US2772972A - Positive diazotype printing plates - Google Patents

Description

Dec. 4, 1956 c. E. HERRlcK, JR., ETAL 2,772,972

POSITIVE DIAZOTYPE PRINTING PLATES Filed Aug. 2o, 1954 INVENToRs cL/FFon f. HE/ze/c/gJ/e.

ATTO EYS United States Patent" POSITIVE DIAZOTYPE PRINTING PLATES Clifford E. Herrick, Jr., Chenango Forks, Peter T.

Application August 20, 1954, Serial No. 451,271

20 Claims. (Cl. 96-33) The present invention relates to a pre-sensitized, positive-Working, offset printing plate derived from a plate having a hydrophobic resinous layer sensitized with,.a diazonium compound, said resinous layer being capable of being rendered hydrophilic, after exposure of the plate, at the light-struck portions of the same, and to the preparation and processing of .such a plate.

A vast amount of duplication. and reproduction is required in modern .business and industrial practice. .In those applications which require the production of fewer than 30 copies from a single original, the dia'zotype process is ideal. This process, as is understood, involves the sensitizationV of a base with a light-sensitive diazonium compound, the exposure of the sensitive element under a pattern, and the treatment of the element with a base in the presence of a coupling component to produce an azo dye in those portions where the sensitized element has not been struck by light. 'To a large degree, the great popularity of this system can be ascribed to the varietyof originals capable of duplication without special preparations.k Thus, any printed, drawn or written material on a from-translucent-to-transparent base serves as a master for the diazotype process.

An increasing number.. of business systems and methods which require, Vthe productionof several kcopies from a single original are being built around the diazotype process.

The common denominator of these diazotype systems is the so-called translucent paper original'which serves as the photoprinting master for the production ofadditional copies. Since these masters diter from ordinary printed,

typed, or written originals only in the higher translucency.

of the paper base stock, itV is clear that, in addition to being highly economical to prepare, they are unexcelled in their over-all versatility `and convenience with special reference to ease of-adding, deleting, or changing information on the master. ing on paper of lrelatively high opacity is successfully reproducedby diazotype since the contrast of the diazo process is` so high. p

Reproduction based on the photocopying of translucent originals by the diazotype process has thus proved to be` a most convenient and economical solution to duplicating problems, provided the number of copies required is not too great. However, in a considerable proportion of the originals encountered, more than 30 copies are required and the reproduction processes requiring the production .of a special master, in spite of their many disadvantages, become attractive because they are capable of producing copies at much greater speeds than with diazotype, once theV special master Ahas been prepared.

The offset printing method is especially interesting since the copies prepared using the offset press possess several advantages over competitive processes. Thus, the image produced by the offset press is composed of a permanent carbon pigment, while. the image in a diazotype or spirit reproduction is composed of dye which in time may fade. `In. a diazotype print, the non-image areas contain photodecomposition `products which are prone -As a matter of fact, matterr appear-` to cause a yellow discoloration, especially if the print be exposed to strong light. In addition, stability against premature color formation in diazotype papers is brought about through the use of a heavy load of ac id in the sensitive layer and some loss of strength of the paper may occur on aging. Finally, the quality of the` printing produced by thevoifset press is outstanding. On the other hand, the use of the offset press has heretofore involved either the manual recopying of an original onto asocalled direct image master plate or the use of expensive, light-sensitive masterplates either negative-working or positive-working. In the type of duplicating application in which the diazotype process has proved so useful, the preparation of master plates usinga negative-working, photosensitive offset plate involves several time-consuming operations and expensive photographic equipment* so-called legitimate graphic arts eld, where the requirements of exceptionally high printingnquality, absolute dimensional stability and long runs justify the use c-f a.

necessarily expensive metal base offset plate. However, the relatively low photographic contrast of these plates andthe consequent critical nature of the exposure `step make it ditiicult to obtain acceptable copy from the average translucent original of the type discussed above. Due basically to their inadequate contrast and their highcost, these metal based plates `have failed to till the need for a low-cost, positive-Working, offset plate with working properties suited to the needs of the duplicating field.

It is thus manifest that an uniilled need of great magnitude exists for an inexpensive, pre-sensitized, positiveworking, otset plate with working properties tailored to the conditions encountered in duplicating Work. Such a plate, which would involve a relatively inexpensive base capable of sensitization with available diazos and amenable to processing with conventional chemicals, could greatly expand to the `area of usefulness of the diazotype process and make possible the creation of new systems and applications based on the translucent paper master. The creation of such a plate, however, presents manifold diculties, particularly in the selection of a substraturn which permits adequate sensitization withvlight-sensitive diazos and with respect to a simple and differential processing leading to the necessary grease and water-receptive areas requisite for printing.

It is proposed in the application of C. E. Herrick et al., Serial` No. 265,046, filed January 4, 1952,` to produce resinous layers having a predeterminate degree or' water sensitivity. According to this method, a suitable substrate, for instancepaper, is lacquered with a mixture comprising a resinous co-polymer of about one mol of a vinyl compound with about one mol of an ethenoid dicarboxylic. acid compound and a hydrophobic resin cornpatible with said co-polymer. As lacquered, these materials are `hydrophobic and areunreceptive to water or water miscible substances. Hydrophilic character may be imparted by treating the, coated surface with an alkali such .as sodium orammoniurn hydroxide and the like.

It has been determined that certain combinations within the broad ambit of the aforesaid application, no-

tably those in which the constituent capable of becoming hydrophilic is derived from a vinyl-ether-maleic anhydride co-polymer, are Well lsuited for use as lithographie surfaces. For example, a mixture of about 60 parts by weight of such a co-polymer and about 40% by weight of a low viscosity cellulose acetate is lacquered onto paper and then rendered hydrophilic with a 5% aqueous solution of ethanolamine. An excess of such aqueous solution is advantageously applied and after a suitable imbition time, amounting to several seconds, is removed with an air knife. Such a layer may be sensitized with a water-so-luble, negative-Working sensitizer such as is described in German patent application Kl67,l30, referred to in PB 1308, page 48, and satisfactory negativeworking plates thus obtained.

