Note: Descriptions are shown in the official language in which they were submitted.
CA 02339735 2001-02-06
RADIATION-HARDENING AND/OR HEAT-HARDENING
SUBSTANCES AND PREPARATIONS
The invention relates to substances and formulations curable thermally and/or
by
high-energy radiation and to their uses in accordance with the invention.
The starting point for the present invention were considerations in the field
of LTV-
curable coating materials for use in liquid form, and powder coating
materials.
Such coating systems are continually acquiring more fields of use on the
grounds
of reduced solvent consumption. A major problem with known UV coating
materials, however, is the inhibiting effect of atmospheric oxygen on curing
at the
film surface. To overcome this inhibition requires lamps with very high energy
density, and accelerated curing by means of amine coinitiators. These amines
are
frequently the cause of odor nuisance.
In the case of UV powder coating materials, in addition, further problems
arise
from the contradictory requirements for good blocking resistance of the
powders on
storage and good leveling of the melted coating film. For good blocking
resistance,
the glass transition temperature and melting point should be as high as
possible,
whereas for good leveling, and to permit use on heat-sensitive substrates,
they
should be as low as possible, in order to prevent a curing reaction before
optimum
surface smoothness has developed and in order to prevent substrate damage.
Likewise for the purpose of improving the surface smoothness, the melt should
have a low viscosity and the reaction should set in only after a delay period.
These
concepts are difficult to realize with powder coating materials whose curing
is
based on one of the known, thermally activated reactions between resin and
hardener, e.g., polyepoxy resin and dicarboxylic acid hardener, since a
viscosity-
increasing reaction sets in simultaneously with the melting process. In the
case of
radiation-curable powder coating materials, on the other hand, it should be
possible
to separate the melting process from crosslinking. In order to meet this
requirement, various attempts have been disclosed in the prior art.
CA 02339735 2001-02-06
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US-A-4,129,488 and US-A-4,163,810 disclose UV-curable powder coating
materials having specific spatial arrangements of ethylenically unsaturated
polymers. Here, the binder consists of an epoxy-polyester polymer in which the
epoxy adduct is arranged spatially such that by means of a linear polymer
chain it is
at a distance from the polyester adduct. In addition, the polymer comprises a
chemically bonded photoinitiator.
EP-A 0 650 978, EP-A 0 650 979 and EP-A 0 650 985 disclose copolymers whose
essential constituent is a relatively high fraction of monomers having the
structural
unit of methacrylic acid. These monomers can be used as binders for UV-curable
powder coating materials, and feature a relatively narrow molecular weight
distribution.
EP-A 0 410 242 discloses binders for UV-curable powder coating materials,
consisting of polyurethanes which have specific (meth)acryloyl groups, can be
crosslinked without crosslinker components or peroxides, and are therefore
stable
on storage. Crosslinking by UV irradiation requires the addition of
photoinitiators.
EP-A 0 636 669, furthermore, discloses a UV-curable binder for powder coating
2 0 materials which consists of unsaturated polymers, which can include cyclo-
pentadiene, and a crosslinking agent which has vinyl ether groups, vinyl ester
groups or (meth)acrylic groups.
WO-A-93/25596 discloses polyacrylates, for use as automotive topcoats, which
are
2 5 functionalized with double bonds in a wide variety of ways.
DE-A 42 26 520 discloses liquid compositions comprising unsaturated polymer,
in
the form of unsaturated polyesters, and compounds containing (meth)acryloyl
groups and/or vinyl ether groups. These compositions can be crosslinked both
by
3 0 means of free-radical initiators and by means of radiation curing, and are
used as
binders for coating materials. In the case of crosslinking by UV radiation it
is
necessary to add photoinitiators.
With the UV coating materials of the cited prior art, problems arise as a
result of
3 5 the need to employ coinitiators, generally amines, in order to provide
high
photosensitivity and to overcome the known oxygen inhibition of the surface.
The
CA 02339735 2001-02-06
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elimination products of these photoinitiators remain in the cured coatings and
are
the cause of odor nuisance.
In addition, EP-A-0 322 808 has disclosed a prior art which reveals a liquid
binder,
curable by means of high-energy radiation, which consists of a mixture of an
ethylenically unsaturated polyester component, which may also include an
ethylenically unsaturated polyester oligorner, and a nonpolymerized vinyl
ether
component. In this case, the vinyl ether component is selected such that per
molecule of the vinyl ether component it contains on average at least two
vinyl
ether groups which are able to react with the ethylenic double bonds of the
polyester component.
Against the background of this prior art, it is an object of the present
invention to
provide substances and formulations whose use in coating systems which are
curable thermally and/or by means of high-energy radiation is unaccompanied by
oxygen inhibition of the film surface, so that it is possible to forego the
use of
malodorous amines and other coinitiators, and which can also be employed more
broadly.
2 0 We have found that this object is achieved by substances with an
oligomeric or
polymeric substructure having in each case terminally and/or laterally at
least one
vinyl ether group a) and at least one, preferably copolymerizable group b)
which is
different from the vinyl ether groups a) but is coreactive with the groups a),
there
being on average at least one vinyl ether group a) and one coreactive group b)
per
2 5 oligomer or polymer molecule.
Coating systems which comprise such substances surprisingly show high UV
reactivity and no oxygen inhibition of the surface when cured in air. This has
the
advantage that it is possible to forego the use of amines and other
coinitiators.
Also possible is curing to a B-stage, i.e., to a partially cured state in
which the
curing is interrupted and can be started again later.
