Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
PROCESS FOR SEALING PHOSPHORIC ACID ANODIZED ALU1ViINUMS
ORIGIN OF INVENTION
The invention described herein was made by employee(s) of the United States
Government and may be manufactured and used by or for the Government for
governmental purposes without the payment of any royalties thereon or
therefor.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a process for depositing a film or coating onto
aluminum
and its alloys that have been phosphoric acid anodized. The coating system
comprises
phosphoric acid anodize aluminums, a supplemental post-treatment or seal
coating,
optimally, an adhesive bond primer or other supplemental coatings. Phosphoric
acid
anodized aluminum coatings are very porous and therefore have poor inherent
corrosion
resistance. These coatings do, however, have excellent adhesive properties.
Accordingly
these anodized coatings would benefit from a post-treatment or seal coating
that enhances
corrosion protection without adversely affecting the adhesion properties. The
performance characteristics of this invention allows the phosphoric acid
anodized
coatings to be used in unpainted applications which are currently unfeasible;
to replace
chromic acid anodize aluminum and FPL Etch, both of which contain chromates
for
corrosion-prone fatigue-sensitive applications; in all adhesive bonding
applications where
2
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
the trani4'libn'to "n6n-cli"rornated'bond primers is made; and, in general use
applications to
reduce fatigue debit and coating weight compared to other general use anodize
coatings.
This invention relates to a process for treating phosphoric acid anodized
aluminum(s) to maintain and improve the corrosion-resistant properties. More
specifically, this invention relates to the process of sealing phosphoric acid
anodized
aluminum and anodized aluminum alloys. The trivalent chromium post-treatment
(TCP)
process comprises an acidic aqueous solution containi.ng effective amounts of
at least one
water-soluble trivalent chromium compound, an alkali metal
hexafluorozirconate, at least
one alkali metal tetrafluoroborate and/or hexafluorosilicate, at least one
divalent zinc
compound, and effective amounts of water-soluble thickeners and/or water-
soluble
surfactants.
Anodized aluminum(s) are generally sealed or post-treated after anodizing by
processes employing a variety of sealing processes and compositions. Current
high-
performance post treatments or sealers for anodized aluminum are based on
hexavalent
chromium chemistry. Hexavalent chromium is highly toxic and a known
carcinogen. As
a result, the solutions used to deposit these protective coatings and the
coating per se are
toxic. These films or coatings do, however, yield good adhesion and improved
corrosion
resistance to the anodized aluminum. Typically, seal coatings are deposited
onto the
anodized coating at elevated temperatures and are usually applied by immersion
or spray
processes. Post treatrnents can be required by the military and by commercial
specifications that govern each coating being treated. As such, there is not a
unique "post
treatment" specification for all anodize aluminums like there is for
"conversion coating"
aluminum.
2
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
Furtfiei; "enviro"inenta~~ 1aws, executive orders, and local occupational,
safety, and
health (OSH) regulations are driving the military and commercial users in the
search for
hexavalent chromium-free treatments. In the case of anodized aluminum, the
anodize
film and base metal are relatively non-toxic. With the addition of the
required hexavalent
chromium treatment, these coatings become toxic. While some other compositions
used
for coating anodized aluminum may not contain hexavalent chromium, their
technical
performance is inferior to the hexavalent chromium-based coatings. In
addition, the use
of hexavalent chromium-treatments is becoming more expensive as regulations
tighten.
Costs may become prohibitive with future restrictions imposed by the EPA.
Thus, while
existing hexavalent chromium-treatments are outstanding in their technical
performance
in that they provide enhanced corrosion protection and adhesion bonding e.g.
with
coatings such as paint at a low application cost, from a life-cycle cost,
environmental, and
OSH perspective, hexavalent chromium coatings are detrimental to both people
and the
environment.
