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
  • B41N3/08—Damping; Neutralising or similar differentiation treatments for lithographic printing formes; Gumming or finishing solutions, fountain solutions, correction or deletion fluids, or on-press development

Definitions

• the present invention relates to method for printing with a diazo-based lithographic printing plate and to a fountain solution for use in said method.
• 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 and the ink-rejecting areas form the background areas.
• a photographic material is made image-wise receptive to oily or greasy inks in the photo-exposed (negative-working) or in the non-exposed areas (positive-working) on a hydrophillic 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 hydrophillic colloids and a large variety of synthetic photopolymers.
• a generally used negative-working diazo-sensitized system is based on the capability of diazo compounds to harden a polymer when exposed to ultraviolet and blue radiation.
• Diazo compounds which have been used for the preparation of lithographic printing plates based on their hardening properties are e.g. diazonium salts whose photolysis products can harden polymers (natural colloids or synthetic resins) directly and diazonium polymers.
• diazonium salts whose photolysis products can harden polymers (natural colloids or synthetic resins) directly and diazonium polymers.
• polymers containing diazonium groups have a large structure they may remain water soluble owing to the presence of the ionic diazonium groups. When these groups are destroyed by exposure to light an insoluble resin is formed.
• the diazo resin or diazonium salt will be dissolved and removed by a suitable solvent, e.g. water, in the non-exposed or insufficient exposed parts of the lithographic printing plate precursor.
• a suitable solvent e.g. water
• the hydrophillic or oleophobic surface of the plate will thus be exposed in the non-exposed or insufficient exposed parts while the oleophillic diazo resin will remain in the exposed parts.
• supports can be used for the manufacturing of a diazo-sensitized lithographic printing plate.
• Common supports are metal supports like Al or Zn.
• a typical hydrophillic layer in these systems is a layer containing polyvinyl alcohol and hydrolyzed tetraethyl orthosilicate and preferably also silicium dioxide and/or titanium dioxide as described in e.g. GB-P-1419512, FR-P-2300354, US-P-3971660 and 4284705.
• additives can be added to the fountain solution.
• hydrophillic substances such as e.g. arabic gum, cellulose derivatives, polyvinyl alcohol, polyvinyl pyrrolidone etc.
• Other additives commonly used in fountain solutions are alcohols e.g. isopropanol, ethyleneglycol, glycol ether, polyols, 3-hydroxymethyl-4-heptanol.
• a fountain solution comprising a dextran of which at least part of the hydroxyl groups have been modified into groups containing ammonium groups and/or amine functions.
• a method for printing with a diazo-based lithographic printing plate using a fountain solution comprising a dextran of which at least part of the hydroxyl groups have been modified into groups containing ammonium groups and/or amine functions.
• scumming and ink staining of a diazo-based lithographic printing plate can be reduced by using a fountain solution comprising a dextran of which at least part of the hydroxyl groups have been modified into groups containing ammonium groups or amine functions.
• Said dextran preferably has a molecular weight between 10000 and 500000.
• dextrans of which at least part of the hydroxyl groups have been modified into groups containing ammonium groups or amine functions are dextrans of which at least some of the hydroxyl groups have been modified into one or more of the following groups: -O-R1 -O-CO-R2 wherein R1 represents an organic residue containing an ammonium group or an amine function, e.g. an amine or ammonium substituted alkyl, an amine or ammonium substituted alkylaryl etc..
• R2 has one of the significances given for R1 or stands for -OR3 or -N(R4)R5, wherein R3 has one of the significances given for R1 and each of R4 and R5 which may be the same or different represents hydrogen, an organic group e.g. an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkylaryl group, an organic residue containing an amine function or ammonium group.
• R3 has one of the significances given for R1 and each of R4 and R5 which may be the same or different represents hydrogen, an organic group e.g. an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkylaryl group, an organic residue containing an amine function or ammonium group.
• dextrans suitable for use in accordance with the present invention are dextrans wherein some of the hydroxyl groups have been modified into one of the groups shown in table 1.
• the modified dextrans can be prepared by reaction of a dextran with e.g. alkylating agents, acid halides, chloroformates, carboxylic acids etc...
• the dextrans are preferably used in a total amount between 0.025g/l and 0.5g/l in the fountain solution as used on a printing machine.
• the fountain solution for use in accordance with the present invention preferably also comprises a glycol preferably in an amount from 0.1g/l to 80g/l.
• glycols suitable for use in accordance with the present invention are e.g. ethylene glycol, propylene glycol, glycol ether, hexylene glycol etc. Hexylene glycol is most preferably used in accordance with the present invention.
• the pH of the fountain solution for use in accordance with the present invention is preferably between 4 and 7.
• the fountain solution is preferably bufferred around the desired pH using a suitable buffer.
• Buffers that can be used in accordance with the present invention are e.g. citrate buffers, acetate buffers, phosphate buffers etc. or mixtures thereof.
• additives such as e.g. hydrophillic colloid binders, organic and inorganic acids e.g. hydrogen chloride, preservatives, corrosion inhibitors, and hardeners into the fountain liquid.
• additives can be used in amounts of from about 0.01 to about 5 percent by volume.
• a diazo-based lithographic printing plate prepared as described in e.g. US-P-3971660 or EP-A-90200801.0 is moistened with the above described fountain solution, supplied with ink and used to print on an offset press.
• Suitable inks for use in accordance with the printing method of the present invention are those inks commonly employed in the art of lithographic printing.
• a comparitive fountain solution consisting of 10% of isopropanol in water was prepared.
• a lithographic printing plate prepared as described in EP-A-90200801.0 was mounted on an Heidelberg GTO 46 offset printing press with a dampening system adapted for alcoholic fountain solutions comprising the above described fountain solution.
• the ink used was Van Son rubberbase 2329 commercially available from Van Son.
• a lithographic printing plate prepared as described in example 1 was used to print under identical conditions as in example 1 with the exception that an aqueous fountain solution having the following composition was used: isopropanol 10% hexylene glycol 4%
• a lithographic printing plate prepared as described in example 1 was used to print under similar conditions as in example 1 with the exception that an aqueous fountain solution having the following composition was used:
• the water supply was set to position 7 at the printing machine for a density of 1.5 at ink supply 15. No scumming nor ink staining was noticed.
• a lithographic printing plate prepared as described in example 1 was used to print under similar conditions as in example 1 with the exception that an aqueous fountain solution having the following composition was used: isopropanol 10% hexylene glycol 4% Dormacid* 0.25% * Dormacid is commercially available from Pfeifer & Langen and is the commercial name for a dextran modified with group 8 of table 1 above.
• the water supply was set to position 5 at the printing machine (less water supply than in example 3) for a density of 1.5 at ink supply 15. No scumming nor ink staining was noticed.
• the fountain solution of this example thus offers the best results since no scumming nor ink staining occurs and since the water supply is less than in example 3 offers more flexibility at the offset press.

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Citations (2)

• 1991
  • 1991-06-10 EP EP91201423A patent/EP0517959A1/fr not_active Ceased

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