Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-09-14
2003-10-28
Zacharia, Ramsey (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S411100, C428S419000, C428S421000, C428S469000, C428S471000, C428S472000, C428S473500
Reexamination Certificate
active
06638600
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a nonstick coating for application to an aluminum surface. More particularly, the present invention relates to a nonstick coating that is formed by applying a ceramic substrate to an aluminum surface and applying a fluorocarbon polymer coating to the ceramic substrate.
BACKGROUND OF THE INVENTION
Fluorocarbon polymers, such as polytetrafluoroethylene (PTFE), polymers of chlorotrifluoroethylene (CTFE), fluorinated ethylene-propylene polymers (FEP), polyvinylidene fluoride (PVF), combinations thereof and the like, are known to have superior nonstick properties. For this reason, they have been used in a wide variety of applications, including forming nonstick coatings on articles of cookware. However, due to the inherent nonstick nature of these fluorocarbon polymers, it has been difficult to form nonstick coatings that adhere well to substrates such as pure aluminum, alloys of aluminum, and aluminized steel. Moreover, due to the inherent softness of fluorocarbon polymers, it has been difficult to form nonstick coatings that resist abrasion.
In an effort to overcome these difficulties, it has been the conventional practice to apply one or more base coats containing adhesive resins in order to better adhere fluorocarbon polymer top coats to substrates (throughout this specification and in the claims, the terms “bases coat” and “primer coat” are used interchangeably). In general, such base coats comprise a combination of high temperature binder resins, such as polyamideimide resins (PAI), polyethersulfone resins (PES) or polyphenylene sulfide resins (PPS), and fluorocarbon polymer resins. The performance of these conventional nonstick coating systems is based upon a stratification of the applied coatings. This stratification results in a coating that is rich in high temperature binder on the bottom and rich in fluorocarbon polymer at the top. The binder-rich bottom provides adhesion to the substrate while the fluorocarbon polymer-rich top provides a layer to which subsequent fluorocarbon polymer top coats can be fused by sintering at high temperature.
The performance of such nonstick coating systems is at best a compromise. The bottom layer of the base coats is not a purely binder resin. Considerable levels of fluorocarbon polymer resins must be included in the base coats in order to provide a layer that is sufficiently rich in fluorocarbon polymer to promote good bonding of subsequent fluorocarbon polymer top coats to the base coat. The presence of fluorocarbon polymer resins in the base coat are disadvantageous because they detract from the adhesion of the base coat to the substrate. Therefore, it has been necessary to roughen substrates by mechanical (e.g. grit blasting) or chemical (e.g. etching) means to assist holding the base coat to the substrate.
Moreover, because both the adhesive resins and fluorocarbon polymers are relatively soft, there have been difficulties in making these nonstick coatings resistant to abrasive wear. Efforts to overcome these deficiencies have included the addition of mica particles, ceramic fillers, or metal flakes to the intermediate and top coat in order to increase the hardness. The presence of these fillers can be disadvantageous. For example, incorporation of metal flakes in the applied coatings can actually promote chemical corrosion of the underlying metal substrate due to dissimilarity between the metals. Moreover, these particulate fillers cannot be incorporated into the nonstick coating at high levels because at high levels they diminish the nonstick properties of the coating and the bonding to the substrate.
Due to the limitations thus described, articles of cookware coated with conventional fluorocarbon polymer nonstick coating systems are prone to damage and abrasive wear during normal use. Cooking utensils, for example, often cause cuts, slices, or gouges in the nonstick coating which permit acids or alkaline foodstuffs and cleaning agents to penetrate to the exposed aluminum substrate and cause corrosion. Corrosion of the underlying aluminum by these materials can further weaken the adhesion of the nonstick coating adjacent to the cut or slice. Moreover, abrasive forces routinely encountered in cooking and cleaning cause the gradual removal of the soft fluorocarbon polymer top coat resulting in diminished nonstick properties. Conventional nonstick coatings simply do not adequately protect the aluminum substrate from corrosion or the fluorocarbon polymer top coat from routine abrasive wear.
SUMMARY OF INVENTION
The present invention provides a new and useful nonstick coating for use on an aluminum surface, a methods of forming such a nonstick coating, and articles of cookware having such a nonstick coating applied thereto. A nonstick coating according to the present invention comprises a ceramic substrate disposed on an aluminum surface and a fluorocarbon polymer coating disposed on said ceramic substrate. The ceramic substrate, prior to firing, comprises at least two layers: a first or bottom layer that is applied to the aluminum surface comprising an enamel ground coat; and a second or top layer applied over the enamel ground coat comprising a blend of one or more glass frits, non-ceramic refractory particles, and non-vitreous inorganic oxide particles. Upon firing, the portion of the ceramic substrate in contact with the aluminum surface comprises a continuous layer of vitreous enamel that is bonded to the aluminum surface, and the exposed surface of the ceramic substrate exhibits a micro-rough texture that is enriched with bonding sides for binder resins in a fluorocarbon polymer primer layer. The ceramic substrate protects the aluminum surface from corrosion and mechanical damage and also protects the fluorocarbon polymer coating from abrasive wear.
A nonstick coating according to the present invention can be applied to an aluminum surface that has been cleaned only. It is not necessary to grit blast or acid etch the aluminum surface in order to attain satisfactory adhesion of the coating. Moreover, a nonstick coating according to the present invention is substantially more durable than conventional nonstick coatings. A nonstick coatings according to the invention is particularly well-suited for use in food preparation applications, but can be used in any application where a durable nonstick coating is desired.
A nonstick coating according to the present invention is formed by applying a ceramic substrate to an aluminum surface and then applying a fluorocarbon polymer coating to the ceramic substrate. In a preferred embodiment, the ceramic substrate is formed by spraying a first layer comprising an enamel ground coat onto the aluminum surface, flash drying the first layer, applying a second layer comprising a blend of one or more glass frits, non-ceramic refractory particles, and non-vitreous inorganic oxide particles, and then firing the applied first and second layers to form a ceramic substrate comprising a continuous layer of vitreous enamel that is bonded to the aluminum surface that has an exposed surface having a micro-rough texture that is enriched with bonding sides for the binder resins in a fluorocarbon polymer primer layer. Next, a fluorocarbon polymer primer layer and one or more fluorocarbon polymer top coats are successively applied to the ceramic substrate by spraying and then sintered to form the nonstick coating.
The foregoing and other features of the invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention provides a nonstick coating for use on an aluminum surface. Throughout the specification and in the appended claims, the term “aluminum surface” is intended to mean any metallic surface that bears a substantial amount of alumin
Gazo Louis J.
Sridharan Srinivasan
Ferro Corporation
Rankin, Hill Porter & Clark LLP
Zacharia Ramsey
LandOfFree
Ceramic substrate for nonstick coating does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ceramic substrate for nonstick coating, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ceramic substrate for nonstick coating will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3150310