TRADUCTION NON-DISPONIBLE

RADIATION CURABLE COATING CMPOSITIONS CONTAINING UNSATURATED ADDITION - POLYMERIZABLE URETHANE RESIN

Abrégé anglais

Abstract
The addition of minor amounts of acrylic acid to radiation
curable compositions containing unsaturated addition-poly-
merizable urethane resin and reactive monomer diluent is
effective in reducing viscosity and thixotropy of the com-
positions and in inhibiting separation of the resin phase from
the diluent phase. In addition, acrylic acid has been found to
render unsaturated addition-polymerizable urethane resins more
compatible with higher molecular weight reactive monomer diluents.

Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A coating composition comprising: a) at least
one unsaturated addition polymerizable urethane resin; (b) a
reactive diluent system containing at least one unsaturated
addition-polymerizable monofunctional monomeric compound selected
from the group consisting of esters having the general formula
<IMG> ;
wherein R° is hydrogen or methyl and R is an aliphatic or cyclo-
aliphatic group having from 6 to 18 carbon atoms; and (c)
acrylic acid, the amount of said unsaturated resin being in the
range from about 30 to about 90 weight percent, based on combined
weight of said unsaturated urethane resin and said reactive
diluent system, the amount of the reactive diluent system being
from 10 to 70% by weight based on the total weight of unsaturated
urethane resin and reactive diluent system, and the amount of
acrylic acid being in the range from about 0.1 to about 10 weight
percent, based on total weight of said unsaturated urethane
resin and said reactive diluent system.
2. A composition according to claim 1, wherein the
amount of said unsaturated resin is in the range from about 50
to about 75 weight percent based on combined weight of said
unsaturated urethane resin and said reactive diluent system.
3. A composition according to claim 2, wherein the
amount of acrylic acid is in the range from about 1 to about 5
weight percent, based on total weight of said unsaturated urethane
resin and said reactive diluent system.
4. A composition according to claim 3, wherein said
unsaturated urethane resin is characterized by the presence of
at least two terminal ethylenically unsaturated groups having
the structure <IMG> .
12

5. A composition according to claim 3, containing an
effective amount of at least one photoinitiator compound.
6. A composition according to claim 4, containing from
about 0.01 to about 30 parts by weight, based on combined
weight of said unsaturated urethane resin and said reactive
diluent system, of at least one photoinitiator compound.
7. A composition according to claim 2, wherein R is an
alkyl or cycloalkyl group having from 6 to 18 carbon atoms.
8. A composition according to claim 2, wherein R is
an alkyl or cycloalkyl group having from 6 to 9 carbon atoms.
9. A composition according to claim 8, wherein said
unsaturated urethane resin is characterized by the presence of
at least two terminal ethylenically unsaturated groups having
the structure <IMG> .
10. A composition according to claim 9 containing from
about 0.01 to about 30 parts by weight, based on combined weight
of said unsaturated urethane resin and said reactive diluent
system, of at least one photoinitiator compound.
11. A composition according to claim 10 wherein the
amount of said unsaturated urethane resin is in the range of
about 50 to about 75 weight percent.
12. A composition according to claim 11, wherein said
unsaturated urethane resin is derived from an isocyanate-
functional prepolymer obtained by reacting a polyol having at
least two hydroxyl groups and a polyisocyanate having at least
two isocyanate groups at an NCO:OH ratio greater than 2:1.
13. A composition according to claim 4 wherein R° is
hydrogen and R is 2-ethyl hexyl.
14. A composition according to claim 6, wherein R°
is hydrogen and R is 2-ethyl hexyl.
15. A composition according to claim 11, wherein R° is
hydrogen and R is 2-ethyl hexyl.
16. A composition according to claim 12, wherein R° is
hydrogen and R is 2-ethyl hexyl.
13

17. A composition according to claim 11, wherein the
amount of acrylic acid is in the range from about 1 to about
5 percent.
18. A composition according to claim 17, wherein said
unsaturated urethane resin is derived from an isocyanate-
functional prepolymer obtained by reacting at least one polyol
having at least two hydroxyl groups and at least one polyisocyanate
having at least two isocyanate groups at an NCO:OH ratio greater
than 2:1.
14

19. A composition according to claim 18, wherein R0 is
hydrogen and R is 2-ethyl hexyl.
20. A method for coating a substrate comprising apply-
ing to said substrate a coating composition according to claim 5;
and exposing said coated substrate to ultraviolet irradiation for
a time sufficient to cure said coating to a hard mar-resistant
surface.
21. A coated substrate having a hard mar-resistant sur-
face which coating is an ultraviolet irradiation cured coating
composition as claimed in claim 5.

