Patent Publication Number: US-2007095719-A1

Title: Multiple portion packaging tray and method of making same

Description:
FIELD OF INVENTION  
      This invention relates to plastic containers for use in packaging. In particular, this invention relates to packaging comprising an array of separably connected plastic containers that are easily separated and methods of making such containers.  
     BACKGROUND OF INVENTION  
      Use of single serve plastic containers is well known in the food product industry. These single serve containers are sometimes manufactured and sold in a multiple portion packaging tray comprising an array of separable containers. The containers are generally connected to one another along their flanges and may be broken apart by breaking the connection at the flanges. These containers work well when made of a relatively brittle plastic. Use of less brittle or more pliable polymers makes the containers more difficult to break apart. For some foods, brittle plastics, such as polystyrene, cannot provide the necessary protection and a high moisture barrier polymer is needed, such as polypropylene or polyethylene. Polypropylene and polyethylene are also generally lower cost materials than polystyrene. Traditionally, single serve packages made from polyolefins include secondary packaging, such as a cardboard sleeve, to form a multiple portion package. Connecting individual containers to form a multiple portion packaging without the use of secondary packaging, however, would deliver a substantial cost benefit. Accordingly, there is a need for an array of separably connected plastic containers made from less brittle and more pliable polymers.  
      Containers in the form of an array of separably connected plastic containers are typically formed from thermoforming processes well known to those of skill in the art. Examples of such thermoforming methods include solid phase pressure forming, melt phase forming, plug assist, vacuum forming, and drape forming. After thermoforming, the containers are transferred to a separate trim station, outside of the thermoforming station, to trim the containers.  
     SUMMARY OF INVENTION  
      This invention addresses the above-described need by providing a multiple portion packaging tray comprising a plurality of pliable polymer containers configured in an array. Each pliable polymer container comprises a receptacle and an integral peripheral flange extending from the receptacle, the flanges integrally connecting adjacent containers.  
      More particularly, this invention comprises perforation lines in the flanges as a means to easily separate the containers. The perforation lines comprise a series of alternating openings and land areas wherein the land areas are sized so that the containers are easily separated by tearing apart the flanges without propagating cracks across the flanges or compromising the containers&#39; integrity and at the same time are robust enough to survive normal handling in a distribution process with out separating incidentally.  
      In addition, this invention encompasses a method for making a multiple portion packaging tray comprising a plurality of pliable polymer containers configured in an array. This method is performed in a former comprising a form station and a separate trim station and comprises the steps of thermoforming a pliable polymer sheet in the form station to create the multiple portion packaging tray and cutting the flanges in the trim station to form perforation lines having a series of alternating openings and land areas.  
      Other objects, features, and advantages of this invention will be apparent from the following detailed description, drawings, and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a plan view of an array of separably connected plastic containers in accordance with an embodiment of this invention.  
       FIG. 2   a  is a partial elevation view of the embodiment in  FIG. 1  illustrating a perforation line.  
       FIG. 2   b  is a partial plan view of the embodiment in  FIG. 1  illustrating a perforation line along its longitudinal length.  
       FIG. 3  is a schematic representation of a system of making an array of separably connected plastic containers in accordance with an embodiment of this invention.  
       FIG. 4  is an exploded schematic representation of a trim station used in the embodiment illustrated in  FIG. 3 .  
       FIGS. 5   a  and  5   b  are elevation views of notched steel rule knives used in the embodiment illustrated in  FIG. 3 .  
    
