Method of manufacturing a printing cylinder

Abstract

A method of manufacturing a printing cylinder. The method comprises providing a moulding apparatus comprising a cylindrical moulding vessel defining a moulding cavity (101). The vessel comprises at least one inlet for the ingress of moulding material. The method comprises performing an injection moulding operation comprising: injecting moulding material through the at least one inlet to substantially fill the moulding cavity with moulding material; and effecting hardening of the moulding material within the vessel (102). The method comprises removing the printing cylinder (103). At least part of the injection moulding operation is performed in the presence of an active pressure being applied to the moulding cavity.

Claims

1. A method of manufacturing a printing cylinder, the method comprising: providing a moulding apparatus comprising a cylindrical moulding vessel defining a moulding cavity, the vessel comprising at least one inlet for the ingress of moulding material; performing an injection moulding operation comprising: injecting moulding material through the at least one inlet to substantially fill the moulding cavity with moulding material; and effecting hardening of the moulding material within the vessel; and removing the printing cylinder, wherein at least part of the injection moulding operation is performed in the presence of an active pressure being applied to the moulding cavity; wherein the active pressure is applied, at least in part, through control of the injection of the moulding material through the at least one inlet, wherein injecting moulding material through the at least one inlet comprises controlling the injection of the moulding material such that mould flow fronts of the injected moulding material collide in a way that generates a plurality of staggered weld lines on the printing cylinder, and wherein the at least one inlet comprises a plurality of inlets, and wherein injecting the moulding material comprises sequentially injecting moulding material through the different ones of the plurality of inlets according to a pre-set sequence.

2. A method as claimed in claim 1, wherein the moulding material is injected under an active injection pressure of at least 150 mega-Pascal, MPa, and the hardening of the moulding material is performed under an active holding pressure of at least 3-5 MPa.

3. A method as claimed in claim 1, wherein the vessel further comprises a removable centrally located spine within the vessel for allowing the moulding material to harden around the centrally located spine; the effecting of hardening of the moulding material within the vessel is such that the moulding material hardens around the centrally located spine; and the printing cylinder comprises the hardened moulding material and spine.

4. A method as claimed in claim 1, wherein, during at least part of the injection moulding operation, the temperature of the moulding vessel or cavity is controlled by at least one of heating or cooling the moulding vessel or cavity.

5. A method as claimed in claim 4, wherein the moulding cavity is heated to a temperature of between 60 and 90 degrees Centigrade.

6. A method as claimed in claim 1, wherein the moulding apparatus comprises a clamping unit, and wherein the method comprises using the clamping unit to apply at least part of the active pressure to the moulding cavity.

7. A method as claimed in claim 6, wherein the clamping unit is a bi-platen or toggle clamping unit.

8. A method as claimed in claim 1, wherein during the injection moulding operation, the only route for the injection moulding material into or out of the cavity is via the at least one inlet.

9. A method as claimed in claim 1, further comprising covering at least part of the printing cylinder with a diamond-like carbon, DLC, layer.

10. A method as claimed in claim 9, further comprising: engraving a printing pattern into the printing cylinder prior to covering the at least part of the printing cylinder with the DLC layer; and/or engraving a printing pattern into the DLC layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

(2) FIG. 1 shows a side cross-sectional view through an existing moulding apparatus;

(3) FIG. 2 shows a process diagram for manufacturing a printing cylinder according to the first aspect of the invention;

(4) FIG. 3 shows a process diagram for manufacturing a printing cylinder according to the second aspect of the invention; and

(5) FIGS. 4a-4d show cross-sectional views through printing cylinders according to aspects of the present invention;

(6) FIGS. 5a-5b show simplified schematic views of a moulding apparatus according to aspects of the present invention.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

(7) Referring to FIG. 2, there is shown a method of manufacturing a printing cylinder according to the first aspect of the invention.

(8) Step 101 comprises providing a moulding apparatus comprising a cylindrical moulding vessel defining a moulding cavity. The vessel comprises at least one inlet for the ingress of moulding material.

(9) In this example, the moulding apparatus comprises an injection unit and a clamping unit.

(10) In this example, the at least one inlet is arranged to introduce moulding material into the vessel from the side of the vessel.

(11) In this example, the at least one inlet comprises a plurality of inlets. The plurality of inlets are spaced apart along all or part of the length of the vessel such that moulding material may be introduced into the vessel for a plurality of different locations, e.g. spaced part along the length of the vessel.

(12) In this example, the vessel further comprises a removable centrally located spine within the vessel. The effecting of setting/hardening of the moulding material within the vessel may be such that the moulding material hardens around the centrally located spine. The printing cylinder thus comprises the hardened moulding material and spine. The spine is hollow in this example.

