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
  • B41C1/1066—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme by spraying with powders, by using a nozzle, e.g. an ink jet system, by fusing a previously coated powder, e.g. with a laser

Definitions

• the present invention relates to a method for the preparation of a lithographic printing plate by means of ink jet printing.
• the image to be printed is present on a plate as a pattern of ink accepting (oleophilic) areas on an ink repellent (oleophobic or hydrophilic) background.
• the required ink repellency is provided by an initial application of a dampening (or "fountain) solution prior to inking.
• Conventional presensitized lithographic printing plates bear a UV sensitive coating based on photopolymer or diazonium chemistry.
• the plates have to be UV-exposed through a mask carrying the image.
• the mask is a graphic arts film prepared by photographic techniques based on silver halide chemistry and involving exposure by a camera or by an image-setter, and further involving wet processing.
• the SETPRTINT material trade mark of Agfa-Gevaert N.V. is based on silver halide DTR chemistry and consists of a polyethylene terephthalate base carrying a photographic coating which after photo-mode exposure and processing produces complementary oleophilic and hydrophilic areas.
• Another system based on photo-mode exposure but with a hydrophilic aluminum base is LITHOSTAR, trade mark of Agfa-Gevaert N.V..
• a system based on heat mode exposure by means of an intense infra-red laser is called THERMOSTAR, also a trade mark of Agfa-Gevaert N.V..
• ink jet printers have replaced laser printers as the most popular hard copy output printers for computers. Some of the competitive advantages of ink jet printers are low cost and reliability.
• the ink jet printing system is a relatively rapid image output system and has a simple construction because it does not require any complex optical system.
• an oleophilic liquid or fluid ink was printed by ink jet printing onto a hydrophilic aluminum surface of a lithographic printing plate. Titanate or silane coupling agents were present in the ink.
• ink jet printing wherein the ink is a solid or phase change type ink instead of a liquid or fluid type ink is described in U.S. Pat. No. 4,833,486 to deposit a hot wax on a surface of an offset plate. Upon cooling of the wax, it solidifies, thereby providing a printing plate.
• Solid ink jet printing has serious disadvantages for lithographic plates in that the wax or resin image has limited durability due to its thermoplastic, chemical, and adhesive properties and the amount and rounded shape of the solidified ink jet droplet on the media do not have the intrinsic image resolution properties found in liquid ink jet printing.
• Japanese Kokai Publication 113456/1981 proposes methods for preparing printing plates whereby ink-repelling materials (e.g. curable silicones) are printed on a printing plate by ink jet printing.
• the printing plate obtained by this method is an intaglio printing plate in which the ink-repelling material formed on the surface of the substrate serves as a non-image part.
• the resolution of the printed images at shadow area or reversed lines is not so good.
• a large amount of ink is needed in this method because the ink-repelling material must be deposited on the whole non-image part which occupies most of the surface of the printing plate, thereby delaying the printing process.
• US-P- 5 511 477 discloses a method for the production of photopolymeric relief-type printing plates comprising: forming a positive or a negative image on a substrate by ink jet printing with a photopolymeric ink composition, optionally preheated to a temperature of about 30°-260°C, and subjecting the resulting printed substrate to UV radiation, thereby curing said ink composition forming said image.
• This is an obnoxious method due to the sometimes high vapour pressure and toxicity of said inks.
• US-P- 5 312 654 discloses a method for making lithographic printing plates comprising: forming an image on a substrate having an ink absorbing layer and a hydrophilized layer between the substrate and the absorbing layer by ink jet printing using a photopolymerizable ink composition, and exposing it to an actinic light in the wavelength region with which said ink composition is sensitized to cure the image.
• the printing endurance of said printing plates is low.
• Japanese Kokai Publication 69244/1992 discloses a method for making printing plates comprising the steps of forming a printed image on a recording material subjected to a hydrophilic treatment by ink jet printing using a hydrophobic ink containing photocurable components, and exposing the whole surface to actinic light.
• the surface of the substrate to be used for the lithographic plate is usually subjected to various treatments such as a mechanical graining, an anodizing or a hydrophilic treatment to obtain good hydrophilic property and water retention property. Therefore, even the use of an ink composition having a very high surface tension results in a poor image on the surface of the substrate because of ink spreading and low printing endurance.
• EP-A- 533 168 discloses a method for avoiding said ink spreading by coating the lithographic base with an ink absorbing layer which is removed after ink printing. This is an uneconomical and cumbersome method.
• Research Disclosure 289118 of May 1988 discloses a method for making printing plates with the use of an ink jet wherein the ink is a hydrophobic polymer latex.
