CA2004988C - Preparation of a multicoat coating, water-thinnable coating compositions, water-thinnable emulsion polymers and preparation of water-thinnable emulsion polymers - Google Patents

Abstract

a process for the preparation of multicoat coatings in which a pigmented aqueous basecoat composition is used which comprises a water-thinnable emulsion polymer as the film-former. The water-thinnable emulsion polymer is prepared in a two-stage emulsion polymerization. The first stage gives rise to a polymer having a glass transition temperature (T G1) of +30 to +110°C. In the second stage a mixture of monomers is polymerized in the presence of the polymer prepared in the first stage which by an exclusive polymerization gives rise to a polymer having a glass transition temperature (T G2) of -60 to +20°C. The hydroxyl value of the emulsion polymer is between 2 and 100.

Description

Preparation of a multicoat coating', water-thinnable coating compositions, water-thinnable emulsion polymers and preparation of water-thinnable emulsion polymers The invention relates to a process for the preparation of a multicoat protective and/or decorative coating on a substrate surface, in 'which process (1) a pigmented aqueous coating composition which comprises as the film-former a water-thinnable emulsion polymer, is applied to the substrate l0 surface as basecoat composition (2) a polymeric film is formed from the composition applied in stage (1) (3) a clear topcoat composition is applied to the basecoat obtained in this manner and subsequently (4) the basecoat and the topcoat are baked together.
The invention also relates to water-thinnable coating compositions, to water-thinnable emulsion polymers and to a process for the preparation of water-thinnable emulsion polymers.
20 The process, described above, for the preparation of multicoat protective and/or decorative coatings is known and is particularly employed for producing metallic finishes on automotive bodies (cf., for example, EP-A-89,497, DE-A-3,628,124 and EP-A-38,127).
Only then is it possible to produce metallic 200~.~~~
- 2 ~-finishes having a satisfactory metallic effect by the process under discussion, if the aqueous basecoat com-positions used are so constituted that they can be applied to the substrate in relatively thin, rapidly drying films - especially when applied with the aid of automatic painting equipment - and if, subsequent to the execution of the process stages (3) and (4) the metallic pigment particles are aligned in parallel with the substrate surface.
Furthermore, the aqueous basecoat compositions must be so constituted that the basecoat of the baked metallic finish adheres well to the substrate and the clear topcoat adheres well to t:he basecoat. In addition, the aqueous basecoat compositions must be so constituted that the baked metallic finish shows no loss of gloss, loss of adhesion or even blistering after exposure to the condensed water steady conditions test.
It is finally desirable that the aqueous basecoat compositions possess a long shelf-life.
DE-A 3,628,124 discloses aqueous basecoat com-positions which comprise a mixture of a water-thinnable emulsion polymer and a water-thinnable polyurethane resin as the film-former. These basecoat compositions fail to meet the above requirements in 'the optimum way possible.
The object forming the basis of the present invention is to prepare aqueous basecoat compositions which are suitable for the process under discussion and meet the above requirements in the optimum way possible.
Surprisingly, this ob ject is achieved via aqueous basecoat compositions which comprise a water-thinnable emulsion polymer, which polymer can be obtained (a) by polymerizing in a first stage 10 to 90 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in aqueous phase in the presence of one or more emul-sifiers and one or more radical-forming initiators, the ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T~1) of + 30 to + 110°C, and (b) by polymerizing in a second stage 90 to 10 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers, after at least 80% by weight of the ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the monomer used in the second stage or the mixture of ethylenically unsaturated - monomers used in the second stage being chosen such that an exclusive polymerization of the monomer used in the second stage or of the mixture of ethylenic-ally unsaturated polymers used in the second stage gives rise to a polymer having a glass transition temperature (T~2) of - 60 to + 20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference TG1 - TG2 is 10 to 170°C.
In another aspect, the invention provides a water-thinnable coating composition which comprises as the film-former a water-thinnable emulsion polymer which can be obtained as described above.
In a further aspect, the invention provides a water-thinnable emulsion polymer which can be obtained as described above, as well as a process for the preparation of such a polymer as described.
In another aspect the invention provides a substrate bearing a multicoat protective and/or decorative coating applied by a process as described above.
The water-thinnable emulsion polymers used according to the invention can be prepared by a two-stage emulsion polymerization in an aqueous medium using known equipment, for example a stirred reaction vessel provided with means of heating and cooling. The addition of the monomers can be effected by first placing a solution comprising the total water, the emulsifier and some of the initiator in the reaction vessel and then slowly adding, at the polymerization temperature, the monomer or the mixture of monomers and, separately but side by side, the remaining initiator.

