Curable coating composition for low curing temperatures and methods for producing coatings at low curing temperatures as well as multi-layer coating systems

Abstract

Curable coating composition for low curing temperature, comprising: a crosslinkable component comprising an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 percent to 12 percent of monomers containing one or more carboxylic acid group(s), wherein the percentages are based on the total weight of the acid-functional acrylic copolymer, a networking component; and A control device for a low firing temperature, comprising a rheology component selected from an amorphous silica gel, a clay or a combination thereof, wherein the rheology component is present in an amount of 0.1 to 10 wt% and 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components.

Description

TECHNICAL AREA

[0001] The present invention relates to curable compositions and in particular to a curable coating composition with low VOC (volatile organic compound) for low curing temperatures, suitable for use in automotive OEM (original equipment manufacturer) and repair applications, and to methods for producing coatings with low curing temperatures. BACKGROUND

[0002] A variety of clear and pigmented coating compositions are used in various coatings, such as primers, basecoats and clearcoats, which are applied in automotive coatings, which are generally solvent-based.

[0003] Multi-layer systems were developed to meet the need for improved aesthetics of the coated substrate. A multi-layer system typically includes a primer coat, followed by a base coat, which is typically pigmented, and then finally a clear coat that provides a glossy, deep appearance commonly referred to as the "wet look".

[0004] To improve manufacturing efficiency and reduce production costs, it is important in a multi-layered system to dry quickly (thus reducing production lead time) and / or to cure intermediate layers (such as basecoats sandwiched between the primer and clearcoats) at lower baking temperatures (thus reducing manufacturing costs). This allows subsequent layers to be applied without negatively affecting coating properties, such as gloss or bleed-through from the basecoat into the subsequently applied clearcoat layer. One way to ensure the aforementioned process is to improve the coating composition, i.e., to increase its resistance to runs, particularly that of the basecoat used for intermediate layers.Runoff resistance is the resistance of a basecoat layer to running or forming runs when applied to an inclined or vertical substrate surface.

[0005] An attempt to improve runoff resistance was disclosed in jointly transferred US application 20060047051 A1. The solution involves including amorphous silica gel in the coating composition. However, there is still a need to provide a coating composition with lower VOCs that can be cured at lower curing temperatures with reduced curing time.

[0006] DE 10 2014 014 988 A1 describes coating compositions with low solids content and rheology-controlling polyurea agents, processes for producing such coating compositions and systems for producing such coating compositions.

[0007] RÖMPP Online, published by Georg Thieme Verlag KG, describes additives for coating compositions of all kinds.

[0008] DE 102 30 406 A1 describes a clear varnish consisting of 10-80 wt.% of a polyester resin containing units derived from an alicyclic polyhydric acid and / or an alicyclic polyhydric alcohol, 5-50 wt.% of a polyisocyanate compound and 0-50 wt.% acrylic resin.

[0009] DE 100 59 856 A1 describes a clear coat obtainable by: (I) applying a non-pigmented intermediate coat to a substrate to be coated; (II) crosslinking the intermediate coat to form an intermediate coat layer; (III) applying a non-pigmented topcoat to the intermediate coat layer; and (IV) crosslinking the topcoat to form a topcoat layer, wherein the intermediate coat layer has a higher flexibility than the topcoat layer, and its use for producing a multi-layer coating.

[0010] DE 100 59 853 A1 describes a coating composition obtainable by polyaddition of a non-aqueous starting mixture containing (1) 10–70 wt.% of a non-aqueous solution of an acrylate-based polymer with an OH index of 100–250; (2) 10–70 wt.% of a non-aqueous solution of a fluorine-modified polymer with a glass transition temperature of 20–40 °C; and (3) 20–60 wt.% of at least one blocked aliphatic or cycloaliphatic polyisocyanate. The weight ratio of component (1) to component (2) is at most 1, and the sum of components (1), (2), and (3) equals 100%, based on the binder content of the starting mixture to be crosslinked.

[0011] DE 44 07 415 A1 describes a coating composition containing (A) at least one hydroxyl-containing polyacrylate resin and (B) at least one crosslinking agent, characterized in that component (A) is obtainable by polymerization of (a) 5 to 80 wt.% at least one cycloaliphatic (meth)acrylic acid ester; (b) 10 to 50 wt.% at least one hydroxyl-containing (meth)acrylic acid alkyl ester; (c) 0 to 25 wt.% at least one further hydroxyl-containing monomer; (d) 5 to 80 wt.% at least one aliphatic (meth)acrylic acid ester; (e) 0 to 40 wt.% at least one vinyl aromatic; and (f) 0 to 40 wt.% of at least one further monomer to form a polyacrylate resin with a Mn of 1000 to 5000, a Mw / Mn ratio of less than 5.0 and an OH number of 60 to 180. The sum of the wt. fractions of all monomers always equals 100 wt.-% and as component (B) only monomers are used which result in a polyacrylate resin with a glass transition temperature of -10 to +6 °C or of +60 to 80 °C when the monomer is polymerized alone.

[0012] US Patent 2011 / 0117379A1 describes a solvent-based coating composition that provides a high-quality basecoat, particularly for automotive substrates, as well as methods for forming a layer from the solvent-based coating composition and substrates coated with the coating composition. The coating composition contains an acrylic polymer that has both acid functional groups and polyether functional groups.

[0013] US Patent 8,357,456 B2 describes a solvent-based coating composition that provides a high-quality basecoat, particularly for automotive substrates, as well as methods for forming a layer from the solvent-based coating composition and substrates coated with the coating composition. The coating composition contains an acrylic polymer that has both acid functional groups and polyether functional groups. SUMMARY

[0014] According to the present invention, a curable coating composition for a low curing temperature includes: a crosslinkable component comprising an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 percent to 12 percent of monomers containing one or more carboxylic acid group(s), wherein the percentages are based on the total weight of the acid-functional acrylic copolymer, a networking component; and A control device for a low firing temperature, comprising a rheology component selected from an amorphous silica gel, a clay or a combination thereof, wherein the rheology component is present in an amount of 0.1 to 10 wt% and 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components.

[0015] According to the present invention, the multi-layer coating system includes: a hardenable basecoat for low baking temperatures, comprising: a crosslinkable component comprising an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 percent to 12 percent of monomers containing one or more carboxylic acid group(s), wherein the percentages are based on the total weight of the acid-functional acrylic copolymer, a networking component; and a control agent for a low firing temperature, comprising a rheology component selected from an amorphous silica gel, a clay, or a combination thereof, wherein the rheology component is present in an amount of 0.1 to 10 wt%, and 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components; and a clearcoat coating composition comprising an acrylic copolymer component comprising one or more acrylic polymers, wherein the clearcoat coating composition comprises primary hydroxyl and secondary hydroxyl groups in a ratio of 30:70 to 80:20, such as 35:65 to 75:25, such as 40:60 to 70:30, such as 45:55 to 70:30, such as 50:50 to 70:30, and wherein the clearcoat coating composition is placed above and in contact with the curable basecoat coating composition for a low baking temperature.

[0016] According to the present invention, a method for producing a coating on a substrate includes: (a) Mixing a crosslinkable component, a crosslinking component and a low-temperature curing control agent of a low-temperature curable coating composition to form a pot mix orMixture, wherein the crosslinkable component comprises an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 wt% to 12 wt% of carboxylic acid group(s) containing monomer, based on the total weight of the acid-functional acrylic copolymer, and wherein the low-curing-temperature control agent is a rheology component selected from an amorphous silica gel, a clay, and a combination thereof, wherein the rheology component is present in an amount of 0.1 wt% to 10 wt% and comprises 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components; (b) Applying a layer of the pot mix or mixture to the substrate; and (c) Hardening of the layer at low firing temperature to the coating on the substrate.

[0017] According to the present invention, a method for producing a multi-layer coating on a substrate includes: (a) Mixing a crosslinkable component, a crosslinking component and a baking temperature control agent to form a basecoat pot mix or mixing batch, wherein the crosslinkable component comprises an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2% to 12% by weight of carboxylic acid group(s) containing monomer, based on the total weight of the acid-functional acrylic copolymer, and wherein the baking temperature control agent comprises a rheology component selected from an amorphous silica gel, a clay or a combination thereof, wherein the rheology component is present in an amount of 0.1% to 10% by weight and comprises 0.1% to 10% by weight of polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components; (b) Applying a layer of the basecoat pot mix or mixture to the substrate; (c) Applying a layer of a clearcoat coating composition, spread over and in contact with a layer of the basecoat pot mix or mixing mixture to form a multi-layer coating composition, wherein the clearcoat coating composition comprises an acrylic copolymer component comprising one or more acrylic polymers, wherein the clearcoat coating composition comprises primary hydroxyl and secondary hydroxyl groups in a ratio of 30:70 to 80:20, such as 35:65 to 75:25, such as 40:60 to 70:30, such as 45:55 to 70:30, such as 50:50 to 70:30; and (d) Hardening of the multi-layer coating composition on the substrate. DETAILED DESCRIPTION

[0018] The features and advantages of the present invention will become more readily apparent to the person skilled in the art upon reading the detailed description below. Emphasis is placed on the fact that certain features of the invention, which are described above and below in the context of separate embodiments for clarity, are also provided in combination in a single embodiment. Conversely, various features of the invention, which are described for the sake of brevity in the context of a single embodiment, may also be provided separately or in each sub-combination. Furthermore, singular references may also include the plural (for example, "a" and "an" may refer to one, or one or more), unless the context indicates otherwise.

[0019] Unless expressly stated otherwise, the use of numerical values ​​in the various ranges disclosed in this application is to be understood as approximations, as if the word "approximately" had been placed before both the minimum and maximum values ​​in the disclosed ranges. In this way, slight variations above and below the disclosed ranges can be used to achieve essentially the same results as values ​​within the ranges. The disclosure of these ranges is also intended to be as a continuous range, including any value between the minimum and maximum values.

[0020] When used herein: A "two-component coating composition" is a thermosetting coating composition with two components stored in separate containers. These containers are typically sealed to enhance their shelf life. The components are mixed shortly before use to form a pot mix, which has a limited pot life, typically ranging from a few minutes (15 to 45 minutes) to several hours (4 to 8 hours). The pot mix is ​​applied as a layer of the desired thickness to a substrate surface, such as a car body. After application, the layer dries and cures at low stoving temperatures to form a coating on the substrate surface with desired properties, such as high gloss, damage resistance, and resistance to environmental etching.The low curing temperature suitable for use herein is in the range of 60°F (15°C) to 200°F (93°C). In one example, the low curing temperature is in the range of 60°F (15°C) to 110°F (43°C) and is referred to as ambient temperatures or ambient conditions. In another example, the low curing temperature is in the range of 60°F (15°C) to 140°F (60°C). In yet another example, the low curing temperature is in the range of 140°F (60°C) to 160°F (71°C). In still another example, the low curing temperature is in the range of 160°F (71°C) to 200°F (93°C).

