US2733653A

US2733653A - Dampening system and method of-

Info

Publication number: US2733653A
Authority: US
Publication date: 1956-02-07
Anticipated expiration: 1973-02-07

Description

Feb. 7, 1956 w. G. MULLEN 2,733,653

DAMPENING SYSTEM AND METHOD OF USING SAME Filed Jan. 14, 1953 LL 0 2 I 2 g. a Q H 7 l5 5 I INVENTOR. Z. 2 /Q/%IZ/7Z ///a//6/(-,

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Application January-14, 1953, Serial No. 331,-292 8 Clfimsa' (Cl.'101147) Thi it? for th applie on,of r epellentto the plate surface.

Ifhe rinciples underlying the-operation of a" litho-" graph c; plate are well: recognized and the same :wvhether,

invention relates to an improvement in theappli-- f e lem--10 tthexsurfa'ce-of ta'lithog'raphie auditrela-tesmore particularly to. apparav in; connection .with a -lithographicprinting press thLZplatt be formed of the old lithographic stone etched metal plate or the-more recently developed I coatedr; papenb lithogra late s r In theory; the imagedportion-of the 1 4i?"P'iwtqesrmk receptive and water repellent-Whilethe non-imaged portion formingqthe remainder of theyplate. 3

l is hydrophilio in character and-preferentially gre- I n op an aqueous repellentd's first-applied to his-generally recognized by those skilled in the ttth 'ticalzconditionsinthe operation of alitho tenan lt is believed that the basic difiiculty which: prevents any pqssihility o f' rnaintainingflthedesired balance of cond5 rece vedonly "by the imaged {portion for onto: the fofiset blanket for the production 'of er and repels the oily or greasydnk composi-; t

t rifaee oi the;.p late,- "When present in the de-. A the t repellent wets oply ,the' ;hydrophilic,- len so that greasy inks will be "repel-led tro ent systems is due in part tothe fact thatwhen' the ate dampeners are wet sufficiently to prevent anyj ei h enin form ming on the-plate moon-to thesabove; t the presentdampening system oi inlet-mm. the plate-image,-they, 'atthesame jettoo-ivet to print properly. 4 As a result it has; to strike a-compr0mise.-;In practice the form pile s vveta suliicient to prevent scumming but'not; peletheink entirelywAs a result, the damp roller becomes -progressively contaminated requ i;res -;increasing amountsof repellent to a.

is subject-1o asnumheraofother objections,;a iew -of which:

willlhereinafterg be specifically mentioned of the-.:=;=r'equirem1ent t for having the dampe properlyewet-wout--with:=repellentbefore contactf withthe I surfaqe; ofthe-plate itris-impossible-to start-operation to duce copy until several-: cycleshavebeen made:pr'opf B us g -rollers" a 2,733,653 Patented Feb. 7, 1956 2 (3) In etfect, the control through thedarnpeningsystem is limited to onedirection only Whileadditional water can be applied; whennecessary no nieans is available for cutting back on the amount of moisture on the plate -isurface other than to dissipate the excess inusegradually by cutting down on the supplyjntihthe desired"conditions are temporarily secured. In the meantime eopy- 3 poor quality is being produced (4) Ihepresence-pi the dampening .roller in contact with the lithographie surface constitutes a ,source of wear and damage tol th image and can materially affect the number of cop; which can be produced 5) Becau s e of the contamination factor andthe removal oi ink by the mol leton or dampening rollers operating in contact w ith the surf i of the p1at e,. t he;molleton covers must be replac d pr cleaned periodically and additional pres s operationsfireq required a he damrs a r n tr-pr a t1 The objectionable features of present darnpening s ys; tems which make use of a rnolletonrollereorloth I dampening f orm roller have, been substantially -com a pletely eliminated by .the nevv and improved dampening system of the type described and claimed in the Mullen Patent No. 2,60%,848, vyhieh issuedion July 2 9," 1 Brieflydeseribed the Mullen systemmakes use ofita water roll which appliesan excess of waterpnto the urface of the plate in advance of the inkinglform rolle excess moisture is removed fromvthe surface oi th by an 'air bladewhich;operatespontinuously?across I plate and may be adjusted'Qsub stantiallyfcompletely H remove the ater frorndhe imagedtsareas ofthe plate I while leaving a fi lmof water of minirnum thickness over the non-imagedareas .Thedescribed Mullen-gsystenripr vidcs an exact control of moisture for each revolutioniof the plate cylinder and independently of the-amount-of moisturepresent on the surface of the plate in thejpre vious cycle. Thus it is possible-to achievet properyve ting in the first cycle of the machine for thelprodu'ction'yf of copy and it is also possible to achieve irnmediate adjustment in the amount ofmoisture ontheplatesurface without juggling the 'ratioo f water to ink asthe printing operation continues. Once the amount of moisture f best operation hasbeen established, it is po ssible, to mai tain the desired conditions substantiallyindefinitelydu ing the operation of the machine. Byreaso'n of thejfact t; that the moistening roll applies an excesslof Water vvithout contact with the surface"of thejplategwear on the, plate is eliminated as, aff actor and. no ink iscapable of ff being transferred back from the surface of the Pie thereby to eliminate the p'roblemsincide'nt to; the transf of ink to the dampening roller 'as in the present systems. if Because the air blade removes all entangling Water from the dot image and establishes{essentiallya dry dot image this system] is better fadapted to the reproductiono sharper as well as full inked dots in tone andhalf-tone printing a a t v Thekdampening system of the type described differs basically from the presentsystemsfin that'it is not ,di pendent upon the amount of water repellentapplie'dt H; the surface of the plate but relies upon, the"appli ation1 of a' controllableexces's of repellent to the plateandythe 4 reduction of the excess 'water "film byjadjusttnetit of pressure to provide a minimum" guantityfo'n the n printing areas and substantially complete absence of 1; moisture on inked areas at the point of contactbetwe'en the plateand the'ink form rollers. I a a a While the described air bladefsystem ffor plate'fjdarn ening provides a vast improvement in the; operation of a p e ostap fcrt nt s a e "ib s an, to i o th' invention t'o providestill j further improvements in thefi'; p n ng y entbti he 'p de ibe I .i be ic x si n' 'nfi i rov d ar mr n system of thety'pe described in which problemsin'cident 2,733,653 a I a to the removal of excess moisture cut from the surface of the plate is substantially eliminated; in which amore uniform and controlled film of repellent is permitted to remain upon the plate surface when brought in contact with the inking form rollers; in which the amount of air capable of being entrapped in the water layer is reduced to a. minimum thereby to provide for a more controlled film of moisture.

