US2637929A - Process for producing lithographic printing plates - Google Patents

Description

y 1953 w. J. HAUSMAN 2,637,929

PROCESS FOR PRODUCING LITHOGRAPHIC PRINTING PLATES Filed April 27, 1950 ATTORNEYS Patented May 12, I953 j PROCESS FOR PRODUCING LITHOG-RAPHVIC V PRINTING PLATES Walter J. Hausman, Washington, D. 0.

Application April 2-7, 1950, Serial No. 158,480

3 Claims. (01. 4149) i The present invention relates to a process for producing lithographic printing plates having improved qualities and characteristics. More particularly the invention relates to a process for treating aluminum sheets to prepare lithographic printing plates which process involves combined mechanical and chemical treatment of the aluminum sheets to produce printing plates which have improved qualities and characteristics not heretofore obtainable.

Among the objects of my invention are to provide aluminum lithographic printing plates which can be used to produce large numbers of copies of printed or other matter, which have indefinite shelf life, which reduce the time and cost of preparation for printing, which resist oxidation, which require no scrubbing, counter-etching or pre-etching by the user, which perform uniformly in all weather conditions and which perform satisfactorily irrespective of the manner in which the image is placed on the plate. ,Another object of the invention is to provide an aluminum printing plate which will reduce the cost of lithographic printing by enabling complete runs to be made with one plate, thereby eliminating remakes and idle presses while remakes are being prepared. Still another object of the invention is to provide a process which imparts absolute uniformity to lithographic plates.

Present conventional metal lithographic plates are marble grained to provide a surface which will retain the image and which will hold a sheen or film of moisture on that portion of the surface of the plate which is not covered by the. Marble graining is accomplished by agi-' Image. tation of marbles on the surface of the plate in the presence of moisture and a powdered abrasive. Such plates must be scrubbed and counter-etched to remove oil which has been adsorbed by the metal during rolling and also to remove particles of abrasive and metal which remain in or on the grained surface. The marble graining process is expensive and requires considerable skill.

Metal lithographic plates have also been produced by subjecting surfaces of the plates to certain chemicals which produce a grain similar in appearance to the marble grained plates. Chemically grained plates are now used almost exclusively for those operations in which the image can be applied directly to the plate, such as by typing. The action of the graining chemical appears to be progressive and such plates have been found to have relatively short shelf life. Both marble grained and chemically grained plates are quite susceptible to oxidation which makes the plates extremely difiicult to handle in tropical climatesand during hot humid weather. Aluminum is exposed to oil during the rolling operation to form sheets. It appears that some of this oil remains adsorbed in the metal of the sheets. In both marble grained and chemically grained plates there is a tendency for this oil to for use to obtain the objects and advantages of r? seep into the grain after the plates have been stored fora short time. It will be apparent that presence of oil in the grain is deleterious in a printing processwhich depends upon immiscibility of water and oil.

I accomplish the objects of my invention and overcome the foregoing deficiencies in prior lithographic plates by. using a novel two step mechanical graining process followed by a chemical treatment.

Referring to the accompanying drawing, which diagrammatically illustrates one form of apparatus for the mechanical treatment of the plates, the reference numeral I designates an aluminum sheet which may be of thesize and configuration of a lithographic printing plate or which may be a larger sheet from which a plurality of such plates are. to be cut. The plate is positioned on a flat horizontal support such as a bed 2 provided with rollers 3 so that it can be moved over a track or support t. The aluminum sheet I is .at least 99% pure aluminum which is known in the trade as purity stock and which is virgin aluminum containing no scrap. The hardness of the sheet is that known in the trade as half hard minus.

A first rotary brush 5 mounted on a power driven shaft 6 is positioned above the bed 2 in position to contact the upper surface of the plate I. A second brush 1 is'mounted on a power driven shaft 8 above the bed and is similarly positioned. to contact the upper surface of the plate. The bed 2 moves in the direction of the arrow 9 and the brushes 5 and l rotate in the direction of the arrows l0 and II respectively.

