Note: Descriptions are shown in the official language in which they were submitted.
CA 02239379 l998-06-03
tlLC, r~ AR~IC(~
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'~ FI/Br PAT95573
BASF Lacke I Farben Aktiengesellschaft, Munster 26.09.1996
Radiation-curable coating composition and its use
for coating
The present invention relates to radiation-
curable coating compositions and to the use of radiation-
curable coating compositions for coating wood, woodbasematerials and paper.
It is known to cure compositions based on acry-
lates by radiation, especially UV radiation. A problem
which occurs here, however, is that the presence of air
is disruptive to the curing of surfaces.
DE-C 26 25 538 discloses photopolymerizable
coating compositions which comprise amines as reducing
agents and/or chain-transferring compounds. The use of a
free amine of this kind has the disadvantage that it may
act as a plasticizer and leads to an unwanted covering on
the surface and to instances of odour nuisance.
By incorporating the amino group into a molecule
which comprises groups which are still polymerizable an
amine is obtained which is incorporated by polymerization
in the course of curing and does not have the above-
mentioned disadvantages. A known method of incorporation
is the addition of amines onto double bond-rich mole-
cules, which takes place in the manner of a Michael
addition and is described, for example, in F. Moller,
Houben-Weyl, Vol. 11/1 (1957), pp. 277-280. US-A
2,759,913 teaches the addition of amines onto activated,
olefinically unsaturated compounds, such as acrylates, in
equimolar amounts, leading to the complete reaction of
the activated ethylenic double bonds. Systematic investi-
gations into the addition of amino alcohols onto acry-
lates have been carried out by N. Ogata and T. Asahara,
Bull. Chem. Soc. Jap. 39, pages 1486-1490, 1966.
DE-C 2 346 424 describes the preparation of
radiation-curable compositions starting from acrylic
esters of polyhydric alcohols and secondary, aliphatic
monofunctional amines. These compositions have the
CA 02239379 1998-06-03
PAT95573 - 2 -
disadvantage of reduced stability on storage. The addi-
tion reaction of a secondary amine, moreover, leads to a
reduction in the acrylic ester functionality of the
molecule and hence also to a reduction in the cross-
5 linking possibilities for the radiation-induced
polymerization.
EP-A-280 222 discloses adducts of esters of
acrylic or methacrylic acid and polyhydric alcohols with
primary monoamines, the molar ratio of monoamine to
(meth)acrylic double bond of the ester being from 0. 05: 1
to 0.4:1. The adducts of EP-A-280 222 are employed in
radiation-curable compositions which cure in the air. The
storage stability of the products known from EP-A-
280 222, however, is inadequate. Thus when the adducts
15 are stored there is a marked increase in viscosity. In
addition, problems of compatibility arise in the case of
adducts of tetrahydric polyols with the primary mono-
amines. Products of this kind are cloudy and/or have a
milky white appearance. A further disadvantage of the
20 amine-modified compositions described in the European
application is that a relatively high proportion of
monoamine is necessary to ensure that the resulting
adducts have sufficiently high nitrogen contents for
systems, for example, which are initiated with benzo-
25 phenone. Sufficiently high nitrogen contents are neces-
sary in order to provide for a photopolymerization which
proceeds to completion and is sufficient in actual
practice at the customary radiation dose.
EP-A-2457 describes plastics for shaped plastics
30 parts, the plastics curing under elevated temperatures.
The plastics are Michael adducts of acrylate monomers and
amines having an amine hydrogen functionality of at least
3. The components are reacted in a ratio of equivalents
of acrylate to amin-e hydrogen of from 0. 5 to 2Ø
US Patents Nos. 4,547,562 and 4,675,374 disclose
radiation-curable solvent-free compositions based on
polyacrylates and mono-, di- or polyamines. Di- and
polyamines specified as being suitable are ~pecies having
more than one primary amino group. When used, these
CA 02239379 1998-06-03
PAT95573 - 3 -
polyamines give highly crosslinked coating compositions
of relatively high molecular mass and hence relatively
high viscosity, which without the addition of reactive
diluents and solvents have too high an application
viscosity or even lead to solid products.
