Note: Descriptions are shown in the official language in which they were submitted.
~Z~72~
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FLUORIDE-FREE ALUMINUM CLEANING
; COMPOSITION AND PROCESS
sACKGROUND OF THE INVENTION
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The present invention broadly relates to the
art of cleaning aluminum surfaces and more particularly,
to the cleaning of drawn and ironed aluminum container
bodies of the types employed in the packaging of food-
stuffs and beverages. Various aqueous acidic and
alkaline cleaning compositions have herefore been used
or proposed for removing residual organic lubricants and
drawing agents from the aluminum surfaces in addition
to any met.allic particles commonly referred to as smut
produced during such forming operations in order that
the container bodies or cans can be effectively processed
through succeeding treating steps to impart satisfactory
corrosion protection and lacquer and ink adhesion while
at the same time preserving the shiny metallic aluminum
appearance of the container.
Among the various aqueous cleaning composi-
tions heretofore used or proposed are those described
in United States Patents Nos. 3,969,135; 4,009,115 and
4,116,853. Such prior art cleaning compositions have
; employed fluoride ions as an essential or as a preferred
ingredient to effect acceleration of chemical attack on
the aluminum surfaces to be cleaned to effect removal
of the metallic particles or smut thereon produced
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during the forming operations achieving a desired etch-
ing ox the metal suX~ace employing modexate tempera-
tures of about 120 to about 140F without impairing
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the bright shiny aluminum appearance thereof. While
the effectiveness of fluoride ions to attack and remove
- the adherent oxide film on aluminum surfaces at moder-
ate cleaning temperatures provides for a substantial
-j savings in energy in comparison to cleaners operating
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at 180F or higher, the presence of fluoride ions in
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commercial waste effluen-ts has become environmentally
disfavored over recent years in many areas and there has
been a continuing need for providing an aqueous clean-
ing composition which is fluoride-free while retaining
the beneficial cleaning characteristics of such prior
art aluminum cleaning compositions. It is also impor-
tant that such a fluoride-free aluminum cleaning compo-
sition can commercially operate at moderate to relatively
low temperatures of about 100 to about 160F to provide
satisfactory cleaning within commercially acceptable
time periods thereby providng substantial savings in
energy costs over cleaners operating at relatively
high temperatures of about 180F and higher.
The benefits and advantages of the present
inVention are achieved by an improved fluoride-free
aqueous acidic cleaning composition which can be effec-
tively employed at moderate temperatures as low as about
- 100 to about 140F and which effectively removes sur
face contamination and smut from aluminum surfaces
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within commercially satisfactory time periods rendering
such surfaces suitable fox further treatment in accor-
dance with convent,ional containeX manufacturing process-
ing. The cleaner compositi,on of the present invention
is further characterized as being of reasonable cost,
simple control, effective performance and overcomes
- environmental problems as$ociated with prior art
fluoride-containing cleaning solutions.
SUMMARY OF THE INVENTION
The benefits and advantages of the present
invention are achieved in accordance with the composi-
tion aspec-ts whereof, by a aqueous acidic cleaning
composition containing controlled effective amounts of
a surfactant or combination of surfactants, sulfate ions,
phosphate ions and hydrogen ions in an amount to provide
an acidic pH of less than about 2. More specifically,
the aqueous acidic cleaning composition contains a
surfactant or combination of surfactants in an amount
s of from about 0.1 up to about 30 grams per liter (g/l),
a combination of phosphate ions and sulfate ions in an
amount of about 2 to about 100 g/l of which about 30
percent to about 80 percent by weight comprise phosphate
ions and hydrogen ions in an amount to provide a pH not
in excess of about 2, and preferably prom about a. 5 to
about 1.2 with a pH of about 0.8 being particularly
satisfactory. on accordance with a preferred embodiment
of the present invention, the surfactant comprises a
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combination of a hydrocarbon derivative surfactant of
the general formula R~o~')noE and an abietic acid de-
rivative surfactant having the general formula
ARC H in substantially equal amounts in accordance
with the description as set forth in United States
Patent 3,969,135 which is assigned to the assignee of
the present invention.
The aqueous acidic cleaning composition can
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readily be prepared and replenished employing a concen-
trated solution of the active constituents as herein-
above set forth containing the surfactant or surfactants
in an amount up to about 200 gel, a controlled combina-
tion of phosphate ions and sulfate ions in an amount
up to about 500 g/l and hydrogen ions to provide a pH
of less than about 0.
