WO1994026517A1

WO1994026517A1 - Dampening systems for lithographic printing

Info

Publication number: WO1994026517A1
Application number: PCT/US1994/005337
Authority: WO
Inventors: Thomas A. Fadner
Original assignee: Fadner Thomas A
Priority date: 1993-05-17
Filing date: 1994-05-16
Publication date: 1994-11-24

Abstract

Apparatus and method are disclosed for lithographic printing whereby the dampening solution input from a non-contact source (41) is conveyed to the printing plate (23) primarily by the inking train of rollers or adjuncts thereof having at least four fully inked nips (1-5) between the dampening solution input receiving roller (42) and all inking form rollers (44, 45), the latter also functioning as dampening form rollers.

Description

DAMPENING SYSTEMS FOR LITHOGRAPHIC PRINTING Background of the invention

1. Field of the Invention. This invention pertains to lithographic printin, and more particularly to dampening methods and apparatus associated with lithographic printing.

2. Description of the Prior Art. Conventional prior art dampening systems for lithographic printing presses are classed primarily as the continuous type or the semi-continuous ductor type, for which a dampening train of rollers makes direct physical contact with an initial water input source on a full-time or part-time basis, respectively, and by means of a dampening form roller in contact with the lithographic printing plate. Certain recent dampening systems utilize a detached input of water by means of a spray or mist applied across a gap onto a receiving roller of the dampener train of rollers. Dampening systems with these detached or gapped water input means are termed discontinuous.

Other dampening systems such as the H. Dahlgren type, U.S. Patent 4,527,479, use similar components to those just described but convey the dampening solution to the plate by way of the first inking form roller instead of by means of a separate dampening form roller. In this indirect system the first inking form roller actually becomes the dampening form roller. Special dampening solution additives were found required for these systems. In virtually all high-speed lithographic printing presses, the dampening water is conveyed by means of the dampening train of rollers directly to the printing plate. By accumulating in the hydrophilic non- image regions of the plate, the water allows transfer of ink from the press inking form rollers only to the oleophilic image regions of the planographic, lithographic printing plate. The resulting image differentiated inked regions of the plate are then transferred to a resilient blanket, then from the blanket to the substrate being printed.

In practice of lithographic printing, nearly without exception, the dampening form roller is located prior to the first inking form roller and after the plate-to-blanket nip, as defined by the rotational direction of the printing plate. This practice is termed water-first dampening. The dominant prior art dampening configuration is termed the water-first, direct-to-plate, continuous type.

Dampening water conveyance to the plate by means of the inking train of rollers or by means of water-last, direct-to-plate dampening systems have been disclosed in the prior art and have been utilized in special types of lithographic presses, as, for instance, depicted in Fadner U.S. Patent 4,690,055. These types have achieved limited commercial success and only in newspaper printing systems which have lower quality demands. Accordingly, both ink train dampening and water-last dampening have gradually been superseded in favor or conventional direct, water-first dampening systems and configurations.

The majority of installed high-volume lithographic printing presses around the world and virtually all of the high-volume lithographic presses currently being manufactured around the world utilize the dominant water-first, direct-to-plate continuous dampening configuration in one manifestation or another. Nevertheless, all versions of this dampening type suffer to a more or less significant degree from water interference with the transfer of ink to the printing plate. For instance, whenever the format to be printed contains low circumferential image content in one region of the plate at a given position of the overall press width and high circumferential image content in another cross-press location there exists no consistent prior art method, practice, or apparatus to assure that dampening of the printing plate remains simultaneously trouble-free in both regions in regard to consistent and predictable ink input to the plate and thence to the substrate being printed. A similar situation occurs when changing from a low image content printing job to a high image content job or vice versa using the same printing press. A similar situation occurs when switching from one ink type or source to another.

The inherent problems with these conventional dampening systems disallow consistent functioning of computerized inking systems. No known automated inking system can accurately be programmed for ink conveyance response to dampener-initiated printing system disturbances because none of the prior art dampening methods can be accurately modeled to account for the disturbances. Even the most sophisticated computerized inking systems are not suitable for every printing condition because there exists no consistent prior art body of dampening technology that correctly allows or accounts for the influence of dampening upon the primary printing process function, which is inking.

This lack of dampening predictability is so pervasive that certain industry suppliers have developed waterless lithographic printing plates and presses in an attempt to obviate these ever-present dampening problems. Unfortunately, the waterless lithography approach requires exceptionally expensive inks, plates, and presses. Also, waterless printing plates and presses are limited in the range of substrates that can be acceptably printed. Fadner U.S. Patent 5,107,762 depicts a lithographic printing process dampening system that utilizes dampening water input elements which are physically separated from a train of two or more direct- to plate oleophilic and hydrophobic dampening solution conveyance rollers, one roller of which is the dampening form roller contacting the printing plate. This dampening train of rollers becomes and remains inked during printing operations. The invention of the 5,107,762 patent was based solely on findings derived from keyless lithographic printing considerations. The disclosure therein is limited to the conventional direct- to-plate dampening configuration, which I have now discovered is not optimal either for keyless lithographic printing or for conventional keyed or zone inked lithographic printing systems. Currently, neither the 4,690,055 nor the 5,107,762 patent is being practiced or even tested using conventional key or zone inked lithographic presses. This is likely due to the preponderance of prior art lore and experience with zone inked printing presses that teaches against applicability of the technologies of these patents for conventional printing presses. I have now discovered that the technologies of these two patents are in fact not advantageously applicable to conventional lithographic presses. The Dahlgren prior art dampening systems utilize dampening solution conveyance to the printing plate by way of the first inking form roller rather than by means of a separate dampening form roller. Having found that direct-to-plate dampening by means of an inked roller was inoperable, Dahlgren uncovered that a water miscible organic liquid such as isopropyl alcohol remedied the practical operating problem. In fact, the alcohol addition proved so useful to the practice of dampening that its incorporation pervaded the industry whether or not the dampener being used was of the

Dahlgren type. This prior art background is summarized in Fadner U.S. Patent 4,278,467, and the technical basis for alcohol's widespread acceptance is documented in "Surface Chemistry Control of Lithography," Colloids and Surfaces in Reprographic Technologies, by T. A. Fadner, ACS Symposium Series 200, pp. 348-57, M. Hair and M. D. Croucher, Ed., 1982.

