Slide 1: Tablet Coating Amit M Gupta
Agnihotri College of Pharmacy, Wardha Slide 2: Objectives of tablet coating
The tablet coating depends on the various objectives as follows :
◙ To mask the taste, odor, or color of the drug.
◙ To provide chemical and physical protection to the
◙ To control the release of the drug from tablet ie;
◙ To protect drug from the gastric environment of the stomach with an acid-resistant enteric coating. Slide 3: ◙ To incorporate another drug or formulate adjuvant in the coating to avoid chemical incapability or to provide sequential drug release.
◙ To improve the Pharmaceutical elegance by use of special colors and contrasting printing. There are three primary components involved in tablet coating: : There are three primary components involved in tablet coating: 1. Tablet properties.
2. Coating process.
→ Coating equipment.
→ Parameters of coating process.
→ Facility and ancillary equipment.
→ Automation in coating process.
3. Coating composition. (A). Tablet properties: : (A). Tablet properties: □ For coating tablet must posses the proper physical characteristic.
□ In coating process, the tablets roll in a coating pan or cascade in the air stream of an air suspension coater as coating composition is applied.
□ Tablets must be resistant to abrasion and chipping (ie; to tolerate intense attrition of tablet – tablet and tablet and wall of equipment ) Slide 6: □ Films coatings adhere to all exposed surfaces, so that any surface imperfection is coated and not eliminated.
□ Quality of thin film coating applied to compressed tablets usually depends much more on the quality of starting tablet than on the time at sugar coatings are applied. Slide 7: □ 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. Slide 8: ◘ 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.
□ Coating composition must wet the surface, to adhere. (B). MATERIALS USED IN FILM COATING: : (B). MATERIALS USED IN FILM COATING: □ Coating materials may be a physical deposition of the materials on tablet surface or they may form a continuous film depending on composition of coating formulation.
Eg : Sugar
Wax coatings Slide 10: □ The different type of coating materials are:
► Synthetic polymers
► Opaquant extenders
► Miscellaneous coating solution Ideal characters of coating material are: : Ideal characters of coating material are: □ Solubility in the coating solution.
□ Solubility required for intended use:
Ex : Free water solubility.
Slow water solubility.
pH- dependent solubility.
□ Capacity to produce elegant looking product.
□ Stability in presence of water, heat, moisture, air, and substrate being coated and no change properties with aging. Slide 12: □ 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.
□ No bridging or filling of the debossed tablet surfaces by the film former.
□ Ease of printing procedure on high-speed equipment.
□ Low cost.
□ Ease of application without specialized equipment. Slide 13: (A). Film Formers:
► Non-enteric Materials :
1. Hydroxypropyl methylcellulose, USP:
It is ideal coater and used as glossing solutions, and polymer has tendency to bridge or fill the debossed tablet surfaces.
HPMC + Plasticizers = eliminate bridge or filling problems.
2. Methyl Hydroxyethyl Cellulose:
Same properties as HPMC but not frequently used due to it’s fewer solvents. Slide 14: 3. Ethyl cellulose, NF:
Various viscosity grades are available depend on the ethoxy substitution and it’s water and GI- Fluid insoluble and so it’s added along with water soluble additives eg: HPMC.
4. Hydroxypropylcellulose, FCC:
It’s water and GI- Fluid soluble and organic solvents below 40ºC and insoluble above 45 ºC.
5. Povidone, USP:
Povidone (K-30) is mostly used as binder and a tablet coating, and forms clear, glossy, and hard film. Slide 15: 6. Sodium carboxymethylcellulose, USP:
7. Polythene glycols.
8. Acrylate polymers Slide 16: Reasons for enteric coating are;
▪ To protect acid-labile drugs.
▪ To prevent gastric distress or nausea due to irritation from a drug.
▪ To deliver drugs intended for local action in the intestine.
▪ To deliver drugs that are absorbed in the small intestine to their primary absorption site in their most concentrated form.
▪ To provide a delayed-release component for repeat-action tablets. Slide 17: Types of enteric`coating materials are :
◊ pH-sensitive materials.
◊ Digestible materials
◊ Emulsified by intestine
◊ Some slowly solvated. ► Enteric Materials: : ► Enteric Materials: 1. Cellulose Acetate Phthalate : (CAP)
CAP has been widely used in industry but has disadvantage of dissolving above pH 6, and thus delays absorption.
