Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2137621
WATER-DILUTABLE TWO-CONPONENT COATING COMPOSITION
Background of the Invention
The present invention relates to a water-
dilutable, two-component coating composition.
Summary of the Invention
It is an object of the present invention to
provide a water-dilutable, two-component coating
composition.
These and other objects according to the
invention are provided by a water-dilutable, two-
component coating composition that comprises:
(a1 a polyisocyanate component that contains at
least one organic polyisocyanate, and
~b) an aqueous polyurethane dispersion prepared
by radical-initiated polymerization of
polyurethane macromonomers that contain:
- at least one carboxyl, phosphono or
sulfo group,
- at least one vinyl group, which group
may be a lateral group or a terminal
group, and
- optionally at least one hydroxyl,
urethane, thiourethane or urea group.
In one embodiment, the aqueous polyurethane
dispersion (b) is prepared by producing a urethane
macromonomer by radical-initiated polymerization of
~A) one or more polyhydroxy compounds selected from
the group consisting of ~A1) polyhydroxy-polyethers,
(A2) polyhydroxy-polyesters, and (A3) polyhydroxy-
polycarbonates, and, optionally (A4) low molecular
--1--
- 2137621
weight polyols, (B) one or more polyisocyanates, ~C)
one or more vinyl monomers that contain at least one
vinyl group, selected from the group consisting of
ICl) vinyl monomers that contain one group which is
reactive toward isocyanate groups, which group is
selected from an amino, hydroxyl and mercapto group,
(C2) vinyl monomers that contain at least two groups
which are reactive toward isocyanate groups,
selected as defined in (Cl), it being possible for
the vinyl monomers ~Cl) and ~C2), if desired, to be
employed in a mixture, ~D) polyhydroxy compounds
that contain at least one acid group selected from
a carboxyl, sulfo and phosphono group, and,
optionally, ~D') acid-group-containing polyamines,
polythiols or amino alcohols or amino thiols, the
acid groups of which are as defined in ~D), and
reacting the urethane macromonomer with at least one
alcohol, amine or thiol, wherein the resulting
polyurethane contains acid groups, terminal hydroxyl
groups and vinyl groups, which vinyl groups may be
terminal or lateral vinyl groups.
The another embodiment, the urethane macromo-
nomer is prepared in the presence of a vinyl com-
pound (E) or in the presence of a mixture of two or
more vinyl compounds (E), the vinyl compounds (E)
being selected from the group consisting of:
- esters of olefinically unsaturated
mono- or polycarboxylic acids with
mono- or polyhydric (cyclo)aliphatic,
aromatic or mixed aliphatic-aromatic
alcohols having 1 to 15 carbon atoms,
- amides or nitriles of the above-defined
carboxylic acids, which in the case of
- 2137621
the amides optionally may be
substituted on the nitrogen atom,
- esters of mono- or polyhydric,
olefinically-unsaturated alcohols with
(cyclo)aliphatic, aromatic or mixed
aliphatic-aromatic carboxylic acids
that have 2 to 15 carbon atom~,
- olefinically-unsaturated aldehydes and
ketones,
- ethers of mono- or polyhydric,
olefinically-unsaturated alcohols with
(cyclo)aliphatic, aromatic or mixed
aliphatic-aromatic alcohols that have 1
to 15 carbon atoms,
- vinyl and vinylidene halides, and
- vinyl aromatic compounds.
In yet another embodiment, the aqueous
polyurethane dispersion (b) is prepared by radical-
initiated polymerization in a mixture of water and
an organic solvent which is inert toward isocyanate
groups, optionally in the presence of unsaturated
monomers (E) which are copolymerizable with the
polyurethane macromonomers, and optionally with
removal of the organic solvent by distillation
before or after the free-radical polymerization.
In still another embodiment, the aqueous
polyurethane dispersion (b) is prepared by radical-
initiated polymerization in an unsaturated monomer
(E) which serves as solvent and is copolymerizable
with the polyurethane macromonomers, optionally in
the presence of further copolymerizable unsaturated
monomers (E).
- - 2l3762l
The objects of the invention also are
provided by a process for the preparation of a
water-dilutable two-component coating composition,
wherein prior to the polymerization of the urethane
macromonomers, at least one vinyl monomer is added
which carries at least one functional group selected
from the group consisting of carboxyl, hydroxyl,
amino, ether and mercapto groups. The unsaturated
monomer (E) may be added before or during
polymerization but after the synthesis of the
urethane macromonomer.
The invention also provides a coating method,
comprising the steps of providing a substrate, and
coating a layer of a composition according to the
invention on the substrate. In a preferred
embodiment, the substrate is a metallic substrate.
Other objects, features and advantages of the
present invention will become apparent from the
following detailed description. It should be
understood, however, that the detailed description
and the specific examples, while indicating
preferred embodiments of the invention, are given by
way of illustration only, since various changes and
modifications within the spirit and scope of the
invention will become apparent to those skilled in
the art from this detailed description.
Description of the Preferred Embodiments
A coating composition according to the
invention comprises
(a) a polyisocyanate component composed of
one or more organic polyisocyanates, and
- - 2137621
(b) an aqueous polyurethane dispersion
prepared by radical-initiated polymerization of
polyurethane macromonomers that contain carboxyl,
phosphono or sulfo groups, lateral and/or terminal
vinyl groups, and, if desired, hydroxyl, urethane,
thiourethane and/or urea groups.
Polyisocyanate component (a) may be any of
the organic polyisocyanates which are liquid at room
temperature and which have free isocyanate groups
attached to aliphatic, cycloaliphatic, araliphatic
and/or aromatic structures. Polyisocyanate
component (a) generally has a viscosity at 23C of
from 1 to 20,000 mPa.s. Polyisocyanate component
(a) particularly preferably comprises
polyisocyanates or mixtures of polyisocyanates which
have isocyanate groups attached exclusively to
aliphatic and/or cycloaliphatic structures and which
have an (average) NCO functionality of between 2.0
and 5Ø
If required, the polyisocyanates can be
employed as a mixture with small quantities of inert
solvents, in order to reduce the viscosity to a
level within the specified ranges. The quantity of
such solvents, however, is generally calculated so
that the coating compositions according to the
invention which are ultimately obtained contain not
more than 30% by weight of solvent, this calculation
including any solvents which may still be present in
the polymer dispersions or solutions. Examples of
solvents which are suitable as additives for the
polyisocyanates are aromatic hydrocarbons such as
~solvent naphtha," or else aprotic solvents such as
aliphatic ethers, (e.g., diethylene glycol dimethyl
- - 2137621
ether, dipropylene glycol dimethyl ether), glycol
ether esters, or amides such as N-methylpyrrolidone
or dimethylformamide.
