Tablet Compression Process

Tablet Compression
Semester V
Industrial Pharmacy I (BP502T)
Unit II
VIDHI MER
Assistant professor
Parul Institute of Pharmacy and Research
Parul University, Vadodara

Introduction
• Direct compression method of tablet production involves thorough mixing of dry ingredients
followed by their compression into tablets. This process eliminates the drying steps involved in
wet granulation method. This process is economical in comparison to wet granulation which
includes increased equipment, labor, time, energy, and process validation.
• Besides being efficient and economical, process of direct compression is also suitable for
producing high quality tablets with adequate hardness, friability, and dissolution rates.
• Additionally, this process is also helpful in improving the physical and chemical stability of
tablets as compared to wet granulation.
• Crystalline substances like sodium chloride, sodium bromide, and potassium chloride may be
compressed directly. Direct compression materials should possess good flowability and
compressibility. They should be inert, tasteless, able to disintegrate, and inexpensive.

Stages of Compression
1. Transitional Repacking:
• The initial packing when the granulation movement occurs at lower pressure can be determined by
the particle size distribution and shape of granules.
• The granules flow along each other, and the finer particles enter the voids between the larger
particles. This increases the bulk density of granules.
• Spherical particles undergo less particle rearrangement in comparison to irregular particles, since
the spherical particles take up much closer initial packing arrangement.

2. Fragmentation and Deformation :
• When the stress within the particles increases due to high pressure, cracks may occur , which
gradually turn into fractures.
• Intrusion of smaller fragments into the void space may further increase the density. Since the
stresses are released by plastic deformation, some materials do not undergo fragmentation.
• In plastic deformation, the group of particles slide to release the stress (visco-elastic flow) and
changes the particle shape.
• New clean surfaces are produced as potential areas during such deformation.

• Deformation at the Point of Contact:
Application of further compression force at the contact point when all the granules are closely
packed, and the voids cannot be filled further results in deformation. It is of two types:
Elastic Deformation: It occurs when the deformation completely disappears and regains its original
shape after the release of stress.
Plastic Deformation: It occurs when the deformation does not recover completely even after the
release of stress.

3. Bonding: Different mechanisms of bonding are considered in the compression process, which are
however not experimentally validated. Therefore, they are not useful in estimating the compressional
properties of materials.
Three theories of bonding are:
• i) The mechanical theory,
• ii) The intermolecular theory, and
• iii) The liquid surface film theory.
4. Deformation of the Solid Body: When the applied pressure is increased further, the bonded solid
is confined to a limited density due to plastic and/or elastic deformation of the tablet within the die.

5. Decomposition: The stresses induced by elastic rebound and the associated deformation processes
during decompression and ejection are responsible for the success or failure of producing an intact
tablet. The radial pressure keeps the tablet in the die after the upper punch is withdrawn from the die
cavity. Therefore, every dimensional change throughout decompression occurs in the axial direction.
6. Ejection: There is a continued residual die wall friction during the rising of lower punch and
upward pushing of the tablet. On removing the tablet from the die, the lateral pressure is relieved. As
a result, the tablet undergoes elastic recovery and increases the volume of the tablet portion removed
from die .

Equipment
• After the preparation of granules (in case of wet granulation) or sized slugs (in case of dry
granulation) or mixing of ingredients (in case of direct compression), they are compressed to get
the final product.
• The compression is done either by
1. single punch machine (stamping press) or by
2. multi-station machine (rotary press)

1. Single Station/Single Punch Press

Single Station/Single Punch Press: Process
1. The powder is kept within the hopper connected to a hopper shoe located at the die table.
2. Once the hopper shoe is positioned over the die, the powder is fed into the die by means of gravitational powder
flow.
3. The position of the lower punch controls the quantity of powder filled into the die.
4. The upper punch descends and compresses the powder when the hopper shoe is positioned near the die.
5. During compression, the lower punch remains stationary. Thus, the upper punch applies pressure which is
controlled by the upper punch displacement.
6. After ejection, the hopper shoe pushes away the tablet by moving back to the die for the next tablet. The output of
200 tablets per minute can be produced from a single punch press.
Therefore, the main use of a single punch press is to produce small batches of tablets during formulation development and
for clinical trials.

