tablet coating

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

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

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

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

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

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

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

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

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

10. Syrup solution formulation
10
Example of Syrup solution formulation

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

29. Fluidized bed coating
29

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

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

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

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

34. Coating materials
34

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

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

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

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

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

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

41. Continued…..
Colorants
Eg-certified FD&C, D&C, Inorganic Material-Iron
Oxides, natural coloring materials-anthocyanins,
caramel, carotenoids, chlorophill, indigo,
flavones, turmeric and carminic acid
Opaquant-extenders
Eg-titanium dioxide, silicates (talc, alumnium
silicate), carbonates (magnesium carbonate),
sulfates (calcium sulfate), oxides (magnesium
oxide) ,hydroxides (aluminium hydroxide)
Miscellaneous coating solution components
Eg-flavors, sweetners antioxidants, antimicrobials41

42. Formulation of coating materials
42

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

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

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

46. Coating methods
46

47. Equipments employed in tablet
coating
47

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

49. 49
Standard coating pan

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

51. Perforated pan systems
51

52. 52
Perforated pan systems

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

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

55. Defects in coating
55

56. Film defects
Sticking and picking
• Sticking-overwetting or excessive film tackiness
causes tablets to stick to each other or to the
coating pan
• Picking- on drying, at the point of contact, a piece
of the film may remain adhered to the pan or to
another tablet, giving a picked appearance to the
tablet surface and resulting in a small exposed
area of the core
• Reduction in the liquid application rate or
increase in the drying air temperature and air
volume usually solve this problem
• Excessive tackiness may be an indiction of apoor
formulation 56

57. Roughness
• A rough or gritty surface is a defect often observed
when the coating is applied by a spray
• Some droplets may dry too rapidly before reaching
the tablet bed, resulting in deposits on the tablet
surface of spray dried particles instead of finely
divided droplets of coating solution
• Moving the nozzle closer to the tablet bed or
reducing the degree of atomization can decrease
the roughness due to spray drying
• Roughness increases with pigment concentration
and polymer concentration in the coating solution
57

58. Orange-peel effects
• Inadequate spreading of the coating solution
before drying causes a bumpy or orange-peel
effect on the coating
• This indicates that spreading is impeded by
too rapid drying or by high solution viscosity
• Thinning the solution with additional solvent
may correct this problem
58

59. Bridging and filling
• During drying the film may shrink and pull
away from the sharp corners of an intagliation
or bisect, resulting in a bridging of the surface
depression
• Changing the plasticizer or plasticizer
concentration can decrease bridging
• Filling is caused by applying too much solution
• Judicious monitoring of the fluid application
rate and thorough mixing of the tablets
prevent filling
59

60. Blistering
• When coated tablets require further druing in
oven, too rapid evaporation of solvent from
the core
• Effect of high temperature on the strength,
elasticity and adhesion of the film may result
in blistering
• Milder drying conditions warranted in this
case
60

61. Hazing/dull film
• Also called as ‘bloom’
• Occurs when too high processing temperature
is used
• Particularly evident when aqueous cellulosic
polymers are applied at high processing
temperature
• Also occurs if the coated tablets are exposed
to high humidity conditions and partial
solvation of film results
61

62. Color variation
• Can be due to improper mixing, uneven spray
pattern, insufficient coating
• Migration of soluble dyes, plasticizers and
other additives during drying may give the
coating a mottled or spotted appearance
• Use of lake dyes eliminates dye migration
• Reformulation with different plasticizers and
additives will solve film instabilities caused by
the ingredients
62

63. cracking
• Occurs if internal stresses in the film exceed
the tensile strength of the film
• Tensile sterngth of the film can be increased
by using higher-molecular-weight polymers or
polymer blends
• internal stresses internal stresses can be
minimized by adjusting the plasticizer type
and concentration, and the pigment type and
concentration
63

64. Debossed and Embossed tablets
64
Debossed Tablets Embossed Tablets