Tablet coating glossary

The vocabulary a coating conversation actually uses, defined plainly. 26 terms, each linked to where it does real work.

Process

Aqueous coatingalso water base: A coating dispersion made up in purified water. It runs on the hotter band, roughly 35 to 40 degrees at the tablet bed against a 75 to 80 degree inlet, and avoids solvent handling entirely. It is the default route unless the core cannot tolerate water. AQ-Z Wb
Non-aqueous coatingalso solvent base, NAQ: A dispersion made up in solvent rather than water, run cooler at around 30 to 35 degrees at the bed with a 60 to 65 degree inlet. It suits moisture sensitive cores, and brings solvent handling and area classification with it. NaQ-Z1Wb
Weight build-upalso weight gain, % build-up: How much coating has been applied, expressed as the percentage the tablet has gained. It is the control variable for a functional coat, because release rate and barrier performance both follow the amount applied rather than the time spent spraying. SR100
Tablet bed temperature: The temperature of the tablets themselves inside the pan, not the air going in. It is the number that governs whether a film forms properly, and on an enteric coat it is held at 30 to 32 degrees because a hot bed softens the polymer and costs gastro resistance.
Inlet temperature: The temperature of the drying air entering the pan. It runs well above bed temperature, typically 75 to 80 degrees for an aqueous film coat and 45 to 50 for an enteric stage.

Equipment

Pan speed: How fast the coating pan turns, in revolutions per minute. It falls as pan size rises, from around 18 to 20 rpm on a 12 inch pan to 3 to 5 rpm on a 48 inch auto coater, because the tablets travel further per revolution.
Tablet charge: The weight of tablets loaded into the pan for a coating run. It scales with pan size, from half a kilogram on a 12 inch pan to well over a hundred kilograms on a 48 inch auto coater.
Conventional coateralso conventional pan: A coating pan without a perforated drum, where drying air passes over the bed rather than through it. Still in daily service across much of Indian manufacturing, and the reason we publish parameters for conventional as well as auto coaters.
Auto coateralso perforated pan: A perforated drum coater that pulls drying air through the tablet bed. It handles larger charges at lower pan speed, which shifts the limiting factor from spray rate to drying capacity.

Materials

Ready-mix coatingalso premix, one step coating: A single dry blend containing everything the film needs, dispersed on site in water or solvent and sprayed. It removes in-house weighing and blending of polymer, pigment, plasticiser and opacifier, which is where batch to batch variation usually enters a validated process.
Enteric coatingalso gastro resistant coating, delayed release: A film that stays intact in stomach acid and dissolves once pH rises in the intestine. Used where the active is destroyed by acid, irritates the stomach, or needs to act further down the tract. Enteric coating system
Seal coatalso pre-coat, sub-coat: A thin layer applied to the core before a functional coat. It isolates the core from the polymer above it and gives that layer an even surface to build on, which matters most on acid labile actives. SC-401
Moisture barrier: A film formulated to slow water vapour reaching the core, rather than simply to cover it. Its job is shelf life inside the pack, which is why it is judged on stability data rather than on appearance. Moisture barrier coating
Opacifier: The component that makes a film hide what is underneath. It is why an extra white grade covers a dark core at a lower build-up than a standard white one.
Plasticiser: An additive that keeps a dried film flexible rather than brittle. Without enough of it a film cracks over embossing and at tablet edges.
HPMCalso hypromellose: The workhorse polymer of immediate release film coating. It forms a clear tough film at low build-up, takes pigment well, and does not delay release. Coating polymers
Methacrylic acid copolymeralso acrylic enteric polymer: The polymer family behind most enteric films. It can be applied from either a water or a solvent base, which is why the same chemistry serves cores that can and cannot tolerate an aqueous process. Coating polymers
Cellulose acetate phthalatealso CAP: An older enteric polymer still named in many dossiers. Where a filing specifies CAP, switching to a methacrylic film is a change control rather than a substitution. EC714
Taste masking: Preventing a bitter active being tasted, usually through solid dispersion rather than flavour alone. In a suspension it is a blending problem with no coating parameters attached. RT-114
Hygroscopic: Readily absorbing moisture from the air. A hygroscopic active sticks, picks and caps on the press and keeps degrading afterwards, which takes an adsorbent in the powder and often a barrier film on the tablet. HR100

Testing

Disintegration timealso DT: How long a tablet takes to break apart under test conditions. A coat that is too heavy pushes it out of specification, which is why dissolution critical products are checked after coating and not only before. RT314
Dissolution profile: How much active has released at each time point under test. For an enteric product it is measured in two stages, an acid stage the film must survive and a buffer stage in which it must release.
Acid stage: The first part of enteric dissolution testing, where the tablet sits in acid and must not release. Failing it means the film lost integrity, usually from a hot bed, a thin coat, or a missing seal layer. Loss of gastro resistance

Defects

Logo bridging: The film lifting out of an embossed logo and spanning across it, so the debossing goes shallow or disappears. Usually a sign of too much build-up over the debossing, or a film drying under stress. Coating defects
Picking and sticking: Tablets adhering to each other or to the pan, pulling away fragments and leaving pitted faces. It means the bed is wetter than the drying can carry, or the active is bringing moisture in before coating starts. Coating defects
Orange peelalso roughness: A dimpled matt surface instead of a smooth gloss, caused by droplets drying before they spread and coalesce. Coating defects