Note: Descriptions are shown in the official language in which they were submitted.
1 21 75530
WATER-DILUTABLE TWO-COMPONENT COATING COMPOSITION
A PROCESS FOR ITS PREPARATION, AND THE USE THEREOF
Background of the Invention
Field of the Invention
The invention relates to an aqueous coating
composition, especially a two-component aqueous coating
~composition, to a process for its preparation, and to its
use in single-coat and multicoat systems.
Description of Detailed Art
On the basis of their outstanding properties, prior
art two-component polyurethane coating materials are of
great importance in the coatings sector. A disadvantage,
however, is that relatively large quantities of organic
solvents are required for processing, which must be
removed by, for example, incineration. In many areas of
application, especially outside industry, such incinera-
tion is impracticable, so that there is increased demand
here for high-solids yet, in particular, water-dilutable
coatings, in order to minimize the emission of solvent
and the associated environmental pollution.
The use of water as liquid phase in two-component
polyurethane coating materials having free isocyanate
groups is in general not readily possible, since
isocyanate groups react not only with alcoholic hydroxyl
groups but also with water to form N-substituted polyurea
compounds, giving off carbon dioxide as they do so.
Because of this, in general, the service life, pot life
and quality of the coatings are reduced to levels
incompatible with their practical use. Nevertheless,
much effort has recently been expended in attempting to
overcome these disadvantages.
For instance, DE-A 42 26 243 describes an aqueous
two-component coating composition based on
21 75530
polyisocyanates and on self-emulsifying, fatty acid-
modified polyesters and polyurethanes. European Patent
Application EP-A 0 496 205, as well describes aqueous
binder combinations based on polyisocyanates and self-
emulsifying polyester resins which possess urethane,carboxyl and hydroxyl groups. DE-C 31 22 030 describes
coating compositions comprising polyisocyanate and water-
dilutable alkyd, melamine and acrylic resins, which
compositions also comprise water-miscible solvents.
Disadvantages of the above-described water-dilutable
-two-component binders is the low achievable solids
content, the relatively low boil limit, and the short pot
life.
Summary of the Invention
It was therefore an object of the present invention
to provide water-dilutable two-component binders that
improve on those already known.
It has surprisingly now been found that selected,
externally emulsified alkyd resins, which are described
in more detail below, are particularly suitable,
outstanding emulsifying partners for combination with
nonblocked polyisocyanate curing agents, and are
distinguished by high solids contents, good pot lives,
and high boil limits.
The invention therefore provides a water-dilutable
two-component coating composition comprising
(a) a polyisocyanate component having a viscosity
at 23C of from 50 to 10,000 mPa s, including
one or more organic polyfunctional isocyanates,
and
(b) an alkyd resin emulsion whose solid component
comprises in each case a mass fraction of
(bl) from 60 to 98% of one or more alkyd resins
and
(b2) from 2 to 40% of one or more hydroxy-
functional emulsifiers, and which
comprises
~ ~ -3- 21 75530
(b3) if desired, up to 15%, based on the mass
of emulsion, of organic solvents, and also
(b4) water.
The invention also provides a process for the
preparation of coating compositions composed of an
aqueous binder combination with or without auxiliaries
and additives which are known from coatings technology,
which comprises first transferring the alkyd resin to the
aqueous phase with the aid of emulsifiers and then
emulsifying into the aqueous emulsion of the alkyd resin
~a polyisocyanate component having a viscosity at 23C of
from 50 to 10,000 mPa s and which includes at least one
organic polyisocyanate. In this process, the proportions
of the two components are preferably chosen such that the
ratio of the number of ~isocyanate groups in the
polyisocyanate component to the number of hydroxyl groups
in the alkyd resin is from 0.3:1 to 5:1. The auxiliaries
and additives used if desired are generally incorporated
into the externally emulsified alkyd resin emulsion prior
to the addition of the polyisocyanate component.
Also, the invention additionally provides for the use
of the novel binder combinations as binders, for example,
for paints, coating compositions, and sealing compounds.
Further objects, features, and advantages of the
present invention will become apparent from the detailed
description of the preferred embodiments that follows.
Throughout this specification, the term "high solids
content" refers to mass fractions of solids of more than
50%, preferably more than 55%, and particularly
preferably more than 60%. "Long pot life" means a pot life
of at least 2 hours, preferably of at least 4 hours.
