WO1989012256A1

WO1989012256A1 - Process for making gravure formes of variable depth or variable depth and area

Info

Publication number: WO1989012256A1
Application number: PCT/EP1988/000496
Authority: WO
Inventors: Peter Markus Franc
Original assignee: Peter Markus Franc
Priority date: 1988-06-03
Filing date: 1988-06-03
Publication date: 1989-12-14
Also published as: JPH02504495A; EP0374153A1; ES2015677A6

Abstract

A process for making metallic or plastic gravure formes of variable depth or variable depth and area makes use of a light-sensitive photoresist coating during the chemical or electrolytic decomposition, or a protective coating which can be washed out and/or selectively removed by high-energy radiation or of a layer of copying lacquer (12). The depth and/or area of the gravure cells are varied preferably to obtain a maximal cell surface area together with optimal tone scale-adapted cell volume by superimposing (or leaving) at least one ''dot core'' (18) inside the wall surrounding the dots. The process, which resembles the automatic gravure printing process, results in an appreciable improvement in printing quality and permits comparatively simple manufacture of the formes, in particular in the case of scanner-controlled cell engraving or in the manufacture of formes using laser beams.

Description

Process for the production of gravure forms which are variable in depth or depth and area

The invention relates to a process for the production of deep or deep and surface variable metallic or plastic intaglio printing forms, in which a photosensitive etching resist layer during chemical degradation or a light sensitive insulation layer during electrolytic degradation or a washable and / or selective by high energy rays removable protective layer or a copy varnish can be used.

In order to explain the task on which the invention is based, the currently most important techniques for the production of gravure forms are briefly explained.

a) In the best known conventional method, halftone positives are used as the starting material and are, for example, transferred to pre-screened pigment papers or pigment films. After development in warm water, with unexposed gelatin portions being washed out, the diffusible relief remaining on the low-pressure cylinder or the low-pressure plate is deep-etched by means of an etching bath (for example iron chloride). The halftone dots of the shadow areas, which hold no or only a little gelatin, etch first and the lighter (lighter) tones, in which the gelatin forms a more or less diffusible barrier between the etchant and the metal of the printing form, become temporal and retained in terms of intensity, whereby a proportional depth gradation is achieved.

With regard to the halftone dots, this method can be referred to as "depth-variable" with (theoretically) equally large halftone dot areas that occupy a maximum between the necessary halftone bars. This conventional gravure printing process offered the highest print quality, but at the same time made the most difficult demands on the mold production.

Benefits:

- Very good print quality due to the large volume of color in the depths and due to the large print surface also in the light tonal values.

- The process overcomes the problems inherent in the print medium, such as e.g. B. pores in the paper surface (so-called "missing dots") or color transfer problems with non-absorbent substrates (eg aluminum) best.

Disadvantage:

- The printing form production is difficult and expensive due to the requirement of halftone positives with a strictly adhered to optical density standardization (e.g. D 0.3 to 1.65). - It has proven to be increasingly difficult to obtain corresponding film material qualities on the market.

- Due to the use of halftone positives before etching, there is no possibility of printing. - The use of diffusible etching reliefs means that the manufacture of the mold is associated with great effort, both in terms of sensitization, handling, the copying process and development and etching.

The high precision required in the etching process is made clear by the fact that a deviation of only 1 μ in the depth of the light tones can render a printing form unusable. b) Derived from the "conventional" etching process, the offset gravure conversion brings about a simplification above all by using screened offset positives instead of the halftone positives. The result is an area and depth variable printing form for prints of good quality except on difficult print carriers (e.g. porous paper surfaces, etc.).

Advantages: - Simple film production with a large market of film materials and set up reproduction studios for the purchase of finished screened and printable color separations.

- Possibility of printing before etching. - More tolerance in the case of etching deviations in the light tones.

Disadvantage:

- Necessity of cylinder production using gelatin reliefs to be differentiated as with the conventional one

Method.

