GB2198085A

GB2198085A - Printing apparatus and process

Info

Publication number: GB2198085A
Application number: GB08628598A
Authority: GB
Inventors: Rudolf August Herbert Heinecke
Original assignee: STC PLC
Current assignee: STC PLC
Priority date: 1986-11-29
Filing date: 1986-11-29
Publication date: 1988-06-08
Anticipated expiration: 2006-11-29
Also published as: DE3739829A1; GB8628598D0; GB2198085B

Description

2198 OISS PRINTING APPARATUS AND PROCESS This invention relates to

printing, and in particular to gravure printing.

Gravure printing is widely used in the production of magazines, particularly those that require colour printing. The technique is an intaglio process, i.e. the printed image is provided by a pattern of recesses in a smooth surfaced rotating roller. The recesses are filled with ink which is transferred to paper to form the image. The roller is supplied with ink from a bath, excess ink being remo-\:,ed from the roller surface by a doctor blade mounted adjacent the roller. For high speed running whilst maintaining print quality it has been found necessary to construct the doctor blade from a hard resilient material such as a h.Lgh quality inclusion-free steel. To minimise roller wear it is also necessary to provide the roller with a hard surface.

Conventionally a print roller comprises a steel roll, the surface of which is coated with a soft metal e.g. copper (a Ballard skin). The pattern to be printed is etched in the copper. Generally a liquid etch or a diamond stylus is used for this purpose. The roller is then surface plated with chromium to provide the necessary wear resistance. At both the copper and the chromium plating stages the roller has to be mechanically housed to ensure accuracy of the surface. This operation is critical to prevent abrasive wear by the doctor blade during the printing operation.

2 - After printing has been completed the chromium and copper layers are stripped from the roller and the process is repeated to form a new image.

Whilst the gravure technique is capable of producing good print quality at high speeds, it suffers from the disadvantage that the production of a print roller prior to each paint run is a slow and difficult process.

The object Of the present invention is to minimise or to overcome this disadvantage.

According to one aspect of the invention there is provided a gravure print roller, including a cylindrical body the surface of which is provided wth an array of recesses wherebv, in use, sele--7aed recesses are filled flusll-A with the cylindrLcal surface w-th a removable 15 material to define a pattern to be printed.

Acccrding to ano-,her aspect of the invention there fact f m a n-.

s provided a method o. - I.-uring a gravure print roller, the method including providing a hard surface layer on a rigid cylindrical- body, and fcrming an array Of recesses Jn the surface layer subsequent tc the pro-,.--sJon of said layer.

According to a further aspect of the invention there is -provided a method of manufacturing a gravure print rc'-er, 'ncluding providing an array of recesses in a cylindrical body, and fillina selected recesses flush with the cylindrical surface with a removable material so as to define a pattern to be printed.

The print roller surface is provided with a regular array of closely packed recesses. The recesses are filled, e.g. with a polymer, and those recesses that are required to form a particular printing pattern are then opened by the removal of the polymer therefrom.

Embodiments of the invention will now be described with reference to the accompanying drawings in which:- Figs. 1 to 5 illustrate a method of manufacturing a gravure print roller.

Referring to the drawings, a steel cylinder 11 is provided with a surface coating 12 of aluminium. Typically 5.

3 this coating is applied by vacuum evaporation and is about 40 microns in thickness. The aluminium layer 12 is then coated with a film 13 tpically 2 microns thick, of silica. A photo-resist pattern 14 (Fig. 2) is deposited on the "I and the assembly is plasma etched silica layer 1. anisotropically through an array of apertures 15 in the photoresist 14 to remove the exposed silica and etch recess 16 in the underlying aluminium. Typically the recess 16 are about 25 microns in depth. The photoresist 14 and remaining silica 13 are next removed, e.g. by plasma etching with an atmosphere of sulphur hexafluoride.

The structure is conformally coated (Fig. 3) with a layer 17 of silicon nitride, e.g. by plasma deposition. The nitride layer 17.is anisotropically etched to leave a layer of nitride 17a only on the sides of the recesses (Fig. 4). The structure is then anodised to convert the upper part of the aluminium metal to hard anodic oxide 18 L-ypically to a depth of 30 microns. The recesses are filled with a plastics mazerial 19 (Fig. 5) and the surplus is removed flush with the oxiae surface using a doctor blade (not shown). Finally a desired printing image is provided by removing the plastics 19 from some of the recesses to define a desired pattern.

The technique differs from conventional processes in that the recesses are formed directly in the hard coating and not in an underlying soft coating. Further, by providing a matrix array of recesses, the'roller may be reused without removing the hard coating simply by refilling the empty recesses and defining a new pattern.

Typically the recesses are provided in an array of 100 to 150 lines per cm. The recesses may be opened to form the desired pattern by removing the plastics material with a laser, e.g. a modulated examiner laser. -By control of the laser power the depth of removal of the plastics may be controlled to provide a grey or intensity scale. Alternatively the recesses may be filled with a negative photoresist resist material followed by exposure of the roller through a mask, the configuration of which corresponds to the pattern to be printed. The exposed photoresist is then removed to form the pattern. With a suitable photoresist this technique may be used to form a photographic image on the roller. It will be appreciated that the depth to which the photoresist of a particular recess is exposed will depend on the light intensity at that recess. This modulates the depth of the recesses and gives the finished image a towed or grey scale quality. This technique is thus an analogue process.

