Note: Descriptions are shown in the official language in which they were submitted.
.
WO96/10612 2 2 J ~ 7 2 4 PCT~S95/13223
AQUEOUS COATING COMPOSITION
Backqround of the Invention
Coatings are applied to the interior of metal food
and beverage cans to prevent the contents from coming
into contact with the metal surfaces of the containers.
Contact of the can contents with the metal surface,
especially where acidic products such as soft drinks,
tomato juice or beer are involved, can lead to corrosion
of the metal container and resulting contamination and
deterioration of the contents. Can interiors are
typically coated with a thin thermoset film to protect
the interior metal surface from its contents. Synthetic
resin compositions which include vinyls, polybutadiene,
epoxy resins, alkyd/aminoplast and oleoresinous
materials have typically been utilized as interior can
coatings. These heat-curable resin compositions are
usually applied as solutions or dispersions in volatile
organic solvents.
The ideal coating should have low extractables to
avoid contamination of the contents and should cure
rapidly to facilitate can manufacture. The cured
coating should be highly resistant to a wide variety of
- food products, both under storage and processing
conditions. The interior coating should be
substantially free of blisters and should have good
adhesion to the metal surface, both on application and
after processing.
Relatively thick films are required to ensure
complete coverage of the metal and to protect the metal
during drawing and forming operations. This is
especially true of coatings applied to metal subst~ates
used to produce the end of a can, where film weights of
about 5 to about 9 mg/in2 are typically required. Side
seam coatings, which are also appiied as thick films and
require blister resistant coatings, have similar
performance characteristics. The coatings used for food
cans and can ends are generally applied and cured into
films on high speed coating lines (e.g., coil coating
lines). Modern high speed coating lines require a
WO96/10612 PCT~S95/13223
2201 ~24
coating material that will dry and cure without defects
within a few seconds as it is heated very rapidly to
peak metal temperatures of about 450F to about 550F
(about 230C to about 300C).
Due to the rapid curing speeds involved, attempts
to utilize aqueous coatings on modern coil coating lines
have encountered particularly difficult problems in
avoiding blistering. Blistering typically occurs as
cure temperature passes through the boiling point of
water. Blistering becomes more acute as the thickness
of the uncured coating layer increases and at higher
heating rates and higher peak metal temperatures. All
of these factors may be present during application of a
coating to can ends on a high speed coating line.
Compositions in which the film producing material
is dispersed or dissolved in organic solvents are
generally used in coating applications where a
relatively thick coating is required. Due to
environmental and economic drawbacks associated with the
use of organic solvents, however, there is an increasing
demand for aqueous-based coatings. In addition to being
less expensive than organic solvent-based coatings,
aqueous-based coatings minimize the environmental impact
of organic solvent release and diminish the need to
incinerate curing oven effluents. Unfortunately, under
rapid, high temperature curing conditions, currently
available aqueous-based coatings do not provide
satisfactory performance. There is, accordingly, a
continuing need for aqueous-based coatings, which will
permit the formation under rapid, high temperature
curing conditions of protective films which are
substantially free of blisters.
SummarY of the Invention
The present invention provides an aqueous coating
composition capable of forming a tough coating,
resistant to hydrolysis and other forms of chemical
attack, while minimizing environmental problems
WO96/10612 PCT~S95/13223
22U 1 724
associated with the use of organic solvents. The
coating composition can be applied and cured without
blistering at high coating weights and high line speeds
to provide a resilient, corrosion resistant, cured film.
In addition to the choice of specific components,
achievement of these properties is dependent on a proper
balance of the solids content, viscosity and water
content of the coating composition.
The coating composition includes a solvent
component and a film forming component. The solvent
component includes water and an organic solvent. The
film forming component includes a curing agent and the
product of the reaction of a carboxy addition polymer
and an epoxy resin in the presence of a tertiary amine
catalyst.
The present invention also provides a method of
coating a metal substrate to provide a cured film on at
least one surface of the substrate. The method includes
applying the aqueous coating composition onto the
surface of the metal substrate to form a coating layer.
The coated metal substrate is then heated so that the
coating layer cures to form a cured film adhered to the
substrate surface. The coated metal substrate is
typically cured by heating for about 2 to about 20
seconds in an oven at a temperature of about 230 to
about 300 C. The cured film is substantially free of
blisters and typically has a film weight of at least
about 5 mg/in2 and, preferably, about 7 mg/in2 to about 9
mg/in2.
The present invention also provides a composite
material which includes a metal substrate having at
least one surface covered with a cured film, which is
the result of coating the substrate surface with the
above-described coating composition and heating the
coated metal substrate for 2 to 20 seconds at a
temperature of 230 to 300C. The cured film preferably
has a film weight of at least about 5 mg/in2.
WO96/10612 PCT~S95/13223
22U~ 7~ -
Detailed Description of the Invention
Coating compositions of this invention are useful
for protecting the interior of food and beverage cans.
The cans are typically formed from metals such as
aluminum, tin, steel or tin-plated steel. The coatings
are generally applied to metal sheets by one of two
processes, each of which involves different coating and
curing conditions. The coated metal sheets may be
fabricated into can bodies or ends in a later stage of
the manufacturing operation. One process, called the
sheet bake process, involves roll coating large metal
sheets. These sheets are then placed up-right in racks
and the racks are typically placed in ovens for about l0
minutes to achieve peak metal temperatures of about
180C to about 205C. In a coil coating process, the
second type of process, large rolls of thin gage metal
(e.g., steel or aluminum) are unwound, roll coated, heat
cured and rewound. During the coil coating process, the
total residence time in the curing ovens will vary from
about 2 seconds to about 20 seconds with peak metal
temperatures typically reaching about 230C to about
300C.
