Coating Technology and Problems encountered

1. M. Pharm Sem-II Presentations
Title : Coating Technology And Problems Encountered
SUBMITTED TO
SAVITRIBAI PHULE, PUNE UNIVERSITY , PUNE
FOR
PARTIAL FULFILMENT OF REQUIREMENTS FOR THE AWARD OF
MASTER OF PHARMACY
IN THE SUBJECT
Pharmaceutical Quality Assurance
IN THE FACULTY OF SCIENCE AND TECHNOLOGY
Bhujbal Knowledge City,
MET’s Institute of Pharmacy,
Adgaon, Nashik, 422003.
Maharashtra, India
Academic Year- 2021-2022 1
Presented By- Pratiksha
Mandlik
Guided By- Dr. Sapna
Ahirrao

2. Contents
• Introduction
• Coating Process
• Coating Techniques
• Coating Equipments
• Coating Defects
2

3. Introduction
• Coating is the process by which a layer of coating material is
applied to the surface of a dosage form in order to obtain
certain benefits that mainly include ease of the product
identification and modifying drug release from the dosage
form.
• Objectives of coating :
 To mask taste, odour, or colour of the dosage form
 To provide physical and chemical protection for the drug.
 To protect the drug from the gastric environment of the
stomach with an acid resistant enteric coating
3

4. Coating Process
• Rotating coating pans are commonly used for coating
purpose.
• Uncoated tablets are placed inside the pan and liquid coating
material is brought into the pan during the tumbling of
tablets.
• Air is passed over the tumbling tablets so that liquid part of
the coating part material gets evaporated leaving the layer of
solid coating material.
4

5. Selection of
type of coating
material
Loading the
tablets into pan
and warming
Spraying of
coating material
to moving bed
of tablets
Drying by
heated air
Cooling and
unloading
5

6. Coating Techniques
• Some essential major techniques for applying coatings to
pharmaceutical solid dosage form are as follows:
1. Film coated tablets
2. Sugar coated tablets
3. Enteric coated tablets
6

7. Film Coating
• A film coating is a thin polymer based coat applied to a solid
dosage form such as a tablet, granule or other particle.
• The thickness of such coating is usually between 20 to 100
µm.
• Film coating formulation usually contain the following
components :
1. Polymer
2. Plasticizer
3. Pigments/opacifier
4. Vehicle
7

8. 1. Polymers
• The vast majority of the polymers used in film coating are
either cellulose derivatives or acrylate polymers and
copolymer
a. Hydroxypropyl methylcellulose(HPMC)
 Due to its solubility in both aqueous media and the
organic solvents, low viscosity and non tacky nature it is
widely accepted and normally used for film coating.
b. Hydroxypropyl cellulose
 It is soluble in water below 40º C, gastrointestinal
fluids and many polar organic solvents. This polymer is
extremely tacky as it dries, may be used as subcoat.
8

9. c. Ethylcellulose
 It is completely insoluble in water in water and GIT and
thus cannot be used alone for tablet coating, usually
combined with water soluble additives eg. HPMC in
preparing sustain released tablets.
d. Acrylate polymers
 Marketed under trademark Eudragit. This material is
available as 1) organic solution in isopropyl/acetone 2)
30% aqueous dispersion 3) solid material . Eudragit RL
and RS are copolymers synthesized from acrylic and
methacrylic acid ester.
9

10. e. Methacrylate ester copolymer
 It resemble to the methacrylic copolymers but are totally
esterified with no free carboxylic acid groups, neutral in
character , insoluble over entire physiological pH range.
 It swell and become permeable to water and dissolve
substances so find application in the coating of
MRDF(Modified release dosage form).
 Enteric polymers
• These are designed to resist the acidic nature of the
stomach contents, yet dissolve readily in the duodenum.
10

11. a. Cellulose acetate phthalate(CAP)
 This is most widely used in industries.
 It is insoluble in water, alcohol and chlorinated
hydrocarbon.
 Dissolve only above pH 6.
 FMC corporation has developed a patented aqueous
enteric coating called Aquateric.
b. Acrylate Polymer
 Two commercially available enteric acrylic resins are
Eudragit L and Eudragit S, both are soluble in intestinal
fluid at pH 6 and 7 respectively.
11

