Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
OLIGOMERIC EPOXY/ISOCYANATE SYSTEMS
BACKGROUND OF THE INVENTION
S This invention concerns coating systems comprising non-isocyanate
and isocyanate components in organic solvents. The non-isocyanate components
being an oligomer or blend of oligomers containing at least two functional
groups,
at least one being epoxy; optionally present is a polyester or oligo-ester or
acrylic
polymer having at /east two hydroxyl groups.
U.S. 5,215,783 discloses a process for coating a substrate with a
waterborne basecoat and a clearcoat containing a polymeric epoxy group.
SUMMARY OF THE INVENTION
It has now been discovered that oligomeric epoxies will react directly
with isocyanates to form well-crosslinked coatings. This reaction occurs
rapidly
at elevated temperatures but relatively slowly at room temperature. This is in
sharp contrast to polymeric acrylic epoxies which react poorly at any
temperature.
The room temperature reaction is enhanced significantly by the use of epoxy
compounds which also include hydroxyl moieties. These epoxies can be used as
diluents in traditional hydroxyU isocyanate coatings. This crosslinking system
results in coatings with very low volatile organic content (VOC) that are
durable
and display good etch and mar resistance.
The invention specifically concerns a curable coating composition of a
binder in organic solvent comprising
A) a non-isocyanate component wherein:
i) 5-100% of the non-isocyanate component is an oligomer or
blend of oligomers with a weight average molecular weight not exceeding
about 3,000, a polydispersity not exceeding 1.7, containing at least two
functional groups with at least one being an epoxy group, the remaining
being epoxy or hydroxyl;
ii) 0-95% by weight of the non-isocyanate component of a
polyester, oligo-ester or acrylic polymer each having at least two hydroxyl
groups; and
B) an oligomeric isocyanate crosslinker containing at least two
isocyanate groups; the equivalents of B to A being 0.5 to 3.0 of isocyanate to
epoxy or epoxy plus hydroxyl.
Contemplated embodiments of the invention are those wherein
component (ii) is absent and cure is accelerated by ambient moisture, and
where
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component (ii) contains at least one hydroxyl group derived from acrylates
andlor
methacrylates, and at least one epoxy group derived from glycidyl methacrylate
and/or glycidyl acrylate.
Also contemplated is the above composition cured at ambient
conditions or baked at elevated temperatures. Such composition can include
hydroxyl and/or epoxy-functional nonaqueous dispersions, and these optional
crosslinkers: aldimines, ketimines, and polyaspartic esters. Catalysts such as
tin
and tertiary amines (alone or in combination with acetic acid) can be
employed.
The disclosed composition is useful in clearcoats and pigmented compositions
to
coat substrates, preferably vehicle bodies and vehicle body parts.
DETAILS OF THE INVENTION
The compositions of this invention show a remarkable combination of
wet-properties and film-properties. The combination of oligomeric epoxies
crosslinked by oligomeric isocyanates have shown
1) the potential for extremely low volatile organic content (VOC).
VOC's below 2.0 lbs/gallon, {0.24 kg/Iiter) and in some cases (with only
epoxy/isocyanate) approaching 1.0 (0.12 kglliter) VOC, have been
successfully sprayed with excellent appearance and cure;
2) the etch resistance of these coatings is superior to standard
hydroxy>rsocyanate systems of similar film Tg (glass transition temperature).
This results in coatings with a superior etch/mar balance which is critical to
today's finishes;
3) the fracture properties ofthese systems, as measured by single-
indentor testing, is superior to standard hydroxyllisocyanate systems; and
4) excellent durability exceeding 7000 hours of acccelerated QUV
exposure (using an FS-40 bulb) has been seen with these coatings.
These epoxy or epoxy/hydroxyl-functional oligomers can be used to
improve the spray solids or film properties of standard polymeric isocyanate-
crosslinked systems.
Binder Components
Representative binder components of these systems include epoxy-
functional oligomers, epoxy/hydroxyl-functional oligomers and isocyanate-
functional oiigomers. Other functional oligomers and polymers can also be
included in the formulations of this invention.
Component A(i)
The oligomeric component contains at least two functional groups
and should have a molecular weight of less than about 3000. Typical epoxy
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components containing a hydroxy functionality or (OH) group include, among
others, sorbitol poiyglycidyl ether, mannitol polygIycidyl ether,
pentaeryihritol
polyglycidyl ether, glycerol polyglycidyl ether, low molecular weight epoxy
resins
such as epoxy resins of epichlorohydrin and bisphenol-A, and polyglycidyl
ethers of
isocyanurates, for example, "Denecol" EX30I from Nagase and DCE-358~
sorbitol polyglycidyl ether from Dixie Chemical. These types of oligomers are
preferred for ambient cure, but are also useful for baked systems.
