Coating technology

PHARMACEUTICAL MANUFACTURING TECHNOLOGY
(MQA 204T)
COATING TECHNOLOGY
Guided by : Presented by:
Dr. Vijay k. Parmar Henisha Patel
Associate professor Department of pharmaceutical science,
M.pharm. sem-II
Quality Assurance
1

CONTENTS
Introduction
Definition
Objective
Coating process
Coating equipment’s
Particle coating
Application
Problem encountered
References
2

Tablet coating can be described as a process of applying an edible paint
on the surface of a pharmaceutical dosage form to achieve specific
benefits.
Tablets covered with one or more layers of mixture of various substances
such as natural or synthetic Resins, gums, inactive and insoluble filler, sugar,
plasticizer, polyhydric alcohol ,waxes, authorized colouring material and
flavouring agents.
Coating can be applied to several kinds of solid dosage forms like tablets,
pellets, pills, drug crystals, etc.
INTRODUCTION
3

Coating process:
Coating should be uniform .
Various techniques were designed for the application of the coating on
the tablet surface.
Generally, the coating solutions are sprayed onto the uncoated tablets
as the tablets are being agitated in a pan, fluid bed, etc. As the solution
is being applied, a thin film is formed which sticks to each tablet. The
liquid portion of the coating solution is then evaporated by passing air
over the surface of the tumbling pans.
The coating may be formed either by a single application or may be
developed in layers through the use of multiple spraying cycles.
DEFINITION
4

To mask the disagreeable odor, colour or taste of the tablet.
To offer a physical and/or chemical protection to the drug.
To control and sustain the release of the drug from the dosage form.
To incorporate another drug which create incompatibility problems.
To protect an acid-labile drug from the gastric environment.
Increasing the mechanical strength of the dosage form.
OBJECTIVE
5

Coating process
Commonly used process
1. Sugar coating
2. Film coating
3. Enteric coating
4. Organic film coating
5. Aqueous film coating
Recent technology in tablet coating
1. Electrostatic coating
2. Vacuum film coating
3. Compression coating
4. Dip coating
6

1) SUGAR COATING
Steps Description
Sealing/ water proofing  provides a moisture barrier and harden the tablet
surface.
 The polymers used are natural gums like shellac, acacia or
derivatives of cellulose like cellulose acetate
phthalate(CAP), PVAP, HPMC.
Why sealing-
 It is aqueous formulations which allow water to
penetrate directly into the tablet core and thus
potentially affecting product stability and possibly
causing premature tablet disintegration.
 To protect the tablet core from adverse effect of
moisture.
8

Subcoating  causes a rapid build-up the tablet size and to round of
the tablet edges.
WHY- build up the core weight with adding a bulking agent
such as calcium carbonate, to the sucrose solution.
Antiadherents- e.g. : Talc may be added after partial drying
to prevent sticking of the tablets together.
Smoothing  smoothes out the subcoated surface and increase the
tablet size to predetermine dimension.( smoothed out
by a thick sucrose syrup coating.)
Coloring  this usually consist of thin sucrose syrup containing the
requisite coloring materials (water-soluble dyes or
water-insoluble pigments may be used.)
 The colours used should be approved by FD and C.
9

Polishing after the colour coating, the tablet surfaces show
a dull or matt appearance. To achieve glossy
finish, application of waxes ( beeswax carnauba
wax) are employed.
Printing Different tablets could be identified by
manufacturer logo, product name, dosage
strength or other appropriate code.
Demerits:
 high cost,
 long coating time and high bulk due to the use of other coating
materials.
 It is tedious,
 time consuming and requires the expertise of highly skilled technician.
10

2) FILM COATING
a thin film of polymer solution around the tablet core.
Types of film coating :
1.Immediate release
2.Modified release
Process: single stage process, which involves spraying a coating solution
containing the following:
polymer
Solvent
Plasticizer
Colourant
The solution is sprayed onto a rotating tablet bed followed by drying,
which facilities the removal of the solvent leaving behind the deposition of
thin film of coating materials around each tablet.
11

Plasticizer  added to film coating formulations to modify
the physical properties of the polymer to make
it more usable.
 One important property is that their ability to
decrease film brittleness.
EXAMPLES:
Polyols, such as polyethylene glycol 400. Organic
esters, such as diethyl phthalate. Oils/glycerides,
such as fractionated coconut oil.
In general only water-miscible plasticizers can be
used for aqueous-based spray systems.
Solvent solvents play an important role in formulation of
coating solution.
13

