1. TABLET COATING
2. CONTENTS INTRODUCTION PURPOSE OF COATING PRINCIPLE OF COATING HISTORY OF COATING GENERAL STEPS TYPES OF COATING SUGAR COATING FILM COATING FILM COATING COMPONENTS ENTERIC COATING POLYMERS POLYMER CHARACTERISTICS TYPES OF TABLET COATING EQUIPMENT FACTORS EFFECTING COATING PROCESS ADVANCE COATING TECHNIQUES
3. INTRODUCTION Coating is a process by which an essentially dry, outer layer of coating material is applied to the surface of a dosage form in order to confer specific benefits over uncoated variety. Coating may be applied to a wide range of oral solid dosage form, such as particles, powders, granules, crystals, pellets and tablets. A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. Many APIs are moisture-sensitive and thus need protection against ambient moisture. Usually, packaging materials are employed that provide a tight enclosure, but this adds costs to the already expensive manufacturing process. A more cost-effective alternative is to use well- formulated moisture protective coatings that reduce water vapour transmission rate (WVTR) WVTR can be described using Fick's first law which states that the amount of water vapour diffusing across a film barrier at a given time is a function of the following, The moisture gradient, which can be calculated based on the specific water activity of the core formulation and the ambient humidity. The water activity of the core is dependent on the excepients present in the core formulation. The diffusion constant and the surface area of the tablet. The layer thickness of the film.
4. PURPOSE OF COATING The objectives of tablet coating are as follows, To mask the disagreeable odor, color or taste of the tablet. To offer a physical/chemical protection to the drug. To control and sustain the release of the drug from the dosage form. To incorporate another drug which create incompatibility problems. To protect an acid-labile drug from the gastric environment. To make easier to swallow. To reducing light sensitivity and atmospheric oxidation, improving stability. To improve the pharmaceutical elegance by use of special colors. To prevent color migration from core i.e. if the active substance is colored and migrates easily to stain hands and clothes. To reduce friction in packaging operation. The coated tablets are packed on high speed packaging machine. Coating reduces friction and increases packaging rate. To modify drug release profile.
5. PRINCIPLE OF COATING Coating solutions are sprayed onto the uncoated tablets as the tablets are being agitated in a pan, fluid bed. Rotating coating pans are used in the pharmaceutical industry. Uncoated tablets are placed in the pan and the liquid coating solution is introduced into the pan while the tablets are tumbling. The liquid portion of the coating solution is then evaporated by passing hot air over the surface of the tumbling tablets. As the solution is being applied, a thin film is formed which sticks to each tablet. In contrast, a fluid bed coater operates by passing hot air through a bed of tablets at a velocity sufficient to support and separate the tablets as individual units. Once separated, the tablets are sprayed with the coating composition.
6. GENERAL COATING PROCESS
7. HISTORY OF COATING “Panning” was the original word for the process of adding a coating to a tablet. The word panning is still a common term which is used in the confectionary business. In past years coating perform basically using a rotating drum (pan) on a stand. A coating solution was added, while the rotation of the pan distributed the solution throughout the bed of tablets. The main disadvantage of this technology was slow waiting for the coating solution to dry and the trick was to get it to dry evenly. With the advent of film coating a film or thin membrane, usually representing 1-3% of the total tablet weight, was sprayed on using a perforated pan. To decrease the overall process time, holes were made through the pan so that treated air (hot or cold) could be pulled through the pan, much like a clothes dryer, allowing the tablets to dry more quickly. With this advent of improved drying came the ability to switch the film coating solution from a solvent based solution to a water based solution.
8. GENERAL STEPS OF COATING PROCEDURE BATCH IDENTIFICATION. PREPRATION OF COATING SOLUTION. LOADING OF TABLETS IN COATING PAN. WARMING OF TABLETS. SPRAYING (APPLICATION AND ROLLING ARE CARRIED OUT. SIMULTANEOUSLY). DRYING OF TABLETS. COOLING OF TABLETS. UNLOADING OF TABLETS.
9. TYPES OF COATING 1. FILM COATING 2. SUGAR COATING CLASSIFICATION OF FIM COATING ON BASIS OF POLYMER i. NON FUNCTIONAL Which does not modify the relase profile of the API. Regular film coatings are for taste masking, odour masking, colour identification and Pearly appearance. EXAMPLES i. Immediate Release Coating/Conventional Film Coating ii. FUNCTIONAL Which modifies the release profile of the API. With regards to functional coatings, most of these are non-water soluble. Moisture protection to hygroscopic molecules. EXAMPLES i. ENTERIC COATING ii. MODIFIED RELEASE COATING
10. TYPES OF COATING SUGAR COATING The act or process of covering tablets with sugar/sucrose solution is called Sugar Coating. Compressed tablets may be coated with coloured or uncoloured sugar layer. sugar coating is a multistep process. Use of labour is more intensive than in film coating and process operators require a fair degree of skill. The ideal shape for sugar coating is a deeply convex core with minimal edges MECHANISM In 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. Example Fillers, Colours, etc. The build up of coating material is due to a transference of coating medium from one tablet to another. Typically a single liquid application will be made which will be allowed to spread over the entire tablet bed utilizing the mixing capability of the particular equipment. At this point, drying, usually in the form of heated air, will be used to dry the application. The whole cycle will then be successively repeated.
11. STEPS OF SUGAR COATING Sugar coating process involves five separate operations SEALING/WATER PROOFING: Provides a moisture barrier and harden the tablet surface. SUBCOATING: Causes a rapid buildup to round off the tablet edges. GROSSING/SMOOTHING: Smoothes out the sub coated surface and increases the tablet size to predetermine dimension. COLOURING: Gives the tablet its color and finished size. POLISHING: Produces the characteristics gloss.
12. STEPS OF SUGAR COATING SEALING/WATER PROOFING Sealing protect the tablet core from the aqueous nature of sucrose applications. Sealing also prevents certain types of materials from migration. The seal coat provides a moisture barrier and hardness the surface of the tablet in order to minimize attritional effects. Core tablets having very rapid disintegration rates conceivably could start the disintegration process during the initial phase of sugar coating. The sealants are generally water-insoluble polymers/film formers applied from an organic solvent solution. The quantities of material applied as a sealing coat will depend primarily on the tablet porosity, since highly porous tablets will tend to soak up the first application of solution, thus preventing it from spreading uniformly across the surface of every tablet in the batch. Hence, one or more further application of resin solution may be required to ensure that the tablet cores are sealed effectively. Common materials used as a sealant include, i. SHELLAC iv. ZINE ii. CELLULOSE ACETATE PHTHALATE (CAP) v. HYROXYLPROPYLCELLULOSE iii. PVAP
13. STEPS OF SUGAR COATING SUBCOATING Sub coating is the actual start of the sugar coating process. Less concentrated sucrose syrup is used. It provides the rapid buildup necessary to round up the tablet edge. During the sugar-coating process the increase in weight achieved can be 30–50% of the weight of the original tablet core. Much of the added weight is applied at the subcoating stage. Subcoating serves to confer on the tablet core a perfectly rounded aspect. There are two methods For Sub Coat i. LAMINATION PROCESS ii. SUSPENSION PROCESS
14. STEPS OF SUGAR COATING LAMINATION PROCESS The Lamination process is that a volume of binder solution is applied to the sealed cores in the coating pan. Once this has spread over the tablet bed an application of powder is dusted into the pan, and when this has evenly distributed itself over the contents, drying air is applied. The drying air process needs to be carefully controlled to prevent too rapid evaporation of the water. The objective should be to create as smooth a coat as possible in order to reduce the time for smoothing the coat in the final stages of process. Excessively rapid drying results in a very uneven surface. Too low an evaporation rate gives rise to a lengthy process and the danger of cores adhering together. SUSPENSION PROCESS In recent years, automation in the sugar-coating process has required the use of a liquid subcoat. These are generally suspensions of the filler materials, e.g. calcium carbonate, talc, sucrose in the gum solutions.The system contains only approximately 23% water and consequently dries quickly.
15. STEPS OF SUGAR COATING GROSSING/ SMOOTHING The grossing/smoothing process is specifically for smoothing and filing the irregularity on the surface generated during sub coating. Thick Sucrose solution is used. It also increases the tablet size to a predetermined dimension. The product at the end of the sub coating will be too rough to continue with color coating. Smoothing is usually achieved by applications of plain 70% w/w syrup. However large degrees of unevenness will require some sub coating solids in the initial smoothing coats. If sub coating is carried out well, then approximately ten applications of 70% syrup will be required for tablets that are suitable for the next stage.