Polyisocyanates suitable as component (a) are
S diisocyanates, particularly the so-called paint
polyisocyanates that contain isocyanate groups
attached to aromatic or ~cyclo)aliphatic structures,
the latter aliphatic polyisocyanates being
particularly preferred.
The diisocyanates are the compounds which are
known in the polyurethane and paints sector, such as
aliphatic, cycloaliphatic or aromatic diisocyanates.
These preferably possess the formula Q(NCO) 2~ where
Q is a hydrocarbon radical that has 4 to 40 carbon
atoms, in particular 4 to 20 carbon atoms, and is
preferably an aliphatic hydrocarbon radical that has
4 to 12 carbon atoms, a cycloaliphatic hydrocarbon
radical that has 6 to 15 carbon atoms, an aromatic
hydrocarbon radical having 6 to 15 carbon atoms or
an araliphatic hydrocarbon radical that has 7 to 15
carbon atoms.
Examples of preferred diisocyanates include
tetramethylene diisocyanate, hexamethylene
diisocyanate, dodecamethylene diisocyanate,
1,4-diisocyanatocyclohexane, 3-isocyanatomethyl-
3,5,5-trimethylcyclohexyl isocyanate ~isophorone
diisocyanate), 4,4~-diisocyanatodicyclohexyl-
methane, 4~,4"-diisocyanato-2,2-dicyclohexyl-
propane, l,4-diisocyanatobenzene, 2,4- or
2,6-diisocyanatotoluene or mixtures of these
isomer~, 4,4~- or2,4~-diisocyanatodiphenyl-methane,
4~,4~-diisocyanato-2,2-diphenylpropane, p-xylylene
diisocyanate and ~, ~, h ~ -tetramethyl-m- or
- - 2137621
-p-xylylene diisocyanate, and mixtures of these
compounds.
Other suitable polyisocyanates are those
which contain heteroatoms in the radical which links
the isocyanate groups. Examples of these are
polyisocyanates which have carbodiimide groups,
allophanate groups, isocyanurate groups, urethane
groups, acylated urea groups or biuret groups. With
regard to other suitable polyisocyanates reference
is made, for example, to DE-A 29 28 552.
Examples of polyisocyanates that are highly
suitable include paint polyisocyanates based on
h e x a m e t h y 1 e n e d i i s o c y a n a t e 8 ,
~ -tetramethyl-m- and -p-xylylene
diisocyanate (TMXDI) or on 1-isocyanato-
3,3,5-trimethyl-4-isocyanatomethylcyclohexane (IPDI)
and/or bis(isocyanatocyclohexyl)methane, especially
polyisocyanates that are based solely on
hexamethylene diisocyanate. Paint polyisocyanates
based on these diisocyanates should be understood as
including known derivatives of these diisocyanates
which possess biuret, urethane, uretdione and/or
isocyanurate groups. Subsequent to their
preparation, these have been freed from excess
starting diisocyanate as required in a known manner,
preferably by distillation, down to a residual
content of less than 0.5% by weight. The preferred
aliphatic polyisocyanates to be used in accordance
with the invention include polyisocyanates which
meet the above mentioned criteria, contain biuret
groups and are based on hexamethylene diisocyanate.
These can be obtained, for example, by the processes
of US-A-3,124,605, 3,358,010, 3,903,126, 3,903,127
2137621
or 3,976,622, and comprise mixtures of
N,NON-tris(6-isocyanatohexyl)biuret with minor
quantities of its higher homologs. Other preferred
aliphatic polyisocyanates are the cyclic trimers of
hexamethylene diisocyanate which conform to the
above mentioned criteria. These can be obtained in
accordance with US-A-4,324,879 and essentially
comprise N,N,N-tris(6-isocyanatohexyl) isocyanurate
in a mixture with minor quantities of its higher
homologs. Particular preference is given to
mixtures, conforming to the above mentioned
criteria, of polyisocyanates which are based on
hexamethylene diisocyanate and which possess
uretdione and/or isocyanurate groups. These
mixtures are formed by catalytic oligomerization of
hexamethylene diisocyanate using trialkylphosphines.
Particular preference is given to the last-mentioned
mixtures having a viscosity at 23C of from 1 to
20,000 mPa.s and having an NCO functionality of
between 2.0 and 5Ø
In the context of the present invention it is
advantageous also to employ polyisocyanates which
are dispersible in water, such as those described,
for example, in EP-B-0 061 628, EP-B-0 206 059 and
EP-B-0 469 389. Such polyisocyanates contain
additional hydrophilic groups which may be nonionic,
e.q., polyoxyalkylene groups, or ionic, preferably
anionic groups, for example, groups derived from
carboxylic, sulfonic or phosphonic acids.
Aromatic polyisocyanates are also suitable,
but are less preferred. Preferred aromatic
polyisocyanates are paint polyisocyanates based on
2,4-diisocyanatotoluene or its technical-grade
- 213762i
mixtures with 2,6-diisocyanatotoluene, or based on
4,4-diisocyanatodiphenylmethane or its mixtures with
its isomers and/or higher homologs. Examples of
such aromatic paint polyisocyanates are the
isocyanates that possess urethane groups, such as
those obtained by reaction of excess quantities of
2,4-diisocyanatotoluene with a polyhydric alcohol
such as trimethylol propane, followed possibly by
removal by distillation of the unreacted
diisocyanate excess. Examples of other aromatic
paint polyisocyanates are the trimers of the
monomeric diisocyanates mentioned, i.e., the
corresponding isocyanato-isocyanurates, which may
subsequent to their preparation have been freed,
preferably by distillation, from excess monomeric
diisocyanates. Polyisocyanate component ~a) also
may comprise any desired mixtures of the
polyisocyanates mentioned.
The polyurethane dispersions (b) are
described in DE-A-41 22 266, DE-A-41 22 265 and
EP-A-0 098 752. The polyurethane macromonomers
required for their preparation are prepared by
polyaddition of polyhydroxy compounds (A) from the
group consisting of polyhydroxy-polyethers (Al),
polyhydroxy-polyesters (A2) andpolyhydroxy-polycar-
bonates (A3), if desired in combination with low
molecular weight compounds (A4) which possess two or
more functional groups selected in each case from
among hydroxyl, amino and mercapto groups;
polyisocyanates (B); monomers tc) that have at least
one vinyl group and that contain one (Cl) or at
least two (C2) groups which are reactive toward iso-
cyanate, such as amino, mercapto or, preferably,
- - 2137621
hydroxyl groups; and also polyhydroxy compounds (D)
which contain acid groups, such as polyhy-
droxycarboxylic acids, polyhydroxyphosphonic acids
or polyhydroxysulfonic acids, and/or, if desired,
acid group-containing polyamine~ or polythiols (D~).
