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
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/03—Chemical or electrical pretreatment
• • 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
  • 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
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/03—Chemical or electrical pretreatment
  • B41N3/036—Chemical or electrical pretreatment characterised by the presence of a polymeric hydrophilic coating
• • 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
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/03—Chemical or electrical pretreatment
  • B41N3/038—Treatment with a chromium compound, a silicon compound, a phophorus compound or a compound of a metal of group IVB; Hydrophilic coatings obtained by hydrolysis of organometallic compounds
• • 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 negative-working non-ablative, thermal lithographic printing plate precursor which comprises a grained and anodized aluminum support characterized by a low surface roughness, as well as to methods for making a lithographic printing plate and methods of lithographic printing wherein said precursor is used.
• a so-called printing master such as a printing plate is mounted on a cylinder of the printing press.
• the master carries a lithographic image on its surface and a printed copy is obtained by applying ink to said image and then transferring the ink from the master onto a receiver material, which is typically paper.
• ink as well as an aqueous fountain solution (also called dampening liquid) are supplied to the lithographic image which consists of oleophilic (or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling) areas.
• driographic the lithographic image consists of ink-accepting and ink-abhesive (ink-repelling) areas and during driographic printing, only ink is supplied to the master.
• Printing masters are generally obtained by the so-called computer-to-film (CtF) method wherein various pre-press steps such as typeface selection, scanning, color separation, screening, trapping, layout and imposition are accomplished digitally and each color selection is transferred to graphic arts film using an imagesetter.
• CtF computer-to-film
• the film can be used as a mask for the exposure of an imaging material called plate precursor and after plate processing, a printing plate is obtained which can be used as a master.
• the so-called 'computer-to-plate' (CtP) method has gained a lot of interest. This method, also called 'direct-to-plate', bypasses the creation of film because the digital document is transferred directly to a plate precursor by means of a so-called plate-setter.
• thermal plates which are sensitive to heat or infrared light, are widely used in CtP methods because of their daylight stability.
• Such thermal materials may be exposed directly to heat, e.g. by means of a thermal head, but preferably comprise a compound that converts absorbed light into heat and are therefore suitable for exposure by lasers, especially infrared laser diodes.
• the heat which is generated on image-wise exposure, triggers a (physico-)chemical process, such as ablation, polymerization, insolubilization by cross-linking of a polymer, decomposition, or particle coagulation of a thermoplastic polymer latex, and after optional processing, a lithographic image is obtained.
• Many thermal plate materials are based on heat-induced ablation.
• a problem associated with ablative plates is the generation of debris which is difficult to remove and may disturb the printing process or may contaminate the exposure optics of the plate-setter. As a result, such ablative plates require a processing step for removing the debris from the exposed material.
• EP-A 770 494 discloses a method wherein an imaging material comprising an image-recording layer of a hydrophilic binder, a compound capable of converting light to heat and hydrophobic thermoplastic polymer particles, is image-wise exposed, thereby inducing coalescence of the polymer particles and converting the exposed areas into an hydrophobic phase which defines the printing areas of the printing master.
• the press run can be started immediately after exposure without any additional treatment because the layer is developed by interaction with the fountain and ink that are supplied to the cylinder during the press run.
• the non-exposed areas are removed from the support and thereby define the non-printing areas of the plate.
• EP 908 784 discloses a method for making lithographic printing plates including the steps of (i) preparing a precursor comprising a top layer which is unpenetrable for a developer containing SiO 2 and which includes a diazonium salt and at least 20% non-proteinic hydrophilic film-forming polymers, (ii) exposing said precursor with actinic light and followed by (iii) developing said precursor.
• EP 1 160 083 discloses a printing plate comprising on a hydrophilic support an image-forming layer which contains a hydrophilic resin, an acid precursor and at least one component selected from fine particles containing a compound having a vinyloxy group or fine particles containing a thermosetting resin.
• heat-induced polymer particle coalescence is the only heat-triggered non-ablative imaging mechanism that requires no separate processing step with alkaline chemicals and that meets all the requirements for making a high-quality printing plate material (Agfa Thermolite®).
• Various improvements of such materials are described in e.g. EP-As 773 112 ; 774 364 ; 802 457 ; 816 070 ; 849 090 ; 849 091 ; 881 095 ; and 931 647 .
• none of the prior art materials, which work according to heat-induced polymer particle coalescence, is suitable for making printing plates that provide a high run length during printing.
• This object is realized by applying the heat-sensitive coating onto a smooth aluminum support, as defined in claim 1.
