CA1206851A - Process for coating a trimetal system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for forming zinc phosphate coatings on articles having ferrous metal, zinc, and aluminum surfaces, such as automobile bodies, comprising contacting such articles with an acidic zinc phosphating solution containing:
from about 0.6 to about 2.0 g/l of zinc ion;
from about 8 to about 30 g/l of orthophosphate ion;
from about 0.5 to about 3.5 g/l of chlorate ion;
from about 0.01 to about 1.0 g/l of nitrite ion; and from about 0.2 to about 0.4 g/l of free fluoride ion.

The resulting zinc phosphate coatings are excellent bases for the electrodeposition of paint or enamel, providing good film adhesion and good corrosion resistance on all three types of metal surfaces.

Description

Amchern Case 1374 I I

PROCESS FOR COATING A TRIMETAL SYSTEM

BACKGROUND OF THY INVENTION

Zinc phosphate coatings have traditionally been em-plowed on both iron and zinc surfaces to enhance their paint adhesion properties and their resistance to corrosion. More recently in the automotive field, automotive components having three types of surfaces have come into use, i.e. components having steel, galvanized steel and aluminum surfaces. Act cordingly there is a need for a zinc phosphating method that will work simultaneously on all three types of surfaces.

US. Patent No. 4,311,535 relates to zinc phosphating compositions which contain a complex fluoride for use on zinc surfaces, ferrous metal surfaces, and aluminum surfaces.
However, while the compositions disclosed in this patent are excellent for use on ferrous metal and zinc surfaces, it has been found that the compositions will not effectively coat aluminum surfaces.

US. Patent No. 3,850,700 discloses a composition and process for the treatment of iron-based and zinc-based sun-faces The zinc phosphate coating solution disclosed in this patent contains either a simple fluoride, a by fluoride or a complex fluoride.

US. Patent Noah teaches the coating of a in-metal system using a phosphating bath containing free fluoride.

Other patents that disclose zinc phosphate baths contain- -in complex fluorides include US. Patent No. 3,676,224; US.
Patent No. 4,?65,677; US. Patent No. 3,297,494; US. Patent No. 3,109,757 and US. Patent No. 3,101,286.

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DESCRIPTION OF TIE INVENTION
.... . _ The present invention relates to a process for apply-in a zinc phosphate coating to a trimetal system comprising ferrous metal,zinc,and aluminum surfaces, or alloys thereof where the named metals are the dominant component The pros en process utilizes a zinc phosphal-ing composition which is low in zinc and which also contains chlorate and nitrite ions to produce an excellent conversion coating on all three metal surfaces.

The zinc phosphating solution utilized in the process of the invention contains the following ingredients and ranges thereof: `

Zinc Phosphating Solution Composition ingredients Range*, g/l Zen 0.6 - 2.0 POX 8 - 30, prey. 8 - 20 C103~ 0.5 - 3.5 15 NOW 0.01 1.0 F 0.2 - 0.4 Optional Ingredients No 0.05 - 1.0 Fe 0.006 - 0.008 approximate.

The above zinc phosphating solution is formulated to have a pi in the. range of about 2.7 to about 3.4, preferably about 3.0 to about 3.2. This can readily be accomplished by adding a portion of the phosphate ion as phosphoric acid.

Thea process of the invention is carried out by contact-in a clean metal component having ferrous metal, zinc, and ~68~i~
aluminum surfaces with the above solution by any technique known to the art, such as by spraying or by dipping the come potent into the solution, at a temperature of from about 100 -to about 160F, preferably about 120 to 130F for a period of from about I seconds to about 2 minutes, parboil aye 45 seconds to about 60 seconds.

Following this step, the metal component is rinsed with tap water and/or deionized water. The metal component can then be treated with a final rinse which can be acidulated and can contain trivalent or hexavalent chromium ions or a combination thereof. The coatings so produced are excellent for the electrode position of paint or enamel. The paint or enamel coating exhibits good film adhesion and good corrosion resistance on all three types of metal surfaces.

