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Slide 1:

-Professor V. Chandrakala Dept. of Pharmaceutics East Point College of Pharmacy Bangalore 1 TABLET COATING

Types of Coating:

Types of Coating Sugar coating Film coating Press coating (Compression coating) 2 Multivitamin tablets

Sugar coating :

Sugar coating Duration-few hrs to few days Depends on skill of coating operator (especially in Pan ladling method- an old method) Quantity of solution to be added Method and rate of pouring When to apply drying air How long/how fast the tablets should be tumbled in pan 3


Continued….. Newer technique utilize spraying systems and varying degrees of automation to improve coating efficiency and product uniformity Basic sugar coating process Sealing/seal coating Subcoating Syruping (smoothing) Finishing Polishing Printing 4

1.Sealing/seal coating:

1.Sealing/seal coating It is applied to prevent moisture penetration into the tablet core Especially needed in pan-ladling process Localized overwetting occurs in pan ladling process but not in spray process Seal coating can be eliminated in spray process Sealant-Shellac Zein 5

2.Subcoating :

2.Subcoating Applied to round the edges and built up the tablet size Increase in weight by 50-100% Steps- Application of sticky binder solution Dusting of subcoating powder Drying Above method is continued until the edges are covered and desired thickness achieved 6


Continued….. Spray process Subcoating suspension containing both the binder and insoluble powder is sprayed For both the methods control of the drying rate is critical to obtain a rapid application of subcoat 7

3.Syrup (smoothing/color) coating:

3.Syrup (smoothing/color) coating This step is To cover and fill in imperfections in the tablet surface caused by subcoating & To impart color Requires most skill First syrup coat-contain suspended powders and are called grossing syrups Dilute colorants can be added to this phase to provide a tinted base that facilitate uniform coloring in later steps 8


Continued….. No color is added until the tablets are quite smooth if not mottled appearance in the coated tablets appear In subsequent syruping steps, syrup solutions containing the dye are applied until the final size and color are achieved In the final syruping or finishing step, a few clear coats of syrup may be applied 9

Syrup solution formulation :

Syrup solution formulation 10 Example of Syrup solution formulation

4. Finishing :

4. Finishing Initial coats of regular colored syrup applied rapidly in 3-4 coats The last coat of regular syrup can be applied without colorant Last coat gives depth to the color and enhances the elegance of the coat A quick jog every few minutes prevent sticking After 15-30 min, stop jogging and leave tablets in pan to dry slowly overnight 11


5.Polishing Desired luster is obtained in this final step of sugar coating Equipments-clean standard coating pan canvas-lined polishing pans Either powdered beeswax or carnauba wax Or Warm solutions of these waxes in naphtha or other suitable volatile solvents 12

6. Printing:

6. Printing Use of indented monograms on sugar coated tablet is not feasible Identification is accomplished by printing Printing process used is offset rotogravure Edible printing inks used 13

Film coating:

Film coating Share same equipment and process parameters Two methods used Pan pour method Pan spray method Pan pour method Used for many years Now supplanted by newer coating techniques that are faster and more reproducible 14


Continued….. Coating compositions were too viscous in earlier pan pour methods These tablets are subjected to alternate solution application, mixing and drying It is relatively slow and relies heavily on the skill and technique of operator They require additional drying steps to remove latent solvents Aqueous based film coating not suitable 15

2. Pan spray method :

2. Pan spray method Versatile and allows automated control of liquid application Spray patterns are selected to provide a Continuous band across the tablet bed surface Broad, flat spray patterns are selected of appropriate nozzle system so that the entire width of tablet bed can be covered 16

Process variables:

Process variables The variables to be controlled in pan-spray film coating process are: Pan variables Pan design/baffling Speed Pan load Process air Air quality Temperature Airflow rate/volume balance Spray variables Spray rate Degree of atomization Interdependent Spray pattern Nozzle-to-bed distance 17

Pan variables :

Pan variables Tablet coating adds an approximate increase in weight of 2-5% to the tablet Unacceptable color uniformity or enteric film integrity is encountered if inadequately coated Tablet shape affects mixing Some mix freely some require baffling If baffles are not carefully chosen provide a source of chipping, breakage Pan speed affects Mixing Velocity at which tablets pass under spray 18