Description

ll~Z~39
This invention relates to radiation curablé coa-ting and
ink composition. More particularly, the invention relates to
radiation curable compositions containing unsaturated addition-
polymerizable urethane resin.
Increasing concern with energy, environmental protection,
and health factors have cooperated to enhance the potential of
radiation curable coatings. In principle, such coatings com-
prise a polymerizable mixture that can be applied as a thin
film to a substrate and polymerized at a rapid rate by exposure
to a radiation source such as an electron beam, plasma arc,
ultra violet light, and the like. Advantages of radiation
curable coatings include a practical method of at least
reducing air pollution from volatile vapor loss, rapid cure
rates at ambient temperatures, reduced operating costs, the use
of heat-sensitive substrates, and improved product performance.
Among the more notable achievements in the field of
radiation curing has been the development of the so-called 100
percent reactive solids systems based on unsaturated addition-
polymerizable urethane resin. A characteristic feature of
such systems is the substantial absence of conventional inert
volatile solvents. Instead, the systems contain reactive diluents
which react during curing to become an integral part of the
cured coating. Such systems have been widely accepted commer-
cially. ~hile such systems provide high-performance coatings
which can be cured at high line speeds, they have also provided
a new set of problems for the coatings formulators.
While unsaturated addition-polymerizable urethane resins
can be prepared by several known reaction routes, the preferred
method of preparation for obtaining premium-quality coatings is
by capping an isocyanate-functional prepolymer with an appropriate
addition-polymerizable monomer having a single isocyanate-
reactive active hydrogen group, with the reaction being effected
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in the presence of a diluent system which is inert with respect
to the capping reaction but which is reactive at cure conditions
with the unsaturated addition-polymerizable urethane resins.
One particularly vexing problem of compositions containing such
polymerizable urethane resins, regardless of how the resin is
prepared, is the high viscosity of the resin compositions which
makes application by conventional industrial techniques difficult,
if not impossible. Because the use of conventional inert sol-
vents such as are employed with moisture-cure polyurethanes is
undesirable, there has been developed the so-called reactive
diluent systems, which generally comprise a mixture of mono-
functional and polyfunctional unsaturated addition-polymerizable
monomeric compounds which are copolymerizable with the addition
polymerizable urethane resin and thus become part of the cured
coating. Certain of the lower molecular weight monomeric
diluents such as butyl acrylate are effective in affording clear
coating compositions which can be applied by conventional indust-
rial techniques; however, their use is often undesirable because
of their relatively high volatility, toxicity, noxiousness and
other hazards. While higher molecular weight diluents such as
2-ethyl hexyl acrylate, octyl acrylate, stearyl acrylate and the
like are preferred because they do not present the volatility,
toxicity and handling problems associated with their lower
molecular weight counterparts, they are not without their
problems. Generally, greater amounts of the preferred higher
molecular weight diluents are required for effective viscosity
reduction. A particularly undesirable phenomenon which is
characteristic of diluent systems containing the higher mole-
cular weight reactive monomer diluents is physical instability
of the composition which results in thixotropy or cloudiness
leading to eventual separation of the compositions into distinct
resin-rich and monomer-rich phases. The adverse phenomena
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appear common to all diluent systems con-taining the higher
molecular diluents and is most likely to occur with compositions
containing hiqher molecular weight resinous components. Thus,
there appears to be a maximum diluent level, which varies with
the amount and composition of higher molecular weight diluent
present in the diluent system, that the unsaturated addition-
polymerizable urethane resins can tolerate before separation
takes place. The abilitv to produce compositions which will
remain homogeneous and which can be readily and uniformly
applied to substrates and rapidly cured to a dried film is of
important commercial importance. It is equally important that
harmful emissions to the atmosphere be minimized and that toxic,
noxious and otherhealth hazards be at least reduced, if not
entirely eliminated.
During the course of an extensive study of the viscosity
and thixotropy of radiation curable compositions, particularly
such compositions containing unsaturated addition-polymerizable
urethane resins, it was discovered that the addition of minor
