Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PRETREATING COMPOSITION CONTAINING S-TRIAZINE COMPOUND
Background of the Inv~ntion
4 Field of the Invention: The present invention relates to a
pretreatment composition whlch i5 free of chromic acid; said compositlon
6 is particularly useful as a final rinse in a metal pretreatment process.
8 Brief DescriRtion of the Prior Art
In the metal pretreatment process, it is known to employ a
10 phosphating conversion coating which is usually followed by a final
rinsing or sealing step. The rinsing composition usually comprises
12 chromic acld. While effective in the rinsing step, chrom~c acid is,
nonetheles6, undesirable because of its toxicity and the attendant
14 problems of disposal.
Hence, considerable work has been done in finding a
16 replacement for chromic acid in the final rinsing step. The present
invention pro~ides a pretreatment compo6ition which is essentially free
18 of chromic acid.
Summary of the Invention
In accordance with the foregoing, the present invention
22 encompasses an aqueous composition comprising an S-triazine having at
least one hydroxyl group on a carbon atom of the triazine ring
24 (hereinafter "S-triazine compound") adapted for use for pretreating a
ferrous or non-ferrous metal surface. The aqueous composltion of the
26 S-triazine compound contains at least about O.Ol percent by weight or
higher of the S-triazine compound based on the total weight of the
28 composition, and can have a pH of about 3.4 to 6 and a temperature
typically from about 30~C to 80~C. The S-triazine compound is preferably cyanuric acid.
The in~ention further encompa6ses a process of pretreat~ng a
metal 6urface comprlsing applying an effective aqueous composition of
32 the S-triazlne compound to the metal surface to produce a corrosion
re6istant surface that can adhere to a subsequently applied coating.
34 Preferably, the aqueous composition of the S-triazine compound is
employed as a final rinse o~er a metal surface comprising a conversion
36 coating such as a phosphate conversion coating.
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Detailed Description of the Invention
2 The S-triazine compound or a modification thereof which,
useful herein, is one that enolizes in a manner that renders the aqueous
4 composition containing the same acidic. While not desiring to be bound
to any particular theory, it is believed that the enolized form of the
6 S-triazine compound is reactable with the metal surface. The enol form
of the preferred S-triazine compound is commonly referred to as cyanuric
8 acid. In accordance with this invention, the S-triazine compound or a
modification thereof useful herein is characterized as having at least
10 one hydroxyl group on a carbon atom of the triazine ring.
The useful S-triazine compound must be compatible with an
12 aqueous medium, i.e., it is mixable to produce an effective aqueous
composition that can be applied to a substrate to produce a corrosion
14 resistant surface that can adhere to a subsequently applied coating.
Typically, it must have solubility of at least about 0.01 gram per 100
16 grams of water at 25~C. The aqueous composition of this invention can
be prepared by mixing the S-triazine compound with an aqueous medium,
18 preferably at a temperature of about 30~C to 80~C and more preferably
about 40~C to 80~C. By an aqueous medium is meant water or water in
20 combination with an adjuvant that can enhance the solubility of the
S-triazine compound. The aqueous composition may also contain an
22 additive such as a pH buffer, phosphate, borate, potassium salt or the
like or a mixture thereof.
24 Accordingly, the aqueous pretreating composition of this
invention can have a pH of about 3.4 to 6 and preferably about 4.0 to
26 5Ø The composition can contain about 0.01 to 0.2 percent by weight
and preferably about 0.05 to 0.15 percent by weight of the S-triazine
28 compound based on the total weight of the composition. While higher
amounts of the S-triazine compound can be employed in the aqueous
30 composition, it does not appear that there is an improvement in
performance of such a composition. However, under certain
32 circumstances, the higher concentration in the form of a concentrate
may be desirable, for reasons such as ease of handling.
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The aqueous composition of the S-triazine compound i8 applied
2 under conditions that produce a corrosion-resistant barrier which is
receptive to a subsequent coating process such as a conventional coating
4 or electrocoating. The temperature of the aqueous compo6ition at ~hich
a substrate i8 treated therewith is typically from about 30~C to 80~C
6 and preferably about 40~C to 60~C. The pH of the-treating composition
during application i8 typically about 3.4 to 6 and preferably about 4
8 to 5Ø
In the process of this invention, the aqueous composition of
10 the S-triazine compound iB employed in treating a ferrous or non-ferrous
metal such a8 cold rolled steel, galvanized steel or the like.
