CA2312917A1

CA2312917A1 - Extrusion device

Info

Publication number: CA2312917A1
Application number: CA002312917A
Authority: CA
Inventors: Andreas Kleinke; Karl-Peter Farwerck; Alfons Jochum; Armin Lange; Harald Krull; Joerg Rosenberg; Werner Maier; Karl Ludwig Jotter; Burkhard Trapp; Jorg Breitenbach
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1997-12-10
Filing date: 1998-12-09
Publication date: 1999-06-17
Also published as: CN1281381A; ATE241425T1; DE59808550D1; DE19754873A1; CN1103628C; JP2001525243A; EP1037703B1; EP1037703A1; WO1999029410A1

Abstract

The invention relates to an extrusion device, particularly an extrusion device for thermoplastic or dough-like masses or highly tenacious melts, and to the use of said device. The extrusion device has a housing (11), at least one conveyor worm (12) arranged in a housing and an outlet (20) disposed on the front face of the housing (11) close to the end of each conveyor screw which is furthest away from the drive end. At least one stripping member (21) is arranged in between the end (14) of each conveyor screw (12) furthest away from the drive end and the outlet (20). The device is particularly suitable for producing granulates, preferably those containing active substances.

Description

EXTRUSION DEVICE
The invention relates to an extrusion arrangement, in particular an extrusion arrangement for thermoplastic or pasty compositions or for high-viscosity melts, and to the use of such an arrangement.
Known extrusion arrangements mostly have an essentially cylindrical housing in which at least one screw is arranged. In the vicinity of one end of the screw, the housing has an inlet through which the extrusion arrangement can be charged with the composition which is to be extruded and which usually is initially in the form of a powder or granules. The screw is driven by a motor shaft. The front of the housing has a die orifice in the vicinity of the screw end remote from the drive.
It is frequently possible to control the temperature of sections of the extrusion arrangement. The composition to be extruded is, during conveyance by the screw, melted, mixed and subsequently forced through the die orifice where it emerges in the form of a continuous strand. The die orifice can be designed, for example, as a perforated plate or perforated strip with a plurality of fine orifices which produce correspondingly fine product strands.
Extrusion arrangements of these types can be used, for example, to produce granules. A particularly important area of application is moreover the production of pharmaceutical granules by melt extrusion. The use of an extrusion arrangement in the pharmaceutical sector is described, for example, in US 4,880,585.
In this case, a polymeric binder and the actual pharmaceutical active ingredient are melted in the extrusion arrangement, where appropriate together with other additives, mixed together and forced through the perforated plate of the extrusion arrangement in the form of numerous continuous product strands. Directly downstream of the extrusion arrangement there is a granulation unit, for example what is called a hot-cut arrangement which divides the product strands continuously emerging from the extruder with rotating knives into small cylindrical pieces (granules) which then fall into a collection unit. At this time, the granules are still thermoformable and may therefore change' their shape while falling or in the collection unit. It is possible by process control for example to round off the edges of the cylindrical granules to result in what are called pellets.
Granules or pellets containing active ingredient are interesting variants of conventional formulations. They can be used, for example, directly as animal feed additives or as plant treatment compositions. Direct intake of active ingredients in granule form is also conceivable in the pharmaceutical sector. However, in pharmacy, granules and pellets are more often packed into capsules or compressed to tablets conventionally. Of particular interest in this connection is the possibility of providing incompatible active ingredients in a single dosage form, for example as capsule or tablet, by mixing the various granules or pellets. Granules and pellets also have the advantage of making dust-free further processing possible.
However, problems are associated with the conventional production of granules by extrusion of the melt and subsequent hot-cut.
After the reduction in size by the knives of the cutting arrangement, the granules are still hot and thermoformable. If granule particles come into contact with one another or with a wall of the apparatus at this time, bonding or adhesion together may occur and eventually leads to the need to switch off the extruder and the hot-cut and clean the apparatus. The production process then has to be started off again.
The adhesion together and bonding of the particles can in the final analysis be prevented only by reducing the temperature of the extruded product strands. Reducing the temperature of the extrudate can, for example, be achieved by lowering the extruder temperature, in particular in the region of the perforated plate, or, if the extruded temperature is unchanged, by raising the output of the extruder. However, the flow properties of the polymeric melt change as the temperature falls. In particular, the viscosity of the melt increases so that, as a consequence, some perforations in the perforated plate may be blocked. This problem arises in particular in the production of pharmaceutical granules, where the perforated plates used on the production scale typically have 50-500 perforations, and the perforations normally have diameters in the range from 0.5 to a few millimeters. The blockage of individual perforations results in a nonuniform melt throughput, with a high melt throughput in the case of unblocked perforations leading to a heating of the melt through shear, while radiation cooling of the melt occurs when the perforations are virtually blocked and accordingly the melt throughput is low. This results in different granule sizes, and the large hot granules produced at perforations with a high throughput are particularly prone to bonding, and the small granule particles produced at perforations with a low throughput lead to an increase in the proportion of fines produced. In this case too it is eventually necessary to switch off the production process and clean the apparatus.