The process of making light-sensitive printing plates in this fashion, however, requires three manufacturing steps, namely, lacquering, producing water sensitivity through use of a base, and finally sensitizing. In the interests of economy, it is essential that the number of operations be materially reduced. It appeared to us that a step in this direction would be achieved were it possible to omit the ethanolamine treatment as above, sensitize the surface in its hydrophobic stage and induce the hydrophilic character after the exposure and as a part of the procedure usual in readying the plate for printing on an offset press.

Following this line of thought, attempts were made to sensitize, in the hydrophobic state, a layer consisting of a co-polvmer of vinyl methyl ether and maleic anhydride (hereinafter sometimes referred to as PVM/MA) or a laver as described in the aforesaid application, Serial No. 265,046 and containing PVM/MA and a hydrophobic resin, While using an aqueous sensitizing solution. The procedure failed for the reason that aqueous solutions are antipathetic to and, hence, fail to wet the hydrophobic surface and no sensitizer can be laid down. However, we determined that if one employs a positiveworking. water-insoluble. solvent-soluble sensitizer. notablv those of the diazo oxide class disclosed, for instance, in Example 7, French Patent 904,255, sensitization occurred readily when using organic solvents as a vehicle with the diazo compound. This is attributable to the abilitv of these solvents to swell or dissolve the resinous underlaver containing PVM/MA so that a good load of sensitizer can be deposited. Unfortunately, this procedure creates other ditiiculties for the reason that if a poor solvent for the underlaver be employed so that a high surface load is obtained, the adhesion of the sensitizer for the underlayer ranges from mediocre to poor. depending upon the sensitizer employed. On the other hand, if a penetrating solvent such as acetone be used so that the sensitizer is deposited within theV underlaver. water development. as described in Example 7 of the aforesaid French patent. cannot be practiced. This is due to the inabilitv of the water to remove the photodecomposition products and` as a consequence. if the resulting plate be then treated to impart hydrophilic character. it is found that the exposed regions are more inkreceptive than normal due to the presence of unremoved photodecomposition products while, at the same time. the unexposed regions are not sufficiently ink-receptive.

Further research demonstrated that a remarkable improvement in the image adhesion obtained when nonpenetrating solvents are used is brought about by including a water-insoluble, solvent-soluble, alkali-resistant adhesive resin in the sensitizing formulation as, for instance, a low molecular weight vinyl polymer, i. e., polyvinyl acetate. Thus, we discovered that a strongly adherent surface coating is 'obtained by sensitizing the hydrophobic surface while using, for example, methyl isobutyl ketone as a solvent, low viscosity, completely acetylated polyvinyl acetate as an adhesive resin and 2-diazo-1-naphthol- S-ethylsulfonate as the sensitizer. ['his discovery, while of great merit, failed to provide the desired solution, however, for the reason that the exposed regions of such a layer can no longer be developed withwater; that is to say, the exposed regions repel water and cannot be removed.

Finally, however, it was ascertained that the sensitizing layer in the exposed regions of such a plate can be removed completely and easily by treating the entire surface of the plate with a solution comprising an aliphatic polyhydroxy compound. The unexposed parts of the sensitizing layer resist the action of such processing reagent and remain behind. Once the photo product is removed, hydrophilic character can be introduced into the layer comprising PVM/ MA by the careful use of one of the methods described in the aforesaid patent application. However, great advantages accrue if hydrophilic character be imparted to the PVM/MA layer by treatment with an amine, preferably an alkylolamine. Thus, by careful correlation of the various observations made, as detailed above, we were able to produce a relatively inexpensive plate which is readily amenable to processing and which is capable of producing a large number of copies in the greatest fidelity.

Our invention, therefore, envisages an article capable of conversion to a positive-working, oiset printing plate comprising an inexpensive base vmaterial bearing a hydrophobic lacquer layer comprising essentially PVM/MA, said lacquer layer being coated with a water-insoluble, solvent-soluble, alkali-resistant adhesive resin and a lightsensitive diazo oxide and the processing of such article to a printing plate by exposure under a pattern, the removal of the outer layer where exposed by an aliphatic polyhydroxy compound and the imparting of hydrophilic character to the lacquer layer by use of an alkylolamine at those points where the outer layer has been removed. Such article, the preparation of the same, the processing thereof to form a positive offset printing plate and such plate constitute the purposes and objects of the present invention.

The present invention will be better understood by reference to the accompanying drawing, Figure I of which is a sectional view of the plate before processing and Figure II of which is a similar view of the offset plate subsequent to processing.

Referring to the drawings and particularly to Figure I thereof, it will be seen that the raw plate comprises a base 1 bearing a lacquer substratum 2 having an outer coating 3 of an adhesive resin and a light-sensitive diazo compound.

The base 1 of such a plate is made of a relativelyinexpensive fibrous material, such as paper, cloth or the like. Preferably we employV a base such as is described in U. S. P. 2,534,588 granted December 19, 1950, `or a wet strength clay-casein surfaced paper. It will be apparent, however, that the specific nature of this base material is not a critical feature of the invention since any relatively inexpensive fibrous material capable of accepting and retaining the lacquer layer 2 is suitable.

The lacquer layer 2 contains as its essential element a l.zo-polymer of vinyl methyl ether and maleic anhydride (PVM/MA) in substantially equi-molar proportions. Such co-polymers are described in U. S. P. 2,047,398 granted July 14, 1936 and are available on the open market.

