Note: Descriptions are shown in the official language in which they were submitted.
127;~61
-- 1 --
PROCESS FOR CLEANING ALUMINUM
BACKGROUND OF THE INVENTION
The present inventlon broadly relates to an
improved process for cleaning aluminum surfaces, and
more particularly, to a process employing a
sequential cleaning cycle including a primary
alkaline cleaning solution for effecting a removal of
organic contaminants and aluminum fines from the
surfaces of the containers and to further enhance the
mobility of the containers facilitating their
transport in high-speed can lines having a capaclty
in excess of about 1,000 cans per minute. The
process of the present invention is particularly
adaptable for cleaning drawn and ironed aluminum
container bodies of the types employed in the
packaging of foodstuffs and beverages. The cup-
shaped and dished integral bottom of such container
bodies, because of their configuration, are
conductive to entrapment of the various cleaning and
rinse solutions during the cleaning cycle which has
in some instances resulted in an objectionable
localized staining of the surfaces thereof during
line stoppages during the cleaning process.
It has previously been discovered that by
employing an aqueous alkaline cleaning solution of a
controlled composition as described in U. S. Patent
No. 4,599,116, issued July 8, 1986, and entitled
"Alkaline Cleaning Process", an elimination of such
localized objectionable staining could be achieved
providing for clean aluminum containers of
commercially satisfactory quality. It was also
discovered, in accordance with the teachings of the
aforementioned U. S. patent, that an improvement in
the mobility of such cleaned containers could be
enhanced by subjecting the containers to a con-
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~Z~3861
-- 2ventional conversion coating treatment following the
cleaning and rinsing steps. Such increased mobility
is important for effecting rapid transfer of such
containers through the conveyorized processing lines
without incurring jamming and disruption of the feed
of the containers to subsequent processing steps such
as lacquering, printing, decorating, and the like.
While an improvement in can mobility has been
achieved by the application of such a conversion
coating, the mobility of such containers in high-
speed can processing lines of a production capacity
in excess of 1,000 cans per minute to as high as
about 1,500 cans per minute has been less than
optimum.
- 15 In accordance with the present invention,
it has been discovered that by using an acidulated
water rinse treatment following the alkaline cleaning
treatment and prior to any subsequent optional
conversion coating treatment, a substantial increase
in the mobility of such containers is achieved
further enhancing their processing through subsequent
stages.
SUMMARY OF THE INVENTION
The benefits and advantages of the present
invention are achieved by a sequential process for
cleaning and treating aluminum surfaces, and
particularly aluminum containers to remove aluminum
fines and residual organic contaminants including die
lubricants remaining on the surfaces thereof
following the several manufacturing steps including
the drawing and ironing of the containers into a
container body. The process in accordance with its
preferred embodiments includes the steps
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1~73861
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of contacting the aluminum containers with a preferred acidic aqueous
pre-wash solution for a period of time sufficient to remove a portion of
the reqidual aluminum fines and organic contaminants on the surfaces
thereof. Thereafter, the pre-washed containers are contacted with an
aqueous primary alkaline cleaning solution containing an alkalinity agent
present in an amount to remove aluminum fines f.a~ the surfaces of the
containers in further combination with a complexing ~gent, one or a
oombination of surfactants to remove the organic soils on the surfaces of
the container and opticn~lly, an antifoaming agent. Following the aLkaline
cl~aning step, the cleaned container are thereafter 3ubjected to one or a
plurality of countorflow d highly acidulated water rinses, with or without
a prior lntn~ng wat-r rinse, to effect the neutralization and removal
of re~idu~l alkaline cleanor thereon of which at least one rinse stage
oor~n~ an acidlty agent present in an amount sufficient to provide a pH
of leJs than about 6, preferably below about 5, depending on whether or not
an acc#lerat~ng agont i8 pre~ent in the acidulated rinse solution. The
acidulated w~tor rin~e, d-pending on the temporature and time of contact,
y optlon~lly and pr~ferably contain free fluoride and/or phosphate ions
to accelerate the oxide and stain removal from the aluminwm container
surface . The acid rin~d oor~ner~ are preferably further water rinsed
with a ~olution at ~ubstantially neutral pH, whereafter, the rinsed
con~L~Yn- aru optionally subjectJd to a 0nversion treatment to i~part a
desir d co m er~ion coating thereon. PaL~ng the conversion coating, if
apQliod~ the conbL~er are again sub; ctRd to one or a plurality of water
rin o~ whereaft~r they are dried and c!an thereafter be further proo#~ed
such aa by lacgu~ring, painting, decorating and the like prior to being
fill~d with appropriate foodstuffs or b Rcn~e-.
