U.S. patent application number 10/351752 was filed with the patent office on 2003-12-18 for pretreatment for aluminum and aluminum alloys.
Invention is credited to Matzdorf, Craig A., Nickerson, William C. JR..
Application Number | 20030230215 10/351752 |
Document ID | / |
Family ID | 32770269 |
Filed Date | 2003-12-18 |
United States Patent
Application |
20030230215 |
Kind Code |
A1 |
Matzdorf, Craig A. ; et
al. |
December 18, 2003 |
PRETREATMENT FOR ALUMINUM AND ALUMINUM ALLOYS
Abstract
Pretreated aluminum and aluminum alloys and the process and
composition for pretreating said aluminum and its alloys to provide
a coating with color recognition for identification purposes and to
improved the corrosion-resistance, electrical conductivity, and
adhesion properties which comprises pretreating said aluminum and
its alloys with an effective amount of an acidic aqueous solution
having a pH ranging from about 2.5 to 5.5 comprising water soluble
trivalent chromium compounds, alkali metal hexafluorozirconates,
divalent zinc compounds, alkali metal fluoro-compounds, and
effective amounts of water soluble thickeners, surfactants or
wetting agents.
Inventors: |
Matzdorf, Craig A.;
(California, MD) ; Nickerson, William C. JR.;
(Hughesville, MD) |
Correspondence
Address: |
NAVAL AIR WARFARE CENTER AIRCRAFT
DIVISION OFFICE OF COUNSEL BLDG 435
SUITE A
47076 LILJENCRANTZ ROAD UNIT 7
PATUXENT RIVER
MD
20670
|
Family ID: |
32770269 |
Appl. No.: |
10/351752 |
Filed: |
January 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10351752 |
Jan 23, 2003 |
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10116844 |
Apr 5, 2002 |
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6521029 |
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10116844 |
Apr 5, 2002 |
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09702225 |
Oct 31, 2000 |
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6375726 |
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Current U.S.
Class: |
106/14.44 ;
106/14.21; 106/14.41; 148/247; 148/267; 148/275; 428/472;
428/472.1 |
Current CPC
Class: |
C09D 5/084 20130101;
C23C 22/34 20130101; C23C 2222/10 20130101; C23C 22/83 20130101;
C09D 5/12 20130101 |
Class at
Publication: |
106/14.44 ;
106/14.21; 106/14.41; 148/247; 148/267; 148/275; 428/472;
428/472.1 |
International
Class: |
C23C 022/05 |
Goverment Interests
[0002] The invention described herein was made by an employee 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.
Claims
1. A process for pretreating aluminum and alloys of aluminum to
provide a coating having color recognition, and improved
corrosion-resistance, electrical conductivity, and adhesion
properties which comprises treating said aluminum and alloys of
aluminum with an effective amount of an acidic aqueous solution
having a pH ranging from about 2.5 to 5.5 and comprises, per liter
of said 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 grams of at least one
water soluble fluoro-compound selected from the group consisting of
alkali metal tetrafluoroborates, alkali metal hexafluorosilicates
and mixtures thereof, about 0.001 to 10 grams of at least one water
soluble zinc compound, and from 0 to 10 grams of at least one water
soluble thickener.
2. A process for pretreating aluminum and alloys of aluminum to
provide a coating having color recognition, and improved
corrosion-resistance, electrical conductivity, and adhesion
properties which comprises treating said aluminum and alloys of
aluminum at about room temperature with an effective amount of an
aqueous solution having a pH ranging from about 3.7 to 4.0 and
comprises per liter of solution from about 0.01 to 10 grams of a
water soluble trivalent chromium salt, about 0.01 to 8.0 grams of
an alkali metal hexafluorozirconate, about 0.0 to 12 grams of at
least one fluoro-compound selected from the group consisting of
alkali metal tetrafluoroborates, alkali metal hexafluorosilicates
and mixtures thereof, and about 0.001 to 10 grams of at least one
water soluble divalent zinc salt.
3. The process of claim 1 wherein the pH of the aqueous solution
ranges from about 3.7 to 4.0 and the temperature of the aqueous
solution ranges from about room temperature to about 200.degree.
F.
4. The process of claim 3 wherein the trivalent chromium compound
ranges from about 5.0 to 7.0 grams, the hexafluorozirconate ranges
from about 6.0 to 8.0 grams, and the tetrafluoroborate ranges from
about 0.01 to 1.2 grams.
