Stable aqueous dispersions of mixed resins and process for use as coating compositions

Aqueous dispersions of mixed resins are prepared by polymerizing in the presence of an aminoplast resin a mixture of polymerizable carboxylic acid monomers and other monomers, adding to the polymerization product an epoxy resin, adding ammonia or an amine to salt the acid groups and dispersing the resin mixture in water. The aqueous dispersions are useful as can coatings.

BACKGROUND OF THE INVENTION 
This invention relates generally to thermosetting coating compositions that 
are useful for coating substrates such as metal surfaces. 
In the manufacture of metal containers, a thin protective synthetic resin 
coating is applied to the interior of the container. The synthetic resins 
employed for coating the interior of the metal container are nominally 
heat-curable polymeric compositions which are applied in the form of a 
solution or dispersion in a volatile organic solvent. During the drying 
and baking cycle of a coating operation, there is the problem of 
contending with the hazard of solvent vaporization and recovery. 
The can manufacturing industry utilizes cans which are fabricated from 
aluminum or steel. The interior of the cans are coated with a thin 
thermoset film to prevent the contact of the interior metal surface of the 
can with its contents. Such coatings ideally should have good adhesion to 
the interior metal surface, low extractables to prevent contamination of 
the container contents, and a rapid cure rate for economy of container 
manufacture. Typical synthetic resin coating compositions include vinyls, 
butadienes, epoxies, alkyl/aminoplasts, and oleoresinous materials. Many 
of these resinous coating systems have the disadvantage that they require 
batch premixing just prior to a coating operation, or they require 
continuous in line mixing in a container coating assembly. 
Various technical investigations have addressed the most serious of the 
problems relating to industrial scale application of protective coatings 
to articles of manufacture. 
U.S. Pat. No. 3,118,848 describes coating compositions which are prepared 
by mixing together a water-soluble salt of a vinyl polymer, and a 
water-soluble epoxy or polyhydroxy compound. One or more water-soluble 
phenol-aldehyde or amino resins, notably water-soluble urea-aldehyde or 
melamine-aldehyde resins, may optionally be included as curing agents 
where low baking temperatures are contemplated. 
U.S. Pat. No. 3,156,740 describes thermosetting acrylic resin compositions 
adapted for application as coatings to protect metal surfaces from the 
action of water, soap, grease, light and prolonged heat. Illustrative of 
the preparation of a thermosetting resin composition, there are co-reacted 
(a) a copolymer of 2-10% of acrylic acid, 4.5-88% styrene and 9-93% of 
2-ethylhexyl acrylate and (b) 1-epoxyethyl-3,4-epoxycyclohexane, and then 
there is mixed therein (c) a melamineformaldehyde resin in an amount of 
5-50% by weight based on the total non-volatile content of the 
composition. 
U.S. Pat. No. 3,215,756 describes heat-curable mixtures of a vinyl polymer 
with an epoxy compound in the presence of an amino resin. For example, a 
methacrylic acid/methyl acrylate copolymer is admixed with a polyglycidyl 
ether of Bisphenol A and a urea-formaldehyde resin in an organic solvent, 
and then coated on a substrate and baked to a thermoset film. 
U.S. Pat. No. 3,403,088 describes water-dispersed coating compositions 
which can be applied by electrodeposition. The coating compositions 
contain an at least partially neutralized acrylic interpolymer and an 
amine-aldehyde condensation product or a polyepoxide or both. 
U.S. Pat. No. 3,418,392 describes a crosslinking composition for an 
interpolymer (e.g., styrene/n-butyl acrylate/methacrylamide) which 
consists of a mixture of a polycycloaliphatic polyepoxide (e.g., 
3,4-epoxy-6-methylcyclohexylmethyl 
2,4-epoxy-6-methylcyclohexanecarboxylate) and a reactive triazine compound 
(e.g., hexamethoxymethylmelamine). The coating composition is recommended 
for use in textile print pastes, padding liquor for pigment dyeing of 
textiles, nonwoven textile impregnation dispersions, and generally as 
solvent based protective coatings for metal surfaces and the like. 
U.S. Pat. No. 3,467,730 describes heat-convertible coating compositions 
which are prepared from carboxy-containing copolymers, epoxide resins and 
aminoplast resins. In an example, 37 grams of a 50% copolymer (72% 
styrene, 20% methyl acrylate and 8% acrylic acid) solution, 6.9 grams of a 
polyglycidyl ether of Bisphenol A and 8.3 grams of a butylated 
urea-formaldehyde resin were blended, drawn down on glass, and cured at 
200.degree. C. for 30 minutes. 
U.S. Pat. No. 3,908,049, describes a method for coating metal surfaces 
which involves preparing an aqueous dispersion containing a mixture of a 
neutralized water-dispersible carboxylic acid containing polymer, a 
water-dispersible heat-curable thermosetting aminoplast or polyepoxide 
resin and a water-insoluble, long chain monohydroxy alcohol having 8-36 
carbon atoms, applying the aqueous dispersion to a metal surface, and 
baking the coating at 350.degree.-450.degree. F. to volatilize the alcohol 
and cure the coating. 
U.S. Pat. No. 3,960,979 describes a fast curing high solids coating 
composition which can be applied to the interior of food and beverage cans 
with a hot melt spray gun. The coating composition is a blend of (a) a low 
molecular weight epoxy resin (b) a liquid nitrogen resin or phenolic 
crosslinking agent, (c) a flexibilizing polyol, (d) and inorganic or 
organic monomeric or polymeric acid which acts both as reactant and 
catalyst, and optionally (e) a surface modifier such as an acrylic polymer 
containing acrylic acid. 
There is continuing research effort directed to the development of improved 
heat-curable resin coating systems adapted for application as protective 
films on metal surfaces and other substrates. 
Accordingly, it is an object of this invention to provide an improved 
water-reducible heat-curable thermosetting coating composition adapted for 
the protective coating of metal surfaces. 
It is another object of this invention to provide a coating system which 
comprises a stable dispersion of heat-curable mixed resin solids in water. 
It is a further object of this invention to provide a stable 
water-reducible epoxy resin dispersion adapted for one package baked 
coating applications. 
Other objects and advantages of the present invention shall become apparent 
from the accompanying description and examples. 
