Note: Descriptions are shown in the official language in which they were submitted.
~065'~
This invention relates to a metal container for containlng a beverage and
having its internal surface coated with an adherent sanitary liner.
Background of the Invention
Beer, carbonated and non-c~rbonated soft drinks, and fruit ~uices
(hereinafter referred to generically as beverages) are often packed in
_I~ ~
'
~06~
containers made from aluminum, tin-free steel, blackplate or tinplate,
which is cold rolled steel to which a thin layer of tin is applied. Many
of these beverages exert corrosive action upon the metal and in order to
adequately protect the container and to prevent contamination of the
packaged material, a sanitary liner must be applied to the internal
surface of the container. Ilowever, the use of such liners also presents
several problems, one of the most troublesome being the residual turb~dity
and taste which tends to result from some liner materials.
Because of their relatively taste-free characteristics, vinyl
polymers based on vinyl chloride have been extensi~ely employed in
sanitary liners in contact with beverages. Wllile sucl- vinyl polymers have
been useful in the past, they possess a serious disadvantage whicll
diminishes their usefulness as sanitary liners at the present time. Thus,
these vinyl polymers are generally applied from volatile organic solvent
solutions at relatively low solids contents and these solvent rich solu-
tions either add to llydrocarbon air pollution or require expensive control
equipment.
In recent times, the increased emphasis on safety and environ-
mental pollution problems have resultcd ln n nccd for water-bused composi-
tions for sucll liners. ~y "water-bascd" it is meallt compositions in
solvents comprised predominantly of water, tllus greatly reducing tlle
handling and emissions oE organic solvent vapors. Ilowever, the types of
solvent-based sanitary liners known and used heretofore are not obtainable
as satisfactory water-based systems; indeed, it has been found that water-
based materials as a class generally provide liners whlch impart undesirable
turbidity and taste characteristics to beverages, even when the otl-er
necessary properties of such liners can be obtained.
The combination of properties whicll is necessary to successful
utiiization of any composition for container liners, and which has not
.
- 2 -
- \
1065~8~
been satisfactorily obtainable in water-based sanitary lining compositions
known heretofore, includes the following:
(A) Properties oE the Cured Liner:
(1) Metal ~dhesion - Excellent adhesion to metals, including
the aluminum, tin-free steel, blackplate and tinplate employed in beverage
containers; this property permits the present CompOsitions to be utilized
either as a one-coat liner or as a primary and/or a topcoat in a two-coat
system.
(2) Taste Characteristics - Taste characteristics at least as
good as the best "tasteless" vinyl polymers applied from solvent solu-
tions and utilized extensively in the container industry at the present
time,
(3) Turbidity Resistance - Beverages after packing, pasteuri-
zation and storage must not develop undesirable turbidity and loss of
appearance.
(4) Fabricating Properties - Fabricating properties represent
a combination of flexibility, extensibility and adhesion so as to permit
forming operations to be carried out on the coated mctal without crack-
ing or otherwise lmpairing the coutinuity of the fil.m.
(5) Pasteurization Resistance - l~eer is generally pasteurized
at a temperature oE 150F. for 15 to 40 minutes; occasionally during
the pasteurization temperatures as high as 160F. to 180F. may be
reacbed.
(6) Low rake Properties - The curing or baklng temperature in
containers of the class described should not be excessively high because
the exterior of some containers may be coated with lithograpllic coatings
qnd inks which may discolor and lose their appearance at high temperatures.
. ' . .
-- 3
~06598B
In addition, some conLainers employ adhesive~s as bonding agents and such
adhesives are adversely affected by higll baking temperatures.
(7) Extractability - No undesirable materials may be extracted
from tlle liner during processing and storage.
(8) Intercoat Adllesion - In order to permit use of primer
or base coat, if desired, or added coats to repair defects, tlle liner com-
position should have good adllesion to itself and other conventionally
utili~ed materials.
(B) ~roperties oL tlle Uncured Composition:
(1) Applicatioll Properties - ~pplication by equipment and
methods conventionally employed in tlle coatings industry. Thus, tl-e
composition sllould be capable of being applied by tnetllods such as dipping,
roll coating, spraying and the like.
(2) Storage Stability - Tlle coating composition must be in
a pl~ysical foml wllicll permits llandling and storage over varying conditions.
Water-based compositions in emulsion form, for example, usually are not
storage-stable unless additives are employed whicll generally are undesirable
in liners for contalners used for comestible produc~s.
.
Compo~itions containing amide lnterpolymers have been suggested
for use on tlle exLerior and, to some extent, on tlle interior of containers,
e.g., see U. S. Yatents Nos. 2,870,117 and 3,117,693 and Canadian Yatent
No. 766,103. However, none of tl~ese patentsdescr1bes a water-based compo-
sition for use as a sanitary liner.
--4--
`" ~0659~8
.
