U.S. patent application number 11/268406 was filed with the patent office on 2007-05-03 for non-chromium conversion coatings for ferrous alloys.
This patent application is currently assigned to The U.S. of America as represented by the Secretarty of the Navy. Invention is credited to James L. Green, Craig A. Matzdorf, William C. JR. Nickerson, Andrew S. Schwartz.
Application Number | 20070095437 11/268406 |
Document ID | / |
Family ID | 37994716 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070095437 |
Kind Code |
A1 |
Matzdorf; Craig A. ; et
al. |
May 3, 2007 |
Non-chromium conversion coatings for ferrous alloys
Abstract
Composition and process for coating ferrous alloys to improve
the corrosion resistance and adhesive bonding strength of the
alloys. The process comprises using the composition for treating
the ferrous alloys such as steel with an acidic aqueous solution
comprising, per liter of solution, from about 0.1 to 22 grams of
hexafluorozirconates, effective amounts of at least one water
soluble divalent zinc compound, and 0.0 to 10 grams of water
soluble thickeners and/or water soluble surfactants.
Inventors: |
Matzdorf; Craig A.;
(California, MD) ; Nickerson; William C. JR.;
(Hughesville, MD) ; Green; James L.; (Lusby,
MD) ; Schwartz; Andrew S.; (Mechanicsville,
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
US
|
Assignee: |
The U.S. of America as represented
by the Secretarty of the Navy
|
Family ID: |
37994716 |
Appl. No.: |
11/268406 |
Filed: |
November 1, 2005 |
Current U.S.
Class: |
148/273 |
Current CPC
Class: |
C23C 22/34 20130101 |
Class at
Publication: |
148/273 |
International
Class: |
C23C 22/34 20060101
C23C022/34 |
Goverment Interests
ORIGIN OF INVENTION
[0001] 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.
Claims
1. Composition for preparing conversion coatings for ferrous alloys
to improve the corrosion resistance and adhesive bonding strength
of the alloys which comprises an acidic aqueous solution having a
pH ranging from about 2.5 to 5.5 and per liter of solution, from
about 0.1 to 22 grams of hexafluorozirconates, and from about 0.1
gram up to the solubility limit of a divalent zinc compound, from
0.0 to about 10 grams of at least one water soluble thickener and
from 0.0 to about 10 grams of at least one water soluble
surfactant.
2. The composition of claim 1 wherein the pH of the aqueous
solution ranges from about 3.7 to 4.0 and the ferrous alloy is
steel.
3. The composition of claim 1 wherein the hexafluorozirconate is an
alkali metal salt ranging from about 1.0 to 12 grams and the zinc
compound is a divalent zinc salt ranging from about 0.1 to 12 grams
per liter.
4. The composition of claim 3 wherein the thickener is a cellulose
compound ranging from about 0.5 to 10 grams and the surfactant is a
non-ionic surfactant ranging from about 0.5 to 10 grams per
liter.
5. Process for preparing conversion coatings on ferrous alloys to
improve the corrosion resistance and adhesive bonding of the alloys
which comprises treating said alloys with an acidic aqueous
solution having a pH ranging from about 3.7 to 4.0 at temperatures
ranging from about ambient to 200.degree. F.; said acidic aqueous
solution comprising, per liter of solution, from about 0.1 to 22
grams of a hexafluorozirconate, and from about 0.1 gram up to the
solubility limits of a divalent zinc compound, from 0.0 to about 10
grams of at least one water soluble thickener and from 0.0 to about
10 grams of at least one water soluble surfactant.
6. The process of claim 5 wherein the alloy is steel.
7. The process of claim 6 wherein the thickener is a cellulose
compound.
8. The process of claim 6 wherein the zinc compound is zinc
sulfate.
9. The process of claim 6 wherein the zirconate is an alkali metal
hexafluorozirconate.
10. The process of claim 6 wherein the hexafluorozirconate ranges
from about 1.0 to 12 grams, and the zinc compound ranges from about
1.0 to 6.0 grams per liter of solution.
11. The process of claim 6 wherein the zinc compound is zinc
acetate.
12. The process of claim 7 wherein the thickener is a water soluble
alkyl cellulose.
13. The process of claim 5 wherein the divalent zinc compound is
zinc sulfate and the zirconate is potassium
hexafluorozirconate.
14. The process of claim 5 wherein the surfactant is a water
soluble non-ionic, surfactant.
