DEVICE FOR THE EXTRUSION OF SULFUR-RECYCLED RUBBER MIXTURES, THE USE OF THE DEVICE AND A METHOD FOR PRODUCE AN EXTRUDED, SULFUR-RECYCLED RUBBER MIXTURE

Description

[0001] The invention relates to a device for extruding sulfur-curable rubber compounds. The invention also relates to the use of the device and a method for producing an extruded, sulfur-curable rubber compound.

[0002] Due to current developments in the rubber industry—particularly in tire manufacturing—to fully automate production processes, the quality requirements for each rubber product are constantly increasing. The weight and geometric dimensions of the extruded rubber compound, which is often in the form of a continuous strip, are of particular importance. In extrusion, a mixed rubber compound is extruded, for example, using screws in a twin-screw extruder, and then formed into a rubber profile using a forming unit such as a pre- and post-die. Deviations from the geometric dimensions or excessively large fluctuations in the weight of the extruded rubber compound, i.e., the rubber profile, often make automation impossible or necessitate discarding a significant portion of the rubber compound.This can unnecessarily burden the environment or prolong the production process.

[0003] EP2338655A2 discloses generally the mixing of rubber compositions such as those used in tire manufacturing, and in particular the continuous production of customer-specific rubber mixtures.

[0004] The JP25192564U aims to improve the function of an extruder by enriching the preheating device, using an ultrafast infrared radiant heater as the preheating device, whereby the extruder, which is fed during the receiving vibration, is not heated.

[0005] EP3431251A1 discloses a method for determining the shrinkage behavior of a rubber compound, the method comprising the following steps: a. providing a rubber compound at a temperature in the temperature range T1, b. extruding the rubber compound at a temperature in the temperature range T1 by means of an extrusion device to form an extruded profile, wherein the rubber compound in the extrusion device has a temperature in the temperature range T2, c. cutting the extruded profile into a profile with a length L1, d. tempering the cut profile with a length L1 at the ambient temperature in the range T3 for a predetermined period, e. measuring the magnitude of the length L2 of the tempered profile.

[0006] JPS5919138A describes the use of an infrared emitter, where the infrared emitter is positioned at the focus of an elliptical or parabolic reflecting surface. The surface of an unvulcanized rubber body containing a foaming agent is rapidly heated to create a vulcanized surface layer, resulting in a rubber article.

[0007] A primary objective underlying the invention is therefore to provide a device for extruding sulfur-curable rubber compounds that does not exhibit the known disadvantages described above and enables the automated extrusion of a rubber compound into a rubber profile. In particular, it was an objective to extrude rubber compounds in such a way that their predetermined weight or dimensions could be adjusted more precisely.

[0008] This problem is solved according to the invention by a device for extruding sulfur-crosslinkable rubber compounds according to claim 1.

[0009] A major achievement of the present invention is that by increasing the temperature of a rubber compound before extrusion in a gear pump, the variations in the weight per meter of the extruded rubber profile can be significantly reduced. The deviations from the targeted weight per meter can be disproportionately reduced by the specific combination of contactless heating using an IR emitter and additional extrusion in a gear pump, compared to a device comprising only an IR emitter with just any extrusion unit, or only a gear pump with just any heating source.Such a reduction in deviations from the target weight per meter results in a productivity increase of 10% to 25% compared to devices not based on the invention, using other heating sources or extrusion units, and thus significantly reduces environmental impact. As described below, for some rubber compounds, the reduction in deviations exceeds 25%, or the present invention even makes the extrusion of certain rubber compounds possible in the first place.

[0010] An IR emitter designed to heat a sulfur-curable rubber mixture located in the temperature control unit to at least 60 °C or even over 80 °C further reduces the aforementioned deviations and enables the processing of highly viscous mixtures.

[0011] Without wishing to be bound to a scientific theory, it is assumed that the synergistic effect occurring here is due to the specific combination of IR emitter as a contactless heating source and the gear pump as an extrusion unit discovered within the scope of the present invention, in order to produce a rubber profile.

[0012] Gear pumps are known from the prior art. A suitable IR emitter within the scope of the previous invention is, for example, the model with the product name "Infrared Spiral Emitter" or with the product name "IP 65 Infrared Emitter" from the company Heraeus, or a corresponding device for contactless heating. Within the scope of the present invention, the IR emitter is preferably suitable for heating an area of ​​0.1 to 1 m³ of a rubber compound fur, wherein the IR emitter particularly preferably has a power output in the range of 1 to 40 kW / m².

[0013] A device according to the invention is preferably as described above or as described above as preferred, wherein the device comprises measuring sensors, wherein one or more of the measuring sensors are designed and arranged to determine the temperature and pressure of the rubber mixture in the gear pump.

