EP0836951B1 - Printing plate for rotary letterpress printing - Google Patents

Description

The invention relates to a printing form for a rotary high-pressure process, at of the printing dots transferring the printing ink form a basic grid and of are superimposed on a superstructure formed by depressions.

In the high-pressure rotary process, the ink is transferred to the Printing material directly through the printing form. This is called the pressure plate manufactured and clamped on the surface of a plate cylinder. At the Printing on a print motif or print image is used to generate so-called semitones in the form of an i.a. regular print grid, whose Raised pressure points form flat pressure areas, which can be adjusted by a suitable Facility to be colored and from which the printing ink on the substrate is transmitted.

A printing form mentioned at the outset is known from DE-C1-43 24 577. The Fine grid, the basic grid there in the form of depressions as a superstructure is superimposed, it allows z. B. Glass one to achieve homogeneous and sufficient color transfer. Both the basic grid as the fine grid is also determined by the so-called grid number, by the number the pressure lines or pressure points per cm, calculated in the direction of the shortest distance is given, and the percentage area coverage clearly established. Because the individual printing areas or printing dots are arranged in lines are usually referred to as lines per cm. The grid number therefore gives the Division or the point spacing. The point size is determined by the percentage Coverage set. The percentage area coverage is the ratio of Area of the raised pressure points to the total area of the screened Print motif. The pressure points do not need to be circular, but rather can basically have any geometric shape.

In the known printing form, it can happen that the outer boundary of the pressure points belonging to the basic grid due to the structure of the fine grid is interrupted and that thereby a well-defined limitation of the Pressure points is no longer guaranteed. This is because when choosing the Fine grids only take into account the number of grids and the percentage area coverage become. In contrast, the areas in which the fine grid is not taken into account is superimposed on the basic grid. So it can happen that fine grid points (Depressions) only partially overlap the pressure points in their marginal areas are, so that the edge region of such a pressure point is interrupted. This Effect becomes especially important in those cases where only a small number of fine grid points each with a relatively large area on a pressure point of the Basic grid is not applicable. This leads to such printing dots in the printed image an irregular boundary is clearly recognizable. Especially with the Manufacture of flat screens using the flexographic process for application the phosphor layer can be used on the glass pane, this affects negative.

The invention is therefore based on the object, a printing form of the beginning mentioned type to achieve an improved print image.

This object is achieved in that the superstructures are relative arranged in the same way to the pressure points and superimposed on the pressure points in this way are that there are no depressions at the edge areas of the pressure points.

The invention is based on the knowledge that when selecting one Do not overstructure the position and size of the pressure points forming the basic grid may be disregarded. The superstructure must be relative to the pressure points be arranged in the same way, i.e. that each superstructure is relative to that of it superimposed pressure point has the same position. The one pressure point superimposed superstructure may also not to the edge of the Reach the pressure point so that the edge area is not interrupted, what would cause that of the wells before printing Let the ink taken up in the printing process preferably in such places can. This would then lead to the aforementioned irregular limitation of the Print image of a print point. The superstructures are so arranged that the edge of a pressure point is not cut by a depression.

In one embodiment of the invention it is provided that the pressure points are arranged periodically and that the superstructures periodically with the same Period or a multiple of this period are arranged. This means that the superstructure superimposed on a pressure point to that of the neighboring one Superstructures superimposed on pressure points have the same spacing as that Pressure point itself. If the period of the superstructures is a multiple of the Period of the pressure points corresponds, this means that some pressure points are not are superimposed by a superstructure, i.e. have no depressions.

In a preferred development of the invention it is provided that the Superstructure formed by at least one annular depression per pressure point is. The annular depressions are preferably each concentric to the Center of the pressure point and arranged with several wells per Pressure points do not intersect each other. One designed in this way Superstructure has the advantage that the color absorbed by the depression when Printing process evenly in all directions across the printing area of the dot runs and gives an even, large color transfer. It can too several annular, preferably arranged concentrically to the center of the pressure point Wells are arranged per pressure point, but for reasons of one largest possible volume of the circular depressions the number of ring-shaped depressions is limited at the top, because on the one hand the flanks of the For reasons of strength, depressions must not be steep. On the other hand the width of the depressions is also limited by the pigment size of the color particles, because the depressions must not be so narrow that there are color particles in them can jam.

