Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITION AND METHOD FOR TREATMENT
OF CONVERSION-COATED METAL SURFACES
t
This invention relates to the treatment of metal
surfaces prior to a finishing operation, such as the
application of a siccative organic coating (also known as
an "organic coating", "organic finish", or simply, "paint")
Specifically, this invention relates to the treatment of
conversion-coated metal with an aqueous solution comprised
of a selected organosilane and a selected Group IVA metal
ion, namely titanium, hafnium, and mixtures thereof with
other Group IVA metal ion. Treatment of conversion coated
metal with such a solution improves paint adhesion and
corrosion resistance.
The primary purposes of applying siccative coatings to
metal substrates (e g, steel, aluminum, zinc and their
alloys) are protection of the metal surface from corrosion
and for aesthetic reasons. It is well-known, however, that
many organic coatings adhere poorly to metals in their
normal state. As a result, corrosion-resistance
characteristics of the siccative coating are substantially
diminished. It is therefore a typical procedure in the
metal finishing industry to subject metals to a
pretreatment process whereby a conversion coating is formed
on the metal surface. This conversion coating acts as a
protective layer, slowing the onset of the degradation of
the base metal, owing to the conversion coating being less
soluble in a corrosive environment than is the base metal.
The conversion coating is also effective by serving as a
recipient for a subsequent siccative coating. The
conversion coating has a greater surface area than does the
base metal and thus provides for a greater number of
adhesion sites for the interaction between the conversion
' coating and the organic finish. Typical examples of such
conversion coatings include, but are not limited to, iron
phosphate coatings, zinc phosphate coatings, and chromate
conversion coatings. These conversion coatings and others
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are well-known in the art and will not be described in any
further detail.
Normally, the application of an organic finish to a
conversion-coated metal surface is not sufficient to
provide the highest levels of paint adhesion and corrosion
resistance. Painted metal surfaces are able to reach
maximum performance levels when the conversion-coated metal
surface is treated with a "final rinse", also referred to
in the art as a"post-rinse" or a "seal rinse", prior to
the painting operation. Final rinses are typically aqueous
solutions containing organic or inorganic entities designed
to improve paint adhesion and corrosion resistance. The
purpose of any final rinse, regardless of its composition,
is to form a system with the conversion coating in order to
maximize paint adhesion and corrosion resistance. This may
be accomplished by altering the electrochemical state of
the conversion-coated substrate by rendering it more
passive or it may be accomplished by forming a barrier film
which prevents a corrosive medium from reaching the metal
surface. The most effective final rinses in general use
today are aqueous solutions containing chromic acid,
partially reduced to render a solution comprised of a
combination of hexavalent and trivalent chromium. Final
rinses of this type have long been known to provide the
highest levels of paint adhesion and corrosion resistance.
Chromium-containing final rinses, however, have a serious
drawback due to their inherent toxicity and hazardous
nature. These concerns make chromium-containing final
rinses less desirable from a practical standpoint, when one
considers such issues as safe handling of chemicals and the
environmental problems associated with the discharge of
such solutions into municipal water streams. Thus, it has
been a goal of the industry to find chromium-free
alternatives which are less toxic and more environmentally
benign than chromium-containing final rinses. It has also
been desirous to develop chromium-free final rinses which
are as effective as chromium-containing final rinses in
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terms of paint adhesion and corrosion resistance
properties.
Much work has already been done in the area of
chromium-free final rinses. Some of these have utilized
.5 either Group IVA chemistry or organosilanes.
US-A-3,695,942 describes a method of treating
conversion-coated metal with an aqueous solution containing
soluble zirconium compounds. US-A-4,650,526 describes a
method of treating phosphated metal surfaces with an
aqueous mixture of an aluminum zirconium complex, an
organofunctional ligand and a zirconium oxyhalide. The
treated metal could be optionally rinsed with deionized
water prior to painting. US-A-4,457,790 describes a
treatment composition utilizing titanium, zirconium and
hafnium in aqueous solutions containing polymers with chain
length from 1 to 5 carbon atoms. US-A-4,656,097 describes
a method for treating phosphated metal surfaces with
organic titanium chelates. The treated metal surface can
optionally be rinsed with water prior to the application of
a siccative organic coating. US-A-4,497,666 details a
process for treating phosphated metal surfaces with
solutions containing trivalent titanium and having a pH of
2 to 7. US-A-5,053,081 describes a final rinse composition
comprising an aqueous solution containing 3-
aminopropyltriethoxysilane and a titanium chelate. In EP-
A-0153973 reactive organosilanes in combination with a
titanium or zirconium-containing component are used to
replace a chromate rinse after conversion coating. In all
of the above examples, the treatment method described
claimed to improve paint adhesion and corrosion resistance.
