METHOD FOR PROCESSING PRODUCTS IN AN EXTRUDER

Abstract

The invention relates to the production of PSA in a planetary gear extruder. During filling and after passing a passage on a dispersing ring using a lateral arm extruder, the products are degassed.

Claims

1.-19. (canceled)

20. A method for processing natural rubber and/or comparable non-thermoplastic elastomers which require mastication before they can be blended with other components of a mixture, comprising: providing an extrusion unit that is composed of at least one planetary roller extruder module having a longitudinal axis and an upstream feed part, wherein the planetary roller extruder module consists of a central spindle having an external toothing, planetary spindles with external toothing that rotate about the central spindle, and a surrounding housing having an internal toothing, wherein the planetary spindles mesh with both the central spindle toothing and with the internal toothing of the housing, and wherein the toothings are helical toothings, such that individual teeth, in accordance with a pitch of the teeth to the longitudinal axis of the extruder, run like screw threads on toothed surfaces; kneading a feedstock of natural rubber and/or comparable non-thermoplastic elastomers between the teeth of the planetary roller extruder module and subjecting the feedstock to deformation in at least one dispersion ring so as to masticate the feedstock until it exhibits a Mooney viscosity of less than 80 in order to allow other components of the mixture to be compounded in; and cooling the feedstock during mastication.

21. The method as in claim 20, wherein the dispersion ring is arranged between surrounding housings of two planetary roller extruder modules, wherein the two planetary roller extruder modules have a common central spindle and wherein the dispersion ring engages a groove of the common central spindle and leaves an open passage for the feedstock in the groove.

22. The method as in claim 21, wherein a gap having a gap width is formed between the dispersion ring and the groove of the common central spindle, and wherein the gap width and a variation of the gap width are based on a construction size of the extruder as follows: TABLE-US-00004 Construction Gap Variations size width plus/minus 50 mm 1.5 mm 1 mm/0.5 mm 70 mn 1.4 mm 1 mm/0.75 mm 100 mm 1.6 mm 1 mm/0.75 mm 150 mm 1.8 mm 1 mm/0.75 mm 180 mm 2.5 mm 1.5 mm/1 mm 200 mm 2 mm 2 mm/1 mm 250 mm 3 mm 1.5 mm/1.5 mm 280 mm 3.5 mm 2 mm/1.5 mm 300 mm 3 mm 1.5 mm/1.5 mm 350 mm 4 mm 1.5 mm/1.5 mm 400 mm 3.5 mm 2 mm/2 mm

23. The method as in claim 20, wherein the feedstock is natural rubber and wherein the natural rubber is cooled to below 140 C. during mastication.

24. The method as in claim 20, wherein the feedstock is a comparable non-thermoplastic elastomer and wherein the feedstock is cooled to below a temperature which, if exceeded, would cause the feedstock to suffer a significant molecular degradation in the absence of mechanical deformation and without chemical mastication agents in a presence of ambient air.

25. The process according to claim 20, wherein the internal toothing of the housing is cooled to a temperature which is no higher than half of a melt temperature in the extruder.

26. The method as in claim 20, wherein the mastication is carried out in the absence of oxygen or in an oxygen-depleted atmosphere.

27. The method as in claim 26, wherein oxygen surrounding the feedstock is at least partially replaced with an inert gas.

28. The method as in claim 20, further comprising: adding at least one non-meltable solid after the natural rubber and/or the comparable non-thermoplastic elastomers have been masticated.

29. The method as in claim 28, further comprising introducing additional components to the feedstock through a side-arm extruder after the natural rubber and/or the comparable non-thermoplastic elastomers have been masticated.

30. The method as in claim 28, wherein the natural rubber and/or the comparable non-thermoplastic elastomers and the at least one non-meltable solid which has been added after the mastication are dispersed and homogenized by further processing in the extruder and by further processing through at least a second dispersion ring.

31. The method as in claim 30, wherein a distance between a feed part through which the non-meltable solid is added and the second dispersion ring is at least 2D, with D being a pitch diameter of the internal toothing in the surrounding housing.

32. The method as in claim 20, further comprising: degassing the feedstock in the extruder prior to mastication.

33. The method as in claim 32, comprising at least one additional degassing step after additional components have been introduced to the feedstock after mastication.

34. The method as in claim 32, wherein degassing is performed by a side-arm extruder that runs empty.

35. The method as in claim 32, wherein degassing is performed by degassing rings that are arranged between two consecutively arranged planetary roller extruder modules.

