Abstract:
A plastic container has a base and a lid hinged together by a hinge. The hinge has a series of relatively thick sections joined together by a series of relatively thin sections. The thin sections are sufficiently thin to be severed upon an initial folding of the hinge. The thick sections are sufficiently thick to remain at least partially intact during the initial folding. The container may be filled with product and closed with the hinge becoming partially severed and weakened and may be later opened with the hinge becoming completely severed to separate the base and the lid.

Description:
TECHNICAL FIELD 
     This invention relates generally to plastic containers having a lid, a base and a hinge joining the lid to the base. 
     BACKGROUND OF THE INVENTION 
     Plastic containers have long been used to carry food from a cafeteria, grocery store or restaurant for consumption at another location. Such containers have typically included a base and a lid sized and shaped to matingly engage the edges of one another for securely enclosing food items prior to storing and transporting the items. These containers are commonly thermoformed from a sheet of thermoplastic material. 
     Some of these containers are manufactured, sold and used in two separate pieces as individual lids and bases. Often the lids and the bases are made of like shapes and sizes so that the lids and the bases may nest within one another when not secured to one another along their edges. A drawback to such two-piece containers is that they are inefficient to use as the lids corresponding to the bases must be matched and aligned to the bases prior to joining them to the bases. 
     Some plastic containers have overcome this drawback by hinging together the bases and the lids. These hinged containers are manufactured, sold and used as integral one piece units. The hinges of such containers are often comprised of one or more fold lines or creases in-between the lid and the base as shown for example in U.S. Pat. No. 5,860,549. The hinges allow the lid to be folded and unfolded repeatedly onto the base along the fold line. This efficiency of the one-piece container is particularly appreciated by persons involved in the packing of food into the containers as they are able to efficiently load food into the base without concern for later locating matching lids, and aligning the edges of the lids with the edges of the bases to close the filled container. 
     While solving the inefficiencies of the two piece containers, such one-piece containers have nevertheless created another drawback. In particular, one seeking to consume food packed in the container will commonly use the base of the container as a dinner plate. As such, the consumer opens the container by raising the lid to expose his or her dinner food placed upon the base. The lid of the opened container, although raised, nevertheless remains cumbersomely attached to the base. This is awkward as the lid may refold upon the base on its own. Even if it remains folded out the lid causes the container to consume twice the table space. Often such space is very limited as in airliners. 
     Recognizing this drawback, some users have attempted to remove the lid from the base with food contained in the base. One method of doing so requires scissors or a sharp knife to cut the hinge into two pieces thereby separating the lid from the base. Such cutting is extremely troublesome and dangerous as the plastic from which such containers are typically made is durable and difficult to cut, particularly while simultaneously trying to prevent food from spilling from such containers. Moreover, it requires a utensil that is not often present. 
     Accordingly, there remains a need for a plastic container that provides the advantages of having a base and a lid hinged together for manufacture, storage and transportation, yet without the disadvantage of remaining intact during consumption of its contents. It is to the provision of such that the present invention is directed. 
     SUMMARY OF THE INVENTION 
     The present invention meets the above-described need in the art by providing in a preferred form of the invention a plastic container having a base and a lid hinged together by a hinge. The hinge has a series of relatively thick sections joined together by a series of relatively thin sections. The thin sections are sufficiently thin to be severed upon an initial folding of the hinge. The thick sections are sufficiently thick to remain at least partially intact during the initial folding. With this construction, the container may be filled with product and closed with the hinge becoming partially severed and weakened and may be later opened with the hinge becoming completely severed to separate the base and the lid. 
     In another preferred form of the invention, a method of packaging and unpackaging food products comprises the steps of placing food in the base of an open plastic container having a lid and a base joined by a hinge, closing the lid onto the base and partially fracturing the hinge, and subsequently re-opening the container and completely fracturing the hinge thereby providing access to the product in the base with the lid unattached. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a container that embodies principles of the invention in its preferred form with the container shown fully opened. 
     FIG. 2 is a perspective view of a blade used to form the hinge of the container illustrated in FIG.  1 . 
     FIG. 3 is a side view of the blade shown in FIG. 2 a showing a sheet of plastic material between the blade and a striker plate. 
     FIGS. 4 a-c  are fragmentary views in cross-sections of the hinge illustrated in FIG.  1 . 
     FIG. 5 is a perspective view of the container shown in FIG. 1 containing food in a partially closed position. 
     FIG. 6 is a perspective view of the container shown in FIG. 5 illustrating the container in a fully closed position. 
