GB2031801A

GB2031801A - Printing sleeve

Info

Publication number: GB2031801A
Application number: GB7931298A
Authority: GB
Original assignee: DRG UK Ltd
Current assignee: DRG UK Ltd
Priority date: 1978-09-13
Filing date: 1979-09-10
Publication date: 1980-04-30
Also published as: EP0009360B1; GB2031801B; EP0009360B2; DE2966610D1; EP0009360A1; JPS5559992A

Description

1 GB 2 031801 A 1

SPECIFICATION

Manufacture of printing sleeves chrome-plating to provide a more durable finish.

The first layer may be provided by spraying molten metal onto the outside surface of the mandrel, the fluid outlet holes having been masked beforehand. Alternatively, the first layer may be applied by straining a preformed metal sheet around the mandrel, with either a helical or a longitudinal butt seam, and weld- ing the seam to secure the layer. In the case of a sprayed metal layer, the fluid outlet holes may be masked before or after application of the release agent, but preferably they are masked after, using metal shim, such as cop- per shim, which is thereby incorporated in the sprayed metal layer.

The metal sleeve is at some suitable point in the process removed from the mandrel. This may be done by applying fluid, for example air, under pressure to the apertures in the mandrel so as to slightly expand the sleeve and allow it to be withdrawn axially This invention relates to printing rolls, and is especially applicable to rolls suitable for accepting photo-originating designs, such as used in the gravure or lithographic printing processes.

Conventionally, a gravure printing surface is provided by etching the surface of a metal printing roll. The production of the roll and the need to replace or discard it after use makes the process very expensive, and only suitable for relatively long printing runs.

Our British Patent Applications Nos.

609/76, 700/76 and 14060/77 describe improved methods of producing printing rolls, particularly for flexographic printing. A sleeve made of plastics material, preferably rein forced plastics material, is fitted onto a roll core which can be of metal construction.

Thus, for different printing jobs different from the smaller diameter end. Removal from sleeves can be used with a common roll core. the mandrel may take place when the electro In order to assist in getting the sleeve on and 90 plated layer has been fully finished. However, off the core, the internal diameter of the it may be desirable to mount the sleeve on sleeve is slightly larger at one end than the different mandrels at different stages during other, and the external diameter of the core is the process; for example for applying the first similarly slightly larger at one end than the metal layer, for the electro-plating, and for the other so that the sleeve can be slid partly onto 95 etching. In such a case, the sleeve can be the core before it wedges. The core is pro- removed, in the manner described, from the vided with apertures in that region which is one mandrel and fitted onto the next mandrel initially covered by the sleeve and through by a process which involves sliding the sleeve which compressed air can be forced to slightly over the mandrel until the fluid outlet holes expand the sleeve so that it can be slid fully 100 are covered and then applying fluid under onto the core. pressure to the fluid outlet holes to slightly The present invention, however, provides a expand the sleeve so that it can be slid fully sleeve substantially as described in the forego- onto the mandrel. This is more completely ing paragraph, but made substantially entirely described in our British Patent Applications of metal so as to provide a conductive path 105 referred to earlier. However, if the sleeve is from the inside to the outside of the sleeve to transferred from one mandrel to another be assist in electro-plating the outer surface of tween applying the first layer and the electro the sleeve. plating application of the second layer, the More particularly, the invention provides a first layer may not be sufficiently strong or method of making such a sleeve, comprising 110 resilient to withstand the fluid pressure with taking a generally cylindrical mandrel the ex- out distortion, and other means may be ternal diameter of which is slightly larger at needed for removing it from the first mandrel one end than the other, and optionally having and fitting it to the second mandrel. This may fluid outlet apertures in a region intermediate be achieved by heating and cooling so as to its ends, coating the outside surface of the 115 take advantage of thermal expansion and con mandrel with a release agent, applying a first traction.

