U.S. patent application number 09/727136 was filed with the patent office on 2001-07-05 for aqueous coating composition.
Invention is credited to Dworak, Gert, Kuttler, Ulrike.
Application Number | 20010006994 09/727136 |
Document ID | / |
Family ID | 3529293 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006994 |
Kind Code |
A1 |
Dworak, Gert ; et
al. |
July 5, 2001 |
Aqueous coating composition
Abstract
Coating composition especially for preparing automotive
surfacers, comprising an anionically stabilized resin, preferably a
condensation product A of a carboxyl group-containing resin A1 and
a hydroxyl group-containing resin A2, and a curing agent C, which
becomes active even at room temperature or slightly elevated
temperature of up to not more than 120.degree. C., and comprises a
mixture of an unblocked isocyanate C1 and a hydrophilic partially
etherified amino resin C2.
Inventors: |
Dworak, Gert; (Graz, AT)
; Kuttler, Ulrike; (Vasoldsberg, AT) |
Correspondence
Address: |
Dougherty & Clements
Suite 400
6230 Fairview Road
Charlotte
NC
28210
US
|
Family ID: |
3529293 |
Appl. No.: |
09/727136 |
Filed: |
November 30, 2000 |
Current U.S.
Class: |
525/123 |
Current CPC
Class: |
C08L 2666/14 20130101;
C09D 175/04 20130101; C09D 175/04 20130101; C09D 201/08
20130101 |
Class at
Publication: |
525/123 |
International
Class: |
C08F 008/30; C08L
075/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 1999 |
AT |
A 2173/99 |
Claims
What is claimed is:
1. A coating composition comprising a condensation product A of a
carboxyl group-containing resin A1 and a hydroxyl group-containing
resin A2, and a curing agent C which becomes active already at
temperatures below 120.degree. C., wherein said curing agent
comprises a mixture of a water-insoluble unblocked isocyanate C1
and a hydrophilic partially etherified amino resin C2.
2. The coating composition as claimed in claim 1, wherein a
carboxyl group-containing resin A1 is replaced by a resin selected
from resins Ae, namely epoxy resins modified with phosphoric acid
or phosphonic acids and reaction products of epoxy resins with
fatty acids that are modified with phosphoric acid or phosphonic
acids, and resins Ap, namely polyesters containing excess acid
groups.
3. The coating composition as claimed in claim 1 or 2, wherein the
component A has an acid number of from 25 to 75 mg/g.
4. The coating composition as claimed in claim 1 or 2, wherein the
component A1 has an acid number of from 100 to 230 mg/g.
5. The coating composition as claimed in claim 1 or 2, wherein the
component A2 has an acid number of from 50 to 500 mg/g.
6. The coating composition as claimed in claim 1 or 2, wherein the
curing agent C is a mixture of mass fractions of from 65 to 95% of
a water-insoluble unblocked polyfunctional isocyanate C1 and from 5
to 35% of a water-dilutable partially etherified and partially
methylolated amino resin C2.
7. The coating composition as claimed in claim 1 or 2, wherein the
curing agent C2 is a partially etherified and partially
methylolated amino resin containing on average from 3 to 5
alkoxymethyl groups per triazine ring.
8. The coating composition as claimed in claim 1 or 2, wherein the
curing agent C1 has a viscosity at 23.degree. C. of from 50 to
20,000 mPa.s.
9. The coating composition as claimed in claim 1 or 2, wherein from
60 to 95% of the carboxyl groups of the resins A have been
neutralized.
10. A process for preparing a coating composition as claimed in
claim 1 or 2, which comprises preparing from the carboxyl
group-containing resins A1 and/or A16 and from the hydroxyl
group-containing resins A2, and the polycondensation conditions, a
resin A whose remaining carboxyl groups are neutralized to the
extent of from 60 to 95%, dispersing the neutralized resin A in
water, and mixing the aqueous dispersion with the curing agent C
prior to application.
11. The use of a coating composition as claimed in claim 1 or 2 to
produce surfacer films on metallic substrates.
Description
BACKGROUND OF THE INVENTION
[0001] 1, Field of the Invention
[0002] The invention relates to an aqueous coating composition
suitable in particular for producing coatings on automobile parts.
The parts thus coated, especially those where the coating
composition described here is used as surfacer coat, are notable
for high hardness and freedom from defects of the coating film and
for high stone-chip resistance.
[0003] 2. Description of the Related Art
[0004] EP-A 0 594 685 relates to the use of condensation products
of carboxyl group-containing polyurethane resins and hydroxyl
group-containing polyester resins, with or without urethane
modification, together with water-insoluble blocked isocyanates for
producing stoving enamels. An improvement of this formulation with
reduced sensitivity to so-called overbaking is known from EP-A 0
548 873, the improvement being achieved by adding a water-soluble
amine resin as crosslinker.
[0005] All of these known systems must be cured by heating to
temperatures at which either the blocked isocyanate curing agent is
at least partly deblocked and so becomes active or the amino resin
curing agents exhibit sufficient (crosslinking) reactivity. The
object was therefore to provide aqueous coating compositions which
are suitable, inter alia, for producing surfacer coats in
automotive finishing and which cure even at room temperature or
only slightly elevated temperature (up to 120.degree. C.,
preferably up to 100.degree. C., and in particular up to not more
than 90.degree. C.) to give paint films having properties at least
equal to those of the prior art.
SUMMARY OF THE INVENTION
[0006] It has now been found that by using a combination of
water-insoluble unblocked isocyanates and water-soluble or
water-dispersible, partly etherified amino resins as curing agents
together with anionically stabilized, hydroxyl group-containing
resins, especially condensation products of hydroxyl
group-containing and carboxyl group-containing resins, it is
possible to obtain coating compositions which, compared to the
known systems, exhibit, after curing, defect-free films, a higher
film hardness and good stone-chip resistance even at low
temperatures.
[0007] The invention therefore provides a coating composition
comprising
[0008] an anionically stabilized, hydroxyl group-containing resin
A,
[0009] and
[0010] a curing agent C comprising a water-insoluble unblocked
isocyanate C1 and a hydrophilic partly etherified amino resin
C2.
[0011] The term "anionically stabilized" here is intended to denote
that the resin in question has acid groups in an amount sufficient
such that, with at least partial neutralization of the acid groups
by addition of alkali in a mixture with water, a solution
(single-phase mixture) or a dispersion (multiphase mixture) is
formed which does not undergo separation spontaneously or on
storage at room temperature for at least 7 days.
[0012] "Water-insoluble" is a term used to refer to those compounds
for which, following the achievement of equilibrium at 20.degree.
C. with an amount of water the mass of which is ten times that of
the compound in question, less than 5% of the mass of the compound
that is used is present in solution in the aqueous phase.
[0013] Further objects, features and advantages of the invention
will become apparent from the detailed description of the preferred
embodiments that follows.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Preferably, the anionically stabilized, hydroxyl
group-containing resin A is a condensation product Ak of a resin A1
containing acid groups and a resin A2 containing hydroxyl groups,
A1 preferably having an acid number of from 100 to 230 mg/g, in
particular from 120 to 160 mg/g, and A2 preferably having a
hydroxyl number of from 50 to 500 mg/g, in particular from 60 to
350 mg/g.
