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
  • B41C1/1025—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 using materials comprising a polymeric matrix containing a polymeric particulate material, e.g. hydrophobic heat coalescing particles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/36—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties
  • B41M5/368—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties involving the creation of a soluble/insoluble or hydrophilic/hydrophobic permeability pattern; Peel development
• • 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
  • B41C2210/22—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 material for preparing lithographic printing plates.
• 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 an ink-repelling background.
• 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.
• thermoplastic polymer particles By image-wise exposure to an infrared laser, the thermoplastic polymer particles are image-wise coagulated thereby rendering the surface of the imaging element at these areas ink accepting without any further development.
• a disadvantage of this method is that the printing plate obtained is easily damaged since the non-printing areas may become ink-accepting when some pressure is applied thereto. Moreover, under critical conditions, the lithographic performance of such a printing plate may be poor and accordingly such printing plate has little lithographic printing latitude.
• EP-A- 770 494, 770 495, 770 496 and 770 497 disclose a method for making a lithographic printing plate comprising the steps of (1) image-wise exposing to light a heat-sensitive imaging element comprising (i) on a hydrophilic surface of a lithographic base an image-forming layer comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder and (ii) a compound capable of converting light to heat, said compound being comprised in said image-forming layer or a layer adjacent thereto; (2) and developing a thus obtained image-wise exposed element by rinsing it with plain water.
• the above mentioned heat-sensitive imaging elements for making lithographic printing plates are not optimal regarding lithographic latitude, more particularly they need a lot of prints before the background area becomes free of printing ink.
• a heat-sensitive material for making lithographic printing plates comprising on a lithographic support an image-forming layer comprising a hydrophilic binder, a cross-linking agent for a hydrophilic binder and dispersed hydrophobic thermoplastic polymer particles, characterized in that said image-forming layer is covered with a layer comprising at least one organic compound comprising cationic groups.
• the organic compounds having cationic groups for use in connection with the present invention are preferably hydrophilic and may be low moleculair weight compounds but are preferably polymers.
• Preferred compounds are those having one or more ammonium groups or amino groups that can be converted to ammonium groups in an acidic medium.
• An especially preferred type of cationic compounds are polysacharides modified with one or more groups containing an ammonium or amino group.
• Most preferred organic compounds having cationic groups are dextrans or pullulan wherein at least some of the hydroxy groups have been modified into one or more of the following groups: -O-R 1 -O-CO-R 2 wherein R 1 represents an organic residue containing an amino or ammonium group, e.g. an amine substituted alkyl, an amine substituted alkylaryl etc..
• R 2 has one of the significances given for R 1 or stands for -OR 3 or -N(R 4 )R 5 , wherein R 3 has one of the significances given for R 1 and each of R 4 and R 5 which may be the same or different and have one of the significances given for R 1 .
• Pullulan is a polysacharide that is produced by microorganisms of the Aureobasidium pullulans type (Pullularia pullulans) and that contains maltotriose repeating units connected by a a-1,6 glycosidic bond. Pullulan is generally produced on industrial scale by fermentation of partially hydrolysed starch or by bacterial fermentation of sucrose. Pullulan is commmercially available from e.g. Shodex, Pharmacosmos.
• dextrans or pullulan suitable for use in accordance with the present invention are dextrans or pullulan wherein some of the hydroxyl groups have been modified in one of the groups shown in table 1.
• the modified dextrans or pullulan can be prepared by a reaction of a dextran with e.g. alkylating agents, chloroformates, acid halides, carboxylic acids etc...
• the organic compound having one or more cationic groups according to the invention is preferably provided in an amount of 10 to 5000 mg/m 2 and more preferably in an amount of 20 to 1000 mg/m 2 .
• an imaging element comprising preferably hydrophobic thermoplastic polymer particles with an average particle size between 40nm and 2000nm. More preferably the hydrophobic thermoplastic polymer particles are used with an average particle size of 40nm to 200nm. Furthermore the hydrophobic thermoplastic polymer particles used in connection with the present invention preferably have a coagulation temperature above 50°C and more preferably above 70°C. Coagulation may result from softening or melting of the thermoplastic polymer particles under the influence of heat. There is no specific upper limit to the coagulation temperature of the thermoplastic hydrophobic polymer particles, however the temperature should be sufficiently below the decomposition temperature of the polymer particles.
• hydrophobic polymer particles for use in connection with the present invention have a Tg above 80°C.
• the polymer particles are selected from the group consisting of polyvinyl chloride, polyvinylidene chloride, polyesters, polyurethanes, polyacrylonitrile, polyvinyl carbazole etc., copolymers or mixtures thereof. Most preferably used are polystyrene, polymethylmethacrylate or copolymers thereof.
• the weight average molecular weight of the polymers may range from 5,000 to 5,000,000g/mol.
• the polymer particles are present as a dispersion in the aqueous coating liquid of the image-forming layer and may be prepared by the methods disclosed in US-P- 3 476 937 .
• Another method especially suitable for preparing an aqueous dispersion of the thermoplastic polymer particles comprises:
