Tablet-coating.pdf

Tablet coating
Tablet coating is the process of application of an
essentially dry outer layer of coating material
onto the surface of a dosage form (tablet) in-
order to confer specific benefits that includes
from product identification to modify drug
release from the dosage forms.

Objectives of coating-Tablet coating
• Protecting the drug substance (API) from the environment
particularly light and moisture and thus improving the
product stability. E.g Ranitidine- highly moisture sensitive
drug is film coated.
• To protect drug from the gastric environment of the
stomach with an acid-resistant enteric coating
• Masking the taste of drug substance that may be bitter or
otherwise unpleasant.
• Masking of any batch differences in the appearance of raw
material, hence making the product in every batch look
consistent.
• To control the release of the drug from tablet ie; control
release.

Objectives of coating-Tablet coating
• Improving easy swallowing of large dosage forms, especially tablets than
uncoated tablets.
• To improve the Pharmaceutical elegance by use of special colors and
contrasting printing.
• Facilitate the rapid identification of product by the manufacturer,
dispensing pharmacist and the patient.
• Enabling the coated product to be more easily handled on high-speed
automatic filling and packing equipment.
• Minimise dust formation and contamination with respect to tablets.
• Coating improves the product flow, increases the mechanical strength of
the product and reduces the risk of cross contamination by minimizing
dusting problems.

Components of tablet coating
There are three primary components
involved in tablet coating:
1. Tablet properties.
2. Coating process.
– Coating equipment
– Parameters of coating process
– Facility and ancillary equipment
– Automation in coating process.
3. Coating composition

1.Tablet Properties
Tablet should have proper physical properties-
• Strength
Tablets must be resistant to abrasion and chipping
(i.e.; to tolerate intense attrition of tablet and tablet,
tablet and wall of equipment during tablet coating
process; the tablets roll in a coating pan or cascade in
the air stream of an air suspension coater as coating
composition is applied ).
• Surface property
Tablets for film coating should have smooth surfaces.
Tablets which are brittle, which soften in presence of
heat or affected by coating composition become
rough during early phase of coating process and are
not acceptable for film coating.
However, for sugar coatings with their high solids
content, dry more slowly and can fill many of the
minor tablets surface imperfections.

1.Tablet Properties
• Shape
– The ideal shape of the tablet for proper
coating is ‘sphere’ that allows tablets to
roll freely in the coating pan, with
minimal tablet to table contact.
– In case of square flat shaped tablet,
coating materials get collected
between the surfaces and glue them
together.
– Therefore, coated tablet should have
rounded surfaces; the more convex the
surface is, the fewer difficulties with
tablets agglomeration.
– Use of deep concave punch or dual
radius punches can aid.

1.Tablet Properties
• Nature of surface
Coating on the surface is successful when
the coating composition wet the surface.
If the tablet is hydrophobic, it is difficult
to coat with aqueous based coatings that
do not wet the surface.
• Addition of appropriate
surfactant in the coating
composition would reduce the
surface tension of the coating
composition and improve coating
adhesion.

2.Coating process-Equipment
• Equipment design is the major factor that
governs the coating process.
• Coating systems are based on three designs:
1. Conventional pan system
2. Perforated pan system
3. Fluidized bed (air suspension) system

2.Coating process -equipment
1. Conventional/standard coating
pan:
– Consists of circular metal pan mounted
some what angularly on a stand.
– The diameter of pan is 8-60 inches and is
rotated in its horizontal axis by a motor.
– Heated air is directed into the pan and
onto the tablet bed surfaces and is
exhausted by means of duct.
– Coating solutions are applied on to the
bed by means of atomizing system that
produces a faster, more even distribution
of the solution or suspension.
– Drying efficiency has been improved by
various designs such as pellegrini pan,
immersion sword and the immersion
tube system.

Fig. Glatt Immersion sword Fig. Immersion tube system

2. Perforated pan system:
– Consists of a perforated or partially perforated drum or pan
that is rotated on its horizontal axis in an enclosed housing.
– Examples are: Accela-Cota, Hicoater, Driacoater and Glatt
coater.
– Accela-Cota, Hicoater:
Drying air is directed in pan and is passed through tablet bed and
exhausted through perforation in the pan.
– Driacoater and Glatt coater:
The drying air is introduce through hollow perforated ribs located at
the inside periphery of the drum.
As the coating pan rotates, the ribs dip into the tablet bed and
drying air is passes up through and dries the tablet bed and
exhausted from back of pan.

