A FLUID FOR PREPARATION OF PRINTING PLATES AND METHOD FOR USE OF SAME

Abstract: A simple and inexpensive direct, computer to plate (CTP) method for producing an offset lithographic plate in a process employing a novel inkjet fluid that, while giving excellent jetting properties with high consistency and quality, can be easily dried on an uncoated lithographic plate. The inkjet fluid has a perselected viscosity and comprises a two-phase emulsion system: an oleophilic inner phase and a continuous, aqueous, external phase. Controlling the viscosity of the inkjet fluid enables controlling the dot size of the fluid deposited on the printing surface, resulting in a high quality, robust printed image even after many runs of the offset press.

Description: A FLUID FOR PREPARATION OF PRINTING PLATES AND METHOD FOR USE OF SAME FIELD OF THE INVENTION The present invention generally relates to the preparation of printing plates using computer-to-plate (CTP) methods involving inkjet printing, and more particularly, to a novel inkjet marking fluid and to a method for direct CTP preparation of offset lithographic printing plates. BACKGROUND OF THE INVENTION Offset lithographic printing has been a popular method of printing for many years, primarily because of the relative ease with which printing plates can be produced. Currently, the most widely- used method for plate preparation has remained that which utilizes specially-prepared masking films through which pre-sensitized printing blanks are selectively hardened or softened — according to the chemistry of the plate — by exposure to ultra-violet light. The plate then undergoes a development process, during which the more soluble regions of the plate are washed away. A detailed description of a typical system and the plates used is found in Chapter 20 of the book entitled: Printing Materials: Science and Technology, by Bob Thompson (Pira Int., Leatherhead, Surrey, UK, 1998). In recent years, various considerations have arisen that point to advantages for modification of hitherto generally-accepted practices. With the advent of computers, information for printing is prepared digitally and it has become preferable to use this digital information as directly as possible in plate preparation. One obvious way would be to eliminate the masking film. Not only are these films a source of expense, but the most widely used films are based on silver chemistry whereby the exposure and handling of the film must be in a light-excluding environment. In addition, the exposed film must be processed with chemical solutions which are unstable, messy, and environmentally problematic. One answer is to be found in computer-to-plate (CTP) systems whereby the offset lithographic plates are directly imaged with a light source which is modulated to correspond to the digital information from the computer. Thus the film intermediate is completely eliminated. In general, such plates still need processing by solution, although attempts are being made to develop CTP systems that are processless. A more-detailed description of the subject of CTP systems is found in Chapter 21 of the above-cited book (Thompson, op.cit). In US Patent 5,339,737, to Lewis, et al, describe the processless preparation of offset lithographic printing plates, wherein the upper layer or layers of the plate are removed by ablation. The upper layer is either oleophobic for waterless plates or hydrophilic for conventional, wet-process plates. The substrate is oleophilic in both cases. Another patent similar to the previous one is US 5,353,705 to Lewis, et al, but this patent describes additional layers for secondary, partial ablation. Yet another patent utilizing ablation is US 5,487,338 to Lewis et al, but it includes the use of reflective layers. All of these prior art inventions involve multiple-layered plates which are expensive and time-consuming to produce. Also, it is more difficult to maintain a consistent standard of quality from plate to plate. Moreover, they utilize laser imaging systems which are in themselves costly. Due to these disadvantages, the prior art inventions do not address the needs of many small to medium-sized enterprises. A plate-making process is required which has the utmost simplicity, eliminates all chemical processing, and can be effected at a minimal cost for the plate production and for associated equipment. The process should also be rapid. Inkjet printing is a non-impact, digital printing method which allows images to be produced and printed under computer control. Inkjet ink is jetted through very fine nozzles and the resultant ink droplets form an image directly on a substrate. There are