Abstract:
A rotary tablet press is provided for the manufacture of water soluble tablets by compression of powdered tablet material which does not include hydrophobic lubricants such as magnesium stearate. The tablet press includes a plurality of dies rotatable around a central axis of the press, and upper and lower punches which are rotatable with the dies and slidably mounted for compressive engagement with the dies. A feeder is provided for introducing the powder tablet material through a feed frame and into the dies. The feed frame includes a cam surface for removing the completed tablets from the dies. A brush is rigidly fastened to the feed frame and adapted to engage the working faces of the upper and lower punches to remove tablet material buildup therefrom after each of the punches has released the tablets. The brush is fabricated from food grade materials and includes bristles which extend obliquely relative to the faces of the upper and lower punches.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to tablet fabrication, and more particularly to the production of tablets through the use of a tableting press that compresses powders and granules. 
     2. Background Information 
     Tableting presses have long been utilized to manufacture tablets by compressing powders and granules. A typical tableting press uses a cylindrical die center made of steel, and steel punches, to compress the powder under relatively high pressures, typically up to about 10 to 15 tons per square inch. One result of the compression is the production of heat. This heat builds up on the face of punches and in the die and, over a relatively short period of time, tends to cause the powder to stick to the faces of the punches and sides of the die. Once the powder begins to stick to the die and/or to the punch faces, the integrity of the tablet is compromised, since as the faces of the punches pull apart to eject the tablet, the tablet sticks to the punch faces and breaks, or is broken or damaged by the friction with the cylindrical walls of the die. Moreover, any powder remaining on the punches and/or die walls tends to add to the volume of powder within the die, to disadvantageously alter the internal pressure of the tablets. Tablets formed under excessive pressure may not dissolve properly, while tablets formed under insufficient pressure tend to break prematurely. 
     In order to reduce the die and face heat, and reduce the sticking on the face of the punches and the sides of the dies, it has been common practice to add powdered lubricants to the powdered tablet composition. These lubricants generally encase the powdered granules to reduce the friction on the face of the punches and the sides of the die. Commonly used lubricants include magnesium stearate and other stearates, such as sodium stearate and calcium stearate. Stearates tend to be useful as lubricants because of their relatively high viscosity and insolubility in water, which helps prevent their breakdown when used to make compressed tablets. 
     While the use of stearates may be satisfactory in some applications, such as in the production of pharmaceuticals, their use tends to be undesirable in tablets that are dissolved in water prior to ingestion. Due to their hydrophobic nature, the stearates tend to float to the top of the water when a tablet made using stearates is dissolved in water, creating an undesirable metallic sheen or film on the surface of the water. 
     Thus, when manufacturing a water soluble tablet it is important to reduce or eliminate any insoluble material in the composition. One attempt to manufacture water soluble tablets involves replacing hydrophobic lubricants, such as stearates, with water soluble lubricants such as polyethylene glycol. While the use of such water soluble lubricants tends to reduce sticking on the sides of the die, these lubricants by themselves do not adequately prevent the tablet composition from sticking to the faces of the punches. This sticking problem is particularly acute when producing relatively large tablets, in which the tablet tends to be pulled apart when the punches separate prior to the tablet&#39;s ejection from the press. In particular, over multiple cycles, the composition adhered to the faces of the punches tends to accumulate to undesirable levels to the point at which uniform tablets may no longer be produced. 
     Thus, a need exists for an apparatus and method for fabricating water soluble tablets which overcomes the drawbacks of the prior art. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of this invention, a tablet press is provided for the manufacture of a tablet by compression of tablet material in the form of powder or granules. The tablet press includes at least one die circuitously moveable about the press and adapted for receiving tablet material therein; and a first punch and a second punch, the first and second punches being circuitously moveable with, and being adapted for operative engagement with, the at least one die. A punch movement device is adapted to alternately move at least one of the first and second punches relatively towards and away from an other of the first and second punches to alternately compress the tablet material in the at least one die to form the tablet, and release the tablet. A punch cleaner is disposed in operative engagement with the first and second punches, the punch cleaner being adapted to remove tablet material from the first and second punches after each of the first and second punches has released the tablet. 
