CH384199A - Process for the manufacture by extrusion of tubular nets of plastic material and device for carrying out the process - Google Patents

Description

Process for the manufacture by extrusion of tubular nets made of plastic material and device for implementing the process The present invention relates to a process for the manufacture by extrusion of tubular nets made of plastic material as well as a device for implementing the process. . Such nets are particularly suitable for making packaging bags for various products.

Such a process and a device are already known for the manufacture of tubular nets of plastics material suitable for making bags. However, such nets are not sufficiently stable to maintain the bag's rectangular dimensions, during and after its filling. For example, the filling of plastic bags with diamond-shaped mesh can become complicated due to the tendency of these bags to stretch under the weight of their contents, which is particularly troublesome when filling the bags. onions, oranges or potatoes. The package then often takes the form of a long tube rather than the usual approximately rectangular bag.

The present invention, which precisely obviates these drawbacks, relates to a process for the manufacture by extrusion of tubular plastic nets composed of three adjacent layers of parallel strands, the strands of a first layer forming a network with the strands of a second adjacent layer.

Said method is characterized by the fact that one of said two first layers, still in the molten and sticky state, is brought into contact with a third layer of strands parallel to each other as well as to the direction of extrusion and by the fact that said layers are united so that the strands of said third layer also intersect the strands of the first two layers and adhere at least to the strands of that of the first two layers which is adjacent to it.

A further subject of the invention is a device for carrying out the above method, characterized in that it comprises at least two concentric members, carriers of dies, having contact surfaces, each member having a series of strand extrusion dies which open in the vicinity of said surfaces towards an extrusion end of said members and means for rotating said members, in combination with means for bringing a third layer of strands, parallel to each other and parallel to the direction of extrusion, and means for bringing said third layer of strands into contact with one of the layers of strands produced by said extrusion dies when the latter emerge from their orifices.

The appended drawings show, by way of example, one embodiment of the device according to the invention, and variants.

fig. 1 is a view of part of an extruded net coated with a third layer.

FIG. 2 is a cross section of an extrusion head showing means intended for introducing a third layer of preformed strands.

fig. 3 is a view similar to FIG. 2 showing a modification in which the third layer of strands is extruded separately.

fig. 4 is a view similar to FIG. 3 showing a modification in which all the layers are extruded individually and united after extrusion.

A tubular net is produced consisting of two layers of parallel strands crossed in networks and then a third layer of parallel strands is deposited on one of the two layers so as to obtain a three-layer net. The third layer is applied tail after the two-ply netting components have been extruded, at a time and distance such that the two-ply netting layers are still melted and sticky.

The reinforcing elements can be filaments or ribbons made of plastic material or threads which are not made of plastic material. They can be fixed either to the junctions, or to the strands of the net, or to the junctions and to the strands. The number, size and shape of the longitudinal auxiliary yarns depend on the amount of reinforcement required.

The chemical nature of the reinforcing elements also depends on the reinforcement desired. In some cases, these strands should be made of the same plastic material as the net. The plastic material is then generally polyethylene, polypropylene, nylon or polyvinyl chloride.

The reinforcing threads, when they are not made of plastic material, can be made of cotton or another fibrous material, even glass or metal. Like the strands of the net, the reinforcing strands can have cross sections of various shapes.

Circular shaped filaments are generally preferred, but they can be square, oval or flat, similar to a capital D.

The fillet portion shown in FIG. 1 has 1, 2 diagonal strands and 3 longitudinal strands.

The layers of diagonal strands are connected together at the intersections 4 while the longitudinal strands are connected at the intersections 5 only to one layer of diagonal strands. From the point of view of the structure, the net of fig. 1 is similar to a net obtained in known manner with longitudinal parallel reinforcing strands arranged on one or the other of the ribs.

fig. 2 illustrates an embodiment of a device in which a layer of preformed filaments, represented by a single filament 3, is brought into contact with the filaments of a freshly extruded net composed of filaments 1 and 2. By preformed filaments, we mean threads, cords, monofilaments, etc...

The molten plastic material of the cavity 6 is extruded through dies 7 and 8 of the members 9 and 10, rotating in the opposite direction. The netting produced is composed of layers of diagonal filaments 1 and 2. A preformed filament 3 is fed from top to bottom of the hollow shaft 11.11 is directed down through the ring 12 and up through and around from the outer side of a ring 13 towards the point where it comes into contact with the filaments 1. This contacting taking place while the filaments 1 are in a pasty and sticky state, a solid bonding takes place which results in the net with three layers of parallel strands shown in fig. 1. Rings 12 and 13 are supported by known means (not shown).

fig. 3 shows a first variant of the device according to FIG. 2, in which the net with two layers of diagonal strands, is extruded in the same way as in FIG. 2 but in which the reinforcing strand 3 is extruded simultaneously with the other two.

