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Uses of Bleached Shellac in
Pharmaceutical Industry.
Dewaxed Bleached Shellac
dissolved in specifically denatured alcohol are the glazes
employed for coating pharmaceutical tablets and confectionery
by the pan method.
The main uses for Dewaxed Bleached
Shellac in the pharmaceutical industry are for coating tablets
and sustained release capsules.
The functions of the shellac, depending on the particular
medicament are:
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- To serve as a moisture barrier, protecting the core
ingredients
- As an enteric coating
- To control disintegration
- As a granulating agent
- As a finishing coat over wax, prior to the printing of
a trademark.
The shellac is normally applied by the
pan method from alcohol solutions, the concentration of
shellac depending on the function to be performed. In practice
the number of coats applied depends on the function of the
shellac coating and varies from as few as 1 or 2 coats for a
moisture barrier, to as many as 16 or 20 coats for enteric
coating.
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Our Dewaxed Bleached Shellac give almost
colourless transparent films of great clarity and brilliance
with increased water-resistance and higher stability. Films
from these do not polymerize and lose their solubility in weak
alkalis so rapidly as those from bleached lac and maintain a
more stable disintegration time upon ageing.
Procedure:
Charge the coating pan, clean and dust-free, with tablets so
that they tumble freely. |
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Start the coating pan at
38-48 r.p.m. and add just enough shellac glaze to cover the
tablets. Mix the tablets by hand to ensure even distribution
of the glaze.
Allow the tablets to roll until they
begin sticking to the pan and to each other. At this point,
add a small amount of dusting agent, such as talc, and again
mix by hand.
When the tablets are rolling freely, blow in air at room temperature for 5 to 10 until most of the
remaining alcohol is driven off and then dry with warm air at
29-39ºC for 25 to 40 minutes. The tablets are then cooled and
the procedure repeated as many times as needed. Allow 48 hours
of air drying before starting to re-coat.
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