What are The Reasons for Tablet Chipping or Breaking at The Edges?

Chipping and Lamination of Tablets:

Common Appearance Defects in Compression Production

Chipping and lamination, manifested as localized edge breakage, missing corners, or a jagged appearance on tablet edges, are common appearance defects in tablet production. The core cause is the weak bonding strength of particles at the tablet edge, or uneven force distribution and stress concentration during the forming process. This can be specifically categorized into four main factors: Material and Excipient Factors, Granulation Process Factors, Compression Parameter Factors, and Tooling Factors. A detailed analysis follows:

I. Material and Excipient Factors

1. Insufficient Particle Bonding Strength

• Cause: Poor compressibility of the active pharmaceutical ingredient (API) or excipients (e.g., highly crystalline drugs where particles bond primarily via van der Waals forces), or insufficient binder addition, leading to an overall loose tablet structure with inadequate strength at the edges.
• Improper Binder Selection: Use of weak binders (e.g., low-concentration starch paste) or uneven distribution of the binder within granules, leaving edge particles lacking adhesion and prone to breaking off.

2. Unreasonable Particle Size and Distribution

• Overly Coarse Granules: Poor flowability prevents uniform filling of the die cavity edges during compression, resulting in sparse particle arrangement and weak bonding at the periphery.
• Excessive Fines Proportion: A high percentage of fine powder (<100 mesh) can lead to "segregation" at the die edges. Air trapped between fines cannot escape timely during compression, forming micro-voids that ultimately cause edge chipping.

3. Improper Lubricant Dosage

• Cause: Excessive use of hydrophobic lubricants like magnesium stearate (>1%) forms a hydrophobic film on particle surfaces, reducing interparticle bonding. This effect is most pronounced at the tablet edges, making chipping likely.

II. Granulation Process Factors

1. Poorly Controlled Wet Granulation Parameters

• Overly Dry Wet Mass: Characterized as "falling apart when lightly pressed," produces porous, weak granules leading to fragile edge structure after compression.
• Overly Wet Wet Mass: Leads to lump formation; these hard lumps cause uneven force distribution at the edges during compression, leading to local cracking.
• Excessive Drying Temperature or Time: Over-dried granules lose elasticity, becoming brittle. Tablets made from them lack韧性 (toughness/pliability) at the edges, causing chipping upon slight vibration.

2. Inappropriate Dry Granulation (Roller Compaction) Pressure

• Excessive Roller Pressure: Produces overly hard granules that cannot undergo sufficient plastic deformation during tableting, resulting in poor edge bonding.
• Insufficient Roller Pressure: Produces loose granules, also leading to insufficient edge strength.

III. Compression Parameter Factors

1. Imbalanced Compression Force

• Excessive Force: Reduces tablet porosity excessively, creating a dense but brittle structure. Stress concentrates at the edges, especially during high-speed compression, causing chipping due to excessive squeezing force from the punches.
• Insufficient Force: Results in overall poor bonding; edge particles are not fully compacted and are prone to breaking off.
• Uneven Force Distribution: Caused by excessive punch-to-die clearance or punch misalignment, leading to uneven pressure on the tablet edge and localized weak spots that chip.

2. Excessive Compression Speed

• Cause: Too high a rotation speed on the press (e.g., >60 RPM) does not allow sufficient time for uniform granule filling of the die cavity, especially at the edges. This creates "void areas" post-compression, leading to chipping.

3. Feeding System Malfunction

• Cause: Hopper blockage or uneven feeder speed causes inconsistent fill volume in the die. This leads to varying edge thickness after compression, and the thinner, weaker sections are prone to breaking off.

IV. Tooling Factors

1. Insufficient Tooling Precision or Wear

Cause:

• Worn, burred, or chipped punch tips cannot uniformly shape the tablet edge, resulting in irregular, easily broken edges (this is also a direct consequence of punch tip damage).
• Excessive punch-to-die clearance (>0.005mm) allows material to flash during compression, creating fragile "feather edges" that break off during subsequent handling.
• Rough die bore walls create excessive friction during ejection, "scraping off" edge particles.

2. Incomplete Tooling Cleaning

• Cause: Residual powder or lubricant on the die bore walls acts as an "isolation layer" during compression, reducing interparticle bonding strength at the tablet edge and causing breakage.

Summary

The core logic behind tablet chipping and lamination is **"weak particle bonding at the edges + uneven force application."** Effective resolution requires a three-pronged approach:

1. **Optimize Granule Quality** (enhance bonding strength).
2. **Adjust Compression Parameters** (ensure uniform force application).
3. **Maintain Tooling Precision** (guarantee proper shaping).