Abstract:
A method and apparatus for vacuum thermoforming disposable drink cups lids including the step of imparting printing to the lids while they are in contact with the vacuum thermoforming platen.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to vacuum thermoformed plastic articles and particularly to a vacuum thermoformed disposable drink cup lid having printed indicia thereon and a method of manufacturing such an article.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is well known to manufacture thin plastic articles such as disposable drink cup lids by vacuum thermoforming. Such articles are manufactured by causing a web of extruded plastic sheet material to contact a metal die having the desired shape of the article formed into a surface thereof. Vacuum is applied to the platen surface through small holes to draw the plastic material over the contours of the die. The articles are thereafter cooled, separated from the web by die cutting, and stacked and/or boxed using conventional automation devices.  
           [0003]    It is also known to vacuum form logos and other indicia on the plastic lids. Such indicia are typically forms of raised surfaces in a central deck area of the lid. Because thermoformed plastic lids are usually white, it is difficult to clearly see such vacuum embossed indicia. To add definition, the raised surfaces of the embossed indicia may be colored in a secondary operation carried out by printing machinery separate from the thermoforming machinery.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    According to the present invention vacuum thermoformed articles such as disposable drink cup lids are thermoformed and printed; i.e., provided with coloring on embossed surfaces and/or printed with logos and other indicia on non-embossed surfaces, in what is essentially a single operation. The invention increases manufacturing efficiency and lowers manufacturing costs.  
           [0005]    general, this is accomplished by extruding a thin web of thermoformable plastic sheet material, contacting the web while hot with a vacuum thermoforming dies configured to form articles such as disposable drink cup lids having printable areas within the boundaries of said articles, applying vacuum to form the articles, immediately thereafter applying ink to the printable areas while the articles remain in the web and at an elevated temperature and, thereafter, separating the fully formed and printed articles from the web. As stated above, the term “printed” is used herein to refer to both adding color to embossed surfaces and placing indicia on essentially flat surfaces.  
           [0006]    In the preferred form hereinafter described, the method is carried out by means of an apparatus which comprises a rotating thermoforming drum carrying a series of plates with die inserts for forming articles, and a multi-surface rotatable printing cylinder which rotates in synchronism with the thermoforming drum. The printing cylinder rotates in synchronism with the drum and with an Anilox roller which carries ink from a supply to the pads on the printing cylinder. Synchronism is preferably maintained by gears to ensure registration between the ink pads and the thermoformed articles. Fully formed and printed articles thereafter pass to a conventional die cutter where they are removed from the web. The articles may be stacked and excess material from the web returned to the extruder supply hopper.  
           [0007]    Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0009]    [0009]FIG. 1 is a schematic view of a system for carrying out the method of manufacturing disposable drink cup lids;  
         [0010]    [0010]FIG. 2 is a perspective view of a portion of the machine of FIG. 1;  
         [0011]    [0011]FIG. 3 is a plan view of a drink cup lid made by the inventive method;  
         [0012]    [0012]FIG. 4 is a sectional view of the FIG. 3 lid;  
         [0013]    [0013]FIG. 5 is a plan view of a second lid made by the inventive method; and  
         [0014]    [0014]FIG. 6 is a sectional view of the FIG. 5 lid. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring to the drawing, FIG. 1 illustrates in schematic fashion an apparatus  10  for manufacturing vacuum thermoformed drink cup lids and simultaneously printing the lids in what is essentially a single and continuous manufacturing operation. The apparatus  10  comprises a hot melt extruder  12  for receiving ground or pelletized plastic material such as polystyrene or polyethylene.  
         [0016]    The extruder is equipped to melt the plastic material and force it through an exit die  14  of convention design to produce a thin web  16  of plastic material. The width of the web may be any desired width; here approximately 24 inches.  
