Tablets aqeuos film coating

Seminar on
Department of pharmaceutics
University College Of Pharmaceutical Sciences,
Kakatiya university,warangal-500609.
Film formation mechanism
 Film formers
 Plasticizers and colours
IT is the application of coating
composition on to the moving bed of tablets with
concurrent use of heated air to facilitate
evaporation of the solvent.
Water Soluble Polymers
Water-soluble coating materials dissolve completely in the gastrointestinal tract and
do not modify the drug release characteristics of the dosage. These polymers are applied
as aqueous solutions.
Hydroxypropyl methylcellulose (HPMC)
Methylcellulose (MC)
Hydroxypropyl cellulose (HPC)
Polyvinylpyrrolidone (PVP)
Food starch (modified)
Hydroxypropyl methylcellulose
• Solubility characteristics of the polymer in gastrointestinal fluid, and in organic
and aqueous solvent systems.
• Noninterference with tablet disintegration and drug availability.
• Flexibility, chip resistance, and absence of taste or odor.
• Stability in the presence of heat, light, air, or reasonable levels of moisture.
• Ability to incorporate color and other additives into the film without difficulty.
The interaction of polymer with colorants is rare.
• It forms a transparent, tough and flexible film that protects fragile tablets, masks
the unpleasant taste of a drug and improves the appearance.
Sustained Release:
• Ethyl cellulose (EC)
• Methacrylic acid copolymers ( Eudragit types)
Enteric Release:
• Cellulose acetate phthalate (CAP)
• Hydroxypropyl methylcellulose phthalate (HPMCP)
• Polyvinyl acetate phthalate (PVAP)
Ethyl cellulose
• This material is completely insoluble in water and
gastrointestinal fluids.
• A combination of ethyl cellulose with water soluble
additives has been widely used in preparing
sustained release coatings of fine particles.
Effect of polymer molecular weight on coating properties
Effect of increasing polymer molecular weight
Tensile strength
Elastic modulus
Film adhesion
Solution viscosity
Significantly increases.
• Film coatings prepared from pure polymers tend to be brittle and crack upon
drying. The addition of plasticizers to the coating liquid decreases the
intermolecular forces along the polymer chains by relieving molecular rigidity.
• The plasticizer improves the flexibility and reduces the brittleness of the film
coating and makes it more resistant to mechanical stress during the coating
Polyethylene glycol (PEG)
Propylene glycol (PG)
Tributyl citrate (TBC)
Acetylated monoglyceride (AMG)
Castor oil
Effects of Plasticizers on the properties of film coatings
Effect of increasing plasticizer concentration
Tensile strength
Elastic modulus
Film adhesion
May be increased, but results often variable.
Solution viscosity
Increased, and magnitude of effect dependent on
molecular weight of plasticizer.
Film permeability
can be increased or decreased, depending on chemical
nature of plasticizer.
Glass-transition temperature
Decreased, but magnitude of effect dependent on
compatibility with polymer.
Primarily used for tablet identification.
• Aluminum lakes
• Iron oxides or natural colours such as riboflavin and
Effects of Pigments on the properties of film coatings
Effect of increasing pigment concentration
Tensile strength
Elastic modulus
Film adhesion
Little effect.
Solution viscosity
Increases, but not substantially.
Film permeability
Decreases, unless critical pigment volume concentration
is exceeded.
Formation of films from aqueous polymeric dispersions
This requires the coalescence of polymer particles into a continuous film.
This process involves:
• Rapid evaporation of water, causing the particles of dispersed polymer to be brought
into close contact with one polymer.
• Development of pressures (associated with capillary forces within the structure) that
overcome repulsive forces between particles and cause deformation of the polymer
• Gradual coalescence of the polymer particles as a result of viscous flow and movement
of polymer molecules across the interfaces between particles.
Aqueous polymeric dispersions must be processed at temperatures in excess of the
glass-transition temperature of the polymer.
