US3557696A - Planographic printing plate with nucleating agent and zirconium salt - Google Patents

Abstract

A planographic printing plate having a water receptive, hydrophilic, lithographic surface, said surface having a combination of silver halide nucleating agents and a salt of zirconium, thorium or titanium.

Description

United States Patent Stasel Keith Hoover l-lampstead, London;

James Thomas Crawford Knowles, Buckinghamshire; Wong Kwong Fa Wong Yan Man, London, England 564,758

July 13,1966

Jan. 26, 1971 A. B. Dick Company Niles, III.

a corporation of Illinois July 20, 1965 Great Britain Inventors Appl. No. Filed Patented Assignee Priority PLANOGRAPHIC PRINTING PLATE WITH NUCLEATING AGENT AND ZIRCONIUM SALT 8 Claims, No Drawings US. Cl 101/459, 101/462; 96/29, 96/76, 96/33 Int. Cl 841m 1/04,

[50] Field olSearch 96/29, 76; 101/1492, 456, 466, 453, 459, 462

[56] References Cited UNITED STATES PATENTS 3,220,837 11/1965 Land et a1 96/29 FOREIGN PATENTS 565,696 7/1960 Belgium 96/19 OTHER REFERENCES Mashev, THE TECHNOLOGY OF COATED AND PROCESSED PAPER 1 Primary ExaminerGeorge P. Lesmes Assistant ExaminerJ. P. Brammer Attorney-McDougall, Hersh, Scott & Ladd ABSTRACT: A planographic printing plate having a water receptive, hydrophilic, lithographic surface, said surface having a combination of silver halide nucleating agents and a salt of zirconium, thorium or titanium.

PLANOGRAPI-IIC PRINTING PLATE WITH NUCLEATING AGENT AND ZIRCONIUM SALT This invention is concerned with improvements in or relating to planographic printing. In particular the invention is concerned with the provision and use of a planographic printing plate.

In planographic printing one employs a printing plate having an oleophilic image superimposed on a hydrophilic background so that on application of a greasy ink to the plate wetted with water the ink preferentially coats the image and the coated image may be used to produce copies by an offset procedure. It is possible to manufacture planographic printing plates having metal bases, the resultant plates being capable of producing tens of thousands of copies, or alternatively where at most only a few hundred copies are required it is more economic to employ the cheaper paper based plates. Plates of other materials, e.g., polyesters have also been proposed.

Before the plates are used to produce copies it is necessary to image them and often the image will be applied thereto by a typewriter or a suitable pen or pencil. However if a specimen of the image is already in existence it would add to the expense of producing copies of this if the image had to be recreated on the plate and it is desirable to be able to transfer the image to a planographic printing plate by physical or chemical means.

A chemical process which was not originally developed for the imaging of masters, but which is extensively used for the production of single copies, is the silver halide diffusion transfer process. This process comprises contacting a positive paper with an exposed negative having a latent image in the presence of a developing and a fixing solution containing a silver halide solvent, whereby the latent image on the negative transfers to the positive and is developed and fixed thereon by the solution.

There have been several proposals to adapt this diffusion transfer process for use in conjunction with offset lithography by substituting, for the positive sheet, a specially coated or prepared sheet which is lithographic or adapted to be made lithographic so that copies can be printed therefrom on a conventional offset lithographic printing machine. For example, aluminum plates, the surface of which has been rendered lithographic by graining or formation of a thin layer of an aluminum compound, have already been proposed for this purpose.

A process has also been proposed in which a paper base planographic printing plate is imaged by a diffusion transfer process in which a special negative paper is exposed to the original and the exposed negative is processed or developed with a special developer solution. The emulsion on the negative paper consists of gelatin, silver halide such as silver bromide and other materials. The light exposed, developed portions of the negative are partially insolubilized and incapable of transferring while the unexposed portions corresponding to the image to be reproduced will transfer on contact from the negative to the paper master surface. This is not a true diffusion transfer process because the colored reduced silver is formed in the gelatin layer, transferring to the master along with the gelatin film.

It is an object of the present invention to provide a planographic printing plate which can be imaged by the silver salt diffusion transfer process and used to produce copies simply and cheaply.

