Thixotropic coating agents based on urea adduct of polyamine and monoisocyanate

A thixotropic coating agent, more especially a binder or coating composition, based on a mixtrue of conventional binder-containing systems, optionally in admixture with liquid solvents or diluents, and a thixotropizing agent containing urea groups, wherein the thixotropizing agent is, in part at least, a urea adduct obtained by reacting (a) primary and, optionally, secondary polyamines, (b) monoisocyanate compounds and, optionally, (c) diisocyanate compounds in the presence of at least part of the binder.

Thixotropic coating agents, especially highly thixotropic coating agents 
based on lacquers, paints or other coatings, can be used with advantage in 
cases where the application of thick-layer lacquer systems is required. In 
this connection, the use of thixotropizing agents can also be of crucial 
significance in obtaining a stable state of admixture in the finished 
coating agent. Several proposals have already been made for thixotropizing 
binder-containing coating systems. For example, it is known that coating 
agents based on drying or non-drying fatty oils can be reacted with 
diisocyanates and heated to high temperatures. According to another 
proposal, triglycerides of drying or non-drying oils are initially 
transesterified with polyalcohols and the reaction mixture subsequently 
reacted with diisocyanates in the presence of catalysts. The diisocyanates 
and polyalcohols are used in equivalent or substantially equivalent 
quantities and are required to have a symmetrical molecular structure. 
According to other proposals, vegetable oils for example are reacted with 
organic amino compounds, for example aliphatic diprimary amines, to form a 
thixotropic substance. Thus, it has been proposed to add certain polyamide 
resins to ester-like lacquer starting materials, followed by boiling, 
optionally in a multistage process, until thixotropic properties appear. 
It is known from German Auslegeschrift No. 1,805,693 that coating agents 
based on a mixture of a solvent-containing lacquer or a paint with 
conventional binders can be thixotropized by the addition of 0.05 to 10% 
by weight of a urea adduct obtained by reading an aliphatic monoamine with 
6 to 22 carbon atoms with an aromatic or aliphatic monoisocyanate or 
polyisocyanate in an organic solvent, the molar ratio of amine to 
isocyanate lying between the stoichiometric ratio and a 40% excess of 
amine. More particularly, German Auslegeschrift No. 1,805,693 proposes 
initially preparing a gel in a separate process, comprising reacting the 
isocyanate compounds with the specified monoamines in a lacquer solvent, 
and subsequently working this gel into the binder-containing coating 
agent. However, the specified urea adduct can also be prepared in situ in 
the presence of the binder. 
The practical requirements which a thixotropizing agent or a thixotropic 
coating system has to satisfy are manifold and, for this reason, are 
difficult to satisfy at one and the same time. In thixotropizing coating 
agents, it is of course not only a question of thickening a coatable 
system, on the contrary a whole range of special properties is required. 
Thus, the thixotropized system is required to be readily stirrable or 
spreadable, in spite of its gel character, whilst on the other hand the 
gel-like character is required to be reformed almost instantaneously once 
the effect of mechanical stressing has been removed. In the fresh 
thick-layer coating, the freshly applied layer of coating agent is 
required to level to a certain extent in order to equalise irregularities 
in the coating by free flow. On the other hand, fresh thick-layer 
thixotropic coatings are in danger of "running", especially when applied 
to vertical walls. Particular problems arise in cases where coating agents 
contain heavy pigments, for example iron mica, as is the case in 
particular with anti-corrosion coatings. However, it is in this very field 
that there is an increasing demand for effective thixotropic coating agent 
systems in order to simplify and shorten the extremely labour-intensive 
work involved in the protection of large steel structures. 
The object of the invention is to provide a thixotropizing agent or 
thixotropic binders and, hence, thixotropic coating agents which are 
distinguished by a wider range of variation in their combination of 
properties than it has been possible to obtain with certain conventional 
thixotropizing agents. 
In broad terms, this object is achieved by reacting primary and/or 
secondary polyamines, i.e. amine compounds containing at least two of the 
aforementioned amino groups, with monoisocyanates and optionally 
diisocyanates; it is also possible by using certain monofunctional 
compounds, to arrest any excess of still free isocyanate groups with these 
monofunctional components. By varying the ratio of polyamine to the 
monofunctional isocyanate compounds and the difunctional isocyanate 
compounds used, if any, it is possible in accordance with the invention to 
provide the thixotropic coating agent specifically with a wider range of 
desirable properties than can be achieved with conventional thixotropizing 
agents. Another essential feature of the invention is that the urea adduct 
is prepared in the presence of at least part of the binder. Accordingly, a 
first embodiment of the invention relates to thixotropic coating agents, 
especially binders or coating compositions based on a mixture of 
conventional binder-containing systems, optionally in admixture with 
liquid solvents or diluents and a thixotropizing agent containing urea 
groups, distinguished by the fact that the thixotropizing agent is, at 
least in part, a urea adduct obtained by reacting (a) primary and 
optionally secondary polyamines with (b) monoisocyanate compounds and 
optionally (c) diisocyanate compounds, in the presence of at least part of 
the binder. 
The thixotropic coating agents according to the invention can be complete 
coating agents in the form of lacquers, paints, varnishes or synthetic 
coatings, although the invention also covers in particular thixotropized 
binders and binder-solvent systems. Thixotropic binders of this kind can 
be directly used by the manufacturer of the complete coating agent to 
prepare ready-to-use thixotropic coating agents. 
According to the invention, the polyurea adduct used as thixotropizing 
agent is present in a quantity of preferably 0.05 to 10% by weight, more 
especially in a quantity of about 0.1 to 5% by weight, based on the 
thixotropized system. 
Another embodiment of the invention relates to a process for producing 
thixotropic coating agents, more especially binders or coating 
compositions, of this kind, distinguished by the fact that a liquid binder 
or a binder-containing liquid mixture is thoroughly mixed with the primary 
and/or secondary polyamines and the resulting mixture subsequently reacted 
with the isocyanate compounds. 
Particularly preferred embodiments of this process will now be described. 
Through the formation of a polyurea system, a more or less heavily 
developed thixotropic effect occurs in many cases almost at once or after 
a certain period of standing, for example after about 24 hours. The extent 
of this thixotropic effect can be predetermined in any one case by simple 
small-scale tests. A wide variation of combined property characteristics 
can be determined in advance and standardised by adapting the quantities 
of components selected for forming the thixotropizing agent and optionally 
by selecting and using particularly appropriate binder systems. 