15. The process of claim 14 wherein the zinc compound is present in
the aqueous solution in an amount ranging from about 1.0 to 6.0
grams per liter of solution.
16. The process of claim 15 wherein the zinc compound is divalent
zinc acetate and the surfactant is a non-ionic surfactant.
17. The process of claim 15 wherein the zinc compound is divalent
zinc sulfate present in the aqueous solution in an amount ranging
from about 1.0 to 6.0 grams.
18. Coated ferrous alloy obtained by the process of claim 5.
19. Coated steel obtained by the process of claim 6.
20. Coated steel obtained by the process of claim 10.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] This invention relates to compositions and to the use of
said compositions for pretreating ferrous alloys with effective
amounts of an acidic aqueous solution comprising at least one
fluorometallic compound such as an alkali metal
hexafluorozirconate, divalent zinc compounds, water soluble
surfactants or wetting agents and water soluble thickeners. This
invention relates to compositions and to the process for treating
ferrous alloys such as steel to improve the adhesion bonding and
corrosion resistant properties of the alloys. More specifically,
the process comprises treating ferrous or iron alloys with a
composition comprising an acidic aqueous solution having a pH
ranging from 2.5 to 5.5 which contains effective amounts of at
least one water soluble metal hexafluorozirconate, at least one
water soluble divalent zinc compound, and water soluble thickeners
and/or water soluble surfactants.
[0003] Current surface preparation of ferrous alloys such as steel
include a variety of mechanical and chemical processes, depending
on the application. Phosphate coatings have been used historically
to improve the adhesion of various outer coatings and corrosion
resistance of steel. For example, grit blasting has been used to
improve the adhesion when phosphate coatings were not practical to
apply. In this case, the desired paint primer is applied directly
to the grit-blasted steel which is referred to as the
"direct-to-metal" process. Many organizations rely on the
direct-to-metal technique as the use of phosphate coatings decline
due to their reliance on hexavalent chromium "rinse" for optimum
adhesion and corrosion resistance. While direct-to-metal coating is
straightforward and does not rely on a chemically-produced coating,
it does not provide an optimum-performing coating system. The
absence of a chemical pretreatment lowers the overall corrosion
resistance of the system by allowing undercutting of the paint
primer and sometimes blistering of the primer. This is partially
due to the near ubiquitous use of non-chromated primers for
painting ferrous alloys such as steel. In addition, while
grit-blasting imparts a sound mechanical base for paint adhesion it
is labor intensive and requires application of the grit over all
the steel surface generating large quantities of spent grit that
must be collected and recycled or disposed.
[0004] Further, where there is no corrosion-resistant conversion
coating on the ferrous alloys such as steel there is the problem of
"flash rusting" that occurs after the steel parts are grit blasted
or cleaned, but before the paint can be applied. The requirement to
keep flash rust from occurring places a tremendous burden on
scheduling and does not allow for components to sit for more than a
few hours before being painted. This prevents the metal parts or
components from being allowed to sit overnight or over the weekend
and therefore prevents the work from being completed by the end of
a shift where the parts cannot be painted before the end of a
particular shift. This renders production less productive than it
ordinarily could be. In addition, parts or components that are
processed, but not yet painted that need to be shipped or moved
before painting requires an elaborate and costly protective coating
that must then be subsequently stripped before application of the
outer coating such as paint. A chemical pretreatment for ferrous
alloys that is analogous to an aluminum pretreatment is not
available but would be desirable. Such a coating would impart good
paint adhesion to the alloy e.g. steel without needing a
grit-blasted surface and thereby increase the corrosion resistance
of the painted steel. Moreover, the pretreatment of the alloy would
serve also to prevent flash-rusting and allow for expanded handling
times of the alloy parts before they need to be painted. Such a
pretreatment could be produced by merely immersing the components
or alloy parts in a tank of the pretreating solution or by spraying
the solution onto the alloy or by wiping the solution onto the
alloy.
SUMMARY OF THE INVENTION
[0005] This invention relates to compositions and the process for
preparing conversion coatings on ferrous alloys at ambient
temperatures e.g. ranging from room temperature up to about
160.degree. F. or higher. More specifically, this invention relates
to a process of preparing conversion coatings on ferrous alloys
such as steel to improve its corrosion resistance and adhesion
bonding properties. Specifically, this invention relates to
preparing chromium and nickel-free compositions and the process to
deposit a film or coating made from the compositions on ferrous
alloys e.g. steel, especially non-stainless alloys that are prone
to red rusting. The compositions are referred to herein as "NCP"
for "Non-Chromium Post-Treatment" or "Non-Chromium Process".
