US2821133A - Method for planographic printing - Google Patents

Description

Jam. 2%, 195@ G. R. BRQDlE METHOD FOR PLANOGRAPHIC PRINTING United States PatentA 2,821,133 li/IETHOD FOR PLANOGRAPHIC PRINTING George Rogers Brodie, Lower Merion Township, Montgomery County, Pa., assignor to Fredk H. Levey Com- ;an, Inc., New York, N. Y., a corporation of New Application December 15, 1954, Serial No. 475,400 3 Claims. (Cl. 101-141) This invention relates to the art of printing and, more particularly, to o-set printing. lt is of particular utility in conjunction with printing operations using planographic or lithographie printing plates to which water and ink are alternately applied.

In this method of printing, the ink customarily used is one containing a relatively volatile organic solvent and for best results the ink must be substantially free from water.

The surfaces of such printing plates are composed of different materials one of which is water-receptive and ink repellant and the other being water-repellant and inkreceptive.

In practice, it is customary to apply water to the printing plate by rotating the plate in rolling contact with the surface of a roller which has been wet with water and thereafter to pass the plate in rolling contact with the surface of one or more form rollers wet with ink. The

ink is usually supplied from a fountain and is conveyed therefrom to the form roller, or rollers, over an ink train composed of a number of cooperating rollers, as is well understood in the art. Frequently, the ink is conveyed from the fountain to the plate cylinder over two parallel trains oi ink-distributing rollers.

I have observed, that in operations of the type described, there is a tendency for the form rollers to pick up substantial amounts of water from the plate cylinder in passing in rolling contact therewith, and a tendency for the water so picked up by the form rollers to accumulate in the ink film thereon and work back through the ink train, or trains, thus polluting the ink films with moisture and detracting from the high quality of the printing.

In accordance with my present invention, I avoid the consequences of the conditions just described by subjecting the ink lilms on the surfaces of the rollers of the ink train, or trains, to continuous or intermittent dehydration and thereby avoid the presence of objectionable amounts of water in the ink lm applied to the printing plate.

I accomplish this dehydration in accordance with the present invention by positively circulating over the ink iilms on the surfaces of the ink distributing rollers, as the ink travels toward the plate cylinder a substantially dehydrated atmosphere containing substantial proportions of the vapors of the organic solvent present in the particular ink being used. By reason of the low of water vapor in this dehydrated atmosphere, the water present in the ink ilm is vaporized and carried oi by the circulating atmosphere.

By this means, I not only prevent objectionable pollution of the ink film by water working back through the form rollers, but l protect the ink lm from moisture normally present in the atmosphere of the press room, especially in damp, humid weather.

A further advantage of my present invention is the retarding of the vaporization of the solvent originally present in the ink, thus preserving the consistency'of the ink and avoiding excessive tackiness due to excessive loss of the ink solvent through evaporation.

partial pressure ice The atmosphere, which is circulated in contact with the ink lm, may consist solely of solvent vapors or this atmosphere may consist primarily of dehydrated air, or other gases to which the solvent vapors have been added, and containing a moisture content sulciently low to promote vaporization of moisture contained in the ink film. The extent to which the air so used, must be dehydrated will, of course, vary with temperature and partial pressures, and the amount of moisture initially present in the air. Such dehydration may be eiected by chilling or by passing the air over a dehydratng agent or by other means well known to the art.

For optimum results, the atmosphere circulated in contact with the ink tilms should be substantially saturated with the solvent vapors. However, good results may be obtained where lower concentrations of the solvent are used. Where little or no solvent vapor is present in the circulated atmosphere, there is a tendency to cause excessive vaporization of the solvent from the ink iilm.

Where the tendency of the water to work backward along the ink train is relatively great, some vaporization of the solvent from the ink iilm may be desirable as it appears to promote the removal of water from the ink film perhaps by forming an azeotrope therewith.

In general, the proportion of ink solvent present in the dehydrated atmosphere Vshould be within the range extending from saturation, under existing temperature and pressure conditions, to not less than about one-fourth that amount.

The atmosphere may with advantage be prepared by dehydrating air, or other gases inert with respect to the ink, by any known method, and passing the dehydrated air, or a predetermined proportion thereof, through, or in contact with a body of the particular solvent used.

These solvents are usually hydrocarbon fractions boiling within a range of 450 to 600 F. Low concentrations of these vapors in the press room are customary and are not particularly objectionable. However, in order to avoid excessive concentrations of these vapors in the press room and to avoid the mixing of the humid atmosphere of the press room with the gases being circulated over the ink films, l enclose the ink train, or at least a portion thereof, over which the dehydrated atmosphere is circulated.

The invention will be further described and illustrated with reference to the accompanying drawings which represent conventionally and diagrammatically a particularly advantageous embodiment of the invention, and of which Fig. l represents a side view of the press, with the supporting side frames omitted for greater clarity, and

Fig. 2 represents a vertical sectional view along the lines 2-2 of Fig. 1 with the position of the side frames indicated.