US-A 4,045,416 and US-A 3,845,056, finally,
relate to radiation-curable coating compositions based on
amine acrylates which are obtained by reacting poly-
acrylates with amines having at least one amine hydrogen.
Amines specified as being suitable are primary and
secondary monoamines and also polyamines. According to
the US patents, the polyamine components specified are
polyamines having more than one primary amino group,
polyamines having exclusively secondary amino groups or
polyamines having secondary and tertiary amino groups.
When polyamines having more than one primary amino group
are used, non-homogeneous adducts of low stability on
storage are obtained, while the use of polyamines having
exclusively secondary amino groups, such as piperazine,
for example, leads to non-homogenous mixtures owing to
inadequate reactivities or to instances of incompatibil-
ity. The use of polyamines having secondary and tertiary
amino groups leads only to a reduction in the acrylate or
methacrylate functionality of the molecule.
Formulations employed to date on the bases of
customary commercial binders exhibit good adhesion to the
usual wood substrates (e.g. walnut, oak, cheery) only in
the case of relatively small proportions of so-called
fillers and additives such as waxes, talc, silicates or
else calcium carbonate, calcium sulphate and barium
sulphate. Substrates regarded as particularly critical
for adhesion are compressed woods coated with melamine
resin (film), and plastics such as PVC, polypropylene.
On the other-hand, especially in the case of
primary coatings, a high proportion of filler is essen-
tial to ensure the good sandability which is required in
woodworking. Customary commercial formulations based on
polyether acrylates have filler contents of not more than
about 15~. A higher proportion of filler in such formula-
CA 02239379 1998-06-03
PAT95573 - 4 -
tions leads, for example, to intolerable losses in
adhesion.
Furthermore, if their filler contents are too
high such formulations tend to settle.
One option of avoiding this is to add binders of
relatively high molecular weight. The increases in
viscosity of the formulations which this entails must
then, however, be compensated with additions of monomers
(reactive diluents). For environmental reasons associated
with the product, however, this is undesirable.
The object on which the present invention is
based was therefore to eliminate the disadvantages
described above; in other words, to provide radiation-
curable coating compositions which have sufficient
stability on storage and are homogeneous even using
tetrafunctional (meth)acrylic esters as precursor. They
should be radiation-curable without the use of external
synergists such as amines, for example. The coating
compositions of the invention should be oligomers
combining low viscosity with comparatively good
radiation-curability and comparatively good resulting
film properties, especially hardness. They should be of
low viscosity so that it is possible to dispense with the
use of reactive diluents and organic solvents. Finally,
good sandability with good adhesion should be ensured
even on critical substrates.
The object on which the present invention is
based is achieved by a radiation-curable coating composi-
tion comprising from 50 to 85, preferably from 60 to 75
by weight of polyether acrylate, from 15 to 40,
preferably from 20 to 30~ by weight of fillers, from 0 to
10, preferably from 0 to 5% by weight of water and, in W
applications, from 0 to 6, preferably from 3 to 5~ by
weight of W initiators.
The polyether acrylate employed in accordance
with the invention is an adduct of oligomers having at
least two acrylate and/or methacrylate groups per mole-
cule and polyamines.
Suitable acrylates and methacrylates are con-
CA 02239379 1998-06-03
PAT95573 - 5 -
structed, for example, with dihydric aliphatic alcohols,
such as ethylene glycol, propylene 1,2- and 1,3-glycol,
1,4-butanediol, 1,2-pentanediol, neopentyl glycol, 1,6-
hexanediol,2-methyl-1,5-pentanediol,2-ethyl-1,4-butane-
diol, dimethylolcyclohexane and diethylene glycol, withtrihydric alcohols, such as glycerol, trimethylolethane,
trimethylolpropane and trimethylolbutane, with tetra-
hydric alcohols, such as pentaerythritol, and with higher
polyhydric alcohols, such as di(trimethylolpropane),
di(pentaerythritol) and sorbitol.
