GB1585510A - Lithographic moisture system and method - Google Patents

Description

(54) LITHOGRAPHIC MOISTURE SYSTEM AND METHOD (71) We, AM INTERNATIONAL, INC, a corporation organised and existing under the laws of the State of Delaware, United States of America, formerly of 20600 Chagrin Boulevard, Cleveland, State of Ohio 44122, United States of America, now of 1900 Avenue of the Stars, Los Angeles, California 90067, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to lithographic duplicating and especially to the control of moisture application to the master during printing.

The problem of moisture control has been a persistent one, and many different types of moisture application systems have been developed with varying degrees of success. One fairly standard construction employs molleton covered rolls which are moisture absorntive and provide a reservoir situation which proves rather effective under the control of a trained operator, but in the hands of untrained people can be difficult to manage. For example, a slightly low moisture setting will eventually cause the molletons to dry out and ultimately ink up which requires a complex molleton changing procedure, and excessively high moisture setting, on the other hand, will eventually cause the molletons to become over-wet and necessitates delaying printing operations until they can be dried out sufficiently to proceed. In addition, of course, molleton covers present the familiar built-in problems of lint production and a tendency to irregularity of the roll surface.

A number of moisture systems which are free of rnolleton coverings (and of the attendant reservoir effects) have been deeloped, and while they escape the abovementioned drawbacks, they are still significantly reliant upon trained operator control because of their sensitivity. That is to say, very slight changes in adjustment, or changes in moisture demand by the master environmental conditions of humidity, run length, ink temperature or condition due to previous running or non-running, can cause the moisture situation to shift quickly either to a low moisture or to an over-wet condition with the result that copies are damaged and tirne can be lost in restabilizing the system, unless a skilled alert operator is available to prevent the condition from maturing unduly, or to reestablish correct operating conditions quickly once the aberration is recognized.

The present invention has as its object the provision of a moisture control arrange ment which will avoid the drawbacks of the previously mentioned molleton and nonmolleton systems, and which will have an inbuilt degree of stability tending to keep the moisture forwarding effect of the system at a value suited to the particular conditions currently existing. This natural stability should be such that within a reasonable range of conditions, the system will be self-adapting for fairly extended periods so as to feed slightly more or slightly less moisture to the master as the occasion demands, without operator intervention, and thereby to permit successful operation of lithographic duplicators by operators who ase not highly experienced.

The invention in one aspect provides a moisture system for a lithographic duplicator including a rotary master cylinder adanted to carry a master, said system comprising: a moisture transfer roll with a hydrophilic surface; means for carrying moisture from said transfer roll to the surface of a master on the master cylinder including a roll with an ink receptive surface means for maintaining on the surface of said ink-receDtive roll a continuous film of lithographic ink; means for positively driving said inkreceptive roll in time with the master; the moisture transfer roll being effective to transfer moisture from its surface to the ink film on the surface of said ink-receptive roll, said moisture transfer roll being solely driven in a rotary direction by nip forming surface contact with the combination of the moisture layers and ink layer between said moisture transfer roll and said ink-receptive roll; means for presenting an adjustably determinable supply of moisture to said moisture transfer roll surface; and means for applying to said moisture transfer roll a preselected retarding torque whose value varies monotonically with the rotary surface speed of said transfer roll, said transfer roll being responsive to the combination of the preselected retarding torque of said applying means and the magnitude of the driving effect of the nip contact of said ink-receptive roll with said transfer roll for developing a surface speed during normal printing operation of between 10 percent and 50 percent of the surface speed of said ink-receptive roll; said surface speed of said moisture transfer roll varying as an inverse function of the thickness of the moisture on said transfer roll such that said transfer roll rotates more rapidly to transfer more moisture to said ink-receptive roll as more moisture is required by the master from said ink-receptive roll and less rapidly to transfer less moisture to said ink-receptive roll as less moisture is required by the master from said ink-receptive roll.