DESCRIPTION OF THE INVENTION 
One or more objects of the present invention are accomplished by the 
provision of a process for preparing a stable aqueous dispersion of mixed 
resins adapted for application as a heat-curable coating composition, 
which process comprises the steps of (1) preparing a solution of an 
aminoplast in a substantially water-miscible organic solvent; (2) heating 
the solution and adding thereto a mixture of vinyl polymerization catalyst 
and .alpha.,.beta.-olefinically unsaturated carboxylic acid monomer and at 
least one other vinyl polymerizable monomer to form a polymerization 
product solution; (3) admixing and heating together the polymerization 
product solution and an epoxy resin; (4) at least partially neutralizing 
and admixture with ammonia or an organic amine; and (5) dispersing the 
admixture into an aqueous medium to provide a stable aqueous dispersion of 
mixed resin solids. 
In another embodiment, the present invention further provides a process for 
the preparation of a stable aqueous dispersion of mixed resins adapted for 
application as a thermosetting protective coating for metal surfaces, 
which process comprises the steps of (1) preparing a solution of an 
aminoplast component in a substantially water-miscible organic solvent; 
(2) heating and maintaining the temperature of the solution in the range 
between about 120.degree.-300.degree. F., and adding to the solution at a 
uniform rate over a period between about 0.5-6 hours, a blend of a vinyl 
polymerization catalyst and monomers comprising (a) between about 20 to 
about 90 weight percent based on total monomer weight of an 
.alpha.,.beta.-olefinically unsaturated carboxylic acid, and (b) 10 to 
about 80 weight percent based on total monomer weight of at least one 
olefinically unsaturated monomer which is copolymerizable with the 
carboxylic acid monomer, thereby forming a polymerization product 
solution; (3) admixing and interacting at a temperature between about 
100.degree. to about 300.degree. F., the polymerization product solution 
and an epoxy resin component, wherein said epoxy resin is a glycidyl 
polyether of a polyhydric phenol or hydrogenated phenol and contains an 
average of more than one epoxide group per molecule and has an epoxy 
equivalent weight in the range between about 150 to about 8000; (4) 
treating and at least partially neutralizing the admixture reaction 
product medium with a basic reagent selected from ammonia and amines, 
thereby forming a substantially homogeneous single phase solution; and 
dispersing the said solution into a sufficient quantity of water to 
provide a stable aqueous dispersion of mixed resins having a solids 
content in the range between about 15 to about 40 weight percent. The 
aminoplast component is present in the amount of about 1 to about 12 
weight percent, the monomers are present in the amount of about 20 to 
about 40 weight percent and the epoxy resin component is present in the 
amount of about 48 to about 79 weight percent, said weight percents being 
based on the total weight of aminoplast, monomers and epoxy resin 
components. Sufficient organic solvent is used to render the resin 
components fluid, generally about 30 to about 85 weight based on the total 
weight of aminoplast, polymerized monomers, epoxy resin and organic 
solvent. 
Aminoplast Component 
The aminoplast component employed can be any of the aldehyde condensation 
products of compounds such as urea, ethylene urea, dicyandiamide, various 
triazines, e.g., melamine, benzoguanamine and acetoguanamine, and the 
like; and mixtures and etherified derivatives of these condensation 
products. 
Procedures for preparing aminoplasts are described in Aminoplasts, C. P. 
Vale (Cleaver-Hume Press, Ltd., London). Further illustration of 
aminoplast preparation and application is set forth in U.S. Pat. Nos. 
2,957,835; 3,501,429; 3,522,159; 3,535,148; 3,773,721; 3,852,375; 
3,891,590; 3,954,715; 3,965,058; 3,979,478; 4,071,578; and the like. 
The aldehyde used in preparation of the aminoplasts may be (1) 
monofunctional or (2) polyfunctional, having an at least two aldehyde 
groups separated by at most one carbon atom; such as formaldehyde, 
paraformaldehyde, polyoxymethylene, trioxane, acrolein, and aliphatic or 
cyclic aldehydes such as glyoxal, acetaldehyde, propionaldehyde, 
butyraldehyde, and furfuraldehyde. Condensation, when using formaldehyde, 
furfuraldehyde, paraformaldehyde, polyoxymethylene or trioxane, is 
generally accomplished with the use of a mildly acid or mildly alkaline 
catalyst. When using acrolein, glyoxal, acetaldehyde, propionaldehyde, or 
butyraldehyde, condensation is generally accomplished by combining the 
reactants in the presence of a strongly acid catalyst, neutralizing the 
reaction product, adding more aldehyde, and further reacting in the 
presence of a mildy acid, or alkaline catalyst. The preferred aldehyde is 
formaldehyde. 
The aldehyde condensation products (i.e., aminoplasts) contain methylol or 
similar alkylol groups, the structure of the alkylol group depending upon 
the particular aldehyde employed. All or part of these alkylol groups may 
be etherified by reaction with an alcohol. Among the preferred 
amine-aldehyde products for use in the present invention are those which 
are substantially alkylated by an etherification reaction, i.e., in which 
at least a major portion of the alkylol groups have been reacted with an 
alcohol. Essentially any monohydric alcohol can be employed for this 
purpose, including such alcohols as methanol, ethanol, propanol, butanol, 
heptanol and other alkanols having up to about 12 carbon atoms or more, as 
well as benzyl alcohol and other aromatic alcohols, cyclic alcohols such 
as cyclohexanol, monoethers of glycols such as the Cellosolves and 
Carbitols, and halogen-substituted or other substituted alcohols, such as 
3-chloro-propanol. 
When using alcohols having more than about 4 carbon atoms, the methylol 
groups are first etherified with a lower alcohol containing 1 to 4 carbon 
atoms followed by ether interchange reaction to replace the lower alcohols 
with the higher ones. The preferred alcohols are methanol, butanol, and 
similar lower alkanols with methanol being most preferred. 
The preferred aminoplasts are those which are soluble or substantially 
hydratable and dispersible in aqueous media. Suitable aminoplasts include 
those which are substantially miscible in all proportions with aqueous 
alcohol solvent media, such as 50/50 1-butanol/water mixture. Particularly 
preferred aminoplasts are those based on melamine, formaldehyde and 
methanol. 
