U.S. patent application number 10/208460 was filed with the patent office on 2003-08-07 for curable composition.
This patent application is currently assigned to Vantico, Inc.. Invention is credited to Francois, Jacques, Rickert, Christoph, Tena, Mireille, Turpin, Francois.
Application Number | 20030149193 10/208460 |
Document ID | / |
Family ID | 4224894 |
Filed Date | 2003-08-07 |
United States Patent
Application |
20030149193 |
Kind Code |
A1 |
Rickert, Christoph ; et
al. |
August 7, 2003 |
Curable composition
Abstract
Powder coating compositions comprise a binder selected from
carboxyl-group-containing polyesters, carboxyl-group-containing
poly(meth)acrylates and mixtures of the said substances, and one or
more novel epoxy compounds.
Inventors: |
Rickert, Christoph;
(Reinach, CH) ; Turpin, Francois; (Huningue,
FR) ; Francois, Jacques; (Saint Louis, FR) ;
Tena, Mireille; (Rheinfelden, CH) |
Correspondence
Address: |
LYON & LYON LLP
633 WEST FIFTH STREET
SUITE 4700
LOS ANGELES
CA
90071
US
|
Assignee: |
Vantico, Inc.
Brewster
NY
|
Family ID: |
4224894 |
Appl. No.: |
10/208460 |
Filed: |
July 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10208460 |
Jul 30, 2002 |
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09697331 |
Oct 25, 2000 |
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6437045 |
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Current U.S.
Class: |
525/523 ;
525/403 |
Current CPC
Class: |
C09D 133/064 20130101;
C08L 63/00 20130101; C08G 59/24 20130101; C09D 167/00 20130101;
C07D 303/40 20130101; C07D 493/10 20130101; C07D 407/14 20130101;
C08G 59/3218 20130101; C09D 133/064 20130101; C08L 2666/14
20130101; C09D 167/00 20130101; C08L 63/00 20130101 |
Class at
Publication: |
525/523 ;
525/403 |
International
Class: |
C08G 065/32 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 1999 |
CH |
2056/99 |
Claims
What is claimed is:
1. A powder coating composition comprising a binder selected from
carboxyl-group-containing polyesters, carboxyl-group-containing
poly(meth)acrylates and mixtures of the said substances, and one or
more epoxy compounds, wherein the epoxy compounds comprise at least
one compound of formula (I) that is solid at 25.degree. C.:
15wherein A corresponds to a group of formula (II), (III), (IV) or
(VI): 16in which B is an x-valent organic radical that is derived
from a polyol having x or more hydroxyl groups by the removal of x
hydroxyl groups; E is a (2x)-valent organic radical that is derived
from a polyol having (2.times.) or more hydroxyl groups by the
removal of (2.times.) hydroxyl groups; and D is a (y+2z)-valent
radical that is derived from a polyol having (y+2z) or more
hydroxyl groups by the removal of (y+2z) hydroxyl groups; R.sub.1
and R.sub.5 are each independently of the other hydrogen, halogen,
C.sub.1-C.sub.4alkyl or C.sub.1-C.sub.4alkoxy or are together a
methylene group; and R.sub.2, R.sub.3, R.sub.4, R.sub.6, R.sub.7,
R.sub.8 and R.sub.9 are each independently of the others hydrogen,
halogen, C.sub.1-C.sub.4alkyl or C.sub.1-C.sub.4alkoxy; and x is an
integer of at least 3; y is an integer from 1 to (x-1) and z is
(x-y).
2. A powder coating composition according to claim 1, wherein A
corresponds to a group of formula (II).
3. A powder coating composition according to claim 2, wherein x is
from 3 to 6, preferably 4.
4. A powder coating composition according to claim 3, wherein B is
a radical that is derived from an aliphatic polyol having from 3 to
20 carbon atoms, a cycloaliphatic polyol having from 5 to 20 carbon
atoms or a mixed aliphatic-cycloaliphatic polyol having from 7 to
20 carbon atoms.
5. A powder coating composition according to claim 1, wherein the
polyol is 1,3-dihydroxy-2,2-di(hydroxymethyl)propane
(pentaerythritol).
6. A powder coating composition according to claim 1, wherein A
corresponds to a group of formula (III).
7. A powder coating composition according to claim 6, wherein x is
from 3 to 6, preferably 3.
8. A powder coating composition according to claim 6, wherein E is
a radical that is derived from an aliphatic polyol having from 3 to
20 carbon atoms.
9. A powder coating composition according to claim 8, wherein the
polyol is selected from mannitol, especially D-mannitol, sorbitol,
especially D-sorbitol, and dulcitol.
10. A powder coating composition according to claim 1, wherein A
corresponds to a group of formula (IV).
11. A powder coating composition according to claim 1, that
furthermore comprises at least one epoxy compound of formula (I)
that is solid at 25.degree. C. in which A corresponds to a group of
formula (II) or (III) and x is2.
12. A powder coating composition according to claim 11, wherein the
epoxy compounds of formula (I) wherein x is at least 3 and the
epoxy compounds of formula (I) wherein x is 2 are present in a
molar ratio of up to a maximum of 1:2 preferably of up to a maximum
of 1:1.
13. A powder coating composition according to claim 1, which is
substantially free of glycidyl compounds, especially TGIC and
glycidyl esters.
14. A process for the preparation of a compound of formula (I)
wherein A corresponds to a group of formula (II), B corresponds to
an x-valent organic radical that is derived from a hydroxyl
compound having x or more hydroxyl groups, and x corresponds to an
integer of at least 1, which comprises the transesterification of a
cyclohexene-3-carboxylic acid ester with an alcohol of formula
B(OH).sub.x, wherein x corresponds to an integer of at least 1, in
the presence of LiNH.sub.2, with continuous removal from the
reaction mixture of the alcohol freed from the
cyclohexene-3-carboxylic acid ester, the transesterification being
followed by the epoxidation of the carbon double bond(s) of the
resulting transesterification product.
15. A process according to claim 14, wherein x is at least 3.
Description
[0001] The invention relates to a powder coating composition
comprising a binder selected from carboxyl-group-containing
polyesters, carboxyl-group-containing poly(meth)acrylates and
mixtures of the said substances, and one or more epoxy compounds as
thermal hardeners, and also to a preferred preparation process for
one type of the epoxy compounds that are to be used.
[0002] Powder coating compositions as referred to at the outset are
used in a wide variety of forms. Triglycidyl isocyanurate (TGIC)
has been successful as an epoxy hardener in such compositions,
especially for external paints, which must have a high weather
resistance. Its solid consistency, inter alia, has resulted in TGIC
being considered today as the standard hardener for powder coating
compositions based on carboxyl-group-containing polyesters as
binders (see, e.g. Ullmann's Encyclopedia of Industrial Chemistry,
5th Ed., Vol A9, p. 559) and on carboxyl-group-containing
poly(meth)acrylates (see, e.g., Johnson Wax Speciality Chemicals
Product Application Bulletin, Powder Coatings).