         [0017]    The web  16  exits the extruder die  14  at approximately 320° F. to 340° F. and passes to a vacuum forming drum  18  which is suitably mounted for rotation by a drive  22  in either direction to cause the web to contact forming dies  20  mounted on the drum  18  for the desired time. Coolant and vacuum are applied to the drum by sources  24  and  26  respectively to control temperatures and to produce vacuum forming.  
         [0018]    After the desired time of contact with the dies  20  on the drum  18  the web  16  with the articles formed therein passes to a die cutter and stacker  28  of conventional design.  
         [0019]    To carry out the printing operation simultaneously and in synchronism with the thermoforming operation, a printing cylinder  30  is mounted above the drum  18  by means to be described with reference to FIG. 2. The printing cylinder  30  is equipped with pads  32  which contact the vacuum formed articles after they have cooled to a temperature of between about 150°-250° F., the elevated temperature being effective to rapidly dry the ink, which is applied to the vacuum thermoformed articles by the pads  32  on the printing cylinder  30 .  
         [0020]    The pads  32  on the printing cylinder  30  are continuously inked by an Anilox roller  34  which picks up ink  36  from an ink fountain  38  having a filler mechanism  40 . Seals and proper ink distribution are provided by Nylon doctor blade  42  and  44  which form the bottom of the ink fountain  38  and engage the upper quadrant of the Anilox roller  34 .  
         [0021]    The drum  18 , printing cylinder  30  and Anilox roller  34  all rotate in precise synchronism as a result of means hereinafter described in detail with reference to FIG. 2. In addition the printing cylinder  30 , Anilox roller  34  and ink fountain  38  adapt for vertical movement by means to be described in order to accommodate the irregular surface of the octagonal thermoforming drum  18 .  
         [0022]    Referring now to FIGS. 3 and 4 a specific thermoformed article  50  is shown to comprise a thin plastic drink cup lid of approximately 3½ inches in diameter and configured to be applied to the upper rim of a standard plastic or paper disposable drink cup  52 . The specific article  50  shown in FIGS. 3 and 4 is a hot drink cup lid producing what is known in the trade as a plug fit by means of a 300° channel  54  which is vacuum thermoformed into the material of the lid  50 . A skirt  56  is also vacuum formed around the periphery of the lid and finally formed by the die cutting operation carried out by device  28  shown in FIG. 1.  
         [0023]    The lid  50  is shown to comprise a drink-through tear-back tab  58  defined by a partially die cut area near the periphery of the lid and within the discontinuity of the plug fit channel  54 . A raised feature  60  is formed in the lid  50  adjacent a shallow hinge  64  such that the raised operating feature  60  may be folded back and locked back into a receiver cavity  62  formed immediately behind the hinge  64 . The details of the tear-back/lock-back features of the lid  50  are more fully described in the co-pending U.S. patent application Ser. No. 09/952,154 filed Sep. 14, 2001 the entire disclosure of which is incorporated herein by reference.  
         [0024]    The lid  50  is shown to comprise a large flat central deck area  66  in which there is embossed during the thermoforming operation a raised logo  68  the features of which have relatively flat raised surfaces. In accordance with the invention coloring is imparted to the raised surfaces of the logo  68  by the printing cylinder  30  and the apparatus of FIG. 1. FIG. 5 and  6  illustrate a second lid  50 ′ of a configuration which is slightly different from the configuration of lid  50 .  
         [0025]    Specifically, the lid  50 ′ has no embossed logo. Accordingly, the pads  32  of the printing cylinder  34  must be formed, like conventional rubber stamps, to carry the desired lettering on other indicia.  
