This document discusses various film defects that can occur during the tablet coating process, including sticking and picking, twinning, roughness, orange-peel effects, bridging and filling, blistering, color variation, cracking, hazing/dull film, chipping, peeling, and erosion. For each defect, the document explains the potential causes and recommends remedies to address the underlying issues, such as reducing the liquid application rate, increasing drying air temperature, thinning the coating solution, adjusting the pan speed, or reformulating the coating solution.

1. PHR 221: Pharmaceutical Technology II
Course Teacher: Mohammad Nasir Uddin
Lecturer, Department of Pharmacy, NSU

2. Tablet Coating

3. Film defects
• Sticking and picking
• Twinning
• Roughness
• Orange-peel effects
• Bridging and filling
• Blistering
• Color variation
• Cracking

4. Sticking and picking
• Over wetting or excessive film thickness causes tablets to stick
to each other or to the coating pan.
• 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.
• Excessive tackiness may be a indication of a poor formulation

5. Sticking and picking
Remedies:
 Reduce liquid application rate.
 Increase drying air temperature
and air volume.

6. Twinning
• This is the term for two tablets that stick together, and it’s a
common problem with capsule shaped tablets
Remedies
 Balance the pan speed and spray rate.
 Reduce the spray rate or increase the pan speed.

7. Roughness
• A rough or gritty surface is a defect which is observed when the
coating is applied by spray.
• Some of the 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.
• Surface roughness also increases with pigment concentration and
polymer concentration in the coating solution.

8. Roughness
Remedies
 Move the nozzle closer to the tablet bed.
 Reduce the degree of atomization

9. Orange-peel effects
• Inadequate spreading of coating solution before drying causes a
bumpy or Orange –peel effects On the coating.
• This indicates that spreading is impeded by too rapid drying or
by high solution viscosity.
• Remedies: Thinning of coating solution with additional solvents
may correct this problem.

10. Bridging and Filling
Bridging
• 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.
• These defect can be so severe that the monogram or bisect is
completely obscured.
• Bridging mainly represents a problem with formulations.
• Remedies: Increasing the plasticizer contents or changing the
plasticizer can decrease the incidence of bridging.

11. Bridging and Filling
Filling
• Filling is caused by applying too much solution, resulting in
thick film that fills and narrows the monogram or bisect.
• In addition, if the solution applied too fast, over wetting may
cause the liquid to quickly fill and be retained in the
monogram.
• Remedies: Judicious monitoring of the fluid application rate .
Thorough mixing of tablets in the pan prevent filling.

12. Bridging and Filling

13. Blistering
• When coated tablets require further drying in ovens, too
evaporation of solvents from the core and the effect of high
temperature on the strength, elasticity and adhesion of the film
may results in blistering.
• Remedies: Milder drying condition is preferred to avoid this
problem.

14. Color variation
• This problem can be caused by processing conditions or the
formulation.
• Improper mixing, uneven spray pattern and insufficient coating may
results in color variation.
• The migration of soluble dyes, plasticizer and other additives during
drying may give the coating a mottled or spotted appearance.
Remedies:
 Use lake dyes
 Reformulate with different plasticizer and
additives.

15. Cracking
• Cracking occurs if internal stresses in the film exceed the
tensile strength of the film.
Remedies:
 The tensile strength of the film can be increased by using
higher molecular weight polymers or polymer blends.
 Internal stresses in the film can be minimized by adjusting the
plasticizer type and concentration, and the pigment types and
concentration .

16. Other types of film defects
Hazing/dull film
 It can occur when too high processing temperature is used for a
particular formulation.
 It can also occur if the coated tablets are exposed to high
humidity conditions and thus partial solvation of film results.
Chipping
 This is the result of high pan speed, a friable tablet core, or a
coating solution that lacks a good plasticizer

17. Other types of film defects
Peeling
 This is a defect where the coating peels away from the tablet
surface in a sheet.
 Peeling indicates that the coating solution did not lock into the
tablet surface.
 This could be due to a defect in the coating solution, over-wetting,
or high moisture content in the tablet core which
prevented the coating to adhering.

18. Other types of film defects
Erosion
 This can be the result of soft or friable tablets (and the pan turning too
fast), an over-wetted tablet surface, inadequate drying, or lack of tablet
surface strength.