Fig. accela cota system fig. hi-coater system
Fig. Driacoater pan

3. Fluidized bed
(Air suspension) system:
– Highly efficient drying system.
– The tablets being coated are
suspended in an upward stream of
air, maximizing the surface
available for coating.
– The coating is applied by atomizer
and which is then dried by fluidized
air.
– There are three methods by which
the coating can be applied-
• A. top spray
• B. bottom spray
• C. Tangential spray

Distribution of coating-spray
application systems
• Two types:
1. High pressure airless system
• In the airless atomization process, high pressure forces fluid through a small nozzle.
• The fluid emerges as a solid stream or sheet at a high speed.
• The friction between the fluid and the air disrupts the stream, breaking it into
fragments initially and ultimately into droplets.
– Liquid is pumped at high pressure (250-3000 pounds per square inch gauze-psig) through a small orifice (0.009-0.020 inch
in diameter) in the fluid nozzle resulting in finely divided spray.
– The degree of atomization is controlled by
• Fluid pressure
• Orifice size
• Viscosity of fluid
• It is suitable for large scale production with organic based coating solution-as it has high delivery rate.

Distribution of coating-spray
application systems
2. Low pressure air-atomized system:
– Liquid is pumped at low pressure (5-50 psig) through
larger orifice (0.020-0.060 inch in diameter.)
– It is used in small scale and in aqueous coating system

2.Coating process:
Parameters of coating process
• During the coating process, tablets move through a coating
application zone where the tablets receive coating to non-
application zone (drying zone) –where the coating
composition may be transferred from coated tablet to
adjacent tablet or even to coating pan walls.
• The coating application and heated air flow can be continuous
or intermediate depending on coating composition and drying
conditions.
• During coating, the coating operation is maintained at
equilibrium, where the rate of application of the coating
composition equals the rate of evaporation of volatile
solvents.
• Deviation from this equilibrium results in serious coating
problems.

2.Coating process
• Mathematical model developed for the aqueous
coating :
– Inlet A (T1,H1)+C1(S)+pSA1 E A (T2,H2)+C2+pSA2 (Exhaust)
where A (T,H) is the air capacity, C(s)-Coating composition, pSA-tablet surface area, and E-equipment
efficiency.
1. A (T,H)-air capacity-it is quantity of solvent or water
than can be removed during coating process-that
depends on the quantity of air flowing through the
bed, temperature of the air (T) and the quantity of air
that inlet air contains (H).
• During the coating operation, water is evaporated from
the applied aqueous coating solution, and the air
temperature falls.

2.Coating process
2. Coating composition C(S):
– It contains coating polymers and carrier (solvent).
– The solvent is removed during coating process by the inlet air
that provides heat and evaporates the solvent.
– Due to which the exhaust air becomes cooler and contains more
water.
– Intermittent coating application may be used- if the coating
composition is more viscous, aqueous –use movement of the
tablets outside the application zone to produce partial
distribution of coating and longer drying period.
– Constant Coating application: If the coating composition is thin,
rapidly dry.

2.Coating process
3. Tablet surface area,(pSA):
– Total surface area per unit weight decreases significantly
from a smaller tablet to larger tablets.
– Smaller tablet having larger surface area required more
coating composition to achieve same thickness as in
larger tablets.
– Example: film coating a 20kg pan load of tablets (0.281
inch round convex tablet, thickness-0.114 inch) requires
40% more coating than when the same coating thickness
is applied to 0.438 inch round convex tablet of 0.202 inch
thickness.

2.Coating process
4. Equipment efficiency (E):
– Coating efficiency- Net increase in coated tablet weight
total non-volatile coating weight applied
– Ideally 90-95% of the applied film coating should be on the tablet
surface.
– Quantity less than this suggests improvement in coating operation.
– For sugar coating: 60% only- as much of the sugar coating gets
collected in coating pan during coating process.
– Causes of low film coating efficiency:
• Application rate is too slow (large tablet surface area, high airflow
and high temperature)-this dries the part of coating composition
before it reaches the tablet surface so that it is exhausted as dust.

