U.S. patent number 3,756,492 [Application Number 05/256,453] was granted by the patent office on 1973-09-04 for high strength open bottom packaging tray.
This patent grant is currently assigned to Diamond International Corporation. Invention is credited to Kenneth D. Bixler, Richard F. Reifers.
United States Patent |
3,756,492 |
Reifers , et al. |
September 4, 1973 |
HIGH STRENGTH OPEN BOTTOM PACKAGING TRAY
Abstract
A tray of molded wood pulp or the like is provided for the
packaging of food, such as produce, preferably in conjunction with
an overwrapped transparent film. The tray bottom is formed of a
plurality of upright U or V shaped ribs joining or intersecting in
two directions and defining open windows therebetween, the height
of each V shaped rib being on the order of several times the
thickness of remainder of the tray, and the total volume of the
inverted V shaped ribs being about equal to the volume of a bottom
of a solid bottom tray of the same size.
Inventors: |
Reifers; Richard F. (New
Canaan, CT), Bixler; Kenneth D. (Huntington, NY) |
Assignee: |
Diamond International
Corporation (New York, NY)
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Family
ID: |
22972297 |
Appl.
No.: |
05/256,453 |
Filed: |
May 24, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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185197 |
Sep 30, 1971 |
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111578 |
Feb 1, 1971 |
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Current U.S.
Class: |
229/407; 426/129;
217/26 |
Current CPC
Class: |
B65D
1/34 (20130101) |
Current International
Class: |
B65D
1/34 (20060101); B65d 001/00 (); B65d 065/00 () |
Field of
Search: |
;229/2.5,29F,29M
;217/26,30 ;206/45.33 ;99/174 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moorhead; Davis T.
Parent Case Text
This is a continuation-in-part of application Ser. No. 185,197
filed Sept. 30, 1971 which is in turn a continuation-in-part of
application Ser. No. 111,578 filed Feb. 1, 1971.
Claims
What is claimed is:
1. In a generally rectangular molded tray primarily for the
packaging of food in conjunction with the transparent overwrap film
heat-sealed thereabout, said tray comprising a pair of upwardly and
outwardly inclined opposite side walls, each of said side walls
forming a long side of said tray; and a pair of upwardly and
outwardly inclined opposite end walls, each said end wall being
adjacent to each said side walls and disposed at generally right
angles thereto and thereby forming the rectangular configuration of
said tray; the improvement comprising:
means for providing visibility to the bottom of the tray and for
supporting the food at the bottom of said tray, said means
comprising a plurality of ribs having an upright V-shaped
cross-section, said ribs extending at least partly across said tray
in at least two directions to define therebetween a plurality of
open windows, said ribs forming the tray bottom having a volume
substantially equal to the volume of a bottom of a tray of equal
size having a flat, solid bottom.
2. A tray in accordance with claim 1 molded of wood pulp.
3. A tray in accordance with claim 1 wherein said end and side
walls are of bowed construction.
4. A tray in accordance with claim 1 further comprising an annular
V-shaped rib extending around the periphery of the bottom portion
and to which said ribs extend.
5. A tray in accordance with claim 4 wherein said annular rib in
the areas of said side walls extend upwardly and directly and
smoothly merge into said side walls.
6. A tray in accordance with claim 1 wherein the thickness of
material from which said tray is made is greater in the area of
said V-shaped ribs such that said ribs are filled in to a large
extent on the inside of said tray.
7. A tray in accordance with claim 1 molded of wood pulp with a
screen textured outer surface.
8. A tray in accordance with claim 1 wherein some of said ribs
extend across said tray generally parallel to said side walls, and
the remainder of said ribs extend across said tray generally
parallel to said end walls, said ribs crossing at substantial right
angles to define said open windows.
Description
FIELD OF INVENTION
The present invention relates to an open bottom food conatiner and,
more particularly, to a food container primarily for use for the
packaging of produce, and overwrapped with a transparent film, and
where the bottom wall is replaced with a plurality of open windows
defined by structural beams.