16. STEPS OF SUGAR COATING COLOUR COATING This is one of the most important steps in the sugar-coating process as it has immediate visual impact. During this step the coating syrup contains the colour solids necessary to achieve the desire shade. This stage is often critical in the successful completion of a sugar coating process and involves the multiple application of syrup solution (60-70 % sugar solid) containing the requisite colouring matter. Soluble dyes were used to give the desired colour as these stick to the surface of the tablet during the drying process.But soluble dye may migrate to the surface during drying so pharmaceutical companies prefer the use of insoluble certified aluminium lake pigments.
17. STEPS OF SUGAR COATING POLISHING The final step in the sugar coating process is a polishing step. After the colour coating process the tablets have a somewhat dull, matt appearance which requires a separate polishing step to give them the high degree of gloss. Polishing is achieved by applying the mixture of waxes like i. BEESWAX ii. CARNUBAWAX iii. CANDELILA WAX iv. HARD PARAFFIN WAX to tablets in polishing pan. PRINTING Finally tablets can be printed on the surface using edible ink.
18. STEPS OF SUGAR COATING
19. ENTERIC SUGAR COATING The sealing coat is altered by adding one of the enteric polymers in sufficient number in order for it to pass the enteric test for dissolution. The sub-coating and succeeding coating steps are for conventional sugar coating. The enteric polymer has the ability to form a direct film during the film coating process. Sufficient weight must be used in order to have an efficient enteric effect.
20. ADVANTAGES OF SUGAR COATING The process requires unsophisticated equipment. It is affordable in terms of running costs as the most common ingredients used are sugar and water. It provides an attractive and glossy finish. Sugar coated tablets are easy to swallow as the sugar masks the taste. DISADVANTAGES OF SUGAR COATING It requires specialized and trained personnel. The process is Labour intensive. It requires long processing time. Sugar coated tablets are not amenable to embossing, use of print for identification or labelling. Sugar coating increases the weight and size of the tablet.
21. PROBLEMS OF SUGAR COATING CHIPPING OF THE TABLET COATING This is often caused by a low concentration or absence of polymer. Add more polymer to the coating solution. Another cause is the excessive use of pigments and insoluble fibres. Reduce the number of fillers. CRACKING Expansion of the tablet during or after coating caused by stress relaxation or moisture absorption – consider the use of seal coat or extend the time between the sugar coating and compaction. NON-DRYING OF THE COATING Excessive presence of invert sugar . Avoid the excess heating of the sucrose syrup under acidic conditions.
22. PROBLEMS OF SUGAR COATING TWINNING High edge walls/flat surface. Modify or alter the punch design. UNEVEN COLOURING Poor distribution of coating solution. Add sufficient liquid and ensure that it is fully mixed. Colour migration due to under/rapid drying Optimize the drying condition and use pigments. Uneven sub coat layer. Achieve the required smoothness during the sub coat application. Wash back of pigment colour coating. Avoid excess colour coating liquid. Excessive drying between colour application. Optimize the drying conditions.
23. PROBLEMS OF SUGAR COATING BLOOMING AND SWEATING Extra moisture in the finished tablet coat. Dry properly to ensure appropriate moisture level. MARBLING Uneven coating surface. Make sure to achieve smooth coating before the polishing step.
24. FILM COATING A film coating is a thin polymer-based coat applied to a solid dosage form such as a tablet, granule or other particle. The thickness of such a coating is usually between 20 and 100 μm. Film coating is the process whereby a tablet, capsule, or pellet is surrounded by a thin layer of polymeric material. MECHANISM OF FILM FORMATION In the wet state the polymer is present as a number of discrete particles, and these have to come together in close contact, deform,coalesce and ultimately fuse together to form a discrete film. During processing, the substrate surface will be wetted with the diluted dispersion. Under the prevailing processing conditions solvent will be lost as vapour and the polymer particles will increase in proximity to each other,a process which is greatly aided by the capillary action of the film of solvent surrounding the particles. Complete coalescence occurs when the adjacent particles are able to mutually diffuse into one another. MINIMUM FILM-FORMING TEMPERATURE (MFT) This is the minimum temperature above which film formation will take place using individual defined conditions. It is largely dependent on the glass transition temperature (Tg) of the polymer,defined as temperature at which the hard glassy form of an amorphous or largely amorphous polymer changes to a softer, more rubbery consistency.
25. THE PROCESS OF FILM COATING Tablets are placed inside the coating drum which is then set to rotate, to mix the tablets. Ambient air is heated and passes through perforations in base of the rotating drum to warm up the tablets. Air is circulated through the tablets as the drum rotates and exhausted through a vent system at the top or side of the drum. A solution or suspension of the coating material is sprayed as fine droplets through the bed of tablets. To achieve uniform coating across the bed, the distance between the spray gun and tablet bed is measured and adjusted accordingly. Once the droplets hit the surfaces of the tablets, it spreads into film on the surface before solvent is removed rapidly by the hot air. The coating thickness on each tablet is increased as the tablets pass underneath the spray gun by the rotating drum.
26. FILM COATING COMPONENTS Film coating formulations usually contain the following components, FILM FORMERS (ENTERIC OR NON-ENTERIC) SOLVENTS/SOLUTIONS PLASTICIZERS COLOURANTS OPAQUANT EXTENDERS OTHER COMPONENTS
27. POLYMER/FILM FORMER Polymers play an important role in film coating. Polymer is major ingredient and have great impact on tablet coating properties. Polymers have different grades determined by Molecular wt and viscosity grades. The vast majority of the polymers used in film coating are either cellulose derivatives, such as the cellulose ethers, or acrylic polymers and copolymers. The polymer is dissolved in an appropriate solvent either water or a non-aqueous solvent for application of the coating to the solid dosage form. On application of heat solvent evaporate leaving behind polymer which form film around tablet core.
28. POLYMER/FILM FORMER
29. POLYMER/FILM FORMER
30. IDEAL PROPERTIES OF FILMFORMER Solubility of the film former in the desired solvent. Allow for the release of the drug in the body. Form a clear, strong, non-tacky film. Film coating demands polymers at the lower end of the viscosity scale. pH-dependence of solubility. Capacity for an well-designed end product. Constancy against outside conditions such as light, heat, moisture and substrate. Stability in terms of taste, colour and smell. Be compatible to the core content of the tablet. Compatibility of the film former with other coating additives. Nontoxic with no pharmacological actions. Resistance to cracking. Film formers should not lead to bridging or filling. Ideally compatible with imprints.
31. POLYMER/FILM FORMER METHYLCELLULOSE (MC) This polymer is used rarely in film coating possibly because of the lack of commercial availability of low viscosity material meeting the appropriate compendial requirements. HYDROXYETHYL CELLULOSE (HEC) It is soluble in water. Insoluble in organic solvents. HYDROXYPROPYL CELLULOSE (HPC) HPC is soluble in both aqueous and alcoholic media. This is water-soluble below 40°C but insoluble above 45°C. It is soluble in other fluids such as gastric and other organic solvents. It is flexible but becomes tacky while drying and is used only as a sub-coat and not for gloss or color coating. Its films unfortunately tend to be rather tacky, which possess restraints on rapid coating. HPC films also suffer from being weak. Currently this polymer is very often used in combination with other polymers to provide additional adhesion to the substrate .
32. HYDROXY PROPYL METHYL CELLULOSE (HPMC) HPMC is soluble in aqueous and organic solvent. HPMC is a polymer that is ideal for processes such as air suspension and pan spray coating due to its solubility in organic, gastric fluid and other liquid solvent matter. It is available in different viscosity levels. HPMC is a white powder or granular material. ADVANTAGES HPMC is cheap, heat, light and moisture resistant, flexible. it has no inherent smell or taste, Does not affect the tablet’s disintegration and drug availability. Colours and other additives can easily be added. DISADVANTAGES When used by itself HPMC is inclined to bridge or fill up the debossed tablet’s surface. For this reason it is recommended that HPMC is used in combination with other polymers.
33. SODIUM CARBOXY METHYL CELLULOSE It is soluble in water but insoluble in organic solvents. It is only useful when dispersed in water in order to form colloidal solutions so is not the right choice as a coating for tablets that are based on organic solvents. Although the solution adheres to the tablet’s surface, the tablet becomes brittle when exposed to the solution. Partially dried films are considered tacky and as such other additives are used to modify the composition. Viscosity levels range from medium, high and extra high. VINYL DERIVATES The most widely used vinyl polymer derivate is PVP. It has a limited use in film coating because of its inherent tackiness. A copolymer of PVP and vinyl acetate forms better films.
