CURING AGENTS FOR AQUEOUS EPOXY RESINS
Field of the Invention
The present invention relates to curing agents for aqueous epoxy
resins and to their use. More particularly, it relates to the reaction product
of polyamines with glycidyl ethers that are useful as curing agents for
aqueous epoxy resin emulsions, which cured resins are, in turn, useful as protective coatings.
Background of the Invention
Solvent based, epoxy resin curing agent systems have been known
for many years. However, these solvent systems often are quite flammable
and many exhibit disagreeable odors. In recent years, increasingly strict
regulation of environmental pollutants has lead to a limitation on the types
and amounts of organic solvents which can be used in epoxy resin curable systems. The first approach to these limitations on the solvent content of
coating systems was simply to employ a surfactant and emulsify or disperse existing solvent-based polymeric systems in water. Examples of such
systems include U.S. Patent No. 3,301 ,804 which discloses the use of the
reaction product of boric acid, an alkylene glycol, and a beta-dialkyl-
substituted aminoalkanol as an emulisfier, U.S. Patent No. 3,634,348
which discloses the use of a phosphate ester as an emulsifying agent, and
U.S. Patent No. 3,249,412 which discloses the use of a combination of a cationic emulsifying agent, selected from the group consisting of
imidazolines and amides, and a non-ionic emulsifying agent.
However, the cured products which result from these emulsions or
dispersions may exhibit poor properties when compared to prior art
solvent-based systems. In particular, the chemical and water resistance of
such systems may be lower because of the high levels of surfactant which
were needed. U.S. Patent No.4, 166,900 discloses cathodic electrodeposition resins
prepared based upon polyepoxides, polyamines and monoepoxides.
Polyepoxide resins are adducted with polyamines which are further reacted
with a monoepoxide or a monocarboxylic acid. It is disclosed that the
resinous adducts are water soluble or water dispersible when salted with an
acid. It is also stated that the resin solutions or dispersions are particularly
useful in cathodic electrodeposition processes for prime coating metal
objects.
U.S. Patent No. 4,246,148 discloses a two component industrial
maintenance coating. The first component is a polyamine terminated epoxy
resin which is end capped with a monoepoxide, at least 25 mole percent of the monoepoxide being an aliphatic monoepoxide. The second component
is a low molecular weight polyepoxide crosslinker. It is disclosed that the
adduct can be dissolved or dispersed in water when salted with an acid. The
polyepoxide crosslinker can then be microemulsified in the system. When
coated on a substrate, the two component mixture is said to cure at room
temperature producing coatings having a balance of chemical and physical
properties.
U. S. Patent No. 4, 608,405 discloses an ambient temperature curing
agent used to cure epoxide resins. The curing agent preferably is prepared
by coreacting under liquid advancement conditions, a diglycidyl ether of a dihydricphenol, a diglycidyl ether of an aliphatic dihydroxy polyether and a
dihydricphenol to produce a product having an average weight per epoxide
(WPE) of about 400 to about 1300. Substantially all of the epoxy groups which remain in the advanced product are then reacted with a polyamine
and at least each primary amine group of the polyamine/diepoxide reaction
product is further reacted with a monoepoxide or a monocarboxylic acid. It
is stated that these curing agents may be salted with a volatile acid and
employed in aqueous systems to provide coatings having superior cured
states film properties. It is also stated that, while the preparations of these
curing agents by the liquid advancement process is preferred, it is also
possible to prepare similar curing agents by starting with the corresponding
dihydric phenol and aliphatic dihydroxy polyether and epoxidizing this
mixture using well known epoxidization techniques.
