Note: Descriptions are shown in the official language in which they were submitted.
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LeA 27,624
AQUEOUS SOLUTIONS OR DISPERSIONS OF OLIGOURETHANES
CONTAINING (METH)ACRYl.OYL GROUPS, A PROCESS FOR
THEIR PRODUCTION AND COATED SUBSTRATES PREPARED THEREFROM
BACKGROUND OF THE INDENTION
Field of the Invention
This invention relates to aqueous solutions or
dispersions of certain ionically modi~Fied aligourethanes
containing (meth)acryloyl groups, to a process far their
production and to coated substrates prepared therefrom.
~.o Description of the Prior Art
Polyurethanes containing (meth)acryloyl groups
{so-called urethane (meth)acrylates) have long been known and
are eminently suitable as binders, for example for paints {cf.
far example DE-OS 2,737,406). The relatively high viscosity of
these products almost always necessitates the use of organic
solvents.
Water-dilutable urethane (meth)acrylates are also
known (cf. for example, DE-OS 2,936,039). The hydraphilicity
of these known systems is based on the presence of ionic
2o centers, particularly sulfonate groups, which contain as
counterions alkali cations or ammonium ions (from tertiary
amines) which at least partly rema in in the coatings ultimately
obtained from the systems and considerably impair their water
resistance.
Accordingly, an object of the present invention is to
provide new aqueous solutions or dispersions of urethane
(meth)acrylates which are stable in storage without the
addition of dispersants or external emulsifiers, without alkali
can ons and without ammonium ions from tertiary amines, and
which may be cured to form coatings combining resistance to
water and chemicals with favorable mechanical properties.
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This object may be achieved in accordance with the
solutions or dispersions of the present invention which are
described in detail hereinafter and by the process for their
production. The principal feature of the invention is that
s carboxyl groups at least partly neutralized with ammonia are
incorporated into the urethane (meth)aerylates using
2,2-bis-(hydroxymethyl)-alkane carboxylic acids.
DE-QS 3,641,494 relates to a process in which
polyurethane elastomers dispersible in water are modified with
to anions. Nevertheless, it can be said that the solution
provided by the present invention to the stated object was not
obvious from this prior publication. The solutions or
dispersions of oligourethanes according to the present
invention, which are described in detail hereinafter, differ
15 from the solutions or dispersions of polyurethanes according to
the reference in several areas:
- The polyurethanes according to the prior publication are
polyurethane elastomers wherein the molecules are based on
structural units attributable to the incorporation of
za relatively high molecular weight compounds containing at
least two isocyanate-reactive groups, particularly
hydroxyl groups. The oligourethanes according to 'the
invention contain no such structural units.
The polyurethanes according to the prior publication
25 contain terminal or lateral polyether chains containing
ethylene oxide units as further hydrophilic centers which
are not present in the oligourethanes according to the
invention.
- In addition to the ammonium carboxylate groups, the
sa oligourethanes according to the present invention also
have a high concentration of (me~th)acryloyl groups, which
is net the case with the polyurethanes according to the
prior publication. It could not have been expected that
it would be possible to produce storable aqueous solutions
s5 or dispersions of oligourethanes containing both high
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concentrations of (meth)acryloyl groups and ammonia in the
form of ammonium groups because it is known that ammonia,
in the same way as primary or secondary amines, reacts
spontaneously with activated double bonds by Michael
addition. Accordingly, it could not have expected that
the principle of ionic modification according to DE-OS
3,641,494 would be applicable to oligourethanes containing
(meth)acryloyl groups of the type present in the solutions
or dispersions according to the present invention.
to ,SUMMARY OF ThE 1NVENT10N
The present invention relates to aqueous solutions or
dispersions of oligourethanes having a pH of 6.0 to 8.5 wherein
the dissolved or dispersed oligourethanes contain carboxyl
groups at least partially neutralized with ammonia and have
l) a double bond content in the form of (meth)acryloyl groups
(expressed as C=C, molecular weight 24) of 3 to 15% by
i~eight and
ii) a content of carboxyl groups, including the carboxyl
groups neutralized with ammonia, which corresponds to an
2o acid value of 20 to 100.
