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Tablet Compression :

Tablet Compression Presented By, Gunjal Sandeep S. M.Pharm



Powder compression:

Powder compression It is defined as the reduction in volume of a powder owing to the application of a forces. Because of the increased proximity of particle surfaces accomplished during compression, bonds are formed between particles which provide coherence to the powder i.e. compact is formed.

Effect of Compression :

Effect of Compression When external mechanical forces applied to a powder mass there is reduction in bulk volume as follows Repacking Particles deformation Elastic deformation-e.g. acetyl salicylic acid, MCC Plastic deformation-at yield point of elastic. Micro quashing-irrespective of larger particles, smaller particles may deform plastically.

Tablet production:

Tablet production Powders intended for compression into tablets must possess two essential properties Powder fluidity The material can be transported through the hopper into the die To produce tablets of a consistent weight Powder flow can be improved mechanically by the use of vibrators, incorporate the glidant Powder compressibility The property of forming a stable, intact compact mass when pressure is applied

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PHYSICS OF TABLET COMPRESSION Unlike other physical states of matter, powder solids are heterogeneous because they are composed of individual particles of widely differing size and shapes, randomly interspersed with air spaces. For this reason it is virtually impossible to characterize these complex system fully in terms of fundamental properties.

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Compaction of powder- It is the general term used to describe the situation in which these materials are subjected to some level of mechanical force. This forces are important in case of the production of tablets and granules. The physics of compaction may be simply stated as “the compression and consolidation of two-phase(particulate solid-gas) system due to the applied force.”

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“Compression means a result of displacement of the gaseous phase.” It is defined as the reduction in volume of a powder owing to the application of a forces.


Difference Compaction Consolidation It is defined as the formation of solid specimen of defined geometry by powder compression. The compression takes place in a die by the action of two punches, the lower and the upper by which compression force is applied. It is in increase in mechanical strength of material from particle particle interactions.




THE SOLID-AIR INTERFACE Atoms or ions at the surface of any solid particle are exposed to a different distribution of intermolecular or intramolecular bonding forces than those within the particle.


ANGLE OF REPOSE Tan ф = 2h/D It is the maximum angle that can be obtained between the freestanding surface of a powder heap and horizontal plane. Such measurements give at least a qualitative assessment of internal cohesive and frictional effects under low level of external loading, as might apply in powder mixing, or in tablet die or capsule shell filling operations.


FLOW RATES Resistance to movement of particles, especially for granular powders with little cohesiveness, can be determine by flow rate. I =[1-v/v₀] I-Compressibility index. v-Volume occupied by a sample powder after tapping. V₀- Volume before tapping.


MASS-VOLUME RELATIONSHIP Measurement of the volume is more complicated because of the presence of air spaces or voids. Air spaces or voids can be distinguished as follows, 1. Open intraparticulate voids- 2. Closed intraparticulate voids- 3. Interparticulate voids-

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Therefore at least three interpretation of powder volume may be proposed; 1. The true volume- 2. The granular volume- 3. The bulk volume-

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volumes Definitions True volume Volume of powder itself Granule volume Volume of powder + voids (inter particle spaces ) Bulk volume Volume of powder + volume of intra particle space+ voids Void volume Bulk volume – true volume (Vb - Vp) 17


DENSITY The ratio of mass to volume True density- Granular density- Bulk density-

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Three types of densities Universally defined as weight per unit volume. True density:- it is the weight of material it self Granule density: Measured by mercury displacement method. Mercury fills the voids, but fails to penetrate internal particles. as it has non weighting properties. Granule volume related to weight of the mercury that displaced by granules in pycnometer. 19

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Bulk density:- Bulk density = mass of the powder (w) bulk volume (Vb) -When particle are loosely packed , lots of gaps in between particle. -Bulk volume increases making powder light. -Bulk density apparatus’ is used to determine bulk volume. 20


EFFECT OF APPLIED FORCES Deformation- When any solid molecule is subjected to opposing forces, there is a finite change in its geometry, depending upon the nature of applied load. The relative amount of deformation produced by such forces is a dimensionless quantity is called strain.


