CA1223182A - Flavor aluminum cleaning composition and process - Google Patents

Abstract

Abstract of the Disclosure An improved aqueous acidic cleaning composition and process for cleaning aluminum surfaces, particularly aluminum beverage containers, to enhance the flavor characteristics of the beverages subsequently packaged therein. The aqueous acidic cleaning solution contains a solution soluble fluoride containing compound, a solution soluble boron containing compound, optionally but preferably one or a combination of surfactants, and hydrogen ions to provide a pH of less than about 3.5. The concentration of boron ions is present in a stoichiometric excess relative to the free-fluoride ions present which are required to form the anion HF-4.

Description

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P30,028 IMPR$VED FLAVOR ALU~Cl~M CIEANING COMPOSITIoN AND PROCE5S

Background of the Invention The present invention broadly relates to an ac~leous cleaning ccmposition for cleaning aluminum surfaces, and more particularly, an aqueous acidic solution for cleaninq aluminum keverage containers to enhance the flavor characteristics of ~he beverages subsequentl~ contained there m .
AlumQnum co~taLners are in widespread cGmmercial use for the packaging of v æ ious food~tuffs including beverages such as soft drinks and beer. It is conven~ional practice in the fabrication of such alum m um containers to form circular blanks from an aluminum sheet which are thereafter for~ed Lnto prelimunary cups employing a sultable die or cupping press whereafter the cups are drawn and ironed in one or more forming stages to form a can of the desired di~ensions. The fon~ed cups are subsequently subjected to a tri~0ing operation and are thereaf~er subjected to various eleaning and treatment steps culminating Ln the application of a sanitary lacquer coating as well as decorative coatings and inks on the exterior surfaces thereof prior to filling with foodstuffs.
It i9 conventional practice to employ varicus lubricants and ooolants during the m lling of the aluminum strip as ~311 as during the forming, draw m g and ironing c~erations to assist in the fabrication of sueh alurninuml containers. The resultant contaLner surfaces usually have residual quantities o such organie lubricants thereon in addition to fine-sized metallic particles of aluminum usually referred to aY smut which are formed ~2~
on the container surface during the form m g operations. It is important that such residual luhricants and smut be removed from the oontainer suraces before the container is subject to chemical treatnent steps prior to coating operations.
Various aqueous acidic and/or alkaline cleam ng solutions have heretofore been used or proposed for cleaning such aluminum surfaces to remGve the residual lubricant and aluminum particulate smut ~rom the Æ fa oe s thereof. Typical of such oompositions is that disclosed in United States Patent No. 3,969,135 granted to Peter F. King et al on July 13, 1976 entitled "Low TemperatNre Aluminum Cleaning Composition and Process".
While such aqueous cleaning compositions have been found effective in removing the residual lubricant and other contamunating substances from the surfaces of such aluminum oontainers, problems have arisen in s e instances due to an off-flavor imparted to the beverages contained in such containers as established by extensive subjective flavor taste panels. This problem is particuLarly vexing because of its sporadic and unpr~dictable oocuxrence and has occasioned rejection of lot.s of such c~ontainers because of pot~ntial of-1avor charact~ istics imparted to the foodstuffs to be packed therein.
The cause for such of~ flavor in aluminum containers is not fully understood a~thou~h it is speculated that certain residual contaminants remaining on the container surfaces follcwing cleaning and pretreatment attribute at least in part to the problen. Adjustments in the concentration of active , 2 ~LW~
constituen~s in such aqueous cleaninq solutions have been unsuccessful m overcoming this problem and the latitude in varying such con oe ntrations is restricted by ad~erse effects on the aluminum substrate such as an cver-etched surface condition imparting a frosty appearance to the container surfaces which is objectionable Ln some instances.
Ihe present invention provides an improved ccmposi~ion and proces~ for cleaning aluminum Æ faces which effectively and efficiently remo~es residual contamunating substances and smut ~rom the surfa oe ~ thereof and further inh~bits or substantially elimLnates off-flavor problems imparted to the foodstuffs contained therein.

