Abstract:
The invention comprises a printing cylinder precursor comprising a plastics cylinder in which is located an immovable spine. The invention further extends to a moulding apparatus for manufacturing a printing cylinder precursor, comprising a cylindrical moulding vessel comprising an inlet for the ingress of moulding material, the vessel further comprising a removable spine located centrally within the moulding vessel. The invention further extends to methods of manufacturing printing cylinder precursors and gravure printing cylinders.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to apparatus and methods for manufacturing printing cylinder precursors, methods of manufacturing printing cylinders, printing cylinder precursors and printing cylinders per se.  
         BACKGROUND TO THE INVENTION  
         [0002]    Printing cylinder precursors may be manufactured from a variety of materials including metals and plastics materials. Metal printing cylinders, such as aluminium printing cylinders display some advantageous characteristics such as strength and toughness, but can be expensive to manufacture and once damaged, difficult to repair. Plastics cylinders on the other hand, are cheap to manufacture and any defects caused by damage or through the manufacturing process, can usually be repaired easily and cheaply.  
           [0003]    There are many methods of manufacturing plastics printing cylinders. One known method is injection moulding of a curable plastics monomer into a cylinder vessel, the monomer being cured to produce a solid plastics cylinder which must then be bored to provide anchor points for connection to a suitable printing apparatus. The need to bore the solid cylinder in a separate apparatus, and the subsequent loss of the bored materials makes this method relatively expensive.  
           [0004]    Another known method of forming a printing cylinder precursor is to spin a plastics fibre outer cylinder coating and build up sufficient layers to form the precursor. The use of fibre spinning technology is again relatively expensive, and only certain plastics materials have the inherent physical properties necessary for spinning into fibres and coatings.  
           [0005]    A third known method of forming a printing cylinder precursor, particularly a gravure printing cylinder precursor is described in U.S. Pat. No. 4,197,798, which describes preparing a plastics cylinder by pouring polypropylene into a mould of the desired shape which includes a tapered plug for providing a keyway shafting bore. The tapered plug allows the production of a bore which gives purchase to connection means of a printing apparatus to which a printing cylinder formed from the precursor, is connected. As the cylinder precursor is entirely constructed from plastics, special techniques are needed for enabling copper, or other metal plating, of the precursor to form the final cylinder, as there is no electrically conductive surface present within or on the precursor.  
           [0006]    It is therefore an aim of preferred embodiments of the present invention to overcome or mitigate at least one problem of the prior art, whether expressly disclosed herein or not.  
         SUMMARY OF THE INVENTION  
         [0007]    According to a first aspect of the present invention there is provided a printing cylinder precursor comprising a plastics cylinder in which is located an immovable spine.  
           [0008]    Preferably the printing cylinder precursor is a gravure printing cylinder precursor.  
           [0009]    Preferably the spine comprises a cylindrical member, more preferably a hollow cylindrical member. Suitably the hollow member is open at both ends of the member.  
           [0010]    Preferably the spine comprises an end member at each end of the spine, wherein at least a portion of each end member has a diameter greater than that of the spine. Suitably the end members comprise a substantially frusto-conical shape or a trumpet shape, tapering inwards towards the spine.  
           [0011]    The end members may be formed integrally with the spine, but preferably the end members are connected to the spine, and more preferably are detachably connected to the spine.  
           [0012]    Preferably the end members are hollow.  
           [0013]    Preferably the spine is constructed from metal (including an alloy), more preferably steel, aluminium, bronze or combinations thereof. In a particularly useful embodiment of the invention, the spine is constructed from steel and comprises end members constructed from bronze.  
           [0014]    The spine may alternatively be constructed from plastics material or a composite material, such as woven or spun glass fibre material.  
           [0015]    The spine may be manufactured by any suitable method, such as die casting, for example.  
           [0016]    In alternative embodiments of the invention the spine may comprise an existing printing cylinder precursor or printing cylinder per se.  
           [0017]    Preferably the outer diameter of the spine has a variance of no more than 10 μm along substantially the length of the spine, preferably no more than 5 μm.  