[0014] An advantage of the aspect of the present invention described above is that, by using the measuring sensors described above, deviations in the weight per meter or from the predefined geometric shape of the resulting rubber profile can be further reduced.

[0015] The device according to the invention, as described above or as preferably described above, additionally comprises a control unit configured to control the temperature of a rubber mixture by means of the IR emitter as a function of the drive power for rotating the gears of the gear pump and / or the pressure of the rubber compound in the gear pump and / or the pressure fluctuations of the rubber compound in the gear pump and / or the meter weight fluctuations of the extruded rubber compound after the gear pump to regulate.

[0016] An advantage of the aspect of the present invention described above is that the reduction or further reduction of deviations in the resulting rubber profile described above can be automated by a control unit described above and can also be achieved more precisely than with a comparable control system. This is particularly advantageous and therefore preferred with the measuring sensors described above in conjunction with the gear pump.

[0017] A preferred device according to the invention is one as described above, wherein the device comprises a mixer for producing sulfur-curable rubber compounds, which is connected upstream of the IR emitter. A particularly preferred device according to the invention is one as described above, wherein a storage unit for storing the rubber compound material mixed by the mixer is provided between the mixer and the IR emitter.

[0018] An advantage of the aspect of the present invention described above is that the components are stored on mixed rubber compounds and thus cool down. Without being bound to a scientific theory, it is assumed that cooling during storage causes particularly high deviations in the weight per meter or from the predefined geometric shape of the resulting rubber profile, making the use of a device according to the invention, as described above or as preferably described above, particularly advantageous.

[0019] A device according to the invention is preferably as described above or as described above as preferred, wherein the device additionally comprises at least one feeding unit for feeding rubber mixtures into the downstream gear pump, wherein the feeding unit comprises a rolling mill or an extruder, wherein the feeding unit is preferably located downstream of the IR emitter.

[0020] An advantage of the aspect of the present invention described above is that a feeding unit described above can further reduce the said deviations in the resulting rubber profile.

[0021] A device according to the invention is preferably as described above or as described above as preferred, wherein the IR emitter is configured to heat a sulfur-curable rubber mixture fed into the feeding unit or into the gear pump in such a way that the temperature of the sulfur-curable rubber mixture when fed into the feeding unit or into the gear pump is at least partially at least 50 °C, preferably at least 60 °C.

[0022] A device according to the invention as described above is particularly preferred, characterized in that the device comprising at least one IR emitter for heating a sulfur-curable rubber mixture and at least one gear pump downstream of the IR emitter for extruding rubber mixtures heated by means of the IR emitter, wherein the IR emitter is designed to heat a sulfur-curable rubber compound to at least 40 °C, where one or more of the measuring sensors are designed and arranged to determine the temperature and pressure of the rubber compound in the gear pump; the device additionally comprises a control unit designed to regulate the temperature of a rubber compound by means of the IR emitter as a function of the drive power for rotating the gears of the gear pump and the pressure of the rubber compound in the gear pump and the pressure fluctuations of the rubber compound in the gear pump and the meter weight fluctuations of the extruded rubber compound after the gear pump; the device has a mixer for producing sulfur-curable rubber compounds, which is connected upstream of the IR emitter; the device additionally comprises at least one feeding unit for feeding rubber compounds into the downstream gear pump, wherein the feeding unit comprises a rolling mill or an extruder.wherein the feeding unit is preferably connected downstream of the IR emitter, the IR emitter being configured to heat a sulfur-curing rubber compound fed into the feeding unit or the gear pump such that the temperature of the sulfur-curing rubber compound at least partially reaches at least 60 °C when fed into the feeding unit or the gear pump.

[0023] The advantageous aspects of an apparatus according to the invention for extruding sulfur-crosslinkable rubber compounds described above also apply to all aspects of a method described below, and the advantageous aspects of methods according to the invention discussed below apply accordingly to all aspects of an apparatus according to the invention for extruding sulfur-crosslinkable rubber compounds.

[0024] The invention also relates to a method for producing an extruded, sulfur-crosslinkable rubber compound, comprising the method steps according to claim 7.

[0025] Within the scope of the present invention, step C) is optional, although it is ensured without measurement that the tempered rubber mixture has a temperature of at least 40 °C, preferably at least 50 °C, when fed into the gear pump in step D).

[0026] Within the scope of the present invention, the rubber mixture can be extruded a second time in a further extrusion unit such as an extruder, a calender or another gear pump, or again by said gear pump, after extrusion in the gear pump, before step D1) described below takes place.