12. • Mechanical Properties Of Polymer
1. Tensile strength : It is the maximum stress applied at the
point at which the film breaks.
2. Modulus of elasticity : This is applied stress divided by
the corresponding strain in the region of linear elastic
deformation. It can be regarded as an index of stiffness
and rigidity of a film.
3. Work of failure: It is an index of the toughness of a film
and is better measure of the film’s ability to withstand a
mechanical challenge.
4. Strain : It is measure of how far the sample elongates
prior to break
12

13. 2. Plasticizers
• These are low molecular weight materials which have the
capacity to alter the physical properties of a polymer making
it softer and more pliable thus useful in performing its
function as a film coating material.
13
Internal Plasticizing External Plasticizing
Chemical modification of the basic
polymer by controlling the degree
of substitution, type of substitution
and the chain length
Incorporated with the primary
polymeric film former, changes the
flexibility, tensile strength or
adhesion properties of the
resulting film.

14. • Mechanism of action :
14
Plasticizer molecule
interpose between the
polymer strands
Breaking down the polymer
-polymer interaction
Polymer – plasticizer interaction
is considered stronger than the
polymer-polymer interaction
Polymer are difficult to
plasticize in this way as
disruption of the
intermolecular structure is
not easy

15. • One fundamental property of a polymer which can be
determined by several techniques is the glass transition
temperature (Tg).
• This is the measure at which a polymer changes from a hard
glassy material to a softer rubbery material. The action of the
plasticizer is to lower the glass transition temperature.
• Examples :
1. Polyols : Glycerol, Propylene glycol
2. Organic ester : Pthalate esters, Dibutyl esters
3. Oils : Castor oil, Fractionated coconut oil
15

16. 3. Opacifier or Colorants
• Colorants aid in the identification of the individual products
by patients, particularly taking multiple medication.
• They may be soluble in the solvent system or suspended as
insoluble powder
• Examples :
1. Organic dyes and their lakes : Tartrazine, Sunset yellow
2. Inorganic color : Titanium dioxide, talc
3. Natural colors : Riboflavin, Carmine, Anthocyanins
16

17. 4. Solvents/Vehicles
• A prerequisite for a solvent would be that it has to interact
well with the chosen polymer, this is needed as high polymer-
solvent interaction permits film properties such as adhesion
and mechanical strength
• Not only thermodynamically based compatibility but also
kinetic considerations of the solvent to penetrate the polymer
more effectively and solvate polymer in such a way that
polymer swelling and dissolution take place effectively are
also very important.
17

18. Sugar Coating
• Sugar coating is a multistep process :
18
Sealing
Sub-coating
Syrup coating
Color Coating
Polishing
1. Sealing
• To prevent moisture penetration into the
tablet core, a seal coat is applied
• Shellac is an effective sealant but tend to
lengthen on aging because of
polymerization of shellac
• Zein is an alcohol-soluble protein
derivative lengthening dissolution times
have not been reported on aging of zein
seal coated tablets.

19. 2. Subcoating
• The subcoating is applied to round the edges and build up the
tablet size.
• Sugar coating can increase the tablet weight by 50-100%.
3. Syrup Coating (Smoothing)
• The purpose of this step is to cover and fill in the imperfection
in the tablet surface caused by the sub coating step.
4. Color coating
• During this step the coating syrup contains the color solids
cover the tablet necessary to achieve the desire shade.
19

20. 5. Polishing
• The desired luster is obtained in this final step of the sugar
coating process
• Example : Beeswax, Carnauba
20

21. Coating Equipments
• Most of the coating processes use one of the three general
types of equipment :
1. The standard coating pan
2. The perforated coating pan
3. The fluidized bed (air suspension)
21

22. Standard Coating Pan
• The standard coating pan system consists of a circular metal
pan mounted some what angularly on the stand.
• Coating solutions are applied to the tablets by spraying the
material onto the rotating tablet bed.
• Heated air is directed into the
pan and onto the tablet bed
surface, exhausted by means
of ducts positioned through the
front of the pan
22

23. • A significant improvement in the drying efficiency of the
standard coating pan is achieved by the :
1. The immersion sword system
2. The immersion tube system
23

