2. DEFINITION
• Tablet coating is the application of a coating
composition to a moving bed of tablets with
the concurrent use of heated air to facilitate
the evaporation of solvents
3. OBJECTIVES OF COATING
1. To mask the taste, odor, or color of the drug
2. To provide physical and chemical protection for
the drug.
3. To control the release of drug from the tablet.
4. To protect the drug from gastric environment of
the stomach with an acid resistant enteric
coating.
5. To incorporate another drug or formula adjuvant
in the coating.
4. Contd..
6. To avoid chemical incompatibilities or to
provide sequential drug release.
7. To improve the pharmaceutical elegance by
use of special colors and contrast printing.
5. PRIMARY COMPONENTS IN
COATING
1. Tablet properties
2. Coating process
Coating equipment
Parameters of coating process
3. Coating compositions
6. 1. TABLET PROPERTIES
• Tablets that are to be coated should possess
specific physical characteristics.
• In coating process tablets roll in a coating pan or
cascade in the air stream of air suspension coater
so, the tablets must be resistant of abrasion and
chipping.
• Tablet surfaces that are brittle , or soften in the
presence of heat or that are effected by coating
composition tend to become rough and are
unacceptable for film coating
7. Tablet properties contd..
• Quality of the starting tablet is also important
as surface imperfections are not eliminated by
film coating. On contrast sugar coating with
high solid content fills many minor surface
imperfections.
• Shape is also important
good- sphere
bad - square flat faced
8. Tablet properties contd..
• A tablet formulation utilizes many additives,
which result in hydrophobic surface.
• For the coating to adhere to the tablet, the
coating composition must wet the tablet surface.
• Hydrophobic tablet surfaces are difficult to coat
with aqueous-based coatings that do not wet the
surface and require the addition of surfactants to
decrease the surface tension of the coating
composition
9. EQUIPMENT
• Most coating process use one of three general
types of equipment.
1. Standard coating pan
2. Perforated coating pan
3. Fluidized bed (air suspension coater)
11. 1. STANDARD COATING PAN
• It consists of a circular metal pan mounted
somewhat angularly on a stand.
• The pan is 8 to 60 inches in diameter and is
rotated on its horizontal axis by a motor.
• Heated air is directed into the pan, and onto the
tablet bed surface, and is exhausted by means of
ducts positioned through the front of the pan.
• Coating solutions are applied to the tablets by
ladling or spraying onto the rotating tablet bed.
12. Standard coating pan contd..
• Improvements of coating pan
a. Pellegrini pan
b. immersion sword
c. immersion tube systems
13. • Pellegrini pan utilizes a baffled pan and a air
diffuser for uniform distribution of dry air.
• In the immersion sword system drying air is
introduced through a perforated metal sword
device that is immersed in tablet bed.
• In the immersion tube system, a tube is
immersed in the tablet bed. The tube delivers
heated air, and a spray nozzle is built in the tip
of the tube.
• During the operation, the coating solution is
applied simultaneously with the heated air
from the immersed tube.
19. 2. PERFORATED COATING PAN
• 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.
• Modifications
a. Accela-cota
b. Hi-coater
c. Dria-coater
20. • In the accela cota and hi coater systems,
drying air is directed into the drum, is passed
through the tablet bed, and is exhausted
through perforations in the drum.
• The dria coater introduces drying air through
hollow perforated ribs located on the inside
periphery of the drum. As the coating pan
rotates, the ribs dip into the tablet bed, and
drying air passes through and fluidizes the
tablet bed. Exhaust is from the back of the
pan
25. 3. FLUIDIZED BED COATER
• Fluidized bed coaters are highly efficient coating and
drying systems.
• Fluidization of tablet mass is achieved in a columnar
chamber by the upward flow of drying air.
• The air flow is controlled to enter at the center causing
the tablets to raise in the center.
• They then fall toward the chamber wall and move
down ward to re-enter the air stream at the botom of
the chamber
• In some units a small column is used to direct the flow
of the tablets.
26.
27.
28.
29. Parameters of coating process
• In a continuous coating operation, the coating
operation is essentially maintained at equilibrium,
where the rate of application of coating composition
equals the rate of evaporation of the volatile solvents.
• Air capacity: This value indicates the quantity of water
or solvent that can be removed during the coating
process, which depends on the quantity of air flowing
through the tablet bed (CFM), the temperature of the
air (T), and the quantity of water the inlet air
contains(H).
30. Parameters contd..
• Coating composition: if tablet surfaces are
permeable to the coating solvent, rapid
removal of solvent is necessary to prevent the
integrity damage of the tablet.
• Viscous coating solutions require longer drying
period. Thin, rapidly drying solutions dry
quickly on the tablet surface, allowing
constant application by efficient atomization
of coating solution.
31. Parameters contd..
• Tablet surface area: The total surface area per
unit weight decreases significantly from
smaller to larger tablets. i.e larger tablets
require less coating solution when compared
to smaller tablets.
• Coating efficiency: value obtained by dividing
the net increase in coated tablet weight by the
non volatile coating weight applied to the
tablets. Ideally 90-95% of the applied film
coating should be on the tablet surface.
