U.S. patent application number 10/603028 was filed with the patent office on 2004-01-01 for packaging bag, and method of and apparatus for manufacturing the same.
This patent application is currently assigned to Cryovac, Inc.. Invention is credited to Montalbano, Antonino, Robbiati, Francesco.
Application Number | 20040001652 10/603028 |
Document ID | / |
Family ID | 29716926 |
Filed Date | 2004-01-01 |
United States Patent
Application |
20040001652 |
Kind Code |
A1 |
Robbiati, Francesco ; et
al. |
January 1, 2004 |
Packaging bag, and method of and apparatus for manufacturing the
same
Abstract
A packaging bag comprises a first ply and a second ply joined
along an edge defining the closed end of the bag and along side
edges of the bag. A mouth of the bag has a first edge on the first
ply and a second edge on the second ply, which projects beyond the
first edge and comprises a folded over film portion. The margin of
the second edge portion is disposed adjacent the first edge so as
to provide a substantially constant thickness of the bag across the
mouth and projecting portion.
Inventors: |
Robbiati, Francesco; (Arluno
(Milan), IT) ; Montalbano, Antonino; (Milan,
IT) |
Correspondence
Address: |
Sealed Air Corporation
P.O. Box 464
Duncan
SC
29334
US
|
Assignee: |
Cryovac, Inc.
|
Family ID: |
29716926 |
Appl. No.: |
10/603028 |
Filed: |
June 24, 2003 |
Current U.S.
Class: |
383/66 ; 383/200;
53/459 |
Current CPC
Class: |
B31B 70/642 20170801;
B65D 75/002 20130101; B31B 70/81 20170801; B31B 2155/00 20170801;
B31B 2160/10 20170801; B65D 75/52 20130101; B65D 75/5827 20130101;
B65D 33/007 20130101; B31B 70/00 20170801; B31B 70/14 20170801;
B31B 70/64 20170801; B65B 9/093 20130101; B65B 61/02 20130101; B31B
70/18 20170801; B65D 75/58 20130101; B31B 2155/003 20170801 |
Class at
Publication: |
383/66 ; 53/459;
383/200 |
International
Class: |
B65D 033/16 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2002 |
EP |
02254428.2 |
Claims
1. A packaging bag comprising opposed first and second film plies
joined at a closed end of the bag and sealed along lateral edges of
the bag, said plies defining an open mouth end having a first edge
of the first ply and a second edge of the second ply which projects
beyond the first edge of the first ply and comprises a folded over
film portion to exhibit double thickness at the exposed end of the
second ply, wherein the margin of the folded over portion of the
second ply is disposed adjacent to the edge of the first ply so as
to provide a substantially constant thickness of the bag across the
mouth and projecting portion.
2. The packaging bag according to claim 1, wherein the length of
the folded over film portion is less than 5% of the total length of
the bag.
3. The packaging bag according to claim 1, wherein the length of
the folded over film portion is less than 3% of the total length of
the bag.
4. The packaging bag according to claim 1, wherein the length of
the folded over film portion is less than 1 cm.
5. The packaging bag according to claim 1, wherein the length of
the folded over film portion is less than 8 cm.
6. The packaging bag according to claim 1, wherein the length of
the folded over film portion is less than 0.5 cm.
7. The packaging bag according to claim 1 wherein the two plies are
joined at a fold line defining the closed end.
8. The packaging bag according to claim 1, including at the closed
end of the bag a first seal line joining the first and second plies
and further seal lines extending from the closed bottom of the bag
and converging toward one another in a direction towards the
further seal line.
9. The packaging bag according to claim 8, wherein said further
seal lines meet at the said additional seal line.
10. The continuous strip of transverse-sealed packaging bags that
can be easily separated one from the other, wherein the
transverse-sealed bags are in accordance with claim 1.