[0003] There have also been known for some time, however, powder
coating compositions stable to outside weathering that are based on
a TGIC-free, solid mixture of epoxy resins as hardener (see, e.g.,
EP-A-0 536 085), where substantial amounts of a liquid,
higher-functional epoxy resin, e.g. trimellitic acid triglycidyl
ester, are incorporated into a solid epoxy resin, e.g. diglycidyl
terephthalate, without the total mixture of epoxy resins taking on
a liquid consistency as a result. In industrial practice, however,
virtually the only solid resins available hitherto for such
hardener mixtures have been difunctional glycidyl esters.
Furthermore, the solid resin makes up the majority of such a
mixture, so that a significant disadvantage of such hardener
mixtures is that their epoxy functionality is appreciably reduced
in comparison with TGIC. In addition, clean glycidylisation of
1,2-dicarboxylic acids is not easy on an industrial scale.
[0004] Accordingly there is still a need for new powder coating
compositions with properties comparable to those of the
above-mentioned powder coating compositions from a surface-coating
technology standpoint, that is to say, for powder coating
compositions that, especially, have good flow behaviour and high
reactivity and with which it is possible to produce coatings having
a high crosslinking density and a high level of stability towards
weathering and UV. The present invention provides such new powder
coating compositions.
[0005] The invention relates especially to powder coating
compositions that comprise a binder selected from
carboxyl-group-containing polyesters, carboxyl-group-containing
poly(meth)-acrylates and mixtures of the said substances, and one
or more epoxy compounds, wherein the epoxy compounds comprise at
least one compound of formula (I) that is solid at 25.degree. C.:
1
[0006] wherein
[0007] A corresponds to a group of formula (II), (III), (IV), or
(VI): 2
[0008] in which
[0009] B is an x-valent organic radical that is derived from a
polyol having x or more hydroxyl groups by the removal of x
hydroxyl groups;
[0010] E is a (2x)-valent organic radical that is derived from a
polyol having (2x) or more hydroxyl groups by the removal of (2x)
hydroxyl groups; and
[0011] D is a (y+2z)-valent radical that is derived from a polyol
having (y+2z) or more hydroxyl groups by the removal of (y+2z)
hydroxyl groups;
[0012] R.sub.1 and R.sub.5 are each independently of the other
hydrogen, halogen, C.sub.1-C.sub.4alkyl or C.sub.1-C.sub.4alkoxy or
are together a methylene group; and
[0013] R.sub.2, R.sub.3, R.sub.4,
[0014] R.sub.6, R.sub.7, R.sub.8
[0015] and R.sub.9 are each independently of the others hydrogen,
halogen, C.sub.1-C.sub.4alkyl or C.sub.1-C.sub.4alkoxy; and
[0016] x is an integer of at least 3;
[0017] y is an integer from 1 to (x-1) and
[0018] z is (x-y).
[0019] The powder coating compositions according to the present
invention are distinguished, inter alia, by a very good flow
behaviour, and yield a cured material that has a high crosslinking
density, a high degree of fastness to weathering and a high gloss.
Epoxy resins of formula (I) are, in addition, toxicologically less
harmful than glycidyl compounds such as are normally used for
powder coating compositions.
[0020] When one of the radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5, R.sub.6,R.sub.7, R.sub.8 and R.sub.9 in formula (I) is
halogen, it is preferably, for example, chlorine or bromine; when
one of those radicals is C.sub.1-C.sub.4alkyl or
C.sub.1-C.sub.4alkoxy, it is, for example, methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl or tert-butyl or an alkoxy group
corresponding to one of those alkyl groups.
[0021] Preferably, the radicals R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5, R.sub.6,R.sub.7, R.sub.8 and R.sub.9 are
C.sub.1-C.sub.4alkyl or, especially, hydrogen.
[0022] At least some of the compounds of formula (I) are known or
are obtainable in known manner or in a manner analogous
thereto.
[0023] Compounds of formula (I) wherein A corresponds to a group of
formula (II) can be obtained, for example, from a polyol of formula
B(OH).sub.x wherein x is as defined hereinbefore, by esterifying
the x hydroxyl groups of the polyol with cyclohexene-3-carboxylic
acid and then epoxidising the carbon double bonds of the resulting
polyester compound in customary manner, for example by means of an
organic peracid, such as, for example, peracetic acid.
[0024] An especially preferred process for the preparation of
compounds of formula (I) wherein A corresponds to a group of
formula (II) comprises the transesterification of a
cyclohexene-3-carboxylic acid ester, especially a
cyclohexene-3-carboxylic acid C.sub.1-C.sub.4alkyl ester, such as
methyl 3-cyclohexenecarboxylate, with a polyol of formula
B(OH).sub.x, wherein x is as defined hereinbefore, in the presence
of LiNH.sub.2 as transesterification catalyst, and with continuous
removal from the reaction mixture of the alcohol freed from the
cyclohexene-3-carboxylic acid ester, the transesterification being
followed by the epoxidation of the carbon double bonds of the
resulting transesterification product, which is carried out in
customary manner, for example by means of an organic peracid, such
as, for example, peracetic acid. The use of LiNH.sub.2 as catalyst
results, inter alia, in especially good yields and a high degree of
product purity. The said process can also be used for epoxy
compounds of formula (I) wherein A corresponds to a group of
formula (II) and x is 1 or 2, and the present invention relates
also thereto.
[0025] Compounds of formula (I) wherein A corresponds to a group of
formula (III) can be prepared, for example, in accordance with
British Patent No. 870 696, by reacting a polyol of formula
B(OH).sub.x, wherein x is as defined hereinbefore, with an aldehyde
of formula (V) 3
[0026] wherein R.sub.1 and R.sub.5, as well as R.sub.2, R.sub.3,
R.sub.4, R.sub.6, R.sub.7, R.sub.8 and R.sub.9, are likewise as
defined hereinbefore, in the presence of a suitable catalyst, such
as, for example, p-toluenesulfonic acid, and epoxidising the carbon
double bonds of the resulting product in customary manner, for
example by means of an organic peracid.
[0027] Compounds of formula (I) wherein A corresponds to a group of
formula (IV) can be obtained, for example, in accordance with
SU-A-1 792 956, by trimerising an aldehyde of the above-mentioned
formula (V) in the presence of an acid, for example phosphoric acid
or nitric acid, and epoxidising the double bonds of the resulting
product, again in customary manner.