Components of a Single Station Press
• Hopper: It is connected to the feed shoe and the granules/powder mixtures are poured into it prior
to compression. Manual or mechanical techniques can be employed for filling the hopper for
tableting process.
• Die Cavity: Here the powder granules are compressed into tablets. The die is responsible for
determining the diameter, size, and thickness of the tablet.
• *
• Punches: Tablets of various shapes can be manufactured by compressing the granules using upper
and lower punches.
• Cam Truck: The position and movement of the punches is guided by a cam truck.
• Tablet Adjuster: It decides the tablet weight by adjusting the amount of powder to be compressed.
• Ejection Adjuster: After compression, the tablets are ejected from the die cavity utilising this part.

Advantages of a Single Station Press
• The structure of a single punch is balanced and small.
• It can be easily operated at a high utilization ratio.
• It can also produce odd-shaped products having a diameter of up to 20mm.
• It is suitable for development of tablets and small batch production.
• It reduces weight variations between tablets by utilizing a high amount of pressure.
• It also maintains a low noise level during operation.

Multi-Station/Rotary Press: Process
Multi-station presses are also termed as rotary presses because 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 head portions holding the upper and lower punches are called the upper and lower turrets, respectively, and
the portion holding the dies is the die table .
At the start of a compression cycle, granules stored in a hopper empties into the feed -frame (A) which has several
interconnected compartments.These compartments spread the granulation over a wide area to provide time for the
dies (B) to fill.
The pull -down cam ( C) guides the lower punches to the bottom of their vertical travel, allowing the dies to over
fill. The punches then pass over a weight –control cam (E) which reduces the fill in the dies to the desired amount.
A wipe-off blade (D), at the end of the feed -frame removes the excess granules and directs it around the turret and
back into the front of the feed-frame.

Components of Multi-Station/Rotary Press
• Hopper: The granules or powder mixture containing API and excipients are poured into the hopper
prior to compression or tableting.
• Die Cavity: Here the powder granules are compressed into tablets. The die is responsible for
determining the diameter, size, and thickness of the tablet.
• Feed Paddle: This rotates at a fast speed to force the feed or granules into the dies.
• Punches: These include the upper and lower punches which move within the die bore to compress
granules into tablets.
• Lower Cam Track: This allows accurate adjustment by permitting the overfilling of die bore by
guiding the lower punch during the filling stage.
• Cam Truck: This guides the position and movement of the punches.

Components of Multi-Station/Rotary Press
• Department of Fill/Capacity Control : This ensures that suitable quantity of granules fills the die
prior to compression process by adjusting the lower punch track during the latter part of the fill
stage.
• Recompression Rollers: These provide an initial compression force to the granules for removing
the excess air entrapped in the die.
• Main Compression : This provides the final compression force required for the formation of
tablets.
• Ejection Cam: This is utilized to facilitate the ejection of tablet from the die cavity after
compression.
• Take-off Blade: This is fitted opposite to the feeder housing and deflects the tablet down the
discharge chute.
• Discharge Chute : After being deflected by the take -off blade , the tablet passes through the
discharge chute for collection.

Advantages of a Multi-Station Press
• This operation is cheaper, less labor intensive, and involves high productivity.
• The process is time saving and is capable of meeting high demand of tablet dosage form. For
example, rotary press has an output of 9000-234000 tab/hour.
• A moving feeder is required for managing the powder filled cavity automatically.
• Rotary press involves minimum wastage of valuable formulation in nonspecific tablets .
• Both weight and hardness can be controlled independently by the rotary press

