Note: Descriptions are shown in the official language in which they were submitted.
CA 02270731 1999-04-29
NOVEL EPOXY - AMINE COATING COMPOSTTIONS
BACKGROUND OF THE INVENTION
to In the current environment of regulations intended to reduce the amount of
volatile
organic compounds (or VOC) that are released into the atmosphere on
application of coatings, it
is very difficult to formulate coating compositions that meet the regulatory
limits without some
kind of crosslinking mechanism that takes place after application. In order to
achieve a suitable
spray application viscosity (20-30 seconds #4 Ford cup @20°C) as VOC
regulations have
15 mandated higher application non-volatiles it has been necessary to use
resins with lower molecular
weights and generally lower Tg. Both of these changes generally have the
effect of lengthening
the dry time of the applied coating since the number of crosslink reactions
required to achieve a
"dry to handle" condition increases significantly. Epoxy/amine coatings
systems are well known
in the art as a class of coatings that is useful as a primer. A low VOC
epoxy/amine system may be
2o achieved through the use of low molecular weight epoxy resins and
optionally the use of low
molecular weight polyamines, polyketimines or polyaldimines. Health concerns
are raised when
considering the use of a low molecular weight epoxy resin, which may,
depending on the
application, preclude its use. The present invention effectively reduces the
VOC of epoxy/amine
coating systems without resorting to use of low molecular weight epoxides.
25 This invention also describes a method to reduce the volatile organic
content (VOC) of a
paint composition by increasing the solids of a paint composition without
adversely affecting the
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sprayable viscosity of the paint and also without significantly decreasing the
durability or
performance of the final paint film so produced.
SUMMARY OF THE INVENTION
Accordingly, the invention described herein relates to a low VOC epoxy based
coating
utilizing the following essential components:
1. An epoxy functional resin component where the average epoxide functionality
is
>1.
2. An aliphatic amine or aliphatic blocked amine fianctional component where
the
1o amine functionality is >1. This includes polyamidoamines, polyamines,
ketimines
and aldimines.
3. An acetoacetonate functional oligomer where the molecular weight is < 1000
and
the acetoacetonate functionality is > 1.
4. Optionally other components that typically constitute a complete coatings
system
such as pigments, catalysts, additives, plasticizers, etc.
This is typically a three-package system however, with modification, it can
become a two-package
2o system.
The low molecular weight polyacetoacetonate component can be prepared by
various methods,
the preferred method being transesterification of a polyol, such as ethylene
glycol or preferably
glycerine, with t-butylacetoacetonate, and then distilling offt-butanol as a
by-product.
DETAILED DESCRIPTION
Accordingly, the invention described herein relates to a low VOC epoxy based
coating
utilizing the following essential components:
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An epoxy functional resin component where the average epoxide functionality is
>1.
2. An aliphatic amine or aliphatic blocked amine functional component where
the
amine functionality is > 1. This includes polyamidoamines, polyamines,
ketimines
and aldimines.
An acetoacetonate functional oligomer where the molecular weight is < 1000 and
the acetoacetonate functionality is > I.
4. Optionally other components that typically constitute a complete coatings
system
such as pigments, catalysts, additives, plasticizers, etc.
This is typically a three-package system however, with modification, it can
become a two-package
system.
The low molecular weight polyacetoacetonate component can be prepared by
various methods,
the preferred method being transesterification of a polyol, such as ethylene
glycol or preferably
glycerine, with t-butylacetoacetonate, and then distilling off t-butanol as a
by-product.
Finding utility in the instant coatings are flow and rheology modifying agents
which
2o include but are not limited to synthetic amorphous hydrophobic silica such
as Degussa Aerosil
8972, synthetic amorphous hydrophilic silica Degussa Aerosil 200, organo
clays, polyethylene
wax dispersions, polypropylene wax dispersions, polyamid wax dispersions,
ethylene vinyl acetate
wax dispersions. Agents such as Byk Anti-terra 202, Byk Anti-terra 204, Byk
Anti-terra V, Byk
W-960, Byk R-405, Byk-P104, Byk P-104s; Troy Chemical Troythix Antisag 4, Troy
Chemical
Troythix Antisettle; Raybo Chemical Raybo 6, Raybo Chemical Raybo 94, and Tego
Chemie ZFS
460.