Summar of the Invention
Y
The present invention relates to a metal container for containing
a beverage and having its internal surface coated with an adherent sanitary
liner, the coating which is intended to be in contact with said beverage being
a cured layer of an amine-neutralized or partially-neutralized interpolyme~
formed in the presence of a vinyl polymerization catalyst and in the absence
of mercaptan, said interpolymer being comprised of:
(1) from about 5 percent to about 25 percent of acryl-
amide or methacrylamide in units of the structure:
Il
R' - C - C - NH - CH2 - OR
C
where R' is methyl or hydrogen and R is hydrogen or lower alkyl
with at least 50 percent of the groups represented by R being
lower alkyl;
(2~ from about 3 percent to about 25 percent of units formed by vinyl
polymerization of ethylenically unsaturated carboxylic acid
selected from the group consisting of acrylic acid, methacrylic
acid, itaconic acid, crotonic acid and maleic acid and half
esters of maleic and fumaric acids;
(3) from about 5 percent to about 75 percent of units derived by vinyl
polymerization of hardening monomer selected from the group
consisting of styrene, vinyl toluene and alkyl methacrylates having
1 to 4 carbon atoms; and
(4) from about 5 percent to about 75 percent of units formed by vinyl
polymerization of flexibilizing monomer selected from the group
consisting of alkyl acrylates having up to 13 carbon atoms in each
~/
~5~
.
~06598~3
alkyl group and alkyl methacrylates having from 5 to 16 carbon
atoms in each alkyl group;
wherein said interpolymer is solubilized by neutralizing or partially
neutralizing the acid groups of said interpolymer with a sufficient amount
of monomeric am me to produce at least 0.200 milliequivalents of salt per gram
of resin solids.
-5a-
1o65g88
In copending divisional application 318,452 filed December 21,
1978, there is provided a novel water-based coating composition for use
as an internal sanitary liner for metal containers adapted for packing
beverages, said composition especially adapted for spray application and
consisting essentially of:
(A) from about 5 percent to about 60 percent by weight of an
amine partially-neutralized interpolymer formed in the presence of a vinyl
polymerization catalyst and in the absence of mercaptan, said interpolymer
being comprised of:
(1) from about 5 percent to about 25 percent of acrylamide or
methacrylamide in units of the structure
l 11
R' - C - C - NH - CH2 - OR
C
wherein R' is methyl or hydrogen and R is hydrogen or
butyl with at least 50 percent of the groups represented
by R being butyl;
(2) from about 3 percent to about 25 percent of units formed
from acrylic acid;
(3) from about 5 percent to about 75 percent of hardening
monomer units derived from styrene; and
(4)~ rom about 5 percent to about 75 percent of flexibilizing
monomer units derived from ethyl acrylate;
wherein the acid groups of said interpolymer are partially neutralized with
a sufficient amount of monomeric amine to solubilize the interpolymer
but with an amount of amine which does not produce more than 0.764 milli-
equivalents of salt per gram of ~esin solids; and
~ -6-
-- ~0655~88
(B) from about 40 percent to about 95 percent by weight of a liquid
medium consisting of a mixture of water soluble or water miscible organic solvents
in water wherein at least 60 percent by weight of the mixture is water.
The above compositions meet all the requirements for cured
sanitary liners set forth above.
Detailed Descri tiOn of the Invention ~ -
p
In formulating a coating composition for use as an internal sani-
tary liner for metal containers in which beverages are to be stored, it is
extremely important that cured films-produced from such coating compositions
do not contain certain materials, even in residual amounts, which can be
extracted by the beverage from the cured film. Thus, it has been found that
certain additives commonly employed in the preparation of prior art coating
compositions may remain in residual amounts in cured films produced from
such compositions and that even residual amounts of such additives can
adversely affect the characteristics of beverages in contact with such films.
For example, residual amounts of such materials as mercaptan chain transfer
agents commonly employed in polymerizing interpolymers such as those used
and described herein; external surfactants or disperslon st~bili~ers; and
external crosslinking agents sucll as amine-aldehyde resins in cured films
- 6a-
~0659~
employed as sanitary liners for beverages such as beer have been found to
exert adverse effects on the turbidity and/or taste characteristics of
the beer. Accordingly, in formulatlng the compositions of tllis invention,
such materials are avoided.
As indicated above, the term "beverage" as used throughout the
specification and claims refers to beer, carbonated and non-carbonated
soft drinks, fruit Juices, and ~he like.
Among tlle units in the interpolymers herein are units derived
from acrylamide or methacrylamide. These units may be formed Erom
substituted amides, suc~l as N-(alkoxyalkyl)acrylamide or meth-
acrylamide. N-(alkoxyalkyl)acrylamides or methacrylamides in wllicll the
alkoxy group is butoxy (i.e., where R in the formula above is butyl) are
especially preferred since interpolymers prepared from such substituted
amides exhibit the best balance of stability and efEicient curing. In
addition, mixtures of N-(alkoxyalkyl)acrylamlde and N-methylolamide can
also be used. 'rhese substituted amides can be prepared by several
methods. One preferred metllod is to react an unsaturated amide (e.g.,
acrylamide) with formaldellydc anù an all~anol (e.~,., butanol) un(ler acidic
conditions and in the presence of a polymerization inhibitor. For a
detailed description oE this method, see Roger M. Christenson et al's U.S.Patent
No. 3,079,434, issued Feb. 26, 1963. The resultsnt N-(alkoxyalkyl)acrylamide
[e.g., N-(butoxymethyl)acrylamide] is tllell interpolylllerized with the other
monomers (ùescribed below) to form the interpolymer containing the substi-
tuted amide units.
