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QPATER-DISPERSIBhE POLYMgR AND
COATING COMPOSITION CONTAINING THE SAME
~ ~~E,T~p OF T8E INYBNTION
The present invention relates to water-
s dispersible polymers and to coating compositions for
metal substrates containing the water-dispersible
polymers. The coating composition comprises a water-
dispersible polymer, a fugitive base, a curing agent,
and a carrier comprising water and a volatile organic
solvent. The water-dispersible polymer is prepared
from: (a) an epoxy compound having about two epoxy
groups, (b) a linking compound having (i) conjugated
carbon-carbon double bonds or a carbon-carbon triple
bond and (a.i) a moiety capable of reacting with an
epoxy group, and (c) acrylic monomers, wherein the
epoxy portion (a) of the polymer is covalently linked
to the polymerized acrylic portion (c) by the linking
compound (b).
BACKGROUND OF THE INVHNTION
It is well known that an aqueous solution in
contact with an untreated metal substrate can result
a.n corrosion of the untreated metal substrate.
Therefore, a metal article, such as a metal container
fn_r a water-bated pr~d'.'~Ct, l ike a 'FE3E3d-~3r ~'8verage~
rendered corrosion resistant in order to retard or
eliminate interactions between the water-based product
and the metal article. Conventionally, corrosion
resistance is imparted to the metal article, or to a
metal substrate in general, by passivating the metal
substrate, or by coating the metal substrate with a
corrosion-inhibiting coating.
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Investigators continually have sought
improved coating compositions that reduce or eliminate
corrosion of a metal article and that do not adversely
affect an aqueous product packaged in the metal
article. For example, investigators have sought to
improve the imperviousness of the coating in order to
prevent corrosion-causing ions, oxygen molecules, and
water molecules from contacting and interacting with
a metal substrate. Imperviousness can be improved by
providing a thicker, more flexible and more adhesive
coating, but often, improving one particular advanta-
geous coating feature is achieved at the expense of
another advantageous coating feature.
In addition, practical considerations limit
the thickness, adhesive properties and flexibility of
a coating applied to a metal substrate. For example,
thick coatings are expensive, require a Longer cure
time, can be esthetically unpleasing, and can adverse
ly affect the process of stamping and molding the
coated metal substrate into a useful metal article.
Similarly, the coating should be sufficiently flexible
such that the continuity of the coating is not de-
stroyed during stamping and molding of the metal
substrate into the desired shape of the metal article.
Investigators also have sought coatings that
possess chemical resistance in addition to corrosion
inhibition. A useful coating for the interior of a
metal container must be able to withstand the solvat-
ing properties of a product packaged in the metal
container. If the coating does not possess sufficient
chemical resistance, components of the coating can be
extracted into the packaged product and adversely
affect the product. Even small amounts of extracted
coating components can adversely affect sensitive
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products, like beer, by imparting an off-taste to the
product.
Conventionally, organic solvent-based
coating compositions were used to provide cured
coatings having excellent chemical resistance. Such
solvent-based compositions include ingredients that
are inherently water insoluble, and thereby effective-
ly resist the solvating properties of water-based
products packaged in the metal container. However,
because of environmental and toxicological concerns,
and in order to comply with increasingly strict
governmental regulations, an increasing number of
coating compositions are water based. The water-based
coating compositions include ingredients that are
water soluble or water dispersible, and, therefore,
cured coatings resulting from water-based coating
compositions often are more susceptible to the solvat-
ing properties of water.
Epoxy-based coatings and polyvinyl chloride
based coatings have been used to coat the interior of
metal containers for foods and beverages because these
coatings exhibit an acceptable combination of adhesion
to a metal substrate, flexibility, chemical resis
tance, and corrosion inhibition. However, epoxy-based
coatings and polyvinyl chloride-based coatings have
serious disadvantages that investigators still are
attempting to overcome.
For example, coatings based on polyvinyl
chloride or related halide-containing vinyl polymers,
~ 30 like polyvinylidene chloride, possess the above-listed
advantageous properties of chemical resistance and
~ corrosion inhibition, and are economical. However,
curing a polyvinyl chloride or related halide-contain
ing vinyl polymer can generate toxic monomers, such as
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vinyl chloride, a known carcinogen. In addition, the
disposal of a halide-containing vinyl polymer, such as
by incineration, also can generate toxic monomers.
The generated vinyl chloride thereby poses a potential
danger to workers in metal can manufacturing plants,
in food processing and packaging plants, and at
disposal sites. Disposal of polyvinyl chloride and
related polymers also can produce carcinogenic dioxins
and environmentally harmful hydrochloric acid.
1.0 Government regulators, therefore, are acting to
eliminate the use of polyvinyl chloride-based coating
compositions that contact food, and thereby eliminate
the environmental and health concerns associated with
halide-containing vinyl polymers.
To overcome these environmental concerns,
epoxy-based coating compositions recently have been
used to coat the interior of food and beverage con-
tainers. However, epoxy-based coatings also possess
disadvantages. For example, epoxy-based coating
compositions are more expensive than polyvinyl chlo-
ride-based coating compositions.
Various patents disclose waterborne coating
compositions for metal cans. In general, prior
patents disclose coating compositions including water-
borne thermoset resins for use as can coatings. The
thermoset, resins can be formulated with a crosslinking
agent to provide crosslinked films during cure, as
demonstrated by the resistance of the cured coating to
the effects of organic solvents such as methyl ethyl
ketone. The cured thermoset resins often do not have
sufficient flexibility for use as can coatings.
Recently, waterborne phenoxy resins were
disclosed as useful in coatings for metal cans. These
waterborne phenoxy resins are high molecular weight
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thermoplastic resins that are difficult to process and
are too expensive for practical commercial use. In
addition, because these phenoxy resins are thermoplas-
tic resins, cured coatings derived therefrom are not
resistant to organic solvents, although the cured
coatings often provide sufficient barrier properties
to water-based compositions for use as can coatings.
Investigators, therefore, have sought a
waterborne coating composition for the interior of
food and beverage containers that retains the advanta-
geous properties of adhesion, flexibility, chemical
resistance and corrosion inhibition, and that is
economical and does not adversely affect the food and
beverages packaged in the container.
Investigators prefer a thermosetting coating
composition because such compositions are easier to
handle and provide better chemical resistance than
thermoplastic coating compositions. A thermosetting
coating composition also requires a crosslinking
agent, generally a phenolic resin, an aminoplast, or
a similar resin, in order to provide a cured coating
having a sufficient molecular weight.
Prior investigators have studied waterborne
epoxy resin-based compositions for application to
metal substrates. Many of these investigators sought
epoxy resin-based aqueous compositions that provide
a
sufficiently flexible cured coating such that the
coated metal substrate can be deformed without de-
stroying film continuity. Often, conventional epoxy
resins provide a rigid cured film thereby making it
difficult to impossible to coat the metal substrate
prior to deforming, i . a . , shaping, the metal substrate
into a metal article, like a metal can. Coating a
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metal substrate prior to shaping the metal substrate
is a standard industrial practice.
For example, Johnson et al. U.S. Patent No.
4,954,553 discloses an aqueous coating composition
comprising a carboxyl-bearing phenoxy resin and a
resin that is soft in comparison to the phenoxy resin,
like a polyester. The carboxyl-bearing phenoxy resin
is prepared by grafting ethylenically unsaturated
monomers to the phenoxy resin. The coating composi-
tion provides flexible cured coatings. Fan U.S.
Patent Nos. 4,355,122 and 4,374,875 disclose a water-
borne phenolic composition wherein an ethylenically
unsaturated monomer including a carboxyl group is
grafted onto a phenoxy resin by standard free radical
polymerization techniques, then the carboxyl groups
are neutralized by a base_
Chu et al. U.S. Patent No. 4,446,258 dis-
closes an aqueous coating composition comprising: (1)
the neutralized reaction product of an epoxy resin
with a preformed addition polymer containing carboxyl
groups, and (2) an acrylic or vinyl polymer, which is
prepared either in situ or added to the composition,
and which is different from the preformed addition
polymer.
Evans et al. U.S. Patent No. 4,212,781
discloses grafting an acrylic monomer or monomer blend
to an epoxy resin to provide a polymeric blend includ-
ing unreacted epoxy resin, an acrylic resin and a
graft polymer of the acrylic resin and epoxy resin.
Steinmetz U.S. Patent No. 4,302,373 discloses a
waterborne coating composition consisting essentially
of the neutralized reaction product of a modified
polyepoxide (e. g., an ester or ether) or a phenolic
and a carboxyl-functional polymer.
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Patel U.S. Patent No. 4,963,602 discloses
aqueous coating compositions including an epoxy resin,
an acrylic resin, a phenoxy resin, a novolac resin,
and a resol resin. Wu U.S. Patent Nos. 3,943,187 and
3,997,694 disclose an organic solvent-based coating
composition consisting essentially of a blend of an
acrylic polymer having hard and soft segments and an
epoxy resin. Salensky U.S. Patent No. 4,638,038
discloses modified phenoxy resins wherein anhydrides
or polycarboxylic acids are grafted onto a phenoxy
resin. Spencer U.S. Patent No. 5,296,525 discloses
(a) the reaction product of an epoxy resin with a
monomer having unsaturated groups, (b) wherein the
reaction product of (a) then is reacted with a pre-
IS formed carboxyl-functional polymer and a tertiary
amine, (c) followed by reacting the reaction product
of (b) with unsaturated monomers in an emulsion
polymerization.
Other patents that disclose epoxy resins
admixed with acrylic resins, or having acrylic resins
grafted thereon, include Matthews et al. U.S. Patent
No. 4,247,439; Evans et al. U.S. Patent No. 4,308,185;
Wu U.S. Patent No. 4,021,396; McCarty U.S. Patent No.
4,444,923; Brown et al. U.S. Patent No. 4,585,813; and
Ting et al. U.S. Patent No. 4,480,058.
