Coating technology

Coating technology

1. 1 PRESENTD BY :- PATIL PRANJAY SADASHIV. FIRST YEAR M.PHARM. DEPARTMENT OF QUALITY ASSURANCE. H. R. Patel Institute of Pharmaceutical Education and Research, Shirpur COATING TECHNOLOGY

2. Content- Coating principle Coating process Equipment Particle coating Fluidized bed coating Application technique Problem encountered 2

3. Coating technology Coating principle To mask the taste. To mask the odor, color of the drug. To provide physical and chemical protection for the drug. To control the release of the drug from tablet. To protect the drug from gastric environment. Coating process Coating is the application of a coating composition to a moving bed of tablet with the concurrent use of heated air to felicitate evaporation of solvent. There are two type of coating process- Sugar coating Film coating 3

4. Sugar coating It involve following steps- Sealing Sub coating Syruping(smoothing) Color coating Polishing Printing Sealing: Objective To prevent moisture penetration into the tablet core, a seal coat is applied. To strengthen the tablet core. Without a seal coat, the over wetted tablets would absorb excess moisture. Leading to tablet softening, and may affect the physical and chemical stability. 4

5. Sub-coating : Objective Sub coating is applied to round the edges and build up the tablet size. Sugar coating can increase the weight by 50-100% at this step. The sub-coating step consist of alternatively applying a sticky binder solution to the tablet followed by dusting of powder and then drying. Smoothing: Objective To cover and fill in the imperfections in the tablet surface caused by sub-coating step. To impart desired color to the tablet. Color coating: Objective To impart an elegant and uniform color. 5

6. Polishing: Objective To produce desired luster on the surface of the tablet. Tablet can be polished in standard coating pan. Printing: In order, to identify sugar coated tablet often it is necessary to print them, Using pharmaceutical grade ink. 6

7. Film coating Film coating adds 2-5%to the tablet weight. Film coating is done by the following methods. Pan-pour method Pan spray method 1) Pan-pour method: Viscous coating materials are directly added from some container into the rotating pan moving with the tablet bed. Tablet are subjected to alternate solution application, mixing and then drying. Disadvantage- The method is relatively slow. It relies heavily on the skill of the operator. Tablet require additional drying to remove the solvent. 7

8. 2) Pan-spray method: Coating material is sprayed over the tablet bed from nozzles and hot air is passed through the tablet bed to dry it. The variables to be controlled is pan-spray film coating process are: a) Pan variable : Uniform mixing is essential to deposit the same quantity of film on each tablet. Pan design: some tablet shapes mixes freely while other shapes may require a specific baffling arrangement to ensure adequate mixing. Disadvantage- Baffles may produce chipping if not selected properly. b) Pan speed: Pan speed affects mixing. Optimum speed: 10-15 rpm for nonaqueous film coating. 3-10 rpm for aqueous film coating. 8

9. c) Spray variable: Rate of liquid application Spray pattern Degree of atomization These are interdependent. Process air variable: The variable are required for optimum drying of the coating by evaporation of solvent. 9

10. Equipment Most coating process use one of three type of equipment: Standard coating pan Perforated coating pan Fluidized bed coater Standard coating pan It consist of circular metal pan mounted on a stand. The pan is 8-60 inch in diameter and rotated on its horizontal axis by motor. Heated air is directed into the pan and on to the tablet bed surfaces and it exhausted by means of dusts positioned in front of the pan. The coated solution are applied by spraying the material on to the rotating tablet bed. Use of atomizing system to spray the liquid. 10

11. Perforated coating pan It consist of perforated drum that is rotated on its horizontal axis in an enclosing housing. In the acceclo-cota and hi-coater system, the drying air is directed in to the drum, is passed through the tablet bed and is pass through perforation in the drum. The hi-coater introduces drying air through hollow perforated ribs located on the inside periphery of the drum. As the coating pan is rotates the ribs dip into the tablet bed and the drying air is passes up through and fluidizes the tablet bed. 11