In the preparation of a present invention coating composition, the 
aminoplast component is dissolved in an organic solvent to form a 
solution. To the solution is subsequently added a selected mixture of 
polymerizable olefinically unsaturated monomers and a free 
radical-generating polymerization catalyst, and the vinyl polymerization 
of the monomer mixture is conducted in the presence of the aminoplast 
component in a manner which is more fully described hereinbelow. The 
amount of aminoplast component will be about 1 to about 12 weight percent, 
preferably about 4 to about 8 weight percent, based on total resin 
component weight, i.e., aminoplast polymerized monomers and epoxy resin 
components. 
Organic Solvent Component 
The organic solvent is preferably one which is substantially 
water-miscible, either in the form of a single polar compound, or as a 
mixture of compounds which can include non-polar constituents. The boiling 
point of the organic solvent component preferably will vary in the range 
between about 150.degree. F. to about 500.degree. F. 
Suitable organic solvents, either alone or in admixture, include diisobutyl 
ketone, methyl isobutyl ketone, hydroxyethyl acetate, 2-ethoxyethyl 
acetate, propylene glycol monomethyl and/or monoethyl ether, ethylene 
glycol monobutyl ether, ethylene glycol, propylene glycol, butylene 
glycol, diethylene glycol, isopropanol, n-butanol, t-butanol, amyl 
alcohol, cyclohexanol, dioxane, tetrahydrofuran, dimethylformamide, 
dimethylacetamide, and the like. Non-polar solvents which can be included 
as a minor constituent of the organic solvent component include aliphatic 
and aromatic hydrocarbons such as naphtha, heptane, hexane, mineral 
spirits, decane, benzene, chlorobenzene, toluene, xylene, and the like. 
In the preparation of the present invention coating composition, the 
organic solvent component is employed in a quantity between about 30 to 
about 85 weight percent, preferably in a quantity between about 40 to 
about 75 weight percent, based on the total weight of the aminoplast, 
monomer mixture, epoxy resin and organic solvent components present during 
the preparation of the coating composition. 
Polymerizable Monomer Mixture Component 
The mixture of monomers employed in the preparation of a present invention 
coating composition comprises between about 20 to about 90 weight percent 
of .alpha.,.beta.-olefinically unsaturated carboxylic acid, and between 
about 10 to about 80 weight percent of at least one olefinically 
unsaturated monomer which is copolymerizable with the carboxylic acid 
monomer. 
The vinyl polymerization of the monomer mixture yields a 
carboxyl-containing acrylic resin. It is advantageous for purposes of the 
present invention (e.g., for the protective coating of metal surfaces) to 
select a monomer mixture which provides a carboxyl-containing acrylic 
resin which exhibits a Tg (glass transition temperature) in the range 
between about 0.degree. to about 130.degree. C., and preferably a Tg in 
the range between about 50.degree. to about 90.degree. C. The Tg parameter 
is that measured for an acrylic resin obtained by the polymerization of a 
monomer mixture under the step (2) conditions of the invention process, 
excluding the presence of the aminoplast components. 
Suitable .alpha.,.beta.-olefinically unsaturated carboxylic acid monomers 
include acrylic acid, methacrylic acid, crotonic acid, itaconic acid (or 
anhydride), maleic acid (or anhydride), fumaric acid, the monoesters of 
the dicarboxylic acid monomers such as methyl hydrogen maleate, ethyl 
hydrogen fumarate, and the like. 
The one or more other constituents of the polymerizable monomer mixture are 
alkyl esters of .alpha.,.beta.-olefinically unsaturated carboxylic acids, 
for example methyl, ethyl, propyl, butyl, hexyl, ethylhexyl and lauryl 
acrylate, methacrylate and crotonate; dimethyl maleate; dibutylfumarate 
and dihexylitaconate; and mixtures thereof. 
The polymerizable monomer mixture can also include one or more monomers 
selected from vinyl aromatic compounds. Illustrative of such compounds are 
styrene, alkylstyrenes, halostyrenes, .alpha.-methylstyrene, 
isopropenyltoluene, vinylnaphthalene, and the like. 
Other suitable vinyl polymerization monomer species include vinyl chloride, 
acrylonitrile, methacrylonitrile, vinyl acetate, vinyl propionate, vinyl 
stearate, acrylamide, methacrylamide, and the like. 
The preferred monomers are methylacrylate, ethyl acrylate and acrylic acid. 
The amount of monomers that are polymerized are that amount which will 
produce a polymer having a weight percentage in the mixed resin system of 
about 20 to about 40 weight percent, preferably about 25 to about 35 
weight percent, said weight percents being based on the total weight of 
aminoplast, polymerized monomers and epoxy resin components. 
Epoxy Resin Component 
The epoxy resins useful in this invention are glycidyl polyethers of 
polyhydric phenols and hydrogenated phenols and contain more than one 
1,2-epoxide group per molecule. Such polyepoxide resins are derived from 
an epihalohydrin and a polyhydric phenol or hydrogenated phenol and have 
epoxide equivalent weights of about 150 to about 8,000. Examples of 
epihalohydrins are epichlorohydrin, epibromohydrin and epiiodohydrin with 
epichlorohydrin being preferred. Polyhydric phenols are exemplified by 
resorcinol, hydroquinone, p,p'-dihydroxydiphenylpropane (or Bisphenol A as 
it is commonly called), p,p'-dihydroxydiphenyl ethane, 
bis(2-hydroxynaphthyl)methane, 1-5-dihydroxynaphthalene, novolak resins 
made from the reaction of mono and diphenols with aldehydes, 
phloroglucinol and the like with Bisphenol A being preferred. Epoxy resins 
made from hydrogenated versions of these phenols are also useful in this 
invention. These epoxy resins are well known in the art and are made in 
desired molecular weights by reacting the epichlorohydrin and the 
polyhydric compound in various ratios or by reacting a dihydric phenol 
with a lower molecular weight epoxy resin. Particularly preferred epoxy 
resins for use in this invention are glycidyl polyethers of Bisphenol A 
having epoxide equivalent weights of about 1000 to about 4000. 
In the preparation of the stable aqueous dispersions of this invention, 
between about 48 to about 79 weight percent, preferably between about 57 
to about 71 weight percent, said weight percents being based on total 
weight of aminoplast, polymerized monomers and epoxy resin components, of 
a selected epoxy resin are admixed and interacted with the product 
solution resulting from the previously conducted polymerization of the 
monomer mixture component in the presence of the aminoplast component. 
