WO2013169871A1

WO2013169871A1 - Aqueous coating composition

Info

Publication number: WO2013169871A1
Application number: PCT/US2013/040094
Authority: WO
Inventors: Werner Bosch; Maren BUHK; Carmen Flosbach; Gabriele Buettner; Ralf Dahm; Astrid Tueckmantel
Original assignee: U.S. Coatings Ip Co. Llc; Coatings Foreign Ip Co. Llc
Priority date: 2012-05-10
Filing date: 2013-05-08
Publication date: 2013-11-14

Abstract

An aqueous coating composition with resin solids consisting of 60 to 80 wt.% of binder solids and 20 to 40 wt.% of cross-linker solids, the binder solids consisting of 20 to 100 wt.% of a urethanized polyester binder having a hydroxyl number of 50 to 250 mg KOH/g and a carboxyl number of 10 to 50 mg KOH/g, and 0 to 80 wt.% of one or more further binders, the sum of the respective wt.% in each case equalling 100 wt.%, wherein the urethanized polyester binder is an esterification product made of a polyurethane resin with a carboxyl number of 50 to 200 mg KOH/g and a polyester polyol with a hydroxyl number of 70 to 300 mg KOH/g.

Description

Title of Invention

AQUEOUS COATING COMPOSITION

Field of the Invention

The invention relates to an aqueous coating composition comprising a hydroxyl-functional urethanized polyester binder.

Background of the Invention

Primer surfacer coating compositions are used in the automotive industry to produce an intermediate coating layer having an antichipping and leveling function and being typically positioned between an electrodeposition coating (EDC) primer and a final color and/or special-effect topcoat which is in the form of a single-layer topcoat or of a two-layer coat comprised of pigmented base coat and protective glossy clear top coat.

Summary of the Invention

The invention relates to an aqueous coating composition with resin solids consisting of 60 to 80 wt.% (weight-%) of binder solids and 20 to 40 wt.% of cross-linker solids, the binder solids consisting of 20 to 100 wt.% of a urethanized polyester binder having a hydroxyl number of 50 to 250 mg KOH/g and a carboxyl number of 10 to 50 mg KOH/g, and 0 to 80 wt.% of one or more further binders, the sum of the respective wt.% in each case equalling 100 wt.%, wherein the urethanized polyester binder is an esterification product made of a polyurethane resin with a carboxyl number of 50 to 200 mg KOH/g and a polyester polyol with a hydroxyl number of 70 to 300 mg KOH/g.

It has been found that the aqueous coating composition of the invention is useful as primer surfacer coating composition. It has also been found that it is particularly useful as primer surfacer coating composition for the production of a primer surfacer layer to be overcoated with a single-layer topcoat; in such case an excellent adhesion between the primer surfacer layer and the single-layer topcoat can be achieved. Detailed Description of the Embodiments

In the description and the claims a distinction is made between "solids", "resin solids", "binder solids" and "cross-linker solids" of the aqueous coating composition of the invention. The solids of the aqueous coating composition comprise any non-volatile constituents including the resin solids and any further components making a solids contribution like, for example, pigments, fillers (extenders) and non-volatile additives. The resin solids itself consists of the binder solids (solids contributions of the binders) and of the cross-linker solids (solids contributions of the cross-linkers). The solids of a volatile matter- containing coating composition or a coating intermediate like, for example, a binder solution or a binder dispersion, can be determined in accordance with DIN EN ISO 3251 (60 minutes 150 °C).

The aqueous coating composition of the invention has a solids content, for example, in the range of 40 to 65 wt.%. In the case of an aqueous primer surfacer coating composition, the solids content is, for example, 45 to 65 wt.%. The resin solids content of the aqueous coating composition of the invention ranges, for example, from 20 to 65 wt.% and, in the case of an aqueous primer surfacer coating composition, from 20 to 45 wt.%, for example. The resin solids consists of 60 to 80 wt.% of binder solids and 20 to 40 wt.% of cross-linker solids, the sum of the wt.% equalling 100 wt.%.

