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FIELD OF THE INVENTION

The subject matter of the present invention is a system for regional microetching of holograms, diffraction gra¬ tings, kinograms, reconstructed wave fronts, stereo- grams, pixelgrams, lexelgrams, variable optics and other 0 on sheets of thermoplastic material or on sheets sur¬ face-treated with thermoplastic coatings, ink, toner or other materials creating film which can be microetched or on any other sheets which can be microetched.

5 STATE OF THE PRIOR ART

There are known systems for performing the microetching of holograms, diffraction gratings etc. on sheets of thermoplastic material or on sheets (for example paper) 0 surface-treated with thermoplastic coatings, inks, toner or other.

When used for performance of microetchings of the re¬ gional type these systems can give rise to shortcomings. Indeed, the printing plate bearing the microetched re- 5 gions can give rise in the etching step to structural alterations of the sheet surface to be treated even in the regions unaffected by the etching of the microgro- oves, due to the strong pressures and heat stresses exerted by the etching unit over the entire surface of 0 the transiting sheet, with resulting alteration of what¬ ever was preprinted with ink, toner or other on these regions .

OBJECTS OF THE INVENTION 5

The subject matter of the present invention is provision

of a microetching system of the above mentioned type free of the above mentioned shortcomings

SUMMARY OF THE INVENTION

To obviate this shortcoming the microetching system in accordance with the present invention essentially pro¬ vides one of the following alternative solutions First solution use of an electroformed printing plate bearing the mi croetchmgs in high relief. Second solution use of an electroformed printing plate bearing the re¬ gional microetchings at the same height as the other re- gions of the plate not microetched and mounting of the plate on an embossing roller of an etching unit m which the counterthrust roller rotates synchronously with the embossing roller and displays high reliefs on the surfa¬ ce of the regions designed to face the microetched re- gions of the printing plate during the etching process

GENERAL DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the invention in accordance with the present invention are set forth in the description of embodiments thereof given below by way of non-limitmg example with reference to the an¬ nexed drawings . In the figures FIG 1 shows a diagrammatic view of an "original cliche", FIG 2 shows a diagrammatic front view of a regionally microetched printing plate, FIG 3 shows a diagrammatic cross-section v ew of the printing plate m accordance with the first mven- tive solution,

FIG 4 shows a diagrammatic cross section of the printing

plate m accordance with the second inventive so¬ lution,

FIG 5 shows a diagrammatic cross section view of an embossing roller assembly in accordance with the first inventive solution, and

FIG 6 shows a diagrammatic cross section view of an embossing roller assembly in accordance with the second inventive solution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A traditional procedure for producing a cliche (also termed hereinafter 'original cliche') for etching of a printing plate (or block) to be used on an etching unit (i.e. for embossing and consisting of a pair of rollers of which one termed 'embossing' bears the printing plate and the other is a counterthrust roller) consists of the following steps:

Step 1) etching of the microgrooves on the plate of sensitive material to receive the information generated by expo¬ sure to laser light (holographic technique) or by e- lectron beam;

Step 2) development of the photoetched plate;

Step 3) baking of the plate;

Step 4) chemical or vacuum metallization of the plate for sub- sequent electroforming;

Step 5) formation of the original cliche on the plate by elec- troformmg, and

Step 6) separation of the plate from the original cliche ("e- lectroformed" ) .

A procedure for producing from the original cliche a re¬ gionally etched printing plate would continue in the traditional manner as follows. Step 7) use of the original cliche or a copy thereof, produced from the original cliche by electroformmg, for regio¬ nal etching (by means of a special press I e an "I- mage duplicator") of a thermoplastic plate having di mensions virtually equal to those of the printing plate to be produced; Step 8) repetition of the above Steps 4, 5 and 6 to produce the electroformed printing plate. The plate thus obtained would lend itself poorly to re- gional microprinting (i.e. the printing of mi¬ croetchings) of a sheet because of the above mentioned surface alterations which would be created in the re gions of the sheet unaffected by the microetchings. To obviate this shortcoming the present invention pro- vides one of the following alternative solutions First solution: use of an electroformed printing plate bearing the mi¬ croetchings m high relief, Second solution use of an electroformed printing plate bearing the re¬ gional microetchings at the same height as the other regions of the plate which are not microetched and mounting of the plate on an embossing roller of an etching unit m which the counterthrust roller rotates synchronously with the embossing roller and displays on its surface high reliefs m the regions designed to face the microetched regions of the printing plate during the etching process. To produce an electroformed plate to be used in the first solution the following alternative systems can be applied.

