US3563445A

US3563445A - Plastic tray structures

Info

Publication number: US3563445A
Application number: US758968A
Authority: US
Inventors: William J Clayton
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1968-09-11
Filing date: 1968-09-11
Publication date: 1971-02-16
Anticipated expiration: 1988-02-16
Also published as: BE733890A

Abstract

A thermoplastic tray characterized by having a series of valleys and ridges arranged on the surface thereof in a herringbone-type pattern. The depth and width of the valleys and ridges, the longitudinal extent thereof, and the angular relationship of rib segments are substantially uniform and selected to achieve maximum tray rigidity in the longitudinal, transverse and diagonal directions of the tray structure.

Description

United States Patent 72] Inventor William J. Clayton Fairport, N.Y. [21} Appl. No. 758,968 [22] Filed Sept. 11, 1968 [45] Patented Feb. 16, 1971 [73] Assignee Mobil Oil Corporation [54] PLASTIC TRAY STRUCTURES 5 Claims, 10 Drawing Figs. [5 2] 0.8. CI. 229/25; 220/72, 220/74; 99/ 174; 220/97 [51 Int. Cl. 865d 1/00, 865d 7/42 [50] Field of Search 226/25; 220/74, 97 (C), 72; 99/174 [56] References Cited UNITED STATES PATENTS 1,945,397 1/1934 Gray (220/72) Primary Examiner-George T. Hall Attorneys- Oswald G. Hayes, Andrew L. Gaboriault and James D. Tierney ABSTRACT: A thermoplastic tray characterized by having a series of valleys and ridges arranged on the surface thereof in a herringbone-type pattern. The depth and width of the valleys and ridges, the longitudinal extent thereof, and the angular relationship of rib segments are substantially uniform and selected to achieve maximum tray rigidity in the longitudinal, transverse and diagonal directions of the tray structure.

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PATENTEU FEB] 8197i SHEET 3 BF 3 PLASTIC TRAY STRUCTURES I. Field of the Invention The present invention relates to thermoplastic trays which are especially adapted for the packaging of fresh meats and produce. The subject trays are constructed in such a manner as to allow for relatively free circulation of air at the interface of the tray surface and the product packaged therein, as well as providing a means to entrain the natural juices and liquids normally exuded from the products which are packaged therein.

2. Description of the Prior Art meats In recent years, it has become commonplace in the retail sales of fresh meats and produce, to package, for example, fresh cuts of meat in individual consumer size packages. Such packages are generally characterized as comprising a shallow, rectangular support tray, the product being retained in this support tray by being overwrapped with a transparent material such as, for example, cellophane or polyethylene film material and the like.

In the past, such support trays have been fabricated from materials such as molded fibrous pulp or thermoplastic materials, polystyrene having been found to be a preferred plastic for the latter type of tray. In the case of molded pulp trays, it has been found that ,when moisture-containing products are packaged therein, the absorbtive nature of the pulp material has a severe dehydrative effect on products such as fresh meat, and, likewise, such water absorption into the pulp fibers of the tray has a weakening effect on the tray structure. It has been found that when support trays are fabricated from plastic materials, the aforenoted deficiencies of pulp trays are eliminated to a great extent. However, in the case of plastic trays which are relatively impervious to the passage of air and moisture vapor, there is a tendency for that portion of the meat in contact with such a plastic tray to rapidly discolor, losing its natural bloom and resulting in the contained products having an unpleasant and unappetizing appearance from the consumers point of view.

Attempts have been made in the past to remedy the aforenoted deficiencies in plastic packaging trays, for example, as disclosed in U.S. Pat. No. 2,918,379 by perforating the tray bottom to provide ventilation holes therethrough. More commonly, as disclosed for example in U. S. Pat. No. 3,151,799, prior art attempts to reduce such discoloration consisted in reducing the surface area of the tray bottom, which was in contact with the meat product supported thereon. As disclosed in U.S. Pat. No. 3,ll,799 this reduction in interfacial contact between the tray bottom and meat product supported thereon may be achieved by embossing the tray bottom to provide a series of elongated, upstanding projections separated by relatively flat tray bottom portions, whereby the meat now rested on only the upper surface of the upstanding projections rather than on I00 percent of tray bottom surface. Such an arrangement allows for the circulation of air intermediate the upstanding projections, whereby the natural bloom of the meat product may be preserved for relatively long periods of time.