Continued….. If speeds are too slow may cause localized overwetting-resulting in sticking to each other and to the pan If speeds are too high may not allow enough time for drying- resulting in rough coating Commonly used speeds in large pan coater for non aqueous film coating 10-15rpm Slower pan speed for aqueous film coating 3-10rpm 19


Continued….. Selection of pan operating conditions depends on Equipment availability Type of tablets being coated Characteristics of the coating solution 20

Spray variables:

Spray variables Airless high pressure system – yields greater atomization Air atomized low pressure system Degree of atomization and spray pattern are affected by Atomizing air pressure Air volume Shape and design of air jets in relation to the fluid stream 21


Continued….. Rate at which coating solution is applied depends on Mixing Drying efficiency Coating formula Core characteristics Overwetting and underwetting to be avoided 22


Continued….. Band of spray should spread evenly In larger pans, more nozzles must be added to cover tablet bed width Tablet need to make many more passes through the spraying area to be adequately coated Spray width can be adjusted by moving the nozzle close or farther away from the tablet bed Nozzle to bed distance affects spray width and quantity of coating applied per pass under spray 23


Continued….. Atomization – Process whereby liquid steam is finely subdivided into droplets Degree of atomization – The size and size distribution of the droplets (not easily controllable) Relationship between Orifce size Nozzle configuration Fluid pressure Atomizing air pressure Air volume Fluid viscosity vary with each coating formulation 24


Continued….. Degree of atomization can be controlled empirically Care to be taken to avoid spray drying of coating solution appearing especially at higher atomization Above situation causes rough surface At lower atomization – localized overwetting occurs (sticking, picking, orange-peel effect) 25

Process air variables :

Process air variables The parameters should be controlled to obtain optimum drying environment for coating process The sensitivity of film former and product core to heat largely determines the upper temperature Higher tablet bed and coating chamber temperatures is important for rapid solvent evaporation and faster coating More efficient the equipment design, the less air volume needed for drying 26


Continued….. Supplied air should be dehumidified Seasonal fluctuation in the moisture content can adversely affect coating Balance between supply and exhaust air flow should be such that all dust and solvent are contained within the coating system 27

Fluidized bed process:

Fluidized bed process Used for rapid coating of tablets, granules and capsules Solution formulations used are similar to those used for pan processes Since air is used to move the tablets, specific process controls unique to air suspension coaters Fluidized pattern depends on 28 Chamber design Process air

Fluidized bed coating:

Fluidized bed coating 29


Continued….. Factors affecting ability of tablet mass to fluidize Tablet shape Tablet size Density Quantity of load Adequate fluidization depends on volume and rate of process air Control of process air is achieved by Adjusting a variable speed blower Using dampers to keep tablet mass in a constant “fluid” motion inside the chamber 30


Continued….. Too high airflow results in excess tablet attrition and breakage Too low airflow mass does not move fast enough through the spray region and overwetting occurs Fluidization may be affected by Increase in weight Change in frictional characteristics Periodic adjustment of the rate and volume will be necessary to maintain optimum fluidization 31


Continued….. During coating operation, both inlet and exhaust air temperatures are monitored Evaporation of the solvent causes the exhaust air temperature to be cooler than the inlet Any change in rate of application of coating solution can be monitored by the difference between the inlet and exit air temperatures 32

Film coating compostion:

Film coating compostion Hydroxypropyl methylcellulose(HPMC) non aqueous formula This formula can be applied by spraying or pouring systems HPMC, 2910,USP, 15cps 4% Propylene glycol, USP 1.2% Ethyl alcohol 45% Methylene chloride qs to 100% Insoluble colorant, opaquants or flavors requires a milling step to facilitate their adequate dispersal 33

Slide 34:

Coating materials 34

Ideal film coating material should have the following attributes: :

Ideal film coating material should have the following attributes: Solubility in solvent of choice for coating preparation Solubility required for intended use, e.g. - free water-solubility , slow water solubility of pH-dependent solubility(enteric coating) Capacity to produce an elegant looking product Stability in presence of heat, light, moisture, air and the substrate being coated (Film property should not change with time) 35


