Aqueous multicomponent polyurethane coating composition, process for its preparation and its use in methods of producing a multicoat finish

The present invention relates to an aqueous multicomponent polyurethane coating composition comprising A) a water-dilutable polyaddition resin (A1) and/or polycondensation resin (A2) containing hydroxyl and carboxylate groups and having an OH number of from 40 to 200 mg of KOH/g, preferably from 60 to 140 mg of KOH/g, an acid number of from 15 to 100 mg of KOH/g, preferably from 25 to 50 mg of KOH/g, and a glass transition temperature of from -40.degree. C. to +60.degree. C., preferably from -20.degree. C. to +40.degree. C., B) a polyisocyanate component (B) as crosslinking agent and C) at least one additive, characterized in that it contains as additive a carbodiimide component (C) which has a content of carbodiimide groups --N.dbd.C.dbd.N-- of from 2 to 30% by weight, on average at least 0.8 carbodiimide groups per molecule and from 0 to 25% by weight, based on solids, of chemically incorporated ethylene oxide and/or propylene oxide units which are present within polyether chains, and/or a polyepoxide component (D).

The present invention relates to an aqueous multicomponent polyurethane 
coating composition, comprising 
A) a water-dilutable polyaddition resin (A1) and/or polycondensation resin 
(A2) containing hydroxyl and carboxylate and/or sulfonate groups and 
having an OH number of from 40 to 200 mg of KOH/g, preferably from 60 to 
140 mg of KOH/g, an acid number of from 15 to 100 mg of KOH/g, preferably 
from 25 to 50 mg of KOH/g, and a glass transition temperature of from 
-40.degree. C. to +60.degree. C., preferably from -20.degree. C. to 
+40.degree. C., 
B) a polyisocyanate component (B) as crosslinking agent and 
C) at least one additive. 
The present invention further relates to a process for the preparation of 
these aqueous coating compositions and to their use in methods of 
producing a multicoat finish, and to coated articles in which at least one 
coat has been produced using these coating compositions. 
For ecological and economic reasons the paint industry is making efforts to 
replace as great as possible a proportion of the organic solvents which 
are employed in paints by water. Especially in automotive finishing there 
is a great requirement for aqueous coatings. This applies both to the 
sector of production-line (OEM) automotive finishing and to the sector of 
automotive refinishing. 
In this context aqueous coating compositions are employed in particular in 
the area of top coats. Top coats are understood here as being coating 
materials which are used to produce the topmost coat. This topmost coat 
may comprise one or more coats, especially two coats. Two-coat top coats 
are composed of a pigmented basecoat and of a clearcoat which is pigmented 
either not at all or only with transparent pigments and is applied over 
the basecoat. 
Two-coat finishes are currently produced by the wet-on-wet method, in which 
a pigmented basecoat is initially applied and the resulting basecoat 
layer, without a baking step, is covered with a clearcoat, and then 
basecoat layer and clearcoat layer are cured together. This method is very 
advantageous in economic terms, but places stringent requirements on the 
basecoat and the clearcoat. 
The clearcoat which is applied to the as yet uncured basecoat must neither 
partially dissolve nor otherwise perturb the basecoat layer, lest finishes 
of poor appearance be obtained. This applies in particular to finishes in 
which basecoats containing special-effect pigments (e.g. metallic 
pigments, especially aluminum flakes, or pearlescent pigments) are 
employed. Furthermore, the top coat compositions must be capable of being 
applied by spraying using automatic coating units. For this purpose their 
solids content at spray viscosity must be high enough for coating films of 
adequate thickness to be obtained with 1 to 2 spray passes (cross passes), 
and they must give baked coating films of good appearance (good evenness, 
high gloss, good top coat holdout and a high degree of hardness) and good 
weathering resistance. 
In the area of automotive refinishing there is the additional requirement 
that the coating compositions employed are able to cure fully at low 
temperatures (generally &lt;80.degree. C.) and lead, even when fully cured at 
these low temperatures, to films having the good mechanical properties 
required. 
EP-B-358 979 discloses aqueous two-component polyurethane coating 
compositions which comprise a hydroxyl group-containing polyacrylate resin 
and a polyisocyanate component. However, these coatings described in 
EP-B-358 979 exhibit great disadvantages with respect to weathering 
resistance, in particular with respect to their resistance in a constant 
humid climate (40.degree. C., 240 h), and processability (fall in 
viscosity and too short pot life). 
It is furthermore known, from EP-B-198 343, to add isocyanate derivatives 
containing carbodiimide groups to aqueous solutions of polymers which 
contain carboxyl groups, to improve the mechanical properties, especially 
the wet strength. However, when the carbodiimides described in EP-B-198 
343 are used in aqueous polyurethane coating compositions, problems of 
compatibility with the binders occur and the resulting coatings have an 
inadequate weathering stability. 
Moreover, EP-A-121 083 describes crosslinking agents based on 
carbodiimides, which are employed to crosslink aqueous resins containing 
carboxyl groups. The addition of carbodiimides to polyurethane coating 
compositions is not described in EP-A-121 083. Furthermore, the 
carbodiimides described in EP-A-121 083 are not polyether-modified. 
Rather, they are incorporated into aqueous dispersions using emulsifiers 
and water-miscible solvents. 
In addition, EP-A-507 407 discloses coating compositions which contain as 
crosslinking agents carbodiimides which contain not only carbodiimide 
groups but also crosslinkable groups. By this means it is possible to 
avoid using a further crosslinking agent. The coating compositions known 
from EP-A-507 407 have the disadvantage, however, that their preparation 
is more time-consuming and cost-intensive than the mixing of different 
crosslinking agents having different functional groups. These coating 
compositions also have the disadvantage of a high VOC (Volatile Organic 
Content), since the processing of the coating compositions requires their 
dilution with organic solvents to a solids content of 50%. Furthermore, 
EP-A-507 407 contains no information on the short-term weathering 
stability of the coatings. 
Finally, EP-A-516 277 discloses aqueous two-component polyurethane coatings 
which contain, as the component which is essential to the invention, a 
polyether-modified polyisocyanate. As binders these aqueous two-component 
coatings contain polyacrylate resins which are conventionally employed. 
The use of polyether-modified polyisocyanates has the disadvantage, 
however, that the resulting coatings have only a low weathering stability, 
and in particular poor results in the constant humid climate test. 
The present invention is therefore based on the object of providing aqueous 
multicomponent polyurethane coating compositions of the type mentioned 
initially which, in relation to the known aqueous polyurethane coating 
compositions, have improved properties and/or give improved coating films. 
The new coating compositions should above all have an improved weathering 
stability. Despite hybrid crosslinking using two or more different 
crosslinking agents, the coating compositions should moreover possess the 
same ease of application as conventional 2-component PUR coating 
compositions. 
The new coating compositions should also be suited to the area of 
automotive refinishing, i.e. they should be able to cure fully at low 
temperatures (generally &lt;80.degree. C.) and should lead to coatings which 
meet at least the requirements conventionally placed on an automotive 
refinish. The coating compositions should therefore have, for example, 
good evenness and good mechanical properties. 
Surprisingly this object has been achieved by aqueous multicomponent 
polyurethane coating compositions of the type mentioned initially, which 
are characterized in that they contain as additive a carbodiimide 
component (C) which has a content of carbodiimide groups --N.dbd.C.dbd.N-- 
of from 2 to 30% by weight, on average at least 0.8 carbodiimide groups 
per molecule and from 0 to 25% by weight, based on solids, of chemically 
incorporated ethylene oxide and/or propylene oxide units which are present 
within polyether chains, and/or a polyepoxide component (D). 
The present invention relates furthermore to a process for the preparation 
of the aqueous multicomponent polyurethane coating compositions in which, 
shortly before application, a component which comprises the isocyanate 
group-containing crosslinking agent and the carbodiimide component is 
mixed with the component which comprises the water-dilutable binder. The 
invention also relates to a method of producing a multilayer, protective 
and/or decorative coating on a substrate surface, in which the top coat 
composition employed comprises the aqueous coating compositions according 
to the invention, and to the coated articles obtained by this method. 
Finally, the present invention also relates to the use of the aqueous 
coating compositions. 
It is surprising and was unforeseeable that the aqueous polyurethane 
coating compositions obtained by using the carbodiimide component and/or 
the polyepoxide component, which is or are employed in accordance with the 
invention, have an improved weathering stability (i.e. good resistance in 
the constant humid climate test and in the water spray test). A further 
advantage is that the coating compositions according to the invention 
exhibit better leveling than conventional 2-component PUR coating 
compositions and that the coating compositions according to the invention 
possess the same ease of application as conventional 2-component PUR 
coating compositions. 
A further advantage, finally, is that the coating compositions lead to 
coatings having good mechanical properties. 