- Printing problems with print carriers with a porous surface or with non-absorbent carriers because of the small contact surface of the small halftone dots.

c) Electronic gravure cylinder engraving by means of a scanner for reading the image information with connected engraving unit has become increasingly important. The cells are engraved directly into the copper surface of the printing form with a diamond stylus. This comparatively young process results in good print quality, except for porous or non-absorbent print media, which makes the color transfer difficult, particularly in the light tones. Benefits:

- In the preliminary stages, electronic engraving enables electronic assembly (page make-up) and further development up to completely film-free cylinder production.

Disadvantage:

- Limited color volume of the individual cells, due to the pyramid-like cell shape due to the diamond stylus.

- "Missing dots" or poor ink transfer on difficult print media due to too small a transfer surface or small volume in the lighter tones. - Only mediocre print quality for fine texts and lines due to the zigzag shape of the engraving line, also due to the diamond-shaped punctures of the diamond stylus.

- Comparatively slow cylinder production and therefore unfavorable profitability factors. For example, only one engraving performance of approx. 0.3 to 0.4 m ^{2 of} engraved surface is achieved per engraving head and hour.

- The copper structure of the printing form must be particularly hard and very even.

d) The printing form engraving by means of a laser beam requires a plastic coating instead of the usual copper surface, since laser engraving on metal is hardly applicable in this sector due to the reflection and crater formation, even with high energy expenditure.

Benefits:

- Electronic preliminary stages, such as electronic image montage up to filmless cylinder production, are possible.

- Great production speed. Disadvantage:

- A plastic coating of a very specific composition is required as the printing form carrier.

- High investments.

5. e) The electron beam engraving should only be mentioned here for the sake of completeness.

f) The autotypical gravure printing plate production should be mentioned in the last place here, because in some respects the process procedure comes closest to the inventive method described below.

In this type of rotogravure plate production, a film provided with rotogravure screens (eg transparent cross lines) and with large and small halftone dots corresponding to the tonal strengths of the image is copied onto a copper cylinder coated with copying varnish (photopolymer). The coating is preferably carried out by means of a spray gun or by immersion. The layer thickness is 1 to approx. 3 μm. The copy is preferably transferred using a rotary copying machine, the coated cylinder with the positive film brought into contact rotating past a light slot and the image information of the film being transferred to the acid-resistant copying layer. After the development, the transparent raster lines and non-printing transparent film parts stand hardened on the metal surface of the cylinder, while the (black) raster points of the film are washed out during development and ver¬ into the copper surface during the subsequent etching process or during the electrolytic degradation process become deep.

Because of its simplicity, the autotypical process is easy to use by using autotypical instead of halftone positives in the conventional process) and because of the uncomplicated "yes / no" copy layer (instead of diffusible gelatin reliefs), particularly in the packaging industry.

However, the print quality is often limited because of the depths of the small halftone dots in relation to their surface. This leads to difficulties in training

ICT print, which is known, inter alia, as the "too short tone scale" of the autotype. This is due, among other things, to the fact that the contact surfaces of the small intaglio printing cells are too small in diameter, which, as already mentioned in some other methods, leads to pressure

15 problems with porous print media or non-absorbent materials (e.g. aluminum).

Benefits:

- Fast, simple and comparatively economical process.

Disadvantage:

- Quality problems with certain print media.

- Necessary work with large-area copying films containing all the benefits 25 (with a few exceptions), which leads to corresponding problems with dust and other environmental influences.

- The process can, due to its type of application, not in an electronic assembly system or even in

30 filmless cylinder production can be integrated.

The invention is therefore based on the object of specifying a simplification and improvement of the methods customary today for producing intaglio printing plates.

35

The method according to the invention, initially generally defined Ren for the production of depth or depth and area variable gravure forms is characterized in that the depth or depth and area variability of the gravure cells by fading in or leaving at least one etching resist called "dot core" , Copy lacquer, insulation or protective layer element within the area of the halftone dots of the etch resist, insulation or protective layer (copy lacquer layer) is influenced at least in the areas of the gravure form intended for lighter tones.