[0006] The compositions comprise an acidic aqueous solution having
a pH ranging from about 2.5 to 5.5 which contains a fluoride source
comprising between 0.1 and 22 grams/liter of an metal complex
fluoride, such as potassium or sodium hexafluorozirconate, and from
about 0.1 gram per liter up to the solubility limits of a
water-soluble divalent zinc compound, and from 0.0 to effective
amounts of thickening agents and surfactants.
[0007] It is therefore an object of this invention to provide an
acidic aqueous solution comprising hexafluorozirconates, divalent
zinc compounds for pretreating ferrous alloys to improve its
adhesion and corrosion-resistance properties.
[0008] 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 comprises an alkali metal hexafluorozirconate and divalent
zinc salts for pretreating ferrous alloys such as steel.
[0009] It is another object of this invention to provide a
pretreatment for steel that has a practical color change and
imparts good adhesion without a grit-blasted surface. The
pretreatment process provides improved corrosion resistance of the
painted alloy compared to the alloy painted by the direct-to-metal
method.
[0010] It is a further object of this invention to provide an
acidic aqueous solution having a pH ranging from about 3.7 to 4.0
comprising hexafluorozirconates and divalent zinc salts for
treating ferrous alloys at about room temperature and higher
wherein said acidic solution is substantially free of chromium.
[0011] These and other object of the invention will become apparent
by reference to the detailed description.
DETAILED DESCRIPTION OF THE INVENTION
[0012] This invention relates to compositions and to the process of
using an acidic aqueous solution having a pH ranging from about 2.5
to 5.5, and preferably from about 3.7 to 4.0 for preparing a
conversion coating on ferrous alloys such as steel to improve
adhesion bonding and the corrosion-resistance properties of the
alloys. The process comprises preparing the pretreatment coating by
using an acidic aqueous solution at temperatures ranging from
ambient up to about 160.degree. F. or higher e.g. ranging from
about 70.degree. F. to 200.degree. F. and comprises, per liter of
solution, from about 0.1 to 22 grams and preferably about 1.0 to 12
grams e.g. 6.0 to 8.0 grams of at least one metal
hexafluorozirconate, and from about 0.1 of a gram up to the
solubility limits of a divalent zinc compound e.g. from about 0.1
to 12 or 1.0 to 6.0 grams, from 0.0 to 10 grams and preferably 0.5
to 10 grams of a water soluble thickener, and from 0.0 to 10 grams
and preferably 0.5 to 10 grams of a surfactant. An advantage of the
process is the formation of a pretreatment coating on the alloy
that has a practical color change and imparts good paint adhesion
without a grit-blasted surface.
[0013] After cleaning and deoxidizing or pickling the alloy e.g.
steel substrate via conventional mechanical or chemical techniques,
the coating solution can be applied at about room temperature to
the substrate via immersion, spray or wipe-on techniques similar to
the process used for aluminum pretreatments. Solution dwell time
ranges from about 1.0 to 60 minutes. With this solution, the 1.0 to
10 minute dwell time yields an optimum film for color change, paint
adhesion, and corrosion resistance. More importantly for this
invention, the 1.0 to 10 minute dwell time yields appreciable color
change to the as-deposited coating that ranges from royal blue to
blue-gray depending primarily on the chemical composition of the
aqueous solution. The remaining unreacted solution is subsequently
rinsed from the alloy with tap or deionized water. No additional
post-treatment of the alloy is necessary. The pretreatment coating
is allowed to dry thoroughly before subsequent painting.
[0014] In some processes, depending on the physical characteristics
of the ferrous alloy i.e. steel substrate such as the physical size
of the substrate, the addition of a thickener to the solution 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. The
addition of thickeners, also aids in proper film formation during
large area applications and mitigates the diluent effect of rinse
water that remains on the substrate during processing from previous
steps. This feature of the process yields films that have no
streaks and are an improvement in coloration and corrosion
protection. Water-soluble thickeners such as the cellulose
compounds are present in the acidic aqueous solution in amounts
ranging from about 0.0 to 10 grams per liter and preferably 0.5 to
1.5 e.g., or about 1.0 gram per liter of the aqueous solution.