The aqueous coating composition of the present
invention is particularly suitable for use in coating
the ends or closures of food and beverage cans or for
can side seam coatings. Can ends are typically roll
coated on coil coating lines to a dry film weight (after
curing) of at least about 5 mg/in2, preferably about 7 to
about 9 mg/in2, and most preferably about 7.5 to about
8.5 mg/in2. The present coating composition may also be
used to coat the interior of the can body, where it
typically is applied via a sheet bake process.
The present aqueous coating composition can be
coated onto a metal substrate at a relatively high film
weight (e.g., 5 to 9 mg/in2). The integrity and
thickness of the uncured film can be sustained despite
the exposure of the coated substrate to translational
WO96/10612 2 2 u 1 7 ~ 4 PCT~S95/13223
forces (e.g., the translational forces generated during
the coating of large rolls of thin gage metal on high
speed coil coating lines). The coated substrate can
then be cured at high coating weights and high line
speeds without forming blisters. Use of the present
coating composition permits formation of a tough,
resilient cured film which is substantially free of
defects. Another advantage of the present aqueous
coating composition is that, despite differences in
performance requirements between the two processes, the
same composition used to form a relatively thick coating
via a coil coating process may also be employed to form
thinner coatings (e.g., a film weight of 3-4 mg/in2)
through a sheet bake process. This avoids the need to
develop separate formuiations to address the differing
requirements of the two application methods.
The aqueous coating composition includes at lea.st
about 50 wt.~ and, preferably, at least about 55 wt.~ of
a solvent component and at least about 30 wt.~ of a film
forming component (based on total weight of the coating
composition). The aqueous coating composition
preferably has sufficient viscosity and solids content
to permit application at a relatively high film weight
(e.g., 5 to 9 mg/in2) on a metal substrate subjected to
translational forces, such as the forces generated
during a coil coating process. Viscosity of the coating
composition should also be low enough to avoid
blistering during cure of the coated substrate.
Preferably, viscosity of the coating composition is
about 13 to about 100 seconds, more preferably about 20
to about 80 seconds and most preferably about 30 to
about 60 seconds (#4 Ford cup at 80F (27C)). Where
the coating composition is to be applied through a coil
coating process, the composition preferably includes at
least about 30 wt.~ and, more preferably, about 35 to
about 45 wt.~ of film forming component and typically
has a viscosity of about 30 to about 60 seconds (#4 Ford
WO96/10612 2 2 0 1 7 ~ 4 PCT~S95/13223
cup at 80F). For those applications where a sheet bake
process is to be utilized and relatively low coating
weight (e.g., 3-4 mg/in2) are desired, the composition
preferably includes about 35 to about 45 wt.~ of film
forming component and typically has a viscosity of about
50 to about 80 seconds (#4 Ford cup at 80F).
The coating composition is in the form of an
aqueous dispersion with the film forming component
substantially present in the form of particles. If
particle size is too large, stability problems may be
experienced with the dispersion. Typical particle size
is about O.l to about 0.6 micron, preferably about 0.2
to about 0;4 micron and, most preferably, no more than
0.35 micron. The pH of the coating composition is
preferably within the range of about 6.C to about 8.0
and more preferably is about 6.5 to about 7.5.
The solvent component includes water and an organic
solvent. Preferably, the solvent component includes
about 70 to about 97 wt.~ , more preferably about 75 to
about 95 wt.~ water and most preferably about 79 to
about 9l wt.~ water (based on the total weight of the
solvent component). In order to minimize cost and
environmental problems, it is desirable to include as
high a percentage of water as possible. Some organic
solvent is necessary, however, to prevent formation of
blisters during curing, particularly where the coating
is applied on a high speed coil coating line. The
solvent component typically includes at least about 3
wt.~, preferably at least about 5 wt.~ and more
preferably at least about 8 wt.~ organic solvent (based
on total weight of the solvent component).
Preferably the organic solvent is substantially
miscible with water and is either in the form of a
singular polar compound or as a mixture of compounds
which may include non-polar components. The solvent
typically is capable of dissolving the resins in the
film-forming component, thereby facilitating their
WO96/10612 2 ~ ~ 1 7 2 4 PCT~S95/13223
dispersion in an aqueous solution. Suitable solvents,
to be used either alone or as part of a mixture, include
glycol ethers and alcohols such as alkanols, monoalkyl
glycols, and alkyl carbitols (diethylene glycol
monoalkyl ethers). Among the most commonly used
solvents are alcohols such as butyl alcohols (e.g., n-
butanol), 2-butoxyethanol, Butyl Carbitol (diethylene
glycol monobutyl ether). Non-polar solvents may also be
included as minor constituents of the organic solvent.
Suitable non-polar solvents which may be used include:
aliphatic and aromatic hydrocarbons, such as naphtha,
heptane, mineral spirits, toluene and the like.
The film forming component includes a carboxy
addition polymer and an epoxy resin, which have been
reacted together in the presence of a tertiary amine
catalyst. A curing agent is then blended with the
resulting reaction product. The amounts (wt.~)
specified for the carboxy addition polymer, the epoxy
resin and the curing agent are expressed as a wt.~ based
on the total weight of the film forming component (i.e.,
the solids content of the coating composition).
The resin mixture includes at least about 7 wt.~,
preferably about 10 to about 40 wt.~ of the carboxy
addition polymer. Most preferably, the resin mixture
includes at least about 15 to about 25 wt.~ of the
carboxy addition polymer. The carboxy addition polymer
may be prepared by conventional polymerization processes
and is preferably a copolymer of at least one
polymerizable, ethylenically unsaturated carboxylic acid
monomer and at least one copolymerizable nonionic
monomer. Suitable ethylenically unsaturated carboxylic
acid monomers include acrylic, methacrylic, maleic,
fumaric and itaconic acids. The ethylenically
unsaturated carboxylic acid monomer is preferably an
~ unsaturated carboxylic acid having from 3 to 10 and,
more preferably, from 3 to 5 carbon atoms. Acrylic acid
and methacrylic acid are particularly preferred.
