Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F27/00—Devices for attaching printing elements or formes to supports
  • B41F27/12—Devices for attaching printing elements or formes to supports for attaching flexible printing formes
  • B41F27/1212—Devices for attaching printing elements or formes to supports for attaching flexible printing formes using pneumatic force
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41P—INDEXING SCHEME RELATING TO PRINTING, LINING MACHINES, TYPEWRITERS, AND TO STAMPS
  • B41P2227/00—Mounting or handling printing plates; Forming printing surfaces in situ
  • B41P2227/60—Devices for transferring printing plates
  • B41P2227/63—Devices for removing printing plates

Definitions

• the present invention relates to a method of releasing a seal formed between a used printing plate and a surface of a plate cylinder of a printing press prior to removal of said printing plate from said surface so as to facilitate the removal of said plate.
• the invention also relates to apparatus for achieving the method of the invention and to a printing press comprising said apparatus.
• a web offset printing press comprises a number of printing units. Each unit is designed to print matter onto a continuous web of paper as it travels through the print unit. The printed web, emerging from each print unit, come together in a folding unit which orientates, folds and cuts each web to produce the finished article such as a newspaper or magazine.
• Each unit contains at least one pair of cylinder groups or print couples comprising a rotatably mounted plate cylinder, to which one or more printing plates are attached for printing and, a rotatably mounted blanket cylinder.
• the printing unit may incorporate a shaft less drive system in which each cylinder group is driven by its own drive motor that directly drives one of the cylinders of a group via a belt or gear drive and the other cylinder of that group is mechanically coupled to the driven cylinder.
• An inking system associated with each print couple is operable to feed ink onto the printing plates attached to the plate cylinder as the plate cylinder rotates. As the cylindrical surfaces of the plate and blanket cylinder are in rolling contact, an inked image is transferred from the printing plates onto the blanket cylinder and from the blanket cylinder onto the medium to be printed.
• multi-colour printing is achieved by providing each print unit with a number of printing couples arranged in pairs which are mounted vertically above one another in a stack so that the paper web travels in a vertically upward direction between each pair of print couples.
• a unit having four print couple pairs, i.e. eight print couples, is able to print up to four colours on each side of the paper web and is often referred to as a "four-high" unit.
• each plate cylinder includes at least one recess or lock-up slot extending longitudinally along the surface of the plate cylinder into which is received the leading and trailing edge of a printing plate.
• a mechanism located in the recess engages the leading and trailing edges of an inserted printing plate and firmly holds the printing plate in position during a print run.
• the number of printing plates that must be attached to the plate cylinder of each print couple depends on the width of the press and whether the plate cylinder carries one or two printing plates around its circumference, i.e. whether it is a "one around" or "two around” plate cylinder.
• the plate cylinder may carry four printing plates across its width and one printing plate extending circumferentially around its cylindrical surface. Therefore, there could be as many as eight printing plates in a single printing couple pair and thirty-two printing plates in a four high printing unit all of which must be replaced before a new print run can be initiated.
• the plate cylinder is of the "two-around" type, the number of printing plates is doubled accordingly. Therefore, it will be appreciated that even in the production of just one newspaper issue, a very large number of printing plates will be required.
• Printing plates tend to adhere to a plate cylinder, especially when they have been bedded down onto the plate cylinder by printing pressures applied to it during a print run. This is largely because a solution of water and gum arabic is applied to both front (printing surface) and back surfaces of the plate to form a protective film that remains in-situ after the water has evaporated.
• the gum arabic prevents oxidation of the aluminium printing plate in the interval between the processing of the plate and its use on the printing press.
• the gum arabic film remaining on the back of the printing plate acts as a mild adhesive that sticks or seals the printing plate to the surface of the plate cylinder.
• the force which the press operator must apply to the plate gripping element to pull a printing plate off the plate cylinder may be excessive and/or beyond his ability.
• the force required may exceed the force generated between the plate gripping element and the surface of the plate cylinder causing the grip to be broken without lifting the printing plate.
