Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N1/00—Printing plates or foils; Materials therefor
  • B41N1/04—Printing plates or foils; Materials therefor metallic
  • B41N1/08—Printing plates or foils; Materials therefor metallic for lithographic printing
  • B41N1/083—Printing plates or foils; Materials therefor metallic for lithographic printing made of aluminium or aluminium alloys or having such surface layers
• • 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
  • B41C1/1008—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by removal or destruction of lithographic material on the lithographic support, e.g. by laser or spark ablation; by the use of materials rendered soluble or insoluble by heat exposure, e.g. by heat produced from a light to heat transforming system; by on-the-press exposure or on-the-press development, e.g. by the fountain of photolithographic materials
  • B41C1/1033—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by removal or destruction of lithographic material on the lithographic support, e.g. by laser or spark ablation; by the use of materials rendered soluble or insoluble by heat exposure, e.g. by heat produced from a light to heat transforming system; by on-the-press exposure or on-the-press development, e.g. by the fountain of photolithographic materials by laser or spark ablation

Definitions

• This invention relates to the formation of images directly from electronically composed digital sources and is particularly concerned with the formation of images on lithographic printing plate precursors. More particularly, the invention relates to lithographic printing plate precursors which incorporate an imaging layer comprising metallic silver, and a method of preparing lithographic printing plates which does not require the use of chemical treatments.
• Lithographic printing is a process of printing from surfaces which have been prepared in such a way that certain areas are capable of accepting ink (oleophilic areas), whereas other areas will not accept ink (oleophobic areas).
• the oleophilic areas form the printing areas while the oleophobic areas form the background areas.
• Plates for use in lithographic printing processes may be prepared using a photographic material that is made imagewise receptive or repellent to ink upon photo-exposure of the photographic material and subsequent chemical treatment.
• this method of preparation which is based on photographic processing techniques, involves several steps, and therefore requires a considerable amount of time, effort and expense.
• Imaging systems are also available which involve a sandwich structure which, on exposure to a heat generating infra-red laser beam, undergoes selective (imagewise) delamination and subsequent transfer of materials.
• peel-apart systems are generally used as replacements for silver halide films.
• a digital imaging technique has been described in US Patent No 4911075 whereby a so-called driographic plate which does not require dampening with an aqueous fountain solution to wet the non-image areas during printing is produced by means of a spark discharge.
• a plate precursor comprising an ink-repellent coating containing electrically conductive particles coated on a conductive substrate is used and the coating is ablatively removed from the substrate.
• the ablative spark discharge provides images having relatively poor resolution.
• Coatings which may be imaged by means of ablation with infra-red radiation have previously been proposed.
• a proofing film in which an image is formed by imagewise ablation of a coloured layer on to a receiver sheet is described in PCT Application No 90/12342.
• This system is, however, disadvantageous in requiring a physical transfer of material in the imaging step, and such methods tend to give rise to inferior image resolution.
• a driographic printing plate precursor is imaged digitally by means of an infra-red diode laser or a YAG laser, and the image is formed directly through the elimination of unwanted material.
• the technique involves exposing a plate precursor, incorporating an infra-red radiation ablatable coating covered with a transparent cover sheet, by directing the beam from an infrared laser at sequential areas of the coating so that the coating ablates and loses its ink repellancy in those areas to form an image, removing the cover sheet and ablation products, and inking the image.
• a heat mode recording material is disclosed in US Patent No 4034183 which comprises an anodised aluminium support coated with a hydrophilic layer. On imagewise exposure using a laser, the exposed areas are rendered hydrophobic, and thereby accept ink.
• Japanese patent application laid open to public inspection No 49-117102 (1974) discloses a method for producing printing plates wherein a metal is incorporated in the imaging layer of a printing plate precursor which is imaged by irradiation with a laser beam modulated by electric signals.
• the plate precursor comprises a metal base, such as aluminium, coated with a resin film, which is typically nitrocellulose, and on top of which has been provided a thin layer of copper. The resin and metal layers are removed in the laser-struck areas, thereby producing a printing plate.