Sumnary of the Invention The benefits and advantages of the present invention are based on the disccn~ry of incorporating a controlled amount of a boron containing conpound in an aqueous acidic cleaning solution which is controlled in concentration relative to the active free-fluoride present in the solution so as to provide a stoichiometric excess of boron relative to the free-fluoride present required to form the anion HF4 . The presencq of such a stoichicmetric excess of boron in th~ fonm of a solution soluble and com~atible boron cantaining compound has been found to subst~antially r.educe the occurrence and severity of such of'f-flavvr problem~ heretofore enc~untered Wlth aqu æ us cleaning compositions of the types hPretofore known.

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The aqueou~ acidi~ cleaning solution in accord~nce with the composition aspects of the present invention con~ains free-fluoride in am~ounts generally less than about 0.4 percent by weisht (less than about 4 g/l) and more usually within a range of about 10 pFm to abcut 100 ppm, a solution soluble boron containing compound s~ch as borate anions present relative to the amount of free-fluuride in the cleaning salution to provide a stoichicmetric ex oe ss of that requiu~d to form the anion ~F4 , generally at a stoichiometric excess of boron of at least a~out 4 ppm relative to the free-fluDride present, hydrogen ions to prcvide a pH of less than akout 3.5 with a pH of about 1 to about 2 heing preferred, optionally but preferably a su~factant or mixture of surfactants present in an amount up to about 10 g/l or higher fos furthex enhancing the cleaning characteristics of the cleaning solution, and optionally, a defoaming agent to m m imize foam formation deFending upon the types of surfactants employed and the manner hy which the cleaning solution is applied to the alumi~uml surfaces to be cleaned.
In accordance with the process aspects of the present invention, aluminum surfaces are cleaned by contacting the surfa oe ~ with the a~orementioned aqueous acidic cleaning solution for periods of tine up bo about 10 minute~ with time periods ranging Prom about 10 seconds up to about 5 minutes being typical.
The clezr~g solution temperature i~ controlled at a level above about 90F, with a temperature range o~ about 110 to abc1t 130~
being usually preferred. The aqyRous cleaning solution is preferably applied ~y spray application particularly in the case : 4 ,.,:.. " :. ' 3~

of alum m um cup-shaped containers facilitat m q uniforn contact with the interior and exterior surfaces thereof achiev mg optLmun cleaning.
A~ditional benefits and advantages of the present invention will ~ecome apparent upon a reading of the Description of the Preferred Eh~xxliments taken Ln conjunction with t~
specific examples prcvided.

Descri~tion of the Preferred ELtxxLu~ents The aq~x~us acidic cleaning solution, in accordance with the oomposition aspects thereof, contains as its essential ingredients a solution soluble fluoride containing ccmpound to pxovide a controlled free-fluoride concentration, a solution soluble bo m n containing compound present in consideration or the concentration of free-fluoride to prcvide a stoichiometric excess of boron to free-fluoride required for formung the anion BF4 , hydrogen ions present ~o provide a pH on the acid side generally less than about 3.5, optionally but preerably, one or a plurality of surfactants to further enhanc~ the cleaning characteristics of th~ solu~ion pre æ nt in an amount up to about 10 g/l or hi~her, optionally, a commercial defoanang agent for nNILumizing fohm formation dependinq upon the particular type of surfactants employed and t~e manner in w~tich the cleaning solution is applied bo the surfaces to be cle~ted.
. The acidity of the cleaning solution should be maintained at a ].evel less than about pH 3.5, preferably within a range of abottt 1 to about 2 depending upon the concentration of other constituents in the solution and the temperature and duration of application of the solution to aluminum surface~.
Hydro~en ion concentrations to provide a pH ~elow about 1 have been found in so~e instances, depending on the fluoride concentration, to cause an undesirable etching of the alum mum surfa oe s i } ting a frosty appearance thereto which is undesirable in th~se instances in which a metallic shiny surface is desired. Qn the other hand, pH values in excess of about 3.5 have been found to increase the time required to acccmplish the desired cleaning and such prolonged time periods are undesirable in com¢ercial cperation. The acidity of the cleaning solution is provided ~y the addition of any suitable bath soluble and cGmpatible inorganic or organic acids of which mineral acids such as sulfuric acid are preferred~ When hydrofluoric acid is employed as a source for the fluoride constituent in the soluticn, the use of hydrofluoric acid provides all or a portion of -the hydrogen ionq in the solution.
The cleaning solution further contains a solution soluble fluoride containing compcund to provide a free fluoride concentration which accelerates the attack upon the alum m um sur~aces bo be cleaned and the rem~oval of smut or fine-sized ~tallic particles from the surfaces thereof. The fluoride oonoentration in tha ~olution can conveniently be provided by the use of hydrofluoric acid itself ag well as the aLkali metal and amnonium simple salts thereof.
The ooncentration of fluoride con~aining compound employed i9 controlled so as to p m vide a free-fluoride "''''': ;' ~3~