WO96/10612 PCT~S95/13223
22 0 ~- 724
Suitable copolymerizable nonionic monomers include
nonionic ethylenically unsaturated monomers, such as
vinyl aromatic compounds and alkyl esters of
ethylenically unsaturated carboxylic acids. Included
among the most commonly used copolymerizable nonionic
monomers are lower alkyl acryla-es (e.g., ethyl
acrylate), lower alkyl methacrylates, styrene, alkyl-
substituted styrenes, vinyl acetate and acrylonitrile.
Preferably, the copolymerizable nonionic monomer is
selected from the group consisting of styrene and Cl to
C6 alkyl esters of ~,~-unsaturated carboxylic acids
having 3 to 5 carbon atoms.
The weight average molecular weight of the carboxy
addition polymer is generally at least about 2,000 and
typically does not exceed about 60,000. More
prefe~ably, the weight average molecular weight of the
addition polymer is about 5,000 to about 25,000 and most
preferably, about 7,000 to about 15,000. Tne carboxy
addition polymer has an acid number of at least about
165, typically about 200 to about 350, and preferably
about 225 to about 325. The acid number is defined as
the amount of potassium hydroxide (in mg) required to
neutralize one gram of polymer (on a solids basis).
Typically, the carboxy addition polymer has a glass
transition temperature (Tg) of no more than about 110C
and, preferably, the glass transition temperature of the
carboxy addition polymer is about 50 to about lO0 C.
If the coating composition includes a relatively large
amount of epoxy resin (e.g., at least about 60 wt.
based on the total weight of the film forming
component), a carboxy addition polymer having a
relatively low Tg, i.e., about 50 to about lO0 C, is
typically employed.
The resin mixture also includes at least about 40
wt.~, and preferably about 50 to about 90 wt.~ of the
epoxy resin (based on the total weight of the film
forming component). Most preferably, the resin mixture
W096/10612 2 2 ~ 1 7 2 4 PCT~S95/13223
includes about 60 to about 80 w~.~ of the epoxy resin.
The epoxy resin may be any organic solvent-soluble resin
containing epoxy groups. Preferably, the epoxy resin
includes glycidyl polyethers having more than one
epoxide group per molecule (i.e., glycidyl polyethers
containing an average of greater than 1.0 epoxy groups
per molecule). Typically, the glycidyl polyethers have
an average of about 2.0 to about 2.5 epoxide groups per
molecule. Diglycidyl ethers of dihydric phenols are
particularly suitable for use in the present coating
composition. Exemplary dihydric phenols include
resorcinol, 1,5-dihydroxy naphthalene and bisphenols,
such as Bisphenol A (p,p'-dihydroxy-2,2-diphenyl
propane). Bisphenol A is the preferred dihydric phenol.
The epoxy resins typically used in the present invention
may be derived from the reaction of the dihydric phenol
and an epihalohydrin, such as epichlorohydrin.
Molecular weight of the initial reaction product may be
increased by reaction with additional dihydric phenol.
Epoxy resins suitable for use in the present inven,ion
typically have epoxide equivalent weights of at least
about 1,000 and no more than about 30,000. The upper
limit for the epoxide equivalent weight of the epoxy
resin is dictated primarily by the viscosity of the
resin that can be accomodated by the processing
equipment employed to prepare the coating composition.
Epoxy resins having an epoxide equivalent weight of
greater than about 30,000 are generally more viscous
than can be handled by conventional processing
equipment. The epoxide equivalent weight is preferably
about 1,500 to about 10,000. Diglycidyl ethers of
Bisphenol A are commonly available in commerce and
commercial materials such as Epon iO09F and Epon 1007F
(both available from Shell Chemical Company, Houston,
TX) are suitable for use in the present invention. Most
preferably, the epoxy resin includes a diglycidyl ether
WO96/10612 22 0 1 7 2 4 PCT~S95/13223
of Bisphenol A having an epoxide equivalent weight of
about 2,500 to about 8,000.
The epoxy resin may include diglycidyl ethers of
dihydric phenols whose molecular weight has been
increased ("upgraded") by reaction with additional
dihydric phenol or with a diacid. The inclusion of a
higher molecular weight epoxy resin improves the
flexibility of the coating composition and, in
particular, improves the resistance of the coating to
crazing during fabrication. It has been found that
incorporation of an epoxy resin which has been upgraded
by reaction with an aliphatic diacid may lower the
viscosity of the epoxy resin as well as improve the
flexibility of the coating ultimately formed from the
coating composition. Suitable aliphatic diacids which
may be employed to upgrade the epoxide equivalent weight
of the epoxy resin include adipic acid, succinic acid,
dimer fatty acid and the like. For example, the epoxy
resin may include a diglycidyl ether of Bisphenol A
which has been upgraded to ar. epoxide equivalent weight
of about 2,500 to about 8,000 by reaction with an
aliphatic diacid such as adipic acid. The weight of
diacid employed in the upgrade will depend on a number
of factors, such as the molecular weight of the diacid,
the epoxide equivalent weight of the starting epoxy
resin and the desired epoxide equivalent weight for the
epoxy resin. Typically, the amount of diacid used to
upgrade the epoxy resin ranges from about 0.5 to about
20 wt.~ and, preferably, from about l.0 to about 15 wt.
of the epoxy resin component.
The epoxy resin may also be partially
defunctionalized by reaction with a phosphorus-
containing acid or with an organic monoacid. The
phosphorus-containing acid is an acid having a P-OH
functionality or an acid that is capable of generating
such a functionality upon reaction with water (e.g., a
compound having a P-O-P functionality). Examples of
WO96/10612 PCT~S95/13223
2201 724
11 ,
suitable phosphorus-containing acids include
polyphosphoric acid, superphosphoric acid, aqueous
phosphoric acid, aqueous phosphorous acid and partial
alkyl esters thereof. The organic monoacid is
preferably an aromatic carboxylic acid having up to ten
carbon atoms or a Cl to C20 alkanoic acid. Examples of
suitable organic monoacids include acetic, benzoic,
stearic, palmitic and octanoic acids. The epoxy resin
is typically defunctionalized by reacting from up to
about S0~ of the epoxy groups present with the organic
monoacid. Where the epoxy resin is defunctionalized by
reaction with the phosphorus-containing acid, up to
about 50% of the epoxy groups are typically reacted with
the acid.