The invention in another aspect provides a method for providing moisture to a master on the master cylinder of a lithographic duplicator comprising the steps of: providing a roll with an ink-receptive surface and positively driving the same in time with the master cylinder, said roll having contact with the master surface, or being part of a roll train having contact with the master surface; placing a hydrophilic transfer roll in driven, nip forming, surface contact with moisture and ink layers lying between the hvdrophilic transfer roll and the ink-receptive roll to transfer moisture from its surface to the surface of the ink-receptive roll so that the ink-receptive roll acts by way of the moisture and ink layers as the sole driving influence on the transfer roll: maintaining on the surface of said inkreceptive roll a continuous film of lithographic ink; making available to the transfer roll surface an adjust ably determinable supply of moisture; applying to the transfer roll a retarding torque whose value varies monotonically with the speed of rotation of the transfer roll; and controlling the driving effect of the nip contact between the transfer roll and the ink-receptive roll and the retarding effect of said retarding torque so as to have a combined effect resulting in a transfer roll surface speed during normal printing operation of between 10 percent and 50 percent of the surface speed of the ink-receptive roll, the surface speed of the transfer roll varying as an inverse function of the moisture on the transfer roll such that the transfer roll rotates more rapidly as more moisture is required by the master and less rapidly as less moisture is required by the master.

The transfer roll will take on, to a certain degree, the character of a self-balancing device and will tend to rotate more rapidly as more moisture is required by the master and less rapidly as less moisture is required by the master, thereby forwarding more or less moisture respectively to the ink covered roll and thus to the master surface. In this fashion the transfer roll tends to remain centered at a speed providing a balanced condition such that the moisture being supplied to the master remains substantially equal to that being required by the master at the moment, and such that the speed of rotation can shift through a certain range of speeds as slight changes in moisture requirement occur, regardless of the reason.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a vertical elevation, partly in section of a portion of a lithographic duplicator showing especially the master cylinder and the ink and moisture trains cooperating therewith; and showing one position of the moisture ductor in broken lines, and another in solid lines; Fig. 2 is a fragmentary elevation showing one type of drive for the fountain roll; and Fig. 3 is a longitudinal section to a larger scale of an exemplary conventional arrangement for providing an axially reciprocatory motion for a moisture roller; Referring to the drawing, the master cylinder 10 is served by a conventional ink train 12 and a moisture system 14.

The moisture system 14 includes a fountain 16 receiving a fountain roll 18 having a hydrophilic surface, a ductor roll 20 mounted on an oscillating arm 22, and a moisture transfer roll 24 which has a hydrophilic surface. The transfer roll is in contact with the surface of a moisture form roll 26 having an olephilic surface which runs in contact with a master M on the surface of the master cylinder 10. A reciprocating distributor roll 28, likewise olephilic, rides in contact with the moisture forme roll 26 and by an internal cam mechanism shifts axially back and forth to level the ink layer and moisture deposit on the surface of the form roll 26 in a known manner. One conventional form of cam mechanism which will serve for this purpose is illustrated in Fig. 3 wherein roller 28 is shown as mounted by bearings 60 on a nonrotary shaft 62 to which is pinned a barrel cam 64 with a double reverse helix groove 66.

A sleeve 68 is integral with the roll 24 and rockably retains a dog 70 which has a tip riding in the groove 66. Members 72 affixed to the ends of the shaft 62 engage loosely in any suitable mating grooves or apertures on the frame and constitute one of several conventional means for preventing rotation of the shaft 62 without influencing its vertical location.

For convenient reference the moisture system is divided into the moisture supply module 14A and the moisture flow control module 14B, and it is with the latter that the present invention is primarily concerned.

Referring to the moisture supply module 14A which is essentially conventional, the surface of the fountain roll is hydrophilic.

Usually this roll is of metal, e.g. aluminium with a matte surface, or has a tin-nickel plating or chrome plating on an aluminium or steel support. However, other hydrophilic materials, including nonmetallic compositions, can be used as the surfacing material for the fountain roll.

In many conventional systems the ductor roll 20 is covered with a molleton cloth which has certain moisture reservoir properties, and such a roll is not altogether unsuitable for the purposes of the present invention. However, the preferred arrangement employs at this location a roll of synthetic elastomeric composition in which has been dispersed a high percentage of short fibres of suitable composition such as regenerated cellulose, and which presents a matte surface that, while not significantly water absorptive, is adequately hydrophilic and oleophobic when wet and exhibits significant moisture attracting and carrying properties.

As is customary, the fountain roll 18 is stepped by a suitable ratchet mechanism in time with the rotation of the master cylinder at a rate (smoothed or average rate, that is) which is adjustable, say between 0 RPM and 30 RPM, to provide for increase or decrease in the amount of moisture being forwarded by the system. A set -ting of perhaps 10 to 20 RPM is representative for moderate circumstances at currently customary machine speeds.

