Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR. PRODUUNG SC RATC H RESISTANT CURED MATERIALS
Field of the 9nvenltaon!
The present invention relates to a new process for producing cured materials.
The present
invention further relates to the use of the cured materials produced by means
of the new
process for the coating, adhesive bonding, sealing, wrapping, and packaging of
bodies of
means of transport, especially motor-vehicle bodies, and parts thereof, the
interior and
exterior of constructions and parts thereof, doors, windows, furniture, hollow
glassware,
coils, freight containers, packaging, small parts, optical, mechanical, and
electrical
components, and components for white goods.
Prior Art
The cured materials are preferably thermoset materials. For the purposes of
the present
invention, thermoset materials are three-dimensionally crosslinked substances
which in
contrast to thermoplastic materials are deformable only to a small extent or
not at all on
heating.
A process for producing cured materials is known from German patent
application
DE 102 02 565 Al. In the known process the cured materials are produced from a
composition, curable thermally and with actinic radiation, by heating and
exposure to UV
radiation, for which
(1) a composition curable thermally and with actinic radiation is used which,
after it
has cured, has a storage modulus E' in the rubber-elastic range of at least
10' S Pa
and a loss factor tan6 at 20 C of not more than 0.10, the storage modu lus E.'
arld
the loss factor having been measured by means of dynamic mechanical
thermoanalysis (DMTA) on free films with a thickness of 40 10 m, and
(2) exposure is carried out with UV radiation whose spectrum comprises, in
addition to
UV-A and UV-B, a UV-C fraction which in the wavelength range from 200 to
280 nm has from 2 to 80% of the relative spectral radiance of the spectrum of
a
medium-pressure mercury vapor lamp within this wavelength range, the relative
spectral radiance of the UV-C fraction in the wavelength range from 200 to 240
nm
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always being smaller than the relative spectral radiance of the spectrum of a
medium-pressure mercury vapor lamp within this wavelength range, and
(3) the radiation dose is from 100 to 6000 mJ cm,2.
For the purposes of the present invention actinic radiation means
electromagnetic
radiation, examples being near infrared (NIR), visible light, UV radiation, X-
rays or gamma
radiation, preferably UV radiation, and also corpuscular radiation, examples
being electron
beams, beta radiation, neutron beams, proton beams, and alpha radiation,
preferably
electron beams. Actinic radiation means, in particular, UV radiation.
The spectrum of UV radiation is known to be divided into three regions:
UV-A: 320 to 400 nm
UV-B: 320 to 290 nm
UV-C: 290 to 100 nm
In general the UV spectrum of UV radiation sources is available only down to a
wavelength of 180 - 200 nm, since the lower-wavelength radiation is absorbed
by the
hollow quartz bodies of the radiation sources (cf. R. Stephen Davidson,
"Exploring the
Science, Technology and Applications of U.V. and E.S. Curing", Sita Technology
Ltd.,
London, 1999, Chapter I, "An Overview", pages 3 to 34).
The yellowing of the resultant known cured materials is low. They are scratch-
resistant
and, after being scratched, display minor loss of gloss. At the same time
their hardness
and chemical resistance are high.
The continually growing demands of the market, however, call for further
improvement in
the scratch resistance of cured materials, particularly their scratch
resistance when
exposed to automatic wash lines. In addition it is necessary to achieve
further
improvement in the adhesion of the cured materials to substrates, particularly
those of
metals, plastics, and other cured materials. A particular need is to further
improve the
intercoat adhesion between coats of cured materials which differ in physical
composition
and/or functions, particularly in multicoat paint systems.
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Problem
It is an object of the present invention to provide a new process for
producing cured
materials that no longer has the disadvantages of the prior art but instead,
in a particularly
simple and particularly reliable way, affords cured materials which meet the
advantageous
profile of requirements set out above and, furthermore, exhibit improved
scratch
resistance, particularly on exposure in wash lines, and also improved adhesion
to
substrates, particularly those of metals, plastics, and other cured materials.
The new
process ought in particular to afford cured materials which have improved
intercoat
adhesion between coats of cured materials which differ in physical composition
and/or
function, particularly in multicoat paint systems, and particularly on
exposure to a steam
jet.
Solution
Found accordingly has been the new process for producing cured materials from
compositions curable with actinic radiation ("compositions") by exposure to UV
radiation,
using UV radiation of the following spectral distribution and dose:
- wavelength lambda = 400 to 320 nm; dose = 500 to 2500 mJ/cm2;
- wavelength lambda = 320 to 290 nm; dose = 700 to 3000 mJ/cm2;
- wavelength lambda = 290 to 180 nm; dose = 100 to 500 mJ/cm2.
The new process for producing cured materials is referred to below as the
"process of the
invention".
Further subject matter of the invention will emerge from the description.
Advantages of the inventiion
In the light of the prior art it was surprising and unforeseeable for the
skilled worker that
the object on which the present invention was based could be achieved by means
of the
process of the invention.
In particular it was surprising that the process of the invention, in a
particularly simple and
reliable way, using conventional UV radiation sources, using conventional
electronic,
optical, and mechanical components, and using conventional irradiation units,
afforded, in
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a particularly simple and particularly reliable way, cured materials,
especially thermoset
materials, which not only exhibited low yellowing, high hardness, and high
chemical
resistance but also, furthermore, had improved scratch resistance,
particularly on
exposure in wash lines, and also had improved adhesion to substrates,
particularly those
of metals and plastics and other cured materials. In particular, the process
of the invention
afforded cured materials which exhibited improved intercoat adhesion between
coats of
cured materials differing in physical composition and/or function,
particularly in multicoat
paint systems, and particularly on exposure to a steam jet.
