2k varnish coating composition

Abstract

The present invention provides a 2K varnish coating composition comprising (A) from 10% to 70% and preferably from 20% to 50% by weight of a first resin having at least one primary hydroxyl group; (B) 2% to 40% by weight and preferably 5% to 25% by weight of a second resin comprising a resin (B-1) having at least one primary hydroxyl group and / or a resin (B-2) having at least one secondary hydroxyl group; and (C) a cross-linking agent comprising at least one polyisocyanate and at least one amino resin, and the weight percentages of components (A) and (B) are based on the total weight of the coating composition, and the weight ratio between components (A) and (B) is in the range of from 6: 1 to 1: 2 and preferably from 4: 1 to 1: 1. The invention also provides an article coated with the coating composition of the invention, and the article preferably has a metal substrate.

Description

Technical Field

[0001] The present invention relates to a coating composition, and more particularly to a 2K clearcoat coating composition for use in the automotive field. Background Art

[0002] The clearcoat as a topcoat provides both decoration and protection for the car, and therefore it needs to have both good appearance and scratch resistance as well as sufficient hardness. In addition, for environmental protection purposes, the coating composition forming the clearcoat is required to have low VOC, that is, high solid content. Taking China as an example, the low VOC regulations require that the ready-to-use VOC value of the 2K coating composition is lower than 420 g / L, which is roughly equivalent to a ready-to-use solid content of at least 57% by weight. However, low VOC or high solid content brings high viscosity to the coating composition, and it is difficult to obtain a good appearance by applying a high viscosity coating composition, not to mention those specific requirements from OEM manufacturers.

[0003] On the other hand, in order to improve the scratch resistance of the clear coat layer, nano silica particles are sometimes added to the coating composition, or Si-OR groups are grafted onto the resin or crosslinker component of the coating composition. However, this usually has a negative impact on the appearance of the clear coat layer, especially in wet-on-wet processes.

[0004] CN 105612227 A discloses a coating composition, which comprises a main agent and a curing agent comprising a polyisocyanate compound, wherein the main agent comprises a hydroxyl-containing acrylic resin having a relatively low glass transition temperature and a hydroxyl-containing acrylic resin having a relatively high glass transition temperature. The coating composition forms a coating film having excellent scratch resistance, hardness, appearance, and adhesion to a plastic substrate, and having resistance to a composition containing a UV absorber. However, the coating film in CN 105612227A is only applicable to plastic substrates, and is not applicable to metal substrates at high baking temperatures (e.g., above 100°C).

[0005] US 7,423,077 B2 discloses a coating material comprising (A) at least one hydroxyl-containing (meth)acrylate (co)polymer, (B) at least one urethane and hydroxyl-functional compound, (C) at least one amino resin, and (D) at least one triazine compound. The amino resin and the triazine compound act as crosslinking agents and release alcohol during the polycondensation reaction, which results in internal stress and strong shrinkage after cooling. As a result, the appearance of the varnish layer is negatively affected, especially in wet-on-wet processes.

[0006] Therefore, there is still a need to provide a coating composition having both a high solid content and a low viscosity, the clearcoat layer obtained or obtainable from the coating composition exhibiting good appearance and scratch resistance as well as sufficient hardness, and being particularly suitable for metal substrates at high baking temperatures (e.g. above 100° C.). Summary of the invention

[0007] In one aspect, the present invention provides a 2K clearcoat coating composition comprising

[0008] (A) 10 to 70% and preferably 20 to 50% by weight of a first resin having at least one primary hydroxyl group;

[0009] (B) 2 to 40% and preferably 5 to 25% by weight of a second resin including a resin (B-1) having at least one primary hydroxyl group and / or a resin (B-2) having at least one secondary hydroxyl group; and

[0010] (C) a crosslinking agent comprising at least one polyisocyanate and at least one amino resin,

[0011] The weight percentages of components (A) and (B) are based on the total weight of the coating composition, and the weight ratio between components (A) and (B) is in the range of 6:1 to 1:2 and preferably 4:1 to 1:1.

[0012] In another aspect, the present invention provides an article coated with the coating composition of the present invention, and the article preferably has a metal substrate.

[0013] Surprisingly, it has been found that the coating composition of the present invention has both low VOC and low viscosity, and the clearcoat layer obtained or obtainable from the coating composition exhibits good appearance and scratch resistance as well as sufficient hardness, and is particularly suitable for metal substrates at high baking temperatures (e.g., above 100° C.). DETAILED DESCRIPTION

[0014] 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.

[0015] Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by one of ordinary skill in the art to which the invention belongs. As used herein, the following terms have the meanings ascribed to them below unless otherwise indicated.

[0016] As used herein, the articles "a" or "an" refer to one or more than one (ie, to at least one) of the grammatical object of the article or component.

[0017] As used herein, the terms "comprise", "comprising", and the like are used interchangeably with "contain", "containing", and the like and are to be interpreted in a non-limiting, open manner. That is, for example, additional components or elements may be present. The expression "consisting of" or "consisting essentially of" or cognates may be included in "comprises" or cognates.

[0018] Unless otherwise indicated, all percentages (%) are "percents by weight," and parts indicate parts by weight.

[0019] 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.

[0020] In the present invention, the acid value is determined in accordance with DIN EN ISO 2114 (date: June 2002).

[0021] In the present invention, the OH value (OHV) is determined in accordance with DIN 53240-2 (date: November 2007).

[0022] In the present invention, the solids content is determined in accordance with DIN EN ISO 3251 (date: June 2008).