In an alternative embodiment of the invention it is provided that the Superstructure formed by a depression located in the center of the pressure points is. Even with such a superstructure, there is an evenly large color transfer achieved without irregular boundaries of the printing dots in the printed image can appear.

When applying the fluorescent layer on the glass pane of screens pressure points designed as particularly circular and hexagonal as proven advantageous. To solve the problem, however, can also be done differently designed pressure points are used, according to the invention a Superstructure of the type mentioned is overlaid from regular, one into the other arranged, not intersecting and self-contained There are depressions that do not intersect the edge of the individual points, but rather preferably run parallel to the borders of the individual pressure points.

The printing form and printing machines according to the invention with such Printing presses are used in rotary high-pressure processes, which also include Flexographic printing counts. Such printing processes can also be used Printing on substrates made of hard, non-absorbent material, especially of glass. Especially for printing on This is suitable for glass panes for screens with a fluorescent layer Flexographic printing. Above all, let flat screens for color television tubes advantageous with an inventive, for printing on flat and Manufacture bendable substrates suitable flexo printing machine.

Another application for the flexographic printing process is the application of z. B. a black matrix of color filters. Conductor tracks, resistance layers, Barrier and spacing structures on the surface of screens in question.

Fig. 1

eine schematische Darstellung einer zum Bedrucken von flachen und biegespröden Bedruckstoffen geeigneten, speziellen Flexodruckmaschine,

Fig. 2

einen Teil einer Druckform für eine Flexodruckmaschine gemäß Fig. 1,

Fig. 3

einen Druckpunkt einer gerasterten Druckform nach dem Stand der Technik in einer Draufsicht,

Fig. 4

einen Druckpunkt einer gerasterten Druckform nach der Erfindung in einer Draufsicht,

Fig. 5

einen Ausschnitt einer Druckform mit einem Druckpunkt gemäß Fig. 4 in einer Seitenansicht,

Fig. 6

die Anordnung mehrerer Druckpunkte gemäß Fig. 4 in einer Draufsicht,

Fig. 7

ein mit den Druckpunkten gemäß Fig. 6 erzieltes Druckmotiv,

Fig. 8

eine weitere Ausführung eines Druckpunktes einer Druckform nach der Erfindung in einer Draufsicht und

Fig. 9

einen Ausschnitt einer Druckform mit Druckpunkten gemäß Fig. 8 in einer Seitenansicht.

The invention is explained in more detail below with reference to the drawings. Show it:

Fig. 1

1 shows a schematic illustration of a special flexographic printing machine suitable for printing flat and flexurally brittle substrates,

Fig. 2

part of a printing form for a flexographic printing machine according to FIG. 1,

Fig. 3

a pressure point of a screened printing form according to the prior art in a plan view,

Fig. 4

2 shows a pressure point of a screened printing form according to the invention in a plan view,

Fig. 5

3 shows a section of a printing form with a pressure point according to FIG. 4 in a side view,

Fig. 6

4 shows a top view of the arrangement of several pressure points according to FIG. 4,

Fig. 7

6 a print motif obtained with the pressure points according to FIG. 6,

Fig. 8

a further embodiment of a printing point of a printing form according to the invention in a plan view and

Fig. 9

a section of a printing form with pressure points according to FIG. 8 in a side view.

In Fig. 1 is a flexographic printing press that is suitable for printing, for example Glass panels suitable for flat screens, shown in a schematic representation. The The actual printing unit comprises an ink tray 1 containing the printing ink, one in the ink dipping roller 2, the printing form or the cliché 3 supporting plate cylinder 4 and a screened inking roller 5, the in turn transfers the printing ink from the dipping roller 2 to the printing form 3. The Dip roller 2, the plate cylinder 4 and the screened inking roller 5 are in Usually stored on a machine frame 6 and in a Drawing not shown gear driven synchronously, so that their Circumferential speeds are the same among themselves.

A device 7 is located behind the plate cylinder 4 on the machine frame 6 arranged with the help of which after the printing process on the printing form 3 adhering ink residues can be removed from the printing plate 3. This device 7 is here just like the sled transport system with one on rails 10 movable carriage 9 on which the glass pane 8 in a precisely defined position positioned and held, are not described in detail. For this, be on the already mentioned DE-C1-43 24 577.

