EP0071108B1

EP0071108B1 - Method of and apparatus for applying ink and dampering fluid to a printing plate

Info

Publication number: EP0071108B1
Application number: EP19820106394
Authority: EP
Inventors: Harold Phillip Dahlgren; James E. Taylor; Dwight W. Peters
Original assignee: Dahlgren Manufacturing Co Inc
Current assignee: Dahlgren Manufacturing Co Inc
Priority date: 1981-07-31
Filing date: 1982-07-16
Publication date: 1987-06-03
Also published as: EP0071108A1; CA1224965A; DD202266A5; DE3227793A1; DE3276469D1; JPS5865664A

Description

The invention relates to a method of applying an emulsified printable mixture of ink and dampening fluid to a lithographic printing plate from a mixture reservoir, whereby a film of emulsified mixture to be delivered to the printing plate is metered at a nip between a rotated transfer roller and a metering member onto the surface of the transfer roller.
The invention further relates to a printing apparatus having a printing plate, a form roller engaging the printing plate, a metering roller engaging a transfer roller and forming a nip between the metering roller and the transfer roller for supplying .printing liquid to the form roller, and a reservoir containing a mixture of ink and dampening fluid building a printing liquid.
A such method and apparatus is known from WO-A-001151.
It is well known in the printing industry that it is extremly difficult to obtain high quality when printing certain forms, such as one-half page, combinations of screens and solids, diagonals, and the like. These forms are difficult to print because of the problems associated with "ghosting", ink starvation and accumulation, linting, or ink slinging. Some of these problems have been partially solved by the inovative inventions disclosed in US-A-4 208 963, 4 233 898, and 4 237 785.
In US-A-3 962 114 and US-A-3 587 463, it has been suggested that a scraping off device be positioned to engage an inking roller in a letterpress to remove the negative ink relief to thus avoid the accumulation of ink on rollers in an ink supply mechanism. In letterpress printing, ink is applied to raised image areas on a printing cylinder while .recessed non-image areas remain free of ink. However, in lithographic printing, ink and dampening fluid are applied to a planog- raphic printing plate. US-A-3 926 114 discloses a device in which ink and dampening fluid scraped off a roller are passed into a separator so that the characteristics of the ink are not altered by the add mixture of dampening fluid. Thus, pure ink was metered to the form roller by the inking system to prevent "greying" or the accumulation of excess dampening fluid within the ink supply as the ink was transferred to the inking roller.
US-A-4211 167 discloses a rod pressed under strong pressure against a soft surface carrying a layer of ink and dampening fluid, the rod forming a barrier only against the dampening fluid while allowing all the residual film of ink remaining on the roller to pass and return to a mass of ink in a reservoir.
WO-A-8 001 151 discloses an apparatus which includes a fountain roller dipping into a reservoir consisting of ink, water and further additives, whereby that fountain roller operates as a metering roller and is in direct contact with a form roller, whereby that form roller is in direct contact with the printing plate. The surface of the form roller moving from the nip between the fountain or metering roller and the form roller to the contact or applicator nip between the form roller and the printing plate is only engaged by a single vibrator roller. It has been proofed that the negative images on the surface of the form roller leaving the nip between the form roller and the printing plate cannot be eliminated by such construction so that no perfect uniform fill of printing liquid is provided on the surface of the form roller when contacting again the printing plate, and accordingly ghosting and other disadvantages appear.
The present invention provides a solution to problems encountered in separating ink and dampening fluid by permitting the emulsified ink and dampening fluid to be used again. It was discovered that if unused ink and dampening fluid are thoroughly mixed with fresh ink to form a substantially homogeneous mixture, ink and dampening fluid removed from a lithographic printing press equipped with an inker and a dampener can be removed from a form roller to prevent accumulation and remetered for application to the form roller provided the emulsified ink and dampening fluid are not kept in a confined area long enough for the ink and dampening fluid to separate.
Accordingly, it is an object of the present invention to provide an ink removal, circulating and distributing system that meters a substantially homogeneous mixture of ink and dampening fluid to a form roller for use in a lithographic printing system wherein an improved distribution system maintains the homogeneous mixture sufficiently agitated to prevent separation of the ink and dampening fluid.
Further, it is an object of the present invention to provide a substantially homogeneous mixture of printing ink and dampening fluid for use in a printing system.
It is a further object of the invention to provide a circulating system which eliminates heat build up in an ink reservoir.
A further object of the invention is to maintain a uniform viscosity consistency of an ink emulsion throughout a printing run.
A still further object of the invention is to provide apparatus to remove the ink and dampening fluid from a form roller and to reapply the ink and dampening fluid to the form roller, in combination with a dampener having a hydrophilic roller adapted to deliver a metered film of dampening fluid to the form roller and to remove excess dampening fluid from. the form roller.

