GB2270279A

GB2270279A - Printing-machine roller.

Info

Publication number: GB2270279A
Application number: GB9317931A
Authority: GB
Inventors: Gerhard Johner; Stefan Hasenzahl; Jurgen Kern
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1992-09-05
Filing date: 1993-08-26
Publication date: 1994-03-09
Anticipated expiration: 2013-08-26
Also published as: GB2270279B; FR2695350B1; DE4229700A1; JPH06182961A; GB9317931D0; JP3432250B2; DE4229700C2; FR2695350A1

Abstract

The roller, e.g. a dampening-medium roller, preferably a motoring roller, comprises a coating containing Si on its outer cylindrical surface. The coating may be applied by sintering, vapour deposition, thermal spraying, hot isostatic pressing, or galvanically, and the roller body may be metal. <IMAGE>

Description

PRINTING MACHINE ROLLER AND METHOD OF PRODUCING SUCH A ROLLER The

invention relates to a printingmachine roller, especially a daLmpening-unit roller, preferably a metering roller, the outer cylindrical surface of which is provided with a coating.

In mechanical engineering there is a demand for surface-coated cylinders, whereby the coating must feature a hydrophile property. In printing technology, for example, the dampening unit of a printing machine is equipped with a plurality of rollers which serve to apply onto the printing forme of a printing-forme cylinder a dampening-medium film which is as thin and uniform as possible. A particularly thin and uniform distribution of the dampening medium ensures a good print quality. Moreover, when feedidg the dampening medium, it is important to prevent any printing ink from getting into the dampening unit. With arrangements in which the inking-unit rollers of the printing machine are connected to the dampening-unit rollers via, at least, one intermediate roller it is particularly critical if printing ink enters a dampening unit.

The better the hydrophile property of the surface of the printing-unit roller (dampening-unit roller), the thinner and uniformer the application of the dampening-medium film.

Top-grade print - for example, art printing - mostly requires an extremely thin dampening-medium film (of 5 pm, for example) surrounding the entire outer cylindrical surface of the roller. For forming such a thin dampening-medium film it has up to now been necessary to add alcohol or alcohol substitutes to the dampening medium in order to reduce the surface tension. As alcohols, for example, isopropanol or ethanol are used. For reasons of environmental protection and/or due to the regulations for the prevention of accidents it is to be expected that, in future, a reduction in the use of alcohol or alcohol substitutes is requested or even required by law. At the same time, there still is a demand for top-grade prints for which an extremely thin and uniform layer of dampening medium is a prerequisite.

So far, in addition to special wetting agents (alcohols), specific surface materials exposed to a selective treatment have been used to obtain hydrophile properties which are as good as possible. It is known to use ground and/or polished stainless steel as surface material for such dampening-unit rollers. Moreover, it is known to galvanically deposit onto a respective cylinder surface a chromium layer which is then ground and/or polished. In connection with the use of alcohols or alcohol substitutes added to the dampening medium the dampening-unit rollers described above produce good print results. If the amount of alcohol or the amount of the alcohol substitute is, however, reduced, the print products are no longer satisfactory.

It is therefore the object of the invention to provide an initially mentioned printing-machine roller having excellent hydrophile properties.

According to the invention this object is achieved in that the coating contains Si or consists of Si. Said inventive coating brings about an extremely small contact angle of the alcohol-free dampening medium. Said contact angle is the angle formed at a dampening-medium drop by the secant and a plane surface on which the drop is located. Due to the extremely small contact angle itis not necessary or hardly necessary to reduce the surface tension of the dampening medium by adding alcohol or alcohol substitutes, since an extremely thin and uniform dampening-medium film is created without alcohol or alcohol substitutes being added. It is possible to coat just one printing-machine roller (dampening-unit roller of the printing machine), or a plurality thereof with the inventive surface material. It is especially advantageous to provide the metering roller of the dampening unit with the inventive coating. For the sake of protection against corrosion and/or the adhesive behaviour between the cylinder surface (outer 3 cylindrical surface) and the coating there can be applied an intermediate layer of nickel and/or chromium and/or aluminum and/or boron and/or silicon and/or titanium and/or molybdenum or similar material. Said layer is preferably applied by the following methods: thermal spraying, Physical vapour deposition, chemical vapour deposition, plasma chemical vapour deposition or galvanizing.

The wording of the main claim "to contaiC does not clearly state as to whether, in addition to Si, the coating also contains other substances. The term ',to consist oC in the present main claim means that the coating is made of Si only.

According to a further development of the invention the coating is built up by a thermal application, in particular by spraying, of Si powder.

Preferably the coating has a thickness of approximately 0.2 to 2 mm, preferably approximately 1 mm.