To form the thixotropizing agent according to the invention, the isocyanate 
compounds as a whole are preferably used in such a quantity that from 40 
to 200 equivalent % of isocyanate groups are present, based on the 
isocyanate-reactive primary and, optionally, secondary amino groups of the 
polyamines. The isocyanate compounds are preferably used in quantities of 
from 80 to 140 equivalent % of isocyanate groups, based on primary and/or 
secondary amino groups. The monoisocyanates and the diisocyanates can be 
used in the following mixing ratios: from 0 to 95 equivalent %, preferably 
from 30 to 70 equivalent %, of isocyanate groups from the diisocyanate 
compounds to 100 to 5 equivalent %, preferably 70 to 30 equivalent %, of 
the monoisocyanate compounds. It can be of particular advantage to limit 
the quantity of diisocyanates present, if any, in such a way that the 
primary and/or secondary amino groups of the polyamine are present in a 
stoichiometric excess relative to the isocyanate groups from the 
diisocyanates. 
An excess of free amino groups or an excess of free isocyanate groups can 
initially be present, depending upon the relative quantitative ratios 
selected between reactive isocyanate groups and primary and/or secondary 
amino groups reacting with those groups. At most as many reactive amino 
groups are used in the polyamine as there are amino groups available for 
the reaction, especially in all cases where the presence of free amino 
groups in the finished coating agent is undesirable. The use of an excess 
of isocyanate groups over reactive amino groups can be of particular 
advantage. One alternative, which falls within the scope of the invention, 
is to use other reactive components which are able to arrest undesirable 
free amino groups. Epoxide compounds are particularly suitable for this 
purpose. 
However, an excess of free isocyanate groups could also give rise to 
undesirable secondary reactions in the binder or coating agent. 
Accordingly, it is preferred in accordance with the invention to block 
this quota of excess free isocyanate groups by using monofunctional 
isocyanate-reactive components. Monofunctional amines and in particular 
monofunctional alcohols or monofunctional oximes can be used for this 
purpose. One particular example of monofunctional amines are alkanolamines 
which actually contain two isocyanate-reactive groups. However, on account 
of the considerably increased reactivity of the amino group, these groups 
will always react first with any isocyanate groups still present so that 
an additional reaction of the hydroxyl group of the alkanolamine could 
only be considered if, after all the amino groups have been consumed, 
there are still some free isocyanate groups which have not been arrested 
by other reaction components in the meantime. In fact, it is preferred in 
accordance with the invention to use even the alkanolamines themselves as 
monofunctional components in this case. 
For forming the thixotropizing urea adduct in accordance with the 
invention, the different reaction velocities between the aforementioned 
components are of significance and the invention makes effective use of 
these very differences in reaction velocity. The highest reaction velocity 
occurs between isocyanate groups and amino groups. By contrast, the 
reaction between isocyanate groups and alcoholic groups proceeds much more 
slowly. If, therefore, the polyamines are initially reacted with 
monoisocyanates and, optionally, diisocyanates in excess, the amino groups 
are completely arrested even in cases where other monofunctional 
components, such as monohydric alcohols or monofunctional oximes, are 
simultaneously added to the reaction mixture. In fact, components of this 
kind can be present in a considerable quantity. The isocyanate used in 
excess initially safely arrests all the amino groups, after which the 
isocyanate excess reacts in a slower, following reaction with for example 
already present or subsequently added monofunctional alcohol which in turn 
can be present in an excess over the quantity required for reaction with 
the isocyanate excess. 
In the context of the invention, polyamines are primary and/or secondary 
amines which contain at least two of these isocyanate-reactive amino 
groups. Diamines, especially diprimary amines (primary diamines), can be 
used with particular advantage. In addition to or instead of these 
diamines, however, it is also possible to use tri- and higher polyamines. 
According to the invention, however, it is preferred only to use these 
higher polyamines in admixture with diamines, for example in such ratios 
that substantially equivalent quantities of diamine and higher polyamine 
are present. 
Examples of higher polyamines include diethylene triamine to pentaethylene 
hexamine, or dipropylene triamine to pentapropylene hexamine. The reactive 
diamines particularly preferred for the purposes of the invention can be 
cycloaliphatic and/or aromatic and, at the same time, optionally 
polynuclear, although it is also possible, either wholly or in part, to 
use aliphatic diamines. 
Polyamines with which favourable results have been obtained in accordance 
with the invention are, for example, 
3,3'-dimethyl-4,4'-diaminodicyclohexyl methane, 4,4'-diamino dicyclohexyl 
methane, 4,4'-diaminodiphenyl methane, ethylene diamine, hexamethylene 
diamine, N-aminoethyl piperazine, xylylene diamines, 
1,3,5-triisopropylbenzene-2,4-diamine, 1,3-diisopropylbenzene-2,4-diamine, 
2,4-diaminomethyl-1,3-dimethylbenzene or 
3-aminomethyl-3,5,5-trimethylcyclohexylamine. One particularly favourable 
and highly active diamine in the context of the invention is 
di-(aminomethyl)-benzene. 
Monoisocyanate compounds in the context of the invention are aliphatic, 
aromatic and/or cycloaliphatic monoisocyanates. The aliphatic 
monoisocyanates can contain for example up to 25 carbon atoms. Both in 
this case, and in the case of the aromatic and cycloaliphatic 
monoisocyanates, it is particularly preferred to use commercially 
available, inexpensive compounds. Examples include: alkyl isocyanates with 
1 to 22 carbon atoms, for example methyl isocyanate, ethyl isocyanate, 
propyl isocyanate, butyl isocyanate, stearyl isocyanate, secondary alkyl 
isocyanates such as tert.-butyl isocyanate and/or aromatic isocyanates 
such as phenyl isocyanate, 1-naphthyl isocyanate, tolyl isocyanates, 
toluene sulphonyl isocyanate or even cycloaliphatic isocyanates, such as 
cyclohexyl isocyanate. 
Suitable diisocyanate compounds include both aromatic and cycloaliphatic, 
optionally polynuclear diisocyanates and/or aliphatic diisocyanates. 
Examples of suitable commercially available compounds of this class 
include aliphatic diisocyanates with at least two carbon atoms, such as 
ethylene-1,2-diisocyanate and hexamethylene-1,6-diisocyanate or an isomer 
mixture of 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate. Aromatic 
diisocyanate compounds are particularly suitable, for example the known 
isomer mixtures of 65% of tolylene-2,4-diisocyanate and 35% of 
tolylene-2,6diisocyanate, and isocyanate mixtures containing 80% of the 
2,4-isomer and 20% of the 2,6-isomer. Other suitable aromatic 
diisocyanates include diphenylmethane-4,4'-diisocyanate or 
naphthylene-1,5-diisocyanate. 3-Isocyanatomethyl-3,5,5-trimethylcyclohexyl 
isocyanate is one example of a cycloaliphatic diisocyanate suitable for 
the purposes of the invention. 
