Can coatings

#The present technology is related in general to polymer coatings for containers.

#A major source of non-occupational human exposure to 2,2-bis(4-hydroxyphenyl)propane) (a/k/a bis-phenol A, or BPA) is from food can coatings. Interior can coatings, also known as lacquers or enamels, are applied to the interior of cans to prevent corrosion of the can and contamination of food with a metallic taste. As these coatings prevent oxidation of the can, the coatings should have good adhesion to the metal of the can, flow well over the metal surface so that there are no eyeholes or inclusions in the coating, and be durable enough to survive lengthy periods of exposure to often acidic food. The process of coating a can typically involves spraying one or two layers of a coating using an airless spray system (depending on the coating system). This coating is then thermally cured at an elevated temperature, e.g. about 210° C.

#While there are several types of can coatings available, many have very limited application due to incompatibilities with food chemistries, or because of their prohibitively high cost. The choice of resin is typically based on cost and the type of product that is inside the can. The vast majority of food and beverage cans produced today are coated with BPA-based phenolic-epoxy resins. However, BPA has been shown to migrate from the coatings on these cans in small amounts into liquids and food products, thereby posing a potential health risk to humans that consume the food. Due to this, coatings with BPA are becoming disfavored, despite their other superior performance properties.

#FIG. 1A is an illustration of a can coated having a micro-impression coating composition, according to one embodiment, and FIG. 1B is a detail of the portion of FIG. 1A noted as A.

#FIGS. 2A and 2B are illustrations of the design of micro-impressions in coating compositions, where the product of P*TB is greater than the product of A*TO (FIG. 2A), and where the product of P*TB is less than the product of A*TO (FIG. 2B).

#FIG. 3 is a schematic representation of the process of can coating using the micro-impression coating compositions, according to one embodiment..

#The illustrative embodiments described in the detailed description and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

#Two-layer coatings are provided in which a base coating layer, including an extractable amount of a toxic component, such as BPA, is overlaid with a second coating layer that is non-toxic. Such two-layer coatings may be useful in coating the interior of containers in which liquids or foodstuffs for ingestion are stored. The base coating layer includes micro-impressions that may provide higher surface area for extracting the toxic components prior to the application of the second coating layer, and/or may also provide additional adhesion of the second coating layer to the base coating layer. The materials used in the base coating and second coating layers are selected such that should the second coating layer delaminate from the base layer, the portions of the second coating layer contacting (i.e. plugging) the micro-impressions will tear from the second coating layer, thereby remaining as “plugs” in the micro-impressions of the base coating layer. By tearing to leave portions as plugs in the micro-impressions, the second coating layer, even upon de-lamination, provides some protection against further extraction of toxic components from the base coating layer and into the liquid or foodstuff

#Thus, in one aspect, a coating composition is provided. The coating compositions may be useful for coating a variety of substrates such as plastics, metals, glasses etc. The compositions provide for the use of a base coating resin, which adheres sufficiently to substrates, such that the base coating does not peel or lift from the substrate. However, such base coating resins tend to include chemicals capable of being extracted by a solution (i.e. a liquid or foodstuff) that is in contact with the coating resin. Therefore, an overlay coating is also provided, to partially or completely prevent such extraction from occurring.