5. The process of claim 1 wherein the thickener is a cellulose
compound ranging from 0.5 to 1.5 grams.
6. The process of claim 2 wherein the tetrafluoroborate is present
in the solution in an amount ranging from about 0.12 to 0.24
grams.
7. The process of claim 2 wherein about 0.5 to 1.5 grams of a
cellulose thickener is added to the pretreatment solution.
8. The process of claim 2 wherein the chromium salt is trivalent
chromium sulfate.
9. The process of claim 1 wherein the alkali metal zirconate is
potassium hexafluorozirconate.
10. The process of claim 2 wherein the zinc compound is divalent
zinc sulfate ranging in an amount from about 0.01 to 5.0 grams per
liter.
11. Pretreated aluminum and alloys of aluminum having a color
recognized coating and improved corrosion-resistance, electrical
conductivity, and adhesion properties comprising said aluminum and
alloys of aluminum treated with an effective amount of an acidic
aqueous solution having a pH ranging from about 2.5 to 5.5 and
comprising per liter of said solution from about 0.01 to 22 grams
of a water-soluble trivalent chromium compound, from about 0.01 to
12 grams of an alkali metal hexafluorozirconate, about 0.0 to 12
grams of at least one fluoro-compound selected from the group
consisting of an alkali metal tetrafluoroborate, an alkali metal
hexafluorosilicate and mixtures thereof, about 0.001 to 10 grams of
at least one water soluble zinc compound and from 0 to 10 grams of
at least one water soluble thickener.
12. Pretreated aluminum and alloys of aluminum having a color
recognized coating and improved corrosion-resistance, electrical
conductivity, and adhesion properties comprising said aluminum and
alloys of aluminum treated with an effective amount of an acidic
aqueous solution having a pH ranging from about 3.7 to 4.0, and
comprising per liter of said solution from about 0.01 to 10 grams
of a water soluble trivalent chromium salt, about 0.01 to 8.0 grams
of an alkali metal hexafluorozirconate, about 0.0 to 12 grams of at
least one fluoro-compound selected from the group consisting of an
alkali metal tetrafluoroborate, an alkali metal hexafluorosilicate
and mixtures thereof, 0.01 to 10 grams of at least one water
soluble divalent zinc salt and from 0 to 10 grams of at least one
water soluble thickener.
13. The pretreated aluminum of claim 11 wherein the thickener
ranges from about 0.5 to 1.5 grams.
14. The pretreated aluminum of claim 11 wherein the zinc compound
is divalent zinc sulfate and the hexafluorosilicate is present in
an amount ranging from about 0.01 to 1.2 grams.
15. The pretreated aluminum of claim 11 wherein the
tetrafluoroborate is present in the solution in an amount ranging
from about 0.01 to 1.2 grams.
16. The pretreated aluminum of Claim 11 wherein about 0.5 to 1.5
grams of a cellulose thickener is present in the solution.
17. The pretreated aluminum of claim 11 wherein the chromium
compound is trivalent chromium sulfate.
18. The pretreated aluminum of claim 11 wherein the alkali metal
zirconate is potassium hexafluorozirconate.
19. The pretreated aluminum of claim 12 wherein the zinc salt is
divalent zinc sulfate.
20. The pretreated aluminum of claim 12 wherein the zinc salt is
zinc acetate.
21. A composition for pretreating aluminum and alloys of aluminum
to provide a color recognizable coating and to improved the
corrosion-resistance, electrical conductivity and adhesion
properties of the coated aluminum which comprises an aqueous
solution having a pH ranging from about 2.5 to 5.5 and per liter of
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 grams of at least one water
soluble fluoro-compound selected from the group consisting of
alkali metal tetrafluoroborates, alkali metal hexfluorosilicates
and mixtures thereof, about 0.001 to 10 grams of at least one water
soluble zinc compound and from 0 to 10 grams of at least one water
soluble thickener.
22. The composition of claim 21 wherein the pH ranges from about
3.7 to 4.0.
23. The composition of claim 21 wherein the trivalent chromium
compound is trivalent chromium sulfate basic.
24. The composition of claim 21 wherein the zinc compound is
divalent zinc sulfate.
