NON-CHROME PASSIVATION OF STEEL
FIELD OF INVENTION
The present invention relates to non-chromate coatings for metals. More particularly,
the present invention relates to non-chromate coatings for steel surfaces to improve
corrosion resistance and adhesion of paints to the surface. The invention provides a
dried in place coating which is particularly effective at treating galvanized steel coil
strip.
BACKGROUND
The purposes of the formation of a chromate conversion coating on the surface of
galvanized steel are to provide corrosion resistance, improve adhesion of coatings and
for aesthetic reasons. Chromate passivation of a galvanized steel surface is done to
provide corrosion resistance and for aesthetic reasons on materials which are not to be
painted. The conversion coating improves adhesion of coating layers such as paints,
inks, lacquers and plastic coatings. Galvanized steel is typically treated with an
aqueous composition containing hexavalent or trivalent chromium ions with other
additives to create a chromium conversion coating.
Growing concerns exist regarding the pollution effects of chromates discharged into
rivers and waterways by such processes. Because of the high solubility and the
strongly oxidizing character of hexavalent chromium ions, conventional chromate
conversion processes require extensive waste treatment procedures to control their
discharge. In addition, the disposal of the solid sludge from such waste treatment
procedures is a significant problem.
Accordingly, there is a need in the art to provide an effective non-chromate treatment
to provide a dried in place conversion or passivation coating to inhibit metal surface
corrosion and enhance adhesion of paint or other coatings that may be applied to the
metal surface.
SUMMARY OF THE INVENTION
The present invention provides a method of treating the surface of metals, such as
steel or galvanized steel, to provide for the formation of a coating which increases the
corrosion resistance and adhesion properties of the metal surface. The passivation or
.conversion coating formed by the present invention may be dried in place or rinsed.
The methods of the invention comprise contacting the requisite metal surface with a
chromate free aqueous treatment composition comprising: (a) a film forming latex
polymer; (b) a fluoacid; (c) phosphoric acid; and (d) a polyoxyethylene/oxypropylene
block copolymer. Other objects and advantages of the invention will be apparent
from the following description and the appended claims.
DETAILED DESCRIPTION
The inventors have found that an improved, non-chromate conversion or passivation
coating can be provided on metal surfaces, particularly galvanized steel surfaces, by
contacting the surface with an aqueous coating solution or dispersion of:
(a) a film forming latex polymer;
(b) a fluoacid;
(c) phosphoric acid; and
(d) a nonionic polymer surfactant.
Compositions of the invention have been found to provide an aqueous pretreatment
agent for the treatment of galvanized metal surfaces which provides improved
corrosion resistance and adhesion of latex applied coating when the treatment is dried
in place.
As to the film forming latex polymer component, this can be chosen from a wide
variety of materials such as styrene - butadiene copolymers, acrylate resins,
polyvinylacetate, urethanes, amido-amine polymers, and similar materials. Some
At present, it is preferred to utilize "U Car Latex 651" as the film forming latex
polymer component. This is commercially available form Union Carbide and is
reportedly an acrylic copolymer resin emulsion having as major latex components
butyl acrylate, methyl methacrylate, and methacrylic acid polymers.
As to the fluoacid that is present in the treatment formulation, this is preferably a
fluoacid of a Group 1VB metal or mixtures thereof. Fluotitanic acid H2TiF6, is
presently preferred with fluozirconic acid, hfcZrFe, also mentioned as exemplary.
- Combinations of these acids are also used.
As stated above, .phosphoric acid, HsPCU, and salts thereof are also present in the
treatment formulation. The phrase "phosphoric acid" used herein, refers to both the •
acid and salt form.
With regard to the non-ionic polymer surfactant, a polyoxyethylene/oxypropylene
block copolymer is exemplary. The ethylene oxide (EO):propylene oxide (PO) repeat
units of the copolymers may be present in a molar ratio of about 1:1-9; preferably 1:5-
9; most preferably 1:9. Molecular weights of these block copolymers will range from
about 2,000-4,000. These copolymers are commercially available from BASF under
the "Pluronic" trademark. Presently, "Pluronic 101" is preferred for use. This
specific copolymer has a ratio of EO:PO blocks of about 1:9 and a molecular weight
of about 3,300.
Compositions in accordance with the invention are chromate free and include
0.01 -50 wt% film forming latex
0.01-40wt% H3PO4
0.01-30wt% fluoacid
0.01-20 wt% non-ionic polymer surfactant
wherein the weight of the composition is, in total, 100 wt%.
More preferred are compositions having the following range (in wt%) of the
components
l-20wt% film forming latex
l-50wt% H3PO4
] -40 wt% fluoacid
0.01 -15 wt% non-ionic polymer surfactant
remainder water.
The sum of all composition components equals 100 wt%. The pH of the
compositions may vary from about 1.0 to 2.0.
The requisite metal surface may be contacted by the treatment in spray, immersion or
roller applications. The treatment is then dried and the metal surface is ready for
painting or other coating applications.
The conversion or passivation treatment of the present invention is applied to result in
a conversion coating weight of greater than about 1 milligram per square foot to
treated surface with a weight of 2-150 milligrams per square foot being more
preferred. For use in commercial applications, working solutions comprising about 3-
100, preferably 10-100 wt% concentrations of the above "More preferred"
formulation are used to contact the desired metal surfaces.
EXAMPLES
The invention will now be described in conjunction with the following examples
which are to be regarded as being illustrative of certain embodiments of the invention
but should not be viewed to restrict the scope of the same.
