Note: Descriptions are shown in the official language in which they were submitted.
i245090 ,
METHODS FOR PREPARI NG FLAT-BOTTOM
TE~ERMOPLASTIC SACR AND ~YSTE~IS T~EREFOR
The present invention relates to methods and
systems for preparing a thermoplastic sack, and, more
particularly, to methods and systems for preparing such a
sack having at least a substantially flat rectangular
bottom.
Such a bag structure comprises front and rear bag
walls connected by gusseted side walls. The bag has an open
mouth top portion, which is characterized by having handles
located at opposite end regions thereof, said handles each
being of two films as a result of being integral extensions
of the front, rear and gusseted side walls. The bag has a
bottom wall planarly extensible so as to form a rectangle
with at least no substantial excess film outside of the bulk
volumetric capacity of the bottom region of said bag. An
alternative manner of describing the bottom of such a bag is
that the bottom is formed from integral extensions of the
front, rear and side walls and the closure thereof is 4 two-
film gusset-to-wall heat seals, when the bottom has a square
configuration, and 4 two-film gusset-to-wall heat seals and
1 two-film front wall-to-back wall heat seals when the
bottom has a rectangular configuration. The present
invention also contemplates forming the same type of bag
without handles.
- 2 - ~45090
The present invention is concerned with the method
and system for preparing a handled, at least substantially
flat, rectangular bottom, thermoplastic film sack
comprising:
(a) forming a tube of a thermoplastic film;
(b) collapsing said tube while simultaneously
forming therein two, oppositely disposed, parallel gussets;
(c) opening, simultaneously or spatially
sequentially, a gusset fold on each side of said collapsed
tube, to their full lay-flat extent;
(d~ simultaneously or spatially sequentially
forming in each of the four gusset folds, a diagonal sealed
seam over the portions of the tube width corresponding to
the gussets along lines diagonal to the length of the tube
so that the ends of the sealed seams of adjacent gusset
folds are at least closely spaced or in contact so as to
form an angle therebetween of at least approximately 9~%;
(e) returning said gusset folds to their original
position so that their seal-pairs are superimposed;
(f) forming a transverse seal and severing seam
across and through said collapsed tube along a line which
includes the inboard ends of said pairs of diagonal seams;
(g) collecting a plurality of the resulting
structures in a stack;
(h) removing from each structure the four folded
triangles of film located between the diagonal sealed seams
~ 3 ~ 12~5~9~
and the transverse sealing and severing seams to complete
the bottom of the sack; and
(i~ forming a pair of handles and a sack mouth
opening at the opposite end of said sack bottom. For a pack
of such bags a tab member is provided as an integral
extension of the bag mouth opening and each tab member has a
pre-weakened region, such as perforations therein, so that
when all tabs are fastened together, individual bags may be
detached from the tab structure.
The present invention is also concerned with a
method and system for preparing a handleless, at least
substantially flat, rectangular bottom, thermoplastic film
sack comprising:
(a) forming a tube of thermoplastic film;
(b) collapsing said tube while simultaneously
forming therein two oppositely disposed, parallel, gussets;
(c) opening, simultaneously or spatially
sequentially, a gusset fold on each side of said collapsed
tube to their full lay-flat extent;
(d) simultaneously or spatially sequentially
forming in each of the four gusset folds, a diagonal sealed-
seam over the portions of the tube width corresponding to
the gussets along lines diagonal to the length of the tube
so that the ends of the sealed seams of adjacent gusset
folds are at least closely spaced or in contact so as to
form an angle of at least approximately 9~;
(e) returning said gusset folds to their original
position so that their seal-pairs are superimposed;
- 4 ~ 1 Z ~5~90
(f) forming a transverse sealed seam across said
tube along a line which includes the inboard ends of said
pairs of diagonal seams and simultaneously forming a pre-
weakened transverse line closely adjacent and parallel to
said transverse sealed seam;
(g) removing the four double film triangular
regions bounded by said diagonal seams, said transverse
seams and the side edges of said tube; and
(h) collecting the resulting structures while
still interconnected at said pre-weakened transverse lines.
Another method according to the present invention
involves continuously preparing a handleless, at least
substantially flat, rectangular bottom, thermoplastic ~ilm
sac~ comprising:
(a) forming a tube of thermoplastic film;
(b) collapsing said tube while simultaneously
forming therein, two oppositely disposed, parallel, gussets;
(c) opening, simultaneously or spatially
sequentially, a gusset fold on each side of said collapsed
tube to their full, lay-flat extent;
(d) simultaneously or spatially sequentially
forming in each of the four gusset folds, a diagonal sealed
seam over the portions of the tube width corresponding to
the gussets along lines diagonal to the length of the tube
so that the ends of the sealed seams of adjacent gusset
folds are at least closely spaced or in contact so as to
form an angle therebetween of at least approximately 90%;
~L~9L5B9~3
(e) returning said gusset folds to their original
position so that their seal-pairs are superimposed;
(f) forming a transverse sealed seam across said
tube along a line which includes the inboard ends of said
pairs of diagonal seams and simul~aneously severing said
tube along a line parallel to said transverse sealed seam;
and
(g) removing the four double film triangular
regions bounded by said diagonal seams, said transverse
sever line and the side edges of said period.
