Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
  • B41C1/1066—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by spraying with powders, by using a nozzle, e.g. an ink jet system, by fusing a previously coated powder, e.g. with a laser
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C1/00—Forme preparation
  • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme

Definitions

• Rotary printing presses use a so-called master such as a printing plate which is mounted on a cylinder of the printing press.
• the master carries an image which is defined by the ink accepting areas of the printing surface and a print is obtained by applying ink to said surface and then transferring the ink from the master onto a substrate, which is typically a paper substrate.
• ink as well as an aqueous fountain solution are fed to the printing surface of the master, which is referred to herein as lithographic surface and consists of oleophilic (or hydrophobic, i.e. ink accepting, water repelling) areas as well as hydrophilic (or oleophobic, i.e. water accepting, ink repelling) areas.
• EP-A 786 337 describes a method wherein dry powder, especially toner, is applied to a support.
• the dry powder is then molten image-wise and removed at non-exposed areas by a mechanical or electrostatic processing device.
• the latter step is necessary because the exposure does not convert the powder from a hydrophilic to an oleophilic state (or vice-versa) but only changes the adherence of the powder to the support by melting said powder.
• a processing device is difficult to implement in a printing press.
• the materials made by the method of the present invention require no processing or can be processed by applying plain water, ink or fountain. Since it is a dry coating method, the method of the present invention is very suitable for computer-to-press applications and on-press coating procedures. Another major benefit of the materials made according to the present invention is the excellent stability : they can be stored during 2 minutes at 100°C without toning (accepting ink in non-exposed areas), contrary to conventional thermal lithographic printing plate precursors which show significant toning when exposed to the above conditions. Some materials made according to the present invention, especially those comprising carbon as a light absorbing compound, can even be stored during 2 minutes at 150°C without noticeable toning.
• the feature "negative working” may be considered as an equivalent of the feature “non-ablative", since in ablative materials the functional layers are completely removed from the underlying (hydrophilic) metal support upon image-wise exposure so as to obtain a positive image (exposed areas are hydrophilic, ink repelling).
• exposed areas are hydrophilic, ink repelling.
• Analysis of the exposed areas of the material made according to the method of the present invention indeed showed that the layer or stack of layers is not or only partially removed upon image-wise exposure but, instead, is converted into a hydrophobic surface on the metal support.
• the unexposed areas are hydrophilic or become hydrophilic after processing with plain water, ink or fountain.
• the exposed areas are oleophilic and form the printing areas of the printing master.
• the dry powder used in the present invention may further comprise non-reactive compounds, i.e. inert components such as e.g. a binder, a matting agent or a filler.
• inert components such as e.g. a binder, a matting agent or a filler.
• inert components such as e.g. a binder, a matting agent or a filler.
• inert components i.e. a binder, a matting agent or a filler.
• inert components such as e.g. a binder, a matting agent or a filler.
• inert components such as e.g. a binder, a matting agent or a filler.
• inert components such as e.g. a binder, a matting agent or a filler.
• inert components such as e.g. a binder, a matting agent or a filler.
• hydrophilic binders e.g. carboxymethyl cellulose, homopolymers and copolymers of vinyl pyrrolidone, vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.
• the amount of hydrophilic binder in the layer applied on the metal support is preferably less than 40% by weight and more preferably between 5 and 20% by weight.
• an anodised aluminium support provided with a 0.1 ⁇ m layer consisting of finely divided carbon particles, which was then cleaned by wiping thoroughly with a dry cloth and image-wise exposed with an infrared laser, still provides an excellent printing master.
• the latter example shows that it may be sufficient to fill the pores present in an anodised aluminium support with light absorbing powder in order to obtain a material having the benefits of the present invention.
• a metal support can be applied with a dry powder by rubbing in the surface of said support with a light absorbing compound, e.g. carbon or an organic dye.
• a light absorbing compound e.g. carbon or an organic dye.
• Alternative dry coating methods can also be used, e.g. sputter-coating of carbon on the metal support or direct electrostatic printing (toner jet).
