Submitted by

D. Srinivasa RaoM.Pharmacy- Pharmaceutics

TABLET COMPRESSION

BySrinivas

• Introduction• Different types of tablet compression machines• Punches and dies• Different shapes of tablets• Compaction profile• Effect of compaction on hardness• Effect of compaction on friability• Effect of compaction on lamination• References

CONTENTS

• What is a TABLET ?A tablet is a pharmaceutical unit dosage form. It comprises a mixture of active substances and excipients, usually in powder form, pressed or compacted from a powder into a solid dose.

INTRODUCTION

• 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.

Powder 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.

– Brittle fracture – e.g. sucrose– Microquashing-irrespective of larger particles,

smaller particles may deform plastically.

Effect of compression

Compaction• 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.

Consolidation • It is in increase in

mechanical strength of material from particle particle interactions.

Difference

• 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

Tablet production

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.

EjectionDuring 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.

Compression process

• 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

Tablet compression machine

Upper andLower Collar

Collar locker

Single Punch Machine (Tablets)

• Dry methods– Direct compression– Dry granulation

• Wet methods– Wet granulation

Tablet production methods

Process Route for Tablet Manufacture

• Tablets are compressed directly from powder blends of the active ingredient and suitable excipients

• No pretreatment of the powder blends by wet or dry granulation procedures is necessary

• Advantages – Economy

• Machine: fewer manufacturing steps and pieces of equipment

• Labor: reduce labor costs• Less process vallidation• Lower consumption of power

Direct compression

Advantages Elimination of granulation process

Heat (wet granulation)Moisture (wet granulation)High pressure (dry granulation) Processing without the need for moisture and heat which is

inherent in most wet granulation proceduresAvoidance of high compaction pressures involves in producing

tablets by slugging or roll compactionElimination of variabilities in wet granulation processing

Binders (temp, viscous, age)Viscosity of the granulating solution (depend on its temp), How long it has been prepared,

Cont..

Advantages Rate of binder addition and kneading can affect the

properties of the granules formedThe granulating solution, the type and length of mixing and

the method and rate of wet and dry screening can change the density and particle size of the granules, which can have a major effect on fill weight and compaction qualities

Type and rate of drying can lead not only to critical changes in equilibrium MC but also to

unblending as soluble active ingredients migrate to the surfaces of the drying granules

More unit processes are incorporated in production, the chances of batch-to-batch variation are compounded

Cont..

• Advantages – Prime particle dissociation

• Each primary drug particle is liberated from the tablet mass and is available for dissolution

• Disintegrate rapidly to the primary particle state– Uniformity of particle size– Greater stability of tablet on aging

• Color• Dissolution rate• Fewer chemical stability problems would be encountered as

compared to those made by the wet granulation process

Cont..

ConcernsExcipient available from only one supplier and often cost more than filler used in

granulationProcedure conservationMachine investmentsLack of material knowledgePhysical limitation of drug

No compressibility No flow ability

Physical characteristics of materials (both drug and excipient) Size and size distribution Moisture Shape and surface Flowability Density

Lot to lot variabilityDusting problemColoring

Cont..

Common materials that have been modified in the chemical manufacturing process to improve fluidity and compressibility

Direct compression fillers

LactoseSpray dried lactose

SucroseNutab: 95.8% sucrose, 4% convert sugar Di-Pac: cocrystallization of 97% sucrose and 3% modified dextrin

DextroseEmdex: spray crystallized

SorbitolMannitolMaltodextrin

Maltrin

Soluble fillers

• Starch– Starch 1500– Spray dried starch

• Celulose– Microcrystalline cellulose (Avicel)

• Inorganic calcium salts– Dicalcium phosphate (Emcompress or DiTab)– Tricalcium phosphate (TriTab)

Insoluble fillers

Heckel plot is density Vs applied pressure.Follows first order kinetics.As the porosity increases the compression force will increase.The Heckel equation is described as follows. It is based on the assumption

that powder compression follows first-order kinetics, with the interparticulate pores as the reactant and the densification of the powder bed as the product.

