COATING TECHNOLOGY

K.SANJEEV KIRAN13080040

LALITHA COLLEGE OF PHARMACY

TABLET COATING

Tablet coating is the application of coating material to the exterior of a tablet with the intention of conferring benefits and properties to a dosage form over the uncoated variety

WHY TABLET COATING?? The core contains a material

which has a bitter taste in the mouth or an unpleasant odor.

Coating will protect the drug from surroundings with a view to improve its stability

Coating will increase the ease by which a tablet can be ingested by the patient.

CONT…..

The core contains a substance which is incompatible in the presence of the light and subject atmospheric oxidation.

The core is inelegant. The active substance is colored and

migrates easily to stain hands and clothes. Coating can modify the drug release

profile. E.g., enteric coating, pulsatile delivery.

BASIC PRINCIPLE OF TABLET COATING

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

TYPES OF TABLET COATING

Sugar coating Film coating Enteric coating Controlled release coating Specialized coating

Compressed coatingElectrostatic coatingDip coating Vacuum film coating

SUGAR COATING

sugar coating is a multistep process.

Its use of labour is more, require a fair degree of skill.

In suitable sugar-coating equipment the tablet cores are successively treated with aqueous sucrose solutions which, depending on the stage of coating reached, may contain other functional ingredients,…e.g. fillers, colors, etc.

ADVANTAGES OF S.C

Constituent raw materials are widely accepted—no regulatory problems.

No complex equipment or services are required.

For high humidity climates, it generally offers a stability advantage over film-coated tablets.

STAGES IN SUGAR COATING

Sugar coating is a multi step process.

1. SEALINGApplied directly to the

tablet core to protect it from the water that is used in the remainder of the coating process.

2 SUB COATINGThe actual sugar coating

which leads to 50-100% increase in weight.

CONT…

3. SMOOTHINGAdditional smoothing prior to color

coating can also be applied to opacify the subcoat to promote a brighter final color

4. COLORINGThe most critical step of sugar coating,

consists of multi-step application of syrup containing the required color(dye/pigment)

CONT……5. POLISHING

Imparts the required gloss to the final product.

In many applications, the sealing &/or smoothing steps may be omitted.

SUGAR COATING FAULTS

A common fault is cracking and splitting of the sugar coat which is caused by excess residual moisture from the processing.

Inversion and stickiness are caused by the presence of inverted sugar which is difficult to dry adequately.

Sugar coatings are unfortunately brittle and are prone to chipping if subjected to an inappropriate mechanical stress.

FILM COATING

Film coating is a thin polymer-based coat applied to a solid dosage form.

The thickness of such a coating is usually between 20 and 100 μm.

Each and every tablet is passed through a spray zone, where the adherent material is sprayed and allowed to dry before the next portion of coating and this process is repeated number of times.

FORMULATION

Film-coating formulations usually contain the following components:

• Polymer.• Plasticizer.• Pigment.• Vehicle.

POLYMERS

The vast majority of the polymers used in film coating are either cellulose derivatives, such as the cellulose ethers, or acrylic polymers and copolymers.

Basically there are two classes of such

material depending upon the method of preparation; true latexes and pseudolatexes.

POLYMER CHARACTERISTICS

Solubility

Viscosity

Permeability

Mechanical properties

Tackiness

PLASTICIZERS

Plasticizers are simply relatively low molecular weight materials which have the capacity to alter the physical properties of a polymer to render it more useful in performing its function as a film-coating material.

There are often chemical similarities between a polymer.

CONT… The commonly used plasticizers can be categorized into three

groups:1. Polyols

(a) glycerol (glycerin);(b) propylene glycol;(c) polyethylene glycols PEG (generally the 200–6000 grades).

2. Organic esters(a) phthalate esters (diethyl, dibutyl);(b) dibutyl sebacete;(c) citrate esters (triethyl, acetyl triethyl, acetyl tributyl);(d) triacetin.

3. Oils/glycerides(a) castor oil;(b) acetylated monoglycerides;(c) fractionated coconut oil.

COLOURANTS

This group of materials are commonly used as ingredients in film-coating formulae.

They obviously contribute to the aesthetic appeal of the product, but they also enhance the product in other ways:

1. Identification of the product

2.They reinforce brand imaging

3.optimize the ability of the coating to protect the active ingredient against the action of light.

CONT….

Organic dyes and their lakesSunset YellowTartrazineErythrosine.

Inorganic colorsTitanium dioxideIron oxide yellow, red and blackTalc.

Natural colorsRiboflavineCarmineAnthocyanins

SOLVENTS/VEHICLES

• water• alcohols• ketones esters• chlorinated hydrocarbons.