Latest CAP is available as Aquateric (composed of solid or semisolid polymer spheres of cellulose acetate phthalate , size- 0.05 to 3 microns)
2. Acrylate polymers :
3. Hydroxypropyl Methylcellulose Phthalate :
4. Polyvinyl Acetate Phthalate. Slide 19: (B). Solvents :
Primarily functions as to dissolve or disperse the polymers and other additives to the substrate surface.
Important considerations of the Ideal solvent system are:
▪ Should dissolve or disperse the polymer system.
▪ Should easily disperse other coating solution components.
▪ Should not create the processing problems.
▪ Should have no color, taste, odor, inexpensive, nontoxic, inert, and nonflammable. Slide 20: ▪ Should be rapidly dry.
▪ Should have environmental friendly.
water, ethanol, methanol, isopropranol, chloroform, acetone, methylethyl ketone, and methylene chloride. Slide 21: (C). Plasticizers :
The two types of the plasticizers are:
▪ INTERNAL MATERIALS : They modify the chemical properties of the polymer and thus changes the chemical properties of the polymer.
▪ EXTERNAL MATERIALS : They are non-volatile or the other polymer, which when include with primary polymeric film former, changes the flexibility, tensile strength, or adhesion properties of the resulting film. Slide 22: ◘Choice of the plasticizer material depends upon the ability of plasticizer material to solvate the polymer, as well as they impart flexibility by relieving the molecular rigidity.
◘ Viscosity of the plasticizer; it’s influences on the final coating solution; it’s effect on
film permeability, tackiness, flexibility, solubility, and taste; and it’s toxicity, compability with other coating solution components, and stability of the film and final coated product. Slide 23: ►CONCENTRATION OF PLASTICIZER EXPRESSED AS :
The amount of polymer being plasticized.
►RECOMMENDED LEVEL OF PLASTICIZER :
1 to 50% by weight of the film former.
►EXAMPLES : Castor oil; propylene glycol of 200 and 400 series; and surfactants eg; Tweens; Spans; and organis acid esters.
WATER- SOLUBLE PLASTICIZER : PEG, propylene glycol.
ORGANIC- SOLUBLE PLASTICIZER : castor-oil and SPANS. Slide 24: (D). Colorants :
◘ Colorants may be soluble in the solvent system or suspended as insoluble powders.
◘ They are used to provide distinctive color and elegance to a dosage form.
◘ To achieve proper distribution of suspended colorants in the coating solutions requires the use of fine-powdered colorants
(< 10 microns ).
◘ Most of colorants are synthetic DYES or LAKES OF DYES approved by the FD & C and D&C . Slide 25: ◘ LAKES : derived from dyes by precipitating with carriers. Eg ; alumina or talc. Lakes contains 10 to 30 % of the pure dye content.
FOR VERY LIGHT SHADE, CONCENTRATION : Less than 0.01 %.
FOR DARK SHADE, CONCENTRATION : More than
2.0 % .
Inorganic materials: iron oxides
Natural coloring materials :Anthocyanins, caramel, carotenoids, chlorophyll, indigo, flavones, turmeric, and carminic acid . Slide 26: Various concentrates promoted as archieving less lot-to-lot color variation :
◊ Opalux – Opaquant color concentrate for sugar coating.
◊ Opaspray- Opaque color concentrate for film coating.
◊ Opadry – Complete film coating concentrate. Slide 27: (E). Opaquant-Extenders :
◊ These are very fine inorganic powders used in the coating solution formulation to provide more pastel colors and increase film coverag.
◊ Opaquant provides a white coating or mask the color of the tablet core, and thus the less amount of the colorants are required .
Examples : Silicates(talc, aluminium silicate)
Oxides(Mg oxides) (2). Tablet coating processes : : (2). Tablet coating processes : Succesfull application of the coating solution formula to a tablet provides the visual charactertics for product; thus, the quality of the product may be judged on the final product. ►SUGAR COATING : : ►SUGAR COATING : ▪ The sugar coating process involves several steps, the duration of which ranges from a few hours to few days. A successful product depends on the skill of the coating operator.
►A successful sugar coating process yields elegant, highly glossed tablets. The basic sugar coating process involves the following step : : The basic sugar coating process involves the following step : (1). SEALING
(3). SYRUPING (SMOOTHING)
(5). POLISHING. Slide 31: (A). SEAL COATING :
Why seal coating is done ?
To prevent the moisture penetration into the tablet core, a seal coat is applied. Slide 32: Need of the seal coating ?
It’s needed in the pan-landing process in which localized overwetting of a portion of the tablet bed occurs.
