LU88604A1 - Infinitely variable patterns, physical and chemical properties produced in foam co-extrusion method - by rotating foamable melts together with variable speed and direction under computer control in rotary casing containing mixing screw to produce firmly-welded but distinct interfaces between masses in composite. - Google Patents

Abstract

This procedure makes foam composites from at least two foamable streams of molten polymer having different physical and/or chemical characteristics. They are brought together in an extrusion tool, after the gas injection stage. The novel feature of this process, is the partial mixture and/or rotation of the streams before they are coextruded, in such a way as to achieve any selected pattern within the mass of the resulting composite. Also claimed is a foam composite made from two melt streams as described.

Description

METHOD AND DEVICE FOR PRODUCING COEXTRUDED FOAM COMPOUND BODIES

The present invention relates to a method and an apparatus for producing coextruded foam composite bodies

From German published patent application DE-OS 4 316 863 a foam composite body is known which is produced from at least two different polymer melts, the individual parallel or concentric layers of the foamed polymer melts in the end product being sharply separated from one another and nevertheless firmly attached to one another at their contact surfaces are connected. In order to prevent mixing of the foamable polymer melts and still to ensure a firm connection between the layers of the foam composite body, the polymer melts in the extruder die are brought into connection with one another at an empirically determined distance before the nozzle outlet, without mixing.

US Pat. No. 5,190,706 describes an apparatus for producing foam composite bodies, two polymer melt streams being brought together in an extruder die and one of the two polymer melt streams being applied to the surface of the second polymer melt stream through an opening in the extruder die. This opening can contain a nozzle, whereby the first polymer melt stream is applied in a specific pattern to the surface of the second polymer melt stream. However, only a very limited number of patterns can be produced on the surface of the second polymer melt stream.

It is therefore an object of the present invention to provide a method for producing foam composite bodies, as a result of which at least two polymer melts can be processed into any desired pattern in the mass of a foam composite body.

This object is achieved according to the present invention by a process for the production of foam composite bodies, wherein at least two foamable polymer melt streams having different physical and / or chemical properties are brought together in an extruder tool after gassing. The method according to the invention is characterized in that the polymer melt streams are at least partially mixed and / or twisted and then coextruded, so that any pattern is formed in the mass of the foam composite body.

In this process, only the polymer melt streams are at least partially mixed and / or twisted, but not the polymer melts themselves. Homogeneous mixing of the polymer melts is not sought, the boundaries between the individual polymer melt streams remain sharp and clearly visible in the finished product. The polymer melt streams are firmly welded together over the entire contact area.

This method enables e.g. To produce foam composite bodies that have any pattern in their mass because of the mixing and / or twisting of the individual polymer melt streams. In the previously known methods, it is only possible to either produce foam composite bodies which have two-color patterns on their surface or else to consist of several different, parallel or concentric layers.

The method according to the invention is less prone to failure. It allows foam composites to be manufactured easily and inexpensively.

The foam composite bodies of the present invention can not only be used for decorative purposes, but also foam composite bodies with new physical and / or chemical properties can be produced. For this purpose, polymer melt streams with different properties are mixed together. Depending on

The type and intensity of the mixing makes it possible to tailor the properties of the foam composite body which are produced by this process to the respective requirements.

Foam composites produced by this method can be used to mark products in different color patterns, as is the case today e.g. is the case with electrical cables.

The foam composite bodies produced in this way can also be used in the packaging or in the leisure industry.

According to a first preferred embodiment, the mixing and / or twisting of the polymer melt streams is carried out by controlled turning of a mixing insert fitted in at least two of the polymer melt streams.

Advantageously, the mixing insert installed in at least two of the polymer melt streams is rotated about its own axis at between 1 and 100 revolutions per minute. The speed of rotation of the mixing insert is best infinitely variable and the mixing insert should be rotatable in both directions about its own longitudinal axis.

Thanks to the rotating mixing insert, an almost unlimited number of different patterns can be produced and changed at any time during production without the need to convert the production facilities.

The polymer melt streams can be brought together upstream of the mixing insert and then passed through the mixing insert. This allows many different polymer melt streams to be mixed and / or twisted.

However, the polymer melt streams can also be led separately to the mixing insert and only brought together within the mixing insert. In this case, however, normally only two polymer melt streams can be mixed and / or twisted.