In connection with the substances of the invention, mention should be made of
the
3 5 problem, known per se to the skilled worker, that in the course of the
customary
polymer synthesis, which takes place under statistical reaction conditions,
and/or in
the case of polymer-analogous functionalization, it is also possible for
polymer
CA 02339735 2001-02-06
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molecules to be formed which are functionalized only in one way, e.g., with
the
vinyl ether groups a), or which are not functionalized at all. Since such
polymeric
substructures with little functionalization or none whatsoever may adversely
effect
the properties of the polymers of the invention, it is preferred to direct the
preparation process such that minimal fractions of such minimally
functionalized
or completely unfunctionalized polymeric substructures are formed. Methods
suitable for this purpose are known to the person skilled in the art of
polymers.
They include the use of excesses of substances which if unreacted can be
separated
off again later, or, if desired, the residence of the excess in the finished
coating
binder. It has been found that any residual fractions which nevertheless
remain
have essentially no adverse effect on the success of the invention when using
the
claimed binders.
The outstandingly high ITV reactivity which is observed when the substances of
the
invention are used in powder coating materials curable thermally and/or by
means
of high-energy radiation, which is unaccompanied by oxygen inhibition of the
surface, is attributed to the fact that functionalization of the polymeric
substructure
in the substances of the invention permits self crosslinking to take place,
whereas
in the prior art the compositions are mixtures of substances which must only
be
2 0 crosslinked with one another.
The schematic structural principle of the substances of the invention can be
illustrated as follows:
a~, or b~, a~ or b~, : Fig.l
a~, or b~ ~ a~, or b~,
. n=0-6
In accordance with the structural principle depicted, the functional groups a)
and b)
can be linked to the oligomeric or polymeric substructure at the same point
and/or
different points, and they may arbitrarily terminate this substructure. The
functional
groups a) and b) may also be present more than once on the same group. Thus,
for
3 0 example, two glycidyl methacrylates can react at a terminal NH2 group, or
one
molecule of ethanolamine divinyl ether at a terminal epoxy group. Furthermore,
polymeric substructures having two or more OH groups laterally or terminally
at
the same site can be vinylated. The value for n here is between 0 and 6,
preferably
1 or 2.
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The oligomeric or polymeric substructure can be formed by C-C linkages which
have double and/or triple bonds and/or are selected from ester, ether,
urethane,
amide, imide, imidazole, ketone, sulfide, sulfone, acetal, urea, carbonate and
siloxane linkages.
In addition, the oligomeric or polymeric substructure may be linear, branched,
annular or dendrimeric.
The binders of the invention are obtained preferably by polymer-analogous
reaction
of functional polymers with compounds having functional groups a) or b) and at
least one further group which are able to react with the functional groups of
the
oligomeric or polymeric substructure.
Particularly suitable coreactive, preferably copolymerizable, functional
groups b)
are maleate, fumarate, itaconate (meth)acrylate, allyl, epoxy, alkenyl,
cycloalkenyl,
vinylaryl and cinnamate groups and/or preferably structural units of the
formula I.
I
~" n= 0-I O
2 0 When structural units of the formula I are used as functional group b),
the coating
systems are notable during preparation for low heat sensitivity and yet good
stoving
curability under atmospheric oxygen, for short curing times with combined use
of
heat and UV light, for good blocking resistance of the powders on storage, in
the
case of powder coating materials, and for very good surface smoothness of the
2 5 resultant coatings.
In one preferred embodiment, the structural units of the formula I in the
coreactive
groups b) can be incorporated in the form of esters of (oligo)dihydro-
dicyclopentadienol with monofunctional or polyfunctional carboxylic acids of
the
3 0 formula II.
CA 02339735 2001-02-06
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B
'' "' O
An important polymer class of the invention is that of the epoxy resins.
Suitable
substructures are multiply epoxy-functional polymeric, oligomeric or monomeric
compounds of the type, for example, of the bisphenol A epoxy compounds or
bisphenol A epoxy resins, by reaction with compounds that are reactive with
epoxy
groups. The epoxy groups can be functionalized with compounds having vinyl
ether groups a) and groups b) coreactive with them and contain at least one
further
group which is able to react with epoxides. Examples of compounds of this kind
according to the invention are the products of partial reactions of
conventional
commercial epoxy resins with (rneth)acrylic acid and/or compounds of the
formula
III below and an aminovinyl compound, such as aminobutyl vinyl ether or
diethanolamine divinyl ether, or the reaction products of polyacrylates with
copolymerized glycidyl (meth)acrylate with such compounds, or the reaction
products of polyurethane resins obtained with such compounds with the
additional
use of hydroxy-functional epoxy compounds, an example being glycidol (2,3-
epoxy-1-propanol).
p-i -~=c-~ -off
'Jn''' O p
n=0-10
2 0 Polyurethane resins constitute a further important class of polymer
according to
the invention, and are obtained by reacting polyfunctional isocyanate
compounds
with acrylates and vinyl compounds, hydroxyacrylates or aminoacrylates, and
hydroxyvinylates or aminovinylates, with or without the additional use of
further,
isocyanate-reactive compounds, such as hydroxy compounds.
Isocyanate compounds which can be used include commercially customary and
conventional compounds, such as tolylene diisocyanate (TDI), 4,4'-
methylenedi(phenyl isocyanate) (MDI), isophorone diisocyanate (IPDI),
hexamethylene diisocyanate (HMDI), further C2-C12 alkylene diisocyanates,
further
CA 02339735 2001-02-06
CZ-C 12 cycloalkylene diisocyanates, naphthalene diisocyanates, further
alkaryl
diisocyanates, such as phenylene diisocyanates, biphenyl diisocyanates, and
the
various positional isomers of these compounds. Also suitable are the
derivatives of
these isocyanates that are of higher isocyanate functionality, the products of
biuretization and isocyanuratization, such as the isocyanates oligomerized or
trimerized by way of uretdione groups, and the higher isocyanates obtainable
from
the simple isocyanates mentioned above by dimerization or oligomerization with
amines or water.
