Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
  • B30B15/0005—Details of, or accessories for, presses; Auxiliary measures in connection with pressing for briquetting presses
  • B30B15/0011—Details of, or accessories for, presses; Auxiliary measures in connection with pressing for briquetting presses lubricating means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B11/00—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses
  • B30B11/02—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a ram exerting pressure on the material in a moulding space
  • B30B11/08—Presses specially adapted for forming shaped articles from material in particulate or plastic state, e.g. briquetting presses, tabletting presses using a ram exerting pressure on the material in a moulding space co-operating with moulds carried by a turntable
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B30—PRESSES
  • B30B—PRESSES IN GENERAL
  • B30B15/00—Details of, or accessories for, presses; Auxiliary measures in connection with pressing
  • B30B15/06—Platens or press rams
  • B30B15/065—Press rams

Definitions

• the invention relates to the manufacture of moulded products, especially tablets and powder plugs for encapsulation, for example, produced by the compression of particulate material, for example, powders and granules.
• tablette includes pharmaceutical tablets, vitamin and/or mineral tablets and confectionery.
• Pharmaceutical tablets are usually prepared by the instantaneous compression of a powder, comprising the active ingredient and an excipient, between two punches m a die.
• the force for compression may be supplied by either the upper punch or by both the upper and lower punches, but m neither case does all of the applied force go into compressing the powder. Although some of the force is lost in heat and sound energy a major proportion is absorbed in overcoming die wall friction.
• magnesium stearate lubricant has, however, given rise to a number of problems, especially m the production of pharmaceutical tablets but also for other moulded products.
• the principal problems are (a) it is an extremely hydrophobic powder which can adversely affect the bioavailability of drugs and is undesirable m soluble tablets where it produces a surface film or scum on the glass of water m which the tablet is dissolved; and
• the mixing time used to incorporate the magnesium stearate m the other ingredients of the tablet formulation is critical and can influence the physico-mechanical properties of the tablets produced.
• the punches and the dies of the moulding devices previously used for the manufacture of tablets are typically formed of steel . Because of the repeated reciprocation of the punches within their associated die, on the repeated compression of the material to be formed into tablets, both the punches and the die are subjected to a high degree of wear. In practice, a hardened steel has been used for the manufacture of the punches and dies. Even with such hardened steel materials, lubricated m the manner described above, the severe abrasion to which the parts are subjected m use results m wear, and may result m the shedding of small amounts of the metal into the substrate.
• Powder plugs for incorporation into hard gelatin capsules may be made using a dosator.
• Dosators of the type conventionally used to make such plugs include a cylindrical casing ("dosage tube”), defining a cylindrical bore m which is located a piston (“dosage punch”) .
• the dosage tube is lowered downwardly into a hopper containing the powder to be compressed by means of relative vertical movement of the hopper and the dosage tube the dosage punch lightly compressing the powder to form a plug which remains withm a lower portion of the dosage tube when that is lifted out of the surrounding powder, and can subsequently be ejected from the tube into an open capsule body by operation of the dosage punch.
• the invention provides a part for use m a moulding apparatus, the part comprising a shaped member comprising zirconia .
• Zirconia has been found to have particularly suitable properties for use those parts m tablettmg machines that will be m contact with the material to be moulded. It s a very hard material, and thus resistant to abrasion.
• the use of zirconia offers significant advantages m terms of wear resistance, and thus m terms of the length of the useful life of the parts.
• Zirconia is substantially non- toxic when ingested m small quantities so that, should any abraded material from the shaped part enter the moulded tablet, that will not detrimentally affect the acceptability of the tablets, whether for pharmaceutical or other use .
• zirconia offers a low coefficient of friction m the context of moulding. It is thought that this unexpectedly low coefficient of friction is accounted for by the fact that the surface of the zirconia attracts a monolayer of water molecules, which acts as a lubricant during the manufacturing process. The present inventors have thus found that zirconia has an advantageous spectrum of properties which, m combination, make it especially effective in the moulding of tablets.
• the part is a punch.