The polyhydroxy compounds A are selected from
the groups consisting of the polyhydroxy-polyethers
(Al), namely compounds of the formula
H- tO- (CHR) n] m~OH
in which
R is hydrogen or a lower alkyl radical, with
various substituents if desired,
n is a number from 2 to 6 and
m is a number from 10 to 120.
Examples are poly(oxytetramethylene) glycols,
poly(oxyethylene) glycols and poly(oxypropylene)
glycols. The preferred polyhydroxy-polyethers are
poly(oxypropylene) glycols having a molar mass in
the range from 400 to 5000 g/mol.
The polyhydroxy-polyesters (A2) are prepared
by esterification of organic polycarboxylic acids or
their anhydrides with organic polyols. The
polycarboxylic acids and the polyols may be
aliphatic or aromatic polycarboxylic acids and
polyols.
The polyols used for the preparation include
alkylene glycols such as ethylene glycol, butylene
glycol, 1,6-hexanediol, neopentyl glycol and other
glycols, for example, dimethylolcyclohexane,
2,2-bis(4-hydroxycyclohexyl)propane and also
trishydroxyalkylalkanes such as e.g.
--10--
- - 2137621
trimethylolpropane, and tetrakishydroxyalkylalkanes
such as pentaerythritol.
The acid component of the polyester
principally comprises low molecular weight
polycarboxylic acids or their anhydrides that have
2 to 18 carbon atoms in the molecule. Examples of
suitable acids are phthalic acid, isophthalic acid,
terephthalic acid, tetrahydrophthalic acid, hexahy-
drophthalic acid, succinic acid, adipic acid,
azelaic acid, sebacic acid, maleic acid, glutaric
acid, hexachloroheptanedicarboxylic acid, alkyl- and
alkenylsuccinic acids such as n-octenylsuccinic acid
and n- or iso-dodecenylsuccinic acid,
tetrachlorophthalic acid, trimellitic acid and
pyromellitic acid. In place of these acids it is
also possible to use their anhydrides where they
exist. Dimeric and trimeric fatty acids can also be
employed as polycarboxylic acids.
The terms polyhydroxy-polyether and
polyhydroxy-polyester also refer to those products
of this kind which - contain monomers with
carboxylate, phosponate or sulfonate groups.
It also is possible to use polyhydroxy-
polyesters which are derived from lactones. These
products are obtained, for example, by reacting an
~-caprolactone with polyols. Such products are
described in US-A-3,169,945.
The polylactone-polyols obtained by this
reaction are distinguished by the presence of a
terminal hydroxyl group and by recurring polyester
units derived from the lactone. These recurring
units in the molecule may conform to the formula
2137621
- C - (CHR)n ~ C~2 ~
in which n is preferably from 4 to 6 and the
substituent R is hydrogen, an alkyl radical, a
cycloalkyl radical or an alkoxy radical, with the
proviso that no substituent contains more than 12
carbon atoms.
The lactone used as starting material may be
any desired lactone or combination of lactones,
provided said lactone contains at least 6 carbon
atoms in the ring, for example, 6 to 8 carbon atoms,
and provided at least 2 hydrogen substituents are
present on the carbon atom attached to the oxygen
group of the ring. The lactone used as starting
material can be represented by the following
formula:
CH2(CR2)n~C =
in which n and R are as already defined.
The preferred lactones are the
~-caprolactones, in which n has the value 4. The
most preferred lactone is unsubstituted
~-caprolactone, in which n has the value 4 and all
substituents R are hydrogen. This lactone is
particularly preferred since it is available in
large quantities and gives coatings having excellent
-12-
- 2137621
properties. Various other lactones may be used
individually or in combination.
Examples of aliphatic polyols which are
suitable for reaction with the lactone are ethylene
glycol, 1,3-propanediol, 1,4-butanediol,
1,6-hexanediol, dimethylolcyclohexane,
trimethylolpropane and pentaerythritol.
Polyhydroxy-polycarbonates (A3) include
polycarbonate-polyols and polycarbonate-diols,
conforming to the formula
o
Il
HO- R- C O- C- O- R) n- OH
in which R is an alkylene radical and n denotes an
integer from 10 to 120. These OH functional
polycarbonates can be prepared by reacting polyols
such as 1,3-propanediol, 1,4-butanediol,
1,6-hexanediol, diethylene glycol, triethylene
glycol, 1,4-bishydroxymethyl-cyclohexane, 2,2-
bis(4-hydroxycyclohexyl)propane, neopentyl glycol,
trimethylolpropane or pentaerythritol with
dicarbonates such as dimethyl, diethyl or diphenyl
carbonate or phosgene. Mixtures of such polyols can
also be employed.
The above-described polyhydroxy-polyethers,
polyhydroxy-polyesters and polyhydroxy-
polycarbonates can also be employed together.
Furthermore, these polyhydroxy compounds may also be
employed together with different quantities of low
molecular weight, isocyanate-reactive polyols,
polyamines or polythiols (A4). Examples of suitable
compounds of this kind are ethylene glycol,
- 21376~1
butanediol, pentaerythritol, trimethylolpropane,
ethylene diamine, propylenediamine,
hexamethylenediamine, ,B-mercaptoethanol and
,~-aminoethanol .
s The monomers (C) contain at least one vinyl
group . They include monomers ( Cl ) that contain one
group reactive toward i socyanate, such as amino,
mercapto or hydroxyl groups, preferably hydroxyl
groups, and monomers (C2) that contain at least two
groups reactive toward isocyanate, such as amino,
mercapto or hydroxyl groups, preferably hydroxyl
groups .
Examples of the monomers (Cl) are the
hydroxyalkyl (meth) acrylates such as hydroxyethyl and
hydroxypropyl (meth) acrylate, the reaction products
of monoepoxides and e,,~-unsaturated carboxylic
acids, such as reaction products of Versatic acid
glycidyl esters and (meth) acrylic acid or of
-unsaturated glycidyl esters and monocarboxylic
acids, for example, reaction products of glycidyl
(meth)acrylate and stearic acid or linseed oil fatty
acid, and finally, for example, acrylic monomers
which contain amino or mercapto groups, for example,
t-butylaminoethyl (meth) acrylate.