BACKGROUND
Molded wood pulp food trays have served the food packaging industry
well for many years for the packaging of food commodities. Such
trays have the advantage, besides low price and cost to the
consumer, of being clean, sturdy and safe; of being biodegradable
so as to minimize the solids pollution problem; of being capable of
assimilating the liquid juices which exude from some food products;
of being soft and relatively flexible so as to protect and prevent
bruising of food products such as fresh fruit and tomatoes; and of
being air and vapor permeable to maintain freshness and permit
passage of liquid vapor. Nevertheless, in spite of the many
advantages of such molded wood pulp trays, certain locals have
effectively outlawed their usage by the requirement that a very
high percentage of certain types of food packaged therein be
visible to the consumer, and since such molded wood pulp trays are
normally opaque, they have not met this legal requirement.
Consequently, in such locals, the only packaging trays utilizable
in view of such laws are clear plastic trays. These clear plastic
trays have many defects, some shared with foam plastic trays,
including reduced strength, increased cost, fabrication of
non-biodegradable material. These plastic trays collect in puddles
any liquids which might be present, thereby not only causing
possible discoloration and rotting of the packaged product, but
also serving as a bacterial breeding ground and further serving to
opacify the package itself and provide distortion in the remaining
transparent areas, thereby contributing to the very problem which
such trays were designed to overcome. In addition, such trays being
formed of non-breathable material, inhibit oxygen transfer to the
food products and moisture vapor transmission from the food
product, thereby in many cases reducing freshness.
Such prior plastic trays have sharp edges which tend to cut the
packaging film and/or hands, as well as the product packaged
therein. Where meat or poultry is packaged there is often the
exudation of bloody liquid which collects in puddles; besides
providing a bacterial breeding ground, such bloody liquid goes
under the tray and acts to release the sealed film causing soiled
hands, soiled check-out counters, leaking packages, etc. The
non-breathing nature of these plastic trays causes discoloration of
the meat, including hamburger, at the bottom of the tray, due to
the lack of oxygen migration through the tray, it being well known
that meat in plastic trays deteriorates on the bottom first. The
non-breathable nature of these plastic trays makes them critically
undesirable for the packaging of produce. Oxygen assimilation and
the release of carbon dioxide and water vapor requires a high vapor
transmission rate in packaging, to maintain product freshness.
Another defect of the clear plastic trays involves their
transmission of light lengthwise through the tray walls to provide
a light pipe or fiber optic effect which increases discoloration of
some food products, such as hamburger and other meats. The light
has a negative effect on meat quality causing discoloration more
quickly than meat which is maintained more in the dark but under
otherwise similar conditions. Because of the light pipe effect,
hamburger and other meat packaged in clear plastic has its botom
exposed to light constantly even when the tray rests on an opaque
object such as the bottom of the meat cooler or an underlying
package or between two packages.
Food packaging trays have evolved substantially over the years. The
earlier trays had essentially straight side walls and a flat
peripheral lip, and these served the trade successfully for many
years, particularly for the packaging of meat. In more recent
years, these earlier trays have been used for the packaging of
produce, such as a half dozen deluxe apples or oranges, provided
with a transparent film overwrap. However, as the nature of
transparent plastic wrap film changed and non-elastic cellophane
was replaced with the more elastic thermoplastic overwrap films,
the tray in accordance with Reifers U.S. Pat. No. 3,185,371 was
developed, and this tray became the leader in the field. In more
recent years there has been an increasing desire for greater
visibility of the food packaged.
One of the earlier attempts to provide visibility through the
bottom wall of the tray involved simply providing one or more
relatively large openings in the bottom of the tray. However, this
was found to weaken the tray and was not a successful approach to
the problem. The next attempt was to utilize a raised lip about the
periphery of the opening(s) in the bottom wall of the tray, the
function, in the packaging of meat, of the upwardly extending lip
being to hold the meat upwardly, to trap juices and to stiffen and
reinforce the sturcture. However, this approach was also not
successful as the structure was still too weak and, in the
packaging of meat, the meat tended to sag through the large
opening(s).