In the drawings appended to this specification:
Figure 1 is a plan view, in schematic form,
illustrating a system and process sequence of one form of
the present invention; and
Figure 2 is a plan view of another form of the
process and system oE the present invention.
As shown in Figure 1, there is illustrated a
system and process sequence 50 for forming a handled,
gusseted flat-bottomed thermoplastic sack. A hollow
cylinder or tube of thermoplastic film 12 is collapsed by
being passed through a combined gusset forming and gusset
opening means 14. This device can be of any construction
which accomplishes the steps of collapsing the tube, forming
oppositely disposed gussets therein and opening one fold of
each gusset to the maximum so ~hat they are spread open in a
lay-flat position. By this is meant, that the gusset, which
normally is folded upon itself at an acute angle approaching
- 6 ~ 5~9~
0, is opened by flipping or turning one of the folds over
so that the gusset lays flat at an angle approaching 180~
Depending upon the size of the gussets, this step can be
accomplished simultaneously. If both gussets are small
enough, they can be opened completely side-by-side in a lay-
flat position. As the gusset depth increases only one
gusset fold can be opened at a time. As shown in Figure 1,
and as suggested by the mid-fold line 16, both gussets were
opened completely by the gusset forming and opening means
14. In a situation where the gussets are too large to be
able to be opened side-by-sider they can be opened spatially
sequentially. By this is meant, first one gusset will be
opened as the tube progresses means 14 and at a point
downstream in the system, after the first gusset returns to
its closed position, the opposite gusset will be opened by
an equivalent means to the lay-flat position. As indicated
above, device 14 can be a sheet-metal device which has an
entrance side for receiving a flexible tube of cylindrical
film. Sheet metal plates therein cause an infolding or
gusset to be fashioned in the structure as the tube passes
therethrough. The exit dimension progressively diminishes
to present a fully collapsed gusseted tube. This device
contains turning plates or rolls so that after the gusset is
formed, the upper fold is progressively opened until it
assumes a lay-flat, 180 position.
The gusset or gussets are opened so that a pair of
diagonal sealed seams can be impressed in each of the four
~Z45~9(:~
-- 7 --
gusset folds as shown at 20. This is a~complished by means
of a heat-sealing member 18 which includes ~Teflon" -coated
resistance wires heated to a temperature which will permit
the two layers of each of the four gusset folds to be heat
sealed together. The diagonal sealed seams extend over the
portions of the tube width corresponding to the gussets
along lines diagonal to the length of the tube. The seal-
pairs of each gusset in the lay-flat position form an angle
of approximately 90 to one another. Thereafter, a gusset
closing device 22 flips or turns the open gusset and folds
it back to the closed position so that the angle there-
- between again approaches 0. In this position the sealed
seams 20 of each gusset are superimposed and in registration
with one another.
As the collapsed tube with its seals 20 progress
through the system, there subsequently is formed a bottom
seal 24 which simultaneously seals and severs the bottom of
the gusseted structure. This is accomplished by means of
bottom sealing and severing device 26. Seal line 24 is a
transverse sealing and severing seam which extends across
and through the collapsed tube along a line which includes
the inboard ends 28 of each pair of diagonal seams.
Transverse sealing and severing device 26 can be any
suitable means which will bond and sever the collapsed tube
along the defined line. This sealing and severing action
will isolate sack blank 30 from the collapsed and gusseted
tube. Sack blan~ 30 will have a seal 32 across the top
thereof and the four triangular regions 34 will be bounded
*Trademark of DuPont for polytetrafluoroethylene resin.
1245&9(~
by seal lines 20, 24 and the side edge of the gusseted
structure.
The sack blank structures 30 may be separately or
collectively converted into bag structures by removal of the
triangular regions 34 and by the formation of bag mouth
opening 36 which simultaneously forms handle loops 38, each
of which are formed of two layers of film by virtue of the
gusseted structure. This will complete the formation of a
handled sack, the bottom of which can be planarly extended
so as to have a flat bottom. sy "planarly extended" is
meant that the bag is extended in internal volume to its
utmost by expanding the gussets fully, thereby forming a
flat-bottom, rectangular in nature, having a length larger
than its width.