• a printing plate precursor comprising a support, typically aluminium, an anodic aluminium oxide layer, and a layer of brass, silver, graphite or, preferably, copper is exposed to a laser beam of high energy density in order to render the exposed areas hydrophilic to yield a printing plate.
• the printing plate precursor is, however, of rather low sensitivity and requires the use of a high energy laser for exposure.
• An alternative heat mode recording material for making a lithographic printing plate is disclosed in European Patent No 609941, which comprises a support having a hydrophilic surface, or provided with a hydrophilic layer, on which is coated a metallic layer, on top of which is a hydrophobic layer having a thickness of less than 50nm.
• a lithographic printing plate may be produced from the said material by imagewise exposing to actinic radiation, thereby rendering the exposed areas hydrophilic and repellent to greasy ink.
• European Patent No 628409 discloses a heat mode recording material for making a lithographic printing plate which comprises a support and a metallic layer, on top of which is provided a hydrophilic layer having a thickness of less than 50nm.
• a lithographic printing plate is produced by imagewise exposing the material to actinic radiation in order to render the exposed areas hydrophobic and receptive to greasy ink.
• difficulties in printing will be encountered.
• the energy is converted to heat in the image areas by interaction with the metallic layer, thereby destroying the hydrophilicity or hydrophobicity - depending on the material employed - of the topmost layer in those areas.
• the surface of the metallic layer becomes exposed, and the success of the printing operation is dependent upon differences in hydrophilicity and oleophilicity between the metallic surface and the hydrophilic or hydrophobic layer, as the case may be. Since the metallic layer functions as the hydrophobic surface in one case, and as the hydrophilic surface in the alternative case, it would be expected that such differences in hydrophilicity and oleophilicity would not be sufficiently clearly defined so as to provide a satisfactory printing surface. Furthermore, when a hydrophilic layer is present, and the metallic surface functions as the oleophilic areas of the plate, image areas will necessarily be printed from the metallic surface; such an arrangement is known to be unsatisfactory, and to result in difficulties in achieving acceptable printing quality.
• a high quality image results from the ablation of a metallic layer from a hydrophilic support, thus providing a high degree of differentiation between hydrophilic and oleophilic areas.
• further treatments to the plate surface are required in order to enhance the ink receptive properties of the metal surface in image areas and the hydrophilic properties of the exposed substrate, typically aluminium oxide, in the non-image areas.
• the metallic surface of the lithographic plate precursor is substantially free from other chemicals prior to exposure by a high intensity laser beam.
• the ablated debris produced on exposure, during which imagewise removal of the metal in non-image areas occurs comprises substantially the metal, and is free from other contaminants. As a consequence, collection of the debris is more easily achieved, and the level of environmental hazard is reduced.
• the exposed plate may be treated with various materials prior to use on the press in order to achieve improved press performance; in particular, it is often desirable to treat the plate such that the oleophilicity of the metallic image areas and the hydrophilicity of the non-image areas, comprising revealed substrate, is enhanced in order that good start-up and clean-up properties can be ensured.
• a method of preparing a lithographic printing plate comprising:
• the substrate employed in the present invention is an aluminium substrate which has been electrochemically grained and anodised on at least one surface in order to enhance its lithographic properties.
• the aluminium may be laminated to other materials, such as paper or various plastics materials, in order to enhance its flexibility, whilst retaining the good dimensional stability associated with aluminium.
• the metallic layer which is applied to the grained and anodised surface of the aluminium, may comprise any of several metals, specific examples of which include copper, bismuth and brass. Most preferably, however, the metallic layer comprises a silver layer.
• the thickness of the metallic layer is preferably from 20 nm to 200 nm most preferably from 40 nm to 100 nm.
• the metallic layer comprises a silver layer
• the most preferred method for applying the layer involves the treatment of a silver halide photographic material according to the silver salt diffusion transfer process.
