WO1993025444A1

WO1993025444A1 - Clamshell carton having an improved latching mechanism and a buckle-proof clamshell carton

Info

Publication number: WO1993025444A1
Application number: PCT/US1993/005533
Authority: WO
Inventors: John F. Sorenson
Original assignee: Perseco Division Of The Havi Group L.P.
Priority date: 1992-06-12
Filing date: 1993-06-10
Publication date: 1993-12-23
Also published as: CA2137362C; AU4531893A; CA2137362A1

Abstract

A paperboard clamshell carton includes a tray and a cover, hingedly connected and latched in the closed position by cooperating latching members. Detents, extending forwardly from adjacent the upper corners of the front wall of the tray, and detent engaging slots and tabs in the cover, located adjacent the lower corners of the front wall of the cover, releasably engage when the cover is folded shut over the tray. The forwardly extending detents are of double thickness, being formed by overlapped extensions of the glue flaps and side walls of the tray. In another aspect of the invention, a clamshell type carton is provided with a cut along the hinge score line connecting the upper cover and lower tray portions. Either a second cut in the back panel of the carton, above or below the hinge score line cut, or a cut-out slot encompassing the hinge score line cut, is utilized to facilitate the easy opening and closing of the carton without buckling occurring in the back panel in the region of the hinge score line. In another aspect of the invention, a clamshell type carton is provided with a cut along the hinge score line connecting the upper cover and lower tray portions. A second cut is placed in the back panel of the carton, above or below the hinge score line cut, wherein the second cut is a continuous curve having a first end point located in the back panel and a second end point intersecting the cut along the hinge score line. The second cut is utilized to facilitate the easy opening and closing of the carton without buckling occurring in the back panel in the region of the hinge score line.

Description

CLAMSHELL CARTON HAVING AN IMPROVED LATCHING MECHANISM AND A BUCKLE-PROOF CLAMSHELL CARTON

FIELD OF THE INVENTION

One embodiment of the present invention generally relates to double cavity "clamshell" containers such as those used in the packaging of hamburgers and other food products. More specifically, the invention concerns an improved latching mechanism for clamshell cartons fabricated from folded paperboard, boxboard or corrugated board.

Another embodiment of the present invention generally relates to double cavity "clamshell" containers such as those used in the packaging of hamburgers and other food products. More specifically, the invention concerns clamshell cartons fabricated from folded paperboard, boxboard or corrugated board, and addresses the problem of buckling which occurs in the center back region of such cartons upon opening and closing.

BACKGROUND OF THE INVENTION

In fast service and carry-out food businesses, it is necessary to package food products in containers which are inexpensive, easy to ship and store, and convenient to use for the retailer and the consumer. When assembled and filled with food products, such containers must be easy to close and open, and yet they must remain shut in transport from the food counter to a table or other carry out location. It is also important, in the design and construction of such containers, to take into account environmental aspects of their use. One form of packaging which has addressed these concerns, and has met with acceptance, is a carton comprised of a joined tray and cover with integral latching means which can be readily formed from a cut and scored blank. The cut and scored blank is made from paperboard, boxboard or corrugated board. When partially folded and glued, the blank forms a hingedly connected tray and cover, each in the form of a truncated pyramid. Such partially folded cartons can be shipped and stored in nested condition. In use, various food products, such as hamburgers, chicken pieces, pizza slices and the like, are placed in the tray portion of the partially folded carton, and the cover portion is folded over the tray portion and latched thereto at a location opposite the fold or hinge in the back panel of the carton. Such double cavity, folded tray and cover, cartons are referred to a clamshell cartons. A clamshell carton is disclosed, for example, in U.S. Patent No. 4,877,178, issued October 31, 1989 to Dopaco, Inc. as assignee.

The design of a suitable latching mechanism for such clamshell cartons has been an object of prior art efforts. The latching mechanism must do more than simply keep the carton closed. It must be foolproof, simple and quick to use, positive and secure in its engagement, and so designed that it will not be prone to damage during transportation of the nested cartons or while being handled by restaurant crew persons or patrons.

A generally accepted prior art clamshell carton which features integral latching means is disclosed, for example, in U.S. Patent No. 4,877,178, issued October 31, 1989 to Dopaco, Inc. as assignee. In the Dopaco carton, two primary detents extend forwardly from slightly above the front wall of the tray portion. The detents are minimal in size and are double laminated during carton fabrication for additional stiffness, which enhances their performance and durability. Upon closing, the detents engage corresponding, triangular-shaped slots in each of the forward cover glue flaps.

While providing a tight and secure fit of the carton portions, the Dopaco latching mechanism has proven to be difficult to open. The natural tendency for the customer has been to pull on the center of the overhanging front panel of the cover portion to open the carton. However, this action draws the outside corners of the triangular-shaped slots into contact with the tray detents, preventing their release. Alternatively, the user can work with each corner of the carton to free the detents; this has proven cumbersome and equally ineffective. Furthermore, the triangular flaps that remain after the cover flap slots are cut in the Dopaco carton do not always pop out when the clamshell is formed and, thus, have been known to interfere with and delay closing of the carton.

Other prior art clamshell cartons have used cover engagement hooks formed from the front panel or side panels of the carton cover. The engagement hooks usually extend beyond the width or length of the carton, and suffer the disadvantage of being subject to damage during shipping and handling.