The reaction between the carboxy addition polymer
and the epoxy resin is carried out in the presence of
about 0.35 to about 1.0 equivalents and, more
preferably, about 0.5 to about 0.& equivalents, of a
tertiary amine catalyst per equivalent of carboxy groups
present in the carboxy addition polymer. ~xamples of
suitable tertiary amines include trialkyl amines (e.g.,
diethylbutyl amine), dialkyl benzyl amines, and cyclic
amines such as N-alkyl pyrrolidine, N-alkyl morpholine
and N,N'-dialkyl piperidine. Tertiary amines containing
at least two methyl groups, such as dimethyl
ethanolamine, trimethylamine and dimethylbenzyl amine,
are preferred.
The film forming component includes at least about
2 wt.% curing agent (based on the total weight of the
film forming component). More preferably, the film
forming component includes about 3 to about 45 wt.~, and
most preferably, about 5 to about 25 wt.% of the curing
agent. The curing agent includes an aminoplast resin
and/or a phenoplast -esin.
Preferably, the curing agent includes a phenoplast
resin. Phenoplast resins are condensation products of
an aldehyde, such as formaldehyde or acetaldehyde, -ir:d 3
WO96/10612 2 2 0 1 7 ~ ¢ PCT~S95/13223
phenol. Suitable phenoplast resins may be derived rrom
an unsubstituted phenol, cresol or other alkyl phenols
as well as from dihydric phenols such as Bisphenol A.
Mixtures of phenols may be used to vary and control
properties of the phenoplast resin. The phenoplast
resin preferably includes at least one of an alkylated
phenol-formaldehyde resin and a bisphenol A-formaldehyde
resin. The melting point of the phenoplast resin is
preferably no more than about 100C. Alkylated phenol-
formaldehyde resins which are suitable for use in thepresent coating compositions include polymeric, solid
resins having low color and a molecular weight of at
least 1000. Such alkylated phenol-formaldehyde resins
are typically based on one or more longer chain
alkylated phenols, e.g., phenols substituted with an
alkyl group having from 4 to 10 carbon atoms.
Representative longer chain alkylated phenols include t-
butylphenol, hexylphenol, octylphenol, t-octylphenol,
nonylphenol, decylphenol and dodecylphenol.
2C The film forming component may also include a
hydrophobic addition polymer. The incorporation of a
hydrophobic addition polymer as an additional component
in the present coating ccmpositions may lead to an
enhancement in the flexibility, adhesion and/or water
resistance of coatings derived from the composition.
When present, the amount of the hydrophobic addition
polymer added to the coating composition typically
ranges from about 5 to about 35 wt.~ and preferably from
about 10 to about 30 wt.~ of the film forming component
("solids content").
The hydrophobic addition polymer has a relatively
high molecular weight and is typically formed by the
polymerization of one Gr more nonionic monomers (i.e.,
monomers which do not include an ionizable functional
group such as a carboxylic acid or an amine). The
weight average molecular weight of the hydrophobic
addition polymer is typically at least about 50,000 and
WO96/10612 PCT~S95/13223
2201 1~4
preferably at least abouL l00,000. Polymers of this
type may be prcduced by an emulsion polymerization
process. The preparation of addition polymers of this
type is disclosed in U.S. Patent Nos. 4,446,258 and
4,476,262, the disclosure of wh,ch is herein
incorporated by reference. Preferably, the hydrophobic
addition polymer is formed in SiLU by emulsion
polymerizing one or more ethylenically unsaturated
nonionic monomers in the presence of an aqueous
dispersion of the carboxy addition polymer/epoxy resin
reaction product.
The hydrophobic addition polymer is preferably
formed from a monomer or monomers which do not include a
hydrophilic group, such as a hydroxyl group or an
ionizable group. Examples of suitable hydrophobic
monomers include hydrophobic ethylenically unsaturated
monomers such as vinyl aromatic compounds or alkyl
acrylate and methacrylate esters. In a preferred
embodiment of the invention, the hydrophobic addition
polymer is formed via emulsion polyrnerization of a
mixture of styrene and butyl acrylate.
The present hydrophobic addition poiymer typically
has a relatively low Tg, e.g., a Tg of no more than about
100C. Preferably, the present hydrophobic addition
polymer has a Tg cf no more than about 40C, and more
preferably no more than about 20C. Hydrophobic
addition polymers which are in a rubbery state at
ambient temperatures are highly effective for use in the
present coating compositions. One example of a suitable
hydrophobic addition polymer which may be employed in
the present coating composition is a polymer formed from
a l:l mixture of styrene and butyl acrylate and having a
calculated Tg of 3C.
Depending upon the desired application, the coating
composition may include other additives such as
lubricants, coalescing solvents, leveling agents,
wetting agents, thickening agents, suspending agents,
-
WO96/10612 PCT~S95/13223
220 1 l24
14
surfactants, defoamers, adhesion promoters, corrosion
inhibitors, pigments and the like. Coating
compositions, which are to be used as a can coating,
typically include a lubricant such as a hard, brittle
synthetic long-chain aliphatic wax, a carnuba wax
emulsion, or a polyethylene/Teflon~ blend.
