Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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EASY TEAR PERFORATION FOR FILM ROLL PRODUCTS
Background of the Invention
This invention relates to thermoplastic handled sacks,
5 dispensed from a roll pack, and a method for separating
individual sacks from the roll.
Handled thermoplastic sacks are well known and find
increasing use as grocery sack and the like. A common type of
thermoplastic handled grocery sack is one made from a gusseted
10 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) discloses a
conventional thermoplastic bag structure comprising a front and
15 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 extension
20 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
25 opening and handles at one end thereof. The resulting bag is
an ungusseted bag which can be unitized into a pack by providing
a detachable, unitizing tab at the bag mouth opening.
U.S. Patent No. 4,790,437 (Pistner) teaches a method
for forming a thermoplastic film handled bag comprising: forming
30 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 towards each other until they meet at a common center
line, folding the structure once again in the same direction
35 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
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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.
Roll packs are commonly employed in dispensing thin film
S 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 typical bag
rolls are difficult to separate by tearing a conventionally
perforated line.
Tear strength of perforated webs depends on both the web
material properties and the perforation design. A particular
perforation design includes an arrangement of cut portions and
a non-cut portion of web material. This invention pertains to
a particular perforation design that reduces the perceived tear
15 strength of perforated webs but retains the in-process stretch
of perforated webs.
Summary of the Invention
The present invention is directed to an improvement
20 in a roll of bags for dispensing handled film bags from a rolled
web having a series of individual bags joined top-to-bottom by
a transverse perforated tear line of film disposed between a
bottom bag seal and top handle seal. The improvement compises:
a perforated tear line including transverse slits separated by
25 short unslit areas sufficient to permit pulling of the
individual bags from a turning bag roll. The tear line extends
transversely across the bag handle width and has terminal nick
portions for initiating tearing by skewed tension motion.
In a preferred embodiment, the bag roll is made by
30 continuously forming ungusseted handle-containing bags from
thermoplatic blown film. This manufacturing process includes
the steps of: a) forming a continuous collapsed tube;
b) forming pairs of closely spaced seals transverse to said tube
at bag length distances apart; c) perforating a tear line to
35 form a transverse line of weakness between each pair of seals;
d) folding the marginal edges of said tube inwardly toward each
other; and e) forming and removing a cut-out region at one end
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of each sealed segment of the tube so that on removal of the
cut-out region, the cut defines loop handles and a bag mouth
region in each bag, wherein the tear line includes tear-
initiating nick portions at opposite sides of each loop handle.
5 Advantageiously, the collapsed tube is produced by extruding a
polymeric material , such as low density polyethylene, high
density polyethylene (HDPE), linear low density polyethylene
(LLDPE) and blends thereof.
Brief Description of the Drawings
Reference may now be had 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 regions and integral bag
handles of Fig. 3 with opposite sides again folded equally
inwardly;
Fig. 5 presents the Fig. 4 embodiment in roll form, in
25 accordance with the present invention;
Fig. 6 is a single detached bag fully unfolded to show the
handles and bag mouth regions of a bag; and
Fig. 7 is a detailed plan view of a handle area and
adjoining bag bottom attached on a roll.
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
35 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
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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
5 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 polyethylene,
10 generically and, specifically, low density polyethylene, high
density polyethylene, including high molecular, high density
polyethylene, linear low density ethylene copolymerized with a
C3-C8 alpha olefin and blends and coextrusions of these
materials. In addition, the polyethylenes can be blended with
15 certain aromatic polymers in order to impart special desirable
physical characteristics thereto. For example, linear low
density polyethylene can be blended with up to about 10% by
weight of polystyrene or poly(paramethylstyrene). A specific
example of a commercially available polyethylene material
20 suitable for use in the present invention is a linear low
density ethylene copolymerized with from about 2 to about 7 wt.
% of octene-1.
This linear low density ethylene-octene-1 copolymer, i.e.,
LLDPE, is melt extruded through an annular orifice and blown up
25 to a tube which will have a lay flat diameter of approximately
24 inches. This tube is then collapsed and formed into heat-
sealed segments approximately 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.
30 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
35 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
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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
5 severed with relatively little force. This technique is
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
10 desired handles. Employing a lay-flat tube having a side-to-
side dimension of approximately 24 inches, the individual handle
widths can range anywhere from about 4 to 8 inches, preferably
from about 5 and 1/2 to 7 inches. When it is desired to produce
a trash ca~ liner product, the side-to-side dimension of the
15 lay-flat tube will be approximately 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
20 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).
25 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
30 between the handles, this portion can be returned for recycle
as usable resin material.
Referring still 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
35 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
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along bag mouth line 30 to concentrate at points below this
line. Thus, stress forces will literally extend through 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-containing 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
10 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 maximum use of the potential volume of the
original collapsed cylinder. As may be appreciated, the
15 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 single handled bag of the present
invention. The preferred large volume bags of the present
invention will find utility in a wide variety of both home and
20 industrial applications, including the disposal of leaves and
yard refuse, garbage, debris, etc. Advantageously, upon being
filled, the handles 34 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
25 provides excellent leak resistance.
A preferred embodiment of the invention is depicted in Fig.
7 wherein a handle portion 32 of a bag is shown attached to the
adjoining bottom portion of the next bag on the roll. The
handle seal 12A is separated from bottom seal 12B by a
30 transverse weakened portion 14 shown as a linear series of
performations or slits extending across the bag member. At
least one extended edge perforation or nick 14A is cut in the
perforation line 14 for the purpose of initiating the tearing
action.
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 (similar to toilet tissue). The
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perceived strength of the perforated material depends on the
angle the consumer uses to tear the material. The greater the
tear angle the less the perceived strength. Consumers have
attached a value to easy tear perforation.
In the processing of bags on a roll, the strength of the
perforated web (in-process strength) is proportional to the
ratio of the non-cut vs. the cut material in a perforation unit
(a cut portion is adjacent to a non-cut portion). The
perforation strength determines the frequency that the web will
10 break during processing and the tightness (density) of the roll
of product. Both of these factors translate directly to product
cost.
The perceived strength of the perforation can be reduced
by pre-cutting the first few non-cut portions of the perforated
15 material. The pre-cut section may be called a nick. The length
of the nick determines the initial tear angle. As mentioned
above, the initial tear angle determines the perceived
perforation tear strength. This alteration to the perforation
design has no effect on the in-process perforation strength
20 since the ratio of non-cut vs. cut length in the perforation
unit is not changed. 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 eight right-hand or left-hand
skewed tension. Thus, the tear initiation can be facilitated
25 from either direction on both handles.
The resulting perforation design allows separate control
of the in-process perforation strength and the perceived
perforation strength within limits. The ratio of non-cut vs.
cut in a perforation unit determines in-process perforation
30 strength. The nick length determines perceived perforation
strength. The optimum perforation design for trash bags on a
roll is a nick on each side of the folded web with perforation
units in between the two nicks. Each nick should be equal in
length to two or more perforation units.
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
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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.