24. The Perforated Pan
• Equipment of this type consists of a perforated or partially
perforated drum that is rotated on its horizontal axis in an
enclosed housing.
• In the Accela-Cota and Hi-Coater system, drying air is directed
into the drum, is passed through the tablet bed, and is
exhausted through perforations in the drum.
24

25. • The Dria-coater introduces drying air through hollow
perforated ribs located on the inside periphery of the drum.
• As the coating pan rotates, the ribs dip into the tablet bed,
and drying air passes up through and fluidizes thr tablet bed.
• Exhaust is from back of the pan
25

26. Fluidized Bed ( Air suspension) System
• Fluidized bed coaters are highly efficient drying system.
26
• 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 tablets to
rise in the centre.
• The movement of tablets is
upward through the center of
the chamber.

27. • They fall towards the chamber wall and move downward to
re-enter the air stream at the bottom of the chamber.
• Coating solution are continuously applied from a spray nozzles
located at the bottom of the chamber or are sprayed onto the
top of the cascading tablet bed by nozzle located at the top of
the bottom.
27

28. Coating Defects
Sr.
No.
Defect Definition Cause Remedy
1 Blistering It occurs when strength,
elasticity & adhesion are
compromised & the film
detaches from the tablet
1. Too rapid
evaporation of the
solvent from core
2. High temp. during
drying
Use milder drying
conditions
2 Sticking and
Picking
It occurs when film
tackiness causes tablets
to stick to each other or
to the coating pan
1. Spray rate too
high & drying air
volume too low
2. Poor film adhesion
1. Reduce liquid
application
2. the drying air
temp. & air
volume
3 Orange peel
effect
Inadequate spreading of
the coating solution
before drying cause a
bumpy or orange peel
effect
1. Too rapid drying
2. High coating
solution viscosity
Thinning coating
solution with
addition of adequate
solvent
28

29. 4 Roughness Tablet has a rough
surface rather than
smooth and glossy film.
When coating is applied
by spray droplets may
dry too rapidly before
reaching tablet bed
1. Moving the nozzle
closer to the tablet
bed
2. the degree of
atomization
5 Bridging and
filling
It is the disappearance
of the tablet logo or
bridging of monogram
on tablet
1. Applying too much
solution
2. Poorly plasticized
film coating
3. If solution applied
too fast, over-
wetting results in
filling of monogram
1. Optimize
adhesiveness &
plasticization
2. Monitor fluid
application rate &
temp.
3. Use logo design
optimized for film
coating
6 Blooming/Hazi
ng/Dull film
It is the dulling of the
tablet colour
1. Too high processing
temp.
2. Use of low
molecular wt.
plasticizer
1. the amount &
the mol. wt. of
plasticizer
2. the processing
temp. and
humidity
29

30. 7 Mottling Variation in the color of
the tablets within a
bath
1. Improper mixing
2. Uneven spray pattern
3. Insufficient coating
1. Use of lake dye
prevent dye
migration
2. Even geometric
mixing
8 Cracking It is splitting of the film
coat especially on the
crown area
1. Internal stresses in the
film exceed the tensile
strength of the film
2. Lack of relaxation time
between tablet
compression & coating
3. Poorly plasticized film
coating
1. Use high mol. wt.
polymer
2. Adjust polymer
type &
concentration
9 Twinning Two or more tablet
cores are stuck
together
1. Overwetting by coating
solution
2. Inappropriate tablet
shape
Placing even a very
subtle amt. of
curvature on an
otherwise flat surface
can minimize twinning
30

31. References
1. The Theory and Practice of Industrial Pharmacy, Roop khar, S
P Vyas et. al. fourth edition, CBS Publisher & Distributors Pvt
Ltd, Pg no. 497-523
2. A Comprehensive Review on Pharmaceutical Film Coating:
Past, Present, Future, Abdel Naser Zaid, Dovepress, Drug
design & development, 2020
3. Tablet Coating Techniques : Concepts & Recent trends, Gupta
Ankit et. al. International Research Journal of Pharmacy, 2012
4. An Overview on Tablet Coating, Arora Rimjhim et. al. Asian
Journal of Pharmaceutical research and development, 2019
31

32. Thank you
32