Note: Descriptions are shown in the official language in which they were submitted.
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P30,028
IMPR$VED FLAVOR ALU~Cl~M CIEANING COMPOSITIoN AND PROCE5S
Background of the Invention
The present invention broadly relates to an ac~leous
cleaning ccmposition for cleaning aluminum surfaces, and more
particularly, an aqueous acidic solution for cleaninq aluminum
keverage containers to enhance the flavor characteristics of ~he
beverages subsequentl~ contained there m .
AlumQnum co~taLners are in widespread cGmmercial use for
the packaging of v æ ious food~tuffs including beverages such as
soft drinks and beer. It is conven~ional practice in the
fabrication of such alum m um containers to form circular blanks
from an aluminum sheet which are thereafter for~ed Lnto
prelimunary cups employing a sultable die or cupping press
whereafter the cups are drawn and ironed in one or more forming
stages to form a can of the desired di~ensions. The fon~ed cups
are subsequently subjected to a tri~0ing operation and are
thereaf~er subjected to various eleaning and treatment steps
culminating Ln the application of a sanitary lacquer coating as
well as decorative coatings and inks on the exterior surfaces
thereof prior to filling with foodstuffs.
It i9 conventional practice to employ varicus lubricants
and ooolants during the m lling of the aluminum strip as ~311 as
during the forming, draw m g and ironing c~erations to assist in
the fabrication of sueh alurninuml containers. The resultant
contaLner surfaces usually have residual quantities o such
organie lubricants thereon in addition to fine-sized metallic
particles of aluminum usually referred to aY smut which are formed
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on the container surface during the form m g operations. It is
important that such residual luhricants and smut be removed from
the oontainer suraces before the container is subject to chemical
treatnent steps prior to coating operations.
Various aqueous acidic and/or alkaline cleam ng
solutions have heretofore been used or proposed for cleaning such
aluminum surfaces to remGve the residual lubricant and aluminum
particulate smut ~rom the Æ fa oe s thereof. Typical of such
oompositions is that disclosed in United States Patent
No. 3,969,135 granted to Peter F. King et al on July 13, 1976
entitled "Low TemperatNre Aluminum Cleaning Composition and
Process".
While such aqueous cleaning compositions have been found
effective in removing the residual lubricant and other
contamunating substances from the surfaces of such aluminum
oontainers, problems have arisen in s e instances due to an
off-flavor imparted to the beverages contained in such containers
as established by extensive subjective flavor taste panels. This
problem is particuLarly vexing because of its sporadic and
unpr~dictable oocuxrence and has occasioned rejection of lot.s of
such c~ontainers because of pot~ntial of-1avor charact~ istics
imparted to the foodstuffs to be packed therein.
The cause for such of~ flavor in aluminum containers is
not fully understood a~thou~h it is speculated that certain
residual contaminants remaining on the container surfaces
follcwing cleaning and pretreatment attribute at least in part to
the problen. Adjustments in the concentration of active
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constituen~s in such aqueous cleaninq solutions have been
unsuccessful m overcoming this problem and the latitude in
varying such con oe ntrations is restricted by ad~erse effects on
the aluminum substrate such as an cver-etched surface condition
imparting a frosty appearance to the container surfaces which is
objectionable Ln some instances.
Ihe present invention provides an improved ccmposi~ion
and proces~ for cleaning aluminum Æ faces which effectively and
efficiently remo~es residual contamunating substances and smut
~rom the surfa oe ~ thereof and further inh~bits or substantially
elimLnates off-flavor problems imparted to the foodstuffs
contained therein.
Sumnary of the Invention
The benefits and advantages of the present invention are
based on the disccn~ry of incorporating a controlled amount of a
boron containing conpound in an aqueous acidic cleaning solution
which is controlled in concentration relative to the active
free-fluoride present in the solution so as to provide a
stoichiometric excess of boron relative to the free-fluoride
present required to form the anion HF4 . The presencq of such a
stoichicmetric excess of boron in th~ fonm of a solution soluble
and com~atible boron cantaining compound has been found to
subst~antially r.educe the occurrence and severity of such
of'f-flavvr problem~ heretofore enc~untered Wlth aqu æ us cleaning
compositions of the types hPretofore known.