The levels of paint adhesion and corrosion resistance
afforded by the treatment solutions in the above examples
do not reach the levels desired by the metal finishing
industry, namely the performance characteristics of
chromium-containing final rinses. I have found that
aqueous solutions containing selected organosilane
compounds and Group IVA metal ions, namely, zirconium,
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titanium, hafnium, and mixtures thereof, provide paint
adhesion and corrosion resistance characteristics
comparable to those attained with chromium-containing final
rinses. In many cases, the performance of
conversion-coated metal surfaces treated with
organosilane-Group IVA metal ion solutions in accelerated
corrosion tests exceeds that of conversion-coated metal
treated with chromium-containing solutions.
It is an object of this invention to provide a method
and composition of an aqueous rinse which will impart an
improved level of paint adhesion and corrosion resistance
on painted, conversion-coated metal. The composition is
comprised of an aqueous solution containing a selected
organosilane and a selected Group IVA metal ion, namely,
titanium, hafnium, and mixtures thereof with other group
IVA metal ion, and provides levels of paint adhesion and
corrosion resistance comparable to or exceeding those
provided by chromium-containing final rinses.
It is a further object of the invention to provide a
method and rinse composition which contains no chromium.
A first aspect of the invention includes a rinse
solution for the treatment of conversion-coated metal
substrates for improving the adhesion and corrosion
resistance of siccative coatings, comprising an aqueous
solution of a Group IVA metal ion selected from titanium,
hafnium and mixtures thereof, and an organosilane selected
from methyltrimethoxysilane, phenyltrimethoxys i lane, and
mixtures thereof, with the Group IVA metal ion
concentration selected to provide a pH in the range of
about 2.0 to about 9Ø
A second aspect of the invention provides a rinse
solution for the treatment of conversion-coated metal
substrate comprising an aqueous solution containing a Group
IVA metal ion including hafnium and an organosilane 35 selected from
methyltrimethoxysilane,
phenyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane
and mixtures thereof, with the Group IVA metal ion
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concentration selected to provide a pH in the range of from
about 2.0 to about 9Ø
The invention also includes a method for treating such
materials by applying the rinse solution to the substrate.
5 The rinse solution of the first aspect of the
invention is an aqueous solution containing a selected
organosilane compound and Group IVA metal ions, namely,
hafnium ions. It is intended that the rinse solution
be applied to conversion-coated metal. The formation of
conversion coatings on metal substrates is well-known
within the metal finishing industry. In general, this
process is usually described as a process requiring several
pretreatment stages. The actual number of stages is
typically dependent on the final use of the painted metal
article. The number of pretreatment steps normally varies
anywhere from two to nine stages. A representative example
of a pretreatment process involves a five-stage operation
where the metal to be ultimately painted goes through a
cleaning stage, a water rinse, a conversion coating stage,
a water rinse and a final rinse stage. Modifications to
the pretreatment process can be made according to specific
needs. As an example, surfactants can be incorporated into
some conversion coating baths so that cleaning and the
formation of the conversion coating can be achieved
simultaneously. In other cases it may be necessary to
increase the number of pretreatment stages so as to
accommodate more pretreatment steps.
Examples of the types of conversion coatings that can
be formed on metal substrates are iron phosphates and zinc
phosphates including mixed phosphates based on iron and/or
zinc with other metal ions. Iron phosphating is usually
accomplished in no more than five pretreatment stages,
while zinc phosphating usually requires a minimum of six
pretreatment stages. The number of rinse stages between
the actual pretreatment steps can be adjusted to insure
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that rinsing is complete and effective and so that the
chemical pretreatment from one stage is not carried on the
metal surface to subsequent stages, thereby possibly
contaminating them. It is typical to increase the number
of rinse stages when the metal parts to be treated have unusual geometries or
areas that are difficult for the
rinse water to contact.
The method of application of the pretreatment
operation can be either an immersion or a spray operation.
