Abstract:
A disposable plate or tray includes a substantially planar bottom portion, a sidewall and a flange. A profile extending from the center to the outer edge article is characterized by a plurality of direction changes having a radius of curvature to diameter ratio of at least about 0.02.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/142,137, filed July 2, 1999.  
         TECHNICAL FIELD  
         [0002]    The present invention relates generally to disposable food service articles such as plates, trays and the like and in preferred embodiments to food serving plates and plates formed from high modulus, mineral-filled polyolefin sheet and most preferably mineral-filled polypropylene.  
         BACKGROUND  
         [0003]    Disposable articles are commonly formed with a curled lip to impart strength to a cup, canister, or carton for example, as is-seen in United States Patent No. 5,184,995 to  Kuchenbecker . The curl tends to give the article a utilitarian look and feel, not necessarily optimally aesthetically pleasing; especially for disposable articles which can be re-used on multiple occasions such as plastic articles.  
           [0004]    There is shown in the United States Patent No. 4,578,296 of  Miyazaki  et al. a thermoformed article manufactured from filled polyolefin sheet. The polyolefin resin composition includes from 30 to 80 percent of resin, from 19 to 69 percent by weight talc and from 1 to 10 percent by weight titanium dioxide. An article formed from the sheet typically includes a curled lip or a severely downwardly projecting outer lip. Note column 9, line 49 through column 10, line 38.  
           [0005]    In accordance with the present invention, there are provided disposable service articles without a curled or severely downturned flange, which features are undesirable in terms of aesthetic qualities and brittleness.  
         SUMMARY OF THE INVENTION  
         [0006]    The invention is described below with reference to the attached figures which show preferred shapes and dimensions. Following the conclusion of the description and claims is an appendix enumerating preferred materials of construction for the articles disclosed and claimed herein.  
           [0007]    The plates of the present invention include in a preferred embodiment a plastic plate with a four- radius profile which balances the need for increased rigidity (strength) and rim stiffness (sturdiness) per given material weight/cost. The ergonomic rim profile provides for ease of holding and carrying, consumer friendly shape denoting Permanentware qualities, without the negative side effect of brittleness encountered when using high modulus / stiffness construction materials. The four-radius disposable plastic plate design has a curvilinear rim surface onto which patterning can be applied for visual, tactile and strength purposes. The plate design is strong but not brittle during use even with the high modulus / stiffness mica filled polypropylene (PP) plastic material.  
           [0008]    Plates produced with other shapes were rigid but often failed by brittle cracking in the flange and downturn areas. The stresses generated in the flange and downturn areas by deflection of the product during use apparently exceeded the highly filled material strength resulting in failure. It is possible that imperfections on the product&#39;s trimmed edge may contribute to brittle cracking by providing failure initiation points for the notch sensitive, highly filled materials preferably used in accordance with the invention and set forth in the attached Appendix.  
           [0009]    It was discovered that plastic plates described in this invention disclosure still had exceptional strength per material weight, but also significantly reduced brittle cracking with the highly filled nonhomogeneous materials. The four-radius design, for example, would not build up the high stress levels during deflection even with trimmed edge may imperfections and was less prone to brittle cracking.  
           [0010]    Plates having a circular configuration as illustrated employ the four-radius plastic plate design. The plastic articles of manufacture may also be square or rectangular in shape having angular comers, such as found in a tray. Further, additional plastic shapes such as triangular, multi-sided, polyhexal, etc. are contemplated including compartmented trays and oval platters.  
           [0011]    It will be appreciated that a salient feature of the inventive articles is the smooth profile as described herein. In general, the transitions between the center, sidewall and flange of the plate are kept free of sharp bends or curves so that mechanical stresses are not concentrated beyond the ability of the material to withstand them. In addition to being operative to avoid undesirable stress regions, the profile is flowing in appearance and provides a pleasing, ergonomic hand feel.  
           [0012]    In general, the invention is directed to disposable food contact articles formed of a polyolefin, mineral-filled sheet and have a characteristic diameter as well as a substantially planar central portion, a sidewall portion and a flange portion. For a circular article such as a plate, the characteristic diameter is simply the diameter of the plate as the term is ordinarily employed, i.e., the distance through the center between opposing outer edges of the flange. For non-circular articles, the characteristic diameter is the average distance through the center between opposing outer edges of the flange of the article. Thus, for a rectangular article the characteristic diameter is the average of the shorter side and the longer side, for an oval article the characteristic diameter is the average of the minor axis length and major axis length of the oval and so forth.  
           [0013]    The inventive articles are characterized by a smooth profile wherein direction changes are accomplished by way of a plurality of arcuate portions, each of which has a radius of curvature. A particularly preferred embodiment is a four radius plate as described herein, characterized in that the ratio of the length of each radius of curvature to the diameter is at least about 0.02. A ratio of at least about 0.03 is preferred with a ratio of at least about 0.035 being still more preferred. Various details will become more understood by reference to the attached Appendix, drawings and detailed description which follows. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    The invention is described in detail below with reference to the various drawings. In the drawings:  
         [0015]    [0015]FIG. 1 is a view in perspective of a plate constructed in accordance with the present invention;  
         [0016]    [0016]FIG. 2 is a view in cross-section and elevation of the plate of FIG. 1 illustrating the profile of the plate; and  
         [0017]    [0017]FIG. 3 is a schematic diagram illustrating the profile of the plate of FIGS.  1  and 2. 
