Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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EPOXIDIZED POLYESTER-BASED
POWDER COATING COMPOSITIONS
This invention relates to powder coating
compositions. In one aspect, the invention relates to
epoxidized, solid resin compositions useful for powder
coatings.
Thermosetting powder coatings with some degree of
exterior durability can be prepared from polyester and
acrylic-based resins combined with suitable co-reactants.
Currently available, exterior grade epoxy group-
containing materials are exemplified by triglycidyl
isocyanurate (TGIC) and glycidyl methacrylate (GMA)
containing acrylic resins. TGIC-based powder coatings,
however, do not have sufficient weatherability, as
evidenced by loss of gloss and discoloration. Although
acrylic materials generally have superior weatherability,
they are known to have poor physical properties( e.g.,
flexibility and impact resistance) and create film
defects in other powder coating materials when present as
a contaminant. While other solid epoxy resins such as
EPON Resins 2002, 2003 and 2004 are available (Epon
Resins are trade marks), they do not provide for exterior
durability, because they consist of aromatic subunits.
Thus, there is a need for improved low aromatic or non-
aromatic, solid epoxy resins that can react with low
aromatic or non-aromatic acrylic resins and polyesters to
produce weatherable powder coatings.
According to the invention, a curable coating powder
composition is provided comprising:
(a) a solid epoxidized polyester prepared by epoxidizing
a polyester having a melting point of at least 90 °C,
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wherein said polyester is a polyester prepared by
reacting a mixture comprising
(i) a tetrahydrophthalic acid or anhydride,
(ii) at least one cycloaliphatic polyol,
(iii) optionally at least one saturated
polycarboxylic acid, and
(iv) optionally at least one other alcohol,
in a mole ratio of (i):(ii):(iii):(iv) such that acid to
hydroxyl equivalent ratio is from 0.8 to 1 to 0.96 to 1,
and an equivalent ratio of (i) to (iii) from 100:0 to 1:4
and an equivalent ratio of (ii) to (iv) of 100:0 to 4:1;
and
(b) a solid carboxylic acid component having an acid
equivalent weight within the range of from 100 to 1500.
Such coating powder provides a cured powder coating
having good resistance to hydrolysis and ultraviolet
light.
The epoxidized polyester must be friable and non-
sintering to be useful for powder coatings applications.
The polyester sinters if it agglomerates (sticks
together) at room temperature within one week and cannot
be readily redispersed. The solid epoxidized polyester
preferably has a melting point of at least 100 °C to
obtain good performance.
It has been found that solid epoxidized polyesters
useful for powder coatings applications can be prepared
by epoxidizing a polyester having a Tg of preferably
greater than 50 °C, a melting point of at least 90 °C and
a viscosity (ICI Cone & Plate viscosity) of at most
50 Poise at 200 °C. Such polyesters can be prepared by
reacting the hereinbefore specified components (i)-(iv)
in the hereinbefore specified molar ratio. Preferably the
total acid to hydroxyl equivalent ratio is from 0.85 to 1
to about 0.95 to 1, the equivalent ratio of (i) to (iii)
from 4:1 to 1:4, and more preferably from about 2:1 to
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1:2; and an equivalent ratio of (ii) to (iv) of 100:0 to
12.5:1. In a preferred embodiment, it is desirable to
have from 2:1 to 1:2 equivalent ratio, of component (I)
to (iii), to obtain a good weatherable formulation.
. 5 The reaction is typically carried out by heating the
mixture at a temperature within the range of from 150 °C,
preferably from 170 °C, to 240 °C, preferably to 230 °C
until the acid value of the reaction mixture reaches 5 or
less, preferably less than 2. Preferably the water
and/or other condensation products formed during the
reaction are continuously removed. The reaction mixture
can also contain inert organic solvents, for example,
ketones such as 2-butanone, 4-methyl-2-pentanone and
hydrocarbons such as xylene and toluene. A catalyst can
be added to facilitate the completion of the reaction.
Such catalysts include for example, those prepared from
titanium, zirconium, tin and antimony, as well as other
conventional catalysts used in polyesterification
reactions. The solid polyester resins produced can be
recovered by conventional methods.
