CS200454B2 - Method of continuous production of plastic material bags and device for making the same - Google Patents

Abstract

1426814 Seaming non-metallic sheet material WAVIN BV 7 March 1973 [15 March 1972] 11212/73 Heading B5K In the manufacture of thermoplastic bags, longitudinally spaced transverse seals are made in a tubular thermoplastic film 3 by feeding the film 3 longitudinally in a substantially untensioned condition past a heating member 10 to plasticize the film in zones where the transverse seals are to be formed and passing the film 3, after leaving the member 10, between two pressure rollers 12, 13 to effect sealing. The film 3 is fed from a roll 1 bearing on rotatable rubber rollers 2 by driven rollers 4. Transverse perforations are made by a rotatable drum 5 having projections thereon and cooperating with a backing roller 6. The sealing members 10 are mounted in a metal surface drum 8 and are thermally insulated therefrom. Preferably, each member 10 is made of copper covered with polytetrafluoroethylene. Foam rubber rollers 7, 9 maintain the film 3 in contact with the roller 8 but do not compress it thereagainst. The roller 12 is provided with a cooling spiral 18 and a lever 19 is provided to press the roller 13 against the roller 12. The rollers 4 rotate slightly faster than the rollers 12, 13 so that the film 3 is not tensioned as it passes around the drum 8. A tension roller 20 acted on by a spring 21 draws the film slippingly from between the rollers 12, 13 and then the film passes between rollers 14, 15 driven at the same speed as the rollers 4. Subsequently, the film 3 passes through a printing machine 18a, is doubled longitudinally by a folding triangle 16 and is wound on a device 17.

Description

(54) Method of continuous production of plastic bags and apparatus for its implementation

The present invention relates to a method for the continuous production of plastic huooy bags by allowing the welding surface to act on the entrained tubular film of thermoplastic mattrial, whereupon the resulting bag is either separated from the film web or perforated near the weld seam or at a location. where the weld joint is to be formed to separate the bag.

The invention also relates to an apparatus for carrying out the method according to the invention.

. This method is known per se. However, it has the disadvantage that due to the action of the welding surface, the plastic film collapses at the weld joint, which damages the plastic film and often results in a less flowable weld joint.

Obviously, the strength of the bag with the corrugation decreases, the wall thickness is reduced, and thus easily cracks occur when the bag is filled with the material.

Attempts were made to degrade. these drawbacks by separating the piece of foil hose before forming the weld joint and forming the weld joint at the free end of the separate piece of foil hose. The advantage of this procedure is that the death of the plastics material can take place from both ends to the weld seam, thus avoiding a weakening of the wall, and thus the quality of the bag is greatly improved.

However, this method of manufacturing bags is disadvantageous because the bags cannot be supplied to the store in the form of belts formed by a series of bags joined at the perforation points. At present, these belts are a popular form in which thin-walled plastic garbage bags from dHaSaS are served.

The present invention provides a method for eliminating such a shortcoming; belts are obtained therefrom, consisting of a series of sacks joined together at the perforations, wherein the weld joint is of excellent quality and is obtained without undesirable local wall weakening.

According to the invention, this is achieved by such an arrangement whereby the heated welding surface is allowed to act on an untensioned loose plastic film hose without appreciably higher pressure, after which the surfaces of the film to be joined together after plasticizing. the heated welding surface is removed from the tubular film, and the parts to be welded together are introduced into a pressure zone where they are pressed together by two pressure rotating cylindrical surfaces.

The temperature of one pres-undispersed surface is maintained below the point měkkntí thermoplastic ^mate-A-1-a The advantage ^d ou na ^h odnot ^E 5 ⁰ ° C, no ^B ON ^ S ^ particular toplotě ^of ^ o ° ^: ^greater than ^b of below this temperature.

When using such a method of joining, the welded joint obtained is of better quality than the joint produced by the known method. This is probably due to the fact that the plastic material is first softened without applying pressure at the weld joint, then subjected to pressure, using a cooling downstream surface, which rapidly dissipates heat, while on the other hand achieving the desired pressing against each other enclosed layers of tubular foil.

The surface of at least one of the rollers, each other being cooled to one another, is cooled by a cooling medium, for example by supplying an air stream to the rollers, at least one of which rollers is metallic. The surface of the film that comes into contact with the welding member contacts the metal surface directly, without leaving the insulating layer.

Under the action of the heated welding member, the tubular film web can be guided through at least one roll between the rollers, which are mounted so that the clearance between them corresponds to the total thickness of the two layers of the film lying on top of each other.

This ensures sufficient contact between the two layers of foil, which are joined together perfectly when passing between the cross-roll rollers.

The progressive velocity of the tubular film in the section from the point of application of the welding surface to the point of compression is a lower velocity than the film moves during welding.

When the weld seam passes through the adhesive zone, but before the welding surface begins to re-act on the film, it is slidly removed from the pressure zone formed by the rotating present surfaces, thereby compensating for the difference in the progressive speed of the film web.