12 Preferably, the aqueous composition is applied to a metal surface
comprising a conversion coating such as a phosphated conversion
14 coating; a zinc phosphate conver~ion coating is preferret herein. The
aqueous composition contn~n~ng the S-triazine compound i8 applied to
16 the metal surface by spraying, immersion or any other convenient
means. After the aqueous composition has been applied, the metal is
18 usually rinsed with deionized water and then coated with a surface
coating, usually after it has been dried.
In a typical pretreatment process, the metal to be treated i8
cleaned by a physical or chemical means and water rinsed in order to
22 remove surface contamination such as grease or dirt. The metal surface
iB then brought into contact with a conversion coating composition,
24 rinsed with water and then rinsed with the composition of this
invention. After the application of the aqueous solution of the
26 S-triazine compound with rinsing and drying, the ferrous or non-ferrous
metal can be coated by any convenient means. It has been found that
28 the pretreatment process of the metal with the aqueous composition of
the S-triazine compound imparts to the coated substrate improved
30 adhesion and corrosion resistance properties.
The invention iB further illustrated by the following
32 non-limiting examples.
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EXAMPLE 1
2 Hot dipped galvanized steel panels were phosphated with
CHEMFOS 710 zinc nickel manganese phosphating solution (from Chemfil
4 Corporation) at an average coating weight of 270 mg/ft2. The panels
were then rinsed with water to remove residual phosphating chemicals
6 and then immersed for 30 seconds in an aqueous solution of cyanuric
acid at 120~F. Two concentrations of the cyanuric acid solutions were
8 employed: 0.1 and 0.2 percent by weight cyanuric acid in city water. The
measured pH's were 4.0 and 3.4, respectively. The panels were dried
10 with a compres6ed air jet and primed the same day with ED3150W
electrodeposition primer (from PPG Industries, Inc., herein "PPG") at
12 about 240 volts giving about 1.2 to 1.6 mils dry film thickness. The
panels were 6ubsequently top coated with HUBC 90270 white basecoat
14 (from PPG) at about .9 mils and then with URC 1000 clearcoat (from PPG)
at about 1.9 mils. The panels were then prepared for testing by
16 scribing and abrading with steel shot according to the "CHRYSLER"
chipping scab test procedure, as follows.
18 1) 4" x 12" test panels were coated as described above.
2) The top half of the panel was scribed with a 12 cm (4.7")
'~" scribe. A strip of pull tape was firmly applied to one
side of the "X" and removed in a rapid vertical motion.
22 Repeat of this procedure was conducted with the other side of
the '~-"
24 3) The air pressure of the gravelometer (from the Q-Panel
Compan~) was adjusted to 205 kPa (30 psi).
26 4) The air valve of the gravelometer was shut off and 200 ml
(32 oz.) of steel shot was collected.
28 5) A test panel was placed in the panel holder with the
coated side facing the gravel projecting mechanism of the
gravelometer. The lid of the test chamber was then closed.
6) The air valve was opened to let the pressure stabilize.
32 Two h~ndred milliliters (200 ml) (32 oz.) of shot was poured
into the hopper. The air was turned off when all of the shot
34 had been spent.
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7) The panel was placed in S percent by weight salt solution (pH of
2 about 6.6 to 7.1) for a ;n~-, of lS minutes.
8) The panel was removed and allowed to recover at lab
4 conditions for 1 hour and lS minutes and then placed in
humidity cablnet for 22.5 hours.
6 An "accelerated" test was conducted as follows:
a) The humidity cabinet was set at 85 percent relative
8 humidity and 60~C (140~F).
b) A cycle program as outlined in steps 7 to 8 was run
over a period of four days.
c) Thereafter (on the fifth day), the panel was removed
12 from the humidity cabinet and within 30 minutes, steps 3
to 8, as set forth above, were followed.
