EP0317656B1 - Cylinder of a printing unit with a rubber layer for use in offset, intaglio, flexographic or letterpress printing - Google Patents

Description

The invention relates to a printing unit cylinder, suitable for high, flexographic, low and web offset printing presses, which has a roller, a tensioning element with a narrowed tensioning channel and a rubber covering, the top layer of which is worn away so far at the channel ends that the remaining ends can be inserted into the tensioning element so that no channel opening is visible on the rubber surface when tensioned.

In the case of high, flexo, gravure and web offset printing, different cylinder types in different functions are covered with rubber as an elastic and ink transfer element. In the case of web offset printing, these are the blanket cylinders (the rubber covering is used for ink transfer). With indirect gravure takes place a so-called rubber cylinder use. In the case of high and flexographic printing, the elevator of the impression cylinder is made of rubber (over which the printing material is guided). In addition, rubber-coated plate printing cylinders and flexo rollers completely covered with rubber (for ink transfer) are used for flexographic printing.

Due to their various tasks, the rubber coverings should withstand the pressure, contain reinforcements with sufficient adhesion to the rubber layer, be easily replaceable and have a long service life, and have sufficient dimensional stability and uniform thickness. Adhesive layers can be used to attach the rubber coverings to the cylinders, but this leads to unsatisfactory results. An improved, but not yet optimal solution for rubber fixation is to set up mechanical holding systems, which are located in the so-called clamping channel of the cylinder.
Measures must be taken to reduce or suppress the bending vibrations of the pressure cylinders at the channel inlet and outlet areas. Because the contact pressure between the cylinders increases the radius in the radial direction, starting from the reversible relaxation of the rubber blanket. As a result of the brief change in the pressing force between the cylinders, the channel impact or engaging shock then occurs when it rebounds onto the counter-rubber blanket or printing cylinder, which leads to vibrations in the printing system. In this case, with a stretched rubber blanket, a gap remains open between the rubber blanket sections lying against the cylinder pit edges. Because of the above processes, the printing process negatively influenced.

European patent application 0 194 618, application number 86103093.3, filing date March 7, 1986, describes this behavior of the bending dynamics of two printing unit cylinders when the tensioning channels overflow, especially in web offset printing presses. It is proposed here to change the blanket or printing unit cylinders so that the axial edges of the tensioning channels are increased relative to the cylinder surface, and in this way the engagement impact or channel impact that occurs when the tensioning channels roll over is greatly reduced. These edge increases on the tensioning channel are achieved by tangential profile rails.

DE-OS 34 37 309.8 attempts to solve the problem of the impact joint or channel run through a special design and configuration of the stiffening strips on the front and rear edge of the rubber blanket on a rubber blanket cylinder.

Finally, in DE-OS 35 40 581 A1 a filling piece arranged in the cylinder pit is proposed.

In the cases mentioned (DE-OS and EP-A), additional complex constructions are necessary, but this only partially solves the problem mentioned.

US-A 2 629 324 relates to a method for producing a printing blanket which comprises a rubber layer on a metal layer. The ends of the metal layer are longer than those of the rubber layer. The printing blanket is used in printing unit cylinders, comprising a tensioning element with an insertion slot for the longer covering end. Such rigid composite films have however, have a low kink resistance and are relatively sensitive to impact. The impact stress can lead to an irreversible deformation of the metallic carrier and thus the surface of the printing unit cylinder, which makes further use of the printing plate questionable.

The invention is therefore based on the object, the construction field clamping channel in the use form, i.e. with the rubber covering in place so that the total radius, taking into account the thickness of the rubber covering, is not increased and in this way there is no longer any impact or channel impact, the system should have good kink resistance and should not be sensitive to impact.

At the same time, the tensioning system must be designed in such a way that the mechanical stability of the cylinder is reduced as little as possible, twisting of screws is not possible, and the surface of the rubber covering is evenly tensioned.

The object is achieved in that the upper layer of the rubber covering of a printing unit cylinder is removed so far at the ends and the remaining lower covering layer is then introduced into the tensioning system in such a way that no stretching channel opening is visible on the rubber surface taking into account the expansion. This means that when the tensioning channel is rolled over the circumferential angular range, the cylinders do not lose the rubber contact, so that no more vibrations occur if the cylinders meet one another after rolling over the channel or the insertion slot. The correction of the rubber covering ends together with the tensioning element according to the invention allows the tensioning channel to be changed so far, that a twist-free clamping system is created with which mechanically stable printing unit cylinders can be produced.

According to the invention, a printing unit cylinder for high, flexo, gravure and web offset printing is thus provided which has a cylinder body (6), a rubber covering (1) - (5), the top layer (3) of which is shorter than the bottom layer (1) - (5), and further comprises a tensioning element (7) with an insertion slot (8) for the longer covering end of the rubber blanket, the upper shorter layer (3) of the covering with the lowest (1) - (5) an angle α smaller or forms 90 °, and the cylinder body (6) has a round recess, the insertion slot (8 ') of which corresponds to the insertion slot (8) of the rotatable and fixable tube (7) serving as a tensioning element (7), which is in the cylinder body (6 ) is attached and the radius corresponds to the inner radius of the recess of the cylinder body (6), the tube (7) having a portion (9) formed over 90 ° of the circumference and about 500 microns thinner in thickness.