amounts of acrylic acid to radiation curable compositions has
the unexpected and inexplainable effects of inhibiting, if not
entirely eliminating, physical instability as the reactive
diluent level increases, causing an increase in flowability;
and affording significant improvements in cured film properties;
the effects being out of proportion to the amount of free acrylic
acid employed. One measure of this inexplainable effect is that
the use of methacrylic acid, among other organic and inorganic
acids, does not afford the same benefits as are obtained with
acrylic acid. The present invention permits the use of higher
molecular weight reactive monomer diluents such as 2-ethyl
hexyl acrylate at hiqher diluent levels than heretofore. As
well, the present invention provides compositionshaving a more
manageable viscosity at higher resin content than heretofore
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possible.
In accordance with the present invention, there are
provided radiation curable compositions comprising
A. at least one unsaturated addition polymerizable
urethane resin;
B. a reactive diluent system comprising at least one
unsaturated addition-polymerizable monoEunctional monomeric
compound selected from the group consisting of esters having
the general formula
O
CH2 = C - C - O - R,
1o
wherein R is hydrogen or methvl and R is an aliphatic or cyclo-
aliphatic, preferably alkyl or cycloalkyl, group having from
6 to 18, preferably 6 to 9, carbon atoms;
C. from about 0.1 to about 10, preferably about 1 to
about 5, weight percent, based on total weight of said unsaturated
addition-polymerizable urethane resin and total reactive diluent
system, of acrylic acid; and optionally,
D. an effective amount of at least one photoinitiator;
the amount of unsaturated addition polymerizable urethane resin
being in the range from about 30 to about 90, preferably from
about 50 to about 75, weight percent, based on combined weight
of unsaturated addition-polymerizable urethane resin and reactive
diluent system. The photoinitiator, which will generally be
employed when curing is effected with a low energy radiation
source such as ultraviolet light radiation, will generally be
in the range from about 0.01 to about 30, preferably about 0.1
to about 15, parts by weight per 100 parts by combined weight
of unsaturated addition-polymerizable resin and reactive diluent
system.
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The unsaturated addition-polymerizable urethane resins
which are suitable for use in the practice of the invention are
characterized by the presence of at least one, preferably at
least two, polymerizable ethylenically unsaturated group(s)
having the structure \ C=C ~ . The polymerizable ethylenically
unsaturated group is preferably a terminal vinyl group having
the structure CH2 = C ~ . Especially preferred unsaturated
addition polymerizable urethane resins are the acrylyl urethane
resins, i.e., urethane resins containing a polymerizable
acrylyl/ methacrylyl, acrylamide, methacrylamide, and the like
moiety in the molecule, characterized by the presence of at
least one, preferably at least two, terminal ethylenically
unsaturated group(s) having the structure CH2=C ~ . For brevity,
the unsaturated addition-polymerizable urethane resins will be
referred to hereinafter in this disclosure and the ensuing
claims as unsaturated urethane resins. Such unsaturated urethane
resins are well-known in the art and do not require further
elaboration herein. A particularly preferred class of unsaturated
urethane resins are those obtained by fully capping an
isocyanate-functional prepolymer with an appropriate unsaturated
addition-polymerizable monomer, e.g., 2-hydroxyethyl acrylate,
especially such unsaturated urethane resins derived from isocyanate-
functional- prepolymers obtained by reacting at least one
polyisocyanate and at least one polyol at an NCO:OH ratio
greater than 2:1.
A further essential ingredient of the coating compositions
of this invention comprises a reactive diluent system. Broadly,
the reactive diluent comprises at least one unsaturated addition-
polymerizable monomer which is copolymerizable with the un-
saturated resin upon exposure to radiation. In the generalcase, such unsaturated addition-polymerizable monomeric diluents
can be monofunctional or polyfunctional with combinations of one
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i~2~)3g
or more monofunctional reactive diluents and one or more poly-
functional reactive diluents heinq presently preferred. In the
case of the present invention, the reactive diluent systems
contain at least one unsaturated addition-polymerizable
monofunctional monomeric compound selected from the group con-
sisting of esters having the qeneral formula
O
CH2 = C - C - O - R,
R
wherein R is hvdroqen or methyl and R is an aliphatic or cvclo-
aliphatic, preferably alkyl or cycloalkyl, group having from 6 .
to 18, preferably 6 to 9 carbon atoms. Representative of such
esters are hexyl acrylate, cyclohexyl acrylate, 2-ethyl hexyl