Lithographic presses are easier to run and are more consistent, particularly as concerns ink/water interactions, when using 10 percent to 25 percent isopropanol in the dampening solution. Substitutive additives have by and large been unsuccessful in emulating this advantageous quality. In any case, all of the organic liquid material additives intended for this purpose are highly to slightly volatile and are environmentally and occupationally hazardous.

It is well known that to carry out conventional lithographic printing practices, two liquids are required, a relatively viscous ink and a relatively fluid aqueous dampening solution. The viscous lithographic ink is essentially a non-volatile liquid insofar as the printing process is concerned. Consequently, for all practical purposes, every bit of ink that is input to the press system is output by the press in the correct positions and amounts on the substrate being printed. Conversely, water is an evaporative liquid under the pressroom operating conditions of temperature, pressure and room ventilation. Water will vaporize from every operating press component upon which it is located.

It is also well known that lithographic ink can and must tolerate and accept some water within its liquid film phase during lithographic printing operations. Conventional lithographic printing is otherwise not possible. Consequently, all roller and cylinder surfaces, whether hydrophobic or hydrophilic and whether ink-covered or water covered, at press operating equilibrium or steady-state will have uppermost liquid/vapor surface layers of water. Water as vapor will be lost by evaporation away from all of these surfaces. In addition, liquid water will be lost by being printed out as part of the intended image of ink. Because of these natural water loss paths, considerably more water must be input to a lithographic press system then that expected required to merely replenish natural water losses directly from the printing plate non-image areas, where, of course, a film of liquid water is required on a steady state basis.

Water can and must enter the ink phase, and it is this interaction between water and ink that constitutes both the efficacy of lithography and the bane of lithography, the latter in terms of adverse effects of imposed or forced interactions.

To achieve optimum lithographic efficiency relative to ink/water interactions, the press system must reach a water input-output equilibrium operating condition or steady-state appropriate for the speed, operating temperature, input rates of consumable ink and dampening solution materials being used, and for the quality parameters of the product being manufactured. A slightly higher rate of dampening water input to the press than the equilibrium value will cause accumulation of additional water in the ink films residing on the various rollers, on the plate, and ont he blanket. This system response must occur because water cannot evaporate faster from the various press components than the already-established equilibrium rate, which is a natural response to ambient pressroom and press operating conditions. Consequently, under any water input rate condition just greater than this naturally occurring loss rate, additional water will be carried to the substrate by way of the ink being printed onto the substrate, and perhaps also by way of the non-image areas of press components that contact the substrate. The substrate path is the only natural path left for extra or excess water to exit the press system without noticeably adverse quality disturbances.

When the water input rate is further increased, a point is reached at which the thin ink films on the rollers cannot assimilate all of the increased water input. Free water may appear on inked surfaces or at inked nips. Free water can interfere directly with the intended smooth transfer of ink to the printing plate image areas and then to the substrate. This higher rate of water input is commonly referred to in the trade as exceeding the upper limit of ink/water balance latitude. The lower limit of ink/water balance latitude is, of course, the dampening water input rate which just fills all of the water loss paths of the press system. Below that rate of dampening water input, the inking form rollers will remove water from the printing plate non- image areas in order to fill the various inking rollers surface evaporative demand, which loss paths have now become water-starved. When insufficient water remains in the non-image areas of the plate to prevent transfer of ink from the inking form rollers, the operating condition is termed toning or sometimes termed tinting. Ink will then reach the substrate in regions that were supposed to remain unprinted. Each of the conventional direct-to- plate dampening systems exhibit these inefficient water- input faults to differing degrees. The industry found long ago that water-last direct-to-plate dampening is impossible for these reasons. With this input inefficiency fault, critical formats cannot be printed routinely at acceptable quality levels. Inking control systems cannot function as desired by design.

At very high water input rates or under inefficient input conditions that therefore require high input rates, slinging or misting loss of liquid water drops from the operating press components can occur, in addition to the natural water vapor losses. When this occurs product quality deterioration is usually observed because more water than lithographically necessary is being forced onto the press. The press system may seem at times to be at a steady-state, so acceptable printed quality may be achieved momentarily because much of the normally detrimental excess water input is exiting the press system as liquid mist or drops. This can be temporarily alleviate interference of the excess water with ink transfer. However, the system will vacillate into and out of acceptable printed output and eventually will require pressman attention to fluid input rates or other controllable factors. This attention is often required during the whole printing run. Any dampening solution conveyance method that places a continuous or even a discontinuous film of water onto any roller that needs to transfer ink, particularly inking form rollers that contact the printing plate, are inherently inefficient dampening systems. Relative to the ink's ability to imbibe or pick up water at a roller nip with, for instance, the plate, any water film, no manner how thin, represents excess water. In fact, that is how lithography works best: by maintaining a finite thin film of water in the plate only in non-image areas. Whenever a similar film occurs between two inked surfaces such as at a form roller/plate image area nip, more water than desired has been input to that nip. There will be ink transfer interference, termed in the industry as ink/water balance problems. The ink/water balance latitude factor for a given lithographic press operating at true equilibrium is therefore dictated primarily by the ink's inherent ability to assimilate and distribute water towards all of natural loss paths. In the optimum system, this dampening water distribution must be accomplished without significantly changing any critical quality property of the ink. When the dampener input or ink input setting is significantly increased or decreased, the time required for a corresponding high or low water input fault to appear in the printed product depends upon this characteristic ink property. The time required also depends upon the number of inking rollers making up the evaporative paths that will become overfilled or will be emptied and to some extent upon the number of rollers between the dampening water input source and the printing plate.

