Coating processes – With post-treatment of coating or coating material – Heating or drying
Patent
1998-03-26
1999-06-29
Lusignan, Michael
Coating processes
With post-treatment of coating or coating material
Heating or drying
165133, 4273884, 524166, 524493, B05D 302
Patent
active
059166355
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
This invention relates to water-based hydrophilic coatings which are suitable for giving hydrophilic nature primarily to the surface of aluminum materials and to a process for manufacturing precoated fin materials for heat exchangers with the use of said coatings.
BACKGROUND TECHNOLOGY
Heat exchangers in air-conditioning equipment installed in buildings and automobiles generally contain fins which are fabricated in a specified shape from aluminum material (hereinafter signifying aluminum or its alloys) and the like. Such fins are arranged at closer intervals for the purpose of raising the heat exchange efficiency or under the influence of size reduction of air-conditioning equipment and, as a consequence, water condenses into globules on the surface of fins and forms a bridge between fins during the cooling operation. This phenomenon produces such undesirable results as increased resistance to air flow and lowered heat exchange efficiency.
A remedial practice has been a surface treatment to give hydrophilicity to the surface of fins as effected by applying hydrophilic coatings to fin materials prior to their fabrication into fins. The aim of this treatment is letting the enhanced hydrophilicity help condensing water to spread over the whole surface of the fins without forming globules and thus preventing the generation of the aforementioned phenomenon of bridging. Fin materials treated prior to fabrication with hydrophilic coatings as mentioned above are usually referred to as precoated fin materials.
Hydrophilic coatings of this kind, for example, contain silica and organic (1978), Japan Kokai Tokkyo Koho No. Sho 55-99976 (1980), and Japan Kokai Tokkyo Koho No. Hei 6-221786 (1994)!. Other examples are hydrophilic coatings containing surfactants in order to enhance initial hydrophilicity obtained by mixing the aforementioned main components with silanes and dialkylsulfosuccinate ester salts and allowing the mixture to react at Kokai Tokkyo Koho No. Hei 1-223188 (1989)!.
The conventional hydrophilic coatings mainly composed of silica and organic polymers exhibit good hydrophilicity in the initial stage, but they tend to lose hydrophilicity gradually with the passage of time as the result of exposure to repeated dry and moist condition and deposition of air-borne hydrocarbons. Hence, there is a demand for sustained hydrophilicity.
Judging from their compositions, the hydrophilic coatings proposed in the aforementioned patent specifications yield an alkaline bath in use and, as described later, they tend to form a relatively smooth surface when applied to fin materials. Fins with such smooth surface not only lack sufficient ability to maintain hydrophilicity, but also generate another phenomenon of repelling water. In Example 1 of the aforementioned Japan Tokkyo Kokai Koho No. Hei 6-221786 (1994), a mixture (alkaline) of a and water is applied to an aluminum plate to provide a fin material precoated with a hydrophilic film containing silica particles averaging 0.5 .mu.m in diameter. The alkaline nature of the film thus formed, however, presents such problems as foaming and degradation of volatile press oil applied during the fabrication of fins, adverse effects on the corrosion resistance of fin materials, and changes in the film structure caused by elution of alkali with the passage of time.
It is described in Japan Kokai Tokkyo Koho No. Hei 7-188585 (1995) that there is no restriction on the kind of surfactants to be used, that the role of the surfactants is mainly to improve the initial hydrophilicity and prevent lowering of hydrophilicity by adsorption of press oil to be applied prior to fabrication, and that addition of crosslinking agents in a suitable amount is effective for securing sustained hydrophilicity over a prolonged period of time. The hydrophilic coatings described in the aforementioned patent specification, however, were not satisfactory to provide sustained hydrophilicity, particularly after application of volatile press oil. Furthermore, it is described in Japan Tok
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Ishii Toru
Takasawa Reiko
Yamazaki Kazuhiko
Lusignan Michael
Nippon Light Metal Company Ltd.
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