[0021] “Low VOC coating composition” means a coating composition that includes the solvent content in the range of 0.1 kilograms (1.0 pounds per gallon) to 0.72 kilograms (6.0 pounds per gallon), preferably 0.3 kilograms (2.6 pounds per gallon) to 0.6 kilograms (5.0 pounds per gallon), and more preferably 0.34 kilograms (2.8 pounds per gallon) to 0.53 kilograms (4.4 pounds per gallon) per liter of coating composition. All VOCs were determined using the method provided in ASTM D3960.

[0022] “High solids composition” means a coating composition with a solids component of above 30 percent, preferably in the range of 35 to 90 percent and more preferably in the range of 40 to 80 percent, all in weight percentages based on the total weight of the composition.

[0023] "Weight-average molecular weight according to GPC" means a weight-average molecular weight measured by gel permeation chromatography. Measurements reported herein were obtained using a high-performance liquid chromatograph (HPLC) obtained from Hewlett-Packard, Palo Alto, California. Unless otherwise stated, the liquid phase used was tetrahydrofuran and the standard was polymethyl methacrylate or polystyrene.

[0024] The “Tg” (glass transition temperature) mentioned herein is measured in °C, determined by DSC (Dynamic Differential Scanning Calorimetry).

[0025] "Polydispersity" means weight-average molecular weight according to GPC, divided by GPC number-average molecular weight. The lower the polydispersity (closer to 1), the narrower the desired molecular weight distribution will be.

[0026] “(Meth)acrylate” means acrylate and methacrylate.

[0027] “Polymer solids” means a polymer in its dry state.

[0028] “Crosslinkable component” means a component that includes a compound, polymer or copolymer with functional groups arranged within the polymer backbone, sideways to the polymer backbone, terminally to the polymer backbone or a combination thereof.

[0029] “Crosslinking component” is a component comprising a compound, polymer or copolymer with groups arranged in the polymer backbone, sideways to the polymer backbone, terminally to the polymer backbone, or a combination thereof, wherein these groups can crosslink with the functional groups on the crosslinkable component (during the curing step) to produce a coating in the form of crosslinked structures.

[0030] In coating applications, particularly automotive refinishing or OEM applications, a crucial factor is productivity, i.e., the ability of a layer of a coating composition to dry quickly to a strike-in resistant or non-mixable state, so that a subsequent coating layer, such as a layer formed from a clear coating composition, does not negatively affect the underlying layer. Once the top layer is applied, the multilayer structure or system should then cure sufficiently quickly without negatively affecting the uniformity of color and appearance. The present invention addresses the aforementioned aspects by utilizing a unique crosslinking technology and an additive. Thus, the present coating composition includes a crosslinkable and crosslinking component.

[0031] The crosslinkable component comprises 2% to 25% by weight, preferably 3% to 20% by weight, and more preferably 5% to 15% by weight of one or more acid-functional acrylic copolymers, all percentages being based on the total weight of the crosslinkable component. If the composition contains more than the upper limit of the acid-functional acrylic copolymer, the resulting composition generally exhibits a higher viscosity than required for application. If the composition contains less than the lower limit of the acid-functional copolymer, the resulting coating would generally exhibit negligible strike-in (or mixing) properties for a multilayer structure or system, or for scale or sheet orientation control.

[0032] The crosslinkable component contains an acid-functional acrylic copolymer polymerized from a monomer mixture containing 2% to 12% by weight, preferably 3% to 10% by weight, and more preferably 4% to 6% by weight of monomers containing one or more carboxylic acid groups, all percentages being based on the total weight of the acid-functional acrylic copolymer. If the amount of the carboxylic acid group-containing monomer in the monomer mixture exceeds the upper limit, coatings resulting from such a coating composition would exhibit unacceptable water sensitivity, and if the amount is less than the lower limit, the resulting coating would exhibit negligible strike-in properties for a multilayer structure or system, or for scale orientation control in general.

[0033] The acid-functional acrylic copolymer preferably has a weight-average molecular weight according to GPC in the range of 8,000 to 100,000, more preferably from 10,000 to 50,000, and more preferably from 12,000 to 30,000. The copolymer preferably has a polydispersity in the range of 1.05 to 10.0, more preferably from 1.2 to 8, and more preferably from 1.5 to 5. The copolymer preferably has a Tg range of -5°C to +100°C, more preferably from 0°C to 80°C, and more preferably from 10°C to 60°C.

[0034] The monomers containing carboxylic acid group(s) suitable for use in the present invention include (meth)acrylic acid, crotonic acid, oleic acid, cinnamic acid, glutaconic acid, muconic acid, undecylenic acid, itaconic acid, fumaric acid, maleic acid, or a combination thereof. (Meth)acrylic acid is preferred. It is understandable that the applicants might also consider providing the acid-functional acrylic copolymer with carboxylic acid groups by generating a copolymer polymerized from a monomer mixture containing anhydrides of the aforementioned carboxylic acids and then hydrolyzing such copolymers to provide the resulting copolymer with carboxylic acid groups. Maleic and itaconic anhydrides are preferred. The applicants further consider hydrolyzing such anhydrides in their monomer mixture prior to polymerizing the monomer mixture to give the acid-functional acrylic copolymer.

[0035] It is assumed without guarantee that the presence of carboxylic acid groups in the copolymer of the present invention appears to increase the viscosity of the resulting coating composition due to the physical network formed by the well-known hydrogen bonds of carboxyl groups. As a result, such increased viscosity supports "strike-in" properties in multilayer structures or systems and scale orientation control in general.

[0036] The monomer mixture suitable for use in the present invention comprises 5 percent to 40 percent, preferably 10 percent to 30 percent, of one or more functional (meth)acrylate monomers, all based on the total weight of the acid-functional acrylic copolymer. It should be noted that if the amount of functional (meth)acrylate monomers in the monomer mixture exceeds the upper limit, the pot life of the resulting coating composition is reduced, and if less than the lower limit is used, it negatively affects the coating properties obtained, such as durability. The functional (meth)acrylate monomer is provided with one or more crosslinkable groups selected from a primary hydroxyl, a secondary hydroxyl, or a combination thereof.

[0037] Some suitable hydroxyl-containing (meth)acrylate monomers have the following structure: where RH is methyl and X is a divalent unit, which can be a substituted or unsubstituted C1 to C18 linear aliphatic unit or a substituted or unsubstituted C3 to C18 branched or cyclic aliphatic unit. Some of the suitable substituents include nitrile, amide, halides such as chloride, bromide, fluoride, acetyl, acetoacetyl, hydroxyl, benzyl, and aryl. Some specific hydroxyl-containing (meth)acrylate monomers in the monomer mixture include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0038] The monomer mixture may also include one or more non-functional (meth)acrylate monomers. When used here, non-functional groups are those that do not crosslink with a crosslinking component. Some suitable non-functional C1 to C20 alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, isodecyl (meth)acrylate, and lauryl (meth)acrylate; branched alkyl monomers such as isobutyl (meth)acrylate, tert-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate; and cyclic alkyl monomers, such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Isobornyl (meth)acrylate and butyl acrylate are preferred.

[0039] The monomer mixture may also include one or more other monomers for the purpose of achieving desired properties such as hardness, appearance, and damage resistance. Some examples of such other monomers include styrene, α-methylstyrene, acrylonitrile, and methacrylonitrile. If included, the monomer mixture preferably contains such monomers in the range of 5 percent to 30 percent, all percentages being expressed as weight percent based on the total weight of the polymer solids. Styrene is preferred.

[0040] Any conventional bulk or solution polymerization process can be used to prepare the acid-functional acrylic copolymer of the present invention. One of the suitable processes for preparing the copolymer of the present invention involves free-radical solution polymerization of the monomer mixture described above.

[0041] The polymerization of the monomer mixture can be initiated by adding conventional heat starters, such as azos, exemplified by Vazo® 64, obtained from DuPont Company, Wilmington, Delaware; and peroxides, such as tert-butyl peroxyacetate. The molecular weight of the resulting copolymer can be controlled by adjusting the reaction temperature and the selection and amount of the starter used, as carried out by a person skilled in the art.

[0042] The crosslinking component of the present invention comprises one or more polyisocyanates, melamines, or a combination thereof. Polyisocyanates are preferred.

[0043] Typically, the polyisocyanate is provided with 2 to 10, preferably 2.5 to 8, and more preferably 3 to 5 isocyanate functionalities. Generally, the ratio of isocyanate functional equivalents to the polyisocyanate per equivalent of all the functional groups present in the crosslinking components is in the range of 0.5 / 1 to 3.0 / 1, preferably 0.7 / 1 to 1.8 / 1, and more preferably 0.8 / 1 to 1.3 / 1. Some suitable polyisocyanates include aromatic, aliphatic, or cycloaliphatic polyisocyanates, trifunctional polyisocyanates, and isocyanate-functional adducts of a polyol and difunctional isocyanates.Some of the special polyisocyanates include diisocyanates such as 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-biphenylene diisocyanate, toluene diisocyanate, biscyclohexyl diisocyanate, tetramethylenexylene diisocyanate, ethylethylene diisocyanate, 1-methyltrimethylene diisocyanate, 1,3-phenylene diisocyanate, 1,5-napthalen diisocyanate, bis-(4-isocyanatocyclohexyl)methane and 4,4'-diisocyanatodiphenyl ether.

[0044] Some suitable trifunctional polyisocyanates include triphenylmethane triisocyanate, 1,3,5-benzene triisocyanate, and 2,4,6-toluene triisocyanate. Trimers of diisocyanates, such as the trimer of hexamethylene diisocyanate, marketed under the trade name Desmodur® N-3390 by Bayer Corporation of Pittsburgh, Pennsylvania, and the trimer of isophorone diisocyanate, are also suitable. Furthermore, trifunctional adducts of triols and diisocyanates are also suitable. Trimers of diisocyanates are preferred, and trimers of isophorone and hexamethylene diisocyanates are preferred even more so.

[0045] Typically, the coating composition can include 0.1% to 40% by weight, preferably 15% to 35% by weight, and more preferably 20% to 30% by weight of melamine, the percentages being based on the total weight of composition solids.