11. An apparatus for manufacturing a plurality of packaging bags
according to claim 1, comprising means for feeding a flattened
tubular film material having first and second marginal folds along
a film path, means for transversely sealing said tubular film at
regularly spaced locations to define the joins between contiguous
transverse-sealed bags to be formed from said tubular film
material, means for taking up said succession of transverse sealed
bags from said transverse sealing station, and means for slitting
one flat wall of said flattened tubular film material in proximity
to said first fold of said film material to define said second
mouth edge extending beyond said first mouth edge, said slitting
means being mounted upstream of said transverse sealing
station.
12. The apparatus according to claim 11, and further including
means defining a tear-initiating formation at said closed end of
the bags by heat sealing said flattened tubular film close to its
second marginal fold.
13. The apparatus according to claim 12 and including an air
introduction nozzle extending transversely across and within said
tubular film material either at said slitting station or downstream
of it but before the heat sealing of the flattened tubular film
close to its second marginal fold, for introducing air into the
space between said superposed plies.
14. The apparatus according to claim 11, wherein said slitting
station comprises an anvil arranged to be disposed within said
tubular film material at said slitting station and to extend
upstream from a carrier, and a slitting blade disposed adjacent
said anvil whereby said slitting blade will slit only said first
ply passing over said anvil.
15. The apparatus according to claim 14, wherein said anvil and
said slitting blade are fixed to said carrier, and including means
for releasably attaching said main carrier to the machine
frame.
16. A method of making a plurality of packaging bags according to
claim 1, comprising a. feeding a flattened tubular film material
along a machine direction while exhibiting first and second
superposed plies extending between first and second marginal folds
of said tubular film material, b. slitting said first ply in
proximity to said first marginal fold of said flattened tubular
film material while leaving said second ply unslit whereby said
second ply has a turned over edge at said first marginal fold of
the tubular film material, c. downstream of said slitting station
transversely sealing said tubular film material along a plurality
of regularly spaced transverse seal lines which extend into said
second ply at said turned over edge in proximity to the first
marginal fold of the tubular film material, and d. delivering the
plurality of transverse-sealed packaging bags thus formed.
17. The method according to claim 16, wherein said transverse
sealing operation applies closely spaced seal lines defining
lateral margins of contiguous transverse-sealed bags, and between
said closely spaced seal lines a line of weakness permitting
subsequent separation of said contiguous bags from one another.
18. The method according to claim 16, and including the further
step of separating said transverse-sealed bags from one another and
presenting them in a package ready for subsequent use at a bag
loader.
19. The method according to claim 16, and including the further
step of applying, at said second marginal fold of the tubular film
material, a longitudinally extending seal line spaced inwardly from
said second fold of the tubular film material, and applying
additional seal lines which extend from said second fold line in a
converging manner towards said additional seal line.
20. The method according to claim 16, wherein said tubular film
material is formed of a heat-shrinkable plastic film.
21. A process of packaging comprising: (A) opening a bag by
pneumatically inflating the mouth of the bag, wherein the bag
comprises first and second film plies joined at a closed end of the
bag and sealed along lateral edges of the bag, said plies defining
an open mouth end having a first edge of the first ply and a second
edge of the second ply which projects beyond the first edge of the
first ply and comprises a folded over film portion to exhibit
double thickness at the exposed end of the second ply, wherein the
margin of the folded over portion of the second ply is disposed
adjacent to the edge of the first ply so as to provide a
substantially constant thickness of the bag across the mouth and
projecting portion; (B) holding the bag open; and (C) introducing a
product into the bag.
22. The process according to claim 21 wherein the bag is produced
by a method comprising: a. feeding a flattened tubular film
material along a machine direction while exhibiting first and
second superposed plies extending between first and second marginal
folds of said tubular film material, b. slitting said first ply in
proximity to said first marginal fold of said flattened tubular
film material while leaving said second ply unslit whereby said
second ply has a turned over edge at said first marginal fold of
the tubular film material, c. downstream of said slitting station
transversely sealing said tubular film material along a plurality
of regularly spaced transverse seal lines which extend into said
second ply at said turned over edge in proximity to the first
marginal fold of the tubular film material, and d. delivering the
plurality of transverse-sealed packaging bags thus formed.