In a preferred embodiment of the process and
system illustrated in the drawing, a linear low density
polyethylene tubular film 12, of about one mil in thickness,
is collapsed and simultaneously gusseted with the gussets
then opened fully to approximately 180 as the tube passes
through the gusset forming an opening means 14. As the
gusseted tube progresses through the system, seals 20 and 24
are simultaneously formed. This action produces bottom seal
24 and top seal 32 at the same time. This step also
isolates sack blank 30. Sack blank 30 can then be removed
to a station which can separately or simultaneously remove
triangular sections 34, form bag mouth opening 36 and form
handles 38. This can be accomplished on individual blanks
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or alternatively, blank 30 can be stacked in vertical
registration and, through the means of a suitable cutting
die mechanism, the triangular regions removed and the handle
and bag mouth opening can be formed.
For the formation of bags which do not contain a
handle, the process and system is as shown in ~igure 2. The
process and system 50a is different from that of Figure 1,
beginning at the point where the bottom of the bag is
sealed. Thus, a bottom seal and perforating mechanism 40 is
shown impressing seal-seam 42 in the flattened gusseted tube
and, simultaneously therewith, perforation line 44 is formed
closely adjacent and parallel to seal line 42. Seal line 42
does not sever the tube, merely seals it. Seal line 42 and
perforation line 44 are impressed in the gusseted tube at
the same time diagonal seals 20 are impressed into the
opened gussets in the next succeeding gusseted tube
structure. Thereafter, by any suitable die cutting
mechanism, the four triangular regions 46 are removed from
the structure. This will yield sack 48 attached by
perforation line 44 to a like structure. Thereafter, these
sacks may be rolled upon themselves to form a cylindrical
package or collected in a zig-zag folded stack arrangement.
Either structure will permit a sack to be torn free along
the perforation lines to yield an open mouth bag which when
extended fully to the total width of the gusset, will yield
a flat-bottomed sack. Instead of rolling or folding this
structure, each bag may be automatically separated at the
perforation line and folded or stacked. The sack resulting
1245(~90
from the process and system of Figure ~ will have a
rectangular bottom with a length larger than its width.
In a modification of the process and system shown
in Figure 2, open mouth handleless structures can be formed
by forming a severance transversely across the tube at the
same time the bottom seal 42 is formed. Thereafter, the
corners of the sack blank corresponding to regions 46 can be
severed to complete the bag structure.
As disclosed, the bag structure formed by the
system and process illustrated in Figures 1 and 2 will yield
a sack having a rectangular bottom when planarly extended,
which bottom will have a length longer than its width. In
other words, the sack bottom will not be a square. In order
to form a square bottom sack either with or without handles
the process and means merely need be modified so that the
gusset folds are both infolded to a maximum. That is, the
collapsed tube will be gusseted to the longitudinal mid-line
of the tube. In this case the center-fold of each gusset
will contact the other and the angle between the therearter
formed diagonal seams will be at least about 90. The
resulting sack will then have a substantially flat square
bottom when planarly extended.
Bags of the structures described can be formed
with a pair of registered tabs as integral extensions of the
bag mouth opening as shown at 39 in Figure 1. The bags can
be stacked in registration to contain 50, 100, 150, etc.,
bags and the tabs 39 fastened together in some suitable
2~5~9~
manner. For example, the tabs can be ultrasonically welded
together. A perforation line across the tab will form a
convenient tear-off site for individual bags to be removed
from the bag pack~
Bags of the structures described can be formed by
employing any suitable thermoplastic material, for example,
polyolefins. In employing the term "polyolefins" it is used
generically to include all forms of the polymer species,
including, for example, low density polyethylene, linear low
density copolymers of ethylene and another olefin, high
density polyethylene, mixtures and blends of the same, and
other monomer counterparts, etc. Thermoplastic coated paper
stock is also contemplated. The bag film can be of any
gauge, for example, from about 0.3 to about 5 mils in
thickness.
In forming the flat-bottomed bag, it is preferred
that the angle between the diagonal seal line and the bottom
seal be at least approximately 135 when said bag is in its
lay-flat conditionO It is also preferred that the open
mouth portion of the handled sacks of the present invention
have stress relief curves or arcs extending from the base of
the handle to a raised portion of the bag mouth. This will
militate against splitting or tears occurring in the bag
mouth during handle extension or when the bag is being
filled with bulky material. The handles and bag mouth
opening can have any configuration.
In forming the bag structure, the pertinent angles
need not be precise. For example, they need not be exactly
12 - 1245~9~
90, 45, or 135. Reasonable processing latitude should
permit some deviation from these guidelines. Likewise in
forming seal seams, the ends thereof can be curved or angled
in order to accommodate or insure good closure at all film
interfaces and joints. Double or plural line seams and
seals also can be employed.
