This is the final serious step in the production tablet . Process selection depends upon which type of coating we want to apply, the hardiness of the tablet core besides the economic of the process.
Sugar coating, still an extensively used coating process as it gives excellent tablet appearance.
Sugar coating:
It involves various steps, the duration ranges from a few hours to go for a few days besides its success depends upon the involvements of the coating operator.
The basic sugar coating involves the following steps:
Sealing/seal coating: A seal coat is applied to stop moisture infusion into the tablet core; otherwise leading to tablet softening or disintegration, affecting the physical & also chemical stability of the product.
Zein(alcohol soluble protein) & shellac, also used as sealant. Propylene/polyethylene glycol etc also used as solvent.
Sub coating: it is applied to round the edges and build up the tablet size (sugar coating increases the tablet weight by 50-100%). The process of subcoating consists of (alternatively): applying a sticky binder to the tablets → dusting of subcoating powders → drying. Example: gelatin, acacia etc are used as subcoating solutions.
Syruping (smoothing): This step is to cover plus to fill in the imperfections in the tablet surface caused by subcoating, and to gives the desired color to the tablet.
Polishing: The tablets are polished in standard coating pans by applying powdered wax (bees-wax or carnauba) in suitable volatile solvent.
Zein(alcohol soluble protein) & shellac, also used as sealant. Propylene/polyethylene glycol etc also used as solvent.
Sub coating: it is applied to round the edges and build up the tablet size (sugar coating increases the tablet weight by 50-100%). The process of subcoating consists of (alternatively): applying a sticky binder to the tablets → dusting of subcoating powders → drying. Example: gelatin, acacia etc are used as subcoating solutions.
Syruping (smoothing): This step is to cover plus to fill in the imperfections in the tablet surface caused by subcoating, and to gives the desired color to the tablet.
Polishing: The tablets are polished in standard coating pans by applying powdered wax (bees-wax or carnauba) in suitable volatile solvent.
Film coating
With some differences film coating comprising of the same equipments & process parameters of sugar coating;
Film coating materials
Criteria of an ideal film coating materials
· Soluble in a suitable solvent.
· Should have required solubility intended use e.g. Free water solubility, slow-water solubility, pH dependent solubility etc.
· Capable of producing an elegant looking product.
· Stable to light, moisture, heat, air plus should not alter with again.
· Essentially have no colour taste or odor.
· Compatiblity with common coating additives.
· Have no pharmacologic activity & also non-toxic.
· Resistance to cracking (i.e. moisture, light etc)
