Manufacture of thermoplastic bags

Abstract

A bag-making machine is disclosed for producing bags from thermoplastic web material. A device (86) for grasping and transferring web segments in an arcuate path for reception by an accumulating device (88) serves to grasp adjacent opposed edges and transfers them through an arc to an accumulating device which includes posts (90).Accumulation of web segments occurs on a bag stack accumulating and transporting device located between laterally spaced radially projected arms of the web transfer device and it includes an indexing system (94) for translating the stacking posts away from the stacking station. The web segments are subsequently cut and/or joined along a line located centrally of the web segments at a station (102) to thereby produce two individual stacks of bags.This invention relates to a method of and apparatus for producing thermoplastic bags.Machines for producing bags from thermoplastic web material come in a variety of configurations depending upon the size and style of bags to be produced and are adaptable to process material of various thicknesses and chemical compositions. Certain bag machines are dedicated to produce one style of bag (side weld or bottom weld) or their design is of a universal character such that by replacement of certain components side weld or bottom weld bags can be made.Directly or indirectly the object of bag machine developments is to decrease the time to produce a bag. The most important consideration in reducing machine cycle time is substantially wholly dependant upon whether the output of the bag machine can be organized such that successive bags are accumulated in neatly registered stacks with each stack containing a predetermined number of bags. One approach currently practiced to produce registered counted stacks is to utilize a bag stack accumulating conveyor, known as a wicketer. Basically, the accumulating conveyor includes a plurality of sets of pins which are successively positioned at a stacking station and remain there until a predetermined number of bags have been deposited on the pins. By using this procedure each individual bag is provided with a pair of holes whose pitch matches the spacing of the wicket pins. After a predetermined number of bags have been accumulated, advance of the web is arrested and the conveyor carrying the set of pins is indexed to transport a completed bag stack away from the stacking station and to position a succeeding pair of pins at the stacking station.Machines utilizing a wicket stacker are in very wide use because stacks of several hundred bags of low gauge high density polyethylene can be quickly and accurately stacked since windage problems have a very minimal effect on proper stacking.According to the present invention in one aspect, there is provided a method of producing thermoplastic bags characterized by the steps of producing segments each defining two bags, transferring the segments successively on one stacking device of an indexing conveyor having a plurality of said stacking devices spaced along its length and engaging the segments on the stacking device at at least one point whereby to retain the segments as a registered stack, and severing the segments of the stack after indexing from the location at which the segments are received on any given stacking device.According to the present invention in a second aspect, there is provided apparatus for producing thermoplastic bags characterized by means for producing segments each defining two bags, means for transferring the segments successively on to one stacking device of an indexing conveyor having a plurality of said stacking devices spaced along its length and means for engaging the segments when on any given one of said stacking devices at at least one point whereby to retain the segments as a registered stack, and means for severing the segments of the stack after indexing from the location at which the segments are received on any given stacking device.When it is desired to produce bags from tubular film, certain considerable advantages result in printing the web on one or both sides. More particularly the pattern achievable by the printing press can be duplicated on either side of the longitudinal median of the web, because processing by the bag machinery constructed in accordance with the principles of this invention allows creation of two bags from a web segment.The rate at which bags made from thermoplastic web material can be produced by both aspects of the invention is double the rate of machine cycle time and the physical characteristics of the material, such as its lack of stiffness, is no longer a factor limiting accurate stacking and stack maintenance when accumulated stacks are transferred to further processing apparatus. More particularly, the process and apparatus of the present invention allow rapid controlled transfer and the creation of stacks containing several hundred web segments when processing the thinnest available low density polyethylene.

Description

Claims

1. A method of making thermoplastic bags from a web roll of thermoplastic material which is continually unwound and divided by a sealing and severing device along equally longitudinally spaced lines transverse to its direction of movement to thereby produce web segments of equal dimensions, the improvement comprising punching at least one hole closely adjacent to and on either side of the longitudinal median of the web before division occurs at intervals such that each resulting web segment contains at least two holes, transferring and accumulating each segment as it is produced on a support including posts projecting through said holes and supporting a central portion of the segments such that the remaining portions of the accumulated segments drape downwardly, and cutting an accumulated group of segments along a line substantially central of each segment and between the holes while on the support and thereby produce two bag stacks from the accumulated web segments.

2. The method according to claim 1, wherein the bag stacks created by cutting are retained on the support by the posts after cutting.

3. The method according to claim 1 wherein punching creates four holes in a pattern such that two holes are closely adjacent to and located on either side of the longitudinal median of the web so that each bag stack created by cutting is retained on the support by posts projecting through each hole.

4. A process of stacking and cutting web segments produced from an elongate web strip unwound from a roll of thermoplastic tubular material or flat material folded in a generally C-shaped configuration so that the lateral edges are equally spaced from the longitudinal median of the strip and providing, closely adjacent to and on either side of the longitudinal median, at least one aperture in each web segment which is produced by transversely severing and sealing the web strip at equally spaced longitudinal intervals; the improvement in said process comprising engaging and grasping each web segment on opposite sides of the apertures as it is produced and transferring it to a stacking station; impaling each segment on upwardly projecting pins arranged to conform to the spacing of the apertures and mounted on a support plate positioned at the stacking station and having a length at least equal to the width of the segments and a width substantially less than the length of the segments; translating the support from said stacking station when a desired number of web segments have been impaled on said pins to a cutting or a cutting and combining station; and cutting or cutting and combining the web segments at said last mentioned station by a heated knife located in a plane normal to and containing the longitudinal median of the web segments and thereby divide the stack of web segments into two bag stacks.

