EP0313510B1 - Device for mounting flexographic printing plates - Google Patents

Description

The invention relates to a device according to the preamble of claim 1.

Such a device is known from US-A-3,983,808. In this known device, the receiving surface is moved relative to the printing cylinder. The arrangement of the cliché on the mounting surface is done solely by a large number of dowel pins and corresponding holes.

From US-A-4,361,091 it is known in principle to provide vacuum openings for temporarily fixing an object on a mounting surface.

Many technical parameters influence the quality of a printed image. In addition to the color balance through optimal masking and a good tonal value gradation through a gradation tailored to the printing press, the register is one of the strongest influencing variables. Any optimal reprotechnical elaboration will result in a poor printing result due to a poor register. In order to be able to print an image, it is separated into the three chromatic colors of the subtractive color mixture yellow, magenta, cyan and black as the fourth in specially designed devices (eg preferably scanners). The raster arrangement takes place with four colors (preferably with flexographic printing in quarter-circle division: cyan = 7.5 °, magenta = 37.5 °, black = 67.5 °, yellow = 82.5 °. In the circular arrangement of 360 ° because of this, four equally strong halftone dots face each other in one color The sluggishness of the human eye is bridged by the area size of the halftone dots of the three glazed colors. For example, the percentage of yellow and cyan in a picture is increased in percentage, compared to magenta (eg 80% yellow, 60% cyan, 10% magenta), so the eye associates green. The more precisely these individual colors match or match each other, the sharper the image appears in the print.

The slightest non-registerers on the one hand show a blurred image in the contours, on the other hand the color mixing spaces change, i.e. Depending on the percentage distribution of the area value of the individual colors, the reflection base (e.g. paper white) becomes larger or smaller in the event of a non-register. If it gets bigger, the color becomes more dominant, if it gets smaller, it associates itself with the color that is denser in the circle arrangement.

For this reason, it is state of the art to work with an inline dowel pin system for quality work in the field of conventional processes. I.e. All films, foils etc. in the various steps of the repro processing area are punched before exposure or further processing and mounted on a suitable fitting rail.

For example, in offset or in the TC area, this system can be used from repro to assembly, plate copying to plate assembly within the machine.

In contrast, the same dowel system can be used, for example, for packaging flexographic printing only up to the matt film required for the production of the plate. At least before the exposure of the matt film registration marks, which are attached to the middle of the side of an image, must be mounted.

If a CAD system was not used at the beginning, manual registration of the four crosses of each film (with 6 colors of a printed image = 24 crosses) means that a misregistration can be accepted. In contrast, centering is achieved with a center hole with an accuracy of +/- 5 to +/- 10 µm depending on the system. Axial parallelism via elongated holes with a height accuracy also depending on the system from +/- 5 to +/- 10 µm.

With the current state of the art in the fine grid area, almost 98% of all work is carried out using fitted crosses. The clichés are mounted on a specially designed device, which consists of a cylinder with paper attached to it, a holder for holding the cliché cylinder and a glass mirror. On the paper attached to the cylinder, a device and an ink pen or the like are used. a rough sketch of the stand. This sketch shows roughly exact dimensions in the axial direction, while in the running direction it only shows the later final print size, with the large tolerances caused by development errors and the line width of the ink stick. In the direction of travel, the center of the printed image is marked by a line or similar marked. The same applies to the route transverse to the running direction. These two lines are reflected on the cliché cylinder provided with double-sided adhesive tape by means of the glass mirror attached over the working width above the cliché cylinder. The main longitudinal and main transverse lines of the cross-over of the cliché are now aligned with the mirrored crossed lines of the drawing. After pressing on the cliché and after the subsequent color printing on the paper (with the stand drawing), all further plates are mounted after the cross-fitting of the first cliché, which is then printed on.

