WO2013113642A1

WO2013113642A1 - Repair process and primer composition

Info

Publication number: WO2013113642A1
Application number: PCT/EP2013/051527
Authority: WO
Inventors: Shashikiran KRISHNADAS; Swarup DAS; Sanjeevappa ANUMOLU
Original assignee: Akzo Nobel Coatings International B.V.
Priority date: 2012-01-30
Filing date: 2013-01-28
Publication date: 2013-08-08

Abstract

The invention relates to a process of repairing the exterior coating of a vehicle comprising the steps of a) applying a first coating composition to an exterior damaged coated area of a vehicle, b) curing the applied first coating composition to form a first layer c) applying and curing at least one further coating composition on the first layer to form at least one second layer, wherein the first coating composition comprises i) a curable material having curable functional groups, and wherein the average equivalent weight of the curable functional groups is in the range of 65 g/mol to 400 g/mol, ii) a curing agent having functional groups reactive with the functional groups of the curable material, wherein the average equivalent weight of the functional groups is in the range of 65 g/mol to 400 g/mol, and iii) at least one organic solvent having a boiling point below 100°C at atmospheric pressure, and wherein the pigment volume concentration of the first coating composition is in the range of 0 to 40%, and wherein at least one of the curable material or the curing agent has an average of at least 3 functional groups per molecule. The invention also relates to a primer coating composition.

Description

Repair process and primer composition

The invention relates to a process of repairing the exterior coating of a vehicle and to a primer coating composition used in the process.

Japanese patent application JP 500092334 A describes that the adhesion of urethane coatings to Al or alloys thereof is improved by coating the substrate with a urethane resin primer coating composition containing an aliphatic isocyanate before top coating.

International patent application WO 02/10241 A relates to a multi-layered coating, consisting of a base coat of a high-molecular, gel-type polyurethane and a top coat consisting of a polyurethane lacquer. The multi-layered coatings are prepared by subsequently introducing the gel-type primer and the top coat in a mould.

A problem of exterior vehicle coating repair processes is the risk of visible repair marks when the damaged area is partly or entirely surrounded by the original coating.

The original coating of an automobile generally comprises several layers, typically a primer layer, a colour and/or effect imparting base coat layer, and a clear top coat layer. Before any layers of repair coatings are applied, the area to be repaired and the original coating adjacent to the area to be repaired are sanded to remove any unevenness and to provide a smooth surface for application of the repair coating layers. As a consequence, the layer boundaries of the original coating are exposed.

A generally known problem of exterior vehicle coating repair processes is the risk of visible repair marks when the damaged area is partly or entirely surrounded by the original coating. It is believed that this is at least partly caused by interaction with the original coating layers caused by solvents or other components of the repair coating compositions. The effect is also known as contour mapping. It is observed when conventional primer-fillers are applied. Such primer-fillers generally have a pigment volume concentration above 40%.

Visible repair marks or contour mapping are of course undesirable.

Therefore, a need exists for processes and coating compositions which reduce or eliminate the occurrence of visible repair marks or contour mapping.

The invention now provides a process of repairing the exterior coating of a vehicle comprising the steps of

a) applying a first coating composition to an exterior damaged coated area of a vehicle,

b) curing the applied first coating composition to form a first layer

c) applying and curing at least one further coating composition on the first layer to form at least one second layer,

wherein the first coating composition comprises

i) a curable material having curable functional groups, and wherein the average equivalent weight of the curable functional groups is in the range of 65 g/mol to 400 g/mol,

ii) a curing agent having functional groups reactive with the functional groups of the curable material, wherein the average equivalent weight of the functional groups is in the range of 65 g/mol to 400 g/mol, and

iii) at least one organic solvent having a boiling point below 100°C at atmospheric pressure,

and wherein the pigment volume concentration of the first coating composition is in the range of 0 to 40%, and wherein at least one of the curable material or the curing agent has an average of at least 3 functional groups per molecule. It has been found that the process of the invention leads to vehicle repair coatings wherein repair marks or contour mapping are significantly reduced or entirely absent. In one embodiment, the primer coating composition is a clear coat composition. This means that the composition is entirely or essentially free of pigments. In a further embodiment, the primer composition is a pigmented coating composition.

The pigmented primer coating compositions typically has a pigment volume concentration in the range of 5 to 40%. Preferably, the pigmented primer composition has a low pigment volume concentration, for example in the range of 5 to 20 %, or 5 to 15%. It has been found that the beneficial effects of the process are most prominent with a low pigment volume concentration. When the pigment volume concentration is low, the technical benefits can also be achieved at lower dry film thickness of the primer coating. The pigment volume concentration is defined as the ratio of the volume of pigments, fillers, extenders, and other non film-forming solid particles to the total volume of non-volatile components of the composition. The primer is generally applied as a first coating layer having a dry film layer thickness in the range of 80 to 200 μηη.