Summary of the Invention
This invention relates to epoxy curing agents comprising the reaction
product of reactants consisting essentially of:
an alkylene polyamine having less than about 12 carbon atoms
(preferably a member selected from the group consisting of lower alkylene
diamines and lower polyalkylene polyamines, said member having from 2 to
8 carbon atoms and, more preferably, only straight-chain alkylene groups),
an aromatic mono-glycidyl ether having less than about 18 carbon
atoms (preferably selected from the group consisting of mono-alkylphenyl
glycidyl ethers and di-alkyl phenyl glycidyl ethers having from 9 to 13 carbon atoms), and
a diglycidyl ether of an aromatic diol having an average degree of
oligomerization of less than about 3.5 (preferably less than about 1.5, and
preferably derived from an alkyl bis-phenol, e.g. bisphenol A), wherein:
the ratio of primary amine equivalents of said alkylene polyamine to
the total epoxide equivalents of said aromatic glycidyl ether and said
diglycidyl ether of an aromatic diol are not less than essentially one, and
the ratio of epoxide equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is greater
than one (preferably greater than 1 .5, more preferably from about 2:1 to
about 6:1 , and most preferably from about 3:1 to 5:1 ). In preferred
embodiments, the alkylene polyamine is not pre-reacted with the diglycidyl
ether of an aromatic diol and, thus, said ratio of epoxide equivalents of said
aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is at no time during the entire course of the reaction, less
than the final product ratio of epoxide equivalents of said aromatic mono- glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic
diol. (By "final product ratio" is meant the ratio of all epoxide equivalents
of said aromatic mono-glycidyl. ether added over the entire course of the
reaction to all epoxide equivalents of said diglycidyl ether of an aromatic diol
added over the entire course of the reaction.) The maintenance of such a
ratio can accomplished by co-addition of proportionally adjusted amounts
said aromatic mono-glycidyl ether and said diglycidyl ether of an aromatic
diol (which will maintain the final product ratio essentially throughout said
reaction) or by pre-reacting the mono-glycidyl ether with the alkylene
polyamine (which will maintain an even greater ratio than the final product
ratio for most of the course of the reaction).
This invention also relates to a first group of preferred embodiments
within the broad scope set forth above wherein the alkylene polyamine is a
polyalkylene polyamine and the ratio of primary amine equivalents of said
alkylene polyamine to the total epoxide equivalents of said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol is essentially one, i.e. the
molar equivalents of primary amine groups of said polyalkylene polyamine
is essentially equal to the molar equivalents of glycidyl groups (e.g. a ratio
of from about 0.85: 1 to about 1 .05: 1 , preferably from about 0.90: 1 to
about 0.95:1 ).
This invention further relates to a second group of preferred embodiments within the broad scope set forth above, wherein the alkylene
polyamine is a mono-alkylene polyamine and the ratio of primary amine
equivalents of said alkylene polyamine to the total epoxide equivalents of
said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol is
greater than essentially one, i.e. the molar equivalents of primary amine
groups of said polyalkylene polyamine are essentially in excess of the molar
equivalents of glycidyl groups (e.g. a ratio of from about 1.05:1 to 2.0:1 ,
preferably from about 1.1 :1 to about 1 .75: 1 , more preferably from about
1.2: 1 to about 1.5:1 ).
This invention also relates to a third group of preferred embodiments
wherein said alkylene polyamine is comprised of a major amount on a molar
basis of a mono-alkylene polyamine and a minor amount on a molar basis of a polyalkylene polyamine (preferably in a molar ratio of from about 6: 1 to
about 2.5:1 , more preferably from about 5: 1 to about 3:1 ).
The reaction product is preferably employed as a curing agent for an
aqueous epoxy resin in a two component coating system wherein said
curing agent, essentially free of acids, is mixed with an aqueous epoxy resin
emulsion and then the resulting mixture is applied as a continuous coating
to a rigid substrate.
Detailed Description of the Invention
The curing agents of this invention are prepared from three major reaction components. The first component is an alkylene polyamine, the
second component is an aromatic glycidyl ether, and the third component
is diglycidyl ether of an aromatic diol. The nature of these components will
be addressed in turn below.
The alkylene polyamines useful in this invention can be characterized
as lower alkylene polyamines and lower polyalkylene polyamines. These
materials are commercially available or can be prepared by conventional
preparative techniques. These contain at least 2 amine nitrogen atoms per
molecule, at least 3 amine hydrogen atoms per molecule and no other
groups which are reactive with epoxide. Useful polyamines typically contain
about 2 to about 6 amine nitrogen atoms per molecule, 3 to about 8 amine
hydrogen atoms, and 2 to about 12 carbon atoms. Mixtures of amines can
also be used.
