Tablet coating concepts

1. TABLET COATING
1
NAGAM SANTHI PRIYA
DEPARTMENT OF PHARMACEUTICS

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CONTENTS
Objectives of tablet coating
Tablet properties
Coating equipments
Types of coating
Coating defects
Coating parameters
References

3. Mask the unpleasant taste and odour ex; Quinine drugs, vitamins
Provide physical and chemical protection
Improve patient acceptability
Control the release of the drug from tablet ex; sustained release.
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OBJECTIVES OF TABLET COATING

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Improve the chemical stability of the drug by protecting it
against light, air , oxidation and moisture.
Protect the drug from gastric environments of stomach
Mechanical strength to the tablet core.
Maintains the shape of the tablet
Identification of a product by the manufacture
Pharmacist and by the patient

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Tablet Properties :
Coating tablet must posses the proper physical
characteristics (size ,shape)
They should easily cascade in the coating pan .
They should be resistant to abrasion and chipping .
Tablets must be in contact motion during early drying phase .
COMPONENTS INVOLVED IN TABLET COATING

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sugar coating with high solid content, fills many
imperfections.
The film coating adheres to all exposed surfaces
surface imperfections are not eliminated

7. COATING PANS FLUIDIZEDBE
D COATER
SPRAY
EQUIPMENT
STANDARD
COATING PANS
PERFORATED
COATING PANS
AIRLESS
SPRAY
AIR
SPRAY
COATING EQUIPMENTS
E.g.; immersion tube system
immersion sword system
E.g.; accela coater pan
hi-coater pan
dria coater pan
glatt coater pan

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Stainless steel – 40 inches in diameter,
with variable speed control, with 2 to 3 atomizing nozzles.
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COATING PAN

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Standard Coating pan

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It is large circular pan of about 8 to 60 inch diameter.
It mounted angularly at an angle 40˚
The pan is rotated on its horizontal axis by means of motor.
Tablets are coated by spraying the coating solution over the rolling
Bed of tablets using spray equipment.
Coated tablets are dried by passing hot air into pan through hot
Air inlet.
Exhausted air is removed through vents or ducts.

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Immersion Tube System

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Tube is immersed in to tablet bed
Hot air is passed in to tablet bed
Air flows In upward direction
Exhaust air removed by exhaust vent or duct.
Coating material and drying air is applied
Simultaneously

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Immersion sword system
Drying air is introduced into the pan
through a sword like device having perforations
It is immersed into the tablet bed
Air flows in upward direction
Exhaust air removed by exhaust vent or duct.

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Accela-Cota System

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Drying air is passed in to perforated cylindrical pan
Air is drawn into tablet bed
Application of coating solution on tablet bed by spraying
Exhausted air is passed through a duct located
At the bottom of the pan

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Hi-Coater System

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Function of Hi- Coater is same as accela coater.
Drying air is passed in to perforated cylindrical pan
through a inlet
Coating solution is applied by spraying nozzles
Exhausted air is passed through perforated plates present
At the bottom of the pan

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Accela coater Hi coater

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Dria-Coater System

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Inside periphery of driacoater is attached with hollow
Perforated ribs .
It provides multidirectional air flow
a) Direct air flow: Air is passed through the ribs located top of
the pan and exhausted through the ribs located below the
tablet bed.
b) Reverse flow : Air is passed through the ribs located below
the tablet bed and exhausted through the outlet at the back
Of the pan.

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Glatt coater
It is latest perforated pan coater
Drying air passed through
tablet bed from the inner side of
the drum
Exhaust through the out let .
Optional split chambered plenum is used to pass the drying air in reverse
Manner through the perforations, for the partial fluidization of tablet bed.

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Fluidized bed coater (Air Suspension Coater)

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Fluidized bed coaters are highly efficient drying
systems.
Fluidization of the tablet mass is achieved in a
Coating chamber.
More air enters into the center of the chamber Causing tablets to
rise in the center.
Then they fall down towards the chamber wall and re enters
into the air stream .
Spray solutions are continuously applied from a spray nozzle
Located at the bottom of the chamber.

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Spray Application systems
High – pressure air less system
Low – pressure air atomized system
Both these systems vary in atomization of liquid.
Airless system: liquid is pumped at a high pressure (250-3000psig)
through a small orifice (0.009 to 0.020 inch)
Degree of atomization depends upon
- Fluid pressure
- Orifice size
- Viscosity of liquid

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Air atomized – Liquid is pumped through large orifice
(0.020 to 0.060inch) at low pressure (5-50 psig).
Air contacts the liquid stream at the tip of the atomizer to obtain
fine spray
degree of atomization depends upon
- Fluid pressure
- Fluid cap orifice
- Viscosity of liquid
- Air pressure
- Air cap design
selection of spray system depends upon composition of the
coating solution

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Types of coating
Conventional
coating process Contemporary
coating process
Specialized
coating process
Sugar coating Film coating
Non –enteric
coating
Enteric
coating
Compression coating
Electrostatic coating
Vacuum coating

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Sugar coating is an effective process for the application of thick
coating layers, primarily for masking taste.
Sugar coating

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Advantages :
Inexpensive and requires simple equipment.
Tablets produced are of High quality ,smooth &
elegant appearance.
Dis advantages:
Time consuming and lengthy process ( it requires
several hours to days to complete)
It requires highly skilled manpower.