Also suitable are cycloaliphatic alcohols, such
as cyclohexanols and 1,4-bis(hydroxymethyl)cyclohexane,
araliphatic alcohols, such as 1,3-xylylenediol, and
phenols, such as 2,2-bis(4-hydroxyphenyl)propane (bis-
phenol A).
It is preferred as oligomers to use esters ofacrylic acid and/or methacrylic acid with tri- to tetra-
hydric alcohols.
The polyhydric alcohols set out above will
preferably have been converted into ether alcohols of
relatively high molecular mass by alkoxylation with, for
example, ethylene oxide or propylene oxide prior to the
esterification with acrylic acid or methacrylic acid.
Polyether acrylates or polyether methacrylates are the
result of this. Such polyether (meth)acrylates are used
with particular preference in the adducts of the inven-
tion.
The hydroxyl-containing polyethers which are
esterified with acrylic acid and/or methacrylic acid are
obtained by reacting di- and/or polyhydric alcohols with
various amounts of ethylene oxide and/or propylene oxide
in accordance with well-known methods (cf. e.g. Houben-
Weyl, Volume XIV, 2, Makromolekulare Stoffe II, (1963)).
The invent-ion -gives particular preference to
polyether acrylates which are prepared from acrylic acid
and a propoxylated trimethylolpropane polyol with subse-
quent reaction with 4-dimethylaminopropylamine.
It is also possible to employ polymerization
products of tetrahydrofuran or of butylene oxide.
CA 02239379 1998-06-03
PAT95573 - 6 -
Further suitable oligomers are polyester acry-
lates and/or polyester methacrylates. The polyester
(meth)acrylates are prepared using hydroxyl-containing
polyesters (polyesterpolyols) as polyhydric alcohols.
These can be prepared by esterification of dicarboxylic
acids with diols and triols in accordance with well-known
methods (cf. e.g. P.J. Flory, J. Am. Chem. Soc. 58, 1877
(1936) and J. Am. Chem. Soc. 63, 3083 (1953)).
The preparation of polyether acrylates and
polyester acrylates is described, for example, in DE-A-
38 36 370.
The polyamines are diamines having a primary and
a tertiary amino group, and the ratio of primary amino
groups to (meth)acrylic double bonds is from 0.01:1 to
0.2:1, preferably from 0.03:1 to 0.1:1.
Suitable diamines having a primary and a tertiary
amino group are N,N-dialkyldiaminoalkanes, such as, for
example, N,N-dimethyl-1,3-diaminopropane, which is
obtainable by catalytic hydrogenation of dimethylamino-
propionitrile. The preparation of this polyamine isdescribed, for example, in Houben Weyl, Vol. 11/1, 1957,
p. 565, in EP-A-316 761 or in P. Lappe, H. Springer and
J. Weber, Chem.-Ztg. 111 (4), pp. 117-125 (1987).
Further suitable dialkylaminopropanes are N,N-
diethyl-1,3-diaminopropane, N,N-di-n-propyl-1,3-diamino-
propane, 4-morpholinopropylamine, 3-(N-piperidine)-
propylamine, N,N-diphenyl-1,3-diaminopropane.
Further compounds suitable as the polyamine
component of the adducts of the invention are: N,N-
dialkyl-1,2-diaminoethanes, such as dimethylaminoethyl-
amine, diethylaminoethylamine, N-~-aminoethylmorpholine
(for preparation see e.g. Houben Weyl, Vol. 11/1, 1957,
p. 563), N,N-dialkyl-1,5-diaminopentanes, which can be
prepared by 1,4-ad-diti-on of secondary amines onto 1-
cyano-1,3-butadiene to form the nitriles, with subsequent
catalytic hydrogenation (for preparation see Houben-Weyl,
Vol. 11/1, 1957, p. 276). Examples of suitable N,N-
dialkyl-1,5-diaminopentanesaredimethylaminopentylamine,
diethylaminopentylamine, 4-morpholinopentylamine.
