WO2006063304A1

WO2006063304A1 - Coating composition

Info

Publication number: WO2006063304A1
Application number: PCT/US2005/044767
Authority: WO
Inventors: Gregory Menovcik; Walter Ohrbom; Swaminathan Ramesh; Paul Lamberty; John Boisseau; Donald Campbell
Original assignee: Basf Corporation
Priority date: 2004-12-10
Filing date: 2005-12-09
Publication date: 2006-06-15

Abstract

A composition comprising a binder polymer with a first functional group that is reactive with a second functional group, a crosslinking agent with the second functional group, and a polymer additive with a third functional group that can react with the second functional group and may optionally contain additional functionality which does not react with the first or second functional group and wherein said polymer additive will concentrate more at a surface interface region of a cured film formed from the composition than in the bulk of the coating.

Description

COATING COMPOSITION

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a PCT application which claims priority to US Provisional application Serial No. 60/635,189 filed December 10, 2004.

BACKGROUND OF THE INVENTION

[0002] In multilayer coatings, it is desired that there be adhesion between the layers of the coating. This is known as intercoat adhesion. In the environment to which the multilayer coating is exposed, a sufficient intercoat adhesion is desired so that the layers of the multilayer coating do not delaminate from each other.

[0003] An example of providing intercoat adhesion can be found in United States Patent Nos. 5,576,063 and 5,639,828, both of which are incorporated herein by reference. In these compositions, an epoxy group containing polymer is provided in the coating composition. When formed into a coating, the epoxy group containing polymer concentrates itself at the surface of the coating. When the coating is cured at a sufficient temperature, the epoxy groups ring open to form hydroxyl groups. The hydroxyl groups provide for intercoat adhesion between the coating and a subsequent coating layer.

[0004] In order to provide intercoat adhesion, the epoxy group-containing polymers in these compositions are substantially free of functional groups that are reactive with other polymers or crosslinkers in the coating composition. By being substantially free of functional groups, the epoxy group containing polymer can migrate to the surface of the coating without reacting with the other materials in the coating, which would limit the epoxy group containing polymer from migrating. Additionally, as the polymer is designed to migrate to the surface, it is desirable to incorporate into it functional groups that will protect the surface.

[0005] In order for the intercoat adhesion to be increased by an epoxy group containing polymer that is substantially free of functional groups, the curing temperature for the coating composition has to be sufficient to ring open the epoxy groups. When lower curing temperatures are used, the epoxy groups do not ring open, and the improvement in intercoat adhesion is less. It would be desirable to provide a material that could provide for intercoat adhesion at a lower cure temperatures. SUMMARY OF THE INVENTION

[0006] The present invention provides a coating composition comprising a binder polymer having a first functional group that is reactive with a second functional group, a crosslinking agent comprising the second functional group, and a polymer additive different than the binder polymer and crosslinking agent, said polymer additive comprising a third functional group that can react with the second functional group, and where said polymer additive migrates to the surface and is present in higher concentration at a surface interface region of a cured film formed from the composition than in the bulk of the cured coating. The polymer additive may also include additional functionality that may or may not react with the binder polymer and/or crosslinker, but which provides improved surface performance. The polymer additive concentrated at the surface improves at least one of repair adhesion, adhesion of window sealant to a painted substrate, etch resistance and coating durability to weathering conditions.

DETAILED DESCRIPTION

[0007] As used throughout, ranges are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. When used, the phrase "at least one of refers to the selection of any one member individually or any combination of the members. The conjunction "and" or "or" can be used in the list of members, but the "at least one of phrase is the controlling language. For example, at least one of A, B, and C is shorthand for A alone, B alone, C alone, A and B, B and C, A and C, or A and B and C.

[0008] The composition includes a binder polymer with a first functional group that is reactive with a second functional group, a crosslinking agent comprising the second functional group, and a polymer additive, different than the binder polymer and crosslinking agent, said polymer additive comprising a third functional group that can react with the second functional group and which will concentrate more at a surface interface region of a cured film formed from the composition than in the bulk of the coating. The bulk of a coating is the remaining portion of the cured coating.

[0009] The surface interface region in a coating is a region that is near the surface of the coating. This is in contrast to an interface between the coating and a substrate or previously applied coating. The surface interface region generally is exposed to the environment, but in some instances may be overcoated, for example, with a repair coating. The surface interface region in a coating is generally the region that extends to about 0 to 10% {0 to 2.5 μm) of the thickness of the coating as measured from the surface of the coating. It should be recognized that the transition from surface interface region to the bulk of the coating is a gradient and can vary from system to system. The cured coating composition, the coating should have a thickness that is sufficient to provide a surface interface region and a bulk region so that the polymer additive can migrate to the surface of the coating. In a preferred embodiment, the coating thickness is at least 30 to 75 μm. It is the surface interface region that determines the degree of repair adhesion, window sealant adhesion, and scratch resistance. While not exclusively a property of the surface interface region, the make up of the surface of a coating can have significant impact on other film properties such as appearance, UV durability and environmental etch resistance.