Polyisocyanates which contain diisocyanurate groups are of particular
importance.
Particular mention may be made here of the trimerization products of the above-
mentioned diisocyanates.
To prepare the binders of the invention, these isocyanates, or mixtures
thereof, are
reactive with compounds which are reactive with the isocyanates and which in
addition to the isocyanate-reactive groups also contain the groups a) and b).
It is
also possible to make use in addition of isocyanate-reactive compounds which
do
not contain the groups a) or b). The compounds to~be reacted with the
isocyanates
can be singly or multiply reactive with isocyanates and can be linear,
branched,
2 0 aromatic, cycloaliphatic, araliphatic or heterocyclic and/or can be
substituted in any
desired manner. Examples are CI-CZO hydroxyalkyl vinyl ethers, such as
hydroxyethyl monovinyl ether, hydroxybutyl monovinyl ether,
cyclohexanedimethanol monovinyl ether, hexanediol monovinyl ether, ethylene
glycol monovinyl ether, propylene glycol monovinyl ether and polyalkylene
glycol
2 5 monovinyl ethers, and also diethanolamine divinyl ether, aminopropyl vinyl
ether,
CI-CZO-hydroxyalkyl (meth)acrylates, such as hydroxyethyl acrylate,
hydroxybutyl
acrylate and also polyalkylene glycol monoacrylates, allyl alcohol,
dihydrodicyclopentadienol, hydroxyl-containing adducts of dicyclopentadienol
(DCPD) with glycols, as per formula scheme V below, ethylene glycol,
3 0 polyethylene glycols, propylene glycol, polypropylene glycols, butanediol
isomers,
hexanediol, neopentyl glycol, trimethylolpropane, glycerol, pentaerythritol,
unsaturated hydroxy compounds, such as allyl alcohol, partially etherified
polyfunctional hydroxy compounds, examples being trimethylolethane monoallyl
ether, trimethylolethane diallyl ether, trimethylolpropane monoallyl ether,
3 5 trimethylolpropane diallyl ether, pentaerythritol monoallyl ether,
pentaerythritol
diallyl ether, alkylenediols, such as 2-butene-1,4-diol, and alkoxylated
alkylenediols, preferably ethoxylated and propoxylated 2-butene-1,4-diol
having a
CA 02339735 2001-02-06
degree of alkoxylation of from 1 to 10 alkylene oxide units per mole of 2-
butene-
1,4-diol.
The selection and combination of the particular starting compounds desired
depends on the desired properties of the substances to be prepared from them.
The
required molecular weight and, if desired, the viscosity can be established by
additionally using monofunctional compounds. The abovementioned measures, and
the selection of a suitable polymerization technique with or without the
additional
use of solvents, and the control of the polymerization by means of catalysts,
are
possible for the skilled worker on the basis of his or her expert knowledge.
For the purposes of this invention, the term polyurethanes is intended to
include
not only those compounds whose main chain is linked by way of urethane
linkages
but also those compounds which have ester or ether chain links, i.e., the
polyester
urethanes and polyether urethanes.
Saturated and unsaturated polyester resins functionalized in accordance with
the
invention with groups a) and b) constitute a further important polymer class
for the
binders of the invention. Suitable for synthesizing the polyester resins are
the
2 0 customary and known carboxylic acids having > 2 carboxyl groups and/or
their
anhydrides and/or their esters, and hydroxy compounds having > 2 OH groups. It
is
also possible to use monofunctional compounds in addition in order, for
example,
to regulate the molecular weight of the polycondensates.
2 5 Examples of suitable carboxylic acid components are a,(3-ethylenically
unsaturated
carboxylic acids, such as malefic acid, malefic anhydride, fumaric acid,
itaconic acid,
citraconic acid, saturated aliphatic carboxylic acids and their anhydrides,
such as
sizccinic acid, adipic acid, suberic acid, sebacic acid, azelaic acid,
naturally
occurring fatty acids and polymerized naturally occurring fatty acids, such as
3 0 linseed oil fatty acid, dimeric linseed oil fatty acid and polymeric
linseed oil fatty
acid, castor oil, castor oil fatty acid, saturated cycloaliphatic carboxylic
acids and
their anhydrides, such as tetrahydrophthalic acid, hexahydrophthalic acid,
endomethylene-tetrahydrophthalic acid, norbonenedicarboxylic acid, aromatic
carboxylic acids and their anhydrides, such as phthalic acid in its isomer
forms,
3 5 also tri- and tetracarboxylic acids and their anhydrides, such as
trimellitic acid,
pyromellitic acid, polycarboxylic acids partially esterified with allyl
alcohol,
examples being monoallyl trimellitate and diallyl pyromellitate; particular
CA 02339735 2001-02-06
_ g _
importance is attached to benzophenonecarboxylic acids, since by way of such
carboxylic acids it is possible to incorporate, copolymerically, structures
which can
be excited by UV light.
Examples of suitable hydroxy components are alkoxylated or nonalkoxylated, at
least dihydric, aliphatic and/or cycloaliphatic alcohols such as ethylene
glycol,
propylene glycol, polyethylene glycols, polypropylene glycols, butanediol
isomers,
hexanediol, trimethylolpropane, pentaerythritol, neopentyl glycol, cyclo-
hexanedimethanol, bisphenol A, hydrogenated bisphenol A, OH-polyfunctional
polymers, such as hydroxyl-modified polybutadienes or hydroxyl-bearing poly-
urethane prepolymers, glycerol, mono- and diglycerides of saturated and
unsaturated fatty acids, especially monoglycerides of linseed oil or sunflower
oil.
