Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2001-07-23
2003-05-06
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S251000, C148S252000, C148S273000, C148S274000, C106S014150, C106S014130
Reexamination Certificate
active
06558480
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to compositions and processes for forming on metals, particularly aluminum and its alloys, a conversion coating that is substantially transparent, so that aesthetically appealing characteristics of the metal surface that is conversion coated are not overly impaired by the conversion coating. (No quantitative test is in common use to measure the degree of preservation of the aesthetic qualities of the metal, but for the principal application area of this invention, aluminum beverage cans, any ordinary consumer can readily judge whether the bright reflectance of the can is as good as usual.)
The following discussion and the description of the invention will be set forth primarily for aluminum cans. However, it is to be understood that, with any obviously necessary modifications, both the discussion and the description of the invention apply also to tin plated steel cans and to other types of metal surfaces over which a transparent conversion coating is practically interesting.
Aluminum cans are commonly used as containers for a wide variety of products, particularly beverages. The exterior cylindrical surfaces of such cans normally are at least partially decorated with lacquer and/or printing ink and the interior surfaces, including the inner dome, normally are protected with sanitary lacquer, but the outer domes of the cans usually do not have lacquer or any similar coating, except possibly for a “rim coat” on its outer margin. It is considered desirable in the market for all exterior parts of the can to have a lustrous surface, even in the parts that are printed or colored, with the reflective properties that are essentially unique to polished metal surfaces. Therefore, for this particular field of use, the conversion coated surface must have adequate adhesion to printing inks and/or lacquer.
In the most widely used current commercial practice, at least for large scale operations, aluminum cans are typically subjected to a succession of six cleaning and rinsing operations as described in Table A below. It is preferable to include another stage, usually called “Prerinse”, before any of the stages shown in Table A; when used, this stage is usually at ambient temperature (i.e., 20-25° C.) and is most preferably supplied with overflow from Stage 3 as shown in Table A and is next most preferably supplied with overflow from Stage 1 as shown in Table A. The prerinse may also be tap water. Any of the rinsing operations shown as numbered stages in Table A preferably includes two, or more preferably three, sub-stages, which in consecutive order of their use are usually named “drag-out”, “recirculating”, and “exit” or “fresh
TABLE A
Stage
Number
Action on Surface During Stage
1
Aqueous Acid Precleaning
2
Aqueous Acid (or Alkali) and Surfactant Cleaning
3
Tap Water Rinse
4
Mild Acid Postcleaning, Conversion Coating,
or Tap Water Rinse
5
Tap Water Rinse
6
Deionized (“DI”) Water Rinse
water” sub-stages; if only two sub-stages are used, the name “drag-out” is omitted. Most preferably, when such sub-stages are used, a blow-off follows each sub-stage, but in practice such blow-offs are often omitted. Also, any of the stages numbered 1 and 4-6 in Table A may be omitted in certain operations.
A conversion coating over the metallic surfaces of beverage cans, prior to any lacquer coating or printing, is generally considered desirable, in order to increase the adhesion of the inner sanitary lacquer and exterior decorative and protective coatings, especially when the cans in process are to be subjected to stressful metal working operations such as necking (i.e., reducing the can diameter in its neck region) and flanging (to provide an anchoring point for a separate cap for the filled container). However, prior art conversion coatings that were sufficiently transparent to preserve the metallic luster of the surfaces coated with them were susceptible to at least one of the following disadvantageous characteristics when subjected to subsequent heating: development of exterior dome staining during pasteurization; loss of luster of the exterior dome surface upon its exposure to steam; and substantially weakened adhesion of lacquers and printing inks, compared with surfaces of otherwise identical aluminum having the same conversion coating not exposed to heat and sometimes even compared to otherwise identical aluminum that never had any conversion coating. A major object of the present invention is to provide a transparent conversion coating that will avoid or reduce at least one, or preferably all, of these disadvantageous characteristics of the prior art. Other objects will be apparent from the further description below.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating 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 or mass; 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 preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word “mole” means “gram mole”, and the word itself and all of its grammatical variations may be 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; the terms “solution”, “soluble”, “homogeneous”, 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 the temperature of the material is maintained within the range of 18-25° C.; and the first definition of an acronym or other abbreviation applies to all subsequent uses of the same acronym or other abbreviation.
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, it has been found that the major object as stated above is achievable with an aqueous conversion coating composition that comprises, preferably consists essentially of, or more preferably consists of, water and the following components:
(A) a component of one or more dissolved transition metal compounds that contains zirconium, hafnium, or both (hereinafter, for brevity, only zirconium will be mentioned, but it is to be understood that zirconium may be partially or totally replaced by hafnium) and may also include titanium, provided that zirconium constitutes a
Banaszak Richard D.
Kelly Timm L.
Rochfort Gary L.
Cameron Mary K.
Harper Stephen D.
Henkel Corporation
Ottmans Andrew L.
Sheehan John
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