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Claims  |
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We claim:
1. A powder coating including a film-forming material consisting
essentially of:
(A) from 19.9 to 90.0 percent by weight of a synthetic resin which contains
epoxide groups and which may optionally contain ethylenically unsaturated
double bonds, or of a mixture of such epoxide group-containing synthetic
resins;
(B) from 9.9 to 80.0 percent by weight of a compound which contains
carboxyl groups and which may optionally contain ethylenically unsaturated
double bonds, or of a mixture of such carboxyl group-containing compounds;
(C) from 0 to 20 percent by weight of a compound which contains
ethylenically unsaturated double bonds, or of a mixture of such compounds;
and
(D) from 0.1 to 3.0 percent by weight of an initiator for free-radical
polymerizations, or of a mixture of initiators for free-radical
polymerizations;
wherein the sum of the percentages by weight of (A)+(B)+(C)+(D) is 100% by
weight, and further wherein the mixture of components (A), (B), (C), and
(D) contains from 0.1 to 6.0 mol of ethylenically unsaturated double bonds
total per 1000 g of mixture.
2. A powder coating according to claim 1, wherein the film-forming material
employed is a mixture of from 39.9 to 80.0 percent by weight of component
(A), from 19.9 to 60.0 percent by weight of component (B), from 0.5 to
10.0 percent by weight of component (C), and from 0.2 to 2.0 percent by
weight of component (D).
3. A powder coating according to claim 1, wherein component (A) is selected
from the group consisting of polyacrylate resins containing epoxide groups
and mixtures thereof.
4. A powder coating according to claim 1, wherein component (B) is selected
from the group consisting of polyester resins containing carboxyl groups
and mixtures thereof.
5. A powder coating according to claim 1, wherein the polyester resin
employed as component (B) is obtained by reacting
(b1) a diol which may optionally be ethylenically unsaturated, or a mixture
of such diols,
(b2) a compound which may optionally be ethylenically unsaturated and which
contains per molecule at least three functional groups selected from the
group consisting of hydroxyl, primary amino, secondary amino, carboxyl,
and acid anhydride groups, and mixtures thereof, with one acid anhydride
group being regarded as equivalent to two carboxyl groups, and
(b3) a dicarboxylic acid which may optionally be ethylenically unsaturated,
a dicarboxylic acid anhydride which may optionally be ethylenically
unsaturated, or mixtures thereof,
wherein the molar ratio of (b1):(b2):(b3) is from 0.0 to 3.0:1.0:1.5 to
9.0, to give a polyester resin having an acid value of from 40 to 300, or
a mixture of such polyester resins.
6. A powder coating according to claim 1, wherein the compound used as
component (B) contains on statistical average from 1.5 to 5.0 carboxyl
groups and from 0 to 20 acid anhydride groups and from 0 to 10
ethylenically unsaturated double bonds per molecule, or a mixture of such
compounds.
7. A powder coating according to claim 5, wherein component (B) comprises a
mixture of from 95 to 5 percent by weight of the polyester resin and from
5 to 95 percent by weight of a second compound containing on statistical
average from 1.5 to 5.0 carboxyl groups and from 0 to 20 acid anhydride
groups and from 0 to 10 ethylenically unsaturated double bonds per
molecule, or a mixture of such compounds; the sum of the proportions by
weight of the polyester resin and of the second compound always being 100%
by weight.
8. A powder coating according to one of claims 1, 6, or 7, wherein maleic
anhydride is employed as component (C).
9. A powder coating according to one of claims 1, 6, or 7, wherein
component (D) has a half-life at 120.degree. C. of at least 5 minutes.
10. A powder coating according to one of claims 1, 6, or 7, wherein the
mixture of components (A), (B), (C), and (D) contains from 0.2 to 4.0 mol
of ethylenically unsaturated double bonds per 1000 g of mixture.
11. A powder coating according to claim 1, wherein the film-forming
material employed is a mixture of from 49.9 to 70.0 percent by weight of
component (A), from 29.9 to 50.0 percent by weight of component (B), from
1.0 to 5.0 percent by weight of component (C), and from 0.5 to 1.5 percent
by weight of component (D).