[0028] Compounds of formula (I) wherein A corresponds to a group of
formula (VI) are likewise known, for example from Batog, A. E.;
Pet'ko, I. P.; Kozlova, L. V.; Pandazi, I. F.; Plast. Massy (1979),
(10), p. 9-10. where, for example, a compound of the
above-mentioned formula (I) is described in which A corresponds to
the group set out below and D is a tetravalent radical derived from
pentaerythritol by the removal of 4 hydroxyl groups: 4
[0029] Preference is given to powder coating compositions according
to the invention wherein A corresponds to a group of formula (II),
especially where x is from 3 to 6 and, preferably, is 4.
[0030] B in formula (II) is preferably a radical that is derived
from an aliphatic polyol having from 3 to 20 carbon atoms, from a
cycloaliphatic polyol having from 5 to 20 carbon atoms or from a
mixed aliphatic-cycloaliphatic polyol having from 7 to 20 carbon
atoms.
[0031] More especially, the radical B in formula (II) is derived
from 1,3-dihydroxy-2,2-di(hydroxymethyl)propane
(pentaerythritol).
[0032] Preference is given also to powder coating compositions
according to the invention wherein A corresponds to a group of
formula (III), especially where x is from 3 to 6 and, preferably,
is 3.
[0033] E in formula (III) and D in formula (VI) are each preferably
a radical derived from an aliphatic polyol having from 3 to 20
carbon atoms, preferably 5 or 6 carbon atoms.
[0034] The radical B in formula (III) is derived especially
preferably from a polyol selected from mannitol, especially
D-mannitol, sorbitol, especially D-sorbitol, and dulcitol.
[0035] Powder coating compositions wherein A corresponds to a group
of formula (IV) also constitute a preferred embodiment of the
invention.
[0036] Another special embodiment of the powder coating
compositions according to the invention is one which comprises at
least one further epoxy compound of formula (I) that is solid at
25.degree. C. wherein
[0037] A corresponds to a group of formula (II) or (III) and
[0038] x is 2.
[0039] For the radicals R.sub.1 to R.sub.9, and also for the groups
B and E, the same applies in the case of epoxy compounds of formula
(I) in which x is 2 as in the case of the other epoxy compounds of
formula (I), in so far as the meanings are compatible with the
value x=2. Examples of epoxy compounds of formula (I) wherein x is
2 that are suitable in accordance with the invention include, inter
alia: 5
[0040] The preparation of such difunctional epoxy compounds can
likewise be carried out in the manner already described above for
the corresponding trifunctional and higher-functional
compounds.
[0041] The epoxy compounds of formula (I) wherein x is at least 3
and the epoxy compounds of formula (I) wherein x is 2 can be
present in the powder coating compositions in a widely variable
molar ratio, for example in a molar ratio of up to a maximum of
1:2, preferably up to a maximum of 1:1, especially a maximum of
1:0.5.
[0042] The powder coating compositions according to the invention
may in principle also comprise, in addition to the epoxy compounds
of formula (I), certain amounts of one or more other epoxy
compounds, e.g. glycidyl esters, such as those described in
EP-A-536 085, EP-A-770 605 and EP-A-770 650. The expression
"certain amount" is to be understood as meaning that a maximum of
60 percent, preferably a maximum of from 5 to 30 percent, of the
total epoxy groups of the powder coating compositions according to
the invention is provided by those other epoxy compounds.
Especially preferably, however, the powder coating compositions
according to the invention are substantially free of such other
epoxy compounds, especially glycidyl compounds, such as TGIC, or
glycidyl esters, such as diglycidyl terephthalate, or the
corresponding glycidyl methacrylates or copolymers thereof.
"Substantially free" means that a maximum of 10 percent, preferably
a maximum of 5 percent, of the total epoxy groups of the powder
coating compositions according to the invention is provided by TGIC
or glycidyl esters. Finally, most preferred are powder coating
compositions according to the invention that are completely free of
glycidyl compounds, especiaclly free of TGIC and glycidyl
esters.
[0043] Suitable binders for the powder coating compositions
according to the invention include, for example,
free-carboxyl-group-containing polyesters having an acid number of
from 10 to 160 mg, preferably from 10 to 70 mg, especially from 20
to 40 mg, of KOH per kilogram of polyester.
[0044] The polyesters are furthermore advantageously solid at room
temperature (from 15 to 35.degree. C.) and have, for example, a
molecular weight (number average Mn) of from 1000 to 10 000. The
ratio of Mw (weight average of the molecular weight) to Mn of those
polyesters is generally from 2 to 10. There are especially
suitable, for example, free-carboxyl-group-containing polyesters
having a molecular weight (weight average Mw from GPC measurement
using polystyrene calibration) of from 4000 to 15 000, especially
from 6500 to 11 000, and a glass transition temperature (Tg) of
from 35 to 120.degree. C., preferably from 50 to 90.degree. C.
[0045] Polyesters such as those mentioned are described, for
example, in U.S. Pat. No. 3,397,254 and EP-A-0 600 546. Polyesters
suitable for the present invention are condensation products of
difunctional, trifunctional and/or polyfunctional alcohols
(polyols) with dicarboxylic acids and, optionally, trifunctional
and/or polyfunctional carboxylic acids, or with corresponding
carboxylic acid anhydrides. The polyols used include, for example,
ethylene glycol, diethylene glycol, the propylene glycols, butylene
glycol, 1,3-butanediol, 1,4-butanediol, neopentanediol, isopentyl
glycol, 1,6-hexanediol, glycerol, hexanetriol, trimethylolethane,
trimethylolpropane, erythritol, pentaerythritol, cyclohexanediol
and 1,4-dimethylolcyclo-hexane. Suitable dicarboxylic acids
include, for example, isophthalic acid, terephthalic acid, phthalic
acid, methyl-substituted derivatives of the said acids,
tetrahydrophthalic acid, methyl-tetrahydrophthalic acids, for
example 4-methyltetrahydrophthalic acid, cyclohexane-dicarboxylic
acids, succinic acid, glutaric acid, adipic acid, pimelic acid,
suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic
acid, fumaric acid, maleic acid and 4,4'-diphenyl-dicarboxylic acid
etc.. Suitable tricarboxylic acids include, for example, aliphatic
tricarboxylic acids, such as 1,2,3-propanetricarboxylic acid,
aromatic tricarboxylic acids, such as trimesic acid, trimellitic
acid and hemimellitic acid, and cycloaliphatic tricarboxylic acids,
such as 6-methylcyclohex-4-ene-1,2,3-tricarboxylic acid. Suitable
tetracarboxylic acids include, for example, pyromellitic acid and
benzophenone-3,3',4,4'-tetracarboxylic acid. Commercially available
polyesters especially are very commonly based on neopentyl glycol
and/or trimethylolpropane as the main alcoholic monomer
constituent(s) and on adipic acid and/or terephthalic acid and/or
isophthalic acid and/or trimellitic acid as the main acidic monomer
component(s).