Where D= relative density of a powder P=compact at pressure P. Constant k = measure of the plasticity of a compressed material.Constant A =die filling and particle rearrangement before deformation and

bonding of the discrete particles.Thus, a Heckel plot allows for the interpretation of the mechanism of

bonding.

Heckel equation

• Single punch press• Rotatory tablet press• Computerised tablet press

DIFFERENT TYPES OF TABLETTING MACHINES

• It posses a die and a pair of punches.• The amount of powder fill in to the die is

controlled by the position of the lower punch.• After ejection of tablet it is displaced by the

shoe of the hopper.as it moves back to the die for next tablet.

• OUTPUT:200 TABS per minute• Used in production of small batches.

Single punch pressSingle punch press

• Developed to increase the out put.• It operates with a number of dies & sets of

punches which can vary considerably.• Both the dies & punches rotate during the

operation.• The vertical movement of the punches is

controlled by tracks that pass over cams and rolls used to control the volume of powder fed in to the die and the pressure applied during compression.

ROTATORY PRESSROTATORY PRESS

• In these the movement of the punches can be controlled and varied considerably.

• Thus the tablet can be prepared under controlled conditions with respect to loading pattern and loading rate.

• Applications: to predict the sensitivity of the drug to such variations, to mimic the loading pattern of production presses to predict scale up problems.

• Because of the later application this is also called as compaction simulator

Computerised hydraulic pressComputerised hydraulic press

Type of Tools Punch Body (mm) Diameter (mm)

D tools 25.35 38.10

B tools 19 30.16

BB tools 19 24

BB toolB toolD tool

International StandardsInternational Standards

• General Terminology of Tooling• Different shapes of dies and punches• International Standards• Materials For Construction• Coating of Dies and Punches• Quality Control• Maintenance of Dies and Punches• New Developments

PUNCHES AND DIESPUNCHES AND DIES

• Upper punch

• Lower punch

• Die

• Keying

GENERAL TERMINOLOGY OF TOOLINGGENERAL TERMINOLOGY OF TOOLING

KEYS ON PUNCHES TERMINOLOGYKEYS ON PUNCHES TERMINOLOGY

Different shapes of tabletsDifferent shapes of tablets

• Round shape punch die set

• Oval shape punch die set

• Capsule shape punch die set

• Geometric shape punch die set

• Irregular shape punch die set

• Core rod tooling punch die set

Different Shapes of punches and DiesDifferent Shapes of punches and Dies

• Used by pharmaceutical and veterinary industry.

• Can manufacture following type of tablets:

Shallow Concave Ball Shape

Deep Concave Flat Faced

Concave with Edges Flat with Bevel Edges

Normal Concave.

Round shape Punch Die SetRound shape Punch Die Set

Applicable to pharmaceutical and ayurvedic industries.

Can manufacture following types of tablets:Flat Faced Flat with bevel

edgesConcave/Deep/Deep

Concave with bevel edges.

Oval Shape Punch Die SetOval Shape Punch Die Set

Applicable to pharmaceutical and ayurvedic industries.

Can manufacture

following types of tablets:Concave with EdgesDeep Concave Flat

Faced Normal concave Flat

with Bevel Edges.

Capsule shape punch die setCapsule shape punch die set

• Applicable to pharmaceutical, confectionery, chemical, industrial powder metallurgy industries.

• Can manufacture following types of tablet:

Triangular Benzene Rhombus Rectangular Square.

Geometric Shape Punch Die SetGeometric Shape Punch Die Set

• Are applicable to confectionery industries.

• Available with different size, concavity, and flat in plain or engraved break line.

Irregular Shape Punch Die SetIrregular Shape Punch Die Set

• Applicable in confectionery and ceramic industries.

• Can manufacture following types of tablets: Tablet with hole in center

& concave rib Tablet with hole in center

& flat rib.