- 4a -However, it is also possible first to introduce some of the water and emulsifier and to form from the remaining water and emulsifier and from the monomer or the mixture of monomers a pre-emulsion which is then slowly added at the polymerization temperature, the initiator being again added separately.
It is preferred in the first stage to add the monomer or the mixture of monomers in the form of a pre-emulsion, and in the second stage to add the monomer or the mixture of monomers as such, i.e. without water or emulsifier, and to add the initiator separately but side 20o~.~~s by side. It is particularly preferred in the first stage to prepare first a seed polymer from some of the pre-emulsion used in the first stage (usually about 30% by weight of the total pre-emulsion to be used), and then to add the remaining pre-emulsion to be used in the first stage.
The polymerization temperature is generally in the range from 20 to 100°C, preferably 40 to 90°C.
The ratio of the monomer to the water can be chosen such that the resultant dispersion has a solids content of 30 to 60% by weight, preferably 35 to 50% by weight.
The emulsifier used is preferably an anionic emulsifier as such or in admixture.
Examples of suitable anionic emulsifiers are the alkali metal salts of hemi-esters of sulfuric acid of alkylphenols or alcohols, also the hemi-esters of sulfuric acid of oxyethylated alkylphenols or oxyethylated alco-hols, preferably the alkali metal salts of the hemi-ester of sulfuric acid of a nonylphenol which has reacted with 4 - 5 mol of ethylene oxide per mol of the phenol, alkyl or aryl sulfonates, sodium lauryl sulfate, sodium lauryl ethoxylate sulfate and secondary sodium alkanesulfonates whose carbon chain contains 8 - 20 carbon atoms. The amount of the anionic emulsifier is 0.1 - 5.0% by weight, based on the monomers, preferably 0.5 - 3.0% by weight.
Furthermore, in order to increase the stability of the aqueous dispersions, a non-ionic emulsifier of the type of an ethoxylated alkylphenol or fatty alcohol, eg. an adduct of 1 mol of nonylphenol and 4 - 30 mol of ethylene oxide, may be additionally used in admixture with the anionic emulsifier.
A peroxide compound is preferably used as the radical-forming initiator. The initiator is soluble in water or the monomer. A water-soluble initiator is preferably used.
Suitable initiators are the usual inorganic percompounds, such as ammonium persulfate, potassium persulfate, ammonium or alkali metal peroxydiphosphate, and organic peroxides, eg, benzoyl peroxide, organic peresters, such as perisopivalate, in some cases in com-bination with reducing agents such as sodium disulfite, hydrazine, hydroxylamine and catalytic amounts of accelerators, such as iron, cobalt, cerium and vanadyl salts, preferably alkali metal or ammonium peroxydi-sulfates. Redox initiator systems which are disclosed in EP-A-107,300, may be likewise used.
In the first stage, 10 to 90, preferably 35 to 65, parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated mono mers is emulsion polymerized. The monomer or mixture of monomers used in the first stage is chosen such that a polymer having a glass transition temperature (TG1) of + 30°C to + 110°C, preferably 60 to 95°C, is obtained when the monomer or the mixture of monomers used in the first stage has fully polymerized. Since the glass transition temperature of emulsion polymers can be calculated approximately from the equation 2004~~3~
- glass i:ransition temperature of n=x _1 Wn the copolymer in °R
W - wei ht g of the nth monomer n=1 glass transition temperature of the homopolymer obtained from the nth monomer x - number of different monomers, a person skilled in the art has no difficulties in selecting the monomer or the mixture of monomers to be used in the first stage such that a polymer having a glass transition temperature (~~1) of + 30 to + 110°C, preferably 60 to 95°C, is obtained, when the monomer or the mixture of monomers used in the first stage has fully polymerized.
Examples of monomers which may be used in the first stage, are: vinylaromatic hydrocarbons such as styrene, a-alkylstyrene and vinyltoluene, esters of acrylic acid or methacrylic acid, in particular aliphatic and cycloaliphatic acrylates or methacrylates having up to 20 carbon atoms in the alcohol radical, eg. methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl, lauryl and cyclohexyl acrylates or methacrylates, acrylic and/or methacrylic acid, acrylamide and/or methacrylamide, N-methylolacrylamide and/or N.-methylolmethacrylamide, hydroxyalkyl esters of acrylic acid, methacrylic acid or another a,p-ethylenically unsaturated carboxylic acid, eg. 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 200 9~8 _ 8 ._ 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate etc.
The ethylenically unsaturated monomers or the mixtures of ethylenically unsaturated monomers used in the first stage are preferably those which are essen-tially free from hydroxyl and carboxyl groups. The term "essentially free" signifies that it is preferred to use monomers or mixtures of monomers which are free from hydroxyl and carboxyl groups, but it also signifies that the monomers or the mixtures of monomers used may also contain small amounts (eg. due to impurities) of hydroxyl and/or carboxyl groups. The hydroxyl and carboxyl groups content should preferably be not greater than would cause a polymer prepared from the monomer or the mixture of monomers used in the first stage to have a hydroxyl value of not more than 5 and an acid value of not more than 3.
It is particularly preferred that a mixture is used in the first stage which consists of (al) 100 to 60, preferably 99.5 to 75, % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0 to 40, preferably 0.5 to 25, % by weight of a monomer which is copolymerizable with (al) or a mixture of such monomers, the total of the weight percentages of (al) and (a2) being always 100% by weight.
Examples of the component ( al ) which can be used, 20U~988 - 9 _.
are: cyclohexyl acrylate, cyclohexyl methacrylate, alkyl acrylates and alkyl methacrylates having up to 20 carbon atoms in the alkyl radical, for example methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl and lauryl acrylates and methacrylates or rnixtures of these monomers .
Examples of the component ( a2 ) which can be used, are vinylaromatic hydrocarbons such as styrene, a-alkyl styrene and vinyltoluene, acrylamide, methacrylamide, acrylonitrile and methacrylonitrile, or mixtures of these monomers.
After at least 80% by weight, preferably at least 95% by weight, of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage have reacted, 90 to 10, preferably fi5 to 35, parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers is emulsion poly-merized in a second stage in the presence of the polymer obtained in the first stage, the monomer or the mixture of monomers used in the second stage being chosen such that an exclusive polymerization of the monomer or of the mixture of monomers used in the second stage gives rise to a polymer having a glass transition temperature (T~z) of -60 to +20°C, preferably -50 to 0°C. This choice poses no difficulties to a person skilled in the art, since the ~ approximate glass transition temperatures of emulsion polymers can be readily approximately calculated - as already stated above.
It is further an essential part of the invention that the nature and amount of the monomer or the mixture zoo~9as of monomers used in the first stage and of the monomer or the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100, preferably 10 to 50, and the difference TG1 - T~Z is 10 to 170, preferably 80 to 150°C.
Examples of monomers which can be used in the second stage, are: vinylaromatic hydrocarbons such as styrene, a-alkylstyrene and vinyltoluene, esters of acrylic acid or methacrylic acid, in particular aliphatic and cycloaliphatic acrylates or methacrylates having up to 20 carbon atoms in the alcohol radical, eg. methyl, .
ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl, lauryl and cyclohexyl acrylates or methacrylates, acrylic and/or methacrylic acid, acrylamide a.nd/or methacrylamide, N-methylolacrylamide and/or N-methylolmethacrylamide, hydroxyalkyl esters of acrylic acid, methacrylic acid or another a,p-ethylenically unsaturated carboxylic acid, eg. 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacry-late, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacry-late etc.
It is preferred that a mixture is used in the second stage which consists of (bl) 47 to 99, preferably 75 to 90, % by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 1 to 20, preferably 5 to 15, % by weight of a monomer which carries at least one hydroxyl group - 11 -.
and is copolymerizable with (bl), (b3) and (b4), or a mixture of such monomers (b3) 0 to 8, preferably 2 to 6, % by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (bl), (b2) and (b4), or a mixture of such monomers, and (b4) 0 to 25, _preferably 2 to 15, % by weight of a further monomer which is copolymerizable with (bl), (b2) and (b3), or a mixture of such monomers, the total of the weight percentages of (bl), (b2), (b3) and (b4) being always 100% by weight.
Examples of the component (bl) which may be used are: cyclohexyl acrylate, cyclohexyl methacrylate, alkyl acrylate and alkyl methacrylate with up to 20 carbon atoms in the alkyl radical, eg. methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl and lauryl acrylates and methacrylates or mixtures o:E these monomers.
Examples of the component (b2) which can be used are: hydroxyalkyl esters of acrylic acid, methacrylic acid or another a,p-ethylenically unsaturated carboxylic acid. These esters may be derived from an alkylene glycol which is esterified with the acid, or they can be obtained by reacting the acid with an alkylene oxide.
Hydroxyalkyl esters of acrylic acid and methacrylic acid in which the hydroxyalkyl group comprises up to 4 carbon atoms, or mixtures of these hydroxyalkyl esters, are preferably used as the component (b2). Examples of such hydroxyalkyl esters are 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 200~0~8 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacry-late, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acry-late or 4-hydroxybutyl methacrylate. Corresponding esters of other unsaturated acids, eg. ethacrylic acid, crotonic acid and similar acids having up to about 6 carbon atoms per molecule, may be also used.
Acrylic acid and/or methacrylic acid and/or acrylamidomethylpropanesulfonic acid are preferably used as the component (b3). However, other ethylenically unsaturated acids having up t:o 6 carbon atoms in the molecule may be also used. Examples of such acids are .
ethacrylic acid, crotonic acid, malefic acid, fumaric acid and itaconic acid.
Examples of the component (b4) which can be used are: vinylaromatic hydrocarbons such as styrene, a alkylstyrene and vinyltoluene,, acrylamide, methacryl amide, acrylonitrile and methacrylonitrile, or mixtures of these monomers.
The emulsion polymer used according to the invention should have a number average molecular mass (determined by gel permeation chromatography using polystyrene as standard) of 200,000 to 2,000,000, prefer ably from 300,000 to 1,500,000.
The person skilled in the art is aware how to choose the reaction conditions during the emulsion polymerization in order to obtain emulsion polymers having the number average molecular masses indicated above (cf. eg. Chemie, Physik and Technologie der Runst stoffe in Einzeldarstellungen, Dispersionen synthetischer Hochpolymerer [Chemistry, Physics and Technology of Plastics in Individual Preparations, Dispersions of Synthetic High Polymers], Part 1, by F. Holscher, Springer Verlag, Berlin, Heidelberg, New York, 1969).
It is preferred that the aqueous basecoat com-positions according to the invention comprise, in addi-tion to the emulsion polymer described above, also a water-thinnable polyurethane resin as film-former.
The basecoat compositions according to the invention preferably comprise water-thinnable poly urethane resins containing urea groups which have a number average molecular weight (determined by gel permeation chromatography using polystyrene as standard) of 1,000 to 60,000, preferably 1,500 to 50,000, and an acid value of 5 to 70, preferably 10 to 30, and which can be prepared by reacting, preferably by chain lengthening, prepolymers comprising isocyanate groups with polyamines and/or hydrazine.
The preparation of the prepolymer containing isocyanate groups can be carried out by reacting poly alcohols having a hydroxyl value of 10 to 1,800, prefer ably 50 to 500, with excess polyisocyanates at tempera tures up to 150°C, preferably 50 to 130°C, in organic solvents which are inert to isocyanates. The equivalence ratio of NCO to OH groups is between 1.5 and 1.0 to 1.0, preferably between 1.4 and 1.2 to 1. The polyols used for the preparation of the prepolymer may be low-molecular and/or high-molecular and they may contain non-reactive anionic groups.

