Coating processes – With post-treatment of coating or coating material – Coating material recirculation or regeneration
Reexamination Certificate
1999-06-30
2001-06-12
Bareford, Katherine A. (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Coating material recirculation or regeneration
C427S235000, C427S236000, C427S348000, C427S424000, C427S434300, C427S439000, C118SDIG003
Reexamination Certificate
active
06245388
ABSTRACT:
BACKGROUND
The invention relates to a process, and to apparatus, for applying a liquid coating to at least one surface of an article. The process produces a high quality, attractive and uniform coating on both flat and contoured surfaces, while minimizing waste of the liquid coating. Preferred articles to be coated using the process are paper plates, cartons, bowls, serving dishes, trays, or similar articles made of molded pulp, pressed or folded paperboard, and the like. While these articles are preferred, essentially any type of article may be coated using the disclosed process and apparatus.
Some manufactured articles can be improved by application of a coating on at least one surface of the article. For example, molded pulp articles used for serving food, such as molded pulp plates and bowls, are light-weight, disposable and low cost. In use, however, these articles can lose their form and/or function in the presence of heat, moisture and/or grease (for example, as in the case of a paper plate weakening when hot, wet food is held in the plate). A protective barrier on a molded pulp or paper article can prevent loss of strength or rigidity due to such factors, which improves the performance of the article in immediate use, and in applications where food is held with or without refrigeration in the article for a period of time, and possibly heated, prior to consumption. Other reasons for coating an article include providing additional surface strength, improving cut resistance, or adding to the aesthetic appearance of the article. For example, one may add color, patterns, textures and sheen to the surface of the article. One may also coat an article to protect an underlying print or to improve its printability.
It is known to pre-apply a wax or polymer coat on the food-contact surface of paperboard, and to thereafter form the paperboard into useful food-service articles. There are problems, however, when attempting to apply coatings to preformed, contoured molded pulp articles rather than to flat paperboard.
GB 1,111,525 (published May 1, 1968) describes some disadvantages of prior art efforts to coat articles, particularly articles with deep contours. For example, dipping an entire article in liquid coating can saturate the article and apply too much coating to the article. Furthermore, it is impractical to dip only the inside (food-contacting) surface of a deeply contoured article into a liquid coating material.
It is also known to spray paper and molded pulp articles with liquid coating materials. See, for example, Canadian Patent Application 2,057,474. Aqueous dispersions or latexes of various plastics, such as acrylic, vinyl and styrene-butadiene, have been sold for many years for use in coating molded pulp articles. Spraying a contoured article with liquid coating, however, can produce uneven coatings, despite the exercise of care in the spray application. Moreover, spray-coating methods used in the prior art generally do not make efficient use of the coating material. Overall, the prior art of coating articles with a protective barrier layer leaves room for improvement.
SUMMARY OF THE INVENTION
The present invention relates to processes, and apparatus, for applying liquid coatings to a surface (or to more than one surface or edge) of an article.
In a first embodiment, the process comprises passing the surface of an article to be coated above an upwardly-directed wave of liquid coating to apply the coating to the surface in excess. Preferably, the wave of coating is applied by one or more upwardly pointed nozzles, which nozzles direct the wave(s) of coating onto the articles to be coated as the articles are passed above the nozzles and through the wave of coating. For example, the articles may be positioned on moving conveyer belt which passes the articles through the wave coating(s), exposing the surface of the articles to be coated to an excess of the coating. After coating the surface of the article, the excess coating is then removed and the coated article is dried.
In a preferred aspect, the wave coating of the article and the removal of excess coating, as described above, are carried out in an atmosphere which is vaporous with the liquid coating vehicle. This can be accomplished by carrying out the coating application and coating removal steps in a closed environment. Inside the closed environment, the water (or other coating solvent) which comprises the vehicle of the liquid coating is caused to permeate the coating atmosphere, to make the closed environment vaporous with the vapor of the coating vehicle. The is preferred coatings are aqueous dispersions, and using these coatings, the closed atmosphere is vaporous with water vapor. Maintenance of a vaporous atmosphere during coating and removal of excess coating has been found to considerably, and surprisingly, enhance the quality of the coating, for example in terms of evenness, lack of streaking and other desirable coating qualities.
It has also been found that, when using a vaporous, closed environment for the application of liquid coating and coating removal steps of the process, it is possible to apply the liquid coating other than by wave-coating. Thus, in a different embodiment of the invention, an excess of liquid coating is applied to a surface of an article, and thereafter the excess coating is removed, wherein the aforesaid coating application and coating removal steps are carried out in a closed environment which is vaporous with the vehicle of the liquid coating. In the vaporous environment of the closed atmosphere, any type of coating application means may be used to apply the liquid coating (which in this embodiment is also preferably an aqueous dispersion) while still obtaining t desired high quality, attractive coatings.
In both embodiments of the process as described above, the excess coating is preferably recovered and reused in the coating process. In a vaporous, closed environment as described, it is possible to apply the coating, remove the excess coating, and reuse the coating, without substantial drying of the coating. This allows for significantly more efficient use and reuse of the liquid coating.
The apparatus of the invention comprises means for applying a wave of liquid coating to a surface of an article, means for removing the excess of liquid coating from the coated surface, means for recovering excess coating for reuse, and means for maintaining a closed environment, which is vaporous with the coating vehicle, during the coating application, coating removal and coating recovery.
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Charny John Allie
Foster Peter D.
Bareford Katherine A.
Connolly Bove & Lodge & Hutz LLP
The Chinet Company Technology
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