CA 02239379 1998-06-03
PAT95573 7
Particularly good results are obtained if the
amine component used is N,N-dimethyl-1,3-diaminopropane.
The adducts of the invention are liquid at room
temperature. They are prepared by adding the diamines
onto an acrylate or methacrylate or onto a mixture of
these esters in a Michael reaction. The resulting amine-
modified oligomers comprise still unreacted acrylate
and/or methacrylate groups and also tertiary amino
groups.
The addition reaction is carried out in liquid
phase at moderate temperature in the absence of a cata-
lyst. The diamine in an appropriate amount is added to
the ester at room temperature with stirring. The tempera-
ture may rise to about 40~C in the course of this addi-
tion. The reaction can be accelerated by raising the
temperature; at 60~C it has subsided after about 12
hours. The viscosity of the resulting mixture is then
constant over time.
For reproducibility the reaction should progress
as completely as possible, which is achieved at reaction
temperatures above 40~C.
The reaction is generally conducted without
solvent, although solvents may also be employed especial-
ly in order to allow solid amines to be metered in as a
solution. The solvent is then removed after Michael
addition has taken place.
So that no unwanted polymerization takes place in
the course of the addition reaction, polymerization
inhibitors are generally added to the reaction mixture.
Suitable polymerization inhibitors include known prod-
ucts, such as substituted phenols, such as 2,6-di-tert-
butyl-p-cresol, hydroquinones, such as methylhydro-
quinones, and thioethers, such as thiodiglycol or
phenothiazine. -- ~
The amine-modified adducts described are used as
film-forming components in radiation-curable coating
compositions of the invention. In addition to the amino-
modified oligomers of the invention, these radiation-
curable coating compositions may, depending on the visco-
CA 02239379 1998-06-03
PAT95573 - 8 -
sity of the esters, comprise further copolymerizable
compounds known for use in radiation-curable coating
compositions, examples being (meth)acrylates, especially
methyl (meth)acrylate, ethyl (meth)acrylate, propyl
(meth)acrylate, butyl (meth)acrylate, isopropyl
(meth)acrylate, isobutyl (meth)acrylate, pentyl
(meth)acrylate, isoamyl (meth)acrylate, hexyl
(meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, octyl (meth)acrylate, 3,5,5-
trimethylhexyl (meth)acrylate, decyl (meth)acrylate,dodecyl (meth)acrylate, hexadecyl (meth)acrylate,
octyldecyl (meth)acrylate, octadecenyl (meth)acrylate and
also the corresponding esters of maleic, fumaric,
tetrahydrophthalic, crotonic, isocrotonic, vinylacetic
and itaconic acid. Preference is given to the use of
monomers having more than 1 double bond per molecule,
examples being ethylene glycol diacrylate, diethylene
glycol diacrylate, propylene glycol diacrylate,
trimethylene glycol diacrylate, neopentyl glycol
diacrylate, 1,3-butylene glycol diacrylate, 1/4-butylene
glycol diacrylate, 1,6-hexamethylene glycol diacrylate,
1,10-decamethylene glycol diacrylate, trimethylolpropane
triacrylate, pentaerythritol tetraacrylate and penta-
erythritol triacrylate and also the corresponding meth-
acrylates. Very particular preference is given to the useof trimethylolpropane triacrylate and acrylates of
propoxylated trimethylolpropane.
The addition of these monomeric copolymerizable
compounds (often also called reactive diluents), however,
is generally unnecessary, since the amine-modified esters
of the invention are of low viscosity.
The advantage of the adducts described is also to
be seen in particular in the fact that by virtue of the
tertiary amino groups they comprise they are dispersible
in water; in other words, it is possible to dispense
entirely with the use of organic solvents. The tertiary
amino groups can be converted into the charged groups by
at least partial reaction with acids. Acids suitable for
neutralizing the basic groups are, for example, lactic
CA 02239379 1998-06-03
PAT95573 9
acid, acetic acid, formic acid, phosphoric acid and
hydrochloric acid.