Continued….. Essentially no color, taste or odor Compatibility with common coating solution additives Nontoxicity with no pharmacologic activity and ease of application to the particles or tablets Resistance to cracking and provision of adequate moisture, light, odor or drug sublimation barrier when desired No bridging or filling of the debossed tablet surfaces by the film former Ease of printing procedure on high-speed equipment 36

Slide 37:

Film formers Nonenteric Eg - Hydroxypropyl methylcellulose, Methyl hydroxyethylcellulose , ethyl cellulose, hydroxypropyl cellulose, povidone , sodium carboxymethyl cellulose, polyethylene glycols, acrylate polymers Enteric- Eg - Cellulose acetate phthalte , Acrylate polymers, Hydroxypropyl Methylcellulose Phthalate, Polyvinly acetate phthalate 37 Material used in film coating

Properties of enteric coating material:

Properties of enteric coating material Resistance to gastric fluid Ready susceptible to or permeability to intestinal fluids Compatibility with most coating solutin components and drug substrates Stability alone and in coating solution Formation of a continuous film Nontoxic Low cost Ease of application without specialized equipment Ability to be readily printed or to allow film to be applied to debossed tablets 38


Solvents Important considerations for Ideal solvent system Should either dissolve or disperse the polymer system Should easily disperse other coating solution components Small concentration of polymers(2-10%) should not result in an extremely viscous solution Should be colorless, tasteless, odorless, inexpensive, nontoxic, inert and nonflammable Should have rapid drying rate Should have no environmental impact 39


Solvents- Eg – water, ethanol, methanol, isopropanol , chloroform, acetone, methylethyl ketone and methylene chloride Plasticizers Eg - Castor oil, propylene glycol, glycerin, low molecular weight polyethylene glycols of 200 to 400 series, surfactants like polysorbates ( tweens ), sorbitan esters (spans), organic acid esters 40 Continued…..


Continued….. Colorants Eg -certified FD&C, D&C, Inorganic Material-Iron Oxides, natural coloring materials- anthocyanins , caramel, carotenoids , chlorophill , indigo, flavones, turmeric and carminic acid Opaquant -extenders Eg -titanium dioxide, silicates (talc, alumnium silicate), carbonates (magnesium carbonate), sulfates (calcium sulfate), oxides (magnesium oxide) ,hydroxides ( aluminium hydroxide) Miscellaneous coating solution components Eg -flavors, sweetners antioxidants, antimicrobials 41

Slide 42:

Formulation of coating materials 42

Development of film coating formulation:

Development of film coating formulation The following questions must be answered concurrently with the decision of coat What is the purpose of coating? What tablet size, shape or color constraints must be place on the developmental work? QA exercises control over the product appearance An experienced formulator usually takes the pragmatic approach and develops a coating formulation as a modification of one that has performed well in the past 43

Film screening study:

Film formulations can be preliminarily screened by spraying or casting films Through the preparation of a series of films with slight changes in formula ingredients, it is possible to eliminate the obvious physical incompatibilities and poor film combinations rather quickly Cast films and sprayed films can have different characteristics Cast films can be prepared by spreading the coating composition on teflon, glass or aluminum foil 44 Film screening study


Sprayed films can be obtained by mounting a plastic-coated surface in a spray hood or coating pan Physical appearance of these films can provide evidence of potential colorant or opaquant separation Films can be subjected to following test Water vapor permeability Film tensile strength 45 Continued…..

Slide 46:

Coating methods 46

Slide 47:

Equipments employed in tablet coating 47

Tablet coating equipments:

Tablet coating equipments Standard coating pan- Pellegrini pan , immersion sword, immersion tube systems(Europe) Perforated coating pan – Accela-Cota , Hi-Coater, Driacoater, Glatt coater Fluidized bed coater Standard coating pan: It consists of circular metal pan mounted somewhat angularly on a stand. Diameter - 8 to 60 inches Rotated in horizontal axis by motor Heated air is directed into the pan and onto the tablet bed surface Air is exhausted by means of ducts positioned through the front of the pan 48