layer of metal over the outside surface of the The invention can be further understood by mandrel, grinding the outside surface of the reference to the accompanying drawings first metal layer to provide it with a uniform wherein:

external diameter, and electro-plating a sec- 120 Figures 1, 2 and 3 show diagrammatically ond metal layer onto the first metal layer. in cross-section the stages in fitting a printing Suitably at least one, and preferably both, of sleeve to a roll core in a manner more particu the metal layers are copper. It is particularly larly described in the above-mentioned British preferred that said second layer is copper. The Patent Applications; outer surface of the second metal layer can be 125 Figure 4 shows a diagrammatically enlarged finished in conventional manner to provide a cross-sectional view of part of one embodi surface suitable for gravure printing. Such ment of sleeve being produced according to finishing may for example take the form of the present invention; grinding, polishing and eventually etching to Figure 5 shows a diagrammatically enlarged provide the imaged surface, and possibly flash 130 cross-sectional view of part of a second em- 2 GB 2031801 A 2 bodiment of sleeve being produced according to the present invention; and Figure 6 shows diagrammatically a cross sectional side view through one end portion of a mandrel and sleeve at the electro-plating stage in an alternative procedure of the pre sent invention.

Referring to Figs. 1 to 3, the sleeve 10 is made from a thermosetting resin, such as polyester or epoxy resin, reinforced with glass fibre, which is preferably spirally wound so as to provide hoop strength for the sleeve. The outside surface 12 of the sleeve is of uniform diameter, but the inside surface 14 has a very small taper from one end to the other. (This taper is greatly exaggerated in the drawing for the sake of clarity in explanation). The sleeve is removably mounted to a roll core 16, shown separately in Fig. 1, suitably made of steel, having an axle 18 for rotatably mount ing the core. The outside surface of the core is similarly slightly tapered, and is dimen sioned so as to allow the sleeve to be manu ally slid onto the core to rather more than half its length before the sleeve wedges on the core as shown in Fig. 2. An air supply pas sage 20 extends axially along the core and emerges at outlets 22 on the surface of the core about half way along its length. These outlets are thus covered by the sleeve at the point where the sleeve wedges onto the core.

Compressed air is then applied through the passage 20 so as slightly to expand the sleeve and allow it to be completely slid onto the core, as shown in Fig. 3. The supply of air is then discontinued and the sleeve is then finally fitted to the core.

Referring to Fig. 4; a steel mandrel 38 on which the sleeve is to be formed has the same general shape and construction as the roll core 16, but its outside diameter, point for pointalong itslength, is very slightly less than that of the roll core to which the sleeve is eventually fitted. In this way, the sleeve thus produced will be slightly undersized with re spect to the roll core, and will therefore be a tight fit on it. The mandrel has air outlets 22 about halfway along its length. In the first stage of construction, the outside surface of the mandrel is covered with a layer 39 of a silicone release agent. Then a strip or hoop of copper shim 40 is fitted around the mandrel so as to cover the outlets 22. Then a particu late copper composition is sprayed on to form a copper layer 41. This can be done by known techniques, for example by feeding copper rod or powder into a spraying head where a plasma electric arc melts it and forms minute droplets of molten copper which are protected from oxidation by an inert gas while 125 they are sprayed onto the surface of the mandrel. The outside surface of this first layer is then ground so as to produce a uniform outside diameter (as compared with the plating bath solution between the sleeve and slightly tapering outside diameter of the manthe mandrel but allowing the end faces of the drel). Then the first copper layer is electroplated to provide a second copper layer 42 of desired thickness, the outside surface of which is ground, polished, etched to produce the gravure printing surface, and finally flash chrome-plated. z The sleeve is removed from the mandrel by applying air under pressure to the outlets 22 which slightly expands the sleeve so that it can be withdrawn lengthwise from the narrower end of the mandrel.

Referring to Fig. 5; in this method, a similar mandrel 38 just is used, and a silicone release agent applied to it. Then a thin sheet of copper 43 is strained around the mandrel so as to provide a butt joint 45 which is secured by plasma welding; that is using a very narrow well- defined electric plasma arc flame produced from a tungsten tip with inert gas protection, to locally melt the copper along the seam and weld the two butting edges together. Thereafter this first copper layer is ground to produce a uniform external diameter, before electro-plating the second layer as previously described.

The all copper sleeves of this invention will generally have a somewhat smaller taper than the corresponding reinforced plastics sleeves described in our British Patent Applications referred to above. For example a taper of about 1:5000 might be appropriate for the sleeves one metre long.