two main types of inkjet processes. In one process, usually termed "continuous inkjet printing", a stream of ink drops is electrically charged and then is deflected by an electric field, either directly or indirectly, onto a substrate. The viscosity of inks used in such systems is typically 2 or 3 centipoise. In the second process, usually called "drop on demand (DOD) inkjet printing", the ink supply is regulated by an actuator such as a piezoelectric actuator of the type used in the Trident Ultrajet Printhead. The pressure produced during the actuation forces a droplet through a nozzle onto the substrate. Inks for DOD inkjet printing do not need to be conductive and their viscosity is typically between 2 and 40 centipoise. The prior art shows several examples of the application of inkjet printing principles to preparing offset lithographic printing plates. In US Patent 4,833,486 to Zerillo, a hydrophobic, solid, inkjet ink - also called a phase-change inking medium - contains waxes held at a sufficiently high temperature to jet the ink through a DOD head. This solid, phase-change ink technology is more fully-described in US Patents 4,390,369 and 4,484,948 to Merritt et al, and 4,593,292 to Lewis. The substrate is a hydrophilic offset plate - either paper or aluminum - onto which the ink is jetted to form an image. When the ink hits the plate it immediately cools and solidifies. One problem, and a serious drawback, of such an approach is the difficulty of obtaining sufficiently good adhesion to the plate of the wax in the ink medium to run multiple impressions during lithographic printing. European Patent EP503621, owned by Nippon Paint Co., describes two approaches. One approach describes jetting inks onto a presensitized plate which then needs further treatment, including a developing stage with a liquid developer. The other approach uses a non-presensitized plate and the inkjet ink is photosensitive so that it can be hardened onto the plate. European Patent EP533168, owned by Nippon Paint Co., describes the use of a photopolymeric-based inkjet ink together with an ink-absorbing layer on the lithographic plate surface. European Patent EP697282, to Leanders and owned by Agfa, describes a two-component system whereby one reactive component is in the ink and the other in the lithographic plate surface so that when the ink hits the plate it produces an oleophilic, reduced silver image that can be used in the offset printing process. In US Patent 5,495,803 to Gerber and owned by Gerber Scientific Products, Inc., a coated, presensitized plate is imaged with a UV-opaque, hot-melt, inkjet ink and the ink is used as a photomask to expose the plate. The unexposed presensitized polymer and the ink are subsequently removed by washing. In US Patent 5,738,013 to Kellet, an inkjet plate-making process is described which involves the use of a reactive inkjet ink which is bonded to the lithographic plate by a chemical reaction activated by radiant energy. This assumes that such inks have very good stability at room temperature so that no ink passing through the nozzles of the inkjet will be blocked. Moreover, it is assumed that the ink will have good reactivity at high temperatures so that the ink becomes insoluble with good adhesion to the offset plate and with good oleophilic properties. Thus, while there have been prior art attempts to use the inkjet process for direct imaging of plates, difficulties have remained in producing satisfactory quality and run lengths while maintaining reasonable costs and operating times. Both water-based and solvent-based inks have problems of spreading of the ink on the high-surface-energy, hydrophilic plate surface due to the properties needed to jet the ink. Phase-change inks have problems with bonding of the wax-like ink to the plate. In addition, there is the need to eliminate further liquid processing and to provide a simple process of plate production, or, to eliminate the plate component altogether and directly image a lithographic press printing surface. SUMMARY OF THE INVENTION Accordingly, it is a principal object of the present invention to overcome the disadvantages associated with prior art computer-to-plate methods, by providing a simple and inexpensive method of producing an offset lithographic printing plate by use of the inkjet process. The method uses a novel inkjet fluid that, while giving excellent jetting properties with high consistency and quality, can be easily dried on an uncoated lithographic printing plate. In accordance with a preferred method of the present invention, there is provided a method for the direct CTP preparation of a printing plate, said