Tablet Coating 3.ppt

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Tablet Coating 3

Dr. Mohammad Shariare

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Coating defects



Sticking and picking



Roughness



Orange –peel effects



Bridging and filling



Blistering

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Coating faults

These arise from two distinct causes:

1.

Processing: for example, inadequate drying conditions will permit Processing:

coating previously deposited on the tablet surface to stick against neighboring tablets. When parted, this will reveal the original core surface underneath.

2. Formulation faults: film cracking or ‘bridging’ of break lines are examples Formulation faults:

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Sticking and picking



Over wetting or excessive film thickness causes tablets

to stick each other or to the coating pan.



On drying at the point of contact, a piece of film may

remain adhered to pan or tablet.



Giving “picked” appearances to the tablet surface.

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Sticking and picking

Remedies:



Reduction

in

liquid

application rate.



Increase in drying air

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Twinning



This is the term for two

tablets

that

stick

together, and it’s a

common problem with

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Roughness

 A rough or gritty surface observed when the coating is applied

by spray.

 Some of the droplets may dry too rapidly before reaching the

tablet bed and deposits on tablet surface.

 On tablet surface spray- dried particles of finely divided

droplets of coating solution.

 Surface roughness also increases with pigment concentration

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Roughness



Remedies

 Moving the nozzle closer to

the tablet bed.

 Reducing the degree of

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Orange – peel effects

 Inadequate spreading of coating solution before drying causes a bumpy or Orange – peel effects on the coating.

 Causes: Indicates that spreading is impaired _Causes: by rapid rate of drying or by high solution viscosity.

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Bridging and Filling



During drying film may shrink and pull away from the

sharp corners of bisect, resulting in a “Bridging” of

surface dispersion.



These defects can be so severe that the monogram or

bisect is completely obscured.



Remedies Increase in plasticizer contents or change

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Bridging and Filling

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Filling

 Applying too much solution, resulting in thick film, causes

filling.

 That fills and narrows the monogram or bisects.

 In addition, if solution applied too fast, over wetting may

cause the liquid to quickly fill and be retained in the monogram.

 Remedies: Judicious monitoring of the fluid application rate.

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Blistering



Evaporation of solvents from the core in the

oven and effect of high temperature on the

strength, elasticity and adhesion of the film

may results in blistering.

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Hazing/Dull film

 Hazing/Dull film is also called as bloom.

 It can occur when too high a processing temperature is used for

a particular formulation.

 Dulling is particularly evident when cellulosic polymers are

applied out of aqueous media at high processing temperature.

 Also occur if the coated tablets are exposed to high humidity

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Color variation

 Problem caused by process conditions or the formulation.

 Improper mixing, uneven spray pattern and insufficient coating

may results in color variation.

 The migration of soluble dyes, plasticizer and other additives

give the coating a mottled or spotted appearance.

 Remedies: Use of lake dyes eliminates dye migration. A

reformulation with different plasticizer and additives is the best

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Cracking

 Cracking occurs if internal stresses in the film exceed the

tensile strength of the film.

 The tensile strength of the film can be increased by using

higher molecular weight polymers or polymer blends.

 Remedies: Adjusting the plasticizer types and concentration

can minimize internal stresses.

 Also adjusting the pigment types and concentration can

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Tablet Coating Problems

Edge Chipping

Core Erosion

Logo Infilling

Picking and Sticking

Peeling

Twinning

Color Variation

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Coating Process

 Tablet coating is the application of a coating composition to a moving bed of tablets with the concurrent use of heated air to facilitate evaporation of the solvent.

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Coating Process

 In addition to smooth surface, the physical shape of tablet is important.

 Tablets in coating pan, become covered with tacky polymeric films and

before surface dries, the applied coating changes from a sticky liquid to a tacky semisolid, and eventually to non-sticky dry surfaces.

 So tablets must be in constant motion during the early drying phase or

tablet agglomeration can occur.

 Coated tablets have rounded surfaces; the more convex the surface is,

the fewer difficulties will be encountered with tablet agglomeration.

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Equipments for Tablet

Coating

Standard (conventional) coating pan system

Perforated coating

pan system Fluidized bed _Systems

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Conventional Pan Systems



It consists of a circular metal pan mounted angularly

on a stand.



Heated air is directed into the pan and onto the tablet

bed and exhausted by means of ducts positioned

through the front of the pan.



Coating solutions are applied by ladling or spraying

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Conventional Pan Systems



Use of atomizing systems produces faster and

suspension.



Spraying can significantly reduce drying time.



Efficient drying is achieved by the pellergrini pan,

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Pellegrini Pan System

 The first coating pan rotating on a horizontal

axis equipped with tapered side walls and an integral baffle system was introduced by Pellegrini and is well-known as the

Pellegrini pan.

 It has a baffled pan and a diffuser that

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Immersion Sword System

 In this system, drying air is introduced

through a perforated metal sword device that is immersed in the tablet bed.

 Air is intimately mixed with the wetted

tablets and a more efficient drying environment is provided.

 Coating solutions are applied by

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Immersion Tube System

 With this 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.

 Coating solution is applied

simultaneously with the heated air from the immersed tube.

 The drying air flows upward and is

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Perforated Pan Systems



These equipments consist of perforated or

partially perforated drums that are rotated on

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Accela-Cota System

 In this system drying air is directed onto the drum, passed

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Hi- Coater System

 In this system drying air is directed onto the drum, passed

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Driacoater System

 It introduces drying air through

hollow perforated ribs located on

the inside periphery of the drum.

 The ribs dip into the bed as the pan

rotates.

 Drying air passes up and fluidizes

the tablet bed.

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Glatt Coater



In the Glatt coater, drying

air can be directed from

inside the drum through

the tablet bed and out an

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Application of Coating

Solution



In all the perforated pan systems the coating

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Fluidized Bed Systems



These are highly efficient drying systems.



Fluidization of the tablet mass is achieved in

columnar chamber by the upward flow of drying air.



Coating solutions are continuously applied from a

spray nozzle located at the bottom of the chamber or

nozzles can also be present at the upper region of

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Fluidized Bed Systems

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Coating Process

Spray Application Systems

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High Pressure, Airless

System

 Liquid is pumped at high pressure (250 to 3000 pounds per

square inch gauge) through a small orifice (0.009inch to 0.020 inch id) in the fluid nozzle which results in finely divided spray.

 The degree of atomization is controlled by the fluid pressure,

the orifice size and the viscosity of the liquid.

 Because of the small orifice, suspended solids in the coating

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Low Pressure, Air Atomized

System

 In this system, Liquid is pumped through a larger orifice

( 0.020 inch to 0.060 inch id) at relatively low pressure (5 to 50 psig)

 Low pressure air contacts the liquid stream at the tip of the

atomizer and finely divided spray is produced.

 The degree of atomization is controlled by the fluid

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