oonoentration in the solution in an amount generally less than about 4 g/l with oon oentrations of frcm abcut 10 ppm up to about 100 ppm keing preferred, while concentrations of from akc~t 20 Fpm up to about 50 ppm are particularly satisfactory and typical. The t~rm "free-fluoride" as herein emplcyed and as set forth in the subjoined claims is intended to encompass that fluoride present in the solution which is not present Ln a co~pl~xed fonm such as stable cc~plexe~ i~cludin~ flubborate, silioofluoride and aluminum fluoride which progressively builds up in ~he bath'during use of the solution. The free-fluoride present in the solution is defined as that measured by a specific fluoride sensitive electrode of the potentic~etric type against a controlled solution oontaininq 40 ppm fluoride ions at a pH of 1.1 and at a temperature of 80~F. A suitable fluoride specific ion electrode is ~escribed Ln U.S. Patent No. 3,431,1~2.

In additicn, the aqueous acidic cleaner solution contains a solution soluble boron containing oompcund the o3ncentration of which will vary depending upon the -particular concentration of the free-fluoride present. The source of the borcn containing oompound preferably oomprises boric acid as well as the simple alkali metal and a~monium salts thereof of which boric acid itself constitutes the preferred material. The ooncentration of the bomn wntaLnm g ozmpound is controlled 50 as to pDovide a stoichiometric excess of boron relative to the anount of free-fluoride present in the cleaning solution over that reouired to produce the anion BF4 . It will be understood, that the anion ~F4 is not necessarily formed in the solution but -~hat this anion is provided as a convenient basis for establishi~g the relativa concentration of the boron to free-fluoride present to achieve the ~enerits of the present inventlon.
The specific free-fluoride level is determined ~y the mQgnitude of cleaning desired or required to renove the aluminum fines, smut and lubricants as well as other con~aminants and 50ils from ~he surfa oe s of the al D um containers being cleaned in further consideraticn of the desired appearance, degree of etching of the aluminum surfaces as well as the types of subsequent treatments and coatings to be applied to the containers. When the desired free-fluoride level is established to provide the requisite clea m ng for any particular situation, the boron level is adjusted so as to prcvide an appropriate stoichianetric excess thereof in accordance with the foregoing definition. Preferably, the stoichiometric excess o boron to free-fluoride to produce the anion BF4 is controlled to provide an excess of boron of at least about 4 ppn to an excess of about 200 ppm or higher, and preferably, an excess with m a range of about 10 ppm to about 75 ppm of the stoichiometric amount.
In addltion to the fore~oing constituents, the cleaning solution optionally but preferably contains one or a mixture of sur~actants which ma~ ba present in concen~ration~ up to about 10 g/l or even higher wi~h concentrations of about 0.1 to about 5 g/l bein~ more usual. Generally, sati~factory cleaning of aluminum surfaces can be obtained at surfactant concen~rations of about 0.5 to abeut 1 g/l. It is also contemplated that any one of a variety ~, ,, :,.: ''' .

