CA1070876A - Method, composition and emulsion for the treatment of image-bearing lithographic printing plates and coated plate - Google Patents

Abstract

ABSTRACT
The invention relates to methods of developing, gumming, gum etching, dampening during printing, cleaning during and after printing, and treatment before storage, of lithographic printing plates, and to compositions therefor which utilize polyacrylamide polymers and blend thereof in place of or as an extender for the traditional gum arabic. The invention also relates to the treated lithographic plates.

Description

~)70876 The invention relates to methods of developing, gumming, gum etching, dampening during printing, cleaning during and after printing, and treatment before storage, of lithographic printing plates, and to compositions therefor which utilize polyacrylamide polymers and blends thereof in place of or as an extender for the traditional gum arabic.
The invention also relates to the treated lithographic plates.
Lithographic printing, which is a type of plano-graphic printing, is a well known and established art. In general, the process involves printing from a flat plate or cylinder having substantially no surface relief (hence, the term "planographic"), and depends upon different properties of the image and non-image areas of the surface for printa-bility. In lithography, the image to be reproduced is im-parted to the plate by any one of several methods well known to those skilled in the art in such a way that the non-image areas are rendered hydrophilic while the image areas are hydrophobic. A widely practiced technique employs a photo-sensitive coating for this purpose. Following exposure of the photosensitive coating to imagewise modulated light, the latent image is developed and a portion of the coating is removed from the plate. Next, the plate is treated with a desensitizing solution to render the plate hydrophilic in the areas from which the photo sensitive coating has been removed. During the actual printing process, an aqueous fountain solution is applied to the plate surface.
The fountain solution keeps moist all portions of the surface not covered by the hydrophobic image. Furthermore, the fountain solution prevents the plate from scumming, i.e. it prevents the non-image areas from becoming at least ~ '.
1,,674B-F -1-~g~70876 partially ink-receptive. The fountain solution may be formulated to gradually etch the surface of the plate just enough to keep the lines sharp and prevent rapid wear.
In a conventional system, the fountain solution is applied S to the plate by one or more rollers. At least one ink roller coated with an oil-based printing ink then contacts the entire surface of the plate but deposits the lithographic ink only on the image area since the hydrophilic non-image areas repel the ink. Hence, for each impression made during a run, the lithographic plate is first dampened with the aqueous fountain solu~ion and then inked with a lithographic ink. Alternatively, the fountain solution and at least a portion of the oil-based ink are applied to the plate simultaneously with a first roller. In this latter system, other rollers, usually smaller in diameter than the first, may contact the plate subsequently to distribute the ink more evenly.
; Finally, the ink image is transferred directly to a paper sheet or other receptive surface to be printed, or to an offset blanket of rubber or synthetic material which in turn transfers the print to the final copy surface.
Gum arabic has long been used in acidic aqueous solutions in the preparation of lithographic plates. Gum arabic has been used, for example, in solutions for developing a latent image; as a desensitizing ingredient in a gumming solution --sometimes in combination with an etchant, in which case the solution is referred to as a gum etch -- to make the non-image areas sharply defined and ink repellent, i.e. hydrophilic rather than hydrophobic; in a fountain solution, again sometimes in combination with an etchant, to keep the non-image 17,674B-F -2-~70876 areas hydrophilic during the press run; as a protective coating during idle periods on the press or even during storage for weeks and months; and in plate cleaner formulations.
Gum arabic is a natural product obtained as an exudate from acacia trees. While the precise structure of gum arabic i8 not known, the main constituent apparently lies somewhere between hemi-cellulose and the simple sugars.
Essentially, it is a mixture of calcium, magnesium, and potassium salts of arabic acid. The average molecular weight of the polymerized arabic acid is in the range of 200,000 to 270,000.
The disadvantages of gum arabic are well recognized in the trade and a suitable substitute has long been sought.
As a natural product it is sub~ect to considerable variation in quality, and it i8 also prone to contain foreign matter of various kinds so that it must first be purified. The fountain solutions of gum arabic employed during printing to maintain the non-printing areas hydrophilic tend to emulsify the ink. Excessive emulsification weakens the resolution of the printing, causes scumming of the plate, and stripping of the ink from the ink rollers. In addition to the technological shortcomings of gum arabic, the con-tinued assured availability of an adequate supply of the product in the United States is in doubt, since nearly all of the domestic supply is imported from the politically unstable Middle East. U.S. Department of Commerce data projects that for 1975, the quantity of gum arabic imported will be only about one half that imported in 1972, and the unit price has more than doubled in the same period. Thus, a substitute for gum arabic is urgently needed.

17,674B-F -3-- . , .

107V~376 Some of the compositions heretofore proposed as gum arabic substitutes for the treatment of image-bearing plates include oxalic acid (U.S. Patent No. 3,489,561), homopolymers and copolymers of itaconic acid (U.S. Patent No. 3,507,647), sodium carboxymethylcellulose (U.S. Patent No. 3,166,421), the copolymer of methyl vinyl ether and maleic anhydride (ibid.), polyacrylic acid (U.S. Patent No. 3,211,686) and the sodium and ammonium salts thereof (Japanese Patent Publication 49-6561 (1974)), alginic acid and the sodium salt thereof, and polyvinyl alcohol (U.S.
Patent No. 3,607,255). None of these proposed substitutes ", seem~ to ha~e realized overwhelming commercial acceptance, at least to this date, as gum arabic continues to be the composition of choice in industry, notwithstanding all of its disadvantages.
Recently, alkaline solutions have been proposed and used with some success as fountain solutions. However, most contain a considerable proportion of surfactants, have a tendency to foam, and cause some emulsification of the ink.
Consequently, they are not always suitable.
British Patent 1,055,711 teaches an improved silver halide diffusion transfer process using a light sensitive material comprising a silver halide emulsion layer covered with a water-soluble colloid top layer.
The light sensitive material is exposed, developed, and only then brought in contact with the metal comprising the lithographic plate, for transfer of the image to the plate. Includ~d in the list of colloids taught to be suitable for use in the top layer are polyacrylamide and polyacrylic acid. It is also taught that the top layer 1,,674B-F -4-~C~7~87t;

may contain more than one of the colloids named in the list. ~owever, the patent contains no suggestion to use polyacrylamide or polyacrylic acid -- either separately or together --- to render hydrophilic the non-image area of the plate once the image has been transferred to the plate: for that purpose, the patentees use carboxymethyl-cellulose. Indeed, the patent contemplates the disappearance of the colloid of the top layer after the transfer is carried out. Moreover, the patent teaches no preference for mixtures of polyacrylamide and polyacrylic acid over the respective compounds employed separately, thereby suggesting that in the process there described, no particular advantage is obtained by employing the compounds in ad-mixture. In contrast, in the hereindescribed processe~
for treating lithographic plates already having an image, it has been found to be critical to employ an active polymer component having the proper ratio of both amide and carboxyl groups as illustrated by the numerous Examples and Comparative Runs hereinafter set forth. Also, the average molecular weight of the active polymer component is critical in the present process.
In addition, the art contains several suggestions to employ polyacrylic acid-containing or polyacrylamide--containing compositions in various ways as more or le~s permanent components of the lithographic plate itself, i.e. in compositions which form part of the plate even before the plate contains an image. For example, Leonard et al., U.S. Patent No. 3,265,504, apply a permanent polyacrylamide-containing coating on the entire surface of ~7,674B-F -5-t~7~876 the plate by contacting the plate with an abrasive poly-acrylamide-containing slurry while simultaneously mech-anically brush graining the surface. Dowdall et al., U.S.
Patent No. 3,136,636, employ polyacrylic acid or water soluble homologs thereof in a stratum between the surface of the plate and the diazo coating. Similar teachings are found in several other U.S. Patents such as No. 3,298,852.
In U.S. Patent No. 3,374,094, Wainer et al. describe a binder for the photosensitive composition for 2 litho graphic plate, the binder containing any of a number of hydrophilic colloids, including polyacrylamide. No attempt has been made, however, so far as the applicants are aware, to utilize polyacrylamide compositions for the treatment of lithographic plates already having an image lS ~latent or developed) thereon, for example, in desensi-tizing or fountain solutions.
The term "image" includes (1) both the hydrophobic, oleophilic, ink receptive areas of a lithographic plate produced, for example, on development on a photolithographic plate following exposure to actinic light, and also (2) the latent image produced in the light sensitive coating of such a photolithographic plate after exposure of the plate to actinic light but prior to development.
The term "non-image" refers to hydrophilic, oleo-phobic, water receptive, ink repelling areas of a lithographic printing plate.
By "image-bearing surface" is meant the entire surface of the lithographic plate exposed to the paper or the blanket in the printing process, including both the image and non-image areas as hereinabove defined.

~7,674B-F -6-: . . .
'~

~70876 "Scumming" refers to the condition that exists on the printing plate or results in the printed image when the water receptive areas of the prin~ing plate become at least partially ink receptive.
The term "blinding" refers to the condition that exists on the printing plate or results in the printed image when the image areas of the printing plate become at least partially water receptive and are not properly ink receptive, e.g. the condition that is exhibited when hydrophilic material from the fountain solution adheres to the plate image instead of or in addition to the non-image areas.
"Toning" or "tinting" refers to emulsification o~ the ink as globule~ in water in the non-image areas which lS results in ink transfer to the print in non-image areas.
"Desensitization" refers to the depositing in the non-image areas of an adequate protective film of a hydrophilic substance to prevent the plate from picking up ink, in such areas, from the inking roller during printing, or, during screening tests, from retaining ink from a sponge or a tissue wiped across the plate surface.
The term "chromium-anion providing agent" refers to one or more compounds selected from the group consisting of chromic acid and the alkali metal- and ammonium- chromates and bichromates.
It is very difficult if not virtually impossible to have an aqueous solution of polyacrylamide wherein all of the carbonyl sites are amide moieties. The term "polyacrylamide"
therefore refers to a polymer comprised of at least 98 percent 7,674B-F _7_ 11~70876 ,c~
H2N ~ O
combining units. Included within the meaning of polyacrylamide are polymers containing 98 percent of the above combining units, and up to 2 percent 2lH
MO O
combining units wherein M is a hydrogen, alkali metal, or ammonium ion.
The terms ~active polymer(s) n and "active polymer-component(s)" mean in a generic sense any one or more of the members (a) through (e) of the Markush group further defined.
The term "caxboxyl group(s)" refers to the moiety -COM wherein M i8 a hydrogen, alkali metal, or ammonium ion.
The term "alcohol," used in reference to the fountain solutions of the present invention, refers generically to lower alkyl mono- and polyhydric alcohols and glycol ethers having a molecular weight of about 170 or less.
By "lower alkyl" is meant having no more than four consecutive carbon atoms.
The abbreviation "cP" refers to the viscosity unit, centipoise. Unless otherwise specified and except for the viscosity measurements relating to characterization of the hydroxypropyl methylcellulose, all viscosity measure-ments were made at ambient temperature using a Brookfield viscometer. Spindle sizes of 1 through 4 were employed at rotations of from 6 to 60 revolutions per minute, as appropriate for each particular solution.