 They serves as a vehicle for dissolving and dispersing the
constituents of coating solutions and helps in the applications of
the coating to the tablet surface.
EXAMPLES of commonly used solvents are water,
alcohol(methanol, ethanol),ketones , esters etc.
Colourant  To improve the aesthetic value of the final product as well as
helps in identifying the product.
EXAMPLES
Iron oxide pigments, titanium dioxide , aluminium lakes.
14

MERITS DEMERITS
 Produce tablets in a single step
process in relatively short period
of time and suitable for diabetic
patients
 They do not have elegance as that
of sugar coated tablets.
15

3) ENTERIC COATING
A tablet that has a special outer covering designed
to dissolve in the small intestine.
This technique is used to protect the tablet from
disintegration in the acid environment of the
stomach for one or more of the following reasons:
1. Prevention of acid attack on active constituents
unusable at low pH,
2. To protect the stomach from the irritant effect of
certain drugs,
3. To facilitate absorption of a drug that is
preferentially absorbed distal to stomach.
4. Polymers are insoluble in aqueous media at low
pH, but as the pH rises they experience a sharp,
well defined increase in solubility at a specific pH.
16

MATERIALS : plant fibres, shellac, fatty acids , plastic and PVAP, HPMCP,
CAP, CAT.
Properties of enteric coating materials:
Resistance and susceptibility
Stability and compatibility
Low cost and non- toxicity
Ease of application without specialized equipment.
Ability to be readily printed or to allow film to be applied to debossed
tablet.
Formation of continues (uninterrupted ) film.
17

Process: After the forming of tablet core, the tablet core are first coated
with separating layer and then with the enteric coating layer.
Components used in enteric coating Description
polymers  These substances often form into a chain-
like structure starch, cellulose, rubber all
possess, polymeric properties.
 They are insoluble in acidic media but
become deprotonated and dissolved in
basic media at pH nearly neutral
values(pH>5).
EXAMPLES: polymethacrylates, polyvinyl
derivatives , cellulose Esters.
plasticizers are a group of auxiliary components that
improve elasticity of the polymeric film.
18

EXAMPLES: phthalate esters, oils, glycerol, glycols,
phosphate esters, other esters like citrates, stearates,
sebacate, oleate, adipate etc.
solvent  solvents are used to dissolve or disperse the polymers
and other additives and convey them to substrate
surface.
• Water
• Alcohols
• Ketones
• Esters
Additives EXAMPLES : pigments/colorant, opacifier, anti-tacking
agent.
19

4) ORGANIC COATING
In liquid coating, a mixture of polymers, pigments and excipients is
dissolved in an organic solvent (for water insoluble polymers) or water (for
water soluble polymers) to form a solution, or dispersed in water to form a
dispersion, and then sprayed onto the dosage forms in a pan coater (for
tablets) and dried by continuously providing heat, typically using hot air,
until a dry coating film is formed .
Organic solvent based coating provides a variety of useful polymer
alternatives, as most of the polymers are soluble in the wide range of
organic solvents. However, there are certain disadvantages like they are
flammable, toxic, and costly and possess environmental issues .
 ICH guidelines also prefer the avoidance of organic solvents in
pharmaceutical dosage formulations considering products safety profile.
20

5) AQUEOUS FILM COATING
All above problems with organic solvents resulted in shift to use of water
as the preferred coating solvent.
The conversion from organic solvent based coating to aqueous based
coating makes the coating process more economical, though initially it
may need a little investment to upgrade the coating facility.
The need of this up-gradation arises due to the need of higher drying
capacity(the latent heat of water is 2200kj as compared to 550kj for
methylene chloride.)
This implies that one would require 4 times more energy as compared to
organic solvent .
21