Epoxy components which typically do not contain significant hydroxy
functionality include, among others, di- and polyglycidyl esters of
polycarboxylic
acids, and di- and polyglycidyl esters of acids, such as Araldite CY-184~
from.
Ciba-Geigy, or XU-71950 from Dow Chemical are preferred since they form high
quality finishes. Cycloaliphatic epoxies can also be used, such as ERL-4221
from
Union Carbide. These oligomers are primarily used in baked systems, but can be
used at low levels in ambient cured systems.
Component B
The composition also contains an organic isocyanate crosslinking
agent in the amount of 0.5 to 3.0 equivalents of isocyanate per equivalent of
epoxy or epoxy/hydroxyl. Optimum film properties are achieved when one epoxy
group reacts with two isocyanate groups. However, it was determined that a
broad
latitude in stoichiometry of isocyanate to epoxy can sometimes be usefial
depending
on final wet- and dry-coating properties desired. Any of the conventional
aromatic, aliphatic, or cycloaliphatic isocyanates; trifunctional isocyanates
and
isocyanate fi.~nctional adducts of a polyol and a diisocyanate can be used.
Typically
useful diisocyanates are i,6-hexamethylene diisocyanate, isophorone
diisocyanate,
4,4'-biphenylene diisocyanate, toluene diisocyanate, bis-cyclohexyl
diisocyanate,
tetramethylene xylene diisocyanate, ethyl ethylene diisocyanate, 2,3-dimethyl
ethylene diisocyanate, 1-methyltrimethylene diisocyanate, I,3-phenylene
diisocyanate, I,5-napthalene diisocyanate, bis-(4-isocyanatocyclohexyl)-
methane,
4,4'-diisocyanatodiphenyl ether and the like.
Typical trifunctional isocyanates that can be used are triphenylmethane
triisocyanate, 1,3,5-benzene triisocyanate, 2,4,6-toluene triisocyanate and
the like,
Trimers of diisocyanates also can be used such as the trimer of hexamethylene
diisocyanate which is sold under the tradename "Desmodur"~ N-3390 and the
trimer of isophorone diisocyanate. Trifunctional adducts of triols and
diisocyanates can be used.
Optional Ingredients
The present coating composition can further comprise a functional
amount of catalyst, generally about 0.1 to 5 weight percent, based on the
weight of
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solids in the formulation. A wide variety of catalysts can be used, such as
dibutyl
tin dilaurate or tertiary amines such as triethylenediamine. These catalysts
can be
used alone or in conjunction with carboxylic acids such as acetic acid. It is
preferred that a catalyst be employed.
The coating compositions of the present invention are formulated into
high solids coating systems dissolved in at least one solvent. The solvent is
usually
organic. Preferred solvents include aromatic hydrocarbons such as petroleum
naphtha or xylenes; ketones such as methyl amyl ketone, methyl isobutyl
ketone,
methyl ethyl ketone or acetone; esters such as butyl acetate or hexyl acetate;
and
glycol ether esters such as propylene glycol monomethyl ether acetate. It is
preferred to employ solvent.
The coating compositions of the present invention can also contain up
to 40% of total binder of a dispersed acrylic component which is a polymer
particle
dispersed in an organic media, which particle is stabilized by what is known
as
steric stabilization. Hereafter, the dispersed phase or particle, sheathed by
a steric
barrier, will be referred to as the "macromolecular polymer" or "core". The
stabilizer forming the steric barrier, attached to this core, will be referred
to as the
"macromonomer chains" or "arms".
The dispersed polymer contains about 10 to 90%, preferably 50 to
80%, by weight, based on the weight of the dispersed polymer, of a high
molecular
weight core having a weight average molecular weight of about 50,000 to
500,000. The preferred average particle size is 0.1 to 0.5 microns. The arms,
attached to the core, make up about 10 to 90%, preferably 10 to 59%, by weight
of the dispersed polymer, and have a weight average molecular weight of about
1,000 to 30,000, preferably 1,000 to 10,000.
The macromolecular core of the dispersed polymer is comprised of
polymerized acrylic monomers) optionally copolymerized with ethylenically
unsaturated monomer(s). Suitable monomers include styrene, alkyl acrylate or
methacrylate, ethylenically unsaturated monocarboxylic acid, and/or silane-
containing monomers. Such monomers as methyl methacrylate contribute to a high
Tg (glass transition temperature) dispersed polymer, whereas such "softening"
monomers as butyl acrylate or 2-ethylhexylacrylate contribute to a low Tg
dispersed polymer. Other optional monomers are hydroxyalkyl acrylates or
methacrylates or acrylonitrile. Optionally, the macromolecular core can be
crosslinked through the use of diacrylates or dimethacrylates such as allyl
methacrylate or post reaction of hydroxyl moieties with polyfunctional
isocyanates.