The present invention also relates to a device for producing foam composite bodies with at least two extruders, which are connected to an extruder die and each feed a foamable polymer melt stream into the extruder die, the polymer melt streams having different physical and / or chemical properties. The device according to the invention is characterized in that the extruder tool comprises a mixing insert which can be rotated about its own axis and which at least partially mixes and / or rotates the polymer melt streams.

The mixing insert preferably comprises a rotationally symmetrical mixer which is mounted in a rotatable housing. Due to the large number of different shapes that are possible for the rotationally symmetrical mixer, the patterns in the foam composite bodies produced can be fundamentally changed by simply exchanging the rotationally symmetrical mixing insert. The device can therefore be used for a whole range of different products.

According to a preferred embodiment, the mixing element is connected to an axial channel which leads a polymer melt stream into the rotationally symmetrical mixer, while the second polymer melt stream is conducted outside the channel to the mixing element. The polymer melt streams are accordingly brought together only in the mixing element. In such a case, one of the polymer melt streams is mixed in a certain pattern by the rotationally symmetrical mixer under the polymer melt stream flowing outside the channel.

However, it is also possible to bring the polymer melt streams upstream, in front of the mixing element in a first section of the extrusion die, and thus to mix several polymer melt streams with one another.

In such a case, it is advantageous to use, as a rotationally symmetrical mixer, a screw that twists and / or at least partially mixes the various polymer melt streams with one another.

According to a further preferred embodiment, the mixing insert can be rotated in both directions about its own axis by a motor via a friction gear. Advantageously, the mixing insert attached in at least one of the polymer melt streams is rotated about 1 to 100 revolutions per minute around its own axis either in one direction or in the other direction, the speed of rotation of the mixing insert being infinitely variable.

In order to make optimum use of the device, it is advantageous to control the motor by means of a computer and thus to drive the mixing operation in a pre-programmed and repeatable manner as often as desired.

The present invention also relates to a foam composite body with any pattern in its mass, which comprises at least two foamable polymer melts with different physical and / or chemical properties.

The polymer melt streams are firmly welded together over the entire contact area. .

According to the present invention, the blowing agent used for direct gassing is preferably i-butane, n-butane, propane, pentane, i-pentane, C02, N2i F142b (difluoro-mono-chloroethane), F22 (difluoro-mono-chloromethane), F134 (tetrafluoroethane) or mixtures thereof.

The same blowing agent is preferably used for the direct gassing of the individual foamable polymer melt streams to be combined, and in such quantities that the foam composite body has a density of less than 100 kg / m3, preferably less than 50 kg / m3.

The foam composite body according to the invention preferably consists of one or more of the polymers from the group of LDPE, (Low Density Polyethylene), LLDPE (Linear Low Density Polyethylene), HDPE (High Density Polyethylene), PP (Polypropylene), PVC (Polyvinylchloride), PS (polystyrene), SAN (styrene acrylonitrile), EVA (ethylene vinyl acetate), and EAA (ethylene ethyl acetate). The foam composite bodies have strands which are firmly connected to one another and have different polymers, colors, bulk densities and / or temperature resistance.

The mechanical and electrostatic properties of the foam composite bodies can be influenced by fillers.

Various preferred embodiments of the device according to the invention are described below with reference to the figures. Show it:

1: an overall view of a device for producing foam composite bodies,

2 shows a section through the extruder die of a first exemplary embodiment of a device for producing foam composite bodies;

3 shows a section through the extruder die of a further preferred embodiment of a device for producing foam composite bodies;

4a-14a are examples of multi-colored foam composites in accordance with the present invention;

Fig. 4b-14b show sections through the Fig. 4a-14a.

15a-18 are examples of dynamic mixers that can be used in the illustrated composite foam manufacturing apparatus of FIG. 3.

15b-17b show sections through FIGS. 15a-17a.

1 shows an overall view of a preferred embodiment of a device for producing foam composite bodies. It comprises three extruders 10, 12, 14 which open into an extruder die 16 which is equipped with an extrusion head 18 and a motor 20. The motor 20 is controlled by an external computer 22.

FIG. 2 shows a partial section through the extruder tool 16 of a first exemplary embodiment of an apparatus for producing foam composite bodies.

The extruder tool 16 consists of a plurality of sections lying one behind the other, the polymer melt streams flowing together in the first section 24, twisted and / or at least partially mixed in the second section 26, and extruded in the third section 28.

