Tray sealing and gas flush apparatus

Apparatus for atmosphere-modifying and sealing individual trays includes a film disposing roller disposed closely adjacent the top of the tray to define a nip region and an elongated gas injection nozzle spanning the nip region for injecting gas through the nip region between the film and the tray. A split conveyor belt advances the trays past the film disposing roller to a sealing unit utilizing band sealers for the longitudinal tray edges and reciprocal "hot bar" sealer for the leading and trailing tray edges. The gas injection nozzle injects the gas substantially perpendicular to the advancing direction, down and into the individual trays. An optional second gas nozzle provides a gas flow curtain across the tray leading edge.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to apparatus for modifying the gas atmosphere 
of individual trays containing e.g., foodstuffs, and for sealing the 
individual trays with the modified gas atmosphere. 
2. Description of the Prior Art 
The modern trend toward increased convenience in preparing meals has caused 
a significant and fundamental change in the way most foodstuffs are 
packaged and sold at retail stores. Rather than sell in bulk quantities, 
supermarkets and convenience stores typically market such foodstuffs as 
meats, poultry, dairy products, etc. in relatively small portions suitable 
for only a few servings. Typically, such foodstuffs are processed at a 
processing plant from bulk quantities into single or multiple serving 
sizes and packaged in individual trays. The trays generally have a flanged 
peripheral edge surrounding a recessed portion, and a clear film cover for 
display purposes. 
A significant problem occasioned by the marketing of smaller sized portions 
of perishable foodstuffs is the possibility of increased spoilage rate and 
reduced shelf life. The smaller portions typically have a larger ratio of 
surface area to volume which accelerates the chemical and bacterial attack 
on the product. This problem has put a premium on the control of the 
atmosphere surrounding the packaged food stuffs. For example, there can 
often result the need to reduce or enrich the oxygen content of the 
atmosphere surrounding the foodstuffs to retard spoilage induced by 
chemical action and bacteria, in order to extend the shelf life and 
appearance of the foodstuffs. 
Conventional tray wrapping/packaging machines, including those which 
attempt to replace or enrich the oxygen atmosphere by the use of a gas 
flush tunnel, vacuum chamber, or other component charged with an 
atmosphere-modifying gas, have not been entirely satisfactory or have 
proved more costly than desired due to the need, for example, of 
associated vacuum pump apparatus. Also, the intermittent motion and 
resulting slow cycle speeds which characterize conventional tray wrapping 
and packaging machines make them economically less attractive to operate. 
These shortcomings are believed to be the result of the additional 
complexity due to the tunnel components and vacuum chambers and the 
inability to completely "flush" the tray even using "vacuuming" 
techniques. 
SUMMARY OF THE INVENTION 
As a consequence of the foregoing, it is an object of the present invention 
to provide a simple, high speed apparatus for modifying the atmosphere in 
individual trays and sealing the trays with film. 
It is a further object of the present invention to provide an apparatus 
which can achieve the atmosphere modification and sealing on a continuous 
basis, such that multiple trays can be processed continuously, rather than 
by intermittent, "batch" processing. 
In accordance with the present invention, as embodied and broadly described 
herein, the apparatus for atmosphere-modifying and sealing trays of the 
type having continuous peripheral edges comprises, a sealing station; 
means for advancing the trays past the sealing station; film supply means; 
and roller means positioned at the sealing station for receiving film from 
the film supply means and for disposing film to cover the trays including 
the edges. The roller means and a respective tray define a nip region 
through which the film passes to cover the tray, and gas flushing means is 
provided including means for injecting a preselected gas into the trays 
through the nip region and between the film and the trays. Means are 
further provided for sealing the disposed film to the edges of the gas 
flushed trays, and the sealing means are positioned proximate and 
downstream of the roller means relative to the advancing direction. 