Summary of the Invention

In accordance with the invention, a method of applying an emulsified printable mixture of ink and dampening fluid to a lithographic printing plate as described above includes the steps of depositing an excess of the emulsified mixture of ink and dampening fluid which has been removed from the form roller after it having engaged the printing plate in an axially central portion of the nip between the transfer roller and the metering member such as that this emulsified mixture flows longitudinally of the nip towards opposite ends of the transfer roller; maintaining the flow of mixture longitudinally of the nip to prevent accumulation of dampening fluid adjacent the nip; causing the mixture to cascade over the opposite ends of the transfer roller into opposite ends of the reservoir to remove the mixture from the nip adjacent opposite ends of the nip; and pumping the mixture from a central portion of the reservoir to the central portion of the nip.
Further, in accordance with the invention, a printing apparatus as described above is-characterized by dispensing means for delivering printing liquid to an axially central portion of the nip between the transfer roller and the metering roller; means for removing excess ink and dampening fluid from the form roller after the form roller has engaged the printing plate; mixing means for mixing ink and the excess ink and dampening fluid removed from the form roller into a substantially homogeneous printing fluid; and pump means circulating the homogeneous printing liquid to and from the nip.
It has been observed that when an abundant quantity of an emulsion of water in ink remains in one given area for a period of time, either between two rollers or between a roller and a blade, that the emulsion will be squeezed and water separated therefrom to cause a resultant non-uniform pick-up of ink or ink stripping from the roller or rollers. It is therefore advantageous to limit the time that the emulsion stays in one given pressure area.
We have found that when supplying the pressure area with an excess of the emulsion, flow must be maintained such that a given quantity of emulsified ink stays in a given pressure area only a limited amount of time sufficient to allow the emulsion to pass along the pressure area, but not allow time for water to be squeezed therefrom and remain in the given pressure area to cause problems.
We have therefore been able to print continuously with a controlled emulsion of dampening fluid and ink wherein before, the emulsion supplied to the pressure area would separate into water and ink, and the water would cause non-uniform ink pick-up and stripping of ink rollers.
Other advantages of the invention will become more apparent upon reading the following detailed description and upon references to the drawings.

Brief Description of the Drawings

Drawings of three embodiments of the invention are annexed hereto wherein like reference characters are used throughout to designate like parts, in which:

FIG. 1 is a fragmentary diagrammatic perspective view of a first embodiment of the invention;
FIG. 2 is a diagrammatic illustration of an inking system constructed according to the present invention as used with a newspaper printing system with the various films of ink and dampening fluid being illustrated;
FIG. 3 is a diagrammatic illustration of an ink removal, circulating and distributing system constructed according to the present invention;
FIG. 4 is a diagrammatic illustration of a second embodiment of an ink removal, circulating and distributing system constructed according to the present invention; and
FIG. 5 is a diagrammatic illustration preferred embodiment of a multi-unit newspaper printing system incorporating the ink removal, circulating and distributing system of FIG. 4.

