US2897875A - Art of forming tubes from thermoplastic sheet material - Google Patents

Description

Aug. 4, 1959 K. A. RUSCH ETAL ART OF FORMING TUBES FROM THERMO-PLASTIC SHEET MATERIAL Original Filed Oct, 5, 1953 INVENTORS ATTORNEYS.

United States Patent Office 2,897,875 Patented Aug. 4, 1959 ART OF FORMING TUBES FROM THERMO- PLASTIC SHEET MATERIAL Kenneth A. Rusch and Erwin Hillman, Milwaukee, Wis.,

assignors to Millprint, Inc., Milwaukee, Wis., a corporation of Delaware Original application October 5, 1953, Serial No. 384,020, now Patent No. 2,780,275, dated February 5, 1957. Divided and this application October 27, 1955, Serial No. 543,200

2Claims. (Cl. 154-42) 7 The present invention relates in general to improvements in the art of making bag-like receptacles, and relates more specifically to improved instrumentalities for effecting longitudinal seals in multi-ply ribbons or webs of thermo-plastic material or the like, to form elongated tubes adapted for fabrication into bags for receiving diverse commodities.

This application is a division of our co-pending application Serial No. 384,020, filed October 5, 1953, and now US. Patent No. 2,780,275, and the primary object of the present invention is to provide improved means for rapidly and effectively longitudinally heat sealing a multi-ply ribbon or elongated loosely folded tube of thermoplastic sheet material preliminarily to the production of successive bag-like containers.

It has heretofore been customary in the commodity packaging and merchandising industry, to produce bags or the like from longitudinally advancing elongated sheets or webs of heat-scalable material such as Pliofilm, polyethylene, or the like, by arranging or folding the sheet material into multi-ply or tubular formation and longitudinally heat-sealing the adjacent loosely overlapped edges thereof, and by subsequently severing the longitudinally seamed tube into successive lengths and thereafter transversely sealing one end of each severed section to complete a bag. Due to the fact that such thermo-plastic sheet materials are subject to static electrification and cling to each other when subjected to frictional contact with fixed and rotating guides, and that the heating at the seals must be continued for relatively prolonged periods of time in order to produce perfect seams, considerable difficulty has previously been encountered in forming longitudinal seams on one wall of a tubularly folded advancing ribbon without sealing the opposite side walls of the tube together at the seam.

It is therefore an important object of our present invention to provide simple but effective and automatically functioning apparatus for obviating these difficulties and for thereby insuring rapid production of longitudinally sealed tubes and successive perfect bags.

A further important object of the invention is to provide an improved device for insuring the production of an effective longitudinal heat sealed seam along the medial portion of one wall of a tubularly folded ribbon of thermo-plastic sheeting, without causing the heat sealing to detrimentally affect the opposite wall of the flat tube by causing the opposed walls to adhere to each other, 7

Still another important object of the present invention is to provide improved automatically functioning mechanism for enabling the handling of relatively thin and highly flexible thermo-plastic sheet material while producing successive bag-like receptacles or containers of diverse sizes and shapes therefrom in rapid succession.

These and other more specific objects and advantages of the invention will be apparent from the following detailed description from which it will be noted that the gist of the I improvement is the provision of devices for rapidly and effectively forming the longitudinal side wall sealed seams in the production of successive bag-like containers produced from thermo-plastic thinand flexible sheet material in a most rapid and continuous manner and without damage or detrimental interference due to heat and static electrification of the advancing stock.

A clear conception of the improved features constituting our invention, and of the construction and operation of typical commercial apparatus embodying the improvements, may be had by referring to the drawing accompanying and forming a part of this specification wherein like reference characters designate the same or similar parts in the various views.

Fig. 1 is a diagrammatic side elevation of a bag-making installation adapted to produce commodity receiving baglike containers in rapid succession from loosely tubularly folded heat-scalable sheet stock;

Fig. 2 is a likewise diagrammatic top View of the bagproducing installation of Fig. 1;

Fig. 3 is a more-or-less enlarged fragmentary side view of a preferred form of transverse bag-bottom heat-sealing apparatus which may be used with our longitudinal seam forming device;

Fig. 4 is a likewise enlarged perspective View of the improved apparatus for producing the longitudinal heatsealed seam on the loosely folded tubular and longitudinally advancing bag-forming thermo-plastic stock; and

Fig. 5 is a further enlarged and somewhat distorted and fragmentary longitudinal section through the bagforming tube illustrating the action of the longitudinal heat-sealing device.