[0015] The acid number is defined in accordance with DIN 53 402 as
the ratio of the mass m.sub.KOH of potassium hydroxide required to
neutralize the sample under analysis to the mass m.sub.B of this
sample (mass of the solids in the sample in the case of solutions
or dispersions); its customary unit is "mg/g". The hydroxyl number
is defined in accordance with DIN 53 240 as the ratio of that mass
m.sub.KOH of potassium hydroxide which has exactly the same number
of hydroxyl groups as the sample under analysis to the mass m.sub.B
of this sample (mass of the solids in the sample in the case of
solutions or dispersions); its customary unit is "mg/g".
[0016] The condensation product Ak preferably has an acid number of
from 25 to 75 mg/g, in particular from 30 to 50 mg/g. Its
Staudinger Index ("limiting viscosity number") is usually from 10
to 20 cm.sup.3/g, in particular from 12 to 19 cm.sup.3/g, and with
particular preference from 13 to 18 cm.sup.3/g. It is prepared
using components A1 and A2 preferably in a mass ratio of from 10:90
to 80:20, in particular from 15:85 to 40:60.
[0017] The formerly so-called "limiting viscosity number", called
"Staudinger Index" J.sub.g in accordance with DIN 1342, Part 2.4,
is the limiting value of the Staudinger function J.sub.v at
decreasing concentration and shear stress, J.sub.v being the
relative change in viscosity based on the mass concentration
.beta..sub.B=m.sub.B/V of the dissolved substance B (with the mass
m.sub.B of the substance in the volume V of the solution); i.e.,
J.sub.v=(.eta..sub.r-1)/.beta..sub.B. Here, .eta..sub.r-1 is the
relative change in viscosity, in accordance with
.eta..sub.r-1=(.eta.-.eta..sub.s)/.eta..sub.s. The relative
viscosity .eta..sub.r is the ratio of the viscosity .eta. of the
solution under analysis and the viscosity .eta..sub.s of the pure
solvent. (The physical definition of the Staudinger Index is that
of a specific hydrodynamic volume of the solvated polymer coil at
infinite dilution and in the state of rest.) The unit commonly used
for J is "cm.sup.3/g"; formerly often "dl/g".
[0018] The resins A1 containing carboxyl groups are preferably
selected from polyester resins A11, polyurethane resins A12, the
so-called maleate oils A13, the graft products A14 of fatty acids
and fatty acid mixtures grafted with unsaturated carboxylic acids,
and the acrylate resins A15. Instead of or in a mixture with resins
containing carboxyl groups, it is also possible to use epoxy resins
modified with phosphoric acid and/or phosphonic acids, or similarly
modified reaction products of epoxy resins with fatty acids,
referred to comprehensively as A16.
[0019] Preferably, the acid number of the resins A1 is from 100 to
230 mg/g, in particular from 70 to 160 mg/g. Its Staudinger Index,
measured in dimethylformamide as solvent at 20.degree. C., is
generally from about 6.5 to 12 cm.sup.3/g, preferably from 8 to 11
cm.sup.3/g.
[0020] Suitable polyester resins A11 may be prepared in a
conventional manner from polyols A111 and polycarboxylic acids
A112, where also some--preferably up to 25% of the amount of
substance--of the polyols and polycarboxylic acids can be replaced
by hydroxycarboxylic acids A113. By appropriate choice of the
nature and amount of the starting materials A111 and A112 it is
ensured that the resulting polyester has a sufficient number of
acid groups, in accordance with the acid number indicated above.
The polyols A111 are preferably selected from aliphatic and
cycloaliphatic alcohols having 2 to 10 carbon atoms and on average
at least two hydroxyl groups per molecule; glycol, 1,2- and
1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol,
di- and triethylene glycol, di- and tripropylene glycol, glycerol,
trimethylolpropane and trimethylolethane are particularly suitable.
Suitable polycarboxylic acids A112 are aliphatic, cycloaliphatic
and aromatic polycarboxylic acids such as adipic acid, succinic
acid, cyclohexanedicarboxylic acid, phthalic acid, isophthalic and
terephthalic acids, trimellitic acid, trimesic acid and
benzophenonetetracarboxylic acid. It is also possible to use
compounds having both carboxylic acid groups and sulfonic acid
groups, such as sulfoisophthalic acid, for example.
[0021] Suitable polyurethane resins A12 may be prepared by reacting
aliphatic polyols A121, as defined under A111,
hydroxyalkanecarboxylic acids A122 having at least one, preferably
two, hydroxyl groups and a carboxyl group which under
esterification conditions is less reactive than those of adipic
acid; preference is given to the use of dihydroxymonocarboxylic
acids selected from dimethylolacetic acid, dimethylolbutyric acid
and dimethylolpropionic acid; oligomeric or polymeric compounds
A125 having on average at least two hydroxyl groups per molecule,
which may be selected from polyether polyols A1251, polyester
polyols A1252, polycarbonate polyols A1253, saturated and
unsaturated dihydroxy-aliphatic compounds A1254, which are
obtainable by oligomerizing or polymerizing dienes having 4 to 12
carbon atoms, especially butadiene, isoprene and dimethylbutadiene,
followed by functionalization in a known manner, and also
polyfunctional isocyanates A123, selected preferably from aromatic,
cycloaliphatic and also linear and branched aliphatic difunctional
isocyanates such as tolylene diisocyanate,
bis(4-isocyanatophenyl)methane, tetramethylxylylene diisocyanate,
isophorone diisocyanate, bis(4-isocyanatocyclohexyl)methane- ,
hexamethylene diisocyanate and 1,6-diisocyanato-3,3,5- and
-3,5,5-trimethylhexane.
[0022] Particular preference is given to those polyurethane resins
A12 which are prepared by reacting a mixture of one or more polyols
A121 with a hydroxyalkanecarboxylic acid A122 and at least one
polyfunctional isocyanate A123 which has been at least partly
blocked, usually to the extent of more than 20%, preferably to the
extent of more than 35% and, in particular, to the extent of 50% or
more with monohydroxy compounds A124 selected from polyalkylene
glycol monoalkyl ethers HO--(R.sup.1--O).sub.n--R.sup.2, where
R.sup.1 is a linear or branched alkylene radical having 2 to 6,
preferably 2 to 4 carbon atoms and R.sup.2 is an alkyl group of
from 1 to 8, preferably 2 to 6 carbon atoms and oximes of aliphatic
ketones having 3 to 9 carbon atoms. The degree of blocking is
stated here as the fraction of the blocked isocyanate groups, based
on the total isocyanate groups present (blocked and unblocked) in
the isocycanate A123. It is further preferred to prepare the
polyurethane resins A12 by reacting a mixture of a polyfunctional
isocyanate and a polyfunctional isocyanate blocked as described
above with the hydroxyalkanecarboxylic acid A122 and the polyols
A121 and A125, the proportions in the mixture being chosen so that
each molecule of the polyurethane A12 contains on average one or
more than one terminal blocked isocyanate group.
[0023] "Maleate oil" A13 is a term used to denote reaction products
of (drying) oils A131 and olefinically unsaturated carboxylic acids
A132, especially dicarboxylic acids. Oils used as A131 are
preferably drying and semidrying oils such as linseed oil, tallow
oil, rapeseed oil, sunflower oil and cottonseed oil, having iodine
numbers of from about 100 to about 180. The unsaturated carboxylic
acids A132 are selected so that under the customary conditions they
graft under free-radical conditions (following addition of
initiators or following heating) onto the initial charge of oils
with a yield (fraction of the unsaturated carboxylic acids bonded
to the oil after reaction, based on the amount used for the
reaction) of more than 50%. Particularly suitable is maleic acid in
the form of its anhydride, as are tetrahydrophthalic anhydride,
acrylic and methacrylic acid, and also citraconic, mesaconic and
itaconic acid.
