U.S. patent application number 09/752678 was filed with the patent office on 2001-10-11 for weathering-stable, radiation-curable polyurethanes.
This patent application is currently assigned to BASF Akiengesellschaft. Invention is credited to Beck, Erich, Jaworek, Thomas, Menzel, Klaus, Reich, Wolfgang, Schwalm, Reinhold, Vollinger, Frank.
Application Number | 20010029272 09/752678 |
Document ID | / |
Family ID | 7627996 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010029272 |
Kind Code |
A1 |
Schwalm, Reinhold ; et
al. |
October 11, 2001 |
Weathering-stable, radiation-curable polyurethanes
Abstract
A water-dispersible, radiation-curable polyurethane composed
essentially of a) organic, aliphatic or alicyclic polyisocyanates,
b) cycloaliphatic diols and/or cycloaliphatic diamines, c)
compounds containing at least one isocyanate-reactive group and at
least one free-radically polymerizable unsaturated group, d)
compounds containing at least one isocyanate-reactive group and at
least one dispersing-active group, e) if desired, compounds
containing at least two isocyanate-reactive groups having a
molecular weight <1000 g/mol, f) if desired, compounds other
than a) to d) containing at least one isocyanate-reactive
group.
Inventors: |
Schwalm, Reinhold;
(Wachenheim, DE) ; Vollinger, Frank; (Edenkoben,
DE) ; Menzel, Klaus; (Ludwigshafen, DE) ;
Reich, Wolfgang; (Maxdorf, DE) ; Beck, Erich;
(Ladenburg, DE) ; Jaworek, Thomas; (Kallstadt,
DE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
BASF Akiengesellschaft
D-67056
Ludwigshafen
DE
|
Family ID: |
7627996 |
Appl. No.: |
09/752678 |
Filed: |
January 3, 2001 |
Current U.S.
Class: |
522/90 ; 522/75;
522/78; 522/84 |
Current CPC
Class: |
C09D 175/16 20130101;
C08G 18/672 20130101; C08G 18/792 20130101; C08G 18/672 20130101;
C08G 18/3212 20130101; C08G 18/0823 20130101 |
Class at
Publication: |
522/90 ; 522/75;
522/78; 522/84 |
International
Class: |
C08F 002/46; C08G
071/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 19, 2000 |
DE |
10002089.5 |
Claims
We claim:
1. A water-dispersible, radiation-curable polyurethane composed
essentially of a) organic, aliphatic or alicyclic polyisocyanates,
b) cycloaliphatic diols and/or cycloaliphatic diamines, c)
compounds containing at least one isocyanate-reactive group and at
least one free-radically polymerizable unsaturated group, d)
compounds containing at least one isocyanate-reactive group and at
least one dispersing-active group, e) if desired, compounds
containing at least two isocyanate-reactive groups having a
molecular weight <1000 g/mol, f) if desired, compounds other
than b) to d) containing at least one isocyanate-reactive
group.
2. A polyurethane as claimed in claim 1, wherein the polyisocyanate
a) is an isocyanurate, a biuret or an allophanate of hexamethylene
diisocyanate or isophorone diisocyanate or is a mixture of the
compounds.
3. A polyurethane as claimed in claim 1, wherein the diol b) is
1,4-bishydroxymethylcyclohexane, bis(hydroxycyclohexyl)propane or
cyclohexanediol or a mixture of at least two of the diols.
4. A polyurethane as claimed in claim 1, wherein the fraction of
the diol b) is from 5 to 40 mol %, based on the isocyanate
groups.
5. A polyurethane as claimed in claim 1, comprising as component c)
at least one of the hydroxyalkyl acrylates hydroxyethyl acrylate,
hydroxypropyl acrylate, hydroxybutyl acrylate or pentaerythritol
triacrylate.
6. A polyurethane as claimed in claim 1, wherein
dimethylolpropionic acid, thioglycolic acid, hydroxyacetic acid,
hydroxypivalic acid or a mixture of at least two of the acids is
present as component d).
7. A polyurethane dispersion comprising a water-dispersible,
radiation-curable polyurethane composed essentially of a) organic,
aliphatic or alicyclic polyisocyanates, b) cycloaliphatic diols
and/or cycloaliphatic diamines, c) compounds containing at least
one isocyanate-reactive group and at least one free-radically
polymerizable unsaturated group, d) compounds containing at least
one isocyanate-reactive group and at least one dispersing-active
group, e) if desired, compounds containing at least two
isocyanate-reactive groups having a molecular weight <1000
g/mol, f) if desired, compounds other than b) to d) containing at
least one isocyanate-reactive group, and if desired g) from 0 to
10% by weight of one or more photochemically and/or thermally
activatable initiators, h) from 0 to 10% by weight of UV absorbers
and HALS compounds.