In immersion operations, the metal articles are submersed
in the various pretreatment baths for defined intervals
before moving on to the next pretreatment stage. A spray
operation is one where the pretreatment solutions and
rinses are circulated by means of a pump through risers
fashioned with spray nozzles. The metal articles to be
treated normally proceed through the pretreatment operation
by means of a continuous conveyor. Virtually all
pretreatment processes can be modified to run in spray mode
or immersion mode, and the choice is usually made based on
the final requirements of the painted metal article. It is
to be understood that the invention described here can be
applied to any conversion-coated metal surface and can be
applied either as a spray process or an immersion process.
The rinse solution of the invention is comprised of an
aqueous solution of a selected organosilane and Group IVA
metal ion. Specifically, the rinse solution is an aqueous
solution containing titanium, or hafnium ions, and mixtures
thereof, whose source can be hexafluorotitanic acid,
hafnium oxychioride and mixtures thereof; and the
organosilane(s) -
One specific titanium source, polyfunctional organic
4k
titanates (significant examples include the reaction
products of tetralkyltitanates with a beta-diketone and an
alkanolamine), has been shown to perform poorly when
combined with organofunctional silanes for use in final
rinse solutions and is therefore preferably not included.
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Where zirconium is also included in the solution, the
source may be, for instance, hexafluorozirconic acid,
zirconium basic sulfate, zirconium hydroxychloride,
zirconium basic carbonate, zirconium oxychloride, zirconium
acetate, zirconium fluoride, zirconium hydroxide, zirconium
orthosulfate, zirconium oxide, zirconium potassium
carbonate.
The rinse solution is prepared by making an aqueous
solution containing the Group IVA metal ion, such that the
pH of the resulting solution is in the range of about 2.0
to 9Ø The salts must be dissolved in 50% hydrofluoric
acid in order to effect dissolution. The rinse solution of
the invention typically contains Group IVA metal ions at a
concentration of at least about 0.005% w/w, i.e. percent by
weight. There is no significant upper limit to the
titanium ion concentration or zirconium, if present. When
hafnium is used in the rinse solution, its concentration
should not exceed about 0.1% w/w. The pH of the rinse
solution is measured; if the pH is outside the desired
range, water or Group IVA metal salt is added to change the
pH to fall within the desired range. Hence, the amount of
Group IVA metal ion present in the finished solution is a
function of the pH. The concentration is not likely to
exceed about 1.0% w/w, and in the case of hafnium, should
not exceed about 0.1% w/w. A selected organosilane in the
concentration range of about 0.1 to 7.0% w/w is added to
the solution containing the Group IVA metal ions described
above. The solution is then mixed for at least 30 minutes
to complete the hydrolysis of the selected organosilane,
after which time the rinse solution is ready to be applied
to conversion-coated metal. The addition of the silane
does not affect the pH of the solution.
A preferred embodiment of the invention is an aqueous
solution containing 0.005 to 0.5% w/w titanium ion and 0.25
to 1% w/w of phenyltrimethoxysilane. The resulting
solution can be effectively operated at pH 2.0 to 5Ø
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Another preferred embodiment of the invention is an
aqueous solution containing 0.005 to 0.1% w/w hafnium ion
and 0.25 to 2% w/w phenyltrimethoxysilane, with the
resulting solution being effectively operated at pH 2.5 to
4.5. -
Another especially preferred embodiment of the
invention is an aqueous solution containing 0.005 to 0.6%
w/w titanium ion and 0.5 to 7%- w/w of
methyltrimethoxysilane. The resulting solution can be
effectively operated at pH 3.0 to 8Ø
Another especially preferred embodiment of the
invention is an aqueous solution containing 0.005 to 0.09%
w/w hafnium ion and 0.25 to 6% w/w methyltrimethoxysilane
with the resulting solution being effectively operated at
pH 3.0 to 5Ø
Another especially preferred embodiment of the
invention is an aqueous solution containing 0.005 to 0.1%
w/w hafnium ion and 0.25 to 1% w/w phenyltrimethoxysilane,
with the resulting solution being effectively operated at
pH 2.5 to 4.5.