- 14 .-In order to raise the hardness of the polyure-thane, it is possible to use low-molecular polyols. They have a molecular weight of 60 to about 400 and may comprise aliphatic, alicyclic or aromatic groups. Amounts of up to 30% by weight, preferably about 2 to 20% by weight, of the total polyol components, are used. The low-molecular polyols have preferably up to about 20 carbon atoms per molecule, such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butylene glycol, 1,6-hexanediol, trimethylolpropane, castor oil or hydro-genated castor oil, di(tri.methylolpropane) ether,.
pentaerythritol, 1,2-cyclohexanediol, 1,4-cyclohexane-dimethanol, bisphenol A, bisphenol F, neopentyl glycol, neopentyl glycol hydroxypivalate, hydroxyethylated or hydroxypropylated bisphenol A, hydrogenated bisphenol A
or mixtures thereof.
In order to obtain a highly flexible NCO prepoly-mer, a high proportion of a mainly linear polyol having a preferred hydroxyl value of 30 to 150, should be added.
Up to. 97% by weight of the total polyol can consist of saturated and unsaturated polyesters and/or polyethers having a molecular mass Mn of 400 to 5,000. Suitable high-molecular polyols are aliphatic polyether diols of ~ the general formula H-(-0-(-CHR)n-)m OH, in which R is hydrogen or a low alkyl which is unsubstituted or sub-stituted by various substituents, n being 2 to 6, prefer-ably 3 to 4, and m being 2 to 100, preferably 5 to 50.
Examples of these are linear or branched polyether diols, 2004 ~~i'~~
- 15 -~ 27293-49 such as poly(oxyethylene) gll~cols, poly(oxypropylene) glycols and/or poly(oxybutylene) glycols. The chosen polyether diols should not introduce an excess of ether groups, since otherwise the polymers formed swell in water. The preferred polyether diols are poly(oxypro-pylene) glycols having a molecular mass Mn in the range of 400 to 3,000. Polyester diols are prepared by esteri-fying organic dicarboxylic acids or their anhydrides with organic diols, or they may be derived from a hydroxycar-boxylic acid or a lactone. To prepare branched polyester polyols, polyols or polycarboxyl.ic acids having a higher valency may be used to a small extent. The dicarboxylic acids and diols may be linear or branched aliphatic, cycloaliphatic or aromatic dicarboxylic acids or diols.
The diols used for the preparation of the poly-esters consist eg, of alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, 1,4-butane-diol, 1,6-hexanediol, neopentyl glycol and other diols such as dimethylolcyclohexane.The acid component of the polyester consists mainly of low-molecular dicarboxylic acids or their anhydrides having 2 to 30, preferably 4 to 18 carbon atoms in the molecule. Examples of suitable acids are o-phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, malefic acid, fumaric acid, glutaric acid, hexa-chloroheptanedicarboxylic acid, tetrachlorophthalic acid and/or dimerized fatty acids. Instead of these acids it is also possible to use their anhydrides, as long as they 20049~i~3 - 16 ~- 27293-49 exist. In the formation of the polyester polyols smaller amounts of carboxylic acids having 3 or more carboxyl groups, for example trimellitic anhydride or the adduct of malefic anhydride and unsaturated fatty acids, may be also present.
Those polyester diols are also used according to the invention ~~ahich are obtained by reacting a lactone with a diol. They are marked by the presence of a ter-urinal hydroxyl group and recurring polyester moiety of the formula -(-CO-(CHR)n-CH2-0-)-, where n is preferably 4 to 6 and the substituent R hydrogen, alkyl, cycloalkyl or alkoxy. No substituent has more than 12 carbon atoms.
The total number of carbon atoms in the substituent does not exceed 12 per lactone ring. Corresponding examples are hydroxycaproic acid, hydroxybutyric acid, hydroxy-decanoic acid and/or hydroxystearic acid. The lactone used as starting material can be represented by the following general formula CH2- ( CR2 ) n-C~~0 I
O_ in which n and R have the meaning defined above. The unsubstituted E-caprolactone in which n is 4 and all R
substituents are hydrogen, is preferred for the prepara-tion of the polyester diols. The reaction with lactone is initiated by low-molecular polyols, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol and dimethylol-cyclohexane. However, other reactants, such as ethylene-diamine, alkyldialkanolamines or even urea, may be also 2004 ~~3~