In the apparatus represented by the drawing, the plate cylinder 1 rotates in Contact with the blanket cylinder 2 which, in turn, rotates in contact with the web passing over impression cylinder 3. The plate cylinder 1 is equipped with means for securing to the periphery thereof, a printing plate to which water is applied by means of rollers indicated at 4 and to which ink is applied by the form rollers 4.

The ink is picked up from the fountain 5 by the fountain roller 6 and is conveyed therefrom by means of the ductor 7 to the ink distributing roller 8 and, from thence, is carried to the form rollers 4 by two parallel trains of ink -distributing rollers 9, 10, 11 and 12.

These various rollers and cylinders are rotatably mounted on parallel axis and are supported at each end by the press frame indicated at 17 in Fig. 2.

The space 13 between the two parallel ink trains is enclosed by the respective parallel trains of rollers, the plate cylinder 1 and side plates 14. The dehydrated atmosphere isintroduced into'V the enclosure 13 by means of inlet duct and passes therefrom `through refuent. duct 16. It is frequently advantageous to provide bales in the enclosure 13 so positioned as to direct the dehydrated atmosphere more uniformly on the ink films, -in ordentopromote of vtheink.l VvHowevensuch use ofmaximum dehydration bales is not essential.

U YIn-operation, the water receptivesurfaces of theprintmg plate, carried` by plate cylinder 1, is wetted -with water The plate then passesinacontactf accumulate toL an extentawhichinterferes with the-5 selecv tivityl of the printing platel surfaces witlrrespectI to waterand ink; Y

By the constant', or v.evenfperiodic circulation lof-the dehydrating atmosphere in contact with the ink lilmslbeing conveyed through the enclosed-area.13, the accumulation of objectionableproportionsof water-in=the i1'1lQ1ilrri-'-mayl beV prevented.

The atmosphere blown through enclosure 13 andfwithdrawn through outlet duct'15 may,z if "desired,-befrecondi tioned-'to the-predeterminedmoisture andsolventvapor;

content and recirculatedin contactwith the' ink Ylilr'n within the enclosure 13.

Thersideplates14 are shown in thedrawingsas--posi- Their arrangement tioned inside vthe press side-frames. may be varied to suit the construction ofthe particular press. While it is desirable to prevent, so farv'as practical,l

the escape of the circulated atmosphere fromthe--en` closure 13 into the press room,someleakage-is usuallypermissbile. In the arrangementshown the. shafts'flS of the respective roller may extend .through openings through the plates or through'notches cut in theedges of` the plates. It is usually desirable that the edges of the` plates appliedY to the f blanketl cylinder f2 extend, at least, to the points of contact between the re- `spective Arollers so as--to forma more perfect-enclosure for the dehydrating atmosphere.

It will be understood that reference herein to dehydrating, or dehydrated, atmosphere is intended to mean an atmosphere of substantially lower relative humidity than the atmosphere of the Pressroom.A Considerable variation is permissible vwithrespect ,to thefmoistnrey content lofi-the ycirculated atmosphere, depending largely upon the temperature and-volume of the. atrnospherez circulated-f; and

the vamounty of fwaterrto be evaporatedfrom the inkilm. Where only-moderate amountsf'oflwaterare to be evaporated from the film, I may, for instance, circulate the dehydrating.v atmosphere .at:r,0omA temperature ,1 and; having a relative humidity of about I claim:

1. In the process of off-set printing wherein an ink containing a volatile organic solvent is applied to the surface .of a` printing: plate, which has lpreviously-beenwetwwith water, by rollinggcontactlwith the. surface of' a formfoller to which alilm of the-,inkv issuppliedover a trainy ofcooperating. ink-distributing rollers Y,the step` of-. preventing f the accumulation of water in the ink filmtbeing conveyed to-the printing :plate `byzcirculating inv contact witha portion' of said ink/film `a :substantially .dehydrated atmosphere comprising aasubstantial proportiontlof :vapors `of the `inlc solvent while shielding said portion of the ink film frompress-room atmosphere;

12. The processfof. claim. l;in which; the 'dehydratedsatf mosphere comprises a.v proportion of thev ink solventvs/ithul therange extending from saturation to not less than. abouti one-quarter the amountrequiredffor saturation .under the existingtemperaturegconditions.`

`3. Process Aof -claim 1., in which the ink ;solvent-.is a. hy; n drocarbon fraction: boilingwithinthe range .of from about,4

ReferencestCitedwnr the `tile ol'"v this"A patent UNITED `STATES PATENTS `643,372 Cornwall Feb.f;13,11900 1,837,702 Canfield Dec. 22, 1931.A

2,347,619 Taylor etal Apr. 25, 1944 2,546,793k Sodomka` Mar.,127, 195,1v

FOREIGN PATENTS 461,042v tItaly; Jan.:1'0,:1195.1

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