method comprising the steps of: providing a digital image generated by a computer system; providing an inkjet marking fluid having a preselected viscosity, wherein said marking fluid is comprised of a two-phase emulsion system consisting of an oleophilic inner phase and a continuous, aqueous, external phase; jetting said marking fluid onto a printing surface; and drying said marking fluid on said printing surface. In the preferred method, inkjet marking fluid is deposited in a pattern that is digitally-determined to provide the information directly from a computer to a plate. In accordance with the Inventive method, the dot size of the inkjet fluid deposited on the printing surface of an offset printing press is controlled by controlling the viscosity of the fluid, thus achieving excellent control over the quality of the image to be printed. In another preferred method, the novel inkjet marking fluid is used directly in a plateless lithographic printing system to form a strong, stable, oleophilic image from which large quantities of good-quality impressions can be printed.. Other features and advantages of the present invention will become clear from the further detailed description and examples. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention with regard to the embodiments thereof, reference is made to the accompanying drawings (not to scale), in which like numerals designate corresponding elements or sections throughout, and in which: Figures la, lb, and lc show enlarged sectional views of a typical, multi-layered offset lithographic printing plate, as known in the prior art, depicting the process of imaging said plate using UN light. Figures 2a, 2b, and 2c show enlarged sectional views of a typical, multi-layered offset lithographic printing plate, as known in the prior art, depicting the process of imaging said plate using an infra-red laser ablation process; Figure 3 shows a computer-to-plate inkjet system, featuring the drop-wise deposition of inkjet marking fluid from an inkjet printing head onto a printing plate in accordance with the present invention; Figure 4 shows a computer-to-plate inkjet system, depicting an offset lithographic plate, prepared in accordance with the present invention, mounted onto an offset printing press; and Figure 5 shows another embodiment of the method of the present invention, wherein the image to be formed is provided by the direct deposition of inkjet marking fluid onto a lithographic printing cylinder in a plateless system. DETAILED DESCRIPTION OF THE INVENTION Referring now to Figures la, lb, and lc, there is shown an example of the steps in the widely-used prior art process of plate-making with presensitized plates. Figure la shows a film 2 which contains, in negative form, the image 4 to be printed. Presensitized printing plate 6 is comprised of a grained, anodized aluminum substrate 8 and coated with a photopolymeric layer 10, which is comprised of a photosensitive pre-polymer and a carrier resin. Film 2 is placed in emulsion-to-emulsion contact with presensitized plate 6 and, as shown in Figure lb, is flood-irradiated with ultraviolet light 12. Transparent areas 4 of negative film 2, which represent the image areas to be printed, permit the penetration of UN light 12 to photopolymeric layer 10 which reacts to form hard, insoluble oleophilic areas 14. The black areas 5 of negative film 2, which correspond to the background areas of the print, prevent UV light 12 from penetrating and thus portions of photosensitive layer 10 remain in the pre-polymer state. Negative film 2 is then removed and plate 6 is processed - usually with a high pH aqueous solution in which the unpolymerized portions of layer 10 are readily soluble. This exposes the grained anodized surface 16 of substrate 8 and provides the hydrophilic background areas for the processed printing plate, as shown in Figure 1 c, now ready to be mounted in a conventional offset lithographic printing press.. Figures 2a, 2b, and 2c show, in an enlarged depiction, the steps in a simplified, infrared-ablatable, computer-to-plate process as known in the prior art. Figure 2a depicts an unprocessed plate 26 comprising: a substrate 8, which may be, for example, aluminum; an infrared-absorbing layer 22; and a hydrophilic, top coating 24. In Figure 2b, plate 26 is imaged by digitally-modulated infrared radiation 28 that is absorbed by layer 22. The energy absorbed causes an extremely fast rise in temperature resulting in ablation of layer 22 which takes with it portions of the hydrophilic coating 24. Figure 2c shows the resulting plate with portions of coating 24 providing the hydrophilic background areas