34. ENTERIC COATING An enteric coating is a polymer barrier applied on oral medication that prevents its dissolution or disintegration in the gastric environment. Some drugs are unstable at the acid gastric pH, and need to be protected from degradation. Enteric coating is also an effective method to obtain drug targeting (such as gastro-resistant drugs). The enteric coating is used to protect the core of the tablet from disintegrating when exposed to the stomach acid, prevent acid sensitive API degradation, and stomach irritation, delivery of the API to the intestine tract and to provide a timed release of the components. Polymers that are used include i. CELLULOSE ACETATE PHTHALATE (CAP) ii. CELLULOSE ACETATE TRIMELLITATE(CAT) iii. ACRYLATES iv. HYDROXY PROPYL METHYL CELLULOSE PHTHALATE (HPMCP) v. POLYVINYL ACETATE PHTHALATE (PVAP) vi. METHYL METHACRYLATE-METHACRYLIC ACID COPOLYMERS vii. SHELLAC viii. SODIUM ALGINATE ix. ZEIN x. ENTERIC COATING AQUEOUS SOLUTION (ETHYLCELLULOSE, MEDIUM CHAIN TRIGLYCERIDES [COCONUT], OLEIC ACID, SODIUM ALGINATE, STEARIC ACID) (COATED SOFTGELS)
35. ENTERIC COATING POLYMERS
36. AQUEOUS ENTERIC COATING POLYMERS
37. ENTERIC COATING POLYMERS CELLULOSE ACETATE PHTHALATE (CAP) This is a common polymer coating used in the industry. Aquateric, a commercial CAP material, comprises a reconstructed colloidal diffusion of latex particles composed of solid or semisolid polymer spheres of CAP that range from 0.05 – 3 microns. CAP is insoluble in water, alcohols and chlorinated hydrocarbons. CELLULOSE ACETATE TRIMELLITATE(CAT) Cellulose acetate trimellitate (CAT) is a similar polymer developed as an ammoniated aqueous formulation and shows a more rapid dissolution than the same formulation of CAP. DISADVANTAGES OF CAP AND CAT INCLUDE Dissolves < pH 6 Delays drug absorption. Permeable to moisture compared with other enteric polymer. Hygroscopic. Acetic acid changes film properties. CAP films are fragile and usually used in conjunction with other hydrophobic films.
38. ENTERIC COATING POLYMERS ACRYLATE POLYMERS There are 2 forms of commercially available enteric acrylic polymer resins i. Eudragit L ii. Eudragit S Both produce films that are resistant to gastric liquids. Both of the resins are soluble in intestinal fluid at pH 6 and 7. The L form is available in organic, solid or aqueous distribution. The S form is only available as an organic and solid solution.
39. ENTERIC COATING POLYMERS METHACRYLIC ACID COPOLYMERS These polymers possess free carboxylic acid groups so find use as enteric-coating materials, forming salts with alkalis and having an appreciable solubility at pH in excess of 5.5 Two organic solvent soluble polymers are i. Eudragit S100 ii. Eudragit L100 It has a lower degree of substitution with carboxyl groups and consequently dissolves at higher pH than Eudragit L100. Pigments and opacifiers are useful additions as they counteract the sticky nature of the polymers. A feature of these polymers is their ability to bind large quantities of pigments approximately two or three times the quantity of polymer used. Polyethylene glycols are frequently added as they provide a measure of gloss to the final product. They also assist in stabilizing the water-dispersible form, Eudragit L30D. Pigment and other additions to the water-dispersible forms Eudragit, L30D and L100–55, should be performed according to the manufacturer’s recommendations to prevent coagulation of the coating dispersion. Both Eudragit L100 and S100 are available in powder form and for convenience purposes they are also available as concentrates in organic solvent solution, which are capable of further dilution in the common processing solvents used in organic solvent-based film coating. Two further commercial forms are available, first, a 30% aqueous dispersion, Eudragit L30D, and, secondly, a water-dispersible powder, Eudragit L100–55.
40. ENTERIC COATING POLYMERS METHACRYLATE AMINOESTER COPOLYMER This polymer is basically insoluble in water but dissolves in acidic media below pH 4. In neutral or alkaline environments, its films achieve solubility by swelling and increased permeability to aqueous media. Formulations intended for conventional film coating can be further modified to enhance swelling and permeability by the incorporation of materials such as water soluble cellulose ethers, and starches in order to ensure complete disintegration/dissolution of the film. This material is supplied in both powder form or as a concentrated solution in isopropanol/acetone, which can be further diluted with solvents such as ethanol, methanol, acetone and methylene chloride. Talc, magnesium stearate or similar materials are useful additions to the coating formula as they assist in decreasing the sticky or tacky nature of the polymer. In general, the polymer does not require the addition of a plasticizer.
41. ENTERIC COATING POLYMERS HYDROXY PROPYL METHYL CELLULOSE PHTHALATE (HPMCP) Commonly used forms of this polymer are HPMCP 50, 55 & 55-s The 55 is recommended for enteric preparation whereas the 50 and the 55-s are for special applications. The polymers dissolve at a pH of 5-5.5. POLYVINYL ACETATE PHTHALATE (PVAP) This polymer is similar to the hydroxyl propyl methyl cellulose phthalate HP-55 in terms of stability and pH dependent solubility.
42. ENTERIC COATING POLYMERS SHELLAC This is a purified resinous secretion of the insect Laccifer lacca. Shellac is insoluble in water but shows solubility in aqueous alkalis. it is moderately soluble in warm ethanol. Shellac suffers from the general drawback that it is a material of natural origin and consequently suffers from occasional supply problems and quality variation. There are also stability problems associated with increased disintegration and dissolution times on storage.
43. APPLICATION OF ENTERIC POLYMER COATING All of the enteric polymers listed above are capable of forming a complete direct film for coating tablets. To ensure that a complete and efficient seal of the tablet core is achieved, sufficient weight of the polymer is needed. To achieve controlled delayed release of drug, the coating can be mixed with polysaccharides which do not react in the stomach but can degrade in the colon. Controlled released coatings are generally prepared using polymers such as modified acrylates and water insoluble cellulose.
44. POLYMER CHARACTERISTICS SOLUBILITY Solubility characteristics of the film-coating polymers show that the following have a good solubility in water, HPMC, HPC, MC, PVP, PEG plus gastrointestinal fluids and the common organic solvents used in coating. Acrylic polymers used for conventional film coating include methacrylate amino ester copolymers.These bcome water soluble by swelling, increasing permeability in aqueous media. These polymers in its unmodified form is however soluble only in organic solvents. Where it is proposed to use an aqueous solvent for film coating it is necessary to consider, first, the need to minimize contact between the tablet core and water and,secondly,the need to achieve a reasonable process time. Both can be achieved by using the highest possible polymer concentration (i.e. the lowest possible water content). The limiting factor here is one of coating suspension viscosity.
45. POLYMER CHARACTERISTICS VISCOSITY Polymer used should have low viscosity for a given concentration. This will result in easy trouble free spraying of solution. HPMC coating polymers are available in a number of viscosity designations defined as the nominal viscosity of a 2%w/w aqueous solution at 20°C. So a 5mPa s grade will have a nominal viscosity of 5 mPa s in 2% aqueous solution in water at 20°C and similarly with 6 mPa s, 15 mPa s and 50 mPa s grades. Commercial nomenclature for these grades describe them as ‘5 cP’ etc. Commercial designations such as E5 (Methocel) or 606 (Pharmacoat) also correspond with the viscosity designation for example Methocel E5 has a nominal viscosity of 5mPa s under the previously described standard conditions. While Pharmacoat 606 would have a nominal viscosity of 6 mPa s under the same conditions.