7,674B-F -8-1~70876 It has now been discovered that a highly sat-isfactory method for treating and composition for rendering hydrophilic the non-image areas of a lithographic plate comprises: water and an active polymer component selected from la) a polyacrylamide-based polymer wherein from about 3 to about 70 percent of the carbonyl sites are carboxyl groups, and the balance of said sites are amide moieties;
(b) a physical blend comprised of from about 97 to about 30 weight percent polyacrylamide and from about 3 to about 70 percent poly-acrylic acid or an alkali metal or ammonium salt thereof:
(c) a physical blend comprised of polyacrylamide, or polyacrylic acid or an alkali metal or ammonium salt thereof, and at least one polyacrylamide-based polymer as described in (a), said polymers being employed in proportions such that of the total carbonyl sites present in the blend, from about 3 to about 70 percent are carboxyl groups and the balance are amide moieties;
(d) a mixture of any two or more of the fore-going;
the average molecular weight of each of said polyacrylamide--based polymer, polyacrylamide, and polyacrylic acid or salt thereof being in the range of from about 5000 to about 1,000,000; or ./,674B-F -9-1070~76 (e) a co-mixture of one or more of the foregoing with up to about 30 weight percent hydroxypropyl methylcellulose based on the total weight of the co-mixture, said hydroxypropyl methyl-cellulose being of a type which produces a 2 weight percent aqueous solution having a viscosity of from about 1 to about 100 cP when measured according to ASTM Method D 2363-72.
By employing various concentrations of the above described active component in an aqueous solution, and, optionally, by employing in addition other components, solutions and/or emulsions are provided for the developlng, gumming, gum etching, cleaning, storage, and the like, of lithographic plates. The method consists in applying the compositions to an image-bearing plate. As a new article, there is produced a lithographic plate bearing an image and having a coating containing the recited active polymer component.
In accordance with the foregoing, the present invention also resides in an aqueous solution for rendering hydrophilic, the non-image areas of an image-bearing litho-graphic printing plate which comprises: water; a phosphate compound selected from ~1) alkali metal phosphates, ammonium phosphate, or mixtures thereof, and (2) phosphoric acid;
and the active pol~mer component.
The present invention further resides in a con-centrated aqueous solution comprising: water; a phosphate compound selected from (1) alkali metal phosphates, 17,674B-F -10-1~'70~76 ammonium phosphate, or mixtures thereof, or (2) phosphoric acid; and the active polymer component, said concentrate, when diluted with additional water, providing a solution containing from 0.001 to 30 weight percent of the active polymer component, which diluted solution is suitable for rendering hydrophilic the non-image areas of an image--bearing lithographic plate.
The present invention further resides in a composi-tion for developing a latent image on a photolithographic plate which has been exposed to imagewise modulated light, of the emulsion type having (1) a water immiscible phase containing a solvent for ~electively removing the non-exposed areas of a negative working photosensitive coating, or the exposed areas of a positive working photosensitive coating, without affecting the respective exposed or non-exposed image areas, and

(2) an aqueous phase containing an agent for rendering hydrophilic the non-image areas of the plate, the aqueous phase comprising the active polymer component.
The invention also resides in a composition for treating lithographic plates, of the emulsion type having (i) a water immiscible phase for maintaining the oleophilicity of the image areas of the plate, containing asphaltum gum or gilsonite and a solvent therefor, and ~ii) an aqueous phase containing an agent for maintaining the hydrophilicity of the non--image areas of the plate, the aqueous phase comprising the active polymer component.

17,674B-F -ll-1~70876 The present invention further resides in an image--bearing lithographic printing plate having a coating on the non-image areas of the plate comprising the active polymer component.
In the method of this invention, the foregoing composition is applied to an image-bearing lithographic plate to render hydrophilic the non-image areas, in aqueous solutions of different concentrations, optionally in combina-tion with other components, depending on the particular function desired. Thus, a very dilute solution, e.g., 0.001-0.5 weight percent active polymer, can be employed as a fountain solution, whereas a more concentrated solution, e.g., 3-30 weight percent active polymer can be employed where the plate is to be desensitized initially, cleaned~ or prepared for storage. The method encompasses application of the solution to a plate manually or by automated means. The composition is used either in an acid solution, in which case it may be regarded as a substitute or extender for gum arabic, in a solution of neutral pH, or in the more recently developed lithographic plate treatment solutions of the alkaline type. Aqueous solutions containing the active polymer can also be employed as one phase of emulsions for developing a latent image in an exposed photosensitive coating on a lithographic plate, and for reconditioning a plate after extended use. Concentrated aqueous solutions comprising the active polymer component can be readily stored and/or transported and then diluted with water when needed for actual use. An image-bearing lithographic printing plate having at least a partial coating comprising the active polymer is also regarded as an aspect of this invention.

17,674B-F -12-~7~876 The method of the present invention is pre-ferably practiced using ball grained, brush grained, or anodized aluminum plates. The invention can also be practiced, however, using copperized aluminum plates or S trimetal chromium/copper/aluminum plates, as well as offset master plates of steel, aluminum, or those having zinc oxide/resin binder or titanium dioxide/resin binder surfaces.
A. he Active Polymer At the heart of all aspects of this invention is the active polymer component.
The active polymer component may be a polyacryl-amide-based polymer wherein from about 3 to about 70 percent of the carbonyl sites are carboxyl groups and the balance are amide moieties. The particular method by which the polyacrylamide-based polymer is prepared is not critical.
It may be formed by copolymerization of acrylamide and acrylic acid, or salts thereof, in proportions and conditions such that of the carbonyl sites in the resulting copolymer, from about 3 to about 70 percent are carboxyl groups. Alternati~ely, a suitable polyacrylamide-based polymer may be obtained by hydrolysis of polyacrylamide. me preparation of both partially hydrolyzed polyacrylamide and copolymers of polyacrylic acid and acrylamide are well known in the art. See, generally, "Acrylamide Polymers,"
Encyclopedia of Polymer Science and Technology, Volume I, pp. t 177ff, Interscience Publishers, N.Y., 1964.
The active polymer component need not be a single polymeric substance, so long as the number of carboxyl groups present in the entire active polymer component 17,674B-F -13-.. ..

107{)~76 constitutes from about 3 to about 70 percent, preferably about 5-50 percent, and most preferably about 5-25 percent, of the total carbonyl sites, i.e., of the sum of the carboxyl groups and amide moieties. Thus, the active polymer component can be a physical blend of polyacrylamide and polyacrylic acid, including the alkali metal and ammonium salts thereof; or a physical blend of polyacrylamide with a polyacrylamide-based polymer of the type described in the preceding paragraph; or any other mixture of poly-acrylamide, polyacrylic acid and the alkali metal and ammonium salts thereof, and polyacrylamide-based polymers, so long a~ the required percentage of carbonyl sites are present as carboxyl groups.
An additional requirement is that each of the poly-acrylamide, the polyacrylic acid or salt thereof, and the poly-acrylamide-based polymers employed in the solution must have an average molecular weight of from about 5000 to about 1,000,000, preferably about 10,000-500,000, and most preferably about 25,000-300,000. As a guide to those practicing this invention, the average molecular weight of the polymers and the perc~ntage of carbonyl sites as car~oxyl groups should be considered together: although the minimum acceptable percentage of carboxyl groups does not appear to vary significantly with molecular weight, the maximum percentage of carboxyl groups at which satisfactory results are obtained generally declines with increasing molecular weight.
Finally, the active polymer component may be a co-mixture of any of the polyacrylamide-based polymers or physical blends hereinabove described, with up to about 30 17,674B-F -14-1~0876 weight percent hydroxypropyl methylcellulose, preferably about 10-25 weight percent. In a typical process for the manufacture of hydroxypropyl methylcellulose, cellulose is reacted with propylene oxide and methyl chloride in the presence of sodium hydroxide to obtain hydroxypropyl sub-stitution on the anhydroglucose units. Hydroxypropyl methylcellulose is a solid at room temperature, but is known and commercially available in a variety of types which produce 2 weight percent solutions having viscosities of up to at least about 75,000 cP when measured at 20C according to ASTM
Method D 2363-72. The type suitable for use herein produces a 2 weight percent solution having a viscosity of from about 1 cP to about 100 cP when measured according to said Method.
B. Solutions Containing the Active Polymer and ~heir Use Having thus described the various forms which the active polymer component may take, solutions containing the active polymer component formulated to accomplish a particular function will now be described. It is to be understood, of course, that while a particular formulation may have another primary function, such as developing a latent imaqe in an exposed photosensitive coating, the active polymer component of such a formulation is employed to render hydrophilic the non-image areas of an imagebearing plate.
l. Developer Formulation The active polymers of the present invention can be used in the aqueous phase of emulsion type formulations employed to develop a latent image on an exposed photo-lithographic plate.