Tablet tooling
• The punches and dies are called tablet tooling that determines the shape, size, and
identification markings of the tablets. The tooling must meet the specific requirements to satisfy
the needs of dosage uniformity, production efficiency, and esthetic appearance.
• Internationally recognized standards for tablet compression tooling are as follow;
1. TSM STANDARD
• TSM is an acronym for the TABLET SPECIFICATION MANUAL widely recognized and
exclusive in the United States. TSM tooling specifications are the sole reference on U.S.
manufacturing standards for tablets and tablet tooling.
• Established by the American Pharmacists Association (APHA). TSM tooling specifications are the
only published standards for the tablet compression industry
2. EU STANDARD
• EU is considered as the European standard and globally applicable. EU, more widely used than
the TSM. EU or Euro norm standard tool configurations are not published or governed by any
organization or association. The EU standard is the most common tooling configuration used
outside the U.S.

Differences between TSM & EU tooling configurations

Tablet
Processing
Problems and its
remedies
An ideal tablet should be free from any visual defect or
functional defect. With the development of technology, the
production process had become more simplified and more
mechanized.
But now the tablet punching machines are all mechanized,
the mechanical feeding of feed from the hopper into the
die, electronic monitoring of the press, but tablet process
problem still persist.
An industrial pharmacist usually encounters number of
problems during manufacturing.
Majority of visual defects are due to inadequate quality or
inadequate moisture in the granules ready for compression
or due to faulty machine setting. Functional defects are due
to faulty formulation.

Tablet Processing Problems and its remedies

1. Capping:
The upper or lower segment of the tablet separates horizontally, either partially or completely from the
main body, and comes off like a cap, during ejection from the tablet press, or during subsequent handling.
Causes: Poorly finished dies, Deep concave punches, Lower punch remains below the face of the die during
ejection, Incorrect adjustment of the sweep-off blade, High turret speed, Due to the air–entrapment in a compact
during compression, and subsequent expansionof tablet on ejection of a tablet from a die.
Remedies: Polish dies properly. Investigate other steels or other materials, Use flat punches, Make the proper
setting of lower punch during ejection, Adjust sweep-off blade correctly to facilitate proper ejection, Reduce the
speed of turret (Increase dwell time).

2. Lamination:
Lamination‘ is the separation of a tablet into two or more distinct horizontal layers.
Reason: Air–entrapment during compression and subsequent release on ejection. The condition is exaggerated
by higher speed of turret.
Causes:
Oily or waxy materials in granules, Too much of hydrophobic lubricant, Magnesium-stearate, Rapid relaxation
of the peripheral regions of a tablet, on ejection from a die, Rapid decompression.
Remedies:
Modify mixing process. Add adsorbent or absorbent, Use a less amount of lubricant or change the type of
lubricant, Use tapered dies, i.e., upper part of the die bore has an outward taper of 3° to 5°, Use pre-compression
step. Reduce turret speed and reduce the final compression pressure.

Tablet Processing
Problems and its
remedies
3. Cracking:
These appear as small, fine cracks on the upper and lower
central surface of tablets, or on the sidewall. The causes and
remedies of cracking are presented in
Causes Remedies
Granules are large Granule size is reduced, and fines
are added
Granules are dry Granules are moistened and proper
amount of
binder is added
Tablets expand Granulation is improved & dry
binders are added
Granulation is too cold Tablets are compressed at room
temperature
Deep concavities cause cracking
while removing tablets
Special take off is used

4. Chipping:
Chipping, or the breakage of small bits of tablet edges, can occur when there are substandard die shapes or
conditions. Wet material, insufficient lubricant, and improper binders that lead to sticking are potential issues in
formulations.
This defect is the presence of scored or rough tablet edges resulting from improperly finished or sized dies
with incorrect clearance or extreme pressure in the tablet press. Formulation-related challenges include
excessive moisture and other granular factors, as well as insufficient lubrication.

