The printing machine (1) comprises: a supporting structure (11); a thermal transfer assembly (20) movable in a predetermined horizontal direction (21) and comprising a rotatable motorized transfer roller (30) and heating means (70, 71) associated to the transfer roller (30), wherein the transfer roller (30) and the associated heating means (70, 71) are movable vertically towards and away from a path of the articles (A) to be printed; and supply means (2; 12-16, 33-40) arranged to advance a printing ribbon (N) which on a side facing the articles (A) carries at predetermined intervals images formed of a thermally transferable ink. The thermal transfer assembly (20) further comprises first and second deviation rollers (35, 36) whose axes of rotation are horizontal and substantially parallel to one another and to the axis of rotation (x) of the transfer roller (30). The deviation rollers (35, 36) are arranged one upstream and the other downstream of the transfer roller (30) on the path of the printing ribbon (N) and are displaceable vertically towards and away from said path of the articles (A). The printing machine (1) further comprises first and second motor means (43, 44) associated each with a respective deviation roller (35, 36), said first and second motor means (43, 44) being controllable independently of one another, whereby each of the deviation rollers (35, 36) is selectively displaceable vertically independently of the other one.