Note: Descriptions are shown in the official language in which they were submitted.
LeA 29 138-PC z 13 5 3 8 5
Aaueous binder mixture and use thereof
The invention relates to an aqueous binder mixture
comprising substantially an aqueous solution and/or
dispersion of a combination of a NCO prepolymer which is
soluble and/or dispersible in water, having blocked
isocyanate groups, and a polyamine component having primary
and/or secondary (cyclo)aliphatically bonded amino groups,
and the use of this binder mixture for the preparation of
coatings on heat-resistant substrates.
The preparation of aqueous PUR dispersions is known and is
described for example in the review article by
J.W. Rosthauser and K. Nachtkamp "Waterborne polyurethanes"
in Advances in Urethanes Science and Technology, Vol. 10,
1987, pp. 121 to 162. The mention here of mixing aqueous
PUR dispersions with melamine formaldehyde resins prior to
application is prior art, as discussed for example in US
Patent Specification No. 4 308 184. This measure imparts
to the thermally cured coating film a cross-linked
duromeric character and resistance to water and solvents.
This cross-linking method has the disadvantage, apart from
the problems involved in handling substances which release
formaldehyde, that PUR dispersions which have been modified
in such a manner have a limited pot life and thus do not
represent a one-pot system.
Genuine one-pot polyurethane-based aqueous binders, i.e.
having virtually unlimited stability in storage, are also
already known (DE-OS 3 345 448). These are constituted by
mixtures of two aqueous PUR dispersions, one containing OH
groups and the other NCO groups blocked with e-caprolactam.
The disadvantage of these aqueous one-pot binders lies in
the necessity for very high temperatures - approximately
170°C - for the thermal cross-linking.
1
z~~53s5
The object of the invention therefore comprises provision
of aqueous binder mixtures which are stable in storage at
room temperature, which are curable at comparatively low
cross-linking temperatures within the range 120 to 150°C,
and which can be utilised for the preparation of high-
performance coatings in terms of the properties required in
lacquer technology.
It was possible to achieve this object by preparing the
l0 aqueous binder mixture according to the invention which is
described in greater detail below.
The object of the invention is an aqueous binder mixture
comprising substantially an aqueous solution and/or.
dispersion of a combination of
a) at least one urethane group-exhibiting NCO prepolymer,
having blocked isocyanate groups, which is soluble
and/or dispersible in water in the presence of
component b), and
b) a polyamine component, comprising at least one organic
polyamine having in total at least two~primary and/or
secondary, aliphatiaally or cycloaliphatically bonded,
amino groups
in a molar ratio of blocked isocyanate groups to primary
and/or secondary amino groups of from 1 : 0.9 to 1 : 1.5.
A further object of the invention is the use of this
aqueous binder mixture, optionally mixed with conventional
auxiliary substances and additives taken from lacquer
technology, for the preparation of coatings on heat-
resistant substrates.
2
-. x135385
The binder component a) according to the invention is
constituted by urethane group-exhibiting, hydrophilically
modified NCO prepolymers having blocked isocyanate groups,
and being soluble and/or dispersible in water at least in
the presence of component b).
NCO prepolymers which are especially highly suitable as
component a) are those which exhibit
per molecule, at least two blocked isocyanate groups, at a
blocked isocyanate group content (calculated as NCO) of
from 2 to 10, and preferably from 3 to 6 wt-%,
a content of from 5 to 20, and preferably from 8 to
15 wt-%, of ethylene oxide units (calculated as CZH40j
incorporated within polyether chains in the end .and/or side
position, and
a content of from l0 to 60, and preferably from 15 to 40,
milliequivalents of carboxyl groups which are at least
partially neutralised by reacting with component b), per
100 g solids,
wherein the total content of ethylene oxide units of the
type named and carboxyl or carboxylate groups must be
calculated in such a manner that the prepolymers are
soluble and/or dispersible in water at least in the
presence of component b).
Preferably, in terms of ionic modification, only
incorporation of carboxyl groups which are at least
partially neutralised in aqueous phase to strongly
hydrophilic carboxylate groups by reciprocal action with
the polyamines b), takes place during preparation of the
prepolymers a), so that the solubility or dispersibility,
respectively, of the component a) in water may be dependent
3
Z1353~5
on the simultaneous presence of component b), but need not
be so if, in fact, component a) is of a sufficiently
hydrophilic character to ensure the solubility or
dispersibility, respectively, of component a) in water even
in the absence of component b).
