Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2000-04-26
2002-12-03
Mulcahy, Peter D. (Department: 1713)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C148S251000, C148S253000, C524S417000, C524S430000, C524S547000
Reexamination Certificate
active
06488989
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a hydrophilicizing treatment for a surface, usually a surface with underlying metal already bearing a corrosion protective conversion coating. Previously known corrosion protective coatings that do not require the use of chromium during their formation can be combined with the characteristic hydrophilicizing treatment according to this invention to form a high quality and durable hydrophilic surface. After treatment according to this invention, water will have a tendency to spread spontaneously over the surface. The invention is particularly advantageously applicable to provide aluminum evaporators, heat exchangers, and condensers with hydrophilic coatings that have good corrosion resistance and little or no tendency to develop undesirable odors during use.
Although any of the common structural metals can be used in constructing practical heat exchanging surfaces, aluminum and its alloys are among those most often used, because of their high heat conductivity. In heat exchanger surfaces, metals are normally used without any relatively thick protective coating such as a paint or lacquer that would generally be used in other types of equipment made from metals and exposed to corrosive environments, to improve the resistance of the equipment, but any such relatively thick protective coating is avoided in heat exchangers because such a coating would also reduce the efficiency of heat exchange.
During the cooling of hot air, a common use of these heat exchangers, moisture contained as vapor in the hot air condenses and initially forms water drops or beads on the fins of the heat exchanger. If the surface of the heat exchanger fins is not sufficiently hydrophilic, these water beads accumulate on the fin surface and tend to bridge across the small spaces between fins, thereby impeding the air flow between fins and reducing the heat transfer efficiency. The condensed water beads also tend to absorb dust and contaminants in the air, such as carbon dioxide, nitrogen oxides, and sulfur oxides, which can promote corrosion of the underlying aluminum, and because of the capillary forces holding in place water drops that have grown sufficiently large to bridge between adjacent fins, the normal drainage of water away from the fins that would otherwise carry away these absorbed contaminants is substantially reduced. Therefore, the formation of water beads on the fins of an aluminum heat exchanger not only decreases heat transfer efficiency but also can physically damage the exchanger.
In order to achieve a desirable combination of a hydrophilic nature and corrosion resistance on metal, particularly aluminum, surfaces, various coatings and treatments have been tried, but no fully satisfactory result has yet been achieved. A chromate conversion coating without any post-treatment usually has inadequate corrosion resistance and often develops an unpleasant odor and poor hydrophilicity. Silicate coating over a chromate conversion coat has often been used but has not satisfied all users. More recently, biocide protected hydrophilic organic polymer films have been used as post-treatments over chromate conversion coatings. While effective, these have proved to be expensive and difficult to control in some commercial operations.
Major alterative or concurrent objects of the invention are to achieve (i) a combination of adequate hydrophilicity and corrosion resistance, compared with the prior art, while avoiding the use of polluting constituents, and of highly volatile constituents, particularly organic solvents, with potential toxicity or unpleasant odors for workers, in the treatment compositions, (ii) durability of the hydrophilicity under thermal aging and/or practical use, and (iii) avoidance of the development of unpleasant odors during practical use. Other objects will be apparent from the description below.
Except in the claims and the specific 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, 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 first definition or description of the meaning of a word, phrase, acronym, abbreviation or the like applies to all subsequent uses of the same word, phrase, acronym, abbreviation or the like and applies, mutatis mutandis, to normal grammatical variations thereof; 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; chemical descriptions of neutral materials apply to the materials at the time of addition to any combination specified in the description and/or of generation in situ in a combination by chemical reactions described in the specification, and do not necessarily preclude chemical changes to the materials as a result of unstated reaction in the combination; specification of materials in ionic form means that the materials are supplied to prepare the compositions containing them in the form of soluble substance(s) containing the ions specified and implies the presence in any composition specified to contain ionic materials 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 counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention.
BRIEF SUMMARY OF THE INVENTION
It has been found that a hydrophilicity can be imparted to a wide variety of surfaces, and a desirable combination of hydrophilicity and corrosion resistance can be achieved on a surface with underlying metal, particularly aluminum and its alloys containing at least 75% by weight of aluminum, by contacting the surface, preferably, if the surface has underlying metal, after this metal has already been supplied with a corrosion protective coating, with an aqueous liquid composition that comprises, preferably consists essentially of, or more preferably consists of, water and:
(A) a sufficient amount of a component of dissolved and/or stably dispersed
1
polymers containing —SO
3
M moieties, where M represents hydrogen, a monovalent cation, or a monovalent fraction of a cation with a valence of two or higher; and, optionally, one or more of the following components:
1
i.e., showing no phase separation evident to normal unaided human vision within a period of observation of 100, or preferably 1000, hours.
(B) a component of one or more dissolved substances which can be made, and preferably actually is made, by dissolving at least one of elemental metals, metal oxides, and metal hydroxides in aqueous phosphoric acid;
(C) a component of pH adjusting substances that are not part of any one of components (A) and (B) as described above; and
(D) an anti-microbial effective amount of at least one anti-microbial agent that is not part of any of components (A) through (C) as described above,
the amount of component (A) being sufficient in a process according to the invention if the specific surface being treated has a smaller spreading contact angle of pure liquid water on the surface after being treated with a composition according to the invention than the same surface had before such treatment; for a composition according to the invention, the amount of component (A) is sufficient if at least one type of surface can be treated with the composition in a process according to the invention so that pure liquid water has a smaller spreading contact angle on the surface after treatment
Harper Stephen D.
Henkel Corporation
Mulcahy Peter D.
Ortiz Daniel S.
LandOfFree
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