All the reactive diamino compounds and diisocyanates mentioned here are 
suitable for thixotropizing. 3,3'-Dimethyl-4,4'-diaminodicyclohexyl 
methane, xylylene diamine and 4,4'-diaminodiphenyl methane, are 
particularly effective. 
Among the isocyanates, diphenylmethane-4,4'-diisocyanate, 
tolylene-2,6-diisocyanate and naphthylene-1,5-diisocyanate in particular 
show pronounced thixotropic effects. In this case, too, however, all the 
described diisocyanates are basically suitable. The only difference 
between them lies in their effectiveness. Allowance can be made for this 
difference in selecting the quantity of polyurea-forming components. Thus, 
it is possible by selecting a larger quantity of components with a weaker 
action to obtain a thickening effect equivalent to that obtained by using 
smaller quantities of components with a stronger thixotropic action. 
In the case of aliphatic diisocyanates, symmetry in structure has a 
positive effect in regard to their effectiveness as thixotropizing 
component. For example, hexamethylene-1,6-diisocyanate is more effective 
than 2,2,4- or 2,4,4-trimethylhexamethylene-1,6-diisocyanate. 
It has also been found that alkyl groups in particular, such as methyl and 
isopropyl radicals as substituents in the vicinity of the NCO-group, i.e. 
in the o-position, have a particularly favourable effect upon the 
thixotropizing properties of aromatic diisocyanates. If two methyl or 
isopropyl groups are symmetrically adjacent the isocyanate groups, the 
effect of the diisocyanate becomes even more favourable. 
1,3,5-Triisopropyl benzene-2,4-diisocyanate for example shows the most 
pronounced thixotropizing properties. The effect of 
1,3-diisopropylbenzene-2,4-diisocyanate, tolylene-2,6-diisocyanate, 
2,4-diisocyanatomethyl-1,3-dimethylbenzene is not quite so strong, whilst 
tolylene-2,4-diisocyanate and hexamethylene-1,6-diisocyanate have an even 
somewhat weaker thixotropizing effect. 
A certain parallel can be found amongst diamines. 3,3' 
-Dimethyl-4,4'-diaminodicyclomethane is significantly more effective than 
4,4'-diaminodicyclohexyl methane, whilst o-phenylene diamine is 
significantly more effective than m- and p-phenylene diamine which produce 
equivalent thixotropic binders. 
Secondary diamines of aliphatic structure which do not contain any primary 
amino groups have to be used in extremely high concentrations to obtain 
even a weak thixotropic effect. Ethylene diamine for example provides a 
strong thixotropic effect, whereas the corresponding N,N'-diethyl 
derivative is considerably less effective. By contrast, heterocyclic 
diamines which secondary amino groups only, for example piperazine, are 
extremely effective. This diamine is as effective as 
3,3'-dimethyl-4,4'-diamino dicyclohexyl methane. 
So far as aliphatic diamines are concerned, it can generally be said that 
not only do short-chain diamines provide particularly favourable effects, 
long-chain diamines, for example 1,12-diaminododecane, are also valuable 
components in accordance with the invention. Tri- and higher polyamines 
suitable for the purposes of the invention include in particular aliphatic 
polyamines with 3 to 6 amino groups in the molecule, of which the terminal 
groups are primary amino groups and the rest secondary amino groups. 
Monoalcohols in the context of the invention are in particular adequately 
volatile monofunctional alcohols of aliphatic and/or cycloaliphatic 
structure. Aliphatic monoalcohols with 1 to 7 carbon atoms and 
cycloaliphatic lower alcohols, especially cyclohexanol, are particularly 
suitable. It is also possible to use alcohols of higher molecular weight. 
In their case, however, one factor which has to be taken into 
consideration is that, as a rule, the alcohols can be used in almost any 
excess so that, in most cases, a considerable proportion of the alcohols 
does not take part in the reaction by which the thixotropizing agent is 
formed. Accordingly, it should be possible for this alcohol excess to be 
able to be evaporated from the binder or from the paint produced with it 
so that it does not leave behind any adverse effects upon the properties 
of the binder or paint. In addition to the aforementioned monoalcohols, it 
is also possible to use lower ether alcohols in particular (monoethers of 
glycols). Examples include methyl-, ethyl-, propyl- or butyl-glycol 
monoether, and the corresponding semi-esters of glycols. 
Similar considerations affect the choice of the oximes as monofunctional 
reaction components. In this case, volatile or evaporating components are 
preferred, ketoximes and aldoximes containing up to 6 carbon atoms being 
particularly suitable. 
Both the monoalcohols and also the oximes can be used in a considerable 
excess over the quantity required for blocking free isocyanate groups. 
This generally does not apply in cases where monoamines are used because 
the monoamine is preferably employed in only such a quantity that no 
appreciable numbers of free amino groups are present after formation of 
the urea adduct. Although basically it is possible to use an excess of 
monoamine, this generally does not produce any improvement in thixotropy. 
In the case of binders which dry by oxidation, an excess of free amino 
groups can be harmful, resulting in particular in much slower drying. 
Suitable monoamines are, in particular, primary monoamines of aliphatic, 
cycloaliphatic and heterocyclic structure. Compounds containing 1 to 25 or 
even more carbon atoms can be considered. Secondary monoamines of 
aliphatic or cycloaliphatic structure, for example dibutylamine or 
dicyclohexyl amine, are also suitable for arresting the still free 
isocyanate groups. However, monoamines of this kind have little or no 
effect in increasing thixotropy, whereas primary monoamines may even 
develop their own effect. 
Among the class of alkanolamines, it is possible to use alcohols containing 
primary or secondary amino groups. The general principles stated above 
apply in this case, too, especially as regards the amino group, namely 
that no appreciable excess over the NCO-groups ready for reaction should 
be used. Lower aliphatic alkanolamines in particular are especially 
significant for practical application. 
In general, the viscosity of the binder or binder-containing system is 
reduced in cases where solvents containing hydroxyl groups are used for 
thixotropizing in accordance with the invention. This makes it easier to 
prepare the thixotropizing agent in the presence of the binder. The same 
applies in cases where the binders are dissolved in non-reactive solvents, 
for example in aliphatic or aromatic hydrocarbons, esters, ketones, ethers 
and the like. However, the coating agents according to the invention are 
generally distinguished by considerable binder contents. Thus, the binder 
is preferably present in the thixotropized system in a quantity of at 
least 20% by weight. It may be of advantage to use even larger quantities 
of binder in the system, for example at least 30% by weight or 40% by 
weight or more. In important applications of the invention, the binder 
makes up more than half the total mixture. 
