AU600689B2 - Process for cleaning aluminum - Google Patents

Description

i AUSTtALIA 68 Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Application Number: 66 cg Lodged: Complete Specification Lodged: Accepted: Int. Class t It I I I Ir it I: i I Publisher.: Priority i i_ nI~C(m m:jl i i ;r i i I ii fXi- Related Art: 1 t APPLICANT'S REF.: P30,054 Name(s) of Applicant(s): PARKER CHEMICAL COMPANY Address(es) of Applicant(s): 32100 Stephenson Madison Heights, UNITED STATES OF Highway Michigan 48071

AMERICA

Actual Inventor(s): Address for Service is: THOMAS H. FICK, SAMUEL T. FARINA PETER F. KING PHILLIPS, ORMONDE AND FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne, Australia, 3000 Complete Specification for the invention entitled: PROCESS FOR CLEANING ALUMINUM The following statement is a full description of this invention, including the best method of performing it known to applicant(s): P19/3/84 Case P30,095 PROCESS FOR CLEANING ALUMINUM Th Present invention broadly relates to an improved process for cleaning aluinum surfaces, and more Particularly, to a process K employing a sequential cleaning cycle including a primary alkaline Cla~jng solution for affecting a removal of orai n alminu fa from -the surfaces of the containers ,and to further enhance the mobility of the containers facilitati.ng their transport in hig-spedcan lines having a capacity in mccess of about 000 cans p.' m mrts. The procs. of the present invention is particularly adaptable for cleaning drawn and ironed aluminm container bodies of the type e loyed Mn the packaging of .7oodsuffs and beverages. The cup-shaped and dished integml bottom of such container bodies, becauset of their cofiuraion ae conducive to enra; my', of the va.r.as cleaning and rinse solutions during the cleaning cycle which h~is in sow~e instances resulted in an objectionable localized staining of the surfaces thereof drig line stoppages during the cleaning process.

it has previously been discovered that by employing an aqueous alkaline cleaning solution of cont=olled contosition as described in -pixnng.s. Patent A-lcatirn Seri"l No. i6g,401. filed November 8, 1984, and entitled "Alkaline Cleaning Process

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an elimination of such 9 '~ocliedobJectionble staining caild be achieved providing for clean i aluminum containers of commercially satisfactory quality. It was also discovered, in accordance with the teachings of the aforementioned U.S.

patent application, that an improvement in the mobility of such cleaned containers could be enhanced by subjecting the containers to a conventional 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 C in excess of 1,000 cans per minute to as high as about 1,500 cans per S minute has been less than optimum.

t 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 INVENTICN t Cc SThe benefits and advantages of the present invention are Sachieved 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 ,H*n aw-. y -A 4 *4 4-V 4 44- 4 J1i t .u4 3- m nyT%-=at-;PFZ- Y IIXI I- I~C- 1 nV-M4:%V-e= Y 1 4 R- -2the drawing and ironing of the containers into a container body.

According to the present invention there is provided a process for cleaning aluminum container surfaces to remove aluminum fines and residual organic contaminants on the surfaces thereof, said process comprising the steps of: contacting the aluminum container surface with an aqueous alkaline cleaning solution for a period of time V sufficient to remove substantially all of the aluminum fines and organic contaminants on the surface thereof; and thereafter (ii) contacting the aluminum container surface with at least one acidulated water-based rinse solution at a pH below 2.5 to neutralize and remove any residual alkaline cleaner thereon and any oxide film on the surface formed Vduring step The present invention also provides a process for cleaning aluminum container surfaces to remove aluminum fines and residual organic contaminants on the surfaces thereof, said process comprising the steps of: 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, (ii) contacting the aluminum 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 less than 6 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.

