CA1295162C

CA1295162C - Method and apparatus for continuous production of bags from thermoplastic film

Info

Publication number: CA1295162C
Application number: CA000577056A
Authority: CA
Inventors: Donald Emil Wogelius
Original assignee: First Brands Corp
Current assignee: Glad Products Co
Priority date: 1987-10-01
Filing date: 1988-09-09
Publication date: 1992-02-04
Anticipated expiration: 2009-02-04
Also published as: JPH01114420A; JPH0764038B2; US4867735A

Abstract

METHOD AND APPARATUS FOR CONTINUOUS PRODUCTION OF
BAGS FROM THERMOPLASTIC FILM
ABSTRACT OF THE DISCLOSURE
A method and apparatus are provided for continuous fabrication of bags from a longitudinally advanced multi-layer thermoplastic film web fed tangentially onto a rotating drum for carrying out transverse web seam welding and severing, the principal novel feature being provision of preliminary heating carried out across at least part of the width of web at which the final seam and sever is to take place. The preliminary heating step is advantageous where the thickness of film layers to be sealed and severed is not uniform across the width of the web or in which the uniform thickness of the film layers is such that seaming and severing in a single step requires an undesirably long time for continuous high speed production. The method can be adapted for production of bags of different widths.

Description

g~

METHOD AND APPARATUS FOR CGNTINUOUS PRODUCT:tON_F BAGS
FROM THERHOPLASTIC FILM

~ack~round of the Invention 1. Field of the Inventio~
Thi~ invention relates to a method ~nd apparatus ~or the continuous production o~ bags from thermoplastic ~ nd is 5 ~ore particularly concerned with improver~ents in the ~ne~hod and apparatus for 'che cont~nuou~ production of bags ~rom a multi-layer continuou~ web of thermc~plastic ~Eilm in which the web i~ passed on to a rotating drum where 6uccess~v~ poxtion~
are ~eam welded and severed in lengths corresponding to the 10 width o~ the desired lbags.

2. Description of the Prior_Art Various method6 ~nd ~pparatus ~ra known in th~ art ~or the continuous production of bag6 6uch as garbag~ bag6 and the like from thermopla6tic ~ilm. One such method, ~nd apparatue ~or 15 c~rrying out the m~thod i5 that described in van der Meulen U.S.
Patent 4,023,470. ~he ~nethod compxises feeding a web o~ a two layer ~hermoplastic ~ilm, in which the layer~ are continuously ~o~ed ~long on~ lonyitudinal ~dge, tanyentially on to a rotating welding drum under t~n6ion. The tension i~ achieved by 20 employing web loop ~ormers which e2~gage the web ~t a location pr~or to itB ~rrivEIl on the dru~. The t~nsic~n serves to ensure that the we~ 1~ drawn on to the druD~ 6urîace in taut and ~laooth _ 3~-~J~ 2 form thus enabling the web t5 be fed at high speeds. At the time of each ~eam weldirlçl and cevering ~tep the we~ tension is release~ momentarily by disenga~ng the web loop i~ormers.
carrying out the weldlng on the unstressed web i6 6aid to ensure 5 a better eeam s~eld and ~v~id da~se to the i~ay or weld which Dight occur i~ ~he web were under ~tres~ during the welding operation .

It has been found that the ~ethod described in the above patent can be employed ~atisfact~rily and 6~lccessfully ~n 10 production o2 bags at relatively high 6peeds 60 long as the web o~ film layers employed has a relatively uniform thickness acros~ the width of the web and ~o long as the thickness of each of the f~m layers doe6 not exceed about 3 ~il8. When these condition~ are not met it is ~ound that problems arise. Thus where, for example, the free edges of the ~ilm layers are folded over to form a hem 60 that there are ~our thicknes6es o~ ~m Along these edges and only two t~icXnesses of ~ilm across -he rest o~ the w~dth o~ the web, it i~ found that sati~factory seam welding and 6everance cannot be achiQved in the four ~lm thicX
region in the time required to w~d ~nd 6ever the two ~.Uffl thick region. Thi~ problem i~ even more ~cute in the cas~ of tra~h bags which ~re provide~ with a draw-6tr~ng. Xn this instance the thickne~s o~ ~wo draw-6trings i~ added to th0 four thicknesses o~ ~m ~n the hems ~hich accommodate the 25 draw-Btrings to make a tot~l thickness of 14 mils or even higher which hafi to be 6eale~ ~nd 6evered. I~ the time ~or ~eam welding and sev~ranc~ increa~ed to permit satisfactory l completion o~ thi~ 6tep in the thicker region the ~ea~ ~or~ed ln the thinner region ~ay ~e affected deleteriou~ly. Further the rate of productlon ~6 reduced as ~ reeult of the 1ncreased time ta~en to accomplish the ~t~p. ~he l~tter i~ also the case where the thlckne~s o~ each of the ~ilm l~y~r~, although uni~orm across the width thereo~, exceed~ o~ the order o~ 3 ~. Such films, which are required for heavy duty bags, reguir~ a ~igni~ican~ly longer perlod in wh~ch to accomplish ~atisfac~ory 6eam welding and 6everance.

lo Attempts have been made to overco~e these problems by carrying out a "preliminary 6eal" at the location on the web at which the ultimate ~ea~ welding and severance step i s to take place. The terms ~preliminary 6eal" and "preli~inary sealing"
as used herein and throughout this ~pecification and clai~s mean ~ preliminary heating step applied ~t designated locations on the ther~plastic material of the web which 6tep serves at least to 60~t~n the ~aterial at the location 60 treated. The term is not intended to i~ply that actual sealing of eome ~r all of the variou 6 layer6 o~ the web takes place.