RECENT TECHNOLOGY IN TABLET COATING
1) ELECTROSTATIC COATING
It is an effective way of applying a coat on conductive substances.
 A strong electrostatic charge is applied to the substrate.
The coating material consisting of conductive ionic species of opposite
charge is sprayed on the charged substrate.
A complete and uniform coating of corners on the substrate is achieved
There are two kinds of spraying units, based on the charging mechanism
a) corona charging and
b) tribo charging.
22

a ) Corona charging
This is done by the electrical breakdown and then ionization of air by
imposing high voltage on a sharp pointed needle like electrode (i.e.
charging pin) at the outlet of the gun.
The powder particles pick up the negative ions on their way from the gun
to the substrate.
The movement of particles between the charging gun and the substrate is
mainly governed by the combination of electrical and mechanical forces.
The mechanical forces produced by the air blows the powder towards the
substrate from the spray gun.
For the corona charging, the electrical forces are derived from the
electrical field between the charging tip of the spray gun and the earthen
substance, and from the repulsive forces between the charged particles.
23

The electrical field can be adjusted to alter the powder's flow, control
pattern size, shape, and powder density as it is released from the gun.
b) Tribo charging
Unlike corona charging guns, the tribo charging makes the use of the
principle of friction charging associated with the dielectric properties of solid
materials and therefore no free ions and electrical field will be present
between the spray gun the grounded substance.
24

For tribo charging guns, the electrical forces are only regarded to the
repulsive forces between the charged particles.
After spraying when charged particles move into the space adjacent to the
substrate, the attraction forces between the charged particles and the
grounded substrate makes the particle to deposit on the substrate.
Charged particles are uniformly sprayed onto the earthen substrate in
virtue of mechanical forces and electrostatic attraction.
Particles accumulate on the substrate before the repulsion force of the
deposited particles against the coming particles increase and exceed the
electrostatic attraction.
Finally once the said repulsion becomes equivalent to the said attraction,
particles cannot adhere to the substrate any more, and the coating
thickness does not increase any more.
25

2)VACCUM FILM COATING
It is new coating technique that employs specially designed baffled pan.
The pan is hot and water jacketed and it can be sealed to achieve a
vacuum system.
The tablets are placed in pan and the air in the pan is displaced by nitrogen
before the desired vacuum level is obtained. The coating solution is applied
by airless spray system.
 The vapours of the evaporated solvents are removed by vacuum system.
 Organic solvents can be effectively used with this coating techniques and
high environment safety is also there .
26

3) COMPRESSION COATING
Not widely used.
It has advantages in some cases in which the tablet core cannot tolerate
organic solvents or water and yet needs to be coated for taste masking, or
to provide delayed or enteric properties to the product.
In addition incompatible ingredients can be conveniently separated by
process.
This type of coating requires a specialized tablet machine .
27

4) DIP COATING
Dip coating technique can be described as a process where the substrate to
be coated is immersed in a liquid & then withdrawn with a well defined
withdrawal speed under controlled temperature & atmospheric condition.
Alternate dipping and drying steps may be repeated several times to
achieve the coating of desired one.
The process lacks the speed, versatility, and the reliability of spray coating
techniques.
28

The equipment’s used for the tablet coating are :
I. Standard coating pan
• Pellegrini pan
• The immersion sword
• Immersion tube systems
I. Perforated coating pan
- Accela-cota system
- Hi coater system
- Dria coater pan
- Glatt coater
II. Fluidized bed coater
Coating equipment's
30

I. STANDARD COATING PAN
It is also known as conventional pan
system
Circular metal pan(mounted angularly
on a stand)
8-60 inches in diameter
Rotated on its horizontal axis by a
motor
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
31

Coating solution are applied to the tablets by ladling or spraying the
material on to the rotating tablet bed.
Use of spraying systems
Produces a faster, more even distribution of the solution or suspension.
Reduces drying time between solution application in sugar coating.
Allows continuous application of the solution in film coating.
32

DRAW BACKS OF STANDARD COATING PAN
Mixing efficiency of tablets was poor.
Drying efficiency was low because much of drying took place on surface of
the tablet bed only.
Improper balance between the introduced & exhausted air increased the
chances of health hazard for the operator & risk of explosion when organic
solvents were used in coating pan.
In standard coating pan ,the drying efficiency is improved by:
Pellegrini pan
The immersion sword
Immersion tube systems 33

Pellegrini pan
Contains baffled pan
Diffuser(distributes the drying air uniformly over the tablet bed surface).
Available in the range of 10-1000kg batch.
Suitable only for sugar coating process but not for film coating due to
limitation in drying capabilities.
Limitation was overcome by installing glatt immersion sword air handling
system to improve drying efficiency.
The immersion sword
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.
34

Immersion tube systems
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
The drying air flows upward through the tablet bed and is exhausted by
conventional duct.
35