[0046] Some of the suitable melamines include monomeric melamine, polymeric melamine-formaldehyde resin, or a combination thereof. The monomeric melamines include low molecular weight melamines containing, on average, three or more methylol groups etherified with a monohydric C1 to C5 alcohol, such as methanol, n-butanol, or isobutanol, per triazine core, and exhibiting a mean degree of condensation up to 2, and preferably in the range of 1.1 to 1.8, and a mononuclear species content of not less than 50% by weight. In contrast, the polymeric melamines have a mean degree of condensation greater than 1.9. Some such suitable monomeric melamines include alkylated melamines, such as methylated, butylated, isobutylated melamines, and mixtures thereof. Many of these suitable monomeric melamines are commercially available. For example, Cytec Industries Inc. supplies..., West Patterson, New Jersey, Cymel® 301 (polymerization level of 1.5, 95% methyl and 5% methylol), Cymel® 350 (polymerization level of 1.6, 84% methyl and 16% methylol), 303, 325, 327, 370 and XW3106, which are all monomeric melamines. Suitable polymeric melamines include high-amino melamine (partially alkylated, -N, -H), known as Resimene® BMP5503 (molecular weight 690, polydispersity of 1.98, 56% butyl, 44% amino), which is sourced from Solutia Inc., St. Louis, Missouri, or Cymel® 1158, supplied by Cytec Industries Inc., West Patterson, New Jersey. Cytec Industries Inc. also supplies Cymel® 1130 with 80 percent solids (polymerization level of 2.5), Cymel® 1133 (48% methyl, 4% methylol and 48% butyl), both of which are polymeric melamines.

[0047] If desired, suitable catalysts contained in the crosslinkable component can accelerate the curing process of a pot mix or mixture of the coating composition.

[0048] If the crosslinking component includes polyisocyanate, the crosslinkable component of the coating composition preferably includes a catalytically active amount of one or more catalysts to accelerate the curing process. Generally, the catalytically active amount of the catalyst in the coating composition is in the range of 0.001 percent to 5 percent, preferably in the range of 0.005 percent to 2 percent, and more preferably in the range of 0.01 percent to 1 percent, all expressed as weight percent based on the total weight of the crosslinkable and crosslinking component solids. A wide variety of catalysts can be used, such as tin compounds, including dibutyltin dilaurate and dibutyltin diacetate; and tertiary amines, such as triethylenediamine. These catalysts can be used individually or in combination with carboxylic acids, such as acetic acid or benzoic acid.One of the commercially available catalysts, marketed under the trademark Fastcat® 4202 Dibutyltin Dilaurate by Arkema North America, Inc. Philadelphia, Pennsylvania, is particularly suitable.

[0049] If the crosslinking component includes melamine, it also preferably includes a catalytically active amount of one or more acidic catalysts to further enhance the crosslinking of the components during curing. Generally, the catalytically active amount of the acidic catalyst in the coating composition is in the range of 0.1 percent to 5 percent, preferably in the range of 0.1 percent to 2 percent, and more preferably in the range of 0.5 percent to 1.2 percent, all expressed as weight percent based on the total weight of crosslinkable and crosslinking component solids. Some suitable acidic catalysts contain aromatic sulfonic acids, such as dodecylbenzenesulfonic acid, para-toluenesulfonic acid, and dinonylnaphthalenesulfonic acid, all of which are either unblocked or blocked with an amine, such as dimethyloxazolidine and 2-amino-2-methyl-1-propanol, N,N-dimethylethanolamine, or a combination thereof.Other acidic catalysts that can be used are strong acids, such as phosphoric acids, especially phenylphosphate, which can be unblocked or blocked with an amine.

[0050] The crosslinkable component of the coating composition can further comprise, in the range of 0.1 percent to 95 percent, preferably in the range of 10 percent to 90 percent, more preferably in the range of 20 percent to 80 percent, and particularly preferably in the range of 30 percent to 70 percent, an acrylic polymer, a polyester, or a combination thereof, all based on the total weight of the crosslinkable component. The applicants have found that by adding one or more of the aforementioned polymers to the crosslinkable component, the resulting coating composition provides a coating with improved run-resistance and flow and leveling properties.

[0051] The acrylic polymer suitable for use in the present invention can have a weight-average molecular weight (GPC) exceeding 2000, preferably in the range of 3000 to 20000 and more preferably in the range of 4000 to 10000. The Tg of the acrylic polymer varies in the range of 0°C to 100°C, preferably in the range of 10°C to 80°C.

[0052] The acrylic polymer suitable for use in the present invention can conventionally be polymerized from typical monomers, such as alkyl (meth)acrylates with alkyl carbon atoms in the range of 1 to 18, preferably in the range of 1 to 12, and styrene and functional monomers, such as hydroxyethyl acrylate and hydroxyethyl methacrylate.

[0053] The polyester suitable for use in the present invention can have a weight-average molecular weight according to GPC exceeding 1500, preferably in the range of 1500 to 100,000, more preferably in the range of 2,000 to 50,000, more preferably in the range of 2,000 to 8,000, and particularly preferably in the range of 2,000 to 5,000. The Tg of the polyester varies in the range of -50°C to +100°C, preferably in the range of -20°C to +50°C.

[0054] The polyester suitable for use in the present invention can be polymerized in the usual manner from suitable polyacids, including cycloaliphatic polycarboxylic acids, and suitable polyols, including polyhydric alcohols. Examples of suitable cycloaliphatic polycarboxylic acids are tetrahydrophthalic acid, hexahydrophthalic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic acid, endomethylenetetrahydrophthalic acid, tricyclodecanedicarboxylic acid, endoethylenehexahydrophthalic acid, camphoric acid, cyclohexanetetracarboxylic acid, and cyclobutanetetracarboxylic acid. The cycloaliphatic polycarboxylic acids can be used not only in their cis form, but also in their trans form and as a mixture of both forms.Examples of suitable polycarboxylic acids that can be used together with the cycloaliphatic polycarboxylic acids, if desired, are aromatic and aliphatic polycarboxylic acids, such as phthalic acid, isophthalic acid, terephthalic acid, halogenated phthalic acids such as tetrachloro- or tetrabromophthalic acid, adipic acid, glutaric acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, trimellitic acid and pyromellitic acid.

[0055] Suitable polyhydric alcohols include ethylene glycol, propanediols, butanediols, hexanediols, neopentyl glycol, diethylene glycol, cyclohexanediol, cyclohexanedimethanol, trimethylpentanediol, ethylbutylpropanediol, ditrimethylolpropane, trimethylolethane, trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol, tris(hydroxyethyl) isocyanate, polyethylene glycol, and polypropylene glycol. If desired, monohydric alcohols, such as butanol, octanol, lauryl alcohol, ethoxylated or propoxylated phenols, may also be included together with polyhydric alcohols. Details of polyesters suitable for use in the present invention are further provided in U.S. Patent No. 5,326,820, which is incorporated herein by reference. One commercially available polyester that is particularly preferred is SCD@-1040 polyester, sourced from Etna Product Inc., Chagrin Falls, Ohio.

[0056] The crosslinkable component may further include one or more reactive oligomers, such as those reactive oligomers disclosed in US 6,221,494, which are incorporated herein by this notice; and non-alicyclic (linear or aromatic) oligomers, if desired. Such non-alicyclic oligomers may be prepared using non-alicyclic anhydrides, such as succinic or phthalic anhydrides, or mixtures thereof. Caprolactone oligomers described in US 5,286,782, which are incorporated herein by this notice, may also be used.

[0057] The crosslinkable component of the coating composition may further include one or more modifying resins, also known as non-aqueous dispersions (NADs). Such resins are sometimes used to adjust the viscosity of the resulting coating composition. The amount of modifying resin that can be used is typically in the range of 10 percent to 50 percent, with all percentages based on the total weight of crosslinkable component solids. The weight-average molecular weight of the modifying resin is generally in the range of 20,000 to 100,000, preferably in the range of 25,000 to 80,000, and more preferably in the range of 30,000 to 50,000.

[0058] The crosslinkable or crosslinking component of the coating composition of the present invention typically contains at least one organic solvent, typically selected from the group consisting of aromatic hydrocarbons, such as petroleum naphtha or xylenes; ketones, such as methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone, or acetone; esters, such as butyl acetate or hexyl acetate; and glycol ether esters, such as propylene glycol monomethyl ether acetate. The amount of organic solvent added depends on the desired solids content and the desired amount of VOCs in the composition. If desired, the organic solvent can be added to both components of the binder. A coating composition with a high solids content and low VOCs is preferred.

[0059] The applicants have surprisingly found that when the low-curing-temperature control element described below is included with either the crosslinkable component, the crosslinking component, or both of the coating composition (preferably with the crosslinkable component), the runoff resistance of the layer applied to a substrate surface can be improved under the low-curing-temperature condition, which is the desired result of the present invention. The low-curing-temperature control element of the present invention includes a rheology component. In an exemplary embodiment, the rheology component includes an amorphous silica gel, a clay, or a combination of both.In another exemplary embodiment, the control means for a low curing temperature includes 0.1 wt% to 10 wt%, preferably 0.3 wt% to 5 wt%, more preferably 0.5 wt% to 2 wt% of the rheology component, and in the range of 0.1 wt% to 10 wt%, more preferably in the range of 0.3 wt% to 5 wt% and more preferably in the range of 0.5 wt% to 2 wt% of polyurea, wherein the wt% percentages are based on the total weight of the crosslinkable and crosslinking components of the low-curing coating composition of the present invention.If too little silica gel and polyurea are used (less than the areas mentioned above), no advantage can be seen, and if too much silica gel and polyurea are used (more than the areas mentioned above), the resulting coating surface will be rough.

[0060] The amorphous silica gel suitable for use in the present invention includes colloidal silica gel which has been partially or completely surface-modified by the silanization of hydroxyl groups on the silica gel particles, thereby rendering part or all of the silica gel particle surface hydrophobic. Examples of suitable hydrophobic silica gel include AEROSIL R972, AEROSIL R812, AEROSIL OK412, AEROSIL TS-100, and AEROSIL R805, all of which are commercially available from Evonik Industries AG, Essen, Germany. Pyrogenic silica gel from Evonik Industries AG, Essen, Germany, available as AEROSIL R 812, is particularly preferred. Other commercially available silica gels include SIBELITE® M3000 (Cristobalite), SIL-CO-SIL®, milled silica gel, MIN-U-SIL®, micronized silica gel, all sourced from US Kieselgel Company, Berkeley Springs, West Virginia.

[0061] The silica gel can be dispersed in the copolymer by a milling process using conventional equipment such as high-speed blade mixers, ball mills, or sand mills. Preferably, the silica gel is dispersed separately in the previously described acrylic polymer, and then the dispersion can be added to the crosslinkable component of the coating composition.