These di.6advantage~ in the prior art ~ethods ar~ overcome by tha method And apparatu~ o~ tha pre6ent invention whlch w~l be described ln deta~ below. ~urther, it has been found ~hat the ~nethod o~ ths present inven~ion enables one to reduce ~igniflcantly the wldth o~ the 6eam formed on the edy2s of the }: ag produced thereby. ~hl~ is an $mportant con~ideration in the cas~ o~ bag~ euch ~ trash baq~ provided Wi'C21 a drawstring ~ 5 ~
c:losur~. Thus th amount by w~ch the bag czln be open2d is reduced by the width o~ the æea~ on elther 6ide of ~hQ ba~.
Any reduction in the 6ize of th~ openin~ makes i5 dif~icult to ~it the bag ~outh over a ~arbage can rllD when the bag le u~ed as S liner. This reduction ln width o~ Beam~ 18 acllieved by the pres~nt invention }: ecause of nccurate regi~tration w~th the preliminary E;e 1 ln 'che ~inal ~eam welding and 6ev~ranc:e 6t~ep.
Thus, ~t ha~; been ~ound that, u~ing the prc>cess and apparatus of the present invention, prellminary ~eal~ having a width as low as about 0.125 inches in the direction o~ move~ent o~ ~he web can be achieved roucinely and ~a'c the width o~ the 6ide seam weld on the bags ~o produced is of the order o~ about 0.062~
inches. These findings represer~t a marked improvement over the results achieved using previous methods availabl~ in the art.

The various advantages discussed above and additional advan~ages which will become apparent ~rom the description which ~ollow6 will be readily underst~od by those ~killed in the art.

SUMMARY OF THE INVENTIC)N

It i~ ~n ob~ect o~ the inv~ntion to provid~ an improv~d process for th~ continuou~ ~abrication o~ bag~ ~rom ~
longiltudlnally advanced multl-layer ther~opla~tic ~ilm web.

It 1B a iFurther ob~ect o~ tbe invention to provide a process for the cont~nuou~ fabrication of bags from a longitudlnally advanced ~ultiple l~yer thermoplastio ~ilm we~ which doe~ not hav~ uniform th$cXne~ across t~ width o~ the web.

~2~ 2 1 It i~ yet another object of the .invention to provide process ~or the continuou6 fabr~cation o~ bag~ from a longitudinally advanced multi-layer th~rmoplastic film web in which each o~ the l~yer6 ha~ a thlckness exceeding about 3 mils.

[t iB also ~n ob~ect of the ~vention to provide ~ process ~or the continuou~ ~abrication o~ bag~ pro~ided with dr~wstring clo~ures from a longitudi~ally ~dvanced ~ulti-layer th~r~o-plastic ~ilm web at a markedly high~r rat~ o~ production thAn hitherto ~c~ieved.

These o~ects, and other objects which will become apparent ~rom the description wh~ch 2~ollow~, are achieved by the proces~
and apparatus of the invention. The process o~ t~e invention comprises, in its broadest aspect, a ~ethod for the continuous production of bags from th~rmoplastic ~ilm in the for~ o~ n continuous longitudinally advanced multi-layer web with the ~ilm layers continuously ~oin~d alo~g one longitudinal Qdge of the web, from the leading end of which web bag~ are 6ucces~ively made by tran6verse 6eam weldiny and severance carried out ~t equally spaced location~ on the web, The method comprise~ t~e step~ o~:
~eediny thQ web tangentially on to the outer ~urface of a conltinuouGly rotating weld~ng drum provid~d with plurality o~ welding anvll~ extendlng parallel to the rotational ~xi~ o~ 'che s~id drum and spaced 6ubstan~ially equally about its circumference;
ef~ect~ng ~ preliminary ~eal o~ the ~ilm layer~ along

3~.6 at leas~ par~ c~f ~ path transverse to the dlrection o~
travel of the we~ dur~ng a predetermined length o~ travel of the 6aid wel:~ on the 6aid drum; and thereafter si~Dultaneously weld~ng and 6evering said web alony th~ whole o~ ~aid transv~rse path inclusiv~ of ~aid prel~min~ry 6eal~

The preliminary 6eal~ng and 'che ~eam welding z~nd ~evering steps are accomplished wh~le said drum has been rotated through an angle of 360/~ where ~ is the number of weldmg ~nv~ls on ~he dru~.

In a particul~r 0mbodiment ~f the ~nvention the distance (X) between the neighborLng anvll~ cn the drum iB greater than the width ~Y) of the bags to be formed and the method o~ the invention compri6es an additional ~tep, carried oul: lmmedlately a~ter completion of the welding and severing ~tep, o~ pulling back the newly ~or~ed leading edge of the 6aid web a distance on ~aid drum circu~ferenca etaual to an amount represanted 6ubstantially by X minu~ Y in tha direction opposite ~o that o~
rotation of ~he dru~D.

The invention a,l50 comprise~ app~ratus for carrying out the Jnethod o~ th3 invention. In itB broade~t aspect the apparatus of the inven~ion compris~ a frame and a weld~ng drum mounted therein, th~ 6aid dru~ having a plurality of elonga~ed welding anvil ele~nent~ ex'cen~ing parall~l tv the axis of ro~ation o~ ~he drum and spaced equally albout the circumferenc2 thereof, each ~9~fi~

1 snv~ element being re~iliently ~ounted on 6aid drum and ~ovable radially owards and ~way ~rom the drum ~xis and bia~e~
outwardly to a normal pos~tion slightly above the drum ~urface~
M~ans are provided ~or continuously rotatinq the drum, ~or feeding ~nd po6itioning ~ continuous web o~ multlolayer thermoplas~ic ~ilm tangentially on to the circu~ferantial surface of the drum, ~nd for retaining the web on the dru~
~urface after it 16 received thereon. Preliminary ealing means ~re provided comprisin~ means ~or bringing at least one heating bar into contact with a portion o~ the web located over one of the anvil elements, ~or moving the heating bar ~ynchronously with ~aid web and underlying anvil while maintainlng said contact during rotation o~ the drum and retained web through a predetermined di6tance, and for removin~ the heating bar from contact with ~aid web. Mean~ are also provided ~or brm ging a welding bar lnto seam weldlng and 6everance contact with the Yull width of 6aid web and underlying anvil in reqi6tration with the location of prior contact with 6aid heating bar and for removing ~aid welding bar ~ro~ contact with said web ~fter completion o~ ~aid 6eam welding and severance. ~eb pull-back ~ean5 i5 provided to pull the web back relative to rotat$on o~
the welding drum by a predeternined di~tance in th~ direction opposite to that o~ rotatlon of the drum. The rotatlon o~ the drum and the ~ovement~ o~ said heating bar, the welding bar ~nd 26 the web pull-back means ar~ a~ driven in appropriate mutually timed relation~hip.