17,674B-F -15-"
. . ; , ~ . ~

1~7~876 In the preparation of a photolithographic plate, a plate having a photosensitive coating is exposed to imagewise modulated light. For example, the plate can be exposed to actinic light through an image-bearing transparency, whereby light and shadow areas are cast upon the plate. The photo-sensitive coating may be of a positive working type, wherein the areas of the coating exposed to light are to be removed from the plate while the shadowed portions of the coating remain adhered to the plate. More frequently, a negative working sensitive coating is employed, wherein the portions of the coating exposed adhere to the plate and become the oleophilic areas of the plate. Representative of the negative working coating are those of the diazo and polyvinyl cinnamate type~.
Regardless of the particular type of photosensitive coating employed, the plate is treated with a developer solution after exposure. While a variety of formulations are employed as developers depending on the particular .ype of photosensitive coating employed, most comprise an emulsion containing at least one water immiscible solvent for selectively removing the photosensitized coating from only those areas of the plate which are not intended to carry the printing ink. Thus, where a negative working photosensitive composition is employed, the solvent removes the shadowed areas of the coating, leaving intact those areas which were actually exposed to light. Con-versely, where the plate has a positive working coating, the developer formulation contains a solvent which removes the coating from the exposed area, leaving the shadowed areas intact. A second phase of the developer emulsion comprises an aqueous solution containing an agent for rendering hydro-philic the non-image areas of the plate. The active polymers 17,674B-F -16-of the present invention can be employed in the aqueous phase of virtually any of such developer formulations in lieu of, or in partial substitution for, the agents here-tofore employed for this purpose, such as gum arabic. Since the particular constituents employed in various developer formulations do vary somewhat, however, it is recom-mended that prior to preparing a large batch employing the active polymer, the compatibility of the active polymer with the remaining constituents be confirmed.
When so employed, the active poly~er component comprises from about 0.1 to about 5 weight percent of the aqueous phase of the emulsion, and the aqueous phase comprises from about 5 to about 75 percent of the total emulsion, by volume.
In addition to the water immiscible selective solvent and the aqueous phase containing an active polymer as herein-above described, the developer emulsion may also contain an agent such as a dye or pigment for rendering easily visible the oleophilic areas of the plate. Also frequently employed in developers are agents for enhancing the properties of the oleophilic areas of the plate, either with respect to dura-~- bility, oleophilicity, or both. The aqueous solutions of the present invention are compatible for use with any of these optional components as well.
The inclusion in the developer of an agent for rendering hydrophilic the non-image areas is not intended to supplant use oE a separate so-called "straight gum" or "gum etch" solution, or substitute, for desensitizing the plate as hereinafter described. It does, however, provide pro-tection against plate sensitization caused, for example, by 17,674B-F -17-oxidation during the time between the exposure and a subse-quent desensitizing step.
2. So- Called "Straight Gum'' Solutions One type of aqueous solution referred to in the trade as a "gum" or "straight gum" solution consists essentially of water and a hydxophilic colloid. A widely used straight gum solution is 14 Baumé (approximately 25%) gum arabic.
Such a solution naturally has a pH of from about 4 to about 5.
This type of solution can be used to desensitize a plate after the plate has been exposed and developed, or after the plate has been cleaned with a plate cleaning etch containing no hydro-philic colloid. It can also be used to treat a plate for storage.
A solution is now provided according to the present invention to be used for substantially the same purpose~ as a conventional straight gum solution, comprising water and from about 3 to about 30 weight percent an active polymer. Such a solution is approximately of neutral pH, but may be slightly acidified with, for example, hydro-chloric, phosphoric, or sulfuric acid, if desired. A
slightly basic straight gum type solution may be pre-pared by including an alkali metal or ammonium phosphate.
A straight gum solution of the present invention is generally characterized by a pH within the range of from at least about 3 to about 9; similar solutions having a pH either above or below the stated range are generally regarded as "gum etch" solutions, hereinafter described.
The amount of active polymer component employed in solutions used as a substitute for a straight gum 7,674B-F -18-,~

~070876 solution depends in part upon the molecular weight of the polymers employed. Those skilled in the art will recognize that within the above range of about 3-30 weight percent, the quantity of a particular active polymer component employed should be such that the viscosity of the solution is from about 40-1000 cP, and preferably from about 50-300 cP, in order to obtain a uniform film on the plate. Where the active polymer component employed is among those described above as preferred, i.e., with respect to molecular weight, percent carbonyl sites as carboxyl groups, and the like, a preferred active polymer concentration range for a solution to be used in lieu of a conventional straight gum solution is from about 5 to about 12 weight percent. ThuR, in most instances, the preferred amount of active polymer com-ponent employed is leRs than half the amount by weight of gum arabic formerly used.

3. So-Called "Gum Etch" Solution Another type of solution, known in the art as a "gum etch" solution, typically comprises 32 parts by weight of a straight gum solution, as hereinabove described, per part of 85% phosphoric acid. Such a solution is employed, for example, in lieu of a straight gum solution to desensitize a plate after the plate has been exposed and developed, or to desensitize a plate after the plate has been cleaned, or to apply a protective coating prior to storage. The distinction between a straight gum solution and a gum etch solution is that the latter can also be used to clean a scummed plate, in which case the two-step pro-cedure of cleaning and thereafter regumming can be reduced to one step.

17,674B-F -19-. : . ~ . . ;. .
: , .. , 107~)876 Both acidic and alkaline substitutes for a conventional gum etch solution are provided by the present invention. Each comprises from about 3 to about 30 weight percent active polymer component and from about 2 to about 4 weight percent (anhydrous basis) of a compound selected from the group consisting of (1) alkali metal and ammonium phosphates and mixtures thereof and (2) phosphoric acid. The acidic gum etch type solution contains phosphoric acid and is characterized by a pH of from about 1 to about 3, whereas the alkaline gum etch type solution ' contains at least one alkali metal or ammonium phosphate and is characterized by a pH of from at least about 9 to about 12.5.
With respect to both the acidic and the alkaline lS solutions, a solution which has a pH which i9 too neutral will not etch the plate sufficiently rapidly to be of any practical use as a cleaning solution, though of course such a solution can be employed as a straight gum type solution, i.e., merely to desensitize a plate rather than to clean or etch the plate. On the other hand, solutions which are too acidic or too basic etch the plate too rapidly, so that portions of the image areas of the plate are destroyed or weakened.
The teachings presented above in describing the substitute for conventional straight gum solutions with respect to solution viscosity and preferred con-centration, are applicable to solutions which are sub-stitutes for conventional gum etch solutions a~ well. Thus, a preferred active polymer component is preferably employed in a concentration of about 5-12 weight percent of the solution.

17,674B-F -20-:1~7~876 As a concentrate, an aqueous solution is provided comprising active polymer component, and phosphoric acid or alkali metal or ammonium phosphates, in proportions so that upon dilution with additional water, a solution is obtained containing said compounds in the amounts hereinabove described as required for the gum etch type solution of this invention.

4. Fountain Solutions Another category of solution require~ in lithographic printing is a fountain solution. Normally, a plate will have been desensitized with a straight gum or gum etch type solution, or a substitute as provided herein, before a press run is begun. A fountain solution contains water to moisten the hydrophilic areas of the plate, and just enough selected additional ingredients to keep the non-image areas of the plate well defined and hydrophilic throughout the press run. On a very short press run, water alone is sufficient since the initially desensitized plate will remain desensitized for at least a few printing cycles. As a practical matter, how-ever, fountain solutions also contain, at the minimum, an agent for maintaining the hydrophilicity of the non-image areas.
Thus, for example, a straight gum solution can be diluted and used as a fountain solution. Often, a fountain solution contains in addition phosphoric acid. Hence, an acidic gum etch type solution can also be diluted to provide a fountain solution. Where an acid fountain solution having a pH of from about 3.5 to about 5.5 is employed, a solution regarded as preferred in the art usually contains a metal nitrate salt, phosphoric acid, and sometimes a chromium-anion providing agent.

17,674B-F -21-1~7~)876 The present invention embraces generally four types of fountain solutions, grouped according to the pH
of the solution and the nature of the solvent system:
acidic aqueous, alkaline aqueous, acidic water/alcohol, and alkaline water/alcohol. Each of the four types comprises, by weight, at least about 97 percent solvent and from about 0.001 to about 0.5 percent, preferably ! , from about 0.0025 to about 0.1 percent, active polymer.
Insufficient active polymer results in inadequate pro-- tection of the plate during long press runs, while an excess can result in an inordinate build-up of a glaze on the rollers.
The solvent comprises at least about 75 volume percent water. In the case of acidic aqueous and alkaline aqueous fountain solutions, the solvent consists essentially of water. ~
It is known in the art, however, that it is some- f times desirable to include an alcohol in the fountain solution, particularly when printing on high quality coated stock, for example, when using a Dahlgren type dampening system.
One advantage of an alcohol is that it changes the wetting angle so that the fountain solution can be carried from the fountain reservoir to the plate surface on rollers of metal, rubber or the like, having no water absorbent wrapping, such as cloth or paper. The fountain solutions of this invention having a water/alcohol solvent system are similar in all respects to the corresponding aqueous fountain solutions, except that an equal amount, by volume, of a low molecular weight (about 170 or less) lower alkyl mono- or polyhydric alcohol or glycol ether is 17,674B-F -22-- - ~ .,, , ; .
.. ~ . . . .

1~7~876 employed in lieu of up to about 25 volume percent of the water. Examples of such compounds are isopropanol, propylene glycol, glycerine, and diethylene glycol ethyl ether.
~epending on the nature and concentration of the active polymer component and the compound selected for use as a solvent in lieu of some of the water, those skilled in the art will recognize that in some instances the water:alcohol ratio must be greater, i.e., more water, than 75:25 lest precipitation of the active polymer component occur. Usually, of course, no more alcohol will be employed than is required to achieve the performance desired, if for no other reason than cost. In this respect, an advantage of the acidic water/alcohol fountain solutions of the present invontion is that a significantly lower proportion of alcohol is generally required to achieve a desired performance than in comparable fountain solutions based on gum arabic.
The acidic fountain solutions of this invention, regardless whether the solvent system consists of water or includes an alcohol, may contain, in addition to the active polymer: a metal nitrate in an amount up to about 0.25 weight percent of the solution, calculated on an anhydrous basis, preferably from about 0.02 to about 0.15 weight percent, and most preferably from about 0.04 to about 0.1 weight percent; phosphoric acid in an amount up to about 0.05 weight percent of the solution, preferably from about 0.004 to about 0.03 percent, and most preferably about 0.008 to about 0.018 weight percent; and a chromium-anion providing agent in an amount up to about 0.02 weight percent of the solution, calculated on an anhydrous basis, preferably from about 0.01 to about 0.02 percent. Ammonium bichromate 17,674B-F -23-1~7~876 is the preferred chromium-anion providing agent. Preferably the pH of the acidic fountain solutions is maintained within the range of from about 3.5 to about 5.5.
Metal nitrates suitable for use in the acidic fountain solutions described herein are those nitrates, the corresponding hydroxide compound of which, e.g., Mg(OH)2, has a solubility product in water at 25C of from about 10 5 to about 10 35, and preferably about 10 10 to about 10 20. Included by way of example are the nitrates of magnesium, calcium, cadmium, berylliumt aluminum, tin, zirconium, nickel, manganese, iron (Fe 2 only), chromium, copper, and lead. Preferably, the metal has a standard reduction potential negative with respect to hydrogen.
Magne~ium and zinc nitrates are most preferred. Those skilled in the art will recognize that where some of the aforementioned metal nitrates are employed, within the above limits the concentrations of the various ingredients and the pH of the solution should be selected so that precipitation detrimental to the quality of the printed image or to the smooth operation of the press is avoided.
It has been found that when the acidic fountain solutions of the present invention are employed, less fountain solution is required to maintain the proper ink-water balance than when corresponding solutions of gum arabic are employed. When an insufficient supply of fountain solution is provided, the plate will not be moistened sufficiently, and scumming occurs. When too much moisture is applied, carryback of the fountain solution occurs on the ink rollers, which leads to uneven ink distribution on the rollers and on the plate. Since the use of less fountain 17,674B-F -24-solution ultimately results in less moisture being transferred from the plate to the surface being printed, faster press speeds are possible with fountain solutions of the present invention than with gum arabic fountain solutions. Moreover, there is less lint accumulation on the press rollers resulting in less frequent shut down for cleaning the press.
Finally, the alkaline fountain solutions employed herein have a pH of from about 7.5 to about 12, preferably from about 8.5 to about 10. In addition to the solvent and the active polymer, the alkaline fountain solutions contain sufficient alkali metal or ammonium phoqphate or mixtures thereof to maintain the pH within a preselected range. Usually, this requires in the solution from about 0.01 to about 0.06 weight percent of the phosphate salt. Generally, the greater the quantity of active polymer employed in the solution, the lower the pH can be maintained with satisfactory results; however, by em~loying somewhat lower amounts of active polymer and operating at somewhat higher pH levels, the press can be restarted with fewer spoiled impressions following periods of brief shut down, such as where a correction must be made on one of the plates on a four color press in the midst of a run.
Since no surfactants of the type which have heretofore caused foaming in conventional alkaline fountains are required in the present invention, a preferred alkaline fountain solution consists essentially of water, the active poIymer component, and the alkali metal or ammonium phosphate in proportions set ~orth above.