According to the present invention, therefore, there is provided a method of producing a planographic printing plate which comprises applying to a base sheet having a water-insoluble, water-receptive, hydrophilic, lithographic surface, an aqueous solution of a silver halide nucleating agent and a metal salt, said metal salt being a salt of thorium, titanium or zirconium, said solution, if desired also containing a stabilizing amount of a water-soluble compatible stabilizing agent to inhibit degradation of the nucleating agent and the salt, whereby said surface is rendered imageable -by the silver halide diffusion transfer process. The base sheet may be of any material used in the production of planographic printing plates, e.g., paper or commercially available metal plates. Where the base sheet is a paper base, the paper preferably has a dry Dennison Wax pick of at least six and preferably over eight.

After the plate has dried it is ready for imaging, either for example by a typewriter, pen or pencil, or alternatively in a conventional silver salt diffusion transfer photocopying procedure from an existing image. The process can be used for the reproduction of line or dot-type material and can also be used together with half tone and continuous tone screens in the preparation of the transfer negative. Thus in order to image the plate by the diffusion transfer technique, a diffusion transfer negative is provided with a negative latent image, by exposure of an original in a photocopy machine, and the exposed negative is passed through the developing section of the machine, containing an offset developer, in contact with the planographic printing plate according to the invention so that the latent negative image on the transfer negative diffuses, on development, to the surface of the printing plate of the invention which has been treated with the aqueous solution of nucleating agent and metal salt. After separating the two sheets, the image is fixed, simply by applying a fixing solution and the printing plate is then ready for use on a conventional offset printing machine after fixing the image.

Coated papers having a lithographic surface, a good wet strength and a dry Dennison Wax pick of eight or higher and preferably above,l1 may conveniently be used as the base sheet. For most purposes we recommend that the pick resistance be over eight.- A high pick resistance facilitates separation of the master from the exposed negative and also results in a cleaner background on the copies printed.

In order to render the surface of paper base sheets lithographic it is necessary to coat the surface with an organic binder and a filler. Various binders such as casein, starch, carboxymethyl cellulose, polyacrylic acid, polyvinyl acetate, alginic acid, polyvinyl pyrrolidone and polyvinyl chloride may be used providing they form a lithographic surface when mixed with a hydrophilic filler. However, casein has been found to provide the best results. The binder may be used as such but is preferably used together with a pigment.

Planographic printing plates according to the invention may be manufactured from the papers termed in the trade as Art Papers, i.e., papers already coated with a binder and filler, provided the surface of the paper has a dry Dennison Wax pick of at least six and is lithographic.

The planographic printing plates may also be prepared from direct image[ paper base planographic printing plates provided these have been coated and filled as described. These plates may then be coated with an aqueous solution of nucleating agent and metal salt as described. These paper base plates, which were primarily intended for use as direct image masters for imaging, e.g., using a typewriter, generally consist of a high wet strength paper coated with a pigment, e.g., clay or zinc oxide and a binder, e.g., casein. The surface of these masters is already lithographic, having been so rendered by any of the conventional methods such as by brushing or treatment with a salt, e.g., zinc chloride.

The planographic printing plates according to the invention may be manufactured by conventional techniques and the metal salt and nucleating agent may be applied at a suitable point during manufacture, i.e., not necessarily after the plate is otherwise finished. Where a proper base is employed the metal salt and nucleating agent may thus be applied before or after a calendering step and before or after the application of a wash coat.

The aqueous composition used in the present invention also preferably contains a stabilizing agent, as stated, in order to prevent deterioration of the composition on the base sheet. lf the base sheet is to bestored for any length of time then the presence of the stabilizing agent may be essential in order to achieve good printing results. Thus, in the absence of the stabilizer under such conditions, a water impermeable coating is formed on the base sheet and this reduces the hydrophilic properties of the latter which are necessary to the success of planographic printing.

Any convenient stabilizing agent may be used always provided it is sufficiently soluble in water and does not oxidize silver. Examples of suitable stabilizing agents (as evidenced by accelerated ageing tests) include strong nonoxidizing acids such as dilute mineral acids, e.g., dilute hydrochloric acid or dilute nitric acid and also compatible soluble phenols such as phenol itself, quinol, pyrogallol, phluoroglucinol or resorcinol. As is known, polyhydric phenols with orthoor para-hydroxy groups and their ethers are antioxidants. Examples of such antioxidants include gallic acid and lower alkyl esters thereof, catechol, various ethers of quinol (e.g., lower alkyl and benzyl ethers) and quinone. Various phenols are unsatisfactory owing to incompatibility with the composition, e.g., due to their forming insoluble precipitates with the nucleating agent or the metal salt or by being per se not sufficiently soluble soluble.

