Tablet coating

Tablet Coating
By –
Vaibhav Tripathi Dr. Anil K. Sahu
Edited By- Dr. Deepak K. Dash

Index
1. Introduction
2. Coating materials
3. types
4. Methods/ equipments of coating
5. Defects
6. References

Introduction
 “panning "was the original word
for the process of adding coating
layer to a tablet.
 Coating is a process by which an
essentially dry/ liquid outer layer
of coating material is applied to
the surface of a dosage form to
achieve specific benefits.

Introduction
 Coating may be applied to a wide
range of dosage form including
tablets, capsules, drug crystals etc.
 Tablet coating is the last critical
step in the tablet production cycle.
 It is the phenomenon of
application of coating to the
tablet.

Introduction
 In this process, coating
composition is applied to a batch
of tablets in a coating pan
 The pan is rotated in order to
uniformly distribute the coating
solution throughout the bed of
tablets.
 As a result tablet surfaces become
covered with a tacky polymeric
film.

Introduction
 Advantages
 Cover the unpleasant taste, odor
and color.
 Physical and chemical protection
in medicine from environment
(light, moisture, and air).
 Control of drug release in the GIT
 increase the tablet strength

Introduction
 Advantages
 To protect drug from the gastric
environment of the stomach with
an acid-resistant enteric coating.
 Improve the appearance of tablets.
 Assist and facilitate the
identification of drug.
 Easing the process of blistering.

Introduction
 Advantages
 improve patient compliance
Increase shelf life of the dosage
form
Limitations
 time taking process
 wt. of tablet is increased
 expensive production cost

Coating materials
1. Solvent
2. Plasticizer
3. Colorant
4. Opaquant-extender
5. Film former

Coating materials
1. Solvent
 It is to dissolve or disperse the polymers
and other additives and convey them to
the substrate surface.
 It should be -
 Colorless, tasteless, odorless,
Inexpensive
 nontoxic, inert and Noninflammable.
 It should have rapid drying Rate.

Coating materials
1. Solvent
 Water, Ethanol, Methanol, Isopropanol,
 Chloroform, Acetone, Methylene chloride
 Methylene ethyl ketone.

Coating materials
2. plasticizer
 It is used to modify the quality of the film
 Plasticizing techniques involve internal
plasticizers and external plasticizers.
I. Internal plasticizers involves chemical
modification of the basic polymer that
alters the physical properties of the
polymers.

Coating materials
2. plasticizer
 Glycerol, propylene glycol, PEG 200
6000 grades.
II. External plasticizers are used to achieve
the desire effect of the film (flexibility tensile
Strength, adhesive properties)
 Diethyl phthalate (DEP), Dibutyl
phthalate (DBP), Tributyl citrate (TBC)

Coating materials
3. Colorant
 It provides the characteristic color and
 appearance to the dosage form.
 The concentration of colorants in the
coating solution depends on the color
shade, intended type of dye and the
concentration of the opaquant
extenders.
 Usually fine powdered colorant(less than

Coating materials
3. Colorant
 In order to achieve uniform distribution of
suspended colorants in the coating
solution.
 For very light shade conc. of less than
0.01% may be used
 For dark shade Conc. more than 2.0%
may be used.

Coating materials
3. Colorant
 Inorganic colorant eg. Iron oxide,
titanium dioxide
 Natural colorant eg. Caramel,
anthocyanin, Carotenoid, Chlorophyll,
indigo,
 Flavones,
 Turmeric and carminic acid.

Coating materials
4. Opaquant- extender
 These are very fine inorganic powders
used in the coating solution formulation
 to provide several tints of colors and
propagate film coverage.
 Titaniundioxide
 Talc, Aluminium silicate
 Magnesium carbonate,
 Calcium sulphate.

Coating materials
5. Film former
 Such materials are used to regulate the
release of API from the dosage form.
 Film formers are used to design enteric
coating.
 Hydroxy propyl methyl cellulose (HPMC)
 Methyl hydroxy ethyl cellulose (MHEC)

Types of Coating
 Mainly 4 types
 Sugar coating
 Film coating
 Enteric coating
 Compression coating

Types of Coating
 Sugar coating (oldest method)
 It uses multiple sucrose based solution
over the tablet.
 Preliminary evaluation such as hardness
and friability should be done before
coating.
 Sugar coating process involves 5
separate steps:

Types of Coating
 Sugar coating

Types of Coating
 Sugar coating
1. Sealing:- it is done for water proofing to
minimize the probability of aqueous solution
of sucrose to penetrate inside the tablet.
 Sealing materials are shellac, oleic acid,
PEG, methylene chloride, alcohol etc.
Shellac is more effective because of
polymerization feature on the other hand
bring about delayed disintegration rate.