Accordingly, it is an object of the present invention to provide a clamshell carton having an improved latching means, which is simpler and more reliable in use.

Another problem which has been encountered with such clamshell cartons, particularly when they are made from thinner grades of paperboard, has been their tendency to buckle in the back as they are being closed by restaurant crew persons or opened by customers. For example, when the top cover portion is lifted and folded back on the center hinge in the rear portion of the carton, the region adjacent the hinge tends to flex and bow. This problem is sometimes referred to as "oil canning" because the back region of the carton can distort as opening begins and then pop back into its proper and intended configuration, in much the same way as an oil can lid pops back into position after being depressed. The buckling problem appears to be caused by the flexible nature of the carton material, the spacing between the front of the carton and the back region where the buckling occurs and the forces applied to the carton portions as they are handled during the closing and opening operations. This problem is a troublesome and awkward one for crew persons trying to rapidly assemble and fill nested and partially folded blanks, and for consumers trying to open the carton and access its contents. Sometimes, a consumer can alleviate the problem during opening by pressing his fingers in the buckled region to realign the carton portions. In other instances, however, trying to fully open the cover and forcibly overcome the buckling can result in a torn container and/or spilled contents.

The prior art has addressed this buckling problem. U.S. Patent No. 4,232,816 discloses the use of one or more slits which are normal to, and bisect, the fold line in the rear wall of a clamshell container. Such slits are said to weaken the center portion of the rear wall and thereby reduce the tendency of that wall to buckle upon opening. U.S. Patent No. 4,266,713 discloses the provision of lines of weakness so positioned relative to the center hinge as to create a separate hinge ridge or an inverted hinge channel upon closing the carton. Such a hinge ridge or hinge channel is said to stabilize the rear carton wall against buckling and/or bowing outwardly. U.S. Patent No. 4,792,085 discloses various diagonal, intersecting incisions above and below the hinge line of a clamshell container, as well as ribs formed above, below and parallel to the hinge line.

These efforts of the prior art, while directed at the buckling problem associated with clamshell cartons, have not been widely accepted; and have been found to be less than entirely satisfactory.

Accordingly, it is an object of this invention to provide a novel clamshell carton construction which can be easily made and conveniently closed or opened without encountering undesirable buckling or "oil canning" effects.

SUMMARY OF THE INVENTION

One or more of the above objects and other objects are realized in the clamshell carton of the present invention, wherein a Dopaco-type container is modified by the elimination of the two interfering flaps and the substitution of sidewise projecting engagement tabs for the walled Dopaco detent receiving slots. The engagement tabs are positioned substantially inboard toward the center of the carton, and are more flexible and consequently less restrictive than the prior art corner slot design. Moreover, the tray detents are held captive by the triangular-shaped, partially walled slot cut out of each of the forward cover glue flaps. The modifications of the present invention, described in greater detail below, have resulted in a more forgiving and more responsive latching mechanism without detracting from any of the advantages inherent in the original Dopaco design.

A principal advantage of the new latching mechanism is that its component parts are readily visible and, therefor, their manner of operation can be perceived easily. If a customer endeavors to open the carton by pulling outwardly and upwardly on the front panel of the cover, the cut-away corners of the cover will permit the sidewise projecting engagement tabs to flex and draw away from engaging contact with the latching detents in the tray portion of the carton. In accordance with the present invention, a clamshell carton having a tray and cover is locked in the closed position by means of a pair of double-walled detents extending forwardly and above the front wall of the tray. The double-walled detents are formed by overlapping extensions of the glue flaps and the side walls of the trays. Sidewise projecting tabs, inboard toward the center of the carton, are formed in the forward glue flaps of the cover and releasably engage the tray detents to latch the cover to the tray in the closed position.

One or more of the above objects and other objects are also realized in the clamshell carton of the present invention, wherein a knife cut is made along the hinge line or hinge score of the blank used to fabricate the clamshell carton. At the same time, a second knife cut is made adjacent the first knife cut in the back panel of the carton. The second knife cut is located either above or below the hinge line. Furthermore, the second cut is a continuous curve having a first end point located in the back panel and a second end point coextensive with the first cut. The second knife cut working in conjunction with the first knife cut along the hinge line have proven to lessen the aforediscussed buckling problem found in prior art clamshell containers.

In certain food packaging applications, a vented carton is neither necessary nor desirable. For example, in a hamburger box, it is desirable that heat be retained and that there be no openings in the carton, particularly in the lower tray portion, for hamburger dressings to leak out during transport. In a preferred embodiment of the invention, intended for use in such applications, a first thin knife cut is made along a portion of the back panel hinge score line and a second thin knife cut is made in the back panel of the carton above the hinge score line. It has been found that the buckling problem is best addressed when the two cuts are adjacent, generally coextensive, generally parallel and centered with respect to a vertical plane bisecting the carton back panel. Excellent results have been achieved in such a hamburger box configuration where the two cuts are spaced apart approximately %-inch and are approximately half the length of the entire hinge score.

As long as one knife cut lies along the hinge score line, the placement and shape of the second knife cut is not critical, and there can be many alternative arrangements within the scope of the present invention. For example, the second cut can be curved or zigzagged. The second cut can be partially parallel to the first cut. The second cut can be spaced at varying distances from the cut along the hinge line. The first and second cuts can have differing lengths. Combinations of such features may likewise be employed within the teachings and scope of the present invention.