of plate 26 and the exposed portions of surface 16 of substrate 8 providing the oleophilic imaged portions of plate 26. Referring now to Figure 3, there is shown a computer-to-plate inkjet printing system 30, constructed and operated in accordance with the principles of the present invention. Using a computer 20, a data pulse train 42 is generated which activates a transducer 45. Transducer 45 emits an electrical signal which actuates a piezo-electric crystal 36. Crystal 36 produces a pressure wave inside ink chamber 38 causing inkjet fluid 32 in ink chamber 38 to be ejected in a stream of droplets 40 through inkjet printer nozzle 34 onto surface 16 of a typical printing plate substrate 8. Substrate 8 may be any type of substrate known to the art from which offset lithographic plates are fabricated, but in the preferred embodiment, it is aluminum-based with a grained, anodized, hydrophilic surface. Although any type of inkjet system is useful in the present invention, Figure 3 shows a generic impulse, drop-on-demand, system as this is the preferred system of the invention. As the inkjet head 39 traverses surface 16, a pattern of dots 44, forming the image to be printed, is deposited on surface 16 of substrate 8. After fluid deposition, plate 46 is heated by any means known to the art to evaporate any water in the fluid and to fuse the resins onto substrate 8. Figure 4 shows a further embodiment of the method of the present invention, wherein a printing plate 46, prepared in accordance with the method of the present invention as described above and as shown in Figure 3, is mounted onto a cylinder 48 of an offset lithographic press 56 used in combination with a CTP inkjet system 30. Inkjet marking fluid is deposited in a pattern that is digitally-determined to provide the information directly from a computer to a plate. A data pulse train 42, generated from computer workstation 20, activates transducer 45 which controls the flow of inkjet marking fluid provided by inkjet system 30 thereby causing said marking fluid to be ejected in a stream of drops 40 through inkjet printer nozzle 34 onto the surface of printing plate 46. Drops 40 produce a pattern of dots 44 as the inkjet head 39 traverses the surface of plate 46, thus forming an image on the surface of printing plate 46. After said marking fluid is deposited onto printing plate 46, drying system 62, which may be any drying system known to the art, is used to heat printing plate 46 to evaporate any water remaining on the surface of printing plate 46 and to fuse the resins to the substrate of printing plate 46. Printing plate 46 is then wetted by fountain solution applied by wetting cylinder 58 and the imaged areas are inked by inking cylinder 60 and transferred to blanket cylinder 50 by rotation of the cylinder press. Thus the inked image is further transferred to paper 54, as it is pressed between blanket cylinder 50 and impression cylinder 52. In a further embodiment of the present invention, as is shown in Figure 5, the printing image is erasable and offset lithographic printing press 56 is plateless. Inkjet system 30 is depicted jetting marking fluid 40 onto the surface of erasable cylinder 48. Erasable cylinder 48 acts as a substrate for the direct deposition of marking fluid drops 40 and is comprised of any type of hydrophilic surface known to the art. In the preferred embodiment, cylinder 48 is comprised of a grained, anodized, aluminum surface. Although any type of inkjet system is useful in this invention, Figure 5 shows a generic impulse, drop-on-demand system 30, as this is the preferred system. Using computer 20, a data pulse train 42 is generated which activates a transducer 45. Transducer 45 emits an electrical signal which controls the jetting of inkjet marking fluid ejected in a stream of droplets 40 from inkjet head 39 via nozzle 34 which produces a pattern of dots 44 as inkjet head 39 traverses the surface of erasable cylinder 48. Thus the inkjet marking fluid in the form of drops 44 is deposited in a pattern that is digitally-determined to provide the information directly from computer workstation 20 to erasable cylinder 48 which is plateless. After marking fluid 44 is deposited onto erasable cylinder 48, it is dried by drying system 62, which can be any method of heating as known to the art, to evaporate the water in the fluid and to fuse the resins to the substrate. In printing, a fount solution is applied to erasable cylinder 48 by wetting cylinder 58 and the imaged areas composed of the pattern of dots 44 are inked by ink cylinder 60 and transferred to blanket cylinder 50 by rotation of the cylinders in lithographic press 56, thus