[0024] Other suitable resins A14 are the graft products of fatty
acids or fatty acid mixtures A141 grafted with the unsaturated
acids specified under A132, said fatty acids or fatty acid mixtures
A141 being obtainable in industrial amounts by saponification of
fats. The appropriate fatty acids have at least one olefinic double
bond in the molecule; those which may be listed by way of example
include oleic acid, linoleic and linolenic acid, ricinoleic acid
and elaidic acid, and also the stated technical-grade mixtures of
such acids.
[0025] Further suitable resins A15 are the acidic acrylate resins
obtainable by copolymerization of olefinically unsaturated
carboxylic acids A151 and other vinyl or acrylic monomers A152. The
carboxylic acids are those already mentioned under A132, and also
vinylacetic acid and crotonic and isocrotonic acid and the
monoesters of olefinically unsaturated dicarboxylic acids, such as
monomethyl maleate and monomethyl fumarate, for example. Suitable
monomers A152 are the alkyl esters of acrylic and methacrylic acid
having preferably from 1 to 8 carbon atoms in the alkyl group,
(meth)acrylonitrile, hydroxyalkyl (meth)acrylates having 2 to 6
carbon atoms in the alkyl group, styrene, vinyltoluene, and vinyl
esters of aliphatic linear and branched carboxylic acids having 2
to 15 carbon atoms, especially vinyl acetate and the vinyl ester of
a mixture of branched aliphatic carboxylic acids having on average
9 to 11 carbon atoms. It is also advantageous to copolymerize the
monomers specified under A151 and A152 in the presence of compounds
A153 which react with the unsaturated carboxylic acids with
addition and formation of a carboxyl- or hydroxyl-functional,
copolymerizable compound. Examples of such compounds are lactones
A1531, which react with the carboxylic acids A151 with ring opening
to form a carboxyl-functional unsaturated compound, and epoxides
A1532, especially glycidyl esters of .alpha.-branched saturated
aliphatic acids having 5 to 12 carbon atoms, such as of neodecanoic
acid or neopentanoic acid, which react with the acid A151 in an
addition reaction to give a copolymerizable compound containing a
hydroxyl group. The amounts of substance of the compounds used
should be such that the required acid number is reached. If this
compound A153 is introduced as the initial charge and the
polymerization is conducted so that this compound is used as (sole)
solvent, solvent-free acrylate resins are obtained.
[0026] The epoxy resins modified with phosphoric acid or phosphonic
acids or the adducts of epoxy resins and fatty acids, modified in
the same way, referred to comprehensively as A16, are prepared by
reacting phosphoric acid or organic phosphonic acids which are at
least dibasic with epoxy resins or adducts of epoxy resins and
fatty acids, preferably in a solvent. The amount of substance of
the phosphoric or phosphonic acid used is normally such that all of
the epoxide groups are consumed by the reaction with the acid and
such that a sufficient number of acid groups is still available
even after the reaction. The resulting resin has hydroxyl groups
(from the reaction of the oxirane group with the acid function),
these hydroxyl groups being positioned .beta. to the ester group,
possibly hydroxyl groups in the glycidyl alcohol residues which are
bonded by ether links in the epoxy resin, and also acid groups of
the phosphoric or phosphonic acid which were not consumed by the
reaction with the epoxide.
[0027] Suitable hydroxyl group-containing resins A2 are, in
particular, polyesters A21, acrylate resins A22, polyurethane
resins A23, and epoxy resins A24. The hydroxyl number of the resins
A2 is generally from about 50 to 500 mg/g, preferably from about 60
to 350 mg/g, and with particular preference from 70 to 300 mg/g.
Their Staudinger Index, measured at 20.degree. C. in
dimethylformamide as solvent, is preferably from 8 to 13
cm.sup.3/g, in particular from 9.5 to 12 cm.sup.3/g.
[0028] The polyesters A21 are prepared like the component A11 by
polycondensation; in this case all that is necessary is to select
the nature and amount of the starting materials such that there is
an excess of hydroxyl groups over the acid groups to arrive at the
hydroxyl number for the condensation products indicated above. This
can be achieved by using polyhydric alcohols containing on average
at least two, preferably at least 2.1, hydroxyl groups per
molecule, with dicarboxylic acids or with a mixture of poly- and
monocarboxylic acids containing on average not more than two,
preferably from 1.5 to 1.95, acid groups per molecule. Another
possibility is to use a corresponding excess of hydroxyl components
(polyols) A211 over the acids A212. The polyols A211 and the
polyfunctional acids A212 which are reacted in the polycondensation
reaction to give the hydroxyl group-containing polyesters A21 are
selected from the same groups as the polyols A111 and the acids
A112. It is likewise possible here to replace some of the polyols
and acids by hydroxy acids in accordance with A113. The aim is for
the acid number of component A2 not to exceed 20 mg/g and to be
preferably below 18 mg/g. The acid number may be reduced, for
example, by reacting the condensed polyester A21 with a small
amount of monofunctional aliphatic alcohols A114 with from 4 to 20
carbon atoms under esterification conditions. The amount of
alcohols A114 is such that, although the acid number is reduced
below the limit, the Staudinger Index does not fall below the
stated lower limit. Examples of suitable aliphatic alcohols are
n-hexanol, 2-ethylhexanol, isodecyl alcohol and tridecyl
alcohol.
[0029] The hydroxyl group-containing acrylate resins A22 are
obtainable by usually free-radically initiated copolymerization of
hydroxyl group-containing acrylic monomers A221 with other vinyl or
acrylic monomers A222 without such functionality. Examples of the
monomers A221 are esters of acrylic and methacrylic acid with
aliphatic polyols, especially diols having 2 to 10 carbon atoms,
such as hydroxyethyl and hydroxypropyl (meth)acrylate. Examples of
the monomers A222 are the alkyl esters of (meth)acrylic acid having
1 to 10 carbon atoms in the alkyl group such as methyl, ethyl,
n-butyl and 2-ethylhexyl (meth)acrylate, (meth)acrylonitrile,
styrene, vinyltoluene, vinyl esters of aliphatic monocarboxylic
acids having 1 to 10 carbon atoms such as vinyl acetate and vinyl
propionate. Preference is also given to those acrylate resins
prepared not, as is usual, in solution but instead in a bulk
polymerization in which the initial charge comprises a liquid
cyclic compound which acts as solvent during the polymerization
reaction and which by means of ring opening forms a copolymerizable
compound on reaction with one of the monomers used. Examples of
such compounds are glycidyl esters of .alpha.-branched aliphatic
monocarboxylic acids, especially the acids or acid mixtures
available commercially as neopentanoic acid or neodecanoic acid,
and also lactones such as .epsilon.-caprolactone or
.delta.-valerolactone. If these glycidyl esters are used, then
during the polymerization it is necessary to use comonomers
containing acid groups, such as (meth)acrylic acid, in an amount
which is at least equimolar to the amount of substance of the
epoxide groups. The lactones may be used, with ring opening, both
with hydroxyl group-containing comonomers and with comonomers
containing acid groups.