Preferably, the gas flushing means includes a preselected gas source and a 
first gas injection nozzle operatively connected therewith. The first gas 
injection nozzle is positioned upstream of the roller means relative to 
the advancing direction and has holes in its bottom or lower side for 
directing gas into the tray. The nozzle is proximate the roller means and 
commensurate with the transverse extent of the nip region. 
The gas flushing means can optionally include a second gas injection nozzle 
operatively connected to the preselected gas source and oriented to flow 
gas across the leading portion of the edges of the advancing trays. The 
second gas injection nozzle has a nozzle opening positioned proximate and 
downstream of the roller means relative to the advancing direction. 
In another aspect the present invention is a process comprising a) moving a 
tray and a sheet of film relative to each other so that the leading edge 
of the tray contacts the sheet of film; b) sealing the film to the tray's 
leading edge; c) injecting a gas into the tray beneath the film proximate 
the sealed leading edge while d) sealing the film to the side edges of the 
tray while continuing to inject gas into the tray; and, e) discontinuing 
the gas injection and sealing the trailing edge of the tray to the film. 
The accompanying drawings, which are incorporated in the constituted part 
of this specification, illustrate a preferred embodiment of the invention 
and, together with the description, serve to explain the principles of the 
invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be made to the present preferred embodiment to the 
invention which is illustrated in the above-described drawings. 
In accordance with the present invention, apparatus for 
atmosphere-modifying and sealing trays of the type having continuous 
peripheral edges includes a sealing station and means for advancing the 
trays past the sealing station. As embodied herein and with initial 
reference to FIG. 1, the atmosphere-modifying and sealing apparatus 
designated generally by the numeral 10 includes sealing station 12 and 
conveyor 14 for advancing trays 16 past sealing station 12 in the 
direction denoted "AD" in the figures. Tray 16, the details of which do 
not form part of the present invention, is depicted in FIG. 3 as having a 
recessed part 18 and an upper continuous flanged edge part 20, including 
leading edge portion 20a, trailing edge portion 20b, and longitudinal side 
edges 20c, 20d, relative to the advancing direction. Tray 16 can be made 
of polystyrene or other suitable packaging materials known to those 
skilled in the art. 
Conveyor 14 depicted in FIG. 1 is a split-belt type conveyor operating at 
essentially constant speed. The individual trays 16 are suspended on the 
split belts by the respective longitudinal edges 20c, 20d and are carried 
past sealing station 12 in end-to-end relationship. Although only two 
trays are shown in the FIG. 1 depiction, it is to be understood that 
apparatus 10 as depicted and otherwise disclosed herein is capable of 
continuous operation. Also, the present invention is not intended to be 
limited to split-belt conveyors, and other advancing means can be 
utilized. 
In accordance with the present invention, the apparatus further includes a 
film supply means and film disposing means positioned at the sealing 
station for receiving the film from the film supply means and for 
disposing the film to cover the tops of the advancing trays including the 
edges of the trays. The film disposing means together with the tray top 
including the edges define a nip region through which the film from the 
film supply means passes to cover the tray. As embodied herein and with 
continued reference to FIG. 1, supply roll 22 is positioned to feed film 
24 to disposing roller 26 which is located near sealing station 12. A 
fixed bar (not shown) or other type of film disposing element could be 
used in place of roller 26 but the roller is presently preferred. One or 
more tensioning rollers, such as roller 28 can be employed to provide 
smooth transport of film 24 between supply roll 22 and disposing roller 
26, as one skilled in the art would appreciate. Film suitable for use in 
the disclosed apparatus can be any of a number of single and multilayer 
films compatible with the modified gas atmosphere and contents of the 
tray. For example, for processing foodstuffs where transparency, heat 
sealability and low oxygen permeability are wanted, various materials 
manufactured and sold by the Cryovac division of W.R. Grace & Co., can be 
used. A Cryovac film material sold under the designation R669B was found 
to perform well when used in conjunction with a polystyrene tray in the 
present invention. 