8. A method of coating substrates, which comprises applying a
polyurethane dispersion as claimed in claim 7, to which typical
coatings additives have been added if desired, to a substrate,
drying it and curing it with electron beams or UV light under
oxygen or, preferably, under inert gas.
9. The use of a polyurethane as claimed in claim 1 or its
dispersion as claimed in claim 7 as a coating composition for
exterior applications.
10. A substrate coated with a radiation-curable polyurethane as
claimed in claim 1.
Description
[0001] The invention relates to water-dispersible,
radiation-curable polyurethanes possessing improved weathering
stability. The invention likewise relates to dispersions comprising
such polyurethanes. The invention further relates to a method of
coating substrates using the polyurethane dispersions, to the use
of the polyurethanes or their dispersions as coating compositions
for exterior applications, and to substrates coated with the
polyurethanes.
[0002] Water-dispersible, radiation-curable polyurethanes are
known, for example, from U.S. Pat. No. 5,905,113, EP-A-801092 and
EP-A-704469. They are generally obtainable by reacting a mixture of
a chain extender, i.e., a component containing at least two OH
groups or at least two NH.sub.2 groups, at least one compound
containing dispersing-active groups, i.e., ionic or ionizable
groups, and containing an isocyanate-reactive group, and at least
one hydroxyalkyl ester of an ethylenically unsaturated carboxylic
acid, especially hydroxyethyl acrylate, with a compound containing
at least two isocyanate groups. Bifunctional compounds containing
two OH groups that are frequently used are hydroxyl-bearing
polyesters or hydroxyl-bearing polyethers. When using
hydroxyl-bearing polyethers, however, unsatisfactory weathering
stabilities are obtained. Polyurethanes containing polyester
structures are unstable to hydrolysis and therefore unsuited to
producing weather-stable coatings. Moreover, the surface tack of
the coatings obtained is high. The use of polycaprolactones leads
to improved weathering stability.
[0003] Aqueous polyurethane dispersions are used predominantly to
coat wood, leather and paper in the interior sector. The use of
radiation-curable coatings in the exterior sector is still
problematic, since aqueous dispersions in particular do not have
the desired weathering and chemical stability.
[0004] U.S. Pat. No. 5,859,135 discloses aqueous dispersions of
polymers containing functional crosslinkable groups and possessing
lipophilic main chains, based in particular on polyesters. Owing to
the high molecular weight of the disclosed lipophilic main chains,
however, the crosslinking densities achieved are inadequate for
good scratch resistance and chemical stability.
[0005] EP-A-26313 and EP-A-554 784 disclose aqueous polyurethane
dispersions and their use as coating compositions. The presence of
sulfonic acid groups and/or sulfonate groups gives these
polyurethanes a high hydrophilicity, leading to inadequate wet
strength of coatings produced from them.
[0006] Polyurethanes containing carboxylic acid groups as
dispersing-active component have also to date been unsatisfactory
in their performance properties. For instance, polyurethane
dispersions in accordance with EP-A-392 352, EP-A-181 486 and
EP-A-209 684 exhibit disadvantages in terms of chemical resistance
and mechanical properties, such as hardness, elasticity and
flexibility of coatings for example.
[0007] Water-dispersible, radiation-curable polyurethanes are also
known from EP-A-704469. The polyurethanes are composed of organic
polyisocyanates, polyesterpolyols, compounds containing at least
one isocyanate-reactive group and at least one carboxyl or
carboxylate group, compounds containing at least one
isocyanate-reactive group and at least one copolymerizable
unsaturated group, and further components if desired. These
polyurethanes represent an improvement in terms of wet strength,
chemical resistance and mechanical properties of the coatings
produced with them.
[0008] There continues to be a need for further improvement,
especially as regards weathering stability, chemical stability,
scratch resistance, flexibility and other mechanical
properties.
[0009] It is an object of the present invention to provide
weathering-stable, radiation-curable, polyurethanes which give
coatings possessing good weathering stability and good chemical
resistance and are therefore suitable for exterior applications.
Moreover, it is intended that the coatings should have high scratch
resistance and good mechanical properties.
[0010] A further object of the present invention is to provide
polyurethane dispersions comprising such polyurethanes and a
process for preparing these polyurethane dispersions.
[0011] We have found that these objects are achieved by means of a
water-dispersible, radiation-curable polyurethane composed
essentially of:
[0012] a) organic, aliphatic or alicyclic polyisocyanates,
[0013] b) cycloaliphatic diols and/or cycloaliphatic diamines,
[0014] c) compounds containing at least one isocyanate-reactive
group and at least one free-radically polymerizable unsaturated
group,
[0015] d) compounds containing at least one isocyanate-reactive
group and at least one dispersing-active group.
