John Norman, mechanical drafter and designer for technical service support at Natoli Engineering, examines the causes and solutions for dark spots in tablet manufacturing.
Can you remember a time when production came to a halt due to dark spots on the tablet post-compression? If you are quick to recall an instance, you’re sitting right alongside the majority of tabletting manufacturers. There are many reasons that these spots can appear and determining the cause is dependent on multiple factors.
One of the most common causes of dark spots is a result of a contaminant, typically a tooling lubricant such as oil or grease, being transferred to the powder. During tablet press operation, it is critical to have proper lubrication on the punch heads and barrels to maintain satisfactory operating conditions. Most modern tablet presses are equipped with oil seals to restrict punch barrel lubricants from entering the compression zone. Regular inspections of these seals should be performed. Uneven or extended wear and damage to the seals may cause lubricant to make its way into the compression zone. Additionally, if the upper punch lubricant is unsuitable for the application, whether an inadequate viscosity or used in excess, the chances of spots, depicted in image 1, within the tablets are increased.