Core Rod Tooling Punch Die SetCore Rod Tooling Punch Die Set

• Dies- HCHC (High carbon High chromium steel )

• Punches- OHNS (Oil Hardened Nitride steel)

• Different types of steel standards: For dies:- AISI-01

For punches:- AISI-S7, AISI-S1, D2(HCHC-D2), SUS 440C.

Materials For ConstructionMaterials For Construction

• Why coating is required?

Sticky material

Corrosive material

Abrasive material

Coating of Dies and PunchesCoating of Dies and Punches

• Titanium Nitride Coating

• Electroless Nickel Plating (ENI)

• Chromium Nitride Coating (CrN)

• Chromium Carbon Nitride (CrCN) Coating

• Diamond Coating of Diamond like Carbon (DLC)

• Cr-CrN-Cr Multilayer Coating (Nano Coating)

Different Types of CoatingsDifferent Types of Coatings

Visual InspectionDimensional

Inspection

Punches:Overall lengthWorking length Cup depthTips – round and capsuleTip and Barrel

concentricityHead, Head flat and NeckBarrel

Dies:Height and outside

diameterDie bore diameter

using expandable, small bore gauges

Die bore major and minor axis using Vernier caliper and expandable, small bore gauges

Die Bore concentricitySquareness

Quality ControlQuality Control

• Why is it required?

To improve the lifespan of toolings.

• How are they Maintained?Fitting instructions usually as per the manual

given.Warm soap water and a soft brush are suitable for

thorough cleaning Not to be touched by bare fingers Thoroughly coated with an acid-free oil in order

to prevent corrosion.

Maintenance of Dies and PunchesMaintenance of Dies and Punches

Toolings should be regularly checked.Polishing –

By hand “Drag Finishing” machine

Storage cabinets for tooling – Clashing Dusting Humidity

Contd..

• Multi-tip punches

• Development in manufacturing different shapes of tablets Polo Teddy Beer, Lion, etc.

• Tablets which can be broken into 4 equal halves

New DevelopmentsNew Developments

Multi-tip PunchesMulti-tip Punches

COMPACTION PROFILECOMPACTION PROFILE

• It has the same causes as weight variations.• Hardness depends on weight of the material and the

space between the upper and lower punch at the moment of compression.

• If the distance between the punches varies hardness is like in consistent.

EFFECT OF COMPACTION ON HARDNESS OF TABLETEFFECT OF COMPACTION ON HARDNESS OF TABLET

• When the punches are in poor condition or worn at their surface edges this problem arises.

• Less compression pressure also leads to increased friability.

Effect of Compaction on Friability of TabletEffect of Compaction on Friability of Tablet

• Rapid relaxation of the peripheral region of a tablet,on ejection from a die.

• This can be prevented by using tappered dies• Rapid decompression also causes lamination.• This can be prevented by doing pre compression

step. And decreasing the final compression pressure.

Effect of compaction on laminationEffect of compaction on lamination

The Kawakita equation is described as follows. This equation describes the relationship between the degree of volume reduction of the powder column and the applied pressure.

The basis for the Kawakita equation for powder compression is that particles subjected to a compressive load in a confined space are viewed as a system in equilibrium at all stages of compression, so that the product of the pressure term and the volume term is a constant.

where C = degree of volume reduction of a powder compact at pressure P. constants (a and b) =evaluated from a plot of P/C versus P. a= total volume reduction for the powder bed [carr’s index] b= constant that is inversely related to the yield strength of the particles.

The data from this study were modeled via the Kawakita equation in an attempt to evaluate the relationship between the volume reduction and applied pressure for each studied DC binder.

Kawakita equation

• www.google.com• Parle-Elizabeth Tools Pvt Ltd.• Encyclopedia of Pharmaceutical Technology,

second and third volumes• http//www.thomaseng.compresstooling.pdf• www.vmindustries.com• Pharmaceutics by Aulton• Pharmaceutical technology by Libermann and

laitman.

References:References: