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, telegraphing roughness through an outer coating to create texture.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 08/362,078 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 textured surface. 
     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, processes 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 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 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. 
     Included in the invention are a method of making an article in which the coatings are applied by spraying coating compositions successively on the substrate and ultimately heating the article to cure the coating, wherein the coating under the discontinuous coating is dried enough before applying the discontinuous coating so that substantial portions of the spattered coating remains on top of said under coating to create the roughness telegraphing through the topcoat. 
    
    
     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 an 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 coming. 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°) 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. Furthermore, mixtures of solid pigments, different colored coated mica, and all of these can be used for unusual optical effects. 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. The temperature being controlled is that of the substrate metal rather than that of the oven, which will vary with the speed of product through the oven and the length of the oven. 
     
                       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                48.33    --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   30.00Hydroxylpropyl  30.00     15.00   20.00cellulose soln.Viscosity in centipoise as           682       608     682measured by Brookfleld#2 spindle, @20 rpm______________________________________ 
    
     
                                           TABLE 4__________________________________________________________________________       White        Gray             Solids Content                          Solids Content       Coating             in Finished                    Coating                          in Finishes       Composition             Article                    Composition                          ArticleSpatter Coats       (Wt. %)             (Wt. %)                    (Wt. %)                          (Wt. %)__________________________________________________________________________PTFB Dispersion       50.29 71.04  50.61 70.63PFA Dispersion       8.91  12.58  8.96  12.52Al.sub.2 O.sub.3 Ceramic Dispersion       4.64  5.46   4.67  5.43TiO.sub.2 Dispersion       9.28  10.92  9.34  10.86Carbon black Dispersion       --    --     0.75  0.52Surfactant-Catalyst Solution       12.99 --     13.07 --Acrylic Dispersion       11.13 --     11.20 --Hydroxyl propyl       2.78  --     1.40  --cellulose soln.Viscosity in centipoise as       682          608measured by Brookfield#2 spindle, @20 rpm__________________________________________________________________________ 
    
     
                       TABLE 5______________________________________                      Solids Content            Coating   in Finished            Composition                      ArticleTopcoat          (Wt. %)   (Wt %)______________________________________PTFB 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     --______________________________________ 
    
     COMPARISON 1 
     The same process is carried out except the discontinuous coat is applied immediately after midcoat application (wet-on-wet) without flash drying. 
     Accelerated abuse cooking results, using 6 pans of each, gave the results of Table 6. The rating of 5 is a standard judged by an experienced tester, based on damage to the coating from a number of standardized cooking tests, using weighted ball point pens to abuse the coatings. This shows the superior durability of the invention. 
     
                       TABLE 6______________________________________       # of cooks to 5 rating______________________________________Ex. 1         97 AvgComparison 1  78 Avg______________________________________