Even more surprising was that the process of the invention could be carried
out with UV-
curable compositions differing very widely in constitution. As a result, in an
unexpectedly
advantageous way, it was possible to tailor the compositions optimally to a
very wide
variety of end uses, so that they could be used with advantage as coating
materials,
adhesives, sealants, and starting materials for moldings and films. In
particular it was
surprising that the coating materials could be used with particular advantage
as
electrocoat materials, surfacers, antistonechip primers, solid-color topcoat,
basecoat, and
clearcoat materials.
A surprise not least was the extraordinarily broad usefulness of the cured
materials as
coatings, adhesive layers, seals, moldings, and films, preferably as coatings,
especially
electrocoats, surfacer coats, antistonechip primer coats, solid-color
topcoats, basecoats,
and clearcoats. They were especially suitable outstandingly for the coating,
adhesive
bonding, sealing, and packaging of bodies of means of transport, especially
motor-vehicle
bodies, and parts thereof, the interior and exterior of constructions and
parts thereof,
doors, windows, furniture, hollow glassware, coils, freight containers,
packaging, small
parts, such as nuts, bolts, wheel rims or hub caps, optical components,
mechanical
components, electrical components, such as windings (coils, stators, rotors),
and
components for white goods, such as radiators, household appliances,
refrigerator
casings or washing-machine casings.
etai8ed description of the invention
The process of the invention serves for producing cured materials, especially
thermoset
materials, from compositions curable with actinic radiation (referred to for
the sake of
brevity below as "compositions") by exposure to UV radiation.
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In accordance with the invention the UV radiation used is of the following
spectral
distribution and dose:
wavelength lambda = 400 to 320 nm; dose = 500 to 2500 and preferably 750 to
2000 mJ/cmz;
- wavelength lambda = 320 to 290 nm; dose = 700 to 3000 and preferably 1000 to
2200 mJ/cm2;
wavelength lambda = 290 to 180 nm; dose = 100 to 500 and preferably 200 to 450
mJ/cmz.
The power may vary widely. The UV radiation used is preferably of the
following spectral
distribution and power:
wavelength lambda = 400 to 320 nm; power = 100 to 600 and preferably 120 to
550 mVr!/cm2;
wavelength lambda = 320 to 290 nm; power = 100 to 600 and preferably 140 to
550 mVi//cm2;
wavelength lambda = 290 to 180 nm; power = 20 to 120 and preferably 30 to 100
mVV/cm2.
For irradiation in the context of the process of the invention, broad
variation is possible in
the distance of the UV radiation source from the surface of the composition.
The distance
is preferably 20 to 250 mm and in particular 40 to 100 mm.
For a given dose, the irradiation period is guided by the belt speed or rate
of advance of
the substrates in the irradiation unit, and vice versa.
As radiation sources for the UV radiation for inventive use it is possible to
use any
conventional UV lamps which as such emit the relevant spectrum. Use may also
be made,
however, of combinations of at least two UV lamps which, although not emitting
the UV
radiation for inventive use, have spectra which nevertheless add to give the
UV radiation
for inventive use. In addition it is possible to use UV lamps where the
desired spectrum is
set by means of filters and/or reflectors. Flash lamps are also suitable.
Examples of suitable flash lamps are flash lamps from the company VISIT.
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As UV lamps it is preferred to use mercury vapor lamps, more preferably low-,
medium-
and high-pressure mercury vapor lamps, especially medium-pressure mercury
vapor
lamps. Particular preference is given to using unmodified mercury vapor lamps
plus
appropriate filters and/or reflectors, or mercury vapor lamps which have been
modified, in
particular by doping.
Examples of suitable modified mercury vapor lamps are gallium-doped and/or
iron-doped
lamps, especially iron-doped mercury vapor lamps, as described, for example,
in
R. Stephen Davidson, "Exploring the Science, Technology and Applications of
U.V. and
E.S. vuring", Sita Technology Ltd., London, 1999, Chapter I, "An Overview",
page 16,
Figure 10, or in ipl.-Ing. Peter Klamann, "eltosch System-Kompetenz, UV-
Technik,
Leitfaden fur Anwender", page 2, October 1998.
Examples of suitable unmodified mercury vapor lamps plus appropriate filters
and/or
reflectors are the UV lamps from Arccure. These lamps are constructed so that
the
compositions for curing are not struck directly by any UV radiation but only
indirectly
reflected radiation in two bundled streaks. For both reflected streaks it is
possible to use
different reflectors, which reflect the entire UV spectrum ("broad"), reflect
the long-wave
component of the UV spectrum more extensively onto the plastic moldings
("A+B"), or
reflect the short-wave component of the UV spectrum more extensively onto the
sample
( 9))_
The arrangement of the radiation sources may be adapted to the spatial
circumstances of
the compositions and/or of the substrates to which they have been applied, and
also the
process parameters. In the case of substrates of complex shape, such as are
envisaged,
for example, for automobile bodies, those regions not accessible to direct
radiation
(shadow regions), such as cavities, folds, and other structural undercuts, can
be cured
using pointwise, small-area or all-round sources, in conjunction with an
automatic
movement means for the irradiation of cavities or edges.
In the context of the process of the invention it is preferred to carry out
irradiation under an
oxygen-depleted atmosphere.