There are other food packaging applications where venting is desirable and/or required. For example, recently fried foods such as fried chicken pieces are often packaged while still very hot. In such instances, it may be desirable that the carton be vented so as to permit the contents to cool slightly before consumption. The present invention encompasses a buckle-proof carton made for such applications. In a preferred embodiment, the first knife cut along the back panel hinge score line forms part of the periphery of a horizontal slot or cut-out. Although not necessary for the present invention, it is preferable that the slot be disposed above the hinge score so that food products resting in the tray portion of the carton can not fall ut of the carton in normal use. The size of the slot can be varied depending on the size of the carton, the size of the food pieces in the carton and the amount of venting desired. Also, the slot can be variously shaped. For ease of manufacturing, and depending on the size of the slot, it may be desirable that the slot have one or more enlarged portions to facilitate the stripping out of paper material during the manufacture of the blank from which the clamshell carton is made. The principal requirement is that the slot must break or interrupt the score line running across the back panel of the carton.

In accordance with the present invention, a stress relief region is created by the adjacent knife cuts or the slot which virtually eliminates oil canning. The full nature of the invention will be understood from the accompanying drawings and the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a stamped and scored paperboard blank for forming the clamshell embodiment of the invention illustrated in FIGS. 2—4.

FIG. 2 is a perspective view showing the blank of FIG. 1 assembled and in the open position.

FIG. 3 is a perspective view showing the carton of FIG. 2 in a closed position.

FIG. 4 is a cross-sectional view taken along the line 4—4 of FIG. 3.

FIG. 5 is a perspective view of a prior art clamshell type carton, and shows buckling in the back panel upon opening.

FIG. 6 is a cross-sectional view taken along line 2—2 of FIG. 5.

FIG. 7 is a cross-sectional view taken along line 3—3 of FIG. 5.

FIG. 8 is a perspective view of an improved clamshell type carton, made according to the present invention, and featuring parallel knife cuts in the back panel, one on the hinge score line.

FIG. 9 is a cross-sectional view taken along line 5—5 of FIG. 8.

FIG. 10 is a rear elevation view of the improved clamshell type carton shown in FIG. 8. FIGS. 11-14 are views of the back panel of the improved clamshell type carton, made according to the present invention, showing other arrangements of cuts which contribute to buckle free opening.

FIG. 15 is a perspective view of a vented prior art clamshell type carton, and shows buckling in the back panel upon opening.

FIG. 16 is a cross-sectional view taken along line 12—12 of FIG. 15.

FIG. 17 is a cross-sectional view taken along line 13—13 of FIG. 15.

FIG. 18 is a perspective view of an improved, vented clamshell type carton, made according to the present invention, and featuring a slot cut out of the back panel and interrupting the hinge score line.

FIG. 19 is a cross-sectional view taken along line 15—15 of FIG. 18.

FIGS. 20—28 are views of the back panel of the improved clamshell type carton, made according to the present invention, showing other configurations which contribute to buckle free opening and closing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now in general to the drawings and in particular to FIGS. 1—4, the novel clamshell carton of this invention is formed of a unitary blank 10 comprising a bottom tray-forming section 11 and a top cover-forming section 12. Fold lines are shown as dashed lines while cut lines are shown as heavy solid lines.

Tray section 11 comprises a bottom rectangular panel 14, a rear wall panel 15, similar side walls 16, 17, and a front wall 18. Rear and front walls 15, 18 are connected to panel 14 along fold lines 19, 20, respectively. Side walls 16 and 17 are connected to panel, 14 along fold lines 21, 22, respectively. A pair of front wall glue flaps 23, 24 are connected to opposite ends of front wall 18 along fold lines 25, 26, respectively.

A pair of latching detents 27, 28 are formed in glue flaps 23, 24, respectively, to project forwardly of front wall 18. A pair of locking detents 29, 30 are formed on side walls 16, 17, respectively, to extend outwardly thereof. As will be explained in connection with FIG. 2, detents 27, 28 and 29, 30 overlap each other in the assembled position to form sturdy, double thickness latching detents.

The cover 12 comprises a top central panel 35 connected to front cover wall 36, rear cover wall 37, and side walls 38, 39 by means of fold lines 40, 41, 42 and 43, respectively. The use of "front" and "rear" is based on the location in the assembled carton. A pair of cover rear wall glue flaps 44, 45 are connected to opposite sides of rear wall 37 along fold lines 46, 47 respectively. A glue flap 48 is connected to side wall 38 along fold line 49. A similar glue flap 50 is connected to side wall 39 along fold line 51.

A detent engaging tab 52 is cut into a section of glue flap 48. The tab 52 is formed by notching out a section along the solid cut line. A similar detent engaging tab 54 is cut into glue flap 50. The cutouts in glue flaps 48 and 50 are such that, when the carton is assembled, detent engaging tabs 52 and 54 will each form the base of a triangular-shaped slot which is open toward the outside of the carton. Thus, tabs 52 and 54 will project sidewise from the center of the carton.

A slotted fold line 55 forms a hinge between rear walls 15 and 37 of the tray and cover to form a hinged clamshell carton.

The cut in rear wall 37 and the cut along fold line 55, both shown in FIG. 1, are not part of the present invention. Rather, the cuts are part of an anti- buckling feature disclosed and claimed in commonly owned and pending Application Serial No. 07/898,026, filed June 12, 1992, the disclosure of which is incorporated herein by reference.