[0023] In the present invention, 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 a value calculated using the equation indicated below:

[0025] 1 / Tg(K)=∑(mi / Tgi)

[0026] Tg(℃)=Tg(K)-273

[0027] Tg: glass transition temperature of copolymer

[0028] mi: M0I score of monomer component i

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

[0030] In addition, the glass transition temperature (K) of the homopolymer of the monomer component i is based on the value obtained by POLYMER HANDBOOK [Polymer Handbook] Fourth Edition, J. Brandrup, Eh Immergut, EA Grulke Edited (1999). For homopolymers of monomers not described in this document, the glass transition temperature can be determined by synthesizing a homopolymer of a monomer having a weight average molecular weight of about 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 and a Tg (glass transition temperature) in the range of -80°C to 0°C, preferably -60°C to -10°C, more preferably -50°C to -20°C, such as -40°C and -30°C.

[0033] The first resin has a hydroxyl value (OH value) in the range of 100 to 240 mg KOH / g, preferably 150 to 200 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, and 230 mg KOH / g.

[0034] The first resin has a weight average molecular weight in the range of 2,000 to 10,000, preferably 4,000 to 8,000, such as 3,000, 4,000, 5,000, 6,000, 7,000, 8,000 and 9,000.

[0035] 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.

[0036] The acrylic resin containing at least one primary hydroxyl group can be synthesized by copolymerizing a primary hydroxyl group-containing acrylic monomer and other copolymerizable monomers by a conventional method such as free radical polymerization.

[0037] Examples of the primary hydroxyl group-containing acrylic monomer include monomers having C1 to C 10And preferably C2 to C6 alkyl (meth) acrylate hydroxyalkyl esters, 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 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 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 primary hydroxyl group-containing acrylic monomers can be used alone or in combination of two or more monomers.

[0038] Preferably, the primary hydroxyl group-containing acrylic monomer is at least one selected from the group consisting of 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 (meth)acrylate, 3-hydroxypropyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

[0039] Examples of other copolymerizable monomers include (meth) acrylic acid C1-C 20 -alkyl esters, preferably (meth)acrylic acid 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) acrylate; (meth) acrylamide or its derivatives, such as N,N-dimethylaminoethyl (meth) acrylamide, N,N-diethylaminoethyl (meth) acrylamide, N,N-dimethylaminopropyl (meth) acrylamide, N-hydroxymethyl acrylamide, N-hydroxymethyl acrylamide methyl ether, N-hydroxymethyl acrylamide butyl ether. Other copolymerizable monomers may be used alone or in combination of two or more monomers.

[0040] Preferably, the other copolymerizable monomers 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, 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 comprises at least 60% by weight, preferably at least 70%, and more preferably at least 80% by weight, such as 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, 85% by weight, 90% by weight, and 95% by weight, etc., of units derived from acrylic monomers based on the total weight of the first resin. The acrylic monomers include any acrylic monomer having at least one primary hydroxyl group as well as other copolymerizable monomers.

[0042] In a preferred embodiment of the present invention, the first resin comprises 60 to 95% by weight, such as 70 to 90% by weight and 75 to 85% by weight, etc., of units derived from acrylic monomers based on the total weight of the first resin.

[0043] The first resin comprises 30 to 50% by weight and preferably 35 to 45%, such as 40% by weight, of units derived from primary hydroxyl group-containing acrylic monomers, based on the total weight of the first resin.

[0044] The first resin contains 50 to 70% by weight and preferably 55 to 65%, such as 60% by weight, of units derived from other copolymerizable monomers, based on the total weight of the first resin.

[0045] The 2K coating composition comprises 10 to 70% by weight and preferably 20 to 50% by weight, such as 10% by weight, 20% by weight, 30% by weight, 40% by weight, 50% by weight, 60% by weight and 70% by weight of the first resin, based on the total weight of the coating composition.

[0046] Preferably, the first 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, 15 KOH / mg / g, and the like.

[0047] The first resin can be produced by conventional methods such as free radical polymerization. Examples of free radical polymerization initiators include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethyl-valeronitrile, 4,4'-azobis-4-cyanovaleric acid, 1-azobis-1-cyclohexanecarbonitrile, dimethyl-2,2'-azobisisobutyrate, and the like, 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)-3,3,5-trimethylcyclohexane,

[0063] The free radical polymerization initiators include tert-butylperoxy)-cyclohexane, 2,2-bis(tert-butylperoxy)octane, tert-butyl hydroperoxide, diisopropyl hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide (DTBP), tert-butylcumyl peroxide, isobutyl peroxide, lauroyl peroxide, benzoyl peroxide, diisopropyl peroxydicarbonate, tert-butyl peroxy-2-ethylhexanoate (TBPEH), tert-butyl peroxyneodecanoate, tert-butyl peroxylaurate, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, etc. One of these free radical polymerization initiators may be used alone, or a combination of two or more types may be used.

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

[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-dimethyl-formamide, N,N-diethylformamide, etc. The organic solvent may be one type, or it may be a mixed solvent of a plurality of types including two or more types.

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

[0051] The polymerization temperature of the above polymerization reaction varies depending on the type of free radical polymerization initiator, but it is preferably carried out at a temperature in the range of 50°C to 200°C, more preferably in the range of 100°C to 160°C, 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, etc.

[0052] Second resin

[0053] The second resin is at least one selected from a resin (B-1) having at least one primary hydroxyl group and a Tg in the range of 0°C to 30°C and a resin (B-2) having at least one secondary hydroxyl group and a Tg of at least 20°C.