Also suitable are unsaturated alcohols, such as polyfunctional hydroxy
compounds
etherified (partially) with allyl alcohol, examples being trimethylolethane
monoallyl ether, trimethylolethane diallyl ether, trimethylolpropane monoallyl
ether, trimethylolpropane diallyl ether, pentaerythritol monoallyl ether,
pentaerythritol diallyl ether, 2-butene-1,4-diol and alkoxylated 2-butene-1,4-
diol.
If monofunctional substances are employed to regulate the molecular weight,
they
2 0 are preferably monofunctional alcohols, such as ethanol, propanol,
butanol,
hexanol, decanol, isodecanol, cyclohexanol, benzyl alcohol, or allyl alcohol.
In the
context of the present invention, the term polyesters includes polycondensates
which in addition to the ester groups feature amide and/or imide groups, as
are
obtained by the additional use of amino compounds. Polyesters modified in this
way are known, for example, from DE-A-15700273 and DE-A-17200323. These
polyesteramides or polyesterimides may in many cases meet certain requirements
-
in terms, for example, of heat stability, chemical resistance, hardness and
scratch
resistance - better than do pure polyesters.
3 0 The double bonds of the unsaturated polyesters used can also be subjected
to an
addition reaction with DCPD, thereby making it possible to incorporate endo-
methylenetetrahydrophthalic acid structures of the formula IV.
IV
Il
O O
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These endomethylenetetrahydrophthalic acid structures can be present at the
chain-
internal double bonds of the polyesters and/or at terminal double bonds, as
are
introduced, for example, by way of substances of the formula III.
Groups a) and b) of the invention can be introduced by cocondensation and/or
by
polymer-analogous reactions on polyesters with functional groups. Examples of
cocondensations are the combined use of trimethylolpropane diallyl and
monoallyl
ethers, pentaerythritol diallyl and monoallyl ethers, and 2-butene-1,4-diol,
alkoxylated 2-butene-1,4-diol and allyl alcohol.
Examples of polymer-analogous reactions on polyesters with functional groups
are
reactions of addition onto incompletely condensed, linear and/or branched,
prepolymeric polyester resins which possess free carboxyl groups and free OH
groups. These resins can be reacted at the carboxyl groups with unsaturated
glycidyl compounds and vinyl ethers. Preferably, first of all, the free
carboxyl
groups are reacted with unsaturated glycidyl compounds in order to prevent
acid-
catalyzed polymerization of the vinyl ethers. Examples of suitable unsaturated
glycidyl compounds are glycidyl (meth)acrylate, glycidyl undecenoate, (meth)-
acrylicization products of polyfunctional epoxy resins and/or allyl glycidyl
ether, in
2 0 which case preferably glycidyl (meth)acrylate is added on. Then, following
these
reactions, the hydroxyl groups are reacted with diisocyanates and hydroxyvinyl
ethers.
It is preferred, however, first to react diisocyanates having isocyanate
groups of
2 5 different reactivity, such as isophorone diisocyanate, with half the
equivalent
amount of hydroxyvinyl ethers and then to react these reaction products with
the
prepolymeric polyesters. In the case of said reactions, hydroxyl-functional
acrylates
rtiay also be used, in addition to the hydroxyvinyl ethers. In the manner
described
lastly, purely hydroxyl-functional prepolymeric polyesters can also be reacted
with
3 0 hydroxyvinyl ethers and hydroxyl-functional compounds having groups b),
examples being hydroxyalkyl (meth)acrylates or allyl alcohol. The introduction
of
groups of the formula I in this way is likewise possible through the
concomitant
use of commercially available dihydrodicyclopentadienol. It is preferred,
however,
to introduce groups of the formula I into polyesters by the cocondensation of
the
3 5 monoesters of malefic acid with dihydrodicyclopentadienol, of the formula
III.
These monoesters are obtainable in an elegant reaction from malefic anhydride
(MA.A), water and dicyclopentadiene (DCPD) or by a direct addition reaction of
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DCPD with MAA. In addition, it is possible to add DCPD directly onto other
acids
and/or acidic polyesters. These reactions, however, are usually less elegant
and
require catalysis with, for example, BF3 etherate.
Furthermore, it is known from US-A-5,252,682, for example, that in the
reaction of
DCPD and MAA there may to a minor extent be side reactions in accordance with
the formula scheme V. These byproducts likewise serve to introduce structures
of
the formula I.
O
o~ + ~ ~ ~ ~ o I
o~ ~ ~ v
off
0 0
to
Hydroxyl-functional compounds for introducing groups of the formula I are
dihydrodicyclopentadienyl alcohol and, preferably, the adducts of DCPD with
glycols, which are obtainable inexpensively by acid catalysis in accordance
with
the formula scheme VI.
I I + HO-R-OH ---.. Hp-~_0
I
Y
Polyacrylate resins, which in accordance with the invention are functionalized
with groups a) and b), constitute a further important class of polymer
according to
2 0 the invention and are obtained by copolymerizing acrylic esters, alone or
with
further copolymerizable compounds.
A preferred method of preparing polyacrylates is that of solvent-free, free-
radical
bulk polymerization in a stirred reactor, at atmospheric or superatmospheric
2 5 pressure or, with particular preference, in continuous through-flow
reactors at
temperatures above the melting point of the resultant polymers, preferably
above
140°C.
This method produces polyacrylates of low molecular weight and narrow
molecular
3 0 weight distribution, which is highly desirable in the case of powder
coating
materials, in particular, owing to the resultant narrower melting range and
the
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lower melt viscosity. In addition, bulk polymerization does away with the need
to
remove an auxiliary solvent, and it is possible to incorporate pigments and
coating
auxiliaries directly into the melt. Alternatively, the polyacrylate resins of
the
invention can be prepared in solvents.
