Tablet press
A tablet press is a mechanical device that compresses powder into tablets of uniform size and weight. A press can be used to manufacture tablets of a wide variety of materials, including pharmaceuticals, illicit drugs such as MDMA, cleaning products, and cosmetics. To form a tablet, the granulated material must be metered into a cavity formed by two punches and a die, and then the punches must be pressed together with great force to fuse the material together.[1]
A tablet is formed by the combined pressing action of two punches and a die. In the first step of a typical operation, the bottom punch is lowered in the die creating a cavity into which the granulated feedstock is fed. The exact depth of the lower punch can be precisely controlled to meter the amount of powder that fills the cavity. The excess is scraped from the top of the die, and the lower punch is drawn down and temporarily covered to prevent spillage. Then, the upper punch is brought down into contact with the powder as the cover is removed. The force of compression is delivered by high pressure compression rolls which fuse the granulated material together into a hard tablet. After compression, the lower punch is raised to eject the tablet.[2]
There are 2 types of tablet presses: single-punch and rotary tablet presses. Most high speed tablet presses take the form of a rotating turret that holds any number of punches. As they rotate around the turret, the punches come into contact with cams which control the punch's vertical position. Punches and dies are usually custom made for each application, and can be made in a wide variety of sizes, shapes, and can be customized with manufacturer codes and scoring lines to make tablets easier to break. Depending on tablet size, shape, material, and press configuration, a typical modern press can produce from 250,000 to over 1,000,000 tablets an hour. [3]
Tablet Machines
Tablets are produced using tablet presses. While these presses vary in their output, from approximately 3,000 tablets per hour to more than 1 million per hour for the fastest machines, the principle of manufacture remains the same. Powder is filled to a specified depth in a die and compressed between two punches. The compression force is ended by removal of the upper punch, and the lower punch then moves upward in the die to eject the tablet. Presses can be divided into two types, single punch (or eccentric) presses and rotary presses.
Single Punch Presses Single punch presses are sometimes referred to as eccentric presses because the movement of punches is controlled by an eccentric cam.
Capacity – around 200 tablets per minute.
Uses - ♦ Product development ♦ Small batch production such as for clinical trials
The powder hopper is attached to a feed shoe which oscillates horizontally. The compression cycle starts with die filling. The lower punch descends in the die. The depth of the descent can be controlled, and this determines the tablet weight. The feed then passes over the die a number of times allowing the die to be filled with powder. As the die shoe moves away, it removes all excess powder away from the die table leaving the die filled to an even level. The upper punch then descends into the die, compressing the powder. The depth to which the punch descends into the die is adjustable, and this controls the compaction pressure applied. The lower punch remains stationary during the compression phase. As the upper punch moves upward at the end of the compression phase, the lower punch will rise in the die, until it is level with the die table. The feed shoe will then begin its oscillatory phase and knocks the tablet off the lower punch and down a collection chute. The lower punch then descends to its filling position as a second cycle commences. Single punch presses are rarely seen in production environments due to their relatively slow production rates, although there are still a number of old products that can only be successfully produced on this type of machine. They are still used in development laboratories because they require only relatively small amounts of material to produce tablets compared to most rotary machines.
Rotary Tablet Machines
Commercial I manufacture of tablets is performed almost exclusively on
rotary tablet machines due to their higher output. On a rotary machine, the
punch and dies are positioned on a rotating turret, and output will depend on
the number of stations positioned around the turret and the speed of
rotation. Machines are available with anything from 4 stations for a
development machine to 79 stations for the largest production machines. All such machines operate using virtually identical principles.
The powder hopper is positioned above a feed frame, a frame that retains a powder bed above the dies when the lower punch is in the filling position. As the lower punches pass below the feed frame, they descend within the die to their lowest possible position so the whole die cavity can be filled with powder. The powder is filled into the dies by the suction effect caused by their descent and gravity from the feed frame above. To optimize filling, the feed frame is designed so that the powder in contact with the die table and following the rotary action of the table is directed in a manner that makes it pass to and fro across the dies. Some machines also have mechanical paddles in the feed frame. As the lower punches approach the end at feed frame, they pass over a weight control cam, this causes the punch to rise, ejecting some of the powder which is scraped off by the edge of the feed frame. Adjusting the height of the cam controls the amount of material remaining in the die as the punch moves toward the compression stage.
