US2773779A - Treating solution for photolithographic printing plates - Google Patents

Description

United States Patent TREATING SOLUTION FOR PHOTOLITHO- GRAPHIC PRINTING PLATES Frederic E. Brinnick and Charles H. Van Dusen, Jr., Westbrook, Maine, assiguors, by mesne assignments, to Addressograph-Multigraph Corporation, Cleveland, Ohio, a corporation of Delaware No Drawing. Original application April 23, 1951, Serial No. 222,523, now Patent No. 2,692,872, dated October 26, 1954. Divided and this application January 25, 1954, Serial No. 406,075.

2 Claims. (Cl. 106243) This application is a division of my application Serial No. 222,523, filed April 23, 1951, now Patent No. 2,692,872, granted October 26, 1954.

In the practice of photolithography a suitable base such as a grained metal plate or a suitably prepared (e. g. mineral-coated) paper sheet having a hydrophilic surface and bearing a Water-soluble photosensitive coating which becomes waterinsoluble and more or less hydrophobic upon exposure to actinic radiation is imaged by exposure to actinic radiation and is then developed. The development serves to remove or wash ofi the unexposed areas of the photosensitive coating and to leave such areas wet with water and repellent to ink and to leave the exposed areas or image repellent to water and wettable by ink. Exposed photosensitive plates have been developed heretofore generally by one or the other of the following methods depending upon the character of the plate.

(a) The exposed plate may be first coated with developing ink and then scrubbed with water to remove the unexposed areas of the photosensitive coating together with the ink adhering thereto and to leave such areas wet with.

water, the exposed areas With the adhering ink remaining unaifected by the scrubbing treatment. The so-developed plate may then be printed by being contacted successively with a wetting roller, an inking roller and the surface to be printed. In the printing process the inked imaged areas will continue to take ink from the inking roller and to repel water and the wetted unimaged areas will continue to take water from the wetting roller and to repel ink. This is the customary procedure with plates having the conventional photosensitive layer of albumin and ammonium bichromate.

(b) The exposed plate is simply washed with water to remove the unexposed areas of the photosensitive coating and then put into the printing machine where it is contacted successively with a wetting roller, an inking roller and the surface to be printed. In this process the plate may be somewhat slow to take ink on the imaged areas so that good prints will not be produced immediately and possibly not until after the machine has run for a considerable length of time during which a number of 'paratively long shelf-life, so that they can be purchased in sensitized condition by the ultimate user and stored for 2,773,779 Patented Dec. 11, 1956 2, a considerable time before actual use. The length of time plates of this type can be stored without apparent deterioration may vary from a few weeks to more than a year, depending upon the particular diazo compound used as sensitizer.

In some cases, and especially in the case of plates capable of long storage, it happens that the plate after exposure and washing with water may be slow to take ink on the imaged areas.

It appears that when the exposed plate is developed by method (b) the exposed areas become to some extent wet with water and as a result repel ink until the water gradually is replaced by ink.

The method commonly used for the development of the albumin-bichromate plates is not suitable for the development of the diazo plates for the following reason. The albumin-dichromate coating is relatively thick amounting to one pound or more per 1,000 square feet of surface so that the developing ink applied to the exposed plate does not penetrate through the coating to the supporting base and is entirely removed from the unimaged areas by the scrubbing with water leaving the unimaged areas clean. In the diazo plates, on the other hand, the coating is relatively thin amounting to only from one to several ounces per 1,000 square feet. Consequently, if a conventional developing ink is applied to the exposed plate it will penetrate through the coating to the supporting base and will not be cleanly removed from the unexposed areas by scrubbing with water. As aresult both the exposed and the unexposed areas will take ink and give defective prints.

The object of my invention therefore is to provide a method and a solution for the development of plates having diazo photosensitive coatings, which method and solution shall avoid the objectionable features of the prior development methods referred to above and will render the imaged areas of the plate immediately wettable by ink while leaving the unimaged areas clean and receptive to water and consequently repellent to ink.

