WO1989005731A1

WO1989005731A1 - Improved rollers

Info

Publication number: WO1989005731A1
Application number: PCT/GB1988/001101
Authority: WO
Inventors: Stanley Fellows
Original assignee: Stanley Fellows
Priority date: 1987-12-18
Filing date: 1988-12-13
Publication date: 1989-06-29
Also published as: AU2906689A; GB8729615D0

Abstract

Ink-retentive rollers for use in printing, especially as metering rollers in printing with oily ink in the presence of water or a wetting additive, are made from rollers having a surface in which a pattern of ink-retaining cells is formed by coating this patterned surface with a thin layer of ink-retentive material and then removing all or part of the excess coating on the surface outside the cells. The method of making these rollers is especially applicable to rollers of solid ceramic or having a surface layer of ceramic on a core, and to sleeves which are carried on base rollers. The preferred ceramic is chromium oxide, and the preferred coating is copper. Rollers with other surfaces, for example chromed surfaces, can also be improved in this way. The main advantage is greatly reduced wear in use.

Description

Title: IMPROVED ROLLERS .

This invention relates to improved rollers for use in printing and more particularly to ink metering rollers for use in printing.

In printing machines, it is customary to use a series of rollers in which one roller has the function of controlling the supply of ink to the printing rollers which bear the main design to be printed. This roller (usually described as the metering roller) has a pattern of depressions or hollows (conveniently described as "cells") formed in its surface and covering most of its surface, and in operation of the printing process these cells are filled with the printing ink from the ink supply and the excess of ink is removed by a doctor blade or roller which sweeps ink away from the general surface of the roller (i.e. those areas of the roller surrounding the cells) and leaves the cells filled with ink. This allows a controlled amount of ink (i.e. substantially that which is in the cells on the metering roller) to be carried on and transferred to the subsequent printing roller which performs the actual printing process itself.

Some printing processes require a purposeful and continuous addition of water to the printing system for good image differentiation. In these, it is desirable to have certain rollers made of, or coated with, a material (for example copper) that has the oleophilic/hydrophobic properties which will accept, retain and maintain an "oily" ink in its surface in preference to water or dampening solution when both ink and water are presented to or forced on to that surface.

Problems can occur in these systems where celled, recessed or anilox-type ink-metering rollers have been used to provide a simplified inking system. Even when a metering roller which has the necessary oleophilic/hydrophobic properties has been provided, problems can still arise because that part of their surface which is exposed to the doctor blade is usually made of metal and wears away unacceptably quickly. The quality of the resulting printing deteriorates as the . surface of the meter ing roller wears ,^* because the . wear . progressively decreases the depth of the cells and , as a consequence, their capacity to hold the required amount of. ink. As this happens, it starves the printing roller of the ink that is required and the printing density falls or becomes irregular.

Alternative materials which are more wear-resistant, .for example ceramics, have been proposed but have the disadvantage that they are so hard that it is difficult to form the cells in them. Also, they can have inadequate ability to retain the .ink because they do not have sufficiently hydrophobic properties- to retain an oil-based ink when water is present..

The problem arises because, in general, materials having good res istance to wear do not have good ink-retentive properties, and materials having good ink-retentive; properties do not have good resistance to wear.

It is therefore highly desirable to have a form of metering ^• roller which can maintain a steady and reliable supply of ink for the printing process without unduly rapid wear. The same applies to any roller which has on its surface a .pattecn (uniforπr or random) of cells, recesses or cavities which can be used for the transfer of ink.

We have now devised a form of printing roller (especially an ink-metering roller) and a method for making it which overcomes these problems.

Thus according to the present invention there is provided an improved printing roller having a surface which comprises a pattern of cells for ink retention, and having a coating of an . ink-retentive material on at least that part of the surface within the cells and optionally on the remainder of the surface. This has the advantage that the material^* which makes up the main surface of the roller can provide the desired wear- resistance while the coating of ink-retentive material in the cells is not subjected to wear and so can be chosen for its ink- retentive properties without the usual concern for its lack of wear-resistance. According to the present invention there is also provided an improved method for making a printing roller, which comprises treating a roller having a surface which bears a pattern of ink- retaining cells by applying a coating material having ink- retentive properties to at least that part of the surface within the cells and optionally on the remainder of the surface.

A particular form of this method comprises:- (a) treating a roller to produce the required pattern of ink- retaining cells in its surface, and (b) coating the patterned surface with a coating material having ink-retentive properties.

The coating stage (b) is preferably such as to coat substantially the whole of the operative surface of the roller

(i.e. the cylindrical surface area, which is used in the printing process) . This gives a covering for the interior of the cells and also the general area surrounding the cells.