12. Fludized bed coating It is highly efficient system. Fluidization of the tablet mass is achieved in a columnar chamber by the upward flow of drying air. The airflow is controlled so that more air enters the centre of the column, causing the tablet to rise in the centre. The movement of the tablet is upward through the centre of the chamber. They then fall toward the chamber wall and downward to reenter the air stream at the bottom of the chamber. Coating solution is applied from the spray nozzle located at the bottom of the chamber. 12

13. Particle coating Particle coating to alter the surface properties. When the thin layer of a substance is places around a core particle it is called coating of particle. Rational of particle coating To modify drug release profile. Improve appearance. Facilitate identification. Mask taste and odor. Protect from external environment. Obtain easier product handling. Type of particle coating Wet particle coating Dry particle coating 13

14. 1) Wet particle coating: This technique used commercially to coat the solid dosage form. Generally mixture of polymers, pigments and excipients is dissolved in an appropriate organic solvent (for water insoluble polymers) or water (water soluble polymers) to form a solution, or dispersed in water to form dispersion, and sprayed onto the dosage forms and dried by continuously providing heat until a dry and smooth film coating film is formed. WPC solution may be volatile and toxic which needs consideration. Apart from that it requires post treatment and waste processing which subsequently increase the cost. Wet particle coating techniques Microencapsulation -Microencapsulation is a versatile and very precise coating technique used to encapsulate individual drug particles. This technique efficiently and uniformly coats drug particles with polymeric membranes of varying degrees of porosity using coacervation/phase separation processes. The size range (2 to 2000 μm approximately) distinguishes them from the smaller nanoparticles or nanocapsules. 14

15. 15 The most commonly employed mechanical methods for the preparation of microcapsules and microspheres are; (1) Multiorifice-centrifugal process, (2) Air suspension coating ( wurster ), (3) Vacuum coating, (4) Spray drying, (5) Spray congealing, (6) Pan coating, (7) Rotary fluidized bed granulator, and (8) Spheronization .

16. Coacervation– Phase separation process This process consists of three steps that are carried out under continues agitation: ( i ) Formation of three immiscible chemical phases (ii) Deposition of the coating (iii) Rigidization of the coating Coacervation: Phase separation process applicable for solids and liquids with particle size ranges from 2- 5000 μ. Step I: Formation of three immiscible chemical phases It involves three immiscible chemical phases which are ( i ) Liquid manufacturing vehicle phase (ii) Core material phase and (iii) Coating material phase. Step II: Deposition of the coating This process consists of depositing the liquid polymer coating upon the core material accomplished by controlled physical mixing of the coating material and the core material in the manufacturing vehicle. Deposition of the liquid polymer coating around the core material occurs if the polymer is adsorb at the interface formed between the core material and the liquid vehicle phase. This adsorption phenomenon results in effective coating. 16

17. Step III: Rigidization of the coating Rigidization of coating is done by thermal, cross- linking or desolvation techniques to form self-sustaining microcapsules. 17 Figure 1: Schematic representation of the coacervation process. Core material dispersion in solution of shell polymer; Separation of coacervate from solution; Coating of core material by microdroplets of coacervate ; Coalescence of coacervate to form Microcapsules

18. Spray drying and spray congealing: Spray drying and spray congealing processes are similar, both involves the dispersion of core material in a liquefied coating substance and spraying or introducing the core coating mixture into some environmental condition, whereby relatively rapid solidification of the coating is affected. Both processes are applicable for solids and liquids. Particle size ranges from 5 to 600 μ. Spray drying: In this method involves the dispersion of core material into coating solution (core material must be insoluble in coating solution). Then spraying the mixture as atomized spray into air stream. The air is usually heated, which provides the latent heat of vaporization required to remove the solvent from the coating material, resulting in the formation of microencapsulated product. Spray congealing: General process and conditions are same as spray drying except that the core material is dispersed into a coating solution melts rather than a coating solution. Microencapsulation is accomplished by spraying the hot mixture into a cool air stream. 18

19. Pan coating The microencapsulation of relatively large particles by pan coating method has become wide spread in the pharmaceutical industry. Solid particles greater than 600 in size are generally considered essential for effective coating. The coating is applied as a solution or as an atomized spray to the desired solid core passed over the coated materials during coatings is being applied in the coating pans. 19