Types of Coating
 Sugar coating
2. Sub- coating:- it is done for rounding- off
the tablet edges and to build up tablet size.
 Large amount of syrup is employed
 As a result tablet volume is increased
about 50- 100 % more than its initial
volume
 Generally two methods are used for sub-
coating:

Types of Coating
 Sugar coating
2. Sub- coating:-
I. The application of gum based solution
followed by dusting with powder and then
drying. This routine is repeated until the
desired shape is achieved.
II. The application of a suspension of dry
powder in gum/sucrose solution followed
by drying.

Types of Coating
 Sugar coating
2. Sub- coating:-
 eg. Acacia, gelatin, sugar powder, corn
syrup, dist. Water.
3. Smoothing / Grossing:-
 It is done to cover the roughness caused
during sub- coating operation.

Types of Coating
 Sugar coating
3. Smoothing / Grossing:-
 It increases tablet size.
 In this step little amount of color is
sometimes added to syrup solution
 To develop tinted base that helps uniform
coating in upcoming step.
 Eg. Ca cabonate, corn starch, sugar
powder, color, dist. water

Types of Coating
 Sugar coating
4. Coloring:-
 It is done to flourish desired color to the
tablet by coating with colored syrup
 Until uniform color shade is obtained
 Eg. Iron oxide, titanium dioxide,
Caramel, anthocyanin, Carotenoid,
Chlorophyll, indigo, Flavones,Turmeric
and carminic acid, syrup

Types of Coating
 Sugar coating
5. Polishing:-
 In this step, coat of polishing solution is
applied to achieve intended luster.
 Polishing solution is comprised of waxy
materials and suitable volatile solvent.
 Eg. Carnauba, bees & paraffin wax,
denatured spirit.

Types of Coating
 Film coating
 It involves, spraying/ pouring of film
coating material on to tablet bed.
In pan pouring tech. coating material is
poured over the rolling tablets
Whereas, in pan spray tech. coating
solution is sprayed onto the rolling tablets
with the aid of automated spray gun

Types of Coating
 Film coating
 film coating process needs keen
observation and expertise personnel.
 Because any sort of minute deviation may
lead to improper coating.
Film coating gives a tablet with less Weight
and small size features as compare to
sugar coating.

Types of Coating
 Film coating
 Provide better mechanical strength and
glossy appearance.
 Film coating materials are hypromellose
 Cellulose-
 caboxymethyl, hydroxyethyl,
hydroxyethylmethyl, hydroxypropyl, ethyl
 PEG

Types of Coating
 Enteric coating
 This technique is used to protect the tablet
core from disintegration in the acid
environment of the stomach for one or
more of the following reasons:
 Prevention of acid attack on API which is
unstable at low pH.
To protect the stomach from the irritant
effect of certain drugs.

Types of Coating
 Enteric coating
 To facilitate absorption of a drug that is
preferentially absorbed distal to the
stomach.
To deliver drugs intended for local Action in
the intestines, e.g. Intestinal antibiotics.
To deliver drugs that are optimally
Absorbed in the small intestine to their
primary absorption site.

Types of Coating
 Enteric coating
 To provide a delayed-release component
for repeat-action tablets.
 Eg. Hypromellose phthalate
 polyvinyl acetate phthalate
 cellulose acetate phthalate
polymethacrylates

Types of Coating
 Use of compression to form coat around a
pre-formed core.
 Used mainly to separate chemically
incompatible materials.
 Also dual release patterns possible
 Compression coating is a dry process.

Types of Coating
process involves compaction of coating
material around a preformed core. The
technique differs from sugar and film
coating process.
 This process enables incompatible
materials to be formulated together, such
that one chemical or more is placed in the
core and the other (s) in the coating
material.

Methods/ equipments of Coating
 On the basis of equipments used
 Coating method/ process can be
classified into 6 types
1. Conventional pan process
2. Perforated pan process
3. Fluid bed coating process

4. Electrostatic dry coating process
5. Magnetically assisted impaction coating

 It is also known as standard pan system
 Circular metal pan(mounted angularly on
a stand) is 8-60 inches in diameter
 Rotated on its horizontal axis by a motor
at a speed of 10 to 15 RPM

 Heated air is directed into the pan & on to the
tablet bed surface and is exhausted by means
of ducts through the front of the pan.
 Coating solution are applied to the tablets by
ladling or spraying the material on to the
rotating tablet bed.