12. A powder coating according to claim 1, wherein the polyester resin
employed as component (B) is obtained by reacting
(b1) a diol which may optionally be ethylenically unsaturated, or a mixture
of such diols,
(b2) a compound which may optionally be ethylenically unsaturated and which
contains per molecule at least three functional groups selected from the
group consisting of hydroxyl, primary amino, secondary amino, carboxyl and
acid anhydride groups, and mixtures thereof, with one acid anhydride group
being regarded as equivalent to two carboxyl groups, and
(b3) a dicarboxylic acid which may optionally be ethylenically unsaturated,
a dicarboxylic acid anhydride which may optionally be ethylenically
unsaturated, or mixtures thereof,
wherein the molar ratio of (b1):(b2):(b3) is from 0.5 to 2.0:1.0:2.0 to
6.0, to give a polyester resin having an acid value of from 80 to 250, or
a mixture of such polyester resins.
13. A powder coating including a film-forming material consisting
essentially of:
(A) from 19.9 to 90.0 percent by weight of a compound selected from the
group consisting of polyacrylate resins containing epoxide groups and
mixtures thereof;
(B) from 9.9 to 80.0 percent by weight of a compound selected from the
group consisting of polyester resins containing carboxyl groups and
mixtures thereof;
(C) from 0 to 20 percent by weight of maleic anhydride; and
(D) from 0.1 to 3.0 percent by weight of an initiator for free-radical
polymerizations, or of a mixture of initiators for free-radical
polymerizations having a half-life at 120.degree. C. of at least 5
minutes;
wherein the sum of the percentages by weight of (A)+(B)+(C)+(D) is=100% by
weight, and further wherein the mixture of components (A), (B), (C), and
(D) contains from 0.1 to 6.0 mol of ethylenically unsaturated double bonds
total per 1000 g of mixture.
14. A powder coating according to claim 13, wherein the polyester resin
employed as component (B) is obtained by reacting
(b1) a diol which may optionally be ethylenically unsaturated, or a mixture
of such diols,
(b2) a compound which may optionally be ethylenically unsaturated and which
contains per molecule at least three functional groups selected from the
group consisting of hydroxyl, primary amino, secondary amino, carboxyl,
and acid anhydride groups, and mixtures thereof, with one acid anhydride
group being regarded as equivalent to two carboxyl groups, and
(b3) a dicarboxylic acid which may optionally be ethylenically unsaturated,
a dicarboxylic acid anhydride which may optionally be ethylenically
unsaturated, or mixtures thereof.
wherein the molar ratio of (b1):(b2):(b3) is from 0.5 to 2.0:1.0:2.0 to
6.0, to give a polyester resin having an acid value of from 80 to 250, or
a mixture of such polyester resins. |
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Claims |
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Description |
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The invention relates to powder coatings which provide coating films having
excellent properties, and in particular coating films of high flexibility
with a high degree of hardness.
Powder coatings are known. Since they contain no solvents, they can be used
for coating in an especially environment-friendly manner. The coating
films which can be produced using powder coatings, however, remain in need
of further improvement in terms of their properties.
The object on which the present invention is based consists in the
provision of new powder coatings which can be used to produce coating
films which, in relation to the prior art, have improved properties, and
in particular a higher flexibility and a higher degree of hardness.
This object is achieved, surprisingly, by the provision of powder coatings
which contain as film-forming material a mixture of
(A) from 19.9 to 90.0 percent by weight of a synthetic resin which contains
epoxide groups and may contain ethylenically unsaturated double bonds, or
of a mixture of such epoxide group-containing synthetic resins,
(B) from 9.9 to 80.0 percent by weight of a compound which contains
carboxyl groups and may contain ethylenically unsaturated double bonds, or
of a mixture of such carboxyl group-containing compounds,
(C) from 0 to 20 percent by weight of a compound which contains
ethylenically unsaturated double bonds and is different from (A) and (B),
or of a mixture of such compounds, and
(D) from 0.1 to 3.0 percent by weight of an initiator for free-radical
polymerizations or of a mixture of initiators for free-radical
polymerizations,
the percentages by weight of (A)+(B)+(C)+(D) being=100% by weight and the
mixture of components (A), (B), (C) and (D) containing from 0.1 to 6.0 mol
of ethylenically unsaturated double bonds per 1000 g of mixture.
