Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 ~ O d~ ~313 PATENT
41961
Stretch Shnnk Package
BACKGROUND OF THE INVENTION
1.Fi~ld of the Invention
This inven~ion relates to an apparatus and method for sealing a tray
filled with a product with a sheet of wrapping material such as thermoplastic
film and ~o the paclcage produced by the method. In par.-icular. the invention
relates ;o a tray and a method of sealing a sheet of wrapping material thereto
so as to produce a substantially leak tight seal while substantiaily reducing the
amount of wrapping material needed.
2. Description of the Related Art
In grocery stores. supermarkets, and butcher shops a paper pulp or
polystyre.~le foam tray with a meat. cheese, or poultry product therein and over-
wrapped by a shee~ of plastic film is a very familiar paclcage. Often these
packages are wrapped manually with the fllm folded or tucked under the bot-
tom of the tray and the tray is then passed over a hot plate to seal lt. In order
to lncrease production and lower labor costs. automatic wrapping devices have
been in~oduced. I'vpical of these is the apparatus described in U. S. Patent
No. 4.63l.903 which issued on December 30, 1986 to Yoshiyuki Takamura.
One of the drawbacks in both hand wrapping and in the automatic ma-
chiner,v processes is that the filrn is not folded smoothlv under the bottom of
the tra,v. When this ocsurs there is a "bunching of the film underneath the
tray. Acditional time rr~ust be taken to seal the thick bunch of film so that a
package cqn be m,ade that w~ll maintain its lntegrity throughout the dlstribu-
tion cycle. In addition. such seals usually will not result in a leak proof pack-
age 50 tha~ iluids from the meat or poultry product will leak through the seals
thus pre~enting an unsightly paclcage which will often be re3ected by the shop-
per. On~ ~olutlon to this pro~lem can be found in U. S. Pa~ent No. 4.796.405
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PATENT
Case No. 4 1 96 1
issued Janu~ry 10, 1989 to Owen et al. This reference discloses an apparatus
for folding the film more smoothly under the tray to avoid "bunching-- and allowfor a better seal to be produced. However, this reference requires that the filmcompletely surround the tray and does not disclose a method of producing a
substantially leak proof seal while simultaneously substantially reducing the
amount of fllm required and eliminate "bunching" altogether.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of this invention to provide an apparatus and method for
sealing a fllm over a food product containing tray which produces a substan-
tially leak proof seal.
It is another object of this invention to provide packages without seals
on the bottom of the packages for easier handling, stacking, and display.
Yet another obJect of this invention is to provide a package which re-
quires a minimum amount of film.
Still another ob~ect of this invention is to provide a tray which, when
sealed with a film, produces shear stress instead of tearing stress on the
tray/fllm seal,
Accordingly, one form of the present invention relates to a method for
sealing a tray -filled with a product with a sheet of thermoplastlc film or the like
comprising: Introduclng a tray having an outer angled lip into a complimentary
shaped tray carrler: placing a product to be sealed into said tray: stretching athermoplastic film over the product and the tray including over the upper sur-
face of the outer angled lip; and sealing said fllm to said upper surface of theouter angled lip of the tray uslng a sealing means: characterized in that the
angle of the outer angled lip Is such that the tensional forces acting on the seal
produced are substantially all shear forces.
Another form of the present invention relates to an apparatus for sealing
a tray filled with a prbduct with a sheet of thermoplastic film or the like com-prising: a means for holdlng a tray fllled with a produc~ and having a angled
outer lip, the holding means having a shape complimentary to the tray: a
means for holding a sheet of thermoplastic fllm horizontally above the tray; a
means for lifting the tray into the fllm while the fllm is so held. the fllm being
stretched over the outer angled lip of the tray: a means for sealing the fllm to
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210 ~ ~1 3 PATENT
Case No. 41961
the angled outer llp of the tray: and a means for detaching the sealed film and
tray from the sheet of thermoplastic fllm. characterized in that the angle of the
outer angled lip is such that the tensional forces acting on the seal produced
are substantially all shear forces.