46. POLYMER CHARACTERISTICS VISCOSITY For example for final polymer solution to be sprayed, a normal HPMC based system would have a viscosity of approximately 500 mPas for this a 5 mPa s grade (E5) is used.A solids concentration of about 15%w/w can be achieved. This has the advantage over a coating solution prepared from a 50 mPa s grade (E50) where only a 5%w/w solids concentration could be achieved. The lower viscosity grade polymer permits a higher solids concentration to be used, with consequent reduction in solvent content of the solution. The practical advantage to be gained is that the lower the solvent content of the solution, the shorter will be the processing time as less solvent has to be removed during the coating procedure. This beneficial interaction between polymer viscosity and possible coating solids is self-limiting in that very low viscosity polymers will suffer from poor film strength due to low molecular weight composition
47. POLYMER CHARACTERISTICS PERMEABILITY The moisture permeability of a simple film may be decreased by the incorporation of water-insoluble polymers, however disintegration and dissolution characteristics of the dosage form must be carefully checked. Permeability effects can be assessed practically by a technique of sealing a sample of cast film over a small container of desiccant or saturated salt solution, the permeability to water vapour being followed by successive weighings to determine respectively weight gain or weight loss. HPMC (606) and polyvinyl alcohol (PVA). Addition of PVA to the HPMC was seen to enhance very effectively the moisture barrier effect of the HPMC. This behaviour is due to possible potentiation of the crystallinity of the HPMC by the PVA.
48. POLYMER CHARACTERISTICS MECHANICAL PROPERTIES Some of the film mechanical properties of concern are, i. TENSILE STRENGTH ii. MODULUS OF ELASTICITY To perform any function a film coat must be mechanically adequate so that in use it does not crack, split or generally fail. Also, during the rigours of the coating process itself the film is often relied upon for the provision of some mechanical strength to protect the tablet core from undue attrition. TENSILE STRENGTH It is the maximum stress applied at the point at which the film breaks. TENSILE STRAIN AT BREAK A measure of how far the sample elongates prior to break.
49. MODULUS (ELASTIC MODULUS) This is applied stress divided by the corresponding strain in the region of linear elastic deformation. It can be regarded as an index of stiffness and rigidity of a film. TACKINESS In a film-coating sense, tack is a property of a polymer solution related to the forces necessary to separate two parallel surfaces joined by a thin film of the solution. It is a property responsible for processing difficulties and is a limitation on the use of some polymers e.g Hydroxypropyl Cellulose.
50. EFFECT OF POLYMER MOLECULAR WEIGHT ON COATING PROPERTIES TENSILE STRENGTH Increases. ELASTIC MODULUS Increases mean coating become less elastic. FILM ADHESION Decrease. SOLUTION VISCOSITY Increases FILM MERMEABILITY Typically uneffected unless structural mechanical properties improve with increase in Mol wt.
51. SOLVENTS Solvents are used to dissolve the polymers and other additives ready for spraying or otherwise coating the surface of the tablet or capsule. The basic solvent requirements are, It should be able to dissolve or disperse the polymer. It should easily dissolve other additives added to the system. Small concentrations of the polymer should not cause any problems for exceedingly viscous solution. It should be non-toxic and non-flammable. It should be odourless, colourless and tasteless. It should not cause any environmental problems. Have high drying rate. Most of the solvents used are by themselves, however some are combined with other solvents. EXAMPLESE i. ETHANOL V. CHLOROFORM ii. WATER VI. METHANOL iii.IPA VII. ACETONE iv. METHYLENE CHLORIDE Due to environmental and health concerns, water is the most commonly used additive,however for drugs that hydrolyze when they come into contact with water, non-aqueous solvents are necessary.
52. CLASSIFICATION OF COATING ON BASIS OF SOLVENT On the basis on solvent used coating is classified into following types, i. AQUEOUS ii. ORGANIC/ALCOHOLIC iii. HYDROALCOHOLIC AQUEOUS SOLVENT USED IS WATER. 12-15 % Dispersion is Suitable. ORGANIC/ALCOHOLIC ORGANIC SOLVENT IS USED. 5-8% Dispersion is Suitable. HYDROALCOHOLIC ORGANIC SOLVENT AND WATER IS USED IN DEFINED RATIO. 8-10% Dispersion is Suitable.
53. AQUEOUS VS SOLVENT COATING AQUEOUS BASED These are now the most common. No safety issues (e.g. can allow mobile vessels). Can release to atmosphere. Takes longer and may lead to mechanical damage as tablets are tumbled for longer. Requires more efficient drying air plant. Advances in drying efficiency has allowed aqueous processes to be developed even for moisture sensitive products. SOLVENT BASED Coating solutions / suspensions are organic e.g. alcohols, methylene chloride. Rapid drying time due to inherent volatility. Can be applied to moisture sensitive products. Operator safety issues. Requires modification to equipment and facility (flame-proofing / intrinsically safe). Environmentally responsible disposal is expensive (solvent recovery). Can impart taste / smell to the product.
54. PLASTICIZERS Plasticizers are 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. Generally the effect will be to make it softer and more pliable. There are often chemical similarities between a polymer and its plasticizer for instance, glycerol and propylene glycol, which are plasticizers for several cellulosic systems, possess OH groups, a feature in common with the polymer. The mechanism of action for a plasticizer is for the plasticizer molecules to interpose themselves between the individual polymer strands thus breaking down to a large extent polymer-polymer interactions. This action is facilitated as the polymer plasticizer interaction is considered to be stronger than the polymer-polymer interaction. Hence, the polymer strands now have a greater opportunity to move past each other. Most of the polymers used in film coating are either amorphous or have very little crystallinity. Strongly crystalline polymers are difficult to plasticize in this fashion as disruption of their intermolecular structure is not an easy matter. The action of a plasticizer is also to lower the glass transition temperature.
55. EFFECT OF PLASTICIZER ON COATING PROPERTIES TENSILE STRENGTH Decrease with increase concentration of plasticizer. ELASTIC MODULUS Decreases mean coating become more elastic. FILM ADHESION May be increased but results are variables. SOLUTION VISCOSITY Increases and depend upon molecular weight of plasticizer. FILM MERMEABILITY Can be increased or decreased depending upon chemical nature of plasticizer. GLASS TRANSITION TEMPWERATURE Decreased but effect depend upon compatibility with polymer.
56. CLASSIFICATION PLASTICIZERS The commonly used plasticizers can be categorized into three groups, POLYOLS i. GLYCEROL (GLYCERIN) ii. PROPYLENE GLYCOL iii. POLYETHYLENE GLYCOLS PEG (GENERALLY THE 200–6000 GRADES) ORGANIC ESTERS i. PHTHALATE ESTERS (DIETHYL, DIBUTYL) ii. DIBUTYL SEBACETE iii. CITRATE ESTERS (TRIETHYL, ACETYL TRIETHYL, ACETYL TRIBUTYL) iv. TRIACETIN OILS/GLYCERIDES i. CASTOR OIL ii. ACETYLATED MONOGLYCERIDES iii. FRACTIONATED COCONUT OIL
57. COLOURANTS FD&C (Food, Drugs and Cosmetics) and D&C (Drugs & Cosmetics) dyes and lakes, also known as artificial colors or certified colors, can be used in a wide range of combinations to produce nearly any color for tablet coating. Pharmaceutical colorants can be classified as water-soluble dyes or water-insoluble Lakes/pigments. For sugar or film coating, lakes are preferred because they produce more reproducible results. The colour shade, dye type and opaquant extender are some of the features that need to considered in ensuring the correct concentration of colouring in the coating solution. Concentrations of < 0.01% generally result in a lighter shade whereas a concentration of 2.0 % results in a darker color. There are a number of reasons to colour tablets, including, i. BRAND IDENTIFICATION ii. COUNTERFEIT PREVENTION iii. QUALITY PERCEPTION CLASSIFICATION OF COLOURS i. ORGANIC DYES AND THEIR LAKES ii. INORGANIC COLOURS iii. NATURAL COLOURS
58. EFFECT OF PIGMENT ON COATING PROPERTIES TENSILE STRENGTH Decreased. ELASTIC MODULUS Increases mean coating become less elastic. FILM ADHESION Little effect. SOLUTION VISCOSITY Increased. FILM MERMEABILITY Decreased. HIDING POWER Increased but effect depend upon refractive index of pigment and light absorbed by pignent
59. ORGANIC DYES AND THEIR LAKES DYE A dye is a chemical that shows color when it is dissolved. They are water soluble and will not mix with oils. Dyes can be bought in a granular version and a dusty light powder form. Will not settle out of suspension. Dyes have a tendency to “bleed”, or migrate from one part of the product to another. LAKE A lake pigment is an insoluble material that colours by dispersion. Lakes are basically a pigment which has been manufactured from a dye by precipitating a soluble dye with a metallic salt.The resulting pigment is called a lake pigment An aluminum lake is not soluble but it colors when dispersed. Lakes are oil dispersive (not oil soluble) and can be mixed with oils, fats, and sugars. They can also be dispersed in other carriers such as propylene glycol, glycerin and sucrose (water and sugar). Lakes are produced in specific concentrations of dye. Thus, Red 40 Aluminum Lake is available in Low Dye (generally 15-17% pure dye) and High Dye (36-42% pure dye). Lakes are available in different concentrations of colors. The major difference between dyes and pigments is the particle size. Therefore dyes are not UV stable whereas pigments are usually UV stable. Pigment colours are usually Ultra-Violet stable and aren’t soluble.
