U.S. patent number 3,563,445 [Application Number 04/758,968] was granted by the patent office on 1971-02-16 for plastic tray structures.
This patent grant is currently assigned to Mobil Oil Corporation. Invention is credited to William J. Clayton.
United States Patent |
3,563,445 |
Clayton |
February 16, 1971 |
PLASTIC TRAY STRUCTURES
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.
Inventors: |
Clayton; William J. (Fairport,
NY) |
Assignee: |
Mobil Oil Corporation
(N/A)
|
Family
ID: |
25053849 |
Appl.
No.: |
04/758,968 |
Filed: |
September 11, 1968 |
Current U.S.
Class: |
229/407; 220/608;
220/669; 426/129 |
Current CPC
Class: |
B65D
81/262 (20130101) |
Current International
Class: |
B65D
81/26 (20060101); B65d 001/00 (); B65d
007/42 () |
Field of
Search: |
;226/25 ;220/74,97 (C)/
;220/72 ;99/174 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hall; George T.
Claims
I claim:
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.degree. to about 120.degree.
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 21/2
inches long, said rib segments joining adjacent segments at an
angle of about 90.degree. 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.
Description
1. 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. 3,151,799 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 100 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. 1 and taken along the reference line 4-4 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. 1 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-to-end 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. 1, applicant has found that by arranging upstanding,
elongated, spaced apart ribs 11, embossed in the internal bottom
surface of the tray in the form of a 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.degree., 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 of locations, 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 thirty-seconds of an inch
and more preferably about three thirty-seconds 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.degree.. It has been found that an angle of
about 90.degree. 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.degree. to about 120.degree., and preferably from
about 80.degree. to about 100.degree., 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.degree., the end-to-end
stiffness increases about 100 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 90.degree. angle.
Conversely, when this angle is increased to 120.degree., the
side-to-side stiffness is increased about 100 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 of these
individual rib segments up to a length of less than about 21/2
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 13 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 areas 15. 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 thirty-second 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 will 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.
* * * * *