17,674B-F -25-11[)70876 !
Concentrates of each of the four types of fountain solutions are provided for convenient transport and storage. These concentrates contain appropriate ingredients in the requisite amounts and proportions 80 that upon dilution of the concentrates with water, or with water and an alcohol, fountain solutions as described herein are obtained.

5. Asphaltum ~um Emulsion When plates are employed in a long press run, or are reused in several runs of more moderate duration, the image areas sometimes tend to deteriorate. When this occurs, the practice in the art has been to treat the plate with an asphaltum gum emulsion comprised of from about 25 to about 75 percent by volume an aqueous phase, and the balance (exclusive of emulsion stabilizers) a water immiscible phase containing asphaltum or other solid tar such as gilsonite, and a solvent therefor such as turpentine or a suitable mineral spirit, e.g. naptha. The asphaltum (or equivalent) enhances the oleophilicity of the image areas of the plate and the aqueous phase, which includes a suitable agent for such purpose, simultaneously imparts a coating to the non-image areas to maintain and/or revitalize the hydrophilicity of such areas.
An asphaltum gum emulsion prepared according to the present invention comprises as the aqueous phase of an emulsion of the type just described, a solution containing from about 3 to about 30 weight percent, preferably about 5-12 percent, active polymer component, and up to about 4 percent, pre-ferably about 2 to about 4 percent, phosphoric acid. When plates are treated with such an emulsion, impressions of premium quality can once again be obtained from the plates. r 7,674B-F -26-~76)876 V. Examples and Comparative Runs The following examples further illustrate the present invention, and in particular illustrate the use of solutions containing the hereinabove described polymers, copolymers, blends and co-mixtures for treating in various ways image--bearing lithographic plates. The examples are illustrative only and are not to be construed so as to limit the scope of the invention. In the tables, "Example" is abbrevia~ed "Ex.", "Comparative Run" is abbreviated "C.R.", and all perc~nts relating to solution concentrations are by weight unless otherwise specified.
A test procedure, hereinafter referred to as the "laboratory scumming test," was devised to evaluate the effectiveness of a composition as a desensitizing or gumming solution. Generally, if a composition adequately protects a plate against scumming in such a test, it will, as a rule, also perform adequately in any other plate treatment application, e.g., in a developer emulsion, in an asphaltum gum emulsion, or when diluted as a fountain solution. In the test, an exposed and developed plate was treated with the solution being evaluated, inked, rinsed with water, and examined for scumming, blinding, or tinting. In particular, brush grained aluminum sheets were coated with a diazo type photosensitive coating. Although the solutions of this invention can be employed with any diazo or other photosensitive coating, the particular diazo coating employed was formed by applying to the plate a solution made up by initially admixing two grams of "Wipe-on Coating Powder" with 56 grams "Negative Wipe-On Coating Solution", each of which was obtained as an item 17,674B-F -27-. . .. . . .

~0~70876 of commerce from RBP Chemical Corporation, Milwaukee, Wisconsin. After the diazo coating had sufficiently dried in warm air, the plate was exposed to a mercury arc 5 KW
ultraviolet lamp at a distance of 38 inches (about 96.5 cm) through a 65-screen combination negative with half tone~
and line copy in a vacuum printer. The resulting latent image was developed and rinsed with water according to the manufacturer's directions using Sure Dot brand wipe-on developer, also obtain~d from RBP Chemical Corporation. An aqueous solution of the substance being evaluated was applied to at least a section of the wet plate with a paper tissue. In some runs, two or more substances were applied to different sections of the plate for simultaneoug evaluation.
me plate was buffed dry and maintained at ambient temper-ature for a duration of, in some runs one hour and in others 24 hours, 72 hours, 96 hours, or longer as hereinafter specified. The plate was then dampened with water and lightly buffed with a moist sponge after which a grease based ink was applied and evenly distributed over the plate. Finally, the plate was rinsed wi$h water and buffed with a wet sponge to remove ink from the non-image areas. The plate was examined under low power magnification for evidence of scumming, blinding, or tinting.
Comparison Run 1 A 14 Baume aqueous solution of gum arabic (equivalent to about 25 weight percent solids) having ;
a pH of 4.7 and a viscosity of about 55 cP was evaluated using the laboratory scumming test. The non-image area of the treated plate was of good quality, showing no scumming after 72 hours.

17,674B-F -28-.

107~876 Examples 1-3 and Comparison Run 2 Aqueous solutions of a polyacrylamide-based polymer having an average molecular weight of about 250,000, obtained by hydrolysis of approximately 10 percent of the carbonyl sites of a corresponding polyacrylamide polymer, were prepared and acidified with sulfuric acid as follows:
TABLE I
Percent Poly- Solution Vis-acrylamide-based cosity, Ambient Run PolymerTemperature pH
Ex. 1 5 50 cP 4.5 Ex. 2 8.5 235 4.5 Ex. 3 12 880 cP 4.5 C.R. 2 20 15,000 cP 4.5 The solutions of Examples 1-3 were evaluated using the laboratory scumming test. In each instance, a sharp, clean image of excellent quality was obtained both on plates inked after one hour and after 72 hours. No scumming was observed in either line copy, solids, or half tones. The plates of Examples 1-3 were judged to be of even better overall quality than those obtained in Comparison Run 1 using gum arabic. The solution of Comparison Run 2 was ~ound to be too viscous to spread uni-formly over the plate at ambient temperature.
Example 4 A 26 percent aqueous solution of a polyacrylamide--based polymer obtained by copolymerization of equal parts acrylamide and acrylic acid and having an average molecular weight of about 25,000 was prepared and the p~ adjusted to 4.3 with sulfuric acid. The visco~ity of the solution was ' :' 17,674B-F -29-1~70~376 measured as 120 cP. No scumming was observed in the lab-oratory scumming test when the plate was inked after 72 hours.
Comparison Runs 3 and 4 In Comparison Run 3, a 15 percent aqueous solution of polyacrylamide (less than 2 percent hydrolysis) having an average molecular weight of 25,000 was prepared and the pH
adjusted to 4.3. The viscosity of the solution was measured as 80 cP. Upon evaluation using the laboratory scumming test, scumming was observed when the plate was inked a~ter 72 hours. Similarly, in Comparison Run 4, an 8 percent aqueous solution of polyacrylamide having an average molecular weight of about 250,000 was prepared and adjusted to pH 4.5. The solution had a viscosity of 190 cP, and did not adequately protect the plate against scumming in the laboratory scumming test. Comparison Runs 3 and 4 demonstrate that polyacrylamide alone having substantially no carboxyl groups at the carbonyl sites is not as effective in a gumming solution as either gum arabic or the compositions of the invention described herein and therefore is not commercially acceptable for such use.
Comparison Runs 5 and 6 In Comparison Run 5, a 0.4 percent aqueous solution having a pH adjusted to 4.5 and a viscosity of 215 cP was prepared from a polyacrylamide-based polymer having an average molecular weight somewhat in excess of about 1,000,000 and having carboxyl groups at about 30 percent of the carbonyl sites. The solution was evaluated using the laboratory scumming test. One hour after the solution was applied to the plate, it was found the plate inked readily, but some scumming was observed. More severe scumming was observed when a still higher molecular weight (1.5 to 2 x 106) poly-mer was tested.

17,674B-F -30-1~70~76 In Comparison Run 6, a series of solutions having a pH adjusted to about 4 and polymer concentrations ranging from about 6 to about 25 percent was prepared from poly-acrylamide and polyacrylamide based polymers having in each instance, molecular weights less than about 5000. None of the compositions performed as well as gum arabic in the laboratory scumming test.
Comparison Runs 5 and 6 demonstrate that solutions based on polymers having an average molecular weight less than about 5000 or more than about 1,000,000 are not as effective as gumming solutions containing similar polymers having average molecular weights within the above range and are not suitable for use as gum arabic sub~titutes.
Examples 5 and 6 In Example 5, an 8 percent aqueous solution was pre-pared from a polyacrylamide based polymer having an average molecular weight of from about 200,000 to about 250,000, and acidified to a pH of about 4.5 with sulfuric acid.
The polymer had been prepared by copolymerization of acrylamide and acrylic acid using proportions such that about 10 percent of the carbonyl sites in the copolymer were carboxyl groups.
I~ Example 6, a similar solution was prepared from `~ a polyacrylamide based polymer having an average molecular weight of 250,000, and approximately the same proportion of amide:carboxyl groups as in Example 5. The polymer in Example 6, however, was obtained not by copolymerization, but rather by hydrolysis of polyacrylamide.
Each solution was applied to two plates, according to the laboratory scumming test procedure. One pair 17 ! 674B-F -31-.. . . .

~C~7~ 76 of plates was inked after one hour, and the other was inked after 96 hours. None of the plates showed any scumming, thereby demonstrating that the method used to provide carboxyl groups in the active polymer component is not critical.
Comparison Run 7 A solution was prepared as described in Examples 5 and 6, except that in lieu of the polyacrylamide-based polymer there was used unhydrolyzed polyacrylamide similar to that which had been hydrolyzed to produce the polym~r used in Example 6. The solution proved unsatisfactory in the laboratory scumming test.
Examples 7-11 and Comparison Run 8 Example 7 shows the use of a solution containing 27 weight percent polyacrylamide-based polymer having an average molecular weight of 25,000 obtained by copolymerization of equal parts acrylic acid and acrylamide.
The pH of the solution was 4.5, and the viscosity was 65 cP. Aliquots of the solution of Example 7 were used as "Solution B" in preparing the various physical blends of Examples 8-11 as set forth in Table II. Used as "Solution A" for Examples 8-11 were aliquots of the solution used in Comparison Run 8, which is of substantially the same composition as the solution described hereinabove in Comparison Run 4, i.e., polyacrylamide having less than 2 percent hydrolysis.