• the shaped member may constitute the whole punch. If preferred, however, the shaped member may constitute a component of the punch, the punch comprising at least one further component, which may be of zirconia or of any other suitable material, for example steel. In that case, it will be appreciated that at least that portion of the surface of the punch that m use contacts the material to be moulded will be constituted by the shaped member comprising zirconia.
• the snaped member comprising zirconia may include a surface having at least one protrusion arranged to form, use, a corresponding recess or recesses an article moulded using the part.
• the shaped member comprising zirconia may include a surface having at least one recessed region arranged to form, use, a corresponding embossed region or regions on an article moulded using the part. Said at least one protrusion or at least one recessed region may be m the form of one or more letters of the alphabet.
• a punch according to the invention enables there to be formed embossed region (s) and/or recess (es) on the surface of the moulded article, for example, tablet, m reproducible fashion, even after many thousands of moulding cycles.
• the shaped member comprising zirconia may be configured and dimensioned to impart to an article to be moulded a feature or features of configuration that is or are substantially invisible to the naked eye.
• the shaped member comprising zirconia may be configured to impart to an article to be moulded a feature of configuration which is suitable for distinguishing the article from a counterfeited article.
• a unique pattern which may for example be the form of a letter or letters of the alphabet identifying the manufacturer or constituting a trade mark associated with the articles, m the form of braille letters enabling blind consumers reliably to distinguish the articles from other similar articles, or in the form of a distinctively shaped design, such as a logo.
• Incorporation of such a unique pattern may have a number of advantages from the point of view of distinguishing the articles from other articles of similar type, but may especially be useful m enabling genuine articles to be distinguished from counterfeit articles.
• the punches of the invention may have a recessed region for generating a complementary embossed region on a moulded article. It has not been possible using the previously known punches to generate such embossed regions satisfactorily and reproducibly on certain types of moulded article, especially tablets. Further, m the case of impressed patterns formed m the tablet surface, such patterns may be deeper than those generally formed m the use of the previously known punches. That is because of the reduced adhesion m the case of the surface of the shaped member, which reduces the tendency of the upper portion of the tablet to be removed when impressing such patterns .
• lubricant in use of the shaped members of the invention, it is possible to use a relatively small amount of lubricant in the moulding process, or even to use no added lubricant. It may also appropriate formulations be acceptable to reduce or even eliminate the amounts of flow aid and/or anti -adherent additives required.
• the part is a die.
• the shaped member may constitute the entire die. It may be preferred, however, for the die to comprise at least one further component (which may be of zirconia or may be of any other suitable material, for example, steel) as well as the shaped member comprising zirconia. In that case, at least that portion of the die that use contacts the material to be moulded will be constituted by the shaped member comprising zirconia.
• the shaped member may be a liner for the interior of the die.
• the shaped member may advantageously consist essentially of zirconia.
• the shaped member advantageously contains at least 90%, preferably 95%, and more preferably 97%, by weight, based on the total weight of the member, of zirconia.
• One or more suitable compounds selected from yttria and other metal oxides may advantageously be present small amounts, for example, up to 10%, preferably up to 5% by weight based on the total weight of the member to stabilise the lattice structure of the zirconia.
• the shaped member may be of zirconia and another suitable material.
• it may be of a blend comprising zirconia and alumina.
• the shaped member may comprise, for example, from 5 to 20% by weight zirconia m admixture with alumina.
• the invention further provides a moulding apparatus comprising at least one punch comprising a shaped member comprising zirconia as defined above and/or at least one die comprising a formed member comprising zirconia as defined above.
• the moulding apparatus comprises at least one pair of punches and a die which are each so configured that they cooperate to form, m use, a moulded article having a plurality of edges and corners.
• Tablettmg machines comprising punches and dies consisting wholly or m part of zirconia as described above offer particular advantages m the manufacture of embossed tablets.
• the use of zirconia parts of suitable configuration will also facilitate the manufacture of tablets of given desired configurations, and may be especially advantageous m the manufacture of tablets having more than the usual number of edges or of unusual shapes, enabling a wider range of tablet shapes to be generated satisfactorily.