The process in accordance with its preferred embodiments includes the steps 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 residual 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 from the surfaces of the containers in further combination with a complexing agent, one or a combination of surfactants to remove the organic soils on the surfaces of the container and optionally, an antifoaming agent. Following the alkaline cleaning step, the cleaned containers are thereafter subjected to one or a plurality of counterflowed highly acidulated water rinses, with or without a prior intervening water rinse, to effect the neutralization and removal Sof residual alkaline cleaner thereon of which at least one rinse stage contains an acidity agent present in an amount sufficient to provide a pH of less than about 6, preferably below about 5, depending on whether or not i an accelerating agent is present in the acidulated rinse solution. The i acidulated water rinse, depending on the temperature and time of contact, may optionally and preferably contain free fluoride and/or phosphate ions to accelerate the oxide and stain removal from the aluminum container surfaces. The acid rinsed containers are preferably further water rinsed with a solution at substantially neutral pH, whereafter, the rinsed 1 containers are optionally subjected to a conversion treatment to impart a desired conversion coating thereon. Following the conversion coating, if applied, the containers are again subjected to one or a plurality of water rinses whereafter they are dried and can thereafter be further processad such as by lacquering, painting, decorating and the like prior to being filled with appropriate foodstuffs or beverages.

-3- The use of the acidulated water rinse stage following the alkaline cleaning step has been found -to markedly increase the mobility of the containers believed to occur as a result of a remroval of an oxide film formed on the container surfaces during the alkaline cleaning step as well, as removing any staining of the surfaces of the containers and greatly enhancing the transferability of the containers such as by rolling and/or sliding through the conveyorized transfer lines and chutes.

Additional benefits and advantages of the present invention will become apparent upon a reading of the description of -the preferred embodiments taken in conjunction with the specific examples provided.

DESMIPTION OF THE~ PF#~hD EODIMENTS In accordance with the practice of the process of the present invention, and with particular emphasis on the cleaning of drawn and is1 ironed aluminum containers, the aluminum containers are transferred from the body-making and trimm~ing apparatus to a multiple stage high-speed cleaning apparatus to effect a remo~val of the residual body-forming lubricants and aluminum fines or smut formed on the surfaces of the containers during the manufacturing operation. The aluminum fines comprise minute particles of aluminup, on the container surfaces and adhered thereto in combination with various lubricants and metal working 'compounds emloyed during the forming operations of the container.

The first stage of the cleaning cycle preferably comprises contacting the surfaces of the containers with an aqueous pre-wash solution, preferably an aqueous acidic pre-wash solution, to effect a removal of at least a portion of the fines and/or organic soils from the container surfaces thereby reducing a buildup of such contaminants in the succeeding primary alkaline cleaning stage.

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9 12 12 The pre-wash solution is applied to the aluminum container 0 surfaces at temperatures ranging from ambient from about 60 F) up 0 0 to about 200 F, and preferably at a temperature below about 150 F, 0 0 such as from about 90 to about 130 F. The pre-wash solution is Scontacted with the aluminum surfaces to be cleaned such as by flooding, Immers ion or spraying of which the latter constitutes the preferred method to assure uniform distribution of the pro,-wash solution on both the interior and exterior surfaces of the container.

Following the pre-wash stage, the preliminarily cleaned 10 aluminum containers are transferred directly to a primary alkaline cleaner stage incorporating an aqueous alkaline cleaning solution of a tt, S99c,116C composition preferably as described in pedn U.S. Patent pIct=- Sezr 6a tlz. 669 ,491 the substance of which is incorporated herein by reference. Typical of suitable aqueous alkaline cleaning compositions are those containing an alkalinity agent present in an amount to achieve T satisfactory removal of residual aluminum fines on the surfaces of the C 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 sufficient to prevent undesirable foaming of the cleaning solution particularly when it is applied by spray application.

In accordance with a preferred practice, the alkaline cleaning solution is 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 alkalinity within the foregoing range, the alkalinity agent such as a mixture of sodium hydroxide and sodim carbonate is employed at concentrations of from about 0.05 up to about 10 g/l.

Coplexing agents suitable for use in the alkaline cleaning solution comprise sugar acids as well as salts thereof such as, for example, sodium gluconate, sodium citrate, sodium tripolyphosphate, as well as other acids including glucoheptanoic acid, tartaric acid, EDTA 4 t and the like as well as the bath soluble and compatible salts and mixtures thereof.

1 The alkaline cleaning solution L further contairr r essential ingzdie at least one or a combination of surfactants which are usually selected from the group comprising hydrocarbon alkoxylated surfactants which are characterized as individually or in their blended combination as having a Hydrophile-Lipophile Balance (HLB racio), i.e.

the balance of the size and strength of the hydrophilic (water-loving or polar) and the lipophilic (oil-loving or non-polar) groups of the molecule within an HLB ratio of at least about 12, preferably at least about 12 to about 15. While other surfactants can be employed to provide for effective cleaning of the alkaline cleaning solution, it has ZS been found that employing surfactants characterized by the foregoing HLB ratios substantially reduces or eliminates a tendency of white staining on the surfaces of the aluminum container occasioned by lLne stoppages L cn frequently occur in high-capacity, high-speed container washers.

