CA1247515A - Method and apparatus for vacuum packaging goods in heat shrinkable plastic bags - Google Patents

Abstract

METHOD AND APPARATUS FOR VACUUM PACKAGING GOODS

IN HEAT SHRINKABLE PLASTIC BAGS
Abstract An improved method and apparatus for evacuating and shrinking a filled heat shrinkable bag including a separate vacuum system to hold the bag in a ballooned out configuration and in contact with heating means before allowing the bag to collapse and shrink onto the goods.

Description

_IELD_OF I7iE ~ rION ~4 ~ S L5 Ihis invention relates to ~ethod and ap~aratus for packaging goods.
In p~rticular, the invention Fertains to vacuum packaging food in heat shrinkable plastic bags.

BACKGRD~D
Specifically, this invention pertains to improvements in the nethod and apparatus of the patent of T~T. Day, W.S. No. 4,132,048 issued on January 2, 1979. In the Day patent, which is owned ~y W.R~ Grace & Co., the assignee of ~e present invention, the bag inside the chamber and the chamber are both evacuated to a relatively low reduced pressure, at which time the bag is sealed inside the chamber. Continued evacuation of the air in the chan~er outside the bag causes the bag to balloon out due to the residual air left therein, and move towards heaters on the inside of the chan~er. m e bag is thus h~ated, and, ~subsequently, the chan~er is vented whereby the bag collapses and shrir~s onto the product.
The Day apparatus ~ld process operate well, and an object of the present invention is to improve its operation further. Among these desired improven~nts are better control of the bag shrir~age. As the bag is heated to a tempexature at which the plastic of the bag material begins contracting, the bag will tend to shrink regardless of wnether or not it is the rn~st opportune time in relation to the degree of evacuation of the surro~mding chamber. S~me uneven shrinkage r~y therefore, occur;
and it is thus an object of the present invention to provide a process in whic'n the bag is more evenly shrunk.
Other objects of the present invention are to provide a process and apparatus in ~nich lawer shrink ten~eratures are used and in which the bag can be heated m~re quickly thus increasing the nun~er of packaging cycles per minute for the apparatus.

~2'~'~5~5 ~ oth th~ preY~nt invention and the a~xlatus of the above n~ntioned Day patent cvercome numerous problems present in the prior are where hot water baths are used to shrink evacuated shrink bags. It has been heretofore known to use pre-formed packaging such as bags for relatively large meat products such as whole rounds of beef or whole pork loins, but heretofore the practive has been to shrink thes~
bags using a hot water bath. There are many disadvantages with hot water systems, including very poor utilization of the energy in the hot water.
It has been est~nat~d that as low as 3% of the heat energy in the water goes into the useful work of bag shrinkage, and the rest is wasted. In addition, handling of the hot water itself is a great problem sin oe this work is done in meat packing cold r3oms. Ihese cold rooms consume enormous amounts of ener~y to keep them refrigerated and thus floor spa oe is very valuable. The present invention is a dry process, which saves all of the slu~iness and n~ss and safety hazards associated with water getting on the floor, and in addition it utilizes much less valuable floor spa oe than is utilized ~y hot water systems.
qhe present invention is related somewhat to general ooncepts in the field of vacuum skin packaging. Re~erence can be had to U.S.
Patent 3,950,919 which issued April 20, 1976 to the present inventor and is assigned to the same assignee for a more detailed explanation of vacuum skin packaging. An idea in U.S. Pat. No. 3,950,919 is the use of a separate vacuum system for controlling the packaging material, which in the vacuum skin packaging art is a sheet of plastic and in the present invention is a bag. Thus, at a general con oeptual level only, the present invention might be characterized as a hybrid of the vacuum skin packaging technology of U.S. Patent 3,950,919 with the vacuum chamber heating of shrink plastic bags as taught in the Day patent 4,132,048. However, it is believed that no such combination has been made heretofore.