[0010] Examples of the functional group selections for the binder polymer and the crosslinker include, but are not limited to, the complementary functional groups where either the binder polymer or the crosslinker includes a proton donor and the other a proton acceptor. Preferred proton donors include primary and secondary hydroxyls, primary and secondary amines, thiols, primary and secondary carbamates, primary and secondary ureas, primary and secondary amides phenolic groups, primary and secondary amides, and organic acids. Primary compounds are preferred. Preferred proton acceptors include isocyanate, Si-OR, where R is a H, alkyl, alkylaryl, or C(O)R where R contains from one to ten carbon atoms, epoxy, cyclic carbonate, tris-alkoxy carbonyl triazine (TACT) or aminoplast groups. Mixtures of the proton acceptor compounds may be used. Aminoplast is defined as the reaction product of an activated amine with either formaldehyde, aldehyde or ketone group. By activated amines is meant electronically activated amines that are activated by groups such as aromatic, triazines, carbamates, ureas, amides as well as other groups that effect the electron cloud around the nitrogen atom. The reaction product of the activated amine described above may optionally be etherified by reaction with an alcohol. The aminoplast used for crosslinking may include mixtures of non-reacted activated amine, the reaction product of the amine with formaldehyde, aldehyde and/or ketone as well as etherified reaction product. However, no more than 50% of the total amount of amine may be the non-reacted activated amine.

[0011] As recognized by one skilled in the art, the hydrogen donated from the proton donor may or may not be incorporated in the film. As further recognized by one skilled in the art, not all proton donors will react with all proton acceptors. For example, hydroxyl and carbamate groups will readily react with aminoplast crosslinkers under normal cure conditions, defined as curing at temperatures below 310⁰F. In contrast, the hydroxyl groups and carbamate groups do not readily react with epoxy or cyclic carbonate groups under normal cure conditions. However, catalyst can be used to initiate or accelerate the cure reaction. Examples of suitable catalysts are Lewis acids and Bronstead acids. In some cases Lewis bases, such as tertiary amines, can also be used.

[0012] In a preferred embodiment, the functional group on the binder polymer and the functional group on the crosslinking agent form a urethane linkage. The reaction may occur for example by reaction of a carbamate functional compound with an aminoplast functional compound, non-activated amine functional compound with cyclic carbonate functional compound or reaction of a hydroxyl functional compound with an isocyanate functional compound. Mixtures of these systems can also be used. Examples of some of these systems are described in United States Patent Nos. 5,639,828 and 5,576,063, which are incorporated herein by reference.

[0013] For the polymer additive to concentrate itself at the interface region, the polymer additive is more non-polar than the binder polymer. The polymer additive contains a sufficient amount of non-polar monomers (i.e., having no interactions such as hydrogen bonding / bridging and other polar interactions) to allow the polymer additive to migrate to the surface. In one embodiment described below, the hydrophobic monomers are alkyl (meth)acrylates. In a preferred embodiment, the amount of hydrophobic monomers in the polymer additive is 30-70% by weight of the total weight of monomers that form the polymer additive, and in another embodiment 45-65%, and in yet another embodiment between 55-65 % of the total weight of monomers that form the polymer additive. The alkyl group preferably is an alkyl group of five (5) or more carbon atoms, preferably eight or more carbon atoms. This group may be a straight chain or branched group. An examples of a branched alkyl group is 2-ethylhexyl and an example of a linear alkyl group are lauryl or decane groups.

[0014] Also, it is preferred that the Tg of the polymer additive be low enough to provide for migration to the surface of the coating and to improve entanglement at the surface of the coating. Entanglement at the surface allows the polymer additive to anchor into the coating to increase intercoat adhesion. The longer the chain length of the polymer additive, the more the polymer additive can anchor itself into the coating. Surface entanglement can also be provided by sufficient molecular weight of the polymer additive. The higher the molecular weight of the polymer additive, the more functional groups per polymer strand there are to provide for intercoat adhesion. In a preferred embodiment, the polymer has a Tg < 0°C, and more preferably < ^"20⁰C. Also in a preferred embodiment, the polymer additive has a number average molecular weight > 10,000, and more preferably > 15,000 daltons. While higher molecular weights are generally preferred, care must be taken that the molecular weight is not so great that when taken together with the functional groups on the polymer it impedes the ability of the polymer additive to migrate to the surface. For this reason, the molecular weights should generally be less than 50,000 Daltons.

[0015] In an alternative embodiment, the Tg can be high enough to provide scratch and mar resistance to the coating. In this embodiment, the molecular weight can be lower. Tg would range from 10 to >100 ⁰C and number average molecular weight from 1000 to 10,000 daltons. It is to be appreciated in this case, it is often desirable to use a polymer additive as described in the preceeding paragraph with the low molecular weight, high Tg polymer additive.