Publications disclosing a water-based
coating compositions including an epoxy resin and an
acrylic resin include:
J_T.K_ Woo et al., "Synthesis and
Characterization of Water-Reducible Graft
Epoxy Copolymers," J. Coat. Tech., 54
(1982), pp. 41-55; and
R.N. Johnson et al., ~~Water-Borne
Phenoxy Resins Low VOC Coatings with Excel-
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lent Toughness, Flexibility and Adhesion,"
presented at the Water-Borne and Higher-
Solid Coatings Symposium, February 3-5, 1988
in New Orleans, LA.
The above-identified patents and publica-
tions disclose waterborne coating compositions com-
prising an epoxy resin and an acrylic resin. The
patents and publications do not disclose a waterborne
coating composition comprising a water-dispersible
polymer comprising an epoxy resin covalently linked to
an acrylic resin by a linking compound having conju-
gated carbon-carbon double bonds or a triple bond.
The present coating compositions, after
curing, demonstrate: (1) excellent flexibility; (2)
excellent adhesion; and (3) excellent chemical resis
tance and corrosion inhibition.
$UP~SARY OF THE INVENTION
The present invention is directed to water-
borne coating compositions that, after curing, effec-
Lively inhibit corrosion of a metal substrate; do not
adversely affect products packaged in a container
having an interior surface coated with the cured
composition; and exhibit excellent flexibility,
chemical resistance and adhesion. The coating compo-
sitions effectively inhibit corrosion of ferrous and
nonferrous metal substrates when the composition is
applied to a surface of the metal substrate, then
cured for a sufficient time and at a sufficient
temperature to provide a crosslinked coating. A
coating composition of the present invention can be ~
used both on the interior and exterior of can ends and
can bodies, and on metal closures for food containers.
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A present coating composition overcomes
disadvantages associated with prior epoxy resin-based
compositions and comprises:
(a) a water-dispersible polymer prepared
f rom
( i ) an epoxy compound having about two
epoxy groups, like an epoxy resin;
(ii) a linking compound having
(A) either conjugated carbon
carbon double bonds or a carbon-carbon
triple band, and
(B) a moiety capable of reacting
with an epoxy group; and
(iii) acrylic monomers, at least a
portion of which are capable of rendering
the polymer water dispersible, wherein the
polymer has at least one epoxy group and the
epoxy portion (i) of the polymer is cova
lently linked to the polymerized acrylic
portion (iii) by linking compound (ii);
(b) a fugitive base, like a tertiary amine;
tc) a curing agent; and
(d) a carrier comprising water and a
volatile organic solvent.
2n particular, the present coating composi-
tions comprise:
(a) about 5% to about 60%, by weight of
nonvolatile material, of a water-dispersible polymer;
(b) a sufficient amount of a fugitive base
to render the water-dispersible polymer water dispers-
ible; and
w (c) about 0.5% to about 25%, by weight of
nonvolatile material, of a curing agent, like a
phenolic resin or an aminoplast.
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The water-dispersible polymer incorporated
into the coating composition is prepared from (i) an
epoxy compound, (ii) a linking compound having an
activated unsaturated carbon-carbon bond moiety and a
moiety capable of reacting with an epoxy group, and
(ii) acrylic monomers, at least some of which are
capable of rendering the polymer water dispersible.
As used here and throughout the specification, the
term "an activated unsaturated carbon-carbon bond
moiety" is defined as either conjugated carbon-carbon
double bonds or a carbon-carbon triple bond.
The epoxy compound has about two epoxy
groups, i.e., about 1.5 to about 2.5 epoxy groups per
molecule of epoxy compound, and an epoxy equivalent
weight (EEW) of about 180 to about 20,000, and is
present in an amount of about 5% to about 95% by
weight of the polymer. The linking compound having an
activated unsaturated carbon-carbon bond moiety and a
moiety capable of reacting with an epoxy group is
present in a sufficient amount to react with at least
about 1% (i.e., about 1% or more) and up to about 50%
of the epoxy groups provided by the epoxy compound_
Alternatively stated, the linking compound is present
in an amount of about 0.3.% to about 5% by weight of
the epoxy compound, or about 0.003% to about 4% by
weight of the water-dispersible polymer.
The polymerized acrylic monomers are present
in an amount of about 5% to about 95% by weight of the
polymer. At least 5% by weight of the polymerized
acrylic monomers have a moiety, like a carboxylic acid
or amide moiety, that render the polymer water dis-
persible. The polymer contains about 0.25% to about
20% by weight of polymerized acrylic monomers having
a moiety capable of imparting water dispersibility.
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The polymerized acrylic monomer portion of the polymer
also can include 0% up to about 95% by weight of vinyl
monomers, like styrene. The polymerized acrylic
J
monomer portion of the polymer also can include 0% up
to about 3% by weight of monomers having more than one
vinyl group, like divinylbenzene.
The water-dispersible polymer, therefore,
has the general structural formula:
E-L-A,
wherein E is the epoxy resin portion of the polymer,
L is the linking portion of the polymer, and A is the
polymerized acrylic portion of the polymer. The
polymer is rendered water dispersible by adding a
base, e.g., a fugitive base, to the polymer.
The epoxy portion of the water-dispersible
polymer provides adhesion, and crosslinking capabili-
ties for mar, chemical, and corrosion resistance. The
acrylic portion of the water-dispersible polymer
provides flow, wetting, and hardness properties, and
24 provides the hydrophilicity that is necessary to
disperse the water-dispersible polymer in water.
Linking the epoxy and acrylic portions provides
enhanced flexibility and resistance properties to the
water-dispersible polymer. The water-dispersible
polymer, therefore, exhibits the excellent flexibility
and formability required a.n a can coating, and exhib-
its improved chemical resistance properties.
Components (a) through {c) of the coating
composition are dispersed in an aqueous carrier such
that a coating composition includes about 5% to about
50%, and preferably about 10% to about 50% of nonvola-
tile components, by weight of the total composition.
Other optional components, such as a pigment, a
filler, or an additive to enhance composition esthet-
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ics or performance, also can be included in the
composition, and accordingly increase the weight
percent of total nonvolatile material in the composi-
tion to above about 60% by weight of the total coating
composition. The carrier of the coating composition
also includes a volatile organic solvent to assist in
dispersing or emulsifying composition ingredients or
to. improve application of the coating composition to
a substrate. A coating composition typically includes
about 15% to about 35% by weight of a volatile organic
solvent.
As used here and hereinafter, the term
"coating composition" is defined as a coating composi-
tion including a water-dispersible polymer, a fugitive
base, a curing agent, and any other optional ingredi-
ents dispersed in the carrier. The term "cured
coating composition" is defined as an adherent poly-
meric coating resulting from curing a coating composi-
tion.
A coating composition, after application to
a metal substrate, and subsequent curing at a suffi-
cient temperature for a sufficient time, provides an
adherent layer of a cured coating composition that
effectively inhibits corrosion; exhibits excellent
flexibility and adhesion to the metal substrate; and
does not adversely affect a product, like a food or
beverage, that contacts the cured coating composition.
Because of these advantageous properties, a cured
coating composition can be used to coat the interior
of food and beverage containers and overcome the
disadvantages associated with conventional polyvinyl
chloride-based compositions and epoxy-based composi- -
tions. A cured coating composition comprises the
water-dispersible polymer and the curing agent essen-
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tially in the amounts these ingredients are present in
the coating composition, expressed as nonvolatile
material. The fugitive base is expelled, or removed,
from a coating composition during the cure cycle.
In accordance with another important aspect
of the present invention, a cured coating composition
demonstrates excellent flexibility, product resis-
tance, and adhesion to a metal substrate compared to
prior epoxy/acrylic resin-based coatings. The excel-
lent adhesion of a cured coating composition to a
metal substrate improves the corrosion-inhibiting
properties of the coating composition. The excellent
flexibility of a cured coating composition facilitates
processing of the coated metal substrate into a coated
metal article, like in molding or stamping process
steps, such that the cured coating composition remains
in continuous and intimate contact with the metal
substrate. A cured coating composition also exhibits
excellent chemical resistance, is sufficiently hard to
resist scratching, and does not adversely affect a
food or beverage packaged in a container having an
interior surface coated with the cured coating compo-
sition.
In accordance with another important aspect
of the present invention, a coating composition
provides a cured coating composition that overcomes
the disadvantages of prior epoxy/acrylic-based coat-
ings and of conventional polyvinyl chloride-based
coatings used to coat the interior of containers for
food and beverages. In addition, a present coating
composition can be used on both the interior and
exterior of can bodies and can ends, and on closures,
thereby obviating the need for a container manufac-
turer to use multiple coating compositions.
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According to one aspect of the present invention,
there is provided a water-dispersible polymer having the
structure
E-L-A,
wherein E is an epoxy portion of the polymer having at least
one epoxy group, A is a polymerized acrylic portion of the
polymer, and L is a linking portion of the polymer which
covalently links E to A, said polymer prepared from (a) an
epoxy compound having an average of 1.5 to 2.5 epoxy groups
per molecule of epoxy compound; (b) a linking compound
having (i) either conjugated carbon-carbon double bonds or a
carbon-carbon triple bond, and (ii) a moiety reactive with
an epoxy group; and (c) acrylic monomers, at least a portion
of which are selected from the group consisting of an
a,(3-unsaturated carboxylic acid, acrylamide, methacrylamide,
and mixtures thereof, to render the polymer water-
dispersible.