Examples of monomers (C2 ) are di- and
poly-hydroxyvinyl compounds such as allyl or vinyl
ethers of polyhydric alcohols or phenols, for
example, trimethylolpropane monovinyl ether,
trimethylol propane monoallyl ether, pentaerythritol
monovinyl or monoallyl ether, esters of polyhydric
alcohols with unsaturated carboxylic acids, for
example, trimethylolpropane mono (meth) acrylate or
glycerol mono (meth) acrylate, adducts of
- 213762i
unsaturated carboxylic acids such as
(meth)acrylic acid, itaconic acid or vinylacetic
acid with diepoxides, for example, bisphenol A
diglycidyl ether or hexanediol diglycidyl ether, and
adducts of dicarboxylic acids, such as adipic acid
or terephthalic acid with glycidyl (meth)acrylates.
Appropriate vinyl compounds containing two or more
amino or mercapto groups are derived, for example,
from polyamines and unsaturated carboxylic acids,
from N-vinyl polyamines or, for example, from
unsaturated polycarboxylic acids which are
esterified with 2-mercaptopropanol, such as
bis-2-mercaptopropyl maleate.
A further component employed for preparation
of the polyurethane dispersions comprises low
molecular weight polyols (D), preferably diols,
which also contain an ionic group in the form of a
carboxyl, phosphono or sulfo group. Examples of
t h i s g r o u p o f m o n o m e r s a r e
~-C2-C10-bishydroxycarboxylic acids, such as
dihydroxypropionic acid, dimethylolpropionic acid,
dihydroxyethylpropionic acid, dimethylolbutyric
acid, dihydroxysuccinic acid, dihydroxybenzoic acid
or 3-hydroxy-2-hydroxymethylpropanesulfonic acid or
1,4-dihydroxybutanesulfonic acid. The components
(D') are analogous polyamines and polythiols
(preferably diamines and dithiols) cont~ining acid
groups, for example, diaminobenzoic acid, lysine,
dimercaptosuccinic acid and dimercap-
topropanesulfonic acid.
Prior to their reaction, these monomers can
be neutralized with a tertiary amine, such as
trimethylamine, triethylamine, dimethylaniline,
2137621
diethylaniline or triphenylamine, in order to avoid
a reaction of the acid group with the isocyanate.
If the probability of such a reaction is only small,
it is also possible for the acid groups not to be
neutralized until after their incorporation into the
polyurethane macromonomer. In this case, neutral-
ization is carried out with aqueous solutions of
alkali metal hydroxides or with amines, for example,
with trimethylamine, triethylamine, dimethylaniline,
d i e t h y l a n i l i n e, t r i p h e n y l a m i n e,
dimethylethanolamine, aminoethylpropanol,
dimethylaminomethylpropanol, dimethyliso-
propanolamine or with ammonia. In addition, the
neutralization can also be undertaken with mixtures
of amines and ammonia.
Examples of suitable polyisocyanates (B) are
trimethylene diisocyanate, tetramethylene
diisocyanate, pentamethylene diisocyanate,
hexamethylene diisocyanate, propylene diisocyanate,
ethylene diisocyanate, 2, 3-dimethylbutylene
diisocyanate, 1-methyltrimethylene diisocyanate,
1,3-cyclopentylene diisocyanate, 1,4-cyclohexylene
diisocyanate, 1,2-cyclohexylene diisocyanate,
1, 3-phenylene diisocyanate, 1, 4-phenylene
diisocyanate, 2, 4-tolylene diisocyanate,
2, 6-tolylene diisocyanate, 4, 4 ~-biphenylene diiso-
cyanate, 1,5-naphthylene diisocyanate,
1,4-naphthylene diisocyanate, 1-isocyanatomethyl-
5 - i socyanato- 1, 3, 3 -trimethylcyclohexane,
bis (4-isocyanatocyclohexyl) -methane,
bis ( 4-isocyanatophenyl ) methane,
4, 4 ~ -diisocyanatodiphenyl ether,
2, 3-bis (8-isocyanatooctyl) -4-octyl-5-hexylcyclohe-
--16--
-
2137621
xene, tetramethylxylylene diisocyanates,
trimethylhexamethylene diisocyanates, isocyanurates
of the above diisocyanates, or allophanates of the
above diisocyanates. Mixtures of polyisocyanates
can also be employed.
It is particularly important for the
polyurethane dispersions ~b) that the macromonomers
which lead to these dispersions contain terminal
and/or lateral vinyl groups. The term "terminal
vinyl groups" refers to those vinyl groups which are
pendant at the beginning or the end of the polymer
chain. The term "lateral vinyl groups" denotes
vinyl groups which are not pendant at the beginning
or end of a polymer chain. The incorporation of
terminal vinyl groups is carried out by reacting a
prepolymer obtained by reaction of the polyols (A)
and the polyhydroxycarboxylic, polyhydroxyphosphonic
or polyhydroxysulfonic acids (D) with the
polyisocyanate (B), which contains free isocyanate
groups, with a vinyl monomer (C) of the above
mentioned type (Cl) containing a group which is
reactive toward isocyanate groups.
The incorporation of lateral vinyl groups is
carried out by addition of vinyl monomers (C2) that
contain at least two groups which are reactive
toward isocyanate as well as at least one vinyl
group.
In this context the monomers (C2) either can
be added directly to the polyhydroxy compounds (A)
prior to reaction with polyisocyanate (B) or they
can be reacted, in a separate reaction step
involving chain extension, with an isocyanto-
functional urethane macromonomer.
-17-
2137621
The macromonomers synthesized from these
monomers additionally may be modified by the
incorporation of amines, alcohols and/or
thioalcohols. For this purpose the initially-
produced intermediate, that contains terminal
isocyanate radicals, is not reacted solely with the
vinyl monomer (C), but rather this monomer is
reacted together with amines, alcohols and/or
thioalcohols. Examples of compounds which are
suitable in this respect are primary amines such as
propylamine, butylamine, pentylamine, 2-amino-
2-methylpropanol, ethanolamine and propanolamine;
secondary amines such as diethanolamine,
dibutylamine and diisopropanolamine; primary
alcohols such as methanol, ethanol, propanol,
butanol, hexanol, dodecanol and stearyl alcohol;
secondary alcohols such as isopropanol and
isobutanol, and the corresponding thioalcohols.