When formulated as a pigmented primer at a pigment volume concentration above 5%, it is preferred that the primer is applied as a first coating layer having a dry film layer thickness in the range of 100 to 200 μηη. When the primer is applied as a clear coat, or when it has a pigment volume concentration not exceeding 5%, it is preferred that the dry film layer thickness is in the range of 80 to 120 μηη.

The above-said primer coating composition is very specific in overcoming such problems as described above. Further, it has been found to be preferable to use a primer composition having a low pigment volume concentration to render the primer layer relatively more non-porous. In addition to this, there is a relation to the binder cross-link network density (per unit volume), primer-filler build thickness, and primer-filler pigment volume concentration (PVC). At lower PVC, a given binder system would be relatively less porous, but if it has large space between functional groups, it would render the film softer and porous. Hence, there is a need to use a primer-filler having binders and crosslinkers of lower equivalent weight. In addition, it is preferred to be rapid-setting to allow it to be sanded as soon as possible after application. In one embodiment, the primer-filler is sandable within 90 minutes or less after application and dries at ambient temperature (23°C). Individually, the features of the primer composition, such as low equivalent weight of the functional groups, low PVC, and presence of a low boiling solvent, will not suffice to achieve the desired effect. Actually, it is the combination of features which is essential to the invention.

It has been found that the problem of contour mapping in vehicle coating repair processes is particularly severe when the original coating of the vehicle comprises a clear top coat layer prepared from a powder coating composition. Accordingly, the process of the invention is particularly beneficial for repairing vehicles having a clear top coat layer prepared from a powder coating composition.

The problem of contour mapping has been found to be even more prominent when such a clear top coat layer has a common layer boundary with a base coat layer prepared from an aqueous base coat composition. Therefore, the process can be used with greatest advantage for repairing vehicles having a clear top coat layer prepared from a powder coating composition, which clear coat layer has a common layer boundary with a base coat layer prepared from an aqueous or solvent borne base coat composition. The process is particularly suitable for the coatings of vehicles which have been damaged due to an accident. Examples of vehicles include trains, buses, trucks, agricultural machines, and in particular automobiles. The repair may include the renewal of the entire coating of a vehicle or a part thereof. The process is particularly suitable for so-called spot repair. Spot repair means the repair of relatively minor damage wherein the spot to be repaired is at least partially surrounded by or adjacent to the original coating layer.

Prior to the process according to the invention, the vehicle in need of repair is suitably prepared for the repair coating process. The preparation steps are those which are usual and which are known to the skilled person. Typical preparation steps include cleaning, filling of larger dents with filling material, or other steps of mechanical repair, sanding, and protection of neighboring portions of the vehicle against spray mist. When the damaged vehicle has been prepared for repair coating, the first coating composition is applied to the damaged area. The first coating composition may also be referred to as the primer coating composition. The first coating composition is typically applied by spraying, although other application methods, such as rolling or brushing, may be used as well.

The first coating composition generally is a fast curing coating composition, leading to a cured coating having a relatively high crosslink density. This is achieved by using a curable material and a curing agent having a high functionality and a low molecular weight. The average equivalent weight of the reactive functional groups in the curable material and in the curing agent is in the range of 65 g/mol to 400 g/mol, calculated on the non-volatile content of the curable material and the curing agent, respectively.

Examples of suitable curable functional groups of the curable material are hydroxyl groups, secondary amino groups, primary amino groups, thiol groups, and mixtures thereof. The curable material may be a relatively low molecular weight multi- functional compound. Alternatively, the curable material may be a polymer or oligomer having pendant functional groups of the above-mentioned type.

The primer coating composition further comprises a curing agent having functional groups reactive with the functional groups of the curable material. It is to be understood that the reactive functional groups in the curable material and the functional groups of the curing agent are not the same. The average equivalent weight of the functional groups is in the range of 65 g/mol to 400 g/mol, calculated on the non-volatile content of the curing agent. A typical example of functional groups for the curing agent are isocyanate groups.

The equivalent weight of the functional groups of the curable material and of the curing agent can suitably be determined by known methods, for example by titration. Methods for the determination of common functional groups, for example hydroxyl groups, amino groups, thiol groups, and isocyanate groups, are laid down in industrial standard methods which are known to the skilled person.