"Oxygen-depleted" means that the oxygen content of the atmosphere at the
surface of the
compositions is lower than the oxygen content of air (20.95% by volume). The
maximum
oxygen content of the oxygen-depleted atmosphere is preferably 18%, more
preferably
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16%, very preferably 14%, with particular preference 10%, and in particular
6.0% by
volume.
The atmosphere may in principle by oxygen-free; that is, it comprises an inert
gas. The
complete or substantial absence of oxygen may also be obtained, however, by
masking
the surface of the compositions with an oxygen-impermeable film.
The absence of the inhibitory effect of oxygen, however, may in such cases
produce a
sharp acceleration in radiation curing, as a result of which inhomogeneities
and stresses
may arise in the coatings of the invention. It is therefore not advantageous
in all cases to
lower the oxygen content of the atmosphere to a volume percentage of zero.
The minimum oxygen content is preferably 0.1 % and in particular 0.5% by
volume.
The oxygen-depleted atmosphere may be provided in a variety of ways. It is
preferred to
produce an appropriate gas mixture and to make it available in pressurized
cannisters.
More preferably the depletion is brought about by introducing at least one
inert gas in the
respective amounts required into the cushion of air situated over the surface
of the layers
that are to be cured. The oxygen content of the atmosphere situated over the
surface in
question can be measured continuously by means of conventional methods and
devices
for determining elemental oxygen, and where appropriate can be adjusted
automatically to
the desired level.
By inert gas is meant a gas which under the curing conditions employed is not
broken
down by the actinic radiation, does not inhibit curing and/or does not react
with the
compositions. Preference is given to using nitrogen, carbon dioxide, helium,
neon or
argon, especially nitrogen and/or carbon dioxide.
The compositions used for the process of the invention are curable with
actinic radiation,
especially UV radiation. This means that they comprise or consist of
constituents which
can be activated with actinic radiation and so undergo free-radical or ionic
polymerization,
especially including free-radical polymerization. This results in three-
dimensional
crosslinking of the compositions to give the cured materials, particularly the
thermoset
materials.
The compositions may additionally be curable physically and/or thermally.
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For the purposes of the present invention the term "physical curing" denotes
the curing of
the compositions, in particular in the form of a film of a coating material,
by filming as a
result of solvent emission from the compositions, with linking within the
coating taking
place via looping of the polymer molecules of the binders (regarding the term
cf. Rompp
Lexikon Lacke und Druckfarben, Georg Thieme Veriag, Stuttgart, New York, 1998,
"Binders", pages 73 and 74). Or else filming takes place via the coalescence
of binder
particles (cf. R mpp Lexikon Lacke und Druckfarben, Georg Thieme Verlag,
Stuttgart,
New York, 1998, "Curing", pages 274 and 275). Normally no crosslinking agents
are
needed for this purpose.
For the purposes of the present invention the term "thermal curing" denotes
the heat-
initiated curing of a composition, in particular of a film of a coating
material, in which
normally a binder and a separate crosslinking agent are employed. This is
normally
referred to by those in the art as external crosslinking. Where the
crosslinking agents are
already incorporated in the binders, the term "self-crosslinking" is also
used. In
accordance with the invention, external crosslinking is of advantage and is
therefore
employed with preference (cf. R mpp Lexikon Lacke und Druckfarben, Georg
Thieme
Verlag, Stuttgart, I~_!ew York, 1998, "Curing", pages 274 to 276, especially
page 275,
bottom).
Those in the art also refer to compositions curable with actinic radiation and
thermally as
dual-cure compositions.
In the process of the invention it is preferred to use compositions which,
after they have
been cured, have a storage modulus E' in the rubber-elastic range of at least
10' 5,
preferably at least 10' 6, more preferably at least 108 , and in particular
at least 108.3 Pa
and a loss factor tanS at 20 C of not more than 0.10, preferably not more than
0.06, the
storage modulus E and the loss factor having been measured by means of
dynamic
mechanical thermoanalysis (DMTA) on free films having a thickness of 40 10
m.
The recoverable energy component (elastic component) in the deformation of a
viscoelastic material such as a polymer, for example, is determined by the
parameter of
the storage modulus E, whereas the energy component consumed (dissipated) in
this
process is described by the parameter of the loss modulus E". The moduli E'
and E" are
dependent on deformation rate and temperature. The loss factor tan8 is defined
as the
ratio of the loss modulus E" to the storage modulus E'. tan8 can be determined
by means
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of dynamic mechanical thermoanalysis (DMTA) and constitutes a measure of the
relationship between the elastic and plastic properties of the film. DMTA is a
widely known
measurement method for determining the viscoelastic properties of coatings and
is
described, for example, in Murayama, T., Dynamic Mechanical Analysis of
Polymeric
Materials, Elsevier, New York, 1978 and Loren W. Hill, Journal of Coatings
Technology,
Vol. 64, No. 808, May 1992, pages 31 to 33. The method conditions relating to
the
measurement of tanb by means of DMTA are described in detail by Th. Frey, K.-
H. Grof3e
Brinkhaus, and U. R ckrath in Cure Monitoring of Thermoset Coatings, Progress
In
Organic Coatings 27 (1996), 59-66, or in German patent application DE 44 09
715 Al or
German patent DE 197 09 467 C2. Preference is given to employing the following
conditions: tensile mode; amplitude: 0.2%; frequency: 1 Hz; temperature ramp:
1 C/min
from room temperature to 200 C.