The zinc phosphating solution composition disclosed above for use in the process of the invention can have the ions present therein from the sources given below. The zinc ion can be supplied in the form of a soluble zinc-containing compound, e.g. zinc phosphate, zinc nitrate, zinc carbonate, zinc hydroxide, zinc oxide or in the form of zinc metal. The phosphate ion can be supplied in the form of a soluble salt and/or an acid, for example, phosphoric acid, alkali metal dihydrogen phosphate, zinc phosphate, nickel phosphate, etc.
The chlorate ion can be supplied in the form of a soluble salt and/or an acid, eye. caloric acid, sodium chlorate, potassium chlorate, and other alkali metal chlorates. The nitrite ion can be supplied in the form of a soluble salt and/or acid; for example, nitrous acid, sodium nitrite, poles-slum nitrite, and other alkali metal nitrites. The fluoride ion can be provided in the form of hydrofluoric acid or an I
alkali metal fluoride salt, erg. sodium fluoride, potassium fluoride, etc. The optional nickel ion can be supplied in the form of a soluble nickel salt; for example, nickel pros-plate, nickel nitrate, nickel carbonate, nickel oxide, etc.
The optional nitrate ion can he supplied in the form of a soluble salt and/or acid; for example, nitric acid, sodium nitrate, potassium nitrate, and other alkali metal nitrates.
The optional ferris ion is preferably added as ferris color-ides The process of the invention will be better understood from the following examples which are given to illustrate the invention and not to limit it.

EXAMPLE I

One thousand metal panels in a ratio of 80~ steel (UP), 15% galvanized steel (Armco minimum spangle) and I aluminum (2036) were treated in accordance with the following pro-seedier:

Prop - 50% solution of a commercial alkaline cleaner, P3-5156* manufactured my Henk~l Corporation.

Stage 1 - Sprayed with 1.2 w/v% solution of REDLINE 1007, ; 20 a cleaner manufactured by Amchem Products, Inc. at 140-150F for 60 seconds.

Stage 2 - water rinse.

Stage 3 - Sprayed with a 1.2 w/v% solution of REDLINE 1007 at 140-150F for 60 seconds.

Stage 4 - water rinse.

Stage 5 - sprayed for 60 seconds at 126-132F with a zinc phosphating solution containing the following ingredients:

*

Trade Mark _~_ Ingredient I
Zen 0.7 - 0.9 C103~ 2 N2 0 . 1 F I 0.285 - 0~370 No 0 4 free acid* 0.7 - 0.9 ml total acid** 19 - 22 ml *Free acid denotes the amount in ml of 0.lN Noah required to neutralize a 10 ml sample of the treat-in bath using a bromphenol blue indicator.
**Total acid denotes the amount in ml of 0.lN Noah required to neutralize a 10 ml sample of the treat in bath using a phenolphthalene indicator.
Stage 6 - water rinse.
Stage 7 - acidulated chromium rinse, Or 6 at 180-260 PAM
pi 4.0 - 4,5.
Stage 8 - deionized water rinse.
Stage 9 - air drying.
Stage 10 - painting with PUG 3002 undercoat by electron deposition, and GM #4 topcoat.
Stage 11 - representative panels were then subjected to the following tests. For comparison purposes, 25 panels were treated according to the above proved urea except that no fluoride was present in -the zinc phosphating bath in Stage 5.

a. I salt spray test ASTM B117.
b. 10 day water soak cross hatch last.
c. Arizona proving ground test -20 cycle, 30 cycle, and 60 cycle -tests were performed Coating weights ox the zinc phosphate coatings applied in Stage 5 were also determined for rep resentative panels whose processing was disco-tinted after Stage 6. The coating weights were determined by immersing a 4 x 6 panel as follows:
steel - a 5% chronic acid solution for 5 minutes at 160F; galvanized steel - a 1% ammonium dip chromates in 28-30% ammonium hydroxide solution for 2 minutes at room temperature; aluminum - a 1:1 solution of concentrated nitric acid for 1 mint vie at room temperature.