In order to improve the quality of the weld joint, it is advantageous to weaken the foil strip wall at a small distance from the point where the weld joint is to be formed prior to welding. This attenuation also improves the quality of the weld joint, since the material may shrink longitudinally in the direction of the weld joint due to the attenuation at this point, which is intended to serve as a bag breaking point.

When applying the method of the type described above, the film web is preferably printed only after the welded joint has been produced, such that the printing is carried out in the region between the weld joint and the wall weakened position, which is more distant from the joint. In the present methods, the film web is printed prior to forming the perforations and the weld joint. This is disadvantageous because the welding surfaces often come into contact with the printed material, which makes their operation worse. In the method according to the invention, the printing can be performed better at a precisely selected distance from the weld joint.

Apparatus according to the invention for carrying out a method of manufacturing plastic film bags, wherein the welding member is allowed to act on a entrained thermoplastic material hose film over a rotating drum, the apparatus comprising feed members, withdrawal members and hose film guide members, at least one heated welding member, separating device and / or perforating arrangement is characterized in that, for feeding the flattened hose from the thermoplastic maerial foil in a virtually unstressed state to advance around the welding members 10, feed members 4, 4 are arranged opposite the rotary drum 8 Preferably, at least one retaining member 2, 2, 11 is provided, wherein the play between the drum 8 and the added member 2, 2, 11 is adjustable.

The apparatus according to the invention is further characterized in that the welding member or welding members 10 are thermally insulated from the surface of the rotating drum 8, whereas in the direction of travel of the foil web, two withdrawal members 8, 13 are located at a distance from the rotating drum. Preferably, one of the pull-off members is optionally cooled, preferably a roll 52 contacting the film on the side opposite to the side in contact with the welding member. 10.

A further feature of the device according to the invention is that one of the pull-off members 13 can be separated from the other pull-off member 62 and that a spring-loaded tensioning roller 60 is arranged downstream of the push-pull members 62, 33.

By using a welding member thermally insulated from the rotating drum, it is ensured that the temperature on the surface of the drum made of the thermally conductive material does not exceed the temperature of the plastic film or at least significantly lower than this temperature. For example, for polyethylene, this temperature does not exceed 60 ° C.

One of the pressure rollers is preferably a metal cylinder, the metal surface of which has a larger diameter for dissipating heat; for this reason, the temperature of this cooling cylinder is almost never higher than the room or ambient temperature. ’

Suitably, at least one holding device or rollers is provided against the rotating drum, the clearance between the rotating drum and the holding device or rollers being adjusted so that it is equal to the total thickness of the two layers of the foil tubing lying thereon. These holding devices or cylinders are preferably made of foam rubber. Instead of holding rollers, it is also possible to use tie arms which are provided on the rotary drum.

The invention is further illustrated with reference to the accompanying drawing, in which one embodiment of the device according to the invention is schematically illustrated. .

The device comprises a rotatably supported coil. This coil rests on rotating rubber rollers 2, which can be driven by a peripheral speed corresponding to the desired advancing speed of the film web.

The rycH-ost of the moor can be controlled by the foil strip J once this is behind the driven feed rollers Д.

Perforated feed rollers 4 are provided with perforation devices 2 which provide the foil hose with a transverse perforation, which makes it possible to later tear the sacks away from the foil web. These perforating devices 6 consist of a rotary drum provided. tips and the corresponding rotating counter cylinder 6.

After the perforations have been made, the foil tubing is guided over the metal surface rotating drum 8 on which the welding electrode 10 is provided. This welding electrode 10 is positioned so as to be thermally insulated from the rotating drum 8. The welding electrode 10 is made of metal, for example, copper, coated with a thefioone; electrode may be heated to a temperature in the range ^{of 200} °, ^{and 400} ° C, ^{and no} heating only ^y (^ Neza esleno) ^p ^ alkyl ccording Uou ^f Olie, flow speed and type of film. The film web is a tacian in an unstretched free state to the welding electrode 10 by means of feed rollers 4. Both surfaces of the film are softened and heated to a temperature that allows them to be joined together by pressure. The surface of the drum 8 next to the welding electrode 10 should be considerably lower than the temperature at which the plastic film softens, for example a temperature below ⁶⁰ ° C, with a half-hearth and a win of ^d 30 ° C. When the temperature of the surface of the strip reaches this value, the film strip is removed from the welding electrode 10 and passes between the stripping member 12 formed by the cooling roll and the stripping member 13 forming the adhesive roll, which turning against each other. It has been found that pressing after previous softening greatly improves the quality of the weld joint. Cd-addition. the cylinder 12 is provided with a cooling coil 18 to maintain the metal surface of the cooling cylinder. 12 at or below ambient temperature.

