US3522062A - Treating solution for planographic printing plates made with electrophotographic recording papers - Google Patents

Description

United States Patent O 3,522,062 TREATING SOLUTION FOR PLANOGRAPHIC PRINTING PLATES MADE WITH ELECTRO- PHOTOGRAPHIC RECORDING PAPERS Sakae Shimizu, Kawasaki-shi, and Takayoshi Tanno, Tokyo, Japan, assignors to Kabushiki Kaisha Ricoh, Tokyo, Japan, a corporation of Japan No Drawing. Filed Mar. 25, 1968, Ser. No. 715,563 Int. Cl. C09k 3/10 U.S. Cl. 106-2 3 Claims ABSTRACT OF THE DISCLOSURE A treating solution for planographic printing plates made with electrophotographic recording papers, said solution comprising an aqueous solution containing a cyanide selected from the group consisting of ferricyanides and ferrocyanides, at least a phosphate, and an organic polybasic acid containing at least two carboxyl radicals, the total concentration of said phosphate and said cyanide contained in said aqueous solution being at least 10% by weight of said solution, the proportion of said cyanide to said phosphate contained in said solution being such that the total cyanide contained in these two salts is in the range of from 5% to 60% by weight of the total of these salts, the pH of said solution being controlled to a value ranging from 3.0 to 7.0 by the addition thereto of said organic polybasic acid.

BACKGROUND OF THE INVENTION Field of the invention The present invention is concerned with a treating solution which is used in making hydrophilic or oilrepellent the non-image areas of an electrophotographic recording paper carrying a copied image produced according to a known electrophotographic copying procedure and intended for use as a planographic printing plate. The term treating solution herein referred to includes also the fountain solution for use in planographic printing, which is obtained by directly diluting said treating solution with water.

Description of the prior art There have been proposed in the past various different compositions for the solutions intended for the treatment of the printing faces of printing plates. However, no treating solution which is satisfactorily applicable to planographic printing plates made with electrophotographic recording papers (hereinafter to be referred to briefly as recording papers) has as yet been reported.

These conventional treating solutions have a number of drawbacks in common. To point out some of them, there are:

(1) They lack sufficient ability for making the printing face of the printing plate oil-repellent, so that the prints will be susceptible to having the background stained with the printing ink during the process of printing;

(2) They are liable to develop cracks in the photoconductive layers of the recording papers during the treatment therewith; and

(3) The treating solutions of the prior art tended to infiltrate, through the aforesaid cracks in the photoconductive layers, into the support sheets of the recording papers, leading to a reduction in the mechanical strength of the support sheets and resulting in the development of wrinkles in the support sheets. These drawbacks of the treating solutions of the prior art appear markedly especially in the offset printing which is performed on a small offset printing machine with Simfio inking system.

SUMMARY OF THE INVENTION The present invention has been made after extensive research conducted by us to overcome the aforesaid drawbacks of the treating solutions of the prior art from an overall viewpoint with respect to both the adaptability of the treating solutions to the faces of the printing plates and the adaptability of the same to the printing operation. More specifically, the treating solution of the present invention contains, as its principal components, a cyanide selected from the group consisting of ferrocyanides and ferricyanides, a salt of phosphoric acid and an organic polybasic acid containing at least two carboxyl radicals (-COOH) in each of the molecules. The present invention is further characterized in that the mixing ratio of ferrocyanide or ferricyanide to phosphate in said treating solution, the concentration of the cyanide and the phosphate, and the pH of the treating solution, are all defined within predetermined ranges, respectively. The present in vention has its object in the provision of a satisfactory planographic printing plate capable of exhibiting an excellent printing eifect, by making the non-image areas of the aforesaid recording paper oil-repellent without the accompaniment of any such undesirable damages of the printing plate as those enumerated above.

The following are the essential and indispensable requirements of the present invention, namely, (1) that the mixing ratio of ferricyanide or ferrocyanide to phosphate is such that the amount of said cyanide present in the total of said phosphate and said cyanide is in the range of from 5% to 60% by weight of said total of these salts, (2) that the total concentration of the cyanide and the phosphate in the treating solution is at least 10% by weight of said treating solution, and (3) that the pH of said treating solution is controlled to a value ranging from 3.0 to 7.0 by the inclusion of said organic polybasic acid.

