Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2196414
DIE-CUT T~ERMOPLASTIC BAG ~IT~ EASY OPEN MOUT~
FIELD OF THE INVENTION
This invention relates to flexible thermopla-stic handled
sacks, such as bag products dispensed from a roll pack, and a
method for separating a blocked, die-cut film bag mouth to
provide easy opening.
BACKGROUND OF THE INVENTION
Handled thermoplastic sacks are well known and find
increasing use as grocery sacks, refuse bags and the like. A
common type o~ thermoplastic handled grocery sack is one made
from a gusseted tube sealed at the top and the bottom with a
suitable bag mouth and handle cutout, which yields a double
layer of film in the handled region.
U.S. Patent No. 4,562,925 (Pistner), incorporated by
reference, discloses a conventional thermoplastic bag
structure comprising a front and rear bag wall, a bottom and
an open mouth top portion, the open mouth portion being
characterized by having two pairs of single film handle loops
each of which are located at opposite ends of the open mouth
portion, the handles of each pair being side-by-side and each
handle is an integral single film loop e~tension of the front
and rear bag walls. The bag structures can be unitized by
providing a detachable tab at the bag mouth opening and
unitizing the bag structures through this tab. The method of
forming the bags involves providing an end sealed collapsed
thermoplastic film tube and removing plastic to form a bag
mouth opening and handles at one end thereof. The resulting
bag is an ungusseted bag which can be unitized into a pac~ by
providing a detachable, unitizing tab at the bag mouth
opening.
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U.S. Patent No. 4,790,437 (Pistner), incorporated by
reference, teaches a method for forming a thermoplastic film
handled bag comprising: forming a continuous collapsed
thermoplastic tube having heat seal lines across the width of
the tube at bag length intervals, longitudinally folding
opposite sides of the heat sealed tube equally to~ards each
other until they meet at a common center line, folding the
structure once again in the same direction along the center
line and removing eight film layers in one of the corner
regions defined by a heat seal line and the spine of the
common center line fold, the film removal yielding a bag
mouth opening and single loop handles at near the opposite
ends of the bag mouth opening. Interconnected bags can be
formed into a roll pack.
In US Patent 4,846,349 (Galimberti~, incorporated by
reference, a method is shown for producing bags on a
continuous roll, starting with collapsed tubular film
material. The production method provides for forming
longitudinal folds with transverse welds forming top and
bottom bag lines. A die cuts multiple layers of plastic film
to create handle and mouth portions, and waste material is
removed from the die-cut plastic.
Such roll packs are commonly employed in dispensing thin
film plastic bags, usually by including a transverse line of
weakened material, such as by perforating the roll or web
between individual bags. It has been found, however, that
adjacent film layers of typical die-cut bags are difficult to
separate. Although die-cut polyolefin film can be fabricated
into handled bags at line speeds greater than 150 cycles per
minute using conventional smooth~ die cutting, this operation
tends to block the individual film layers together, rendering
the bag mouth difficult to open manually. Non-blocking film
cutting techniques, such as reciprocal serrating, are
significantly slower than die cutting.
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Summary of the Invention
The present invention is directed to an improvement in
handled thermoplastic bag manufacture, wherein the bag is
formed by die cutting a multiple film bag structure to form a
central mouth portion and integral handles at lateral
portions of a collapsed tubular film. Opening of the bag
mouth is facilitated by providing a central mouth portion
with roughened edges to obviate film blocking.
In the preferred embodiment, an improved roll of
flexible thermo~lastic bags is-provided for dispensing
handled film bags. The product is made from a rolled
collapsed tube web having a series of individual bottom-
sealed bags joined top-to-bottom by a transverse perforated
tear line of film disposed between the bottom bag seal and a
pair of lateral loop handles disposed on opposite sides of a
U-shaped bag mouth.
The improvement comprises an easy-open bag mouth having
opposing major inside edge portions die-cut from adjacent bag
walls formed by the collapsed tube of thermoplastic film and
forming the inside edges of the lateral handles; and a minor
bag mouth edge portion centrally located between the opposing
major edge portions, said minor bag mouth edge portion
comprising a torn perforation line formed by tearing scrap
thermoplastic film from the die-cut bag mouth. This
technique provides a series of torn film edge discontinuities
in the perforated minor bag mouth edge portion to facilitate
separation of blocked adjacent film layers during opening of
the bag mouth.