[0054] In one embodiment of the present invention, the second resin is resin (B-1) having at least one primary hydroxyl group and a Tg in the range of 0°C to 30°C, preferably 5°C to 20°C (eg, 10°C, 15°C, and 25°C, etc.).

[0055] Resin (B-1) has a hydroxyl value in the range of 100 to 240 mg KOH / g, preferably 150 to 200 mg KOH / g, such as 110 mg KOH / g, 120 mg KOH / g, 130 mg KOH / g, 140 mg KOH / g, 150 mg KOH / g, 160 mg KOH / g, 170 mg KOH / g, 180 mg KOH / g, 190 mg KOH / g, 200 mg KOH / g, 210 mg KOH / g, 220 mg KOH / g and 230 mg KOH / g.

[0056] Resin (B-1) has a weight average molecular weight in the range of 2,000 to 10,000, preferably in the range of 3,000 to 7,000, such as 3,000, 3,500, 4,000, 4,500, 5,000, 5,500, 6,500, 7,000, 7,500, 8,000, 8,500 and 9,000.

[0057] In a preferred embodiment of the present invention, the resin (B-1) is an acrylic resin containing at least one primary hydroxyl group in the molecule.

[0058] The resin (B-1) comprises a 10 And preferred are monomer units of primary hydroxyalkyl (meth)acrylate of C2-C6 alkyl.

[0059] The acrylic resin containing at least one primary hydroxyl group can be synthesized by copolymerizing a primary hydroxyl group-containing acrylic monomer and other copolymerizable monomers by a conventional method such as free radical polymerization.

[0060] Examples of the primary hydroxyl group-containing acrylic monomer include hydroxyalkyl (meth)acrylates having an alkyl group with a carbon number ranging from 1 to 10, preferably ranging from 2 to 6, 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, Ester, 9-hydroxynonyl (meth)acrylate; and the ethylene oxide and / or propylene oxide adducts of the following items: 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 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 monomer containing primary hydroxyl groups can be used alone or in combination of two or more monomers.

[0061] Preferably, the primary hydroxyl group-containing acrylic monomer is at least one selected from the group consisting of 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 (meth)acrylate, 3-hydroxypropyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate.

[0062] Examples of other copolymerizable monomers include (meth) acrylic acid C1-C 20 -alkyl esters, preferably (meth)acrylic acid 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)acrylate; (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 copolymerizable monomers can be used alone or in combination of two or more monomers.

[0063] Preferably, the other copolymerizable monomers 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 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 and styrene.

[0064] Resin (B-1) contains at least 60% by weight and preferably at least 70% by weight, such as 75% by weight, 80% by weight, 85% by weight, 90% by weight, 95% by weight, etc., of units derived from acrylic monomers based on the total weight of resin (B-1). The acrylic monomers include any primary hydroxyl group-containing acrylic monomers and other copolymerizable monomers.

[0065] In a preferred embodiment of the present invention, resin (B-1) comprises 60 to 95% by weight, such as 65 to 75% by weight, of units derived from acrylic acid monomers, based on the total weight of resin (B-1).

[0066] The resin (B-1) contains 30 to 50% by weight and preferably 35 to 45%, such as 40% by weight, of units derived from a primary hydroxyl group-containing acrylic monomer, based on the total weight of the resin (B-1).

[0067] The resin (B-1) contains 50 to 70% by weight and preferably 55 to 65%, such as 60% by weight, of units derived from other copolymerizable monomers, based on the total weight of the resin (B-1).

[0068] In another embodiment of the present invention, the second resin is a resin (B-2) having at least one secondary hydroxyl group and a Tg of at least 20°C, preferably at least 25°C, and more preferably at least 30°C, for example, in the range of 20°C to 150°C, preferably 25°C to 100°C, more preferably 30°C to 50°C, such as 35°C, 40°C, 45°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 110°C, 120°C, 130°C and 140°C, etc.

[0069] The resin (B-2) has a hydroxyl value in the range of 100 to 200 mg KOH / g, preferably 130 to 170 mg KOH / g, such as 100 mg KOH / g, 120 mg KOH / g, 130 mg KOH / g, 140 mg KOH / g, 150 mg KOH / g, 160 mg KOH / g, 170 mg KOH / g, 180 mg KOH / g, 190 mg KOH / g and 200 mg KOH / g.

[0070] The resin (B-2) has a weight average molecular weight ranging from 2,000 to 10,000, preferably from 3,000 to 7,000, such as 3,000, 3,500, 4,000, 4,500, 5,000, 5,500, 6,500, 7,000, 7,500, 8,000, 8,500 and 9,000.

[0071] In a preferred embodiment of the present invention, the resin (B-2) is an acrylic resin containing at least one secondary hydroxyl group in the molecule.

[0072] The resin (B-2) comprises a 10 And preferably, the monomer unit is a hydroxyalkyl (meth)acrylate of a C2-C6 alkyl group.

[0073] The acrylic resin containing at least one secondary hydroxyl group may be synthesized by copolymerizing a secondary hydroxyl group-containing acrylic monomer and other copolymerizable monomers by a conventional method such as free radical polymerization.

[0074] Examples of the secondary hydroxyl group-containing acrylic monomer include hydroxyalkyl (meth)acrylates having an alkyl group with a carbon number ranging from 2 to 10, preferably ranging from 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; and the following ethylene oxide and / or propylene oxide adducts: (meth) acrylate 1-hydroxyethyl, (meth) acrylate 1- or 2-hydroxypropyl, (meth) acrylate 1-, 2- or 3-hydroxybutyl, preferably (meth) acrylate 1-hydroxyethyl, (meth) acrylate 1- or 2-hydroxypropyl and methacrylate 1-, 2- or 3-hydroxybutyl. Acrylic monomers containing secondary hydroxyl groups can be used alone or in combination of two or more monomers.