[0016] The polymer additive can be present in the composition in any amount to provide for any desired level of intercoat adhesion. In a preferred embodiment, the polymer additive is present in the composition in an amount from about 0.1% to about 10% by weight based on the weight of nonvolatile content (fixed vehicle) of the coating system.

[0017] The polymer additive contains a functional group (the third functional group). The functional group is selected to be reactive with either the binder polymer or the crosslinking agent in the coating composition containing the polymer additive. Examples of the functional group include, but are not limited to, hydroxy, SH (thiol), CN (cyano nitrile), ether RO-, carbamate, urea -NHCONH- , or Si-OR, wherein R is an organic radical. Most preferred are hydroxyl groups. While this functional group is reactable with either the crosslinker or binder polymer, it is critical that it reacts at a slower rate than the reaction rate of the binder polymer and crosslinker. This allows the polymer additive to migrate to the surface.

[0018] Three techniques can be used to insure that the functional group on the polymer additive reacts at a slower rate. The first technique is to use a secondary functional group on the polymer additive and a primary functional group on the binder polymer. The second technique is to use a functional group on the polymer additive that can form a bond that has a higher degree of reversibility than the bond formed from the reaction of the binder resin with the crosslinker. An example of this is a hydroxyl group on the polymer additive and a carbamate group on the binder polymer and an aminoplast crosslinker. The third technique is to use steric hinderance and/or low stoichiometry, (i.e. less than 10% by weight functional monomers, based on total monomer weight), to kinetically hinder the reaction with the crosslinker. Preferably less than 6 % by weight functional monomers that can react with either the binder polymer or crosslinker, based on total monomer weight are used.

[0019] It is often preferable to use all three techniques at the same time. For example, when used with a primary carbamate functional binder resin crosslinked with an aminoplast crosslinker, the functional polymer additive is most preferably obtained from monomers that comprise secondary hydroxyl groups, where said monomers are used in less than 10% by weight based on total monomer weight and wherein at least 30% or more of the monomers making up the polymer additive comprise bulky side groups. Bulky side groups are alkyl groups of at least five, and preferably eight or more carbon atoms. While the use of all three procedures is desirable, it is not required to use all three. For example, when there is a need to have high concentrations of primary functionality on the surface, the other two techniques (i.e. reversible crosslinks and steric hinderance and/or low stoichiometry) can be used to allow it to migrate.

[0020] Even though it is preferred that the polymer additive contain only secondary groups, commercially available monomers often contain mixtures of primary and secondary functionality. This mixture can be used as long as approximately 80% or more of the functionality is secondary. Alternatively, the small amount of primary functionality can be further reduced by reaction with a mono-functional group that preferentially reacts with a primary functionality. This reaction can occur before, during or after polymerization. For example, when 2-hydroxypropyl methacryalate is used, the small amount of primary groups can be removed by reaction with a monofunctional isocyanate. Other suitable compounds may be used to preferentially react with the primary groups on the compound.

[0021] The polymer additive can also contain additional functional groups that are essentially non-reactable with the binder polymer or crosslinker. Essentially non-reactable as used herein means that less than 10% total of the non-reactable functional groups react with the binder polymer and/or crosslinker. Examples of these include epoxy, ultraviolet absorber compounds (UVAs), hindered amine light stabilizers (HALS), cyclic carbonates, Si-OR, where R is a H, alkyl and alkylaryl, C(O)R, where R is alkyl, alkylaryl. As will be obvious to one skilled in the art, selection of the non-reactable group on the polymer additive is dependent on the functional groups on the binder polymer and crosslinker. For example, when the binder polymer comprises functionality such as primary amine and crosslinker comprises functionality such as cyclic carbonate, the non-reactable group on the polymer additive cannot be epoxy. However, when the binder polymer functionality is primary carbamate and the crosslinker is an aminoplast, the non-reactable functional group on the polymer additive can be epoxy.

[0022] The capping agents used to reduce the level of primary functional groups on the polymer additive which can react with either the binder polymer or crosslinker can contain additional functional groups that impart desired properties to the polymer additive. An example of this is the half capping of a di-isocyanate with a UVA to form a monofunctional isocyanate that contains the light stabilizer. This material can then be used to reduce the overall level of primary groups on the polymer additive available to react with the binder resin or crosslinker and at the same time incorporate a light stabilizer into the polymer additive.

