U.S. patent application number 10/786340 was filed with the patent office on 2005-08-25 for method of improving the performance of organic coatings for corrosion resistance.
Invention is credited to Gandour, Richard D., Kim, Hyung-Joon, Yoon, Roe-Hoan, Zhang, Jinming.
Application Number | 20050183793 10/786340 |
Document ID | / |
Family ID | 34750486 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183793 |
Kind Code |
A1 |
Kim, Hyung-Joon ; et
al. |
August 25, 2005 |
Method of improving the performance of organic coatings for
corrosion resistance
Abstract
This invention pertains to a method of modifying polymeric
coating materials by adding organosulfur compounds, so that the
metallic substrates coated with the modified polymeric materials
become more resistant to corrosion. The organosufur compounds are
alkane thiols with a general formula R(CH.sub.2).sub.nSH, where R
represents H, NH.sub.2, HOOC, and HO groups and n is in the range
of 10 to 21. The reagents are designed to increase the adhesion
between the polymeric coating materials and the metallic
substrates, which may be conducive to increased corrosion
resistance.
Inventors: |
Kim, Hyung-Joon;
(Pohang-city, KR) ; Zhang, Jinming; (Blacksburg,
VA) ; Gandour, Richard D.; (Blacksburg, VA) ;
Yoon, Roe-Hoan; (Blacksburg, VA) |
Correspondence
Address: |
Donald J. Perreault
Grossman, Tucker, Perreault & Pfleger, PLLC
55 South Commercial Street
Manchester
NH
03101
US
|
Family ID: |
34750486 |
Appl. No.: |
10/786340 |
Filed: |
February 25, 2004 |
Current U.S.
Class: |
148/248 |
Current CPC
Class: |
C09D 5/086 20130101 |
Class at
Publication: |
148/248 |
International
Class: |
C23C 022/05 |
Claims
1. A method of improving the performance of organic conversion
coatings, whose primary ingredients are polymeric resins,
comprising the steps of a. dissolving an organosulfur compound in a
solvent, b. mixing the solution in which said organosulfur compound
is dissolved with a solution in which said polymeric resins are
dissolved, c. coating a metallic substrate with the mixture of the
solutions containing said organosulfur compound and said polymeric
resins, d. curing the metallic substrate coated with said mixture
of the solutions, and thereby increasing the corrosion resistance
of said metallic substrate without using chrome.
2. The method according to claim 1 wherein said organosulfur
compound is selected from the group consisting of alkyl, aryl, and
alkyl-aryl thiols, xanthates, sulfides, disulfides, thiocarbamates,
dithiocarbamates, thioureas, thiophenols, mercaptopyridines,
mercaptoanilines, mercaptoimidazoles, thiophenes, and
thiophosphates.
3. The method according to claim 1 wherein said organosulfur
compound is an alkanethiol with a general formula
R(CH.sub.2).sub.nSH, where R is a terminal group selected from the
group consisting of H--, NH.sub.2--, HOOC--, and HO--, and n
represents the number of hydrocarbons, which can range from 10 to
21.
4. The method according to claim 1 wherein said organosulfur
compound is 1-octadecanethiol.
5. The method according to claim 1 wherein said polymeric resins
are selected from the group consisting of acrylic,
acrylic-urethane, epoxy, polyester, epoxy-polyester or fluorovinyl
polymers, and combinations thereof.
6. The method according to claim 1 wherein said metallic substrate
includes a substrate selected from the group consisting hot rolled
and pickled steel sheet, cold-rolled steel sheet, stainless steel
sheet, hot-dipped metallic coated steel sheets, electroplated
metallic coated steel sheets, aluminum sheets and aluminum alloy
sheets, zinc sheets, zinc alloy sheets, copper sheets, copper alloy
sheets, gold, and silver.
7. The method according to claim 1 wherein said metallic substrate
includes coatings of one or more layers selected from the group
consisting of lead, lead alloy, nickel, nickel alloy, zinc, zinc
layer, tin, and tin alloy.
