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

TABLET COATING

TABLET COATING PRINCIPLES To mask the taste,odor,color of drug. To providephysical and chemical protection

for the dru. To control the release of the drugfromthe

tablet. To protect the drug from the gastric

environmentof the stomach with an acid-resistant enteric coating

Sugar coating Film coating Functional coating Enteric coating Specialized coating Compressed coating Electrostatic coating Dip coating Vacuum film coating

TYPES OF TABLET COATNG

Sugar coating process involves five separate operations:-

1. Sealing/water proofing2. Sub coating3. Grossing/smoothing4. Colouring5. Polishing.

SUGAR COATING

It provides a moisture barrier and harden the tablet surface Eg:• Shellac• Zinc• Cellulose acetate phthalate(CAP)• Polyvinyl acetate phthalate• Hydroxlypropylcellulose• Hydroxypropylmethylcellulose.. etc

1. SEALING / WATER-PROOFING

It causes a rapid buildup to round off the tablet edges and build the tablet size.

It is done by adding bulking agents such as calcium carbonate or talc in combination with sucrose solution .

Generally two methods are used for sub coating1.Application of gum based solution followed by dusting with powder and then drying.2.The application of a suspension of dry powder in gum /sucrose

followed by drying.

2.SUBCOATING

It is specially for smoothing and filling the irregularity on the surface generated during sub coating.

It also increases the tablet size to a predetermined dimension with the application of sucrose syrup.

4. COLOURING It gives the tablet its colour & finished size and it is done for

aesthetic purposes often titanium based pigments are included.

3.GROSSING /SMOOTHING

Produces the characteristics gloss and the desired lustre.Polishing is achieved by applying the mixture of waxes like

bees wax, carnauba wax, candelia wax or hard paraffin wax to tablets in polishing pan.

5.POLISHING

Coating tablets by surrounding them with a thin layer of polymeric material .

MATERIALS USED IN FILM COATING Film formers which may be enteric or non enteric. Polymers used are cellulose derivative,methacrylate amino

ester copolymers Plasticizer used are – Polyols- Polyethylene glycol 400 Organic ester –Diethyl phthalate Oils/glycerides – Fractional coconut oil Colorants are Iron oxide pigment, Titanium di-

oxide,Aluminium lakes. Solvents Miscellaneous.

FILM COATING

COATING PROCESS

Coating machine and process Standard coating pan Perforated coating pan Fluidized bed coaters Process parameters Inlet temperature,oulet temp.,pan speed, spray rate ,pan load,solid content of coating solution, atomization pressure ,nozzle to

bed distance, drying time. Coating Solution

SUGAR COATING ADVANTAGES DISADVANTAGE

Rounded with high degree of polish and shiny appearance .

Sweet in taste . Easily accepted by children

Weight increases 30-50% due to coating material

Difficult to automatedeg. Traditional coating pan Considerable training

operation required Multistage process Not able to be used for

controlled release

FILM COATING ADVANTAGES DISADVANTAGES

Produces tablet in a single step process.

Takes relatively short period of time.

Process enables functional coatings to be incorporated into the dosage form.

There are environmental and safety implication of using organic solvents.

Financial expenses are relatively more .

This technique involved protection of tablet core from disintegration in the acidic environment of the stomach by employing pH sensitive polymer, which swells or solubalise in response to an increase in pH to release the drug.

AIMS OF ENTERIC PROTECTION To mask taste or odour . Protection of active ingredients from the acidic environment

of the stomach. Protection from the local irritation of the stomach mucosa. Release of active ingredient in specific target area within the

GIT.

ENTERIC COATING

COMPREESION COATING

Requires specialised machine.Not widely used,but it has advantages in

some cases in which the tablet core cannot tolerate organic solvents or water and yet needs to be coated for taste masking,or to provide delayed or enteric properties to the product.

VACCUM FILM COATINGNew coating process.The pan used is hot water jacketed,and can

be sealed to achieve a vaccum system.Coating efficiency is high and organic

solvents can be used with minimal environmental and safety concerns.

DIP COATING Coating is applied to the tablet core by

dipping them into the coating liquid. The wet tablets cores are dried in a

conventional manner in coating pans. Alternate dipping and drying steps may be

repeated several times to obtain the desired coating.

This process lacks the speed and reliability of spray coating techniques.

ELECTROSTATIC COATING

Efficient method of applying coating to conductive substrates.

A strong electrostatic charge is applied to the substrate.

The coating material containing conductive ionic species of opposite charge is sprayed onto the charged substrate.

Complete and uniform coating of corners is achieved.

Sticking and picking Roughness Orange peal effects Bridging and filling Blistering Mottling Hazing /dull fill Wrinkling Sweating Flaking Blooming Spotting Colour variation Cracking.

FILM DEFECTS

FILM DEFECTS STICKING AND PICKING Overwetting or execessive film tackiness causes

tablets to stick to each other or to the coating pan. On drying,at the point of contact,a piece of the film

may remain adhered to the pan or to another tablet,giving a picked appearance to the tablet surface and resulting in a small exposed area of the core.

Reduction in liquid application rate or increases in the drying air temperature and air volume can solve this problem.

ROUGHNESS Roughness is observed when coating is

applied by a spray. Some droplets may dry too rapidly before

reaching the tablet bed,resulting in deposits on the tablet surface instead of finely divided droplets of coating solution.

Moving the nozzle closer to the tablet bed can decrease the roughness due to spray drying.

ORANGE PEEL EFFECTS Inadequate spreading of the coating

solution before drying causes orange-peel effect on the coating.

Thinning the solution with additional solvent may correct the problem.

BLISTERING When coated tablets require further drying

in ovens,too rapid evaportaion of the solvent from the core and the effect of high temp on the strength,elasticity,and adhesion of the film may result in blistering.

Milder drying conditions can reduce this defect.

COLOR VARIATION Improper mixing,uneven spray pattern,and

insufficient coating may result in color variation.

The migration of soluble dyes,plasticizers and other additives during drying may give the coating a mottled or spotted appearance.

Reformulation with different plasticizers and additivesis the best way to solve the problem.

CRACKING Occurs if internal stresses in the film

exceed the tensile strength of the film. The tensile strength can be increased by

using higher-molecular weight polymers. Internal stresses in the film can be

minimised by adjusting the plasticizer type and concentration and the pigment type and concentration.

Presence of wrinkles on the surface of the coating tablet indicates improper drying or natural tendencies of the film forming agents .Wrinkling are magnified when the film is to thick.

* Sweating It occurs due to exclusion of plasticizers and surfactants from

the film due to strong cohesive forces of die ploymers or several drying temperature.

* Wrinkling

THANKS….By

Shruti & Geetanjali