SPECIFIC ASPECTS OF DISPERSION PREATION 
The aminoplast component is admixed with the organic solvent and heated 
until the aminoplast is essentially completely dissolved. In some cases, 
the aminoplast may only partly dissolve with the undissolved portion 
remaining dispersed. 
The organic solvent medium coating the aminoplast is heated to a 
temperature in the range between about 120.degree. to about 300.degree. F. 
To the heated solvent medium is added the monomer mixture component which 
contains a vinyl polymerization catalyst, i.e., a free radical producing 
catalyst. The catalyst is employed in a quantity between about 0.2 to 
about 14 weight percent, based on the weight of the monomer mixture. The 
quantity of catalyst must be sufficient to promote the copolymerization of 
the monomer constituents under the processing conditions. A preferred 
polymerization catalyst is an organic peroxide which is free 
radical-generating under the polymerization conditions, e.g., benzoyl 
peroxide, tertiary-butyl peroctoate, and the like. Other useful catalysts 
are the azo catalyst, e.g., azobisisobutyryl nitrile. 
The homogeneous blend of polymerization catalyst and monomer mixture is 
added slowly to the heated solvent medium at a uniform rate. The period of 
addition can vary in the range between about 0.5 to about 6 hours, and, on 
the average, the addition period will vary in the range between about 1 to 
about 4 hours. 
While not wishing to be bound by any theory or mechanism of reaction, there 
is some evidence that during the course of the vinyl polymerization 
reaction, some interaction occurs between one or more of the monomer 
constituents and the aminoplast component, and there is some linkage 
formed between the aminoplast and the acrylic copolymer which 
concomitantly has formed during the polymerization reaction. 
Upon the completion of the polymerization reaction period, in a preferred 
embodiment the resultant polymerization medium is in the form of a clear 
homogeneous solution. While maintaining the said product solution at a 
temperature in the range of about 100.degree. to about 300.degree. F., the 
epoxy resin component is added to the heated solution with the aid of 
efficient stirring. The heating and stirring is continued for an 
additional period between about 0.1 to about 2 hours to permit interaction 
and equilibration between the aminoplast and acrylic copolymer and epoxy 
resin components to be completed. Alternatively, the polymer solution can 
be added to the epoxy resin with heating and stirring as described above. 
Depending on the combination of factors involved, the reaction product 
medium will vary between being a clear solution or a solution which 
exhibits a milky iridescence. It is highly preferred that the reaction 
product medium does not contain any filterable solids when it is subjected 
to the neutralization step of the invention process. 
The reaction product medium is treated with a basic reagent to at least 
partially neutralize the carboxylic acidity which is present. It is 
essential that the degree of neutralization be sufficient to provide a 
product medium pH which is in the range between about 2 to about 10, and 
preferably in the range between about 4 and about 8. The resultant 
neutralized product medium normally is in the form of a clear single phase 
solution. Besides improving the solubility properties of the resinous 
constituents of the product medium, the neutralization step suppresses the 
level of functional group interaction and imparts stability to the product 
medium. 
As another important aspect of the present invention, it is essential that 
the nuetralized carboxylic acid groups in the dispersion coating 
composition be converted to free carboxylic acid groups during any 
subsequent heat-curing cycle to which the coating composition is 
subjected. In order to satisfy this requirement, it is preferred to employ 
a basic reagent for the neutralization step which is either ammonia or an 
organic amine. 
Illustrative of suitable basic reagents are primary, secondary and tertiary 
amine compounds, such as ethylamine, butylamine, dimethylamine, 
diisopropylamine, dimethylethylamine, cyclohexylamine, allylamine, 
benzylamine, m-toluidine, morpholine, ethanolamine, diethanolamine, 
triethanolamine, and the like, and other basic reagents such as ammonium 
hydroxide. 
Having obtained a neutralized product medium which is nominally a single 
phase solution containing solubilized mixed resin solids, the said 
solution is admixed with an aqueous phase and agitated vigorously to 
effect a stable aqueous dispersion of the mixed resin solids in the form 
of an emulsion. The average particle size of the dispersed mixed resin 
solids is preferably less than one micron. 
An aqueous dispersion of mixed resins produced in accordance with the 
present invention process inherently has exceptional phase stability and 
shelf-life. A typical aqueous dispersion coating composition of the 
present invention can remain substantially unchanged for more than one 
year at 77.degree. F. An invention aqueous dispersion coating composition 
is capable of tolerating a 120.degree. F. temperature for more than three 
months without any apparent visible change in the dispersion phases. 
The quantity of water employed for the dispersion-forming procedure can 
vary over a broad range as dictated by practical considerations. A typical 
aqueous dispersion will have a solids content in the range between about 
15 to about 40 weight percent, and preferably in the range between about 
20 to about 30 weight percent, based on the total weight of the aqueous 
dispersion. 
Optionally there can be incorporated into the invention aqueous dispersion 
coating composition other components which do not interfere with the 
stability and other advantageous properties of the coating composition. 
Illustrative of an additional component which may be employed is between 
about 0.05-5 weight percent of a plasticizer, based on the weight of the 
resinous film-forming solids in a coating composition. Typical 
plasticizers include butyl benzyl phthalate, dibutyl phthalate, triphenyl 
phosphate, dicyclohexyl phthalate, dibenzyl phthalate, mixed benzoic acid 
and fatty oil acid esters of pentaerythritol, diethyleneglycol dibenzoate, 
butyl phthalyl butyl glycolate, tricresyl phosphate, toluene ethyl 
sulfonamide, hexamethylene diphthalate, and the like. Additional other 
components are colorants, waxes and the like. 
As noted previously, during the baking and curing phase the volatile basic 
reagent employed to neutralize the coating composition evolves from the 
applied coating, thereby providing free reactive carboxyl groups. The said 
reactive carboxyl groups interact with the epoxy groups of the epoxy 
component to yield crosslinked ester linkages. Hydroxyl groups which are 
initially present and which are formed in situ during the baking cycle are 
highly reactive and condense with the aminoplast component, thereby 
providing an additional crosslinking mechanism. 
The coating compositions of this invention are particularly useful as 
coating compositions for the interior of aluminum and steel cans and can 
be applied to the interior of said cans by airless spray application. The 
closures of such cans can also be coated with the compositions of this 
invention, such coatings being applied by roller coating processes. The 
coatings for cans are applied to dry film thicknesses of 0.1 to 0.5 mil 
and are cured by passing the metal through gas fired ovens heated to 
315.degree. to 425.degree. F. in stages. The total residence time in these 
ovens is a matter of seconds, 30 seconds to 4 minutes. 