The alcohol is preferably a polyhydric alcohol having
5-50 carbon atoms and two to four hydroxyl groups per
molecule. Small amounts, at most 15 equivalent percent,
preferably less than 10 equivalent percent, if any, of
the total hydroxyl content, of polyhydric alcohols having
4 carbon atoms or less or monohydric alcohols may also be
present in the reaction mixture.
Examples of the tetrahydrophthalic acids or
anhydrides useful for preparing the solid polyester
include, cyclohex-4-ene-1,2-dicarboxylic anhydride,
3-methylcyclohex-4-ene-1,2-dicarboxylic anhydride,
4-methylcyclohex-4-ene-1,2-dicarboxylic anhydride,
cyclohex-4-ene-1,2-dicarboxylic acid, 3-methylcyclohex-
4-ene-1,2-dicarboxylic acid, 4-methylcyclohex-4-ene-
1,2-dicarboxylic acid, and mixtures thereof. Examples of
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the cycloaliphatic polyols useful for preparing the solid
polyester include cyclohexanedimethanol and hydrogenated
bisphenol A, and mixtures thereof. Examples of the
saturated polycarboxylic acids useful for preparing the
solid polyester include hexahydrophthalic anhydride,
hexahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid,
the dimethylester of cyclohexanedicarboxylic acid, and
mixtures thereof. Examples of the polyhydric alcohols,
component (iv), include trimethylolpropane, neopentyl
glycol, trimethylolethane, pentaerythritol, and mixtures
thereof. Examples of the polyhydric alcohol having
4 carbon atoms or less include ethylene glycol,
1,3-propanediol, 1,4-butanediol. Examples of the
monohydric alcohols include butanol, 2-ethyl-1-hexanol
and cyclohexanol.
The solid polyesters can be epoxidized by any
conventional epoxidation method such as disclosed in U.S.
Patent Nos. 5,244,985, 3,493,631 and 2,928,805. For
example, the solid polyesters can be epoxidized by
treatment with acid solutions such as peracetic acid,
performic acid, generated separately or in-situ from
formic acid and hydrogen peroxide in the presence of a
strong acid or an acidic resin, or mixtures of molybdic
acid and hydrogen peroxide, in the presence of a
sufficient quantity of a base such as sodium carbonate,
sodium bicarbonate or disodium hydrogen phosphate to
neutralize the contained strong acid, at a temperature
within the range of from 0 °C, preferably from 20 °C, to
70 °C, preferably to 40 °C. The resulting epoxidized
solid polyesters preferably have WPE (weight per
equivalent of epoxy functionality) values within the
range of 350 to 1500. The solid, friable epoxidized
polyesters are recovered by conventional methods.
The carboxylic acid curing agent must also be solid
and friable to be useful for powder coatings
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applications. It has been found that such a carboxylic
acid component useful as a curing agent for powder
coatings application must have an acid equivalent weight
within the range of from 100 to 1500 and preferably from
110 to 900. Such a carboxylic acid preferably has 10 to
100 carbon atoms and two to four carboxyl groups, more
preferably two carboxyl groups per molecule on average,
provided it has an acid equivalent weight within the
range of from 100 to 1500.
l0 Examples of the polycarboxylic acids include,
straight or branched chain solid, preferably crystalline,
alkanoic acids such as dodecanedioic acid and sebacic
acid. Another preferable polycarboxylic acid can be
prepared by reacting a mixture, including at least one
cycloaliphaticdicarboxylic acid or anhydride and at least
one polyhydric alcohol having 5-50 carbon atoms in an
acid to hydroxyl equivalent ratio of less than 2:1,
preferably 1.2:1, to 2:1, preferably to 1.4:1. A mixture
of more than one polyhydric alcohol is preferred to
obtain optimum performance and ease of handling.
Examples of the cycloaliphatic dicarboxylic acid or
anhydride and polyhydric alcohols are listed above.
A curable coating powder composition comprises (a)
the solid epoxidized polyester and (b) the acid
functional component. The amount of (a) to (b) will
generally be within plus or minus 35 percent of the
stoichiometric amount. The ratio may be adjusted to
compensate for the type of catalyst, cure conditions, and
desired coating properties. Ratios outside the range can
lead to low molecular weight, poorly cross-linked
products with less than optimum properties. Conventional
powder coating additives such as flow control agents,
anti-popping agents, powder flow materials, fillers and
pigments may also be included. The curable coating
powder composition may further include a small percentage
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of catalysts such as phosphonium salts (e. g.,
ethyltriphenylphosphonium iodide), imidazoles and tin
salts (e.g., dibutyltin oxide) in order to increase the
crosslinking rate of the coating composition depending on
the desired application.