[0027] A preferred method according to the invention is as described above or as described above as preferred, wherein the method additionally comprises the following step D1): D1) Forming the rubber compound extruded in step D) in the gear pump or in an extrusion unit by means of a forming unit as described above, so that a rubber profile is formed, preferably so that a rubber profile for the manufacture of a vehicle pneumatic tire is formed.

[0028] The inventive method as described above, or as preferably described above, additionally comprises the following step E): E) Controlling the temperature of a rubber mixture using the IR emitter as a function of the drive power for turning the gears of the gear pump and / or the pressure of the rubber compound in the gear pump and / or the pressure fluctuations of the rubber compound in the gear pump and / or the meter weight fluctuations of the extruded rubber compound after the gear pump.

[0029] A preferred method according to the invention is as described above or as described above as preferred, wherein the sulfur-curable rubber mixture tempered in step B) has at least a partial temperature in the range of 40°C to 150°C immediately before the gear pump or in the feed unit, preferably in the range of 50°C to 110°C or 70°C to 100°C.

[0030] An advantage of the aspect of the present invention described above is that, by using a gear pump according to the invention, even particularly hot rubber compounds of over 40 °C, over 50 °C, or even over 70 °C can be extruded in the gear pump without the rubber compound reaching a temperature of over 150 °C in the gear pump. Without wishing to be bound by a scientific theory, it appears that this interplay between heat and the pretreatment in the gear pump further reduces the deviations in the resulting rubber profile described above.

[0031] A preferred method according to the invention is as described above, or as described above as preferred, wherein the sulfur-curing rubber compound fed in step D) is extruded through the gear pump at a throughput in the range of 10 kg / h to 1000 kg / h, preferably in the range of 200 kg / h to 1000 kg / h. Such a throughput is only achieved due to preheating and the use of the gear pump.

[0032] A preferred method according to the invention is as described above or as described above as preferred, wherein the sulfur-crosslinkable rubber mixture fed in step D) is at least partially a temperature in the gear pump in the range of 20 °C to 100 °C, preferably in the range of 40 °C to 70 °C, and / or a pressure in the range of 5 to 400 bar, preferably in the range of 70 to 200 bar, particularly preferably in the range of 80 to 150 bar, most preferably in the range of 90 to 110 bar.

[0033] An advantage of the aspect of the present invention described above is that, by using a gear pump according to the invention, rubber compounds can be extruded at very high pressures without the rubber compound reaching a temperature above 100°C in the gear pump. This makes it possible to extrude rubber compounds at higher temperatures and thus reduce the aforementioned deviations. Without wishing to be bound to a scientific theory, it appears that this interplay between heat and the pretreatment in the gear pump at high pressures further reduces deviations in the resulting rubber profile as described above. Furthermore, for highly viscous compounds with a Mooney viscosity [ML1+4] at 20°C of >100 MU and compounds with a high natural rubber content (NR), i.e.,The phr content of NR is greater than 70 phr. Heating significantly reduces the viscosity before the mixture enters the gear pump. This viscosity reduction via contactless heating enables the processing of this mixture. In particular, it reduces or prevents changes in the mixture properties, specifically the degradation of the polymer chains due to shear forces during extrusion, as the mechanical stress from the gear pump and extruder is significantly lower compared to known devices in the prior art. In the prior art, it is common practice to plasticize highly viscous mixtures, especially those with a high NR content of > 70 phr, using an extruder and / or rollers before feeding them into the preform extruder. Degradation of the polymer chains is undesirable because it alters the mixture properties and, moreover, this degradation is not controlled.Unless otherwise specified, the Mooney viscosities referred to in the present invention are always those measured at 20 °C using the [ML1+4] method.

[0034] A preferred method is one according to the invention as described above or as described above as preferred, wherein the sulfur-curable rubber mixture, when measuring the temperature in step C), has a Mooney viscosity [ML1+4] in the range of 40 MU to 170 MU, preferably in the range of 100 MU to 170 MU, and the sulfur-curable rubber mixture added in step D) has a Mooney viscosity [ML1+4] in the range of 30 MU to 150 MU, preferably in the range of 100 MU to 150 MU.

[0035] An advantage of the aspect of the present invention described above is that, in particular, rubber compounds with the high viscosities described above exhibited particularly high deviations in the previous process. With the present invention, it is possible to significantly reduce these large deviations in the aforementioned rubber compounds, or even to make extrusion possible in the first place for rubber compounds with the viscosity ranges described above as preferred.