[0016] Preferably, the water-dispersible, radiation-curable
polyurethane further comprises one or more of the following
constituents:
[0017] e) compounds containing at least two isocyanate-reactive
groups having a molecular weight <1000 g/mol, preferably <500
g/mol,
[0018] f) compounds other than b) to d) containing at least one
isocyanate-reactive group.
[0019] The dispersions of the polyurethanes, optionally,
comprise
[0020] g) from 0 to 10% by weight of one or more photochemically
and/or thermally activatable initiators,
[0021] h) from 0 to 10% by weight of UV absorbers and light
stabilizer compounds based on sterically hindered amines.
[0022] The polyurethanes, and their aqueous dispersions, are
suitable as coating compositions for exterior applications. The
coatings obtained exhibit high weathering stability and chemical
resistance and no surface tack.
[0023] Component a)
[0024] Suitable polyisocyanates a) are preferably those having an
NCO functionality of at least 2, in particular at least 3.
[0025] Suitable examples include linear or branched
C.sub.4-C.sub.14 alkylene diisocyanates, cycloaliphatic
diisocyanates having in all 6 to 12 carbon atoms, polyisocyanates
containing isocyanurate groups, uretdione diisocyanates,
polyisocyanates containing biuret groups, polyisocyanates
containing urethane and/or allophanate groups, polyisocyanates
containing oxadiazinetrione groups, uretonimine-modified
polyisocyanates, or mixtures thereof.
[0026] Examples of suitable diisocyanates that may be mentioned
include tetramethylene diisocyanate, hexamethylene
diisocyanate(1,6-diisocyanatoh- exane; HDI), octamethylene
diisocyanate, decamethylene diisocyanate, dodecamethylene
diisocyanate, tetradecamethylene diisocyanate, trimethylhexane
diisocyanate or tetramethylhexane diisocyanate, cycloaliphatic
diisocyanates such as 1,4-, 1,3- or 1,2-diisocyanatocyclohexane,
4,4'-di(isocyanatocyclohexyl)methane,
1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane
(isophorone diisocyanate; IPDI) or 2,4- or
2,6-diisocyanato-1-methylcyclohexane.
[0027] The polyisocyanates containing isocyanurate groups comprise,
in particular, simple trisisocyanato isocyanurates, which
constitute cyclic trimers of the diisocyanates, or mixtures with
their higher homologues containing more than one isocyanurate ring.
The isocyanato isocyanurates generally have an NCO content of from
10 to 30% by weight, in particular from 15 to 25% by weight, and an
average NCO functionality of from 3 to 4.5.
[0028] The uretdione diisocyanates are cyclic dimerization products
of diisocyanates. The uretdione diisocyanates may be used, for
example, as sole component or in a mixture of other
polyisocyanates, especially the isocyanates containing isocyanurate
groups.
[0029] Suitable polyisocyanates containing biuret groups preferably
have an NCO content of from 18 to 22% by weight and an average NCO
functionality of 3 to 4.5.
[0030] Polyisocyanates containing urethane and/or allophanate
groups may be obtained, for example, by reacting excess amounts of
diisocyanates with simple polyhydric alcohols such as
trimethylolpropane, glycerol, 1,2-dihydroxypropane or mixtures
thereof. These polyisocyanates containing urethane and/or
allophanate groups generally have an NCO content of from 12 to 20%
by weight and an average NCO functionality of from 2.5 to 3.
[0031] Polyisocyanates containing oxadiazinetrione groups may be
prepared from diisocyanate and carbon dioxide.
[0032] Said polyisocyanates may also be used with preference in a
mixture.
[0033] Preferred polyisocyanates are diisocyanates and
(cyclo)aliphatic polyisocyanates of higher functionality.
[0034] Particular preference is given to polyisocyanates containing
isocyanurate, allophanate and biuret groups, especially those of
hexamethylene diiosocyanate, isophorone diisocyanate, or 1,3- or
1,4-bis(isocyanatomethyl)cyclohexane.
[0035] Particular preference is also given to mixtures of
diisocyanates, e.g., hexamethylene diisocyanate and isophorone
diisocyanate, with higher-functional polyisocyanates in a weight
ratio of from 95:5 to 5:95, in particular from 95:50 to 5:50.
[0036] The isocyanate groups may also be present in capped form.
Examples of suitable capping agents for NCO groups are oximes,
phenols, imidazoles, pyrazoles, pyrazolinones, diketopiperazines,
caprolactam, malonic esters or compounds as stated in the
publications by Z. W. Wicks, Prog. Org. Coat. 3 (1975) 73-99 and
Prog. Org. Coat. 9 (1981), 3-28, and in Houben-Weyl, Methoden der
Organischen Chemie, vol. XIV/2, 61 ff. Georg-Thieme-Verlag,
Stuttgart, Germany 1963.