The thermosetting coating powder compositions can be
prepared by the various methods known to the powder
coating industry: dry blending, melt compounding by two
roll mill or extruder and spray drying. Typically the
process used is the melt compounding process: dry
blending the ingredients in a planetary mixer and then
melt blending the admixture in an extruder at a
temperature within the range of 80 °C to 130 °C. The
extrudate is then cooled and pulverized into a
particulate blend.
The thermosetting coating powder composition can then
be applied directly to_a substrate of, e.g., a metal such
as steel or aluminium. Non-metallic substrates such as
plastics and composites can also be used. Application
can be by electrostatic spraying or by use of a fluidized
bed. Electrostatic spraying is the preferred method.
The coating powder can be applied in a single sweep or in
several passes to provide a film thickness after cure of
2.0 to 15.0 mils.
The substrate can optionally be preheated prior to
application of a coating powder composition to promote
uniform and thicker powder deposition. After application
of the coating powder, the powder-coated substrate is
baked, typically at 120 °C, preferably from 150 °C, to
205 °C for a time sufficient to cure the powder coating
composition, typically from 1 minute to 60 minutes,
preferably from 10 minutes to 30 minutes.
The coating powder compositions can be applied
directly upon bare metal or plastics or composites (e. g.,
upon untreated, unprimed steel) or upon pretreated
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surfaces (e.g., phosphatized, unprimed steel). The
powder coating compositions can also be applied upon
phosphatized steel having a thin (0.8 mils to 2 mils)
layer of an electrodeposited primer, cured or uncured
before the application of the coating powder composition
or over a chip-resistant coating layer as a top coating
layer. Examples of a chip-resistant layer is described,
for example in U.S. Patent Nos. 5,115,029 and 5,264,503.
The electrodeposited primer coating upon the metal
substrate can be, for example, a cathodic
electrodeposition primer composition. In one aspect of
the present invention, it is contemplated that the
coating powder composition can be applied directly upon
an uncured electrodeposited primer coating and the
coating powder can be co-cured by heating at temperatures
between 150 °C to 180 °C from 10 minutes to 30 minutes.
The powder coating compositions of this invention
exhibit good W resistance, which can be seen by good
retention of gloss at 60°, good chemical resistance and
have good flow under cure conditions useful for exterior
durable powder coatings for automobiles, for general
metal surfaces such as wheel covers and architectural
components such as window frames. The powder coating
compositions of the invention are desirable over
conventional liquid systems because they have essentially
no volatile organic content.
The following illustrative embodiments describe the
novel epoxy resin composition of the invention and are
provided for illustrative purposes and are not meant as
limiting the invention.
Tetrahydrophthalic anhydride was obtained from
Janssen Chemical. Hexahydrophthalic anhydride and
hydrogenated bisphenol A were obtained from Milliken
Chemical. 1,4-Cyclohexanedimethanol was obtained from
either Aldrich Chemical Co. or from Eastman Chemical Co..
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1,4-Cyclohexane dicarboxylic acid was provided by Eastman
Chemical Co.. Trimethylolpropane mentioned in the
examples below was obtained from Aldrich Chemical Co.. _
Tin catalyst (Fascat 4100) was obtained from Elf Atochem.
Equilibrium peracetic acid (35%) was purchased from
Aldrich Chemical Co..
Examples 1-8
Preparation of solid ~ d ox~r1 -fllnct~ nna~
Solid polyesters containing multiple sites of
olefinic unsaturation were prepared by reacting varying
amounts of the reactants listed in Table 1, (CHDA =
cyclohexanedicarboxylic acid; THPA = tetrahydrophthalic
anhydride; HHPA = hexahydrophthalic anhydride; CHDM =
1,4-cyclohexanedimethanol; HBPA = hydrogenated
bisphenol A; TMP = trimethylolpropane). Two procedures
were used to add the reagents.