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The use of the acidulated water rinse stage ollcwing the
alkaline cleaning step ha~s been found to m ~kedly increase the mobility
of the containers believed to occur as a result of a remcval o~ an oxide
film formed on the container surfaces during the alkaline cleaning step
S as well.as remcving any staining of the surfaces of the conta m ers and
greatly enhancing the transferability of the containe~s such as by
rolling and/or sliding through the conveyorized transfer lines and
chutes.
A~ditional benefits and advantages of the present invention
will become apparent upon a reading of the description of the preferred
embod~ments taken in conjunction with the speci~ic examples provided.
CESC~IPTloN OF THE PY~KK~ EMBODIMENTS
In accordance with the practice of the process of the present
invention, and with -particul æ emphasis o.n the cleam ng of drawn and
ironed aluminum containers, the aluminum containers are transferred from
the body-making and trimming apparatus to a multiple stage high-speed
cleanLng apparatus to effect a removal of the residual body-forming
lubrlcants and aluminum fines or smut formed on the surfaces of the
ccnta1ners dur mg the manufacturing operation. The aluminum fines
comprise minute particles of alum mum on the container surfaces and
adhered thereto in combination with various lubricants and metal warking
ccqpound~ employed during the form mg operations of the container.
The first stage of the cleaning cycle preferably comprises
contacting the surfacYs of the ecntainer~ with an aqueous pre-wash
solution, preferably an aqueous acidic pre-waih solution, to effect a
remcval of at lea~t a portion of the fines and/or organic soils from the
contaLner surfaces thereby reducing a buildup of such contamln3nts in
- the succeeding primary alkaline clea m ng stage.
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The pre-wash solution is applied to the
aluminum container surfaces at temperatures ranging
from ambient (i.e. from about 60F) up to about
200F, and preferably at a temperature below about
150F, such as from about 90F to about 130F. The
pre-wash solution is contacted with the aluminum
surfaces to be cleaned such as by flooding, immersion
or spraying of which the latter constitutes the
preferred method to assure uniform distribution of
the pre-wash solution on both the interior and
exterior surfaces of the container.
Following the pre-wash stage, the pr~-
liminarily cleaned aluminum containers are
transferred directly to a primary alkaline cleaner
stage incorporating an aqueous alkaline cleaning
solution of a composition preferably as described in
U. S. Patent No. 4,599,116. Typlcal of suitable
aqueous alkaline cleaning compositions are those
containing an alkalinity agent present in an amount
to achieve satisfactory removal of residual aluminum
fines on the surfaces of the containers without
incurring undesirable etching of the surfaces.
Generally, the pH of the alkaline cleaning solution
ranges from at least about 11 up to about 13. The
alkalinity agent may comprise an alkali metal
hydroxide and/or alkali metal carbonate in further
combination with a suitable complexing agent present
in an amount effective to complex at least some of
the metal ions present in the cleaning solution which
otherwise tend to form solution insoluble
precipitates. The alkaline cleaning solution can
optionally further contain a foam-suppressant agent
of any one of the types conventionally employed which
is utilized in consideration of the types and
concentration of the surfactants employed. The foam
suppressant agent is used at a level
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lZ7386~
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sufficient to prevent undesirable foam mg of the cleam ng solution
particularly when it is applied by spray application.
In accordance with a preferred practice, the alkal me cleamng
solution LS controlled at a pH ranging from about 11 up to about 13 with
a pH of from about 11.5 to about 12.5 being preferred. In order to
achieve an alkalin~ty within the foregoLng range, the alkalinity agent
such as a mixture of sodium hydroxide and sodium carbonate LS employed
at concentration~ o frcm about 0.05 up to about 10 g/l.