Description
[0001] The present invention relates to a packaging bag,
particularly a transverse- or side-sealed bag of plastics film.
[0002] In the manufacture of transverse- or side-sealed plastic
packaging bags a problem arises from time to time in that the mouth
edge of the bag may tend to curl during the manufacturing process.
This problem is particularly noticeable when producing the bags
from a shrink film, due to the application of heat to achieve the
transverse or side seal between contiguous bags in a stream being
produced, particularly when working with film thicknesses of
smaller values. One solution to this problem has been to add a
final step of trimming off the mouth edge material after formation
of the transverse-sealed bags, in order that freshly exposed mouth
edge will have a straight, uncurled configuration in the finished
bag.
[0003] It is an object of the present invention to provide a novel
packaging bag which is resistant to the curling experienced with
the prior art bags.
[0004] A further object of the present invention is to provide a
method of producing packaging bags which are resistant to the
curling problem of the prior art.
[0005] Yet a further object of the present invention is to provide
an apparatus for producing packaging bags which are resistant to
this curling problem.
[0006] According to a first aspect of the present invention there
is provided a packaging bag comprising opposed first and second
film plies joined at a closed end of the bag and sealed along
lateral edges of the bag, said plies defining an open mouth end
having a first edge of the first ply and a second edge of the
second ply which projects beyond the first edge of the first ply
and comprises a folded over film portion to exhibit double
thickness at the exposed end of the second ply, wherein the margin
of the folded over portion of the second ply is disposed adjacent
to the first edge of the first ply so as to provide a substantially
constant thickness of the bag across the mouth and the projecting
portion.
[0007] The turned over lip defines the mouth edge of a longer side
of the bag which thus slightly projects beyond the edge of the
shorter opposite side of the bag. The turned over lip also
therefore presents a rigidifying effect, which is particularly
helpful in the case of packaging bags with a thickness at the
smaller end of the available range of materials to be used, i.e. a
light weight of film.
[0008] The packaging bags according to this first aspect may be
presented as discrete, separate, bags, possibly reassociated in
shingled or imbricated form on guide tapes, or stacked vertically
and delivered as a wicket of stacked bags. They may also be
presented in the form of a continuous strip of contiguous bags that
can be easily separated one from the other, e.g. due to the
presence of weakening lines such as pre-perforated lines,
positioned between the transverse seals of each bag and the
transverse seals of the immediately preceding and following
bags.
[0009] A further aspect of the present invention provides an
apparatus for manufacturing a bag according to the first aspect,
comprising means for feeding a flattened tubular film material,
having first and second marginal folds, along a film path, means
for transversely sealing said flattened tubular film at regularly
spaced locations to define the joins between contiguous
transverse-sealed bags formed from said tubular film material,
means for taking up said succession of transverse sealed bags from
said transverse sealing station, and means for slitting one flat
wall of said flattened tubular film material in proximity of said
first fold of said film material to define said second mouth edge
extending beyond said first mouth edge, said slitting means being
mounted upstream of said transverse sealing station.
[0010] A third aspect of the present invention provides a method of
manufacturing a bag according to the first aspect, comprising
feeding a flattened tubular film material along a machine direction
while exhibiting first and second superposed plies extending
between first and second marginal folds of said tubular film
material, slitting said first ply in proximity of said first
marginal fold of said flattened tubular film material while leaving
said second ply unslit whereby said second ply has a turned over
edge at said first marginal fold of the tubular film material,
downstream of said slitting station transversely sealing said
tubular film material along a plurality of regularly spaced
transverse seal lines which extend into said second ply at said
turned over edge in proximity to the first marginal fold of the
tubular film material, and delivering the plurality of
transverse-sealed packaging bags thus formed.