In regard to adhesive bonding, phosphoric acid anodize is being implemented as
an alternative to chromic acid anodize. Phosphoric acid anodize coatings
provide
excellent adhesive bonding performance, but fail to adequately protect the
base aluminum
from corrosion. While anodize sealers are typically applied to various other
anodize
coatings to boost corrosion performance, they are generally not applied to
phosphoric acid
anodize coatings because the adhesive bonding performance is significantly
reduced. As
a result, the corrosion protection of a phosphoric acid anodized coating is
provided by
chromated bond primers or general use primers. Phosphoric acid anodize
coatings are
characteristically columnar and porous, thus promoting excellent adhesive
bonding
performance. However, the columnar, porous structure also promotes corrosion
making
3
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
blids0h6i'ie''kfid"ctidftgs particularly difficult to protect against
corrosion. For
example, phosphoric acid anodized "honeycomb" core, commonly used in military
aircraft, corrodes quickly in service when its protective coating is damaged
and would
greatly benefit from a corrosion protective sealer that does not adversely
impact the
adhesive bonding characteristics of the anodize coating.
SUMMARY OF THE INVENTION
This invention relates to a process of post-treating or sealing phosphoric
acid
anodized aluminum and its alloys at ambient temperatures or higher e.g.
ranging up to
about 200 F. More specifically, this invention relates to post-treating
phosphoric acid
anodized aluminum and its alloys to improve the corrosion-resistance and
maintain
adhesion bonding properties e.g. paint adhesion and the like. The trivalent
chromium
post-treatment (TCP) composition of this invention comprises an acidic aqueous
solution
having a pH ranging from about 2.5 to 5.5 and preferably 2.5 to 4.5 or 3.7 to
4.0, and per
liter of said acidic solution, from about 0.01 to 22 grams of a water-soluble
trivalent
chromium compound, about 0.01 to 12 grams of an alkali metal
hexafluorozirconate,
about 0.0 to 12 or 0.001 to 12 grams of at least one fluorocompound selected
from the
group consisting of an alkali metal tetrafluoroborate, an alkali metal
hexafluorosilicate
and various combinations or mixtures thereof in any ratio, 0.001 to 10 grams
of a water
soluble divalent zinc compound, from about 0 to 10 grams and preferable 0 to
2.0 grams
of at least one water-soluble thickener, and from 0 to 10 and preferably 0 to
2.0 grams of
at least one water-soluble non-ionic, cationic or anionic surfactant or
wetting agent.
4
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
~ It'i's'fher'efa'r'e an'objecf'of this invention to provide an acidic aqueous
solution
comprising a trivalent chromium compound, an alkali metal hexafluorozirconate,
and a
tetrafluoroborate and/or hexafluorosilicate for treating phosphoric acid
anodized
aluminum and its alloys to maintain its adhesion and improve its corrosion-
resistance
characteristics.
It is another object of this invention to provide a stable acidic aqueous
solution
having a pH ranging from about 2.5 to 5.5 which contains effective amounts of
a trivalent
chromium salt and a hexafluorozirconate for seali.ng phosphoric acid anodized
aluminum
and its anodized alloys.
It is a further object of this invention to provide a stable acidic aqueous
solution
having a pH ranging from about 3.7 to 4.0 containing a trivalent chromium salt
and a
hexafluorozirconate for treating or sealing phosphoric acid anodized aluminum
and its
alloys at about room temperature and higher wherein said acidic solution
contains
substantially no hexavalent chromium.
These and other objects of the invention will become apparent by reference to
the
detailed description when considered in conjunction with the accompanying
Figs. 1-9
(photos).
DESCRIPTION OF THE DRAWINGS
Fig. 1 is a photo of phosphoric acid anodized aluminum, 2024-T3 with no post
treatment after exposure to 24 hours (1 day) of ASTM-B 117 neutral salt fog
test.
5
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
Fig: ''is'a plioto of pnospfioric acid anodized 2024-T3 post treated with the
composition of Example 5 (10 minute immersion at about 75 F) after exposure to
96
hours (4 days) of ASTM-B 117 neutral salt fog test.
Fig. 3 is a photo of a phosphoric acid anodized 2024-T3 post treated with the
composition of Example 6(10 minute immersion at about 75 F) after exposure to
96
hours (4 days) of ASTM-B 117 neutral salt fog test.
Fig. 4 is a photo of phosphoric acid anodized 2024-T3 post treated with the
composition of Example 5 (10 minutes at 100 F) after exposure to 1000 hours
(42 days)
of ASTM-B 117 neutral salt fog test.