Examples of components for synthesizing polyacrylate resins are the known
esters
of acrylic and methacrylic acid with aliphatic, cycloaliphatic, araliphatic
and
aromatic alcohols of 1 to 40 carbon atoms, such as, for example, methyl
(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl
(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tent-butyl
(meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl
(meth)acrylate,
2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate,
dodecyl
(meth)acrylate, tridecyl (meth)acrylate, cyclohexyl (meth)acrylate,
methylcyclohexyl (meth)acrylate, benzyl (meth)acrylate, tetrahydrofizrfuryl
(meth)acrylate, furfuryl (meth)acrylate and the esters of 3-phenylacrylic acid
and
the various isomeric forms thereof, such as methyl cinnamate, ethyl cinnamate,
butyl cinnamate, benzyl cinnamate, cyclohexyl cinnamate, isoamyl cinnamate,
tetrahydrofurfuryl cinnamate, furfuryl cinnamate, acrylamide, methacrylamide,
methylolacrylamide, methylolmethacrylamide, acrylic acid, methacrylic acid, 3-
2 0 phenylacrylic acid, hydroxyalkyl (meth)acrylates, such as ethyl glycol
mono(meth)acrylate, butyl glycol mono(meth)acrylates, hexanediol
mono(meth)acrylate, glycol ether (meth)acrylates, such as methoxyethyl glycol
mono(meth)acrylate, ethyloxyethyl glycol mono(meth)acrylate, butyloxyethyl
glycol mono(meth)acrylate, phenyloxyethyl glycol mono(meth)acrylate, glycidyl
2 5 acrylate, glycidyl methacrylate, and amino (meth)acrylates, such as 2-
aminoethyl
(meth)acrylate.
Further suitable components are free-radically copolymerizable monomers, such
as
styrene, 1-methylstyrene, 4-tert-butylstyrene, 2-chlorostyrene, vinyl esters
of fatty
3 0 acids of 2 to 20 carbon atoms, such as vinyl acetate, vinyl propionate,
vinyl ethers
of alkanols of 2 to 20 carbon atoms, such as vinyl isobutyl ether, vinyl
chloride,
vinylidene chloride, vinyl alkyl ketones, dimes, such as butadiene and
isoprene,
and also esters of malefic acid and crotonic acid. Further suitable monomers
are
cyclic vinyl compounds, such as vinylpyridine, 2-methyl-1-vinylimidazole, 1-
vinyl-
3 5 imidazole, 5-vinylpyrrolidone and N-vinylpyrrolidone. Monomers with
allylic
unsaturation can also be employed, examples being allyl alcohol, allylalkyl
esters,
CA 02339735 2001-02-06
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monoallyl phthalate and allyl phthalate. Acrolein and methacrolein, and
polymerizable isocyanates, are also suitable.
Vinyl ether groups a) and coreactive groups b) can be incorporated by
copolymerization during the preparation of the polyacrylates or, preferably,
by
subsequent polymer-analogous reaction. Examples of readily polymerizable
compounds which additionally are reactive with vinyl ethers are
copolymerizable
epoxy compounds, such as glycidyl (meth)acrylate or dihydrodicyclopentadienol
(meth)acrylate, dihydrodicyclopentadienyl ethacrylate and dihydrodi-
cyclopentadienyl cinnamate. The epoxy groups of copolymerized glycidyl (meth)-
acrylate are able to polymerize with vinyl ethers directly by a cationic
mechanism,
but are also anchor groups for polymer-analogous functionalization reactions
of the
polymers, for the purpose, for example, of introducing acrylic double bonds by
reaction with (meth)acrylic acid and/or for introducing vinyl ether groups by
reaction with amino vinyl ether compounds, such as, for example,
diethanolamine
divinyl ether.
Dihydrodicyclopentadienyl groups of copolymerized dihydrodicyclopentadienyl
compounds can be crosslinked or copolymerized directly with vinyl ether groups
2 0 by initiation with UV irradiation and/or thermally, using free-radical
donor
compounds.
In principle, the invention is not restricted to the abovementioned classes of
polymer. It can be an advantage to use mixtures of different polymer classes.
In this
2 5 case, particular preference is given to mixtures of relatively soft and
elastic
polyurethane resins or polyacrylate resins, which per se do not form blocking-
resistant powders, with hard polyester resins having good blocking resistance
properties.
3 0 The various functionalization methods referred to can be carried out in
arbitrary
combination in uniform polymeric precursors or mixtures of different polymeric
precursors. This provides a kind of modular system which permits the
properties of
the powder coating materials to be adapted to a very wide variety of
requirements.
3 5 The substances of the invention can also be mixed with further, preferably
solid
compounds which are reactive with the vinyl ether groups a) and/or with the
groups
b) that are coreactive with said groups a), examples of such compounds being
CA 02339735 2001-02-06
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unsaturated, preferably partially crystalline polyesters, monomeric and/or
polymeric acrylates, vinyl esters, vinyl ethers, allyl esters and allyl
ethers, e.g.,
polyester acrylates, polyether acrylates, polyurethane acrylates and
polyurethane
vinyl ethers. In such mixtures as well, the disruptive oxygen inhibition of
the
surface is advantageously suppressed.
The substances of the invention can comprise copolymerically incorporated
photoinitiators, as are set out in more detail further below.
The invention also provides formulations which comprise the substance of the
invention. The formulation of the invention can comprise at least one compound
which on heating or under high-energy irradiation provides free radicals
and/or
cations.
The invention also provides for uses of the formulation of the invention.
These
include its use as or in a binder for liquid coating systems, with or without
the use
of solvents, coating dispersions or powder coating materials.