Suitable binders include almost all the components that have already been 
proposed in the coating art. A thixotropizing effect can be obtained in 
almost every case. Examples of particularly suitable binders include 
long-oil, middle-oil or short-oil or even oil-free alkyd resins, stand 
oils, linseed oil/linseed oil-stand oil combinations, urethane-, epoxy 
resin-, acrylic resin- and styrene-modified alkyd resins, PVC-copolymers, 
cyclorubbers, oil-modified epoxides, water-dilutable alkyd resins in their 
non-neutralised form and similar components. 
However, the invention can also be applied with advantage for example in 
the case of unsaturated polyester resins or mixtures thereof with 
copolymerisable monomers, such as styrene, methacrylate or similar 
ethylenically unsaturated compounds. Another interesting field of 
application for the invention are the so-called solvent-free binder 
systems, i.e. comparatively low-viscosity condensates which are used 
without, or only with small quantities of, solvents. Suitable acid binders 
in non-neutralised form are, for example, binders of this kind with acid 
numbers of from 20 to 120, preferably from about 30 to 90. However, the 
system according to the invention is also suitable for thixotropizing 
water-dilutable binders which are neutralisation products or at least 
partially neutralised products of binders which, in their non-neutralised 
form, have an acid number of 20 to 120, preferably 30 to 90. From the 
extensive prior art on the quality of binders, reference is made to 
British Patent Specification No. 1,230,605 and the literature quoted 
therein, and to the book by Wagner-Sarx "Lackkenstharze", 5th Edition, 
1971, Carl Henser Verlag, Munich. 
Individual binders can respond differently to the thixotropizing effect. If 
it is desired to intensify the effect of binder systems having only a weak 
response in thixotropizing according to the invention all that is 
necessary is for example to use limited quantities of a compatible and, at 
the same time, high-response binder in order overall to obtain a highly 
thixotropic composition. 
In another embodiment of the invention, it is possible to thixotropize only 
part of the binder of the finished composition in the presence of the 
reactive components of the invention. In this embodiment, exaggerated 
thixotropy is obtained in regard to this part of the binder. The gel thus 
obtained is subsequently mixed with non-thixotropized binder and/or 
solvent or diluent until the required state is reached. This possibility 
embodies another important simplification for adjusting predeterminable 
property combinations in the end products. 
Well developed thixotropic properties and, in most cases, clear gels are 
obtained by initially introducing the diamine into the binder and 
subsequently adding the monoisocyanate and optionally diisocyanate, 
optionally diluted with solvent. According to one particularly important 
aspect of the invention, however, the properties of the thixotropizing 
agent can be influenced by a sequence of certain process stages. 
In this embodiment, not only is the polyamine together with the 
monofunctional components present, if any, mixed with a binder before 
polyurea formation, the isocyanates are also preferably combined with part 
of the binder or binder-containing mixture before the components are 
reacted. 
In the particularly important embodiment referred to above, the reaction is 
carried out by homogeneously distributing the monoisocyanates and 
optionally diiocyanates in part of the liquid binder or binder-containing 
liquid mixture and subsequently introducing the polyamines, again best 
dissolved in binder, into the diisocyanate immediately afterwards. This 
ensures that isocyanate groups are present in excess at least during the 
greater part of the urea-forming reaction. It can be of particular 
advantage for this purpose to establish an excess of isocyanate during 
selection of the stoichiometric ratio of reactive amino groups and 
isocyanate groups, so that free isocyanate groups are present in excess up 
to the end of the reaction of the amino groups. The isocyanate groups that 
are not arrested by amino groups are reacted with the monofunctional 
components also used in this case. 
The special addition of the polyamide to the isocyanate excess, as 
described above, results in the formation of thixotropic materials which, 
hitherto, it has not been possible to obtain in the combination of their 
favourable properties. The thixotropized coating agent or binder has a 
soft-pasty consistency, i.e. it is easy to spread. Nevertheless, it does 
not run, even in thick layers, when applied to vertical surfaces. On the 
other hand, this soft-pasty material levels to an adequate extent so that 
irregularities arising out of application of the coating agent to the 
substrate to be coated are satisfactorily equalised in the required 
manner. Thixotropized coating agents prepared in this way are clearly 
distinguished in the particularly advantageous combination of their 
properites from those in whose case the diisocyanate is introduced into 
the polyamine-containing reaction component. 
Reaction of the polyamines with the diisocyanate compounds and, optionally, 
the monofunctional components in the presence of the binder can be carried 
out at room temperature. However, the effect of the thixotropizing 
additive can be considerably increased in many cases by carrying out the 
reaction at elevated temperatures. Temperatures in the range from about 
40.degree. to 100.degree. C. are particularly suitable for this purpose, 
temperatures in the range from 50.degree. to about 80.degree. C. being 
particularly preferred. Another possibility for intensifying the effect of 
the gel is to carry out the reaction at room temperature and subsequently 
to heat the thixotropized material for example to temperatures of up to 
about 80.degree. C. Temperatures in the range from room temperature to 
about 100.degree. C., more particularly in the range from room temperature 
to about 70.degree. C., are generally suitable for preparation of the 
polyureas. The thixotropic gel formed in the presence of binders is 
remarkably stable and, in particular, represents an irreversible gel 
largely unaffected by temperature. 
This resistance of the thixotropic state to temperature, even high 
temperatures such as those normally applied for stoving purposes, makes 
the invention particularly suitable for use in the field of heat-drying or 
heat-reactive binders and coating systems. Accordingly, one particularly 
preferred aspect of the invention is the use of the addition products 
containing urea groups prepared in the presence of polymeric compounds as 
heat-stable thixotropizing agents in heat-drying polymer compositions, for 
example in so-called stoving lacquers. 
One particularly interesting field of the kind in question here is the 
production of heat-hardened coatings on metal components for example by 
applying so-called heat-drying lacquers and, in particular, stoving 
lacquers and primers. These processes are widely used in industry, for 
example in the manufacture of car bodies, domestic appliances, such as 
washing or rinsing machines, refrigerators or in the production of 
so-called band coatings by the coil-coating technique. Industry has 
developed a large number of thermosetting systems which are normally 
hardened at temperatures of from about 70.degree. to 300.degree. C. or 
even higher. The invention is particularly suitable for this field of 
heat-reactive coating agents, more especially heat-drying lacquers, 
stoving lacquers and primers based for example on thermosetting 
aminoplasts, autocrosslinking or crosslink-assisted acrylate resins, 
thermosetting alkyd resins and/or epoxide resins. The heat-reactive binder 
systems mentioned here can be used as known per se in admixture with other 
binder components, as known from the numerous proposals for the production 
of heat-hardenable systems. Among the extensive literature, reference is 
made in this connection to "Ullmann's Enzyklopadie der Technischen 
Chemie", 3rd Edition, Urban und Schwarzenberg, vol. 11, pages 279 to 364, 
and to the already mentioned book by Wagner-Sarx entitled 
"Lackkunstharze", in particular pages 61 to 80 and 230 to 235. 