[0030] Hydroxyl group-containing polyurethane resins A23 are
obtainable in a known manner by addition reaction of oligomeric or
polymeric polyols A231 selected from polyester polyols, polyether
polyols, polycarbonate polyols and polyolefin polyols, and, if
desired, low molar mass aliphatic diols or polyols A233 having 2 to
12 carbon atoms, such as ethylene glycol, 1,2- and 1,3-propylene
glycol, 1,4-butanediol, 1,6-hexanediol, di- and triethylene and/or
-propylene glycol, neopentyl glycol, trimethylolpropane,
pentaerythritol, ditrimethylolpropane, and dipentaerythritol, and
polyfunctional isocyanates A232, the latter being used in a
substoichiometric amount such that the number of hydroxyl groups in
the reaction mixture is greater than the number of isocyanate
groups. Suitable polyols are, in particular, oligomeric and
polymeric dihydroxy compounds having a number-average molar mass
M.sub.n of from about 200 to 10,000 g/mol. By means of polyaddition
with polyfunctional, especially difunctional, isocyanates, the
molecules are enlarged up to the target value for the Staudinger
index of at least 8 cm.sup.3/g, preferably at least 9.5
cm.sup.3/g.
[0031] Epoxy resins A24 obtainable by reacting epichlorohydrin with
aliphatic or aromatic diols or polyols, especially bisphenol A,
bisphenol F, resorcinol, novolaks or oligomeric polyoxyalkylene
glycols having 2 to 4, preferably 3 carbon atoms in the alkylene
group, have at least one hydroxyl group per epichlorohydrin
molecule used. Instead of the reaction of epichlorohydrin with
diols, it is also possible to prepare the appropriate epoxy resins
by the so-called advancement reaction from diglycidyl ethers of
diols (such as those mentioned above) or diglycidyl esters of
dibasic organic acids with the stated diols. All known epoxy resins
may be used here, provided they satisfy the condition for the
hydroxyl number.
[0032] As anionically stabilized resins A it is also possible to
use polyesters Ap which may be prepared in a known manner by
condensing polyfunctional acids and polyfunctional compounds
containing hydroxyl groups. The excess of acid groups needed for
anionic stabilization may be achieved by using either acids or
hydroxyl group-containing compounds having a functionality of more
than 2, the amounts of the components being chosen such that the
amount of substance of the acid groups exceeds that of the hydroxyl
groups to the desired extent, or by using hydroxyl group-containing
compounds which in addition carry acid groups whose participation
in the polycondensation reaction is zero or only minimal (not more
than 20% of the acid groups are esterified under the condensation
conditions). These polyesters Ap also preferably have an acid
number of from about 10 to 60 mg/g, more preferably from 15 to 55
mg/g, and in particular from 20 to 50 mg/g. The amount of hydroxyl
groups in Ap corresponds to a hydroxyl number of at least 10 mg/g,
preferably from 15 to 200 mg/g, and in particular from 25 to 150
mg/g. The polyester Ap usually has a Staudinger index J.sub.0 of
from 5 to 25 cm.sup.3/g, preferably from 7 to 22 cm.sup.3/g, and in
particular from 10 to 20 cm.sup.3/g, measured in dimethylformamide
at 20.degree. C.
[0033] Further anionically stabilized resins Ae which may be used
for the invention are the epoxy resins modified with phosphoric
acid or phosphonic acids, or adducts of epoxy resins and fatty
acids modified with phosphoric acid or phosphonic acids, as already
mentioned above in connection with A16. They are prepared by
reacting phosphoric acid or organic phosphonic acids which are at
least dibasic with epoxy resins or adducts of epoxy resins and
fatty acids, preferably in a solvent. The amount of substance of
the phosphoric or phosphonic acid used is usually such that all of
the epoxide groups are consumed by reaction with the acid and such
that a sufficient number of acid groups is available even after the
reaction. The resulting resin has hydroxyl groups (from the
reaction of the oxirane group with the acid function), these
hydroxyl groups being positioned .beta. to the ester group, and
also acid groups of the phosphoric or phosphonic acid which were
not consumed by the reaction with the epoxide. In this case as
well, the target acid number is from about 10 to 60 mg/g,
preferably from 15 to 55 mg/g, and in particular from 20 to 50
mg/g. The amount of hydroxyl groups in Ae corresponds to a hydroxyl
number of at least 10 mg/g, preferably from 15 to 200 mg/g, and in
particular from 25 to 150 mg/g.
[0034] The curing agents C comprise a combination of
water-insoluble unblocked isocyanates C1 and highly reactive
partially etherified amino resins C2. The mass fractions of the
curing components C1 and C2 (mass of the individual component C1,
and C2, respectively, divided by the total mass of the curing
agents used) are preferably from 65 to 95% of component C1 and from
35 to 5% of component C2, with the sum of the mass fractions
necessarily being 100%, of course.
[0035] The unblocked isocyanates C1 are any desired organic
polyfunctional isocyanates which are liquid at room temperature and
have free isocyanate groups attached to aliphatic, cycloaliphatic,
araliphatic and/or aromatic moieties. The isocyanate component C1
generally has a viscosity of from 50 to 20,000 mPa.s at 23.degree.
C. With particular preference, the isocyanate component C1
comprises polyfunctional isocyanates or mixtures of such
isocyanates with isocyanate groups attached exclusively to
aliphatic and/or cycloaliphatic moieties and having an (average)
NCO functionality of between 2.0 and 5.0.
[0036] If necessary, the isocyanates may be used as a blend with
small amounts of inert solvents in order to reduce the viscosity to
a level within the stated ranges. The amount of such solvents,
however, is generally such that in the coating materials of the
invention obtained ultimately the mass fraction of solvents does
not exceed 30%, calculated to include any solvents still present in
the polymer dispersions or polymer solutions. Examples of solvents
suitable as additives for the polyisocyanates are aromatic
hydrocarbon mixtures such as solvent naphtha.
[0037] Isocyanates suitable as component C1 are, in particular,
diisocyanates or, preferably, the so-called paint polyisocyanates
having isocyanate groups attached to aromatic or (cyclo)aliphatic
moieties, particular preference being given to the last-mentioned
aliphatic isocyanates.
[0038] The diisocyanates comprise the compounds known in the fields
of polyurethanes and paints, such as aliphatic, cycloaliphatic or
aromatic diisocyanates. They preferably possess the formula
Q(NCO).sub.2, where Q is a hydrocarbon radical having 4 to 40
carbon atoms, especially 4 to 20 carbon atoms, and preferably an
aliphatic hydrocarbon radical having 4 to 12 carbon atoms, a
cycloaliphatic hydrocarbon radical having 6 to 15 carbon atoms, an
aromatic hydrocarbon radical, having 6 to 15 carbon atoms, or an
araliphatic hydrocarbon radical having 7 to 15 carbon atoms.
Examples of such diisocyanates to be used with preference are
tetramethylene diisocyanate, hexamethylene diisocyanate,
dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane,
3-isocyanatomethyl-3,5,5-trime- thylcyclohexyl isocyanate
(isophorone diisocyanate), 4,4'-diisocyanatodicyclohexylmethane,
2,2-bis(4,4'-diisocyanatodicyclohex- yl)propane,
1,4-diisocyanatobenzene, 2,4- or 2,6-diisocyanatotoluene and/or
mixtures of these isomers, 4,4'- or 2,4'-diisocyanatodiphenylmetha-
ne, 2,2-bis(4,4'-diisocyanatodiphenyl)propane, p-xylylene
diisocyanate and .alpha.,.alpha.,.alpha.',.alpha.'-tetramethyl-m-
or -p-xylylene diisocyanate, and mixtures of these compounds.