     
    
     DETAILED DESCRIPTION  
       [0018]    The invention is described in detail below with reference to the figures and attached appendix. Such description is for purposes of illustration only and is not limitative of the invention in any way.  
         [0019]    Illustrated in FIGS.  1  through 3, there is a plate 180 which includes a planar center 182 which, in turn, includes an outer peripheral surface 184. This center region  182  may have a slight convex crown to improve plate stability during use. The planar center  182  forms a bottom for the plate  180 . An outwardly projecting sidewall  186  includes a first rim portion  188  which is joined to the outer peripheral surface  184  of the planar center  182 . A second rim portion  190  is joined to the first rim portion  188 . The first rim portion  188  and the second rim portion  190  form the outwardly projecting sidewall  186  which forms the sidewall of the plate  180 . A rim  192  includes a third rim portion  194  which is joined to the second rim portion  190  of the outwardly projecting sidewall  186 . A fourth rim portion  196  is joined to the third rim portion  194 . The fourth rim portion  196  forms the outer edge of the plate  180 .  
         [0020]    [0020]FIG. 3 illustrates a partial cross-sectional view of a plate, diameter D, according to the present invention. The plate  180  defines a center line  204 . A base or bottom-forming portion  200  extends from the center line  204  to an outer peripheral surface  202 .  
         [0021]    From the center line  204  a predetermined distance X 12  extends toward the outer peripheral surface forming portion  202 . A distance Y 12  extends a predetermined distance from the base or bottom-forming portion  200  upwardly therefrom. A radius R 12  extends from the intersection point of the distance X 12  and Y 12  to form a first rim portion  206  of the outwardly projecting sidewall  205 . The first rim portion  206  is defined by an arc A 12  which extends from a substantially vertical line defined at the outer peripheral surface  202  to a fixed point  210 . The arc A 12  may be approximately 60°.  
         [0022]    A distance X 22  extends from the center line  204  to a predetermined point. A distance Y 22  extends from the base or bottom-forming portion  200  of the plate  180  downwardly a predetermined distance. A radius R 22  extends from the intersection of the lines X 22  and Y 22  to form a second rim portion  208  of the sidewall  205 . The radius R 22  extends from the first fixed point  210  to the second fixed point  212  through an arc A 22 . The arc A 22  may be approximately 4 °.  
         [0023]    A distance X 32  extends from the center line  204  to a predetermined distance. A distance Y 32  extends from the base or bottom-forming section  200  of the plate  180  to project upwardly a predetermined distance. A radius R 32  extends from the intersection of the lines X 32  and Y 32  to form the third rim portion  214  of the rim  216 . The radius R 32  extends from the second fixed point  212  to a third fixed point  218 . An arc A 32  is formed between the second fixed point  212  and the third fixed point  218  to extend a predetermined distance. The arc A 32  may be approximately 55°.  
         [0024]    A distance X 42  extends a predetermined distance from the center line  204 . Similarly, a distance Y 42  extends from the base or bottom-forming section  200  of the plate  180  to project upwardly. A radius R 42  extends from the intersection of the lines X 42  and Y 42  to form a fourth rim portion  217  of the rim  216 . An arc A 42  is formed between the third fixed point  218  and a fourth fixed point  220  at diameter D from the center line. The arc A 42  may be approximately 60°. A section  220  forms the outer edge of the plate.  
         [0025]    The article made according to the present invention may have any particular size as desired by the user so long as the relative profile dimensions are maintained. More specifically, square or rectangular with rounded comers, triangular, multi-sided, polyhexyl and similar shapes may be made having the profile described above, including compartmented trays and plates. In various embodiments of the present invention the container may be a 9-inch or 11-inch plate with profile coordinates as illustrated in FIGS. 1 through 3 having the dimensions, angles, or relative dimensions enumerated in Tables 1 through 3.  