When the formulations of the invention are used, such coating systems can be
2 0 crosslinked with a surprisingly high reactivity and even without
coinitiators exhibit
no oxygen inhibition of the surface. Furthermore, they can be cured by baking
with
compounds which on heating produce free radicals.
These coating systems are cured with conventional photoinitiators of Norrish
type I
2 5 or II or with catalysts which on heating produce free radicals, such as
peroxides,
azo initiators or C-C-labile compounds, such as those of the pinacol type, for
example. Furthermore, combinations featuring malefic andlor fumaric acid
groups
are in many cases curable in customary coat thicknesses by baking in air.
3 0 Particularly preferred photoinitiators are those which are bonded
copolymerically.
Examples of copolymeric photoinitiators which can be employed are copoly-
merizable derivatives of benzophenone and compounds which are known from EP-
A-486 897, DE-A-38 20 463, DE-A-40 07 318 and which embrace in particular
those compounds derived from aromatic or partially aromatic ketones and have
3 5 thioxanthone structures. Copolymeric photoinitiators can also be
incorporated by
the addition reaction of, for example, hydroxybenzophenone onto copolymerized
epoxy compounds, such as glycidyl (meth)acrylate, for example. Polymers which
CA 02339735 2001-02-06
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have, for example, copolymerically bonded benzophenone groups, in particular,
can be crosslinked with high sensitivity by UV. This reactivity is further
enhanced
if at the same time structural units of the formula I are present as
functional group
b).
If the coating systems comprising the formulations of the invention include
compounds which on heating or under high-energy radiation provide free
radicals
and/or cations, curing can take place by purely thermal means, for example, by
baking in air, and/or by means of high-energy radiation, with initiators, such
as
peroxides, azo initiators or C-C-labile compounds.
Such coating systems can be used for coating a wide variety of surfaces. These
surfaces can, quite generally, be flat or shaped, fibrous or particulate
substrates of
any desired materials, such as metal, wood, plastic, glass, ceramic, silicon,
etc. The
selection of the polymeric substructure to be combined and of the coreactive
groups b) for the binder of the respective powder coating material takes place
in
accordance with the requirements of the intended use in such a way that the
finished coatings meet the set requirements. The basic principles governing
the
selection of the polymeric substructure and the coreactive groups b) of the
2 0 constituent monomers for establishing the basic properties of the coating
materials
are known to the polymer chemist and to the skilled worker.
The requirements imposed on the finished coatings can be very different. For
clear
topcoats of automotive metallic finishes, for example, the utmost yellowing
2 5 resistance and weathering stability, scratch resistance and gloss
retention are called
for along with a high level of hardness.
In the case of a coil coating material, i.e., a coating material with which
metal
strips are coated, then wound up and processed further later, with
deformation,
3 0 important parameters are very high elasticity and adhesion. The price of
the
monomers may also be a selection criterion if for certain applications high
quality
of the coatings is not a particular requirement but a low price is.
For example, the hardness, glass transition temperature and softening point of
the
3 5 polymers can be increased by using higher proportions of "hard" monomers,
such
as styrene or the (meth)acrylates of C 1 to C3 alcohols, whereas, for example,
butyl
acrylate, ethylhexyl acrylate or tridecyl acrylate, as "soft" monomers,
attenuate
CA 02339735 2001-02-06
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these properties but at the same time improve the elasticity. Minor
proportions of
(meth)acrylic acid or (meth)acrylamide improve the adhesion.
The influences of the molecular weight, the molecular weight distribution, the
control of the polymerization by means of regulators, temperature sensing and
cata
lyst selection are fundamentally known.
Monomers which in addition to the double bond carry further functional groups
can
also be used for an additional heat-activatable crosslinking reaction. In
general,
however, they are employed in minor amounts in which they improve, for
example,
the adhesion, electrostatic chargeability, flow behavior of the coating
materials, and
surface smoothness. Derivatives of the 3-phenylacrylic acids, moreover, as
incorporated stabilizers, improve the weathering stability of the coatings.
The coating formulations may additionally comprise pigments and/or customary
coating auxiliaries, such as leveling assistants, devolatilizing assistants,
other
wetting agents and dispersants, dyes, and fillers. Also possible are aqueous
dispersions of the coating powders, known as powder slurries, in order to open
up
application in liquid form to the powder coating materials.
2 0 It is also possible to prepare aqueous dispersions, for example, by
(partial)
neutralization of polymer-bound amino groups or dispersion with the aid of
protective colloids. In this case it is advantageous to establish a pH of > 7
in order
to prevent acid-catalyzed hydrolysis of the vinyl ethers.
2 5 The invention also provides for the use of the formulation of the
invention as or in
adhesives. These adhesives can be applied from the melt, as liquid systems, or
as a
solution or dispersion in appropriate solvents or water. In this case too,
curing can
be carried out thermally and/or with high-energy radiation, preferably UV
light.
3 0 In addition, the formulation of the invention can be used in the form of
casting and
impregnating compositions for electronics and/or electrical engineering. In
this
case, the formulations can be applied from the melt, as systems liquid at room
temperature, or as solutions or dispersions in appropriate solvents or water.
Here
again, curing can be carried out thermally and/or with high-energy radiation,
3 5 preferably UV light.
CA 02339735 2001-02-06
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A further use in accordance with the invention relates to the preparation of
formulations for producing moldings, which can comprise fibrous reinforcing
materials in flat formation andlor present randomly. Examples of possible such
reinforcing materials are glass fibers and/or other fillers and reinforcing
substances.
Pigments may also be included.