The coating composition of the present invention
may be prepared by conventional methods. For example,
the coating composition may be prepared by adding the
epoxy resin to a solution of the carboxy addition
polymer in a solvent mixture which includes an alcohol
and a small amount of water. During the addition, an
inert gas blanket is maintained in the reactor and the
solution of the carboxy addition polymer is warmed,
typicaliy to about 100C. The mixture is maintained at
that temperature and stirred until the epoxy resin is
dissolved. The tertiary amine (e.g., dimethylethanol
amine) is then added and the resulting mixture stirred
for a period of time at elevated temperature. The
curing agent, which typically includes a pher,oplast
resin, is then added and the batch is held for roughly
30 minutes at a temperature of about 90 to 100C.
Deionized water is added under maximum agitation to
emulsify the resin and the temperature is allowed to
drop. Additional deionized water is typically added at
a uniform rate over a period of about one hour while the
batch is cooling. The final visccsity is adjusted to
the desired value (typically 30-60 seconds (#4 Ford cup
at 80F) by further addition of deionized water. The
coating composition that is produced may be used as is
or other additives (e.g., a lubricant) may be blended in
to form the final coating composition.
The present invention also provides a method of
coating a metal substrate to provide a substantially
continuous film on at least one surface of the
substrate. The method includes applying the above
described aqueous coating composition onto the metal
WO96/10612 PCT~S9S/13223
2 2 ~ 4
surface to form a coating layer and heating the coated
substrate so that the coating layer cures to form a
cured film which adheres to the substrate surface. The
cured film has a film weight of at least about 3 mg/in2,
preferably at least about 5 mg/in2, and is substantially
free of blisters. The present coating compositions are
typically used to produce blister free cured films
having films weights of about 7 mg/in2 to about 9 mg/in2.
The coating composition may be applied to the substrate
surface using a variety of well-known techniques. For
example, the composition may be roll coated, bar coated
or sprayed onto the surface. Where large rolls of thin
gauge metal are to be coated, it is advantageous to
apply the coating composition via reverse roll coating.
Where large metal sheets are to be coated, the coating
composition is typically direct roll coated onto the
sheets as part of a sheet-bake process. The sheet-bake
process is typically used to form a coated metal
substrate where a relatively low (e.g., about 3-4
mg/in2), cured film weight is desired. If the coating is
applied using a sheet-bake process, the coated metal
substrate is typically cured at a temperature of about
180C to about 205C for about 8 to about lO minutes.
In contrast, when the coating is carried out using a
coil-coating process, the coated metal substrate is
t-ypically cured by heating for about 2 to about 20
seconds at a temperature of about 230OC to about 300C.
If the coil-coating process is used to produce material
to be fabricated into can ends, the cured film on the
coated metal substrate typically has a film weight of at
least about 5 mg/in2 and preferably, about 7 to about 9
mg/in2.
The present invention may be further described by
reference to the foliowing examples. Parts and
percentages, unless otherwise designated, are parts and
percentages by weight.
WO96/10612 PCT~S95/13223
22~ ~ ~24
16
Examples
Example 1
Carboxy Addition Polymer A
A five liter reactor was fitted with stirrer,
condenser, heater, and thermometer with inert gas inlet.
An inert gas blanket was introduced to the reactor.
n-Butanol (3636 parts) and 403 parts deionized water
were charged to the reactor and the solvent mixture was
heated under agitation to reflux (95-97C). In a
separate vessel, a monomer premix was prepared from 1160
parts ethyl acrylate, 1864 parts acrylic acid, 2480
parts styrene and 432 parts 70~ benzoyl peroxide. The
monomer premix was added to the reactor over four hours
while maintaining the temperature at 95-97C. After the
addition was complete, the batch was cooled to 93C and
held at that temperature for one hour. After the one
hour hold period, 31 parts 70~ benzoyl peroxide were
added and the batch was held for another two hours at
g3C to ensure complete reaction. The final product had
an acid number of 248 and contained 57.9 wt.
nonvolatile components.
ExamPles 2-7
Carbox~ Addition Polymers B-G
Using a simi'ar procedure to that described in
Example 1, a solution of a carboxy addition polymer
(CAP) in 3636 parts n-butanol and 403 parts deionized
water was prepared from ethyl acrylate, styrene and
either acrylic acid or methacrylic acid (the parts by
weight of the monomers used to prepare each specific CAP
are shown in Table I) with 463 parts 70~ benzoyl
peroxide. The final products were characterized as
shown in Table I.
WO96/10612 PCT~S95/13223
2201 /~4
ExamPle 8
Coatinq Com~osition 1
A reaction flask was prepared with a stirrer,
condenser, heater and thermometer with an inert gas
inlet. An inert gas blanket was introduced and 112.6
parts Epon 828 (Shell Chemical; Houston, TX), 59.4 parts
Bisphenol A, 9.1 parts diethylene glycol monobutyl ether
(Butyl Carbitol) and 0.15 parts
ethyltriphenylphosphonium iodide were charged to the
reactor. The mixture was heated with agitation to 121C
and allowed to exotherm to 170-180C. Following the
exotherm, the batch was held at 155-160C until an epoxy
value of 0.050 was attained. Then 16.0 parts diethylene
glycol monobutyl ether was added. Then 155.0 parts of
the solution of the carboxy addition polymer from
Example E was added and the temperature was allowed to
drcp to 96C. The batch was stirred to achieve
uniformity. After the batch was uniform,
dimethylethanol amine (22.0 parts) was added at a
2C uniform rate and the batch was held for thirty minutes
at 90-98C. An exotherm was seen immediately following
the amine addition. After the thirty minute hold, 86.0
parts t-butylphenol-formaldehyde resin (average degree
of polymerization of 6) was added and the batch was
stirred for thirty minutes at 90-98C. The heat was
then turned off and 103 parts deionized water were added
at a uniform rate to emulsify the resin. The batch was
held for one hour, then 240 parts deionized water were
added over one hour at a constant rate. The resulting
epoxy/acrylate/phenolic composition contained 4.19 wt.
nonvolatile components.
The epoxy/acrylate/phenolic composition (100 parts)
from above was charged to a mixing vessel equipped with
an agitator. Deionized water, 7.44 parts, was added
under agitation and mixed until uniform. The resulting
coating composition had a theoretical nonvolatile
component of 39.0 wt.~.
