Pharmaceutical Manufacturing Handbook: Production and

982 TABLET DESIGN
E: This ensures that the bore of the die is fi lled with as exact volume of the
material to be used, and the next stage can begin.
2. Compression Pressure is applied to form the granule into a solid (Figure
4 b ):
F: The upper punch is lowered into the bore of the die.
G: Precompression gives the powder an initial “ punch ” to remove excess
air.
H: The powder is fully compressed.
I: The correct pressure is reached.
J: The upper punch is lifted out of the way ready for tablet ejection.
3. Ejection The tablet is ejected and the next tablet will be formed (Figure
4 c ):
K: The lower punch begins to rise in the bore of the die lifting the tablet until
step L is reached.
L: Its base is level with the tap of the die.
M: The tablet is pushed aside into the take - off chute by passing under a static
blade.
N: The lower punch moves to its lowest position ready for fi lling ( O ), similar
to A and the entire cycle is repeated.
Guidance on compression levels for each tablet type (series 1, 2, and 3) and maximum
punch pressures are given in Table 1 :
Series 1 : Flat fl ace, normal concave, shallow concave tablets
Series 2 : Double radius, bevel and concave tablets
Series 3 : Flat beveled edge, deep concave, ball or pill
In Figure 4 the tablets progress from start to fi nish from left to right. On an actual
machine this will be determined by the direction in which the entire turret rotates
in relation to the fi xed item, such as the fi ll hopper precompressions and compression
rollers. It is important to note that this direction may vary from machine to
machine, but as a general rule, British, American, and some Asian machines
rotate in a clockwise direction while European machines rotate anticlockwise
(see Figure 5 ).
6.3.3
LIMITATIONS FOR DIRECT COMPRESSION
In tablet formulation, a range of excipient materials are normally required along
with the active ingredient in order to give the tablet the desired properties. For
example, the reproducibility and dose homogeneity of tablets are dependent on the
properties of the powder mass. The tablet should also be suffi ciently strong to
withstand handling but should disintegrate after intake to facilitate drug release.
The choice of excipients will affect all these properties:
1. Filler illers are used to make tablets of suffi cient size for easy handling by
the patient and to facilitate production. Tablets containing a very potent active