In the text below the intention is to illustrate the invention further with
reference to
examples:
Examples
Example 1: Polyurethane with vinyl ether and acrylate groups
3 87 g of hexamethylene diisocyanate
(2.3 mol)
185 of vinyl cyclohexyl ether
g
1.50 g of tert-butylcresol
0.75 g of hydroquinone monomethyl
ether
0.15 g of phenothiazine
0.6 g of dibutyltin dilaurate
2 0 are weighed out into a stirring flask equipped with feed vessel and reflux
condenser. The mixture is heated to 80°C under a gentle stream of
nitrogen and
over an hour a dissolved mixture of
90 g of 1,4-butanediol (1 mol)
2 5 174 g of hydroxyethyl acrylate (1.5 mol)
58 g of 1,4-butanediol monovinyl ether (0.5 mol)
30 g of trimethylolpropane (0.22 mol)
50 g of vinyl cyclohexyl ether (solvent)
is added dropwise. There is an exothermic reaction. The temperature is held at
3 0 from 80 to 90°C by gentle cooling and following the end of the
addition is held at
80°C for a further hour. Thereafter, isocyanate can no longer be
detected in the IR
spectrum. Cooling gives a waxy, pale yellowish substance having a melting
point
of about 80°C.
CA 02339735 2001-02-06
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Example 2: Polyurethane with vinyl ether and acrylate groups
289 g of Basonat HI 100 (trimerized hexamethylene diisocyanate with 21.8%
NCO)
111 g of vinyl cyclohexyl ether
1 g of tert-butylcresol
0.5 g of hydroquinone monomethyl ether
0.1 g of phenothiazine
0.4 g of dibutyltin dilaurate (as catalyst)
are weighed out into a stirring flask equipped with feed vessel and reflux
condenser. The mixture is heated to 80°C under a gentle stream of
nitrogen and
over an hour a dissolved mixture of
11.4 g of 1,4-butanediol (0.125 mol)
87 g of hydroxyethyl acrylate (0.75 mol)
58 g of 1,4-butanediol monovinyl ether (0.5 mol)
is added dropwise. There is an exothermic reaction. The temperature is held at
from 80 to 90°C by gentle cooling and following the end of the addition
is held at
80°C for a further hour. Thereafter, isocyanate can no longer be
detected in the IR
spectrum. Cooling gives a clear, colorless resin solution.
Example 3: Polyacrylate with aminovinyl ether and acrylate groups
486 g of butyl acetate
are weighed out into a stirring flask equipped with feed vessel and reflux
2 5 condenser, and this initial charge is brought to 85°C. Then, as
feed stream I, .
300 g of methyl methacrylate
200 g of glycidyl methacrylate (1.41 mol)
300 g of butyl acrylate
200 g of ethyl hexyl acrylate and
3 0 10 g of mercaptoethanol
are added over 90 minutes and, as feed stream II,
g of 2,2'-azobis(2-methylbutyronitrile)
Wako-Starter V59, dissolved in
190 g of butyl acetate,
are added over 120 minutes. Polymerization is continued at 85°C for 3
hours, after
which the batch is cooled to 50°C and
67.6 g of acrylic acid (0.94 mol)
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0.7 g of tert-butylcresol
0.35 g of hydroquinone monomethyl ether
0.07 g of phenothiazine and
0.7 g of dimethylaminopyridine
are added and the mixture is stirred at 95 to 100°C for 8 hours.
Thereafter, a resin
solution with an acid number of 6.2 is obtained. This solution is cooled to
60°C
and
74 g of diethanolamine divinyl ether (0.47 mol)
are added dropwise over one hour. There is a slightly exothermic reaction.
After a
further 3 hours at 80°C, the mixture is cooled. This gives a viscous,
yellowish resin
solution.
Example 4: Polyacrylate with aminovinyl ether and dihydrodicyclo-
pentadienyl groups
486 g of butyl acetate
are weighed out into a stirring flask equipped with feed vessel and reflux
condenser, and this initial charge is brought to 85°C. Then, as feed
stream I,
200 g of methyl methacrylate
2 0 106.5 g of glycidyl methacrylate (0.75 mol)
300 g of butyl acrylate
200 g of ethyl hexyl acrylate
100 g of dihydrodicyclopentadienyl acrylate and
10 g of mercaptoethanol
2 5 are added over 90 minutes and, as feed stream II,
30 g of 2,2'-azobis(2-methylbutyronitrile)
Wako-Starter V59, dissolved in
1$0 g of butyl acetate,
are added over 120 minutes. Polymerization is continued at 85°C for 3
hours, after
3 0 which the batch is cooled to 60°C and
118 g of diethanolamine divinyl ether (0.75 mol)
are added dropwise over one hour, with a slightly exothermic reaction. After a
further 3 hours at 80°C, the result is a viscous, pale yellowish resin
solution.
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Example 5: Polyacrylate with aminovinyl ether, acrylate and dihydrodi-
cyclopentadienyl groups
486 g of butyl acetate
are weighed out into a stirring flask equipped with feed vessel and reflux
condenser, and this initial charge is brought to 85°C. Then, as feed
stream I,
200 g of methyl methacrylate
100 g of dihydrodicyclopentadienyl acrylate
200 g of glycidyl methacrylate (1.41 mol)
300 g of butyl acrylate
200 g of ethyl hexyl acrylate and
10 g of mercaptoethanol
are added over 90 minutes and, as feed stream II,
30 g of 2,2'-azobis(2-methylbutyronitrile)
Wako-Starter V59, dissolved in
180 g of butyl acetate,
are added over 120 minutes. Polymerization is continued at 85°C for 3
hours, after
which the batch is cooled to 50°C and
67.6 g of acrylic acid (0.94
mol)
2 0 0.7 of tent-butylcresol
g
0.35 g of hydroquinone monomethyl
ether
0.07 g of phenothiazine and
0.7 g of dimethylaminopyridine
are added and the mixture is stirred at 95 to 100°C for 8 hours.
