GB2280148A

GB2280148A - Inking roller

Info

Publication number: GB2280148A
Application number: GB9414291A
Authority: GB
Inventors: Peer Dilling
Original assignee: MAN Roland Druckmaschinen AG
Current assignee: Manroland AG
Priority date: 1993-07-17
Filing date: 1994-07-15
Publication date: 1995-01-25
Anticipated expiration: 2014-07-15
Also published as: GB9414291D0; DE9310713U1; FR2707555A1; CH688410A5; GB2280148B; FR2707555B1

Abstract

In order to improve the damping properties of an inking roller (1) the roller coating (5) is given a thicker portion (7) in the circumferential region contacted by a cylinder gap (3), when a forme cylinder (2) rolls over the roller. The core (4) of the inking roller has a corresponding recess (6). The thicker portion of the coating gives the required lower absolute hardness without the disadvantages which would be entailed by the use of a different material. <IMAGE>

Description

Inking Roller The invention relates to an inking roller with an elastic roller coating applied to a core for a short inking unit for applying printing ink to a forme cylinder.

A printing machine with a short inking unit is known, for instance, from WO 91/13761. The short inking unit is equipped with a chambered doctor blade system from which a screen roller transports printing ink to an inking roller. The inking roller transfers the printing ink to a forme cylinder which has the same diameter as the inking roller.

The inking roller is coated with an elastic roller coating. It has proved necessary to use a roller coating of great hardness, typically with a Shore hardness of 55 to 60 , in order to achieve an optimum print result. The disadvantage here is that with each rotation of the inking roller this hard roller coating rolls over the cylinder gap of the forme cylinder. The inking roller thus falls in at the front edge of the cylinder gap and is propelled out of it again by the following edge of the cylinder gap. The inking roller is thus excited into oscillation, which has an effect on the print widths between the forme cylinder and the inking roller on the one hand, and the inking roller and the screen roller on the other hand, so that the ink density values which can be achieved on the printed copies are not constant.

To overcome this problem attempts have been made to reduce the oscillation behaviour of the inking roller by inserting a strip of an elastic material of lesser hardness, for instance of 35 Shore hardness, into the roller coating of the inking roller in the zone which lies opposite the cylinder gap of the forme cylinder when the inking roller rolls over the forme cylinder. However, the material of lesser hardness forming the strip has a much higher plasticiser content than the other part of the roller coating. The roller coating therefore has different swelling and shrinking characteristics. Under the action of the printing ink this could lead to greater changes in the diameter and in the hardness of the roller coating in the zone of the softer material than in the zone of the harder material, which again has a negative effect on the damping characteristics of the inking roller and on the line forces. If the inserted strip shrinks then a depression is produced in the surface of the inking roller; because of the increase in rubber hardness this leads to an increase in the line forces and to poorer damping. On the other hand, if the inserted strip swells then the inking roller has a thicker portion opposite the cylinder gap of the forme cylinder as a result of which the inking roller "jumps" over the forme cylinder. The thicker portion increases the line forces and the squeezing work additionally introduced because of the thicker portion of the forme cylinder, and the heat thus produced, quickly destroy the strip.

It is the aim of the present invention to produce an inking roller with an elastic roller coating which rolls over the forme cylinder with a high degree of damping and hence almost free from vibration.

According to the invention the aim is achieved by providing the core of the inking roller on its casing surface with a recess in its contour in the region rolling over the cylinder gap of the forme cylinder, this recess being filled by a thicker portion of the roller coating so that the inking roller has a substantially cylindrical casing on its outer circumference.

By this measure the hardness of the zone of the inking roller opposite the cylinder gap of the forme cylinder is reduced and at the same time its damping properties are improved. The absolute hardness of a roller coated with a roller coating, for instance of rubber, is determined from the hardness of the rubber mixture, and its thickness with respect to the core and the rigidity of the core itself. With the invention only the thickness of the roller coating of the inking roller in the region opposite the cylinder gap of the forme cylinder is increased, and the thickness of the core is correspondingly reduced so that the inking roller rolls elastically over the forme cylinder without the roller coating on its surface being inhomogeneous.

The recess is preferably of uniform section along the length of the cylinders, this section being of any suitable shape. Possibilities are a simple flatteningoff of the cylinder surface along a chord, or a flatbottomed bowl-shaped section. The width of the recess will broadly correspond to that of the cylinder gap.

An embodiment of the invention will now be described in detail with reference to the accompanying drawing, which shows a section through an inking roller using the invention.

An inking roller 1 rolls over a forme cylinder 2.

In order to avoid ghosting the inking roller 1 preferably has the same diameter and circumference as the forme cylinder 2 when it is covered with a single printing forme, as the forme cylinder 2 shown here.