The macromonomer arms attached to the core can contain
polymerized monomers of alkyl methacrylate, alkyl acrylate, each having 1 to
12
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carbon atoms in the alkyl group, as well as glycidyl acrylate or glycidyl
methacrylate or ethylenically unsaturated monocarboxylic acid for anchoring
andlor crosslinking. Typically useful hydroxy-containing monomers are hydroxy
alkyl acrylates or methacrylates as described above.
Additional crosslinkers can be included in this formula such as
aldemine, including the reaction product of isobutyraldehyde with diamines
such as
isophorone diamine and the like; ketimines such as the reaction product of
methyl
isobutyl ketone with diamines such as isophorone diamine; and polyaspartic
esters.
The coating compositions of the present invention can also contain
conventional additives such as pigments, stabilizers, ultraviolet light
stabilizers,
antioxidants, rheology control agents, flow agents, toughening agents and
fillers.
Such additional additives will, of course, depend on the intended use of the
coating
composition. Fillers, pigments, and other additives that would adversely
effect the
clarity of the cured coating will not be included if the composition is
intended as a
clear coating.
Component Aliil:
The coating compositions of the present invention can also an acrylic
polymer of weight average molecular weight greater than 3,000, or a
conventional
polyester such as SCD~ - 1040 from Etna Product Inc. for improved properties
and appearance, sag resistance, flow and leveling and such. The acrylic
polymer
can be composed of typical monomers such as acrylates, methacrylates, styrene
and the like and functional monomers such as hydroxy ethyl acryiate, glycidyl
methacrylate, or the like.
Representative hydroxyl-functional oligomers that can be employed as
component A(ii) include the reaction product of multifunctional alcohols such
as
pentaerythritol, hexanediol, trimethylol propane, and the like, with cyclic
monomeric anhydrides such as hexahydrophthalic anhydride,
methylhexahydrophthalic anhydride, and the like, said reaction product further
extended by reaction with monofunctional epoxies such as butylene oxide,
propylene oxide, and the like to form hydroxyl oligomers.
Non-alicyclic oligomers (linear or aromatic) can include succinic
anhydride- or phthalic anhydride-derived moieites such as described above.
Caprolactone oligomers which can be made by reacting caprotactone with a
cycloaliphatic, aliphatic or aromatic polyol can also be used. Particulary
useful
caprolactone oligomers are described in columns 4 to 5 of U.S. Patent
5,286,782.
Preferred oligomers A(ii) have weight average molecular weights not
exceeding about 3,000 with a polydispersity not exceeding about 1.7; more
preferred oligomers have molecular weights not exceeding about 2,500 and
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polydispersity not exceeding about 1.4; most preferred oligomers have
molecular
weights not exceeding about 2,200, and polydisperity not exceeding about I.25.
The coating compositions are typically applied to a substrate by
conventional techniques such as spraying, electrostatic spraying, roller
coating,
dipping or brushing. The present formulations are particularly useful as a
clear
coating for outdoor articles, such as automobile and other vehicle body parts.
The
substrate is generally prepared with a primer and/or a color coat or other
surface
preparation prior to coating with the present compositions.
After application to a substrate, the present compositions can be cured
by heating to a temperature of about 120° to 150°C for a period
of about 15 to 90
minutes or with the proper formulation can be cured at ambient conditions
(about
60° to 110°F, depending on the geographical location, usually
65° to 90°F).
The performance characteristics of the final cured coating composition
are excellent, providing a combination of excellent gloss and durability to
abrasion,
sunlight and acidic rain. At the same time, the compositions provide low
volatile
organic content and ease of handling. The ability to apply the present
compositions by spraying techniques with the unusually low VOC content is
surprising.
The present invention is further illustrated by the following specific
examples, in which parts and percentages are by weight unless otherwise
indicated.