25. The composition of claim 21 wherein the zinc compound is
divalent zinc acetate.
Description
CONTINUATION APPLICATION
[0001] This application is a continuation-in-part of co-pending
application Ser. No. 10/116,844 filed Apr. 5, 2002 which in turn is
a continuation-in-part of co-pending application Ser. No.
09/702,225 filed Oct. 31, 2000 by Matzdorf et al., now U.S. Pat.
No. 6,375,726B1 issued Apr. 23, 2002.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention relates to the protection and pretreatment of
aluminum and aluminum alloys and to the surface treatment of
aluminum and its alloys with novel compositions and to the process
of using these compositions for the pretreatment of aluminum and
aluminum alloys at ambient and higher temperatures. The
pretreatment coatings provide color recognition, improved corrosion
resistance, adhesion of overlaying coatings e.g. paints and
maintains low electrical contact resistance in a corrosive
environment. More specifically, this invention relates to corrosion
resistant compositions and to the process of using the compositions
on aluminum and aluminum alloys which comprises an acidic aqueous
solution containing effective amounts of at least one water soluble
trivalent chromium salt, an alkali metal hexafluorozirconate, at
least one fluoro-compound, at least one zinc compound and at least
one water soluble thickener.
[0005] 2. Description of Prior Art
[0006] It is current practice to improve the corrosion resistance
and bonding of subsequent coatings to aluminum and its alloys by
initially coating or pretreating the metal surface with protective
films. The conversion coating enhances the corrosion resistance of
the untreated metal surface and prepares the surface for a finish
coating including paints and the like. These conversion or
pretreatment coatings are most often applied by using hexavalent
chromium-containing solutions: While these coatings provide good
corrosion resistance, attempts have been made to provide a more
acceptable non-chromate derived coating because of concern
regarding the occupational, safety, health and environmental
effects of hexavalent chromium. Hexavalent chromium is highly toxic
and is a known carcinogen. Therefore, the solutions used to deposit
these protective films, and the films per se are toxic and
carcinogenic. Chromate films, however, provide outstanding adhesion
and corrosion resistance and are easy to apply by various methods
including immersion, spraying or by the wipe-on technique.
Moreover, the environmental laws and OSH regulations are forcing
the military and commercial users to find other non-toxic,
non-chromate pretreatments. In addition, the use of chromate
conversion coatings is becoming more expensive as the regulations
are being enforced and costs become prohibitive because of the
restrictions being imposed by the EPA. For example, certain
processes such as spraying chromate conversion coatings are
forbidden because of OSH regulations, thereby forcing the use of
less than optimum alternative methods.
[0007] It is generally known that aqueous chromate solutions
contain chemicals that partially dissolve the surface of the metal
e.g. aluminum and form insoluble films known as a pretreatment or a
chromate conversion coating. These coatings are corrosion resistant
and protect the metal from various elements which cause corrosion.
Although these conversion coatings enhance corrosion resistance and
improve the bonding or adhesion properties, the coatings have
serious drawbacks, i.e., the toxic nature of the solutions from
which they are made and the presence of hexavalent chromium in the
applied films. This is a serious problem for the operators handling
the solution e.g. disposing the used chromate solution, the
chromate-contaminated rinse water, and the coating systems
contaminated with chromates. These problems, however, can be
avoided by eliminating hexavalent chromium from the process.
However, this method is expensive and can be a major cost factor in
the overall metal treating process. Therefore, it is highly
desirable to provide processes and protective coatings which are
free of hexavalent chromium, but at the same time capable of
imparting corrosion resistant and bonding properties which are
comparable to those imparted by conventional chromate-based
conversion coatings. Of particular interest is the use of chromate
conversion coatings for aluminum and its alloys e.g. the coating of
large objects such as aircraft. Therefore, it would be desirable to
provide a protective coating for aluminum and its alloys utilizing
relatively non-toxic chemicals that serve as an alternative to the
toxic hexavalent chromium coatings.