[0037] Component b)
[0038] Used in accordance with the invention instead of the prior
art polyethers and polyesters are comparatively short-chain diols
containing cycloaliphatic structural elements. Cycloaliphatic
diamines may also be used.
[0039] The cycloaliphatic diols and diamines comprise, in
particular, compounds of the formula I:
H--X--R.sup.1--X--H
[0040] where
[0041] R.sup.1 is C.sub.1-C.sub.12 alkylene interrupted by 1, 2 or
3 C.sub.3-C.sub.8 cycloalkyl 35 groups; C.sub.3-C.sub.8
cycloalkylene; or bicyclic C.sub.6-C.sub.10 cycloalkylene, it being
possible for the cycloalkyl groups and the bicyclic cycloalkyl
groups to be substituted by 1, 2 or 3 C.sub.1-C.sub.4 alkyl
groups;
[0042] X is 0 or NR.sup.2;
[0043] R.sup.2 is H or C.sub.1-C.sub.4 alkyl,
[0044] and if X=NR.sup.2, R.sup.1 may also be --(CH.sub.2).sub.m--
and the two radicals R.sup.2 may together be --(CH.sub.2).sub.m--,
m and n independently of one another being 1, 2 or 3.
[0045] The alkylene chain may be linear or branched. It is
preferably a C.sub.2-C.sub.6 alkylene chain. The cycloalkyl
group(s) may be arranged at any point in the alkylene chain.
Preferably, two cycloalkyl groups are arranged terminally on the
alkylene chain or one cycloalkyl group is arranged internally in
the alkylene chain.
[0046] The cycloalkyl group is preferably a cyclopentyl or
cyclohexyl group.
[0047] The bicyclic cycloalkyl group is preferably a norbornane,
pinane or decalin group.
[0048] Other suitable cycloaliphatic diols are esters of the
formula II:
H--X--R.sup.1--X--CO--A--CO--X--R.sup.1--X--H
[0049] where R.sup.1 is as defined above, X is O and A is
C.sub.2-C.sub.6 alkylene, cyclopentylene, cyclohexylene, phenylene
or O--CO--O.
[0050] In preferred diols, OH groups are attached to the cyclic
moieties of the molecule.
[0051] Particularly preferred diols are diols of the formula III:
1
[0052] (where R independently of each other represents H, CH.sub.3
or C.sub.2H.sub.5) and 1,4-bishydroxymethylcyclohexane,
1,3-bis(4-hydroxycyclohexyl)propane,
2,2,4,4-tetramethylcyclobutane-1,3-d- iol, 1,3- and
1,4-cyclohexanediol, cyclooctanediol, norbornanediol, pinanediol,
decalindiol and their carbonates and esters of the formula II. As
dicarboxylic acids it is preferred to use adipic acid and
1,4-cyclohexanedicarboxylic acid.
[0053] The preparation of these esters and carbonates takes place
in a customary manner and is known to the skilled worker.
[0054] Preferred diamines are methylene- or
isopropylidene-bis(cyclohexyla- mine), piperazine,
1,4-diaminocyclohexane or 1,4-bisaminomethylcyclohexane- .
[0055] Particularly preferred components b) are
1,4-bishydroxymethylcycloh- exane and
1,3-bis(4-hydroxycyclohexyl)propane.
[0056] Particularly preferred diols b), moreover, are
perhydrogenated bisphenol A and other compounds comprising two
cyclohexanol units connected by an alkylene bridge.
[0057] Component c)
[0058] Examples of suitable components c) are esters of
monoethylenically unsaturated C.sub.3-C.sub.6 monocarboxylic acids,
preferably esters of acrylic or methacrylic acid with polyols, in
which at least one hydroxyl group remains unesterified. Preference
is given to C.sub.2-C.sub.12 hydroxyalkyl (meth)acrylates,
especially C.sub.2-C.sub.6 hydroxyalkyl (meth)acrylates, in which
the alkyl chains may be linear or branched.
[0059] Moreover, suitable components c) are vinyl ethers, allyl
ethers and methallyl ethers of polyols, preferably of aliphatic
polyols having 2 to 10 carbon atoms or of cycloaliphatic diols
having a free hydroxyl group.
[0060] Particularly preferred components c) are hydroxyalkyl
acrylates, such as hydroxyethyl, hydroxypropyl and hydroxybutyl
acrylate, pentaerythritol triacrylate, trimethylolpropane
diacrylate and hydroxyethyl vinyleethers, such as hydroxybutyl
vinyl ether, cyclohexanedimethanol monovinyl ether.
[0061] Component d)
[0062] Compounds used as component d) contain at least one,
preferably one or two isocyanate-reactive groups, such as hydroxyl
groups, primary or secondary amino groups or mercapto groups, and
at least one dispersing-active group. Dispersing-active groups are
preferably carboxyl groups and/or sulfonic acid groups or the salt
forms of these.