[0015] In addition, depending on the characteristics of the ferrous
alloy, 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 10 grams and preferably from 0.5
to 1.5 grams e.g. 1.0 gram per liter of the acidic solution. There
are many water soluble surfactants known in the prior art and
therefore for purpose of this invention one or more water soluble
surfactants can be selected from the group consisting of non-ionic,
cationic and anionic surfactants.
[0016] The solution contains effective amounts of at least one
divalent zinc compound to provide color and also to improve
corrosion protection of the alloy when compared to other treatment
and compositions that do not contain zinc. For example, the amount
of the zinc compounds can be varied to adjust the color imparted to
the coating, from as little as about 0.1 grams per liter up to 12
grams per liter e.g. 1.0 to 6.0 grams of Zinc.sup.2+cation. The
divalent zinc can be supplied by any chemical compound e.g. salts
that dissolves in the water in amounts ranging up to the zinc salts
solubility limits and are compatible with the other components in
the acid solution. Divalent zinc compounds that are water soluble
at the required concentrations preferably include, for example,
zinc acetate which is soluble in the solution up to 300 grams per
liter at 20.degree. C., zinc telluride, zinc tetrafluoroborate,
zinc molybdate, zinc hexafluorosilicate, and zinc sulfate which is
soluble in the solution up to 577 grams per liter at about
25.degree. C. and any combination thereof in any ratio.
[0017] The pretreatment or coating of the ferrous alloys can be
carried out at various temperatures including the temperature of
the solution which ranges from ambient e.g. from about room
temperature up to about 160.degree. F. or higher. Room temperature
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 including, for example, oven drying,
forced-air drying, exposure to infra-red lamps, and the like. For
purposes of this invention, the term "ferrous alloys" includes any
iron alloy such as steel containing small but effective amounts of
various other metals and non-metals such as carbon.
[0018] The Examples illustrate the stable solutions of this
invention, and the method of using the solutions in providing color
recognition, improved adhesion bonding and corrosion-resistant
coatings for ferrous alloys.
EXAMPLE 1
[0019] A stable acidic aqueous solution having a pH ranging from
about 3.7 to 4.0 for pretreating steel to provide a
corrosion-resistant and a color recognized coating thereon
comprises, per liter of solution, from about 1.0 to 12 grams of
potassium hexafluorozirconate and about 0.1 to 12 grams of zinc
sulfate.
EXAMPLE 2
[0020] A stable acidic aqueous solution of deionized water for
treating steel to form a corrosion-resistant coating thereon
comprises, per liter of solution, about 4.0 grams of sodium
hexafluorozirconate, about 3.0 grams of zinc sulfate and about 1.0
gram of methyl cellulose.
EXAMPLE 3
[0021] A stable acidic aqueous solution having a pH ranging from
about 2.5 to 5.5 for treating steel to provide a
corrosion-resistant and a color recognized coating thereon
comprises, per liter of solution, about 8.0 grams of potassium
hexafluorozirconate, about 6.0 grams of divalent zinc sulfate and
about 0.1 gram of cellulose (Methocel F4M).
[0022] The conversion coatings were applied to 4130 steel by the
following method:
[0023] The coupons were cleaned in a standard alkaline cleaner
(Turco HTC) at 140-160.degree. F. for 10 minutes. Coupons were then
rinsed and immersed directly into the composition set forth in
Example 1. Coupons were allowed to dwell in the NCP-6 for
approximately 10 minutes, removed, and thoroughly rinsed in
deionized water. Coupons were then allowed to dry in a rack at
ambient conditions overnight. The resulting coating was a dark gray
in color, easily visible from across the laboratory. This is
critical for quality control during processing so that processors
have an easy way to tell that a coating is present. In addition to
the NCP coated 4130 steel, control sets of 4130 were prepared by
cleaning in the same solution and treating with TCP-P (potassium
hexafluorozirconate). A subset of these were grit blasted with
alumina grit media to produce an average profile of 1.0 to 1.5
mils, standard for direct to metal painting. These coupons were
then painted with MIL-C-53022 primer to approximately 1.0 mil
thick. One sub-set was painted with Aqua Zen.TM. "wash primer"
before the primer. Aqua Zen.TM. is an industry standard coating
used to promote adhesion and improve corrosion performance of
coating systems. The painted coupons sat for 14 days at ambient
conditions to allow for the paint to cure. After curing, the
coupons were subjected to paint adhesion and painted corrosion
tests.
