US2753796A - Ink-repellant applying method for rotary lithographic printing apparatus - Google Patents

Description

y 1956 w. H. wooo ET AL 2,753,796

INK-REPELLANT APPLYING METHOD FOR ROTARY LITHOGRAPHIC PRINTING APPARATUS Filed Feb. 10, 1951 3 Sheets-Sheet l HIGH POTENHAL 8 ac. Souncz INVENTOR. Wu lAM W000 /ro wmeo A- Pmrcmeo Afro sys July 10, 1956 w. H. WOOD ET AL 2,753,796 INK-REPELLANT APPLYING METHOD FOR ROTARY LITHOGRAPHIC PRINTING APPARATUS Filed Feb. 10, 1951 3 Sheets-Sheet 2 HIGH IUTENTIAL DC. 5OURCE PIEZO ELECTRIC CRYS'TAL INVENTOR. W/LL/AM H W000 12 BY Hownno IQPEITcHAED ATTORNEYS July 10, 1956 w. H. wooo ET AL 2,753,796 INK-REPELLANT APPLYING METHOD FOR ROTARY LITHOGRAPHIC PRINTING APPARATUS Filed Feb. 10, 1951 3 Sheets-Sheet 3 HIGH Fornnm.

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INVENTOR. W/LL/AM 1% W000 y Haw/:20 4- Pena/men WWW wm HTTOR Na s INK-REPELLANT APPLYING METHOD FOR R- TARY LITHOGRAPHIC PRINTING APPARATUS William H, Wood, Aurora Township, and Howard A. Pritchard, Hiram, Ohio, assignors to Harris-Seybold Company, Cleveland, Ohio, a corporation of Delaware Application February 10, 1951, Serial No. 210,392 2 Claims. (Cl. 101-147) This invention relates to printing apparatus, and more particularly to methods and means for maintaining inkrepellent the non-printing areas of planographic printing surfaces, such as are utilized in lithography, collotype, aquatone, or other similar printing processes wherein the image and non-image areas lie substantially in the same plane and are maintained in printing condition by the alternate application of ink and ink-repellent material to the printing surfaces. This application is a continuation-in-part of our former application No. 597,420, filed June 4, 1945, now abandoned.

The invention will bedescribed herein as applied to lithographic printing, and it has particular utility therein, but it is to be understood that wherever the context permits reference to lithographic printing is intended to include similar kinds of printing wherein the printing surface is substantially planographic in character.

In such processes it has been customary to apply both the ink (usually a greasy ink) and the ink-repellent material (usually water or an aqueous solution) by means of rollers. The use of rollers for applying the ink has been quite satisfactory, but much trouble has been experienced in the use of rollers for applying the inkrepellent material. These rollers, usually composed of fibrous material, damage the image areas by abrasion, get out of round, are difficult to adjust to proper contact with the printing surface, pick up ink and redeposit it in non-image areas, require frequent and laborious cleaning, require recovering and give up loose fibers to the image areas.

Much effort has been expended in efforts to find Ways of eliminating the use of rollers for applying ink-repellent material, such as spraying, putting the ink-repellent material in the ink, the use of refrigeration and the use of steam. None of these proposals has proven commercially practical, so that planographic printing as practiced commercially today still requires the use of rollers for applying the ink-repellent material with all the attendant difficulties.

Accordingly one of the objects of this invention is the provision of improved methods and means for applying ink-repellent material to a planographic printing surface.

Another object is the provision of methods and means of the kind described wherein electric force is employed to convey finely divided ink-repellent material from a source to a planographic printing surface.

Another object is the provision of methods and means for producing electrified fog, mist or vapor of ink-repellent material and for applying the same to a planographic printing surface.

A further object is the provision of an improved method and means for controlling the amount and distribution of the ink-repellent material applied to a planographic printin surface, in accordance with various conditions encountered in printing.

Still another object is the provision of an improved method and means for producing fog, mist or vapor of hired States Patent 0 ink-repellent material for application to a planographic printing surface.

Other objects will appear as we proceed with the description of those embodiments of the invention which we have selected for purposes of illustration and which are shown in the accompanying drawings, in which- Fig. 1 is a diagrammatic elevational view, partly in vertical section, of a lithographic printing unit embodying a form of the invention.

Figs. 2, 3 and 4 are forms of the invention.

Fig. 5 is a similar view illustrating a modified means for producing an electrical field of force, and

Fig. 6 is a fragmental diagrammatic view illustrating apparatus similar to that of Fig. 3.