• a silver halide emulsion layer is transformed, by treatment with a so-called silver halide solvent, into soluble silver complex compounds which are then allowed to diffuse into an image receiving layer and are reduced therein by means of a developing agent, generally in the presence of physical development nuclei, to form a metallic silver layer.
• Two such systems are available: a two sheet system in which a silver halide emulsion layer is provided on one element, and a physical development nuclei layer is provided on a second element, the two elements are placed in contact in the presence of developing agent(s) and silver halide solvent(s) in the presence of an alkaline processing liquid, and subsequently peeled apart to provide a metallic silver layer on the second element; and a single sheet system wherein the element is provided with a physical development nuclei layer, a silver halide emulsion layer is provided on top thereof, the element is treated with developing agent(s) and silver halide solvent(s) in the presence of an alkaline processing liquid, and the element is washed to remove spent emulsion layer and leave a metallic silver layer which is formed in the layer containing physical development nuclei.
• the diffusion transfer process may be used to apply a metallic silver layer by overall exposing a positive working silver halide emulsion layer to form a latent negative image which is then developed in contact with a physical development nuclei layer to form a metallic silver layer.
• the process may be carried out using either a single sheet or a double sheet system.
• the precursor is imaged by a beam of radiation, preferably from a laser operating in the infra-red region of the spectrum.
• suitable infra-red lasers include semiconductor lasers and YAG lasers, for example the Gerber Crescent 42T Platesetter with a 10W YAG laser outputting at 1064 nm.
• Exposure to the beam of radiation causes ablation of the metallic layer to occur in the radiation-struck areas.
• the plate is treated with a composition comprising materials which enhance the oleophilic character of the metal forming the image areas and also improve the hydrophilic nature of the exposed anodic aluminium oxide layer comprising the non-image areas.
• Typical components would include enzymes, oleophilic agents and desensitising compounds. Additional components, having a beneficial effect on other aspects of plate performance, may also be included, for example, storage gums and surfactants; other typical ingredients could include pH buffering agents and biocides.
• the compositions comprise aqueous solutions of the various components.
• Suitable enzymes which may be incorporated in the finishing compositions utilised in the present invention include proteolytic enzymes such as trypsin, pepsin, ficin, papain or the bacterial proteases or proteinases.
• the enzyme is generally present in the composition in an amount of from 0.1% to 10.0% by weight.
• oleophilising agents are suitable for use in the present invention and, in particular, the materials disclosed on pages 105 to 106 of "Photographic Silver Halide Diffusion Processes" by Andre Rott and Edith Weyde find such application.
• mercapto compounds and cationic surfactants such as quaternary ammonium compounds are of especial value.
• Such materials are generally present at a level of from 0.05% to 5.0% by weight of the total composition.
• desensitising agents are of value in the finishing compositions finding application in the method of the present invention, with carbohydrates such as gum arabic, dextrin and inorganic polyphosphates such as sodium hexametaphosphate being particularly effective in ensuring that background areas remain free from contamination.
• the desensitisers are typically incorporated in the finishing compositions at a level of from 1.0% to 10.0% by weight.
• the method of the present invention also provides press ready plates showing high image quality, good press properties and high durability on press without the requirement for the use of costly intermediate film and developer chemistry and the attendant inconvenience resulting from the use of these materials.
• Alcalase ® 2.5L is a proprietary bacterial protease.
• the printing plate precursors were separately loaded on to a Gerber Crescent 42T Platesetter and fully (blanketwise) exposed to a 10 W YAG laser outputting at a wavelength of 1064 nm and peak power density of 6.5% mW/cm 2 .
• the debris and pyrolysis products generated on exposure were collected and analysed. In each case, silver was recovered, with the following materials also being detected:

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

Applications Claiming Priority (3)

Publications (1)

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• 1997
  • 1997-06-03 GB GBGB9711392.2A patent/GB9711392D0/en active Pending
• 1998
  • 1998-06-03 JP JP50158999A patent/JP2002508717A/ja active Pending
  • 1998-06-03 GB GB9811833A patent/GB2325890A/en not_active Withdrawn
  • 1998-06-03 WO PCT/EP1998/003480 patent/WO1998055331A1/en not_active Application Discontinuation
  • 1998-06-03 EP EP98929438A patent/EP0986484A1/de not_active Withdrawn

Non-Patent Citations (1)

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