We find that while satisfactory plates can be produced where the layer 2 consists of PVM/MA, best results are achieved when said layer 2 is composed of a solid solution of PVM/MA and a hydrophobic resin compatible therewith. The hydrophobic resin serves the functions of imparting toughness and exibilityto the plate and of eliminating tendencies of the layer 2 to crack or craze. Where a hydrophobic resin is utilized, it may be present in the lacquer layer 2 in a quantity as high as 60% of the lacquer layer. For best results, however, the quantity of the hydrophobic resin should not exceed 40% by weight of the solid contents of the lacquer layer 2.

Where a hydrophobic resin is used in the lacquer layer, the llacquer layer exists as a solid solution of PVM/MA and said hydrophobic resin,fwhi'ch1.is compatiblewwithlthe PVM/MA. Compatability of the resins is,-`of course, a. Acondition precedent `to Ithe :obtainingof a true `solicl solution and not a heterogeneous mixture of the resins. It is manifest that the latter` would offer a variable surface to the processing solutionspthusleading to nonuniformity in the creation of; hydrophilic character in said layer.

Hydrophobic resins compatible with thei-co-polymer includewthe various vcellulose esters-such as cellulose acetate, cellulose propionate, `cellulose butyrate, the mixed esters such as celluloseacetatepropionate, celluloseacetatebutyrate and thel like,.polyvinyl resins such` as polyvinylacetate, polyvinylacetals' such as polyvinylbutyral, methylacrylate, methylmethacrylate and the like. Within the series of commercially available cellulose esters, grades which contain combined acetic acid from as low as 52% to as high as 61.8%k (triacetate) can be employed. If a cellulose esteri bebused,` it is recommended that it be of lhigh acyl content. --We have good reason to believe that since-'the maleic anhydride copolymers are reactive materials, they can, in the course of time, react with the unesteried hydroxyls of a low acyl ester. The result of such a reaction is usually a change in the degree-to which the layer can be rendered hydrophilic. Thus, a freshlyl lacquered sample containing a low acyl cellulose ester `may respond dilerently to the processing solution than a sample some weeks old. In' any case, irrespective of the-mechanism, we have found that greater uniformity and-consistency -of response are attained when cellulose esters of the highestdegree of acylation are utilized. It should be further pointed out that when a high acyl cellulose ester is used, a relatively higher proportion-offoo-polymer'is required for optimum results than when a low acyl cellulose ester is employed. i

It is clear that the hydrophobic resins, the use of which we contemplate, are all commercial materials, the solubility properties -of which are known. vThe same is true of PVM/ MA. It is, therefore, a very simple matter to determine the suitability of any-hydrophobic resinfor use with PVM/MA in forming thelacquer layer 2.

Various solvents and solvent-mixtures may be utilized for laying'down the lacquer coating and,'in this connection, attention is directed to the solvents described in the aforesaid application, Serial No. 265,046. Solvents which we have Ifound to be suitable are liquid relatively low boiling organic solvents such as methyl cellosolve, acetone, methylene chloride,dioxane,` tetrahydrofurane, cyclohexanone, methylethylketone-and various mixtures of the same. Such mixtures include, for example, methylene chloride, methylcellosolve -and acetone, rnethylcellosolve and dioxane, methylcellosolve and cyclohexanone, methylcellosolve and tetrahydrofurane and the like.

These solvents, because of their relatively low boi-ling point, are readily removed'toyield a dry lacquer ilm. This filmfgenerally has a thickness ranging from about .l -to .4 mil, preferably .2 mil.

The outer layer 3 contains as tthe sensitizing component a diazo oxide which is water insoluble but which is soluble to the extent of at least 1% in a solvent which is a liquid and is an aliphatic-ester, an aliphatic ketone or an aliphatic alcohol, i. e., alcohols in which the -OH group is aliphatically linked. Examples of such solvents are ethylacetate, butylacetate, amylacetate and-the like, acetone, diethylketone, methylpropylketone, lmethylisobutylketone, dipropylketone, methylethylketone, methylbutylketone andthe like, ethyl alcohol, isopropyl alcohol, butyl alcoliol,=diacetone alcoholfbenzyl alcohol-and the like. Many diazo-oxides of extremely highmolecular weight and complex structure areof such4 a mixed', polarnon-polar characterthat Vthey are `only soluble -in such powerful solvents as dimethylformamide, dimethylacetamide,dioxane or methyl cellosolve. Such solvents would penetrate and dissolvethe lacquenlayer 2. Consequently, isuch'diazo oxides `which are onlysoluble in thesefpowerful solvents are unsuitablefor use in the sensitization of the plate. On the other hand, any diazoV oxide which is soluble tothe extent indicated in any of the above simple solvents may be employed.

Diazo oxides within the broad'class which we have found to be particularly suitable are those derivedby esterication or amidation of Z-diazo-l-naphthol-S-sulfonyl chlorides or Z-naphthol-l-diazo-S-sulfonyl chlorides with comparatively simple amines or alcoholsV or `with more complex compounds which possess a saturated, unconjugated, non-polar molecule such as rosin amines, rosin alcohols andtheir derivatives.

The above diazo oxides may be formulisticallyrepresented as follows:

SO2R

and

SIOrR wherein R1 isV alkoxy, i. e., methoxy, ethoxy, propoxy, aryloxy such as phenoxy, naphthoxy and the like, ammo such as primary amino, alkyl amino, i. e., methylamino,

dimethylamino, ethylamino, diethylamino, propylamino, dipropylarnino, butylamino, dibutylamino, arylamino such as phenylamino, naphthylamino and the like, aralkylaminosuch as benzylamino, dehydroabietylamino, didehydroabietylamino and the like, carbalkoxyalkyl amino such -as carbmethoxymethylamino, carbethoxymethylamino, Vcarbethoxyethylamino and the like. Speciiic examples of such diazo oxides embraced by these formulae are:

The aforementioned diazo oxides, excepting for those containing the rosin amine structure, are known compounds and are prepared `by a simple esterication or amidation of the sulfonyl chloride in the presence of an acid binding yagent such as pyridine. The rosin derivatives, on the other hand, are prepared according to the method described .in the application of Ralph G.` D.

