Patent Abstract:
Anodized aluminum cookware having an exposed copper base or ring is formed by anodizing the completed vessel using a protective cap to cover most of the copper. The portion of copper that is exposed to the anodizing bath only tarnishes slightly and is preferably polished off after a protective lacquer is applied, creating a clean even margin with the anodized aluminum portion of the vessel.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     None 
     BACKGROUND OF INVENTION 
     The present invention relates to a method of manufacturing cookware having a decorative design. 
     Copper and copper clad cookware are well know. However, the copper cladding hides the beauty of copper. Some styles of copper cookware have a base that is a laminate of copper with other metal, such as aluminum and stainless steel for protection. 
     Exposing at least a portion of the copper core normally hidden behind cladding is desirable as a decorative effect, but also helps the cook differentiate the cookware from similar cookware that does not have a highly conductive base or sidewalls. 
     One such novel design, now the subject of a commonly owned U.S. design patent application no. 29/313,712 filed Feb. 3, 2009, now U.S. Design Pat. No. D652,670, is shown in  FIG. 1 . As disclosed further herein and not admitted as prior art, such an ornamental appearance of cookware vessel  100  can be provided by an anodized aluminum portion that forms a vessel  110  for containing fluid, which is dark grey in color and a generally matte finish. The base  105  or bottom of vessel  100  is a laminate of copper cap which is attached to the aluminum vessel body  110  followed by a protective cap of stainless steel  130  attached to the copper base or cap  130 . The stainless steel cap  130  does not extend upward to the anodized aluminum, but exposes an annular rim  114  of copper metal. This construction thus produces a decorative design of a grey body, with a bright copper rim between the bright silvery stainless steel base.  FIG. 2A  shows the construction of the vessel  100  in cross-section, with  FIG. 2B  showing a magnified partial view of the cookware wall adjacent the rim thereof. 
     This construction is preferred for protecting the copper layer with the stainless steel cap, and the scratch resistance of the anodized alumina body, as well as the higher thermal conductivity of the copper. However, similar appearing cookware can be made using paints or finishes to provide the matte color of the alumina; or plating can be used to create the visual impression of a thick copper layer in the cap. 
     It is therefore a first object of the present invention to provide an improved method for fabricating a cookware article having a portion of exposed copper adjacent an anodized aluminum layer. 
     It is also an object of the invention to provide improved method for fabricating a cookware article having a portion of exposed copper adjacent an anodized aluminum layer wherein a steel cap protects the lower portion of the exposed copper so that only a band or ring remains visible. 
     It is a further object of the invention to provide such methods wherein the seams or margins between the different layers, and in particular between the copper and aluminum has a regular sharp transition along the entire periphery of the vessel, and to do so in a cost effective manufacturing process. 
     SUMMARY OF INVENTION 
     In the present invention, the first object is achieved by a process for fabricating anodized cookware comprising the steps of providing a cooking vessel having an exposed aluminum upper portion and an exposed copper lower portion, attaching a protective cap to cover substantially all of the exposed copper portion without covering the exposed aluminum portion, immersing the vessel in an anodizing bath, applying electrical current to the vessel to anodize the exposed aluminum portion thereof creating an alumina coating thereon, wherein the exposed portion of the copper not covered by said cap remains intact, having formed thereon a thin layer of copper oxides. 
     The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of the embodiments thereof taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an exterior elevation of cooking vessel having a decorative color pattern formed from the sidewall and the dual layer base of copper and stainless steel. 
         FIG. 2A  is a cross-sectional elevation of the vessel of  FIG. 1 .  FIG. 2B  is a cross-sectional elevation of the portion of the vessel indicated in  FIG. 2A . 
         FIG. 3A  is a cross-sectional elevation of just a portion of the base of the vessel in  FIGS. 1 and 2  to show a first embodiment for a masking boot and a method of anodizing and finishing the vessel. 
         FIG. 3B  is cross sectional elevation of the vessel in  FIG. 3A  after anodizing. 
         FIG. 3C  is a cross sectional elevation of the vessel in  FIG. 3B  after applying protective lacquers or finishes on the entire outer surface to hide the un-anodized layer. 
         FIG. 4A  is a cross-sectional elevation of just a portion of the base of the vessel in  FIGS. 1 and 2  to show a preferred deployment of the masking boot. 
         FIG. 4B  is a cross sectional elevation of the vessel in  FIG. 3A  after anodizing. 
         FIG. 5A  is a cross sectional elevation of  FIG. 4B  after coating with a protective organic finish. 
         FIG. 5B  is a cross sectional elevation of  FIG. 5A  after polishing the base. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 through 5 , wherein like reference numerals refer to like components in the various views, there is illustrated therein a new and improved Anodized Aluminum Cookware with Exposed Copper, generally denominated  100  herein. 