In this device, a stationary central die-carrying member 14 is provided with an annular groove 15 fed by the molten plastic material coming from the cavity 6 through several supply holes 16 located in a rotating die-carrying member 10.

At the base of the notch or of the annular groove 15 is a ring of die orifices serving for the extrusion of the third layer of reinforcing strands 3. The third layer of strands extruded through the orifices 17 comes into contact with the inner layer of the extruded net of the dies 7 and 8 in the vicinity of a gauge of cylindrical shape 18. The carrier member of the central dies being stationary, the strands 3 produced are parallel and longitudinal. The device of FIG. 3 can be further modified to include extensions on the lifeline orifices 17 so as to introduce the reinforcing strand into the net at a point closer to the discharge orifices of the lifelines 7 and 8.

fig. 4 represents a second variant of the device of FIG. 2. The main difference from the device according to fig. 3 is that the dies 7 and 8 are separate orifices which do not form integrally extruded intersections. In this modification, all the layers of strands are united outside the dies in the vicinity of the cylindrically shaped gauge 18.

In all the above figures, the die bearing members can be rotated by appropriate means, not shown. Rotary means, plastic feed means and other suitable mechanisms are known to those skilled in the art.

Although the layer of reinforcing strands is applied by the device described above inside the extruded tubular net, it can be applied by appropriate means to the outer strands of the net.

These reinforcing strands can be extruded separately from different sources of plastic material, which allows the use of a polymer different from that which is used in the net.

The process and the device described are satisfactory for the preparation of reinforced plastic nets. Bags made from such nets are much more suitable than others for packaging, since they eliminate the low dimensional stability which is one of the most serious drawbacks encountered in the use of plastic net bags.

In figs. 2, 3 and 4 of the drawing, the strands pass through a water bath below the spinnerets, the broken line 20 represents the water level.

CLAIMS I. Process for the manufacture by extrusion of tubular plastic nets composed of three adjacent layers of parallel strands, the strands of a first layer forming a network with the strands of an adjacent second layer, characterized in that one brings one of said first two layers, still in the molten and sticky state, into contact with a third layer of parallel strands between them, as well as in the direction of extrusion, and by the fact that said

**WARNUNG** Ende DESC Feld konnte Anfang CLMS uberlappen**.

Claims (6)

