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
  • B41C1/1008—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
• • 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
• • 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
  • B41C1/1016—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 characterised by structural details, e.g. protective layers, backcoat layers or several imaging layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
  • B41C2201/04—Intermediate layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
  • B41C2201/12—Location, type or constituents of the non-imaging layers in lithographic printing formes characterised by non-macromolecular organic compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
  • B41C2201/14—Location, type or constituents of the non-imaging layers in lithographic printing formes characterised by macromolecular organic compounds, e.g. binder, adhesives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
  • B41C2210/04—Negative working, i.e. the non-exposed (non-imaged) areas are removed
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
  • B41C2210/08—Developable by water or the fountain solution
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
  • B41C2210/20—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by inorganic additives, e.g. pigments, salts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
  • B41C2210/22—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by organic non-macromolecular additives, e.g. dyes, UV-absorbers, plasticisers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
  • B41C2210/24—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by a macromolecular compound or binder obtained by reactions involving carbon-to-carbon unsaturated bonds, e.g. acrylics, vinyl polymers

Definitions

• the present invention relates to a heat sensitive imaging element. More specifically the invention is related to a heat sensitive imaging imaging element for preparing a lithographic printing plate which can be imaged by rub-off or on the press.
• Lithography is the process of printing from specially prepared surfaces, some areas of which are capable of accepting lithographic ink, whereas other areas, when moistened with water, will not accept the ink.
• the areas which accept ink define the printing image areas and the ink-rejecting areas define the background areas.
• a photographic material is made imagewise receptive to oily or greasy inks in the photo-exposed (negative-working) or in the non-exposed areas (positive-working) on a hydrophilic background.
• lithographic printing 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.
• printing plates are known that include a photosensitive coating that upon image-wise exposure is rendered soluble at the exposed areas. Subsequent development then removes the exposed areas.
• a typical example of such photosensitive coating is a quinone-diazide based coating.
• the above described photographic materials from which the printing plates are made are exposed in contact through a photographic film that contains the image that is to be reproduced in a lithographic printing process.
• Such method of working is cumbersome and labor intensive.
• the printing plates thus obtained are of superior lithographic quality.
• GB- 1 492 070 discloses a method wherein a metal layer or a layer containing carbon black is provided on a photosensitive coating. This metal layer is then ablated by means of a laser so that an image mask on the photosensitive layer is obtained. The photosensitive layer is then overall exposed by UV-light through the image mask. After removal of the image mask, the photosensitive layer is developed to obtain a printing plate.
• This method however still has the disadvantage that the image mask has to be removed prior to development of the photosensitive layer by a cumbersome processing.
• 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- 580 393 disclose a lithographic printing plate directly imageable by laser discharge, the plate comprising: (a) a topmost first layer; and (b) a second layer underlying the first layer; wherein the first layer is characterized by efficient absorption of infrared radiation; and (d) the first and second layer exhibit different affinities for at least one printing liquid selected from the group consisting of ink and an abhesive fluid for ink.
• printing plates for wet offset and printing plates for waterless offset can be prepared.
• the plates for wet offset have a poor endurance.
• WO 94/18005 discloses a heat mode recording material having a high recording speed comprising on a support having an ink receptive surfaceor being coated with an ink receptive layer a substance capable of converting light into heat and a hardened hydrophilic surface layer having a thickness not more than 3 ⁇ m.
• the substance capable of converting light into heat is present in the support or in a separate recording layer. This is detrimental for a high sharpness of the image due to lateral diffusion of the heat and the light diffraction.