Using the powder coatings provided in accordance with the invention it has,
surprisingly, been possible to produce coating films which, in relation to
the prior art, have improved properties, and in particular higher
flexibilities and higher degrees of hardness.
EP-A-38 635 describes powder coatings which contain, as film-forming
material, a synthetic resin containing epoxide groups and a linear
polyester containing carboxyl groups. Coating films prepared using these
powder coatings possess, in comparison to coating films which have been
produced using the powder coatings provided in accordance with the
invention, poorer properties, and in particular poorer flexibilities and
degrees of hardness.
The film-forming material of the powder coatings according to the invention
comprises from 19.9 to 90.0 percent, preferably from 39.9 to 80.0 percent
and particularly preferably from 49.9 to 70.0 percent by weight of
component (A), from 9.9 to 80.0 percent, preferably from 19.9 to 60.0
percent and particularly preferably from 29.9 to 50.0 percent by weight of
component (B), from 0 to 20 percent, preferably from 0.5 to 10.0 percent
and particularly preferably from 1.0 to 5.0 percent by weight of component
(C) and from 0.1 to 3.0 percent, preferably from 0.2 to 2.0 percent and
particularly preferably from 0.5 to 1.5 percent by weight of component
(D), the percentages by weight being based on (A)+(B)+(C)+(D)=100% by
weight and the mixture of components (A), (B), (C) and (D) containing from
0.1 to 6.0 mol, preferably from 0.2 to 4.0 mol and particularly preferably
from 0.3 to 2.5 mol of ethylenically unsaturated double bonds per 1000 g
of mixture.
As component (A) it is possible in principle to employ any synthetic resin
which contains epoxide groups and may contain ethylenically unsaturated
double bonds, which can be employed for the production of powder coatings
and has a melting point of from 20.degree. to 100.degree. C., preferably
from 30.degree. to 80.degree. C. and particularly preferably from
30.degree. to 60.degree. C., or a mixture of such synthetic resins.
Examples of epoxide group-containing synthetic resins which may be
employed are epoxide group-containing polyacrylate resins, polyglycidyl
ethers of aliphatic or cycloaliphatic alcohols such as ethylene glycol,
diethylene glycol, 1,2-propylene glycol, 1,4-butylglycol,
1,2-cyclohexanediol, 1,4 cyclohexanediol,
1,2-bis(hydroxymethyl)cyclohexane and hydrogenated bisphenol A, or
polyglycidyl ethers of polyphenols such as bisphenol A,
1,1-bis(4-hydroxyphenyl)ethane and
2-methyl-1,1-bis(4-hydroxyphenyl)propane, and the compounds containing
epoxide groups which are listed in U.S. Pat. No. 4,102,942 in column 3,
lines 1 to 16.
As component A) it is preferred to employ an epoxide group-containing
polyacrylate resin or a mixture of epoxide group-containing polyacrylate
resins.
The term epoxide group-containing polyacrylate resin refers to a polymer
which can be prepared by copolymerization of at least one ethylenically
unsaturated monomer, containing at least one epoxide group in the
molecule, with at least one further ethylenically unsaturated monomer
which contains no epoxide group in the molecule, at least one of the
monomers being an ester of acrylic acid or methacrylic [sic] acid.
Epoxide group-containing polyacrylate resins are known (cf. e.g. EP-A-299
420, DE-B-22 14 650, U.S. Pat. No. 4,091,048 and U.S. Pat. No. 3,781,379).
Examples of ethylenically unsaturated monomers containing at least one
epoxide group in the molecule are glycidyl acrylate, glycidyl methacrylate
and allyl glycidyl ether.