5. The method according to claim 4 wherein removal of a central strip from one panel of the tubular material produces bags having uneven edges.

6. The method according to claim 4, further comprising forming, in a central zone of the tubular material, continuous lines of perforation through both panels to produce even edge bags.

7. The method according to claim 4 wherein the knife at said cutting or cutting and combining station is heated in the range of from 93.degree.-105.degree. C., to effect cutting without joining the adjacent plies of web.

8. The method according to claim 4 wherein the knife at said cutting or cutting and combining station is heated to approximately 575 degrees F., to effect combining of the adjacent plies of web to produce a block of interconnected bags.

9. A method of producing thermoplastic bags comprising the steps of forming successive web segments from an elongate strip of thermoplastic film material by intermittently advancing equal lengths of the strip to a transfer station adjacent a severing and sealing device operative to sever and seal the advanced portion to produce the web segment,

forming at least one hole on either side of the longitudinal median of the web strip prior to severing and sealing,

transferring and accumulating each segment on a support including posts projecting through each of the holes formed in the segment and supporting a central portion of the segments such that the remaining portion drapes downwardly,

and cutting an accumulated group of segments along a line substantially central of each segment and thereby produce two bag stacks retained on said support by the posts.

10. A method of converting an elongate strip of tubular or folded thermoplastic web material to produce bags comprising the steps of forming at least two holes at regularly spaced intervals and on opposed sides of the longitudinal median of the web material, transversely severing and sealing the web material to produce substantially identical web segments each of which contain said two holes, deploying a selected length of the web on a generally planar support surface before severing and sealing and thereby produce said web segment, said support surface defining a transfer station, transporting the segment in a generally circular path approximately equal to an arc subtended by a central angle of 180.degree., depositing the transferred segment on posts projecting through said holes, and cutting the segment along a line between said holes while on the posts.

11. An apparatus for producing thermoplastic bags from a roll of tubular thermoplastic web material comprising means for intermittently advancing equal increments of the web, means extending transversely to the path of web advance for severing and sealing the advanced leading portion of the web and thereby define a web segment, means for forming at least one aperture on either side of the longitudinal median of the web during periods of web repose and before severing and sealing occurs, means for accumulating a predetermined number of web segments on one of a plurality of stacking devices mounted on an indexable conveyor operable to locate successive stacking devices at a stacking station, said conveyor being operable, on accumulating a predetermined number of web segments on one of said stacking devices located at a stacking station, to index said conveyor and position a successive one of said stacking devices at the stacking station, means for transferring each web segment as it is produced on to one of said stacking devices located at the stacking station, mounting posts on each stacking device on which each web segment is impaled, said posts being positioned to correspond to the apertures formed in each web segment, and means in the path of said conveyor and remote from said stacking station for cutting said web segments along the longitudinal median.

12. A bag producing apparatus according to claim 11 wherein said aperture forming means comprises two reciprocable pneumatic actuators each mounting two hole punches, said actuators being spaced longitudinally to produce a pattern of four holes in each web segment.

13. A bag producing apparatus according to claim 11 wherein said stacking device comprises a generally rectangular plate supporting a central portion of the web segments, and a deformable platen penetrated by said cutting means to preserve the edge thereof.

14. A bag producing apparatus according to claim 11 wherein said cutting means comprises a reciprocating knife holder mounting an elongate serrated knife, means for electrically heating said holder and said knife to a desired temperature, and means substantially coextensive with and located on opposite sides of said knife for compressing the accumulating web segments before and while cutting occurs.

15. A bag producing apparatus according to claim 11 wherein said transferring means comprises a pair of arms located on either side of the apertures of said web segments.

16. An apparatus for making two bags from a segment of tubular thermoplastic web material wherein said web segment has a generally rectangular configuration defined by transversely sealing and severing the web at equally spaced longitudinal intervals, removing a narrow strip from the central portion of one web ply and forming apertures located on either side of the longitudinal median and in the central portion of the remaining ply, said apparatus comprising means, having posts mounted on a platform, for accumulating a plurality of web segments with the central portion assuming a generally planar condition and the outer opposed portions draped downwardly, and means for cutting the accumulated segments along a line between the apertures.

17. An apparatus for producing thermoplastic bags from web segments provided with at least one hole on either side and closely adjacent its longitudinal median, said apparatus comprising means for intermittently advancing an elongate web of thermoplastic material, means operable during the period of web repose for forming said one hole on either side of its longitudinal median, means for severing and sealing a portion of said elongate web along a line transverse to the direction of web advance to produce a web segment containing said one hole, means for transferring the segment in an arcuate path to a stack accumulating device, said stack accumulating device comprising upwardly extending posts fixed to a rigid platform, said posts being located to correspond to the spacing of said one hole on either side of the longitudinal median of said web segment so that each segment transferred to said accumulating device is disposed on said posts such that a central area of the segment overlies said rigid platform, means operable upon the accumulation of a selected number of web segments on said rigid platform for translating said accumulating device to a location remote from the location where the accumulation of said web segments occurs, and means at said remote location for cutting or cutting and combining the accumulated web segments along a line between and substantially equally spaced from said holes on either side of the longitudinal median of the web material, said cutting or cutting and combining produces two bag stacks retained on said accumulating device by said posts.