Patent GB-1044042-A (GB)
Title: Method and means for dampening lithographic offset printing plates
IPC: B41F7/26
Filed: 1963-07-01
Abstract: 1,044,042. Printing processes. H. P. DAHLGREN. July 1, 1963 [July 1, 1963], No. 26056/63. Heading B6C. A process for dampening the plate cylinder A, Fig. III, on a lithographic offset rotary printing press comprises the steps of providing a dampening liquid transfer roller 14 having a polished surface thereon treated to render same hydrophilic, applying a film of dampening liquid 9 to the surface of roller as it rotates, contacting the film 15 of dampening fluid with a forme roller 6, which is in rotative contact with the plate cylinder A, said forme roller having a coating of ink thereon of greater viscosity than the dampening fluid and rotating the transfer and forme rollers 14 and 6, respectively, to deposit a portion 16 of the dampening fluid 9 on the surface of the ink coating. In operation, a fountain roller 7 picks up a film of dampening fluid 9 from a fountain 8 and deposits it on an oscillating messenger roller 10, which transfers the fluid via a first transfer roller 11 to a sponge roller 12 having an elastic, flexible, absorbent sleeve 13 thereon, such as sponge rubber or synthetic plastic. The sponge roller 12 is impressed into the surface of a hydrophilic, polished, chromium plated transfer roller 14 to deposit a film 15 thereon. The surface of the transfer roller 14 is treated by bathing it with a solution of one part hydrochloric or sulphuric acid, one part gum arabic water solution 14 degree Baume and one part water to render the surface hydrophilic. The transfer roller 14 is subsequently contacted with a forme roller 6, having a coating of ink thereon applied by an ink messenger roller 2, so as to deposit a portion 16 of the dampening fluid on the coating. The film 16 is in turn transferred to the plate 20 of the cylinder A as indicated at 18 to thereby dampen the non-printing area of the plate. When the plate has been dampened the remaining forme rollers 3, 4 and 5 inked by ink messenger rollers 1 and 2, respectively, are brought into contact with the plate cylinder A, which co-operates with a conventional rubber offset blanket extended about the cylinder B. The paper on which the image is printed passes between the cylinder B and impression cylinder C (Fig. I, not shown). The dampening liquid consists of a watersoluble, volatile organic liquid such as ethyl or methyl, esters or ketones. A 10% mixture with water works satisfactorily. In one embodiment of the apparatus the oscillating messenger roller 10 is mounted on an arm 24, Fig. IV, in turn pivotally mounted on a shaft 25 and having a cam follower 23 spring-urged into contact with the surface of a cam 22 by a spring 22c. Rotation of the cam alternately brings the messenger roller 10 into contact with the fountain roller 7 and transfer roller 11. For shifting the transfer roller 14 away from and into engagement with forme roller 6 and for shifting the forme roller 6 away from and into engagement with the plate cylinder separately from shifting of the other forme rollers 3, 4 and 5 into and away from engagement with the plate cylinder the transfer roller 14 and forme roller 6 are mounted pivotally on roller hanger 38 and offset arm 40, respectively. By operating an arm 31 of an overcentre toggle 28, whereby a recess 33 in a latching arm 32 engages a stub shaft 34, the roller hanger 38 is pivoted anti-clockwise by an associated rod 26 to move the transfer roller away from the forme roller 6 (Fig. V, not shown). As the transfer roller 14 is moved away a spring 41 on the arm 40 pivots the arm about the shaft 2a in anti-clockwise direction shifting the forme roller 6 out of contact with the plate cylinder A. Pivoted movement of the forme roller 6 is limited by stop 45, 46. In another embodiment in Fig. VIII the intermediate rollers 10, 1] and 12 are omitted and the transfer roller 14 is in direct contact with the fountain roller 7. Both rollers are mounted on frames 50, having slots 51 for sliding movement on pins 52. By operation of the handle 58 an arm 60 shifts the frames 50 to and fro horizontally to bring the roller 14 in and out of contact with the forme roller 6. Horizontal movement of the frames 50 is limited by stops 62, 63 and pivotal movement of the forme roller 6 mounted on an arm 64 is limited by adjustable stops 68, 69. Adjustment of stops 94, 68 and 69 adjusts the amount of dampening liquid transferred to the plate cylinder A. The amount of liquid transferred may also be controlled by a variable speed drive 72, whereby the transfer roller 14 and the forme roller 6 are rotated at different peripheral speeds, the forme roller 6, however, being rotatable at the same peripheral speed as the plate cylinder A.