2 shows, in a greatly enlarged illustration, schematically how ink is applied to the glass pane 8 in a printing form 3. The printing form 3, which is applied to the plate cylinder 4, consists in a known manner of a carrier film 30 and a photopolymer layer 32 with the printing dots 33, which are arranged periodically with a basic grid period in a basic grid forming the print motif. In order to compensate for any unevenness in the systems involved in the ink transfer to the printing substrate, the printing form 3 is drawn onto the plate cylinder 4 in a known and preferred manner via an elastic foam adhesive film 31.
Two pressure points 33 can be seen in FIG. A superstructure is superimposed on the pressure points 33, which here is formed by depressions 34 and extends as far as the edge region 35 of the pressure points 33. The color that is held on the surface of the printing dots 33 is transferred to the glass pane 8 during the rolling process, so that color areas 40 result on the upper side of the glass pane 8.

A pressure point 33 of a printing form shown in FIG. 2 is in a plan view in Fig. 3 shown. It can be seen that the superstructure caused by Wells 34 is formed, the pressure points is superimposed so that also in the edge regions are depressions 34. The outer limit of the Pressure point 33 is therefore interrupted by the superstructure and it is not well-defined limitation of the pressure point 33 more guaranteed. This effect, which is particularly important in cases where only a small number of Wells 34 of the superstructure on a pressure point 33 can be omitted from the already described photolithographic manufacturing process of the printing form occur. It comes about by producing the basic grid and superimposed two films on top of each other and exposed at the same time with one film (the basic grid film) being the basic grid and the second film (the superstructure film) carries the grid for the superstructure. However, this will only to the desired number of rasters (number of lines per cm) and the desired one Area coverage respected. Where and how the two grids are overlay is not taken into account.

The effect mentioned leads to the colored areas on the glass pane irregular outer boundary and no uniformly high color transfer over have the whole pressure point. When using those shown in Fig. 3 Pressure points 33, for example, do not result in an exactly round color spot 40, but instead at the points at which there are 33 depressions 34 on the outer edge of the pressure point are located, the color can run very easily during color transfer, so that these places deviate from the round shape.

A pressure point 33 for a printing form according to the invention with an annular, In FIG. 4, depression 341 extending around the center of pressure point 33 is shown in FIG shown in a top view. The pressure point 33 is here hexagonal designed. A section of a side view of a printing form with such 5 shows pressure points.

It is important when dimensioning the annular recess 341 that it is does not extend to the edge region 35 of a pressure point 33. This would be too the disadvantages mentioned, namely that no regular and defined Limitation of the color area on the glass pane could be achieved. Moreover Adequate stability of the pressure point must be guaranteed to a to avoid undesirable squeezing of the pressure point. This will do so achieved that the raised points of the pressure point 33, that is, the edge areas 35th and the central region 36. is not too thin. The width and depth of the annular depression 341 must match the pigment size of the paint used be adjusted to ensure adequate filling and emptying of the printing ink guarantee. Has proven itself for a shown hexagonal pressure point 33 with an annular recess 341 dimensioning in such a way that the radius of the central raised area 36, the width of the recessed ring 341 and dimensioned the narrowest point of the outermost edge region approximately the same size are. The width of the annular recess should be about six times the do not fall below the mean pigment diameter of the color used. In a practical application of such a printing form for printing on glass panes for flat screens, fluorescent suspensions are used, in which the Fluorescent grains have an average diameter of 4.6 µm. There of course, the phosphor suspension also fluorescent grains with larger Diameter contains, in one embodiment, the annular recess 341 40 microns wide and 50 µm deep. The middle area has a diameter of 80 µm, the pressure point 33 has a largest diameter of 300 µm.

If a low viscosity paint is used, it will still form Hexagon shape of the pressure point 33 a color spot with approximately one uniform circular shape. At higher viscosities of the color forms the hexagonal structure, on the other hand, which in some applications also may be desired.

6 shows the arrangement of a plurality of pressure points shown in FIG. 4 on one Printing form shown in a plan view. A print motif that can be achieved with this is shown in Fig. 7 shown. You can see e.g. from the second horizontal row, that the pressure points are arranged in a line and always along the line have the same distance, ie are periodically arranged on the printing form. The pressure points along two adjacent lines (e.g. A1, A3 and B0, B2, B4) are staggered in the example shown. The pressure points are the indicated manner distributed over the entire printing form.