While the improved bag-making apparatus has been shown and described as having been applied to an installation especially adapted to produce successive bottom sealed flat bags 'having longitudinal seams medially disposed along one wall thereof from loosely folded tubular thermo-plastic stock, it is not desired or intended to unnecessarily restrict the use of the improved features by virtue of this limited embodiment; and it is also contemplated that specific descriptive terms employed herein be given the broadest possible interpretation consistent with the disclosure.

. Referring to the drawing, and more especially to Figs. 1 and 2, the improved bag-producing installation shown therein comprises in general, a pair of guide rollers 7 for receiving loosely folded flat tubular heat-scalable bag stock 8 from a folder or former, and for delivering the tube longitudinally beneath a rotary heating element or seam forming wheel 9 coacting with a resilient reaction pad 10 fixedly supported within the tubular stock 8 by a bracket 11 to produce a continuous longitudinal heat seal or seam 12; a pair of draw rolls 13 coacting with the opposite walls of the longitudinally seamed flat tube to constantly advance the same; a set of cooperating cut-off knives 14 for cutting the flat tubular and longitudinally seamed stock 8 into successive open ended bag lengths or sections 15 and for delivering the severed sections onto the upper deck of a transfer belt 16; a rotor 17 having thereon a series of parallel heating elements or heat sealing bars 18 revolvable about the rotor axis across the path of advancement of the tube sections 15 and cooperating with an endless backing conveyor 19 to produce a transverse heat seal 20 across one end of each successive bag section 15; an elongated bag releasing member or tape 21 movable along the path of advancement of the bag sections 15 about the rotor 17 and through the heat sealing zone, while travelling between the conveyor 19 and the successive end sealed bags 22, and thereafter extending beyond the heat sealing rotor; and a final bag delivery belt 23 cooperating with the tape 21 to deposit the successive finished bags 22 into a receptacle 24.

The former for initially converting the ribbon of thin and flexible thermo-plastic material into loosely folded bag stock 8 as it travels continuously toward the heat sealing installation, is of old and well known construction, but the longitudinal seam forming apparatus is an improved and important assemblage capable of most effectively producing the longitudinal heat seal 12. The thermo-plastic material used in the production of these bags is preferably transparent Pliofilm, polyethylene, or the like which is subject to static electrification and consequent sticking or clinging to adjacent surfaces of the same material when frictionally engaged by fixed metallic guides or guide rollers, so that great care must be exercised for preventing the opposed walls of the tubular stock 8 from contacting each other and being heat sealed together at the longitudinal seal forming zone. The heating at this zone should also be applied for a relatively prolonged period of time in order to insure a perfect longitudinal seam 12, and all of these desirable results are obtained with the improved apparatus shown in detail in Figs. 4 and 5.

The heating element or wheel 9 is preferably formed of relatively large diameter in order to insure extensive peripheral contact between its heated periphery and the outer free edge 26 of the upper wall 27 of the flatly folded tubular stock 8, and this wheel 9 may be heated in any suitable manner and is swingably supported by an arm 28 so that it may rock up and down in order to compensate for slight unevenness in the stock or to permit removal thereof from active position. The inner reaction pad 10 is formed of relatively softand resilient material and of considerable width in the direction of travel of the stock 8, in order to provide a support for the stock 8 throughout the entire sealing zone and to also insure maximum dwell between the wheel 9 and the outer edge 26 of the advancing tube, and the inner free edge 29 f the tubular stock 8 is overlapped by the outer free edge 26 of the upper wall 27 and advances over the top of the pad 10 while the lower wall 30 advances beneath this pad and is therefore separated from the upper wall 27 by a considerable space at the heat-sealing zone, see Figs. 4 and 5. The fixed pad supporting bracket 11 may be secured to the frame of the machine and reaches into the longitudinally advancing loosely folded flat tubular stock 8 between the upper and lower overlapped free edges 26, 29; and the free end of this bracket 11 has a laterally extending arm 31 secured thereto beyond the inner tube edge 29 and which carries a supporting shelf 32 for the pad 10. This shelf additionally spaces the lower wall 30 from the upper wall 27 of the tube, thus doubly protecting the lower tube wall from engagement with the upper wall 27 at the sealing zone.