• said printing plates have a bad ink acceptance and a low printing endurance.
• EP-A- 003 789 discloses a process for the preparation of offset printing plates by means of an ink jet method with oleophilic inks. There is not indicated how said inks are made but from the examples it is clear that it concerns artificial latices, which are difficult to prepare.
• JP-A- 57/038142 discloses a method of preparing a printing plate by forming an ink image on a blank printing plate, and also by fixing this image thermally by making toner to adhere to this image-formed area.
• the composition of the ink is not mentioned, only the composition of the toners is disclosed.
• JP-A- 07/108667 discloses a plate-making method forming an ink image containing a hydrophilic substance on a conductive support whose surface layer is made hydrophilic according to an electrostatic attraction type ink set system to dry or cure the same, by applying bias voltage to the conductive support at the time of ink jet writing. This is a cumbersome process.
• US-P- 5,213,041 discloses a method for preparing a reusable printing plate for printing, projecting an imaging deposit on the plate surface by jet printing using an ejectable substance containing a heat fusible component.
• the image forms an imaging deposit which is fused to the surface of the printing plate using a variable frequency and variable power induction heater.
• a lithographic printing plate is manufactured by means of an ink jet fluid comprising reactive components selected from the group consisting of transition metal complexes and organic carbonyl compounds.
• the reactive compound comprises one or more chromium complexes of an organic acid.
• the present invention extends the teaching on the preparation of a lithographic printing plate whereby an oleophilizing fluid is directly applied onto a lithographic receiver by means of ink jet printing.
• a method for the preparation of a lithographic printing plate comprising dispensing information-wise by means of ink jet printing droplets of a fluid onto a surface of a lithographic receiver, characterized in that said fluid contains an oleophilizing compound represented by following general formula (1) : wherein Y represents C or N; Q represents the necessary atoms to complete an aromatic or hetero-aromatic 5- or 6-membered ring; X represents the necessary atoms to complete a hetero-aromatic 5- or 6-membered ring; Z is selected from oxygen or sulphur ; M is selected from a proton or a counterion to compensate negative charge.
• Y represents C or N
• Q represents the necessary atoms to complete an aromatic or hetero-aromatic 5- or 6-membered ring
• X represents the necessary atoms to complete a hetero-aromatic 5- or 6-membered ring
• Z is selected from oxygen or sulphur
• M is selected from a proton or a counterion to compensate negative
• the essence of the present invention is the presence in the ink jet fluid of an oleophilizing compound represented by general formula (I) as defined above.
• Preferred compounds are 8-hydroxyquinolines, 7-hydroxybenzimidazoles, and 7-hydroxybenztriazoles, and their corresponding thio-analogues.
• the most preferred compounds are 8-hydroxyquinolines.
• the oleophilizing agent may be present in the ink in an amount from 0.01 to 6, preferably from 0.02 to 3 % by weight.
• the oleophilizing agent is in the form of a homogeneous solution or a stable colloidal dispersion, so that it can pass through the nozzles of the printer head.
• the liquid carrier is water or an organic solvent or combinations thereof. Choice of the specific liquid carrier depends on the specific ink jet printer and its compatibility with the ink jet printing head and cartridge being used for the ink jet printing. Both aqueous based and solvent based fluids can be used in the present invention depending on the ink jet technology that is being used : piezo, thermal, bubble jet or continuous ink jet.
• the aqueous composition may comprise one or more water miscible solvents e.g. a polyhydric alcohol such as ethylene glycol, diethylene glycol, triethylene glycol or trimethylol propane.
• the amount of aqueous carrier medium in the aqueous composition may be in the range from 30 to 99.995, preferably from 50 to 95 % by weight.
• organic solvents may be used as a carrier medium for the ink jet fluid, e.g. alcohols, ketones or acetates.
• Ink jet fluids suitable for use with ink jet printing systems may have a surface tension in the range from 20 to 60, preferably from 30 to 50 dyne/cm. Control of surface tensions in aqueous ink jet fluids may be accomplished by additions of small amounts of surfactants. The level of surfactants to be used can be determined through simple trial and error experiments. Several anionic and nonionic surfactants are known in the ink jet art.
• the viscosity of the fluid is preferably not greater than 20 mPa.s, e.g. from 1 to 10, preferably from 1 to 5 mPa.s at room temperature.
• the ink jet fluid may further comprise other ingredients.
• a cosolvent may be included to help prevent the ink from drying out in the orifices of the print head.
• a biocide may be added to prevent unwanted microbial growth which may occur in the ink over time. Additional additives that may be optionally present in the ink include thickeners, pH adjusters, buffers, conductivity enhancing agents, drying agents and defoamers.
• dyes may be added.
