US3548722A

US3548722A - Manufacture of valve bags

Info

Publication number: US3548722A
Application number: US757207A
Authority: US
Inventors: Elwyn David Jones; Edward Kenneth Rowley; Douglas Reynolds Shepherd
Original assignee: Canadian Industries Ltd
Current assignee: PPG Architectural Coatings Canada Inc
Priority date: 1967-08-21
Filing date: 1968-08-16
Publication date: 1970-12-22
Anticipated expiration: 1987-12-22
Also published as: CH507807A; GB1232028A; IL30569A; FR1577706A; IL30569A0

Description

United States Patent lnventors Elwyn David Jones;

Edward Kenneth Rowley; Douglas Reynolds Shepherd, lBeloell, Quebec, Canada Appl. No. 757,207

Filed Aug. 16, 1968 Patented Dec. 22, 1970 Assignee said Jones and said Rowley assignors to Canadian Industries Limited Montreal, Quebec, Canada Priority Aug. 21, 1967 Great Britain No. 38464/67 MANUFACTURE OF VALVE BAGS 51 Int. Cl .1 B31b 1/00 [50] Field of Search 93/8, 8(V B). 35

[56] References Cited UNITED STATES PATENTS 3,115,072 12/1963 Kaplan et al 93/8 3,214,312 10/1965 Gattrugeri 93/8UX Primary Examiner-Hemard Stickney Attorney-Alexander 0. Mc Intosh ABSTRACT: Valve bags having the valve formed of overlapping end panels are fabricated from a two-ply web of film employing a modification of a known bagmaking machine. The valve panels are sealed to the longitudinal edges of the 10 claims 13 Drawing Figs web of film thus minimizing the operations carried out at film [1,3,0] 93/8,93/35; edges separating individual bags, thereby permitting an in- 1 229/625 creased rate of production.

1a ,22 729 3 2 m" z I I I PATENTED DEM-2197B 3.548; 722

SHEET 1 [IF 6 INVENTORS Elwyn David JONES Edward Kenneth ROWLEY Douglas Reynolds SHEPHERD Ma hum PATENT AGENT PATENTEDUEB22|970 3548.722

SHEET 3 [1F 6 H- INVENTORS Elwyn Duv id JONES Edward Kenneth ROWLEY Douglas Reynolds SHEPHERD mamw PATENT AGENT PATENTED [m2 I978 SHEEI 5 [IF 6 lNVFZiVTORS ".11 um I Elwyn David JONES Edward Kenneth ROWLEY Douglas Reynolds SHEPHERD M19. flaw PATENT AGENT PATENTEB UEE22 I970 SHEET 8 [IF 6 PATENT AGENT the valve panels and the free edges *1 MANUFACTURE or VALVE mics manufactured on commercial bag making machines they normally are made end' to end and the 'formingof the valve element between successive bags is complicated. This results in slowa'nd costly operation. There is thus need fora simpler method of manufacmring plastic valve bags using automatic bagrnaking machinery. v 1

It has now been discovered that valve bags can be made from a double ply 'web of heat-scalable plastic film by a novel method'whereby the valve element is attachedto the double edge of the web prior to scaling and severing the individual bags. In the novel method the bottom and mouthof the bag thus are fonned from the edges of the webL The apparatus for making bags by'this method operates'automatically, is relatively simple and can be operated at high-production rates relative to the cost of the equipment. I v

It is therefore a primary object of this invention to provide an automatic and rapid method for the manufacture of valve bags from heat-scalable plastic film. Additional objects will appear hereinafler. 1 f

The valve bagof this invention comprises front and back panels joined along two opposed edges toform a flattened tube, the remaining two opposed edges of the front and back panels forming the bag bottom and valved bag closure respectively, said valved closure being formed of two end panels joined to lengths less than the length of bag end andoverlapping at their inner extremities, the inner extreme edge of each end panel being free, thus fonning thevalve'. It is convenient toemploy thinner gauge-film at the free extremities of the valve panels, the thinner extension in being folded-back to lie incontact'withthe internal valve panel. The preferred design of ,valve'bag is described in Pat. application Ser'. No. 7 30,384.A suitable heat-scalable plastic ispolyethylene' V The method formanufacturing the valve bag comprises;

l. proving a two-ply web a fold along one edge, theopposefd edge of the web being on; 2. h eit-sealing the opposed edges of overlapping rectangular panels of plastic film to the corresponding open edges of the web toforrn a tube, the unsealed extremities of said panels overlapping in the direction of the web edge, each panel having a length greater than one' bag width but less than two bag widths, the overlapping panels constituting valve elements, v

the fron t and back panels,'said. end panelshaving the case of the external valve panel of heat-sealable-plastie film'having 3. heat-sealing the thus formed tube transversely of the web by a double seal at the position intermediate the positions of overlap'of the valve panels; and Y 4. severing the film between the double 'sverse seal positions. i I