[0011] By leaving the turned over lip in place at the mouth edge of
the finished bag, it is possible to utilize all of the film
material of the flattened tubular film used as starting material
for the manufacture of side-sealed bags, and this both provides
better economy of material and also eliminates the complication of
the need to remove the trimmed mouth edge as has been conventional
as a way of avoiding curling in the finished bags.
[0012] A fourth aspect of the invention provides a method of
packaging, comprising taking a bag according to the first aspect,
or a bag made by the method of the third aspect, and pneumatically
inflating the mouth of said bag to separate the edge of said
shorter first ply from said projecting edge of the second ply to
initiate opening of the bag, and subsequently holding the bag open
and introducing a product article into a respective said open
bag.
[0013] In order that the present invention may more readily be
understood the following description is given, merely by way of
example, with reference to the accompanying drawings in which:
[0014] FIG. 1 is a top plan view of an embodiment of packaging bag
in accordance with the first aspect of the present invention, in
this case incorporating an optional easy open (EZO) feature;
[0015] FIG. 2 is a side sectional view of the bag of FIG. 1, taken
along the line 11-II of FIG. 1;
[0016] FIG. 3 is a perspective view of a prior art form of bag
making apparatus and process;
[0017] FIG. 4 is a view corresponding to FIG. 3 but showing an
embodiment of the bag making process and apparatus in accordance
with the present invention in the special case of the EZO bag
embodiment of FIG. 1; and
[0018] FIG. 5 is a sectional view, taken on the line V-V of FIG. 2,
showing the knife and anvil of the slitting station of the
apparatus of FIG. 4.
[0019] The improved packaging bag shown in FIG. 1 is a transverse-
or side-sealed bag 1 having a closed end 1a at which are joined
together first and second superposed main panels 2 and 3 which are
sealed along opposite edges 4 and 5 by a heat-sealing operation. In
this embodiment the closed end 1a is a first fold in the film
material providing the two plies defining the panels 2 and 3.
[0020] The mouth of the bag is at the end opposite the closed end
1a and is formed by a singly folded portion 7 of the second main
panel 3 and a cut edge 6 of the first main panel 2. The manufacture
of the mouth end involves slitting the flattened tubular film of
the plastic material used for the bag (12 in FIGS. 3 and 4) in
proximity of the second of the two folds thereof, the first fold
being to define the closed end 1a, described above, of the bag.
[0021] The production of the mouth end involves forming a cut at 7a
in one of the two flat plies of the flattened tubular film in
proximity to the second fold 7 referred to above, in order to
separate the first main ply from the co-planar folded over part of
the film margin at the fold 7. As a result, at the mouth end the
folded end of the second main ply exhibits a double thickness of
the film in one wall which projects beyond the end 6 of the first
main ply (other wall), thereby (i) allowing easier pneumatic
inflation of the bag mouth in order to open the bag 1 for loading
purposes, and (ii) resisting wrinkling in that the increase in
thickness of the end of the panel 3 at the folded end of the second
ply helps to resist the tendency, which the bag material would
otherwise have, to curl, as described above.
[0022] In the bag according to the present invention the bag mouth
is created by cutting only one of the plies of the flattened tubing
along a line which is parallel to and in proximity of the second of
the two longitudinal folds of the flattened tubing, no material is
removed and the transverse seals to give the discrete bags are made
directly on the longitudinally (machine direction) tensioned slit
tubing. Therefore, there will be essentially a zero space between
the edge 6 of the first ply and the margin 7a of the folded over
portion of the second ply, i.e. said two edges will be adjacent one
to the other.
[0023] Close to the end 1a of the bag are optional seal lines 8, 9a
and 9b the purpose of which will be described later.