The draw rolls 13 coact with the longitudinally heatsealed tubular stock 8 to advance the latter past the first heat-sealing zone and to deliver the flat tube to the knives 14 which are operable in a well known manner to sever the stock 8 into successive sections 15 of the desired length. In order to prevent the upper draw roll 13 from contacting the freshly formed longitudinal heat-sealed seam 12, this roll is preferably provided with a medial gap 34 of reduced diameter, as shown in Fig. 2; and the endless transfer belt 16 is adapted to promptly remove the successive severed bag sections 15 from the cutting zone and is driven at such speed that it will endwise space the sections 15 apart for proper cooperation with the successive transverse heat-sealing elements or bars 18 of the rotor 17 to which the belt 16 delivers these bag sections in rapid succession.

The heat-sealing bars 18 of the rotor 17 may be heated in any suitable manner and are slidably confined within radial slots 36 formed in the rotor. As shown diagrammatically in Fig. 3, each bar 18 has one or more inwardly extending stems 37 each provided with a plate 38 engaged by a spring 39 which constantly urges the corresponding bar inwardly into the slots 36 and toward the rotor axis, and the inner end of each stem 37 carries a roller 40 coacting with a stationary cam 41 formed to force the adjacent bars 18 outwardly beyond the rotor periphery and into sealing position but only after each tube section 15 which is to be transversely sealed has been brought into advancing engagement with the rotor periphery by the backing conveyor 19. This endless conveyor 19 is formed of relatively heavy and durable belting and has an arcuate advancing portion 42 snugly engageable with the periphery of the revolving rotor 17 and terminating in a horizontally disposed reversely curved lower portion 43 coacting with a reversing drum 44 disposed considerably beyond the lowermost periphery of the rotor. The arcuate belt portion 42 is adapted to press the successive bag sections 15 against the successive outwardly projected heat-sealing bars 18 and coacts with the rotor periphery to frictionally advance the sections 15 while the transverse end or bottom seams 20 are being formed, and this frictional propulsion tends to produce static electrification of the final bags 22.

The endless bag releasing member or tape 21 is provided in order to positively release the successive final bags 22 from the revolving drum or rotor 17 and more particularly from the belt conveyor 19 due to static electrification and possible adhesion due to heat sealing, and this tape 21 may be of relatively narrow width preferably coacting with the bags along the seams 12 where it will not interfere with the production of effective end seams 20. The tape 21 travels around and beyond the rotor 17 between the conveyor portions 42, 43 and the successive bags 22; and when it leaves the rotor periphery, it cooperates with the bag delivery belt 23 to engage each of the opposite side walls 27, 30 of each succeeding final bag 22. Both the tape 21 and the belt 23 extend along the reversely curved conveyor portion 43 and around the drum 44, and travel considerably beyond the lower stretch of the portion 43 so as to insure positive release of the bags 22 from the conveyor 19 and delivery thereof to the receptacle 24.

While the construction and normal functioning of the improved bag making apparatus should be apparent from the foregoing detailed description, a short resum of the operation will be given. The heat-sealing wheel 9 and bars 18 may be heated and energized electrically so that they will function only while bag stock 8 is being supplied, and will be de-energized when no stock is being fed. The revolving wheel 9 normally cooperates with the internal stationary pad 10 to form a continuous longitudinal heat-sealed seam 12 along the overlapped edges 26, 29 of the upper wall 27 of the flat loosely folded tubular stock being rapidly advanced through the initial heat-sealing zone by the draw rolls 13, and the pad 10 and shelf 32 prevent the lower wall 30 from engaging the upper wall 27 at this initial zone. The draw rolls 13 deliver the longitudinally seamed stock 8 to the knives 14 which sever the successive sections 15 and deposit them upon the transfer belt 16. This transfer belt 16 endwise spaces the successive bag sections 15 and delivers them in properly spaced relation to the final transverse heatsealing zone.

