Pharmaceutical Manufacturing Handbook: Production and

COATING SYSTEMS 1019
ences between the individual sugar - coated tablets. This is one of the reasons why
sugar - coated products always show a much wider weight distribution than fi lm -
coated tablets.
Several authors have made proposals for the most convenient size of tablet for
sugar coating. A further rule has been established according to which the convex
radius should be between 0.7 and 0.75 times the tablet diameter and the band height
between 0.07 and 0.12 times that diameter. However, for calculation of the band
height only a factor of 0.12 is advisable, since, otherwise, the minimum value of
1 mm will be fallen short of by far [53, 57 – 60] . For fi lm coating the recommended
convex radius is 1.5 times the tablet diameter (less curved tablets are preferred).
Numerous formulation are available for all fi lm - forming polymers offered in the
market. Thus, it is possible to dispense with many of the preliminary tests and
concentrate development work on the special problems of the formulation in question.
In this chapter, we will focus on SEPIFILM and Kollidon VA 64. Table 16
presents proven basic formulations reported on in the literature [61] and polymers
used for the most important commercially available fi lm formers, which also can be
used as a basis for further tablet coating.
The major operational coating process parameters related to fi lm coating are able
to be measured and monitored continuously in some pan - type coaters. The inlet
airfl ow rates infl uence the coating process and the subsequent quality of the coated
tablets. Increasing the inlet airfl ow rate accelerated the drying of the tablet surface.
At high inlet airfl ow rate, obvious fi lm coating defects, that is, unacceptable surface
roughness of the coated tablets, are observed and the loss of coating material
increased.
Today advantages of aqueous fi lm coating are well recognized and fi lm coating
technology is much developed to successfully perform these types of coatings.
Process automation and monitoring of critical process parameters can be utilized
to increase the overall process effi ciency and predictability and to improve the
homogeneity and reproducibility of the tablet batches. This will ensure high quality
and safety of the fi nal coated products, which are mandatory requirements of tablet
manufacturing.
6.3.8.1 Subcoating of Tablet Cores as a Barrier to Water
As tablets are nowadays coated mostly with aqueous solutions or dispersions, it has
become increasingly necessary to provide the tablet cores with a barrier layer prior
to sugar or fi lm coating. This is mainly to protect water - sensitive drugs against
hydrolysis and chemical interactions, for example, between different vitamins, and
to prevent the swelling of high - performance tablet desintegrants that are very sensitive
even to small quantities of water. It can be especially useful when controlled -
release systems with hydrophilic polymer are studied and the water contained can
change the dissolution profi le. Kollidon VA 64 also can be used to improve the
adhesion of subsequent coatings by hydrophilization of the surface.
6.3.8.2 Kollidon VA 64
We are studying the ability of Kollidon VA 64 as a subcoating in a combined hydrophilic
(dextran – HPMC) – hydrophobic (cetyl alcohol) matrix core prior to sugar