The brush 5 is provided with hardened steel bristles I2 having diameters of .008 inch to .009 inch. The brush '5 is provided with hardened steel bristles of .005 inch diameter. The shafts B and 0 are driven at such speeds that the outer end of the bristles l2 and I3 have peripheral or linear speeds of approximatly 1400 feet per minute. In actual practice the brushes 5 and l are equal in diameter and the shafts 6 and 8 are driven at equal speeds. I have obtained the advantages of my invention by using brushes of 6 inches diameter rotating at speeds of 900 revolutions per minute, which causes the ends of the bristles l2 and 13 to have linear speeds of about 1414 feet per minute. The bed 2 and the plate I are moved in the direction of the arrow 9 at a speed of approximately 17.5 feet per minute,

The bristles ll! of the roller 5 break the skin of the aluminum sheet and produce. a decided grain which is relatively coarse. The bristles l3 of the brush 1 appear to modify or subdue the coarse grain produced by the brush 5 and the sheet is left with a beautifully uniform grain.

The aluminum sheet is then ready for the chemical treatment which modifies the mechanically produced grain and conditions the plate 3 the invention. I-add calcium hydroxide to hot water in an amount in excess of that which can be dissolved. The temperature of the bath is accurately maintained at 180 F. by means of thermostatically controlled electric heaters, A saturated solution of calcium hydroxide and; water is thus produced. I have found it advisable to permit the freshly prepared solution to age on season:

at the 180 F. temperature for about one hour before use. The aging or seasoning'is'also'found desirable after additional calcium hydroxide has been added to a bath which has already been used. The aging or seasoning eliminate any tendency toward-the formation of a coating on the plates or sheets.

The brush grained sheet'which has been mechanically prepared as described above is immersed in the aged or seasoned bath for 4Q seconds, the bath being maintained at the temperature of 180 These values have given the best results and thetemperature oi the bath the time of immersion of the aluminum sheets appear to be quite critical. It is possible to use temperatures as low as 175 or as high 185 but the time of immersion must be adiusted accordingly. At temperatures belowv 1T5 F. the bath is not effective. If the tempo C-i the bath is elevated above about 1821. or ii the plate is l ft'in the bath for too long an interval, the plate will be chemically grained the ad.- vantages of the mechanical pretreatinentwill be Immersion times of from 25 to 55 econds lull advanobtained with lost. are possible but I have found that the tages of the, invention be immersion times below 85 or above seconds.

The aluminum sheets or plates withdrawn iromthe bath and promptly scrubbed with a re.- tary brush having fibre bristles operating under a constant spray of fresh water. The plates may then be passed between wringer rolls to remove excess water, force dried by mild heat or air blast, inspected and packed.

Plates produced according to the foregoing .irocessare remarkably resistant to oxidation. One of my plates was placed in a tropical room maintained by the United S .tes Army for test purposes under conditions of high temperature and excess humidity. After a period or days the plate was found to be in perfect condition. The chemical treatm nt appears to, remove or cficctively seal any residual '18 metal of the plates and this eliminates the oil hazard and the necessity for: scrubbing and counter-etching the p prior to I am not. aware or" the precise 11 re of the chemical action which occurs during immersion of the latesthe There is consi" foam while the sheets are immersed the -ne appearance of'the grained is somewhat changed. although no coatii appears to be formed on the sheets. The r stance to oxidation is greatly increased and th s enables the plates to be stored indefinitelybefore use and causes the plates to handle and produce eniciently under even the lllOStadVGl'SE weather eon. ions;

My plates are sensitiveto all known image forming materials-and at the some time are quite susceptibleto action of all. standard plate etches My plates may be uniformlysensitized" f. .-p1atQ bar-ha and H WP QwSi 21 quitethj'e whirlinglaction iota whirler; However, if desired the plates can be sensitized by wetting with water, placed on a whirler and sensitized in the manner conventional with marble grained plates,

My plates have been used to produce 215,000 colliesgoflprinted matter Without remakes and without loss of quality of reproduction. This numberis-far-in'excess of the numbers which it hasheretofore been possible to produce with a single plate and is of tremendous practical and economic advantage because it enables extremely large runs to be made without remakes."