14 d) At the conclusion of a five-week cycle of steps a - c
(after step 6), the panels were washed with sponge and
16 water (a mild detergent could be used). Excess water
was removed and the panel(s) were allowed to recover for
18 30 minutes.
e) The target areas was covered with pull tape and
removed as outlined in step 2.
f) The percent paint loss in the target area was
22 estimated.
CONTROL: Control panels were also prepared wlth CHEMSEAL 20
24 chrome rinse (from Chemfil Corporation) and with a deionized water
rinse for comparison purposes. Triplicate panels were prepared for
26 each system and subjected to the same CHRYSLER chipping scale test as
described above. The total test period was 10 weeks. The panels were
28 evaluated according to the amount of paint removed by taping with #898
3M SCOTCH tape after the test period. The results of the tests are
30 reported in Table I hereinbelow.
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TABLE I
~F~uLTsPAINT ADHESION LOSS
4 .1% aqueous composition
of cyanuric acid rinse 4%
.2% aqueous composition
8 cy~n~ric acid rinse 4%
C~M.~AT. 20 chrome rinse 10%
12 Deionized water rinse 2470
14
EXAMPLE 2
16 Cold rolled steel (CRS) and hot dipped galvanized (HDG)
panels were phosphated with CHEMFOS 86 zinc nickel phosphate (from
18 Chemfil Corporation) at about 230 mg/ft2. After rinsing with water,
the panels were immersed for 30 seconds in a .1 percent by weight solution of
20 cyanuric acid in water at 120~F, pH at 4.1.
Control6 for comparison were made with CHEMSEAL 20 chrome
22 rinse and with deionized water. The series were rinsed with deionized
water, dried with a compressed air jet, and primed with UNI-PRIME
24 electrocoat (from PPG) at 240 volts for 1.2 mils thicknes6 on cold
rolled steel. The panels were top coated with HUBC 90270 white
26 ba6ecoat at 1.0 mils and URC 100~ clearcoat at 1.6 mils. Triplicate
panels were prepared and tested according to the CHRYSLER chipping scab
28 test described in Example 1. The results of the test are reported in
Table II hereinbelow.
TABLE II
32
RESULTS PAINT ADHESION LOSS ON:
34 HDGl cRs2
.1% aqueous composition of
36 cyanuric acid rinse 6% 1770
38 CHEMSEAL 20 Rinse .5% 24%
Deionized Water Rinse 12% 24%
42 (1) Hot dipped galvanized steel.
(2) Cold rolled steel.
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EXAMPLE 3
2 Heavy gauge hot rolled steel panel6 were pretreated with
CHEMFOS 86 zinc nickel pho6phate coating at about 240 mg/ft2, rinsed
4 with water, and immersed for 30 seconds in .1 percent by weight aqueous
composition of cyanuric acid at 120~F. The panels were then rinsed
6 again with water, dried with compressed air, and then painted with a
single coat of ED 4201 black electrocoat primer (from PPG) at about .8
8 mil6 dry thickness.
Control panels were prepared with CHEMSEAL 20 chrome and with
10 deionlzed water rin6es. Triplicate panels were prepared for each
system and tested in essentially the same manner a6 described in the
12 CHRYSLER scab test cabinet for eight weeks. The results of the test
are reported in Table III hereinbelow.
14
TABLE III
16
SCRIBE CREEPAGE FACE CORROSION
18 RESULTS (ASTM D610-85~*
.1% by weight Cyanuric Acid Rinse 1/4 inch 7
22 CHEMSEAL 20 Rinse 5/16 " 6
24 Deionized Water Rinse 1/2 + " 7
26
*The numerical rating for this aspect of the te6t is ba6ed on a scale
28 of 0 to 10, with 10 indicating no failure and 0 indicating the total
failure from rusting accompaning blistering which is not initially
30 evidenced by vi6ible rust.
32 While the illustrative embodiments of the invention have been
described hereinabove, it will be understood that various modifications
34 will be apparent to and can be made by those skilled in the art without
departing from the scope or spirit of the invention. Accordingly, it
36 is intended that the claims directed to the invention be construed as
encompassing all aspects of the invention which would be treated as
38 equivalents by those skilled in the art to which the invention
pertains.
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