Film disposing roller 26 is positioned substantially transverse to the 
advancing direction and in close proximity to plane 30 defined the tray 
top including tray edges 20. See FIG. 3 showing a dotted line 
representation of the plane 30. Positioning disposing roller 26 no more 
than three-four film thicknesses from plane 30 enables continued contact 
to be more easily and stably maintained between edges 20 and film 24 after 
it has passed through nip region 32. This both improves the quality of the 
seal and also the retention of the modified gas atmosphere in tray 16 
following the sealing operation to be discussed hereinafter. 
Further in accordance with the present invention, the apparatus includes 
gas flushing means including means for injection a preselected gas into 
the trays through the nip region and between the film and the trays. As 
embodied herein, gas flushing means designated generally 34 includes a gas 
source 36 connected via conduit system 38 to gas injection nozzle 40. The 
particular type of gas will depend upon the particular application, such 
as the use of nitrogen gas to purge trays containing perishable foodstuffs 
in order to eliminate as much oxygen as possible or oxygen to enrich the 
oxygen content, depending on the particular application. However, the 
present invention is not limited to the particular gas or to applications 
involving packaging foodstuffs. 
Nozzle 40 which comprises the gas injection means is positioned adjacent 
the nip region 32 and upstream of disposing roller 26 and has a transverse 
width 42. Nozzle 40 is positioned and oriented such that at least a 
portion of the gas flowing through the nozzle is directed substantially 
through nip region 32 below film 24 and into tray 16. Nozzle 40 can be 
fabricated from spaced apart plates such as plates 44, 46 (see FIG. 2A), 
and transverse width 42 should substantially span nip region 32. 
As embodied herein, and as best seen in FIGS. 2A and 2B, nozzle 40 includes 
a series of holes 48 (five being shown in FIG. 1) for delivering the gas 
flow through nip region 32 in a direction substantially perpendicular to 
the advancing direction and directly down into tray 16. It has been found 
that a significant increase in the efficiency of the flushing operation in 
terms of modifying the atmosphere of the trays can be achieved utilizing a 
nozzle constructed as shown in FIGS. 2A and 2B, which provides a flushing 
gas flow downward, perpendicular to the advancing direction, into tray 16. 
However, the present invention is not to be limited to this particular 
construction or orientation of the passages through which the modifying 
gas flows into the trays. 
As embodied herein, gas flow means 34 optionally can include gas injection 
nozzle 50 positioned slightly downstream of the disposing roller 26, below 
conveyor 14, and oriented to flow gas upward across leading edge 20a each 
tray 16 as it passes nip region 32. Nozzle 50 can be supplied from the 
same gas supply source 36 through conduit 52, as shown in FIG. 1, or from 
a separate gas source. While nozzle 50 is not critical to the operation of 
the disclosed apparatus, more complete flushing occurs. It is believed 
that nozzle 50 acts to provide a gas curtain to prevent return flow of air 
into the flushed tray across the leading edge after it passes through nip 
region 32 and before it is permanently sealed by components to be 
discussed hereinafter. However, the theory of operation of nozzle 50 is 
not to be taken as a limitation on the invention defined by the appended 
claims. 
The particular gas flow rate and pressures are a function of the tray size, 
conveyor speed, etc. For example, N.sub.2 purging tests run with Formpac 
BT 972 trays having dimensions of 9"(1), 7"(w), and 2"(d), a film 71/4 
inches wide, allowed 60 trays per minute to be processed using a N.sub.2 
flow rate of about 220 CFH. The nozzle 40 was configured with a transverse 
width 42 of about 7 inches and had a total of 104 holes 48 each 0.12" I.D. 
Nozzle 50 had a single opening of 3/8" dia. The residual O.sub.2 content 
in the sealed trays was determined to be less than about 0.50%. One 
skilled in the art would be able to select suitable parameters for a 
particular application with a minimum of experimentation, given the 
present disclosure. 