As the ferrocyanides which can be applied to the present invention, the employment of such cyanides as sodium ferrocyanide, namely, Na [Fe(SN) and potassium ferrocyanide, namely, K [Fe(CN) is desirable. As the ferricyanides which are applicable to the present invention, the employment of such cyanides as sodium ferricyanide, namely, Na [Fe(CN) and potassium ferricyanide, namely, K [Fe(CN) is desirable. As the phosphates which can be used in the present invention, there can be enumerated ammonium dihydrogen phosphate, namely, NH H PO diammonium hydrogen phosphate, namely, (NH HPO sodium dihydrogen phosphate, namely, NaH PO and disodium hydrogen phosphate, namely, Na HPO As the organic polybasic acids which are applicable to the present invention, there can be used those organic acids having at least two carboxyl radicals which include dibasic acids such as oxalic acid, malonic acid, succinic acid and adipic acid; unsaturated dibasic acids such as maleic acid and itaconic acid; and polybasic hydroxy-acids such as tartaric acid and citric acid.

It is to be noted that by diluting one part of the treating solution of the present invention into several parts with water, the resulting diluted treating solution can be utilized as the fountain solution for use in planographic printing.

In case a planographic printing is performed while making oil-repellent the non-image areas of the recording paper carrying a copied image formed thereon according to a known electrophotographic copying technique by the application thereto of the treating solution of the present invention and while using the fountain solution prepared by diluting one part of said treating solution into the order of five parts with water, there are provided the advantages that all of the aforesaid drawbacks inherent to the conventional treating solutions are greatly im- 3 proved and that the fear of the occurrence of those t-roubles such as the staining of the backgrounds of the prints, the staining of the prints due to the cracks developing in the photoconductive layers of the recording papers or due to the development of wrinkles in the support sheets are completely eliminated.

While no theoretical explanation has been made yet as to the function of the ferrocyanides or ferricyanides, the phosphates and the polybasic acidswhich are the fundamental components of the treating solution of the present invention-to make the non-image areas of the recording papers oil-repellent, it has been observed by us that the Zinc oxide contained in the photoconductive layer of the recording paper is caused to react upon these aforesaid components when they are placed in an acidic state, thereby producing an organic acid salt of zinc, ferrocyanide of zinc and zinc phosphates-such as Zn [Fe(CN) NH Z11PO and Zn (PO )in the form of an oil-repellent film covering the surface of the nonimage areas of the photoconductive layer. It has been confirmed from experiments, however, that in case the mixing ratio of a ferrocyanide or a ferricyanide to a phosphate is such that the amount of the cyanide with respect to the total of these salts exceeds 60% by weight, the resulting treating solution will be liable to develop changes due to exposure to light and due to temperature, and that thereby the ability of the treating solution to make the non-image areas of the printing plate oil-repellent is reduced. On the other hand, in case the concentration of the salts, namely, the cyanide and the phosphate, drops to a level below not only there will arise an economical disadvantage that the percentage of the dilution of the treating solutionwhen it is intended to prepare a fountain solution for use in planographic printing from said treating solution-will inevitably become small, but also there will be apt to occur troubles in the process of printing due to the resulting excessively low concentration of these salts contained in the fountain solution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 An electrophotographic recording paper prepared with a specifically processed strongly built support paper sheet provided on one surface thereof with a photoconductive layer of about in thickness consisting of a mixture of a zinc oxide and a silicone resin or a zinc oxide and a silicone plus styrenated alkyd resin which is prepared in the form that zinc oxide is dispersed in the resin, was

used. This recording paper was then charged with electricity according to a known manner by the use of an ordinary electrophotographic copying apparatus. Thereafter, the recording paper was exposed to light through an original placed thereon, and the same was developed. After heat-fixation of the same, a copied image was obtained.