Detailed Description of the Preferred Embodiments
The polyisocyanate component (a) comprises any
desired organic polyisocyanates having at least two
isocyanate groups per molecule, particularly those which
are liquid at room temperature and, generally, whose
isocyanate groups are in each case bonded to an
aliphatic, cycloaliphatic, araliphatic, or aromatic
21 75530
carbon atom. In general the polyisocyanate component (a)
has a viscosity of from 50 to 10,000 mPa s, preferably
from 50 to 1000 mPa s, at 23C. It is particularly
preferably a polyisocyanate or polyisocyanate mixture
containing only aliphatically and/or cycloaliphatically
bonded isocyanate groups and having a (mean) NCO func-
tionality of between 2.2 and 5.0 and a viscosity at 23C
of from 50 to 500 mPa s.
The polyisocyanates can if required or desired be
used as a blend with small quantities of inert solvents,
~in order to reduce the viscosity to a value within the
stated ranges. However, the quantity of such solvents is
preferably calculated such that, in the novel coating
compositions ultimately obtained, the mass of solvents is
not more than 20% of the mass of water, this calculation
includes any solvents which may still be present in the
alkyd resin emulsion. Examples of solvents suitable for
addition to the polyisocyanates are aromatic or aliphatic
hydrocarbons, such as, for example, "Isopar~ H", ketones,
esters or aprotic water-miscible solvents, for example N-
methylpyrrolidone.
Polyisocyanates particularly suitable as component
(a) are the so-called paint polyisocyanates having
aromatically or (cyclo)aliphatically bonded isocyanate
groups; in this context, the latter aliphatic polyiso-
cyanates are, as already mentioned, particularly
preferred. It is preferred to employ only isocyanates
derived from aliphatic polyfunctional isocyanates.
Highly suitable examples are paint polyisocyanates
derived from hexamethylene diisocyanate, 1-isocyanato-
3,3,5-trimethyl-4-isocyanatomethylcyclohexane (IPDI) and
bis(isocyanatocyclohexyl)methane, especially hexamethy-
lene diisocyanate. "Paint polyisocyanates" based on
these diisocyanates are to be understood as being the
derivatives of these diisocyanates which are known per
se, comprise biuret, urethane, uretdione and/or
isocyanurate groups and, following their preparation,
have been freed in a known manner, preferably by
distillation, from excess initial diisocyanate down to a
-5~ $30
residual content of less than 0.5% by mass. Particularly
preferred paint polyisocyanates are those which are
completely free of monomer fractions.
Preferred aliphatic polyisocyanates to be used in
accordance with the invention include the hexamethylene
diisocyanate-based, biuret-containing polyisocyanates
which meet the above criteria, as can be obtained, for
example, by the processes of U.S. Patents No. 3,124,605;
No. 3,358,010; No. 3,903,126; No. 3,903,127; and
No. 3,976,622 (all hereby incorporated by reference),
which comprise mixtures of N,N,N-tris(6-isocyanatohexyl)-
biuret with minor amounts of its higher homologs, and the
cyclic hexamethylene diisocyanate trimers which meet the
above criteria, as can be obtained in accordance with
U.S. Patent No. 4,324,879 (hereby incorporated by
reference), which essentially comprise N,N,N-tris(6-
isocyanatohexyl) isocyanurate in a mixture with minor
amounts of its higher homologs. Particular preference is
given to mixtures which meet the criteria specified and
comprise hexamethylene diisocyanate-based polyisocyanates
containing uretdione and/or isocyanurate groups, as are
formed by the catalytic oligomerization of hexamethylene
diisocyanate using trialkylphosphines. Among these
latter mixtures, particular preference is given to those
having a viscosity at 23C of from 50 to 500 mPa s and a
mean NC0 functionality of between 2.2 and 5Ø
The aromatic polyisocyanates, which are likewise
suitable in accordance with the invention as isocyanate
component (a), but are usually less preferred, are in
particular paint polyisocyanates based on 2,4-diiso-
cyanatotoluene or its technical-grade mixtures with 2,6-
diisocyanatotoluene or based on 4,4-diisocyanatodiphenyl-
methane or its mixtures with its isomers and/or higher
homologs. Examples of aromatic paint polyisocyanates of
this type are the isocyanates containing urethane groups,
as are obtained by reaction of excess quantities of 2,4-
diisocyanatotoluene with polyhydric alcohols such as
trimethylolpropane and subsequent distillative removal of
the unreacted diisocyanate excess. Examples of further
6 21 75530
aromatic paint polyisocyanates are the trimers of the
monomeric diisocyanates mentioned by way of example,
i.e., the corresponding isocyanatoisocyanurates, which,
following their preparation, are likewise freed from
5excess monomeric diisocyanates, preferably by distilla-
tion.
