LU86146A1 - EXTRUSION METHOD AND DEVICE FOR PRODUCING A WIRE COATED WITH FOAM PLASTIC - Google Patents

Description

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The present invention relates to an extrusion process and a device for producing a wire coated with foam plastic, in which a plastic melt consisting essentially of thermoplastics, cell former and a physical blowing agent, and optionally dyes, is extruded together with the wire continuously introduced into the extrusion tool.

From DE-OS 15 15 805 a wire insulated with a foamed plastic is known. However, the disadvantage of this wire coated with foam plastic is that the binding of the foam jacket to the wire is unsatisfactory.

The object of the present invention is therefore to provide a wire coated with foam plastic, in which the foam plastic sheath firmly encloses the wire.

This object is achieved according to the invention in that a wire cooled below room temperature, preferably below 0 ° C., is used.

In the manufacture of such a wire provided with a foam plastic sheath according to the invention, a device is used which is characterized according to the present invention in that the extrusion tool is provided with a wire feed attachment which protrudes into the extrusion tool without contact and which includes most of the wire feed channel which in turn cantilevered from the exit from the wire feed attachment into the mandrel tip, the wire feed channel in the wire feed attachment being surrounded by V4 a cooling chamber in order to continue to keep the supplied wire, already cooled down in the cooling device, in the extrusion tool until it is cool he comes into contact with the plastic melt.

The present invention thus relates to an extrusion process for the production of a wire coated with foam plastic, in which a plastic melt consisting essentially of thermoplastics, cell former and a physical blowing agent, and optionally dyes, is extruded together with the wire which is continuously introduced into the extrusion die, which characterized in that a wire cooled at room temperature is used.

Furthermore, the subject of the present invention includes the device described above for carrying out the method according to the invention, and the product, i.e. the wire coated with foam plastic and the use of this foamed wire for binding plant parts such as stems, stems, twigs, branches and the like. In addition, according to the invention, electrical conductors insulated with foam plastic sheath can also be produced.

The invention is further explained below with reference to FIGS. 1 and 2, which represent a preferred embodiment, and the following parts of the description.

Fig. 1 shows in section the extrusion tool with a flanged wire feed attachment.

2 shows a schematic representation of an overall device according to the invention.

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In the figures, the reference symbols have the following meaning: 1 extruder 2 extrusion tool 3 wire feed attachment 4 wire feed channel 5 exit from the wire feed attachment (3) 6 mandrel tip 7 cooling chamber 8 mandrel opening 9 spacer 10 extruder nozzle 11 nozzle outlet opening 12 nozzle antechamber 13 feed of the plastic melt 14 cooling device 15 wire straightening device 16 wire drum

As shown in FIG. 1, the wire feed attachment 3 is flanged to the extrusion tool 2. There is a spacer 9, preferably made of a thermally insulating material, between the wire feed attachment 3 and the extrusion tool 2, so that the part of the wire feed attachment 3 protruding into the extrusion tool 2 does not come into contact with the extrusion tool 2. The space between the extrusion tool 2 and the wire feed attachment 3 thus also serves for thermal insulation.

The wire feed channel 4 located in the wire feed attachment 3 is surrounded by the cooling chamber 7, through which the cooling liquid is passed. This cooling liquid not only cools the major part of the wire feed channel 4, but also the parts of the wire feed attachment 3 protruding into the extrusion tool, by heat dissipation. In this way, the wire which has already cooled down before entering the wire feed attachment 3, while maintaining its temperature, reaches the mandrel opening 8, where it comes into contact with the hot plastic melt in the nozzle antechamber 12. The plastic melt coming into contact with the wire is quenched and a thin layer is formed on the wire, which encloses it tightly. In order for this layer to form on the wire by quenching, but on the other hand to avoid reheating or melting of the plastic layer formed on the wire during the quenching, it is important that the distances between mandrel opening 8 and nozzle outlet opening 11 meet the process conditions, e.g. the speed of the wire feed and the prevailing temperature conditions in the melt.

The main cooling of the wire takes place - as already mentioned - before entry into the wire feed attachment 3. This can be done in the manner shown in Fig. 2 by continuously pulling the wire from the wire drum 16 and '·' after passing the wire straightening device 15 through the Cooling device 14 leads from where the wire, preferably directly, without coming into contact with the outside air, reaches the wire feed attachment 3.

Of course, you can also cool down the entire wire drum in a corresponding freezer or freezer and from there through a special lock extractor into a, preferably under vacuum and possibly also cooled, wire straightening "device 15 and then directly into the wire feeder - lead essay 3.

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An essential inventive feature of the method can thus be seen in the use of the cooled wire. Due to the preferably strongly cooled wire, there is still in the nozzle, i.e. in the nozzle antechamber 12, the plastic melt to be foamed is quenched, which then deposits as a thin, non-foamed layer on the wire and thus creates the connection between the wire and the foam. If you use an uncooled wire, the foam sheath does not fit tightly against the wire. Even in this case, the wire has a certain amount of play in the foam casing and can be moved back and forth easily.