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polishing
Finishing
syruping
Basic steps involved in sugar coating :
sealing
Sub coating

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SEAL COATING
Why seal coating is done ?
Need of the seal coating ?
To prevent the moisture penetration into the tablet core.
It is needed in the pan-ladling process in which localized over
wetting of a portion of the tablet bed .
Examples:
Shellac (natural product derived from scale insects, laccifer lacca)
Zein : is an alcohol-soluble protein derivative from corn used
as an effective sealant. Lengthening
dissolution time not reported

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SUBCOATING
Why sub-coating is necessary?
It is applied to round the edges and build up the tablet size &
weight ( 50 to 100 %)
Steps involved in sub-coating:
Binder solution and dusting of subcoating powders are
alternately applied on tablets and dried.
Same procedure is done until the desired thickness is achieved
In spray process the subcoating suspension contains both
binder and insoluble powders.
Subcoating solutions : Gelatin, Acacia in syrup & water
Subcoating powders : Kaolin, Dextrin sugars etc

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SMOOTHING(SYRUPING OR COLOURING):
What is the need of syruping ?
It covers the imperfections on the tablet surface caused by the
subcoating and imparts the desired colour to the tablet.
First syrup coat contains some suspended powders are called
grossing syrups, colourants can be added in this step.
In the second step, syrup solution containing the
dye is applied until the final size and colour is achieved.
In the final step, a few clear coats of syrup may be applied.

33. POLISHING:
Tablets can be polished in clean standard
coating pans or Canvas –lined polishing pans,
Polishing can be done by applying powdered
wax (bees wax, carnauba) or warm solutions
of these waxes in naptha or other suitable
Volatile solvents.

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FORMULATION OF SUGAR COATING SOLUTION :
seal coating Sub coating Syrup coating polishing
Zein / shellac Gelatin Colorant Carnauba
wax(yellow)
Oleic acid Acacia Sub coating
powder
Bees wax(white)
Propylene glycol Sugar cane powder Calcium carbonate Paraffin wax
PEG Corn syrup Cane sugar powder Naphtha
Methylene chloride syrup Corn starch
alcohol Distilled water syrup
Distilled water

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Ethanol , methanol, isopropanol , chloroform, acetone
Methylene chloride , methylene ethyl ketone,
Solvents used for sugar coating :
Enteric coating polymers :
Cellulose acetate phthalate , acrylate polymers, hydroxypropyl
methyl cellulose phthalate, poly vinyl acetate phthalate,

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Sugar coated pills

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FILM COATING
latex particles dispersed
in aqueous phase
formation of thin film with
evaporation of water
through film
Formation of continuous
film
Mechanism of Film formation
Application and deposition of thin film of polymer solution
Around the tablet surface

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COMPOSITION OF FILM
COATING
solvent
Film
formers plasticizer
Opaquant
extenders
colorants

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Ideal characters of film coating material:
Should be soluble in aqueous fluids
Solubility required for the intended use e.g. freely water soluble,
Slow water soluble , pH- dependent soluble(enteric coating)
Capacity to produce an elegant look
Must be stable in the presence of heat, light,moisture,air
Should not have color, taste, and odour
Non toxic and ease to application
Should be resistance to cracking

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FILM FORMERS (non – enteric materials ):
Hydroxy propyl methyl cellulose(HPMC),USP
Soluble in organic , aqueous and gastro intestinal fluids.
It has flexibility and chip resistance ,
Polymer has tendency to bridge or fill the tablet surfaces
HPMC+Plasticizers or other polymer = eliminate bridging or
filling problem
Methyl hydroxy ethyl cellulose :
It is soluble in fewer organic solvents.

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Ethyl cellulose , NF
It is insoluble in water and gastrointestinal fluids.
Ethyl cellulose + HPMC = used in tablet coating
Ethyl cellulose + water soluble additives are mostly used
In preparing sustained released coating for fine particles and tablets.
Hydroxy propyl cellulose:
It is soluble in water , gastro intestinal fluid and organic solvents at
below 40˚c and insoluble at above 45˚c.
Hydroxy propyl cellulose + other polymers = improve film character

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Povidone ,USP
Povidone k30 is mostly used as binder and also as tablet coating
polymer
It forms a clear ,glossy and hard film.
Sodium carboxy methyl cellulose,USP
It is easily dispersed in water and form colloidal solutions
Insoluble in organic solvents
Not used for coating solution.

