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
  • B41N3/036—Chemical or electrical pretreatment characterised by the presence of a polymeric hydrophilic coating

Definitions

• the present invention relates to a lithographic base. More particularly the present invention relates to an hydrophilic lithographic surface layer with improved mechanical properties.
• 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 form the printing image areas, generally hydrophobic areas, and the ink-rejecting areas form the background areas, generally hydrophilic 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 lithographic base that has affinity to water or obtains such affinity by chemical treatment is coated with a thin layer of a photosensitive composition.
• compositions for that purpose include light-sensitive materials such as light-sensitive polymers, diazonium salts or resins, a photoconductive layer, a silver halide emulsion etc. These materials are then image-wise exposed to actinic radiation and processed in the appropriate manner so as to obtain a lithographic printing plate.
• a silver precipitating (nucleating) agent is located in or on top of the hydrophilic surface.
• An image is obtained on the precipitating layer according to the silver salt diffusion transfer process by contacting said precipitating layer with an exposed silver halide emulsion in the presence of a silver halide developing agent and a silver halide solvent.
• a heat mode imaging element for making a lithographic printing plate comprising on a lithographic base with a hydrophilic surface a first layer including a polymer, soluble in an aqueous alkaline solution and a top layer on the same side of the lithographic base as the first layer which top layer is IR-sensitive and unpenetrable for an alkaline developer wherein said first layer and said top layer may be one and the same layer.
• a hydrophilic receiving layer can also be used for xerography, electrography, thermosublimation, thermal transfer and other image-forming techniques.
• supports can be used for the manufacturing of a lithographic imaging printing plate.
• Common supports are for example organic resin supports, e.g.polyesters,and paper bases, e.g. polyolefin coated paper. These supports are first coated with a hydrophilic layer forming the hydrophilic lithographic background of the printing plate.
• hydrophilic layer a layer containing polyvinyl alcohol and hydrolyzed tetra(m)ethyl orthosilicate and titanium dioxide and preferably also silicium dioxide as described in e.g. GB-P- 1 419 512, FR-P- 2 300 354 , US-P- 3 971 660 and 4 284 705, EP-A- 405 016 and 450 199 .
• drying stress results in materials with superior physical qualities.
• these drying stress caused by the pressure gradient in the liquid phase, results in the occurance of microscopic fractures.
• the exterior of the gel shrinks much faster than the interior so that tensile stresses arise that tend to fracture the network at the exterior. These fractures propagate easily during the further drying process.
• a lithographic base comprising a support and a hydrophilic layer thereon containing a hydrophilic binder , TiO 2 particles and wherein said layer is cross-linked, characterized in that the total volume of pores of said lithographic base is more than 0.0007 cm 3 /g.
• the total volume of pores of said lithographic base is at least 0.0010 cm 3 /g.
• the lithographic base having a hydrophilic surface comprises a flexible support, such as plastic film, provided with a cross-linked hydrophilic layer.
• a particularly suitable cross-linked hydrophilic layer may be obtained from a hydrophilic binder cross-linked with a cross-linking agent such as formaldehyde, glyoxal, polyisocyanate, zirconium compounds, titanates or a hydrolysed tetra-alkylorthosilicate. The latter is particularly preferred.
• hydrophilic binder there may be used hydrophilic (co)polymers or mixtures such as for example, homopolymers and copolymers of vinyl alcohol,polyvinyl pyrrolidone,starch or modified starch, acrylamide, methylol acrylamide, methylol methacrylamide, acrylate acid, methacrylate acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.
• hydrophilic (co)polymers or mixtures such as for example, homopolymers and copolymers of vinyl alcohol,polyvinyl pyrrolidone,starch or modified starch, 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 0.8 parts by weight and 3 parts by weight.
• a cross-linked hydrophilic layer in a lithographic base 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.
• a cross-linked hydrophilic layer in a lithographic base used in accordance with the present embodiment also contains in addition inert particles of larger size than the colloidal silica i.e. particles having an average diameter of at least 100 nm which are particles of titanium dioxide.