In a preferred method of manufacturing the valve bag the two-ply web of film is provided from {flattened tubular film,

- one edge of which has been opened "by slitting or trimming border encompassing the edge fold. Alternaaway a narrow formed by center folding'a wide sheet of tively the web can be single-ply film to form free film on the other side. The valvelieleme'nt is formed by joining the two free edges of the web together with a series of overlapping panels of film. These panels preferably are composed of two'sdjacent sections, the main section being of film of the lap type which provide greater strength. With the valve panels sealed in place a tube with a series of valved openings is provided. Gusset folds are next formedin both the valve sec tion and the oppositely located web fold, such folds defining the depth of a square ended bag. With'the gussets in flattened configuration V-shaped seals are made at transversely adjacent positions in the two gussets, theapex ofthe seal being inward, the seals extending from the corner fold to the reentrantangleofthegusset. w

These V-shaped seals are made 5 in-' pairs at distances separated by one bag width and at a position intermediate the overlap of the valve panels. The triangular sections external to the V-shaped gusset folds are removed. Finally transverse double seals are made across the web between the apices of I matching V-shaped gusset seals and "the film is' severed between the double seals. The resultinggvalve bag when. filled will be square ended with transverse and diagonal seals located in side panels. f

The valve bag may be manufactured asing-known bagmalring'equipment to which has been. added apparatus for attaching the valve panels to the web. The means for activating the valve attaching apparatus isco'ntrolled by the control of the parent bagmaking machine.

The joining of. the overlapping valve panels to the free edges of the web may be carried out automatically, employing an apparatuscomprising: 1. means for separating the free edges-oftheweb; 2. means for providing a panel of adapted to form the matching parts of valves in twozsuccessively produced s 1 I 3. means for joining said panel along its'longitudinal edges to the adjacent free edges of the web; and 4. control means for actuating the joining means at times corresponding to positions of successively produced bags. The forming of the transverse seals and transverse severing of the film may be carried out convenientlyernploying an apparatus as described in Canadian Pat. No. 746,689 issued on Nov. 22, 1966, with the modificationthat there be used a doublesealing bar for making the transverse seal in the nongusseted region. I j I i v The invention is illustrated by the accompanying drawings wherein FIG. 1 is a perspective view of filled bag, 3 FIG. 2 is a perspective/view of the bag of FIG. 1 in a-collapsed configuration, V

FIG. 3 is a sectional view of simple valve,

FIG. 4' is a sectional view-of a-valve having anextensionof v operation of the invention,

acrease on one side'and two edges of or the same thickness as that of the web, the smaller section forming the inner lip of the valve comprising film of lighter gauge to provide effective valve closure. The seals between panels of a bag panel is disposed in parallel relationship-to the front panel.

Front and back panels are joined along longitudinal seams 2a e and 2b. At 3 are shown diagonal seals in th'egusset region. Theof the web preferably are diagonal seals assume a V-shaped configuration when the bag FIG. 10 is a side elevation, partly in section, of an apparatus for metering plastic filmfor valve panels and heat sealing the panels to the lower ply of a two-ply web of plastic film,

FIG. 1 1 is a rear elevation of the apparatus of FIG. 10,

FIG. 12 is a rear elevation'of the metering roll assembly of FIG.'10, and

.' FIG. 13 is a front perspective view of the valve panel metering assembly of FIG. 10. I v a inFIGS. 'l and 2 front and back Referring to the drawings,

are shown at l and 2 respectively. The back FIG. 8 is a diagrammatic plan view 'of apparatus of FIG.

FIG. 9 is a diagrammatic view of the panel attaching is filled. At 4 is shown a bag bottom. A valve structure is shown at 5 and 6, 5 being the outer portion of the valve and 6 the inner portion of the valve. It is to be noted that the two portions of the valve overlap at their inner extremities. The two valve portions are sealed to the front and back panels along seals 3 and 9.