~2~

_IEF DESCRIPTION OE THE DRAWINGS

FIGURE 1 18 a 6ide elevation view, partially broken ~way and part~ally ~chematic ln r~pre6~ntation, of appar~tu~ ~or carrying out the ~nethod o~ ~nd incorporat~ng ~achlne a~pect~ o~ the 5 invention, FIt;URE 2 is a fragmentary ~ection of the welding drum shown in FIGURE 1 and taXen in a plane perpendicular to the drum axis and through an edge of the web on which a preliminary ~eal is ~eing form~d.

FIGURES 3 A-D illustrate in sch~r~atic form the ~equence of ~;teps in produclng ~ bag in 2ccordance with the method of the invention .

FIGURE 4 is a perspective view, partially cut away, of one embodimant o~ ~ preliminary sealins~ device in accordance with the ~nvention.

FIGURE 5 i6 a cros~ ~ectlonal view taken along the line 5-5 in FIGURE 40 DETAILED DESCRIPTION OF THE VENI'IQ~

The method ~nd apparatus o~ the inventioll will now be illustrated by referenc~ to ~he acc~mpanying drawing~ wh$ch ~how ~n embodiment in whicb a portion of one edge of a web o~

~5~

1 ~hermoplas~ic ~ilm, in which the edge in question is o2 thicknes~ greater than the rest of the web, i$ sub~ected to prelimlnary Gealing prior to the final ~sam welding ~nd 6ever~nce to form a bag from the web. It ls to be under~tood however that the ~nvention iB not limited to thi partlcular ~mbod~ent.

In the ~bodiment ~hown generally in FIGURE 1 ~ continuous two-layered 6ynthetic thermopl~stic ~il~ web 2, having the film layers con~inuously joined along one lon~itudinal edge of the we~ and having a folded he~ wi~h drawstring enclosed therein on each o the edges shown in the side view presented ln the FIGURE, is fed between the opposing halves ~ and 6 of a web loop former 6hown generally a~ 8 and via gulde roll 10 on to the ~ircumfer~ntial sur~ace o a continuously rotating welding dru~
15 12. The latter ie rotatably ~upported in the parallel opposite vertical Prame sides 22a and 22b o~ fra~e ~4 and ls provided with ~our elongated anvil~ or 6eal p~d~ 14, 1~, 18 And 20 aub~tantially ~u~lly spaced about th~ circu~ference of the drun~. Each anv$1 traverses the width oiE the drum ~ur~ace with 20 its longitudinal a.xi5 par~llel to th~ ~xis ~ o~ dnlm ~. Al60 r~tationally ~ounted in ~ram~ j~ with it6 axi~ Z~ vertically a~bovo ~nd ~ligned parall~l to a~ j~ o~ th~ dru~ n open cylindrically ~haped fr~me 3~ which ~upport~ two diametrically o~posed welding bar~ ~ and ~. The latter are p~votally 25 mounted at their ends and ~xtend aoro~s the width of fra~e 30 with th~ir longitudinal axes parallel to axis 2B. Frame ~0 rotate~ ln the vpp~site direction (~hown by arrow3 to dru~n 12 . 2 ~nd the speed of rotation of the two i~ ~ychronized by mean~; of a gear chain mechani~DI (not shown). The circum~2rential distance between welding bars 3~ and ~ is equal to the ~ircumferent~al distance between each of ~nv~ls 14, 1~ ~ and 5 ~û ~nd the pos~tion of welding bars ~ ~nd ~4 relative to 'che latter anvils is s~ach that, during ~ach 90 rotation of drum 1~ one of the welding b~r~ register~ with an anv~l and a~akes 6eam welding ~nd eeverance contact with th~ web ~ acros~ the whole width thereo~.

A preliminary ~ealing device ~hown generally ~n sche~nati~
~orm as ~6 co~prises a frame 38 pivotally ~upported at 40 on frame 24. Frame 38 i8 provided with rollers 42, ~, and 46 which together 6uppo:rt 2 continuous belt 48. Two welding bars 50 and 52 are carried by ~aid belt 48 and are ~paced apart from 15 each other by a di~tance precisely egual to the circum~erential distance be~ween the centers of any o~ the neighboring pairs of anvils 1~, 16, 18 and ~0. The belt 48 traverse~ ~ path between roller~ ~6 ~nd 42 which i~ spaced ~ predetermined distance ~rom the surfaca of the drum ~ nd matche~ the contour thereo~.
20 E~elt 48 i~ conformed to this p~th by cooperation with guldes mounted on th~ periphery oP drum ~ shown ln deta~ in FIGUX~
S discussed below. Th~ rate of trav~l of belt 48 i8 6ychronized with that vI the circumferential 6llrface o~ drum ;L~ (by drive mechanisms described below). The position~ of heating bar~ 50 25 and 52 are 80 ad~usted that each in turn registers precisely with one oi~ the anvil~ 14, 16, 1~ and 20 as each 6ai~ bar begins the path between roller~ ~ ~nd 42. ~ieating bar~ 50 - 1 2 - ~
and ~ are . liqned w~th their longitudinal ~xe~ parallel to ~o~e of Invll~ ~, .1., ;L~L and 2Q ~nd are 6Q orient~d ~nd o~
~UCh 2i length that, when each bar i5 ~n r~gistry with arl anvil, ~e bar ~ ln ~ealins~ contac~ w~th whate~r portion o~ the widkh 5 o~ the w~b i~ to receive the preli~ eal. In the ~nbodimen~ ~howr~ ~n Figure~ 1-5, th~ heating bar~ .~0 and 5 are ~ingle bar~ located a8 '1:O regi6ter with one edge c~ we2~
~ Where the web i6 to re~eive 8 preliDIinary ~eal ~ aore than one loc~tion across the width thereof an ~ppropriatQ number o~
10 heating bar~ o~ the desired dimen8ions 1~ provided ln place of, or in ~ddition to, the bar~ 50 and 52. Where the prelimir~ary seal is to ~xtend ~ub6tantially completely acro~ the width of web 2 thQ bars ~LQ and ~2 will themselve~ extend the appropriate di~tance across the width c~f the w~b.