• the latter technique can be used to apply the dry powder image-wise on a metal support and after intense overall heating, e.g. by infrared laser exposure, a printing master is obtained.
• Said infrared laser can be mounted on the same carriage as the direct electrostatic printing head.
• the method of the present invention can be used in computer-to-plate (off-press exposure) or computer-to-press (on-press exposure) procedures.
• the method may also involve on-press coating, i.e. applying a dry powder according to the present invention directly on the metal surface of a cylinder of a rotary printing press.
• Said on-press coating can also be performed indirectly by applying the dry powder on a metal support which is mounted on a cylinder of a rotary printing press.
• said composition can be applied on a metal sleeve which, after image-wise exposure and optional processing, is then transferred to a cylinder of a rotary printing press.
• the dry powder may also be applied on the metal support by contacting the surface of said support with another material, which carries a dry layer containing a light absorbing compound which is then transferred to the metal support.
• the method of this embodiment can be automated easily, e.g. by incorporating a supply roll of such a transfer material, such as a ribbon impregnated with light absorbing compound, in a print station of a digital press similar to the configuration which is described EP-A 698 488.
• the transfer material can be unwound from said supply roll and the layer containing the light absorbing compound can then be brought in direct contact with the surface of a plate cylinder by one or more contact rollers.
• the whole surface of said cylinder passes the dry coating unit and a layer is coated along a spiral path around the cylinder. Since the laser exposure unit moves together with the dry coating unit, an area which has been coated during one revolution of the cylinder is exposed by the laser exposure unit a number of revolutions later, i.e. coating and image-wise exposing can be carried out almost simultaneously during the same scan procedure.
• the materials made according to the present invention can be exposed to light by a light emitting diode or a laser such as a He/Ne or Ar laser.
• a laser emitting near infrared light having a wavelength in the range from about 700 to about 1500 nm is used, e.g. a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser.
• the required laser power depends on the pixel dwell time of the laser beam, which is determined by the spot diameter (typical value of modern plate-setters at 1/e 2 of maximum intensity : 10-25 ⁇ m), the scan speed and the resolution (i.e.
• ITD image-setters are typically characterised by very high scan speeds up to 500 m/sec and may require a laser power of several Watts. Satisfactory results have also been obtained by using XTD image-setters having a typical laser power from 100 mW to 500 mW at a lower scan speed, e.g. from 0.1 to 10 m/sec.
• post-bake i.e. an overall heating treatment after image-wise exposure and optional processing so as to increase the run length of the plate.
• the materials made according to the present invention allow to achieve satisfactory run lengths without a post-bake.
• anodised aluminium support was covered with a soot layer by contacting said surface with the flame of a Bunsen burner fed with natural gas. After coating the whole support, the layer was rubbed off with a dry cloth so as to obtain a uniform thin layer of soot.
• the plate precursor thus obtained was image-wise exposed with a Nd:YLF (1060 nm) external drum (XTD) laser having a power of 738 mW and a scan speed of 80 m/sec.
• the plate was mounted on the cylinder of an AB Dick 360 (trade name) printing press and cleaned with a sponge that was moistened with plain water.
• a print job of 25000 copies was started using Rubber Base Plus VS2329 Universal Black ink, trade name of Van Son, and Tame EC 7035 fountain, trade name of Anchor, the latter diluted with water 50-fold. The print quality was very good throughout the press run.
• Cpd 2, Cpd 3, Cpd 10 and Cpd 11 were each rubbed in as a dry powder on the surface of an anodised aluminium plate.
• the four materials thus obtained were image-wise exposed with a XTD laser diode (830 nm) with a power of 60 or 80 mW and a scan speed of 1, 2 or 4 m/sec (six combinations exposed at different areas of each plate).
• the plates were used as a master in a print job using the same press, ink and fountain as in Example 1. All masters provided good printing results over the whole area of the plate.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Manufacture Or Reproduction Of Printing Formes (AREA)
• Printing Plates And Materials Therefor (AREA)

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Cited By (3)

Citations (5)

• 1999
  • 1999-06-23 EP EP19990202010 patent/EP0974455B1/de not_active Expired - Lifetime

Patent Citations (5)

Non-Patent Citations (1)

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