These and other objects and advantages of this system will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawing in which- Figure 1 is a schematic elevational view of a portion of a planographic printing press embodying features of this invention;

Figure 2 is an enlarged sectional elevational view of the mechanism for removing excess moisture from the surface of the plate;

Figure 3 is a chart comparingthe efiiciency of the effusor at various angles, and

Figure 4 is a fragmentary elevational view showing a modification in a repellent applicator means.

In accordance with practice of this invention, the operation of a' dampening system of the type described has been found to'begreatly improved by the use of an air blade or eifusor set to operate upon the surface of the plate at a negative angle with respect to the radius of the plate cylinder at the line of contact between the air blade and the plate and in the use of a vacuum means to dispose of the excess repellent rolled back by the air blade operating to remove the excess moisture from the surface of the plate. Optimum conditions have been found to result when the angle of the knife blade ranges from to -30 with the normal at a point of engagement but improvements are still secured when the air blade is. setat less than zero but greater than -3 from normal.

When the use of a negative angle within the range described, negative pressures following the Bernuli principleare found to exist in the area of the slick and that the slick is shortened to the extent that the wake moves up to permit positioning of the vacuum removal means closer to the blade thereby to minimize the difficulties relating to the removal of the excess moisture a the tail end of the plate. In the event that the distance between the air blade or efiusor and the wake were large, it would be difiicult to achieve proper moisture control in the end portion of the plate.

When a plus angle is used, the air issuing from the effusor dividesin favor of flowing back and the excess moisture out from the surface of the plate becomes turbulent with a resulting loss in control and with the introduction of excessive amounts of air bubbles with the consequent non-unformity in the moisture layer which remains on the plate. When turbulence occurs and air in excessive amounts is entrained within the repellent, it then becomes necessary to make use of special equipment to separate the air from the repellent for subsequent recirculation in the dampening system. With a plus angle, the vacuum means adapted for removal of the excess moisture rolled back upon the surface of the plate would of necessity be located far back on the cylinder with the result that the air would interfere with the operational characteristics of the plate.

For purposes of illustrating the improvement described and claimed herein, reference will now be made to the accompanying schematic drawing in which 10 indicates the plate cylinder of a conventional printing press used for direct or offset printing.

The plate cylinder 10 is adapted to support the usual imaged lithographic plate 11 which is secured at its leading edge and at its trailing edge 12 within a depression 13 formed to extend across a portion of the plate cylinder.

Ink distributing rolls 14 of the conventional type function to transfer ink from a fountain 15 to an ink form roller 16 which engages the surface of the plate 11 for transfer of ink to the imaged portion in the production of copy. e

The improvement embodying the concepts of this invention relates to the means in advance of the inking system for the application of repellent and control of the amount which remains on the surface of the plate to repel transfer of ink to the non-imaged areas without interfering with the transfer of ink to the imaged areas whereby copy of good quality can be secured repeatedly with minimum wear on the imaged plate and without contamination of the elements functioning incooperation therewith.