2: -6- 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 sflwhite-staining problems. By employing surf actants of the appropriate HIS ratio, such white-staining S has been substantially eliminated.

The aqueous alkaline cleaning solution can also be applied, as in the case of the acidic pre-wash solution, by flood~ing, irrnersion and preferably by spray application for a period of time sufficient to effect a cleaning of the surf aces thereof. Generally, the aqueous alkaline cleaning solution is employed at moderate temperatures below 0 about 150 F to about amibient temperature with temperatures of from 0 about 90 to about 130 F being preferred.

Following the aqueous alkaline cleaning stage, the cleaned containers are transferred to a water rinse stage, preferably a mrultiple stage water rinse section of the conveyorized washer. in accordance with the process as described in-pend4M- U.S. Patent i ?l tL.n 3=ia1 No 656,49, 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 br fl 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 Vt about 7.5 as a result of carry-over of alkaline cleaning solution into the water rinse stage, brown staining 4rf the aluminum container surf-aces 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 alkaline cleaning step, with or without an intervening water rinse step, not only brown staining is prevented, but 42 -7a further substantial improvement in the mobility of the cleaned aluminum containers is obtained. It is believed that this increased mobility is a result of the substantial reduction of or removal of an aluminum oxide f ilm formed on the aluminum container surfaces during the alkaline cleaning step.

substantial reduction of the aluminum oxide f ilm on the aluminum surfaces also effects a substantial or complete removal of objectional stains that may have formed o~a the aluminum container surfaces during and following the alkaline cleaning stage. Because of this, the containers following the alkaline c',aning stage and prior to the acidulated water rinse stage can be subjected to a conventional tap water rinse to remove a substantial portion of the residual alkaline cleaner from the surfaces thereof prior to the acidulated water rinse stage. Any staining occurring in the tap water rinse stage, which may beccxne saniewhat alkaline because of drag-in, as a result of line stoppages, can be substantially and/or completely removed in the following acidulated water rinse stage producing containers of acceptable commercial quality. In order to achieve such further improvement, it has been found that the acidulated water rinse solution should be at an acid pH low enough for the specific contact time and ri: ise solution teniperature, method of application and concentration, if any, of accelerating agents to achieve removal of substantially all stains formed during any prior stages. The acidulated rinse solution should be at a pH of less than about 6, preferably less than about 5, in the presence of f ree-f luoride and/or phosphate ions and below about 2.5, preferably below about 2, in the absence of free-fluoride and/o phosphate ions. When tertiary stage acidic water rinse section is employed, the secondrecirculating stage of the three-stage water rinse should contain the rinse solution at the required maximum pH. The water rinse solution fran the -7

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third or last rinse stage can conveniently be counterfiowed to the preceding stages such as in a three-stage water rinse section. The acidulated water rinse solution is applied to the containers 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 emloing any one or comibinations of commionly available organic and inorganic acids of which sulfuric and/or hydrofluoric acids constitute the preferred materials. The presence of free-fluoride through the addition of hydrofluoric acid or simple or complex fluoride and soluble salts may also be employed in amounts sufficient to enhance mobility or improve stain suppress ion/rmval.

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 contact of the acidulated rinse is5 solution with the container surface. The method of application of the acidulated rinse solution also constitutes a variable with spray application at high pressure (high volume) constituting the preferred practice. In commercial can washers of the general types presently employed, pre-wash contact times of about 20 seconds up to about one minute are usual while alkaline cleaner contact times generally range from about seconds up to about one minute. Acidulated water rinse stages have normal contact times ranging frain about 10 up to about 30 seconds. Under sane manufacturing conditions, the can washers will operate at one-half speed for certain time intervals under which conditions the aforementioned contact times are doubled.

