GB2040229A - Inking unit for printing machine - Google Patents

Abstract

An inking unit for, inter alia, offset rotary printing machines, includes an inking cylinder (1) which is in contact with a plate cylinder (2). On one side of the inking cylinder (1) facing away from the plate cylinder (2), there are provided several distributor rollers (3 to 8) the diameters of which are different from one another. The distributor rollers (3 to 8) are entrained by friction contact with the inking cylinder (1), or may be driven. The diameter of the largest distributor roller (5) is preferably less than twice the diameter of the smallest distributor roller (6), and the other distributor rollers (3, 4, 7) are graduated in approximately equal arithmetical intervals. By this gradation, a substantially uniform, thin layer of ink can be applied to the plate cylinder (2), and the formation of transverse stripes of different ink density may be avoided. The distributor rollers are preferably axially reciprocated, and arranged in pairs reciprocated out of phase. Rider rollers may be provided bridging the distributor rollers. Damping liquid may be applied, as shown, to roller 1, or to plate cylinder 2. <IMAGE>

Description

SPECIFICATION Inking unit for printing machine This invention relates to an inking unit for a printing machine, and having a plurality of vibratory distributor rollers which bear against an inking cylinder which is for transferring ink to a plate cylinder, and is for use with an ink-feed roller which supplies the inking cylinder with ink.

In an inking unit of this type for a high pressure machine, as known from German patent specification 1 176 674, an inking cylinder is used having a diameter which corresponds to the diameter of the plate cylinder and having an elastic covering stretched thereover, with the result that, in the same way as the plate cylinder, it has a groove which extends in the longitudinal direction of the cylinder for the purpose of receiving the stretching means. Several distributor rollers of equal size rest against the inking cylinder.

When, with an arrangement of this type, during operation the groove of the inking cylinder passes a distributor roller, then there is an imperfection on the layer of ink located on the distributor roller, which following one rotation of the distributor roller, is transferred back onto the inking cylinder. This imperfection affects the printing carrier in such a way that the latter displays a first, narrow, transverse stripe in which too little ink is applied and, immediately after this, a further transverse stripe in which too much ink is applied. It is not possible to prevent the formation of these transverse stripes simply by vibrating the distributor rollers, as only distribution of ink in the longitudinal direction of the cylinder, and not the necessary eveness in the circumferential direction, is achieved thereby.Neither can imperfection occurring at the first distributor roller when a groove passes by be prevented by the following distributor roller, since the imperfection occurs in the same manner with this distributor roller and, after one rotation thereof, is transferred back again to precisely the same point of the inking cylinder upon which the preceding friction roller has already left the uneven layer of ink.

If an inking cylinder having a continuous casing without a groove is used, then certainly the cylinder itself cannot cause any imperfection in the thickness of the layer of ink, over the circumferential area of the inking cylinder over which the groove of the plate cylinder passes, ceases, whilst all other areas of the inking cylinder supply ink to the plate.If a fresh layer of ink is subsequently applied to the inking cylinder by means of the ink feed roller, then this layer of ink is heavier in the area which passes by the groove of the plate cylinder than the other points of the inking cylinder. if this heavier layer of ink passes by a distributor roller, then although it is reduced slightly, that area of the distributor roller against which the heavier layer of ink begins in the first instance, takes on a narrow stripe of ink of greater thickness, and after one rotation of the distributor roller, transfers this to the inking cylinder again. In this respect, the phenomenon of the formation of a transverse stripe on the printing carrier, as described above, again appears here. It is true that this phenomenon can be avoided by the arrangement of additional ink-reducing rollers.

However, rollers of this type, which do not take any part in distributing the layer of ink of the inking cylinder between the ink feed roller and the plate cylinder, reduce the circumferential area of the inking cylinder along which distributor rollers can be provided.

The present invention aimsto provide a generally improved inking unit.

According to the present invention, there is provided an inking unitfora printing machine, the unit comprising an inking cylinder for transferring ink onto a plate cylinder, and a plurality ofvibratory distributor rollers of different diameters bearing against the inking cylinder.

To assist in understanding the invention and to show how it may be carried out, two embodiments thereof will now be described, by way of example, with reference to the accompanying drawing, in which Figures 1 and 2 each show a schematic side view of an inking unit in a printing machine.

The inking unit represented in Figure 1 comprises an inking cylinder 1 which is driven in the direction of an arrow a and which is in contact with a plate cylinder 2. The surface of the inking cylinder 1 consists of an elastic ink-receptive material. Its circumference corresponds to the length of the printing face of a printing plate which is stretched over the plate cylinder 2, and defines a groove 14.

There are provided on the side of the inking cylinder 1 which is remote from the plate cylinder 2 several distributor rollers 3 to 8. The distributor rollers 3 to 8 have metallic, ink-receptive surfaces and are entrained by frictional contact with the inking cylinder 1. The distributor rollers 3 to 8 vibrate or oscillate along their longitudinal axes during rotation, by means knownperse (not shown).

Advantageously, the arrangement is such that the distributor rollers oscillate in pairs in opposite directions, with the result that, for example, when the distributor roller 3 moves in one direction in parallel with the axis of the inking cylinder 1, then the distributor roller 4 moves in the opposite direction. The diameter of the largest distributor roller 5 is less than twice the diameter > . ahe smallest distributor roller 6. The diameters of the other distributor rollers 3,4,7,8 are gradua-d therebetween in approximately equal, arithmetic intervals.