the inked image is transferred to the print surface consisting, in the example shown, of paper 54, which is pressed between the blanket cylinder 50 which receives the inked image and impression cylinder 52. After the printing process, the dried image can be erased either by abrasion or with the aid of an aqueous fluid of either high or low pH or by application of high temperature to decompose the cured image remaining and to clean erasable cylinder 48 which is then ready to accept a new image. In accordance with the principles of the present invention, the inkjet medium is provided in the form of a dispersion since it is known to those skilled in the art that true solutions, whether they be water-based, oil-based, or solvent-based, give poor imaged plates because of their tendency to spread over the surface of the plates. The present invention comes to solve this difficulty by utilizing a two-phase fluid comprising a combination of resin dispersion in water. On contact with a printing plate, the outer, aqueous phase of the inkjet fluid is separated from the internal phase by both capillary action onto the hydrophilic plate surface, and by evaporation, leaving the relatively high-viscosity internal phase of the dispersion which coalesces to give a smooth sharp print image on the printing plate. The preferred embodiment of the invention utilizes an inkjet marking fluid which is based on an internal, dispersion phase and a continuous aqueous, external phase. The particle size of the internal phase is from 4 nm to 3 microns. The inkjet marking fluid in the preferred embodiment is characterized by a viscosity greater than 2 centipoise and less than 40 centipoise, and, more specifically, by a viscosity of between 3 and 25 centipoise. Surface tension of the marking fluid should be within the range of between 28-60 dyne/cm. The amount of polymer binder which constitutes the internal phase of the dispersion should be at least 5% and, in the preferred embodiment, in the range of between 8- 20% by weight. In the preferred embodiment, the internal phase of the dispersion is a polymer selected from the following group: Urethanes Acrylates Methacrylates Styrene Vinyl Acetate and other vinyl esters(e.g. laurate) Ethylene Butadiene Vinyl chloride Vinylidene chloride Copolymers of the above materials Other ingredients present in the inkjet fluid are those known to the art. These include humectants, dyes, pigments, cosolvents, and coalescing agents. A preferred additive in these fluids is a water-soluble, low molecular-weight polymer that acts as a surfactant in stabilization of the system and at the same time helps maintain the sharpness of print on the finished, imaged plate. Another preferred type of ingredient is a coalescing agent which is necessary to ensure that the dispersed polymer particles form a smooth image after the image coalesces on the surface of the plate and the water leaves the system. Although some coloration or dye substance is needed in the system so that the image on the plate is visible, in the preferred embodiment, carbon black, which is in itself oleophilic, serves this purpose, but it is limited to a concentration of not greater than 15% by weight in order to optimize the mechanical resistance of the image to the printing process. The above rheological properties enable the inkjet marking fluid to produce small (down to 3 picoliter) droplets to give high resolution. At the same time, the combination of the high viscosity and surface tension of dispersions restricts spreading of the inkjet marking fluid on the high surface-energy face of the hydrophilic plate. Thus the particle dot size in the image may be controlled by a suitable combination of marking fluid properties, especially by controlling the viscosity of the marking fluid. It is possible to further improve the abrasion resistance of the jetted image to increase run length by means of injecting various forms of energy. This may be done by heating the image-bearing printing plate up to approximately 200° C to increase the cross-linking density of the polymer. In the preferred embodiment, the imaged printing plate is heated to a temperature between 100-140° C. Alternatively, drying is done by exposure of the imaged plate to UN light when the composition of the inkjet marking fluid is based on photosensitive monomers or oligomers in conjunction with photoinitiators. The inkjet printing system can operate on its own, functioning solely as a plate-maker, or it can be incorporated directly into a lithographic printing press. In the latter case, printing may commence immediately after application of the image to a blank plate and