5. Picking and Sticking:
This problem occurs due to material adhesion to the punch faces. If material adhesion is localized, some
portions of the tablet surface are found to be missing and this defect is referred to as picking. If the entire tablet
adheres to the punch face, the tablet appears rough and dull, and this defect is referred to as sticking.
• Causesand Remedies of Sticking of Tablets
Causes Remedies
Granules are not dried properly Granules are properly dried, and limits are evaluated by moisture
analysis
Lubrication is not done properly Lubricant is either increased in quantity or changed
Binder is present excessively Binder is either decreased in quantity or changed
Granular material is hygroscopic Granulation is modified and compressed under controlled humidity
Materials are oily or waxy Mixing process is modified by adding an absorbent
Granules are soft or weak Amount of binder and granulation technique is optimised
Causes and Remedies of Sticking Related to Machine (Dies, Punches, and Tablet Press)
Pressure is low Pressure is increased
Compression speed is fast Speed is reduced

6. Binding:

7. Excessive Weight Variation:
This involves separation of granule constituents due to poor granular flow . Weight variation occurs due to
the presence of under dried granules, too large granules , too fine granules , large proportion of fines,
improperly lubricated granules , or granules with variable densities or sizes . A faulty rotary machine with a
suitable granular flow indicates that one or more punches are of different length due to unintentional mixing of
bottom punch sets.
8. Fissured or Pitted Surface:
This problem occurs due to the presence of uniformly sized granules which lack the fines required to fill up
the voids . The remedy for this problem is using granules of a broader size distribution. However, this should
not result in problems like capping or lack of tablet weight uniformity

Tablet Processing
Problems and its
remedies
9. Double impression: Double impression means embossing or
break or score line appears two time.

Tablet Processing
Problems and its
remedies
10. Mottling:
Uneven distribution of colour in tablets is termed mottling which
occurs due to discontinuous granule size distribution . This is
because the finer particles present a slightly different background
against the larger particles present on the surface. This defect is
commonly observed in colored tablets due to migration of dye.
Causes Remedies
Colored drug is used along
with
colourless or white-coloured
excipients
Appropriate colourants are used
Dye migrates to the granulation
surface
while drying
Solvent and the binder system is
changed; drying temperature is reduced;
particles of small size are used
Dye is improperly mixed,
especially
during direct compression
Dye is improperly mixed, especially
during direct compression
Colored binder solution is
improperly
mixed
Dry colour additive is added during
powder blending followed by adding fine
powdered adhesives (acacia and
tragacanth) and mixing well; finally, the
granulating liquid is added

7. Variation of Medicament Content:
Standards are set for the drug content of individual tablets. If the content varies widely and the factors
responsible for this variation can be eliminated, the most common sources of variation are migration of solute,
physical adsorption with separation at some stage of the production,and inefficient mixing.
8. Drug Instability:
Generally, water is present and is also purposely added in various air-dried drugs and tablet excipients . This
water may also be present even after the moist granulation process. To ensure drug stability and to comply with
technical reasons associated with the physical processes of tablet production, it is necessary to control the
moisture content.

Capping
Lamination Chipping
Mottling
Double impression
Cracking
Binding

Content outline
Types of coating Coating materials
Formulation of coating
composition
Method of coating
Equipment employed
and defects in coating

Introduction
• Coated tablets are defined as tablets covered with one or more layers of mixture of various
substances such as natural or synthetic resins, gums, inactive and insoluble fillers, sugar,
plasticizers, polyhydric alcohol, waxes, authorized coloring materials, and sometimes flavoring
agents. Coating may also contain active ingredients.
• Substances used for coating are usually applied as solution or suspension under conditions in
which the vehicle evaporates. In tablet coating, the moving tablet bed is applied with coating
solution along with the simultaneous use of heated air for rapid solvent evaporation.
• Coating of tablets is an essential step involved in manufacturing controlled and delayed release
tablet dosage forms. There are many advantages associated with tablet coating like masking
obnoxious odour, bitter taste, and unpleasant colour of the drug; protecting the drug from gastric
environment; and physically and chemically protecting the drug.