Typically, the reactive functional groups of the curable material and the curing agent are selected to be mutually reactive upon mixing at room temperature, optionally in the presence of a curing catalyst.

In a further embodiment, the curable functional groups of the curable material are acetoacetate groups and the functional groups of the curing agent are selected from amino groups, ketimine groups, acrylate groups or mixtures thereof. In order to further enhance the fast curing and fast setting characteristics of the primer coating composition, it comprises at least one low boiling organic solvent having a boiling point, at atmospheric pressure, below 100°C. Examples of suitable organic solvents are acetone, ethyl acetate, and methyl ethyl ketone. The amount of this low boiling organic solvent in the coating composition typically, is in the range of 10-40% by weight, calculated on the total weight of the primer coating composition. In one embodiment, the primer coating composition is a clear coat composition. This means that the composition is entirely or essentially free of pigments / extenders. In a further embodiment, the primer composition is a pigmented coating composition. The pigmented primer coating compositions typically has a pigment volume concentration in the range of 5 to 40%, preferably 10 to 35%.

Suitable pigments / extenders are generally known to the skilled person and include anti-corrosive pigments and fillers.

As mentioned above, at least one further coating composition is applied on the first layer. When the first layer is a pigmented primer composition, it is preferred that the further coating composition is a colour and/or effect imparting base coat composition, followed by a clear coat composition. Alternatively, the further coating composition is a pigmented top coat composition.

If the first coating composition is a clear coating composition, it is preferred that the first layer is followed by a pigmented primer-filler layer or a putty filler compound, which is further sanded after application and drying. This would be followed by a base coat and clear coat or a pigmented single layer top coat as described above.

The invention further relates to a primer coating composition for use in the process. It concerns a primer coating composition comprising

i) a curable material having an average of at least 3 curable functional groups, and wherein the average equivalent weight of the curable functional groups is in the range of 65 g/mol to 400 g/mol, ii) a curing agent having functional groups reactive with the functional groups of the curable material, wherein the average equivalent weight of the functional groups is in the range of 65 g/mol to 400 g/mol, and

and wherein the pigment volume concentration of the primer coating composition is in the range of 0 to 40%. In a preferred embodiment, the curable functional groups of the curable material are selected from hydroxyl groups, secondary amino groups, primary amino groups, thiol groups, and mixtures thereof, and the functional groups of the curing agent are isocyanate groups. Suitable curable materials include polyols. Examples of suitable polyols include compounds comprising at least three hydroxyl groups. These may be monomers, oligomers, polymers, and mixtures thereof. Examples of hydroxy-functional oligomers and monomers are castor oil and trimethylol propane. Examples of suitable polymers include polyester polyols, polyacrylate polyols, polycarbonate polyols, polyurethane polyols, melamine polyols, and mixtures and hybrids thereof. Such polymers are generally known to the skilled person and are commercially available. Suitable polyester polyols, polyacrylate polyols, and mixtures thereof are for example described in International patent application WO 96/20968 and in European patent application EP 0688840 A. Examples of suitable polyurethane polyols are described in International patent application WO 96/040813.

Further examples include hydroxy-functional epoxy resins, alkyds, and dendrimeric polyols such as described in International patent application WO 93/17060. Examples of amine-functionai curable materials are in particular "poly aspartic acid derivatives" based on the addition reaction of amines and maieic or fumaric acid derivatives. Examples of suitable amine-functional curable materials include 1 ,4- diaminobutane, 1 ,6-diaminohexane, 2,2,4- and 2,4,4-trimethyl-1 ,6-diaminohexane, 1 -amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane, 4,4'-diamino-dicyclohexyl methane or 3,3-dimethyl-4,4'-diamino-dicyclohexyl methane.

Suitable polyamines include ethylene diamine, 1 ,2-diaminopropane, 1 ,4- diaminobutane, 1 ,6-diaminohexane, 2,5-diamino-2,5-dimethylhexane, 2,2,4-and/or 2,4,4-trimethyl-1 ,6-diaminohexane, 1 ,1 1 -diaminoundecane, 1 ,12-diaminododecane, 1 -amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane, 2,4-and/or 2,6- hexahydrotoluylene diamine, 2,4'-and/or 4,4'-diamino-dicyclohexyl methane and 3,3'-dimethyl-4,4'-diamino-dicyclohexyl methane. Aromatic polyamines such as 2,4- and/or 2,6-diaminotoluene and 2,4'-and/or 4,4'-diaminodiphenyl methane are also suitable. Relatively high molecular weight polyether polyamines containing aliphatically bound primary amino groups, for example, the products marketed under the Jeffamine® trade designation, are also suitable.

