Process Of Using Multi-purpose Lithographic Solution

Abstract

A multi-purpose lithographic solution is provided adapted for use in concentrated form and in different ratios of aqueous dilution as conversion, start-up, fountain solution, or the like for a plurality of different types of planographic printing masters, such as electrostatic, direct-image, and photographic planographic masters, both projection speed and conventional. The solution preferably comprises glycerin, monosodium phosphate, potassium ferrocyanide, and water as solvent. The amounts of the dissolved components in the concentrated form must be present within fairly narrow ranges. Similarly, when the concentrated solution is diluted for use, for example as a fountain solution, the dilution with water must be carried out in definite ratios of concentrated solution to water.

Description

BACKGROUND OF THE INVENTION

Planographic printing involves the preparation of a printing plate having water-receptive, non-image or non-print areas and water-repellent, ink-receptive areas constituting the image to be reproduced. In use, the plate is moistened by a water-base liquid which is repelled by the image areas but maintains the non-image areas ink repellent. When printing ink is applied to the plate, the ink-receptive image areas are coated but the water-receptive, non-image areas repel the ink. Ink from the image areas only is then transferred to a suitable copy sheet to reproduce the image. The process is repeated as often as desired up to the life of the planographic plate.

Various lithographic solutions are used in the preparation and/or treatment of planographic masters prior to a run on a printing press as well as while the master is being used to print a desired image as described. For example, start-up solutions are used to prepare a master for subsequent printing, while fountain solutions maintain the non-image areas moist to repel the ink during a printing operation. At present, such solutions can differ substantially in composition depending on how they are to be used and on what type of master. It has long been an objective in the planographic art to realize a single lithographic solution for substantially universal application, that is, one which might be applied to all types of planographic masters and for different functions, such as a conversion, start-up, or fountain solution.

There are in current use three basic types of planographic printing plates or masters: electrostatic, direct-image, and photographic planographic masters. To prepare an electrostatic planographic master, for example, a recording element is prepared by coating a surface of a suitable backing with a photo-conducting, insulating material such as zinc oxide dispersed in an electrically-insulating, film-forming, water-insoluble material such as a silicone resin. An electrostatic charge is produced over the entire surface of the material, and a light image is focused on the charged surface, thereby discharging those portions irradiated by the light rays while leaving the remainder of the surface in a charged condition. This forms an electrostatic image. The image is rendered visible by next applying a developer powder which is held electrostatically to the charged areas of the sheet. The powder image so formed may be fixed directly to the photo-conductive coating, or it may be transferred to another surface upon which the reproduced image may then be fixed.

The developer powder used to prepare the electrostatic planographic master is a hydrophobic material. Upon fixing the powder image to the photo-conducting coating, the resulting element may be used for lithographic printing after treatment with a known converter solution.

A direct-image planographic master usually comprises a paper or plastic base having a coating of a finely divided filler or pigment such as clay and an adhesive, hydrophilic colloid such as casein which serves as a binder. The direct-image master is prepared for printing by directly marking on the master as by typing, drawing, marking, or the like, to form image areas.

An oleophilic design on a hydrophilic surface may also be obtained by photographic means, for example, by differentially hardening a light sensitive organic colloid layer on a lithographic surface with actinic rays and removing the unhardened areas to bare hydrophilic non-printing areas. A "projection speed" method for preparing a photographic planographic printing plate is described in Yackel et al. U.S. Pat. No. 3,146,104, issued Aug. 25, 1964, which provides formation of a developable silver halide image, as by exposure to a line or halftone subject, of a hydrophilic, organic colloid-silver halide film such as a gelatino-silver halide sensitized plate, followed by silver halide development. No additional steps, such as etching or washing off the unhardened areas, are required for producing the plate. Moreover, the process in its various forms can be adapted to the production of positive plates from either positive or negative subjects.

This process is popularly known by the trademark "PHOTO-DIRECT," owned and registered by Addressograph-Multigraph Corporation. Hereinafter, the term "photographic master" is used to designate this type of planographic master.

Previously, the fountain, conversion, rubbing, start-up solutions, etc., were formulated for use with a particular type of printing plate in mind and were not generally suitable for universal use on all types of planographic masters and for different purposes. As a result, solutions already present in a printing press must be removed and replaced whenever a change to a different type of planographic master is desired, causing loss of valuable down time on the press.

SUMMARY OF THE INVENTION

In accordance with the present invention, a multi-purpose lithographic solution is provided that can be compatibly used, either in concentrated or diluted form, with various types of planographic masters and especially with electrostatic, direct-image, and photographic planographic masters. The present solution can be used as a conversion solution or start-up solution or a rubbing solution, where those are needed, as well as being used as a fountain solution. It is, therefore, not necessary to change a solution in a press each time it is desired to use a different type of planographic plate.

