EP0548501B1 - Device for cleaning a flexographic printing cylinder - Google Patents

Description

The device relates to an object as specified in the preamble of claim 1.

The flexographic printing cylinder, which carries a relief-like printing form, becomes dirty during the printing process due to contact with the printing material, from which particles pass onto the printing form. The inherently low-viscosity flexographic printing ink, with which the flexographic printing cylinder is usually inked by means of an anilox roller, deposits on the bottom of the printing elements in an aging manner. After a certain printing time, the appearance of the printing form is such that the permanently contacting projecting partial areas of the elastic or partially elastic printing form show largely freely visible material, but dirt is accumulated below the above contact areas. Depending on the image structure, it is possible that soiling is irrelevant and that the substrate is removed more or less without interference. In raster areas, however, the dirt can clog the printed image or the fine writing.

If the printing form is otherwise suitable for production printing, the production printing must therefore be interrupted and the printing form cleaned. Apart from waste, it is then difficult to bring the printing process back into sync.

It is known to clean the soiled printing form provided with the printing relief by mechanical means. In addition, it is known to use the printing nip traversed by the material web in a flexographic printing machine for the throughput of a cleaning sheet. When the cylinders are rotating, the so-called cleaning sheet is gripped in the inlet gap, whereupon it moves through the pressure zone. When the cliché is imprinted on the cleaning sheet made of resilient material, they get caught deeply soiled spots in contact with the surface of the cleaning sheet. This contact cleans the soiled areas with more or less success by transferring the dirt from the printing form to the cleaning sheet.

A disadvantage of this measure is the complex provision of the cleaning sheet and the non-harmless passage of the cleaning sheet through the cylinder gap, the cleaning sheet in the worst case not exiting freely from the outlet gap of the cylinders, but getting into the inking unit.

It is therefore the task of making the cleaning of the forme cylinder of a flexographic printing unit more machine-reliable and more reliable with the aid of a cleaning material.

This object is achieved by the features stated in patent claim 1.

The solution includes the installation of a cleaning device opposite the outer surface of the forme cylinder, with which the cleaning material or the cleaning tool can be brought and rolled in the position required for a perfect cleaning of the printing blocks. There is no need to use the pressure gap for the throughput of the cleaning sheet. The handling of the printing material web remains unaffected by the addition of the cleaning device to the forme cylinder. Damage to the printing unit due to undesired introduction of the cleaning sheet into the inking unit is excluded. With the shifting of cleaning to a separate cleaning device, cleaning is limited to an accompanying process in which there is no intervention in the printing nip and in the web processing and accordingly the extent of the overall impairment is inevitably reduced.

The rolling of the cleaning material on the printing form allows repeated cleaning contact when the endless material is applied continuously on a cleaning cylinder placed against the forme cylinder. Different diameters of the forme cylinder and cleaning cylinder ensure a shifting coverage of the printing form and the rolling cleaning material that preserves the contours of the printing form.

The adjusting body, which can be forcibly moved into a rest and working position, can be finely positioned with respect to the working position, as a result of which the adjusting forces of the cleaning material can be adjusted against the printing form. The higher the force, the lower the indentation of the flexible material.

The cleaning material is provided in various ways. When the cleaning material is pulled onto the jacket of a cylindrical rotating body, the use is limited to a certain number of revolutions or rollovers. It is possible to store the cleaning material in web form in the interior of the rotating body on a supply roll and to wind it up on a consumption roll likewise arranged in the interior of the rotating body. By means of external control, the cleaning path running over the outer surface of the rotating body can be successively advanced.

A simple clamping device for the cleaning material on the rotating body allows the cleaning device to be loaded from a magazine with cleaning material in stock. The new material is housed in a roll or Z-Z shape in the cassette.