As diazo compounds suitable for the new process there can be used diazo compounds of a higher molecular weight of the following general formula RYAr-N2-X wherein R means an aryl, aralkyl, a higher alkyl or an aroyl residue, Y means 0, S, NH or NR1, R1 standing for alkyl,

aralkyl or aryl, Ar means an aromatic residue, and X an equivalent of an anion of an acid.

Under the term aroy I understand the acyl radicals of aromatic carboxylic acids, e. g. benzoyl, and the expression equivalent of an anion of an acid is intended to designate radicals such as Cl, SO4/ 2, ZnCl4"/ 2, CeHsSOs, and the like.

The substituent Y and the diazo group N2 may preferably be in a para-position to each other. The aromatic residue Ar, the group R and the NH-group may contain further substituents. In the most cases it is advantageous if the residues R and Ar are substituted by alkoxy, aroxy or N-aryl-sulfamido groups or by one or more halogen atoms. When using a diazo compound of the formula but it is not desirable to have sulfo groups as substituents in any of R, R1 and Ar.

' 3'; Plaza-ecorpundsowhjcbn re.obtainedbyo re tiastha diazo compounds mentioned above with carbonyl compounds such as formaldehyde may be used. Thus higher sadenseddia esc mpe nds r i btai ed whieharet spew ndy-valuable r henew p oc ss,

The; Q-.a ledezo f at h ch an :be; o ine by trea n he. .d a dn p uuds. r i th d y erdiazo compound reaction products with alkali metal sulfites also mavv e sedur h az nompo nds hi h an-nbepbtained; by causing the, diazo compounds in qBQsfionio-react with guanidine, taur-ine orsimilar com:

pounds may be used. The light sensitivityof these con-, densation; products isv usually weaker than :that .of the before-mentioned ;-products1 and the shelf-lifeof plates coated threwith; is correspondingly-longer.

Typical diazo compounds which when applied to paper and exposed. toactinio radiation yield. images which are benefited by treatment according ,to the invention include the ,dia z o. compounds of 4-(N-benzyl-N-ethyl)amino-am; HD5251 41(N -2,6,-.dichlorob.enzyl amino-aniline, '4.-'(NrCyCl.ohexyll-aminq-aniline, 4:arnino.2,5,4'=tribromo-diphenyla1 mine, 4-aminoj2', 4f,6rtrichloro diphenylamine, 41amino- LEN-(2,5-diethoxy-phenyl)-sulfamid0] diphenylaminc, 4eaminor3,6-dirnethoxy-diphenylamine-ZT-carboxylic acid, l-arnino- 2,5 dim-propwry-4'-methyl diphenylsulfide, N-' (2,6 dichloro benzyl) 3 amino carbazol, 4 (N- 2,3,,4,6 tetrachloro benzyD-amino aniline, 4-(N'-2, 6.di-' chloro-vbenzyl, N ethyl)-amino-2,S-diethoxy-aniline and 4- aminoi,5,4-triethoxy-diphenyhether. V

Myinventionis; applicable to any diazo image whic ismot suificientlywater-repellent but is more particularly adapted for use with diazo images derived-from the sul fonates formed by-reacting'an alkali metal 'sulfite, e. g. sodium. sulfite,- with=the :reaction'products of aldehydes such as formaldehyde with diazo compounds of the type defined above, said-sulfonates generally giving plates havinga relatively long shelf-life but yielding images which'tend tobe deficient in Water-repellence.