Examples of ethylenically unsaturated monomers containing no epoxide group
in the molecule are alkyl esters of acrylic and methacrylic acid which
contain 1 to 20 carbon atoms in the alkyl radical, and in particular
methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate,
butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate and 2-ethylhexyl
methacrylate. Further examples of ethylenically unsaturated monomers
containing no epoxide groups in the molecule are acids, for example
acrylic acid and methacrylic acid, acid amides, for example acrylamide and
methacrylamide, aromatic vinyl compounds such as styrene,
.alpha.-methylstyrene and vinyltoluene, nitriles such as acrylonitrile and
methacrylonitrile, vinyl halides and vinylidene halides, such as vinyl
chloride and vinylidene fluoride, vinyl esters, for example vinyl acetate,
and monomers containing hydroxyl groups, for example hydroxyethyl acrylate
and hydroxyethyl methacrylate.
The epoxide group-containing polyacrylate resin usually has an epoxide
equivalent weight of from 400 to 2500, preferably from 500 to 1500 and
particularly preferably from 600 to 1200, a number-average molecular
weight (determined by gel-permeation chromatism [sic] using a polystyrene
standard) of from 1000 to 15,000, preferably from 1200 to 7000 and
particularly preferably from 1500 to 5000, and a glass transition
temperature (T.sub.G) of from 30.degree. to 80.degree. C., preferably from
40.degree. to 70.degree. C. and particularly preferably from 40.degree. to
60.degree. C.
The epoxide group-containing polyacrylate resin can be prepared in
accordance with generally well-known methods, by free-radical
polymerization.
Components (A) containing ethylenically unsaturated double bonds can be
prepared by using components which contain ethylenically unsaturated
double bonds for the preparation of component (A), and/or by reacting
functional groups, for example hydroxyl groups or epoxide groups, with
compounds which contain ethylenically unsaturated double bonds (e.g.
acrylic acid, methacrylic acid and unsaturated fatty acids). Preferred
components (A) containing ethylenically unsaturated double bonds are
prepared by reacting polyacrylate resins containing hydroxyl and/or
epoxide groups with acrylic acid, methacrylic acid or with an unsaturated
fatty acid.
The powder coatings according to the invention can in principle contain as
component (B) any compound which contains carboxyl groups and may contain
ethylenically unsaturated double bonds, which can be employed in powder
coatings and has a melting point of from 20.degree. to 100.degree. C.,
preferably from 20.degree. to 80.degree. C. and particularly preferably
from 20.degree. to 60.degree. C., or a mixture of such compounds. Examples
of compounds containing carboxyl groups which can be employed are carboxyl
group-containing polyester resins, polyanhydrides of polycarboxylic acids,
and especially polyanhydrides of dicarboxylic acids. As component (B) it
is preferred to employ a polyester resin containing carboxyl groups, a
mixture of such polyester resins, a compound which contains on statistical
average from 1.5 to 5.0 and preferably from 2 to 4 carboxyl groups and
from 0 to 20 and preferably from 2 to 15 acid anhydride groups and from 0
to 10 and preferably from 0 to 5 ethylenically unsaturated double bonds
per molecule, or a mixture of such compounds. As component (B) it is very
particularly preferred to employ a mixture of from 95 to 5 percent,
preferably from 95 to 20 percent and particularly preferably from 90 to 50
percent by weight of a carboxyl group-containing polyester resin and from
5 to 95 percent, preferably from 5 to 80 percent and particularly
preferably from 10 to 50 percent by weight of a compound which contains on
statistical average from 1.5 to 5 and preferably from 2 to 4 carboxyl
groups and from 0 to 20 and preferably from 2 to 15 acid anhydride groups
and from 0 to 10 and preferably from 0 to 5 ethylenically unsaturated
double bonds per molecule, the sum of the proportions by weight in each
case being 100 percent by weight.