While mineral acids such as sulfuric acid itself is effective to reduce the oxide film when employed at temperatures approaching 200 0 F, such elevated temperatures are energy intensive, and for this reason, temperatures below about 150OF' are preferred. It has been -9found, however, that at acidulated water rinse temperatures below about 0 160 F employing 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 i peratures are emloyed, 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 removal properties of the acidulated rinse solution has been found necessary and prefered& practice under conventional commnercial operations. Of the foregoing, free-fluoride constitutes the preferred matarial due to the relatively small quantities required to achieve the necessary accel eration in comparison to phosphate ions which mrust be aded in amo~unts substantially higher than fluoride to achieve equivalent results. Generally, free-fluoride ions in amounts as low as i. 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 being usable subject to Kenvironmental restrictions. Excessive free-fluoride concentrations, that is, above about 200 ppm under crtain 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 1, preferably controlled at a level below about 3.00 ppm. Generally, free-fluoride in amounts of less than about 40 ppm are satisfactory and preferred from both an economic and environmental standpoint.

The free-fluoride ions can be added as hereinbef ore set for-th to the acidulated water rinse solution as simple or complex fluorides 10 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 S thir-d-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 enhanicement 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 bae on chromium phosphate or titanium or zirconium with or without tannin. Exemplary of such conversion coatings suitable for use in the present process are is those described in U.S. Patent Nos. 4,017,334; 4,054,466 and 4,338,140, the teachings of which are incorporated here by reference.

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 subj oined claims.

EXAMPLE 1 In order to demonstrate the effectiveness of the present process in improving can mobility in high-speed can processing lines, an 11 7-

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experimental field test was conducted employing 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. Co~ntainers. The multiple stage washer contained three primary stages in which Stage 1 comprised an aqueous prewr-sh emloying a solution at a pH of about 10.5; Stage 2 comprised an aqueous alkaline primrary cleaning solution of the type previously described at a pH of about 11.9; an aqueous acidulated water rinse stage controlled at a pH of about 2.5 which was followed by a tap water flush-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 iater rinse and were thereafter oven dried. Following drying, the cans were transferred by conveyorized transfer lines and chutes to a printer at a nominal rate of about 980 to about 1,000 cans per minute. Under the foregoing operating conditions, the mobility of the cans was acceptable providing for high-speed printing.

By reducing the acidity in Stage 3 of the acidulated rinse solution from an operating pH of about 2.5 to a pH of about 5, can mobility was signiificantly reduced whereby the capacity of the printer had to reduced to a rate of 710 cans per minute to provide satisfactory operation. When the acidulated rinse solution was again further acidified to restore its pH at a level of about 2.5, the mobility of the cans improved and the rate of printing was also restored to a level of about 980 to about 1,000 cans per minute.

The benefits of applying a conversion treatment to the alumninumi containers following the acidul~ated rinse step in accordance with a preferred practice was also demonstrated by omitting the conversion treatment for a 24 hour test period. Can mobility was 12 27 reduced apparently due to an oxide build-up on ThE and chutes such that the rate of printing had to bE of about 820 cans per minute. When the conve3 restored, can mobility was again restored and the p to normal.

conveyorized rails Sreduced to a level :sion treatment was :inting rate r~curned EXAMPLE 2 In order to demonstrate the effectiveness 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 application employing 19 liters of cleaning solution. The cleaning solution consisted of sodium hydroxide dissolved in water to provide a 0 pH of 12.1. The cleaning solution was heated to 12Q F and spray applied to the aluminumw containers for a period of one minute. The containers were inverted so that the concave dome retained a residual 1S quantity of cleaning solution which was al~lowed to stand on the container for a period of one-half hour. The containers were thereafter subjected to a tap water rinse. An objectionable brown stain was present in the dome of the container along the periphery of residual alka.1ine cleaning solution that was retained 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 0 solution at a temperature of 120 F was applied for one minute to the stained aluminum containers whereafter the containers were water rinsed and inspected for stain removal. A rating system was employed in which a rating of 1 indicates no stain removal while a rating of 5 indicates a complete stain removal. An inspection of the aluminum container revealed a stain rating of 1 indicating no stain removal.

13 i 1 EXAMPLE 3 To the acidulated water rinse solution as described 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 o aluminum containers was 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 containing the hydrofluoric acid was increased to 4.8 indicating almost complete stain rempval'.