[0075] 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).

[0076] Examples of other copolymerizable monomers include (meth) acrylic acid C1-C 20 -alkyl esters, preferably (meth)acrylic acid 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)acrylate; (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 copolymerizable monomers can be used alone or in combination of two or more monomers.

[0077] Preferably, the other copolymerizable monomers 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 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 and styrene.

[0078] Resin (B-2) contains at least 70% by weight, preferably at least 80% and more preferably at least 90% by weight, such as 75% by weight, 80% by weight, 85% by weight, 90% by weight and 95% by weight, etc., of units derived from acrylic acid monomers based on the total weight of resin (B-2). The acrylic acid monomers include any secondary hydroxyl group-containing acrylic acid monomers and other copolymerizable monomers.

[0079] In a preferred embodiment of the present invention, the resin (B-2) comprises 85 to 95% by weight of units derived from acrylic acid monomers, based on the total weight of the resin (B-2).

[0080] The resin (B-2) contains 30 to 50% by weight and preferably 35 to 45%, such as 40% by weight, of units derived from a secondary hydroxyl group-containing acrylic monomer, based on the total weight of the resin (B-2).

[0081] The resin (B-2) contains 50 to 70% by weight and preferably 55 to 65%, such as 60% by weight, of units derived from other copolymerizable monomers, based on the total weight of the resin (B-2).

[0082] The coating composition comprises 2 to 40% by weight and preferably 5 to 25% by weight, such as 5% by weight, 10% by weight, 15% by weight, 20% by weight, 25% by weight, 30% by weight and 35% by weight, etc., of the second resin, based on the total weight of the coating composition.

[0083] 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.

[0084] The weight ratio between the first resin and the second resin in the coating composition is in the range of 6:1 to 1:2 and preferably 4:1 to 1:1, such as 2:1, 3:1, 4:1, 5:1 and the like.

[0085] The second resin can be produced by conventional methods such as free radical polymerization, and the method used to prepare the first resin is also applicable to the second resin.

[0086] Crosslinking agent

[0087] In the present invention, the crosslinking agent comprises at least one polyisocyanate and at least one amino resin.

[0088] Polyisocyanates having at least two and preferably at least three isocyanate groups may be used as the crosslinking agent in the coating composition of the present invention, and one type of polyisocyanate or a combination of two or more types of polyisocyanates may be used.

[0089] 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, the isocyanurate form, the oligomeric or polymeric isocyanates of these compounds, or mixtures thereof.

[0090] 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.

[0091] In a preferred embodiment, the polyisocyanate is an oligomeric isocyanate compound, such as an isocyanate dimer, an isocyanate trimer, and the like.

[0092] In a particular embodiment, the polyisocyanate is a trimer of HDI, such as Desmodur 3390 from Covestro.

[0093] 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 1.6:1 to 0.7:1 and preferably 1.35:1 to 1.05:1.

[0094] 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.

[0095] 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.

[0096] Such crosslinkers are described in patents U.S. Pat. No. 4,710,542 A and EP 0 245 700 B1, and also in the article by B. Singh and co-workers, “Carbamylmethylated Melamines, Novel Crosslinkers for the Coatings Industry”, 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 “Lack additive” [Additives for Coatings], 1988, pages 242 to 250, in the section on “Melamine-resin-crosslinking systems”.

[0097] It is preferred that the crosslinking agent comprises at least 60%, preferably at least 70%, and more preferably at least 80% by weight of melamine resin based on the total weight of the crosslinking agent comprising melamine resin and amino resin.

[0098] 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.

[0099] An example of a suitable relatively low molecular weight, highly etherified melamine resin containing free imino groups is CYTEC® from Cytec Corporation. 325 and 327 (methanol etherified), Cymel 202 and 203 (mixture of methanol and butanol etherified) and 1158 (butanol etherified) from BASF AG 062 (methanol etherified), 018 (butanol etherified) and 014 (butanol etherified, with relatively high viscosity) from Solutia 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 from Akzo Resins US138 and US146 (butanol etherified).

[0100] Examples of suitable relatively low molecular weight, partially etherified melamine resins are BASF AG's 012, 016, 015 and 010 from Solutia MF 590 and 600, and from Akzo Resins US 132 and 134.

[0101] The amount of the amino resin is in the range of 1 to 30% by weight, preferably 5 to 15% by weight, such as 3% by weight, 8% by weight, 10% by weight, 12% by weight, 16% by weight, 18% by weight, 20% by weight and 25% by weight, etc., based on the total weight of the coating composition.

[0102] In a preferred embodiment according to the present invention, the 2K coating composition comprises (A) a first resin having at least one primary hydroxyl group and a Tg in the range of -50°C to -20°C; (B) a second resin having at least one primary hydroxyl group and a Tg temperature in the range of 5°C to 20°C; and (C) a crosslinker comprising at least one polyisocyanate and at least one amino resin.

[0103] In a specific embodiment according to the present invention, the 2K coating composition comprises (A) an acrylic resin having at least one primary hydroxyl group and a Tg in the range of -50°C to -20°C; (B) an acrylic resin having a primary hydroxyl group and a Tg in the range of 5°C to 20°C; and (C) a crosslinker comprising an aliphatic polyisocyanate and a melamine resin.