Moore, entitled Rosin Derivatives of Diazonaptholsulfonamides and Diazophenolsulfonamides, Serial No. 451,294, led August 20, 1954.

It has been previously noted that we cannot employ complex high molecular weight diazo oxides which can only be dissolved in powerful solvents which would penetrate and `dissolve the lacquer layer 2. Since such penetration would destroy the plate, it is essential in coating the diazo oxide to not only eliminate the aforesaid high molecular weight diazo oxides but also to select a solvent which will dissolve the diazo oxide in an amount of at least 1% and which will not penetrate and dissolve the lacquer layer 2. To this end, we may employ (l) any liquid aliphatic ester; (2) any liquid aliphatic ketone boiling above 100 C.; and (3) any liquid aliphatic or araliphatic alcohol containing at least four carbon atoms. This would exclude from the solvents previously listed such entities as acetone, ethyl alcohol and isopropyl alcohol. The remaining listed solvents meet the above prerequisites and, hence, are illustrative of those which we have employed.

A word of caution is deemed necessary to avoid any confusion between the purpose of the two groups of solvents mentioned in connection with the diazo oxides. The broader class embracing the liquid aliphatic esters, ketones and alcohols offers a criterion of the suitability of a diazo oxide for our purposes. Thus, any diazo oxide which dissolves to the extent of at least 1% in any solvent in these classes will have the requisite structure for our use. However, certain of such solvents, notably acetone, if used to lay down the diazo oxide would penetrate the lacquer layer 2. Consequently, in coating the diazo oxide, a solvent in the more restricted class must be selected.

The light-sensitive diazo oxide as noted is laid down with an alkali-resistant adhesive resin in order to ensure adequate adhesion of the image to the lacquer layer 2. As such resin there may be employed any water-insoluble, alkali-resistant resinous material which is soluble in any of the aforementioned limited classes of solvents for the diazo oxide, at least to an extent of 1% by weight. In addition, the resin must be resistant to or impervious to the action of aliphatic polyhydroxy compounds and alkylolamines which are utilized in the processing Vof the raw plate to the nshed offset printing plate. The resin should thus withstand a contact time of one-half minute or longer with such reagents and resist removal from the lacquer layer 2 during such period of contact in the absence of the photodecomposition products. It is advantageous but not essential that the resin be of low or moderate molecular weight since such resins have improved adhesive character and are more readily removed in the presence of the photodecomposition products.

Many resins available on the open market manifectly fit these requirements and, in this connection, reference is made to polyvinyl resins such as phenol modied coumarone-indene resins, polyvinyl acetate, polymethylacrylate, polymethylmethacrylate, cellulose derivatives such as ethyl cellulose, cellulose acetate, cellulose propionate, mixed esters and the like. Here, again, it is a very simple test, the solvents being identified, to determine a suitable resin having adhesive characteristics which may be utilized for application with the light-sensitive diazo compound.

Figure II of the drawing indicates the condition of the article of Figure l after processing thereof. lt will be observed from Figure II that the outer coating 3 has been locally removed at those areas 4 which were lightstruck. In these areas, the processing solvents have penetrated the lacquer substratum 2, as indicated by reference numeral 5, imparting hydrophilic character thereto, making such areas water attractive. The printing areas 6 of layer 3 which have not been removed or atfected by the processing solutions remain hydrophobic and greasereceptive. By application of a printing ink, the, plates in the condition shown in Figure II are ready for use on an offset press:

The processing of the article of Figure 1 to produce the product of Figure II is brought about by exposure of the plate under a pattern which permits light to pass where the patternV is transparent or translucent and which blocks the passage of light where the pattern is opaque. Where the light strikes the plate, decomposition of the diazo oxide ensues.

It has been ascertained, and this is one of the key points of our invention, that the photodecomposition products of the `diazo oxide are soluble or swellable in liquid aliphatic polyhydroxy compounds, thus permitting the selective removal of the photodecomposition products and thc adhesive resin commingled therewith from the lacquer layer 2.

The phenomenon permitting the achievement of this result has been studied and it is believed to be attributable to the following circumstances.

It hasV been conclusively demonstrated that the action of actinic light on compounds containing the grouping causes the loss of nitrogen accompanied by a rearrangement to form a ketene intermediate. It is well known that ketenes may react with compounds containing an active hydrogen. `In the case of hydroxyl-containing compounds, esters are formed. It is our considered opinion that the liquid polyhydroxy compounds react with the diazo oxide photodecompositon product to form an ester derivative of the polyhydroxy reagent, only a portion of the hydroxyls being so converted. The resulting compound bears sufcient resemblance to the polyhydroxy solvent to promote a tendency toward mutual solubility. The generality of the solubility behavior is thus explicable.

It is to be recognized that this is a theory of operation which is offered in explanation of the changes which ensue in the removal of the photodecomposition products and the adhesive resin. Despite the accuracy of this theory, it is a fact that the diazo photodecomposition products play a crucial role in creating permeability to the various polyhydroxy compounds and this factor will be subsequently elaborated upon.

The polyhydroxy compound utilized for removal of the decomposition products and the adhesive resin is any liquid aliphatic polyhydroxy compound such as the various alkyl glycols, i. e., ethylene glycol, propylene glycol, diethylene glycol, l-3-butylene glycol, 2-3-butyleneglycol, dipropylene glycol, hexylene glycol, trihydric alcohols such as glycerin and the like. Such polyhydroxy compounds may be used alone or in admixture and as suitable mixtures we have used ethylene glycol with glycerin, hexylene glycol with glycerin, 2,3-butylene glycol with glycerin, propylene glycol with ethylene glycol and the like. It has been our finding that the solubility or swellability of the diazo oxide photodecomposition products in liquid aliphatic polyhydroxy compounds is a general phenomenon and, hence, any such solvent is suitable for use.