SUMMARY
It is, accordingly, an object of the present invention to overcome
the defects of the prior art.
It is another object of the present invention to provide a molded,
nestable tray, preferably of wood pulp or the like, primarily for
the packaging of soft produce or the like and which, in spite of
being made of generally opaque or translucent material, provides a
relatively high degree of visibility of the packaged product.
It is another object of the present invention to provide for the
clean, safe and effective packaging of food products.
It is another object of the present invention to provide a food
tray which, although being primarily open on the bottom is
sufficiently strong to be handled under all conditions.
It is another object of the present invention to provide a food
packaging tray which is not only effective but which is
inexpensive.
It is another object of the present invention to provide a food
packaging tray which may provide from a minimum of 55 percent total
visibility (entire surface of food packaged) up to about 85 percent
on certain round fruits, and which also tends to softly support the
food without bruising or other damage thereto.
It is another object of the present invention to provide a high
visibility food tray having an open bottom which has increased,
rather than decreased, strength even when overwrapped with
stretchable, transparent plastic film which acts to compress and
sometimes collapse a conventional tray; and which also has high
beam strength.
These and other objects and the nature and advantages of the
instant invention will be more apparent from the following
description:
In our parent application, Ser. No. 111,578, we described a tray
primarily intended for the packaging of meat and similar products,
which tray had a bottom of inverted U or V cross-section shaped
ribs extending thereacross. It was stated in such parent
application that the V ribs may be upright rather than inverted.
Parent application Ser. No. 111,578 is an improvement over the
construction shown in the earlier Bixler application Ser. No.
53,545 which uses a plurality of intersecting inverted V shaped
ribs. The Bixler construction provides maximum visibility with a
relatively strong construction and is, in many respects, a
successful approach to the problem, although under certain
conditions there has been found to be a need to provide increased
strengthening of the Bixler construction, particularly in the area
where the V ribs meet the side walls of the tray where "fault
lines" may exist.
The present invention provides such an improved structure in a food
packaging tray primarily intended for the packaging of produce,
although it may be used for packaging of other food products such
as meat, particularly hamburger. The construction of the present
invention utilizes high and strong ribs on the nature of the ribs
in parent application Ser. No. 111,578, but they are upright rather
than being inverted. It is found in accordance with the present
invention that in order to provide the maximum strength desirable
in all packaging situations, the upright V or V shaped ribs should
be of substantial height to provide a thick platform or pallet upon
which the food product is supported, and wherein the total volume
of the ribs forming the platform is about equal to the volume of a
bottom of a conventional tray of the same size, such as that shown
in the Reifers U.S. Pat. No. 3,185,371.
Certain food products, such as meat, have increased shelf life as
the oxygenation to the food product is improved. By providing more
open space, the construction according to the present invention not
only improves visibility of the product, but improves oxygen
transmission to the food product packaged therein in conjunction
with a plastic overwrap film. In addition, the raised ribs provide
an immediately available supply of trapped oxygen to the
package.
By use of the upright V shaped ribs, there is utilized a different
type of transition zone between the side walls of the tray and such
ribs of upright V cross-section. This transition zone is such that
no "fault lines" or notches are provided in the side or end wall
and the transition zone, and this may be accomplished by providing
a rounded transition zone from the end and side walls, which in
turn merges into a peripheral gutter, such peripheral gutter
forming the furthest point to which the upright V ribs extend. It
is preferably accomplished by extending the side walls directly
into the peripheral rib.
The characteristics of the package provided in accordance with the
present invention, some of which are indicated above, are
accomplished by the use of relatively high support beams, namely
the upright U or V cross-section ribs of about 3/16 inch height or
more, which are themselves strong, which are coupled to the side
and end walls in a way that maintains high side walls beam
strength, for highest total package strength. The transition
between the ribs and the inner periphery of the tray being
relatively smooth and uninterrupted without notches, the strength
provided is high and failure sites are reduced to a minimum. This
is in contrast with rib forms which have been previously suggested
in trays of uniform material thickness, such as plastic, that have
the liability of an interrupted edge which provides a fault
site.
