Tablet Coating Related Problems and Solutions

Coating Related Problems and Solutions.

         

Here is a list of common defects associated with coated tablets and some likely causes—

Capping:

This is when the tablet separates in laminar fashion. The problem stems from improper tablet compression, but it may not reveal itself until you start coating. How you operate the coating system, however, can exacerbate the problem. Be careful not to over-dry the tablets in the preheating stage. That can make the tablets brittle and promote capping.

Chipping:

This is the result of high pan speed, a friable tablet core, or a coating solution that lacks a good plasticizer.

Picking & Sticking:

This is when the coating removes a piece of the tablet from the core. It is caused by over-wetting the tablets, by under-drying, or by poor tablet quality.

Bridging:

This occurs when the coating fills in the lettering or logo on the tablet and is typically caused by improper application of the solution, poor design of the tablet embossing, high coating viscosity, high percentage of solids in the solution, or improper atomization pressure.

Erosionp:

This can be the result of soft tablets, an over-wetted tablet surface, inadequate drying, or lack of tablet surface strength.

Mottled color:

This can happen when the coating solution is improperly prepared, the actual spray rate differs from the target rate, the tablet cores are cold, or the drying rate is out of spec.

Peeling & Frosting:

This is a defect where the coating peels away from the tablet surface in a sheet. Peeling indicates that the coating solution did not lock into the tablet surface. This could be due to a defect in the coating solution, over-wetting, or high moisture content in the tablet core.

Twinning:

This is the term for two tablets that’s stick together, and it’s a common problem with capsule shaped tablets. Assuming you to change the tablet shape, you can solve this problem by balancing the pan speed and spray rate. Try reducing the spray rate or increasing the pan speed. In some cases, it is necessary to modify the design of the tooling by very slightly changing the radius. The change is almost impossible to see, but it prevents the twinning problem.

Orange peel:

This refers to a coating texture that resembles the surface of an orange. It is usually the result of high atomization pressure in combination with spray rates that are too high. T & C this photo shows multiple defects. The initial problem is erosion of the tablet edge due to a soft or friable tablet or because the pan was turning too fast or both. Peeling and breakage also appear here. I attribute the peeling in this photo to excessive moisture within the tablet, which preserved the coating from adhering. However, the tablet coating also pulled the granulation out of the tablet, a picking defect. That is usually caused by over-wetting the tablet or by a tablet that is too fast.

Just one broken tablet can distribute particles to all other tablets and mar their appearance. These tablets likely broke because they had poor hardness. This photo shows a very porous tablet that prevented the coating from adhering to the surface. These tablets should have been coated longer, and atomization pressure should have been reduced to decrease the slight orange peel, or textured, surface.   

**Labels: Coating Tablet Defects, Cause and Remedies, Formulation, Solution, Tablet coating Problems, Tablet properties, polymers, plasticizers

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