Description of the Invention

A printing system 1 is illustrated in FIGS. 1 and 2 which includes an inking system 2, a scraping-off means 26, a reservoir 14, a pump 32 and motor 34, by-pass line 38, a distributor line 20 and nip N' between two adjacent rollers 12 and 13 in pressure indented relation and a suitable . dampener 200.
Ink is supplied to nip N' via ink distributor line 20 to the mid-point between the ends of rollers 12 and 13 in an adundant quantity such that the excess flows towards the roller ends and cascades therefrom to be collected and supplied to reservoir 14 by gravity feed. Blended in reservoir 14 with ink, the mixture or emulsion of ink and dampening fluid removed from form roller 90 by roller 94 and scraping-off means 26 is pumped back to distributor line 20 to complete the circuit. By-pass 38 is provided to enable pump 32 to run at a high rate of speed to thoroughly mix and circulate the emulsion further. Pump 32 is preferably a constant displacement auger-type screw pump driven by a variable speed air motor 34. Pump 32 and by-pass 38 provide adequate mixing through circulation to form and maintain a homogeneous mixture of the ink and dampening fluid.
Water and ink excess 128 left on the form roller 90 of the inker 2, after printing, is applied to roller 94 and wiped off by scraping off means 26. This non-uniform mix of water and ink is then preferably moved to reservoir 14 and through pump 32 where it is throughly mixed with fresh new ink and/or previously conditioned ink before returning to distributor tube 20. The dampener 200 is of the general form roll contact-type disclosed in the U.S. Pat. No. 3,168,037, entitled "Means For Dampening Lithographic Offset Printing Plates" which issued February 2, 1965 to Harold P. Dahlgren. The disclosure of U.S. Pat. No. 3,168,037 is incorporated herein by reference in its entirety for all purposes.
The inker generally comprises a form roller 90, ink idler roller 10, ink transfer roller 12, ink metering roller 13, and ink pan 14. Form roller 90, ink idler roller 10 and ink transfer roller 12 are generally supported between side frames (not shown) as disclosed in PCT International Application No. 79/00948 filed June 3, 1980, entitled "Inker For Newspaper Press", the disclosure of which is incorporated herein by reference in its entirety for all purposes.
Suitable means are provided, as hereinbefore described, for delivering an abundant supply of ink to the ink metering nip N' between adjacent surfaces of ink metering roller 13 and ink transfer roller 12. In the particular embodiment of the invention illustrated in FIG. 1, a distribution tube 20 discharges a substantially homogeneous printing liquid 22 at the junction between rollers 12 and 13 with the liquid being metered at the ink metering nip N' and carried by the surface of the roller 12 to thereby provide ink at ink transfer nip N. A sufficient flow of liquid 22 is provided at the junction of rollers 12 and 13 to maintain a flow of excess liquid over the ends of rollers 12 and 13 into ink pan 14, as will be hereinafter more fully explained.
Idler roller 10 and metering roller 13 are preferably hard and have an exterior surface which may be smooth or textured and which are ink receptive or oleophilic, such as copper or plastic. The surface of ink idler roller 10 and ink metering roller 13 may be either hard or resilient, depending upon the characteristics of the surface of form roller 90. If the form roller 90 has a resilient surface, then the surfaces of the idler roller 10 and metering roller 13 are preferably hard.
Transfer roller 12 preferably comprises a hollow tubular sleeve 12a with a resilient cover 12c secured about the outer surface of the sleeve. This cover material of ink transfer roller 12 is selected so as to be oleophilic and the surface may be textured.
. It should be readily apparent that if desired, the material of idler roller 10, ink transfer roller 12 and ink metering roller 13 may be alternately hard and soft.
Ink idler roller 10 is preferably positioned in pressure indented relationship with form roller 90, which has a metal tubular core 91 as described in U.S. Pat. No. 4,233, 898.
Form roller 90 has a smooth outer cover 96 which may be non-absorbent or absorbent, hard or soft, depending upon the nature of construction of printing plate 112.
In one embodiment, form roller 90 has a smooth outer cover 96 which may have a resilient non-absorbent surface. Another embodiment of form roller 90 includes a resilient surface and has a molleton type of cover which absorbs the ink and will reject dampening fluid. However, if plate 112 has raised image areas and is constructed of resilient material, form roller 90 could be provided with a hard surface of, for example, copper or a hard thin plastic covering.
ink roller 94 preferably a traversing oscillating idler roller with associated scraping off-means 26, is adapted to remove excess ink from areas 128" from ink film 128 on the surface of form roller 90 and transfer some of the ink to depleted areas 128' thereby creating a more uniform film of ink 130 on the surface of roller 90 moving from nip 120 towards nip 106 to be later explained more fully.
A second ink roller 95, similar to roller 94, is positioned between plate cylinder P and dampener 200 to smooth the ink film upon reversal of form roller 90 as will be more hereinafter fully explained.