[0063] As component d), suitable compounds are therefore carboxylic
acids or sulfonic acids containing at least one hydroxyl, amino or
mercapto group. Preference is given to aliphatic mono- or
dihydroxy-, monomercapto- or monoamino-carboxylic acids or sulfonic
acids, such as mercaptoacetic acid (thioglycolic acid),
mercaptopropionic acid, thiolactic acid, mercaptosuccinic acid,
glycine, iminodiacetic acid, sarcosine, alanine, leucine,
isoleucine, aminobutyric acid, hydroxyacetic acid, hydroxypivalic
acid, lactic acid, hydroxydecanoic acid, hydroxydodecanoic acid,
hydroxyhexadecanoic acid, hydroxyethane sulfonic acid,
hydroxypropane sulfonic acid, mercaptoethane sulfonic acid,
mercaptopropane sulfonic acid, aminomethane sulfonic acid, taurine,
aminopropane sulfonic acid, bis(hydroxyalkyl)carboxylic acids, such
as dimethylolpropionic acid, preferably thioglycolic acid,
hydroxyacetic acid, dimethylolpropionic acid and hydroxypivalic
acid.
[0064] By virtue of component d) the polyurethanes are dispersible;
i.e., for dispersion in water no dispersing auxiliaries, such as
protective colloids or emulsifiers, are necessary. Prior to or
during dispersion in water, the carboxyl groups and/or sulfonic
acid groups may be neutralized using organic and/or inorganic
bases, such as alkali metal hydroxides, carbonates and hydrogen
carbonates, ammonia, or primary, secondary or--preferably--tertiary
amines, such as triethylamine.
[0065] Component e)
[0066] Optimal compounds used as component e) are hydrolytically
stable short-chain diols, especially C.sub.2-C.sub.12 diols, such
as ethylene glycol, butanediol, hexanediol and decanediol. Also
suitable are diols and/or diamines having short-chain ether, ester,
carbonate or urethane segments composed of the diols specified for
components b) or e).
[0067] Component f)
[0068] If desired, it is possible for the composition of the
polyurethanes of the invention to use a further component different
than components b) to e). This component comprises, in particular,
mono-C.sub.1-C.sub.12 alcohols, mono-C.sub.1-C.sub.12 mercaptans or
mono-C.sub.1-C.sub.12 amines, such as methanol, ethanol,
cyclohexanol, cyclohexylamine, etc.
[0069] Component g)
[0070] Suitable as component g) are from 0 to 10% by weight,
preferably from 0.1 to 5% by weight, based on the weight of the
radiation-curable polyurethane, of one or more photochemically or
free-radically activatable initiators, especially photoinitiators
which exhibit little or no yellowing. These include the
phenylglyoxylic esters of the formula: 2
[0071] where the two radicals R.sup.1 independently of one another
are a radical of the formula 3
[0072] R.sup.2, R.sup.3 and R.sup.4 independently of one another
are H, C.sub.1-C.sub.6 alkyl unsubstituted or substituted by OH,
OC.sub.1-C.sub.6 alkyl or OCOC.sub.1-C.sub.6 alkyl, or are OH or
OC.sub.1-C.sub.6 alkyl;
[0073] A is C.sub.2-C.sub.6 alkylene or a radical of the formulae 4
5 6
[0074] the radicals R.sup.5 independently of one another are H or
COCOR.sup.1, and A.sup.1 is C.sub.2-C.sub.6 alkylene or 7
[0075] The phenylglyoxylic esters are described in DE 19913353 and
may be prepared by the process described in WO 98/33761.
[0076] Photoinitiators which exhibit little or no yellowing are
also the phenylglyoxylic acids of the formula 8
[0077] where
[0078] R.sup.1 is a hydrogen atom or a C.sub.1-C.sub.18 alkyl
group, and
[0079] R.sup.2 and R.sup.3 independently of one another are a
hydrogen atom or a C.sub.1-C.sub.18 alkoxy group.
[0080] These compounds are described in DE 19826712 and in Angew.
Makromol. Chem. 1981, 93 (1), 83-95. Further suitable
photoinitiators are, for example, benzophenone, alkylbenzophenones,
halomethylated benzophenones, Michler's ketone, anthron and
halogenated benzophenones. Also suitable are benzoin and its
derivatives. Likewise effective photoinitiators are anthraquinone
and many of its derivatives, such as .beta.-methylanthraquinone,
tert-butylanthraquinone and anthraquinonecarboxylic esters, for
example, and acylphosphine oxides, e.g.,
2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin.RTM.
TPO).