Another especially preferred embodiment of the
invention is an aqueous solution containing 0.005 to 0.1%
w/w hafnium ion, 0.005 to 0.3% w/w zirconium ion, 0.005 to
0.5g w/w titanium ion and 0.1 to 2% w/w
phenyltrimethoxysilane, with the resulting solution being
effectively operated at pH 2.5 to 4Ø
Another especially preferred embodiment of the
invention is an aqueous solution containing 0.005 to 0.1%
w/w hafnium ion, 0.005 to 0.6% w/w zirconium ion, 0.005 to
0.4% w/w titanium ion and 0.5 to 6-% w/w
methyltrimethoxysilane, with the resulting solution being
effectively operated at pH 2.5 to 6Ø
An especially preferred embodiment of the second
aspect of the invention is an aqueous solution containing
0.005 to 0.1% w/w hafnium ion and 1 to 3% w/w 3-
glycidoxypropyltrimethoxysilane, with the resulting
solution being effectively operated at pH 2.5 to 4Ø
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Another especially preferred embodiment of the second
aspect of the invention is an aqueous solution containing
0.005 to 0.1% w/w hafnium ion, 0.005 to 0.4% w/w zirconium
ion, 0.005 to 0.4% w/w titanium ion and 0.25 to 4% w/w 3-
.5 glycidoxypropyltrimethoxysilane, with the resulting
solution being effectively operated at pH 2.5 to 5Ø
Another preferred embodiment of the second aspect of
the invention is an aqueous solution containing 0.005 to
0.1% w/w hafnium ion and 0.25 to 6% w/w 3-
glycidoxypropyltrimethoxysilane, with the resulting
solution being effectively operated at pH 2.5 to 4Ø
The rinse solution of the invention can be applied by
various means, so long as contact between the rinse
solution and the conversion-coated substrate is effected.
The preferred methods of application of the rinse solution
of the invention are by immersion or by spray. In an
immersion operation, the conversion-coated metal article is
submersed in the rinse solution of the invention for a time
interval from about 15 sec to 3 min, preferably 45 sec to
1 min. In a spray operation, the conversion-coated metal
article comes in contact with the rinse solution of the
invention by means of pumping the rinse solution through
risers fashioned with spray nozzles. The application
interval for the spray operation is about 15 sec to 3 min,
preferably 45 sec to 1 min. The rinse solution of the
invention can be applied at temperatures from about 5 C to
85 C, preferably 16 C to 32 C. The conversion-coated metal
article treated with the rinse solution of the invention
can be dried by various means, preferably oven drying at
about 130 C for about 5 min. The conversion-coated metal
article, now treated with the rinse solution of the
invention, is ready for application of the siccative
coating.
EXAMPLES
The following examples demonstrate the utility of the
rinse solution of the invention. Comparative examples
include conversion-coated metal substrates treated with a
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chromium-containing rinse and conversion-coated metal
substrates treated with an organosilane-organotitanate
final rinse solution as described in US-A-5,053,081,
specifically 3-glycidoxypropyltrimethoxysilane at 0.35%
.5 w/w. The TYZOR CLA at 0.5% w/w. The TYZOR CLA is used to
promote adhesion. Throughout the examples, specific
parameters for the pretreatment process, for the rinse
solution of the invention, for the comparative rinses and
the nature of the substrate and the type of siccative
10 coating are described.
All treated and painted metal samples were subjected
to accelerated corrosion testing. In general, the testing
was performed according to the guidelines specified in ASTM
B-117-85. Specifically, three identical specimens were
prepared for each pretreatment system. The painted metal
samples received a single, diagonal scribe which broke
through the organic finish and penetrated to bare metal.
All unpainted edges were covered with electrical tape. The
specimens remained in the salt spray cabinet for an
interval that was commensurate with the type of siccative
coating that was being tested. Once removed from the salt
spray cabinet, the metal samples were rinsed with tap
water, dried by blotting with paper towels and evaluated.
The evaluation was performed by scraping away the loose
paint and corrosion products from the scribe area with the
flat end of a spatula. The scraping was performed in such
a manner so as only to remove loose paint and leave
adhering paint intact. In the case of some organic
finishes, like powder coating, removal of the loose paint
and corrosion products from the scribe was accomplished by
means of a tape pull as specified in ASTM B-117-85. Once õ
the loose paint was removed, the scribe areas on the
specimens were then measured to determine the amount of
paint lost due to corrosion creepage. Each scribe line was
measured at eight intervals, approximately 1 mm apart,
measured across the entire width of the scribe area. The
eight values were averaged for each specimen and the
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averages of the three identical specimens were averaged to
arrive at the final result. The creepage values reported
in the following tables reflect these final results.