751~i Another feature of the present invention pertains to apparatus means to permit interchan~ing platens so that different sizes and shapes of food products or other goods can be accommodated in one machine with minimal changes.
There are many different sizes and shapes of large cuts of beef and there are many different sizes of processed meat such as salami, thus interchangeability of platens is an important advantage of the present invention over the prior art in general.
Another important advantage of the invention resides in its utilization of a rack in the chamber between the heated platen, and the filled bag resting thereon. By controlling the size and the spacing of the wlres or other material making up the rack the amount of heat imparted ~o the product by the heated platen can be well controlled. Thls ls very lmportant with aertain proclu~ts, such a cheese and certain processecl ~oods, whereln more than a predetermined small amount of heat would be unacceptable.

STATEMENT OF INVENTION
The present invention relates to an improvement in an apparatus for vacuum packaylng goods in heat shrinkable plastic bags, which apparatus generally comprises a vacuum chamber, a pump for evacuating the chamber, a platform for holding a product in a heat shrinkable bag so that the bag may be evacuated through its unsealed mouth as the chamber is evacuated, radiant heaters or movable contact heaters within the chamber for heating the bag when the bag has ballooned outwardly from the product as the chamber is evacuated, and seal bars ~or sealing the bag after it has been evacuated.

~;~4~7~i~5 The said improvement is characterized by the fact that the seal bars can close and clamp the mouth of the bag without sealing the bag while the chamber is evacuated so that the bag will balloon outwardly. The improvement is further characterized by a heated platen generally conforming to the shape of the ballooned bag so that when the bag balloons outwardly it conta~ts the heated platen which impar~s heat to the bag so that it will shrink after which the heater bars are opened so that the shrinking force of the bag will force the air out through the now unclamped bag mouth and evacuate the hag as the bag collapses and shrlnlcs tightly around the product. The improvement is characterized still further in that electrical resistance heate.rs are included in the seal bars which can be activated as the seal bars again close, thus sealing the bag.

DESCRIPTION Ok' THE DRAWINGS
The above and other advantages of the lnvention wlll be pointed out or will become evident in the following summary of the lnvention, detalled descripti.on, and clalms, and in the accompanying drawing also forming a part of the disclosure, in which, Figures 1 to 4 lnclusive are a series of views illustrating the method of the invention as used in a first embodiment of the apparatus according to the invention; and Figures 5 and 6 are vlews similar to certain ones of Flgures 1 to ~ lllustratlng the method applied to second embodiment of apparatus.

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SU~RY OF THE lNVENTION
In one aspect the present invention i5 a ~ethod of vacuum packing gcods in a heat shrinkable bag comprising the steps of:
(1) causing the bag to balloon outwardly from the g~ods by creating a pressure differential between the outside of the bag and the inside of the bag;

(2) using said pressure differential to ~ositively hold said bag in its ballooned condition and in contact with a heating means;
t3) heating said bag to its shrinking temperature while held in contact with the heating means;
(4) evacuating said bag around the gocds therein; and, (5) closing a~ sealing the bag shut.

In another aspect the present invention is a machine for vacuum packing goods in heat shrinkable b~gs, the combination comprising vac~lum chamber means, heated plat~n menas in said chamber means for receiving pre-bagged goods, mr~ns to cause the bag to balloon outwardly from the goods into contact with said heated platen means, means to cre~te a pressure diffe~ential to hold the bag in its ballooned condition in contact with said heating means, means to evacuate the inside of the bay ar~und the gcods, means to oontrol the evacuating means, the heating means and the pressure differential holding said ballooned bag in order to cause said kag to collapse and to shrink onto said goods in a controlled manner; and means to close and seal the bag.

