DK144208B - METHOD AND APPARATUS FOR MANUFACTURING PLASTIC BAGS - Google Patents

Description

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DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No. 2351/74 (51) IntCI.3 B 31 B 1/54 (22) Filing date 30 · Apr. 1974 B 31 B 29/00 (24) Race day 30 Apr. 1974 (41) Aim. available Nov. 2 1974 (44) Submitted Jan 18 1982 (86) International application # - (86) International filing day - (85) Continuation day - (62) Master application no -

(30) Priority 1 May 1973, 20676/73, OB

(71) Applicant NATIONAL PETRO CHEMICALS CORPORATION, New York, US.

(72) Inventor Herbert Edward Brock, US: Glenroy Gregor Blatz, US:

James Burley Hon, US.

(74) Associate Engineer Hofman-Bang & Bout ard.

(54) Method and apparatus for making plastic bags.

The present invention relates to a process for producing plastic bags of the kind set forth in the preamble of claim 1.

The invention further relates to an apparatus of the kind specified in claim 3 for the production of plastic bags in the practice of the method according to the invention.

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From the disclosure of U.S. Patent No. 3,606,822, a method and apparatus for producing such a bag or sack are known. The problem lies in the rapid, continuous and automatic preparation of

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The bags, since the prior art is essentially based on piecewise operation which is inherently slow and therefore uneconomical.

Ω 2 144208

Certain of the advantages associated with thermoplastic materials present difficulties in bag making, especially in folding, as electrostatic effects will tend to keep a laid web in unfolded state and the flexibility of the material discourages the formation of folds and layers, especially when at high speed many and complicated folds must form within a small area.

The present invention has for its object to provide a method and apparatus for the automatic and continuous production of folded bags with a folded bottom of a thermoplastic web or tubular film and which enable mass production with greater production speed and precision than has been achieved by means of the invention. prior art.

This object is achieved by the fact that the method is peculiar to the features of claim 1, and that the apparatus has the features of claim 3.

The bags made by the method and by means of an apparatus according to the invention have an approximately rectangular, flat base and, using a plastic material of appropriate rigidity, the bags can be made with self-supporting walls which allow the bags to be placed upright in an open position on a substrate. , eg. for filling, which has not so far been possible in mass production of plastic bags.

For the manufacture, a flattened tube of plastic film, preferably HD polyethylene film, which is formed with lateral layers, is used, the upper and lower sides along each longitudinal edge being joined by a sheet in the form of a single inlaid fold. Such material is delivered from a supply roll under controlled tension to an apparatus for welding, cutting and bottom folding, the material web being passed through the apparatus by means of conveying means in the form of gripping means which grip the lower leg edges. During feeding, the web is periodically closed with transverse welds by means of movable heat rails and then cut by the welding seam, preferably by means of a rotary shaving cutter, which acts against a soft plastic abutment roller so that the cut plastic webs are not interconnected. This provides a series of consecutive bag blanks which are closed at one end by the weld seam. While the individual bag items are still carried and driven by gripping means at the same velocity as the web, they according to the invention are opened by blowing in air which is preferably ionized, separating the top and bottom sides of the web so that the bag blank is easily accessible to the gripping means. This opening of the bag blank will also facilitate the feeding of the upper leg edge to a gripping action for folding the bottom. The bottom of each bag is then folded raw as the bag blank is advanced, the two folding edges at each side of the bag blank being gripped at certain locations at the closed end of the blank as further specified in claim 1.

The respective folding edges are then moved forward at different speeds, whereby one set of gripping means, cf. Claim 5 is adapted to move forward at a speed corresponding to the feed rate of the bag blanks in the apparatus so as to ensure a smooth and smooth folding of the bag bottom. The closed edge may conveniently comprise the front portion of the bag, and the folding edges are then gripped by separate sets of movable gripping means which move at different speeds, so that the upper folding edge is retracted behind the bottom thereby forming a raw bottom, which essentially contains cross folds and attach to the gripping means. Possible air is then removed from the individual bags and these are flattened to compress the bottom folds, after which the bags are released and stacked.

All of these operations are continuous and automatic and are synchronized to produce high speed bags or bags.

