US 3409199 A
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C. LAKE PACKAGING TRAY Nov. 5, 1968 2 Sheets-Sheet 1 Filed Sept. 29, 1966 FIG! INVENTOR. CONNIE LAKE Nov. 5, 1968 c. LAKE 3,409,199
PACKAGING TRAY Filed Sept. 29, 1966 2- Sheets-Sheet 2 '0 IIIIIIIIIIIIM \\\\\\\\\\\W '0 INVENTOR. CONNIE LAKE United States Patent 3,409,199 PACKAGING TRAY Connie Lake, Pittsford, N.Y., assignor to Mobil Oil Corporation, a corporation of New York Filed Sept. 29, 1966, Ser. No. 583,029 2 Claims. (Cl. 229-25) ABSTRACT OF THE DISCLOSURE The present invention relates to molded containers, and more particularly, it relates to molded containers which are suitable for packaging food for example and to a process for manufacturing such trays.
A common and conventional problem in the utilization of containers of any type resides in the storage of such containers. In order to store or ship containers, without utilizing a great deal of space, it is necessary that they be nested one within the other, which practice is conventional.
In general, prior art packaging tray structures have been characterized in having a bottom wall and side and end walls of a constant and uniform thickness. Additionally, the angle formed between the side and end walls of the tray with the tray bottom is such that the upstanding side and end walls function to retain product positioned in the tray after it has been overwrapped with, for example, protective plastic or cellophane overwrap material, and prevents product from slipping or sliding outside of the confines of the tray walls. Such trays, i.e. trays with uniform cross section thickness and having side and end walls disposed at a certain minimum angle with respect to the tray base, when they are stacked or nested together contact each other only at the interface of the respective side and end walls, there being an opening or dead space between adjacent tray bottom Walls. This dead space results, in addition to increased stack heights which necessitate increased storage space and shipping costs, in permanent deformation of the tray if pressure i applied to the top or bottom of such a stack. The deformation is caused by the tray bottoms being forced closer together causing a bending or bowing outwardly of the upstanding tray walls.
The support tray structures of the present invention have overcome the aforenoted deficiencies of the prior art trays by providing advantages hitherto unavailable in such trays. The new support trays of the present invention may be fabricated from materials, such as plastics or foamed plastics, which materials, since they are compressible, allow tray fabrication from an integral piece of stock material utilizing a one-step molding technique wherein the individual thicknesses of the tray bottom and side and end walls of a tray may be varied. Furthermore, the unique construction of the present support trays re sults in a tray which may be stacked or nested during storage to give stack heights lower than that achievable with prior art tray constructions resulting in obvious advantages with respect to, for example, shipping costs and warehouse space savings.
The tray structures of the present invention comprise molded trays of thermoplastic material comprising a bottom wall, upstanding side and end walls integral with said bottom wall, the side and end walls of the tray terminating in arcuate corners. The trays are further characiceterized in that the bottom wall of the tray is thicker than the side and end walls of the tray.
A better understanding of the invention may be had from the following description read in conjunction with the accompanying drawings wherein:
FIGURE 1 illustrates a top plan view of one form of the support tray of the present invention;
FIGURE 2 is a vertical section taken substantially 0n the plane of line 22 of FIGURE 1;
FIGURE 3 is a vertical section taken substantially on the plane of line 33 of FIGURE 1;
FIGURE 4 is a perspective view of a modified embodiment of the novel food trays of the present invention;
FIGURE 5 is a vertical section taken substantially on the plane of line 5--5 of FIGURE 4.
FIGURE 6 is a cross-sectional view in elevation of a stack of typical prior art trays;
FIGURE 7 is a cross-sectional view in elevation of a stack of the novel trays of the present invention such as the tray illustrated in FIGURE 1.
As illustrated in the drawings, the support tray of the present invention comprises a substantially fiat tray base, generally indicated as 11. Side and end Walls 12 and 12 extend upwardly and slightly outwardly from base 11 nd are integrally joined to the periphery of tray base 11, said side and end walls terminating in arcuate corners 12" which integrally join side and end wall members 12 and 12. Side and end walls 12 and 12' are inclined outwardly at a slight angle from the vertical to permit nesting of a plurality of trays for stacking purposes as illustrated in FIGURE 7. This angle. indicated as B in FIGURE 7, may vary from about 15 up to about 60, however, it has been found preferable if t? is from about to about Side and end walls 12 and 12' terminate in an out wardly flared continuous lip 10 which imparts increased rigidity to the tray structure.