           [0018]    The plastics cylinder suitably comprises polyurethane.  
           [0019]    Suitably the thickness of the cylinder wall is at least 5 mm, preferably at least 10 mm and more preferably at least 15 mm. In particularly preferred embodiments the thickness of the cylinder wall is at least 20 mm.  
           [0020]    Preferably at least a portion of the exterior surface of the spine comprises an adhesion means, which in use allows the plastics cylinder to adhere to the spine.  
           [0021]    Suitably the adhesion means comprises a roughened portion of the spine. Roughening of the spine may be effected by any suitable method, such as rubbing with an abrasive material, or, if the spine is metal, electrograining the surface of the spine.  
           [0022]    It has been found that by only providing the spine with adhesion means on certain sections of the spine, optimal adhesion and uniform stress distribution can be achieved for the printing cylinder precursor. Thus preferably the spine comprises adhesion means on portions of the surface of the spine adjacent to either end of the spine and optionally, substantially centrally on the spine.  
           [0023]    Suitably each of the three portions extends for substantially 10% of the length of the spine. The adhesion means on the surface of the spine adjacent to either end of the spine may further cover at least a portion of the end members of the spine.  
           [0024]    Suitably the surface of the spine comprises, in regions not comprising adhesion means, a release agent, arranged in use to prevent adhesion of the plastics cylinder to the spine in said regions. Suitable release agents include R525B Bulk Release Agent and Acmos 82-2405 sold by ECL Chemicals Limited, UK.  
           [0025]    During subsequent plating of the printing cylinder precursor with copper (or other metal) to produce a gravure cylinder, it has been found by the applicant that the heat generated during the plating process may sometimes expand the spine in diameter at both ends by an unacceptable amount (generally 750 μm), which pushes the plastics cylinder out. When the plating process is finished the spine may cool down and contract to its original size but the plastics cylinder may not, the result being an increase in diameter of the plastics cylinder at the cylinder ends.  
           [0026]    To overcome this disadvantage, preferably the spine comprises a compressible material on at least a portion of the surface of the spine. Suitably the compressible material is located in the region of either or both end(s) of the spine, and may be located on a portion of the spine substantially midway along the spine. Suitably the compressible material also functions as the adhesion means, and preferably is located as described hereinabove for the adhesion means.  
           [0027]    Suitably the compressible material comprises bitumen or polymerised bitumen.  
           [0028]    Preferably the compressible material has a thickness of at least 100 μm, more preferably at least 200 μm and most preferably at least 300 μm. In a particularly preferred embodiment of the invention, the compressible material has a thickness of substantially 500 μm.  
           [0029]    The compressible material may be laminated with one or more layers of aluminium foil, suitably substantially 20 μm in thickness. The aluminium foil may be overlaid with one or more layers of polyester, preferably between substantially 15 μm and substantially 20 μm in thickness. The aluminium and/or polyester layers are suitably roughened or otherwise treated, to function as the adhesion means of the spine.  
           [0030]    An advantage of a printing cylinder precursor of the invention, comprising a plastics cylinder in which is located an immovable spine, is the property that the cylinder can be turned down to a different diameter by a printer if desired. The printer may turn down the precursor per se or turn down a printing cylinder produced from the precursor, thus recycling the cylinder and/or precursor, savings costs, resources and time. The immovable spine allows the plastics cylinder to be turned down by providing strength against the pressure involved in the turning process, alleviating pressure on the plastics cylinder, thus reducing the likelihood of cracking or shearing of the cylinder. The precursor and/or printing cylinder produced therefrom, may also be cast up to a larger size, again allowing printers to recycle precursors and cylinders.  
           [0031]    A second advantage of utilising an immovable spine within the plastics cylinder is that the increased strength effected by the spine allows precursors of much greater length to be manufactured, as would otherwise be possible without a spine. During the manufacturing process, an immovable spine allows adhesion of the plastics material of the cylinder so that the cylinder is prevented from flexing or bending axially when removed from the manufacturing apparatus, thus preventing possible cracking or shearing of the plastics material.  