EXAMPLE 4 j The interrelationship of acidity, free-fluoride concentration, temperature and time of the acidulated water rinse treatment relative to the effectiveness of stain removal was evaluated by forming an acidulated water rinse solution containing sulfuric acid in variable amounts to provide the desired pH. Stained aluminum containers prepared as previously described in connection with Example 2 were acid rinsed 0 O ei-loying such solutions at variable temperatures of 90 F and 120 F for time periods of 15 seconds and one minute to determine the concentration of free-fluoride present to provide a stain rating of The results obtained are set forth in the following table:

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i 't ppm Free-Fluoride Required For Stain Rating of pH 3 pH 2.14 pH 1.7 pH 0.4 0 0 0 0 0 0 TEMPERATURE, 90 120 120 120 90 120 TIME, 15 sec. 171 68 64 69 190 109 TIME, 60 sec. 68 23 13 18 14 The results as set forth in the foregoing table indicates that t as temperature increases or -time incr-ases, the concentration of free-fluoride in ppm to effect a rating of 5 decreasets. 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 of from about 2 to about 3. The foregoing test data indicates that when moderate acidulated rinse solution temperatures are employed and are accelerated by employing free-fluoride ions, the optimum pH for removing brown stains ranges from about 1.5 to about The interrelationship of acidity, solution temperature and time of contact at a constant free-fluoride concentration was evaluated relative to the effectiveness of stain removal by forming an acidulated is water-based rinse solution containing 1, 000 ppm free-fluoride added as sodium fluoride and containing sulfuric acid in variable amounts to provide the desired pH. Separate groups of drawn and ironed aluminum containers were processed through a conveyorized laboratory pilot can washer including a first cleaning stage employing an alkaline cleaning 2 0 solution containing sodium hydroxide, a chelating agent and -a surf actant, at a pH ranging from about 12.0 to about 12.2 at a temperature of 130 F for a period of 45 seconds by spray application. 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 of 20 minutes containing alkaline cleaner in the dome sections thereof simulating a line stoppage.

Following the 20 minute dwell, one can was removed and the stain in the dome section was inspected. The remainder of the containers were ii I~ 1

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retained in stage two whereafter the tap-water sprays were turned on for a period of 15 seconds at room temperature and the water rinsed containers were thereafter transferred to a third-stage containing an acidulated highly accelerated rinse solution containing 1, 000 ppm free-fluoride. A series of tests were conducted at each pH level cormencing at a pH of 7 at two different temperatures and at two 0 0 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 employing -the longest contact time at the highest temperature to evaluate the effectiveness of stain removal compared to the container removed from the second-stage prior to tap-wqater rinsing. if only a ma~rginal improvement was-obtained under such conditions, the remaining tests of that series employing lower temperatures and/or lower contact times were not run in anticipation 115 that the results would be less favorable than those obtained at the higher temperature and contact time condition.

Following the acceleratkd acidulated third rinse stage, the containers were transferred to a fourth stage containing a deionized water rinse whereafter the containers were dried and the stain remaining in the dome section thereof was compared to the control sample removed from the second tap-water rinse stage. In accordance with the rating system described in Eample 4, a stain rating of 1 was assigned to those containers in which no perceptible stain removal was obtained while a stain rating of 5 was assigned to test samples exhibiting a subtantially complete stain removal. In addition to an inspection of the degree of stain removal, the aluminum container surfaces were also inspected for undesirable etching which in some commrercial operations would result in a rejection of such containers as unacceptable. The results of the five 16

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groups of separate test runs are suxrrarized in the following table including an indication as signified iy the letter whether the surfaces were highly etched.

pH 7 pH 6 0 0 0 0 Temp. F. 90 F 120 90 1; Time, 15 sec. Time, 60 sec. 1 undesirable etching of surface pH 5 PH 4.5 0 0 0 0 0 0 90 120 90 120 2 5 5 1 2 5 5 5 pH 4_ 0 0 90 120 5 5E It is apparent from the data as set forth in the foregoing Table under the specific conditions employed, that the acidulated rinse solution at a pH of about 7 was ineffective to remosve any stain from the dome of the container employing a temp-rature 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 solution was ineffective to remove any 0 so.lution temperature of 120 F and a Accordingly, the remaining three tests of At a pH of 5, however, at a temperature Sof 60 seconds, the highly accelerated effective to remove substantially all of stain rating of 2 was obtained when the seconds or when the solution temperature accelerated appreciable stain employing a contact time of 60 seconds.

that group were rnot conducted.