reacted with caprolactone.
Suitable higher-molecular diols are also polylac-tam diols, which are prepared by reacting for example e-caprolactam with low-molecular diols.
Aliphatic, cycloaliphatic and/or aromatic poly-isocyanates having at least t:wo isocyanate groups per molecule, are used as typical multifunctional isocyan-ates. The isomers or isomeric mixtures of organic diiso-cyanates are preferred. Suitable aromatic diisocyanates are phenylene diisocyanate, toluylene diisocyanate, xylylene diisocyanate, biphenylene diisocyanate, naph-thylene diisocyanate and diphenylmethane diisocyanate.
Because of their good resistance to ultraviolet, (cyclo)aliphatic diisocyanates give rise to products having little tendency to ;yellowing. Corresponding examples are isophorone diisocyanate, cyclopentylene diisocyanate and the hydrogenation products of aromatic diisocyanates,such as cyclohexylene diisocyanate, methyl-cyclohexylene diisocyanate and dicyclohexylmethane diiso-cyanate. Examples of aliphatic diisocyanates are trimethy-lene diisocyanate, tetramethylene diisocyanate, penta-methylene diisocyanate, hexamethylene diisocyanate, pro-pylene diisocyanate, ethylethylene diisocyanate,dimethyl-ethylene diisocyanate, methyltrimethylene diisocyanate and trimethylhexane diisocyanate. Isophorone diisocyanate and dicyclohexylmethane diisocyanate are particularly preferred as diisocyanates. The polyisocyanate component used for the formation of the prepolymer can also contain a proportion of higher-valent golyisocyanates, provided 200~9~38 no yellowing is caused thereby., Products which are formed by trimerization or oligomerization of diisocyanates or by reacting diisocyanates with polyfunctional compounds containing OH or NH groups, have been found satisfactory as triisocyanates. Examples of such products are the biuret of hexamethylene diisocyanate and water, the isocyanurate of hexamethylene diisocyanate or the adduct of isophorone diisocyanate with trimethylolpropane.
If desired, the average functionality can be reduced by adding monoisocyanates. Examples of such chain-terminating monoisocyanates are phenyl isocyanate, cyclohexyl isocyanate and stearyl isocyanate.
Polyurethanes are in general not compatible with water, if in their synthesis special components are not incorporated and/or if special preparative steps are not undertaken. Thus, the acid value which has been incor-porated is such that the neutralized product is disper-sible in water to give a stable dispersion. Such com-pounds are those which comprise two H-active groups which are reactive toward isocyanate groups and at least one group capable of forming anions. Suitable groups which react with isocyanate groups are in particular hydroxyl groups as well as primary and/o:r secondary amino groups.
Groups which are capable of forming anions are carboxyl, sulfonic acid and/or phosphoric: acid groups. Carboxylic acid or carboxylate groups are preferably used. They should be so slow to react that the isocyanate groups of the diisocyanate preferably react with the other groups of the molecule which are reactive toward isocyanate 2004~~88 _ lg _ 27293-49 groups. Alkanoic acids having two substituents in the cY-position carbon atom are used for this purpose. The substituent may be a hydroxyl group, an alkyl group or an alkylol group. These polyols have at least one, in general 1 to 3, carboxyl groups in the molecule. They have two to about 25, preferably 3 to 10 carbon atoms.
Examples of such compounds are dihydroxypropionic acid, dihydroxysuccinic acid and dihydroxybenzoic acid. A
particularly preferred group of dihydroxyalkanoic acids are the a,a-dimethylolalkanoic acids which possess the structural formula RC(CHZOH)ZC00H where R is hydrogen or an alkyl group having up to about 20 carbon atoms.
Examples of such compounds are 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid and 2,2-dimethylolpentanoic acid. The preferred di-hydroxyalkanoic acid is 2,2-dimethylolpropionic acid.
Examples of amino-containing compounds are cx,b -diamino-valeric acid, 3,4-diaminobenzoic acid, 2,4-diamino-toluenesulfonic acid and 2,4-diaminodiphenylethersulfonic acid. The carboxyl-containing polyol can form 3 to 100%
by weight, preferably 5 to 50% by weight, of the total polyol component in the NCO pre;polymers.
The amount of ionizable carboxyl groups available in salt form by the neutralization of the carboxyl groups ~ is generally at least 0.4% by weight, preferably at least 0.7% by weight, based on the solids content. The upper limit is about 6% by weight. The amount of dihydroxy-alkanoic acids in the non-neutralized prepolymers pro-duces an acid value of at least 5, preferably at least 10. The upper limit of the acid value is in the neighbor-hood of 70, preferably in the neighborhood of 40, based on the solids content.
Prior to reacting with isocyanates, these di hydroxyalkanoic acids are advantageously neutralized at least in part with a tertiary amine in order to prevent a reaction with the isocyanates.
The NCO prepolymers used according to the inven tion may be prepared by simultaneously reacting the polyol or polyol mixture with an excess of diisocyanate.
Otherwise the reaction may be also carried out in the .
prescribed sequence in stages.
Examples are disclosed in DE 2,624,442 and DE 3,210,051. The reaction temperature may be as high as 150 °C, a temperature in the range of 50 to 130 °C being preferred. The reaction is continued until practically all hydroxyl functions have reacted.
The NCO prepolymer contains at least about 0.5%
by weight of isocyanate groups, preferably at least 1% by weight of NCO, based on the solids content. The upper limit is in the neighborhood of about 15% by weight, preferably 10% by weight, particularly preferably 5% by weight. The reaction may be carried out in the presence or absence of a catalyst, such as organotin compounds and/or tertiary amines. In order to maintain the coreac-tants in a fluid state and to make possible a better tem-perature control during the reaction, organic solvents which contain no Zerewitinoff-active hydrogen, may be added. Examples of suitable solvents are dimethylformamide, 2UU~ 98~~

esters, ethers such as diethylene glycol dimethyl ether, ketoesters, ketones such as methyl ethyl ketone and acetone, ketones having substituted methoxy groups such as methoxyhexanone, glycol ether ester, chlorinated hydrocarbons, aliphatic and alicyclic hydrocarbon-pyrroli-dones, such as N-methylpyrrolidone, hydrogenated furans, aromatic hydrocarbons and mixtures thereof. The amount of solvent can vary within wide limits and should be suffi-cient to form a prepolymer solution of suitable viscosity.
0.01 to 15% by weight of solvent, preferably 0.02 to 8%
by weight of solvent, based on the solids content, is sufficient in most cases. If the boiling point of any water-insoluble solvents which may be present, is lower than that of water, these solvents may be carefully distilled off by vacuum distillation or thin-layer evaporation after preparation of the urea-containing polyurethane dispersion. Higher-boiling solvents should be water-soluble and remain in the aqueous polyurethane dispersion in order to facilitate the coalescing of the polymer particles during film formation. N-Methylpyrroli-done, as such or in admixture with ketones such as methyl ethyl ketone, is a particularly preferred solvent.
The anionic groups of t:he NCO prepolymer are at least partly neutralized by a tertiary amine. The in crease in dispersibility in water achieved by this step provides for an infinite thinnability. It is also sufficient to disperse the neutralized urea-containing polyurethane to form a stable dispersion. Examples of suitable tertiary amines are t:rimethylamine, triethyl-20U49~8 amine, dimethylethylamine, diethylmethylamine, N-methyl-morpholine. The NCO prepolymer is thinned after being neutralized with water and forms then a finely divided dispersion. Soon afterwards the isocyanate groups still present are reacted with diamines and/or polyamines containing primary and/or secondary amino groups as chain extenders. This reaction leads to a further linkage and to an increase of the molecular weight. The competing reaction between amine and water with the isocyanate must be well adjusted (duration, temperature, concentration) in order to obtain optimum properties and must be care-fully supervised to achieve reproducible production conditions. Water-soluble compounds are preferred as chain extenders, since they increase the dispersibility of the polymeric end product in water. Hydrazine and organic diamines are preferred, since they usually produce the highest molecular mass without causing the resin to gel. However, it is assumed for this purpose that the ratio of the amino groups to the isocyanate groups is expediently chosen. The amount of the chain extender will depend on its functionality, the NCO
content of the prepolymer and on reaction time. The ratio of the active hydrogen atoms in.the chain extender to the NCO groups in the prepolymer should usually be less than 2 :1 and preferably in the range of 1.0 : 1 to 1.75 : 1.
The presence of excess active hydrogen, especially in the form of primary amino groups, may give rise to polymers having undesirably low molecular mass.
The polyamines are essentially alkylene polyamines having 1 to 40 carbon atoms, preferably about 2 to 15 carbon atoms. They can carry substituents which are free from any hydrogen atoms which are capable of reacting with isocyanate groups. Examples are polyamines with a linear or branched aliphatic, cycloaliphatic or aromatic structure and at least two primary amino groups. Suitable diamines are ethylenediamine, propylenediamine, 1,4-butylenediamine,piperazine,l,4~-cyclohexyldimethylamine, 1,6-hexamethylenediamine, trimethylhexamethylenediamine, methanediamine, isophoronediamine, 4,4'-diaminodicyclo-hexylmethaneandaminoethylethanolamine.Preferreddiamines are alkyldiamines or cycloalkyldiamines such as propylene-diamine and 1-amino-3-aminomethyl-3,5,5-trimathylcyclo-hexane.
The chain lengthening can be carried out at least in part using a polyamine which contains at least three amino groups having a reactive hydrogen. The amount of this type of polyamine which can be used is such that unreacted amine nitrogen atoms with 1 or 2 reactive hydrogen atoms are present after the lengthening of the polymer. Polyamines which can be used for this purpose are-diethylenetriamine, triethylenetetramine, dipropyl-enetriamine and dibutylenetriamine. Preferred polyamines are the alkyltriamines or cycl.oalkyltriamines such as diethylenetriamine. In order to prevent gel formation during the chain lengthening, small amounts of mono-amines, such as ethylhexylamine, may be also added.
The water-thinnable polyurethane resins to be used according to the invention and their preparation are 200498L~