           [0032]    A conductive metal spine also provides, an electrically. conductive surface which can be utilised to electroplate the surface of the precursor to form a gravure printing cylinder.  
           [0033]    According to a second aspect of the invention there is provided a gravure printing cylinder comprising a printing cylinder precursor of the first aspect of the invention, on which is coated a deformable layer of metal (including alloy).  
           [0034]    The deformable layer of metal is thus suitable for etching by conventional gravure printing methods.  
           [0035]    Suitably the metal layer is copper.  
           [0036]    Preferably the gravure printing cylinder comprises a conductive metal layer between the precursor surface and the deformable metal layer. Suitable conductive metals include nickel and conductive alloys thereof, for example.  
           [0037]    According to a third aspect of the present invention there is provided a moulding apparatus for manufacturing a printing cylinder precursor, comprising a cylindrical moulding vessel comprising an inlet for the ingress of moulding material, the vessel further comprising a removable spine located centrally within the moulding vessel.  
           [0038]    Preferably the vessel comprises air egress means, which may comprise an air outlet. Suitably there are a plurality of air egress means.  
           [0039]    The vessel preferably comprises moulding material egress means, which may comprise a moulding material outlet. Preferably there are a plurality of moulding material egress means.  
           [0040]    In an especially preferred embodiment, the air egress means and the moulding material egress means are the same means.  
           [0041]    Suitably the vessel comprises a spine locating member, arranged in use to enable location of the spine substantially centrally within the vessel. Preferably the spine locating member comprises an elongate member extending between both ends of the cylinder through the central axis of the cylinder. The elongate member may comprise a bar or rod, and is preferably a threaded bar or rod.  
           [0042]    The moulding vessel preferably comprises a bottom plate and a top plate spaced apart by way of a continuous side wall, and wherein at least one of the top plate and bottom plate is removably connected to the side wall.  
           [0043]    Suitably the air egress means is located in the top plate. Preferably the moulding material egress means is located in the top plate.  
           [0044]    Suitably the spine locating member is fixedly connected to one of the top plate or bottom plate, preferably the is bottom plate.  
           [0045]    At least one of the top plate and bottom plate may comprise a spine connecting member, arranged in use to cooperate with a corresponding connecting member on the spine. Preferably the spine connecting member comprises a male connection member which protrudes into the vessel from the top plate and/or bottom plate, and is cooperable with a female connection member of the spine. Most preferably the spine connecting member comprises a spigot which, is cooperable with a female connection member of the spine in the form of a recess.  
           [0046]    Suitably the spine is as described for the first aspect of the invention.  
           [0047]    The end members preferably comprise a moulding vessel connecting member, arranged in use to operably cooperate with a corresponding spine connecting member on the moulding vessel.  
           [0048]    Preferably the interior surface of the moulding vessel is substantially smooth, and is more preferably coated with a release agent which, in use, prevents moulding material adhering to the interior surface at the mould. Suitable release agents include R525B Bulk Release Agent and Acmos-82-2405 sold by ECL Chemicals Limited, UK.  
           [0049]    Preferably at least a portion of the exterior surface of the spine is roughened to form a key for adhesion of moulding material injected into the moulding vessel, in use of the moulding apparatus. The exterior surface of the spine may be roughened by any suitable method, such as rubbing with an abrasive material, such as emery paper, for example. If the spine is composed of a metal, roughening of the spine may be effected by electrogaining the surface of the spine.  
           [0050]    According to a fourth aspect of the present invention there is provided a method of manufacturing a plastics printing cylinder precursor, the method comprising applying a plastics material to a spine such that the spine is immovably fixed within the plastics material of the cylinder precursor.  
           [0051]    The plastics material may be applied to the spine by any suitable method, such as spin coating, injection moulding, or placing the spine in a cylindrical moulding vessel and introducing plastics moulding material to the vessel, before hardening of the material, for example.  
           [0052]    Suitably, the spine and plastics material are as described for the first aspect of the invention.  
