Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR PRODUCING A FLAT BOTTOM
PLASTIC BAG
The pres~nt invention relates to a new and
useful improvement in the method of forming side gusseted
square bottomed stand-up bags. More particularly the
present invention relates to a method for forming a
side gusseted square bottomed stand-up bag fabricated
from suitable thermo plastic material having innerent
heat-sealing characteristics, such as polyethylene,
polypropylene, and the like.
The advent of relatively low cost plastic
film has not gone unnoticed, and in fact, plastic film
has been utilized to fabricate plastic bags in areas
conventionally dominated by paper and similar materials.
For example, plastic bags have found such use as grocery
bags, shopping bags, garbage bags, and coat bags, either
disposable or semi-durable. Various types of bag con-
structions and methods have been proposed in the patent
literature. ~erely as illustrative, the following
U.S. Patents disclose various methods and bag con-
structions. U.S. Patents 3,980,225; 3,855,907; 3,023,679;
3,606,822 and 3,669,347. Other pa~ents in the field
include U.S. Patents 3,690,221; and 3,590,698. The
type of bag constructions included in the above patents
fall generally into two categories, i.e., those whicn
do not form square corners by themselves such as Johnson,
U.S. Patent 3,855,907 or Kan, U.S. Patent 3,980,225; or
those which emulate the "paper sack" but vary in their
closure method. The present invention is particularly
concerned with flat bottom self-standing plastic bags
such as disclosed for example in U.S. Patents 3,606,822
and U.S. Patent 3,669,347.
Heretofore prior art methods for for~ing
square bot~omed plastic bags have utilized "paper sack"
technology. The i'paper sack" technology when applied to
plastic bags made from plasti.c film is generally complex.
I have discovered a simple and efficient method for forming
a square bottomed bag and conventional plastic bag making
equipment can be utilized for the method with only simple
modifications to the conventional equipment. The method
utilizes a side gusseted tube such as conventionally
manufactured by al.most all tubular film extruders.
Alternatively, such a tube could be produced by folding
and heat-sealing flat sheets along the side. ~he tube
is thereafter carried through a conventional "bag maker"
such as manufactured by numerous commercial firms. Only
slight changes need be made to the conventional bag making
machine to make it adaptable for connection to a unit for
in-tucking the corner bag gussets to form a square bottom
bag.
It is therefore a major object of the present
invention to provide a method for generating a side
gusseted squared bottom plastic bag.
It is an additional important object of the
invention to provide a bag of the character under dis-
cussion ~lich may be produced with particular economy,
can compel:e successfully with prior-art paper bags and
can be used with particular facility in grocery and
supermarket operations and the like.
Still another object of the invention is to
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provide a method for forming a side gusseted self-standing
square bottomed plastic bag wherein no contact adhesives,
tapes, patch additions or hot melt adhesives are required
during fabrication.
These and other objects of the invention will
become apparent from the description ta~en in conjunction
with the accompanying drawings in which:
Fig. 1 is a perspective view of a partially
opened plastic envelope produced ~rom an extruded length
of thermoplastic seamless tubing having a gusset in each
longitudinal edge thereof and heat sealed transversely
across the full width thereof, including the opposed
gussets, to provide a sealed bottom edge;
Fig. 2 is a view illustrating the first step
in generating the flat-bottom plastic bag of the present
invention, i.e., clamping the front and back walls in a
central longitudinal region and illustrates one form of
clamping mechanism operable to clamp the front and back
walls and to advance the bag and also illustrating
stationary sheet metal guides above and below the side
gussets;
Fig. 3 is a view taken along the lines 3-3 of
Fig. 2;
Fig. 4 is a view taken along line 4-4 of Fig. 2
and also lllustrating an air jet to assist in unblocking
the film.
Fig. 5 is a view taken along line 5-5 of Fig. 2
and showing one position in the gradual spreading of the
side gussets from 0 towards 180 and illustrating one
form of a spreader mechanism operable to gradually spread
the gussets as the bag and spreader is advanced.