20. 2) Dry particle coating Dry particle coating is used to create new-generation materials by combining different powders having different physical and chemical properties to form composites, which show new functionality or improve the characteristics of known materials. Materials with relatively large particle size (1–200 μm ) form a core and these core (host) particles are mechanically coated with fine submicron (guest) particles; no liquid of any kind (solvents, binders or water) is required. Multi orifice centrifugation The liquid material to be coated is extruded through the nozzle of the inner tube into the coating fluid contained in the outer tube. Initially, the fluid extrudes as a rod surrounded by the coating fluid, but the rod ultimately breaks up into droplets, which are then immersed, in the coating fluid. As the extruded droplets pass through the nozzle orifice of the outer tube, the coating fluid forms a surface coat, which encases the extruded particle. 20

21. 21 Dry particle coating involves mechanically fixing fine particles (guests) onto the surface of relatively larger particles (hosts).

22. Dry Particle coating techniques Supercritical fluid coating Vapor coating of powders Electrostatic fluidized bed coating d) Rotating (Centrifugal) fluidized bed granulator/coater e) Hot melt coating Hot melt coating: A hot-melt coating material, as its name implies, is applied in its molten state over the substrate and then solidified upon cooling. Generally, materials with molten viscosities less than 300 centipoise and melting points less than 80°C. b) Supercritical fluid coating: Carbon dioxide is an ideal supercritical medium for pharmaceutical purposes due to its relatively low critical temperature (31.1°C) and critical pressure (72 bar). For a successful coating, the supercritical fluid ideally dissolves only the coating material, leaving the core completely undissolved. 22

23. c) Vapor coating of powders: A liquid or powder material can be dispersed by the application of electrostatic fields. d) Electrostatic fluidized bed coating: In such systems, the powder material which is essentially 100% solids is kept fluidized in a bed by dry air passing through a porous base plate. The powder particles are charged either by means of an electrode in the fluid bed beneath the surface of the fluidizing powder or by charge transfer from the pre-ionized air. 23

24. 24 Rotating fluidized bed coater/granulator e) Rotating (Centrifugal) fluidized bed granulator/coater It consists of a chamber and a porous cylindrical air distributor made of stainless sintered mesh. The horizontal cylinder (air distributor) rotates around its axis of symmetry inside the chamber. There is a stationary concentric cylindrical metal filter inside the air distributor to retain any elutriated fine powder. A binary spray nozzle mounted on the metal filter sprays mist of coating material into the powder bed. A pulse air-jet nozzle is also placed inside the metal filter, which cleans the surface of the metal filter in order to prevent it from clogging .

25. f) Spheronization Melt-able materials are utilized for coating in such processes with a core up to 0.5 mm in diameter. It is more suitable for smooth continuous coating with improved flow properties. The particles are rapidly passed through an intensely heated area; the outside material melts, flows, and, as it cools, forms a smooth surface. If there are small melt-able particles on the outside of the core material, these will melt and flow to provide a better coating. If the core is thermoplastic, it softens and allows the coating particles to become more strongly adhered . 25

26. Application technique:  Roller coating Flow coating. Spray painting. Electrode position. Plural component systems. 26

27. Problem encountered Sticking and picking: Excessive film thickness causes tablet to stick to each other. Remedy- Reduction in the liquid application rate or Increase in the drying air temperature. Orange peel effect: In adequate spreading of coating solution before drying causes orange peel effect. Remedy- Thinning the polymer solution with additional solvent. Bridging and filing: During drying, the film may shrink and pull away from the sharp corners called bridging. Remedy- Increase the plasticizer content. Or change the plasticizer. 27

28. Remedy- Milder drying conditions are adopted. Blooming: It can occur when too high a processing temperature is used for particular formulation. . Color variation: Improper mixing, uneven spray pattern. Insufficient coating may result in color variation. 28 Blistering: When coated tablet require further drying in oven to rapid evaporation of solvent from the core.

29. Reference Lachman L, Libermen H.A, Kanig J. The Theory and practice of industrial pharmacy, third edition varghees publisher; page no. 346-374. Banker GS . Film coating theory and practice. J pharm Sci 1996;55:81-9. 29

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