As shown in Fig. 1, the fountain roll 18 is stepped in a rotary direction opposite in sense to that of the transfer roll 24.

Therefore, as the ductor roll 20 swings back and forth it is driven in opposite directions, first in one direction (counterclockwise as seen in Fig. 1) by its contact with the fountain roller, and then in the opposite direction (clockwise as seen in Fig. 1) by its contact with the transfer roller 24.

Fig. 2 illustrates such a conventional adjustable drive mechanism wherein the fountain roll 18 (not shown in this view) is driving connected to the ratchet wheel 40 which is stepped in the customary fashion by an oscillating drive link 42 carrying a drive pawl 44 meshable with the teeth of the ratchet and urged towards the same by a spring (not shown). The link 42 is powered by any suitable rotary machine element 46 through a connecting link 48 to rcciprocate, for example, at about 7 cycles per second. In order to manually adjust the amount of rotation derived from each stroke of the pawl 44, a cam or shroud 50 is arranged to coact with a follower pin 52 on the pawl to prevent its meshing with the ratchet except where the surface of the cam is relieved, as at 54, to permit such contact. The point of first contact of the nawl with the ratchet can be determined by the angular setting of the cam 50, and this is controlled by the handle 56, the cam setting being held by a suitable detent mechanism 58.

While the conventional type of drive for the fountain roll has been described it will be understood that other arrangements will work equally well, and one alternative that suggests itself is an arrangement for continuously rotating the fountain roll by means of a separate variable speed electric motor powering the shaft of the fountain roll 18, with suitable manual speed setting control for the motor.

The oscillating motion of the arm 22 which carries the ductor roll 20 is also caused by a conventional drive from the duplicator mechanism, the arm oscillating at a fairly high rate, for example about 2.8 cycles per master revolution or about 7 cycles per second for machine speeds currently in common use.

Turning now to the moisture flow control module 14B, the moisture forme roll 26 is smooth surfaced and of a rubbery material, preferably a synthetic elastomer of durometer in the range of 20 to 40 on the Shore A scale. The roll 26 is driven by conventional gearing, preferably at the same surface speed as the master cylinder 10.

Running in friction contact with the forme roll 26 is a distributor roll 28 of material similar to that used for the roll 26. Before the duplicator is put in operation, light films of ink 30, 32 are placed on the rolls 26 and 28, and these rolls, being oleophilic, remain inked up at all times when the machine is operating, since the roll 26 runs in contact with the master which continually receives an ink supply from the ink train 12. As previously noted the roll 28 has a cam-inspired axially reciprocating movement to maintain the ink film at a uniform thickness at all times.

The transfer roll 24 is constructed of a material providing a suitable hydrophilic surface as discussed above for the hydrophilic fountain roll 18, and is driven only by the influence it receives from the roll 26 via the nip between itself and the roll 26 which experiences only nominal or nonfilm-control pressure. In normal operation the roll 24 carries a film of moisture on its surface as shown at 34. This moisture is supplied and continuously replenished by the moisture supply module 14A and as the roll 24 rotates, it transfers portions of this film, via the ink layer 30, to the surface of a master M on the master cylinder 10, which captures the moisture and carries it away as rapidly as the background areas of the master require added moisture. It is thought that the transferred moisture perhaps in part forms an emulsion with at least the surface of the ink layer 30 and in part supplies a water film 36 overlying the ink layer. Whatever the exact mechanism, however, moisture is indeed carried to the surface of the master by this composite layer of ink and moisture. While not necessarily required, the preferred arrangement provides a roll 24 which is equipped with a cam for axial reciprocation to improve the levelling action of the moisture deposit on roll 24, which arrangement may be, for example, identical with that shown in Fig.

3 for distribution roll 28.

It has been discovered in connection with the present invention that the roll 24 does not necessarily rotate at a constant surface speed in spite of the fact that roll 26 is driven at a substantially constant speed for any given speed setting of the duplicator, and that this variation in speed does indeed perform an important function in relation to the improved operation of the system.

It appears likedly that the thickness of the moisture film 34 (indicated as tin Fig.