also disclosed in EP-A 89,497 and US-PS 4,719,132.
The mixture of emulsion polymer and polyurethane resin, contained in the preferred aqueous basecoat compositions as film-former, consists of 95 to 40% by weight of emulsion polymer and 5 to 60% by weight of polyurethane resin, the weight percentages being in each case based on the solids content and their total being always 100% by weight.
In addition to the emulsion polymer or the mixture of emulsion polymer and polyurethane resin, the aqueous basecoat compositions according to the invention contain advantageously furtherc:ompatible water-thinnable synthetic resins, eg. aminoplast resins, polyesters and polyethers which generally serve as grinding resins for the pigments.
The aqueous basecoat compositions according to the invention preferably contain 5 to 20, particularly preferably 10 to 16, % by weight, based on the total solids content of the basecoat compositions, of a water-thinnable aminoplast resin, preferably melamine resin, and 5 to 20, preferably 8 to 15, % by weight of a water-thi~inable polyether (eg. polypropylene glycol having a number average molecular weight. of 400 to 900).
The basecoat compositions according to the ~ invention may comprise as pigments inorganic coloring pigments, eg. titanium dioxide, iron oxide, carbon black etc., organic coloring pigments as well as the usual metal pigments (eg. commercial aluminum bronzes, alloy steel bronzes ...) and non-metallic effect pigments (eg.

2004~)~g nacreous luster pigments and interference pigments). The basecoat compositions according to the invention prefer-ably comprise metal pigments and/or effect pigments. The degree of pigmentation falls within the usual ranges.
Furthermore, crosslinked polymeric microparticles, such as those disclosed in EP-A 38,127, and/or the usual rheological inorganic or organic additives may be added to the basecoat compositions according to the invention.
Thus, for example, water-soluble cellulose ethers, such as hydroxyethylcellulose,methylcelluloseorcarboxymethyl-cellulose, and synthetic polymers having ionic and/or associatively acting groups, such as polyvinyl alcohol, poly(meth)acrylamide, poly(meth)acrylic acid, polyvinyl-pyrrolidone, styrene-malefic anhydride or ethylene-malefic anhydride copolymers and their derivatives, as well as hydrophobically modified ethoxylated urethanes or poly-acrylates, may act as thickeners. Carboxyl-containing polyacrylate copolymers having an acid value of 60 to 780, preferably 200 to 500, are particularly preferred.
The basecoat compositions according to the invention have generally a solids content of about 15 to 50% by weight. The solids content varies with the end use of the coating compositions. In the case of metallic paints, for example, it is preferably 17 to 25% by weight. For solid-color paints the solids content is higher, for example 30 to 45% by weight.
The coating compositions according to the inven-tion may additionally contain the usual organic solvents .
Their amount is kept as low as possible, for example 2004~1~9 - 2 6 ~-below 15% by weight.
The pH of the basecoat compositions according to the invention is generally adjusted to between 6.5 and 9Ø The adjustment can be carried out using the usual amines, eg. ammonia, triethylamine, dimethylaminoethanol and N-methylmorpholine.
The object outlined at the outset is achieved by the preparation of the basecoat compositions according to the invention.
The basecoat compositions according to the invention provide high-quality coatings even without being themselves coated with a clear topcoat composition.
The basecoat compositions according to the invention may be applied to any substrate, ecz. metal, wood, plastics or paper.
The examples below explain the invention in greater detail.
A. Preparation of the emulsion polymers Emulsion polymer dispersion 1 1344 g of deionized water and 12 g of a 30%
aqueous solution of the ammonium salt of penta(ethylene glygol) nonylphenyl ether sulfate (Fenopon' EP 110 from GAF Corp., emulsifier 1) are introduced into a cylindri-cal glass vessel with double walls, provided with a stirrer, reflux condenser, stirrable feed vessel, dropp-ing funnel and thermometer, and the mixture is heated to 82°C. An emulsion is prepared in the stirrable feed vessel from 720 g of deionized water, 24 g of emulsifier 1, 10.8 g of acrylamide, 864 g of methyl methacrylate and 200 ~~