[0039] Suitable polyisocyanates, in addition to these simple ones,
include those containing heteroatoms in the radical linking the
isocyanate groups. Examples of such polyisocyanates are those
containing carbodiimide groups, allophanate groups, isocyanurate
groups, urethane groups, acylated urea groups, or biuret groups.
For further suitable polyfunctional isocyanates, reference may be
made, for example, to DE-A 29 28 552.
[0040] Highly suitable polyisocyanates are, for example, "paint
polyisocyanates" based on hexamethylene diisocyanate or on
1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane (IPDI)
and/or bis(isocyanatocyclohexyl)methane, especially those based
exclusively on hexamethylene diisocyanate. By "paint
polyisocyanates" based on these diisocyanates are meant the
conventional derivatives of these diisocyanates containing biuret,
urethane, uretdione and/or isocyanurate groups which following
their preparation have if necessary been freed in a known manner,
preferably by distillation, from excess starting diisocyanate down
to a residual mass fraction of less than 0.5%. The preferred
aliphatic polyfunctional isocyanates for use in accordance with the
invention include the polyfunctional isocyanates based on
hexamethylene diisocyanate, containing biuret groups and conforming
to the abovementioned criteria, as may be obtained, for example, by
the processes of U.S. Pat. Nos. 3,124,605, 3,358,010, 3,903,126,
3,903,127 or 3,976,622, which comprise mixtures of
N,N,N-tris(6-isocyanatohexyl)biuret with minor amounts of its
higher homologues, and also the cyclic trimers of hexamethylene
diisocyanate which meet the aforementioned criteria, as may be
obtained in accordance with U.S. Pat. No. 4,324,879, which comprise
essentially N,N,N-tris(6-isocyanatohexyl) isocyanurate in a mixture
with minor amounts of its higher homologues. Particular preference
is given to the mixtures of polyfunctional isocyanates based on
hexamethylene diisocyanate which contain uretdione and/or
isocyanurate groups and meet the abovementioned criteria, these
isocyanates being as formed by catalytic oligomerization of
hexamethylene diisocyanate using trialkylphosphines. Particular
preference is given to the last-mentioned mixtures with a viscosity
at 23.degree. C. of from 50 to 20,000 mPa.s and an NCO
functionality of between 2.0 and 5.0.
[0041] The aromatic polyfunctional isocyanates, which are likewise
suitable in accordance with the invention but are less preferred,
comprise in particular "paint polyisocyanates" based on
2,4-diisocyanatotoluene or its technical-grade mixtures with
2,6-diisocyanatotoluene or based on 4,4-diisocyanatodiphenylmethane
or its mixtures with its isomers and/or higher homologues. Aromatic
paint polyisocyanates of this kind are, for example, the
isocyanates containing urethane groups as obtained by reacting
excess amounts of 2,4-diisocyanatotoluene with polyhydric alcohols
such as trimethylolpropane with possible subsequent distillative
removal of the unreacted diisocyanate excess. Further aromatic
paint polyisocyanates are, for example, the trimers of the
monomeric diisocyanates given as examples, i.e., the corresponding
isocyanato isocyanurates, which following their preparation may
preferably have been freed, preferably by distillation, from excess
monomeric diisocyanates.
[0042] Furthermore, the isocyanate component C1 may comprise any
desired mixtures of the isocyanates given by way of example.
[0043] As a further curing component, use is made of a
water-dilutable amino resin C2 especially in a mass fraction of
from 5 to 35%, preferably from 10 to 30%, and with particular
preference from 15 to 25%, based on the mass of the total curing
component. The amino resin C2 is used preferably in partly
etherified form. Particularly suitable are partly etherified and
partly methylolated melamine resins containing on average from 3 to
5, preferably about 4, methoxymethyl or other alkoxymethyl groups
per triazine ring, such as tetramethoxymethylmelamine, and also
varieties etherified with butanol or with mixtures of butanol and
methanol, and also the corresponding benzoguanamine,
caprinoguanamine or acetoguanamine resins. "Methylolated" resins
are those where at least one amino hydrogen group is replaced by a
N-methylol group formed by addition of formaldehyde to the amino
compound. "Etherified" resins are those amino resins where at least
a part of the methylol groups are etherified with lower alcohols,
preferably aliphatic alcohols of from 1 to 6, especially preferred
from 1 to 4 carbon atoms. These resins are also called
"alkoxymethyl" melamine (or the respective guanamine) resins.
Especially preferred are methoxymethyl, butoxymethyl and
isobutoxymethyl resins (those etherified with methanol, n- or
iso-butanol, or also mixtures thereof). "Partly etherified" as
preferred herein means that from 20 to 80%, preferably from 35 to
65% of all methylol groups are replaced by alkoxymethyl groups in
the resin.
[0044] The resins A are prepared from the polyhydroxy components A1
and the polycarboxyl components A2 under condensation conditions,
i.e., at a temperature of from 80 to 180.degree. C., preferably
between 90 and 170.degree. C., preferably in the presence of
solvents which form azeotropes with the water formed during the
condensation. The condensation is continued until the resins A have
acid numbers of from about 25 to about 75 mg/g, at which point the
Staudinger Index is from about 13.5 to 18 cm.sup.3/g, preferably
from 14.5 to 16.5 cm.sup.3/g, in each case measured in
dimethylformamide as solvent at 20.degree. C. Following at least
partial neutralization of the remaining carboxyl groups (with
preferably from 50 to 95% of the carboxyl groups, with particular
preference from 60 to 85%, being neutralized), the resins A are
dispersible in water. During the condensation it may be observed
that the initially cloudy reaction mass clarifies and forms a
homogenous phase.
[0045] The curing agent is added preferably directly prior to the
processing of the binder. It is also possible to add the amino
resin C2 before the neutralization of the condensate A; the
isocyanate C1 should in any case not be added until shortly before
processing. The addition of the isocyanate C1 is made preferably
with intensive mixing, for example, in high-speed mixers
(rotor-stator mixers), or not until during application in known
dual-fluid nozzles.
[0046] The ready-formulated dispersion may be adapted to the
intended application by means of customary additives such as
pigments, corrosion inhibitors, levelling agents, antisettling
agents, adhesion promoters and defoamers.
[0047] For the formulation of clearcoat materials, all that are
added are the customary levelling systems, defoamers and, if
desired, catalysts which accelerate the curing reaction. The
compounds used for this purpose are commonly salts or complex
compounds of transition metals such as titanium and cerium or of
main-group metals which exist in different valence states, such as
antimony, tin or lead.
[0048] For the formulation of surfacers, organic or inorganic
fillers as well are added to the dispersion, such as carbon black,
titanium dioxide, finely divided silica, silicates such as kaolin
or talc, chalks, heavy spar or iron oxide pigments; organic fillers
which may be used are ground thermoplastics such as polyolefins,
polyesters or polyamides; preference is also given to polymers of
olefinically unsaturated monomers that are obtainable by emulsion
polymerization, including crosslinked polymers in particular.
[0049] The surfacer compositions may further comprise the customary
solvents, especially water-miscible solvents. These surfacers are
normally prepared by grinding the fillers and pigments with a
portion of the dispersion and with the addition of dispersing
auxiliaries, defoamers and other additives in appropriate
dispersing equipment such as a bead mill. The particle size of the
fillers and pigments is preferably reduced to less than 15 .mu.m.