[0046] Also suitable as binders are carboxyl-group-containing
poly(meth)acrylates, which can be prepared in known manner by the
copolymerisation of acrylic and/or methacrylic monomers, for
example, C.sub.1-C.sub.12alkyl(meth)acrylates, such as methyl,
ethyl, propyl; butyl, pentyl, hexyl, octyl, 2-ethylhexyl, decyl and
dodecyl(meth)acrylates, C.sub.1-C.sub.4alkyl(meth)acrylates being
preferred, or (meth)acrylamide with acrylic acid and/or methacrylic
acid and, where appropriate, other ethylenically unsaturated
comonomers, such as vinyl aromatic compounds, e.g. styrene,
a-methylstyrene, vinyltoluene or also .beta.-halogenated styrenes,
in addition. The copolymerisation can be carried out in known
manner. For example, the monomers can be dissolved in suitable
organic solvents and thermally reacted in the presence of a
suitable initiator that is soluble in the solvent, such as dicumyl
peroxide, and in the presence of a suitable chain-transfer reagent.
such as thioglycolic acid (solution polymerisation), or the monomer
mixture can be suspended in water together with a solution of the
initiator in an organic solvent and polymerised, or the monomer
mixture can also be emulsified in water with the aid of
surfactants, e.g. sodium lauryl sulfate, and reacted in the
presence of a water-soluble polymerisation initiator, such as
K.sub.2S.sub.2O.sub.8 (emulsion polymerisation). The prepared
poly(meth)acrylic resin is in each case then isolated in solid form
from the solvent or water. The reaction can also be carried out
without using solvents or water, for example according to JP-A-Sho
53-140 395. Suitable poly(meth)acrylic resins are solid at
temperatures in the region of room temperature (from 15 to
25.degree. C.). They generally have a molecular weight of from 1000
to 50 000 (weight average M.sub.w), preferably from 5000 to 20
000.
[0047] The Tg value (glass transition temperature) of the
poly(meth)acrylates, determined by DSC (heating rate 10.degree.
C./minute), is preferably-from 40 to 75.degree. C. The acid number
of the resins, quoted in mg equivalent KOH per g of (meth)acrylate
resin, is preferably from 20 to 160, especially from 20 to 80.
[0048] In certain cases it may also be advantageous to use, as
binders, a mixture of free-carboxyl-group-containing polyesters and
free-carboxyl-group-containing poly(meth)acrylates.
[0049] The powder coating compositions according to the invention
comprise epoxy compounds and binders preferably in such an amount
that the ratio of epoxy groups to carboxyl groups of the binder is
from 2:1 to 0.5:1, preferably from 1.3:1 to 0.7:1. The compositions
according to the invention may especially have a slight molar
excess of epoxy groups. The molar ratio of epoxy groups to carboxyl
groups in the compositions is thus preferably from 1.3:1 to 1:1,
e.g. approximately from 1.2:1 to 1.1:1.
[0050] Preferably, the powder coating compositions according to the
invention also comprise a catalyst for the reaction of epoxy groups
with carboxyl groups. Such a catalyst is commonly an organic amine
or a derivative of an amine, especially a tertiary amine or a
nitrogen-containing heterocyclic compound. Preferred catalysts for
the reaction of epoxy groups with carboxyl groups are
phenylimidazole, N-benzyldimethylamine and
1,8-diazabicyclo[5.4.0]-7-undecene, optionally on a silicate
support or triphenylphosphine, alkyltriphenylphosphonium halide,
Actiron.RTM. NXJ-60 (2-propylimidazole), Actiron.RTM. NXJ-60 P (60
% by weight of 2-propylimidazole on 40% by weight of solid
support). Beschleuniger.RTM. DT 3126 (alkylammonium salt in
polyester). The catalyst or a catalyst mixture is preferably added
in such an amount that the gel time of the mixture at 180.degree.
C. (determined according to DIN 55990) is approximately from 70 to
400 seconds, preferably from 90 to 300 seconds. Generally,
approximately from 0.1 to 10 percent by weight, especially from 0.5
to 5 percent by weight, of catalyst will be required for that
purpose. Of course some commercially available polyesters that can
be used as binders for the powder coating compositions according to
the invention will already contain a certain amount of one of the
above-mentioned catalysts or of a comparable catalyst, and that
amount should be taken into account in the above percentage by
weight figure for the catalyst; the mentioned preferred gel times
can be used to provide an indication of how much catalyst still
needs to be added.
[0051] The powder coating compositions according to the invention
may also comprise further additives customary in the
surface-coating industry, for example light stabilizers, dyes,
pigments, for example titanium dioxide pigment, degassing agents,
for example benzoin, and/or flow agents. Suitable flow agents
include, for example, polyvinyl acetals, such as polyvinyl butyral,
polyethylene glycol, polyvinylpyrrolidone, glycerol and acrylic
mixed polymers, such as, for example, those available under the
names Modaflow.RTM. and Acrylron.RTM..
[0052] Powder coating compositions according to the invention can
be prepared simply by mixing the constituents together, for example
in a ball mill. Another, more preferred possibility comprises
melting together, blending and homogenising the constituents,
preferably using an extrusion machine, such as a Buss co-kneader,
and cooling and comminuting the resulting mass. In that procedure,
the fact that either immediately after extrusion, or at least after
they have been left to stand for a few hours, for example from 24
to 48 hours, the powder coating compositions according to the
invention become so hard and brittle that they can readily be
ground, has proved especially advantageous. The powder coating
composition mixtures preferably have a particle size in the range
from 0.015 to 500 .mu.m, especially from 10 to 75 .mu.m. In
some-cases it may also be advantageous first of all to prepare a
masterbatch from portions of the binder, the epoxy resins and,
optionally, further components, the masterbatch then being mixed
and homogenised in a second step with the remainder of the binder
and the remaining constituents to yield the finished powder coating
composition.
[0053] After application to the article to be coated. the powder
coating compositions are cured at a temperature of at least
approximately 100.degree. C., for example from 150 to 250.degree.
C. Curing generally takes approximately from 10 to 60 minutes. All
materials that are stable at the temperatures required for the
curing, especially ceramics and metals, are suitable for coating.
The substrate may already have one or more base surface-coatings
that are compatible with the powder coating composition.
[0054] The powder coating compositions exhibit good flow behaviour
combined with good mechanical properties, good weather resistance
and good resistance to chemicals.