drying, thereby reducing press set-up time considerably. The inkjet imaging system can be configured either as a flatbed printing system or as a cylinder printing sytem wherein the lithographic plate blank is mounted on the flatbed or attached to the exterior of the cylindrical surface. In another embodiment of the method of the present invention, the inkjet marking fluid is deposited directly onto an erasable cylinder in an offset printing press which serves as the printing surface in a plateless system. The following are examples of preferred embodiments of the marking fluid used in the printing process of the present invention in which all parts are given by weight. EXAMPLE 1 An inkjet marking fluid consisting of 7 parts of acrylic polymer emulsion, sold under the trade name of Joncryl 538 by S.C Johnson, 12 parts of Ethylenglycol, 1 part of di-propyleneglycol-monomethylether (DPM), 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Bayscript Magenta by BAYER) and 12 parts of deionized water, was prepared. A 200 micron thick grained anodized aluminum plate was then placed on an XY bed where it was imaged (600 dpi image) using the inkjet printhead described in EP640481 assigned to Scitex using the above liquid. The plate was then heated to 140°C for 2 minutes and then mounted on a Heidleberg GTO printing machine where 50,000 good impressions were printed on high-quality coated paper. EXAMPLE 2 An inkjet marking fluid consisting of 7 parts of acrylic polymer emulsion, sold under the trade name of Joncryl 537 by S.C Johnson, 12 parts of Ethylenglycol, 1 part of DPM, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Bayscript Magenta by BAYER) and 13 parts of de-ionized water, was prepared. Imaging, heat treatment, and testing were performed as described in Example 1. This process gave results similar to those reported in Example 1. EXAMPLE 3 An inkjet marking fluid consisting of 7 parts of acrylic emulsion, sold under the trade name of Joncryl 2177 by S.C Johnson, 12 parts of Ethylenglycol, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Bayscript Magenta by BAYER) and 13 parts of de-ionized water, was prepared. Imaging , heat treatment, and testing as described in Example 1 gave results similar to those reported there. EXAMPLE 4 An inkjet marking fluid consisting of 7 parts of acrylic emulsion polymer, sold under the trade name of Lucidene 366 by Morton, 12 parts of Ethylenglycol, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Magenta Bayscript by BAYER) and 14 parts of de-ionized water, was prepared. Imaging , heat treatment, and testing as described in Example 1 gave results similar to those in Example 1. EXAMPLE 5 An inkjet marking fluid consisting of 8 parts of acrylic emulsion polymer, sold under the trade name of Lucidene 388 by Morton, 12 parts of Ethylenglycol, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Magenta Bayscript by BAYER) and 13 parts of de-ionized water, was prepared. Imaging, heat treatment and testing as described in Example 1 gave results similar to those in Example 1. EXAMPLE 6 An inkjet marking fluid consisting of 11 parts of styren/acrylic emulsion polymer, sold under the trade name of Lucidene 410 by Morton, 12 parts of Ethylenglycol, 1 part of DPM , 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Magenta Bayscript by BAYER) and 9 parts of de-ionized water, was prepared. Imaging, heat treatment, and testing as described in Example 1 gave results similar to those in Example 1. EXAMPLE 7 An inkjet marking fluid consisting of 7 parts of styrene/acrylic emulsion polymer, sold under the trade name of Lucidene 5025 by Morton, 12 parts of Ethylenglycol, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Magenta Bayscript by BAYER) and 13 parts of de-ionized water, was prepared. Imaging, heat treatment, and testing as described in Example 1 gave results similar those reported in Example 1. EXAMPLE 8 An inkjet marking fluid consisting of 6 parts of vinylidene chloride acrylic copolymer emulsion, sold under the trade name of Permax 801 by BF-Goodrich, 12 parts of Ethylenglycol, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Magenta Bayscript by BAYER) and 13 parts of de-ionized water, was prepared. Imaging , heat treatment, and testing as described in Example 1 gave results similar to those in Example 1. EXAMPLE 9 An inkjet marking fluid consisting of 10 parts of aliphatic urethane polymer dispersion, sold under the trade name of Sancure 776 by BF-Goodrich, 0.6 parts from the polymer dispersion solids of the photoinitiator Melamine, 12 parts of Ethylenglycol, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta Dye sold under the trade name of Bayscript