EXAMPLE 1
Cold-rolled steel test panels from Advanced Coating
Technologies, Hillsdale, Michigan were processed through a
five stage pretreatment ope,r,ation The panels were cleaned
*
with Ardrox, Inc. Chem Clean 1303, a commercially available
alkaline cleaning compound. Once rendered
water-break-free, the test panels were rinsed in tap water
and phosphated with Ardrox, Inc. Chem Cote* 3011, a
commercially available iron phosphate. The phosphating
bath was operated at about 6.2 points, 60 C, 3 min contact
time, pH 4.8. After phosphating, the panels were rinsed in
tap water and treated with various final rinse solutions
for 1 min. The comparative chromium-containing rinse was
Ardrox, Inc. Chem Seal" 3603, a commercially available
product. This bath was run at 0.25% wfw. In accordance
with normal practice in the metal finishing industry,
panels treated with the chroinium-containing final rinse (1)
were rinsed with deionized water prior to dry off. The
comparative chromium-free final rinse (2) contained 0.35%
w/w 3-glycidoxypropyltrimethoxysilane and 0.5% w/w TYZOR
CLA. All panels were then dried in an oven at 130 C for 5
min.
The conversion-coated test panels were painted with a
melamine polyester organic finish. The various final
rinses are summarized as follows.
1. Chem Seal 3603, chromium-containing final rinse.
2. Comparative chromium-free final rinse.
3. phenyltrimethoxysilane, 0.25% w/w, pH 2.88, Ti
concentration, 0.026% w/w.
4. phenyltrimethoxysilane, 0.5% w/w, pH 4.32, Ti
concentration, 0.0144 w/w
5. phenyltrimethoxysilane, 1.0% w/w, pH 3.20, Ti
concentration, 0.0464 w/w.
* trade-mark
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The salt spray results are described in Table 1. The
values represent total creepage about the scribe area in
mm. The numbers in parentheses represent the exposure
interval for that particular organic finish.
TABLE I
Final Rinse No. Melamine-Polyester (336 hr)
1 2.6
2 37.1
3 5.1
4 2
5 4.4
EXAMPLE 2 _
Another set of cold-rolled steel test panels was
prepared using the parameters described in Example 1. The
conversion-coated test panels were painted with the
melamine polyester organic finish that was used in Example
1. The various final rinses are summarized as follows.
1. Chem Seal 3603, chromium-containing final rinse.
2. Comparative chromium-free final rinse.
6. methyltrimethoxysilane, 0.5% w/w, pH 4.15, Ti
concentration, 0.035% w/w.
7. methyltrimethoxysilane, 1.0% w/w, pH 8.00, Ti
concentration, 0.042% w/w.
8. methyltrimethoxysilane, 2.0% w/w, pH 4.81, Ti
concentration, 0.030% w/w.
9. methyltrimethoxysilane, 6.0% w/w, pH 3.06, Ti
concentration, 0.053% w/w.
10. methyltrimethoxysilane, 7.0% w/w, pH 4.76, Ti
concentration, 0.026% w/w.
The salt spray results are described in Table II. The
values represent total creepage about the scribe area in
mm. The numbers in parentheses represent the exposure
interval for that particular organic finish.
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TABLE II
Final Rinse No. Melamine-Polyester (336 hr)
1 2.6
2 37.1
6 1.1
7 2.5
8 2.8
9 2.5
2.3
EXAMPLE 3
Another set of cold-rolled steel test panels was
prepared using the parameters described in Example 1. The
conversion-coated test panels were painted with the
melamine polyester organic finish that was used in Example
1, a high solids polyester (designated as High-Solids
Polyester), and a baking enamel. The various final rinses
are summarized as follows.
1. Chem Seal 3603, chromium-containing final rinse.
11. phenyltrimethoxysilane, 0.25% w/w, pH 3.72, Hf
concentration, 0.055% w/w.
12. phenyltrimethoxysilane, 0.5% w/w, pH 4.22, Hf
concentration, 0.10% w/w.
13. phenyltrimethoxysilane, 1.0% w/w, pH 2.56, Hf
concentration, 0.082% w/w.
14. phenyltrimethoxysilane, 2.0% w/w, pH 3.97, Hf
concentration, 0.051% w/w.