8. The method according to claim 1 wherein said solvent for said
organosulfur compound is selected from the group consisting of
alcohols, acetone, turpentine, benzene, ethyl and butyl acetate,
toluene, petroleum ester, xylene, alkane, mineral spirit, and
water.
9. The method according to claim 8 wherein a preferred solvent is
selected from the group consisting of ethanol, 1-propanol,
1-butanol, and mixtures thereof.
10. The method according to claim 1 wherein the concentration of
said organosulfur compound in said polymeric resins is in the range
of 0.001-0.5 moles per liter.
11. The method according to claim 1 wherein said metallic substrate
is coated with said mixture of the solutions containing said
organosulfur compound and said polymeric resins by means of a roll
or a bar coater, cured at a temperature in the range of 100 to
350.degree. C. to obtain a desired coating thickness.
12. A method of improving the performance of organic conversion
coatings, whose primary ingredients are polymeric resins,
comprising the steps of a. mixing an organosulfur compound with a
polymeric resin, b. coating a metallic substrate with said
polymeric resin containing said organosulfur compound, c. curing
the metallic substrate coated with said mixture of the solutions,
and thereby increasing the corrosion resistance of said metallic
substrate without using chrome.
13. A method according to claim 12 wherein said metallic substrate
is electrogalvanized steel.
14. A method according to claim 12 wherein said organosulfur
compound is selected from the group consisting of alkyl, aryl, and
alkyl-aryl thiols, xanthates, sulfides, disulfides, thiocarbamates,
dithiocarbamates, thioureas, thiophenols, mercaptopyridines,
mercaptoanilines, mercaptoimidazoles, thiophenes, and
thiophosiphates.
15. The method according to claim 12 wherein said polymeric resins
are selected from the group consisting of acrylic,
acrylic-urethane, epoxy, polyester, epoxy-polyester or fluorovinyl
polymers, and combinations thereof.
Description
FIELD OF THE INVENTION
[0001] This invention applies to polymeric resins that are used to
coat metallic substrates for corrosion protection, and to a method
of modifying the resins with organosulfur compounds for improved
corrosion resistance. In particular, the invention pertains to
preparing a homogeneous mixture of the resin and the organosulfur
compound.
BACKGROUND OF THE INVENTION
[0002] Metals that are exposed to the ambient for prolonged periods
of time require coatings to protect the exposed surface from
corrosion. Steel producers use various organic and inorganic
coatings to protect cold-rolled steel (CRS) sheets from corrosion
during shipment and storage. The common practice in providing
temporary corrosion protection for steel sheets is to apply a
conversion coating. Traditionally, conversion coatings are produced
by exposing untreated or galvanized CRS sheets to phosphoric acid
or chromic acid treatment or both. The latter provides the most
effective corrosion protection. However, increased environmental
and safety concerns on the use of chrome have generated strong
interest in developing chrome-free conversion coatings. Most of the
new developments are based on replacing chromation with organic
coatings.
[0003] It is well known that coating steel with a resin solution
containing an organosilane coupling agent provides corrosion
protection. Woo, et al. (U.S. Pat. No. 5,077,354) disclosed a
method of mixing a silicon resin with ethylenically unsaturated
monomers in a solvent, heating the solution to 50-150.degree. C.,
and agitating the solution until polymerization is complete.
According to van Ooij (U.S. Pat. No. 5,455,080), this method
suffers from the weak bonding between the paint and steel
substrate. The reason is that silicone resin has already been
reacted with the ethylenic monomers when forming the acrylic
polymer, which in turn prevents the silicon resin from acting as a
coupling agent between the outer acrylic layer and the steel
substrate.
[0004] Van Ooij, et al. (U.S. Pat. Nos. 5,455,080; 5,498,481;
5,539,031) disclosed methods of coating CRS or electrogalvanized
(EG) steel with a blended powder mixture comprising a thermosetting
resin, a pigment and non-hydrolyzed organosilane coupling agent.
The mixture contains 0.01-10% by weight of an organosilane whose
melting temperature is lower than the curing temperature of the
resin. It is believed that organosilanes can diffuse toward a metal
surface and form a crosslinked layer during curing step.
