Coating technology

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• PRESENTD BY :-
• PATIL PRANJAY SADASHIV.
• FIRST YEAR M.PHARM.
• DEPARTMENT OF QUALITY ASSURANCE.
H. R. Patel Institute of Pharmaceutical Education
and Research, Shirpur
COATING TECHNOLOGY

2. Content-
 Coating principle
 Coating process
 Equipment
 Particle coating
 Fluidized bed coating
 Application technique
 Problem encountered
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3. Coating technology Coating principle
1. To mask the taste.
2. To mask the odor, color of the drug.
3. To provide physical and chemical protection for the drug.
4. To control the release of the drug from tablet.
5. To protect the drug from gastric environment.
 Coating process
Coating is the application of a coating composition to a moving bed of
tablet with the concurrent use of heated air to felicitate evaporation of solvent.
There are two type of coating process-
1. Sugar coating
2. Film coating 3

4. Sugar coating
It involve following steps-
1. Sealing
2. Sub coating
3. Syruping(smoothing)
4. Color coating
5. Polishing
6. Printing
Sealing:
Objective
1. To prevent moisture penetration into the tablet core, a seal coat is applied.
2. To strengthen the tablet core.
3. Without a seal coat, the over wetted tablets would absorb excess moisture.
Leading to tablet softening, and may affect the physical and chemical stability.
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5. Sub-coating :
Objective
1. Sub coating is applied to round the edges and build up the tablet size.
2. Sugar coating can increase the weight by 50-100% at this step.
The sub-coating step consist of alternatively applying a sticky binder solution to
the tablet followed by dusting of powder and then drying.
Smoothing:
Objective
1. To cover and fill in the imperfections in the tablet surface caused by sub-coating
step.
2. To impart desired color to the tablet.
Color coating:
Objective
To impart an elegant and uniform color.
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6. Polishing:
Objective
1. To produce desired luster on the surface of the tablet.
2. Tablet can be polished in standard coating pan.
Printing:
In order, to identify sugar coated tablet often it is necessary to print them,
Using pharmaceutical grade ink.
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7. Film coating
 Film coating adds 2-5%to the tablet weight.
 Film coating is done by the following methods.
1. Pan-pour method
2. Pan spray method
1) Pan-pour method:
1. Viscous coating materials are directly added from some container into the
rotating pan moving with the tablet bed.
2. Tablet are subjected to alternate solution application, mixing and then drying.
Disadvantage-
1. The method is relatively slow.
2. It relies heavily on the skill of the operator.
3. Tablet require additional drying to remove the solvent.
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8. 2) Pan-spray method:
Coating material is sprayed over the tablet bed from nozzles and hot air is
passed through the tablet bed to dry it.
The variables to be controlled is pan-spray film coating process are:
a) Pan variable:
Uniform mixing is essential to deposit the same quantity of film on each tablet.
Pan design: some tablet shapes mixes freely while other shapes may require
a specific baffling arrangement to ensure adequate mixing.
Disadvantage-
Baffles may produce chipping if not selected properly.
b) Pan speed:
Pan speed affects mixing.
Optimum speed: 10-15 rpm for nonaqueous film coating.
3-10 rpm for aqueous film coating.
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9. c) Spray variable:
1. Rate of liquid application
2. Spray pattern
3. Degree of atomization
These are interdependent.
d) Process air variable:
The variable are required for optimum drying of the coating by evaporation
of solvent.
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10. Equipment
Most coating process use one of three type of equipment:
1. Standard coating pan
2. Perforated coating pan
3. Fluidized bed coater
Standard coating pan
 It consist of circular metal pan mounted on a stand.
 The pan is 8-60 inch in diameter and rotated on its horizontal axis by
motor.
 Heated air is directed into the pan and on to the tablet bed surfaces and it
exhausted by means of dusts positioned in front of the pan.
 The coated solution are applied by spraying the material on to the rotating
tablet bed.
 Use of atomizing system to spray the liquid.
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11. Perforated coating pan
 It consist of perforated drum that is rotated on its horizontal axis in an
enclosing housing.
 In the acceclo-cota and hi-coater system, the drying air is directed in to the
drum, is passed through the tablet bed and is pass through perforation in the
drum.
 The hi-coater introduces drying air through hollow perforated ribs located
on the inside periphery of the drum.
 As the coating pan is rotates the ribs dip into the tablet bed and the drying
air is passes up through and fluidizes the tablet bed.
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12. Fludized bed coating
 It is highly efficient system.
 Fluidization of the tablet mass is achieved in a columnar chamber by the
upward flow of drying air.
 The airflow is controlled so that more air enters the centre of the column,
causing the tablet to rise in the centre.
 The movement of the tablet is upward through the centre of the chamber.
 They then fall toward the chamber wall and downward to reenter the air
stream at the bottom of the chamber.
 Coating solution is applied from the spray nozzle located at the bottom of
the chamber.
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13. Particle coating
 Particle coating to alter the surface properties.
 When the thin layer of a substance is places around a core particle it is
called coating of particle.
 Rational of particle coating
1. To modify drug release profile.
2. Improve appearance.
3. Facilitate identification.
4. Mask taste and odor.
5. Protect from external environment.
6. Obtain easier product handling.
 Type of particle coating
1. Wet particle coating
2. Dry particle coating
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14. 1) Wet particle coating:
This technique used commercially to coat the solid dosage form.
Generally mixture of polymers, pigments and excipients is dissolved in an
appropriate organic solvent (for water insoluble polymers) or water (water
soluble polymers) to form a solution, or dispersed in water to form dispersion,
and sprayed onto the dosage forms and dried by continuously providing heat
until a dry and smooth film coating film is formed. WPC solution may be
volatile and toxic which needs consideration. Apart from that it requires post
treatment and waste processing which subsequently increase the cost.
Wet particle coating techniques
 Microencapsulation-Microencapsulation is a versatile and very precise coating
technique used to encapsulate individual drug particles. This technique
efficiently and uniformly coats drug particles with polymeric membranes of
varying degrees of porosity using coacervation/phase separation processes.
The size range (2 to 2000 μm approximately) distinguishes them from the
smaller nanoparticles or nanocapsules.
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The most commonly employed mechanical methods for the preparation of
microcapsules and microspheres are;
(1) Multiorifice-centrifugal process,
(2) Air suspension coating (wurster),
(3) Vacuum coating,
(4) Spray drying,
(5) Spray congealing,
(6) Pan coating,
(7) Rotary fluidized bed granulator, and
(8) Spheronization.