The circular dots situated at various locations on blank 10 represent glue deposits which are spread and join the various parts together; however, other joining means such as heat sealing may also be employed. As shown in FIG. 2, it has been found desirable to adhere glue flaps 23, 24, 31 and 32 to the outside of the tray walls. This is so the flaps do not act as a wick for food oils and other liquids which may be present in the assembled and filled carton.

The assembled carton is shown in FIG. 2 in an open position. Note the open truncated pyramid shape of the tray and cover. This construction enables easy nesting of a stack of cartons. The detents 27, 29 and 28, 30 can be seen projecting forwardly of front tray panel 18 on an upper portion thereof. Having the detents at this location increases the volume of the container in comparison with prior art constructions. Also, the double thickness detent construction increases the resistance of the carton to deformation when filled cartons are stacked. Detent engaging tabs 52 and 54 can be seen adjacent an upper portion of front wall 36, projecting sidewise therefrom but still inboard with respect to the carton side walls.

FIG. 3 shows the carton in a closed position. The truncated pyramidal-shaped top cover 12 extends over the smaller truncated pyramidal-shaped tray 11 to form a closed carton. The cover is latched to the tray when detent engaging tabs 52 and 54 ride over the latching detents in the front tray panel and are captured thereby.

FIG. 4 is a view from the inside of the closed container. Detent 30, which is part of side wall 17 is shown projecting slightly forward of detent engaging tab 54 and front cover wall 36.

The carton of the present invention is easily opened by pulling upward on the center of the overhanging front panel of the cover. Alternatively, projecting tabs 52 and 54 can be bent away from the carton, and the cover easily lifted. Significantly, the customer can easily view the latching components and readily determine a quick and efficient way to open the carton. Moreover, the cantilevered tabs 52 and 54 are sufficiently flexible to accommodate different ways of opening the carton.

It will be appreciated that the detents and corresponding detent engaging tabs can be switched in terms of their placement on the tray and cover portions of the carton, and that they can be cut to shapes other than the ones shown in the Figures. Moreover, the present inventions may be utilized in connection with different sizes and types of paperboard cartons (e.g.. for hamburgers, chicken pieces, pizza and so on) .

Reference is now made to FIG. 5 for the general details of a typical prior art clamshell type carton used for sandwiches and the like. There is shown a carton which is assembled from a unitary cut and scored blank. In its assembled form, the carton 56 has a hingedly connected tray 58 and cover 60, each in the form of a truncated pyramid, joined by an integral back panel 62. In use, food product is placed in tray 58 and the cover 60 is folded over the tray 58 and latched thereto at the forward end of the carton. FIG. 5 also shows the hinged connection of the tray 58 and cover 60 defined by the scored hinge line 64 extending horizontally across the center of back panel 62. The scored hinge line 64 may be formed by a crease, a perforation or a combination thereof; however, it must be sufficiently strong so as to permit repeated opening and closing and to maintain the structural integrity of the container.

The particular latching mechanism illustrated in FIG. 5 was disclosed previously in reference to the embodiment of the carton illustrated in FIGS. 1-4.

As will be seen in FIGS. 5-7, the prior art clamshell type carton of FIG. 5 is prone to buckling in the back panel 62 when the cover 60 is lifted and folded back on the center hinge in the back panel 62. It should be noted that the buckling problem is an equally troublesome one during the carton closing operation.

FIG. 8 shows an improved clamshell type carton according to the present invention. The parts of the illustrated carton perform similar functions to the parts shown in the carton of FIG. 5, and are identified with like numbers. Unlike the prior art, however, the improved clamshell container of the present invention has a cut 66 along a portion of the scored hinge line 64 and an adjacent cut 68 in the back panel 62 above cut 66. In practice, it has been found advantageous to place the cut 66 generally in the vicinity of the midpoint of hinge line 64 as it runs from one side of the container 56 to the other. Such placement enables the use of a cut 66 which is as long as possible without severing or destroying the integrity of hinge line 64. Generally, it has been found suitable to make cut 66 a length equal to approximately half the length of the hinge line 64. As illustrated in FIG. 8, cut 68 is parallel to and coextensive with cut 66. Also, they are adjacent, meaning that they may be closely spaced apart from each other. It has been found expeditious to space cuts 66 and 68 approximately %-inch apart.

Alternative versions of cooperating cuts are shown in FIGS. 10-14. FIG. 10 and FIGS. 11—14 show the use of cartons having perforated hinge lines. FIG. 11 further shows placement of the second cut at a location on back panel 62 which is below hinge line 64. FIG. 12 shows that cuts can be made above and below the hinge line, so long as there exists a cut along the hinge line. FIGS. 13—14 show that the cut or cuts corresponding to the hinge line cut may be curved. Furthermore, it is within the teachings and scope of this invention that the respective cuts can be of different lengths, sizes and shapes so long as at least one knife cut lies along the hinge score line.

FIGS. 15—17 are illustrative of prior art clamshell type containers used in applications where it is desirable to provide an opening in the container to vent the contents. Thus, FIG. 15 shows a carton construction similar to that shown in FIG. 5, but more rectangular and having vent holes 70 and 72 in the back panel. Prior art vented cartons such as the one shown in FIGS. 15—17 experience the same buckling or oil canning phenomenon in use.