Sections 24 and 28 are equipped with heating tapes 30 and temperature probes 32 to ensure that the polymer melts can be kept at the optimum temperature during the entire process.

The polymer melts of the extruders 10, 12, 14 are brought together in the first section 24 of the extruder die 16, the connections of the extruders 10 and 14 each being provided with a shut-off valve 34 which allow the polymer melt streams from the two extruders 10, 14 to be interrupted. As a result, this device can be used for the extrusion of foam bodies which consist of one, two or three different polymer melts, without the entire apparatus therefore having to be dismantled or converted.

In the second section 26 of the extruder die 16, the polymer melt streams are mixed with one another or twisted into one another. For this purpose, this section 26 contains a mixing insert 36 which comprises a housing 38 in which an elongated rotationally symmetrical mixer is attached. In this case, the elongated rotationally symmetrical mixer is designed as a screw 40, which is sealed against the inner housing 38. The polymer melt streams are twisted into one another by rotations of the mixing insert 36 and / or at least partially mixed with one another

The inner housing 38 is rotated about its longitudinal axis by the motor 20 by means of a belt pulley 42. The rotation of the inner housing 38 rotates the screw 40, which is in solidarity with the inner housing 38, about its own axis within the polymer melt streams, so that the polymer melt streams are mixed with one another and / or twisted into one another. Since the motor 20 can be controlled by a computer 22 and the mixing insert 36 can thus be rotated about its longitudinal axis in both directions, any number of patterns can be produced and varied as desired during production. For this purpose, the speed of rotation and / or the direction of rotation of the mixing insert 36 is changed. The preferred rotational speed is between 1 and 100 revolutions per minute.

The forces of the motor 20 are, in this example, transferred from a friction gear or roller bearing to the mixing insert 36. The motor 20 is equipped with a drive pulley 44, which transmits the movement to a pulley 42. The movement of the pulley 42 is transmitted to the inner housing 38 and thus to the mixing insert 36 by means of an output pulley 46 which is in solidarity with the inner housing 38. The friction wheel transmission is particularly advantageous in this case because it is simple in construction and thus allows an inexpensive construction and can simultaneously serve as an overload clutch.

The inner housing 38 is rotatably supported by a roller bearing 48 in the second section 26 and sealed by seals 50.

After flowing through the individual polymer melts through the mixing insert 36, the twisted and / or mixed

Polymer melt streams are extruded through a conventional extrusion head 18 into a standard pressure atmosphere.

The extrusion head 18, which in this example is designed for the production of composite foam pipes, essentially consists of a bolt 52 arranged in the polymer melt stream and a tool disk 56 connected to the third section of the extruder tool 16 by centering screws 54. The bolt 52 and the tool disk 56 form an extrusion die through which the polymer melts are extruded, the polymer melts flowing around the bolt 52 and being delimited to the outside by the tool disk 56.

In the bolt 52 a compressed air supply 58 is attached which opens within the polymer melt stream.

When carrying out the method, it is important that the extruder tool 16, in particular the extrusion head 18, is tempered uniformly and homogeneously. This is particularly important in the production of foam composite pipes, since in the extruder die 16 an additional bolt 52 is required which extends to the nozzle outlet and which must be tempered from the inside with compressed air. Make sure that the air is not too cold, otherwise the extrusion nozzle will freeze. In practice, good empirical values have been achieved with air temperatures that are approximately 50 ° C below the freezing temperatures of the polymer melts used.

FIG. 3 shows a section through the extruder tool 16 of another preferred embodiment of a device for producing foam composite bodies. In this particular embodiment, composite foam pipes can be produced with two different polymer melts. Instead of as in the embodiment shown in FIG. 2, the polymer melt streams do not flow together before the mixing insert, but rather are led separately to the mixing insert.

The input of the first extruder 12 is connected to an axially arranged channel 60 which leads the polymer melt into the mixing insert 62. The mixing insert 62 comprises an inner housing 64 in which an elongated rotationally symmetrical mixer 66 is attached. In this case, the elongated, rotationally symmetrical mixer 66 is accommodated in an extension 68 of the channel 60, the transition between the channel 60 and the extension 68 being sealed radially outward by means of seals 70. The extension 68 of the channel 60 is connected to the rotatable housing by one or more webs 72. The housing 64, the extension 70 and the elongated rotationally symmetrical mixer 66 are accordingly rotatable with respect to the polymer melt stream which flows around the channel 60 on the outside.

