Patent Publication Number: US-6662996-B2

Title: Cup and method for making cup with integrally formed u-shaped bottom channel

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of leakproof paper cups and the making thereof. 
     Volume production of paper cups and plastic coated paper cups has achieved considerable success in the United States of America and abroad. One deficiency inherent in the cups formed using a layer of insulating foam is that the leak rate per million cups is almost double when compared to cups formed using plain paper stock. However, insulating foam cups have proven to be very popular. An unsolved problem is how to produce a better bottom seam seal for insulating foam cups since most of the leaks occur where the side seam adjoining a lower cylindrical portion of the cup attaches to the bottom blank. 
     FIG. 1A shows a cross section of a prior art cylindrical cup  100 . The peripheral wall  150  of cup  100  has its lower edge  160  curved inwardly and upwardly forming a channel. 
     The circular bottom blank  110  is typically a single layer of board and has a downwardly extending skirt  120  formed about its periphery. 
     FIG. 1A also shows where the prior art applies heat to seal the bottom blank  110  to the peripheral wall  150 . Heat is applied at  130  to the interior of the shallow hollow formed below the ascending sidewall  140  and the bottom blank  110 . 
     FIG. 1B shows a more detailed cutaway of an X-point  180  where five layers of board come together. The X-point  180  is especially prone to leaks. 
     Typically, a single layer of board is shaped to form a peripheral wall  150  of a cup  100 . The two edges of the peripheral wall board meet and overlap to form a side seam  170 . The side seam  170  is created by overlapping the two edges of the board and sealing them together. Because the board is overlapped to form the side seam  170 , the side seam  170  is two layers thick. Because the peripheral wall  150  has its lower edge  160  curved inwardly and upwardly to form the channel, a double layer of the peripheral wall  150  is thus also curved inwardly and upwardly at the seam  170 . 
     At all points where the peripheral wall  150  meets the bottom blank  110 , except at the X-point  180 , there are three layers of board. To seal the peripheral wall  150  to the bottom blank  110 , the heat must penetrate two layers of board. The two layers of board are the peripheral wall&#39;s  150  single layer and the bottom blank&#39;s  110  single layer. 
     But, at the X-point  180  is where side seam  170  meets the periphery of bottom blank  110 , the side seam  170  is four layers thick, two layers on the outside and two layers on the inside where the side seam  170  is folded upward. When the bottom blank  110  is then coupled to the top blank, the X-point  180  becomes five layers thick. To seal at the X-point  180 , the heat must penetrate three layers of board. The three layers of board are the side seam&#39;s  170  two outer layers and the bottom blank&#39;s  110  single layer. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a cup less likely to leak by forming a u-shaped channel about a periphery of a bottom blank, forming a top blank into a generally cylindrical shape, and coupling an edge of the top blank to the u-shaped channel of the bottom blank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the invention will be more apparent from the following detailed description wherein: 
     FIG. 1A (Prior Art) is a cross sectional, elevational view of a conventional paper cup viewed at a side seam showing the X-point which is prone to leaking; 
     FIG. 1B (Prior Art) is a cross sectional, elevational view of a prior art cup showing the X-point being five layers thick; 
     FIG. 2A is a cross sectional, elevational view of a bottom blank of one embodiment of this invention having a first bend forming a circular flange; 
     FIG. 2B is a cutaway of a bottom blank of one embodiment of this invention having a fully formed u-shaped channel; 
     FIG. 3 is a plan view of a bottom blank of one embodiment of this invention with scores making it easier to form part of the bottom blank into a u-shaped channel; 
     FIG. 4 is a schematic showing the placement of the polyethylene coatings; 
     FIG. 5 is a cross sectional, elevational view showing where heat is applied to fuse the polyethylene coatings to their surfaces; 
     FIG. 6 is a cross sectional, elevational view of a top blank coupled to a bottom blank in a u-shaped channel; 
     FIG. 7 is a cross sectional, elevation view showing where heat is applied to join a top blank and a bottom blank together; 
     FIG. 8 is a perspective view showing how a top blank and a bottom blank are coupled in a u-shaped channel; and 
     FIG. 9 is a cutaway perspective view of a side seam and X-point of a cup. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention comprises an improved cup where the bottom periphery of a generally cylindrical top blank without a lower channel fits into a bottom blank having a preformed, generally u-shaped channel about its periphery. 
     FIG. 2A shows a bottom blank  200  having an upper surface  220 . The bottom blank  200  has a first bend  210  and a second bend  240  to create an edge  230  about the periphery of the bottom blank  200 . FIG. 2B shows a completely formed bottom blank  250  with the first bend  210  and the second bend  240 . The second bend  240  is completed to form a u-shaped channel  260  about the periphery of the bottom blank  250 . 