The binder solids itself consists of 20 to 100 wt.% of the urethanized polyester binder and 0 to 80 wt.% of one or more further, in particular, hydroxyl-functional binders, the sum of the wt.% equalling 100 wt.%. In an embodiment, it consists of 30 to 100 wt.% of the urethanized polyester binder and 0 to 70 wt.% of one or more further, in particular, hydroxyl-functional binders, the sum of the wt.% equalling 100 wt.%.

The urethanized polyester binder has a hydroxyl number of 50 to 250 mg KOH/g, preferably 70 to 200 mg KOH/g and a carboxyl number of 10 to 50 mg KOH/g, preferably 10 to 40 mg KOH/g. Its weight average molar mass may be, for example, 5000 to 10000.

The term "weight average molar mass" is used herein. It shall mean the weight average molar mass determined by gel permeation chromatography (GPC; divinylbenzene-cross-linked polystyrene as the immobile phase, tetrahydrofuran as the liquid phase, polystyrene standards).

The urethanized polyester binder is an esterification product made of a polyurethane resin with a carboxyl number of 50 to 200 mg KOH/g and a weight average molar mass of, for example, 3000 to 9000, and a polyester polyol with a hydroxyl number of 70 to 300 mg KOH/g, a carboxyl number of, for example, 0 to 30 mg KOH/g and a weight average molar mass of, for example, 2000 to 4000. The urethanized polyester binder is typically free of free and blocked isocyanate groups (isocyanate groups blocked by

monofunctional blocking agents as are conventionally used for permanently or reversibly blocking isocyanate, such as monoalcohols, ketoximes, phenols, lactams, CH-acidic compounds, pyrazoles, etc.).

Polyurethane resins with a carboxyl number of 50 to 200 mg KOH/g can be produced, as is known to a person skilled in the art, by reacting polyisocyanates with hydroxycarboxlic acids and, optionally, polyols at a stoichiometric ratio of isocyanate groups and hydroxyl groups.

Linear polyurethane resins with terminal carboxyl groups

corresponding to a carboxyl number of 50 to 200 mg KOH/g are preferred; especially preferred are linear polyurethane resins with terminal and lateral carboxyl groups corresponding to a carboxyl number of 50 to 200 mg KOH/g. Polyurethane resins of this type can be produced by reacting diisocyanates with monohydroxycarboxylic acids and diols or with monohydroxycarboxylic acids and dihydroxycarboxylic acids and, optionally, although less preferred, diols. Said addition reactions can be carried out in the absence or in the presence of an organic solvent (mixture) which is inert to isocyanate groups. Generally, the addition reactions are carried out at a temperature ranging from 60 to 100 °C.

Examples of polyisocyanates which may be used to produce the carboxyl-functional polyurethane resins include polyisocyanates having two or more than two free isocyanate groups corresponding to a content of free isocyanate of, for example, from 10 to 50 wt.%.

Examples of suitable polyisocyanates include diisocyanates, such as, phenylene, toluylene, xylylene, naphthylene or diphenylmethane diisocyanate, 1 ,6-hexane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, trimethylhexane diisocyanate, cyclohexane diisocyanate, cyclohexanedimethylene diisocyanate and tetramethylenexylylene

diisocyanate.

Examples of polyisocyanates having more than two isocyanate groups comprise trisisocyanatononane and polyisocyanates derived from the diisocyanates stated in the preceding paragraph. Such examples comprise oligomers of the diisocyanates or isocyanurate, uretdione or biuret derivatives of the diisocyanates or isocyanate-functional adducts of the diisocyanates and compounds having at least three groups containing active hydrogen per molecule, in particular, polyols, polyamines and/or aminoalcohols, such as, for example, trimethylolpropane, glycerol, diethylene triamine and 1 :1 -adducts of dialkanolamines and cyclic carbonate.

Examples of hydroxycarboxylic acids which may be used to produce the carboxyl-functional polyurethane resins include monohydroxycarboxylic acids, such as, glycolic acid (hydroxyacetic acid), malic acid, 12- hydroxystearic acid, 4-hydroxybenzoic acid, citric acid, or 1 :1 -adducts of monoepoxy compounds and dicarboxylic acids, for example, corresponding adducts of glycidyl ethers or glycidyl esters, such as, glycidyl versatate with dicarboxylic acids, and polyhydroxycarboxylic acids, such as, tartaric acid, dimethylolpropionic acid and dimethylolbutyric acid.