36. The method as in claim 32, further comprising: checking the dispersion and degassing by visually inspecting a compound sample for inclusions, wherein the compound sample is compressed to a layer thickness of less than 1 mm before inspection thereof.

37. The method as in claim 20, wherein the feedstock comprises dry rubber and/or a comparable non-thermoplastic elastomers and no more than 15 wt % of a liquid slip agent.

38. The method as in claim 20, wherein mastication occurs in absence of a solvent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0198] FIG. 1 is a schematic diagram of an exemplary extrusion unit,

[0199] FIG. 2 is a cross sectional view of an exemplary dispersion ring.

DETAILED DESCRIPTION

[0200] An embodiment of the invention is illustrated in the drawing. The drawing shows in FIG. 1 an extrusion unit, consisting of a drive 1, a feed part 2, a planetary roller extruder module 3, a planetary roller extruder module 4 and a planetary roller extruder module 5. In the embodiment the modules 3, 4, 5 are each 400 mm long. Each module 3, 4, 5 possesses an externally toothed central spindle (not shown), externally toothed planetary spindles (not shown) and a housing with an inner toothed liner. The planetary spindles mesh with the toothing of the liner and simultaneously with the toothing of the central spindle. The toothing is a helical toothing, here an involute toothing, such that the individual teeth run correspondingly with the pitch of the teeth to the longitudinal axis of the extruder like screw threads on the toothed surfaces.

[0201] All the modules 3, 4, 5 possess a common central spindle that continues as a feed-screw in the feed part. This means that a common central spindle penetrates all the modules and forms the feed screw in the feed part 2 designed in the form of a single-screw extruder. Moreover, one end of the central spindle is connected to the drive 1.

[0202] The housings of all the modules and the feed part are equipped with a temperature control system. In the embodiment water serves as the temperature control agent. The temperature control agent flows in channels between the housing and the liner that is seated therein. The channels are created by grooves on the periphery of the liners and which run like screw threads on a screw. The grooves become channels when the liners are pushed into the housing. The temperature control agent is fed through supply lines 6 to the channels and through pipes 7 from the channels to a heat exchanger, in which, as needed, heat is supplied to or removed from the temperature control agent.

[0203] The housings of the modules 3, 4, 5 and of the feed part 2 have a cylindrical design and are equipped on both ends with a collar. The collar serves to connect the housings together. The connection between the feed part 2 and the module 3 is identified with 8.

[0204] The planetary spindles are held in position in the machine direction of the extrusion unit by slide rings. In the embodiment the slide rings are held at the coupling joints 9 and 10 of the modules 3, 4, 5 between the housing ends. The slide ring of the planetary spindles of module 5 is held at 19 between the associated end and an extrusion die (not shown). Incidentally, the planetary spindles are held between the central spindle and the surrounding liner.

[0205] The slide ring at position 9 between the modules 3 and 4 serves not only to position the planetary spindles but in the embodiment also a special ring construction with a dispersion ring. The dispersion ring is made of two halves that can be inserted into a corresponding recess of the ring construction. The dispersion ring is inserted after positioning the ring construction with the slide ring. The dispersion ring engages into a groove (not shown) of the central spindle. The dimensions of the groove are greater than those of the part of the dispersion ring that engages into the groove. After having inserted the dispersion ring there thus remains a gap, through which the feedstock must flow. The ring construction, as the usual slide rings, is clamped between the ends of the modules/ends of the housing.

[0206] An airtight lock is mounted on the feed part 2. The lock is made of two hopper-shaped chambers 11 and 12. The lower chamber 11 is connected to the feed opening. A dosing device in the form of a toothed wheel air lock is provided between the lower chamber 11 and the feed opening. The upper chamber 12 possesses a connection to the lower chamber. A slider is provided at the connection point. The feedstock is supplied to the upper chamber through a pipeline 13. Another slider is provided at the entrance into the upper chamber. The sliders enable an airtight closure of the chamber 12.

[0207] The chamber 12 is also connected to a suction line 16. Another slider 17 is provided in the suction line 16. The air enclosed in the chamber 12 can be partially suctioned off with the device. A side-arm extruder 14 is mounted on the module 4. The side-arm extruder 14, by standing vertically above the module 4, differs from the conventional horizontal position. Moreover, the side-arm extruder does not serve to feed in material, but rather serves for degassing. For this, the side-arm extruder 14 runs empty in the operational mode.

[0208] A suction line 15 as attached to the side-arm extruder. Just as in the suction line 16, a slider 17 is provided in the suction line 15. Both suction lines 15 and 16 run into a common suction line 18.