     FIG. 7 is an end view of a portion of the container in its fully closed position. 
     FIG. 8 is an enlarged cross-sectional side view of the container taken along the plane  8 — 8 . 
     FIG. 9 is an enlarged cross-sectional side view of the container taken along the plane  9 — 9 . 
     FIG. 10 is a top view of the container shown in FIG. 1 illustrating the hinge being severed. 
    
    
     DETAILED DESCRIPTION 
     Referring now in more detail to the drawings in which like numerals refer to like parts throughout the several views, FIG. 1 illustrates a container  10  having a base  12 , a lid  14  and a hinge  16  joining the lid to the base. The container  10  is thermoformed from a sheet of thermoplastic material preferably including a polypropylene or polyethylene resin. The base  12  has a bottom  18  and sides  20  that border the bottom. A bottom lip  22  extends from an upper portion of the sides  20 . A protrusion  24  is formed in the bottom lip  22 . The lid  14  has a top  26  and sides  28  that border the top. A top lip  30  extends from an upper portion of the sides  28 . A groove  32  is formed in the top lip  30 . The protrusion  24  and the groove  32  are sized and shaped to matingly engage one another in a tongue and groove manner. 
     The hinge  16  is integrally formed to a side edge  34  of the base  12  and to a side edge  36  of the lid  14 . The hinge  16  has a series of thin sections  38  and a series of thick sections  40 . The hinge  16  extends along an axis  42  between the base  12  and the lid  14 . The axis  42  is the fulcrum about which the base  12  and the lid  14  pivot. The axis  42  is preferably positioned to enable the flange  24  of the base  12  to engage the groove  30  of the lid  14 . 
     A brief description of some of the tools used to form the hinge  16  facilitates an understanding of the construction of the hinge. FIG. 2 illustrates a blade  44  used to impregnate or coin a sheet of plastic material to form the hinge  16 . The blade  44  has a series of upper teeth  46  and a series of lower teeth  48  attached to a ridge  50 . The ridge  50  is mounted to a block  52 . The upper teeth  46  are preferably 1.4 millimeters in height as measured from the block  52 . The lower teeth  48  are preferably 1.1 millimeters in height as measured from the block  52 . 
     FIG. 3 illustrates a side view of the blade  44  and of a striker plate  54  against which the blade coins a sheet of plastic material  56 . During the process of thermoforming the container  10 , the plastic material  56  is squeezed between the blade  44  and the striker plate  54 . The compressive force of the upper teeth  46  against the striker plate  54  forms the thin sections  38  of the hinge  16 . The compressive force of the lower teeth  48  against the striker plate  54  forms the thick sections  40  of the hinge  16 . In addition, the compression of the teeth  46  and  48  against the striker plate  54  carves out large and small indentations  58  and  60  in the plastic sheet  56  as best shown in FIGS. 4 a-c.    
     FIG. 4 a  is a cross-sectional view of a section of the hinge  16  taken along the plane  4   a — 4   a  in FIG.  1 . Each of the thin sections  38  includes a pair of upper inclined walls  62  that intersect at an upper crease  64 . Each of the thin sections  38  extends between the upper inclined walls  62  and a top hinge surface  66 . The top hinge surface  66  is preferably a planar surface formed by the striker plate  54 . Each of the thick sections  40  includes a pair of lower inclined walls  68  that intersect at a lower crease  70 , and a pair of side walls  72 . Each of the thick sections  40  extends between the lower inclined walls  68  and the top hinge surface  66 . 
     The gauge of the sheet of thermoplastic material  56  from which the container  10  is formed is preferably  25  to 70 microns. The depths d 1  of the thin sections  38  between the upper crease lines  64  and the top hinge surface  66  are preferably about 25 percent to 50 percent of the gauge of the thermoplastic sheet  56 . The depths d 2  of the thick sections  40  between the lower crease lines  70  and the top hinge surface  66  are preferably between about 75 percent and 95 percent of the gauge of the thermoplastic sheet  56 . The lengths l 1  of the thin sections  38  between the side walls  72  are preferably about 4 millimeters. The lengths  12  of the thick sections  40  between the side walls  72  are preferably about 2 millimeters. 