It has been found, however, that such prior art trays as aforediscussed are not entirely satisfactory. In the case of plastic trays which have been perforated to allow for adequate product ventilation, products packaged therein may become prematurely dehydrated as a result of moisture loss through such ventilation holes. Additionally, such apertures in the tray bottom may result in undesirable seepage of liquids therethrough. In the case of the aforediscussed prior art tray structures wherein the tray bottoms have been embossed to reduce the tray contact area, it has been found that there is a tendency for such trays to bend or collapse along lines corresponding to the embossed ridges in the tray bottom. Such a tendency is especially prevalent in the case of trays formed from relatively thin plastic sheet material on the order of less than about 20 mils, for example.

SUMMARY OF THE INVENTION The plastic trays of the present invention comprise a generally rectangular bottom surface surrounded by four upstanding and adjoining tray walls which are integral extensions of the tray bottom. The surface of the tray bottom is characterized by having a series of contiguous valley segments and contiguous ridge segments arranged thereon in a preselected pattern which simulates a herringbone type of design. The depth and width of the valleys and the ridges are substantially uniform and preselected, dependent upon desired tray thickness and size, to achieve maximum tray rigidity in both the longitudinal, transverse and diagonal directions of the tray structure. In addition, the valleys in the surface of the tray bottom serve to entrain liquids exuded from moisture-emitting products contained therein; and the ridges provide a discontinuous supporting surface of minimal contact area allowing for relatively free circulation of air on the undersurface of the packaged product.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a plastic tray construction in accordance with the present invention.

FIG. 2 is a side elevational view of the tray shown in FIG. 1.

FIG. 3 is an end elevational view of the tray shown in FIG. 1.

FIG. 4 is an enlarged fragmentary cross-sectional view of the tray shown in FIG. I and taken along the reference line 44 thereof, and further illustrating a meat product and a film overwrap.

FIG. 5 is an enlarged fragmentary cross-sectional view of the tray shown in FIG. I and taken along the reference line 5-5 thereof.

FIG. 6 is a top plan view of a modified form of a tray constructed in accordance with the present invention.

FIG. 7 is a side elevational view of the tray shown in FIG. 6.

FIG. 8 is a schematic illustration, illustrative of modifications of corner portions of the tray illustrated in FIG. 6.

FIG. 9 is a fragmentary cross-sectional view of two nested trays and illustrative of the tray corner modifications schematically depicted in FIG. 8.

FIG. 10 is a top plan view of a still further modification of the tray constructions according to the principles of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS The tray structures of the present invention are formed from moisture-resistant plastic material. Thermoplastic or thermosetting resin polymers may be employed to fabricate the structures of the present invention, however, thermoplastic materials are preferred. Suitable thermoplastic resins include vinylaromatic polymers such as polystyrene; polyolefins such as polyethylene, polypropylene, polybutene, etc. polyvinyl chloride, polyvinylidene chloride, rubber hydrohalides, polyesters and copolymers, and mixtures of these resins.

Standard forming techniques such as, for example, vacuum or blow molding may be employed to form the tray structures of the present invention from preformed plastic sheet. Alternatively, the trays may be formed directly from unformed resinous materials utilizing, for example, injection molding or rotational molding techniques. As hereinbefore discussed, the novel tray structures of the present invention comprise a rectangular bottom wall surrounded by four integral and upstanding sidewalls. A preferred material of construction for the tray structures of the present invention has been found to be oriented polystyrene film. The thickness of the tray structure may vary within wide limits, principally dependent upon the end use intended for such trays. However, for purposes of the present invention, polystyrene film thicknesses on the order of from about 3 mils to about 30 mils, and preferably from about 5 mils to about 15 mils, have been found to be satisfactory.

