GB1059753A - Apparatus and method for flexographic printing - Google Patents

Abstract

1,059,753. Printing machines. H. H. HARTWIG. June 18, 1965 [June 30, 1964; May 28, 1965], No. 25788/65. Heading B6C. Ink is applied to the plate cylinder 21 of a flexographic printing-machine by an inking roller 32 or belt having a rigid indented or cellular surface and to which an excess of ink is applied, the amount of ink on the part of the roller 32 contacting the plate being controlled by a resilient-surfaced doctor roller 35 or belt which moves in the reverse direction to the roller 32 at their line of contact C. As applied to a multicolour web-printing flexographic machine, Fig. 1 (not shown), employing halftone synthetic-rubber printing plates, four printing units (11 . . . 14) co-operate with an impression cylinder 19, the units (11, 12) being constructed as shown in Fig. 2 and the units (13, 14) having a modified construction, Fig. 3 (not shown), referred to below. The plate cylinder 21 and inking roller 32 are driven at the same surface speed as the impression cylinder 19, but the doctor roller 35 may be rotated at a surface speed preferably less than that of the inking roller 32. The relative speeds of the rollers 30, 35 may be varied by changing the sprockets 43, 44 over which a drive-chain 45 passes, but a change-speed drive box may be employed. A pool of ink 47 is provided in the nip of the rollers 32, 35 by a wall 48 which has a doctor blade 41 diverting excess ink into a pan 42. A conduit 46 supplies ink to the pool. The doctor-roller bearing 38 is adjusted by a screw 39 so that a constant light but positive pressure occurs between the rolls 32, 35. In the arrangement illustrated in Fig. 3 (not shown) the cellular-surfaced inking roller (51) dips into a reservoir of ink (54). The doctor roll (55) corresponding to the roll 35 is engaged by a doctor blade (60) which diverts excess ink back into the reservoir (54). The relative speeds of the rollers (51, 55) can be adjusted by means of a gear-box (64). According to the Specification, with the devices described, the variation of the thickness of ink applied to the plates lies within permissible limits with variation of press speed, so that the relative speed of roll 35 to the roll 32 and the pressure between the two rolls can be adjusted according to the thickness of ink required while the press is running at a low speed, and the press can then be set to run at normal working speed without further adjustments being necessary. The level of the ink in the pool 47 may be raised as the speed is raised, to prevent turbulence. The inking rollers 32 &c. have a rigid surface of steel treated by milling &c. to provide indentations or cells, and subsequently chromeplated.