SUMMARY OF THE INVENTION
[0008] This invention relates to an acidic aqueous trivalent
chromium pretreatment (TCP) of aluminum and aluminum alloys and to
the process for providing color recognition, and identification of
the coating and to improve the adhesion and corrosion resistant
properties of the aluminum surfaces. Specifically, this invention
relates to pretreating aluminum and to the composition and process
of pretreating aluminum and aluminum alloys at ambient or higher
temperatures ranging up to about 200.degree. F. The pretreatment
solutions comprise an acidic aqueous solution having a pH ranging
from about 2.5 to 5.5 and preferably from 3.7 to 4.0, and contain
per liter of said 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 grams and
preferably 0.01 to 1.2 e.g. 0.12 to 0.24 grams of at least one
fluoro-compound selected from the group consisting of an alkali
metal tetrafluoroborate, an alkali metal hexafluorosilicate and
various combinations or mixtures thereof, from about 0.001 to 10
grams of at least one zinc compound, from about 0.0 to 10 grams per
liter and preferably 0.5 to 1.5 grams of at least one water-soluble
thickener, and from 0.0 to 10 grams per liter and preferably 0.5 to
1.5 grams of at least one water-soluble non-ionic, cationic or
anionic surfactant.
[0009] One shortcoming of the compositions and processes described
by the prior TCP coatings is the lack of a significant color change
or color recognition in the as-deposited coating, especially when
used as a pretreatment for aluminum alloys. Chromate-based coatings
typically have an iridescent gold to brown color that is easily
identified by processors, quality control personnel, and other
users in the field. A gold color on aluminum components generally
means that a chromate pretreatment is present and the color is
useful for this type of quality control irrespective of technical
coating performance such as resistance to corrosion or paint
adhesion. The TCP coatings described heretofore typically have a
light bluish to purplish to tan color, depending on the process
conditions, that is very difficult to see in mixed light such as
inside a production facility, in a repair depot or manufacturing
plant. TCP on some surfaces like clad aluminum alloys is virtually
colorless. Therefore, to provide a means of color identification or
recognition of the coating, this invention relates to compositions
and processes for preparing a corrosion-resistant coating for
aluminum and aluminum alloys. The compositions comprise treating
the aluminum substrates with an acidic aqueous solution containing
trivalent chromium sulfate basic, an alkali metal
hexafluorozirconate, and optionally a cellulose-based thickener and
an alkali metal tetrafluoroborate and/or an alkali metal
hexafluorosilicate stabilizer. In addition, the composition must
also contain a zinc-based compound e.g. divalent salt to impart
color recognition to the as-produced coating.
[0010] It is therefore an object of this invention to provide
pretreated aluminum and its alloys by treating said aluminum with
an aqueous solution comprising a trivalent chromium compound, an
alkali metal hexafluorozirconate, effective amounts of an alkali
metal tetrafluoroborate and/or hexafluorosilicate and at least one
zinc compound to improve the electrical resistance, adhesion, and
corrosion resistance properties and to provide color recognition
for identification of the coated aluminum.
[0011] It is another object of this invention to provide a process
of pretreating aluminum and aluminum alloys with 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,
hexafluorozirconate and a divalent zinc salt to provide color
recognition for identification of the coating
[0012] It is a further object of this invention to provide a stable
acidic aqueous solution having good "shelf life" containing
trivalent chromium salts, hexafluorozirconates, divalent zinc salts
and a pH ranging from about 2.5 to 5.5 for pretreating aluminum and
its alloys at ambient temperatures wherein said acidic pretreating
solution contains substantially no hexavalent chromium.
[0013] These and other objects of the invention will become
apparent from a further and more detailed description of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] This invention relates to an acidic, aqueous stable solution
of trivalent chromium compounds having a pH ranging from about 2.5
to 5.5 and preferably from 3.7 to 4.0 and the use thereof at
ambient temperatures or higher for pretreating aluminum and
aluminum alloys. The stable aqueous solutions comprise from about
0.01 to 22 grams, per liter of solution, and preferably about 0.01
to 10 grams per liter e.g. 5-7 grams of at least one water soluble
trivalent chromium compound, about 0.01 to 12 grams and preferably
about 0.01 to 8.0 grams e.g. 6-8 grams per liter of solution of at
least one alkali metal hexafluorozirconate, about 0.001 to 10 grams
and preferably 0.1 to 5.0 grams per liter of at least one divalent
zinc compound, about 0.0 to 12 grams and preferably from about 0.01
to 1.2 grams e.g. 0.12 to 0.24 grams of at least one alkali metal
tetrafluoroborate, 0.0 to 12 grams and preferably from 0.01 to 1.2
grams e.g. 0.12 to 0.24 grams of an alkali metal hexafluorosilicate
and any combination of said borates and silicates, from about 0.0
to 10 grams per liter of the solution and preferably from about 0.5
to 1.5 grams per liter of at least one water soluble thickener e.g.
water soluble organic thickener and 0 to 10 grams of at least one
surfactant or wetting agent.