     The present invention provides, in a second aspect, a rotary tablet press for the manufacture of a tablet by compression of tablet material in the form of a powder or granules. The rotary press includes a plurality of dies rotatable around a central axis of the press; a plurality of first and second punches rotatable with the dies; a feeder for introducing tablet material to each of the dies at a filling station; and a punch movement device adapted to alternately move the first and second punches relatively towards and away from one another to alternately compress the tablet material in the dies between working faces of the upper and lower punches to form tablets, and release the tablets. An ejector is provided for removing the released tablets from the plurality of dies; and a punch cleaner is disposed in operative engagement with the plurality of upper and lower punches, the punch cleaner being adapted to remove tablet material buildup from the working faces after each of the upper and lower punches has released the tablets. 
     The present invention provides, in a third aspect, a method is provided for fabricating a water soluble tablet adapted to dissolve in non-carbonated water. The method includes the steps of: 
     (a) providing a tablet press including: 
     at least one die circuitously moveable about the press and adapted for receiving tablet material therein; 
     a first and second punch, the first and second punches being circuitously moveable with, and being adapted for operative engagement with, the at least one die; 
     a punch movement device adapted to alternately move at least one of the first and second punches relatively towards and away from an other of the first and second punches to alternately compress the tablet material in the at least one die to form the tablet, and release the tablet; 
     a punch cleaner disposed in operative engagement with the first and second punches, the punch cleaner being adapted to remove tablet material from the first and second punches after each of the first and second punches has released the tablet; 
     (b) introducing tablet material in the form of powder or granules to the at least one die; 
     (c) moving the at least one of said first and second punches relatively towards the other of said first and second punches to compress the tablet material within the at least one die to form the tablet; 
     (d) moving the at least one of said first and second punches relatively away from the other of said first and second punches to release the tablet; 
     (e) engaging the punch cleaner with said first and second punches to remove tablet material therefrom. 
     The above and other features and advantages of this invention will be more readily apparent from a reading of the following detailed description of various aspects of the invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic developed plan view, viewed from the interior, of a rotary press incorporating the present invention; 
     FIG. 2 is an enlarged view of a portion of the rotary press of FIG. 1; and 
     FIG. 3 is a schematic top view of a portion of the press of FIG. 1, taken generally along  3 — 3  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the figures set forth in the accompanying Drawings, the illustrative embodiments of the present invention will be described in detail hereinbelow. For clarity of exposition, like features shown in the accompanying Drawings shall be indicated with like reference numerals and similar features as shown in alternate embodiments in the Drawings shall be indicated with similar reference numerals. 
     Where used in this disclosure, the term “axial” shall refer to a direction substantially parallel to rotational axis  12  (FIG.  3 ). The term “radial” shall refer to a direction substantially orthogonal to the axial direction. The term “coaxial”, when used in connection with an element described herein, shall refer to a direction relative to the element, which extends through its geometric center and is substantially parallel to rotational axis  12  of table  11 . The terms “downstream” and “upstream” respectively refer to the direction of arrow a (as the dies  15  move through filling station  20 ) and a direction opposite thereto. 
     Turning now to the Figures, the rotary press shown in FIGS. 1-3 is in many respects conventional. The press  10  has a circular die table  11  disposed for rotation in direction a about its central axis  12  (FIG.  3 ). A plurality of generally cylindrical dies  15  are spaced circumferentially within the table  11 . Above and coaxially aligned with each die  15  is an associated upper punch  16  mounted for coaxially slidable movement into and away from a die  15  in an upper punch holder  19 . The upper punch holder is in turn, arranged for rotation with the die table  11 . Each of the upper punches  16  are thus sized for slidable receipt within a corresponding die  15 . Similarly, below and coaxially aligned with each die  15  is an associated lower punch  17  disposed for sliding movement into and away from the die  15  in a lower punch holder  25 . This lower punch holder is in turn, disposed for rotation with the die table  11  about axis  12 . The proximal end of each punch  16  and  17  has a working face  22  which is adapted for engaging and compressing the powder  14  to form tablets  13  as will be discussed hereinbelow. Moreover, each of the upper punches  16  has a cam follower  40  disposed at its distal or upper end, while each of the lower punches  17  has a cam follower  42  at its distal or lower end. The cam followers  40  are supported by and slidably moveable along a stationary upper cam track  44 , while the cam followers  42  are similarly supported by, and adapted for slidable movement along stationary lower cam track  46 . The die table  11 , dies  15 , punches  16  and  17  and punch holders  19  and  25  may be fabricated from any suitable material commonly used for fabrication of dies and the like, such as metals and metal alloys, and/or composites, etc. 