The storage modulus E' can be adjusted by the skilled worker through the
selection of
particular actinic radiation-curable and also, where appropriate, physically
and/or thermally
curable constituents, the functionality of the constituents, and their
proportion as a fraction
of the composition for inventive use.
The storage modulus E' can generally be adjusted, by means of constituents
curable with
actinic radiation, by selecting the nature and amount of the constituents
preferably such
that for each gram of composition soiids there are 0.5 to 6.0, preferably 1.0
to 4.0, and
more preferably 2.0 to 3.0 meq of bonds which can be activated with actinic
radiation.
For the purposes of the present invention the "solids" means the sum of those
constituents
of a composition that build up the cured material produced from said
composition.
For the purposes of the present invention a bond which can be activated with
actinic
radiation is a bond which when exposed to actinic radiation becomes reactive
and,
together with other activated bonds of its kind, enters into polymerization
reactions and/or
crosslinking reactions which proceed in accordance with free-radical and/or
ionic
mechanisms. Examples of suitable bonds are single carbon-hydrogen bonds or
single or
double carbon-carbon, carbon-oxygen, carbon-nitrogen, carbon-phosphorus or
carbon-
silicon bonds. Of these, the double carbon-carbon bonds are particularly
advantageous
and are therefore used with very particular preference in accordance with the
invention.
For the sake of brevity they are referred to below as "double bonds".
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Particularly preferred compounds containing double bonds are compounds
containing
acrylate groups.
The compositions may contain acid groups. Where the latter are used they are
present in
an amount of more than 0.05, preferably more than 0.08, very preferably more
than 0.15,
and in particular more than 0.2 meq/g solids. The amount of acid groups
present should
not exceed 15, preferably 10, more preferably 8, and in particular 5 meq/g
solids.
Where acid groups are used they are selected preferably from the group
consisting of
carboxyl groups, phosphonic acid groups, sulfonic acid groups, acidic
phosphate ester
groups, and acidic sulfate ester groups, especially carboxyl groups.
The physical constitution of the compositions for use in the process of the
invention is not
critical; instead, all conventional compositions curable with actinic
radiation, especially UV
radiation, and also, if desired, curable physically and/or thermally, can be
used.
Suitable constituents of such compositions, the suitable compositions
themselves, and the
processes for preparing them are known, for example, from German patent
application DE
102 02 565 Al, page 4, paragraph [0029], to page 8, paragraph [0079], or from
German
patent DE 197 09 467 C2.
The process of the invention affords particular advantages if carried out with
compositions
comprising at least one free-radically crosslinkable or curable component
which
(i) contains one or more oligourethane and/or one or more polyurethane
(meth)acrylates and which has
(ii) on average more than one olefinically unsaturated double bond per
molecule,
(iii) a number-average molecular weight of 1000 to 10 000 daltons,
(iv) a double bond content of 1.0 to 5.0 double bonds per 1000 g of free-
radically
crosslinkable component,
(v) on average per molecule > 1 branch point,
(vi) 5 to 50% by weight, based in each case on the weight of the component, of
cyclic
structural elements, and
(vii) at least one aliphatic structural element having at least 6 carbon atoms
in the
chain,
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the free-radically crosslinkable component containing carbamate and/or biuret
and/or
allophanate and/or urea and/or amide groups.
The free-radically crosslinkable component preferably contains at least 50% by
weight,
more preferably contains at least 70% by weight, and very preferably contains
at least
80% by weight, based in each case on the solids content of the free-radically
crosslinkable
component, of one or more oligourethane (meth)acrylates and/or one or more
polyurethane (meth)acrylates. In particular, the free-radically crosslinkable
component is
composed of 100% of one or more oligourethane (meth)acrylates and/or one or
more
polyurethane (meth)acrylates.
The free-radically crosslinkable component also contains preferably not more
than 50% by
weight, more preferably not more than 30% by weight, and very preferably not
more than
20% by weight, of further monomers, but preferably oligomers and/or polymers,
especially
polyester (meth)acrylates, epoxy (meth)acrylates, (meth)acryloyl-functional
(meth)acrylic
copolymers, polyether (meth)acrylates, unsaturated polyesters, amino
(meth)acrylates,
melamine (meth)acrylates and/or silicone (meth)acrylates, preferably polyester
(meth)acrylates and/or epoxy (meth)acrylates and/or polyether (meth)acrylates.
Preference is given here to polymers which in addition to the double bonds
also contain
hydroxyl, carboxyl, amino and/or thiol groups. In the great majority of cases
the use of
further free-radically crosslinkable constituents is superfluous.
The free-radically crosslinkable component contains preferably less than 5% by
weight,
more preferably less than 1% by weight, based in each case on the weight of
the free-
radically crosslinkable component, and in particular contains substantially no
detectable
free isocyanate groups.
Additionally it is preferred for the free-radically crosslinkable component to
comprise a
mixture of different oligourethane and/or polyurethane (meth)acrylates, which
may also
have different double bond contents, molecular weights, double bond equivalent
weights,
branch point contents and levels of cyclic and also relatively long-chain
aliphatic structural
elements, and different amounts of carbamate, biuret, allophanate, amide
and/or urea
groups.
This mixture may be obtained by mixing different oligourethane or polyurethane
(meth)acrylates or by the preparation of different products simultaneously
during the
preparation of a corresponding oligourethane and/or polyurethane
(meth)acrylate.