In another procedure of the present invention, the mandrel coated with a silicone re- lease agent is heated to about 1 00C above ambient temperature. An electrically conductive metal, preferably zinc, is sprayed onto the release coated mandrel to form a metal base sleeve. A typical wall thickness is of the order of 0.5 to 0.8 mm. The mandrel is heated in order to accept more easily the sprayed metal and also to assist in removing the metal base sleeve from the forming mandrel by contraction of the mandrel on cooling.

The metal base sleeve on the forming mandrel is then machined to a uniform external diameter and is ready for removal from the forming mandrel. The temperature of the mandrel in the meantime has cooled down and in order to remove the metal base sleeve its temperature is raised quickly and it is slidw lengthwise off the forming mandrel. Air is not used at this stage for the removal of the metal base sleeve from the mandrel, particularly if the metal base sleeve is made of zinc, since zinc is too soft and the sleeve would be distorted.

The metal base sleeve 48 is expanded by heat and slid onto a plating mandrel 50 (Fig. 6). The ends of the sleeve extend beyond the body of the mandrel and are closed by end plugs 52, e.g. of acetal resin, with O-ring seals 54 to prevent the migration of the 3 GB 2031801 A 3 sleeve to be plated. For this purpose a gap 55 is left between the end faces and the plugs. The metal base sleeve is then plated with copper to a required thickness and is then ground to a finish diameter. The copper layer strengthens the sleeve to such an extent that the sleeve can be removed from the plating mandrel and mounted and demounted from a printing roll core by compressed air as de- l 0 scribed above.

Claims

1. A printing sleeve for fitting to a printing roll one end of which is of slightly larger diameter than the other end, the sleeve being similarly dimensioned so that it can be mounted on the roll by sliding it on lengthwise until it covers fluid outlet openings in the roll intermediate the ends of the roll, applying fluid under pressure to the outlets to slightly expand the sleeve, and then sliding the sleeve the rest of the way onto the roll; the sleeve being made entirely of metal and has an inner metal layer which contacts the roll and an electro-plated outer metal layer.

2. A printing sleeve according to claim 1 wherein both the inner layer and said electroplated layer are of copper.

3. A printing sleeve according to claim 1 wherein the inner layer is of zinc and said electro-plated layer is copper.

4. A method of making a printing sleeve for fitting to a printing roll one end of which is of slightly larger diameter than the other end, the sleeve being similarly dimensioned so that it can be mounted on the roll by sliding it on lengthwise until it covers fluid outlet openings in the roll intermediate the ends of the roll, applying fluid under pressure to the outlets to slightly expand the sleeve, and then sliding the sleeve the rest of the way onto the roll; the method comprising taking a generally cylindrical mandrel the external diameter of which is slightly larger at one end than the other, coating the outside surface of the mandrel with a release agent, applying a first layer of metal over the outside surface of the mandrel, grinding the outside surface of the first metal layer to provide it with a uniform exter- nal diameter, and electro-plating a second metal layer onto the first metal layer.

5. A method according to claim 4 wherein said first layer is provided by spraying molten metal onto the outside surface of the mandrel.

6. A method according to claim 4 or claim 5 wherein the sleeve is removed from the ' mandrel by applying fluid under pressure to said fluid outlet apertures to slightly expand the sleeve and allow it to be withdrawn axially from the smaller diameter end of the mandrel.

7. A method according to claim 5 wherein after applying the first metal layer the sleeve is transferred from the first mandrel to a plating mandrel at which the second layer is electro-plated.

8. A method according to claim 7 wherein the sleeve is removed from the first mandrel by heating it to a higher temperature than the mandrel so that it expands relative to the mandrel and can be withdrawn axially therefrom.

9. A method according to claim 8 wherein the sleeve is slid axially onto the plating mandrel whi, le at a relatively higher tempera- ture so that it contracts to fit the plating mandrel tightly on cooling.

10. A method according to any one of claims 7, 8 and 9 wherein the end portions of the sleeve extend beyond the body of the plating mandrel, the ends of the sleeves being closed by members which seal against the inside surface of the sleeve, whereby the end faces of the sleeve are exposed for plating.

11. A printing sleeve substantially as de- scribed herein with reference to the accompanying drawings.

12. A method of making a printing sleeve substantially as described herein with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd.-1 980. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.