Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Patent
1998-06-15
2000-02-22
Willis, Prince
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
148261, 148272, C23F 712
Patent
active
060275804
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydrophilicizing treatment for a chromate conversion coating over underlying metal, particularly aluminum or an aluminum alloy containing at least 75% of aluminum. After treatment of a surface 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, especially those used for automobile air conditioning, with hydrophilic coatings that have good corrosion resistance and a durably hydrophilic character with little or no tendency to develop undesirable odors during use.
2. Statement of Related Art
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 normally be used to improve the resistance of the metals to corrosion in most other types of metal structures, but 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, the water beads accumulate on the fin surface and impede the air flow between fins and also reduce 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. Therefore, the formation of water beads on the fins of 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. 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.
DESCRIPTION OF THE INVENTION
The principal object of the invention is to provide metal heat exchanger surfaces with adequate hydrophilicity and corrosion resistance, while avoiding or at least mitigating at least one of the following problems sometimes observed with prior art hydrophilicizing treatments: dissolution of environmentally undesirable hexavalent chromium from the underlying chromate coating; dust in the passenger compartment of automobiles equipped with air conditioners bearing a prior art coating on its heat exchangers; unpleasant odors in the vicinity of the heat exchanger surface when operating; a need for expensive materials to form the hydrophilic surface; and complicated maintenance requirements for the process of forming the hydrophilic coating. Other objects will be apparent from the 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, unless expressly stated to the contrary: percent, "
REFERENCES:
patent: 3097978 (1963-07-01), Newell et al.
patent: 4110129 (1978-08-01), Matsushima et al.
patent: 4146410 (1979-03-01), Reinhold
patent: 4797183 (1989-01-01), Yamamoto et al.
patent: 5350791 (1994-09-01), Hsu
Henkel Corporation
Jaeschke Wayne C.
Oltmans Andrew L.
Szoke Ernest G.
Willis Prince
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