GB2269136A

GB2269136A - Dampening-unit roller of a printing machine

Info

Publication number: GB2269136A
Application number: GB9314093A
Authority: GB
Inventors: Gerhard Johner; Stefan Hasenzahl; Jurgen Kern
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 1992-07-09
Filing date: 1993-07-08
Publication date: 1994-02-02
Anticipated expiration: 2013-07-08
Also published as: GB9314093D0; FR2693944B1; JP3165560B2; FR2693944A1; JPH06171060A; GB2269136B

Abstract

A dampening-unit roller includes, an outer cylindrical surface (13) provided with a hydrophilic coating (14) containing a zirconium oxide and/or an yttrium oxide. Zirconium silicate may also be used. Suggested methods of application of the coating layer include thermal spraying, physical vapour deposition (PVD), chemical vapour deposition, plasma chemical vapour deposition or galvanizing. The zirconium or yttrium oxide may be part of an enamel layer. A corrosion protection layer may be provided between the outer cylindrical surface (13) and the hydrophilic coating (14).

Description

2269136 Dampening-unit roller of a printing machine The invention relates

to a dampening-unit roller, in particular a metering roller, of a dampening unit of a printing machine, in particular an offset printing machine, comprising a coating on its outer cylindrical surface.

The dampening unit of a printing machine mostly comprises a plurality of rollers serving 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 result. Moreover, when feeding 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 dampening-unit roller, the thinner and uniformer the application of the dampening-medium film.

It is known to use ground and/or polished stainless steel as surface material for such dampening-unit rollers in order to obtain a surface which is as hydrophile as possible. Moreover, it is known to galvanically deposit on the outer cylindrical surface of a dampening-unit roller a chromium layer which may then be ground and/or polished.

The US Patent 4,991,501 discloses a method with which a flame sprayed layer of ceramic material is applied onto a metal roller, said flamesprayed ceramic layer being subjected to a pore-sealing treatment in order to improve its hydrophile 2 property. After a certain service life the pore-sealing layer requires re- hydrophilizing.

In order to improve the hydrophile condition of the surface of the dampening-unit roller it is also known to add to the dampening water alcohol (isopropanol or ethanol, for example) and/or alcohol substitutes. Environmental protection and future legislation call for a reduction in the use of alcohol. At the same time, there still is a demand for topgrade prints for which an extremely thin and uniform layer of dampening medium is a prerequisite.

It is therefore the object of the invention to provide a dampening-unit roller of the type initially mentioned having excellent hydrophile effects by adding to the dampening medium only little alcohol or none at all.

According to the invention this object is achieved in that the coating features a zirconium oxide or a yttrium oxide. Coating a respective roller with the material according to the invention results in an extremely small contact angle of the 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. With the coating according to the invention it is not necessary or hardly necessary, due to the extremely small contact angle, to lower the surface tension of the dampening medium by adding alcohol or the like, since an extremely thin and uniform dampening-medium film is created without alcohol or the like having to be added. It is possible to coat just one dampening-unit roller of the printing machine or a plurality thereof with the material according to the invention. It is especially advantageous to provide the metering roller of the dampening unit with the inventive coating.

The wording of the main claim "to contain" does not clearly state as to whether, in addition to the zirconium oxide andlor the yttrium oxide, the coating comprises also other substances. However, the term "to consist oC used within the framework of this application is meant to state that the coating may be made of zirconium oxide and/or yttrium oxide only.

According to a further development of the invention the zirconium oxide used is Y 0 2 3 According to a further development of the invention the yttrium oxide used is Y 0 2 3 According to a further development of the invention the coating consists of or contains ZrSiO 4. Said coating may be formed, for example, by dissolving in the ZrO 2 crystal lattice an appropriate amount of SiO 2, thus forming ZrSiO 4 from ZrO which is highly stabilized by SiO 2 Of course, it is also conceivable to produce the ZrSio 4 coating differently. According to the aforementioned specimen embodiments it is also possible, for example, to introduce a relatively high concentration of the stabilizing MgO - for example, 24 percent by weight, in the form of magnesium zirconate - into the ZrO 2 crystal lattice similar to the case of SiO 2 and zirconium silicate; zirconium silicate having excellent hydrophile properties.