• the gripping force applied must be high, otherwise they simply detach from die plate when the plate loading head is lifted.
• the present invention seeks to provide a method and apparatus that substantially overcomes or alleviates the problems discussed above and enables easier and faster removal of printing plates from the surface of a plate cylinder of a printing press.
• a method of releasing a seal formed between a used printing plate and a curved surface of a plate cylinder of a printing press to facilitate removal of said printing plate from said surface including the step of directing a jet of compressed air towards the surface of the plate cylinder adjacent to an edge of a printing plate mounted on said cylinder.
• the edge of the printing plate is preferably the longer edge that extends in a circumferential direction around the curved surface of the plate cylinder.
• the method includes the step of directing said jet of compressed air towards the surface of the plate cylinder between edges of adjacent printing plates.
• the plate cylinder may have a trailing edge lock-up slot in which is received the trailing edge of a printing plate, and the method preferably includes the step of directing said jet of compressed air towards the surface of the plate cylinder between adjacent printing plates at location circumferentially spaced away from said trailing edge lock-up slot.
• the method includes the step of directing the jet of compressed air in a direction towards the plate cylinder at an angle which is substantially perpendicular to the axis of the plate cylinder.
• the method includes the step of directing the jet of compressed air in a direction towards the plate cylinder at an angle which is between 0 and 90 degrees to the axis of the plate cylinder.
• the method may involve directing multiple pulses of compressed air towards the surface of the plate cylinder.
• the printing press comprises a plate removal apparatus and at least one nozzle mounted to the plate removal apparatus connected to a supply of compressed air through which the jet is emitted.
• the method may include the step of moving the plate removal apparatus into a position in which the or each nozzle is positioned above the surface of the plate cylinder between adjacent printing plates.
• the plate removal apparatus may comprise a plurality of plate gripping elements movable into contact with the surface of a printing plate to be removed from the plate cylinder. If so, the method preferably includes the step of directing a jet of compressed air towards the surface of the plate cylinder between adjacent printing plates prior to moving said plate gripping elements into contact with the surface of a printing plate.
• the method may then include the step of firing said nozzles consecutively or simultaneously.
• the method may include the step of directing a jet of compressed air towards the surface of a plate cylinder for a controlled period of time of typically one second or less.
• apparatus for releasing a seal formed between a used printing plate and a surface of a plate cylinder of a printing press to facilitate removal of said printing plate from said surface comprising a nozzle for directing a jet of compressed air towards the surface of a plate cylinder adjacent to an edge of a printing plate.
• said edge of the printing plate is an edge that extends in a circumferential direction around the curved surface of the plate cylinder.
• the nozzle is configured to direct said jet of compressed air towards the surface of the plate cylinder between edges of adjacent printing plates.
• the plate cylinder has a trailing edge lock-up slot in which is received the trailing edge of a printing plate, the nozzle being positioned relative to a plate cylinder so as to direct a jet of compressed air towards the surface of said plate cylinder between adjacent printing plates at location circumferentially spaced away from said trailing edge lock-up slot.
• the nozzle may be configured to direct a jet of compressed air in a direction towards a plate cylinder at an angle, said angle being substantially perpendicular to the axis of said plate cylinder.
• the apparatus may include means to control the nozzle to direct multiple pulses of compressed air towards the surface of a plate cylinder.
• a printing press comprising apparatus for releasing a printing plate according to the invention.
• the printing press can include a plate cylinder and apparatus for removing printing plates from said plate cylinder, the nozzle being mounted to the plate removal apparatus such that the nozzle is moved into a position in which the or each noz2le is positioned above the surface of the plate cylinder between adjacent printing plates when the plate removal apparatus is moved into a plate removal position adjacent to a plate cylinder of the printing press.
• the plate removal apparatus comprises a plurality of printing plate gripping elements movable into contact with the surface of a printing plate to be removed from the plate cylinder after a jet of compressed air has been directed towards the surface of the plate cylinder between adjacent printing plates.