[0062] The clay suitable for use herein may include clay, dispersed clay, or a combination thereof. Examples of commercially available clay products include bentonite clay, available as BENTONE® from Elementis Specialties, London, UK, and GARAMITE® clay, available from Southern Ton Products, Gonzales, TX, USA, under appropriately registered trademarks. BENTONE® 34 dispersion, described in U.S. Patent No. 8,357,456, and GARAMITE® dispersion, described in U.S. Patent No. 8,227,544, and a combination of the two are suitable. A combination of silica gel and clay, such as the aforementioned BENTONE®, GARAMITE®, or dispersions thereof, may also be used.

[0063] The polyurea suitable for use in the low-temperature control agent is obtained from the polymerization of a monomer mixture comprising 0.5 to 3 wt. percent of amine monomers, 0.5 to 3 wt. percent of isocyanate monomers, and 94 to 99 wt. percent of a moderating polymer. The amine monomer is selected from the group consisting of a primary amine, secondary amine, ketimine, aldimine, or a combination thereof. Benzylamine is preferred. The isocyanate monomer is selected from the group consisting of an aliphatic polyisocyanate, cycloaliphatic polyisocyanate, aromatic polyisocyanate, and a combination thereof. The preferred isocyanate monomer is 1,6-hexamethylene diisocyanate. The moderating polymer may be one or more of the polymers described above. Acrylic polymers or polyesters are preferred.

[0064] Preferably, the polyurea is produced by mixing one or more of the moderating polymers with the amine monomers and then adding isocyanate monomers over time under ambient conditions.

[0065] The sag resistance of a layer made from a pot mix, resulting from blending the crosslinkable and crosslinking components of the coating composition, when applied to a substrate, ranges from 5 mils (127 micrometers) to 20 mils (508 micrometers) when measured using ASTM test D4400-99. The higher the number, the greater the desired sag resistance.

[0066] The coating composition is preferably formulated as a two-component coating composition, wherein the crosslinkable component is stored in a separate container from the crosslinking component, which are mixed to form a pot mix or a mixing batch shortly before use.

[0067] The coating composition is preferably formulated as an automotive OEM composition or as an automotive repair composition. These compositions can be applied to a substrate as a basecoat or as a pigmented single-coat topcoat. These compositions require the presence of pigments. Typically, a pigment-to-binder ratio of 1.0 / 100 to 200 / 100 is used, depending on the color and type of pigment applied. The pigments are formulated in granules by conventional methods such as milling, sand milling, and high-speed blending. Generally, the granules comprise pigment and a dispersant in an organic solvent. The granules are added to the coating composition in an appropriate quantity and blended to form a pigmented coating composition.

[0068] Any of the commonly used organic and inorganic pigments, such as white pigments (e.g., titanium dioxide), colored pigments, metallic flakes (e.g., aluminum flakes), special effect pigments (e.g., coated mica flakes and coated aluminum flakes), and extender pigments, can be used.

[0069] The coating composition may also include other conventional formulation additives, such as wetting agents, leveling agents, and flow control agents, for example, Resiflow® S (polybutyl acrylate), BYK® 320 and 325 (high molecular weight polyacrylates), BYK® 347 (polyether-modified siloxane), defoamers, surfactants, and emulsifiers to aid in stabilizing the composition. Other additives, which generally improve damage resistance, may be included, such as silsesquioxanes and other silicate-based microparticles.

[0070] To improve the weather resistance of the clear finish of the coating composition, 0.1% to 5% by weight, based on the weight of the composition solids, of an ultraviolet light stabilizer or a combination of ultraviolet light stabilizers and absorbers may be added. These stabilizers include ultraviolet light absorbers, screeners, quenchers, and special hindered amine light stabilizers. Likewise, 0.1% to 5% by weight, based on the weight of the composition solids, of an antioxidant may also be added. Most of the aforementioned stabilizers are sourced from BASF, Florham Park, NJ.

[0071] The coating composition of the present invention is preferably formulated as a two-component coating composition. The present invention is particularly suitable as a basecoat for outdoor objects, such as motor vehicles and other vehicle body parts. A typical motor vehicle or truck body is manufactured from a sheet steel or a plastic or composite substrate. For example, the fenders may be made of plastic or a composite material, and the main body part may be made of steel. When steel is used, it is first treated with an inorganic corrosion inhibitor, such as zinc or iron phosphate, called an E-coating, and then a primer coating is generally applied by electroplating.Typically, these electrodeposition primers are epoxy-modified resins crosslinked with a polyisocyanate and applied by a cathodic electrodeposition process. Optionally, a primer can be applied over the electrodeposition primer, usually by spraying, to provide a better appearance and / or improved adhesion of a basecoat or monocoat to the primer.

[0072] The present invention also relates to a method for producing a multilayer structure or system on a substrate. The method includes the following process steps: The crosslinkable component of the coating composition described above is mixed with the crosslinking component of the coating composition to form a pot mix or mixing batch. Generally, the crosslinkable component and the crosslinking component are mixed shortly before application to form a pot mix or mixing batch. Mixing can take place via a conventional mixing nozzle or separately in a container.

[0073] A layer of the pot-mix is ​​generally applied to a substrate, such as a motor vehicle body or chassis, with a thickness ranging from 15 to 200 micrometers. This substrate may have been pre-coated with a conventional e-coating followed by a conventional primer. The preceding application step can be conventionally carried out by spraying, electrostatic spraying, a commercially available robotic spraying system, roller coating, dipping, flooding, or brushing the pot-mix onto the substrate. After application, the layer is allowed to evaporate, i.e., be exposed to air, to reduce the solvent content of the pot-mix layer, thus producing a strike-in resistant or non-mixable layer. The evaporation period ranges from 5 to 15 minutes.Then, a layer of a conventional clearcoat composition with a thickness in the range of 15 micrometers to 200 micrometers is applied in the usual manner by the previously described applicator over the strike-in resistant or non-mixable layer to form a multilayer system on the substrate. Any suitable conventional clearcoat compositions can be used in the multilayer structure or system of the present invention. For example, clearcoats suitable for use over the basecoat of this invention include a solvent-based clearcoat composition containing organosilane polymers, disclosed in US 5,244,696; a solvent-based clearcoat composition crosslinked with polyisocyanate, disclosed in US 6,433,085; and clear thermosetting compositions containing epoxy-functional polymers, disclosed in US 6,485,788; all of which are included herein by reference.

[0074] In another variant, a layer of the pot-mix, generally with a thickness ranging from 15 to 200 micrometers, is applied to a substrate, such as a motor vehicle body or a motor vehicle body pre-coated with a conventional e-coating followed by a conventional primer. The preceding application step can be conventionally carried out by spraying, electrostatic spraying, a commercially available robotic spraying system, roller coating, dipping, flooding, or brushing the pot-mix onto the substrate. After application, the layer is allowed to evaporate, i.e., be exposed to air, to reduce the solvent content of the pot-mix layer, thus producing a strike-in resistant layer. The duration of the evaporation step is in the range of 5 to 15 minutes.

[0075] Unless explicitly stated otherwise below, features of this variant will be described preferentially.

[0076] In some embodiments, one or more layers of a conventional clearcoat composition with a thickness in the range of 15 micrometers to 200 micrometers are applied in a conventional manner by the previously described applicator over the strike-in resistant or non-mixing layer to form a multilayer system on the substrate. As with the application of multiple layers of basecoat, a flash-off time, such as 60-120 seconds, may be required between the application of a first and second layer of clearcoat. Any suitable conventional clearcoat composition can be used in the multilayer structure or system of the present invention.For example, suitable clearcoats for use over the basecoat of this invention include a solvent-based clearcoat composition containing organosilane polymers, disclosed in US 5,244,696; a solvent-based polyisocyanate crosslinked clearcoat composition, disclosed in US 6,433,085; and clear thermosetting epoxy-functional polymer-containing compositions, disclosed in US 6,485,788; all of the preceding patents being incorporated herein by reference.

[0077] Some embodiments described herein employ a crosslinkable clearcoat composition comprising an acrylic copolymer (i.e., an acrylic resin) polymerized from a monomer mixture including monomers containing ethylene-unsaturated hydroxyl functionality. The clearcoat composition of this disclosure may comprise one or more acrylic copolymers having primary and secondary hydroxyl groups. In one example, the acrylic copolymers may comprise an acrylic polymer polymerized from a monomer mixture comprising a first acrylic monomer comprising a primary hydroxyl group and a second acrylic monomer comprising a secondary hydroxyl group. In another example, the acrylic copolymers may comprise an acrylic polymer comprising both primary and secondary hydroxyl groups.In yet another example, a mixture of polymers with primary and secondary hydroxyl groups can also be suitable. A polymer containing primary hydroxyl groups can be polymerized from monomers with primary hydroxyl groups. A polymer containing secondary hydroxyl groups can be polymerized from monomers with secondary hydroxyl groups. A polymer containing both primary and secondary hydroxyl groups can be polymerized from a mixture of monomers containing both primary and secondary hydroxyl groups. Monomeric isoforms with mixed primary and secondary hydroxyl groups can also be suitable.The ratio of primary and secondary hydroxyl groups in the clear coat composition can be adjusted by polymerizing acrylic polymers of a predetermined ratio of monomers, which in one example have the primary and secondary hydroxyl groups, or in another example by mixing predetermined amounts of one or more polymers having the primary hydroxyl groups with one or more polymers having secondary hydroxyl groups, or a combination thereof.

[0078] Monomers containing ethylene-unsaturated hydroxy functionality include hydroxyalkyl acrylates and hydroxyalkyl methacrylates, wherein the alkyl group has 1 to 4 carbon atoms. Suitable monomers include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyisopropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyisopropyl methacrylate, hydroxybutyl methacrylate, and the like, as well as mixtures thereof. In some embodiments, the clear lacquer coating composition comprises primary hydroxyl groups and secondary hydroxyl groups in a ratio of 30:70 to 80:20, such as 35:65 to 75:25, such as 40:60 to 70:30, such as 45:55 to 70:30, such as 50:50 to 70:30, such as 55:65 to 70:30, such as 60:40 to 70:30, such as 65:35 to 70:30.

[0079] In some embodiments, the acrylic copolymer component of the clear coat composition comprises a single acrylic resin. In alternative embodiments, the acrylic copolymer component comprises a variety of acrylic resins. In some embodiments, the acrylic copolymer component comprises an acrylic resin with a Tg (theoretical) of 45°C to 95°C, such as 55°C to 85°C, or 65°C to 75°C. Emphasis is placed on the fact that in embodiments in which the acrylic copolymer component comprises a variety of acrylic resins, the types and relative amounts of monomers present in each acrylic resin may be selected such that the cumulative primary and secondary hydroxyl groups in the clear coat composition are in a ratio of 30:70 to 80:20, such as 35:65 to 75:25, such as 40:60 to 70:30, such as 45:55 to 70:30, such as 50:50 to 70:30, such as 55:65 to 70:30, such as 60:40 to 70:30, such as 65:35 to 70:30.In some embodiments, where the acrylic copolymer component comprises a plurality of acrylic resins, the acrylic copolymer component comprises a first acrylic resin having a primary to secondary hydroxyl group ratio of 45:55 to 80:20. In some embodiments, where the acrylic copolymer component comprises a plurality of acrylic resins, the acrylic copolymer component comprises an acrylic resin with a Tg (theoretical) of 25°C to 95°C, such as 55°C to 85°C, or 65°C to 75°C.