    
     DETAILED DESCRIPTION  
      As summarized above, this invention encompasses a multiple portion packaging tray comprising a plurality of pliable polymer containers configured in an array. Such containers are frequently used to package individual servings of food products, although other uses are well known in the art. The containers are easily separable from the multiple portion packaging tray through the exertion of tensile force by hand. Embodiments of this invention are described in detail below and illustrated in  FIGS. 1-5 .  
      A multiple portion packaging tray  10  made in accordance with an embodiment of this invention is illustrated in  FIG. 1 . The multiple portion packaging tray  10  comprises a plurality of pliable polymer containers  12  configured in an array. The individual containers  12  comprise receptacles such as cups  14  surrounded by peripheral flanges  16 . The flanges  16  integrally connect adjacent containers  12  to one another. The flanges  16  comprise perforation lines  18  wherein the perforation lines provide a means to easily separate the individual containers  12  from the multiple portion packaging tray  10 . The perforation lines  18  may be formed within channels  19  formed in the flanges  16 , as shown in  FIGS. 1, 2   a  and  2   b , or directly in non-channeled flanges. The channels  19  can be formed by any suitable means including but not limited to coining, and the like. The perforation lines  18  comprise a series of alternating openings  20  and land areas  22 . The land areas  22  are sized so that the individual containers  12  are easily separated by tearing apart the flanges  16  at the tear lines  18  using tensile forces without propagating cracks across the flanges  16 . Desirably, the land areas  22  can be easily pulled apart by hand yet are strong enough to survive normal handling and shipping. The perforation lines  18  extend along the flanges  16  in a longitudinal direction D as illustrated in  FIG. 2   b . The length L of the land areas  22  in the longitudinal direction D of the perforation lines  18  preferably ranges from about 15 mils to about 32 mils, more preferably from about 18 mils to about 22 mils. The length L of the land areas  22  in the longitudinal direction D of the perforation lines  18  is most preferably about 20 mils.  
      The multiple portion packaging tray  10  preferably comprises a pliable polymer material which is desirable in some packaging applications. For example, polyolefins are suitable pliable polymer materials for forming the packaging tray  10 . Preferred polyolefins include polypropylene, high density polyethylene, and low density polyethylene. The most preferable polyolefin is polypropylene. The pliable polymers also may be coextruded with other materials. For example, polypropylene may be coextruded with ethylene vinyl alcohol by using ethylene vinyl acetate based tie layers for adhesion to the polypropylene. Other pliable polymer materials are also suitable.  
      The thickness T of the pliable polymer can vary and is preferably at least 3 mils and desirably ranges from 3 mils to about 40 mils, and more desirable ranges from about 5 mils to about 30 mils. As illustrated in another embodiment in  FIG. 2   a , the flanges  16  may be coined to form channels  19  so that the material thickness t at the perforation lines  18  is less than or equal to that of the remaining portion of the flanges.  
      The method of making the multiple portion packaging tray  10  is illustrated in  FIG. 3 . The multiple portion packaging tray  10  can be made using any suitable polymer sheet or film forming process, but is desirably made using a thermoforming process  24 . Suitable thermoforming methods include solid phase pressure forming, melt phase forming, plug assist, vacuum forming, and drape forming. The thermoforming process  24  occurs in a former  28  comprising a form station  30  and a separate trim station  32 . A pliable polymer sheet  26  is indexed through the form station  30  to create the formed multiple portion packaging tray  10  using thermoforming methods known to those skilled in the art. Desirably, the mold temperature of the former  28  is controlled using cold water flow through internal channels in the mold to quench the formed multiple portion packaging tray  10  so that there is crystallization of the polymer. The cooling process is well known to those of skill in the art.  
      The trim station  32 , illustrated in an exploded schematic in  FIG. 4 , comprises steel rule knives  40  to cut the perimeter of the formed multiple portion packaging tray  10 . The trim station  32  further comprises notched steel rule knives  42   a  and  42   b , best shown in  FIGS. 5   a  and  5   b  to create a series of alternating openings  20  and land areas  22  in the longitudinal direction of the respective tear lines  18 . As illustrated in  FIG. 5 , the notched knives  42   a  and  42   b  comprise standard straight blade steel rule knife material with notches  44   a  and  44   b  sized to create land areas of a predetermined size so that the individual containers  12  are easily separated by tearing apart the flanges  16  at the perforation lines  18  without propagating cracks across the flanges  16 . The perimeter knives  40  can also have small notches to create tabs attaching the multiple portion packaging tray  10  to the polymer sheet  26 . The steel knives  40  and  42   a  and  42   b  touch a striker plate  46  to trim the perimeter of the multiple portion packaging tray  10  and to create the openings  20  and land areas  22  of the perforation lines  18 . In another embodiment, the trim station  32  further comprises a punch and die system, well known to those of skill in the art, at the points where the individual containers  12  meet on the multiple portion packaging trays  10 . The cutting by the steel knives  40  and  42   a  and  42   b  and punch and die system may be done simultaneously or in separate steps.  
      The multiple portion packaging trays  10  may be indexed to a stacking station  36  where the perimeter tabs are broken by pushing the array of containers  10  through the sheet  26  to a stacking chamber where they are counted and pushed to a packaging station  38 .  
      The present invention is further illustrated by the following example, which is not to be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof which, after reading the description therein, may suggestion themselves to those skilled in the art without departing from the spirit of the present invention and/or the scope of the appended claims.  
     EXAMPLE  
      A 30 mil 100% polypropylene sheet is used to make a multiple portion packaging tray. The polypropylene sheet is heated to 160° C. as it indexes through an oven into the form station at 4 second cycles. In the form station, the hot sheet may be formed using a variety of methods. The formed multiple portion packaging tray leaves the forming station, still attached to the sheet. The formed multiple portion packaging tray enters the trim station approximately 8 seconds after leaving the forming station. At the trim station, a lower platen moves up to the sheet level to capture the individual containers in a die plate. An upper platen containing steel rule knives, notched steel rule knives, and punches moves downward until it just touches the die plate and trims the perimeter of the multiple portion packaging tray as well as forms the tear lines in the flanges with alternating opening and land areas. The notches of the notched steel rule knives are desirably 20 mils in length. The upper and lower platens return to their initial positions and the multiple portion packaging tray proceeds to the stacking station. In the stacking station, a ram below sheet level pushes the multiple portion packaging tray up through the sheet, separating the multiple portion packaging tray from the sheet, and feeds the multiple portion packaging tray into a stacking chamber. The multiple portion packaging trays are collected in the stacking chamber and pushed onto a conveyor for packing.  
      It should be understood that the foregoing relates to particular embodiments of the present invention, and that numerous changes may be made therein without departing from the scope of the invention as defined from the following claims.