The invention will be explained in greater detail by the following description of an embodiment, with reference to the drawing, in which fig. 1 is a schematic side view of the components of a plant for carrying out the method according to the invention; FIG. 2 is a side view of a machine for welding, cutting and bottom folding; FIG. 3 shows the same from above; FIG. 4 is an enlarged view of a portion of an upper gripper assembly; FIG. 5 is a sectional view taken along line 5-5 of FIG. 4 through a gripper; 6 is a sectional view taken on line 6-6 of FIG. 3, showing inflation means; FIG. 7 is a sectional view taken along line 7-7 of FIG. 3, showing cutting means; 8 is a sectional view taken along line 8-8 of FIG. 3> showing welding means, FIG. Figs. 9, 10 and 11 are schematic sections showing the progressive folding of the bag bottom by means of different gripping sets at different speeds; 12, 13 and 14 are perspective views, respectively, of the laid web, a welded and cut portion thereof and the finished bag with folded bottom, fig. 15 on a large scale, partly schematic, part of a lower gripper assembly; FIG. 16 and 17 section along the line 16-16 of FIG. 15, with the parts in different positions, while FIG. 18 on a large scale, perspective, partly in section, showing a spacer or separator in FIG. 15th

FIG. 1 shows the components for carrying out the method according to the invention for producing a bag with a folded and folded bottom of a roll of HDPE in the form of a laid tube film or laid web GW, see fig. 12. The material is in the form of a flat web with following extending leg G, see fig. 12, and is in the form of one or more rollers 16, 16 'suspended in a roller holder 22 with brake means 24 for braking the shaft of the roller and thus regulating the tensile stress in the t released path. A voltage sensor 26 at the path provides feedback to the brake 24 for controlling the voltage in the path to the desired value.

A burner 28 is arranged so that, by heat treatment, it can prepare one face of the web for printing. The web GW is then rectified by an automatic web guide 30 of the pivotal type controlled by edge sensors 32 which senses the web edge position and reports back to the guide of guide 30. The web is then imprinted in a suitable printing press 34 and passes therefrom directly. in a bag molding machine 36 designed in accordance with the invention. The printing press, the tension control means, and other units in front of the machine 36 are conventional units mounted together as shown.

The machine 36 comprises a welding station 38, a cutting station 40, a bottom folding station-42, which supplies a stacking unit 44 at a packing and dispatching station 46.

The machine 36 is supported by a machine frame 48 which may consist of a plurality of pins 50 connected at the top by transverse rails 52. The laid web GW, fig. 12, the machine 36 is first converted into a closed bottom bag by welding and cutting, fig. 13, and then into a folded bottom bag, FIG. 14. The web is introduced into the machine 36 by clamping rollers 53 operated at a speed slightly higher than the web speed through the machine, to remove tensile stress on the welds and to compensate for shrinkage during welding or heat closure.

The introduced web and the resulting parts are "all passed through the production line continuously, quickly and at the same speed, by grippers disposed on each side of the web · GW. These gripper means comprise side gripper chains 54 with grippers or gripper tongs 56 which is guided to grasp the lower edge of the leg GEL, Fig. 12, into the web as it enters the machine at the right end, as seen in Figs. 2 and 3. Spacer fingers 60 or additional grippers also engage. The open grippers are guided towards the edge GEL r by guide 61 so that one cover of the gripper enters the leg and the other under the track, and the guide 61 also opens the leg G so that the gripper can enter.

The first step in the treatment of the laid web GF is that, while the web is in motion, closures are made across the web and the legs, with distances corresponding to the length of the desired bags. This is done at the welding station 38, where there are a number of transverse heat rails 62, fig. 2, 3 and 8, carried by a chain 64 running over sprocket 66 and arranged so that the lower bar of the chain keeps each rail in contact with the surface of the web. Further, lower heat rails 68 are provided. corresponding to the rails 62 located on chains 70 over sprocket 72 running synchronously with the chains 64. The chains are operated such that the rails run at substantially the same speed as the web. The sprockets and chains of the welding mechanism are carried by a rack 74, which also carries no electrical equipment shown for supplying electrical pulses to the heat rails or one set thereof, for pulse welding. The heat rails 62 and 68 are arranged on the chains so that they meet to hold the web therebetween, see fig. 2 and 8. To apply the proper pressure during welding, a pair of adjustable push rods 76 are arranged at least behind the upper heat rails 62 for direct control of the position and pressure of these rails. Each of the heat rails 62 carries on the outside a heatable portion which will come into contact with the web along the area to be welded. Electric power for heating is delivered from a sectional bus bar 78, fig. 8, arranged between the push rods 76 and coming into contact with brushes 80 carried by the heat rails 62, e.g. for electrical impulse welding.