acrylate, octvl acrylate, nonyl acrylate, stearyl acrylate, and
the corresponding methacrylates. Optionally, the diluent systems
can contain one or more of the known reactive monofunctional
monomeric diluents in addition to the required acrylic and meth-
acrylic esters havinq at least 6 carbon atoms inthe non-acid
moiety of the molecule. In many instances, the reactive diluent
systems advantageously will include one or more reactive poly-
functional monomeric diluents. Suchoptional reactivemonofuncti~nal
andpolvfunctional monomericdi~luents include,wi~hout limitation
thereto,styrene, methylmethacrylate, butylacrylate, isobutylacrylate,;
dicyclopentenyl acrylate, 2-phenoxyethylacrylate, 2-methoxyethyl
acrylate, 2-(N,N-diethylamino)-ethyl acrylate, the corresponding
methacrylates, acrylonitrile, methacrylonitrile, methacrylamide, ' :
neopentyl glycol diacrylate, ethylene qlycol diacrylate, hexylene
glycol diacrylate, diethylene glycol diacrylate, trimethylol
propane triacrylate, pentaerythritol di-, tri-, or tetra-
acrvlate, the corresponding methacrylates, vinyl acrylate, vinylmethacrvlate and the like. Generally, the reactive diluent
system will comprise from about 10 to about 70, preferably about
25 to about 50, weiqht percent, based on total weight of
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1~2~S'39
unsaturated urethane resin and reactlve diluent system of the
radiation curable compositions of the invention. It is presently
preferred that the diluent system contain at least 50 weight per-
cent of acrylic and methacrvlic esters havina at least 6 carbon
atoms in the non-acid moiety of the molecule. Reactive
diluent systems are well-known to those skilled in the art of
radiation curing and the selection of an appropriate diluent
system in any given instance is sufficiently encompassed by such
knowledge as to require no further discussion here.
As previously indicated, a photoinitiator system will
generally be employed when curinq is effected by exposure to
low energy radiation sources such as ultra violet light. Any
of the known photoinitiators can be used within the concentration
ranges previously set forth. Illustrative photoinitiators,
without limitation thereto, include benzophenone, benzoin,
acetophenone, benzoin methyl ether, ~lichler's ketone, benzoin
butyl ether, xanthone, thioxanthone, propiophenone, fluorenone,
carbazole, diethoxyacetophenone, the 2-, 3- and 4-methylaceto-
phenones and methoxyacetophenones, the 2- and 3-chloroxanthones
and chlorothioxanthones, 2-acetyl-4-methylphenyl acetate,
2,2'-dimethoxy-2-phenylacetophenone, benzaldehyde, fluorene,
anthroquinone, triphenylamine, 3- and 4-allylacetophenone, p-
diacetylbenzene, 3-chloro-2-nonylxanthone, and the like, and
mixtures thereof.
~ The invention compositions can also include pigments,
fillers, wetting aqents, flatting agents, and other additives
typically present in coating compositions, with the exception of
inert volatile solvents or diluents. These are well-known to
those skilled in the art and do not require further elaboration
herein. Also well-known are the concentrations at which such
additives are used.
The radiation curable compositions of the present invention
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have an increased flowability and fluidity, and exhibit a
markedly improved viscositv stabilitv, i.e., a substantially
reduced tendency to phasing, at any diluent level in comparison
to compositions which do not contain any free acrylic acid.
Thus, the invention compositions can be applied to wood, metal
fabric and plastic substrates in a more economical and efficient
manner to afford a smoother and more uniform film. In addition,
the modulus andultimate film properties or cured films derived
from the compositions of this invention arenoticeably better
than the corresponding properties of cured films derived
from radiation curable compositions which do not contain any
free acrylic acid.
The improved coating compositions of this invention can
be applied and cured by any of the conventional known methods.
Application can be by roll coating, curtain coating, airless
spray, dipping or by any other procedure. The cure can be
effected by exposure to anv high energy source, such as ionizing
radiation, or low eneray source, such as ultraviolet light
radiation. The equipment utilized for curing, as well and the
appropriate time for curing, and the conditions under which the
curing is effected are well-known to those skilled in the
art of radiation curing and do not require further elaboration
herein.
The invention is illustrated in greater detail by the
following Examples, but these examples are not to be construed
as limiting the present invention. All parts, percentages and
the like are in parts by weight, unless otherwise indicated.
Example I
An unsaturated acrylvl urethane resin composition is
prepared by reacting methylene-bis(cvclohexyl isocyanate) and
polycaprolacetone triol having an average molecular weight of
about 900 in the presence of 2-ethyl hexyl acrylate and