1) organic polyisocyanates, 2) higher molecular weight
polyhydroxyl compounds, optionally 3) low molecular weight
chain extenders, 4) hydrophilic structural components and
5) blocking agent for isocyanate groups are utilised for
the preparation of the NCO prepolymers a).
Suitable polyisocyanates 1) are the known aromatic or
(cyclo)aliphatic polyisocyanates, such as are described,
for example, in Houben-Weyl, Methoden der organischen
Chemie [organic chemistry methods], Vol. 14/2, pp. 61 to
70, and in the article by W. Siefken in Justus Liebigs
Annalen der Chemie 562, pp. 75 to 136. The following
compounds may be named as examples of aromatic poly-
isocyanates: 2,4-diisocyanatotoluene, industrial mixtures
of this with up to 35 wt-% of 2,6-diisocyanatotoluene,
calculated on the mixture, 4,4'-diisocyanatodiphenyl-
methane, industrial mixtures of this with up to 50, and
preferably up to 40 wt-x of 2,4' diisocyanatodiphenyl-
methane, calculated on the mixture, and optionally up to
5 wt-% of 2,2'-diisocyanatodiphenylmethane, calculated on
the mixture, mixtures of the named diisocyanatodiphenyl-
methane isomers with their higher homologues exhibiting
more than 2 isocyanate groups, wherein these mixtures
generally exhibit at least 80 wt-% of the named
diisocyanatodiphenylmethane isomers, and any mixtures of
the polyisocyanates named by way of example. The following
may be named as examples of aliphatic polyisocyanates:
hexamethylene diisocyanate (HDI), 2-methylpentamethylene
diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate
(THDI), isophorone diisocyanate (IPDI),
4
°
~ 2135385
1,4-diisocyanatomethyl cyclohexane, tetramethylxylylene
diisocyanate (TMXDI). The known "lacquer polyisocyanates",
in particular those based on HDI and/or IPDI, in particular
the known biuret groups, isocyanurate groups and/or
uretdione group-exhibiting derivatives of these
diisocyanates may also be utilised as starting component 1)
for the preparation of the blocked polyisocyanates a). Any
mixtures of the polyisocyanates named by way of example may
also be used.
The polyhydroxyl compounds 2) are constituted in particular
by those polyester polyols and/or polyether polyols, known
per se from polyurethane chemistry, which exhibit per
molecule at least 2, and preferably from 2 to 4, hydroxyl
groups and a molecular weight of from 400 to 10,000, and
preferably from 500 to 3,000, calculable from OH content
and OH functionality. Either corresponding polyester
polyols or mixtures of polyester polyols and polyether
polyols are preferably used.
25
Suitable polyester polyols are also polyactone diols, for
example reaction products of hexanediol-1,6 with
e-caprolactone, in particular within the molecular weight
range 500 to 1,500.
Polyester polyols which are also suitable are polycarbonate
diols, in particular hexanediol-1,6 polycarbonate diols
within the molecular weight range 500 to 2,000, such as are
obtainable by condensation.of diols, in particular 1,6-
hexanediol, with Biphenyl carbonate or dimethyl carbonate
in a manner which is known per se.
A portion of the polyester polyols may also comprise
difficultly-saponifiable oligo-esters of long-chain,
hydroxyl group-containing carboxylic acid. Castor oil
should be named as an example.
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2135385
The polyhydroxy polyethers are constituted by the products,
which are known per se, of polyaddition reactions between
epoxides, for example ethylene oxide and/or propylene
oxide, and low molecular weight polyols of the type already
named above as examples of starting material in the context
of the polyester polyol. Those polyether polyols which
correspond to the molecular weight data indicated and which
are prepared by propoxylation of bisphenol A or
trimethylolpropane in a manner which is known per se, are
especially preferred.
The optionally co-utilised chain extenders 3) are
constituted by either simple low molecular weight polyols
of a molecular weight below 400, such as the multivalent,
preferably bivalent, alcohols named as examples of starting
materials in the context of the preparation of the
polyester polyols, and/or by amino group-exhibiting
compounds such as hydrazine or hydrazine hydrate or organic
diamines within the molecular weight range 60 to 400, such
as ethylenediamine, hexamethylenediamine, 4,4'-
diaminodicyclohexylmethane or 3,3'-dimethyl-4,4'-diamino-
dicyclohexylmethane. The low molecular weight chain
extenders 3) are utilised in quantities of up to 10 wt-%,
calculated on the weight of the higher molecular weight
hydroxyl compounds 2), if they are utilised at all.