2.Coating process:
Facility and Ancillary equipment:
– Should be designed to meet requirement of current GMP.
– Should have adequate space-for coating equipment, solution
preparation and in process storage.
– If the coating solvent is explosive or toxic concentration being
used-specific safety requirement for coating areas is must (i.e
electrical explosive proofing and specialized ventilation are
required).
– Use of aqueous based film coating-less expensive and less
detrimental to environment as compared to organic solvent.
– Other equipment used in coating solution preparation requires-
tanks, jacketed tanks (to keep solution at elevated
temperature), filters, and mixer (colloid mill, ball mill).

2.Coating process:
Automation:
– Full automation has been achieved for sugar and film
coating (aqueous and non-aqueous ).
– Feed back control of the system is maintained through a
series of sensor and regulating devices for temperature,
airflow, spray rate and pan speed.

Tablet coating processes
1. Sugar Coatings
• This traditional coating involves
successive application of sucrose-based
coating formulations, usually to tablet
cores, in suitable coating equipment.
• It imparts a smooth, rounded, elegant
appearance to the tablet.
Ideal characteristics of sugar coated tablets:
• Should posses a smooth, rounded
contour, with even coverage and a
glossy finish.
• Should be compliant with finished
product specifications and any relevant
compendial requirements.

Coating processes-sugar coating
Advantages:
• Produce tablets with characteristically smooth rounded contour
with even colour coverage.
Disadvantages
• Time consuming process-which ranges from a few hours to few
days.
• successful product depends on the skill of the coating operator
• Functional coatings are usually possible other than enteric coatings
• 30-50% weight increase due to coating material
• logo or break lines not possible.

• It is multistage process-involving 6 separate
operations.

Tablet coating processes-sugar coating
1. Sealing tablet core-
– Sugar coating are aqueous formulations.
– Water can penetrate directly into the tablet cores,
potentially affecting product stability and causing
premature tablet disintegration.
– To prevent this, application of a water impermeable
polymer in alcoholic solution such as Shellac, cellulose
acetate phthalate and polyvinyl acetate phthalate,
which protects the core from moisture, increasing its
shelf life.
– The amount of sealing coat has to be calculated to
obtain desire release pattern (modified/immediate).

2. Sub coating –
– It is applied to round the edges and build up the tablet
size.
– It increase the tablet weight by 50 to 100%.
– Is done by adding bulking agents such as calcium
carbonate or talc in combination with sucrose solution.
– In addition antiadherents such as talcum may be used to
prevent tablets sticking together.
• Polysachharide gums such as gum acacia may be added
as a binder in order to reduce brittleness.

3. Smoothing process
– remove rough layers formed in step 2 with the
application of sucrose syrup and to impart desired colour
to the tablet.
– This step requires skill.
• The first syrup coats usually containing some suspended
powders, called grossing syrups.
• Dilute colorant (titanium dioxide) may be added and smoothing
tablet surface to promote uniform colouring in later stages.

4. Colouring –
• For aesthetic purposes often titanium based
pigments are included.
• Application of colours to rough surface leads to
mottling problem in the final coated tablets.
• Syrup containing dye/pigments are applied until the
final size and colour are achieved.
• Few clear coats of syrup may be applied in the
finishing step.
5. Polishing –
• Effectively polished to give characteristic shine,
commonly using beeswax, carnauba wax or warm
solutions of these waxes in suitable volatile solvents
in clean standard coating pan.
6. Printing -edible ink for characterisation.

Tablet coating processes-film
coating
Film coating:
• Modern approach to coating tablets, capsules, or pellets by surrounding them with a thin
layer of polymeric material and only adds up to 2-6% of the tablet weight with negligible
increase in tablet size (thickness of the film ranging from 20-200µm).
• Description of tablets: Shape dictated by contour of original core.
• Process: Single stage process, which involves spraying a coating solution containing the
following;
1. Polymer
2. Solvent
3. Plasticizer
4. Colourant
• The solution is sprayed onto a rotating tablet bed followed by drying, which facilitates the
removal of the solvent leaving behind the deposition of thin film of coating materials around
each tablet.