The frame 3a can be pivoted away ~rom the circum~erential ~urface of drum ~ by operation o~ pneumatically drlven plston ~ssem~ly ~0 ~Dounted by ~astener ~ on ~rame 24 and connected via rod~ 5~ and ~6 ~nd connectlng pln ~oint ~ to the upper corner oi~ 2~rame ~. This reature o~ th~ ~pparatu~, namely th~ D~ean~ to 20 pivot preliminary ~ealer ~ ~way :Erom the periphery of drum ~, 13 ~ I;afety ~eature to be operated liF and whQn the production o~
bag~ i8 interrupt0d Ior any ~ignificant amount o~ time. When ~uch an in~erruptlon occ~lr~ it la de~irable ~nd nece~sary to removQ the ho~ welding barG~ nd ~2 ~rom pro~im$ty ~o ~he web 25 i~ ln order to avold heat damag~ to the latter cau3ed by prolonged local expo~3urq~ o~ the web to th~ hearc o~ ~aid bar.

6~

The w ~ pull-back ~eans o~ 1:he embodiment ~hown ln ~igure 1 comprises the web loop ~ormer ~. Th~ latter comprises ~ ~irsk ~et t4) 0~ roller6 64 rotatably ~ounted on frame 66 and aligned ~n p~rallel wlth their longitudin~l ~xa~ par~llel to th~ plane of web j~ and perpendicular to the ~ire~ion o~ travel o~ eaid web. Frame ~Ç i~ rigidly mounted; by mean~ not ~hown, on ~r~me ~4 thu6 31o~ding roller~ Ç~ ixed po~it~on relative to w~b ~.
A ~econd ~et of rollers 68 ~ rotatably ~ounted on ~ras~e 7Q
which is adapted ~o:r reciprocating movement between paix~ of gulde roll~ 71 ln a direction vertical to the direction o~
znovement o~ web ;j~. The upward ~novement o~ roller6 5~ in contact with the underside o~ web ~2. pu~h~s loops o~ the latter upward between roller~ 6~ ~nd ~pplies tenslon to the web. A~ discussed more ~ully below, the ~mount by which w2b 2 can b~ pulled back relative to rot~tion of drum 1~ $8 a function of the numb~r of roller6 in each of ~et~ ~ and ~ ~nd thQ distance through which the lower se~ capabl~ o~ moving ln contack w~th the web ~.
Reciprocating ~ov~ment of rollers 6q on fram~ ~Q i8 ~ctuated ~y rod 7~ pivotally ~ounted at one Qnd 74 to frame 70 and pivotally ~ount8d at the o~her end 7~ to rotatable ca~ 7a. Ca~ 7~ i~
rot~te~ in care~ully timed relation~h~p to rotation o~ drum 1 ~nd belt ~ ~y ~ 8erie~ 0~ drivo ele~ent~ euch ~ belt~ or chain~ and coopera~ing ~prockets the whol0 syste~ being driven by el~ctric ~otor ~Q. The latter, through its driv2 sprocket ~, drive element ~ and ~h~t ~procket ~6, drives intermediate drive ehaft ~ ~ppropriately rotatably 6upported on bracket~
~ixed to ~r~m~ ~g. FroDD sprocket ~Q al~o located on dr~ve ha~t ~ and ~ eacond ~riv~ ele~Dent 92, motion 1~ tr~nsmltted 1 ~imultaneously to ~procket~ ~4 and ~ mounted on dr~v~ ~hafts 9B
~nd lO0, respsctlvely, Qach o~ wh~ch latter ~ al80 rotatably mount~d on ~upport brackets a~fixed to frame 24. Sprocket lo?
also mounted on drive sha~t ~8 l~part~ ~otion to ~ thlrd drive element 104 whlch 1~ ~ounted over ten610n pulley 106 and idler pulley 108 to provlde between ~proc~et .lP2 and pulley ~Q~ ~n upper reach whi~h drivingly en~ages dru~ ~ and C~U62~ rotation thereof. Si~sultaneously 6procket ~ ~ounted on drive ~haft 100 acting through a ~ourth drive element la2 and a ~procket ~not shown) mounted on the end of roller 46 imparts motion to drive belt 48 to move the latter at a rate 6ychronized with the rate of travel of the periphery of drum 12.

As wlll be discus~ed in deta~ below, the rotation o~ cam wheel 78 is 60 timed with respect to said dru~ 12 that the upward movement of roller~ 68 to apply web loop former tension to web 2 occurs immediately after the 6eam welding and 6everance contact betwe~n welding bars 32 or 34 and a corresponding anvi h~s been completed. The cam wheel 78 i~ cau6ed to make one ~omplete revolution for each rotation of 90 imparted to drum l~- As will be obviouo to on2 ~k~l~d in the ~rt th~ rot~tion o~ drum ;L~ through 90 represent the completion o~ on~
complete cycle, i.~. the formation o~ one bag, becau~e in the par~icular embodi~ent ~hown ln Figure 1 there are four t4) ~nv~l~ eub6tantially ~gually ~paced about the drum ~t which the ~eaming and ~evQrance 6tep at the end of ~ bag forming cycle occur~. IP there srQ le~s than or ~ore than ~our an~ils loc~ted on the drum the angle through which the drum rotate6 during ~95~&~
~ 15 -1 completion o$ a single cycle ~n the formation Qf a bag is 360 divided by the number of anv ~ present and the relat~onship between rotatlon o~ the cam wheel ?8 and that of drum L~ i~
~djusted accordLngly ~o that the cam wheel ~ke~ o~e co~plete rotation ~or ~ach cycle in the ~or~tion o~ a bag. ~im~larly, when there ~re le~s than or more than ~our anv~s located on drum 12 the rate of rotation of ~rame 1~ ~nd or 1ts dimen6ions and ~r the number of weld bar~ located thereon ~s/are ~dju~ted 80 that a weld bar is brought Lnto registration w$th eaoh anv~
10 as the dru~ 1~ and ~rame ~Q are rotated in the ~anner described a~ove.