An angle error of the mirror of 0.5 °, which over the working width of the cylinder e.g. of 1.50 m or 2.20 m results in a registration error depending on the cylinder circumference, i.e. in the length of the printed image up to 1.5 mm. Since the cliché is glued to the cylinder by hand, the angle of view of the assembler varies from color to color, i.e. from cylinder to cylinder, different. The slightest changes in the viewing angle have the result that the registration cross is incorrectly mirrored or seen, with the result that the six colors cannot be fitted to each other with a perfect fit. Due to the constantly changing viewing angle alone, registration errors of 0.5 to 0.75 mm are the result, depending on the working width and length. These errors increase with the number of panels on a cylinder.

It is state of the art today to be able to assemble and assemble only transversely to the direction of travel because other suitable methods are not available.

With today's state of the art, the annoying, otherwise also printed, fitting crosses are cut off after assembly. In the case of repeat orders, the image should only be assembled according to the selected pixels. This means that, in addition to a time-consuming assembly, high losses in accuracy of the inaccuracy of registration, which is otherwise already to be complied with when fitting the cross-piece, must be accepted. The resulting increased inaccuracy of registration is to be given a factor of 3.

In the current state of the art, the cliché is placed on the cylinder, for example, with double-sided adhesive tape, and pressed lightly with the palm of the hand without exerting partial pressure. You avoid heavier pressure marks, as they become apparent later in production.

In this type of installation, an attempt is made to spread out the air between the cliché and the adhesive tape with the open palm from the center in the axial direction of rotation.

However, this is only partially possible.

In the printing process, the cliché is then put under stress, with the theoretical distance e.g. reduced by approx. 50 µm between the surface of the printing cylinder and the printing surface of the substrate.

However, since the cliché sticks to the adhesive tape with the carrier film, it is no longer possible to change the direction of rotation of the cylinder. The change in the development of this 50 µm causes a deformation of the plate and thus an extreme bulge formation before and after the printing zone and accordingly a deformation in the ink-bearing layer of the plate.

In most cases there is only a small distance of a few millimeters between the leading and trailing edge of an image in the circumference of the cylinder.

The advantage of drilling in an axial line and fitting over round holes is small because the strip carrying the hole is cut off before the final fastening and is not available for repetitive tasks. The invention is therefore based on the object to provide a device according to the preamble of claim 1, which also enables the mounting of the cliché on the printing cylinder with the help of the known trim strips with dowel pins, in order to substantially improve the print quality and even with flexographic printing in particular to ensure that the clichés for the individual plates print exactly on top of each other, on the other hand that for the first time it can be installed regardless of the direction of rotation.

The perforation is always in the "dead" space not required for printing - either on the long or short side - and is retained for subsequent editions.

In the case of repeat orders of difficult, multi-use registration work, no new plates need to be manufactured. In addition to high quality increases, this also results in high cost and time savings.

This object is basically achieved by the characterizing part of claim 1.

In claims 2 and 3, advantageous embodiments of the device according to claim 1 are protected.

The mounting device according to the invention makes it possible to fasten the clichés precisely and securely on the printing cylinder and, in particular, to arrange the clichés of the individual colors so precisely that a print image is produced in such a way that a correspondingly exact print takes place, i.e. the arrangement is reproducible. Once the first cliché is locked onto the mounting surface and sucked in with the help of the vacuum, the subsequent clichés are arranged in exactly the same place, so that the individual colors are assembled precisely and printed on top of each other in the printing machine.

The use of a mounting film with graduation, which is preferably a millimeter graduation, enables an exact fixation of the cliché (which is transparent) before locking the mounting bar and switching on the vacuum.

A parallel development of a process that uses a much thinner polymer cliché than was previously possible enables the cliché to be punched precisely in accordance with the reprotechnical intermediate work such as positive films and the final film and the shape and position of the dowel for final plate assembly.

The invention is explained in more detail below with reference to the drawing using an exemplary embodiment.

Fig. 1

eine perspektivische Ansicht einer Ausführungsform einer Montagevorrichtung nach der Erfindung;

Fig. 2

eine perspektivische Ansicht der Montagefläche mit Klischee und Montagefolie;

Fig. 3

eine der Fig. 2 entsprechende Ansicht, jedoch eine Ansicht der Montagefläche ohne Montagefolie und Klischee.