Also preferred are those polyfunctional isocyanates
which, in order to facilitate dispersion in the aqueous
phase, are modified at least in part with polyoxyalkylene
10glycols, such as polyoxyethylene glycol and polyoxypropy-
lene glycol, or with ionic groups. With particular
preference, the mass fraction of polyfunctional
isocyanates which have been hydrophilically modified in
this way is at least 5~ of the overall mass of the
15isocyanate component. Such ;socyanates are obtainable by
reacting diisocyanates with hydrophilic compounds con-
taining at least two isocyanate-reactive groups and at
least one group selected from polyoxyethylene and poly-
oxypropylene groups and also ionic or ionogenic groups.
20For use according to the invention as component (a),
particular preference is given to sterically hindered
polyisocyanates having 4 to 25, preferably 4 to 16,
carbon atoms, which contain in position 2 relative to the
NCO group one or two linear, branched or cyclic alkyl
25groups having 1 to 12, preferably 1 to 4, carbon atoms.
Examples thereof are 1,1,6,6-tetramethylhexamethylene
diisocyanate, l,5-dibutylpentamethylene diisocyanate, and
p- or m-tetramethylxylylene diisocyanate (TMXDI).
It is of course also possible in principle to use
30unmodified polyisocyanates of the type mentioned by way
of example, provided they conform to the statements made
regarding viscosity.
The polyisocyanate component (a) may in addition
comprise any desired mixture of the polyisocyanates
35mentioned.
Any desired resin can be used as alkyd resin (bl).
Suitable alkyd resins generally have hydroxyl numbers
(OHN, mass of KOH with the same number of OH groups as a
unit mass of resin) in the range of 30 to 200 mg/g, pre-
- _7_ 21 75530
ferably of 50 to 150 mg/g. Especially suitable in
accordance with the invention are polyesters modified
with any desired fatty acids. They are prepared from
saturated and/or unsaturated fatty acids or oils,
polyalcohols and polycarboxylic acids. The fatty acids
can be replaced at least in part by other monocarboxylic
acids. Any desired fatty acids, polyalcohols, and
polycarboxylic acids can be used to make the alkyd
resins.
The term fatty acids includes in general linear or
-~branched monocarboxylic acids having 6 to 35 carbon
atoms. The fatty acids may be non-drying or drying.
Examples of suitable non-drying fatty acids are, prefer-
ably, saturated and monounsaturate`d, linear or branched
aliphatic monocarboxylic acids, with a number of carbon
atoms which is preferably from 6 to 18.
Examples of suitable drying fatty acids are
unsaturated fatty acids or fatty acid mixtures which
comprise at least one monocarboxylic acid having at least
two isolated or conjugated double bonds and an iodine
number of more than 125 g/(100 g). Preference is given
to unsaturated fatty acids having a linear carbon chain
of from 16 to 18 carbon atoms.
Specific examples of suitable nondrying fatty acids
are 2-ethylhexanoic acid, isononanoic acid, Versatic acid
or coconut fatty acid and also oleic acid. Preferred
examples of what are understood to be drying fatty acids
are unsaturated monocarboxylic acids having an iodine
number of more than 125 g (100 g) and 18 carbon atoms.
These include, in particular, unsaturated fatty acids
having two or three isolated double bonds and various
steric configurations, or corresponding polyunsaturated
fatty acids with conjugated double bonds. Such fatty
acids are present, for example, in natural oils, such as
linseed oil, soya oil, safflower oil, cottonseed oil or
castor oil, sunflower oil, groundnut oil, wood oil and
dehydrated castor oil. The unsaturated fatty acids
obtained therefrom are linseed oil fatty acid, safflower
oil fatty acid, tall oil fatty acid, cottonseed fatty
5S`~l~
- --8--
acid, groundnut oil fatty acid, wood oil fatty acid,
ricinenic fatty acid or sunflower oil fatty acid.