• t will be preferable for the tablettmg machine to incorporate a pair of punches and a die which together cooperate to form the tablet, and at least those portions of the opposed punches that m use contact the tablet will comprise zirconia.
• the tablettmg machine is a rotary press.
• a multiplicity of pairs of punches operate sequentially and the pressing cycle is initiated by a cam mechanism which acts on a portion of each punch (that portion being referred to below as a "cam follower") .
• cam follower it may be advantageous for the cam follower to comprise zirconia, rendering the cam follower more resistant to wear. It may also be advantageous for the cam to comprise zirconia .
• the moulding apparatus may be suitable for use m the manufacture of powder plugs for encapsulation m gelatin capsules, for example, it may be a device of the type known as a dosator.
• the shaped member advantageously constitutes the dosage tube of the dosator. It may be preferred, however, for merely the tip of the dosage tube, m particular the portion that m normal use comes into contact with the composition to be compressed, to comprise zirconia.
• the invention provides a method of making a moulded article, which is admmistrable to a human or animal, especially an mgestible article, comprising introducing a zirconium-containing compound into a mould with the material to be moulded.
• the lubricating properties of the zirconium-containing compound may render the use of other lubricating materials unnecessary (although the presence of such other lubricants is not excluded, if desired) .
• the use of zirconium-conta mg compounds, especially zirconia, as a lubricating ingredient offers advantages over conventional lubricants, such as magnesium stearate, m particular m that it has a lesser effect on the solubility characteristics of the other ingredients of the moulded article.
• the zirconium-contammg compound should be a physiologically tolerable compound.
• the zirconium-contammg compound may be introduced into the mould m admixture with the material to be moulded. As well, or instead, the zirconium-contammg compound may be introduced into the mould advance of the material to be moulded.
• the zirconium-contammg compound may be zirconia, but is preferably zirconium hydroxide or a physiologically tolerable zirconium salt.
• Zirconium- contammg compounds for use the manufacture of moulded articles according to the invention will advantageously be in the form of powders, of which the maximum particle size is not more than lO ⁇ m.
• Zirconia powder for use m the manufacture of the moulded articles may be made by calcination of finely divided zirconia.
• the moulded article is a tablet.
• the moulded article is a pharmaceutical tablet.
• the invention further includes a tablet comprising a zirconium- contammg compound .
• the moulded article may be a powder plug for encapsulation m a gelatin capsule.
• the invention further provides a hard gelatin capsule including an encapsulated composition comprising a zirconium-contammg compound.
• the zirconium-contammg compound to be incorporated m the moulded article may be the form of a gel or of small particle size particulates, which may be obtained for example by means of spray drying, lyophilisation or size reduction from larger particles.
• the zirconium-contammg compound may be incorporated m mixtures of drugs or drug formulations m amounts of, for example 0.05% to 20%, and preferably not more than 10%, more preferably not more than 5%, by weight based on the total weight of the combined components.
• zirconium-contammg compound exceeding 20% by weight are not excluded, although it is believed that no further significant improvement m lubrication will be obtained if greater amounts are used.
• the presence of the zirconium-contammg compound may improve the flow, adherence and lubrication properties of such mixtures.
• the zirconium-contammg compounds may be used m combination with, or as alternatives to, materials currently used for flow improvement, adherence or lubrication.
• a rotary press tablettmg machine including a multiplicity of dies and punches embodying the invention will now be described with reference to the accompanying drawings, of which:
• Fig. 1 is a schematic developed view of a rotary press ;
• Fig. 2 is a vertical section through a punch having a zirconia tip
• Fig. 3 is a vertical section through a die having a zirconia lining
• Fig. 4 is a graph which the ejection forces m a steel die and a zirconia die are compared m respect of micro-crystallme cellulose tablets;
• Fig. 5 is a graph corresponding to Fig. 4 respect of silicified micro-crystallme cellulose tablets
• Fig. 6 is a graph corresponding to Fig. 4 respect of lactose tablets
• Figs. 7a to 7e are graphs of ejection force against ejection time for a microcrystallme cellulose tablet previously compacted at compaction speed 100mm per second and at a compaction force of 2kN(F ⁇ g. 7a), 4kN (Fib. 7b), 8kN (Fig. 7c), 12kN (Fig. 7d) , and 16kN (Fig. 7e) ;
• the rotary press shown m the drawing is entirely conventional, except for the punches and dies which, as described further below, are m accordance with the invention.