For W applications, the radiation-curable
coating compositions also comprise photoinitiators which
are normally employed in radiation-curable coating
compositions, examples being benzophenones, benzoins or
benzoin ethers. The use of synergists can be dispensed
with, since the esters present in the coating
compositions have been amine-modified and hence exhibit
a synergistic effect.
The coating materials of the invention can also
be cured with electron beams. In the corresponding
formulations it is possible to dispense with the addition
of W initiators.
In addition to the amine-modified reaction
products of the esters and the diamines, the radiation-
curable compositions of the invention can additionally
comprise further photopolymerizable binders, which may
likewise have been amine-modified. Examples of suitable
such further, amine-modified binders are the radiation-
curable binders known from EP-A-280 222 and those known
from US Patents Nos. 4,045,416, 4,547,562 and 4,675,374.
Suitable further binders which have not been
amine modified are the epoxy acrylates and epoxy meth-
acrylates, urethane methacrylates, urethane acrylates,polyester methacrylates, polyester acrylates, polyether
methacrylates and polyether acrylates described above by
way of example of the oligomer component.
The radiation-curable coating compositions of the
invention comprise customary auxiliaries and additives,
examples being extenders, defoamers, levelling agents and
film-forming auxiliaries, lubricants, adhesion promoters.
Suitable fillers are in accordance with the
invention silicates, carbonates and sulphates. The former
include in particular kaolins, talc, siliceous chalk,
micas, e.g. micaceous iron ore, silicon carbide and
quartz flour.
Suitable carbonate fillers are calcium carbonates
and calcium magnesium carbonates (dolomite).
CA 02239379 1998-06-03
PAT95573 - 10 -
Barium sulphates (heavy spar) and potassium
sulphates (light spars) are employed as sulphate fillers.
In addition to the substances mentioned it is
also possible to use wood flour and cellulose deriva-
tives.
Substances which impart colour are also suitable
in accordance with the invention. These include both
inorganic pigments, e.g. carbon black, TiO2 and organic
pigments.
Filler contents of from 20 to more than 30~ by
weight have been realised in the formulations of the
invention. In the prior art, such high filler contents
were considered impossible.
It is surprising according to the invention that
there are no losses in adhesion in a range of more than
15% by weight filler content. Moreover, the coating
compositions of the invention show no tendency whatsoever
towards irreversible settling. Further surprisingly
advantageous properties are the good sandability and very
good adhesion even on critical substrates, such as
plastics or woodbase materials coated with melamine
resins, for example.
In one variant of the invention the viscosity and
reactivity can be established within certain limits by
simple addition of amine prior to application. If about
48 h elapse between the addition of amine and the appli-
cation of the coating composition, the amine is no longer
present in free form but is bonded physically or chemi-
cally to the remaining constituents of the coating
composition. In this case the reactivity of the mixture
produced with addition of amine increases relative to the
base formulation described above. Experiments have shown
that, depending on amounts, an approximately double rate
of reaction is found under W radiation. The viscosity
can also be very nearly doubled.
In a preferred embodiment of the invention the
coating composition consists accordingly of from 95 to
100~ by weight, preferably from 98 to 100% by weight of
the above-described coating material and from 0 to 5,
CA 02239379 1998-06-03
PAT95573 - 11 -
preferably from 0 to 2~ by weight of polyamine added
prior to application.
Suitable polyamines are the compounds already
described above. In other words, mention should be made
here primarily of diamines having a primary and tertiary
amino group. Particular preference is given in this
context to the addition of dimethylaminopropylamine.
Lubricants can be present in a proportion of from
0.8 to 1.2~ and levelling agents in a proportion from 0.2
to 0.8~ by weight in the coating composition. In this
case the remaining amount of filler is reduced according-
ly .