A material conditioning roller 86, preferably an oscillating idler roller, is rotatably supported as disclosed in U.S. Pat. No. 4,233,898. Roller 86, 94 and 95 are mounted in pressure indented relation with form roller 90 each having a surface of preferably similar material to that of form roller90 such that the surface has the same affinity for ink as does the surface of form roller 90.
As the ink film 100 emerges from nip 106 between form roller 90 and idler roller 10, it may be slick and calendared. A slick film of ink is not particularly receptive to dampening fluid since the surface tension of the molecules of ink may reject the thin layer of dampening fluid to be applied by dampener 200.
Material conditioning roller 86 will receive a portion of the film 100 of ink thus splitting the film 100 of ink and producing a film 100' on roller 86 thus leaving film 100a with a matte finish having microscopic cavities or indentations. The matte surface upon film 100a will readily accept the thin film 204 of dampening fluid.
Rollers 86, 94 and 95 are preferably provided with drive means (not shown) to oscillate the rollers in a longitudinal direction. Suitable oscillator drive means are well known to persons skilled in the printing art and further description is not deemed necessary. Rotation is provided through friction contact with adjacent surfaces.
Dampener 200 is diagrammatically illustrated in FIG. 2 and comprises a hydrophilic transfer roller 212 and a resilient metering roller 213 mounted in a manner similar to inker 2 as described in U.S. Pat. No. 3,168,037. Metering roller 213 meters dampening fluid 214a from pan 214 onto transfer roller 212 through flooded nip Na. Water film controlled by pressure between rollers 213 and 212 forms a thin layer of dampening fluid 204 which is metered through dampening fluid transfer nip D onto the matte finish of ink film 100a on the surface of form roller 90.
Dampener metering roller 213 is driven by a variable speed reversible motor as described in U.S. Pat. No. 4,233,898.
For the purpose of graphically illustrating the function and results of the process of the mechanism hereinbefore described, a diagrammatic view of idler roller 10, transfer roller 12, metering roller 13.and form roller 90 is shown in FIG. 2. Ink and water films are exaggerated for clarity.
Metering roller 13 is rotatably mounted in pressure indented relation with transfer roller 12 and transfer roller 12 is rotatably mounted in pressure indented relation with idler roller 10. The pressure between adjacent roller surfaces is adjusted such that the surface of metering roller 13 and idler roller 10 are actually impressed into the surface of transfer roller 12.
At the point of tangency, or cusp area between rollers 12 and 13, an excess 22 of ink is piled up. The greatness of the excess of ink extending longitudinally of rollers 12 and 13 is regulated by virtue of the fact that the excess ink will fall into pan 14 by gravity to virtually create a "waterfall" of ink at opposite ends of the nip between adjacent surfaces of rollers 12 and 13, and by virtue of the amount of flow of liquid 22 from discharge tube 20. The excess of ink 22 in the flooded nip becomes the reservoir from which ink is drawn by transfer roller 12. As rollers 12 and 13 rotate in pressure indented relation, a layer of ink is metered between adjacent surfaces of the two rollers separated by a thin lubricating layer of ink. Since transfer roller 12 has a smooth, oleophilic surface thereon, a portion of the film adheres to the surface of roller 12 to form a film 104, the remaining portion being rotated on the surface of roller 13 back into the excess. A film of ink 104 is distributed on the surface of transfer roller 12 by reason of the rotating, squeezing action between rollers 12 and 13 at their tangent point at ink metering nip N'.The film of ink 104 rides on the surface of transfer roller 12 and comes in contact with ink film 116 on idler roller 10 at ink transfer nip N to form a film of printing ink 104a on idler roller 10.
The film of ink 104a rides on the surface of idler roller 10 and comes in contact with uniform film 130 of ink on form roller 90 at the inking nip 106 between idler roller 10 and form roller 90.
It is important to note that idler roller 10 may or may not be positively driven. If positively driven, it may be driven at a fixed ratio slower than the surface speed of the adjacent form roll 90. In any event, the surface of idler roller 10 is driven in the same direction as the adjacent surface of form roller 90. Idler roller 10 serves as an intermediate applicator roll between form roller 90 and transfer roller 12.
At nip 106 and N, it will be observed that idler roller 10 is impressed into the resilient surface of form roller 90 and transfer roller 12 and that the film of ink 104 has an outer surface 108, which contacts ink film 116, and an inner surface 110 which adheres to the surface of transfer roller 12. The outer surface 108 of film 104 and te outer surface 117 of the film of ink 116 on idler roller 10 are urged together to create a hydraulic connection between rollers 12 and 10 as they rotate in close relationship, but there is no physical contact between the roller surfaces. It is an important fact to note that the relatively thick film of ink 104 permits rollers 12 and 10 to be rotated at different surface speeds. Preferably, the form roller 90, which is normally press driven and rotated at the same surface speed as the printing plate 112 is rotated at a greater surface speed than the surface speed of roller 12. By regulating the differential surface speed between transfer roller 12 and form roller 90 the amount of ink applied to plate 112 may be regulated.