[0023] Once concentrated on the surface, the functional group non-reactable with the crosslinker or binder, can react with other materials which migrate to the surface. Optionally^ a catalyst that migrates to the surface can be used to accelerate this reaction. At this point, the non-reactable functional group can be transformed to a functional group that can react with either the binder polymer or crosslinker. It will be recognized that at this point the coating is cured and migration of the polymer additive away from the surface is impossible. For example, when the functional group that is nonreactive with the binder or crosslinker is epoxy, it can react with a fatty acid present in the coating composition to form a beta-hydroxy ester. A fatty acid is defined as an organic acid that has at least seven carbons per acid group. Premature reaction of the polymer additive with the materials designed to react with polymer additive on the surface can be minimized by using low concentrations of polymer additive and material designed to react with the polymer additive. Generally the combined weight of the polymer additive and material designed to react with the polymer additive is from 0.1% to about 10% by weight based on the total nonvolatile weight of the coating composition. However, once on the surface, the concentration is great enough to allow reaction to occur.

[0024] A preferred polymer additive is an epoxy group containing polymer that includes at least one epoxy group. The epoxide may be of the general formula:

O,

where Rl, R2, R3, and R4 are each independently H (with the proviso that at least one of Rl-

R4 is other than H), an organic radical, which may be polymeric or non-polymeric and may contain unsaturation and/or heteroatoms, or one of Rl or R2 together with one of R3 or R4 may form a cyclic ring, which may contain unsaturation and/or heteroatoms. [0025] Useful epoxides can be prepared from alcohols, e.g., butanol, trimethylol propane, by reaction with an epihalohydrin (e.g., epichlorohydrin), or by reaction of an allyl group with peroxide. Oligomeric or polymeric polyepoxides, such as acrylic polymers or oligomers containing glycidyl methacrylate or epoxy-terminated polyglycidyl ethers such as the diglycidyl ether of bisphenol A (DGEBPA), can also be used. Epoxidized polyurethane resins or polyester resins can be prepared by reacting OH group-containing polyurethanes or polyesters, as are known in the art, with an epihalohydrin. Epoxides can also be prepared by reacting an isocyanate-terminated component such as a monomeric polyisocyanate or polymer or oligomer with glycidol. Other known polyepoxides, e.g., epoxy-novolacs, may also be used.

[0026] In one preferred embodiment, the epoxy group containing polymer additive is an acrylic-containing polymer or oligomer, preferably deriving its epoxy groups from glycidyl methacrylate monomer, glycidyl acrylate, allyl glycidyl ether, cyclohexyl monoepoxyy methacrylate, the epoxide of the dimer of cylopentadiene methacrylate, or epoxidized butadiene, more preferably glycidyl methacrylate. In another preferred embodiment, both the epoxy group containing polymer additive and one of the components that reacts to form urethane linkages are acrylic polymers or oligomers.

[0027] In one preferred embodiment, the epoxy group containing polymer additive is a reaction product of glycidyl (meth)acrylate, a hydroxyalkyl (meth)acrylate, an alkyl (meth)acrylate, and, optionally a vinyl aromatic. Preferably, the glycidyl (meth)acrylate is glycidyl methacrylate. In a preferred embodiment, the epoxy equivalent weight is between 350 and 2000 grams per equivalent.

[0028] Examples of the hydroxyalkyl (meth)acrylate include, but are not limited to hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate. When reference is made to hydroxyalkyl (meth)acrylates, the reference includes a reference to all possibilities where the hydroxyl group may be attached to the alkyl group. In a preferred embodiment, the hydroxyl equivalent weight is between 1500 and 15,000 grams per equivalents.

[0029] Examples of the alkyl (meth)acrylates include, but are not limited to, reaction products of ethylenically unsaturated carboxylic acids and C₁ to C20 alcohols. Examples of these (meth)acrylates include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isodecyl (meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate, 4-tertbutylcyclohexyl (meth)acrylate, 3,3,5- trimethylcyclohexyl (meth)acrylate, dimethyl maleate, n-butyl maleate, alkylene glycol di(meth)acrylates, ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4- butylene glycol di(meth)acrylate, propylene glycol (meth)acrylate, 1,6-hexanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, cyclopentadienyl (meth)acrylate, carbodiimide (meth)acrylate, t-butylaminoethyl (meth)acrylate, 2-t-butylaminoethyl (meth)acrylate, and N,N-dimethylaminoethyl (meth)acrylate. Preferred alkyl (meth)acrylates include 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isodecyl methacrylate, lauryl methacrylate, and methyl methacrylate.

[0030] Examples of vinyl aromatics include, but are not limited to, styrene, α-methyl styrene, o-chlorostyrene, chloromethyl styrene, α-phenyl styrene, styrene sulfonic acid, salts of styrene sulfonic acid, para-acetoxystyrene, divinylbenzene, diallyl phthalate, vinyl toluene, and vinyl naphthalene. Preferably, the vinyl aromatic is styrene.