Z~39
stannous octoate at an NCO:OH mol ratio of 2.5:1. The reaction
is terminated at an end point corresponding to 100 percent
depletion of hydroxyl value, as determined by isocyanate
titration. When the end point is reached there is immediately
added to the isocyanate-functional prepolymer-containing reaction
mixture sufficient 2-hydroxyethyl acrylate to react with the
free isocyanate functions of the prepolymer. Radiation curable
compositions are prepared at several diluent (2-ethyl hexyl
acrylate) levels with the following results:
Composition A B C
Unsaturated urethane resin 70 65 60
2-ethyl hexyl acrylate30 35 40
Time to separationa2 mos 30 days 24 hrs
Viscosity, cps 27,500 12,000 8,400
a = separation of composition into distinct resin-rich
and monomer-rich phases
The data are demonstrative of the physical instability
of radiation curable compositions comprising unsaturated urethane
resin and reactive diluent system containing acrylic and meth-
acrylic acid esters having at least 6 carbon atoms in the non-
acid moiety of the ester molecule.
Example II
Composition C of Example I is heated at 58C for 30
minutes with constant stirring. The resin phase is redispersed
into the diluent phase to form a homogeneous system. The
composition is now separated into four separate portions. After
standing for 24 hours, phasing has occurred in each portion.
To three portions, there is added acrylic acid at 1, 3 and 5
percent levels. In each instance, the addition of acrylic acid
results in resolubilization of the separated unsaturated urethane.
Also in each instance, the addition of acrylic acid significantly
reduces the viscosity and thixotropy of the composition to
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marked increase the flow abilityof the compositions. The results
are tabulated below:
Composition C C-l C-2 C-3
Unsaturated urethane 60 60 6060
2-ethyl hexyl acrylate 40 40 4040
Acrylic acid, weight percent 0 1 3 5
Viscosity, cps 8,400 5,600 3,8003,000
Time to separation 24 hrs 2 mos >2 mos >2 mos
To each of compositions C, C-l, C-2 and C-3 is added an
effective amount of a henzoin-type photoinitiator. The com-
positions are then coated onto aluminum panels and cured by
exposure to ultravoilet radiation (200 watts/in.) at a line
- speed of 50 feed per minute for three passes. Compositions C-l,
C-2 and C-3are sianificantlyless viscous and are more easily
and uniformly applied to the substrate than is composition C,
which contains no acrylie acid. In the ease of Composition C,
phasing aqain oecurs within 24 hours; nodiscernible phasing is
observed with anv of compositions C-l, C-2 and C-3 after two
months storage. The properties of the cured films are tabulated
helow:
Composition C C-l C-2 C-3
Tensile strength, psi 3816 3065 3570 4480
Youngs modulus, psi 77000 75000 92000 118000
The data demonstrate the unexpected effects afforded by
the present invention in reducing viscosity and thixotropy of
radiation curable eompositions, improvina viscosity stability,
and significantly improving cured film properties.
Example III
Emplovinq the unsaturated acrylyl urethane resin composition
of Example I, the following formulation is prepared:
: Unsaturated urethane 60
2-ethyl hexyl acrylate 40
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The formulation is divided into several portions. After
24 hours at room temperature, phase separation has occured with
each portion. There is added to individual portions acrylic
acid, methacrylic acid, acetic acid, p-toluene sulfonie acid
and hydrochloric acid, respectively, at a level of 3 weight
pereent, based on total weight of urethane resin and diluent
system. Acetie acid, p-toluene sulfonie aeid and hvdroehlorie
aeid do not resoluhilize the resin phase. The resin phase is
resolubilized by the addition of methaerylic acid but phasing
again occurs within 24 hours. The resin phase is resolubilized
by the addition of acrylic aeid and substantially no phasing
has oeeurred after 2 months storage. The data demonstrates the
eompletely unexpeeted results whieh are obtained by the addition
of minor amounts of acrylie acid to radiation curable compositions.
~r
~,, - 11 -