• the preferred materials of the present invention are capable of providing a lithographic printing master that can be used for a press run of at least 30 000, and more preferably at least 60 000 copies without visible wear of the image. The best embodiments even enable a press run of more than 100 000 copies.
• the support of the plate precursor of the present invention is a grained and anodized aluminum support having a hydrophilic surface that is characterized by a low surface roughness, expressed as arithmetical mean center-line roughness (Ra), sometimes also referred to as CLA (center-line average).
• the apparatus used for measuring Ra was a Talysurf 10 from Taylor Hobson Ltd.
• the Ra value of the hydrophilic surface of the grained and anodized aluminum support used in the material of the present invention is lower than 0.45 ⁇ m, preferably lower than 0.4 ⁇ m and even more preferably lower than 0.3 ⁇ m.
• a grained and anodized aluminum support having a hydrophilic surface characterized by the mentioned low Ra values is briefly referred to herein as a "smooth support".
• the lower limit of the Ra value may be 0.05 ⁇ m, preferably 0.1 ⁇ m.
• the grained aluminum support used in the material of the present invention is preferably an electrochemically grained support.
• the acid used for graining can be e.g. nitric acid.
• the acid used for graining preferably comprises hydrogen chloride. Also mixtures of e.g. hydrogen chloride and acetic acid can be used.
• the grained and anodized aluminum support may be post-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 an organic acid and/or salt thereof, e.g. carboxylic acids, hydroxycarboxylic acids, sulfonic acids or phosphonic acids, or their salts, e.g. succinates, phosphates, phosphonates, sulfates, and sulfonates.
• a citric acid or citrate solution is preferred. 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.
• a further post-treatment involves rinsing the aluminum oxide surface with a bicarbonate solution. Still further, the aluminum oxide surface may be treated with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid, polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinyl alcohol, and acetals of polyvinyl alcohols formed by reaction with a sulfonated aliphatic aldehyde.
• the coating provided on the support is heat-sensitive, thereby providing a plate precursor which can be handled in normal working lighting conditions (daylight, fluorescent light) for many hours.
• the coating comprises an image-recording layer which contains hydrophobic thermoplastic polymer particles.
• suitable hydrophobic polymers are e.g. polyethylene, poly(vinyl chloride), poly(methyl (meth)acrylate), poly(ethyl (meth)acrylate), poly(vinylidene chloride), poly(meth)acrylonitrile, poly(vinyl carbazole), polystyrene or copolymers thereof.
• the thermoplastic polymer comprises at least 50 wt.% of polystyrene, and more preferably at least 60 wt.% of polystyrene.
• the thermoplastic polymer preferably comprises at least 5 wt.%, more preferably at least 30 wt.% of nitrogen containing monomeric units or of units which correspond to monomers that are characterized by a solubility parameter larger than 20, such as (meth)acrylonitrile or monomeric units comprising sulfonamide and/or phthalimide pendant groups.
• nitrogen containing monomeric units are disclosed in EP-A-1 219 416 .
• a specific embodiment of the hydrophobic thermoplastic polymer is a homopolymer or a copolymer of (meth)acrylonitrile and/or styrene, e.g. a copolymer consisting of styrene and acrylonitrile units in a weight ratio between 1:1 and 5:1 (styrene:acrylonitrile).
• a 2:1 or 3:2 ratio provides excellent results.
• the weight average molecular weight of the thermoplastic polymer particles may range from 5,000 to 1,000,000 g/mol.
• the hydrophobic particles preferably have a number average particle diameter below 200 nm, more preferably between 10 and 100 nm.
• the amount of hydrophobic thermoplastic polymer particles contained in the image-recording layer is preferably between 20 wt.% and 65 wt.% and more preferably between 25 wt.% and 55 wt.% and most preferably between 30 wt.% and 45 wt.%.
• the hydrophobic thermoplastic polymer particles can be provided as a dispersion in an aqueous coating liquid of the image-recording layer and may be prepared by the methods disclosed in US 3,476,937 .
• Another method especially suitable for preparing an aqueous dispersion of the thermoplastic polymer particles comprises:
• the image-recording layer further may comprise a hydrophilic binder, e.g. 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 hydrophilic binder e.g. homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylic 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
• the image-recording layer may also contain other ingredients such as additional binders, surfactants, colorants, development inhibitors or accelerators, and especially one or more compounds that are capable of converting infrared light into heat.