1) particularly its thickness at the nip of the rolls 24 and 26, is what controls this speed, and that as t increases the torque necessary to generate shearing action in the film 34 decreases so that the drive becomes less positive and the roll 24 tends to exhibit increased slip and to turn more slowly. On the other hand, as t decreases, it appears that the torque necessary to generate shearing action in the film 34 increases so that the drive becomes more positive and roll 24 tends to exhibit decreased slip and thus to speed up. In fact if the roll 24 dries out completely so as to receive its drive directly through the film of tacky lithographic ink 30 on the roll 26, its surface speed becomes substantially identical to that of the roll 26. As the postulated thickness t of the moisture layer is gradually increased, this results in progressively slower rotation of the hydrophilic transfer roll 24, which appears to be directly responsive to this thickness.

As can be seen from the foregoing discussion, the pressure between the rolls 24 and 30 is quite light since it in no sense controls the moisture film thickness or interferes materially with the changes in thickness above-described. It is merely sufficient to insure the possibility of an effective drive at virtually equal surface speeds of the two rolls 24 and 26 if the moisture film were not present. As such, the pressure in question is herein identified as nominal or "nonfilm-control pressure".

In order for the roll 24 to slow down promptly as t increases and driving torque decreases, there must of course be certain retarding factors, and these are found to act most effectively when they are of such character that their torque value increases monotonically as the speed of the transfer roll 26 increases (or, conversely, decreases as the speed of the roll decreases). While this would undoubtedly be very effective if the increase were directly proportional to speed, this is not seen as a requirement, and any arrangement showing significant increase in retarding torque with increase in the speed of roll 24 is thought to give an effective and filly operative result in terms of causing the speed of roll 24 to approximate proportionally to the water film thickness in an inverse relationship. It is noted, however, that conventional bearing friction loadings and the like, customarily present in machinery of this sort, normally provide a restraining torque answering the above description.

In the particular arrangement shown, retarding torque is applied in various ways.

For one, the bearings of the shaft supporting the trunnions of the roll 24 present a significant retarding friction. Primarily, however, the ductor roll 20 which is periodically in contact with the roll 24 is so adjusted that its arc of motion will tend to carry it slightly beyond the point of surface contact with the roll 24 and thereby place a momentary interference pressure on the transfer roll. Other frictional components may enter into the picture as well, such as the friction in the standard cam drive arrangement if the roll 24 is caused to reciprocate axially as above-described, plus the viscous resistance generated with the composite layer when thus reciprocated.

The combined effects of these various loadings respond to the above description and provide the type of restraining torque preferred. Certain of these retarding effects, particularly that of the ductor contact, can be arranged to be mechanically adjustable by conventional means so as to provide for initial set-up of the system to optimum restraining values.

It will be understood, of course, that other types of mechanisms for generating the requisite type of restraining torque are also contemplated, for example, fluid dynamic braking means applied to the shaft of the roll 24, electromagnetic braking, and any other sort of restraint torque generating device providing the properties described above will serve the purpose.

To ilustrate generally how a system is set up to operate in accordance with the invention, the means, whatever it may be, for aplying restraining torque to the transfer roller 24, is adjusted by the assembler or serviceman to provide, in normal operation, a load sufficient to significantly reduce its surface speed below that of the ink carrying roll with which it is in contact and by which it is driven. This restraint might be stated in terms of torque values, but since these are extremely difficult to measure, interpret and apply, it is deemed more effective to identify the load in practical mechanical terms. For example, the transfer roll should normally run in a range of between 10% and 50% of the surface speed of the inked roll. This can be readily determined by actually measuring the RPM of each, converting to surface speed and comparing. As a practical matter, however, in the construction shown, the transfer roll 24 and the distributor roll 28 are about the same diameter and are in sufficiently close proximity that the assembler or service technician can readily make a visual comparison of their speeds and determine that the speed relationship is well within the range indicated. The effective moisture supply setting of the handle 56 will depend, of course, on the particular location of the speed ratio within this range of speed ratios, but assuming that the proper complementary moisture supply setting is identified in each case, the operation at one speed ratio is altogether as effective as at any other within the range. The normal speed ratios referred to are, of course, under circumstances of normal stable state running while producing copies of acceptable quality.

In practice, of course, the appropriate loading adjustments are predetermined by laboratory tests and specified in terms of adjustment settings for the particular design of equipment under consideration.

Such specified settings are effective, because the range of permissible loading values has very substantial latitude allowing for any reasonable degree of variation in the equip ment., To summarize the operation briefly, the system described will be understood as providing an improved type of moisture application for lithographic duplicators which avoids the overrun problems assignable to molleton or other reservoir type systems, and on the other hand provides a quick reponse device which, nevertheless, avoids undue sensitivity and affords operating latitude sufficient in amount that moisture settings can be easily made without undue demands on the skill of the operator.