Standard coating pan:

49 Standard coating pan

Slide 50:

Pellegrini pan It has a baffled pan Diffuser to distribute the drying air uniformly 50

Perforated pan systems:

Perforated pan systems 51

Perforated pan systems:

52 Perforated pan systems


Driacoater 53 Driacoater Drying air is introduced through hollow perforated ribs located on the inside periphery of the drum As coating pan rotates the ribs dip into the tablet bed Drying air passes up through and fluidizes tablet bed Exhaust is from back of the pan

Glatt Pan coating:

54 Glatt Pan coating Similar to accela-cota A divided air plenum located beneath the moving tablet bed enables air to be blown into or exhausted from the pan through either or both the two sections In addition, another air plenum, connected to an opening above the door (similar to that in a hi-coater) also allows air to be blown into or exhausted from the pan It is expensive

Spray Application Systems:

Spray Application Systems High pressure airless Low pressure, air atomized 55 Sl . No. High pressure airless Low pressure, air atomized 1 Liquid pumped at high pressure (250 to 3000 psig) Liquid pumped at low pressure (5 to 50 psig) 2 Liquid passed through a small orifice (0.009 inch to 0.02 inch id) Liquid passed through a larger orifice (0.020 inch to 0.060 inch id) 3 Degree of atomization and spray rate are controlled by fluid pressure, orifice size and viscosity of liquid Degree of atomization is controlled by fluid pressure, fluid cap orifice, viscosity of liquid, air pressure, air cap design

Slide 56:

56 High pressure airless nozzle Low pressure air atomized nozzle Continued…..

Slide 57:

Defects in coating 57

Film defects:

Film defects Sticking and picking Sticking- overwetting or excessive film tackiness causes tablets to stick to each other or to the coating pan Picking- 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 the liquid application rate or increase in the drying air temperature and air volume usually solve this problem Excessive tackiness may be an indication of a poor formulation 58

Slide 59:

59 Picking Sticking Continued…..

Slide 60:

Roughness A rough or gritty surface is a defect often observed when the coating is applied by a spray Some droplets may dry too rapidly before reaching the tablet bed, resulting in deposits on the tablet surface of spray dried particles instead of finely divided droplets of coating solution Moving the nozzle closer to the tablet bed or reducing the degree of atomization can decrease the roughness due to spray drying Roughness increases with pigment concentration and polymer concentration in the coating solution 60

Slide 61:

61 Continued…..

Slide 62:

Orange-peel effects Inadequate spreading of the coating solution before drying causes a bumpy or orange-peel effect on the coating This indicates that spreading is impeded by too rapid drying or by high solution viscosity Thinning the solution with additional solvent may correct this problem 62

Slide 63:

Bridging and filling During drying the film may shrink and pull away from the sharp corners of an intagliation or bisect, resulting in a bridging of the surface depression Changing the plasticizer or plasticizer concentration can decrease bridging Filling is caused by applying too much solution Judicious monitoring of the fluid application rate and thorough mixing of the tablets prevent filling 63

Slide 64:

64 Continued…..

Slide 65:

Blistering When coated tablets require further drying in oven, too rapid evaporation of solvent from the core and Effect of high temperature on the strength, elasticity and adhesion of the film may result in blistering Milder drying conditions are warranted in this case 65

Slide 66:

Hazing/dull film Also called as ‘bloom’ Occurs when too high processing temperature is used Particularly evident when aqueous cellulosic polymers are applied at high processing temperature Also occurs if the coated tablets are exposed to high humidity conditions and partial solvation of film results 66

Slide 67:

Color variation Can be due to improper mixing, uneven spray pattern, insufficient coating Migration of soluble dyes, plasticizers and other additives during drying may give the coating a mottled or spotted appearance Use of lake dyes eliminates dye migration Reformulation with different plasticizers and additives will solve film instabilities caused by the ingredients 67

Slide 68:

Cracking Occurs if internal stresses in the film exceed the tensile strength of the film Tensile strength of the film can be increased by using higher-molecular-weight polymers or polymer blends Internal stresses can be minimized by adjusting the plasticizer type and concentration, and the pigment type and concentration 68

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