• the printing press may comprise multiple nozzles mounted to the plate removal apparatus, each nozzle being located above the plate cylinder between adjacent printing plates when the plate removal head is moved into a plate removal position above the plate cylinder.
• the plate cylinder comprises a groove or scalloped surface that extends from beneath a printing plate towards an adjacent printing plate mounted on said plate cylinder, said groove being configured to direct the jet of compressed air from said nozzle under the printing plate that extends over said groove.
• FIGURE 1 illustrates a side sectional view of a printing plate unloading head disposed above the surface of a plate cylinder of a printing press to which a printing plate is mounted;
• FIGURE 2 illustrates a top view of the plate cylinder shown in Figure 1 having four printing plates mounted thereto in side-by-side relation, but with the plate loading head omitted;
• FIGURE 3 illustrates a section along line X-X in Figure 2;
• FIGURE 4 illustrates an alternative section, showing a modified plate cylinder, along line X-X in Figure 2; and FIGURE 5 illustrates a section along line X-X of Figure 2 using angled compressed air nozzles.
• FIG. 1 a portion of a plate cylinder 1 and blanket cylinder 2 forming a single print couple of a printing unit which is equipped with an automatic plate removal apparatus comprising a plate removal head 3 that extends across the width of the plate cylinder 1.
• an automatic plate removal apparatus comprising a plate removal head 3 that extends across the width of the plate cylinder 1.
• the plate removal head 3 may also be used in an automatic or semi-automatic plate loading procedure to mount unused printing plates in position on the plate cylinder of the press prior to initiation of a print run.
• the plate removal head 3 can be moved using compressed air between a raised position, in which it is spaced away from the plate cylinder 1 when no plate unloading or loading operations are being performed and the printing unit is in use and, a lowered position for carrying out printing plate loading or unloading operations on the plate cylinder 1.
• the plate removal head 3 includes an elongate support frame 5 that extends substantially across the entire width of the plate cylinder 1.
• An array of plate gripping elements 6 are mounted to and depend from the support frame 5 so as to face the curved cylindrical surface Ia of the plate cylinder 1.
• the plate gripping elements 6 When the plate gripping elements 6 are activated, they are operable to engage the surface of a printing plate 7, or set of printing plates 7 placed side-by-side across the width of the plate cylinder 1 (see Figure 2), to enable the printing plates 7 to be manipulated by the plate removal head 3.
• the plate removal head 3 may also include a pusher element 8 that is independently movable relative to the support frame 5 and to the plate gripping elements 6 in a direction towards and away from the surface Ia of the plate cylinder 1.
• the pusher element 8 is generally only used in a plate loading procedure and so no further reference to it will be made here.
• a printing plate 7, or a set of printing plates 7, such as those shown in side-by- side relation in Figure 2 are to be removed from the plate cylinder 1
• the plate cylinder 1 is indexed into a position in which the trailing edges 7a of the printing plates 7 are proximal to the plate removal head 3. This preferred position is as shown in Figure 1.
• the plate removal head 3 is lowered so that the plate gripping elements 6 contact the surface of the printing plates 7 adjacent to their trailing edges 7a and the plate gripping elements 6 are then activated to grip the printing plates 7.
• the plate removal head 3 is then lifted (in the direction of arrow "X" in Figure 1), with the intention of pulling or lifting the printing plates 7 off the surface Ia of the plate cylinder 1 and the trailing edges 7a of the printing plates 7 out of their lock-up slot 9 in the plate cylinder 1.
• the plate gripping elements 6 instead of lifting the entire print head 3, it is also possible for the plate gripping elements 6 to be retractably mounted to the print head 3 so that they retract relative to the print head 3 to lift the trailing edges 7a of the printing plates 7 out of the lock-up slot 9.
• the plate cylinder 1 is rotated (in the direction of arrow "Y" in Figure 1) until the leading edge (not shown) is located beneath the plate removal head 3 for removal, or at least partial removal, of said leading edge using the suction elements 6. If the leading edge is only partially removed from its lock up slot, the plate cylinder 1 is rotated once again so that the leading edge is fully removed from its lock up slot by a plate extraction element (not shown) that contacts the partially removed leading edge as the plate cylinder 1 rotates and leaves the printing plates 7 hanging by their leading edges on the extraction element.