[0031] In a preferred embodiment, the amount of the alkyl (meth)acrylate in the epoxy group containing polymer additive is sufficient to allow the epoxy group containing polymer additive to migrate to the surface of the coating. In a preferred embodiment, the alkyl (meth)acrylate is present in the epoxy group containing polymer additive in an amount that is at least about 50% by weight of the_. polymer additive and the amount of hydrophobic monomer in the polymer additive is 30 - 70% by weight of the total weight of monomers that form the polymer additive, and more preferably 45 - 65% More preferred between 55 - 65 %. Preferably, the amount is between 58 -62% so as to allow for a sufficient amount of glycidyl (meth)acrylate and hydroxyalkyl (meth)acrylate in the polymer additive.

[0032] The coating composition can be provided as a one-component or a multiple component composition. In a one-component composition, the functional groups on the crosslinking agent can be blocked to prevent premature reaction with the binder polymer. Preferably, the composition is a two-component composition with the binder polymer and crosslinking agent provided in separate components. The polymer can be provided in the binder polymer containing component. [0033] The coating composition can be used as any layer in a multilayer coating. A multilayer coating can include any of the following layers, electrocoat, primer, basecoat, topcoat, or clearcoat. More than one type of layer can be present in the multilayer coating. Preferably, the coating composition can be applied as a clearcoat.

[0034] The coating composition can be cured at a temperature lower than the temperature needed to ring open epoxy groups to form hydroxyl groups. Even at this lower cure temperature, the intercoat adhesion of the coating is at least equal to the intercoat adhesion provided by a coating composition that contains an epoxy group containing polymer additive that is substantially free of reactive groups that is cured at a temperature sufficient to ring open the epoxy groups. Preferably, the curing temperature for the coating is from about 180 to 310⁰F, from about 5 minutes to about 50 minutes.

[0035] The coating composition used in the practice of the invention may include a catalyst to enhance the cure reaction. For example, when aminoplast compounds, especially monomeric melamines, are used as a crosslinking agent, a strong acid catalyst may be utilized to enhance the cure reaction. Such catalysts are well-known in the art and include, organic acids containing at least 8 carbon atoms, phosphoric acids and derivatives thereof, sulfonic acids and derivatives thereof and tin and mixtures thereof. Examples of these include, without limitation, p-toluenesulfonic acid, dinonylnaphthalene disulfonic acid, dodecylbenzenesulfonic acid, phenyl acid phosphate, monobutyl maleate, butyl phosphate, and hydroxy phosphate ester. Strong acid catalysts are often blocked, e.g. with an amine. Other catalysts that may be useful in the composition of the invention include Lewis acids, zinc salts, and tin salts.

[0036] The coating composition containing epoxy functionality in the crosslinker can contain catalysts that promote the ring opening of an epoxy group at lower temperatures. Examples of these catalysts include, but are not limited to, organic acid catalysts and octanoic acid, tin, butyl acid phosphate, and dodecylbenzene sulfonic acid (DDBSA). When the crosslinking mechanism does not involve reaction with an epoxy functionality, it is required that the rate of epoxy ring opening be slower than the rate of crosslinking. In some cases, the catalyst used to accelerate the reaction of the binder polymer to the crosslinker can be used to accelerate a reaction of the polymer additive once it is concentrated on the surface.

[0037] A solvent may optionally be utilized in the coating composition used in the practice of the present invention. Although the composition used according to the present invention may be utilized, for example, in the form of substantially solid powder, or an aqueous or organic dispersion, it is often desirable that the composition is in a substantially liquid state, which can be accomplished with the use of a solvent. This solvent should act as a solvent with respect to the components of the composition. In general, the solvent can be any organic solvent and/or water. In one preferred embodiment, the solvent is a polar organic solvent. More preferably, the solvent is selected from polar aliphatic solvents or polar aromatic solvents. Still more preferably, the solvent is a ketone, ester, acetate, aprotic amide, aprotic sulfoxide, aprotic amine, or a combination of any of these.

[0038] Examples of useful solvents include, but are not limited to, organic solvents, methyl ethyl ketone, methyl isobutyl ketone, m-amyl acetate, ethylene glycol butyl ether-acetate, propylene glycol monomethyl ether acetate, xylene, N-methylpyrrolidone, blends of aromatic hydrocarbons, and mixtures of these. In another preferred embodiment, the solvent is water or a mixture of water with small amounts of co-solvents.

[0039] In a preferred embodiment of the invention, the solvent is present in the coating composition in an amount of from about 0.01 weight percent to about 99 weight percent, preferably from about 10 weight percent to about 60 weight percent, and more preferably from about 30 weight percent to about 50 weight percent.