In order to obtain the desired thickness of the foam casing, it is necessary to choose a certain ratio of the diameter of the nozzle outlet opening and the wire. This ratio is preferably 2.5: 1. In a preferred embodiment according to the present invention, a foam jacket with a diameter of 10 mm is obtained at this ratio of 2.5: 1 with a wire diameter of 1 mm. Of course, the diameter of the foam shell also depends on the composition of the plastic melt to be foamed.

In general, the casing is obtained from a foamed plastic by extrusion using a screw extruder. A chemical blowing agent, e.g. Azodicarbonamide and 4,4'-oxybis- (benzenesulfonyl hydrazide), or an inert gas such as nitrogen, argon and carbon dioxide gas, or a gaseous or liquid hydrocarbon from the group consisting of methane, propane, butane, pentane and hexane or a gaseous or liquefied fluorocarbon, such as Trichloromonofluoromethane, dichloride fluoromethane, trichlorotrifluoroethane and dichlorotetrafluoroethane are used. The plastic is generally polyolefin, such as e.g. low density polyethylene, medium polyethylene - 9 -

Density, high density polyethylene, polypropylene and a butyl rubber or a mixture of at least two of these materials. Polyethylene and polypropylene are the most common plastic materials.

According to a preferred embodiment according to the invention, the procedure is such that to achieve a foam density below 60 kg / cm and a rough surface of the plastic sheathing, the ratio of wire diameter to diameter of the plastic sheathing being at least 1: 8, (a) the physical blowing agent in an amount of 20 to 30%, based on the thermoplastic, is metered directly into the melt in the extruder; (b) uses high density, low density polyethylene as the thermoplastic; (c) allowing the mixture to be foamed to emerge from the extruder nozzle together with the wire at a temperature of 60 to 105 ° C; (d) operate at an ejection speed of at least 50 m / min; and (e) uses a soft iron wire of quality class DIN 17140 as the wire, which has a temperature of 10 ° C.

Of course, in the method according to the invention, an adhesion promoter in the form of a wafer-thin coating can also be applied to the wire before the cooled wire is introduced into the plastic melt, which in certain cases can additionally improve the adhesion of the foam plastic sheath to the wire. In general, however, this is not necessary.

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In the preferred embodiment specified above, the distance from mandrel opening 8 and nozzle outlet opening 11 is preferably 18.5 cm.

Claims (10)

1. Extrusion process for the production of a wire coated with foam plastic, in which one melts a plastic, consisting essentially of thermoplastics, cell former and a physical blowing agent, and optionally dyes, together with the wire continuously introduced into the extrusion tool, characterized in that uses a wire cooled at room temperature. 2. Extrusion process according to claim 1, characterized in that one obtains a foam density below 60 kg / cm and a rough surface of the plastic sheathing, the ratio of wire diameter to diameter of the plastic sheathing being at least 1: 8, (a) the physical blowing agent in an amount of 20 to 30%, based on the thermoplastic, is metered directly into the melt in the extruder; (b) uses high density, low density polyethylene as the thermoplastic; (c) allowing the mixture to be foamed to emerge from the extruder nozzle together with the wire at a temperature of 60 to 105 ° C; (d) operate at an ejection speed of at least 50 m / min; and (e) uses a soft iron wire of quality class DIN 17140 as the wire, which has a temperature of 10 ° C. i - 2 - 3. Extrusion method according to claim 1 and 2, characterized in that one introduces a supercooled wire into the extrusion die, which is coated with an adhesion promoter. 4. Device for carrying out the method according to claims 1 to 3, characterized in that the extrusion tool (2) is provided with a wire feed attachment (3) which projects into the extrusion tool (2) without contact and most of the wire feed channel ( 4), which in turn protrudes from the outlet (5) from the wire feed attachment (3) cantilevered into the mandrel tip (6), the wire feed channel (4) in the wire feed attachment (3) being surrounded by a cooling chamber (7) in order to keep the supplied wire, which has already cooled down in the cooling device (14), in the extrusion tool (2) until it comes into contact with the plastic melt. 5. The device according to claim 4, characterized in that a thermal insulation material (9) is arranged between the wire feed attachment (3) and extrusion tool (2) in the flange region. 6. Apparatus according to claim 4 and 5, characterized in that the mandrel in the extrusion tool (2) is arranged so that the mandrel opening (8) arranged in the mandrel tip (6) is so far away from the nozzle outlet opening (11) that on the one hand a homogeneous cooled layer is formed on the wire and on the other hand this layer does not melt again. - 3 - 9 7. Device according to claims 4 to 6, characterized in that the diameter of the nozzle outlet opening (11) to the diameter of the wire is in a ratio of 2.5: 1. 8. Apparatus according to claim 4 to 7, characterized in that a separate cooling device (14) for continuously cooling down the wire to be foamed is arranged in front of the extrusion tool (2). 9. Foamed wire, produced by the method according to claims 1 to 3 above. 10. Use of the foamed wire according to claim 9 v for tying plant parts, such as stems, stems, branches, branches and the like.