The control which the operator exerts on the moisture supply in a system of this type normally relates to the speed of rotation of the fountain roll 18. The conventional ratchet mechanism heretofore described can be set, using the handle 56, to step the roll at a wide range of speeds, forwarding more or less moisture along the moisture train. If the setting made by the operator corresponds exactly to the amount of moisture being taken up by the surface of the master under prevailing conditions, then there is proper operation and no flooding or starving occurs. Consequently, properly printed copies issue continuously from the duplicator. However, with the usual moisture system which is devoid of reservoir properties (i.e. the usual non-molleton system) any deviation from the proper setting quickly shows up as flooding and weakening of the image if too high, or starvation and the appearance of spreading, plugging and background if too low, so that the operator must be alert to keep the system in proper balance, and adjust it periodically to accommodate changing conditions.

While the system as above-described does not totally relieve the operator of the necessity for making moisture control settings, the requirement placed on the operator is merely that he find an adjustment for the speed of the fountain roll (or the output of some other moisture supplying module) so that at least sufficient moisture is being made available to the roll 24 to meet the needs of the master, plus an extra safety margin of a small amount to remove any possibility of temporary moisture starvation.

When a setting such as the foregoing is achieved, the system 14B of Fig. 1 will exert the requisite control as follows.

1. If conditions should change slightly so that the master is demanding and taking slightly less moisture, the thickness t of the moisture film 34 on the roll 24 will slightly increase. This causes the speed of the roll to slightly diminish. Due to its diminshed speed the roll 24 will take slightly less moisture per unit time of contact from the surface of the ductor roll 20, and will pass slightly less mois ture per unit time to the surface of the forme roll 26.

2. Conversely if the conditions should change so that the master requires and takes more moisture, the thickness t of the moisture film 34 on the roll 24 will slightly decrease. This causes the speed of the roll to slightly increase. Due to its increased speed the roll 24 will with- draw slightly more moisture per unit time of contact from the surface of the ductor roll 20, and will pass slightly more moisture per unit time to the surface of the forme roll 26.

it wil be understood that if the setting of the moisture supply being provided by the module 14A is totally out of scale in either direction with the requirements of the master under the existing humidity, ink temperature and ink working conditions, then the balancing action provided by the module 14B will probably be unable to compensate for this discrepancy with sufficient alacrity to be functional. However, so long as the setting of the moisture supply is a reasonable approximation of the requirements at the master, the accommodation will be substantially complete, and further attention to the moisture adjustment will be required only as a gross change in conditions occurs.

The significance of the foregoing paragraph is illustrated by the fact that it has been found possible to operate with the system illustrated and described under circumstances such that, with fairly continuous running, a duplicator will frequently run all day long without adjustment of the moisture system except for a few settings to gradually increase the moisture supply during the initial warm-up period. It has even occurred that with a fortuitous high limit setting at the outset, a single additional increased setting of the moisture system after partial warm-up was all that was required during a day of fairly continuous running.

The latitude provided by the system described is indeed sufficient that the instruction manual for the operator can provide a table of settings for the moisture supply module based on relative humidity, ambient temperature running condition (e.g. startup, 300 to 1000 copies, over 1000 copies, etc.), and these settings will normally provide a sufficiently accurate guide that, if carefully applied will make refinements in the setting on the basis of observed operation virtually unnecessary.

Since one of the most troublesome responsibilities for the operator of a lithographic duplicator is the monitoring of the moisture system, and because the failure to successfully execute this responsibility is so costly in lost time and copy paper, it can be understood that this invention provides an important advantage to the operator, and opens up the use of the lithographic duplicator, on a practical basis to operators of much less skill than heretofore required.

In the non-molleton form of the present invention, the benefit common to such non molleton, fast response systems, namely the quick transition from dry condition to printready condition, (requiring perhaps 15 to 20 revolutions), is present here. The fast response, however, is obtained without incurring highly objectionable sensitivity which is so characteristic of systems of this character.