EXAMPLE 1a
Reaction of D-mannitol with 1,2,3,6-tetrahydrobenzaldehyde
[0055] 6
[0056] A mixture of D-mannitol (182.18 g,1.0 mol),
1,2,3,6-tetrahydrobenza- ldehyde (800 ml, 7.0 mol) and
p-toluenesulfonic acid monohydrate (1.9 g, 10 mmol, p-TSA) is
heated under reflux (100.degree. C./200 mbar) and water is
continuously removed azeotropically. The theoretically calculated
amount of water (53 ml) is collected in the course of 2 hours, and
the mixture is subsequently cooled to room temperature. The mixture
is then filtered through Dowex (Fluka 44340). The removal of excess
1,2,3,6-tetrahydrobenzaldehyde yields 460.5 g (100%) of the desired
product in the form of a viscous oil.
EXAMPLE 1b
Reaction of D-sorbitol with 1,2,3,6-tetrahydrobenzaldehyde
[0057] In the same manner as that described in Example 1a,
D-sorbitol (54.50 g, 0.30 mol) and 1,2,3,6-tetrahydrobenzaldehyde
(250 ml, 2.2 mol) are reacted in the presence of p-toluenesulfonic
acid monohydrate (0.57 g, 3 mmol), yielding 119.0 g (87%) of the
corresponding product, likewise in the form of a viscous oil.
EXAMPLE 1c
Trimerisation of 1,2,3,6-tetrahydrobenzaldehyde
[0058] 7
[0059] 1,2,3,6-Tetrahydrobenzaldehyde (200 g, 1.8 mol) is
introduced into a reactor. With vigorous stirring, ortho-phosphoric
acid is added dropwise, the temperature being maintained at
20.degree. C. After reaction for 25 minutes, the entire mixture
forms a solid mass and 500 ml of water are added. The solid residue
is washed five times with 800 ml of water each time, then washed
with 500 ml of NaHCO.sub.3 solution (5% in water), then washed
twice with 800 ml of water each time again, and finally washed
twice with 800 ml of ethanol each time. The precipitate is filtered
off and dried overnight at 60.degree. C. 162.8 g (81%) of a white
powder having a melting point of 170.degree. C. are obtained.
EXAMPLE 1d
Reaction of Pentaerythritol with 1,2,3,6-tetrahydrobenzaldehyde
[0060] 8
[0061] A mixture of pentaerythritol (81.76 g, 0.60 mol),
1,2,3,6-tetrahydrobenzaldehyde (250 ml, 3.5 mol) and
p-toluenesulfonic acid monohydrate (1.14 g, 6 mmol, p-TSA) is
heated under reflux (100.degree. C./500 mbar) and water is
continuously removed azeotropically. 17 ml of water are collected
in the course of 2.5 hours, and the mixture is subsequently cooled
to room temperature. The mixture is then diluted with 300 ml of
ethyl acetate and washed first with 250 ml of NaHCO.sub.3 solution
(5% in water) and then twice with 250 ml of saturated NaCl
solution. The organic layer-is removed and dried over MgSO.sub.4.
After removal of the solvent, the mixture that remains is shaken in
1.5 litres of cold ethanol, and the precipitate that forms is
filtered off, washed with ethanol and dried overnight at 70.degree.
C. 110.3 g (57%) of the desired product are obtained in the form of
a yellow powder having a melting point of 97.degree. C.
EXAMPLE 2a
Epoxidation of the Product of Example 1a
[0062] 9
[0063] A mixture of the product of Example 1a (114.6 g, 0.25 mol)
in 750 ml of dichloromethane is cooled to 10.degree. C. A solution
of peracetic acid (39% in acetic acid, 172 g, 0.88 mol) and
anhydrous sodium acetate (8.79 g, 0.11 mol) is added dropwise to
the mixture in the course of 1 hour. During the addition, the
temperature is maintained below 30.degree. C. The mixture is then
reacted for 3 hours at room temperature. The mixture is washed with
500 ml of water, 500 ml of NaOH solution (1 N) and with 500 ml of
saturated NaCl solution. The organic phase is removed, stirred with
sodium sulfite and dried over MgSO.sub.4. Removal of the solvent
yields 122.8 g (97%) o the product in the form of a viscous yellow
resin (epoxy value: 5.46 eq./kg).
EXAMPLE 2b
Epoxidation of the Product of Example 1b
[0064] The product of Example 1b (101 g, 0.22 mol), peracetic acid
(39%, 151.4 g, 0.78 mol), sodium acetate (7.72 g, 94 mmol) and
dichloromethane (500 ml) are reacted in the same manner as that
described in Example 2a, and yield 98.0 g (88%) of the
corresponding end product in the form of a viscous oil (epoxy
value: 5.53 eq./kg).
EXAMPLE 2c
Epoxidation of the Product of Example 1c
[0065] 10
[0066] The product of Example 1c (99.1 g, 0.30 mol), peracetic acid
(39%, 207.1 g, 1.06 mol), sodium acetate (10.61 g, 129 mmol) and
dichloromethane (1000 ml) are reacted in the same manner as that
described in Example 2a, and yield 106.1 g (94%) of the
corresponding end product in the form of a white powder having a
melting point of 201.degree. C. (epoxy value: 7.55 eq/kg).
EXAMPLE 2e
Epoxidation of a Mixture of the Products of Examples 1b and 1c in a
Molar Ratio of 1:1
[0067] The product of Example 1b (114.7 g, 0.25 mol) and the
product of Example 1c (82.6 g, 0.25 mol), peracetic acid (39%,
343.8 g, 1.76 mol), sodium acetate (17.36 g, 212 mmol) and
dichloromethane (1000 ml) are reacted in the same manner as that
described in Example 2a, and yield 215.8 g (97%) of the
corresponding mixture of epoxy compounds of formula (I) in the form
of a yellow powder (epoxy value: 6.08 eq./kg).
EXAMPLE 2f
Epoxidation of a Mixture of the Products of Examples 1a and 1c in a
Molar Ratio of 42:58
[0068] The product of Example 1a (33.0 g, 72 mmol) and the product
of Example 1c (33.0 g, 100 mmol), peracetic acid (39%, 118.0 g, 607
mmol), sodium acetate (6.03 g, 73 mmol) and dichloromethane (500
ml) are reacted in the same manner as that described in Example 2a,
and yield 69.1 g (97%) of the corresponding mixture of epoxy
compounds of formula (I) in the form of a white powder (epoxy
value: 6.55 eq./kg).
EXAMPLE 2g
Epoxidation of a Mixture of the Products of Examples 1c and 1d in a
Molar Ratio of Approximately 1:1
[0069] The product of Example 1c (50.0 g, 156 mmol) and the product
of Example 1d (50.0 g, 151 mmol), peracetic acid (39%, 196.1 g, 1.0
mol), sodium acetate (10.0 g, 122 mmol) and dichloromethane (800
ml) are reacted in the same manner as that described in Example 2a,
and yield 98.4 g (87%) of the corresponding mixture of epoxy
compounds of formula (I) in the form of a white powder (epoxy
value: 5.72 eq./kg).