216 g of n-butyl methacrylate. 30% by weight of this emulsion are added to the mixture in the glass vessel, followed by a dropwise addition, in the course of 5 minutes, of 28% by weight of a solution of 3.1 g of ammonium peroxodisulfate (APS) in 188 g of deionized water. An exothermic reaction sets in. The reaction temperature is kept between 82 and 88°C. 15 minutes after the addition of the ammonium peroxodisulfate solution has been completed, the remaining 70% by weight of the emulsion are added together with the remaining 72% by weight of the ammonium peroxodisulfate solution in the course of one hour, the temperature being kept at 85°C.
The reaction mixture is then cooled to 82°C, and a mixture of 842 g of n-butyl acrylate, 108 g of hydroxy-propyl methacrylate, 43 g of methyl methacrylate, 43.2 g of methacrylic acid, 32.4 g of acrylamide and 5.4 g of eicosa(ethylene glycol) nonylphenyl ether (Antarox CO 850 from GAF Corp., emulsifier 2) as well as 343 g of deionized water are added in the course of 2 hours. When the addition has been completed, the reaction mixture is kept for a further 1.5 hours at: 85°C. It is then cooled and-the dispersion is passed through a fabric with a ~m mesh size. A finely divided dispersion is obtained which his a non-volatile content of 45% by weight, a pH
25 of 3.4, an acid value of 13 and a hydroxyl value of 20.
Emulsion polymer dispersion 2 1344 g of deionized water and 12 g of a 40%
aqueous solution of the ammonium salt of penta(ethylene glycol) nonylphenyl ether sulfate (Fenopon' EP 110 from _ 2s _ GAF Corp., emulsifier 1) are introduced into a cylindri-cal glass vessel with double walls, provided with a stirrer, reflux condenser, stirrable feed vessel, drop-ping funnel and thermometer, and the mixture is heated to 80°C. An emulsion is prepared in the stirrable feed vessel fom 720 g of deionized water, 24 g of emulsifier 1, 10.8 g of acrylamide, 518 g of methyl methacrylate, 292 g of n-butyl methacrylate and 205 g of styrene.
30% by weight of this emulsion are added to the mixture in the glass vessel, followed by a dropwise addition, in the course of 5 minutes, of a solution of 0.9 g of ammonium peroxodisulfate APS in 55 g of de ionized water. An exothermic, reaction sets in. The reaction temperature is kept between 80 and 85°C. 15 minutes after the addition of the above APS solution has been completed, a solution of 2.2 g of APS in 480 g of water is added in the course of 3 hours and the remaining 70% by weight of the above emulsion are added in the course of one hour, the reaction temperature being kept at 80°C. After the addition of the emulsion has been completed, the reaction mixture is cooled to 77°C and a mixture of 745 g of n-butyl acrylate, 119 g of methyl methacrylate, 108 g of hydroxypropyl methacrylate, 54 g of styrene, 42.7 g of ethylhexyl acrylate, 42.7 g of methacrylic acid, 21.6 g of acrylamide and 2.2 g of emulsifier 2 is added in the course of 2 hours. After the addition has been completed, the reaction mixture is kept for a further 1.5 hours at 80"C. It is then cooled and the dispersion is passed through a fabric with a 30 ~m 200~0~~
- 2g ._ mesh size. A finely divided dispersion is obtained which has a non-volatile content of 45% by weight, a pH of 3.8, an acid value of 13 and a hydroxyl value of 19.
Emulsion polymer dispersion 3 1109 g of deionized water and 10 g of a 30%
aqueous solution of the ammonium salt of penta(ethylene glycol) nonylphenyl ether sulfate (Fenopon EP 110 from GAF Corp., emulsifier 1) are introduced into a cylindri-cal glass vessel with double walls, provided with a stirrer, reflux condenser, stirrable feed vessel, dropp-ing funnel and thermometer, and the mixture is heated to 82°C. An emulsion is prepared in the stirrable feed vessel from 748.2 g of deionized water, 20.3 g of emul-sifier 1, 9.0 g of acrylamide, 718.1 g of methyl meth-acrylate and 179.5 g of n-butyl methacrylate. 30% by weight of this emulsion are added to the mixture in the glass vessel, followed by a dropwise addition, in the course of 5 minutes, of 10% by weight of a solution of 7.2 g of ammonium peroxodisulfate in 305 g of deionized water. An exothermic reaction sets in. The reaction temperature is kept between 82 and 88°C. 15 minutes after the addition of the ammonium peroxodisulfate solution has been completed, the remaining 70% by weight of the emulsion are added together with the remaining 90% by weight of the ammonium peroxodisulfate solution in the course of one hour, the temperature being kept at 82°C.
A mixture of 700 g of n-butyl acrylate, 89.8 g of hydroxypropyl methacrylate,35.9 g of methyl methacrylate, 2oo49~s 35.9 g of methacrylic acid, :!6.9 g of acrylamide and 4.5 g of eicosa(ethylene glycol) nonylphenyl ether (Antarox CO 850 from GAF Corp., emulsifier 2) is then added in the course of 2 hours. When the addition has been completed, the reaction mixture is kept for a further 1.5 hours at 82°C. It is then cooled and the dispersion is passed through a fabric with a 30 ~m mesh size. A finely divided dispersion is obtained which has a non-volatile content of 45% by weight, a pH of 2.5, an acid value of 14 and a hydroxyl value of 20.
Emulsion polymerization dispersion 4 1344 g of deionized water and 12 g of a 30%
aqueous solution of the ammonium salt of penta(ethylene glycol) nonylphenyl ether sulfate (Fenopon° EP 110 from GAF Corp., emulsifier 1) are introduced into a cylindri-cal glass vessel with double walls, provided with a stirrer, reflux condenser, stirrable feed vessel, dropp-ing funnel and thermometer, and the mixture is heated to 82°C. An emulsion is prepared in the stirrable feed vessel from 477 g of deionized water, 66.7 g of emul-sifier 1, 10.8 g of acrylamide, 864 g of methyl methacry-late and 216 g of n-butyl methacrylate. 30% by weight of this emulsion are added to the mixture in the glass vessel, followed by a dropwise addition, in the course of 5 minutes, of 3.6% by weight of a solution of 8.6 g of ammonium peroxodisulfate in 183 g of deionized water. An exothermic reaction sets in. The reaction temperature is kept between 82 and 88°C. 15 minutes after the addition of the ammonium peroxodisulfate solution has been com-- 31 ~-pleted, the remaining 70% by weight of the emulsion together with the remaining 96.4% by weight of the ammonium peroxodisulfate solution are added in the course of one hour, the temperature being kept at 82°C. A
mixture of 842 g of n-butyl acrylate, 108 g of hydroxy-propyl methacrylate, 43.2 g of methyl methacrylate, 43.2 g of acrylamidomethylpropanesulfonic acid, 32.4 g of acrylamide, 66.7 g of emulsifier 1 and 5.4 g of eicosa-(ethylene glycol) nonylphenyl ether (Antarox CO 850 from GAF Corp., emulsifier 2) is then added in the course of 2 hours. When the addition has been completed, the -reaction mixture is kept for a further 1.5 hours at 82°C.
It is then cooled and the dispersion is passed through a fabric with a 30 ~m mesh size. A finely divided disper-sion is obtained which has a non-volatile content of 46%
by weight, a pH of 2.5, an acid value of 6 and a hydroxyl value of 19.
Emulsion pol3nner dispersion 5 1344 g of deionized water and 12 g of a 30%
aqueous solution of the ammonium salt of penta(ethylene glycol) nonylphenyl ether sulfate (Fenopon EP 110 from GAF_Corp., emulsifier 1) are introduced into a cylindri cal glass vessel with double walls, provided with a stirrer, reflux condenser, stirrable feed vessel, dropp ing funnel and thermometer, and the mixture is heated to 82°C. An emulsion is prepared in the stirrable feed vessel from 720 g of deionized water, 24 g of emulsifier 1, 43.2 g of acrylamide, 907 g of methyl methacrylate, 216 g of n-butyl methacrylate, 842 g of n-butyl acrylate, - 3 2 .-108 g of hydroxypropyl methacrylate, 43.2 g of meth-acrylic acid and 5.4 g of emulsifier 2. 10% by weight of this emulsion are added to the mixture in the glass vessel, followed by a dropwise addition, in the course of 5 minutes, of a solution of 0.87 g of ammonium peroxo-disulfate in 53 g of deionized water. An exothermic reaction sets in. The reaction temperature is kept between 82 and 88°C. 15 minutes after the addition of the APS solution has been completed, the remaining 90$ by weight of the emulsion is added in the course of 3 hours and a solution of 2.23 g of APS in 478 g of deionized water is added in the course of 3.5 hours, the tempera-ture being kept at 82°C.
After the addition has been completed, the reaction mixture is kept for a further 1.5 hours at 82°C.
It is then cooled and the dispersion is passed through a fabric with a 30 ~m mesh size. A finely divided disper sion is obtained which has a no:n-volatile content of 45$
by weight, a pH of 5.8, an acid value of 13 and a hydroxyl value of 20.
B. Preparation of the Dolvurethane resins used according to the invention Polvurethane resin dispersion 1 570 g of a commercial polyester prepared from caprolactone and ethylene glycol., having a hydroxyl value of 196, are stripped of water by being heated for 1 hour at 100°C under reduced pressure. 524 g of 4,4'-dicyclo hexylmethane diisocyanate are added at 80°C and the mixture is stirred at 90°C until the isocyanate content 20049t3~3 - 3 3 ~-is 7.52% by weight, based on the total weight. The reaction mixture is cooled to 60°C, a solution of 67 g of dimethylolpropionic acid and 50 g of triethylamine in 400 g of N-methylpyrrolidone is added and the mixture is stirred for 1 hour at 90°C. The resultant mass is poured into 1840 g of cold deionized water with vigorous stirr-ing. To the resultant dispersion there are added, in the course of 20 minutes, 86 g of 15% hydrazine solution with vigorous stirring. The resultant finely divided disper-sion has a solids content of 35% and an efflux time of 27 seconds in DIN cup No. 4.
Polyurethane resin dispersion ~
830 g of a polyester from neopentyl glycol, 1,6-hexanediol and adipic acid, having a hydroxyl value of 135 and an acid value of less than 3, are stripped of water by being heated for 1 hour at 100°C under reduced pressure. 524 g of 4,4'-dicyclo;hexylmethane diisocyanate are added at 80°C and the mixture is stirred at 90°C
until the free isocyanate groups content is 6.18% by weight, based on the total weight. The reaction mixture is cooled to 60°C, a solution of 67 g of dimethylpro-pionic acid and 50 g of triethylamine in 400 g of N-methylpyrrolidone is added and the mixture is stirred for 1 hour at 90°C.
The resultant mass is poured into 2400 g of cold deionized water with vigorous stirring. A finely divided dispersion is obtained. To this dispersion there are added, in the course of 20 minutes, 80 g of a 30% aqueous solution of ethylenediamine with vigorous stirring. The 2004~~3~3 - 3 4 ~-resultant very finely divided dispersion has a solids content of 35% and an efflux time of 23 seconds in the DIN cup No. 4.
C Preparation of the basecoat compositions 18.2 g of butyl glycol, 3.7 g of a commercial melamine-formaldehyde resin (Cymel° 301), 3.1 g of poly-propylene glycol (average molecular weight - 400) and 7.2 g of an aluminum bronze according to DE-OS 3,636,183 (aluminum content: 60% by weight) are stirred for 15 minutes using a high-speed stirrer at 300-500 rpm.
Mixture 1 is obtained.
27.2 g of emulsion polymer dispersion 1, 2, 3 or 4 are mixed with 11.6 g of polyurethane resin dispersion 1 and 19.6 g of deionized water. The pH of the mixture is adjusted to 7.7 using a 5% aqueous dimethylethanolamine solution, and 9.4 g of a 3.5% solution of a commercial polyacrylic acid thickener (Vi.scalex°HV 30 from Allied Colloids, pH: 8.0) are added. Mixture 2 is obtained.
To prepare the basecoat paint according to the invention, mixtures 1 and 2 are mixed for 30 minutes at 800-1000 rpm and the pH of the mixture is then adjusted to 7.7 using a 5% aqueous dimethylethanolamine solution.
The viscosity is then adjusted to an efflux time of 25 seconds in the DIN cup No. 4 by adding deionized water.
The basecoat compositions BC1, BC2, BC3 and BC4 according to the invention are obtained.
The basecoat composition BC5 is obtained by incorporating 36.2 g of the emulsion polymer dispersion 20049&8 1 into mixture 2. BC5 contains no polyurethane resin dispersion.
The basecoat compositions obtained in this manner possess excellent shelf life.
The basecoat compositions are sprayed by well-known methods onto phosphated steel panels (Bonder 132) which have been coated with a commercial electrocoating paint and a commercial filler; after a 10 minutes' flash-off period they are then coated with a commercial clear-coat and are baked for 20 minutes at 140°C.
The metallic finishes obtained in this manner have a good metallic effect, good adhesion to the filler, good intercoat adhesion between the basecoat and the topcoat, good gloss and good :resistance to exposure to the condensed moisture steady conditions test according to DIN 50 017. BC1, BC2, BC3 and BC4 exhibit a better metallic effect than BCS.
Some of the coated panels are recoated with the basecoat compositions BC1, BC2, BC3, BC4 and BC5 and are then coated with a commercial clearcoat. The coatings obtained in this manner are baked for 40 minutes at 80°C.
The_coatings baked at 80°C adhere very well to the coatings baked at 140°C.
Comparative Example A basecoat composition prepared according to the above description using the emulsion polymer dispersion 5 possesses inadequate shelf life.