Advantages of coating
1) The tablet coating process prevents sticking of tablets.
2) It follows the fine contours of embossed characters or logos on tablets.
3) It maintains its stability and strength during tablet handling.
4) It provides a smootherfinishing to tablets.
5) It aids in swallowing larger tablets.
6) It also conceals the unpleasant taste of certain drugs.
7) Tablet printing can also be accomplished by coating.

Disadvantages of coating
1) Other coating materials are preferred over sugar coating because it is an expensive technique and requires
prolonged time.
2) The tablet coating process is tiresome and requires prolonged time for completion.
3) It cannot be performed without the guidance of highly skilled technicians.

Types of coating
1. Sugar Coated Tablets(SCT):
These tablets are usually used for children to mask the unpleasant smell
and taste of some drugs. In the process of sugar coating, sucrose-based
coating formulations are applied successively onto the tablet cores in
coating equipment. During the process , water evaporates from the syrup
and a thick sugar layer is left around each tablet.
2. Film Coated Tablets(FCT):
This type of coating is used to make the tablets attractive with various
colors. Film coating protects the tablet to remain stable and masks the
unpleasant taste and uneven colour of some drugs (such as the herb al
extracts). In the process of film coating, a thin uniform film of a
polymer formulation is deposited on the tablet by spraying method.

Types of coating
3. Enteric Coated Tablets (ECT): These tablets contain
drugs that undergo best absorption in intestines (and not in
gastric). Thus, they are coated such that they withstand the
pH of stomach acid and slowly release the drug only in the
small intestine.
4. Compression Coating: This type of coating is less
popular; however, it gained increased interest for creating
modified -release products. In the process of
compression coating, granular materials are compacted
around a pre -formed tablet core using specially designed
tableting equipment.
5. Gelatin Coated Tablets: These are capsule -shaped
compressed tablets coated with gelatin layer.

Coating Materials and Formulation of Coating Composition
The formulation of coating solution includes:
1) Film forming materials (enteric or non-enteric),
2) Solvents,
3) Plasticisers,
4) Colourants,
5) Opaquants,and
6) Miscellaneous coating solution components.
Materials Types Examples
Film formers Enteric, non-enteric HPMC, ethyl cellulose, sodium CMC, polyethylene glycol,
cellulose acetate phthalate, and HPMCP
Solvent - IPAand methylene chloride
Plasticisers Internal and external
Plasticising
Castor oil, propylene glycol, glycerine, surfactants, and
polysorbates
Colourants Inorganic and natural
colourants.
FD and C colors, D and C colors, iron oxides, caramel, and
turmeric
Opacifiers - Titanium dioxide, talc, and aluminium silicate.

1. Sugar coating
Tablet coating processes are of the following two types:
1) Sugar coating, and
2) Film coating.
1. Sugar Coating
Compressed tablets may be coated with colored or uncolored sugar layer. The coating is water-
soluble and quickly dissolves after swallowing. Sugar coat protects the enclosed drug from the
environment and provides a barrier to objectionable taste or order. The sugar coat also enhances the
appearance of compressed tablet and permits imprinting manufacturer’s information.
Sugar coating provides a combination of insulation, taste masking, tablet core smoothening, coloring,
and modifying drug release.
The disadvantages of sugar coating are the time and expertise required in the coating process, and
thus, increases size, weight, and shipping costs.

1. Sugar coating
Sugar coating process involves five separate operations:
1. Sealing/Water Proofing: It provides a moisture barrier and hardens the tablet surface.
2. Sub-Coating: It causes a rapid build-up to round off the tablet edges.
3. Grossing/Smoothing: It smoothens the sub-coated surface and increases the tablet size to
predetermined dimension.
4. Coloring: It provides the desired colour to tablets.
5. Polishing:It produces the characteristic gloss.
6. Printing: It utilizes edible inks for tablet characterization.