According to a further development of the invention the coating has a surface roughness Rz of ú 5 jum, preferably Rz % 1.0 m. This surface roughness can be produced by respective treatment of the Si coating, in particular by grinding, polishing, and pore-sealing after-treatment (e.g. through an anaerobically curing gumming process).

In particular it is conceivable to provide a coating formed by physical vapour deposition. in particular, it is possible to provide an electron beam physical vapour deposition.

Alternatively the coating may be a layer of sintered powder.

Further, the coating may also he a layer formed in a heat isostatic pressing process.

4 Further, the coating may be a layer formed galvanically.

According to a preferred specimen embodiment the cylinder consists of metal.

Moreover, the invention relates to a method for coating a cylinder of a printing machine, Si or a substance containing Si being applied onto the outer cylindrical surface of the cylinder.

Preferably Si or s substance containing Si is applied onto the outer cllindrical surface of the cylinder in a thermal process, in particular in a thermal spraying process.

According to a further process step the surface of the coating is processed in order to reduce the roughness. In particular, the surface roughness is reduced by being processed mechanically. Preferably the surface is ground and polished after having been ground, thereafter it is exposed to a pore-sealing after-treatment (impregnation), if necessary.

The surface is processed up to a roughness of preferably!5 1.0 )L= - The surface of the coating is abraded, in particular after the aforementioned leveling treatment (such as grinding and/or polishing) with the aid of a basic agent, especially a slightly basic cleaning liquid. In so doing, the surface is activated and causes the formation of a hydrophile layer.

According to a further development of the invention the roughness of the surface consisting of Si or containing Si is set such that a dampening medium which is free of alcohol or alcohol substitutes and used in the printing process features a contact angle.<50, in particular<40.

1 Furthermore, the invention relates to the application of Si to be used for a surface coating of a printing-machine roller having a hydrophile property.

The drawings illustrate the invention.

Fig. 1 is a schematic view of the rollers of an offset printing machine; Fig. 2 is a perspective cut through a coated dampening-unit roller, and Fig. 3 is a diagram.

Fig. 1 is a schematic view of printing-unit rollers 1 of a of an offset printing machine. The rollers 2 through 6 are part of a dampening unit 7 and the other rollers, illustrated in Fig. 1, are part of an inking unit 8. The roller 6 is an intermediate roller via which the dampening unit 7 and the inking unit 8 are connected to each other. An ink fountain 9 from where the printing ink is supplied is assigned to one of the rollers of the inking unit 8. A water pan 10 - from where the dampening medium (dampening water) is taken and fed to a roller 3 designed as a metering roller - is assigned to the roller 2 of the dampening mediuú which is designed as the water-pan roller. The roller 3 rolls off on the roller 5 designed as a rubber-covered roller cooperating with the roller 4 serving as a friction cylinder. Roller 5 transfers the dampening medium in the form of a thin and uniform film onto a plate cylinder 11 carrying a printing forme on its circumference. For the sake of simpilicity further rollers such as a blanket cylinder etc. are not illustrated in Fig. 1.

At least one of the rollers, namely the metering roller 3, is provided with a coating having excellent hydrophile properties ensuring an extremely thin and uniform dampening-medium f ilm, doing without the addition of alcohol or alohol substitutes or 6 using only considerably reduced amounts of alohol or alcohol substitutes. The alcohol usually having 10 to 15 per cent by volume is thus reduced to an essentially lower percentage or is totally dispensed with. This is of great importance with respect to the regulations for the prevention of accidents and the environmental protection.

The invention is, however, not limited to the arrangement of rollers of the dampening unit 7 as represented in Fig. 1; it can be applied with any type of printing-machine rollers - provided said rollers feature hydrophile properties.

Fig. 2 shows a perspective cross-cut through roller 3 (metering roller). Said roller has a hollow cylindrical body 12 made of metal, the outer cylindrical surface 13 of which is provided with a coating 14. Said coating 14 contains Si or, according to a further specimen embodiment, consists of Si.

In a thermal spraying process preferably pure Si powder is applied as a preferably approximately 1-mm-thick layer having very few pores. Thereafter said coating 14 is mechanically ground and polished until a roughness Rz of approximately 1.0 pm, in particular< 1.0 pm, is reached. If necessary, the surface is then exposed to a pore-sealing aftertreatment. The thus obtained surface features an excellent hydrophile property. Said hydrophilism is reproducible and remains in perfect condition, even after the surface has dried.

After having been polished and prior to its first use the surface of the coating 14 is preferably abraded with a slightly basic cleaning liquid. In so doing, the surface is activated by forming a hydrophile layer.

According to the method of the invention a coating 14 of a dampening-unit roller onto which dampening medium containing no 7 alcohol and/or alcohol substitutes is applied has a contact angle which is smaller than 400 (see Fig. 3).