[0104] In another specific embodiment according to the present invention, the 2K coating composition comprises (A) an acrylic resin having at least one primary hydroxyl group, a Tg in the range of -50°C to -20°C, and a weight average molecular weight in the range of 4,000 to 8,000; (B) an acrylic resin having at least one primary hydroxyl group, a Tg in the range of 5°C to 20°C, and a weight average molecular weight in the range of 3,000 to 7,000; and (C) a crosslinker comprising an aliphatic polyisocyanate and a melamine resin.

[0105] In a preferred embodiment according to the present invention, the 2K coating composition comprises (A) a first resin having at least one primary hydroxyl group and a Tg in the range of -50°C to -20°C; (B) a second resin having at least one secondary hydroxyl group and a Tg in the range of 30°C to 50°C; and (C) a crosslinker comprising a polyisocyanate and an amino resin.

[0106] In a specific embodiment according to the present invention, the 2K coating composition comprises (A) an acrylic resin having at least one primary hydroxyl group and a Tg in the range of -50°C to -20°C; (B) an acrylic resin having at least one secondary hydroxyl group and a Tg in the range of 30°C to 50°C; and (C) a crosslinker comprising an aliphatic polyisocyanate and a melamine resin.

[0107] In another specific embodiment according to the present invention, the 2K coating composition comprises (A) an acrylic resin having at least one primary hydroxyl group, a Tg in the range of -50°C to -20°C, and a weight average molecular weight in the range of 4,000 to 8,000; (B) an acrylic resin having at least one secondary hydroxyl group, a Tg in the range of 30°C to 50°C, and a weight average molecular weight in the range of 3,000 to 7,000; and (C) a crosslinker comprising an aliphatic polyisocyanate and a melamine resin.

[0108] Various additives may be added as needed, such as leveling agents, sag control agents, defoaming agents, light stabilizers, UV 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, internal cross-linking resin fine particles, etc.

[0109] The coating composition of the present invention can be used as a clear varnish or a colored paint to which a dye, a pigment or the like is added.

[0110] 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 roller coater, a flow coater or a dip coater, or a brush coater or a bar coater, or an applicator, etc. And spray painting is preferred in the present invention.

[0111] The thickness of the paint film obtained by applying the coating composition of the present invention is not particularly limited, but the thickness of the paint film after drying is preferably in the range of 10 μm to 150 μm, and more preferably 30 μm to 60 μm.

[0112] In addition, examples of substrate materials for painting the coating composition of the present invention include both inorganic and organic materials, such as metal, wood, glass, cloth, plastic, foam, elastomer, paper, ceramic, concrete, gypsum board, etc., and metal substrates are preferred. These substrate materials may or may not be pre-treated.

[0113] Examples of the obtained or obtainable coated articles 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 (e.g., car bodies, bumpers, spoilers, mirrors, wheels, interior decoration parts, etc., which are made of various materials), metal sheets (such as steel sheets), bicycles, bicycle parts, materials used on roads (e.g., guardrails, traffic signs, sound insulation walls, etc.), materials used in tunnels (e.g., side wall panels, etc.), ships, railway rolling stock, aircraft, furniture, musical instruments, household electrical goods, building materials, containers, office accessories, sports accessories, toys, etc., and metal products are preferred.

[0114] Example

[0115] Although the following detailed description sets forth specific preferred embodiments, those skilled in the art will appreciate that these embodiments are by way of example only and that the invention may be practiced in alternative forms.

[0116] Example 1

[0117] A 2K clearcoat coating composition comprising

[0118] (A) 10 to 70% and preferably 20 to 50% by weight of a first resin having at least one primary hydroxyl group;

[0119] (B) 2 to 40% and preferably 5 to 25% by weight of a second resin including a resin (B-1) having at least one primary hydroxyl group and / or a resin (B-2) having at least one secondary hydroxyl group; and

[0120] (C) a crosslinking agent comprising at least one polyisocyanate and at least one amino resin,

[0121] The weight percentages of components (A) and (B) are based on the total weight of the coating composition, and the weight ratio between components (A) and (B) is in the range of 6:1 to 1:2 and preferably 4:1 to 1:1.

[0122] Example 2

[0123] The coating composition according to embodiment 1, wherein the first resin has a Tg of -80°C to 0°C, preferably -80°C to -10°C, and more preferably -40°C to -20°C.

[0124] Example 3

[0125] A coating composition according to any one of embodiments 1 to 2, wherein the first resin has a hydroxyl value in the range of 100 to 240 mg KOH / g and preferably 150 to 200 mg KOH / g.

[0126] Example 4

[0127] 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 2,000 to 10,000 and preferably 4,000 to 8,000.

[0128] Example 5

[0129] A coating composition according to any one of embodiments 1 to 4, wherein the first resin is at least one acrylic resin and preferably has a C1-C 10 And a C2-C6 alkyl hydroxyalkyl (meth)acrylate resin is preferred.

[0130] Example 6

[0131] The coating composition according to any one of embodiments 1 to 5, wherein the resin (B-1) has a Tg in the range of 0°C to 30°C and preferably 5°C to 20°C.

[0132] Example 7

[0133] The coating composition according to any one of embodiments 1 to 6, wherein the resin (B-1) has a hydroxyl value in the range of 100 to 240 mg KOH / g and preferably 150 to 200 mg KOH / g.

[0134] Example 8

[0135] The coating composition according to any one of embodiments 1 to 7, wherein the resin (B-1) has a weight average molecular weight in the range of 2,000 to 10,000 and preferably in the range of 3,000 to 7,000.

[0136] Example 9

[0137] The coating composition according to any one of embodiments 1 to 8, wherein the resin (B-1) is at least one acrylic resin and preferably has a C1-C 10 And a C2-C6 alkyl hydroxyalkyl (meth)acrylate resin is preferred.