2. Film Coating
Film coating involves deposition of a thin film of polymer surrounding the tablet core.
Conventional pan equipment may be used , but nowadays more sophisticated equipment are
employed to have a high degree of automation and coating time. The polymer is solubilized into
solvent, other additives (like plasticizers and pigments) are added, and the resulting solution is
sprayed onto a rotated tablet bed. The drying conditions cause removal of the solvent, giving thin
deposition of coating material around each tablet core.
Usually spray process is employed in the preparation of film coated tablets.
Accela Cota is the prototype of perforated cylindrical drum providing high drying air capacity.
Fluidized bed equipment has made considerable impact where tablets are moving in a stream of air
passing through the perforated bottom of a cylindrical column. With a smaller cylindrical insert, the
stream of cores is rising in the center of the device together with a spray mist applied in the middle of
the bottom. For fluidized bed coating, very hard tablets must be used.

2. Film Coating
Characteristics of Film Coating:
1. It results in minimum weight gain (2-3%) of tablets.
2. The film coat affects tablet disintegration to a lesser extent.
3. It is a single stage process, thus, quick.
4. It is easy to automate (less reliance on skilled operator/easier to meet GMP requirements of
SOPs, validation, etc.).
5. It maintains the original shape of core and allows embossing.
6. It requires expensive equipment, and the plant requires a large space.
7. It demands high installation and energy costs.

2. Film Coating
The ideal requirements for film coating materials are:
1. They should be soluble in the solvent selected for coating preparation.
2. They should dissolve freely in water, possess low water solubility, or show pH - dependent
solubility depending on their use.
3. They should be capable of creating products having graceful appearance.
4. They should be stable against heat, light, moisture, air, and the substrate being coate d.
5. They should not take over any colour, taste, or odourduring the process.
6. They should be compatible with other excipients in the coating solution.
7. They should be non-toxic and possess no pharmacological activity.
8. They should be resistant against cracking.
9. They should not provide bridging or filling appearance to de -bossed tablets.
10.They should be compatible with printing methods involved in the process.

3. Equipment Employed in Coating
Most coating processes use one of the three
general types of equipment:
1) Standard coating pan
i) Pellegrini pan system,
ii) Immersion sword system, and
iii) Immersion tube system.
2) Perforated coating pan
i) Accela Cota system,
ii) Hi-coater system,
iii) Glatt coater system, and
iv) Dria coated system.
3) Fluidized bed (air suspension) coater
The general trend has been toward energy-
efficient, automated systems to shorten the
total coating time and reduce operator
participation in the coating process.

Quality Control Tests for
Tablets

Quality Control Tests for Tablets
General appearance: Size, shape, and thickness: This is important to facilitate packaging and to
decide which tablet compressing machine to use.
Organoleptic properties: which include color, odor and taste of the tablets.
Weight uniformity and Content uniformity: The tablet should contain the correct dose of the drug.
Dissolution test: Drug should be released from tablet in a controlled and reproducible way.
Weight variation, thickness & diameter: The appearance of tablet should be elegant & its weight,
size & appearance should be consistent.
Hardness & friability: The tablet should show sufficient mechanical strength to withstand fracture
& erosion during manufacture & handling.
These factors must be controlled during production and verified after production, hence called In-
process control

Official Standards as per I.P.
A) Uncoated tablet:
• Uniformity of container content and
Content of active ingredient
• Uniformity of weight and Uniformity of
content
• Disintegration test
B) Enteric coated tablet:
C) Dispersible tablet:
• Uniformity of dispersion
D) Soluble tablet:
E) Effervescent tablet:
• Disintegration/Dissolution/Dispersion test

1. Weight Variation
This test is based on the fact that, if the weight variation is within the limits, then it can be said that the amount
of medicament will uniform considerably. Conversely, if the weight variation is not in limits, then it can be
concludedthat the active medicament will ununiformconsiderably.
Sources of weightvariation
Weight variation is solely dependent on the poor flow property of granules and filling of die cavity. Poor flow
properties arise from:
(a) improperlubrication, (b) size of granules and (c) adjustment of lower punch.
Weight variation test
The U.S.P. weight variation test is run by weighing 20 tablets individually, calculating the average weight, and
comparing the individual tablet weights to the average. The tablets meet the USP test if “not more than 2 tablets
are outside the percentage limit and if no tablet differs by more than 2 times the percentage limit.”