Once the photodecomposition products and resin have been removed from the lacquer layer 2, there remains the feature of rendering the lacquer layer hydrophilic at those areas Where the photodecomposition product has been removed. We find that this result is very advantageously effected 'by the utilization of an alkylolamine soluble in the aforesaid aliphatic polyhydroxy compounds which, when primary or secondary, we have good reason to believe operates to yconvert the PVM/MA in the lacquer layer, at least in part, to an amide. It is to be emphasized that the alkylolamine should be applied as such or in a solution of an aliphatic polyhydroxy compound. Thus, it has been found that if an. aqueous solution Ofaaalkylolamine ,beusedrininparting hydrophilic character to thelacquerflayer;great welts appear on the surface ydue toexcessivewswelling. Damage to the surfaceoccurs because of the tender nature of the water-swollen surface, damage to the image is occasioned, and toning on start-up is almost impossible to eliminate. The ability of a casually spread `solution of an alkylolaminevin-the substantial absence of water to bring about a hydrophilic character which isuniform not only in directions parallel to thersurface but which also appears to be uniform and limited in depth is remarkable. In passing, it might also .be noted that by using substantially non-aqueous solutions vofthe'alkylolamines, it is possible to employ a much higherproportion of PVM/ MA in the lacquer layer` Zthan is possible in the procedure outlined in the aforementioned application, Serial No. 265,046.

We may use asthe alkylolamine any. aliphatic a'lkylol-` amine Which is soluble in the aforementioned polyhydroxy compounds, preferably .one.having a reactive fhydrogen atom attached tothe amino nitrogen, such as ethanolamine, diethanolamine, propanolamine, di-isopropanol amine, butanolamine, ethanolisopropanolamine, ethanolisobutanolamine and the like. Tertiary alkylolamines, such as triethanolarnine,- may Ibe employed but are less effective, which prompted the conclusion previouslyV expressed that the induction of hydrophilic character in the lacquer layer 2 when using a non-tertiary alkylolamine is the result of at least apartial amidation of the carboxy groups in the PVM/ MA.

It has beenindicated above that the removal of the decomposition products from layer 3 and the-induction of hydrophilic character in layer 2 are sequential operations. We have found, however, that both operations may be effected simultaneously by lreplacing a part of the polyhydroxy compound by a substantially equivalent amount of the selected alkylolamine. Since the alkylolamine combines the functions of an alcohol with that of an amine, its presence in the polyhydroxy compound serves to compensate for the quantity of the polyhydroxy compound it replaces. The combination of the two solvents for effecting these two functions manifestly permits a simplification of the processing procedure.

When the plate has been processed to the stage indicated in Figure II, it is recommended that before starting the press rapid pickup bythe image be promoted by treating the plate with an acidic -solutionof lthe type used commercially which generally contains a desensitizing gum such as gum arabic or cellulose gum,` a buffer designed to give a pH of 3 to 4 and, if desired, an alkali metal dichromate. Such solutions are marketed, for instance, by the -Addressograph Multigraph Company, Cleveland, Ohio under the trademark Platex The use of a solution of this type is not a necessity butits `em-` ployment facilitatesthe operation of the plate and, hence,y

its use is preferred.

A further important factor of our invention involves the use of our offset plate for reproduction of half-tone originals or the preparation of prints by projecting anY enlarged or reduced image onto the light-,sensitive sur` face. .The superior results in these applications can be secured by applying to the iibrous base an antihalation coating of a dyestuif of the typeused in the manufacture Example` I The diazo `oxide of; ExampleJ, French Patent No.

-10 904,255, is dissolved to `form a coating solution having the following composition:

2.0 grams of 2-diazo-1-naphthol-S-sulfuric acid ethyl ester 2.0 grams of phenol modified coumarone-indene resin sold as Nevillac Soft by the Neville Co., Pittsburgh 25, Pa., and OO mls. of methyl isobutyl ketone This solution is coated by dip beading onto the lacquered surface of a wet strength clay-resin surfaced paper which had been coated and dried to yield adry lm thickness of about 0.3 with a lacquer of the following composition:

1.2 grams of polyvinylmethyl ether-maleic anhydride copolymer speciic viscosity in methyl ethyl ketone:

1.8-2.5) 0.3 gram of high acetyl, high viscosity cellulose acetate (61.8% combined-acetic acid) 20 mls. of methylene chloride 5 mls. of methyl Cellosolve and 75 mls. of acetone Following exposure beneath a positive translucent carbon-backed paper original at about speed 10 ona white print machine sold by General Aniline & Film Corporation, Johnson City, New York, under the trademark Ozamatic, the plate is attached to the plate cylinder of an offset duplicator and then swabbed for a few seconds with a pad moistened with the following solu tion:

77 mls. of ethylene glycol 23mls; of glycerin The sensitizing layer is thus rapidly removedV in the regions of the plate which were unprotected during the exposure by opaque portions of the original. The cornpleteness of this removal can be conveniently followed by the presence of color on the exposed surface since the exposed sensitizing layer is brownish in hue.

Hydrophilic character is imparted to the resin underlayer by next swabbing the surface of the plate with a solution containing l0 parts of diethanolamine and 90 parts of, glycerin.

Before starting the press, the plate is treated with an acidic Platex solution to facilitate ink pickup by the image.

This example serves to stress several important featuresof our invention, to wit:

l. Diazo oxides of high molecular weight are not essential. This is contrary to the notion presently advanced that for printing plates it is essential that there be employed diazo oxides ofexcessively high molecular weight.

2. Resins resistant to or stable to alkalies are employed in the sensitized layer.

'3. lt is unnecessary to employ aqueous alkaline solutions `for removal of the light-struck sensitized layer.

In these fundamental respects, the plate Vconstructed by us shows a distinct improvement over plates previously known or described.