Fig. 5 is a photo of a phosphoric acid anodized 2024-T3 post treated with the
composition of Example 7(10 minutes at 100 F) after exposure to 1000 hours (42
days)
of ASTM-B 117 neutral salt fog test.
Fig. 6 is a photo of a phosphoric acid anodized 2024-T3 post treated with the
composition of Example 5 (40 minutes at ambient (75 F)) after exposure to 1000
hours
(42 days) of ASTrv1-B 117 neutral salt fog test.
Fig. 7 is a photo of a phosphoric acid anodized 2024-T3 post treated with the
composition of Example 7(40 minutes at ambient (75 F)) after exposure to 1000
hours
(42 days) of ASTM-B 117 neutral salt fog test.
Fig. 8 is a photo of a phosphoric acid anodized 2024-T3 post treated with the
composition of Example 5 (5 minutes at 150 F) after exposure to 1000 hours (42
days)
of ASTM-B 117 neutral salt fog test.
Fig. 9 is a photo of a phosphoric acid anodized 2024-T3 post treated with the
composition of Example 6 (5 minutes at 150 F ) after exposure to 1000 hours
(42 days)
of ASTM-B 117 neutral salt fog test.
6
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
...... _. ..,.. .. .._. .;. ,_.
OE'TAII.~~ ~~SORIP'TiO~ OF" ~HE IliNENTION
More specifically, this invention relates to the process of using an acidic
aqueous
solution having a pH ranging from about 2.5 to 5.5, and preferably from about
2.5 to 4.5
or 3.7 to 4.0 for sealing phosphoric acid anodized aluminum and its alloys to
maintain its
adhesion bonding and to substantially improve the corrosion-resistance
properties of the
anodized aluminum(s). The process preferably comprises the use of an acidic
solution
comprising from about 0.01 to 22 grams and preferably from about 4.0 to 8.0
grams e.g.
6.0 grams of at least one water soluble trivalent chromium compound e.g.
chromium
sulfate, about 0.01 to 12 grams and preferably about 6.0 to 10 grams e.g. 8.0
grams of at
least one alkali metal hexafluorozirconate, about 0.0 to 12 or about 0.001 to
12 grams and
preferably about 0.12 to 1.2 grams e.g. 0.24 to 0.36 grams of at least one
fluorocompound
selected from the group consisting of alkali metal tetrafluoroborates, alkali
metal
hexafluorosilicates and various mixtures or combinations thereof in any ratio,
and from
about 0.001 to 10 grams and preferably 0.1 to 5.0 or 1.0 to 2.0 grams of at
least one
divalent zinc compound such as zinc sulfate.
In some processes, depending on the physical characteristics of the anodized
aluminum e.g. the physical size of the anodized substrate, a feature is the
addition of a
thickener to the solution that aids in optimum film formation during spray and
wipe-on
applications by slowing down solution evaporation. This also mitigates the
formation of
powdery deposits that degrade paint adhesion. Moreover, the addition of
thickeners, aids
in proper film formation during large area applications and mitigates the
diluent effect of
rinse water remaining on the substrate during processing from previous steps.
This
additive yields films that have no streaks and have better coloration and
corrosion
7
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
~iuble'tbickeners such as the cellulose compounds are known and
pibtectia: rt'Tlie*dter=s,f
can be present in the acidic aqueous solution in amounts ranging from about
0.0 to 10
grams and preferably from 0.0 to 2.0 grams and more preferably from 0.5 to 1.5
e.g.,
about 1.0 gram per liter of the aqueous solution. Depending on the
characteristics of the
anodized almninuin, an effective but small amount of at least one water-
soluble surfactant
or wetting agent can be added to the acidic solution in amounts ranging from
about 0.0 to
grams and preferably from 0.0 to 2.0 grams and more preferably from 0.5 to 1.5
grams
e.g. 1.0 grams per liter of the acidic solution. These water soluble
surfactants or wetting
agents are known in the prior art and are selected from the group consisting
of non-ionic,
10 cationic and anionic surfactants.