The polyester resins containing carboxyl groups which can be employed as
component (B) can be prepared by well-known methods, by reacting
(b1) a diol which may be ethylenically unsaturated, or a mixture of such
diols,
(b2) optionally, a compound which may be ethylenically unsaturated and
which contains per molecule at least three functional groups selected from
hydroxyl, primary amino, secondary amino, carboxyl and acid anhydride
groups, with one acid anhydride group being regarded as equivalent to two
carboxyl groups, or a mixture of such compounds, and
(b3) a dicarboxylic acid which may be ethylenically unsaturated, a
dicarboxylic acid anhydride which may be ethylenically unsaturated, or a
mixture of such dicarboxylic acids and/or dicarboxylic acid anhydrides;
where either the carboxyl group-containing component is employed in excess
or, in a first step, a polyester resin containing hydroxyl groups is
prepared which is then further reacted with a carboxylic acid anhydride to
give a polyester resin containing carboxyl groups. The carboxyl
group-containing polyester resins employed as component (B) should have a
number-average molecular weight (determined by gel-permeation
chromatography using a polystyrene standard) of from 300 to 5000,
preferably from 500 to 3000 and particularly preferably from 500 to 1700,
a glass transition temperature of from 15.degree. to 100.degree. C.,
preferably from 20.degree. to 80.degree. C. and particularly preferably
from 20.degree. to 60.degree. C., and an acid number of from 40 to 300 and
preferably from 80 to 250. Carboxyl group-containing polyester resins
which it is particularly preferred to employ are obtained by reacting
components (b1), (b2) and (b3) in a molar ratio of (b1):(b2):(b3)=from 0.0
to 3.0:1.0:1.5 to 9.0, preferably from 0.0 to 2.0:1.0:2.0 to 8.0 and
particularly preferably from 0.5 to 2.0:1.0:2.0 to 6.0.
The reaction of (b1), (b2) and (b3) is carried out by the well-known
methods of polyester resin preparation. The reaction temperatures are
usually from 140.degree. to 240.degree. C. and preferably from 160.degree.
to 200.degree. C.
As component (b1) a diol which may be ethylenically unsaturated or a
mixture of such diols is employed. The term diol refers to an organic
compound which contains two hydroxyl groups per molecule. Examples of
diols which can be employed are ethylene glycol, propylene glycol,
neopentyl glycol, 1,6-hexanediol, cyclohexanediol, cyclohexanedimethanol,
hydrogenated bisphenol A, and ethylene oxide or propylene oxide addition
products with bisphenol A, hydrogenated bisphenol A and diethylene glycol.
As component (b1) it is preferred to employ aliphatic or cycloaliphatic
diols having from 2 to 16 and preferably from 2 to 12 carbon atoms in the
molecule, or mixtures of such diols.
The compound employed as component (b2) may be ethylenically unsaturated
and contains per molecule at least three functional groups selected from
hydroxyl, primary amino, secondary amino, carboxyl and acid anhydride
groups, one acid anhydride group being regarded as equivalent to two
carboxyl groups, or a mixture of such compounds.
Examples of compounds which can be employed as component (b2) are those
containing per molecule at least three hydroxyl groups. Examples of such
compounds are trimethylolpropane, pentaerythritol, trimethylolethane and
glycerol.
As component (b2) it is also possible to employ compounds which contain two
primary amino and one hydroxyl group per molecule. An example of such a
compound is diaminopropanol.
Compounds which can be employed as component (b2) are also those containing
per molecule at least three carboxyl groups or at least one acid anhydride
group and one carboxyl group. Examples of such compounds are trimellitic
acid, trimellitic anhydride, pyromellitic acid and pyromellitic anhydride.
As component (b3) a dicarboxylic acid which may be ethylenically
unsaturated, a dicarboxylic acid anhydride-which may be ethylenically
unsaturated or a mixture of such dicarboxylic acids and/or dicarboxylic
acid anhydrides is employed. Examples of dicarboxylic acids which can be
employed are saturated and ethylenically unsaturated aliphatic or
cycloaliphatic dicarboxylic acids, such as adipic acid, sebacic acid,
azelaic acid, dodecanedioic acid, maleic acid, fumaric acid, succinic
acid, hexahydrophthalic acid and tetrahydrophthalic acid. Examples of
dicarboxylic acid anhydrides which can employed are the anhydrides of the
stated acids.
As component (b3) it is also possible to employ aromatic dicarboxylic acids
and their anhydrides, for example phthalic acid, isophthalic acid and
terephthalic acid. The use of aromatic dicarboxylic acids and their
anhydrides is less preferred.
