CA1273861A - Process for cleaning aluminum - Google Patents

Abstract

Abstract of the Disclosure A process for cleaning aluminum surfaces to remove aluminum fines and residual organic contaminants on the surfaces thereof which is particularly applicable for cleaning drawn and ironed aluminum containers of the type employed in the packaging of foodstuffs and beverages. The process includes a sequential cleaning cycle including a primary alkaline cleaning step for effecting the removal of organic contaminants and aluminum fines followed by at least one acidulated water rinse treatment in which the solution is at a pH of below about 6, when the rinse solution contains an accelerating agent, and below about 2.5 when the rinse solution does not contain any accelerating agent, optionally followed by treatment with an aqueous solution adapted to apply a conversion coating on the surface thereof. The combination of treating steps has been found to surprisingly enhance the removal of stains from the surfaces and the mobility of the aluminum containers facilitating their transport in high-speed can lines having capacities in excess of about 1,000 cans per minute.

Description

127;~61 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-, .

~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 h . . . . .
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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 . ' ' -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 A

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1273~36i - 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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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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~ ;~r7 I~8~1 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 ~ ' 1 2'73~f~6 1 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.

'~ '' . ' ' ' ' - lla -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.
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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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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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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:
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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 ' ~,, : .~

~ 2~Y386~
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.

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 _ ,,5 _ . . :

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- ~ ' f~ ~27~!36i 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 ~, ~ - 16 -~:, - - -` ' . -' .' " ' ' , ' ' ' ` ' ` ~` 127~6~

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~

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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.

Claims (29)

The embodiments of the invention, in which an exclusive property or privilege is claimed, are defined as follows:

1. A process for cleaning aluminum container surfaces to remove aluminum fines and residual organic contaminants on the surfaces thereof comprising the steps of the contacting the aluminum container surface with an aqueous alkaline cleaning solution for a period of time sufficient to remove substantially all of the aluminum fines and organic contaminants on the surface thereof, and thereafter contacting the cleaned aluminum container surface with at least one acidulated water-based rinse solution at a pH below about 2.5 to neutralize and remove any residual alkaline cleaner thereon and any oxide film on the surface formed during the alkaline cleaning step.

2. The process as defined in Claim 1 including the further step of contacting the aluminum container surface with an aqueous pre-wash solution for a period of time sufficient to remove at least a portion of the aluminum fines and residual organic contaminants on the surface thereof prior to the step of contacting the aluminum container surface with the aqueous alkaline cleaning solution.

3. The process as defined in Claim 1 in which at least one said acidulated water rinse solution is at a pH of about 2.

4. The process as defined in Claim 1 in which the step of contacting the cleaned aluminum container surface with the at least said one acidulated water-based rinse solution is performed in a plurality of contact stages with the second downstream stage being of a pH of below about 2.5.

5. The process as defined in Claim 4 in which a portion of the at least said one acidulated water-based rinse solution in the last downstream stage is counterflowed to the adjacent upstream stage.

6. The process as defined m Claim 1 including the further step of controlling the pH of at least said one acidulated water-based rinse solution at a level below about 2.5 by the addition of an acidity agent thereto.

7. The process as defined in Claim 6 in which said acidity agent comprises at least one acid selected from the group consisting of sulfuric acid and hydrofluoric acid.

8. The process as defined in Claim 1 including the further step of controlling the temperature of at least said one acidulated water-based rinse solution within a range of about 60° to about 200° F.

9. The process as defined in Claim 1 including the further step of controlling the temperature of at least said, one acidulated water-based rinse solution at a temperature below about 150° F.

10. The process as defined in Claim 1 including the further step of controlling the temperature of at least said one acidulated water-based rinse solution within a range of about 90° to about 130° F.

11. The process as defined in Claim 1 including the further step of contacting the aluminum container surface with a flush-off water rinse immediately following the step of contacting the aluminum container surface with the at least said one acidulated water-based rinse solution.

12. The process as defined in Claim 1 including the further step of controlling the pH of said aqueous alkaline cleaning solution within a range of about 11 to about 13.

13. The process as defined in Claim l in which the step of contacting the aluminum container surface with the at least said one acidulated water-based rinse solution is performed by spray application.

14. The process as defined in Claim 1 including the further step of contacting the cleaned and acidulated water-based rinsed aluminum container surface with a treating solution to apply a conversion coating thereon.

15. The process as defined in Claim 1 including the further step of water rinsing the cleaned and acidulated water-based rinsed aluminum container surface.

16. The process as defined in Claim 1 including the further step of drying the cleaner and rinsed aluminum container surface.

17. The process as defined in Claim 1 wherein the acidulated water-based rinse solution contains soluble fluoride salts.

18. The process as defined in Claim 1 including the further step of contacting the aluminum container surface with an aqueous water rinse solution following the alkaline cleaning solution and prior to the at least one acidulated water-base rinse solution to remove at least a portion of the residual alkaline cleaner thereon.

19. The process as defined in Claim 1 in which at least said one acidulated water-based rinse solution contains fluoride ions in an amount of at least about 1 ppm.

20. The process as defined in Claim l in which at least said one acidulated water-based rinse solution contains phosphate ions in an amount effective to accelerate the removal of oxide film from the aluminum containers.

21. A process for cleaning aluminum container surfaces to remove aluminum fines and residual organic contaminants an the surfaces thereof comprising the steps of contacting the aluminum container surface with an aqueous alkaline cleaning solution far a period of time sufficient to remove substantially all of the aluminum fines and organic contaminants on the surface thereof, and thereafter contacting the cleaned alum mum container surface with at least one acidulated water-based rinse solution containing free-fluoride and/or phosphate ions present in an amount effective to accelerate the removal of any oxide film on the surface of the aluminum container at a pH low enough and for a period of time in consideration of the temperature of said acidulated rinse solution sufficient to neutralize and remove any residual alkaline cleaner thereon and to substantially reduce any oxide film on the aluminum surface.

22. The process as defined in claim 21 in which at least said one acidulated water-based rinse solution contains free-fluoride ions in an amount of about 1 to about 1000 ppm.

23. The process as defined in claim 21 in which at least said one acidulated water-based rinse solution contains free-fluoride ions in an amount below about 100 ppm.

24. The process as defined in claim 21 in which at least said one acidulated water-based rinse solution contains free-fluoride ions in an amount of about 1 to about 40 ppm.

25. the process as defined in claim 21 in which at least said one acidulated water-based rinse solution contains phosphate ions present in an amount effective to accelerate removal of any oxide film on the surface of the aluminum container.

26. The process as defined in claim 21 in which said at least one acidulated water-based rinse solution is controlled at a pH less than about 6.

27. The process as defined in claim 21 in which said at least one acidulated water-based rinse solution is controlled at a pH less than about 5.

28. The process as defined in claim 21 including the further step of contacting the aluminum container surface with an aqueous pre-wash solution for a period of time sufficient to remove at least a portion of the Aluminum fines and residual organic contaminants on the surface thereof prior to the step of contacting the aluminum container surface with the aqueous alkaline cleaning solution.

29. The process as defined in claim 21 including the further step of contacting the aluminum container surface with an aqueous water rinse solution following the alkaline cleaning solution and prior to the at least one acidulated water-base rinse solution to remove at least a portion of the residual alkaline cleaner thereon.