When made of molded wood pulp, the construction of the present
invention is particularly satisfactory. The upright V ribs may be
filled at their upper surface, the extent of filling being
determined by the V angle, the type of wood or paper fiber from
which the tray is formed, and the weight and rib height. These
factors may be selected to optimize window visibility, strength and
nesting of the tray. For a tray intended for packaging of produce,
the steepest practical "V" angle should be selected, to maximize
filling to create a soft and relatively flat pallet surface; in
practice an included V-angle of 5.degree. to 35.degree. has been
shown to be satisfactory.
The fundamental aspects of the tray in accordance with the present
invention may be said to be: spaced beam members, the spacing being
open between such beam members to allow for viewing the tray
contents between each beam of relatively solid material. The
section modulus of the beams must be such that in combination with
the end and side walls, the total strength equals or exceeds the
beam strength of a tray of the same material of equal weight with a
flat, solid bottom.
For a better understanding of the invention, possible embodiments
thereof will now be described with reference to the attached
drawings, it being understood that these embodiments are to be
intended as merely exemplary and in no way limitative.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of an embodiment of a tray in accordance with
the present invention;
FIG. 2 is a bottom plan view of the tray of FIG. 1;
FIG. 3 is a section taken along line 3 -- 3 of FIG. 1;
FIG. 4 is a plan view of a second embodiment in accordance with the
present invention;
FIG. 5 is a bottom plan view of the tray of FIG. 5;
FIG. 6 is a section taken along line 6 -- 6 of FIG. 4;
FIG. 7 is a top plan view of a third embodiment in accordance with
the present invention;
FIG. 8 is a bottom plan view of the tray of FIG. 7;
FIG. 9 is a section taken along line 9 -- 9, partly broken
away;
FIG. 10 is a section taken along line 10 -- 10 of FIG. 7;
FIG. 11 is a top plan view of a fourth embodiment in accordance
with the present invention;
FIG. 12 is a bottom plan view of the tray of FIG. 11;
FIG. 13 is a sectional view partly broken away along line 13 -- 13
of FIG. 11; and
FIG. 14 is a sectional view taken along line 14 -- 14 of FIG.
11.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
Noting FIG. 1, it will be seen that a tray 10 is provided,
primarily intended for the packaging of produce, although any food
product may be packaged therein, in association with an overwrap
film of transparent material such as plastic film or heat-sealable
cellophane. As is conventional, the food tray 10 has two upwardly
and outwardly inclined opposite side walls 16 and two upwardly and
outwardly inclined opposite end walls 18, both the end walls and
side walls being preferably bowed as described in the Reifers U.S.
Pat. 3,185,371. As is conventional, each adjacent end and side wall
merges as at a rounded corner 20, and the side and end walls
terminate at their upper end in a downwardly and outwardly
extending peripheral lip 22.
Instead of having a flat bottom wall as is conventional, the tray
10 is provided with a plurality of ribs 24 extending along the
bottom generally parallel to the side walls 16; and, preferably at
right angles thereto, a plurality or ribs 26 extending generally
parallel to the end walls 18. As best seen in FIG. 3, these ribs
form, in cross-section, an upright V-shape the walls of which are
generally inclined at an angle of about 5.degree. to 15.degree.
with their apices 28 forming the external bottom of the tray; if
desired, however, the ribs may be made fatter or wider in which
case the external bottom of the tray lies in a plane above the
true, imaginary apices of the ribs.
It is also clear from inspection that the terminal portions 30 of
the V-legs form the internal bottom of the tray upon which the
produce or other food product rests. The terminal portions 30 of
the upright V-legs are not so sharp that the food product is in any
way cut, bruised or otherwise damaged. When the tray is intended
for produce or hamburger, it is preferred that it be fabricated so
that the interior of the V-ribs be essentially "filled in."