Example : Zein is an alcohol-soluble protein derivative from corn that has also been used as an effective sealant.
Lengthening dissolution times have not been seen on aging of zein seal coated tablet. Slide 33: (B). SUBCOATING :
Why subcoating is necessary ?
It’s is applied to round the edges and build up the tablet size. It increase the tablet weight by 50 to 100%. Slide 34: Steps of the subcoating :
Alternatively applying a sticky binder solution to the tablets followed by a dusting of the subcoating powders and then drying, and further more the same procedure is done to increase the thickness of the tablet to the desired one.
Subcoating is also done by the spraying method.
In both methods the drying rate is very critical. Slide 35: (C). SYRUP SMOOTHING) :
What is the need of syruping ?
It covers and fill the imperfection in the tablet surface caused by the subcoating step, and to impart the desired color to the tablet. Slide 36: GLOSSING SYRUP :
The first syrup coats which contains the suspended powders are called Glossing syrup.
Colorants can be added to this syrup.
No color can be added untill the tablet are quite smooth.
► In the second step, syrup solution containing the dye are applied until the final size and color are achieved.
► In the final step, a few clear coats of syrup may be applied. Slide 37: (D). POLISHING :
► The tablets can be polished in clean standard coating pans, or canvas-lined polishing pans, by carefully application of the powdered wax (beeswax or carnauba) or warm solution of these waxes in naphtha or other suitable volatile solvents.
Example : An infinite no of variation in the materials and processes are possible, the complexity of the process can be explained by these example : Slide 38: MATERIALS AND EQUIPMENT :
Coating pans :
Stainless steel – 40 inches in diameter, with variable speed control, with 2 to 3 atomizing nozzles.
Tablet core :
55 to 70 kg of 3/8-inch standard convex tablets. Slide 39: Tablet coating machine 2. PROCESS : : 2. PROCESS : A. SEAL COAT : Here the spray coating is applied and it has faster distribution and also even one is obtained.
PAN SPEED : 10 rpm.
AIR SUPPLY TEMP: 30˚C .
THREE APPLICATION OF THE ZEIN SOLUTION.
ALLOW 15 TO 20 MINS BETWEEN EACH APPLICATION TO
ALLOW TO DRY TABLET Slide 43: B. SUBCOAT:
1. TURN HEAT AND INLET AIR OFF PAN SPEED AT 10 RPM.
2. APPLY 3 TO 9 COATS. USE 1.5 L OF WARM GELATIN/ ACACIA SOLUTION AND REDUCE AMOUNT TO OBTAIN CORRECT THICKNESS, AND ALSO TO COVER EDGES. Slide 44: 3.APPLY SUBCOATING POWDER UNTILL TABLETS ROLL FREELY AND SHOW NO SIGNS OF TACKINESS. AND ALLOW 20 MINS. GAP BETWEEN COATS TO PERMIT ADEQUATE DRYING.
4. ATLAST, JOG THE PAN FOR ATLEAST 2 TO 4 HOURS TO ENSURE DRYING. Slide 45: C. SYRUP (SMOOTHING/COLOR) COAT :
► THE SYRUPING COAT INVOLVES THREE BASIC PHASES :
→ GROSSING SYRUP.
→ HEAVY SYRUP.
→ REGULAR SYRUP. Slide 46: ▪ EACH STEP IS IN THE SEQUENCE :
1. REMOVE THE EXCESS DUST IN PAN BEFORE STARTING.
TURN ON EXHAUST OUTLET AIR.SET INLET AIR TEMPERATURE TO PROVIDE AN EXHAUST TEMPERATURE TO PROVIDE AN EXHAUST TEMPERATURE OF 45˚C TO 48˚C. SET PAN SPEED AT 12 RPM. Slide 47: 2. APPLY THE 5 TO 15 COATING B’COZ SOLUTION DRIES RELATIVELY QUICK, UNIFORM, RAPID DISTRIBUTION MUST BE PROVIDED.
APPLY SUCCESSIVE AMOUNTS OF GROSSING SYRUP IMMEDIATELY AFTER EACH PRECEDING APPLICATION IS DRYING AND SLIGHTLY DUSTY. Slide 48: 3. APPLY SEVERAL HEAVY-COLORED SYRUP COATS IN A SIMILAR MANNER UNTIL A SPECIFIC TABLET VOLUME IS ATTAINED.