Thepractice of my process is inexpensive and the cost of producing the improved plates is rela-. ive y lcw-.. The pro es n e ond cted in a mor r le co ti us rrie me i.v h appa tus which has been described aboveis exemplary only and it is apparent'th'at'othjer arrangements of apparatus would be suitable so long as the action on the aluminum sheets or plates remains essentially unaltered.

Having thus described my invention, 1 claim:

1. A process'for producinga lithographic plate which comprises brushing one side of a sheet of at least 99% pure aluminum with, a first brush having relatively coarse steel bristles to tear the shin of thje sheet and to .form a coarse rain, brushing said side of said sheet with a steel brush having relatively finer bristles to subdue the coarse grain formed by said first brush,v immersing said sheet in a saturated aqueous solution of.

calcium hydroxide maintained at a temperature between F. and,l 85. F. for a period. of vfrom about 25, seconds to about ,55 seconds, and water s ru bin nd. rying. a d plate.

2.. A process. fQI'producing a lithographic plate which comprises brushingone side of a sheet of, at leastfli? percent pure aluminium wit-ha first brush having steel,,bristles approximately .008 inch in diameter movin a a, spee of. about .1400 feet per minute, brushing said sheet with a sec.-

ond brusnhaving steel bristles approximat ly .005" inch in diameter .movin iat, a speed of aboutMOo feet. per. minute, immersing Said plate for from 35 to 45 secondsin ,a saturated. aqueous solution of 5 calcium hydroxide maintained, atabout 1.30.: 5., andWatenscrubbing and drying said plate.

3. A process for producing a lithographic printing latewhich comprisespassing a sheet ,otat

lea t pure aluminum into contact with afirst. brush having steel bristles, of a diamctenot ap proximatelmbw inch mOViIIg' at a spe d eras p mately %00 feet p r. minute. p ssing, the h et beneath a cond brush hav steel bristles f pp ximately. fl l5inchdiametcr moi/inset a. sp d f p roximately 0.0 feet p r minute, said plate being movedoppositely to the direction. of

movement of the engaging bristles; ata linearne of approximately 7.5fee perminu e. imn

m r e' said plate for approximatel 40 seconds in a bath n istingof a saturated aqueous olu tion ofcalcium hydroxide ma taincdat about.

180 F2, and waterscrubbing and drying said plate.

WALTER J. hAUsMAN.

References Cited in the-file .ofothis paten

Claims (1)

1. A PROCESS FOR PRODUCING A LITHOGRAPHIC PLATE WHICH COMPRISES BRUSHING ONE SIDE OF A SHEET OF AT LEAST 99% PURE ALUMINUM WITH A FIRST BRUSH HAVING RELATIVELY COARSE STEEL BRISTLES TO TEAR THE SKIN OF THE SHEET AND TO FORM A COARSE GRAIN, BRUSHING SAID SIDE OF SAID SHEET WITH A STEEL BRUSH HAVING RELATIVELY FINER BRISTLES TO SUBDUE THE COARSE GRAIN FORMED BY SAID FIRST BRUSH, IMMERSING SAID SHEET IN A SATURATED AQUEOUS SOLUTION OF CALCIUM HYDROXIDE MAINTAINED AT A TEMPERATURE BETWEEN 175* F. AND 185* F. FOR A PERIOD OF FROM ABOUT 25 SECOND TO ABOUT 55 SECONDS, AND WATER SCRUBBING AND DRYING SAID PLATE.

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