According to the invention, the superstructure, ie here the annular depressions, is the Pressure points with the same period superimposed in such a way that on the No depressions are arranged at the edge areas of the pressure points. In the shown For example, this means that all ring-shaped depressions are visible are arranged as centrally as possible only on the pressure point and not its Interrupt the edge area. This can be achieved in that on the Superstructure film the grid points for the superstructure the same distances (the same period) from each other as the halftone dots on the basic halftone film for the pressure points.

The advantage of the hexagonal pressure points arises for Flat panel displays. With the pressure points of the invention Printing form is supposed to put a color on the substrate, which is generally glass, be applied, the color pigments under suitable lighting fluoresce. In order to be able to generate the brightest possible images, the one with fluorescent color pigments colored area portion of a flat screen be as large as possible and that for switching the individual pressure points on and off necessary switching lines as small or narrow as possible. Hexagonal Pressure points result in dividing bars of uniform width and thus one greatest possible surface coverage with light-emitting or translucent points.

When used for printing on glass panes for color television screens three such printing forms must be used, the first printing form only has pressure points at positions A1, B4, C1, which is the first Fluorescent suspension, for example, the red color transferred and the red Color spots R result. A second printing form then only has pressure points on the Place A3, B0, C3, which then create the green patches G, a third Printing form has pressure dots at position B2, which finally have a blue one Color spot B created.

8 shows a further embodiment of a pressure point 33 in one Top view and the associated side view shown in FIG. 9. The pressure point 33 here has a central region 342, which is recessed relative to the edge region 35 on. A lot of color can accumulate here before printing is transferred to the glass pane during the printing process. The recess 342 is like this arranged and only so large that the edge region 35 is not interrupted by it is, so that the disadvantages mentioned are avoided even with such a printing form become.

According to the invention, any number of differently designed superstructures are conceivable, which can be superimposed on the pressure points, for example triangular, rectangular or linear depressions. Even several can annular depressions can be arranged on a pressure point. The superstructure can also be done by raising the pressure point instead of by depressions are formed, always with the stated requirements for the stability of the Pressure points and dimensioning to prevent constipation Fluorescent grains must be observed. The outer shape of the pressure points can also other than circular or hexagonal, for example square or polygonal with more than six corners.

A printing form according to the invention is produced in DE-C1-43 24 577 in a known manner by photochemical means. When using two films, one for the basic grid and a second for the superstructure, Take special care to ensure that the negative films with high accuracy are produced and the negative film (superstructure film) with the grid of Overstructure the negative film with the basic grid for the exposure of the Printing form is superimposed precisely

The production of a printing form according to the invention using only is preferred of a film that both superimposes the negative of the basic grid and that Contains negative of the superstructure. Such a negative film would correspond to that Negative to Fig. 6: The areas bright there would be black in the negative film, those in Fig. 6 parts shown dark would be transparent in the negative film and d. H. bright.

Claims (7)

1. A printing form (3) for a rotary relief-printing method, in which the printing dots (33) transferring the printing ink constitute a half-tone screen and are superimposed by a relief structure constituted by indentations (34), characterized in that the relief structures are arranged homogeneously relative to the printing dots (33) and are superimposed on the printing dots (33) in such a way that no indentations (34) are present at the border areas (35) of the printing dots (33).
2. A printing form as claimed in claim 1, characterized in that the printing dots (33) are arranged periodically, and the relief structures (34) are arranged periodically with the same period or a multiple of this period.
3. A printing form as claimed in claim 1 or 2, characterized in that the relief structure is constituted by at least one annular indentation (341) per printing dot (33).
4. A printing form as claimed in claim 1 or 2, characterized in that the relief structure is constituted by an indentation (342) situated in the center of the printing dot (33).
5. A printing form as claimed in any one of the preceding claims, characterized in that the printing dots (33) are circular or hexagonal.
6. A printing machine, particularly a flexographic printing machine with a printing form as claimed in claim 1.
7. Use of the printing machine as claimed in claim 6 for printing hard, non-absorptive materials, particularly glass, particularly for printing glass plates of display screens having a luminescent material coating.

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