NOTE: The tests referred to in Stage 11, a., b., and cut were carried out as follows:

5% Salt Spry Test ASTM B117 Y _ _ .
This method is carried out in accordance with ASTM B117 specification, and is also in accordance with Federal Test Standard lSlb, Method 811.1 and Federal Test Method Standard 141, Method 6061. The evaluation of the test specimens was carried out according to ASTM D1654.

Water Soak Cross Hatch Test This test is used to determine the degree of resistance of automotive paint systems to accelerated water immersion by measuring paint adhesion. The test specimens are immersed to one half of their total area in a water immersion bath maintained at 122 1F and contains distilled or deionized ~2~68~i~

waker maintained with slight agitation. The test specimens are hung with nonconducting hooks so that at least 1/2ll of space is maintained between the specimens. The test specie miens are allowed to remain in the heated water bath for a period of 10 days. After 10 days, the -test specimens are removed, dried with absorbent paper and cross-hatched with a 2 millimeter separation. Scotch brand ~710 tape is then applied to the cross-hatched area immediately so that the test panel temperature remains above room temperature. The tape is then removed and the results evaluated according to ASTM D-3359.
Arizona Proving Ground Test This test is a scab blister test which accelerates the development of scab-type corrosion blistering on paint soys-terms. The painted test specimens are aged for a minimum of 72 hours. The test specimens are then X scribed with a mini-mum scribe area of 3 x 5", allowing a half inch between the scribe and all edges. Then all sheared or unpainted edges are taped and the test specimens suspended from a rack in such a manner as to insulate them from all metal contact which could set up a galvanic cell, including contact with each other. Each scribed test specimen is then subjected -to the riven number of test cycles. Each test cycle is car-fled out by first immersing the test specimen in an aerated I solution of sodium chloride at room temperature for 15 minute. The test specimen is then removed from the salt immersion and allowed to drain for 1 hour and 15 minutes at room temperature and room humidity. The test specimen is next placed in a constant humidity cabinet at 120F and 85 relative humidity for the remainder of the 24-hour period, i.e. for 22-1/2 hours At the conclusion of the last cycle, the test specimens are removed from the humidity cabinet, rinsed in tap water, scraped with a spatula, rinsed in tap water, the scribe cleaned with a Scotch-Brite* pad and a powdered cleanser, and rinsed in tap water. The tested specimens axe ennui rated descriptively using average and maximum paint loss or film eruption from the scribe. The ratings are expressed in millimeters. The test specimens are rated within 2 hours of the completion of the last cycle.

The results obtained from the above tests are given in Table I which follows:

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The following terms used in the above table have the meanings given below:

"Trace" denotes the extent of Scribe Failure, "NSF" means No Scribe Failure "M" - means Maximum Scribe Creep age "A" - means Average Scribe Seepage "T-P" - means Top Coat to Prime Failure I Med." - means Size #8 Field Blistering (#8 being smallest; #2 largest) and of Medium Density "Cons." - means Considerable Field Blistering As can be seen from the above table, when the zinc phosphating bath does not contain fluoride first three panels), the coating weight and test results for aluminum are unseats-factory. However, when the process of the invention is followed ~1~5 (remaining panels the results for all three metals are well within commercial acceptability EXAMPLE II

This example is given for purposes of comparison, using a complex fluoride (HBF4) instead of the simple fluoride required to achieve the results of the present invention.