• Particularly useful light-to-heat converting compounds are for example infrared dyes, carbon black, metal carbides, borides, nitrides, carbonitrides, bronze-structured oxides, and conductive polymer dispersions such as polypyrrole, polyaniline or polythiophene dispersions.
• Anionic cyanine dyes are preferred.
• the colorants are preferably dyes or pigments which provide a visible image after processing.
• the coating may also contain one or more additional layer(s), adjacent to the image-recording layer.
• additional layer can e.g. be an adhesion-improving layer between the image-recording layer and the support; or a light-absorbing layer comprising one or more of the above compounds that are capable of converting infrared light into heat; or a covering layer which is removed during processing.
• the materials of the present invention are suitable for off-press and on-press exposure.
• the printing plate precursors of the present invention are exposed to heat or to infrared light, e.g. by means of a thermal head, LEDs or an infrared laser.
• a laser emitting near infrared light having a wavelength in the range from about 700 to about 1500 nm is used, e.g. a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser.
• the required laser power depends on the sensitivity of the image-recording layer, the pixel dwell time of the laser beam, which is determined by the spot diameter (typical value of modern plate-setters at 1/e 2 of maximum intensity : 10-25 ⁇ m), the scan speed and the resolution of the exposure apparatus (i.e. the number of addressable pixels per unit of linear distance, often expressed in dots per inch or dpi; typical value : 1000-4000 dpi).
• Two types of laser-exposure apparatuses are commonly used : internal (ITD) and external drum (XTD) plate-setters.
• ITD plate-setters for thermal plates are typically characterized by a very high scan speed up to 500 m/sec and may require a laser power of several Watts.
• the hydrophobic thermoplastic polymer particles fuse or coagulate so as to form a hydrophobic phase which corresponds to the printing areas of the printing plate. Coagulation may result from heat-induced coalescence, softening or melting of the thermoplastic polymer particles.
• the coagulation temperature of the thermoplastic hydrophobic polymer particles 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.
• the coagulation temperature is at least 10°C below the temperature at which the decomposition of the polymer particles occurs.
• the coagulation temperature is preferably higher than 50°C, more preferably above 100°C.
• the material After exposure, the material is developed. "Developing” and “processing” are used herein as equivalent terms. Development can be carried out by supplying to the coating a liquid comprising a hydrophilic phase, thereby removing the coating from the support at non-exposed areas. Said liquid can be selected from the group consisting of water, an aqueous liquid, gum, fountain and single-fluid ink. According to one embodiment, the material is developed by supplying fountain and/or printing ink, preferably by supplying first fountain and subsequently ink. This method is preferably used in combination with an on-press exposure step. Another development method, also suitable for on-press development, especially in driographic presses, is performed by supplying single-fluid ink.
• a suitable single-fluid ink comprises an ink phase, also called the hydrophobic or oleophilic phase, and a polyol phase as described in WO 00/32705 . More information on the development with single-fluid ink can be found in EP-A- 1213 140 .
• the material When exposed in an off-press plate-setter, the material can be processed on-press by supplying ink and/or fountain as mentioned before or off-press, e.g. by supplying water, an aqueous liquid or a gum solution.
• a gum solution is typically an aqueous liquid which comprises one or more surface protective compounds that are capable of protecting the lithographic image of a printing plate against contamination or damaging. Suitable examples of such compounds are film-forming hydrophilic polymers or surfactants. More information on the development with a gum solution can be found in EP-A-1342568 .
• the plate can be dried and baked.
• the plate can be dried before baking or is dried during the baking process itself.
• the baking process can proceed at a temperature above the coagulation temperature of the thermoplastic polymer particles, e.g. between 100°C and 230°C for a period of 5 to 40 minutes.
• the exposed and developed plates can be baked at a temperature of 230°C for 5 minutes, at a temperature of 150°C for 10 minutes or at a temperature of 120°C for 30 minutes.
• a preferred baking temperature is above 60°C. Baking can be done in conventional hot air ovens or by irradiation with lamps emitting in the infrared or ultraviolet spectrum.
• run length is defined as the number of copies printed when the degradation, due to image wear, of a 60% screen of a high quality image (200 lpi) exceeds 5%. Unless indicated otherwise, all the plates described below were on-press processed by the ink and fountain supplied to the plate during the first ten to fifteen revolutions of the press.
• a 0.30 mm thick aluminum foil was degreased by immersing the foil in an aqueous solution containing 40 g/l of sodium hydroxide at 60°C for 8 seconds and rinsed with demineralized water for 2 seconds.