60. INORGANIC COLOURS Stability towards light is an important characteristic displayed by these materials, some of which have a useful opacifying capacity, e.g. titanium dioxide. Another great advantage of inorganic colours is their wide regulatory acceptance, making them most useful for multinational companies. One drawback to their use is that the range of colours that can be achieved is rather limited NATURAL COLOURS As a generalization, natural colours are not as stable to light as the other groups of colours. Their tinctorial powers are not high and they tend to be more expensive than other forms of colour. They do, however, possess a regulatory advantage in that they have a wide acceptability. Even with these advantages their penetration into the pharmaceutical area has not been great. i.Riboflavine ii.Carmine
61. ADVANTAGES OF LAKE PIGMENTS OVER DYES MIGRATION Drying is an integral part of the coating process and, as a consequence, water will leave the film coat continuously as the coat is formed. If the colour is in the form of insoluble particles, then no migration takes place. However, a water-soluble colour(dye) tends to follow the escaping water molecules to the tablet surface and produce a mottled finish to the coating. OPACITY Pigments are much more opaque than dyes, hence they offer a much greater measure of protection against light than dye-coloured film coats. PERMEABILITY Pigments decrease the permeability of films to water vapour and oxygen thereby offering the possibilities of increased shelf-life. COATING SOLIDS Pigments contribute to the total solids of a coating suspension without significantly contributing to the viscosity of the system. Thus faster processing times by virtue of more rapid drying is possible.This is particularly significant with aqueous-based processes.
62. ADVANTAGES OF LAKE PIGMENTS OVER DYES ANTI-TACK ACTIVITY Tack is a concept that is widely used to describe the forces involved in the separation of two parallel surfaces separated by a thin film of liquid. Such considerations are important during the coating process as excess tack can cause troublesome adhesion of tablets to each other or to the coating vessel. Since the early days of film coating it has been appreciated that solid inclusions, including lake pigments, in the formula have a part to play in combating the effects of tack. Action of titanium dioxide, talc and indigo carmine lake on the tackiness of coating polymer solutions is well known. At high polymer concentrations, increasing the pigment concentration and decreasing the pigment particle size, reduced the effect of tack, whereas at low polymer concentration only talc was effective in reducing tack
63. EFFECTS OF LAKE PIGMENTS ON FILM-COATING SYSTEMS MECHANICAL EFFECTS The presence of lake pigments will reduce the tensile strength of a film, increase the elastic modulus and decrease the extension of the film under a tensile load. All of these are, of course, negative effects. However, as pigments consist of discrete individual particles the need for efficient pigment dispersion should be emphasized. Another generalization is that the lower the particle size of the pigment concerned, the smaller will be the deleterious effect on film properties. Acrylic film-coating polymers bind substantially higher quantities of pigment than is possible for example with the cellulos polymers.
64. OPAQUANT/EXTENDERS These extenders are fine inorganic powder used to increase the fill coverage and provide more pastel colour shade to the tablet. The white coat covers the core of the tablet. The colourants are expensive and a high level is needed,however the inorganic materials are more affordable. In the presence of the inorganic matters, the level of colourants decreases. Common inorganic powders include, i. TITANIUM DIOXIDE ii. SILICATES (ALUMINUM SILICATES INCLUDING TALC) iii. CARBONATES (E.G., MAGNESIUM CARBONATES) iv. OXIDES (E.G., MAGNESIUM OXIDE) v. HYDROXIDES (E.G., ALUMINUM HYDROXIDES) The pigments have excellent hiding power for intagliations in film-coated tablets.
65. FLAVORS AND SWEETENERS These are added to mask unpleasant odours or to develop the desired taste. For example, aspartame, various fruit spirits (organic solvent), water soluble pineapple flavour (aqueous solvent) etc. SURFACTANTS These are supplementary to solubilize immiscible or insoluble ingredients in the coating. For example, Spans,Tweens etc. ANTIOXIDANTS These are incorporated to stabilize a dye system to oxidation and colour change. For example oximes, phenols etc. ANTIMICROBIALS/PRESERVATIVES Antimicrobials/Preservatives are added to put off microbial growth in the coating composition. Some aqueous cellulosic coating solutions are mainly prone to microbial growth, and long-lasting storage of the coating composition should be avoided. For example alkylisothiazloinone, carbamates, benzothiazoles etc.
66. ADVANTAGES OF FILM COATING Minimal weight gain (2-3% as opposed to 60-80 % for sugar coating) Coat is less likely to affect disintegration. Single stage process an so generally quicker. Easy to automate (less reliance on skilled operator / easier to meet GMP requirements of SOPs, validation etc) Maintains original shape of the core & allows for embossing. DISADVANTAGES OF FILM COATING Expensive equipment & plant requires large space. High installation & energy costs.
67. TABLET COATING DEFECTS AND THEIR REMEDIES BLISTERING Definition: Blistering of a surface film occurs when its elasticity or adhesive properties are compromised. The result is that the film becomes detached from the tablet’s substrate. Cause: Blistering is usually a result of high temperatures that may occur during the drying process, during the spraying stage or at the end of the coating process Remedy: Use mild drying conditions, and ensure moderate temperatures at other stages of the coating process. CHIPPING Definition: Chipping occurs when the film becomes dented and chipped and this is most notably visible on the edges of the tablet. Causes: Chipping may be related to pan speed. Or a poor polymer or coating solution – e.g., an incorrect amount of plasticizer is used in the coating solution,. Remedy: Increase the hardness of the film by adjusting the proportion of plasticizer in the coating solution or selecting a polymer with a higher molecular weight.
68. TABLET COATING DEFECTS AND THEIR REMEDIES CRATERING Definition: Cratering happens when a defect on the film’s coating results in craters appearing on the tablet which in turn results in the exposure of the tablet’s surface. Causes: Cratering can occur in certain instances where there is insufficient drying time to seal the film or a high volume of coating solution is applied. In these cases excess polymer solution can penetrate to the surface of the tablet, especially in the crown area, causing the disruption of the coating and degeneration of the tablet’s core. Remedy: Check the efficiency of the drying process and optimise drying conditions. PICKING Definition: Picking happens when part of the film sticks to the pan resulting to some of the tablet pieces being detached from the core. Causes: Picking occurs when there is overwetting of tablets by the polymer solution, making the film become tacky which results to the tablets sticking to one another. Remedy: Overwetting can be avoided by increasing the efficiency of the drying process e.g, by increasing the air inlet temperature. Alternatively, the rate of applying coating solution can be decreased, or the solution viscosity increased.
69. TABLET COATING DEFECTS AND THEIR REMEDIES PITTING Definition: Pitting is the deformation of the core of the tablet without any visible signs of disruption of the film coating. Causes: Pitting can occur when the tablet core becomes hotter than the melting point of the materials used in its preparation. . Remedy: Dispense with preheating procedures at the start of coating and modify the drying (inlet air) temperature such that the temperature of the tablet core does not become greater than the melting point of the batch of additives used. BLOOMING Definition: Blooming is the fading or dulling of a tablet colour after a prolonged period of storage at a high temperature. Causes: The tablet colour can become dull as a result of changes in the composition of the surface film. It is usually the result of using too much plasticiser or of using a plasticiser with a low molecular weight. Remedy: Decrease the concentration and increase the molecular weight of the plasticiser in the polymer.
70. TABLET COATING DEFECTS AND THEIR REMEDIES BLUSHING Description: Blushing is a haziness or appearance of white specks in the film. Causes: Haziness or white specks are particles of polymer that has precipitated in the film. It usually forms as a result of an excessively high coating temperature. Alternatively it may be formed by gelation of the polymer when used in certain combinations with other materials. Remedy: Decrease the drying temperature to avoid precipitation of polymer. Avoid the use of sorbitol with polymers such as hydroxy propyl cellulose, hydroxy methyl cellulose, methyl cellulose and cellulose ethers. COLOR VARIATION Description: Variation in the colour of tablets within a batch. Causes: Colour variations may occur by a number of different faults in the preparation e.g., poor mixing, uneven spray patterns of the machinery, insufficient coating, migration of soluble dyes-plasticizers and other additives during drying. Remedy: Aim for even geometric mixing, reformulate with different plasticizers and additives and/or use mild drying conditions.