There is provided, between the point of contact of the inking cylinder 1 with the plate cylinder 2, and the first distributor roller 3 as viewed in the direction of rotation a of the inking cylinder 1, an ink-feed roller 9 to which the ink is continuously fed from a duct roller 10 by way of an intermediate roller 11.

There is provided between the last distributor roller 8 and the point of contact of the plate cylinder 2 with the inking cylinder 1 a dampening roller 12 which is in contact with a water tank roller 13. In place of these means for feeding ink and dampening fluid, other known arrangements could be used.

If, when the inking unit is in operation, the groove 14 passes by the inking cylinder 1, then no ink is taken by the plate cylinder in the groove area. The original ink application is therefore preserved on the ink cylinder. In the course of further rotation of the inking cylinder 11, fresh ink is applied over this area by means of the ink feed roller 9. If this layer of ink having increased thickness now runs counter two the distributor roller 3, then this roller also takes a narrow stripe of ink having increased thickness, which it then transfers to the inking cylinder 1 again, at any rate partially, after one complete rotation.

Both the imperfection originating from the groove 14 being passed over and the imperfection transferred back from the distributor roller 3 in the even ink layer thickness are further reduced by each of the following distributor rollers 4 to 8. As a result of the unequal diameters of the distributor rollers 3 to 8, a thicker stripe of ink is prevented from being again applied by each of the following distributor rollers onto the thicker stripe of ink which is transferred back from the distributor roller 3 onto the inking cylinder 1, such that this stripe of ink passes, scarcely changed, to the plate cylinder 2.

In the case of the embodiment of Figure 2, there is used an inking cylinder 20 which has a diameter equal to that of the plate cylinder 21. The two cylinders 20, 21 each have a groove 22, 23. In this respect, the groove 22 is due to a stretched elastic covering. In addition to this, the groove 22 is intended to prevent ink from being applied to the inking cylinder 20 in the area in which no ink can be transferred onto the plate cylinder 21. Several distributor rollers 24 to 29 are again provided along a circumferential area of approximately 1800 which faces away from the plate cylinder 21, and are designed in the same way as in the first embodiment.There is provided between each two distributor rollers, for example 24 and 25, which oscillate in opposite directions, a respective one of three rider rollers 30 to 32, which result in further evening out of the layer of ink on the distributor rollers 24 to 29.

Alternatively, rider rollers can also be provided between all of the distributor rollers or can each rest against only one distributor roller. In this embodiment, the distributor rollers 24 to 29 are driven, with a surface speed which corresponds approximately to the surface speed ofthe inking cylinder 20.

An ink-feed roller 33, which is constructed as a lifting roller which moves to and fro, serves to supply the ink, and receives the ink from a duct roller 34. Unlike the first embodiment, dampening fluid is supplied by way of a dampening roller 35 of a film dampening device, placed directly against the plate cylinder 21.

When this arrangement is in operation, it is again ensured by graduating the diameters of the friction rollers 24 to 29 that lamellarvariations of the layer of ink on the inking cylinder 20, which can occur as a result of the ink feed roller 33 coming only into periodic contact with the inking cylinder 20 or by the groove 22 passing by the distributor rollers 24 to 29, are reduced to such an extent that an even layer of ink is fed to the plate cylinder 21.

The illustrated inking units may transfer an even, thin layer of ink, also suitable for offset printing, onto the plate cylinder, and prevent transverse stripes of different thicknesses of ink from forming.

They may also permit a space-saving type of construction, in spite of a plurality of possibie friction points between the distributor rollers and the inking cylinder, as space is required only in the immediate proximity of the inking cylinder.

Claims (11)

1. An inking unit for a printing machine, the unit comprising an inking cylinder for transferring ink onto a plate cylinder, and a plurality of vibratory distributor rollers of different diameters bearing against the inking cylinder.

2. An inking unit according to claim 1, including an ink-feed roller for supplying the inking cylinder with ink.

3. An inking unit according to claim 1 or 2, wherein the diameter of the largest distributor roller is less than twice the diameter of the smallest distributor roller, and the diameters of any other distributor rollers are graduated in approximately equal arithmetical intervals therebetween.

4. An inking unit according to claim 1,2 or 3, wherein rider rollers bear against the distributor rollers.

5. An inking unit according to any preceding claim, wherein the distributor rollers are arranged to be driven.

6. An inking unit according to any preceding claim, wherein the distributor rollers are arranged in pairs, and the rollers of each pair are arranged to vibrate in opposite directions.

7. An inking unit according to claim 2 orto any of claims 3 to 6 as appendent thereto, wherein the distributor rollers are distributed over an area of approximately 180 of the circumference of the inking cylinder, a dampening roller is arranged at one side of the distributor rollers, and the ink-feed roller is arranged at the other side of the distributor rollers, such that a plate cylinder may contact the inking cylinder at a point intermediate the dampening roller and ink-feed roller.

8. An inking unit according to any preceding claim, including a plate cylinder in contact with the inking cylinder.

9. An inking unit according to claim 8, wherein the plate cylinder carries a printing plate and the circumference of the inking cylinder is at least equal to the length of the printing face of the printing plate and at most equal to the circumference of the plate cylinder.

10. An inking unit for a printing machine, the unit being substantially as hereinbefore described with reference to the accompanying drawing.

11. A printing machine having an inking unit according to any preceding claim.