II. PERFORATED PAN SYSTEMS
In general all equipment of this type consist of a perforated or partially
perforated drum that is rotated on its horizontal axis in an enclosed housing.
The coating solution is applied to the surface of the rotating bed of tablets
through spraying nozzles, which are present inside the drum.
Perforated pan coaters are efficient drying systems with high coating
capacity.
PERFORATED PAN SYSTEM HAS
- Accela-cota system
- Hi coater system
- Dria coater pan
- Glatt coater
36

ACCELACOTA SYSTEM
Baffles/mixing blades ensure the
tablets mix freely within the
drum as it rotates.
Spray gun atomizes the coating
solution & directs it to the
tablets.
 Drying air is directed in to the
drum,
Passed through tablet bed,
Exhausted through perforations
in drum.
37

HI COATER SYSTEM
Although the design of HI-coater
systems may be different, the
working principle is similar to that
of the ACCELA-COTA.
The machine directs both the
coating solution and drying air
downwards.
The drying air, then leaves the
coating system through the
perforations below the coating
drum.
38

DRIACOATER PAN
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.
39

GLATT COATER
In there extremely short processing time.
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
Normally , the air passes through the tablet bed & leaves via exhaust duct.
Its unique design minimizes turbulence that may occur around the spray
nozzle.
This ensures an even distribution of the coating solution on the tablets.
Moreover, its drum has unique geometrical shapes with baffles on the
periphery.
This ensures an effective mixing of tablets while protecting the product
from damage at the same time.
Give accurate coating but quite expensive.
40

Coating of particles is an important unit operation
in the pharmaceutical industry.
There are numerous applications of coating,
including drug layering, modified release coating,
physical and chemical protection, aesthetic
purposes, taste masking, and enhanced
identification of drugs.
Particle coating
41

Particle coating
Wet particle
coating
Dry particle
coating
 either aqueous or non-aqueous solution.
 An innovative method to replace the wet
coating process is to directly coat fine
particles on target particles (dry particle
coating) using strong mechanical forces.
Drawbacks :WPC solution may be volatile and
toxic
 Requires post treatment & waste processing
it increase cost
 Used to create new-generation
materials by combining
different powders having
different physical and chemical
properties to form composites,
which show new functionality
or improve the characteristics
of known materials.
42

Materials with relatively large particle size (1–200 μm) form a core and
these core (host) particles are mechanically coated with fine submicron
(guest) particles; no liquid of any kind (solvents, binders or water) is
required.
In this technology, powdered coating materials are directly coated onto
solid dosage forms without using any solvent, and then heated and cured
to form a coat.
43

PARTICLE COATING TECHNIQUES:-
MICROENCAPSULATION:-
A process of applying relatively thin coating to small particles of solids,
droplets of liquids and dispersions, using various coating agents, such as
gelatin, povidone, hydroxyethyl cellulose, ethyl cellulose, bees wax,
carnauba wax and shellac.
It is a versatile & precise coating technique used to encapsulate individual
particles.
This process results in individual particles of a drug substance being
enveloped into a membrane.
The type & level of membrane applied is determined by release rate
requirements, organoleptic features & the dosage form application.
44

Microencapsulation also increases the stability of the drug. It can be
accomplished by a variety of methods, including
45

FLUIDIZED BED COATING:- (AIR SUSPENSION COATER)
In fluidized bed powder coating, heated parts are either dipped directly
into a container of fluidized powder or passed through an electrically
charged cloud of powder, which is created above a container of fluidized
powder.
Highly efficient drying system.
The airflow is controlled so that more air enters the centre column,
causing the tablets to rise in the centre.
The movement of the tablets is upward through the centre of the
chamber.
They then fall toward chamber wall & move downward to re enter the
air stream at the bottom of the chamber.
46

Coating solution are continuously applied from a spray nozzle located in
the upper region of chamber.
There are two types of system to apply a finely divided spray of coating
solution or suspension onto tablets
A. High pressure ,airless
B. Low pressure , air atomized
HIGH PRESSURE, AIR LESS: the liquid is pumped at high pressure(250-
3000psig) through a small orifice of 0.009-0.020 in each diameter in fluid
nozzle, which result in finely divided spray. The degree of atomization &
spray rate are controlled by fluid pressure, orifice size and viscosity of the
liquid.
47