DE~AILED DE RIPTION ~L24 7515 Referring now in detail to the drawings, Figs~ 1 through 4 show a first form of the apparatus comprising an outer vacuum chanber made up of an upper half 10 and a lower half 12. Other means not shown are provided to form air tight seals and the like, all as is well knc~n to those skilled in these arts. An upper double walled platen 14 is mounted in the upper half 10, and a lower double walled platen 16 is mDunted in the lower half 12. ~unting means, which may comprise yokes, nuts and bolts and the like, are provided to removably mount the platens 14 and 16 in the upper halves, and these means also permit interchanging sizes of the platens as is well known to those skilled in these arts.
The inside surfaces of the platens 14 and 16 are provided with a plurality of air access cpenings 20, throught which vacuum pressure can be drawn via conduits 22 which connect to suitable sleeve~s 24 in the upper and lower chamber halves 10 and 12~
Ihe bag, B, is evacuated by vac~lum applied through oonduit 26 when its mouth is placed within closure and sealing means 30. Of course, the sealing halves of the closure mean 30 are not closed upon the bag mouth when vacuum V~ is applied. The assemblage of the p rts 22 and 24 also facilitates interchanging of different sized platens in the machine halves lC and 12.
By way of example, the drawings show a turkey "T" which has ~een pre-~acka~ed in a bag "B" and has been put inside the chamber. A rack 28 is provided on the inside surface of the bottom platen 16 on which the turkey "T" or other food product rests.
Ihe rack 28 will create an unheated section in the bag and will also control the heating of the food product thereon. With, for example, cheese, and certain other products, heat must be very closely controlled or the product`'s esthetics or even its fitness as food can ke adversely effected. Ihe invention contemplates making racks of different sizes and types to control the degree to which the food product is heated lower platen 16. FDr example, if the bars or other elements used to fabricate rack 28 were made thicker and/or Fositioned closer together, then the food prGduct resting thereon would be heated less by the heat frGm the lo~er platen 16. However, 2 concurrent disadvantage is that that portion of the bag cn the rack is not heated as much as other portions of the kag.
This will cause an irregularity in the n~nner in which the bag shrinks arGund the product as is explained below.
It is anticipated that this problem can be overcome in a nwmber of ways. Firstly, for oe rtain products, this irregular area may not matter, i.e., products ~hich have top and bottom surfaces. For exam~le, if a quantity of chicken Farts were to be shrink wrapped on a flat tray or cardboard or the like, the underside of the tray or cardboard does not matter and its contact with the rack and any resultant irregularity of the shrink has no effect. However, in some products this oould make a difference, i.e., whole poultry. This problem can be overcome, as one Fossible solution, by providing a very large degree of shrink. Ihat is~ if t~,e VariOIlS parameters of the bag both before and after shrinking are controlled such that the bag will have to shrink a great deal, then this large amount of shrinkage can literally "cverpcwer" any Fossible irregu-larity created by the rack.
muS~ the advantage of controlling the heat imparted to the foGd so that no adverse effect is experienced by the f3cd is obtained. Any problem of irregular shrink of the bag, if there is any, is overccme by other aspects of the teaching of the invention.
In general, the present invention solves the problems of exoe ssive wrinkling of the bag, excessive non-uniform fitting of the bag mateiral onto the goods, and limitations of the size of the g~od relative to the chamber size which can be accon~odated.
The bag may ~e made of any suitable packaging material including but not limited to thermoplastics such as Folyethylene, cross-linked et~ lene Folymers and ccpolymers, ~olypropylene, saran, ethylene vinyl alc~hol oopolymers, nylon, Folyvinyl fluoride, polyester and the like, and laminates of these materials. 0~ course, other materials known to those skilled in the art can also be used.