[0024] The film used for manufacturing the bag 1 may be a
mono-layer film, but is preferably a multi-layer film having
different functions for the individual layers of the bag. For
example, (i) one of the intermediate layers of the bag material may
be a barrier layer in order to control the transmission of gas (for
example O.sub.2) between the interior and exterior of the bag when
sealed, (ii) another of the layers of the bag material on the
inside of bag will be a sealing layer facilitating sealing to a
similar material for the purposes of closing the bag when loaded,
and (iii) a third layer will be an abuse-resistant layer giving
strength to the bag material. Other functions may also be provided,
for example there may be tie layers between any of the above
mentioned layers. The thickness of films suitable for the
manufacture of transverse-sealed bags, including those according to
the present invention, is typically comprised between about 35 and
about 120 .mu.m, preferably between about 40 and about 100 .mu.m.
Thicker films as well as thinner films, e.g. films 15, 20, 25, 30
.mu.m thick may however be employed in the process of the present
invention.
[0025] The apparatus for producing a bag of the type shown in FIGS.
1 and 2 will now be described with reference to FIGS. 3 and 4, FIG.
3 showing a prior art apparatus for manufacturing a continuous
strip of transverse- or side-sealed contiguous packaging bags, and
FIG. 4 showing a modification which produces the bags in accordance
with the present invention.
[0026] In FIG. 3 there is shown bag making apparatus 10 which
processes a flattened tubular film 12 which may either have come
straight from a bubble extrusion manufacturing plant or may have
been previously formed by bubble extrusion and then rolled up for
reuse at a later date at which point the roll is unwound so that
the film can be fed to the bag making apparatus 10. Initially the
tubular material 12 arrives at a bag opening station 14 which
includes a horizontally arranged knife blade 16 which can serve to
slit the film 12 at the right-hand marginal fold as shown in FIG.
3. Next the film 12 arrives at an optional air introduction station
18 including an air nozzle 20 which is supported on the machine
frame and is cantilevered to extend across the width of the flat
folded film to introduce air near the left-hand fold line (which
corresponds to the closed end 1a in FIGS. 1 and 2). This may be
helpful in case bags with the optional EZO feature, which will be
described later, are manufactured.
[0027] Next the film 12 arrives at a bottom forming station 22
which is optional but which in the present embodiment creates the
seal lines 8, 9a and 9b to provide a particular easy open (EZO)
configuration to the closed or bottom end of the bag so that the
bag is substantially in accordance with U.S. Pat. No. 6,260,705.
The operation of this closed end will be described later with
reference to the use of the finished bags.
[0028] The already slit film material then arrives at a transverse
sealing station 24 including vertically closable and openable seal
bars 26 and 28 which operate in synchronisation with stepwise
advance of the tubular film material 12 so as to define a plurality
of spaced transverse seal lines 30 which each include two spaced
lines parallel sealing contiguous bags, one of such lines being
associated with each of the contiguous bags, and between them a
perforation line to allow the bags to be separated from one another
at a downstream station.
[0029] As can be seen in FIG. 3, the bag material just at the
slitting station 14 and downstream therefrom, undergoes
considerable curling particularly at the mouth end of the bag, and
this results in pleats and wrinkles at the transverse sealing
operation at station 24, particularly when the film material is of
a heat shrinkable nature. In order to remove the unsightly curled
mouth region from the bag, and to guard against the possibility of
that curling leading to difficulties in opening the bag by a
pneumatic opening device at the loading station, the selvage 34 of
the film material along the right-hand fold of the tubular material
12 is removed in its entirety by means of a vertically aligned
trimming knife blade 32 which separates the selvage 34 to be sucked
into an aspiration nozzle 36.
[0030] The chain of perforated and transverse-sealed bags
downstream of the knife 32 can then either be wound up for
subsequent use, or be separated and reassociated in shingled or
imbricated form on guide tapes, or possibly stacked vertically and
delivered as a wicket of stacked bags, depending upon the type of
bag loader for which they are to be used.