In accordance with the process aspects of the
present invention, aluminum surfaces to be cleaned are
contacted with the aqueous acidic cleaning composition
at toe normal operating strength at temperatures
preferably from about 110 to about 140F for energy
conservation considerations and for time periods of
from about 10 seconds up about 5 minutes or longer with
time periods of less than about 2 minutes normally
being sufficient. While the aqueous cleaning solution
can also be applied by immersion and flooding techniques,
it is usually preferred, in view of the configuration
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of aluminum container bodies, to apply the cleaning
solution and subsequent rinse and treating solutions
by conventional spray application.
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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.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
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The manufacturing sequence for producing
aluminum container bodies or cans conventionally com-
prises providing an aluminum strip which passes througha cupping press which forms a preliminary cup-shaped
disc which is transferred to a draw and ironing press
producing an elongated cup shaped body. During the
cupping press and draw and ironing operation, various
; organic lubricants as well as coolants including water
or dilute aqueous emulsions are applied to the surfaces
of the part to facilitate the forming operations. The
container bodies or cans thereafter are transferred to
a trimmer in which the upper edge is trimmed whereafter
the trimmed can passes through a washer containing a
plurality of cleaning, rinsing and treatment stages.
At the conclusion of the washing and treating cycle,
the treated cans are transferred to a dry-off oven and
` 25 the interior and exterior surfaces of the can are sub-
jected to one or a plurality of lacquering steps and
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exterior decorative printing steps. Typically, the
exterior surface of the can is first provided with a
., decorative ink printing of suitable indicia which after
drying is followed by a conventional exterior can lac-
quer coating and a curing of the coating by heating to
an elevated temperature such as about ~00F for a period
of about 10 minutes in a recirculating air oven. After
' cooling, the interior can lacquer coating is applied to
the interior surfaces of the can and the lacquer come
` 10 prises any of the types conventionally employed which
are selected so as to chemically resist the foodstuff
or beverages to be placed wi.thin the can in a subsequent
willing station. The interior lacquer coating is again
cured at an elevated temperature and the can may further
optionally be subjected to a second exterior lacquer
coating followed by an additional curing step before
transfer to the filling station.
In many instances, the filled cans after
,.~ sealing are subjected to a pasteurization treatment in
order to destroy bacteria. Such pasteurization treat-
` ment typically comprises immersing the filled and sealed
cans in water heated to about 150 to about 16~F for
a period of about 30 minutes. Such a pasteurization
treatment does not effect the over-varnished side walls
of the can but unvarnished exterior bottom of the con-
tainer has in many instances undergone discoloration
: during pasteurization which is highly objectionable.
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In order to assure excellent ~ualit~ and
durability ox such decorated, yarnished and filled cans
during processing, shipment, storage and ultimate end
use not only with respect to appearance but also with
S respect to durability, various tests have been devised
for measuring adhesion ox the lacquer coating to the
can surfaces, resistance to corrosion when subjected to
. high humidity at elevated temperatures, corrosion re-
sistance of the can surfaces and discoloration of the
varnished ana unvarnished exterior surfaces under
various conditions. It is apparent that the cleaning
of the can surfaces to remove the contaminating sub-
stances thereon rendering the surfaces susceptible Eor
further treatment and lacquering comprises an impor-tant
lS step in the manuEacturing sequence and insuring that
the cleaned can surfaces are receptive to such post
treatments. Typically, the trimmed can body from the
trimming operation enters the multiple stage washer in
which after pre-washing, the can body is exposed to the
cleaner of the present inVention which is applied such as
by spray application for a period of about 1 minute at a
temperature preferably ranging from about 110 to about
140F whereafter the cleaned çan is spray water rinsed
at about 120F for a period of about 15 seconds. There-
after the cleaned and rinsed can body is subjected to
a treatment of any of the Various types known in the
art to improve the surface characteristics thereof and
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to enhance corrosion resistance and other desirable
properties wherea~ter the treated can is again spray
water rinsed at about 120F followed by a 15 second
deionized water spray rinse normally at room temprature
(70 - 80F) whereafter the can is dried in a hot air
recirculating oven usually at about 380 to about 400F
for a period of 5 minutes. After cooling, the can
thereafter is decorated and lacquered as previously
described.
It has been discovered that effective clean-
ing and preconditioning of the aluminum can surface can
be obtained in the absence of any fluoride ion activat-
ing agents in the cleaner in accordance with the com-
position of the present invention ale aqueous acidic
cleaning composition in accordance with the present
invention contains a surfactant or combination of sur-
factants present in an amount of about 0.1 to about 30
g/l with amounts of about 0.5 to about 10 g/l being pre-
ferred. The particular type of surfactant or combina-
tion oE surfactants employed will depend to some extenton the types of organic and inorganic contaminants
present on the can surfaces to be cleaned and can be
adjusted to provide optimum removal of such soils.