Claims (27)

1. A process for the preparation of a multicoat protective and/or decorative coating on a substrate surface, in which process (1) a pigmented aqueous coating composition which comprises as the film-former a water-thinnable emulsion polymer, is applied to the substrate surface as basecoat composition (2) a polymeric film is formed from the composition applied in stage (1) (3) a clear topcoat composition is applied to the basecoat obtained in this manner and subsequently (4) the basecoat and the topcoat are baked together, wherein the basecoat composition comprises a water-thinnable emulsion polymer, which polymer can be obtained (a) by polymerizing in a first stage 10 to 90 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T G1) of +30 to +110°C, and (b) by polymerizing in a second stage 90 to 10 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers, after at least 80% by weight of the monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the monomer used in the second stage or the mixture of ethylenically unsaturated monomers used in the second stage being chosen such that an exclusive polymerization of the monomer used in the second stage or of the mixture of ethylenically unsaturated polymers used in the second stage gives rise to a polymer having a glass transition temperature (T G2) of -60 to +20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T G1 T G2 is 10 to 170°C.

2. The process as claimed in claim 1, wherein the basecoat composition or compositions comprises a metallic pigment.

3. The process as claimed in claim 1, wherein the basecoat composition or compositions comprises an aluminum pigment.

4. The process as claimed in claim 1, 2, or 3, wherein the film-former consists of 95 to 40% by weight of the emulsion polymer and 5 to 60% by weight of a water-thinnable polyurethane resin, the weight percentages in each case referring to the solids content and their sum being always 100% by weight.