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In order to obtain effective crosslinking it is preferred to use free-
radically crosslinkable
components whose functional groups are of high reactivity, more preferably
free-radically
crosslinkable components containing acrylic double bonds as functional groups.
The urethane (meth)acrylates can be prepared in a way which is known to the
skilled
worker, from a compound containing isocyanate groups and from at least one
compound
containing groups that are reactive toward isocyanate groups, preparation then
taking
place by mixing of the components in any order, where appropriate at an
elevated
temperature.
It is preferred to add the compound containing groups that are reactive toward
isocyanate
groups to the compound containing isocyanate groups, preferably in two or more
steps.
In particular the urethane (meth)acrylates are obtained by initially
introducing the
diisocyanate or polyisocyanate and subsequently adding at least one
hydroxyalkyl
(meth)acrylate or hydroxyalkyl ester of other olefinically unsaturated
carboxylic acids, so
;giving rise to reaction initially of some of the isocyanate groups.
Subsequently a chain
extender from the group of the diols/polyols and/or diamines/polyamines and/or
dithiols/polythiols and/or alkanolamines is added and in this way the
remaining isocyanate
groups are reacted with the chain extender.
A further possibility is to prepare the urethane (meth)acrylates by reacting a
di- or
polyisocyanate with a chain extender and subsequently reacting the remaining
free
isocyanate groups with at least one olefinically unsaturated hydroxyalkyl
ester.
It will be appreciated that all forms intermediate between these two
techniques are also
possible. For example, some of the isocyanate groups of a diisocyanate can
first be
reacted with a diol, subsequently a further portion of the isocyanate groups
can be
reacted with the olefinically unsaturated hydroxyalkyl ester, and thereafter
the remaining
isocyanate groups can be reacted with a diamine.
In general the reaction is carried out at temperatures between 5 and 100 C,
preferably
between 20 to 90 C, and more preferably between 40 and 80 C, and in particular
between 60 and 80 C.
It is preferred here to operate under anhydrous conditions. "Anhydrous" means
here that
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the water content of the reaction system is not more than 5% by weight,
preferably not
more than 3% by weight, and more preferably not more than 1% by weight. In
particular
the water content is below the detection limit.
In order to suppress polymerization of the polymerizable double bonds it is
preferred to
operate under an oxygen-containing gas, more preferably air or air/nitrogen
mixtures.
As an oxygen-containing gas it is possible with preference to use air or a
mixture of
oxygen or of air and a gas which is inert under the conditions of use. As the
inert gas use
may be made of nitrogen, helium, argon, carbon monoxide, carbon dioxide,
steam, lower
hydrocarbons, or mixtures thereof.
The oxygen content of the oxygen-containing gas can be, for example, between
0.1% and
22% by volume, preferably from 0.5% to 20%, more preferably 1% to 15%, very
preferably 2% to 10%, and in particular 4% to 10% by volume. It will be
appreciated that, if
desired, higher oxygen contents can also be used.
The reaction can also be carried out in the presence of an inert solvent,
examples being
acetone, isobutyl methyl ketone, methyl ethyl ketone, toluene, xylene, butyl
acetate or
ethoxyethyl acetate.
Through the selection of the nature and amount of di- and/or polyisocyanate,
chain
extender, and hydroxyalkyl ester employed, control is exerted over the further
variables of
the urethane (meth)acrylates, such as, for example, double bond content,
double bond
equivalent weight, amount of branch points, amount of cyclic structural
elements, amount
of aliphatic structural elements having at least 6 carbon atoms, and amount of
biuret,
allophanate, carbamate, urea and/or amide groups, and the like.
Through the selection of the particular amounts of di- or polyisocyanate and
chain
extender that are employed and also through the functionality of the chain
extender it is
also possible, furthermore, to prepare urethane (meth)acrylates which as well
as the
ethylenically unsaturated double bonds also contain other functional groups,
examples
being hydroxyl groups, carboxyl groups, amino groups and/or thiol groups or
the like.
Especially if the urethane (meth)acrylate is to be used in aqueous
compositions, some of
the free isocyanate groups present in the reaction mixtures are also reacted
with
compounds which contain an isocyanate-reactive group, selected preferably from
the
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group consisting of hydroxyl, thiol, and primary and secondary amino groups,
especially
hydroxyl groups, and also at least one, especially one, acid group, selected
preferably
from the group consisting of carboxyl groups, sulfonic acid groups, phosphoric
acid
groups, and phosphonic acid groups, especially carboxyl groups. Examples of
suitable
compounds of this kind are hydroxyacetic acid, hydroxypropionic acid or gamma-
hydroxybutyric acid, especially hydroxyacetic acid (glycolic acid).
For the process of the invention the compositions may be present in any of a
very wide
variety of physical states and three-dimensional forms.
For instance, at room temperature, the compositions may be solid or liquid or
fluid. They
may also, however, be solid at room temperature and fluid at higher
temperatures, with
preferably a thermoplastic behavior being displayed. In particular they may be
conventional compositions comprising organic solvents, aqueous compositions,
substantially or entirely solvent-free and water-free liquid compositions
(100% systems),
substantially or entirely solvent-free and water-free solid powders, or
substantially or
entirely solvent-free powder suspensions (powder slurries). The dual-cure
compositions
may additionally be one-component systems, where the binders and crosslinking
agents
are present alongside one another, or two-component or multicomponent systems,
where
the binders and crosslinking agents are separate from one another until
shortly before
application.