[0138] Example 10

[0139] The coating composition according to any one of embodiments 1 to 5, wherein the resin (B-2) has a Tg of at least 20°C and preferably at least 30°C.

[0140] Embodiment 11

[0141] The coating composition according to any one of embodiments 1 to 10, wherein the resin (B-2) has a hydroxyl value in the range of 100 to 200 mg KOH / g and preferably 130 to 170 mg KOH / g.

[0142] Example 12

[0143] The coating composition according to any one of embodiments 1 or 11, wherein the resin (B-2) has a weight average molecular weight in the range of 2,000 to 10,000, preferably in the range of 3,000 to 7,000.

[0144] Example 13

[0145] The coating composition according to any one of embodiments 1 to 12, wherein the resin (B-2) is at least one acrylic resin and preferably has a C2-C 10 And a C2-C6 alkyl hydroxyalkyl (meth)acrylate resin is preferred.

[0146] Embodiment 14

[0147] The coating composition according to any one of embodiments 1 to 13, wherein 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 1.6:1 to 0.7:1 and preferably 1.35:1 to 1.05:1.

[0148] Embodiment 15

[0149] The coating composition according to any one of embodiments 1 to 14, wherein the amount of the amino resin is in the range of 1 to 30%, preferably 5 to 15% by weight based on the total weight of the coating composition.

[0150] Example 16

[0151] Embodiment 1: The coating composition of any one of embodiments 1 to 15, wherein the amino resin is a melamine resin.

[0152] Embodiment 17

[0153] A coating composition according to any one of embodiments 1 to 16, wherein the coating composition further comprises a hydroxyl-containing polyester resin.

[0154] Embodiment 18

[0155] An article coated with the coating composition according to any one of embodiments 1 to 17, wherein the article preferably has a metal substrate.

[0156] Examples

[0157] The present invention is described below in a more practical manner by means of illustrative examples, but the present invention is not limited in any way to these illustrative examples.

[0158] The properties of the paint films obtained with the coating compositions of the invention were determined in the manner indicated below.

[0159] Performance testing of varnish

[0160] (1) Appearance

[0161] The appearance of the dried and cured varnish is evaluated by its surface texture, which is measured by a BYK wave-scan dual. The surface texture is a mixture of various textures ranging from very fine to very coarse. BYK wave-scan dual measures the surface texture at different scale levels, which are divided into six categories (Du, Wa, Wb, Wc, Wd, We) by wavelength. Based on these measured data, Lw, Sw are calculated by the device and indicate the appearance level of the paint layer. Lower Lw, Sw values ​​indicate better appearance properties. Usually, good appearance properties are defined by Lw < 5 and Sw < 20 at the same time.

[0162] (2) Scratch resistance

[0163] Scratch resistance is evaluated by the 20° gloss retention after dry scratching. Dry scratches are produced by a crockmeter equipped with PERSI sandpaper (grain size: 10 microns). During the test, 15 back and forth repetitions are performed. The 20° gloss before and after dry scratching is compared. A higher gloss retention indicates better scratch resistance. The 20° gloss retention of a conventional polyurethane 2K clearcoat measured by the above method is about 40%.

[0164] (3) Hardness

[0165] The hardness of the coating was evaluated by pencil hardness following GB / T standard 6739-2006.

[0166] (4) VOC

[0167] VOC was evaluated based on solid content measurement according to the methods described in GB / T 38597 / 2020, GB / T 1725-2007 and GB / T 23985-2009. Solid content was measured by weighing 1 g of sample in an aluminum pan with a diameter of 75 mm, which was then baked at 105°C for 1 h. VOC calculations were performed according to the equation listed below. For all samples of the present invention and comparative samples listed in the present invention, the density ρ of the coating sample measured was 0.97 g / mL.

[0168] ρ(VOC)=(100–NV)×ρ×10

[0169] ρ(VOC) = Sample VOC (calculated value), g / L

[0170] NV = solid content of the sample, expressed as mass fraction (%)

[0171] ρ = density of the coating sample measured at 23°C, g / mL

[0172] The polyacrylates in the following preparation examples were prepared according to the monomer compositions and weight ratios shown in Table 1.

[0173] Material

[0174] 91756VS-60YA is a sag control agent from Allnex

[0175] 327 is an amino resin crosslinker from Allnex

[0176] 018 is an amino resin crosslinker from BASF

[0177] 4045 is a catalyst from Allnex

[0178] BYK355 is a leveling agent from BYK Chemie

[0179] Disperbyk 161 is a leveling agent from BYK Chemicals

[0180] BYK 325 is a leveling agent from BYK Chemicals

[0181] BYK 315 is a leveling agent from BYK Chemicals

[0182] OX-883HF is a defoamer from King Industries

[0183] 5248 is a light stabilizer from BASF

[0184] Preparation Example 1

[0185] A stainless steel reactor equipped with a reflux condenser and an N2 inlet was charged with a mixture of 27.9 parts by weight of solvent naphtha 160 / 180 (SN) and caprolactone, and this initial charge was heated to 140°C. Thereafter, an initiator solution (5.1 parts by weight of tert-butyl peroxy-2-ethylhexanoate (TBPEH) in 3.7 parts by weight of solvent naphtha 160 / 180 (SN)) was metered in at a uniform rate over a period of 4.75 hours under stirring. A monomer mixture containing 6.4 parts by weight of styrene (St), 30.1 parts by weight of 2-ethylhexyl acrylate (EHA), and 23.1 parts by weight of 2-hydroxyethyl acrylate (2-HEA) was metered in at a uniform rate over a period of 4 hours under stirring. Thereafter, the reaction mixture was heated to 160°C and maintained for 4 hours. The reaction mixture was then cooled to 60°C and diluted by adding 5.4 parts by weight of solvent naphtha 160 / 180 (SN). The solid content of the obtained polyacrylate solution was 65% by weight. The obtained polyacrylate (ie, low Tg resin-1 in Table 1) had a weight average molecular weight (M W ), an OH value of 175 mg KOH / g and a Tg of -30°C.