According to another aspect of the present
invention, there is provided a water-dispersible polymer
prepared by a method comprising: (a) reacting (i) an epoxy
compound having an average of 1.5 to 2.5 epoxy groups per
molecule of epoxy compound with (ii) a sufficient amount of
a linking compound to consume at least 1% and up to
about 50% of epoxy groups provided by the epoxy compound,
said linking compound having (A) either conjugated carbon
carbon double bonds or a carbon-carbon triple bond, and (B)
a moiety reactive with an epoxy group, to provide a modified
epoxy compound having at least one epoxy group and wherein
the linking compound is covalently bonded to the epoxy
compound; and (b) reacting the modified epoxy compound of
step (a) with (iii) a sufficient amount of an acrylic
monomer, such that the acrylic monomer copolymerizes with
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the conjugated carbon-carbon double bonds or the carbon-
carbon triple bond of the linking compound to provide the
water-dispersible polymer.
According to still another aspect of the present
invention, there is provided a coating composition
comprising: (a) about 5% to about 60%, by weight of
nonvolatile material, of a water-dispersible polymer having
the structure
E-L-A,
wherein E is an epoxy portion of the polymer, said epoxy
portion E derived from an epoxy compound having an average
of 1.5 to 2.5 epoxy groups per molecule of epoxy compound; L
is a linking portion of the polymer, said linking portion L
derived from a linking compound having (A) either conjugated
Carbon-carbon double bonds or a carbon-carbon triple bond,
and (B) a moiety reactive with an epoxy group; and A is a
polymerized acrylic portion of the polymer, said acrylic
portion A comprising polymerized acrylic monomers, at least
a portion of which were selected from the group consisting
of an a,(3-unsaturated carboxylic acid, acrylamide,
methacrylamide, and mixtures thereof, to render the polymer
water-dispersible, and wherein the epoxy portion E of the
polymer is covalently linked to the acrylic portion A by the
linking portion L; (b) a sufficient amount of a fugitive
base to disperse the water-dispersible polymer in water; (c)
about 0.5% to about 25%, by weight of nonvolatile material,
of a curing agent; and (d) a carrier comprising water and a
volatile organic solvent.
According to yet another aspect of the present
invention, there is provided a method of coating a metal
substrate comprising: (i) applying a coating composition as
described herein to at least one surface of the metal
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substrate; and (ii) heating the metal substrate having the
coating composition applied thereon for a sufficient time
and at a sufficient temperature to remove the fugitive base
and the carrier from the composition and provide a
crosslinked cured coating composition.
According to a further aspect of the present
invention, there is provided a metal article having at least
one surface thereof coated with an adherent layer of a cured
coating composition as described herein.
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These and other aspects and advantages of
the present invention will become apparent from the
following detailed description of the preferred
embodiments.
DETAILED DESCRIPTION OF THE PREFERRED ED~ODIb~NTS
The coating compositions of the present
invention, after curing, provide cured coating compo-
sitions that effectively inhibit the corrosion of
metal substrates, such as, but not limited to, alumi-
num, iron, steel and copper. The cured coating
compositions, after curing, also demonstrate excellent
adhesion to the metal substrate; excellent chemical
resistance and scratch resistance; and excellent
flexibility.
In general, a coating composition of the
present invention comprises: (a) a water-dispersible
polymer, (b) a fugitive base, and (c) a curing agent
in (d) a carrier comprising water and organic sol-
vents. In addition, the present coating compositions
can include optional ingredients, like lubricants,
that improve the esthetics of the composition, that
facilitate processing of the composition, or that
improve a functional property of the composition. The
individual composition ingredients are described in
more detail below.
(s) The Water-Disoersib3.e Polymer
The water-dispersible polymer is prepared
from: (i) an epoxy compound having about two epoxy
groups, (ii) a linking compound having an activated
unsaturated carbon-carbon bond moiety and a moiety
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capable of reacting with an epoxy group, and (iii)
acrylic monomers, at least a portion of which are
capable of rendering the polymer water dispersible.
The linking compound (a.i) provides a covalent link
between the epoxy compound (i) and the polymerized
acrylic monomers (iii).
In accordance with an important feature of
the present invention, the water-dispersible polymer
is present in the coating composition in an amount of
about 5% to about 60%, and preferably about 10% to
about 50%, by weight of nonvolatile material.
As demonstrated hereafter, the epoxy portion
of the water-dispersible polymer imparts adhesion
properties, and chemical and mar resistance, to a
cured coating composition. The acrylic portion of the
water-dispersible polymer provides the functionality
necessary to disperse the polymer in water and also
imparts flow, hardness, and wetting properties.
Flexibility and chemical resistance of the cured
coating composition is improved over previous ep-
oxy/acrylate-based compositions because a water-
dispersible polymer having covalently linked epoxy and
acrylic portions is present in the coating composi-
tion. The cured coating composition exhibits the
advantageous properties of a combination of an epoxy
resin and an acrylic resin, with the added advantage
that the epoxy and acrylic portions of the polymer are
covalently linked.
The flexibility of a cured coating composi
- 30 Lion is an important feature because the coating
composition then can be applied to a metal substrate,
and cured, prior to shaping the metal substrate into
a metal article, such as a can end, a can body, or a
closure. The flexibility imparted to a cured coating
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composition overcomes rigidity problems associated
with prior epoxy-based compositions. The chemical and
mar resistance of the cured composition are important
properties with respect to resisting scratching of the
cured coating composition during manufacture into a
metal article and to resisting the corrosive effects
of materials packaged in the metal article.
The water-dispersible polymer is prepared
from the epoxy compound, the linking compound, and
acrylic monomers. These components are reacted to
provide a water-dispersible polymer having an EEW of
about 360 to about 20,000, and preferably about 1,000
to about 12,000. The water-dispersible polymer has a
weight average molecular weight {N!w) of about 35,000
to about 75,000, and preferably about 45,000 to about
65,000; and a number average molecular weight (NIa) of
about 6,000 to about 25,000, and preferably about
7,000 to about 16,000.
The individual components of the water
dispersible polymer are described in more detail
below.
(i) Spoxy Compound Haviag About
Two Epoxy Groups
An epoxy compound having about two epoxy
groups is present in an amount of about 5% to about
95%, and preferably from about 10% to about 90%, by
weight of the water-dispersible polymer. To achieve
the full advantage of the present invention, the epoxy _
compound is present in an amount of about 15% to about
85% by weight of the water-dispersible polymer.
During preparation of the water-dispersible
polymer, a portion of the epoxy groups provided by the
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epoxy compound are consumed in a reaction with the
linking compound. However, as discussed hereafter,
the epoxy compound, after modification by reaction
with the linking compound, contains at least one epoxy
group.
The epoxy compound contains an average of
about 1.5 to about 2.5 epoxy groups per molecule of
epoxy compound. If the average number of epoxy groups
exceeds about 2.5, excessive crosslinking of the
20 composition can result in a cured coating that is too
hard or brittle. The epoxy compound has an EEW of
about 180 to about 20,000, and preferably about 1,000
to about 12,000. To achieve the full advantage of the
present invention, the epoxy compound has an EEW of
about 2,000 to about 8,500_
The epoxy compound imparts chemical and mar
resistance to the cured coating composition. If the
epoxy compound is present in an amount below about 5%
by weight of the water-dispersible polymer, the cured
coating composition is brittle and can form cracks or
lose adhesion during manufacture of a metal article.
In addition, crosslinkable moieties are present in an
insufficient amount to achieve proper cure of coating.
If the epoxy-containing compound is present in an
amount above about 95% by weight of the water-dis-
persible polymer, the cured coating composition does
not have sufficient flow and wetting properties, and
dispersion of the polymer in water is increasingly
difficult. Within the above weight ranges, the cured
coating composition is sufficiently flexible to permit
deformation of a cured coating composition without
forming cracks, and is sufficiently hard to exhibit
excellent chemical and mar resistance.
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The epoxy compounds having about two epoxy
groups typically is a linear epoxy resin terminated at
each molecular end of the resin with an epoxy group.
The epoxy compounds having about two epoxy groups,
therefore, average about 1.5 to about 2.5 epoxy groups
per molecule of epoxy compound.
The epoxy compound can be an aliphatic epoxy
compound or an aromatic epoxy compound. The preferred
epoxy compounds are aromatic, like epoxy resins based
on the diglycidyl ether of bisphenol A. The epoxy
compound has an EEW of about 180 to about 20,000, and
preferably about 1,000 to about 12,000. The epoxy
compounds have a weight average molecular weight (Mw)
of about 400 to about 50,000. An epoxy compound can
be used in its commercially available form, or can be
prepared by advancing a low molecular weight epoxy
compound by standard methods well known to those
skilled in the art, e.g., advancing an epoxy compound
having an EEW of about 180 to about 500 with bisphenol
A to produce an epoxy compound having an EEW of about
1,000 to about 12,000.
Exemplary epoxy compounds include, but are
not limited to, DER 664, DER 667, DER 668, and DER
669, all available from Dow Chemical Co., Midland,
Michigan, and EPON 1004, EPON 1007, and EPON 1009, all
available from Shell Chemical Co., Houston, Texas. An
exemplary low molecular weight epoxy compound that
used in its commercial form, or can be advanced with
bisphenol A, is EPON 828, available from Shell Chemi-
cal Co. -
In general, suitable epoxy compounds are
aliphatic-, cycoaliphatic-, or aromatic-based epoxy -
resins, such as, for example, epoxy resins represented
by structural formulae I and II:
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WO 97/31044 PCT/US97/00728
- 19 -
cX7, OH CX7,
Ii~C~ ~-CH ~0-CHS-~-CHs 0~0-CHr-C~o~Ns CI>
l
a.
<x7, <x~, oa cx7, <x7,
e, ~~crS,-~a~"~e ea, - i - cH, - o~<a~" eat-c~\ H, <In
R J.
.
wherein each A is, independently, a divalent hydro-
carbyl group having 1 to about 12, preferably 1 to
about 6, and most preferably 1 to about 4, carbon
atoms; each R is, independently, hydrogen or an alkyl
group having 1 to about 3 carbon atoms; each X is,
independently, hydrogen, a hydrocarbyl or hydrocarbyl-
oxy group having 1 to about 12, preferably 1 to about
6, and most preferably 1 to about 4, carbon atoms, or
a halogen atom, preferably chlorine or bromine; n is
0 or 1, and n' has an average value of 0 to about 150,
and preferably 0 to about 100.