           [0053]    According to a fifth aspect of the invention there is provided a method of manufacturing a plastics printing cylinder precursor, method comprising the steps of:  
           [0054]    (a) providing a moulding apparatus comprising a cylindrical moulding vessel comprising an inlet for the ingress of moulding material, the vessel further comprising a removable centrally located spine within the vessel;  
           [0055]    (b) effecting passage of a moulding material through the inlet to substantially fill the moulding vessel with moulding material;  
           [0056]    (c) effecting hardening of the moulding material within the vessel such that the moulding material hardens around the centrally located spine; and  
           [0057]    (d) removing the cylinder precursor comprising the hardened moulding material and spine.  
           [0058]    The moulding vessel may comprise air egress means, and the method may comprise effecting egress of air through the air egress means as the vessel is filled with moulding material.  
           [0059]    The moulding vessel may comprise moulding material egress means, and the method may comprise overfilling the vessel with moulding material such that a portion of the moulding material is ejected through the moulding material egress means in order to ensure complete filling of the vessel.  
           [0060]    Preferably the moulding vessel, spine, air egress means and moulding material egress means are as described for the first aspect and third aspects of the invention.  
           [0061]    Suitably the moulding material comprises a heat curable material, a radiation curable material or a heat and radiation curable material.  
           [0062]    Suitable moulding materials include plastics materials, such as polyurethane, for example. Examples of suitable polyurethane materials include slow reacting, water blown polyurethane foam or carbon dioxide (CO 2 ) blown MDI based foam. The moulding material may also comprise the plastics material of the fourth aspect of the invention.  
           [0063]    The method preferably comprises, after step (d), turning the cylinder precursor to remove any flaws in the outer surface of the precursor.  
           [0064]    The method may comprise, after step (d), turning the cylinder precursor to reduce the diameter of the cylinder precursor in order to allow subsequent coating of the precursor to its initial cylindrical diameter.  
           [0065]    According to a sixth aspect of the present invention there is provided a printing cylinder precursor manufactured by the method of the fourth or fifth aspect of the invention.  
           [0066]    According to a seventh aspect of the present invention there is provided a method of manufacturing a gravure printing cylinder from a precursor of the sixth aspect of the invention, the method comprising the steps of:  
           [0067]    (a) coating the precursor with a conductive metal (including alloy); and  
           [0068]    (b) plating the metal-coated cylinder precursor with a deformable metal.  
           [0069]    Suitably the deformable metal is copper.  
           [0070]    Preferably step (a) comprises applying a coating of electroconductive paint, which may be applied by brushing, rollering, spraying, dip-coating or doctor-blading the precursor with the electroconductive paint. Suitably the paint is electroconductive nickel-based paint.  
           [0071]    Alternatively step (a) may comprise electrodepositing a coating of conductive metal, such as nickel or copper for example.  
           [0072]    Step (a) may comprise spinning a coating of copper tape or film onto the surface of the precursor.  
           [0073]    Step (a) may comprise adhering a copper sheet to the precursor using any suitable adhesive.  
           [0074]    Step (a) may comprise spraying a coating of molten metal onto the precursor.  
           [0075]    Step (b) preferably comprises electrodeposition of copper from a copper salt. Suitably the copper salt is an aqueous solution of copper salt and is preferably an aqueous solution of copper sulphate.  
           [0076]    Step (b) may comprise immersing the precursor in an aqueous solution of copper salt and effecting an electronic current through the electroconductive coating of the precursor.  