71. TABLET COATING DEFECTS AND THEIR REMEDIES INFILLING Description: This refers to the filling of intagliations - i.e., the distinctive words or symbols formed on the tablet. Causes: Infilling is caused when a polymer solution that is sprayed onto the table is unable to disperse. When sprayed with air, bubbles can form in the solution leading to a foam. Unlike a liquid, foams may accumulate within the intagliations rather than dispersing over the whole tablet. The result is that droplets of liquid become concentrated in the intagliations. This leads to a higher concentration of polymer within the intagliations. If the droplets build up, they can coat the whole pellet giving rise to an uneven polymer film. Remedy: Add alcohol to the polymer solution to improve dispersion, or use a spray nozzle capable of finer atomization. ORANGE PEEL (ROUGHNESS) Description: The tablet has the appearance of an “Orange Peel” on account of having a rough surface, which may also have a matt rather than glossy texture. Causes: Orange peel can be the result of poor tablet composition causing it to become soft. It can also be caused by too high a spray pressure combined with a fast spray rate, leading to uneven coating of the tablet. Remedy: Use mild drying conditions or use additional solvents to decrease the viscosity of the polymer solution so that spraying rate can be reduced.
72. TABLET COATING DEFECTS AND THEIR REMEDIES CRACKING (SPLITTING) Description: Cracking occurs when the film coating the tablet cracks in the crown area or splits around the edges. Causes: Cracking occurs when the film’s internal stress exceeds the tensile strength of the film. This is common with higher molecular weight polymers or polymeric blends. Remedy: Use lower molecular weight polymers or polymeric blends. Also adjust plasticiser type and concentration.
73. TABLET COATING DEFECTS AND THEIR REMEDIES SUMMERY Blistering is caused by entrapment of gases in or underneath the polymer film due to overheating either during spraying or at the end of the coating run. Use of mild drying conditions can solve this problem. Chipping is related to higher degree of attrition associated with the coating process. Increase in hardness of the film by increasing the molecular weight of the polymer can solve this problem. Cratering is related to penetration of the coating solution into the surface of the tablet, often at the crown where the surface is more porous, causing localized disintegration of the core and disruption of the coating. Decrease in spray application rate and use of optimum and efficient drying conditions can solve this problem. Pitting is a defect in which the temperature of the tablet core is greater than the melting point of the materials used in tablet formulation. Dispensing with preheating procedures at the initiation of coating and modifying the drying (inlet air) temperature can solve this problem. Blooming or dull film is generally a result of using of high concentrations and lower molecular weight of plasticizer. To avoid blooming, use lower concentrations and a higher molecular grade of plasticizer. Blushing/Whitish specks/Haziness of the film is related to precipitation of polymer exacerbated by the use of high coating temperature at or above the thermal gelation temperature of the polymers. Colour variation arises through poor mixing, uneven spray pattern, insufficient coating or migration of soluble dyes during drying. Address problem this by opting for geometric mixing, using mild drying conditions and reformulate with different plasticizers. Infilling arises through bubble/foam formation during air spraying of a polymer solution. Addition of alcohol or use of spray nozzle capable of finer atomization can solve this problem. Orange peel/Roughness is related to inadequate spreading of the coating solution before drying. A decrease in viscosity of coating solution can reduce this defect
74. TABLET COATING DEFECTS AND THEIR REMEDIES
75. TABLET COATING DEFECTS AND THEIR REMEDIES
76. TYPES OF TABLET COATING EQUIPMENT Depending on the working principle, you may classify all the existing tablet coating machines as 1. STANDARD COATING PAN 2. PERFORATED COATING PAN 3. FLUIDIZED BED COATER 1. STANDARD COATING PAN Standard coating pan is also known as the conventional pan system is a popular accessory in most pharmaceutical industries. Basically, the design of this type of tablet coating machine is such that there is a circular metal pan whose diameter may range from 6 to 80 inches (15 to 200 cm). The pan is slightly tilted to an angle of about 45°C to the bench top.
77. TYPES OF TABLET COATING EQUIPMENT STANDARD COATING PAN The standard coating pan has an electric motor that rotates the circular metal pan horizontally to its axis. It is the motion of this pan that causes a batch of tablets to tumble. The conventional pan system has an inlet air supply. This inlet port supplies heated air. It must be ensured that the air temperature does not initiate any chemical reaction on the tablets from the tableting machines. At times, very high temperature may decompose or degrade essential chemical constituents of the tablets. It is the hot air that dries the coating solution. During the process, all exhaust air will exit the system through the front section of the standard coating pan. This air leaves by means of the duct system. This machine uses spraying or ladling mechanism to supply the coating solution.
78. DRAWBACKS OF CONVENTIONAL PAN SYSTEMS Improper balance of inlet and exhaust air that may further complicate the process. This can be risky whenever using inorganic solvents. Since a greater percentage of the drying takes place on the surface, the process may not be efficient. Tablets may not mix properly and this may cause uneven coating. For a fact, by adopting spraying system, it can solve improper mixing and uneven coating. To improve the drying efficiency,modify the conventional pan system.
79. IMPROVING THE DRYING EFFICIENCY OF STANDARD COATING MODIFICATION OF STANDARD COATING PAN This type of modification can improve drying efficiency. i. IMMERSION TUBE SYSTEM ii. BAFFLED PAN AND DIFFUSER iii. IMMERSION SWORD
80. i. IMMERSION TUBE SYSTEM In immersion tube system a tube is immersed in the tablet bed. This tube has a spray nozzle that delivers both the hot air and coating solution.The immersion tube system delivers heated air and coating solution simultaneously. It is basically a long tube with a spray nozzle at its tip. The design is such that the drying air (heated air) flows upwards and leaves the system by conventional duct. By incorporating an immersion tube system in standard coating pan, it will increase the drying efficiency. It is a technique that is handy for both sugar coating and film coating machines.
81. IMMERSION TUBE SYSTEM
82. ii. BAFFLED PAN AND DIFFUSER A baffled pan and diffuser, which is also called the pellegrini, also improves the drying efficiency of standard coating pan. In this process, the tablet coater can distribute drying air uniformly on the coated tablets. However, the standard coating pan with baffled pan and diffuser are only suitable for a sugar coating process. This is due to the limited drying capability.
83. BAFFLED PAN AND DIFFUSER
84. iii. IMMERSION SWORD SYSTEM/ PERFORATED METAL SWORD This is basically a perforated metal sword that is immersed in the tablet bed. The working principle is such that, During the drying process,it will introduce drying air which flows through perforated metal sword then upwards through the bed. This way, it will improve the drying efficiency in standard coating pan systems.
85. IMMERSION SWORD SYSTEM
86. 2. PERFORATED COATING PAN Perforated coating pan is also popular among many pharmaceutical companies. In most cases, this type of tablet coating equipment has either a full or partial perforated drum. Like the standard coating pan, the drum of this tablet coater rotates on a horizontal axis. In this the coating drum is an enclosed housing with various spray nozzles. It is the spray nozzles that atomize the coating solution. However, unlike most conventional pan machines, perforated pan coaters have an efficient drying system. These are high capacity tablet coating machines. There are following types of perforated coating pan i. ACCELA-COTA SYSTEM ii. DRIA COATER PAN iii. HI COATER SYSTEM iv. GLATT COATER
87. i. ACCELA-COTA SYSTEM There are a number of processes that take place within the drum. Baffles/Mixing blades ensure the tablets mix freely within the drum as it rotates. Spray gun atomizes the coating solution and directs it to the tablets. Dry inlet air flows from the upper section of the drum, passing in between the tablets. It leaves the drum through the perforations. This increases the overall efficiency of this type of tablet coating machine.
88. ACCELA-COTA SYSTEM
89. ii. DRIA COATER PAN A Dria coater pan has hollow perforated ribs, which are locate on the inside periphery tablet coating drum. Therefore, as the drum rotates, the spray nozzle atomizes coating solution and directs it to the tablets from the top section. This is the same scenario like for the accela-cota machines. However, the drying air enters the coating drum from below the tablets and flows upwards, then exits the system through the back of tablet coating pan. Basically, in Dria coater, the drying air fluidizes the tablets.
90. DRIA COATER PAN
91. iii. HI-COATER SYSTEM Although the design of Hi-coater systems may be different, the working principle is similar to that of the accela-cota. The machine directs both the coating solution and drying air downwards. The drying air, then leaves the coating system through the perforations below the coating drum.