Suitable hydrophilic structural components 4) are
monovalent, ethylene oxide unit-exhibiting polyether
alcohols, in particular within the molecular weight range
350 to 5,000, such as are obtainable by addition of
ethylene oxide and optionally other alkylene oxides to
monofunctional starter molecules, for example methanol,
n-propanol, n-butanol or butyldiglycol, in a manner which
is known per se. In the event that other alkylene oxides
such as propylene oxide are also utilised in this
alkoxylation reaction, in addition to ethylene oxide, care
6
'~, ~1353~5
must be taken to ensure that the proportion of ethylene
oxide, calculated on the total quantity of alkylene oxides,
is at least 40, and preferably at least 80 wt-%., In the
event of more than one alkylene oxide being utilised, the
latter may be utilised in a mixture and/or in succession
for the alkoxylation reaction.
Further hydrophilic structural components 4) are organic
carboxylic acids which exhibit in addition to the carboxyl
groups at least one, and prefeably two, reactive groups
which exhibit a greater readiness to react with isocyanate
groups than that exhibited by carboxyl groups. These
reactive groups are preferably constituted by primary
and/or secondary amino groups and in particular alcoholic
hydroxyl groups. Hydrophilic structural components of this
type that are particularly highly suitable are a-a-
dimethylolalkane carboxylic acids having in total from 5 to
8 carbon atoms, in particular dimethylolpropionic acid.
Also suitable are, for example, hydroxypivalic acid or
products of addition reactions between diamines (e. g.
ethylenediamine or isophorone diamine) and acrylic acid in
accordance with DE-OS 2 034 479.
Both ethylene oxide unit-exhibiting monovalent alcohols of
the type named by way of example and also amino- or
hydroxycarboxylic acids of the named type are preferably
utilised in the preparation of the prepolymers a) in
quantities such that ethylene oxide units and carboxyl
groups (or, after combination with component b), at least
some carboxylate groups) are present in the prepolymers
within the aforementioned ranges. The hydrophilic
polyether chains are situated in the end position or (if
branching-acting higher-functional structural components
are co-utilised) on the side, because monovalent polyether
alcohols which exhibit ethylene oxide units are used as a
part of component 4).
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2135385
Phenols, such as phenol, lactams, such as e-caprolactam,
oximes, such as butanone oxime and secondary amines, such
as diisopropylamine, imidazole, pyrazole or 1,2,4-triazole
may be utilised as blocking agent 5). Butanone oxime and
diisopropylamine are preferred according to the invention.
The higher molecular weight polyhydroxyl compounds 2) are
generally utilised in a quantity of from 20 to 60, and
preferably from 30 to 55 wt-%, calculated on the total
weight of starting components 1) to 5), for the preparation
of the prepolymers a). The equivalent ratio of component
1) isocyanate groups to groups of components 2) to 4) which
are reactive vis-a-vis isocyanate groups (not including the
carboxyl groups present in component 4)) is generally from
1.5 : 1 to 2.5 : 1. The quantity of blocking agent 5) is
generally calculated in such a manner that at least 90%,
and preferably 100%, of the isocyanate excess then still
present reacts with the blocking agent. It is in principle
possible, but is by no means preferred, to use a small
excess of blocking agent, so that the NCO prepolymers
initially still exhibit free isocyanate groups which then
react off with the water or part of component b) during the
dispersion stage.
Component b)'which is essential to the invention is
constituted by (cyclo)aliphatic polyamines having in total
at least two primary and/or secondary amino groups within
the molecular weight xange 60 to 400, and preferably 100 to
250. Examples which may be named are ethylenediamine,
hexamethylenediamine, diethylenetriamine, 4,4~-
diaminodicyclohexylmethane, 1,4-diaminocyclohexane, 3,3,5-
trimethyl-5-aminomethylcyclohexylamine (IPDA) or also
perhydrated triaminodiphenylmethanes such as are utilised
according to DE-oS 3 417 683 for the preparation of the
corresponding cycloaliphatic triisocyanates. Any mixtures
8
--~ 2~35~85
of such polyamines may also be used. 3,3'-dimethyl-4,4'-
diamino-dicyclohexylmethane is preferred.
The polyamines b) are utilised in the preparation of the
binder mixtures according to the invention in quantities
such that the molar ratio of blocked isocyanate groups of
component a) to primary and/or secondary amino groups of
component b) is from 1 : 0.9 to 1 : 1.5, and preferably
from 1 : 1 to 1 : 1.1.
The binder mixtures according to the invention may be
prepared, for example, by bringing to reaction, stepwise or
by way of a single-pot reaction, the starting poly-
isocyanates 1) and the starting components 2) to 5).at a
temperature of from 60 to 110°C, until the theoretical NCO
value of the reaction mixture (generally complete
disappearance of free isocyanate groups) is reached.