The trivalent chromium is added as a water-soluble trivalent chromium
compound, preferably as a trivalent chromium salt. Specifically, in
formulating the acidic
aqueous solutions of this invention, the chromium salt can be added,
conveniently, to the
solution in its water soluble form wherein the valence of the chromium is plus
3. For
example, some of the preferred chromium compounds can be prepared in solution
in the
form of Cr2(S04)3, (NHa)Cr(S04)a or KCr2(SO4)2 and any mixtures or combination
of
these compounds. The aluminum substrates are either phosphoric acid anodized
aluminum or anodized aluminum alloys containing about 60% or more by weight of
aluminum. A preferred example of trivalent chromium concentration is within
the range
of about 4.0 to 8.0 grams or 6.0 grams per liter of the aqueous solution. It
has been found
that particularly good results are obtained when the trivalent chromium
compound is
present in solution in these preferred ranges. The preferred metal
fluorozirconate addition
to the acidic solution ranges from about 6.0 to 10 grams or 8.0 grams per
liter of solution.
8
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
1"'lid i&atffient'br'seMffig=of the phosphoric acid anodized aluminum can be
carried
out at low temperatures e.g. about ambient or room temperature or at
temperatures
ranging up to about 200 F. Room temperatare treatment is preferred in that
this
eliminates the necessity for heating equipment. The seal coating may be air
dried by any
of the methods known in the art, for example, oven drying, forced air drying,
exposure to
infra red lamps, and the like. For purposes of this invention, the terms
phosphoric acid
anodized alumimun and anodized aluminum alloys include alumi.num and its
alloys
phosphoric acid anodized by methods known in the art.
In some treatments, the alkali metal tetrafluoroborates and/or
hexafluorosilicates
can be added to the acidic solution in amounts as low as 0.001 grams per liter
up to the
solubility limits of the compounds. For example, about 50% weight percent of
the
fluorosilicate is added based on the weight of the fluorozirconate. In other
words, for 8.0
grams per liter of the fluorozirconate salt, about 4.0 grams per liter of
fluorosilicate is
added to the solution. For example, an alternative is to add about 0.01 to 100
weight
percent of the fluoroborate salt based on the weight of the fluorozirconate
salt.
Preferably, about 1 to 10 weight percent e.g. about 3% of the fluoroborate
salt can be
added based on the weight of the fluorozirconate salt. A specific example
comprises
about 8.0 grams per liter of potassium hexafluorozirconate, about 6.0 grams
per liter of
chromium III sulfate basic, about 0.1 to 5.0 grams per liter of divalent zinc
sulfate and
about 0.12 to 1.2 grams per liter of potassium tetrafluoroborate and/or
hexafluorosilicate.
An important result of the addition of the stabilizing additives i.e.
fluoroborates and/or
fluorosilicates is that the solution is stable while the pH is maintained
between about 2.5
and 5.5. However, in some cases the pretreatment solutions may require small
9
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
adju'r's~' fb"tYib' pl T'bY tii~"Adtiition of effective amounts of a dilute
acid or base to
maintain the pH in the range of about 2.5 to 5.5 or lower e.g. from about 3.25
to 3.5..
The composition or acid solution can also contain zinc compounds to further
improve the corrosion protection of the phosphoric acid anodized coatings
compared to
compositions that do not contain divalent zinc compounds. The components of
the
solution are mixed together in water and can be used with no further chemical
manipulation. The divalent zinc can be supplied by any chemical compound that
dissolves in water at the required concentrations ranging from 0.001 to 10
grams and is
compatible with the other components in the solution. Compounds that are
particularly
preferred include, for example, zinc acetate, zinc telluride, zinc
tetrafluoroborate, zinc
molybdate, zinc hexafluorosilicate, zinc sulfate and the like or any
combination thereof in
any ratio.
The following Examples illustrate the stable seal-coating solutions of this
invention, and the method of using the solutions in maintaining the adhesion
properties
while improving the corrosion-resistance of phosphoric acid anodized aluminum
and its
alloys.
EXAMPLE 1
TCP5PZ2
A stable acidic aqueous solution having a pH ranging from about 3.45 to 4.0
for
post-treating phosphoric acid anodized aluminum and aluminum alloys to provide
a
corrosion-resistant and a color recognized coating thereon which comprises,
per liter of
solution, about 3.0 grams of trivalent chromium sulfate basic, about 4.0 grams
of
potassium hexafluorozirconate and about 1.0 gram zinc sulfate.