Advantageous further developments and additions to the idea of the invention and the procedure are characterized in the subclaims and, insofar as these are not immediately understandable to the person skilled in the art, are also explained in more detail in the following description.

The invention is initially based on the knowledge that, as can be seen from the above description of the known processes a), b), c), d) and f), it is desirable to achieve a gradation of depth of the gravure cells, each but with the largest possible contact surface, even in the light tones.

The invention solves this problem while avoiding or eliminating disruptive elements in the methods known today for producing rotogravure printing forms, the following advantages in particular resulting:

- No halftone positives with precisely prescribed densitometric density values are required;

- Diffuse, difficult to control etch reliefs of pigment paper or film material are eliminated;

the process can be carried out as quickly as in known economical processes for the production of gravure printing, ie the profitability is good; - tightly tolerated requirements for copper hardness and uniformity of the copper structure of the gravure form are not made;

- The aforementioned difficult plastic coating of a printing form support is not given;

the processing of large-area utility films with corresponding handling and dirt problems is not necessary;

- With certain procedures, the integration of electronic preliminary stages or filmless processing is possible.

Examples of a method according to the invention are explained below with reference to the drawing. To make it clear:

Figure 1 shows a conventional method in the manufacture of a depth or depth and area variable printing form.

2 shows the phenomenon of so-called "under-etching" which is feared in the conventional production of intaglio printing forms;

3 shows a first basic type of process control according to the invention in comparison to conventional processes;

4 (A / B) shows the production of an intaglio printing cell according to the invention in comparison to the production of such an intaglio printing cell according to an autotypical method;

5 shows an example of a method according to the invention using a dot core in each pressure cell center, with a gray scale for autotypical Rasterization is accepted;

6 shows the change in pressure cell volumes for a typical gray scale, which determines the number of point cores to be provided;

7 (A / B / C / D) shows an advantageous method according to the invention in the production of an otherwise purely autotypical printing form;

Fig. 8 shows an embodiment of a method for generating depth variability, the

Print result roughly the same as the one above

Position (under a)) corresponds to "conventional" gravure printing;

9 shows the lateral deflection, for example of a laser beam in path widths of z. B. 2 mm at a comparatively slow cylinder rotation speed if a

Rotating mirror or an opto-electronic deflection unit is used;

10 shows the deflection of a laser beam in the engraving unit by means of opto-electronics; and

11 the deflection of a serious laser beam by means of a polygon mirror.

Corresponding parts, cell recesses, layers, etc. are identified in the individual figures with the same references.

The reference notes used have the following meaning: 10: etching resist layer, protective layer or insulating layer for electrolytic degradation of this layer or for waste er / dissolving the protective layer in a plastic printing form.

11: Metal layer of the printing form (usually copper) or plastic. The printing form is cylindrical or plate-shaped.

12: Resist, insulating or protective layer developed or removed with high-energy beam (laser, electron beam).

13: Metal or plastic surface, exposed after the resist, insulating or protective layer has been removed.

14: Etched or electrolytically degraded intaglio printing cell or, in the case of plastic printing form, cell washed out or released.

15: Effect of the stop of sections of the printing form caused by the dot core or dot core with lateral effects of the degradation means.

16: "Normal" halftone dot on film template or in raster generator (RIP) for filmless processing.

17 or 18: rotogravure cell (17) with a plurality of dot cores (dot cores 18) depending on the tone scale on film template or in the RIP for filmless processing.

19: "Normal" printed halftone dot on print carrier with autotypical process.

20: Printed halftone dot of the same tone strength when the dot-core method is used according to the invention.

21: A printing cylinder to be engraved, which is shown in FIGS. 9 to 11 in different dimensions.

22: A laser beam generator indicated in FIGS. 10 and 11. 23: A deflecting mirror that is as totally reflective as possible.

24: A light beam (laser) modulator.

25: An opto-electronic deflection unit.

26: Laser beam focusing optics.