In accordance with the invention ink-repellent material, for example water or a water solution including other suitable or known ingredient such as gum arabic, chromic acid, phosphoric acid, etc., is provided in finely dispersed form adjacent the planographic printing surface, and electrical force is applied to the elements of the dispersed material to cause them to move to said surface. Preferably an electrical charge is provided or induced upon said elements, as by a strong electrostatic field or corona discharge, and the printing surface is maintained at an electrical potential such that the charged elements are driven or attracted by electrical force to the printing surface where they are deposited and give up their charge For example the minute elements of dampening fluid may be positively charged by means of a relatively high potential device and the printing surface may be at ground potential or at a potential of opposite sign, depending upon conditions and the results desired.

In the drawings 14) is the usual metal plate cylinder of a rotary lithographic offset printing press, upon which a lithographic plate 11 is secured in known manner. Plate 11 may be of any known construction, either of metal or of non-metallic material such as cellulose. 12 is the blanket cylinder and 13 is the impression cylinder of the printing unit. The plate cylinder turns in the direction indicated by the arrow, and ink from an ink fountain and ink distributing rollers, not shown, is applied to plate 11 by form inking rollers 14.

Various methods and means may be employed to disperse the ink-repellent fluid and to apply electrical force to the elements of the dispersed fluid. Certain particular dispersing means and certain particular electrical means are shown combined in the drawings, but other combinations may be used satisfactorily, and hence we do not desire to be limited in this respect.

Referring now to the different methods and means illustrated in the drawings for effecting dispersion of the dampening fluid, and in the first place to the disclosure of Fig. 1, the outer wall 15 of an elongated housing extends transversely of the machine adjacent to and across the width of the plate cylinder 10. This housing also has an inner wall 16 providing a chamber 17 which in cross section is a flattened annulus. Chamber 17 is closed at its ends and is open along one side adjacent cylinder 10. The outer wall 15 also has an opening along the bottom of the chamber, which opening is closed normally by a pool of ink-repellent liquid 18 within a pan 19 which extends transversely of the press and is of substantially the same length as housing 15, 16. The level of liquid 18 is preferably maintained constant by a suitable automatic means, not shown. A series of spray or atomizing nozzles 20 suitably spaced lengthwise of the cylinder 10 are furnished with compressed air from flexible conductors 21 and draw liquid from the supply 18 through pipes 22. The finely divided particles of moisture delivered to chamber 17 from these nozzles, due to the shape similar view illustrating other of the chamber and the initial direction of the particles, are caused to circulate through the chamber, and this action may be augmented if desired by means of an impeller 23 at the top of the chamber rotated in the direction indicated by the arrow. The mist emitted by the nozzles may contain some heavy particles, and these may fall quickly and return to the liquid in the pan. Others may be deposited on the opposite upwardly extending wall of the chamber and drained back into the pan. The finer particles however travel in the current of air provided by the nozzles upwardly in the portion of chamber 17 nearest the cylinder 10, and any particles not deposited on the cylinder by electrical action may then travel downwardly in the return portion of the chamber farthest from the cylinder. Thus a circulating cloud of fine mist may be provided.

In Fig. 3 an elongated housing 24 holds a small quantity of dampening liquid 25 above which, during the opera-- tion of the press, there is a cloud or fog 26 of dispersed fluid elements. Housing 24 is set down into an oil bath 27 contained in a pan 28. Within the oil bath there are placed one or more vibrating devices 29 capable of generating ultrasonic vibrations in the oil bath. Any suitable devices of this character may be employed. We have shown such devices as each comprising a piezoelectric crystal 30 with conduction plates 31 on opposite sides thereof connected by wires 32 with a source of high frequency electric oscillations 33. Any suitable frequency may be employed, and preferably the natural frequency of vibration of the crystal 30 and of the oscillator 33 are chosen to substantially coincide. Frequencies of the order of 100,000 to 300,000 cycles may be employed to produce the desired result.

The action of the vibrating crystal 30 is to produce ultrasonic vibrations in the oil bath 27, which vibrations are transmitted through the walls of housing 24 to the dampening liquid 25, thereby causing a portion of the latter to rapidly disperse into finely divided form comprising discrete elements of dampening material. Thus housing 24 becomes filled with a fog 26 of dampening material which may travel to the plate 11 through the opening in the side of the housing. If desired a series of devices 29 may be arranged along the length of housing 24 to produce fog uniformly therein.

In Fig. 4 housing 35 is provided with an opening 36 which may be closed off to a greater or lesser extent by means of adjustable gates or shields 37 which are slidably secured to housing 35 at a point above the opening 36. Preferably a series of such gates, about 2" wide for example, are arranged adjacent each other along the full length of housing 35 so as to permit variation of the effective width of opening 36 transversely of the machine for varying the amount of dampening fluid applied to the plate, which is a feature that is frequently of great benefit in printing operations where certain parts of the plate may have much greater inked areas than others. This feature of the invention is equally applicable to the forms of the housing illustrated in Figs. 1, 2 and 3.