As indicated, in the above metllod tlle substituted amide Utlits of
the interpolymer herein are formed by first separately preparing Llle
substituted amide and then interpolymerizing it with tlle other monomers.
Alternativcly, these substituted amide unlts can be formed in situ, that
'~J '
-- 7 --
106591~3~
is, the substituted amide units can be formed subsequent to the formation
of the interpolymer. Thus, the unsaturated amide (e.g., acrylamide
or metllacrylamide) can first be interpolymerized witl~ the other monomers
and tlle resultant product then reacted with the aldellyde (e.g., formal-
dehyde) and alkanol (e.g., butanol). For a more detailed discussion
of tllls reaction, see Roger M. Christenson's U.S. Patent No. 3,037,963 issued
June 5, 1962. Th1s method has the disadvantage of requiring removal of
any excess formaldel~yde wl~icll has a troublesome odor, and in tllis method
the degree of etherification of tlle methylol groups is more difficult
to control; thus, in the above structure, the proportion oE R groups
which are alkyl ratller tl-an hydrogen may not be as desired. For good
stability at least 50 percent of these groups sllould be alkyl, and usually
it is preferred that all or nearly all be al~yl.
As described above, the acrylamide or methacrylamide is in
units of polymerized ami~e substituted wlth alkoxymethyl groups, with tlle
alkoxymethyl substituent introduced either as part of the amide reactant
or by reacting the polymeri~ed amide with formAl~el-yde and alkanol. It
has been the practice in the art to describe tlle proportlon of amicle in
these interpolymers by referellce to the unsubstituted ami~!e, e.g., acrylamlde
or methacrylamide. l`his is because the alkoxymethyl groups may or may not
be present in tl;e monomer mixture used to form the interpolymer, and if
present may be oE difEerellt m(>lecular weigllt depcnding on the particular
group, and also because these groups split off and are substantially lost
during the baking of the interpolymer coating. That practice is followed
throughout tl-e sl~ecification and claims herein in referring to tbe propor-
tion of amide. Thus, for example, an interpolymer described as containing
lO percent acrylamide may be formed from a monomer mixture containing lO
yercent acrylamide itself (and the interpolymer later reactcd witll
'Z`
0,~,~ 5, .
- i3 -
~(~6S988
formaldehyde and alkanol), or the interpolymer may be formed from a
monomer mixture containing N-(alkoxymethyl)acrylamide in an amount which
would provide an interpolymer containing 10 percent of the acrylamide
moiety if the aikoxymetllyl groups were removed. Where the latter is the
case in the examples, it is so indicated by stating the component as
"Acrylamide as NBMA".
The interpolymer of the compositions of this invention conta`ins
from about 5 percent to about 25 percent of acrylamide or methacrylamide,
with the preferred range being from about L0 percent to about 15 percent.
For similar reasons, the levels of salt groups in the partially-
neutralized interpolymers, as described in detail below, are calculated
herein based on interpolymers containing unsubstituted amide~ i.e., not
having alkoxymethyl substituents. The calculated values correspond
closely to experimental values based on the non-volatile solids content
of the interpolymer as obtained by lleating at 150C. for 2 hours, thus
simulating the losses incurred in the baking operation during which
alkoxymethyl groups are evolved.
The units of the interpolymer derived from ethylenically
unsaturated carboxylic acid are best formed from acrylic acid or metll-
acrylic acid, but itaconic acid, crotonic acLd, and maleic acid, and half
esters of maleic and fumaric acids may also be used. In the half esters,
one of the carboxyl groups is esterified with an alcohol, the identity of
which is not significant so long as it does not prevent polymerization or
preclude the desired utilization of the product. ~utyl hydrogen maleate
and ethyl hydrogen fumarate are examples.
The interpolymer of the compositions of this invention may contain
from about 3 to about 25 percent of such acid units. llowever, for the best
balance of curing and ease of solubilization, it is preferred that tlle
interpolymer contain from 5 to ]5 percent of the acid units. It shall be
_ g _
~0655~8~3
noted that interpolymers of the compOsitiOns in some instances con-
tain more acid than is normally required for solubilization purposes.
This is often desirable in order to obtain satisfactory curing of the
interpolymer.
The other units in the interpolymer are derived from a combina-
tion of hardening and flexibilizing monomers, to provide the desired
combination of properties. The hardening monomer is generally styr~ne"
but otl-ers such as vinyl toluene or alkyl methacrylates having from 1
to 4 carbon atoms can also be used.
The interpolymer of the compositions of this invention may
contain from about S to about 75 percent of units derived from hardening
monomers with a preferred range being from about 40 to about 60 percent
of such units.