Advantageously the coating contains both an amount of zirconium oxide and an amount of yttrium oxide, the zirconium oxide making up for the larger portion, especially in view of weight percentage. Within the framework of ths application "zirconium oxide" and "Yttrium oxide" are to be understood in broader terms i.e. as "an oxide of zirconium" and as "an oxide of yttrium".

A good hydrophile surface condition is achieved by a coating containing approximately 80 percent by weight of zirconium oxide and approximat-ely 20 percent by weight of yttrium oxide.

Advantageous is a coating containing approximately 90 to 95 percent by weight of zirconium oxide and approximately 10 to 5 percent by weight of yttrium oxide.

According to further developments of the invention the coating contains, in addition to zirconium oxide and/or yttrium oxide, one or more of the following substances: CaO, Ceo 2, M90, Hfo 2 CaF Sio Particulary good hydrophile properties can be obtained with a coating having a surface roughness (Rz) which is smaller than 5 pm, in particular smaller than 1jum.

The coating can be designed as a layer formed by thermal spraying, in particular by flame spraying or atmospheric plasma spraying or vacuum plasma spraying, i.e. it is applied onto the outer cylindrical surface of a cylinder after a thermal spraying process.

In an alternative development the coating may also be a PVD layer which is applied onto the outer cylindrical surface of a cylinder by physical vapour deposition (PVD layer). In a further alternative development the layer may be applied by a chemical vapour deposition (M layer). According to a further development a layer formed by plasma chemical vapour deposition is provided. According to still further developments such a coating may be a sintered layer, or a layer produced galvanically or by hot isostatic pressing. Applying the coating by electron beam physical vapour deposition is also possible. It is also conceivable to form a coating formed by diffusion of zirconium, for example, in that Zr atoms diffuse at a high temperature, thus being oxidized and forming ZrO. X Alternatively, it is possible to form a layer by 2 laser-caused melting, i.e. the surface is remelted by simultaneously adding to the melt ZrO 2 particles, for example. According to another alternative the layer may be formed by enamelling; thus ZrO 2 particles, for example, may be added to the enamel composition and burnt afterwards. Finally, it is possible to plate steel-made bodies by blasting; for example, metal sheets made of zircalloy 4 may be used which are then subjected to an oxidization treatment, thus forming ZrO 2 layers. Although the aforementioned specimen embodiments mostly refer to the use of zirconium, this does not represent a limitation. Of course, all methods also permit the application of yttrium.

The cylinder onto which the coating is applied is preferably made of metal or of plastic material the fibres of which may be reinforced.

Moreover, the invention relates to the novel application of a material which as such is known, by using this material/these materials to make the surface condition of a printing-machine roller hydrophile, said material/materials being a zirconium oxide and/or an yttrium oxide.

The drawings illustrate the invention by means of specimen embodiments.

Fig. 1 is a schematic view of rollers of an offset printing machine, Fig. 2 is a perspective cut through a coated dampening-unit roller, and Fig. 3 is a diagram of the contact angle as a function of the amount of alcohol A or the like contained in a dampening medium given various surface conditions of dampening-unit rollers.

Fig. 1 is a schematic view 1 of printing-unit rollers of an offset printing machine. The rollers 2 through 6 are part of a dampening unit 7, whereas the remaining rollers, illustrated in Fig. 1, are part of an inking unit 8. The roller 6 is an 6 intermediate roller via which the dampening unit 7 and the inking unit 8 are connected with 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 containing dampening-medium additives) is taken and fed to a roller 3 designed as a metering roller - is assigned to roller 2 of the dampening unit 7 which is designed as a water-pan roller. Roller 3 rolls off on roller 5 designed as a rubber-covered roller cooperating with 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 simplicity 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 film, doing without the addition of alcohol or alcohol substitutes, or using only considerably reduced amounts of alcohol or alcohol substitutes. Thus, the alcohol usually having 10 to 15 percent by volume is lowered to an essentially smaller percentage or totally dispensed with. As alcohols there are preferably used isopropanol or ethanol.