0050/48627 CA 02312917 2000-os-3o It is an object of the present invention to indicate a novel extrusion arrangement with which it is possible in particular to extrude thermoplastic or pasty compositions or high-viscosity melts reliably even through fine die orifices. It is moreover intended that the arrangement be suitable in particular for producing granules or pellets, and the temperature of the product strands should be lower than with conventional extrusion arrangements so that bonding of the granules or pellets both with one another and with the wall of the extrusion arrangement after the hot-cut is reliably prevented.
We have found that this object is achieved by an extrusion arrangement having a housing, having at least one screw arranged in the housing and having a die orifice arranged at the front of the housing in the vicinity of the end, remote from the drive, of each screw, wherein at least one stripper device sweeping over the inside of the die orifice is arranged between the end, remote from the drive, of each screw and the die orifice.
With the novel extrusion arrangement, the composition to the extruded, for example a polymeric binder, a pharmaceutical active ingredient and further additives are first melted in a conventional way and mixed together during conveyance by the screw. Active ingredients, binders and additives which can be used are disclosed, for example, in DE 195 39 363 A1. The melt is extruded through a die orifice and the extrudate is finally reduced in size to individual granule particles. In contrast to conventional extrusion of strands, however, the extrudate is not discharged by the pressure generated in the extrudate, but is conveyed by a special stripper device through the die orifice of the extrusion arrangement. The novel arrangement therefore differs from known extrusion arrangements only by the additional stripper device so that it is essentially no more costly to produce and even extrusion arrangements which are already installed can easily be retrofitted with the stripper device proposed by the invention. Retrofitting of this type can be implemented relatively simply, in particular because even in conventional extrusion arrangements the screw does not extend right up to the die orifice, for example the perforated plate, and a space is almost always provided in between, and the stripper device proposed by the invention can now be arranged therein.
Numerous advantages are associated with the novel arrangement.
The temperature of the extrudate and/or of the die orifice of the extruder can be reduced so that bonding or adhesion together of the granules which have been reduced in size is reliably prevented. Unlike conventional extrusion arrangements, however, lowering the temperature of the extrudate does not, despite the increased viscosity of the extrudate, lead to blockage of the perforations of the die orifice. On the contrary, such blockage is reliably prevented by the continuous stripping of the inside of the fine perforations of the die orifice. Since the stripper device acts only on the extrudate located immediately on the inside of the die orifice, there is virtually no additional energy input into the melt so that there is also no unwanted increase in temperature due to the conveying operation. It is even possible with the novel arrangement to extrude pasty compositions and high-viscosity melts without difficulty even on use of perforated plates with very small diameter perforations.
The optimal process parameters for this are normally determined using a laboratory-scale extruder with 1-5 perforations. Scale-up to an industrial production scale with some hundreds of perforations entails no additional problems.
The extrusion at comparatively low temperature markedly extends the range of applications of melt extrusion. For example, it is now possible also to extrude melts which contain active ingredients and which comprise heat-sensitive consituents which would be damaged by the temperatures used in conventional extruders.
In order to take account of the unavoidable play in the individual components of the extrusion arrangement and possible changes in temperature and pressure during the process, but especially when the extrusion process starts off, the stripper device is preferably pushed elastically against the inside of the die orifice. This can be achieved, for example, by a compression spring acting on the stripper device.
The stripper device is advantageously connected to rotate with the assigned screw so that the inside of the die orifice is continuously stripped. The stripper device may, for example, have a shaft which is fastened to the tip of the screw. The screw preferably has for this purpose a recess in which this shaft engages in order to rotate therewith. The abovementioned compression spring can be arranged between the base of the recess and the shaft of the stripper device. The novel arrangement can therefore be implemented by a simple modification of the tip of the screw of a conventional extrusion arrangement.
The novel arrangement operates without dead space so that there is no risk of degradation of the polymeric active ingredient melt.
The stripper device is advantageously designed as a traversing knife. The knife can in this case consist, for example, of a 5 hardened material, preferably a hardened metal.
The die orifice of the extruder is advantageously designed as a perforated plate, the perforated plate typically having between 50 and 500 perforations whose diameter is in the range 0.5 -10 mm. It is advantageous for the temperature of the perforated plate itself to be controllable.
If the extruder is, for example, a twin screw extruder, each screw is preferably assigned a separate stripper device.
The novel arrangement is particularly suitable for producing granules, in which case a granulating unit, for example a cut-off unit with rotating knives, is located downstream of the extrusion arrangement. The novel arrangement is particularly preferably used to produce granules containing active ingredients, for example pharmaceutical granules, plant treatment compositions, animal feed additives and supplements or human food supplements.
The present invention is described in more detail below by means of an example described with reference to the appended drawing.
In the drawing, Figure 1 shows part of an axial cross-section of a first embodiment of the novel extrusion arrangement;
Figure 2 shows a front view of a second embodiment, designed as twin-screw extruder, of the novel extrusion arrangement in detail.
Figure 1 depicts part of a cross-section of a preferred embodiment of the novel extrusion arrangement. Like a conventional extrusion arrangement, the novel extruder 10 comprises a cylindrical screw housing 11 in whose interior a screw 12 is rotatably arranged. The screw shaft 13 of the screw 12 terminates in a shaft tip 14 before a perforated plate 18. The temperature-controllable perforated plate 18 is arranged in a perforated plate holder 19 and forms the front termination of the extruder 10. The perforated plate 18 has orifices 20 through which the screw 12 conveys the molten extrudate. Not depicted are the charging units which are known from conventional extruders and which can be used to feed, for example, a powdered polymeric binder and a powdered active ingredient to the extruder, which are then melted by heating elements (likewise not depicted) to give the extrudable melt. The screw 12 in this case simultaneously acts as mixing device for homogeneous mixing of the individual components of the melt.
To produce pharmaceutical granules, the orifices 20 in the perforated plate 18 have a diameter of only a few mm. The perforated plate 18 may have a few 100 orifices 20.
A stripper device designed as a traversing knife 21 is fixed in the shaft tip 14 of the screw 12 in order to rotate therewith. In the depicted example, the traversing knife 21 has two essentially diametrically opposite knife blades 22, 23. The knife shaft 24 of the traversing knife 21 is held by a fastening screw 26 in a hole 15 bored in the shaft tip 14. The hole has an internal thread 16 which cooperates with a complementary external thread on the fastening screw 26. A compression spring is arranged on the base of the central recess 27 of the fastening screw 26 and acts against the shaft 24 of the traversing knife 21 and presses the latter against the inside of the perforated plate 18.
Figure 2 shows a partial depiction of a front view of a second embodiment of the novel extruder 10. The variant depicted in Figure 2 is a twin-screw extruder with each of the two screws 12 being provided with a traversing knife 21. The perforated plate 18 with orifices 20 arranged circularly therein is depicted in partial detail.
To carry out the novel process, the extruder 10 is charged in a conventional way with polymeric binder and active ingredient, and these components are mixed and melted and conveyed by the screw 12 into the intermediate space 28 bounded by the shaft tip 14 and perforated palte 18. The rotating traversing knife 21 in this intermediate space 28 forces the extrudate through the orifices 20 in the perforated plate 18 and thus prevents these orifices becoming blocked even if the temperature of the molten extrudate is lowered in order to prevent later bonding of the granule particles.
The extrudate leaves the orifices 20 in the form of a continuous product strand which is reduced in size by a (not depicted) hot-cut device known per se into small cylindrical granule particles. Depending on the process control, the granule particles can solidify in this cylindrical shape or, as long as they are still thermoformable, be rounded off to pellets.