EXAMPLE 3
[0070] The powder coating composition indicated in the following
Table 3/1 is homogenised using an extruder (laboratory extruder
from PRISM, The Old Stables, England). The cooled extrudate is
ground to give the finished powder coating composition having a
particle size of approximately 40 micrometers.
1TABLE 3/1 Powder coating composition formulation Formulation A[g]
Uralac P 3485.sup.1) 60.00 Epoxy compound according to 5.80 Example
2a Benzoin 0.20 Acrylron.sup.2) 1.00 TiO.sub.2[Cronos 2160] 33.00
.sup.1)Polyester based on terephthalic acid, isophthalic acid and
neopentyl glycol having an acid number of 28 and a glass transition
temperature Tg of 71.degree. C.; .sup.2)Acrylic mixed polymer as
flow agent.
[0071] Using an electrostatic spray gun, the powder coating
composition is applied to a Q panel as substrate. The coated panel
is then placed in an oven in order to melt and fully cure the
powder coating composition. The gel time, the curing temperature
and the curing time, and also the thickness of the resulting powder
resin coating, are indicated in the following Table 3/2 together
with properties of the resulting coatings that are important from
the standpoint *of surface-coating technology.
2 TABLE 3/2 Property A Gel time 180.degree. C. [sec.] 210 Full cure
15 min./200.degree. C. Layer thickness [mm] 55 Substrate Q panel
Gloss 60.degree. 94 Gloss 20.degree. 84 Yellowness value Yi 4.8
Flow [rating].sup.3) 12 Acetone test.sup.5), 1 min. 3 [rating]
.sup.3)Empirical scale from 0 (very good) to 18 (orange-peel)
.sup.5)According to DIN 53320. The specimen is kept in acetone for
1 minute. The result is evaluated in accordance with the following
scale of five ratings: 0 = unchanged; 1 = resistant, cannot be
scratched with a finger nail; 2 = difficult to scratch, may stain
cottonwool pad; 3 = softened, easily scratchable; 4 = beginning to
separate or dissolve; 5 = complete dissolution.
EXAMPLE 4
[0072] The powder coating compositions indicated in the following
Table 4/1 are homogenised using an extruder (laboratory extruder
from PRISM, The Old Stables, England). The total amount of powder
coating composition in each case is approximately from 100 to 200
grams. The cooled extrudates are ground to give the finished powder
coating composition having a particle size of approximately 40
mm.
3TABLE 4/1 Powder coating composition formulations Formulation B
[g] C [g] D [g] E [g] Uralac P 3485.sup.1) 59.05 58.11 58.71 59.17
DGT.sup.6) -- 1.80 4.37 4.41 Epoxy compound according to 5.92 4.56
1.38 1.39 Example 2b DT 3126.sup.7) -- 0.50 0.50 -- Benzoin 0.20
0.20 0.20 0.20 Acrylron.sup.2) 1.50 1.50 1.50 1.50 TiO.sub.2
[Cronos 2160] 33.33 33.33 33.33 33.33 .sup.6)Diglycidyl
terephthalate .sup.7)Alkylammonium salt in polyester
[0073] The properties found for the coatings are indicated in the
following Table 4/2.
4TABLE 4/2 Property B C D E Gel time @ 180.degree. C. 165 265 400
530 [sec.] Full cure 15 min./ 15 min./ 15 min./200.degree. C. 15
min./ 180.degree. C. 200.degree. C. 200.degree. C. Layer thickness
[mm] 54 55 56 55 Substrate Q panel Q panel Q panel Q Panel Gloss
60.degree. 95 95 96 96 Gloss 20.degree. 84 84 88 88 Yellowness
value Yi 2.7 4.8 1.7 0.3 Flow.sup.3)[rating] 10 10 10 6 Acetone
test.sup.5), 1 min. 3 3 3 4 [rating]
EXAMPLE 5
[0074] The powder coating compositions indicated in Table 5/1 are
prepared in accordance with Example 4.
5TABLE 5/1 Powder coating composition formulations Formulation F
[g] G [g] H [g] Uralac P 3485.sup.1) 58.38 59.91 59.91 Epoxy
compound according to 4.59 4.89 4.89 Example 2c DT 3126.sup.7) 2.00
-- -- Benzoin 0.20 0.20 0.20 Crylcoat 164.sup.9) -- 1.00 --
Acrylron.sup.2) 1.50 1.00 1.00 TiO.sub.2 [Cronos 2160] 33.33 33.00
33.00 .sup.9)Alkyltriphenylphosphonium bromide in polyester
[0075] The properties found for the coatings are indicated in the
following Table 5/2.
6TABLE 5/2 Property F G H Gel time @ 180.degree. [sec.] 150 160 s
90 Full cure 15 min./180.degree. C. 15 min./200.degree. C. 15
min./200.degree. C. Layer thickness [mm] 53 48 51 Substrate Q panel
Q panel Q Panel Gloss 60.degree. -- 95 95 Gloss 20.degree. -- 83 71
Yellowness value Yi -- 2.4 0.0 Flow [rating].sup.3) 8 10 10 Acetone
test.sup.5), 1 min. 3 3 3 [rating]
EXAMPLE 6
[0076] The powder coating composition indicated in Table 6/1 is
prepared in accordance with Example 4.
7TABLE 6/1 Powder coating composition formulation Formulation I [g]
Uralac P 3485.sup.1) 59.54 Epoxy compound according to 5.43 Example
2e Benzoin 0.20 Acrylron 1.50 TiO.sub.2 [Cronos 2160] 33.33
[0077] The properties found for the corresponding coating are
indicated in the following Table 6/2.
8 TABLE 6/2 Property I Gel time 180.degree. C. [sec.] 285 Full cure
15 min./180.degree. C. Layer thickness [mm] 86 Substrate Q panel
Gloss 60.degree. 91 Gloss 20.degree. 75 Yellowness value Yi 3.3
Flow [rating].sup.3) 10-12 Acetone test,.sup.5) 1 min. 2
[rating]
EXAMPLE 7
[0078] The powder coating compositions indicated in Table 7/1 are
prepared in accordance with Example 4.
9TABLE 7/1 Powder coating composition formulations Formulation J
[g] K [g] Uralac P 3485.sup.1) 60.66 59.79 Epoxy resin according
5.14 6.01 to Example 2f Benzoin 0.20 0.20 Acrylron.sup.2) 1.00 1.00
TiO.sub.2 [Cronos 2160] 33.00 33.33
[0079] The properties found for the corresponding coating are
indicated in the following Table 7/2.