EXAMPLES
KEY FOR EXAMPLES
Tradename or identifier Chemical Description
Tinuvin~384 (UVA) substituted benzotriazole (Ciba-Geigy)
Tinuvin~292 (HALS) hindered amine derivative (Ciba-Geigy)
BYK~306 silane flow additive (BYK-Chemie)
Tolonate~HDT or HDT-LV isocyanurate oligomers of hexamethylene
diisocyanate (Rhone-Poulenc)
Procedure 1
TETRAI-iYDROXY-FUNCTIONAL OLIGOMER
Preparation of Acid Oii~gomer
To a 12-liter flask fitted with an agitator, condenser, heating mantle,
nitrogen inlet, thermocouple and an addition port was added 2447.2 gms of
propylene glycol monomethylether acetate, 792.4 gms of pentaerythritol and
1.36
gms of triethylamine. The reaction mixture was agitated and heated to
140°C
under a nitrogen blanket at which time 3759 gms of methyl hexahydrophthalic
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anhydride was added over 6 hrs. The reaction mixture was then held at
140°C
until no anhydride bands were observed on an infrared spectroscopic trace.
Preparation of Hvdroxy Oligomer
To a 5-liter flask fitted with an agitator, condenser, heating mantle,
nitrogen inlet, thermocouple and an addition port was added 2798.4 gms of acid
oligomer prepared above and 2.76 gms of triethylamine. The mixture was
agitated
and heated to 64°C under nitrogen. Then, 696.9 gms of 1,2-epoxy butane
was
added over 120 mins, after which the temperature was raised to 105°C
and held at
that temperature until the acid number dropped to about 10 or Iess. Percent
weight solids were 71.5, Gardner viscosity V, number average molecular weight
895 and weight average molecular weight 1022 as determined by GPC
(polystyrene standard).
Procedure 2
The hydroxy-functional acrylic component was made as follows:
a stirred, heated reactor is charged with
I Methyl amyl ketone 148.05 parts
This mixture was heated to reflux (about 150-155°C)
The following feed was then added simultaneously with part III
uniformly over 5 hours while maintaining reflux:
II Isobutyl methacrylate monomer 182.56
2-ethylhexyl methacrylate monomer 237.37
2-hydroxyethyl methacrylate 129.16
The following feed was fed simultaneously with part Ii over 150
minutes. When addition is complete cool reactor to 130°C.
III Methyl amyl ketone 58.64
t-butyl peroxyacetate 70% soln 26.51
After the previous feed the following was added over 30 minutes while
maintaining reflux (hold temperature at 130°C. Cool and fill sample
IV Methyl amyl ketone 14.81
t-butyl peroxyacetate initiator 6.55
The batch was then cooled and filled out.
Total 804.00
Solids - 68.0%
Viscosity = W to Y Gardner-Holdt
Gallon Weight =8.04
Example 1
Two-Component Oligomeric EpoxylIsocyanate clear - bake system
Component !i7
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Diglycidyl ester of 1,2 cyclohexane dicarboxylic acid 189.78
Tinuvin~384 (UV Screener from Ciba-Geigy) 11.01
Tinuvin~292 (Hindered Amine Light Stabilizer from
Ciba-Geigy) 8.26
10% BYK-301 ~ (flow additive from BYK Chemie)
in Propylene Glycol Monomethyl ether acetate 2.76
10% DiButyl Tin Dilaurate (DBTDL) in Butyl Acetate 1.38
Butyl Acetate 50
Component B
Tolonate HDT-LV~ (Isocyanurate trimer of
hexamethylene diisocyanate from Rhone-Poulenc) 361.06
Components (i) and (B) are mixed, the clear is then thinned to a Zahn
#2 viscosity of 30 seconds with butyl acetate, The clear is spray-applied over
a
black solvent-borne basecoat which has already been baked for 30 minutes at
130°C (265°F). The coating is cured for 30 minutes at
141°C (285°F). This
coating exhibits excellent cure, hardness, and appearance.
Example 2
Oligomeric Epoxy/Oligomeric Hydroxyl/Isocyanate clear - bake
system
Components li) and (ii)
Diglycidyl ester of 1,2 cyclohexane dicarboxylicI02.b
acid
Tetra Hydroxyl functional oligomer (from Procedure141.71
#1)
Tinuvin~384 (LIV Screener from Ciba-Geigy) 10.82
Tinuvin~292 (Hindered Amine Light Stabilizer 8.12
from Ciba-Geigy)
10% BYK-301~ (flow additive from BYK Chemie)
in Propylene Glycol Monomethyl ether acetate 2.16
10% DiButyl Tin Dilaurate in Butyl Acetate 1.35
Butyl Acetate 67
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Component (B)
Tolonate HDT-LV~ (Isocyanurate trimer of
hexamethylene diisocyanate from Rhone-Poulenc) 335.92
The components are mixed, the clear is then thinned to a Zahn #2
viscosity of 30 seconds with butyl acetate. The clear is spray-applied over a
black
water-borne basecoat which has already received a warm air flash of 5 minutes
at
82°C (180°F). The coating is cured for 30 minutes at
141°C (285°F). This
coating exhibits excellent cure, hardness, and appearance.