Examples of optionally substituted maieic or fumaric acid esters suitable for use in the preparation of the poly aspartic acid derivatives include dimethyl, diethyl, and di-butyl esters of maieic acid and fumaric acid and the corresponding maieic or fumaric acid esters substituted by methyl in the 2- and/or 3-position.

The preparation of the "poly aspartic acid derivatives" from the above-mentioned starting materials may be carried out, for example, at a temperature of 0 to 100°C, using the starting materials in such proportions that at least 1 , preferably 1 , olefinic double bond is present for each primary amino group. Excess starting materials may be removed by distillation after the reaction. The reaction may be carried out solvent-free or in the presence of suitable solvents such as methanol, ethanol, propanol, dioxane, and mixtures of such solvents. Examples of suitable commercially aspartates are Desmophen® N H 1 220, Desmophen®NH 1420, and Desmophen® NH 1520, all ex Bayer.

The curable functional groups of the curable material may also comprise thiol- functional groups. Suitable thiol-functional compounds include esters of a thiol- functional carboxylic acid with a polyol, such as esters of 2-mercaptoacetic acid, 3- mercaptopropionic acid, 2-mercaptopropionic acid, 1 1 -mercaptoundecanoic acid, and mercaptosuccinic acid. Examples of such esters include pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (2-mercaptoacetate), trimethylol propane tris (3-mercaptopropionate), trimethylol propane tris (2- mercaptopropionate), and trimethylol propane tris (2-mercaptoacetate). A further example of such a compound consists of a hyperbranched polyol core based on a starter polyol, e.g. trimethylol propane and dimethylol propionic acid, which is subsequently esterified with 3-mercaptopropionic acid and isononanoic acid. These compounds are described in European patent application EP-A-0 448 224 and International patent application WO 93/17060.

Addition products of H₂S to epoxy-functional compounds also give thiol-functional compounds. These compounds may have a structure of the following formula: T[(O-CHR-CH₂-O)nCH₂CHXHCH₂YH]_m, with T being a m-valent organic moiety, R being hydrogen or methyl, n being an integer between 0 and 10, X and Y being oxygen or sulfur, with the proviso that X and Y are not equal. An example of such a compound is commercially available from Cognis under the trademark Capcure^® 3/800. Other syntheses to prepare compounds comprising thiol-functional groups involve: the reaction of an aryl or alkyl halide with NaHS to introduce a pendant mercapto group into the alkyl and aryl compounds, respectively; the reaction of a Grignard reagent with sulfur to introduce a pendant mercapto group into the structure; the reaction of a polymercaptan with a polyolefin according to a nucleophilic reaction, an electrophilic reaction or a radical reaction; and the reaction of disulfides.

Preferred thiol-functional compounds are pentaerythritol tetrakis(3-mercapto propionate), trimethylol propane tris(3-mercaptopropionate), and Capcure® 3/800.

In another embodiment of the invention, the thiol groups can be covalently attached to a resin. Such resins include thiol-functional polyurethane resins, thiol-functional polyester resins, thiol-functional polyaddition polymer resins, thiol-functional polyether resins, thiol-functional polyamide resins, thiol-functional polyurea resins, and mixtures thereof. Thiol-functional resins can be prepared by the reaction of H₂S with an epoxy group or an unsaturated carbon-carbon bond-containing resin, the reaction between a hydroxyl-functional resin and a thiol-functional acid, and by the reaction of an isocyanate-functional polymer and either a thiol-functional alcohol or a di- or polymercapto compound.

In a further embodiment, the curable material comprises amine-functional groups. Especially suitable are polyaspartic acid derivatives, which are commercially available, for example under the trade designation Desmophen®.