The remainder of the dispersion and any further additives are added
to this preparation in accordance with the target pigment/binder
mass ratio of from 0.5:1 to 2.5:1. The mass of the pigments here
also includes the mass of the fillers.
[0050] The finished formulation may be applied to the substrate by
the customary techniques, such as by roller, by spraying or by roll
coating. Particular preference is given to spraying application
techniques, such as compressed air spraying, airless spraying or
what is known as "ESTA high-speed rotation spraying". After a short
flash-off time at room temperature or elevated temperature of up to
about 80.degree. C., the film is baked at from about 90 to about
130.degree. C. The film thickness after baking is usually from
about 15 to about 120 .mu.m, preferably between 25 and 70
.mu.m.
[0051] The combination of water-insoluble and hydrophilic curing
components in accordance with the invention brings about a markedly
improved quality of the baked clearcoat films, which are free from
defects such as hazing and pinholing. Despite the fact that in the
automotive coating system the surfacer film is coated with at least
one further film (solid-color topcoat) or two further films (in the
case of metallic paint: pigmented paint film containing color
pigment and metallic effect pigment, and a clearcoat film), the
markedly improved quality of the surfacer film (reduction in the
frequency of defects) also has a substantial influence on the
appearance of the finished coating system. The resistance to stone
chipping is not adversely affected.
[0052] The specific epoxide group content "SEC" is defined as the
ratio of the amount of substance of epoxide groups n(EP) and the
mass m.sub.B of the substance (and is thus the reciprocal of the
so-called "EV value" or "epoxide equivalent weight" (EEW)); the
customary unit of measurement is "mmol/kg":
SEG=n(EP)/m.sub.B
[0053] In the reaction of epoxide compounds with primary or
secondary amines R.sup.1R.sup.2--NH (R.sup.1 and R.sup.2 being
independently selected from alkyl residues preferably of from 1 to
20 carbon atoms, where R.sup.2 in the case of a primary amine is
H), addition is followed by the formation, with ring opening, of
.beta.-hydroxyamines of structure
--CH(OH)--CH.sub.2--NR.sup.1R.sup.2. Since one .beta.-hydroxyamine
group is formed for each epoxide group reacted, the sum of the
amount of substance of .beta.-hydroxyamine groups (calculated from
the "EPA value", amount of substance of the .beta.-hydroxyamine
groups divided by the mass of the sample) and of that of the
unreacted epoxide groups after the reaction is equal to the amount
of substance of epoxide groups originally present.
[0054] In the examples below, as in the text which precedes them,
all figures with the unit "%" are mass fractions (ratio of the mass
of the substance in question to the mass of the mixture), unless
stated otherwise. "Parts" (abbreviated "pbm") are always mass
fractions. Concentration figures in "%" are mass fractions of the
dissolved solid in the solution (mass of the dissolved solid,
divided by the mass of the solution).
EXAMPLES
[0055] 1 Preparing the Carboxyl Component A (PCPU1)
[0056] 675 g of dimethylolpropionic acid, 180 g of ethyl glycol,
543 g of diglycol dimethyl ether and 271 g of methyl isobutyl
ketone were weighed out into a reaction vessel with stirring,
cooling and heating equipment and were heated to 100.degree. C. At
100.degree. C., 1044 g of tolylene diisocyanate were added
dropwise, account being taken of the exothermic reaction, and the
temperature was maintained until the mass fraction of free
isocyanate groups had fallen to below 0.1%. The batch was
subsequently diluted with approximately 540 g of diglycol dimethyl
ether and approximately 270 g of methyl isobutyl ketone. This gave
a clear resin solution having a viscosity of 500 mPa.s (measured at
23.degree. C. in accordance with DIN EN ISO 3219 on a solution of
46 g of resin in 100 g of solution in diglycol dimethyl ether), a
mass fraction of solids of approximately 60% and an acid number of
140 mg/g.
[0057] 2. Preparing the Carboxyl Component B (PCLM)
[0058] 300 g of linseed oil were mixed with 100 g of maleic
anhydride under a nitrogen atmosphere and the mixture was heated to
200.degree. C. over 4 hours. The temperature of 200.degree. C. was
maintained until free maleic anhydride could no longer be detected.
After cooling to 85.degree. C., the batch was admixed with a
mixture of 30 g of fully deionized (DI) water and 3 g of
triethylamine and held until an acid number of 200 mg/g was
reached. Subsequently, it was diluted with 85 g of
methoxypropoxypropanol. The resulting resin solution had a mass
fraction of solids of approximately 80%.
[0059] 3. Preparing the Hydroxyl Component C (PHEP)
[0060] 838 g of methoxypropoxypropanol, 1800 g of .RTM.Epikote 1007
(epoxy resin based on bisphenol A, having a weight-average molar
mass M.sub.W of 2900 g/mol and a specific epoxide group content
"SEC" of approximately 5300 mmol/kg) and 56 g of tall oil fatty
acid 150, plus an added esterification catalyst, were held at
170.degree. C. until an acid number of less than 1 mg/g was
measured. After the mixture had cooled to 100.degree. C., 84 g of
diethanolamine were added and the temperature was maintained until
the specific amount of .beta.-hydroxyamine groups ("EPA value",
amount of substance of hydroxyamine groups, divided by the mass of
the sample) plus the specific amount of unreacted epoxide groups
(amount of substance of epoxide groups, divided by the mass of the
sample) had fallen to 360 mmol/kg. Following the addition of 50 g
of .RTM.Cardura E 10 (glycidyl ester of neodecanoic acid), the
temperature was raised to and held at 160.degree. C. This phase was
ended when the specific amount of .beta.-hydroxyamine groups ("EPA
value") plus that of the unreacted epoxide groups in the sample was
340 mmol/kg.
[0061] 4 Preparing the Hydroxyl Component D (PHPU1)
[0062] In an appropriate reaction vessel, 183 g of dipropylene
glycol, 35 g of isononanoic acid, 68.5 g of pentaerythritol, 175 g
of isophthalic acid and 0.5 g of dibutyltin dilaurate as catalyst
were esterified at 220.degree. C. to an acid number of less than 5
mg/g. At 70.degree. C., the batch was diluted with methyl ethyl
ketone to a mass fraction of solids of 65%, and 60 g of tolylene
diisocyanate were added. The temperature was held until free NCO
groups were no longer detectable.
[0063] 5 Preparing the Hydroxyl Component F (PHES1)
[0064] 106 g of tripropylene glycol, 87 g of hexanediol and 104 g
of trimellitic anhydride were esterified at 180.degree. C. with 0.2
g of dibutyltin dilaurate as catalyst to an acid number of
approximately 20 mg/g. At the end of the reaction, the viscosity of
a solution of 55 g of resin in 100 g of solution in butyl glycol,
measured in accordance with DIN EN ISO 3219 at 23.degree. C., was
approximately 500 mPa.s.
[0065] 6 Preparing the Hydroxyl Component G (PHES2)
[0066] 79 g of dipropylene glycol, 87 g of hexanediol and 90 g of
trimellitic anhydride were esterified at 180.degree. C. with 0.2 g
of dibutyltin dilaurate as catalyst to an acid number of
approximately 20 mg/g. At the end of the reaction, the viscosity of
a solution of 55 g of resin in 100 g of solution in butyl glycol,
measured in accordance with DIN EN ISO 3219 at 23.degree. C., was
500 mPa.s.
