Pharmaceutical Manufacturing Handbook: Production and

1134 TABLET COMPRESSION
stages involved in the compaction of a two - phase system due to the application of
an external force. It is defi ned as the reduction in the bulk volume of a material as
a result of gaseous phase [1, 2] . The second stage is consolidation, which is described
as an increase in the mechanical strength of the material resulting in particle -
to - particle interaction [1, 2] .
It is suggested that four mechanisms are basically involved in the process of
compression of particles: deformation, densifi cation, fragmentation, and attrition.
The process of compression is briefl y described as follows: small solid particles are
fi lled in a die cavity and a compression force is applied to it by means of punches
and then the formed monolithic dosage form is ejected. The shape of the tablet is
dictated by the shape of the die while the distance between the punch tips at the
point of maximum compression governs the tablet thickness, and the punch tip
confi guration determines the profi le of the tablet. The compression cycle in a conventional
rotary tablet press will be described in detail in this chapter and is illustrated
in Figure 1 .
The physical and mechanical properties of tablets, such as density and mechanical
strength, are signifi cantly affected by the process. Since tablet compression relies on
the ability of particulates to be compacted, the need to control the critical properties
of the materials with respect to readiness or ability to compact is an important issue
to the formulator.
In order to compress a powder or granulation product into a tablet of specifi c
hardness, a defi ned compression force must be applied. As pointed out by Shlieout
et al. [3] , by compressing a constant mass of powder, any variation in the applied
force causes a change in the measured force. In addition, the substance itself plays
an important role, that is, if it is of good compressibility, then the force needed for
compression would be low. It is well known that this compressibility will depend on
powder characteristics such as crystal habit and thermodynamic behavior.
The structure and strength of tablets are often discussed in terms of the relationship
between the properties of the particulate material and the properties of the
formed tablet. The properties of a powder that control its evolution into a tablet
(a) Creating thecavity
Fill cam
(e) Precompression
Solid formation
FIGURE 1
(b) Filling the cavity
Suction
gravity
feeder
(f) Compressing
Solid formation
(c) Metering thecavity
Weight adjustment ramp
and head
scraper
(g) Removing solid
Ejection cam
Compression cycle. (Courtesy of Thomas Engineering.)
(d) Containing the fill
Tail over die
Pull down after
weightcontrol
Punch-holding device