The flexibilizing monomer component is one or more alkyl or
substituted alkyl esters of acrylic acid or methacrylic acid, the alkyl
groups having l to 13 carbon atoms in the case of acrylic esters and
5 to 16 carbon atoms in the case of methacrylic esters. Ethyl acrylate,
butyl acrylate, and 2-ethylhexyl acrylate, 2-ethyl.tlexyl methacrylate,
decyl methacrylate and lauryl metllacrylate arc examllc~. Uthyl acrylate
is especially preferred. The interl)olymer of the compositions of this
invention may contain from about 5 to about 75 percent of units derived
from flexibilizing monolners with a preferred range being from about 20 to
about 50 percent of such units.
The com~?ositions of this invention may contain from about 5
percent to about 60 percent by weight, preferably 15 to 40 percent by
weigllt, of tbe interpolymer, the balance being the liquid medium.
The interpolymer is formed by polymerization in the presence of
a vinyl polymerization catalyst. Thc preferred catalysts are azo compounds,
-- 10 --
1~)6S98~
such as, for example, alpha, alpha'-azobis(isobucyronitrile). Otl-er
useful catalysts are tertiary-butyl perben~oate, tertiary-butyl pivalate,
isopropyl percarbonate and similar compounds. In some instances, Gther
free radical catalysts such as benzoyl peroxide and cumene hydroperoxide
may also be useful.
As indicated above, the polymerization is carried out in the
absence of a mercaptan. This is an important consideration because it
has been tlle practice, as illustrated by the above patents, to employ
small amounts (e.g., one percent to 3 percent) of a mercaptan as a chain
transfer agent in the preparation of amide interpolymers of this desired
type. It ilas been found that the presence of even these small amounts of
mercaptan in the interpolymer composition results in compositions which
are unsuitable for use in sanitary liners for beer and similar beverages.
When a mercaptan is present, the lining imparts an undesirable taste
characteristic to the beverage, especially on storage for a period of
6everal weeks. Since packed beverages are normally packed for some period
of time before they are used, this precludes the utilization of such
interpolymer compositions ss liners for the~e containers.
The compositions of thls lnvention are composed of dispersions
of the above-described interpolymers in a liquid medium. The liquid
medlum may consist entirely of water in some cases but, more commonlyj
will conslst of a mixture containing a major proportion of water and a
minor proportion of water-soluble or water-miscible organic solvents.
Sultable organic solvents are the etl~er type alcohols, such as ethylelle
glycol monobutyl ether (butyl Cellosolve~), ethylene glycol mono-ethyl ether
~ethyl Cellosolve~) and the like, and lower alkanol~ having ~ to 4 carbon atoms
~uch as ethanol, lsopropanol, butanol, and the like. ~lnor proportlons o~ hydro-
carbon solvent~ such as xylene, toluene, and the like may also De pre~ ln tlle
liq~id medium. Mixtures
* Trade Mark~
- 11 -
~)6598~
of the ether type alcohols and lower alkanols can also be used. The
preferred water-soluble, or water-miscible organic solvents are mixtures
of butyl Cellosolve and isopropyl alcohol. The liquid medium portion
of the CompositiOnS of this invention may contain from about 60 percent
to about 100 percent, preferably 80 percent, by weight of water and
from about 0 percent to about 40 percent, preferably 20 percent, by weight
of water-soluble or water-miscible organic solvent. In any event, thç
liquid medium will contain at least 60 percent by weight of water. It
should be noted that while ordinary tap water can be used in the composition
of this invention, deionized or distilled water is preferred. Based on
total weight of tl-e composition, the composition may contain from ahout 40
percent to a~out ~5 percent, preferably 60 to 85 percent, by weight of the
liquid medium.
The interpolymer herein is rendered water-reducible or disper-
sible by the addition of a monomeric amine solubilizing agent. As is
known in the art, acid group-containing interpolymers such as those
employed in tlle present compositions can be rendered water-soluble or
water-reducible by neutralizing or partially neutralizing the acid
groups therein with amines. In general, the monomerLc amines employed
herein for tllat purpose may be any of the allllnes used for solubilizing
resin systems known heretofore, including an~nonia, ethyl amine, butylamine,
dimethylamine, cycloliexylamine, morpholine, monocthanolallline, diethanol-
amine, diethylethanolamine, and the like. The preferred amines herein
are monoethanolamine and dimethyletllanolamine with dimethylethanolamine
being particularly preferred since it has been found to provide the best
results. While, as indicated above, amines may in general be used, there
are certain considerations which should be taken into account in choosing
the amine used to neutralize any particular system; for example, some
amines are morc effective than others in providing stable compositions,
depending upon the degree of neutralization of the interpolymer.
,
~ - 12 -
~0655~8~
The term "degree of neutralization" refers to the amount of
acid in the interpolymer (as determined theoretically) which has been
neutralize~ with amine. Thus, for example, if 20 percent of the
theoretical amount of acid in the interpolymer has been neutralized with
amine, the degree of neutralization is 20 percent theoretical neutrali-- -
zation; if 30 percent of the theoretical amount of acid has been
neutralized, the degree of neutralization is 30 percent theoretical
neutralization, and so forth. In all cases, the degree of neutralization
and the amount of amine is sufficient to provide a stable composition,
which is defined as one which does not separate into distinct phases, and
retains its application properties on storage. When it is desired that
this be accomplished at a relatively low degree of neutralization, i.e.,
below about 30 percent, tlle preferred amines, dimethylethanolamine and
monoethanolamine, should be used. At higher degrees of neutralization
(i.e., 30 percent or above), other amines are effective. Thus, for
example, at 30 percent theoretical neutralization, diethylethanolamine
produces good results and at say 50 percent theoretical neutralization,
essentially all of the above-listed amines are suitable.