Advantageously, the collapsed tube is produced by
extruding a polymeric material , -~uch as low density
polyethylene, high density polyethylene (HDPE), linear low
density polyethylene (LLDPE) and blends thereof. -
Brief Description of the Drawinqs
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Reference is made to the following detailed
description of exemplary embodiments of a layflat plastic bag
with integral handles in accordance with the present
invention, taken in conjunction with the accompanying
drawings; in which:
Fig. 1 is a plan view of a collapsed thermoplastic tube;
Fig. 2 is a plan view of the sealed tube of Fig. 1 with
opposite sides folded equally inwardly;
Fig. 3 is a plan view of the folded sealed tube of Fig. 2
having cut out portions to produce bag mouth regions and
integral bag handles for a plurality of bags;
Fig. 4 is a plan view of the folded sealed tube having cut
out portions to produce bag mouth and integral bag handles
of Fig. 3 with opposite sides folded equally inwardly;
Fig. 5 presents the Fig. 4 embodiment in roll form;
Fig. 6 is a plan view of a single detached bag fully unfolded
to show the handles and bag mouth regions of a bag; and
Fig. 7 is an enlarged view of a portion of the bag mouth.
Detailed Description of the Invention
It is well known in the plastics art to continuously
melt extrude thermoplastic resin through an annular orifice,
apply internal fluid pressure to the tube thus extruded and
thereby expand the tube and reduce the wall thickness thereof
to appropriate dimensions while cooling and solidifying the
extruded thermoplastic film. This technique and any
equivalent technique of forming a thermoplastic film tube,
can be employed in providing the starting material for the
bags and bag packs of the present invention.
- The contemplated thermoplastic film can be of any type
having the characteristics necessary for a handled bag which
will be required to carry items totaling up to about 45 lbs.
or more. While not limited to the polyolefins, these
materials have proven in the past to be excellent films from
which bags can be made. Preferred materials include
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polyethylene, generically and, specifically, low density
polyethylene, high density polyethylene, including high
molecular, high density polyethylene, linear low density
ethylene copolymerized with a C~-C8 alpha olefin and blends
and coextrusions of these materials. In addition, the
polyethylenes can be blended with certain aromatic polymers
in order to impart special desirable physical characteristics
thereto. Linear low density polyethylene can be blended with
up to about 10% by weight of polystyrene. Suitable examples
of a commercially available polyolefin material suitable for
use in the present invention include high density homopolymer
polyethylene (HDPE) or linear low density polyethylene
(LLPDE), which comprises ethylene copolymerized with from
about 2 to about 7 wt. % of octene-l. The polyolefin is melt
extruded through an annular orifice and blown up to a tube
which will have a lay flat diameter of approximately 60 cm
(24 inches) and single film thickness of about 10 to 20
microns (0.4-0.8 mil). This tube is then collapsed and
formed into heat-sealed segments approximately 90 cm. (36
inches) long. This will produce what is known as a sealed
"pillowcase" 10 as shown in Fig. 1. The sides 26 are
seamless and the ends 12 are heat-sealed. Heat-seal 12
constitutes a thermal merging of the two films of the
collapsed tube. The seals 12 can be made so that they
simultaneously seal and sever through the films or the seals
may be made not to sever through but merely weaken the region
adjacent to line 12 so they may be subsequently severed with
comparatively little force. As depicted in Fig. 1, another
technique which is particularly preferred is to provide pairs
of relatively closely spaced heat seals 12, the spacing
generally on the order of about one-half to one inch between
individual heat seals 12. Advantageously placed between the
pairs of heat seals 12 is a transverse line of weakness or
perforation line 14 effective to permit individual bags to be
severed with relatively little force. This technique is
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preferred because the next step of the method of the present
invention requires that the seamless sides of the tube 26 be
folded over in a continuous process, as shown at 16 of Fig.
2. The degree of foldover is related to the ultimate width
of the desired handles. Employing a lay-flat tube having a
side-to-side ~i~Dnsion of approximately 60 cm, the individual
handle widths can range anywhere from about 10-20 cm,
preferably from about 12-18 cm. When it is desired to
produce a trash can liner product, the side-to-side dimension
of the lay-flat tube will be approximately 75 cm (30 inches).