• the foil was then electrochemically grained during 15 seconds using an alternating current in an aqueous solution containing 12 g/l of hydrochloric acid and 38 g/l of aluminum sulfate (18-hydrate) at a temperature of 33°C and a current density of 130 A/dm 2 .
• the aluminum foil was then desmutted by etching with an aqueous solution containing 155 g/l of sulfuric acid at 70°C for 4 seconds and rinsed with demineralized water at 25°C for 2 seconds.
• the foil was subsequently subjected to anodic oxidation during 13 seconds in an aqueous solution containing 155 g/l of sulfuric acid at a temperature of 45°C and a current density of 22 A/dm 2 , then washed with demineralized water for 2 seconds and post-treated for 10 seconds with a solution containing 4 g/l of polyvinylphosphonic acid at 40°C, rinsed with demineralized water at 20°C during 2 seconds and dried.
• the support thus obtained was characterized by a surface roughness Ra of 0.46 ⁇ m and had an anodic weight of 2.9 g/m 2 of Al 2 O 3 .
• the same procedure as above was followed with the proviso that the current density during graining and anodizing was 90 A/dm 2 and 30 A/dm 2 respectively.
• the support thus obtained was characterized by a surface roughness Ra of 0.22 ⁇ m and had an anodic weight of 4.0 g/m 2 of Al 2 O 3 .
• a comparative printing plate precursor 1 and an printing plate precursor 2 according to the invention were produced by preparing a coating composition and coating it onto the above described lithographic supports 1 and 2 respectively.
• an image-recording layer was coated from an aqueous coating solution at a wet thickness of 30 g/m 2 .
• the layer consisted of 600 mg/m 2 of a copolymer of styrene and acrylonitrile (weight ratio 60/40) having an average particle size of 65 nm, stabilized with an anionic wetting agent, 60 mg/m 2 of infrared absorbing dye I and 120 mg/m 2 of polyacrylic acid (Glascol D15 from Allied Colloids, molecular weight 2.7x10 7 g/mole).
• the plate precursors thus obtained were exposed with a Creo Trendsetter (plate-setter available from Creo, Burnaby, Canada), operating at 330 mJ/cm 2 and 150 rpm. After imaging, the plates were mounted on a MO printing press (available from Heidelberger Druckmaschinen AG), and a print job was started using K+E800 ink and 4% Combifix XL with 10% isopropanol as a fountain liquid.
• Creo Trendsetter plate-setter available from Creo, Burnaby, Canada
• a continuous web of aluminum having a thickness of 0.30 mm and a width of 500 mm was degreased by immersing the web in an aqueous solution containing 10.4 g/l of sodium hydroxide at 38°C for 35 seconds and then rinsing with demineralized water for 30 seconds.
• the aluminum web was then electrochemically grained for 30 seconds using an alternating current at a current density of 826 A/m 2 in a mixed acid aqueous solution containing 9.5 g/l of hydrochloric acid and 21 g/l of acetic acid at a temperature of 29°C.
• the support thus obtained had an average center-line roughness Ra of 0.24 ⁇ m.
• the aluminum web was etched to remove smut with an aqueous solution containing 124 g/l of phosphoric acid at 43°C for 35 seconds and then rinsed with demineralized water for 30 seconds.
• the aluminum web was subsequently subjected to anodic oxidation for 30 seconds in an aqueous solution containing 137 g/l of sulfuric acid at a temperature of 48.5°C, using a DC voltage at a current density of 1173 A/m 2 to form an anodic oxidation film of 3.4 g/m 2 of Al 2 O 3 , then washed with demineralized water for 30 seconds and post-treated for 15 seconds with a solution containing 2.2 g/l of polyvinylphosphonic acid at 52°C, rinsed with demineralized water for 30 seconds and dried.
• the same procedure as for support 3 was followed with the proviso that the current density during graining was 2125 A/dm 2 .
• the support thus obtained was characterized by a surface roughness Ra of 0.53 ⁇ m.
• the anodic weight was the same as for support 3.
• Printing plate precursors 3 and 4 were prepared by coating the same composition as described above for the preparation of printing plate precursor 1 and 2. Also the exposure, on-press processing and printing procedure was the same.
• Plate 4 showed a run length of 30 000 copies while plate 3 did not show any image wear after 50 000 copies, when the run length tests was stopped.
• a continuous web of aluminum having a thickness of 0.30 mm and a width of 500 mm was degreased by immersing the web in an aqueous solution containing 10 g/l of sodium hydroxide at 39°C for 35 seconds and then rinsing with demineralized water for 30 seconds.