[0081] The photoinitiators, which depending on the intended use of
the compositions of the invention are used generally in amounts of
from 0.05 to 20% by weight, preferably from 0.05 to 5% by weight,
based on the polyurethane, may be used as the individual substance
or, owing to frequent advantageous synergistic effects, in
combination with one another.
[0082] Advantageous additives which may lead to a further increase
in the reactivity are tertiary amines such as triethylamine and
triethanolamine, for example. They are also used generally in
amounts of up to 5% by weight, based on the polyurethane.
[0083] Component h)
[0084] Compounds suitable as component h) are UV absorbers and HALS
(Hindered Amine Light Stabilizer) compounds, as described for
example in U.S. Pat. No. 5,369,140. These are UV absorbers from the
class of the 2-hydroxyphenyl-s-triazines and light stabilizers from
the class of the sterically hindered amines, especially those from
the class of the 2,2,6,6-tetramethylpiperidines.
[0085] The fractions of the structural components are preferably as
follows:
[0086] b) 0.05 to 0.4 equivalent, with particular preference from
0.1 to 0.3 equivalent of hydroxyl groups, based on one equivalent
of polyisocyanate a) (from 5 to 40 mol %);
[0087] c) Component c) is used in an amount such that the double
bond content of the polyurethanes is from 0.15 to 0.6, preferably
from 0.2 to 0.5 mol/100 g of polyurethane.
[0088] d) Component d) is used in an amount such that the
polyurethane 20 has a dispersing-active group content of from 0.005
to 0.1, with particular preference from 0.01 to 0.03 mol per 100 g
of polyurethane.
[0089] e) From 0 to 0.2 equivalent, with particular preference from
0 to 0.1 equivalent, based on one equivalent of polyisocyanate
a);
[0090] f) from 0 to 0.4, with particular preference from 0.1 to
0.3, equivalent of isocyanate-reactive groups.
[0091] The molar ratio of isocyanate groups to the
isocyanate-reactive groups of all structural components b) to f) is
preferably from 1:0.8 to 1:1.2, with particular preference
approximately 1:1.
[0092] The polyurethanes of the invention are prepared by reacting
components a), b) and c) and, if desired, e) in a
solvent-containing precursor prior to dispersion and, if desired,
adding component h) (light stabilizers based on sterically hindered
amines) to the solvent-containing precursor. The course of the
reaction may be monitored by the consumption of the functional
groups, especially the isocyanate groups.
[0093] The reaction is preferably conducted in an inert,
water-miscible solvent, such as acetone, tetrahydrofuran, methyl
ethyl ketone or N-methylpyrrolidone. The reaction temperature is
generally from 20 to 100.degree. C., preferably from 50 to
80.degree. C.
[0094] The reaction of the isocyanates may be accelerated using the
customary catalysts, such as dibutyltin dilaurate, tin(II) octoate
or diazabicyclo[2.2]octane.
[0095] Component d) and, if desired, component f) is preferably not
added until toward the end of the reaction. Then, an amine, an
example being triethylamine, or a mixture of amines is used for
neutralization. The solvent may then be removed by distillation and
the water required for dispersing the polyurethane is added.
Usually afterwards, component g) and, if desired, h) are added.
These components, however, may also be added at an earlier
point.
[0096] The solids content of the resulting dispersion is preferably
from 25 to 60%, with particular preference from 30 to 50%.
[0097] The average particle size (determined using a Zetasizer,
from Malvern Instruments) is below 10 .mu.m, preferably below 3
.mu.mm and with very particular preference below 1 .mu.m. The lower
average particle size limit is generally about 30 nm.
[0098] The dispersions of the invention may include further
additives, examples being pigments, dyes, fillers and customary
coatings auxiliaries.
[0099] The dispersions of the invention may also be crosslinked
thermally if they contain initiators which form free radicals at
elevated temperatures. Use may be made, for example, of dibenzoyl
peroxide, cumene hydroperoxide or azodiisobutyronitrile.
[0100] The polyurethanes and polyurethane dispersions of the
invention may be used to produce moldings and, preferably,
coatings.
[0101] The dispersions of the invention are found particularly
suitable for coating substrates such as wood, paper, textile,
leather, nonwoven, plastics surfaces, glass, ceramic, mineral
building materials, such as shaped cement products and fiber cement
slabs, and metals or coated metals.
[0102] The present invention accordingly also provides a method of
coating substrates, and the coated substrates obtainable by this
method. The substrates are generally coated by applying at least
one dispersion of the invention, to which typical coatings
additives may have been added, to the target substrate in the
desired thickness and removing any solvent present. If desired,
this operation may be repeated one or more times. The
radiation-curable formulations are applied to the substrate in a
known manner, for example, by spraying, troweling, knife coating,
brushing, rolling, roller coating, or flow coating. The coating
thickness is generally in the range from 3 to 1000 g/m.sup.2 and
preferably from 10 to 200 g/m.sup.2. Application may be made either
at room temperature or at elevated temperature, but preferably not
above 100.degree. C.