     Of course, the depths d 1  and d 2  and the lengths l 1  and l 2  vary depending upon the type, the durability and the gauge of thermoplastic material used to form the hinge  16 . Also, there is some variation in the exact measurements of thermoplastic material from which the containers  10  are made. Based upon the differences in the dimensions of the teeth  46  and  48  of the blade  44 , the depths d 1  of the thin sections  38  are preferably about 15-25 percent less than the depths d 2  of the thick sections  40 . The lengths l 1  of the thin sections  38  are preferably about twice the lengths l 2  of the thick sections  40 . 
     FIGS. 4 b  and  4   c  are cross-sectional views of the hinge  16  taken along the planes  4   b — 4   b  and  4   c — 4   c  in FIG.  1 . The thin sections  38  and the thick sections  40  align along the axis  42 . The widths w 1  of the thin sections  38  and the widths W 2  of the thick sections  40  are preferably 1.2 millimeters. However, the widths w, of the thin sections  38  and the widths w 2  of the thick sections  40  need not be the same. The upper inclined walls  62  of the thin sections  38  form a V-shape. The lower inclined walls  68  of the thick sections also form a V-shape. The side walls  72  of the thick sections  40  together with the upper inclined walls  62  of the thin sections  38  define the large indentations  58 . The lower inclined walls  68  define the small indentations  60 . 
     The operation of the container  10  is understood with reference to FIGS.  1  and  5 - 10 . Beginning with FIG. 1, the container  10  is typically used initially from its open position as shown in FIG.  1 . Food or other items are placed in the base  12  and the lid  14  is moved pivotally about the axis  42  from an open position to a partially closed position as shown in FIG.  5 . As the lid  14  is further moved pivotally about the axis  42  to a fully closed position upon the base  12 , as shown in FIG. 6, tensile stress is applied to the hinge  16  transverse to the axis  42 . The thin sections  38  are sufficiently thin so that the tensile stress caused by this pivotal movement of the lid  14  toward the base  12  weakens and severs them into two pieces  38   a  and  38   b  as shown in FIGS. 7 and 8 as the container  10  is closed. The thick sections  40  are sufficiently thin so that the tensile stress applied to them transverse to the axis  42  during the initial closing action of the lid  14  upon the base  12  does not sever the thick sections. 
     In the fully closed position shown in FIGS. 6-9, the thick sections  40  of the hinge  16  are at least partially intact. Thus, even though the thin sections  38  are being severed while the container  10  is being closed, the thick sections  40  provide some stability to the container  10  so that the tongue  24  may be aligned and engaged to the groove  32  prior to the hinge  16  fully severing. 
     Upon reopening of the container  10  by disengaging the tongue  24  from the groove  32  and pivotally moving the lid  14  away from the base  12 , the thick sections  40  sever into two pieces  40   a  and  40   b  as shown in FIG.  10 . The thick sections  40  are sufficiently thin so that they cannot withstand the force caused by pivotally reopening the container  10 . It should be noted that the initial closing action of the container  10  partially weakens the thick sections  40 . Thus, upon reopening the container  10 , the thick sections  40  are further weakened and severed into two pieces  40   a  and  40   b.    
     In this manner, the container  10  converts from a one-piece container to a two-piece container after one full cycle of closing and re-opening. Once re-opened, the separate lid  14  and the separate base  12  may be fitted or nested together with the lid placed directly under the base. In this nested configuration, the top lip  30  and the bottom lip  22 , the top sides  28  and the bottom sides  20 , top  26  and the bottom  18  each lie in essentially parallel planes to one another. Thus, the lid  14  may be compactly stored under the base  12  to provide double the support and double the insulation of the base. This is particularly useful where the container  10  is used to carry hot or heavy food. Also, the base  12  may be used apart or together with the lid  14  to contain and heat food as in a microwave. 
     Preferably the thick sections  40  fully sever as the lid  14  is moved to a fully opened position as shown in FIG.  10 . However, because of the variations in thermoplastic material and in the manufacturing process, the thick sections  40  may not fully sever as shown in FIG.  10 . In such circumstances, the lid  14  and the base  12  may be pulled slightly apart to complete the severing of the thick sections  40 . 
     The preferred thermoplastic material  56  used to form the container  10  includes a polypropylene or polyethylene blend of resins. Some of such thermoplastic materials include polystyrene, oriented polystyrene, polyethylene terephthalate, amphbrous polyethylene terephthalate (APET), and crystallized polyethylene terephthalate (CPET). However, plastic sheets comprised of other plastic resins may be used to form the container. 
     It thus is seen that a plastic container is now provided that overcomes problems long associated with those of prior art. It should be understood however that many modifications, additions and deletions may be made thereto without departure from the spirit and scope of the invention as set forth in the following claims.