Another form of the present invention relates to an apparatus for sealing
a tray fllled with a product with a sheet of thermoplastic film or the like com-prising: a means for holding a tray filled with a product and having a angled
outer llp. the holding means having a shape complimentary to the tray: a
means for holding a sheet of thermoplastic film horlzontally above the tray: a
means for lowering the fllm over the tray while the fllm is so held. the fllm be-
ing stretched over the outer angled lip of the tray: a means for sealing the film
to the angled outer lip of the tray: and a means for detaching the sealed film
and tray from the sheet of thermoplastic film. characterized in that the angle of
the outer angled llp is such that the tensional forces acting on the seal pro-
duced are substantially all shear forces.
Preferred forms of the invention. as well as other embodiments. ob~ects.
features and advantages of this invention, will be apparent from the following
detaiied description whlch is to be read in connection with the accompanying
drawings.
BRIEF DESCRIPIION OF THE DRAWlNGS
FIG. 1 ls a cross-sectlonal view of a food product containing tray before
the fllm is sealed over the open portion of the tray.
FIG. 2 is a cross-sectional view of a food product containing tray with
the film stretched over said tray and the sealing means sealing said film to said
tray.
FIG. 3 is a cross-sectional view of a sealed food product containing tray
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The present invention will be better understood from the specification
taken in conjunction with ~he accompanying drawings in which like reference
numerals refer to like parts.
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Case No. 41961
Referring now to FIG. l. tray l, having an outer angled lip 2, ls placed
into tray carrier 3. tray 1 having a food product 4 introduced therein either be-
fore or after tray l is introduced into tray carrier 3. The tray carrier 3 contain-
ing tray l with food product 4 therein is then positioned under stretch fllm 5
held in position bv film stretch rolls 6. A sealing bar ring 7 is positioned above
both the stretch fllm 5 and tray carrier 3 holding tray l containing food prod-
uct 4. Throughout this detailed description. reference will be made to required
parts and a description will be given of their operating features. Descrlption of
items such as the main machine drive. other drive motors. switches. gears. etc.
is omitted as such detalls can readiiy be supplied by those skilled in the art
using this specification as a guide and will not be described where such de-
scription is not necessary for an understandlng of the present invention. Rep-
resentative of prior art machines wlth various operating mechanisms is U. S.
Patent No. 4.631.903 issued to Yoshiuki Takamura and U. S. Patent No.
4.796.405 issued to Dave L. Owen et al. It is to be understood that the appa-
ratus of the present invention may be incorporated into machinery well known
in the package sealing art without undue experimentation by those skilled in
thls art.
Continuing with the description of the apparatus shown In FIGS. l and
2, wrapplng fllm ls fed from a roll (not shown) and is gripped by the f~lm stretch
rolls 6 whlch hold the edges of the film therebetween. In this position the fllmls tightiy held between the fllm stretch rolls 6 horizontally above the tray 1 in
tray carrier 3.
It should be noted that the apparatus as described baslcally works on
lndexed or intermittent motion. The infeed apparatus (not shown) moves a
food product 4 containlng tray 1 in tray carrier 3 ~nto the sealing station and
then stops until the tunction of the sealing station has been completed. Like-
wise, when the food product 4 contalning tray 1 in tra~v carrler 3, has been
placed in the seallng station the film stretch rolls 6 operate to transfer and hold
a sheet of fllm over the fllled tray 1. In the present apparatus. these mecha-
nlsrns may be controlled by a timing camshaft which. as it rotates. actuates thevarious drive mechanlsms in the proper sequence. It is also ~,vithin the skill of
the art to substltute for the timing camshaft a microprocessor to actuate and
stop each drive mechanism in programmed sequence.