Fig. 6 is a view taken along line 6-6 of Fig. 2
showing the further ~mfolding of the spreader mechanism
and the resultant opening of t:he side gussets towards a
flat configuration;
Fig. 7 is an isometric view of the plastic en-
velope shown in Fig. 6 with the gussets fulLy flared
(omitting the clamping mechanism, the sheet metal guides
and spreader mechanism from the view) to provide a hood
or triangular tuck on ~he sealed end and showing the
gusset fold line and transverse seal in juxtaposition and
further showing one form of mechanism, i.e., a stationary
plow to aid in holding the triangular tuc~ in position;
Fig. 7A is a view showing the gusset being
refolded towards 0;
Fig. 8 is an isometric view of the plastic
envelope with the side gussets returned to their original
position thereby providing inwardly folded corner tucks;
Fig. 9 is a view similar to Fig. ~ but showing
the creasing of the bag at the terminal ends of the seal
to form creases as a means for defining the periphery of
the bottom of the bag; and
Fig. 10 is a view showing a fully opened bag made
in accordance with the method of the instant invention.
Broadly contemplated, the present invention
provides a method of producing a flat-bottom bag from
thermoplastic material which includes the steps of:
(a) providing a length of flattened, heat
sealable tubular material having front and back walls
and united along each longitudinal edge by a gusset
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including a longitudinal gusset fold line, said length
having been heat sealed transversely adjacent one
extremlty to provide a bag having a closed bottom and
an open mouth;
(b) clamping the front and back walls in a
central longitudinal region;
(c? flaring the gussets until the position
of the transverse heat seal common to the gusset
coincides with the gusset fold line;
(d) and maintaining the fold line and hea~
seal in juxtapositi.on while returning the gussets to the
non-flared position thus providing a gusset tuck on each
corner of said closed bottom.
Optionally a line can be generated transversely
at the terminal ends of the seal to form creases for
defining the periphery of the bottom of the bag.
; For a clearer understanding of the invention
ref~rence is made to the drawing and particularly to
Fig. 1 which illustrates a tube which has been heat
sealed transversely along the bottom edge to form a
; bag 10 after being severed from a length of seamless
thermoplastic tubing produced by an extrusion process
and flattened as is well known in the art. The severed
b.ag includes a front wall 11 and a rear wall 12 united
; along the longitudinal edges thereof by gussets 13 and
14, the latter being folded around gusset fold lines
13A and 14A respectively. The thermoplastic material is
heat sealed transversely, from edge to edge thereof as
indicated at heat seal line 15 and severed immediately
beyond the seal 15, thereby provi.ding a bottom closure
for the initial bag and an opened mouth edge for the
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next adjacent bag, the invention contemplating the
successive production of bags from a continuous length
of tubing. It will be noted that the transverse heat
seal 15 securely unite.s or welds the bottom edges of
the front and rear walls or panels 11 and 12 to each
other and that this seal also includes the gusseted
portions 13 and 1~. Thus, in the central portion of
the seal tube there are 2 layers of thermoplastic
materlal, constituting the front and rear walls of the
bag; however, in the marginal portions of the seal 15
there are 4 layers of thermoplastic material, the ~
opposed layers forming each gusset 13 and 14 being sealed
to each other and between the front wall 11 and the rear
wall 12.
The seal 15 constituting the bottom closure
can be produced by numerous methods known in the art,
including hot wire or hot knife cut-off seals, stationary
or traveling bar seals, traveling heating bands, rotary
discs, or ultrasonic sealers. The significant result
should be a strong, leak tight seal.
The material for the bag could be any one of
a variety of plastics, e.g., high or low density poly-
ethylene or blends thereof, polyvinyl chloride, poly-
propylene, ethylene-ethylacrylate, polyvinylacetate,
or a variety of laminates such as different polymeric
films, paper extrusion coated with polymers, scrim
reinforced structures, coated textiles or nonwovens,
etc.
As the bag travels through the bag machine, it
can travel with either the open or sealed end leading.
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The latter is preferred however, since the open end could
scoop up air which would be trapped causing later pro-
cessing difficulties.