As more clearly illustrated in FIGURES 2 and 3, the thicknesses of the tray base 11 and continuous lip 10 are substantially equal, while the thicknesses of side and end wall members 12 and 12', although substantially uniform with respect to each other, are considerably thinner than the thickness of tray base 11 or continuous lip 10.
As more clearly illustrated in FIGURE 7, which shows a nested arrangement of trays fabricated in accordance with the present invention, as a result of decreasing the thickness of the side and end Wall members 12 and 12' the individual tray base members 11 are in complete interface contact with one another. This eliminates the dead space or intervals between the respective tray base portions which are present in prior art tray nesting arrangements, as illustrated in FIGURE 6, thereby offering the aforediscussed advantages or reduced stack height and attendant savings on shipping costs and warehouse storage.
In addition to the foregoing advantages, the increased thickness of the tray base results in the tray when nested being in base to base contact with adjacent tray structures. Accordingly, when pressures, which are normally encountered during the handling, shipping and storage of such tray structures, are applied to a nested stack of trays, the side and end walls are not deformed or bowed out as in the case of prior art trays since the bottom to bottom contact of the trays resist such deformative pressures. It has been found that in order to achieve the foregoing advantages, the tray base must be at least 1.3 times as thick as the tray side and end wall members. Although the tray base may be much thicker than this, it has been found that when the tray base is over four times the thickness of said side and end walls, excessive stack height of the nested trays results which eliminates the aforediscussed advantages. Furthermore, it has been found that the increased base thickness of the trays of the present invention, i.e. increased thickness with respect to the side walls thereof, results in an increase of the rigidity of the tray structures of the present invention as compared to trays having a uniform profile of thickness.
As will be discussed more 'fully hereinafter, the structural strength and integrity of the tray is not reduced or sacrificed as a result of forming the tray with side and end walls of reduced thickness, moreover, the method employed for achieving this reduced side and end wall thickness in members 12 and 12' results in a tray which exhibits greater resistance to deformation than that generally exhibited by a tray of .uniform cross section, i.e. with the side and end wall members being of substantially the same thicknessas the tray base 11.
Depending upon the particular end-use application intended for the tray structures of the present invention, the tray base may vary in thickness from about 50 mils up to about 250 mils while the thickness of the side and end wall members of the tray may also vary from about 15 mils up to about 150 mils, provided that the tray base thickness is maintained atabout at least 1.3 :times the thickness of the side and end wall members.
FIGURES 4 and 5 illustrate still another embodiment of the novel tray structures of the present invention. In this instance the inner surface of tray base 11 isprovided with a plurality of recesses 14, the bottom portion of each recess terminating at a point 9 above the undersurface of tray base 11.
As illustrated in FIGURE 4, the recesses may take the form of a square. However, it should be noted the specific shape of recesses 14 shown in the drawings is merely for purposes of illustration and that recesses 14 may be of any geometrical configuration such as rectangular, triangular, circular, or the like. The side walls 16 of recesses 14 are substantially vertical withrespect to the inner surface of tray base 11, the upper edges of recesses 14 being defined by the fiat non-recessed portion of the inner tray surface of tray base 11. As shown in FIGURES 4 and 5, the undersurface of tray base 11 is substantially smooth and non-interrupted. As also illustrated in FIGURE 5, the base 11 is of a greater thickness than side and end wall members 12 and 12' as in the case of the tray embodiment illustrated in FIGURES 1 through 3 described hereinbefore.