The present invention also relates to a process for
the preparation of aqueous solutions or dispersions of
oligourethanes by reacting
a) 20 to 80% by weight of an alcohol component containing at
2s least ane monohydric alcohol having one or more
(meth)acryloyl groups and a molecular weight of 116 to
1,000,
b) 4.5 to 20% by weight of at least one 2,2-bis-(hydroxy-
methyl)-alkane carboxylic acid having at least 5 carbon
ao atoms and
c) 15 to 75% by weight of at least one polyisocyanate
component containing at least one organic polyisocyanate
having a molecular weight of 168 to 1,000,
by initially introducing components a) and b), then reacting
~5 these components with component c) at a temperature of 50 to
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100°C until the reaction mixture contains no more free
isocyanate groups and subsequently dissolving or dispersing the
reaction mixture in water, the carboxyl groups being at least
partly neutralized by addition of ammonia during the dissolving
or dispersing step so that the resulting solution or dispersion
has a pH value of 6.0 to $.5, wherein
A) the percentages of a), b) and c) add up to 100, based on
the weight of a), b) and c),
B) the amounts of a), b) and c) correspond to an NCO: OH
1o equivalent ratio of 0.5:1 to 1:1 and
C) the amounts of a), b) and c) are otherwise selected within
the stated limits so that the resulting oligourethanes
have
i) a double bond content in the form of (meth)acryloyl
groups (expressed as C=C, molecular weight 24) of 3
to 15% by weight and
ii) a content of carboxyl groups, including the carboxyl
groups neutralized with ammonia, which corresponds to
an acid value for the oligourethanes of ZO to 100.
2o Finally, the present invention is directed to coated
substrates prepared from these solutions or dispersions of
oligourethanes.
DETAILED DESCRIPTION OF THE INVENTION
Component a) contains at least one monohydric alcohol
containing one or mare (meth)aeryloyl groups. Examples include
esters which contain on average one free hydroxyl group and
which are prepared from acrylic acid or methacrylic acid and
polyhydric alcohols. The esters have a molecular weight of 116
to 1,000, preferably 116 to 750. Examples of such ethyl-
Oo enically unsaturated esters are hydroxyethyl (meth)acrylate, 2-
and 3-hydroxypropyl (meth)acrylate, 2-, 3- and 4-hydroxybutyl
(meth)acrylate and reaction products of trimethylol propane or
alkoxylated trimethylol propane with (meth)acrylic acid, such
as the reaction product of 2 moles of acrylic acid with 1 mole
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of an ethoxylated trimethylol propane (OH value 550, degree of
ethoxylation approx. 4).
Component b) contains at least one 2,2-bis-(hydroxy
methyl)-alkane carboxylic acid having at least 5 carbon atoms,
s preferably 2,2-bis-(hydroxymethyl)-propionic acid.
Component c) contains at least one organic po7yiso-
cyanate. Suitable polyisocyanates include any organic
polyisocyanate known from polyurethane chemistry having
aliphaticaliy, cycloaliphatically and/or aromatically bound
to isocyanate groups and a molecular weight of 168 to 1,000,
preferably 168 to 300. Examples of suitable polyisocyanates
include 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyi
cyclohexane (IPUI); 4,4'-diisocyanatodicyclahexyl methane;
4,4'-diisocyanatodiphenyl methane and mixtures thereof with
15 2,4'-diisocyanatodiphenyl methane and, optionally, the higher
homologs of these diisocyanates; and 2,4-diisocyanatotoluene
and mixtures thereof with 2,6-diisocyanatotoluene.
Biuret-, isocyanurate- or urethane-modified
polyisocyanates based on these monomeric polyisocyanates are
2o also suitable. These derivatives generally have a molecular
weight less than 1,000. The preparation of these derivatives
is described, for example, in U.S. Patents 3,124,604,
3,183,112, 3,919,218 and 4,324,879.
The oligourethanes present in the solutions or
a5 dispersions according to the invention have the above-mentioned
content of olefinic double bonds. This content is preferably
between 4 and 10% by weight. The oligourethanes have an ac id
value of 20 to 100, preferably 25 to 80 mg K0H/g; the acid
value encompasses both the free carboxyl groups and also the
30 carboxyl groups neutralized with ammonia. At least some,
preferably 45 to 100% and more preferably 60 to 100%, of the
carboxyl groups are neutralized with ammonia, i.e., are present
as carboxylate groups. At the same time, it is impor'tan't
during neutralization of the carboxyl groups to ensure that the
35 pH value of the aqueous solutions or dispersions is between 6.0
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and 8.5, preferably between 6.5 and 8Ø The solutions or
dispersions according to the invention generally have a solids
content of 30 to 55% by weight, preferably 35 to 50% by weight.
The oligourethanes according to the invention are
reaction products of comparatively low molecular weight
starting materials in the presence of large quantities of
chain-terminating synthesis components. Accordingly, there is
every justification to refer to these reaction products not as
°'polyurethanes," but instead as "oiigourethanes°' which have an
average molecular weight calculated from the stoichiometry of
to the starting materials of 700 to 5,000, preferably 700 to
2,000.