An important feature of the present invention involves the height
of the upright V-shaped ribs 24 and 26. It will be noted best from
FIG. 3 that the height of such ribs is on the order of about five
times the thickness of the material forming the side and end walls
of the tray, in this illustrated embodiment. From this it will be
understood that the ribs 24 and 26 are of substantial height to
provide a fixed platform or pallet upon which the food product is
supported. It will also be noted that the material forming the ribs
in cross-section is thicker than the material forming the side
walls, and such thickness may be controlled during the molding
operation. The volume of material provided in the upright V-shaped
ribs 24 and 26 which form the platform is about equal to the volume
of a flat, solid bottom of equal area which would be found in a
conventional tray of equal size, wherein such flat, solid bottom
would have a material thickness about the same as the side and end
wall thickness. By providing a ribbed construction of such volume
in accordance with the present invention, a sufficient section
modulus is obtained so that the tray 10 will have proper strength
to resist normal handling, to prevent inward collapse during
overwrapping, and to provide sufficient beam strength.
In accordance with the present invention, and to insure that there
are no fault lines as the ribs approach the end to end side walls,
there is provided a peripheral gutter-like bottom portion 32 which
has an internal depth the same or approximately the smae as the
internal depth of the V-ribs 24 and 26. This peripheral groove 32
is formed by two walls, an inner peripheral wall 34 and an outer
peripheral wall 36. The inner peripheral wall 34 is preferably of
the same slope and the same height as one of the inner walls of the
V-shaped ribs 24 and 26; however, the outer peripheral wall 36 is
relatively steep and does not rise to as great a height, i.e., it
terminates in a plane lower than a plane passing through the upper
terminal portions 30 of the V-ribs 24 and 26.
The outer peripheral wall 36 of the peripheral groove or
gutter-like portion 32 in turn merges with a generally annular,
planar bottom portion 38. As best seen in FIG. 1, it will be
understood because of the bowed nature of the side and end walls 16
and 18, the annular planar bottom wall 38 becomes very small, in
many cases disappearing, in the area of the corner portions 20. The
annular bottom wall 38 in turn blends into the side walls 16 and
the end walls 18 along a rounded or curved portion 40.
Referring to the outer surface of the tray 10, as best seen in
FIGS. 2 and 3, it will be noted that the annular, planar bottom 38,
lying outside of the groove 32, is provided with a bottom surface
38' which is raised a considerable distance above the true bottom
of the tray defined by the outer apices 28 of the upright V-shaped
ribs 24 and 26. A relatively steep outer annular wall 36' is
provided which connects the outer apex 32' of the peripheral groove
32 with the bottom 38' of the annular planar bottom wall 38, such
annular wall 36' laying opposite groove wall 36 through the
thickness of such groove wall.
Noting FIGS. 4-6, there is shown a tray 100, particularly designed
for the packaging of soft produce, intended to be overwrapped by a
suitable transparent film. The tray 100 has two opposite upwardly
and outwardly inclined side walls 116 and two opposite upwardly and
outwardly inclined end walls 118, such end walls 118 extending
upwardly to a greater height than the side walls 116 to afford
greater protection to easily bruised fruit intended to be packaged
therein. Adjacent end and side walls merge at rounded corners 120.
If desired, suitable denesting ledges 112 and 114 may be provided
at the corners of the end walls 118 and along the side walls 116,
respectively.
As with the embodiment of FIGS. 1-3, the tray 100 has a plurality
of ribs 124 along the bottom generally parallel to the side walls
116 and a plurality of ribs 126 generally parallel to the end walls
118, defining open windows of generally rectangular configuration
therebetween, although such windows may be circular. As seen in
FIG. 6, such ribs are V-shaped in cross-section having walls
inclined at an angle of about 5.degree. and with the inside of the
V-ribs being almost completely "filled in."