When smooth, flat bottom trays are fabricated from such film material, the trays have a very neat and attractive appearance. However, such trays are impractical in that, in addition to causing product discoloration as aforediscussed, they lack the requisite rigidity for packaging applications. For example, when slight compressive forces are applied either in the transverse or longitudinal direction or obliquely across the tray from corner to corner, the tray has a tendency to buckle and collapse in the direction of the applied forces. It has been found that when the bottom surface of such trays are embossed to provide therein a series of ridges and valleys, the tray becomes more rigid, resisting deformation forces applied thereto. It has further been found that when elongated parallel ridges extending in the transverse direction of the tray are embossed in the tray bottom, such transverse ridges effectively resist deformation forces applied across the tray in a direction parallel to such ridges. However, when deformation forces are applied longitudinally to such an embossed tray, for example distortional forces perpendicular to said transverse ribs, there is a definite tendency for the tray to buckle and fold along lines generally parallel to such transverse ribs. Applicant has found, likewise, that when such trays are fabricated with the embossed upstanding parallel ribs extending longitudinally of said tray, the tray is strengthened in the longitudinal direction. However, when compressive forces are applied transversely of the tray, the tray will buckle and bend along the longitudinally extending ribs.

In an effort to remedy the structural deficiencies of the aforediscussed embossed trays, trays were constructed wherein a plurality of crisscrossing, upstanding ribs were embossed in the tray bottom. A portion of these ribs extended parallel to one another in a longitudinal direction from end-toend of the tray. The other portion of the ribs extended, parallel to one another, transversely across said longitudinal ribs and from side-to-side of said tray, whereby a checkerboard" rib pattern was embossed upon the tray bottom. Although such an embossment pattern proved to be superior to the aforediscussed embossed tray designs in that it exhibited greater resistance to structural deformation forces, in both the longitudinal and transverse direction of the tray, such an arrangement resulted in weak spots in the tray at those portions in the tray bottom where longitudinal ribs intersected the transverse ribs resulting in unsatisfactory tray strength.

Referring now to an embodiment of the structure as illustrated in FIG. I, applicant has found that by arranging upstanding, elongated, spaced apart ribs 11, embossed in the internal bottom surface of the tray in the form ofa herringbone pattern wherein each of the ribs comprised a series of contiguous rib segments, each of said segments meeting an adjacent segment at an angle of approximately 90, support trays may be formed which exhibit outstanding strength characteristics as well as other desirable packaging characteristics, as will be more fully described hereinafter. The herringbone, or chevron, ribbed pattern embossed on the bottom surface of the tray structures of the present invention results in an extremely rigid tray which will resist deformation forces applied to the tray in either a longitudinal or transverse direction, and, since there is no crisscrossing of the ribs, weak sport spots in such a tray bottom are nonexistent.

Additionally, it has been found that overall tray stiffness is dependent to a great extend upon the number of upstanding ribs which are embossed in the tray bottom. Since the chevron rib arrangement illustrated in FIG. 1 results in a maximum number of rib segments per given area of tray bottom, and since such rib segments extend in directions which impart, simultaneously, strength in both longitudinal and transverse directions, the resultant tray structure is one which, for equivalent amounts, i.e. weight, of construction material, is far superior to any hitherto commercially available support trays.

Although, as hereinbefore outlined, it is extremely desirable in trays of the type herein contemplated to exhibit as much rigidity as possible in both the longitudinal and transverse direction, as well as diagonally across the tray structures, it

will be understood that, by virtue of the relatively thin material from which the subject trays are fabricated, a certain degree of flexure of component parts of the tray structure, e.g. the tray sidewalls, will inevitably occur during normal handling and usage of such trays. Accordingly, it is essential that such flexure results in the sidewalls bending and not breaking or buckling. As a result of the novel construction of the tray structures of the present invention, there is provided a plurality oflocations, at points along the side and endwalls of the tray structures, which act to distribute bending stresses applied thereto across substantially the entire tray length or width, whereby single stress points are eliminated which would otherwise result in the tray breaking or buckling when forces are applied to the walls thereof.

It will be obvious to those skilled in the art that the specific dimensions and spacing of the individual contiguous rib segments may vary within wide limits. It has been found, however, for purposes of the present tray structure, that the spacing between ribs may vary from about 0.12 inch up to about 2 inches, and is preferably about 0.25 inch. The height of the individual rib segments is preferably at least about two thirtyseconds of an inch and more preferably about three thirtyseconds of an inch.

