Abstract:
Cookware with a multi-layer, non-stick coating on its cooking surface has a random spattered pattern of raised dots or globules in an inner coat, made by spraying the globules on at an angle to create a random, stone-like appearance.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 08/362,079 filed Dec. 22, 1994 abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention concerns non-stick coated cookware, with a decorative pattern visible through a light transmitting topcoat. More specifically, it concerns such cookware with a pattern formed by irregular discontinuous globules. 
     U.S. Pat. No. 4,259,375--Vassiliou (1981 ) discloses an article of cookware with a 3-layer coating having a discontinuous speckled or spattered pattern in a partial layer directly beneath the topcoat. The spattered coating is deliberately sprayed directly on the layer under it while the under layer is still wet and soft so that the spattered layer sinks into the under layer and does not provide roughness that could telegraph through the surface. It was said that roughness would provide a place for a fork or other utensil to catch in the coating and tear the coating. The spattered layer dots were also sprayed on directly, such as at 90 degrees from the substrate, so as to form more or less round dots. This patent is incorporated by reference herein for its disclosure of materials and equivalents suitable for the present invention. 
     U.S. Pat. No. 3,961,993--Palisin (1976) discloses spraying multilayer polymer coatings on a substrate, one layer being sprayed on top of the layer under it after the under layer has become tacky. A tacky underlayer permits the successive layer to adhere better without completely merging indistinguishably with the underlayer. Still, any roughness in the upper layer would tend to smooth out as the two layers interact. 
     U.S. Pat. No. 3,655,421--Long (1972) describes means of keeping globules of an intermittent coating from flowing out to make a uniform layer, by controlling surface tension relations. 
     It is desirable to have a superior non-stick, decorative coating for cookware optionally with a raised or textured surface and with greater flexibility for aesthetic design than just to make smooth round dots. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of making an article of cookware having a cooking surface which comprises a multi-layer, non-stick coating which minimizes sticking by food residues and which is heat resisting by being stable at temperatures above 300° C. on a substrate, wherein the coating comprises a primer adhered to the substrate, a non-stick, heat-resisting, light-transmitting topcoat, and optionally one or more intermediate coats, with the topcoat adhered to any such intermediate coats which are adhered to the primer or, in the absence of intermediate coats, the topcoat being adhered directly to the primer, with the coating under the topcoat having a first color or darkness, wherein a discontinuous layer of raised globules is present on and covers no more than 80% of the area of the coating under the topcoat, said globules having at least one color or darkness which is visibly different than said first color or darkness as seen through said topcoat, said discontinuous layer creating a texture or roughness in said topcoat wherein the globule coating is sprayed onto the substrate at an angle of the center of the spray stream to the substrate in the range of 30 to 75 degrees, creating a spattered pattern of non-round dots. 
    
    
     DETAILED DESCRIPTION 
     An important part of the process for obtaining the present invention is the drying or &#34;flashing&#34; the primer or intermediate coat before applying the discontinuous coat, adequately so the spattered dots do not sink into the primer or the intermediate coat. In normal application, air flow for 30 seconds or longer, or preheating the substrate or the air with a shorter time of air flow, will suffice. 
     Those skilled in the art know how to select the ingredients of each coating to avoid wetting which might cause the globules to run together. Wetting is generally not a problem with most heat resistant materials useful for cookware coatings, especially perfluoropolymers such as polytetrafluoroethylene and (PTFE) and copolymers of TFE and fluorovinyl ethers (PFA). 
     Preferably the coatings contain oxide-coated mica, and preferably the oxide in TiO 2 , as described in U.S. Pat. Nos. 3,087,827--Klenke et al., 3,087,828 and 3,087,829--both to Linton, and granted 1963. 
     In the examples which follow, parts, percentages and proportions are given by weight except where stated otherwise. 
     EXAMPLE 1 
     A primer having the composition of Table 1 is sprayed on a clean, lightly etched aluminum substrate to a dry film thickness (DFT) of 7.5 to 10 microns, the primer is dried at 66° C. for 3 minutes and a black midcoat of Table 2 is applied to a DFT of 17.5 to 20 microns. The midcoat is allowed to dry at ambient temperature for 45 seconds and three separate inks or spatter coatings are applied using a DeVilbiss spatter gun to provide a discontinuous coating. The inks of Table 3 or 4 are colored to be significantly different than the black midcoat background and are sprayed at a 45° angle (or at an angle of from 30° to 75°, preferably 45° to 60°) to provide irregular shapes on the spinning substrate. The effect is to provide an appearance of natural stone. The inks are not limited to solid color pigments but also include color achieved by reflectance with coated mica. A topcoat of Table 5 is then applied wet-on-wet over the spattered particles. The topcoat, in this example, contains mica particles in a 1-15 micron particle size range so as not to interfere with the aesthetics of the spatter coat. The entire system is sintered at 427° to 435° C. for 5 minutes, with the measured temperature being that of the metal substrate. 
     
