Manufacturing container or tube from paper; or other manufacturi – Container making – Pliable container
Reexamination Certificate
1997-10-14
2001-07-03
Vo, Peter (Department: 3721)
Manufacturing container or tube from paper; or other manufacturi
Container making
Pliable container
C493S238000, C493S248000, C493S226000
Reexamination Certificate
active
06254520
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and apparatus for the manufacture of plastic bags, e.g., for use as bin liners.
2. The Prior Art
It is well known to manufacture plastic bags from a continuous tube of extruded polyethylene. The extruded tubing is expanded to reduce the thickness of the polyethylene film, flattened, heat sealed and severed across the width of the tubing, such that the heat seals form the bottoms of the bags. Handles can be formed by removing an upper central section of the bags, and by providing a series of transverse perforation lines rather than severing the tubing, a series of bags which an be wound into a roll may be produced. In order to reduce the width of the rolls of bags, an to reduce the size of the machinery required for the bag manufacture, it is known to fold the sides of the tubing inwardly to form gussets prior to sealing. It is also known to fold the gusseted tubing prior to sealing as described in GB-A-1584746, which enables an especially strong seal to be produced. However, this folding method is not suitable for the manufacture of rolls of interconnected bags formed with hands, as the folding operation superimposes the handles at the same side of the folded tube, and the resulting string of bags cannot be satisfactorily wound into a roll. Handles at the open end of a bag are often desirable for tying closed the bag after it has been filled, e.g., with refuse, or to facilitate carrying the bag.
GB-A-2 274 446 addresses the drawbacks of the aforementioned folding method by providing a bag having laterally opposed gusseted side portions folded about longitudinal fold liens onto opposite sides of a medial portion.
The method of bag folding described in GB-A-2 274 446 secures the advantage of a strong base seal. It also enables manufacture of a bag with handles that, in its folded form, is considerably narrower than previously known bags with handles, and the handles of the folded bag may be located at laterally opposed sides of the bag which is desirable when a string of bags is to be wound into a wall.
SUMMARY OF THE INVENTION
The present invention relates to an improved folding method and it provides a method of manufacturing a bag from layflat tubing comprising steps of first folding the longitudinal edges of the tubing to form inwardly extending gussets, further folding the flattened gusseted tubing to reduce the tubing's width, transversely sealing the folded and gusseted tubing to form a base seal, and forming handles between the folding operations by removing a central section of the gusseted tubing and by transversely sealing the tubing at a position corresponding to the ends of the handles, characterised in that the gusseted portions are folded successively about respective longitudinal fold lines to lie against opposite sides of a medial portion of the tubing between the gusseted portions.
In the preferred method the gusseted portions are each folded by passing the flattened tubing over a discrete arcuate folding ramp having a lateral edge around which the gusseted portion is folded, nips are provided upstream of and downstream of each folding ramp, the tension of the tubing as it passes over the folding ramp is controlled by adjusting the relative speed of the nips, and the orientation of the nips is adjusted to maintain a substantially uniform tension across the width of the tubing as it passes over the folding ramp. The adjustment of the orientation of the nips allows satisfactory folds to be achieved despite the asymmetry of the two stage second folding process.
Although the order in which steps of removing the central section of the gusseted tubing and sealing the tubing at the position corresponding to the ends of the handles are performed is readily interchangeable, it has been found that the bag manufactured process is easier to control when the tubing is transversely sealed at the position corresponding to the ends of the handles before the central section of the gusseted tubing is removed.
Further in the preferred method, a series of bags are formed from a continuous length of layflat tubing, the handles on one bag being connected to the base of the next bag, and a transverse line of weakness is formed between adjacent base and handle seals to facilitate separation of individual bags, said line of weakness being produced after folding of the two bag joined at the line of weakness has been completed. By providing the transverse line of weakness, e.g., a row of perforations, after the tubing is folded, the tubing can be subjected to greater tension during folding than would otherwise be possible, and hence the speed of the tubing and the rate of production of bags can be increased.
The present invention also provides apparatus for manufacturing a series of bags from layflat tubing comprising: first folding means for folding the longitudinal edges of the tubing to form inwardly extending gussets, second folding means for further folding the gusseted tubing to reduce the tubing's width; means for transversely sealing the folded and gusseted tubing thereby to form a base seal; and means for producing a transverse line of weakness extending across the tubing to facilitate separation of individual bags; cutting means for removing a central section of the tubing for forming handles, and sealing means to seal the tubing transversely at a position corresponding to the ends of the handles are provided between the first and second folding means, characterised in that the second folding means is arranged to fold the gusseted portions about respective longitudinal fold lines in succession to lie against opposite sides of a medial portion of the tubing between the gusseted portions.
A clear understanding of the invention will be gained form the following description of the preferred embodiment, which is given with reference to the accompanying drawings.
REFERENCES:
patent: 3263901 (1966-08-01), Hoelzer
patent: 3518810 (1970-07-01), Steeves
patent: 3670953 (1972-06-01), Leventhal
patent: 3682051 (1972-08-01), Sengewald
patent: 4666423 (1987-05-01), Herrington
patent: 4759742 (1988-07-01), Achelpohl
patent: 4923436 (1990-05-01), Gelbard
patent: 5000728 (1991-03-01), Dreckmann et al.
patent: 5573489 (1996-11-01), Letendre et al.
patent: 5890810 (1999-04-01), Barlow
patent: 2274446 (1994-07-01), None
Dykema Gossett PLLC
Huynh Louis K.
Poly-Lina Limited
Vo Peter
LandOfFree
Manufacture of bags does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Manufacture of bags, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Manufacture of bags will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2471491