27: A rotating polygon mirror. 28: The schematically indicated beam path of the laser beam from the laser generator 22 to the surface of the Cylinder 21. 29: In the greatly enlarged partial image representation of FIG. 9, the juxtaposition of z. B. 200 cells engraved by the laser beam within an engraving track width a.

1 shows the known removal effect, which is normally perceived as a "defect" and acts radially and not only vertically (in depth), which occurs with chemical etching, electrolytic removal and, to a certain extent, also when washing out or dissolving of plastic printing forms.

This effect (see. Fig. 2) is in chemical etching z. B. referred to as "under-etching" and leads to the dreaded "web collapse" in its last phase if the etching process is not terminated in time, so that a perfect doctoring of the gravure form is no longer possible during the printing process.

The above-mentioned effect of the lateral (area-changing) etching is used in a controlled manner in the method according to the invention in order to deal with non-diffusing layers which only act as protection against the chemical action of the etching solution or as an insulating layer in the case of electrolytic degradation. to achieve a depth and / or volume reduction of certain cells. This gives a significantly better prerequisite for the color transfer in the print.

As an example, an autotypical fine raster dot is once etched normally (FIG. 3, left) and once using the dot-core method according to the invention (FIG. 3, right). The volume reduction of the cell (FIG. 3, right) allows a corresponding enlargement of the cell surface and thus a significantly improved prerequisite. for the color transfer without increasing the original color volume of an autotypical etching (eg FIG. 1). On the contrary, the color volume is rather reduced.

4 (A) and 4 (B) again illustrate on the left a "normal" autotypical cell with an assigned pressure surface (FIG. 4 (B), left), while on the right a pressure cell modified in accordance with the present invention is shown correspondingly enlarged printing surface, which also applies here again that the color volume of the individual cells remains the same or is even reduced.

5 illustrates a gray scale for gravure printing with auto-typical screening, in which case a dot core of the same size is provided in the center of each printing cell.

As can be seen from the sectional illustration in FIG. 5 (B), the dot core in the etched printing form has a different degree of efficiency depending on the corresponding cell size. While the "remaining" cell nucleus in the small cell (right), in which a reduction in the cell volume is desired, the effect of the point nucleus makes up a relatively large percentage of the cell volume, so the "full" cell results (left) an overall insignificant reduction in cell volume. The degree of change in volume of the individual cells within a gray scale can be influenced by enlarging, changing the geometry, grouping into larger units or by a skillful "strategic" distribution of the point nuclei.

6 shows an example of the change in cell volumes in an autotypical gray scale. There is no point nucleus for the largest cell (left) because there the entire volume is used and desired; full color transfer is ensured due to the large cell surface. The medium-sized grid point (FIG. 6, center) has a grouping of several point cores _y in order to achieve a corresponding volume reduction in the cell produced. The smallest grid point (right) contains only a single point core, which occupies a considerable space in the overall diameter of the cell. With a correspondingly selected grouping or a change in size of the dot cores, a gray scale with regard to the color volume obtained can be adapted exactly to the necessary printing conditions, in particular also to the material to be printed. This is a very important advantage of the invention.

FIG. 7 shows an advantageous application of a dot core distribution according to the invention in an otherwise purely autotypical printing form. The illustrated method can, however, also be used in the manufacture of depth-variable and area- and depth-variable shapes.

The top view of FIG. 7 (A) shows the point core placement only on the flanks of the largest cells, in which "undercutting" and a reduction in the web width in the middle between two web crosses are normally to be feared and often occur. This is indicated by the dashed line in the sectional view of FIG. 7 (B). The solid lines clearly show the reduction in the undercut effect.

FIG. 7 (C) shows the geometry of a cell surface after the etching using the dot-core method according to the invention, while FIG. 7 (D) shows a corresponding cell geometry after a "normal" etching of a conventional type . The embodiment variant of the invention according to FIG. 8 illustrates an approach to a depth variable cylinder production variant that is close to conventional gravure printing in the print result. The cell surfaces of all tone levels (largely) of the same size (largely) of z. B. 100 x 100 microns are provided depending on the desired cell olumen either with a more or less large dot core or with a plurality of dot cores corresponding to the respective gray value. These point cores can be grouped in different ways and / or can have different sizes, e.g. B. in the range of 5 microns to 10 microns in diameter.