In particular, the preferred epoxy resins
are the (diglycidyl ether/bisphenol-A) resins, i.e.,
polyether diepoxides prepared by the polymeric adduc
tion of bisphenol-A (III)
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CH3
HO ~C~ OH CIII>
\~~J/ CH \~~/y
and the diglycidyl ether of bisphenol-A (IV).
p CH
HrC C-CHZ-O~C~O_CH2-C CHg C I V )
CH3
The diglycidyl ether can be preforrned by reacting two
molecules of epichlorohydrin with one molecule of the
bisphenol-A in the presence of a base, such as sodium
hydroxide. Preferably, however, this reaction is
carried out in such a manner that the resulting
diglycidyl ether molecules react in si to with bis-
phenol molecules to produce the epoxy resin.
In this case, the epoxy resin a.s a mixture
including polymeric species corresponding to different
values of n' in the following idealized formula V:
CN CH, 0
NpC~CN~CyI,O ~ ~O~CN~CN-CH=-O ~ ~ O~CH~C~ ~ H (V) -
~/ [
CH, H ~H~
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wherein n' is a number from 0 to about 150.
In addition to bisphenol-A, useful epoxy
resins can be prepared by advancing a diglycidyl ether
of a bisphenol listed below with an exemplary, but
nonlimiting, bisphenol listed below:
OH OH OH
OH
OH
OH
DH
C3
0H
OH
H
Br
0H
HD ~ CH2 ~ . OH
CH OH
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C1 CH3 C1
HD ~ C ~ OH
C H3
Br H3 $r
HO ~ C ~ OH
l
Br CHI 8r
H C GH3
CCH3>3C CCCH3)3
CH
HO ~ C ~ OH
H
CH3 CH
C F3
HO ~ CH-CH= ~ OH
CHa HO ~ C ~ OH
C F3
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HD HO HO HO
CHQ ~ ~ CHz
CH3 CFi3 C1
HD OH OH
~CH2--~ HO ~ CHI
HO CHa OH Br HD OH
C H2
CH3 Br
Br OH OH 9r CCH3>ZHC OH OH Cl
CHQ ~ ~ CH2
CHI CH3 C1 r
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aH off a
IH
H ~ HO C ~ OH
Cl C1
0
HO~S~OH
HO ~ S ~ OH
D
CH3
HO ~ OOH
HO ~ O ~ OH
H0~ CH3 CH3
OH
HD ~ CHQ ~ DH
CCHt)=CHI CCHL)=CH3
Other epoxy resins that can be used as a
component of the water-dispersible polymer are pre-
pared from the following starting epoxy-containing
materials. These epoxy-containing materials are
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reacted with bisphenol-A or another bisphenol to
adjust the molecular weight of the epoxy compound to
a sufficiently high range.
-o_ 'o_
H2C/ \\CHCH20CCH2120CHaCH/ \\CH2
I
O 0 O O
CH2 CH-CHQ CHg-CH CHp
0 w
O 0 0 () 0
GHp-O-C
CH- CH2
(ii) Linking Compouad Having an
Activated Unsaturated Carbon-
Carbon Bond Moiety and a Moiety
Capable of Reacting With an Epoxy
group
The linking compound used to prepare a
water-dispersible polymer has two functional groups
and covalently links the epoxy portion of the water-
dispersible polymer to the polymerized acrylic monomer
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portion of the polymer. The linking compound is
present in the water-dispersible polymer in an amount
of about 0.003% to about 4%, and preferably about
0.003% to about 2.5%, by weight of the water
s dispersible polymer.
In accordance with another important feature
of the present invention, the linking compound is
present in a sufficient amount to react with at least
1% and up to about 50% of the epoxy groups provided by
the epoxy compound. Preferably, the linking compound
is present in a sufficient amount to react with about
5% to about 40%, and most preferably about 5% to about
25%, of the epoxy groups provided by the epoxy com-
pound. Accordingly, a reaction between the epoxy
compound and the linking compound does not consume all
the epoxy groups, and sufficient epoxy groups remain
such that the water-dispersible polymer contains at
least one epoxy group.
As previously stated, the linking compound
is a bifunctional monomer. One functionality is a
moiety capable of reacting with an epoxy group. The
second functionality is a moiety having an activated
unsaturated carbon-carbon bond. As used herein, the
term ~~activated unsaturated carbon-carbon bond" refers
to a carbon-carbon triple bond, i.e., an acetylenic
bond, or to conjugated carbon-carbon double bonds.
The linking compounds have the general
structural formulae VI or VII
R1-CH=CH-(-CH=CH-)-r (CH2) ~-Y (VI) .
R1-C~C~C~C-~S(CH2)p-Y, (VTI) .
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wherein R1 is hydrogen, an aliphatic hydrocarbyl
group, an aliphatic cyclohydrocarbyl group, or an
aromatic hydrocarbyl group; r is a numeral from 1 to
6; s is a numeral from 0 to 6; p is a numeral from 0
to 18; and Y is a moiety capable of reacting with an
epoxy group. Preferably, the linking compound has a
maximum of twelve carbon atoms.
In particular, R~ can be an aromatic hydro
carbyl group, like phenyl, or a substituted aromatic
hydrocarbyl group, like a C1-C1~ alkoxy-substituted
phenyl, a halo-substituted phenyl, or a CZ-Ci8 alkyl-
substituted phenyl. As used herein, the term "halo"
includes fluoro, chloro, bromo, and iodo. The R1
group also can be an aliphatic hydrocarbyl group or an
aliphatic cyclohydrocarbyl group, either substituted
or unsubstituted. Nonlimiting examples of R1 are
hydrogen; a C1 to Ct8 alkyl group, and preferably a
Ci-C10 alkyl group; a C$ to C7 cycloalkyl group; a
phenyl-substituted CI-C1g alkyl or CS-C~ cycloalkyl
group; and a halo-substituted alkyl or cycloalkyl
group. The R1 group also can be an unsaturated C1 to
Clg aliphatic hydrocarbyl group or an unsaturated CS to
C~ cycloaliphatic hydrocarbyl group, i.e., the group
contains one or more carbon-carbon double bonds or
carbon-carbon triple bonds. Such unsaturated aliphat-
ic hydrocarbyl and cyclohydrocarbyl groups can be
substituted or unsubstituted. Any substituent groups
on R1 are sufficiently nonreactive such that the sub-
- stituents do not interfere in the preparation of the
modified epoxy compound or the water-dispersible
' polymer. To achieve the full advantage of the present
invention, R1 is hydrogen, a C1-C4 alkyl group, a CS-C~
cycloalkyl group, or phenyl.
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The identity of the Y group is not limited,
except that the Y group is capable of reacting with an
epoxy group . Theref ore , the Y group can be, but is
not limited to, carboxyl (-C02H), amido (-CON(R2)2)~
amino ( -N (R2) 2) , hydroxyl ( -OH) , or mercapto ( -SR3) ,
wherein R2 groups are, independently, hydrogen, C~-C4
alkyl , or phenyl , and R3 is hydrogen, C1- C4 alkyl , or
phenyl.
Specific linking compounds include, but are
not limited to, sorbic acid, sorbic alcohol, dicyclo-
pentadiene acids, conjugated unsaturated fatty acids
(e.g., eleostearic acid), 3-pentyn-1-ol, 2-pentyn-1-
ol, 4-pentynoic acid, 4-pentyn-I-ol, 4-pentyn-2-ol, 1-
pentyn-3-ol, heptacose-10,12-diynoic acid, heptadeca-
2,4-diynoic acid, heneicosa-2,4-diynoic acid, 2-
heptynoic acid, 2-hexynoic acid, nonacosa-10,12-
diynoic acid, nonadeca-1,4-diynoic acid, 2-nonynoic
acid, pentadeca-2,4-diynoic acid, pentacosa-10,12-
diynoic acid, phenylpropiolic acid, propiolic acid,
tetrolic acid, tricosa-10,12-diynoic acid, 10-
undecynoic acid, 1-butyn-3-ol, 2-butyn-1-ol, 3-butyn-
1-oI, 2-decyn-1-oI, 3-decyn-1-ol, 3,6-dimethyl-1-
heptyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 3,4-dimethyl-
1-pentyn-3-o1,3-ethyl-1-heptyn-3-o1,4-ethyl-1-hexyn-
3-o1,3-ethyl-5-methyl-1-heptyn-3-o1,4-ethyl-1-octyn-
3-o1,3-ethyl-1-pentyn-3-ol,l-ethynyl-1-cyclohexanol,
1-heptyn-3-ol, 2-heptyn-1-ol, 3-heptyn-1-ol, 4-heptyn-
2-0l, 5-heptyn-3-ol, 1-hexyn-3-ol, 2-hexyn-1-ol, 3-
hexyn-1-ol, 4-hexyn-2-ol, 5-hexyn-1-ol, 5-hexyn-3-ol,
3-methyl-1-butyn-3-ol, 5-methyl-1-hexyn-3-ol, 3-
methyl-1-pentyn-3-ol, 3-nonyn-1-ol, 1-octyn-3-ol, 3-
octyn-1-ol, 1-phenyl-2-propyn-1-ol, 2-propyn-Z-ol, 10-
undecyn-1-ol, 3-aminophenylacetylene, propargylamine,
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and mixtures thereof. A preferred linking compound is
sorbic acid, having the structure (VTII).
CH3-CH=CH-CH=CH-C02H {VIII)
( i i i ) A~1 i c ~2oaomers
The acrylic monomers, after polymerization,
are present in an amount of about 5% to about 95%, and
preferably about 10% to about 90%, by Weight of the
water-dispersible polymer. To achieve the full
advantage of the present invention, the polymerized
acrylic monomers are present in an amount of about 15%
to about 85%, by weight of the water-dispersible
polymer.
