Printing Machine Having A Central Impression Drum

A printing machine having a central impression drum, comprising:

• a rotary central impression drum (35) having an outer surface suitable for supporting a web substrate (S) between a substrate entry point (11) located on an entry side (35a) of said central impression drum (35) and a substrate exit point (12) located on an exit side (35b) of the central impression drum (35);
• a plurality of printing groups (51-60) distributed along said entry side and said exit side of the central impression drum (35), each printing group (51-60) having a printing cylinder (20) depositing a respective water-based ink or solvent-based ink at a corresponding impression point (1-10) on said web substrate (S) supported on said central impression drum (35), said printing groups (51-60) including a first printing group (51) adjacent to said substrate entry point (11) and a last printing group (60) adjacent to said substrate exit point (12) with respect to the forward movement direction of the web substrate (S);
• and a plurality of drying units (61-69) configured and arranged for applying a drying agent to the web substrate (S) supported on the central impression drum (35) for drying by evaporating the water or solvent the ink deposited on the web substrate (S), at least one of said drying units (61-69) being arranged between each pair of adjacent printing groups (51-60), wherein:
• between the impression point (1) corresponding to said first printing group (51) and the impression point (3) corresponding to a subsequent printing group (53) and/or between the impression point (10) corresponding to said last printing group (60) and the impression point (8) corresponding to a preceding printing group (58) there is an angular distance with respect to the circumference of the central impression drum (35) at least two times greater than an angular distance between the impression points (3-5) corresponding to each remaining pair of adjacent printing groups (53-55) located on said entry side (35a) of the central impression drum (35) and than an angular distance between the impression points (6-8) corresponding to each remaining pair of adjacent printing groups (56-58) located on said exit side (35b) of the central impression drum (35);
• and
• in a space provided by said angular distance between the impression point (1) corresponding to the first printing group (51) and the impression point (3) corresponding to said subsequent printing group (53) and/or between the impression point (10) corresponding to the last printing group (60) and the impression point (8) corresponding to said preceding printing group (58), there is installed at least one extensive drying unit (61, 69) dimensioned for providing an exposure time of the web substrate (S) to the drying agent applied by said at least one extensive drying unit (61, 69) at least two times longer than an exposure time of the web substrate (S) to the drying agent applied by each of the remaining drying units (63-67).