This ppt discuss about the CPP impacting the coating process parameters & optimisation. U can find validated excel sheet which calculates the CPP for the scale up/down or changing the equipment.

1. Discussion on Critical process parameters (CPP) of film coating and Prediction
of CPP on scale up/scale down & changing the coating equipment
Dr. Satish Puttachari
E mail id: satishputtachari@gmail.com

2. Contents

3. What is coating process
The coating is the process of applying a film of solid is applied on to the surface of tablets or an intermediate (granule
or particle). The coating vehicle used are aqueous or non aqueous and combination of both.
The different types of coating.
1. Film coating – Aesthetic purposes, masking the bitter taste, easy of swallowing, protect from water, oxygen etc.
2. Sugar coating – Masking the bitter taste of drug product, Aesthetic purposes
3. Function coating – Delayed release, modified release.
Equipment's used for coating:
1.Conventation coating pan
2. Side vented coating pan
3. Fluid bed processor

4. What is coating process
3. Fluid bed processor – Bottom spray, tangential spray, preferred for smaller tablets.
During the coating in FBP, the tablets are subjected to more attrition as compared to coating pan.

5. Factors affecting the coating process
Factors affecting the coating process:
They are many variables affect the film coating process, they are classified based on their source

6. Scale up of coating process
Optimisation and Scale up of coating process: They are many factors influence the quality of coated tablets. The
formulation scientist are facing challenges in optimising process parameters and finding the range of critical process
parameters, they are as follows
1. They are many factors effect the film coating process (core tablet, coating equipment's settings, process parameters,
environments). Some of these parameters are interdependent. We need to understand each factors, accordingly the
process to be designed.
2. Optimisation of coating process: Many trials to be taken based on DOE to study the factor and fixes its minimum and
maximum range. Planning the many trials at higher scale is time consuming, laborious and costly.
3. The coating is still considered as ‘Science and Art’ and very less attempt was made for use of scale up parameters to
calculate the process parameters at higher scale up and on changing the coater. Generally the process parameters are
decided on new coater by trial and error method or by experience.
Attempt was made make the task easier, the validated automated Excel sheet is prepared, it will gives the process
parameters in the changed coater on entering the parameters of current equipment.

7. Scale up of coating process
Scale up of coating process:
During the product development, the coating trial was taken in the smaller lab equipment, on optimisation of
process parameters it is transferred to bigger equipment at scale up and then commercial scale.
Challenges in scale up of coating.
1. They are many factors influencing in the coating process, they are core tablet physical parameters, shape,
size etc.
2. The coating solution parameters like Viscosity, consistency, spray rate, solid content
3. Coating equipment parameters like Number of spray guns, size of pan, baffle design,
4. Process parameters like Inlet air volume, inlet air temperature,
5. Environmental factors like Dew point of drying air, Relative humidity.
6. Batch size, % occupancy, spray time
The scale up of coating process and prediction of coating process parameters in the changed
equipment, batch size is quite complex and difficult as compared to other unit operation like compression,
blending etc.

8. Scale up of coating process
Scientific method of scale up of coating process.
Step I: Comparison of two coating equipment's:
A. Geometrical similarity:
Check the following critical equipment's components of the equipment
1. Pan length to diameter ratio (h/D)
2. Shape and size of the coater
3. Baffle design
4. Spray gun nozzle
If the current and proposed coating equipment are similar for above parameters, then they are called as
Geometrically similar equipment's.
B. Kinematic similarity: Keeping the same velocity across the scales
1. Movement of tablets in the pan
2. Spray droplet velocity

9. Scale up of coating process
C. Dynamic similarity
The dynamic similarity refers to ratio of forces at corresponding points in the pan coater is similar across all location.
They are two forces are involved they are
1. Inertial force
2. Gravitational force
The Froude No. is the Dimensionless number that refer the Dynamic similarity.
Fr = w2 D/g
Where w – Pan speed
D – Diameter of the pan
G- Gravitational force

10. Calculation of critical coating process parameters
Calculation of coating critical process parameters
1. Pan load/occupancy: The pan load is calculated as follows.
Maximum Pan load = Brim volume X Bulk density of the tablets
Minimum Pan load = Brim volume (lts) X Bulk density of the tablets (g/ml) X 0.6
Ex: The occupancy of the 36 inches coater for the BD of the tablet 0.55 gm/ml is as follows.
Max pan load = 100 lts X 0.55 g/ml = 55 kg
Minimum pan load =100 lts X 0.55 g/ml X 0.6 = 33 kg
The Brim volume is the volume of the water when the pan is fully filled at current position it is different from the total
volume of the pan.
The pan load should be optimised.
• If the pan load is at higher level, it leads to improper drying of tablets
• If the pan load is at minimum level, the baffles, coating pan receives the coating spray leads tablet sticking and
other problems