[0080] Surprisingly, it was found that certain combinations of basecoat and clearcoat, such as those combinations comprising a basecoat as described herein and a clearcoat coating composition comprising primary hydroxyl groups and secondary hydroxyl groups in a ratio of 30:70 to 80:20, such as 35:65 to 75:25, such as 40:60 to 70:30, such as 45:55 to 70:30, such as 50:50 to 70:30, such as 55:65 to 70:30, such as 60:40 to 70:30, such as 65:35 to 70:30, interact advantageously, such that a multi-layer coating with improved properties is provided. In embodiments, a basecoat / clearcoat multi-layer system can be cured under suitable conditions, such as 160°F for a suitable period of time, such as 20 minutes, to provide a hard, dry film.In particular, a multi-layer system as described herein exhibited an R-value (orange peel effect) of less than 6, such as 4 to 6, for a dry film thickness of 1.5 mils (as measured by ASTM D3451). In some embodiments, some multi-layer compositions as described herein exhibited a Distinctness of Image (DOI) value greater than 85 (e.g., 85 to 95), such as greater than 89 (e.g., 89 to 95), for a film thickness of 1.5 mils (as measured by ASTM D5767). In some embodiments, some multi-layer compositions as described herein exhibited gloss values ​​of at least 88 (e.g., 88 to 95) at 20°C and at least 90 (e.g., 90 to 99) at 60°C for a dry film thickness of 1.8 mils. In some embodiments, certain multi-layer compositions as described herein exhibited a shortwave value of less than 30 (e.g., 30 to 25) on a wave scan, such as less than 27 (e.g., 27 to 25) for a dry film of 1.8 mils. The base coating is clear.

[0081] It should be noted that the present invention, if desired, also includes a method for applying one or more layers of the basecoat pot mix or mixture described above, followed by the application of one or more layers of the clearcoat composition described above (i.e., a clearcoat composition with primary and secondary hydroxyl groups in a ratio of 30:70 to 80:20, such as 35:65 to 75:25, such as 40:60 to 70:30, such as 45:55 to 70:30, such as 50:50 to 70:30, such as 55:65 to 70:30, such as 60:40 to 70:30, such as 65:35 to 70:30), which is then cured to produce a multi-layer coating on a substrate, which may contain other previously applied coatings, such as an e-coating or a Primer coat, whether it can be included or not.

[0082] The following applies to all embodiments and variants of the present invention.

[0083] The multi-layer system is then cured to form the multi-layered structure or system under low curing temperatures. In typical automotive OEM applications, the multi-layer system can typically be cured at low curing temperatures in 10 to 60 minutes. It is understood that the actual curing time may depend on the thickness of the applied layer, the curing temperature, humidity, and any additional mechanical aids, such as blowers, which help to continuously circulate air over the coated substrate to accelerate the curing rate. It is also understood that the actual curing temperature would vary depending on the catalyst and its quantity, the thickness of the layer to be cured, and the amount of the crosslinking component used.For example, the hardening step can be accelerated by adding a catalytically active amount of a catalyst or acidic catalyst to the composition.

[0084] It should be noted that the present invention, if desired, also includes a method for applying a layer of the above-described pot mix or mixture, which is then cured to produce a coating, such as a base coat, on a substrate which may or may not include other previously applied coatings, such as an e-coating or a primer.

[0085] Suitable substrates for applying the coating composition of the present invention include, but are not limited to, motor vehicle bodies and any items manufactured and painted by motor vehicle suppliers, longitudinal beams, truck and heavy-duty vehicle bodies, including beverage trucks, pickup truck beds, ready-mix concrete mixer bodies, waste disposal vehicle bodies and fire and emergency vehicle bodies, as well as any potential accessories or components for such truck bodies, buses, agricultural and construction equipment, truck covers and covers, truck trailers, car trailers, motorhomes, including but not limited to large motorhomes, caravans, campervans, vans, horse-drawn carriages, houseboats, snowmobiles, off-road vehicles, passenger watercraft, motorcycles, boats and aircraft.The substrate further includes industrial and commercial new construction and maintenance work; cement and wood flooring; leather; walls of commercial and residential buildings, such as office buildings and houses; amusement park equipment; concrete surfaces, such as parking lots and driveways; asphalt and concrete road surfaces; wood substrates; ship surfaces; outdoor structures, such as bridges and towers; coil coating; passenger train carriages; printed circuit boards; machinery; OEM tools; signage; fiberglass carriers; sporting goods; and sports equipment.

[0086] Preferred embodiments of the present invention are described in the following paragraphs. 1. A low-temperature curable coating composition comprising: a crosslinkable component comprising an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 percent to 12 percent of monomers containing one or more carboxylic acid group(s), the percentages being based on the total weight of the acid-functional acrylic copolymer; a crosslinking component; and a low-temperature control agent comprising a rheology component selected from an amorphous silica gel, a clay, or a combination thereof, the rheology component being present in an amount of 0.1 to 10 percent by weight; and 0.1 to 10 percent by weight of polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components. 2. The coating composition of paragraph 1, wherein the acid-functional acrylic copolymer has a weight-average molecular weight according to GPC in the range of 8000 to 100000 and a polydispersity in the range of 1.05 to 10.0. 3. The coating composition of paragraph 1 or 2, wherein the acid-functional acrylic copolymer has a Tg in the range of -5°C to +100°C. 4. The coating composition of paragraph 1, wherein the monomer mixture comprises one or more functional (meth)acrylate monomers and one or more non-functional (meth)acrylate monomers. 5. The coating composition of paragraph 4, wherein the monomer mixture comprises 5 percent to 40 percent, based on the total weight of the acid-functional acrylic copolymer, of the functional (meth)acrylate monomers. 6. The coating composition of paragraph 5, wherein the functional (meth)acrylate monomer is provided with one or more crosslinkable groups selected from the group consisting of a primary hydroxyl, secondary hydroxyl and a combination thereof. 7. The coating composition of paragraph 5, wherein the functional (meth)acrylate monomer is selected from the group consisting of hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyisopropyl (meth)acrylate, hydroxybutyl (meth)acrylate and a combination thereof. 8. The coating composition of paragraph 1, wherein the monomer containing the carboxylic acid group(s) comprises one or more carboxylic acids selected from the group consisting of (meth)acrylic acid, crotonic acid, oleic acid, cinnamic acid, glutaconic acid, muconic acid, undecylenic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid and a combination thereof. 9. The coating composition of paragraph 1, wherein the crosslinking component comprises a polyisocyanate, melamine or a combination thereof. 10. The coating composition of paragraph 1, wherein the polyurea is produced by polymerizing a monomer mixture comprising one or more amine monomers, one or more isocyanate monomers and one or more moderating polymers. 11. The coating composition of paragraph 10, wherein the amine monomer is selected from the group consisting of a primary amine, secondary amine, ketimine, aldimine or a combination thereof. 12. The coating composition of paragraph 10, wherein the isocyanate monomer is selected from the group consisting of an aliphatic polyisocyanate, cycloaliphatic polyisocyanate, aromatic polyisocyanate and a combination thereof. 13. The coating composition of paragraph 10, wherein the monomer mixture comprises 0.5 to 3 percent by weight of the amine monomer and 0.5 to 3 percent by weight of the isocyanate monomer, the percentages by weight being based on the total weight of the crosslinkable component. 14. The coating composition of paragraph 10, formulated as a two-component coating composition, wherein the crosslinkable component and the crosslinking component are stored in separate containers. 15. The coating composition of paragraph 10, formulated as a motor vehicle OEM composition, motor vehicle repair composition or industrial coating composition. 16. The coating composition of paragraph 1, wherein the crosslinkable component comprises between 2% and 25% by weight of the acid-functional acrylic copolymer, all percentages being based on the total weight of the crosslinkable component. 17. Method for producing a coating on a substrate, comprising: (a) mixing a crosslinkable component, a crosslinking component and a low-curing-temperature control agent of a low-curing-temperature coating composition to form a pot mix or(a) Mixture, wherein the crosslinkable component comprises an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 wt% to 12 wt% of carboxylic acid group(s) containing monomer, based on the total weight of the acid-functional acrylic copolymer, and wherein the low-curing temperature control agent is a rheology component selected from an amorphous silica gel, a clay, or a combination thereof, wherein the rheology component is present in an amount of 0.1 wt% to 10 wt% and comprises 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components; (b) applying a layer of the pot mix or mixture to the substrate; and (c) curing the layer at a low-curing temperature to form the coating on the substrate. 18. The method of paragraph 16, wherein the low curing temperature is in the range of 60°F (15°C) to 200°F (93°C). 19. The method of paragraph 16, wherein the substrate is a motor vehicle body, industrial equipment or construction equipment.