Within housing 35 there is a quantity of water 38 or other suitable vaporizable ink-repellent material. The water 38 is heated by an electric heating device 39 immersed in the water and connected by wires 40 to a suitable source of electric power and to suitable control mechanism for maintaining the Water at an even temperature. The temperature is not critical but is preferably above room temperature and below boiling temperature, and is chosen to produce the amount of vapor required. The heating of the water 38 causes it to give off vapor which may remain in that form until it reaches the plate, or may condense to form a cloud of fluid particles.

In Fig. 6 the means for effecting a dispersion of fluid elements is the same as that of Fig. 3, and no additional description is necessary.

the plate 11 of cylinder 10 by electrical means. This result may be accomplished in different ways. As illustrated in Fig. 1 an electrode which may take the form of a conducting wire 45 extending the length of chamber 17 is arranged within the latter in the path of the stream of mist particles and adjacent the lateral opening in the housing member 15. Wire 45 is of a diameter suitable for the production of corona discharge which, according to generally accepted practice, is of the order of .005 to .012 inch. It is connected by Wire 46 with one terminal of a high potential source 47 of direct current electricity. Such a source may comprise a power pack of known type including the usual high voltage transformer, choke coils, condensers, resistances and mechanical or electron tube rectifier. The other terminal of source 47 may be connected by a wire 48 to ground, and from ground another wire 49 may lead to a brush 50 in engagement with a conductor ring 51 on cylinder 10. Alternatively, wire 43 may lead directly to brush 50. The first arrangement provides a high positive or negative potential in wire 45, depending upon the polarity selected, and ground potential in ring 51. The second may provide potentials of opposite signs in wire 45 and cylinder 10 without reference to ground potential. Normally the plate 11 is metallic and is electrically connected to the cylinder 10, so that it will be at the same potential as the cylinder. The actual potential difference which it is desirable to employ varies with the size of the particles of mist, the amount of dampening material required by the plate, the speed of rotation of the cylinder, the size of the opening between the chamber 17 and the cylinder 10, the diameter and location of wire 45 and other prevailing conditions. Potential differences in the range of 10,000 to 60,000 volts may be used, other conditions being properly chosen, but the invention contemplates the use of any potentials capable of accomplishing the desired result of influencing the movement of particles of ink-repellent fluid without disruptive arcing or spark discharge.

As illustrated in Fig. 2, additional wires 45 having the same connections as wire 45 may be employed if desired,

their purpose being to charge the particles of ink-repellent fluid as they pass such wires on their way toward the point of deposition on cylinder 10. Also, if desired, a further electrode in the form of a plate 45 may be provided adjacent cylinder 10 for increasing the strength of the electric field applied to the charged particles of dampening fluid. This plate may be connected to the high potential source so as to have a charge of like sign to that on wire 45 and of the same or difierent potential.

In Fig. 3 the means illustrated for charging the fog particles 26 is the same as that described in connection with Fig. l, and as in Fig. 1 the connection between the high potential source and the ring 51 may be made either directly or through ground, depending upon conditions. For the sake of simplicity the electrical means for creating this potential difference between wire 45 and ring 51 is omitted from the drawing.

While in connection with the means illustrated in Fig. 4 for producing particles of the dampening liquid in the form of vapor or fog, the charged wire of Figs. 1 and 3 may be used for causing flow of such particles toward the printing plate 11, We have shown in Fig. 4 a somewhat dilferent means for the purpose, that is to say the dampening liquid 38 is electrically charged by means of a plate 55 immersed therein and connected by a wire 56 to one side of a high potential direct current source 57 of the kind described in connection with Fig. l, the other side being connected by a wire 58 to a brush 59 running on ring 51 of cylinder 10. Alternatively the connection from source 57 to brush 59 may be made through ground in the manner illustrated in Fig. l. The liquid 38 thereby functions as an electrode. Thus the vapor or fog particles retain a charge of like kind to that existing in the liquid dampening material when the vapor is separated therefrom by the heating of the material. Being thus charged and being disposed in the electrical field between the liquid dampening material and the oppositely charged or grounded cylinder 10, the vapor or fog particles are attracted to the cylinder where they are deposited and dampen the plate 11. The temperature of the water, the potential difference between the plate 55 and the cylinder or plate 11, and the width of the opening 36 are chosen or adjusted to provide the amount of moisture on the plate required by other operating conditions.