This means that the forme cylinder 2 has a single cylinder gap 3 for clamping the printing forme.

The inking roller 1 comprises a core 4 and a roller coating 5 covering the core 4. In the region which rolls over the cylinder gap 3 of the forme cylinder 2 the core 4 has a recess in its contour which is formed either by a flattened portion of the core 4 extending in the longitudinal direction of the inking roller 1 or by the channel 6 shown here. The channel 6 is filled by a corresponding thicker portion 7 of the roller coating 5. The channel 6 extends in the longitudinal direction over the entire casing surface of the inking roller 1. It is produced, for instance, by milling out the core 4. The depth of the channel 6 is selected so that the impact exerted by the cylinder gap 3 on the inking roller 1 when the forme cylinder 2 rolls over the inking roller 1 is almost completely compensated for by the thicker portion 7 of the roller coating 5. The channel 6 or other form of recess in the contour of the core 4 has a width which corresponds substantially to the width of the cylinder gap 3.

Instead of the channel 6 shown here it is also possible to flatten the core 4 along its length inwardly from its casing surface. The roller coating 5 preferably has a Shore hardness of 55 to 60 ; it is made, for instance, of nitrile rubber.

If the forme cylinder 2 is covered on its circumference by several printing formes lying one behind the other, i.e. the forme cylinder 2 has a corresponding number of cylinder gaps 3, an inking roller 1 can be used which has a smaller circumference than the forme cylinder 2, the circumferential ratio between the forme cylinder 2 and the inking roller 1 being given by the number of cylinder gaps 3, e.g. two.

The only prerequisite is that the thicker portion 7 in the roller coating of the inking roller 1 rolls in each case after a half rotation of the forme cylinder 2 over one of its two cylinder gaps 3. It is also possible in this case, however, to use an inking roller 1 which has the same circumference as the forme cylinder 2 and which correspondingly has two thicker portions 7 in its roller coating 5 which roll respectively over the two cylinder gaps 3 of the forme cylinder 2.

If the inking roller 1 rolls over a forme cylinder 2 which is covered on its circumference by at least two printing formes lying next to each other and whose cylinder gaps 3 are offset with respect to each other, the inking roller 1 accordingly has two offset and adjacently arranged thicker portions 7 of the roller coating 5 which roll with the same offset over the cylinder gaps 3 of the forme cylinder 2.

Claims

Claims:

1. An inking roller (1) having a core (4) and an elastic roller coating (5) applied to the core (4), the core (4) of the inking roller (1) having a recess in its surface corresponding to the cylinder gap (3) of a forme cylinder (2) and the coating (5) having a thicker portion (7) corresponding to this recess so that the inking roller (1) has a cylindrical outer circumference.

2. An inking roller according to claim 1, in which the roller coating (5) has a Shore hardness of 55 to 60".

3. An inking roller according to claim 1 or 2, in which the recess is formed by a flattened section of the surface of the core (4).

4. An inking roller according to claim 1 or 2, in which the recess is formed by a channel (6) milled into the core (4).

5. An inking roller according to any preceding claim, in which the material of the coating (5) is homogeneous.

6. A short inking unit including a forme cylinder (2) with a cylinder gap (3), and an inking roller (1) according to any preceding claim.

7. An inking roller according to claim 6, in which the recess in the contour corresponds substantially to the width of the cylinder gap (3) of the forme cylinder (2).

8. An inking unit according to claim 6 or 7, in which the inking roller has the same circumference as the forme cylinder (2).

9. An inking unit according to claim 6 or 7, in which the inking roller has a smaller circumference than the forme cylinder (2) over which it rolls, the forme cylinder (2) having at least two printing formes and cylinder gaps (3) around its circumference, and the ratio of the circumference of the forme cylinder (2) to the circumference of the inking roller (1) is given by the number of cylinder gaps (3) of the forme cylinder (2) so that the thicker portion (7) in the roller coating (5) of the inking roller (1) always rolls over the cylinder gaps (3) of the forme cylinder (2).

10. An inking unit according to claim 6 or 7, in which the forme cylinder (2) is covered on its circumference by at least two printing formes lying next to each other, the cylinder gaps (3) of which are offset with respect to each other, characterised in that the core (4) of the inking roller (2) has recesses in the contour correspondingly offset and lying next to each other which are filled by respective thicker portions (7) of the roller coating (5) and which roll with the same offset over the cylinder gaps (3) of the forme cylinder (2).

11. An inking roller substantially as described herein with reference to the accompanying drawings.

12. A method of producing an inking roller, in which a core (4) is formed with an axial recess in its surface, and the core is then covered with a homogeneous elastic coating in such a way as to present a uniform outer circumference.