Also finding utility are pigment wetting and dispersing aids which include but
are not
limited to ICI Solsperse hyperdispersants such as Solsperse 5000, Solsperse
12000, Solsperse
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22000 and Solsperse 24000; Troy Chemical Troysol CDI, Troy Chemical Troysol
CD2 and Troy
Chemical Troysol 98C; Daniel Products DispersAyd 9100; Raybo Chemical Raybo
63; Byk Anti-
terra U, Byk Anti terra 202, Byk W-960, Byk p 104 Disperbyk 160, Disperbyk
162, Disperbyk
163; Nuodex Nuosperse 657; Nuodex Nuosperse 700. Also finding utility in these
coatings are
ultraviolet light absorbers and stabilizers which include but are not limited
to Sandoz Chemicals
Sanduvor 3206, Sanduvor VSU, Sanduvor 3050; Ciba Geigy Corp. Tinuvin 123,
Tinuvin 292,
Tinuvin 328, Tinuvin 440, Tinuvin 900, Tinuvin 1130.
Also finding utility in these coatings are various types pigments common to
the art which
include but are not limited to titanium dioxide, graphite, carbon black, zinc
oxide, cadmium
Io sulfide, chromium oxide, zinc sulfide, zinc chromate, strontium chromate,
barium chromate, lead
chromate, lead cyanamide, lead silico chromate, chromium oxide, zinc sulfide,
yellow nickel
titanium, yellow chromium titanium, red iron oxide, transparent red iron
oxide, yellow iron
oxides, transparent yellow oxide, black iron oxide, naphthol reds and browns,
anthraquinones,
dioxazine violet, isoindoline yellows, arylide yellow and oranges, ultramarine
blue, phthalocyanine
complexes, amaranth, quinacridones, halogenated thioindigo pigments, extender
pigments such as
magnesium silicate, aluminum silicate, calcium silicate, calcium carbonate,
fumed silica, barium
sulfate.
The coating composition can be applied using conventional spray equipment or
high
volume pressure spray equipment resulting in a high quality finish. Other
modes of application are
2o roller coating, brushing, sprinkling, flow coating, dipping, electrostatic
spraying, or
electrophoresis. Exemplary metal substrates include such things as steel,
aluminum, copper, zinc,
magnesium and alloys thereof. Exemplary non-metallic substrates include such
things as the rigid
CA 02270731 1999-04-29
and non-rigid plastics common to the art. The components of the compositions
can be varied to
and non-rigid plastics common to the art. The components of the compositions
can be varied to
suit the temperature tolerance of the substrate material. For example, the
components can be
constituted for ambient or room temperature drying (e.g. less than
100°F), force drying or low
temperature baking (e.g. 100°F. - 180°F.), or high temperature
baking (e.g. over 180°F.). The
coatings may be formulated to meet the requirements of the equipment intended
for use during
application.
The pigments can be introduced by first forming a mill base with the resin
utilized in the
composition or with other compatible polymers by conventional techniques, such
as sand-
to grinding, ball-milling attritor grinding, two roll milling and the like, to
disperse the pigments. The
mill base is then blended with other film forming constituents as shown in the
examples which
follow:
Coating compositions described by the present invention find utility in
applications of
ambient or room temperature drying (e.g. less than 100°F), force drying
or low temperature
baking (e.g. 100° F. - 180° F.), or high temperature baking
(e.g. over 180° F.). The coating cure
process for the present invention may also be accelerated by the utilization
of radiant heating or
Infra red emitting devices known to the art.
The following examples are intended to illustrate the invention. All
quantities are shown
on a weight bases unless otherwise indicated.
Example 1
Preparation of Acetoacetate-Functional Oligomer GDAA) from Eth~rlene Glycol
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A 2-liter, 3-necked flask was fitted with a heating mantle, stirrer,
thermocouple, NZ inlet,
distillation head with thermometer, condenser and receiver. The flask was
charged with 173.9
gams of ethylene glycol and 930.2 gams of tert-butyl acetoacetate. It was
heated slowly to
140°C under a N2 gas purge. When the temperature reached about
140°C, distillation of
byproduct t-butanol was initiated at a head temperature of about 90°C.