A~ter the web ~ has been received on the circum~erential sur~ace o~ drum 12 it is held fir:mly ln place thereon, at least until a~ter flnal 6eam welding and ~everance i~ complete, by 15 ~eans of vacuum applied to the under~de o~ the web via multiple per~orations 114 as 6hown in the partial cross-sectional view shown in FIGURE 2. Elements common to FIGURES 1 and 2 are ~ho~n by the ~ame numeral~ in ~oth lnstancas. As also ~hown in FIGURE
2 the space between adjacent anvil elements and immediately beneath th~ perforated 6urfaca of the drum 1~ i~ divided into ~emi-~eg~ented c~amber~ ~lÇ and 11~ by ~ longitudinal plate 12Q
in chord-llke disposition over the width o~ th~ drum and a oentral longitudinal partition plate 1~ extending between plate 120 and the inner ~ur~ace o~ the drum. Each o~ chambers ~ llnd 25 118 communicates throu~h on~ or more apertures with a respective conduit 1?4 or ~ 26. Each o~ the latter runs to, ~nd opens through, ~ouths at dru~ wall end 13 ~or application o~ vacuum or pressurized air ~8 the ~nouth~ pass respectively ~ vacuum ~anifold ~28 or ~ pressurized a~r ~ani~old l~ ence, as web ~
is fed on to the dru~ 6urface the mouth~ the cs~nduits 124 and ;L~ lead~g tc~ the c:hamber~ ~ and L~. beneat~ the per~orated surface o~ the dru~, b~g~n~g ~t th~ poink oi! f~rst contact o~
the web and cont~ nulAg unt~l WQll pa~t the point at which ~eam welding and ~evera.nce takes pl~ce, ar~ ln communlcatlDn with vacuum manlfold ;~ whereby the portion of the web in quest~on iq held firmly in place.

At ~he particular point in the production cycle represented in FIGURE 1, a first bag ~ has been ~or~ed ~nd the cycle i~
well ~dvanced in the formation of a new bag. Seam welding and severance of bag ;L~ has taken place by combined action of welding bar 32 and anvil 14. Further, as expla~ned in more deta;l below, the web lc>op fonDer mechanism ~ has already been activated to apply necessary tens~on to web ~ to pull back the new lead~ng edge .;L~ Of the web ~ c$rcumferentl~1 distance 'la"
this di6tance ~eing the differ2rlce between the c~rcumferential di~tance (X) separa~ing the centerpoint of anvils 14 and 20 and ~he width ~Y) o~ he bag to ~ Formed. The conduit6 ;L~L and 126 in contact with the chambcr~ and 118, both of which at ~ome poin~ ~r~ underlying the newly formed bag 1~, are in contact with the pres6uri2ed nir ~Danifold thu~ ~acili~a~ing r~leAse of the bag 1~ ~ro~ the surface o~ drum 1~. ~he bay 132 iB removed fron the surface by re3~oval means which comprises ~ hollow rotating roll~r 1~4 aligned w$th it6 longitudirlal AXi6 parallel to the axi~ j~ of dna~ ~. The surfacQ of the roller over chamber 1~6 bounded by ra~ial plates ~ and 140 is perforated and a sl~ght vacuum i6 applied to ch~mber 13 6 by an appropriatP
conduit (not 6hown) co~Dmun~ cat~g with the ~ame or a different vacuum sol~rce as 3DaniiEold ~, The rotation s:f roller 1~4 ls so ti~ed that the section oX it3 6urface co~unicating with chamber contact6 the leading çldge OI bag ;L~. The combined actlon of low v~cuum via chamber .;L~ arld pres6urized ~lr through the surface of dru~ L2 facilitates removal of the leading 2dge of bag ~ from the drum eur~ace ~ollowed by in~ertion o~ ~;aid 10 leading edge between continuous aloYing belts ~ and ~ which remove the bag to a 6torage and or packaging zone ~not ~howrl).

As shown ln FIGURE 2 each of ~he anvil elements (of wh$ch only 14 and 2 O are shown in the figure) compri6e ~he anv11 element itself, 6hown as 14 or ~0, received ln the top channel of a composite ~-shaped ~upport bar co~prised of a pair of flat botto~ed channel element6 146 and 148 dispo~ed ln back to back relationship. Stud bolt l~Q ha~ on~ end secured in channel memb2r 148 and the other one extending through a guide aperture in box sec~ion 152 and provide~ with termlnal nut 154. Helical 20 compression spring 1~ around bolt lS0 i6 interposed between the bot~o~ o~ channel ~48 ~nd the upper surface of box ~ection 152 to ~ias anvil element 1~ outwardly ~nd c~U5e it to pro~ect outwardly and slightly abovQ the ~urface o~ drum ;L~. As ~hown ~or anv~l ele~ent ~Q in FIGURE 2, when heating bAr 50 1~ ln 25 oontact with ~he ~nv~l element ~he downward pressure exerted by the bar 1~ insu~iclent to bia~ the anvil ele~Dent slightly downwardly agaln6t the action of 6prlng 156. However, when weld ~3S~

bar 32 later comes into ~ea~n welding and 6evering contact with anvil 20 tha pressure exerted by lthe bar ~ ls 6ufflclerlt to bias the an-.ril ? downwardly aga~nst the action of spring lS6.
Thi$ ensures tllat excellent seam welding contact o~ the bar with 5 the weh DCCUr6.