As compounds which contain on statistical average from 1.5 to 5.0 and
preferably from 2.0 to 4.0 carboxyl groups and from 0 to 20 and preferably
from 2 to 15 acid anhydride groups and from 0 to 10 and preferably from 0
to 5 ethylenically unsaturated double bonds per molecule it is possible to
employ polyanhydrides of saturated or ethylenically unsaturated
polycarboxylic acids, in particular dicarboxylic acids, or polyanhydrides
of mixtures of saturated or ethylenically unsaturated polycarboxylic
acids, in particular dicarboxylic acids. Such polyanhydrides can be
prepared by removing water from the polycarboxylic acid or mixture of
polycarboxylic acids, each two carboxyl groups being converted to one
anhydride group. Such preparation procedures are well known and therefore
require no further discussion. It is also possible to employ
polyanhydrides modified with a polyol, as described in EP-A-299 420, and
this polyol modification can also be effected during the extrusion
procedure.
Compounds of the type described above which it is preferred to employ are
linear polyanhydrides of aliphatic or cycloaliphatic dicarboxylic acids
having from 3 to 20 and preferably from 6 to 12 carbon atoms in the
molecule, or linear polyanhydrides of mixtures of such dicarboxylic acids.
Specific examples of polyanhydrides which it is preferred to employ are
poly(adipic anhydride), poly(azelaic anhydride), poly(sebacic anhydride),
poly(dodecanedioic anhydride) and poly(cyclohexanedicarboxylic anhydride).
As component (C) it is possible in principle to employ any compound which
contains ethylenically unsaturated double bonds and can be employed in
powder coatings, or a mixture of such compounds. Examples of compounds
which can be employed as component (C) are: maleic anhydride, fumaric
acid, acrylamide, methacrylamide, methacrylic acid, crotonic acid,
methylenebisacrylamide, methylenebismethacrylamide, styrene, methyl
methacrylate, methyl acrylate, butyl acrylate, divinylbenzene, hexanediol
diacrylate, trimethylolpropane triacrylate and divinyldioxane. It is also
possible to employ as component (C) polyurethane, polyester or
polyacrylate resins which contain hydroxyl groups and are modified with
acrylic or methacrylic acid. It is preferred to employ maleic anhydride as
component (C).
As component (D) an initiator for free-radical polymerizations or a mixture
of initiators for free-radical polymerizations is employed. Initiators for
free-radical polymerization are compounds which, at elevated temperatures
or under the effect of high-energy radiation, especially under the effect
of UV radiation, decompose to give free radicals. These free radicals are
able to initiate free-radical polymerizations. Examples of initiators
which can be employed are azo compounds, for example azoisobutyronitrile,
peroxides, for example dibenzoyl peroxide, dilauroyl peroxide and
di-tert-butyl peroxide, and hydroperoxides, for example cumene
hydroperoxide. As component (D) it is preferred to employ initiators which
have a melting point of above 30.degree. C. and a half-life at 120.degree.
C. of at least 5 and preferably at least 20 minutes.
It is essential to the invention for the mixture of components (A), (B),
(C) and (D) to contain from 0.1 to 6.0 mol, preferably from 0.2 to 4.0 mol
and particularly preferably from 0.3 to 2.5 mol of ethylenically
unsaturated double bonds per 1000 g of mixture, with component (A)
containing from 0 to 50 mole-percent, preferably from 0 to 10 mole-percent
and particularly preferably from 0 to 5 mole-percent, component (B)
containing from 0 to 100 mole-percent, preferably from 40 to 100
mole-percent and particularly preferably from 60 to 95 mole-percent and
component (C) containing from 1 to 100 mole-percent, preferably from 1 to
60 mole-percent and particularly preferably from 5 to 40 mole-percent of
the ethylenically unsaturated double bonds contained in the mixture.
The powder coatings according to the invention can also contain, in
addition to the mixture of components (A), (B), (C) and (D) employed in
accordance with the invention, other components conventional for powder
coatings, for example crosslinking catalysts, pigments, UV stabilizers and
leveling assistants.