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
~LE 2
TCP5B3
A stable acidic aqueous solution for post-treating phosphoric acid anodized
aluminum and aluminum alloys to form a corrosion-resistant coating thereon
which
comprises, per liter of solution, about 3.0 grams of trivalent chromium
sulfate basic,
about 4.0 grams of potassium hexafluorozirconate, and about 0.12 grams of
potassium
tetrafl.uoroborate.
EXAMPLE 3
TCP5B3Z4
A stable acidic aqueous solution for post-treating phosphoric acid anodized
aluminum and aluminum alloys to provide a corrosion-resistant and a color
recognized
coating thereon which comprises, per liter of solution, about 3.0 grams of
trivalent
chromium sulfate basic, about 4.0 grams of potassium hexafluorozirconate,
about 0.12
grams of potassium tetrafluoroborate and about 2.0 grams of divalent zinc
sulfate.
Table 1 shows the corrosion ratings of three Examples for post-treating
phosphoric acid anodized aluminum alloys of this invention in comparison to
the
composition of Example 2 coatings. Example 3 (TCP5B3Z4) and Example 1(TCP5PZ2)
on average had higher ratings.
11
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
TABLE 1
Corrosion Resistance of Phosphoric Acid Anodize with Sealer on 2024-T3
Aluminum
Alloy After 1,000 Hours of Exposure to ASTM B 117 Neutral Salt Spray
Immersion conditions
Applicable TCP SeaCer Ambient/10 Ambient140 IOOF/1 O- 1 S0FO5-
Patents composition minute minute minute minute
;USP 6,500,532 xample 2
B3 0 6,7 5.7 3
's Invention, Example 3
SP 6,663,700, ,5B3Z4
,[JSP 6,669,764 1 0 1 0 8
iThis Invention, xample 1
UI~-SP 6,663,700 , P~
~L7SP 6,669,764 0 7.7 7.7 6
Note: Each rating is the average of 3 identically coated and exposed panels
Corrosion rati~per ASTM D 1654
~ EXAMPLE 4
Add 3.0 grams per liter of chromium III sulfate basic and 4.0 grams per liter
of
potassium hexafluorozirconate to specific volume of deionized water. Maintain
pH
between 3.25 and 3.60 for 14 days using dilute potassium hydroxide or dilute
sulfuric
acid. After 14 days, adjust pH to 3.90 +1-0.05 and let sit overnight. Solution
is ready to
use.
EXAMPLE 5
Add 3.0 grams per liter of chromium IIl sulfate basic, 4.0 grams per liter of
potassium hexafluorozirconate, and 0.12 grams per liter potassium
tetrafluoroborate to
12
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
SpdC"iiYC vdl'M "deiofflied''Watef. Let solution stand for approximately 10
days, or
until pH rises to between 3.75 and 4.00. Solution is ready to use.
EXAMPLE 6
To Example 4, add 1.0 grams per liter of zinc sulfate during initial mixing.
Solution is ready to use.
EXAMPLE 7
To Example 5, add 2.0 grams per liter of zinc sulfate during initial mixing.
Solution is ready to use.
EXAMPLE 8
Post treatment coatings were applied to anodized aluminum as follows. The
phosphoric acid anodize process per ASTM D 3933, "Standard Practice for
Preparation
of Aluminum Surfaces for Structural Adhesives Bonding (Phosphoric Acid
Anodizing),"
was followed throughout. Immediately after anodizing 3" by 10" by 0.32"
aluminum
panels of 2024-T3 aluminum alloys by the Phosphoric Acid Anodize process, the
panels
were rinsed thoroughly two times in deionized water. Immediately after
rinsing, the
panels were immersed into a solution of either Example 6 or 7 for 10 minutes
at ambient
conditions. The immersion was immediately followed by two deionized water
rinses.
The panels were air-dried at ambient conditions before being subjected to
neutral salt fog
per ASTM B 117. The coupons were held in a rack at 15 degrees for the duration
of the
13
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
testGontrol'coupons of pliosphoric acid anodized (PAA) not sealed were tested
alongside the subject coatings.