A repellent roller 17 rotating out of contact with the peripheral surface of the plate 11, but spaced a very short distance therefrom, is partially immersed in a bath 1% of repellent contained in a suitable trough 19. The

roller may be rotated in the same direction but is. pref- I erably rotated opposite that of the plate cylinder so that a film of water or repellent 20 in excess of that required is transferred from the roller 17 onto the surface of the plate 11. The amount of repellent appliedmay be varied in accordance with. the distance between the surface of the plate and the repellent roller and the relationship between their linear speeds but it will be apparent that application is effected without contact between the repellent roller and the surface of the plate thereby to avoid wear -or deterioration of the imaged plate andprevent transfer back of ink composition from the surface of the plate to the repellent system.

This notonly provides for the production of a greater number of copies of good quality from the imaged plate but eliminates the necessity for a molleton system and the consequent difficulties of replacing molleton covers and breaking in the molleton rollers for operation. It

also greatly simplifies the repellent system since the amount of repellent applied is not critical so longas an excess is present on the surface of the plate thereby to eliminate the necessity for taking special precautions to control and distribute the repellent on the form or molleton rollers, as in present systems. While the use of a repellent roller out of contact with the surface of the plate is preferred, excess repellent can be applied onto the surface of the plate by other means such as aspray gun or shower-head or by a wick 17 for transmitting repellent from a bath 18 in a container 19" to the sur which terminates at its forward end into an elongate slot 23 shaped to make most efficient use of the air pa'ssing therebetween under pressure to cut repellent from U the surface of the plate in amounts which depend upon the air pressure and the distance between the slot and the surface of the plate. It has been found that conditions which require minimum air pressure provide for best operation, as will hereinafter be more specifically defined. For most efiicient utilization of the air, itappears best to provide an outlet opening in the .form of v a slot 23 of substantially uniform dimension for a distance sufficient to channel the air stream and minimize spread or divergence upon issuing from the slot. Air under pressure is admitted into the chamber 22 through a conduit 24 which communicates a source of'air under high pressure with the air chamber through an mletopem ing 25 in the rear of the housing.

new and novel concept of this invention resides in theuse of vacuum means 26 for constantlyremoving repellent rolled back upon the surface of the pla'te by; the air knife or effuser thereby to eliminate problems the normal.

ditiiiiiii. iirfail pref; l at ,the po nt where the ffwalce Illustration is @3215 oneforiribf tl fic 'liii m ll repbll awn -fi'o t 'plate "to drain "into means associated 1th the described xtracto'r' "for separating the'i I p air ffom to enable recirculation of the repellent facfi oiit02003"i'r'ich" ceat the point of contact between the air'knife andrepenent 'oii the surface o? the plate;= and in theifwak rforrrled m the rear thereof withwtheeresult thateles a irsbecomes entrappedyin the. repellent layerand a smoother-coating witli mpletecontrolis"securedin the amount of rp'e'l' f'i len lia s permitted to remairr on the *surface" oftlief h "advanced'to the 'airformroll'er. A reuse-r f .pi'es'sure'and vacuumofair also preveiit'slo'ss; of thecentrbl 'iavhichmight'arise'by evaporation of repel lent from the surface of the plate after the excess has onto the plate surface beyond the repellent applying meansbeen removed by the air knife. and at an angle with'the normal from the plate which is In the past, the air knife has been positioned to direct less than zero but greater than -30 whereby repellent the blade of air back upon the surface of the plate in from the imaged portions of the plate and the excess the direction opposite rotation or at a plus angle with repellent from the non-printing portions of the plate is When using a plus angle, substantial displaced rearwardly onto the plate, and suction means amounts of the air divide and flow back onto the plate having aninlet opening in parallel relation with the blade and create such turbulence that an uneven and streaky of air engaging the. plate and located immediately rearfilm of repellent is left on the plate and the excess rolled wardly thereof and extending crosswise in parallel relaback becomes uncontrollable and an excessive amount tion with the plate for removal of repellent displaced of air becomes entrained. rearwardly by the blade from the surface of the plate.