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The aqueou~ acidi~ cleaning solution in accord~nce with
the composition aspects of the present invention con~ains
free-fluoride in am~ounts generally less than about 0.4 percent by
weisht (less than about 4 g/l) and more usually within a range of
about 10 pFm to abcut 100 ppm, a solution soluble boron containing
compound s~ch as borate anions present relative to the amount of
free-fluuride in the cleaning salution to provide a stoichicmetric
ex oe ss of that requiu~d to form the anion ~F4 , generally at a
stoichiometric excess of boron of at least a~out 4 ppm relative to
the free-fluDride present, hydrogen ions to prcvide a pH of less
than akout 3.5 with a pH of about 1 to about 2 heing preferred,
optionally but preferably a su~factant or mixture of surfactants
present in an amount up to about 10 g/l or higher fos furthex
enhancing the cleaning characteristics of the cleaning solution,
and optionally, a defoaming agent to m m imize foam formation
deFending upon the types of surfactants employed and the manner hy
which the cleaning solution is applied to the alumi~uml surfaces to
be cleaned.
In accordance with the process aspects of the present
invention, aluminum surfaces are cleaned by contacting the
surfa oe ~ with the a~orementioned aqueous acidic cleaning solution
for periods of tine up bo about 10 minute~ with time periods
ranging Prom about 10 seconds up to about 5 minutes being typical.
The clezr~g solution temperature i~ controlled at a level above
about 90F, with a temperature range o~ about 110 to abc1t 130~
being usually preferred. The aqyRous cleaning solution is
preferably applied ~y spray application particularly in the case
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of alum m um cup-shaped containers facilitat m q uniforn contact
with the interior and exterior surfaces thereof achiev mg optLmun
cleaning.
A~ditional benefits and advantages of the present
invention will ~ecome apparent upon a reading of the Description
of the Preferred Eh~xxliments taken Ln conjunction with t~
specific examples prcvided.
Descri~tion of the Preferred ELtxxLu~ents
The aq~x~us acidic cleaning solution, in accordance with
the oomposition aspects thereof, contains as its essential
ingredients a solution soluble fluoride containing ccmpound to
pxovide a controlled free-fluoride concentration, a solution
soluble bo m n containing compound present in consideration or the
concentration of free-fluoride to prcvide a stoichiometric excess
of boron to free-fluoride required for formung the anion BF4 ,
hydrogen ions present ~o provide a pH on the acid side generally
less than about 3.5, optionally but preerably, one or a plurality
of surfactants to further enhanc~ the cleaning characteristics of
th~ solu~ion pre æ nt in an amount up to about 10 g/l or hi~her,
optionally, a commercial defoanang agent for nNILumizing fohm
formation dependinq upon the particular type of surfactants
employed and t~e manner in w~tich the cleaning solution is applied
bo the surfaces to be cle~ted.
. The acidity of the cleaning solution should be
maintained at a ].evel less than about pH 3.5, preferably within a
range of abottt 1 to about 2 depending upon the concentration of
other constituents in the solution and the temperature and
duration of application of the solution to aluminum surface~.
Hydro~en ion concentrations to provide a pH ~elow about 1 have
been found in so~e instances, depending on the fluoride
concentration, to cause an undesirable etching of the alum mum
surfa oe s i } ting a frosty appearance thereto which is
undesirable in th~se instances in which a metallic shiny surface
is desired. Qn the other hand, pH values in excess of about 3.5
have been found to increase the time required to acccmplish the
desired cleaning and such prolonged time periods are undesirable
in com¢ercial cperation. The acidity of the cleaning solution is
provided ~y the addition of any suitable bath soluble and
cGmpatible inorganic or organic acids of which mineral acids such
as sulfuric acid are preferred~ When hydrofluoric acid is
employed as a source for the fluoride constituent in the soluticn,
the use of hydrofluoric acid provides all or a portion of -the
hydrogen ionq in the solution.
The cleaning solution further contains a solution
soluble fluoride containing compcund to provide a free fluoride
concentration which accelerates the attack upon the alum m um
sur~aces bo be cleaned and the rem~oval of smut or fine-sized
~tallic particles from the surfaces thereof. The fluoride
oonoentration in tha ~olution can conveniently be provided by the
use of hydrofluoric acid itself ag well as the aLkali metal and
amnonium simple salts thereof.