The salt spray results are_ described in Table III.
The values represent total creepage about the scribe area
in mm. The numbers in parentheses represent the exposure
interval for that particular organic finish.
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TABLE III
Fina1 Rinse No. Melamine-Polyester High-Solids Polyester Baking Enamel
(240 hr) (168 hr) (240 hr) 1 9.1 4.3 4.2
11 6 3.4 9.5
12 4.7 4.3 9.9
13 2 5 12.9
14 11.8 5.1 9.3
IF 10 EXAMPLE 4
Another set of cold-rolled steel test panels was
prepared using the parameters described in Example 1. The
conversion-coated test panels were painted with the three
organic finishes used in Example 3. The various final
rinses are summarized as follows.
1. Chem Seal 3603, chromium-containing final rinse.
15. methyltrimethoxysilane, 0.25% w/w, pH 3.53, Hf
concentration, 0.034% w/w.
16. methyltrimethoxysilane, 0.5% w/w, pH 4.05, Hf
concentration, 0.066% w/w.
17. methyltrimethoxysilane, 1.0% w/w, pH 4.44, Hf
concentration, 0.017% w/w.
18. methyltrimethoxysilane, 2.0% w/w, pH 3.91, Hf
concentration, 0.071% w/w.
19. methyitrimethoxysilane, 4.0% w/w, pH 3.41, Hf
concentration, 0 058% w/w.
20. methyltrimethoxysilane, 6.0% w/w, pH 4.53, Hf
concentration, 0.087% w/w.
The salt spray results are described in Table IV. The
values represent total creepage about the scribe area in
mm. The numbers ln parentheses represent the exposure
interval for that particular organic finish.
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TABLE IV
Final Rinse No. Melamine-Polyester High-Solids Polyester Baking Enamel
, (240 hr) (168 hr) (240 hr)
1 9.1 4.3 4.2
15 4.2 1.4 4.3
5 16 1.3 0.8 1.6
17 0.7 0.9 1.3
18 0.5 0.5 1.1
19 0.5 0.7 0.9
0.5 0.5 1.1
EXAMPLE 5
Another set of cold-rolled steel test panels was
prepared using the parameters described in Example 1. The
conversion-coated test panels were painted with the three
organic finishes used in Example 3. The various final
rinses are summarized as follows.
1. Chem Seal 3603, chromium-containing final rinse.
2. Comparative chromium-free final rinse.
21. 3-glycidoxypropyltrimethoxysilane, 0.25% w/w, pH 3.23,
Zr concentration, 0.35% w/w, Hf concentration, 0.080% w/w.
22. (comparative) 3-glycidoxypropyltrimethoxysilane, 0.5%
w/w, pH 3.72, Zr concentration, 0.48% w/w.
23. 3-glycidoxypropyltrimethoxysilane, 1.0% w/w, pH 3.25,
Zr concentration, 0.18% w/w, Ti concentration, 0.39% w/w,
Hf concentration, 0.050% w/w.
24. 3-glycidoxypropyltrimethoxysilane, 2.0% w/w, pH 4.02,
Ti concentration, 0.02% w/w, Hf concentration, 0.090% w/w.
The salt spray results are described in Table V. The
values represent total creepage about the scribe area in
mm. The numbers in parentheses represent the exposure
interval for that particular organic finish.
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TABLE V
Final Rinse No. Melamine-Polyester High-Solids Polyester Baking Enamel
(240 hr) (168 hr) (240 hr)
1 6.9 4.3 4.2
2 32 26.3 28.3
21 4.4 1.9 5.7
22 8 2.5 5.3
23 12.5 3.2 6.3
24 6.7 2.8 2
EXAMPLE 6
Another set of cold-rolled steel test panels was
prepared using the parameters described in Example 1. The
conversion-coated test panels were painted with the three
organic finishes used in Example 3. The various final
rinses are summarized as follows.
1. Chem Seal 3603, chromium-containing final rinse.
2. Comparative chromium-free final rinse.
25. phenyltrimethoxysilane, 0.1% w/w, pH 2.98, Zr
concentration, 0.23% w/w, Hf concentration, 0.060% w/w.
26. phenyltrimethoxysilane, 0.5% w/w, pH 3.54, Ti
concentration, 0.46% w/w.