An important feature of this invention resides in the 2. A dampening system for a planographic printing discovery that the operational characteristic of the air plate mounted for rotational movement on a plate cylinknifeis greatly improved if, instead of positioning the tier, comprising means for applying an excess of liquid knifeblade' at a plus angle, the knife blade operates at repellent onto the surface of the plate and means for rea negative angle of between Zero and 32 with the normoving the repellent from the imaged areas of the plate mal and preferably within the range of 10 to 30. Opand for removing the excess from the non-printing porplate or dir ,;st met at tlmllm Conditions are Secured With respect to P tions of the plate including an air nozzle having an outlet sure, moisture control, reduction in turbulence, reduction of the length of the slick, and smoothness and uniformity of the rep l y permitted to remain as a to direct the stream of air issuing as a continuous blade coating on the non-imaged areas of the P The therefrom onto the surface of the plate at an angle less Movement resulting from Positioning the blade at than zero but greater than -30 with the normal of the a negative angle Within the limits Prescribed is graphically plate whereby the excess of the repellent on the surface illustratedin the c rt of Figure 3 Which p re th of the plate and repellent on the imaged portions thereof air pressure required to secure a predetermined thicki displaced rearwardly onto the oncoming portions of Hess of repellent on the Surface of the Plate When the the plate, and means for removing repellent displaced air blade is positioned at various angles. It will be obearwardly onto the plate comprising a housing having served that optimum conditions exist when the air blade the inlet opening aligned with the outlet of the air nozzle is positioned at a negative angle of between 20 to and closely spaced rearwardly thereof in closely spaced -25 and that a sharp break occurs when the knifeblade relation with the plate surface to remove repellent disis positioned at an angle beyond 32 to 33, which placed rearwardly onto the surface of the plate.

opening extending continuously crosswise of and in closely spaced relation with the surface of the plate and positioned as a result forms the lower limit of setting. These con- 3. A dampening system for a planographic printing M ws.

plate mounted for-movement inone direction on a sup? crosswise of and in closely spaced relation withth'e surface 7 of the plate, said air nozzle being positioned'to direct the streamof' air as afcontinous air blade onto the surface of the plate at an angle of less than zero but greater than. 30 with the normal to the plate whereby the excess repellent on the'surface of the plate and repellent on theimagedportionsthereofis displaced r'earwardly onto theoncoming portions'of the plate, means for removing the'repellent' displaced rearwardly ontothe plate comprising a housing having an ,inlet opening aligned with the outlet 'openin'gof the'air n'ozzzle and inclosely spaced parallel relation therewith and in closely spaced relation with the plate surface to'remove repellent displaced rear-wardly 'onto'the surface of the plate, means for introducing air into "the air nozzzle for passage through theoutlet'opening as an air stream of high velocity, and means for withdrawing air from the suction housing to withdraw repellent through the inlet opening from the surface of the plate.

4. Adampening system as claimed in claim 3 which includes means for adjusting thepressure of the air introduced into the blade housing to adjust the pressure of airi'rr the air lblade extending across the surface of the plate.

5. A dampening system as claimed in claim 3 in which the air nozzle is positioned to direct the airhlade' onto the plate at an angle between- 10" and -30."

6. The method of dampening a planographic printing plate bythe use of apparatus of the type described which comprises moving the printing plate continuously in one direction, applying a liquid repellent onto the surface of the plate in excess of the amount required for use in the printing operation, directing 'a stream of air which extends continuously crosswise of the plate as a blade onto the surface of the plate at an angle less' than zero but greater than +30" with the normal to theplate whereby the port,means for applying an'excess of liquid repellent onto the surface of theplate and means for removing" repellent excess repellent. onthe non-printing portionsof theplate andlrepellent on the imaged portio'ns isdisplaced rear wardly ontotheplate' fronrthe line of management the 'air blade and the plate and removing repellent di's'-' placed rearwardly "onto the'plate'by suctionmeansfhaving itsinlet opening aligned with the blade and positioned immediately rearwardly thereof. 7 V I 7'. The method of dampening a' planographicprinting plate by the use of apparatus of. the type described which comprises the steps of moving the plate continuously in one direction, applying liquid repellent onto the surface of the plate in excess of the amountjrequiredf foruse in the printingoperation,directing a stream of air ex f tending continuously crosswise of the plate as ablade' onto the surface of the plate from an air nozzlehaving its exit opening extending continuously crosswise'of the j 1' plate and positioned "to direct the air stream onto the blade at an angleless than zero but greater than, l-.30" to the normal of the plate whereby the'excess repellent. on the non-printing portions of the plate, and repellent on f the imaged portions is displaced rearwardlyfrom the point of contact, and removing repellent displaced rearwardly onto the plate by suction means through a housing having its inlet opening co-extensive with an aligned with the I exit opening of the nozzle and spaced immediately rea'rwardly thereof, introducing air into the nozzle forissuance under pressure from the exitopening as a continuous blade, and withdrawing air from the housing to such the excess repellent displaced rearwardly by the blade through the inlet opening into the housing for removal.

8, The method as claimed in claim 16 in which the air nozzle is' positioned to direct the stream of air as a blade j onto the surfaceot the plate at an angle between '10 and with the'normal.

References Cite d in the file of this patent UNITED STATES PATENTS 2,139,628 Terry Doc. 6,1938 J 2,366,926 Melton Q. Ian. 9, 1945 2,590,429 Ras .Mar. 25, 1952 2,604,848 Mullen July 29, 2 2,679,231 Pomper et al. L ...L May 25, 19 54