10TABLE 7/2 Property J K Gel time @ 180.degree. C. [sec.] 200 200
Full cure 15 min./200.degree. C. 15 min./200.degree. C. Layer
thickness [mm] 45 89 Substrate Q panel Q panel Gloss 60.degree. 95
96 Gloss 20.degree. 82 77 Yellowness value Yi 2.0 7.9 Flow
.sup.3)[rating] 10 6-8 Acetone test.sup.5), 1 min. 3 3 [rating]
EXAMPLE 8
[0080] The powder coating compositions indicated in Table 8/1 are
prepared in accordance with Example 4.
11TABLE 8/1 Powder coating composition formulations Formulation J K
Uralac P 3485.sup.1) 91.27 60.78 Epoxy compound according to 7.53
5.02 Example 2e Benzoin 0.20 0.20 Acrylron.sup.2) 1.00 1.00
TiO.sub.2 [Cronos 2160] -- 33.00
[0081] The properties found for the corresponding coatings are
indicated in the following Table 8/2.
12 TABLE 8/2 L M Gel time @ 180.degree. C. [sec.] 180 180 Full cure
15 min./200.degree. C. 15 min./200.degree. C. Layer thickness [mm]
55 55 Substrate Q panel Q panel Gloss 60.degree. 108 96 Gloss
20.degree. 76 81 Yellowness value Yi -- 6.8 Flow.sup.3) [rating] 2
6-8 Acetone test.sup.5), 1 min. 3 3 [rating]
EXAMPLE 9
Preparation of an Epoxy Compound of the Following Formula
[0082] 11
[0083] Step A) 12
[0084] 100 ml of xylene (purissimum, stored over a 4.ANG. molecular
sieve, water content<0.02%), 146.3 g (1.04 mol) of methyl
3-cyclohexenecarboxylate and 27.1 g (0.20 mol) of pentaerythritol
are introduced into a well-insulated reaction vessel equipped with
a thermometer, a mechanical stirrer and a distillation bridge. The
resulting suspension is heated at a temperature of from 145 to
150.degree. C. for 30 minutes under nitrogen and with stirring
further xylene gradually being added to the reaction vessel at the
same rate as that at which xylene is distilled off. 0.23 g (0.01
mol) of LiNH.sub.2 is then added. After approximately 30 minutes
the methanol begins to distill off. The total distillation time is
approximately 6 hours, during the course of which 150 ml of xylene
are added. The reaction vessel is then cooled to room temperature.
The reaction mixture is diluted with 200 ml of toluene and washed
with 200 ml of water. The organic phase is dried over MgSO.sub.4
and filtered. The solvent and excess methyl
3-cyclohexenecarboxylate are then removed using a rotary evaporator
(120.degree. C./5 mbar). 110 g (97% yield) of reaction product are
obtained in the form of a colourless, viscous liquid, which
crystallises on being left to stand. The melting point of the
crystallisate is 65.degree. C.
[0085] Step B) 13
[0086] A mixture of 90.0 g (0.16 mol) of the reaction product
obtained according to Step A in 700 ml of dichloromethane is cooled
to a temperature of 10.degree. C., and a suspension of 148 g (0.76
mol, 39% in acetic acid) of peracetic acid and 7.3 g (0.088 mol) of
anhydrous sodium acetate is added dropwise thereto over a period of
approximately 45 minutes. During the addition, the temperature is
maintained below 30.degree. C. The solution is subsequently allowed
to react further for approximately 3 hours at room temperature
(25-30.degree. C.). The resulting reaction mixture is washed twice
with 200 ml of water, then twice with 200 ml of a 5% NaHCO.sub.3
solution and finally a further twice with 200 ml of water. The
organic phase is subsequently stirred with sodium sulfite until a
peroxide test is negative, and is subsequently dried over
MgSO.sub.4. After removal of the solvent a colourless, viscous
liquid is obtained which slowly crystallises on being left to
stand. Recrystallisation from 200 ml of MeOH yields 80 g (80%
yield) of the desired product in the form of a white, crystalline
powder (epoxy value: 6.1 eq./kg; melting point: 95.degree. C.).
EXAMPLE 10
[0087] The powder coating compositions indicated in Table 10/1 are
prepared in accordance with Example 4.
13TABLE 10/1 Powder coating composition formulations Formulation N
[g] O [g] P [g] Q [g] Uralac P 3485.sup.1) 56.26 58.89 58.80 58.82
DGT.sup.6) -- 2.74 -- -- HHDGP10) -- -- -- 1.12 HHDGT.sup.11) -- --
1.14 -- Epoxy compound according to 5.71 2.84 4.53 4.53 Example 9
DT 3126)) -- 0.50 0.50 0.50 Benzoin 0.20 0.20 0.20 0.20
Acrylron.sup.2) 1.50 1.50 1.50 1.50 TiO.sub.2 [Cronos 2160] 33.33
33.33 33.33 33.33 .sup.10)Hexahydrodiglycidyl phthalate (Araldite
PY 284) .sup.11)Hexahydrodiglycidyl terephthalate
[0088] The properties found for the corresponding coatings are
indicated in the following Table 10/2.
14 TABLE 10/2 N O P Q Gel time @ 180.degree. C. [sec.] 190 280 195
195 Full cure 15 min./ 15 min./ 15 min./ 15 min./ 180.degree. C.
180.degree. C. 180.degree. C. 180.degree. C. Layer thickness [mm]
62 48 58 60 Substrate Q panel Q panel Q panel Q panel Gloss
60.degree. 95 95 96 95 Gloss 20.degree. 86 83 88 85 Yellowness
value Yi 0.4 -1.3 -0.4 -0.6 Flow.sup.3)[rating] 10 10 10 11 Impact,
reverse.sup.4) [kg cm] 100 >160 140 120 Impact, front.sup.4) [kg
cm] 160 >160 160 160 Acetone test.sup.5), 1 min. 3 3 3 3
[rating] .sup.4)The impact deformation is determined by dropping
onto the coated face, from a specific height from behind (reverse
side) or from the front, a punch weighing 2 kg, having a 20 mm
diameter ball on its underside, with the underside leading. The
value indicated is
[0089] the product of the weight of the punch in kg and the test
reignt in cm at which there is still no detectable damage to the
coating
EXAMPLE 11
[0090] The powder coating compositions indicated in Table 11/1 are
prepared in accordance with Example 4.