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 dampening unit.

Fig. 2 is a perspective cross-cut through roller 3 (metering roller). Said roller has a hollow cylindrical body 12 made of metal or plastics, the outer cylindrical surface 13 of which is provided with a coating 14. Said coating 14 contains a zirconium oxide and/or a yttrium oxide or consists of one or both of said oxides. Depending on the substance(s) and the amount(s) thereof used various specimen embodiments are conceivable.

7 For the sake of protection against corrosion and/or the adhesive behaviour between surface 13 (outer cylindrical surface) and c oating 14 there can be applied an intermediate layer of Ni and/or Cr and/or Al and/or B and/or Si and/or Ti and/or Mo or the like. Said layer is preferably applied by the aforementioned methods: thermal spraying, physical vapour deposition, chemical vapour deposition, plasma chemical vapour deposition or galvanizing.

Examples a) Very good wetting results are obtained with a coating 14 containing approximately 80 percent by weight of zirconium oxide and approximately 20 percent by weight of yttrium oxide.

b) According to a further specimen embodiment it is also advantageous of the coating 14 contains approximately 93 percent by weight of zirconium oxide and approximately 7 percent by weight of yttrium oxide.

c) According to a further specimen embodiment the coating 14 contains 98 percent by weight of zirconium oxide and 2 percent by weight of yttrium oxide.

d) According to further specimen embodiments of the invention the coating 14 may also consist 100 percent by weight of zirconium or 100 percent by weight of yttrium oxide.

e) Moreover, according to further specimen embodiments, the coating 14 may contain CaO, Ceo 2, MgO, HfO 2, and/or CaF in addition to zirconium oxide and/or yttrium oxide.

Experiments have shown that - according to specimen embodiment b, for example - a contact anglec( of 29 degrees is obtained with the dampening medium containing 0 percent by volume of alcohol. If a dampening medium containing 10 percent by volume of alcohol (isopropanol) is used, the contact angle c is reduced to 20 degrees. The surface roughness R of the coating 14 is z preferably smaller than 5 pm. Values which are smaller than 1 Mm are particularly advantageous.

The surface of the coating 14 is preferably treated mechanically, in particular it is subjected to a grinding and/or polishing treatment. Recommended are surface roughnesses R of approximately -0.5 pm extending in longitudindal direction, z i.e. in grinding direction, and of approximately 1 um extending transversely thereto.

The diagram of Fig. 3 shows the contact anglec< at the surface of the metering roller (roller 3) featuring a coating according to the specimen embodiment b. In said diagram the contact angleo<, indicated in degrees, is mentioned as a function of the amount of isopropanol A plotted as percent by volume on the abscissa. With the coating according to the invention there is a functional relation with respect to line 15. The diagram clearly shows an extremely small contact angle a, even if no alcohol is added, whereas Fig. 3 shows contact-angle values of dampeningunit rollers featuring known surfaces. Thus, line 16 shows the relation betweenc< and A with respect to a silicium-coated roller. Line 17 shows the result produced with a roller as disclosed in the US Patent 4,991,501. And line 18 shows the result produced by a dampening-unit roller having a stainless-steel surface.

Various methods are conceivable to apply the coating 14 onto the outer cylindrical surface 13 of the cylinder 12. Advantageously the following methods are used: thermal spraying, physical vapour deposition, chemical vapour deposition, plasma chemical vapour deposition, sintering, hot isostatic pressing and galvanizing.