         [0026]    Referring now to FIG. 2, the octagonal drum  18 , the printing cylinder  30 , the Anilox roller  34  and the ink fountain  38  are shown in greater detail. A continuous gear surface  74  is formed around the left peripheral end of the drum  18  with teeth extending parallel to the axis of rotation of the drum  18 . The gear surface  74  is in constant contact with a print cylinder gear  76  which is mechanically attached to the printing cylinder  30  to rotate the printing cylinder  30  and the ink pad  32  in precise synchronism with the rotation of the drum  18  thereby to ensure continuous registry of the ink pad  32  with the locations of the mold inserts or dies  20  which are carried by plates  21  attached by machine screws to the flat surfaces of the drum  18 . In this instance there are three lid forming dies  20  across each of the plates  21  but this number is merely illustrative. The molding features of the inserts  20  may differ from insert to insert but it is desirable that all of the inserts be male dies and have essentially the same height so as to be properly engaged by the printing surfaces of the pads  32 . The feature  60  shown in FIGS. 3 and 4 of the drawings requires that the ink pads be sized and located to clear the feature  60  as they engage the top surfaces of the logo  68  during the printing operation.  
         [0027]    The printing cylinder  30  with the associated gear  76  is mounted on a print head frame  70  which is adapted for pivotal rotation about an axle  72 . Cam rollers  78  mounted on both sides of the frame  70  for rotation relative thereto contact cam surfaces  84  formed on the drum  18 . The cam surfaces are continuous, and, although essentially octagonal, have machined corners to permit smooth and continuous contact between the cam surfaces and the associated rollers  78 . The clearance between the rollers  78  and the cam surfaces  84  may be adjusted by means of adjustment screws  88  shown in FIG. 2 to vary the pressure of the ink pads  32  on the molded plastic articles during the printing operation.  
         [0028]    To ensure a synchronous drive relationship between the printing cylinder  30  and the Anilox roller  34 , the gear  90  is mounted on the printing cylinder  30  inboard of the gear  76  and meshes with a gear  92  mounted on the left end of the Anilox inking roller  34  as shown in FIG. 2. The Anilox roller  34  is mounted on the frame  70  by conventional bearings.  
         [0029]    The ink fountain  38  may be adjusted in relationship to the surface of the Anilox roller  34  by means of a plate  96  which lies between opposite lateral sections of the frame  70  and carries spacing adjustment screws  98 . The drum  18  is mounted on a frame  100  for rotation as previously described.  
         [0030]    Operation  
         [0031]    In a typical operation plastic material is forced from the extruder through the die  14  to form the hot web  16 , the web being continuously drawn from the extrusion die  14  by clockwise rotation of the drum  18 . It will be understood that this drum may rotate in the counter-clockwise direction if desired to extend the web  16  around the bottom of the drum and thereafter to the die cutter  28 .  
         [0032]    Substantially as soon as the web  16  encounters the mold inserts  20  of the drum  18  vacuum is applied and the material of the web is drawn by vacuum over the contours of the dies  20  to form the lids  50  or such other articles as it may be desired in any particular operation to make. The web material cools to between approximately 140° F. to 250° F. for application of the ink  36  by way of the pads  32  on the printing cylinder  30 . The web material with the articles now formed therein and printed remains in contact with the drum  18  and the dies  20  and plates  21  long enough to cool to between about 70° F. and 110° F. whereupon they are separated from the drum surface and conveyed to the die cutter apparatus  18 . Extra material from the web not formed into articles  50  may be recovered and ground and returned to the hot melt extruder  21 .  
         [0033]    While the invention has been described with reference to a specific article and a specific apparatus for carrying out the manufacturing method of the article, it is to be understood that it may be carried out using apparatus of different style and design and also that articles other than molded plastic drink cup lids may be manufactured and printed in accordance with the teachings of this patent. While the adjustable cam rollers and gears described above with reference to the illustrative embodiment are preferred at this time, it is to be understood that other and equivalent drive devices such as belts, chains and the like may also be used to synchronize the rotation of the various components of the thermoforming and printing system. Alternatively or additionally a speed control and synchronization may be achieved electronically using high resolution encoders and variable speed motors and the like. A key consideration is to avoid slip between the rotating drum  18  and the inking cylinder  30  as such slip will deregister the pads  32  from the article  50  being printed.