Examples of polyols which may be used to produce the carboxyl- functional polyurethane resins include diols, such as, ethylene glycol, the isomeric propane- and butanediols, 1 ,5-pentanediol, 1 ,6-hexanediol, 1 ,10- decanediol, 1 ,12-dodecanediol, neopentyl glycol, butylethylpropanediol, trimethylhexane diol, diethylene glycol, triethylene glycol, tripropylene glycol, the isomeric cyclohexanediols, the isomeric cyclohexanedimethanols, hydrogenated bisphenols, tricyclodecanedimethanol, dimer fatty alcohol, bisphenol A, and polyols with more than two hydroxyl groups, such as, glycerol, trimethylolpropane, trimethylolethane, pentaerythritol,

dipentaerythritol, ditrimethylolpropane, sorbitol and mannitol.

Polyester polyols with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g can be produced by polycondensation of polyols with polycarboxylic acids or with suitable polycarboxylic acid derivatives, such as, for example, corresponding esters or anhydrides. Hydroxycarboxylic acids, monoalcohols, monocarboxylic acids and/or epoxide compounds may, optionally, be included in the polyester synthesis. Polycondensation may be carried out by the conventional methods known to the skilled person, for example, in the presence of conventional esterification catalysts and at elevated temperatures of, for example, 180 to 250 °C, for example, in the melt. Optionally, entrainers, such as, for example, xylene, may also be used.

Examples of polyols which may be used to produce polyester polyols with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g are the same as those which have been previously mentioned as examples of polyols which may be used to produce the carboxyl-functional polyurethane resins.

Examples of polycarboxylic acids which may be used to produce polyester polyols with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g include dicarboxylic acids, such as, phthalic acid, isophthalic acid, terephthalic acid,

tetrahydrophthalic acid, hexahydrophthalic acid, 1 ,3- and 1 ,4-cyclohexane dicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, maleic acid, fumaric acid, dimer fatty acids, and polycarboxylic acids with more than two carboxyl groups, such as, trimellitic acid and pyromellitic acid.

The polyester polyols with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g may be linear, in which case they are polyesterdiols. However, branched polyester polyols with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g are preferred.

The urethanized polyester binder can be produced by esterifying a carboxyl-functional polyurethane with a carboxyl number of 50 to 200 mg KOH/g with a polyester polyol with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g. A person skilled in the art knows how to carry out esterification reactions of this type; for example, these reactions may be performed under the conditions mentioned with regard to the production of polyester polyols with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g.

Once the esterification reaction between the carboxyl-functional polyurethane resin and the polyester polyol with a hydroxyl number of 70 to 300 mg KOH/g and a carboxyl number of, for example, 0 to 30 mg KOH/g is finished, the formed urethanized polyester binder may, after the addition of a neutralizing agent, be converted, by the addition of water, into an aqueous urethanized polyester binder dispersion with a solids content of, for example, 35 to 55 wt.%. It is also possible to provide the urethanized polyester binder, neutralized or non-neutralized, as a solution in water-dilutable organic solvent and to use it in such form to prepare an aqueous coating composition of the invention.

As has already been mentioned, the binder solids of the aqueous coating composition of the invention may comprise up to 80 wt.% of one or more further binders, i.e. binders that are different from the urethanized polyester binder. This concerns hydroxyl-functional binders in particular.

Examples of corresponding further binders comprise resins conventionally used as binders for coating compositions, such as, for example, (meth)acrylic copolymer resins, polyester resins, polyurethane resins as well as resin hybrids of two or more of said resin types. (Meth)acryl or (meth)acrylic is to be understood, both here and in the following, as acryl and/or methacryl or as acrylic and/or methacrylic.