                                           TABLE 1                           Dimensions and Angles For 9″ Plate                DIMENSION and ANGLES   VALUE (inches or degrees)                            R12   0.537           X12   3.156           Y12   0.537           R22   2.057           X22   5.402           Y22   0.760           R32   0.564           X32   4.167           Y32   0.079           R42   0.385           X42   4.167           Y42   0.258           A12   60.00°           A22   4.19°           A32   55.81°           A42   60.00°           D   9.00           BOTTOM CONVEX CROWN   0.06                      
 
         [0026]    [0026]                                           TABLE 2                           Dimensions and Angles For 11′ PLATE                DIMENSION/ANGLES   VALUE (inches or degrees)                            R12   0.656           X12   3.857           Y12   0.656           R22   2.514           X22   6.602           Y22   0.929           R32   0.689           X32   5.093           Y32   0.097           R42   0.470           X42   5.093           Y42   0.315           A12   60.00°           A22   4.19°           A32   55.81°           A42   60.00°           D   11.00           BOTTOM CONVEX CROWN   0.06                        
         [0027]    [0027]                                                                         TABLE 3                           Dimensions For 9 and 11 INCH PLATE                DIMENSION               RATIO OR   VALUES (Dimensionless or degrees)                ANGLE   PREFERRED   MINIMUM   MAXIMUM                            R12/D   0.060   0.045   0.075           X12/D   0.351   0.280   0.420           Y12/D   0.060   0.045   0.075           R22/D   0.228   0.180   0.275           X22/D   0.600   0.480   0.720           Y22/D   0.084   0.065   0.100           R32/D   0.063   0.050   0.075           X32/D   0.463   0.370   0.555           Y32/D   0.009   0.007   0.011           R42/D   0.043   0.034   0.052           X42/D   0.463   0.370   0.555           Y42/D   0.029   0.023   0.035           A12   60.00°   55.00°   75.00°           A22   4.19°   1.00°   10.00°           A32   55.81°   45.00°   75.00°           A42   60.00°   45.00°   75.00°                        
         [0028]    Salient features of the plate illustrated in FIGS. 1 through 3 generally include a substantially planar center portion (which may be crowned as noted above and illustrated throughout the various figures) with four adjacent rim portions extending outwardly therefrom, each rim portion defining a radius of curvature as set forth above and further noted below. The first rim portion extends outwardly from the planar center portion and is convex upwardly as shown. There is defined by the plate a first arc A 12  with a first radius of curvature R 12  wherein the arc has a length S 1 . A second rim portion is joined to the first rim portion and is downwardly convex, subtending a second arc A 22 , with a radius of curvature R 22  and a length S 2 . A third, downwardly convex, rim portion is joined to the second rim portion and subtends an arc A 32 . There is defined a third radius of curvature R 32  and a third arc length S 3 . A tangent to the third arc at the upper portion thereof is substantially parallel to the planer center portion as shown in FIG. 20. A fourth rim portion is joined to the third rim portion, which is also downwardly convex. The fourth rim portion subtends a fourth arc A 42  with a length S 4 , with a radius of curvature R 42 .  
         [0029]    The length of the second arc, S 2  is generally less the length of the fourth arc S 4 , which, in turn, is less than the length S 1  of the first arc A 12 . The radius of curvature R 42  of the fourth arc is less than the radius of curvature R 32  of the third rim portion, which in turn, is less than radius of curvature R 22  of the second rim portion. The angle of the first arc, A 12  is generally greater that about 55 degrees, while, the angle of the third arc, A 32  is generally greater than about 45 degrees as is set forth in the foregoing tables. The angle of the fourth arc A 42  is generally less than about 75 degrees and more preferably is about 60 degrees.  
         [0030]    Typically, the length S 1  of arc A 12  is equivalent to the length S 3  of arc A 32  and R 12  of the first rim portion is equivalent in length to the radius of curvature R 32  of the third rim portion.  
         [0031]    Generally speaking, the height of the center of curvature of the first arc (that is the origin of ray R 12 ) above the central planar portion is substantially less than, perhaps twenty five percent or so less than, the distance that the center of curvature of the second rim portion (the origin of ray R 22 ) is below the central planar portion. In other words, the length Y 12  is about 0.75 times or less the length Y 22 .  
         [0032]    So also, the horizontal displacement of the center of curvature of the second rim portion from the center of curvature of the first rim portion is at least about twice the length of the first radius of curvature R 12 . The height of the center of curvature of the third rim portion above the central planar portion is generally less than the height of the center of curvature of the fourth rim portion above the plane of the central planar portion. The horizontal displacement of the center of curvature of the second rim portion is generally outwardly disposed from the center of curvature of the third and fourth rim portions.  
         [0033]    A further noteworthy feature of the plate of FIGS. 1 through 3 is that the height of the center of curvature of the third rim portion above the planar central portion is less than about 0.3 times the radius of curvature R 42  of the fourth rim portion; while the height of the center of curvature of the fourth rim portion above the plane of the central portion is at least about 0.4 times the first radius of curvature R 12 . The plates are preferably made from mineral-filled polyolefin sheet such as polyethylene or polypropylene mineral-filled sheet as described in the appendix attached hereto.  
         [0034]    As will be appreciated from the foregoing data tables as well as from the drawings and discussion above, the ratio of the fourth radius of curvature to the diameter of the plate is preferably at least about 0.03, while the ratio of the third radius of curvature to the diameter of the plate is preferably at least about 0.050. The ratio of the second radius of curvature to the diameter of the plate is preferably at least about 0.2 and the ratio of the length of the first radius of curvature to the diameter of the plate is preferably at least about 0.045.  
         [0035]    While the invention has been exemplified and described in detail, numerous modifications to specific examples within the spirit and scope of the invention will e apparent to those of skill in the art. The invention is defined in the appended claims.