[0031] During the bag closing operation the mouth of the bag along
the right-hand edge, corresponding to the right-hand end 7 of the
bag in FIGS. 1 and 2, is closed by any convenient mechanism,
preferably by heat seal bars, and then the bag can be subjected to
a heat-shrinking operation which serves to tidy the structure of
the bag around a product article which was loaded therein before
the bag closing operation. Where the optional bottom forming device
22 is present, the shrinking operation also results in formation of
loose tabs or ears, illustrated by the portions 8a and 8b (FIG. 1)
of the bag bottom to either side of the central V-notch shown
therein (defined by the seal lines 9a and 9b), at which tearing of
the bag can be initiated by pulling the two ears 8a and 8b apart
from one another. This particular easy open feature is very useful
for a shrink package but, as indicated above, is optional and can
be used with or without the curl-preventing mouth structure in
accordance with the present invention.
[0032] In order to complete description of the prior art apparatus
of FIG. 3, it is sufficient to indicate that initially the
flattened tubular film 12 is withdrawn from the supply and pulled
past the slitting station 14, the optional air introduction station
18, the optional bottom forming station 22, the mouth separating
blade 40 and the heat sealing station 24 while its jaws 26 and 28
are open so that the film material 12 can be inserted therebetween.
Then the right-hand edge of the tubular film material at the film
slitting station 14 is slit and the tubular material is placed over
the horizontal knife blade 16 such that the blade enters the slit
which has thus been formed, and then subsequent movement of the
tubular film material in the machine direction illustrated by arrow
21 will cause the blade 16 to continue slitting the film passing
thereover.
[0033] Finally the leading end of the continuous perforated strip
of bags is drawn to the slitting blade 32 where another slit is
formed by the blade 32 to isolate the selvage 34 for continuous
removal of the selvage 34 as the machine 10 continues to operate
with stepwise advancing of the film material synchronised with
intermittent operation of the transverse sealing station 24.
[0034] The difference between the prior art apparatus of FIG. 3 and
the embodiment of the present invention shown in FIG. 4, which
provides a bag in accordance with the present invention, resides in
the fact that the film opening station 14 of FIG. 3 is replaced by
a modified bag slitting station in FIG. 4, where the knife blade 17
is vertically aligned as compared with the horizontal alignment of
the knife blade 16 at the film slitting station 14 of FIG. 3. In
FIG. 4 the tube-slitting blade 17 is associated with a support 19
which carries both the knife blade 17 on the outside of the tubular
film material 12 and an anvil (46 in FIG. 5) inside the tubular
material so that the blade 17 can form a slit (illustrated at 7a in
FIG. 2) in the upper ply 2 of the film 12 without penetrating the
lower ply 3 of the film. It will be readily understood that this
slit 7a formed by the knife blade 17 in FIG. 4 forms, at a single
stroke; the bag mouth in accordance with the present invention. The
support 19 carrying the tube-slitting blade 17 and the anvil 46 is
mounted on the machine frame so as to be released when desired, and
so as to be adjustable in position in a direction transverse to the
machine direction (i.e. to the direction of movement of the film
web 12).
[0035] The apparatus of FIG. 4 again includes the optional
bottom-forming station 22 which may be used in conjunction with the
optional air-introduction station 18 also shown in FIG. 3.
Preferably the optional air introduction station 18 can be located
on the carrier 19 of the slitting station 15. However, it is
equally possible for the air introduction station 18 to be
positioned downstream of the slitting station 15 but upstream of
the optional bottom forming station 22.
[0036] The transverse sealing station 24 in FIG. 4 is identical to
that of FIG. 3 and will not be described in more detail.
[0037] A further difference between the device of FIG. 4 in
accordance with the present invention and the prior art embodiment
of FIG. 3 is that there is no longer any need to remove the selvage
material as shown at 32, 34, 36 in FIG. 3 because the reinforcement
of the mouth portion, relying on the staggered mouth edges 6 and 7
(FIG. 2) and the folded over configuration of the projecting edge 7
(FIG. 1), rigidifies the bag structure sufficiently to eliminate
the curling, and the absence of curling can be readily appreciated
from the drawing of FIG. 4.