[0005] Purnel, et al. (U.S. Pat. No. 5,389,405) and Morris, et al.
(U.S. Pat. No. 5,412,011) disclosed chromium-free conversion
coatings for metal surfaces such as aluminum, steel, and galvanized
steel, which are applied on the surfaces as aqueous solutions of
anionic polyacrylamide copolymer, inorganic silicate, and
organofunctional silane.
[0006] There have been a few attempts to incorporate surfactants
into polymer or other coatings to increase corrosion resistance.
Sankaranaryanan and Subbaiyan (1993) added 1 g/l octadecyl
dithiocarbamate (C.sub.18H.sub.37NHCSSH) to a phosphating bath to
improve the corrosion resistance of phosphated steel. Van Alsten
(1999) added 1,000 ppm of an alkyl bis-phosphonic acid and zinc
acetate to an ethylene and methacrylic acid copolymer. The mixture
is melt-pressed onto CRS panels to form a film of approximately 2
mm in thickness. The film was subsequently cured in a vacuum oven
at 150.degree. C. to allow for the surfactant (i.e., octadecyl
dithiocarbamate) to form self-assembled monolayers (SAMs). Although
the process of forming SAMs from a rather thick polymer melt was
sluggish, using alkyl bis-phosphonic acid and zinc acetate as
additives to polymeric resin improved the coating properties after
several minutes of annealing time.
[0007] Shimakura, et al. (EP 1,002,889) disclosed an anticorrosive
coating composition, comprising a silane coupling agent and an
aqueous resin solution (or suspension). Additionally,
phosphorus-containing ions and/or sulfur-containing compounds can
be added to the coating solution. The sulfur-containing compounds
disclosed in this invention may be selected from the groups
consisting of thio-carbonyls, triazine thiols, sulfide ions, and
persulfate ions.
[0008] Kanai and Shimakura (U.S. Pat. No. 6,607,587) disclosed an
anticorrosive coating for metals, which comprises a resin, water,
water-dispersible silica, and a thio-carbonyl compound.
[0009] Organosulfur compounds have a strong affinity for metal
substrates and can form close packed SAMs on the surface. There
have been attempts to use this SAMs to produce a
corrosion-resistant coating (Jenning, 1996; Nozawa, 1997; Aramaki,
1999; Taneichi, 2001). The invention described herein uses
sulfur-containing organic compounds to modify resin solutions for
forming a durable coating with enhanced corrosion resistance.
SUMMARY OF THE INVENTION
[0010] The instant invention describes a method of improving the
performance of organic conversion coatings for metals by modifying
the compositions of the organic resins by adding an organosulfur
compounds. The improved performance of the modified resin
compositions can protect metal substrates from corrosion without
chromation. Several possible mechanisms may operate to enhance the
properties of the coating:
[0011] i) The sulfur-containing surfactants disclosed in the
instant invention chemisorb on the surfaces of the metallic
substrates, and give rise to improved adhesion of the organic
resins on the substrates.
[0012] ii) The surface free energies of the metallic substrates are
reduced and, therefore, render the substrates less susceptible to
corrosion.
[0013] iii) The small organosulfur compounds as compared to the
molecules of the resins can readily fill the pores of polymer
matrix, thereby increasing the barrier effect for corrosion
protection.
[0014] iv) The organosulfur compounds of the invention may be more
readily oxidized than the substrates, thereby serving as
anti-oxidants.
[0015] The aforesaid organic resins to be used in the instant
invention may be chosen from, but not limited to, acrylic,
acrylic-urethane, epoxy, polyester, epoxy-polyester or fluorovinyl
polymers. The resins may be a single resin or a combination of
several resins that are designed to coat metal substrates for the
purpose of corrosion protection.
[0016] The aforesaid organosulfur compounds that can be used as
modifiers of the organic resins may be selected from but not
limited to thiols, xanthates, alkyl sulfides, alkyl disulfides,
thiocarbamates, dithiocarbamates, thioureas, thiophenols,
mercaptbpyridines, mercaptoanilines, mercaptoimidazoles,
thiophenes, and thiophosphates. Moreover, bifunctional compounds
with two terminal groups, one sulfur-containing and the other a
non-sulfur containing polar group, can serve as modifiers, provided
that both groups are compatible with the afore said organic
resins.