In the text below a closer description will first be given of the 
individual components of the aqueous coating composition according to the 
invention. Before the preparation of the polyacrylate resins to be 
employed in accordance with the invention is described more closely, two 
explanations of terms are dealt with beforehand: 
1. (Meth)acrylic acid is occasionally used as an abbreviation for 
"methacrylic acid or acrylic acid". 
2. The formulation "essentially free from carboxyl groups" is intended to 
express the fact that components (a1), (a2), (a4), (a5) and (a6) may have 
a small carboxyl group content (but no more than would give a polyacrylate 
resin prepared from these components a maximum acid number of 10 mg of 
KOH/g). It is preferred, however, for the carboxyl group content of 
components (a1), (a2), (a4), (a5) and (a6) to be kept as low as possible. 
It is particularly preferred to employ carboxyl group-free components 
(a1), (a2), (a4), (a5) and (a6). 
The coating compositions according to the invention contain as binder a 
water-dilutable polyaddition resin (A1) and/or polycondensation resin (A2) 
which contains hydroxyl and carboxylate and/or sulfonate groups and has an 
OH number of from 40 to 200 mg of KOH/g, preferably from 60 to 140 mg of 
KOH/g, an acid number of from 15 to 100 mg of KOH/g, preferably from 25 to 
50 mg of KOH/g, and a glass transition temperature of from -40.degree. C. 
to +60.degree. C., preferably from -20.degree. C. to +40.degree. C. 
The polycondensation resins which are suitable as binders are known perse 
sic! and are described in, for example, EP-A-542 105. Polyester resins 
are preferably employed as (A2). The sulfonate groups can be introduced 
into the polyester by using, for example, 5-(lithiumsulfo)isophthalic 
acid. 
Polyacrylate resins are preferably employed as binders in the coating 
compositions according to the invention. These polyacrylate resins are 
preferably prepared by polymerizing, in an organic solvent or solvent 
mixture and in the presence of at least one polymerization initiator, 
a1) a (meth)acrylate which is different from (a2), (a3), (a4), (a5) and 
(a6), is copolymerizable with (a2), (a3), (a4), (a5) and (a6) and is 
essentially free from carboxyl groups, or a mixture of such monomers, 
a2) an ethylenically unsaturated monomer which is copolymerizable with 
(a1), (a2) sic!, (a3), (a4), (a5) and (a6), is different from (a5), 
carries at least one hydroxyl group per molecule and is essentially free 
from carboxyl groups, or a mixture of such monomers, 
a3) an ethylenically unsaturated monomer which carries at least one 
carboxyl group and/or sulfonate group per molecule and is copolymerizable 
with (a1), (a2), (a4), (a5) and (a6), or a mixture of such monomers, and 
a4) if desired one or more vinyl esters of .alpha.-branched monocarboxylic 
acids having from 5 to 18 carbon atoms per molecule, and/or 
a5) if desired at least one reaction product of acrylic acid and/or 
methacrylic acid with the glycidyl ester of an .alpha.-branched 
monocarboxylic acid having from 5 to 18 carbon atoms per molecule, or, 
instead of the reaction product, an equivalent amount of acrylic and/or 
methacrylic acid which is then reacted during or after the polymerization 
reaction with the glycidyl ester of an .alpha.-branched monocarboxylic 
acid having from 5 to 18 carbon atoms per molecule, 
a6) if desired an ethylenically unsaturated monomer which is 
copolymerizable with (a1), (a2), (a3), (a4) and (a5), is different from 
(a1), (a2), (a4) and (a5) and is essentially free from carboxyl groups, or 
a mixture of such monomers, 
and, after the end of the polymerization, at least partially neutralizing 
the resulting polyacrylate resin and dispersing it in water, the nature 
and quantity of (a1), (a2), (a3), (a4), (a5) and (a6) being selected such 
that the polyacrylate resin (A1) has the desired OH number, acid number 
and glass transition temperature. 
The preparation of the polyacrylate resins which are employed in accordance 
with the invention may employ as component (a1) any ester of (meth)acrylic 
acid which is copolymerizable with (a2), (a3), (a4), (a5) and (a6) and is 
essentially free from carboxyl groups, or a mixture of such 
(meth)acrylates. Examples are 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 acrylate and 
methacrylate, and cycloaliphatic (meth)acrylates such as cyclohexyl 
methacrylate. It is preferred to employ as component (a1) mixtures of 
alkyl acrylates and/or alkyl methacrylates, of which at least 20% by 
weight are composed of n-butyl and/or t-butyl acrylate and/or n-butyl 
and/or t-butyl methacrylate. 
As component (a1) it is also possible to employ ethyltriglycol 
(meth)acrylate and methoxyoligoglycol (meth)acrylate having a 
number-average molecular weight of preferably 550 or other ethoxylated 
and/or propoxylated derivatives of (meth)acrylic acid which are free from 
hydroxyl groups. 
As component (a2) it is possible to employ ethylenically unsaturated 
monomers which are copolymerizable with (a1), (a2) sic!, (a3), (a4), (a5) 
and (a6), are different from (a5), carry at least one hydroxyl group per 
molecule and are essentially free from carboxyl groups, or a mixture of 
such monomers. Examples are hydroxyalkyl esters of acrylic acid, 
methacrylic acid or another .alpha.,.beta.-ethylenically unsaturated 
carboxylic acid. These esters may be derived from an alkylene glycol which 
is esterified with the acid, or they may be obtained by reacting the acid 
with an alkylene oxide. As component (a2) it is preferred to employ 
hydroxyalkyl esters of acrylic acid or methacrylic acid in which the 
hydroxyalkyl group contains up to 20 carbon atoms, reaction products of 
cyclic esters, e.g. .epsilon.-caprolactone, and these hydroxyalkyl esters, 
or mixtures of these hydroxyalkyl esters and/or 
.epsilon.-caprolactone-modified hydroxyalkyl esters. 
Examples of such hydroxyalkyl esters are 2-hydroxyethyl acrylate, 
2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl 
methacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 
4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, hydroxystearyl 
acrylate and hydroxystearyl methacrylate. Corresponding esters of other 
unsaturated acids, for example ethacrylic acid, crotonic acid and similar 
acids having up to about 6 carbon atoms per molecule, can also be 
employed. It is also possible to employ olefinically unsaturated polyols 
as component (a2). Preferred polyacrylate resins (A) are obtained when 
trimethylolpropane monoallyl ether is employed as at least part of 
component (a2). The proportion of trimethylolpropane monoallyl ether is 
usually from 2 to 10% by weight, based on the total weight of the monomers 
(a1) to (a6) employed in the preparation of polyacrylate resin. In 
addition, however, it is also possible to add from 2 to 10% by weight, 
based on the total weight of the monomers employed in the preparation of 
the polyacrylate resin, of trimethylolpropane monoallyl ether to the 
finished polyacrylate resin. The olefinically unsaturated polyols such as, 
in particular, trimethylolpropane monoallyl ether may be employed as the 
sole hydroxyl group-containing monomer, but are employed in particular in 
proportions in combination with other of the hydroxyl group-containing 
monomers mentioned. 
As component (a3) any ethylenically unsaturated monomer which carries at 
least one sulfonyl and/or carboxyl group per molecule and is 
copolymerizable with (a1), (a2), (a4), (a5) and (a6), or a mixture of such 
monomers, can be employed. It is preferred to employ acrylic acid and/or 
methacrylic acid as component (a3). However, it is also possible to employ 
other ethylenically unsaturated acids having up to 6 carbon atoms in the 
molecule. Examples of such acids are ethacrylic acid, crotonic acid, 
maleic acid, fumaric acid and itaconic acid. It is also possible to employ 
as component (a3) mono(meth)acryloyloxyethyl maleate, 
mono(meth)acryloyloxyethyl succinate and mono(meth)acryloyloxyethyl 
phthalate. Examples of monomers containing sulfonyl groups are 
2-acrylamido-2-methylpropanesulfonic acid and vinylsulfonic acid. 
As component (a4) one or more vinyl esters of .alpha.-branched 
monocarboxylic acids having from 5 to 18 carbon atoms in the molecule are 
employed. The branched monocarboxylic acids can be obtained by reacting 
formic acid or carbon monoxide and water with olefins in the presence of a 
liquid, strongly acid catalyst; the olefins may be products from the 
cracking of paraffinic hydrocarbons such as mineral oil fractions, and may 
contain both branched and straight-chain acyclic and/or cycloaliphatic 
olefins. The reaction of such olefins with formic acid or with carbon 
monoxide and water produces a mixture of carboxylic acids in which the 
carboxyl groups are predominantly located on a quaternary carbon atom. 
Examples of other olefinic starting substances are propylene trimer, 
propylene tetramer and diisobutylene. The vinyl esters may, however, also 
be prepared from the acids in a manner known per se, for example by 
reacting the acid with acetylene. 