As conventionally taught, lithographic problems are said to be dependent upon whether the printing plate is being overdamped or underdampened. While this statement is correct, it will become apparent from the disclosures herein that optimum trouble-free dampening requires that none of the inking or dampening roller or printing plate surfaces anywhere in the press system be overdampened or underdampened at any time during printing operations. It will become apparent that optimal lithographic dampening is coincident with minimum practical water input rate and therefore is automatically coincident with minimal number and severity of adverse ink/water interactions.

Virtually all of the prior art dampening systems, which are of the direct-to-plate, water first type, are designed and tested to convey a more or less continuous film of dampening water solution toward the printing plate. This practice renders the first inking form roller nearest the dampening form roller totally or at least largely incapacitated as an inking form roller. This readily demonstrated condition follows logically from the fact that the first inking form roller subsequent in the printing plate rotational direction to a water-first dampening form roller encounters at its nip with the printing plate a film of dampening water that is being input at a rate at least equivalent to the naturally required water input rate for distribution to all of the press system's water loss paths. This required water input rate is far greater than that which would be required merely to replace water losses only from the lithographically critical component of the press system which is the printing plate. The required rate of water input being applied in the prior art directly to the printing plate is generally also far greater than that which can readily be assimilated by the thin film of ink residing on the first inking form roller, merely by passing through its single low-residence time, narrow nip with the printing plate. The reality of this view is substantiated by the well known and demonstrable fact that the water-last direct-to-plate dampening, for which the dampening form roller is placed subsequent to the last inking form roller and therefore rotationally prior to the plate/blanket nip, transfer of ink from the plate to the blanket is either completely lost, because of the water film placed on the inked image areas by the dampening form roller, or at best is uncontrollable.

Since the ink film on the first inking form roller of, for instance, a set of four inking form rollers, cannot continuously carry away from the plate surface sufficient of the excess water input, the second inking form roller may be affected similarly though less extensively. Perhaps also the third inking form roller. Finally, at the fourth or perhaps at the third inking form roller the water input to and from those rollers will closely approximate a natural water flow loss path equilibrium condition. One or both of the last inking form rollers will then be able to function properly and predictably as ink delivery rollers with little or no adverse interference from the presence of dampening water associated with the ink that resides on the contiguous rollers and the excess dampening water initially input to the printing plate. Isopropyl alcohol assists the process of filling the evaporative loss paths by rendering more efficient water movement into and out of ink films. A conventionally dampened press operates with less attention to dampener related faults then without the alcohol additive. These factors explain the virtual dependence of much of the industry on this additive.

When using for demonstration purposes a multiple inking form roller printing press carrying a printing form not subject to mechanical ghosting that normally could occur because of differing inking form rollers and plate cylinder diameters, it is well known that the printed ink density decreases markedly as the number of inking form rollers being employed is decreased, other factors being held constant. It is also well known that the last inking form roller, the one farthest from a conventional, direct, water-first dampening form roller, delivers during normal operation the smoothest and most water-interference-free ink film of the inking form roller set.

These observable factors using prior art practices are primarily dampening design-related and only secondarily inker-design related. These less than optimal inking conditions are the result of the inherently inefficient direct-to-plate conventional dampening practices which partially to severely negate what would otherwise be efficient conveyance of ink to the printing plate by all of the press system's inking form rollers. The excess rate of water input using these prior art conventional dampening systems coincides with the presence of one or more free water films at the plate/inking form roller nips both in image and in non- image regions of the plate.

The oleophilic and hydrophobic dampener roller system of U.S. Patent 5,107,762 is advantageously functional for keyless lithographic systems. In keyless systems both the ink and the water inputs are continuously uniform. In conventional systems only the latter is input uniformly. That portion of the ink not used by the plate, and coincidentally some water, is continuously scraped off the return side of an inking roller for reuse by the keyless press system. However, as will be shown, the dampener means of the 5,107,762 patent is not optimal nor perhaps even useful as the dampener input means for conventional zoned ink input printing presses wherein all of the ink being input must of necessity be printed out.

In practice, the oleophilic and hydrophobic dampening rollers of the 5,107,762 patent become ink covered only in circumferential bands located at cross- press positions directly corresponding to the cross-press locations of images on the printing plate. The greater the circumferential image content at any given cross- press location, the more complete is the corresponding circumferential ink film band observed on the dampener rollers, that is, the more likely that specific region will carry the maximum amount of ink possible, namely, that carried on average by the inking form rollers. Obviously, it is only these bands of ink on the dampener rollers that can participate in emulsifying water into the ink for conveyance to the plate, and only for the correspondingly located portions of the uniformly input dampening solution. Only those specific inked regions of the dampener rollers of the 5,107,762 patent can participate in what is disclosed therein as inked roller conveyance of dampening water to the plate. Since normal image content varies primarily between about 0 to 50 percent for most printing jobs, most of the 5,107,762 dampening roller surface area will not carry ink. The primarily uninked portions of the dampening system of the 5,107,762 patent operate exactly like a conventional direct-to-plate, non-inked dampening system, with its inherent excess-water-induced interference with ink transfer. This adverse condition will be particularly severe with low-image content formats, particularly if applied to conventional zoned inking presses. Prior art examples of attempts to obviate these pervasive dampening water input problems in conventional presses include, for instance, the Alcolor Dampening system marketed by Heidelberger Druchmaschinen Aktiengesellschaft of Germany. A roller diagram reproduced from Heidelberg's April 1990 brochure titled

M-Offset CP Tronic is illustrated together with the press inking rollers as Figure 1. Dampening system 10 utilizes a differential speed nip 11 to meter a thin water film onto hydrophilic roller 12 which film is then transferred in whole or part to inked dampening form roller 13 thence to the printing plate mounted on cylinder 14. As in any printing press, the inking form and dampening form rollers must be covered with rubber or similar material because of mechanical and material considerations of their contact with the hard-surfaced printing plate. Rubber coincidentally is oleophilic and hydrophobic; therefore roller 13 would normally carry ink in cross- press regions corresponding to images as just previously described herein for the technology of the 5,107,762 patent. Hydrophilic roller 15 is described to impart additional metering and/or smoothing action to the water film on roller 13. Oleophilic and hydrophobic copper roller 16 is somewhat unique for this otherwise conventional prior art dampener in that it creates an inked roller bridge between form roller 13 and the inking system of rollers 16 by means of inking form roller 19. To the extent that ink transfers from roller 19 to roller 13 by means of roller 17, those may nearly operate as fully inked rollers in this particular system. Nevertheless dampening form roller 13 must of necessity carry a more-or-less continuous water film on its surface.