     The lower cam track  46  is interrupted at one position by a ramp  48  the height of which may be screw-adjusted, and at another position by the head of an ejection knob  50  which may also be screw adjustable. A pair of compression rolls  52  are also associated with the upper and lower cam tracks  44  and  46 , as will be discussed in greater detail hereinbelow. Since FIG. 1 is a developed view, portions of one end of the drawing, namely compression rolls  52  and one set of punches and a die  15  are duplicated in phantom at the opposite end of the drawing to help illustrate the movement of the punches  16  and  17 . 
     The press  10  includes a hopper (not shown) for feeding powder or granules  14  to be tableted into one or more (two as shown in FIG. 1) dies  15  located at a filling station  20 . Powder  14  may include a water soluble lubricant in a preferred embodiment, as will be discussed in greater detail hereinbelow. The hopper feeds the powder into the dies  15  located at the fill station  20  through a feed frame  32  superposed with the top surface  54  of the table  11 . The feed frame  32  includes stationary blades  56  which extend radially across the dies for scraping excess powder or granules away from the dies  15  located within the fill station  20  as the dies rotate with table  11  relative to the stationary feed frame  32 . This action will be discussed in greater detail hereinbelow with respect to the operation of the present invention. 
     As best shown in FIGS. 2 and 3, feed frame  32  also includes a tablet cam or ejector  23  which serves to cam the completed tablet  13  radially outward and off of table  11  as the table rotates about its access  12  in direction a. Also disposed on ejector  23  is a brush  28  which includes an elongated base  36  which, as shown in FIG. 3, is adapted to extend transversely or radially across substantially the entire diameter of each die  15  as each die rotates past the ejector  23 . As also shown, brush  28  includes a pair of bristle arrays  38  extending from opposite sides of the base or block  36  to respectively engage the faces  22  of punches  16  and  17 . As best shown in FIG. 2, the bristle arrays  38  are disposed to resiliently engage and clean the faces  22  of upper and lower punches  16  and  17  as the punches rotate past the brush  28 . The bristles within each bristle array  38  are fabricated from any suitable material. In a preferred embodiment the bristles are fabricated from a food grade nylon (polyamide) or polypropylene. Block  36  may be fabricated from any suitable material, such as various metals (i.e steel, stainless steel. etc.) or polymers, (i.e. acetal, nylon, polytetrafluoroethylene, etc.). The bristles are retained within base  36  in any suitable manner familiar to those skilled in the art of brush making. The diameters of the individual bristles as well as the bristle count per cross-sectional unit area are predetermined in conjunction with the elastic modulus of the particular material used, to form bristles which effectively remove any buildup of powder  14  from the punch faces  22 , nominally without scoring or otherwise damaging the faces. As also shown in FIG. 2, bristle arrays  38  are preferably angled obliquely towards the incoming punches  16  and  17  (i.e. the bristles extend obliquely towards the upstream direction) to provide a relatively aggressive angle of incidence of the bristles onto faces  22 . In a preferred embodiment, bristles are positioned on the block at a 10 degree angle α relative to axis  12 , to provide a relatively firm and aggressive contact with the faces  22  of the punches as they rotate through the bristles. In this embodiment, as the faces of the punches rotate through the bristles, the firmness and orientation of the bristles tend to push the punches axially away from the brush, against the bias of the cam tracks  44  and  46  and force any built up powder composition to be removed from the face of the punches  16  and  17 . The clean punch faces are then presented to the fill station  20 , as will described in greater detail hereinbelow with respect to the operation of the present invention. 
