Coating processes – With pretreatment of the base – Heating or drying pretreatment
Patent
1998-08-12
2000-11-28
Short, Patricia A.
Coating processes
With pretreatment of the base
Heating or drying pretreatment
427209, 4273743, 427386, 4273881, 428 358, 428418, 428458, 525176, 525177, 525437, 525438, 525444, B05D 302
Patent
active
061532649
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to extrusion coating compositions for metal substrates that, after application, demonstrate excellent adhesion, weather-ability, barrier properties, and flexibility; to a method of extrusion coating a metal substrate; and to a metal article, such as a metal can or container, or a material of construction, like aluminum siding, having at least one surface coated with an adherent layer of an extrusion coating composition. An extrusion coating composition comprises: (a) a polyester having a weight average molecular weight of about 10,000 to about 50,000, and optionally, (b) a modifying resin, for example, an epoxy or phenoxy resin having an epoxy equivalent weight of about 500 to about 15,000. The extrusion coating composition is applied to a metal substrate as a film having a thickness of about 1 to about 40 microns.
BACKGROUND OF THE INVENTION
It is well known that an aqueous solution in contact with an untreated metal substrate can result in corrosion of the untreated metal substrate.
Therefore, a metal article, such as a metal container for a water-based product, like a food or beverage, is rendered corrosion resistant in order to retard or eliminate interactions between the water-based product and the metal article. Generally, corrosion resistance is imparted to the metal article, or to a metal substrate in general, by passivating the metal substrate, or by coating the metal substrate with a corrosion-inhibiting coating.
Investigators continually have sought improved coating compositions that reduce or eliminate corrosion of a metal article and that do not adversely affect an aqueous product packaged in the metal article. For example, investigators have sought to improve the imperviousness of the coating in order to prevent corrosion-causing ions, oxygen molecules and water molecules from contacting and interacting with a metal substrate. Imperviousness can be improved by providing a thicker, more flexible and more adhesive coating, but often, improving one advantageous property is achieved at the expense of a second advantageous property.
In addition, practical considerations limit the thickness, adhesive properties and flexibility of a coating applied to a metal substrate. For example, thick coatings are expensive, require a longer cure time, can be esthetically unpleasing and can adversely affect the process of stamping and molding the coated metal substrate into a useful metal article. Similarly, the coating should be sufficiently flexible such that the continuity of the coating is not destroyed during stamping and molding of the metal substrate into the desired shape of the metal article.
Investigators also have sought coatings that possess chemical resistance in addition to corrosion inhibition. A useful coating for the interior of a metal container must be able to withstand the solvating properties of a product packaged in the metal container. If the coating does not possess sufficient chemical resistance, components of the coating can be extracted into the packaged product and adversely affect the product. Even small amounts of extracted coating components can adversely affect sensitive products, like beer, by imparting an off-taste to the product.
Conventionally, organic solvent-based coating compositions were used to provide cured coatings having excellent chemical resistance. Such solvent-based compositions include ingredients that are inherently water insoluble, and thereby effectively resist the solvating properties of water-based products packaged in the metal container. However, because of environmental and toxicological concerns, and in order to comply with increasingly strict governmental regulations, an increasing number of coating compositions are water based. The water-based coating compositions include ingredients that are water soluble or water dispersible, and, therefore, cured coatings resulting from water-based coating compositions often are more susceptible to the solvating properties of water.
In addition, water-based coa
REFERENCES:
patent: 4012363 (1977-03-01), Bruning et al.
patent: 4246378 (1981-01-01), Kometanie et al.
patent: 5407702 (1995-04-01), Smith et al.
Chemical Abstracts, Registry File RN118330-58-8.
Jimenez Artemia
Jung Rolf
Lu Martin
Postle Stephen
Schmid Christina
Short Patricia A.
The Dexter Corporation
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