[0209] The feedstock is introduced into the unit with the feed part 2. In the embodiment for producing a PSA the feedstock includes acrylic polymers as the elastomer and diverse additives. The feedstock initially arrives into the chamber 12. There, the air that was entrained with the feedstock into the chamber 12 is essentially suctioned off. During the extraction by suction the chamber 12 is sealed from the chamber 11 and the supply line 13.

[0210] After a desired reduced pressure in the chamber 12 has been achieved, the chamber 12 is opened, such that the material may flow into chamber 11. After the chamber 11 has been filled the chamber 12 is again sealed from chamber 11. The material is dosed from chamber 11 into the feed part 2. The feed screw in the feed part compresses the material and presses it into the module 3. The material is kneaded therein at a temperature between 100 and 120 C. by the planetary spindles. The kneading step is essentially determined by the toothing of the module parts. In the embodiment all parts have a standard toothing.

[0211] After being processed in the module 3 the material is pressed through the gap at the dispersion ring. This is associated with a high mechanical deformation of the elastomers. The elastomers are masticated, such that the additives can be permanently blended into the elastomers. At the same time degassing is carried out by the side-arm extruder 14 that is designed as a twin-screw extruder. In other embodiments a planetary roller extruder is provided as the side-arm extruder. However, a single-screw extruder is also suitable for use as the side-arm extruder that fulfils the subsequent conditions.

[0212] The side-arm extruder 14 runs empty. The side-arm extruder serves to thrust back the material under pressure in module 4 and any material that surges through the housing opening. The side-arm extruder has also to evacuate the released gas. The side-arm extruder is thus gas permeable. This is achieved by a correspondingly large clearance between the two screws in the side-arm extruder housing surrounding the screws. Planetary roller extruders and single-screw extruders can be configured to be exactly as gas permeable as the twin-screw extruder.

[0213] For the degassing, a suction line 15 is attached to the side-arm extruder. The induced draft is controlled by the valves provided in the suction lines 15 and 16, such that the reduced pressure of the induced draft is made to remain within acceptable limits independently of the source of the induced draft. The processing of the material in the modules 4 and 5 is known as homogenization. In this regard, only standard toothing is provided in module 4. The module differs only in its planetary spindles. The above described transport spindles are provided there.

[0214] In other embodiments degassing also occurs between the modules 4 and 5 and optionally between additional modules. At these positions ring constructions are provided, which have still more additional functions than a thrust ring, namely a degassing function. For this the ring construction has an annular degassing channel that opens in the downstream direction of the material, i.e. towards the inner space of the module 5. During extrusion, due to the partial filling of the module, a cavity is formed there that is suitable for the degassing. Moreover, the ring construction/annular space is connected to a suction line. The suction line can be easily guided between the ends of the modules 4 and 5.

[0215] FIG. 2 shows a detail of a ring construction between two modules. The ring construction is clamped between adjacent housing ends 15 and 16 of the modules. Inner toothed liners 18 and 19 are seated in the housing ends 15 and 16. The liners 18 and 19 are recessed somewhat in the housing ends 15 and 16 and leave a space that is filled by a ring construction 20. The ring construction 20 consists of two halves that are combined around the already installed central spindle 17 to form a ring before installing the housing with the end 15. The ring construction 20 engages into a groove of the central spindle 17. An annular gap remains between the outer periphery 23 of the ring construction 20 and the base 26 of the groove. The annular gap is composed from an entry-side taper 24, a constant passage 22 and a discharge-side broadening 25.

[0216] At the same time the ring construction 20 forms a thrust ring and a dispersion ring. As the thrust ring the ring construction 20 forms a support for carbide annular parts 21. During the operation of the extruder the planetary spindles (not shown) slide with their front face on the carbide annular parts 21. During the operation of the extruder the planetary spindles run in the free volume between the inner toothed liners 18 and 19 and the outer toothed central spindle 17. In this regard the planetary spindles in the free volume of the inner toothed liner 18 come into contact with the carbide ring parts 21, whereas the planetary spindles in the free volume of the inner toothed liner 19 circulate at a distance from the ring construction 20. In the view shown in FIG. 2 the feedstock flows from right to left. As the dispersion ring, the ring construction has the task of distributing additive components in the compound. Here, the compound is a rubber or a comparable elastomer that is to be masticated, in order for the added components to be initially dispersed as desired.

[0217] The compound is pressed through the illustrated annular gap and is thus subjected to a considerable deformation, which together with the deformation from the repeated rolling of the compound between the teeth of the planetary roller extruder module, causes a mastication of the rubber or other comparable elastomers.