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
  • B41C1/1041—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by modification of the lithographic properties without removal or addition of material, e.g. by the mere generation of a lithographic pattern
• • 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

• Lithographic printing is the process of printing from specially prepared surfaces, which contain a lithographic image consisting of areas that are capable of accepting ink (oleophilic areas) and areas that do not accept ink but are water-accepting (hydrophilic areas).
• a lithographic image consisting of areas that are capable of accepting ink (oleophilic areas) and areas that do not accept ink but are water-accepting (hydrophilic areas).
• wet lithographic printing methods both water or an aqueous dampening liquid (also called fountain solution) and ink are applied to the plate surface that contains the hydrophilic and oleophilic areas.
• the hydrophilic areas are soaked with water or the dampening liquid and are thereby rendered oleophobic.
• DE-A-2 448 325 discloses a laser heat-mode 'direct negative' printing plate comprising e.g. a polyester film support provided with a hydrophilic surface layer.
• the disclosed heat-mode recording material is imaged using an Argon laser thereby rendering the exposed areas oleophilic.
• An offset printing plate is thus obtained which can be used on an printing press without further processing.
• the plate is called a 'direct negative' plate because it is suitable for direct exposure by a laser beam ("computer-to-plate", no film mask required) and because the areas of the recording material that have been exposed to the laser are rendered ink-accepting and define the image areas, i.e. the printing areas.
• EP-A-580 393 discloses an ablative lithographic printing plate directly imageable by laser discharge, the plate comprising a topmost first layer and a second layer underlying the first layer wherein the first layer is characterized by efficient absorption of infrared radiation and the first and second layer exhibit different affinities for at least one printing liquid.
• This object is realized by the material defined in claim 1. Preferred embodiments thereof are defined in the dependent claims.
• said organic compound comprises an organic radical corresponding to one of the following formula : R1-(O) n -PO 3 A 2 R2-(O) n -SO 3 A wherein n is 0 or 1 and A is hydrogen, a counter ion or an alkyl group.
• a groups can have any of the latter meanings independently from one another or can together represent a divalent counter ion or an alkylene group.
• R1 and R2 are an organic radical.
• R1 can be a low molecular or a macromolecular radical.
• R2 is a macromolecular organic radical.
• Briquest 3010-25K ([(oxidonitrilo)tris(methylene)]tris-Phosphonic acid, potassium salt)
• Briquest 281-25S ([[(2-ethylhexyl)imino]bis(methylene)]bis-Phosphonic acid, sodium salt)
• Briquest 422-33N [1,2-ethanediylbis[nitrilobis(methylene)]]-tetrakis-Phosphonic acidtetraammonium salt
• Briquest 785 ([[(phosphonomethyl)-imino]bis[2,1-ethanediyl[(phosphonomethyl)-imino]-2,1-ethanediylnitrilobis(methylene)]] Phosphonic acid, tetrakis-, sodium salt)
• Briquest ADPA 60AW ((1-hydroxyethylidene)-bis-Phosphonic acid, potassium salt)
• Briquest 221 [[[bis[
• the lithographic base may be an anodized aluminum support.
• a particularly preferred lithographic base is an electrochemically grained and anodized aluminum support.
• the anodized aluminum support may be treated to improve the hydrophilic properties of its surface.
• the aluminum support may be silicated by treating its surface with a sodium silicate solution at elevated temperature, e.g. 95°C.
• a phosphate treatment may be applied which involves treating the aluminum oxide surface with a phosphate solution that may further contain an inorganic fluoride.
• the aluminum oxide surface may be rinsed with a citric acid or citrate solution. This treatment may be carried out at room temperature or may be carried out at a slightly elevated temperature of about 30 to 50°C.
• the lithographic base can also be a flexible support, which is provided with a hydrophilic layer, hereinafter called 'base layer'.
• the flexible support is e.g. paper, plastic film or aluminum.
• the base layer is preferably a cross-linked hydrophilic layer obtained from a hydrophilic binder cross-linked with a hardening agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolyzed tetra-alkylorthosilicate. The latter is particularly preferred.
• the hydrophilic binder for use in the base layer is e.g. a hydrophilic (co)polymer such as homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylate acid, methacrylate acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.
• the hydrophilicity of the (co)polymer or (co)polymer mixture used is preferably the same as or higher than the hydrophilicity of polyvinyl acetate hydrolyzed to at least an extent of 60% by weight, preferably 80% by weight.
• the heat-sensitive imaging material can be covered with an additional hydrophilic layer, provided on top of the hydrophilic upper layer discussed above, which comprises an organic compound containing cationic groups as described in EP-A no. 99202110, filed on 29.06.99.
• a preferred additional wet processing step is a gumming step as is commonly used for conventional plates.
• a gumming step is normally not regarded as a processing step, but rather as a treatment which protects the hydrophilic areas from fingerprints or other contamination which may affect the water-acceptance of these areas. Upon gumming the remaining ablation dust on the plate is removed thereby avoiding contamination of the press. At the same time the hydrophilic areas are covered with a thin layer of the gumming solution inducing a better start-up performance.
• Image-wise exposure in connection with the present invention is preferably an image-wise scanning exposure involving the use of a laser or L.E.D.
• lasers are used that operate in the infrared or near-infrared, i.e. wavelength range of 700-1500 nm.
• laser diodes emitting in the near-infrared with an intensity higher than 0.1 mW/ ⁇ m 2 .
• the plate is then ready for printing without an additional development and can be mounted on the printing press.
• a 0.30 mm thick aluminum foil was degreased by immersing the foil in an aqueous solution containing 5 g/l of sodium hydroxide at 50°C and rinsed with demineralized water.
• the foil was then electrochemically grained using an alternating current in an aqueous solution containing 4 g/l of hydrochloric acid, 4 g/l of hydroboric acid and 5 g/l of aluminum ions at a temperature of 35°C and a current density of 1200 A/m 2 to form a surface topography with an average center-line roughness Ra of 0.5 ⁇ m.
• the aluminum foil was etched with an aqueous solution containing 300 g/l of sulfuric acid at 60°C for 180 seconds and rinsed with demineralized water at 25°C for 30 seconds.
• the imaging layer was coated on the lithographic base at a wet coating thickness of 20 ⁇ m from a solution having the following composition:
• the materials 1-3 were prepared in an identical way as the comparative material described above with the proviso that polymers having sulfonic acid or phosphonic acid pendant groups have been added to the coating solution of the hydrophilic upper layer. The details are given in table 1.
• the materials 8 and 9 were prepared in an identical way as the reference material with the proviso that polymers which contain a sulfonic acid pendant group or the salt thereof were added to the solution of the hydrophilic layer resulting in a layer composition as shown in table 3.
• the exposure, printing and evaluation method was the same as used in the above examples 1-3.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Printing Plates And Materials Therefor (AREA)

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Citations (3)

• 2001
  • 2001-10-18 EP EP01000543A patent/EP1208974B1/fr not_active Expired - Lifetime

Patent Citations (3)

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