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Poly ethylene glycols
Poly ethylene glycols are used as plasticizers in coating
solution
Poly ethylene glycols combine with cellulose acetate
phthalate forms gastro intestinal soluble films

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ENTERIC COATING:
These are intact with stomach but will dissolve and
release the contents of dosage form once it reaches the
small intestine.
Important reasons for enteric coating:
Protects the acid labile drugs from the gastric fluids e.g. enzymes&
antibiotics.
Prevents gastric distress or nausea due to irritation from a drug e.g.
sodium salicylate
Intended for local action in the intestine e.g. diclofenac sodium

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ENTERIC COATING MATERIALS:
Cellulose acetate phthalate (CAP)
Widely used in the industry.
These films are brittle and formulated with hydrophobic
film forming materials to achieve better enteric coating.
Acrylate polymers:
Two trade forms of resins eudragit L and eudragit S, produce
gastric acid resistance films
Soluble in intestinal fluid at pH 6 to 7.

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Hydroxy propyl methyl cellulose phthalate(HPMCP)
These polymers are dissolved at pH at 5 to 5.5.
Poly vinyl acetate phthalate (PVAP)
These polymers are similar to hydroxy propyl cellulose
phthalate.
Ideal enteric polymer should dissolve or become permeable
near and above pH 5.0

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SOLVENTS:
Primary function of a solvent system is to dissolve or disperse the
polymers and other additives to substrate surface.
Should dissolve or disperse the polymer system.
Should easily disperse other coating solution components.
Should be colorless, tasteless, odourless, inexpensive, nontoxic,inert.
Should be easily dried.
Should be eco -friendly.
Examples: water, ethanol, methanol, isopropanol, chloroform,
acetone, methylethyl ketone and methylene chloride.
Important Characters:

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PLASTICIZERS:
These are added to film coating to modify the physical
Properties of the polymer.
Ability to decrease the film brittleness, polymer-
polymer interactions
It gives the stability to film and final coated product
Concentration of plasticizer is expressed as the
amount of Polymer being plasticized.
Recommended level of plasticizer – 1 to 50% by
weight of film Former.

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Examples of plasticizers:
Castor oil, propylene glycol of 200 and 400 series and surfactants e.g.
Tweens, Spans and organic acid esters.
Water- soluble plasticizer : PEG, propylene glycol.
Organic- soluble plasticizer : castor-oil and Spans.

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COLOURANTS:
Used to provide distinctive color and elegance to a
dosage form
Most of colorants are synthetic dyes (soluble) & lakes
( insoluble)Approved by FD&C, D&C.
LAKES : derived from dyes by precipitating with
Carriers e.g. alumina, talc
Lakes contains 10 to 30 % of pure dye content
For very light shade, concentration : less than 0.01 %.
For dark shade, concentration : more than 2.0 %
Examples
Inorganic materials : iron oxides
Natural coloring materials :Anthocyanins, caramel,
carotenoids, chlorophyll, indigo, flavones, turmeric
and carminic acid.

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OPAQUANT EXTENDERS:
These are very fine inorganic powders used in the coating solution
formulation to provide more pastel colors and increase film coverage.
Examples: Titanium di oxide, Silicates (talc, aluminum silicate);
Carbonates (magnesium carbonate); Sulfates (calcium sulfate); Oxides
(Mg oxides)

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Film coated pills

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FILM DEFECTS
Sticking and picking
Roughness
Orange –peel effects
Bridging and filling
Blistering
Hazing/Dull film
Colour variation
Cracking

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STICKING AND PICKING:
Over wetting and excessive film thickness causes tablets to
Stick each other or to the coating pan.
On drying a piece of film remain Adhere to pan or tablet
gives “picked” appearance of tablet surface,
resulting a small portion of tablet core is exposed
Remedies
Reduce the liquid application rate.
Increase in drying air temperature and air volume.

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ROUGHNESS
A rough or gritty surface observed when the coating is applied
by spray. Some of the droplets may dry too rapidly before
reaching the tablet bed and deposits on tablet surface.
Deposition of spray particles instead
of fine particles of coating solution
Surface roughness also increases with pigment
concentration and polymer concentration in the coating
solution.
Remedies
• Moving the nozzle closer to the tablet bed.
• Reducing the degree of atomization can decrease the
roughness due to spray drying.

