Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
2000-06-14
2002-07-16
Barr, Michael (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S224000, C427S241000, C427S309000, C427S321000, C427S329000, C427S347000, C427S367000, C427S368000, C427S383700, C427S406000, C427S409000, C427S433000, C427S486000, C427S220000, C427S142000
Reexamination Certificate
active
06419992
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method of protecting articles having a bare ferrous base surface and, more particularly, to a method wherein a thermosetting powder is electrostatically applied to a galvanized metal layer covering a bare ferrous based substrate.
BACKGROUND ART
Parking meter housings include several different parts made of metal based material. To enable the parking meter housing parts to withstand the abuse to which they are subjected, the parts are usually made of cast iron or zinc, and electrostatically powder coated. Housings of other outdoor token accepting devices, such as consoles for accepting credit and debit cards for several adjacent parking spaces, include parts having a steel base. These token accepting devices are subject to many adverse conditions, such as vandalism and harsh environmental conditions. The vandalism is frequently of the petty type, such as cutting the housing surface with a knife. The harsh environmental conditions include oxidation, leading to rusting of housing parts having a ferrous base, and/or hydrocarbon deposits resulting from automotive vehicle tailpipe emissions, for example. Because of these adverse conditions, parking meters housings and other outdoor token accepting devices generally must undergo substantial maintenance after only five to seven years of use. However, the maintenance usually only includes spray painting the housings, which does not put the meters and other token handling devices back into anything resembling new condition.
Officials of several jurisdictions have also decided that parking meters, and the like, can be used for beautification purposes. For example, officials in seashore communities have decided parking meter housings should have a teal color to complement the color of the adjacent sea. Other communities have decided the usual battleship gray color of parking meter housings is inappropriate and have decided the housings should be a silver like color. The expectation is that an attractive color for parking meter housings and the housings of related devices will be attractive to visitors and might reduce petty vandalism.
I am aware of the prior art disclosing the combination of a ferrous substrate, a galvanized coating on the ferrous substrate and an organic powder coating over the galvanized coating. For example, Geary et al., U.S. Pat. No. 4,540,637 indicates a steel surface must be thoroughly cleaned of dirt, oil, oxidation products and other foreign matter prior to the deposition of a powder coating on the steel. Geary et al. also discloses applying such coatings over mild or “black” steel. The '637 patent also states surface preparation systems have been developed for mild steel. The preparation systems typically include first cleaning the steel and sometimes roughening it, then rinsing the steel with a solution which deposits a microscopic layer of crystalline material, such as zinc phosphate, on the steel. The microscopic layer passivates the surface against corrosion and provides bonding sites for the powder. Geary et al. specifically states that hot dipped or electroplated galvanized coatings on steel substrates are not normally recommended as a base for thermosetting organic powder coatings. This is so despite the superior resistance to corrosion provided by the zinc cladding of the galvanized layer. Geary et al. states previous experience has shown the thermosetting organic powders do not bond as well to the inherently smooth zinc cladding as to properly prepared mild steel.
This problem was previously recognized by Wlodek in U.S. Pat. No. 3,674,445. Wlodek attempts to solve the problem by vacuum vapor depositing zinc onto the steel substrate. As Geary et al. points out, vacuum vapor depositing zinc is an exotic technique which produces microscopically rough surfaces as compared to galvanized steel. Vacuum vapor deposition can only occur in vacuum processing facilities at very low pressures, on the order of 10
−5
Torr or less. Such processes are not generally suitable for large scale deposition on large products, but are generally used extensively in processing of small articles, such as integrated circuits.
Geary et al. points out that the problem of depositing a thermosetting organic powder on a zinc coating covering a ferrous base has previously been dealt with by Gemmer in U.S. Pat. No. 3,090,696 and Wamant et al., UK Patent 815 756, both of which say coating adhesion is improved by roughening the surface prior to applying the coating. In Wamant et al., “anchor cavities” are created on the surface to achieve good adherence. Bannister, in UK Patent 1 009 055, recommends blasting the surface to be coated with abrasive particles, such as steel shot, to clean the surface and, presumably, to roughen it.
Geary et al. deals with this problem by avoiding the roughening steps through a four-step pretreatment process, including immersing a ferrous workpiece into an acidified rinse including chromium compounds. However, the use of a substantial amount of chromium compounds is inadvisable in large scale manufacturing processes because of the environmental problems associated therewith.
It is, accordingly, an object of the present invention to provide new and improved housings for parking meters and for other similar metal based token accepting devices which are primarily in an outdoor environment.
Another object of the present invention is to provide a new and improved method of protecting metal based parts of parking meter housings and housings of other related token accepting devices.
A further object of the invention is to provide a new and improved method of refurbishing metal based parts of parking meter housings and the housings of other token accepting devices which are primarily used outdoors.
A further object of the invention is to provide a new and improved parking meter housing which is able to withstand vandalism to a greater extent than existing parking meter housings and is less subject to adverse effects of the environment, such as oxidation and/or deposition of organic compounds on the housing.
THE INVENTION
In accordance with one aspect of the present invention, the problems with the prior art processes are obviated by centrifuging parking meter and other outdoor token accepting device parts while a hot dipped zinc layer is still in a molten state on a clean, bare ferrous base or substrate of the part. The meter parts are then processed the same as in conventional galvanizing operations, i.e. washed in HCl, then pickled in a Zn—Pb bath including some Al and then washed in a water bath including some chromate. The galvanized parts then dry, perhaps for many days, but for considerably more than six hours, before being electrostatically powder coated with a non-epoxy organic, electrical insulating electrically charged thermosetting powder. The powder is applied directly to the thus treated galvanized layer on the cast iron substrate, without requiring the use of phosphoric acid which forms and randomly distributes small amounts of zinc phosphate crystals over the substrate surface prior to application of the powder. Hence, certain problems of the Geary et al. patent are avoided.
By centrifuging the parking meter parts under these conditions, excess zinc is removed from the parts to form a somewhat smooth and somewhat rough zinc surface covering the substrate. Such a surface enables a non-epoxy, organic electrical insulating, electrically charged thermosetting powder to adhere to the oppositely charged zinc layer covering the bare ferrous substrate. The powder is then heated to a molten state and cooled. The organic powder cannot be an epoxy because epoxy powders do not have the ability to withstand the harsh environmental conditions to which parking meters and other similar outdoor metal based consoles are exposed.
It has been found, through actual use and experimentation, that excellent adherence properties are attained as a result of the foregoing process. Theoretical analysis leads to the conclusion that a parking meter or ot
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