• the rotary press may, for example, be a rotary press of the Type RB3 (trade mark) manufactured by Manesty Machines Ltd.
• the press has a circular die table 1 mounted for rotation about its central axis.
• a plurality of dies 2 are located m the table 1.
• Above and aligned with each die 2 is an associated upper punch 3 mounted for sliding movement into and away from the die in an upper punch holder 4 which, m turn, is arranged for rotation with the die table 1.
• each die 2 below and aligned with each die 2 is an associated lower punch 5 mounted for sliding movement into and away from the die m a lower punch holder 6 which, m turn, is arranged for rotation with the die table 1.
• Each of the upper punches 3 has a cam follower 7 at its upper end and similarly each of the lower punches 5 has a cam follower 8 at its lower end.
• the cam followers 7 rest on a stationary fixed upper cam track 9 while the cam followers 8 rest on a stationary fixed lower cam track 10.
• the die table 1, dies 2, punches 3, 5 and punch holders 4, 6 are made of metal .
• the lower cam track 10 is interrupted at one position by a ramp 11 the height of which can be screw-adjusted and at another position by the head of an ejection knob 12 which is also screw-adjustable.
• a pair of compression rolls 13 are also associated with the upper and lower cam tracks 10 and 11.
• the press has a main hopper 14 for feeding the powder or granules to be tabletted. In a conventional arrangement this powder would include lubricant particles but in the described apparatus that may not be necessary (although it is not excluded) .
• the hopper 14 has an outlet leading to a stationary feed frame or a force feeder with moving paddles 15 immediately about the die table 1.
• the base of the frame 15 lies immediately adjacent to the top of the die table 1 and has apertures which allow powder or granules to pass from the compartment into the dies 2.
• a stationary blade 16 is provided for scraping excess powder or granules away from the dies 2.
• a given die 2 having an associated lower punch 5 and upper punch 3, moves to a position underneath the feed frame 15 where the die is filled with powder.
• the cam follower 8 is caused to move down by the downwardly sloping cam track 10 so that the lower punch 5 only just projects into the die and the die is therefore almost entirely filled with powder.
• the cam follower 8 subsequently reaches the ramp 11 and is driven upwardly thereby expelling powder.
• the cam follower 8 subsequently reaches the ramp 11 and is driven upwardly thereby expelling powder from the die. While the cam follower 8 is on the top of the ramp 11 the blade 16 scrapes away excess powder from above the die.
• the lower punch 5 is lowered as the cam follower 8 returns to the cam track 10 and the upper punch 3 drops as the cam follower 7 slides down the inclined upper cam track 9.
• the upper and lower punches 3, 5 are finally force ⁇ together by the compression rollers 13 compressing the powder the die 2 and forming a tablet .
• the upper punch 3 is raised and the lower punch 5 also raised until the tablet is swept away into a collector (not shown) by a wall. The cycle of operation is then repeated.
• a punch 3 suitable for use m the machine of Fig. 1 may have a steel body 17, to which is fixedly attached a tip 18, which is of zirconia. If desired, the end portion of the punch opposed to the tip 17 (which opposed end portion includes at least the cam follower surface 7) may also be of zirconia, although such a construction is not illustrated m Fig. 2. The punch 3 may, instead, be wholly of zirconia, and may then be monolithic .
• a die 2 suitable for use the machine may have an outer casing 19 of steel and a lining 20 of zirconia defining a cylindrical bore 21.
• the die may, however, be wholly of zirconia and may then be monolithic.
• the punch tip diameter and the die internal diameter may each be 10 mm.
• a die or punch or a shaped die lining or punch tip according to the invention may be of stabilised zirconia which may be manufactured from a tetragonal zirconia powder which may contain for example 3mol% ytt ⁇ a m solid solution, the presence of ytt ⁇ a contributing to the stability of the tetragonal phase.