The cross-linker solids of the aqueous coating composition of the invention may comprise conventional cross-linkers known as cross-linkers for coating compositions containing hydroxyl-functional binders. Examples of such cross-linkers include aminoplast resins, interesterification cross-linkers and cross-linkers with reversibly blocked isocyanate groups. Examples of aminoplast resins include benzoguanamine resins and, in particular, melamine resins. Examples of interesterification cross-linkers include trisalkoxycarbonylaminotriazines. Examples of cross-linkers with reversibly blocked isocyanate groups include the conventional blocked polyisocyanate cross-linkers known as cross-linkers for coating compositions. The aqueous coating composition of the invention may comprise fillers and/or pigments. If the aqueous coating composition of the invention is an aqueous primer surfacer coating composition, conventional fillers and, optionally, color and/or special-effect pigments are contained; the weight ratio of pigment plus filler/resin solids may then be, for example, 0.6 : 1 to 1 .5 : 1 . Examples of fillers are silicon dioxide, barium sulphate, talcum and kaolin. Examples of inorganic or organic color pigments are titanium dioxide, iron oxide pigments, carbon black, azo pigments, phthalocyanine pigments, quinacridone pigments, pyrrolopyrrole pigments and perylene pigments.

Examples of special-effect pigments are metal pigments, e.g. of aluminum, copper or other metals; interference pigments such as metal oxide-coated metal pigments, e.g. titanium dioxide-coated aluminum, coated micas such as titanium dioxide-coated mica, platelet-like iron oxide and platelet-like copper phthalocyanine pigments.

The aqueous coating composition of the invention comprises water in a proportion of, for example, 20 to 60 wt.%. If an aqueous primer surfacer coating composition is concerned, the water content is, for example, from 20 to 55 wt.%.

In addition to water, the aqueous coating composition of the invention may also comprise one or more organic solvents, for example, 1 to 15 wt.% of organic solvent(s). Examples are C1 -C4 alcohols, 2-ethyl hexanol, benzyl alcohol, isodecanol, ethylene glycol, propylene glycol, diethylene glycol, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, methoxypropanol, butyl glycol, butoxypropanol, butyl diglycol, hexyl glycol, methoxybutanol, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether,

methoxypropyl acetate, butyl glycol acetate, butyl diglycol acetate, ethyl glycol acetate, N-ethylpyrrolidone and aliphatic, aromatic or terpene hydrocarbons.

In addition to one or more neutralizing agents, such as, in particular, amines and/or aminoalcohols, the aqueous coating composition of the invention may comprise conventional paint additives in a total quantity of, for example, 0.1 to 10 wt.%, based on the resin solids content of the coating compositions. Examples of such additives are wetting agents, adhesion- promoting substances, catalysts, levelling agents, anti-cratering agents and thickeners.

The aqueous coating composition of the invention can in particular be used to apply the primer surfacer coating layer of primer surfacer/base coat/clear coat multi-layer coatings or, in particular, the primer surfacer coating layer of primer surfacer/top coat two-layer coatings, wherein the base coat layer or, respectively, the top coat layer represents the coating layer which imparts the color to the finished multi-layer or two-layer coating. In case of a primer surfacer/base coat/clear coat multi-layer coating this may be a solid color (color independent on the observation angle) or an effect color (color having a color and/or lightness flop dependent on the observation angle), while in case of a primer surfacer/top coat two-layer coating said color is typically a solid color. Cured primer surfacer layers applied from an aqueous coating composition of the invention fulfill the technological requirements of primer surfacers posed by motor vehicle manufacturers. They exhibit excellent adhesion to an overcoated color-imparting single-layer topcoat.

The invention is also related to a process for the production of a primer surfacer/base coat/clear coat multi-layer coating, wherein the primer surfacer layer is applied from an aqueous coating composition of the invention onto a substrate. The process comprises the steps:

(1 ) providing a substrate to be provided with a primer surfacer/base coat/clear coat multi-layer coating,

(2) applying a layer of the aqueous coating composition of the invention on the substrate to form the primer surfacer layer,

(3) curing the primer surfacer layer,

(4) applying and curing a base coat/clear coat two-layer coating on the cured primer surfacer layer.

The substrate provided in process step (1 ) is made of one or more materials which are sufficiently stable at the object temperatures prevailing when the applied coating layers are cured. The substrate may consist of one single material or of a plurality of different materials which are combined together in the manner of a mixed construction. Generally, metal or plastics material substrates are concerned. These are generally pre-coated, i.e.

plastics materials substrates may, for example, be provided with a plastics primer, metal substrates generally have an EDC primer, in particular a cathodic EDC primer. Examples of substrates include in particular automotive substrates, such as car bodies or car body parts, in particular car bodies or car body parts provided with an EDC primer.