Fig's.2 and 3 (photos) show the performance of post treatments from the
compositions of Examples 5 and 6. Fig. 1 (photo) shows an unsealed PAA panel
after
exposure to ASTM B 117 neutral salt fog. The post treatments of Fig's. 2- and
3 provide
improved corrosion resistance compared to the no post-treatment coating of
Fig. 1.
EXAMPLE 9
Test specimens were anodized as in Example 8. In this example, the
compositions (solutions) from Examples 5 and 7 were heated to 100 Fahrenheit
and the
panels were immersed for a total of 10 minutes. Fig's. 4 and 5(photos) show
corrosion
performance of these coatings after 1000 hours of neutral salt fog per ASTM B
117. It is
evident that the composition of example 7 is an improvement compared to the
composition of Example 5.
EXAMPLE 10
Test specimens were anodized as in Example 8. In this example, the
compositions (solutions) from Examples 5 and 7 were kept at ambient
conditions, about
75 Fahrenheit, and the panels were immersed for a total of 40 minutes. Fig's.
6 and 7
(photos) show the improved corrosion resistance of these coating after 1000
hours of
iieutral salt fog per ASTM B 117.
14
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
EXAMPLE 11
Test specimens were anodized as in Example 8. In this example, the
compositions (solutions) from Examples 5 and 6 were heated to 150 Fahrenheit,
and the
panels were immersed for a total of 5 minutes. Fig's. 7 and 8 (photos) show
the corrosion
resistance of these coatings after 1000 hours of neutral salt fog per ASTM B
117.
Table 2 compares the corrosion resistance results of the Examples based on
numerical ratings from ASTM D 1654. In the ASTM rating method, the best
possible
score is 10, meaning substantially no corrosion is evident on the test panel.
Ratings
decrease to 1, which represents substantially 100% corrosion of the panel
surface. From
the data in Table 2, it is evident that the process of this invention is an
improvement over
previous processes used for post treating or sealing phosphoric acid anodized
aluminum
and its alloys.
TABLE2
Numerical corrosion ratings of the panels treated with the compositions
(solutions) and the process of this invention, based on ASTM D 1654, had
ratings as high
as 10 (no corrosion) to a low of 1(fially corroded) where there was no post-
treatments.
The ratings comprise an average of three rated panels for each condition.
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
...,,..
'e'oinposi~ions'iit iT,e .t '-" PROCESS CONDI?7ONS
Aqueous Acidic A~knt 1Ambient 00 F and 10 150 F and S
So[ution Tr_emperature ,temp-erature minute minute
75 1) and #5 P) and unmersion mmersion
~10 minute 40 minute le 9) ( le 11)
. l~mP~-riP
imnmersion nunersion
le8 ~ 1e10
Control (no post 0 after 24 hours rA A ;;~A
~treatment
-~xample 5 NA 6.7 after 1000 ~5.7 after 1000 3 after 1000
1 ours NSF ours NSF ours NSF
xample 6 after 96 hours ~.7 after 1000 ~7.7 after 1000 after 1000
SF I ours NSF ~iours NSF ours NSF
xample 7 0 after 96 hours 1 after 1000 after 1000 8 after 1000
,~SF ours NSF ours NSF ~ours NSF
For purposes of this invention, the water soluble surfactants or wetting
agents can
be added to the t.rivalent chromium solutions in amounts ranging from about 0
to 10
grams per liter and preferably 0.5 to about 1.5 grams per liter of the
trivalent chromium
25 solution. The surfactants are added to the aqueous solution to provide
better wetting
properties by lowering the surface tension thereby insuring complete coverage,
and a
more uniform film on the coated substrate. The surfactants include at least
one water
soluble compound selected from the group consisting of the non-ionic, anionic,
and
cationic surfactants. Some lcnown water soluble surfactants having the
solubility at the
30 required concentrations include the monocarboxyl imidoazoline, alkyl
sulfate sodium
salts (DUPONOL ), tridecyloxy poly(alkyleneoxy ethanol) ethoxylated or
propoxylated
alkyl phenol (IGEP.AL(g), alkyl sulfonamides, alkaryl sulfonates, palmitic
alkanol amides
(CENTROL ), octylphenyl polyethoxy ethanol (TRITON ), sorbitan monopalmitate
(SPAN ), dodecylphenyl polyethylene glycol ether e.g. TERGITROL , alkyl
35 pyrrolidone, polyalkoxylated fatty acid esters, alkylbenzene sulfonates and
mixtures
thereof. Other known water soluble surfactants include the alkyl phenol
alkyloxylates,
16
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
preferably tfie 'nonylpheriol etl~yloxylates, and the various anionic
surfactants, having at
least one sulfonate substituent in the phenyl ring, and the adducts of
ethylene oxide with
fatty amines. Other known water soluble compounds are found in "Surfactants
and
Detersive Systems", published by John Wiley & Sops in Kirk-Othmer's
Encyclopedia of
Chemical Technology, 31 Ed.