                       TABLE 1______________________________________                Coating  Solids Content                Composi- in Finished                tion     ArticlePrimer               (Wt. %)  (Wt %)______________________________________Furfuryl Alcohol     1.82     --Polyamic acid salt in N-Methyl Pyrrolidone                18.10    24.48Water                43.33    --Mica coated with TiO.sub.2                0.05     0.24PTFE Dispersion      7.93     22.19FEP Dispersion       5.88     15.08Colloidal Silica Dispersion                3.58     5.00Ultramarine blue dispersion                13.74    32.06Aluminum silicate dispersion                0.58     0.94______________________________________ 
    
     
                       TABLE 2______________________________________                      Solids Content            Coating   in Finished            Composition                      ArticleIntermediate     (Wt. %)   (Wt %)______________________________________PTFE Dispersion  56.34     77.43PFA Dispersion   10.21     14.22Water            4.62      --Carbon black dispersion            2.71      3.79Ultramarine blue dispersion            0.49      3.22Mica coated with TiO.sub.2            0.75      1.73Surfactant catalyst soln.            12.63     --Acrylic dispersion            12.23     --______________________________________ 
    
     
                       TABLE 3______________________________________Typical spatter ink formulation composition (parts by weight)       A (white) B (gray)                         C (brown)______________________________________PTFE Dispersion         542.0       542.0   542.0PFA Dispersion         96.0        96.0    96.0Ceramic Dispersion         50.0        50.0    --TiO.sub.2 Dispersion         100.0       100.0   20.0Iron Oxide Dispersion         --          --      80.0Channel Black Dispersion         --          8.0     2.0Solvent Surfactant Blend         110.00      110.00  110.00Acrylic Dispersion         120.00      120.00  120.00Solvent-Surfactant Blend         30.00       30.00   30.00Hydroxyl propyl         30.00       15.00   20.00cellulose soln.Viscosity in centipoise as         682         608     682measured by Brookfield#2 spindle, @ 20 rpm______________________________________ 
    
     
                       TABLE 4______________________________________    White        Gray      Coating Solids Content                         Coating                               Solids Content      Compo-  in Finished                         Compo-                               in Finishes      sition  Article    sition                               ArticleSpatter Coats      (Wt. %) (Wt. %)    (Wt. %)                               (Wt. %)______________________________________PTFE Dispersion      50.29   71.04      50.61 70.63PFA Dispersion      8.91    12.58      8.96  12.52Al.sub.2 O.sub.3 Ceramic      4.64    5.46       4.67  5.43DispersionTiO.sub.2 Dispersion      9.28    10.92      9.34  10.86Carbon black      --      --         0.75  0.52DispersionSurfactant-Catalyst      12.99   --         13.07 --SolutionAcrylic Dispersion      11.13   --         11.20 --Hydroxyl propyl      2.78    --         1.40  --cellulose soln.Viscosity in      682            608centipoise asmeasured by Brook-field #2 spindle,@ 20 rpm______________________________________ 
    
     
                       TABLE 5______________________________________                     Solids Content           Coating   in Finished           Composition                     ArticleTopcoat         (Wt. %)   (Wt %)______________________________________PTFE Dispersion 66.73     94.04PFA Dispersion  3.51      4.95Water           3.77      --Mica coated with TiO.sub.2           0.43      1.01Surfactant catalyst soln.           12.52     --Acrylic dispersion           13.04     --______________________________________