In a preferred embodiment, the present lithographic solution adapted for such interchangeable use comprises in concentrated form, by weight per cent, an aqueous solution of 20 per cent glycerin, 15 per cent monosodium phosphate, and 2 per cent potassium ferrocyanide. These amounts can be varied only slightly, as hereinafter described, and still obtain an effective solution as herein contemplated. Similarly, when the concentrated form of the solution is diluted with water for other lithographic applications, the dilution must be made within relatively narrow ranges of volumetric ratios of the concentrated solution to water.

The concentrated solution is used as a conversion solution for electrostatic masters and as a start-up solution for direct-image masters and photographic masters, even though the concentrated form of the solution causes temporary blindness in photographic masters.

The concentrated solution, diluted about one volumetric part of solution to about 0.5 part to 1.5 volumetric parts of water, may be used as a rubbing solution for blinded photographic masters which surprisingly removes the temporary blindness.

The concentrated solution, diluted about one volumetric part of solution to about 2.5 to about 3.5 volumetric parts of water, may be used as a fountain solution for any of the electrostatic, direct-image, or photographic planographic masters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, a solution having the varied application and interchangeability sought comprises the following in weight per cent:

Component Range __________________________________________________________________________ Glycerin 18 to 22 Buffered, ionizable, hydrogen-containing alkali metal phosphate 14 to 18 Alkali metal ferrocyanide 1 to 3 Water Balance __________________________________________________________________________

A preferred embodiment comprises the following in weight per cent:

EXAMPLE 1

Component Per Cent __________________________________________________________________________ Glycerin 20 Monosodium phosphate 15 Potassium ferrocyanide 2 Water Balance __________________________________________________________________________

Optionally, from about 0.1 to about 1.5 weight per cent of a sequestering agent may be included to reduce the tendency of a blue precipitate to form from the ferrocyanide radical on standing or aging of the solution. Various materials may be used for this purpose such as the tetrasodium salt of ethylene diamine tetraacetic acid. Addition of a sequestering agent may be accompanied by a corresponding reduction in the amount of water. Another exemplary composition of the present solution and one which includes a sequestering agent comprises the following in weight per cent:

EXAMPLE 2

Component Per Cent __________________________________________________________________________ Glycerin 20 Monosodium phosphate monohydrate 17.25 Postassium ferrocyanide 2 Ethylene diamine tetrasodium acetate 0.10 __________________________________________________________________________

The ethylene diamine tetrasodium acetate may be purchased as a powder under the trademark VERSENE.

The glycerin hydrophilic as a humectant. As such, in view of its hygroscopic character and its aid to viscosity, the glycerin keeps clean the hydrophilic non-image areas of a master. In the case of direct-image masters having paper backs, the glycerin also retains the solution on the surface of a master and prevents it from soaking into the paper which can result in curling of the master.

Similarly, the glycerin retains the phosphate ion of the alkali metal phosphate, hereinafter described, on the non-image areas of a master where it can perform its useful and intended functions. Accordingly, it is desirable to have as much humectant present as possible, as long as the functions of the other components are not adversely affected. Particularly desirable is a high weight ratio of the phosphate ion to a humectant, so that the best features of both components are happily combined.

Although in some lithographic solutions and especially fountain solutions, other materials have been substituted for glycerin, such as ethylene glycol and diethylene glycol, such substitution is not possible with the present solutions. The desired results are obtained only when glycerin is used as the humectant.

It is known that the phosphate ion, .tbd.PO.sub.4, is admirably suited for maintaining the non-image areas of a master in a hydrophilic condition. The effect of the phosphate ion, as well as the latitude of application of a solution containing it, particularly a concentrate, are directly related to the amount of phosphate ion that can be dissolved. Not many phosphate compounds are water soluble. Those that are have such a limited solubility in glycerin-water solution that for a relatively concentrated solution, such as that contemplated for the present solution concentrate, not enough phosphate can be dissolved to meet the objective sought. On the other hand, phosphoric acid, H.sub.3 PO.sub.4, is readily soluble in water. In this case, however, dissolving enough acid to produce the desired amount of phosphate ion in a concentrate renders the solution so strongly acidic that it is impractical for use.

To place by dissolution sufficient quantities of the phosphate ion in the solution concentrate without unduly lowering the acid pH, a buffered phosphate compound is used. Although U.S. Pat. No. 3,398,002 to Bondurant et al teaches that monoammonium phosphate can be used in the fountain solution of that patent in place of monosodium phosphate, monoammonium phosphate is not useful in the present solutions. It cannot provide the phosphate solubility requirements. More seriously, when ammonium phosphate contacts a photographic master, the master picks up ink throughout the plate, in both image and non-image areas.