[0186] Preparation Example 2

[0187] A stainless steel reactor equipped with a reflux condenser and an N2 inlet was charged with a mixture of 27.9 parts by weight of solvent naphtha 160 / 180 (SN) and caprolactone, and this initial charge was heated to 140°C. Thereafter, an initiator solution (5.1 parts by weight of tert-butyl peroxy-2-ethylhexanoate (TBPEH) in 1.9 parts by weight of solvent naphtha 160 / 180 (SN)) was metered in at a uniform rate over a period of 4.75 hours under stirring. A monomer mixture containing 6.4 parts by weight of styrene (St), 30.1 parts by weight of 2-ethylhexyl acrylate (EHA), and 23.1 parts by weight of 2-hydroxyethyl acrylate (2-HEA) was metered in at a uniform rate over a period of 4 hours under stirring. Thereafter, the reaction mixture was heated to 160°C and maintained for 4 hours. The reaction mixture was then cooled to 60°C and diluted by adding 5.4 parts by weight of solvent naphtha 160 / 180 (SN). The solid content of the obtained polyacrylate solution was 65% by weight. The obtained polyacrylate (ie, low Tg resin-2 in Table 1) had a weight average molecular weight (M W ), an OH value of 175 mg KOH / g and a Tg of -30°C.

[0188] Preparation Example 3

[0189] 27.9 parts by weight of solvent naphtha 160 / 180 (SN) were charged to a stainless steel reactor equipped with a reflux condenser and an N2 inlet, and this initial charge was heated to 140°C. Thereafter, an initiator solution (5.1 parts by weight of tert-butyl peroxy-2-ethylhexanoate (TBPEH) in 3.7 parts by weight of solvent naphtha 160 / 180 (SN)) was metered in at a uniform rate over a period of 4.75 hours under stirring. A monomer mixture containing 15.2 parts by weight of styrene (St), 19.6 parts by weight of n-butyl acrylate (nBA), and 23.7 parts by weight of 2-hydroxyethyl methacrylate (2-HEMA) was metered in at a uniform rate over a period of 4 hours under stirring. Afterwards, the reaction mixture was heated to 160°C and maintained for 4 hours. The reaction mixture was then cooled to 60°C and diluted by adding 5.4 parts by weight of solvent naphtha 160 / 180 (SN). The solid content of the resulting polyacrylate solution was 60% by weight. The resulting polyacrylate (ie, the medium Tg resin in Table 1) had a weight average molecular weight (M) of 5,700 g / mol. W ), an OH value of 175 mg KOH / g and a Tg of 12°C.

[0190] Preparation Example 4

[0191] A stainless steel reactor equipped with a reflux condenser and an N2 inlet was charged with 28 parts by weight of solvent naphtha 160 / 180 (SN), and this initial charge was heated to 160°C. Thereafter, an initiator solution (0.9 parts by weight of di-tert-butyl peroxide (DTBP) in 3.4 parts by weight of solvent naphtha 160 / 180 (SN)) was metered in at a uniform rate over a period of 4.75 hours under stirring. A monomer mixture containing 13.9 parts by weight of styrene (St), 23.6 parts by weight of 2-hydroxyethyl acrylate (2-HEA), 6.7 parts by weight of n-butyl acrylate (nBA), 11.4 parts by weight of cyclohexyl methacrylate (CHMA) and 1.4 parts by weight of acrylic acid (AA) was metered in at a uniform rate over a period of 4 hours under stirring. Afterwards, the reaction mixture was kept for 4 hours. The reaction mixture was then cooled to 60°C and diluted by adding 16.9 parts by weight of butyl acetate (BA). The solid content of the obtained polyacrylate solution was 60% by weight. The obtained polyacrylate (ie, high Tg resin-1 in Table 1) had a weight average molecular weight (M W ), an OH value of 167 mg KOH / g and a Tg of 32°C.

[0192] Preparation Example 5

[0193] A stainless steel reactor equipped with a reflux condenser and an N2 inlet was charged with 28 parts by weight of solvent naphtha 160 / 180 (SN), and this initial charge was heated to 150°C. Thereafter, an initiator solution (0.9 parts by weight of di-tert-butyl peroxide (DTBP) in 3.4 parts by weight of solvent naphtha 160 / 180 (SN)) was metered in at a uniform rate over a period of 4.75 hours under stirring. A monomer mixture containing 5.1 parts by weight of styrene (St), 20.3 parts by weight of 2-hydroxypropyl methacrylate (2-HPMA), 7.7 parts by weight of n-butyl methacrylate (nBMA), 17.2 parts by weight of tert-butyl acrylate (tBA) and 0.4 parts by weight of acrylic acid (AA) was metered in at a uniform rate over a period of 4 hours under stirring. Afterwards, the reaction mixture was kept for 4 hours. The reaction mixture was then cooled to 60°C and diluted by adding 16.9 parts by weight of butyl acetate (BA). The solid content of the obtained polyacrylate solution (ie, high Tg resin-2 in Table 1) was 53% by weight. The obtained polyacrylate (ie, high Tg resin-2 in Table 1) had a weight average molecular weight (M) of 5,500 g / mol. W ), an OH value of 150 mg KOH / g and a Tg of 40°C.