61 Metal panels in a ratio of 21 steel PI 20 gal-vanlzed steel (Armco minimum spangle) and 20 aluminum (2036) were treated according to the procedure of EXAMPLE I except that in Stage 5 an aqueous zinc phosphating solution was employed which was maintained within the following composition range:

Ingredient q/l Zen 0.6-0.8 Cloy 0.8-1.6 NO 0.1-0.2 IIBE'4 1.2 No 0 3-0 4 g_ I

Ingredient free acid 0.7-1.2 ml total acid 15-25 ml The resulting panels, after completion of Stage 10, were then evaluated in Stage 11 according to the following texts, the results riven being an average result of the panels used in each test.
a. 5% salt spray test ASTM B117 (1000 hour exposure).
d. 10 cycle scab corrosion test. This test is a scab type corrosion blister test for paint systems. The painted test specimens are aged for a minimum of 72 hours. The test specimens are then scribed horizontally approximately 2 inches long at a point four inches down from the top. The scribed test specimens are then subjected to 10 of the following test cycles: I' (it 24 hours salt spray (ASTM B117);
(ii) without rinsing, four 24 hour humidity tests; each test comprising 8 hours at 100% relative humidity at 100+ 2F, and 16 hours at room temperature and relative humidity; and ; lit 48 hours at room temperature and relative humidity.
The panels are then rinsed with water, dried, and evaluated within 2 hours after completion ox the Thea cycle. The measurement taken is of the maximum corrosion creep in millimeters from the scribed line.

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The number of panels used in each test is as hollows:
(a) Salt Spray, (d) 20 Cycle Scab _1000 hours _ _ I
Steel 12 9 Gal. 12 8 Al~inum 12 8 The zinc phosphate coating weights for steel were in the range of 120-180 mg/ft2; for galvanized steel in the range of 250-350 mg/ft ; and for aluminum in the range of only 10-40 10 mg/ft2.
The results obtained are set forth in Table II below:
TABLE II
.. . ...
Metal Salt Spray 10 Cycle Scab Panel 1000 Hours Corrosion Test Steel 1/32-1/16 0~5-2.0 mm Gal. 1/16-1/4 0.5-Z.0 mm Aluminum Trace 1~10 mm*
*Filiform corrosion noted in all cases.
: As can be seen prom the above table/ the results obtained or aluminum are very unsatisfactory, and are commercially unacceptable.

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Claims (9)

What is claimed is:

1. A process for forming a zinc phosphate coating on articles containing ferrous metal, zinc, and aluminum surfaces com-prising contacting a clean article having ferrous metal, zinc, and aluminum surfaces with an acidic zinc phosphat-ing solution comprising from about 0.6 to about 2.0 g/l of zinc ion, from about 8 to about 30 g/l of orthophosphate ion, from about 0.5 to about 3.5 g/l of chlorate ion, from about 0.01 to about 1.0 g/l of nitrite ion, and from about 0.2 to about 0.4 g/l of free fluoride ion.

2. A process in accordance with Claim 1 wherein the article is contacted with the acidic zinc phosphating solution for a period of from about 30 seconds to about 2 minutes at a temperature in the range of from about 100° to about 160°F.

3. A process in accordance with Claim 1 wherein the coated article is subsequently treated with an acidulated rinse containing trivalent or hexavalent chromium ions or a mixture of such ions.

4. A process in accordance with Claim 1 wherein the coated article is subsequently coated with an electrodeposited paint film.

5. A process in accordance with Claim 1 wherein the ortho-phosphate ion is present in from about 8 to about 20 g/l.

6. A process in accordance with Claim 1 wherein the article is contacted with the acidic zinc phosphating solution for a period of from about 45 seconds to about 60 seconds at a temperature in the range of from about 102° to about 130°F.

7. A process in accordance with Claim 1 wherein the zinc phosphating solution also contains from about 0.05 to about 1.0 g/l of nickel ion.

8. A process in accordance with Claim 1 wherein the zinc phosphating solution also contains from about 3 to about 8 g/l of nitrate ion.

9. A process in accordance with Claim 7 wherein the zinc phosphating solution also contains from about 3 to about 8 g/l of nitrate ion.