WARNUNG* Anfang CLMS Feld konnte Ende DESC uberlappen *. such that the layers of the two-ply net are still melted and sticky. The reinforcing elements can be filaments or ribbons made of plastic material or threads which are not made of plastic material. They can be fixed either to the junctions, or to the strands of the net, or to the junctions and to the strands. The number, size and shape of the longitudinal auxiliary yarns depend on the amount of reinforcement required. The chemical nature of the reinforcing elements also depends on the reinforcement desired. In some cases, these strands should be made of the same plastic material as the net. The plastic material is then generally polyethylene, polypropylene, nylon or polyvinyl chloride. The reinforcing threads, when they are not made of plastic material, can be made of cotton or another fibrous material, even glass or metal. Like the strands of the net, the reinforcing strands can have cross sections of various shapes. Circular shaped filaments are generally preferred, but they can be square, oval or flat, similar to a capital D. The fillet portion shown in FIG. 1 has 1, 2 diagonal strands and 3 longitudinal strands. The layers of diagonal strands are connected together at the intersections 4 while the longitudinal strands are connected at the intersections 5 only to one layer of diagonal strands. From the point of view of the structure, the net of fig. 1 is similar to a net obtained in known manner with longitudinal parallel reinforcing strands arranged on one or the other of the ribs. fig. 2 illustrates an embodiment of a device in which a layer of preformed filaments, represented by a single filament 3, is brought into contact with the filaments of a freshly extruded net composed of filaments 1 and 2. By preformed filaments, we mean threads, cords, monofilaments, etc... The molten plastic material of the cavity 6 is extruded through dies 7 and 8 of the members 9 and 10, rotating in the opposite direction. The netting produced is composed of layers of diagonal filaments 1 and 2. A preformed filament 3 is fed from top to bottom of the hollow shaft 11.11 is directed down through the ring 12 and up through and around from the outer side of a ring 13 towards the point where it comes into contact with the filaments 1. This contacting taking place while the filaments 1 are in a pasty and sticky state, a solid bonding takes place which results in the net with three layers of parallel strands shown in fig. 1. Rings 12 and 13 are supported by known means (not shown). fig. 3 shows a first variant of the device according to FIG. 2, in which the net with two layers of diagonal strands, is extruded in the same way as in FIG. 2 but in which the reinforcing strand 3 is extruded simultaneously with the other two. In this device, a stationary central die-carrying member 14 is provided with an annular groove 15 fed by the molten plastic material coming from the cavity 6 through several supply holes 16 located in a rotating die-carrying member 10. At the base of the notch or of the annular groove 15 is a ring of die orifices serving for the extrusion of the third layer of reinforcing strands 3. The third layer of strands extruded through the orifices 17 comes into contact with the inner layer of the extruded net of the dies 7 and 8 in the vicinity of a gauge of cylindrical shape 18. The carrier member of the central dies being stationary, the strands 3 produced are parallel and longitudinal. The device of FIG. 3 can be further modified to include extensions on the lifeline orifices 17 so as to introduce the reinforcing strand into the net at a point closer to the discharge orifices of the lifelines 7 and 8. fig. 4 represents a second variant of the device of FIG. 2. The main difference from the device according to fig. 3 is that the dies 7 and 8 are separate orifices which do not form integrally extruded intersections. In this modification, all the layers of strands are united outside the dies in the vicinity of the cylindrically shaped gauge 18. In all the above figures, the die bearing members can be rotated by appropriate means, not shown. Rotary means, plastic feed means and other suitable mechanisms are known to those skilled in the art. Although the layer of reinforcing strands is applied by the device described above inside the extruded tubular net, it can be applied by appropriate means to the outer strands of the net. These reinforcing strands can be extruded separately from different sources of plastic material, which allows the use of a polymer different from that which is used in the net. The process and the device described are satisfactory for the preparation of reinforced plastic nets. Bags made from such nets are much more suitable than others for packaging, since they eliminate the low dimensional stability which is one of the most serious drawbacks encountered in the use of plastic net bags. In figs. 2, 3 and 4 of the drawing, the strands pass through a water bath below the spinnerets, the broken line 20 represents the water level. CLAIMS I. Process for the manufacture by extrusion of tubular plastic nets composed of three adjacent layers of parallel strands, the strands of a first layer forming a network with the strands of an adjacent second layer, characterized in that one puts one of said first two layers, still in the molten and sticky state, into contact with a third layer of parallel strands between them, as well as in the direction of extrusion, and by the fact that said layers are united in such a way that the strands of said third layer also intersect the strands of the first two layers and adhere at least to the strands of that of the first two layers which is adjacent to it. II. Device for applying the method according to claim I, characterized in that it comprises at least two concentric members, carriers of dies, having surfaces in contact, each member having a series of extrusion dies for the strands which open in the vicinity of said surfaces towards an extrusion end of said members and means for rotating said members, in combination with means for bringing a third layer of strands, parallel to each other and parallel fi, the direction of extrusion , and means for bringing said third layer of strands into contact with one of the layers of strands produced by said extrusion dies when the latter emerge from their orifices. SUB-CLAIMS 1. A method according to claim 1, wherein said third layer of strands is a layer of preformed filaments. 2. A method according to claim 1, wherein said third layer of strands is separately extruded from the extruder which produces the other two layers. 3. A method according to claim I, wherein all three layers of strands are extruded separately and wherein said first two layers are brought into contact with each other after they emerge from the extruder to form a net, the third layer of strands being extruded from the same extruder and being brought into contact with one of the two layers of strands of the net. 4. Apparatus according to claim II, wherein the means for introducing the third layer of strands comprises a series of stationary die orifices extruding the strands, concentric with said rotating die members. 5. Device according to claim II, in which the means for introducing the third layer of strands comprises means for guiding the pre-formed filaments downwards from the hollow central shaft of the said device and means for guiding the said filaments and placing them in contact with one of the layers of said extruded strands of the net. 6. Device according to claim II, characterized in that it comprises three concentric members carrying dies, each member having a series of strand extrusion dies, the central member being stationary and the two outer members having means to rotate them in opposite directions, means for bringing the layers of strands extruded from the two external rotating members into contact when they emerge therefrom to form a tubular net and means for bringing the layer of strands extruded from of the stationary central member with the layers of one of the adjacent layers of strands of the net when they emerge from the extrusion device.