Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1999-05-26
2001-03-13
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S388100, C427S379000, C427S493000, C427S410000, C427S189000, C427S195000
Reexamination Certificate
active
06200650
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to drying of primer (primer/surfacer) coating compositions for automotive coating applications and, more particularly, to multi-stage processes for drying primer coating compositions which include a combination of infrared radiation and convection drying.
BACKGROUND OF THE INVENTION
Today's automobile bodies are treated with multiple layers of coatings which not only enhance the appearance of the automobile, but also provide protection from corrosion, chipping, ultraviolet light, acid rain and other environmental conditions which can deteriorate the coating appearance and underlying car body.
The formulations of these coatings can vary widely. However, a major challenge that faces all automotive manufacturers is how to rapidly dry and cure these coatings with minimal capital investment and floor space, which is valued at a premium in manufacturing plants.
Various ideas have been proposed to speed up drying and curing processes for automobile coatings, such as hot air convection drying. While hot air drying is rapid, a skin can form on the surface of the coating which impedes the escape of volatiles from the coating composition and causes pops, bubbles or blisters which ruin the appearance of the dried coating.
Other methods and apparatus for drying and curing a coating applied to an automobile body are disclosed in U.S. Pat. Nos. 4,771,728; 4,907,533; 4,908,231 and 4,943,447, in which the automobile body is heated with radiant heat for a time sufficient to set the coating on Class A surfaces of the body and subsequently cured with heated air.
U.S. Pat. No. 4,416,068 discloses a method and apparatus for accelerating the drying and curing of refinish coatings for automobiles using infrared radiation. Ventilation air used to protect the infrared radiators from solvent vapors is discharged as a laminar flow over the car body.
FIG. 15
is a graph of temperature as a function of time showing the preferred high temperature/short drying time curve
122
versus conventional infrared drying (curve
113
) and convection drying (curve
114
). Such rapid, high temperature drying techniques can be undesirable because a skin can form on the surface of the coating that can cause pops, bubbles or blisters, as discussed above.
U.S. Pat. No. 4,336,279 discloses a process and apparatus for drying automobile coatings using direct radiant energy, a majority of which has a wavelength greater than 5 microns. Heated air is circulated under turbulent conditions against the back sides of the walls of the heating chamber to provide the radiant heat. Then, the heated air is circulated as a generally laminar flow along the inner sides of the walls to maintain the temperature of the walls and remove volatiles from the drying chamber. As discussed at column 7, lines 18-22, air movement is maintained at a minimum in the central portion of the inner chamber in which the automobile body is dried.
A rapid, multi-stage drying process for automobile coatings is needed which inhibits formation of surface defects and discoloration in the coating, particularly for drying primer/surfacer coatings.
SUMMARY OF THE INVENTION
The present invention provides process for drying a liquid primer coating composition applied to a surface of a metal substrate, comprising the steps of: (a) exposing the liquid primer coating composition to air having a temperature ranging from about 10° C. to about 50° C. for a period of at least about 30 seconds to volatilize at least a portion of volatile material from the liquid primer coating composition, the velocity of the air at a surface of the primer coating composition being less than about 4 meters per second; (b) applying infrared radiation and warm air simultaneously to the primer coating composition for a period of at least about 1 minute, the velocity of the air at the surface of the primer coating composition being less than about 4 meters per second, the temperature of the metal substrate being increased at a rate ranging from about 0.2° C. per second to about 2° C. per second to achieve a peak metal temperature of the substrate ranging from about 30° C. to about 120° C.; and (c) applying infrared radiation and hot air simultaneously to the primer composition for a period of at least about 2 minutes, the temperature of the metal substrate being increased at a rate ranging from about 0.1° C. per second to about 1° C. per second to achieve a peak metal temperature of the substrate ranging from about 40° C. to about 155° C., such that a dried primer coating is formed upon the surface of the metal substrate.
Another aspect of the present invention is a process for drying a powder slurry primer coating composition applied to a surface of a metal substrate, comprising the steps of: (a) applying infrared radiation and warm air simultaneously to the powder slurry primer coating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the powder primer coating composition being less than about 4 meters per second, the temperature of the metal substrate being increased at a rate ranging from about 0.5° C. per second to about 1° C. per second to achieve a peak metal temperature of the substrate ranging from about 90° C. to about 110° C.; and (b) applying infrared radiation and hot air simultaneously to the powder primer composition for a period of at least about 2 minutes, the temperature of the metal substrate being increased at a rate ranging from about 0.25° C. per second to about 1° C. per second to achieve a peak metal temperature of the substrate ranging from about 125° C. to about 140° C., such that a coalesced dried primer coating is formed upon the surface of the metal substrate.
Yet another aspect of the present invention is a process for curing a powder primer coating composition applied to a surface of a metal substrate, comprising the steps of: (a) applying infrared radiation and warm air simultaneously to the powder primer coating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the powder primer coating composition being less than about 4 meters per second, the temperature of the metal substrate being increased at a rate ranging from about 0.5° C. per second to about 1° C. per second to achieve a peak metal temperature of the substrate ranging from about 90° C. to about 110° C.; and (b) applying infrared radiation and hot air simultaneously to the powder primer composition for a period of at least about 2 minutes in which a temperature of the metal substrate is increased at a rate ranging from about 0.5° C. per second to about 1.5° C. per second to achieve a peak metal temperature of the substrate ranging from about 160° C. to about 200° C. and maintaining the peak metal temperature for at least about 15 minutes.
Another aspect of the present invention is a process for drying a liquid primer coating composition applied to a surface of a polymeric substrate, comprising the steps of: (a) exposing the liquid primer coating composition to air having a temperature ranging from about 10° C. to about 30° C. for a period of at least about 30 seconds to volatilize at least a portion of volatile material from the liquid primer coating composition, the velocity of the air at a surface of the primer coating composition being less than about 4 meters per second; (b) applying infrared radiation and warm air simultaneously to the primer coating composition for a period of at least about 1 minute, the velocity of the air at the surface of the primer coating composition being less than about 4 meters per second, the temperature of the polymeric substrate being increased at a rate ranging from about 0.2° C. per second to about 0.4° C. per second to achieve a peak temperature of the substrate ranging from about 30° C. to about 50° C.; and (c) applying infrared radiation and hot air simultaneously to the primer composition for a period of at least about 2 minutes, the temperature of the polymeric substrate being increased at a rate ranging from about 0.1
Altman Deborah M.
Cannoni Ann M.
Padgett Marianne
PPG Industries Ohio Inc.
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