In FIG. 3 is shown a section through a valve of configuration of that illustrated in FIGS. 1 and 2. In FIG. 4 an extension of thinner gauge film 7 is joined to the inner wall 6. In FIG. 5 thinner gauge extensions to both walls of the valve are shown, extension 8 being folded back to lie parallel to the inner side of outer walls. FIG. 6 is a sectional view showing the lap sealitig of valve portions 5 and 6 to the front and back panels along seal 9.

The valve bag is conveniently manufactured employing a bagrnaking machine wherein a web offilm is advanced intermittently in units of one bag dimension (width or length of bag), the sealing operations taking place during stationary periods of the web.

In FIGS. 7 and 8 illustrating an apparatus suitable for the manufacture of the valve bag, a reel of lay-flat tubing is shown at ll). Tubing unwound from reel 10 passes over feed rolls 11 and 12 and floating accumulator roll 13. Roll 13 serves to maintain the film taut as it advances intermittently in steps equal to bag widths. The flattened tubing next passes over edge guide roll 14 and proceeds to edge slitter 15 which slits the tube at the fold position. Alternatively the device at 15 could be adapted to trim away a narrow border encompassing the edge fold. The edge slitter serves also to separate the cut edges of the two plies of film. The upper ply of the web must be raised sufficiently to avoid fouling the sealing element of the-valve inserting station. The slit tube shown at 16, next passes to valve inserting station 17 where one longitudinal edge of.-a valve panel is inserted under the edge of the lower ply'of film and under the trailing edge of the valve panel of the preceding bag. The lower ply of the web and the previously inserted valve panel can be raised by a mechanical guide or by an air jet so that the valve panel edge can be inserted beneath them. The extent of valve panel overlap is dependent upon the unit of web advance. The overlapping valve panel is next heat sealed to the superimposed edge of the lower ply of the web. The valve inserting apparatus is shown in greater detail in FIGS. 10,11, 12 and 13. In FIG. 7 are seen the reels of film for the two' thicknesses of film used in valve panels, 18 being thin gauge film for the trailing edge of the valve panel and 19 being of the same gauge as the two ply web. At 20 is shown the unit for joining the two parts of the valve panel by heat-sealing. Valve inserting station 17 operates when the film is stationary.

The two-ply web of film with overlapping valve panels 21 sealed to the edge of the lower ply next passes over a forming plate 22. This plate is anchored to the frame of the bagmaking machine at 23. The plate 22 floats between the two plies of the web, the lower ply of the web passing over rolls not shown. As the web of film with valve panels attached to the lower ply advances the valve panels 21 pass over folding device 24 which folds the valve panels so that their free longitudinal edges lie above the edge of the upper ply of the web, the said upper ply riding on forming plate 22. The web and overlapping valve panels next pass to sealing station 25. At 25 a heat sealing element 26 seals the upper edges of the overlapping valve panels to the edge of the upper ply of the plastic-web, former 22 serves as anvil for the sealing element. The sealing operation takes place while the web is stationary. The operations involved in attaching the valve panels are shown in greater detail in FIG. 9.

At this stage of the manufacture the product comprises a flattened plastic tube having a strip of overlapping panels inserted along one edge. Be sealing transversely it is possible to form pillow-type bags from the tube as it is at this stage, but bags with gusseted tops and bottoms are preferred. The next operation serves to form gussets in both edges of the flattened tube. Four sets of

double discs

27 and 28 are carried inside the tube by support linkage 29 which is attached to former 22.

Discs

27 and 28 shape the tube into a rectangular cross section. Gusset forming discs 30 fit between double discs 28 and cooperate therewith to from a gusset fold in each edge of the web. The gusseted' tube is next flattened by matching rolls 31 and double plates 32. The flattened gusseted tube next passes through drive rolls 33 which are adapted to run intermittently so as to advance the plastic web in units of one bag width. The rolls are actuated in response to a photoelectric cell mounted in monitoring unit 34 which responds to fiduciary marks printed on the film web at distances equivalent to one bag width. 4

The flattened tube next passes to gusset sealing station 35 where V-shaped seals are made between the four comer folds of the gussets at positions separated by units of one bag width and intermediate the overlap positions of the valve panels. The film external to the V-shaped seals is cut out at this station. The apex of the V-shaped seal is located at the position of the reentrant fold of the tube gusset. During the forming of the gusset seals adhesion between the external surfaces of the gusset can be prevented by either the insertion of an anvil into the gusset as in Canadian Pat. No. 746,689, or by using film having printing in the gusset area.