An additional benefit is the manner in which the system identifies itself to the operator as being substantially in proper running condition. At the start of operation, or if there should be an interruption for any reason, such as a paper jam, the operator can merely direct his attention to the hydrophilic roll 24 upon starting up. If the system is in an excessively dry condition, ink deposits will appear on the roll surface. When adequate moisture has been moved to the nip the deposits will promptly disappear and paper feed can be started. On the other hand, if aberrant operation has somehow flooded the system, the roll 24 will have stopped turning or will be turning very slowly, in which case the operator merely waits until the roll 24 attains substantial speed and then is free to start the paper feed.

While the foregoing description has proceeded on the basis of employing a special inked up roll 26 as being the moisture form

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. takes more moisture, the thickness t of the moisture film 34 on the roll 24 will slightly decrease. This causes the speed of the roll to slightly increase. Due to its increased speed the roll 24 will with- draw slightly more moisture per unit time of contact from the surface of the ductor roll 20, and will pass slightly more moisture per unit time to the surface of the forme roll 26. it wil be understood that if the setting of the moisture supply being provided by the module 14A is totally out of scale in either direction with the requirements of the master under the existing humidity, ink temperature and ink working conditions, then the balancing action provided by the module 14B will probably be unable to compensate for this discrepancy with sufficient alacrity to be functional. However, so long as the setting of the moisture supply is a reasonable approximation of the requirements at the master, the accommodation will be substantially complete, and further attention to the moisture adjustment will be required only as a gross change in conditions occurs. The significance of the foregoing paragraph is illustrated by the fact that it has been found possible to operate with the system illustrated and described under circumstances such that, with fairly continuous running, a duplicator will frequently run all day long without adjustment of the moisture system except for a few settings to gradually increase the moisture supply during the initial warm-up period. It has even occurred that with a fortuitous high limit setting at the outset, a single additional increased setting of the moisture system after partial warm-up was all that was required during a day of fairly continuous running. The latitude provided by the system described is indeed sufficient that the instruction manual for the operator can provide a table of settings for the moisture supply module based on relative humidity, ambient temperature running condition (e.g. startup, 300 to 1000 copies, over 1000 copies, etc.), and these settings will normally provide a sufficiently accurate guide that, if carefully applied will make refinements in the setting on the basis of observed operation virtually unnecessary. Since one of the most troublesome responsibilities for the operator of a lithographic duplicator is the monitoring of the moisture system, and because the failure to successfully execute this responsibility is so costly in lost time and copy paper, it can be understood that this invention provides an important advantage to the operator, and opens up the use of the lithographic duplicator, on a practical basis to operators of much less skill than heretofore required. In the non-molleton form of the present invention, the benefit common to such non molleton, fast response systems, namely the quick transition from dry condition to printready condition, (requiring perhaps 15 to 20 revolutions), is present here. The fast response, however, is obtained without incurring highly objectionable sensitivity which is so characteristic of systems of this character. An additional benefit is the manner in which the system identifies itself to the operator as being substantially in proper running condition. At the start of operation, or if there should be an interruption for any reason, such as a paper jam, the operator can merely direct his attention to the hydrophilic roll 24 upon starting up. If the system is in an excessively dry condition, ink deposits will appear on the roll surface. When adequate moisture has been moved to the nip the deposits will promptly disappear and paper feed can be started. On the other hand, if aberrant operation has somehow flooded the system, the roll 24 will have stopped turning or will be turning very slowly, in which case the operator merely waits until the roll 24 attains substantial speed and then is free to start the paper feed. While the foregoing description has proceeded on the basis of employing a special inked up roll 26 as being the moisture forme roll, it is important to understand that this particular arrangement is not essential to the operativeness of the invention. The hydrophilic transfer roll may make contact with any ink-covered roll, for example with the forme roll forming a portion of the ink train, or with one of the other ink-covered rolls of the ink train, and such an arrangement is to be considered as the full equivalent of that described herein. WHAT WE CLAIM IS:

1. A moisture system for a lithographic duplicator including a rotary master cylinder adapted to carry a master, said system comprising: a moisture transfer roll with a hydrophilic surface; means for carrying moisture from said transfer roll to the surface of a master on the master cylinder including a roll with an ink receptive surface; means for maintaining on the surface of said ink-receptive roll a continuous film of lithographic ink; means for positively driving said inkreceptive roll in time with the master; the moisture transfer roll being effective to transfer moisture from its surface to the ink film on the surface of said ink-receptive