     Moreover, the bristles are preferably provided with a variable length, so that relatively downstream bristles extend further from surface  50  than relatively upstream bristles as shown in FIGS. 1 and 2. Also as shown, the bristles of array  38  which extends towards lower punches  17  are preferably substantially shorter than those of the bristle array  38  adapted to engage the upper punches  16 . This configuration compensates for the relatively small clearance between base  36  of the brush and the surface  50  of table  11 . In one example, the bristles have a diameter within a range of from 0.003-0.030 inches (0.007-0.07 cm), with a preferred diameter within a range of approximately 0.0050-0.006 inches (0.012-0.015 cm), with a bristle length within a range of about 0.3-0.5 inches (0.7-1.3 cm) i.e. about 0.5 inches (1.3 cm) on upper array  38 , 0.3 inches (0.7 cm ) on lower array  38 . 
     As best shown in FIG. 1, in operation, a given die  15 , having an associated upper punch  16  and a lower punch  17 , is moved with table  11  to the filling station  20  (i.e. a position axially aligned with feed frame  32 ) where the die is filled with powder  14 . As the die moves to the fill station  20 , the cam follower  42  is moved down (axially away) from surface  50  of table  11  by the slope of the cam track  46  so that the lower punch  17  only slightly projects into the die and the die is thus almost entirely filled with powder  14 . As table  11  continues to rotate in direction a, the cam follower  42  subsequently reaches the ramp  48  and is driven upwardly (axially towards the surface  50 ) to expel powder from the die. By the time the cam follower  42  is on top of the ramp  48  (i.e. at the point closest to the working surface  50 ) the blades  56  will have scraped away any excess powder from the surface of the die which is generally co-planar with surface  50 . Thereafter, the lower punch  17  is lowered as the cam follower  42  returns to the cam track  46  and the upper punch  16  drops towards table surface  50  as the cam follower  40  slides down the inclined upper cam track  44 . The upper and lower punches  16  and  17  are finally forced together by the compression rollers  52  to compress the powder  14  within the die  15  to form a tablet  13 . As table  11  continues to move in direction a, the upper punch  16  is raised until it disengages both the die  15  and the tablet  13 . The lower punch  17  is also raised until face  22  thereof is flush with surface  50  of the die table  11 , at which stage the tablet is cammed radially outwardly by ejector  23  as best shown in FIGS. 2 and 3. The tablet is then collected by a suitable collection device (not shown). As the tablet  13  is being cammed away from table  11  by ejector  23 , the faces  22  of upper and lower punches  16  and  17  are moved into engagement with the bristle arrays  38 . This engagement serves to remove a majority of any build up of powder  14  thereon as the punches and die move into the fill station  20  where the cycle of operation is repeated. 
     Although the present invention is shown and described in conjunction with a single stage rotary press  10 , the invention may be incorporated into a conventional multi-stage press in which a plurality of tablets are produced during each revolution thereof. Moreover, the cycle of the press  10  may be modified to include various additional steps such as precompression of the powder  14 , etc. 
     The present invention as shown and described herein, may be utilized with powder material  14  either with or without a lubricant. The present invention has been shown to be particularly effective in manufacturing water soluble tablets  13  without the use of conventional hydrophobic lubricants such as magnesium stearate. When fabricating such water soluble tablets  13 , the present invention may be utilized either with or without lubricants. In a preferred embodiment however, any suitable water soluble lubricant such as polyethylene glycol (PEG) may be mixed with the powder  14  prior to being fed into dies  15  as discussed hereinabove. Examples of additional water soluble lubricants which may be used in the present invention include crystalline maltitol, sodium benzoate, 1-leucine, starch, and sodium lauryl sulfate. 
     In a further variation of the subject invention, the powdered or granular material  14  may be pre-ground prior to being fed into the dies  15 . For example, the powder  14  may be ground to a predetermined mesh size, preferably to a U.S. standard mesh size within a range of about 10 to 30 to provide a grit size of approximately 0.1356 to 0.0365 inches (3460 to 930 microns). This pre-grind step serves to provide the powder with a substantially homogeneous consistency to advantageously reduce the tendency of the powder to stick to either the dies or faces  22 . Such pre-grinding may be utilized with either lubricated or unlubricated powder  14 . In a still further embodiment, rather than being substantially cylindrical as shown, the inner surface of the dies  15  may be tapered to have a slightly frusto-conical configuration (not shown) to facilitate removal of the tablets  13  therefrom. In such an embodiment, the inner surface of dies  15  are provided with a predetermined diameter at a point substantially flush with surface  50  of die table  11 , with the diameter tapering radially inwardly further from surface  50 . 