27. phenyltrimethoxysilane, 1.0% w/w, pH 3.98, Zr
concentration, 0.09% w/w, Ti concentration, 0.47% w/w.
The salt spray results are described in Table VI. The
values represent total creepage about the scribe area in
mm. The numbers in parentheses represent the exposure
interval for that particular organic finish.
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TABLE VI
Final Rinse No. Melamine-Polyester High-Solids Polyester Baking Enamel
(240 hr) (168 hr) (240 hr)
1 6.9 4.3 4.2
2 32 26.3 28.3
25 3.2 1.5 3.4
26 5.3 2.7 11.7
27 3.2 1.6 9
EXAMPLE 7
Another set of cold-rolled steel test panels was
prepared using the parameters described in Example 1. The
conversion-coated test panels were painted with the three
organic finishes used in Example 3. The various final
rinses are summarized as follows.
1. Chem Seal 3603, chromium-containing final rinse.
2. Comparative chromium-free final rinse.
28. methyltrimethoxysilane, 0.5% w/w, pH 3.47, Zr
concentration, 0.53% w/w, Ti concentration, 0.18% w/w, Hf
concentration, 0.030% w/w.
29. methyltrimethoxysilane, 1.0% w/w, pH 4.46, Zr
concentration, 0.17% w/w, Ti concentration, 0.14% w/w, Hf
concentration, 0.080% w/w.
30. methyltrimethoxysilane, 3.0% w/w, pH 3.54, Hf
concentration, 0.070% w/w.
31. methyltrimethoxysilane, 6.0% w/w, pH 4.86, Zr
concentration, 0.09% w/w, Ti concentration, 0.31% w/w, Hf
concentration, 0.040% w/w.
The salt spray results are described in Table VII.
The values represent total creepage about the scribe area
in mm. The numbers in parentheses represent the exposure
interval for that particular organic finish.
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TABLE VII
Final Rinse No. Melamine-Polyester High-Solids Polyester Baking Enamel
(240 hr) (168 hr) (240 hr)
1 6.9 4.3 4.2
2 32 26.3 28.3
28 2.8 1.7 2.4
29 1.3 1 1
30 1.2 0.4 1.1
31 2.2 0.9 1.9
EXAMPLE 8
Another set cold-rolled steel panels was prepared
using the parameters described in Example 1. The
conversion-coated test panels were painted with the
melamine-polyester organic finish that was used in Example
1, and the high solids polyester and baking enamel used in
Example 3. The various final rinses are summarised as
follows:
1. Chem Seal 3603, chromium-containing final rinse.
32. 3-glycidoxypropyltrimethoxysilane, 0.25% w/w, pH 2.83,
Hf concentration, 0.088% w/w.
33. 3-glycidoxypropyltrimethoxysilane, 1.0% w/w, pH 3.84,
Hf concentration, 0.098% w/w.
34. 3-glycidoxypropyltrimethoxysilane, 2.0% w/w, pH 2.69,
Hf concentration, 0.069% w/w.
35. 3-glycidoxypropyltrimethoxysilane, 3.0% w/w, pH 3.25,
Hf concentration, 0.040% w/w.
36. 3-glycidoxypropyltrimethoxysilane, 6.0% w/w, pH 2.90,
Hf concentration, 0.034% w/w.
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19
TABLE VIII
Final Rinse No. Melamine-Polyester High-Solids Polyester Baking Enamel
(240 hr) (168 hr) (240 hr)
1 9.1 4.3 4.2
32 13.2 4.6 11.3
33 5.9 2.3 3.0
34 4.3 1.9 2.9
35 6.9 3.8 6.1
36 5.5 4.6 6.1
CONCLUSIONS
The results from accelerated corrosion testing
demonstrated in Examples 1 to 8 show that rinse solutions
containing a selected organosilane and the selected Group
IVA metal ion(s) provided substantially better performance
than the comparative chromium-free rinse. The results
demonstrated in Examples 1 to 8 also- show that rinse
solutions containing a selected organosilane and Group IVA
metal ion, namely titanium, hafnium and mixtures thereof
with each other and with zirconium, provided, in many
cases, corrosion resistance comparable to that of a
chromium-containing rinse, such as Final Rinse No. 1. In
several instances, the rinse solutions provided
significantly higher levels of corrosion resistance than
that achieved with a chromium-containing rinse.