If desired, the coating material may be left on all of the surface to which it has been applied, but preferably all or part of it is removed from the surface surrounding the ink-retaining cells. This leaves the coating on the interior walls of the cells.

The material from which the main surface of the roller is made (in which the pattern of ink-retaining cells is formed) may be a material which has wear-resistant properties, and may be for example a microporous ceramic material. The roller may be made of a solid ceramic material or may be made with a ceramic layer on a metal core, for example a steel core.

The microporous ceramic material should be such that its porosity is sufficient to allow it to be easily made or fabricated, and also to provide a sufficiently textured or "rough" surface (in the microscopic sense) to provide a good basis for the applied coating to adhere or "key on" to it, without being so highly porous as to be unduly absorbent or rough-surfaced to have an adverse effect on its use or strength for the printing process. Such materials in general are well known and their suitability may be determined by simple trial. Alternatively, the main surface of.the-.roller'may be mad of a hard: metal, for example a chromed 'surface' (i.e.. a surface of hard chromium metal or a chromium-containing material)^'.

The invention may be applied to a base roller itself or, when the roller is in the form of a base roller with a surface sleeve (which may optionally be detachable) , it may be applied to the surface sleeve.

In this form of the invention, the sleeve (which provides the effective working surface for the printing operation) should first have a layer of the ceramic material applied to its surface and this layer of ceramic material should be treated to form the required pattern of ink-retaining cells.

The base roller may be made of conventional materials, for example mild steel or stainless steel, with or without copper plating. Likewise a surface sleeve may be made of conventional materials, for example nickel and/or polymer or resin composites.

The ceramic material may be alumina, chromium oxide," or other metal oxides, carbides or nitrides, or mixtures or combinations thereof, but is preferably chromium oxide. These may be applied to the base roller or the sleeve by conventional methods, for example plasma spraying, to form an adherent layer on the surface of the base roller or its 'sleeve_* ~ ^~

The thickness of the ceramic layer may be varied over a wide range, but should be at least enough to take the engraving with the desired cells.

The pattern of the cells may be conventional, for example a regular pattern of square, rectangular, round or linear, cells or any combination of these. The method, when using a laser, lends itself especially to a regular pattern of cells which provides good coverage of the surface.

The pattern of cells for ink retention may be formed in the surface of the roller in various ways, according to the materials used and the procedures preferred. For example, when the roller is made of microporous ceramic material or has a surface of such material, the roller may be subjected to a treatment which introduces or forms the pattern of cells in it. When the roller is made of a base metal, for example copper, its surface is preferably pre-treated to give it a layer of a hard-wearing material to improve its wear resistance, before the coating of ink-retentive material is applied. This hard-wearing material may be for example a microporous ceramic material or a chrome coating, and this pre-treat ent may be carried out using known procedures. For example it may be done by "flash coating" procedures, whereby a microporous ceramic material is applied as a powder in a flame which turns it into an adherent layer on the metal base, or electrolytically in the case of a hard chrome coating (chromium plating) . In such cases, it is preferred that the desired pattern of cells is formed in the surface of the roller prior to application of the layer of hard-wearing material; this may be done by conventional means, for example engraving or etching (for example by mechanical or electrolytic means) or a combination of these.

The treatment for producing the pattern of ink-retaining cells in a ceramic surface is preferably by means of a laser which, by impinging on the surface, evaporates the ceramic locally to form the cells. This method has the advantage that the size and shape of the cells can be controlled very accurately by regulation of the laser parameters. It also avoids the problems of heavy wear which are met when using a mechanical cutting or engraving tool (for example even a diamond engraving tool) to make the cells, though the more conventional engraving techniques may be used if desired and their shortcomings can be accepted.

The ink-retentive material may be any material which has the desired degree of ink-retention for the particular type of ink used. Such materials are themselves well known in the art. As the material coats the cells and is subjected to relatively little direct wear during use in printing, it may be chosen with more concern for its surface properties than for its wear- resistance, so giving the user a greater freedom of choice. Of the various materials conventionally used, copper is the most preferred but other materials may be used if desired. The deposition of the ink-retentive material may be. achieved by any method which provides a good adherent coating on the surface of the ceramic without adversely affecting it. : One very convenient and effective method is by sputtering or vapo r- deposition, and another is by chemical deposition from solution (for example non-electrolytic deposition of a metal, for example copper, from solution). Of these methods, chemical- deposition from solution is strongly preferred. Many chemical compositions and processes for carrying it out are well known in the art. The thickness of the layer of ink-retentive coating material should be sufficient to coat the cells and provide the desired surface coating within them, and also can be based on the required ink-carrying capacity for the substrate to be printed. In this second aspect, the deposited coating layer reduces the initial volume of the cells but has the advantage of reducing the need to control the cell-forming stage so accurately, that the desired cell size is made initially. A convenient thickness ;is of the order of 2 to 4 microns, but greater or lesser thicknesses may be used if desired. The method of the present -invention .provider a- ery convenient way for determining and .controlling the: size and capacity of the cells, which can be very .useful for. securing high-quality printing. By making the original cells deeper than finally required and then depositing the layer of ink-retentive material to a thickness which takes up the excess depth, it is possible to achieve the desired final depth by abrading the deposited material from the "high" areas outside the cells. ;

