Tablet Coating
Tablet Coating
Tablet Coating
Disadvantages:
✓ Time consuming process.
✓ Logo or break lines not possible.
✓ 30-50% weight increase due to coating material.
Sugar coating process involves following steps:
✓ Sealing
✓ Subcoating
✓ Smoothing
✓ Colouring
✓ Polishing
✓ Printing
Sealing:
✓Application of one or more coats of water impermeable polymer
such as shellac, cellulose acetate phthalate and polyvinyl acetate
phthalate.
✓The main purpose of sealing is to prevent the penetration of moisture
in to the tablet core.
✓The lengthening of tablet disintegration and dissolution times may
occur with the usage of shellac as a sealant due to polymerization of
shellac.
Subcoating:
✓ By adding bulking agents such calcium carbonate or talc in
combination with sucrose solution.
✓ Used in order to round of the tablet edges.
✓ It tyically increases the tablet weight by 20%
Smoothing:
✓By the application of the thick sucrose syrup, it removes the rough
surfaces formed during the sub coating.
Colouring:
✓It usually consists of thin sucrose syrup containing the requisite
coloring material (water soluble dyes or water insoluble pigments)
✓Water insoluble pigments along with the opacifier such as titanium
dioxide develop desired colour more rapidly, thus resulting in thinner
color coat.
Polishing:
After coloring step, the tablet surfaces are smooth but with
dull appearance, to achieve glossy finish, waxes are used.
Ex: Bees wax, Carnauba wax.
Printing:
For sugar coated tablets, edible ink is used for printing
different identification marks such as manufacturer logo, product
name, dosage strength etc.
2. FILM COATING:
It involves spraying a solution of polymer along with the
plasticizer and pigments on a rotated, mixed tablet bed forms a thin
uniform film on the tablet surface.
continuous film
Mechanism of film formation:
In the wet state, the polymer is present as a no. of discrete particles,
and these have to come together in close contact, deform, coalesce
and ultimately fuse together to form a discrete film. During
processing, the substrate surface will be wetted with the diluted
dispersion. Under the prevailing processing conditions, water will
be lost as water vapour and the polymer particles will increase in
proximity to each other, a process which is greatly assisted by the
capillary action of the film of water surrounding the particles.
Complete coalescence occurs when the adjacent particles are able to
mutually diffuse into one another.
Film forming ingredients:
✓ Polymers
✓ Plasticizers
✓ Colorants
✓ Solvents
✓ Opacifier
Polymers:
A film former is capable of producing smooth thin films
reproducible under the prescribed coating conditions.
Plasticizers:
Affords flexibility and elasticity to the coat and thus
provide durability.
Internal plasticizer:
Chemical modification of the polymer alters;
Degree of substitution
Type of substitution
External plasticizer:
They are non-volatile or other polymers, which when
combine with the primary polymeric film former alters;
Flexibility
Tensile strength
Adhesion properties of resulting film
Colorants:
These provide an elegant appearance. They may be soluble
in the solvent systems or suspended as insoluble powders.
Ex: Iron oxide pigment, Titanium dioxide.
Opaquant –extenders:
These are fine inorganic powders used in coating solution
formulation to increase film coverage.
Process: Process:
✓ Can be automated. ✓ Difficult to be automated.
e.g. Accela Cota e.g. Traditional coating pan
✓ Easy training operation ✓ Considerable training operation
✓ Single stage process required.
✓Easily adaptable for ✓ Multistage process.
controlled release allows for ✓Not able to be used for
functional coatings. controlled release apart from
enteric coating.
3. ENTERIC COATING:
The technique involved in enteric coating is protection of
the tablet core from disintegration in the acidic environment of the
stomach by employing pH sensitive polymer, which swell or
solubilize in response to an increase in pH to release the drug.
Aim:
✓ To mask taste or odour.
✓ Protection from local irritation of the stomach mucosa.
✓ Release of active ingredient in specific target site.
✓ Protection of active ingredients from acidic environment of the
stomach.
Enteric Coating
Examples of Enteric coated products:
Pellegrini pan
Immersion sword systems
Immersion tube systems
Conventional pans
Immersion-
tube system
Immersion
sword system
Pellegrini
pan system
Pellegrini pan:
The side walls of this pan are shaped with a pronounced
taper, which increases the efficiency of particle movement by
forcing the cores into an additional lateral movement. This results
in a composite core movement yielding improved exposure of the
core to the coating material.
Immersion Sword System:
• With the immersion sword system, drying air is introduced
through a perforated metal sword device that is immersed in the
tablet bed.
• The drying air flows upward from the sword through the bed.
Since the air is more intimately mixed with the wetted tablets, a
more efficient drying environment is provided.
.
Immersion Tube System
• In this type of system, the immersed tube delivers the heated air
and a spray nozzle is built in the tip of the tube. During this
operation , the coating solution is applied simultaneously with the
heated air from the immersed tube.
• The drying air flows upward through the tablet bed and is
exhausted by a conventional duct.
2. PERFORATED PAN COATING:
It consists of a perforated drum that is rotated on its
horizontal axis in an enclosed housing.
In 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.
Cracking:
This occurs if internal stresses in the
film exceeds the tensile strength of the film.
The tensile strength of the film can be
increased by using high molecular weight
polymers or polymer blends.
Roughness:
This is observed when coating is applied by
spray. Some of the tablets 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.
2. Laminated coating
4. Electrostatic coating
1. Dip coating:
➢ In this, cores to be coated are held in a suitable device. eg:
Baskets.
In Technology:
✓ To reduce the influence of moisture.
✓ To avoid dust formation.
✓ To improve drug stability.
✓ To prolong shelf-life.
✓To reduce friction and increase the production rate in high speed
packaging systems.
In Marketing:
✓ Improve product identity.
✓ Improve appearance and acceptability.
CONCLUSION