FIG. 18 shows a buckle-proof clamshell type carton made, according to the present invention, for applications where venting of the carton contents is desirable or required. A generally elliptical, horizontal slot 74 is cut out of back panel 62 at a location which interrupts hinge line 64. As shown in FIGS. 20—24, the slot 74 can be cut to a number of different shapes and sizes. However, the slot must always break or interrupt the hinge line 64 on the back panel 62. Depending on the size of the slot, and the equipment used to strip excess paper material away from the cut and scored blank used to make the carton, it may be necessary to configure the slot with a protuberance or enlargement that the stripper barbs can engage during a stripping operation. One or more such enlarged portions 76 may be employed, as shown in FIGS. 21 and 23.

In FIG. 25, another embodiment of the present invention is shown. As with the embodiment of FIG. 8, a continuous cut 66 is positioned along a portion of the scored hinge line 64. Cut 66 generally is centrally located with respect to the hinge line 64 as it runs from one side of the container 56 to the other. Such placement enables the use of a cut 66 which is as long as possible without severing or destroying the integrity of hinge line 64. Generally, it has been found suitable to make cut 66 a length equal to approximately one half the length of the hinge line 64.

Located on both sides of the cut 66 are a plurality of cuts 86, 88, 90, and 92. Hinge line 64 and line 84, which bisects and is perpendicular to hinge line 64, define four quadrants I, II, III, and IV at which cuts 86, 88, 90, and 92 are respectively located. Cuts 86 are continuous curves having a first end point 94 located in the back panel and a second end point 96 which intersects or is adjacent to the cut 66. Cuts 86 have a height H of approximately 1/4" and a radius of curvature of approximately 5/8" R. Cuts 86 have a negative slope throughout their length from the first end point to the second end point. Located in quadrant II are a plurality of cuts 88 which are mirror images of cuts 86 with respect to line 84. Furthermore, there may be cuts 86 and 88 in which their second end points 96 intersect each other at line 84. In the case of the cuts 86 and 88 not intersecting each other at line 84, those cuts 86 and 88 nearest line 84 are separated from each other by approximately 1/4". Cuts 86 are evenly spaced from each other by approximately 1/2". Likewise, cuts 88 are evenly spaced from each other by approximately 1/2".

Cuts 90 are located in quadrant III and are below the hinge line 64. Cuts 90 are evenly spaced from each other by approximately 1/2" and are mirror images of cuts 86 with respect to the hinge line 64. Similarly, cuts 92 located in quadrant IV are evenly spaced from each other by approximately 1/2" and are mirror images of cuts 92 with respect to hinge line 64. As with cuts 86 and 88, there may be cuts 90 and 92 in which their second end points 94 intersect each other at line 84.

Two other embodiments of the present invention are shown in FIGS. 26 and 27. As with the embodiment of FIG. 25, a continuous cut 66 is positioned along a portion of the scored hinge line 64. Cut 66 generally is centrally located with respect to the hinge line 64 as it runs from one side of the container 56 to the other. In the embodiment of FIG. 26, cut 66 has a length equal to approximately eight tenths of the length of the hinge line 64. In the embodiment of FIG. 27, cut 66 has a length equal to approximately one half of the length of the hinge line 64. Located on both sides of the cut 66 are a plurality of cuts 86, 88, 90, and 92. Cuts 86 are continuous curves having a first end point 94 located in the back panel and a second end point 96 which intersects or is adjacent to the cut 66.

In the embodiment of FIG. 26, cuts 86 are J- shaped having a curved section 98 and a straight section 100. Straight section 100 has a length of approximately 1/2" and is parallel to the hinge line 64. Cuts 86 have a height H of approximately 1/4" and curved section 98 has a radius of curvature of approximately 1/8" R. Located in quadrant II are a plurality of cuts 88 which are mirror images of cuts 86 with respect to line 84. Cuts 86 are spaced from each other by approximately 7/8". Likewise, cuts 88 are spaced from each other by approximately 7/8". Cuts 86 and 88 nearest line 84 are separated from each other by approximately 1 1/2".

In the embodiment of FIG. 26, cuts 90 are located in quadrant III and are below the hinge line 64. Cuts 90 are J-shaped in a manner similar to that described with cuts 86. However, cuts 90 are offset with respect to cuts 86 and are spaced from cuts 86 approximately between two adjacent cuts 86. Cuts 90 are spaced from each other by approximately 7/8". Cuts 92 located in quadrant IV are mirror images of cuts 90 with respect to line 84. Cuts 90 and 92 nearest line 84 are separated from each other by approximately 7/8".

In the embodiment of FIG. 27, cuts 86 are continuous having a first end point 94 and a second end point 96 which intersects or is adjacent to cut 66. Cuts 86 have a height H of approximately 1/4" and a radius of curvature of approximately 5/8" R. Cuts 86 have a negative slope throughout their length from the first end point to the second end point. Located in quadrant II are a plurality of cuts 88 which are mirror images of cuts 86 with respect to line 84. However, there are no cuts 86 and 88 in which their second end points 96 intersect each other at line 84. Cuts 86 are evenly spaced from each other by approximately 1/2". Likewise, cuts 88 are evenly spaced from each other by approximately 1/2". Cuts 86 and 88 nearest line 84 are separated from each other by approximately 5/8".