The end walls 118 and side walls 116 curve and merge into the
bottom along an annular transition zone 138. Such annular
transition zone 138 in turn merges into the outer peripheral rib
132'. If desired, a slight indentation 132 may be provided along
the top of the outer peripheral rib 132' thereby providing a
peripheral gutter as in the embodiment of FIGS. 1-3.
The embodiment of FIGS. 7-10 is similar in many respects to the
embodiment of FIGS. 4-6. The tray 200 of FIGS. 7-10 is primarily
designed for the packaging of soft produce, such as three tomatoes.
The tray 200 has two opposite upwardly inclined side walls 216
which extend directly from the bottom of the tray in a manner
described below in greater detail. Extending out from the side
walls 216 are denesting ledges 214. The tray 200 also has two
opposite upwardly and outwardly inclined end walls 218 which extend
upwardly to a greater height than the side walls 216 to afford
greater protection to the easily bruised fruit intended to be
packaged therein.
As with the other embodiments, the tray 200 has a plurality of ribs
224 along the bottom generally parallel to the side walls 216 and a
plurality of ribs 226 generally parallel to the end walls 218,
thereby defining open windows of generally rectangular
configuration. As clearly seen in FIGS. 9 and 10, such ribs are
almost U-shaped with the inside of the U-ribs being almost
completely "filled in." In this embodiment the ribs are about 3/16
inch in height.
It will be noted, particularly from FIGS. 8, 9 and 10 that each rib
224 and 226 has respectively associated therewith a horizontal
flange portion 224' and 226'. The width of such flanges 224' and
226' varies from a narrow point at the midpoint between two rib
intersections to a maximum thickness at the point closest to the
rib intersection, and this gives the ribs a slightly undulating
configuration. At the point where the horizontal flange portions
224' and 226' are narrowest, namely midway between rib
intersections, the width or thickness of the ribs including the
flange portions are, in the present embodiment, about 5/16 inch;
and the openings between ribs are about 13/16 inch square.
One of the major differences between the tray 100 of FIGS. 4-6 and
the tray 200 of FIGS. 7-10 involves the greater window area in the
tray 200. This is primarily accomplished by extending the windows
very close to the end walls 218 and immediately adjacent to the
side walls 216. Here the transition zone between the open bottom
portion and the side and end walls constitutes an annular or
boundary rib 232'. As can best be seen in FIG. 10 the outer edge of
the peripheral or boundary rib 232' continues to extend upwardly to
form a continuous surface of constant slope with that portion of
the side wall 216 below the denesting rib 214.
The tray 300 of FIGS. 11-14 is essentially the same as the tray 200
of FIGS. 7-10, except that it is larger. These two trays 200 and
300 constitute a preferred form of the present invention. Like tray
200, it will be understood that tray 300 has end walls 318 and side
walls 316, and open bottom portion defined by intersecting U or
V-shaped ribs 324 and 326 wherein the open windows extend very
close to the side and end walls to maximize visibility. The
transistion zone between the open bottom portion and the side and
end walls is defined by an annular boundary rib 332'.
It will be understood that the method of fabrication does not
constitute a part of the present invention and that any known
fabrication method may be used. Normally, the preferred methods of
fabrication involve various molding procedures.
While the tray of the present invention is preferably formed of
conventional wood pulp stock which may be molded from a water
slurry, it will be understood that the ribs may be made of harder
paper stock, or such ribs may be specially pressed or otherwise
treated. If desired, the tray may be formed of other, equivalent
material, it being understood that the scructural advantages of the
tray of the present invention derives from its geometrical
configuration. For example, the tray may be formed of a structural
plastic foam, such as cellular polystyreen foam comprising on the
order of 70 percent void space, or porous polyolefin material or
other open cell plastic, or a biodegradable plastic such as special
biodegradable foam polystyrene. If formed of material having
different characteristics than the preferred molded wood pulp,
various changes in the configuration may be necessary and,
depending upon the material, certain advantages may be absent.
