METHOD AND DEVICE FOR EXTERNAL LUBRICATION OF PRESS ROLLS OF A ROLLER COMPACTION DEVICE AND APPLICATION OF THE METHOD

Abstract

In a method for external lubrication of the press rolls (2 or 2.1) of a roller compaction device (1) by means of a continuous coating of said press rolls (2 or 2.1), a thin layer of a lubricant and/or an anti-adhesive are continuously provided to coat the press rolls (2 or 2.1). This coating preferably contains magnesium stearate or a mixture containing magnesium stearate. To carry out the method, at least one coating device (13, 14, 15 or 13.1, 14.1, 15.1) is arranged in a housing in which the press rolls (2 and 2.1) are arranged, by means of which coating device at least one press roll is provided with a thin coating of a lubricant and/or an anti-adhesive, preferably with magnesium stearate or a mixture containing magnesium stearate. The method is used for the manufacture of dry granules in the pharmaceutical and food industries.

Claims

1-12. (canceled)

13. A method for the external lubrication of rotating press rolls of a roller compaction device by continuous coating of the rotating press rolls, comprising coating the press rolls with a thin layer of a lubricant and/or an anti-adhesive in a continuous and solvent-free manner.

14. The method according to claim 13, wherein the coating is performed with a magnesium stearate powder.

15. The method according to claim 13, wherein the coating is performed with a magnesium stearate-containing powder mixture.

16. The method according to claim 13, wherein the coating is performed with one or more pressed articles consisting of a magnesium stearate-containing mixture.

17. The method according to claim 13, wherein the press roll surfaces exhibit a surface roughness ranging from 0.5 m to 1.5 m.

18. The method according to claim 13, wherein the press roll surfaces exhibit a surface roughness ranging from 0.8 m to 1.2 m.

19. The method according to claim 14, wherein the amount of magnesium stearate collected from the press roll surfaces by the product to be roller compacted ranges from 0.015 mg to 0.2 mg per square centimeter press roll surface.

20. The method according to claim 14, wherein the amount of magnesium stearate collected from the press roll surfaces by the product to be roller compacted ranges from 0.03 mg to 0.05 mg per square centimeter press roll surface.

21. The method according to claim 13, wherein the concentration of lubricant and/or anti-adhesive, particularly magnesium stearate, in the dry granules increases by less than 0.01% to 0.2% (w/w).

22. The method according to claim 13, wherein the concentration of lubricant and/or anti-adhesive, particularly magnesium stearate, in the dry granules increases by less than 0.04% to 0.1% (w/w).

23. The method according to claims 13, wherein the apparent density of the ribbons located between the press rolls whilst under pressure can be determined with an accuracy of better than 3%.

24. The method according to claims 13, wherein the apparent density of the ribbons located between the press rolls whilst under pressure can be determined with an accuracy of better than 2%.

25. The method according to claims 13, wherein the apparent density of the ribbons located between the press rolls whilst under pressure can be determined with an accuracy of better than 1.5%.

26. A device for the external lubrication of press rolls in a roller compaction device resulting in continuous coating of the rotating press rolls, comprising a housing in which the press rolls are arranged, the housing comprising at least one coating device based on rolls or a coating device based on pressed articles by which at least one press roll is coated.

27. The device according to claim 26, wherein a transfer roll is arranged between a ribbon scraper and an auger.

28. The device according to claim 27, wherein the pressed articles are pressed onto the press roll surfaces between the ribbon scraper and the auger.

29. A method of manufacturing dry granules, comprising a step of roller compacting powders into dry granules with the device according to claim 26.

Description

[0032] The invention is to be described in more detail with the aid of drawings as follows:

[0033] FIG. 1 shows the method of the invention

[0034] FIG. 2 shows the device according to the invention

[0035] FIG. 3 shows a variant of the device according to the invention

[0036] In FIG. 1 reference sign 1 denominates a process housing. Press rolls 2 and 2.1 are arranged inside said process housing 1. The related measuring device 2.2 measures the number of revolutions, or rotations, of press rolls 2 and 2.1. In the lower part of process housing 1, a granulation roll 3, or granulator, with a screen basket 3.1 is arranged. The press roll force is measured using measuring device 4, and the roll gap, or gap, (=smallest effective distance between the press rolls) with measuring device 5. Beneath the process housing 1, a drum 6 is positioned for collecting the dry granules, the drum standing on a scale 7, which is connected to a computer 8 via collector line 9. More than one collector line may be required, depending on how many load cells are required.