It is surprising that the good adhesion mentioned
on the various substrates is obtained without the use of
typical adhesion promoters. In specific cases, however,
additional adhesion promoters can be employed. Examples
are alkoxysilanes, such as, for example, N-~-aminoethyl-,
-aminopropyltrimethoxysilane, -N-methyl-~-aminopropyl-
trimethoxysilane or triamino-modified propyltrimethoxy-
silane (e.g. adhesion promoter DYNASYLAN type "TRIAMO",commercial product of Dynamit Nobel Chemie).
The coating films are cured by means of radi-
ation, preferably by means of W or electronic radiation.
Accordingly, the W-cured coating compositions of the
invention comprise W initiators. These are preferably
benzophenone, benzoin alkyl ethers, benzil ketals,
hydroxyalkylphenones, thioxanthones and also phosphine
oxide derivatives and bisacylphosphine oxide derivatives.
The curing of the coating films takes place
directly following application or following the evapor-
ation of any water present by means of W or electron
beams. The equipment and conditions for these curing
methods are known from the literature (cf. e.g. R.
Holmes, U.V. and E-.B. ~uring Formulations for Printing
Inks, Coatings and Paints, SITA Technology, Academic
Press, London, United Kingdom 1984, pp. 79 to 111) and
require no further description.
The coating compositions can be applied to the
substrate, preferably to wood, to woodbase materials or
CA 02239379 1998-06-03
PAT95573 - 12 -
to paper, by spraying, rolling, flowcoating, dipping,
knifecoating, spreading, by casting or by Vakumat appli-
cation.
The radiation-curable coating compositions of the
invention exhibit an excellent stability on storage, have
a transparent appearance and good radiation-curability,
and following radiation curing lead to films having
excellent properties. The films obtained are notable for
excellent transparency.
In the text below the invention is illustrated
further with reference to working examples. Parts are by
weight unless stated otherwise:
Example 1
Base formulation:
15 1. Polyether acrylate 68.5%
prepared from propoxylated
trimethylolpropane polyol
(Desmophen550U from Bayer),
acrylic acid and
subsequent reaction with 4%
of dimethylaminopropylamine
2. Phyllosilicate 2.0%
3. Talc 10.0%
4. Calcium carbonate 10.0
25 5. Lubricant (Lanco wax) 1.0%
6. Levelling agent (Byk 306) 0.5%
7. Water 4-0%
8. Benzophenone 4.0%
Total 100%
Viscosity 42-45 seconds flow viscosity in accordance with
DIN6/20~C.
CA 02239379 1998-06-03
PAT95573 - 13 -
Example 2
Adjusting viscosity, adjusting reactivity
1. Base formulation see above 99.5%
2. Dimethylaminopropylamine 0.5%
5 Total 100%
1. and 2. are mixed with one another and then
left for 48 h.
Result: The reactivity of the mixture has risen to
15 m/min relative to the base formulation of 9 m/min per
80 W mercury W radiator. The viscosity has risen from 44
to 72 seconds (flow in accordance with DIN6/20~C).
ExamPle 3
1. 70.30 parts of binder as in Ex. 1
2. 4.10 parts of benzophenone
3. 8.30 parts of talc
4. 10.30 parts of chalk (CaCO3)
(5. 3.00 parts of phyllosilicate for matting)
(6. 3.50 parts of phyllosilicate)
5. 6.50 parts of phyllosilicate
6. 0.50 parts of levelling agent
100 . O
In addition to the advantages referred to, the
formulation also meets the chemicals test of DIN68861 B.
Comparative examples with customary commercial binders
For Example 1 - -
1) Item 1: 68.50 parts of Laromer PO84F (obtainable
from BASF AG)
Phyllosilicate 2.0
Talc 10.0
CA 02239379 1998-06-03
PAT95573 - 14 -
Calcium carbonate 10.0
Lubricant (Lanco wax) 1.0
Levelling agent (Byk 306) 0 .5%
Water 4.0
Benzophenone 4.0g6
Result: Viscosity too high, DIN6>120 sec., hence cannot
be processed in practice.
2) Item 2: 68. 50 parts of Laromer PO83F
Result: Viscosity acceptable but coating material not
stable on storage, severe irreversible tendency towards
settling.