Referring now to Fig. 3, in forming the bags
contemplated by the present invention, the side-folded,
sealed and perforated structures, shown in Fig. 2, are
serially provided with cut-out regions 18 by the use of a
suitable cutting mechanism, the handles and bag mouth opening
thus formed by the removal of plastic film from cut-out
region 18. As may be appreciated by those skilled in the
art, it is necessary, in order to create the carrying handles
of the present invention, to open the upper left and right
sides of the structures as at 32 (see Fig. 6). This is
uniquely accomplished by having the side-folded regions 18
extend far enough into the cut-out region 18 for each bag.
As shown, the cutting member which thus remove a hand-
accommodating slice from each pillowcase structure to yield
openings at 32. As with the portion removed from the region
between the handles, this portion can be returned for recycle
as usable resin material.
Referring again Fig. 3, it should be appreciated that a
preferred embodiment of the present invention includes the
use of a handle/bag mouth cutout of a more complex design.
The handles and bag mouth opening show that at the base of
the handles there are stress relief regions 28 which function
to cause stress forces which ordinarily would be brought to
bear along bag mouth line 30 to concentrate at points below
this line. Thus, stress forces will literally extend through
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the film space between the bottoms of the arcs of stress
relief regions 28. As indicated above, the preferred handled
bags of the present invention are relatively large bags.
Referring now to Figs. 4 and 5, in forming handle-
cont~ ~;ng bags in roll-form, such as is illustrated in Fig.
5, the marginal edges of the tube are once again folded
inwardly toward each other to form folded regions 20. Then,
the twice folded tube structure is convolutely winded to form
severable bags on a roll 22.
As may be seen by reference to Fig. 6, a bag of the
present structure makes ~x;mum use of the potential volume
of the original collapsed cylinder. The subsequent severing
of an individual bag 24 and the unfolding of the folded over
regions 20 (see Fig. 4) and 16 (see Fig. 2), ultimately yield
the handled bag of the present invention. The die-cut mouth
has a relatively short central portion having a discontinuous
edge segment (see enlarged view Fig. 7) adapted for easy
manual opening. The opposing handles 32 and side portions 31
of the bag mouth are preferably smooth die-cut.
The preferred large volume bags of the present invention
will find utility in a wide variety of both home and
industrial applications, including the disposal of leaves and
yard refuse, garbage, debris, etc. Advantageously, upon
being filled, the bag handles may be tied together to close
the bag, eliminating the need for bag ties of the type
typically employed. The ungusseted construction of the bag
bottom provides excellent leak resistance.
In preferred embodiment of the invention, the handle
portion of a bag. The handle seal is separated from the
adjacent bottom seal by a transverse weakened portion formed
as a linear series of uniform perforations having
predetermined slit length and extending across the bag
handles. At least one extended edge perforation or nick is
cut in the perforation line at the handle edges for the
purpose of initiating the tearing action.
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Bags held together by perforations wound on a roll are
dispensed by the consumer one at a time by un-rolling and
tearing the perforation lines adjacent the bag handles. By
placing nick portions in the tear lines across each bag
handle at opposite sides, each handle may be torn from the
adjacent bag by skewed tension. The ratio of non-cut vs.
slit cut in a perforation line determines in-process
perforation strength.
Referring to Fig. 7, an enlarged segment of the bag
mouth portion 130 is depicted prior to removal of die-cut
scrap 118. A minor bag mouth edge portion is provided
centrally located between the opposing major smooth die-cut
edge portions 131 between the bag handles for ease of
separation. This minor bag mouth edge portion 130 comprises
a perforation line having a uniform series of slits 136 of
predetermined length (ie - about 0.5 to 2 cm.) and ratio (ie -
S:l to 20:1) to alternating uncut land portions 138. Theland portions 138 result in a spaced series of small tabs
formed by tearins scrap thermoplastic film 118 from the die-
cut bag mouth 130; thereby providing a series of torn film
edge discontinuities in the perforated minor bag mouth edge
portion to facilitate separation of blocked adjacent film
layers during opening of the bag mouth.
Although the present invention has been described and
exemplified with respect to preferred embodiments, it is to
be understood that modifications and variations may be
utilized without departing from the spirit and scope of this
invention. Such modifications and variations are considered
to be within the purview and scope of this invention.