It has been found that recesses 14 in the upper surface 13 of tray base 11 function to mechanically entrap and retain therein liquids, for example meat or poultry juices,which may be exuded from the meat or poultry products packaged in such trays. At the same time, as
a result of the inherently hydrophobic character of the plastic material from which the tray is fabricated, these juices will not penetrate the tray beyond the confines of recesses 14, thereby avoiding the dehydrative effects of moisture absorbing tray materials as well as maintaining the structural integrity and strength of the tray structure. It has been found that the size of the cross-sectional area of recesses 14 contributes to a great extent to the ability of the recesses to trap and hold liquids. The recesses are preferably about V8" in diameter and may vary from about to about 7 in diameter and still function to entrap and retain liquids. However, below these limits there is a tendency for the liquids not to flow into the recess and, conversely, above these limits although liquids will enter the recess they will not be entrapped therein and will have a tendency to flow out of the recess when the tray is tilted or inverted during handling. The depth of recesses 14 has been found to have little or no effect on the mechanical functioning of the recess and may vary within wide limits depending only upon the tray thickness (i.e. the recess must terminate prior to penetrating completely through the tray) and the relative amounts of liquid it is desired to entrap and retain therein.
Among some of the types of plastic materials which are suitable for fabrication into the tray structures of the present invention are polyolefins such as polyethylene,
polypropylene, and polybutene; polystyrene; high impact polystyrene; polyurethane; polyvinylchloride and others. A particular material which has been found to be well suited for fabrication of the present tray structures is foamed polystyrene. The closed-cell structure of the foamed polystyrene prohibits absorption or penetration of liquids into the tray body' and the foam material itself is extremely light weight permitting ease of handling and transport. i
As hereinbefore indicated, a preferred material employed in the formation of the" tray structures of the present invention is plastic and in particular foam thermoplastic materials and especially polystyrene foam. The polystyrene foam may be manufactured utilizing anyone of the number of conventional extrusion techniques, for example, extrusion of foamable polystyrene be ads,. i.e. beads which have a blowing agent already incorporated in them prior to delivery to an extrusion apparatus. or, for example, by direct injection extrusion techniques wherein a foamable agent isadded to a molten mass of polystyrene contained within an extruder prior to extrusion thereof from a die orifice. A
'After the polystyrene foam sheet material has been produced utilizing conventional extrusion techniques as discussed above, it may be molded to form the tray structures of the present invention. In general, it is desirable to preheat the foamed polystyrene sheet before it is molded in order to assure that the sheet will be at a sufficiently elevated temperature to permit rapid forming of the desired tray structure in the mold. h
After preheating the formed polystyrene foam sheet, the support tray structures of the present invention may be conveniently formed utilizing a molding operation such as match molding, for example. 3
The thickness of the tray base portion of the tray structures of the present invention may vary within wide limits depending primarily upon the nature of the tray material, the side and end wall members of the tray being of a reduced thickness relative to the thickness of the' tray base portion. For example, trays fabricated from a relatively dense tray material such as high-impact polystyrene which is extremely rigid would require less thickness than trays fabricated from low density polyethylene. Utilizing the preferred tray forming material of the present invention, i.e. polystyrene foam, it has been found that thicknesses of from about mils, for high density polystyrene foam, to about 400 mils, for low density polystyrene foam, may be employed, the specific thicknesses depending primarily upon foam density. When foam'material having preferred density of about 4 pounds per cubic foot is employed, an average tray base thickness of from about to about 250 mils has been found to be satisfactory. i
The process employed for forming the present trays may best be understood by a description of a specific embodiment as illustrated in the following example, however, such a description is solely for purposes of illustration and is not to be construed in a limiting sense. For example, the following embodiment sets forth rather specific process and operating conditions employed when preformed polystyrene foam is employed as the starting material for the tray structure and, of course, such'con- 'ditions will normally vary when other plastic tray materials are employed. l
' Example I v A preformed sheet of polystyrene foam material with an average density of about 4 pounds per cubic ft. and approximately mils thick was fed into a radiant preheat oven and heated to a temperature of approximately 275 F. Upon emerging from the preheat oven, the polystyrene sheet was approximately 200 mils thick as a re.- sult of the expanding action of the residual blowing agent, in this case pentane, which remains entrapped within the polystyrene cells after it is extruded. The residencetime of the polystyrene in the oven was approximately 5 to 20 seconds and the average line speed was about 45 ft. per minute. Immediately upon emergence from the preheat oven, the polystyrene foam sheet passes into a tray forming mold. The thermoforming mold employed is essentially an internally cooled female mold base member and an upper male tray forming member. As the match mold is cycled, the upper mold member presses down on the heated polystyrene foam forcing it to assume the traylike configuration of the female base member. The cleartance between the mold members is such that the base of the tray formed is approximately 200 mils thick and the side and end wall members are approximately 100 mils thick. The side and end wall members of the tray comprise a compressed form of the polystyrene foam formed as a result of compressive forces acting against these wall members while in the thermoforming device. The peripheral lip bordering the side and end wall members is approximately 200 mils thick.