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of suitable commercial defoami~g agents of the types known in the art can also be employed depending upon the particular type or types of surfactants used to minimize an undesirable degree of foaming of the cleaning solution partieularly when applied by spray applieation.
A particularly satisfactory combination of surfactants suitable for use in the cleaner composition is that as described in United States Patent No. 3,969,135. m e afore~entioned U.S.
patent teaches the use of a hydroearbon-derivative surfactant in combination with an abietic acid-derivative surfactant in which each of the surfactants can be employed in amounts of about .1 up to about 50 g/l with amounts of about 0.5 to about 2 g/l being preEerred. The combination of the two surfactants functions to remove all of the various types of organic eontaminants and soils present on the aluminum surfaces enhancing the efEiciency and perforrnance of the cleaning solution.
The surfaetants whieh can satisfactorily be employed may comprise nonionic, anionic or cationic surfactants of whieh nonionie surfaetants are generally preferred. Typieal of suitable surfaetants whieh ean be satisfaetorily employed and are eornmer-eially avallable are:
Surfaetant AR* 150 available from ~lereules, Ine. and reported to eomprise an ethoxylated ab:ietie aeid deriva-tive eon-taining about ]5 mols ethoxylation.
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PEGOSPERSE* 700-~O available fron G1YCD Chemicals, Inc.
reported to comprise an ethoxylated abietic acid derivative oontaining ab3ut 14 bo 16 mols ethoxylation.
qRTqON* CF-10 available frcm Rohm & Haas Co. reportedly oomprising an alkylaryl polyether having a carbon chain of about 14 carbon atoms and abcut 16 mols of ethoxylation.
PLURONIC* Lr61 availahle from BASF Wyandotte, Inc.
~ep~rtel1y oomQrising a condensa~e oonta ~ only ethylene oxide and propylene oxide chains.
ANTAROX* IF-330 a~ailable from GAF Cbrporation reportedly cc~,prising an aLkyl poly(ethyleneoKy) ethanol.
ANTAROX* BL~330 also avail~ble frcm G~F Corporation reportedly camprising an alkyl poly(ethyleneoxy) ethanol.
IGEPAL* C~-630 available fr3m G~F Corporation reportedly comprising an aLkyl pheno~y poly(ethyleneox;y) ethanol.
~ RYCOL* LF~l avail~ble fr3m Emery Ind~stries, Inc.
reForbedly ocmPrising an aLkyl polyether.
PLURAFAC* D-25 cc~mercial1y available fram B~SF
Wyandot~e, Inc. reportedly comprising a m~dified oxyethylated straight chain alcohol.
'tRI'nON* X-102 avail~ble from Rohm & ~aas Co. r~portedly com2rising ,m octyl phenoxy p,oly ethoxy ethanol.
PLURAFAC* R~-30 avaiL~ble from BA5F Wyandotte, Inc.
reportedly oomprisLng a modified oxyethylated straight chain alcoho1.

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POLYDETERGEN~ S-505LF available from Oline Corp.
reportedly oomprism g a mcdified polyethoxylated straight chain alcohol.
SURFONIC* LF-17 available frcm Jefferson ~ ical Cb.
reæortedly ccmprising an alkyl polyethoxylated ether.
TRIION*~F~16 available from Rohm ~ Haas Cb. reportedly oompris ~ a modified polyethoxylated straight chain alcohol.
Ill~KGIT~L~Anionic-08 available from Union Carbide Corp.
reportedly comprising soditDm 2-ethyl hexyl sulfate, or the like.
In accordance with the process aspects of the prese~tt i~on, the aqueous acidic clean~r~ solution can be applied to the al~ni~ surfaoe by any of the com~ltional techniques alth~gh Sp~dy appLication is particul~rly desirable when cleaning alumirmm containers in view of their configuratio~ in order to achieve ~iform cle~ning of the interior as well as exterior surfaces thereof. $~e cleaning solution is heated to a te~erature abava the cl~d point which deper~ding upan the types and ~nc~ttrations of surfactants enplc~yed, is generally at least about 90F or higher. Typically, tes~eratures of a}~ut 110 up to about 130F are errployed with a te~erature of abaut 120F being preferred. Higher tsrperatureq can be ~ployed but are n~re energy intensive and are l~sg desirable for this reason~
me solution is applied to the al~ni ~ surfaces to be clean3d for p~riods up bo about 10 mlnutes although time periods of about 10 seoonds up to about S mlnutes are more usual.
Typically, satisfactory cleaning of the alumlnum sur-faoe s can be achieved in pe~riods o less than about 2 minutes.
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In order to fuxther illustrate the present invention, the follow m g example is prcvided. It will be understood that the ~ample is provided for illustrative purposes and is not Lntended to be limiting of the scope of this i~vention as herein described and ~s set forth in the subjoined cla.ums.