Tablet coating process-film coating
Advantages
• Produce tablets in a single step process in
relatively short period of time.
• Process enables functional coatings to be
incorporated into the dosage form.
Disadvantages
• There are environmental and safety
implications of using organic solvents as well
as their financial expense.

Why film coating is favoured over
sugar coating?
Tablet appearance
 Retains shape of original core
 Small weight increase of 2-
3% due to coating material
 logo or ‘break lines’ possible
Process
 Can be automated e.g. Accela
Cota
 Easy training operation
 Single stage process
 Easily adaptable for
controlled release allows for
functional coatings.
• Film coating • Sugar coating
Tablet appearance
 Rounded with high degree of
polish
 Larger weight increase 30-50%
due to coating material
 Logo or ‘break lines’ are not
possible
Process
 Difficult to automated e.g.
traditional coating pan
 Considerable training
operation required
 Multistage process
 Not able to be used for
controlled release apart from
enteric coating.

Tablet coating processes-film coating
Pan spray method:
• Film coating can be applied using spray-atomization technique.
• Spray patterns-broad flat spray selected using appropriate nozzle
systems so that the entire width of the tablet bed can be covered
by the spray from 1-5 nozzles.
Process variables:
• The process variables to be controlled in pan spray film coating
processes are:
– Pan variables: pan design/baffling, speed and pan load.
– Process air: air quality, temperature, air flow rate/volume/balance
– Spray variables: Spray rate, degree of atomization, spray pattern, nozzle to bed
distance.

• Pan variables:
– Mixing of tablet mass is affected by pan shape, baffling,
rotational speed and pan load.
– Uniform mixing is essential to deposit the same quantity of
film on each tablet-that otherwise can result in
unacceptable color uniformity or enteric film integrity.
– Certain tablet shape requires a specific baffling
arrangement to ensure adequate mixing.
– Baffles, however, increase the chance of attritional forces
causing chipping and breakage if not carefully selected and
used.

– Pan speed affects mixing as well as the velocity of the
tablets passing under the spray.
– Too slow pan speed causes localized over-wetting,
resulting in tablet sticking to each other.
– Too high pan speed may not allow time for sufficient
drying before the tablets are reintroduced to the spray,
thus results in a rough coating appearance.
– Coating speed of 10-15 rpm are used for large pan coater
non-aqueous film coating.
– Pan speeds of 3-10 rpm (slower) are used for aqueous film
coating primarily to accommodate slower application rate
and drying of coating liquid.

• Pan load is defined in terms of volume fill, rather than by
weight.
• Thus optimum pan load by weight will vary frm product to
product depending upon apparent density of the product.
• When the pan is underloaded, the side walls of the coating
pan and even baffles become more exposed to the spray,
causing liquid to buid up on exposed metal surfaces-results
in sticking of the tablets to the surfaces.
• This can be minimized by:
– Minimising gun-tablet bed distance-to ensure optimal and
reproducible bed coverage
– Guns spacing
– Minimising gun spacing

Process air variables:
• Optimum drying efficiency for a coating process depends
on temperature, volume, rate and quality of air.
• Sensitivity of the film former and product core to the heat
determines the upper temperature at which the coating is
successful.
• In general, higher tablet bed and coating chamber
temperatures-results in rapid solvent evaporation, and
consequently faster coating rate.
• Air volume and rate determines by AHU and coating
equipment.
• Less air volume required for drying in case of efficient
coating equipment.

• Supply air should have some degree of
dehumidification-seasonal fluctuations of
moisture content of oncoming air can alter
coating and drying conditions-affects tablet
quality.
• Therefore, balance between supply and
exhaust air flows should be such that all dust
and solvent are contained within the coating
system.

Spray variables:
• Rate of liquid application, spray pattern and degree of
atomization are three interdependent spray variables.
• In the air-less high pressure system, all the three
variables are affected by fluid pressure and nozzle
design.
• In the air-atomized, low pressure systems, the rate of
liquid flow is affected by liquid pressure and orifice
size.
• Degree of atomization and spray pattern are affected
by atomizing air pressure, air volume and shape and
design of air jet in relation to fluid stream.