The tray of the present invention has many advantages, a number of
which have been delineated above. In brief, however, it may be
noted:
Visibility -- Both sides of the packaged food, such as produce or
hamburger, may be viewed, providing up to 55-85 percent view of
contents depending in part upon the height of the opaque side and
end walls. The bottom of the food product viewed through the
windows between ribs is very easy to see since the light, passing
along the sides of the ribs, fully illuminates the bottom of the
packaged product without casting any shadows. In actuality, an
improved visibility may be provided compared to clear plastic trays
which introduce an added layer of plastic in addition to the
overwrap film, and which collect moisture often impairing
vision.
Strength -- Added beam of structural members across bottom adds
stiffening. Tray easily resists all types of normal handling: (1)
The tray has sufficient strength to resist handling during
wrapping; compression of film on the inward side wall is the main
force which tends to cause side wall deformation or collapse, but
the present tray resists such deformation or collapse. (2) The tray
resists handling in the store and by consumer at home; insufficient
beam strength of package for weight of contents may tend to deform
or break the package when it is lifted, but the tray of the present
invention tends to resist such deformation or breakage.
Breathability -- The open structure promotes oxygen transfer which,
for the packaging of meat in particular, maintains better food
product color. This provides for maintenance of meat bloom and
quality over the extended period for store sale and home
storage.
Juice Control -- When the material is made of wood pulp or other
porous material exuding liquid tends to be accepted. This
controlled acceptance of free liquids enhances appearance and
prolongs the life of the food.
Nestable with Automatic Denesting -- Trays nest closely for
economical storage and shipping; yet the partially or completely
filled-in ribs provide for automatic denesting.
Refrigeration -- Beam bottom construction holds food products
suspended, providing improved air circulation for oxygenation,
improved cooling and water evaporation where it occurs, such as in
meats, without loss of nutrients.
The trays of the present invention also have no problem of either
cutting overwrap film or causing any damage to the packaged food
product, particularly when the tray is formed of molded wood pulp.
This is so because the edges of the wood pulp are soft and provide
a soft support for the food product and also protect the film which
contacts the tray.
When formed of the preferred material, molded wood pulp, the tray
of the present invention is preferably formed or preformed using a
female die, directly contrary to the normal practice wherein a male
die is used as the deposition form for molded wood pulp food trays.
By the expedient of using such a female die, the screen or finished
surface is provided on the outside of the tray, while the inside
has a rougher and softer finish, such softer finish serving to
enhance the protection of the food product packaged therewithin,
while minimizing bruising or other damage. Also, by using a female
die, the pulp deposits to a greater thickness in the troughs of the
V-shaped ribs, and this may be easily controlled, as indicated
above, by the angle of the V, it being understood that the narrower
the angle, the greater the pulp will fill in on the interior of the
V-shaped ribs 24 and 26, thereby providing more of a cushion
surface on the inside of the tray.
A characteristic of molding a tray from wood pulp followed by free
drying, is the tendency of the tray bottom to warp upwardly during
drying to provide a convex bottom on the inside. This
characteristic is disadvantageous since the finished trays - unless
specially treated such as by form drying, after pressing, etc. --
will have a slightly concave external bottom which tends to inhibit
film sealing when overwrapping the package. This also occurs in a
ribbed open bottom tray when a male die is used.
The use of a female die, on the other hand, tends to produce a
downward arch which pushes against the flat drying support during
free drying, tending to produce a virtually warpage free bottom at
improved manufacture speed, without adversely affecting film
selaing during packaging.
It is to be understood that the invention is not limited to the
embodiments disclosed which are offered illustratively, and that
modifications may be made without departing from the invention; for
example, variations in the spacing, height and arrangement of the
ribs and the windows may be made (e.g., the windows may be round,
rectangular, diamond-shaped, etc.; the ribs may join rather than
cross so as to provide a "brick-work" or staggered rectangular
window pattern), and variations in the merger configuration between
the walls and bottom of the tray may be made.
* * * * *