TABLETING
Moisture content and particle size distribution can affect sticking
STICKING AND PICKING
Sticking and picking are common issues within tablet production, this article explores how the right technology can circumvent the problem
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ticking is a common issue, it occurs when particles adhere to the punch cup while picking occurs where particles
stick in or around the embossing on the punch face. When sticking or picking is noticed,
their location will help in identifying the root cause. Photos or sample tablets are helpful.
TABLET DESIGN Cup depth is a critical parameter in optimising a tablet design. Often, sticking and picking is caused by a ‘soft zone’ across the crown of the tablet owing to a deep cup depth.
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Shallower cup depths improve tablet hardness uniformity, which can reduce or eliminate the ‘soft zone’.
FONT DESIGN Picking is affected by the font style and letter spacing. Serif fonts are more prone to picking problems than Sans Serif fonts. Fonts should have a letter height
at least five times (preferably 6 to 7.5 times) stroke width to allow for adequate island and peninsula sizes. Inside corners within the font should have a fillet radius at least 20% of the stroke width. Opening up the shape and flair of
peninsulas rather than a more closed ‘pinch’ look is helpful. This may often be achieved by widening the letter, such as an ‘N’ or ‘M’, or uncurling the ends of an ‘S’.
ENGRAVING DETAILS Section thru engraving views detail stroke width, stroke angle, stroke depth, the blend radius, and the stroke radius. Wider stroke angles reduce picking, Avoid 30° for sticky formulations. 35° to 40° stroke angles are recommended with 37.5° or 40° used when adequate stroke depth can still be achieved. For sticky products, stroke depth
should be the minimum necessary to achieve visual clarity. Stroke depths between 0.007” to 0.009” are preferred. For larger characters, use a flat bottom engraving to minimise stroke depth. The blend radius is most often
overlooked. Picking begins at the transition between the cup and logo. Larger blend radii improve resistance against picking. Specifying a blend radius that consumes 30% to 35% of the stroke depth is ideal for sticky products.. The formula to optimise break radius is:
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