coated defects2


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SIGNIFICANCE OF COATING Mask taste and smell Protect from environment Provide protection from gastric acid — enteric coating Make easy to swallow Provide identification Give aesthetic appeal Hide surface defects Smooth tablets Stable Sustained/controlled release tablets Incorporate incompatible drugs


FORMULATION • Polymer • Solvent • Plasticizer • Other ingredients • Anticacking agent • Antifoam agent • Colorant • Filler/extender • Flavor • Surfactant

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Parameters like Inlet air temperature and spray rate are major events in coating technology, If any deviation in above said it leads to defective tablets naming blistering (wrinkling), chipping, cratering, picking, and pitting . The knowledge of process conditions and film-coating formulation Is must to get ideal coating across surface of the process, attention not follows leads to creation of odd events called as blooming, blushing, color variation, infilling, mottling, and orange peel (roughness). Bridging, cracking, flaking, peeling, and splitting —defects associated with high internal stresses within the film coating.


CHIPPING The edges of tablet coat becomes dented and detaches from corners/edges of coated tablet. It occurs due to high temperature, long drying rate. High degree of attrition associated with the coating process as in the case of fluidized bed coating of large tablets. Problem overcome by changing the polymer(high mol.wt.),increase the hardness of film, close attention towards monitoring drying and temperature conditions.


Cratering The coating solution penetrates the surface of the tablet, often at the crown where the surface is more porous, causing localized disintegration of the core and disruption of the coating. The coating solution penetrates the surface of the tablet, often at the crown where the surface is more porous, causing localized disintegration of the core and disruption of the coating. the rate of application of the coating solution is too high is leads to cratering.

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The defect is often alleviated by increasing the drying (inlet air) temperature and decreasing the spray application rate, increasing the viscosity of the coating solution by increasing the polymer concentration It may be necessary to slow the rate of penetration of the solution into the tablet surface.


PITTING pits occur on the surface of a tablet core without any visible disruption of the film coating. This is in contrast to “pinholing,”whereby the film contains minute holes, resulting in a loss of film integrity. It only occurs when the temperature of the tablet core exceeds the melting point of the stearic acid, implying that it is the melting point of the particles/aggregates of the stearic acid in the surface of the tablet that causes the pitting to occur.


PICKING Picking with picking, isolated areas of film pull away from the surface when the tablets stick together and then part. It produces an overly wet tablet bed where adjacent tablets can stick together and then break apart. Corrective measures involve decreasing the spray application rate and increasing the inlet air temperature. It is initiation step for sticking . Obliterated by subsequent application of more polymer.


BLUSHING Coated tablet appears as whitish specks or haziness in the film. The white specks or haziness in the film is thought to be due to precipitated polymer exacerbated by the use of high coating temperatures. It may be eliminated by decreasing the drying air temperature.


BRIDGING & CRACKING film pulls out of the intagliation or monogram in the tablet core, forming a bridge across the edges of the mark. This renders the intagliation indistinct and illegible, thus losing the advantage of using intagliated tablets for product identification

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Diagram of the stresses in a film coating applied to a tablet and the causes of cracking/splitting and bridging of the intagliations


BLOOMING Coated tablets subjecting prolonged storage at high temperatures, dulling of the coating . Preventive steps involve not using hot air to dry the tablets at the end of the coating run, the decrease in plasticizer concentration, and the increase in the plasticizer molecular weight. Due to the collection on the surface of low-molecular-weight ingredients.


Infilling Inability of a foam, formed by air spraying of a polymer solution, to break . The foam droplets on the surface of the tablet breakdown readily due to attrition. The intagliations form a protected area, allowing the foam to accumulate and “set. However, the addition of alcohol and the use of spray nozzles capable of finer atomization have both been found to be effective.

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SEM of a Bridged intagliation

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