In terms of method the preparation of the compositions for inventive use has
no
peculiarities but instead takes place by the mixing and homogenization of the
above-
described constituents by means of conventional mixing techniques and
apparatus such
as stirred tanks, agitator mills, extruders, compounders, Ultraturrax devices,
inline
dissolvers, static mixers, micromixers, toothed-wheel dispersers, pressure
release nozzles
and/or microfluidizers, preferably in the absence of actinic radiation. The
selection of the
method that is optimum for a given individual case is guided in particular by
the physical
state and the three-dimensional form which the composition is to have. Where,
for
example, a thermoplastic composition is present in the preferred form of a
film or a
laminate, extrusion through a slot die is particularly appropriate for
producing the
composition and shaping it.
For the purposes of the process of the invention the compositions are used for
producing
cured materials, especially thermoset materials, which serve a very wide
variety of end
uses.
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The compositions are preferably starting products for moldings and films or
are coating
materials, adhesives, and sealants.
The cured materials are preferably moldings, films, coatings, adhesive layers,
and seals.
The coating materials are employed in particular as electrocoat materials,
surfacers,
antistonechip primers, solid-color topcoat materials, aqueous basecoat
materials and/or
clearcoat materials, especially clearcoat materials, for producing single-coat
or multicoat
color and/or effect, electrically conductive, magnetically shielding or
fluorescent paint
systems, especially multicoat color and/or effect paint systems. The multicoat
paint
systems can be produced using the conventional wet-on-wet techniques and/or
extrusion
techniques and also the conventional paint or film construction systems.
To produce the cured materials, in the process of the invention, the
compositions for
inventive use are applied to conventional temporary or permanent substrates.
For producing films and moldings it is preferred to use conventional temporary
substrates,
such as metallic and plastic belts and sheets or hollow bodies of metal,
glass, plastic,
wood or ceramic, which can be easily removed without damaging the moldings and
films
that are produced from the compositions.
Where the compositions are used for producing coatings, adhesives, and seals,
permanent substrates are used, such as bodies of means of transport,
especially motor-
vehicle bodies, and parts thereof, the interior and exterior of constructions
and parts
thereof, doors, windows, furniture, hollow glassware, coils, containers,
packaging, small
parts, optical, mechanical, and electrical components, and components for
white goods.
The films and moldings produced by means of the process of the invention may
likewise
serve as permanent substrates.
In terms of method the application of the compositions for use in the process
of the
invention has no peculiarities but can instead take place by all conventional
application
methods suitable for the composition in question, such as, for example,
extrusion,
electrocoating, injecting, spraying, including powder spraying, knifecoating,
brushing,
pouring, dipping, trickling or rolling. Preference is given to employing
extrusion methods
and spray application methods. During application it is advisable to operate
in the absence
of actinic radiation, in order to prevent premature crosslinking of the
compositions.
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In one preferred embodiment of the process of the invention the compositions
are used in
the form of films, particularly in the form of planar laminates, comprising at
least one film
of a composition and also, where appropriate, at least one backing film,
preferably of a
thermoplastic.
In one particularly preferred embodiment of the process of the invention the
films or
laminates are shaped before being cured.
Shaping takes place preferably by thermoforming and/or by injection
backmolding with
thermoplastics or reactive precursors of plastics (reaction injection molding)
in
conventional injection molding machines. This results in shaped films or
laminates, still
curable, on correspondingly shaped plastic substrates.
Where the curable films or laminates comprise at least one thermoplastic
backing film, the
films or laminates are preferably connected with the substrates or precursors
thereof in
such a way that the backing films are facing away from the UV radiation
sources.
Following their application the compositions are cured in the manner described
at the
outset.
The resultant cured materials, particularly the resulting films, moldings,
coatings, adhesive
layers, and seals, are outstandingly suitable for the coating, adhesive
bonding, sealing,
wrapping, and packaging of bodies of means of transport, especially motor-
vehicle bodies,
and parts thereof, the interior and exterior of constructions and parts
thereof, doors,
windows, furniture, hollow glassware, coils, containers, packaging, small
parts, such as
nuts, bolts, vvheel rims or hub caps, optical components, mechanical
components,
electrical components, such as windings (coils, stators, rotors), and also
components for
white goods, such as radiators, household appliances, refrigerator casings or
washing-
machine casings.
The process of the invention affords very particular advantages when used for
producing
clearcoats.
The clearcoats are normally the outermost coats of multicoat paint systems or
of films
and/or laminates, substantially determining the overall visual appearance and
protecting
the substrates and/or the color and/or effect coats of multicoat paint systems
or films
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and/or laminates from mechanical and chemical damage and from damage by
radiation.
Consequently, deficiencies in the hardness, scratch resistance, chemical
resistance, and
yellowing stability in the clearcoat are manifested to a particularly marked
extent.
However, the clearcoats produced by the procedure of the invention exhibit no
more than
a low level of yellowing. They are highly scratch-resistant and, after being
scratched,
exhibit only very low levels of loss of gloss. In particular the loss of gloss
in the
Amtec/Kistler carwash simulation test is very low. At the same time they have
a high level
of hardness and a particu-arly high chemical resistance. Not least, they
exhibit outstanding
substrate adhesion and intercoat adhesion, particularly in connection with
exposure to a
steam jet.