17,674B-F -32-10~0876 ,~ o ,I t-- tO N
~ O ~
~ O U~ ~

_~ ~r tn o o~ u~ o X ~ ~
~:
U~ :~
~r CO
O . ,.
_~ O
~ o ~r o 11'~
~ ~ _I 0~ ~1 1~ N 'I 'I .
:
Lt~
Cr~ ~D O _~ O O
~I t~
. ~ N ~t ~ Ul H CO

m u~
~; ~0 E~- co N O u') O
~ ~1 _I _I O ' 1~ U~ N N
~i O~
: .
0:~ ~

: ~ o a 1-~
. . _I _I N
.,' C.) '.
~ m .
.. , . U~ -,~,., U~ ~ ~ o ~ X
s~
~ ~I o :: ~ ~ P' 3 :, .~
O _I ~
~ o ~ ' s~
~ o ; P~

:
., 17, 674B--F --33--Plates were treated with each of the solutions described in Table II according to the laboratory scumming test procedure. When inked after seven days at ambient temperature and humidity, the plates of Examples 7-11 showed no scumming, while that of Comparison Run 8 showed severe scumming.
Example 12 Another blend comparable to that described in Examples 8-11 was successfully employed in the same manner.
The blend contained 4 weight percent each of polyacrylamide and partially (10 percent) hydrolyzed polyacrylamide, each having an average molecular weight of 250,000. Thus, of the total carbonyl sites in the blend, about 5 percent were carboxyl groups. Solution viscosity was 120 cP.
Example 13 A 4 percent solution of a polyacrylamide-based polymer having an average molecular weight of about 750,000 and about 20 percent of the carbonyl sites as carboxyl was prepared and acidified to pH 4.5. Viscosity of the solution was about 120 cP. Plates were treated and inked as per the laboratory scumming test. No scumming was observed on the plate when inked after 1 and 96 hour intervals. While certainly usable within the scope of this invention, the polymer solution was somewhat stringy and is not considered a perferred embodiment.
Examples 14-17 Aqueous solutions each containing approximately the same weight percent of polyacrylamide hydrolyzed to various degrees, were prepared and successfully employed in the laboratory scumming test. The solutions are summarized ln Table III.

17,674B-F -34-- , -, .
.~, ..

~1 ~70876 TABLE III
Ex.14 Ex.15 Ex.16Ex.17 Percent Hydrolysis 8.7 14.2 19.5 28.9 Percent Active7 7 7 7.5 Polymer Solution Viscosity 105 110 115 155 Polymer3Ave.M.Wt. 250 250 250 250 Bxamples 18-20 and Comparison Runs 9 and 10 The series of Examples and Comparison Runs in-cluded under this caption relate to the actual use in a lithographic printing process of solutions coming within the scope of the present invention. A separate Example or Comparison Run number has been designated for each ~olution employed. The solutions will be described first, followed by a description of their application.
The solutions shown in Table IV were prepared for use as straight gum type solutions. The gum arabic solution of Comparison Run 9 naturally has a pH of about 4.5. The solutions of Examples 8-20 were adjusted to their respective hydrogen ion concentrations using sulfuric acid.

` ;, ~.
.

~7,674B-F -35-. :~ . : , .

O p o o o o .
u~
. .
o ~
a~
h ~ f~ , .
~ O ,.~
O cO r~
o _I
.1 Ul ".~, ~l' ~ ,q ~ ~ ~
a) ~ N N 1'~7 1 ~3 ~ ~ ~ r O tJ '~
E~
: ~ O O O O
,. S~ O O O O
o O O
O O O O
~1 aJ Il'~ In In ~
: & ~ ,, ~, ~ N
. . , .
,: C~
W O ~ ~ h .S: h .' ~1 O ~ E~ I
~\ ~ ~ ~ O O n1 a~
p ~ 'a ~ I Q~
u ~:a~ ~ ~ h tJ~ ~ O
.~ I¢ H m ~

o q~
~ r~l r-l N
a~ . . . P:
H X X X ~

17, 674 3-F -36 Substitute solutions for conventional gum etch solutions, designated as Examples 18-GE, l9~GB, and 20-GE respectively were prepared by mixing 32 parts by weight of the respective gumming solutions of Examples 18, 19, and 20, with one part of 85 weight percent phosphoric acid.
A control gum etch solution, Comparison Run 10, contained 32 - parts of 7 Baumé gum arabic and one part of 85 weight percent phosphoric acid.
Four different fountain solutions, designated as Examples 18-F, l9-F, 20-F, and Comparison Run 9-F, were pre-pared by diluting to one gallon (3.78 liters): 1 fluid ounce (29.6 ml) of the respective desensitizing solutions of Examples 18-20 and Comparison Run 9, and 2 fluid ounces (59.1 ml) of a so-called etch concentrate. The particular etch concentrate employed was an aqueous solution consisting of (in addition to water), per liter, 90 grams of zinc nitrate and 8.5 ml of 85 weight per cent phosphoric acid.
; Having described the solutions employed, the press runs will now be described.
A series of latent images was established on a com-mercially available aluminum plate having a presenqitized diazo coating, by exposing the coating to an ultraviolet light source through a negative comprised of solids, 120 line screen, a screen step wedge, and a 40 percent tint scale. The plate was developed with the recommended chemicals for this commercial plate. The plate was divided into four parallel sections.
To each of the four sections was applied a different desensi-tizing solution described above as Examples 18-20 and Com-parison Run 9. The plate was maintained for 16 hours at ambient temperature and humidity and was then mounted on a Miehle 7,674B-F -37-~70876 Favorite litho press for scumming tests. To simulate varying rates of wear on the plates, paper packing of 0.008 inch, 0.0055 inch, 0.004 inch, and 0.002 inch thicknesses was in-terposed between the plate and the plate roller in such a manner that the four sections of the plate which had been treated with four different desensitizing solutions would each be subjected to four different printing pressures. Thus, 16 different combinations of plate treatment and pressure were evaluated simultaneously. The dampening solution con-sisted only of water in order to provide a rigorous test for the desensitizing composition. The paper printed upon was Mountie brand Offset Enamel #70, sold by the Northwest r Paper Company. The ink employed was Hanco Offset Super Nax Arid Black BK 4664 Litho manufactured by Handschy Chemical Company. The test cycle was comprised of 10 cycles of inking and cleaning the plate with water, followed by the printing of 100 sheets. A total of 180 test cycles, each of 100 sheets, was run.
Scumming occurred throughout most of the press run in all of the sections of the plate under the excess pressure of the 0.008 inch packing, but after 180 test cycles, all the sections printed under normal press conditions (0.004 inch packing) were printing cleanly and showed no scumming.
Similarly, substantially no difference was observed in the performance of the four desensitizing solutions in the portions of the plate having the 0.002 inch and 0.0055 inch paper packing. The sections of the plate treated with the solutions of Examples 18-20 were equivalent or better in print quality to that treated with the gum arabic solution of Comparison Run 9.

l7,674B-F -38-lG70876 The portions of each of the four plate sections upon which scumming had developed were cleaned with the respective gum etch type solutions of Examples 18-GE through 20-GE and Comparison Run 10. The scum cleaned off with equal ease in all sections, and clean, high quality printed images were once again obtained from the plate, demonstrating that the active polymers of the present invention can be employed as a substitute for gum arabic in plate cleaning solutions.
Another test employing some of the same specific solutions hereinabove described under this caption was per-formed as follows. Four plates were exposed and developed in the same manner as described in the preceding press test.
Each plate was desensitized using, in four parallel sections on the plate, the gum etch type solutions of Examples 18-GE
through 20-GE and Comparison Run 10. The four identically prepared plates were maintained under ambient conditions for 40 hours and each was then mounted on the press for successive :
; runs. For each run a different one of the four fountain solutions of Examples 18-F through 20-F and Comparison Run 10 was employed. The pressure applied to different ` parts of the plates was again varied using different thicknesses of paper between the plate roller and the plate itself as hereinabove described.
On initial inking, the image areas in those portions of the plates desen~itized with the substitute gum etch solutions of Examples 18-GE through 20-GE accepted ink more readily than those portions treated with the gum arabic counterpart, Comparison Run 10; i.e. there was less initial blinding with the compositions of the present invention.
With each fountain solution, 5000 sheets were printed at a press speed of 4000 sheets per hour.

17,674B-F -39-~070876 With the gum arabic fountain solution, satisfactory results were obtained in 15 of the 16 parts of the plate.
In that portion of the plate which was desensitized with the gum ara~ic solution of Comparison 10 and which was subjected to the highest pressure during the prass run, con-siderable scumming occurred in the half tones.
The fountain solutions of the Examples performed in a manner comparable to one another, and each proved - superior to the gum arabic fountain solution. Less fountain solution of the Examples was required to maintain the proper ink~water balance, and cleaner, better quality half tones were obtained, especially in the high pressure areas, than with the gum arabic fountain solution.
Example 21 A fountain solution similar to that of Example 18-F
was employed in a press run of 60,000 impression6 on newspaper stock using a Harris Cottrell 15A web offset press. Prints of excellent quality were obtained throughout the run. No foaming of the fountain solution occurred, nor was there any indication that the ink was emulsified by the fountain solution. A suitable fountain solution may also obtained by substituting, for example, an equal amount by volume of isopropyl alcohol, propylene glycol, glycerine, diethylene glycol ethyl ether, and the like, for up to about 25 percent `25 of the water employed in solutions such as those described in Examples 18-F through 20-F. In particular, a press run of 60,000 impressions was made on a Harris Cottrell LTZ
printing press using a fountain solution such as Example 18-F except that isopropanol was substituted for about 25 percent of the water.

17,674B-F -40-~070876 Examples 22-27 Several alkaline concentrate and fountain solutions were prepared as summarized in Table V. The particular source of the active polymer component was an 8 percent aqueous solution of partially hydrolyzed (approximately 10 percent) polyacrylamide having a molecular weight of about 250,000, although any of the polymers, copolymers, and blends hereinabove described may be used as well. The fountain solution of Example 26 was successfully employed in a press run of 300,000 impressions on newspaper stock.
The fountain solutions of Examples 22-25 and 27 can be employed in a similar manner.