• other additives for example one or more other oxides, may be used to stabilise the zirconia product.
• the powder, including any additives may then be pressed into shape by any suitable technique, for example, die pressing or hydrostatic pressing or both of those techniques used sequentially. Other methods such as slip casting may be used.
• the green body (that is, the shaped powder compact) may then be sintered, for example, by heating in a furnace under a controlled heating cycle to a maximum temperature between 1300°C and 1600°C, preferably in the range 1400°C to 1500 °C, and maintaining this temperature for 2 to 12 hours. The temperature may then be lowered slowly to room temperature.
• the shaped member so obtained may then be machined to the precise final configuration and dimensions required, to give a close fit between the cooperating punch and die, for example, using diamond grinding techniques. It is in particular desirable to ensure that sharp edges are removed by imparting in their place a small radius of curvature as the presence of sharp edges would lead to regions of stress concentration in use.
• the desired pattern may be generated on the punch tip by any suitable method, for example, by machining the tip using suitable diamond tooling, or by appropriate modification of the method of manufacture of the tip.
• the pattern may be introduced during manufacture by green machining the pattern onto the tip surface to a calculated shape and size and subsequently sintering (the densification on sintering causing shrinkage of dimensions with the pattern being essentially retained) , or by impressing the pattern, to a calculated shape and size, into the powder compact and sintering to full density. It will be appreciated that, in each case, when calculating the appropriate shape and size, allowance will have to be made for the shrinkage that will occur on sintering.
• the patterns so produced are of relatively high definition.
• the liner m the form of a thin walled cylinder is, after sintering, diamond machined such that its diameter is slightly larger than the internal diameter of the outer die casing.
• the casing which may be of, for example, tooled steel, may be heated to expand its internal diameter and the zirconia insert may then be inserted and the casing shrink fitted onto the liner, imposing compressive stresses on the liner, both holding it in place and strengthening it.
• the inner diameter of the lining may then be diamond honed to give it the desired final dimensions.
• the tip may be held in place by any suitable means, for example, mechanical means, any suitable adhesive or metallic braze, or a suitable combination of one or more of those means.
• suitable mechanical means may include the provision of cooperating means on the tip and the punch body, for example, means permitting an interlocking fit or a screw fit.
• Suitable adhesives are preferably organic-based adhesives. Because the stresses on the tip are mainly compressive nature, it is m general unnecessary to take any special measures to ensure that the affixment of the tip to the remainder of the punch is of very high strength.
• Fig. 4 is a graph of the ejection force required to eject from a die a compressed portion of microcrystallme cellulose powder against the compaction force previously applied to the compressed portion to be ejected.
• the powder did not contain any conventional lubricant additives
• the upper line represents measurements made using as the die a steel die
• the lower line represents measurements made using as the die a zirconia die according to the invention.
• the lower opening of the die is closed by a lower punch, arranged to be stationary, and the material is compacted by an upper, vertically movable puncn.
• the upper and lower punches are, m each case, of the same material as the die, that is, of steel or zirconia, respectively.
• the ejection force required in the case of the steel die is significantly greater than in the case of the zirconia die.
• the measurements were obtained by compressing a portion of the microcrystallme cellulose m the die by advancing the upper punch downwardly at a speed of 10 mm per minute until the desired compaction force is reached and thereafter inverting the die together with the compressed portion contained therein and advancing the punch downwardly onto the compressed portion and determining the ejection force required to eject it.
• the compaction force and ejection force were measured using an Instron tensile testing machine, having a load cell arranged to measure the force transmitted through the punch.
• the compaction force and the ejection force are the peak force, determined m each case by the load cell, during compaction and ejection, respectively.
• Fig. 5 is a corresponding graph of the ejection force against compaction force for compressed portions of silicified microcrystallme cellulose, without added lubricant and Fig. 6 is an analogous graph for compressed portions of lactose containing 1% by weight magnesium stearate as added lubricant.
• the upper line represents measurements made using as the die a steel die
• the lower line represents measurements made using as the die a zirconia die according to the invention
• the relative positions of the lines show that the ejection force required the case of the steel die is significantly greater than the case of the zirconia die.