(13) Step 102 comprises performing an injection moulding operation comprising: injecting moulding material through the at least one inlet to substantially fill the moulding cavity with moulding material; and effecting hardening of the moulding material within the vessel.

(14) At least part of the injection moulding operation is performed in the presence of an active high pressure being applied to the moulding cavity.

(15) In this example, the active pressure comprises an injection pressure during the injection stage and/or (preferably and) a holding pressure after the injection stage. The injection pressure is a clamping pressure, i.e. is provided at least in part by the clamping unit, and often in combination with pressurised injecting. In other words, the method comprises using the clamping unit to apply at least part of the active pressure to the moulding cavity. In particular, the clamping unit may act to keep two halves (or, generally, parts) of the moulding vessel together.

(16) In this example, the clamping unit is a bi-platen or toggle clamping unit.

(17) In this example, the moulding apparatus including the clamping unit and the moulding vessel are designed to withstand the high active pressure applied during the moulding operation.

(18) Other ways of providing the active pressure are within the scope of the invention and may be used in addition to or separately to the application of clamping pressure as described above.

(19) In this example, the moulding cavity is also heated during at least part of the moulding operation. The moulding cavity is heated to a temperature of between 80 and 100 degrees Centigrade in this example. The moulding apparatus comprises a control unit for controlling the heating of the moulding cavity such that the temperature within the moulding cavity remains at a predetermined temperature or within a predetermined temperature range.

(20) In this example, heating the moulding cavity comprises heating the spine.

(21) In this example, injecting moulding material through the at least one inlet comprises controlling the injection of the moulding material such that the mould flow fronts of the injected moulding material collide in a way that generates a plurality of staggered weld lines on the printed article. It will be appreciated that the weld lines are not visible under the naked eye. The material may be mixed sufficiently by this method so that the weld lines are not perceptible.

(22) In more detail, a sequential injection moulding operation is performed such that moulding material is injected through the different ones of the plurality of inlets according to a pre-set or otherwise adaptable sequence. The controller of the moulding apparatus in this example thus acts to control the valves of the inlets so as to allow/prevent moulding material to be injected through the inlets according to the pre-set sequence or otherwise adaptable sequence.

(23) Step 103 comprises removing the printing cylinder.

(24) In this example, the cylinder has a length between 800 mm and 1800 mm.

(25) The removed plastics printing cylinder is of high quality, and may be machined to provide a highly finished engraveable surface. The body of the printing cylinder can be machined at any one or many points within its diameter so that, significantly, the size of the printing cylinder is variable—i.e. the diameter can be varied. The high quality finish is such that the plastics printing cylinder may be engraved directly with the printing pattern. The printing cylinder may have less than 5% voids on the outer surface of the printing cylinder, less than 4% voids on the outer surface of the printing cylinder, less than 3% voids on the outer surface of the printing cylinder, less than 2% voids on the outer surface of the printing cylinder, or ideally less than 1% voids on the outer surface of the printing cylinder, and even less than or equal to 0.3% voids.

(26) In this example, after the plastics printing cylinder has been removed, the method comprises engraving the printing pattern onto the outer surface of the plastics printing cylinder using a laser engraving process.

(27) In this example, the outer surface of the plastics printing cylinder is then covered with a diamond-like carbon (DLC) layer.

(28) In this example, a nickel layer is sputtered onto the outer surface of the plastics printing cylinder before the DLC layer is applied.

(29) In another example, the outer surface of the plastics printing cylinder may be covered with the DLC and then the printing pattern may be engraved into the DLC layer using laser engraving.

(30) The DLC layer provides a hard wearing outer surface for the printing cylinder. The finished printing cylinder may then be used in printing operations.

(31) Referring to FIG. 2, there is shown another method of manufacturing a printing cylinder according to the second aspect of the invention. The example of FIG. 2 is similar to the example of FIG. 1 described above, but does not require the application of an active pressure during the moulding operation. Instead, the example of FIG. 2 achieves the advantageous high quality finish of the printing cylinder through use of the application of heat during the moulding operation.

(32) Step 201 comprises providing a moulding apparatus comprising a cylindrical moulding vessel defining a moulding cavity. The vessel comprises at least one inlet for the ingress of moulding material.

(33) Step 202 comprises performing an injection moulding operation comprising: injecting moulding material through the at least one inlet to substantially fill the moulding cavity with moulding material; and effecting hardening of the moulding material within the vessel.

(34) During at least part of the injection moulding operation the moulding cavity is heated.

(35) Step 203 comprises removing the printing cylinder.