The preparation of the intermediates in the
first steps is carried out by the conventional
methods as are known in urethane chemistry. In
these methods the catalysts employed may be tertiary
amines such as triethylamine, dimethylbenzylamine
and diazabicyclooctane, and also dialkyltin(IV)
compounds, such as dibutyltin dilaurate, dibutyltin
dichloride and dimethyltin dilaurate. The reaction
takes place without solvent in the melt, in the
presence of a solvent, or in the presence of a so-
called reactive diluent, as disclosed below.
Suitable solvents are those that can later be
removed by distillation, examples being dioxane,
methyl ethyl ketone, methyl isobutyl ketone,
acetone, tetrahydrofuran, toluene and xylene. These
-18-
2137621
solvents can be distilled off in whole or in part
after the preparation of the polyurethane
macromonomers or after the free-radical
polymerization. In addition, the reaction also can
be carried out in a high-boiling, water-dilutable
solvent, for example, in N-methylpyrrolidone, which
then remains in the dispersion. Prior to the
process of dispersion it is also possible to add
further solvents such as glyco ethers and their
esters. Examples of suitable glycol ethers are
butylglycol, butyldiglycol, methoxypropanol,
dipropylene glycol monomethyl ether or diglycol
dimethyl ether. The reactive diluents (E) are ~
unsaturated monomers which, in the final stage, are
lS copolymerized with the macromonomers that contain
vinyl groups. Examples of such reactive diluents
are ~,~-unsaturated vinyl monomers such as alkyl
acrylates, alkyl methacrylates and alkyl crotonates,
that have 1 to 20 carbon atoms in the alkyl radical,
di-, tri- and tetraacrylates, methacrylates and
crotonates of glycols, tri- and tetrafunctional
alcohols, substituted and unsubstituted acrylamides
and methacrylamides, vinyl ethers, ~,~-unsaturated
aldehydes and ketones, vinyl alkyl ketones that have
1 to 20 carbon atoms in the alkyl radical, vinyl
ethers, vinyl esters, diesters of ~,~-unsaturated
dicarboxylic acids, styrene and styrene derivatives,
such as ~-methylstyrene.
The polyurethane macromonomers can be
prepared by a variety of routes. The first method
of preparation entails reaction of polyhydroxy
compounds ~A) with polyisocyanates (B) under the
conditions specified in the previous paragraph. The
--19--
2137G21
further monomers, namely the polyhydroxy acids (D)
or the polyamino or polymercapto acids (D') and the
vinyl monomers ~C2) which carry at least two groups
which are reactive toward isocyanate, are added to
the monomer (A) from the start. In this context,
the proportions of the reactants, especially the
polyisocyanate, are chosen so that a macromonomer
having terminal hydroxyl groups is produced. This
macromonomer, which additionally contains carboxyl,
phosphono or sulfo groups and lateral vinyl groups,
is transferred to an aqueous dispersion. It is then
polymerized via the vinyl groups, using free-radical
initiators, to form the polyurethane dispersion, the
polyurethane in this case still cont~in;ng hydroxyl
groups.
A second method of preparation corresponds to
the first procedure except that the proportions are
chosen so that a macromonomer that has terminal
isocyanate groups i8 produced. In addition, this
macromonomer also contains carboxyl, phosphono or
sulfo groups and lateral vinyl groups. The free
isocyanate groups of this macromonomer then are
reacted with primary or secondary amines, alcohols
or thioalcohols to form urea, urethane or
thiourethane groups. The macromonomer thus modified
is then likewise polymerized via the vinyl groups
using free-radical initiators.
A third method of preparation is analogous to
the second method, except that the free isocyanate
groups of the macromonomer are reacted with a vinyl
monomer (Cl) which carries a group which is reactive
toward isocyanate, if desired in a mixture with
primary or secondary amines, alcohols or
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2137621
thioalcohols. In this way, a urethane macromonomer
is obtained which has lateral and terminal vinyl
groups.
Urethane macromonomers that have only
terminal vinyl groups are obtained by reacting
polyhydroxy compounds (A), polyhydroxy acids (D)
and/or polyamino or polymercapto acids (D') and the
monomers (Cl), having a group which is reactive
toward isocyanate and a vinyl group, with the
polyisocyanates (B). In the polyaddition reaction,
the monomers (Cl) act as chain terminators. These
urethane macromonomers also can be prepared in a
plurality of reaction steps, for example, by
reacting an isocyanato-terminal urethane
macromonomer which is free from vinyl groups and
which is compo~ed of the units (A), (B) and (D)
and/or (D') with monomers (Cl).
A fifth method of preparation entails
subsequent incorporation of the polyhydroxy
acids (D) into the previously-formed urethane
macromonomer that contains isocyanate end groups.
In this method the first step is reaction of a
mixture of the polyhydroxy compounds (A) with the
polyisocyanates ~B) and with the vinyl monomers (C)
which are reactive toward isocyanate, the quantities
employed being selected so that macromonomers that
have isocyanate end groups are obtained. In the
following step these products are reacted with the
polyhydroxy acids (D) or with the polyamines or
polythiols (D') which contain acid groups.
A preferred procedure is not to incorporate
the dihydroxyvinyl compound during the polyaddition,
at the same time as the polyol, but instead first to
2137621
react a prepolymer composed solely of polyol,
polyisocyanate and, if desired, polyhydroxy acid to
give an OH- or NCO-terminal prepolymer. In a second
step this prepolymer i8 then reacted with the
dihydroxyvinyl compound and further polyisocyanate
to give the vinyl-containing, OH- or NCO-terminal
macromonomer.
In this reaction, the proportions are chosen
so that the polyisocyanate is in excess, in which
case the prepolymer formed contains not only
carboxyl, phosphono and/or sulfo groups, but also
free isocyanate groups. A preferred procedure is
initially to employ the polyisocyanate in excess, in
order to obtain a prepolymer cont~i n; ng free
hydroxyl groups. In an additional step this
prepolymer is then reacted with further polyisocya-
nate, in order likewise to obtain a prepolymer that
contains free isocyanate groups.
The macromonomers obtained by these various
routes are then neutralized, unless the acid groups
in the monomers that carry such groups were employed
in neutralized form from the start. Neutralization
is carried out with aqueous solutions of alkali
metal hydroxides or with amines, for example, with
trimethylamine, triethylamine, dimethylaniline,
d i e t h y l a n i l i n e , t r i p h e n y l a m i n e ,
dimethylethanolamine, aminomethylpropanol,
dimethylaminomethylpropanol, dimethylisopropanol-
amine or with ammonia. Neutralization also can be
undertaken with mixtures of amines and ammonia.