Mechanism of film formation

ENTERIC COATING

An enteric coating is a barrier applied to oral medication that controls the location in the digestive system where it is absorbed.

Enteric refers to the small intestine, therefore enteric coatings prevent release of medication before it reaches the small intestine.

Composition of coatings

methyl acrylate-methacrylic acid copolymers cellulose acetate succinate hydroxy propyl methyl cellulose phthalate hydroxy propyl methyl cellulose acetate

succinate (hypromellose acetate succinate) polyvinyl acetate phthalate (PVAP) methyl methacrylate-methacrylic acid

copolymers Sodium alginate and stearic acid

Specialized coating

Electrostatic coatingElectrostatic coating is a

manufacturing process that employs charged particles to more efficiently coat a tablet.

Dip coating Dip coating is a popular way of

creating thin films for research purposes. Uniform films can be applied onto flat or cylindrical substrates.

CONT….

Vacuum film coatingVacuum coating is a mechanized process for applying coatings to lengths of materials. The product to be coated is motivated or conveyed in a lengthwise fashion at a constant speed, and these speeds can be as high as 500 feet per minute.

IDEAL CHARACTERS OF COATING MATERIAL

Solubility in the coating solution. Low cost

Ease of application without specialized equipment.

Capacity to produce elegant looking product.

Stability in the presence of water, heat, air, moisture and substrate being coated and no change properties with aging.

CONT….

Essentially no color, odor or taste. Compatibility with common coating

solution additives. Nontoxic and ease of application. Resistance to cracking and should act as

barrier. Ease of printing procedure on high speed

equipment

METHODS OF PREPARATION- COATING SOLUTION

1. EMULSION-SOLVENT EVAPORATION

2. PHASE INVERSION

EMULSION-SOLVENT EVAPORATION

Polymer is first dissolved in water-immiscible organic solvent and then mixed with an aqueous phase containing surfactant and stabilizer.

The mixture is then emulsified to form an o/w type of emulsion which is then subjected to ultrasonification or homogenization to generate a fine emulsion containing submicron droplets

Solvent is evaporated (EX-aquacoat)

PHASE INVERSION Polymers and plasticizer first undergoes

hot melting or solvent gelation and combined with long chain fatty acids to form a homogenous mixture.

A dil Alkali solution is slowly added to the mixture under vigorous agitation to form initially a w/o type of emulsion (water in polymer)

As more aqueous alkali is added, phase inversion occurs and a dispersion of polymers in water is produced

COATING DEFECTS PICKING & STICKING BRIDGING CAPPING EROSION TWINNING PEELING AND FROSTING CHIPPING MOTTLED COLOR ORANGE PEEL WAITING PERIOD BATCH SIZE SOLUTION PREPARED GUN GEOMETRY SPRAY GUN CALIBRATION GUN NOZZLES PAN LOADING CLEANING

. PICKING & STICKING

This is when the coating removes a piece of the tablet from the core. It is caused by over wetting the tablet or by poor tablet quality

BRIDGING

This occurs when the coating fills in the lettering or logo on the tablet and is typically caused by improper application of the solution, poor design of tablet embossing, high viscosity, high %age of solids in the solution etc.

. CAPPING

This is when the tablet separates in laminar fashion. This occurs due to improper tablet compression

EROSION

This can be the result of soft tablets, an over wetted tablet surface, inadequate drying or lack of tablet surface strength

TWINNING

2 tablets stick together.

Common problem with capsules.

Reduce spray rate or increase the pan speed.

PEELING & FROSTING

The coating peels away from the tablet surface in a sheet.

This indicates the coating solution didn’t lock into the tablet surface.

Due to over wetting, defect in coating solution or high moisture content in the tablet core.

CHIPPING

This is the result of high pan speed, a friable tablet core or a coating solution that lacks plastizer.

MOTTLED COLOR

Happens when coating solution is improperly prepared, the actual spray rate differs from target rate.

TABLET QUALITY

Tablets must have the proper porosity, surface, hardness and moisture content.WAITING PERIOD

Most tablets cannot be coated after being compressed. The energy within the tablet will be pretty high, in fact it will be warm. Hence the tablet should be kept aside for sometime.

SPRAY GUN CALIBRATION

Must check the calibration of the guns every time you change products.

Means checking the gun’s overall condition, its filter, nozzle alignment and needle condition.

CLEANING

Each component of the spraying system must be cleaned and dried.

GUN NOZZLES

The spray gun nozzles must be kept clean and free of product buildup.

Use a flash light during coating to look into the cabinet and check the nozzles.

PAN LOADING

While loading the tablets look for tablets that are broken, capped, chipped.