[0040] Without being bound to a theory, it appears that the polymer additive changes the properties of the cured surface interface, while leaving the overall properties of the bulk cured coating unaltered, thus allowing for improved overall properties. The polymer additive can be used to bring to the surface, functional groups that are not found in the binder polymer or crosslinker. For example, when the functional group on the binder resin is carbamate and the crosslinker is aminoplast, the polymer additive can be used to place hydroxyl groups on the surface for repair adhesion. Other groups such as epoxy groups can augment window sealant adhesion in coating systems where the binder polymer and crosslinker do not contain these groups. As discussed, the polymer additive can be used to concentrate on the surface functional groups that can impart improved light stability, scratch resistance, and appearance as well as other properties such as environmental etch resistance. The polymer additive can be used to incorporate more than one desirable surface effect. For example, the polymer additive can contain hydroxyl groups, epoxy groups as well as light stabilizers. Alternatively, different polymers that focus on just one attribute can be used. In addition, the polymer additive can be used to change the physical properties (i.e. Tg) on the surface of the coating when compared to the bulk coating. For example, better flow and leveling may be obtained by using a polymer additive that has a Tg of < 20⁰C without affecting the overall cured film Tg. Better scratch and etch resistance may be obtained by using a polymer with Tg > 80⁰C to increase the surface interface Tg without making the overall Tg of the cured resin high enough so that it is susceptible to cold cracking.

[0041] Coating compositions can be coated on an article by any of a number of techniques well-known in the art. These include, for example, spray coating, dip coating, roll coating, curtain coating, brush coating and the like. For automotive body panels, spray coating is preferred.

[0042] Additional agents, for example surfactants, fillers, stabilizers, wetting agents, dispersing agents, adhesion promoters, UV absorbers, hindered amine light stabilizers, pigments, etc. may be incorporated into the coating composition. While such types of agents may also be incorporated into the polymer additive, it is often desirable to add these agents so that they can be in the bulk of the coating.

[0043] The coating composition according to the invention is preferably utilized in a high- gloss coating and/or as the clearcoat of a composite color-plus-clear coating. High-gloss coatings as used herein are coatings having a 20°gloss (ASTM D523-89) or a DOI (ASTM E430-91) ofat least 80.

[0044] When the coating composition of the invention is used as a high-gloss pigmented paint coating, the pigment may be any organic or inorganic compounds or colored materials, fillers, metallic or other inorganic flake materials such as mica or aluminum flake, and other materials of kind that the art normally includes in such coatings. Pigments and other insoluble particulate compounds such as fillers are usually used in the composition in an amount of 1% to 100%, based on the total solid weight of binder polymer components (i.e., a pigment-to- binder ratio of 0.1 to 1).

[0045] When the coating composition according to the invention is used as the clearcoat of a composite color-plus-clear coating, the pigmented basecoat composition may any of a number of types well-known in the art, and does not require explanation in detail herein. Polymers known in the art to be useful in basecoat compositions include acrylics, vinyls, polyurethanes, polycarbonates, polyesters, alkyds, and polysiloxanes. Preferred polymers include acrylics and polyurethanes. In one preferred embodiment of the invention, the basecoat composition also utilizes a carbamate-functional acrylic polymer. Basecoat polymers may be thermoplastic, but are preferably crosslinkable and comprise one or more type of crosslinkable functional groups. Such groups include, for example, hydroxy, isocyanate, amine, epoxy, acrylate, vinyl, silane, and acetoacetate groups. These groups may be masked or blocked in such a way so that they are unblocked and available for the crosslinking reaction under the desired curing conditions, generally elevated temperatures. Useful crosslinkable functional groups include hydroxy, epoxy, acid, anhydride, silane, and acetoacetate groups.

[0046] Basecoat polymers may be self-crosslinkable, or may require a separate crosslinking agent that is reactive with the functional groups of the polymer. When the polymer comprises hydroxy functional groups, for example, the crosslinking agent may be an aminoplast resin, isocyanate and blocked isocyanates (including isocyanurates), and acid or anhydride functional crosslinking agents.

[0047] The coating compositions described herein are preferably subjected to conditions so as to cure the coating layers. Although various methods of curing may be used, heat-curing is preferred. Generally, heat curing is effected by exposing the coated article to elevated temperatures provided primarily by radiative heat sources. Curing temperatures will vary depending on the particular blocking groups used in the cross-linking agents, however they generally range from 90⁰C to 180⁰C. The curing time will vary depending on the particular components used, and physical parameters such as the thickness of the layers, however, typical curing times range from 15 to 60 minutes, and preferably 15-25 minutes for blocked acid catalyzed systems and 10-20 minutes for unblocked acid catalyzed systems.

[0048] It should be appreciated that the present invention is not limited to the specific embodiments described above, but includes variations, modifications and equivalent embodiments. The invention is further described in the following non-limiting examples.