• diluents selected from microcrystallme cellulose, silicified microcrystallme cellulose and lactose, and Figs. 4 to 6 demonstrate the benefit of the advantageous frictional behaviour of zirconia m the manufacture of tablets. In the presence of added lubricant, the superior performance of zirconia will still be observable, at a given lubricant content.
• Figs. 7a to 7e are graphs showing the relationship between ejection force and ejection time for a microcrystallme cellulose tablet, incorporating 0.5 wt % magnesium stearate as added lubricant, the tablet having previously been compacted m the compaction simulator.
• Compaction of the tablets was accomplished using a sawtooth profile compaction cycle, with a punch tip velocity of 100mm per second, at a selected compaction force. (Punch tip velocity the compaction simulator may be determined using a linear variable displacement transducer.)
• Fig. 7a relates to tablets previously compacted at compaction force 2kN, Fig. 7b to tablets compacted at 4kN, Fig. 7c to tablets compacted at 8kN, Fig. 7d to tablets compacted at 12kN and Fig. 7e to tablets compacted at 16kN.
• each curve represents the averaged results for at least five tablets.
• the area under each curve represents the work needed to overcome die wall friction during ejection, and it will be seen that, m each of Figs. 7a to 7e, the area under the curve representing tablets ejected from zirconia tools is less than that under the curve representing tablets ejected from steel tools, indicating a significant reduction m ejection forces.
• Microcrystallme cellulose used m the above methods was of the type known as EMCOCEL 90M, obtainable from Mendell UK Ltd. Where magnesium stearate was used as an additive, it was incorporated in the powder before compaction by mixing for five minutes in a Turbula mixer at slow speed. All powders were stored before use for at least one day m the desiccator at room temperature and relative numidity 44%. Where used, the compaction simulator was fitted with 10mm diameter flat-faced round F-toolmg manufactured from zirconia or steel. The compaction speed used was lOOmm/sec corresponding to the ma compaction time of 0.345 seconds. A single saw-tooth control profile was chosen to provide the mam compaction pressures. The die was filled manually, sufficient powder being used to produce a tablet thickness of about 2.5mm at zero porosity. During tabletmg, relative humidity was withm the range of 35 to 45% and temperature with the range 20 to 25 °C.
• Shaped members comprising zirconia according to the invention have also been found to exhibit excellent wear resistance, and have high strength, high fracture toughness and high nardness .
• Other properties of zirconia which it is thought may contribute to its excellent performance the manufacture of tablets are its anti-static properties, non-magnetic nature, low thermal conductivity and good corrosion resistance.
• a consequence of the advantageous combination of properties is that the amounts of material shed into the tablet formulation are likely to be considerably reduced as compared with the steel parts conventionally used, and may be substantially eliminated.
• the tablets manufactured using zirconia members according to the invention may, moreover, be of improved strength.
• a part comprising a shaped member comprising zirconia m a device for moulding powder plugs for subsequent encapsulation.
• the forces to which the part will be subjected use will be lower than m a tablettmg machine.
• a moulding device of the type known as a dosator it may be appropriate to use a single walled cylindrical tube of zirconia, for example of wall thickness 1mm, as the dosage tube itself or as the tip portion of the dosage tube.
• the following Examples are illustrative of those methods of the invention m which a zirconium-contammg compound is incorporated m a tablet composition. In the Examples, references to % are % by weight based on the total weight of the composition.
• determination of particle size may be carried out by any method suitable having regard to the material and particle size, for example, by low angle laser light scattering using an apparatus such as the Malvern Mastersizer X (trade mark) .
• zirconia there may be used instead of zirconia m the above formulations (or any other formulation according to the invention) any zirconium-contammg compound that is pharmaceutically acceptable.

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• 1999
  • 1999-11-18 EP EP99972151A patent/EP1140479B1/de not_active Expired - Lifetime
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  • 1999-11-18 GB GB9927318A patent/GB2343862A/en not_active Withdrawn
  • 1999-11-18 DE DE69906577T patent/DE69906577D1/de not_active Expired - Lifetime
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