     The present invention thus enables the successful production of relatively large production runs (i.e. 200,000 tablets or more) of tablets which are water soluble and thus suitable for non-carbonated soft drinks and sports drinks, etc. Moreover, the invention enables production of relatively large tablets, within a range of about 0.5 to 1.5 inches (1.2 to 3.8 cm) in diameter, having sufficient structural integrity to prevent them from breaking inadvertently during handling, while enabling them to efficiently dissolve in water. In a preferred embodiment, the tablets resist breakage forces within a range of from 8.5 to 14 kilopounds (Kp) using a test well known to those in the tableting industry. Additional steps such as lubricating the tablet material with various water soluble lubricants, pre-grinding the particulate to improve homogeneity, as well as tapering the die walls and lubricating the die walls and/or punch faces may be utilized either individually or in various combinations, with the brush  28  of the present invention to effect consistent and repeatable tableting of water soluble powder material. 
     Although a unitary punch cleaner or brush  28  has been shown and described to clean the punch faces  22 , one skilled in the art should recognize that a punch cleaner may be fabricated from one or a plurality of discrete components, such as resilient wipers, sponges, scrapers, brushes, etc., adapted to clean the first and/or second punch faces, without departing from the spirit and scope of the present invention. 
     The foregoing description is intended primarily for purposes of illustration. Although the invention has been shown and described with respect to an exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the invention. 
     The following illustrative examples are intended to demonstrate certain aspects of the present invention. It is to be understood that these examples should not be construed as limiting. 
     EXEMPLIFICATION 
     Example 1 
     Water soluble drink mix powder including sucrose, dextrose, malto dextrin, citric acid, gum arabic, flavor, salt, acetic acid, and sodium citrate was mixed in four batches with 1 percent crystalline maltitol, 3 percent crystalline maltitol, 1 percent sodium benzoate and 2 percent sodium benzoate by weight, respectively, and fed into a conventional tablet press similar to tablet press  10  without brush  28 . All four powder formulations stuck to the walls of the dies. The compositions were tableted on a stokes model “T” single station press. 
     Example 2 
     Control 
     Powder formulations including the drink mix of Example 1 were prepared in five batches including 5 percent mannitol, 0.5 percent 1-leucine, 1 percent 1-leucine, 2 percent 1-leucine, and 10 percent starch by weight, respectively. All five formulations were fed into a tablet press in the manner described in Example 1 and all five formulations resulted in sticking on the die and/or punch face surfaces. 
     Example 3 
     A pre-blend of sodium benzoate, PEG 800 and sugar was milled through a number 1 plate. The pre-blend was added to the base drink mix granulation and fed to the tablet press as described in Example 1. The powder stuck to the die wall and/or punch faces. 
     Example 4 
     A tablet powder formulation was provided utilizing the drink powder of Example 1 and PEG 3350 lubricant at 0.5 weight percent. The formulation was fed to a stokes rotary DD-2 press having a brush  28  mounted onto the feed frame. The brush had bristles approximately 0.006 inches in diameter fabricated from food grade nylon. A production run of approximately 50,000 tablets was completed with minimal sticking. The size of the tablets was approximately 1 ⅜ inches by 0.5 inches. 
     Example 5 
     Seven tablet compositions are provided using the drink powder of Example 1, and 1 weight percent crystalline maltitol, 3 weight percent crystalline maltitol, 1 weight percent sodium benzoate, 2 weight percent sodium benzoate, 1 weight percent 1-leucine, 2 weight percent 1-leucine and 10 percent starch, respectively. All of these formulations are respectively fed to a rotary tablet press substantially as described Example 4. Production runs of at least 50,000 tablets are successfully completed with minimal sticking. 
     Example 6 
     The formulations of the previous Example 5 are pre-ground and screened with a screen having a U.S. mesh size of 20, and then tableted substantially as described in the previous Example 5. Successful production runs of at least 50,000 tablets are completed. Example 7 
     Control 
     Tablets were fabricated substantially as described in Example 1 in which the die wall and faces  22  were electroplated with a non-stick coating of beryllium. The coating wore off during the production run and generated unacceptable levels of sticking to the punch faces.