The polymer melt streams are rotated into one another by rotations of the mixing insert 62 and / or at least partially mixed with one another. The polymer melt from the extruder 12 is divided into different streams by the mixing insert 62 and below the polymer melt from the second extruder 14, which is outside the channel 60 in Direction extrusion head 18 flows, mixed. In this case too, the mixing insert 62 is set in rotation by a computer-controlled motor 20 via a friction gear, so that foam composite bodies with different patterns, which are dependent on the speed of rotation and the direction of rotation, can be produced.

4a-14a are examples of multi-colored foam composites in accordance with the present invention;

Fig. 4b-14b show sections through the Fig. 4a-14a.

The products of FIGS. 4-10 were produced with the extruder according to FIG. 3, with FIGS. 4-7 having round products with a wavy pattern. FIGS. 8a and 8b show a composite foam pipe, while FIGS. 9a and 9b show a flat product with a wave pattern. However, more complex shapes such as 10, are produced.

11-14 were produced with an extruder according to FIG.

All of these examples show only a limited selection from a large number of different patterns and shapes that can be produced using the described method and extrusion tools.

15a-18 are examples of mixers that can be used in the illustrated device for producing foam composite bodies according to FIG. 3.

15b-17b show sections through FIGS. 15a-17a.

FIGS. 15a and 15b show a cylinder blunted on both sides with peripheral recesses and central bores. A rotationally symmetrical mixer with a star-shaped cross section is shown in FIGS. 16a and 16b.

17a and 17b show a cylindrical mixer with an inner lattice structure, while FIG. 18 shows a mixer with a cylindrical section which has corrugated surface depressions.

Claims (16)

1. A process for the production of foam composites in which at least two foamable polymer melt streams with different physical and / or chemical properties are brought together in an extruder die after gas injection, characterized in that the polymer melt streams are at least partially mixed and / or twisted and then coextruded , so that any pattern in the mass of the foam composite body. 2. A process for the production of foam composite bodies according to claim 1, characterized in that the polymer melt streams are at least partially mixed and / or twisted by controlled rotation of a mixing insert fitted in at least two of the polymer melt streams. 3. A method for producing foam composite bodies according to claim 2, characterized in that the rotational speed of the mixing insert is infinitely variable. 4. A process for the production of foam composite bodies according to one of claims 2 or 3, characterized in that the polymer melt streams are brought together upstream before the mixing operation. 5. A method for producing foam composite bodies according to one of claims 2 or 3, characterized in that the polymer melt streams are brought together within the mixing insert 6. Device for the production of foam composite bodies with at least two extruders which are connected to an extruder die and each feed a foamable polymer melt stream into the extruder die, the polymer melt streams having different physical and / or chemical properties, characterized in that the extruder die has one of which its own axis rotatable mixing insert which at least partially mixes and / or rotates the polymer melt streams. 7. The device for producing foam composite bodies according to claim 6, characterized in that the mixing insert comprises a housing and a rotationally symmetrical mixer which is attached in the housing. 8. Device for the production of foam composite bodies according to claim 6 or 7, characterized in that the mixing insert attached in at least one of the polymer melt streams can be rotated in both directions about its own axis at between 1 and 100 revolutions per minute. 9. A device for producing foam composite bodies according to claim 7 or 8, characterized in that the housing is connected to an axial channel which leads a polymer melt stream to the rotationally symmetrical mixer. 10. The device for producing foam composite bodies according to claim 7 or 8, characterized in that the polymer melt streams are brought upstream, in front of the housing in a first section of the extruder die. 11.Device for producing foam composite bodies according to one of Claims 6 to 10, characterized in that the rotationally symmetrical mixer is a screw. 12. Device for producing foam composite bodies according to one of claims 6 to 11, characterized in that the extruder die comprises a motor which rotates the mixing insert in both directions about its own axis. 13. A device for producing foam composite bodies according to claim 12, characterized in that the motor is controlled by a computer. 14. Foam composite body with any patterns in its mass from at least two foamable polymer melt streams with different physical and / or chemical properties. 15. Foam composite body according to claim 14, characterized in that the foam composite body has a density below 100 kg / m3, preferably below 50 kg / m3. 16. Foam composite body according to claim 14 or 15, characterized in that the foam composite body comprises one or more of the polymers from the group LDPE, LLDPE, HDPE, PP, PVC, PS, SAN, EVA, and EAA