[0103] In the case of porous substrates, such as leather, paper or
wood, for example, the times required for physical drying are
generally very short, since the majority of the water is absorbed
by the substrate.
[0104] In general, the coatings are subsequently cured by exposure
to high-energy radiation.
[0105] If desired, if two or more coats of the coating composition
are applied atop one another, radiation curing may be carried out
after each coating operation.
[0106] Radiation curing takes place by exposure to high-energy
radiation, i.e., UV radiation or daylight, preferably light with a
wavelength of from 250 to 600 nm, or by bombardment with
high-energy electrons (electron beams; from 150 to 300 keV).
Examples of radiation sources used are high-pressure mercury vapor
lamps, lasers, pulsed lamps (flashlight), halogen lamps, and
excimer emitters. The radiation dose commonly sufficient for
crosslinking in the case of UV curing is in the range from 80 to
3000 mJ/cm.sup.2.
[0107] Irradiation may also be conducted, if desired, in the
absence of oxygen, under an inert gas atmosphere, for example.
Suitable inert gases are, preferably, nitrogen, noble gases, carbon
dioxide, or combustion gases. Furthermore, irradiation may be
carried out by covering the coating composition with transparent
media. Examples of transparent media are polymer films, glass or
liquids, e.g., water.
[0108] In one preferred process, curing takes place continuously by
passing the substrate treated with the formulation of the invention
past a radiation source at a constant speed. This requires the
curing rate of the formulation of the invention to be sufficiently
high.
[0109] Even after physical drying only, the polymethanes of the
invention give an essentially tack-free, dry coating. After
radiation curing, the coating possesses very good weathering
stability, chemical stability and scratch resistance with at least
comparable mechanical properties such as hardness, tensile
strength, elasticity, flexibility, and adhesion.
[0110] The invention is illustrated below with reference to
examples.
EXAMPLE 1
[0111] Preparation of a Weathering-Stable Polyurethane Acrylate
Dispersion
[0112] Preparation of the Precursor:
[0113] A stirred vessel was charged with 455 parts of hydroxyethyl
acrylate, 377 parts of 2,2-bis(4-hydroxycyclohexyl)propane, 2.3
parts of 2,6 di-t-butyl-p-cresol, and 1.2 parts of hydroquinone
monomethyl ether, 0.5 part of dibutyltin dilaurate and 1500 parts
of the isocyanurate of hexamethylene diisocyanate are added, and
the mixture was stirred at 60.degree. C. for 5 hours. The batch was
diluted with 500 parts of acetone. The NCO value was 1.05%.
[0114] Preparation of Polyurethane Dispersion:
[0115] 882 parts of this solution were admixed with 9.7 parts of
thioglycolic acid and 3.7 parts of methanol and the mixture was
left to react at 40.degree. C. for 8 hours, after which 11 parts of
triethylamine were added. The batch was dispersed in water and the
acetone was removed by distillation. The particle size was 75
nm.
COMPARATIVE EXAMPLE 1
[0116] (Example 1 of EP 704469):
[0117] A stirred vessel was charged with 6.74 g of a polyester
prepared from isophthalic acid, 1,6-hexanediol and adipic acid,
having a molecular weight of approximately 2000 (number average)
and approximately 10,000 (weight average), 3.26 kg of
1,4-butanediol, 7.83 kg of 2-hydroxyethyl acrylate, 1.6 kg of
acetone, 31.2 g of hydroquinone monomethyl ether, 19.4 g of
dibutyltin dilaurate and 58.2 g of 2,6-di-t-butyl-p-cresol. The
contents were heated initially to 60.degree. C. and a mixture of
15.91 kg of isophorone diisocyanate with 4.94 kg of Basonat PLR 8
638 (trimerized HDI) was added dropwise over the course of two
hours. After the isocyanate content had fallen to 1.15%, 3.16 kg of
PUD salt (Michael adduct of acrylic acid with ethylenediamine) were
added in the form of a 40% strength aqueous solution. Finally, 47.7
kg of distilled water were added, the vessel interior was heated to
65.degree. C., and an acetone/water mixture was removed by
distillation. The water lost by distillation was replaced by adding
more. The particle size was 65 nm.
[0118] Performance Testing
[0119] Production of Films
[0120] The dispersions from Example 1 and comparative Example 1
were admixed with 4% by weight of photoinitiator Irgacure 500
(Ciba) (benzil dimethyl ketal), applied to various substrates in
film thicknesses of approximately 40 .mu.m, and treated as follows:
ventilation at room temperature overnight, then heat treatment at
60.degree. C. for 15 minutes and exposure in an IST UV unit on a
conveyor belt at 10 m/min with 2 UV lamps (120 W/cm). Both films
were physically dry and through-cured (fingernail test).