As illustrated in FIG. 1, the angle that is formed at the apex of the chevron formed by the individual contiguous rib segments is optimally about 90. It has been found that an angle of about 90 results in a tray which exhibits relatively balanced strength, i.e. rigidity, in both the transverse and longitudinal direction. However, this angle may vary within limits from about 60 to about 120, and preferably from about to about 100, dependent upon packaging applications intended therefor, without too great an adverse effect on the overall requisite rigidity of the tray. It has been found that when this angle is reduced to 60, the end-to-end stiffness increases about I00 percent and the side-to-side stiffness is decreased to about 50 percent as that exhibited by a tray having the rib segments merging at a angle. Conversely, when this angle is increased to 120, the side-to-side stiffness is increased about percent and the end-to-end stiffness is decreased by about 50 percent.

It will be noted from FIG. 1, and as specifically illustrated therein, that sets of ribs, each set comprising a series of four coextensive rib segments (a, b, c and d) extend completely across preselected areas of the tray bottom surface. The length of each of these individual rib segments may vary dependent upon the transverse dimension of the tray and are preferably from about 1 inch to about 1.5 inches in length. It is within the purview of the present invention to provide in the bottom of the tray structure any number of such contiguous rib segments from at least about two up to about 20 or more. In the case of relatively wide packaging trays, i.e. on the order of more than 10 inches in width, it has sometimes been found desirable to limit the length ofthese individual rib segments up to a length of less than about Z /inches and preferably less than 2 inches. Longer rib segment lengths have been found to result in the undesirable tendency of valleys 12 to buckle upwardly into the tray interior when pressures encountered in normal tray handling and usage are applied to the undersurface of the tray.

As hereinbefore noted, in addition to imparting strength to the tray, the upstanding chevron rib pattern in the bottom of the present trays provides air spaces, in the form of valleys 12 intermediate the upstanding support ribs 11 for circulation of air therethrough to minimize product discoloration and to maintain the natural bloom of meat products packaged thereon. It will be apparent that such interrib spacing likewise allows for continuous valleys 12 to entrain liquids exuded from the meat products packaged in such trays resulting in a neater appearing package.

It will also be noted, particularly from FIGS. 2 and 3 of the drawings, that upstanding ribs 11 embossed in the bottom surface of the tray, rather than terminating at the juncture of the tray bottom with the upstanding sidewalls of the tray, may extend further upwardly, preferably substantially vertically, into the sidewalls l3 and endwalls .14 whereby the side and endwalls 13 and 14 are further rigidified. It has been found that satisfactory widewall strength may be achieved by extension of the embossed ribs up the tray sidewalls a distance equivalent to at least one-third of the tray wall height.

As also shown in FIG. 1, in order to rigidify the corner portions of the tray illustrated therein, the tray may be provided with upstanding plateaus or flat areaslS. Such an upstanding area in each of the corners of the tray structures of the present invention, although not an absolute necessity, is desirable in those instances where it is desired to have a tray which exhibits rigidity in the corner areas thereof.

Additionally, as more clearly illustrated in FIGS. 6, 7, 8 and 9, another embodiment of the tray structure of the present invention comprises providing flat or planar areas 16, in the bottom portion of the tray. As illustrated in FIG. 6, such flat or planar portions 16 may be provided adjacent opposite ends of the tray structure or, although not illustrated, such planar portions may be provided anywhere on the tray bottom surface, for example in the middle thereof. Planar tray bottom portion 16, in addition to providing a decorative effect to the overall appearance of the tray structures of the present invention, more practically is provided to provide a flat, unembossed area on the tray bottom whereon advertising indicia or tray size information, for example, may be clearly imprinted or embossed.

As further illustrated in FIG. 6, the tray structures of the present invention may be provided with stacking lugs located in positions A, B or C, which stacking lugs comprise relatively small recesses or depressions located along the edge of tray corner portions 15. As more clearly illustrated in FIG. 9, when a series of trays are nested together one inside the other, these stacking feet serve to maintain a slight separation between adjacent trays whereby said trays may be more easily denested one from the other. Obviously, as illustrated in FIG. 9, the stacking lugs in a adjacent trays should be offset one with respect to the other, i.e. a tray with stacking feet positioned at A as illustrated in FIG. 8 is maintained separate or apart from the adjacent tray which has stacking feet located at position B as illustrated in FIG. 8.