Aqueous Film Coating
Film Coating Composition
Film-forming polymer
Process Parameters
Many quality aspects of the final coated product are greatly
influenced by the combined effect of process parameter values
used in aqueous film coating.
• Coating process parameters affect the spreading, penetration
and drying (i.e. evaporation of water) of the coating liquid on
the tablet surface and, subsequently, the surface roughness
and the residual moisture of the coated tablets.
Process Parameters
Spraying air pressure:
The spraying air pressure disperse the coating liquid into droplets and effects
the droplet size distribution and droplet spreading and penetration on the tablet
The formation of adequate and adhesive film coat, the atomized droplets have
to spread completely over the surface of the tablet.
Increasing the spraying air pressure decreases the surface roughness of coated
tablets and produces denser and thinner films.
If spraying air pressure is excessive the spray loss is great. The formed droplets
are very fine and could spray dry before reaching the tablet bed, resulting in
inadequate droplet spreading and coalescence.
Spraying air pressure is insufficient, the film thickness and thickness variation
greater possibly due to change in film density and smaller spray loss.
Flow rate of coating solution
• Successful aqueous coating process, the flow rate of the coating liquid is
equal to the rate of water evaporation from the coated tablet surface.
• Increasing the flow rate allows greater number of droplets to be spread on
to the tablet bed per time and increases droplet size.
• The flow rate is important parameter since it impacts the moisture
content and the quality and uniformity of the film.
• Low coating liquid flow rate causes incomplete coalescence of polymer
due to insufficient wetting, which result in brittle films.
• High coating liquid flow rate may result in over wetting of the tablet surface
and subsequent problems such as picking and sticking.
Pan air temperature
• The
pan air temperature effects drying efficiency of the
coating pan and
the uniformity of the coatings.
• High inlet air temperature increases drying efficiency
of aqueous film
coating process and decreases in water penetration into
the tablet coating.
• Excessive air temperature increases premature drying
of the spray during
application and subsequently decreases the coating
Rotating speed of the pan
• Increasing
rotating speed of the pan improves mixing
of the tablets.
• The pan speed effects the time the tablet spend on the
spraying zone and subsequently, the homogenous
distribution of the coating solution on the surface
of each tablet throughout the batch.
• Increasing the pan speed decreases thickness variation
and improves the uniformity of the coating.
• Too rapid rotating speed of the pan will cause the
tablet to undergo excessive attrition and breakage.
Application of the film
• Aqueous film coating requires equipment with high air flow and excellent control
over the coating process.
• Aqueous film coating needs tighter control of the coating process than organic
solvent-based coating systems.
• The tablets are normally designed to disintegrate in water, so the rate of application of
coating composition is critical;
Too slow or too rapid application of the coating will
cause the tablet to undergo excessive erosion and breakage.
The following coating pans can provide adequate air flow and control to be used for
aqueous film coating:
1.Accela Cota.
3.Dria Coater.
Accela Cota
This is an angular pan
operating on a horizontal
axis. Drying air is directed
into the pan, through the
tablet bed, and exhausted
out the perforations in the
periphery of the pan.
This is similar to Accela
Cota, but only a portion of
the pan periphery has
perforations. Like the Accela
Cota, continuous venting of
the exhaust air from the
pan is still attained.
General procedure
The aqueous coating liqid is commonly applied by pnemutic (air) spray systems
where the pressure of the spraying air disperses the coating liqid as appropritely
sized droplets
The coating of tablets in a coating pan involves spraying the coating compositions
through one or more spray guns onto rotating bed of tablets.
Coating process consists of the continuous application of coating liquids to a small
portion of the tablets in the pan.
The applied coating must dry before it touches the coating pan or receives its next
To attain a continuous coating operation, the rate of water evaporation from the
coated tablets must equal the rate of water applied in the coating liquid.