Because of their ready availability, it is particularly preferred to employ 
vinyl esters of saturated aliphatic monocarboxylic acids having from 9 to 
11 carbon atoms, which are branched on the .alpha. carbon atom. 
As component (a5) the reaction product of acrylic acid and/or methacrylic 
acid with the glycidyl ester of an .alpha.-branched monocarboxylic acid 
having from 5 to 18 carbon atoms per molecule is employed. Glycidyl esters 
of strongly branched monocarboxylic acids can be obtained under the trade 
name "Cardura". The acrylic or methacrylic acid can be reacted with the 
glycidyl ester of a carboxylic acid having a tertiary .alpha. carbon atom 
before, during or after the polymerization reaction. Preference is given 
to employing as component (a5) the reaction product of acrylic and of 
methacrylic acid with the glycidyl ester of Versatic acid. This glycidyl 
ester is commercially available under the name "Cardura E10". 
As component (a6) it is possible to employ all ethylenically unsaturated 
monomers which are copolymerizable with (a1), (a2), (a3), (a4) and (a5), 
are different from (a1), (a2), (a3) and (a4) and are essentially free from 
carboxyl groups, or mixtures of such monomers. Preferably employed as 
component (a6) are vinyl aromatic hydrocarbons such as styrene, 
.alpha.-alkylstyrene and vinyltoluene. 
As component (a6) it is also possible to employ, in combination with other 
monomers mentioned as being suitable as component (a6), polysiloxane 
macromonomers. Suitable polysiloxane macromonomers are those having a 
number-average molecular weight of from 1000 to 40,000, preferably from 
2000 to 10,000, and on average from 0.5 to 2.5 and preferably 0.5 to 1.5 
ethylenically unsaturated double bonds per molecule. Suitable examples are 
the polysiloxane macromonomers described in DE-A-38 07 571 on pages 5 to 
7, in DE-A-37 06 095 in columns 3 to 7, in EP-B 358 153 on pages 3 to 6 
and in U.S. Pat. No. 4,754,014 in columns 5 to 9. Also suitable, 
furthermore, are other acryloxysilane-containing vinyl monomers having the 
abovementioned molecular weights and contents of ethylenically unsaturated 
double bonds, for example compounds which can be prepared by reacting 
hydroxy-functional silanes with epichlorohydrin and subsequently reacting 
the reaction product with methacrylic acid and/or hydroxyalkyl esters of 
(meth)acrylic acid. 
Preferred polysiloxane macromonomers for employment as component (a6) are 
those of the following formula: 
##STR1## 
where R.sup.1 .dbd.H or CH.sub.3 
R.sup.2, R.sup.3, R.sup.4, R.sup.5 =identical or different aliphatic 
hydrocarbon radicals having from 1 to 8 carbon atoms, especially methyl, 
or a phenyl radical. 
n=from 2 to 5, preferably 3 
m=from 8 to 30 
Particular preference is given to employing the .alpha., -acryloxy sic! 
organo-functional polydimethyl-siloxane of the formula 
##STR2## 
where n.apprxeq.9, with an acryloxy equivalent of 550 g per equivalent, an 
OH number of 102 mg of KOH/g and a viscosity of 240 mPas (25.degree. C.). 
Also preferably employed as component (a6) are polysiloxane macromonomers 
which have been prepared by reacting from 70 to 99.999 mol-% of a compound 
(1), represented by the formula (I) 
##STR3## 
in which R.sup.1 represents an aliphatic hydrocarbon group having from 1 
to 8 carbon atoms or a phenyl radical and R.sup.2, R.sup.3 and R.sup.4 
each represent a halogen radical or an alkoxy radical having 1 to 4 carbon 
atoms, or a hydroxyl group, with from 30 to 0.001 mol-% of a compound (2), 
represented by the formula (II) 
##STR4## 
in which R.sup.5 represents a hydrogen atom or a methyl radical, R.sup.6, 
R.sup.7 and R.sup.8 each represent halogen, OH-- or an alkoxy radical 
having from 1 to 4 carbon atoms, or an aliphatic hydrocarbon group having 
from 1 to 8 carbon atoms, at least one of the radicals R.sup.6, R.sup.7 or 
R.sup.8 representing OH-- or an alkoxy group and n representing an integer 
from 1 to 6. 
Examples of suitable compounds (1) and (2) are mentioned in WO 92/22615 on 
page 13, line 18 to page 15, line 9. 
The reaction between compounds (1) and (2) is brought about by the 
dehydrating condensation of the hydroxyl groups which these compounds 
contain and/or the hydroxyl groups which can be attributed to the 
hydrolysis of the alkoxy groups in these compounds. Depending on the 
reaction conditions the reaction comprises in addition to the dehydration 
reaction a dealcohalizing sic! condensation. If compounds (1) or (2) 
contain halogen radicals the reaction between (1) and (2) is brought about 
by dehydrohalogenation. 
The conditions under which the reaction between compound (1) and compound 
(2) is carried out are likewise described in the international patent 
application having the international publication no. WO 92/22615 on page 
15, line 23 to page 18, line 10. 
The amount of the polysiloxane macromonomer(s) (a6) employed to modify the 
acrylate copolymers (A1) is less than 5% by weight, preferably from 0.05 
to 2.5% by weight and particularly preferably from 0.05 to 0.8% by weight, 
based in each case on the total weight of the monomers employed in the 
preparation of the copolymer (A1). 
The use of such polysiloxane macromonomers leads to an improvement in the 
slip of the aqueous polyurethane coating composition. 
The nature and quantity of components (a1) to (a6) is selected such that 
the polyacrylate resin (A1) has the desired OH number, acid number and 
glass transition temperature. Particular preference is given to employing 
acrylate resins obtained by polymerizing 
(a1) from 20 to 60% by weight, preferably from 30 to 50% by weight, of 
component (a1) 
(a2) from 10 to 40% by weight, preferably from 15 to 35% by weight, of 
component (a2) 
(a3) from 1 to 15% by weight, preferably from 2 to 8% by weight, of 
component (a3) and 
(a4) from 0 to 25% by weight, preferably from 2 to 15% by weight, of 
component (a4) 
(a5) from 0 to 25% by weight, preferably from 2 to 15% by weight, of 
component (a5) 
(a6) from 5 to 30% by weight, preferably from 10 to 20% by weight, of 
component (a6), 
the sum of the proportions by weight of components (a1) to (a6) being in 
each case 100% by weight. 
The polyacrylate resins (A1) employed in accordance with the invention are 
prepared in an organic solvent or solvent mixture and in the presence of 
at least one polymerization initiator. The organic solvents and 
polymerization initiators employed are those solvents and polymerization 
initiators which are conventional for the preparation of polyacrylate 
resins and suitable for the preparation of aqueous dispersions. Examples 
of solvents which can be used are butylglycol, 2-methoxypropanol, 
n-butanol, methoxybutanol, n-propanol, ethylene glycol monomethyl ether, 
ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, 
diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 
diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethyl 
2-hydroxypropionate and 3-methyl-3-methoxybutanol, and derivatives based 
on propylene glycol, for example ethyl ethoxypropionate, methoxypropyl 
acetate, dipropylene glycol monomethyl ether and the like. Examples of 
polymerization initiators which can be used are free radical initiators 
such as, for example, t-butyl perethylhexanoate, benzoyl peroxide, 
azobisisobutyronitrile and t-butyl perbenzoate. The polymerization is 
expediently carried out at a temperature of from 80.degree. to 160.degree. 
C., preferably from 110.degree. to 160.degree. C. The preferred solvents 
employed are ethoxyethyl propionate, dipropylene glycol monomethyl ether 
and butyl acetate. 
The polyacrylate resin (A1) is preferably prepared by a two-stage process, 
since in this way the resulting aqueous coating compositions have a better 
processability. Preference is therefore given to employing polyacrylate 
resins which can be obtained by 
I. polymerizing a mixture of (a1), (a2), (a4), (a5) and (a6), or a mixture 
of part-amounts of components (a1), (a2), (a4), (a5) and (a6) in an 
organic solvent, 
II. after at least 60% by weight of the mixture composed of (a1), (a2), 
(a4), (a5) and if desired (a6) have been added, adding (a3) and any 
remaining amount of components (a1), (a2), (a4), (a5) and (a6) and 
continuing polymerization, and 
III. after the end of the polymerization, at least partially neutralizing 
the resulting polyacrylate resin and dispersing it in water. 
In addition, however, it is also possible initially to charge components 
(a4) and/or (a5) together with at least a part-amount of the solvent and 
to meter in the remaining components. Furthermore it is also possible to 
include in the initial charge only part of components (a4) and/or (a5) 
together with at least part of the solvent, and to add the remainder of 
these components as described above. It is preferred, for example, 
initially to charge at least 20% by weight of the solvent and about 10% by 
weight of components (a4) and (a5) and if desired part-amounts of 
components (a1) and (a6). 