0050/48627 ca o23i29m Zooo-os-3o The advantages of the novel extrusion arrangement are also clear from the comparative investigation described below:
Examples:
The following formula was processed using a Werner & Pfleiderer ZSK 40 twin-screw kneader:
Component ~ by weight Theophylline 50 Eudragit RS 10 Kollidon VA-64 40 A Werner & Pfleiderer MWG 260/90 pelletizer was used to cut the extrudates.
Comparative Example 1:
In order to obtain a homogeneous discharge from the perforated strip (15x1 mm}, the extruder of conventional design was run with the following temperature profile:
Zone 1 Zone Zone 3 Zone Zone 5 Head Die The product came uniformly out of the perforated strip but bonded to the knives and to the housing so strongly that the process had to be stopped after a short running time.
Comparative Example 2:
In order to couteract the bonding, the processing temperature was reduced:

Zone Zone 2 Zone 3 Zone Zone 5 Head Die The tendency to bond decreased markedly, but the throughput through the perforations varied greatly so that the resulting granule particles varied in size. After a short time, some perforations were completely blocked.
Example 3:
The extruder was fitted with the novel stripper device. Retaining the temperature profile described in Comparative Example 2, nonadhesive, uniform granule particles were obtained. The throughput through the individual perforations was very uniform, and no perforations became blocked even after a lengthy time.

Claims

We claim:

1. The use of an extrusion arrangement having a housing (11), having at least one screw (12) arranged in the housing and having a die orifice (20) arranged at the front of the housing (11) in the vicinity of the end (14), remote from the drive, of each screw, wherein at least one stripper device (21) sweeping over the inside of the die orifice (20) is arranged between the end (14), remote from the drive, of each screw (12) and the die orifice (20), which is elastically pressed against the inside of the die orifice (20), for producing granules containing active ingredients, selected from pharmaceutical granules, plant treatment compositions, animal food additives and supplements and human food supplements.

2. The use as claimed in claim 1, wherein the stripper device (21) is connected to rotate with the assigned screw (21).

3. The use as claimed in either of claims 1 or 2, wherein the stripper device (21) is designed as a traversing knife.

4. The use as claimed in any of claims 1-3, wherein the die orifice (20) is designed as a perforated plate.

5. The use as claimed in any of claims 1-4, wherein a granulating unit is arranged downstream of the die orifice (20).