Examples of such amines are the alkylene polyamines ethylene
diamine, 1 ,2-propylene diamine, 1 ,3-propylene diamine, 1 ,2-butylene
diamine, 1 ,3-butylene diamine, 1 ,4-butylene diamine, 1 ,5-pentylenediamine,
1 ,6-hexylene diamine, 1 ,7-heptylene diamine, 1 ,10-decylene diamine, and
the like. Preferred amines for use in this invention are polyamines of the formula H2N-R(-NH-R)n-NH2 wherein n is 0 to 4 and R is an alkylene group
containing 2 to 8 carbon atoms, provided the total carbon atoms do not
exceed 12. Examples of the preferred mono-alkylene polyamines include
1 ,4-butylene diamine (tetramethylene diamine), 1 ,6-hexylene diamine
(hexamethylene diamine), and 1 ,8-octylene diamine (octamethylene
diamine) . The polyalkylene polyamines have at least one secondary amine
group. Examples of polyalkylene polyamines include diethylene triamine,
triethyiene tetramine, tetraethylene pentamine, pentaethylene hexamine,
dipropylene triamine, tributylene tetramine, trimethylhexamethylene diamine,
hexamethylene triamine and the like. The more preferred polyalkylene
polyamines are the polyethylene polyamines with the most preferred being
triethyiene tetramine and diethylene triamine.
Cyclic diamines can also be included in the diamine component,
preferably, however only in minor amounts, e.g. at less than 10%, and
preferably less than 5%, of the primary amine equivalents. Examples of
cyclic diamines include 1 ,4-diaminocyclohexane, 1 ,2-diaminocyclohexane,
o, m and p-phenylene diamine, 4,4'-methylene dianiline, meta-xylylene
diamine, and isophorone diamine.
In certain embodiments of the invention, the amine component is
comprised of a major amount on a molar basis of a mono-alkylene polyamine
and a minor amount on a molar basis of a polyalkylene polyamine (preferably
in a molar ratio of from about 6:1 to about 2.5:1 , more preferably from
about 5:1 to about 3: 1 ). It has been found that the use of both a mono-
alkylene polyamine and a polyalkylene polyamine has certain advantages
over the use of a mono-alkylene polyamine alone. One important advantage
is that the polyalkylene polyamine appears to prevent precipitation of the
curing agent that can occur upon storage. Without wishing to be bound by
any theory, unless expressly noted otherwise, it is thought that the
molecular structure of a mono-alkylene polyamine, such as hexamethylene
diamine, may allow the molecular species of curing agent prepared
therefrom to associate in a manner that allows the curing agent to crystallize
or otherwise precipitate. The use of an amount of a polyalkylene polyamine in an amount sufficient to inhibit such precipitation (e.g. a molar ratio of
mono-alkylene polyamine to polyalkylene polyamine of less than about 4:1 )
thus allows one of ordinary skill to extend the shelf life of the curing agent,
if so desired.
The polyepoxide materials useful in this invention are glycidyl
polyethers of dihydric phenols and contain, on average, more than one, but
not more than two 1,2-epoxide groups per molecule. Such polyepoxide
materials are derived from an epihalohydrin and a dihydric phenol and have
an epoxide equivalent weight of about 100 to about 4000, preferably from
about 125 to about 525, and more preferably from about 150 to about 350. Examples of epihalohydrins are epichlorohydrin, epibromohydrin and
epiiodohydrin with epichlorohydrin being preferred. Dihydric phenols are
exemplified by resorcinol, hydroquinone, p,p'-dihydroxydiphenylpropane (or
Bisphenol A as it is commonly called), p,p'-dihydroxybenzophenone,
p,p'-dihyd roxydipheny I, p,p'-dihydroxy pheny I ethane,
bis(2-hydroxynaphthyl)methane, 1,5-dihydroxynaphthaleneandthe like with
Bisphenol A being preferred.
These polyepoxide materials are well known in the art and are made in desired molecular weights by reacting the epihalohydrin and the dihydric
phenol in various ratios or by reacting a dihydric phenol with a lower
molecular weight polyepoxide material. Preferred polyepoxide materials are
glycidyl polyethers of Bisphenol A having epoxide equivalent weights of
about 150 to about 525 and, thus, have from just greater than 1.0 (e.g.
from about 1 .1 ) to just less than 3.5 (e.g. up to about 3.4) dihydric phenol groups per polyether molecule, and more preferably have epoxide equivalent
weights of less than 400.
The third component is an aromatic mono-glycidyl ether, i.e., a
compound having at least one aromatic ring having attached thereto an
glycidyl functional group and no other reactive functional groups.