in order to provide the paper basewith a layer of the light sensitive diazo compounds there can be used solutions or suspensions of the, diazo compounds which are appliedtothe paper surface by coating, spraying, or

a sponge dampened or wet with water, the unexposed areas are easily wiped clean of both the still soluble unexposed diazo-sulfonate sensitizer and any overlying water-repellent powder which may be adhering thereto. It will be noted that during the;cleaning or washing operation the image areas, to which the water-repellent powder particles adhere; are not wet by the. wash water because the water is repelled bythe said water-repellent or watersheddingparticles.v Likewise the image is notrwet by; subsequently applied aqueous lithographic :wet-out ;or dampening solutiom, Consequently when .the' plate; is put on an otfset printing press the image is still dry and in. condition to pick. upink .upon first contact with. the inkingarolls, thus avoiding, loss -of time hitherto. required for ink to. 'displacewater on -untreated imageswhichhave adsorbed water or aqueous lithographic'solution.1

A1ternatively,instead of a water-repellent powder, there may 'be used a non-penetrating, water-repellent, oily liquid, suchas oleic acid, any of various vegetable oils havingviscosities approximating that of. oleic .acid'or liquid silicones havingviscosities at least ashigh-as that of oleic acid. In fact-,oxidized or polymerized turpem tine, ifsufiiciently viscous, can be used successfully.

However, in theuseof. the. latter substance care must be taken that thev oxidation or. polymerization has proi-.

ceeded far .enoughuthat the material will not penetrate throughthe diazo-sulfonate coatingto contaminate the underlying base. To treat the plate with" the hydrophobic liquid aswab wet with oleic acid orsimilar oily material is-wiped over the exposed surface of the plate, whereby theimagednareasare-wetby the saidoily material and consequently are rendered non-water-wettable- When the :surface issubsequently wiped with a sponge-wet with foundthat the oil-treated image immediately picks up by; means. of appliance-rollers or brushes or a pad. A

surplus may be removed by doctor knives, by blowing with air, by flowi-ng or by. centriiuging. The coating solution should have a neutral or weakly acidic reaction.

in practicing my present invention, I provide a suitable a base, such as a coated paper base and preferably a waterimpervious paper base, with a thin photosensitive layer of diazo-compound of the type previously mentioned; I expose the sensitized surface through a transparency to the action of actinic radiation; I treat the exposed surface with non-penetrating, hydrophobic, oleophilic' material and thereby render the exposed or imaged areas waterrepellent; and-I wash the entire surface with aqueous inlctrom; an inking-roll. passed thereover, so that prints can be.--made'therefrom without delay. In place-of the oleic acid mentioned there may be substituted with very similar. results oliveoilycotton-seed oil, rapeseed oil; peanutoil or the like.

It is frequently=found advantageous todissolve an oil soluble dyestulf in' the oleic acid or other oil used according to the invention. The resultingsolution makes the imageon the platemore readily visible before it is inked,

' andprobably likewise makes 'it slightly more water;-

repellent. Such dyestufis are usually'only sparingly soluble-in oleic acidor vegetable oils, and may in; general be added up to the limit of their solubility: Alternatively or iII-COHjllllCtiOll; smallquantitiesof water-insoluble metal- 1 lic soap maybedissolved in the hydrophobic oilymaterial, therebyincreasing the viscosity-and decreasing the penetrating qualities thereof, as well as, increasing to some extent the water-repellenoyof-the'image treated therewith. The useful quantity'of metal soap to be dissolved in the oleic acid or other oil in general falls withinthe range of fronrtll to 5 percentof the weightof solvent. For example,-solutions of 0.25 percent of aluminum oleate, 1.,0

' percent of zinc o1eate-,- and 2.5'percent 'of magnesium orit may be (2) anoilymaterial of at least medium I means'of a soft brush or 21 ,pledgetof cotton. It is found that hydrophobic powder so applied adheres firm ly to the-exposed "or-imaged areas of the plateL, When the sotreated plate is subsequently washed'or wiped with oleate have all given good results. Stearates and palmtates may be used in place of oleate soapsif desired;

