Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2001-04-30
2002-10-15
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S247000, C148S274000, C148S276000, C148S251000, C252S393000
Reexamination Certificate
active
06464800
ABSTRACT:
BACKGROUND OF THE INVENTION
Conversion coating in general is a well known method of providing aluminum and its alloys (along with many other metals) with a corrosion resistant coating layer. The most effective method of controlling the thickness of the conversion is by measurement of its mass per unit area coated, a characteristic that is usually called “coating weight”, but some users who do not require the most careful control of this property prefer a visual indication of the thickness of the coating, because it is sufficiently accurate for their purposes and is faster and cheaper than measurements of coating weight. Both traditional types of conversion coatings for aluminum, the chromate and phosphate types, are capable of providing a visual indication of thickness. However, both chromium and phosphorus are often environmentally objectionable, so that their use should be minimized for that reason. Conversion coating compositions and methods that do not need the use of chromium or phosphorus are taught in U. S. Pat. Nos. 5,356,490 and 5,281,282, both of which are assigned to the same assignee as this application. These compositions and processes have been successful when the coating weight produced by using them is controlled, but these compositions form substantially colorless and transparent conversion coatings that do not provide any adequate visual indication of coating thickness.
Accordingly, a major object of this invention is to provide a conversion coating and composition and process therefor that gives a visual indication of coating weight that is at least as reliable as that from conventional chromate conversion coating but minimizes, or most preferably entirely avoids, the use of chromium and phosphorus. Still other concurrent and/or alternative objects will be apparent from the description below.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities used in the description of the invention to indicate amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, “parts of”, and ratio values are by weight; the term “polymer” includes “oligomer”, “copolymer”, “terpolymer”, and the like; 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 or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not necessarily preclude unspecified 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 preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterons may be freely selected, except for avoiding counterions that act adversely to the objects of the invention; the word “mole” means “gram mole” and the word itself and all of its grammatical variations may by used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; and the terms “solution”, “soluble”, “homogeneous phase”, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed; and, unless otherwise explicitly stated or necessarily implied by the context, the simple term “aluminum” includes pure aluminum and those of its alloys that contain at least, with increasing preference in the order given, 55, 65, 75, 85, or 95 atomic percent of aluminum atoms.
BRIEF SUMMARY OF THE INVENTION
It has been discovered that alizarine dyes can be added to treatment compositions as otherwise taught by U. S. Pat. Nos. 5,356,490 and 5,281,282 to generate treatment compositions that maintain most of the other properties of these previously known compositions but produce a strongly colored conversion coating instead of a substantially colorless one. These colored conversion coatings have the beneficial corrosion protective properties of those produced according to the teachings of these U. S. Pat. Nos. 5,356,490 and 5,281,282 and have the additional benefit of a readily visible indication of their presence and at least their approximate thickness.
DETAILED DESCRIPTION OF THE INVENTION
A composition according to this invention begins with a precursor composition that comprises, preferably consists essentially of, or more preferably consists of, water and:
(A.1) a first initial reagent component of at least one dissolved fluoroacid of an element selected from the group consisting of titanium, zirconium, hafnium, boron, aluminum, silicon, germanium, and tin; and
(A.2) a second initial reagent component of one or more of dissolved, dispersed, or both dissolved and dispersed finely divided forms of (i) elements selected from the group consisting of titanium, zirconium, hafnium, boron, aluminum, silicon, germanium, and tin and (ii) all of oxides, hydroxides, and carbonates of all of titanium, zirconium, hafnium, boron, aluminum, silicon, germanium, and tin.
These necessary initial reagent components are caused to chemically interact in such a manner as to produce a homogeneous composition that is itself useful for metal treatment but is not normally a composition according to this invention because it does not yet contain dye. If initial reagent component (A.2) is present in dispersion rather than solution, as is generally preferred, the precursor composition normally will not be optically transparent, because of the scattering of visible light, in a thickness of 1 centimeter (hereinafter usually abbreviated as “cm”), and completion of the desired chemical interaction is indicated by the clarification of the composition. If reagent components (A.1) and (A.2) as defined above are both present in the precursor aqueous composition in sufficiently high concentrations, adequate chemical interaction between them may occur at normal ambient temperatures (i.e., 20-25° C.) within a practical reaction time of 24 hours or less, particularly if component (A.2) is dissolved or is dispersed in very finely divided form. Mechanical agitation may be useful in speeding the desired chemical interaction and if so is preferably used. Heating, even to relatively low temperatures such as 30° C., is often useful in speeding the desired chemical interaction, and if so is also preferred. (The chemical interaction needed is believed most probably to produce oxyfluro complexes of the elements or their compounds of necessary initial reagent component (A.2), but the invention is not limited by any such theory.) The desired chemical interaction between components (A.1) and (A.2) of the mixed composition eliminates or at least markedly reduces any tendency toward settling of a dispersed phase that might otherwise occur upon long term storage of the initial mixture of water and components (A.1) and (A.2) as defined above.
In addition to a product of reaction between initial reagent components (A.1) and (A.2) as described above,
Carlson Lawrence R.
Dolan Shawn E.
Niemi Therese E.
Scalera Patrick A.
Harper Stephen D.
Henkel Corporation
Oltmans Andrew L.
Sheehan John
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