EXAMPLES

Example 1- Polymer Additive

15.6 parts of amyl acetate and 15.6 parts of ethyl ethoxy propionate were loaded into a reactor and heated to 110⁰C under a nitrogen blanket. A solution of monomers including 36.1 parts of ethyl hexyl acrylate, 19.4 parts of glycidyl methacrylate, 0.6 parts styrene, 0.6 parts of methyl methacrylate, 1.2 parts of hydroxyethyl acrylate, 1.2 parts of hydroxyl propyl methacrylate, 1.2 parts of hydroxylethyl methacrylate and 0.5 parts of free radical initiator from (Vazo® 67 from Du Pont) were added over a three hour period. Then a solution of 0.2 parts of Vazo® 67 in 4.9 parts of aromatic S-100 (Solvesso aromatic solvent) was added over a one hour period. Then 3.2 parts of amyl acetate was added. The reaction mixture was held at 110⁰C for 75 minutes. The final resin had a NV of 60.6%, Mn of 10175 Daltons. It had an epoxy equivalent weight of 440 grams per equivalents and an OH equivalent weight of 2264 grams per equivalents.

Comparative Polymer Additive

A GMA resin having a molecular weight between 10,000 and 15,000 Daltons, no hydroxyl functionality, an epoxy equivalent weight of 440 grams per equivalent and a Tg of less than -20 ⁰C was used as the comparative polymer additive.

Example 3- Coating Composition

BASF Corp. proprietaiy carbamate acrylic resin having a Tg 100⁰C, an idealized carbamate equivalent weight of 406 and used in 70% solution.

² BASF Corp. proprietary carbamate acrylic resin having a Tg of > 15O⁰C, an idealized carbamate equivalent weight of 340 and used in 31% solution.

CIearcoat Examples

Three clearcoats were prepared from the above coating composition.

Coating A -1.62% of a commercial epoxy resin having no hydroxyl functionality, Mw greater than 10,000 daltons and a Tg of < ^'20⁰C was added.

Coating B-1.62% of the hydroxyl-functional epoxy was added.

Coating C- no epoxy was added.

Repair Adhesion Evaluation

Each resultant clearcoat was evaluated for repair adhesion with the following process, using a commercial BASF high solids basecoat and electrocoated, cold-rolled steel panels: Apply OEM basecoat layer to 0.5-0.7 mils thickness

Apply OEM clearcoat layer to 1.0-1.4 mils thickness

Bake panel for 5 minutes at 25O⁰F

Apply repair basecoat layer, varying film thickness from 0 to 2.0 mils thickness Apply repair clearcoat layer to 1.0-1.4 mils thickness

Cooled panels were scribed along its entire length using a 2mm Crosshatch cutting tool Scotch 898 adhesive tape was applied to the scribes and pulled

Percent adhesion was recorded for scribes at 0, 0.5, and 1.0 mils of repair basecoat thickness.

Adhesion to Window Sealant

MVSS (Motor Vehicle Safety Standard) testing is required to insure that the windshield properly adheres to the vehicle, since it is a structural component. The standard requires that the windshield adhesive adhere to the painted surface, and failure must be cohesive within the adhesive bead. Generally, a "quick-knife" method is used to test this property. This method is described as follows:

1. To a cured, painted steel panel coated with the clearcoat to be tested, a bead of urethane windshield adhesive (specifically DOW Betaseal 15625) was applied using a caulking gun.

2. The adhesive, which reacts with moisture was allowed to cure for several days in a controlled humidity environment.

3. When cured, the adhesive and underlying coat was cut using a razor knife at about 1/8 inch intervals along the length of the test panel, while at the same time applying a constant upward force.

In areas where there is adhesive weakness between the adhesive and the clearcoat layer, or cohesive weakness within the underlying coating layers, the adhesive bead is released from the panel. For a passing rating, there will be an adhered layer of adhesive on the test panel, and the top portion of the bead will be removed (cohesive failure of the adhesive).

Clearcoat samples B and C as described above were evaluated for MVSS testing. Clearcoats were sprayed on electrocoated steel panels and baked at two temperatures. The above "quick- knife" test was then run with the following result:

MVSS Adhesion Testing Results

Claims

WHAT IS CLAIMED IS:

1. A composition comprising a. a binder polymer with a first functional group that is reactive with a second functional group, b. a crosslinking agent with the second functional group, and c. a polymer additive with a third functional group that can react with the second functional group and may optionally contain additional functionality which does not react with the first or second functional group and wherein said polymer additive will concentrate more at an interface region of a coating formed from the composition along the surface of the coating than in the bulk of the coating.

2. The composition of claim 1, wherein the polymer additive is present in the composition in an amount from about 0.1% to about 10% by weight of a combined amount of the binder polymer and the polymer additive in the coating composition.

3. The composition of claim 1, wherein the polymer additive is a reaction product of monomers in which 30 to 70 % by weight of the total monomers used to form the polymer addditive are hydrophobic monomers.

