Three moves of the press
A tablet press turns granules into discs with a repeating three-stroke cycle. The shaping parts — the punches and die — are the tooling, and their shape becomes the tablet's shape, score line, and any embossed logo.
- Fill. Granules pour by gravity into the die cavity; the fill depth sets the tablet weight. Steady glidant-aided flow here is what keeps weight variation tight.
- Compress. The upper and lower punches squeeze the powder between them — often at several tonnes — forcing the particles into contact until they bond into a coherent solid. This compression force sets the tablet's hardness.
- Eject. The lower punch rises and pushes the finished tablet out of the die. Clean ejection depends on the lubricant; without it the tablet sticks and tears (capping or picking).
Dressing the tablet: coating
Many tablets get a thin polymer skin sprayed on in a rotating coating pan. [[film-coating|Film coating]] is the modern default: a fine mist of polymer (such as HPMC) dries into a coat a few hundredths of a millimetre thick. It masks bitter taste, adds colour and a swallowable gloss, protects against light and moisture, and prints a brand — all without much changing how fast the drug releases.
The clever cousin is [[enteric-coating|enteric coating]]. The polymer is chosen to stay intact in the acid of the stomach and dissolve only when it reaches the higher pH of the small intestine. This pH-responsive trick protects acid-sensitive drugs and shields the stomach from irritants — a simple form of delayed release.