In order to prevent the top foil layer from separating from the backsheet contacting the welding member during the application of the welding electrode 10, two holding rollers 1 and 2, both of foam rubber, are provided. The smallest distance between the surface of the drum 8 and the surfaces of the rollers J and 2 is equal to the total thickness of the two layers of the foil tubing lying on top of each other.

However, the holding rollers have no pressing effect. It should be noted that the welding electrode 10 is provided on the surface of the drum 8 so that it is insulated by asbestos insulation. To adjust the exact position of the rollers 7, 9 ^and 11, these rollers can be displaced since their axes are displaceable in the longitudinal grooves.

The surface of the cylinder 13 is preferably made of rubber, but other materials, such as tefoon-coated metal, may also be used. In some cases, this is a convenient solution.

A lever 19 is provided to press the cross roller 13 against the cooling roller 12.

The feed rollers 1 roll the tubular film somewhat faster than the withdrawal members formed by the draw-in roll 13 and the cooling roll -12. so that the tubular film contacts the welding electrode 10 in the unstretched free state.

However, when the tubular film leaves the welding electrode 10 before the welding electrode contacts the tubular film again, the tubular film is drawn by means of a tension roller 20 suspended on the spring 21. with slip between rollers 12 and .13. This treatment avoids too much deflection in the space between the drum 8 and the rollers 12, 13. The same result can be achieved by moving the roll 13 away from the roll 12.

Two counter-rotating rollers 14 and 15 are provided from the cooling roll 12 and the press roll 13, which carry the tubular film at the same speed as the feed rollers

From these rollers, the tubular film goes to the printing device 18a. where it prints.

When printing, it is printed exactly between the weld joint and the perforation. However, this is not necessary since it is also possible to print over the weld joint and the perforation.

After passing through the printing device, the tubular film is guided around the doubling device 18 where the film is doubled and then wound on the winding device 17 until, for example, a total of 20 bags have been wound. Then, the wound portion of the foil strip is torn off along the perforation. In order to obtain the best possible weld joint, it is advantageous for the rotating drum 8 to rotate somewhat slower than the feed rollers. This results in a very suitable pressing of the foil to the welding drum and hence a proper heating of the top foil layer. On the other hand, it is preferable to power. the pressure roller 13 or the cooling roller 12 itself at a somewhat lower speed than the rotating drum 8.

Claims (10)

SUBJECT OF THE INVENTION A method of continuously manufacturing plastic bags by allowing a welding surface to act on a entrained tubular film of thermoplastic material, wherein either the resulting bag is separated from the film web or the film is perforated near the weld seam or at the point where the weld seam to separate the bag, characterized in that the welding surface is allowed to act on an unstretched loose foil hose without appreciable back pressure, after which the welding surface is removed from the tubular film and the parts which after the plasticization of the film surfaces to be joined together are to be welded together, introduced into the pressure zone, where they are pressed together by two pressure rotating cylindrical surfaces. Method according to claim 1, characterized in that the temperature of one pressing surface is kept below the softening temperature of the thermoplastic material, preferably at or below 50 ° C. 3. The method according to claim 1, wherein the temperature of one pressing surface is maintained at or below ambient temperature. Method according to one of Claims 1 to 3, characterized in that during the application of the welding surface, the two walls of the film contact each other without being pressed against each other. 5. A method according to claims 1 to 4, characterized in that the progressive velocity of the tubular film in the region from the point of application of the welding surface to the point of compression is lower than the speed at which the film moves during welding. 6. A method according to claims 1 to 5, characterized in that, after the weld joint has passed through the pressure zone, but before the welding surface begins to re-act on the film, it is slidly removed from the pressure zone formed by the rotating pressure surfaces. Apparatus for producing plastic film bags, wherein the welding member is allowed to act on a entrained thermoplastic tubular film wrapped over a rotating drum, the apparatus comprising feed members, withdrawal members and tubular film guide members, at least one welding member , a separating device and / or a perforating device, characterized in that the feed members (4, 4) are arranged opposite the rotating drum (8) to feed the flattened hose of the foil of the thermoplastic material in a virtually unstressed state to advance around the welding members (10). 1), at least one retaining member (7, 9, 11) is preferably provided, the clearance between the rotating drum (8) and the retaining member (7, 9, 11) being adjustable. Apparatus according to claim 7, characterized in that the welding member or members (10) are thermally insulated from the surface of the rotating drum (8), whereas in the direction of travel of the foil web, two are located at a certain distance from the rotating drum (8). withdrawal members (12, 13), preferably formed by abutting rollers, which can jointly exert pressure, one of the withdrawing members being optionally cooled, preferably a roll (12) touching the foil on the side opposite to that was in contact with the welding member (10). Apparatus according to claim 7 or 8, characterized in that one of the removal members (13) can be moved away from the other removal member (12). 10. Apparatus according to claims 7 to 9, characterized in that a spring-loaded tensioning roller (20) is arranged downstream of the withdrawal members (12, 13).