[0067] 7 Preparing the Carboxyl Component H (PCPU2)
[0068] 270 g of dimethylolpropionic acid, 134 g of dipropylene
glycol, 180 g of ethyl glycol, 367 g of diglycol dimethyl ether and
183 g of methyl isobutyl ketone were weighed out into a reaction
vessel with stirring, cooling and heating equipment and were heated
to 100.degree. C. At 100.degree. C., 696 g of tolylene diisocyanate
were added dropwise, account being taken of the exothermic
reaction, and the temperature was maintained until the mass
fraction of free isocyanate groups had fallen to below 0.1%. The
batch was subsequently diluted with approximately 260 g of diglycol
dimethyl ether and approximately 130 g of methyl isobutyl ketone.
This gave a clear resin solution having a viscosity of 200 mPa.s
(measured at 23.degree. C. in accordance with DIN EN ISO 3219 on a
solution of 46 g of resin in 100 g of solution in diglycol dimethyl
ether), a mass fraction of solids of approximately 60% and an acid
number of 95 mg/g.
[0069] 8 Preparing the Binder 1
[0070] 65 g of component C (PHEP) and 35 g of component A (PCPU1)
were mixed and heated to 150.degree. C. The solvent present was
substantially removed prior to the condensation reaction, by
distillation under reduced pressure, and at the beginning of the
reaction the mass fraction of solid of the reaction mixture was
approximately 75%. The temperature was held until an acid number of
from 40 to 45 mg/g and a viscosity of 450 mPa.s (measured in
accordance with DIN EN ISO 3219 at 23.degree. C. on a solution of
26 g of resin in 100 g of solution in butyl glycol) was reached.
The batch was neutralized with dimethylethanolamine and adjusted
using DI water to a mass fraction of solid of 30%.
[0071] 9 Preparing the Binder 2
[0072] 70 g of component D (PHPU1) and 30 g of component B (PCLM)
were mixed. The mixture was condensed at a reaction temperature of
100.degree. C. until an acid number of from 65 to 70 mg/g was
reached; the viscosity of a solution of 40 g of resin in 100 g of
solution in butyl glycol, measured in accordance with DIN EN ISO
3219 at 23.degree. C., was 450 mPa.s. The batch was subsequently
neutralized with dimethylethanolamine and adjusted with fully
deionized (DI) water to a mass fraction of solids of 35%.
[0073] 10 Preparing the Binder 3
[0074] 137 g of diethylene glycol were mixed with 152 g of
trimethylolpropane, 109 g of isophthalic acid, 96 g of adipic acid
and 198 g of phthalic anhydride under a nitrogen atmosphere and the
mixture was heated to 180.degree. C., water of reaction being
removed via a water separator. The temperature was held until the
acid number was 60 mg/g. After cooling to 160.degree. C., the batch
was diluted with approximately 370 g of butyl glycol. The resulting
resin solution had a mass fraction of solids of 60% and a viscosity
of approximately 4000 mPa.s, measured in accordance with DIN EN ISO
3219 at 23.degree. C.
[0075] 11 Preparing the Binder 4
[0076] Stage a Fatty Acid Ester
[0077] An esterification catalyst was added to 57 g of epoxynovolak
.RTM.DEN 431 (Dow Chemical; average functionality 2.2; specific
epoxide group content approximately 5700 mmol/kg) and 18.5 g of
linseed oil fatty acid, and the mixture was heated to 150.degree.
C., account being taken of the exothermic reaction. The temperature
was held until the acid number had fallen below 1 mg/g.
Subsequently, 44 g of diacetone alcohol and 25 g of epoxy resin
.RTM.DER 664 (Dow Chemical; epoxy resin based on bisphenol A; type
4; specific epoxide group content approximately 1100 mmol/kg) were
added. Following thorough homogenization, the batch was cooled to
50.degree. C.
[0078] Stage b Phosphoric Ester
[0079] A mixture of 10 g of phosphoric acid (75% strength solution
in water) and 25 g of diacetone alcohol was heated to 50.degree. C.
Subsequently, the fatty acid ester from stage a was added in
portions at a rate such that the exothermic reaction occurring
allowed the temperature to be maintained. Stirring was continued
until the specific epoxide group content had fallen below 0.1
mmol/g. The batch was adjusted using diacetone alcohol to a mass
fraction of solids of 60%; the viscosity, measured in accordance
with DIN EN ISO 3219 at 23.degree. C. in a solution of 45 g of
resin in 100 g of a solution in methoxypropoxypropanol, was 500
mPa.s.
[0080] 12 Preparing the Binder 5
[0081] 75 g of component G (PHES2) and 25 g of component H (PCPU2)
were mixed and heated to 150.degree. C. The solvent present was
substantially removed, by distillation under reduced pressure. The
temperature of 150.degree. C. was held until an acid number of from
35 to 40 mg/g and a viscosity of 600 mPa.s (measured in accordance
with DIN EN ISO 3219 at 23.degree. C. on a solution of 45 g of
resin in 100 g of a solution in butyl glycol) was reached. After
cooling to 95.degree. C., the batch was neutralized with
dimethylethanolamine and adjusted using DI water to a mass fraction
of solid of 30%.
[0082] 13 Preparing the Binder 6
[0083] 75 g of component F (PHES1) and 25 g of component H (PCPU2)
were mixed and heated to 150.degree. C. The solvent present was
substantially removed, by distillation under reduced pressure. The
temperature of 150.degree. C. was held until an acid number of from
35 to 40 mg/g and a viscosity of 600 mPa.s (measured in accordance
with DIN EN ISO 3219 at 23.degree. C. on a solution of 45 g of
resin in 100 g of a solution in butyl glycol) was reached. After
cooling to 95.degree. C., the batch was neutralized with
dimethylethanolamine and adjusted using DI water to a mass fraction
of solid of 30%.
[0084] 14 Preparing Clearcoat Materials
[0085] The clearcoat materials 1 to 12 were prepared in accordance
with the formulas summarized in Table 1 (masses of the respective
components used, in g). The substances used were as follows:
[0086] .RTM.Maprenal VMF 3921: partially etherified highly reactive
melamine resin (on average 4 methoxymethyl groups per molecule of
melamine) from Vianova Resins GmbH & Co. KG
[0087] .RTM.Bayhydur 3100: hydrophilically modified
(water-dispersible) polyfunctional isocyanate from Bayer AG based
on hexamethylene diisocyanate having a mass fraction of isocyanate
groups of approximately 17.4%
[0088] .RTM.Desmodur N 3600: aliphatic polyfunctional isocyanate
from Bayer AG based on hexamethylene diisocyanate, solution of 90 g
of the isocyanate in 100 g of solution, the solvent is a mixture of
butyl acetate and "Solvent Naphtha 100" in a mass ratio of 1:1
[0089] .RTM.Basonat P LR 8878: solvent-free hydrophilic
polyfunctional aliphatic isocyanate from BASF AG based on
hexamethylene diisocyanate having a mass fraction of isocyanate
groups of from 17 to 18%
[0090] .RTM.Proglyde DMM: dipropylene glycol dimethyl ether
[0091] Crosslinking catalyst: zirconium complex compound .RTM.K-Kat
XC 6212 (King Industries)
[0092] .RTM.Additol XW 392: curing accelerator based on organic
phosphates (Vianova Resins GmbH & Co. KG)
[0093] The clearcoat materials thus prepared were applied to clean
glass plates using a 200 .mu.m coating bar. After a flash-off time
of 15 minutes, the films were subjected to forced drying at
90.degree. C. for 20 minutes.