Suitable isocyanate-functional curing agents for use in the primer coating composition are isocyanate-functional compounds comprising at least two isocyanate groups. Preferably, the isocyanate-functional crosslinker is a polyisocyanate, such as an aliphatic, cycloaliphatic or aromatic di-, tri- or tetra- isocyanate. Examples of diisocyanates include 1 ,2-propylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, 2,3-butylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, dodecamethylene diisocyanate, ω,ω'-dipropylether diisocyanate, 1 ,3-cyclopentane diisocyanate, 1 ,2-cyclohexane diisocyanate, 1 ,4- cyclohexane diisocyanate, isophorone diisocyanate, 4-methyl-1 ,3- diisocyanatocyclohexane, trans-vinylidene diisocyanate, dicyclohexyl methane- 4,4'-diisocyanate (Desmodur^® W), toluene diisocyanate, 1 ,3-bis(isocyanatomethyl) benzene, xylylene diisocyanate, α,α,α',α'-tetramethyl xylylene diisocyanate (TMXDI^®) , 1 , 5-dimethyl-2,4-bis(2-isocyanatoethyl) benzene, 1 ,3,5-triethyl-2,4- bis(isocyanatomethyl) benzene, 4,4'-diisocyanato-diphenyl, 3,3'-dichloro-4,4'- diisocyanato-diphenyl, 3,3'-diphenyl-4,4'-diisocyanato-diphenyl, 3,3'-dimethoxy- 4,4'-diisocyanato-diphenyl, 4,4'-diisocyanato-diphenyl methane, 3,3'-dimethyl-4,4'- diisocyanato-diphenylmethane, and diisocyanatonaphthalene. Examples of triisocyanates include 1 ,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 1 ,8- diisocyanato-4-(isocyanatomethyl) octane, and lysine triisocyanate. Adducts and oligomers of polyisocyanates, for instance biurets, isocyanurates, allophanates, uretdiones, urethanes, and mixtures thereof, are also included. Examples of such oligomers and adducts are the adduct of 2 molecules of a diisocyanate, for example hexamethylene diisocyanate or isophorone diisocyanate, to a diol such as ethylene glycol, the adduct of 3 molecules of hexamethylene diisocyanate to 1 molecule of water (available under the trademark Desmodur® N of Bayer), the adduct of 1 molecule of trimethylol propane to 3 molecules of toluene diisocyanate (available under the trademark Desmodur® L of Bayer), the adduct of 1 molecule of trimethylol propane to 3 molecules of isophorone diisocyanate, the adduct of 1 molecule of pentaerythritol to 4 molecules of toluene diisocyanate, the adduct of 3 moles of m-a,a,a',a'-tetramethyl xylene diisocyanate to 1 mole of trimethylol propane, the isocyanurate trimer of 1 ,6-diisocyanatohexane, the isocyanurate trimer of isophorone diisocyanate, the uretdione dimer of 1 ,6-diisocyanatohexane, the biuret of 1 ,6-diisocyanatohexane, the allophanate of 1 ,6-diisocyanatohexane, and mixtures thereof. Furthermore, (co)polymers of isocyanate-functional monomers such as α,α'-dimethyl-m-isopropenyl benzyl isocyanate are suitable for use.

In the coating composition according to the invention the equivalent ratio of functional groups of the curing agent to functional groups of the curable material suitably is between 0.5 and 4.0, preferably between 0.7 and 3.0, and more preferably between 0.8 and 2.5. Generally, the weight ratio of curable material to isocyanate-functional crosslinker in the coating composition, based on non-volatile content, is between 85 : 15 and 15 : 85, preferably between 70 : 30 and 30 : 70.

In a further embodiment, the curable functional groups of the curable material are acetoacetate groups and the functional groups of the curing agent are selected from amino groups, ketimine groups, acrylate groups or mixtures thereof. Examples of suitable curable materials having acetoacetate groups include an acetoacetoxy-functional derivative of a low molecular weight polyol, especially a monomeric polyol. As used herein, the term "acetoacetoxy-functional derivatives of polyols" means acetoacetoxy-functional compounds generally obtained by the chemical conversion of at least some of the hydroxyl groups of the polyol to an acetoacetoxy group or to a group containing one or more acetoacetoxy groups. These acetoacetoxy-functional derivatives of low molecular weight polyols help provide additional crosslinking sites and reduce the overall viscosity of the final curable composition. The polyol starting material should have an average of at least two hydroxy-functionai groups per molecule and should have a number average molecular weight of less than 1 ,000 and preferably less than 500. Preferred polyols are the aliphatic, polyether, polyester, and polyurethane polyols, especially diols and triols. Suitable polyols, for example, include diols such as ethylene glycol, dipropylene glycol, 2,2,4-trimethyl 1 ,3-pentanediol, neopentyl glycol, 1 ,2-propanediol, 1 ,4-butanediol, 1 ,3-butanediol, 2,3-butanediol, 1 ,5- pentanediol, 1 ,6-hexanediol, 2,2-dimethyl-1 ,3-propanediol, 1 ,4-cyclohexane- dimethanol, 1 ,2-cyclohexanedimethanol, 1 ,3-cyclohexanedimethanol, 1 ,4-bis(2- hydroxyethoxy)cyclohexane, tri methylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, norbornylene glycol, 1 ,4- benzenedimethanol, 1 ,4-benzenediethanol, 2,4-dimethyl-2-ethylenehexane-1 ,3-diol, 2-butene-1 ,4-diol, and polyois such as trimethylolethane, trimethylolpropane, trimethylolhexane, triethylolpropane, 1 ,2,4-butanetriol, glycerol, pentaerythritol, dipentaerythritol, poiycaproiactone polyois, etc. The acetoacetyiation to convert the hydroxyl groups of the polyois to the corresponding acetoacetoxy-functional derivatives can be conveniently accomplished by transesterification with a suitable acetoacetoxy ester, by direct reaction with diketene, or any other method known in the art. The acetoacetoxy-functional derivative generally has an average of at least 2 acetoacetate groups per molecule and, preferably, at least 3.0 acetoacetoxy groups per molecule.