The advantage of the coating according to the invention is the fact that it requires no wetting agents such as alcohol or acohol substitutes at all or only very small amounts thereof, permitting nevertheless excellently thin and uniform wetting. A reduced consumption of agents promoting the wetting process is beneficial to the environment. The very thin and uniform dampening-medium film which can be provided according to the invention produces top-grade print results. As no further substances have to be applied onto the cylinder surface, no re-hydrophilization is required, as is periodically the case with the subject-matter of US Patent 4,991,501. Thus, offset printing using very little alcohol or none at all and featuring dampening-medium films which are as thin as possible is of lasting quality and beneficial to the environment.

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.

Claims

CLAIMS:

1. A roller for a dampening unit of a printing machine, comprising an outer cylindrical surf ace provided with a coating, containing a zirconium oxide and/or a yttrium 5 oxide.

2. A roller according to claim 1, wherein the zirconium oxide used is Zr02.

3. A roller according to claim 1 or 2, wherein said coating consists of or contains ZrSi04.

4. A roller according to any one of the preceding claims, wherein the yttrium oxide used is Y203. is

5. A roller according to any one of the preceding claims, wherein said coating contains an amount of zirconium-oxide and an amount of yttrium oxide, the zirconium making up for the larger amount by percentage weight. 20

6. A roller according to any one of the preceding claims, wherein said coating contains approximately 80 percent by weight of zirconium oxide and approximately 20 percent by weight of yttrium oxide. 25

7. A roller according to any one of the preceding claims 1-5, wherein said coating contains approximately 90 to 95 percent by weight of zirconium oxide and approximately 10 to 5 percent by weight of yttrium oxide. 30

8. A roller according to any one of the preceding claims, wherein, in addition to zirconium oxide and/or yttrium oxide, said coating contains one or more of the following substances: CaO, Ce02. MgO, Hf02. CaF2. S'0235

9. A roller according to any one of the preceding claims, wherein said coating features a surface roughness (Rz) which is smaller than 5gm.

11

10. A roller according to any one of claims 1-8, wherein said coating has a surf ace roughness (Rz) smaller than 1 gm.

11. A roller according to any one of the preceding claims, wherein said coating is a layer formed by thermal spraying.

12. A roller according to claim 11, wherein the thermal spraying is plasma spraying or flame spraying.

13. A roller according to any one of the preceding claims 1-10, wherein said coating is a layer f ormed by physical vapour deposition.

14. A roller according to any one of the preceding claims 1-10, wherein said coating is a layer f ormed by chemical vapour deposition.

15. A roller according to any one of the preceding claims 110, wherein said coating is a layer f ormed by plasma chemical vapour deposition.

16. A roller according to any one of the preceding claims 110, wherein said coating is a sintered layer.

17. A roller according to any one of the preceding claims 1-10, wherein said coating is a layer formed by hot isostatic pressing.

18. A roller according to any one of the preceding claims 1-10, wherein said coating is a layer formed galvanically.

19. A roller according to any one of the preceding claims 1-10, wherein said coating is a layer formed by electron beam physical vapour deposition.

20. A roller according to any one of the preceding claims l-io, wherein said coating is a layer formed by diffusion.

12

21. A roller according to any one of the preceding claims 1-10, wherein said coating is a layer formed by laser-caused melting.

22. A roller according to any one of the preceding claims 1-10, wherein sa id coating is a layer of enamel to which zirconium oxide and/or yttrium oxide has/have been added.

23. A roller according to any one of the preceding claims 1-10, wherein said coating is a layer plated by blasting.

24. A roller according to any one of the preceding claims, wherein the basic cylinder body is made of metal or plastic 15 material.

25. A roller according to claim 24, wherein the metal or plastics material incorporates fibres which are reinforced.

26. A roller, substantially as hereinbef ore described with reference to the accompanying drawings.

27. A dampening unit for a printing machine and having a metering roller as claimed in any one of claims 1-26.

28. A method of producing a hydrophile surface condition on a roller for metering the dampening medium in a dampening-unit of a printing machine, wherein a zirconium oxide andlor a yttrium oxide is applied to the surface of 30 the roller.