Tablet compression stages

Like lubricants, glidants are fine powders and may be required for tablet compression at high production speeds to improve the flow properties of the material into the die or during initial compression stages. They are added in the dry state immediately prior to compression and, by virtue of their low adhesive potential, reduce the friction between particles. Colloidal silica is popular, as are starches and talc. 

Tablets are the most important pharmaceutical dosage from and their design has always been of great interest to pharmaceutical engineering. Since tablets are made by a process of die compaction, although commonly called tablet compression, many investigations have been involved in the task to describe the mechanisms involved in this process. Nevertheless, some considerations should be taken regarding the definitions of stages involved in tablet compression. Compression is one of two...

The process of tablet compression is divided into three stages filling, compression, and ejection of the tablet (see Figure 1). 

Irrespective of the type of press that is used, the process of tablet compression can be divided into three stages, as shown in Fig. 1. 

The upper punch is withdrawn from the die, and so the force being applied to the tablet is removed. The effect of this might be to cause the deformed particles to return to their former shape, which would result in a decrease in interparticulate contact and hence tablet strength. It is essential that this does not occur. As the upper punch leaves the die, the lower punch moves upwards, pushing the tablet before it. During the compression stage, the particles are forced into intimate contact with the interior die wall. It follows that attempts to remove the tablet will be opposed by frictional forces and so successful ejection demands lack of adhesion between the tablet and the diewall. 

If you monitor punch displacement and compression force, you can make pretty accurate assessment of the compactibility of your material. If LVDTs are attached to both upper and lower punches, it is possible to actually measure in-die thickness of the tablet at various compression levels. In Fig. 12, one can see how the tablet thickness rapidly decreases in the compression stage and then gains some thickness during the decompression stage of the tableting cycle. The degree of this increase in thickness is indicative of the elastic recovery as the pressure is removed from the tablet. 

For some tablets, compression marks the final stage of the production process, but many formulations involve coating the compressed tablet. There are several reasons for applying a coat ... 

Developmental stability Stability studies conducted in the early stages of product development where an assessment of various formulations is being made with the intent of selecting the formulation that will have the longest shelf life. Other factors, such as tablet compressibility, and target product profile, may influence these studies. These studies may or may not be protocol driven, depending upon the stage of development. 

During the preformulation stage, the chemical and physical properties of the dmg moiety are studied exhaustively to ensure stabdity, safety, bioavadabdity, and therapeutic efficacy. Tablets are produced directly by compression of powder blends or granulations, which include a small percentage of fine, particle-sized powders. 

Since the SIR of disintegration time after storage depends on the compression load as well as on the disintegrant concentration, these factors should both be taken into account, when the SIR of disintegration time is used as a measure for the physical stability of tablets after storage, in the developing stage of tablet formulations. 

The specific material properties of most import to the compaction operation are elastic deformation behavior, plastic deformation behavior, and viscoelastic properties. These are also referred to as mechanisms of deformation. As mentioned earlier, they are equally important during compression and decompression i.e., the application of the compressional load to form the tablet, and the removal of the compressional load to allow tablet ejection. Elastic recovery during this decompression stage can result in tablet capping and lamination. 

Water content of the bulk tablets irrespective of the drying process was higher than at the final mix stage (Table 2). This is probably due to the compression room environment and the low initial moisture of the powder. Still, the specification limit of 2% is easily met. 

FIGURE 4 Stages of tableting process (a) filling (b) compression (c) ejection. 

The manufacturing process of tablets principally consists of three stages filling the die with the powder, compressing the powder, and ejecting the tablet from the die. 

The compression event is the central stage of tablet production. Compression not only depends on the machine but to a great deal on the material properties of a tablet formulation. The principal stages of compression have been described above. Principally, from the machine manufacturing side two different possibilities of compression exist. Either the lower punch is closing the die from the bottom side and the upper punch moves downward for compression or both upper and lower punches move simultaneously toward each other and the powder is compressed from both sides. In the first case the surface hardness of the tablet is not the same on the upper... 

There are different stages of tablet production which happen simultaneously for several tablets. The central stage of tableting occurs when the punches pass the upper and lower compression wheels and the compression wheels determine the downward movement of the upper punch and the upward movement of the lower punch The tablet is formed by the resulting punch forces. The compression wheels can be positioned either by a flexible swing or more seldom by an eccentric valve [40]. 

After formation of the tablet by application of a compression force follows the decompression stage, where the compression force is removed and the upper punch leaves the die. Then, the formed tablet undergoes a sudden elastic expansion followed by a viscoelastic recovery during ejection when the lower punch moves upward. 

At present, knowledge bases for aerosols, IV injection solutions, hard gelatin capsules, and direct compression tablets have been completed. Other knowledge bases for coated forms, granules, freeze-diied formulations, and pellets are in different stages of development. Trials have demonstrated that the system proposes formulations that are acceptable to formulators, and in December 1996, the system was first introduced for field trials in a pharmaceutical company. 

Precompression and Main Compression Rollers. After die fill and scrape-off, the punches rotate to the precompression station where an initial force is applied to the compact. The tablet is frequently partially formed during the precompression stage. Subsequently, the upper and lower punches move together under the main compression rollers where the final tablet is formed. The main compression roller is usually larger than the precompression roller. However, latest advances suggest that similar sizes for precompression and main compression rollers with the ability to apply similar loads may result in optimal tablet formation. The compression rollers are made of premium tool steels and are surface hardened. 

There are three methods of tablet manufacture designed to confer these essential attributes to a tablet formulation. Wet granulation and direct compression are the most important, with dry granulation (also known as precompression or slugging) used in some circumstances. Fig. 1 shows the processes of wet granulation and direct compression broken down into their constituent stages. 

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