The clamping device for the cleaning material consists of a transversely fixed clamping rail arranged below the tip circle of the rotating body, with which the head side of the cleaning material section clamped on the outer surface of the rotating body is clamped. Fixing the cleaning material downwards from the nip is not critical because the section runs on and cannot free itself. However, the flexible cleaning material allows holding by means of pick-up tips, such as with Velcro, or sticking with double-sided adhesive tape. If the cleaning material lies freely on the rotating body after the clamping point, one or more guide rollers can be arranged, which ensure that the cleaning material is pressed down onto the outer surface of the rotating body.

Another form of holding the cleaning material on the rotating body consists of guide slots on the lateral peripheral edges of the rotating body, into which the side edges of the cleaning material are inserted and then held in their position. The structure with guide slots on the peripheral edges of the rotating body is suitable for automated lifting of the cleaning material onto the rotating body.

Instead of a rotating body with mounted cleaning material, it is possible to arrange a roller mill in relation to the forme cylinder, the roller mill serving as a transport device for the curved or endless, loop-shaped cleaning material. One of the rollers of the roller mill serves as a counter roller to form the cleaning gap with respect to the forme cylinder.

The process of the positive connection between the resilient, partially elastic cleaning material and the high-pressure printing form, which itself has a certain deformability, is based on the compression and compression set in the gap inlet, which is followed by the reforming in the outlet gap. Depending on the material properties of the cleaning material and also the printing form, a certain permanent deformation and also a certain temporal behavior play a role for the reforming process. Taking into account the temporal, local processes in the cleaning gap, it is therefore appropriate to continuously rotate the rotating body with the cleaning material when the forme cylinder is rolled over several times to adjust. Force sensors or optical sensors, the signals of which can be fed to a control structure, can be used as a control device for the superimposed readjustment of the rotating body to be carried out during the mutual cylinder adjustment.

The flexible cleaning material preferably consists of polyvinyl alcohol. This material can be substituted by similar, foam-like plastics, which are suitable for limited reversible impressions and also in their adhesive properties for flexographic printing inks. One method of restricting the consumption of soiling cleaning material made of relatively voluminous, expensive elastomer is that this elastomer merely forms a soft layer on the rotating body and a thin layer of cleaning tissue is provided for contact with the printing form. The consumable is not the elastomer, but the cleaning fabric. It sits tubularly on the rotating body or is unwound as a thin web. An arrangement for this shows the processing with two rollers inside the rotating body and the fabric literally as an elevator on the cleaning cylinder, another arrangement consists of an unwinding arrangement external to the cleaning cylinder. The take-up roll and the supply roll are on both sides of the cleaning gap. The thin layer of the dirt track must be moved at the peripheral speed of the forme cylinder.

An exemplary embodiment follows with the aid of figure representations.

Fig. 1:

Ausschnitt eines Flexodruckwerks mit Reinigungsvorrichtung;

Fig. 2:

Anordnungsschema der Halterung sowie Verstellung des Drehkörpers am Flexodruckwerk;

Fig. 3:

Anordnungsschema des Reinigungsmaterials gegenüber dem Reinigungszylinder

• A) Einspannung eines Umfangsabschnittes;
• B) zylinderinterne Abwicklung;

Fig. 4:

externe Bevorratung und Führung des Reinigungsmaterials;

Fig. 5:

Reinigungszylinder mit weicher Beschichtung und daraufliegender Schmutzbahn.

Show it:

Fig. 1:

Section of a flexographic printing unit with cleaning device;

Fig. 2:

Arrangement diagram of the holder and adjustment of the rotating body on the flexographic printing unit;

Fig. 3:

Arrangement diagram of the cleaning material in relation to the cleaning cylinder

• A) clamping a peripheral portion;
• B) in-cylinder processing;

Fig. 4:

external storage and management of cleaning materials;

Fig. 5:

Cleaning cylinder with soft coating and dirt track on top.

The printing unit shown in FIG. 1 is a printing unit of a flexographic printing machine, in which a printing material web 4 is printed with a flexographic plate 1.1 seated on a forme cylinder 1. The inking takes place via an inking and immersion roller 3. In this arrangement, the printing nip exists between the forme cylinder 1 and a printing cylinder 2. The printing unit can be reversed. Particles from the printing material web 4 and from ink settling in the flexo plate 1.1 deteriorate the printing result over time.