When large surfaces do not permit immersion or where vertical surfaces are to
be
sprrayed, thickening agents are added to retain the aqueous solution on the
surface for
sufficient contact time. The thickeners employed are known inorganic and
organic water
soluble thickeners which can be added to the trivalent chromium solutions in
effective
amounts e.g. a sufficient concentration ranging from about 0 to 10 grams per
liter and
preferably 0.5 to 1.5 grams per liter of the acidic solution. Specific
examples of some
preferred thickeners include the cellulose compounds, e.g. hydroxypropyl
cellulose (e.g.
Klucel), ethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose,
methyl
cellulose and mixtures thereof. Some of the less preferred thickeners include
the water
soluble inorganic thickeners such as colloidal silica, clays such as
bentonite, starches,
gum arabic, tragacanth, agar and various combinations.
After preparing the surface to be treated via conventional phosphoric acid
anodizing techniques, the solution can be applied by immersion, spray or wipe-
on
techniques. The solution also can be used at elevated temperatures up to 65 C
and
optimally applied by immersion to fizrther improve the corrosion resistance of
phosphoric
acid anodize coatings. Solution dwell time is about I to 60 minutes, depending
on the
solution temperature and concentration of the solution. After dwelling, the
remaining
solution is then thoroughly rinsed from the substrate with tap or deionized
water. No
additional chemical manipulations of the deposited film are necessary for
excellent
17
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
perfoimance. " However~ an application of a strong oxidizing solution can
yield a film
with improved corrosion resistance. The additional corrosion resistance is
presumed to
be due to the hexavalent chromium formed in the film from the trivalent
chromium. The
aqueous sealer composition may be sprayed from a spray tank apparatus designed
to
replace immersion tanks. This concept also reduces active chemical volume from
about
1,000 gallons to about 30 to 50 gallons.
Another feature of this invention is the ability of this protective seal
coating to
provide the phosphoric acid anodized coatings with corrosion resistance better
or at least
equivalent to other known sealed anodic coatings produced with sulfuric,
chromic, boric-
sulfuric, or other known compositions. This capability has not been available
before and
offers new potential applications for phosphoric acid anodized in corrosive
environments
that were not previously possible. Phosphoric acid anodized aluminums have a
major
advantage over these other coatings in that its coating weights are typically
10 to 50 times'
lower. This yields significant weight savings and lower fatigue debit to
structural
aluminum alloys. In addition, this invention has the ability to enhance the
performance of
phosphoric acid anodize coatings currently being implemented as an adhesive
bonding
alternative to chromic acid anodizing. Phosphoric acid anodize coatings that
have not
been post treated are known to have inferior corrosion resistance, but are
known also to
have excellent bonding characteristics. This invention increases the corrosion
performance of the anodized aluminums, while maintaining the adhesive bonding
strength of the coatings. The terms, for purposes of this invention,
"solubility" and
"water soluble" mean water solubility of the chemical compounds used in the
solutions of
this invention at least at the concentrations set-forth herein.
18
CA 02598390 2007-08-14
WO 2006/088520 PCT/US2005/041425
Whi:1e"'t"his inventionIas''been described by a number of specific examples,
it is
obvious that there are other variations and modifications which can be made
without
departing from the spirit and scope of the invention as particularly set forth
in the
appended claims.
15
19
