CA2143911A1 - Easy tear perforation for film roll products - Google Patents

Abstract

An improved roll of bags for dispensing handled film bags from a rolled web, and manufacturing technique. The roll has a series of individual bags joined top-to-bottom by a transverse perforated tear line disposed between a bottom bag seal and top handle seal. The improvement provides a perforated tear line including transverse slits separated by short unslit areas sufficient to permit pulling of the individual bags from a turning bag roll, the tear line extending transversely across the bag handle width and having terminal nick portions for initiating tearing.

Description

` F-7300-L 2143911 -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 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 2I~3911 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 -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 F-7300-L 21 439~1 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 F-7300-L 21 ~ 39I l 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 F-7300-~ 21~3911 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 ~ F-7300-L 21~3911 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.

Claims (7)

1. A method for forming ungusseted handle-containing bags, comprising:
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 form a transverse line of weakness between each pair of seals;
d) simultaneously or thereafter folding the marginal edges of said tube inwardly toward each other; and e) forming and removing a cut-out region at one end of each sealed segment of said tube so that on removal of said cut-out region, the cut defines loop handles and a bag mouth region in each bag, wherein said tear line includes tear-initiating nick portions at opposite sides of each loop handle.

2. The method of claim 1, wherein said continuous collapsed tube is produced by extruding a polymeric material selected from the group consisting of low density polyethylene, high density polyethylene, linear low density polyethylene and blends thereof.

3. A thermoplastic bag structure produced in accordance with claim 1.

4. A method for forming handle-containing bags in roll-form comprising:
a) forming a continuous collapsed tube;
b) forming pairs of closely spaced seals transverse to said tube at bag length distances apart;
c) forming a perforated line of weakness between each pair of seals having at least one nick portion for initiating tearing alone the perforated line;
d) simultaneously or thereafter folding the marginal edges of said tube inwardly toward each other;
e) forming and removing a cut-out region at one end of each sealed segment of said tube so that on removal of said cut-out region, the cut defines loop handles and a bag mouth region in each bag;
f) again folding the marginal edges of said tube inwardly toward each other; and g) convolutely winding the structure to form severable bags on a roll.

5. The method of Claim 4 wherein in each of said loop handles has at least one nick portion.

6. The method of Claim 5 wherein each loop handle has two nick portions disposed at opposite ends of the perfortion line for each handle.

7. 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 which comprises: a perforated tear line including transverse slits separated by short unslit areas sufficient to permit pulling of the individual bags from a turning bag roll;
said tear line extending transversely across the bag handle width and having terminal nick portions for initiating tearing by skewed tension motion.