[0087] Preferred embodiments of the present invention are described in the following paragraphs. 1. A multi-layer coating system comprising: a low-temperature curable coating composition comprising: a crosslinkable component comprising an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 percent to 12 percent of monomers containing one or more carboxylic acid group(s), the percentages being based on the total weight of the acid-functional acrylic copolymer; a crosslinking component; and a low-temperature control agent comprising a rheology component selected from an amorphous silica gel, a clay, or a combination thereof, the rheology component being present in an amount of 0.1 to 10 percent by weight; and 0.1 to 10 percent by weight of polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components.and a clearcoat composition comprising an acrylic copolymer component comprising one or more acrylic polymers, wherein the clearcoat composition comprises primary hydroxyl and secondary hydroxyl groups in a ratio of 30:70 to 80:20 and wherein the clearcoat composition is placed above and in contact with the curable basecoat composition for a low curing temperature. 2. The multi-layer coating composition of paragraph 1, wherein the acrylic copolymer comprises an acrylic polymer polymerized from a monomer mixture comprising a hydroxyalkyl acrylate, a hydroxyalkyl methacrylate or a mixture thereof, wherein an alkyl group in the hydroxyalkyl acrylate and / or hydroxyalkyl methacrylate has 1 to 4 carbon atoms. 3. The multi-layer coating composition of paragraph 1, wherein the acrylic copolymer of the clearcoat coating composition comprises an acrylic polymer polymerized from a monomer mixture comprising hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyisopropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyisopropyl methacrylate, hydroxybutyl methacrylate or a mixture thereof. 4. The multi-layer coating composition of paragraph 1, wherein the acrylic copolymer of the clearcoat coating composition comprises an acrylic polymer polymerized from a monomer mixture comprising styrene, isobutyl methacrylate (IBMA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA) or a mixture thereof. 5. The multi-layer coating composition of paragraph 1, wherein the acrylic copolymer of the clear lacquer coating composition comprises a single acrylic resin. 6. The multi-layer coating composition of paragraph 1, wherein the acrylic copolymer of the clear lacquer coating composition comprises a variety of acrylic resins. 7. The multi-layer coating composition of paragraph 1, wherein the acrylic copolymer of the clear lacquer coating composition comprises an acrylic resin having a theoretical glass transition temperature (Tg (theoretical)) of 25°C to 95°C. 8. The multi-layer coating composition of paragraph 1, wherein the acrylic copolymer of the clear lacquer coating composition comprises an acrylic resin having a ratio of primary hydroxyl groups to secondary hydroxyl groups of 35:65 to 75:25. 9. A method for producing a multi-layer coating on a substrate, comprising: (a) mixing a crosslinkable component, a crosslinking component and a control agent for a baking temperature to produce a basecoat pot mix orto form a mixture, wherein the crosslinkable component comprises an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 wt% to 12 wt% of carboxylic acid group(s) containing monomer, based on the total weight of the acid-functional acrylic copolymer, and wherein the control agent for a curing temperature is a rheology component selected from an amorphous silica gel, a clay or a combination thereof, wherein the rheology component is present in an amount of 0.1 wt% to 10 wt% and comprises 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components; (b) applying a layer of the basecoat pot mix or-mixture onto the substrate; (c) applying a layer of a clearcoat coating composition, spread over and in contact with a layer of the basecoat pot mix or mixture to form a multi-layer coating composition, wherein the clearcoat coating composition comprises an acrylic copolymer component comprising one or more acrylic polymers, wherein the clearcoat coating composition comprises primary hydroxyl and secondary hydroxyl groups in a ratio of 30:70 to 80:20; and (d) curing the multi-layer coating composition on the substrate. 10. The method of paragraph 17, wherein applying a layer of the basecoat pot mix or mixing mixture includes applying a plurality of layers of the basecoat pot mix or mixing mixture, applying a layer of a clearcoat composition, applying a plurality of layers of the clearcoat composition, or both. 11. The method of paragraph 17, wherein the hardening is carried out at a curing temperature of 60°F (15°C) to 200°F (93°C). 20. The method of paragraph 17, wherein the substrate is a motor vehicle body, industrial equipment or construction equipment. EXAMPLES of testing procedures

[0088] Runoff resistance: Runoff resistance was measured using ASTM test D4400-99.

[0089] Distinctness-of-Image (DOI): DOI was measured using a Hunterlab RS 232 model (HunterLab, Reston, VA).

[0090] Surface roughness: The orange peel (R) of basecoat dry film was measured using ASTM D3451. Process 1: Production of acrylic polymers

[0091] Acrylic polymers were formed, as described above, by similar free-radical copolymerization with different monomer ratios, as described below. A reactor equipped with a stirrer, reflux condenser, and under nitrogen was charged with 13.7 parts of tert-butyl acetate and heated under reflux at approximately 96°C. A monomer mixture of 14.6 parts by weight of methyl methacrylate, 5.9 parts by weight of styrene, 11.7 parts by weight of hydroxyethyl methacrylate, 14.6 parts by weight of n-butyl methacrylate, 11.7 parts by weight of 2-ethylhexyl methacrylate, and 1.2 parts by weight of tert-butyl acetate was premixed. A starter mixture of 3.4 parts Vazo®67 heat starter (Vazo®67 is available from E.I. DuPont de Nemours and Company, Wilmington, Delaware, USA) and 23.2 parts tert-butyl acetate was premixed. The monomer mixture was fed simultaneously with the starter mixture under reflux for 360 minutes. The starter mixture continued to be fed for 390 minutes.After the starter mixture had been completely added, the reaction mixture was held under reflux for 60 minutes and then cooled to room temperature.

[0092] The acrylic polymer obtained herein had the following properties: a calculated Tg of + 17.6°C, solids content 60%, Gardner-Holdt viscosity Y + 1 / 4, and weight mean molecular weight (Mw) of 10000. Method 2: Production of polyurea

[0093] In a reactor, 1.7 parts by weight of benzylamine (available from BASF, Florham Park, NJ) were added to 1.34 parts by weight of 1,6-hexamethylene diisocyanate in the presence of 96.36 parts by weight of the acrylic polymer (Tg = 17.6°C) from Process 1. The mixture was stirred for 5 minutes to produce the polyurea. Method 3: Production of control devices for a low firing temperature

[0094] In a conventional milling apparatus, 9 parts by weight of Aerosil® R 805 calcined silica gel powder, obtained from Evonik Industries AG, Essen, Germany, were milled with 30 parts by weight of the acrylic polymer from Process 1 and 61 parts by weight of butyl acetate to a fineness of 7.5 to 8.0, as measured on a Hegman gauge. Then, 50 parts by weight of this silica gel dispersion were mixed with 50 parts by weight of the polyurea from Process 2 to produce the low-temperature control agent of the present invention. The BENTONE® dispersion, GARAMITE® dispersion, or a combination thereof can also be mixed at 50 parts by weight with 50 parts by weight of the polyurea. A combination of the silica gel dispersion, BENTONE® dispersion, and GARAMITE® dispersion can also be used.

[0095] The tables below show the wording of the comparative examples and an example of the present invention:

[0096] [Base coat with a dry-cured coating thickness of 1.5 mils (38.1 micrometers), coated with Imron® Elite clear coat with a dry-cured coating thickness of 2 mils (50.8 micrometers), both simultaneously baked-cured for 30 minutes at a high baking temperature of 180°F (82.2°C)] Table 1 Coating system of comparative example 1 Basecoat components in grams Polyurea binder, produced by process 2 0 Control device for a low firing temperature, produced by process 3 0 silica gel dispersion (1) 0 Acid-functional acrylic copolymer (2) 250 Polyester (3) 197 Imron ® Yellow tint PT 144 3 Imron ® magenta tint PT 164 6 Imron® Black tint PT 105 19 Imron® Transparent Yellow Oxide Tint PT 183 101 Imron® medium-fine aluminum tint PT 110 159 Ethyl acetate from Eastman Chemical, Kingsport, Tennessee 65 Imron® Activator 15305S (in crosslinking component) 250 in total 1051 Test results Basecoat runoff dry film thickness 2 mils (50.8 micrometers) R (orange peel) at BC dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D3451 5 DOI for basecoat dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D5767 65 Test observations weak runoff resistance

[0097] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware. Note: (1) The silica gel dispersion was produced in accordance with US Patent Publication 2006 / 0047051, Table 6,

[0080] -

[0081] , incorporated herein by this reference. (2) The acid-functional acrylic copolymer was prepared according to Acid-functional Acrylic Copolymer 2: Styrene / Butyl Acrylate / 2-Ethylhexyl Acrylate / Isobornyl Acrylate / Hydroxypropyl Methacrylate / 2-Hydroxyethyl Methacrylate / Methacrylic Acid: 15.0 / 30.0 / 20.0 / 15.0 / 7.5 / 7.5 / 5.0 wt%. The polymer solution obtained was clear and had a solids content of about 65.5% and a Gardner-Holt viscosity of W-1 / 2. The polymer had a GPC Mw of 15.049 and a GPC Mn of 4.789, based on GPC using polystyrene as the standard, and a Tg of +3.7°C, as measured by DSC, as described in [reference to document], incorporated herein by this notice. (3) Polyester was produced in accordance with , Table 5,

[0078] -

[0079] , incorporated herein by this reference.

[0098] [Base coat with a dry-cured coating thickness of 1.5 mils (38.1 micrometers), coated with Imron® Elite clear coat with a dry-cured coating thickness of 2 mils (50.8 micrometers), both simultaneously baked-cured for 30 minutes at a high baking temperature of 180°F (82.2°C)] Table 2 Coating system of comparison example 2 Basecoat components in grams Polyurea binder, produced by process 2 0 Control device for a low firing temperature, produced by process 3 0 silica gel dispersion (1) 224 Acid-functional acrylic copolymer (2) 76 Polyester (3) 146 Imron ® Yellow tint PT 144 3 Imron ® magenta tint PT 164 6 Imron® Black tint PT 105 19 Imron® Transparent Yellow Oxide Tint PT 183 101 Imron® medium-fine aluminum tint PT 110 159 Ethyl acetate from Eastman Chemical, Kingsport, Tennessee 65 Imron® Activator 15305S (in crosslinking component) 250 in total 1049 Test results Basecoat runoff dry film thickness 4 mils (101.6 micrometers) R (orange peel) at BC dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D3451 5 DOI for basecoat dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D5767 75 Test observations Good runoff resistance, very smooth, and good DOI.

[0099] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware.

[0100] Note: (1)-(3) are the same as in Table 1.

[0101] [Base coat with a dry-cured coating thickness of 1.5 mils (38.1 micrometers), coated with Imron® Elite clear coat with a dry-cured coating thickness of 2 mils (50.8 micrometers), both simultaneously baked-cured for 30 minutes at a high baking temperature of 180°F (82.2°C)] Table 3 Coating system of comparative example 3 Basecoat components in grams Polyurea binder, produced by process 2 400 Control device for a low firing temperature, produced by process 3 0 silica gel dispersion (1) 0 Acid-functional acrylic copolymer (2) 0 Polyester (3) 50 Imron ® Yellow tint PT 144 3 Imron ® magenta tint PT 164 6 Imron® Black tint PT 105 19 Imron® Transparent Yellow Oxide Tint PT 183 101 Imron® medium-fine aluminum tint PT 110 159 Ethyl acetate from Eastman Chemical, Kingsport, Tennessee 65 Imron® Activator 15305S (in crosslinking component) 250 in total 1054 Test results Basecoat runoff dry film thickness 3 mils (76.2 micrometers) R (orange peel) at BC dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D3451 6 DOI for basecoat dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D5767 78 Test observations Good runoff resistance, very smooth, and good DOI.

[0102] Note: (1)-(3) are the same as in Table 1.