The amount of amine employed in producing the water-based coating
compositions of tllis invelltioll is an impot~allt asl)ect of the invention.
This amount is partlcularly sigllificant at lower degrees of neutralization
of the interpolymer if a stable composition is to be obtained.
The amount of amine employed in producing the water-based coating
composition of tllis invention may in some cases be as low as an amount
sufficient to produce 0.180 milliequivalent of salt per gram of resins
solids, but ordinarily will be an amount sufficient to produce at least
0.200 milliequivalent of salt per gram of resin solids. The term "milli
equivalents of salt Rer gram of resin solids" refers to the number of
acid milliequivalents per gram of resin solids of the interpol~ner which
'
- 13 -
. , . . , .. . _ . _ _ _
~O~;S~8
have been neutralized with a base (i.e., an amine). The number of
milliequivalents of salt per gram of resin solids can be determined by
calculation using the following formula:
WeiglIt fraction of acid x 10 N ~lilliequivalents of salt per
Equivalent weight of acid gram of resin solids
wherein N is the degree of neutralization. A degree of neutrali~ation
greater than 100 percent indicates that excess base has been used. In
this latter situation, tlle value of 100 percent is used in the above
calculation. As indicated above, the compositions of this invention will
ordinarily contain at least 0.200 milliequivalents of salt per gram of
resin solids.
The upper limit in the amount of amine employed is somewhat less
important and is governed to a large degree by the method of application.
Thus, for example, if the composition is to be applied by brushing, roll
coating or dipping, the amine may be used in an amount which will produce
as much as 3.47 milliequivalents of salt per gram of resin solids. IIowever,
preferably, even in the above metllods the amount of amine employed does not
exceed an amount which will produce 1.910 milliequivalents of salt per
gram of resin solids. Moreover, when the composition is to be applied by
spraying, the amount of amine employed ordinarily should not produce more
than 0.764 milliequivalents of salt per gram of resln solids although in some
instances an amount of amine whicll will produce ~Ip to about 1.40 milliequiva-
lents of salt per gram of resin solids may be used.
The preferred method for producing water-based coating composi-
tlons of this invention comprises the steps of (a) polymeri~ing the
substituted amide, ethylenically-unsaturated acid, hardening and flexibil-
i~inb monomers in an escess of a mixture of water-soluble or water-miscible
organic solvents, the solvent mixture consisting essentially of an ether-
type alcohol selected from the group consisting of ethyl Cellosolve and
butyI Cellosolve and a lower alkanol selected from the group consisting of
. : .
.
- 14 -
_ _ .. ., . .. .. .... . . _ _ ~ . .. .. . _
-
~O~S5~8~
ethanol, propanol, isopropanol and butanol, wherein the excess solvent in
the mixture is essentially the lower alkanol, in the presence of a
polymerization catalyst to form the interpolymer in solution; (b) strip-
! ping off the e~cess solvent consisting essentially of lower alkanol by
distillation at atmospherlc pressure, under vacuum, or both; (d) adding
monomeric amine to tlre interpolv.ner solution; (d) adding water to the .
interpol~mer solution under conditions of agitation to form a dispersion
of the interpolvmer; and (e) heat aging the dispersion at temperatures of
from about 70C. to about 90C., while maintaining conditions of agitation
until the viscosity of the dispersion is substantially constant.
Tlle term "excess" as employed with reference to the organicsolvent mixture in step (a) above means that the total amount of organic
solvent mixture employed in the polvmerization process exceeds the total
amount of organic solvent desired in the final composition. The period
of heat aging, i.e step (e), depends upon several factors, such as the
composition of the interpolymer, the solids content of the composition,
the initial viscosity of the interpolymer formed, the degree of agitation
and the like. In general, the heat aging period can range from one hour
or less up to about 11 hours.
In a partlculaLLy preferred emL~odL~nent oE the above method, the
above-described monomers are polymeri%ed in an excess of a solvent mixture
consisting essentially of butyl Cellosolve and isopropanol, wllerein the
excess solvent of the mixture is essentially isopropanol, in tlle presence
of an azo polymerization catalyst to form the interpolymer in solution.
Then, the excess solvent consisting essentially of isopropanol is stripped
off by distillation at atmospheric pressure or under vacuum, or both,
following which the monomeric amine is added to the interpolymer solution.
Then deionized vater at a temperature ranging from 50C. to 99C. (i.e.,
,
,
- 15 -
1()65~88
hot water) is added to the solution to form a dispersion of the inter-
polvmer and finally the interpolymer dispersion is heat aged as in step
(e) above.
