Multi-layer tablet with recess, device and method for compacting such a tablet

A method of producing a compacted tablet having at least two layers using a rotary press device, comprising the following successive steps:

• E1. Taking a first mixture in powder form and placing said first mixture in an open space formed by a lower punch and a die arranged in a rotary table, so as to cover an active surface of said lower punch and a central rod projecting from said active surface, said central rod being mounted within a longitudinal cavity of the lower punch movable in translation with respect to said lower punch, wherein the central rod is coupled to the lower punch via a resilient link provided along the translation axis of the central rod to hold, in a rest position, the central rod in a deployed position in which the central rod projects with respect to the active surface of the lower punch;
• E2. Moving an upper punch close to the lower punch so as to apply a compaction stress on the first mixture to form a first compacted layer, said compaction stress further allowing movement of the central rod towards inside the longitudinal cavity;
• E3. Moving the upper punch away from the lower punch so as to remove the compaction stress on the first mixture so that the central rod returns to said deployed position with respect to the lower punch, the central rod thereby piercing the first layer so as to form a through cavity;
• E4. Taking a second mixture in powder form and placing said second mixture in the open space formed by the lower punch and the die, so as to cover the first layer;
• E5. Moving the upper punch close to the lower punch so as to apply a compaction stress on the second mixture and the first layer to form a second compacted layer on the first layer;
• E6. Moving the upper punch away from the lower punch so as to remove the compaction stress on the compacted assembly formed by the first and second layers;
• E7. Ejecting the compacted assembly out of the die by translation of the lower punch so that the active surface of said lower punch lies flush with the surface of the rotary table, the compacted assembly thus ejected forming the compacted tablet.