This Alcolor bridge variation of conventional, water-first, direct-to-press dampening is consistent with the inherent lithographic printing need that the water be purposefully mulled into the ink. However, the use of only one fully inked roller nip 17 between the water input source, hydrophilic roller 12, and the first inking form roller 19 is far from sufficient to mull all of the input water into the relatively small volumes of ink on these rollers. Consequently, but perhaps less severely than non-bridged counterparts, the Alcolor system encounters all of the typical adverse lithographic ink/water interactions already described herein. Recent Heidelberg literature is consistent with this and other explanations herein. The manufacturer has modified the inking train of rollers to place considerably more ink on the first two inking form rollers than on the last two. Apparently, the combination of the Alcolor dampener and the extra ink input to the two form rollers that are exposed by the dampener to the greatest ink transfer water interference was found to improve press operations, particularly when inking has been automated (Heidelberg Speed aster CD, CP Tronic, distributed publicly April 1993) .

The Koromatic Dampener system marketed by Komori Corporation of Japan and illustrated in their July 1991 brochure titled New Lithrone is reproduced for use on their sheet-fed presses as Figure 2. This direct-to- plate, continuous, water-first dampening system 20 utilizes a reverse slip nip 21 to meter a thin water film to the rubber dampening form roller 22 for subsequent transfer to the printing plate mounted on cylinder 23. This system employs an oleophilic copper roller 24 riding on. rubber form roller 22, but unlike the Heidelberg system of Fig. 1, the Komori copper roller 24 does not bridge with inking system 25. As with the Figure 1 system, a hydrophilic chrome roller 26 is required to prevent ink feeding back to water fountain 27 because of the direct connection between rollers 21, 22, 26, and 28. If copper roller 24 is oscillated, the small amount of ink picked up by rubber dampening form roller 22 will be spread out somewhat, thereby nearly approximating the Heidelberg bridged roller advantage. However, typical prior art dampening interference with inking does and will persist for reasons already presented.

Graphic Systems Division of Rockwell International Corporation, a domestic company, had marketed lithographic presses to newspaper printers which included ink-train dampening systems (ITD) , shown schematically in Figure 3. This unpatented dampening configuration was prompted but customer demand that dampening components be readily accessible for cleaning and maintenance. This dampening system 30 has separated spray water input 31. Input is to a single dampening roller 32 riding on a first copper inking drum 33 of the inking system 34. This system functioned reasonably well since there are almost enough fully inked nips available to mull water into the ink on its way to the printing plate mounted on cylinder 35. The three water path nips are numbered sequentially in Figure 3. Adverse field experience relative to increased demand for improved printed quality prompted gradual withdrawal of this dampening system in favor of more conventional direct systems. There remains need for a consistent, repeatable, predictable, and efficient means for conveying to a lithographic plate the water required to maintain image differentiation at the plate without introducing significant adverse influence of the dampening water on the delivery of ink to the image area of the plate. Summary of the Invention In accordance with the present invention, a method and apparatus for assuring optimal input of dampening water to any lithographic printing press are provided that are independent of printing plate format, of practical printing speed, and of ambient operating conditions.

The method and apparatus of my invention utilize the concept that water as a necessary but evaporative lithographic printing operations material can and will escape by evaporation from every operational surface of the press system during printing. This roller surface evaporative loss of water plus an additional amount lost as part of the ink film image printed onto the substrate account for all of the input water required to operate lithographically. It is technically correct for all cases of efficient lithographic operations, as hereinafter defined, that the rates per unit area of water evaporation from every press roller surface whether inked or not and from the surface of the substrate being printed are for all practical purposes identical. This logical factor greatly simplifies understanding the basic concepts of my invention.

With these principles as the basis, I have determined that four criteria must be satisfied to achieve the lithographically most efficient operation condition:

1. The means for initial input of dampening solution to the press system must be physically separated from the press system and that means should provide reasonably uniform input in both cross-press and substrate travel directions.

2. The ink being used in the practice of this invention must be able to assimilate some water as hereinafter defined. 3. No portion of the dampening system should cause or allow a significantly higher rate of dampening water conveyance to any critical inking component of the press system than the rate required for replacing the natural evaporative path losses, and any printed out losses as applicable, associated with than given component.

4. The dampening water must be conveyed to the printing plate by means of inked rollers that provide a sequence of four or more fully inked roller nips between the input means of criteria 1 and the printing plate.

These criteria are readily met by means of my present invention. Only when operating within these criteria can the condition of minimum water input required for image differentiation be achieved for any lithographic printing press system. Meeting these criteria allows optimum latitude in low to high image content operability with the attendant improvements in operations and in consistent printed product quality over the prior art.

Meeting the indicated criteria allows minimal operator attention to dampener input settings because the press always operates at essentially the same conditions insofar as dampening is concerned. In addition, the absence of a need for severe dampening input changes because of differing formats allows optimal control of automated press inking systems. The control system variables are no longer adversely influenced by spurious and unpredictable dampening-related operational changes or differences.

