DE68907475T2 - System for the continuous production of bags made of polypropylene, polyethylene, PVC or similar plastic materials. - Google Patents

Abstract

Plastic bags are fashioned by sealing two layers of polypropylene, polythene or PVC film along two, three or four sides, often with holes punched along one of the longitudinal edges, the continuous film being uncoiled from a bulk supply turned out by chill-roll extrusion methods. The plant disclosed comprises a folding station (5), then in sequence, a heat-seal station (11), a cooling stage and a cutting station (40), and turns out the bags in an entirely continuous process.

Description

The present invention relates to systems for the continuous production of bags using polypropylene, polyethylene, PVC and similar plastic material.

The conventional process includes a variety of systems for forming plastic bags by heat sealing, all of which are disruptive in that they involve the introduction, generally via a conveyor belt, of previously cut and folded pieces of film into the sealing device, which consists of a reciprocating plate arranged transversely to the conveyor, the film material being held motionless in the device until two, three or four sides have been sealed together to form the bag.

The plastic bags of the type in question are, due to the need for the film piece to remain static in the heat-sealing device, must be costly to produce, and there is no way to speed up this production step.

Another disadvantage of systems of this type is the waste generated, since a horizontal strip of the film must be cut off in order to ensure opening and finishing.

US-A-2 866 392 shows an apparatus for producing bags made of cellophane or the like, including a folding device, at least one welding device with electrically heated, roller-supported welding irons, and a cutting device with a roller-supported blade which cooperates with a fixed blade.

A problem with the welding device is that the plastic film comes into direct contact with the heated irons and, in addition, there is no effective device for cooling the heat-welded film.

US-A-4 599 926 shows a punching roll for cutting holes in running fabrics and sucking out the waste parts inside through an axial passage in the roll.

The document shows neither a cooling device, nor an application of the roll to a system for continuous production of bags or similar.

The purpose of the present invention is to realize a plant for the continuous production of bags using one or more film rolls, or alternatively and due to the same ability for continuous production, to combine it with a cast continuous production plant in which continuous film is produced by extrusion.

Another purpose of the invention is to increase the number of bags produced by the system per hour without compromising quality.

Another purpose of the invention is to reduce the waste generated during production.

When using a system according to the present invention, it is also possible to produce bags continuously with reinforcing ribs and, if desired, with perforations, which are either applied as additional film layers or produced directly during extrusion.

The purposes listed are set out in Annexes in accordance with of the present invention, which has the characteristic features according to claim 1).

The invention is described in detail below by way of example and with the aid of accompanying drawings in which:

Fig. 1 is a schematic representation of the disclosed invention in plan view.

Fig. 2 is another schematic representation of the invention in side view.

Fig. 3 shows the hot welding device in side view.

Figure 4 shows a section through the hot welding device through III - III on Figure 3.

Fig. 5 is a side view of the cutting and punching device.

Figure 6 is a section through the punching device through IV - IV in Figure 5.

Figure 7 is a section through the cutting device along V - V in Figure 5.

With reference to Figures 1 and 2, it can be noted that the system described provides for the use of continuous plastic film (polypropylene) folded into two layers.

(1) indicates the feed roller carried by a holder (2) and from which the film is unwound, which passes through guide rollers 4 and is guided to a folding device (5) of conventional type, shown schematically in the drawings.

The folding device serves to fold the film into two identical sandwich layers and is indicated at (6) which are guided by the guide rollers (7) and passed around a roller (8) which has a pressure roller (8a) which has the function of flattening the fold and preparing the film for passage through a series of units or devices to which the present invention effectively relates.

(9) denotes a drive unit consisting of two driven pull rollers (19) by which the film is pulled from the feed roller and guided into the following devices.

(11) refers to a heat welding device in its entirety following the drive unit and how it is aligned.

With reference to Figures 3 and 4, it can be noted that the heat-welding device (11) comprises an upper roller (12) and a lower roller (13), both driven by a belt (14) which passes around two pulleys (15) and (16) mounted on the respective shafts (17) and (18) and rollers (12) and (13). The belt (14) is kept taut by a tensioner (19) and driven by a pulley (20) which is moved by a pair of bevel gears (21) which in turn is driven by a shaft (22) driven by a gear motor (23) (see Fig. 2).

The shafts (17) and (18) are hollow to accommodate the electric power cables (24) of the resistors (25) that heat the rollers (12) and (13).

In the example illustrated, the resistors are arranged according to two parallel lateral rings (26) and (27) whereby two endless longitudinal welds are carried out along the outer edges of the folded, running film, and according to a transverse element (28) for carrying out transverse welds on the film.

The two shafts (17) and (18) are supported by two bearings (29) and (29a) connected by brackets (30) and (31) to two corresponding rails (32) and (33) mounted on columns (34) are mobile.