The acrylic monomers are polymerized in a
free radical polymerization reaction, in the presence
of the linking compound, to covalently bond the
acrylic portion of the water-dispersible polymer to
the linking compound through the activated unsaturated
carbon-carbon bond moiety. Preferably, the acrylic
monomers are polymerized in the presence of the
linking compound after the linking compound has been
covalently bound to the epoxy compound.
In accordance with an important feature of
the present invention, at Least a portion of the
acrylic monomers are capable of rendering the polymer
dispersible in water. These monomers are defined as
monomers that yield either water-soluble homopolymers
- or homopolymers that are rendered water soluble by
neutralization with a base. The acrylic monomers can
- include 0% up to about 95%, by total weight of mono
mers, of vinyl monomers. To avoid excessive branch
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ing, the amount of polyvinyl monomers is 0% to about
3% by total weight of monomers.
The acrylic monomer typically comprises an
~,~-unsaturated carboxylic acid. The a-/S unsaturated
carboxylic acid renders the polymer water dispersible
after neutralization with a base. Suitable a,,8-
unsaturated carboxylic acid monomers include, for
example, acrylic acid, methacrylic acid, crotonic
acid, itaconic acid, malefic acid, mesaconic acid,
citraconic acid, sorbic acid, fumaric acid, and
mixtures thereof. The acrylic monomer also can
include acrylamide or methacrylamide which can render
the polymer water dispersible.
The a,~-unsaturated carboxylic acid conven
tionally is copolymerized with a vinyl or an acrylic
monomer, like styrene or an acrylic acid ester.
Polymerizable vinyl and acrylic monomers suitable for
copolymerization with an a,(3-unsaturated carboxylic
acid include, for example, aromatic and aliphatic
compounds including vinyl moieties and esters and
amides of a,~-unsaturated carboxylic acids. Nonlimit-
ing examples of suitable vinyl and acrylic monomers
include styrene and halostyrenes; isoprene; conjugated
butadiene; a-methylstyrene; vinyl toluene; vinyl
naphthalene; the methyl, ethyl, propyl, isopropyl,
butyl, isobutyl, pentyl, isoamyl, hexyl, ethylhexyl,
lauryl, and other C4-Cl2 alkyl acrylates, methacrylates
and crotonates; dimethyl maleate, dibutyl fumarate and
similar diesters of a,~-unsaturated dicarboxylic
acids; and mixtures thereof. Other suitable polymer- -
izable vinyl monomers include vinyl chloride, acrylo-
nitrile, methacrylonitrile, vinyl acetate, vinyl
propionate, vinyl stearate, isobutoxymethyl acryl-
amide, and the like.
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The preferred acrylic monomers are methyl
acrylate, methyl methacrylate, ethyl acrylate, butyl
acrylate, acrylic acid, methacrylic acid, and mixtures
' thereof. A preferred vinyl monomer is styrene. The
most preferred acrylic and vinyl monomers are styrene,
methacrylic acid, acrylic acid, and mixtures thereof.
The acrylic monomers are polymerized and
covalently bonded to the linking compound by subject-
ing the acrylic monomers and the linking compound to
free radical polymerization conditions known to
persons skilled in the art. Therefore, the acrylic
monomers axe polymerized and covalently bonded to the
linking compound in the presence of a free radical
initiator. Useful free radical initiators include,
but are not limited to, redox initiators, peroxide-
type catalysts, like, for example, cumene hydroperox-
ide, or azo compounds, like, for example, azobisiso-
butyrontrile.
In general, any free radical initiator can
be used in preparing the water-dispersible polymer.
One commonly used, and preferred, free radical initia
tor is potassium persulfate. In addition to potassium
persulfate, other useful free radical polymerization
catalysts include, but are not limited to, redox
initiators, such as a sulfite or bisulfite of an
alkali metal, ammonium sulfite, ammonium metabi-
sulfate, ammonium bisulfite, a persulfate of an alkali
metal or ammonium persulfate; a peroxy compound, such
as a peroxide or a peroxy acid, like t-butyl hydro-
- 30 peroxide, di-t-butyl hydroperoxide, benzoyl hydro-
peroxide, t-butyl peroxide, lauroyl peroxide, methyl
ethyl ketone peroxide, chlorobenzoyl peroxide, t-butyl
perbenzoate, t-butyl peroxy isopropyl carbonate, and
peroxy-3,3,5-trimethylcyclohexane, or a mixture
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thereof. Also useful are free radical thermal initia-
tors such as azobisisobutyronitrile; 4-t-butylazo-4'-
cyanovaleric acid; 4,4'-azobis(4-cyanovaleric acid);
2,2'-azobis(2-amidinopropane)dihydrochloride; 2,2'-
azobis(2,4-dimethylvaleronitrile); dimethyl 2,2'-
azobisisobutyrate; 2,2'-azodimethyl bis(2,4-dimethyl-
valeronitrile); (1-phenylethyl)azodiphenylmethane;
2,2'-azobis(2-methylbutyronitrile); 1,1'-azobis(1-
cyclohexanecarbonitrile); 2-(carbamoylazo)-isobutyro-
nitrile; 2,2'-azobis(2,4,4-trimethylpenta-2-phenylazo-
2,4-dimethyl-4-methoxy)valeronitrile; 2,2'-azobis(2-
methylpropane); 2,2'-azobis(N,N'dimethyleneiso-
butyramidine)dihydrochloride; 4,4'-azobis(4-cyano-
pentanoic acid); 2,2'-azobis(2-methyl-N-[1,1-bis-
(hydroxymethyl)-2-hydroxyethyl] propionamide); 2,2'-
azobis(2-methyl-N-[1,1-bis(hydroxymethyl)-
ethyl]propionamide); 2,2'-azobis[2-methyl-N(2-hydroxy-
ethyl)propionamide]; 2,2'-azabis(isobutyramide) dehy-
drate, and the like. These types of initiators,
redox, peroxy, and thermal, can be used singly or in
a suitable mixture.
The water-dispersible resin is prepared
either by reacting the linking compound with an epoxy
compound or by advancing a low molecular weight epoxy
compound to a desired EEW while simultaneously react-
ing the advanced epoxy resin with the linking com-
pound, followed by polymerizing the acrylic monomer in
the presence of the linking compound bonded to the
epoxy compound. The preferred method simultaneously
advances a low molecular weight epoxy compound while -
reacting the advanced epoxy compound with the linking
compound. ,
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For purposes of illustrating the preparation
of a water-dispersible polymer, the following experi-
ments and reactions were performed.
First, the ability of a linking compound to
covalently bond to an epoxy group without disrupting
the activated unsaturated carbon-carbon bond moiety of
the linking compound was demonstrated by reacting 1,2
epoxy-3-phenoxypropane (IX) with sorbic acid (VIII) to
provide compound (X).
/ 0 - CHr - CH - CHI * HO - C - CH = CH - CH = CH - CHg
CIX> CYIII)
OH 0
0 - CHp - CH - CHE - 0 - C - CH = CH - CH = CH - CH9
CX>
In particular, compound (X) was prepared by
admixing 74.0 gram (g) (0.49 equivalents) of compound
IX, 55.38 (0.49 equivalents) of sorbic acid, 0.0068
(500 ppm) tetraethylammonium bromide (TEAB), and 208
methyl ethyl ketone in a reaction flask to form a
reaction mixture. The initial acid number of the
reaction mixture was about 184.1. A blanket of
nitrogen gas (N2) was applied over the reaction
mixture, then the reaction mixture was heated to
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200°F, and held at 200°F until the acid number was
reduced to less than one_ During the reaction, a
second portion of 0.068 TEAB as added to the heated
reaction mixture. After the acid number dropped below
one, the reaction mixture was cooled, and the methyl
ethyl ketone was stripped from the reaction mixture to
provide compound (X). The structure of compound (X)
was confirmed by nuclear magnetic resonance (Nt~t)
spectroscopy.
In experiments wherein sorbic acid was
reacted with an advanced epoxy resin (e.g., EEW of
about 1,000), the reaction mixture often was too
viscous to completely dissolve the advanced epoxy
resin and allow a homogeneous reaction with the sorbic
acid. To overcome this problem, sorbic acid (VIII)
and bisphenol-A (III) were admixed with a low molecu-
lar weight epoxy compound, and allowed to react
simultaneously with the epoxy compound. The structure
of the resulting epoxy-sorbate polymer was confirmed
by NMR spectroscopy. The conjugated diene portion of
sorbic acid was not effected during the reaction. The
sorbate-modified epoxy compound, therefore, has the
structure (XI).
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' o
H3
H2C CH-CH20 ~ C ~ 0-CHp-CH-CHI-0
CHa OH
t
CNg O H H
C-(( ]r--0-CH2-CH-CHp-0-C-C=C-C=C-CH3
CH3 OH H H
CXI>
wherein t is 0 to about about 70. The sorbate-modi-
fied epoxy compound (XI), therefore, has epoxy groups
available for reaction with a crosslinlcing agent and
an activated unsaturated carbon-carbon bond moiety
available for reaction with the acrylic monomers.
In other embodiments, the epoxy ring remain-
ing in sorbate-modified epoxy compound (XI) is opened
prior to reacting the sorbate-modified epoxy compound
with the acrylic monomers. For example, the epoxy
ring in compound (XI) can be hydrolyzed to provide the
corresponding «-glycol compound, wherein the epoxy
ring at the terminal end of the sorbate-modified epoxy
compound is converted to structure (XII).
