Punch sticking is a common problem during the tablet compression process. It happens when powder or granules stick to the surface of the punch, especially the upper punch tip. This would cause the material to build up over time.
- Why is punch sticking serious?
- What causes punch sticking?
- How to optimize the making process?
- How to prevent punch sticking?
Why is It A Serious Issue in Tablet Production?
Punch sticking could be caused by many factors. This problem is serious because it can stop production unexpectedly. Operators may need to clean the punches frequently, which increases downtime. If the sticking continues, it may cause wear on the punches or damage to the tablets.
Moreover, punch sticking directly affects the appearance and quality of tablets. It may cause rough or uneven surfaces, broken edges, or missing logos. Some tablets may even break during ejection if the sticking is severe.
When it comes to production, punch sticking reduces efficiency. It interrupts the flow of production, and may lead to more rejected tablets. In large-scale manufacturing, even short delays or product defects can lead to higher costs and missed delivery times.
What Causes Punch Sticking?
Material properties
Some materials used in tablet production absorb moisture easily from the air. These are known as hygroscopic materials. Once they absorb moisture, they can become sticky and may begin to cling to the punch surface during compression. Common hygroscopic materials include certain herbal extracts, amino acids, and sugar-based ingredients. These materials can cause sticking even when the rest of the process is well-controlled.
For common materials, drying is important. If the granules are not dried evenly or thoroughly, moisture may remain on the surface. It increases the chance of sticking during compression.
Insuffcient force
When the compression force is too low, the powder cannot be fully compacted. When the bonding force between particles is weak, it is easier for residue to remain on the punch surface. This often occurs in formulations that contain sticky materials or a high proportion of fine powders. It increases the chance of adhesion.
Insufficient pressure may also result in soft, and loose tablets. In this case, broken pieces from these weak tablets may stick to the punch face, leading to sticking problems.
Damaged punch tooling
If punches have scratches, dents, or worn edges, they are more likely to collect powder during operation. Surface damage reduces the smoothness of the punch face. It creates small areas where powder sticks easily. If you don’t conduct proper maintenance during daily use, it may lead to wear and cause sticking.
No lubricant
Polished punches have smoother surfaces that help reduce sticking. If punches are rough, powder can begin to stick. So many manufacturers coat the punches for more smoothness. Some special coatings like chrome and nitriding are always applied. They are especially useful in high-speed machines for non-sticking.
How to Optimize the Manufacturing Process to Prevent Punch Sticking?
A good tablet compression process can help reduce or eliminate punch sticking. The following steps focus on key areas that can be adjusted or controlled for your smooth production.
Modify your formula
In manufacturing, small changes in formulation can help improve flow and reduce buildup on the punches. Many factories choose to increase the particle size of sticky actives or excipients. Because milling too fine can make some materials more cohesive. You may use coarser grades to improve powder movement and reduce adhesion to the tooling.
You may also add excipients that improve flowability. Ingredients like glidants help improve blend uniformity and reduce bridging in the feeder. This also lowers the chance of overfilling and sticking. When you find the blend becomes too dense or sticky, reduce the binder. Excess binder can make granules too soft and cause them to stick to punch tips.
Adjust dwell time
Dwell time, or the time the punch remains in the compression position, is also important. A slightly longer dwell time can help the powder form a better bond. It help reduces the chance of particles sticking to the punch surface. If you want to improve dwell time, it is a good idea to adjust the turret speed or compression cam profile.
Proper powder filling
Uneven powder feeding or overfilling can create pressure points on the punch surface. If the die is overfilled, excess powder may get trapped between the punch and die wall. It then causes sticking. If powder feeding is inconsistent, some dies may receive too little or too much powder. It also increases variability and the chance of sticking.
Add suitable lubricants or anti-sticking agents
Lubricants reduce friction between the powder and the metal surfaces of punches and dies. They form a thin barrier that helps prevent sticking. However, their concentration must be carefully controlled. Too much lubricant can affect tablet hardness or disintegration time.
Regular punch polishing and maintenance
Polishing smooths out small scratches and wear marks on punch surfaces. A polished punch is less likely to trap powder or moisture. Common maintenance should include routine cleaning after every batch, scheduled inspection for surface damage and replacing punches as needed.
Use of punches with special coatings
Coated punches provide a smoother and more resistant surface. Common coatings include
- Hard chrome plating. It adds a layer of hardness and corrosion resistance.
- Nitriding. This creates a hard surface through heat treatment. This method is often used in high-volume production.
- DLC. It offers excellent non-stick properties and long tool life.
How to Prevent Punch Sticking?
Regular inspection
Worn or damaged punches can increase sticking and affect tablet weight, thickness, and hardness. You may make a checklist weekly or monthly to inspect the punch. Common inspections include surface wear like scratches and dents, sticking residue, or misalignment. If you find these problems, solve them immediately.
Staff training
Operators and technicians are the first to notice sticking. So it is a good idea to train them to recognize early signs. It allows faster action and reduces scrap or rework. They should know how to stop the machine for a quick inspection, and report the issue clearly. They are also required to assist in documenting the conditions when the sticking occurred, such as the formula and machine speed. This helps trace patterns and adjust both materials and settings.
The End
Punch sticking should be considered when you make tablets. A good solution to this problem will greatly improve your production efficiency and consistency. Meanwhile, a high-quality tablet press may be a big help to this problem. You can customize the machine for better performance. HUADA Pharma specializes in various designs of tablet press machines. We have a professional technical team to meet your different customization needs.