Examples
Preparation example 1
The preparation of a free rad ecafly curable or crosslinkable urethane
acrylate
A urethane acrylate was prepared from the synthesis components specified
below, by
coarsely dispersing hydrogenated bisphenol A in 2-hydroxyethyl acrylate at 60
C with
stirring. Added to this suspension were the isocyanates, hydroquinone
monomethyl ether,
1,6-di-tert-butyl-para-cresol, and methyl ethyl ketone. Following the addition
of dibutyltin
dilaurate there was an increase in the temperature of the batch. It was
stirred at an
internal temperature of 75 C for a number of hours until there was virtually
no longer any
change in the NCO value of the reaction mixture. Any free isocyanate groups
still present
after the reaction were converted by adding a small amount of methanol.
Synthesis components:
104.214 g of hydrogenated bisphenol A (corresponding to 0.87 equivalent of
hydroxyl
groups);
147.422 g (corresponding to 0.77 equivalent of isocyanate groups) of Basonat
HI 100
from BASF AG = commercial isocyanurate of hexamethylene diisocyanate having an
NCO
content of 21.5%-22.5 / (DIN EN ISO 11909);
147.422 g (corresponding to 0.77 equivalent of isocyanate groups) of Sasonat
HB 100
from BASF AG = commercial biuret of hexamethylene diisocyanate having an NCO
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content of 22%-23% (DIN EN ISO 11909);
124.994 g (corresponding to 0.51 equivalent of isocyanate groups) of Vestanat
T1890
from Degussa = commercial isocyanurate of isophorone diisocyanate having an
NCO
content of 11.7%-12.3% (DIN EN ISO 11909);
131.378 g of 2-hydroxyethyl acrylate (corresponding to 1.13 equivalents of
hydroxyl
groups);
0.328 g of hydroquinone monomethyl ether (0.05% on solids);
0.655 g of 1,6-di-tert-butyl-para-cresol (0.1 % on solids);
methyl ethyl ketone (70% solids);
0.066 g of dibutyltin dilaurate (0.01% on solids);
4.500 g of methanol (corresponding to 0.14 equivalent of hydroxyl groups).
The characteristics of the resulting urethane acrylate (free-radically
crosslinkable
component) were as follows:
- on average 2.2 ethylenically unsaturated double bonds per molecule;
- a double bond content of 1.74 double bonds per 1000 g of urethane acrylate
solids;
- on average 2.2 branch points per molecule;
- 25% by weight of cyclic structural elements, based on the solids content of
the
urethane acrylate.
Preparation example 2
The preparation of aW-curab@e clearcoat materba9
A suitable stirrer vessel was initially charged with 100.00 parts by weight of
the above-
described organic solution of the urethane acrylate from preparation example
1.
Added to the initial charge over the course of 30 minutes was a mixture of 1.0
part by
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weight of Tinuvin0 292 (commercial HALS light stabilizer from Ciba Specialty
Chemicals,
based on a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate and
methyl(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate), 2.0 parts by weight of
Tinuvin0 400
(commercial light stabilizer from Ciba Specialty Chemicals, based on a mixture
of
2-(4-((2-hydroxy-3-dodecyloxypropyl)oxy)-2-hydroxyphenyl)-4,6-bis(2,4-
dimethylphenyl)-
1,3,5-triazine and 2-(4-((2-hydroxy-3-tridecyloxypropyl)oxy)-2-hydroxyphenyl)-
4,6-bis-
(2,4-dimethylphenyl)-1,3,5-triazine), 0.8 part by weight of Lucirin0 TPO-L
(commercial
photoinitiator from BASF Aktiengesellschaft, based on 2,4,6-
trimethylbenzoyldiphenyl-
phosphine oxide), 2.40 parts by weight of Irgacure0 184 (commercial
photoinitiator from
Ciba Specialty Chemicals, based on 1-hydroxycyclohexyl phenyl ketone) and 0.2
part by
weight of SykO 306 (commercial additive from Byk Chemie, based on a polyether-
modified polydimethylsiloxane) with continual stirring at room temperature,
and the
resulting mixture was dissolved in 3-butoxy-2-propanol and adjusted with 3-
butoxy-
2-propanol to a solids content of 48%. It was then stirred at room temperature
for
30 minutes.
Preparation examp@e 3
The production of a coated thermoplastic backing film
The backing film used was a thermoplastic film of LuranO S 778 TE from BASF
Aktiengesellschaft with a thickness of 800 pm. The surface of the backing film
that was to
be coated was subjected to a corona pretreatment at 0.5 kilowatt.
The film was coated on one side with a metallic aqueous basecoat material
(color: "silver
metallic"). The basecoat material was applied to the backing film using a box-
type coating
bar with a width of 37 cm at a belt speed of 0.5 m/min. Application was
carried out with a
gentle airflow of 0.2 m/s, at a constant temperature of 21 1 C, and at a
constant relative
humidity of 65 5%. The thickness of the resulting wet basecoat film (first
basecoat film)
was 100 pm. The wet first basecoat film was flashed off under these conditions
for
3 minutes and then dried to a residual volatiles content of 4% by weight,
based on the first
basecoat film. The resulting conditioned first basecoat film, with a thickness
of
approximately 20 pm, was adjusted with chill rolls to a surface temperature <
30 C.
Applied to the conditioned and temperature-adjusted first basecoat film was
the same
basecoat material, under the following conditions, using a system for
pneumatic spray
application:
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- outflow rate: 100 ml/min;
- air pressures: atomizer air: 2.5 bar; horn air: 2.5 bar;
- rate of travel of the nozzles: high enough to result in a spray-jet overlap
of 60%;
5- nozzle/film distance: 30 cm.