The invention can be of particular importance in the field of thermosetting 
stoving lacquers based on aminoplasts, more especially corresponding urea 
resins and/or melamine resins. The multicomponent lacquers plasticised by 
the addition of other binder systems are of particular importance in this 
respect. Plasticising systems of this kind are, for example, polyesters, 
drying or non-drying alkyd resins, epoxide resins, polyacrylates, also 
nitrocellulose or silicone-, acryl-, styrene-, vinyltoluene-modified alkyd 
resins or even oil-free alkyd resins. 
The mixing ratios of the polymeric binders lie within the usual limits. 
Accordingly, the thermosetting, more especially etherified urea or 
melamine resin is preferably used in a deficit in relation to the other 
constituents of the binder. 
It has proved to be of advantage in this very field of aminoplast-based 
stoving lacquers for the various process stages involved in the production 
of the thixotropized material to follow a certain order. Thus, it is of 
particular advantage to carry out in situ production of the urea adduct 
from isocyanate compounds and amines in the plasticising binder component 
rather than in the aminoplast component. The aminoplasts can readily show 
incompatibility with urea adducts if an attempt is made to carry out in 
situ formation of the urea in the aminoplast phase. This gives rise to 
hazing phenomena which may be attributable to some precipitation of the 
polyurea molecule formed and the effect of which can be that the 
thixotropic effect is not fully developed. Accordingly, it is more 
effective to carry out in situ formation of the urea adduct in the 
plasticising binder component and subsequently to mix the binder 
thixotropized in this way with the heat-reactive aminoplast component. In 
this way, the thixotropic effect is no longer impaired. 
In addition, the invention is of particular importance in connection with 
acrylate resins both of the autocrosslinking and of the crosslink-assisted 
type. Both types can be satisfactorily thixotropized by in situ formation 
of urea adduct in their presence so that they can be used either as such 
or in admixture with components introduced into them, for example alkyd 
resins and/or other binder components as listed above, as binding phase 
for the thixotropizing agent. The autocrosslinking acrylate resins can be 
mixed for example in known manner with epoxide resins, alkyd resins or 
melamine resins, whilst the crosslink-assisted acrylate resins require in 
particular products containing methylol ether, such as urea resins or 
melamine resins, as stoving lacquers. 
In cases where binders according to the invention containing methylol ether 
groups are directly thixotropized, it can be of advantage to bear the 
following in mind: binders of this kind, such as amino resins or 
acrylamideformaldehyde resins can obviously interact with the amines used 
to form the urea adduct. Accordingly, it is advisable in this and similar 
cases to add the isocyanates immediately after the binder has been mixed 
with the amines. By virtue of the particularly high reactivity of the 
isocyanate group with the amino groups, the urea adduct is formed before 
undesirable secondary reactions or interactions can occur. 
In selecting the components for forming the urea adducts, it can be of 
advantage, especially in accordance with the stoving conditions required 
later on, to take into account colour stability in dependence upon the 
stoving temperature. It is known, for example from polyurethane chemistry, 
that aromatic diisocyanates, such as tolylene diisocyanate, can give rise 
at elevated temperatures to undesirable changes in colour reflected in the 
form of yellowing in the field of stoving lacquers in question here. 
Accordingly, in cases where high colour stability, especially at high 
temperatures, is required, it can be of advantage to use non-aromatic 
diisocyanates, for example cycloaliphatic and, in particular, aliphatic 
diisocyanates. 
It has also been found that certain monoisocyanate compounds are 
particularly suitable for obtaining the required combination of properties 
in the thixotropized material by reaction with polyamines, especially 
diamines, in the presence of the binder. The monoisocyanates which are 
used for preparing the polyurea adduct in this embodiment are in turn 
reaction products of polyisocyanates and monoalcohols obtained by 
separately reacting polyisocyanates in the absence of the binder with such 
quantities of monoalcohols that about one free isocyanate group is left in 
the molecule. The monoisocyanates obtained in this way are then reacted 
with polyamines and, optionally, polyisocyanate compounds in the presence 
of all or at least part of the binder or coating agent to be 
thixotropized. 
These monoisocyanates can be prepared for example with any of the 
diisocyanate compounds listed above for direct use. Diisocyanate compounds 
suitable for this purpose include both aromatic and cycloaliphatic, 
optionally polynuclear diisocyanates and/or aliphatic diisocyanates. 
The production of monoisocyanate compounds of this kind with approximately 
one free isocyanate group in the molecule by reacting polyisocyanates and 
monofunctional alcohols is known per se. Reference is made in this 
connection to British Patent Specification No. 1,230,605 which describes a 
process for the production of thixotropic resins and resin solutions. In 
this process, corresponding monoisocyanate compounds are prepared by 
reacting polyisocyanates with monofunctional alcohols in a separate 
operation, followed by reaction with the binder itself and/or with water 
in the presence of the binder. Thixotropic binders are actually formed in 
this case, too. However, it has been found that the reaction cannot be 
adequately controlled, with the result that it is not possible with any 
degree of certainty to obtain reaction products with predetermined and 
required combinations of properties. In particular, the quantity of 
isocyanate compound required in this conventional process for obtaining 
adequate thixotropy is also relatively high. 
It has surprisingly been found that monoisocyanates of the kind described 
here and in British Patent Specification No. 1,230,605 give particularly 
favourable combinations of properties in the thixotropized binder in a 
particularly reliable manner if, instead of being directly reacted with 
the binder or with water, they are reacted, in accordance with the 
invention, with polyamines in the presence of at least part of the binder 
to be thixotropized. The effect of the particularly fast reaction between 
isocyanate-reactive primary and/or secondary amino groups and the 
isocyanate groups is that it is possible, in accordance with the 
invention, to form polyurea adducts of exactly predetermined constitution 
which provide the binders or coating agents with the required combinations 
of properties in predetermined manner. 