[0017] A distinguishing feature of the instant invention is the
simplicity in coating a metal surface with the modified-resins.
There are no needs to add additional steps or equipment. A mixture
of the resin and organosulfur compounds can be directly applied to
a metal surface by any means that is usually employed for the
original resin. Also, there are no needs to modify the procedures
or equipment involved in curing the coated surface. In fact, the
process as disclosed in the instant invention simplifies the
process by eliminating the chromation step.
[0018] The aforesaid modified resin can contain 0.001-0.5 moles per
liter (M) of organosulfur compounds, preferably in the range of
0.02-0.05 M. This concentration may be used for electrogalvanized
steel. For other metals, the optimal concentrations may differ
slightly.
[0019] The modified-resins can be applied to metal surfaces by a
roll or a bar coater and be cured at a temperature in the range of
100-350.degree. C. The coating thickness may be controlled
according to the needs. For galvanized steels, coating thickness in
the range of 1-2 .mu.m may be sufficient as conversion coatings for
cold-rolled steels.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate an embodiment of
the invention, and, together with the description, serve to explain
the principles of the invention:
[0021] FIG. 1 shows the photographs of the EG steel panels after
250 hours of salt spray tests. The unprotected panel showed red
rust, while the EG steel coated with unmodified resin shows white
rust. The panel coated with a resin containing 1-octadecanthiol
(ODT) shows no sign of rust.
[0022] FIG. 2 is a schematic illustration of a metal substrate
coated with a resin that has been modified with an organosulfur
compound. The triangles, squares and circles represent the
components of the polymer. The rods represent the organosulfur
modifier.
[0023] FIG. 3 shows the hotographs of the EG steel panels after 144
hours of salt spray tests. The unprotected EG steel showed red
rust, while the panel coated with unmodified resin shows signs of
corrosion. The EG steel coated with a resin containing
16-mercaptohexadecanoic acid (MCA) shows no sign of corrosion.
[0024] FIG. 4 shows the photographs of the EG steel panels after
168 hours of salt spray tests. The panels were coated with i) resin
alone, ii) resin mixed with ODT dissolved in ethanol, iii) resin
mixed with ODT dissolved in 1-butanol, and iv) resin mixed with ODT
in 1:1 blend of ethanol and 1-butanol. All ODT solutions were at
0.1 M, and the resin and ODT solutions were blended at 70:30 ratio
by volume.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] A preferred embodiment of the present invention will
hereinafter be described in detail with reference to the
accompanying drawings.
[0026] According to the instant invention, four steps are involved
to coat a metal substrate with the aforesaid modified resin. First,
a solution of organosulfur compound is prepared with a proper
solvent. A separate resin solution is also prepared according to
the prescribed procedure for a particular resin. Second, the
solution of the organosulfur compound is mixed with the resin
solution at an optimal ratio. Third, the mixed solution is then
applied to a metal surface by means of a suitable coating
technique, for example, rolling, dipping, brushing, and spraying.
Fourth, the coating is cured at an appropriate temperature to
solidify the film on the metal substrate. As an alternative to
steps one and two above, the organosulfur compound may be directly
dissolved into the resin solution.
[0027] The organosulfur compounds that can be used for modifying
resins may be selected from thiols, xanthates, alkyl sulfides,
alkyl disulfides, thiocarbamates, dithiocarbamates, thioureas,
thiophenols, mercaptopyridines, mercaptoanilines,
mercaptoimidazoles, thiophenes, and thiophosphates. These reagents
can be of alkyl or aryl compounds, but straight chain alkyl
compounds are preferred. Moreover bifunctional compounds with two
terminal groups, one sulfur-containing and the other non-sulfur
containing polar group, can serve as modifiers, provided that both
groups are compatible with the resin.