[0194] Table 1 Resin characteristics

[0195]

[0196] St: styrene; 2-HEA: 2-hydroxyethyl acrylate; EHA: 2-ethylhexyl acrylate; 2-HEMA: 2-hydroxyethyl methacrylate; n-BA: n-butyl acrylate; nBMA: n-butyl methacrylate; CHMA: cyclohexyl methacrylate; AA: acrylic acid; t-BA: tert-butyl acrylate; 2-HPMA: 2-hydroxypropyl methacrylate

[0197] Preparation of 2K varnish composition

[0198] Table 2 describes the composition of component I of the 2K clearcoat composition. All components listed in the table were subsequently mixed to obtain component I. To obtain component II, Desmodur 3390 (from Covestro) was diluted to 80% by weight in a mixture of solvent naphtha and butyl acetate (1:1 by weight). The molar ratio of NCO of component II to the total OH of component I was 1.2:1.

[0199]

[0200] Preparation of dried and cured films

[0201] Component I and component II of each 2K clearcoat composition were mixed, and the mixture was stirred to homogeneity; the mixture was sprayed onto a steel plate and baked at 140° C. for 20 minutes.

[0202] Evaluation of clearcoat films was performed in a multi-coat coating including a black waterborne primer produced from a commercial black waterborne primer material (Colorbrite) from BASF Shanghai Coating Ltd. The black primer was chosen because it allowed for the best observation of changes in the appearance of the multi-coat coating system.

[0203]

[0204] As can be seen from Table 3, only the examples of the present invention simultaneously exhibit high solid content (ie, low VOC) and low viscosity. And the obtained varnish layer exhibits good appearance and scratch resistance and sufficient hardness, while the comparative examples exhibit one or more disadvantages.

[0205] It will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. It is intended that the embodiments and examples be considered as illustrative only. Therefore, 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 clearcoat coating composition comprising (A) 10 to 70% and preferably 20 to 50% by weight of a first resin having at least one primary hydroxyl group; (B) 2 to 40% and preferably 5 to 25% by weight of a second resin including a resin (B-1) having at least one primary hydroxyl group and / or a resin (B-2) having at least one secondary hydroxyl group; and (C) a crosslinking agent comprising at least one polyisocyanate and at least one amino resin, The weight percentages of components (A) and (B) are based on the total weight of the coating composition, and the weight ratio between components (A) and (B) is in the range of 6:1 to 1:2 and preferably 4:1 to 1:

1.

2. The coating composition according to claim 1, wherein The first resin has a Tg of -80°C to 0°C, preferably -80°C to -10°C, and more preferably -40°C to -20°C.

3. The coating composition according to any one of claims 1 to 2, wherein The first resin has a hydroxyl value in the range of 100 to 240 mg KOH / g and preferably 150 to 200 mg KOH / g.

4. The coating composition according to any one of claims 1 to 3, wherein The first resin has a weight average molecular weight ranging from 2,000 to 10,000 and preferably from 4,000 to 8,000.

5. The coating composition according to any one of claims 1 to 4, wherein The first resin is at least one acrylic resin, and preferably has a C1-C 10 And a C2-C6 alkyl hydroxyalkyl (meth)acrylate resin is preferred.

6. The coating composition according to any one of claims 1 to 5, wherein The resin (B-1) has a Tg in the range of 0°C to 30°C and preferably 5°C to 20°C.

7. The coating composition according to any one of claims 1 to 6, wherein The resin (B-1) has a hydroxyl value within a range of 100 to 240 mg KOH / g and preferably 150 to 200 mg KOH / g.

8. The coating composition according to any one of claims 1 to 7, wherein The resin (B-1) has a weight average molecular weight ranging from 2,000 to 10,000 and preferably ranging from 3,000 to 7,000.

9. The coating composition according to any one of claims 1 to 8, wherein The resin (B-1) is at least one acrylic resin, and preferably has a C1-C 10 And a C2-C6 alkyl hydroxyalkyl (meth)acrylate resin is preferred.

10. The coating composition according to any one of claims 1 to 5, wherein The resin (B-2) has a Tg of at least 20°C and preferably at least 30°C.

11. The coating composition according to any one of claims 1 to 10, wherein The resin (B-2) has a hydroxyl value within a range of 100 to 200 mg KOH / g and preferably 130 to 170 mg KOH / g.

12. The coating composition according to any one of claims 1 or 11, wherein The resin (B-2) has a weight average molecular weight in the range of 2,000 to 10,000, preferably in the range of 3,000 to 7,000.

13. The coating composition according to any one of claims 1 to 12, wherein The resin (B-2) is at least one acrylic resin, and preferably has a C2-C 10 And a C2-C6 alkyl hydroxyalkyl (meth)acrylate resin is preferred.

14. The coating composition according to any one of claims 1 to 13, wherein 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 1.6:1 to 0.7:1 and preferably 1.35:1 to 1.05:

1.

15. The coating composition according to any one of claims 1 to 14, wherein The amount of the amino resin ranges from 1 to 30%, preferably from 5 to 15% by weight, based on the total weight of the coating composition.

16. The coating composition according to any one of claims 1 to 15, wherein The amino resin is a melamine resin.

17. The coating composition according to any one of claims 1 to 16, wherein The coating composition further comprises a hydroxyl-containing polyester resin.

18. An article coated with the coating composition according to any one of claims 1 to 17, wherein The article preferably has a metal substrate.

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