In order to incorporate the fatty acids into the
alkyd resins, it is possible on the one hand to esterify
the fatty acids with the alcohol components or, on the
other hand, to introduce them into the alkyd resin by
transesterification reactions of the oils.
It also is possible to employ so-called technical-
grade oils as fatty acids, these oils generally being
mixtures of cis-linolenic acid, linoleic acid, oleic acid
~and stearic acid. The technical-grade oils or fatty
acids can be employed as such or can be incorporated into
the alkyd resin through transesterification reactions or
after dehydration reactions (ricinenic fatty acid).
Where polyunsaturated fa'tty acids are used, particu-
lar preference is given to employing mixtures of fatty
acids containing isolated and conjugated unsaturation,
for example having a mass fraction of from 10 to 80% of
fatty acids containing conjugated unsaturation.
The mass fraction of saturated and unsaturated fatty
acids incorporated, based on the mass of the solid resin,
is generally from 10 to 80%, preferably from 20 to 70%.
Of the mass of saturated and unsaturated fatty acids,
with particular preference, from 10 to 60~ is accounted
for by unsaturated fatty acids containing conjugated
double bonds. For nonyellowing resins, saturated
monocarboxylic acids or fatty acids containing one or two
isolated double bonds are preferred. The fatty acids
obtained can be chemically optimized by means of
fractional distillation, isomerization or conjugation.
In order to modify the properties of the alkyd resin, up
to 15% by mass of the unsaturated fatty acids may be
replaced by other monocarboxylic acids, such as benzoic
acid, tert-butylbenzoic acid, hexahydrobenzoic acid,
ethylhexanoic acid or abietic acid.
The monocarboxylic acids which can be used together,
at least in part, with the fatty acids are understood as
being, for example, alicyclic or aromatic monocarboxylic
21 75530
g
acids having 6 to 35 carbon atoms. They may, if desired
be substituted.
Suitable polycarboxylic acids used to make the alkyd
resins contain, for example, two or more carboxyl groups
on a hydrocarbon structure having, for example, from 4 to
36 carbon atoms. It is also possible to employ the
esterifiable derivatives of the polycarboxylic acids,
such as anhydrides or methyl esters. The dicarboxylic
acids which are preferably employed include linear or
branched aliphatic, alicyclic or aromatic in structure.
Suitable examples of dicarboxylic acids and
derivatives thereof are phthalic anhydride, isophthalic
acid, lower alkyl(C1-C6-alkyl)-substituted isophthalic
acid, dimethyl terephthalate, tetrahydro- and hexahydro-
phthalic anhydride, succinic'anhydride, methyltetrahydro-
phthalic anhydride, fumaric acid, maleic anhydride,
adipic acid, 2,2,4-trimethyladipic acid, azelaic acid,
sebacic acid, dimerized fatty acids, cyclopentanedi-
carboxylic acid, 1,3- and 1,4-cyclohexanedicarboxylic
acids, norbornenedicarboxylic acid, endoethylenecyclo-
hexanedicarboxylic acid or halogenated dicarboxylic
acids, such as chlorophthalic anhydride and hexachloro-
endomethylenetetrahydrophthalic anhydride, or mixtures
thereof.
Polycarboxylic acids of higher functionality, and
their derivatives, such as trimellitic anhydride,
pyromellitic anhydride or bisanhydrides, can be
incorporated proportionately; preferably, up to 10~ of
the dicarboxylic acids can be replaced by polycarboxylic
acids or derivatives thereof. An appropriate tricar-
boxylic acid can also be obtained by substituted addition
or Diels-Alder reaction of maleic anhydride or
(meth)acrylic acid with an unsaturated fatty acid.
Alcohols preferred for the synthesis of the alkyd
resins are aliphatic, cycloaliphatic and araliphatic
alcohols having 2 to 6 hydroxyl groups and 2 to 24 carbon
atoms per molecule and a molar mass of from 62 to 434 g/
mol. The alcohols may have primary, secondary and terti-
ary hydroxyl groups. The linear or branched, substituted
21 75530
10--
or unsubstituted carbon chain can be interrupted if
desired by ether or ester groups.