WO96/10612 PCT~S95/13223
2201-724
18
Example 9
Coatinq Composition 2
A l liter reaction flask was fitted as described in
Example 8 and 247 parts of the carboxy addition polymer
prepared in Example E was charged. The resulting
mixture was heated with agitaticn to approximately 100C
under an inert gas blanket. Epon lOO9F epoxy resin
(Shell Chemical; Houston, TX; 138 parts) was added to
the reaction flask and the mixture was stirred at 100C
until the epoxy resin dissolved. After the batch was
uniform, stirring was continued until the batch was
96C. Dimethylethanol amine (32.0 parts) was then added
at a uniform rate and the resulting mixture was stirred
for thirty minutes at a temperature of 90-98C. t-
Butylphenol-formaldehyde resin (average degree of
- polymerization of 6; 68.8 parts) was then added. The
batch was held thirty minutes at 90-98C and 94 parts
deionized water was added under maximum agitation to
emulsify the resin The temperature was allowed to drop
to 80-82C while the batch was held for sixty minutes.
The heat was turned off and deionized water (220 parts)
was added at a uniform rate over one hour and the batch
was allowed to cool. The resulting
epoxy/acrylate/phenolic composition had a nonvolatile
content of 43.1 wt.~.
The epoxy/acrylate/phenolic composition (100 parts)
was charged to a mixing vessel equipped with an
agitator. Deionized water (13.4 parts) was added under
agitation and mixed until uniform to produce a coating
composition with a theoretical nonvolatile component of
38.0 wt.~.
Examples 10-31
Coatinq Compositions 3-20
Using a procedure similar to that described in
either Examples 8 and 9, coating composition 3-20 were
prepared from a t-butylphenol-formaldehyde resin
WO96/10612 PCT~S95/13223
2201 72~ -
19
(average degree of polymerization of 6) and the carboxy
addition polymers and epoxy resins indicated in Table
II.
Two of the epoxy resins used, Epon lOO9F and Epon
1007F, were obtained from a commercial source. Epon
lOO9F (Shell Chemical Company, Houston, TX) is an epoxy
resin derived from Bisphenol A and epichlorohydrin
having an epoxide equivalent weight of about 3000 and an
epoxy value of 0.026-0.043. Epon 1007F (Shell Chemical
Company, Houston, TX) is an epoxy resin derived from
Bisphenol A and epichlorohydrin having an epoxide
equivalent weight of 1700-2300 and an epoxy value of
0.043-0.059.
The other epoxy resins were obtained by reacting a
commercial epoxy resin (Epon 828) with Bis-phenol A.
Epon 828 (Shell Chemical Company, Houston, TX) is an
epoxy resin derived from Bisphenol A and epichlorohydrin
having an epoxide equivalent weight of 185-192 and an
epoxy value of 0.52-0.54. Epoxy resin H is an epoxy
resin having an epoxy value of 0.038 and was obtained by
reacting Epon 828 and Bisphenol A (in a weight ration of
64.80/35.20) using the procedure described in Example 8.
Epoxy resin M is an epoxy resin having an epoxy value of
0.050 and was obtained by reacting Epon 828 and
Bisphencl A (in a weight ration of 65.65/34.35) as
described in Example 8. Epoxy resin L is an epoxy resin
having an epoxy value of 0.115 and was obtained by
reacting Epon 828 and Bisphenol A (in a weight ration Gf
70.25/29.75) using the procedure described in Example 8.
In each instance, the carboxy addition polymer and
epoxy resin were reacted by heating after the addition
of dimethylethanol amine catalyst (0.65 equivalent per
equivalent of carboxy groups present in the carboxy
addition polymer). The t-butylphenol-formaldehyde resin
was then added followed by dilution with water as
described in Examples 8 and 9 to form an intermediate
coating composition. The coating compositions based on
WO96/10612 2 2 J 1 7 2 4 PCT~S95/13223
either Epon lO09F or Epon 1007F were prepared in a n-
butanol/water solvent system according to the procedure
described in Example 9. The coating compositions based
on either Epoxy Resin H, Epoxy Resin M, or Epoxy Resin L
were prepared in a Butyl Carbitol/n-butanol/water
solvent system according to the procedure described in
Example 8. The wt.~ nonvolatile components (solids),
viscosity, pH and particle size for each of the
intermediate coating compositions are shown in Table
III.
The intermediate coating compositions described
above were diluted with water (where necessary) to
obtain a final coating composition having a viscosity
and wt.~ solids within the desired ranges (viscosity -
about 30 to about 60 seconds (#4 Ford cup at 80F);about 30 to about 45 wt.~ solids). Using an
app~opr-ately sized barcoater, each of coating
compositions 1-20 were applied to aluminum metal panels
to form a "blister panel." The blister panels were
cured by baking for lO seconds in a 450F oven (peak
metal temperature of 450F) to produce cured coated
metal panels having a cured film weight of 7.5 to 8.0
mg/in' The cured coated metal panels were evaluated for
the forma.ion of blisters. The results of these
evaluations are summarized in Table II. The results
shown in Table II demonstrate that the aqueous coating
compositions of the present invention are capable of
being applied at high coating weights and cured at high
line speeds without blistering to provide a resilient,
cured film.
Particle Size Determinations
The measurement of the average particle size of the
polymer~c dispersions reported in Table III were carried
out using a Spectronic 20 ~ausch & Lomb 33-39-61-62
spectrophotometer. About one-half to one drop of the
coating composition under evaluation was added to 50 ml
WO96/10612 2201 /~ PCT~S95/13223
distilled water. The sample cell of the
spectrophotometer was filled from 1/4 to 1/2 full with
the resulting solution. The solution was then further
diluted by adding distilled water to fill approximately
3/4 of the cell. After shaking the cell to produce a
homogeneous solution, the percent transmittance of the
diluted solution was measured at a wavelength of 375
millimicrons. The concentration of dispersed polymer in
the solution was then adjusted so that the solution had
an optical density between 0.50 and 0.54 at 375
millimicrons. The optical density of the solution was
then measured at 375, 450, 500 and 550 millimicrons.