Example 11 The formed tray fabricated in accordance with Example I after being removed from the thermoforming device was passed through a heated die punch employed for forming recesses on the inner surface of the tray bottom as illustrated in FIGURES 4 and 5 of the attached drawings. The die punch is formed from metallic materials and preferably a metallic material which exhibits good thermal conductivity properties. Aluminum has been found to be an effective material. The face of the die carries a plurality of integrally connected projecting aluminum lugs arranged on the face of the die in a predetermined pattern depending upon the the tray recess pattern desired. The lugs may be coated with a material such as Teflon, for example, to avoid sticking to the polystyrene work material during the recess forming operation. The size and shape of the lugs may vary depending upon the size and shape of recesses desired upon the tray surface. However, the cross-sectional area of the recess forming lugs must be within the crosssectional ranges discussed above, i.e. between about and 7 which are necessary to insure proper functioning of the tray recesses. The temperature of the die is regulated according to the die cycling speed which in turn is dependent upon the in-line speed of the forming operation. Hence, when the die-punch is cycling at 0.3 second, for example, it has been found advantageous to employ die temperatures of from about 575 F. to about 625 F. On the other hand, if the line speed is comparatively slow and the die punch is cycling at three second intervals, for example, die temperatures as low as about 250 F. have been found to be sutficient for forming the recesses on the inner surface of the tray bottom. As the recess-forming die-punch is cycled, the heated lugs on the die face come into contact with the inner surface of the alreadyformed tray bottom, each heated lug advancing through the polystyrene to a point just above the lower surface of the tray bottom whereupon the die is removed. The resultant, finished tray now carries a plurality of recesses, corresponding to the shape and patterned arrangement of the lugs on the surface of the die-punch.
The number, arrangement and spacing of the recesses on the interior surface of the tray bottom may vary depending upon the size of the tray and the quantities of liquid it may be necessary to entrap. Generally, for most meat and poultry packaging operations, the recesses will occupy a total area ranging from about 5 percent to about percent of the total surface area of the tray bottom and preferably about 15 percent to about 25 percent of the total surface area of the tray bottoms interior surface.
When recesses on the order of A; in width are employed, it has been found convenient to space them on A centers on the interior surface of the tray bottom.
Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be resorted to, without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of the appended claims.
What is claimed is:
1. A molded rectangular tray of foam polystyrene material comprising a fiat bottom wall, upstanding side and end walls integral with said bottom wall and extending upwardly and slightly outwardly from said bottom wall, said side and end walls terminating in arcuate corners, said tray being further characterized in that the bottom wall has a thickness of from about 1.3 to about 4 times the thickness of said side and end walls, said side and end walls being further characterized as comprising a higher density foam polystyrene material than said bottom wall, said tray being further characterized by being nestable so that in nested form the upper surface of the bottom portion of one tray is in substantial contact with the bottom surface of the bottom portion of an adjacent tray.
2. A molded tray in accordance with claim 1 wherein said tray base is characterized by having a plurality of liquid entrapping recesses arranged in a predetermined pattern on the surface thereof.
References Cited UNITED STATES PATENTS 2,893,877 7/1959 Nickolls 99174 3,040,949 6/ 1962 Foote 2292.5 3,220,631 11/1965 Reifers 229-2.5 3,264,120 8/1966 Westcott 229-2.5. X 3,305,158 2/ 1967 Whiteford 2292.5
OTHER REFERENCES Koppel-s: Bulletin C-9-273, Apr. 15, 1962, page 3.
DAVID M. BOCKENEK, Primary Examiner.