[0015] In some pretreatments, the alkali metal tetrafluoroborates
and/or hexafluorosilicates can be added to the 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 grams per liter of the fluorozirconate salt,
about 4.0 grams per liter of fluorosilicate is added to the
solution. 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. 3% of the
fluoroborate salt can be added based on the weight of the
fluorozirconate salt. A specific example comprises about 8 grams
per liter of potassium hexafluorozirconate, about 6 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 0.24 grams per liter of
potassium tetrafluoroborate. An important result of the addition of
the stabilizing additives i.e. fluoroborates and/or fluorosilicates
is that the solution is stable and the pH is maintained between
about 2.5 and 5.5. However, in some cases the pretreatment
solutions may require small adjustments to the pH by the addition
of effective amounts of a dilute acid or base to maintain the pH in
the range of about 2.5 to 5.5.
[0016] The trivalent chromium may be added to the solution as any
water-soluble trivalent chromium compound, preferably as a
trivalent chromium salt. Specifically, in formulating the aqueous
coatings of this invention, the chromium salt is added conveniently
to the solution in its water soluble form wherein the valence of
the chromium is plus 3. Some preferred chromium compounds are
incorporated in the aqueous solution in the form of
Cr.sub.2(SO.sub.4).sub.3, (NH4)Cr(SO.sub.4).sub.2, Cr(OH)SO.sub.4,
Cr.sub.2O.sub.3, or KCr(SO.sub.4).sub.2 and various combinations of
these compounds. A preferred trivalent chromium concentration is
within the range of about 0.01 to 10 grams per liter of the aqueous
solution and it has been found that particularly good results are
obtained economically when the chromium is present in this
preferred range. A preferred alkali metal fluorozirconate addition
to the solution ranges from about 0.01 to 8.0 grams per liter.
[0017] The amount of zinc salt can be varied to adjust the color
imparted to the coating, from as little as 0.001 grams per liter up
to 10 grams per liter. Zinc.sup.2+ cation or divalent zinc can be
supplied by any chemical compound that dissolves in water and is
compatible with the other components in the composition. Some
compounds that are particularly preferred include zinc acetate,
zinc telluride, zinc tetrafluoroborate, zinc molybdate, zinc
hexafluorosilicate, zinc sulfate and any combination thereof in any
ratio.
[0018] The pretreatment of aluminum and its alloys can be carried
out at various temperatures including the temperature of the
pretreatment solution which ranges from ambient e.g. from about
room temperature up to about 200.degree. F. Room temperature
treatment is preferred, however, in that this eliminates the
necessity for heating equipment. The 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 term "aluminum" is intended to
include substantially pure aluminum, and any aluminum alloy
containing various other metals and particularly any aluminum alloy
containing over 60% by weight aluminum.
[0019] The following Examples illustrate the stable pretreatment
solutions of this invention and the method of using the solutions
in providing color recognition and improved adhesion and
corrosion-resistant coatings on aluminum and its alloys.
EXAMPLE 1
TCP5P
[0020] A stable acidic aqueous pretreating solution having a pH
ranging from about 3.45 to 4.0 for pretreating 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, and about 4.0 grams of potassium
hexafluorozirconate.
EXAMPLE 2
TCP5PZ2
[0021] A stable acidic aqueous solution having a pH ranging from
about 3.45 to 4.0 for pretreating 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.
EXAMPLE 3
TCP5B3
[0022] A stable acidic aqueous solution for pretreating 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
tetrafluoroborate.
EXAMPLE 4
TCP5B3Z4
[0023] A stable acidic aqueous solution for pretreating 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.
EXAMPLE 5
TCP5PZA
[0024] A stable acidic aqueous solution for pretreating 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 5.0 grams of
divalent zinc acetate.