With the Laer exposure systems available on the market today with a resolution of 2400 d.p.i. (d_ot p_er _inch; approx. 1000 dots per cm) the requirements of the method according to the invention can be met. With a conventional gravure screen of z. B. 70 lines per cm results in a side length of a cell surface of about 100 microns. This results in the possibility of up to 100 point cores with a diameter of z. B. 5 to 8 microns to plazie¬ to achieve a volume reduction for all levels of a gray scale by the dot-core effect according to the invention. FIG. 8 (A) illustrates the copy of a printing form produced in this way, while FIG. 8 (B) shows the section of an etched or electrolytically degraded printing form and clearly shows the dot-core effect of a depth and Er¬ volume reduction can be known.

A system structure for carrying out the method on which the invention is based is briefly explained below with reference to FIGS. 9 to 11, laser exposure or laser pre-engraving or electron beam exposure or engraving being used.

In conventional processes with laser or electron Beam engraving, in which an entire cell is of course exposed or engraved without one or more of the point cores according to the invention, must be based on comparatively very high speeds of rotation for the cylinder 21 in order to achieve even reasonably acceptable production speeds.

In contrast, in the embodiment variant of the invention described here, a large number of cells are exposed or (pre-) engraved per revolving track of the cylinder 21 by means of a very rapid lateral deflection, for example with a track width a = 2 mm, with the result that per track in the longitudinal direction of the cylinder 200 points each with point elements of z. B. 10 microns in diameter. Together with the speed of rotation of the cylinder 21, which can now be reduced considerably, a spiral machining is achieved, which can be seen clearly from FIG. 9 on the left.

The width of the lateral deflection (i.e. in the axial direction of the cylinder 21) can be chosen so that the resulting rotational speed corresponds approximately to that in today's engraving machines. This results in the possibility of converting existing engraving machines to laser processing using an additional electronic control and laser equipment.

10 shows a first basic arrangement example for a laser exposure, in which a deflection unit 25 electronically controlled by a variable frequency generator is used, for example in the form of a (modified) Bragg cell or another known electro-optical deflection unit becomes.

11, the side deflection of the laser beam 28, ie in the representation perpendicular to the plane of the drawing and in the axial direction of the cylinder 21, by means of the rotating polygon mirror 27, the speed of which is synchronized with the rotational speed of the cylinder 21.

Finally, the special advantages of the method according to the invention compared to the currently known production methods are to be summarized in key words.

Dot-core process versus "conventional" gravure process: production method according to FIG. 8:

- No diffusing etching layers (pigment paper or film).

- Possibility of integration for electronic preliminary stages up to filmless cylinder production.

Dot-core process versus offset / gravure conversion: manufacturing method according to FIGS. 5 and 6:

- No diffusing etching layer (pigment paper or film).

Dot-core process versus electronic engraving: Manufacturing method according to FIGS. 5 and 6:

- The production speed is several times higher; - Color volume increased significantly;

- copper hardness and structure is not critical;

- The quality of fine lines / fonts is excellent;

- Problems with the wear of styluses and their adjustment are eliminated. Dot-core process versus laser engraving on plastic coating:

Production method according to FIGS. 5 and 6:

- The printing form is a conventional, proven copper form, 5 / z. B. with the usual chrome plating.

Dot-core process versus autotypical process:

Production method according to Fig. 7 (as well as possible Fig. 5 and 6): 10. - Significantly improved print quality due to depth and area-variable printing form;

Surface enlargement of the small dots (see, for example, FIG. 4, right) and thus improvement of the color transfer during printing; 15 - Possibility of integration for electronic pre-stages up to filmless cylinder production and thus avoidance of film repetition copies to obtain large format copy films.