FI :;URES 3 A-D ~llu~trate ln ~chealatic form the variou~ lcey Gteps in forming of ~ b~g in accordanca with the m2thod oi~ the lnvention. FIGURE 3A show~ the 6ituation in whlch weld bar 32 and anvil 14 are in exact registration with each other ~nd ~e~m 10 welding and 6everance are taking place across the width of web to form bag 158. FIGURE 3~ 6how~ the ~ituation ilDmediately following the ~eam welding and severance 6hown ~n th~ 3; revious figure. Drum ;L~ ha~ rc~tated through approximately 10 and contact between weld bar ~ and anvil 1~ ha~ ~u~t ceased. The 15 leading edge oî bag 15~ is being taken up on roll ~
preparatory to being guided between continuously mov~ng belts 14~ and ~. At this ~uncture the web loop former ~ (not 6hown ~n ~IGURES 3 ~-D) i6 activat~ to apply tension to web i! and cause the new leading edge o~ the latter to be pulled back (i.e.
20 ~n the oppo~ite directlorl to thAt ln which th~ drum fiur~ace i8 ~noving) relative to rotation o~ th~ drum 6ur~ace a clrcumferenti~l distance Na~ as ~llu~trated in FIGURE 313. The d~stancc "~" through which the web ~ i~ pullea back in any given ~nstance ~s the di~fQrence betwQen (l) the distance between 25 neighbor~nçl anvils a.g. between anvils 14 and ~0 and (2) the length o~ the bag to be formed. It will be 6een from FIGURE 3C
that, at the complet-~on o~ the pull-baclc, the weld bar 50 on the ~2~S~6~

preliminary seale~ about to ~ake contact with anvil ~ 0. :In FIGURE 3D the drum li~ has rotated approxilDat~aly 45 beyond the ~ituation ~hown in FIGURE 3A and the weld bar ~Q and ~nvil 20 h~Ye moved synchronou~ly ln ~;eaDI weldlng cont~ct with the web 5 ~or approxlmat~ly two thirds of the di~tance in which they travel ln 6uch contact. At thi~ ~tage the leading ~dge of the previously ~ormed bag 1~ ha~ been received between the moving belts 14? and 144 and 6hortly thereaft~r will have been completely removed from the dru~.

When drum 1~ has turned a full 90 from the position shown in FIGURE 3A the 6eam welding contact between heating bar 50 and anv~l 20 in the preliminary ~e~ng 6tep ha~ ended and weld bar 3~ ha~ registered accurately with the anvil ~0. Seam welding and ~everance contact i~ taking place across the web at the precise location ~n which the prelimin~ry 6eal has been made. A
new bag i~ thereby being formed and the cycle ~hown in FIGURES 3 A-D is beginninq ~new. It $~ to ~e ~oted that, during the whole o~ the time ~n whlch the preliminary se~ belng formed and thereafter unt~l the ~eam welding ~nd severance ~tep i5 co~plete, thc portion of the web undergoing thesQ ~teps is being held ~ir~ly ~n place on the 6urface o~ the drum by appllcatlon o~ vacuu~ in the ~anner di6cusssd ~bove. This ensure~ that no movement Or the web relativ~ to the ~ru~ takes place ~nd hence precise regi~tration can be achieved between the preliminary ~eal and the ~inal ~eal and s~verance. Thi~ permi~s ~he actual wldth o~ the prelim~nary ~eal to be kept to a mini~um generally a8 low as a~out l/B~.

~2~

1 Further, ~t w~l be apparent ~rom the illu~tration o~ the ~ethod of the invention given ~n FIGURES 3 A-D that the meth4d and apparatus can be e~ployed to produce bags of various widths without significant modification of the apparatus. ~hus the only change whloh hAs to be made, ln changing from production of bags o~ one width to tho~e o~ ~nother, i~ in the amount of pull-back "a". A~ previously noted this latter i6 controlled by appropriate ad~u~tment of the web loop for~er 8. As will be readily apparent ~o one skilled ln the art the amount by which the web is pulled bac~ can be changed by increasing or decreasing the number of rollers in both the 6tationary ~et 4 ~nd reciprocating 6et 6 and or by increasing or decreaslng the distance through which the reciprocating ~et 6 of rollers moves after contacting the web.

Advantageously the temperature at which the heating bars 50 ~nd 52 are ~aintained i~ ln the range of about 600F to 1200F tha particular temperature ~mployed ln any givQn instance being determined by the natur~ o~ the thermopla~tlo ~ or ~ilms employed and tha total thic~ness o~ the f~
layers at the location o~ the preliminary ~eal. Tha temperature e~ployed ln weld b~rs ~ and 34 i~ within tha range o~ ~bout 600 to 1000F the particul~r temperatur2 employed in any niven instance bainq ~ub~ect to the ~ame ~c*ors dlscussed above.

FIG~RE 4 ~ a partial per6psctive vlew o~ the preliminary 6ealer 36 ~howing ~he hsating bar 50 in contact wit.h web 2 and underlylng anv~ ~Q in the 6ame phase of the preliminary ~ealing ~ 29~

aode as t~t 6hown in cros~-~ectlon ln FIGVRE 1. The ~ame numerals are u6ed to de~ignate ele~enta whlch ~re com~on to both figures. Heat~ng b~r 50 1~ mounted on 6UFlpOrt bar l~Q which is a'ctached by bolts ;L~ to bracket L~ b~hich latter is a~ x2d to 5 ~lexible belt or chain 4~ by thr~aded sGrew~ ~R. The under~ide o~ the outer end of bracket 1~6 i~ ~upported in ~lidlng engagemen~ wilth 'che upper Gurface o~ guide rail 1~. mounted on the outer edge of drum 12. Bar 160 i6 transversely disposed above the ~urface 21 of drum 12 and carries a series of contacts 170, 1?2, and 174 which maka electrical conducting contas:t with ~ymmetrically aligned plates 176, ;LZ~ and ~. Each of the latter is shaped to have a profile which approximates the total path travelled by endles~ flexible belt 48 as shown ln FIGURE
1. Plate ;L~ is connected to a source of 120 voltage AC
15 current, plate 180 i5 connected to ground and plate ~ is neutral. Contacts 170, 17~ and 174 are connected by wires ~o appropriate terminal~ on the heating bar 50 and 6erve to maintaln eqectrical contact bet~een the latter ~nd plate~ ~26, ~ and 180 as the heating bar 50 moves ~ynchronously with an~i 20. FIGURE 5 16 a cross-~ectional view taken along the line 5-5 in FIGURE ~ and ~hows ln ~ore detail the ~nner ln wh$ch heating b~r 50 and oontacts ;~Q, ;L~ and ;~ are mount~d on bar ;L~Q ~nd attached thereby to brAcXet ;U~ on belt ~.