Also preferred is the preparation of the polyacrylate resins (A1) which are 
employed in accordance with the invention by a two-stage process in which 
stage (I) lasts from 1 to 8 hours, preferably from 1.5 to 4 hours, and the 
addition of the mixture of (a3) and any remaining amounts of components 
(a1), (a2), (a4), (a5) and (a6) is made over a period of from 20 to 120 
min, preferably over a period of from 30 to 90 min. When the addition of 
the mixture of (a3) and any remaining amounts of components (a1), (a2), 
(a4), (a5) and (a6) is complete polymerization is continued until all of 
the monomers employed have undergone essentially complete reaction. 
The quantity and rate of addition of the initiator is preferably chosen 
such that a polyacrylate resin (A1) having a number-average molecular 
weight of from 2500 to 20,000 is obtained. It is preferred to commence the 
addition of the initiator about 5 minutes before adding the monomers and 
to terminate it about half an hour after the addition of the monomers has 
been ended. The initiator is preferably added in a constant quantity per 
unit time. When the addition of initiator has ended the reaction mixture 
is maintained at polymerization temperature for a time (generally 11/2 h) 
until all the monomers employed have undergone essentially complete 
reaction. "Essentially complete reaction" is intended to denote that 
preferably 100% by weight of the monomers employed have been reacted, but 
that it is also possible for a small proportion of residual monomer of no 
more than up to about 0.5% by weight, based on the weight of the reaction 
mixture, possibly to remain unreacted. 
The resulting polyacrylate resin (A1) has an OH number of from 40 to 200 
and preferably from 60 to 140 mg of KOH/g, an acid number of from 20 to 
100 mg of KOH/g, preferably from 25 to 50 mg of KOH/g, and a glass 
transition temperature of from -40.degree. to +60.degree. C., preferably 
from -20.degree. to +40.degree. C. This glass transition temperature can 
be calculated by the following formula: 
##EQU1## 
Tg=glass transition temperature of the polyacrylate resin (A) 
X=number of different monomers copolymerized in the polyacrylate resin 
Wn=weight proportion of the nth monomer 
Tgn=glass transition temperature of the homopolymer of the nth monomer 
For calculating the glass transition temperature the Tg of the homopolymer 
of the reaction product of acrylic acid and Cardura E10 is taken to be 
equal to the glass transition temperature of the homopolymer of isodecyl 
methacrylate (-41.degree. C.). 
When the polymerization is over the resulting polyacrylate resin is at 
least partially neutralized and dispersed in water. The degree of 
neutralization to be applied in each case depends on the acid number of 
the acrylate and is in general, for acid numbers &lt;70 mg of KOH/g, between 
50 and 90% and, for acid numbers &gt;70 mg of KOH/g, between 30 and 80%. Both 
organic bases and inorganic bases can be used for the neutralization. It 
is preferred to use primary, secondary and tertiary amines such as, for 
example, ethylamine, propylamine, dimethylamine, dibutylamine, 
cyclohexylamine, benzylamine, morpholine, piperidine, diethanolamine and 
triethanolamine. It is particularly preferred to employ tertiary amines as 
neutralizing agents, in particular dimethylethanolamine, triethylamine, 
dimethylisopropylamine, tripropylamine and tributylamine. 
The neutralization reaction is generally carried out by mixing the 
neutralizing base with the polyacrylate resin. In this context it is 
preferred to employ a quantity of base such that the top coat composition 
has a pH of from 7 to 8.5, preferably from 7.2 to 7.8. 
The partially or completely neutralized polyacrylate resin is then 
dispersed by adding water. This produces an aqueous polyacrylate resin 
dispersion. If desired some or all of the organic solvent can be distilled 
off. The polyacrylate resin dispersions according to the invention contain 
polyacrylate resin particles whose average size is preferably between 60 
and 300 nm (method of measurement: laser diffraction; measuring 
instrument: Malvern Autosizer 2 C). The polyacrylate resin (A1) employed 
in accordance with the invention is conventionally employed in the coating 
compositions in an amount of from 30 to 50% by weight (calculated as 
solids, i.e. without the water content), based on the total weight of the 
coating composition. 
The polyisocyanate component (B) is any organic polyisocyanate having free 
isocyanate groups which are bonded to aliphatic, cycloaliphatic, 
araliphatic and/or aromatic structures. Preferably employed are 
polyisocyanates having from 2 to 5 isocyanate groups per molecule and 
having viscosities of from 200 to 2000 mPas (at 23.degree. C.). If desired 
small amounts of organic solvent may also be added to the polyisocyanates, 
preferably from 1 to 25% based on pure polyisocyanate, in order thus to 
improve the ease of incorporation of the isocyanate and if appropriate to 
reduce the viscosity of the polyisocyanate to a value within the 
abovementioned ranges. Examples of solvents which are suitable as 
additives for the polyisocyanates are ethoxyethyl propionate, butyl 
acetate and the like. 
Examples of suitable isocyanates are described by way of example in 
"Methoden der organischen Chemie", Houben-Weyl, volume 14/2, 4th edition, 
Georg Thieme Verlag, Stuttgart 1963, page 61 to 70, and by W. Siefken, 
Liebigs Ann. Chem. 562, 75 to 136. Suitable examples are 1,2-ethylene 
diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene 
diisocyanate, 2,2,4- or 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 
1,12-dodecane diisocyanate, .omega.,.omega.'-diisocyanatodipropyl ether, 
cyclobutane 1,3-dilsocyanate, cyclohexane 1,3- and 1,4-diisocyanate, 2,2- 
and 2,6-diisocyanato-1-methylcyclo-hexane, 
3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone 
diisoyanate" sic!), 2,5- and 
3,5-bis(isocyanatomethyl)-8-methyl-1,4-methano-decahydronaphthalene, 1,5-, 
2,5-, 1,6- and 2,6-bis(iso-cyanatomethyl)-4,7-methanohexahydroindane, 
1,5-, 2,5-, 1,6- and 2,6-bis(isocyanato)-4,7-methanehexahydro-indane, 
dicyclohexyl 2,4'- and 4,4'-diisocyanate, 2,4-and 2,6-hexahydrotolylene 
diisocyanate, perhydro-2,4'-and -4,4'-diphenylmethane diisocyanate, 
.omega.,.omega.'-diisocya-nato-1,4-diethylbenzene, 1,3- and 1,4-phenylene 
diisocyanate, 4,4'-diisocyanato-biphenyl, 
4,4'-diisocy-anato-3,3'-dichlorobiphenyl, 
4,4'-diisocyanato-3,3'-dimethoxy-biphenyl, 
4,4'-diisocyanato-3,3'-dimethylbiphenyl, 
4,4'-diisocyanato-3,3'-diphenyl-biphenyl, 2,4'- and 
4,4'-diisocyanato-diphenylmethane, naphthylene 1,5-diisocyanate, tolylene 
diisocyanates such as 2,4- and 2,6-tolylene diisocyanate, 
N,N'-(4,4'-dimethyl-3,3'-diisocyanatodiphenyl)uretdione, mxylylene 
diisocyanate, dicyclohexylmethane diisocyanate, tetramethylxylylene 
diisocyanate, but also triisocyanates such as 2,4,4'-triisocyanatodiphenyl 
ether and 4,4',4"-triisocyanatotriphenylmethane. It is also possible to 
employ polyisocyanates having isocyanurate groups and/or biuret groups 
and/or allophanate groups and/or urethane groups and/or urea groups. 
Polyisocyanates having urethane groups are obtained, for example, by 
reacting some of the isocyanate groups with polyols such as, for example, 
trimethylolpropane and glycerol. 
Aliphatic or cycloaliphatic polyisocyanates are preferably employed, 
especially hexamethylene diisocyanate, dimerized and trimerized 
hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexyl-methane 
2,4'-diisocyanate or dicyclohexylmethane 4,4'-diisocyanate or mixtures of 
these polyisocyanates. Very particular preference is given to employing 
mixtures of polyisocyanates based on hexamethylene diisocyanate which 
contain uretdione and/or isocyanurate groups and/or allophanate groups, as 
are formed by catalytic oligomerization of hexamethylene diisocyanate 
using suitable catalysts. Polyisocyanate component (B) may otherwise be 
composed of any desired mixtures of the polyisocyanates mentioned by way 
of example. 
It is essential to the invention that the coating compositions contain a 
carbodiimide component (C) and/or a polyepoxide component (D). The coating 
compositions preferably contain a carbodiimide component (C) or a mixture 
of a carbodiimide component (C) and a polyepoxide component (D). The 
carbodiimide component (C) which is employed may in each case be a 
carbodiimide or else a mixture of 2 or more carbodiimides. Likewise, the 
polyepoxide component (D) which is employed may in each case be a 
polyepoxide or a mixture of 2 or more polyepoxides. 