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Inadequate spreading of coating solution before
drying causes a bumpy or Orange –peel effects On
the coating
Causes : rapid rate of drying , high
solution viscosity.
ORANGE PEEL EFFECT
Remedies
• Thinning of coating solution with additional solvents may
correct this problem.
• Adjust the speed of coating pan

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BRIDGING
During drying the film may shrink and pull away from
the sharp corners and bisects, which resulting in
“Bridging” of surface dispersion
Remedies
Increase in plasticizer contents
Changing plasticizer
Application of too much solution, resulting
formation of thick film, that fills and narrows the
monogram or bisect.
FILLING:
Remedies
-Judicious monitoring of the fluid application rate.

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BLISTERING :
Local detachment of film from the substrate forming blistering
Remedies
Maintains the milder drying conditions.
Reason :entrapment of the gases in or underneath of film due to
Overheating during spraying .

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HAZING & DULL FILM
HAZING (bloom): It occurs when too high processing
temperature is used for a particular formulation.
DULLING: it is observed when cellulosic polymers are
applied at high processing temperature.
Also occur if the coated tablets are exposed to high
humidity conditions results partial solvation of the film.

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it is caused by Improper mixing, uneven spray pattern and
insufficient coating may results in color variation.
The migration of soluble dyes, plasticizer and other additives gives
the coating a mottled or spotted appearance.
Remedies
Use of lake dyes eliminates dye migration.
Reformulation with different plasticizer and additives is the best way
to solve film instability.
COLOR VARIATION

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Cracking occurs when internal stress in the film
exceed the tensile strength of the film.
The tensile strength of the film can be increased by
using higher molecular weight polymers or polymer
blends.
CRACKING
Remedies
• Adjusting the plasticizer type and concentration can minimize
internal stress.
• Adjusting the pigment types and concentration can minimize
internal stress

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SPECIALIZED COATINGS :
Electrostatic coating : it is efficient method for application of
coating solution to conductive substrates.
A strong electrostatic charge is applied to the substrate,
Coating material containing opposite charged ions were sprayed
on the charged substrate.
Complete and uniform coating of corners is achieved .
Vacuum film coating :
It normally done in specially designed sealed baffled pan
the pan is surrounded by a hot water jacket to dry the coated tablets
air is displaced inside with nitrogen to create vacuum environment
Coating solution is applied by airless spray system.
Vapors caused by pan can be removed by vacuum system.

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Compression coating :
It requires specialized coating equipment
It characterized by two component system (tablet with in a
tablet) or three component system (tablet with in a tablet
with in tablet)
Reasons
If substrates are physically or chemically incompatible with
each other
If Substrate is sensitive to organic solvents or water
Provide prolonged action , repeat action products.

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COATING PARAMETERS :
Rate of coating composition application = rate of evaporation of
volatile solvents.
Deviation from this equilibrium results in serious coating problem
Mathematical modeling for aqueous automated coating process
Inlet A(T1, H1) +C1 (S) +pSA1 A (T2,H2)+ C2+Psa2 exhaust
AIR CAPACITY: quantity of water or solvent removed During
coating process, it depends upon
1) quantity of air flow through tablet bed
2) Temperature of air
3) Water content of inlet air

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COATING COMPOSITION :
Inlet air provides heat to evaporate the water ,the exhaust air
Becomes cooler and contains water.
Tablet surfaces are permeable to applied coating solution which
Cause coating difficulties, so rapid removal of solvent is done by
Increase in temperature .
TABLET SURFACE AREA :
Size and presence of debossed feature affects the coating solution
The size of the atomized coating droplets must be smaller .

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EQUIPMENT EFFICIENCY:
Equipment efficiency =
Net increase in coated tablet weight
Total weight of non volatile coating
applied to the tablets
FACILITY & ANCILLARY EQUIPMENT:
Facility require should meet to requirements of cGMP.
Adequate space is required for equipment , solution preparation
and in- process storage.
Safety requirements depending on nature of solvent,
electrical explosion proofing, specialized ventilation.
Exhaust air treatment to recover solvent or to prevent entry to
atmosphere.

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CONCLUSION :
By the usage of tablet coating process we may conclude
that the following advantages :
Mask the unpleasant taste & odour of the drug
Provide protection to physical & chemical properties
of drugs from enzymes, pH,
Better patient acceptance
Bio availability of drug can be can be controlled

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REFERENCES:
LEON LACHMAN HERBERT A.LIEBERMAN ‘S Theory
and practice of industrial pharmacy , special Indian edition 2009,
Pg no; 346 to 372.
HERBERT A.LIBERMAN ,LEON LACHMAN AND
JOSEPH B SCHWARTZ’S Pharmaceutical dosage forms tablet
Volume 3 , 2nd edition revised and expanded , pg no 78 to 158.
M.E. AULTON’S Pharmaceutics, the science of dosage form
Design, 2nd edition ,pg no 441 to 448.