4. The composition of claim 1, wherein the polymer additive has a Tg of <0°C.

5. The composition of claim 1, wherein the polymer additive has a Tg of <-20°C.

6. The composition of claim 1, wherein the polymer additive has a number average molecular weight >10,000 daltons.

7. The composition of claim 1, wherein the polymer additive has a number average molecular weight > 15,000 daltons.

8. The composition of claim 1, wherein the polymer additive is a reaction product of monomers in which 30 to 70 % by weight of the total monomers are hydrophobic monomers, the polymer has a Tg of <0°C, and the polymer has a number average molecular weight >10,000 daltons.

9. The composition of claim 1, wherein the third functional group is selected from the group consisting of hydroxyl, carbamate, acid, and Si-OR, wherein R is an organic radical.

10. The composition of claim 1, wherein the polymer additive comprises an epoxy group containing polymer, wherein the epoxy group is essentially non-reactable with the binder polymer or crosslinker during the cure cycle.

11. The composition of claim 1, wherein the polymer additive is a reaction product of glycidyl (meth)acrylate, a hydroxyalkyl (meth)acrylate, an alkyl (meth)acrylate, and, optionally a vinyl aromatic.

12. The composition of claim 11, wherein the glycidyl (meth)acrylate is glycidyl methacrylate having an epoxy equivalent weight between 350 and 2000 grams per equivalent.

13. The composition of claim 11, wherein hydroxyalkyl (meth)acrylate is present in the polymer and has a hydroxyl equivalent weight between 1500 and 15,000 grams per equivalents.

14. The composition of claim 11, comprising hydroxyalkyl (meth)acrate containing primarily secondary hydroxyl functionality.

15. The composition of claim 14, wherein the level of primary functional groups is reduced by reaction with a mono-functional capping agent that preferentially reacts with pimary hydroxyl groups over secondary hydroxyl groups.

16. The composition of claim 15 wherein the capping agent is at least one of mono- functional isocyanate, mono-functional aminoplast, and anhydride.

17. The composition of claim 16 wherein the capping agent is a poly-functional agent comprising capping groups wherein all but one of the capping groups on average is pre-reacted with a material having additional functional groups reactive with said polyfunctional agent.

18. The composition of claim 17 wherein the material having additional functional groups contains functional groups which would not react with the functional group(s) on the capping agent or the polymer additive.

19. The composition of claim 1 wherein the polymer additive comprises compounds selected from the group consisting of ultraviolet absorbers, hindered amine light stabilizers,

Si-OR, where R is alkyl, aryl, alkyl aryl, and C(O)R where R contains between one to ten carbon atoms, and mixtures thereof.

20. The composition of claim 1 wherein the Tg of the polymer additive is from 10⁰C to 15O⁰C and the number average molecular weight is from 1000 to 10,000 Daltons. .

21. The composition of claim 10, wherein the composition further comprises materials that promote ring opening of an epoxy group when concentrated on the surface.

22. The composition of claim 1, wherein the composition is free of materials that promote the ring opening of an epoxy group.

23. The composition of claim 1, further comprising compounds selected from the group consisting of organic acids containing at least 8 carbon atoms, phosphoric acids and derivatives thereof, sulfonic acids and derivatives thereof and tin and mixtures thereof.

24. The composition of claim 1, wherein the composition is free from organic acids containing at least 8 carbon atoms, phosphoric acids and derivatives thereof, sulfonic acids and derivatives thereof and tin.

25. The composition of claim 1, wherein the first functional group and the second functional group form a urethane linkage when reacted together.

26. The composition of claim 25, wherein the first and second functional groups are selected from the group consisting of (i) a first functional group that is primary carbamate and a second functional group that is an aminoplast, (ii) a first functional group that is hydroxyl and a second functional group that is isocyanate (free or blocked), (iii) a first functional group that is amine and a second functional group that is a cyclic carbonate, and mixtures of any of (i)-(iii).

27. The composition of claim 1, further comprising a solvent.

28. The composition of claim 17, wherein the solvent comprises water.

29. The composition of claim 1, further comprising compounds selected from the group consisting of ultraviolet light absorbers, hindered amine light stabilizers and mixtures thereof.

30. The composition of claim 1, wherein a coating formed from the composition has a 20° gloss, as measured by ASTM D523-89, of at least 80.

31. The composition of claim 1, wherein a coating formed from the composition has a DOI, as measured by ASTM E430-91, of at least 80.

32. A multilayer coating comprising more than one layer on a substrate, wherein at least one layer is formed from the composition of claim 1.

33. The multilayer coating of claim 32, wherein a concentration of the polymer additive is higher at a surface interface region of the coating film than in a bulk region of the coating film..

34. The multilayer coating of claim 32, wherein the coating formed from the composition of claim 1 is capable of being cured at a temperature of from 180⁰F to 31O⁰F. with a bake time between 5 minutes to 50 minutes.

35. The multilayer coating of claim 32, wherein the at least one layer is a clearcoat layer.