Then, the image-carrying face of said recording paper was wiped with a piece of absorbent cotton impregnated with a treating solution having the following composition, to thereby make the non-image areas of the recording paper oil-repellent, with the result that the recording paper became capable of use as a planographic printing plate. The composition of the treating solution was as follows:

K Fe(CN) 5 Na HPO 5 NaH PO 5 Water 85 (The pH of the treating solution was controlled to 5.0 by the addition of citric acid).

The planographic printing plate having been given this oil-repelling treatment was then applied to a planographic printing press. Printing was performed by using a fountain solution which was prepared by diluting one part of the aforesaid treating solution with 5 to 6 parts of water. Thus, more than 3000 clear prints were obtained with stability. There was noted no prints in which the non-image areas were stained with the printing ink or stained due to cracks occurring in the printing face or due to wrinkles of the support paper.

In order to compare the ability of the treating solution of the instant example with a conventional one, there was prepared a control treating solution having the following composition:

Weight percent Potassium ferrocyanide 2.0 Polyacrylic acid 1.5 Water, proper volume (The pH of the treating solution was controlled to 5.0 by the addition of trisodium phosphate.)

In a manner similar to that described above, a planographic printing plate was prepared from a recording paper. When this printing plate was subject to printing, there occurred cracks in the photoconductive layer of this control recording paper and also wrinkles in the support sheet at the end of about 2000 runs. It was noted that no further printing would be possible. This result was confirmed by the comparative experiment of the abilities of these two treating solutions, which was performed repeatedly on several scores each of the recording papers of both.

Example 2 The non-image areas of the recording paper carrying an image which was formed in the same manner as described in Example 1 were made oil-repellent by using a treatment solution having the following composition:

Na Fe(CN) 6 2 NaH PO 4 (NH HPO 6 Water 38 (The pH of this treating solution was controlled to 6.0 by the addition of succinic acid.)

As a result, a planographic printing plate was obtained. Then, a fountain solution was prepared by diluting one part of this solution into 5 to 6 parts of water. Using this fountain solution, printing was performed in a manner similar to that described in Example 1. More than 3000 clear prints were obtained without causing any trouble.

Example 3 A treating solution having the following composition was prepared:

KgFe 6 1 NH H PO 3 Na HPO 5 Na-H2PO4 1 Water (The pH of this treating solution was controlled to 3.5 by the addition of adipic acid.)

This treating solution was used in the preparation of the planographic printing plate and the preparation of a fountain solution. It was found that both the treating solution and the fountain solution made with the same were of abilities which were substantialy equal to those of Examples 1 and 2, permitting more than 3000 clear prints to be produced.

What is claimed is:

1. A solution for treating a planographic printing plate made of an electrophotographic recording paper in order to render hydrophilic the non-image areas of the plate without affecting the hydrophobic nature of the image areas, said recording paper being comprised of a support paper and a photoconductive layer formed on one surface of said paper, said photoconductive layer being comprised of a resin binder having suspended therein finely divided photoconductive zinc oxide, said solution consisting essentially of an aqueous solution of:

(a) a cyanide selected from the group consisting of alkali metal salts of ferricyanides and ferrocyanides, (b) at least one water-soluble phosphate selected from the group consisting of alkali metal and ammonium salts of monoand di-hydrogen phosphate, and (c) an organic acid selected from the group consisting of oxalic acid, malonic acid, succinic acid, fadipic acid, maleic acid, itaconic acid, tartaric acid and citric acid; the ratio of said cyanide present in said solution to said phosphate present in said solution being such that the amount of said cyanide is in the range of from 5% to 60% by weight of the total amount of said cyanide and said phosphate, the pH of said solution being controlled to a value ranging from 3.0 to 7.0 by the addition thereto of said organic acid.

References Cited UNITED STATES PATENTS 10 2,988,988 6/1961 Kurz 101-451 3,211,686 12/1965 Uber et a1. 101-451 XR 3,398,002 8/1968 Bondurant et al. 1062 JULIUS FROME, Primary Examiner 5 L. B. HAYES, Assistant Examiner US. Cl. X.R.