EXAMPLE 6
[0025] Pretreated aluminum and alloys of aluminum having improved
corrosion-resistance and adhesion properties comprising said
aluminum and alloys of aluminum treated with an effective amount of
an acidic aqueous solution having a pH ranging from about 3.7 to
4.0, and containing per liter of said solution from about 0.01 to
10 grams of a water soluble trivalent chromium salt, about 0.01 to
8 grams of an alkali metal hexafluorozirconate, about 0.01 to 1.2
grams of at least one fluoro-compound selected from the group
consisting of an alkali metal tetrafluoroborate; an alkali metal
hexafluorosilicate and mixtures thereof, from 0 to 10 grams of at
least one water soluble thickener and from 0 to 10 grams of at
least one water soluble surfactant.
EXAMPLE 7
[0026] An acidic aqueous solution having a pH ranging from about
2-6 for preparing corrosion-resistant coatings on aluminum, and
aluminum alloys consisting essentially of, per liter of solution,
from about 3.0 grams to 22 grams of a water soluble trivalent
chromium salt, about 1.5 grams to 11.5 grams of an alkali metal
hexafluorozirconate, from 0 to 10 grams of at least one water
soluble thickener and from 10 grams of at least one water soluble
surfactant.
[0027] Prior to forming the trivalent chromium pretreatment, the
aluminum substrates were treated by cleaning the aluminum for about
15 minutes at temperatures ranging from about 100.degree. to
140.degree. F. with an alkaline phosphate cleaner Turco 4215 NC-LT,
rinsed in tap water and subsequently immersed in a non-chromate
deoxidizer (Turco Smut Go NC) for about 1 to 15 minutes under
ambient conditions, and then rinsed again in ambient tap water. The
cleaned substrates were then immersed in an acidic trivalent
chromium sulfate solution at ambient conditions for about 30
seconds to 60 minutes and subsequently rinsed in ambient tap water
and let stand until dry. In an alternative process, the aluminum
substrates were sprayed with an alkaline phosphate cleaner for
about 15 minutes at elevated temperatures, then rinsed in cold tap
water and sprayed With (Turco Smut Go NC) for about 30 seconds
under ambient conditions.
[0028] Coating the aluminum substrates with the trivalent chromium
solutions of this invention can be accomplished by spraying, wiping
or immersing the aluminum panels. The duration of contact ranges
from about 30 seconds to about 5 minutes, but longer contact, e.g.,
up to sixty minutes or more, may be required where the trivalent
chromium concentration or temperature of the solution is relatively
low. The aqueous solution temperature is normally below 100.degree.
C., e.g. in the range of 15.degree. to 75.degree. C. e.g. about
25.degree. C. The aluminum temperatures ranges from about
15.degree. to 30.degree. C.
TABLE A-1, A-2 AND A-3
[0029] Colorimetry Results
[0030] (All readings taken on Hunterlabs D25PC2 Colorimeter)
1TABLE A-1 Aluminum alloy 2024-T3 Pretreatment L a b TCP5P 42.7
-0.3 -7.1 TCP5P 42.6 -0.4 -6.7 EX. 1 TCP5PZ2 34.9 -0.6 0.2 TCP5PZ2
36.0 -0.4 0.5 EX. 2
[0031]
2TABLE A-2 Aluminum alloy 7075-T6 Pretreatment L a b TCP5P 38.4 0.1
-3.7 TCP5P 37.0 -0.2 -3.6 TCP5PZ2 34.3 -0.4 -0.1 TCP5PZ2 33.8 -0.9
0.2
[0032]
3TABLE A-3 Aluminum alloy 2219-T87 Pretreatment L a b TCP5P 52.1
-2.2 -4.9 TCP5P 51.2 -1.0 -4.1 TCP5PZ2 41.4 -0.8 0.6 TCP5PZ2 43.6
-0.7 4.2
[0033] In Tables A-1, A-2, and A-3, L is the grayscale, wherein
L=100 is pure white, L=0 is pure black, and L=50 is gray. Where "a"
is the red to green scale, and wherein 0 is a neutral value, +50 is
pure red, and -50 is pure green. Where "b" is the yellow to blue
scale, and wherein 0 is a neutral value, +50 is pure yellow, and
-50 is pure blue. Combining the "a" and "b" values gives the
desired color (for example: where -"b", +"a" is purplish, "b"=-50
and "a"=-50 is pure purple) and the L value shows the darkness of
the panels.