Magenta by BAYER) and 11 parts of de-ionized water, was prepared. Imaging , heat treatment, and testing as described in Example 1 gave results similar to those in Example 1. The plate can be cured in order to give extra abrasion resistance by crosslinking the polymeric system. EXAMPLE 10 An inkjet marking fluid consisting of 10 parts of aliphatic urethane polymer dispersion, sold under the trade name of Sancure 850 by BF-Goodrich, 0.6 parts from the polymer dispersion solids of the photoinitiator sold under the trade name Quantacure ITX by Biddle Sawyar, 12 parts of Ethylenglycol, 1 part of black pigment sold under the trade name of Hostafine Black TS by Clariant GmbH (or magenta dye sold under the trade name of Magenta Bayscript by BAYER), and 11 parts of de-ionized water, was prepared. Imaging , heat treatment, and testing as described in Example 1 gave results similar to those in Example 1. The plate can be UN-cured in order to give extra abrasion resistance by crosslinking the polymeric system. EXAMPLE 11 This Example most-clearly demonstrates the relationship between the viscosity of the inkjet marking fluid and the dot size on a commercially-available, brush-grained and post-anodic treated, uncoated aluminum offset plate. An inkjet marking fluid consisting of variable parts of acrylic polymer emulsion, sold under the trade name of Joncryl 538 by S.C Johnson and other components as described in Example 1 was prepared and imaged. Table I shows the dot diameter (in microns) obtained by using the above-described inkjet marking fluid in different viscosities. Table I Joncryl 538 Viscosity Dot Diameter Amount [parts] [cP] [μm] Exp. 11A 1.4 3.5 225 Exp. 1 IB 7 5.7 125 Exp. 11C 10.5 7.9 90 Exp. 11D 14 13.5 75 EXAMPLE 12 This Example demonstrates the relationship between the viscosity of the inkjet marking fluid and the dot size on a commercially-available, brush-grained and post-anodic-treated, uncoated aluminum offset plate. An inkjet marking fluid consisting of variable parts of aliphatic urethane polymer dispersion, sold under the trade name of Sancure 850 by BF-Goodrich and other components as described in Example 10, was prepared and imaged. Table II shows the dot diameter (in microns) obtained by using the above-described inkjet marking fluid with different viscosities. Table H Sancure 850 Viscosity Dot Diameter Amount [cP] [μm] [parts] Exp. 12A 4.8 3.3 250 Exp. 12B 9.6 4.1 175 Exp. 12C 14.5 7.8 100 Exp. 12D 19.3 12.6 65 Having described the present invention with regard to certain specific embodiments thereof, it is to be understood that the description is not meant as a limitation, since further modifications may now suggest themselves to those skilled in the art, and it is intended to cover such modifications as fall within the scope of the present invention.

Claims: CLAIMS: 1. A method for the direct CTP preparation of printing plates, said method comprising the steps of: providing a digital image generated by a computer system; providing an inkjet marking fluid having a preselected viscosity, wherein said inkjet marking fluid is comprised of a two-phase emulsion system comprised of an oleophilic inner phase and a continuous aqueous external phase; jetting said marking fluid onto a printing surface using an inkjet printing device; and drying said marking fluid on said printing surface. 2. The method of claim 1, wherein said inner phase of said marking fluid comprises any combination of a resin dispersion in water. 3. The method of claim 1, wherein said inner phase of said marking fluid comprises a binder having between 8-20% by weight of the liquid medium in said marking fluid. 4. The method of claim 1, wherein said inner phase of said marking fluid is characterized by a particulate size of between 4 nm to 3 microns. 5. The method of claim 1, wherein said marking fluid has a viscosity between 2-40 centipoise. 6. The method of claim 1, wherein said marking fluid has a surface tension within the range of 28-60 dyne/cm. 7. The method of claim 2, wherein said dispersion consists of a polymer selected from the group comprising: urethanes, acrylates, methacrylates, styrene, ethylene, butadiene, vinyl chloride, vinylidene chloride, vinyl acetate and other vinyl esters, copolymers of these materials and mixtures thereof. 8. The method of claim 2, wherein said dispersion comprises photosensitive monomers combined with photoinitiators where, upon exposure to UV light, said marking fluid is cured onto said printing plate. 9. The method of claim 2, wherein said dispersion comprises photosensitive oligomers combined with photoinitiators where, upon exposure to UV light, said marking fluid is cured onto said printing plate. 