           [0077]    According to a eighth aspect of the invention there is provide a gravure printing cylinder produced by the method of the seventh aspect of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0078]    For a better understanding of the various aspects of the invention, and to show how embodiments of the same may be put into effect, the invention will now be described by way of example, with reference to the accompanying drawings, in which:  
         [0079]    [0079]FIG. 1 illustrates a side cross-sectional view through a moulding apparatus of the invention, with the removable spine located centrally within the vessel;  
         [0080]    [0080]FIG. 2 illustrates a blown up perspective view of the moulding vessel of the moulding apparatus of FIG. 1;  
         [0081]    [0081]FIG. 3 illustrates a side view of the spine of the moulding apparatus of FIG. 1;  
         [0082]    [0082]FIG. 4 illustrates a blown-up perspective view of a portion of the spine of FIG. 3, showing an end member and part of the spine;  
         [0083]    [0083]FIG. 5 illustrates a spine of a second embodiment of the moulding apparatus of FIG. 1;  
         [0084]    [0084]FIG. 6 illustrates a side cross-sectional view of a printing cylinder precursor. of the invention produced in the moulding vessel of FIG. 1; and  
         [0085]    [0085]FIG. 7 illustrates a side cross-sectional view of a gravure printing cylinder of the invention manufactured from the printing cylinder precursor of FIG. 5. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0086]    Referring firstly to FIG. 1, 2 and  3  a moulding apparatus  2  of the invention comprises a moulding vessel  4 , and a removable hollow spine  6 .  
         [0087]    As illustrated in FIG. 2, the moulding vessel  4  comprises a cylindrical side wall  8  and top  10  and bottom  12  plates which are removably attached to the side wall  8 . The bottom plate  12  includes a central locating collar  14  dimensioned to connect to one end of the side wall  8 . At the centre of the locating collar there is provided a raised spigot  16 . The raised spigot  16  is substantially semi-circular in shape, with the circumference of the spigot nearest the collar  14  being substantially equal to the inner circumference of the spine  6 , to provide a tight seal when the spine  6  is mounted on the spigot  16 . Extending from the centre of the spigot is a spine locating member in the form of an elongate shaft  18  which is threaded at its free end.  
         [0088]    The top plate  10  includes air egress means and moulding material egress means in the form of apertures  20  which perform both functions. The top plate  10  also includes connection aperture  21  which, in use is arranged to be located over the free end of the elongate shaft  18 .  
         [0089]    The side wall  8  also includes a moulding material ingress means in the form of an inlet  26  located towards the end of the side wall  8  which in use is mounted on the bottom plate  12 .  
         [0090]    Referring now to FIGS. 1, 3 and  4 , the removable spine  6  comprises a spine body  28 , to which are connected at either end thereof, first  30  and second  32  end members having a substantially trumpet shape. Each of the spine body  28  and first  30  and second  32  end members are hollow, having a bore  34  running therethrough.  
         [0091]    Referring to FIG. 4, the end members  30  and  32  comprise a distal frusto-conical portion  36  and a proximal shoulder portion  38  which is disc-shaped. Extending from the shoulder portion  38  is an end member connection means in the form of a hollow spigot  40 , which in use is arranged to fit into the bore  34  at one end of the spine body  28  until the shoulder portion  38  of the end member  30  or  32  abuts the end of the spine body  28 .  
         [0092]    The spigot  40  is dimensioned to provide a tight seal with the bore  34  of the spine body  28 .  
         [0093]    Use of the apparatus will now be described with reference to FIGS. 1, 2,  3  and  4 .  
         [0094]    The top plate  10  of the vessel  4  is removed by first removing the nut  22  and washer  24  from the elongate shaft  18  and lifting off the plate  10 . The spine  6  is then lowered over the elongate shaft  18  such that the shaft  18  is within the bore  34  of the spine  6 . The spine  6  is lowered into the vessel  4  such that the end member  32  is arranged to sealingly fit over the raised spigot  16  in order to secure the spine  6  to the bottom plate  12  of the vessel  4  as illustrated in FIG. 1. The spigot  16  and/or end member  32  may include ‘O’-rings which effect a tight seal between the two components.  
         [0095]    When the spine  6  is in position in the vessel  4 , the top plate  10  is fitted back onto the top of the vessel  4  and the nut  22  and washer  24  screwed onto the elongate shaft  18  and tightened to ensure that the top plate  10  is sealed to the vessel  4 .  
         [0096]    Curable moulding material, such as polyurethane foam is then injected into the vessel  4  through the inlet  26 . As the moulding material enters the vessel  4 , it displaces air within the vessel  4  which is forced out of the vessel  4  through the apertures  20 . The vessel  4  is slightly overfilled with moulding material such that some moulding material is forced out of the vessel  4  through the apertures  20 , in order to ensure complete filling of the vessel  4 .  