The powder coatings according to the invention can be prepared by generally
well-known methods. The preparation is in general carried out by extruding
the mixture of components (A), (B), (C), (D), optionally together with
further conventional additives, and milling the extrudate obtained. It is
also possible to add component (D) after the extrusion of components (A),
(B) and (C) and to mill the components (A), (B), (C) and (D) in unison.
The powder coatings according to the invention can be used both without
pigments (i.e. as clearcoats) and with pigments for the coating of any
desired substrates, for example metal, wood, glass or plastic.
The powder coatings according to the invention can also be used to coat car
bodies. They can be employed in particular, possibly as clearcoats, in
two-coat finishes of the basecoat/clearcoat type.
The powder coatings according to the invention can be applied using the
application techniques which are customary for powder coatings. The
coating films produced using the powder coatings according to the
invention are stoved at from 120.degree. to 220.degree. C., preferably
from 140.degree. to 200.degree. C. and particularly preferably from
140.degree. to 180.degree. C. The stoving time is from 5 to 60 and
preferably from 5 to 30 minutes. When an initiator is employed, as
component (D), which can be activated with the aid of high-energy
radiation, preferably UV radiation, the coating film must additionally
also be irradiated with the corresponding radiation. The irradiation is
carried out preferably after the storing procedure.
The invention is illustrated in more detail in the examples below. All
parts and percentages are by weight, unless expressly stated otherwise.
1. Preparation of Component (A)
Over a period of 4 hours a mixture of 37.06 parts by weight of methyl
methacrylate, 14.40 parts by weight of glycidyl methacrylate, 9.00 parts
by weight of n-butyl acrylate and 6.54 parts by weight of styrene is added
at 120.degree. C. to 30.0 parts by weight of xylene. Commencing with the
addition of the monomer mixture, 3.0 parts of tert-butyl
per-2-ethylhexanoate (TBPEH; manufacturer: Peroxid Chemie) are added over
a period of 4.5 hours. During the addition of the monomer mixture and the
peroxide the reaction temperature is 140.degree. C. This temperature is
maintained after completing the addition of the peroxide for a further
hour. The xylene is then removed under reduced pressure, and the synthetic
resin is heated to 180.degree. C. and drained off from the reaction
vessel. The resulting polyacrylate resin has an epoxide equivalent weight
of 686 g/mol.
2. Preparation of Component (B)
2.1 A mixture of 447 parts by weight of hexane-1,6-diol, 338 parts by
weight of trimethylolpropane, 792 parts by weight of hexahydrophthalic
anhydride and 504 parts by weight of maleic anhydride is slowly heated,
and the water formed is removed from the reaction mixture with the aid of
a water separator. As soon as the reaction product has reached an acid
number of 160, the batch is cooled and at 100.degree. C. is drained off
from the reaction vessel. The resulting polyester resin, which contains
double bonds and carboxyl groups and can be polymerized by a free-radical
mechanism, has a glass transition temperature (T.sub.G) of 20.degree. C.
2.2 A mixture of 722 parts by weight of hexane-1,6-diol, 307 parts by
weight of trimethylolpropane and 1240 parts by weight of fumaric acid is
slowly heated and the water which forms is removed from the reaction
mixture with the aid of a water separator. As soon as the reaction product
has reached an acid number of 160, the batch is cooled and at 100.degree.
is drained off from the reaction vessel. The resulting polyester resin,
which contains double bonds and carboxyl groups and can be polymerized by
a free-radical mechanism, has a glass transition temperature (T.sub.G) of
22.degree. C.
2.3 67.2 parts by weight of dodecanedioic acid are weighed out together
with 29.8 parts by weight of acetic anhydride and charged to a reaction
vessel having a reflux condenser. The mixture is slowly heated until
reflux sets in and is left for 3 hours under reflux. The acetic acid which
has formed is then removed by distillation. Subsequently a further 3.00
parts by weight of acetic anhydride are added to the reaction product, and
the mixture is heated for one hour at reflux temperature. Finally, the
acetic acid which has formed is removed by distillation and the reaction
product is drained off at 90.degree. C. from the reaction vessel.