Nucleating agents for silver halides in diffusion transfer processes are known for example from US. Pat. No. 2,352,014 and British Pat. No. 614,155 and are able to reduce silver halides in the absence of light. They are also known as fogging agents. The preferred nucleating agents are the stannous halides, e.g., stannous chloride, fluoride or bromide particularly stannous chloride.

The nucleating agent and metal sat salt may be coated onto the base sheet from two separate solutions, one of which may conveniently contain the stabilizers, antioxidants or pigments etc.

Since suitable lithographic paper base sheets are already commercially available and further since the nucleating agent and metal salt are prone to degradation as stated, it may be preferable to treat the surface of e.g., a direct image master or an Art Paper with the aqueous solution just prior to imaging by the diffusion transfer process.

It is thus also an object of the present invention to provide a solution suitable for converting a base sheet having suitable characteristics as stated, to a planographic printing plate which can be imaged by the silver salt diffusion transfer process.

According to the present invention therefore there is provided an aqueous solution comprising a silver halide fogging or nucleating agent and a salt of thorium, titanium or zirconium (the metal salt). The fogging agent and the metal salt can also be applied to the base sheet in separate solutions and if the master is not to be used reasonably soon thereafter the water compatible stabilizer may be incorporated into one or other of the solutions preferably into the metal salt solution. In any case a short period should be allowed in between applying the solutions, and also before the master is used, to allow it to dry off.

The air dry weight of the coating of nucleating agent, metal salt, and stabilizer when present, is variable over a wide range, e.g., from 0.6 to 16 grams per square metre. A preferred range for the weight of the coating is 0.6 to 14 g.s.m. The optimum coating weight will depend on the nature of various factors including the ability of the substrate to absorb the aqueous solution. In general absorbent base sheets, e.g., absorbent papers, will require more solution to be used than relatively nonabsorbent base sheets. However preliminary trial and error experiment will soon indicate the optimum coating weight. For less absorbent base sheets coating weights of from 0.6 to 3 g.s.m. are convenient and for more absorbent base sheets, especially certain papers, not less than 2.45 g.s.m., e.g., 5 to 9 preferably 6 to 8 g.s.m. may be used.

The amount of stabilizer used will depend on the required shelf life of the master but will generally be at least 10 percent and not more than 60 percent by weight of the coating. Satisfactory results can be obtained in most instances by using about 50 percent.

The ratio by weight of nucleating agent to metal salt in the coating may be with the range of from l.0:O.87 to l.O:l0.4, e.g., from 1.0:l.0 or 1.0:] .3 up to l.0:2.0 or 1.020.87 to 1.8:;064, l.O:5.2 and a particularly preferred ratio being about I.

Apart from the ratio limitations too little nucleating agent or metal salt will result in a brown nonink receptive image whilst too much nucleating agent will initially produce a dense bronzy image on the master but an image which is easily washed off during the fixing and etching processes. This has been attributed to the film forming properties of the metal salt used.

The actual amount of nucleating agent, metal salt and optionally stabilizer in the aqueous cooling solution or solutions is thus adapted to provide an air dried coating having the characteristics set forth above. The solution must not be of such a concentration that the compounds in the solution are liable to precipitate at room temperature. Conversely if the dilution is too great an excessive amount of the solution will have to be applied.

The preferred concentration of the compounds in the aqueous solution depends on the desired coating weight and the solubility of the constituents but may conveniently be from 2.6 percent to 17 percent by weight. Particularly preferred weight percentages for the concentration of the coating solution are from 5.25 percent to 9.6 percent and especially from 6.25 percent to 8.6 percent by weight. In the solution the ratio by weight of nucleating agent to metal salts and the amount of stabilizer will be as for the respective amounts in the coating to be laid down on the base sheet.

The metal salt used may be an acetate, chloride or nitrate, e.g., zirconyl acetate, zirconyl nitrate, thorium nitrate, thorium chloride, titanium dichloride or zirconyl chloride. The metal salt used must not be one which destroys the lithographic properties of the surface of the master.