roll, said moisture transfer roll being solely driven in a rotary direction by nip forming surface contact with the combination of the moisture layers and ink layer between said moisture transfer roll and said ink-receptive roll; means for presenting an adjustably determinable supply of moisture to said moisture transfer roll surface; and means for applying to said moisture transfer roll a preselected retarding torque whose value varies monotonically with the rotary surface speed of said transfer roll, said transfer roll being responsive to the combination of the preselected retarding torque of said applying means and the magnitude of the driving effect of the nip contact of said ink-receptive roll with said transfer roll for developing a surface speed during normal printing operation of between 10 percent and 50 percent of the surface speed of said ink-receptive roll; said surface speed of said moisture transfer roll varying as an inverse function of the thickness of the moisture on said transfer roll such that said transfer roll rotates more rapidly to transfer more moisture to said ink-receptiye roll as more moisture is required by the master from said ink-receptive roll and less rapidly to transfer less moisture to said ink-receptive roll as less moisture is required by the master from said inkreceptive roll.

2. A moisture system as set forth in Claim 1 wherein the driving effect of the nip contact is due in part to force means acting on the rolls to urge them towards contact, and wherein said force means is arranged to urge said moisture transfer roll and said ink-receptive roll into nip contact with force which results in the combination of the moisture and ink layers between said rolls substantially determining the spacing between said rolls.

3. A moisture system as set forth in Claim 1 or Claim 2 which further includes, in rolling contact with said ink-receptive roll, an axially reciprocating distributor roll whose surface is also ink-receptive.

4. A moisture system as set forth in Claim 1 in which means is provided for causing axial reciprocation of said moisture transfer roll.

5. A moisture system as set forth in Claim 3 in which means is provided for causing axial reciprocation of said moisture transfer roll.

6. A moisture system as set forth in Claim 1 in which there is provided adjustable means for exerting on said moisture transfer roll a controlled retarding torque which varies as a direct function of the speed of rotation of said transfer roll.

7. A moisture system as set forth in Claim 1 wherein said means for presenting moisture to said transfer roll surface comprises: a moisture fountain; a rotatable fountain roll running in contact with the liquid in said fountain; a freely rotating ductor roll and means for oscillating said ductor roll to alternately contact said fountain roll and said transfer roll; means for rotating said fountain roll; and means for adjusting the operation of said rotating means to control the speed of rotation of said fountain roll.

8. A moisture system as set forth in Claim 7 in which, in use, said fountain roll rotates in a direction opposite in sense to that of said transfer roll.

9. A moisture system as set forth in Claim 7 in which said means for applying a retarding torque includes said ductor roll and said means for oscillating said ductor roll and in which said means for oscillating said ductor roll is provided with adjustment means settable to cause said ductor roll to exert a selected force against said moisture transfer roll so as to develop said preselected retarding torque.

10. A method for providing moisture to a master on the master cylinder of a lithographic duplicator comprising the steps of: providing a roll with an ink-receptive surface and positively driving the same in time with the master cylinder, said roll having contact with the master surface, or being part of a roll train having contact with the master surface; placing a hydrophilic transfer roll in driven, nip forming, surface contact with moisture and ink layers lying between the hydrophilic transfer roll and the ink-receptive roll to transfer moisture from its surface to the surface of the ink-receptive roll so that the ink-receptive roll acts by way of the moisture and ink layers as the sole driving influence on the transfer roll; maintaining on the surface of said inkreceptive roll a continuous film of lithographic ink; making available to the transfer roll surface an adjustably determinable supply of moisture; applying to the transfer roll a retarding torque whose value varies monotonically with the speed of rotation of the transfer roll; and controlling the driving effect of the nip contact between the transfer roll and inkreceptive roll and the retarding effect of said retarding torque so as to have a combined effect resulting in a transfer roll surface speed during normal printing operation of between 10 percent and 50 percent of the surface speed of the ink-receptive roll, the surface speed of the transfer roll varying as an inverse function of the moisture on the transfer roll such that the transfer roll rotates more rapidly as more moisture is required by the master and less rapidly as less moisture is required by the master.

11. A method as set forth in Claim 10 wherein the driving effect of the nip contact is due in part to the exerting of force upon the rolls to urge them towards contact, and which includes the step of maintaining said force at a value which results in the combination of moisture and ink layers between said rolls substantially determining the spacing between said rolls.

12. A moisture system for a lithographic duplicator substantially as herein described with reference to the accompanying drawings.

13. A method for providing moisture to a master on the master cylinder of a lithographic duplicator substantially as herein described with reference to the accompanying drawings.