 In standard coating pan ,the drying
efficiency is improved by:-
I. Pellegrini pan
II. The immersion sword
III. Immersion tube systems

I. Pellegrini pan
 Baffled pan
 Diffuser(distributes the
 drying air uniformly over
 the tablet bed surface).

II. Immersion sword pan
 Perforated metal sword device immersed in the
tablet bed.
 Drying air is introduced through this device and
flows upward from the sword through the tablet
bed.

II. Immersion sword pan
 Coating material
 is applied through
 an atomized
 spray gun

II. Immersion tube system
 Tube immersed in the tablet bed.
 Tube delivers the heated air.
 In immersion tube system the coating solution is
applied with the heated air from the immersed
tube

II. Immersion tube system
 Coating material is
 delivered Through
 spray nozzle

2. Perforated pan process
 Perforated or partially perforated drum.
 Rotated on its horizontal axis in an enclosed
housing.
 The coting solution is applied to the surface of
the rotating bed of tablets through spraying
nozzles, which are present inside the drum.

2. Perforated pan process (PPC)
 Perforated pan coaters are efficient drying
systems with high coating capacity.
 PPC utilizes 4 types of equipments:-
I. Accela- cota
II. Hi- coater
III. Dria- coater IV. Glatt- coater

I. Accela- cota
 Drying air is directed in to the drum
 Passed through tablet bed
 Exhausted through perforations in drum.

I. Accela- cota

II. Hi - coater system
 Working is similar to that of Accela- cota
 But only one side has perforated design

II. Hi - coater system

III. Dria- coater system
 Drying air enters through hollow perforated ribs
located on inside periphery of the drum.
 As the coating pan rotates, the ribs dip into the
tablet bed and drying air passes up through
 Exhaust is from the back of pan.

III. Dria- coater system

IV. Glatt- coater system
 It is the latest perforated pan coater to be
introduced in the industry.
 In this, drying air can be directed from inside the
drum through tablet bed
 Exhausted out through an exhaust duct.

IV. Glatt- coater system

3. Fluidized bed coating
 In this system fluidization of the tablet mass is
achieved in a columnar chamber by the upward
flow of drying air.
 The air flow is controlled, so that more air
enters the center of the column, causing the
tablets to rise in the center.

 The movement of tablets is upward trough the center of
the chamber.
 They then fall towards the chamber wall, Move
downwards to reenter the air stream At the bottom of
the chamber.
 Coating solutions are applied from a spray nozzle which
is located either at the bottom or upper region of
chamber

 It is a dry coating process .
 In this tech. electrically charged coating
material is sprayed over the tablet bed
and then heat is applied to fix the coat.

 Now a days, this tech. is gaining
popularity as an alternative method to
aqueous or solvent based coating
process.
 According to charging mechanism,
spraying units are of 2 types:

I. Corona charging:-
 In this mechanism, high electrical voltage
is developed with the help of electrode
through a spray gun for electrical
breakdown & ionization of air.
 As a result, coating material pick up the

 Negative ions on
 their way from
 the gun to
 tablet bed.

 The electric field can be adjusted :
 To regulate the movement of particles,
powder flow & density.

II. Tribo charging:-
 this tech. uses the principal of friction
charging associated with the dielectric
properties of coating material
 Apart from free ions & electrical field

 Electric force is only used to produce
repulsive force among charged particles.

5. Magnetically Assisted Impaction Coating
 Coating is done with the aid of magnetic
force.
 Coating process is as followed:
 Excitation of magnetic particles
 De- agglomeration of guest particles(coating
material)

 Shearing & spreading of coating materials
onto host material (tablet)
 Magnetic host- host particles interaction
 Magnetic host- guest interaction
 Formation of coated products

IMPORTANT PROCESSING PARAMETERS
 Inlet & Outlet of bed temperatures.
 Relative humidity.
 Atomization air pressure.
 Pan speed.
 Liquid spray rate.
 Gun nozzles check.

IMPORTANT PROCESSING PARAMETERS
 Spray gun calibration.
 Solid content of coating solution.
 Nozzle-to-bed distance.
 Droplet size.
 Drying time

Coating defects
 An ideal coated tablet should be free from
any visual defect or functional defect.
 But some imperfections are seen in the
tablet coating for different kinds of
reasons
 Such imperfections are known as tablet
coating defects .