4TABLE B Representative Compositions and Processes to Produce Color
Change and Recognition of the Coating Documentation Name
Composition Process Comments Comparison TCP5P 3 grams/liter
chromium 2 to 5 minute Baseline Example 7 III sulfate basic and 4
dwell of composition and grams/liter potassium composition on
process that yields hexafluorozirconate aluminum surface coating
without EX 1 at ambient practical color conditions change TCP5B3
TCP5P and 0.12 2 to 5 minute Stabilized Example 6 grams/liter
potassium dwell of composition and tetrafluoroborate composition on
process that yields EX 3 aluminum surface coating without at
ambient practical color conditions change TCP5PZ2 TCP5P and 1.0 1
to 10 minute Baseline Invention grams/liter zinc sulfate dwell of
composition and EX 2 composition on process that yields aluminum
surface coating with at ambient practical color conditions change
TCP5B3Z4 TCP5B3 and 2.0 1 to 10 minute Stabilized Invention
grams/liter zinc sulfate dwell of composition and EX 4 composition
on process that yields aluminum surface coating with at ambient
practical color conditions change TCP5PZA TCPSP and 5.0 1 to 10
minute Buffered baseline Invention grams/liter zinc acetate dwell
of composition and EX 5 composition on process that yields aluminum
surface coating with at ambient practical color conditions
change
[0034] The term "practical color change" means a readily visible
recognizable color that does not have a detrimental effect on the
corrosion performance of the coating. The term "chromium III
sulfate basic" is defined in the Kirk-Othmer Encyclopedia of
Chemical Knowledge: Volume 6, 3.sup.rd edition (pps 95-96).
[0035] The advantage of the composition and process is the readily
visible color change and recognition imparted to the as-deposited
coating compared to previously disclosed trivalent chromium-based
aluminum pretreatments. Tables A-1, A-2 and A-3 detail colormetric
measurements of various aluminum alloys coated with the TCP
solutions described by this invention compared to those previously
disclosed without the zinc compound. Table B describes
representative compositions and the processes used to deposit the
pretreatment coatings of this invention in comparison to prior TCP
coatings without a zinc salt.
[0036] Where large surfaces of aluminum do not permit immersion or
where vertical surfaces are to be sprayed, thickening agents can be
used to retain the aqueous solutions on the surface for sufficient
contact time. The thickeners employed are known water soluble or
dispersible thickeners which can be added to the trivalent chromium
solutions of this invention in amounts ranging from about 0.0 to
about 10 grams per liter and preferably from about 0.5 to 1.5 grams
per liter of the solution. Specific examples of these additives
include the preferred cellulose thickeners e.g. hydroxypropyl
cellulose (e.g. Klucel), ethyl cellulose, hydroxyethyl cellulose,
hydroxyethyl cellulose, methyl cellulose, and some of the other
known water soluble thickeners such as colloidal silica, clays such
as bentonite, starches, colloidal alumina, gum arabic, tragacanth,
agar and any combination thereof.
[0037] For purposes of this invention, the water soluble
surfactants are used in amounts ranging from about 0.0 to about 10
grams per liter and preferably about 0.5 to 1.5 grams per liter of
the TCP solution. The surfactants are added to the aqueous
solutions to provide better wetting properties by lowering the
surface tension thereby insuring complete coverage, and a more
uniform coating on the substrate. The surfactants include at least
one water soluble compound selected from the group consisting of
the non-ionic, anionic and cationic surfactants. Specific water
soluble surfactants include the monocarboxyl imidoazoline, alkyl
sulfate sodium salts (DUPONOL.RTM., tridecyloxy poly(alkyleneoxy
ethanol), ethoxylated or propoxylated alkyl phenol (IGEPAL.RTM.),
alkyl sulfoamides, alkaryl sulfonates, palmitic alkanol amides
(CENTROL.RTM.), octylphenyl polyethoxy ethanol (TRITON.RTM.),
sorbitan monopalmitate (SPAN.RTM.), dodecylphenyl polyethylene
glycol ether (e.g. TERGITROL.RTM.), alkyl pyrrolidone,
polyalkoxylated fatty acid esters, alkylbenzene sulfonates and
mixtures thereof Other known water soluble surfactants are
disclosed by "Surfactants and Detersive Systems", published by John
Wiley & Sons in Kirk-Othmer's Encyclopedia of Chemical
Technology, 3.sup.rd Ed.
[0038] While this invention has 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.
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