The reaction temperature
was slowly increased in stages to 180°C, at which point 98% of the
calculated amount of t-
butanol byproduct had been removed. Yield of ethylene glycol diacetoacetate
(EGDAA) was
680 grams. The product was a light-colored liquid with 18 cps Brookfield
viscosity and having
molecular weight of 230 and an acetoacetate equivalent weight of 115.1.
Example 2
Preparation of Acetoacetate-Functional Oligomer from Glycerol (GTAA~
Into a 2-liter, 3-necked flask set up as described in Example lwas charged
138.1 gams of
glycerol and 759.4 gams of t-butylacetoac;etate. Under a nitrogen flow the
flask was heated in
stages to 175° C. Distillation of byproduct t-butanol began at a head
temperature of 95°C and
was completed when about 97% of the theoretical amount of t-butanol was
collected. Yield of
approximately 98% pure glycerol triacetoacetate (GTAA) was 537 gams. The
product was a
light-colored mobile liquid with a viscosity of 85 - 90 cps (Brookfield), a
molecular weight of
approximately 344 and an acetoacetate equivalent weight of 114.8.
2o Low molecular weight acetoacetyl derivatives of pentaerythritol,
trimethylol propane, Tone~
301 and several other low molecular weight polyols were made by similar
procedures. All were
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low-viscosity light-colored liquids with molecular weights below 1000 and are
suitable for use in
low VOC coatings of the type described herein.
Example 3
Low VOC Coatings from Epoxy Resins, Low Molecular Weight Acetoacetates.
Aldimines and
Other Ingredients
Primer coating compositions were formulated from a resin base, DE15, which is
a standard BASF
epoxy-resin primer base that also contains pigment and other additives in
addition to the epoxy
resin; AEP (aminoethylpiperazine), which is a standard epoxy curing agent (the
control used
PA16, a polyamidoamine curing agent) ; and PR70, which is a standard BASF
toluene/butyl
acetate reducer. The experimental coatings were modified with varying amounts
of low
molecular weight acetoacetate reactive diluents and an aldehyde blocked amine
(aldimine) curing
2 0 agent for the acetoacetate. In the experimental resins some of the PR70
reducer was replaced by
methyl ethyl ketone, which stabilizes the aldimine hardener. The table below
shows a
representative sample of such coatings compared with an epoxy primer control
that does not
incorporate the acetoacetate-blocked amine reactive reducer modifcation. The
table also shows
VOC results and other important system properties.
Ingredient Coating A Exper. Coating Exper. Coating Exper. Coating
(grams) (control) B C D
DE15 252.0 252.0 252.0 252.0
GTAA 0 36.0 22.5 27.0
EGDAA 0 0 10.0 11.4
3 0 PR70 33.0 18.0 18.0 15.0
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MEK* 0 19.5 19.5 19.5
PA16 hardener 67.0 0 0 0
AEP 0 4.5 4.8 4.8
CE4072 Aldimine 0 44.8 17.5 23.6
*Methyl ethyl
ketone
Properties:
Visc. (#4Cup) 17.5 sec 18 sec l9.Ssec 19.5sec
Wt.(lb. per gal.) 11.1 11.1 11.6 11.6
VOC(Ib. per gal) 4.7 3.1 3.48 3.24
Pot life for the control and the experimental coatings was at least one hour
for each one. All
coatings were drawn down over bare steel plates or sprayed on to these plates
and compared for
dust-free and tack-free times. The control and experimental compositions were
dust-free in less
than 30 minutes and tack-free in less than two hours. As primers, all systems
could be
overcoated with white basecoats in 30 minutes and demonstrated enough holdout
of the basecoat
to prevent any dieback of the white basecoats.
2o Note that all the experimental primer coatings have at least a 25% lower
volatile organic
content (VOC) than the control, while retaining adequate performance as a
primer coating..
The low molecular weight (< 1000) of these acetoacetates results in the low
viscosity properties
that allow for incorporation as reactive diluents or reducers. Higher
molecular weight
2s acetoacetate-functional compounds would not have given the low viscosities
that would permit
practical use as modifiers for epoxy coating systems.
s