By means of the present invention, a set of fully inked rollers is used to mull dampening water into the ink on its way to the printing plate. The prior art advantages of alcohol additives are thereby achieved without requiring occupationally or environmentally hazardous additives to the dampening solution.

With virtually all of the most serious prior art dampening-related lithographic problems obviated by means of my invention, there remains little need for the much more expensive, substrate-limited waterless lithographic systems, such as marketed by Toray and Komori Industries of Japan.

The first and second of the aforementioned invention criteria are readily met using initial water input devices and inks that are already available from suppliers to the industry. Generally, the water input Criterion 1 can be satisfied using any of several appropriately-designed pressurized nozzle or spiral brush water droplet spray devices. A water assimilation capability by the ink of at least about five percent by volume will generally suffice to meet Criterion 2. The ink should also have an upper limiting value of water assimilation capability which in the industry conventionally is in the range of about 30 percent to 40 percent by volume of the resulting mixture. The water take-up test termed the Surlyn Test utilizing, for instance, a Duke Custom Systems apparatus, will suffice to establish these test values. Providing that Criteria 1 and 2 are met,

Criterion 3 may be satisfied primarily by proper selection of the configurational position of the press system at which the dampening water is introduced. This criterion is one of the new and novel elements of the present invention and its efficacy will be illustrated subsequently in this disclosure.

Criterion 4 is another new and novel element of this invention, particularly when considered in conjunction with Criterion 3. The only prior art involving inked rollers is the ink train dampening and inked dampening rollers technologies previously cited. The former prior technology has an incorrect number and configuration of inked rollers to meet the stated criteria, as will be shown presently, and the rollers of the latter technology are, in practice, not fully inked, as previously explained herein.

Criteria 3 and 4 focus on solving the crux of the prior dampening system problems and form the primary novel basis for the printing and dampening systems disclosed herein. The dampening system of U.S. patent 5,107,762 meets certain of the criteria herein previously set down for the present invention, namely criteria 1 and 2. However, criteria 3 and 4 cannot be satisfied merely by using oleophilic and hydrophobic rollers primarily because of the direct-to-plate dampening configuration called for in that reference, despite the possibility that under very high overall ink coverage conditions the rollers could become ink covered.

In view of the principles set forth in this disclosure, the failure of the ink-trained dampening system of the Graphic Systems Division of Rockwell

International Corporation can be used to illustrate the necessity for meeting criterion 3 set forth earlier herein. All of the water required to continuously fill all of the water evaporation paths is input by the Figure 3 system into the nip between main inking roller 33 and dampening roller 32. Forcing more water into that nip than required as makeup to the inking system water loss paths at that roller position tends to disallow roller 33 and therefore inking form roller 36 to smoothly convey and transfer ink to the plate. An actual film of water appears at that nip. The corresponding printed faults cause pressmen to increase ink feed in order to maintain printed optical density, which in turn necessitates even greater water input to avoid toning. The attendant operating fault was unacceptable. Excess ink and excess water accumulated at and would sling off from press components near the ink input system 37.

As noted previously in this disclosure, optimal lithographic dampening requires that no critical component of the press inking system be forced to receive, convey, or handle significantly more water than is required to replenish the natural water loss paths associated with that component of the press system. An important corollary of this requirement is that no critical inking portion of the press must be required to receive, convey or handle any free water whether in the form of continuous film or discrete water droplets. The best way to meet this criteria water requirement is to mull the incoming water into the ink to form either a semi-stable, two-phase fluid or preferably to form a microemulsion of water in the ink phase. The latter likely is the naturally occurring result of my invention and the water as the discontinuous phase exists as extremely small readily mobile clusters. Simple pressure at any of the inked roller nips temporarily makes water available for transfer to and from the two rollers involved. Accomplishing this mulling action requires that dampening, that is, the process of conveying water to the printing plate, be carried out by means of a sufficient number of fully inked rollers in a train of rollers. These statements correspond to the previously stated criterion 4.

A logical and systematic method to evaluate which of all possible dampening alternatives is best and most efficient for any given lithographic printing press inking configuration can be employed as disclosed herein. This method leads directly to the basis for my invention. The concepts presented can be quantified and modeled when appropriate experimental data is collected but as herein disclosed there exists no essential reason to do so. The practice of my invention renders dampening a trivial

830801 factor relative to optimal maintenance of the operational and printed qualities traditionally expected from the practice of conveying ink to a lithographic printing plate. Meeting the need for a consistent, repeatable, predictable, and efficient means for conveying to a lithographic plate the water required to maintain image differentiation at the plate without introducing significant adverse influence of the dampening water on the delivery of ink to the image area of the plate is a primary objective of this invention.

It is another objective to provide method and apparatus whereby the minimum required water input to any lithographic press can be achieved. Still another objective is to optimize the inking efficiency of conventional zoned or keyed lithographic printing presses.

Another objective is to minimize dampener- related operating and quality problems in the practice of lithographic printing.

A further objective of this invention is to eliminate need for organic additives to the aqueous dampening solution, such as isopropyl alcohol or intended substitutes. Additionally, it is an objective of this invention to provide dampening means whereby the applicable operating range of computerized inking systems may be extended to virtually any practical lithographic printing condition. Examples of this disclosure's novel technology will be presented utilizing extant press system configurations, modified according to the principles of this invention insofar as the dampening process of the press system is concerned. Brief Description of the Drawings

Fig. 1 is a roller diagram of a typical prior art lithographic press.

Fig. 2 is a roller diagram of another prior art lithographic press.

Fig. 3 is a roller diagram of a third prior art lithographic press.

Fig. 4 is a roller diagram of the Fig. 2 lithographic press advantageously modified to incorporate the present invention.

Fig. 5 is a roller diagram generally similar to Fig. 4, but showing an alternative embodiment of the present invention.

Fig. 6 is a roller diagram generally similar to Figs. 4 and 5, but showing a further embodiment of the present invention.