The diffusion transfer negative used is of the conventional type and may be one of those commercially available and intended for use in the production of single copies by the diffusion transfer method. In particular the following can be used: Gevart GS (Gevart Photo Production Antwerp, Belgium) Oricopy (Oriental Photocopy Company, Tokyo, Japan) and Anken Photo Rapid negative made by Anken Chemical Company, New Jersey, USA.

The developer used may be any of the conventional offsettype developers. These are reducing solutions which contain a solvent for the silver halide, a synthetic gum, an antioxidant and other stabilizers. A typical example is the offset developer made for the Diffusion Transfer Process by Gevart and also A. B. Dicks developer formula 59B9.2. 9.2.

The fixing solution is again conventional and may for example be CT Offset Fixer made by Kodak (Trade Mark). This fixer appears to contain inter alia carboxy methyl cellulose, sodium nitrate, sodium thiosulfate, ammonium phosphate, ethyl alcohol a small amount of a mercapto compound and water. Solutions of this type are described in British Pat. No. 934,691.

The invention will now be illustrated with reference to the following Tables of experimental results.

EXPERIMENTAL Table I illustrates the invention with respect to various types of paper which may be used.

In examples 1 to 6 inclusive and 8 the base sheets used were commercial wet strength papers coated with a pigment and a binder as specified. The surface of the paper was then made lithographic by conventional means, e.g., by brushing or washing with a salt such as zinc chloride.

In examples 7and 9 art type papers were used. In all cases the following solution was used:

Stannous Chloride 1 gram.

Zirconyl Acetate 20 of 13 percent solution in water. Phenol 4 grams.

Water ml.

The solution was applied by conventional coating means such that the air dried coating weight was 6 to 8 grams per square metre. The coated and dried sheet was then calendered until the surface was smooth and the sheet flat. The paper master, so made, was contacted with a properly exposed Gevart type GS negative sheet and passed through Gevart Offset Developer solution of the instructed dilution in an A. B. Dick M. 120 Photocopier. After about 14 seconds the two sheets were separated. The image on the master was fixed by applying a Kodak (Trade Mark) CT Offset developer solution using a cotton pad. The imaged master was then used to produce copies on a conventional offset duplicator.

The wet strength papers coated as above can give up to 2,000 good copies.

TABLE I Resist- Ex. ance No. Pick Type of coating Comments 1. 12 Casein-Pigment Very good copy, long run. 2..... 11 .....do Good copy, short run. 3. 14 Starch-Pigment Do. 4..... 8 Polyacrylic acid-pigment Fair to poor copy. 5. 12 Polyvinyl copolymers-pigment Fair to poor. 6... 11 Carboxymethyl cellulose-pigment... Fair copy. 7... 6 Casein Fair to poor copy. very short run. 8.. 12 Casein-pigment Very good co y, medium run. 9".-. 9 Casein-latex-pigment Good copy, s ort run.

When stannous fluoride was substituted for stannous chloride in example No. 2 a master was obtained which gave incomplete transfer but the copy was otherwise fair. Likewise use of stannous bromide resulted in incomplete transfer and fair to poor copy.

Table II gives the results obtained when example 2 was repeated using other metal salts according to the invention in place of zirconyl acetate:

TABLE IL-SUBSTITUTION FOR ZIRCONYL ACETATE IN STANDARD FORMULA No. Zirconyl acetate substitute Comments 10. Zirconium nitrate Dense bronzy image. Fair copy.

11 Thorium nitrate Ptgirttransier. Slightly bronzy image. Some copy u poor.

12.... Thorium nitrate heated one hour at 100 C Better transfer and copy than Example 11.

Thorium chloride Fair transfer. Fair copy.

Titanium chloride..... Fair bronzy image. Fair to good copy. 15 Zirconyl chloride Uneven transfer. Fair to good copy. Image bronzy in some areas. 16 Zirconyl chloride heated one hour at 100 0...... Fairly dense bronzy image. Fair to good copy.

TABLE IIL-PRESERVING AGENTS Aging. hrs. at Ex. No. Preservative 100 0. Comments 17 None None Good bronzy image on Master. Good copy. Clear background. 18 o 1 Fair bronze image on Master. Poor copy. Specky background. 19 ..d 17 Faint image. No copy. 20 PhenoL. 1 Good bronzy image and copy. Specks. 21 ..do 17 Fair bronzy image. Fair copy. 22 Resorcinol 17 Bronzy image. Fair copy. Scums. 23.. Phloroglucinol.-.. 17 Bronzy image in areas. Fair copy. 24.. Hydroquinone. 17 Good bronzy image. Good copy. Some scum. 25.. None Fair bronzy image. Fair copy. 26 17 Slight bronzy image. Poor copy. 27 17 Good bronzy image. Fair to good copy. 28 17 Weak bronzy image. Fair copy. Clean background. 29 17 Fair bronzy image. Fair copy. Clean background. 30... 17 Good bronzy image and copy. Clean background.