In order to prepare the polyurethane
dispersions (b), macromonomers that contain vinyl
groups are transferred by addition of water to an
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2137621
aqueous dispersion and are polymerized using methods
known per se by means of free-radical initiator
systems. In this polymerization it is possible to
incorporate monomers of this kind as described
above, if not present from the start in the form of
so-called reactive diluents (E), by polymerization
into the polyurethane. It is also possible to add
carboxyl-, hydroxy-, amino-, ether- and mercapto-
functional ~,~-unsaturated vinyl monomers directly
before or during the free-radical polymerization.
Examples of such monomers include hydroxyethyl
(meth)acrylate, hydroxypropyl (meth)acrylate,
(meth)acrylic acid, crotonic acid, glycidyl
methacrylate, t-butylaminoethyl methacrylate or
dimethylaminoethyl methacrylate. The content of
copolymerized vinyl monomers preferably is from 0 to
95% by weight, preferably from 5 to 70% by weight,
based on the solids content of the polyurethane
dispersion. The ratio of soft to hard segments in
the polyurethane macromonomers preferably is from
0.30 to 6, particularly preferably from 0.8 to 3.
Suitable initiators for the polymerization include
known free-radical initiators, such as ammonium
peroxodisulfate, potassium peroxodisulfate, sodium
peroxodisulfate, hydrogen peroxide, organic
peroxides such as cumene hydroperoxide, t-butyl
hydroperoxide, di-tert-butyl peroxide, dioctyl
peroxide, tert-butyl perpivalate, tert-butyl
perisononanoate, tert-butyl perethylhexanoate,
tert-butyl perneodecanoate, di-2-ethylhexyl
peroxodicarbonate and diisotridecyl peroxodicar-
bonate, and also azo compounds such as
azobis(isobutyronitrile), azobis~4-cyanovaleric
-23-
2137621
acid), or the customary redox systems, for example,
sodium sulfite, sodium dithionite, ascorbic acid and
organic peroxides or hydrogen peroxide, if desired
in conjunction with accelerators such as iron salts
or cerium salts. It is also possible to add
regulators (thiols), emulsifiers, protective
colloids and other conventional auxiliaries.
If the preparation of the macromonomer was
carried out in a solvent which can be removed by
distillation and which forms an azeotrope with water
or can be removed by fractionation from the aqueous
phase, for example, in acetone, dioxane, methyl
ethyl ketone, methyl isobutyl ketone,
tetrahydrofuran, toluene or xylene, then this
solvent is removed from the dispersion by
distillation. In every case an aqueous polyurethane
dispersion is obtained.
The acid numbers of these polyurethanes
preferably are within the range from 5 to 80,
particularly preferably in the range from 10 to 40,
mg of ROH per g of solid resin. The hydroxyl
numbers of these polyurethanes preferably are within
the range from 5 to 150, and more preferably from 10
to 120, mg of ROH per g of solid resin.
Further details on the preparation of the
macromonomers and their polymerization to give the
polyurethane dispersions according to the invention
are evident from the following general process
descriptions. These process conditions represent
preferred embodiments. In addition, all documents
mentioned in this application are incorporated by
reference herein in their entirety.
-
2137621
1. æolvent-free polyurethane dispersion
a. pro~ ~ithout a--Y; 1; ary solvents
At temperatures of from 100 to 150C, prefer-
ably from 120 to 135C, the polyhydroxy acid (D)
and, if desired, low molecular weight polyols (A4)
are dissolved in a polyol (A) having an average
molecular weight of from 400 to 5000 and are reacted
with a polyi~ocyanate (B) or a mixture of
polyisocyanates to give an OH-terminal product that
has an average molar mass (Mn) of from 500 to
12,000, particularly preferably from 600 to 8000.
After the reaction mixture has been cooled to a
temperature of from 30 to 100C, preferably from 50
to 80C, a vinyl monomer (E) which is not iso-
cyanate-reactive is added. Further polyisocyanate
is added at this temperature to produce an NCO-
terminal resin which is subsequently reacted with an
NCO-reactive vinyl compound (Cl and/or C2) to give
a polyurethane macromonomer having an average molar
mass of from 700 to 24,000, preferably from 800 to
16,000, g/mol. If desired, amines, alcohols or
thiols are also added at this point, which react
with any isocyanate groups still present to form
terminal urea, urethane or thiourethane groups. The
resin solution obtained in this way is neutralized
with amines or other bases and then dispersed in
water. Further vinyl comonomers (E) can be added to
the resulting dispersion before or during the free-
radical polymerization which follows. The free
vinyl compound is then polymerized in the aqueous
dispersion using free-radical initiators at a
temperature of from O to 95C, preferably from 40 to
95C, or at a temperature of from 30 to 85C if
-25-
-
2137621
redox systems are used. This produces a solvent-
free polyurethane dispersion.
b. pro~ e~ with al-Y;1iary ~olvent
In contrast to method l.a., in this case all
of the polyol components (A), (D) are dissolved in
a solvent which can be fractionated from the aqueous
phase or which forms an azeotrope with water, and
are reacted directly with polyisocyanate (B) or
mixtures of polyisocyanates to give the NCO-terminal
product. The content of solvent is between 1 and
80% by weight, preferably between 10 and 50% by
weight, based on the solids content of the
polyurethane macromonomer. The temperature for this
step is between 30 and 100C, preferably between 50
and 80C. After the reaction with an isocyanate-
reactive vinyl compound (C1 and/or C2) to give a
polyurethane macromonomer that has a molar mass of
from 500 to 30,000, preferably from 700 to 20,000,
g/mol, amines, alcohols or thiols are added, if
desired, which react with any isocyanate groups
still present to form terminal urea, urethane or
thiourethane groups. The resin solution obtained in
this way is neutralized with amines or other bases
and then dispersed in water. The auxiliary solvent
is subsequently distilled off from the aqueous
pha~e, possibly under a slight vacuum. Vinyl
comonomers (E) can be added to this solvent-free
dispersion before or during the free-radical
polymerization which follows. Polymerization is
subsequently carried out with free-radical
initiators at a temperature of between 0 and 95C,
particularly preferably between 40 and 95C, or
-26-
2137621
using Redox systems at a temperature of between 30
and 85C, to give a solvent-free polyurethane
dispersion.
2 . 801vent-contai ni n~ polyurethane dispersion
When a non-distillable auxiliary solvent such
as N-methylpyrrolidone is used, the procedure is
exactly as in method l.b. except that distillation
after the dispersion is omitted and, if desired,
vinyl monomers (E) can be added before or during the
free-radical polymerization. The polymerization is
carried out as in method l.b. The content of
solvent is in the range from 0.1 to 30% by weight,
particularly preferably from 1 to 15% by weight,
based on the overall binder dispersion.