The tube with V-shaped gusset seals completed, next passes under a second photoelectric monitor 36 which responds to the fiduciary marks on the film and serves to control drive rolls in transverse sealing unit 37. Unit 37 is fitted with double transverse sealing elements whose action is controlled to make a double transverse seal between the two-ply web lying between the apices of two matching V-shaped gusset seals. These two transverse seals form the sidewall seals of two consecutive bags. Unit 37'is equipped with a transverse cutting device whose action is controlled to sever the two-ply web at a transverse position lying between the two transverse seals, thus separating consecutive bags. A separated bag is shown at 38;

Although it is possible to manually feed precut valve panels into position at the appropriate position in the operation and make the lower valve panel seal with a standard sealing element, automatic operation is desirable. In FIGS. 10, 11, 12 and 13 is illustrated an apparatus for automatically sealing two thicknesses of film to form composite valve panels, metering a predetermined length of valve panel, positioning the panel in correct position with respect to the two-ply web and the preceding valve panel, and sealing overlapping valve panels to the edge of the lower ply of the web. Referring to FIGS. 10 and l 1 reels of lengths of plastic film l8 and 19 are shown supported by brackets 39 and 40 fixed to the frame 41 of the apparatus. Film from reel 19 passes over feed roll 42 to

rolls

43 and 44 where it overlaps film from reel 18. Sealing device 20 located between

rolls

43 and 44 seals the two strips of film together at the position of overlap to form a length of film of two thicknesses suitable for valve panels. Sealing device 20 is constituted by heat-sealing element 45 carried by frame 46. Frame 46 is mounted in yoke 47 to pivot about a midpoint of the frame. The pivoting action of the frame 46 is controlled by air piston and cylinder unit 48 acting against springs 49. Heatsealing element 45 acts against an anvil attached to the end of plate 50 which yoke 47, air piston 48 and springs 49 also are attached. Plate 50 is fixed to the frame of the apparatus.

The sealed length of film next passes between matching metering rolls 51 and 52. FIGS. 12 and 13 show the details of the valve panel metering device. The metering rolls are mounted rotatably on shafts 53 and 54 which fit in hearings in matching support plates 55. Shaft 53 is free to rotate with respect to support plates 55, but shaft 54 is fixed rigidly to said plates preventing its rotation. Support plates 55 are fastened to side plates 56 of the upper frame of the apparatus. Rectangular cutouts in plates 56 expose the shaft bearing positions of the metering rolls. Each metering roll carries a spur gear 57, 58. These gears being in mesh assure that the metering rolls turn with the same peripheral speed but in reverse sense. Metering roll shaft 53 carries affixed to each extremity spur gears 59. These gears engage matching racks 60 which slide horizontally in guides 61 attached to side plates 55. The endsof racks 60 are attached at the output side of the metering rolls to a film support plate 62. The action of racks 60 are such that when the metering rolls discharge a length of valve panel, film support plate 62 moves forward supporting the film.

Also attached to side plates 55 is a valve panel cutoff device. This comprises a movable clampinggmember 63 carried by U-shaped frame 64 and fixed slotted cutting member 65. Frame 64 is hinged about set in side plates 55. Clamping member 63 is forced into I contact with cutting member 65 by the action of air cylinder. and piston units 67 whose pistons press against pins 68 carried by frame 64. Helical springs 69 acting against the pressure of the pistons of 67 tend to maintain clamping member 63 in araised position.

Cutting member 65 carries a movable knife 70 mounted on pivoted links 71 and 72. Helical spring 73 attachedto the lower extremity of link 72 tends to maintain knife 70 in a retracted position. Air cylinder and piston unit 74, connected to the lower extremity of link' 71, when actuated raises the knife upwards through the opening in '65. The lower surface of clamping member 63 is slotted corresponding to the slot in 65 so that knife 70 when raised will cut film clamped between 63 and 65.

The metering rolls are driven by arack75 and pinion 76,

actuated by air cylinder 77. Pinion 76 is mounted on the extremity of shaft 53 of lower metering roll 51. Pinion 76 meshes with rack 75 being held ,in mesh by theaction of roller 78.