It shows:

Fig. 1

a perspective view of an embodiment of a mounting device according to the invention;

Fig. 2

a perspective view of the mounting surface with cliché and mounting film;

Fig. 3

a view corresponding to FIG. 2, but a view of the mounting surface without mounting foil and cliché.

The assembly device shown in the drawing shows an assembly table 10 with a mounting surface 7. To the side of the mounting surface 7, racks 3 are arranged.

A drive 6 with a receptacle 4 for the pressure cylinder 1 can be moved over the mounting surface 7, specifically in the direction of the toothed racks 3.

The pressure cylinder 1 is mounted in the two receptacles 4 with the help of bearing pins 5. The receptacles 4 are adjustable in height so that printing cylinders with different diameters can be accommodated.

The gear wheel 2 of the pressure cylinder 1 engages in a rack 3.

The drive 6 also engages via a gear with a gear in one or both racks in order to move the pressure cylinder 1 over the mounting surface, the engagement between the gear 2 and the rack 3 ensuring a corresponding rolling movement of the pressure cylinder, that of the actual one Pressure corresponds.

As is particularly clear when looking at FIG. 3, three mounting grooves 15, 16 and 17 are provided in the mounting surface 7. The mounting grooves 15 and 17 run perpendicular to the axis of the printing cylinder 1, whereas the mounting groove 16 in turn runs perpendicular to the mounting grooves 15 and 17.

The known mounting strips 11, 12 and 13 can be arranged in the mounting grooves.

Furthermore, first vacuum openings 18 and second vacuum openings 19 are provided in the mounting surface 7. The two groups of vacuum openings 18 and 19 can be supplied with negative pressure independently of one another.

1 and 2, the mounting film 8 and the cliché 9 are indicated on the mounting surface 7.

If a cliché is to be mounted, the drive 6 is moved to one end of the assembly table 10. The pressure cylinder, which is already provided with an adhesive tape or with spray adhesive, is inserted in the receptacle 4 so that the gearwheel 2 engages with the one rack 3.

Depending on the desired print image that is defined in advance, a mounting strip 11 for the mounting film 8 is then inserted, for example, into the mounting groove 15. This mounting bar is then locked by a fastener, not shown. With the help of this mounting bar and its dowel pins 14, a mounting film 8 is then placed, which is provided with appropriate punched holes. For universal use, the mounting film is provided on two mutually perpendicular sides with corresponding perforations and holes for the vacuum 18.

The applied mounting film is then sucked in with the help of the second vacuum openings 19 so that it is immovably fixed.

Through the possible use of different cliché strengths, e.g. 0.51; 0.64 or 0.76 mm etc. on the same machine, the different expansion factors are taken into account by changing the mounting foils, i.e. one film each for the plate thickness 0.51, as well as one film for 0.64 or one film e.g. for 0.76 mm etc.

If, on the other hand, only a cliché thickness is used, the use of an assembly film can be dispensed with. In this case, the assembly division is applied directly to the foundation. In such a configuration, the vacuum openings 19 and 18 are connected in parallel.

Now a mounting strip 12 with dowel pins 14 is inserted into the free mounting groove 16, which runs perpendicular to the mounting groove 11 already used. The cliché with its punched holes is then placed on the dowel pins 14, this assembly bar 12, the side of the cliché which is later to be used for the color pointing downwards, ie the Assembly film is facing. The mounting bar 12 is now moved with the cliché in the direction of the mounting groove 16 until the cliché - which is transparent - assumes the desired and exact position, taking into account the dimensions. If this is the case, the first vacuum openings are supplied with vacuum so that the cliché is sucked in and can no longer be moved.

Now the printing cylinder with its adhesive surface with an additional value of preferably + 50 microns is moved over the cliché, synchronized with this movement, the vacuum in the corresponding row of the first vacuum openings 18 is switched off, so that wherever the bonding begins, the cliché of the mounting foil can be lifted off. The interruption of the vacuum always takes place in a row parallel to the axis of the printing cylinder and depending on the progressive movement of the printing cylinder.