• Rate of application is dependent on:
– Mixing and drying efficiency of the system
– Coating composition
– Tablet core properties
• A spray pattern that is too wide results in loss of
coating material to the pan surface, resulting lower
coating efficiency (high wastage).
• Too narrow spray pattern causes localized over-wetting
and the tablet-tablet uniformity will be poor.
• spray width can be adjusted by moving the nozzles
closer or farther away from the tablet bed.

• Degree of atomization can also be controlled.
• High pressure yield greater atomization.
• Atomization that is too fine causes some droplets
to dry before reaching the tablet bed, resulting in
• Rough tablet surface,
• also excessive dust production
• Insufficient atomization – too large droplet
reaching tablet surface and causing localized
wetting –leading to sticking and picking or a
“orange peel” effect.

Tablet coating-Coating composition
• Film coating formulation has following
important ingredients:
1. Film former
2. Solvents
3. Plasticizer
4. Colorants
5. Opaquant extenders
6. Miscellaneous coating solution

1. Film former:
Ideal characters of coating material
• Solubility in the coating solution
• Solubility required for intended use- Free water solubility, Slow water solubility,
pH- dependent solubility
• Capacity to produce elegant looking product
• Stability in presence of water, heat, moisture, air, and substrate being coated and
no change in properties with aging.
• Essentially no color, odor, or taste
• Compatibility with common coating solution additives
• Nontoxic and ease of application
• Resistance to cracking and should act as barrier
• No bridging or filling of the debossed tablet surfaces by the film former
• Ease of printing procedure on high-speed equipment
• Low cost &
• Ease of application without specialized equipment

• A single polymer may not fulfill all of the
above qualities of an ideal film coating
material.
– Therefore proper blend of two or more polymers
may be used.
Non-enteric film polymers Enteric film formers
• Hydroxypropylmethylcellulose
•Methylhydroxyethylcellulose
•Ethylcellulose
•Hydroxypropylcellulose
•Povidone
•Sodium Carboxymethyl Cellulose
•Polyethylene Glycols
•Acrylate polymers
•Cellulose acetate pthalate
•Acrylate Polymers
•Hydroxypropylmethylcellulose pthalate
•Polyvinylacetate pthalate

Polymers for film coating
1. Cellulose derivative
• Widey used cellulose is HPMC-
– Readily soluble inaqueous
medium
– Forms film with good
mechanical properties
(strength, flexibility and
adhesion to the tablet core)
– Easy application of the coat.
• E.g.MC, HPC
2. Vinyl derivatives
PVP-tackiness
PVP+vinyl acetate-better film.
• Immediate release
coating polymers
• Modified release coating polymers
Extended-release polymers and Enteric
coating
• Dissolve in organic solvent or
disperse in aq. Medium.
1.Methacrylic acid-Copolymers
• Cellulose derivatives
The presence of Highly substituted
cellulosic carboxylic acid gr. Ether,
making polymer water Insoluble
. E.g. Ethylcellulose
2. pthalate ester
Insoluble in Water at low pH (stomach)
but gradually becomes soluble as pH
rises (intestine). e.g. CAP (Cellulose
acetate pthalate)

Summary of Polymers used in pharmaceutical
formulations as coating materials.
Polymer Trade name Application
Shellac EmCoat 120 N
Marcoat 125
 Enteric Coatings
 Taste/Odor Masking
Cellulose acetate Aquacoat CPD®
Sepifilm™ LP
Klucel®
Aquacoat® ECD
Metolose®
 Enteric Coatings
 Taste masking
 Sustained release coating
 Sub coat moisture and barrier
sealant pellet coating
Polyvinylacetate phthalate Sureteric®  Enteric Coatings
Methacrylate Eudragit®  Enteric Coatings
 Sustained Release Coatings
 Taste Masking
 Moisture protection
 Rapidly disintegrating Films

Enteric coating
• Reasons for enteric coating:
1. To protect acid-labile drugs from the gastric fluids, e.g.
antibiotics (penicillin), omeprazole etc.
2. To prevent gastric distress or nausea due to irritation
from a drug. E.g. sodium salicylate
3. To deliver drugs intended for local action in intestines.
4. To deliver drugs that are optimally absorbed in the
small intestine to their primary absorption site in their
most concentrated form.
5. To provide a delayed-release component for repeat
action tablet.