' Example 1I The procedure is the same asin Example I excepting that the plate after exposure is treated with the following solution:

l0 partis of diethanolamine 67parts of ethylene glycol and 23 parts of glycerin With this solution the removalV of the photodecompositionV products and the imparting of hydrophilic character to the lacquer layer 2 are combined in one operation. The results obtained with this plate are the same as thosewith -,Example I.

. Example IIIY p The procedure is the same as in Example I excepting that coumarone-indene resin is replaced by an equalV weight of a low viscosity polyvinyl acetate such as that sold by Carbide and Carbon Chemicals Corporation under the trademark "Vinylite AYAC. The plate ob tained has characteristics simulating those of Examples I and II.

Example IV and thoroughly dried.

After exposing beneath a positive original, the photoproduct and resin in the exposed areas were removed by swabbing the plate with a solution of l5 parts of isopropanol and 85 parts of ethylene glycol. The nonimage areas were then rendered hydrophilic by treating the plate with a solution of l5 parts of diethanolamine and 85 parts of ethylene glycol. The plate was then treated with the conventional acidic press solution and printing was started. In excess of 500 excellent copies were obtained.

In place of using the ethylene glycol-isopropanol mixture used above, the photoproduct and resin were removed in the non-image areas by any of the following solutions:

The procedure is the same as in Example IV excepting that the plate directly after exposure was treated with a solution containing l5 parts of diethanolamine and 85 parts of ethylene glycol, the plate thereby being rendered ready for printing.

Example VI The procedure is the same as in .Example IV except-' ing that the plate directly after exposure was treated with a soution containing 2 parts of monoethanol amine and 98 parts of ethylene glycol. The plate so processed yielded over 590 copies of excellent fidelity.

Example VII A paper base was lacquered and sensitized as in Example lV except that the polyvinyl acetate in the sensitizing solution was replaced by an equal amount of a methyl acrylate polymer (marketed by Rohm and Hass Company, Philadelphia, Pa., under the trademark Acryloid C-l0). After exposure beneath a positive original, the plate was treated with ethylene glycol, the photoproduct and resin thereby being removed in the nonimage areas. To render the non-image areas hydrophilic and ready the plate forrprinting, a solution containing 85 parts of ethylene glycol and 15 parts of diethanolamine was applied. When put on the os'et press, ovel 500 excellent positive copies were obtained.

ln place of ethylene glycol, any of the following solutions may be used to remove photoproduct and resin from the non-image areas:

l. parts of hexylene glycol and 70 parts of glycerin 2. Propylene glycol 3. Diethylene glycol 4. 70 parts of dipropylene glycol and 30 parts of glycerin 12 5. 1,3-butylene glycol. 6. 2,3-buty1ene glycol Example VIII Av paper base was lacquered as `in Example I. The dried, lacquered base was then sensitized by bead-coating with a solution of the following composition:

The dried, sensitized plate was then exposed beneath a positive original, andtreated with a solution composed of parts of ethylene glycol and l5 parts of diacetone alcohol. A positive yellow image upon a white background was obtained(v The plate was then rendered hydrophilic in the non-image areas by treatment with a solution of l5 parts of diethanolamine in 85 parts of ethylene glycol. Theplate was now inked.v Over 500 excellent positive copies were obtained.

In place of the ethylene glycol-diacetone alcohol mixture used above, the photoproduct and resin were revmoved in the non-image vareas with any of the following solutions:

. 50 partsof hexylene glycol and 50 parts of glycerin Propylene glycol Diethylene glycol 70 parts of dipropylene glycol and 30 parts of glycerin 1,3-butylene glycol 2,3-butylene glycol Example IX The procedure is the same as in Example VIII excepting that the plate directly after exposure was readied for printing by treatment with a solution composed of 72 parts of ethylene glycol, 13 parts of diethanolamine and l5 parts of diacetone alcohol. Over 500 excellent copies were obtained. v

Example A paper base was lacquered as in Example I. The dried, lacquered base was then sensitized by bead-coating with a solution containing:

parts of methyl ethyl ketone f l part of cellulose acetate (S50-56.0% combined acetic acid) and l part N-dehydroabietyl Example XI The procedure was the same as in Example X excepting that the plate after exposure was directly readied for printing by treatment withV a solution containing:

l5 parts of diethanolamine and 85 parts of Vdiethylene glycol This plate gave results on a par with those previously described.

Example XII A lacquered paper base prepared as in Example l '1113 was sensitized, by .bead-coating with a solution .of the following composition:

10() parts of. methyl isobutyl ketone 4l parts ofpolyvinyl acetate andy 2 parts of the diazo compound having the structure:

| SOzNH The. thoroughly dried plate was exposed beneath a positive original, and then treated with -a solution of 75 parts of ethylene glycol and 25 parts of glycerin. The plate, from which the photoproduct and resin in the non-image areas had thus been Aremoved was then rendered hydrophilic in theA non-image areas-by treatment with a solution of 60 parts of ethylene glycol, 20 parts of glycerin and 20 parts of diethanolamine. The plate was now ready for printing.

It was found that the plate could equally well be readied for printing by treating the exposed plate only with a solution of 60 parts of ethylene glycol, 20 parts of glycerin and 2G parts of diethanolamine. Several hundred copies '(in excess of 500) of excellent quality were obtained.

Example XIII A lacquered paper prepared as in Example I was beadcoated with -a solution having the following composition:

2 parts of polyvinyl acetate lOO parts of methyl isobutyl ketone 2 parts N,Ndidehydroabietyl-N,Nethylene diazo-S (6) -oxo-1naphthalenesulfonamidel `The thoroughly dried` platewas exposed beneath a posiitve original and then treated with a solution of 81 partsof ethylene glycol, 9 parts of hexylene glycol and 10fparts of diethanolamine. The photoproduct and resin were thus removed from the non-image areas, leaving a yellow image on a'white background, and the non-image areas werefound to be hydrophilic. The plate was now ready for printing, and after a brief treatment with Platex, in excess of -500 excellent copies were obtained.