The monoisocyanate compounds can be prepared for example as described in 
British Patent Specification No. 1,230,605. In general, the 
polyisocyanate, preferably the diisocyanate selected, is reacted with the 
stoichiometrically necessary quantity of monoalcohol. The reaction can be 
carried out at room temperature, although it is preferably carried out at 
elevated temperatures. Temperatures of from 50.degree. to 120.degree. C. 
for example are particularly suitable. It can be of advantage to carry out 
this reaction in an inert solvent. It is preferred for this purpose to use 
solvents which, subsequently, can actually be left behind in the reaction 
system during thixotropizing of the binder or coating agent. The 
polyisocyanate is preferably initially introduced and the monoalcohol 
added with stirring in such a way that the reaction temperature lies for 
example in the range from about 50.degree. to 100.degree. C. 
According to the invention, monoalcohols for the production of these 
monoisocyanate compounds are preferably primary monoalcohols, although 
basically it is also possible to use secondary or tertiary alcohols. 
According to the invention, it can be of advantage to use monoalcohols 
with at least 5 and preferably with at least 8 carbon atoms. Monoalcohols 
with 8 to 25 and more particularly with 9 to 17 carbon atoms for example 
are particularly suitable. The alcohols can be aliphatic, cycloaliphatic 
and also aromatic. The aliphatic alcohols can be linear or branched. 
Branched aliphatic alcohols can have particular significance. Instead of 
using simple alcohols of the kind described here, it is also possible to 
use semi esters and semi ethers of glycols. The alcohols themselves can be 
saturated or even unsaturated. Reference is made in this connection to 
British Patent Specification No. 1,230,605, page 5, line 50 to page 6, 
line 18. For details of the polyisocyanates, see page 5, lines 25 to 50 of 
the aforementioned British Patent Specification. All the polyisocyanates 
mentioned in addition to those already specified can also be used in 
accordance with the invention. 
The advantage of using linear longer-chain monoalcohols for producing the 
monoisocyanate compounds is inter alia that they are less hygroscopic and, 
for this reason, contain less water than short-chain alcohols. In cases 
where more than traces of water are present during adduct formation, 
hazing can occur through the formation of insoluble polyureas. This is 
undesirable so far as the subsequent use of these monoisocyanates for 
thixotropizing is concerned. The adducts of polyisocyanates, especially 
diisocyanates and short-chain alcohols, tend to crystallise out even more 
quickly than monoisocyanates obtained by reacting for example tolylene 
diisocyanate, isophorone diisocyanate or hexamethylene diisocyanate with 
nonyl alcohol, isotridecyl alcohol or stearyl alcohol. The alcohol can be 
selected in particular in accordance with the binder to be thixotropized. 
Particularly high compatibility levels and, hence, stabilisation of the 
thixotropic state can be obtained by adapting the alcohol component in the 
monoisocyanate to the type of binder. 
In this case, thixotropizing is preferably carried out by mixing the binder 
component to be thixotropized with the polyamine and subsequently stirring 
in the isocyanate compounds. In this case, too, the effect of the 
thixotropizing addition is considerably enhanced if the reaction is 
carried out at the elevated temperatures referred to above. Accordingly, 
it is possible to obtain highly thixotropic binders with only small 
quantities of the thixotropizing constituent. Thus, the technically 
desired results can be obtained with only 0.1 to about 2% by weight, 
preferably with about 0.1 to 1% by weight, of the thixotropizing 
constituent, based on solvent-free binder. This represents a significant 
improvement over all the corresponding proposals of the prior art. 
It has proved to be of advantage to use the isocyanate compounds and, in 
particular, the monoisocyanates in an excess over the primary and/or 
secondary amino groups ready for reaction. This ensures that no free amine 
is actually left in the binder. Free amino groups can give rise to 
undesirable effects. The excess of free isocyanate groups is harmless. In 
many cases, standard commercial binder systems contain other 
isocyanate-reactive constituents such as alcohols, oximes and, above all, 
generally limited quantities of moisture. The quota of isocyanate groups 
present in excess over the reactive amino groups reacts more slowly with 
such compounds and/or with any reactive groups of the binder that are 
present. In any event, the isocyanate groups disappear completely after a 
short time so that no troublesome effects need be expected from them. The 
decisive factor is that, by virtue of their particularly high reactivity 
with isocyanate groups, the reactive amino groups are always the first to 
react, thus ensuring formation of the predetermined polyurea adduct. It 
can be of advantage to use the isocyanate in an excess of 10 to 100 
equivalent % over the reactive amino groups. It is generally preferred to 
use an excess of 15 to 50 equivalent %. 
The monoisocyanates of the kind just described can be used in admixture 
with other monoisocyanate compounds. 
According to the invention, it is also possible, even with very small 
quantities of the polyurea adduct formed in situ, to obtain favourable 
anti-sedimentation properties without at the same time producing a heavily 
pronounced gel character. This can be of importance in a number of 
applications; reference is made for example to fibre-reinforced 
unsaturated polyester resins or pigmented coating agents in whose case a 
high degree of flowability is required. 
In one preferred embodiment of the invention, substantially anhydrous 
conditions are applied at least up to formation of the urea adduct 
involving reaction of all the isocyanate groups. The quantities of 
moisture normally present in the components of the coating agent are 
harmless in this embodiment. In fact, formation of the urea adduct can 
even be carried out in the presence of relatively small or relatively 
large quantities of water. In this case, it is necessary to ensure, 
preferably by rapidly mixing isocyanate and amine component, that the 
reaction between these two reactive groups is the preferred reaction. 
According to the invention, it is readily possible to thixotropize not only 
binders as such or their solutions, but also complete paints which, in 
addition to the binder, contain pigments and additives for example. 
In this case, the reactants are added to the finished paint. However, it is 
more favourable to thixotropize the binder alone or in admixture with a 
solvent or diluent, and subsequently to process the gel formed with the 
pigments and other additives, for example by grinding on a roll stand, in 
a bead mill or in a dissolver, to form the paint.

