coating Flashcards
what happens in the film coating process?
droplet formation impingement wetting and spreading coalescence adhesion drying is continuous
what influences droplet formation?
type of nozzle:
pneumatic nozzle- use of compressed gas, usually air to atomize the liquid to small droplets
hydraulic nozzle- droplets are formed when a highly pressurized liquid flowing out of a small nozzle port
movement of the cores
heat
exhaust
how is coating preformed in a perforated coating pan?
1- liquid fed and compressed air fed in
2- heated air supplied
3- perforated air in the center of cabinet because of this
4- flows out through exhaust air
how is coating done in the fluid bed system?
top spray
bottom spray
tangential spray
what are the critical coating process variables?
- Type of equipment
- Equipment dimension & batch size
- Pan or rotor speed
- Method of spraying and spray rate •Atomising air pressure
- Nozzle distance
- Inlet, exhaust and product temperatures
- Drying air volume
- Drying time
what are the type of defects in a film coat?
- Picking and cratering
- Rough or ‘Orange skin’
- Cracking and splitting •Peeling and flaking
- Bridging
- Pitting
what mechanisms are drugs released by?
diffusion
osmosis
dialysis
erosion
what does the sugar coating process involve?
- Involves successive application of sucrose solutions to tablets
- Sealing–To protect tablet from overwetting–Water‐impermeable polymers
- Sub‐coating –To form the typical shape of sugar coated tablets–Syrups with other excipients–Dusting powder
- Smoothing
- Colouring
- Polishing
what are the common problems in sugar coating?
- Visual defects
- Sugar inversion
- Sticking of coated tablets
what are the BP stds for coated tablets?
- Some similar requirements for uncoated & coated tablets
- But there are differences:
- Film coated tablets must comply with uniformity of weight test •Even for a dose of 2mg/2% or less, where uniformity of content is required
- Disintegration time limit 30 min (film coated tablets) or 60 min (all other immediate release coatings)•Coated tablets are not tested for ‘resistance to crushing’ or ‘friability’, but the cores should be tested in this way
- Special disintegration and/or dissolution test requirements apply of coating are functional
what are the two types of coaters?
(perforated pan and fluid bed coater)
what would be the possible reasons for coating of solid dosage forms?
- Improve in dosage form stability and protective function
- Masking of unpleasant taste and odour
- Improvement in dosage form appearance
- Ease of swallowing
- Ease of identification
- Ease of handling and packaging
- Modification of drug release (enteric coating, modified release, drug targeting)
what are the types of coatings available?
- Film coating
- Sugar coating
- Press coating
- Hot melt coating
- Electrostatic coating
what is film coating?
•Depositing a thin polymeric film onto surface of dosage form
what does a formulation of a film coating usually consist of?
–Polymer
–Plasticizer
–Colorant/opacifier
–Vehicles (solvent or suspending liquid
what are the ideal characteristics of a film coating polymer?
–Solubility
–Viscosity
–Permeability
–Mechanical properties(elasticity, tensile strength and crystalinity etc.)
what are the different choices of polymers?
Cellulose derivatives or acrylic polymers and co‐polymers
Non‐functional film forming polymers,
Functional polymers / pH sensitive
Functional polymers / extended release (water insoluble)
what is a true latex system?
rue latex–e.g. acrylic polymers and copolymers (EudragitRL and RS)
–Manufactured by an emulsion polymerization process
–Initiate polymerisation by adding an initiator molecule
–Quenching of polymerization process
–Particle size: 50 to 200nm
what is a pseudolatex system?
–Prepared from an existing water‐insoluble polymer
–Dissolution of polymer in organic solvent
–Addition of solution to water containing emulsifying agent
–Homogenisation of emulsion
–Evaporation of organic solvent
what are the two types of vehicles?
organic solvent and aqueous solvent
what are the properties of an organic solvent?
–Wide range of suitable polymers
–Low coating temperature
–Good quality film coating
–Suitable for water‐sensitive materials
what are the properties of an aqueous solvent?
–Non‐flammable, non‐toxic, no environmental hazard
–Lengthy processing time
–Limited range of suitable polymers
what role do colorant and opacifiers have?
- Contribute to aesthetic appeal of the product
- Product identification
- Water soluble dyes–Sunset yellow, patent blue
- Water insoluble pigments–Aluminium lakes–Titanium dioxide–Iron oxide
what do plasticizers do?
- Improve film flexibility
- Reduce film cracking/ brittleness
- Improve adhesion of the film to the surface of the dosage form
- Must show high degree of compatibility with the polymer
- Often chemically similar (e.g. OH‐, COOH‐groups)
what is the MOA of a plasticizer?
–Plasticizer molecules interpose themselves between individual polymer strands
–Breakdown of polymer‐polymer interaction
–Increase opportunity for polymer strands to move past each other
–Reduce of glass transition temperature
what properties do film formation have?
glass transition temperature
crystalline materials
amorphous materials
transition phase
what is a glass transition temperature?
–Transition from the ‘glassy’ into the ‘rubbery’ state
–a property of amorphous materials (e.g. polymers)
–Glass state = materials are brittle, hard and stiff
–Rubbery state = materials are limp and flexible
what advantage do crystalline materials have in film formation?
rapid increase in molecular movement when melting point is reached
what advantage do amorphous materials have in film formation?
molecular movement increases gradually, whereby the physical properties of the material changes dramatically
what influence do plasticizers have on Tg values?
- Effect depends on chemical structure of plasticizer, e.g. ethylcellulose,–M.P. = 175oC; Tg= 129‐133oC
- Reduction of Tgof ethyl cellulose when adding plasticizer in a concentration of 25%, –Oleic acid ~45oC–PEG 400 ~70oC
- Minimum film forming temperature (MFT)
what is MFT?
Minimum film forming temperature (MFT)
–Minimum temperature above which film formation takes place
–Depends on Tg
–Coating temperature should be 10‐20oC above MFT
what effect does plasticiser have on contact angle and surface tension?
inc contact angle
decrease surface tension
what is the mechanism of film formation for a solution?
- All components of the formulation are dissolved
- Rapid evaporation of solvent from both the liquid droplets and the surface of the coated substrate
- Increase in polymer concentration and contraction in volume of the coating liquid on the surface of the substrate
- Further loss of solvent as solvent diffuses to surface of coating
- Concentration of polymer in the coating increases to a point where the polymer molecules become immobile
- Final loss of solvent due to diffusion of residual solvent through an essential dry membrane
what is the MOA of film formation for an aqueous dispersion?
- Components of coating formulation are present as discrete particles dispersed in the solvent
- Droplets adhering to substrate surface lose water due to simultaneous drying
- Particles form contacts and capillary forces initiate coalescence
- Residual water escapes at very slow rate by diffusion through capillary channels between the particles
- Complete coalescence as a result of viscous flow
- Coalescence further enhanced by thermal treatment after drying (‘curing)