Cuts 90 are located in quadrant III and are below the hinge line 64. Cuts 90 have the same magnitude for their height and radius of curvatures as cuts 86. Cuts 90 are evenly spaced from each other by approximately 1/2" and are offset with respect to cuts 86. Cuts 90 have their second end points 96 located approximately halfway between the second end points 96 of adjacent cuts 86. Cuts 92 located in quadrant IV are evenly spaced from each other by approximately 1/2" and are mirror images of cuts 90 with respect to line 84. As with cuts 86 and 88, there are no cuts 90 and 92 in which their second end points 96 intersect each other at line 84. Cuts 90 and 92 nearest line 84 are separated from each other by approximately 3/16".

In the embodiment of FIG. 28, cuts 86 are continuous having a first end point 94 and a second end point 96 which intersects or is adjacent to cut 66. Cut 66 has a length equal to approximately seven tenths of the length of the hinge line 64. Cuts 86 have a height H of approximately 1/4" and a radius of curvature of approximately 5/8" R. Cuts 86 have a negative slope throughout their length from the first end point to the second end point. Cuts 86 are evenly spaced from each other by approximately 1/2". Located in quadrant II are a plurality of cuts 88 which have the same shape and spacing as cuts 86. The second end points 96 of cuts 86 and 88 nearest line 84 are each separated from line 84 by approximately 3/16".

Cuts 90 are located in quadrant III and are below the hinge line 64. Cuts 90 have the same magnitude for their height and radius of curvatures as cuts 86. Cuts 90 are evenly spaced from each other by approximately 1/2" and are offset with respect cuts 86. Cuts 90 have their second end points 96 located halfway between the second end points 96 of adjacent cuts 86. Located in quadrant IV are a plurality of cuts 92 which have the same shape and spacing as cuts 90. The second end points 96 of cuts 90 and 92 nearest line 84 are each separated from line 84 by approximately 3/16". It should be noted that if the pattern of cuts in quadrants I and III of FIG. 27 were continued into quadrants II and IV of FIG. 27, then the embodiment of FIG. 28 would be a substantial result thereof.

Although the invention has been described above by reference to preferred embodiments thereof, it will be appreciated that the foregoing and other changes may be made without departing from the scope and spirit of the invention as defined by the claims appended hereto. Therefore, it is not intended to limit the present invention to the details of the illustration or terms of description of the preferred embodiments shown above. It will be appreciated by those skilled in the art that various modifications and alterations may be made within the scope and spirit of the present invention. For example, the values of the height, radius of curvature, and spacing of the cuts may well vary on the size of the carton.

Claims

I claim:

1. A clamshell carton having a tray, a cover fitting over said tray, a fold line hinge connecting said tray and cover and means for latching the cover and tray in a closed position, said latching means comprising: double wall detents projecting forwardly above the front wall of said tray; and cooperating slot and cantilevered tab pairs in said cover for releasably engaging said double wall detents.

2. A carton according to claim 1, wherein said double wall detents in said tray are located generally adjacent upper corners of said tray front wall and said slot and cantilevered tab pairs are located generally adjacent lower corners of said front wall of said cover.

3. A carton according to claim 2, wherein each of said tabs of said slot and cantilevered tab pairs has a free end projecting generally away from the other of said tabs.

4. A carton according to claim 3, wherein said cover has side walls that extend outwardly beyond said free end of each of said tabs when said carton is closed.

5. A carton according to claim 3, wherein each of said slots of said slot and cantilevered tab pairs is generally triangular in shape, having a bottom portion defined by said cantilevered tab and a generally open portion adjacent said free end of said tab.

6. A carton formed from a unitary blank of cut and foldable paperboard comprising: a tray, a cover fitting over said tray, and a fold line hinge connecting said tray and cover; said tray comprising a bottom panel, two side walls, a front wall and a rear wall, said front and rear walls each having two glue flaps, each of said glue flaps being adhered to an end of one of said side walls, each of said glue flaps on said front wall having a detent in an upper portion of said front wall extending forwardly and above said front wall, each of said side walls having a detent in an upper portion thereof extending forwardly and above said front wall, each of said detents on each of said glue flaps on said front wall and each of said detents on each of said side walls being in overlapped joined relation to form a pair of double thickness detents; and said cover comprising a top panel, two side walls, a rear wall and a front wall, said front wall having both a slot and a cantilevered detent engaging tab adjacent each end portion thereof; said cover slots and detent engaging tabs releasably engaging said pair of tray detents when said cover is closed to latch said cover to said tray.

7. A carton according to claim 6, wherein each said tray glue flap is folded over and adhered to an outside portion of said tray side walls.

8. A carton according to claim 6, wherein said cover slots and cantilevered detent engaging tabs are formed in said cover front wall glue flaps.

9. A carton according to claim 6, wherein said cover rear wall has two glue flaps, each of said glue flaps being adhered to an adjoining end of one of said cover side walls.

10. A carton according to claim 6, wherein each of said cantilevered detent engaging tabs projects generally away from the other and is generally perpendicular to an adjacent cover side wall.

11. A carton according to claim 10, wherein said cover side walls extend outwardly beyond the ends of said cantilevered detent engaging tabs when said carton is closed.

12. A carton according to claim 10, wherein each said slot is generally triangular in shape, having a bottom portion defined by said cantilevered detent engaging tab and a generally open portion adjacent the free end of said cantilevered detent engaging tab.