In other applications, i.e., as metal primer coatings, the coating 
compositions are cured at a temperature of about 300.degree. F. to about 
500.degree. F. for a time sufficient to obtain a cure. The coating 
compositions can be formulated into clear coatings as hereinbefore 
described or into pigmented coatings. Pigments can be added using well 
known formulating procedures. Other additives which can be incorporated in 
the coating compositions are coalescing solvents, leveling agents, wetting 
agents, dispersions of other resins, water soluble resins, thickening 
agents, suspending agents, surfactants, defoamers, adhesion promoters, and 
the like.

The following examples are presented to more clearly define the invention. 
Parts and percentages unless otherwise designated are parts and 
percentages by weight. 
EXAMPLE 1 
To a suitable reactor equipped with a stirrer, temperature recording 
device, reflux condenser and dropping funnel were added 60 parts of 
hexamethoxymethyl melamine (Cymel 300 available from American Cyanamid 
Co.), 220 parts of ethylene glycol monobutyl ether and 406 parts of 
n-butanol. To the dropping funnel were added 128 parts of methacrylic 
acid, 80 parts of styrene, 88 parts of ethyl acrylate and 40 parts of a 
50/50 blend of benzoyl peroxide and tricresyl phosphate. Heat and stirring 
were applied raising the reactor contents to 85.degree. C. At this 
temperature, the slow addition of the monomer-catalyst solution from the 
dropping funnel was begun. The addition was completed after 90 minutes 
with the temperature rising to 104.degree. C. The temperature was held at 
104.degree.-107.degree. C. for 90 minutes to complete the polymerization 
reaction. 696 Parts of pulverized glycidyl polyether of Bisphenol A having 
an epoxide equivalent weight of 2700 and a melting point of about 
150.degree. C. were then added. Heating and stirring were continued until 
the glycidyl polyether was dissolved, a period of about 45 minutes. 
N,N-dimethylaminoethanol, 114 parts, was then added. After 25 minutes and 
with the temperature at 96.degree. C., 1000 parts of deionized water were 
added. Ten minutes later, 1750 parts of deionized water were added. When 
thoroughly mixed, the emulsion product was cooled and stored in 
appropriate containers. The stable emulsion product had a Brookfield 
viscosity of 22.5 cps. at 25.degree. C. (a Zahn 2 viscosity of 19 
seconds,) a solids content of 23.02%, a weight per gallon (wt/gal) of 8.54 
lbs. and a pH of 8.15. After 3 weeks at room temperature, the composition 
gelled. 
The insides of 12 ounce aluminum and electrolytic tin plated (ETP) steel 
cans were coated with the coating composition using airless spray, to a 
dry film weight of 115 to 125 mg. per can (beer weight). The coatings were 
cured by baking for 60 seconds at a peak metal temperature of 188.degree. 
C. The continuity of the coatings was determined by a conductivity test 
carried out by filling the coated can with a 10% solution of sodium 
chloride in water and then determining the milliamperes of leakage current 
through the coating 30 seconds after a potential of 12 volts is applied 
between the salt solution and the can exterior. High readings indicate 
defects in the coating, e.g., craters, voids, bubbles, etc., which in use 
could result in contamination of the can contents and/or corrosion of the 
container. A milliamp reading (also referred to as Enamel Rater reading) 
of 0 to 25 is acceptable. The conductivity of the coatings was found to 
vary from 0-20 milliamps (ma) with an average, based on 24 cans, of 6.2 
ma. When applied at beverage weights, i.e., 175 to 185 mg. per can, the 
milliamp reading was 0 for 24 cans. 
The blister threshold, i.e., the applied dry film weight at which blisters 
or bubbles form in the film from escaping solvent or water, was greater 
than 180 mg. 
Films were cast from the coating composition onto electrolytic tin plated 
(ETP) steel panels to a dry film thickness of 0.2 mil using a wire wound 
Meyer rod. After baking at 188.degree. C. for one minute, the films were 
well cured. After 10 minutes immersion in a water bath heated to 
82.degree. C., the film exhibited no blushing and passed the wet adhesion 
test with a rating of 10. The wet adhesion test was conducted as follows: 
within one minute of removal from the water bath described above, the film 
surface was dried with a cloth and scribed with a cross-hatch pattern. A 
high tack cellophane tape was applied over the scribed portion and was 
removed with a jerk. The amount of film which remained on the panel was 
visually estimated and was rated as 10 for no removal and 0 for total 
removal. 
The double coat adhesion was tested by applying a second coating over the 
first cured coating using the same film weight and curing conditions as 
used for the first coating. The wet adhesion was rated as 7-8. 
In all of the following examples the wet adhesion as described above of 
single coatings was excellent. The adhesion tests reported in these 
examples pertain to double coated panels and cans. 
EXAMPLE 2 
Using the same procedure described in Example 1, 60 parts of 
hexamethoxymethyl melamine (Cymel 303 available from American Cyanamid 
Co.) were dissolved in 228 parts of ethylene glycol monobutyl ether and 
342 parts of n-butanol. To this solution heated to 93.degree. C., was 
added over a 90 minute period a mixture of 128 parts of methacrylic acid, 
80 parts of styrene, 88 parts of ethyl acrylate and 40 parts of a 50/50 
blend of benzoyl peroxide and tricresyl phosphate. After holding at 
93.degree. C. for 3 hours to complete the polymerization, 696 parts of 
pulverized glycidyl polyether described in Example 1 were added. After one 
hour with the temperature at 93.degree. C., the glycidyl polyether had 
dissolved. N,N-dimethylaminoethanol, 57 parts, was added followed by 47 
parts of triethylamine. After holding at 95.degree. to 112.degree. C. for 
30 minutes, 3186 parts of deionized water were added over a 15 minute 
period. When thoroughly mixed, the resulting emulsion was cooled and 
stored in an appropriate container. The emulsion product had a solids 
content of 21.96%, a wt/gal. of 8.57 lbs., a pH of 7.7, an acid value of 
49.8 and a Zahn 2 viscosity at 25.degree. C. of 23 seconds. The product 
exhibited no instability after 2 months at room temperature, 100.degree. 