[0038] As in the case of the FIG. 3 embodiment, the perforated
chain of bags delivered at the far end of the apparatus as viewed
in FIG. 4 can then either be immediately separated into individual
bags for wicketing or imbricating or can remain as a chain of
transverse-sealed bags for rolling up and storage.
[0039] Both the FIG. 3 prior art embodiment and the FIG. 4
embodiment of the present invention include also a mouth separating
blade 40 which serves merely to hold the right-hand edges of the
upper 2 and lower 3 plies of the folded film 12 apart from one
another and to guide them into the area between the jaws 26 and 28
of the transverse sealing station 24. As in the FIG. 3 apparatus,
the sealing station 24 in FIG. 4 operates in an intermittent manner
synchronously with the stepwise movement of the bag chain.
[0040] The modified apparatus 11 of FIG. 4 is threaded up in a
similar manner except that the combined tube slitting station 15
and the optional air introduction station 18 provide for (i) the
support 19 with the blade 17 to be removed from the bag path and
for the nozzle then to be introduced between the opposed plies 2
and 3 of the centre folded film 12 once a slit (7a in FIG. 2) has
been formed manually, and (ii) the air introduction station 18
(where fitted) to be similarly removed and then replaced after
slitting the tube manually. The film material can then be advanced
such that the anvil (46 in FIG. 2) at the slitting station 15 and
the air nozzle 20a of the optional air introduction station 18 can
be introduced into the space between the two opposed plies (2 and 3
in FIG. 1) while the knife blade 17 is positioned above the upper
ply 2 and is able to slit only the upper ply while leaving the
lower ply intact as illustrated in FIG. 2. The rest of the
threading-up operation is the same for the apparatus 11 of FIG. 4
as it is for the apparatus 10 of FIG. 3, except that there is no
need to form the downstream slit at knife blade 32 for the
selvage-removing operation.
[0041] The anvil 46 and the slitting blade 17 of FIG. 4 are also
adjustable in a direction perpendicular to the machine direction
for accommodating flattened tubular films 12 of different
widths.
[0042] The length of the transverse-sealed bags (that corresponds
to the width of the flattened tubing 12) is typically comprised
between about 15 and about 65 cm, preferably between about 16 and
about 60 cm, and more preferably between about 18 and about 50
cm.
[0043] The distance between the cut edge 6 of the first main panel
2 and the fold 7 of the second main panel 3, that corresponds to
the length of the turned over lip, is typically below about 5%, and
preferaby below about 3% of the total length of the bag. Preferably
the length of the turned over lip is anyway less than 1 cm, more
preferably less than 0.8 cm and even more preferably less than 0.5
cm. As an example, the bag represented in FIG. 1 is 18 cm long and
has a turned over lip of 0.4 cm, corresponding to less than 3% over
the total length of the bag.
[0044] The slitting blade will thus be positioned at a distance
from the second fold 7 of the flattened tubing 12 that corresponds
to the desired length of the turned over lip, i.e. preferably less
than 1 cm, more preferably less than 0.8 cm and even more
preferably less than 0.5 cm.
[0045] In order to illustrate more clearly the operation of the
combined air introduction station 18 and the film slitting station
15 in FIG. 4, reference will now be made to FIG. 5 which shows the
knife blade 17 on the carrier 19 and in the process of forming the
cut 7a in the upper ply 2 of the material 12a and leaving the
underneath ply 3 uncut.
[0046] In order to establish the precise configuration for FIG. 5
it should be noted that this drawing is taken on the line V-V of
FIG. 2, in other words at the location of the slit 7a of FIG. 2,
and for that reason a sub-carrier 42 which has a clamp (not shown)
to support the blade 17 thereon is illustrated in broken lines in
FIG. 5 but in fact this is just in front of the plane of the paper
and would therefore, strictly speaking, not be visible in FIG. 5.
In other words, the blade 17 is clamped to the back face of the
sub-carrier 42, and that face is in the plane of the paper of FIG.
2.
[0047] The sub-carrier 42 is bolted to the main carrier 19 by means
of bolts (not shown) which engage in holes 44 of the main carrier
19.