The ooncentration of fluoride con~aining compound
employed i9 controlled so as to p m vide a free-fluoride
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oonoentration in the solution in an amount generally less than
about 4 g/l with oon oentrations of frcm abcut 10 ppm up to about
100 ppm keing preferred, while concentrations of from akc~t 20 Fpm
up to about 50 ppm are particularly satisfactory and typical. The
t~rm "free-fluoride" as herein emplcyed and as set forth in the
subjoined claims is intended to encompass that fluoride present in
the solution which is not present Ln a co~pl~xed fonm such as
stable cc~plexe~ i~cludin~ flubborate, silioofluoride and aluminum
fluoride which progressively builds up in ~he bath'during use of
the solution. The free-fluoride present in the solution is
defined as that measured by a specific fluoride sensitive
electrode of the potentic~etric type against a controlled solution
oontaininq 40 ppm fluoride ions at a pH of 1.1 and at a
temperature of 80~F. A suitable fluoride specific ion electrode
is ~escribed Ln U.S. Patent No. 3,431,1~2.
In additicn, the aqueous acidic cleaner solution
contains a solution soluble boron containing oompcund the
o3ncentration of which will vary depending upon the -particular
concentration of the free-fluoride present. The source of the
borcn containing oompound preferably oomprises boric acid as well
as the simple alkali metal and a~monium salts thereof of which
boric acid itself constitutes the preferred material. The
ooncentration of the bomn wntaLnm g ozmpound is controlled 50 as
to pDovide a stoichiometric excess of boron relative to the anount
of free-fluoride present in the cleaning solution over that
reouired to produce the anion BF4 . It will be understood, that
the anion ~F4 is not necessarily formed in the solution but -~hat
this anion is provided as a convenient basis for establishi~g the
relativa concentration of the boron to free-fluoride present to
achieve the ~enerits of the present inventlon.
The specific free-fluoride level is determined ~y the
mQgnitude of cleaning desired or required to renove the aluminum
fines, smut and lubricants as well as other con~aminants and 50ils
from ~he surfa oe s of the al D um containers being cleaned in
further consideraticn of the desired appearance, degree of etching
of the aluminum surfaces as well as the types of subsequent
treatments and coatings to be applied to the containers. When the
desired free-fluoride level is established to provide the
requisite clea m ng for any particular situation, the boron level
is adjusted so as to prcvide an appropriate stoichianetric excess
thereof in accordance with the foregoing definition. Preferably,
the stoichiometric excess o boron to free-fluoride to produce the
anion BF4 is controlled to provide an excess of boron of at least
about 4 ppn to an excess of about 200 ppm or higher, and
preferably, an excess with m a range of about 10 ppm to about 75
ppm of the stoichiometric amount.
In addltion to the fore~oing constituents, the cleaning
solution optionally but preferably contains one or a mixture of
sur~actants which ma~ ba present in concen~ration~ up to about 10
g/l or even higher wi~h concentrations of about 0.1 to about 5 g/l
bein~ more usual. Generally, sati~factory cleaning of aluminum
surfaces can be obtained at surfactant concen~rations of about 0.5
to abeut 1 g/l. It is also contemplated that any one of a variety
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of suitable commercial defoami~g agents of the types known in
the art can also be employed depending upon the particular type
or types of surfactants used to minimize an undesirable degree
of foaming of the cleaning solution partieularly when applied
by spray applieation.
A particularly satisfactory combination of surfactants
suitable for use in the cleaner composition is that as described
in United States Patent No. 3,969,135. m e afore~entioned U.S.
patent teaches the use of a hydroearbon-derivative surfactant
in combination with an abietic acid-derivative surfactant in
which each of the surfactants can be employed in amounts of about
.1 up to about 50 g/l with amounts of about 0.5 to about 2 g/l
being preEerred. The combination of the two surfactants functions
to remove all of the various types of organic eontaminants and
soils present on the aluminum surfaces enhancing the efEiciency
and perforrnance of the cleaning solution.