[0121] The chemical stability was determined in accordance with DIN
68861 (chemical resistance of furniture surfaces) for 10 chemicals
(cleaning agent, ballpoint pen paste, disinfectant, lipstick,
mustard, butyl acetate, blackcurrant juice, coffee, red wine,
sodium carbonate; substrate: black-colored basecoat on metal)
(rating 0: no visible change to rating 5: test area destroyed).
[0122] The scratch resistance was determined in an abrasion test in
which 50 double strokes were performed using a Scotch Brite fabric
under a weight of 750 g. The level of scratching of the coating on
a black-colored glass plate was determined by measuring the drop in
gloss in % (before and after corresponding exposure).
[0123] The weathering stability was determined by applying films of
the dispersions approximately 35 .mu.m thick to a barium fluoride
crystal and curing them. These samples were then exposed to
UV-water cycles of 8 hours' irradiation at 70.degree. C. and 4
hours' dark condensation at 50.degree. C. in a QUV Weather-o-meter
UVA-A-340 with fluorescent lamps. After 300 hours, the decrease in
the C--H (2951 cm.sup.-1) and C--N (1531 cm.sup.-1)bands in the IR
spectrum was measured. Alternatively, samples of coating material
were irradiated in the Xenon test 1200 from Heraeus in accordance
with ISO/DIS 11341 (dry period 17 min/irrigation period 3 min) and
the drop in degree of gloss was measured.
[0124] The pendulum hardness was determined in accordance with DIN
53157 (substrate: black-colored glass plate). It is a measure of
the hardness of the coating (high values: high hardness).
[0125] The Erichsen indentation was determined in accordance with
DIN ISO 1520 (substrate: Bonder panel). It is a measure of the
flexibility and adhesion of the coating (high values: high
flexibility).
1 Weathering stability Chemical (reduction in stability Scratch
resistance C-H, (rating) (Loss of gloss, %) C-N bands, %) Example 1
0.70 29 4/0 Comparative 1.05 61 7/15 Example 1
[0126] With an equal level in terms of mechanical properties
(pendulum hardness Example 1: 114 swings/comparative Example 1: 105
swings; Erichsen indentation Example 1: 7.8 mm/comparative Example
1: 8.6 mm) and initial physical drying (pendulum hardness before UV
irradiation Example 1:8 swings/comparative Example 1:12 swings),
there are clearly improvements in the chemical, scratch and
weathering stability.
COMPARATIVE EXAMPLES 2 TO 6
[0127] In Example 1, the bis(hydroxycyclohexyl)propane fraction was
replaced by other diols, short-chain polyethers, polyesters,
polycarbonate and polymethacrylate diols:
[0128] C2: polyether of tetrahydrofuran (poly-THF 1000)
[0129] C3: polycarbonate Desmodur 2020 (Bayer AG)
[0130] C4: aromatic polyester prepared from isophthalic acid,
adipic acid and hexanediol (M=1000)
[0131] C5: Polymethacrylate: BD 1000 from Goldschmidt
[0132] C6: aliphatic polyester prepared from adipic acid and
neopentyl glycol (M=3024).
2 Weathering stability Decrease in C-H band Decrease in C-N band
(in %) (in %) C2 24 18 C3 10 19 C4 11 22 C5 6 18 C6 11 23 Example 1
4 0
EXAMPLE 2
[0133] The procedure of Example 1 was repeated but using a mixture
of 75% of the isocyanurate of HDI with 25% of the isocyanurate of
IPDI, instead of the isocyanurate of HDI.
[0134] The initial physical drying is markedly improved: Pendulum
hardness before UV: 21 swings. In the Xenon test, there is no drop
in gloss after 300 hours.
EXAMPLE 3
[0135] Preparation of a Weathering-Stable Polyurethane Acrylate
Dispersion Based on Allophanate.
[0136] A stirred vessel was charged with 43 parts of acetone, 92
parts of 2,2-bis(4-hydroxycyclohexyl)propane, 0.4 part of
2,6-di-t-butyl-p-cresol and 0.2 part of hydroquinone monomethyl
ether, 0.1 part of dibutyltin dilaurate and 333 parts of an
allophanate of hydroxylethyl acrylate and hexamethylene
diisocyanate were added, and the mixture was stirred at 65.degree.
C. for 5 hours. The batch was diluted with 50 parts of acetone. The
NCO value was 0.68%. 8.5 parts of thioglycolic acid are added and
the mixture was left to react at 60.degree. C. for 6 hours, after
which 94 parts of triethylamine were added. The batch, then, was
dispersed in water and the acetone was removed by distillation (28%
solids content). There was no drop in gloss in the Xenon test after
300 hours.
* * * * *