Complexing agents suitable fo~ use m the alkaline cleaning
solut~on comprise sugar acids as well as salts thereof such as, for
example, sodium gluconate, sodium citrate, sodium tripolyphosphate, as
well as other acids includ~ng glucoheptanoic acid, t~rtaric acid, ~DI~
- and the like as well as the bath soluble and compatible salts and
mixture~ thereo.
The alkaline cleaning solution further contains as an
e~sential ingredie~ at le~t one or a comblnation d surfactants which
are u~u~lly ~lected from the group comprising hydro 3 bon alkcxylated
surfactant~ wbich ar~ charactorized as 1n~vidually or in their blended
combination a~ having a Hydrophile- ~ ile aalance (HLB ratio), i.e.
the balance of the slze and strength o the hydrophilic ~water-lov my or
polar~ and tha lipophilic (oil-loving or non-polar) groups of the
molecule within an HLB ratio o at least about 12, preferably at l~.Ct
about 12 to abcut 15. While other surfactants can be employed to
provide for effective cleaning of the aLkaline clea m ng colution, it has
been found that employing surfactanto characterized ~y the foregoing HL~
rati4~ subotantially reduces or eliminates a tondency of white stalning
on the sur~ace~ of the alumioum con~r occasioned by line stoppages
~ whi~ fr~tly occur in high-capacity, hi~h-~peed conta~ner wa~h~rg.
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lZ73E~61
Such line stoppages may range from about one-half
minute to as long as about one hour and the presence
of residual cleaning solution on the container
surfaces has occasioned such white-staining problems.
5 By employing surfactants of the appropriate HLB
ratio, such white-staining has been substantially
eliminated.
The aqueous alkaline cleaning solution can
also be applied, as in the case of the acidic pre-
wash solution, by flooding, immersion and preferablyby spray application for a period of time sufficient
to effect a cleaning of the surfaces thereof.
Generally, the aqueous alkaline cleaning solution is
employed at moderate temperatures below about 150F
to about ambient temperature with temperatures of
from about 90 to about 130F being preferred.
Following the aqueous alkaline cleaning
stage, the cleaned containers are transferred to a
water rinse stage, preferably a multiple stage water
rinse section of the conveyorized washer. In
accordance with the process as described in U. S.
Patent No. 4,599,116, it was discovered that by
maintaining the pH of the water rinse solution at a
level below about pH 7.5, a further elimination of
any tendency to form brown stains on the container
bodies was achieved during the rinsing stage. As
demonstrated in the prior pending application, if the
pH of the aqueous rinse stage rises to a level above
about 7.5 as a result of carry-over of alkaline
cleaning solution into the water rinse stage, brown
staining of the aluminum container surfaces occurs
particularly when line stoppages occur in the rinsing
stage.
It has now been further discovered that by
increasing the acidity of the water rinse solution
employed in the rinse stage following the primary
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- 7a -
alkaline cleaning step, with or without an
intervening water rinse step, not only brown staining
is prevented, but
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a further ~ubstantial improvement in the mobility of the cleaned aluminum
containers is obtained. rt is believed that this increased mobility is a
result of the substantial reduction of or removal of an aluminum oxide film
fo~med on the aluminum oontainer surfaoes during the aIkaline cleaning step.