~Z~
It is conventional in this art to provide means inside the vacuum chamber to close, to seal, and to cut off exoe ss b~g material outboard of the seal. Ihese means are well developed and can be found, for example, in the description of the above identified patent, and all of these means are indicated herein by reerence numeral 30. So far as pertinent to this invention, these means 30 include the ability to close in an air tight manner, but not to seal the bag, and to later re-open and then seal the bag. As an ex~mple these means can ~e a pair of opposed electrically heated ~eal bars or clipping means to apply a metal closure clip. Both means are well known in the art.
Means are also provided to heat the upper and lower platens 14 and 16. Ib this end a platen heater energy source means 32 is provided and is shown connected by wires 34 to the two platens. Heating of platens is known in this art, referen oe may be had to these Day and Perdue patents referenced above as needed. m e energy source 32 may be electric cul~ent supplied throught wires 34 to an electrically resistant wire mesh or strips on the cuter surface of the platens which are preferably constructed of a highly conductive material and as aluminum to transfer heat to their inner surfaces in close proximity to the bagged product.
It is sufficient to say that the heating means can deliver enough heat to shrink the bag.
Ihe method of the invention ooTprises the following steps, which will ke acooTpanied by references to Figs. 1, 2, 3 and 4 as they appear in the sequence of steps:
(1) The preloaded bag "B~ with the turkey "T" is placed on the rack 28 in the open machine, with the mDuth of the bag positioned over the closing, æ aling, and cutting means 30. ~his is the oondition shown in Fig. 1.
(2) In Fig. 2 the machine is closed onto the bag and the means 30 are closed on the uth of the bag, but the bag is not sealed.

7~:~5

3) me platen heaters are activated to begin heating. (the platen heaters, once activated, may be continuously heated, particularly if quick cycle time is desired.)

4) Vacuum pressure is provided to the perforated double wall platens to cause the bag to balloon out into contact with the heated platens. This condition is shown in Fig. 2.

5) In Fig. 3, means 30 are separated to oQen the bag mouth to the environment inside the closed chamber defined by the halves 30a and 30b which is evacuated through conduit 26 as indicated by V .

6) The vacuum pressure at the platen V is stopp~d while the vacuum pressure in the chamber Vc continues. This causes a controlled collapsing of the bag onto the product and is the condition shown in Fig. 3.

7) me bag is then permanently sealed or clipped shut. Clipping means are well known in this art, see U. S. patent 3,832,824 which issued on September 3, 1974 to Burrell and is assigned to the same assignee as the present invention. In fact tho~e clipping means are particularly adapted for use in the second embodLment of this invention shown in Figs. 5 and 6 and described in detail below.

8) V is turned off and the chamber vented to the atmosphere which causes an additional final tight collapse of the bag onto the product.

9) The chamber is open and the package may be removed as shown in Fig. 4.
It is important to note that a great deal of the flexibility of the invention is provided at step 6). The time at which V is turned off controls the amount of build up of shrink force within the plastic of the bag created by the heating which in turn is an important factor in controlling the speed and uniformity of the shrinkage. Likewise, the continued application ~'2,,~75i5 of V to the ~ag interior after V is re]eased and ~ented also has a c P
large effect on this con~rol. V can be totally or partially released giving precise control over film shrinkage. Thus, the invetnion provides several separate paranE~ters which can be controlled to contxol the shrinXing of the bag to the product without any wrinkles or aix pockets or the like is achieved. lrnese E~xaneters are: a) the tern2erature to which the platen is heated; b) the time the bag is alla~ed to re~ain in contact with the heated platens; c) the timing of the turning off of Vp; d) the value of Vc at this point; and, 3) the rate of increase of Vc after the heater and V
are t~lrned off.
Referring now to Figs. 5 and 6, there is shown a second embodLm~nt of apparatus ada~ted to carry out the method. T~lis apparatus is a rr~dification of a machine currently marketed by the assignee of the present invention and is described and clain~d in the aforementioned U. S. patent 3,832,824. Commexcially, in the form shown in the Fatent but not as r~dified as in Figs. 5 and 6 of this application, this rnachine is known as the CRYOVAC* ~lodel 8200 dual charr~er vacuumizing machine. One of its principal uses is for large cuts of beef, large t~rkeys and the like. Tb the extent parts in this apparatus 40 are the s~ne as or similar to parts described above in regard to the first e~kodiment, such parts are indicated by the same reference nun~rals followed by "An.
Fig. 5 corresponds to Fig. 1, the beginning of a process wherein the turkey "T" already positioned within the bag "B" is placed within the rnachine 40, with the neck portion of the bag extending across a pair of walls 42 and 44 and into a second chamber on the right hand side of the walls. me clipping or æaling means 30A are provided between the walls 42 and 44. As can be readily appreciated ~y those skilled in the art, and by looking at Fig. 6, the only conceptual difference ~etween the second eTbodim~nt and the first embodiment of Fi~s. 1 through 4 is that the entire left hand chamber to the left of the wall 42 is subject to the vacuum pressure V , and the *Reg. U. S. Patent & Tradernark Office ~4~7S~ S