Within limits, if the surface speed of transfer roller 12 is increased, the ink film 104 is presented at the inking nip N at a faster rate and more ink is transferred by the surface roller 90 to lithographic printing plate 112, and the opposite is true, if the surface speed of roller 12 is decreased.
The film of ink 104, existent between adjacent surfaces of rollers 12 and 10, permits the rollers 12 and 10 to be rotated at different speeds in sliding relationship because the film of ink 104 actually provides lubrication which permits slippage between adjacent surfaces of rollers 12 and 10 without frictional deterioration. By reason of the slippage between rollers 12 and 10, the ink film 104 is calendared, smoothed out, metered and distributed by shearing the ink between adjacent surfaces of rollers 12 and the film 116 on idler roller 10, to create a printing liquid film 104a. The thickness of printing liquid film 104a is controlled by the relative pressures between metering roller 13 and transfer roller 12, and idler roller 10 and the relative speeds of rollers 12 and 10.
Transfer roller 12 preferably is driven at a surface speed which is slower than the surface speed of form roller 90. For example, if a printing press has paper travelling therethrough at a surface speed of about 275 m/min, the surfaces of printing plate 112 and form roller 90 will ordinarily have the same surface speed, while the surface speed of transfer roller 12 would preferably be less than 10% thereof.
Films 104 and 116 will be combined at inking nip N and will split when sheared as rollers 12 and 10 rotate away from inking transfer nip N. The fresh film 104a of printing ink adheres to the surface of idler roller 10. Ink rejected by idler roller 10 forms a feedback film 104b of ink which may be slightly irregular. Film 104b adheres to the surface of transfer roller 12 and is conveyed back to the ink metering nip N' to be remetered. Feedback film 104b may not be uniform because the starved areas on form roller 90 and consequently idler roll 10, from which ink was removed by image areas on plate 112, removed different quantities of ink from film 104 in order to form film 100 on form roller 90. Film 128 has starved areas 128' from ink removed by image areas 122 on plate 112, thus rendering film 128 irregular.
Actually ink film 130 generated at nip X is quite uniform and consequently films 100 and 116 and 104a and 104b resulting therefrom will be substantially uniform as explained later herein.
The lithographic printing plate 112 has hydrophilic or water liking non-image areas 121 and oleophilic, ink receptive, image areas 122 formed on the surface thereof. If printing plate 112 is provided with raised image areas, the dampener 200 would not be required to prevent transfer of ink to non-image areas.
At the nip 120 between applicator roller 90 and printing plate 112, the combined film 216 and 100a is split to form thin films 125 of ink and dampening fluid over oleophilic surfaces 122 on the printing plate. The layer 216 of dampening fluid is carried on and in the film 100a of printing liquid and is also distributed to form a thin film 226 of dampening fluid over hydrophilic areas 121 of the printing plate.
Some dampening fluid remains on the surface of form roller 90 which is moving away from nip 120 towards nip X, but such dampening fluid as does remain thereon is transfered with the excess liquid film 128 to become liquid film 130a on the ink roller 94. A doctor blade 26 has one of its edges supported by holder 28 and a edge engaging roller 94 for removing as much of the excess liquid from the roller as possible thereby forming a uniform and thin film 130b on roller 94. The removed dampening fluid and ink (liquid) is gravity fed onto a deflector shield 30 which in turn permits gravity feed into a liquid reservoir 14a in ink pan 14.
The non-uniform excess liquid film 128 remaining on form roller 90 is combined with the ultra thin uniform film 130b on ink roller 94 and actually "printed" onto roller 94. Explained again, the excess ink and dampening fluid 128 remaining on the surface of form roller 90, after printing to the lithographic printing plate 112, is virtually entirely removed therefrom by transferring or "printing" the irregular film 128 to the ultra-thin doctored film 130b on the surface of idler roller 94. The ultra-thin and uniformly doctored film 130b is formed from a reservoir 23 of accumulated excess 130a. Idler roller 94 now functions as an endless doctoring surface which allows the film 128" to be completely transferred to the surface of roller 94 just as ink film 100a was initially transferred or "printed" to the plate 112.
The layer of dampening fluid 216 is applied in substantially the same manner as the ink film 100 is applied. An excess of dampening fluid 214a is supplied to bead 201 and metered at Na between rollers 213 and 212 to form a film 204 of dampening fluid which is applied to ink film 100a on form roller-90 at nip-D. The film 204 of dampening fluid on hydrophilic dampening fluid transfer roller 212 and dampening fluid on film 100a combine at nip D to form film 216 on form roller 90. The film 217 of excess dampening fluid is removed from form roller 90 and is returned to bead 201 to be remetered at nip Na.