Suitable ketimine compounds are typically prepared by the reaction of ketones with amines. Representative ketones which may be used to form the ketimine include acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, diethyl ketone, benzyl methylketone, diisopropyl ketone, cyclopentanone, and cyclohexanone. Representative amines which may be used to form the ketimine include ethylene diamine, ethylene triamine, propylene diamine, tetramethylene diamine, 1 ,6-hexamethylene diamine, bis(6-aminohexyl)ether, tricyclodecane diamine, Ν,Ν'-dimethyldiethyltriamine, cyclohexyl-1 ,2,4-triamine, cyclohexyl- 1 ,2,4,5-tetraamine. 3,4,5-triaminopyran, 3,4-diaminofuran, and cycloaliphatic diamines. The ketimines are conveniently prepared by reacting a stoichiometric excess of the ketone with the polyamine in an azeotropic solvent and removing water as it is formed. In order to minimize side reactions, and to avoid delays due to prolonged processing, it is frequently desirable to avoid the prolonged heating necessary to remove all of the excess ketone and unreacted starting materials, provided that their presence does not adversely affect the performance of the final product.

One preferred type of ketimine compound for reaction with acetoacetoxy-functional materials in the practice of this invention is an adduct obtained by reacting an ketimine having an additional reactive group other than a ketimine, such as a hydroxyl group or, preferably, an amine group, with a compound, such as an isocyanate, or an epoxide, having one or more chemical groups or sites capable of reaction with the additional reactive group. One commercial ketimine having an additional reactive group is Epicure® 3501 , which is the reaction product of diethylene triamine and methyl isobutyl ketone.

Polyisocyanates useful for reaction with the hydroxyl or amine group of the ketimine in the preferred configuration have an average of at least two isocyanate groups per molecule. Representative polyisocyanates are those mentioned above. For reaction with the imines having unreacted amine groups, representative useful monoepoxides include the monoglycidyl ethers of aliphatic or aromatic alcohols such as butyl glycidyl ether, octyl glycidyl ether, nonyl glycidyl ether, decyl glydicyl ether, dodecyl glycidyl ether, p-tertbutylphenyl glycidyl ether, o-cresyl glycidyl ether, and 3-glycidoxypropyl trimethoxysilane. Monoepoxy esters such as the glycidyl ester of versatic acid (commercially available as CARDURA® E), or the glycidyl esters of other acids such as tertiary-nonanoic acid, tertiary -decanoic acid, tertiary- undecanoic acid, etc. are also useful.

Additionally, epoxidized oils can also be used. Preferred as the poiy-functionai epoxy compounds, due to their reactivity and durability, are the polyepoxy-functional novalac, bisphenol, and cycloalphatic epoxies. Preferably, the polyepoxies will have a number average molecular weight of less than about 2,000 to minimize the viscosity of the adduct.

The coating composition of the invention may comprise catalyst for the reaction between the functional groups of the curable material and the curing agent. Suitable catalysts are known to the skilled person. The catalyst is generally used in an amount of 0.001 to 10 weight-%, preferably 0.002 to 5 weight-%, more preferably in an amount of 0.01 to 1 weight-%, calculated on the non-volatile matter of the coating composition.

Suitable metals in the metal based catalyst include zinc, cobalt, manganese, zirconium, bismuth, and tin. It is preferred that the coating composition comprises a tin based catalyst. Well-known examples of tin based catalysts are dimethyl tin dilaurate, dimethyl tin diversatate, dimethyl tin dioleate, dibutyl tin dilaurate, dioctyl tin dilaurate, and tin octoate.