Example 1 - Treatment Formulations
One tested treatment candidate formulation "A", was a latex emulsion including the
following components:
1) . U Car Latex 651 5.8 wt% (65% actives)
2) H3PO4 22.0 wt%
.3) Fluotitanic acid 10wt%
4) PluroniclOl 0.5 wt%
5) Water remainder
U Car Latex 651 is an acrylic copolymer resin emulsion having a viscosity 20°C, cP
.(Brookfield, LVT #3, 50 rpm) of 400 and a particle size in microns of 0.45. It is
available from the Union Carbide Corporation of Danbury, Connecticut. Its major
constituents are 1) butyl acrylate, methyl methacrylate, methacrylic acid polymers in
an amount or <65 wt%; 2) water - 35%; 3) glycols, polyethylene, mono [(1,1,3,3-
tetramethylbutyl)phenyl] ether in an amount of less than 2%; and 4) ammonia in 0.2
wt%. It is a white liquid.
PJuronic 101 is a difunctional block copolymer surfactant terminating in primary
hydroxy groups and is available from BASF Corporation in Mount Olive, New Jersey.
It is a block copolymer having hydrophobic propylene oxide (PO) repeat units and
hydrophilic ethylene oxide (EtO) repeat units in a molar ratio of about 9:1. The
overall molecular weight of the copolymer is about 3300.
Test panels for the examples were prepared as follows: G70/70 hot dipped galvanized
steel test panels purchased from ACT Laboratories were spray cleaned with a 3%
aqueous solution of an alkaline surfactant product and then rinsed with DI water and
subsequently coated with the test treatment formulations by spin coat application,
followed by forced air drying.
A. NSS - Neutral Salt Spray Test per ASTM B 117 and rated according to ASTM
D-l 654 (% white rust).
B. Water Resistance - ASTM D 4585 - Water Resistance of Coatings Using
Controlled Condensation wherein condensation is produced by exploring one surface
of a coated specimen tp a heated, saturated mixture of air and water vapor while the
reverse side of the specimen is exposed to the cooling effect of room temperature. (%
white rust).
C. Water Resistance of Coatings' in 100% Relative Humidity according to ASTM
2247-97 (% white rust).
Test Results
Test & Result
Treatment ASTM B117/D1654 ASTM D4585 ASTM D2247 -97;
100% Rel Humidity
48Hrs. NSS 240HrsQCT
408 hours
A 1 0 0
C-l 1 0 0
C-2 100 1 10
C-l is a state of the art, chrome containing hexavalent chromium passivation.
C-2 is commercially available non-chrome passivation.
While this invention has been described with respect to particular embodiments
thereof, it is apparent that numerous other forms and modifications of this invention
will be obvious to those skilled in the art. The appended claims and this invention
generally should be constmed to cover all such obvious forms and modifications
which are within the true spirit and scope of the present invention.
What is claimed is:

CLAIMS
1. A method of forming a conversion or passivation coating on a metal surface
comprising contacting said metal surface with an aqueous treatment composition
comprising:
(a) a film forming latex polymer;
(b) a fluoacid;
(c) phosphoric acid; and
(d) a non-ionic polymeric surfactant.
2. A method as recited in claim 1 wherein said non-ionic polymeric surfactant
comprises a polyoxyethylene/oxypropylene block copolymer.
3. A method as recited in claim 2 wherein said latex polymer comprises an
aery] ate resin.
4. A method as recited in claim 3 wherein acid acrylate resin comprises butyl
acrylate, methyl methacrylate, and methacrylic acid polymers.
5. A method as recited in claim 2 wherein said fluoacid comprises a fluoacid of a
Group IVB metal.
6. A method as recited in claim 2 wherein said poiyoxyethylene/polypropylene
block copolymer comprises a mole ratio of ethylere oxide (EO):propylene oxide (PO)
groups of about 1:1-9.
7. A method as recited in claim 6 wherein said EO:PO molar ratio is about 1:5-9.
8. A method as recited in claim 7 wherein said polyoxyethylene/polypropylene
block copolymer has a molecular weight of about 2,000-4,000.
9. A method as recited in claim 2 wherein said metal surface is a zinc covered
metal surface.
10. A method as recited in claim 2 wherein said metal surface is galvanized steel.
11. A method as recited in ciaim ^ wnerein said metal surface is aluminum.
12. A method as recited in claim 2 wherein said treatment composition is
chromate free.
13. A method as recited in claim 2 further comprising drying said metal after said
coating has been brought into contact with said metal, then painting said metal.
14. Composition for treating metal surfaces to form a conversion or passivation
coating thereon, said composition comprising (a) a film forming latex polymer; (b) a
fi.uoacid of a Group IVB metal; (c) phosphoric acid; and (d) a non-ionic polymeric
surfactant, and water.
15. Composition for treating metal surfaces to form a conversion or passivation
coating thereon, said composition comprising:
0.01-50 wt% of a film forming latex polymer;
0.01-40wt%H3PO4;
0.01-30 wt% fiuoacid;
0.01-20 wt% polyoxyethylene/oxypropylene block copolymer;
remainder water, wherein said composition eauals 100 wt%.
16. Composition as recited in claim 15 wherein said composition is devoid of
chromate, said polyoxyethylene/oxypropylene block copolymer comprising a mole
ratio of ethylene oxide (EO):propylene oxide (PO) groups of about 1:1-9.
17. Composition as recited in claim 16 wherein said EO:PO molar ratio is about
1:5-9 and wherein said polyoxyethylene/oxypropylene block copolymer has a
molecular weight of about 2,000-4,000:
] 8. Composition as recited in claim 17 wherein said EO:PO molar ratio is about
] :9 and said molecular weight is about 3300.
19. Composition as recited in claim 15 wherein said fluoacid comprises fluotitanic
acid.
20. Composition as recited in claim 15, wherein said film forming latex polymer
comprises an acrylate resin.
21. Composition as recited in claim 20 wherein said acrylate resin comprises butyl
acrylate / methyl methacrylate and rhethacrylic acid polymers.