• the amount of hydrophobic thermoplastic polymer particles contained in the image-forming layer is preferably between 2 and 40 % by weight and more preferably between 10 and 20 % by weight of the total weight of said layer.
• Suitable hydrophilic binders for use in an image-forming layer in connection with this invention are water soluble (co)polymers for example synthetic homo- or copolymers such as polyvinylalcohol, a poly(meth)acrylic acid, a poly(meth)acrylamide, a polyhydroxyethyl(meth)acrylate, a polyvinylmethylether or natural binders such as gelatin, a polysaccharide such as e.g. dextran, pullulan, cellulose, arabic gum, alginic acid, inuline or chemically modified inuline.
• water soluble (co)polymers for example synthetic homo- or copolymers such as polyvinylalcohol, a poly(meth)acrylic acid, a poly(meth)acrylamide, a polyhydroxyethyl(meth)acrylate, a polyvinylmethylether or natural binders such as gelatin, a polysaccharide such as e.g. dextran,
• a cross-linked hydrophilic binder in the heat-sensitive layer used in accordance with the present embodiment also contains substances that increase the mechanical strength and the porosity of the layer e.g. oxide particles having an average diameter of at least 100 nm. Incorporation of these particles gives the surface of the cross-linked hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys.
• these particles are oxides or hydroxydes of beryllium, magnesium, aluminium, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth or a transition metal.
• titanium dioxide used in 20 to 95 % by weight of the heat-sensitive layer, more preferably in 40 to 90% by weight of the heat-sensitive layer.
• the image-forming layer also comprises crosslinking agents.
• crosslinking agents such as formaldehyde, glyoxal, polyisocyanate or a hydrolysed tetraalkylorthosilicate. The latter is particularly preferred.
• the imaging element can further include a compound capable of converting light to heat.
• Suitable compounds capable of converting light into heat are preferably infrared absorbing components having an absorption in the wavelength range of the light source used for image-wise exposure.
• Particularly useful compounds are for example dyes and in particular infrared dyes as disclosed in EP-A- 908 307 and pigments and in particular infrared pigments such as carbon black, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides and oxides structurally related to the bronze family but lacking the A component e.g. WO 2.9 .
• conductive polymer dispersion such as polypyrrole or polyaniline-based conductive polymer dispersions.
• the lithographic performance and in particular the print endurance obtained depends i.a.on the heat-sensitivity of the imaging element. In this respect it has been found that carbon black yields very good and favorable results.
• a light-to-heat converting compound in connection with the present invention is most preferably added to the image-forming layer but at least part of the light-to-heat converting compound may also be comprised in a neighbouring layer.
• the imaging layer preferably contains surfactants which can be anionic, cationic, non-ionic or amphoteric.
• Perfluoro surfactants are preferred. Particularly preferred are non-ionic perfluoro surfactants. Said surfactants can be used alone or preferably in combination.
• the weight of the imaging layer ranges preferably from 0.5 to 20 g/m 2 , more preferably from 3 to 15 g/m 2 .
• the lithographic base according to the present invention can be aluminum e.g. electrochemically and/or mechanically grained and anodised aluminum.
• the lithographic base can be a flexible support.
• flexible support in connection with the present embodiment it is particularly preferred to use a plastic film e.g. substrated polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film, polyethylene film, polypropylene film, polyvinyl chloride film, polyether sulphone film.
• the plastic film support may be opaque or transparent.
• the plastic film is preferably subbed with subbing layers as described in EP-A- 619 524, EP-A- 619 525 and EP-A- 620 502.
• Still further paper or glass of a thickness of not more than 1.2 mm can also be used.
• the imaging element is image-wise exposed. During said exposure, the exposed areas are converted to hydrophobic and oleophilic areas while the unexposed areas remain hydrophilic.
• Said image-forming can be realized by direct thermal recording wherein the thermal transfer is effected by heat radiation, heat conductivity or inductive heat transport. It is believed that on the heated areas the hydrophobic polymer particles coagulate and form a hydrophobic area while on the non-heated areas the hydrophobic polymer particles remain unchanged and said area remains hydrophilic.re
• Said image-forming can also effected by irradiation with high intensity light.
• the heat-sensitive material should then comprise a compound capable of converting light into heat.
• the plate is then ready for printing without an additional development and can be mounted on the printing press.
• the imaging element is first mounted on the printing cylinder of the printing press and then image-wise exposed directly on the press. Subsequent to exposure, the imaging element is ready for printing.
• the resulting imaging elements were imaged on a CREO 3244 Trendsetter TM at 2400 dpi operating at a drum speed of 140 rpm and a laser output of 15.5 Watt.
• the plates were mounted on a GTO 52 press using K + E 800 as ink and rotamatic as fountain.
• the press was started by allowing the print cylinder with the imaging element mounted thereon to rotate.
• the dampener rollers of the press were first dropped on the imaging element so as to supply dampening liquid to the imaging element and after 10 revolutions of the print cylinder , the ink rollers were dropped to supply ink. After 10 further revolutions ink was feeded.
• the Dmin and the dot areas of the 50 % screen at 200 lpi were measured at prints 5, 25, 50.
• the Dmin and the dot area were measured with a Macbeth RD918-SBTM.

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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)
• Materials For Photolithography (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)

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Cited By (4)

Citations (6)

• 2000
  • 2000-05-24 EP EP20000201854 patent/EP1065049B1/de not_active Expired - Lifetime

Patent Citations (6)

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