The shape of a tablet significantly affects compression, coating, blistering, and various physical-mechanical properties, as well as product identification. From traditional round tablets to more complex shapes like capsule, oval, or uniquely customized designs, this article delves into essential factors such as shape, surface configuration, engraving, and bisect lines in tablet design

Tablet Design

• Tablet shape design serves more than an aesthetic purpose; it directly impacts product quality, manufacturing processes, and patient experience. The required compression force should be determined during the R&D phase of a new product. For high compression forces, a shallow cup or standard cup shape is preferred to maintain tooling durability and meet quality standards.
• During compression, force is applied vertically and horizontally on the die walls. Excessive pressure may cause permanent deformation or damage the punch head. To reinforce the punch head for high compression forces:

1. 1. Increase the flat area on the punch head for enhanced durability
   2. Reduce the punch head hardness, allowing for flex without breakage
   3. Increase the cup radius or reduce the cup depth to eliminate bending stresses and minimize internal abrasion on the die

• The flat-face bevel edge (FFBE) tablet configuration also experiences lateral force. Reinforcement can be applied by implementing steps 1 and 2, or by increasing the radius between the flat surface and bevel edge, typically 0.010–0.015 inches. The flat-face radius edge (FFRE) configuration provides a stronger punch head than FFBE and reduces edge chipping by softening sharp angles on the tablet face. Another common design is the compound cup.

Tablet Shapes

Tablets come in a variety of shapes, from traditional round shapes to unique forms like capsule, oval, square, triangular, and customized shapes like animals or hearts.

• Round Shape: The most common shape due to its manufacturability and reduced technical issues during compression and storage.
• Special Shapes: Unique shapes usually hold a larger volume and and are more unique than round shapes. Unique shapes improve tablet identification, thereby maintaining consumer interest and recognition. For film-coated tablets, modified capsule shapes are preferred over traditional capsule shapes as they reduce twinning during coating.

• Near-round Shapes: Such shapes can lead to punch-to-die binding or self-locking, which should be avoided to ensure productivity and tooling longevity.

• Corner Radius: For specific shapes like square or triangle, the corner radius is crucial to maintaining tooling integrity. A radius smaller than 0.032 inches can cause excessive stress and damage punches and dies.

Tablet face configurations

• The surface configuration of a tablet, commonly called the “cup” of the punch, dictates the contour of the tablet’s upper and lower faces. TSM defines the depth of the cup by “cup depth,” while the EU standard uses “cup radius”.

• The “TSM” (USA) standard outlines depth specifications for six of the most common round configurations.

• The surface configuration of the tablet (cup) significantly affects the manufacturing process. Some common die configurations include:
  • Single Radius Cup: The simplest and most widely used design. Its depth provides products with high durability, strength, and low deformation.
  • Compound Cup: This configuration has two radius, increasing tablet volume for a thinner appearance that is easier to swallow, while minimizing internal edge abrasion during coating. However, compound cups are prone to high-stress points at the radius intersection, leading to potential punch wear under heavy load. Compound cups may also lead to capping or delamination from trapped air. Solutions include reducing press speed or increasing compression force. Compound cup sides are steeper, making them susceptible to abrasion and reducing punch life.

• 3D Cup Designs: Common in vitamins and candies, 3D configurations add features to product surfaces, providing opportunities for character or detail engraving.

Engraving

• Tablets can be identified by printing or engraving, with engraving being the most common method. There are two main types:

  • Debossed: Characters are recessed into the tablet.
  • Embossed: Characters are raised on the tablet surface.

• Company logos are often engraved on tablets for brand recognition. For smaller ones, engraving size should be selected carefully to ensure readability across different tablet sizes.
• Character designs should minimize sticking to punches by rounding sharp edges and enlarging closed-in areas to prevent sticking.

• For products prone to sticking, pre-pick engraving (removing surplus material around characters) can facilitate ejection from the die. However, pre-pick engraving may pose challenges for film coating, as rough surfaces hinder uniform coating adhesion.

• Engraving corner radius may contribute to sticking and punch wear. This radius should be approximately one-third the depth of the cut, and the standard engraving angle is 30°. For products that tend to stick, increasing the angle to 35–40° can improve ejection from the die.

Bisect

• Bisect lines allow the tablet to be split into two parts. The design should enable easy splitting without compromising drug efficacy (note: equal content distribution between halves requires supporting data). The TSM standard provides two types of bisects for curved tablets—protruding and flush bisects. In contrast, the “cut-through bisect” design common in Europe makes tablets easier to split.

Conclusion

Tablet shape design is a complex process requiring a precise balance of technical properties (tablet mechanics) and aesthetics. Features such as surface configuration, engraving, bisect lines, and product shape must be carefully optimized to ensure high product quality, manufacturing efficiency, and a positive consumer experience.

References

1. Y. Qiu, Y. Chen, G. G. Zhang, L. Yu, and R. V. Mantri, Developing solid oral dosage forms: pharmaceutical theory and practice. Academic press, 2016.

For more articles on punches and dies, visit SEN Pharma’s website:

• Terminology of punch and die structures
• Cấu tạo chày cối trong máy dập viên
• Bản chất chày cối trong ngành công nghiệp sản xuất dược phẩm.