For each solution, log(optical density) was plotted
versus log(wavelength) and the average particle size was
determined from the slope of the plot, where
Log(OD3~5) - Log(oDsso)
Slope = -------------------------
0.167
and
20Average Particle Size = Antilog [0.055 - 0.2615
(Slope)].
Viscosity Measurements
For the purposes of this application, #4 Ford cup
viscosity was determined using a slightly modified
version cf ASTM D-1200-54, which is a procedure used for
determining the viscosity of paints, varnishes and
related liquid materials. The procedure is carried out
with a #4 Ford-type efflux viscosity cup (available from
Scientific Instrument Co., Detroit, MI). The liquid
material (as a solution or dispersion) and the #4 Ford
cup are brought to a constant temperature of 80F. The
orifice at the bottom of the viscosity cup is closed and
the liquid material to be tested is then poured into the
viscosity cup to a slight overflowing of the inner cup.
After any excess material is allowed to flow into the
outer cup, the orifice at the bottom of the cup is
opened. The time interval required for the appearance
WO96/10612 2 2 0 1 7 ~ 4 PCT~S95/13223
of the first break in the stream of material flowing
from the orifice is measured using a stopwatch. The
viscosity is reported as the elapsed time to the
appearance of the first break in the stream.
In some instances, viscosity was determined using a
Brookfield Model LVF viscometer (Brookfield Engineering
Laboratories, Inc.). The Brookfield viscometer measures
the torque required to rotate a spindle head immersed in
the coating composition at a given angular velocity.
The viscosity is reported in units of centipoises.
RESISTANCE TO BLISTERING
The coating composition to be evaluated (100-150
g.) was placed in a 9 oz. jar and agitated for 20
seconds with a plastic prop attached to a high speed
motor. The coating composition was then bar coated onto
an aluminum panel to form a "blister panel" having a
7.5-8.0 mg/in2 thick coating. A "blister panel" is only
coated in the middle of the panel. This enables more
heat to be appl~ed to the coating and ir.creases the
severity of the blister test.
The coated bliste r panel is air dried for 5 seconds
and then immediately placed in a coil coating oven with
a peak metal temperature of lO seconds at 450F. After
removal from the oven, the cured coated panel in water
quenched and visually inspected for blisters. The
resistance of the coating to blistering is rated on a
pass/fail scale.
Exam~le 32
Coatinq Com~osition 25
An inert gas blanket was introduced to a reaction
flask fitted with a stirrer, condenser, heater,
thermometer and a gas inlet. The flask was charged with
572.4 parts of coating composition 6 (described in
Example 13) and agitation was started. Deionized water
(159.8 parts) was added and the resulting mixture was
WO96/10612 PCT~S95/13223
2 2 ~
st ^red until uniform. Styrene (25.6 parts) and butyl
acrylate (25.6 parts) were then added and the inert gas
blanket was converted to an inert gas sparge. The
mixture was heated to 75C and the gas sparge was
converted back into an inert gas blanket. Benzoin (0.51
parts) was added and the mixture was heated. When the
temperature of the mixture reached 80C, a 30~ hydrogen
peroxide solution (2.56 parts) was added and the
resulting mixture was maintained at 83-86C for 2 hours.
Additional portions of styrene (12.8 parts) and benzoin
(0.13 parts) were then added and the batch was stirred
for 5 minutes. Another portion of 30~ hydrogen peroxide
solutior. ~0.64 parts) was added and the reaction mixture
was maintained at 83-86C for another 4 hours. The
resulting coating composition included the t-
butylphenol-formaldehyde resin, the reaction product
formed from epoxy resin H and carboxy addition polymer A
(as described in Example 13), and a styrene/butyl
acrylate hydrophobic addition polymer. The
styrene/butyl acrylate hydrophobic addition polymer had
a calculated Tg of 3C.
Exam~le 33
Carboxy Addition Polymer H
Acrylic acid (2542 parts), styrene (748 parts) and
ethyl acrylate (2208 parts) were reacted according to
the procedure described for the preparation of carboxy
addition polymers B-G in Example 2-7. The resulting
carboxy addition polymer ("H") had an acid number of 339
and a solids content of 57.0 wt.~.
Example 34
Coatinq Com~osition 26
An inert gas blanket was introduced to a reaction
flask fitted with a stirrer, condenser, heater,
thermometer and a gas inlet. The flask was then charged
with ~98.1 parts Epon 828 (Shell Chemica'; Hcuston, TX),
WO96/10612 2 2`iO-1 7 2 4 PCT~S95/13223
Bisphenol A (268.1 parts), Butyl Carbitol (57.4 parts)
and ethyltriphenylphosphonium iodide (0.65 parts). The
mixture was heated with agitation to 130C and allowed
to exotherm to 170-180C. Following the exotherm, the
batch was held at 155-160C until an epoxy value of
0.041 was attained. The temperature was allowed to drop
to 145-150C and diethylene glycol monobutyl ether (57.3
parts) was added followed by adipic acid-(8.8 parts) and
tri-n-butyl amine (0.5 parts). The reaction mixture was
then maintained at 145-150C until an epoxy value of
0.025 was attained. The temperature of the reaction
mixture was then allowed to drop to about 135C while
diethylene glycol monobutyl ether (177.2 parts) was
added.
A solution of carboxy addition polymer H (175.4
parts) prepared according to the procedure described in
Example No. 33 was added. The resulting mixture was
stirred at 102C until the batch was uniform. After the
batch had become uniform, dimethylethanolamine (27.0
parts) was added at a uniform rate over a period of 7
minutes. The resulting mixture was maintained at 95-
100C for 30 minutes. A mixture of bisphenol A-
formaldehyde resin (average degree of polymerization of
about 2) was added and the resulting mixture was stirred
until all of the solids had dissolved. Deionized water
(1067 parts) was then added over 2 hours and the
resulting coating composition was allowed to cool to
room temperature.