Properties of an Ideal enteric coating
material
1. Resistance to gastric fluids.
2. Ready susceptibility to or permeability to intestinal fluids.
3. Compatibility with most coating solution and the drug
substances.
4. Stability alone and in coating solution. The film should not
change on aging.
5. Formation of a continuous film.
6. Non-toxicity
7. Low cost
8. Ease of application without specialized equipment.
9. Ability to be readily printed or to allow film to be applied
to debossed tablets.

2. Solvents:
• Dissolve or disperse the polymers and other additives and add
them to the tablet surface.
Ideal solvent systems:
• Should dissolve /disperse the polymer system.
• Should easily disperse other coating solution components into the
solvent system.
• Polymer concentration range from 2-10% should not produce
viscous system greater than 3000cps –resulting in processing
problems.
• Should be colorless, tasteless, odorless, inexpensive, non-toxic,
inert, and non-flammable.
• Should have rapid drying rate(300kg load coat in 3-5 hr).
• Should have no environmental impact.

• Widely used solvents used alone or in
combinations are as follows:
– Water
– Ethanol
– Methanol
– Isopropanol
– Chloroform
– Acetone
– Methylethylketone
– Methylene chloride

• Water is best solvent of choice due to
economic and environment issue.
• However, several polymers cannot be applied
from aqueous systems.
• Drugs hydrolyzed in water can be effectively
coated with non-aqueous solvent based
coating.

3. plasticizers:
• Two types of plasticizers used:
– Internal
– External
• Internal :
– Modify the chemical properties of polymer.
• External:
– Non-volatile or other polymer which when includes with primary
polymeric film former, changes the flexibility, tensile strength and
adhesive properties of resulting film.
– Choice of the plasticizer material depends on the ability of plasticizer
material to solvate the polymer and impart flexibility by relieving the
molecular rigidity.

• Type of plasticizers, its ratio to polymer-optimized to
achieve the desired film properties.
• Viscosity of the plasticizers-its influence on the final coating
solution, its effect on film permeability, tackiness, flexibility,
solubility and taste and its toxicity, compatibility with other
coating solution components and stability of the film and
final coated product.
• Concentration of plasticizer is expressed as: amount of
polymer being plasticized.
• Recommended level of plasticizer: 1-50% by weight of film
former. E.g. castor oil, propylene glycol 200 and 400 series
and surfactant (tweens, spans, and organic acid esters)

– Water soluble plasticizer: PEG, propylene glycol,
– organic soluble plasticizer: castor oil, and spans.
4. Colorants:
– May be soluble in solvent system or suspended as insoluble powder.
– Concentration used: (2.5-8)%
– Used to provide distinctive color and elegance to a dosage forms.
– Use of fine powdered colorants (<10µm)-help to achieve proper
distribution of suspended colorant in coating solution.
– Common colorants are certified (FD&C) and (D&C) colorants.
– Synthetic dyes and their corresponding lakes.
– Lakes-reproducible color achieved, colorant of choice for sugar/film
coating.

• Lakes-(10-30)% of pure dye content
– For light shades: conc. Less than 0.01% may be adequate.
– For dark color : concentration more than 2%.
Organic dyes &
their lakes
Inorganic color Natural color
Sunset yellow Iron oxide red, black Carmine
Erythrosine Titanium dioxides Anthocyanin
Tartrazine Riboflavin

• Various color concentrate promoted to
achieve less lot to lot color variation.
– Opalux: opaquant color concentrate for sugar coating.
– Opaspray: paque color concentrate for film coating.
– Opadry: complete film coating concentrate.

5. Opaquant Extender:
– Very fine in-organic powders used in coating solution to
provide more pastel colors and increase film coverage.
– Provide absolute coating or mask the color of tablet core
and thus less amount of colorants are required.
– Silicates (talc, Al. silicate), titanium dioxide,
carbonates (magnesium carbonate),
– Sulfate (calcium sulfate)
– Oxides(Magnesium oxides)

6. Miscellaneous :
• Flavors and sweeteners:
– Mask objectionable odor and enhance desire taste.
• Surfactants:
– Solubilize immiscible or insoluble ingredients
– To facilitate faster dissolution of coating.
• Antioxidants:
– Prevent dyes from oxidation and color change.
• Antimicrobials:
– To prevent microbial growth in coating composition preparation and
storage.
– Aqueous cellulosic coating solution prone to microbial contamination.