CA 02245100 1998-07-30
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OH OH
CH2-CH-
(xII)
Similarly, the epoxy ring of compound (XI)
can be opened with a nitrogen compound having the
structure (R4)2NH, wherein the R4 groups are, indepen-
dently, hydrogen, phenyl, or an alkyl or hydroxyalkyl
group having one to six carbon atoms. Examples of
such nitrogen compounds are ammonia, a primary amine,
or a secondary amine. Opening the epoxy ring with a
nitrogen compound provides an «-aminoalcohol at a
terminal end of the modified epoxy compound (XI).
In addition, the epoxy ring of a modified
epoxy compound can be opened with a hydroxyl-contain-
ing compound having the structure RSOH, wherein RS is
an alkyl group or a hydroxyalkyl group having one to
six carbon atoms, or R$ is phenyl. Opening the epoxy
ring with an alcohol provides an «-hydroxy ether at a
terminal end of the modified epoxy compound.
Furthermore, the epoxy ring of the modified
epoxy compound can be opened with phosphoric acid
having the structure (XIII),
0
fR~O)zPOH
(XIII)
wherein the RS groups are, independently, hydrogen, an
alkyl group or a hydroxyalkyl group having one to six
carbon atoms, or phenyl. Opening the epoxy ring with
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a phosphoric acid of structure (XIII) provides an «-
hydroxy phosphate ester having the structure (XIV)
0
I I
R60-i-OR6
0 OH
CtiE-CHp -
{XIV)
at the terminal end of the modified epoxy compound
{XI) .
To demonstrate that the linking compound
copolymerizes with the acrylic monomers, sorbic acid
was reacted with acrylic monomers and vinyl monomers
under free radical polymerization conditions. The
conjugated diene moiety of sorbic acid was not ob-
served in the resulting polymer. In particular, the
following example demonstrates the copolymerization of
sorbic acid, acrylic monomers, and vinyl monomers.
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Ingredient Amouat (wt) '
(a) Butyl Cellosolve 316g
(b) n-Butyl Alcohol g6g
(c) Styrene 5.1g
(d) Sthyl Acrylate 113.48
(e) Methyl Methacrylate 33.98
(f) Acrylic Acid 21.38
(g) Methacrylic Acid 25.58
(h) Sorbic Acid 3g
(i) 2,2'-Azobisisobutyronitrile 3g
(j) Butyl Cellosolve 5pg
(k) 2,2'-Azobisisobutyronitrile 1.38
(1) 2,2'-Azobisisobutyronitrile 1.38
(m) 2,2'-Azobisisobutyronitrile 1.38
Ingredients (a) and (b) were charged into a
reaction flask and heated to 230°F. Ingredients (c)
through (i) were premixed, then added dropwise to the
heated mixture of (a) and (b) over a 90-minute period,
with agitation and while maintaining a temperature of
230°-235°F. Residual amounts of the monomer premix
(c)-(i) were washed into the reaction flash with
ingredient (j). The resulting reaction mixture was
held at 230°F for 30 minutes, then ingredient (k) was
added. After another 30-minute hold at 230°F, ingre-
dient (1) was added. After a third 30-minute hold at
230°F, ingredient (m) was added. The reaction mixture
then was held at 230°F for an additional 60 minutes,
then allowed to cool.
The solvents were evaporated from the
reaction mixture, and the resulting copolymer was
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- 39 -
assayed by NNgt for the presence of the sorbic acid
dime moiety. No evidence of a diene moiety was
observed.
As illustrated hereafter, a sorbate-modified
epoxy compound of structural formula (XI) was reacted
with acrylic and vinyl monomers to provide a water-
dispersible polymer. The resulting water-dispersible
polymer had the structure:
E-L-A,
wherein E a.s the epoxy portion of the polymer, A is
the acrylic portion, and L is the linking portion
which covalently links E to A.
(b) The Fugitive Base
The water-dispersible polymer contains a
sufficient amount of acrylic monomers capable of
. rendering the polymer dispersible in water. These
acrylic monomers typically are o~, ~i-unsaturated carbox
ylic acids and these monomers render the polymer water
dispersible by neutralizing the carboxylic acid moiety
with a fugitive base.
A fugitive base is included in a sufficient
amount such that about 20% to about 100% of the
carboxylic acid groups of the acrylic portion of the
water-dispersible monomer are neutralized. An excess
amount of fugitive base does not adversely affect the
coating composition, but the excess amount of fugitive
base provides no advantages and, therefore, is wasted.
A fugitive base preferably is present in an amount
sufficient to neutralize at least about 35% to about
?5% of the carboxylic acid groups present in a water-
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borne coating composition. The precise amount of
fugitive base added to the composition is determined
from the acid number of the water-dispersible polymer
and from the basicity of fugitive base.
A fugitive base is a relatively volatile
compound that is expelled from a coating composition
during cure_ Accordingly, a coating composition,
during cure, reverts to a more water insoluble form
and, therefore, provides a cured coating composition
that exhibits excellent chemical resistance and
excellent blush resistance.
A fugitive base usually is a primary,
secondary or tertiary amine, either aromatic or
aliphatic, or a primary, secondary or tertiary
alkanolamine, or ammonium, an alkylammonium hydroxide,
or an arylammonium hydroxide, or mixtures thereof.
Nonlimiting examples of a fugitive base include
ammonium hydroxide, a tetraalkylammonium hydroxide,
wherein an alkyl group has one to about 4 carbon atoms
(e. g., tetramethylammonium hydroxide), monoethanol-
amine, dimethylamine, methyldiethanolamine, benzyl-
amine, diisopropylamine, methylethanolamine, butyl-
amine, piperazine, dimethylethanolamine, diethyl-
ethanolamine, diethanolamine, morpholine, N-methyl-
morpholine, N-ethylmorpholine, triethylamine, 2-
dimethy!amine-2-methyl-1-propanol, diisopropanolamine,
trimethylamine, N-methylpiperidine, 2-amino-2-methyl-
1-propanol, piperidine, pyridine, dimethylaniline, and
similar amines and alkanolamines, and mixtures there-
of .
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(c) The Curiaa Aaea
A coating composition of the present inven-
tion also includes a curing agent, such as a phenolic
resin or an aminoplast. The coating composition
contains about 0 _ 5% to about 25%, and preferably about
1% to about 20%, by weight of nonvolatile material of
the curing agent. To achieve the full advantage of
the present invention, the coating composition con-
tains about 1% to about 10%, by weight, of a curing
agent.
The curing agent can be a phenolic resin, an
aminoplast, a carbodiimide, or a similar curing agent.
The phenolic resin is a condensation product resulting
from a reaction between a phenol and formaldehyde, and
has a low weight average molecular weight of about 800
to about 8,000, and preferably about 1,200 to about
5,000. Phenol or essentially any other compound
including a hydroxyphenyl moiety can be used as the
phenol component of the phenolic resin. Nonlimiting
examples of suitable phenol compounds include phenol,
cresylic acid and bisphenol A. Bisphenol A is the
preferred phenol component of the phenolic resin.
Similarly, an aminoplast can be used as the
curing agent. An aminoplast generally is a low
molecular weight partially or fully alkylated conden
sation product, like urea-formaldehyde, melamine
forma.ldehyde, and benzoguanamine-formaldehyde resins.
Commercially available aminoplasts include,
for example, CYMEL 301, CYMEL 303, CYMEL 370, and
CYMEL 373, all being melamine-based and commercially
available from American Cyanamid, Stamford, Connecti
cut, e.g., CYMEL 301 is hexamethoxymethyl melamine.
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Other examples of aminoplast resins are of
the type produced by the reaction of aldehyde and
formoguanamine, ammeline, 2-chloro-4,6-diamine-
1,3,5'triazine; 2-phenyl-p-oxy-4,6-diamino-1,3,5-
triazine; and 2,4,6-triethyl-triamino-3.,3,5-triazine.
The mono-, di, or triaryl melamines, for instance,
2,4,6-triphenyltriamine-1,3,5-triazine,are preferred.
Other aldehydes used to react with the amino compound
to form the resinous material are crotonic aldehyde,
acrolein, or compounds which generate aldehydes, such
as hexamethylene-tetramine, paraldehyde, and the like.
(d) The Carrier
The carrier of a present coating composition
is water based, but also can include a volatile
organic solvent. In general, the volatile organic
solvents included in the coating composition have
Buff icient volatility to evaporate essentially entire-
ly from the coating composition during the curing
process, such as during heating at about 350°F to
about 500°F for about 6 seconds to about 15 minutes.
The volatile organic solvents are included
as a portion of the carrier to help dissolve, disperse
and emulsify composition ingredients, and thereby
provide a more stable composition. The volatile
organic solvents also are included to improve the
physical properties of the composition, like surface
tension, flow out during the bake and viscosity, and
thereby provide a composition that is easier to apply
and that provides a more uniform cured coating. The
volatile organic solvents improve the flow properties
of a coating composition and facilitates spraying of
a coating composition.
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Numerous volatile organic solvents can be
' included in a present coating composition. Suitable
volatile organic solvents have a sufficiently low
' vapor pressure to resist evaporation during storage
and a sufficiently high vapor pressure to be evaporat
ed from the coating composition during cure. Exempla-
ry, nonlimiting volatile organic solvents include, but
are not limited to, the methyl, ethyl, propyl, butyl,
hexyl or phenyl ether of ethylene glycol, diethylene
glycol, triethylene glycol, propylene glycol or
dipropylene glycol; ethylene glycol methyl ether
acetate; ethylene glycol ethyl ether acetate; ethylene
glycol butyl ether acetate; diethylene glycol ethyl
ether acetate; diethylene glycol butyl ether acetate;
propylene glycol methyl ether acetate; dipropylene
glycol methyl ether acetate; n-butanol; hexyl alcohol;
hexyl acetate; methyl n-amyl ketone; butylene glycol;
propylene glycol; diisobutyl ketone;. methyl propyl
ketone; methyl ethyl ketone; methyl isobutyl ketone;
2-ethoxyethyl acetate; t-butyl alcohol; amyl alcohol;
2-ethylhexyl alcohol; cyclohexanol; isopropyl alcohol;
and similar organic solvents, and mixtures thereof.