11. Calculation of critical coating process parameters
2. Pan speed: The pan rotation such that it will uniformly mix the tablets in the pan such that individual tablets receives the
similar amount of coating solution and tablets are uniformly dried.
In general, if the tablets are friable, the pan speed shall kept at minimum at initial level and once the initial coating layer is
applied increase the speed gradually.
3. Spray rate calculation: on scaling to bigger coater, the pan speed and spray rate to be increased as the probability of the
tablet in the coating zone is decreases in the bigger coater. So it will gives enough drying time for drying of the coating
solution so the spray rate to be increased appropriately.
If there is no significant change in air flow pattern, pan shape, the following equation shall be used for calculating the spray
rate.
S2 = (S1XV2)/V1
Where S2- Spray rate in proposed equipment
S1 - Spray rate in existing equipment
V2- Inlet air volume in proposed equipment
S1 - Inlet air volume in existing equipment
3.

12. Calculation of critical coating process parameters
4. Temperatures: Inlet temperature, Product temperature & Exhaust temperature
In most of the coater, the inlet temperature is controlled to keep the product temperature at required level.
The mechanism of film formation as follows.
The coating solution is sprayed on the tablet surface, The water vapour partially evaporates and the polymers undergoes
‘Coalescence’ and they join together to form the thin over the tablets surface and subsequent drying makes it firm film.
The Glass transition temperature (Tg) of polymer is decided by the properties of the polymer and concentration and type of
Plasticizer.
The Tg determines the minimum film forming temperature (MFET). The product temperature shall be kept more than this
temperature.
In the scale up of coating process, the product temperature shall be kept at same level as followed at lower capacity coater
but it also dependent on the overall drying efficiency of the coater.

13. Calculation of critical coating process parameters
5. Gun to bed distance: It is the distance between the spray gun nozzle to tablet surface.
If the distance is higher might leads to spray drying of coating solution, rough surface on the tablets, higher coating
duration.
If the distance is lesser might leads to over wetting of tablets, twinning and surface dissolution.
Normally around 10 cm is maintained for the smaller coater and 25 cm for higher coater.
6. Number of guns to be used: Select the number of guns in the pan to fulfil the following criteria.
a. The full width of tablet bed is covered and spray on the coating pan.
b. The distance between the coating guns are fixed so that no overlap of coating of two adjacent of guns

14. Factors effecting the coating process
Miscellaneous factors affecting the coating process
1.Dew point : The moisture content in the air impact on the tablet drying efficiency.
If the air is uncontrolled, there will be seasonal variation in the humidity leading to impact on the tablets drying and
film formation.
Its better to use the controlled humidity air for the coating of functional coating.
The humidity in the inlet air is indicated by Dew point. It is calculated by knowing the inlet air temperature and humidity.
2. Droplet size distribution: The drop let size should be optimised to give better coating.
 If the droplet size is higher leads to wetting of tablet bed leading to picking/twinning
 If the droplet size is too small leads to spray drying leading to Orange peel effect on the tablets.
 Typical droplet size is varies from 5 to 250 micron.

15. Automatic calculation of coating process parameters
Calculation of coating process parameters
unit Current
equipme
nt
Proposed
equipmen
t
No of guns
of proposed
coater
Spray rate
per gun
(gm/min)
Pan size inches 60 24
Brim volume
of the pan
lts 400 30
Tablet density gm/ml 0.6 0.5
Actual Pan
load
kg 200 15.00
Working capacity of the Pan
Max capacity kg 240 15
Minimum
capacity
kg 144 9
Pan rpm rpm 6 9.49
Spray rate gm/min 700 131.25 2 65.6
Inlet air flow CFU 6000 1125.00
Atomisation
air pressure
Bar 2.6 1.40
Pattern air
pressure
Bar 2.5 1.40
Note:
1. The data to be entered in the Cell marked in
Blue colour.
2. The data in the yellow colour Cell, calculates
the value automatically
3. If u r knowing the Bulk density of the tablet to
be coated enter the same or otherwise keep it as
0.6 gm/ml.
4. Enter the Brim volume of coater from the
equipment Brochure, if it is not known add the
value from the above table given in the
reference table.
5. The coating process consist of ramping
(change in parameters on time), enter the value
of lower scale and get the values for higher
scale/
5. The downloadable Excel sheet in this slide,
the sheet can be used for calculating the
process parameters.
Prediction of
coating parameters