In the following Examples, the quality of the thixotropic state was 
assessed according to three aspects, namely the thixotropy adjusted, the 
viscosity developed and the flow properties of the product. The marks 
awarded are defined as follows: 
thixotropy: 
6=very heavily thixotropic 
5=heavily thixotropic 
4=satisfactorily thixotropic 
3=weakly thixotropic 
2=very weakly thixotropic 
1=non-thixotropic 
viscosity: 
4=very difficult to stir 
3=difficult to stir 
2=satisfactorily stirrable 
1=readily stirrable 
flow properties: 
4=heavily ointment-like, pasty 
3=ointment-like, pasty 
2=weakly ointment-like, pasty 
1=non-ointment-like, pasty 
TABLE 1 
______________________________________ 
1 2 3 4 
______________________________________ 
Component (1) 
long-oil linseed-oil alkyd, 
300.0 300.0 300.0 300.0 
60% in white spirit 
cyclohexylisocyanate 8.0 
ethylglycol 10.0 10.0 
3,3'-dimethyl-4,4'-diamino 
5.3 5.3 8.0 
dicyclohexylmethane 
Component (2) 
3,3'-dimethyl-4,4'-diamino 8.0 
dicyclohexylmethane 
tolylene diisocyanate 
3.26 3.26 
white spirit 20.0 20.0 20.0 20.0 
cyclohexylisocyanate 
2.15 
stearylisocyanate 5.06 
Thixotropy 5 5 2-3 2-3 
Viscosity 3 3-2 2 2 
Flow properties 
1 1 1-2 1-2 
clear opalescent- 
slightly 
slightly 
hazy hazy hazy 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
5 6 7 8 9 10 
__________________________________________________________________________ 
Component (1) 
linseed oil varnish 
300.0 
epoxide ester, 50% in 300.0 
xylene (60% epoxide 
resin, 40%, ricinene 
fatty acid) 
coal-tar pitch, 85% 300.0 
in xylene 
Gilsonite asphalt, 300.0 
60% in xylene 
hydroxyl-group-containing 300.0 
polyester, viscosity at 
75.degree. C. 550-750 cP, 6.2-6.7% 
hydroxyl content 
hydroxyl-group-containing 300.0 
polyester-polyether, approx. 
5000 cP, 100% 
5% hydroxyl content 
xylylene diamine (0.1 val) 
6.8 6.8 6.8 6.8 6.8 6.8 
(70% m- and 30% p-isomer) 
Component (2) 
cyclohexylisocyanate (0.102 val) 
12.8 12.8 12.8 12.8 12.8 12.8 
Thixotropy 1-2 1-2 1-2 1-2 2 2-1 
Viscosity 2 2-3 2 2 2 1-2 
Flow properties 3 4 4 4 4 3 
slightly 
slightly 
homogeneous 
homogeneous 
slightly 
opalescent, 
hazy opalescent, opalescent 
hazy 
hazy 
__________________________________________________________________________ 
Component (2) is slowly added with stirring to component (1). The 
thixotropic and pasty properties appear immediately and up to 30 minutes 
after the two components have been mixed. 
- 11 12 13 14 15 
__________________________________________________________________________ 
Component (1) 
unsaturated polyester resin, 300.0 
73% in styrene, viscosity 
900-1100 cP at 20.degree. C. 
Copolymer, 75% of polyvinyl 300.0 
chloride/25% of polyvinyl 
isobutyl ether, 30% in xylene, 
softening point of the solid 
resin 48 to 52.degree. C. 
alkyd resin dilutable with water 300.0 
after neutralisation, 63% in 
butyl glycol, oil content 49%, 
acid number 46 
methyl silicone resin, 50% in 300.0 
xylene/butanol 8:2 
hydroxyl-group-containing branched 300.0 
polyether, viscosity 650 .+-. 100 cP 
xylylene diamine (0.1 val) 6.8 6.8 6.8 6.8 6.8 
Component (2) 
cyclohexylisocyanate (0.102 val) 
12.8 12.8 12.8 12.8 12.8 
Component 2 is slowly added with stirring to component 1. 
Thixotropy 1-2 2 1 1 1 
Viscosity 1-2 2 1 1 1 
Flow properties 3 4 2-3 3 4 
opalescent, 
opalescent, 
very hazy 
very hazy 
very opalesecent, 
hazy hazy hazy 
__________________________________________________________________________ 
EXAMPLE 1 
A thixotropized binder is prepared from components (1) and (2) in 
accordance with the following recipe: 
______________________________________ 
Component (1) 
300.0 g 
or long-oil linseed-oil alkyd resin, 60% in 
white spirit 
viscosity: 190-240 cP, 50% in white spirit 
oil content: 63%, phthalic acid anhydride content: 23% 
6.8 g 
of xylylene diamine 
306.8 isomer mixture: 70% m- and 
30% p-xylylene diamine 
Component (2) 
13.0 g 
of cyclohexyl isocyanate 
20.0 g 
of white spirit 
33.0 g 
______________________________________ 
Component (2) is slowly added with stirring to component (1). A very pasty, 
thixotropic binder is immediately formed. 
A white surface lacquer is then prepared with this thixotropic material in 
accordance with the following recipe: 
______________________________________ 
240.0 g 
of long-oil linseed oil alkyd, 60% in white spirit 
viscosity: 190-240 cP, 50% in white spirit 
oil content: 63%, phthalic acid anhydride content: 23% 
1.5 g of calcium naphthenate, 4% Ca 
1.8 g of silicone oil, 2% in xylene 
140.0 g 
of titanium dioxide rutile 
10.0 g 
of barium sulphate, precipitated 
393.3 g 
Grind once on a 3-roll mill 
0.7 g of methylethyl ketoxime (anti-skin agent) 
stir 
6.0 g of dry substance solution 
100.0 g 
of thixotropic alkyd resin according to the invention 
500.0 g 
stir thoroughly 
______________________________________ 
The lacquer thus obtained is subsequently diluted with white spirit to a 
spreadable consistency. The lacquer obtained is highly to heavily 
pasty-thixotropic and does not show any tendency to run when applied to 
vertical surfaces. 
EXAMPLE 2 
A complete, pigment-containing surface lacquer as a whole is thixotropized 
in this Example. The following procedure is adopted: 
______________________________________ 
Component (1) 
340.0 g 
or long-oil linseed-oil alkyd, 60% in white spirit 
viscosity: 190-240 cP, 50% in white spirit 
oil content: 63%, phthalic acid anhydride content: 23% 
1.5 g of calcium naphthenate, 4% Ca 
1.8 g of silicone oil, 2% in xylene 
140.0 g 
of titanium dioxide rutile 
10.0 g 
of barium sulphate, precipitated 
493.3 g 
Grind once on a 3-roll mill 
0.7 g of methylethyl ketoxime (anti-skin agent) 
stir 
6.0 g of dry substance solution 
500.0 g 
Component (2) 
3.4 g of xylylene diamine 
isomer mixture: 70% m- and 
30% p-xylylene diamine 
Stir component (1) and component (2) 
Component (3) 
6.5 g of cyclohexyl isocyanate 
10.0 g 
of white spirit 
16.5 g 
______________________________________ 
Component (3) is slowly added with stirring to the mixture of component (1) 
and component (2). After 1 hour, white spirit is added for spreadability. 