The preferred embodiment of preparing the water-based coating
compositions of this invention provides a number of significant and
important advantages. First, the use of butyl Cellosolve and isopropanol
as tlle solvent mixture provides a significant advantage because of tile
wide difference in the boiling points of these materials (i.e., butyl
Cellosolve = 171.2C., isopropanol ~ 8Z.4C.). This difference is boiling
points permits the ready removal (e.g., by distillation) of isopropanol
from the mixture, Accordingly, where as here, the excess solvent (as
defined above) employed in tlle polymerization procedure is essentially
isopropanol, such excess is readily removable and the total solvent content
of tlle final composition is more easily controlled. Secondly, the iso-
propanol in the solvent mixture functions as a chain-transfer and molecular
weight control agent in this system. I~ence, in the preferred embodiment,
isopropanol effectivel~ controls the molecular weight of the interpolymer
without the necessity of using an external or adcled cllain transfer agent,
such as the mercaptall chain transfer agellt~s normal?y cmpLoyed in polymer-
izing lntcrpolylllers oL thls type. l~lnlllly, the adtllt:loll of hot water to
the lnterpolylller solutioll is advantageous in that lt aids in the formation
of the interpolvmt!r disperslon and permits thc morc rapid attaimnent of
coating composition viscosity.
As indicated, the above-described methods are dirccted to the
preparation of the preferred water-based coating compositions in which a
portion of the or~anic solvent originally employed in the polymerization of
the interpolymer remains in the final resin composition. Ilowever, as indi-
cated previouslv in the specification, water-based coating compositions in
whicll tl-e liquid medium is entirely water are also contem~)lated as being
,
- 16 -
106S988
witllin the scope of this invention. Such compositions may be obtained by
following the above-described metllods and then employing an additional
separation procedure following step (e). Thus, for example, the organic
solvent remaining in the composition after step (e) can be removed bv
various separation procedures such as distillation, liquid cllromatography
and the like.
The water-based coating compositions of this invention can b'e
applied by methods conventionally employed in the coatings industry, such
as brushing, dipping, roll coating, spraying, and the Like and they are
particularly adapted to be applied by the metllods used to coat containers. -
In this regard, it should be observed that the exact formulation of the
coating composition employed herein (e.g., total solids, viscosity, etc.)
will depend upon the desired manner in which the composition is to be
applied. Thus, within the compositional limitations set forth in the
specification above, compositions having suitable application properties
(e.g., solids contents, viscosity, etc.~ can be readily selected for the
the method of applicatlon desired. Such a determLnation is well within
the skill of those in the coating art.
After applicatlon, the compositioll~ are ordLn~rily dried and
cured by baklng at elevated temperatures to yroduce a hard, thermoset
film. 'l'he baking schedules depend upon the nature of the particular
composition, the nature of the substrate, and the manner in which it
is to be used. In general, the water-based coating compositions of this
invention can be cured by using typical baking schedules employed in the
container industry. Typical baking schedules for such container coatings
employ temperatures ranging from about 300~F. to about 420F. and times
ranging from about 2 minutes to about 15 minutes.
The following examples are submitted to further illustrate the
nature oE the present invention and are not intended as a limitation on
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... . , . ~
106S988
the scope thereof. All parts and percentages used in the examples and
throughout the specification, are by weight unless otherwise indicated.
The solids contents reported in the examples were run at 105C. as a
quality control test.
,
XAMPLE 1
This example illustrates the preparation of a water-based
coating composition of this invention.
Into a reactor equipped with reElux condenser, heating means,
stirrer, thermometer and nitrogen feed liner were charged 159.0 grams of
ethyl Cellosolve, 325.0 grams of isopropanol, and 290 grams of a monomer
mixture consisting of 5.9 percent glacial acrylic acidj 28.2 percent of a
61.5 percent solids solution of N-(butox~methyl)acrylamide (NBMA) in a 1:3
solvent mixture of toluene and butanol, 32.I percent of styrene, 32.5
percent of ethyl acrylate and 1.3 percent alpha, alpha'-azobis(isobutyro-
nitrile) catalyst (based on monomer solids, the monomer charge contains 10
percent acrylamide as N~MA, 41 percent styrene, 41.5 percent ethyl
acrylate and 7.5 percent acrylic acid). The charged mixture was then
heated under nitrogen to reflux temperature (about 90C-93C.) in a
period of about 45 minutes. Afte.r reflux llad hesill, nn ad~itional ln81
grams of the above mOIlomer m:Lxture were ad~e(l to the reactor over a perlod
of about 3 hours. Thell 12.0 grams of t-butyl perbenzoate were added in 3
equal increments (i.e., 4 grams eacll) over a period of about 6 hours with
each increment being added at two-hour intervals. At the end of the six-
llour period, 337 grams of solvent (slightly more than the ori~inal amount
of isopropanol used) were stripped from the resultant interpolymer solu-
tion by distillation at atmospheric pressure at a temperature of about
94C. over a period of about 75 minutes. At this point, a sample of the
reaction mixture was analyzed for total solids content and found to have
a solids content measured at 150C. of 73 percent by welght. Then 49.8
grams (50 percent theoretical neutralization) of dimethyl ethanolamine
,
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~06S~88
were added to the reaction mixture (temperature of the mixture about
97C.). After addition of the dimethyl ethanolamine was completed, 1939
grams of deionized water preheated to 75C. was added to the reaction
mixture with stirring and the stirring was continued for about one hour
after the addition of deionlzed water was completed.