Example XIV The clay-casein surface layer of the paper base as described in Example I was provided withgan antihalation coating by impregnating it with a solution containing 4 parts of Fast Light Red BA, 2 parts of Diazo Fast Yellow in 100 parts of water. After drying, the pinkorange surface was lacquer-coated and sensitized as in Example IV.

The sensitized plate was exposed to a 35-ampere carbon arc at a, distance of 3 feet for 45 seconds beneath a screened film positive (133 lines per inch). The exposed plate was treated with a solution containing S parts of ethylene glycol and 15 parts of diethanolamine, then treated with Platex, and copies run on the offset l dried,lacquered base was then sensitized by bead-coating with the following solution:

2 parts of polyvinyl acetate parts of methyl isobutyl ketone and 2'partslof the diazo compound havingtl'ieV structurer The dried plate was then exposed beneath a `positive original. The exposed plate was, swabbed with a solution containing:

42.5 parts of ethylene glycol 42.5 parts of glycerin 15 parts of diethanolamine resulting in. a yellow ink-receptive image on a white, hydrophilic background. Over 500 excellent copies .were obtained on the offset press.'

The removal of the photodecornposed areas was found to be equally. well carried out by treating the exposed plate with a solution of:

57.5 parts of ethylene glycol 42.5 parts of glycerin The plate was then readied for printing by swabbing with a solution of:

42.5 parts of ethylene glycol 42.5 parts of glycerin 15 parts. of diethanolamine Example XVI The procedure is the same as in Example X excepting that the high acetyl, high viscosity, cellulose kacetate employed to form the'lacquer layer 2 is replaced by an Several aluminum offset plates having a surfaceprepared according to the teachings of U. S. P. 2,637,929

were sensitized by whirler-coating with a 2% solution of N,N-4,4biphenylenebis [6 5 -diaz0-5 6)-0xo-1-naphthalenesulfonamide] in dimethyl foramide and dried. `Several different exposures were made on such plates, using as a positive original a letter typed on translucent paper. After exposure, the image on these plates was developed using a 10% solution of disodium phosphate, thev plates being thereafter treated with Platex and run on the press.

Positive-working metal plates manufactured by the Azo- Plate Corporation of Summit, New Jersey were exposed using the above original at several different exposure times and then processed with the reagents furnished bythe manufacturer.

Paper plates made according to the procedure of Example IV hereof were exposed for sevreal different `lengths of time beneath the same translucent original and thereafter developed using either the one or two step procedure of the example noted. A comparison of the offset printing behavior of the platespprepared and processed as above shows the following results:

l. The optimum exposure for the paper base plate of Example IV was faster by about a factor of 2 than 4that for the metal plates.

2. At the optimum exposure, the paper.y plate faithfully captured all of the detail of the original, doing this with a substantial increase in contrast and yielding prints having a clean white background. With the metal plates, on the other hand, the whole of the image of the original could be captured only by printing from an underexposed plate which resulted in the presence of appreciable background tone in the VVcopy. No exposure could be found at which the performance of the paper plate could be duplicated in the metal plate. l

We believe that the all or nothing contrast behavior of our materials is a consequence of the unique correlation of reagents and type of light-sensitive layers which we employ. Thus, if, in the time allowed for development the reagent fails to diffuse or penetrate through a given light-struck area, the subsequent application of water and acid terminates the action of the developer. Such an area will accept ink and print well. In another region which has received only a slightly longer exposure, the slightly increased permeability allows penetration of the developer to the interface between the sensitizing layer and the carrier layer, in the time allotted, with a result that the entire sensitizing layer can be removed and in such a region ink is rejected.

The unique correlation of the various factors in the production of our plates is also illustrated by the following, which stresses the crucial role played by the diazo photodecomposition products in creating permeability of the layer 3 to the aliphatic polyhydroxy compounds.

Polyvinylacetate used in Example IV was coated alone from methyl isobutyl ketone on the lacquer base of said example. The dried coated plate was then treated with the ethylene-glycol isopropanol mixture of said example but it was found that the resin layer was not removed. An attempt was made to render the plate hydrophilic with the diethanolamine-ethylene glycol mixture of Example IV but the plate failed completely to respond to such treatment, remaining completely hydrophobic and ink-receptive.

Similar experiments were carried out using the ethyl cellulose resin of Example VIII, the polymethylacrylate of Example VII, the coumarone-indene resin of Example I and the cellulose acetate resin of Example X. It was dis covered that in every case, in the absence of the diazo photodecomposition products, the resin completely resisted the treating solutions used in these examples. It is, therefore, manifest that operability of our printing plates depends in no way on the solubility of the adhesive resins in the processing reagents but rather on the specific fact that such decomposittion products create a permeability for the processing solutions, Vallowing the adhesion between the resin and the lacquer layer 2 to be destroyed.

The salient features of our invention, explaining the above unique correlation, may, therefore, be expressed in paraphrase as follows: Y

We employ water-insoluble diazo oxides soluble in the aforesaid usual commercial relatively low boiling solvents together with a water-insoluble, alkali-resistant adhesive resin coated from a non-penetrating solvent onto a substrate largely composed of PVM/MA, a substance which is not ink-receptive but water-receptive after contact with alkylolamines and which remains behind after processing. Our sensitizing layer contains no coupler either before or after development and is entirely a surface layer. Our sensitized layer may advantageously contain much more resin than is employed in the plates using alkali soluble resins as a binder.

All of these factors add up to a relatively inexpensive "paper plate capable of being simply processed to yield offset plates which reproduce in the greatest fidelity.