Instead, in the present solutions, buffered alkali metal phosphate salts, such as sodium and potassium phosphates, that still contain an ionizable hydrogen atom, are used. Although di-substituted phosphoric acid salts, such as disodium acid phosphate, may be used, it is preferred to use the mono-substituted salts because of the required pH values. The preferred buffered phosphate compound is monosodium phosphate. The hydrated form of an alkali metal acid phosphate may be used to promote the dissolving action.

Although the alkali metal ferrocyanide may be sodium ferrocyanide, it is preferred to use potassium ferrocyanide. Usually potassium ferrocyanide trihydrate is used to facilitate its dissolution in the water solvent. As indicated, it is because of the ferrocyanide component that a sequestering agent is desirably used if the solution is apt to stand for an extended period of time. The ferrocyanide ingredient is apt to decompose and form a ferro-ferrocyanide compound which, in the absence of a sequestering agent, can form a blue precipitate.

To prepare a solution of the present invention, the indicated components may be added to water, which preferably is distilled water, in any order desired with accompanying stirring until solution is obtained. In general, the buffered, ionizable, hydrogen-containing alkali metal phosphate, the alkali metal ferrocyanide, and the sequestering agent, when one is used, are added together to the water which is then stirred until all components are dissolved. The glycerin is next added with continued stirring until homogeneity is obtained. Preferably, the pH of the solution is adjusted to about 4.0 at 25.degree. C. by adding either ammonium hydroxide or phosphoric acid as may be necessary. One solution prepared with the composition of Example 1 had a specific gravity of 1.180 to 1.190 at 25.degree. c./4.degree. C. and a pH of 3.9 to 4.10 at 25.degree. C. For shipment to a point of use, the present solutions may be packaged in translucent brown polyethylene containers.

The amounts of the components of the present concentrated solutions can be varied surprisingly little and still obtain the desired universal applicability. The same is true with respect to the volumetric ratios of concentrated solution to water in diluting the former for various applications as herein described.

Arbitrarily beginning the use of the present solutions with an electrostatic master, the solution is used initially in concentrated form, that is, as first given, supra, to convert the master. It is the ferrocyanide radical which converts an electrostatic master for use in a printing press. Prior to conversion, both the image and non-image areas of an electrostatic master are hydrophobic and oleophilic. During conversion, the ferrocyanide radical reacts with the photo-conductive metal in the non-image areas, such as zinc oxide, which has not been affected by the hydrophobic electrostatic developer powder, and renders the non-image areas hydrophilic and oleophobic by depositing, for example, zinc ferrocyanide. Thereafter, another portion of the concentrated solution is diluted about one volumetric part of the solution to about 2.5 to about 3.5 volumetric parts of distilled water, and the resulting diluted solution operates well as a fountain solution for the same electrostatic master. The preferred ratio of concentrated solution to water for this purpose is 1 to 3, respectively.

The acceptable use of a solution containing a ferrocyanide in contact with a photographic planographic master is most surprising. Indeed, such a master does go blind, that is, the image areas do not pick up ink after initial contact with the present solutions. More particularly, if a fountain solution of the present concentrated solution, diluted about one volumetric part to about 2.5 to 3.5 volumetric parts of distilled water, is used on a photographic planographic master, the master goes blind and does not pick up ink. However, if the present concentrated solution is diluted about one volumetric part of solution to about 0.5 to 1.5 volumetric parts of water, and the solution so diluted is worked as by rubbing into the image areas of the photographic planographic master; the master unexpectedly operates well thereafter even though the same fountain solution is used, that is, the present concentrated solution diluted with water in a volumetric ratio of about 1:2.5 to 3.5. The preferred ratio for the rubbing solution is one volumetric part of concentrated solution to one volumetric part of water.

The reason for this reversal of results is not clear. It may be that the rubbing operation works sufficient ink, which is on the plate from the attempted start-up operation, into the image areas without affecting the hydrophilic background and that the present solutions, diluted 1:2.5 to 3.5 with water, are thereafter compatible with the operation of such a plate. The dilution of the rubbing or working solution into the approximate 1:0.5 to 1.5 volumetric ratio is important. If, for example, a concentrated solution is used to rub the plate, or if such solution is diluted 1:2.5 to 3.5 as for a fountain solution, the described results for a photographic planographic master are not obtained.

If a direct-image master is to be used, the concentrated solution (undiluted) is used as a start-up solution. Thereafter, a concentrated solution is diluted about one volumetric part of solution per about 2.5 to 3.5 volumetric parts of distilled water, and the solution so diluted then used as a fountain solution for the direct-image master.