In the practical application of the process according
t o the invention, component a) is preferably used in a quantity
of 25 to 75% by weight, component b) is preferably used in a
quantity of 5 to 19% by weight and component c) is preferably
used in a quantity of 20 to 70% by weight, the percentages of
a), b) and c) adding up to 100, based on 'the weight of a), b)
and c). In addition, it is important in accordance with the
present invention to ensure that the starting components are
2o used within the stated limits so that an NCO: OH equivalent
ratio of 0.5:1 to 1:1, preferably 0.7:1 to 1:1 is maintained.
The polyisocyanate c) is generally used in slightly less than
the stoichiometric quantity so that the end of the reaction is
reached when no more isocyanate groups can be detected in the
reaction mixture. Finally, the reactants and their amounts are
suitable selected within the stated limits to ensure that 'the
oligourethanes have the required double bond content and acid
number.
The reaction according to the invention is preferably
carried out in 'the presence of inert solvemts at solids
contents of 60 to 95% by weight. Suitable solvents include
dimethyl diglycol, N-methyl pyrrolidone, N-methyl caprolactane,
ethyl glycol acetate, n-butyl acetate, acetone and mixtures of
these solvents.
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To carry out the reaction, the alcohol component a)
containing the (meth)acryloyi groups, the 2,2-bis-(hydroxy-
methyl)-alkane carboxylic acid b) and the solvent preferably
used are homogenized, the polyisocyanate c) is added over a
s period of 1 minute to 2 hours at 50 to 100°C and the reaction
mixture is then stirred at 60 to i00°C utilizing the exothermic
reaction until a resin having the characteristics mentioned is
obtained. The reaction is preferably carried out in the
presence of oxygen, for example, by passing air through the
~o reaction mixture.
The reaction may be accelerated by the addition of
suitable catalysts (such as dibutyl tin dioxide, dibutyl tin
dilaurate and triethylamine) in quantities of 0.01 to 2.5% by
weight, based on the weight of the reaction mixture as a whole.
i5 The reaction product may be protected against
premature and unwanted polymerization by the addition of
suitable inhibitors and antioxidants each in quantities of
0.001 t o 0.3°'° by weight, based on the mixture as a whole.
Where the residual organic solvent content has to
zo meet particularly stringent requirements, the solvent may be
partly removed by distillation before, during and/or after
neutralization or dissolution or dispersion of the resin in
water. Removal of solvents from the solution or dispersion by
distllation is only appropriate far solvents which form an
z5 azeotrope with water.
After the urethanization reaction, small quantities
of other organic solvents (such as ethanol, n-propanol,
isopropanol, n-butanol, tert.-butanol, pentanol, hexanol,
octanol, butyl glycol, ethyl glycol, butyl diglycol, ethyl
ao diglycol, methyl diglycol and methoxypropanol) may be added to
obtain certain properties.
The reaction products, which preferably accumulate in
the form of 60 to 95% by weight solutions in organic solvents,
are dissolved or dispersed in 'the form of these solutions in a
05 mixture of water and ammonia, 'the ammonia preferably being used
Mo-3552
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in such a quantity that 45 to 100%, preferably 60 to 100% of
the carboxyl groups are neutralized. At the same time, it is
important to ensure that the pH value of the solution or
dispersion formed is between 5.0 and 8.5, preferably between
6.5 and 8Ø The quantity of water used is gauged so that a
solids content within the limits mentioned above is abstained.
The aqueous solutions or dispersions obtained in
accordance with the present invention are valuable aqueous
binders for coating compositions. They may be used as such or
in combination with auxiliaries and additives known from paint
to technology (such as fillers, pigments, solvents, flow control
agents and the like) for the production of coatings on any
substrate.
Suitable substrates include paper, paperboard,
leather, wood, plastics, nonwovens, textiles, ceramic
materials, mineral materials, glass, metal, artificial leather,
photographic materials, for example, paper coated with a
photographic layer.
The coating compositions may be applied in known
manner by spray coating, knife coating, roll coating, spread
2o coating, dip coating or casting. After evaporation of the
water and any inert solvents present, the coatings may be
crosslinked either by high-energy radiation (such as UV light,
electron beams or gamma rays) or by curing with metal salts of
siccative acids and (hydro)peroxides or with metal salts of
25 siccative acids or with (hydro)peroxides alone at temperatures
of 80 to 250°C. At temperatures above 150°C, it is generally
not necessary to add (hydro)peroxides and/or metal salts.