32. SUGAR COATING
• The basic sugar coating process involves the
following steps:
1. Sealing
2. Sub-coating
3. Syruping (smoothing)
4. Finishing
5. Polishing
33.
34. 1. Seal coating:
-To prevent moisture penetration into tablet
core seal coat is applied.
-Without a seal coat over wetted tablets would
absorb excess moisture, leading to softening
or disintegration and effecting the physical &
chemical stability.
-Shellac is an effective sealant, but
disintegration time lengthens on aging.
-Zein is a alcohol soluble protein derivative from
corn and is a efficient sealant.
35. 2. Sub-coating
-it is applied to round the edges of tablet and to
build up the size.
-Sugar coating can increase the tablet weight by
50 to 100%
-The step consists of alternatively applying a
sticky binder solution followed by dusting of
sub coating powders & then drying.
-The process is continued till the tablet attains a
desired thickness.
36. 3. Syruping (smoothing):
-This step is done to cover& fill the imperfections
in surface of tablet caused by sub coating step,
and to impart the desired color to the tablet.
-The first syrup coat contain some suspended
powders and are called grossing syrups.
-Color is not added till the tablets attain a smooth
surface. In subsequent syruping steps, syrup
solutions containing the dye are applied until
the final size and color are achieved.
-In the final syrup coating a clear coat is applied.
37. 4. Finishing and polishing:
-The desired luster is obtained in the final step
of the sugar coating process.
-The tablets can be polished in clean standard
coating pans or canvas lined polishing pans.
-By carefully applying powdered wax or warm
solutions of these waxes in naptha or other
solvents.
38.
39. Film coating
• More or less sugar coating and film coating contains same
equipments and processes
Pan-pour methods:
• Traditionally, it is the most used method for film coating.
• Coating compositions used earlier were too viscous to be
sprayed effectively.
• Tablets coated by pan pour methods are subjected to
alternate solution application, mixing and drying similar to
sugar coating.
• Aqueous coating solutions are not suitable due to various
problems like surface erosion and altered stability of the
product.
40. Pan-spray method: introduction of spraying
equipment revolutionized the process of
tablet coating.
• Spraying lends versatility and automation of
the process.
• Broad, flat spray patterns may be selected as
per the need.
41.
42. Process variables
• In the coating process, certain elements need
to be controlled to ensure consistent product
quality.
43. • The variables to be controlled in pan-spray film coating
processes are
1. Pan variables
pan design/ baffling
speed
pan load
2. Process Air
air quality
temperature
air flow rate/volume
3. Spray variables
spray rate
degree of atomization
spray pattern
nozzle-to-bed ratio
44. Pan variables
• Pan shape, baffling, rotational speed, loading all
effect the mixing of tablets.
• Uniform mixing is essential for depositing same
quantity of film on each tablet.
• Unacceptable color uniformity may occur due to
poor tablet movement.
• Tablet shape can also affect mixing. Some tablet
shapes allow free mixing while others require baffles.
• Baffles are reason for chipping and are to their
design is to be carefully selected.
45. • Low pan speed causes localized over wetting
and results in sticking problem.
• Too high speeds may not allow enough time
for drying.
• Pan speed of 10 to 15 rpm are commonly
used.
Pan variables contd..
46. Spray variables
• The variables to be controlled are
rate of liquid application
spray pattern
degree of atomization
These three are interdependent variables.
• The proper rate at which coating solution should be
applied depends on mixing and drying efficiency of
the system.
• A band of spray should be spread evenly over tablet
mass. In larger pans, more nozzles are to be used to
cover the tablet bed width.
47. • A spray pattern that is too wide results in application
of coating to pan.
• A spray pattern that is too narrow results in localized
over wetting.
• Atomization is the process by which liquid stream is
finely divided into droplets.
• Adjustment of fluid pressure or air pressure can give
the desired results.
• Higher the pressure greater is the atomization.
• Too fine droplets may cause “spray-drying” problem
Spray variables contd..
48. Process air variables
• The temperature, volume, rate, quality and balance
are parameters of the process air that need to be
controlled to obtain an optimum drying environment.
• The sensitivity of film former and drug core to heat
determines the upper temperature at which coating
process is successful.
• Capacity of air handling system determines the air
volume and rate.
• Supply air should have some degree of
dehumidification to avoid seasonal fluctuations and
adverse effect on quality of tablet coating.
49. FILM DEFECTS
Problem
name
Reason / Problem solution
Sticking &
picking
Over wetting or excessive film
tackiness resulting in picked
appearance after drying
•Reduction in liquid application rate
•Increase in drying temp.
•Increase in air volume.
•Modifying formulation
Roughness Rapid drying of spray solution
before reaching tablet bed,
resulting in deposition of spray
dried particles on tablets.