After the formation of such cross-welds, the web is cut in synchronism with the weld, close to each weld seam, by cutting means 82, see FIG. 2. These cutting means comprise a rotating knife 84 and a pressure roller 86 disposed on either side of the web. The rotary knife 84 carries in blocks 90 along the circumferentially interchangeable razor blades 88, see FIG. 7 · A cog connection 92 drives the rotating knife 84 and roller 86 at the same speed. The roller 86 7 144208 has a soft polyurethane replaceable 94 which the knives 88 cut into. This arrangement addresses a very difficult problem arising from cutting HDPE webs with a thickness of 0.05 to 0.08 mm, i.e. the cut surfaces are interconnected so that the web cannot be easily opened. With the one shown in FIG. 7, the web can be easily opened, which is necessary before the folding step, where grippers must grasp the upper leg edge. To fold the bottom of the closed and cut bag to the one in FIG. 14, the bag must be opened slightly.

The bags are opened at a blowing station 96, see fig. 3 · The blowing station has an air nozzle 98, fig. 6, mounted on a transverse support 100 and connected to a suitable source of compressed air, the air nozzle is directed toward the open end of the bag which has just been cut, and blows toward this end to open the bag for the subsequent bottom fold. Various means may be used to assist in inflating the bag, e.g. For example, the underside of the web GW can be held down by another set of square lower grippers not shown, or by suction means in the form of a vacuum box 102, fig. 6, connected through a line 104 to a vacuum source, over which runs a perforated belt 106 driven by synchronized drive means at the same speed as the feed chains 54.

Above the web is a restriction plate 108 which, as shown in FIG.

6 is suspended on a transverse support 110 at an oblique angle which serves to determine the extent to which the bags are opened.

When the bags leave the blowing station 106, they will be opened to a degree determined by the distance between the trailing edge 109 of the plate 108 and the conveying plane of the web GW. (In an alternative embodiment, the blow-up may occur in the following zone, or when the first and second sets of grippers have grasped the web, in which case these grippers themselves will provide the desired restraining effect).

The bag thus opened then enters the bottom folding station 42, where the upper leg edge GEU is gripped by upper gripper mechanisms 112;

2 and 3, located on either side of the web, with grippers 114 carried on chains 116 running over sprocket 118, see FIG. 3 and 4. The trailing edge 109 of the plate 108 places the upper leg edge GEU and guides the grippers 114 in position to grasp this edge.

8 144208

FIG. Figures 4 and 5 show the details of the grippers 114, which can substantially correspond to the grippers 56 for the lower leg edge, however they are in the reverse position. The lower grippers 56 may also, as shown in Fig. 15, be provided with a cutter piece 162 which will open the insert so that the upper grippers 114 can clamp properly around the upper part of the insert. The grippers each have a fixed jaw and a movable jaw. The grippers 114 shown in FIG. 4 and 5, has a fixed jaw 120 and a movable jaw 122 which, as shown in the dash lines of FIG. 5 can be opened so that only the fixed jaw 120 passes into the web of the web, after which the movable jaw 122 can be closed around the outside of the web to hold the web edge and advance it. The fixed jaw 120 forms part of a block 124 which is secured to the chain 116. At a suitable pin 126, the movable jaw 122 is secured to a cam follower bar 128 which can be displaced vertically in the block 124 and which is pressed closed by a spring 130. position. A cam follower roller 132 is mounted on the end of the rod 128 and is positioned to contact a stationary cam 134 on a housing 136 at the position where the grippers must open to engage or leave the shank. Thus, there is a stationary cam 134 at each end of the housing 136 where the grippers 114 respectively engage and away from the web, as shown in FIG. 3 · Similarly, stationary lugs on housings 138 and 140 are located around the sprockets of the chains 54 for opening the grippers 56 which grip the lower leg edge GEL of the web. The jaws of the lower grippers 56 may be formed in the same way as the jaws of the grippers 114. As shown in FIG. 15, the lower grippers 56 may comprise a fixed jaw 120 and a movable jaw 176 which also serves to carry the end seam S. of the bag.

FIG. 9, 10 and 11 show schematically how the two sets of grippers 56 and 114 grip and fold the bottom of the one in FIG. 13 to form the bag shown in FIG. 14. The chains 116 of the upper gripper mechanisms 112 are driven at a lower speed than the chains 54 carrying the lower grippers 56. This speed difference is indicated by the size of arrows in FIG. 9-11. The chains are synchronized such that the grippers 56 and 114 grasp the upper and lower leg edges in the positions shown in FIG. 3 and 9, where the upper grippers 114 are in the front and grip directly at the seam S, while the grippers 56 follow and grip at a position at the desired folding line. When the grippers are closed around the respective edges, as shown in FIG. 9> the velocity difference will cause the upper grippers 114 to fall backwards relative to the lower grippers 56 as shown in Figs. ). Furthermore, the upper grippers 114 move upwards relative to the plane of the web due to oblique positioning of the gripper mechanism 112, FIG. 2nd

During this movement, the bottom of the bag is opened and bent to form a raw folded bottom FB. 11 and 14. Put another way, the fold is there but is not pressed down as the bag still contains some air from the inflation station and since the HPPE does not fold in the same way as Kraft paper.