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210~13
PATENT
Case No. 41961
Still viewing FIGS. 1 and 2 at the point where the film 5 is positionedabove the tray l. it should be noted that. in general. any heat sealable flexible
wrapping material in sheet form can be used with the present invention but
preferably the fiIm 5 will be thermoplastic film which is heat sealable. These
types of films are readily available in the marketplace and are well known to
those skilled in the packaging arts and are usually fllms formed from poly-
ethylene. ethylene homo- or copolymers. e.g.. ethylene-propylene copolymers
and ethylene-vinyl acetate copolymers. linear low density polyethylenes. very
low density polyethylenes. polyvinyl chlorides. and polyvinylidene chlorides.
and various copolymers and blends of any of the foregoing polymers. In the
present invention it is desirable that the fllm be stretchable so that as the
product ls forced or llfted into the film or the film is stretched down over thetray the film will give and stretch. The foregoing listed films can be
compounded to have these types of properties which can be selected to meet
various packaging needs. In addition. for some applications it is desirable thatthe fllm also be heat shrinkable. Films of the foregoing listed polymers are
available which are both stretchable for the packaging process and then after
the package has been formed these can be heated to heat shrink the tightly
around the product for handling and appearance purposes. Some of the films
are multi-layer fllms having layers of one or more of the aforementioned poly-
mers and may even Include a gas barrier layer. if. for packaging tne particular
product such a property is desirable.
Wlth the tray 1 located under the heat sealing rlng 7 and tilm sheet 5
positioned above tray 1. tray 1 will be lifted by the actuation of a lifting
mechanism (not sho~,vn) in the direction of the arrow in FIG. 2 upwardly to a
position where the outer angled lip 2 is above the fllm stretch rollers 6.
stretching the film 5 over the food product 4 and the ollter angled lip 2. Con-
tinued upward motion of the tray 1 forces the film 5 to be pressed between
outer lip 2 and seallng bar ring 7. Sealing bar ring 7 seals the fllm 5 to the
outer angled lip 2 and CLltS the fllm 5 free of fllm stretch rollers 6, thereby pro-
ducing a sealed food product containing package. The now sealed package is
moved downwardly away from the sealing bar ring 7 and is removed using a
transporting means (not shown). It is to be appreclated that the tray carrler 3
preferably has a shape compllmentary to the outside shape of the tray 1 such
that the forces encountered ln the seallng operation do not distort the tray l or
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PATENT
Case No. 41961
Interfere with the formation of an acceptable seal 9 (see Fl&. 3) between film 5and outer angled lip 2.
Turning now to the sealed package. shown in FIG. 3. the film 5 Is sealed
by seal 9 to tray 1 along outer angled lip 2. The outer angle of lip 2 is suc
that the tensional forces of the film 5 are tangential to the seal 9. This meansthat the tensional forces are shear forces rather than tear forces which sub-
stantlally improves the integrity and strength of the seal 9. The relatively small
excess of fllm material 8 is allowed to shrink under the outer angled lip 2,
thereby eliminating the need to underwrap the tray 1. or perform a separate
film cutting operation. Thls most advantageously accomplished when the
sealing bar ring 7 is a heat sealing bar ring having a sealing face 10 which is at
an angle which produces seal 9 on angled outer lip 2 in such a position that
substantially all of the tensional forces on the seal 9 are shear forces. It is to
be appreciated. however, that adhesive sealing and adhesive sealing in con-
junction with heat sealing is also suitable for use in the present invention. It is
to be further appreciated that a separate fllm cut-ting apparatus and/or step
may be utillzed to cut the sealed film free of the sheet of film held by film
stretch rollers 6.
Suitable trays 1 for use in the present invention are preferably polysly-
rene foam tray. However. it Is to be appreciated that anv tray material which
allows for heat sealing or adhesive sealing or both of the film 5 may be used
ulith the present inventlon. Thus~ paper pulp trays and trays of other poly-
mers. both foamed and unfoamed may be used. The shape of the tray is not a
critical part of the present invention. Generally. in the food paclsaging industry
these trays are rectangular in shape. but other shapes. such as for example.
square and round are also suitable.
The tray carriers 3 which are suitable for use in the present invention
may be made of any suitable material. including for e~ample. stainless steel.
steel. plastic. and alumlnum. The presently preferred tray carrier material is
stainless steel.
Although the illustrative embodiments of the present invention have
been descfibed hereln with reference to the accompanving drav.~ings it is to be
understood that the inventlon is not limited to those precise embodlments. and
that various other changes and modifications may be effected therein by one
skilled in the art without departing from the scope or spirit of the invention.
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