Examples of the compounds employed as diols are
glycols, such as ethylene glycol, propylene glycol, 1,4-
butanediol, 1,6-pentanediol, 1,6-hexanediol, 1,2-decane-
diol, 2,2-ethylbutyl-1,3-propanediol, 2,2-dimethyl-1,3-
propanediol, cyclohexanedimethanol, l,l-isopropyli-
denebis(p-phenoxy)di-l-ethanol, l,l-isopropylidenebis(p-
phenoxy)di-2-propanol, di(hydroxyethyl)-5,5-dimethyl-
hydantoin, and the hydrogenated bisphenols A and F. As
~ether alcohols use is made, for example, of diethylene
glycol, triethylene glycol, dipropylene glycol or
tripropylene glycol, and ethoxylated or propoxylated
bisphenol A or F products.
Examples of higher-functional polyols are glycerol,
trimethylolethane, trimethylolpropane, trimethylolhexane,
ditrimethylolpropane, 2,2-dimethylolbutan-3-ol, 2,2-
bis(hydroxymethyl)butan-l-ol, pentaerythritol, dipenta-
erythritol, tripentaerythritol, tris(2-hydroxyethyl)
isocyanurate, and also ethoxylated or propoxylated
polyhydric alcohols such as trimethylolpropane, penta-
erythritol, and sugar alcohols, such as mannitol or
sorbitol, and mixtures thereof.
Primary monoalcohols having a chain-terminating
action, such as isodecanol, cyclohexanol, benzyl alcohol
or fatty alcohols, can be incorporated by condensation in
certain fractions, preferably when carboxylic acids
having a basicity of more than two are used.
The alkyd resins can be prepared by polycondensation
in accordance with known methods, as are described, for
example, in S. Paul, Surface Coatings, pp. 70 to 139,
John Wiley & Sons, New York, 1985, hereby incorporated by
reference.
For example, the polycondensation can be carried out
by heating in the melt or by an azeotropic method, with
elimination of water. The desired number of hydroxyl and
acid groups can be introduced by an appropriate choice of
the ratios of equivalents, a suitable reaction regime
and, if desired, by working in steps. The appropriate
21 75530
--11--
process conditions and solution criteria are familiar to
the person skilled in the art.
Any desired hydroxy-functional emulsifiers (b2) can
be used in the composition of the invention. Suitable
hydroxy-functional emulsifiers include alkylphenols and
alkylphenol ethoxylates, alkyl ethoxylates, alkyl
glycosides, as described for example in DE 34 04 558,
alkyl polysaccharides, sorbitol mono- and diesters,
ethoxylated sorbitol esters, sorbitol hexaesters,
propylene -oxide-ethylene oxide copolymers, polyvinyl
~alcohols or partially hydrolyzed polyvinyl acetates, and
water-soluble hydroxy-functional polymers formed by
addition polymerization, condensation polymerization or
polyaddition.
Suitable hydroxy-functiohal polyesters include water-
soluble polyesters whose solubility in water derives from
the fact that polyethylene glycol has been used as hydro-
philic component and/or from the high acid number.
Particular preference is given to hydroxyl-cont~;n;ng
polyurethanes or polyurethane-polyureas which can be
prepared by reacting polyfunctional isocyanates with,
inter alia, hydroxy-functional polyesters or polyethers
as hydrophobic component, the polyesters being obtained
by condensation from the polycarboxylic acids and polyols
already described above, and polyethylene glycol and/or
dihydroxy acids, for example dimethylolpropionic acid, as
hydrophilic components, with or without chain extension
using polyamines. These polyurethanes or polyurethane-
ureas can be prepared, for example, in bulk or in inert
solvents by adding diisocyanates to the hydroxy compon-
ents or by chain extension of isocyanate-functional
prepolymers in the aqueous phase, using polyamines.
Attention is directed to copending application Attorney
Docket No. 016878/0686, filed on the same date as this
application, hereby incorporated by reference, for
examples of useful emulsifiers.
In order to prepare the alkyd resin emulsions, these
alkyd resins are first of all mixed with the above-
described emulsifiers or emulsifier dispersions, in the
21 75530
-12-
presence or absence of the inert solvents described
above.