A highly to heavily pasty-thixotropic lacquer is formed which is easy to 
spread and does not show any tendency to run. 
EXAMPLE 3 
(a) 200 parts by weight (1 val) of isotridecyl alcohol are added with 
stirring at room temperature to 174 parts by weight (2 val) of tolylene 
diisocyanate (65% 2,4-isomer, 35% 2,6-isomer). Approximately one quarter 
of the alcohol is initially added at such a rate that the mixture has a 
reaction temperature of 60.degree. to 80.degree. C. The rest of the 
alcohol is then added over a period of another 30 minutes. The 
aforementioned temperature range is maintained by cooling. If necessary, 
heating at 80.degree. C. is continued until the reaction product has an 
NCO-content of 11.2%. 
The reaction described here is best carried out in the presence of an inert 
solvent. Aromatic or aliphatic hydrocarbons or even esters adapted to the 
subsequent application envisaged can be used as the solvents. The inert 
solvent is used for example in such a quantity that equivalent quantities 
of inert solvent and reactive isocyanate compound are present in the 
monoisocyanate reaction product. 
(b) 168 parts by weight (2 val) of hexamethylene diisocyanate are reacted 
with 200 parts by weight (1 val) of isotridecyl alcohol in xylene or 
another high-boiling solvent. The reaction product has an NCO-content of 
11.4%. 
(c) 4 conventional binders are thixotropized with the monoisocyanates 
according to (a) and (b). 
A vinyltoluene-modified alkyd resin, in the form of a 60% solution in 
xylene, is used as binder 1. Binder 2 is a long-oil linseed-oil alkyd 
resin diluted to a solids content of 60%. Binder 3 is a short-oil coconut 
alkyd resin with a solids content of 60% in xylene. Finally, binder 4 is a 
short-oil air-drying alkyd resin, again with a solids content of 60% in 
xylene. 
300 g batches of the solvent-containing binders are mixed separately with 
1.5 g of xylylene diamine, after which 12 g batches of the monoisocyanate 
compound dissolved in 12 g of solvent are stirred in. 
TABLE 3 
______________________________________ 
Binder 1 300.0 
Binder 2 300.0 
Binder 3 300.0 
Binder 4 300.0 
xylylene diamine 
1.5 1.5 1.5 1.5 
Stir ! 
Adduct 
Example 3a 12.0 12.0 
Adduct 
Example 3b 12.0 12.0 
White spirit 12.0 
Xylene 12.0 12.0 12.0 
325.0 325.0 325.0 325.0 
______________________________________ 
All the products are clear, pasty gels. Binders 1 and 2 are typical 
air-drying systems. Binder 3 is a synthetic resin suitable for stoving 
purposes. Resistance to yellowing remains favourable where stoving is 
carried out with a melamine resin (for 20 minutes at 140.degree. C.). 
Binder 4, which can be used both in air-drying systems and also for 
stoving resins, does not produce any signs of yellowing either. 
EXAMPLE 4 
Binders and binder systems typical of the field of stoving lacquers are 
thixotropized in the following. Three binder components (binders 1 to 3) 
according to the invention are initially thixotropized: 
Binder 1 
Short-oil, non-drying alkyd resin, 60% in xylene 
oil content as triglyceride: 26% 
phthalic acid anhydride content: approximately 49% 
specific gravity at 20.degree. C.: 1.19 g/cc. 
acid number: 8 
viscosity, 50% in xylene: 300-400 cP 
Binder 2 
Autocrosslinking thermosetting acrylate resin, 50% in butanol/xylene 1:1 
acid number below 2 
flow-out time from a DIN-cup 6=40-60 seconds (DIN 53211) 
stoving temperature 
30 minutes at 180.degree. C. 
or 20 minutes at 190.degree. C. 
or 10 minutes at 200.degree. C. 
Binder 3 
Crosslink- assisted acrylic resin, 50% in butanol/xylene 2:8. 
Binders 1 and 3 are used in combination with melamine resins, urea resin or 
autocrosslinking acrylic resins for stoving lacquers. 
In Examples 4a to c, these binders are thixotropized with urea adducts 
obtained by reacting a diamine with a monoisocyanate and small quantities 
of tolylene diisocyanate (isomer mixture of about 65% of 
tolyene-2,6diisocyanate and 35% of tolyene-2,4-diisocyanate) in the 
presence of the binder. Details are given in Table 4 below (where the 
figures quoted are parts by weight). 
TABLE 4 
______________________________________ 
Examples 4 5 6 
______________________________________ 
Binder 1 300.0 
Binder 2 300.0 
Binder 3 300.0 
3,3'-dimethyl-4,4'-diamino- 
6.0 6.0 6.0 
dicyclohexylmethane 0.05 val 
tolylene diisocyanate 0.0253 val 
2.2 2.2 2.2 
1-naphthyl isocyanate 0.0253 val 
4.3 4.3 4.3 
312.5 312.5 312.5 
Solids content 52.0% 52.0% 52.0% 
______________________________________ 
The binder is thoroughly stirred with the diamine. The isocyanate 
components are then slowly added with stirring. The binders immediately 
become heavily pasty-thixotropic after stirring. 
The thixotropized binders are then each worked up into a white lacquer. 
Binders 1 and 3 are processed with a melamine resin and pigment in 
accordance with the following basic receipe: 
______________________________________ 
Basic recipe parts by weight 
______________________________________ 
Binder 41.0 
Melamine resin, 55% in butanol/xylene 
16.5 
Titanium dioxide rutile 
30.5 
Ethylglycol 12.0 
100.0 
______________________________________ 
The white stoving lacquers produced with the above thixotropic binders were 
ground once on a one-roll stand, applied to sheet metal and, in an upright 
position, were stoved in an oven for 30 minutes at 150.degree. C. after an 
evaporation time of 5 minutes. The samples obtained did not show any signs 
of running, and the films were high-gloss and streak-free. After stoving, 
the colour was pure white. The dry layer thickness amounted to between 
0.05 and 0.08 mm (single coating). 
The thixotropic binder of Example 4b based on an autocrosslinking acrylic 
resin is mixed with the same, but non-thixotropized acrylic resin in a 
ratio of 1:1 (based on solids). This mixture is pigmented with 100% by 
weight of titanium dioxide rutile (based on binder). The paint thus 
obtained was applied in a thick layer to metal sheets and stoved upright 
for 30 minutes at 150.degree. C. The lacquer films did not show any signs 
of running in a dry film thickness of 0.05 to 0.08 mm (single coating). 
Stoving did not produce any yellowing or reduction in gloss.