The substantial reduction of the aluminum oxide film on the aluminum
surfaces also effects a substantial or complete removal of objectional
stains that may have formed on the aluminum container surfaoes during and
following the aLkaline cleaning stage. Because of this, the containers
following the alkaline cleaning stage and prior to the acidulated water
rin~e stage can be subjected to a conventional tap water rinse to remove a
sub~tantial portion of the residual alkaline cleaner from the surfac~s
thereof prior to the acidulated water rin~e stage. Any staining occurring
in the tap water rinse stage, which may become somewhat aLkaline because of
drag-in, as a result of line stoppages, can be substantially and/or
completely removed in ~h~ following acidulated water rinse stage producing
containers of acceptable commercial qyality. In order to achieve such
further improvement, it has been found that the acidulated water rinse
~i solution should be at an acid pH Jow enough for the specific contact time
and rin~e solution tenperature, method of application and conoe ntration, if
any, d accelerating agents to achieve remcval of substantially all stains
for~ed during any prior stage~. The acidulated rinse solution should be at
a p~ of le~s than about 6, preferably less than about 5, in the presence of
free-fluoride and/or phosphate ions an~ below about 2.5, preferably below
about 2, in the absence of free-fluoride and/or phosphate ions. When
tertiary stage acidic water rin9e section is employed, the second-
recilcul eing stage of the tbree-stag water rinse should contain the rinse
- solution at the required maximu~ p~. The water rinse solution from the
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127~61
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third or last rinse stage can conveniently be counterflowed to the
preceding stages such a~ in a three-stage water rinse section. The
acidulated water rinse solution is applied to the oontainers in the same
manner and at the same temperatures employed for the pre-wash and alkaline
cleaning solutions. Acidulation of the water rinse solution can be
achieved by employing any one or combLnations of ~_.u~y available organic
and inorganic acids of which sulfuric and/or bydrofluoric acids cDnstitute
the preferred ~aterials. The presence of free-fluoride through the
addition of hydrofluoric acid or simple or complex fluoride an~ soluble
~alt~ y aI3o be employed in amounts sufficient to enhance mobility or
imprcqe stain suppression/removal.
; The effectiveness of the reduction of oxide film to an
acceptable level in the acidulated water rinse stage is related to the
temperature employed and the duration of oontact of the acidulated rinse
solution witn the container surface. The method of application of the
acidulated rinse solution also con~titutes a variable with spray
application at high pres~ure (high volume) constituting the preferred
practice. In comoercial can waahers of the general types presently
e~plcyed, pre-wash contact ti~as of about 20 seconds up to atout one minute
are u8u~1 while alkaline cleaner contact tines generally range from about
10 second~ up to about one minute. Acidulated water rinse stages have
norm~l contact times ranging from about 10 up to about 30 seconds. Under
sc~e manu~acb~nq conditions, the can washers will operate at one-half
speed for certain time intervals under which conditions the aforementioned
2S contact ti_s are dcubled.
While mineral acids such as sulfuric acid itself is effective
to reduc~ the oxide film when employed at temperatures approaching
200P, such elevated temperatures are energy intensive, and for this
r ason, temperatures below about 150F are preferred. It has been
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found, however, that at acidulated water rinse temperatures below about
160 F employ mg usual contact times, sulfuric acid itself is only
marginally effective to remove the necessary quantity of oxide film and
any prior staining that may have occurred on the container surfaces.
Accordingly, when lower acidulated water rinse temperatures are
o o
employed, such as from about 90 F to about 130 F, the addition of an
effective amount of free fluoride and/or phosphate ions to accelerate
the oxide film remcNal properties of the acidulated rmse solution has
~een found necessary and prefe~red practice under conventional
commercial operations. Of the fore~oing, frcc-fluoride constitutes the
preferred material due to the relatively small qua~tities requi-ed to
achieve the necessary acceleraticn in comparison to phosphate ions which
must be added in amDunts substantially higher than fluoride to achieve
eqyivalent results. Generally, free-fluoride ions in amcunts as low as
1 ppm provide for an increase in acceleration with amounts as high as
100 ppm or higher to as high as about 1,000 ppm be mg usable subject to
environmental restrictions. Excessive free fluoride concentrations,
that is, above about 200 ppm under certa m processing conditions have
been observed to cause an undesirable etching of the aluminum container
surface which detracts from the shiny metallic appearance of the
surface. Because of this, the free-fluoride ion concentration is
preferably controlled at a level below about 100 ppm. Generally,
free-fluoride in amounts of less than about 40 ppm are satisfactory and
preferred from both an econcmic and environmental standpoint.
The free-fluoride ions can be added as hereinbefore set forth
to the acidNlated water rinse solution as simple or complex fluorides
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and/or soluble salts of which hydrofluoric acid
itself constitutes the preferred material.