Generally, the mixtures comprise from 40 to 97,
preferably from 50 to 95, parts by weight of the hydro-
phobic alkyd resins mentioned in a blend with from 3 to
60, preferably from 5 to 50, parts by weight of the
specified emulsifiers or emulsifier dispersions.
However, it is often important to select the nature and
proportions of the individual components, within the
scope of the comments made, such that the mass fraction
~of ethylene oxide originating from component (b2) in the
water-dispersible mixtures is not more than 20%,
preferably not more than 15%, of the mass of the solid
(bl + b2).
The mixtures can be pre~ared simply by blending the
synthetic resins with the emulsifiers or aqueous emulsi-
fier dispersions, with or without the presence of further
solvents, for example hydrocarbons, alcohols, ketones,
glycol ethers or N-methylpyrrolidone.
The aqueous synthetic-resin dispersions according to
the invention are prepared by dispersing the novel
mixtures in water, which can be done either simply by
stirring water into the initially introduced mixture of
the synthetic resins with the emulsifier, using customary
dissolvers or stirrers, or else by pouring the mixture
into water, with vigorous stirring. If desired, it is
possible first to add part of the water to the above-
described mixture and then to pour this mixture, with
stirring, into the remaining quantity of water. In this
way, stable oil-in-water emulsions can be obtained.
To prepare the alkyd resin emulsion, it is also
possible first to prepare an aqueous solution of the
emulsifier, into which the alkyd resin is then stirred
under heavy shearing.
The ready-to-use coating compositions can be obtained
by emulsifying the polyisocyanate component (a) in the
aqueous emulsion of the alkyd resin (b), the alkyd resin
emulsion taking over the function of an emulsifier for
the added polyisocyanate (a). As polyisocyanate
_ -13- 21 7553~
component (a) it is possible, but generally not
preferable, to use hydrophilically modified polyiso-
cyanates which, because of the incorporated ionic or
nonionic hydrophilic centers, are autodispersible.
Thorough mixing can be achieved simply by stirring,
generally, at room temperature. In this context, the
quantity of polyisocyanate component is calculated such
that the resulting ratio of the number of isocyanate
groups of component (a) to the number of alcoholic
hydroxyl groups of component (b) is generally from 0.3:1
~to 5:1, preferably from 0.5:1 to 4:1 and, with particular
preference, from 0.8:1 to 3:1.
Prior to the addition of the polyisocyanate component
(a), it is possible to incorporate into the externally
emulsified alkyd resin emulsion (b), the auxiliaries and
additives which are customary in coating technology.
These auxiliaries and additives may also be present in
the polyisocyanate component (a).
If desired, the dispersions according to the inven-
tion can be modified, prior to, during or after their
preparation, by the addition of other polymers, for
example polyacrylates, polyurethanes, hard resins or
polyesters in solution or dispersion form. If the
additional binders carry reactive groups, for example
hydroxyl groups, then these groups should be taken into
account in connection with the mixing ratio of components
(a) and (b).
The coating compositions according to the invention
include the above-described usually hydroxyl-containing,
water-dispersible binders and the isocyanates. As
auxiliaries and additives they can also comprise, for
example, pigments, fillers, coatings additives,
emulsifiers which are preferably incorporated into the
network via reactive double bonds or hydroxyl groups
during film formation, especially nonionic emulsifiers,
leveling agents, antifoams, rheological auxiliaries,
catalysts, siccatives and further binders. The purpose
of the additives is to influence coatings properties such
as, for example, curing times and surface quality, or to
21 75530
-14-
influence applications-related properties, for example
the viscosity.
In order to achieve ready dispersibility of the
polyisocyanates it is possible to establish a suitable,
low viscosity. This goal is also served by dissolving
highly viscous or solid polyisocyanates in water-miscible
organic solvents which react slowly or not at all with
isocyanates. Examples of useful unreactive solvents are
glycol dialkyl ethers, such as glycol dimethyl ether,
esters, such as ethylglycol acetate, ketones, such as
~acetone, cyclic ethers, such as dioxane, or lactams, such
as N-methylpyrrolidone. Preference is given to alcohols
containing sterically hindered alcohol groups, ketone
alcohols or alkoxy alcohols, such as butoxyethanol,
butyldiglycol, methoxyisoprbpanol or diacetone alcohol.