The invention has been described with reference to
various specific and preferred embodiments and
techniques. It should be understood, however, that many
variations and modifications ma-y be made while remaining
within the spirit and scope of the invention.
WO 96/10612 2 2 0 1 7 2 4 PCT/US95/13223
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WO96/10612 PCTrUS95/13223
2201 724
TABLE II
COATING COMPOSITIONS
COATING EPOXY EPOXY CAP CAP PHENOLIC
COMPOSITION TYPE LEVEL TYPE LEVEL LEVEL BLISTERS
1 M 50 E 25 25 PASS
2 1009/F 40 E 40 20 PASS
3 1009/F 53 A 30 17 PASS
4 1007/F 53 C 30 17 PASS
1009/F 53 D 30 17 PASS
6 H 60 A 20 20 PASS
7 H 60 B 20 20 PASS
8 H 60 D 20 20 PASS
9 M 60 A 20 20 PASS
M 60 F 20 20 PASS
;1 H 70 A 20 10 SLIGHT
i2 H 70 D 20 1~ SLIGHT
13 H 75 A 20 5 PASS
'4 M 75 C 20 5 FAIL
1009/F 50 D 40 10 PASS
-5 L 50 F 25 25 PASS
7 1007/F 50 B 30 20 PASS
_8 H 50 E 30 20 PASS
;9 H 40 - 15 5 PASS
H 40 G 15 45 PASS
21 1009/F 60 D 35 5 SLIGHT
22 1007/F 60 G 35 5 FAIL
23 H 80 C 15 5 PASS
24 H 80 G 15 5 FAIL
SUBSTITUTE SHEET (RULE ~6~
WO96/10612 2 2 0 1 7 2 4 PCT~S95/13223
TABLE III
PXYSICAL CONSTANTS OF
INTERMEDIATE COATING COMPOSITIONS
In~ermedia_e Soiids Viscosity pH Part Size
Coatinc (cps)
C~osit__
1 41.9~18300 7.0 0.23
2 43.~8500 7.1 0.57
3 ~3.3%5560 6.8 0.27
q 42.9~58000 6.5 0.34
43.4~6510 7.1 0.28
6 ~2.6%224 7.0 0.27
7 43.~96000 7.0 0.23
8 42.0~ 83 7.4 0.26
9 43.4~9180 7.0 0.26
41.6'~1300000 6.8 0.25
11 43.8~7520 7.0 0.18
12 42.3~12~ 7.1 0.18
13 44.5~1370C 7.0 0.19
14 35.5~10960 6.8 0.16
42.6~1840 7.0 0.40
16 35.~%590000 7Ø 0.25
17 36.5~22400 7.C 0.28
1~ 4~.7~3600 7.2 0.37
_ G ~1.6~ 65 6.7 Q.52
2~ ~1.7~565 7.~ 0.32
21 42.9~1640 7 3 n, 22
22 30.6%8800 7.5 0.14
23 38.5%1848 6.8 C.17
24 31.7%2000 7.7 ~.15
SUaSTlTUTESHEET (RUEE 26)
WO96/10612 PCT~S95/13223
~ o ~ 4
28
TABLE IV `
COATING COMPOSITION SOLVENT COMPONENTS
AND FINAL SOLIDS
Ir.termediate
Coating Final Coating Composition
Com~os;.lon
Coating Solids Organic
Composition Water/Organic (Theoretical) Water/Organic Component~
1 80.55/'9.45 39.6 82.84/17.16 3uOH/BuC
2 ,,.46!2-.-4 38.0 82.01/17.99 BuOH
3 -:.7;,~':E.,7 40.6 84.17/15.83 3uOH/BuC
4 92.53/:7.32 36.6 87.27/12.73 BuOH/BuC
50.53/'C.32 40,0 83.30/16.70 3uOH/BuC
6 ^C.:3,'C.E7 42.6 80.13/19.87 3uOH/BuC
7 8^.21/'iC.7.- 38.0 84.05/15.95 3uOH/BuC
8 -^.;5/2C.-_ 42 0 79.45/20.55 3uOH/BuC
9 EC.:3'15.'7 40.0 82.82/17.13 BuOH/BuC
lC E:.98/;E.02 32.0 88.30/11.70 BuOH/BuC
11 E^.:3/'.-^7 40.0 83.11/16.8S BuOH/3uC
:2 7,-.45/2C.5_ 42.3 79.45/20.55 3uOH/BuC
13 8C.13/1C.87 40.0 83.59/16.4; BuOH/BuC
~4e- . 9- /14 . o - 32.0 88.01/11.59 3uOH/BuC
7^.17!2c.s3 40.0 81.41/18.59 BuCH
:5 8~.C9,~12 -: 30.0 90.02/9.98 3uOH/3uC
;7 E-.75,':^.~_ 32.0 88.74/11.2~ 3uOH/BuC
:3 E:.3C/:E.'. 38.0 84.10/15.50 3uOH/3uC
:9 5~.07,:5,,-_ 41.6 80.07/19.9} 3uOh-JBuC
7,-.5,'2C.'4 40.0 81.28/18.7^ 3uOH/3uC
2' E_.36,~:E.-4 40.0 E3.56/16.4~ 3uOH/3uC
22 E~.'7/11.-3 28.0 89.97/10.03 BuO:-
23 82.E9,~:7.:- 36.0 E4.68/15.3~ 3uOH/BuC
24 85.99/ 3.0: 31.7 86.99/13.01 3~0H/BuC
UOr: - n-Butar,ol
3uC - r.-3utyl Carb:~o
SUBSTITUTE SHE'T ~P.ULE 2~)