In one procedure, the acid-functional reactants, HBPA
and toluene were placed in a 5.0 litre flask, equipped
with a Dean-Stark trap and condenser, thermocouple and
overhead stirrer assembly. The flask and its contents
were briefly purged with nitrogen; then, a positive
pressure of nitrogen was maintained until initiation of
sparge. The components were heated to reflux and held
for one hour. Afterwards, a solution of 2-butanone
(800 grams) and the remaining hydroxyl components were
added, allowing for continuous removal of solvent. In
the alternative procedure, cyclohexanedimethanol was
added along with the other reactants prior to heating.
The reaction mixture was warmed slowly to 200 °C,
removing solvent and by-product water as required. The
reaction mixture was maintained at reflux to facilitate
removal of water until the evolution rate of water
diminished. Fascat 4100 (a butylated tin oxide) was added
all at once, either at the beginning of the reaction or
after the initial evolution of water of condensation
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9
slowed. After maintaining a temperature of 200 °C for
1-2 hours, the reaction mixture was further warmed to
220 °C and was sparged with nitrogen. This was maintained
until the acid number of the resin was less than 1. Acid
number was measured by titration of a 50:50 (w/w)
toluene/isopropanol solution of resin with O.1N ethanolic
potassium hydroxide. The polyester resin produced was
isolated by transferring the contents of the flask to
aluminium pans.
Properties of the resultant solid polyesters are
listed in Table 2. Viscosity was measured at 200 °C,
unless noted otherwise, by ICI Cone & Plate. Mettler
melting point (M. P. in degree centigrade) and final acid
value are listed.
m m., , ,. , 1
Example CHDA THPA HHPA CHDM HBPA TMP Acid/OH~
1 10.1 8.6 16.7 3.3 0.935/1
2 1.19 1.81 3.02 0.24 0.92/1
Comp. 1.9 1.66 0.34 0.95/1
a
Comp. 2.4 4.48 0.54/1
b
3 0.86 1.01 1.67 0.33 .935/1
4 5.16 6.06 10.4 2.06 0.9/1
Comp. 9.35 8.35 1.65 0.935/1
c
5 10.1 8.6 16.7 3.35 0.3 0.92/1
1) Values represent equivalents employed:
MOLECULE EQUIV. WT.
CHDA 86
THPA 76
HHPA 77
CHDM. 72
HBPA 120
TMP 44.7
AMENDED SHEET
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2) Ratio based on equivalents employed
Table 2
Ex. Acid M.P. Melt Degree of Mn2
No. (C) Viscosity Olefin
(Poise/ Functionality)
C)
1 0.88 101.7 21/200 7.7 4400
80/175
2 0.43 107.5 75/175 6.6 4768
Comp. a 1.9 138.1 >250/200 19 5752
Comp. b 5.1 66.6 13/150 4.1 1231
3 1.5 108 52/175 7.8 4400
4 0.5 90.8 22/175 4.9 2827
Comp. c 0.9 103 14/200 14.4 4385
47/175
0.9 104.3 29/175 7.5 4246
1) Degree of functionality is the theoretical value
2) Mn is the theoretical number average molecular weight
As can be seen from the Tables above, the polyesters
of Examples 1-2 and 5-8 have melting points of above
90 °C and viscosity measurements of less than 50 Poise at
5 200 °C. Comp. example b is provided as an example with
the melting point too low. Comp. example a is provided as
an example with the viscosity too high during powder
coating curing, due to a too high reactivity. Although
the acid to OH ratio of Comp. example c is such as to
obtain a low viscosity value suitable for processing in
powder coating applications, the reactivity of the epoxy
resin is too high, which causes a poor flow out of the
powder coating composition under curing conditions.
A~IEtdDE~ ~~ 1EET
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Examples 9-13
Preparation of solid epoxidized olyester
The polyesters obtained above were dissolved in
toluene or methylene chloride (25/75-40/60 w/w) and
reacted with equilibrium 35% peracetic acid at 25 to
40 °C for two to three hours. The reaction mixture was
treated with sufficient sodium carbonate to neutralize
the sulfuric acid contained in the peracetic acid.
Subsequent to reaction, the epoxidized polyester was
isolated in one of two ways. In one method (method A),
the reaction mixture was condensed under reduced pressure
to remove water, unreacted hydrogen peroxide, peracetic
acid and acetic acid as well as some solvent. The residue
was diluted to 25o solids with toluene or methylene
chloride and either filtered or washed 4-5 times with
water to remove solid impurities. The resin solution was
then condensed by distillation of volatiles under reduced
pressure and at elevated temperature (200 °C max.). The
residue was optionally sparged with nitrogen to remove
the final traces of volatiles to render a product more
acceptable as a coating powder vehicle.