F. and 120.degree. F. 
The interiors of 12 ounce aluminum and ETP steel cans were coated, cured 
and tested using the procedure described in Example 1. The Enamel Rating 
at beer weights was 44.5 ma. and at beverage weights, 4.6 ma. The blister 
threshold was less than 170 mg. 
The wet adhesion of coatings on aluminum panels, double coated and cured as 
described in Example 1, was 7-8 and on ETP steel panels the wet adhesion 
was 4-6. The solvent resistance of the cured coating was determined by 
rubbing the coating with methylethyl ketone (MEK). The coating passed 21 
double rubs. 
EXAMPLE 3 
Using the same procedure as described in Example 1, a monomer-catalyst 
solution of 128 parts of methacrylic acid, 80 parts of styrene, 88 parts 
of ethyl acrylate and 36 parts of t-butyl peroctoate was polymerized in a 
solution of 60 parts of hexamethoxymethyl melamine (Cymel 303), 228 parts 
of ethylene glycol monobutyl ether and 324 parts of n-butanol. When the 
polymerization was completed, 696 parts of the glycidyl polyether 
described in Example 1 were added and dissolved in the reaction mixture, 
followed by 114 parts of N,N-dimethylaminoethanol and then by 3204 parts 
of deionized water. The resulting stable emulsion had a solids content of 
21.85%, a wt/gal of 8.54 lbs., a pH of 7.9 and an acid value of 46.25. The 
product was still stable after 3 months at room temperature, 100.degree. 
F. and 120.degree. F. 
The solids were adjusted with water to 19% and the viscosity to 19 seconds 
(Zahn 2 at 25.degree. C.). The interiors of 12 ounce aluminum ETP steel 
cans were coated, cured and tested using the procedure described in 
Example 1. The Enamel Rating at beer weights was 10.2 ma. and at beverage 
weights, 2.4 ma. The blister threshold was 155 mg. 
The wet adhesion of coatings on aluminum and ETP steel panels, double 
coated and cured as described in Example 1, was poor. The double coat wet 
adhesion of the coatings on the interior of aluminum cans was also poor, 
but on ETP steel cans, the cured coat adhesion was perfect. The solvent 
resistance of the cured coatings was 100 MEK double rubs. 
EXAMPLE 4 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 128 parts of methacrylic acid, 80 parts of styrene, 88 parts 
of ethyl acrylate and 20 parts of benzoyl peroxide was polymerized in a 
solution of 68 parts of Cymel 370 available from American Cyanamid Co. 
(hexamethoxymethyl melamine at 88% solids in isopropanol), 228 parts of 
ethylene glycol monobutyl ether and 334 parts of n-butanol. When the 
polymerization reaction was completed, 696 parts of pulverized glycidyl 
polyether described in Example 1 were added followed by 114 parts of 
N,N-dimethylaminoethanol and 3204 parts of deionized water. The resulting 
stable emulsion had a solids content of 22.18%, a wt/gal. of 8.59 lbs., a 
pH of 7.6 and an acid value of 52.6. The product was stable after 2 months 
at room temperature, 100.degree. F. and 120.degree. F. 
The interiors of 12 ounce aluminum and ETP steel cans were coated, cured 
and tested using the procedure described in Example 1. The Enamel Rating 
at beer weights was 10.3 ma. and at beverage weights, 1.1 ma. The blister 
threshold was 145-150 mg. 
The wet adhesion of coatings on aluminum and ETP steel panels, double 
coated and cured as described in Example 1, was poor. The double coat wet 
adhesion of the coatings on the interior of aluminum cans was also poor, 
but on ETP steel cans, the double coat adhesion was perfect. The cured 
coatings passed 50 MEK double rubs. 
EXAMPLE 5 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 137 parts of methacrylic acid, 86 parts of styrene, 94 parts 
of ethyl acrylate and 22 parts of benzoyl peroxide was polymerized in a 
solution of 280 parts of hexamethoxymethylamine (Cymel 303) in 220 parts 
of ethylene glycol monobutyl ether and 330 parts of n-butanol. When the 
polymerization reaction was completed, 645 parts of the glycidyl polyether 
described in Example 1 were added, followed by 123 parts of 
N,N-dimethylaminoethanol and 3147 parts of deionized water. The resulting 
stable emulsion had a solids content of 24.34%, a wt/gal. of 8.61 lbs., a 
pH of 7.7 and an acid value of 47.2. The dispersions were still stable 
after 3 months at room temperature and at 100.degree. F., but had settled 
out at 120.degree. F. 
The solids and viscosity (Zahn 2 at 25.degree. C.) were adjusted to 22% and 
30 seconds respectively with water. 
The interiors of 12 ounce aluminum and ETP steel cans were coated, cured 
and tested using the procedure described in Example 1. The Enamel Rating 
at beer weights was 2.3 ma., and at beverage weights, 1.5 ma. The blister 
threshold was 135 mg. 
The wet adhesion of double coatings on aluminum and ETP steel panels and on 
ETP steel cans was poor. The wet adhesion, however, on aluminum cans had a 
rating of 7-8. The solvent resistance of the cured coatings was 28 MEK 
double rubs. 
EXAMPLE 6 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 137 parts of methacrylic acid, 87 parts of styrene, 95 parts 
of ethyl acrylate and 22 parts of benzoyl peroxide was polymerized in a 
solution of 19 parts of hexamethoxymethyl melamine (Cymel 303) and 28 
parts of hexabutoxymethyl melamine in 220 parts of ethylene glycol 
monobutyl ether and 330 parts of n-butanol. When the polymerization 
reaction was completed, 793 parts of the glycidyl polyether described in 
Example 1 were added followed by 123 parts of N,N-dimethylaminoethanol and 
3150 parts of deionized water. The resulting stable emulsion had a solids 
content of 24.44, a wt/gal. of 8.62 lbs. and an acid value of 46.6. The 
dispersion was stable after 3 months at room temperature, but exhibited 
slight settling after 3 months at 100.degree. F. and complete instability 
at 120.degree. F. 
The interiors of 12 ounce aluminum and ETP steel cans were coated, cured 
and tested using the procedures described in Example 1. The Enamel Rating 
at beer weights and at beverage weights was 7.7 ma. The blister threshold 
was 135 mg. 