• inert particles of larger size than the colloidal silica i.e. particles having an average diameter of at least 100 nm which are particles of titanium dioxide.
• the amount of titanium dioxide is at least 55%, more preferably at least 62 % of the total amount of the hydrophilic layer.
• the weight of a cross-linked hydrophilic layer in a lithographic base in accordance with this embodiment may vary in the range of 0.2 to 25 g/m 2 and is preferably 1 to 15 g/m 2 .
• paper or polyolefin paper can be used as flexible support of a lithographic base in connection with the present embodiment. It is particularly preferred to use a plastic film e.g. subbed polyethylene terephthalate film, subbed polyethylene naphthalate 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 at least 500 m 2 per gram.
• the hydrophilic layer also contains drying control chemical additives.
• DCCA's As DCCA following classes of chemical compounds can be used:
• Said DCCA's can be used in combination and are preferably used in an amount between 100 and 1500 mg/m 2 .
• Said hydrophilic layer are suitable for heat mode imaging elements, ink jet printing, electrostatic printing, thermal transfer printing, laser ablation transfer, thermal ablation transfer, laser transfer printing, electrographic printing, pen plotter, manual writing, xerographic printing, tonerjet printing.
• a 0.175 mm thick polyester foil was coated with a layer from a 23.6 % aqueous solution at pH 4, with a wet coating thickness of 50 ⁇ m. This layer was after chilling for 30 sec at 10°C dried at a temperature of 50°C with a moisture content of the air of 4 g/m 3 for at least 3 minutes.
• the resulting hydrophilic layer contained 8990 mg/m 2 TiO 2 , 900 mg/m 2 SiO 2 , 990 mg/m 2 polyvinylalcohol, 81.6 mg/m 2 SAPONIN TM, 36.8 mg/m 2 of HOSTAPON T TM and 605 mg/m 2 of FT248 TM.
• TiO 2 with average particle size between 0.3 and 0.5 ⁇ m was used.
• the used polyvinyl alcohol is hydrolyzed polyvinyl acetate, commercially available at Wacker Chemie GmbH, Germany under the trademark POLYVIOL WX TM.
• the SiO 2 mentioned above is added as a dispersion of hydrolyzed tetramethyl orthsilicate to the dispersion.
• SAPONIN is a nonionic surfactant mixture consisting of esters and polyglycosides, commercially available at Merck.
• HOSTAPON T is an anionic surfactant, commercially available at Hoechst AG.
• FT248 is an anionic perfluoro surfactant, commercially available at Bayer AG.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 500.0 mg/m 2 of glycerol.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 90.0 mg/m 2 of glycerol and 100 mg/m 2 of acetamide.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 90.0 mg/m 2 of glycerol and 200 mg/m 2 of acetamide.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 460.0 mg/m 2 of glycerol and 100 mg/m 2 of acetamide.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 460.0 mg/m 2 of glycerol and 100 mg/m 2 of acetamide.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 460.0 mg/m 2 of glycerol and 1000 mg/m 2 of acetamide.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 90.0 mg/m 2 of glycerol and 560 mg/m 2 of oxalic acid.
• composition was prepared in the same way as this described in example 1, with the exception that the hydrophilic layer comprised also 90.0 mg/m 2 of glycerol and 1130 mg/m 2 of oxalic acid.
• the total pore volume of the lithographic base was measured by a Micromeritics ASAP 2400 apparatus. Therefore, the material, including the support, was cut in little pieces and brought into the apparatus, then a sorption/desorption of the material was measured with nitrogen gas as adsorbate.
• the total pore volume was calculated by the method of Barett, Joyner and Hallender.
• the physical properties of the imaging element were evaluated by measuring the scratch resistance. In this test the mechanical properties and the adhesion of the coating to the support become clear.
• Example 2 11 0.000087
• Example 3 0 0.000768
• Example 4 0 0.001067
• Example 5 0 0.000790
• Example 6 0 0.001612
• Example 7 3 0.000912
• Example 8 0 0.001272
• Example 9 0 0.001872
• Example 10 31 0.000070
• Example 11 18 0.000079

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• Materials For Photolithography (AREA)
• Printing Plates And Materials Therefor (AREA)
• Printing Methods (AREA)

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Citations (5)

• 1998
  • 1998-10-26 EP EP19980203608 patent/EP0997317B1/de not_active Expired - Lifetime
  • 1998-10-26 DE DE69818827T patent/DE69818827T2/de not_active Expired - Lifetime
• 1999
  • 1999-10-26 JP JP11304556A patent/JP2000127645A/ja active Pending

Patent Citations (5)

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