3. Preparation of Powder Coatings According to the Invention
3.1 800 parts by weight of component (A) prepared as in section 1. are
comminuted in a precutting mill together with 280 parts by weight of
component (B) prepared as in section 2.1, 31 parts by weight of component
(B) prepared as in section 2.3, 19 parts by weight of maleic anhydride, 5
parts by weight of monobutyltin oxide, 6 parts by weight of a leveling
assistant based on polyacrylate resin (Perenol.RTM. F 40, manufacturer:
Henkel KgaA), 10 parts by weight of benzoin, 26 parts by weight of a first
light stabilizer (Tinuvin.RTM. 900, manufacturer: Ciba Geigy AG) and 16
parts by weight of a second light stabilizer (Tinuvin.RTM. 144,
manufacturer: Ciba Geigy AG) and subsequently premixed. The resulting
mixture is then extruded in a co-kneader from Buss (type PLK 46), the
temperature in the center of the extrusion chamber being from
90.degree.-100.degree. C. The extrudate is cooled rapidly to room
temperature and comminuted using a precutting mill. It is then admixed
with 5.9 parts by weight of dicumyl peroxide (Perkadox BC, manufacturer:
Akzo), the resulting mixture is ground in an impact mill (ACM 2L from
Hosokawa MikroPul) to give a powder having an average particle diameter of
from 30-40 .mu.m, and is screened through a sieve having a pore size of
125 .mu.m.
3.2 800 parts by weight of component (A) prepared as in section 1. are
comminuted in a precutting mill together with 280 parts by weight of
component (B) prepared as in section 2.1, 31 parts by weight of component
(B) prepared as in section 2.3, 19 parts by weight of maleic anhydride, 5
parts by weight of monobutyltin oxide, 6 parts by weight of a leveling
assistant based on polyacrylate resin (Perenol.RTM. F 40, manufacturer:
Henkel KgaA), 10 parts by weight of benzoin and 353 parts by weight of
titanium dioxide, and subsequently premixed. The resulting mixture is then
extruded in a co-kneader from Buss (type PLK 46), the temperature in the
center of the extrusion chamber being from 90.degree.-100.degree. C. The
extrudate is cooled rapidly to room temperature and comminuted using a
precutting mill (particle diameter from 1 to 3 mm). It is then admixed
with 7.6 parts by weight of dicumyl peroxide (Perkadox BC, manufacturer:
Akzo), the resulting mixture is ground in an impact mill (ACM 2L from
Hosokawa MikroPul) to give a powder having an average particle diameter of
from 30-40 .mu.m, and is screened through a sieve having a pore size of
125 .mu.m.
3.3 800 parts by weight of component (A) prepared as in section 1. are
comminuted in a precutting mill together with 295 parts by weight of
component (B) prepared as in section 2.2, 31 parts by weight of component
(B) prepared as in section 2.3, 19 parts by weight of maleic anhydride, 5
parts by weight of monobutyltin oxide, 6 parts by weight of a leveling
assistant based on polyacrylate resin (Perenol.RTM. F 40, manufacturer:
Henkel KgaA), 10 parts by weight of benzoin and 358 parts by weight of
titanium dioxide, and subsequently premixed. The resulting mixture is then
extruded in a co-kneader from Buss (type PLK 46), the temperature in the
center of the extrusion chamber being from 90.degree.-100.degree. C. The
extrudate is cooled rapidly to room temperature and comminuted using a
precutting mill (particle diameter from 1 to 3 mm). It is then admixed
with 7.6 parts by weight of dicumyl peroxide (Perkadox BC, manufacturer:
Akzo), the resulting mixture is ground in an impact mill (ACM 2L from
Hosokawa MikroPul) to give a powder having an average particle diameter of
from 30-40 .mu.m, and is screened through a sieve having a pore size of
125 .mu.m.
4. Application of the Powder Coatings According to the Invention
The powder coatings prepared as in sections 3.1, 3.2 and 3.3 are applied
electrostatically to degreased steel panels. After the application the
panels are stoved for 30 minutes at 180.degree. C. The stoved coating
films have a film thickness of from 40 to 60 .mu.m. They are notable in
particular for their high flexibility (T-bend: 2 mm) with a high degree of
hardness (pencil hardness: 3H-5H, Buchholz hardness 100-125).
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