[0103] [Base coat with a dry-cured coating thickness of 1.5 mils (38.1 micrometers), coated with Imron® Elite clear coat with a dry-cured coating thickness of 2 mils (50.8 micrometers), both simultaneously baked-cured for 20 minutes at a low baking temperature of 160°F (71.1°C)] Table 4 Coating system of comparison example 4 Basecoat components in grams Polyurea binder, produced by process 2 0 Control device for a low firing temperature, produced by process 3 0 silica gel dispersion (1) 0 Acid-functional acrylic copolymer (2) 250 Polyester (3) 197 Imron ® Yellow tint PT 144 3 Imron ® magenta tint PT 164 6 Imron® Black tint PT 105 19 Imron® Transparent Yellow Oxide Tint PT 183 101 Imron® medium-fine aluminum tint PT 110 159 Ethyl acetate from Eastman Chemical, Kingsport, Tennessee 65 Imron® Activator 15305S (in crosslinking component) 250 in total 105149 Test results Basecoat runoff dry film thickness 1 mil (25.4 micrometers) R (orange peel) at BC dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D3451 4 DOI for basecoat dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D5767 50 Test observations weak expiry time and reduction of DOI

[0104] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware.

[0105] [Base coat with a dry-cured coating thickness of 1.5 mils (38.1 micrometers), coated with Imron® Elite clear coat with a dry-cured coating thickness of 2 mils (50.8 micrometers), both simultaneously baked-cured for 20 minutes at a low baking temperature of 160°F (71.1°C)] Table 5 Coating system of comparative example 5 Basecoat components in grams Polyurea binder, produced by process 2 0 Control device for a low firing temperature, produced by process 3 0 silica gel dispersion (1) 224 Acid-functional acrylic copolymer (2) 76 Polyester (3) 146 Imron ® Yellow tint PT 144 3 Imron ® magenta tint PT 164 6 Imron® Black tint PT 105 19 Imron® Transparent Yellow Oxide Tint PT 183 101 Imron® medium-fine aluminum tint PT 110 159 Ethyl acetate from Eastman Chemical, Kingsport, Tennessee 65 Imron® Activator 15305S (in crosslinking component) 250 in total 1049 Test results Basecoat runoff dry film thickness 4 mils (101.6 micrometers) R (orange peel) at BC dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D3451 3 DOI for basecoat dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D5767 61 Test observations Good runoff resistance, but flaking.

[0106] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware.

[0107] Note: (1)-(3) are the same as in Table 1.

[0108] [Base coat with a dry-cured coating thickness of 1.5 mils (38.1 micrometers), coated with Imron® Elite clear coat with a dry-cured coating thickness of 2 mils (50.8 micrometers), both simultaneously baked-cured for 20 minutes at a low baking temperature of 160°F (71.1°C)] Table 6 Coating system of comparative example 6 Basecoat components in grams Polyurea binder, produced by process 2 400 Control device for a low firing temperature, produced by process 3 0 silica gel dispersion (1) 0 Acid-functional acrylic copolymer (2) 0 Polyester (3) 50 Imron ® Yellow tint PT 144 3 Imron ® magenta tint PT 164 6 Imron® Black tint PT 105 19 Imron® Transparent Yellow Oxide Tint PT 183 101 Imron® medium-fine aluminum tint PT 110 159 Ethyl acetate from Eastman Chemical, Kingsport, Tennessee 65 Imron® Activator 15305S (in crosslinking component) 250 in total 1054 Test results Basecoat runoff dry film thickness 2 mils (50.8 micrometers) R (orange peel) at BC dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D3451 5 DOI for basecoat dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D5767 65 Test observations medium runoff resistance and smooth

[0109] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware.

[0110] [Base coat with a dry-cured coating thickness of 1.5 mils (38.1 micrometers), coated with Imron® Elite clear coat with a dry-cured coating thickness of 2 mils (50.8 micrometers), both simultaneously baked-cured for 20 minutes at a low baking temperature of 160°F (71.1°C)] Table 7 Coating system of Example 1 of the present invention Basecoat components in grams Polyurea binder, produced by process 2 0 Control device for a low firing temperature, produced by process 3 3000 silica gel dispersion (1) 0 Acid-functional acrylic copolymer (2) 0 Polyester (3) 146 Imron ® Yellow tint PT 144 3 Imron ® magenta tint PT 164 6 Imron® Black tint PT 105 19 Imron® Transparent Yellow Oxide Tint PT 183 101 Imron® medium-fine aluminum tint PT 110 159 Ethyl acetate from Eastman Chemical, Kingsport, Tennessee 65 Imron® Activator 15305S (in crosslinking component) 250 in total 1049 Test results Basecoat runoff dry film thickness 5 mils (127 micrometers) R (orange peel) at BC dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D3451 7 DOI for basecoat dry film thickness of 1.5 mils (38.1 micrometers), measured by ASTM D5767 80 Test observations good expiry resistance and very good DOI

[0111] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware.

[0112] Note: (1)-(3) are the same as in Table 1.

[0113] [Comparison examples 7 and 8: Coatings were cured for 24 hours at ambient temperature in the range of 60°F (15°C) to 110°F (43°C) (component in grams)] Table 8 Ambient temperature hardness Comparison 7 Comparison 9 silica gel dispersion (1) 10,0 0,0 BENTONE ® -Dispersion (4) 0,0 0,0 GARAMITE® dispersion (5) 0,0 0,0 Control device for a low firing temperature, produced by process 3 0,0 37,0 Acid-functional acrylic copolymer (2) 8,8 4,0 Polyester (3) 18,0 15,0 Violet tint PT 120 0,1 0,1 Black tint PT 105 0,5 0,5 Blue tint PT 122 3,9 3,9 Red-shade-blue tint PT 124 11,2 11,2 Aluminum tint PT 114 10,9 10,9 Methyl amyl ketone 14,0 10,0 Ethyl acetate 10,9 5,0 butyl acetate 6,5 3,0 Heptane 1,7 1,7 3-Ethoxypropionic acid ethyl ester 2,1 2,3 Dibutyltin dilurate 0,01 0,01 Imron® Activator 15305S 35,0 36,0 Total [grams] 133,6 140,6 Test results Minimum dry film thickness for runoff [mil] 4 3 R (orange peel) of dry film thickness of 1.5 mils, measured by ASTMD3451 5 8 DOI of dry film thickness of 1.5 mils, measured by ASTM D5767 70 75 Mottling measurement (6) 6,7 4,5 Coating appearance Good runoff resistance, but flaking and poor mottling resistance. Medium runoff resistance, smooth and good mottling resistance

[0114] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware.

[0115] Note: (1)-(3) are the same as in Table 1.

[0116] (4) The BENTONE clay was manufactured by Elementis Specialties, London, United Kingdom, under the appropriate registered trademark. BENTONE 34 dispersion was manufactured in accordance with, and is incorporated herein by this notice.

[0117] (5) GARAMITE clay was manufactured by Southern Clay Products, Gonzales, TX, USA, under the appropriate registered trademark. GARAMITE dispersion was manufactured in accordance with [relevant legal provision], incorporated herein by this notice.

[0118] (6) Mottling measurement was performed using Cloud Runner, available from BYK-Gardner GmbH, Geretsried, Germany.

[0119] [Examples 2-4 coatings were cured for 24 hours at ambient temperature in the range of 60°F (15°C) to 110°F (43°C) (component in grams)] Table 9 Ambient temperature hardness Example 2 Example 3 Example 4 silica gel dispersion (1) 4,0 0,0 0,0 BENTONE ® -Dispersion(4) 0,0 10,0 0,0 GARAMITE ® - Dispersion (5) 0,0 0,0 10,0 Control device for a low firing temperature, produced by process 3 18,0 18,0 18,0 Acid-functional acrylic copolymer (2) 3,9 2,0 2,0 Polyester (3) 16,7 13,0 13,0 Violet tint PT 120 0,1 0,1 0,1 Black tint PT 105 0,5 0,5 0,5 Blue tint PT 122 3,9 3,9 3,9 Red-shade-blue tint PT 124 11,2 11,2 11,2 Aluminum tint PT114 10,9 10,9 10,9 Methyl amyl ketone 10,0 14,0 14,0 Ethyl acetate 15,0 10,9 10,9 butyl acetate 4,1 6,5 6,5 Heptane 1,8 1,7 1,7 3-Ethyl ethoxypropionic acid 1,2 2,1 2,1 Dibutyltin dilurate 0,01 0,01 0,01 Imron® Activator 15305S 35,5 35,0 35,0 Total [grams] 136,8 139,8 139,8 Test results Minimum dry film thickness for runoff [mil] 4 4 4 R (orange peel) of dry film thickness of 1.5 mils, measured by ASTM D3451 7 7 7 DOI of dry film thickness of 1.5 mils, measured by ASTM D5767 73 75 76 Mottling measurement (6) 5,1 5,0 5 Coating appearance Good runoff resistance, very smooth, good DOI and good Good runoff resistance, very smooth, good DOI and good Good runoff resistance, very smooth, good DOI and good Mottling resistance Mottling resistance Mottling resistance

[0120] Unless otherwise stated, all components were sourced from Axalta Coating Systems, LLC of Wilmington, Delaware. Note: (1)-(6) are the same as in Table 7.

[0121] From the foregoing, it becomes clear to the expert that: 1. It is a unique combination of components in the low baking-curing temperature control agent that results in increased runoff resistance of the obtained coating. 2. The low baking-curing temperature curing agent also simultaneously provides desired coating properties, such as a smooth surface and very good DOI (Distinctness of Image). 3. The low-curing-temperature curing agent produces a coating composition with low VOC at low curing temperatures in shorter curing times than the state of the art.

[0122] Multi-layer coatings, comprising a low-bake-temperature basecoat and a low-bake-temperature clearcoat, were also investigated. An example is provided below.

[0123] A low-bake-temperature clear coat was prepared by manufacturing an initial acrylic resin by feeding the components listed in Table 10 into a 12-liter reactor equipped with a stirrer, nitrogen inlet, condenser, dual top surface feeders, and a heat source. Table 10. Components in initial acrylic resin Table 10. Components in first acrylic resin Portion I. Quantity (grams) Methyl amyl ketone 1249,44 Portion II. Styrene (Sty) monomer 1140,4 Isobutyl methacrylate (IBMA) monomer 1900,16 2-Hydroxyethyl methacrylate (HEMA) monomer 1013,68 2-Hydroxypropyl methacrylate (HPMA) monomer 1013,68 Methyl amyl ketone 130,56 Portion III. Methyl amyl ketone 60,24 Portion IV. Methyl ethyl ketone 529,2 t-Butyl peroxyacetate 593,12 Portion V. Methyl ethyl ketone 46,16 Portion VI. butyl acetate 323,36 In total 8000

[0124] The first acrylic resin was prepared as follows. Portion I was added to the reactor and heated to reflux temperature. The monomers of Portion II were premixed and added to the reactor at a uniform rate over a 240-minute period, maintaining the components in the reactor at their reflux temperature. Simultaneously, Portion IV, the starter feed, was started and added with the monomers of Portion II at a uniform rate over the 240-minute period. After Portions II and IV had been added, Portions III and V were used to purge the feed vessels and added to the reactor. The resulting polymer solution was held at its reflux temperature for an additional 60 minutes. The polymer solution was then diluted with Portion VI and cooled to room temperature.