In an alternative, digital, technique, selected recesses may be exposed, one or more moves at a time, to light directed on the roller via a striplike mask structure. Typically we employ a strip of liquid crystal cells disposed adjacent the roller parallel to the roller is axis. The roller is rotated in a stepwire manner, one step advancing one row of recesses, and appropriate ones of the liqu-'Ld cryszal cells are enabled to expose the photoresist in the corresponding recesses. Data is entered into the licuid crvstal cell array in a serial manner and is transferred in parallel to the roller. The rate at which the roller is prepared may be increased by using a number of masks and' exposing a corresponding number of rows of recesses 'n marallel.

In a further technique the recesses are Eilled with a polymeric materiall and the roller surface is then printed with a similar material to form a 'negative' image. The assembly is then plasma etched to ablate the printed polymer to the roller surface and at the same time to ablate polymer from exposed recesses, i.e. those not covered by the printed negative image. In this way the profile of the printed polymer is transferred to the roller. Again, tonal quality is provided by depth modulation of the recess.

After a print roller has been used it may be refurbished for a new print run. The plastics material in the recesses is removed e.g. by exposure of the roller surface to a radio frequency oxygen plasma. The recesses 1 are then refilled and selected ones are opened as before to form the new print pattern.

In a further application, e.g. where a long print run is anticipated, the roller may be printed with a predetermined or committed surface pattern. In this technique the roller is coated with a hard material and is then provided with a photoresist mask having windows corresponding to the desired print pattern. The assembly is plasma etched through the mask openings to form the corresponding pattern of recesses. After removal of the mask the roller can then be used for printing.

The roller is used in a printing machine, either alone or with similar rollers, in the same manner as a conventional roller, i.e. it provides a direct replacement.

Further, the roller described herein can be run together with conventional rollers in the same printing machine.

6 -

Claims

CLAIMS:

1. A method of manufacturing a gravure print roller, the method including providing a hard surface layer on a rigid cylindrical body, and forming an array of recesses in the surface layer subsequent to the provision of said layer.

2. A method of manufacturing a gravure print roller, including providing an array of recesses in a cylindrical body, and filling selected recesses flush with the cylindrical surface with a removable material so as to define a pattern to be printed.

3. A method of manufacturing a gravure print roller, the method including providing a cylindrical steel body, providing a hard surface coating on the cylindrical surface is of said steel body, and forming in said coating an array of recesses each adapted to receive a quality of printing ink and filling selected recesses with a plastics material so as to deffine a print image corresponding to the unfilled recesses.

4. A method as claimed in claim 3, wherein said surface coating comprises anodic aluminium oxide.

5. A method as claimed in claim 3 or 4, and which includes filling said recesses with a negative photoresist, exposing selected recesses to light, and removing the exposed photoresist to form a print pattern.

6. A method as claimed in claim 5, wherein said selected recesses are exposed via a liquid crystal mark.

7. A method as claimed in claim 3 or 4, wherein said recesses are filled with a plastics material, and wherein the plastics material is removed from selected recesses by laser evaporation to form a print pattern.

8. A method of manufacturing a gravure print roller substantially as described herein with reference to the accompanying drawings.

7 -

9. A gravure paint roller, including a cylindrical body the surface of which is provided with an array of recesses whereby, in use, selected recesses are filled flush with the cylindrical surface with a removable material to define a pattern to be printed.

10. A print roller for gravure printing, the roller including a cylindrical steel body, means for rotatably mounting said body, a hard coating providing on the cylindrical surface of the steel body, and a regular array of recesses formed in the hard coating, said recesses being adapted to receive a plastics material already in use, by filling selected recesses with the plastics material, a print image is defined by the unfilled recesses.

11. A print roller as claimed in claim 2, wherein said hard coating comprises anodic aluminium oxide.

12. A gravure print roller substantially as described herein with reference to and as shown in the accompanying drawings.

13. Printing apparatus provided with one or more print rollers as claimed in any one of Claims 9 to 12.

14..4. method of gravure printing, includinE providing a roller having an array of Eurface recesses, filling the th a zlas'ics -na'er4al flusl-i witt the roller recesses w. LI G JL -L surface, removing material from selected recesses so as to 4 define a cattern to be Dri-nted, applying ink to the roller wtereby the opened recesses are filled with ink, removing surplus ink from the roller surface, and contaCtinE a substrate with the roller so as to transfer ink from the recesses to the substrate to form a printed imaEe.

Published 1988 at Trhe Patent Office, State House, 65.171 High Holborn, London WC1R 4TP. PUrther copies may be obtained from The Patent office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/87.

14. A method of gravure printing, including printing a roller having an array of surface recesses, filling the recesses with a plastics material flush with the roller surface, removing material from selected recesses so as to define a pattern to be printed, applying ink to the roller whereby the opened recesses are filled with ink, removing surplus ink from the roller surface, and contacting a substrate with the roller so as to transfer ink from the recesses to the substrate to form a printed image.

15. A method of printing as claimed in claim 14 and substantially as described herein.

8 Claims 3 and 14 above have been textually amended as follows:- -1 ler, 3. A method of manufacturing a gravure print ro- the rret"riod includinE provding a cylindrical steel body, providing a hard surface coating on the cylindrical surface of said steel body, and forming in said coating an array of recesses each adapted to receive a quantity of printing ink and filling selected recesses with a plastics material so as to define a -,rj--nt image corresponding to the unfilled recesses.