As illustrated in FIG. 10, there is shown a still further modified form of the tray structures of the present invention comprising a tray having a series of spaced apart reinforcing ribs 17 which are positioned parallel to one another and perpendicular to the tray endwall members 14. It has been found that, especially in the case of larger size trays, i.e. trays having an increased bottom surface area which are employed, for example in the packaging of relatively large cuts of meat such as roasts and the like, there is a tendency for the endwall members 14 to flex outwardly to an undesirable extent when such large size trays are handled with the relatively heavy meat products supported on the surface thereof. Applicants have found that this undesirable flexure of endwall member 14 may be eliminated or substantially reduced by forming reinforcing rib members 17, as illustrated in FIG. 10, perpendicular with respect to the endwall members 14 of the tray and substantially parallel with respect to one another. As illustrated in FIG. 10, reinforcing rib members 17 extend into sidewall member 14 at one end of each of said reinforcing ribs and the opposite ends of reinforcing ribs 17 are tied into and are integral with upstanding rib members 11 located in the bottom surface of the tray. Upstanding rib members 17 may be either coextensive in height with rib members 11, or slightly higher, i.e. on the order of about one thirty-second to two thirtysecond inch higher than rib members 11, or alternatively reinforcing ribs 17 may taper with respect to their height relationship with upstanding rib members 11, whereby that portion of reinforcing rib 17 adjacent tray endwall 14 is higher than the terminal end of reinforcing rib 17 which terminates integrally with at least one of upstanding rib members 11 and is coextensive in height at said terminal end with rib member 11.

It WIII be noted, from FIG. 5, that the sidewalls of upstanding rib members 11, rather than being substantially parallel, may be inclined at a slight angle to the vertical. Although not absolutely essential, such inclination of the sidewalls of rib members 11 facilitates the removal of the tray structures of the present invention from the molds employed in their forming process.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.

Iclaim: I

1. A thermoplastic tray comprising an internal bottom surface with upstanding side and end wall members integrally joined thereto, a series of substantially parallel, elongated, spaced apart ribs extending upwardly from said bottom surface, each of said ribs comprising a plurality of integrally joined segments forming a herringbone configuration, each of said segments being segments disposed at an angle of from about 60 to about 120 in relationship with its adjacent segment.

2. A thermoplastic meat tray in accordance with claim 1 wherein said rib segments which are adjacent to said sidewall members extend upwardly in a, vertical direction into said sidewall members to a height intermediate the lower and upper margin of said sidewalls.

3. A thermoplastic meat tray in accordance with claim I wherein said ribs are spaced apart a distance of from about 0.12 inch to about 2 inches, said rib segments being approximately one to Zlfiinches long, said rib segments joining adjacent segments at an angle of about and said rib segments being at least two thirty-seconds inch in height.

4. A thermoplastic tray in accordance with claim I wherein said thermoplastic is transparent.

5. A packaged food product comprising a tray, as described in claim I, and a food product supported on the inner surface of the tray bottom.

Claims

1. A thermoplastic tray comprising an internal bottom surface with upstanding side and end wall members integrally joined thereto, a series of substantially parallel, elongated, spaced apart ribs extending upwardly from said bottom surface, each of said ribs comprising a plurality of integrally joined segments forming a herringbone configuration, each of said segments being segments disposed at an angle of from about 60* to about 120* in relationship with its adjacent segment.

2. A thermoplastic meat tray in accordance with claim 1 wherein said rib segments which are adjacent to said sidewall members extend upwardly in a vertical direction into said sidewall members to a height intermediate the lower and upper margin of said sidewalls.

3. A thermoplastic meat tray in accordance with claim 1 wherein said ribs are spaced apart a distance of from about 0.12 inch to about 2 inches, said rib segments being approximately one to 2 1/2 inches long, said rib segments joining adjacent segments at an angle of about 90* and said rib segments being at least two thirty-seconds inch in height.

4. A thermoplastic tray in accordance with claim 1 wherein said thermoplastic is transparent.

5. A packaged food product comprising a tray, as described in claim 1, and a food product supported on the inner surface of the tray bottom.