In accordance with conventional practice,
the cleaned and acidulated water rinsed containers
may be subjected to a final third-stage-exit water
flush-off rinse upon emerging from the acidulated
rinse section, which serves to remove residual
acidulated rinse solution therefrom, as well as
supplying fresh make-up water to the rinse stage.
Following the water rinsing of the cleaned
aluminum containers, if further mobility enhancement
is desired and/or an improvement in the
pasteurization characteristics of the filled
containers, one may optionally subject the containers
to a conversion treatment such as by employing
treating solutions based on chromium phosphate or
titanium or zirconium with or without tannin.
Exemplary of such conversion coatings suitable for
use in the present process are those described in
U.S. Patent Nos. 4,017,334; 4,054,466 and 4,338,140.
The cleaned and treated containers can
thereafter be dried and subjected to the application
of one or a plurality of sanitary lacquer coatings,
decorative coatings, inks, and the like in accordance
with conventional practice prior to the filling and
sealing thereof with appropriate food stuffs or
beverages.
In order to further illustrate the improved
process of the present invention the following
specific examples are provided. It will be
understood that the examples are provided for
illustrative purposes and are not intended to be
limiting of the scope of the present invention as
herein described and as set forth in the subjoined
claims.
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EXAMPLE 1
In order to demonstrate the effectiveness
of the present process in improving can mobility in
high-speed can processing lines, an
~ i27386~ ?
experimental field test was conducted employ mg a multiple stage
high-speed cleaning apparatus to effect a removal of residual
body-making lubricants and aluminum fines from the surfaces of drawn and
ironed aluminum contaLners. The multiple stage washer contained three
primary stages m which Stage 1 comprised an aqueous prewash employing a
solutian at a pH of about 10.5; Stage 2 comprised an aqueous alkaline
primary clea m ng solution of the type previously descr~hc~ at a pH of
about 11.9; an aqueous acidulated water rinse stage controlled at a pH
of about 2.5 which was followed b~ a ~ap water 1ush-off rinse stage
prior to transfer to a conversion treatment stage operated at a pH of
from about 2.8 to about 3.2. Following the conversion treatment, the
; containers were water rinsed followed by a deionized water rinse and
were thereafter oven dried. Following drying, the cans were transferred
by conveyarized transfer lines and chutes to a printer at a nominal rate
af about 980 to about 1,000 cans per minute. Under the foregoing
operating conditions, the mobility of the can~ was a ~ ble providing
for highrspeed printing.
By reducing the acidity in Stage 3 of the acidulated rinse
soluticn from an op~at~ pH of about 2.5 to a pH of about 5, can
ncbility was significantly reduced whereby the capacity of the printer
had to b~ reduced to a rate of 710 cans per minute to provide
satisfactory cperation. When the acidulated rinse solution was again
acidi~ied to re~tore its pH at a level of about 2.5, the
mobility of the cans ins~raved and the rate of printing was also restored
to a level a~ a~out 980 to about 1,000 cans per m~nute.
j:
rhe benefits of Qlying a ~version treatment to the
alunir~ contain~s follow~ the aci~ulated rinse step in accordance
;~ with a preferred practice was also demanstrated by ~mitting the
~ ~ sil t~eatment far a 24 hour te~t period. Can mability was
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reduced apparently due to an oxlde build-up on the conveyorized rails
and chutes such that the rate of printing had to be reduced to a level
of about 820 cans per minute. When the conversion treatment was
restored, can mobility was agam restored and the printing rate returned
to normal.
EXAMPLE 2
In order to demonstrate the effertiveness of free-fluoride
ions to accelerate the removal of oxide film from aluminum container
surfaces, aluminum cans were cleaned in a laboratory can washer by spray
aFplication employing 19 liters of clean m g soluticn. The cleaning
solution consisted of sodium hydraxide dissolved in water to provide a
pH of 12.1. ~he cleaning solution was heated to 12Q ~ and spray
aFplied to the aluminum conta m ers for a period of one minute. The
oontainers were inverted so that the concave dome retained a residual
quantity of cleaning solutian which was allowed to stand on the
container for a period of one-half hour. me cont~-ners were thereafter
subjected to a tap water rinse. An abjectionable brcwn stain was
present in the dome of the conta m er alang the periphery of residual
alkaline cleaning solution that was re~ P~ therein.