They are used, shortly before processing and without
heating, to prepare a polyisocyanate solution which has
a solids content of more than 40% by mass, preferably
from 50 to 95% by mass, with a viscosity of from 0.5 to
2000 mPa s, preferably from 1 to 20 mPa s.
Suitable pigments are the customary pigments, for
example those described in DIN 55 944: preferably carbon
black, titanium dioxide, finely disperse silica, aluminum
silicate, metal powders or flakes, organic and inorganic
color pigments, anticorrosion pigments, such as lead
compounds and chromate compounds, and metal-effect
pigments. In addition to the pigments and fillers it is
possible if desired to employ customary organic dyes. It
is likewise possible to add proportions of crosslinked
organic microparticles.
The methods for preparing the coating compositions
from the individual components are known. For example,
it is possible to disperse the pigments in a particularly
appropriate grinding resin and, if desired, to mill them
to the required particle size. Another procedure envis-
ages milling the pigments in the aqueous dispersion of
the binder component (b).
In this context care should be taken to ensure that
the stability of the aqueous dispersion remains
~ 7~5~i~
-15-
unaffected during the milling process. Following the
dispersion of the pigments it is possible to add further
binder components. These may comprise the externally
emulsified alkyd resins of the invention and, if desired,
other binders of those described above. If desired,
further coatings auxiliaries can be added in order to
influence properties such as, for example, dispersi-
bility.
In accordance with another preferred procedure, the
externally emulsified alkyd resins or, if desired, other
~customary paint resins are first of all mixed with a
little water, with or without the addition of fillers,
pigments, colorants and the like, and this mixture is
dispersed on a roller bed or in a ball mill, to form
pastes. These pastes can thén be diluted with water and,
if desired, admixed with further resin emulsion and
additives to prepare the ready-to-use coating formula-
tions.
If desired, pigments or coatings auxiliaries may also
be present in component (a). This coatings component is
generally nonaqueous. However, it is dispersible in the
aqueous alkyd resin emulsion. It may if desired contain
small fractions of organic solvents in order to establish
an appropriate viscosity for dispersion. Care should be
taken to ensure that the additives are unable to react
with the isocyanate component. The brief mixing of iso-
cyanates with alcohols, such as butoxyethanol or diace-
tone alcohol, is possible.
The coating compositions according to the invention
can be applied to the materials to be coated in any
desired manner, such as using customary techniques, for
example dipping, spraying or rolling. The applied film
subsequently crosslinks.
Crosslinking of the coating can be effected at
temperatures of, for example, from 0C to 150C. The
coating compositions according to the invention can
advantageously be cured at relatively low temperatures,
for example at temperatures between 10C and 80C,
~1 755~0
-16-
especially below 60C. If appropriate, a flash-off time
can be allowed to elapse before crosslinking.
The thicknesses of the coats applied depend on the
intended use of the coating composition. For example,
clearcoats generally have a thickness of up to 60 ~m,
pigmented basecoats or topcoats generally have a thick-
ness of from 10 to 50 ~m, coatings as fillers or stone-
chip resistance coats a thickness generally from 30 to
100 ~m, and anticorrosion primer coatings generally a
thickness of from 20 to 70 ~m.
The coating composition according to the invention
is suitable for single-coat finishes, topcoats and
primers.
Any desired substrates can be suitably coated in
accordance with the invention, examples being metal
substrates such as iron, aluminum or zinc, nonmetallic
substrates, such as mineral substrates (e.g., concrete,
glass), wood, plastics substrates, such as polyolefins,
polycarbonates and polyurethanes, and, if desired,
substrates provided with a preliminary coating. Applica-
tion can be made to a dried or crosslinked coated sub-
strate. It also is possible to operate by the "wet-on-
wet" method. For this purpose the coating composition of
the invention can be applied, if desired after a short
flash-off phase, to a substrate provided with a noncross-
linked coating composition. It is also possible to apply
a further coating composition to the novel coating
composition, without drying or crosslinking beforehand
and, if desired, after a short flash-off phase. The
further coating composition may comprise a coating
composition on the basis of the present invention or
another coating composition. Subsequently, the coating
films are crosslinked together.