17,674B-F -41-~0876 u~ In _~ o r~
W : .. ;

~ a:~ ~ >
~ O ~ N
. '1 ~1 _ :
~i .
01~

: '~n O P~ U~ o o o ~ O
O O ~D ~ ~ C~ CO a~
U~ r~
t~ . .~
. ~ ' ~
O~ O O O
O~r tTl ~
. K~ tn ~ ~ N

~ .1 Z O
~ Z

~1 _I
O O
~U~
O
~) O N ~ ~r In ~D 1~
~i N N N N N N

17, 674B-F -42-Exampl ~ n Runs 11-14 Solutions containing a blend of hydroxypropyl methylcellulose ("HPMC" in the table which follows) and par-tially hydrolyzed (about 10 percent) polyacrylamide having a molecular weight of about 250,000 were prepared, adjusted to a pH of 4.5 with sulfuric acid, and evaluated using the laboratory scumming test. Results are tabulated in '~ Table VI.

'' ,;, ;.

17,674B-F -43-, . .. ..

~7~76 ~n S~ ~
~ ~ o N t~
I` U~ ~-I 0 ~1 S U~ O-~ d 3 b o~S ~o~ o~ o~
o ~ ~ o o~q o ~nO ~ ~ ~ e~ o rl q~ O q~
o ,, o ~ n ~o o ~Q
0~ d O ~ ~ ~ O ~ ~
P ~ ~S~ :~ ~ ~ P In P~

Ul O O O O tN 1~ N O O ~ ~r O
o 8 ". o ~ ." ~ ~ rl .. , N r` O
E-~ :~
O
U~
, U-P ~ u~
h ~ ~1 C~lN N N ~ D O u~\ Ul ~ Q~ ,~ O ~1 ~
P~ ~
m _ m ~o a~
o ~ OU~ O U~ O U~ O U~U~ O Ln o rl _I ~ t` Il) N ~ ~ 1~1~ 1~ 0~ r`
0~ ~ O11~ 0It~ O ~ O1~ ~ O 11 ~I NIt'l1` --I N u~N N _I N
~e;

~ .
~0 W O . . . . .. .
dP~J ~ I N t~l O O O
N
EL~-rl ~p 4ol _I N t" ~r coa~ o _I~I N
NN~ ~ ~ ~ '~') X X P P; X ~ ~ X X W X P~
~ ~Y ~d U U ~ W U ~ ~ ~ U

17, 674B-F -44-1CI37~876 Example 36 Fountain solutions containing hydroxypropyl methyl-cellulose are prepared in a manner similar to the fountain solutions described in Examples 18-F through 20-F by employing solutions such as those of Examples 28-35 in lieu of the solutions in Examples 18-20. As a specific example, 0.5 ounce (14.8 ml) of a solution such as that of Example 29, except containing 8 percent solids and having a viscosity of 165 cP, was admixed in 1 gallon (3.785 liters) of water with 1 fluid ounce (29.6 ml) of an etch concentrate com-parable to that described in the preparation of Examples 18-F through 20-F, to form a fountain solution which was used in the printing of excellent quality prints of an ANPA Faximile Test Sheet on an offset press.
Example 37 Another fountain solution is prepared by dissolving in 1 liter of water, about 4 milliliters of an "A" solution, hereinafter described, and about 8 milliliters of a "B" solution, also hereinafter described, and about 4 milliliters of the solutions of any of Examples 1-17, 18, 19, 20, and 28-35. The ~A" solution comprises 1 liter of water, about 45 grams of ammonium bichromate, and about 24 ml of 85~ phosphoric acid. The "B" solution comprises about 120 grams of magnesium or zinc nitrate dissolved in 1 liter of water.
Example 38 A plate was treated as described in the laboratory scumming test with a solution such as that of Example 31, except containing 8 percent total active polymer component and having a solution viscosity of 165 cP. After storage for one month 17,674B-F -45-~70876 r at ambient temperature and humidity, the plate was inked.
No scumming was detected.
Examples 39-42 An "A" solution having a pH of 12.3 was prepared S by dissolving 7 grams of Na3PO4-12H2O in 100 grams water.
A "B" solution having a pH of 10.65 was prepared by dissolving

6 grams Na3PO4-12H2O in 100 grams of an aqueous solution initially adjusted to pH 4.5 and containing 6.5 weight percent partially (about 10%~ hydrolyzed polyacrylamide having an average molecular weight of about 250,000. Four alkaline aqueous fountain concentrates were prepared by combining solutions "A" and "B" in different proportions as summarized in Table VII.
TABLE VII

Weight Ratio A/B pH
Ex. 3910/1 12.15 Ex. 4010/3 12.0 Ex. 412/1 11.85 Ex. 421/1 11.6 Sixteen fountain solutions were prepared by diluting 0.5 fluid ounce (14.8 ml), 1 oz (29.6 ml), 2 oz (59.1 ml), and 3 oz (88.7 ml) of each of the four concentrates to 1 gallon (3.785 liters) with water. The pH of each of the resulting fountain solutions is shown in Table VIII.
TABLE VIII
Amount of Each Source of Concentrate ---Concentrate---Diluted to One Gallon Ex.39 Ex.40 Ex.41 Ex.42 0.5 oz 11 10.87 10.7 10.58 1 oz 11.35 11.28 11.15 11 2 oz 11.6 11.55 11.45 11.28 3 oz 11.73 11.65 11.55 11.38 17,674B-F -46-~7~876 Example 43 An alkali solution comparable to that prepared as described in the preceding set of examples by diluting one ounce of the concentrate of Example 39 to one gallon was employed as the fountain solution throughout a press run of about 300,000 impressions on newspaper stock using a Harris Cottrel 15A web offset press. Impressions of high quality were obtained throughout the run, except for a small quantity of unsatisfactory impressions obtained immediately after periods of brief shut down which is normal for alkaline fountain solutions. No significant foaming of the fountain solution was encounted during the run.
Comparison Runs 15 and 16 In Example 2 of British Patent 1,055,711, here-inabove discussed, an approximately 1 weight percent solution of medium viscosity polyacrylamide was employed to form the colloid top layer described therein. A 5 percent aqueous solution of the polyacrylamide of the type employed therein was taught to have a viscosity at 25C
of between 280 and 600 cP.
For Comparison Run 15, a 5 weight percent aqueous solution of polyacrylamide was prepared, which had a viscosity of 3 55 cP at ambient temperature. The pH of the solution was 7.19. For Comparison Run 16, a portion of the solution of Comparison Run 15 was diluted with water to obtain a 1 weight percent solution. The latter had a viscosity of 15 cP and a pH of 7.15.
Two substantially identical image-bearing plates were treated according to the laboratory scumming test 17,674B-F -47-1~70876 procedure with the respective compositions of Comparison Runs 15 and 16. To assure that any scumming which might be observed with the Comparison compositions could not be attributed to defects in the plates or other extraneous S factors, a third substantially identical image-bearing plate was treated with a composition which was substantially that of Example 6, i.e., an 8 weight percent solution of a polyacrylamide-based polymer having a carboxyl group at approximately 10 percent of the carbonyl sites. When inked 24 hours later, the plate treated with the 5 percent solution of Comparison Run 15 showed severe scumming, and that treated with the 1 percent solution of Comparison Run 16 was much worse still. That plate treated according to the present invention showed no evidence of scumming whatsoever.
Although the solution employed according to the present invention happened to be an 8 percent solution whereas those employed in the Comparison Runs were but 5 and 1 percent, that alone does not account for the remarkable difference in performance since as is described in Example 13, no scumming was observed, even after 96 hours, when a plate was treated with a 4 percent solution according to the present invention.

17,674B-F -48-

Claims (105)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for the treatment of an image-bearing lithographic printing plate to render hydrophilic the non-image areas of the plate, comprising applying to the image-bearing plate an aqueous solution comprising water and an active polymer component selected from (a) a polyacrylamide-based polymer wherein from 3 to 70 percent of the carbonyl sites are carboxyl groups and the balance of said sites are amide moieties;
(b) a physical blend comprising from 97 to 30 weight percent polyacrylamide and from 3 to 70 weight percent poly-acrylic acid or an alkali metal or ammonium salt thereof;
(c) a physical blend comprising polyacrylamide, or polyacrylic acid or an alkali metal or ammonium salt thereof, and at least one polyacrylamide-based polymer as described in (a), said polymers being employed in proportions such that of the total carbonyl sites present in the blend are from 3 to 70 percent carboxyl groups and the balance are amide moieties;
(d) a mixture of any two or more of the fore-going;
the average molecular weight of each of said polyacrylamide--based polymer, polyacrylamide, and polyacrylic acid or salt thereof being in the range of from 5000 to 1,000,000; or (e) a co-mixture of one or more of the foregoing with up to 30 weight percent hydroxypropyl methylcellulose based on the total weight of the co-mixture, said hydroxypropyl methylcellulose being of a type which produces a 2 weight percent aqueous solution having a viscosity of from 1 to 100 cP when measured according to ASTM Method D 2363-72;
said solution being applied in an amount sufficient to render substantially all the non-image areas hydrophilic.

2. The method of Claim 1, wherein the active polymer component is item (e), and the hydroxypropyl methylcellulose comprises from 10 to 25 per cent by weight of the total active polymer component.

3. The method of Claim 1, wherein the average molecular weight of each of the polyacrylamide based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is within the range of from 10,000 to 500,000.

4. The method of Claim 3, wherein the average molecular weight of the recited components is in the range of from 25,000 to 300,000.

5. The method of Claim 4, wherein the active polymer component is item (e), and the hydroxypropyl methylcellulose comprises from 10 to 25 percent by weight of the total active polymer component.

6. The method of Claim 1, wherein from 5 to 50 percent of the carbonyl sites in the active polymer component are carboxyl groups.

7. The method of Claim 6 wherein of the carbonyl sites in the active polymer component, from 5 to 25 percent are carboxyl groups.

8. The method of Claim 7 wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is in the range of from about 25,000-300,000.

9. The method of Claim 7 wherein the active polymer component is item (e), and the hydroxypropyl methylcellulose comprises from 10 to 25 percent by weight of the total active polymer component.

10. The method of Claim 1, wherein the aqueous solution contains from 0.001 to 30 percent active polymer component.

11. The method of Claim 10, including a pre-liminary step of diluting with water a concentrated aqueous solution containing the active polymer, to obtain the solution applied to the plate.

12. The method of Claim 10, wherein the aqueous solution contains from 3 to 30 percent active polymer component.

13. The method of Claim 12, wherein the solution contains gum arabic, the active polymer being employed as an extender for the gum arabic.