A preferred volatile organic solvent is n
butanol because coating composition components are
easily dispersed in n-butanol. Another preferred
volatile organic solvent is ethylene glycol monobutyl
ether, i.e., butyl cellosolve.
The carrier also can include a relatively
low amount of a nonpolar organic solvent, such as up
. 30 to about 10% by weight of the carrier, without ad
versely affecting a coating composition, either prior
to or after curing. Exemplary nonpolar organic
solvents include a chlorinated hydrocarbon, an ali-
phatic hydrocarbon, or an aromatic hydrocarbon, like
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toluene, ethylbenzene, benzene, xylene, mineral
spirits, kerosene, naphtha, heptane, hexane, and
combinations thereof.
The amount of carrier included in the
coating composition is limited only by the desired, or
necessary, rheological properties of a coating compo
sition. Usually, a sufficient amount of carrier is
included in a coating composition to provide a compo
sition that can be processed easily, that can be
applied to a metal substrate easily and uniformly, and
that is sufficiently evaporated from a coating compo-
sition during cure within the desired cure time.
A carrier, therefore, is included in the
composition in a sufficient amount to provide a
coating composition including about 5% to about 60%,
and preferably about 10% to about 50%, by weight of
the nonvolatile material. To achieve the full advan-
tage of the present invention, a waterborne coating
composition includes about 15% to about 45% by weight
of the nonvolatile material. The addition of optional
fillers can increase the amount of nonvolatile materi-
al above about 60%.
Therefore, essentially any carrier compris
ing a major portion of water and a minor portion of
volatile organic solvents is useful in the present
coating composition as long as the carrier adequately
disperses, emulsifies and/or solubilizes the composi-
tion components; is inert with respect to interacting
with composition components and thereby adversely
affecting the stability of the coating composition or
the ability of the coating composition to effectively
cure; and evaporates quickly, essentially entirely and "
relatively rapidly to provide a cured coating composi-
tion that inhibits the corrosion of a metal substrate,
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that does not adversely affect a food or beverage that
contacts the cured coating composition, and that
demonstrates sufficient physical properties, like
adhesion and flexibility, for use as a coating on the
interior or exterior of a container or a closure.
(e) Other Optional Ingredients
A coating composition of the present inven-
tion also can include other optional ingredients that
do not adversely affect the coating composition or a
cured coating composition resulting therefrom. Such
optional ingredients are known in the art, and are
included in a coating composition to enhance composi-
tion esthetics; to facilitate manufacturing, process-
ing, handling, and application of the composition; and
to further improve a particular functional property of
a coating composition or a cured coating composition
resulting therefrom.
Such optional ingredients include, for
example, dyes, pigments, extenders, fillers, addition
al anticorrosion agents, flow control agents, thixo
tropic agents, dispersing agents, antioxidants,
adhesion promoters light stabilizers, and mixtures
thereof. A nonionic or an anionic surfactant is
included in a coating composition to improve flow
properties. A wax emulsion and/or dispersion of a
synthetic lubricant is included to improve the slip
properties of a cured coating composition. Each
optional ingredient is included in a sufficient amount
to serve its intended purpose, but not in such an
amount to adversely affect a coating composition or a
cured coating composition resulting therefrom.
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A coating composition of the present inven-
tion is prepared by first preparing the water-dis-
persible polymer. The water-dispersible polymer
preferably is prepared by simultaneously advancing the
epoxy compound and reacting the epoxy compound with
the linking compound. The resulting modified epoxy
compound is reacted with acrylic monomers under free
radical polymerization conditions to provide the
water-dispersible polymer.
The water-dispersible polymer then is
admixed with the fugitive base, curing agent, and
carrier, i.e., water and volatile organic solvent.
The carrier is present in a sufficient amount to
adjust the amount of nonvolatile material a.n the
coating composition to a predetermined level. Option-
al ingredients can be added to the coating composition
either prior to or after the addition of the carrier.
To demonstrate a coating composition of the
present invention, the following Examples and Compara
five Examples were prepared, then applied to a metal
substrate, and finally cured to provide a coated metal
substrate. The coated metal substrates then were
tested, comparatively, for use as a food or beverage
container. The cured coatings were tested for an
ability to inhibit corrosion of a metal substrate; for
adhesion to the metal substrate; for chemical resis-
tance; for flexibility; and for scratch and mar
resistance. A composition of the present invention
was compared to a commercial vinyl organosol composi-
tion (i.e., Comparative Example 1) that is widely used -
in coating metal substrates for food and beverage
applications.
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~mnarative ExamSle l
Commercial Viayl Orgaaosol
Composition
% % (by
Iagredieat (by Weight) weight NVMl)
Xylene 29.45 --
Diisobutyl Ketone 13.77 --
Diacetone Alcohol 20.90 --
Solution Vinyl 2 11.61 34_32
Phenolic Resin 3 2_02 2.99
Epoxy Resin 4 1_01 2.99
Lubricant 5 1.31 0.77
Vinyl Chloride Dispersion 19.93 58.92
Res in6
NVM is nonvolatile material;
2 UCAR Solution Vinyl VMCC, available as a 100% active
material, from Union Carbide Corp., Danbury, CT;
50% nonvolatile material;
EPON 828, available as a 100% active material, from
Shell Chemical Co., Houston, TX;
POLYSPERSE°, 20% active material; and
~ OXY 1730, available as a 100% active material, from
Occidental Chemical Co., Houston, TX.
The composition of Comparative Example 1 contains
about 33.8% nonvolatile material.
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Lxample 1 '
% (by
Ingredient % (by weightD weight NvMl)
Water-Dispersible
Polymer/Fugit~ve 91.46 97.0
Base Solution.
Curing Agent 8 1.52 2.3
Lubricant 9 0.92 0.7
N-Butyl Alcohol 1.22
Deionized Water 4.88
~ Aqueous solution of water-dispersible polymer
solubilized with dimethylethanolamine, 35% solids
content, see Example 2;
8 Phenolic resin, based on phenol and paraformalde-
hyde, 50% active; and
9 MICHEM 160, Michelman Chemical Tnc., Cincinnati, OH,
a 25% active emulsion of carnauba wax.
The composition of Example 1 is a coating
composition of the present invention containing about
33% nonvolatile material. The composition of Example
1 is prepared by simply admixing composition ingredi-
ents until homogeneous. The composition of Example 1
is based on the water-dispersible polymer prepared as
set forth below in Example 2.
ple 2
Water-Dispersible Palymer/Fucritive Base Solution
An epoxy compound, i.e., EPON 828, a digly- '
cidylether of bisphenol-A, (EEW 187, 180 pounds) was
added to a nitrogen-blanketed reactor fitted with a '
reflux condenser. The epoxy compound was heated to
about 170°F to about 175°F, then a sufficient amount
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of bisphenol-A was added to the heated epoxy compound
to provide an epoxy resin of EEW of about 3000 (e. g.,
about 99 pounds). In addition, 464 grams (g) of
sorbic acid and 77g of a phosphonium salt catalyst
(i.e., SHELL Catalyst 1201, available from Shell
Chemical Co., Houston, TX) were added to the reactor.
The resulting mixture was heated to 240°F
while maintaining a nitrogen blanket. After reaching
240°F, the mixture was allowed to cool to 100°F. An
exothermic reaction raised the temperature to 270°F,
and the temperature then was allowed to raise at the
rate of about one to about one and one-half Fahrenheit
degrees per minute by cooling the mixture until the
temperature reached about 350°F (peak temperature was
about 365°F). After the exotherm subsided, the
mixture was held at about 350°F to about 360°F, by
heating, for about one hour. When the epoxy resin
attained an EEW of greater than about 3000, butyl
cellosolve (176 pounds) was added to the mixture, and
the mixture was allowed to cool to about 250°F.
Then, n-butyl alcohol (32.8 pounds) was
added to the mixture, and the resulting mixture was
further cooled to 230°F. A premix of styrene (790g),
ethyl acrylate (38.7 pounds), methyl methacrylate
(11.6 pounds), acrylic acid (3,299g), and methacrylic
acid (3,950g), and having an acid number of about 166,
was prepared. Azobisisobutyronitrile initiator (464g)
was added to the monomer premix, then the resulting
acrylic monomer/initiator mixture was added to the
- 30 reactor over a 90-minute time period, while maintain
ing a temperature of about 230°F. Residual amounts of
. acrylic monomers were flushed into the reaction vessel
with 14.4 pounds of butyl cellosolve and held at about
230°F for an additional 30 minutes.
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Next, a premix of 2018 of azobisisobutyro- ,
nitrite and 4028 of butyl cellosolve was added to the
reactor, and the resulting mixture was held for an
additional 30 minutes at about 230°F. This procedure
was repeated two additional times to ensure that the
acrylic monomers were polymerized.
The contents of the reactor then were cooled
to about 220°F, followed by the addition of 40908 of
deionized Water. The contents of the reactor were
cooled to 212°F, then a premix of water (40908) and
dimethylethanolamine (40908) was added to the reactor.
After a 10-minute hold, heated deionized water (262
pounds, 200°F) was added to the reactor over a one-
hour time period. The reaction product was allowed to
cool to about 195°F to about 200°F during the Water
addition. Next, deionized water (135 pounds) was
quickly added to cool the reaction product to about
105°F. The reaction product then was adjusted to the
desired solids content by the addition of deionized
water.
The polymer solution of Example 2 had a
solids content of about 35%, by weight; a pH of about
7.25; a viscosity of 350 cps (centipoise) measured on
a #3 spindle at 25°C and 20 rpm; an acid number on
solids of about 32.5, and a base number on solids of
about 16.2. The water-dispersible polymer/fugitive
base solution of Example 2 was used as the major
component of the composition of Example 1.