entire right hand chamber is conceptually identical to the overall chamber outside the double walls of the first form, and is subject to the vacuum pres Æ e V . Otherwise, the method is implemented identically in this second form as it is in the fixst, with only minor changes being necessary to accommodate this slight difference in the form of the apparatus.
Fig. 6 corresponds most closely to a step just prior to the end of the step shown in Fig. 2, that is the use of V to balloon the bag after the bag has been shut but not sealed. For this purpose, the arrow indicated Vc in Fig. 6 is shown dotted, that is, it is not yet active.
Mbunting means 18A are also provided so that here again this apparatus can have interchangeable platens. The major structural difference is in the uppex and lowex platens 14A and 16A which are formed with openings 20A. thus, the dual chamb~x machine is more economical to mcdify for use with the invention in that the platens are of simpler construction, i.e., they are single walled rather than the double walled platen structures reguired in the first embc~lin~nt of the invention in Figs. l through 4.
This form also uses the rack 28A as in the first embcdim~nt to achieve those same advantages.
The word "platen" as used in tlle specification and claims herein shall be understood to include various sizes and shapes of such means useful in the invention and note be limited to flat devices as the word is sometimes defined in dictionaries.
While the invention has been described in detail above, it is to be undexstood that this detailed description is by way of example only, and the protection granted is to be limited only within the spirit of the invention and the scope of the following claims.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Improvement in an apparatus for vacuum packaging goods in heat shrinkable plastic bags said apparatus comprising a vacuum chamber, a pump for evacuating the chamber, a platform for holding a product in a heat shrinkable bag so that the bag may be evacuated through its unsealed mouth as the chamber is evacuated, radiant heaters or moveable contact heaters within the chamber for heating the bag when the bag has ballooned outwardly from the product as the chamber is evacuated, and seal bars for sealing the bag after it has been evacuated, characterized by the fact that the seal bars can close and clamp the mouth of the bag without sealing the bag while the chamber is evacuated so that the bag will balloon outwardly and further characterized by a heated platen generally conforming to the shape of the ballooned bag so that when the bag balloons outwardly it contacts the heated platen which imparts heat to the bag so that it will shrink after which the heater bars are opened so that the shrinking force of the bag will force the air out through the now unclamped bag mouth and evacuate the bag as the bag collapses and shrinks tightly around the product and characterized still further in that electrical resistance heaters are included in the seal bars which can be activated as the seal bars again close thus sealing the bag.

2. The improved apparatus of claim 1 characterized by the fact that the heated platen substantially surrounds the loaded bag and is of a predetermined size and shape adapted to cooperate with the particular size and shape of the goods in the bags being packed.

3. The improved apparatus of claim 2 characterized by the fact that the heated platen is removably mounted thereby permitting packaging of different sizes and shapes of goods in bags.

4. The apparatus of claim 1 characterized by the fact that the clamping or seal bars comprise a clamp to clamp the bag mouth while the chamber is initially being evacuated and characterized by the clipper to apply a metal clip around the bag mouth.

5. The apparatus of claim 1 further characterized by a platen having double-walls with a space between the walls and the inner-wall having apertures therein so that the evacuation of the chamber draws the bag against the inner perforated walls.

6. The improved apparatus of claim 1 characterized by the fact that the vacuum chamber is divided into two chambers, the first chamber being for receiving the product within the bag and the second for receiving the mouth of the bag, each chamber having a vacuum cord connected to a vacuum pump.