The carbodiimides which are employed in accordance with the invention have 
the following characteristic properties: 
1. The incorporation of hydrophilic ethylene oxide and/or propylene oxide 
units enables the carbodiimides employed in accordance with the invention 
to be added without problems to aqueous solutions and, in particular, 
dispersions of synthetic resins containing carboxylate and/or carboxyl 
groups and/or sulfonate groups. 
2. In dependence on the content of carbodiimide groups in the carbodiimide 
component employed in accordance with the invention, which content can 
easily be varied by a simple choice of the nature and proportions of the 
starting materials employed, the degree of crosslinking of the 
two-dimensional structure ultimately obtained can be adjusted. 
Starting materials for the carbodiimides employed in accordance with the 
invention are: 
a) organic polyisocyanates having an average NCO functionality of from 2.0 
to 2.5 or mixtures of organic poly- and monoisocyanates having an average 
functionality of from 1.3 to 2.5 and, if desired, 
b) compounds which are mono- or polyfunctional in terms of the isocyanate 
addition reaction and have groups which are reactive toward isocyanate 
groups. 
Structural components a) include: 
a1) any desired aliphatic and/or cycloaliphatic and/or aromatic 
polyisocyanates such as, in particular, the diisocyanates which are easily 
accessible industrially such as hexamethylene diisocyanate, 
1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcy-clohexane and 
m-tetramethylenexylylene diisocyanate (m-TMXDI). 
If aromatic polyisocyanates are employed then it is preferred to employ 
those in which the isocyanate groups are bonded to aliphatic radicals. 
Particularly preferred isocyanates for preparing the carbodiimides are 
those of the general formula (I) 
##STR5## 
in which X represents a divalent, aromatic hydrocarbon radical, preferably 
for a naphthylene, diphenylene or 1,2-, 1,3- or 1,4-phenylene radical 
which is optionally substituted by halogen, methyl or methoxy, 
particularly preferably a 1,3-phenylene radical, and R.sub.1 and R.sub.2 
represent an alkyl radical having 1-4 carbon atoms, preferably a methyl 
radical. Diisocyanates of the formula (I) are known (their preparation is 
described in, for example, EP-A-101 832, U.S. Pat. Nos. 3,290,350, 
4,130,577 and 4,439,616) and some are commercially available 
(1,3-bis-(2-isocyanatoprop-2-yl)benzene for example is sold by the 
American Cyanamid Company under the trade name TMXDI (META).RTM.). 
The exclusive employment is preferred, as component (a1), of a diisocyanate 
of the formula (I) or a mixture of such diisocyanates. It is particularly 
preferred to employ as component (a1) a diisocyanate of the formula (II) 
##STR6## 
These isocyanates are also designated as tetramethylxylylene diisocyanates 
(TMXDI). Very particular preference is given to the employment as 
component (a1) of a diisocyanate of the formula (II) in which the 
--C(CH3).sub.2 NCO groups are in the meta position (MTMXDI). 
Further starting materials (a) are: 
a2) Hydrophilically modified polyisocyanates. 
These include mono- or diisocyanates which contain polyethylene oxide 
and/or polypropylene oxide units incorporated within polyether chains, as 
are described in, for example, DE-A-23 14 512, DE-A-23 14 513, DE-A-25 51 
094, DE-A-26 51 506, U.S. Pat. Nos. 3,920,598 or 3,905,929. 
Particularly preferred hydrophilically modified polyisocyanates, however, 
are NCO prepolymers as are obtained by reacting excess amounts of the 
diisocyanates mentioned as examples under a1) with diols. In the 
preparation of these NCO prepolymers the starting materials are generally 
brought to reaction while observing a ratio of NCO to OH equivalents of 
from 1.2:1 to 10:1 at from 20.degree. to 150.degree. C. 
Diols which are suitable for the preparation of NCO prepolymers are in 
particular those of the general formula 
##STR7## 
in which A and B represent identical or different divalent aliphatic 
hydrocarbon radicals having from 1 to 6 carbon atoms, R represents 
hydrogen, an aliphatic hydrocarbon radical having from 1 to 4 carbon atoms 
or a phenyl radical, n and m represent identical or different numbers from 
0 to 30 and o and p each represent 0 or 1. 
Further starting materials (a) are, for example: 
a3) organic monoisocyanates, such as, for example, n-hexyl isocyanate, 
phenyl isocyanate or p-tolyl isocyanate. As already mentioned above these 
monoisocyanates are possibly employed as a mixture with organic 
polyisocyanates of the kind mentioned by way of example, the mixture 
having an average NCO functionality of from 1.3 to 2.5, preferably from 
1.3 to 2. 
In addition, other modified polyisocyanates may also be present in 
component (a), for example reaction products of excess amounts of organic 
diisocyanates of the kind mentioned by way of example under (a1) with di- 
or trihydroxyalkanes having a molecular weight of less than 400, for 
example ethylene glycol, propylene glycol, tetramethylene diols, 
hexamethylene diols, trimethylolpropane and/or glycerol. 
Examples of the structural components (b) which are also used if desired 
are 
b1) polyhydric, especially dihydric alcohols, for example ethylene glycol, 
propylene glycol, tetramethylene diols, hexamethylene diols, octamethylene 
diols, neopentyl glycol, 2-methyl-1,3-dihydroxypropane, glycerol, 
trimethylolpro-pane, diethylene glycol, triethylene glycol, tetraethylene 
glycol, polyethylene glycols of the molecular weights mentioned, 
dipropylene glycol, tripropylene glycol or any desired mixtures of such 
polyhydric alcohols. 
It is preferred to employ methoxypolyethylene glycol having an average 
molecular weight of 550 g/mol with 1 free OH group and 1 methyl-etherified 
OH group. 
Examples of further structural components (b) which are also used if 
desired are: 
b2) Hydrophilically modified mono- or dihydric alcohols, for example the 
compounds which have ethylene oxide units and the general formula 
##STR8## 
in which 
R lacuna! a divalent radical as obtained by removing the isocyanate groups 
from a diisocyanate of the formula R(NCO)2 of the kind mentioned above 
under (a1), 
R' lacuna! hydrogen or a monovalent hydrocarbon radical having 1-8 carbon 
atoms, preferably hydrogen or a methyl group, 
R" lacuna! a monovalent hydrocarbon radical having 1-12 carbon atoms, 
preferably an unsubstituted alkyl radical having 1-4 carbon atoms, 
X lacuna! a polyalkylene oxide chain having 5-90 and preferably 20 to 70 
chain members of which at least 40%, preferably at least 65%, are composed 
of ethylene oxide units and which in addition to ethylene oxide units may 
also represent propylene oxide, butylene oxide or styrene oxide units, 
with propylene oxide units being preferred among the last-mentioned units, 
Y lacuna! oxygen or --NR'"--, where R'" in terms of its definition 
corresponds to R". 
The compounds of the abovementioned formulae may be prepared in accordance 
with the procedures of DE-A-23 14 512 and/or DE-A-23 14 513; in order to 
supplement the disclosure made therein reference is made to the fact that, 
instead of the monofunctional polyether alcohols mentioned therein as 
starting material, it is also possible to employ those polyether alcohols 
whose polyether segment also has, in addition to ethylene oxide units, 60% 
by weight based on the polyether segment of a sic! propylene oxide, 
butylene oxide or styrene oxide, preferably propylene oxide units. 
The proportion of such "mixed polyether segments" may in specific cases be 
accompanied by specific advantages. 
Examples of the hydrophilic monohydric alcohols which are suitable in 
accordance with the invention include compounds of the formula 
H--X--Y--R", in which X, Y and R" have the meaning just mentioned. 
These monohydric, hydrophilically modified alcohols can be prepared by the 
methods described in U.S. Pat. Nos. 3,905,929 or 3,920,538, for example by 
the alkoxylation of suitable starter molecules, for example n-butanol with 
ethylene oxide and if desired other alkylene oxides, for example propylene 
oxide. 
The isocyanate derivatives which contain carbodiimide groups, are employed 
in accordance with the invention and are prepared from the starting 
materials mentioned by way of example have a content of from 2 to 30% by 
weight, preferably from 5 to 15% by weight, of carbodiimide groups 
--N.dbd.C.dbd.N--, and have on average per molecule from 0.8 to 30, 
preferably from 1 to 25 and particularly preferably from 1.3 to 20 such 
carbodiimide groups. Their content of incorporated ethylene oxide units 
present within polyether chains is from 0 to 25% by weight, preferably 
from 2 to 20% by weight and particularly preferably from 5 to 15% by 
weight, based on solids. The hydrophilic groups mentioned are preferably 
present in the carbodiimides in amounts so as to ensure their solubility 
or dispersibility in water. It is however also possible, but by no means 
preferred, to use--in addition to the chemically incorporated, hydrophilic 
groups mentioned--external emulsifiers which are mixed with the 
carbodiimides in order to ensure their solubility or dispersibility in 
water. 
