Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2000-01-31
2002-04-09
Koehler, Robert R. (Department: 1775)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S260000, C148S261000, C148S262000, C148S273000
Reexamination Certificate
active
06368426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to zinc phosphate coatings for metal surfaces and to processes for phosphatizing a metal surface with acidic aqueous phosphate solutions. The invention is applicable to a variety of substrates including cold rolled steel (“CRS”), zinc alloys, and aluminum.
2. Statement of Related Art
Present day phosphate coating solutions are generally dilute aqueous solutions of phosphoric acid and other chemicals which, when applied to the surface of an active metal, react with the metal surface to form on the surface of the metal an integral layer of a substantially insoluble amorphous or coating. Generally, the crystalline coatings are preferred.
Typically the solutions include phosphate ions, zinc and other metal ions, especially manganese, nickel, and other divalent metal cations, to provide specific characteristics desired in the final coating. Other ions typically present may be nitrate, nitrite, chlorate, fluobotate or fluosilicate. A typical phosphating process comprises the following sequence of process steps: (1) cleaning and conditioning; (2)phosphating itself; and (3) post treating. Rinses are generally employed between each of the noted steps to prevent or at least reduce carry over of materials to the next step.
Despite advances in both the composition of the phosphate coating solution and the phosphating process, there is a continued demand for still further improvements in the compositions and processes, in order to provide more control over the process, assure adequate coating weights, reduce formation of scale or white spots, and reduce adverse environmental impact and safety hazards.
DESCRIPTION OF THE INVENTION
In this description, except in the claims and operating examples or where explicitly otherwise indicated, all numbers describing amounts of ingredients or reaction or usage conditions are to be understand as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred.
Also, unless expressly stated to the contrary:
percent, “parts of”, and ratio values are by weight;
the term “polymer” includes oligomer;
the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred;
description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed;
specification of materials in ionic form implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole (any counterions thus implicitly specified should preferably be selected from among other constituents explicitly specified in ionic form, to the extent possible, otherwise such counterions may be freely selected; and
except for avoiding counterions that act adversely to the stated objects of the invention): and the term “mole” and its variations may be applied to elemental, ionic, and any other chemical species defined by number and type of atoms present, as well as to compounds with well defined molecules.
SUMMARY OF THE INVENTION
It has now been discovered that certain zinc phosphate compositions containing both nickel and manganese along with hydroxylamine sulfate (“HAS”) as an accelerator provide polycrystalline coatings and retain the advantages of the use of manganese and nickel and the accelerator properties of the HAS, without changing the platelet or needle like crystalline morphology, as described in U.S. Patent 4,865,653. The HAS accelerated zinc phosphating compositions of the present invention produce a desirable uniform gray manganese and nickel modified zinc phosphate coating on a variety of substrates including ferrous alloys, zinc alloys and aluminum and its alloys at desirable temperatures in the range of 38 to 66° C., preferably 46 to 54° C., and can be applied by both spray and/or immersion and by any other method that establishes contact between the compositions and the substrates. The hydroxylamine sulfate accelerator can be incorporated into the makeup and replenishing mixtures, when needed, without the need of traditional supplemental accelerators, such as nitrite, which are undesirable because of their chemical instability and consequent unsuitability to single package concentrates from which a complete working composition can be prepared by dilution with water only. Compositions according to the invention ate also highly tolerant of sulfate ions, which may be introduced into the compositions during use.
In addition to providing overall desirable advantages, without many of the disadvantages previously encountered in the art, the present invention provides for improved process uniformity at the low temperature and reduces adverse environmental impact and safety hazards associated with nitrite. The polycrystalline coating contains Zn, Mn and Ni in the coating, and Fe in coatings on ferrous surfaces.
The present invention also includes as one embodiment a make-up or concentrate composition, which may then be diluted with water to form an aqueous, acidic coating solution for a spray or immersion coating process.
DESCRIPTION OF PREFERRED EMBODIMENTS
In general, a composition according to the invention, used for actual contact with a metal substrate to form a phosphate conversion coating, preferably will contain, more preferably will consist essentially of, or still more preferably will consist of water and:
INGREDIENT
CONCENTRATION (WT %)
PO
4
ions
0.5 to 2.5%
Zn ions
0.05 to 0.2%
Ni ions
0.02 to 0.15%
Mn ions
0.02 to 0.15%
HAS
0.1 to 0.25%
NO
3
ions
0 to 0.2%
Fluoride ions
0 to 0.15%
Sulfate ions
0 to 1.4%
The stoichiometric equivalent as fluoride ions of any content of complex fluoride ions such as fluosilicate, fluotitanate, fluobotate, and the like is to be understood as included within the content of fluoride ions for the purpose of the preferred concentration ranges noted above.
“The coating solution may be formed by diluting a concentrate. The concentrate is accordingly formulated to provide a coating solution preferably containing, more preferably consisting essentially of, or still more preferably consisting of water and:
(A) from 0.5 to 2 g/l, more preferably from 0.8 to 1.2 g/l of zinc ions;
(B) from 5 to 25 g/l, more preferably from 10 to 15 g/l, of phosphate ions;
(C) from 0.2 to 1.5 g/l, more preferably from 0.5 to 1 g/l, of manganese ions;
(D) from 0.2 to 1.5 g/l, more preferably from 0.5 to 1 g/l, of nickel ions;
(E) from 1 to 2.5 g/l, more preferably from 1.5 to 1.75 g/l, of hydroxylamine accelerator; and, optionally,
(F) up to 1.5 g/l of total fluoride ion with, more preferably, a free fluoride content of 400-600 parts per million; and, optionally,
(G) up to 2 g/l of nitrate ions; and, optionally,
(H) up to 14 g/l, more preferably no more than 9.0 g/l, still more preferably no more than 6.0 g/l, of sulfate ions.
In the phosphating solutions, it is preferable that the weight ratio of zinc ion to phosphate ion be in the range from 1.0:10 to 1.0:25 and the weight ratio of zinc to the sum of manganese and nickel be in the range from 1.0:0.5 to 1.0:2.5, with the ratio of manganese to nickel being most preferably 1.0:1.0, with a ratio in the range from 1.0:0.5 to 1.0:1.5 being satisfactory.”
The “free fluoride content” noted above is defined and can conveniently be measured by means of a fluoride sensitive electrode as described in U.S. Pat. No. 3,431,182 and commercially available from Orion Instruments. “Free fluoride content” as this term is used herein was measured relative to a 120E Activity Standard Solution commercially available from the Parker+Amchem (“+A”) Division of Henkel Corporation, Madison Heights, Mich. by a procedure described in detail in P+A Technic
Cormier Gerald J.
Sienkowski Michael L.
Harper Stephen D.
Henkel Corporation
Jaeschke Wayne C.
Johnson Lance G.
Koehler Robert R.
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