[0028] It should be understood that a proper solvent has to be
chosen to make the solution of organosulfur compound compatible
with the resin solution. The compatibility may mean that both
solutions are miscible when mixed together, and a mixture of both
solutions can produce a satisfactory coating without defects. A
proper solvent should be chosen so that the aforesaid
resin-organosulfur mixture can remain stable for a desired period
of time and also have a suitable fluidity. Of course, the solvents
should be environmentally acceptable and have a pleasant odor. The
preferred solvents include, but are not necessarily limited to,
alcohols, acetone, turpentine, benzene, ethyl and butyl acetate,
toluene, petroleum ester, xylene, alkane, mineral spirit, and
water. The particularly preferred solvents of the present invention
are ethanol, 1-propanol, 1-butanol, or their mixture.
[0029] Another critical aspect of the invention is the mixing ratio
between the solutions of the resin and the modifier. The mixing
ratio controls the concentration of modifier in the
resin-organosulfur mixture. In a preferred embodiment, the
concentration of the modifier in the mixture can be in the range of
0.001-0.5 M, preferably in the range of 0.02-0.05 M.
[0030] Another feature of the instant invention is that the
modifiers can be added to a paint, which is a blended resin mixture
containing one or more additional additives such as a pigment and a
filler.
[0031] The modified resin of the invention can provide corrosion
resistance in a variety of metal substrates including, but not
limited to, hot rolled and pickled steel sheet, CRS sheets,
stainless steel sheet, hot-dipped metallic coated steel sheets,
electroplated metallic coated steel sheets, aluminum sheets and
aluminum alloy sheets, zinc sheets, zinc alloy sheets, copper
sheets, copper alloy sheets, gold, and silver. The metallic coating
may include one or more layers of lead, lead alloy, nickel, nickel
alloy, zinc, zinc layer, tin, tin alloy, and the like. A phosphate
conversion coating may also be applied to these steel sheets prior
to being coated with the resin-organosulfur mixture. The metal
substrates may include continuous strip and foil, sheets cut to
lengths as well as bars, angles, tubes and beams.
[0032] As depicted in FIG. 2, the organosulfur modifier may
chemically bind with metal surface and, therefore, enhance the
adhesion between the coating and substrate, giving an improved
resistance to chemical attack, mechanical stress and weathering.
The small organosulfur molecules may also fill the pores present in
the matrix of resin and help reduce the diffusion rate of corrosive
media such as water, oxygen and ions to metal surface. Another
effect of the additives is that organosulfur molecules can orient
over the topmost surface of the resin coating where the terminal
groups of the surfactant may protrude. The orientation of
organosulfur molecules over the topmost surface may be such that
the coating has a lower surface free energy and act as the first
protection against attack by corrosive media. The organosulfur
compounds may also serve as anti-oxidants. The modified resin
coating can significantly improve corrosion resistance when
compared with pure resin coatings because of synergistic effects
between the organosulfur compounds and the cured resin.
[0033] In a preferred embodiment, the organosulfur compound used as
a modifier of a resin to form a protective coating on metal surface
comprise an alkanethiol having the general formula
R(CH.sub.2).sub.nSH, where R is a terminal group, which can be, but
not necessarily limited to. H--, NH.sub.2--, HOOC--, HO--. The
number n represents the length of hydrocarbon chain, which can
range from 7 to 21, and is most preferably 10 and 18. A
particularly preferred embodiment of the present invention is
1-octadecanethiol (ODT, CH.sub.3(CH.sub.2).sub.17SH). Details of a
blended resin-organosulfur mixture of the invention will be better
understood from the following examples.