The content of polyurethane resin (b)
(calculated as solids) in the aqueous coating
composition is generally from 5 to 40% by weight,
preferably from 15 to 30% by weight, based on the
overall coating composition.
In addition to the polyurethane resin, the
agueous coating composition also may contain, as a
binder, up to 60% by weight, preferably up to 30% by
weight, based on the polyurethane resin, of other
oligomeric or polymeric materials, such as water-
soluble or water-dispersible phenolic resins,
polyester resins, epoxy resins, melamine resins or
acrylic resins, etc., as described, for example, in
EP-A 089 497.
In order to prepare a ready-to-use coating
compositions the polyisocyanate component (a) is
emulsified in the aqueous dispersion/solution of the
polyurethane resin (b), the dissolved or dispersed
-
2137621
polyurethane resin taking on the function of an
emulsifier for the added polyisocyanate ~a).
Nixing can be effected simply by stirring at
room temperature. Preferably, however, a suitable
apparatus is used in order to achieve very highly
homogenous mixing of components ~a) and (b),
examples of such apparatus being high-speed-Qtirrers
or high-speed dispersion units. Also suitable are
the units known to those skilled in the art for two-
component application, in which both components are
mixed by means of appropriate mixing chambers
shortly before application. In this case the
quantity of the polyisocyanate component i8
calculated so as to result in a ratio of NCO/OH
equivalents, based on the isocyanate groups of
component ~a) and the alcoholic hydroxyl groups of
component (b), of from 0.5:1 to 5:1, preferably from
0.8:1 to 4:1.
Prior to the addition of the polyisocyanate
component (a) it is possible to incorporate the
conventional auxiliaries and additives of paint
technology into the polyurethane resin dispersion
(b) of the polymers. Examples of such auxiliaries
and additives include antifoams, leveling agents,
slip agents, wetting agents, dispersion auxiliaries,
organic and inorganic fillers and pigments, organic
and inorganic acids and baQes, protective colloids,
emulsifiers, preservatives, etc.
The coating compositions according to the
invention which are obtained in this way are
suitable for virtually all applications in which
solvent-cont~;n;ng, solvent-free or other kinds of
aqueous paint or coating systems having an improved
-28-
-
2137621
profile of properties are desired. The substrates
to be coated include, for example, metal, such as
iron and also nonferrous metals, mineral materials
such as lime, cement or plaster, fiber-cement
building materials, concrete, wood or wood
materials, paper, asphalt, bitumen, plastics of
various kinds, composite materials, glass, ceramic,
textiles or leather. The metallic substrates are
preferably automobiles and rail-bound vehicles. The
coating compositions according to the invention are,
for example, sealers, primers, fillers or pigmented
or transparent topcoats and/or clearcoats.
The coating compositions according to the
invention can be applied by any methods known to
lS those skilled in the art, for example, by brushing,
rolling, flow-coating, knife-coating, dipping and,
in particular, by spraying. It is possible to
employ a very wide variety of spraying methods, such
as pressurized-air spraying, airless, air-mix or
electrostatic spraying and using 1- or 2-component
spraying units.
The drying and/or curing of the binder
combinations according to the invention or of the
coatings based thereon is/are carried out for a
sufficiently long time at temperatures of 10 -
250C, preferably 10 - 100C.
The invention is illustrated in more detail
by the examples given below:
Example 1:
An amount of 252.0 g of a polyester prepared
from 1,6-hexanediol, isophthalic acid, adipic acid
and dodecenylsuccinic anhydride and having a
- 2137621
hydroxyl number of 84 and an acid number of less
than 2, together with 50.2 g of dimethylolpropionic
acid, are heated to 130C and maintained at this
temperature until a homogenous solution is obtained.
Subsequently 106.0 g of tetramethylxylylene
diisocyanate are metered in with stirring over a
period of from 20 to 25 minutes and stirring is
continued at 130C until no further free isocyanate
groups are present. After the mixture has been
cooled to 70C, 2.5 g of 1,4-butanediol, 11.8 g of
glycerol methacrylate, 131.3 g of methylmethacrylate
and 0.3 g of 2,6-di-tert-butyl-4-methylphenol are
quickly added and the mixture is homogenized.
Thereafter 81.6 g of tetramethylxylylene
diisocyanate are metered in over a period of 20
minutes and the mixture is reacted at 70C until the
content of free isocyanate groups i8 1. 39% by
weight, based on the weight of all the components.
Diethanolamine (21.6 g) is added quickly to the
resulting prepolymer solution, which is homogenized
for 10 minutes. Following the metered addition of
28.4 g of triethylamine, 15.9 g of methyl
methacrylate at 28.0 g of 2-hydroxyethyl
methacrylate, 1087.6 g of water at a temperature of
70C are added to the prepolymer solution with
intensive stirring. The temperature subsequently is
raised to 80C and 0.7 g of tert-butyl hydroperoxide
(80% strength in di-tert-butyl peroxide) are quickly
added dropwise. After a further 30 minutes a
solution of 1.3 g of ascorbic acid in 130 g of water
is metered in over a period of 90 minutes. The
temperature is maintained at 80C for a further
hour.
-30-
- 2137621
The resulting polyurethane-acrylic hybrid
dispersion is cooled to room temperature and
filtered through a 5 ~m filter cloth. The
dispersion has a solids content of 36% and a pH of
7Ø
Bxample 2:
An amount of 252.0 g of a polyester prepared
from 1,6-hexanediol, isophthalic acid, adipic acid
and dodecenylsuccinic anhydride and having a
hydroxyl number of 84 and an acid number of below 2,
together with 50.2 g of dimethylolpropionic acid,
are heated to 130C and maintained at this
temperature until a homogenous solution is obtained.
Subsequently 106.0 g of tetramethylxylylene
diisocyanate are metered in with stirring over a
period of from 20 to 25 minutes and stirring is
continued at 130C until no further free isocyanate
groups are present. After the mixture has been
cooled to 70C, 2.5 g of 1,4-butanediol, 11.8 g of
glycerol methacrylate, 131.3 g of methylmethacrylate
and 0.3 g of 2,6-di-tert-butyl-4-methylphenol are
quickly added and the mixture is homogenized.
Thereafter 81.6 g of tetramethylxylylene
diisocyanate are metered in over a period of 20
minutes and the mixture is reacted at 70C until the
content of free isocyanate groups is 1.39% by
weight, based on the weight of all the components.
