Parameters Influences in Tablet Coating Process

Tablet coating is a complex process that is affected by many variables. Some of those variables can be evaluated or controlled, others can’t.

Here are some of the parameters you should check when evaluating coating process to determine the source of defective coated tablets.

1. Control. Many problems occur in coating when you can’t control every important parameter, such as temperature, pan pressure, spray rates, and atomization pressure. But, the tablet’s surface temperature can be measure with additional tools (out from the coating equipment) by using infra red thermometer (laser thermometer).

2. Tablet quality. Tablets must have the proper porosity, surface, hardness, and moisture content. You can’t have consistent coating without consistent tablet quality.

3. Waiting period. Most tablets cannot be coated immediately after they’ve been compressed. The energy within the tablets is still fairly high and they are still warm. In addition, tablet hardness changes over 24 to 48 hours. Let the tablets rest at least that long before you coat them meanwhile you can check the uncoated tablet for assay, dissolution or other specification by quality control. After the QC released the tablet, then you can start the coating process.


4. Batch size. Variation in batch size changes the required pan speed, gun geometry, spray rates, and temperature. The more your batch sizes vary, the more quality issues that will arise in the coating process. Usually, the greater batch size or the greater number of tablets in pan coating the pan speed to spin faster. Vice versa, if the number of tablets or the smaller the batch size, pan speed spin also reduced.

5. Coating Solution preparation. Does your company prepare coating solutions the same way, regardless of the batch, the shift, or the operator? Track the solution temperature, mixer speed, and storage time. Better if you had standard operation procedure for the coating solution manufacturing.

6. Spray gun calibration. You should calibrate or check the calibration of the guns every time you change products. This means checking the gun’s overall condition and its filter, nozzle alignment, and needle condition.

7. Spray Gun Position/Geometry. Geometry refers to the gun-to-gun alignment, gun-to-tablet bed alignment, and distance from the gun to the end of the pan. Furthermore, make sure all the guns are pointed in exactly the same direction and are maintaining the same spray pattern. Make certain that the tubing and connections are tight and do not interfere with alignment.

8. Gun nozzles. The spray gun nozzles must be kept clean and free of product buildup. Use a flashlight during coating to look into the cabinet and check the nozzles.

9. Pan loading. A visual inspection is critical when coating tablets that are friable or that chip or break easily. That’s why, while loading the tablets, you can search for tablets that are broken, capped, chipped, or covered with black specks. Well, of course you don’t have to check it one by one, as long as your eyes can see. Doing so will help you pinpoint the source of any defects that occur. You can also check the tablets during initial pan rotation, or after preheating.

10. Cleaning. Make sure you’ve cleaned and dried each component of the spraying system before re-installing it after a product changeover.

In tablet coating, small changes in almost any parameter can lead to big differences in results. The more consistent you make operations, and the tablet, the less you must rely on the skill of the operator. Coating may be something of an art, but you’ll get better results when you apply a little science to it.