With such a construction using a covering without metal foils, a mechanically stable printing unit cylinder can be provided without channel runout and engagement butt, which enables the printing plate to be used further and has a long service life on the printing presses.

The invention is explained in more detail below.

I. Printing unit cylinder for high, flexo, gravure and web offset printing

The claimed printing unit cylinder essentially consists of a roller, a tubular tensioning channel and a tubular tensioning element, each with insertion slots and a flat fabric, which, after being shortened at the channel ends in the tensioned state, completely covers the roller body. In this way, it is not the entire backing layer rubber composition, which is usually used as a pressure coating, that is fixed in the tensioning device, but the main strength backing. The mechanical stress in the tensioning channel region, in particular on the rubber-rubber joint, is then largely absorbed by the strength between the carrier layer and the rubber layer.

For the printing unit cylinder claimed, such a rubber covering is preferably selected which has a high strength between the carrier layer and the rubber layer and has good dimensional stability, so that the printing properties of the printing unit cylinder claimed are further improved.

For this purpose, composite films are used, which consist of a carrier layer, preferably a polyester film, such as e.g. Polyethylene terephthalate, which is crosslinked on one or both sides using known adhesion promoters, at least with a layer of NBR or other elastomers. These composite films produced under normal vulcanization conditions are in one piece, of high dimensional stability and strength due to the chemical bond achieved between the various components.

FIGS. 1-4 show four embodiments of such composite films which can be used as flat structures in the printing unit cylinder claimed. Here, (2) is the adhesive layer.

For example, the backing layer (1) (preferably polyethylene terephthalate) can be cross-linked on one side with an elastomer layer (3) (Fig. 1), on one or both sides with one or two elastomer layer (s) (3 + 4) of different Shore A hardness ( Fig.2).

The flat structure can furthermore consist of a carrier layer (1), two elastomer layers (3 + 4) and a driven layer (5) arranged between them (Fig. 3), or also have an elastomer layer (4) with incorporated raster (Fig. 4) .

The invention is illustrated by the following examples.

example 1

A rubber covering according to FIG. 1 is selected as a flat structure for the construction of the printing unit cylinder claimed. The arrangement shown in FIG. 5 results between the roller body and the flat structure.

To prevent the impact impact or channel impact, the upper layer (in the example the elastomer layer (3)) is now at the clamping edges of the rubber covering, e.g. by planing, milling or grinding to such an extent that the part still occupied corresponds exactly to the circumference of the cylinder and the planed, milled or ground ends are of equal length. Now the elastomer layer (3) is shortened again on one or both sides to the extent that the stretching under the tensioning force. The situation shown in FIG. 6 results for the flat structure.

The elastomer mass (3) located above the base point B determines the extent of the increase in the total radius, ie the elevation depends on the angle α. If the angle α is 90 ° or more, there is no exaggeration, the purpose according to the invention is not achieved in the latter case.

If the fabric shortened according to the invention at the covering ends is inserted in accordance with FIG. 7 and the tensioning elements are actuated, the edges are pressed together in such a way that a tangential bulge arises over the tensioning channel and the elastomer surface is closed with the exception of the press-on edge. This is shown in Figures 7a-7c. The correction required due to the stretching when the rubber covering is tensioned can also be applied, e.g. with increasing tension, layer by layer using a planer, milling cutter or scraper. If the rubber covering is tensioned, its curved surface above the clamping channel is increased to the total radius by means of a radial planer, radial milling cutter, radial scraper or radial grinding device, adjusted to the same or below it, and, as far as necessary, the tangential outlet into the Total radius considered. In this way, it is possible to prevent the interference shock or channel blow.

The minimum channel width required to clamp the ends of the rubber covering remaining after abrasion of the layer (3) depends on the total thickness of the covering.

When using the rubber covering on one side as shown in Fig. 1 (example 1) with a backing layer thickness (1) of 250 µm and complete abrasion of the elastomer layer (3) and the adhesive layer (2), the minimum channel width is calculated as follows:
generally 2 x base layer thickness
2 x 250 µm = 500 µm minimum channel width.

Example 2

When using a 1.95 mm thick rubber covering on both sides with elastomer layers of the same thickness with a backing layer thickness of 0.250 mm and complete abrasion of an elastomer layer (3) with adhesive layer (2), the minimum channel width is calculated
generally 2 x covering thickness minus 2x abrasion thickness
2x1.95 mm - 2x0.85 mm = 2.2 mm minimum channel width
Printing unit cylinders for web offset printing (blanket cylinder), for high and flexographic printing (printing plate and impression cylinder) and also for indirect gravure printing (blanket cylinder) can be equipped with the rubber covering which has been corrected and subsequently fixed in the manner described.