The surfaetants whieh can satisfactorily be employed
may comprise nonionic, anionic or cationic surfactants of whieh
nonionie surfaetants are generally preferred. Typieal of suitable
surfaetants whieh ean be satisfaetorily employed and are eornmer-
eially avallable are:
Surfaetant AR* 150 available from ~lereules, Ine. and
reported to eomprise an ethoxylated ab:ietie aeid deriva-tive eon-
taining about ]5 mols ethoxylation.
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PEGOSPERSE* 700-~O available fron G1YCD Chemicals, Inc.
reported to comprise an ethoxylated abietic acid derivative
oontaining ab3ut 14 bo 16 mols ethoxylation.
qRTqON* CF-10 available frcm Rohm & Haas Co. reportedly
oomprising an alkylaryl polyether having a carbon chain of about
14 carbon atoms and abcut 16 mols of ethoxylation.
PLURONIC* Lr61 availahle from BASF Wyandotte, Inc.
~ep~rtel1y oomQrising a condensa~e oonta ~ only ethylene oxide
and propylene oxide chains.
ANTAROX* IF-330 a~ailable from GAF Cbrporation reportedly
cc~,prising an aLkyl poly(ethyleneoKy) ethanol.
ANTAROX* BL~330 also avail~ble frcm G~F Corporation
reportedly camprising an alkyl poly(ethyleneoxy) ethanol.
IGEPAL* C~-630 available fr3m G~F Corporation reportedly
comprising an aLkyl pheno~y poly(ethyleneox;y) ethanol.
~ RYCOL* LF~l avail~ble fr3m Emery Ind~stries, Inc.
reForbedly ocmPrising an aLkyl polyether.
PLURAFAC* D-25 cc~mercial1y available fram B~SF
Wyandot~e, Inc. reportedly comprising a m~dified oxyethylated
straight chain alcohol.
'tRI'nON* X-102 avail~ble from Rohm & ~aas Co. r~portedly
com2rising ,m octyl phenoxy p,oly ethoxy ethanol.
PLURAFAC* R~-30 avaiL~ble from BA5F Wyandotte, Inc.
reportedly oomprisLng a modified oxyethylated straight chain
alcoho1.
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POLYDETERGEN~ S-505LF available from Oline Corp.
reportedly oomprism g a mcdified polyethoxylated straight chain
alcohol.
SURFONIC* LF-17 available frcm Jefferson ~ ical Cb.
reæortedly ccmprising an alkyl polyethoxylated ether.
TRIION*~F~16 available from Rohm ~ Haas Cb. reportedly
oompris ~ a modified polyethoxylated straight chain alcohol.
Ill~KGIT~L~Anionic-08 available from Union Carbide Corp.
reportedly comprising soditDm 2-ethyl hexyl sulfate, or the like.
In accordance with the process aspects of the prese~tt
i~on, the aqueous acidic clean~r~ solution can be applied to
the al~ni~ surfaoe by any of the com~ltional techniques
alth~gh Sp~dy appLication is particul~rly desirable when cleaning
alumirmm containers in view of their configuratio~ in order to
achieve ~iform cle~ning of the interior as well as exterior
surfaces thereof. $~e cleaning solution is heated to a
te~erature abava the cl~d point which deper~ding upan the types
and ~nc~ttrations of surfactants enplc~yed, is generally at least
about 90F or higher. Typically, tes~eratures of a}~ut 110 up to
about 130F are errployed with a te~erature of abaut 120F being
preferred. Higher tsrperatureq can be ~ployed but are n~re
energy intensive and are l~sg desirable for this reason~
me solution is applied to the al~ni ~ surfaces to be
clean3d for p~riods up bo about 10 mlnutes although time periods
of about 10 seoonds up to about S mlnutes are more usual.
Typically, satisfactory cleaning of the alumlnum sur-faoe s can be
achieved in pe~riods o less than about 2 minutes.
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In order to fuxther illustrate the present invention,
the follow m g example is prcvided. It will be understood that the
~ample is provided for illustrative purposes and is not Lntended
to be limiting of the scope of this i~vention as herein described
and ~s set forth in the subjoined cla.ums.