13. A carton formed from a unitary blank of cut and foldable paperboard comprising: a tray, a cover fitting over said tray, and a fold line hinge connecting said tray and cover; said tray comprising a bottom panel, two side walls, a front wall and a rear wall, said front and rear walls each having two glue flaps, each of said glue flaps being adhered to an end of one of said side walls, each of said glue flaps on said front wall having a detent in an upper portion thereof extending forwardly and above said front wall, each of said side walls having a detent in an upper portion thereof extending forwardly and above said front wall, each of said detents on each of said glue flaps on said front wall and each of said detents on each of said side walls being in overlapped joined relation to form a pair of double thickness detents; and said cover comprising a top panel, two side walls, a rear wall, a front wall, generally triangular-shaped slots adjacent lower corners of said cover front wall and cantilevered detent engaging tabs adjacent said slots and projecting generally away from each other and generally perpendicular to said cover side walls adjacent thereto; said cover slots and cantilevered detent engaging tabs releasably engaging said pair of tray detents when said cover is closed to latch said cover to said tray.

14. In a clamshell type container having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising: a first cut along said hinge line, said cut being continuous and approximately half the length of said hinge line; and a second cut in said back panel above said first cut.

15. A container according to claim 14, wherein said first cut is centrally disposed along said hinge line.

16. A container according to claim 14, wherein said second cut is curved.

17. A container according to claim 14, wherein said first and second cuts are generally coextensive with each other.

18. A container according to claim 14, wherein said first and second cuts are approximately %-inch apart.

19. In a clamshell type container having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising: a cut along said hinge line; and at least one cut in said back panel generally coextensive with said hinge line cut.

20. A container according to claim 19, wherein said hinge line cut is approximately half the length of said hinge line.

21. A container according to claim 19, wherein said hinge line cut is centrally disposed along said hinge line.

22. A container according to claim 19, wherein said generally coextensive back panel cut is adjacent said hinge line cut.

23. A container according to claim 19, wherein said generally coextensive back panel cut is generally parallel to said hinge line cut.

24. A container according to claim 19, wherein both said hinge line cut and said back panel cut are centrally disposed across said back panel.

25. A container according to claim 19, wherein said hinge line cut and said back panel cut are approximately -inch apart.

26. A container according to claim 19, wherein said generally coextensive back panel cut is curved.

27. In a clamshell container having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising: a first cut along said hinge line, said hinge line cut centrally disposed along said hinge line and having a length equal to approximately half the length of said hinge line; and a second cut in said back panel adjacent said hinge line cut; said second cut being generally coextensive with and generally parallel to said first cut; whereby buckling of said back panel is avoided when said cover portion is folded about said back panel hinge line.

28. A container according to claim 27, wherein said generally coextensive and generally parallel cut is above said hinge line.

29. A container according to claim 27, wherein either of said cuts is sufficiently wide to permit venting of the container.

30. In a clamshell type container formed from a paperboard blank and having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising a single slot cut out of said back panel and interrupting said hinge line, said single slot encompassing approximately half the length of said hinge line.

31. A container according to claim 30, wherein a portion of said slot is defined by a cut along said hinge line.

32. A container according to claim 30, wherein said slot is generally elliptical.

33. A container according to claim 30, wherein said slot includes at least one enlarged region to facilitate stripping out of paper material during fabrication.

34. A container according to claim 30, wherein said slot is centrally disposed along the length of said hinge line.

35. A container according to claim 30, wherein said slot includes at least one straight edge defined by a straight cut along said hinge line.

36. A container according to claim 35, wherein said slot includes a curved portion adjacent said hinge line cut.

37. A container according to claim 30, wherein said slot has a minimum width at any point along its length of approximately Vβ-inch.

38. In a clamshell container having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising a slot cut out of said back panel and horizontally disposed with respect thereto, said slot defined in part by a cut coincident with said hinge line and extending approximately half the length of said hinge line; whereby buckling of said back panel is avoided when said cover portion is folded about said back panel hinge line.

39. A container according to claim 38, wherein said hinge line cut defines a lowermost portion of said slot.

40. A container according to claim 38, wherein at least one portion of said slot is curved.

41. A container according to claim 38, wherein said slot is generally elliptical.

42. A container according to claim 38, wherein said slot includes at least one enlarged region to facilitate stripping out of paper material during fabrication.

43. A container according to claim 38, wherein said slot is centrally disposed along the length of said hinge line.

44. In a clamshell type container having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising: a first cut along said hinge line; a second cut in said back panel positioned to one side of said first cut, wherein said second cut is a continuous curve having a first end point located in said back panel and a second end point intersecting said first cut.

45. The clamshell type container of claim 44, wherein said second cut comprises a negative slope.

46. The clamshell type container of claim 44, wherein said second cut comprises a negative slope throughout its length from said first end point to said second end point.

47. The clamshell type container of claim 44, wherein said first cut is continuous.

48. The clamshell type container of claim 47, wherein said first cut has a length of approximately three fourths of the length of said hinge line.

49. The clamshell type container of claim 47, wherein said first cut is centrally located with respect to said hinge line.

50. The clamshell type container of claim 44, comprising a third cut in said back panel and above said hinge line.

51. The clamshell type container of claim 50, wherein said third cut is a mirror image of said second cut with respect to a line which is perpendicular to said hinge line.