In addition to the low boiling organic solvent mentioned above, the primer composition may comprise other organic solvents. Examples of suitable volatile organic solvents are alcohols such as iso-butanol, hydrocarbons, such as toluene, xylene, Solvesso 100, ketones, terpenes, such as dipentene or pine oil, halogenated hydrocarbons, such as dichloromethane, ethers, such as ethylene glycol dimethyl ether, esters, such as ethyl propionate, n-butyl acetate, ether esters, such as methoxypropyl acetate or ethoxyethyl propionate. Also mixtures of these compounds can be used.

If so desired, it is possible to include one or more so-called "exempt solvents" in the coating composition. An exempt solvent is a volatile organic compound that does not participate in an atmospheric photochemical reaction to form smog. It can be an organic solvent, but it takes so long to react with nitrogen oxides in the presence of sunlight that the Environmental Protection Agency of the United States of America considers its reactivity to be negligible. Examples of exempt solvents that are approved for use in paints and coatings include acetone, methyl acetate, parachlorobenzotrifluoride (commercially available under the name Oxsol® 100), and volatile methyl siloxanes. Also tertiary butyl acetate is being considered as an exempt solvent.

The non-volatile content of the primer coating composition of the invention preferably is in the range of 60 - 80% by weight, calculated on the weight of the entire composition.

In addition to the components described above, other compounds can be present in the primer coating composition according to the present invention. Such compounds may be binders and/or reactive diluents, optionally comprising reactive groups which may be crosslinked with the aforesaid hydroxy-functional compounds and/or isocyanate-functional crosslinkers. Examples of such other compounds are ketone resins, and latent amino-functional compounds such as oxazolidines, ketimines, aldimines, and diimines. These and other compounds are known to the skilled person and are mentioned, int. al., in US 5214086.

The coating composition may further comprise other ingredients, additives or auxiliaries commonly used in coating compositions, such as pigments, dyes, surfactants, pigment dispersion aids, levelling agents, wetting agents, anti-cratering agents, antifoaming agents, antisagging agents, heat stabilizers, light stabilizers, UV absorbers, antioxidants, and fillers.

The curable material and the curing agent are generally mutually reactive upon mixing. Therefore, the coating composition has a limited pot life after mixing all components. The coating composition can suitably be prepared by a process comprising mixing a binder module comprising the curable materials and a crosslinker module comprising the curing agent. Therefore, the composition is suitably provided as a multi-component composition, for example as a two-component composition or as a three-component composition. Therefore, the invention also relates to a kit of parts for preparing the coating composition. Examples

Starting materials

Desmodur® N-75 Polyisocyanate ex Bayer NCO equivalent weight is 191

NCO content 16.6%. g/equivalent

Average functionality is above 3

Desmodur® N-3390 Polyisocyanate ex Bayer NCO equivalent weight is 192

NCO content 15.5% g/equivalent

Avg Functionality->3 Average functionality is above 3

Desmophen ®1420 Aspartate based sterically Used as such as a cross-linkable hindered amine material

Eq wt-276g. 100% solids

TAPE Tetra-acetoacetate of penta- Acac equivalent weight 132.5 erythritol. g/equivalent

Average functionality is 4

M400NS Tetrafunctional acrylate ex Acrylate equivalent weight is 90

Sartomer g/equivalent

Average functionality is 4 Example 1 : 30% PVC Polvurea Primer-Filler

Binder module

The above formulation at 2:1 weight ratio Part A: Part B, is a pigmented primer-filler of preferably 0-30% PVC formulation. Such a primer-filler is spray applied over a spotted original equipment (OE) panel with 2-3 coats applied at 4-6 minutes flash off between the coats. The primer-filler is applied such that the dry film thickness is about 150-200 μηη. The primer-filler is later sanded after 2 hrs and refinished with base coat and clear coat. In this Example 1 , the primer-filler is tailored to the specific requirement by lowering PVC, increasing cross-link density per unit volume, and having a rapid set binder, all being relative when compared to a standard colour build plus (primer-filler from AkzoNobel), and is applied. There is no intermediate clear binder coat in between the primer-filler and the OE spot panel. Example 2: 30% PVC Acetoacetate-Acrylate primer-filler

Binder module

The above-said primer-filler at 2:1 weight ratio Part A: Part B has a PVC of less than 30%. Such primer-filler is spray applied over a spotted OE substrate and applied 2-3 coats with 5 minutes of flash-off time, such that the dry film thickness is built above 150 μηη and up to 200 μηη. Later the primer-filler is allowed to cure for 2 hrs and sanded with a P400 sand paper to a final dry film thickness of 150-200 μηη. After sanding, primer-filler is wiped with hexane, is refinished with a solvent borne base coat (Auto base plus from AkzoNobel), and further applied with ACIII (clear coat from AkzoNobel) to complete the refinish. Example 3

Polyurea clear coating composition prior to application of conventional primer-filler Binder module

Crosslinker module

The above-said clear binder formulation is added at 1 :1.2 weight ratio of Part A: Part B, spray applied over the spotted OE panel, and allowed to dry for 15-50 minutes. Later the layer is sanded with P400 grit sand paper and a conventional primer-filler is spray applied. The application of clear binder is such that the thickness of the layer is not less than 80 μηη after sanding.