The composition of Example 1 was applied to
both sides of an aluminum substrate at a rate to -
provide about 5.2 to about 7 milligrams per square
inch (msi) interior dry film weight and about 2.3 to
about 2.8 msi exterior dry film weight. The composi-
tion of Example 1 was applied at a rate of about 150
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feet per minute, and was cured at about 450°F for
about L1 seconds. The composition of Example 1 was
easy to apply, exhibiting excellent flow, no foaming,
no skinning, no significant solvent loss, and no
apparent rise a.n viscosity after two hours. The cured
coating composition exhibited excellent gloss.
The composition of Example 1 was compared to
the composition of Comparative Example 2. Comparative
Example 1 was used as a control. The composition of
Comparative Example 2 was similar to the composition
of Example 1, except sorbic acid was omitted from the
composition of Example 2. The composition of Compara-
tive Example 2, therefore, does not include a linking
compound to covalently bond the epoxy portion of the
polymer to the polymerized acrylic portion of the
polymer.
In summary, Comparative Example 2 contains
97%, by weight of nonvolatile material, of an epoxy-
acrylic dispersion. The epoxy-acrylic dispersion
.20 contains 33% nonvolatile material, and is based on an
advanced epoxy resin, styrene, ethyl acrylate, methyl
methacrylate, and methacrylic acid. The epoxy-acrylic
dispersion of Comparative Example 2 is prepared in an
essentially identical manner as Example 2, except that
sorbic acid is omitted and the epoxy resin used in
Comparative Example 2 is advanced prior to the synthe-
sis, rather than as a first step of the synthesis.
The composition of Comparative Example 2 contains the
same curing agent and lubricant, in the same amounts,
as Example 1; and contains 30% nonvolatile material.
The compositions of Example 1 and Compara-
tive Examples 1 and 2 were applied to a metal sub-
strate (e. g., an aluminum substrate), and then cured
to provide a coated metal substrate. The coated metal
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substrates then were tested, comparatively, for use as
the interior surface of a food or beverage container.
As will be demonstrated more fully hereinafter, a
Y
cured coating composition resulting from curing a
coating composition of the present invention is
suitable as the interior or exterior coating of a
metal container for food or beverages, or for a
closure.
In particular, a coating composition of the
present invention is applied to a metal substrate,
then cured for a sufficient time at a sufficient
temperature, such as for about 3 to about 5 minutes at
about 350°F to about 500°F, to provide an adherent
cured coating composition on the metal substrate. The
coated metal substrate then is shaped into a container
or other metal article.
Therefore, the compositions of Example 1 and
Comparative Examples 1 and 2 were individually applied
to a clean, untreated aluminum substrate in a suffi-
cient amount to provide a cured film thickness of
about 0.1 mil. Each composition was reduced to a
solids content of about 28% by weight with deionized
water before applying the composition to the metal
substrate. After individually applying a composition
of Example 1 or a composition of Comparative Examples
1 and 2 to an aluminum substrate, the composition was
cured through an HVHT coil oven at 450°F for about 15
seconds. Each of the cured coating compositions had
a smooth, glossy appearance and was defect free.
Table I summarizes the results of different
tests performed on the cured coating compositions.
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TaHL~ Z
Cosiparative
Tests
Film pencil
Cc~positicas lieightlHardness IfFZ 11p (H/H)(H/a)
3
le 1 9.3 2H-3H 0.3, 0.3 100/100 80/100
Comparative 7.3 2H-3H 0.3, 0.5 100/100 100/100
8x. 2
Comparative 7.2 2H 0, 0 100/100 60/100
8x. i
(control)
1 In milligrams per square inch of substrate;
A wet feathering (t~PF) test, the coated panels,
after immersion in 150°F water for 15 minutes, were
tested for an ability to resist forming torn or
protruding edges when a tab of the coated metal
substrate is removed from the coated metal substrate,
the test simulates removal of a tab from an easy-open
aluminum can, 0 (best results)--5 (worst results);
3 H/A is blush/adhesion, 100-excellent, 90-good, 0
total loss, WP is wet pasteurization, the coated
substrate is tested after immersion in 180°F water for
minutes. Dow refers to a standard test wherein the
coated substrate is tested by immersing the coated
aluminum substrate in a boiling aqueous solution
including 1 Weight % DowfaxTM 2A1 (aa anionic surfac-
25 tart) for 15 minutes, then testing for blush and
adhesion.
The results summarized in Table I show that the
composition of Example 1 has a better blush resistance
than a presently used commercial composition (Coaapara
30 tive Example 1).
The compositions of Example 1 and Compara-
tive Example 2 also were tested for process resis-
tance. In these tests, liquids are placed in contact
with the coated substrate for a predetermined period
of time under different conditions, then the sub-
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strates are tested for resistance to the effects of
these various liquids in an enamel rating test.
The enamel rating tests the continuity of a
cured coating film applied to a can part, such as a
can end or a can body. A can end or can body is
formed after the metal substrate is coated. There-
fore, the cured coating has been deformed during this
manufacturing step. The data presented in Table II
show that the enamel rating for a composition of the
present invention (Example 1) is substantially better
than the enamel rating of Comparative Example 2.
The enamel rating test measures the passage
of current from an electrode through an electrolyte to
the formed can part. The coating functions as an
Z5 insulator, and, accordingly, no current flows if film
continuity is perfect. The lower the milliamp read-
ing, the more continuous the coating on the metal
substrate. The data in Table II shows a relatively
low milliamp reading for can parts coated with the
composition of Example 1, therefore, showing good film
continuity. The composition of Example 1 showed
substantially better process resistance because of a
better enamel rating.
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TABhE II
Comparative Testiag
Comparative
Testl Example 1 Example 2
Coated substrate 0.39 t 0.29 1.68 t 0.91
(as made?
After 5 minutes in 4.75 t 1.76 10.62 t 2.61
boilin Dowfax 2A1
3 days c~ 120F 2.49 t 1.25 6.65 t 2.16
Diet Coke
7 days ~ 100F -- 5.0 t 2.53
Diet Coke
3 days ~ 120F 1.70 t 0.97 4.48 t 1.43
Diet Sprite
i All tests are enamel ratings, in milliamps. Tests
were performed after subjecting a coated substrate to
the indicated conditions.
In general, the composition of Example 1
demonstrates improved flexibility, adhesion, and
enamel rating over the composition of Comparative
Example 2. Example 1 also exhibited properties
comparable to the presently used commercial vinyl
organosol composition of Comparative Example 1. In
addition, the compositions of the present invention
exhibit an improved solids/viscosity relationship
permitting the formulation of a high solids composi
tion having an acceptable viscosity for handling and
application. The present coating compositions,
therefore, have exhibited coating properties at least
equal to current commercial compositions for similar
end uses.
The data summarized in Tables I and II
illustrate that a coating composition of the present
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invention provides a cured coating composition useful
as the interior or exterior coating of a food or
beverage container, or a closure for a food product ,
container. The present compositions demonstrate
excellent blush resistance and excellent adhesion.
The blush resistance test demonstrates the ability of
a cured coating to resist attack by a hot detergent
solution and other liquids. A coating composition for
a metal container must demonstrate excellent adhesion
and flexibility because metal containers are manufac-
tured by first coating flat sheets of the metal
substrate, then forming the coated sheets into a
desired shape. Coatings having poor adhesion proper-
ties can separate from the metal substrate during the
shaping process. A lack of adhesion, therefore, can
adversely affect the ability of the cured coating
composition to inhibit corrosion of the metal sub-
strate. A present coating composition exhibits an
excellent adhesion to a metal substrate, and, there-
fore, the coating composition can be applied to a
metal substrate, cured, and the metal substrate
subsequently can be deformed without adversely affect-
ing continuity of the coating film.
The present coating compositions also
provided a cured coating composition having excellent
flexibility. Flexibility is an important property of
a cured polymeric coating because the metal substrate
is coated prior to stamping or otherwise shaping the
metal substrate into a desired metal article, such as
a metal container. The coated metal substrate under- '
goes severe deformations during the shaping process,
and if a coating lacks sufficient flexibility, the
coating can form cracks or fractures. Such cracks
result in corrosion of the metal substrate because the
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aqueous contents of the container have greater access
to the metal substrate. Metal substrates coated with
a present coating composition were deformed into the
shape of a metal can. No cracks or fractures were
observed. In addition, as previously described, a
cured coating provided by a coating composition of the
present invention is sufficiently adherent to the
metal substrate, and remains sufficiently adherent
during processing into a metal article, and, there-
fore, further enhances corrosion inhibition.
The comparative tests illustrated in Tables
I and II demonstrate that a cured coating composition
of the present invention maintains adhesion to the
metal substrate; is flexible; is sufficiently hard
and, therefore, is scratch and mar resistant; resists
blush; and resists chemical attack.
As an added advantage, a composition of the
present invention can be cured over a relatively wide
temperature range of about 350°F to about 500°F, and
over relatively wide time period of about 3 minutes to
about 5 minutes, without adversely affecting the
advantageous physical and chemical properties of the
cured coating composition. A container manufacturer,
therefore, does not have to design the coating process
around the curing characteristics of the coating
composition; nor does the coating manufacturer have to
tailor the curing characteristics of the coating
composition to a particular coating process. The
present coating composition, therefore, has a more
universal range of applications. Furthermore, the
wide curing range and the chemical and physical
properties demonstrated by the present coating compo-
sitions makes a waterborne coating composition useful
for both the exterior and interior of can bodies and
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_ 5$ _
can ends. Conventionally, different coating composi
tions are used for the can body and can end, and for
the exterior and interior of the container. This
further expands the range of applications for the
present composition.
Obviously, many modifications and variations
of the invention as hereinbefore set forth can be made.
without departing from the spirit and scope thereof
and, therefore, only such limitations should be
imposed as are indicated by the appended claims.