Exam",ple 3
Oligomeric Epoxy/Aldimine/Isocyanate clear - bake system
Component (i)
ERL 4299 (cycloaliphatic epoxy from Union Carbide) 101.5
Desmophen~ XP-7069 (Aldimine from Bayer) 101.5
Tinuvin~384 (LJV Screener from Ciba-Geigy) 10.64
Tinuvin~292 (Hindered Amine Light Stabilizer from
Ciba-Geigy) 7.98
10% BYK-301~ (flow additive from BYK Chemie)
in Propylene Glycol Monomethyl ether acetate 2.13
10% Octanoic acid in Propylene Glycol Monomethylester acetate 3.73
Butyl Acetate 92
Component fB)
Tolonate HDT~ (Isocyanurate trimer of
hexamethylene diisocyanate from Rhone-Poulenc) 340.04
Components (i) and (B) are mixed, the clear is then thinned to a Zahn
#2 viscosity of 30 seconds with butyl acetate. The clear is spray-applied over
a
black water-borne basecoat which has already received a warm air flash of 5
minutes at 85°C (180°F). The coating is cured for 30 minutes at
141°C (285°F).
This coating exhibits excellent cure, hardness, and appearance.
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Exam In a 4
Oligomeric Epoxy/Hydroxyl with Isocyanate Clearcoat - bake/ambient
system
ComQonent (i)
DC E 358~ Sorbitol ether epoxy/hydroxyl compound
from Dixie Chemical 12.86
10% BYK-301~ (flow additive from BYK Chemie)
in Propylene Glycol Monomethyl ether acetate 0.49
1% DiButyl Tin Dilaurate in Methyl Ethyl Ketone 2.45
Butyl Acetate 18.06
Component [B)
Tolonate HDT~ (Isocyanurate trimer of
hexamethylene diisocyanate from Rhone-Poulenc) 36.14
Components (i) and (B) are mixed. The clear is drawn down over
primed steel panels and TEDLAR~ to a thickness of about 2 mils. The coating is
cured for 30 minutes at 141°C (285°F). This coating exhibits
excellent cure,
hardness, mar resistance, and appearance. The percent gel fraction as measured
by
boiling the free film of this coating in acetone for 6 hours is 97.7%, which
is
excellent.
This same coating was cured at ambient conditions and found to give
good hardness, appearance and cure. The gel fraction on the air dried system
after
days of room temperature aging was 94.7%. The "surface dry time" as
measured by a BK dry time tester was 260 minutes.
25 Example 5
Oligomeric Epoxy/Isocyanate clearcoat - bake system
Component (i)
ERL - 4221~ (cycloaliphatic epoxy from Union 13.14
Carbide)
10% BYK-301~ (flow additive from BYK Chemie)
30 in Propylene Glycol Monomethyl ether acetate 0.49
i% DiButyl Tin Dilaurate in Methyl Ethyl Ketone 2.45
Butyl Acetate 18.06
Component fBl
Tolonate HDT~ (Isocyanurate trimer of
hexamethylene diisocyanate from Rhone-Poulenc)35.86
Components (i) and (B) are mixed. The clear is down over
drawn
primed steel panels and TEDLAR~ to a thickness The coating
of about 2 mils. is
cured for 30 minutes ai 141C (285F). This coating
exhibits excellent cure,
CA 02297808 2000-O1-24
WO 99105193 PCT/US98115230
hardness, and appearance. The gel fraction as measured by boiling the free
film of
this coating in acetone for 6 hours is 96.2%.
Examples 6 and 7
In redient Wei ht 6 Wei ht 7
IBMA/EHMfA/HEMA Resin 96.93 114.98
rocedure 2
XUGY-3581 6.58 6.95
MEK 43.46 26.38
TinuvinT"" 1130 UV screener 3.31 3.39
TinuvinT"" 123 hindered amine2.21 2.26
light
stabilizer
BYKT"" 306 flow additive 1.60 1.60
silane
10% DBTDL in MEK 0.44 0.45
acetic acid 1.00 1.00
Tolonate I~TT"' 32.16 30.79
lene 12.32 12.19
viscosi -initial Zahn #2 19 sec 28 sec
cu
viscosi - 4 hours 32 sec #2 Zahn 41 sec #3
Zahn
BK d time #22 1.00 hour 0.875 hour
BK d time #32 I.2S hours 1.50 hours
VOC 0.42 k iter 0.43 k iter
Tukon hardness o0 2.95 7.70
ISorbitol Ether Epoxy-hydroxyl from Dixie Chemical
z..,a s-Surface dry time using BK dry time tester
11