The film~ which ~loay be employed ~ the web in the practice ~ thQ ~nvention lnclude ~ny thre2-dimensional material which possesses two opposite ~3cing ~urfaces ~eparated by edging ~ur~aces. The opposite :eacing surface~ may be Dono- or ~g5~2 1 poly-planar ~nd the com~ined 6urfaces typicall~ ~and preferably) posse6s many t~mes the ~rea o~ the edge 6urfaces. The Pilm employed in the practlce o~ the invention may be ~ade of ~ny ~aterial capable of being ~ealed by a her~al ~ealing process, and m~y be ~ade o~ plnsti~, re6in, metal, t~xtile, ~iber reinforced plastic or resln, compo~ite~ ther~of, and ths like.
The preferred ~heeting u~ed ~n the practice o~ the inventlon are thermoplastic f~lms ~uch ag one or ~ore layer6 of one or more of polye~hylene tlow den~ity, high densi~y, linear low density lo and/or combinations), polypropylene, polyethylene copely~ers (low density, linear low dansity andJor combinations), poly-butylenes, ABS polymer~, polyurethane~, polycarbonates, poly-~ulphones, aliphati~ polyamides, polya~ylamides, polyarylether-ketones, polyarylimideamides, polyaryletherimides, polyesters, polyarylates, polyoxymethylene, poly(epsilon-caprolactone), and the like, alone or composited with a variety of material~ such as metal f~ms, paper cardboard, textile ctructures, and the like.

The various embodl~ents of the method and apparatu~ of the lnvention which have been ~et forth abov0 ~ave been given for purpo6e6 o~ illustratlon only ~nd ~re not to be construed as llmitlng. Various modifications and improvements which can ~e made ln respec~ o~ these v~rious embodiments without departing ~rom the sc~pe o~ ~he invention will be readlly ~pparent to one 2 5 ~kllled ln the art.

Claims

WHAT IS CLAIMED:

1. In a method for production of bags from thermoplastic film in the form of a continuous longitudinally advanced web having at least two layers with the film layers continuously joined along one longitudinal edge of the web, from the leading end of which web bags are successively made by transverse seam welding and severance carried out at substantially equally spaced locations on the web, the steps comprising:
feeding said web tangentially on to the outer surface of a continuously rotating welding drum provided with a plurality of welding anvils extending parallel to the rotational axis of said drum and spaced equally about its circumference;
effecting a preliminary seal of the film layers along at least part of a path transverse to the direction of travel of the web during a predetermined length of travel of said web on said drum; and thereafter simultaneously welding and severing said web along the whole of said transverse path inclusive of said preliminary seal.

2. A method in accordance with Claim 1 wherein said preliminary sealing and said welding and severing steps are accomplished and the formation of each bag is completed during the time taken for said drum to rotate through an angle equal to 360° divided by the total number of welding anvils on said drum.

3. A method in accordance with Claim 1 wherein said preliminary seal is formed by bringing a heating bar into contact with a portion of the web located over one of said anvils and maintaining said contact during said predetermined travel of said web.

4. A method in accordance with Claim 3 wherein, after said contact has been discontinued and said heating bar has been withdrawn, a welding bar is brought into welding and severing contact with said web and underlying anvil across the whole width of said web and in accurate registration with said preliminary seal.

5. A method in accordance with Claim 1 wherein the distance (X) on the drum surface between neighboring anvils is greater than the width (Y) of the bags to be produced, which method comprises the additional step, after completion of the welding and severing step, of pulling back said web relative to rotation of said drum by a distance on said drum circumference substantially equal to an amount represented by X minus Y in the direction opposite to that of rotation of the drum.

6. A method in accordance with Claim 5 wherein said pull-back is achieved by means of a plurality of cooperating web loop former rolls adapted to engage said film web in a location adjacent that where said web is being fed to said drum.

7. A method in accordance with Claim 6 wherein actuation of said cooperating web loop former rolls is achieved by cam means sychronized with the rotation of said welding drum.

8. A method in accordance with Claim 1 wherein said web has a cross-section such that the number of film layers in one portion is greater than in the thickness of the remainder of said cross section and the preliminary seal is formed across said portion of the web.

9. A method in accordance with Claim 1 wherein said web comprises two film layers each of the free longitudinal edges of which is provided with a hem.

10. A method in accordance with Claim 9 wherein a drawstring tape is enclosed by each of said hems.

11. A method in accordance with Claim 10 wherein said drawstring tape is formed of a thermoplastic material other than that of said film layers.

12. A method in accordance with Claim 1 wherein the film layers of said web are of a substantially uniform thickness greater than about 3 mils and said preliminary seal is made across the whole width of said web.

13. A method in accordance with Claim 1 wherein said web is held firmly in contact with the surface of said drum during the whole of the preliminary sealing and the final welding and severance of said web.

14. A method in accordance to Claim 1 wherein the width of said preliminary seal in the direction of movement of the web is less than about 0.125 inches.

15. A method in accordance to Claim 1 wherein the width of the side seam weld on the finished, separated bag is less than about 0.0625 inches.

16. In a method for continuous production of bags from thermoplastic film in the form of a continuous longitudinally advanced two layer web with the film layers continuously joined along one longitudinal edge of the web, from the leading end of which web bags are successively made by transverse seam welding and severence carried out at substantially equally spaced locations on the web, the steps which comprise:
feeding said web tangentially on to the outer surface of a continuously rotating welding drum provided with a plurality of welding anvils extending parallel to the drum axis of rotation and spaced substantially equally about its circumference by a distance (X) greater than the width (Y) of the bags to be formed;
effecting a preliminary seal of said film layers along at least part of a path transverse to the direction of travel of the web by bringing a heating bar into contact with a portion of the web located over one of said anvils and maintaining said contact during a predetermined length of travel of said web in contact with said drum circumference;
thereafter simultaneously welding and severing said web along the whole of said path traversing said web inclusive of said preliminary seal; and after completion of the welding and severing step, pulling back the newly sorted leading edge of said web relative to rotation of said drum by a distance on said drum circumference substantially equal to X minus Y in the direction opposite to that of rotation of the drum.