LOW PRESSURE, AIR ATOMIZED SYSTEM: the liquid is pumped through a
somewhat larger orifice (0.020-0.060inch) at relatively low pressure (5-
15psig)
The lower pressure air contacts the liquid stream at the tip of the atomizer
and finely divided spray is produced.
FLUIDIZED BED COATER
48

Application technique
Application Process Examples of tablet used in
particular process
To mask the disagreeable
odor, colour or taste of
the tablet.
Sugar coating 1. Brufen – available in 200mg and
400mg strength
2. Premarin – conjugated oestrogens
625µgm and 1.25µgm.(yellow)
3. Colofac – mebeverine hcl 100mg
Round, white
Protection of active
ingredients, from the
acidic environment of the
stomach.
Enteric coating Micropirin- 75mg EC tablets
49

To control and sustain
the release of the drug
from the dosage form.
Film coating Diltiazem HCL, Ephedrine
HCL, Theophylline ,
Neomycin sulphate etc
To protect an acid-labile
drug from the gastric
environment.
Enteric coating -
50

Defects Definition Causes Remedies
Picking and
sticking
This is when the
coating removes
a piece of the
tablet from the
core.
It is caused by over-wetting the
tablets, by under-drying, or by
poor tablet quality.
A reduction in the
liquid application rate
or increase in the
drying air temp. & air
volume usually solved
this problem.
Bridging This occurs when the coating fills
in the lettering or logo on the
tablet is typically caused by
excess application of the solution,
poor design of the tablet
embossing, high coating viscosity,
high percentage of solids in the
solution, or improper atomization
Increase the plasticizer
content or changing
the plasticizer can be
decrease the
incidence of bridging.
Problem encountered
51

Chipping It is defect where
the film becomes
chipped & dented,
usually at the
edges of tablet.
high pan speed, a friable
tablet core or a coating
solution that lacks a good
plasticizer.
Be careful not to over
dry the tablets in the
preheating stage.
Erosion This can be the result of soft
tablets, an over-wetted
tablet surface, inadequate
drying, or lack of tablet
surface strength.
Be careful in drying .
Mottled
colour
In even
distribution of
colour on the
surface of tablet,
with dark or light
patches of it.
It is mainly due to different
coloration of the excipient
or the degradation product
of the tablet is coloured.
Coating solution is
prepared properly in
sufficient quantity.
52

Capping and
lamination
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.
Air entrapment ,
deep concave punch
Friability test is the
quickest way of
revealing such
problems. Or
reducing final
compression force
Roughness Involves presence of
previously dried spray
coating solution droplets
onto the core
Drying of coating
solution before
reaching the surface
of the tablet during
spraying.
Excessive pigment
concentration.
Moving the nozzle
closer enough.
Reducing the degree
of atomization.
53

Twinning This is the term for two
tablets which stick
together, and it’s a
common issue with
capsule shaped tablets.
- Changing the pan
speed and rate
Orange peel It is surface defect
resulting in the film being
rough & non glossy.
Appearance is similar to
that of an orange.
Rapid drying,
High solution
viscosity
Use mild drying
condition ,decrease
viscosity of solution.
Blistering
When coated tablets
require further drying in
ovens , too rapid
evaporation of solvent
from the coated tablets
the effect of high
temperature on the
strength and
elasticity of the film
may cause blistering.
Milder drying
conditions are
required in this
case.
54

Conclusion
 From the last three decades, coating of pharmaceutical formulations
including tablet coating have been subject of remarkable developmental
efforts aiming to ensure and enhance the final product quality.
 Improvements regarding energy consumption, film distribution, drying
efficiency and continuous processing have contributed to significantly
develop this technology with improved safety profiles.
 In future there is enormous possibility of developments in the area of
tablet coating to achieve specific benefits.
56

REFERENCES
1.Kamble N. et al. Innovations in tablet coating technology: A review.
International Journal of Applied Biology and Pharmaceutical Technology.
2011: 214-218.
2. Lachman Leon et al. The Theory and Practice of Industrial Pharmacy.
Second edition, Fourth Indian Reprint, Published by Varghese Publishing
house, Bombay. 1991: 346-372.
3. Remington’s The Science and Practice of Pharmacy. Volume-I. 21st ed.
Indian Edition, Lippincott Williams And Wilkins. 2005: 929-938.
References
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