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

Definitions

• the present invention relates to a method for making lithographic printing plates. More specifically the invention relates to a method using a heat-sensitive imaging element that requires no separate processing and that can be imaged on-press.
• Lithographic printing is the process of printing from specially prepared surfaces, some areas of which are capable of accepting ink, whereas other areas will not accept ink.
• a photographic material is made imagewise receptive to oily or greasy ink in the photo-exposed (negative working) or in the non-exposed areas (positive working) on a ink-repelling background.
• lithographic plates also called surface litho plates or planographic printing plates
• a support that has affinity to water or obtains such affinity by chemical treatment is coated with a thin layer of a photosensitive composition.
• Coatings for that purpose include light-sensitive polymer layers containing diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely used.
• the exposed image areas become insoluble and the unexposed areas remain soluble.
• the plate is then developed with a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.
• EP-A- 444 786, JP- 63-208036 ,and JP- 63-274592 disclose photopolymer resists that are sensitized to the near IR. So far, none has proved commercially viable and all require wet development to wash off the unexposed regions.
• EP-A- 514 145 describes a laser addressed plate in which heat generated by the laser exposure causes particles in the plate coating to melt and coalescence and hence change their solubility characteristics. Once again, wet development is required.
• EP-A- 652 483 discloses a lithographic printing plate requiring no dissolution processing which comprises a substrate bearing a heat-sensitive coating, which coating becomes relatively more hydrophilic under the action of heat Said system yields a positive working printing plate.
• EP-A- 609 941 describes a heat-mode recording material comprising on a substrate a metallic layer and a thin hydrophobic layer which becomes hydrophilic upon exposure. However the lithographic performance of the obtained printing plate is poor.
• EP-A- 770 495 discloses a heat-sensitive material and method for making lithographic printing plates that can be imaged on-press. However a wet processing step is required.
• lithographic printing plates comprising the steps of:
• the present invention also provides a method for making multiple copies of an original comprising the steps of:
• Metallic layers or metal oxide layers suitable for use in accordance with the invention comprise metals or metal oxides converting the actinic radiation to heat so that the oleophobicity of the oleophobic top-layer is destroyed.
• the thickness of the metallic layer or metal oxide layer is preferably from 0.01 ⁇ m to 2 ⁇ m, and most preferably from 0.05 ⁇ m to 1.5 ⁇ m.
• Specific examples of metal layers or metal oxide layers are aluminum, titanium oxide, bismuth and silver of which the latter three are preferred.
• a silver layer for use in this invention as the metallic layer can be made according to the principles of the silver complex diffusion transfer reversal process, hereinafter called DTR-process, having been described e.g. in US-P 2,352,014 and in the book “Photographic Silver Halide Diffusion Processes” by André Rott and Edith Weyde - The Focal Press - London and New York, (1972).
• DTR-process the silver complex diffusion transfer reversal process
• non-developed silver halide of an information-wise exposed photographic silver halide emulsion layer material is transformed with a so-called silver halide solvent into soluble silver complex compounds which are allowed to diffuse into an image-receiving element and are reduced therein with a developing agent, generally in the presence of physical development nuclei, to form a silver image having reversed image density values ('DTR-image') with respect to the black silver image obtained in the exposed areas of the photographic material.
• a developing agent generally in the presence of physical development nuclei
• a silver halide emulsion disposed on a hydrophilic substrate is strongly exposed to actinic radiation and then developed, or otherwise processed to maximum blackness.
• the black opaque emulsion is converted to a reflective recording material by heating at least to 270 °C in an oxygen containing environment until the emulsion coating assumes a shiny reflective appearance.
• Such method is disclosed in US-P-4 314 260 .
• the metal is provided using vapour or vacuum deposition.
• the metallic layer can be a bismuth layer that can be provided by vacuum deposition.
• a drawback of the method of preparation of a thin bismuth recording layer by vacuum deposition is the fact that this is a complicated, cumbersome and expensive process.
• a thin metal layer is formed by the following steps :
• a metal oxide layer preferably a titanium oxide layer is used. This layer can be applied to the substrate by vacuum deposition, electron-beam evaporation or sputtering.
• the oleophobic layer provided on top of the metallic layer or metal oxide layer preferably comprises of a polymer containing phenolic groups.
• Preferred polymers containing phenolic groups are phenolic resins (e.g. novolac) or hydroxyphenyl substituted polymers (e.g. polyhydroxystyrenes).
• the oleophobic layer has a thickness of less than 5 ⁇ m. As a consequence a highly sensitive heat-sensitive imaging element is obtained.
• the use of a polymer containing phenolic groups furthermore improves the lithographic performance ( ink acceptance, scratch resistance, durability) of the lithographic printing plates obtained according to the present invention.
• Suitable compounds preferably for a silver layer, to be used in the oleophobic layer are compounds which contain a mercapto or a thiolate group and one or more hydrophobic substituents e.g. an alkyl containing at least three carbon atoms.
• these compounds for use in accordance with the present invention are e.g. phenyl mercaptotetrazoles or those described in US-P- 3 776 728 and US-P- 4 563 410 .
• the most preferred compounds are described in EP-A 609 941 .and correspond to one of the following formulas: wherein R 5 represents hydrogen or an acyl group, R 4 represents alkyl, aryl or aralkyl. Most preferably used compounds are compounds according to one of the above formulas wherein R 4 represents an alkyl containing 3 to 16 C-atoms.