EXAMPLE 1
[0034] A 0.1-M ODT solution was prepared in ethanol. The resin
solution was prepared by mixing 99 parts of polymer solution and 1
part of inorganic hardener solution, both of which were provided by
a chemical company. The ODT solution and resin solution were
subsequently mixed together in the ratio of 30:70 by volume. The
resultant mixture solution was applied to a test panel of
12.times.7.5 cm by means of a No. 5 bar coater. The panel was an
electrogalvanized (EG) CRS sheet from Pohang Iron and Steel Company
(POSCO). The coated panel was then cured in an oven at a
temperature of 150.degree. C. for 5 minutes. As a result, a
uniform, lightly gray-colored coating was formed on the steel panel
with thicknesses in the range of 1-2 .mu.m. For comparison, another
EG steel panel was coated with the aforesaid resin solution without
ODT. The test panels coated with the resins with and without ODT
were subjected to salt spray test (SST) by following the test
procedures of ASMT B117. Also subjected to SST was another EG steel
panel without any treatment (control).
[0035] FIG. 1 shows the photographs of the three test panels after
250 hours of salt spray tests. White rusts appeared on the surface
of the control panel after 2-4 hours, while the resin coated panel
showed white rusts after 48-72 hours. In contrast, the EG steel
panels that had been coated with ODT-modified resin remained rust
free after 250 hours of SST. The water beads present in the surface
indicate that the surface was still hydrophobic and still remained
resistant to the attack of salt fogs. This example demonstrated
that the corrosion resistance of resin coating on EG steel sheets
can be improved by at least three times with the addition of
ODT.
EXAMPLE 2
[0036] This example illustrates the optimization of the
concentration of ODT as a modifier in the resin. The coatings of
ODT-modified resins were prepared in the same manner as described
in Example 1, but the mixing ratio between resin solution and ODT
solution (0.1M in ethanol) was varied in the range of 90:10 to
40:60 by volume.
[0037] The EG steel panels coated with the ODT-modified resins were
subjected to salt spray tests.
[0038] For comparison, two other EG steel panels were also
subjected to salt spray tests. One was without any treatment, and
the other was coated with the unmodified resin. Still another panel
was treated with chromate rinsing prior to coating it with the
unmodified resin.
[0039] The results of the salt spray tests are given in Table 1. As
shown, even a small amount of ODT added to the resin increased
corrosion resistance considerably. As the ODT dosage was increased,
the corrosion resistance was further increased. At very high
dosages of ODT, the resistance decreased. It appears that the
optimal mixing ratio between the resin solution and 0.1M ODT
solution lies in the range of 70:30 and 60:40 by volume. Under the
optimal conditions, the EG steel coated with ODT-modified resin
were superior to the chrome-rinsed EG steel that had been coated
with unmodified resin.
1TABLE 1 The Results of the Salt Spray Tests Conducted on the EG
Steel Panels Treated with Resins Containing Varying Amounts of 0.1
M ODT-in- Ethanol Solution Composition Initiation of of Mixture
White Surface Resin ODT Rust Free Test Panels and Solution Conc. in
SST Energy Treatment (vol. %) (M) (hours) (mJ/m.sup.2) Ranking EG
-- -- 2-4 45.25 9 EG + Resin 100 0 48-72 44.99 8 EG + Resin/ODT
(90:10) 90 0.01 72-96 44.03 7 EG + Resin/ODT (80:20) 80 0.02
168-192 42.53 5 EG + Resin/ODT (70:30) 70 0.03 264-288 39.93 1 EG +
Resin/ODT (60:40) 60 0.04 264-288 38.13 2 EG + Resin/ODT (50:50) 50
0.05 216-240 42.04 4 EG + Resin/ODT (40:60) 40 0.06 144-168 41.77 6
EG + Chrome + Resin -- -- 240-264 42.89 3
[0040] Also shown in Table 1 are surface free energies of the test
panels. Interestingly, the corrosion resistance was maximum when
the surface free energy of the coated surface was minimum. Thus,
the improvement of corrosion resistance may be partially attributed
to the decrease of surface free energy of the coating.
[0041] Table 2 shows the results of the Tafel studies conducted on
the test panels coated with modified resins. As shown, the density
of the corrosion current reaches a minimum at the optimal mixing
ratios and, hence, at the maximum corrosion resistance. Thus, there
was a clear correspondence between the results of the Tafel studies
and the salt spray tests.