92. HI-COATER SYSTEM
93. PERFORATED COATING PAN
94. iv. GLATT COATER The design of a Glatt coating pan machine resembles that of the accela-cota. This type of tablet coating machine is known for following High spray rates. Extremely short processing time. Its design is such that you can direct the drying air from inside the tablet coating drum. Normally, the air passes through the tablet bed and leaves via exhaust duct. Its unique design minimizes turbulence that may occur around the spray nozzle. This ensures an even distribution of the coating solution on the tablets. Moreover, its drum has unique geometrical shapes with baffles on the periphery. This ensures an effective mixing of tablets while protecting the products from damage at the same time. So far, it is one of those tablet coating machines that ensures consistent and accurate coating. The working principle of all these tablet coating machines is the same. For instance, in all the perforated pan systems, the spray nozzle atomizes coating fluid. The only difference is how the machine supplies and removes the drying air.
95. GLATT COATER
96. GLATT COATER
97. 3. FLUIDIZED BED COATER The working principle of fluidized bed or air suspension system is basically similar to that of the other spraying systems. Normally, the key aspects about these coating machines are, It has a vertical cylinder. A column of drying air flows upwards suspending all the tablets.This causes the tablets to move upwards, outwards and then downwards, a process we refer to as fluidization. Spray nozzle atomizes and introduces the coating fluid into a fluidized bed. The nozzle’s position can either be at the top mid or bottom of the fluidized bed coater. This process will continue until you achieve the right coating on your tablets. Basically,we can choose any of the three types of tablet coating machines. The degree of coating fluid atomization in any of these machines will depend on, i. Type, design and size of the nozzle ii. Fluid pressure iii. Orifice size
98. FLUIDIZED BED COATER
99. BASIC PARTS & COMPONENTS OF FILM COATING MACHINE A coating machine is an assembly of many parts and components. Depending on the size, functionality and model of the tablet coating equipment, the number of parts may vary broadly. Following are the basic parts and components of film coating machine, AUTOMATED CONTROL SYSTEM(PLC) Technological advancements increase accuracy and consistency. Most advanced machines have microprocessor based programmable control system. As a result, machine can automatically be controlled. Selection of running/operation state. Various parameters such as speed, temperature and negative pressure. Recording and printing working state of the machine. Displaying of process data. Spraying gun and atomization.
100. AUTOMATED CONTROL SYSTEM
101. ELECTRIC MOTORS To perform various operations such as creating negative pressure, blowing air, mixing tablets, etc., the tablet coating machines have different types and sizes of electric motors. For instance, in coating machines have electric motors in the following key sections, Peristalsis pump Hot air equipment Air exhaust section Coating drum Remember, these are not the only sections. A single machine can have more than three motors, depending on its complexity and design.
102. ELECTRIC MOTORS
103. TOUCH SCREEN OPERATION PANEL(HMI) This is part of the technological advancements in the modern tablet coating machines. It provides a user-friendly human machine interface (HMI). In most designs, the HMI is fully enclosed and allows for easy and seamless operation of the tablet coating machine. GUIDE PLATE This process involves mixing tablets with the right solution. The drying process requires that hot air blow through each tablet. For this he coating system features an agitator of streamline guide plate. This allows all tablets to tumble smoothly. During the process, tablets collide with the solvent from the spraying nozzle while preventing possible breakage or chipping.The narrow surface of the guide plate prevents possible adhesion of the coating material.
104. PERISTALTIC PUMP Modern coating systems have peristaltic pumps. These pumps guarantee the following unique features. Constant pressure variable thereby eliminating the use of return pipes Ability to stabilize atomization by making spray system simple and easy to automate
105. SPRAYING SYSTEM The spraying section, which includes the tank, nozzle and pumps have a simple design. So, it is easier to conduct the following, Clean and maintain the spraying gun. Stabilize atomization. Prevent plugging-up of the spraying gun. Saves tablet coating solution. Efficient and even atomization with a large coverage of spraying. Universally adjustable head for easy adaptability.
106. SPRAYING SYSTEM
107. OTHER PARTS AIR DISTRIBUTING DEVICE COMPONENTS FORMING THE INTERNAL STRUCTURE OF THE DRUM ELECTRONIC PULSE VALVE AIR HEATING UNIT MAGNETIC STIRRER DRUM FILTER MOVABLE HOLDER AIR PIPES AND FITTINGS EXHAUST DUST COLLECTOR SOLUTION TANK DISCHARGING DEVICE
108. BASIC PARTS & COMPONENTS OF FILM COATING MACHINE
109. FACTORS EFFECTING TABLET COATING
110. FACTORS EFFECTING TABLET COATING
111. FACTORS EFFECTING TABLET COATING
112. FACTORS EFFECTING TABLET COATING
113. FACTORS EFFECTING TABLET COATING
114. FACTORS EFFECTING TABLET COATING
115. FACTORS EFFECTING TABLET COATING SPRAY RATE At one extreme, a high spray rate may cause coating defects such as twinning, picking and sticking, and logo bridging. At the other extreme, a low spray rate may cause spray drying and a loss in coating efficiency. Spray rate is one of the most important coating process parameter. Spray rates are especially important if the tablet formulation or API is moisture-sensitive as residual water content in the coated tablets has been shown to be directly related to the spray rate. The rate at which the coating formulation is applied to the tablets influences the bed temperature and, thus, the rate of solvent evaporation. Spray rate, in conjunction with atomization air pressure, has been shown to affect spray characteristics, such as droplet size. Larger droplets are more likely to dissolve the outermost region of the tablet, potentially resulting in drug migration into the film coat As the spray rate is increased, the amount of water/solvent sprayed onto the tablets at any given time is also increased which result in increased tablet bed RH and tablet temperature is decreased.
116. FACTORS EFFECTING TABLET COATING SPRAY TARGET POSITION
117. SPRAY RATE AND BATCH SIZE
118. STEPS OF FILM FORMATION
119. STEPS OF FILM FORMATION
120. FACTORS EFFECTING TABLET COATING THE ATOMIZATION AIR PRESSURE The atomization air pressure used in coating processes dictates the droplet size and velocity of the solution or suspension exiting the spray nozzle. Excessive atomization air pressure can result in the production of smaller droplets that dry completely before reaching the tablet surface, leading to spray drying, loss of efficiency, and, in some cases, logo infilling or “orange peeling” coating defects. On the other hand, a low atomization air pressure can lead to ineffective atomization of the coating suspension, leading to bigger droplets that may not get spread and dried appropriately after they contact the tablet substrate. Reduced atomization air pressure should result in larger droplets and, hence, would likely result in a higher tablet bed RH. The pattern air flattens out the spray cone and enables better and more uniform spray coverage across the tablet bed, which in turn improves coating uniformity between tablets . The size of the spray droplet impacts the drying kinetics as the droplet moves from the nozzle toward the tablet cores. Pattern air pressure (or flow rate) should be chosen such that there is uniform spray coverage across the tablet bed without an overlap of the spray zones between the multiple guns. An overlap of spray regions would result in regions with much wetter conditions than desired, and tablets passing through those regions would receive additional spray, which could then lead to coating defects. As the atomization air pressure decreases, the droplet velocity also decreases, thereby increasing the transit time of the droplet and thus allowing for more solvent evaporation to occur. A slight increase in tablet bed temperature was also noted when the atomization air pressure was reduced.
121. FACTORS EFFECTING TABLET COATING
122. FACTORS EFFECTING TABLET COATING GUN TO GUN DISTANCE
123. FACTORS EFFECTING TABLET COATING INLET AIRFLOW RATE The inlet air (flow rate, T, and RH) dictates the drying kinetics of the spray droplets as they travel from the spray nozzle to the tablet surface and thus is another critical processing parameter in film coating. Inlet air RH can significantly impact both tablet bed and exhaust air RH. Insufficient drying can result in overly wet tablet surfaces, producing detrimental effects such as twinning, tablet agglomeration, and surface dissolution. At the other extreme, if drying occurs too rapidly, the polymer-containing droplets may dry prior to hitting the tablet surface (spray drying) or not sufficiently spread across the tablet surface, resulting in a rougher film surface. In addition to the flow rate, the humidity conditions of the inlet air also play a significant role in film formation. Maintaining the inlet airflow-to-spray rate ratio constant allows for closer correlation between inlet and exhaust temperature. This ratio is defined as the drying capacity. A higher drying capacity would be expected to result in a drier environment and vice versa Drying capacity may be a good indicator of the RH in the tablet bed, although the relationship does not seem to be linear.