         [0097]    As the spine  6  is sealed to both the top  10  and bottom  12  plates of the vessel  4 , no moulding material may enter the spine  6  and thus the moulding material is forced to encase the spine  6 .  
         [0098]    The moulding material is then cured and the vessel allowed to stand for a minimum of 2 hours to ensure complete curing of the material. The curing technique and standing time will vary depending on the moulding material, but will be well known to persons skilled in the art.  
         [0099]    When the moulding material is completely set, the nut  22  and washer  24  are unscrewed and removed from the elongate shaft  18  and the top plate  20  removed from the vessel  4 .  
         [0100]    The spine  6  which is now immovably encased by a cylinder of cured plastics material  41  as shown in FIG. 5, is then withdrawn from the vessel  6 . The plastics encased spine forms a printing cylinder precursor  42  of the invention, having an immovable spine.  
         [0101]    The printing cylinder precursor is then allowed to stand at ambient temperature for a minimum of 72 hours to stabilize the cured moulding material.  
         [0102]    The frusto-conical portion  36  of each end member  30  and  32  has a diameter greater than that of the shoulder portions  38  and serves to allow attachment of the cylinder precursor  42  to apparatus having varying sized cylinder connection means (not shown).  
         [0103]    The diameter of the precursor  42  is then lowered by shaving off a layer of the cured moulding material  41 , in order that subsequent coating and plating does not increase the diameter of the precursor  42  beyond its original diameter.  
         [0104]    The precursor  42  is then coated with a conductive metal by blade coating, spraying or hand brushing an electroductive nickel based paint, to form a conductive coating on the cylinder precursor  41  surface, as illustrated in FIG. 6.  
         [0105]    To manufacture a printing cylinder  44  as shown in FIG. 6, a layer of copper plating  48  is deposited on the conductive nickel layer  46  by electrodeposition from an aqueous solution of copper sulphate. To copper plate the precursor  41 , a conductive shaft is passed through the spine  6  which makes electrical contact with the surface of the conductive bore  34  or conductive end members  30  or  32 .  
         [0106]    Rubber seals are then placed over the end members  30  and  32  to prevent any solution entering the bore  34 . The spine  6  is then lowered into a vessel of copper sulphate. solution and an electrical current is passed down the shaft within the bore which passes through the spine  6  onto the conductive coating  46 . Copper is then deposited onto the conductive coating  46  to form a copper plate layer  48  on the surface thereof, as shown in FIG. 6.  
         [0107]    The current is initially low [approx 2-5 A/dm 2 ] and is increased once a thin layer of copper plate has formed on the conductive surface  46  to a maximum current of 20 A/dm 2 .  
         [0108]    The printing cylinder  44  is then removed from the copper solution, dried and cleaned, ready for use as a gravure printing cylinder of the invention, for example.  
         [0109]    We refer now to FIG. 5. In an alternative embodiment of the moulding apparatus of the invention, and a printing plate precursor of the invention the spine  6  may include compressible portions  50  and  51 , located around the surface of the spine  6 , at either end of the spine adjacent to the end members  30  and  32 , and substantially centrally round the spine. The compressible areas  50  and  51  may be formed of bitumen, and are laminated with layers of aluminium and polyester, the latter of which is roughened to provide an adhesion means for the polyurethane cylinder to adhere to.  
         [0110]    The compressible portions  50  and  51  allow the spine to expand and contract during plating without causing the polyurethane cylinder to expand, and thus prevents loosening and cracking of the cylinder during plating.  
         [0111]    The surface areas  52  and  55  of the spine adjacent to the compressible portions which do not comprise compressible material are coated in a release agent to prevent adhesion by the polyurethane cylinder. This allows for a more uniform pressure to be exerted on the spine during plating, and prevents expansion of the spine and cylinder adjacent to and on the end members  30  and  32 .  
         [0112]    The reader&#39;s 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.  
         [0113]    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.  
         [0114]    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.  
         [0115]    The invention is not restricted to the details of the foregoing embodiment(s). The invention extend 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.