0 of 120 F and at a contact time acidulated rinse solutioni was the stain on the containers. A contact time was reduced to was reduced to 90 F. In view acidulated rinse of these results, the test at 90 F and 159 second omitted.

contact time was 17 AapHof 4.5, stain ratings of 5 were obtained under all of the temperature and contact conditions specified. As the pH was further reduced to 4, undesirable etching was observed except for the test 0 conducted at 90 F and 15 second contact time.

It is apparent from the relationship of the results as set forth in the foregoing Table, that optimumIn stain removal without experiencing undesirable etching can be achieved by an appropriate correlation of the pH, temperature, contact time, concentration of the accelerating agent, and manner of application of the acidulated rinse solution in accordance with routine 6asting for any specific~ cormercial iristal1laticn.

While it will be apparent that the preferred embodiments 'of the invention disclosed are well calculated to fulfill the objects above *stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subj oined claims.

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Claims (24)

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

2. The process as defined in claim i, including the i 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 or claim 2 in which at least one said acidulated water rinse solution is at a pH of about 2. S4. The process as defined in any one of claims 1 to 3 in which the step of contacting the aluminum container surface with the at least 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 The process as defined in claim 4 in which a portion of the at least one acidulated water-based rinse solution in the last downstream stage is counterflowed to the adjacent upstream stage.

6. The process as defined in any one of claims 1 to including the further step of controlling the pH of the at 39 -19- r *I i I i 'i -l t-ne~=l~in( i. -rl;ll ~llrl*LI~.. I i. C C C I- least one acidulated water-based rinse solution at a level below 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 any one of claims 1 to 7 including the further step of controlling the temperature of the at least one acidulated water-based rinse solution within a range of 60° to 200°F.

9. The process as defined in any one of claims 1 to 7 including the further step of controlling the temperature of the at least one acidulated water-based rinse solution at a temperature below 150°F.

10. The process as defined in any one of claims 1 to 7 including the further step of controlling the temperature of the at least one acidulated water-based rinse solution within a range of 90° to 130°F.

11. The process as defined in any one of claims 1 to 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 one acidulated water-based rinse solution.

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

13. 13. The process as defined in any one of claims 1 to 12 in which the step of contacting the aluminum container surface with the at least one acidulated water-based rinse solution is performed by spray application.

14. The process as defined in any one of claims 1 to 13 including the further step of contacting the acidulated water-based rinsed aluminum container surface with a treating solution to apply a conversion coating thereon. The process as defined in any one of claims 1 to 14 including the further step of water rinsing the cleaned 39 AB -I ca U$- 4 and acidulated water-based rinsed aluminum container surface.

16. The process as defined in any one of claims 1 to including the further step of drying the cleaned and rinsed aluminum container surface.

17. The p ess as defined in any one of claims 1 to 16 wherein the acidulated water-based rinse solution contains soluble fluoride salts.

18. The process as defined in any one of claims 1 to 17 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. S19. The process as defined in any one of claims 1 to 18 i: in which the at least one acidulat-d water-based rinse j solution contains fluoride ions in an amount of at least 1 ppm.

20. The process as defined in any one of claims 1 to 19 in which at least said one acidulated water-based rinse solution contains phosphate ions in an amount effective to Saccelerate 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 Son the surfaces thereof, said process comprising the steps of: 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, (ii) contacting the aluminum 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 less than 6 9 -21- I i 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 the at least one acidulated water-based rinse solution contains ree-fluoride ions in an amount of 1 to 1000 ppm.

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

24. The process as defined in claim 21 in which the at least one acidulated water-based rinse solution contains free-fluoride ions in an amount of 1 to 40 ppm. The process as defined in claim 21 in which the at least one acidulated water-based rinse solution contains t 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 any one of claims 21 to o in wlich at least one acidulated water-based rinse solution is controlled at a pH less than

27. The process as defined in any one of claims 21 to 26 ,including the further step of contacting the aluminum container surface with an aqueous pre-wash solu':ion 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.

28. The process as defined in any one of claims 21 to 27 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.

29. The process according to claim i, substantially as 39 -22- .I N AD C n.l-liili :__L.irr hereinbefore described with reference to any one of the examples. The process according to claim 21, substantially as hereinbefore described with reference to any one of the examples. DATED: 5 JUNE, 1990 PHILLIPS ORMONDE FITZPATRICK Attorneys For: PARKER CHEMICAL COMPANY 1381Z -1 m 9, -23-