An acidulated water rinse solution totaling 19 liters was
prepared containing one gram per liter of tartaric acid which was
adjusted to a pH of 1.91 by sulfuric acid. The acidulated rinse
solution at a temperature of 120 F was applied for one munute to the
stained al _ containers whereafter the containers were water rinsed
~r~ Lnspect d for stain remcval. A rating system was employed in which
a rating of 1 indicates no stain removal while a rating of 5 ;n~;cates a
oomplete stain removal. An inspectiDn af the aluminum container
revealed a stain rati~g of 1 indicating no stain remcval.
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EXAMPLE 3
To the acidulated water r mse solution as descri~ed in Example
2, 0.5 milliliters of 50 percent hydrofluoric acid was added to the 19
liters of rinse solution. An acidulated water rinsing of stained
aluminum containers wa~ repeated at a temperature of 120 F for a period
of one minute. Following the acidulated water rinsing, the containers
were water rinsed and inspected. The stain rating of the aluminum
containers conta m m g the hydrofluoric acid was mcreased to 4.8
indicat mg almost complete stain rempval.
EXAMP$E 4
The interrelationahip of acidity, free-fluoride concentration,
temperature and time of the acidulated water rinse treat~ent relative to
the effectiveness of stain remcval was evaluated by forming an
acidulated water rinse solution containing sulfuric acid Ln variable
amounts to provide the desired pH. Stained aluminum containers prepared
as previously described in connection with Example 2 were acid rinsed
o o
employ m g such solutions at variable bemperatures of 90 F and 120 F
for time periods of 15 seconds and one minute to determlne the
concentration of free-fluoride present to provide a stain rating of 5.
The results obtained are set forth in the following table:
$~E
ppm Free-Fluoride Required For Stain Rating of S
pH 3 pH 2.14 pH 1.7pH 0.4
o o o o o o
~E~PER~U~, 90 120 120 120 90 120
TIME, 15 sec. 171 68 64 69 190 109
TIME, 60 sec. 68 23 13 18
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me results as set forth m the foregoing table mdicates that
as temperature increases or time increases, the concentration of
free-fluoride in ppm to effect a rating of S decreases. As the pH of
the acidulated rinse solution decreases below a pH of about 2, as
evidenced by the data provided for the acidulated rinse solution at a pH
of 0.4, the concentration of free-fluoride increases in comparison to
that required at a pH Oe from about 2 to about 3. me foregoing test
data indicates that when moderate acidulated rinse solution temperatures
are employed and are accelerated by em~loying free-fluoride ions, the
optimum pH for removing brcwn sta ms ranges from about 1.5 to about 2.5.
EXAMPIE 5
T.he interrelationship of acidity, solution temeerature and
time of contact at a constant free-fluoride concentration was evaluated
relative bo the effectiveness of stain removal by forming an acidulated
water-based rinse solution containing 1,000 ppm free-fluoride added as
sodium fluoride and oontaining sulfuric acid in variable amounts to
prcvide the desired pH. Separate groups of drawn and ironed aluminum
oontainers were processed through a conveyorized laboratory pilot can
washer includin~ a f~rst cleaninq stage ~l~loying an alkaline cleaning
; 20 solution conta m mg sodium hydroxide, a chelating agent and a surfactant
at a pH ranging from about 12.0 to about L2.2 at a temperature of 130 F
for a period of 45 seconds by spray appli Q tion. Following the alkaline
cleaning stage, the containers were transferred into a second tap-water
: rinse stage with the rinse water turned off and the cleaned containers
were permitted to stand for a period Oe 20 minutes containing alkaline
: cleaner in the dome sections thereof simNlating a line stoppage.