•Moving nozzle closer to tablet bed
•Reducing degree of atomization
•Decreasing pigment and polymer
concentration in solution
Orange-peel Inadequate spreading of coating
solution before drying
•Decrease the drying rate
•Decreasing the high solution viscosity
Bridging Shrinking of film from sharp
corners resulting in bridging
•Increase or modify the plasticizer
Filling Too much solution filling bisects
and monograms
•Altering fluid application rate
•Thorough mixing of tablets
50. Problem
name
Reason / Problem solution
Blistering Too rapid evaporation of solvent
from core & high temperatures
in drying ovens resulting in
altered strength and elasticity of
film
• Mild drying conditions
Hazing •High processing temperature
•Cellulose polymers
•High humidity leading to partial
solvation of film
•Decrease the temperature
•Change the polymer
•Control the humidity
Color variation •Improper mixing
•Uneven spray pattern
•Migration of soluble dyes
•Modify the mixing pattern
•Change the spray pattern
•Use lake dyes
Cracking If internal stresses exceed the
tensile strength of film
Tensile strength of film can be
increased by using high molecular
weight polymers
51.
52.
53. COATED TABLETS EVALUATION
• Adhesion test:
This test is done with tensile strength testers and it measures the
force required to peel the film from the tablet surface.
• Diametrical crushing strength or hardness:
The relative increase in tablet crushing strength provided by the
film is measured
• Disintegration or dissolution:
Unless the coating is intended to control the release of drug , it
should have minimal effect.
• Stability studies: To determine if temperature and humidity
changes will cause film defects
54. Polymers used in film coating
Film formers
Non enteric Enteric
1. HPMC
2. MHEC
3. EC
4. HPC
5. POVIDONE
6. SOD.CMC
7. PEG
8. ACRYLATE
POLYMERS
1.CAP
2.ACRYLATE
POLYMERS
3.HPMCP
4.PVAP
55. • HPMC- Hydroxy propyl methyl cellulose
-wide range of solubility.
-noninterference with tablet properties.
-flexible, chip resistance.
-absence of taste, odour, color.
-stable in heat, light, air & moisture.
-ability to incorporate color & additives.
-requires plasticizer for avoiding bridging
and filling problems.
56. • MHEC- Methyl hydroxy ethyl cellulose
- Soluble in fewer organic solvents.
• EC- Ethyl cellulose
- This is completely insoluble in water and gi
fluids.
- Combined with water soluble polymers in
preparing S.R coatings.
- Soluble in organic solvents.
- Non-toxic, colorless, odorless, tasteless
57. • HPC-Hydroxy propyl cellulose
- Solubilty in all solvents below 40⁰ C.
- Extremely tacky.
- Yields very flexible films.
- Used in combination to improve film properties
• Povidone
-four grades K-15, K-30, K-60, K-90.
-Indication of Mol.Wt 10,000,
40,000,
160,000,
360,000.
58. -used as tablet binder and in tablet coating.
-excellent solubility in wide variety of solvents.
-povidone films are clear, glossy and hard.
• Sodium carboxy methyl cellulose
-easily dispersed in water to form colloidol soln.
-insoluble in most organic solvents.
-films are brittle and require plasticizers
59. • PEG-Polyethylene glycol
-mol.wt 200-600 occur as liquids
-mol.wt 900-8000 occur as waxy solids
- Used In combination to modify film proprties
- Coats are sensitive to elevated temperature
• Acrylate polymers
-Eudragit- RL , RS produce films for delayed
action.
- Cationic polymer dimethyl aminoethyl
metacrylate.
60. • ENTERIC COATING MATERIALS
- To protect acid liable drugs - enzymes
- To prevent gastric distress - sodium salicylate
- To deliver drugs for local action –intestinal antiseptics
- To provide delayed release
• CAP-Cellulose acetate phthalate
-films are brittle.
-dissolves above pH 6
61. • Acrylate polymers
- Eudragit L & S soluble in pH 6 and 7
• HPMCP-Hydroxy propyl methyl cellulose
phthalate
-These polymers dissolve at low pH at 5
-used for general enteric preparations
-Higher bio-availabilty than CAP
62. • SOLVENTS
- The primary function of a solvent system is to
dissolve or disperse the polymers or other
additives and convey them to the substrate
surface.
- Ex: water, ethanol, methanol, isopropanol,
chloroform, acetone, methylethyl ketone and
methylene chloride.
- Because of environmental and economic
considerations water is the solvent of choice.
- Several polymers cannot be applied from
aqueous systems.
63. • PLASTICIZERS
- The quality of film can be modified by using
internal or external plasticizer.
- Internal plasticizer means chemical
modification of the basic polymer.
- External plasticizer can be a non volatile liquid
or another polymerwhich can be incorporated
with the primary polymeric film former
- Ex: castor oil, propylene glycol, glycerin, peg-
200, Tweens and spans.
64. • COLORANTS
-They may be soluble in the solvent system or
suspended as insoluble powders.
-Used to provide distinctive color and elegance
to the dosage form.
-To achieve proper distribution of suspended
colorants in the coating solutions requires the
use of fine powdered colorants < 10 microns.
-The most common colorants in use are certified
Food Drug and cosmetic (FD&C) or Drug and
Cosmetic (D&C) colorants.
- They are synthetic lakes or dyes.