Compression takes place when the upper and lower punches pass between compression rollers. During compression, the upper and lower punches move together, in contrast to the single punch machine, where only the upper punch moves. The compression force is controlled by moving the lower compression roller up or down, thus adjusting the distance between the punches at the point of maximum compaction. Some machines are fitted with two sets of rollers, a small roller being positioned between the feed frame, and the main compression roller allowing a small degree of compression to take place. This is termed recompression, and was introduced to minimize capping and lamination by removing air from the powder bed and effectively increasing the dwell time of the compression phase.
Following compression, the upper punches are removed by the upper punch cam track, and the lower punches pass over an ejection cam, a gentle ramp that moves the lower punches vertically within the die until the tablet is fully ejected. The tablets are removed from the punch tip by a scraper blade positioned on the edge of the feed frame, and the punch then descends to allow die filling to occur for the next cycle.
When developing formulations, it is usual for the early batches to be manufactured on either single punch machines or small rotary machines, due to the batch sizes being produced and the limited availability of new drug substances. It should be borne in mind that formulations that are being developed may ultimately be required to run on larger rotary machines, and there are great differences in the rate of compression between the machines generally found in formulation laboratories and those found in production. These differences are summarized in Table-2 & 3. Table-2 Approximate specifications of some small single station laboratory presses. Manufacturer: Model Number: Fette Exacta 1 Killian SP 300 Korsch EK-O/DMS Manesty F3 Max output (Tabs/ min) 75 80 60 85 Max tab diam (mm) 15 18 20 22 Max fill (mm) 16 16 20 17 Max appl force (kN) 15 25 30 40 Motor (HP) 0.75 1.1 0.5 2.0 Weight (Kg) 250 300 200 476 Apprx. dwell time (ms) 133 125 100 118
Table-3 Comparative specifications of some high output tablet presses.
Manufacturer: Model: Fette PT3090 Kikusi Gemini Korsch PH 800 Manesty Rotapress Max output (Tabs/ min) 16,750 10,720 18,360 13,360 Number of stations 79 67 85 75 Max turret speed (rpm) 106 80 108 89 Max tab diam (mm) 34 25 34 25 Max fill depth (mm) 18 16 22 20.6 Max compression force (kN) 100 80 80 100 Precompression (KN) 100 80 80 10 Net Weight (Kg) 4500 3900 4000 3700
The differences in punch speed at initial contact and dwell times, the period at which the compact is held at maximum compression, are likely to affect the nature of any tablets which have any viscoelastic components. Compaction simulators that are able to reproduce the punch speeds of production machines, yet only require small quantities of powder for testing, can have a valuable role to play in formulation development.
COMPRESSION, CONSOLIDATION, COMPACTION
COMPRESSION: reduction in the bulk volume of a material as a result of the removal of the gaseous phase (air) by applied pressure. CONSOLIDATION: increase in the mechanical strength of a material resulting from particle-particle interactions. COMPACTION: The compression and consolida-tion of a two phase (solid + gas) system due to an applied force, resulting in the formation of a compact but porous mass of definite geometry.
See also
References
- ^ Schwartz, Joseph; Lieberman, Herbert A.; Lachman, Leon (1989). Pharmaceutical dosage forms--tablets. New York: Dekker. ISBN 0-8247-8044-2.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ Isadore Kanfer; Shargel, Leon; Kanfer, Izadore (2005). Generic drug product development: solid oral dosage forms. New York, N.Y: Marcel Dekker. ISBN 0-8247-5460-3.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ Nash, Robert J.; Wachter, Alfred H; Berry, Ira R. (2003). Pharmaceutical process validation. New York, N.Y: Marcel Dekker. ISBN 0-8247-0838-5.
{{cite book}}: CS1 maint: multiple names: authors list (link)