~ eferring again to Fig. 1, it will be seen
that the heat sealed bag has a central zone 16. The
method of the instant invention requires that the central
zone 16 of the ~ront and back walls be held ~irmly in
order to prepare for the next operation. The front
and back walls can be held firmly or clamped by direct-
ing the bag between two feed belts of somewhat lesserwidth than the central zone 16. Thus referring to Fig. 2
it will be seen that two such feed belts are shown and
designated as upper feed belt 17 and lower feed belt 18
driven by a power source (not shown) and that the tubular
bag is directed between the two feed belts so that the
central zone 16 of the bag is clamped between the feed
; belts. ~he belts preferably have a roughened surface
to provide a more secure grip such as molded conveyor
belting and can also be optionally provided with pressure
rolls ~not shown) to increase the holding power. Various
other techniques can be utilized which can serve an
equivalent function such as power roller beds, vacuum
caps, etc. Whatever device or technique is utilized,
it should be sufficient to clamp the bag in the designated
area and also serve as a means to transport the bag
through the subsequent method steps.
As best seen from Figs. 2, 4, 5 and 6, the
bag 10 travels in between upper and lower -stationary
guides 19 and 21 respectively attached to a gusset tucker
unit and which are disposed above and below each gusset
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13 and 14. The stationary gu:ides which can be fabricated
from plastic or metal are adapted to deEine a path
conforming means corresponding to the ~laring of the
gussets towards a nominal 180 and a subsequent reolding.
The nominal 180 could be more than 180 or less than
180 depending upon the modulus and resiliency o~ the
polymers used in the bag construction; however, experi-
ments indicate no commercial materials were found
to require more than + 25 from the nominal. The opening
to the nominal 180 of the side gussets under suitable
restraint, forces the corners 22 of the sealed end lS to
adapt to the dimensional restraints and forms a "hood"
or a triangular tuck 23 disposed on each side of the bag
(Fig. 7) whereby the transverse hea~t seal 15 common
to the gussets coincides with the gusset fold lines 13A
arLd ~4A respectively. In order to aid in the outward
flaring of the gussets and to urge the gussets towards
the conforming means, i.e., upper and lower stationary
guides 19 and 21, use is made of a spxeader mechanism.
Various types of spreader mechanisms can be utilized for
the intended purpose and merely as illustrative Figs. 5
and 6 illustrate ohe such type mechanism by reference
numeral 24. The spreader mechanism illustrated in Figs.
5 and 6 is an umbrella type linkage device which can be
activated by cams or small fluid controlled devices (not
fully showlL) and is designed to travel along with the
bag during its spreading motion, i.e., the outward flaring
of the side gussets. The umbrella type linkage device is
attached to a corner tucking unit and includes member 25
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extending from support 26 and which slideably accommodates
pivot arms 27. Pi~ot arms 27 are adapted to urge plates
28 either towards or away from the confronting surfaces
of upper and lower stationary guides 19 and 21 thereby
causing gussets 13 and 14 sandwiched in between plates
28 and stationary guides 19 and 21 to follow a path
defined by the surface of ~he stationary plates. Prior
to contacting the gussets with the spreader mechanism,
however, the gussets may be "sticking to each other"
as a result of chemical interaction or electrostatic
forces caused by unwinding film from a roll, and in
order to overcome any blocking tendency of the ~ilms
it is sometimPs desirable to have a power assist to
separate the film such as a vacuum lift or an air jet.
~us, as shown in Fig. 4, air jet 30 is disposed in a
~anner such as to be capable of deli~ering a jet of air
in between the inner confronting surfaces of gussets 13
and 14 so that the inner confronting surfaces can be
sep æ ated to permit subsequent contact with the plate 28
of the spreader mechanism 24.
As the gussets are forced into their outwardly
flared position, as shown in Fig. 7, a hood or triangular
tuck 23 is formed at each lower corner of the bag. At
this point the transverse heat seal line 15 common to
the gusset and frant wall and rear wall coincldes with
gusset fold line 13A and 14A. The tuck 23 now ~ust be
held in tE~is position while the gussets are refolded
with the triangular tucks 23 sandwiched in between. As
~- shown in Fig. 7, a stationary plow 29 ~s proYLded to
hold the tuck while effecting return of the gussets to
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their original starting position. Plows 29 are mounted
~o contact each side of gusset 13 and 14 so that the
contacting edge 31 applies sl.iding press~lre to the gusset
fold lines 13A and 14A and to the heat seal line 15
which coincides with gusset fold lines 13A and l~A.