Examples of such emulsifiers are ethoxylated nonylphenol, polyoxyethylene, 
lauryl ethers or polyoxyethylene laurate, oleat or stearate, these 
compounds generally having from 8 to 50 oxyethylene units per molecule. 
The fact that the carbodiimides contain the groups mentioned which are 
essential to the invention is ensured by the corresponding choice of the 
nature and proportions of the starting materials and of the degree of 
carbodiimidization. The term degree of carbodiimidization is to be 
understood here as meaning the percentage of isocyanate groups, present in 
the starting isocyanates (a), which undergo the carbodiimidization 
reaction. The compounds employed in accordance with the invention 
preferably have no further free isocyanate groups after their preparation. 
The compounds employed in accordance with the invention can be prepared by 
different variants. 
The most simple method of preparation comprises reacting mixtures of 
organic polyisocyantes sic!, preferably diisocyanates, with complete 
carbodiimidization of the isocyanate groups, polyether alcohols or 
alcohols containing ethylene oxide units also being employed in a quantity 
such that the resulting product has a content of ethylene oxide groups 
which is within the abovementioned limits, and the proportion of 
polyisocyanate to monoisocyanate, i.e. the average functionality of the 
isocyanate mixture, being chosen such that chain termination takes place 
during the carbodiimidization reaction, so that the resulting products 
have a content of carbodiimide groups which is within the abovementioned 
ranges. 
Chain termination of this kind always occurs when the average NCO 
functionality is less than 2.0. Thus by simply choosing the average NCO 
functionality of the isocyanates employed as component (a) it is possible 
to adjust the molecular weight and thus the number of carbodiimide groups 
present on average in the process products. 
According to a further variant only some of the isocyanate groups of 
starting component (a) are carbodiimidized, and the free isocyanate groups 
which are then still present are reacted with groups which are reactive 
towards isocyanate groups, of the kind mentioned above by way of example 
under (b), the degree of carbodiimidization of the first stage of the 
reaction being chosen such that the quantity of carbodiimide groups 
present in the ultimate process product obtained corresponds to the 
statements made above. In this context the quantity of component (b) is 
always such that, for each isocyanate group of the partially 
carbodiimidized isocyanate, at least 1 group which is reactive towards 
isocyanate groups is available. 
The number of carbodiimide groups present on average in the process 
products can also in this context be predetermined by a suitable choice of 
the functionality of the starting components, i.e. by adjusting the 
molecular weight as is possible in this way. If, for example, the number 
of carbodiimide groups in the partially carbodiimidized isocyanate has 
already been reached, then a chain-lengthening reaction will be avoided in 
the reaction with component (b), i.e. exclusively chain-terminating 
structural components of the type mentioned by way of example will be used 
as component (b). Conversely, if at least a proportion of difunctional 
structural components (b) is used, a chain lengthening reaction can be 
induced by means of which, of course, on average the number of 
carbodiimide groups present per molecule in the process products is 
increased. 
In this varianat sic! of the process component (a) preferably possesses 
prior to the carbodiimidization reaction an NCO functionality of from 1.8 
to 2.5. Using this procedure it is also possible to prepare valuable 
process products which have a multiplicity of carbodiimide units, 
corresponding on average to the statements made above with respect to the 
number of carbodiimide units. 
The ethylene oxide units which may if desired be present in the process 
products are also incorporated into the process product, in the second 
variant of the preparation process, by the additional use of components 
(a) containing ethylene oxide units and/or by the additional use of 
components (b) which contain ethylene oxide units and are of the kind 
mentioned above by way of example. 
In both variants of the process the at least partial carbodiimidization of 
the isocyanate groups of component (a) is carried out in a manner known 
per se, for example in analogy with the previously known teaching of the 
prior art, as is evident for example from U.S. Pat. Nos. 2,840,589, 
2,941,966 or German Offenlegungsschriften 25 04 400, 25 52 350 or 26 53 
120. The at least partial carbodiimidization of the isocyanate groups of 
component (a) is carried out particularly advantageously using 
carbodiimidization catalysts as are described, for example, in U.S. Pat. 
Nos. 2,941,966, 2,853,581 or 2,853,473 or in DE-A-26 14 323. The 
carbodiimidization is particularly preferably carried out using 
1-methyl-1-phospha-2-cyclopentene 1-oxide or 
1-methyl-1-phospha-3-cyclopentene 1-oxide or mixtures of these compounds 
as catalysts. 
It is of course also possible to use any other carbodiimidization 
catalysts. The at least partial carbodiimidization of component (a) is 
carried out in general using from 0.01 to 5% by weight, preferably from 
0.2 to 2% by weight, based on component (a), of carbodiimidization 
catalysts of the type mentioned, within the temperature range from 
0.degree. to 200.degree. C., preferably 20.degree.-150.degree. C. If the 
desire is for only a partial carbodiimidization of the isocyanate groups 
of component (a) it is recommended to terminate the carbodiimidization 
reaction at the particular degree of carbodiimidization required, by 
adding a catalyst poison. Examples of suitable catalyst poisons are 
described in DE-A-26 14 323. 
In order to obtain partially carbodiimidized isocyanates which are 
storage-stable at room temperature it may be advisable to carry out the 
carbodiimidization reaction at 50.degree.-200.degree. C. with the specific 
use of catalysts which only contain sic! their catalytic activity in this 
increased temperature range. This is described, for example, in EP-B-198 
343. 
The progress of the carbodiimidization reaction can be monitored via the 
evolution of carbon dioxide and the drop in the NCO content of the 
reaction mixture. The partial carbodiimidization generally does not 
produce uniform process products, but mixtures of carbodiimides with 
different contents of carbodiimide units per molecule and possibly still 
containing unreacted starting isocyanate. 
All statements made above with regard to the content of carbodiimide groups 
in the process products and with regard to the number of carbodiimide 
groups per molecule therefore relate to average values. 
The carbodiimidization reaction can be carried out in the presence or else 
in the absence of solvents. Examples of suitable solvents are toluene, 
xylene, cyclohexane, chlorobenzene, O-dichlorobenzene sic!, 
dimethylformamide, perchloroethylene, ethyl acetate, butyl acetate, 
diethylene glycol dimethyl ether, tetrahydrofuran, acetone, methyl ethyl 
ketone, cyclohexanone or any desired mixtures of such solvents. The 
solvent-free carbodiimidization product prepared solidifies to give a hard 
resin which is ground down to a powder and is subsequently used in 
accordance with the invention or can be processed further by reaction with 
component (b). 
The reaction with component (b) which is possibly still to be carried out 
following the carbodiimidization reaction likewise takes place in the 
presence or in the absence of solvents of the type mentioned by way of 
example, within a temperature range of from 0.degree. to 150.degree., 
preferably from 20.degree. to 100.degree. C. 
In this context, when using different components (b), the reaction 
components can be reacted either simultaneously or in succession, the 
ratio of the isocyanate groups of the carbodiimidized component (a) to the 
groups of component (b) which are reactive towards isocyanate groups being 
from 1:1 to 1:1.5, preferably from 1:1 to 1:2. 
Particularly preferred is a procedure which comprises carrying out the 
carbodiimidization reaction up to a degree of carbodiimidization such 
that, in the process product ultimately obtained, the required amount of 
carbodiimide groups is present. The product thus obtained is reacted with 
compounds (b) which contain ethylene oxide units and which may be 
difunctional, while observing a ratio of equivalents of NCO groups to 
groups which are reactive towards NCO groups of from 1.05:1 to 10:1, and 
subsequently reacting the free NCO groups which are then still present 
with chain terminators of the type mentioned by way of example under (b), 
while observing a ratio of equivalents of NCO groups to groups which are 
reactive towards NCO of from 1:1 to 1:1.5, preferably 1:1, or with a high 
excess of chain lengthening agents of the type described under (b), 
preferably while maintaining a ratio of equivalents of NCO groups to 
groups which are reactive towards NCO groups of at least 1:2, to give an 
NCO-free product. 
Substantially equivalent to this particularly preferred procedure would be 
a procedure which comprises reacting the partially carbodiimidized 
diisocyanates having a mixture of difunctional hydrophilic structural 
components with chain terminators, while maintaining a ratio of 
equivalents of NCO groups to groups which are reactive to NCO groups of 
from 1:1 to 1:1.5. 
After the reaction the solvent which may also have been used can be 
removed, for example by distillation. The solvent-free reaction product is 
generally a solid which can be taken up at any time in an organic solvent 
or else can be used in accordance with the invention without using 
solvents. For this purpose the carbodiimides can be added to the coating 
compositions in the form of aqueous solutions or dispersions, or else in 
bulk. 