4. TURN OFF HEAT, AND REDUCE INLET AND EXHAUST AIR. Slide 49: 5. APPLY SEVERAL COATS OF THE REGULAR COLORED SYRUP SOLUTION TO ACHIEVE A FINAL SMOOTHNESS, SIZE, AND COLOR DEVELOPMENT.
6. EACH COAT OF REGULAR COLORED SYRUP IS APPLIED AS SOON AS THE TABLETS EXHIBIT A SLIGHLY FROSTED APPEARANCE. Slide 50: D. FINISHING
MAKE SURE THAT THE PAN IS CLEAN.
2. OPERATE THE PAN WITH THE HEAT TURNED OFF, NO SUPPLY, AND GREATLY REDUCED EXHAUST AIR. SET PAN SPEED AT 12 RPM.
3. APPLY 3 TO 4 COATS OF REGULAR COLORED SYRUP RAPIDLY, WITHOUT PERMITTING THE TABLET BED TO FROST OR BECOME DUSTY. Slide 51: 4. THE LAST COATS OF REGULAR SYRUP CAN BE APPLIED WITHOUT COLORANT. THIS GIVES “DEPTH” TO THE COLOR AND ENHANCES THE ELEGANCE OF THE COAT.
5. SHUT OFF EXHAST AIR BEFORE APPLYING THE LAST COAT.APPLY COAT; MIX UNIFORMLY AND SHUT OFF PAN WHILE THE TABLETS ARE STILL DAMP. Slide 52: E. POLISHING :
IT CAN BE DONE IN THE SAME PAN BUT THE BEST RESULTS ARE OBTAINED IN THE CANVAS-LINED PANS:
SUPPLY AIR, EXHAUST AIR, AND HEAT SHOULD BE TURNED OFF. PAN SPEED 12 RPM.
2. APPLY 3 TO 4 COATS OF WARM POLISHING SOLUTION, APPROXIMATELY 300ml PER APPLICATION.
3. ALLOW THE SOLUTION TO EVAPORATE. Slide 53: TABLET COATINGS ACHIEVE THEIR LUSTER DURING THE POLISHING PHASE. IN THE CANVAS LINED PAN, IT’S USED TO TRANSFER THE WAXES TO THE TABLET SURFACE AND TO PROVIDE A BUFFING ACTION. Slide 54: Film defects
Sticking and picking
Orange –peel effects
Bridging and filling
Cracking Slide 55: 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 adhere to pan or tablet.
- Giving “picked” appearances to the tablet surface.
- Resulting in a small exposed area of the core. Slide 56: Remedies
- Reduction in liquid application rate.
- Increase in drying air temperature and air volume. Slide 57: 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 and polymer concentration in the coating solution. Slide 58: Remedies
Moving the nozzle closer to the tablet bed.
Reducing the degree of atomization can decrease the roughness due to spray drying Slide 59: Orange –peel effects
Inadequate spreading of coating solution before drying causes a bumpy or Orange –peel effects On the coating. Slide 60: Causes
Indicates that spresding is impaired by rapid rate of drying or by high solution viscosity.
Thinning of coating solution with additional solvents may correct this problem. Slide 61: 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. Slide 62: Remedies
Increase in plasticizer contents or change in plasticizer concentration can decrease the bridging Slide 63: 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.
Judicious monitoring of the fluid application rate .
Thorough mixing of tablets in the pan prevent filling. Slide 64: 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.
Controlled drying conditions. Slide 65: Hazing/Dull film
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 conditions and partial solvation of film results. Slide 66: Colour variation
Problem caused by process conditions or the formulation
Improper mixing, uneven spray pattern and insufficient coating may results in colour variation.
The migration of soluble dyes, plasticizer and other additives give the coating a mottled or spotted appearance.
Use of lake dyes eliminates dye migration.
A reformulation with different plasticizer and additives is the best way to solve film instability. Slide 67: 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.
Adjusting the plasticizer types and concentration can minimize internal stresses
Also adjusting the pigment types and concentration can minimize internal stresses Equipments : Equipments Three general type equipment:
1. The standard coating pan
2. The perforated coating pan
The fluidized bed
(air suspension) coater The standard coating pan : The standard coating pan Simplified diagram of Hi-coater system : Simplified diagram of Hi-coater system Simplified diagram of Di-coater system : Simplified diagram of Di-coater system Glatt coater : Glatt coater Slide 74: Fluidized bed
( air suspension )
coater Slide 75: Simplified diagram of Rotating Fluidized bed ( air suspension ) coater Slide 77: Thank you