(36) Referring to FIG. 4a, there is shown a printing cylinder 300a according to aspects of the present invention.

(37) The printing cylinder 300a comprises a plastics cylinder 301 and a spine 303. The spin 303 may otherwise be known as an axle. In other examples, the spine 303 may be an external shaft of an internal bore or sleeve configuration. The plastics cylinder 301 may be manufactured using an injection moulding operation as described above in relation to the first or second aspect of the present invention.

(38) Referring to FIG. 4b, there is shown a printing cylinder 300b according to aspects of the present invention.

(39) The printing cylinder 300b comprises a plastics cylinder 301, a spine 303, and a diamond-like carbon, DLC, layer 305 covering at least part of the plastics cylinder. The DLC layer 305 is a DLC sub-layer 305 is formed with a substantially cylindrical outer surface.

(40) Referring to FIG. 4c, there is shown a printing cylinder 300c according to aspects of the present invention.

(41) The printing cylinder 300c comprises a plastics cylinder 301, a spine 303, a DLC sub-layer 305 and a DLC outer-layer 307. Together, the DLC sub-layer 305 and the DLC outer layer 307 form a DLC layer. The DLC of the DLC sub-layer 305 has a lower intrinsic compressive stress than the DLC of the DLC outer layer 307.

(42) The DLC layer has a thickness of more than 3 microns, or more than 5 microns. More specifically, the DLC layer has a thickness of more than 8 microns. More specifically, the DLC layer has a thickness of more than 15 microns. In the present example, the DLC outer layer has a thickness of between 2 and 3 microns and the DLC sub-layer has a thickness of between 12 and 13 microns. In other examples, the DLC sub-layer has a thickness of between 17 and 18 microns. In other example, an outer DLC layer thickness may be between 3 and 8 microns.

(43) In other examples, the DLC layer comprises a single layer of DLC, for example, having the substantially the same intrinsic compressive stress throughout.

(44) Referring to FIG. 4d, there is shown a printing cylinder 300d according to aspects of the present invention.

(45) The printing cylinder 300d comprises a plastics cylinder 301, a spine 303, a DLC sub-layer 305 and a DLC outer-layer 307. Together, the DLC sub-layer 305 and the DLC outer layer 307 form a DLC layer. The DLC of the DLC sub-layer 305 has a lower intrinsic compressive stress than the DLC of the DLC outer layer 307.

(46) Additionally, the DLC outer layer 307 has been engraved with a printing pattern 309. The printing pattern 309 is engraved directly in the DLC layer. In other examples, the printing pattern is engraved into the outer surface of the plastics cylinder 301 rather than the DLC layer.

(47) Referring to FIG. 5a, there is shown a moulding apparatus 400 for implementing one or more method aspects of the present invention. The apparatus 400 comprises a cylindrical moulding vessel 401 defining a moulding cavity. The vessel 401 comprises a plurality of inlets 403a-403c for the ingress of moulding material. The inlets 403a-403c are arranged to introduce moulding material into the vessel 401 from the side of the vessel 401. The inlets may, in some examples, be arranged on both sides of the vessel. The moulding apparatus 400 further comprises a means for applying the active pressure to the moulding cavity and thus the moulding material. In this example, the means is a clamping unit 402 for the application of a clamping pressure/clamping force to the cavity and thus the moulding material within the cavity. The clamping unit 402 may be controlled as discussed above to provide the active pressure.

(48) Referring to FIG. 5b there is shown additional components of the moulding apparatus 400 including: a temperature control system 404 to ensure that during at least part of the injection moulding operation the moulding cavity is heated and/or cooled; a controller or control system 405 to control the flow of the moulding material; and an injection unit 406 for injecting the moulding material.

(49) Some example operating conditions for aspects of the present invention will now be described.

(50) In some examples, during the moulding operation, the internal plastic pressures may be between 200-400 bar.

(51) In some examples, during the moulding operation, the plastic temperature may be between 240-310 degrees Centigrade.

(52) In some examples, the vessel may be heated to a temperature of between 80-200 degrees Centigrade.

(53) In some examples, the plastic and cylinder annealing temperatures may be between 200 to 60 degrees Centigrade. That is, the temperature may start at 200 degrees and may be ramped down to 60 degrees.

(54) In some examples, the finished cylinder has a percentage of voids of less than 1% and optionally less than 0.3%.

(55) In some examples, the clamping force is between 600-2000 tons,

(56) In some examples, the mould temperature is between 60-90 degrees Centigrade.

(57) The method of manufacturing a printing cylinder described herein is especially appropriate to rotogravure and flexography printing forms/cylinders.

(58) Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

(59) Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

(60) All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

(61) Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

(62) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.