• a heat-sensitive imaging element for providing a lithographic printing plate, comprising a lithographic base with a hydrophobic oleophilic surface and a top layer layer comprising a compound capable of converting light into heat and a hydrophilic polymer, characterized in that said hydrophilic polymer is crosslinked.
• the lithographic base comprises a hydrophobic oleophilic surface.
• Preferred bases are plastic films such as polyethylene film, polypropylene film, polyvinylchloride film, polycarbonate film, polystyrene film, polyethylene terephthalate film and polyethylene naphthalate film.
• 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 at least 500 m 2 per gram.
• the lithographic base has preferably a thickness between 0.13 and 0.50 mm.
• the top layer layer comprises a compound capable of converting light into heat and a crosslinked hydrophilic polymer.
• Suitable compounds capable of converting light into heat are preferably infrared absorbing components although the wavelength of absorption is not of particular importance as long as the absorption of the compound used is in the wavelength range of the light source used for image-wise exposure.
• Particularly useful compounds are for example dyes and in particular infrared absorbing dyes and pigments and in particular infrared absorbing pigments. Examples of infrared absorbing dyes are disclosed in EP-A- 97 203 131.4.
• Preferred dyes are cyanine dyes, more preferably cyanine dyes with at least two sulphonic acid groups, most preferably cyanine dyes with at least two sulphonic acid groups and two indolenine groups. Particularly preferred are the following two structures:
• infrared absorbing pigments are carbon black, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and oxides structurally related to the bronze fatly but lacking the A component e.g. WO 2.9 . It is also possible to use conductive polymer dispersion such as polypyrrole or polyaniline-based conductive polymer dispersions.
• Said compound capable of converting light into heat is present in the imaging element preferably in an amount between 1 and 25 % by weight of the total weight of the image forming layer, more preferably in an amount between 2 and 20 % by weight of the total weight of the image forming layer.
• the compound capable of converting light into heat is most preferably present in the imaging element in an amount to provide an optical density at a wavelength between 800 nm and 1100nm of at least 0.35.
• a particularly suitable crosslinked hydrophilic layer may be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolysed tetra-alkylorthosilicate. The latter is particularly preferred.
• a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolysed tetra-alkylorthosilicate. The latter is particularly preferred.
• hydrophilic binder there may be used hydrophilic (co)polymers such as for example, 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 percent by weight, preferably 80 percent by weight.
• the amount of crosslinking agent, in particular of tetraalkyl orthosilicate, is preferably at least 0.2 parts by weight per part by weight of hydrophilic binder, more preferably between 0.5 and 5 parts by weight, most preferably between 1.0 parts by weight and 3 parts by weight.
• a cross-linked hydrophilic layer used in accordance with the present embodiment preferably also contains substances that increase the mechanical strength and the porosity of the layer.
• colloidal silica may be used.
• the colloidal silica employed may be in the form of any commercially available water-dispersion of colloidal silica for example having an average particle size up to 40 nm, e.g. 20 nm.
• the amount of colloidal silica lies preferably between 0.05 and 10 parts by weight versus the amount of hydrophilic binder.
• inert particles of larger size than the colloidal silica may be added e.g. silica prepared according to Stöber as described in J. Colloid and Interface Sci., Vol.
• alumina particles or particles having an average diameter of at least 100 nm which are particles of titanium dioxide or other heavy metal oxides.
• the crosslinked hydrophilic polymer yields a top layer which is insoluble in water or in an aqueous fountain solution.
• the image forming layer is preferably applied in a thickness between 0.25 and 5 ⁇ m, more preferably in a thickness between 0.5 and 3 ⁇ m.
• the hydrophilic binder is preferably a hydrophilic colloid, usually a protein, preferably gelatin. Gelatin can, however, be replaced in part or integrally by synthetic, semi-synthetic, or natural polymers.
• Said silica is a colloidal silica with a mean number diameter between 0.01 and 1 ⁇ m.
• a latex is defined as a stable colloidal dispersion of a polymeric substance in an aqueous medium.
• the polymer particles are usually approximately spherical and of typical colloidal dimensions: particle diameters range from about 20 to 1000 nm.
• the dispersion medium is usually a dilute aqueous solution containing substances such as electrolytes, surfactants, hydrophilic polymers and initiator residues.
• the polymer latices are classified in various way. By origin, they are classified as natural latices, produced by metabolic processes occuring in the cells of certain plant species; synthetic latices, produced by emulsion polymerization of monomers; and artificial latices, produced by dispersing a polymer in a dispersing medium.