     FIG. 3 is the bottom blank  250  in a plan view, with scoring  300  to assist with the forming of the bends  210 ,  240  shown in FIGS. 2A and 2B. 
     FIG. 4 shows the surfaces of the top and bottom blanks coated with polyethylene. When forming a foam-generated cup as disclosed in the following U.S. Pat. Nos. 5,766,709, 5,840,139, 5,993,705, 6,030,476, 6,129,653, 6,139,665, 6,142,331, 6,308,883, 6,319,590, and 6,328,557, the entire disclosures of which are incorporated herein by reference, the top blank  310  is coated on an inner surface  320  with polyethylene, preferably a blend of high density polyethylene (HDPE) and low density polyethylene (LDPE). The blend of HDPE and LDPE is used because it forms a better seal and bond under heat with the LDPE on an inside part  400  of the u-shaped channel  260  as well as with the outer surface  330  where side seam  800 , as shown in FIGS. 8 and 9, is formed. When forming non-foam-generated cups the inner surface of the top blank is commonly coated with LDPE. 
     An upper surface  220  of the bottom blank  250  and an outer surface  330  of the top blank  310  are coated with polyethylene, preferably a low density polyethylene (LDPE). The coating is applied before any bending and therefore lines the u-shaped channel  260 . 
     FIGS. 5 and 6 show how the top blank  310  and the bottom blank  250  are joined together so a bottom edge  510  of the top blank  310  fits within the u-shaped channel  260  of the bottom blank  250 . FIG. 5 further shows different methods of heat application prior to joining the top blank  310  to the bottom blank  250 . Both methods fuse the polyethylene coating on the top blank  310  to the bottom blank  250 . First, heat can be applied at  520 , the outer  330  surface of the top blank  310 , and at  500 , the inner  320  surface of the top blank  310 . Second, heat can be applied at  530 , the inside of the u-shaped channel  260 . FIG. 6 shows a bottom edge  510  of the top blank  310  fitting into the u-shaped channel  260  of the bottom blank  250  after either method of heat application. 
     FIG. 7 shows two more methods of heat application that occur after joining the top blank  310  to the bottom blank  250 . First, heat can be applied at  730 , an outer portion of the exterior of the u-shaped channel  260 . 
     Second, heat can be applied at  700 , an inner portion of the exterior of the u-shaped channel  260 . To reach the first joining layer of polyethylenes  710 , the heat at  700  need only penetrate one layer of board. However, to reach the second joining layer  720  of polyethylenes the heat at  700  needs to penetrate two layers of board. At the X-point  600 , the heat at  700  needs to penetrate three layers of board to reach the second joining layer  720  of polyethylenes. 
     Both seals bond polyethylene to polyethylene creating a stronger bond. 
     FIG. 8 is an exploded perspective showing schematically how the top blank  310  lines up with the bottom blank  250  and how the bottom edge  510  of the top blank  310  fits into the u-shaped channel  260 . FIG. 8 further shows a side seam  800  along the top blank  310 . 
     Prior art cups are manufactured by forming a frustral conical top, wrapping a bottom blank around a lower outer portion of the top, and curling the edges of the bottom blank inwardly. 
     Unlike the prior art where a bottom edge of the top blank is folded inwardly and upwardly (See FIG.  1 A), the present invention does not fold the bottom edge  510  of the top blank  310  (See FIG.  8 ). Therefore, there is one layer of board around the entire top blank  310  except at the side seam  800  where there are two layers of board joined to form the side seam  800 . 
     An embodiment of the present invention is constructed by forming a bottom blank  250  into a frustral conical shape (See FIG.  2 A), then wrapping a top blank  310  around the bottom blank  250  so that the bottom edge  510  of the top blank  310  fits into what will become the u-shaped channel  260  (See FIG.  5 ). Next, the outer edge of the bottom blank  250  is curled around the bottom edge  510  of the top blank  310  forming the u-shaped channel  260  (See FIG.  6 ). 
     FIG. 9 shows a cross-sectional cutaway of a completely formed cup  900  having a side seam  800  two layers thick. The X-point  600  is 4 layers thick. 
     The side seam&#39;s  800  two layers  910 ,  920  are shown within the u-shaped channel&#39;s two layers  930 ,  940  making the X-point  600  four layers thick. Having an X-point only four layers thick is a reduction by one layer of board over the prior art. This reduction in the number of board layers at the X-point aids in the final joining process and discloses a cup less likely to leak. 
     While certain exemplary embodiments have been described in detail it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention is not to be limited to the specific arrangements and constructions shown and described, since various other modifications may occur to those with ordinary skill in the art.