Capping, Sticking & Weight Variations - tableting problems

Weight Variation
Weight variation occurs because at higher press speeds the time for a homogeneous die filling is too short. Forced feeding in nearly all cases improves the situation dramatically. This feature can be activated at most modern tablet presses and makes homogeneous die filling less dependent on the flowability of raw materials.

Capping
Capping occurs either because air is entrapped in the tablet or too much elastic energy is stored after main compression. Increase of the pre-compression-time either by the use of larger rollers, the use of punches with mushroom heads or the utilization of presses allowing equal force compression; all assuring a better removal of entrapped air. Keeping the upper punch in contact with the tablet after the main compression as long as possible allows the stored mechanical energy to be released without destroying the tablet. 

Sticking
Sticking in most cases is a result of materials (partially) melting. Influences therefore include surface properties of punches and dies, raw material properties as well as temperatures inside the press. Utilization of tablet presses with the ability to control the temperature in the compression section helps in many cases.

ECA has developed a new course on tableting for those who want to go deeper into the details. Aim of this course is to explain the route courses of these problems plus to show solutions for improvement. Also Quality Assurance topics like the validation of a tableting process are adressed. More information can be found here.