From the foregoing it should be readily apparent that the improved apparatus for applying ink to printing systems offers control of metering at ink metering nip N and N' to provide a film 100 of ink of precisely controlled thickness by adjusting pressure between rollers 10, 12 and 13, and further by controlling surface speeds of rollers, 12 and 10 relative to each other. The rate at which the metered film 104 of ink is offered to film 116 on idler roller 10 at inking nip N and also the hydraulic force of obtaining the desired film split are controlled.
To eliminate conditions which could cause accumulation of ink, when printing unusual forms or on only one-half-of a web, rendering it impossible to form a film 100 of precisely controlled thickness, the doctor blade 26 engages roller 94to remove as much as possible of the ink and dampening fluid in film 128. When roller 94 engages roller 90 a thinner uniform thickness of printing liquid 130 moves into nip 106 and thereby assists in preventing an accumulation on idler roller 10.
As best seen in FIGS. 1 and 2, the mixture of dampening fluid and ink thus removed by doctor blade 26 is fed by gravity onto deflector shield 30 and from there into ink pan 14. Ink pan 14 has a central drain outlet 14b located in the center of pan 14, which communicates through appropriate pipes 14c and pump 32, driven by motor 34, to distributor tube 20 to regulate the flow of printing liquid onto metering roller 13 at 22. The provision of the bottom in pan 14 with sections sloping downwardly toward the central opening assures constant circulation of ink 14a in the pan. The ink flows from tube 20 into the center of nip N' forming excess 22 and then flows outwardly along nip N' to cascade over the ends of metering roller 13 and ransfer roller 12 into opposite ends of pan 14. Thereafter, the ink is mixed with the contents of the reservoir including the non-uniform mix of ink and dampening fluid removed from roller 94. A bypass line 38 is branched from distributor tube 20 to discharge printing liquid into ink pan 14. Thus, by continuous operation of pump 32, a substantially honogeneous mixture of ink and dampening fluid is provided as printing liquid 22 and deposited onto metering roller 13 and/or transfer roller 12.
Tests have revealed that when printing at 275 m per minute using a two plate wide lithographic newspaper press, approximately 0.13 liter per minute of letterpress-type ink was printed onto a web which was 83 cm (thirty inches) wide. The plate printed directly to the web.
The pump 32 delivered about 7.5 liter per minute of homogeneous mixture of ink and dampening fluid through line 38 to reservoir 14 and about 11 liter per minute through distributor tube 20 to the nip N'. Thus, the pump capacity was about 19 liter per minute which was sufficient to maintain a homogeneous mixture of ink and dampening fluid. The flow of about 7.5 liter was sufficient to prevent separation of dampening fluid from ink in nip N' or to remove any dampening fluid from nip N' that was separated from the ink. Thus, dampening fluid was not present in nip N' in a form which would displace ink and cause stripping.
To replenish the printing liquid used in the system, an ink supply tank 40, FIG. 3, is provided in the circulating system with a pump 42 having an inlet in communication with the fresh ink and an outlet in fluid communication through line 41 with a float valve 44 which permits communication with distribution tube 20. Float valve 44 is controlled by a float 46 disposed within ink pan 14 to add fresh ink to liquid 14a when the level of liquid drops below a predetermined quantity. Since float valve 44 is closed except when the level of ink in pan 14 is low, a return line 41a a having a valve 41b therein extends between ink supply line 41 and ink container 40 to permit circulation of ink from pump 42 through supply line 41 and return line 41 a when float valve 44 is closed.
Further, when desired, this circulation system is operable on a complete printing couple as shown in FIG. 3: When employed in forward printing couples, the first printing unit is operable as previously described in relation to the embodiment of the invention shown in FIG. 1.
Further, for an adjacent couple in the forward printing mode only, a doctor blade 26 supported by holder 28' is disposed to engage roller 94 to remove a portion of the ink and dampening fluid film carried thereon. This portion of ink is then gravity fed through deflector shield 30' into ink pan 14'. Pan 14' includes an outlet 14b' which is in fluid communication through appropriate piping with pump 32' powered by motor 34' which discharges into distributor tube 20'. A control valve 36' is provided to control the flow of homogeneously mixed printing liquid 22' onto meter roller 13 for application to form roller 90 and from there onto printing cylinder P. Pump 32' is continuously supplying printing liquid through distributor tube 20' and the printing liquid is then either discharged onto metering roller 13' or through bypass tube 38' to thereby provide a continuous circulation of the printing liquid which creates the homogeneous mixture of ink and dampening fluid for discharge as the printing liquid 22'.