First system:

- covering with photosensitive lacquer an electroformed plate produced m the traditional manner in accordance with the above mentioned steps 1 to 8, - baking of the plate thus covered,

- masking the plate with a mask (for example of the pho¬ tomechanical type) reproducing the map of the affected regions (i.e. masking the photoetched regions if the lacquer has positive photosensitivity or the other re- gions if the lacquer has negative photosensitivity) ,

- exposure of the plate to ultraviolet light,

- developing of the lacquer for removing the same m the unetched regions of the electroformed plate,

- chemicalbath for the erosion of the plate m the above mentioned unetched regions,

- washing and removal of the residual lacquer protecting the icrogrooves,

Second system:

- regional milling of a thermoplastic plate having di- mensions virtually equal to those of the printing pla¬ te to be produced in accordance with a map correspon¬ ding to the regions to be microetched so as to produce low reliefs at the regions to be microetched,

- etching of the above mentioned low relief regions by means of an original cliche mounted on a press of the

"image duplicator" type,

- gluing of the microetched plate on a ground plate,

- repetition of the above mentioned electroformmg steps 4 to 6 and production of a sandwich consisting of the assembly "metal plate-thermoplastic plate-electroform" ,

- any flushing, flattening and grinding of the sandwich,

- separation of the "electroformed" from the metallic and thermoplastic plates.

Third system: - regional masking of a thermoformable photoetchable plate (of the 'photopolymer' or 'Nylonprint' etc

types) having dimensions virtually equal to those of the printing plate to be produced, according to a map corresponding to the regions to be microetched,

- exposure of the plate to ultraviolet light, - developing and resulting formation of low reliefs in the regions of the plate subject to photopolymer remo¬ val,

- etching of the above mentioned regions m low relief by means of an original cliche mounted on a press of the "image duplicator" type,

- gluing of the microetched plate on a ground plate,

- repetition of the above mentioned electroforming steps 4 to 6 and production of a sandwich consisting of the assembly "metal plate-thermoplastic plate-electroform" , - any flushing, flattening and grinding of the sandwich, and

- separation of the "electroformed" from the metal and thermoplastic plates.

Another solution could be using an electroformed plate produced by the traditional process (steps 1 to 8 de¬ scribed above) and mounting the original cliche on the above mentioned "image duplicator" press and exerting on the printing plate a pressure greater than that necessa ry for microetching m such a manner as to create a dif- ference in height of the plate surface This way in the subsequent steps, as described for the First, Second and Third solutions, there is already, in addition to the microetchings, a low relief thickness variation (in high relief on the electroformed copy) on the plate surface of the "electroformed" , designed to separate the contact regions from the neutral regions.

This method makes critical the gauging and compatibility of the temperatures and pressures suitable for producing the two effects so that although they are possible the solutions described previously are preferable

To produce a counterthrust roller to be used m the se-

cond solution and displaying high reliefs on its surface in the active regions designed to face the microetched regions of the printing plate during the etching process it is sufficient to mount on the roller a ground metal plate displaying the above mentioned high reliefs which can be produced by milling of the inactive regions of the plate .

For greater clarity of the differences between the First and Second solutions reference is made to the annexed drawings.

The first solution is represented in FIGS 3 and 5 where FIG 3 shows diagrammatically in cross section the prin¬ ting plate of FIG 2 sectioned along a vertical plane passing through two microetched regions and where FIG 5 shows an etching assembly consisting of an embossing roller 1 bearing the printing plate and of a counter- thrust roller 2.

The second solution is represented in drawings 4 and 6 where FIG 4 again shows diagrammatically in cross section the printing plate of FIG 2 sectioned along a vertical plane passing through two microetched regions

(shown in broken lines in the figure) and where FIG 6 shows an etching unit consisting of an embossing roller

1 bearing the printing plate (in this plate the micro- etched regions are shown in broken lines) and of a counterthrust roller 2 bearing a metal plate milled as set forth above .

It is clear that numerous modifications, adaptations, variations, and replacements of elements with others functionally equivalent can be made to the embodiments described above by way of nonlimiting example without thereby going beyond the protective scope of the fol¬ lowing claims. One of such modifications could concern for example the second solution which is capable of the following virtually equivalent variation. Instead of mounting on

the counterthrust roller a metal plate displaying high reliefs in the active regions designed to face the mi¬ croetched regions of the printing plate of the embossing roller it would be possible to mount this metal plate on the embossing roller beneath the printing plate in such a manner that for each high relief there is a correspon¬ ding relative overlying microetched region of the prin¬ ting plate. It is also clear that to produce a printing plate bea- ring the high relief microetchings (first solution) or to produce a metal plate displaying high reliefs in the active regions designed to be superimposed over the mi¬ croetched regions or which to be beneath the microetched regions (second solution) the chemical erosion step could be replaced by an erosion step performed in any manner, for example by mechanical milling, mechanical erosion with plasma, electroerosion or laser erosion etc .