     One method of creating a cookware vessel with the appearance shown in  FIG. 1  and  FIG. 2  is to anodize the vessel  100  after attachment of a copper base or cap layer  130 , as well as a final stainless steel cap  120  to the bottom of the aluminum vessel  110 . This leaves the interior of the vessel  110   a  and the exterior portion  110   b  above the copper layer  130  with an exterior of alumina or an aluminum oxide coating  115 , which has a matte grey color However, as the anodizing treatment occurs by passing current through the vessel in a hot concentrated sulfuring acid solution, the none aluminum portions of the vessel, i.e. the copper and stainless steel, should be masked to avoid their undesirable and extensive corrosion in this media. While the masking can be painted on the stainless steel cap  120  and exposed ring of the copper base  130  very precisely, this is time consuming. 
     It is far easier to cover the base with a conforming rubber base or boot  310  as shown in  FIG. 3A . As any misalignment in the boot or, variations in manufacture of either the boot  310  or the article  100 , might leave some portion of the base exposed, the boot can be slightly oversized to cover a small extra portion  113  of the aluminum. This produces a portion of the aluminum  113  that is not anodized, which in contrast to anodized coating on the exterior  112 , would thus stand out, being a highly reflective metal. Fortunately protective lacquers or finishes can be applied to the entire outer surface to hide this imperfection, the result of which is shown in  FIG. 3C . However the precise application of this material  116 , to avoid covering the copper  130 , can also be time consuming. However, such a coating  116  is still preferred as it offers other benefits, as for example when it incorporates silicones, fluorocarbon polymers and the like provide a relatively heat resistant non-stick finish. Examples of such coatings include organic materials that may comprise of other polymers and resins, as well as inorganic pigmenting agents, filler and reinforcing agents such as described in U.S. Pat. Nos. 5,250,356 and 5,194,336 as well as combined inorganic—organic coatings systems as disclosed in U.S. Pat. No. 7,244,502, all of which are incorporated herein by reference. The fillers in the coating  116  can give an appearance comparable to anodized aluminum, or alternatively create a different decorative finish if desired. It should be appreciated that a different non-stick finish  116  can be used in the interior of  110   a  of the vessel  100 , which can include multiple layers to increase durability. 
     An improved masking means has been discovered to avoid leaving this region  113  of un-anodized aluminum adjacent the copper band  114 . Rather than trying to cover the entire copper base  130  that appears externally as a circumferential band  114 , it is beneficial to provide as shown in  FIG. 4A , a protective boot  310 ′ that is sized just smaller than the nominal combined thickness of the copper  130  and stainless steel  120  bases, leaving only a small portion  401  of the copper exposed. 
     It has been surprisingly discovered that the conventional anodizing bath does not as aggressively attack the copper  130  when only a small portion  401  is exposed, and that the oxidation that does occur is easily removed in the final polishing step of the stainless steel  120  and copper base  130 . 
     This is remarkable in light of the observations that if the entire copper base  130  is exposed it will be completed corroded, usually delaminating the bond with the aluminum portion  110  and allowing attack into the stainless steel cap  120  from what was the copper interface therewith. 
     Not wishing to be bound by theory, it is believed that this remarkable reduction in oxidation of the copper occurs uniquely in this configuration because the heat of oxidation is quickly removed by conduction through the unexposed copper so that the reaction never auto accelerates from the heat that is generated. In other words, when the entire copper base is exposed to an anodizing condition, the rate of oxidation of bulk copper is auto-catalytically accelerated due to the heat of reacting and thus increasing the reaction rate. However, when just a small amount of copper is exposed, the heat of reaction is removed by the copper bulk such that the reaction rate remains low and never accelerates. Thus, the aluminum surfaces  110   a  and  110   b  are oxidized at a faster rate to produce the protective alumina coating  115  that is durable, while producing only a very thin superficial layer of copper oxides  411  on the exposed rim or exterior  114  of the copper base  130 . 
     Whatever method is used to mask the copper and stainless steel bases, it is preferable to cover at least the anodized aluminum with the exterior protective lacquer  116 , as well as a similar non-stick coating on the interior, as shown in  FIGS. 3C and 5B . 
     In a further preferred embodiment of the invention, illustrated in  FIGS. 5A and 5B , the exterior protective lacquers  116  is applied to the entire exterior of the vessel, without concern that portion of the stainless steel cap  120  and copper base or band  130  are covered ( FIG. 5A ). Next the base  117  of the vessel  110  is polished to remove the portion  116   a  that cover the copper band  130  and steel cap  120 . This polishing step also removes the thin strip of copper oxides or tarnish  411 , resulting in the completed vessel  100  shown in  FIG. 5B . 
     Other embodiments of the invention include an anodized aluminum vessel with a copper cap, or other exposed copper portions and do not necessarily require a steel cap  120 . 
     While the invention has been described in connection with several preferred embodiments, it is not intended to limit the scope of the invention to the particular form set forth. On the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be within the spirit and scope of the invention as defined by the appended claims.

Technology Classification (CPC): 0