16. Coacervation– Phase separation process
This process consists of three steps that are carried out under continues agitation:
(i) Formation of three immiscible chemical phases
(ii) Deposition of the coating
(iii) Rigidization of the coating
 Coacervation: Phase separation process applicable for solids and liquids with particle
size ranges from 2- 5000 μ.
Step I: Formation of three immiscible chemical phases
 It involves three immiscible chemical phases which are
(i) Liquid manufacturing vehicle phase
(ii) Core material phase and
(iii) Coating material phase.
Step II: Deposition of the coating
This process consists of depositing the liquid polymer coating upon the core
material accomplished by controlled physical mixing of the coating material
and the core material in the manufacturing vehicle. Deposition of the liquid
polymer coating around the core material occurs if the polymer is adsorb at the
interface formed between the core material and the liquid vehicle phase. This
adsorption phenomenon results in effective coating.
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17. Step III: Rigidization of the coating
Rigidization of coating is done by thermal, cross- linking or desolvation
techniques to form self-sustaining microcapsules.
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Figure 1: Schematic representation of the coacervation process.
a) Core material dispersion in solution of shell polymer;
b) Separation of coacervate from solution;
c) Coating of core material by microdroplets of coacervate;
d) Coalescence of coacervate to form Microcapsules

18. Spray drying and spray congealing:
 Spray drying and spray congealing processes are similar, both involves the
dispersion of core material in a liquefied coating substance and spraying or
introducing the core coating mixture into some environmental condition,
whereby relatively rapid solidification of the coating is affected. Both
processes are applicable for solids and liquids. Particle size ranges from 5 to
600 μ.
Spray drying:
 In this method involves the dispersion of core material into coating solution
(core material must be insoluble in coating solution). Then spraying the mixture
as atomized spray into air stream. The air is usually heated, which provides the
latent heat of vaporization required to remove the solvent from the coating
material, resulting in the formation of microencapsulated product.
Spray congealing:
 General process and conditions are same as spray drying except that the core
material is dispersed into a coating solution melts rather than a coating solution.
Microencapsulation is accomplished by spraying the hot mixture into a cool air
stream.
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19. Pan coating
 The microencapsulation of relatively large particles by pan coating method has
become wide spread in the pharmaceutical industry. Solid particles greater than
600 in size are generally considered essential for effective coating. The coating is
applied as a solution or as an atomized spray to the desired solid core passed over
the coated materials during coatings is being applied in the coating pans.19