' Rack 75 is connected to piston 79 working in air cylinder 77.

The lower extremity of rack 75 is joined to rod 80 which carries an adjustable collar 81. Rod 80 passes at its lower extremity through a bore in bracket. 82. Collar ,81 is too large to pass through the bore of bracket 82 and so acts to limit the travel of rack 75 andthus the rotation of metering rolls 51 and 52. Piston 79 can be controlled to occupy either an advanced or retracted position, however only during advance does it cause motion of the metering rolls. This is because metering rolls 51 and 52 are connected to shafts 53 and 54 respectively by

unidirectional clutches

83 and 84. Shaft 54 remains stationary, the motion of roll 52 being linked to that of roll 51 by meshing spur gears 57. and 58. Shaft 53 however rotates in both senses so that support plate 62 is extended and retracted as piston 79 is extended and retractdfThe rack and pinion unit (75 and 76) with its actuating piston and air cylinder are attached to plate 85 which is fastened to the side plate 56 of the upper frame of the apparatus. I

After passing through the metering rolls the valve panel film passes between raised clamping element [63 and cutting a member 65, being supported, by plate 62. The film is advanced until its extreme edge lies over anvil 86 but underneath the edge of the lower ply of the web and; the'trailing edge of the preceding valve panel. Heat-sealing element 87 carried in frame 88 is adapted to press the layers of film against anvil 86 to produce a heat seal. Frame 88 is geherally U-shaped being linked to main frame 56 by hinge 89 so as to permit raising and lowering the heat-sealing element 87. The motion of frame 88 is controlled by two

pistons

90 and 91 working in air cylinders 92 and 93. Air cylinders 92 and 93 are linked-to frame crosspiece 94, and the cooperating

pistons

90 and 91 are linked to the forward part of heat-sealer frame 88. j

The valve panel inserting apparatus can conveniently be film clamping and severing device. The air supply to these cylinders is controlled by the programmed controller 103 of the bagmaking machine so that the operationof'the valve in serter is coordinated with the operation of the other units of the machine. This is necessary sincethe sealing of the valve panels takes place while the web is stationary.

In operation the valve panel inserting and attaching apparatus goes through the following cycle.

The web of two-ply film being stationary and both heat-sealing element 87 and clamping element 63 being in raised positions, air is admitted to cylinder 77 to drive rack 75 down. Rack 75 rotates metering rolls 51 and 52 to advance a length of valve panel to a position where its advanced edge lies on anvil 86 and under the edge of the lowerply of the web and under the trailing edge of the preceding valve panel. Asthe valve panel advances it is supported by support plate 62. The rotation of the metering rolls terminates when collar 81 comes in contact with bracket 82.

Air is then admitted to cylinders 92 and 93 to force heatsealing element 87 against the superimposed layers of film lying on anvil 86 to'heat-seal the valve panel edge to the edge of the lower ply of the web in a lap seal.

Air is next admitted to cylinder 77 to retract the piston 79 and draw rack 75 upward and retract support plate 62 to a position interior to cutting member 65. Owing to the action of

clutches

83 and 84 rolls 51 and 52 remain stationary.

Air is then admitted to air cylinders 67 to force clamping member 63 against cutting member 65, followed by admission of air to air cylinder 74 to raise knife 70, and cutting the clamped valve panel film to-the desired panel size. When air pressure-to

cylinders

67 and 74 is released springs-69 and 73 return clamping member 63 and knife 70 respectively to their original positions.

During the operation of sealing the valve panel to the web air has been admitted to cylinder 48 to force heat-sealing element 45 against overlapping valve panel film lying over the anvil attached to plate 50. This seals the two portions of the valve panel material in a lap seal'of length corresponding to the length of film metered by rolls 51 and 52. With release of air from cylinder 48, heat-sealing element45 is lifted from the sealed film by the action of springs 49. 1

Air is next admitted to air cylinders 92 and 93 so as to retract

pistons

90 and 91 and raise heat-sealing element 87.

The coordinated controls of the bagmaking machine next advance the two ply web with valve panel attached by a distance equivalent to one bag width andfthe cycle-of the valve panel attachment is repeated while the web is stationary.