The surface active agents which can be satis-
factorily employed can be anionic, cationic or nonionic.
Typical examples of such surfactants are: T~RGITOL
ANIONIC - 08 (trade mark, Union Carbide Corporation) an
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anionic surfactant believed to be sodium 2-ethyl hexyl
sulfate, '~RITO~ DF-16 (trade mark; Rohm & Haas Co.) a
nonionic surfactant believed to be a modified poly-
ethoxylated straight chain alcohol, POLYTERGE~T S-505
LF (trade mark, olin Corp.) a nonion:ic surfactant
believed to be a modified polyethoxylated straight
chain alcohol; SURFONIC LF-17 (trade mark, Jefferson
Chemical Co.) a nonionic surfactant believed to be an
alkyl polyethoxylated ether, PLURA~AC RA-30 (trade mark,
BASF Wyandotte Corp.) a nonionic surfactant, believed
to be a modified oxyethylated straight chain alcohol,
TRITO~ X-102 (trade mark, Rohm & Haas Co.) a nonionic
surfactant believed to be an octyl phenoxy poly ethoxy
ethanol, PLURONIC L-61 (trade mark, BASF Wyandotte,
Inc.) a nonionic surfactant, and believed to be a
condensate containing only ethylene oxide and propylene
oxide chains, RENEX 20 (trade mark, I.C.I. United
States, Inc.~ a nonionic, polyoxyethylene ester of
mixed fatty acids and resin acids.
In accordance with a preferred embodiment of
the present invention, the surfactant preferably com-
prises a combination of a hydrocarbon-derivative sur-
factant and an abietic acid-derivative surfactant which
are present in substantially equal quantities.
The hydrocarbon-derivative surfactant prefer-
ably employed in the cleaner may be represented by the
following general formula:
R(OR~ )nOH
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Wherein R is an alkyl or alkylaryl group of 8-22
carbon atoms; R' i.s a divalent radical selected from
ethyl, propyl and combinations thereof and n i5 an
integer from 7 to 22. The desired concentration of
this surfactant is bound at the lower end by the extent
of cleaning required and at the upper end by the stabi-
lity of the surfactant in the aqueous acidic cleaner.
The range of about 0.1 to about 30 g/l or higher has
been found suitable with a range of about 0.5 to about
2.1 g/l being preferred and concentration of about 1.3
g/l being most preferred. Commercially available sur-
factants believed to fall within the above general
formula include T~ITON CF-10 (trade mark, Rohm & Haas
Company), A~TAROX LF-330, ~NTAROX BL-330 and IGEPAL CA-
630 (trade marks, GAF Corporation), TRYCOL LF-l (-trade
mark, Emery Industries, Inc.) and PLURAFAC D-25 (trade
mark, BASF Wyandotte Corporation). These surfactants
contain both alkyl and alkylaryl R groups, ethoxy and
propoxy R' groups with n values ranging from to 16.
The abietic acid-derivative surfactant may
be represented by the general formula:
A(R')n~
wherein R' and n are as defined above and A is the
abietie acid radical. The abietic acid-derivative sur-
faetant functions conjointly with the hydrocarbon-
derivative surfactant to remove all of the types of
organie contaminants whieh may remain on the surface
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subsequent to ordinary cold forming operations. The
desired concentration ranges are the same as those for
the hydrocarbon-derivative surfactants. Commercially
available surfactants are SURFACTANT AR 150 (trade mark)
supplied by Hercules, Inc. and PEGOSPERSE 700-T0 (trade
mark) supplied by Glyco Chemicals, Inc. Both of these
commercially available surfactants serve as source of
an abietic acid ester containing approximately 14 to 16
mols of ethoxylation.
It has been found that variations in the
alkylene oxide end groups of either of the above sur-
ac-tants does not adversely affect their efficacy. The
final hydroxy group may be replaced, for example, by a
chloride substituent. Alkyl or aryl substitutions may
also be made.
The cleaner composition in addition to the
surfactant further contains as essential constituents,
a combination of phosphate ions and sulfate ions present
in an amount of about 2 to about 100 g/l with amounts of
about 5 to about 35 g/l being preferred. The phosphate
ions preferably comprise from about 30 percent to
about 80 percent by weight of the combined weight of
phosphate and sulfate ions present.