In the event that the second printing couple is used in a reverse printing mode only, doctor blade 26' is disengaged from roller 94 and a doctor blade 26a is supported by holder 28a for removing a portion of the ink and dampening fluid carried by roller 95. This removed portion of ink and dampening fluid is gravity fed to an ink collection pan 14" which has a discharge outlet 14b" in fluid communication through appropriate piping with discharge outlet 14b' and the inlet of pump 32'.
A float control valve 44' is provided with an inlet in fluid communication with the outlet of the pump 42 driven by motor 43 and an outlet in communication with distributor tube 20' so that fresh ink may be added to the system when necessary. Valve 44' is controlled by a float 46' mounted within ink pan 14' so that when the level of liquid 14a' drops below a predetermined amount, fresh ink is supplied to the system. This arrangement permits the adding of fresh ink to the system for both forward and reverse printing by use of a single float control valve controlling the addition of fresh ink.
It should be noted that when reversing a printing couple the direction of rotation of roller 90 and, therefore, roller 10 is reversed although the directions of rotation of rollers 13 and 12 may remain the same.
A second embodiment for multiple printing couples 1 and 2 is shown in FIG. 4. This embodiment is similar to the embodiment shown in FIG. 3, except that a single pump 50 driven by motor 52 has its inlet in fluid communication through conduits or similar piping with the outlets of pans 14, 14' and 14". The outlet of pump 50 is in fluid communication through conduits or similar piping through a mixing tank 54 which receives, mixes and stores a quantity of the printing liquid. Stirring apparatus 56 having paddles 58 disposed within the printing fluid 55 continuously mixes the fluid to ensure a homogeneous mixture of ink and dampening fluid for the printing liquid used in the printing system.
A quantity of fresh ink is stored within tank 60 which includes an outlet 62 in fluid communication through appropriate piping to a float valve 64 disposed in fluid communication within tank 54 to add fresh ink to the printing liquid 55 when needed. A second pump 66 driven by motor 68 includes an inlet in fluid communication through appropriate piping with the interior of tank 54 and outlet in fluid communication through appropriate discharge tubes 20 and 20'.
In this embodiment, pump 66 has a discharge sufficient to provide the required amount of flow of printing liquid to metering rollers 13 and 13' with some flow through bypass tubes 38 and 38' into ink pans 14 and 14', respectively. Further, this embodiment in addition to a single pump moving the homogeneous printing liquid to both metering rollers 13 and 13', includes a separate and distinct mixing apparatus to ensure that the ink and dampening fluid is continuously mixed to provide a homogeneous mixture of printing liquid 55.
The third embodiment of the invention illustrated in FIG. 5 is preferred for multiple printing units which incorporates the system and described in relation to the second embodiment illustrated in FIG. 4.
In this embodiment, six printing couples 1-6 (three printing units) are illustrated with the first printing unit being capable of forward and reverse printing. It will be noted that couple 2 is illustrated with blade 26a positioned for reverse printing.
As illustrated, a single tank 54' is provided for receiving a quantity of printing liquid 55' therein. Mixing apparatus 58' is then used for continuously mixing the ink and dampening fluid contained within the mixing tank 54' to ensure a homogeneous mix of printing liquid from removed ink and dampening fluid from a multiple of printing units. Further, a remote supply tank 60' is provided for supporting a quantity of fresh ink and an outlet 62' is in fluid communication through appropriate piping to a float valve 64' disposed within tank 54' for adding the fresh ink into printing liquid 55' when necessary.
Each printing unit shown in FIG. 5 is then in fluid communication through appropriate piping to return and supply pumps in a manner similar to that previously described in relation to the embodiment illustrated in FIG. 4.
In this embodiment, varying combinations of printing, having varying mixes of excess ink and dampening fluid; namely, couples running forward and reverse, couples running half-webs and those having ordinary and extraordinary printing formats, are joined together by removal of excess ink and dampening fluid from respective form rolls of each printing couple, circulated and mixed with fresh ink to form a honogeneous mixture of - printing liquid and then distributed back to each printing unit.
Extensive testing has revealed that at no time was "greying" noticed throughout the period of test runs which lasted several hours and ink used on one day could readily be used again. It was seen that emulsification in printing is not a detriment when controlled as described herein. Dampening fluid when properly dispersed in ink had shown that it can be beneficial and not a contaminant to the lithographic printing process.
It should be appreciated that filters could easily . be added to this system for removal of foreign particles of dried ink, dust paper lint, etc. which if allowed to accumulate could cause problems in addition to those primarily solved by this invention. The system also readily provides that ink additives and ink heating and/or cooling may be incorporated for any purpose required, primarily at tanks 54 or 54'.