[0036] Particularly preferred is a process as described above or as described above as preferred, wherein the sulfur-crosslinkable rubber mixture prepared or produced in step A) comprises at least 70 phr natural rubber (NR), since in these rubber mixtures the polymer degradation of the natural rubber is reduced by a process according to the invention and this can lead to a further reduction of the deviations described above.

[0037] The advantageous aspects of an apparatus according to the invention for extruding sulfur-crosslinkable rubber compounds and a method according to the invention for producing an extruded, sulfur-crosslinkable rubber compound described above also apply to all aspects of a use described below, and the advantageous aspects of uses according to the invention discussed below apply accordingly to all aspects of an apparatus according to the invention for extruding sulfur-crosslinkable rubber compounds and a method according to the invention for producing an extruded, sulfur-crosslinkable rubber compound.

[0038] The invention also relates to the use of a device as described above or as preferably described above for reducing the fluctuations in the weight per meter of extruded, sulfur-crosslinkable rubber compounds.

Claims

1. Apparatus for extrusion of sulfur-crosslinkable rubber mixtures, characterized in that the apparatus comprises - at least one IR emitter for heating sulfur-crosslinkable rubber mixtures and - at least one gear pump arranged downstream of the one IR emitter for extrusion of rubber mixtures heated using the one IR emitter, wherein the IR emitter is configured for heating a sulfur-crosslinkable rubber mixture to at least 40°C, characterized in that the apparatus additionally comprises a control unit configured for controlling the temperature of a rubber mixture by means of the IR emitter according to - the propulsive power for rotating the gears of the gear pump and / or - the pressure of the rubber mixture in the gear pump and / or - the pressure variations of the rubber mixture in the gear pump and / or - the weight-per-meter variations of the extruded rubber mixture downstream of the gear pump. zu regeln.

2. Apparatus according to Claim 1, wherein the apparatus comprises measurement sensors, wherein one or more of the measurement sensors are configured and arranged for determining the temperature and the pressure of the rubber mixture in the gear pump.

3. Apparatus according to any of the preceding claims, wherein the apparatus comprises a mixer for producing sulfur-crosslinkable rubber mixtures which is upstream of the IR emitter.

4. Apparatus according to any of the preceding claims, wherein the apparatus additionally comprises at least one feed unit for supplying rubber mixtures into the downstream gear pump, wherein the feed unit comprises a roller mill or an extruder, wherein the feed unit is preferably downstream of the IR emitter.

5. Apparatus according to any of the preceding claims, wherein - the IR emitter is adapted for heating a sulfur-crosslinkable rubber mixture supplied to the feed unit or to the gear pump such that the temperature of the sulfur-crosslinkable rubber mixture upon supplying to the feed unit or to the gear pump is at least partially at least 50°C, preferably at least 60°C.

6. Use of an apparatus as defined in any of the preceding claims for reducing the variations in the weight-per-meter of extruded, sulfur-crosslinkable rubber mixtures.

7. Process for producing an extruded sulfur-crosslinkable rubber mixture comprising the process steps of: A) producing a sulfur-crosslinkable rubber mixture using a mixer or providing a sulfur-crosslinkable rubber mixture, wherein the sulfur-crosslinkable rubber mixture preferably comprises at least 70 phr of natural rubber, B) heating the sulfur-crosslinkable rubber mixture produced or provided in step A) to at least 40°C using an IR emitter, C) optionally measuring the temperature of the rubber mixture in the heating unit, D) supplying the sulfur-crosslinkable rubber mixture heated in step B) or measured in step C) to a gear pump at a temperature of 35°C or more and extruding the supplied rubber mixture in the gear pump and E) controlling the temperature of a rubber mixture using the IR emitter according to - the propulsive power for rotating the gears of the gear pump and / or - the pressure of the rubber mixture in the gear pump and / or - the pressure variations of the rubber mixture in the gear pump and / or - the weight-per-meter variations of the extruded rubber mixture downstream of the gear pump.

8. Process according to either of Claims 7 and 8, wherein the sulfur-crosslinkable rubber mixture heated in step B) at least partially has a temperature in the range from 40°C to 150°C, preferably in the range from 50°C to 110°C, immediately upstream of the gear pump or in the feed unit.

9. Process according to any of Claims 7 to 9, wherein the sulfur-crosslinkable rubber mixture supplied in step D) - at least partially has a temperature in the gear pump in the range from 40°C to 70°C and / or - at least partially has a pressure in the gear pump in the range from 5 to 400 bar, preferably in the range from 70 to 200 bar, particularly preferably in the range from 80 to 150 bar, very particularly preferably in the range from 90 to 110 bar and / or - is extruded through the gear pump at a throughput in the range from 10 kg / h to 1000 kg / h.