ROLE OF MOISTURE As little as 0.02% moisture can affect the proportion of the applied force transmitted to lower punch, and at 0.55% moisture, the behavior is actually the reverse of that for totally dry material.

Physics of compression :

Physics of compression A tablet is formed by reducing tile volume of a set of autonomous particles until they are consolidated into a solid body Tablet consolidation occurs when the punches and die go between two compression rollers The complete tablet manufacturing cycle occurs in four steps: (I) the die is filled, (ii ) the fill weight is adjusted, (iii) the tablet is compacted. and (iY) the tablet ejected from the die . From a material point of view, a compaction process is normally described by a series of sequential phases

Compression :

Compression Tableting procedure Filling Compression Ejection

Compression process:

Compression process Filling By gravitational flow of powder from hopper via the die table into die. The die is closed at its lower end by the lower punch. Compression The upper punch descends and enters the die and the powder is compressed until a tablet is formed. During the compression phase, the lower punch can be stationary or can move upwards in the die. After maximum applied force is reached, the upper punch leaves the powder i.e. the decompressed phase. Ejection During this phase, the lower punch rises until its tip reaches the level of the top of the die. The tablet is subsequently removed from the die and die table by a pushing device.

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Tablet compression machines Hopper for holding and feeding granulation to be compressed Dies that define the size and shape of the tablet Punches for compressing the granulation within the dies Cam tracks for guiding the movement of the punches Feeding mechanisms for moving granulation from the hopper into the dies 1. Single punch machine The compression is applied by the upper punch Stamping press

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Upper and Lower Collar Collar locker

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Common stages occurring during compression Stage 1: Top punch is withdrawn from the die by the upper cam. Bottom punch is low in the die so powder falls in through the hole and fills the die Stage 2: Bottom punch moves up to adjust the powder weight-it raises and expels some powder Stage 3: Top punch is driven into the die by upper cam. Bottom punch is raised by lower cam. Both punch heads pass between heavy rollers to compress the powder Stage 4: Top punch is withdraw by the upper cam. Lower punch is pushed up and expels the tablet. Tablet is removed from the die surface by surface plate Stage 5: Return to stage 1

Multi-station rotary presses:

Multi-station rotary presses The head of the tablet machine that holds the upper punches, dies and lower punches in place rotates As the head rotates, the punches are guided up and down by fixed cam tracks, which control the sequence of filling, compression and ejection. The portions of the head that hold the upper and lower punches are called the upper and lower turrets The portion holding the dies is called the die table

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Procedure for compression Granulation stored in hopper- Transferred to feed frame(A) Which having several compartments. Spread granule into the die Pull down cam (D) guides the lower punch. Allowing dies to overfill Punches pass over a weight control cam (E). It reduce fill in die to desired amount Swipe off blade remove excess granulation.

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The lower punches travel over the lower compression roll (F) while simultaneously the upper punches ride beneath the upper compression roll (G) The upper punches enter a fixed distance into the dies, while the lower punches are raised to squeeze and compact the granulation within the dies After the moment of compression, the upper punches are withdrawn as they follow the upper punch raising cam (H) The lower punches ride up the cam (I) which brings the tablets flush with or slightly above the surface of the dies

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At the same time, the lower punches re-enter the pull down cam (C) and the cycle is repeated. The tablets strike a sweep off blade affixed to the front of the feed frme (A) and slide down a chute into a receptacle

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-Theory and practice of industrial pharmacy by Leon lachmann -Dosage form design by Dr. Javed Ali, Dr. R.K. khar, Dr. Alka Ahuja -Pharmaceutics –The science of dosage form design by M.E. Aulton -Pharmaceutical dosage form: Tablet by Lieberman, lachmann -Bentleys textbook of pharmaceutics References

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