Component b) is then stirred in and dilution takes place
with water to the desired solids content, which is
generally from 35 to 55 wt-%. The reaction is generally
started in the melt and a water-miscible solvent which is
inert to isocyanate groups, and which can subsequently be
removed by distillation, for example acetone, is added as
required. The solvent which has been added may, if
desired, be removed by distillation following admixture of
the water of dispersion. The binder mixtures according to
the invention are finally obtained in the form of an
aqueous solution or dispersion.
The conventional auxiliary substances and additives taken
from lacquer technology, for example pigments, flow
promoters, W stabilisers, antioxidants, fillers,
thixotropic agents or plasticisers, may be admixed to the
binder mixtures according to the invention. Ready-to-use
aqueous coating agents which can be stored at room
temperature for virtually unlimited periods and which cure
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2135385
at relatively law temperatures of from 120 to 150°C to form
lacquer films having excellent mechanical properties are
obtained in this manner. Since the polyamines b) fulfil
the dual function of hardener for the blocked NCO
prepolymers and neutralising agent for the incorporated
carboxyl groups in the coating agents according to the
invention, there is during thermal curing no dissociation
of tertiary amines, which would otherwise normally serve as
the neutralising agents in the chemistry of aqueous
polyurethane dispersions. The neutralising agent is
instead incorporated in the lacquer film. It is for this
reason that only relatively small quantities of volatile
organics are released during the stowing operation.
The binder mixtures according to the invention are
particularly preferred for the preparation of under-floor
protective coatings and stone-chip resistant fillers for
motor vehicles.
All percentages indicated in the following Examples are by
weight.
2.35385
Example 1
50% dispersion of a binder mixture according to the
invention, based on an aromatic isocyanate component.
Component a), which represents the reaction product of the
first 6 starting substances named, contains 8.7 wt-% of
ethylene oxide units incorporated within polyether chains
in the end or side position, and 30.4 milliequivalents of
carboxyl groups per 100 g of solids.
Formulation
323.0 g (0.380 Val) of an adipic acid-hexanediol-1,6-
neopentylglycol polyester of
OH
number 66,
240.0 g (0.240 Val) of a polyether polyol of OH number
56, prepared by propoxylation
of
trimethylolpropane,
90.0 g (0.040 Val) of a monovalent polyether polyolol
of OH number 25 (dispersing agent),
prepared by ethoxylation of
n-butanol,
42.0 g (0.626 Val) of dimethylolpropionic acid,
63.8 g (0.734 Val) of butanone oxime,
271.0 g (2.020 Val) of a tube MDI type having a two-
nucleus proportion of approx.
90 wt-%, approx.l0 wt-% of which
represents 2,4'-diphenyl-
methanediisocyanate and approx.
10 wt-% higher-nucleus proportions,
NCO content approx. 31.3%,
96.0 g (0.800 Val) of bis-(4-amino-3-methyl-
cyclohexyl)-methane,
1126.0 g of water (equivalent to 50% solids
content)
2251.8 g binder dispersion
viscosity at 23°C approx. 1000 mPas
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2135385
Method
MDI is placed in approx. 500 ml of acetone at room
temperature and the polyester, both polyethers in anhydrous
form, dimethylolpropionic acid and butanone oxime are
introduced consecutively with stirring. The reaction
mixture is heated slowly - causing an exothermic reaction
of MDI and butanone oxime - to a reflux temperature of
approx. 65°C, and is reacted under reflux conditions for
approx. 10 h. At the end of this reaction time only a
small NCO band can generally still be observed in the IR
spectrum. Where this is the case a further 10 ml of
butanone oxime are added and retesting takes place after 30
minutes fox any residual NCO content. When no further NCO
is present, the diamine is stirred into the cooling
formulation. Water is then added with vigorous stirring at
approx. 45°C. A milky blue dispersion is formed which
still, however, contains acetone. The latter is distilled
off at approx. 45°C under reduced pressure (final value
approx. 150 mbar) over a period of approx. 4 hours.
A milky blue, finely-particulate 50% dispersion is
obtained, having a viscosity of approx. 1,000 mPas
(at 23°C) .
Properties
This one-pot binder dispersion is stable in storage, for
example no change during 6 months storage at 50°C. The
dispersion is coloured grey with pigment, and is then
applied to test plates. After evaporation of the water and
stowing at 120°C (for 30 minutes) a film thickness of, for
example, 364 ~,m is determined. Adhesion is good. The
caating withstands 2 minutes and 40 seconds of bombardment
with shot (Saablux test) without damage, an excellent
score.