14. The method of Claim 12, wherein the aqueous solution contains from 5 to 12 percent active polymer component; wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is in the range of from 10,000 to 500,000; and wherein of the carbonyl sites in the active polymer component, from about 5 to about 50 percent are carboxyl groups.

15. The method of Claim 14, including a pre-liminary step of diluting with water a concentrated aqueous solution containing the active polymer to obtain the solution applied to the plate.

16. The method of Claim 14, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is within the range of from 25,000 to 300,000, and wherein of the carbonyl sites in the active polymer component, from 5 to 25 percent are carboxyl groups.

17. The method of Claim 16, wherein the solution has a viscosity of from 50 cP to 300 cP.

18. The method of Claim 17, wherein the solution has a pH within the range of from at least 3 to 9.

19. The method of Claim 14, wherein the solution contains gum arabic, the active polymer being employed as an extender for the gum arabic.

20. The method of Claim 12, including a pre-liminary step of diluting with water a concentrated aqueous solution containing the active polymer, to obtain the solution applied to the plate.

21. The method of Claim 12, wherein the solution has a viscosity of from 40 cP to 1000 cP.

22. The method of Claim 21, wherein the solution has a viscosity of from 50 cP to 300 cP.

23. The method of Claim 12, wherein the solution contains up to 4 weight percent of a compound selected from (1) alkali metal phosphates, ammonium phosphates, or mixtures thereof, or (2) phosphoric acid.

24. The method of Claim 23, wherein the phosphorous-containing compound comprises from 2 to 4 weight percent of the solution.

25. The method of Claim 24, wherein the solution contains phosphoric acid and has a pH of from 1 to 3.

26. The method of Claim 25, including a pre-liminary step of diluting with water a concentrated aqueous solution containing the active polymer and phosphoric acid, to obtain the solution applied to the plate.

27. The method of Claim 25, wherein the solution contains gum arabic, the active polymer being employed as an extender for the gum arabic.

28. The method of Claim 25, wherein the aqueous solution contains from 5 to 12 percent active polymer component; wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is in the range of from 10,000 to 500,000; and wherein of the carbonyl sites in the active polymer component, from 5 to 50 percent are carboxyl groups.

29. The method of Claim 28, where the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is within the range of from 25,000 to 300,000, and wherein of the carbonyl sites in the active polymer component, from 5 to 25 percent are carboxyl groups.

30. The method of Claim 29, wherein the viscosity of the solution is from 50 cP to 300 cP.

31. The method of Claim 24, wherein the solution contains an alkali metal phosphate, ammonium phosphate, or mixtures thereof, and wherein the pH of the solution is from 9 to 12.5.

32. The method of Claim 31, wherein the aqueous solution contains from 5 to 12 percent active polymer component; wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is in the range of from 10,000 to 500,000; and wherein of the carbonyl sites in the active polymer component, from 5 to 50 percent are carboxyl groups.

33. The method of Claim 32, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is within the range of from 25,000 to 300,000, and wherein of the carbonyl sites in the active polymer component, from 5 to 25 percent are carboxyl groups.

34. The method of Claim 33, wherein the solution has a viscosity of from 50 cP to 300 cP.

35. The method of Claim 31, including the preliminary step of diluting with water a concentrated aqueous solution containing the active polymer and at least one alkali metal phosphate or ammonium phosphate, to obtain the solution applied to the plate.

36. The method of Claim 12, wherein the solution has a pH of at least 3 up to 9.

37. The method of Claim 10, wherein the solution contains gum arabic, the active polymer being employed as an extender for the gum-arabic.

38. The method of Claim 10, wherein the image bearing plate is treated with a solution comprising, by weight, at least 97 percent solvent and from 0.001 percent to 0.5 percent active polymer, wherein the solvent consists essentially of at least 75 volume percent water and up to 25 volume percent of a compound selected from lower alkyl mono- and polyhydric alcohols or glycol ethers having a molecular weight of 170 or less, or mixtures thereof.

39. The method of Claim 38, wherein the solution contains from 0.0025 to 0.1 weight percent active polymer.

40. The method of Claim 38, wherein the solution contains, in addition, at least one of: phosphoric acid in an amount up to 0.05 weight percent of the solution; a chromium-anion providing agent in an amount up to 0.02 weight percent of the solution; and a metal nitrate in an amount up to 0.25 weight percent of the solution, wherein said metal nitrate is selected from those metal nitrates, the corresponding hydroxide com-pound of which has a solubility product in water at 25°C
of from 10-5 to 10-35, and mixtures thereof.

41. The method of Claim 40, wherein the solution contains gum arabic, and the active polymer is employed as an extender for the gum arabic.

42. The method of Claim 40, including a pre-liminary step of diluting with water a concentrated aqueous solution, to obtain the solution applied to the plate.

43. The method of Claim 40, wherein the solution has a pH of from 3.5 to 5.5.

44. The method of Claim 40, wherein the solution contains from 0.02 to 0.15 weight percent metal nitrate.

45. The method of Claim 40, wherein the solution contains from 0.004 to 0.03 weight percent phosphoric acid.

46. The method of Claim 45, wherein the solution contains from 0.008 to 0.018 weight percent phosphoric acid.

47. The method of Claim 45, wherein the solution contains from 0.02 to 0.15 weight percent metal nitrate.

48. The method of Claim 45, wherein the solution contains at least one metal nitrate and the metal nitrate is selected from those metal nitrates, the corresponding hydroxide compound of which has a solubility product in water of from 10-10 to 10-20.

49. The method of Claim 48, wherein the metal ion of the metal nitrate has a standard reduction potential negative with respect to hydrogen.

50. The method of Claim 49, wherein the metal nitrate is zinc nitrate or magnesium nitrate.

51. The method of Claim 50, wherein the solution contains from 0.04 to 0.1 weight percent magnesium or zinc nitrate and from 0.008 to 0.018 weight percent phosphoric acid.

52. The method of Claim 51, wherein the solution contains from 0.0025 to 0.1 weight percent active polymer.

53. The method of Claim 52, wherein the solution contains ammonium bichromate as the chromium-anion pro-viding agent.

54. The method of Claim 53, wherein the solution contains from 0.01 to 0.02 weight percent ammonium bi-chromate.

55. The method of Claim 50, wherein the solvent consists essentially of at least 75 volume percent water and up to 25 volume percent isopropanol.

56. The method of Claim 55, wherein the solution contains from 0.04 to 0.1 weight percent magnesium- or zinc nitrate and from 0.008 to 0.018 weight percent phosphoric acid.

57. The method of Claim 56, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is from 25,000 to 300,000, and wherein 5 to 25 percent of the carbonyl sites in the active polymer component are carboxyl groups.

58. The method of Claim 56, wherein the solvent consists essentially of water.

59. The method of Claim 38, wherein the solvent consists essentially of water.

60. The method of Claim 38, wherein the aqueous solution contains, in addition, sufficient alkali metal or ammonium phosphate to maintain the solution at a pH
within the range of from 7.5 to 12.

61. The method of Claim 60, wherein the pH of the solution is from 8.5 to 10.

62. The method of Claim 61, wherein the solution contains from 0.01 to 0.06 weight percent of the phosphate compound, and from 0.0025 to 0.1 weight percent active polymer.

63. The method of Claim 62, wherein the solution consists essentially of water, the active polymer and the phosphate compound.

64. The method of Claim 63, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is from 25,000 to 300,000, and wherein from 5 to 25 percent of the carbonyl sites in the active polymer component are carboxyl groups.

65. The method of Claim 60, including the preliminary step of diluting with water a concentrated aqueous solution, to obtain the solution applied to the plate.

66. The method of Claim 1, wherein the solution includes gum arabic and the active polymer component is employed as an extender for the gum arabic.

67. The method of Claim 1, wherein the active polymer component is employed in the aqueous phase of an emulsion for treating lithographic plates.

68. The method of Claim 67, wherein the emulsion is of the asphaltum gum type having (a) a water immiscible phase to maintain the oleophilicity of the image areas of the plate, containing asphaltum gum or gilsonite and a solvent therefor, and (b) an aqueous phase containing an agent for maintaining the hydrophilicity of the non-image areas of the plate.

69. The method of Claim 68, wherein the aqueous phase comprises from 25 to 75 percent, by volume, of the total emulsion.

70. The method of Claim 69, wherein the aqueous phase contains from 3 to 30 weight percent active polymer component.

71. The method of Claim 70, wherein the aqueous phase contains up to 4 weight percent phosphoric acid.

72. The method of Claim 70, wherein the aqueous phase contains from 5 to 12 weight percent active polymer component; wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is from 10,000 to 500,000; and wherein from 5 to 50 percent of the carbonyl sites in the active polymer component are carboxyl groups.

73. The method of Claim 72, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is in the range of from 25,000 to 300,000, and wherein of the carbonyl sites in the active polymer component, from 5 to 25 percent are carboxyl groups.

74. The method of Claim 72, wherein the aqueous phase contains up to 4 weight percent phosphoric acid.

75. The method of Claim 74, wherein the aqueous phase contains from 2 to 4 weight percent phosphoric acid.

76. The method of Claim 75, wherein the average molecular weight of each of the polacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is in the range of from 25,000 to 300,000, and wherein of the carbonyl sites in the active polymer component, from 5 to 25 percent are carboxyl groups.

77. The method of Claim 67, wherein the emulsion is employed for developing a latent image on a photolitho-graphic plate which has been exposed to imagewise modulated light, said emulsion being of the type having (a) a water immiscible phase containing a solvent for selectively removing the non-exposed areas of a negative working photosensitive coating, or the exposed areas of a positive working photosensitive coating, without affecting the respective exposed or non-exposed image areas, and (b) an aqueous phase containing an agent for rendering hydro-philic the non-image areas of the plate.

78. The method of Claim 77, wherein the aqueous phase comprises from 5 to 75 percent of the emulsion, by volume.

79. The method of Claim 78, wherein the aqueous phase of the emulsion contains from 0.1 to 5 weight percent active polymer component.

80. The method of Claim 79, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is in the range of from 25,000 to 300,000, and wherein 5 to 25 percent of the carbonyl sites in the active polymer component, are carboxyl groups.

81. The method of Claim 79, wherein the emulsion contains in addition, one or more of: an agent for rendering easily visible the oleophilic areas of the plate; and an agent for enhancing the properties of the oleophilic areas of the plate with respect to durability or oleophilicity.