It will be clear to one skilled in the artof bag manufacture that modifications can be made in the operation of the bag making machine. For example instead of layfl'at tubing a wide sheet of single ply film can be center folded to form a crease on one side with two edges of free film on the other side. Such procedure may have advantage as to the; printing of information on the film. It is also clear that the valve panels of uniform gaugefilm may be employed to form bags with the simple valves illustrated in FIGS. 1, 2 and 3. The transverse seals on I the bags likewise maybe adjusted to form skirted side seals or mounted to travel on rails fastened to the bagmaking machine.

'- operation of

air cylinders

48, 67, 74,77, 92 and 93. The advance of the length of valve panel filmis controlled by the action of air cylinder 77. Air cylinders 47, 92 and 93 operate heat-sealing members. Air cylinders 67. and 74 operate the seals without film external to the seal line. Alternatively, the transverse severing cuts may be replaced by perforations so that the product can be transported on reels or as folded packs. An additional alternative is to provide bags in web form without transverse perforations, a form which may have advantage in automatic filling machinery. It is clear also that the machine described may be modified to form valved pillow bags by omitting the gusseting and gusset sealings steps.

The method of the present invention has the advantage that it permits the manufacture of valve bags in a continuous manner from a web of plastic film, the valve being inserted automatically in the edge of the web. The method is readily car ried out by a modification of known bagmaklng machines.

We claim: 7 1. A method for manufacturing valve bags which comprises the steps:

1. providing a two-ply main web of heat-scalable plastic film having a fold along one edge, the opposed edge of the web being open;

2. providing a supply of rectangular panels, each having a length greater than one bag width but less than two bag widths;

3. feeding the valve panels to a position adjacent to the open edges of the main web of film;

4. heat-sealing the opposed edges of each valve panel to the corresponding open edges of the main web with the unsealed extremities of the panels overlapping in the direction of the web edge, thus forming a tube;

5. heat-sealing said tube transversely by a double seal at positions intermediate each position of overlap of the valve panels; and

6. severing the film between the double transverse seal positions, thus separating successively fabricated valve bags.

2. A method of manufacturing valve bags as claimed in claim 1 wherein, subsequent to the sealing of the valve panels to the main web, gusset folds are formed in the two edges of the web including the edge constituted by the valve panels.

3. A method of manufacturing valve bags as claimed in claim 2 wherein the transverse seal of the gusset if formed by sealing each gusset fold in a V-shaped seal having its apex continuous with the double transverse seal of the two-ply region of the tube.

4. A method of manufacturing valve bags as claimed in claim 1 wherein the valve panels are preformed in two sections of different film thickness by sealing together the two film sections along a seal direction perpendicular to the edge of the main web of film.

5. A method of manufacturing valvebags as claimed in claim 1 wherein the valve panels are sealed to the edges of the main web of film by lap seals.

6. In an apparatus for the manufacture of bags from heatscalable plastic film in which a folded two-ply main web of film is advanced through the machine intermittently in increments equal to a bag width and during the stationary periods of the web transverse double seals and corresponding intermediate severing cuts are made to seal and sever consecutively produced bags the improvement for attaching a valved end panel to the bag which comprises (1) means for separating the free edges of the web, (2) means for providing a rectangular panel of film adapted to form the matching parts of valves in twosuccessively produced bags, (3) means for joining said panel along its longitudinal edges to the adjacent free edges of the main web at a position corresponding to two successively produced bags, and (4) control means for actuating the joining means at times corresponding to positions of successively produced bags.

7. Inan apparatus as claimed in claim 6 wherein the means for providing valve panels comprises means for metering from stock sufficient film to form the panel and means for cutting off the metered panel.

8. In an apparatus as claimed in claim 6 wherein the means for providing valve panels comprises means for sealing together portions of film of different thickness along a seal line running perpendicular to the direction of travel of the main web of film, thus to form composite valve panels.

9. In an apparatus as claimed in claim 6 wherein the means for joining the valve panel to the main web comprises a heatsealing bar and cooperating anvil adapted to seal the longitudinal edges of the panel and main web in a lap seal.

10. In an apparatus as claimed in claim 6 wherein the joining of the valve panel to the main web is carried out in two stages comprising means for heat-sealing the first longitudinal edge of the valve panelto the lower free edge of the main web, means for folding the second longitudinal edge of the valve panel over the upper free edge of the main web and means for heatsealing the second longitudinal edge of the valve panel to the upper free edge of the main web.