Modifications of the invention will occur to persons skilled in the art. Thus, we may use, in lieu of the diazo oxides of the examples, any of the diazo oxides referred Y to herein, including any of the rosin derivatives ofthe aforesaidvMoore application in which the Yrosin radical Yis linked to a naphthalene nucleus. We, therefore, do not intend to be limited in the-patent granted except as necessitated by the appended claims.

We claim:

l. A plate capable of conversion to an offset printing plate comprising a base, a hydrophobic layer on said base comprising essentially a copolymer of vinyl methyl ether and maleic anhydride on said base and an overcoating on said hydrophobic layer of a water-insoluble, alkali-resistant adhesive resin and a light-sensitive, water-insoluble diazo oxide which is soluble in a solvent selected from the class consisting of liquid aliphatic esters, aliphatic ketones and aliphatic alcohols.

2. A plate capable of conversion to an offset printing plate comprising a base, a layer on said base comprising a solid solution of a co-polymer of vinyl methyl ether and maleic anhydride and a hydrophobic resin compatible therewith, and a coating on said layer of a water-insoluble adhesive resin and a light-sensitive, water-insoluble diazo oxide which is soluble in a solvent selected from the class consisting of liquid aliphatic esters, aliphatic ketones and aliphatic alcohols.

3. The product as defined in claim l wherein said diazo oxide is selected from the class consisting of esters and amides of l-diaZo-Z-naphtholand 2-diazo-1-naphtol-5- sulfonic acids.

4. The product as defined in claim 1 wherein the adhesive resin is a polyvinyl compound.

5. The product as defined in claim 1 wherein the adhesive resin is selected from the class consisting of cellulose esters and ethers.

6. The product as defined in claim 2 wherein said diazo oxide is selected from the class consisting of esters and amides of 1-diazo-2-naphtholand 2-diazo-1-naphthol-5- sulfonic acids.

7. The product as defined in claim 2 wherein the adhesive resin is a polyvinyl compound.

8. The product as defined in claim 2 wherein the adhesive resin is selected from the class consisting of cellulose esters and ethers.

9. The process of producing a plate capable of conversion to an offset printing plate which comprises coating a base with an organic solvent solution of PVM/ MA, drying the base to form a hydrophobic film essentially comprising PVM/MA and overcoating the film with a solution in an organic solvent selected from the class consisting of a liquid aliphatic ester, an aliphatic ketone boiling above C. and an aliphatic alcohol containing at least four carbon atoms of an alkali-resistant, water-insoluble adhesive resin and a water-insoluble, diazo oxide.

l0. The process as defined in claim 9 wherein the solution coated on said base contains a hydrophobic resin compatible with the PVM/MA.

1l. The process as defined in claim 9 wherein the lightsensitive diazo oxide is selected from the class consisting of amides and esters of l-diazo-Z-naphtholand 2-diazo-1- naphthol-S-sulfonic acid.

l2. An offset printing plate having grease-receptive printing portions comprising a water-insoluble, alkaliresistant synthetic resin and a water-insoluble, light-sensitive diazo oxide soluble in a liquid solvent selected from the class consisting of aliphatic esters, aliphatic ketones and aliphatic alcohols and water-receptive, non-printing portions essentially comprising PVM/MA rendered hydrophilic by treatment with an alkylalamine.

13. The article as defined in claim 12 wherein the adhesive resin is Va polyvinyl compound.

14. The article as defined in claim 12 wherein theadhesive resin is selected from the class consisting of cellulose esters and ethers.

15. The article as defined in claim l2 wherein the diazo oxide is selected from the class consisting of esters and amides of l-diazo-Z-naphtholand 2-diazo-l-naphthol-5- sulfonic acid. v

i6. The article as defined in claim l2 wherein the water-receptive portions are defined by a solid solution of 17 PVM/ MA and a hydrophobic resin compatible Vwith said copolymer said solid solution have been rendered hydrophilic by treatment with an alkylolamine.

17. The article as defined in claim 15 wherein the water-receptive portions are dened by a hydrophilic modiication of a solid solution of PVM/MA and a hydrophobic resin compatible therewith.

18. The process of producing an olset printing plate from a plate comprising a base, a hydrophobic film of PVM/MA on said base and an overcoating on said lm of a water-insoluble, alkali-resistant resin and a waterinsoluble, light-sensitive diazo oxide soluble in a liquid organic solvent selected from the class consisting of aliphatic esters, aliphatic ketones and aliphatic alcohols which comprises exposing said plate under a pattern,

locally removing by means of a liquid, aliphatic polyhy- 18 droxy compound the outer coating where exposed to light and imparting hydrophilic character to the PVM/ MA lm in the areas where the outer coating is removed by treatment with an alkylolamine soluble in the aforesaid aliphatic polyhydroxy compound.

19. The process as dened in claim 18 wherein the polyhydroxy compound is a glycol. 20. The process as defined in claim 18 wherein the hydrophobic lm consists of a solid solution of PVM/ MA and a hydrophobic resin compatible therewith.

References Cited inthe le of this patent UNITED STATES PATENTS 2,667,415 Neugebauer et al. Ian. 26, 1954

Claims (1)

1. A PLATE CAPABLE OF CONVERSION TO AN OFFSET PRINTING PLATE COMPRISING A BASE, A HYDROPHOBIC LAYER ON SAID BASE COMPRISING ESSENTIALLY A COPOLYMER OF VINYL METHYL ETHER SAID MALEIC ANHYDRIDE ON SAID BASE AND AN OVERCOATING ON SAID HYDROPHOBIC LAYER OF A WATER-INSOLUBLE, ALKALI-RESISTANT ADHESIVE RESIN AND A LIGHT-SENSITIVE, WATER-INSOLUBLE DIAZO OXIDE WHICH IS SOLUBLE IN A SOLVENT SELECTED FROM THE CLASS CONSISTING OF LIQUID ALIPHATIC ESTERS, ALIPHATIC KETONES AND ALIPHATIC ALCOHOLS.

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