[0048] As mentioned earlier, the entire carrier 19 is releasably
mounted on the machine frame so that it can be introduced into the
already slit tubular film so that subsequent operation of the
apparatus will continue the slitting action.
[0049] The carrier 19, and the sub-carrier 42 and the air
introduction nozzle 20a carried thereby, are in this way able to be
rigidly mounted on the machine frame once it has been introduced
into the already pre-positioned tubular film.
[0050] It should be noted that the lower film ply 3 is shown in
section along its entire length in FIG. 5 and the upper film ply 2
is only shown in section up to the point where it arrives at the
tip of the slitting blade 17. Thereafter it has been slit and the
exposed face 6 of the ply 2 can be seen, except where it is
concealed behind the rear surface of the main carrier 19.
[0051] In order to explain in more detail the way in which the tear
initiation formation provided by the bottom-defining means 22 is
structured, reference will now again be made to FIG. 1 which shows
this optional characteristic as comprising a first seal line 8
which is parallel to and disposed inwardly of the fold defining the
bottom end 1a of the bag, and a pair of additional seal lines 9a,
9b which start from the bottom end 1a of the bag and converge
towards one another in a direction towards the seal line 8. In this
particular embodiment these additional lines 9a and 9b meet at the
seal line 8, but this is not essential to the operation of the easy
open means defined by the lines 8, 9a, 9b.
[0052] An "easy-open" (EZO) pre-cut line 9c extends longitudinally
of the bag (i.e. perpendicularly to the seal line 8 and to the
bottom end 1a of the bag so as to define a point of initiation of a
tear when the bag is to be open. This opening operation will occur
after the open end of the bag at 6, 7 has been sealed and the thus
sealed bag has been subjected to a shrinking operation.
[0053] It is possible for the bag closing operation to involve
placing the loaded bag into a vacuum chamber which exposes the
exterior of the sealed bag to reduced pressure causing the bag to
balloon slightly, and causing the sealed pockets 8a, 8b of the
bottom end of the bag to inflate slightly to present the tabs or
ears mentioned above. Subsequently the thus partially evacuated and
sealed bag is subjected to a heat shrinking operation, either in a
hot air shrink tunnel or in a shrink bath, whereupon the bag
material between the seal line 8 and the closed mouth end of the
bag will hug the contours of the product within the bag to provide
a tidy package, but the pockets 8a, 8b will protrude from the
surface, in the manner described in U.S. Pat. No. 6,260,705.
[0054] The fact that there is air within these pockets 8a and 8b,
due to the action of the air introduction nozzle 20a applying air
at the fold line which defines the closed end 1a of the bag helps
to ensure that these pockets 8a, 8b will appear inflated in
relation to the shape of the rest of the bag which will have shrunk
down onto the surface of the product article, and thus the two
pockets 8a, 8b define respective tabs or ears which can be pulled
laterally away from one another (i.e. in a direction away from and
transversely to the perforation line 9c of FIG. 1). This initiates
a tear near the point of convergence of the two converging seal
lines 9a, 9b to allow the bag to be opened.
[0055] It will of course be understood that the existence of the
perforation line 9c is optional, and that instead some other form
of tear-initiating formation could be provided. One possibility
would be for a hole to be formed centrally in the triangular region
defined between the fold line 1a of the tubular film material and
the converging additional seal lines 9a, 9b. Another would be to
provide a notch at the fold line 1a, again within the triangular
zone defined between the fold line 1a and the converging additional
seal lines 9a, 9b. However, such a tear-initiating means could be
omitted and one could rely simply on the fact that it is easy to
apply tearing tension to the film material simply by grasping the
two ears defined by the pockets 8a, 8b and pulling them apart.
[0056] As indicated above, the tear-initiating bottom formation 8,
8a, 8b, 9a, 9b, 9c is optional and it would have been possible for
the bag to be finished with simply the fold line 1a defining the
closed end of the product compartment of the bag.
* * * * *