Representative examples of aromatic mono-glycidyl ethers include the
monoglycidyl ethers of monohydric aromatic alcohols such as phenol and
naphthanol, mono- or dialkyl-substituted monoglycidyl ethers of monohydric aromatic alcohols, said alkyl groups having from about 1 to about 4 carbon
atoms, such as the monoglycidyl ether of o-cresol, m-cresol, p-cresol, o- ethyl-phenol, m-ethyl-phenol, p-ethyl-phenol, o-(n-propyl)-phenol, m-(n-
propyD-phenol, p-(n-propyl)-phenol, o-isopropyl-phenol, m-isopropyl-phenol,
p-isopropyl-phenol, o-(n-butyl)-phenol, m-(n-butyl)-phenol, p-(n-butyl)-
phenol, m-(t-butyl)-phenol, p-(t-butyl)-phenol, 2,4-dimethyl-phenol, 3,5-
dimethyl-phenol, 3-methyl-5-ethyl-phenol, 2-methyl-4-(n-propyl)-phenol, or
2-methyl-4-(t-butyl)-phenol. The preferred aromatic mono-glycidyl ether is o-cresyi glycidyl ether.
The ratios of the reactants are selected so that the primary amine
equivalents of said alkylene polyamine to the total epoxide equivalents of
said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol are
essentially equal. This means that, on average, all of the primary amine
groups will be converted to secondary amines (i.e. a group still having a
reactive secondary amine hydrogen, albeit less reactive than a primary amine
hydrogen). Preferably less than 10% and more preferably less than 5% of primary amine hydrogens will remain in the curing agent.
As discussed above, in preferred embodiments, the alkylene
polyamine is not pre-reacted with the diglycidyl ether of an aromatic diol
and, thus, said ratio of epoxide equivalents of said aromatic mono-glycidyl
ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is at no time during the entire course of the reaction, no less than the final
product ratio of epoxide equivalents of said aromatic mono-glycidyl ether to
epoxide equivalents of said diglycidyl ether of an aromatic diol. (By "final
product ratio" is meant the ratio of all epoxide equivalents of said aromatic mono-glycidyl ether added over the entire course of the reaction to all epoxide equivalents of said diglycidyl ether of an aromatic diol added over
the entire course of the reaction.) The maintenance of such a ratio can
accomplished by co-addition of proportionally adjusted amounts said
aromatic mono-glycidyl ether and said diglycidyl ether of an aromatic diol
(which will maintain the final product ratio essentially throughout said reaction) or by pre-reacting the mono-glycidyl ether with the alkylene
polyamine (which will maintain an even greater ratio than the final product
ratio for most of the course of the reaction). Of course, because of the possibility of differing rates of reactivity with the alkylene polyamine, the
ratio of mono-glycidyl ether to aromatic diol may vary somewhat over time
in the reaction medium. Because the mono-glycidyl ether is present in the
reaction from the beginning of the reaction, however, the resulting reaction
product will have a relatively smaller degree of polymerization, for example,
as compared with the use of a mono-glycidyl ether solely as a capping agent for an adduct of a polyamine and a polyepoxide.
Moreover, the ratio of epoxide equivalents of said aromatic mono¬
glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic
diol is greater than 1 , preferably greater than 1.5, and more preferably from
about 2:1 to about 6:1 , and most preferably from about 3:1 to 5: 1 . Thus,
the reaction product will be comprised predominantly (e.g. greater than 60%
by weight) of species derived from the reaction of two mono-glycidyl ether
molecules with one alkylene polyamine and only a minor amount (e.g. less
than 35% by weight) of species derived from the reaction of one diglycidyl
ether of an aromatic diol with two alkylene polyamine molecules and two aromatic mono-glycidyl ether molecules. Further, because the secondary
amine hydrogen atoms of a polyalkylene polyamine are reactive, there is the possibility for some branching of the molecule, but use of a relatively high
ratio of mono-glycidyl ether to diglycidyl ether of an aromatic diol (optionally
along with a low reaction temperature) will reduce such a possibility
dramatically, such that the reaction product will be essentially free of
branched species.
While not wishing to exclude any other components unnecessarily, it
is noted that the use of glycidyl ethers of polyoxyalkylenes and/or volatile
acids to salt the curing agent are not needed in the curing agent and so
should be excluded. Further, it is believed that the selection of components
is so important to the performance of the curing agent that other
components which would affect the essential attributes of the curing agent,
or cured epoxy resins prepared therefrom, should be excluded. The skilled
artisan will, with the aid of the following description, be able to determine
whether a particular component in a particular amount will affect the
attributes of the curing agent in an essential manner, i.e. will prohibit its use
as a curing agent for an aqueous epoxy emulsion used to prepared a protective coating when cured.
