Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
1999-05-26
2001-04-24
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S378000, C427S379000, C427S388100, C427S409000, C427S189000, C427S202000
Reexamination Certificate
active
06221441
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to drying of liquid basecoats for automotive coating applications and, more particularly, to multi-stage processes for drying a liquid basecoat which include a combination of infrared radiation and convection drying for subsequent powder topcoat application.
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 use with liquid basecoats to be overcoated with powder topcoat.
SUMMARY OF THE INVENTION
The present invention provides a process for coating a metal substrate, comprising the steps of: (a) applying a liquid basecoating composition to a surface of the metal substrate; (b) exposing the basecoating composition to air having a temperature ranging from about 10° C. to about 50° C. for a period of at least about 5 minutes to volatilize at least a portion of volatile material from the liquid basecoating composition, the velocity of the air at a surface of the basecoating composition being less than about 0.5 meters per second; (c) applying infrared radiation and hot air simultaneously to the basecoating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the basecoating composition being less than about 4 meters per second, the temperature of the metal substrate being increased at a rate ranging from about 0.4° C. per second to about 1.2° C. per second to achieve a peak metal temperature of the substrate ranging from about 120° C. to about 165° C., such that a dried basecoat is formed upon the surface of the metal substrate; and (d) applying a powder topcoating composition over the dried basecoat.
Another aspect of the present invention is a process for coating a metal substrate, comprising the steps of: (a) applying a liquid basecoating composition to a surface of the metal substrate; (b) applying infrared radiation and warm air simultaneously to the basecoating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the basecoating composition being less than about 4 meters per second, the temperature of the metal substrate being increased at a rate ranging from about 0.05° C. per second to about 0.3° C. per second to achieve a peak metal temperature ranging from about 30° C. to about 60° C., such that a pre-dried basecoat is formed upon the surface of the metal substrate; (c) applying infrared radiation and hot air simultaneously to the basecoating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the basecoating composition being less than about 4 meters per second, the temperature of the metal substrate being increased at a rate ranging from about 0.4° C. per second to about 1.2° C. per second to achieve a peak metal temperature of the substrate ranging from about 120° C. to about 165° C., such that a dried basecoat is formed upon the surface of the metal substrate; and (d) applying a powder topcoating composition over the dried basecoat.
Yet another aspect of the present invention is a process for coating a polymeric substrate, comprising the steps of: (a) applying a liquid basecoating composition to a surface of the polymeric substrate; (b) exposing the basecoating composition to air having a temperature ranging from about 10° C. to about 50° C. for a period of at least about 5 minutes to volatilize at least a portion of volatile material from the liquid basecoating composition, the velocity of the air at a surface of the basecoating composition being less than about 0.5 meters per second; (c) applying infrared radiation and hot air simultaneously to the basecoating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the basecoating composition being less than about 4 meters per minute, the temperature of the polymeric substrate being increased at a rate ranging from about 0.4° C. per second to about 1.2° C. per second to achieve a peak polymeric substrate temperature ranging from about 120° C. to about 165° C., such that a dried basecoat is formed upon the surface of the polymeric substrate; and (d) applying a powder topcoating composition over the dried basecoat.
Another aspect of the present invention is a process for coating a polymeric substrate, comprising the steps of: (a) applying a liquid basecoating composition to a surface of the polymeric substrate; (b) applying infrared radiation and warm air simultaneously to the basecoating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the basecoating composition being less than about 4 meters per second, the temperature of the substrate being increased at a rate ranging from about 0.05° C. per second to about 0.3° C. per second to achieve a peak substrate temperature ranging from about 30° C. to about 60° C., such that a pre-dried basecoat is formed upon the surface of the polymeric substrate; (c) applying infrared radiation and hot air simultaneously to the basecoating composition for a period of at least about 2 minutes, the velocity of the air at the surface of the basecoating composition being less than about 4 meters per second, the temperature of the polymeric substrate being increased at a rate ranging from about 0.4° C. per second to about 1.2° C. per second to achieve a peak polymeric substrate temperature ranging fro
Cannoni Ann Marie
Padgett Marianne
PPG Industries Ohio Inc.
Uhl William J.
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