Fig. 7 is a roller diagram of the lithographic press of Fig. 1 altered to incorporate the present invention. Fig. 8 is a view similar to Fig. 7, but showing an alternative embodiment of the present invention incorporated thereinto.

Fig. 9 is a roller diagram of another typical prior art lithographic press modified to incorporate the present invention.

Fig. 10 is a roller diagram of Figure 3 prior art lithographic press modified to incorporate the present invention.

Fig. 11 is a roller diagram similar to Fig. 10, but showing a variation of the present invention incorporated into the lithographic press of Fig. 3.

Detailed Description of the Invention

Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention, which may be embodied in other specific structures. The scope of the invention is defined in the claims appended hereto.

Figure 4 schematically depicts the Komori Lithrone Press of Figure 2 fitted with one of the allowable dampening means 40 selected according to the criteria set forth in the practice of this invention. In this variation, the original dampening system is removed and unconnected water input device 41 sprays dampening solution uniformly across of gap onto added oleophilic and hydrophobic receiving dampening roller 42 or into the vicinity of the nip formed by roller 42 and already existing inking roller 43, both of which become fully inked during operation. As indicated by numerals 1 through 5 on the Figure 4 diagram, there exist at least four fully inked roller nips between the dampening solution receiving roller 42 and the nearest inking form rollers 44 and 45. Accordingly, no only will the amount of water being transferred to each of the four inking form rollers correspond closely to the minimal amount required to maintain full the natural water loss paths associated with the form rollers so that the natural lithographic equilibrium will maintain, but the total required input water will be readily assimilated by the overall ink film on inking roller 43 and by all of the fully inked contiguous inking rollers. No interfering free water film appears anywhere in the press system except in the printing plate non-image areas. As a direct result, all four ink form rollers will be able to deliver the calculated quantity of ink to the plate that is expected in the absence of dampening water interference.

A somewhat more efficient dampening water input selection using the same press inking configuration as Figure 4 is illustrated in Figure 5. In this variation 50, two oleophilic and hydrophobic rollers 42 and 56 are added to the inker as a rider pair on existing roller 43. This enables having at least five fully inked roller nips in the water's path to the nearest inking form rollers on its way to the plate.

To further illustrate the versatility of my invention, an equally efficient location for a dampening water input which meets the criteria already presented is shown in Figure 6 utilizing the same press inking configuration as in Figures 4 and 5. In this variation two oleophilic and hydrophobic dampening rollers 52 and 53 and the detached water spray input means 51 make up the add-on dampening water input components 50, and in this variation oleophilic and hydrophobic rider roller 54 is added to the inking system to assure having at least four fully inked roller nips between the water input 51 and the nearest but rotationally last inking form roller 56.

Another adaptation of these dampening principles can be used to affix inked dampening water input rollers to the Heidelberg press of Figure 1, as depicted in Figure 7, with minimal change to the configuration of the press. In this case, the original dampener form roller 13 is utilized in essentially the same position as in Figure 1. Oleophilic and hydrophobic rollers 101, 102, and 103 are added as the bridge from roller 13 is first inking form roller 19. Riding on added roller 101 is one of a pair of oleophilic and hydrophobic rollers 106 and 107. Detached water input system 108 sprays water onto roller 106 or into the nip formed by rollers 106 and 107. With this modified dampening water input configuration there again exist at least four fully inked roller nips between the input roller 106 and the nearest inking form roller 19 as well as the existing dampening form roller 13. In this or any of the alternatives depicted or suggested herein, any practical combination of dampening rollers and inking rollers can be advantageously oscillated laterally by means well known in that industry.

An even less obtrusive change to the Figure 1 press configuration is illustrated in Figure 8. Oleophilic and hydrophobic rollers 110, 11 and 112 are added, with roller 110 riding on existing copper bridging roller 16 of Figure 1. In this alternative there again are at least four fully inked nips between the water input roller 112 and inking form rollers 19 and 105 and dampening form roller 13.

Both of these Figure 7 and Figure 8 alternatives involving inked rollers for conveying dampening solution to inking form rollers also convey dampening solution essentially directly to the plate. These alternatives will not be as free of water interference problems as the alternatives exemplified by Figures 4, 5, and 6 wherein the dampening solution is conveyed to the plate by means only of the inking form rollers. The Figures 7 and 8 alternatives will feed much of the required water directly to the plate as in prior art water-first direct-to-plate dampeners. To maintain full the water loss paths in the inking set of rollers, more water will need to be input to the plate than if all of the input water is to the plate by means of the inking rollers, as in Figures 4, 5, and 6, for which the inker loss paths are already filled whenever the dampening solution is input by means of the inking system of rollers as herein described that is in the downstream direction as regards ink travel from its input towards the printing plate.

Of course, dampening systems such as depicted in Figures 4, 5, and 6 can be utilized with the inking system of Figures 7 and 8 instead of those depicted.

Yet another example of practicing the present invention is illustrated in Figure 9, which shows a three-ink-form roller printing press configuration marketed by Solna Web International under the trademark SOLNA 224. Two dampener configurations 60 and 61, according to this invention, are shown together with the inking train of rollers in Figure 9. Either of these alternatives could be used alone with this press configuration. It should be recognized that both dampener systems 60 and 61 could be employed at the same time with significant operational advantages. Dampener components 60 consist of two added oleophilic and hydrophobic rollers 62 and 63 and detached water input system 64. System 61 uses three oleophilic and hydrophobic add-on rollers 65, 66, and 67 together with detached water input device 68.

An example of a more or less conventional web lithographic newspaper press generally similar to those marketed by Mitsubishi Kubaku Ku of Japan, Rockwell Graphic Systems of USA, and MAN-Roland of Germany is shown with various dampening system alternatives according to this invention in Figures 10 and 11. In Figure 10, oleophilic and hydrophobic roller 71 is added in rotational contact with existing ink transfer roller 73. Roller 71 plus water input device 72 make up the add-on dampening components 70 of this alternative. In this alternative there are at least four fully inked nips between dampening solution receiving 'roller 71 and inking form rollers 74 and 75, as noted on the drawing.