The diagram in Fig. 3 shows the contact angle a at the surf ace of the metering roller (roller 3) which is coated according to the description. In said diagram the contact angle a indicated in degrees is mentioned as a function of the amount of isopropanol A plotted on the abscissa as percent by volume. with the coating according to the invention there is a functional relation with respect to line 16. The diagram clearly shows an extremely low contact angle a, even if no alcohol is added, whereas Fig. 3 shows contact-angle values of dampening-unit rollers featuring known surfaces. Line 17 shows the outcome produced by a chromium-plated roller. And line 18 reveals the outcome produced by a dampening-unit roller having a stainless-steel surface.

Especially advantageous is the fact that a Si coating applied in a thermal spraying process can be ground and polished very qu:kkly and easily up to a roughness Rz of approximately 1.5 pm, preferably 1.0 pm. It is readily conceivable to obtain with such a coating a dampening- medium film having a thickness of 5 pm, for example even without adding a wetting agent to the dampening medium so that a perfect print is produced without a tear of the dampening-medium film.

In addition to the aforementioned thermal spraying method further methods of applying the coating 14 onto the outer cylindrical surface 13 of a respective cylinder 12 are conceivable. It is advantageous to use the following methods: physical vapour deposition, electron beam physical vapour deposition, chemical vapour deposition, plasma chemical vapour deposition, sintering, hot isostatic pressing and/or galvanizing.

it will of course be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

8

Claims

CLAIMS:

1. A printing machine roller having a coating on its outer cylindrical surface which contains Si or consists of Si.

2. A printing machine roller according to claim 1, wherein the coating is formed by a thermal application.

3. A printing machine roller according to claim 2, wherein Si powder is thermally sprayed onto the roller to provide the coating.

4. ' A printing machine roller according to claim 1, wherein the coating is a layer formed by physical vapour deposition.

5. A printing machine roller according to claim 1, wherein the coating is a layer formed by electron bean physical vapour deposition.

6. A printing machine roller according to claim 1, wherein the coating is a layer formed by chemical vapo ur deposition.

7. A printing machine roller according to claim 1, wherein the coating is a layer formed by plasma chemical vapour deposition.

8. A printing machine roller according to claim 1, wherein the coating is a sintered layer.

9. A printing machine roller according to claim 1, wherein the coating is a layer formed by hot isostatic pressing.

10. A printing machine roller according to claim 1,, wherein the coating is a layer formed galvanically.

9

11. A printing machine roller according to any one of the preceding claims, wherein the cylinder consists of metal.

12. A printing machine roller according to any one of the preceding claims, wherein the coating has a thickness of approximately 0. 2 to 2 mm.

13. A printing machine roller according to claim 12, wherein the thickness of the coating is 1 mm.

14. A printing machine roller according to any one of the preceding claims, wherein the coating has a surface roughness Rz of:5 5 pm.

is

15. A printing machine roller according to claim 14, wherein the surface roughness is:5 1.0 pm.

16. A printing machine roller substantially as hereinbefore described with reference to the accompanying 20 drawings.

17. A method of coating a cylinder of a printing machine, wherein Si or a substance containing Si is applied onto the outer cylindrical surface of the cylinder.

18. A method according to claim 17, wherein si or si powder or a substance containing si is applied onto the outer cylindrical surface in a thermal spraying process.

19. A method according to claim 17 or 18, wherein the surface roughness of the cylinder is reduced by processing the surface of the coating.

20. A method according to claim 19, wherein the surface 35 of the coating is ground.

21. A method according to claim 19, wherein the surface of the coating is polished.

22. A method according to claim 21, wherein the coating is polished after having been ground.

23. A method according to any one of the preceding claims 17-22, wherein the surface of the coating is impregnated with a pore-sealing agent in order to reduce its porosity.

24. A method according to any one of the preceding claims 17-23, wherein the surface of the coating is processed up to a roughness Rz:5 1.0 gn.

25. A method according to any one of the preceding claims 17-24, wherein the surface of the coating is abraded, after levelling treatment, with a basic agent.

26. A method according to claim 25, wherein the basic agent is a cleaning liquid.

27. A method according to any one of the preceding claims 17-26, wherein the surface roughness of the coating, consisting of or containing Si, is set such that a dampening medium which is to be used in the printing process and to which there has not been added any alcohol andlor alcohol substitutes has a contact angle of < 500.

28. A method according to claim 27, wherein the contact angle is < 35.

29. A method of coating a cylinder of a printing machine according to claim 17, and substantially as hereinbefore described with reference to the accompanying drawings.

30. Application of si or a substance containing Si for the production of a surface coating of a printing machine roller featuring hydrophile properties.