The reaction medium is typically maintained at moderate temperatures
during the reaction. Such temperatures avoid degradative side reactions
which can affect the appearance (e.g. by excessive color formation) of the
reaction product. Typical temperatures that will be maintained during the reaction range from about 35 °C. to about 80°C, preferably from about
40°C to about 75 °C, for a time sufficient to bring the reaction to
completion, typically about 5 minutes to 3 hours. Lower temperatures may
be employed at the expense of increasing the reaction time. The reaction
medium is also typically treated to exclude oxygen to a practicable degree,
e.g. by blanketing and/or sparging the reaction zone with an inert gas, e.g.
dry nitrogen.
The product which results after the epoxide material has been reacted
with the polyamine is extremely viscous and it is preferred that an
oxygenated solvent be present in the reaction medium or added to the
reaction product to reduce its viscosity. The preferred solvents are the
glycol ethers such as the various lower alkyl ethers of ethylene and
propylene glycol. Typically, about 20 to about 50 percent by weight of an
alkoxy-alkanol, e.g. 2-propoxy ethanol, or another oxygenated solvent may
be used.
The second major component of the coating system is a water
dispersible (either alone or in the presence of a co-solvent) epoxy resin
having more than one terminal epoxide group. The epoxy resins suitable for use in the second component include the glycidyl polyethers of dihydric
phenols as well as epoxy novolac resins. The dihydric phenols employed to
prepare the epoxy resins are further described in U.S. Pat. No. 4,246,148.
It is particularly preferred to employ those glycidyl polyethers wherein the
dihydric phenol is bisphenol-A. Examples of suitable resins include those disclosed in U.S. Patent No. 4,315,044, the disclosure of which is
incorporated herein by reference. Particularly preferred epoxy resins are
those disclosed in U.S. Serial No. (Case No. M 5308 FPD/CO), filed
concurrently herewith, the disclosure of which is incorporated by reference.
The maximum molecular weight of the epoxy resins is limited by the fact that the amount of epoxy resin employed in the second component is
usually selected to achieve stoichiometric equivalence of epoxy groups with
the amine hydrogen equivalents of the curing agent. Consequently, as the
molecular weight of the epoxy resin increases, thereby increasing the
epoxide equivalent weight, more of the epoxy resin is required to satisfy the
stoichiometric requirement. However, the use of large amounts particularly
of higher molecular weight epoxy resins is not preferred because they are
water insoluble and become increasingly more difficult to microemulsify or
disperse as the amount thereof is increased.
In view of the above, it is preferred to characterize the epoxy resin
also in terms of its epoxide equivalent weight. Thus, the epoxide equivalent
weight (WPE) of the glycidyl polyethers of dihydric phenols is not greater
than about 1000, preferably from about 180 to about 700.
As described above, the amount of epoxy resin which is present in
the coating composition is preferably sufficient to achieve substantially
stoichiometric equivalence with the reactive amino hydrogens on the end
capped epoxy-amine adduct. In general, it is preferred to employ the epoxy
resin in an amount sufficient to achieve an epoxy to reactive amine
hydrogen equivalent weight ratio of from about 0.5: 1 .0 to about 1 .5:1 .0,
and, preferably, from about 0.8:1.0 to about 1.2:1.0.
The epoxy resins which are useful herein, may be either liquids or
solids, so long as the resin is in the form of a stable aqueous dispersion.
Preferred aqueous epoxy resins are disclosed in U.S. patent application Serial No. (Case No. M5308), filed on even date herewith, entitled "Self-Dispersing
Curable Epoxy Resins, Dispersions Made Therewith, And Coating
Compositions Made Therefrom", by John G. Papalos et al., the disclosure
of which is incorporated herein by reference.
When the epoxy resin and the curing agent are mixed, the resulting
coating composition exhibits a useful pot life at room temperature, e.g. from
about 2 hours to about 12 hours, and more typically from about 3 hours to
about 8 hours. The pot life of the coating composition is herein defined to
be the elapsed time from mixing the components together until the resulting
composition is no longer suitable, with normal thinning, for application by
spray, brush, or roll coating techniques to a substrate. The suitability for
application by common techniques can be expressed in terms of the
viscosity of the coating composition. Thus, the pot life of unpigmented
coatings can be characterized as the elapsed time from mixing the two
components to the time when the viscosity of the coating compositions
drops below A1 or increases above Z6 as determined by the Gardner-Holdt
method. For pigmented coatings, useful applications viscosities are between
50 and 140 Kreb Units (K.U.) as determined with a Stormer viscometer.