52. The clamshell type container of claim 45, comprising a third cut in said back panel and above said hinge line.

53. The clamshell type container of claim 52, wherein said third cut is a mirror image of said second cut with respect to a line perpendicular to said hinge line.

54. The clamshell type container of claim 46, comprising a third cut in said back panel and above said hinge line.

55. The clamshell type container of claim 54, wherein said third cut is a mirror image of said second cut with respect to a line perpendicular to said hinge line.

56. The clamshell type container of claim 44, comprising a third cut in said back panel and below said hinge line, wherein said third cut is a mirror image of said second cut with respect to said hinge line.

57. The clamshell type container of claim 45, comprising a third cut in said back panel and below said hinge line, wherein said third cut is a mirror image of said second cut with respect to said hinge line.

58. The clamshell type container of claim 46, comprising a third cut in said back panel and below said hinge line, wherein said third cut is a mirror image of said second cut with respect to said hinge line.

59. The clamshell type container of claim 51, wherein said perpendicular line bisects said hinge line.

60. The clamshell type container of claim 50, comprising a fourth cut in said back panel and below said hinge line.

61. The clamshell type container of claim 60, wherein said fourth cut is a mirror image of said second cut with respect to said hinge line.

62. The clamshell type container of claim 51, comprising a fourth cut in said back panel and below said hinge line.

63. The clamshell type container of claim 62, wherein said fourth cut is a mirror image of said second cut with respect to said hinge line.

64. The clamshell type container of claim 54, wherein said second and third cuts have a common end point.

65. The clamshell type container of claim 55, wherein said second and third cuts have a common end point.

66. The clamshell type container of claim 61, wherein said second and third cuts have a common end point.

67. The clamshell type container of claim 62, wherein said second and third cuts have a common end point.

68. The clamshell type container of claim 44, comprising a plurality of second cuts.

69. The clamshell type container of claim 68, wherein said plurality of second cuts are evenly spaced from each other.

70. The clamshell type container of claim 50, comprising a plurality of third cuts.

71. The clamshell type container of claim 70, wherein said plurality of third cuts are evenly spaced from each other.

72. The clamshell type container of claim 71, comprising a plurality of second cuts.

73. The clamshell type container of claim 72, wherein said plurality of second cuts are evenly spaced from each other.

74. The clamshell type container of claim 44, wherein said second cut is positioned above said hinge line.

75. In a clamshell type container having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising: a first cut along said hinge line; a second cut in said back panel positioned at one side of said first cut, wherein said second cut is J- shaped having curved section and a straight section.

76. The clamshell type container of claim 75, wherein said first cut is continuous.

77. The clamshell type container of claim 76, wherein said first cut has a length of approximately three fourths of the length of said hinge line.

78. The clamshell type container of claim 77, wherein said first cut is centrally located with respect to said hinge line.

79. The clam shell type container of claim 75, wherein said straight section is parallel to said hinge line.

80. The clamshell type container of claim 75, comprising a third cut in said back panel and above said hinge line.

81. The clamshell type container of claim 80, wherein said third cut is a mirror image of said second cut with respect to a line which is perpendicular to said hinge line.

82. The clamshell type container of claim 75, comprising a third cut in said back panel and below said hinge line, wherein said third cut is J-shaped having a straight section and a curved section.

83. The clamshell type container of claim 82, wherein said third cut is offset with respect to said second cut.

84. The clamshell type container of claim 83, comprising a fourth cut which is a mirror image of said third cut with respect to a line which is perpendicular to said hinge line.

85. The clamshell type container of claim 81, wherein said perpendicular line bisects said hinge line.

86. The clamshell type container of claim 75, wherein said second cut is positioned above said hinge line.

87. In a clamshell type container having a top cover portion, a bottom tray portion and an integral back panel, wherein said cover portion and said tray portion are hingedly connected through a hinge line extending across said back panel, the improvement comprising: a first cut along said hinge line; a second cut in said back panel positioned at one side of said first cut, wherein said second cut is a continuous curve having a first end point located in said back panel and a second end point intersecting said first cut; and a third cut in said back panel below said first cut and offset with respect to said second cut.

88. The clamshell type container of claim 87, wherein said second cut comprises a negative slope.

89. The clamshell type container of claim 88, wherein said second cut comprises a negative slope throughout its length from said first end point to said second end point.

90. The clamshell type container of claim 87, wherein said first cut is continuous.

91. The clamshell type container of claim 87, wherein said first cut has a length of approximately three fourths of the length of said hinge line.

92. The clamshell type container of claim 91, wherein said first cut is centrally located with respect to said hinge line.

93. The clamshell type container of claim 87, comprising a fourth cut in said back panel and above said hinge line, wherein said fourth cut is a mirror image of said second cut with respect to a line which is perpendicular to said hinge line.

94. The clamshell type container of claim 87, comprising a fourth cut in said back panel and below said hinge line, wherein said third cut is a mirror image of said third cut with respect to a line which is perpendicular to said hinge line.

95. The clamshell type container of claim 87, comprising a plurality of second cuts evenly spaced from each other.

96. The clamshell type container of claim 95, comprising a plurality of third cuts offset from said plurality of second cuts.

97. The clamshell type container of claim 96, wherein said plurality of third cuts are evenly spaced.