Coating defects
1. Twinning 7. Blistering 14. Erosion
2. Color variation
8. Bridging 15. Blushing
3. Orange peel
9. Cracking
4. Roughness
10. Sticking &
Picking
5. Filling
11. Blooming
6. Chipping
12. Pitting

Coating defects
 Twining
 Two tablets stick together.
 Most common in capsule shaped tablets.
Cause Redress
Due to tablet shape
other than spherical
Changing the shape of
tablet
Improper spraying Altering spray rate
Inappropriate pan drying Regulating pan speed

Coating defects
 Color variation
 Imperfect color shed onto tablet surface
Cause Redress
Improper mixing
Proper mixing of all
additives
Uneven spray pattern
Selection of suitable
spraying process
Migration of soluble
dyes during drying
Use of lake dyes
eliminates dye migration

Coating defects
 Orange peel
 The texture of tablet surface looks like
surface of an orange
Cause Redress
Rapid Drying Use mild drying
conditions
High solution viscosity Use additional solvents
to decrease viscosity
of solution.

Coating defects
 Roughness
 The surface becomes rough and no
glossy
Cause Redress
Uneven atomization
tech.
Alter the degree of
atomization
Insufficient quantity of
plasticizer
Makeup the quantity as
per requirement

Coating defects
 Chipping
 where film become chipped and dented
usually at the edges of tablet .
Cause Redress
Excessive
attrition during
coating process
Increase
hardness of the
film.

Coating defects
 Filling
 The monogram or bisect is filled and
become narrow.
Cause Redress
Applying too
much solution
Adjust the
volume of coating
solution
Higher solution
applying rate
Control fluid
application rate

Coating defects
 Blistering
 Detachment of film from the substrate
forming a blister .
Cause Redress
Over heating
during spraying
coating solution
Use mild drying
condition

Coating defects
 Bridging
 Unwanted filling of coating material in the
letter or logo embossed on the tablet .
Cause Redress
High percentage of
solid in coating
solution
Increase plasticizer
contents or change
plasticizer
concentration
High coating
viscosity
Reduce viscosity
of coating solution

Coating defects
 Cracking
 Small, fine flaws observed on the upper and lower
central surface of tablets
 Rarely find on the sidewall
Cause Remedy
Use of higher
molecular weight
polymers or
polymeric blends
Use low molecular
weight polymer
Higher internal
stresses in the film
Adjust the
plasticizer &
pigment types and
concentration to
minimize internal
stresses

Coating defects
 Sticking & Picking
 Area of film are pulled away from the surface
when the tablet sticks together and then part.
Cause Remedy
Higher rate of
application of
coating solution
Reduce liquid
application rate
Over wetting
Increase in drying
air temperature
and air volume.
Excessive film
thickness
Use of sufficient
quantity of
opaquant-
expander

Coating defects
 Blooming
 Coating becomes dull immediately or after a
prolonged storage .
 Normally it occurs together with surface
roughness.
Cause Remedy
using low molecular
weight plasticizer
Use of plasticizer
with high MW &
concentration

Coating defects
 Pitting
 When pits occur in the surface of tablet core
Cause Remedy
Non-continuous
spreading of film
Selection of
suitable spreading
mechanism for
uniform coating
temperature of the
tablet core is
greater than the
melting point of the
materials used in
tablet formulation
Control drying
temperature

Coating defects
 Blushing
 The defect best described as whitish specks or
haziness of the film .
Cause Remedy
Excessive
precipitation of
polymer exacerbated
Proper use of coating
polymer
High coating
temperature at or
above the thermal
gelation
temperature of the
polymers.
Control coating
temperature

Coating defects
 Erosion
 Gradual destruction of coating layer
Cause Remedy
Over-wetted tablet
surface
Use of suitable solvent
Inadequate drying Control drying rate &
temperature
Lack of tablet surface
strength
Use of suitable
polymer in coating
solution to improve the
tensile strength

References
1. Ankit G, Ajay B, Kumar KM, Neetu K, Bihani SG. Tablet coating
techniques: Concepts and recent trends. International Research Journal of
Pharmacy. 2012;3(9):50-3.
2. Augsburger LL, Hoag SW, editors. Pharmaceutical dosage forms-tablets.
CRC press; 2016 Apr 19.
3. Doerr DW, Serless ER, Deardorff DL. Tablet coatings: Cellulosic high
polymers. Journal of the American Pharmaceutical Association. 1954
Jul;43(7):433-6.
4. Tripathi DK, Industrial Pharmacy: A Comprehensive Approach, (2018),
Pharma Med. Press/BSP Books, Andhra Pradesh.
5. Lachman L., Lieberman H.A., Theory And Practice of Industrial
Pharmacy, (2009), Indian Edition, CBS Publication And Distributors, New

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