15TABLE 11/1 Powder coating composition formulations Formulation
R[g] S[g] T[g] U[g] V[g] Uralac P 3485.sup.1) 58.53 58.21 58.60
57.99 58.49 Epoxy compound according to 4.51 4.84 4.51 5.12 4.78
Example 9 Epoxy compound.sup.12) 1.43 1.42 -- -- -- Epoxy
compound.sup.13) -- -- 1.36 1.36 -- Epoxy compound.sup.14) -- -- --
-- 1.20 DT 3126.sup.7) 0.50 0.50 0.50 0.50 0.50 Benzoin 0.20 0.20
0.20 0.20 0.20 Acrylron.sup.2) 1.50 1.50 1.50 1.50 1.50 TiO.sub.2
[Cronos 2160] 33.33 33.33 33.33 33.33 33.33
[0091] 14
[0092] The above epoxy compounds (2) 13) and 14 are obtained in
accordance with the same preparation procedure as in Example 9
[0093] The properties found for the corresponding coatings are
indicated in the following Table 11/2.
16 TABLE 11/2 R S T U V Gel time @ 180.degree. C. 240 230 210 215
215 [sec.] Full cure 15 min. 15 min. 15 min. 15 min. 15 min.
180.degree. C. 200.degree. C. 200.degree. C. 200.degree. C.
200.degree. C. Layer thickness [mm] 48 47 72 47 47 Substrate Q
panel Q panel Q panel Q panel Q panel Gloss 60.degree. 91 94 94 94
95 Gloss 20.degree. 86 84 87 77 82 Yellowness value Yi -2.3 -2.1
2.0 -2.8 -1.9 Flow.sup.3)[rating] 10 10 10 11 9 Impact,
reverse.sup.4) [kg cm] >160 >160 >160 >160 >160
Impact, front.sup.4) [kg cm] >160 >160 >160 >160
>160 Acetone test.sup.5), 1 min. 3 3 3 3 3 [rating]
EXAMPLE 12
[0094] The powder coatings indicated in Table 12/1 are prepared in
accordance with Example 4.
17TABLE 12/1 Powder coating composition formulations Formulation X
[g] Y [g] Z [g] Uralac P 3485 58.56 57.86 57.55 Epoxy compound,
prepared in accordance with 2.90 2.15 5.13 Example 2b (5.60 eq./kg)
Epoxy compound.sup.12) 3.01 4.46 -- Epoxy compound.sup.13) -- --
1.80 DT 3126.sup.7) 0.50 0.50 0.50 Benzoin 0.20 0.20 0.20
Acrylron.sup.2) 1.50 1.50 1.50> TiO.sub.2 [Cronos 2160] 33.33
33.33 33.33 .sup.12), 13), 7), 2)See corresponding definitions
hereinbefore.
[0095] The properties found for the corresponding coatings are
indicated in the following Table 12/2.
18 TABLE 12/2 X Y Z Gel time @ 180.degree. C. [sec.] 245 sec. 410
sec. 220 sec. Full cure 15 min./180.degree. C. 15 min./180.degree.
C. 15 min./180.degree. C. Layer thickness [mm] 60 59 69 Substrate Q
panel Q panel Q panel Gloss 60.degree. 95 94 95 Gloss 20.degree. 88
86 86 Yellowness value Yi 4.5 3.3 5.1 Flow.sup.3)[rating] 10 10 10
Acetone test.sup.5), 1 min. 3 3 3 [rating]
EXAMPLE 13
[0096] A clear powder coating composition (W) according to the
invention and three clear powder coating compositions used for
comparison purposes (W1, W2, W3), each based on Uralac 3489.sup.14)
and the epoxy compounds indicated in the following Table 13/1
(molar ratio of the COOH groups of the polyester to the epoxy
groups of the epoxy compound in each case 0.95 to 1) as well as 0.2
percent by weight of benzoin and 1.5 percent by weight of acrylon
(all compositions without curing accelerator) are homogenised by
extrusion twice using a laboratory extruder from PRISM, The Old
Stables, England, (T1=30.degree. C./T2=80.degree. C.). The
following are determined in each case: the gel time at 180.degree.
C.; the percentage of gelled material (gelled amount) in the cured
composition after curing for 15 min. at 200.degree. C., the Tg
value of the cured composition and the viscosity of the cured
systems at 180.degree. C. The values are likewise indicated in
Table 13/1.
19TABLE 13/1 Powder coating composition formulations Gel time @
Gelled Epoxy compound 180.degree. C. amount.sup.18) Tg after
curing. Viscosity Formulation (% by wt.) [sec.] [% by wt.] onset
[.degree. C.] [Pa.s] W according to Epoxide according 375 93.5 76
10700 the invention to Example 9 (7.8%) Comparison W1 PT
910.sup.15) 450 80.4 72 510 (7.2%) Comparison W2 XB 912.sup.16) 390
89.0 73 2100 (7.2%) Comparison W3 PT 810.sup.17) 210 95.2 76 9050
(5.2%) .sup.14)Uralac P3489 is a polyester based on Terephthalic
acid, Isophthalic acid and Neopentylglycol with an acid value of 28
mg KOH/g and a Tg of 70.degree. C. .sup.15Araldite PT910 is a solid
mixture of 75% by wt. of diglycidyl terephthaiate and 25% by wt. of
triglycidyl trimellitate according to US-A-5 457 168. .sup.16)XB
912 is a solid mixture of 60% by wt. of diglycidyl terephthalate
and 40% by wt. of triglycidyl trimellitate according to US-A-5 457
168. .sup.17)Araldite PT810 = triglycidyl isocyanurate .sup.18)The
gelled amount is determined as follows: A specimen, weighing 1 g,
of a 50 .mu.m thick film of the powder coating composition, which
has been cured for 15 minutes at 200.degree. C., is extracted for 2
hours three times with 50 ml of acetone each time. The value quoted
corresponds to the undissolved residue that remains, quoted in
percent by weight. .sup.19)Measurement of the (dynamic) viscosity
is determined using a rheometric measuring apparatus. The specimen
is subjected between two parallel plates (diameter 50 mm) to an
oscillating shearing stress (1 Hz; shearing stress (strain) 15%).
The viscosity is determined at 180.degree. C. as a function of the
time. The values quoted in the Table correspond to the viscosity of
the cured system.
[0097] The gelled amount of the powder coating composition (W)
according to the invention, which is significantly increased
compared with the comparison compositions based on Araldite PT910
(Comparison W1) and XB 912 (Comparison W2), is a clear indication
of the surprisingly increased crosslinking density in cured
material based on the composition according to the invention under
the same curing conditions (15 min./200.degree. C.). The
crosslinking density, which with the same curing time is increased,
also makes clear the higher reactivity of the systems according to
the invention, that reactivity being comparable with compositions
based on Araldite PT810 (Comparison W3). Likewise, the viscosity of
the system according to the invention after curing is significantly
increased compared with all three comparison systems (W1, W2 and
W3), demonstrating the comparatively high crosslinking density and
reactivity of the powder coating compositions according to the
invention.
* * * * *