When the coatings are crosslinked by UV 'irradiation,
photoinitiators have to be added to 'the coating compositions.
so Suitable photoinitiators include known compounds such as those
which are described, for example, in the book by J. Korsar,
Light-Sensitive Systems, J. Wiley & Sons, New York-London-
Sydney, 1965.
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Other suitable photoinitiators include benzoin ethers
such as benzoin isopropyl ether, benzil ketals such as benzil
dimethyl ketal, and hydroxyalkyl phenones such as 2-hydroxy-2-
methyl-1-phenylpropan-1-one. The photoinitiators are used in
quantities of 0.1 to 10% by weight, preferably 0.1 to 5% by
weight, depending upon the particular application for the
compounds according to the invention. The photoinitiators may
be used either individually or, by virtue of favorable syner-
gistic effects, in combination with one another.
to The siccatives which are optionally used include
cobalt, lead or manganese salts of acids such as linseed oil
Fatty acid, tall oil fatty acids and soybean oil fatty acids;
resinic acids such as abietic acid and naphthenic acid; acetic
acid; and isooctanoic acid. When they are used, they are used
i5 in the form of organic solutions in such quantities that the
metal content, based on the weight of the dispersed hydrophilic
and hydrophobic polymers, corresponds to between 0.001 and 1%
by weight.
Examples of suitable (hydro)peroxides include dicumyl
2o peroxide, di-tart. butyl peroxide, benzoyl peroxide, cyclo-
hexanone peroxide, methyl ethyl ketone peroxide, acetyl acetone
peroxide, dinonyl peroxide, bis-(4-tart.-butyl-cyclohexyl)-
peroxydicarbonate, tart. butyl hydroperoxide, 2,5-dimethyl-
hexane-2,5-hydroperoxide, diisopropylbenzene monohydroperoxide
2s and hydrogen peroxide. These (hydro)peroxides are preferably
used in quantities of 1 to 10% by weight, based on the weight
of the dispersed or dissolved oligourethanes.
rn the following examples, all parts and percentages
are by weight unless otherwise ind'ica'ted.
~a ~XAMIPI.ES
The quantities of components a) and b) set forth ~in
Table 1 were dissolved in butyl acetate together with 0.2% tin
diactoate and 0.1% 2,6-di-tart. butyl-p-cresol (see Table 1)
and the resulting solution was heated to 60°C while air was
35 passed through. The quantity of component c) set forth in
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Table 1 was then added dropwise. After 1 hour, the temperature
was increased to 80"C and the mixture was kept at that
temperature until the NCO content had fallen to below 0.1%
A solution of ammonia in water was 'then added to 'the
solution of the oligourethane containing (meth)acryloyl groups
obtained in a quantity sufficient to obtain a solids content of
50%. Ammonia was then added to provide a degree of neu~tral-
ization of 80%n, based on dimethylal propionic acid. A solution
of ammonia in water was then added in an amount which resulted
to in an aqueous dispersion or solution having a pH value of
approx. 7. The solids contents obtained and the pH values are
set forth in Table 1.
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_Application Examples
a) photochemical curing
5% 2-hydroxy-2-methyl-1-phenylpropan-1-one was added
to the product of Examples 1, z, 3 and 4 beFore the final
addition of ammonia water.
The aqueous dispersions were then applied to a glass
plate in a wet film thickness of 60 ~cm. After evaporation of
the water, the film was cured beneath two 1ST lamps (impulse
lamps manufactured by Strahlentechnik Fiildebrancl, Warner and
io Pfleiderer, output 80 watts/cm, arranged at a distance from the
film of 20 cm) at a processing speed of 14 m/minute.
Clear, extremely hard (Konig pendulum hardness in
accordance with DIN 53 157: approx. 200 sacs.) and
scratch-resistant coatings which were resistant to water and
chemicals were obtained.
Scratch resistance was determined by the finger nail
test while resistance to water and chemicals was tested by the
application of cotton wool plugs impregnated with
- water (16 hours)
- ethanol, 50% (I hour)
- detergent (1 hour)
- acetone (10 seconds).
b) Thermal curin--tc
The aqueous dispersions of Examples 2, 3, 5 and 6
2s were applied to a glass plate in a wet film thickness of 60 ~Cm
and cured for 30 minutes and 180°C. Clear, hard,
scratch-resistant and water-resistant coatings were formed.
Although the invention has been described in detail
in the foregoing for the purpose of illustration, it is to Ibe
understood that such detail is solely for that purpose and ~tha~t
variations can be made therein by those skilled in the art
without departing from the spirit and scope of the invention
except as it may be limited by the claims.