The water-based coating composition resultlng from the above
procedure is a dispersion of interpolymer in a liquid medium, the compo-
sition has the following formulation:
Interpolymer Units
Interpolvmer (Percent)
Acrylamide as N~ 10.0
Styrene 41.0
¢thyl acrylate 41.5
Glacial acrylic acid 7.5
Liquid Medium Percent by Weight
Deionized water 83.8
Organic solvents** 16.2
* - N-(butoxymethyl)acrylamide
** - A mixture consisting of ethyl Cellosolve,
isopropanol, toluene and butanol.
The composition ha8 thc foLlowing properties:
Polymer solids: 33.4 percent by weight of total composition
Liquid Medium: 65.6 percent by weigllt of total composition
Viscosity: 140 centipoises, Brookfield viscosity
at 77F., Spindle #4 at 20 r.p.m.
Acid No. 16.1
Milliequivalents of salt per gram of resin solids: 0.521
Stability: Good
-- 19 --
106S9~
The composition was drawn down on a metal substrate and
baked for two minutes at 375F., producing a smooth, hard and durable
film.
EXAMPI,E 2
In this example, Example 1 was repeated except that the
amount of dimethyl ethanolamine used to neutralize the interpolymer
was reduced by 40 percent (to 30 percent theoretical neutralization)
and the amount of isopropanol increased by 10 percent to adjust the
viscosity. The finis~led composition had the following properties:
Polymer solids: 35 percent by weight of total compositlon
Liquid medium*: 65 percent by weight of total composition
Viscosity 100 centipoises, Brookfield viscosity
at 77F., #4 spindle at 20 r.p.m.
Acid No.: 17.43
Milliequivalents of salt per gram of resin solids: 0.314
Stability: Good
* - 85 percellt bv welgllt of delonized water and
15 percent by weight of organlc solvents.
The composition when drawn down on a metal substrate and baked
for two minutes at 375F. produced a smooth, hard and durable film.
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~0~:;59~
~ ~IPLE 3
This example illustrates tlle preparation oE a preferred water-
based coating ccmposition of the invention in whicll Lhe ether-type alcohol
employed was butyl Cellosolve.
Into a reactor having the same equipment as in Example 1 were
cllarged 477 grams butyl Cellosolve, 975 ~rams of isopropallol and 870 grams
of the monomer mixture of ~xample 1 with ~he alpha, alpha'-azobis(isobutyro-
nitrile) catalyst removed. The chargcd Tnix~ure was tllen heated under nitrogen
to reflux employing the same conditions as in Example 1. After the onset
of reflux, an additional 3189 grams of the monomer mixture of Example 1 and -
54 grams of alpha, alplla'-azobis(isobutyronitril.e) catalyst were added to the.
reactor over a three-llour period as in Example 1. Following this addition,
12.0 grams of.t-butyl perbenzoate were added to the reactor using tl~e addition
procedure of Example 1. Then 981 grams of organic solvent were removed by
distillation at atmospherlc yressure at temperattlres ranging from about 95C.
to about 120C. Subsequently, 89.4 grams (30 percent theoretical neutraliza-
tion) of dimethyL ethanolamlne were added to tl~e reaction mixture. After
this addiLioll~ 5085 grams of deionized water preheated to 75C. were added
to the reaction mi.xture with stirring as in Example 1.
The resultant water-based coating composition has tl~e following
formulation:
nterpolymerYercent by welgl~t to~al solids ~ 38.5
Interpolymer Units
(E~ercent)
Acrylalllide as NB~I~ 10.0
Styrene 41.0
Ethyl acry.l.ate 4L.5
Glacial acrylic acid7.5
. .
1065S~88
Liquid ~ledium Percent by weight total liquid = 61.5
Percent by wei~
Deionizecl water 83.5
Organic solvents* 16.5
*Consisting of butyl Cellosolve, isopropanol, toluene and
- butanol.
' The composition had the following properti,es:
Total solicls: ' 38.5 percent
Acid number: 17.7
Visc06ity: 300 centipoises, l3rookEielcl viscosity at
77F., No. 4 Spindle at 20 r.p.m.
~lilliequivalents of salt per gram of resin solicls: 0.313
Stability: Good
The composition when drawn down on a metal substrate and cured as
in the preceec!ing examples produced a smooth, har(l and durable film.
- EX~'LE 4
In this example a water-~ased eoating omposltlatl was prepared ln
accordanee ~ h the manner used in Example 3, except tllat additional butyl
Cellosolve wns empLoyecl to increase the orgnnic solvent content of tlle
composition. The COIllpOsitioll had the following Eormulation:
Total Weigllt
Interpolymer as in Example 3 37.$X
Liquld medium 62.5X
Percent by Weigllt
Deionized water 79.5
Organic Solvents 20.5
.. . .
- 22 -
1(~6S~88
The composition had the following ?roperties:
Total solids: 37.5 percent
Viscosity: 16.5 seconds, #4 Ford cup
Acid No. 18.6
Milliequivalents of salt per gram of resin solids: 0.313
Stability Good
The CompositiOn when applied to a metal substrate and cured as
in Examples 1-3 produced a smooth, hard and durable rilm.