The wet adhesion of double coatings on both aluminum and ETP steel panels 
and cans was poor. The solvent resistance of the cured coatings was 50 MEK 
double rubs. 
EXAMPLE 7 
To a suitable reactor equipped as described in Example 1 were added 280 
parts of n-butanol and 280 parts of ethylene glycol monobutyl ether. To 
the dropping funnel were added 129 parts of methacrylic acid, 131 parts of 
styrene, 197 parts of ethyl acrylate and 24 parts of benzoyl peroxide. 
Heating and stirring were begun and at 93.degree. C., the addition of the 
monomer-catalyst solution was begun. After 90 minutes, all of the 
monomer-catalyst solution had been added and heating at 
93.degree.-95.degree. C. was continued for 3 hours. After this heating 
period, 624 parts of pulverized glycidyl polyether of Bisphenol A having 
an epoxide equivalent weight of 1850 and a melting point of about 
130.degree. C. were added. Heating and stirring were continued and after 1 
hour and 25 minutes at 108.degree. C., 114 parts of 
N,N-dimethylaminoethanol were added followed 30 minutes later by 96 parts 
of hexamethoxymethyl melamine (Cymel 303). Heating was discontinued and at 
88.degree. C., 3128 parts of deionized water were added. The resulting 
dispersion after cooling had a solids content of 24.3%, a wt/gal. of 8.59 
lbs., a pH of 7.7 and an acid value of 51.0. The dispersion was not 
stable. It completely settled out after 2 weeks at room temperature, 
100.degree. F. and 120.degree. F. 
The interiors of aluminum and ETP steel cans were spray coated, cured and 
tested as described in Example 1. The material was foamy and had poor 
atomization. The Enamel Rating at beer weights and at beverage weights was 
9.3 and 4.4 ma. respectively. The blister threshold was 155 mg. 
The wet adhesion on aluminum and EPT steel panels was excellent. The wet 
adhesion on aluminum cans was poor but on ETP steel cans, it was almost 
perfect. The solvent resistance of the cured coatings was 18 MEK double 
rubs. 
EXAMPLE 8 
Using the same procedure described in Example 1, 4.2 parts of methacrylic 
acid, 2.8 parts of styrene and 3.11 parts of ethyl acrylate were 
copolymerized with 0.65 part of benzoyl peroxide in a solution of 2.16 
parts of hexamethoxymethyl melamine (Cymel 303), 6.54 parts of ethylene 
glycol monobutyl ether and 9.8 parts of n-butanol. When the polymerization 
was completed, 23.04 parts of pulverized glycidyl polyether of Bisphenol A 
as described in Example 1 were added and dissolved. 
N,N-dimethylaminoethanol, 3.7 parts, was added followed by 93.8 parts of 
deionized water. The resulting dispersion had a solids content of 24.08%, 
a wt/gal. of 8.62 lbs., a pH of 7.7 and an acid value of 59.9. 
The solids and viscosity (Zahn 2 at 25.degree. C.) were adjusted with water 
to 23% and 24", respectively. The interiors of aluminum and ETP steel cans 
were spray coated, cured and tested as described in Example 1. The Enamel 
Rating at beer and beverage weights was 14.2 and 1.3 ma., respectively. 
The blister threshold was 210 mg. 
The wet adhesion on aluminum panels was good, a 7-8 rating, but was poor on 
ETP steel panels. The wet adhesion on aluminum and ETP steel cans was 
poor. Solvent resistance was 16 MEK double rubs. 
EXAMPLE 9 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 140 parts of methacrylic acid, 122 parts of styrene, 133 parts 
of ethyl acrylate and 25 parts of benzoyl peroxide was polymerized in a 
solution of 72 parts of hexamethoxymethyl melamine (Cymel 303) in 326 
parts of n-butanol and 218 parts of ethylene glycol monobutyl ether. When 
the polymerization reaction was complete, 708 parts of the glycidyl 
polyether described in Example 1 were added followed by 123 parts of 
N,N-dimethylaminoethanol and 3132 parts of deionized water. The resulting 
stable emulsion had a solids content of 24.21%, a wt/gal. of 8.61, a pH of 
7.8 and an acid value of 54.5. The stability was excellent after 3 months 
at room temperature and 100.degree. F. with slight settling at 120.degree. 
F. 
The solids and viscosity (Zahn 2 at 25.degree. C.) were adjusted with water 
to 23.2% and 25 seconds respectively. The interiors of aluminum and ETP 
steel cans were spray coated, cured and tested as described in Example 1. 
The Enamel Rating at beer and beverage weights was 20.9 and 5.8 ma., 
respectively. The blister threshold was 135 mg. 
The wet adhesion on aluminum panels was excellent but poor on ETP steel 
panels. The wet adhesion on aluminum can interiors was poor and was just 
slightly better on the interiors of ETP steel cans. Solvent resistance of 
the cured coatings was 19 MEK double rubs. 
EXAMPLE 10 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 100.1 parts of acrylic acid, 91 parts of methyl acrylate, 91 
parts of ethyl acrylate and 23.2 parts of a catalyst blend of 78% benzoyl 
peroxide and 22% water was polymerized in a solution of 72 parts of 
hexamethoxymethyl melamine (Cymel 303) in 408.5 parts of n-butanol and 273 
parts of ethylene glycol monobutyl ether. When the polymerization reaction 
was completed, 828 parts of the glycidyl polyether described in Example 1 
were added followed by 111.4 parts of N,N-dimethylaminoethanol and 3001.1 
parts of deionized water. The resulting stable emulsion had a solids 
content of 24.63%, a wt/gal. of 8.6 lbs. and a pH of 7.0. After 2 months 
at room temperature, 100.degree. F. and 120.degree. F., the dispersion 
exhibited medium to large settling which could be stirred back in. 
The interiors of aluminum and ETP steel cans were spray coated, cured and 
tested as described in Example 1. The Enamel Ratings at beer and beverage 
weights was 0.1 and 0.04 ma., respectively. The blister threshold was 
245-250 mg. 
The wet adhesion on aluminum panels and on the interior of aluminum and ETP 
steel cans was perfect. The wet adhesion on ETP steel panels was almost 
perfect. The solvent resistance was 4 MEK double rubs. 