[0125] The first acrylic resin obtained had a theoretical solids content of 62.5% and Sty / IBMA / HEMA / HPMA monomers in a weight ratio of 22.5 / 37.5 / 20.0 / 20.0. Gel permeation chromatography (GPC) was used to determine a weight-mean molecular weight of 3766 and a number-mean molecular weight of 1675. Formulated as above, the first acrylic resin comprised primary and secondary hydroxyl groups in a ratio of approximately 64:36 and had a theoretical glass transition temperature (Tg (theoretical)) of 68°C, calculated based on the weight average of the literature values ​​of the glass transition temperatures of the individual homopolymers.

[0126] The first acrylic resin was then used to formulate a clear coat formulation with a low baking-curing temperature, as provided in Table 11. Table 11. Clearcoat formulation with low baking-curing temperature Components Weight (grams) first acrylic resin (1) 776,6 second acrylic resin (2) 79,4 Methyl amyl ketone 96,2 2-ethylhexyl acetic acid ester 52 mixed dimethyl esters of succinic, glutaric and adipic acids 23,4 Acrylic polymer solution (3) 3,9 Ultraviolet light absorber (4) 11,6 Light stabilizer (5) 11,6 Urethane catalyst solution (6) 14,2 Cocoalkyldimethylamin (7) 1,2 Benzoic acid 10,0 silica gel dispersion (8) 92,1 Imron ® -Activator (9) 423,0 In total 1595,2 (1) The production of the first acrylic resin is described above. (2) The second acrylic resin was a type of acrylic resin typically used in the manufacture of conventional clear coatings and was obtained from Axalta Coating Systems, Philadelphia, PA. The second acrylic resin contained primary and secondary hydroxyl groups in a ratio of approximately 25:75 and had a theoretical glass transition temperature (Tg) of approximately 2.4°C. (3): The acrylic polymer solution: RESIFLOW S was available from Estron Chemical, Calvert City, KY. (4): The ultraviolet light absorber TINUVIN 328 was available from BASF CORPORATION, Ludwigshafen, Germany. (5): The light stabilizer: TINUVIN 292 was available from BASF CORPORATION, Ludwigshafen, Germany. (6): The catalyst: FASCAT (R) 4202 CATALYST (Dibutyltin Dilaurate), available from PMC ORGANOMETALLIX INC, Mount Laurel, NJ, was used as a 2% solution in ethyl acetate. (7): The cocoalkyldimethylamine: ARMEEN DMCD is available from AKZO NOBEL, Malvern, PA. (8): Silica gel dispersion was obtained from Axalta Coating Systems, Philadelphia, PA. (9): Imron® activator contained aliphatic polyisocyanate resin (60-100%) and was obtained from Axalta Coating Systems, Philadelphia, PA.

[0127] Thus, the exemplary clearcoat formulation for a low baking temperature provided in Table 11 comprised first and second acrylic resins in a ratio of approximately 10:1. These results are available in a clearcoat coating composition with primary and secondary hydroxyl groups in a ratio of approximately 60:40.

[0128] An exemplary multi-layer coating system was prepared using the basecoat described above in Example 4 and the clearcoat formulation provided in Table 11. The basecoat was applied to a metal substrate using conventional spraying techniques typical in the automotive coating field. The clearcoat formulation was applied wet-on-wet over the basecoat layer to form a clearcoat. The basecoat / clearcoat system was cured at 160°F for approximately 20 minutes, resulting in a dry, hard film.

[0129] Consequently, various embodiments of low VOC (volatile organic compound) curable coating compositions for low curing temperatures, suitable for use in automotive OEM (original equipment manufacturer) and refinish applications, and methods for producing coatings at low curing temperatures are described herein. In particular, multi-layer coatings comprising a low-curing basecoat and a clearcoat composition comprising primary and secondary hydroxyl groups in a ratio of 30:70 to 80:20, such as 35:65 to 75:25, 40:60 to 70:30, 45:55 to 70:30, 50:50 to 70:30, 55:65 to 70:30, 60:40 to 70:30, and 65:35 to 70:30 are provided.

Claims

[1] Curable coating composition for a low curing temperature, comprising: a crosslinkable component comprising an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 percent to 12 percent of monomers containing one or more carboxylic acid group(s), wherein the percentages are based on the total weight of the acid-functional acrylic copolymer, a networking component; and A control device for a low firing temperature, comprising a rheology component selected from an amorphous silica gel, a clay or a combination thereof, wherein the rheology component is present in an amount of 0.1 to 10 wt% and 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components. [2] Coating composition according to claim 1, wherein the acid-functional acrylic copolymer has a weight-average molecular weight according to GPC in the range of 8000 to 100000 and a polydispersity in the range of 1.05 to 10.0 and / or the acid-functional acrylic copolymer has a Tg in the range of -5°C to +100°C. [3] Coating composition according to claim 1, wherein the monomer mixture comprises one or more functional (meth)acrylate monomers and one or more non-functional (meth)acrylate monomers, preferably wherein the monomer mixture comprises 5 percent to 40 percent, based on the total weight of the acid-functional acrylic copolymer of the functional (meth)acrylate monomers. [4] Coating composition according to claim 1, wherein the monomer containing the carboxylic acid group(s) comprises one or more carboxylic acids selected from the group consisting of (meth)acrylic acid, crotonic acid, oleic acid, cinnamic acid, glutaconic acid, muconic acid, undecylenic acid, itaconic acid, crotonic acid, fumaric acid, maleic acid and a combination thereof. [5] Coating composition according to claim 1, wherein the polyurea is produced by polymerizing a monomer mixture comprising one or more amine monomers, one or more isocyanate monomers and one or more moderating polymers, preferably wherein the amine monomer is selected from the group consisting of a primary amine, secondary amine, ketimine, aldimine or a combination thereof, and / or wherein the isocyanate monomer is selected from the group consisting of an aliphatic polyisocyanate, cycloaliphatic polyisocyanate, aromatic polyisocyanate and a combination thereof; and / or wherein the monomer mixture comprises 0.5 to 3 weight percent of the amine monomer and 0.5 to 3 weight percent of the isocyanate monomer, the weight percentages being based on the total weight of the crosslinkable component. [6] Coating composition according to claim 1, formulated as a two-component coating composition, wherein the crosslinkable component and the crosslinking component are stored in separate containers. [7] Coating composition according to claim 1, formulated as an automotive OEM composition, automotive repair composition or industrial coating composition. [8] Method for producing a coating on a substrate, comprising: (a) Mixing a crosslinkable component, a crosslinking component and a low-temperature curing control agent of a low-temperature curable coating composition to form a pot mix orMixture, wherein the crosslinkable component comprises an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2 wt% to 12 wt% of carboxylic acid group(s) containing monomer, based on the total weight of the acid-functional acrylic copolymer, and wherein the low-curing-temperature control agent is a rheology component selected from an amorphous silica gel, a clay, or a combination thereof, wherein the rheology component is present in an amount of 0.1 wt% to 10 wt% and comprises 0.1 wt% to 10 wt% polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components; (b) Applying a layer of the pot mix or mixture to the substrate; and (c) Hardening of the layer at low firing temperature to the coating on the substrate. [9] The method of claim 8, wherein the low curing temperature is in the range of 60°F (15°C) to 200°F (93°C) and / or wherein the substrate is a motor vehicle body, industrial equipment or construction equipment. [10] Multi-layer coating system, comprising: a curable basecoat composition for a low baking temperature according to any one of the preceding claims 1 to 7; and a clearcoat composition comprising an acrylic copolymer component comprising one or more acrylic polymers, wherein the clearcoat composition comprises primary hydroxyl and comprising secondary hydroxyl groups in a ratio of 30:70 to 80:20, wherein the clear coat composition lies above and is in contact with the curable base coat composition for a low baking temperature. [11] Multi-layer coating composition according to claim 10, wherein the acrylic copolymer of the clear coat coating composition comprises an acrylic polymer polymerized from a monomer mixture comprising a hydroxyalkyl acrylate, a hydroxyalkyl methacrylate or a mixture thereof, wherein an alkyl group in the hydroxyalkyl acrylate and / or hydroxyalkyl methacrylate has 1 to 4 carbon atoms; or wherein the acrylic copolymer of the clear lacquer coating composition comprises an acrylic polymer polymerized from a monomer mixture comprising hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyisopropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyisopropyl methacrylate, hydroxybutyl methacrylate or a mixture thereof, or wherein the acrylic copolymer of the clear lacquer coating composition comprises an acrylic polymer polymerized from a monomer mixture comprising styrene, isobutyl methacrylate (IBMA), 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA) or a mixture thereof. [12] Multi-layer coating composition according to claim 10, wherein the acrylic copolymer of the clear coat coating composition comprises an acrylic resin having a theoretical glass transition temperature (Tg (theoretical)) of 25°C to 95°C. [13] Method for producing a multi-layer coating on a substrate, comprising: (a) Mixing a crosslinkable component, a crosslinking component and a baking temperature control agent to form a basecoat pot mix or mixing batch, wherein the crosslinkable component comprises an acid-functional acrylic copolymer polymerized from a monomer mixture comprising 2% to 12% by weight of carboxylic acid group(s) containing monomer, based on the total weight of the acid-functional acrylic copolymer, and wherein the baking temperature control agent comprises a rheology component selected from an amorphous silica gel, a clay or a combination thereof, wherein the rheology component is present in an amount of 0.1% to 10% by weight and comprises 0.1% to 10% by weight of polyurea, the percentages being based on the total weight of the crosslinkable and crosslinking components; (b) Applying a layer of the basecoat pot mix or mixture to the substrate; (c) Applying a layer of a clearcoat coating composition, spread over and in contact with a layer of the basecoat pot mix or mixing mixture to form a multi-layer coating composition, wherein the clearcoat coating composition comprises an acrylic copolymer component comprising one or more acrylic polymers, wherein the clearcoat coating composition comprises primary hydroxyl and secondary hydroxyl groups in a ratio of 30:70 to 80:20; and (d) Hardening of the multi-layer coating composition on the substrate. [14] Method according to claim 13, wherein applying a layer of the basecoat pot mix or mixing mixture comprises applying a plurality of layers of the basecoat pot mix or mixing mixture, applying a layer of a clearcoat composition, applying a plurality of layers of the clearcoat composition, or both. [15] Method according to claim 13, wherein the hardening is carried out at a curing temperature of 60°F (15°C) to 200°F (93°C) and / or wherein the substrate is a motor vehicle body, industrial equipment or construction equipment.