5. The process as claimed in any one of claims 1 to 4, wherein a mixture is used in the first stage which consists of (a1) 100 to 60% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0 to 40% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

6. The process as claimed in any one of claims 1 to 4, wherein a mixture is used in the first stage which consists of (a1) 99.5 to 75% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0.5 to 25% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

7. The process as claimed in any one of claims 1 to 6, wherein a mixture is used in the second stage which consists of (b1) 47 to 99% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 1 to 20% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3) and (b4), or a mixture of such monomers (b3) 0 to 8% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 0 to 25% by weight of a further monomer which is copolymerizable with (b1), (b2) and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

8. The process as claimed in any one of claims 1 to 6, wherein a mixture is used in the second stage which consists of (b1) 75 to 90% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 5 to 15% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3) and (b4), or a mixture of such monomers (b3) 2 to 6% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 2 to 15% by weight of a further monomer which is copolymerizable with (b1), (b2) and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

9. A water-thinnable coating composition which comprises as the film-former a water-thinnable emulsion polymer which can be obtained (a) by polymerizing in a first stage 10 to 90 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T G1) of +30 to +110°C, and (b) by polymerizing in a second stage 90 to 10 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers, after at least 80% by weight of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the monomer used in the second stage or the mixture of ethylenically unsaturated monomers used in the second stage being chosen such that an exclusive polymerization of the monomer used in the second stage or of the mixture of ethylenically unsaturated polymers used in the second stage gives rise to a polymer having a glass transition temperature (T G2) of -60 to +20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T G1 - T G2 is 10 to 170°C.

10. The coating composition as claimed in claim 9, which comprises a metallic pigment.

11. The coating composition as claimed in claim 9, which comprises an aluminum pigment.

12. The coating composition as claimed in claim 9, 10, or 11, wherein the film-former consists of 95 to 40% by weight of the emulsion polymer and 5 to 60% by weight of a water-thinnable polyurethane resin, the weight percentages in each case referring to the solids content and their sum being always 100% by weight.

13. The coating composition as claimed in any one of claims 9 to 12, wherein a mixture is used in the first stage which consists of (a1) 100 to 60% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0 to 40% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

14. The coating composition as claimed in any one of claims 9 to 12, wherein a mixture is used in the first stage which consists of (a1) 99.5 to 75% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0.5 to 25% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

15. The coating composition as claimed in any one of claims 9 to 14, wherein a mixture is used in the second stage which consists of (b1) 47 to 99% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 1 to 20% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3), and (b4), or a mixture of such monomers (b3) 0 to 8% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 0 to 25% by weight of a further monomer which is copolymerizable with (b1), (b2), and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

16. The coating composition as claimed in any one of claims 9 to 14, wherein a mixture is used in the second stage which consists of (b1) 75 to 90% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 5 to 15% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3), and (b4), or a mixture of such monomers (b3) 2 to 6% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 2 to 15% by weight of a further monomer which is copolymerizable with (b1), (b2), and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

17. A water-thinnable emulsion polymer which can be obtained (a) by polymerizing in a first stage 10 to 90 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T G1) of +30 to +110°C, and (b) by polymerizing in a second stage 90 to 10 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers, after at least 80% by weight of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the monomer used in the second stage or the mixture of ethylenically unsaturated monomers used in the second stage being chosen such that an exclusive polymerization of the monomer used in the second stage or of the mixture of ethylenically unsaturated polymers used in the second stage gives rise to a polymer having a glass transition temperature (T G2) of -60 to +20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of the monomers used in the first stage and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T G1 - T G2 is 10 to 170°C.

18. The emulsion polymer as claimed in claim 17, wherein a mixture is used in the first stage which consists of (a1) 100 to 60% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0 to 40% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

19. The emulsion polymer as claimed in claim 17, wherein a mixture is used in the first stage which consists of (a1) 99.5 to 75% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0.5 to 25% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

20. The emulsion polymer as claimed in any one of claims 17 to 19, wherein a mixture is used in the second stage which consists of (b1) 47 to 99% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 1 to 20% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3), and (b4), or a mixture of such monomers (b3) 0 to 8% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 0 to 25% by weight of a further monomer which is copolymerizable with (b1), (b2), and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

21. The emulsion polymer as claimed in any one of claims 17 to 19, wherein a mixture is used in the second stage which consists of (b1) 75 to 90% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 5 to 15% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3), and (b4), or a mixture of such monomers (b3) 2 to 6% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 2 to 15% by weight of a further monomer which is copolymerizable with (b1), (b2), and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

22. A process for the preparation of a water-thinnable emulsion polymer, which comprises (a) polymerizing in a first stage 10 to 90 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers in aqueous phase in the presence of one or more emulsifiers and one or more radical-forming initiators, the ethylenically unsaturated monomer or the mixture of ethylenically unsaturated monomers being chosen such that the first stage gives rise to a polymer having a glass transition temperature (T G1) of +30 to +110°C, and (b) polymerizing in a second stage 90 to 10 parts by weight of an ethylenically unsaturated monomer or a mixture of ethylenically unsaturated monomers, after at least 80% by weight of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage has reacted, in the presence of the polymer obtained in the first stage, the monomer used in the second stage or the mixture of ethylenically unsaturated monomers used in the second stage being chosen such that an exclusive polymerization of the monomer used in the second stage or of the mixture of ethylenically unsaturated polymers used in the second stage gives rise to a polymer having a glass transition temperature (T G2) of -60 to +20°C, the reaction conditions being chosen such that the resultant emulsion polymer has a number average molecular mass of 200,000 to 2,000,000, and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the first stage and the nature and amount of the ethylenically unsaturated monomer or the mixture of monomers used in the second stage are chosen such that the resultant emulsion polymer has a hydroxyl value of 2 to 100 and the difference T G1 - T G2 is 10 to 170°C.

23. The process as claimed in claim 22, wherein a mixture is used in the first stage which consists of (a1) 100 to 60% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0 to 40% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

24. The process as claimed in claim 22, wherein a mixture is used in the first stage which consists of (a1) 99.5 to 75% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters, and (a2) 0.5 to 25% by weight of a monomer which is copolymerizable with (a1) or a mixture of such monomers, the total of the weight percentages of (a1) and (a2) being always 100% by weight.

25. The process as claimed in any one of claims 22 to 24, wherein a mixture is used in the second stage which consists of (b1) 47 to 99% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 1 to 20% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3) and (b4), or a mixture of such monomers (b3) 0 to 8% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 0 to 25% by weight of a further monomer which is copolymerizable with (b1), (b2) and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

26. The process as claimed in any one of claims 22 to 24, wherein a mixture is used in the second stage which consists of (b1) 75 to 90% by weight of a cycloaliphatic or aliphatic ester of methacrylic acid or acrylic acid or a mixture of such esters (b2) 5 to 15% by weight of a monomer which carries at least one hydroxyl group and is copolymerizable with (b1), (b3) and (b4), or a mixture of such monomers (b3) 2 to 6% by weight of a monomer which carries at least one carboxyl or sulfonic acid group and is copolymerizable with (b1), (b2) and (b4), or a mixture of such monomers, and (b4) 2 to 15% by weight of a further monomer which is copolymerizable with (b1), (b2) and (b3), or a mixture of such monomers, the total of the weight percentages of (b1), (b2), (b3) and (b4) being always 100% by weight.

27. A substrate surface bearing a multicoat protective and/or decorative coating applied by a process according to any one of claims 1 to 8.