The bag sections 15 discharged by the transfer belt 16 are not acted upon by the heat-sealing bars 18 until a substantial portion of each succeeding section 15 has been introduced between the periphery of the rotor 17 and the backing conveyor 19, whereupon the cam 41 acts to force the bars 18 outwardly against the action of the springs 39 and into heat-sealing contact with the adjacent ends of the sections 15 to form the end or bottom seams 20. The final bags 22 are thereafter conveyed away from the rotor 17 and are positively removed from the belt conveyor 19 by the tape 21 which travels medially between this conveyor and the successive bags 22, and the tape 21 subsequently coacts with the conveyor belt 23, to deliver the finished bags 22 in rapid succession from the installation,

It is to be noted that both the longitudinal seam 12 and the transverse seams 20 are effectively formed by subjecting the bag stock to the heating elements 9, 13 for prolonged periods of time; and that the internal pad positively prevents exposure of bag wall 30 to detrimental heat in the initial sealing Zone, While the tape 21 insures positive release of the completed bags 22 from the backing conveyor 19 after they leave the final heatsealing Zone. The relatively heavy and large heating wheel 9 co acts with the soft and resilient pad it to produce considerable contact between the Wheel periphery and the bag stock 8, while the large diameter of the rotor 17 cooperates with the elongated arcuate conveyor portion 42 to likewise provide a long sealing period between each bar 18 and the adjacent bag section 15.

From the foregoing detailed description it will be apparent that the present invention in fact provides improved and automatically functioning apparatus for rapidly and effectively heat-sealing a multi-ply ribbon or elongated loosely folded tube of thermo-plastic material longitudinally prior to formation of the transverse seals so as to produce successive bag-like containers with utmost precision and with least waste of the material. The successive bags 22 are formed without interference due to static electrification of the thin and flexible stock, and are positively removed from the installation by the tape 21 coacting with the longitudinal seams 12 so as to prevent interruption of the transverse end seals or seams 20. The improved mechanism may be used to produce bag-like containers from diverse sheet materials and of various sizes and shapes, and has proven highly satisfactory and successful in actual commercial use. While the apparatus has been shown and described herein as operating on successive tube sections 15, it can of course be readily modified to effectively longitudinally and transversely seal a continuous ribbon by simply relocating the knives 14 to a position beyond the sealing rotor 17. Likewise, when the tube is cut into successive sections prior to introduction to the rotor 17, it is a mere matter to adjust the timing so that the transverse sealing bars 18 coact with the trailing edges of the successive sections instead of with the leading edges thereof as shown.

It should be understood that it is not desired to limit this invention to the exact details of construction and operation of the precise apparatus herein shown and described, for various modifications Within the scope of the appended claims may occur to persons skilled in the art.

We claim:

1. In a device for longitudinally heat seaming thermoplastic tubular stock, means for longitudinally and rectilinearly advancing tubular folded flat thermo-plastic stock with its opposite side edges loosely overlapped medially of one wall of the flat tube, a relatively fiat pad fixedly confined within the advancing tube between both of said overlapped edges and the opposite tube wall, a unitary thin L-shaped support having one leg fixedly mounted externally of the tube and extending from a point out wardly of the tube transversely between the loosely overlapped tube edges to a point internally of the tube laterally beyond said edges while its other leg extends longitudinally within the tube beyond said overlapped edges and away from the inner end of said first mentioned leg between said pad and said opposite tube wall to support the pad and to space it from said opposite wall, and a heat sealing element coacting externally with said overlapped tube edges in opposition to said pad to form a longitudinal seam on the tube along said edges.

2. In a device for longitudinally heat seaming thermoplastic tubular stock, means for longitudinally and rectilinearly advancing tubular folded flat thermo-plastic stock with its opposite side edges loosely overlapped medially of one wall of the flat tube, a relatively flat pad fixedly confined within the advancing tube between both of said overlapped edges and the opposite tube wall, a unitary thin -L-shaped support having one leg fixedly mounted externally of the tube and extending from a point outwardly of the tube transversely between the loosely overlapped tube edges to a point internally of the tube laterally beyond said edges while its other leg extends longitudinally within the tube beyond said overlapped edges and away from the inner end of said first mentioned leg in the direction of advancement of said tube and between said pad and said opposite tube wall to support the pad and to space it from said opposite wall, and a heat sealing element coacting externally with said overlapped tube edges in opposition to said pad to form a longitudinal seam on the tube along said edges.

References Cited in the file of this patent UNITED STATES PATENTS 2,170,364 Bergstein Aug. 22, 1939 2,595,421 Spalding May 6, 1952 2,680,471 Mercer June 8, 1954 2,718,915 Piazze Sept. 27, 1955

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