In accordance with the present invention, the apparatus further includes 
means for sealing the disposed film to the edges of the gas flushed trays. 
The sealing means are positioned proximate and downstream of the roller 
means relative to the advancing direction. As embodied herein, and as 
depicted schematically in FIG. 1, apparatus 10 includes sealing unit 60 
positioned closely proximate and downstream of disposing roller 26. It is 
important to have the sealing unit 60 positioned as close as practicable 
to disposing roller 26, to achieve the best results in terms of 
maintaining the modified atmosphere and providing a good seal. Sealing 
unit 60 utilizes a pair of conventional band sealers (not shown) to 
continuously seal film 24 to longitudinal edges 20c, 20d. Sealing unit 60 
also includes an intermittent, vertically and horizontally reciprocal "hot 
bar" sealer apparatus 62 to seal leading and trailing edges 20a, 20b. In 
the preferred embodiment of sealing unit 60, the conventional band sealers 
are positioned to act on the film covered tray before the leading and 
trailing edge sealer 62. 
As embodied herein, and with reference to FIG. 4, leading and trailing edge 
sealer 62 includes a heated top die 64 and a complementary opposing bottom 
die 66 configured to engage a film-covered leading or trailing edge 20a, 
20b (not shown in FIG. 4) positioned therebetween. In the FIG. 4 
embodiment, dies 64 and 66 are constrained for vertically reciprocal 
motion in opposite directions by a pair of rack and pinion assemblies 68, 
70 disposed transversely to conveyor 14. Assemblies 68, 70 are driven by 
double-acting pneumatic units 72, 74 relative to frame 76 which is 
constrained to move horizontally along a pair of parallel slide rails 78, 
80 in the longitudinal direction relative to conveyor 14. Horizontal 
reciprocal movement of frame 76 on slide rails 78, 80 is provided by drive 
unit 82 (shown schematically). 
In operation, drive unit 82 moves frame 76 upstream relative to the 
conveying direction of conveyor 14 to a point closely adjacent the 
downstream end of the conventional band sealers, whereupon cylinders 77, 
74 are activated to capture a film-covered edge 20a or 20b between 
vertically travelling opposing dies 64, 66. Drive unit 82 then moves frame 
76 downstream at the same rate as conveyor 14 with the film-covered edge 
of tray 16 remaining captured until sealing has been accomplished. 
Cylinders 72, 74 are then activated in the reverse direction causing dies 
64, 66 to release the film-covered edge and clear the tray, and drive unit 
82 returns frame 76 upstream and the cycle is repeated for the next 
film-covered trailing or leading edge to be sealed. For a close tray-tray 
spacing, it has been found advantageous to simultaneously seal the 
trailing edge of one tray and the leading edge of the adjacent tray. One 
skilled in the art given the present disclosure, would readily be able to 
construct a suitable sealing unit and coordinate its operation with the 
balance of apparatus 10. 
As further embodied herein, apparatus 10 includes trimming unit 84 disposed 
downstream of sealing unit 60 to conform the disposed film to the outer 
shape of tray edges 20 and to sever the film linking adjacent sealed 
trays. Although shown separately in the FIG. 1 depiction for clarity, the 
operation of trimming unit 84 could be combined with that of the sealing 
unit 60. Such a combination is particularly advantageous where minimum 
trimming occurs, such as where the transverse extent of the film coincides 
with the width of the trays and wherein the tray corners are reasonably 
square. In such a case, the remaining function of the trimming unit, 
namely severing of the film between adjacent trays, can be accomplished by 
incorporating a knife blade trimmer with the "hot bar" sealer 62 to sever 
the film linking the adjacent trays either during or immediately after the 
leading and trailing edges are sealed. 
It will be apparent to those skilled in the art that various modifications 
and variations can be made in the above-described embodiment of the 
present invention without departing from the scope or spirit of the 
invention. Thus, it is intended that the present invention covers such 
modifications and variations provided they come within the scope of the 
appended claims and their equivalents.