The coating composition according to the invention
is particularly suitable for use in multi-coat finishing,
with at least one coat being prepared using the coating
composition of the invention. In this context it is
possible, depending on the pigmentation, to produce, for
example, clearcoat compositions, basecoat or topcoat
21 75530
- -17-
compositions and also stone-chip resistance compositions,
fillers or primers. A preferred use is that as clearcoat
compositions applied to a basecoat which is based on an
aqueous solvent-containing coating composition. The
coatings thus obtained are distinguished by high mar
resistance, a high gloss retention capacity and enhanced
resistance properties.
The examples which follow illustrate the invention,
but do not limit it. All contents, parts and numerical
percentages below are fractions by mass unless otherwise
~specified.
EXAMPLES
;
Hydroxy-functional emulsifier E1
26.8 g of dimethylolpropionic acid are suspended at
about 80C in 100 g of polyethylene glycol 1000 (mean
molar mass Mn about 1000 g/mol). Then, after heating to
70C, 51 g of tetramethylxylylene diisocyanate (TMXDI)
and 36.6 g of tolylene diisocyanate (TDI) are added
dropwise at a rate such that the temperature does not
exceed 70C (about 30 min). Once all of the isocyanate
has been added, the admixture is stirred at the tempera-
ture for one hour and the reaction temperature is then
raised to 90C. The temperature is maintained until the
isocyanate content has fallen to 3.8~. Then 30 g of
Genapol~ O-100 (ethoxylated fatty alcohol) and 60 g of a
polyester made from isophthalic acid, adipic acid,
neopentylglycol and trimethylolpropane (OH number
107 mg/g, acid number 3 mg/g) are added and the mixture
is stirred at 90C until the NCO content has fallen to
1.4%. Then, with vigorous stirring, 400 g of heated
deionized water are added over the course of 10 minutes.
This is followed directly by the rapid (about 5 min)
dropwise addition of 3.75 g of triethylenetetramine
dissolved in 37.5 g of deionized water. Following the
addition of 4.5 g of triethylamine and a reaction time of
3 hours at 80C, a further 4.4 g of triethylamine and
21 75530
-18-
1000 g of deionized water are added and the mixture is
then cooled. A pastelike dispersion is obtained.
Alkyd resin emulsion A1
220 g of the above-described emulsifier emulsion El
are added to 200 g of a commercial alkyd resin having an
oil content of 34% (e.g., Alftalat~ AF 342 100~) and the
mixture is stirred at 70C for about 60 min until it is
homogeneous.
After adding 1 ml of ammonia water (25%), 70 g of
deionized water heated at 70C are added dropwise very
slowly with vigorous stirring (about 2 hours). A milky,
pseudoplastic dispersion is obtained.
;
Alkyd resin emulsion A2
40 g of Genapol~ O-100 (ethoxylated fatty alcohol)
and 10 g of butylglycol are added to 200 g of a
commercial alkyd resin having an oil content of 42%
(e.g., Alftalat~ AM 424 100%) and the mixture is stirred
at 70C for about 60 min until it is homogeneous.
After adding 2 ml of ammonia water (25%), 230 g of
deionized water heated at 70C are added dropwise very
slowly with vigorous stirring (about 4 hours). A milky
dispersion is obtained.
Coating composition
19.5 g of the externally emulsified alkyd resin
emulsion A1 are diluted with 2 g of methoxypropyl acetate
and mixed with 6 g of a polyisocyanate (Bayhydur~ LS
2980). The pot life of this mixture is more than 4
hours. The films, cured at room temperature, were free
from tack, clear and crosslinked and exhibited good
evenness. After drying at 80C for 30 minutes and at
60C for 16 hours, pendulum hardnesses of more than 100
s were measured, which rose to more than 150 s after a
further week at room temperature. The solvent resistance
(xylene, 5 minutes) of the films cured in this way was
excellent.
21 75530
., --19--
Similar results are obtained with the alkyd resin
emulsion A2.
Although only a few exemplary embodiments of this
invention have been described in detail above, those
skilled in the art will readily appreciate that many
modifications are possible in the exemplary embodiments
without materially departing from the novel teachings and
advantages of this invention. Accordingly, all such
modifications are intended to be included within the
~scope of this invention.