• the lithographic base comprises a flexible support, such as e.g. paper or plastic film, provided with a hardened hydrophilic layer.
• a particularly suitable hardened rough hydrophilic layer may be obtained from a hydrophilic binder hardened with a hardening agent such as formaldehyde, glyoxal, polyisocyanate or preferably a hydrolysed tetra-alkylorthosilicate.
• hydrophilic binder there may be used hydrophilic (co)polymers such as for example, homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.
• hydrophilic (co)polymers such as for example, homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.
• a hardened hydrophilic layer on a flexible support used in accordance with the present embodiment preferably also contains substances that increase the mechanical strength and the porosity of the layer e.g. colloidal silica.
• inert particles of larger size than the colloidal silica can be added e.g. silica prepared according to Stöber as described in J. Colloid and Interface Sci., Vol. 26, 1968, pages 62 to 69 or alumina particles or particles having an average diameter of at least 100 nm which are particles of titanium dioxide or other heavy metal oxides. Incorporation of these particles gives the surface of the hardened hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys.
• the thickness of the hardened hydrophilic layer may vary in the range of 0.2 to 25 ⁇ m and is preferably 1 to 10 ⁇ m.
• plastic film e.g. substrated polyethylene terephthalate film, cellulose acetate film, polystyrene film, polycarbonate film etc.
• the plastic film support may be opaque or transparent.
• the amount of silica in the adhesion improving layer is between 200 mg per m 2 and 750 mg per m 2 .
• the ratio of silica to hydrophilic binder is preferably more than 1 and the surface area of the colloidal silica is preferably at least 300 m 2 per gram, more preferably a surface area of 500 m 2 per gram.
• the heat-sensitive imaging material is mounted on the press and image-wise exposed.
• the printing press is then started and while the print cylinder with the imaging element mounted thereon rotates, the dampener rollers that supply dampening liquid are dropped on the imaging element and subsequent thereto the ink rollers are dropped.
• the dampener rollers that supply dampening liquid are dropped on the imaging element and subsequent thereto the ink rollers are dropped.
• the first clear and useful prints are obtained.
• the ink rollers and dampener rollers may be dropped simultaneously or the ink rollers may be dropped first.
• a dry or wet cleaning step is performed by applying brush rollers or rollers that supply plain water to avoid contamination of the dampening solution and ink.
• the printing plates of the present invention can also be used in the printing process as a seamless sleeve printing plate.
• This cylindrical printing plate wich has as diameter the diameter of the print cylinder is slided on the print cylinder instead of applying in a classical way a classically formed printing plate. More details on sleeves are given in 'Grafisch Nieuws' ed. Keesing, 15, 1995, page 4 to 6.
• the heat-sensitive imaging element is image-wise scanning exposed using a laser, preferably a laser that operates in the infrared or near-infrared, i.e. wavelenght rang of 700-1500nm.
• a laser preferably a laser that operates in the infrared or near-infrared, i.e. wavelenght rang of 700-1500nm.
• laser diodes emitting in the near-infrared.
• the laser used is a multibeam laser.
• This layer contained 82.7% of titaniumdioxide, 9.1% of polyvinylalcohol, 8.2% of hydrolysed tetramethylorthosilicate and 0.17 ⁇ of palladiumsulphide (particle size 2-3 nm).
• an emulsion layer and top layer were simultaneously coated by means of the cascade coating technique.
• the emulsion layer was coated with a wet thickness of 30 ⁇ m and such that the silver halide coverage expressed as AgNO 3 was 2.50 g/m 2 and the gelatin content was 1.50 g/m 2 .
• the toplayer was coated with a wet thickness of 15 ⁇ m such that the gelatin content was 0.7 g/m 2 .
• the top layer further contained 61 mg/m 2 of Levanyl Rot and 0.14 g/m 2 matting agent.
• the unexposed DTR material as described above was developed for 12s at 24 °C in an aqueous alkaline solution having the following ingredients: Anhydrous sodium sulphite 120 g Sodium hydroxide 22 g Carboxymethylcellulose 4 g Potassium bromide 0.75 g Anhydrous sodium thiosulphate 8 g Aluminum sulphate.18H 2 O 8 g Ethylene diamine tetraacetic acid tetrasodium salt 4.2 g Hydroquinone 20 g Methylfenidon 6.25 g Demineralized water to make 1L pH (25°C) > 12.5
• the initiated diffusion transfer was allowed to continue for 18 s to form a silver layer, whereafter the material was rinsed with water containing 0.03 ⁇ of trypsine at 50 °C.
• This material was imaged with an Isomet diode external drum platesetter at 3.2 m/s and 3600 dpi.
• the power level in the image plane was 253 mW.
• the plate was printed on a Heidelberg GTO46 printing machine with a conventional ink (Van Son rubberbase) and fountain solution (Rotamatic), by first applying dampening liquid to the surface of the imaging element by dropping the dampening rollers of the printing press and after 5 revolutions the ink rollers were dropped as well.
• the DTR material was prepared as described in example 1.
• the unexposed DTR material was developed for 12s at 24 °C in an aqueous alkaline solution as described in example 1.
• the initiated diffusion transfer was allowed to continue for 18 s to form a silver layer, whereafter the material was rinsed with water at 50 °C.
• the thus obtained metallic silver layer was coated with a novolac layer (2 g/m 2 Alvonol SPN452).
• This material was imaged with an Isomet diode external drum platesetter at 3.2 m/s and 3600 dpi.
• the power level in the image plane was 253 mW.
• the plate was printed on a Heidelberg GTO46 printing machine under more critical conditions than example 1 with a conventional ink (K+E) and a fountain solution of 5% G671c (commercialy available from Agfa-Gevaert N.V.) + 10% isopropanol, by first applying dampening liquid to the surface of the imaging element by dropping the dampening rollers of the printing press and after 5 revolutions the ink rollers were dropped as well.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)
• Printing Plates And Materials Therefor (AREA)

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Citations (4)

• 1999
  • 1999-01-18 EP EP99200197A patent/EP0934824A1/de not_active Withdrawn

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