Hard Capsules


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Two-piece hard gelatine capsules are one of the major pharmaceutical oral dosage forms.
The manufacturing process of hard capsules consists in dipping stainless steel forms called “pins” into a gelatine solution (~30% solution). Once removed from the gelatine solution, the uniform gelatine film that has formed on the pins gels. A drying step allows to obtain dried thin film (capsule walls) showing the adequate mechanical resistance. Capsules are then stripped from the pins and cut. The body and cap are assembled and sorted for obtained pre-locked empty hard gelatine capsules.

The key features of gelatine in this application are:

  • A workable viscosity at high concentration allowing high machinability
  • A gelling power forming thermo-reversible gel
  • A low and suitable setting point
  • A film-forming power forming the capsules walls
  • High clarity and brightness

 


The gelatines used for making hard capsules are of two different types either alkaline (Type B) or acid (Type A) with high gel strength (high Bloom). Both types are used in combination or separately:

 

  • Type B gelatines are limed bone gelatine, limed hide gelati
  • Type A gelatines are pig skin gelatine and fish gelatine



Pharmaceutical grade gelatine is the main ingredient in hard capsules manufacture but several other ingredients are also involved including coloring agents and processing aids.

A typical dipping solution formula for making hard gelatine capsules would be:


  • Gelatine 30%
  • Water 65%
  • Surface active substance as needed, (SLS,SDS..)
  • Dye / Pigment as needed
  • Opacifier as needed

 

After drying, the hard capsules exhibit the following typical composition:

 

  • Gelatine ~ 80% to 85%
  • Moisture ~ 15%
  • Other excipients ~ 0% to 5%



The resistance, the elasticity and the solubility of the hard capsules shell will depend on physical characteristics of the gelatine.

Pharmaceutical manufacturers will fill the capsules mainly with powders or solid forms but new sealing technologies allow to fill hard capsules with liquids and pastes when this application was formerly dedicated to soft capsules only. Several functionalities of gelatine are usefully requisite in these innovative techniques (thermo-reversibly of gel, banding film).