1TABLE 1 Clearcoat Examples Coating material (CM) CM1 CM2 CM3 CM4
CM5 CM6 CM7 CM8 Binder 3 50 50 50 50 50 50 50 50 (40% in water)
.RTM. Maprenal VMF 3921 5.9 5.9 5.9 5.9 -- 5.9 5.9 5.9 .RTM.
Bayhydur 3100 25 .RTM. Desmodur N 3600 25 25 25 .RTM. Basonat P LR
8878 25 .RTM. Proglyde DMM 6.25 6.25 6.25 6.25 6.25 Deionized water
25 25 11 16 17 15 15 15 Cross-linking 0.2 0.2 0.2 catalyst .RTM.
Additol XW 392 1.25 Appearance of the Clear, Clear, Clear, Clear,
Cloudy, Clear, Clear, Clear, cured coating film no film no film no
film no film pinholes, no film no film no film defects defects
defects defects film defects defects defects defects Pendulum
hardness.sup.1 18 21 18 93 68 21 18 16 in s Pendulum
hardness.sup.24 95 91 176 176 92 24 21 20 in s
[0094] Pendulum hardness measured in accordance with Konig (DIN 53
157) following forced drying (20 minutes at 90.degree. C., and
storage for 1 ("pendulum hardness") or 24 ("pendulum
hardness.sup.24") hours under standard conditions
2TABLE 1 Clearcoat Examples (continued) CM9 CM10 CM11 CM12 Binder 4
46.5 46.5 46.5 46.5 (35% in water) .RTM.Maprenal VMF 3921 4.7 4.7
4.7 -- .RTM.Desmodur N 3600 8 -- -- 8 .RTM.Basonat P LR 8878 -- 8
-- -- N-methyl- 2 2 -- 2 pyrrolidone Deionized water 18.5 20.5 18.5
18.5 Crosslinking 0.16 0.16 -- 0.16 catalyst Additol XW 392 1 1 1 1
Appearance of the Clear, Clear, Clear, Cloudy, cured coating film
no film no film no pinholes, defects defects film film defects
defects Pendulum hardness.sup.1 136 59 20 91 in s Pendulum 153 70
28 112 hardness.sup.24 in s
[0095] Result:
[0096] The clearcoat materials which are cured only with melamine
resin, even in combination with different catalysts (coating
materials 6,7,8, and 11) do not give sufficiently high film
hardnesses after 20 minutes of curing at 90.degree. C. and are
therefore unsuitable for use in practice.
[0097] Crosslinking with unblocked isocyanate curing agents only
(Examples 5 and 12) leads to better film hardness; owing to the
incompatibility between binder and isocyanate, however, there are
film defects, which likewise rule out use in practice.
[0098] Defect-free coating films, however, were obtained with the
combination of melamine resin and hydrophilic isocyanate curing
agent (Examples 1, 2 and 10); in these cases, however, the degree
of hardness achieved was still inadequate.
[0099] All these examples are included for comparison, and to
illustrate the advantage brought about by the present
invention.
[0100] Only the combination of a binder of the invention with a
melamine resin and unblocked isocyanate leads to the desired
defect-free films possessing high pendulum hardnesses (Examples 3,
4 and 9). The presence of a crosslinking catalyst results in high
hardness even after a short period of storage; without a catalyst,
the hardness develops only after about 24 h of storage under
standard conditions, following the forced drying (20 minutes at
90.degree. C.) which preceded this storage in all cases.
[0101] 15 Preparation of Surfacer Materials
[0102] Using the formulations stated in Table 2 (masses of the
relevant components in grams), aqueous surfacer materials were
prepared in accordance with the procedure known to the skilled
worker. These coating materials were applied to cleaned glass
plates using a 200 .mu.m coating bar. Coating materials 13 and 14
were flashed off for 15 minutes and then subjected to forced drying
at 90.degree. C. for 20 minutes.
3TABLE 2 Surfacer materials Comparison: Coating Coating Ex. 4 from
material 13 material 14 EP-B 0 594 685 Binder 4 (35% in water) 50
Binder 5 (35% in water) 50 Wetting agent 0.3 0.3 Titanium dioxide
15 11.7 Fillers 15 18.3 .RTM.Additol VXW 4971 0.3 0.3 Deionized
water 18.5 18.5 Methoxypropoxy- propanol 1.5 1.5 .RTM.Mapranal VMF
3921 5.1 5.1 .RTM.Desmodur N 3600 8.55 6.85 .RTM.Basonat P LR 8878
1.7 N-methyl-pyrrolidone 1.45 1.45 Crosslinking catalyst 0.17 0.17
.RTM.Additol XW 392 1.05 1.05 Appearance of the cured defect-free
defect-free coating film Dry film thickness in .mu.m 42 42 40
Pendulum hardness.sup.1 in s 98 51 60 Pendulum hardness.sup.24 in s
106 95 74 .RTM.Additol VXW4971: levelling and wetting additive
(Vianova Resins GmbH & Co. KG)
[0103] The comparative example comprises an aqueous surfacer in
accordance with EP-A 0 594 685, Example 4). This was applied and
flashed off as for coating materials 13 and 14 but then was baked
at 165.degree. C. for 20 minutes.
[0104] Test Panels for Stone-Chip Test:
[0105] Test system: Bonder 26 60 OC as substrate, 25 .mu.m of a
standard electrocoat primer, 35 .mu.m of aqueous surfacer based on
coating material 13, 14 or comparison of table 2, 40 .mu.m of
standard commercial acrylic-melamine topcoat
4 Baking conditions for 30 minutes at 165.degree. C. electrocoat
primer: Baking conditions for Coating materials 13 and 14:
surfacers: 20 minutes at 90.degree. C., Comparison: 20 minutes at
165.degree. C. Baking conditions for 30 minutes at 140.degree. C.
topcoat:
[0106] The metal test panels so painted and prepared were stored
under standard conditions for 24 hours and then subjected to a
stone-chip test in accordance with the VDA [German Automakers'
Association] Standard 621-487 (2 passes each with 0.5 kg of angular
shot material, pressure: 0.1 MPa (=1 bar))
5 Test panel 1: Electrocoat primer, surfacer based on coating
material 13, topcoat Test panel 2: Electrocoat primer, surfacer
based on coating material 14, topcoat Test panel 3: Electrocoat
primer, comparative surfacer, topcoat
[0107] Result:
[0108] Following forced drying (20 minutes at 90.degree. C.), the
two surfaces crosslinked with unblocked isocyanate and melamine
resin give defect-free coatings whose film hardness is higher in
both cases than that of the aqueous baking surfacer (state of the
art), which was baked at 165.degree. C. for 20 minutes. Despite the
"equalizing" effect of the topcoat film, the quality of the surface
in the case of test panels 1 and 2 (in accordance with the
invention) was better than in the case of the comparative surfacer
which was baked at a higher temperature.
[0109] The stone-chip ratings listed in Table 3 show that in the
coating system described the results achieved with the surfacers of
the invention following forced drying (20 minutes at 90.degree. C.)
were approximately equal to those obtained with the state of the
art surfacer (baked at 165.degree. C. for 20 minutes).
6TABLE 3 Stone-chip test Test panel Test panel Test panel 1 2 3
Stone chip 1-2 1 0-1 rating Evaluation as per the Standard: Topcoat
adhesion (0 = no flaking of the topcoat from the surfacer; 10 = no
adhesion between topcoat and surfacer)
* * * * *