[0037] In FIG. 2 and FIG. 3, same reference signs denominate same parts as in FIG. 1. In FIG. 2, two press rolls 2 and 2.1 are arranged inside the process housing 1. The product is fed via an auger 12, forming a ribbon or flakes 10 after the compaction process between the counter-rotating press rolls 2 and 2.1.

[0038] One lubricant feed each is arranged at storage tanks 15 and 15.1 in the lateral area of press rolls 2 and 2.1. Below each storage tank 15 and 15.1, a transfer roll 13 and 13.1 and a conveyor roll 14 and 14.1 are arranged, respectively. The lubricant and/or anti-adhesive feed 15 and 15.1 are positioned on process housing 1 of the roller compaction device in such a way that transfer rolls 13 and 13.1 each touch the press rolls in areas 16 and 16.1, respectively, behind the ribbon scrapers 11 and 11.1 and in front of the auger 12. In this area namely, during roller compaction no ribbons or flakes are expected to be present on the press roll surfaces anymore. It should be emphasised that these ribbon scrapers do not touch the press roll surface, so that abrasion between the press roll surface and the ribbon scrapers is prevented, fundamentally.

[0039] The application of a thin layer of lubricant and/or anti-adhesive with the help of a conveyor- and a transfer roll may also take place with a device consisting of more than two rolls, such as for instance two conveyor rolls and one transfer roll. Also, each press roll may be equipped with several of such application devices in order to apply a thin layer of powder to the press roll surface. The diameters of conveyor- and transfer-rolls may be identical or different. It is irrelevant whether the diameter of the conveyor roll is larger or smaller compared to the one of the transfer roll.

[0040] During compaction, the lubricant feed storage tanks 15 and 15.1 (FIG. 2) contain a suitable lubricant and/or anti-adhesive, preferably magnesium stearate or a magnesium stearate containing powder mixture, which is transferred by the conveyor roll 14, respectively 14.1, to the transfer roll 13, respectively 13.1. The transfer roll 13, respectively 13.1, then applies the lubricant and/or anti-adhesive to the surface of press roll 2, respectively 2.1.

[0041] The object of the invention may also be achieved with the aid of pressed articles containing a suitable lubricant and/or anti-adhesive, preferably magnesium stearate. These pressed articles may for example be produced by compaction of magnesium stearate containing powders with the aid of suitable (tablet) presses. During manufacture it has to be ensured that the lubricant and/or anti-adhesive properties of the substances used are maintained at an adequate level. For this reason, extrusion-or melt processes are not acceptable for the manufacture of such magnesium stearate containing pressed articles, because this will substantially reduce the lubricant and/or anti-adhesive properties of magnesium stearate.

[0042] The lubricant and/or anti-adhesive containing pressed articles are denominated with reference signs 19, respectively 19.1 (FIG. 3). These sufficiently strong pressed articles are pressed directly onto the surface of the press rolls 2, respectively 2.1, with an adjustable, preferably constant force, schematically represented by the spring assembly 18, respectively 18.1, in FIG. 3. The device by which these pressed articles are pressed onto the press roll surface as well as the pressed articles themselves are arranged in housing 17, respectively 17.1. As a matter of principle, the housing containing the pressed articles is also arranged in the press roll area, in which no ribbons or flakes or only small, for the process irrelevant amounts of ribbons or flakes are expected to be present on the respective press roll surfaces. Accordingly, the device by which these pressed articles are pressed onto the press roll surface as well as the pressed articles comprised therein are arranged in the area between the respective ribbon scraper (11, respectively 11.1) and the auger (12), which in FIG. 3 is schematically represented by the shaded areas 16 and 16.1.