Application was carried out under a gentle airflow of 0.5 m/s (impinging
vertically on the
film), at a constant temperature of 21 1 C, and at a constant relative
humidity of
65 5%. The thickness of the resulting wet basecoat film (second basecoat
film) was
50 2pm. The second basecoat film was flashed off under these conditions for
3 minutes
and then dried to a residual volatiles content of 4% by weight, based on the
second
basecoat film. The air temperature was 90 C, the humidity 10 g/min, and the
air speeds
10 m/s. The resulting conditioned second basecoat film, with a thickness of
about 10 pm,,
was adjusted with chill rolls to a surface temperature < 30 C.
Atop the conditioned and temperature-adjusted second basecoat film was applied
the
UV-curable clearcoat material of preparation example 2, using a box-type
coating bar with
a width of 37 cm. Application was carried out with a gentle airflow of 0.2
m/s, at a constant
temperature of 21 1 C, and at a constant relative humidity of 65 5%. The
thickness of
the resulting wet clearcoat film was 120 pm. It was flashed off under the
stated conditions
for 6 minutes and then dried to a residual volatiles content of 2.5% by
weight, based on
the clearcoat film. The air temperature in the oven was 119 C for all drying
stages. The
resulting dried but not yet fully cured coating, with a coat thickness of 60
pm, was adjusted
with chill rolls to a surface temperature < 30 C and coated with the
polypropylene
protective film described in DE 103 35 620 Al, example 1 (commercial product
GH-X 527
from Bischof + Klein, Lengerich).
The multilayer film which resulted was wound up into a roll and stored in this
form until
further use.
ExampBes 1 to 3
The production of plas4ac moldings
Plastic moldings were produced in accordance with the following general
instructions:
The multilayer film of preparation example 3 was preformed. Subsequently the
transparent
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coating, as yet not fully cured, was stripped of its protective film and then
crosslinked fully
using UV radiation. The positive mold used was a cube. The resulting preformed
part was
inserted into a mold. The mold was closed and the cube was injection
backmolded with a
liquid plastic material.
Irradiation was carried out using a UV lamp from Arccure (undoped mercury
tube). The
construction of this lamp was such that there was no direct impingement of UV
radiation
on the plastic moldings; instead, only indirectly reflected radiation impinged
on the
moldings, in two bundled streaks. Different reflectors could be used for both
reflected
streaks, which reflected the total UV spectrum ("broad"), which reflected the
long-wave
component of the UV spectrum more extensively onto the plastic moldings
("A+13"), or
which reflected the short-wave component of the UV spectrum more extensively
onto the
sample ("C"). In the case of examples 1 and 3 to 6 the reflector arrangement
selected,
viewed in the direction of travel of the plastic moldings through the UV
exposure unit, was
as follows: 1. "broad" and 2. "C". In the case of example 2 the reflector
arrangement
chosen was as follows: 1. "A+B" and 2. "A+B"
The plastic moldings were irradiated in an oxygen-depleted carbon dioxide
atmosphere.
The table gives an overview of the shortest distances employed between the UV
radiation
source and the surface of the clearcoat film on the plastic moldings, the
oxygen content of
the atmosphere over the clearcoat film, the spectral distribution, with the
associated dose
and power, and the scratch resistance and adhesion of the resulting clearcoats
on the
plastic moldings.
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Table: Curing of the clearcoat films with UV radiation, and important
properties
of the clearcoats
Example Dost,a) 02 b) se') Powerd) Amtece) sif)
No. (mm) (% by v i,) (Mj/cM2) (MW/cMZ) (residual (index)
gloss %)
0!!-A l0l9-B UF1-C UV-A UV-B U!1-C
1 40 0.5 782 1058 205 - - - 79.3 sat.
2 40 0.9 915 1240 251 474 467 77 81 sat.
3 40 0.8 854 1194 235 470 474 78 87.7 sat.
a) distance between UV radiation source and clearcoat film surface;
b) oxygen content of atmosphere above the clearcoat film;
c), d) measured using a PowerPuck from EIT;
e) residual gloss after exposure in the Amtec/Kistler carwash simulation test
with
cleaning (wiping with petroleum ether);
f) steamjet test;
In the case of the carwash simulation test a laboratory wash line from Amtec
Kistler was
used (cf. T. Klimmasch, T. Engbert, Technologietage, Cologne, DFO, report
volume 32,
pages 59 to 66, 1997). The stress induced was determined by measuring the
residual
gloss of the sample after the carwash simulation test and subsequent wiping
with a wipe
soaked with petroleum ether. Residual gloss levels of more than 80% were
achieved.
For the steamjet test, in accordance with the Daimler-Benz steamjet testing
instructions
that are known in the art, a St. Andrew's cross was scored into the clearcoats
of each of
examples 1 to 6. The scored areas were subjected to a waterjet spray (Walter
instrument
model LTA2; pressure: 67 bar; water temperature: 60 C; nozzle tip/test
specimen
distance: 10 cm; exposure time: 60 seconds; instrument setting: F 1).
The degree of flaking and subfilm migration was assessed visually. In all
cases the result
was sat. (satisfactory).
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The results in the table underline the fact that the clearcoats on the plastic
moldings of
examples 1 to 6 exhibited very good intercoat adhesion and high scratch
resistance,
especially under realistic conditions.
In other respects the clearcoats on the plastic moldings of examples 1 to 6
were bright
and had a very high gloss (20 ) in accordance with IN 67530. They were hard,
fiexible,
chemical-resistant, and free from disruptive yellowing.