Thereafter, a resin
2 5 solution with an acid number of 6.2 is obtained. This solution is cooled
to 60°C
and
74 g of diethanolamine divinyl ether (0.47 mol)
are added dropwise over one hour. There is a slightly exothermic reaction.
After a
further 3 hours at 80°C, the mixture is cooled. This gives a viscous,
yellowish resin
3 0 solution.
Comparative Example 1: Comparative Example: Polyacrylate with
acrylate groups only
3 5 486 g of butyl acetate
are weighed out into a stirring flask equipped with feed vessel and reflux
condenser, and this initial charge is brought to 85°C. Then, as feed
stream I,
CA 02339735 2001-02-06
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300 g of methyl methacrylate
200 g of glycidyl methacrylate (1.41 mol)
300 g of butyl acrylate
200 g of ethyl hexyl acrylate and
10 g of mercaptoethanol
are added over 90 minutes and, as feed stream II,
30 g of 2,2'-azobis(2-methylbutyronitrile)
Wako-Starter V59, dissolved in
180 g of butyl acetate,
are added over 120 minutes. Polymerization is continued at 85°C for 3
hours, after
which the batch is cooled to 50°C and
101 g of acrylic acid (1.39 mol)
0.7 g of tert-butylcresol
0.35 g of hydroquinone monomethyl ether
0.07 g of phenothiazine and
0.7 g of dimethylaminopyridine
are added and the mixture is stirred at 95 to 100°C for 8 hours. After
cooling, a
clear, viscous resin solution with an acid number of 7.9 is obtained.
2 0 Test coating materials
L1 100 g B1 + 50 g TEGDVE + 5 g BDMK
L2 100 g B 1 + 50 g HDA + 5 g BDMK
L3 100 g B2' + 3 g BDMK
L4 100 g B2 + 50 g TEGDVE + 5 g BDMK
L5 100 g B2 + 50 g HDA + 5 g BDMK
L6 156 g B3 (about 100 g resin content) + 3 g BDMK
L7 156 g B3 (about 100 g resin content) + 50 g TEGDVE + 3 g BDMK
L8 156 g B3 (about 100 g resin content) + 50 g HDA + 3 g BDMK
L9 156 g B4 (about 100 g resin content) + 3 g BDMK
L10 156 g B4 (about 100 g resin content) + 50 g TEGDVE + 3 g BDMK
L11 156 g B4 (about 100 g resin content) + 50 g HDA + 3 g BDMK
L12 156 g B5 (about 100 g resin content) + 3 g BDMK
CA 02339735 2001-02-06
- 22 -
L13 156 g BS (about 100 g resin content) + 50 g TEGDVE + 3 g BDMK
L14 156 g BS (about 100 g resin content) + 50 g HDA + 3 g BDMK
VL 162 g VB 1 (about 100 g resin content) + 3 g BDMK
1
VL 162 g VB1 (about 100 g resin content) + 50 g TEGDVE + 3 g BDMK
2
VL 162 g VB 1 (about 100 g resin content) + 50 g HDA + 3 g BDMK
3
BDMK - benzil dimethyl ketal (photoinitiator)
TEGDVE - triethylene glycol divinyl ether
HDA - hexanediol diacrylate
The test coating materials were formulated, and the test panels produced, in a
LJV-shielded laboratory. The constituents of the test coating materials were
pre-
mixed in glass bottles using a stirring spatula, and these mixtures were
stored in a
drying cabinet at 50°C for one hour and then thoroughly stirred again.
After
cooling to room temperature, clear viscous solutions resulted in all cases.
The
solutions were then applied using a coating bar with a gap height of 60 ~,m to
degreased, bright steel panels. The panels with the solutions L6 to L14 and
VL1 to
VL3 were then stored overnight in a vacuum drying cabinet at 40°C to
remove the
solvent, butyl acetate. Thereafter, liquid viscous resin films are present on
all test
panels. The panels were then irradiated under a LJV mercury vapor lamp having
an
emission maximum at about 365 nm and an energy output of 19 mJ/cm2 in the
plane of exposure until the films obtained were unattacked after 10 minutes of
2 0 subjection to a cotton pad wetted with acetone. If surface inhibition of
the films
was observed, then the uncrosslinked, acetone-soluble layer present in that
case
was first of all wiped off and the swellability of the underlying, crosslinked
layer
was assessed.
CA 02339735 2001-02-06
- 23 -
Test findings
Co-ahn~ Finding after UV irradiation
material
L1 30 s: acetone resistant, no surface inhibition*
L2 60 s: acetone resistant, no surface inhibition
L3 90 s: acetone resistant, no surface inhibition
L4 30 s: acetone resistant, no surface inhibition
LS 60 s: acetone resistant, no surface inhibition
L6 90 s: acetone resistant, no surface inhibition
L7 30 s: acetone resistant, no surface inhibition
L8 60 s: acetone resistant, no surface inhibition
L9 120 s: acetone resistant, no surface inhibition
L10 30 s: acetone resistant, no surface inhibition
L11 60 s: acetone resistant, no surface inhibition
L12 30 s: acetone resistant, no surface inhibition
L13 30 s: acetone resistant, no surface inhibition
L14 30 s: acetone resistant, no surface inhibition
VLl 300 s: acetone resistant with tacky surface inhibition
VL2 240 s: acetone resistant, no surface inhibition
VL3 240 s: acetone resistant with tack-free surface inhibition
* Surface inhibition: beneath a thin tacky or tack-free surface layer which
remains uncrosslinked and soluble in acetone, the layers are insoluble in
acetone.
The examples show that the approach in accordance with the invention achieves
extremely high UV sensitivity and prevents oxygen inhibition of the surface.