Diethanolamine (21.6 g) is added quickly to the
resulting prepolymer solution, and the mixture is
homogenized for 10 minutes. Following the metered
addition of 28.4 g of triethylamine, 22.9 g of
methyl methacrylate, 7.0 g of methacrylic acid and
2137621
14.0 g of 2-hydroxyethyl methacrylate, 1087.6 g of
water at a temperature of 70C are added to the
prepolymer solution with intensive stirring. The
temperature is subsequently raised to 80OC and 0.7 g
of tert-butyl hydroperoxide ~80% strength in di-
tert-butyl peroxide) are quickly added dropwise.
After a further 30 minutes a solution of 1.3 g of
ascorbic acid in 130 g of water is metered in over
a period of 90 minutes. The temperature is
maintained at 80C for a further hour.
The resulting polyurethane-acrylic hybrid
dispersion is cooled to room temperature and
filtered through a 5 ~m filter cloth. The
dispersion has a solids content of 36% and a pH
of 6.7.
~xample 3:
An amount of 261.0 g of a polyester prepared
from neopentyl glycol, l,6-hexanediol, isophthalic
acid and adipic acid and having a hydroxyl number of
41 and an acid number of less than 2, with 43.0 g of
dimethylolpropionic acid, 3.5 g of 1,6-hexanediol
and 120.5 g of N-methyl-2-pyrrolidone, are heated to
80C. 8ubsequently 119.1 g of isophorone
diisocyanate are metered in with stirring over a
period of from 25 to 30 minutes and the mixture is
stirred at 80C until the content of free isocyanate
groups is 1.38% by weight, based on the total weight
of all the components. 2-hydroxyethyl methacrylate
(23.4 g) and 0.2 g of 2,6-di-tert-butyl-
4-methylphenol are added to the resulting prepolymer
solution. Reaction is carried out until there are
no more free isocyanate groups present. After
-32-
- - 2137621
addition of 99.7 g of methyl methacrylate, 33.2 g of
2-ethylhexyl acrylate and 60.0 g of 2-hydroxyethyl
methacrylate and following a 5-minute homogenization
phase, the mixture is neutralized with 24.4 g of
triethylamine. Water (1091.8 g) at a temperature of
75C is then added to the prepolymer solution with
intensive stirring. Subsequently, at a temperature
of 80C, 0.7 g of tert-butyl hydroperoxide (80%
strength in di-tert-butyl peroxide) are quickly
added dropwise. After a further 30 minutes a
solution of 1.3 g of ascorbic acid in 130.0 g of
water is metered in over a period of 90 minutes.
The resulting polyurethane-acrylic hybrid
dispersion is cooled to room temperature and
filtered through a 5 ~m filter cloth. The
dispersion has a solids content of 32% and a Ph
of 7.1.
Acrylic polyurethane dispersions prepared in
accordance with Examples 1 to 3, in combination with
a commercial polyisocyanate curing agent (Desmodur~
VPLS 2032 from Bayer AG, a water-emulsifiable
aliphatic polyisocyanate based on hexamethylene
diisocyanate), were tested with regard to their
properties in a clear coat formulation. The
comparison substance used was a commercial, nonacry-
lic OH-functional polyurethane dispersion (Daotan~
VTW 1225 from Hoechst AG).
Application Example 1.1:
one part by weight of a commercial levelling
agent (Additol~ XW 390 from Hoechst AG), 5 parts by
weight of butyl glycol and 3.5 parts by weight of
213762~
deionized water are added with thorough stirring to
80.5 parts by weight of a polyurethane dispersion
according to Example 1. Shortly before application
the batch is mixed with the curing agent solution,
comprising 14.5 parts by weight of Desmodur~ VPLS
2032, 2.5 parts by weight of butyl acetate and 0.9
part by weight of white spirit, using a high-speed
stirrer, and is then ready for application.
Application Example 2.1:
One part by weight of a commercial levelling
agent (Additol~ XW 390 from Hoechst AG), 5 parts by
weight of butyl glycol and 3.5 parts by weight of
deionized water are added with thorough stirring to
80.5 parts by weight of a polyurethane dispersion
according to Example 2. Shortly before application
the batch is mixed with the curing agent solution,
comprising 14.5 parts by weight of Desmodur~ VPLS
2032, 2.5 parts by weight of butyl acetate and 0.9
part by weight of white spirit, using a high-speed
stirrer, and is then ready for application.
Application Example 3.1:
one part by weight of a commercial levelling
agent (Additol~ XW 390 from Hoechst AG), 5 parts by
weight of butyl glycol and 3.5 parts by weight of
deionized water are added with thorough stirring to
80.5 parts by weight of a polyurethane dispersion
according to Example 3. 8hortly before application
the batch is mixed with the curing agent solution,
comprising 12.9 parts by weight of Desmodur~ VPLS
2032, 2.2 parts by weight of butyl acetate and 0.8
2137621
part by weight of white spirit, using a high-speed
stirrer, and is then ready for application.
Comparative application example:
one part by weight of a commercial levelling
agent (Additol~ XW 390 from Hoechst AG), 5.2 parts
by weight of butyl acetate and 5.6 parts by weight
of deionized water are added with thorough stirring
to 86.2 parts by weight of the OH-functional,
nonacrylic polyurethane dispersion Daotan~ VTW 1225
~Hoechst AG). Shortly before application the batch
is mixed with the curing agent solution, comprising
17.3 parts by weight of Desmodur~ VPLS 2032, 3.3
parts by weight of butyl acetate and 1.1 parts by
weight of white spirit, using a high-speed stirrer,
and is then ready for application.
The finished clearcoat formulations were
applied to glass panels and polycarbonate panels,
respectively, at a wet-film thickness of 150 ~m
(corresponding to a dry-film thickness of
approximately 30 to 40 ~m), and the panels were
flashed off at room temperature for 10 min and then
dried at 80C for 30 min and then at 60C for 16 h.
After the coatings had cooled, the following
properties were tested (results are given in Table
1):
- general appearance of the coating, by
subjective assessment
- adhesion to the substrate with crosshatch
in accordance with DIN 53 151
- - 213762i
- pendulum hardness according to Ronig, in
accordance with DIN 53 157
- resistance to selected solvents (columns 6
through 10), the value given being the period
of action after which the coatings are soft
and no longer scratch-resistant
- resistance to selected chemicals (columns
11 and 12), the period of action being 16 h:
the following evaluation scale was used:
- satisfactory = no attack
- largely satisfactory = slight attack
but coating still intact
- not satisfactory = coating very
heavily attacked or completely
destroyed.
2137621
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