124. INLET AIRFLOW RATE
125. FACTORS EFFECTING TABLET COATING EXHAUST TEMPERATURE Adjustment of inlet air temperature to maintain a desired exhaust temperature is commonly used. The factors affecting the required inlet air temperature include spray rate, percent solids in coating solution, inlet airflow rate, and inlet air RH. The exhaust temperature is one of the process parameters that are generally kept constant during the pan coating process scale-up. In early literature, the exhaust temperature was assumed to be the same as the tablet bed temperature. Later studies using infrared gun measurements showed that the tablet bed temperature is generally 2–3°C cooler than the exhaust air temperature. In more recent studies utilizing PyroButtons the exhaust temperature is shown to be up to 10°C higher than the tablet bed temperature. In the absence of tablet bed temperature data, the exhaust temperature provides a rough estimate of the tablet bed temperature. The tablet bed temperature decreased and RH increased when the exhaust temperature is lowered
126. FACTORS EFFECTING TABLET COATING
127. FACTORS EFFECTING TABLET COATING
128. FACTORS EFFECTING TABLET COATING GUN-TO-BED DISTANCE It refers to the distance between the tip of the nozzle and an imaginary flat surface on the cascading bed of tablets. Therefore, this variable can be somewhat subjective and operator-dependent. The reduction in gun-to-bed distance result in a significant increase in tablet bed RH and a reduction in tablet bed temperature. As the droplets move in this region, the solvent can evaporate, leading to a decrease in size, or the droplets can coalesce, thus increasing in size. In general, a reduction in droplet size is observed. However, since the pattern air flattens the spray, there is also a significant droplet coalescence occurring and the size of the droplet hitting the tablet surface is dependent on process parameters. If the gun-to-bed distance is too large, spray drying can be observed where smaller droplets dry completely before hitting the tablet surface, which in turn can lead to lower process efficiency and tablet defects such as rough surface or logo infilling. On the other hand, if the spray nozzle is placed too close to the tablet bed, relatively large droplets may reach the tablets, creating an over-wetted surface and thus increasing the chance for tablet defects, including twinning and surface dissolution.
129. FACTORS EFFECTING TABLET COATING GUN-TO-BED DISTANCE
130. FACTORS EFFECTING TABLET COATING GUN TO WALL DISTANCE
131. SUSPENSION OR POLYMER CONCENTRATION The concentration of a polymer in solution significantly influences the viscosity of the liquid. since coating materials (both polymer solutions and dispersions) must be atomized into a fine mist for coating processes, the viscosity of the material should generally be lower than 400 cP as the liquid can be delivered to the spray gun and atomized into droplets more readily. On the other hand, a higher polymer concentration can reduce the total coating time necessary to achieve the same coating weight gain, and therefore is more cost-effective. Additionally, shorter processing times are advantageous if the tablet cores are somewhat friable as more coating material deposited faster can enhance the mechanical strength of such tablets. In order to understand the impact of solids concentration on the tablet bed conditions, a coating run was done using a 10% (w/w) total solids level (run I) and compared to the batch coated at 15% (w/w) total solids level (run A), with all other parameters held constant. A decrease in solution/suspension viscosity will make the atomization more effective (at the same spray rate) and create smaller droplets a significant increase in tablet bed RH from 26.3% to 39.0% was observed when the solids content of the suspension was decreased, similar to the effect of increasing the spray rate. This observation was likely due to the increase in the amount of water sprayed on the tablet bed with the coating suspension at the lower solids level.
132. FACTORS EFFECTING TABLET COATING TABLET MOVEMENT WITHIN THE COATING PAN/PAN SPEED Pan speed will affect attritional effects within the process (and hence mechanical damage to the tablets) and coating distribution uniformity across a batch of tablets. Tablet movement may impact drying within the tablet bed, because the faster the tablets move, the shorter the time in the spray zone, the less coating material each tablet picks up, and the faster that amount of coating material can dry. Generally, as long as the tablet cores and coating formulation are suitably robust, the faster the tablet motion within the coating pan.
133. ADVANCE TABLET COATING TECHNIQUES Environmental Protection Agency and Occupational Safety and Health administration (OSHA) have strict requirement regarding use of solvent in pharmaceutical industry. Thus,aqueous based coating is increasingly used compared to organic based coa ting. However aqueous based coating also having following drawbacks, DEGRADATION OF CERTAIN DRUGS DUE TO USE OF HEAT AND WATER. VALIDATION OF COATING DISPERSION FOR CONTROLLING MICROBIAL PRESENCE. HIGH ENERGY CONSUMPTION AND LONG PROCESSING TIME. In order to overcome the drawbacks of liquid coating technology, solventless coating has emerged. Solventless coating eliminates many problems associated with the use of solvent i.e., residual solvent, solvent exposure, solvent disposal in coating. As there is no use of solvent, it eliminates the solvent evaporation step and thus reduces the processing time also solventless coating reduces overall cost because it eliminates the tedious and costly process of solvent disposal and treatment.
134. ADVANCE TABLET COATING TECHNIQUES i. COMPRESSION COATING ii. DIP COATING iii. Electrostatic spray powder coating iv. PHOTOCURING v. SUPERCRITICAL COATING vi. VACUUM FILM COATING
135. COMPRESSION COATING The coating requires a specialized tablet press machine. This type of coating is not popular but has some advantages including the ability to coat the tablet to mask the taste and protect the core from organic solvent or water. Other advantages include delaying the enteric properties and preventing the separation of the incompatible ingredients. DIP COATING In this method the tablet’s core is simply dipped into the coating liquid. Once dipped in the solution, the tablets are then placed in a traditional coating pan to dry. The steps are repeated until the desired coating is achieved. Disadvantages for this process include the lack of versatility, low speed as well as low reliability compared with the spraying methods. Although specialized equipment has been developed for dip coating, no commercial application for it has been attained.
136. ELECTROSTATIC SPRAY POWDER COATING Electrostatic spray powder coating, uses powdered raw materials that have been electrostatically charged through the application of high voltage. These materials are sprayed onto a neutrally charged seed pellet and will adhere to the surface by electrostatic forces. The coating is then fixed in place by temperature or exposure to infrared radiation for approximately 1 to 2 minutes. The main advantage of the process is that the coating forms and hardens quickly. The coating and tablet core must possess certain conductive properties, or be modified using additional steps to introduce electric charge. The conductivity of the core particle can by increased by wetting it with water to decrease resistance, although this method introduces moisture into the tablet and can lead to instability. Another way to improve conductivity is to modify the surface of the API substrate using polar groups. This method is usually achieved by dissolving the polar groups in a volatile solvent before spraying the solution onto the tablet core, thereby, reintroducing a solvent step into the process.
137. PHOTOCURING Fundamental stage in the coating process is the fixation of the coating to form a solid, protective layer. In many cases, this step involves the use of heat. This increase in temperature requires costly energy and many APIs become more susceptible to degradation as temperature increases. Photocuring attempts to avoid these problems by employing a method of fixation dependent on light energy rather than heat. As such, it does not require any heating or drying steps and is ideal for temperature-sensitive APIs. The process hinges on the use of light energy to trigger a polymerization reaction to convert a liquid or granulate surface coating into a solid material. The technique has been successfully used in pharmaceutical coating to create immediate and sustained-release dosage forms.
138. SUPERCRITICAL COATING One way to avoid the downsides of traditional liquid coating is to use supercritical liquids, which have properties between liquids and gases Like liquids, they can be used to dissolve the excipients and API, thereby facilitating the mixing and formation of a homogeneous coating. Carbon dioxide is most widely used because of its low critical temperature (31 °C) and pressure (74 bar), making it easy to manipulate under manufacturing conditions.
139. VACUUM FILM COATING This procedure uses a specially designed baffled pan/drum, whereby the pan is heated by a hot water jacket, and sealed so that it can be evacuated. Tablets are then placed in the pan and the air in the pan/drum is displaced by nitrogen before it is evacuated to a desired level of vacuum. Once the target vacuum level is achieved, the coating solution is applied to the tablets via an airless spray system. Evaporation of the water from the sprayed film is driven by the heated pan whereas organic vapors are removed via the vacuum system. As there is no high velocity heated air for drying the product, the energy required by vacuum film coating is low and the coating efficiency is higher. Organic rather than aqueous solvents are effective and ideal for the vacuum film coating system as there are minimal safety and environmental concerns.
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