The following examples are intended to illustrate the invention and should not be construed as limiting the claims. Percentages are by weight.

EXAMPLE 3

An electrostatic master was mounted in a standard offset printing press for planographic masters. The electrostatic master had a paper back coated with a photo-conducting composition including about 100 to 900 parts by weight of photo-conducting zinc oxide and about 100 parts by weight of a vehicle consisting essentially of about 5 per cent to about 25 per cent of zinc acetate and about 95 per cent to about 75 per cent of resinous polyvinyl alcohol. An electrostatic image had been formed and developed in a known manner.

The electrostatic master was contacted on the printing press with the concentrated solution of Example 1. The potassium ferrocyanide reacted with the zinc oxide in the non-image areas and converted them to hydrophilic and oleophobic areas. The solution did not change the character of the image areas which remained hydrophobic and oleophilic.

Thereafter, the printing press was provided with a fountain solution consisting essentially of the composition of Example 1 diluted about one part of the solution to about three parts of distilled water by volume. The printing press ran continuously and produced an acceptable long run of copies from the converted electrostatic master.

EXAMPLE 4

The electrostatic master was removed from the printing press of Example 3 and replaced by a photographic planographic master. This master had been produced in accordance with the teachings of Yackel et al U.S. Pat. No. 3,146,104 and involved the formation of a silver halide image. The fountain solution was not drained from the printing press of Example 3 but was allowed to remain. When the press was started, the fountain solution and ink were sequentially applied to the photographic master in the usual manner. As anticipated the master ran blind after a few impressions because of the presence of potassium ferrocyanide.

The press was then stopped and the photographic master rubbed with a solution corresponding to the composition of Example 1 diluted in substantially equal volumetric parts with distilled water. This appeared to cause the image areas to take some of the ink which had been left on the plate by the initial run. Thereafter, the press was restarted and ran well, although the fountain solution was the same which had been used in Example 3 and which was initially used in this example, namely, the composition of Example 1 diluted about one volumetric part to about three volumetric parts of water.

These results of a successful run were quite surprising, especially in view of the fact that varying the amount of dilution or concentration of the present solutions in either direction produced undesirable results At higher concentrations of the solutions, the entire master became ink-receptive; while at lower concentrations than those described the image remained blind.

EXAMPLE 5

The photographic planographic master of Example 4 was removed from the printing press of Examples 3 and 4 and replaced by a direct-image master. This master comprised a kraft paper backing having a coating of finely divided clay and an adhesive hydrophilic colloid of finely divided clay and an adhesive hydrophilic colloid of guar gum which served as a binder. The direct-image master contained as an image typing legend extending across the master. The master was first contacted with the concentrated solution of Example 1, that is, undiluted, as a start-up solution. Thereafter, the same fountain solution was used as that previously employed, namely, the solution of Example 1 diluted one volumetric part to three volumetric parts of distilled water. The printing press produced many acceptable copies from the direct-image master.

For best results when interchanging the above-indicated types of masters, it is recommended that the electrostatic master should be converted in an Addressograph-Multigraph Converter. PHOTO-DIRECT masters should be processed in the normal manner.

The present concentrate solution is a shippable commodity which can be diluted, if and when desired, at a point of application for use with a plurality of different types of masters without losing its ability to perform in the manner indicated.

The present solutions, either in concentrated or diluted form as described, serve as a converter solution for electrostatic masters; as a start-up solution for direct-image and photographic masters; as a rubbing solution to remove the temporary blindness imparted thereby to photographic masters; and as a fountain solution for all three types of planographic masters.

Although the foregoing describes several embodiments of the present invention, it is understood that the invention may be practiced in still other forms within the scope of the following claims.

Claims

What is claimed is:

1. In a process of printing with a photographic planographic master having an image formed from a developable silver halide, the steps of contacting said master with a solution consisting essentially in weight per cent of:

2. In a process of using sequentially in any order desired on the same printing press a plurality of types of planographic masters including electrostatic, direct-image, and photographic planographic masters without having to remove fountain solution from said press or otherwise prepare it for a change from one type of planographic master to another, the improvements comprising:

a. first applying to any of said masters a lithographic solution consisting essentially in weight per cent of:

wherein said alkali metal ferrocyanide is selected from the group consisting of potassium ferrocyanide and sodium ferrocyanide, thereby causing temporary blindness in said photographic master,

b. using said solution diluted about one volumetric part of solution to about 0.5 to 1.5 volumetric parts of water as a rubbing solution to remove said blindness, and

c. thereafter using said solution in dilution as a fountain solution for any of said planographic masters.