Fig. 5 illustrates a further means for applying electrical force to the dispersed elements of dampening solution. This means comprises a high potential conductor 60 to which are connected a series of electrodes consisting of closely spaced conducting wires or rods 61 having sharp points. These pointed Wires 61 are located at least partly within chamber 62, which contains the dispersed dampening fluid, with their pointed ends directed toward the plate 11 and spaced a suitable distance therefrom. The plate 11 is either grounded or maintained at an opposite potential to that of conductor charge from the points 61 toward the plate causes the mist or vapor particles to be charged and to travel toward plate 11 and dampen the latter. In this form, the movement of the particles due to their charge and the electric field is augmented by the effect of the electric wind produced by the discharge from points 61. Any means for creating a fog or mist or vapor of fluid elements may be utilized with this particular means for charging the elements.

In Fig. 6 the means for imparting an electrical charge to the dispersed fluid is the same as that of Fig. 4, namely by charging the liquid before the dispersion takes place. Hence no additional description is necessary.

The various methods and means described herein may be combined in different ways than are illustrated in the drawings. For example devices for regulating the size of the opening of the chamber adjacent the plate cylinder, such as the gates 37 of Fig. 4, may be employed in connection with any of the chambers shown herein or with any chamber suitable for carrying out the invention, and the various methods and devices for applying electrical force to the elements of the dispersed dampening fluid may be employed in any suitable combinations with the various methods and means for dispersing the dampening material.

In practice suitable control devices may be provided to automatically turn on and off and vary the degree of high potential employed, and to initiate the dispersing devices, in accordance with operating conditions. For example, means may be provided for varying the potential difference applied to the dispersed dampening material with variations in the speed of rotation of cylinder 10, for the purpose of applying the proper amount of moisture to the plate. Increasing speed in general requires the application of increasing amounts of moisture, although such increases may not be in direct proportion to the increase in speed. Means for this purpose may, for example, comprise a governor driven by the press drive gears or a gear on the plate cylinder and suitably connected to the source of potential difference to vary the potential difference as the speed of the cylinder changes.

Means may also be provided for reducing the potential difference to a predetermined value when, as is customary in offset lithographic printing, the press is tripped from running speed to slow idling speed, and the form rollers 14 are lifted from the plate cylinder 11. During such slow idling of the press the plate 11 must be kept damp,

60, and the escape of electrical but only a relatively small amount of moisture is required, since none is removed by the rollers 14 or blanket cylinder 12. A predetermined value of potential may be chosen to cause only the required amount of moisture to be impelled to the plate.

As a further refinement means may be provided also for momentarily reducing the potential difference at a time corresponding with the passage of the gap in plate 11 past the chamber containing the dispersed dampening material, the purpose being to avoid deposition of a surplus of moisture in the gap of the cylinder. Such change in potential difference may consist in a reduction of the potential of both the plate 11 and the wire 45 or rods 61, as the case may be, so that less electrical force acts upon the moisture particles, or such change may consist in momentarily applying potential of like sign to the plate cylinder 10 and the wire 45, so that the moisture particles will be repelled away from the plate cylinder 10.

Similarly, means may be provided for disconnecting the source of high potential, for grounding the plate 11 and the wire 45, and for turning off the heating device 39, the vibrating device 30 or the nozzles 20, as the case may be, when the press stops.

Having thus described our invention, we claim:

1. The method of dampening a lithographic plate mounted upon a rapidly rotating cylindrical support preparatory to inking image areas thereof by contact with inking rollers, transferring the ink to a blanket cylinder and printing therefrom on print receiving material by pressure exerted against an impression cylinder, which method comprises establishing an electrical field of force adjacent said cylindrical support and across the Width thereof of substantially uniform effect over adjacent image and non-image areas or" said lithographic plate and of limited extent circumferentially of said support, and providing finely divided elements of aqueous lithographic plate dampening material suspended in air in said field, said elements being electrically charged, said field being of such potential gradient as to influence the movement of electrically charged particles suspended in air in said field toward said support while avoiding spark discharge, said finely divided electrically charged elements being impelled by said field toward said support and onto the surface of said rotating lithographic plate to dampen said plate preparatory to contact thereof with inking rollers.

2. The method substantially as defined in claim 1, wherein the charging of the particles takes place in said field.

References Cited in the file of this patent UNITED STATES PATENTS 1,335,026 Pitkin Mar. 30, 1920 1,798,850 Moe et al. Mar. 31, 1931 1,939,302 Heaney Dec. 12, 1933 2,108,984 Grembecki Feb. 22, 1938 2,191,827 Benner et al. Feb. 27, 1940 2,196,412 Grembecki Apr. 9, 1940 2,221,776 Carlson Nov. 19, 1940 2,224,391 Huebner Dec. 10, 1940 2,394,656 Beregh Feb. 12, 1946 2,394,657 Beregh Feb. 12, 1946 2,408,143 Huebner Sept. 24, 1946 2,451,288 Huebner Oct. 12, 1948 2,551,582 Carlson May 8, 1951 2,633,796 Pethick Apr. 7, 1953

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