EXAMPLE 11 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 115.5 parts of acrylic acid, 88.1 parts of methyl 
methacrylate, 22.0 parts of 2-ethylhexyl acrylate and 18.5 parts of a 
blend of 78% benzoyl peroxide and 22% water were polymerized in a solution 
of 72 parts of hexamethoxymethyl melamine (Cymel 303) in 424.9 parts of 
n-butanol and 283.3 parts of ethylene glycol monobutyl ether. When the 
polymerization reaction was completed, 888 parts of the glycidyl polyether 
described in Example 1 were added followed by 85.7 parts of 
N.N-dimethylaminoethanol and 3002 parts of deionized water. The resulting 
stable dispersion had a solids content of 25.4%, a wt/gal. of 8.6 lbs. and 
a pH of 6.67. The dispersion exhibited no instability after 3 months at 
room temperature, 100.degree. F. and 120.degree. F. 
The interior of aluminum and ETP steel cans were spray coated, cured and 
tested as described in Example 1. The Enamel Rating at beer and beverage 
weights was 5.8 and 0.4 ma., respectively. The blister threshold was 160 
mg. 
The wet adhesion on aluminum panels was almost perfect (9-10) and on ETP 
steel panels, it was 7-8. The wet adhesion of coatings on the interior of 
aluminum cans was perfect (10) and on ETP steel cans almost perfect 
(9-10). The solvent resistance was 13 MEK double rubs. 
EXAMPLE 12 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 115.5 parts of acrylic acid, 90 parts of methyl methacrylate, 
22.5 parts of 2-ethylhexyl acrylate and 15.4 parts of a blend of 78% 
benzoyl peroxide and 22% water was polymerized in a solution of 72 parts 
of hexamethoxymethyl melamine (Cymel 303) in 433.5 parts of n-butanol and 
289 parts of ethylene glycol monobutyl ether. When the polymerization 
reaction was completed, 888 parts of the glycidyl polyether described in 
Example 1 were added, followed by 71.4 parts of N,N-dimethylaminoethanol 
and 3006.2 parts of deionized water. The resulting stable dispersion had a 
solids content of 24,83%, a wt/gal. of 8.56 lbs. and a pH of 6.1. The 
dispersion exhibited soft settling after 3 months at room temperature, 
100.degree. F. and 120.degree. F. 
Using the procedure described in Example 1, the interior of aluminum and 
ETP steel cans were spray coated, cured and tested. The Enamel Rating at 
beer and beverage weights was 1.5 and 0.8 ma. respectively. The blister 
threshold was 200 mg. 
The wet adhesion on the interior of aluminum and ETP steel cans was perfect 
(10), on aluminum panels almost perfect (9-10) and on ETP steel panels 
4-6. The solvent resistance was 15 MEK double rubs. 
EXAMPLE 13 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 112.6 parts of acrylic acid, 102.3 parts of methyl acrylate, 
102.3 parts of ethyl acrylate and 26 parts of a blend of 78% benzoyl 
peroxide and 22% water was polymerized in a solution of 81 parts of 
hexamethoxymethyl melamine (Cymel 303) in 461.3 parts of n-butanol and 
307.5 parts of ethylene glycol monobutyl ether. When the polymerization 
reaction was completed, 931.5 parts of the glycidyl polyether described in 
Example 1 were added followed by 139.2 parts of N,N-dimethylaminoethanol 
and 2737.3 parts of deionized water. The resulting stable dispersion had a 
solids content of 28.0%, a wt/gal. of 8.62 lbs. and a pH of 7.95. The 
dispersion exhibited soft settling after 3 months at room temperature, 
100.degree. F. and 120.degree. F. 
The solids and viscosity (Zahn 2 at 25.degree. C.) were adjusted with water 
to 26.8% and 21 seconds respectively. The interior of 12 ounce aluminum 
and ETP steel cans were spray coated using the procedure described in 
Example 1. The Enamel Rating at beer and beverage weights was 0.4 and 0 
ma. respectively. The blister threshold was 230-235 mg. 
The wet adhesion on aluminum and ETP steel panel and can interiors was 
perfect. The solvent resistance was 50 MEK double rubs. 
EXAMPLE 14 
Using the same procedure described in Example 1, a monomer-catalyst 
solution of 403.6 parts of acrylic acid, 366.6 parts of methyl acrylate, 
366.6 parts of ethyl acrylate and 93.2 parts of a catalyst blend of 78% 
benzoyl peroxide and 22% water was polymerized in a solution of 290.3 
parts of hexamethoxymethyl melamine (Cymel 303) in 887.8 parts of 
n-butanol and 591.7 parts of ethylene glycol monobutyl ether. 
To another reactor were added 165.2 parts of the diglycidyl ether of 
Bisphenol A having an epoxide equivalent weight of 190 and 83.2 parts of 
Bisphenol A. Heat was applied raising the temperature to 121.degree. C. 
Potassium hydroxide, 0.042 part of a 45% aqueous solution, was added, and 
heating was continued raising the temperature to 177.degree. C. Heating 
was discontinued and the temperature was allowed to rise to 204.degree. C. 
due to the exothermic reaction. The temperature was then held at 
204.degree. C. for 3 hours and 45 minutes. Heating was discontinued and 
69.9 parts ethylene glycol monobutyl ether were added over a five minute 
period with the temperature dropping to 177.degree. C. N-butyl alcohol 
104.7 parts was then added with the temperature dropping to 131.degree. C. 
The temperature was then lowered to 99.degree. C. and 223.2 parts of the 
hexamethoxymethyl melamine/polymer solution, described in the first 
paragraph of this example, were added over a 5 minute period with the 
temperature dropping to 82.degree. C. The temperature was raised to 
93.degree. C. and was held at 93.degree. C. for 45 minutes. 
Dimethylethanol amine, 15.8 parts, and triethylamine, 17.9 parts were then 
added. The temperature was held at 93.degree.-96.degree. C. for 15 
minutes. Deionized water, 1500 parts, was then added over a 10 minute 
period. The reaction product was cooled to 38.degree. C., was filtered and 
stored. The resulting product was a stable dispersion having a solids 
content of 24.34%. Coatings on steel and aluminum cans, prepared as 
described in the preceding examples, exhibited excellent coating 
properties. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the foregoing specification. The 
invention which is intended to be protected herein, however, is not to be 
construed as limited to the particular forms disclosed, since these are to 
be regarded as illustrative rather than restrictive. Variations and 
changes may be made by those skilled in the art without departing from the 
spirit of the invention.