Primer-filler for clear binder applied OE Panel.

Colorbuild Plus (AkzoNobel Primer Filler) was spray applied as a primerfiller over sanded clear binder coated OE as per the instructions of TDS. The primer-filler is sanded after 2 hrs, wiped with hexane to remove loose primer particles, and then a refinish base coat is spray applied, with a final clear coat application (ACIII™ from AkzoNobel). Example 4 low PVC High build Primer-Filler (30% PVC and 102% cross-lining) Binder module

The above formulation is spray applied at 3: 1 Part A:Part B ratio by volume and allowed to cure for 2 hrs at room temperature. The dry film build is such that the thickness after sanding is above 200 μηη. After sanding the primer-filler, Autobase plus (AkzoNobel base coat) and Autoclear I I I (AkzoNobel clear coat) are spray applied to complete the refinish coating process. Comparative Example A (50-60% PVC)

Popular Primer-filler which do not overcome CCM.

Binder module

The above formulation is spray applied at 3: 1 Part A:Part B ratio by volume and allowed to cure for 2 hrs at room temperature. The dry film build is such that the thickness after sanding is above 200 μηη. After sanding the primer-filler, Autobase plus (AkzoNobel base coat) and Autoclear III (Akzonobel clear coat) are spray applied to complete the refinish coating process.

Claims

A process of repairing the exterior coating of a vehicle comprising the steps of a) applying a first coating composition to an exterior damaged coated area of a vehicle,

b) curing the applied first coating composition to form a first layer

wherein the first coating composition comprises

and wherein the pigment volume concentration of the first coating composition is in the range of 0 to 40%, and wherein at least one of the curable material or the curing agent has an average of at least 3 functional groups per molecule.

A process according to claim 1 , wherein the pigment volume concentration in the first coating composition is in the range of 5 to 40%.

3. A process according to claim 1 or 2, wherein the dry film layer thickness of the first coating layer is in the range of 80 to 200 μηη.

A process according to any one of the preceding claims, wherein the pigment volume concentration in the first coating composition does not exceed 5% or wherein the first coating composition is a clear coat composition.

A process according to claim 4, wherein the dry film layer thickness of the first coating layer is in the range of 80-120 μηη.

A process according to any one of the preceding claims, wherein the exterior coating of the vehicle comprises a clear top coat layer prepared from a powder coating composition.

A process according to claim 6, wherein the clear top coat layer has a common layer boundary with a base coat layer prepared from an aqueous or organic solvent borne base coat composition.

A process according to any one of the preceding claims, wherein the curable functional groups of the curable material are selected from hydroxyl groups, secondary amino groups, primary amino groups, thiol groups, and mixtures thereof, and wherein the functional groups of the curing agent are isocyanate groups.

A process according to any one of the preceding claims, wherein the curable functional groups of the curable material are acetoacetate groups and wherein the functional groups of the curing agent are selected from amino groups, ketimine groups, acrylate groups or mixtures thereof.

10. A primer coating composition comprising

ii) a curing agent having functional groups reactive with the functional groups of the curable material, wherein the average equivalent weight of the functional groups is in the range of 65 g/mol to 400 g/mol, and iii) at least one organic solvent having a boiling point below 100°C at atmospheric pressure,

and wherein the pigment volume concentration of the primer coating composition is in the range of 0 to 40% wherein at least one of the curable material or the curing agent has an average of at least 3 functional groups per molecule.

1 1. A primer coating composition according to claim 10, wherein the pigment volume concentration is in the range of 10-35%.

12. A primer coating composition according to claim 10 or 1 1 , wherein the curable functional groups of the curable material are selected from hydroxyl groups, secondary amino groups, primary amino groups, thiol groups, and mixtures thereof, and wherein the functional groups of the curing agent are isocyanate groups.

13. A primer coating composition according to claim 10 or 1 1 , wherein the curable functional groups of the curable material are acetoacetate groups and wherein the functional groups of the curing agent are selected from amino groups, ketimine groups, acrylate groups or mixtures thereof.