Follcwnng the 20 minute dwell, one can was remcved and the stain Ln the
dome section was inspected. me remainder of the containers were
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retained in stage two w;hereafter the tap-water sprays were turned on for
a period of 15 seconds at rccm temperature and the water rinsed
containers were thereafter transferred to a third-stage containing an
acidulated hiqhly accelerated rinse solution containing 1,000 ppm
free-fluoride. A series of tests were conducted at each pH level
commencing at a pH of 7 at two different temperatures and at two
o o
different contact times. The temperatures selected were 90 F and 120 F
and the spray contact times were selected at 15 seconds and 60 seconds.
Each series of tests started employ mg Ue longest contact time at the
highest temperature to evaluate the effectiveness of stain removal
ccmpared to the ~a~;nPr removed from the seoond-stage prior to
tap-water rinsing. rf only a marginal improvement was ~lb~;ned under
such conditions, the remo m ing tests of that series employing lower
tem4eratures and/or lower contact times were not run in anticipation
that the results would be less favorable than those obtained at the
higher temperature a~ c~ntact time conditiQn.
~ Pollowing ths accelerated aci~lated third rinse stage, the
; conta~ners were transferred to a fourth stage containing a deionizedwater rinse whereafter the con~nPr~ were dried and the stain remaining
in the dome section thereof wa~ compared to the control sample removed
fron tbe second tap-water rinse stage. ~n acoordance with the rating
system descrlbed in Example 4, a stain rating of 1 ~was assigned to those
cantainlers in which no per~eptIble stain removal was obtained while a
stain rating oOE S wos assigned to test samples exhibiting a subtantially
ocmplete stain removal. In addit~on to an insFection Oe the degree of
stain rsmoval, the aluminum container surfaces were also Lnspected for
~;~ undb~irable etching which in some commercial operations would result Ln
a Dejection oOE such cantainers as unacceptable. me results of the five
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groups of separate test runs are summarized Ln the following table
Lncluding an indication as signified by the letter "E" whether the
surfaces were highly etched.
TABLE
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pH 7 pH 6 pH 5 pH 4.5 pH 4
o o o o o o o o o o o
Temp., F. 90 F 120 90 120 90 120 90 120 90 120
Time, 15 sec. ~ 2 5 5 5 5E*
Tlme, 60 sec. - 1 - 1 2 5 5 5 5E SE
*~ ~ undesirable etching of surface
10It is app rent from the data ~-~ set forth in the foregoing
Table under the specific conditions employed, that the acidulated rinse
solution at a pH of about 7 wa~s meffective to remove any stain from the
dome o the contam er e~ploying a temperature of 120 F and a contact
time of 60 seconds. Accordingly, the remaining three tests at pH 7 were
not run in anticipation that the results would even be poorer.
Similarly, at a pH of 6, the highly acceleratF~ acidulated rinse
solution was meffective to remcve any appreciable stain ~l~loying a
solution temperature of 120 F and a contact time of 60 seconds.
Accordingly, the ~emain1ng three tests of that group were not conducted.
At a pH of 5, hcwever, at a temFerature of 120 F and at a contact time
d 60 seconds, the highly accelerated acidulated rinse solution was
effective to remove substantially all of the stain on the containers. A
;stain rating of 2 was obtained when the contact time was reduced to 15
seconds or when the solution temQerature was reduced to 90 F. In view
o
of these results, the test at 90 F and 15 second contact time was
omlt~
'
~ - 17 -
.
.
.- .
- . , - - , :
27~61
At a pH of 4.5, sta m rat mgs of 5 were obtained under all of
the temperature and contact conditions specified. AS the pH was further
reduced to 4, undesirable etching was cbserved except for the test
conducted at 90 F and 15 second contact tLme.
It is apparent fr~l~ the relationship of the results as set
forth in the foregoing Table, that optimum stain remcval without
experiencing undesirable etching can be achieved by an appropriate
correlation of the p~, temperature, contact time, concentration of the
accelerating agent, and manner of application of the acidulated rinse
olution in accordance with routine tèsting for any specific commercial
inctallation.
Khile it will be apparent that the preferred embodiments of
the invention disclose~ are well calculated to fulfill the objects above
stated, it will be appreciated that the invention is suscep~ihle to
modification, variation and changa without departing from the proper
scope or fair meaning of the subjoined claims.
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