II printing cylinder for flexo printing

The printing unit cylinder according to the invention, consisting of a roller, a tensioning element with a narrowed tensioning channel and a flat structure laid out in the manner described, is also suitable for functioning as a flexographic printing roller.

The production of flexographic printing rollers today is very time-consuming and expensive and requires a large number of operations, the roller core with the Elastomeric covering is firmly connected. This means that in order to produce a new printing form, the roller core must be cleaned, coated with adhesive, the elastomer plate wound up and bandaged. After vulcanization, the bandages are unwound, the elastomer surface is sanded and then laser-engraved with the subject, cf. book: "Technik des Flexodrucks" Coating specialist books, 1986, Coating-Verlag, Thomas and Co., CH-9001 St.Gallen.

The type of the new pressure element allows the elastomer covering to be replaced in the shortest possible time. It is even conceivable to do without changing the printing roller. This is possible if the subject is laser-engraved separately and the elastomer printing form component is placed and clamped on the printing roller or core installed in the machine. A prerequisite for such a mode of operation is the dimensional identity and the same mechanical behavior of the cylinder in the laser engraving unit and that in the printing press.

The surface of the rubber covering can also be designed in a known manner in relief, as is done in so-called cliché machines by pressing and vulcanizing. In this case, the printing unit cylinder described is a printing form cylinder.

To use the printing unit cylinder in web offset, high, low and flexographic printing, the elastomer plate joint can be closed with adhesives or a suitable adhesive.

The mechanical stability of a printing unit cylinder, which in the conventional designs is due to the installation of the clamping elements and the cutout for the Clamping channel is reduced is not reduced in the claimed printing unit cylinder, because the rotatable part of the clamping device, the clamping element, together with the clamped carrier layer, fills the clamping channel and thereby stabilizes the printing unit cylinder.

In addition, the rotatable part, the tensioning element, cannot be twisted due to its shape and dimensions, and its guidance in the tensioning channel. This makes it possible to create mechanically stable, twist-free clamping systems. This is done by the configuration of the printing unit cylinder according to the invention shown in FIGS. 8a-8d.

Fig.8a): The cylinder body (6) contains a round recess and the slot for the carrier layer (6/8 ').

Fig. 8b): A tube with the same size slot (7/8) as (6/8 ') on the cylinder (6) serves as the tensioning element (7) and corresponds in radius to the cylinder recess (6). This tube is reduced in thickness by approximately 500 µm (9) over 90 ° of the circumference from the outside.

Fig. 8c): The clamping element (7) is inserted into the cylinder body (6). If the slots (7/8) and (6/8 ') are one above the other, the rubber covering ends (10) machined according to the invention are inserted and provided with tensioning rails (11).

Fig.8d): By turning the tensioning element (7) the rubber covering (12) is tensioned and the tensioning element is fixed (13).

The advantage of the claimed printing cylinder is in the fact that no special devices are to be installed in order to bring about the exaggerations required to prevent the channel impact or interference.

The correction of the rubber covering ends according to the invention can be carried out in a simple manner (planing, milling, grinding) and in the laid-on state. By narrowing the clamping channel, twist-free clamping elements and thus mechanically stable printing unit cylinders can be created.

The printing unit cylinder can be used in web offset printing (blanket cylinder) in indirect gravure printing (rubber cylinder), in high and flexographic printing (impression cylinder) or also in flexographic printing (printing form cylinder, flexographic printing roller).

Claims (6)

1. Printing unit cylinder for relief, flexographic, intaglio and web offset printing, comprising a cylinder body (6), a rubber covering (1) - (5), the top layer (3) of which is shorter than the bottom layer (1) - (5), and a tensioning element (7) with an insertion slot (8) for the longer covering end of the rubber blanket, characterised in that the top shorter layer (3) of the rubber covering forms with the bottom layer (1) - (5) an angle α which is smaller than or equal to 90°, and the cylinder body (6) comprises a round recess whose insertion slot (8') corresponds to the insertion slot (8) of the rotatable and fixable tube (7), which serves as a tensioning element (7), is fitted in the cylinder body (6) and corresponds in radius to the inner radius of the recess of the cylinder body (6), the tube (7) comprising a part (9) which is formed over 90° of the circumference and is approximately 500 µm thinner than the rest of the tube.
2. Printing unit cylinder according to claim 1, characterised in that the rubber covering consists of a base layer (1) which, using an adhesion promoter (2) which is known per se, is chemically joined on one or both side(s) to at least one layer (3, 4) of NBR or another elastomer by a cross-linking reaction.
3. Printing unit cylinder according to claims 1 and 2, characterised in that the base layer (1) is polyethylene terephthalate of a thickness of 0.250 - 0.35 mm.
4. Printing unit cylinder according to claims 1 - 3, characterised in that the rubber covering comprises a laserengraved elastomer layer (4).
5. Printing unit cylinder according to claims 1 - 4, characterised in that the rubber covering is a moulded elastomer layer.
6. Printing unit cylinder according to claims 1 - 5, characterised in that the rubber covering comprises an embossed layer (5).

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