EX~MPLES 5-8
These examp]es illustrate tile crltical efrcct of the degree of
neutralization and thus the amount of salt procluced per gram of resin solids
on the stability of the water-based coating compositions of this invention.
In this evaluation, compositions were prepared in substantially
the same manner and using the same interpolymer as in Examples 3-4 except
that the amount of dimethyl ethanolamine employed was such that the degree of
neutralizatioll of the interpolymer was 30 percent of theoretical neutralization
(hereafter TN) in Example 5, 25 pereent TN in Ex;llllplc 6, 20 percent TN in
~xample 7 an~ 15 percellt 'I'N in i~xample 8. ~8lllce tha lower dagrees of neutrali-
zation resulted in higll composition viscosity (i.e., Examples 6-8), tlle solids
content o~ these compositions were recluced by aclding adclit:ional solvent in the
form of an 80/20 mixture of deionized water anci butyl Cellosolve. The resul-
LanL co~pDtitions ha~l the follouing Lormal~Lions and properties:
:'
.' ' - , .
- - 23 -
~0659-88
E X A M P L E
5 _ 6 7 8
Interpolymer ~ (As in ~xample 4, above)~
Percent Lheoretical neutralization 30 25 20 15
Total s()lids (weight percent) 36.4 33.1 18.0 25
Total liquid medium (weight percent) 63.6 66.9 82.0 75
Viscosi~y, #4 Ford cup, seconds
at 77~ 26 31 25 __
Acid number 18.G 19.4 12.9 12.1
Millie(luivalents of salt per gram
resin solids 0.312 0.261 0.20~ 0.156
Stability Good Cood ~air-Slight Bad - two
settling phase
separation
As can be seen from these examples, the stability of the composition
depends upon the degree of neutralization and thus the amount of salt per gram
oE resin solids produced.
lhe above examples were repeated Usillg monoethanolamine in place of
dimethyl ethanolamille and showed similar stabi]ity results.
` ~XA~II1.1~ 9
This example illustrates a water-based coating composition of this
invelltion having Low temperature bal~ing propertieY.
ln thiY example, the composition was prepared in substantialLy the
same manner as in ~xamples 1-8 except that tl~e monomer charge consisted of 10
percent acrylamide as N~IA, 10 percent acrylic acid, 30 percent etllyl acrylate
alld 50 percellt styrene; the stripping procedure was carried out under vacuum,
and the degree of neutralization of the acid groups of tl-e interpolymer was
27 percent TN. Tl~e resultant composition had tlle following formulation and
proPerties:
- 24 -
~065~38
Interpolymer (composition as above): 35 percent by weight
Liquid medium*: 65 percent by weight
Viscosity: 340 centipoises, Brookfield viscosity at
77F., #4 spindle at 20 r.p.m.
Acid number: 25.3
Milliequivalents of salt per gram of resin solids: 0.375
Stability: Good
* - 82.3 percent by weight of deionized water and 17.7
percent by weight of organic solvents consistlng
of butyl Cellosolve, isopropanol, butanol and xylene.
The above composition when applied to a metal substrate can be
cured in 4 minutes at 320F. to produce a smooth, hard and durable film.
As indicated above, the compositions of this invention are especi-
al;y adapted for use as internal sanitary liners for beverage containers.
- As indicated at the beginning of the specification, the sanitary
liner of such beverage containers are subjected to a number of tests.
These tests are performed on the liner both prior to and after the container
is backed with beverages te.g., beer). When such a container is packaged
with beer and sealed, the beer ls sub~ected to pasteurization and other
normal processing operations. After the containers have been subjected to
storage, they are opened and both the beer and the liner are evaluated. The
following are some of the more important tests which have been developed
to measure the sanitary liner compositions for beverage containers:
(a) metal adhesion;
(b) turbidity;
(c) extractability;
(d) taste; and
(e) pasteurization resistance.
.
.. . . .
- 25 -
~06~ 8~
In the following examples, designated 10-13, samples of the water-
based coating compositions of Examples 1, 2 ? 4 and 9 (Examples 10-13 below)
were applied to beverage container stock used to package beer and cured as
indicated above. The cured sanitary liner compositions of the invention
were then evaluated to determine their effectiveness in the above tests.
Results are shown below.
EXAMPLES 10-13
E X A M P L E
11 12 13
Formulation Ex. 1 Ex. 2 Ex. 4 Ex. 9
Type Test and Result:
Metal adhesion P P P P
Turbidity P P P P
Extractability P P P P
Taste P P P P
Pasteurization resistance P P P P
P = Passed.
As can be seen from the above, the compositions of this invention
passed all of the important testæ for sanitary liners.
It should be observed that a composition similar in formulation
to Example 1, except that it contained 2.5 percent mercaptoethanol chain
transfer agent, falled to pass the taste test.
According to the provisions of the Patent Statutes, there are des-
cribed above the invention and what are now considered to be its best
embodiments. However, within the scope of the appended claims, it is to be
understood that the invention can be practiced otherwise than as specifically
descrlbed .
,
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