2TABLE 2 Corrosion Currents of the EG Steel Panels Coated at
Different Mixing Ratios between Resin and 0.1 M ODT-in-Ethanol
Solutions Corrosion Current Density (.mu.A/cm.sup.2) Before Soaking
After Soaking in in 1 M NaCl 1 M NaCl solution Treatment solution
for 100 hours EG + Resin 4.21 21.03 EG + Resin/ODT(90:10) 0.09
18.98 EG + Resin/ODT(80:20) 0.08 8.22 EG + Resin/ODT(70:30) 0.002
4.85 EG + Resin/ODT(60:40) 0.003 6.02 EG + Resin/ODT(50:50) 0.02
8.70 EG + Resin/ODT(40:60) 2.28 12.72
EXAMPLE 3
[0042] In this example, a 16-mercaptohexadecenoic acid (MCA,
HS(CH.sub.2).sub.15COOH) was used instead of ODT as a resin
modifier. This reagent was different from ODT in that it was a
bi-functional sulfur-containing compound. A 0.025 M MCA solution
was prepared with ethanol and then mixed with the resin solution at
a ratio of 1:1 by volume, which was not necessarily the optimal
mixing ratio. At this ratio, the resin-organosulfur mixture
contained 0.0125 M MCA. The modified resin was used to coat an EG
steel panel with a No. 5 bar coater. The coated panel was cured at
150.degree. C. for 5 minutes. Under this condition, the coating
thickness would be approximately 1-2 .mu.m. The EG steel panel
coated with the modified resin was subjected to salt spray test.
For comparison, salt spray tests were also conducted on an uncoated
EG steel panel and an EG steel panel that had been coated with the
unmodified resin.
[0043] After 144 hours of salt spray tests, the untreated EG steel
panel showed red rusts, while the panel coated with unmodified
resin showed white rusts. On the other hand, the EG steel panel
coated with the resin modified with MCA exhibited no sign of
corrosion, as shown in FIG. 3.
EXAMPLE 4
[0044] In this example, ODT was dissolved in different solvents and
mixed with the resin solution. The resin-ODT mixtures were used to
coat EG steel panels, which were subsequently subjected to salt
spray tests. The photographs of FIG. 4 were taken after 168 hours
of the salt spray test for the EG steel panels coated with the
following:
[0045] i) resin alone,
[0046] ii) resin-ODT mix (70:30) with 0.1 M ODT-in-ethanol
solution,
[0047] iii) resin-ODT mix (70:30) with 0.1 M ODT-in-1-butanol
solution;
[0048] iv) resin-ODT mix (70:30) with 1:1 mixture of 0.1 M
ODT-in-ethanol and 0.1 M ODT-in-1-butanol solution.
[0049] As shown in FIG. 4, ODT-modified resin greatly increased the
corrosion resistance of the EG steel. Both ethanol and 1-butanol
served as satisfactory solvents for ODT. The resin-ODT mixtures
exhibited low viscosities, but they were not very stable when
ethanol was used as the solvent for ODT. 1-butanol was a better
solvent for ODT and, hence, the resin-ODT mixture was more stable.
However, the resin-ODT mixtures prepared with 1-butanol tended to
be more viscose than the case of using ethanol as solvent. As a
compromise, a blend of ethanol and 1-butanol provided stable
resin-ODT mixtures with low viscosities. Other solvents may be used
as solvents for ODT. It should also be noted here that when
shorter-chain thiols are be used as resin modifiers, solvents of
higher dielectric constants, including water, may be used.
[0050] While this invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not
limited to the disclosed embodiments, but, on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
REFERENCES CITED
[0051] Aramaki, K., Protection of iron corrosion by ultrathin
two-dimensional polymer film of an alkanethiol monolayer modified
with alkylethoxysilanes, Corrosion Science, 41(1999),
1715-1730.
[0052] Jennings, G. K., Paul E. Laibinis, Self-assembled monolayers
of alkanethiol on copper provide corrosion resistance in aqueous
environments, Colloids and Surface A: Physicochemical and
Engineering Aspects, 116(1996) 105-114.
[0053] Nozawa, K., H. Nishihara and K. Aramaki, Chemical
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