82. An image-bearing lithographic printing plate having a coating on the non-image areas of the plate comprised of an active polymer component selected from (a) a polyacrylamide-based polymer wherein from 3 to 70 percent of the carbonyl sites are carboxyl groups and the balance of said sites are amide moieties;
(b) a physical blend comprised of from 97 to 30 weight percent polyacrylamide and from 3 to 70 percent polyacrylic acid or an alkali metal or ammonium salt thereof;
(c) a physical blend comprised of polyacrylamide, or polyacrylic acid or an alkali metal or ammonium salt thereof, and at least one polyacrylamide-based polymer as described in (a), said polymers being employed in proportions such that of the total carbonyl sites present in the blend, from 3 to 70 percent are carboxyl groups and the balance are amide;
(d) a mixture of any two or more of the fore-going; the average molecular weight of each of said polyacrylamide-based polymer, polyacrylamide, and polyacrylic acid or salt thereof being in the range of from 5000 to 1,000,000, or (e) a co-mixture of one or more of the foregoing with up to 30 weight percent hydroxypropyl methylcellulose based on the total weight of the co-mixture, said hydroxypropyl methylcellulose being of a type which produces a 2 weight percent solution having a viscosity of from 1 to 100 cP when measured according to ASTM Method D 2363-72.

83. The coated plate of Claim 82, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and/or the polyacrylic acid or salt thereof comprising the coating, is in the range of from 10,000 to 500,000.

84. The coated plate of Claim 83, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and/or the polyacrylic acid or salt thereof comprising the coating is in the range of from 25,000 to 300,000.

85. The coated plate of Claim 84, in which the active polymer in the coating is the co-mixture of item (e) and hydroxypropyl methylcellulose comprises from 10 to 25 weight percent of the active polymer component.

86. The coated plate of Claim 82, wherein from 5 to 50 percent of the carbonyl sites in the active polymer component are carboxyl groups.

87. The coated plate of Claim 86, wherein of the carbonyl sites, from 5 to 25 percent are carboxyl groups.

88. The coated plate of Claim 87, wherein the average molecular weight of each of the polyacrylamide-based polymer, the polyacrylamide, and/or the polyacrylic acid or salt thereof comprising the coating is in the range of from 25,000 to 300,000.

89. The coated plate of Claim 87, wherein the active polymer component in the coating is the co-mixture of item (e), and hydroxypropyl methylcellulose comprises from 10 to 25 weight percent of the active polymer component.

90. The coated plate of Claim 82, wherein the coating contains, in addition, one or more of: a compound selected from the group consisting of (1) phosphoric acid and (2) alkali metal phosphates and ammonium phosphates and mixtures thereof; a chromium providing agent, or a metal nitrate, said metal nitrate being selected from those metal nitrates, the corresponding hydroxide compound of which has a solubility product in water of from 10-5 to 10-35.

91. The coated plate of Claim 90, wherein the metal nitrate is magnesium or zinc nitrate, and wherein the chromium providing agent is ammonium bichromate.

92. The coated plate of Claim 91, wherein 5 to 25 percent of the carbonyl sites in the active polymer component are carboxyl groups, and wherein the average molecular weight of each of the polyacrylamide based polymer, the polyacrylamide, and/or the polyacrylic acid or salt thereof is within the range of from 25,000 to 300,000.

93. An aqueous solution for rendering hydro-philic, the non-image areas of an image-bearing litho-graphic printing plate which comprises: water; a phos-phate compound selected from (1) alkali metal phosphates, ammonium phosphate, or mixtures thereof, and (2) phos-phoric acid; and the active polymer component being selected from (a) a polyacrylamide-based polymer wherein from 3 to 70 percent of the carbonyl sites are carboxyl groups and the balance of said sites are amide moieties, (b) a physical blend comprised of from 97 to 30 weight percent polyacrylamide and from 3 to 70 weight percent polyacrylic acid or an alkali metal or ammonium salt therof (c) a physical blend comprised of polyacrylamide, or polyacrylic acid or an alkali metal or ammonium salt thereof, and at least one polyacrylamide-based polymer as described in (a), said polymers being employed in proportions such that of the total carbonyl sites present in the blend, from 3 to 70 percent are carboxyl groups and the balance are amide moieties, (d) a mixture of any two or more of the fore-going, the average molecular weight of each of said polyacrylamide--based polymer, polyacrylamide, and polyacrylic acid or salt thereof being in the range of from 5000 to 1,000,000, or (e) a co-mixture of one or more of the foregoing with up to 30 weight percent hydroxypropyl methylcellulose based on the total weight of the co-mixture, said hydroxypropyl methylcellulose being of a type which produces a 2 weight percent aqueous solution having a viscosity of from 1 to 100 cP when measured according to ASTM Method D 2363-72.

94. A concentrated aqueous solution comprising:
water; a phosphate compound selected from (1) alkali metal phosphates, ammonium phosphate, or mixtures thereof, or (2) phosphoric acid; and an active polymer component selected from (a) a polyacrylamide-based polymer wherein from 3 to 70 percent of the carbonyl sites are carboxyl groups and the balance of said sites are amide moieties, (b) a physical blend comprised of from 97 to 30 weight percent polyacrylamide and from 3 to 70 weight percent polyacrylic acid or an alkali metal or am-monium salt thereof, (c) a physical blend comprised of polyacrylamide, and at least one polyacrylamide-based polymer as described in (a), the polyacrylamide and polyacrylamide-based polymers being employed in proportions such that of the total carbonyl sites present in the blend, from 3 to 70 percent are carboxyl groups and the balance are amide moieties, (d) a mixture of any two or more of the fore-going, the average molecular weight of each of said polyacrylamide--based polymer, polyacrylamide, and polyacrylic acid or salt thereof being in the range of from about 5000 to 1,000,000, or (e) a co-mixture of one or more of the foregoing with up to 30 weight percent hydroxypropyl methylcellulose based on the total weight of the co-mixture, said hydroxypropyl methylcellulose being of a type which produces a 2 weight percent aqueous solution having a viscosity of from 1 to 100 cP when measured ac-cording to ASTM Method D 2363-72;
said concentrate, when diluted with additional water pro-viding a solution containing from 0.001 to 30 weight percent of the active polymer component, which diluted solution is suitable for rendering hydrophilic the non--image areas of an image-bearing lithographic plate.

95. A composition for developing a latent image on a photolithographic plate which has been exposed to imagewise modulated light, of the emulsion type having (1) a water immiscible phase containing a solvent or selectively removing the non-exposed areas of a negative working photosensitive coating, or the exposed areas of a positive working photosensitive coating, without affecting the respective exposed or non-exposed image areas, and (2) an aqueous phase containing an agent for rendering hydrophilic the non-image areas of the plate, the aqueous phase comprising an active polymer component selected from (a) a polyacrylamide-based polymer wherein from 3 to 70 percent of the carbonyl sites are carboxyl groups and the balance of said sites are amide moieties;
(b) a physical blend comprised of from 97 to 30 weight percent polyacrylamide and from 3 to 70 weight percent poly-acrylic acid or an alkali metal or ammonium salt thereof;
(c) a physical blend comprised of polyacrylamide, or polyacrylic acid or an alkali metal or ammonium salt thereof, and at least one polyacrylamide-based polymer as described in (a), said polymers being employed in proportions such that of the total carbonyl sites present in the blend, from 3 to 70 percent are carboxyl groups and the balance are amide moieties;
(d) a mixture of any two or more of the fore-going;
the average molecular weight of each of said polyacrylamide--based polymer, polyacrylamide, and polyacrylic acid or salt thereof being in the range of from 5000 to 1,000,000 or (e) a co-mixture of one or more of the foregoing with up to 30 weight percent hydroxypropyl methylcellulose based on the total weight of the co-mixture, said hydroxypropyl methylcellulose being of a type which produces a 2 weight percent aqueous solution having a viscosity of from 1 to 100 cP when measured according to ASTM Method D 2363-72.

96. The developer emulsion of Claim 95, wherein the aqueous phase comprises from 5 to 75 percent of the total emulsion, by volume.

97. The developer emulsion of Claim 96, wherein the aqueous phase comprises from 0.1 to 5 percent by weight active polymer component.

98. The developer emulsion of Claim 97, wherein 5 to 50 percent of the carbonyl sites in the active polymer component are carboxyl groups.

99. The developer composition of Claim 97, con-taining in addition one or more of (A) an agent for rendering easily visible the oleophilic areas of the plate, and (B) an agent for enhancing the properties of the oleophilic areas of the plate with respect to durability or oleophilicity.

100. A composition for treating lithographic plates, of the emulsion type having (i) a water immiscible phase for maintaining the oleophilicity of the image areas of the plate, containing asphaltum gum or gilsonite and a solvent therefor, and (ii) an aqueous phase containing an agent for maintaining the hydrophilicity of the non--image areas of the plate, the aqueous phase comprising an active polymer component selected from (a) a polyacrylamide-based polymer wherein from 3 to 70 percent of the carbonyl sites are carboxyl groups and the balance of said sites are amide moieties;
(b) a physical blend comprised of from 97 to 30 weight percent polyacrylamide and from 3 to 70 percent poly-acrylic acid or an alkali metal or ammonium salt thereof;
(c) a physical blend comprised of polyacrylamide, or polyacrylic acid or an alkali metal or ammonium salt thereof, and at least one poly-acrylamide-based polymer as described in (a), said polymers being employed in proportions such that of the total carbonyl sites present in the blend, from 3 to 70 per-cent are carboxyl groups and the balance are amide moieties;
(d) a mixture of any two or more of the fore-going;
the average molecular weight of each of said polyacrylamide--based polymer, polyacrylamide, and polyacrylic acid or salt thereof being in the range of from 5000 to 1,000,000; or (e) a co-mixture of one or more of the foregoing with up to 30 weight percent hydroxypropyl methylcellulose based on the total weight of the co-mixture, said hydroxypropyl methylcellulose being of a type which produces a 2 weight percent aqueous solution having a viscosity of from 1 to 100 cP when measured according to ASTM Method D 2363-72.

101. The emulsion of Claim 100, wherein the aqueous phase comprises from 25 percent to 75 percent of the total emulsion, by volume.

102. The emulsion of Claim 101, wherein the active polymer component is item (e) and hydroxypropyl methylcellulose comprises from 10 to 25 weight percent of the total active polymer component, by weight.

103. The emulsion of Claim 101, wherein the aqueous phase comprises from 3 to 30 percent by weight active polymer component.

104. The emulsion of Claim 103, wherein the aqueous phase contains, in addition, up to 4 weight percent phosphoric acid.

105. The emulsion of Claim 103, wherein the aqueous solution comprises from 5 to 12 weight percent active polymer component; wherein the average molecular weight of each of the polyacrylamide--based polymer, the polyacrylamide, and the polyacrylic acid or salt thereof is from 10,000 to 500,000; and wherein of the total carbonyl sites in the active polymer component, from 5 to 50 percent are carboxyl groups.