[0043] With both the devices shown in FIG. 2 and in FIG. 3, thin layers of lubricant and/or anti-adhesive, preferably magnesium stearate, are reproducibly applied to the press roll surface. In this respect, only one of these surface coating devices per press roll would suffice, but of course it is also possible to use combinations thereof.

[0044] The precise amount of lubricant and/or anti-adhesive, preferably magnesium stearate or a magnesium stearate containing mixture, which are applied by these coating devices and finally are collected from the press roll surface by the powder to be roller compacted, depends on the process conditions selected, e.g. on the surface constitution of the conveyor- and the transfer rolls (nos. 13, respectively 13.1, in FIG. 2), the contact pressure and mechanical strength of the pressed articles (nos. 19, respectively 19.1, in FIG. 3), the constitution of the surface of the press rolls (nos. 2, respectively 2.1, in FIG. 3) (e.g. smooth, roughened, knurled or pocket-type press roll surfaces) and the properties of the powder to be compacted.

[0045] This causes fluctuations in the amount of lubricant and/or anti-adhesive, in particular magnesium stearate, finally collected from the press roll surface by the powder, ranging from 0.015 mg to 0.2 mg, particularly between 0.03 mg and 0.05 mg magnesium stearate per square centimetre press roll surface. And this in turn, depending on the roll force, or press force, and the gap selected, results in an increase in the magnesium stearate concentration in the ribbon, respectively the granulate, ranging between 0.01% and 0.2% (w/w), and particularly between 0.04% and 0.1% (w/w). And thus, the amount of magnesium stearate introduced into the product by this solvent-free coating is significantly smaller than the amount needed in case of an internal lubrication for preventing completely or almost completely sticking/caking on the press roll surfaces. In order to prevent this sticking/caking by internal lubrication, internal concentrations between 0.5% and 1.5% (w/w) are normally required, depending on product properties and surface properties of the press roll.

[0046] With such magnesium stearate application devices, several substances could be roller compacted and milled immaculately without material build-up, or sticking/caking, on the press rolls. In general, it was not necessary to accept essential limitations regarding the possible process parameters such as roll force (or press force), roll gap and/or press roll speed (number of roll revolutions per time unit), also called manufacturing parameters, which are relevant concerning dry granulation based on roller compaction.

[0047] For instance, when using smooth press roll surfaces, the sticking/caking-prone substance citric acid could be processed without addition of the (internal) lubricant magnesium stearate over the same range of manufacturing parameter as employed for magnesium stearate coated press rolls. In fact, by coating with magnesium stearate sticking/caking was prevented completely or reduced to an irrelevant level. For gaps up to 24 mm per metre press roll diameter, roll forces, or press forces, up to 80 kN per centimetre press roll width and per meter press roll diameter were possible, being the whole force range of the roller compaction device being used.

[0048] Although by adding 1% magnesium stearate to this powder (so-called internal magnesium stearate) sticking/caking could also be largely prevented, the range of possible manufacturing parameter was considerably reduced thereby. In this case, when using press rolls with a smooth surface, only roll forces up to 48 kN per centimetre press roll width and per metre press roll diameter could be achieved irrespective of the selected gap. And at a gap of 18 mm per metre press roll diameter, a roll force of only up to 20 kN per centimetre press roll width and per metre press roll diameter could be applied.

[0049] The same smooth press roll surface was also used for compacting citric acid without internal magnesium stearate but with magnesium stearate coated press rolls. Upon externally coating with magnesium stearate, the ribbons indeed contained clearly less than 1% magnesium stearate, namely between 0.01% and maximum 0.1% (w/w) magnesium stearate, depending on the selected press rolls of the powder coating unit or the contact pressure of the pressed articles (the latter ones being prepared from a magnesium stearate containing powder mixture) and their mechanical strength.

[0050] Also when compacting mannitol using smooth, magnesium stearate coated press roll surfaces, in comparison to non-lubricated powder, no significant limitations to the manufacturing parameters were observed which are relevant for dry granulation with a roller compaction device. Also with mannitol, external coating of the press roll surfaces enabled a reduction of the magnesium stearate concentration in the roller compacted product by at least a factor of 10 to 0.1% (w/w). Generally, concentrations of 0.02% to 0.05% (w/w) were achieved, which is up to a factor of 50 less than with internal lubrication.