[0024] Table 1 describes paint adhesion results. Ratings of 4 and 5
are considered passing, 0 to 3, failing. As shown by the data, NCP
provides excellent paint adhesion to the 4130 steel whether or not
the steel is grit blasted. The NCP also shows better overall
performance than the two controls which are commonly used on DOD
equipment. In this case, the NCP is a better alternative to Aqua
Zen.TM. and shows excellent performance with the MIL-C-53022 primer
without grit blast, where the paint adhesion is very poor with only
the primer. TABLE-US-00001 TABLE 1 COATINGS AND PAINT ADHESION
RESULTS Coating Paint Adhesion Results Grit Blast System Dry 1-day
Wet 4-day Wet 7-day Wet No MIL-C-53022 4 4 0 0 primer only No Aqua
Zen 5 4 3 3 plus MIL-C- 53022 primer No TCP-P plus 5 4 4 4
MIL-C-53022 primer No NCP plus 5 5 5 NA MIL-C-53022 primer Yes
MIL-C-53022 5 5 5 3 primer only Yes Aqua Zen 4 4 3 1 plus MIL-C-
53022 primer Yes TCP-P plus 5 5 5 4 MIL-C-53022 primer Yes NCP plus
5 5 5 NA MIL-C-53022 primer
[0025] In preparing the acidic solutions of this invention, the
water soluble surfactants can be added to the acidic solutions in
amounts ranging from about 0 to 10 grams per liter and preferably
about 0.5 to 1.5 grams or 1.0 gram per liter. 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 iron alloy substrates. The
surfactants include at least one water soluble compound selected
from the group consisting of non-ionic, anionic, and cationic
surfactants. Some known water soluble surfactants include the
monocarboxyl imidoazoline, alkylsulfate sodium salts
(DUPONOL.RTM.), tridecyloxypoly(alkyleneoxy ethanol), ethoxylated
or propoxylated alkylphenols (IGEPAL.RTM.), alkylsulfonamides,
alkaryl sulfonates, the alkylaryl polyether alcohols such as
octylphenoxypolyethoxy ethanol (TRITON.RTM.), sorbitan
monopalnitate (SPAN.RTM.), polyoxyethylenealkylphenyl ethers,
dodecylphenyl polyethyleneglycol ether (TERGITOL.RTM.), alkyl
pyrrolidones, polyalkoxylated fatty acid esters, alkylbenzene
sulfonates and mixtures thereof. Other water soluble surfactants
include the alkylphenol alkoxylates, preferably the nonylphenol
ethoxylates, and adducts of ethylene oxide with fatty amines; see
the publication: "Surfactants and Detersive Systems", published in
Kirk-Othmer's Encyclopedia of Chemical Technology, 3.sup.rd Ed.
[0026] When large surfaces do not permit immersion or where
vertical surfaces are to be sprayed, thickening agents are added to
retain the aqueous solution on the surface for sufficient contact
time. The thickeners employed are preferably the organic water
soluble thickeners added to the coating solutions at sufficient
concentrations ranging from about 0 to 10 grams or 0.5 to 10 grams
per liter and preferably 0.5 to 1.5 grams or 1.0 gram per liter of
the acidic solution. Specific examples of some preferred thickeners
include the cellulose compounds, such as hydroxypropyl cellulose
(Klucel), methyl or ethyl cellulose, hydroxyethyl cellulose,
hydroxymethyl cellulose and mixtures thereof Other water soluble
inorganic thickeners include colloidal silica, clays such as
bentonite, starches, gum arabic, tragacanth, agar and various
combinations thereof.
[0027] After preparing the iron alloy surface to be coated via
conventional techniques, the solution can be applied via immersion,
spray or wipe-on techniques. The solutions can be used at elevated
temperatures ranging up to 160.degree. F. or higher and optimally
applied via immersion to further improve the corrosion resistance
of the coatings. Solution dwell time ranges from about 1 to 60
minutes, and preferably 5 to 15 minutes at about 80.degree. F.
After dwelling, the remaining solution is then thoroughly rinsed
from the alloy with tap or deionized water. No additional chemical
manipulations of the deposited films are necessary for excellent
performance. Moreover, aqueous solutions 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.
[0028] 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.
* * * * *