• the plate loading head 3 is provided with a number of compressed air nozzles 10 spaced along its length (only one of which is shown in Figure 1). These nozzles 10 are located on the plate removal head 3 so that, when the plate cylinder 1 has been indexed into its trailing edge loading position, as shown in Figure 1, the compressed air nozzles 10 are positioned directly above the circumferentially extending long edges 7b of two adjacent printing plates 7 close to, but preferably not directly above the trailing edge lock-up slot 9. Ideally, the nozzles 10 are spaced in a circumferential direction away from the trailing edge 7a of the plates 7 by a short distance in the region of between 30 to 200mm.
• a jet of compressed air (indicated by "J" in Figure 1) is emitted from the nozzles 10 towards the printing plates 7 and impinges on the surface Ia of the plate cylinder 1 directly between the long edges 7b of the plates 1. It has been found that a short blast of compressed air directed towards the plate cylinder 1 in this way has the effect of breaking the seal between each adjacent plates 7 and the plate cylinder surface Ia caused by, for example, the presence of arabic gum and/or a vacuum caused by bedding down of the plates 7 onto the surface Ia of the plate cylinder 1.
• the compressed air jet need only last a fraction of a second to fulfil its purpose of loosening the plates 7 so that, when the plate gripping elements 6 are subsequently activated, they can easily lift the plates 7 off the surface Ia of the plate cylinder 1 and draw the trailing edges 7a out of their lock-up slots 9.
• compressed air it is envisaged that compressed air will be used, it is also possible that some other compressed gas could be fired from the nozzles 10 instead. It is also possible to direct a jet of compressed air into the lock-up slot, rather than towards the plate cylinder at an orientation spaced from the lock-up slot.
• Figure 2 shows a plan view of the plate cylinder 1 shown in Figure 1, but with the plate loading head 3 omitted for clarity.
• the nozzles 10 are positioned such that the air jet "J" impinges the plate cylinder 1 between adjacent plates 7 at the points marked "A". It has been found that, in a press having four printing plates 7 extending in side-by-side relation across the width of the plate cylinder 1, two nozzles 10, positioned with one between the two left hand plates and one between the two right hand plates, as shown in Figure 2, is sufficient to break the seal between each printing plate 7 and the plate cylinder 1, although it will be appreciated that any number of nozzles 10 may be employed.
• the effectiveness of the air jet can be improved if small grooves or scallops 12 are formed in the surface of the plate cylinder 1 to re-direct the air jet up against the underside of the printing plates 7, as shown by arrows "E" in Figure 4.
• the air jet is suff ⁇ cent to release the plates even if no modification to the plate cylinder 1 is made.
• an air jet positioned as described above, so as to be close to one corner of each of two adjacent plates 7 is sufficient to achieve the desired release of the plates 7 from the surface of the plate cylinder 1.
• an operator may simply pass a compressed air hose across the surface of the printing plates 7 so that a jet of compressed air is directed in roughly the same place as the jet of air emitted from the nozzle 10 attached to the plate removal head 3, prior to placing a plate gripping elements 6 on each printing plate 7 and pulling the plate off the surface of the plate cylinder 1.
• the jet of compressed air will be fired in a substantially radial direction towards the surface of the plate cylinder and printing plates, i.e. so that the air jet impinges at an angle of substantially 90 degrees to the surface of the plate cylinder 1 immediately below the nozzle 10, as shown in Figures 3 and 4, it is possible for the nozzles 10 to be angled so that the air jet impinges against the surface at an angle of less than 90 degrees, as shown in Figure 5. If the nozzles 10 are angled in this way, the jet is more closely directed towards the edge of a printing plate 7 where it meets the surface of the plate cylinder 1. However, it will be appreciated that a second nozzle 10 is then required which is angled towards the edge of the adjacent printing plate 7, when an automatic plate removal apparatus is used.

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• Supply, Installation And Extraction Of Printed Sheets Or Plates (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

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ID=39284652

Family Applications (1)

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Citations (5)

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• 2008
  • 2008-02-27 GB GB0803577A patent/GB2457902A/en not_active Withdrawn
• 2009
  • 2009-02-27 CN CN2009801065424A patent/CN101970234A/zh active Pending
  • 2009-02-27 EP EP09714455A patent/EP2282892A1/en not_active Withdrawn
  • 2009-02-27 JP JP2010548122A patent/JP2011513091A/ja active Pending
  • 2009-02-27 WO PCT/EP2009/052368 patent/WO2009106614A1/en active Application Filing

Patent Citations (5)

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