[0051] Even though by coating the press roll surface with magnesium stearate usually no significant limitations to roller compaction parameters have to be accepted which are relevant to dry granulation using roller compactionin comparison to non-lubricated powderthis does not apply for each powder to be roller compacted. Limitations regarding compaction between the press rolls may for instance be caused by a thin magnesium stearate layer leading to so-called draw-in problems. Especially, when using smooth press roll surfaces, for certain materials, like e.g. corn starch, this phenomenon is so pronounced that roller compaction is only possible at low forces and/or gap widths.

[0052] During the roller compaction of corn starch using smooth press roll surfaces, the manufacturing parameter range was already massively constrained at an internal magnesium stearate quantity of 0.1% (w/w). With corn starch, an internal magnesium stearate quantity of only 0.1% whilst using with smooth press rolls only a roll force of maximally 28 kN per centimetre press roll width and per metre press roll diameter could be applied at a gap of 4 mm per metre press roll diameter. From a gap of 8 mm per metre press roll diameter, a roll force of only 12 kN per centimetre press roll width and per metre press roll diameter could be exerted. From a gap of 12 mm per metre press roll diameter no significant roll force could be exerted, anymore.

[0053] However, if the surface of a smooth roll was roughened in such a way that the press rolls thereafter exhibited a surface roughness from 0.5 m to 1.5 m thereafter, and particularly from 0.8 m to 1.2 m, then the internal magnesium stearate concentration of 0.1% in the corn starch product still caused a reduction in the possible roller compaction parameter range compared to the non-lubricated product, but this reduction was and generally is of little practical significance for dry granulation by roller compaction. Also upon addition of 1% internal magnesium stearate together with the above-mentioned smooth but roughened press roll surfaces, the manufacturing parameter range was still sufficiently large (although slightly less than with an internal magnesium stearate concentration of 0.1% (w/w)), but the external lubrication of the press roll surfaces resulted not only in a slightly larger manufacturing parameter range than with an internal quantity of magnesium stearate of 1% but also in a much smaller concentration of magnesium stearate in the roller compacted product. The latter was lowered by a factor of 10 to 50, namely 0.1% to 0.02% depending on the constitution of the transfer rolls when using the roll-based coating device (refer to FIG. 2). Further, the press roll surfaces remained free of sticking/caking.

[0054] These results clearly show that the use of roughened press roll surfaces, characterized by press roll surfaces exhibiting a surface roughness from 0.5 m to 1.5 m, preferably from 0.8 m to 1.2 m, in combination with a device for applying a thin layer of a lubricant and/or an anti-adhesive, in particular magnesium stearate, are excellently suited for the compaction of powders with the aid of a roller compaction device, whereupon not only a sufficiently broad manufacturing parameter range is guaranteed, but whereupon also the magnesium stearate concentration in the granulate increases by only 0.01% to 0.2% (w/w), particularly by only 0.04% to 0.1% (w/w). At the same time, the press roll surfaces remain free of sticking/caking or the level of sticking/caking is so small that it has no influence on granulate quality or only an irrelevant one. In addition, this also ensures that the at gap density can be determined with an accuracy of 1.5% or better, but in any case better than 3%.

[0055] In some cases (e.g. for the product Neosorb), it was surprisingly noted that external lubrication even resulted in a minor extension of the roller compaction parameter range (though only of little practical relevance for dry granulation). In this case smooth but roughened press rolls were used. By externally applying a thin layer of magnesium stearate on the press rolls using the device by which magnesium stearate containing pressed articles were pressed onto the surface as shown in FIG. 3, the manufacturing parameter range could be extended from 72 kN to 80 kN per centimetre press roll width and per metre press roll diameter at a gap of 16 mm per metre press roll diameter. Also in this case, only small concentrations of magnesium stearate were measured in the roller compacted product, namely 0.04% to maximally of 0.12% (w/w).