The coating composition is also significant factor in establishing the tablet coating
rate. Coating compositions that are quite tacky during the drying phase must be
applied at a slower rate to avoid tablets sticking to pan surface or other tablets.
Common Coating Defects &
Rough/Orange Peel Appearance
Not enough vehicle.
High atomization air.
Moving the nozzle closer to the tablet bed or
reducing the degree of atomization
• Tablets are too wet.
Possible Causes:
• Spray rate too high.
• Guns too close together.
• Insufficient atomizing air.
• Pan speed too low.
REMEDY:Reduction in the liquid application rate or
increases in air dry temparature
Film Cracking
Small cracks appear in the coating.
Wrong plasticizer.
Insufficient plasticizer.
Solution too concentrated (Thick).
Insufficient atomizing air.
Film Chipping
Coating gone from the tablet edge.
High pan rpm.
Low spray rate.
Both together.
Sharp tablet edges.
Bridging of the Logo
• The letters and numbers fill in with dried
• High spray rate
• Inadequate atomizing air.
• Poor tooling design.
Twins or Twinning
Tablets stick together.
High spray rate.
Inadequate drying capacity.
Tablet shape/design.
Tablet too long.
Logo Erosion
Tablet erodes before coating can adhere to
the surface.
Spray rate too slow.
Pan speed too fast.
• Cracking occurs if internal stress in the
film exceed the tensile strength of the film
can be increased by using highermolecular –weight polymers or polymer
blends .
• It can occur when to high processing
temperature used for a particular
• Dulling is particular evident when cellulosic
polymers are applied out of aqueous
media at high processing temperature.
• Aqueous coatings are in many ways less expensive than organic solvent coatings.
•The removal of water from water soluble films such as hydroxypropylmethyl
cellulose, methylcellulose, gelatin, or starch requires the use of higher drying
temperatures than does the removal of methanol from a film. This is not surprising
when one considers their heats of evaporation.
• Another comparison between aqueous and organic film coating systems has to relate
to time. The processing time for any film coating application is extremely important to
meet production goals. Aqueous coatings require longer processing time than organic
solvent systems.
• Water and organic solvents differ in their support facilities. Because of their volatile
and toxic nature, organic solvent must be handled and stored in areas designed for this
• Stability and bioavailability are greatly influenced by the selection of coating and the
solvent system from which it is applied. Many drugs react in the presence of water; thus,
residual moisture in the film coated product may present more of a problem than residual
organic solvents. Although moisture can be eliminated by heat, some products are
unstable at higher temperatures or the combination of heat and moisture.
• Aqueous films also tend to have a lower gloss level than the same polymers applied
from organic solvents.
Cellulosic and acrylic polymeric films have been used to coat pharmaceutical drug
products for decorative, protective and purposes. These materials are generally
applied using a spray-atomization technique. Additional excipients, including
plasticizers, pigments, anti adherents, and surfactants, may be incorporated into the
coating formulation to aid in processing or to improve the esthetic appearance of
the coated solid.
The addition of these excipients, however, may alter polymer properties and affect
drug release rates. In the development of a film coating formulation, various
polymer properties are commonly evaluated and these data are used to make
predictions regarding the dissolution characteristics and long-term stability of the
final product. Adhesion of the polymer is critical to the performance of the film and
may be affected by the physicochemical properties of the substrate, additives in the
coating formulation, and processing conditions.
Sub coats have been used to improve polymer adhesion as well as to separate
reactive components in the film and substrate.
Defects in the polymeric film may be eliminated by adjusting processing
parameters or by reformulating the coating and/or the substrate.
Aging of coated solids may cause changes in the drug release characteristics and
polymer films should be completely coalesced to minimize aging problems.
• Encyclopedia of pharmaceutical technology by
James Swarbrick, James C.Boyane volume – 1
• The Theory And practice of Industrial Pharmacy
by Leon Lachmann and Herbert . A.
• Pharmaceutical dosage forms : Tablets volume3 –Liebermann series.

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