Claims

Patent claims

1. A process for the production of deep or deep-variable and surface-variable metallic or plastic intaglio printing forms, in which a light-sensitive etching resist layer during chemical degradation or a light-sensitive insulation layer during electrolytic degradation or a washable and / or through High-energy radiation selectively removable protective layer or copy varnish is used, characterized in that the depth or depth and area variability of the gravure printing cells (14, 17) by fading in or leaving at least one as a "dot core" "(Dot Gore) (18) designated etching resist copying lacquer 5 or protective layer element within the area of the halftone dots of the etching resist or protective layer (copying lacquer layer) (10) is influenced at least in the areas of the gravure form intended for lighter tone levels .

2. The method according to claim 1, characterized in that in the full depths of the rotogravure form no dot cores and for the lighter tones depending on the tones increasing to more bright tones with the same screen dot size either increasingly larger individual dot cores and / 5 or one a correspondingly increasing number of dot cores is provided per raster dot.

3. The method according to claim 1 or 2, characterized gekenn¬ characterized in that the point cores are formed as round points with a 0 diameter between 5 microns to 100 microns.

4. The method according to claim 1 or 2, characterized gekenn¬ characterized in that the point cores are oval, designed as a polygon, star-shaped or as a wrinkled grain, and that their distribution over the surfaces of the individual gravure cells is symmetrical or random (random Distribution).

5. The method according to any one of the preceding claims 1 to 4, characterized in that the dot cores for strengthening the raster bars in the edge region of the raster dots are arranged in particular for cells with a large ink absorption volume.

6. The method according to claim 1, characterized in that when using a film, the dot cores are faded in by means of a contact or glass grid or by scanner scanning by an additional program in the raster generator of a film scanner.

7. The method according to any one of the preceding claims, characterized in that in the case of metallic printing form this is provided with a light-sensitive, acid-resistant copy varnish (10), the screened image provided with dot cores is copied thereon and the printing form developed thereafter with an etchant the necessary depth is etched.

8. The method according to any one of the preceding claims 1 to 6, characterized in that in the case of metallic printing form this is provided with a light-sensitive copying varnish which is resistant to the subsequent electrolytic removal, and the developed printing form is lowered to an electrolytic degradation process.

9. The method according to any one of the preceding claims 1 to 6, characterized in that a photosensitive plastic layer is applied as a printing form on a plate template or on a serving as a base cylinder (21).

10. The method according to any one of the preceding claims 1 to 6, characterized in that as a printing form

Plastic layer in plate or cylinder shape used which is provided with a light-sensitive protective layer which is resistant to the subsequent development, washing or dissolving process.

_y - 11. The method according to claim 1, characterized in that a laser beam or a copying device with light-emitting diode matrix is used to copy the rotogravure.

12. The method according to any one of claims 1 to 5, characterized in that (a) non-light-sensitive protective or insulating layer (s) is (are) used, and the dot information of the printing form by local removal of the layer by means of a laser beam or other high-energy beam is achieved without attacking the underlying metal surface.

13. The method according to claim 12, characterized in that the laser beam or the other high-energy beam transversely to the direction of movement of the printing form, ie in a printing cylinder approximately in the axial direction laterally over a certain track width (a) is deflected at high speed and is excited in a clock-controlled manner .

14. The method according to claim 13, characterized in that the lateral deflection over a width of about a = 2 mm and with a point sequence of about 200 points, based on the deflection track width (a) and a point diameter of 10 microns is processed.

15. The method according to claim 12, characterized in that the protective or insulation layer consists of a Keramik¬ layer, which remains on the printing form for the subsequent printing process.

16. The method according to claim 1 or 2, characterized gekenn¬ characterized in that an etching or galvano-resistant protective layer with the image information is applied by means of an electrostatic process, and after the protective layer has hardened, the halftone dots are either deeply etched or removed galvanically (electrolytically).

17. The method according to claim 1 or 2, characterized gekenn¬ characterized in that an etch or galvano-resistant protective layer with the image information is applied by means of an inkjet printing process to the gravure printing plate and that the free zones corresponding to the halftone dots are subsequently applied by chemical etching or electrolytic abrasion are deep.