20. 2) Dry particle coating
Dry particle coating is 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. 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.
Multi orifice centrifugation
The liquid material to be coated is extruded through the nozzle of the inner
tube into the coating fluid contained in the outer tube. Initially, the fluid
extrudes as a rod surrounded by the coating fluid, but the rod ultimately
breaks up into droplets, which are then immersed, in the coating fluid. As the
extruded droplets pass through the nozzle orifice of the outer tube, the coating
fluid forms a surface coat, which encases the extruded particle.
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Dry particle coating involves mechanically fixing fine particles (guests) onto
the surface of relatively larger particles (hosts).

22. Dry Particle coating techniques
a) Supercritical fluid coating
b) Vapor coating of powders
c) Electrostatic fluidized bed coating
d) Rotating (Centrifugal) fluidized bed granulator/coater
e) Hot melt coating
a) Hot melt coating:
 A hot-melt coating material, as its name implies, is applied in its molten
state over the substrate and then solidified upon cooling. Generally,
materials with molten viscosities less than 300 centipoise and melting
points less than 80°C.
b) Supercritical fluid coating:
 Carbon dioxide is an ideal supercritical medium for pharmaceutical
purposes due to its relatively low critical temperature (31.1°C) and critical
pressure (72 bar). For a successful coating, the supercritical fluid ideally
dissolves only the coating material, leaving the core completely
undissolved.
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23. c) Vapor coating of powders:
 A liquid or powder material can be dispersed by the application of
electrostatic fields.
d) Electrostatic fluidized bed coating:
 In such systems, the powder material which is essentially 100% solids is
kept fluidized in a bed by dry air passing through a porous base plate. The
powder particles are charged either by means of an electrode in the fluid
bed beneath the surface of the fluidizing powder or by charge transfer from
the pre-ionized air.
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24. 24Rotating fluidized bed coater/granulator
e) Rotating (Centrifugal) fluidized bed granulator/coater
It consists of a chamber and a porous cylindrical air distributor made of stainless
sintered mesh. The horizontal cylinder (air distributor) rotates around its axis of
symmetry inside the chamber. There is a stationary concentric cylindrical metal
filter inside the air distributor to retain any elutriated fine powder. A binary spray
nozzle mounted on the metal filter sprays mist of coating material into the
powder bed. A pulse air-jet nozzle is also placed inside the metal filter, which
cleans the surface of the metal filter in order to prevent it from clogging.

25. f) Spheronization
 Melt-able materials are utilized for coating in such processes with a core up
to 0.5 mm in diameter. It is more suitable for smooth continuous coating
with improved flow properties. The particles are rapidly passed through an
intensely heated area; the outside material melts, flows, and, as it cools,
forms a smooth surface. If there are small melt-able particles on the outside
of the core material, these will melt and flow to provide a better coating. If
the core is thermoplastic, it softens and allows the coating particles to
become more strongly adhered.
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26. Application technique:
1. Roller coating
2. Flow coating.
3. Spray painting.
4. Electrode position.
5. Plural component systems.
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27. Problem encountered
 Sticking and picking:
Excessive film thickness causes tablet to stick to each other.
Remedy-Reduction in the liquid application rate or
Increase in the drying air temperature.
 Orange peel effect:
In adequate spreading of coating solution before drying causes orange
peel effect.
Remedy-Thinning the polymer solution with additional solvent.
 Bridging and filing:
During drying, the film may shrink and pull away from the sharp
corners called bridging.
Remedy- Increase the plasticizer content.
Or change the plasticizer.
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28. Remedy-Milder drying conditions are adopted.
 Blooming:
It can occur when too high a processing temperature is used for
particular formulation.
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 Color variation:
Improper mixing, uneven spray pattern.
Insufficient coating may result in color variation.
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 Blistering:
When coated tablet require further drying
in oven to rapid evaporation
of solvent from the core.

29. Reference
 Lachman L, Libermen H.A, Kanig J. The Theory and practice of industrial
pharmacy, third edition varghees publisher; page no. 346-374.
 Banker GS . Film coating theory and practice. J pharm Sci 1996;55:81-9.
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