By Bill Turner and Kevin Queensen
Sticking is one of the most common problems of tablet manufacturers. It occurs when granules or particles from the formulation attach and stick to the face of a punch cup, resulting in defective tablets. Picking is a specific type of sticking that refers to material becoming stuck on the faces of the compression tooling due to embossed designs, such as the letter or numerals of the tablet logo or identifier. Sticking or picking issues are often not detected until transferring the product from research and development to production. Although sticking and picking are frequently related to deficiencies in tablet design, remediation does not always require changing the design (and thus the tools used for tablet manufacturing).
When powder sticks in the punch cup or embossed characters, one of the first things to check is the moisture level of the formulation. Excess formulation moisture or excessive humidity in the compression suite can initiate sticking or picking.
Insufficient compression force is also a potential source of sticking/picking because the compaction of the powder is not complete. When this occurs, the adhesive forces of the punch are stronger than the cohesive forces of the inadequately compressed tablet.
Another potential cause of sticking and picking is a deficiency in the amount of lubricant within the formulation. An increase of lubricant will impart greater release of the compressed tablet from the punch cup surface.
Careful inspection of the punch cups is also essential to ensure there are no surface scratches to capture small particles of formulation. Scratches will lead to filming, which is an initial slow form of sticking, often due to fines and excess moisture in the granulation. If surface scratches are identified, punches should be polished. Additionally, a specialized polishing compound can be used to impart greater lubricity and better product release properties.
When simple or environmental fixes are not enough, a full tablet design review may be necessary. Tablet design plays a pivotal role in oral solid dosage manufacturing, although it’s often overlooked. Typically, a pharmaceutical company’s marketing department pushes for certain tablet shapes and logos with the end goal of promoting brand recognition. However, those designs may not be optimal for manufacturing requirements and demands. Compression tooling suppliers, who are often highly experienced tablet design experts, can identify potential sticking and picking issues before tablet designs have been finalized, thus reducing production challenges.