In another method (method B), the reaction mixture
after completion of the epoxidation reaction was diluted
to 25o solids as above then filtered; afterwards, the
mixture was washed 4-5 times with water and condensed by
distillation and sparging as described above.
The WPE (weight per equivalent of epoxy
functionality), Mettler melting point (M. P. in degree
centigrade) and ICI Cone & Plate viscosity at 200 °C are
listed below in Table 3. The WPE was determined by
titration of a dichloromethane/acetic acid solution of
resin and tetraethylammonium bromide with standardized
0.1 N perchloric acid in acetic acid to a crystal violet
endpoint.
AMENDED SHEET
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- 12 -
Table 3
Melt Mettler
Example Polyester WPE Viscosity M.P. (C)
Prepared in (Poise/C)
Examr~le
9 2 852 142/175 107.7
3 783 69/175 107.7
11 4 721 68/175 105.3
13 5 682 36/175 112
Examples 14-17
Preparation of Acid Functional Component
Acid functional components (polyester curing agents)
were prepared by reacting varying amounts of the reagents
5 listed in Table 4 in equivalents, (CHDA = cyclohexane
dicarboxylic acid; HHPA = hexahydrophthalic anhydride;
CHDM = 1,4-cyclohexanedimethanol; TMP = trimethylol-
propane) in a manner similar to that used to prepare the
polyesters described above in Tables 1 and 2. All
10 reagents were placed in a four neck flask fitted with an
overhead stirring assembly, a thermocouple, a Dean-Stark
trap and condenser, and a source of nitrogen. Xylene was
optionally added to the reactants to serve as a carrier
for the water to be formed. After briefly purging the
flask and its contents with nitrogen, a positive pressure
of nitrogen was applied and the mixture was heated to
reflux, if xylene was employed, or to 150 °C. For
MCS22/TH0274PCT
AMEI~'DED SHEET
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Examples 15-17, 0.1-0.2 wt.% Fascat 4100 catalyst was
added. After one hour at this temperature, the mixture
was warmed to 175 °C and maintained at that temperature
until approximately 75% of the water had evolved. After
this time, the mixture was warmed to 200 °C. After water
evolution again slowed, the mixture was sparged with
nitrogen until the theoretical acid number was attained
or exceeded. The total Acid/OH ratio and melting point of
each product is listed in Table 4.
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a o ~ y .n
~r m m ,
O un
U . y m
u~ p 'n o
-rl a, N rl r-I
J-t , M tll~ Lfl
Cr M ~ 01
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tr' ~,..~~-1r-i
W
r1
p ~ Lf1N b
_~ O ~ , r-1rlM
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N
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x
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d' ll7lDL~
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Examples 18 and 1,,~
r
cured prod
Exams 1 Examp
Example 13, Oxirane Component a 18 ----
395
Example 17, Curing Coreactant 296 ----
Polyester ResinA, DSM P-3900 ---- 596
TGICB
---- 45
Modaflow Powder IIIC 7 6
Benzoin __-_ 3
Ethyltriphenylphosphonium 2 _-__
Iodide
Titanium Dioxide (Exterior
Grade)
TOTAL 1000 1000
A Acid functional polyester resin from DSM. Acid
Value=32-38.
B Araldite PT 810 from Ciba-Geigy.
C Acrylate copolymer from Monsanto.
Ma_n_mfactur~ ng Proc
The above compositions were processed using a typical
coating powder manufacturing process: Intensive premix,
high shear melt compounding (extrusion), grinding and
sieving through a 200 mesh screen.
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WO 98/49215 PCTlEP97/02234
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.r-I ~I~-I
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A Powder Coating Institute (PCI) Test Procedure #6.
B ASTM D2794.
C ASTM D522
D ASTM D3363
E PCI #8.
F ASTM D523
G ASTM D2244
H PCI #20
I ASTM D4141
As can be seen from the Table above, the powder
coating of the invention, Example 18, has superior
weatherability and other performance properties at least
equivalent to a typical TGIC-polyester powder, Example
19. 60° gloss retention was 97o after 1000 hours for the
invention versus 30o after 200 hours for the TGIC-
polyester powder.