From a commercial standpoint masters made as above described would be expected to have a shelf life of at least 1 year if stored under normal conditions. In order to short cut Table IV shows the effect using varying quantities of stabil izer according to the present invention. Examples 31-33 usethe paper and solution of example 25 and examples 34-36 the length of time required to evaluate preservatives. an acuse the paper and solution of example 22. In both cases the 4 percent of phenol used in the solution of earlier examples was replaced by the amounts of phenol shown in table 1V.

8. We claim: 1. A planographic printing plate having a water insoluble,

The effect of changing the air dried weight of the coating is shown in the following table V. In examples 37-39 the solution and paper of example 8 was used.

TAB LE V Air dry coating weight,

g.s.m. Comments Fair bronzy image. Fair to poor copy. Good bronzy image. Fair copy. Fair bronzy image. Fair to poor copy.

TABLE VI water receptive, hydrophilic, lithographic surface, said plate having on the lithographic surface the combination of a nucleating agent for silver halide and a water soluble salt of zirconium as a component separate and apart from the nucleating agent to render said surface imageable by the silver halide diffusion transfer process, the materials being present in the ratio of one part by weight nucleating agent to 0.87 to 10.4 parts by weight of the zirconium salt.

2. A plate as claimed in claim 1 in which the combination on the lithographic surface contains 10-60 percent by weight of a water soluble compatible stabilizing agent to inhibit degradation of said nucleating agent and said salt.

3. A plate as claimed in claim 2 in which the stabilizing agent is a compatible water-soluble phenolic compound.

4. A plate as claimed in claim 1 having a paper base, said base having a coating of an organic binder and a filler on the surface thereof and having a dry Dennison wax pick of at least SIX.

5. A plate as claimed in claim 1 wherein said lithographic surface is in the form of a coating containing a binder of casein.

6. A plate as claimed in claim 1 wherein said metal salt is zirconyl acetate, zirconyl nitrate or zirconyl chloride.

Percent in solution image washes off. Very slight poor copy.

Although the above examples illustrate the application of 7. A plate as claimed in claim 1 wherein the nucleating the invention with paper base masters, it is to be understood agent isastannous halide.

that the invention is not limited thereto and that other lithographic masters having, for example, metal or plastic substrates may be used. An example of a plastic base master is the 8. A plate as claimed in claim 1 wherein the nucleating agent and zirconium salt are present in separate coatings on the surface of the plate.

polyester based Transmaster D1 of the Ozalid Company.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,557 696 Dated January 26 1971 Inventor) Stasel Keith Hoover et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3 lines 73 and 74 cancel "1 0:0 .87 to 1 .0:10 .4" Column 4 line 5 after "attributed" insert in some cases line 45 after "59B9. 2" cancel "9 2"; line 68 after "20" insert m1 Column 5 line 2 "14" should read 1S Signed and sealed this 15th day of June 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, J Attesting Officer Commissioner of Patent

Claims (7)

1. 2. A plate as claimed in claim 1 in which the combination on the lithographic surface contains 10-60 percent by weight of a water soluble compatible stabilizing agent to inhibit degradation of said nucleating agent and said salt.
2. 3. A plate as claimed in claim 2 in which the stabilizing agent is a compatible water-soluble phenolic compound.
3. 4. A plate as claimed in claim 1 having a paper base, said base having a coating of an organic binder and a filler on the surface thereof and having a dry Dennison wax pick of at least six.
4. 5. A plate as claimed in claim 1 wherein said lithographic surface is in the form of a coating containing a binder of casein.
5. 6. A plate as claimed in claim 1 wherein said metal salt is zirconyl acetate, zirconyl nitrate or zirconyl chloride.
6. 7. A plate as claimed in claim 1 wherein the nucleating agent is a stannous halide.
7. 8. A plate as claimed in claim 1 wherein the nucleating agent and zirconium salt are present in separate coatings on the surface of the plate.