10. The method of claim 2, wherein said marking fluid further comprises humectants, dyes, pigments, co-solvents, and coalescing agents. 11. The method of claim 10, wherein said humectants are selected from the group comprising glycols, glycol ethers, glycol ether acetates, N-methylpirrolidone, and substituted pirrolidone. 12. The method of claim 10, wherein said dyes comprise less than 15% concentration by weight of carbon black. 13. The method of claim 10, wherein said pigments comprise less than 15% concentration by weight of carbon black. 14. The method of claim 10, wherein said coalescing agents are selected from the group comprising glycol ethers, glycol acetates, and butyl carbitol. 15. The method of claim 1, wherein said printing surface is hydrophilic. 16. The method of claim 1, wherein said printing surface comprises a polyester plate. 17. The method of claim 16 wherein said polyester plate comprises a grained, anodized aluminum substrate. 18. The method of claim 16, further comprising the step of incorporating said printing plate into an offset lithographic printing press system. 19. The method of claim 18, wherein said printing press system comprises a lithographic printing flatbed system. 20. The method of claim 18, wherein said printing press system comprises an offset lithographic cylinder-plate system. 21. The method of claim 1, wherein said drying step is performed by exposure to UV light. 22. The method of claim 1, wherein said drying step is performed by thermal processing. 23. The method of claim 22, wherein said thermal processing is performed by heating of said printing surface to a temperature between 100-140°C. 24. The method of claim 1 wherein said inkjet printing device comprises a drop-on-demand system. 25. The method of claim 1 wherein said inkjet printing device comprises a continuous system. 26. The method of claim 1, wherein said printing surface comprises a plateless, lithographic press cylinder. lb 27 The method of claim 1 , wherein said printing surface comprises a plateless, flat-bed lithographic press 28 An inkjet marking fluid for use in a method for the direct CTP preparation of printing plates, said marking fluid comprising a two-phase emulsion system having an oleophilic inner phase and a continuous aqueous external phase. 29 The marking fluid of claim 28, wherein said inner phase comprises any combination of a resin dispersion in water 30 The marking fluid of claim 28, wherein said inner phase comprises a binder having between 8-20% by weight of the liquid medium in said marking fluid 31 The marking fluid of claim 28, wherein said inner phase is characterized by a particulate size of between 4 nm to 3 microns 32 The marking fluid of claim 28 having a viscosity between 2-40 centipoise 33 The marking fluid of claim 28 having a surface tension within the range of 28-60 dyne/cm 34 The marking fluid of claim 29, wherein said dispersion consists of a polymer selected from the group comprising urethanes, acrylates, methacrylates, styrene, ethylene, butadiene, vinyl chloride, vinylidene chloride, vinyl acetate and other vinyl esters, copolymers of these materials and mixtures thereof 35 The marking fluid of claim 29, wherein said dispersion comprises photosensitive monomers combined with photoinitiators where, upon exposure to UV light, said marking fluid is cured onto said printing plate 36 The marking fluid of claim 29, wherein said dispersion comprises photosensitive oligomers combined with photoinitiators where, upon exposure to UV light, said marking fluid is cured onto said printing plate. 37 The marking fluid of claim 29, further comprising humectants, dyes, pigments, co-solvents, and coalescing agents. 38. The marking fluid of claim 37, wherein said humectants are selected from the group comprising glycols, glycol ethers, glycol ether acetates, N-methylpirrolidone, and substituted pirrolidone. 39 The marking fluid of claim 37, wherein said dyes comprise less than 15% concentration by weight of carbon black. 40 The marking fluid of claim 37, wherein said pigments comprise less than 15% concentration by weight of carbon black. 41 The marking fluid of claim 37, wherein said coalescing agents are selected from the group comprising glycol ethers, glycol acetates, and butyl carbitol.

Inventors: FIGOV MURRAY, FRENKEL MOSHE, KIMELBLAT JANKIEL, NITZAN BOAZ, FIGOV, MURRAY, FRENKEL, MOSHE, KIMELBLAT, JANKIEL, NITZAN, BOAZ
Applicants: APRION DIGITAL LTD, FIGOV MURRAY, FRENKEL MOSHE, KIMELBLAT JANKIEL, NITZAN BOAZ, FIGOV, MURRAY, FRENKEL, MOSHE, KIMELBLAT, JANKIEL, NITZAN, BOAZ
Application year: 2000
Main classification: B41C1
IPC codes: B41C1, B41J2, C09D11