In process step (2) the substrate is coated, typically, spray-coated with the aqueous coating composition of the invention to form a primer surfacer layer. The aqueous coating composition of the invention is applied in a dry film thickness of, for example, 15 to 50 m.

In process step (3), the primer surfacer coating layer is cured at an object temperature of, for example, 130 to 170 °C, in particular, 140 to 160 °C, typically by baking.

In process step (4) a base coat/clear coat two-layer coating is applied on the cured primer surfacer layer and then cured in the conventional manner known to the skilled person. The base coat layer is the coating layer which imparts the color to the finished multi-layer coating. The color may be a an effect color or a solid color. The clear coat layer is the outer protective and glossy coating layer.

In another and particular embodiment, the invention is also related to a process for the production of a primer surfacer/top coat two-layer coating, wherein the primer surfacer layer is applied from an aqueous coating composition of the invention onto a substrate. The process comprises the steps:

(1 ') providing a substrate to be provided with a primer surfacer/top coat two-layer coating,

(2') applying a layer of the aqueous coating composition of the invention on the substrate to form the primer surfacer layer,

(3') curing the primer surfacer layer,

(4') applying and curing a top coat to form the single-layer top coat on the cured primer surfacer layer.

With regard to the substrate provided in process step (1 ') the same is true as has previously been mentioned regarding the substrate provided in process step (1 ) of the process for the production of the primer surfacer/base coat/clear coat multi-layer coating.

In process step (2') the substrate is coated, typically, spray-coated with the aqueous coating composition of the invention to form a primer surfacer layer. The aqueous coating composition of the invention is applied in a total dry film thickness of, for example, 15 to 50 μιτι.

In process step (3'), the primer surfacer coating layer is cured at an object temperature of, for example, 120 to 160 °C, in particular, 130 to 150 °C, typically by baking.

In process step (4') a top coat is applied on the cured primer surfacer layer and cured in the conventional manner known to the skilled person. The top coat layer is the outer coating layer which imparts the color to the finished two-layer coating. The color is typically a solid color.

If the top coat composition used in process step (4') is a top coat composition that comprises one or more aminoplast cross-linkers as the predominant or even only cross-linker(s), i.e. a top coat composition with cross-linker solids consisting of >50 to 100 wt.% of aminoplast cross-linkers, the use of the aqueous coating composition of the invention to form the primer surfacer layer is of special value with regard to achieving excellent adhesion between primer surfacer layer and single-layer top coat.

Examples

Example 1 (preparation of a solution of a carboxyl-functional polvurethane):

412.5 g dicyclohexylmethane diisocyanate, 180 g 12-hydroxystearic acid, 180 g dimethylolpropionic acid and 600 g methyl ethyl ketone were introduced into a flask equipped with stirrer, thermometer and reflux

condenser. The mixture was heated to 60°C and stirred for 30 minutes.

Thereafter the reaction mixture was heated to 70°C and stirred for further 30 minutes. Then the reaction mixture was heated to reflux while stirring, until the NCO content was <0.4 wt.%. After cooling the contents of the flask were diluted by addition of 127.5 g methyl ethyl ketone. Example 2 (preparation of a polyester polvol):

375 g 1 ,6-hexanediol, 1 18 g trimethylolpropane, 389 g isophthalic acid and 1 18 g adipic acid were introduced into a flask equipped with stirrer, thermometer, column and distillation bridge. The contents were condensed while water of condensation was distilled off. The condensation was stopped by cooling to 80°C, after the carboxyl number of the reaction mixture had reached 10 mg KOH/g.

Example 3 (preparation of an aqueous dispersion of a urethanized polyester binder):

At 80°C 451 g of the product of example 1 were added to the polyester polyol of example 2 and the reaction mixture was heated to 160°C while distilling off the methyl ethyl ketone. Esterification was carried out until an carboxyl number of 18 mg KOH/g was achieved. After cooling to 100°C a 78 g butyl diglycol were added and the contents of the flask were neutralized. To this end 25 g dimethylethanolannine were homogeneously mixed in and the contents of the flask were cooled to 75°C. Deionized water was added portionwise to produce a 42 wt.% aqueous urethanized polyester binder dispersion.