The phosphate ions can be introduced in the
form of any one of a variety of bath compatible alkali
metal and ammonium phosphate salts although phosphoric
acid itself constitutes the preferred material.
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As in the case of the phosphate ionS, the
sulfate ions can be introduced in the foxm of any one
of a variety of bath compatible salts including alkali
metal and ammonium salts although sulfuric acid itself
comprises the preferred material. In either event, the
phosphate and sulfate ions are introduced to preferably
; provide a hydrogen ion concentration to provide an
acidity of the operating cleaner composition of a pH
not in excess of 2 with a pH of about 0.5 to about 1.2
being preferred and a pH of about 0.8 being particularly
satisfactory. The appropriate concentration of hydrogen
ions to provide the desired acidity can conveniently be
achieved by appropria-te additions of phosphoric acid and
sulfuric acid which simultaneously introduces the requisite
quantity of phosphate and sulfate ions in the solution.
When a bright shiny aluminum appearance is
required, the concentration of the combined phosphate and
sulfate ions is preferably maintained at a level below
about 17 g/l. When a frosty, etched aluminum surface
appearance can be tolerated as in the case of over-all
painted or decorated containers, the combined concentra-
tion of phosphate and sulfate lons can be increased up to
about 100 g/l. Since the efficacy of cleaning and
etching of the aluminum surface is related to the time,
temperature, and acidity of the cleaning treatment, the
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:. concentration of toe actiVe constituents can be adjusted
for any specific situation within the parameters herein-
above defined to attain the desired cleaning and appear-
ance of the aluminum surfaces.
In accordance with the process aspects of
the present invention, the aqueous acidic cleaning com-
position is applied to the aluminum surface to be
cleaned by immersion, flooding and preferably by spray
application in view of the configuration of the con-
tainers. The cleaner solution is applied at moderate
temperatures ranging from about 100 up to about 160F
with temperatures of about 110 to about 140F being
preferred for energy conservation considerations. the
contact time of the cleaner with the aluminum surface
will vary depending upon the magnitude and nature of
; the contaminants present thçreon and Jill usually range
from as low as about 10 seconds up to about 5 minutes
with contact times of less than about 2 minutes such as
about 30 seconds to about 1 minute being sufficient for
most conditions.
The cleaning composition may also optionally
contain any one of a variety of commercially available
anti-foaming agents in usual amounts in the event ob-
~ectionable foaming of the cleaning solution occurs
depending upon the particular mode of application.
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A so-called "TR-4" test procedure has been
developped to evaluate the resistance to discoloration
of a cleaned and treated but unlacquered aluminum sur-
face, also called "Bare Corrosion Test" which simulates
exposure of the unpainted exterior bottom of an aluminum
can during a commercial Pasteurization process. For
this purpose, an aqueous solution is prepared simulat-
ing a typical water composition employed in the Pas-
teurization process containing 82.4 parts per million
(ppm) sodium chloride, 220 ppm sodium bicarbonate,
2180 ppm of a water conditioner and the balance de-
ionized water to form one liter. The water conditioning
agent employed is a proprietary product supplied by
DuBois Chemicals, Inc. under the trade mark DUBOIS 915
which exhibits a total alkalinity of 5.8 percent Na20
and on analysis contains sodium nitrate, carbonate,
triethanolamine and a dodecylphenyl polyethylene glycol.
The test procedure employing the aforementioned TR-4
test solution involves subjecting the treated and un-
lacquered containers to the solution for a specified
time, e.g. 30 minutes while maintained at a specified
elevated temperature such as 150F plus or minus 5F.
Following the test, the test specimen is removed,
rinsed with water, dried and visually inspected for
discoloration. Test specimens are rated from 1 no
staining or discoloration) to 10 (dark gold to grey-
black discoloration or extensive non-uniform mottling
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of the surface). Ratings of l through 4 are generally
considered commercially acceptable in the aluminum can
industry whereas ratings of 5 through 10 are not accep-
table.
In order to further illustrate the improved
-I fluoride-free cleaner composition and method of the
present invention, the following specific examples are
I, provided It will be understood that the examples are
provided for illustrative purposes and no-t intended to
be limiting of the scope of the present invention as
herein described and as set forth in the subjoined
claims.
EXAMPLE 1
For comparison purposes, a fluoride-free
aqueous acidic cleaning solution is prepared containing
7.7 g/l sulfuric acid (100~), about 2 g/l of an abietic
acid-derivative surfactant commercially designated as
AR-150, about 2 g/l of a hydrocarbon-derivative surfac-
tant commercially available under the designation
Trycol LF-l, and the balance water. A total of 19 liters
of the cleaning solution is provided at a nominal pH
of about 1.2.