The method for the removal of the .ink- etentive¹ material from the surface surrounding the ink-retaining cells may be "by any procedure which removes the coating material without unduly affecting or roughening the surface (for example, ceramic material) beneath it. Thus, it may be removed for example by grinding, but it is preferred to use relatively mild abrasive techniques, for example a polishing action — especially by use of polishing belt, often known in the art as a linishing belt. The extent of the removal should be whatever degree is required, and is preferably such as to remove substantially all the ink-retentive material from that part of the surface outside the cells, and expose the material beneath, for example the ceramic. It should also produce a substantially smooth surface on the surrounding surface, for example the ceramic, into which the ink-retaining cells are set.

The method of the present invention has the advantage of overcoming the printing problems normally due to the wear of a copper ink-metering roller, especially when used in conjunction with a doctor blade. As, in the present invention, the layer of ink-retentive material outside the cells is worn off, the final surface will be substantially free from undesired irregularities.

Claims

CLAIMS :-

1. A printing roller having a surface which, comprises .a pattern of cells for ink retention, and having a- coating of an ink- retentive material on at least that part of the surface.within^{^} the cells and optionally on the remainder of the surface.

2. A printing roller as claimed in Claim 1, wherein the surface which comprises a pattern of cells for ink retention is .formed of a microporous ceramic material.

3. A printing roller as claimed in Claim 2, wherein the microporous ceramic material is chromium oxide.

4. A printing roller as claimed in Claim 1, wherein the surface which comprises a pattern of cells for ink retention is a. chromed surface.

5. A printing roller as claimed in any of Claims 1 to 4, wherein the ink-retentive material is copper.

6. A printing roller as claimed in any of claims 1 to 5, wherein- the thickness of the layer .of ink-retentive material is in the^• range 2 to 4 microns.

7. A printing roller as claimed in any of Claims 1 to 6,^' herein. the roller comprises a metal core.

8. A printing roller as claimed in any of Claims 1 to 7, wherein- the roller is in the form of a base roller with a surface sleeve to which the coating of ink-retentive material is applied.

9. A printing roller as claimed in Claim 8, wherein the surface sleeve has a coating of a microporous ceramic material to which ^• the coating of ink-retentive material is applied.

10. A sleeve for a printing roller, having a surface which comprises a pattern of cells for ink retention and a coating of * an ink-retentive material on at least that part of its surface within the cells and optionally on the remainder of its surface, adapted for carrying on a base roller to form a printing roller as claimed in Claim 8 or Claim 9.

11. A sleeve as claimed in Claim 10, wherein the coating of an ink-retentive material is applied over a layer of microporous ceramic material.

12. A method for making an ink-retentive printing roller, which comprises treating a roller having a surface which bears a pattern of ink-retaining cells by applying a coating material having ink-retentive properties to at least that part of the surface within the cells and optionally on the remainder of the surface.

13. A method as claimed in Claim 12, wherein the coating material having ink-retentive properties is deposited on the surface by chemical deposition.

14. A method as claimed in Claim 12 or Claim 13, wherein all or part of the coating material having ink-retentive properties is removed from the surface surrounding the ink-retaining cells.

15. A method as claimed in Claim 14, wherein the method for removing coating material having ink-retentive properties from the surface surrounding the ink-retaining cells is by the action of polishing or linishing.

16. A method as claimed in any of Claims 12 to 15, which comprises:

(a) treating a roller to produce the required pattern of ink- retaining cells in its surface, and

(b) coating the patterned surface with a coating material having ink-retentive properties.

17. A method as claimed in Claim 16, wherein the roller has a surface of microporous ceramic material in which the required pattern of ink-retaining cells is produced.

18. A method as claimed in Claim 16 or Claim 17, wherein the treatment for producing the pattern of ink-retaining cells is by means of a laser.

19. A method as claimed in Claim 16 or Claim 17, wherein the treatment for producing the pattern of ink-retaining cells is by means of etching or engraving.

20. A method as claimed in any of Claims .12. to 19, wherein the application and/or removal of the coating.material', having ink- retentive properties is carried out? on a sleeve having a surface layer of ceramic material thereon and adapted to be carried on a base roller.

21. A method for making a printing roller, substantially as described.

22. A printing roller or sleeve therefor whenever made by a method as claimed in any of Claims 12 to 21.

23. A printing roller substantially as described.