If desired, after introducing ethylene oxide and/or propylene oxide units, 
it is also possible for example to employ the carbodiimides described in 
DE-A-41 26 359, especially on page 2, line 1 to page 3, line 45. 
The carbodiimides employed in accordance with the invention are 
particularly suitable for modifying polyurethane which contains 
carboxylate and/or carboxyl groups and/or sulfonate groups and is present 
in dispersion or dissolved in water, and for modifying polyester resins, 
polybutadienes or polyacrylate resins which are present in dispersion or 
dissolved in water and contain carboxylate groups and/or carboxyl groups 
and/or sulfonate groups. 
The quantity of the carbodiimides employed in accordance with the invention 
depends, on the one hand, on the content of carboxylate groups and/or 
carboxyl groups in the dissolved or dispersed polymer and, on the other 
hand, on the desired range of properties of the coatings. For instance it 
may on the one hand be desired to select the ratio of carboxylate groups 
and/or carboxyl groups and/or sulfonate groups in the dissolved or 
dispersed binder to the carbodiimide groups so as to be greater than 1:1 
in order, especially when using carbodiimides having more than 2 
carbodiimide groups per molecule, to prevent excessive crosslinking of the 
product; on the other hand the use of at least equivalent amounts of 
carbodiimide groups, especially carbodiimides which (on average) are at 
least difunctional, enables the reaction time during the drying of the 
coatings ultimately obtained to be shortened. 
Furthermore, the coating compositions according to the invention may 
contain as additive, together with or instead of the carbodiimides, a 
polyepoxide component (D). Examples of suitable polyepoxides are all known 
aliphatic and/or cycloaliphatic and/or aromatic polyepoxides, based for 
example on bisphenol A or bisphenol F. 
Suitable examples of component (D) include the polyepoxides which are 
commercially available under the names Epikote.RTM. from Shell, Denacol 
from Nagase Chemicals Ltd., Japan, for example Denacol Ex-411 
(pentaerythritol polyglycidyl ether), Denacol EX-321 (trimethylolpropane 
polyglycidyl ether), Denacol EX-512 (polyglycerol polyglycidyl ether) and 
Denacol EX-521 (polyglycerol polyglycidyl ether). 
In the coating compositions according to the invention the polyepoxide 
component (D) is preferably employed in an amount such that the weight 
ratio of binder solids to polyepoxide solids is between 60:40 and 90:10, 
preferably between 70:30 and 85:15. 
In order to prepare the ready-to-use, aqueous polyurethane coating 
composition, a mixture of polyisocyanate component (B) and carbodiimide 
component (C) and/or of polyepoxide component (D) is mixed shortly before 
application with binder component (A). The components can be mixed simply 
by stirring them together at room temperature or else by dispersion. The 
polyisocyanate component (B) is here employed in an amount such that the 
weight ratio between binder solids and polyisocyanate solids is from 60:40 
to 90:10, particularly preferably from 70:30 to 85:15. The ratio of the 
number of free OH groups of component (A) to the number of isocyanate 
groups of component (B) is usually in the range from 1:2 to 2:1 in this 
context. 
It is preferred to employ the carbodiimide component in an amount such that 
the weight ratio between binder solids (A) and carbodiimide solids (C) is 
between 60:40 and 90:10, preferably between 70:30 and 85:15. The ratio of 
the number of acid groups of binder (A) to the carbodiumide groups of 
component (C) is usually in the range between 1:2 and 2:1 in this context. 
The aqueous polyurethane resin coating compositions according to the 
invention may also contain, in addition to the polyaddition and/or 
polycondensation resin employed in accordance with the invention, 
crosslinked polymer microparticles as disclosed in, for example, EP-A-38 
127, and/or further compatible resins such as, for example, 
water-dilutable or water-soluble polyacrylate resins, polyurethane resins, 
polyester resins, alkyd resins or epoxy resin esters. The proportion of 
these further resins is usually between 1 and 10% by weight, based on the 
total weight of the coating composition. For instance, up to 30% by weight 
based on the binder solids of an acrylate prepared by emulsion 
polymerization and having an OH number which is preferably between 40 and 
200 mg of KOH g may be added to the coating compositions according to the 
invention. The preparation of such emulsion polymers is described in, for 
example, DE-A-40 09 000, although the OH number of the acrylates is to be 
raised correspondingly. 
Over and above this, the coating compositions according to the invention 
may also contain other conventional auxiliaries and additives such as, in 
particular, thickeners and wetting agents. It is preferred to add to the 
aqueous coating compositions according to the invention a nonionic 
polyurethane thickener, since this leads to a better transparency and 
better emulsifiability of the polyisocyanate. Preferably, the aqueous 
coating compositions according to the invention also have added to them a 
wetting agent based on an alkyl-modified polyether, since this likewise 
improves the transparency of the coating composition and the gloss and 
levelling of the coating composition. 
Furthermore the aqueous coating compositions may also contain other 
conventional auxiliaries and additives, for example antifoams and the 
like. The quantity of auxiliaries and additives (incl. wetting agents and 
thickeners) employed is conventionally between 1 and 5% by weight, based 
on the total weight of the coating compositions. 
The aqueous coating compositions according to the invention may also 
contain conventional organic solvents, whose proportion is kept as low as 
possible. This proportion is conventionally below 15% by weight, based on 
the total content of the volatile constituents. 
The coating compositions according to the invention are generally adjusted 
to a pH of between 6.5 and 9.0. The pH can be adjusted using conventional 
amines such as, for example, triethylamine, dimethylaminoethanol and 
N-methylmorpholine. 
The coating compositions according to the invention can be applied using 
conventional application methods such as, for example, spraying, knife 
coating, brushing, dipping, to any desired substrates such as, for 
example, metal, wood, plastic or paper. The coating compositions according 
to the invention are preferably employed for the production of top coats. 
The coating compositions according to the invention can be employed both 
in the production-line finishing and in the refinishing of car bodies. 
They are, however, preferably employed in the refinishing sector. The 
aqueous coating compositions according to the invention can be employed as 
fillers and for producing one-coat top coats, and as pigmented basecoats 
or as clearcoats in a process for the production of a multilayer finish 
(basecoat/clearcoat method). The coating compositions according to the 
invention are, however, preferably employed as clearcoats. 
If the coating compositions according to the invention are employed for the 
production of single-coat top coats or as basecoats, then they can be 
pigmented with pigments such as, for example, pigments with an inorganic 
basis, for example titanium dioxide, iron oxide, carbon black etc. and/or 
pigments with an organic basis and/or metallic pigments such as, for 
example, aluminum bronzes, and/or pearlescent or interference pigments. 
Aluminum bronzes and pearlescent or interference pigments are examples of 
special-effect pigments. If the coating compositions according to the 
invention are employed as pigmented basecoats then they can be covered 
over with the coating compositions according to the invention which 
contain no pigments or only transparent pigments, although they can also 
be covered with conventional clearcoats based on organic solvents, with 
aqueous clearcoats or else with powder clearcoats. 
The top coat compositions according to the invention 
have a solids content at spray viscosity which is high enough (20 to 50% by 
weight, preferably 32 to 45% by weight) to obtain, with 1 to 2 spray 
passes (cross passes), coating films of adequate thickness (the thickness 
of the baked coating film should preferably be between 25 and 70 .mu.m) 
and 
give coating films having a very good appearance (good evenness, high 
gloss, good top coat holdout), good weathering resistance and good 
mechanical properties, and 
have a relatively low content of organic cosolvents (less than 35% by 
weight based on the total solids content of binders and crosslinking 
agents). 
If the top coat compositions according to the invention are used together 
with water-dilutable base coat compositions in order to produce metallic 
finishes, then in the metallic finishes obtained the transparent top coat 
adheres particularly well to the basecoat. Suitable basecoats are, for 
example, the aqueous basecoat described in DE-A-40 09 000. Also suitable 
are all conventionally employed aqueous basecoats. 
The following examples describe the invention in more detail. All parts and 
percentages are by weight unless expressly stated otherwise.

EXAMPLES 1 TO 4 
Comparative Examples 1 and 2 
1. Preparation of a water-dilutable acrylate resin employed in accordance 
with the invention (A1) 
24 parts by weight of ethoxyethyl propionate (EP) are introduced into a 
steel vessel fitted with monomer feed, initiator feed, thermometer, oil 
heating and reflux condenser and heated to 120.degree. C. Then a solution 
of 6.0 parts by weight of t-butyl perethylhexanoate in 6.0 parts by weight 
of ethoxyethyl propionate is added at a rate such that the addition is 
concluded after 4 h 30 min. The commencement of the addition of the 
t-butyl perethylhexanoate solution is accompanied by the beginning of the 
addition of the monomer mixture of (a1), (a2), a3) and (a4) 
(a1): 20.0 parts by weight of n-butyl methacrylate 17.4 parts by weight of 
methyl methacrylate, 10.0 parts by weight of lauryl acrylate (commercial 
product Methacrylester 13 from Rhoim AG, Darmstadt) 
(a6): 15.0 parts by weight of styrene 
(a2): 32.5 parts by weight of hydroxyethyl methacrylate 
(a3): 5.1 parts by weight of acrylic acid. 