2. Content Uniformity test
Weight variation test is applicable when the amount of medicament in the tablet is high.
In potent drug the medicament is less in amount in comparison to the other excipients. The weight variation may
meet the pharmacopeial limitation, but this will not ensure the correct variation of potency. hence, in this case
the weight variation test is followed by content uniformity test.
Procedure:
1. In this test 30 tablets are randomly selected for sample, and at least 10 of them are assayed individually
accordingto the official assay method.
2. 9 of the 10 tablets must have potency within 15 % of the labelled drug content.
3. Only 1 tablet may be within 25%.
4. If this condition is not met, then the tablets remaining from the 30 must be assayed individually and none
may fall outside 15% of the labeled content.

3. Disintegration Test of Tablets
The time a tablet takes to disintegrate is the disintegration time.
To test the disintegration time one tablet is placed in each tube, and the basket rack assembly is positioned in a
1-litre beaker of water, simulated gastric fluid or simulated intestinal fluid, at 370C 20C, such that the tablet
remains 2.5 cm from the bottom of the beaker.
A standard motormoves the basket up and down through a distance of 5 to 6 cm at a frequency of 28 to 32 cpm
(cycles per minute).

4. Dissolution study
Disintegration test simply identifies the time required for the tablet to break up under the condition of the test,
but it does not ensure the drug release in the bulk of the fluid.
Rate of dissolution is directly related to the efficacy of the drug. Rate of dissolution is a good index for
comparingthe bioavailability of two tablet products of the same drug.
Apparatus-I (Basket)
In general, a single tablet is placed in a small wire mesh basket and immersed in the dissolution medium (as
specified in the monograph) contained in a 1000 ml flask at 37°±0.5°C. Generally, it is rotated at 50 rpm unless
otherwise specified.
Apparatus-2 (Paddle)
The same equipment is used. Instead of basket a paddle is introduced as the stirring element. The tablet is
allowed to sink at the bottom of the flask before stirring.
Limit: A value of t₉₀ (i.e., 90% drug release) within 30 minutes is often considered satisfactory and is an
excellent goal since a common dissolution tolerance in the USP/NF is not less than 75% dissolved in 45
minutes.

5. Hardness of the tablet
The resistance of the tablet to chipping, abrasion or breakage under conditions of storage, transportation and
handling before usage depends on its hardness.
Method:
A tablet is taken between the 2nd and 3rd finger and pressing it with the thumb as fulcrum. If the tablet breaks
with a “sharp snap”, yet it does not break when it falls on the floor – is said to possess properhardness.
Instrumentsused:
a) Monsanto Hardness Tester
b) Strong Cobb Hardness Tester -Manual mode.
c) Pfizer Hardness Tester.
d) Erweka Hardness tester. – Automatic.
e) Schleuniger Apparatus.– Operates without manual involvement.
Hardness of a tablet:
The hardnessat which the tablet crushes is the hardness of the tablet.
• Unit of hardness: Kg/sq.in. or lb/ sq.in
• Limit: Generally maximum 5 kg/sq.in. hardnessis required.

6. Friability
Tablet hardness is not an absolute indicator of strength since some formulations, when compressed into very
hard tablets may produce chipping, capping and lamination problems. Therefore, another measure of tablet
strength i.e., friability is often measured, i.e., the friability.
Instrument:Roche Friabilator
Objective of friability test:
This apparatus is designed to evaluate the ability of the tablet to withstand abrasion, in handling, packaging and
shipping operation.
Method: 20 tablets, previously weighed are taken in the plastic chamber of the laboratory friability tester. In the
plastic chamber the tablets are subjected to abrasion and shock by rotating the plastic chamber at 25 rpm for 4
mins (i.e., total 100 revolutions). The tablets are dedusted and reweighed.
Limit: For conventional compressed tablet, the weight loss should be within 0.5 to 1.0 %.

Tablet Compression Process

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