All columns (34) are partially threaded so that two ring nuts (37) can be screwed on, which act on bushings (38) that are movably mounted on the columns and allow the position of the shafts to be adjusted.

(39) designates one of the four pneumatic cylinders, which are located between the rails (32) and (33) and by which the heated rollers are elastically compressed during operation and separated when stopped.

(35) designates a belt surrounding the lower heated roller (13) which has the task of completely isolating the folded film from the surface of the roller and thus avoiding direct contact between the two; the belt is driven by the roller (13) itself and tensioned by the device (36).

A plant according to the present invention comprises a cutting and piercing device located behind the hot-welding device. As can be seen from Figures 5, 6 and 7, the device in question, which is designated in its entirety by (40), comprises two separate Devices: a cross cutter 40a, by which the continuous film is separated into individual bags, and a punching device (40b) which produces a plurality of holes along a longitudinal edge of each bag.

The cutting device (40a) comprises an upper roller (41a) and a lower roller (41b), of which the upper roller (41a) is elastically brought into contact with the lower roller (41b) by a spring device made of rubber (42).

(43) designates a diagonally arranged blade, which is carried by the lower roller (41b) which acts together with a stop (44) inserted in the upper roller (41a).

The blade and the stop are fixed and adjustable by the corresponding devices (43a) and (44a).

The shafts (45) and (46) of the cutting device (40a) are hollow to allow the passage of a cooling liquid to and from the rollers through corresponding intake and exhaust pipes and are driven using a system identical to that previously described for the hot-welding rollers.

The punching device (40b) also comprises two rollers, of which the upper roller (51) has a plurality of holes (52) arranged in a circle and containing corresponding balls (53), each of which is held in its seat by a retaining ring (54) and pressed against the ring by register screws (55).

The lower roller (56) of the device is equipped with a plurality of hollow, cylindrical cutting edges (57) which are arranged to correspond with the balls of the upper roller and thus punch circular holes in each bag. The lower roller is supported by a hollow shaft (60) to allow connection to a suction system (61) which removes the punched material generated during production. Like the two rollers of the cutting device, the two punching rollers (51) and (56) are elastically brought into contact by a rubber spring device (62).

At the exit of the last device, a conveyor belt collects and counts the bags produced.

Alternative realizations of the invention are possible without affecting the validity of the enclosed requirements. For example, the number of resistances of the heat sealing rollers can be changed to adapt to other types and sizes of bags.

Claims (6)

1) Device for the continuous production of bags using polypropylene, polyethylene, PVC and similar plastic films, consisting of: - a transport unit (9) for unrolling an endless film from one or more conveyor rollers; - a continuously operating rotary welding device (11) consisting of drive rollers (12) and (13) whose shafts are arranged parallel and coincident with the path taken by the film, in which the welds of the parallel longitudinal edges of the film, also in the transverse direction, are carried out; - rotating devices (40) for cutting and separating the individual bags transversely and/or longitudinally, characterized in that the drive rollers (12) and (13) have electrical resistors on the outside which coincide in circumference and with the rectilinear generator of the roller geometry; the lower roller (13) is surrounded by a belt (35) which serves to ensure direct contact between the rollers and the continuous To avoid foil. 2) Device according to claim 1), equipped with: Rotary welding machines (11) consisting of two driven rollers (12) and (13) fixed to respective tubes (17) and (18) through which the supply cables are passed to the electrical resistances and where the roller shafts are held between rails (32) (33) adjustable in height so that the respective position of the shafts can be changed and connected to one another by pneumatic cylinders in such a way that the rollers can be held elastically together during operation and separated from one another during standstill. 3) Device according to claim 1), characterized in that it is equipped with: Rotary cutting device or cutting and punching device for punching a long side of the bags, equipped with: cutting device (40a) consisting of two rollers (41a) and (41b) with parallel, perpendicular to the path of the film Axles whose surfaces carry at least one blade and at least one stop plate which correspond to the cylindrical and/or rectilinear generator of the roller geometry. 4.) Device according to claim 1), characterized in that it is equipped with: Rotary cutting and punching device, equipped with a punching device (40b) consisting of an upper roller (51) having a plurality of bores (52) receiving corresponding balls (53) each held by a ring (54), and a lower roller (56) having a plurality of cylindrical cutting edges which are mounted in such a way that they cooperate with the balls (53) of the upper roller. 5.) Device according to claim 4), characterized in that the cylindrical cutting edges (57) are hollow and are connected through the inner cavity of the lower roller (56) to an extraction system which is also connected through the hollow shaft which supports the roller itself to the inner cavity of the roller (56). 6.) Device according to claim 1), characterized in that the belt (35) is driven by the roller (13) itself and is equipped with a tensioning device (36).