Claims

1. A method of applying an emulsified printable mixture of ink and dampening fluid to a lithographic printing plate (P) from a mixture reservoir (14), whereby a film of emulsified mixture to be delivered to the printing plate (P) is metered at a nip (N') between a rotated transfer roller (12) and a metering member (13) onto the surface of the transfer roller (12), characterized by depositing an excess of the emulsified mixture of ink and dampening fluid which has been removed from a form roller (90) after it having engaged the printing plate (P) in an axially central portion of the nip (N') between the transfer roller (12) and the metering member (13) such that the emulsified mixture flows longitudinally of the nip (N') towards opposite ends of the transfer roller (12); maintaining the flow of mixture longitudinally of the nip (N') to prevent accumulation of dampening fluid adjacent the nip (N'); causing the mixture to cascade over the opposite ends of the transfer roller (12) into opposite ends of the reservoir (14) to remove the mixture from the nip (N') adjacent opposite ends of the nip (N'); and pumping the mixture from a central portion (14c) of the reservoir (14) to the central portion of the nip (N').

2. The method of claim 1, characterized by adding a portion of a second emulsified mixture of ink and dampening fluid which was not transferred to the lithographic printing plate (P) with the first mixture and mixing the first mixture with the second mixture to form a homogeneous mixture having a smaller percentage of dampening fluid than the second emulsified mixture.

3. The method of claims 1 or 2, characterized by pumping a portion of the mixture through a first line (20) to the central portion of the nip (N'), and pumping a portion of the mixture into the reservoir (14) such that the mixture is removed from the reservoir (14) at a faster rate than it is deposited in the central portion of the nip (N').

4. The method of claim 3, characterized by delivering fresh ink to the reservoir (14) to replenish the mixture applied to the lithographic printing plate (P).

5. The method of one or more of the preceding claims, characterized by removing mixtures from a central portion (14c) of a plurality of reservoirs (14), mixing the mixtures to form a homogeneous mixture, and pumping the homogeneous mixture to a central portion of a plurality of nips (N').

6. Printing apparatus having a printing plate (P), a form roller (90) engaging the printing plate (P), a metering roller (13) engaging a transfer roller (12) and forming a nip (N') between the metering roller (13) and the transfer roller (12) for supplying printing liquid to the form roller (90), and a reservoir (14) containing a mixture of ink and dampening fluid building a printing liquid, characterized by dispensing means (20) for delivering printing liquid to an axially central portion of the nip (N') between the transfer roller (12) and the metering roller (13); means (26, 94) for removing excess ink (128) and dampening fluid from the form roller (90) after the form roller (90) has engaged the printing plate (P); mixing means (14, 32) for mixing ink and the excess ink (128) and dampening fluid removed from the form roller (90) into a substantially homogeneous printing fluid; and pump means (32) circulating the homogeneous printing liquid to form the nip (N').

7. The printing apparatus of claim 6, characterized in that the removing means (26, 94) includes a doctor blade (26) and means (30) for directing the flow of removed ink and dampening fluid to the mixing means (14, 32).

8. The printing apparatus of one or more of the claims 6 or 7, characterized by a hydrophilic roller (212) delivering a film of dampening fluid to the form roller (90) and removing excess dampening fluid from the form roller (90).

9. The printing apparatus of claim 8, characterized by a dampening fluid metering roller (213) in pressure intended relation with the hydrophilic roller (212) to form a dampening fluid metering nip (N_a) the excess dampening fluid removed from the form roller (90) by the hydrophilic roller (212) being carried by the hydrophilic roller (212) to the dampening fluid metering nip (N_a), and means to maintain an abundant supply of dampening fluid adjacent the dampening fluid metering nip (N_a).