A rotating body 5 is arranged parallel to the axis of the forme cylinder 1 and can be rotated about the axis 5.1 by means of a drive (not shown) and can be set against the flexographic plate 1.1. The peripheral speed of the rotating body 5 is matched to the peripheral speed of the forme cylinder 1.

According to Figure 2, the axis 5.1 between a rest position A and an operating position B, in which the rotating body 5 is set against the forme cylinder 1, is displaceable. The shift takes place with the help of an eccentric adjusted by a servo cylinder. To form a stop of the rotating body 5 against the forme cylinder 1, a pin connected to the positioning curve can be moved against an adjustable, adjustable stop C. In order to place a resilient cleaning material 7 (see FIG. 1), which may have a permanent indentation, with the same or increasing pressing action against the flexographic plate 1.1, the stop C during the cleaning process, in which the Cleaning material 7 is pressed against the flexo plate 1.1, can be moved by means of a fine adjustment 19. A displacement of the stop C which is superimposed on the engagement process permits a corresponding swelling increasing or decreasing impression of the cleaning material 7, which can be programmed depending on the cleaning requirements.

The frame-fixed bracket for massive adjustment of the rotating body 5 against the forme cylinder 1 is created by a suspension 6.

The clamping of new versus old sections of cleaning material 7 around the circumference of the rotating body 5 is possible with a tensioning shoe 9, which holds the front edge of the section, that is to say the inlet side, in a slot and fastens it to the rotating body 5. The front edge is also bent and held by the part above the slot by a radial movement of the tensioning shoe 9 towards the axis 5.1. The front is ejected by moving the tensioning shoe 9 outwards. Guide rollers 8 serve to hold down the cleaning material 7 on the rotating body 5.

FIG. 3b shows a solution in which the cleaning material 7 can be renewed piece by piece via a take-up roll 10 arranged internally in the rotating body 5 with a supply roll 11 on the circumference of the rotating body 5. When the cleaning device is operating, there is a synchronous speed between the rotating body 5 or cleaning material 7 and the peripheral speed of the forme cylinder 1, including a feed of the cleaning material 7 by rotating the winding roller 10. For reasons of expiration, the cleaning material 7 can only be advanced relative to the surface of the rotating body 5 during operation only when the channel section is passing through. However, the arrangement tolerates slight slippage between the cleaning material 7 and the flexo plate 1.1 if the cleaning material 7 is slowly advanced on the outer surface of the rotating body 5.

For a feed from rotation to rotation or from cleaning cycle to cleaning cycle, a winding drive 12 is provided which can be operated manually or automatically. The winding drive 12 engages the core of the winding roll 10 via a gear.

3a can be loaded from a magazine 13 in which a plurality of sections of the cleaning material 7 are stacked. After a section has been placed on the tensioning shoe 9, the section is either fastened to the lateral surface of the rotating body 5 or the section is conveyed into the cleaning gap 18 by a feed movement which is brought about by rotation of an arranged feed roller 14.1 and the rotating body 5. To remove the section of cleaning material 7 from the outlet gap between the rotating body 5 and the flexo plate 1.1, there is a removal roller 14.2 near the surface of the forme cylinder, the direction of rotation of which opposite to that of the forme cylinder 1 results in a repelling effect.

The supply and discharge of the cleaning material 7 into the cleaning gap 18 or to the clamping point of the rotating body 5 is controlled by guiding devices 20.

With the dashed line in Fig. 4, a loop 17 is indicated, which shows the use of the cleaning material 7 in endless form. The loop 17 has the advantage of a material offering in which a relatively large amount of new material for lubricating the dirt is offered by the flexo cliché 1.1.