Example 1.''In a typical case a-planographic printing plate wasused which comprised a water-impervious paper base -provided by a. suitable water-barrier coating and having on one side a super-calendered "coating ,of casein I Ph uylamiueisee..U. 8.; Pa ent .No.., 2,063.,6 1.),...-, T s plate was exposed through aanegative transparency to y r. v

the action of actinic radiation, whereby the exposed areas of the diazo-sulfonate product were rendered insoluble in Water but did not become unwettable by water. The exposed surface was wiped over with a cotton swab moistened with oleic acid. Next the surface was swabbed with a pad moistened with water which removed from the unexposed areas the still soluble photosensitive material together with any overlying oleic acid. The surface was then wiped over with a swab wet with a standard lithographic starting solution (Platex manufactured by the Addressograph-Multigraph Corporation of Cleveland, Ohio). Thereafter the plate was immediately placed in a rotary offset duplicator where the plate at once satisfactorily picked up ink on the imaged areas, and at once gave satisfactory black prints therefrom.

Similar results are obtainable by substituting the following for the oleic acid of the foregoing example:

a. Powdered aluminum stearate.

b. Powdered Oil Red (color index No. 258).

c. Powdered Hausa Yellow (a lake) suspended in olive oil.

d. General Electric Companys Silicone Oil 9981 LT70NV.

e. Polymerized turpentine.

f. Cottonseed oil.

g. Oil Orange (color index No. 24) dissolved in oleic acid.

h. Oleic acid containing 2% of dissolved magnesium oleate.

Example 2.The supercalendered clay-coated paper base of Example 1 was washed with a 3 percent aqueous solution of the sulfonate formed by reacting sodium sulfite in aqueous solution with the diazo compound of 4-amino-2',4',6-trichloro-diphenylamine. The product was dried at moderate temperature and exposed through a. negative to actinic radiation. The surface was wiped over with a cotton swab moistened with oleic acid. Then the surface was swabbed with a pad moistened with water, which removed from the unexposed areas the still soluble photosensitive material together with any overlying oleic acid. The surface was then wiped over with a swab wet with a standard lithographic starting solution (Platex) and the plate was placed in a rotary ofiset duplicator where the imaged areas at once satisfactorily picked up ink, while the background remained satisfactorily clean.

Example 3.-A supercalendered clay-coated paper similar to that used in Example 1 was coated with about 3 02. dry weight, per thousand square feet, of the guanidide of the diaxo compound of 4-(N-2,6-dichloro-benzyl) -aminoaniline deposited from aqueous medium. The sheet was dried at moderate temperature and exposed through a negative to radiation from an arc-lamp. The surface was then wiped with a swab moistened with oleic acid, and was then washed with water. The resulting plate was then wet with a standard lithographic starting solution (Platex) and run in a rotary ofiset duplicator where the imaged areas immediately took up ink satisfactorily while the unimaged areas remained satisfactorily clean.

We claim:

1. A liquid desensitizer solution for planographic printing plates composed of oleic acid having dissolved therein from 0.1 percent to 5 percent of a water-insoluble soap selected from the group consisting of aluminum, zinc, calcium and magnesium salts of oleic, stearic and plamitic acids.

2. A liquid desensitizer solution for planographic printing plates composed of oleic acid having dissolved therein about 2.5 percent of magnesium oleate.

References Cited in the file of this patent UNITED STATES PATENTS 430,274 Edison June 17, 1890 437,780 Higgin Oct. 7, 1890 2,342,713 Wescott Feb. 29, 1944 2,409,950 Meyer Oct. 22, 1946 2,420,127 Doelling May 6, 1947 2,525,984 Weston Oct. 17, 1950 2,692,827 Brinnick Oct. 26, 1954

Claims (1)

1. A LIQUID DESENSITIZER SOLUTION FOR PLANOGRAPHIC PRINTING PLATES COMPOSED OF OLEIC ACID HAVING DISSOLVED THEREIN FROM 0.1 PERCENT TO 5 PERCENT OF A WATER-INSOLUBLE SOAP SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, ZINC, CALCIUM AND MAGNESIUM SALTS OF OLEIC, STEARIC AND PLAMITIC ACIDS.