An improved version of the Figure 10 alternative is shown in Figure 11. One additional oleophilic and hydrophobic roller 81 is added to make up dampening input system 80 so that the water path to inking form rollers 74 and 75 includes at least five fully inked nips. To further minimize potential water interference with the critical ink transfer at otherwise single ink path nips 76 and 77, inking roller 78 is also added. Thus, it is apparent that there has been provided, in accordance with the invention, dampening systems for lithographic presses that fully satisfy the aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace. all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.

Claims

I claim:

1. In a printing press having at least one cylinder carrying thereupon at least one lithographic printing plate and utilizing at least one train of oleophilic and hydrophobic inking rollers to convey ink from an ink input device to the printing plate, the train of inking rollers including at least one inking form roller in contact with the printing plate, apparatus for conveying aqueous dampening solution to the printing plate comprising: a. a train of oleophilic and hydrophobic dampening solution input rollers including at least one dampening solution receiving roller and including at least one dampening solution conveyance roller that is in rotational contact with at least one of the inking rollers, wherein the train of dampening solution input rollers cooperates with the train of inking rollers to provide during printing operations at least one path of fully inked rollers for conveying dampening solution from the dampening solution receiving roller to the printing plate, wherein the dampening solution path of fully inked rollers contains at least four nips of fully inked rollers between the dampening solution receiving roller and the inking form roller; and b. dampening solution input means for supplying the dampening solution across a gap to the dampening solution receiving roller.

2. The printing press of claim 1 wherein: a. the apparatus for conveying aqueous dampening solution to the printing plate further comprises at least one dampening form roller in contact with the lithographic printing plate; and b. at least one dampening solution conveyance roller of the train of oleophilic and hydrophobic dampening solution input rollers is in rotational contact with at least one selected inking roller of the train of inking rollers and at least one oleophilic and hydrophobic dampening solution conveyance roller is in contact with the dampening form roller.

3. In a printing press having at least one cylinder carrying thereupon at least one lithographic printing plate and utilizing at least one train of oleophilic and hydrophobic inking rollers to convey ink from an ink input device to the printing plate, the training of inking rollers include at least one inking form roller in contact with the printing plate, apparatus for conveying aqueous dampening solution to the printing plate comprising: a. an oleophilic and hydrophobic dampening solution receiving roller in rotational contact with at least one of the inking rollers, wherein the dampening solution receiving roller and the train of inking rollers provide during printing operations at least one path of fully inked rollers for conveyance of dampening solution from the dampening solution receiving roller to the printing plate, wherein the dampening solution path of fully inked rollers contains at least four nips of fully inked rollers between the dampening solution receiving roller and the inking form roller; and b. dampening solution input means for supplying the dampening solution across a gap to the dampening solution receiving roller.

4. In a printing press having at least one cylinder carrying thereupon at least one lithographic printing plate and utilizing at least one train of oleophilic and hydrophobic inking rollers to convey ink from an ink input device to the printing plate, the train of inking rollers including at least one inking form roller in contact with the printing plate, apparatus for conveying aqueous dampening solution to the printing plate comprising: a. a train of oleophilic and hydrophobic dampening solution input rollers including at least one dampening solution receiving roller and at least one conveyance roller that is in rotational contact with at least one selected inking roller of the train of inking rollers to thereby render the train of dampening solution input conveyance rollers fully inked, wherein the train of fully inked dampening solution input rollers and the inking rollers cooperate to define at least one continuous path of fully inked rollers for conveying dampening solution from the dampening solution receiving roller to the printing plate, wherein the train of dampening solution input conveyance rollers defines at least four nips of fully inked rollers; and b. dampening solution input means for supplying the dampening solution across a gap to the dampening solution receiving roller.

5. In a printing press comprising at least one cylinder carrying thereupon at least one lithographic printing plate, at least one inking form roller in contact with the lithographic printing plate, and an initial dampening solution input, means for conveying the dampening solution from the initial dampening solution input to the inking form roller along at least one continuous path of fully inked rollers having at least four fully inked nips therealong.

6. In a printing press comprising at least one cylinder carrying thereupon at least one lithographic printing plate, at least one inking form roller in contact with the lithographic printing plate, and an initial dampening solution input, apparatus for conveying the dampening solution from the initial dampening solution input to the inking form roller comprising: a. dampening roller means for receiving the dampening solution from the initial dampening solution input; b. a source of ink; and c. a train of fully inked oleophilic and hydrophobic inking rollers that convey ink in a downstream direction from the source of ink to an output inking roller in rotational contact with the inking form roller, a selected one of the inking rollers of the train of inking rollers being in rotational contact with the dampening roller means thereby to receive and to convey the dampening solution in the downstream direction along at least one continuous path of fully inked rollers of the train of inking rollers that contains at least four fully inked nips between the dampening roller means and the inking form roller.

7. The printing press of claim 6 wherein the dampening roller means comprises a train of oleophilic and hydrophobic dampening solution rollers than convey the dampening solution in a downstream direction from the initial dampening solution input to the selected inking roller of the train of inking rollers, the train of dampening solution rollers including at least one dampening solution receiving roller and at least one dampening solution conveyance roller that is in rotational contact with the selected inking roller of the train of inking rollers.

8. In a printing press comprising at least one cylinder carrying thereupon at least one lithographic printing plate, at least one inking form roller in contact with the lithographic printing plate, and an initial dampening solution input, apparatus for conveying the dampening solution from the initial dampening solution input to the inking form roller comprising: a. an oleophilic and hydrophobic dampening roller that receives a dampening solution across a gap from the initial dampening solution input; b. a source of ink; and c. a train of fully inked oleophilic and hydrophobic inking rollers that convey ink in a downstream direction from the source of ink to an output inking roller in rotational contact with the inking form roller, a selected one of the inking rollers of the train of inking rollers being in rotational contact with the dampening roller to receive the dampening solution therefrom and to convey the dampening solution in the downstream direction along at least one continuous path of fully inked rollers of the train of inking rollers that contains at least four fully inked nips between the dampening roller and the inking form roller.