• Preferred latices in connection with the invention are synthetic and artificial latices. These artificial latices are rather referred to as polymer dispersions. These polymers or oligomeric species could be dispersed in water either before their polymerization and/or crosslinking or afterwards.
• the colloidal stability of the dispersion can be improved by the addition of dispersion agents (surface-active compounds) or by ionic groups incorporated via the monomeric species or via modification.
• the dispersions of the polymers (or oligomers) can contain crosslinking agents, polymerization catalyst, or incorporated species which can give self-crosslinking of the polymer, to obtain sufficient mechanical strength
• a hydrophobic polymer for use in a latex according to the present invention has preferably a Tg of at least 30°C, more preferably a Tg of at least 35°C.
• the hydrophobic polymer latex for use in the present invention may contain conventional emulsifiers.
• Hydrophobic polymers for use in synthetic latices according to the present invention are, for example, polystyrene, polyacrylates such as polymethyl methacrylate and polybutyl acrylate, copolymers of butyl acrylate and methyl methacrylate, copolymers of butyl acrylate and styrene, homopolymers of butadiene, copolymers of butadiene and methyl methacrylate.
• Hydrophobic polymers for use in artificial latices according to the present invention are, for example polyurethanes such as the condensation product of polyester and isoforon diisocyanate.
• Imaging in connection with the present invention is preferably done with an image-wise scanning exposure, involving the use of a laser, more preferably of a laser that operates in the infrared or near-infrared, i.e. wavelength range of 700-1500 nm. Most preferred are laser diodes emitting in the near-infrared. Exposure of the imaging element can be performed with lasers with a short as well as with lasers with a long pixel dwell time. Preferred are lasers with a pixel dwell time between 0.005 ⁇ s and 20 ⁇ s.
• the exposure of the imaging element can be carried out with the imaging element already on the press.
• a computer or other information source supplies graphics and textual information to the laser via a lead.
• the printing plate of the present invention can also be used in the printing process as a seamless sleeve printing plate.
• This cylindrical printing plate has such a diameter that it can be slided on the print cylinder. More details on sleeves are given in " Grafisch Nieuws” ed. Keesing, 15, 1995, page 4 to 6.
• the image-wise exposed imaging element can be developed by a dry rub-off or by a wet rub-off using water or an aqueous solution.
• the image-wise exposed imaging element after optional wiping is mounted on a print cylinder of a printing press with the backside of the imaging element (side of the support opposite to the side having the photosensitive layer).
• 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 may be dropped simultaneously or the ink rollers may be dropped first.
• An exposed imaging element in accordance with the present invention is preferably mounted on a printing press and used to print shortly after the exposure. It is however possible to store an exposed imaging element for some time before using it on a printing press to print copies.
• Suitable dampening liquids that can be used in connection with the present invention are aqueous liquids generally having an acidic pH and comprising an alcohol such as isopropanol and silica.
• dampening liquids useful in the present invention there is no particular limitation and commercially available dampening liquids, also known as fountain solutions, can be used.
• Polyacrylamide IR-2 CARBOPOL 801 is a trade name of Goodrich for polyacrylic acid.
• MOWIOL 5698 is a trade name of Hoechst for 98 % hydrolyzed polyvinyl acetate.
• PRINTEX L6 is a trade name of Degussa for carbon black.
• the plates were exposed on a CREO TRENDSETTER 3244T TM (trade name of Creo for a plate setter) with an energy in the writing plane of 558 mJ/cm 2 at a speed of 45 m/min.
• the exposed areas could be removed by rubbing with a dry cotton pad, revealing the hydrophobic background.
• the plates were printed on an AB-Dick 360 press, using Van Son rubberbase VS 2329 as ink and 2% Tame as fountain.
• An imaging element 8 is prepared in an identical way as imaging element 1 with the exception that the 50 g of a dispersion containing 30% silica was replaced by 50 g of water. It was exposed, developed and printed as example 1. The ink acceptance was good and the run length was >10 000 but the plate showed a slight scumming. It is clear that the addition of silica to the top layer improves the scumming of the printing plate.

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

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Cited By (4)

Citations (6)

• 1999
  • 1999-05-10 EP EP19990201520 patent/EP0967077B1/fr not_active Expired - Lifetime

Patent Citations (6)

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