The lower grippers may be equipped with special folding members 160, see fig. 15, 16 and 17, which follow the lower gripper, grasp the outer edge of the upper leg edge behind the upper gripper and pull a portion of the web forward and below the raw folded bottom FB

The particular folding means 160 are hinged on the underside of the fixed gripper jaw 120 by a bracket 172 and actuated by a lever mechanism comprising a spring-loaded bolt 166 and an angular bar 164 mounted on a pin I68 and connected to the bracket 172 by a joint system 170. cam follower roller 174 is mounted at the end of lever 164 and positioned so that it comes into contact with stationary lugs not shown for opening and closing of folding members 160. The folding member 160 is mounted so that it is openly over the upper leg edge and in the closed position. position rests against the upper side of the upper calf. The folding member 160 can be actuated to close simultaneously with the lower gripper 56.

It will be appreciated that in order to form a square bottom pouch, it is necessary that the lower grippers grasp at a point whose distance from the end seam is equal to the inserted width of the leg so that the required fold effect. The upper grippers must grip the upper part of the calf at a point up to the end seam and within a distance equal to the width of the calf.

In other words, the upper grippers grasp the web at the same point as the lower grippers or in front of it, relatively straight at the end seam. If the apparatus is operated in such a way that the closed end of the bags is at the rear of the movement, the upper grippers will be brought to run faster than the lower grippers.

To promote the formation of regular uniform folds, the upper and lower grippers are angular, i.e. the fixed jaw inserted in the insert is cut off at the rear end of the upper grippers, as shown in FIG. 4, and at the front end of the lower grippers, as shown in FIG. 15 · Preferably, the cross-section is of triangular shape, usually at an angle of 45 °, with the perpendicular leg in the front of the upper grippers and in the rear of them. lower grippers.

After the bottom folding station there is one of venting means 142, fig. 3 which, in the embodiment shown, consists of a pair of brushes 144 arranged in a V-shape, with the angular tip leading towards the center of the folded bottom. These brushes press on the raw folded bag and vent it.

After the deaeration station, a pressing station 146 is found. 2nd

This station has a center press band 148 which runs over rollers 150 and is positioned at the center of the folded bottom of the bag, and a pair of edge press strips 152 which runs over rollers 154 and are placed along the edges of the bag over the legs. These belts are operated at a rate higher than the velocity of the chains 54 such that the bags are removed from the bottom folding station at a rate higher than that at which they are folded and are quickly removed from the grippers as the upper grippers 54 open as they pass around about the sprockets. The bags are now finished and delivered to the stacking station 44, whereupon they are transported to the wrapping station 46, where they are bundled and placed on pallets for shipment to grocery stores or the like.

A machine designed according to the invention has satisfactorily produced 1/6 bl goods bags of 0.076 mm HDPE with print, at a production rate of more than 200 bags per day. minute.

Although a machine has been disclosed for the manufacture of standard size HDPE bags with a folded base, it will be clear that the stated principles will be applicable to

Claims (2)

11 144208 similar bags of other sizes and that, instead of HDPE, any other suitable rigid thermoplastic material may be used. The term "bag" and "bag" have been used interchangeably in the foregoing for no other difference than the size. A method of making folded bottom bags from a flattened thermoplastic tube film, the side edges of which are each folded by two outwardly folding edges, and wherein the tube film is passed through an apparatus having a zone in which it is provided with transverse seals with prior art. spaced apart and cut near the seals to form a number of consecutive open-ended and closed-end bag blanks, characterized in that the two fold edges on each side of the bag blank are gripped by each gripping member to hold one fold edge of said gripper means over a distance approximately corresponding to the depth of the seam and starting from a location close to the seal, while the second folding edge is held by its gripping means at a distance, from the seal approximately corresponding to the depth of the seam, and the gripping means for the two folding edges during the further feeding of the bag item in the apparatus is moved forward at mutually different speed, into to there. thereby forming a folded bottom folded against the adjacent portion of the bag. A method according to claim 1, characterized in that the bag blank is opened, by blowing in air, to a position in which it is easily accessible to the gripping means before gripping the fold edges of the side edges. Apparatus for carrying out the method according to claim 1, characterized in that they are equipped with two sets of gripping means (56, 114) on each side of the feeding path of the bag blanks, one of the sets (56) being adapted to grip the bag piece one. folding edge and retaining it over a distance approximately equal to the depth of the bag blank, while the second set of grips