9. A method of conveying ink and dampening solution to at least one inking form roller in rotational contact with the printing plate of a lithographic printing press comprising the steps of: a. conveying ink in a downstream direction from a source of ink along a first continuous path to the inking form roller; b. conveying dampening solution from a source of dampening solution to a selected location on the first path; c. conveying the dampening solution and ink together along the first path from the selected location thereon to the inking form roller; and d. mulling the dampening solution into the ink in at least four locations along the first path between the selected location thereon and the inking form roller.

10. The method of claim 9 wherein: a. the step of conveying ink comprises the step of conveying ink along a train of inking rollers from the source of ink to at least one inking form roller; and b. the step of conveying dampening solution comprises the steps of: i. applying dampening solution from the source of dampening solution across a gap to a train of dampening solution conveying rollers; and ii. contacting a selected dampening solution conveying roller of the train thereof with a selected inking roller and thereby conveying dampening solution from the source of dampening solution to the train of inking rollers.

11. The method of claim 9 wherein: a. the step of conveying ink comprises the step of conveying ink along a train of inking rollers from the source of ink to the inking form roller; and b. the step of conveying dampening solution comprises the steps of: i. applying dampening solution from the source of dampening solution across a gap to a train of dampening solution conveying rollers; ii. contacting at least one inking roller with at least one dampening solution conveying roller of the train of dampening solution rollers; iii. contacting the printing plate with at least one dampening form roller; and iv. contacting the dampening form roller with at least one dampening solution conveying roller of the train of dampening solution conveying rollers.

12. A method of conveying ink and dampening solution to at least one inking form roller in rotational contact with the printing plate of a lithographic printing press comprising the steps of: a. conveying ink in a downstream direction from a source of ink along a train of inking rollers that defines a first continuous path from the source of ink to the inking form roller; b. applying dampening solution from a source thereof across a gap to a dampening solution conveying roller; c. contacting the dampening solution conveying roller with a selected inking roller of the train of inking rollers to thereby convey dampening solution from the source thereof to the train of inking rollers; d. conveying the dampening solution and ink together along the first path from the selected inking roller of the train of inking rollers to the inking form roller; and e. mulling the dampening solution into the ink in at least four locations along the first path between the selected inking roller and the inking form roller.

13. In a lithographic printing press having a printing plate, at least one inking form roller in rotational contact with the printing plate, a train of oleophilic and hydrophobic inking rollers that convey ink from a source thereof along at least one first path of fully inked rollers to the inking form roller, and a source of dampening solution, the improvement comprising: means for conveying dampening solution from the source of dampening solution to the inking form roller for subsequent distribution to the printing plate along a second path that has a selected portion thereof common with a selected portion of the first path, the portion of second path that is common with the selected portion of the first path having at least four fully inked nips therealong.

14. The lithographic printing press of claim

13 wherein the means for conveying dampening solution from the source of dampening solution to the printing plate comprises: a. an oleophilic and hydrophobic dampening solution receiving roller that is in rotational contact with a selected roller of the inking train of rollers, the dampening solution receiving roller and the selected roller of the inking train of rollers cooperating to convey dampening solution to the portion of the second path that is common with the selected portion of the first path and the dampening solution receiving roller cooperating with the selected inking roller to form one of the fully inked nips along the second path; and b. means for applying dampening solution across a gap to the dampening solution receiving roller.

15. The lithographic printing press of claim 13 wherein the means for conveying dampening solution from the source of dampening solution to the printing plate comprises: a. a train of oleophilic and hydrophobic dampening rollers comprising: i. a dampening solution receiving roller; and ii. a dampening solution conveyance roller in rolling contact with a selected inking roller of the train of inking rollers to thereby render the train of dampening rollers fully inked, the train of dampening rollers cooperating with the selected inking roller to convey dampening solution to the portion of the second path that is common with the selected portion of the first path, and the train of dampening rollers cooperating with the train of inking rollers along the common portions of the first and second paths to form at least four fully inked nips; and b. means for applying dampening solution across a gap to the dampening solution receiving roller.

16. A lithographic printing press comprising: a. a printing plate; b. at least one inking form roller in rotational contact with the printing plate; c. an inking train of rollers for conveying ink in a downstream direction from a source of ink to the inking form roller, respective adjacent rollers of the inking train of rollers defining fully inked nips therebetween, there being at least three fully inked nips between a selected roller of the inking train of rollers and the inking form roller; d. a source of dampening solution; and e. a dampening roller that receives dampening solution from the source of dampening solution and that is in rotational contact with the selected roller of the inking train of rollers to thereby convey dampening solution to the selected roller of the inking train of rollers at a fully inked nip therewith, so that dampening solution is conveyed by the inking train of rollers in the downstream direction from the source of dampening solution to the inking form roller along a continuous path that contains at least four fully inked nips.

17. A lithographic printing press comprising: a. a printing plate; b. an inking form roller in rotational contact with the printing plate; c. an inking train of rollers for conveying ink in a downstream direction from a source of ink to the inking form roller; d. a source of dampening solution; and e. a train of dampening solution rollers including a dampening solution receiving roller that receives dampening solution across a gap from the source of dampening solution and a dampening solution conveyance roller that is in rotational contact with a selected roller of the inking train of rollers to thereby render the train of dampening rollers fully inked and to thereby form a continuous path of fully inked rollers between the dampening solution receiving roller and the inking form roller, therebeing at least four fully inked nips along the path between the dampening solution receiving roller and the inking form roller.

18. The lithographic printing press of claim 17 wherein there are four fully inked nips between the dampening solution receiving roller and the selected roller of the inking train of rollers.