Tablet Capping and Lamination: Causes, Troubleshooting and Prevention

What is Tablet Capping?

Tablet capping occurs when the upper or lower portion of a tablet separates from the main body after compression or during ejection.

Lamination is similar, but the tablet separates into multiple horizontal layers.

Both defects can lead to production losses and unstable tablet quality.

Importantly, capping is rarely caused by one parameter alone.

1. Common Causes of Capping

The most common causes can be divided into four groups:

1. Formulation and granule properties

2. Compression parameters

3. Tooling condition

4. Tablet press operation

Formulation-related factors

Poorly formed granules may contain excessive air or have insufficient bonding strength.

Excessive fines can also reduce powder flow and increase air entrapment.

Equipment-related factors

A rotary tablet press operating at high speed gives the material less time for deaeration and compression.

If the formulation cannot deform and consolidate quickly enough, internal stress may remain in the compact.

2. Why High Compression Force Does Not Always Help

A common troubleshooting method is to increase compression force when tablets are weak.

This may work temporarily, but excessive force can make capping worse.

The compression cycle involves:

Filling → Pre-compression → Main compression → Decompression → Ejection

During compression, powder particles deform and form interparticle bonds.

During decompression, elastic recovery occurs.

If the compact stores too much internal stress, the tablet may separate when compression force is released.

Therefore, the solution may involve improving granulation, pre-compression, or machine speed rather than continuously increasing main compression force.

3. Tooling and Machine Factors

Punches and dies should be inspected for:

· Wear

· Scratches

· Incorrect dimensions

· Poor alignment

· Damaged punch tips

· Material buildup

· Improper lubrication

Punch and die geometry also affects compression behavior.

For shaped tablets, the punch profile and cup depth can significantly influence force distribution.

4. A Practical Troubleshooting Sequence

When capping occurs, avoid changing multiple variables at the same time.

A useful sequence is:

This makes it easier to identify the actual cause.

5. Why High-Speed Tablet Presses Require Better Granules

High-speed rotary presses increase production capacity, but they also reduce the available time for filling, deaeration, compression, and ejection.

The formulation therefore needs predictable:

· Flow

· Density

· Compressibility

· Plastic deformation

· Elastic recovery

This is one reason why a formulation that performs well on a laboratory single-punch machine may behave differently on a high-speed rotary tablet press.

FAQ

Is capping always caused by excessive compression force?

No. Granule properties, trapped air, machine speed, tooling, moisture, and formulation can all contribute.

Can reducing machine speed help?

Yes. Lower speed can increase the available time for powder filling, deaeration, and compression, although the root cause should still be investigated.

Does pre-compression help prevent capping?

Pre-compression can help remove entrapped air and improve powder consolidation, depending on the formulation and machine configuration.