The mixture (a1), (a2), (a3) and (a6) is added at a rate such that the 
addition is concluded after 4 hours. When the addition of the t-butyl 
perethylhexanoate solution is over the reaction mixture is maintained at 
120.degree. C. for a further 2 h. The resin solution is then cooled to 
80.degree. C. and neutralized over a period of about 30 min with 
dimethylethanolamine, to a degree of neutralization of 60 %. 
Then a quantity of water is added until the solids content of the 
dispersion is about 40% by weight. Organic solvent is removed by 
azeotropic distillation under vacuum from this dispersion until no more 
than 3% can be detected (by GC). Whereas the organic solvent was sic! 
separated off, the water is returned to the reactor. 
At the end of the distillation the dispersion is adjusted, by adding 
deionized water, to the following final parameters: 
Acid number of the total solids: 40 mg of KOH/g of solids; 
OH number of the total solids: 140 mg of KOH/g of solids; 
solids content (1 h, 130.degree. C): 39.0%. 
2.1 Preparation of a carbodiimide 1 employed in accordance with the 
invention (C1) 
475 parts of (1,3-bis(2-isocyanatoprop-2-yl)benzene (commercial product 
TMXDI (Meta).RTM. from American Cynamid sic! Comp.) and 119 g of 
isophorone diisocyanate together with 14 parts of 
3-methyl-1-phenyl-2-phospholene 1-oxide are placed in a reactor. They are 
heated under a nitrogen atmosphere at 155.degree. C. until the isocyanate 
content has reached 6.5% (approximately after 19 h). The reaction mixture 
is then cooled to 50.degree. C. before 143 parts of methoxy polyethylene 
glycol having a molecular weight of 550 and 0.6 parts of dibutyl tin 
dilaurate are added. The mixture is stirred at 50.degree. C. until a 
constant isocyanate content of about 4.2% has been reached. Then at 
50.degree. C. 142 parts of ethanol are added and the mixture is stirred 
until no free NCO is determined. 
The remaining ethanol is distilled off under vacuum and the batch is 
diluted with metoxypropyl sic! acetate to a solids content of 79%. 
2.2 Preparation of the carbodiimide 2 employed in accordance with the 
invention 
50 parts of a tetraisopropyldiphenyl-methanecarbodiimide (prepared 
according to DE-A 41 26 359), in which the remaining NCO groups had been 
partially urethanized with ethanol (8% free NCO groups) were reacted with 
25 parts of a commercially available polyether alcohol of the propylene 
glycol type having an average molecular weight of 900 (commercial product 
Pluriol.RTM. P 900 from BASF AG) and 0.1 parts of dibutyl tin dilaurate 
(DBTL) for 6 hours at 80.degree. C. The solids content was adjusted to 60% 
using methoxypropyl acetate and the product was drained off. 
3.) Preparation of transparent aqueous top coat compositions according to 
the invention 
Transparent top coat compositions are prepared from the acrylate dispersion 
prepared according to point A, an 80% strength solution of a commercially 
available water-dilutable polyisocyanate resin in ethyl ethoxypropionate, 
based on hexamethylene diisocyanate dimer/trimer, containing uretdione 
groups (commercial product Desmodur.RTM. N 3400 from Bayer AG), if desired 
the carbodiimide 1 or 2, if desired a commercially available aromatic 
polyepoxide having an epoxide equivalent weight of 231 (commercial product 
Denacol EX-411 from Nagase Chemical Ltd., Japan), butylglycol, methyl 
isobutyl ketone, ethoxyethyl propionate, a 10% strength aqueous solution 
of a commercially available polyurethane thickener (Dapral T 210 from 
Akzo), distilled water, a commercially available siloxane-modified surface 
additive (commercial product Tego Flow 425 from Goldschmidt, Essen) and a 
surface-active agent based on silicone (commercial product Byk 331 from 
Byk), and these compositions are adjusted using distilled water to spray 
viscosity (22 to 25 s efflux time from the DIN-4 cup (in accordance with 
DIN 53 211, 1974)). The composition of the top coat compositions is shown 
in Table 1. 
4.) Application of the transparent top coat compositions according to the 
invention and testing of the baked coating films 
A water-dilutable basecoat composition pigmented with aluminum flakes, 
according to EP-A-279 813, is applied to a phosphatized steel panel coated 
with a commercially available electrodeposition coating and a commercially 
available filler so as to give a dry film thickness of from 12 to 15 
.mu.m. The applied basecoat composition is dried for 10 min at room 
temperature and 10 min at 60.degree. C. A top coat composition obtained as 
in point B) is then sprayed onto the basecoat in 3 spray passes with a 
flashoff time of 15 min in between. The panel is finally dried for 60 min 
at room temperature and baked for 30 min at 60.degree. C. in a 
circulating-air oven. The resulting multilayer coatings were subjected to 
a number of tests. The test results are shown in Table 2. 
TABLE 2 
______________________________________ 
Composition of the transparent, aqueous top coat compositions 
from Examples 1 to 3 and Comparative Examples 1 and 2 
Com- Com- 
parative 
parative 
Exam- Exam- Exam- Exam- Exam- Exam- 
ple 1 ple 2 ple 3 ple 4 ple 1 ple 2 
______________________________________ 
Acrylate 56.6 56.1 56.1 56.1 58.0 60.0 
dispersion 
Distilled 
5.7 5.6 5.6 5.6 5.9 6.0 
water 
Daspral T210 
1.4 1.4 1.4 1.4 1.4 1.4 
(10%) 
Butyl glycol 
1.1 1.1 1.1 1.1 1.1 1.1 
Methyl isobutyl 
1.1 1.1 1.1 1.1 1.1 1.1 
ketone 
Ethoxyethyl 
2.3 2.3 2.3 2.3 2.3 2.3 
propionate 
Byk 331 0.1 0.1 0.1 0.1 0.1 0.1 
Tego Flow 425 
0.1 0.1 0.1 0.1 0.1 0.1 
Distilled water 
2.3 2.2 2.2 2.2 2.3 2.3 
Desmodur 13.0 12.9 12.9 12.9 13.5 -- 
N3400 
Carbodiimide 1 
1.1 
1.1 
7.0 
Carbodiimide 2 
-- 1.2 
Denacol -- 
1.0 2.8 
EX-411 
Ethoxyethyl 
3.2 3.2 3.2 3.2 3.2 6.1 
propionate 
Distilled water 
12.0 12.7 11.8 11.1 11.0 12.5 
Solids content 
40 39 41 41 39 39 
(%) 
Solvent (%) 
12.2 12.2 12.0 12.0 12.0 14.0 
Viscosity (DIN 
23 22 23 24 25 22 
4 cup)s 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
Test results 
Example 1 
Example 2 
Example 3 
Example 4 
Comp. Ex. 1 
Comp. Ex.2 
before after 
before after 
before after 
before after 
before after 
before after 
Exposure 
Exposure 
Exposure 
Exposure 
Exposure 
Exposure 
__________________________________________________________________________ 
Solids content.sup.1) 
40% 39% 41% 41% 39% 39% 
Coat thickness 
50 50 50 50 50 50 
(lm).sup.2) 
CC test.sup.3) (3 days) 
Blistering 
m0/g0 
m1/g1 
m0/g0 
m2/g1 
m0g/0 
m1/g1 
m0/g0 
m2/g1 
m0/g0 
m2/g2 
m0/g0 
m3/g3 
Swelling 0 4 0 4 0 2 0 4 0 5 0 5 
Cratering 
0 0 0 0 0 0 0 0-1 0 1 0 1 
CC test.sup.3) (10 days) 
Blistering 
m0/g0 
m2/g1 
m0/g0 
m3/g3 
m0/g0 
m2/g1 
m0/g0 
m3/g3 
m0/g0 
m4/g3 
m0/g0 
m5/g3 
Swelling 0 5 0 5 0 3 0 5 0 5 0 5 
Cratering 
0 0 0 0 0 0 0 1 0 2 0 3 
WS test.sup.4) (5 cycles) 
Blistering 
m0/g0 
m0/g0 
m0/g0 
m0/g0 
m0/g0 
m0/g0 
m0/g0 
m1/g1 
m0/g0 
m1/g1 
m0/g0 
m3/g2.sup.4) 
Swelling 0 2-3 0 2-3 0 1-2 0 3 0 3-4 0 4.sup.4) 
Pendulum hardness 
Konig RT 105 97 118 119 103 55 
30' 60.degree. C. 
126 120 145 148 126 74 
__________________________________________________________________________