Packaging apparatus for forming specially shaped packages

Packaging apparatus for making hermetically sealed vacuum packages from two continuous webs of plastic packaging material supplied as roll stock. The lower web is formed into product receptacles, and the upper web is applied over the receptacles to serve as the top. The apparatus includes a single-station evacuate-and-seal head where the two webs are initially sealed together around the flanges of the receptacle. The resulting package is then evacuated through a slit in the lower web, and the evacuation slit is sealed off to complete the package. During evacuation, the upper web is shifted up to engage a heated plate to raise the web temperature to a level permitting forming of the plastic material. After final sealing, the spaces above and below the packages are sequentially vented to atmosphere so as to control the formation of the upper web to produce a crowned effect, wherein a portion of the product extends upwardly a small distance above the flanges of the package.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to packaging apparatus. More particularly, this 
invention relates to the making of packages from two continuous webs of 
plastic packaging material, wherein the final package has a shape 
configured for improved handling or other purposes. 
2. Description of the Prior Art. 
Packaging apparatus is known for converting continuous web roll stock into 
sealed packages. A wide variety of machines have been disclosed for this 
general purpose. For example, U.S. Pat. No. 3,805,486 shows one such 
machine wherein a bottom web of flexible packaging material is transported 
in a horizontal direction by means of edge-clamp conveyors, the web being 
operated on at successive stations to produce product-receiving 
receptacles. A top web of semi-rigid material is simultaneously 
transported along a generally circular path by means of a rotary turret 
having means to form the web into cups which at a station just beneath the 
turret, are mated, in inverted disposition, with the lower web receptacles 
carrying the product. The package thus defined is evacuated and sealed. 
When the evacuation head is evacuated, the atmospheric pressure beneath 
the flexible lower web forces the web and product up against the inner top 
surface of the inverted semi-rigid cup. In carrying out this procedure, 
the evacuated spaces beneath the lower web were evacuated first, and then 
the spaces above the upper web were evacuated. 
SUMMARY OF THE INVENTION 
In an embodiment of the invention to be described below in detail, there is 
provided packaging apparatus having conveyor means for transporting a 
bottom web of flexible packaging material past a series of operating 
stations. Conventional means are used to form this web into 
productreceiving receptacles. After the product has been placed in the 
receptacle, the web is advanced to an operating station where an unformed 
top web of flexible packaging material is laid over the product and the 
bottom web. This operating station includes an evacuation and seal head 
having vertically-reciprocable upper and lower members. The two members 
are brought together to make an initial heat-seal between the two webs 
along a flange area around the receptacle mouth, and to form an evacuation 
chamber to evacuate the package through an evacuation slit in the bottom 
web. During this operation, the top film is drawn up to an inner heated 
surface of the upper member to raise the web temperature to a level 
providing for subsequent forming. After evacuation is complete, a final 
heat seal is made to form an hermetically sealed package. Thereafter, the 
spaces above and below the package are sequentially vented. The resulting 
final package has a "crowned" configuration, wherein upper portions of the 
product are located above the flange line where the two plastic sheets are 
sealed together. 
Other objects, aspects, and advantages of the invention will in part be 
pointed out in, and in part apparent from the following detailed 
description considered together with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is shown a bottom web 10 of flexible plastic 
packaging material which is conveyed from right-to-left along a horizontal 
path past a series of stations. At one such station (not shown herein, but 
located off to the right from FIG. 1), conventional means are utilized to 
form the lower web into cup-like receptacles 12 the upper openings of 
which can be seen in FIG. 1. Around these openings are the usual flanges 
14, in the plane of the web. 
The formed receptacles 12 are loaded with product, in this case shingled 
bacon 16. A top web 18 of flexible packaging material then is moved down 
towards the bottom web 10 and applied thereto, as by the usual lay-down 
roll. The two webs, and the contained product, are then advanced to a 
seal-and-evacuation head generally indicated at 20 in FIG. 3, and 
comprising vertically-reciprocable upper and lower members 22, 24. 
As can be seen from FIG. 3, the bottom web 10 is supported for horizontal 
conveying movement by edge-clamps 26 of usual construction. The top web 18 
rests somewhat limply on the product 16 which in this case protrudes a bit 
above the flanges 14 of the receptacle 12, e.g. a distance of perhaps 1/8 
to 3/16 inch. 
The upper member 22 comprises an outer part 30 carrying conventional heater 
elements 32 so that the downwardly-extending sides 34 of this part serve 
as an initial seal bar to seal the two webs 10 and 18 around the flange 
surrounding the receptacle opening when the members 22, 24 are 
reciprocated together as shown in FIG. 4. The upper member 22 also 
includes an inner web-heating insert 36, made of aluminum, and in 
non-insulated, heat-transfer contact with the outer initial seal-bar part 
30; the function of this insert will be described below. 