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2135385
Example 2
Binder mixture according to the invention, based.on an
aliphatic polyisocyanate. The NCO prepolymer a) forming
the reaction product of the first 7 starting components
named contains 13.7 wt-% of ethylene oxide units
incorporated in polyether chains in the end or side
positions, and 15.2 milliequivalents of carboxyl groups per
100 g solids.
l0
Formulation
336.0 g (0.3 Val) of an adipic acid-butanediol-1,4-
polyester of OH number 50,
135.0 g (0.06Val) of dispersing agent according-to
Example 1,
20.1 g (0.30Val) dimethylolpropionic acid,
99.9 g (0.90Val) IPDI
270.0 g (1.35Val) of an isocyanurate group-exhibiting
polyisocyanate based on hexamethyl-
diisocyanate (NCO content 21%)
117.6 g (1.23Val) of butanone oxime,
10.0 g (0.4 Val) of hydrazine hydrate
114.7 g (1.35Val) IPDA,
1345.0 g of water (equivalent to 45% solids
content)
2448.3 g binder dispersion
Method
Polyester and polyether are taken and are dewatered with
stirring at a temperature of 110°C and a pressure of 15 mbar
for approx. 1 hour. Cooling takes place to approx. 60°C and
both isocyanate components and the dimethylolpropionic acid
are stirred in, the former in one shot, the latter portion-
wise. Smallish portions of butanone oxime are then added,
whereupon the reaction becomes exothermic. Heating takes
place and reaction occurs in the melt at from 100 to 110°C,
until just less than the calculated NCO content of 1.5% is
reached after approx. 2 hours. Cooling takes place to
13
. 2135385
approx. 70°C, followed by dissolution in approx. 1000 ml
acetone and addition of the hydrazine hydrate to extend the
chain length. Stirring of the acetone solution continues
at approx. 50°C for a further 3 hours, the IR spectrum
indicates a minimal NCO band, mixed with IPDA and free of
acetone, as already described in Example 1. A milky blue,
finely particulate 45% dispersion is obtained having a
viscosity of approx. 2,000 mPas at 23°C. This one-pot
binder dispersion is stable in storage.
Example 3
Binder mixture according to the invention, based on
aliphatic polyisocyanates. The NCO prepolymer a)
representing the reaction product of the first 7 starting
components named contains 13.2 wt-% of ethylene oxide units
incorporated within polyether chains in the end or side
position and 27.9 milliequivalents of carboxyl groups per
100 g solids.
Formulation
448.0 g (0.40 Val) of an adipic acid-butanediol-1,4
polyester of OH number 50,
180.0 g (0.08Val) of the dispersing agent according
to
Example 1,
133.2 g (1.20Val) of IPDI,
360.0 g (1.80Val) of polyisocyanate according to
Example 2,
26.8 g (0.40Val) of dimethylolpropionic acid,
165.6 g (1.64Val) of diisopropylamine,
120.0 g (0.4 Val) of a product of an addition reaction
between 1 mol IPDA (170 g) and
1 mol
acrylic acid (72 g) in water
(242 g); 1 Val of incorpo_ratable
NH/NHZ in this aminocarboxylic
acid
equates to 300 g,
153.0 g (1.8 Val) of IPDA,
1623.0 g of water, equivalent to 45% solids
content
3209.6 g binder dispersion
14
213535
Method
Polyester and polyether are dewatered with stirring at a
temperature of 110°C and a pressure of 15 mbar for approx.
1 hour. Cooling takes place to approx. 7o°C, dilution takes
place with 120 g N-methylpyrrolidone, the isocyanates are
added in a single shot, the dimethylolpropionic acid is
introduced portion-wise and diisopropylamine is added
dropwise to the well-stirred formulation. The internal
temperature is then increased to 100°C. After a reaction
time of approx. 1 hour, an NCO content just below the
calculated value of 1.45% is obtained. Cooling takes place
to approx. 60°C, dilution follows with approx. 1,200 ml of
acetone and the aqueous solution of the IPDA-acrylic acid
addition product is stirred in. After approx. 30 minutes
at 40°C no further NCO content is detectable (IR spectrum)
in the acetone solution. IPDA is added and dispersion with
water follows. Acetone is then distilled off over a period
of 4 hours, as indicated in Example 1 (45°C at 150 mbar).
A milky blue dispersion having a solids content of 50%, an
organic solvent content of 3.7% and a viscosity at 23°C of
approx. 2,000 mPas is obtained.