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The benefits of the aqueous clean m g solution of the
present invention in enhancing the flavor of foodstuffs packaged
in alum m um contaLners and overcoming off-flavor problems i5
demonstra~ed by the foll~wing tests. Aluminum beverage containers
of the type employed for packag~ng beer were cleaned employing a
sLx-stage washer in which stage one ccmprised a prewash employing
solution counterflowed from the second stage and was at a pH of
about 2.5 to abcut 3. In stage two, an aquecus cleaning solution
of the type compris m g the present invention was employed in which
the ooncentration of boron was varied relative to the
free-fluoride oonoentration to evaluate its effectiveness on
overoo~ing of~-flavor problems. Stage three ccnprised a triple
r m se stage while stage four employed a proprietary alkaline
cleaning treatment and rinse followed by stage ive comprising a
~hrea-skage water rinse and f m ally stage six ccmprisin~ a dual
water rinse with the lask sec*ion employing deionized water.
Alun~ln~n containers proces~ed through the foregoiny
cleaning seqyenoe were evaluated by a ta~te panel co~prising a
group of taste exFerts to establish the effect o~ the can cleaning
process on the flavor of beer. For this purpose, reshly brewed
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unpasteurized beer was placed in a glass beaker and used as the
con~rol. The same draft beer was pLaced in the processed alum m um
contaiNers for a period of 15 minutes and was then tasted and
scored relative to the taste of the control. The control
typically receives a a~mposite score ranging about 3 to about 4.
In rating flavor of the aluminum containers, the more closely the
beer in the aluminum container approximates that of the control,
the bet*er the flavor rating.
Ths composite scores assigned cc~prise a weighted
averaye of 8 flavor "notes" by the individual taste panelists
including oily, woDdy, mouthfeel, aftertaste, bitterness, e~c. in
accordance with conventional taste practices. Generally, a rating
of about 6 to 6.5 is considered as the nurLI~Im ccmmercially
acoeptable; a composite rating of about 5.5 to 6 comprises a good
flavor rating; a composite rating of about 5 bo 5.5 corres~onds to
a rating which is virtlally psrfect and equivalent to the control
while ratings below about 5 are so perfect as indicating that the
results are suspect.
The aqueous acidic cleaning solution in the second stage
of the washer was continucusly monitored over a six-day test run
for composition and processing paramsters with the conoentration
o~ ooron ~Itroduced by way o~ boric acid being vari~d and the
concentration correla ed to the flavor panel oomposite rating on
cans produced thxeby. The aqueous acidic clea m ng solution was
applied at a te~perature ncmlnally oontroll~d at 125F at a free
acid of about 7.5 to 9ml (a pH of ahout 1.4 to about 1.5) and at a
free-1uoride concentration of about 25 ppm. The free fluoride
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was introduced in the fonm of hydrofluoric acid and pH control was
provided by the addition of sulfuric acid. The aqueous acidic
cleaner further contained about 0.7 g/l of surfactant Trycol LF-l
and 0.7 g/l of Surfactant AR-160. The aqueous acidic solution as
well as each of the rinse and pretreatment solutions following
w~re spray applied ~against the conta~ner surfa oe s. The duration
of treatment of the containers in stage two incorporating ~he
aqueous acidic clea~ing solutions was about 30-60 seconds, which
varied with l;ne-speed and averaged abcut 45 seconds. Ihe results
of these tests are summarized in Table l.
TABLE 1
Test Stoichiometric Cb~posite
n No. Excess B,~pl~l Flavor Score
l 0 5.7
2 0 5.9
3 0 5.9
Average 5.8
4 1 5.5
3 5.7
6 6 5.4
7 30 5.2
8 28 5.2
9 26 5.2
5.0
Average 5.3
~ rhe foregoing results clearly demonstrate an enhancement
o~ the flavor of be0r relative bo the controL by emplcying boron
in the aq~ux~u9 acidic cleaning .;olution which is in stoichicmetric
exces~ over that theoretically required relative to the
~re~-fluoride pre~ent to produce the anion BF~ .
While it will be apparent that the pre~erred embodiments
o~ the invention disclosed are well calculated to ful~ill thP
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objects a~cve stated, it will be appreciated ~lat the invention is
susceptible to modification, variation and change without
departinq from the propar scope or fair mean m g of the subjoined
claims~
