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How to preserve tablet surface

Who never runs into coating surface defects? Roughness, peeling, orange skin and scuffing are some of the difficulties encountered while coating tablets. Discover how to overcome these obstacles and obtain a perfectly coated tablet surface.

November 30, 2016
Caterina Funaro
Massimo Malavolti

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The answers of the coating experts

Which is the best core shape to obtain a perfect coating?
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The ideal shape would be a sphere because it moves in the best way inside the coater. Tablets with flat surfaces are the worst case and should be avoided. Of course, all other core shapes that are close to spherical are the ideal situation.

Does the spray time influence the quality of the coating?
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Most of the customers would like to speed up the process reducing the spray time. In order to do this thermodynamic limitations and core capability to receive the solution without being damaged have to be considered. To define the right flow rate to be sprayed on the tablets preliminary trials have to be performed to check which is the best compromise between spray rate and final quality of the tablet surfaces.

Are cosmetic and functional coating formulation different with reference to surface defects?
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These surface defects are more frequent when applying a cosmetic formulation because:

  1. The viscosity is higher. Sometimes the formulation is based on HPMC and it is used with the highest concentration.
  2. Cosmetic formulation is applied to mask the core. Higher quantity of titanium dioxide is used and weight gain is normally below 4%.

In the enteric formulation the weight gain is double and time to recover the defects is longer. Importantly, tablet shape is normally designed without the logo or the breaking line. In the enteric formulation it is also more frequently present the problem of polymer coagulation in the spray line.

Do we increase surface defects using new formulations with up to 35% solids dispersion? Is it difficult to control the process in these conditions?
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No, luckily the modern formulations that can be used at 30-35% solids content also prove a very low viscosity and very easy spray ability. Adjusting the parameters in the proper way makes it possible to work perfectly even in this condition.

Does end polishing with transparent coating help in solving surface defects?
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No, unfortunately any polishing step maximize the surface finishing in both a positive and a negative way. If the surface is smooth after the coating process, polishing can confirm it, but if the surface is rough any type of glossy agent (wax, clear coat, shellac, Capol, etc….) makes the defect more and more evident like a magnifier.

Should we always foresee the relaxation time when designing a tableting and coating process? Is it common?
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Relaxation of cores and tablets is needed only by a few excipients when subjected to compression. So it is not really very popular and normally the time existing between compression and coating is more than enough to enable it as far as batch coating is concerned.

Meet our webinar speakers

Caterina Funaro
Process R&D Laboratory Manager
Caterina Funaro got her degree in Chemistry and Pharmaceutical Technology at the University of Bologna in 1998. She is actually employed at IMA Active Division as process laboratory manager and her main responsibilities are technical assistance to sales for all solid dose equipment, after sales process assistance, R&D, training and cleaning support for solid dose manufacturing equipment.
Massimo Malavolti
Product Manager for Coating Equipment
Massimo Malavolti got his degree in Technological Institute specialized for electronical and mechanical applications in 1990 in Bologna. He is employed at IMA since 1990. At the beginning he supported validation development and calibration strategy for coating equipment, actually he is Product Manager for coating equipment and his main responsibilities are sales technical support and projects management.
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