When the upper and lower members 22, 24 are together, as shown in FIG. 4, 
they form an airtight evacuation chamber surrounding the package. Vacuum 
is applied to the spaces 40, 42 above and below the package through the 
use of valves 44, 46 controlling vacuum lines 48, 50. The upper line 48 
communicates with the spaces 40 through channels 52 in the insert 36 (see 
also FIG. 2), and through holes leading down from those channels. The 
valves 44, 46 apply vacuum at about the same time, as indicated in FIG. 7 
which shows the actual timing relationship for a machine constructed in 
accordance with this invention. The lower chamber timing line is shown 
with curved leading and trailing edges only because the actual machine for 
which this chart applies used a cam-operated valve 46. The other valve was 
solenoid-operated giving rise to sharp leading and trailing-edges. In 
actuality, the vacuum from each may be applied at about the same rate, 
notwithstanding the more gentle curve shown for the lower chamber. 
When vacuum is applied, the interior of the package is evacuated through an 
evacuation slit 60 (see also FIG. 1) positioned just above the outlet of a 
vacuum line 62 connected to line 50, at the side of the head 20. The 
spaces 40, 42 above and below the package are evacuated more rapidly than 
is the interior of the package, and for that reason the top web 18 is 
pushed up by the resulting differential pressure between the package 
interior and the upper spaces. The top web approaches and may 
advantageously momentarily engage the heated surface of the insert 36 as 
illustrated in FIG. 4. This surface preferably is polished to provide good 
heat transfer to the web. The temperature of the web is raised to a 
relatively high level providing for forming of the plastic material. The 
top web also will be slightly stretched, as it is forced against the 
smoothly contoured surface of the insert, thus serving to provide an 
amount of slack in the material. 
After the package is evacuated, a final seal bar 64 is shifted down by 
conventional air-cylinder operating means, to seal off the evacuation slit 
60 as shown in FIG. 5. Almost simultaneously, the spaces above the top web 
18 are vented to atmosphere (see FIG. 7, "top web crowning"), and the 
vacuum valve to the lower chamber is closed but the vacuum line is not yet 
vented to atmosphere, as indicated by the curve "lower chamber main 
vacuum" in FIG. 7. The initial inrush of air above the package tends to 
drive down both the top web 18 (already stretched somewhat by having been 
drawn up towards the insert 36), and the bacon 16, which is somewhat 
compressible. As can be seen from FIG. 5, the product and the top web now 
are about even with the plane of the flanges of the receptacle. In some 
cases, the product and top web may be below that plane. 
After a further short period of time, the lower valve 46 is shifted from 
vacuum-off to vent position, at the time indicated by "lower chamber vent" 
in FIG. 7. The resulting inrush of atmospheric pressure applies an 
upwardly-directed force against the bottom web and the product, tending to 
move the product up. The final seal bar 64 then is retracted, and the vent 
to the lower spaces is closed. The upper and lower head members 22, 24 
then move apart, and the completed package is shifted out from the head to 
be cut from the web, as illustrated in FIG. 1. 
FIG. 6 shows a cross-sectional view of the finished package where, it will 
be observed, an upper portion 70 of the product is located above the 
flanges surrounding the mouth of the receptacle. This upward disposition 
of the product has been referred to as "crowning," and provides 
significant benefits for certain products. In bacon packaging, for 
example, the resulting package is much better able to be placed in a 
conventional board-type container for presentment to the customer. 
Although a specific preferred embodiment has been described in detail 
herein, this is not intended to be limiting of the invention since many 
modifications can be made without departing from the scope and spirit of 
the invention. For example, products other than bacon can be usefully 
crowned, for special applications. The products may in many instances lie 
initially within the receptacle with their upper surfaces below the flange 
line. Different types of packaging material also can be used, depending on 
a variety of factors. For such different products and different 
conditions, the timing of the sequential venting of the upper and lower 
spaces will differ from those shown herein. In some cases, the lower 
spaces should be vented before the upper spaces, since the intended result 
depends upon an upward force being directed against the lower web after 
the package has been sealed. Alternatively, as in the present application, 
the upper spaces may be vented first, in order to apply an initial 
downward force against the top web and the product, e.g. to prevent 
excessive force, due to venting the lower spaces, from jamming the product 
tightly up against the interior surface of the insert 36 and thereby badly 
misshaping the product. Thus in general it can be said that the desired 
results are achieved by selective sequential venting of the upper and 
lower spaces, in conjunction with heating of the upper web, especially in 
the same chamber in which the evacuation and final sealing take place.