Tablet adhesion often appears unexpectedly at a late stage and can be difficult to solve. Merlin has developed a test to quantify the risk of sticking which we call the “Picking Index”.
We run tests using our specialist equipment on our compaction simulator to measure adhesion risk and can troubleshoot potential root causes. Merlin can also check the suitability of punch-coating solutions for existing products.
Merlin offers the capability of measuring punch sticking using our instrumented adhesion punch. We can make tablets at a fast speed, mimicking the real conditions to measure production-relevant sticking. This testing involves compressing compacts of the material at selected forces and compressing enough compacts for the sticking signal to stabilise. Sticking varies with punch force and therefore it is useful to assess at least 3 forces in the range of interest. There is no need to wait until visible sticking is seen in production. The measurements can detect the risk of sticking at levels below the level needed to see visible effects.
There are other methods of evaluating sticking, however, this method uses a real punch face, compressing the material in a real die and gets very close to copying the conditions in production to give a fair assessment that has real-life relevance.
Measuring adhesion force is part of the picture. It measures Adhesion, the interaction between the upper punch and the tablet surface. It is also important to measure the strength of the compact and the cohesion. Balancing the risk factors: Adhesion between punch face and compact and compact and the cohesion of the compact allows the risk of sticking to be determined.
Sticking and picking is a common problem during tablet development and manufacture. It occurs when particles of the tablet formulation adhere to the punch face. Using an adhesion punch specifically designed for this application, the risk of sticking of new formulations or troubleshooting solutions for existing products can be quantified.
Sticking is not specific to the tooling’s embossing as it can occur on any area of the tooling face. In contrast, picking is generally related to tooling’s embossing and occurs mostly within the logo and island areas.
Picking occurs within the “closed” numbers and letters, these numbers are 0,4,6,8 and 9 some of the letters are A, B, D, and e.
Temperature
Merlin has the ability to change the temperature of the die during compression to simulate the effects of heat on sticking.
Humidity
Merlin uses humidity chambers to condition samples to specify humidity to predict how the materials will behave under different environmental conditions.
Punch Surface and Coatings
The surface of the punch can affect sticking. There are a number of different anti-stick coatings available. Choosing the most effective coatings can be difficult due to different solutions working with different products.
Merlin offers an option to evaluate the most effective punch coatings to prevent sticking. We have a range of iHollands coated punch surfaces to provide quantitative data to help select the most appropriate coating option.
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