Tablet coating-Coating film defects
• Sticking and picking
• Roughness
• Orange –peel effects
• Bridging and filling
• Blistering
• Hazing/Dull
• film Colour variation
• Cracking

• Sticking and picking –
– Over wetting or excessive film
thickness causes tablets to stick
each other or to the coating pan.
– On drying at the point of contact, a
piece of film may remain adhere to
pan or tablet.
– Giving “picked” appearances to the
tablet surface.
– Resulting in a small exposed area of
the core.
• Remedies
– Reduction in liquid application rate.
– Increase in drying air temperature
and air volume.

• 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.
– 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.

Orange –peel effects :
• It is surface defect resulting in the
film being rough and non-glossy.
• Appearance is similar to that of an
orange.
– Inadequate spreading of coating solution
before drying causes a Orange –peel
effects on the coating.
Causes :
– Indicates that spreading is impaired by
rapid rate of drying or by high solution
viscosity.
Remedies :
– use mild drying conditions
– Thinning of coating solution with
additional solvents may correct this
problem.

• Bridging and filling :
– During drying film may shrink
and pull away from the sharp
corners of bisect, resulting in a
“Bridging” of surface dispersion.
– These defects can be so severe
that the monogram or bisect is
completely obscured.
• Remedies :
– Increase in plasticizer contents
or change in plasticizer
concentration can decrease the
bridging

• Filling :
– Applying too much solution, resulting in thick film, causes
filling.
– That fills and narrows the monogram or bisects.
– In addition, if solution applied too fast, over wetting may
cause the liquid to quickly fill and be retained in the
monogram.
• Remedies :
– Judicious monitoring of the fluid application rate
– Thorough mixing of tablets in the pan prevent filling.

• Blistering:
• It is local detachment of film from the substrate forming
blister.
Reason:
• Entrapment of gases in or underneath the film due to
overheating either during spraying or at the end of the
coating run.
• Causes:
– Evaporation of solvents from the core in the oven.
– And effect of high temperature on the strength, elasticity and adhesion of
the film may results in blistering.
• Remedies:
– Controlled drying conditions.

• Hazing/Dull film :
– Also called as bloom.
– It is defect where coating becomes dull immediately or after
prolonged storage at high temperatures.
• Causes:
– It can occur when too high processing temperature is used for a
particular formulation.
– high concentration and low molecular weight plasticizer is used.
– High humidity exposure of coated tablet-resulting in partial solvation
of film.
• Remedy:
– Decrease plasticizer concentration and increase molecular weight of
plasticizer.
– Decrease air temperature.

• Colour variation:
– Problem caused by process conditions or the formulation.
– Improper mixing, uneven spray pattern and insufficient coating
may results in colour variation.
– The migration of soluble dyes, plasticizer and other additives
give the coating a mottled or spotted appearance.
• Remedies:
– Use of lake dyes eliminates dye migration.
– A reformulation with different plasticizer and additives is the
best way to solve film instability.

• Cracking:
– Cracking occurs if internal stresses 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.
• Remedies:
– Adjusting the plasticizer types and concentration can
minimize internal stresses .
– Also adjusting the pigment types and concentration can
minimize internal stresses

• Capping and Lamination:
– This is when the tablet separates in
laminar fashion.
– Capping is partial or complete separation of top or bottom crowns of
tablet main body.
– Lamination is separation of a tablet into two or more distinct layers.
– Friability test can be used to reveal these problems
Causes
– Improper tablet compression, but it may not reveal itself until coating
starts. Operation of the coating system, however, can exacerbate the
problem.
Remedy : not to over-dry the tablets in the preheating stage that can
make the tablets brittle and promote capping.

QUALITY CONTROL ALREADY DEALT IN LAB.
THE END
Dryer/vet/tab/coat/dye

Tablet-coating.pdf

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