As the bag travel continues and the gussets are returned
to the non-flared condition by action of the upper and
Lower stationary plates (as shown in Fig. 7A), the re-
sultant bag, shown in Fig. 8 is produced. As will be
seen from Fig. 8, the gussets have been refolded thus
maintaining the triangular tucks or hood 23 trapped within
the gusset.
After the bag, as shown in Fig. 8., is pro-
duced, it is desirable that the bag thereafter be
directed through a creasing operation. Additionally it
i5 highly desirable to generate a transverse crease or
fold Line on the bag (in some materials also called score
line~. This transverse line should be near the widest
point of the corner tucks or at the terminal ends of the
seal. The crease or fold line could be produced by
numerous conventional devices including pressure blades
or rolls. A simple way to implement a crease or fold
line is illustrated in Figure 9 wherein a fold over of
~he bag end defines a trapezoidal bottom portion of the
bag which could be produced by a folding bar in conjunction
with a set of pressure rolls. The transverse fold line
together with the corners now defines a square bottom
bag after opening.
In a typical mode o operation and with
reference to the accompanying drawing, a tube formed from
a Length of seamless thermoplastic tubing produced by .
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an extrusion process has been sealed transversely along
the bottom edge to form a bag 10. The bag so formed on
a continuous bag mak-ing machine is directed between feed
belts 17 and 18 of somewhat lesser width than the central
zone 16 of the bag. The upper and lower feed belts serve
to clamp the bag in the central zone and direct the bag
between upper and lower stationary guides 19 and 21
respectively disposed above and below each gusset 13
and 14. The bag continues its travel with the closed
end leading and streams of air are directed towards
the gussets 13 and 14 from air jets 30 as shown in
Fig. 4 to assist in unblocking the film. As the bag
continues its travel, spreader mechanism 24 is activated
; and travels along with the bag during its spreading
motion, i.e., the outward flaring of the side gussets.
Pivotal arms 27 urge the gussets, sandwiched in between
plates 28 and stationary guides 19 and 21 toward the surface
of the stationary plates thereby initiating the flaring of
the gussets as shown in Fig. 5. As the gussets are fully
spread as shown in Fig. 6 stationary plows 29 shown in Fig.
7 apply sliding pressure along gusset fold line 13A and
14A and to the triangular tucked-in corners or hood 23 formed
by flaring the gussets as explained previously and as shown
in Fig. 6. As the bag continues its advance the gusset
folds begin to return to their original folded position
as a result of the action of stationary guides 19 and 21.
The spreader mechanism ~4 folds and returns to enter and
flare the gusset of the next bag. The bag with the
gussets refolded and the corners tucked in as shown in
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Fig. 8 continues its travel through a pair of nip rolls
or other pressure device (not shown) to form permanent
creases in the tucked-in triangles 23 of the bag. There-
after the bag proceeds to a scoring or creasing operation
transversely applied across the terminal ends o~ the seal
to orm the creases 35 and 36 for defining the periphery
of the bottom of the bag as shown in Figure 10. Alter-
natively the bag can be transversely folded at the terminal
ends of the seal to form the creases 35 and 36 for defining
the periphery of the bottom of the bag as sho~ in Fig. 9.
The bag can thereafter be directed to a conventional
palletizer or alternatively it can be directed to a con-
ventional carton folder where the bags are folded and
packed in a carton. A view o an opened bag produced
by the method of the present invention is shown in Fig. 10.
It will be obvious to those skilled in the
art that various changes may be made in the invention
without departing from the spirit and scope thereof.
Thus, the invention is not considered limited by that
which is shown in the drawings and described in the
specification and reference is had to the claims for
summaries of the essentials of the invention, novel
features of construction, and novel methods of operation,
for all of which protection i9 desired.
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