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The benefits of the aqueous clean m g solution of the present invention in enhancing the flavor of foodstuffs packaged in alum m um contaLners and overcoming off-flavor problems i5 demonstra~ed by the foll~wing tests. Aluminum beverage containers of the type employed for packag~ng beer were cleaned employing a sLx-stage washer in which stage one ccmprised a prewash employing solution counterflowed from the second stage and was at a pH of about 2.5 to abcut 3. In stage two, an aquecus cleaning solution of the type compris m g the present invention was employed in which the ooncentration of boron was varied relative to the free-fluoride oonoentration to evaluate its effectiveness on overoo~ing of~-flavor problems. Stage three ccnprised a triple r m se stage while stage four employed a proprietary alkaline cleaning treatment and rinse followed by stage ive comprising a ~hrea-skage water rinse and f m ally stage six ccmprisin~ a dual water rinse with the lask sec*ion employing deionized water.
Alun~ln~n containers proces~ed through the foregoiny cleaning seqyenoe were evaluated by a ta~te panel co~prising a group of taste exFerts to establish the effect o~ the can cleaning process on the flavor of beer. For this purpose, reshly brewed ::

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unpasteurized beer was placed in a glass beaker and used as the con~rol. The same draft beer was pLaced in the processed alum m um contaiNers for a period of 15 minutes and was then tasted and scored relative to the taste of the control. The control typically receives a a~mposite score ranging about 3 to about 4.
In rating flavor of the aluminum containers, the more closely the beer in the aluminum container approximates that of the control, the bet*er the flavor rating.
Ths composite scores assigned cc~prise a weighted averaye of 8 flavor "notes" by the individual taste panelists including oily, woDdy, mouthfeel, aftertaste, bitterness, e~c. in accordance with conventional taste practices. Generally, a rating of about 6 to 6.5 is considered as the nurLI~Im ccmmercially acoeptable; a composite rating of about 5.5 to 6 comprises a good flavor rating; a composite rating of about 5 bo 5.5 corres~onds to a rating which is virtlally psrfect and equivalent to the control while ratings below about 5 are so perfect as indicating that the results are suspect.
The aqueous acidic cleaning solution in the second stage of the washer was continucusly monitored over a six-day test run for composition and processing paramsters with the conoentration o~ ooron ~Itroduced by way o~ boric acid being vari~d and the concentration correla ed to the flavor panel oomposite rating on cans produced thxeby. The aqueous acidic clea m ng solution was applied at a te~perature ncmlnally oontroll~d at 125F at a free acid of about 7.5 to 9ml (a pH of ahout 1.4 to about 1.5) and at a free-1uoride concentration of about 25 ppm. The free fluoride 3~8~
was introduced in the fonm of hydrofluoric acid and pH control was provided by the addition of sulfuric acid. The aqueous acidic cleaner further contained about 0.7 g/l of surfactant Trycol LF-l and 0.7 g/l of Surfactant AR-160. The aqueous acidic solution as well as each of the rinse and pretreatment solutions following w~re spray applied ~against the conta~ner surfa oe s. The duration of treatment of the containers in stage two incorporating ~he aqueous acidic clea~ing solutions was about 30-60 seconds, which varied with l;ne-speed and averaged abcut 45 seconds. Ihe results of these tests are summarized in Table l.