Example 4 (preparation of an aqueous coating composition and its application as primer surfacer coating):

a) A blend was prepared by mixing together 18.0 pbw (parts by weight) of the aqueous dispersion of example 3, 3.3 pbw deionized water, 0.4 pbw dimethylethanolannine, 0.9 pbw Surfynol® 104 (surfactant), 16.9 pbw titanium dioxide, 2.7 pbw barium sulphate, 2.0 pbw talc, 0.3 pbw fumed silica and 3.4 pbw mineral spirit. Thereafter the mixture was homogenized and dispersed in a beadmill. b) The paste from a) was mixed with 26.2 pbw of the aqueous dispersion of example 3, 1 .5 pbw Cymel® 303 (melamine formaldehyde resin), 9.2 pbw of a 50 wt.% butyl diglycol solution of a reversibly blocked polyisocyanate cross-linker (1 :1 mixture by weight of trimeric 1 ,6-hexane diisocyanate and trimeric isophorone diisocyanate, each blocked with methyl ethyl ketoxime), 0.1 pbw of Nacure®2500 (catalyst) and 15.1 pbw deionized water to form an aqueous coating composition.

The coating composition was spray-applied at 30 μιτι dry film thickness on steel panels provided with an electrocoating primer. The coating so applied was baked for 20 minutes at 160°C (object temperature) to form a cured primer surfacer layer which was then overcoated with a blue water-borne polyester/nnelannine top coat at a dry film thickness of 35-45 μιτι. The top coat layer was then bake-cured for 30 minutes at 130°C (object temperature).

The cross cut (2mm) adhesion test according to DIN EN ISO 2409 resulted in a rating 1 regarding adhesion between the primer surfacer layer and the top coat layer.

Claims

Claims What is Claimed is:

1 . An aqueous coating composition with resin solids consisting of 60 to 80 wt.% of binder solids and 20 to 40 wt.% of cross-linker solids, the binder solids consisting of 20 to 100 wt.% of a urethanized polyester binder having a hydroxyl number of 50 to 250 mg KOH/g and a carboxyl number of 10 to 50 mg KOH/g, and 0 to 80 wt.% of one or more further binders, the sum of the respective wt.% in each case equalling 100 wt.%, wherein the urethanized polyester binder is an esterification product made of a polyurethane resin with a carboxyl number of 50 to 200 mg KOH/g and a polyester polyol with a hydroxyl number of 70 to 300 mg KOH/g.

2. The aqueous coating composition of claim 1 , wherein the binder solids consist of 30 to 100 wt.% of the urethanized polyester binder and 0 to 70 wt.% of the one or more further binders, the sum of the wt.% equalling 100 wt.%.

3. The aqueous coating composition of claim 1 or 2, wherein the polyurethane resin is a linear polyurethane resin with terminal carboxyl groups.

4. The aqueous coating composition of claim 1 or 2, wherein the polyurethane resin is a linear polyurethane resin with terminal and lateral carboxyl groups.

5. The aqueous coating composition of any one of the preceding claims, wherein the polyester polyol is a branched polyester polyol.

6. The aqueous coating composition of any one of the preceding claims comprising 20 to 60 wt.% of water.

7. A process for the production of a primer surfacer/base coat/clear coat multi-layer coating comprising the steps: (1 ) providing a substrate to be provided with a primer surfacer/base coat/clear coat multi-layer coating,

(2) applying a layer of the aqueous coating composition of any one of the preceding claims on the substrate to form the primer surfacer layer,

(3) curing the primer surfacer layer,

8. A process for the production of a primer surfacer/top coat two-layer coating comprising the steps:

(1 ') providing a substrate to be provided with a primer surfacer/top coat two- layer coating,

(2') applying a layer of the aqueous coating composition of any one of claims 1 to 6 on the substrate to form the primer surfacer layer,

(3') curing the primer surfacer layer,

9. The process of claim 8, wherein the top coat composition used in process step (4') comprises a cross-linker comprised of 50 to 100 wt.% of at least one aminoplast cross-linker.

10. The process of claim 7, 8 or 9, wherein the substrate is a car body or a car body part.