17. A method in accordance with Claim 16 wherein said pull-back is achieved by means of a plurality of cooperating web loop former rolls adapted to engage said film web in a location adjacent that where said web is being fed to said drum.

18. A method in accordance with Claim 17 wherein actuation of said cooperating web loop former rolls is achieved by cam means sychronized with the rotation of said welding drum.

19. A method in accordance with Claim 16 wherein, after said contact in formation of said preliminary seal has been discontinued and said heating bar has been withdrawn, a welding bar is brought into welding and severing contact with said web and underlying anvil across the whole width of said web and in accurate registration with said preliminary seal.

20. A method in accordance with Claim 16 wherein said web has a cross-section such that the number of film layers in at least one portion is greater than in the remainder of said web and the preliminary seal is formed across said portion of the web.

21. A method in accordance with Claim 16 wherein each of the free longitudinal edges of said two layers of film is provided with a hem.

22. A method in accordance with Claim 21 wherein a drawstring tape is enclosed by each of said hems.

23. A method in accordance with Claim 22 wherein said drawstring tape is formed of a thermoplastic material other than that of said film layers.

24. A method in accordance with Claim 16 wherein each of the film layers has a uniform thickness greater than about 3 mils and said preliminary seal is made across the whole width of said web.

25. A method in accordance with Claim 16 wherein said web is held firmly in contact with the surface of said drum during the whole of the preliminary sealing and the final welding and severance of the web.

26. A method according to Claim 16 wherein the width of said preliminary seal in the direction of movement of the web is less than about 0.125 inches.

27. A method according to Claim 16 wherein the width of the side weld on the finished separated bag is less that about 0.0625 inches.

28. Apparatus for fabrication of bags by transverse seam welding and severance from the leading edge of a longitudinally advanced web having at least two layers of thermoplastic film and having the film layers continuously joined along one longitudinal edge of the web, said apparatus comprising:
a frame and a welding drum mounted therein;
said drum having a plurality of elongated welding anvil elements extending parallel to the axis of rotation of said drum and spaced substantially equally about the circumference thereof each anvil element being resiliently mounted in said drum and movable radially toward and away from said drum axis and biased outwardly to a normal position slightly above the drum surface:
means for continuously rotating said drum;
web feeding and positioning means spaced from said drum including a driven feed roll and n web guide for directing said web tangentially on to the surface of said drum;
means to retain said web on said drum surface after it has been received thereon;
preliminary sealing means comprising means for bringing a heating bar into contact with a portion of said web located over one of said anvils, for moving said heating bar synchronously with said anvil during rotation of said drum and retained web through a predetermined distance and for removing said heating bar from contact with said web;
means for bringing a welding bar into seam welding and severance contact with the full width of said web and underlying anvil in registration with the location of prior contact with said heating bar and for removing said welding bar from contact with said web after completion of said seam welding and severance;
web pull-back means located adjacent to said web prior to said preliminary sealing means;
actuating means for causing said web pull-back means to engage said web and apply tension thereto sufficient to pull back the web relative to rotation of said welding drum by a predetermined distance in the direction opposite that of rotation of said drum after said welding bar has been removed from contact with said web; and means for coordinating the rotation of said drum and the movements of said heating bar, said welding bar and said web pull-back means in mutually timed relationship.

29. Apparatus in accordance with Claim 28 wherein said web pull-back means comprises web loop forming means located upstream of said web positioning means.

30. Apparatus in accordance with Claim 28 which also comprises means for removing finished bags from said welding drum.

31. Apparatus in accordance with Claim 28 wherein said heating bar is mounted on an endless flexible drive member supported on sprockets and provided with drive means to move said belt continuously in a path which includes an arc conforming to the contour of the surface of said welding drum and spaced therefror a distance such that said heating bar is brought into contact with said web and underlying anvil at the beginning of said arc and moves in synchronism with said web and anvil thereby maintaining said contact while transversing said arc.

32. Apparatus in accordance with Claim 31 wherein said endless belt while traversing said arc is supported on a guide rail mounted on the periphery of said surface of said drum.

33. Apparatus in accordance with Claim 28 wherein said welding bar is one of a plurality of such bars supported on a hollow cylindrical frame aligned with its axis parallel to that of said welding drum at a location spaced about the latter in the rotation direction away from said preliminary sealing means, said welding bars extending parallel to said axis of said frame, said frame being provided with means for rotating the same in mutually timed relationship with rotation of said welding drum so as to bring each of said welding bars in turn into seam welding and severance contact with and across the whole width of said web and an underlying anvil after withdrawal therefrom of said heating bar of said preliminary sealing means.

34. Apparatus in accordance with Claim 33 wherein there are two welding bars in substantially diametrically opposite locations on said frame and four anvils substantially equally spaced apart on the periphery of said welding drum, said welding bars and anvils being so arranged that, as each anvil reaches the location at which the surfaces of the said drum and said frame are closest, said anvil is in registration with a welding bar.

35. Apparatus in accordance with Claim 29 wherein said web loop forming means comprises a first set of spaced parallel loop former rolls disposed in fixed position on one side of said web prior to said web positioning means and a second set of spaced parallel loop former rolls shiftable reciprocatingly in parallel disposition to said fixed loop former rolls and engageable with the other side of the web to form web tensioning loops.

36. Apparatus in accordance with Claim 35 wherein the reciprocating movement of said second set of loop former rolls is effected by cam means the operation of which is coordinated with rotation of said welding drum.

37. Apparatus in accordance with Claim 36 wherein the distance through which said second set of loop former rolls is movable and or the number of former rolls in each of the first and second sets thereof is adjusted so that the tension exerted on the web when said web loop forming means is actuated is such that the web is pulled back relative to rotation of said drum a distance substantially equal to the difference between the distance between neighboring anvils on said welding drum and the width of the bag to be formed.