Coatings based on the compositions described herein can be
formulated into easily handled two-package systems which blend together
as easily as their solvent based counterparts. Application by brush, spray
and roller-coating are typically free of bubbling and other film imperfections.
The coating systems described herein should also exhibit good
adhesion to such widely varied substrates as galvanized metal, cold rolled steel (untreated and phosphate treated), hot rolled steel, and aluminum.
Flash rusting is not a problem over untreated steel and, therefore, there is
no need for special additives as in some water reducible epoxy systems.
Adhesion should also be excellent to three and four-year old alkyd and epoxy
ester enamel films. Such systems may therefore be employed for repaint
purposes in food processing plants and dairies and can also be used as
adhesive compositions per se.
As pointed out above, a major advantage of the coating compositions
of the instant invention is that they are useful in preparing solvent and
chemically resistant coating compositions from aqueous based systems.
These systems do not exhibit the traditional solvent related problems shown by solvent based systems and accordingly are preferred in end-use
applications where nonpolluting or nonflammable coatings systems are
necessary. In addition, the cured state properties of compounds made from
the curing agents disclosed herein are generally equivalent or superior to the
properties of compounds prepared from prior art solvent based systems.
The following examples will serve to further illustrate the invention,
but should not be construed to limit the invention, unless expressly set forth
in the appended claims. All parts, percentages, and ratios are by weight
unless otherwise indicated in context.
EXAMPLES
EXAMPLES 1-4
Curing agents were prepared by charging to a flask the amine
reactants diethylenetriamine (DETA), 1 ,2-diamino-cyclohexane (DACH),
hexamethylenediamine (HMDA) in the molar amounts set forth Table 1 ,
below, along with the solvent 2-propoxyethanol, with mixing and under dry
nitrogen gas. The contents were heated to 40°C. The epoxide reactants
cresyl glycidyl ether (CGE) and a bisphenol A diglycidyl ether homopolymer
having an average of 1.15 bisphenol A groups per molecule and available from the Dow Chemical Co. as DER 331 , were pre-mixed in the molar
amounts shown in Table 1 and the pre-mixture was added dropwise to the
charge flask to maintain the temperature within the flask to less than 70°C.
Once the addition of epoxide reactants was complete, the flask was held at
50°C for about 2 hours.
Table 1 Curing Agent Composition
Example DETA DAGH HMDA CGE DER 331 (moles) (moles) (moles) (moles) (moles)
1 1.00 0.04 0.04 1.72 0.22
2 1.00 0.04 0.04 1.30 0.43
3 0.17 0.03 0.80 0.96 0.12
4 0.17 0.03 0.80 1.20 0.15
Example 5
The curing agent of Example 1 was used to cure an epoxy resin from
an aqueous dispersion as follows. The epoxy resin dispersion of Example 3 of U.S. patent application Serial No. (Case M5308 FPD/CO), referred to
above, in an amount of 200 parts by weight was ground with 123.7 parts
by weight of titanium dioxide pigment (DuPont R-960) along with 17 parts
by weight of oxygenated solvent (Ektasolve EP), and 103.9 parts by weight
of water. To this grind paste was added 44.7 parts by weight of the curing
agent of Example 1 , above. The resulting white epoxy paint thus had a ratio
of epoxy equivalents to active amine hydrogen equivalents of 1 :1 , a pigment
to binder ratio of 0.85:1 , and 55% non-volatiles (by calculation). This
coating composition was applied to cold rolled steel at a thickness of 56
micrometers to 62 micrometers. The coating was cured at room temperature for 14 days and then evaluated. The cured coating exhibited
a Crosshatch adhesion of 100% (5B), a pencil hardness of HB, Impact
Direct/Reverse strength of 160/120 in-lbs., passed the conical mandrel test,
survived 500 methyl ethyl ketone double rubs, and exhibited no salt spray corrosion until about 500 hours. This performance was superior to a
commercial water-borne epoxy resin (Epi-Rez WJ-5522 cured with CMD J60-8290, both available from. Hi-Tek), but still inferior in a number of
respects to a solvent-borne epoxy resin DER 671X75, available from Dow
Chemical Co. cured with Versamid 115, available from Henkel Corporation,
Ambler, PA).