Aluminum cans from the can trimming operation
having residual organic lubricants and coolants on the
- 25 surface thereof are cleaned with the cleaner for a
period of 1 minute by spray application at a tempera-
ture of about 140F. The cleaned cans thereafter are
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subjected to a warm tap water rinse at about 120F or
a period of 15 seconds.
The cleaned and rinsed cans are thereafter
subjected to a surface treatment employing an aqueous
chromium-free treating solution sold under the designa-
tion BONDERITE K-780 (trade mark) available from
Parker Division of looker Chemicals & Plastics Corpora-
tion. The treating solution is applied at a pH of 3.7
by spray application for a period of 15 seconds at a
temperature of about 120 F.
The treated cans following the treatment are
again spray water rinsed for a period of 15 seconds
with tap water at 120F followed by a 15 second cle-
toted water spray rinse whereafter the can is dried
in a recirculating hot air oven for a period of 5
minutes at 380F
The bottom portion of the can is removed as
a test sample ancl is subject to the TR-4 test in accor-
dance with the procedure previously described. An in-
spection of the unlacquered exterior bottom surface ofthe test specimen at the conclusion of the TR-~ test
reveals a rating of about 10 which is generally
commercially unacceptable. At the completion of the
cleaning treatment and prior to the conversion coating
treatment, the can was observed to the water break-free
with no etching of the surfaces thereof.
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EXAMPLE 2
A cleaning solution is prepared identical to
that described in Example 1 with the exception that the
solution contained an additional 4.5 g/l of phosphoric
acid (100%) and a trimmed aluminum can was processed in
accordance with the same sequence as described in Exam-
ple 1. At the completion of the clean:ing treatment, the
;l surface of the can was observed to be water break-free
I, with a little etching of the surface thereof. Exposure
of the bottom of the can to the TR-4 test evidenced a
rating of 4.
EXAMPLE 3
A cleaning solution is prepared similar to
that of Example 1 with the exception that 9 g/l of
phosphoric acid (100%) is added and trimmed aluminum
cans are processed in accordance with the same sequence
as in Examples l and 2. At the completion of the
cleaning treatment the surface of the can was water
break-free with a desirable degree of etching. The
can bottom after subjection to the TR-~ test had a
rating of 0 which is commercially acceptable.
EXAMPLE 4
An aqueous cleaning solution was prepared
similar to thak described in Example 3 except that the
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phosphoric acid concentration was increased to 13.5 g/l
and the temperature of the cleaning solution was reduced
from 140F to 130~. The results obtained at the lower
temperature and at the higher phosphate ion concentra-
tion were similar to those obtained on the test specimen
processed in accordance with Example 3.
The results of Examples 2-4 clearly evidence
the unexpected synergistic effect of sulfate and phos-
phate ions in combination with a surfactant to effect
satisfactory cleaning and etching of an aluminum can
surface to remove organic soils and metallic smut while
at the same time retaining the attractive shiny metallic
appearance of the can and without excessive etching.
Tests conducted employing a solution similar to that of
Example 1 to which 19 g/l of hydrochloric acid (100%)
were added produced excessive etching of the surface
resulting in a blacked-streaked and frosty undesirable
exterior appearance and the TR~4 tes-t results were
.~ commercially unsatisfactory. Similarly, the addition
of 10.4 g/l of nitric acid to the cleaner formulation
of Example 1 resulted in substantially no etching of the
surface and TR-4 test results which were commercially
unsatisfactvry.
The make-up and replenishment of operating
aqueous cleaning solutions in accordance with the
present invention can conveniently be achieved employ-
ing a concentrate containing each of the essential
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constituents in appropriate proportions such that upon
dilution with water, an operatiny bath of the appropri-
ate concentration is attained and is maintained. The
maximum concentration of the various constituents in
the concentrate will to some extent depend upon the
stability and compatibility of the ingredients at such
higher concentrations. Conventionally, aqueous concen-
trates containing up to about 200 g/l surfactant, up to
about 500 g/l of a controlled combination of phosphate
ions and sulfate ions are suitable for dilution with
an appropriate amount of water to produce an operating
cleaning solution of the desired concentration.
While it will be apparent that the preferred
embodiments of the invention disclosed are well calcu-
lated to fulfill the objects above sta-ted, 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 subjoined
claims.
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