Test Stoichiometric Cb~posite n No. Excess B,~pl~l Flavor Score l 0 5.7

2 0 5.9

3 0 5.9 Average 5.8

4 1 5.5 3 5.7 6 6 5.4 7 30 5.2 8 28 5.2 9 26 5.2

5.0 Average 5.3 ~ rhe foregoing results clearly demonstrate an enhancement o~ the flavor of be0r relative bo the controL by emplcying boron in the aq~ux~u9 acidic cleaning .;olution which is in stoichicmetric exces~ over that theoretically required relative to the ~re~-fluoride pre~ent to produce the anion BF~ .
While it will be apparent that the pre~erred embodiments o~ the invention disclosed are well calculated to ful~ill thP

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objects a~cve stated, it will be appreciated ~lat the invention is susceptible to modification, variation and change without departinq from the propar scope or fair mean m g of the subjoined claims~

Claims (19)

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

1. An aqueous acidic cleaning solution including a solution soluble boron containing compound, a solution soluble fluoride containing compound, and hydrogen ions to provide a pH of less than about 3.5, the amount of boron in said cleaning solution being present relative to the amount of free-fluoride in said cleaning solution to provide a stoichiometric excess of that required to form the anion HF4-.

2. The cleaning solution as defined in claim 1 further containing a surfactant.

3. The cleaning solution as defined in claim 1 in which said free-fluoride is present in an amount of about 10 ppm up to about 4 g/l.

4. The cleaning solution as defined in claim 1 in which said free-fluoride is present in an amount of about 10 ppm to about 100 ppm.

5. The cleaning solution as defined in claim 1 in which said free-fluoride is present in an amount of about 20 to about 50 ppm.

6. The cleaning solution as defined in claim 1 in which said boron is present in a stoichiometric excess to said free-fluoride of at least about 4 ppm.

7. The cleaning solution as defined in claim 1 in which said boron is present in a stoichiametric excess to said free-fluoride of up to about 200 ppm.

8. The cleaning solution as defined in claim 1 in which said hydrogen ions are present in an amount to provide a pH of about 1 to about 2.

9. The cleaning composition as defined in claim 1 further containing a surfactant present in an amount up to about 10 g/l.

10. The cleaning composition as defined in claim 1 further containing a surfactant present in an amount of about 0.1 to about 5 g/l.

11. The cleaning composition as defined in claim 1 further containing a surfactant present in an amount of about 0.5 to about 1 g/l.

12. An aqueous acid cleaning solution including a solution soluble boron containing compound, a solution soluble fluoride containing compound, a surfactant present in an amount of about 0.1 to about 10 g/l, hydrogen ions to provide a pH of about 1 to about 2, said fluoride containing compound present in an amount to provide a free-fluoride concentration of about 10 ppm to about 100 ppm, said boron containing compound present in an amount to provide a stoichiometric excess of boron to free-fluoride ranging from about 10 ppm to about 75 ppm above that required to produce the anion HF4-.

13. A process for cleaning aluminum surfaces which comprises the step of contacting the aluminum surfaces with an aqueous acid cleaning solution as defined in claim 1.

14. The process as defined in claim 13 including the further step of controlling the temperature of said cleaning solution at a temperature above about 90°F.

15. The process as defined in claim 13 in which the step of contacting the aluminum surfaces with said aqueous cleaning solution is performed for a period of time ranging from about 10 seconds to about 5 minutes.

16. The process as defined in claim 13 including the further step of controlling the temperature of said cleaning solution within a range of about 100°F to about 130°F.

17. The process as defined in claim 13 including the further step of controlling the temperature of said cleaning solution at about 120°F.

18. The process as defined in claim 13 in which the step of contacting the aluminum surfaces with said aqueous cleaning solution is performed by spray application.

19. The process as defined in claim 13 in which the aluminum surfaces are in the form of cup-shaped containers.