• the aluminum web was then electrochemically grained for 30 seconds using an alternating current at a current density as indicated in Table 1 in a mixed acid aqueous solution containing 8.1 g/l of hydrochloric acid and 21.7 g/l of acetic acid at a temperature of 30°C.
• the aluminum web was etched to remove smut with an aqueous solution containing 128 g/l of phosphoric acid at 43°C for 35 seconds and then rinsed with demineralized water for 30 seconds.
• the aluminum web was subsequently subjected to anodic oxidation for 30 seconds in an aqueous solution containing 154 g/l of sulfuric acid at a temperature of 50°C, using a DC voltage at a current density as indicated in Table 1, then washed with demineralized water for 30 seconds and post-treated for 15 seconds with a solution containing 2.45 g/l of polyvinylphosphonic acid at 53°C, rinsed with demineralized water for 30 seconds and dried.
• Printing plate precursors 5-9 were prepared by coating the same composition as described above for the preparation of printing plate precursor 1 and 2 onto the supports 5-9 respectively. Also the exposure, on-press processing and printing procedure was the same.
• Table 1 gives the current densities for graining (GR) and anodizing (AN), surface roughness Ra and the anodic weight (AW) of lithographic supports 5-9 and the run length achieved with plates 5-9.
• Table 1 Example no. current GR (A/m 2 ) Ra ( ⁇ m) current AN (A/m 2 ) AW (g/m 2 ) Run length 5 (comp.) 2740 0.53 2350 4.8 11 000 6 (inv.) 1300 0.28 2350 4.8 55 000 7 (inv.) 1300 0.28 1750 3.5 50 000 8 (inv.) 1300 0.28 2900 6.3 70 000 9 (inv.) 1000 0.21 2350 4.8 >90 000
• Example 5 The data for Example 5, 6 and 9 in the above table demonstrate that for a given anodic weight (4.8 g/m 2 ), the run length significantly improves by reducing Ra. For a given Ra value (Examples 6-8 : 0.28 ⁇ m), a further improvement is achieved by increasing the anodic weight. Plate 9 still showed no image wear after 90 000 copies when the press run was stopped.
• thermoplastic polymer was a homopolymer of styrene having an average particle size of 70 nm.
• Plates 10 and 11 were prepared from precursors 10 and 11 respectively by exposure and processing as described in the previous examples with the proviso that the on-press processing and run length test was preformed on a GTO printing press (Heidelberger Druckmaschinen), using K+E800 ink and 4% Combifix XL with 10% Isopropanol as a fountain liquid.
• Plate 12 was prepared from precursor 2 using the same procedure as for plates 10 and 11.
• Table 2 Example no. Ra ( ⁇ m) Polymer Run length 10 (comp.) 0.46 styrene homopolymer 21 500 11 (inv.) 0.22 styrene homopolymer 85 000 12 (inv.) 0.22 styrene/acrylo-nitrile copolymer > 100 000
• the aluminum foil was electrochemically grained during 4 seconds in an aqueous solution containing 12.4 g/l of nitric acid and 67 g/l of aluminum nitrate (9-hydrate) at a temperature of 40°C, using an alternating current at a current density of 36 A/dm 2 .
• the Ra value of the nitric acid grained support thus obtained was 0.38 ⁇ m.
• Printing plate precursor 16 was prepared by coating the same composition as described in Example 2 on the above support 16. Plates 16 and 17 were prepared by exposing plate precursors 16 and 2 respectively with a Creo Trendsetter (plate-setter available from Creo, Burnaby, Canada), operating at 330 mJ/cm 2 and 150 rpm. After imaging the plates 16 and 17 was mounted on a MO printing press (available from Heidelberger Druckmaschinen AG), and printing was started using K+E800 ink and 4% Combifix XL with 10% Isopropanol as a fountain liquid.
• Creo Trendsetter plate-setter available from Creo, Burnaby, Canada
• Plate 17 (nitric acid graining) showed ink built-up on the blanket of the SM-74 during printing while plate 16 (chloric acid graining) was running on the SM-74 without any ink built up on the blanket throughout the whole press run.
• Plate 18 was prepared as described in Example 2 with the proviso that the exposed plate was off-press processed with a gum solution using RC520 baking gum from Agfa (HWP450 processor, 1 minute immersion time, room temperature).
• Plate 19 was prepared similarly, but after processing the plate was baked during 2 minutes at 270 °C.

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• 2002
  • 2002-04-26 DE DE2002624642 patent/DE60224642T2/de not_active Expired - Lifetime
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