Immediately after switching off the vacuum, compressed air is placed in the same or in a second hole. This reversal means that even the zones that have no ink-bearing layers, ie do not stick directly through the pressure contact, come into parallel contact with the cylinder due to the air pressure.

Another very significant advantage of this invention over the current state of the art is that the cliché is assembled under stress, with the additional printing that will later be used in the production press.

This means that Bead formation, which lead to vibration stripes, is avoided and thus inaccurate registration is eliminated. Air inclusions, which result in an increased pressure increase and thus a poor print image, are avoided by this stress assembly.

When the first cliché for the first color is mounted in this way, the printing cylinder is removed and the process is repeated for the cliché for the second color, which is correspondingly mounted on the second printing cylinder. Since the fitting strips are immovably fixed and have been locked accordingly, it is ensured that the clichés are successively assembled one above the other for printing.

The mounting film has the same scale as the cliché. A millimeter graduation is often provided. This millimeter graduation corresponds to the actual conditions in the direction of the axis of the printing cylinder 1. Perpendicular to this direction, i.e. in the direction of rotation of the printing cylinder, there is distortion, i.e. a reduction by the percentage of the stretching of the cliché - matched to the circumference or diameter of the printing cylinder -.

The arrangement of the mounting bar for the mounting film takes place in coordination with the printed image, i.e. as cheaply as possible to the place where the cliché is to be arranged. If the mounting block for the cliché on one side, i.e. are arranged perpendicular to the axial direction of the printing cylinder, the mounting strip for the mounting film is arranged in the mounting groove running perpendicular to this.

After placing and fixing the mounting film, the cliché is put on and moved with its mounting bar until the desired position on the mounting film is reached. Then the mounting bar is locked by a mechanical fastener and the first vacuum openings 18 are supplied with negative pressure.

In the embodiment described above, a mounting table 10 with a mounting surface 7 has been described. The assembly table can also be cylindrical, i.e. the mounting surface is then curved. Whether designed as a table or as a cylinder, precise assembly is only possible if compressed air is counteracted at the same time as the vacuum is switched off (during the assembly process) in order to adhere the non-contact parts of the cliché to the pressure cylinder.

Claims (4)

1. Device for mounting flexographic blocks with the aid of a double-sided adhesive tape on an impression cylinder with a pinion, which is mounted on a receptacle (4), which is located on a drive (6) and which by means of a mounting surface (7) carrying the printing side of the block (9) is movable relative to said mounting surface, the pinion (2) of the impression cylinder (1) engaging with a rack (3) or the like on the mounting table, in which are provided register pins (14) corresponding to the holes punched in the block, characterized in that the mounting surface (7) is provided with a plurality of first vacuum openings (18) connectable to a vacuum source and which in series parallel to the impression cylinder axis and as a function of its movement over the mounting surface (7) can be separated from the vacuum source and in that simultaneously with the disconnection of the vacuum compressed air is countercontrolled.
2. Device according to claim 1, characterized in that in the mounting surface (7) are formed mounting grooves (15,16,17) for receiving mounting ledges (11,12,13) and which run parallel and perpendicular to the axis of the impression cylinder (1), the register pins (14) being provided on the mounting ledges.
3. Device according to claim 1 or 2, characterized in that with the aid of a mounting ledge (11) between the mounting surface (7) and the block (9) is provided a mounting foil (8) with graduations, which is subject to suction action through second vacuum openings (19), which are supplied with vacuum independently of the first vacuum openings (18), and having passage openings corresponding to the first vacuum openings (18), the mounting ledge (11) for the mounting foil (8) being located in a mounting groove (15), which is perpendicular to the mounting groove (16) for receiving the mounting ledge (12) for the block (9).
4. Device according to claim 3, characterized in that the graduations of the mounting foil (8) have the same scale as the block and parallel to the axis of the impression cylinder (1) are provided the actual dimensions, whereas perpendicular to the impression cylinder axis there is a shortening by the percentage of the expansion of the block (9), matched to the impression cylinder circumference.

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