• Many dyes and pigments are known to be suited for the ink jet technology. Suitable dyes are further selected based on their compatibility in the carrier medium (i.e. aqueous based or solvent based) and on the compatibility with the oleophilizing agent, i.e. they should not lead to coagulation.
• aqueous inks are anionic dyes such as acid black
• the support may be any support suitable for printing plates.
• Typical supports include metallic and polymeric sheets or foils.
• a support having a metallic surface is used.
• the metallic surface is oxidised.
• a support having an anodised aluminium surface is employed.
• the support for the lithographic printing plate is typically formed of aluminium which has been grained, for example by electrochemical graining, and then anodised, for example, by means of anodising techniques employing sulphuric acid and/or phosphoric acid. Methods of both graining and anodising are very well known in the art and need not be further described herein.
• the printing plate After writing the image the printing plate can be inked with printing ink in the normal way, and the plate can be used on a printing press. Before inking the plate can be treated with an aqueous solution of natural gum, such as gum acacia, or of a synthetic gum such as carboxymethyl cellulose, as it is well known in the art of printing.
• natural gum such as gum acacia
• synthetic gum such as carboxymethyl cellulose
• the lithographic base with a hydrophilic surface comprises a flexible support, such as e.g. paper or 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, melamine type cross-linkers, ammonium zirconyl carbonate, titanate crosslinkers, or a hydrolysed tetraalkylorthosilicate. 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.
• a cross-linked hydrophilic binder in the heat-sensitive layer used in accordance with the present embodiment also contains colloidal inorganic pigments that increase the mechanical strength and the porosity of the layer e.g. metal oxide particles which are particles of titanium dioxide or other metal oxides. It is believed that incorporation of these particles gives the surface of the cross-linked hydrophilic layer a uniform rough texture consisting of microscopic hills and valleys which serve as storage places for water in background areas.
• these particles are oxides or hydroxydes of beryllium, magnesium, aluminium, silicon, gadolinium, germanium, arsenic, indium, tin, antimony, tellurium, lead, bismuth, titanium or a transition metal.
• Particularly preferable inorganic particles are oxides or hydroxides of aluminum, silicon, zirconium or titanium, used in at most 75 % by weight of the hydrophilic layer.
• the inorganic pigments may have have a particla size ranging from 0.005 ⁇ m to 10 ⁇ m.
• the thickness 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 ⁇ m and is preferably 1 to 10 ⁇ m.
• 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.
• ink jet printing tiny drops of ink fluid are projected directly onto an ink receptor surface without physical contact between the printing device and the receptor.
• the printing device stores the printing data electronically and controls a mechanism for ejecting the drops image-wise. Printing is accomplished by moving the print head across the paper or vice versa.
• Early patents on ink jet printers include US 3,739,393, US 3,805,273 and US 3,891,121.
• the jetting of the ink droplets can be performed in several different ways.
• a continuous droplet stream is created by applying a pressure wave pattern. This process is known as continuous ink jet printing.
• the droplet stream is divided into droplets that are electrostatically charged, deflected and recollected, and into droplets that remain uncharged, continue their way undeflected, and form the image.
• the charged deflected stream forms the image and the uncharged undeflected jet is recollected.
• several jets are deflected to a different degree and thus record the image (multideflection system).
• the ink droplets can be created “on demand” (“DOD” or “drop on demand” method) whereby the printing device ejects the droplets only when they are used in imaging on a receiver thereby avoiding the complexity of drop charging, deflection hardware, and ink recollection.
• DOD on demand
• the ink droplet can be formed by means of a pressure wave created by a mechanical motion of a piezoelectric transducer (so-called “piezo method”), or by means of discrete thermal pushes (so-called “bubble jet” method, or “thermal jet” method).
• the oleophilizing capacity of representatives of the different chemical substances described above was tested using the following procedure.
• the oleophilizing agent was dissolved in isopropanol or in N-methylpyrrolidone in a concentration of 0.1 to 2 % w/w.
• a 6 ⁇ l droplet of the ink fluid was jetted on a lithographic electrochemically grained and anodised aluminum receiver as described above.
• the local oleophilicity was tested by mounting the plate on an ABDICK 360 press and using VAN SON RUBBERBASE as ink (registered trade mark of van Son Co.) and 2 % TAME (trade mark of Anchor/Lithchemko Co.) as fountain.
• the ink uptake of the droplet image was evaluated.

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Cited By (10)

Citations (2)

• 2000
  • 2000-05-26 EP EP20000201860 patent/EP1157827B1/fr not_active Expired - Lifetime
  • 2000-05-26 DE DE2000622010 patent/DE60022010T2/de not_active Expired - Fee Related
• 2001
  • 2001-05-25 JP JP2001156796A patent/JP2002046362A/ja active Pending

Patent Citations (2)

Non-Patent Citations (1)

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