Instead of the resilient cleaning material 7 made of, for example, PVA, an elastic or partially elastic coating 16 can be applied to the rotating body 5, which coating is pressed against the flexographic plate 1.1 on contact. Between the coating 16 and the flexo cliché 1.1, a waste fabric 15 pulled off at synchronous speed is moved. With regard to the stretching of the waste fabric 15, the guidance of the speed is the Take-up roll 10 can be tolerated by means of a take-up drive (not shown), which relates to deviations in the speed of the abrasive fabric 15 compared to the peripheral speeds of the rotating body 5 and the forme cylinder 1.

The desired offset between the cliché 1.1 and the cleaning material 7, with which the same coincidence of parts of both surfaces is to be avoided, is achieved with the uneven, odd diameter ratio given for the rotating body 5 and forme cylinder 1. The arrangement of an axially acting traversing mechanism on the axis 5.1 of the rotating body (not shown) provides additional offset in the axial direction to avoid rolling of the same surface parts.

Claims (11)

1. Device for cleaning a forme cylinder with a relief forme, using a flexible cleaning material which can be brought into contact against the relief forme in a pressing-on gap,
   characterised in that
   there is disposed, axially parallel to the forme cylinder (1), a rotationally driven rotating body (5) which can be moved into a rest position (A) and into an operating position (B) against the forme cylinder (1) and with which a holding and guiding arrangement (8, 9) for the cleaning material (7), which can be channelled through the gap (18) between the rotating body (5) and the forme cylinder (1), is associated, that the rotating body (5) substantially has the same peripheral speed as the forme cylinder (1), and that the axial distance between the rotating body (5) and the forme cylinder (1) in the operating position (B) can be varied by a fine-resetting system (19) which is deployed.
2. Device according to claim 1,
   characterised in that
   the diameter of the rotating body (5) is unequal to the diameter of the forme cylinder (1).
3. Device according to claims 1 and 2,
   characterised in that
   the cleaning material (7) can be clamped, in the form of a length, onto the rotating body (5).
4. Device according to claims 1 and 2,
   characterised in that,
   next to the cleaning device, there is a guiding-in and also a guiding-away arrangement (10, 11, 14.1, 14.2, 20) for the cleaning material (7) in respect of the rotating body (5) or the cleaning gap (18).
5. Device according to claim 4,
   characterised in that
   the cleaning material (7) can be unwound and wound in the interior of the rotating body (5) and that the advance of the cleaning material (7) relative to the superficies of the rotating body (5) has an external drive (12) which can be actuated when the rotating body (5) is at a standstill or, in the event of rotation, is in operation.
6. Device according to claims 3 and 4,
   characterised in that
   a supply arrangement (13) for the cleaning material (7) to be guided in is disposed on the run-in side of the gap (18) between the rotating body (5) and the forme cylinder (1), and a receiving arrangement for the cleaning material (7) to be guided away is disposed on the run-out side of the said gap.
7. Device according to claims 4 and 6,
   characterised in that
   the cleaning material (7) can be guided to the cleaning gap (18) via a run-in guide with a pair of entry rollers (5, 14.1) and can be transported, with the aid of a run-out guide (5, 14.2, 20), out of the cleaning gap (18) and into the receiving arrangement.
8. Device according to claim 7,
   characterised in that
   the cleaning material forms a loop (17) between the pair of entry rollers (5, 14.1) and the run-out guide (5, 14.2, 20).
9. Device according to claim 1,
   characterised in that
   the rotating body (5) can be offset in the axial direction, it being possible to admit offsetting at intervals or periodic offsetting.
10. Device according to claim 1,
    characterised by the building-up of a flexible cleaning material from a lower layer (16) of compressible elastomer and a ply, which is located thereon, of thin, replaceable or unwindable fabric (15).
11. Device according to claims 6 and 10,
    characterised in that
    the layer (16) of elastomer is connected to the rotating body (5) and the thin ply of fabric (15) can be unwound from the supply arrangement (11) onto the receiving arrangement (10) at about the same speed as the peripheral speed of the forme cylinder (1).

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