US3161508A

US3161508A - Process of lithographic printing

Info

Publication number: US3161508A
Application number: US836077A
Authority: US
Inventors: Hepher Martin; Marriage Anthony; Vincent Alan Maurice; Williams Leslie Alfred
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1958-08-29
Filing date: 1959-08-26
Publication date: 1964-12-15
Anticipated expiration: 1981-12-15
Also published as: GB934692A; BE582160A; BE582161A; GB934694A; FR1243430A; FR1242943A; GB934691A; GB934693A

Description

3,15 L58 Patented Dec. 15, 1964 United States Patent 655cc 3,161,508 PROQESS F LITHUGRAPHEC PRINTING Martin Hepher, Anthony Marriage, Alan Maurice Vincent, and Leslie Alfred Williams, all of Harrow, England, assignors to Eastman Kodak Lompany, Rochester,

N.Y., a corporation of New Jersey No Drawing. Filed Aug. 26, 1959, Ser. No. 836,977 Claims priority, application Great Britain Aug. 29, 1958 11 Claims. (Cl. 96-29) The present invention relates to lithographic processes and to lithographic printing plates made photographically.

In lithography a greasy ink is employed and the printing plate comprises a support which when wet is oleophobic and carries a line or dot image which is oleophilic.

The oleophilic properties of the image and the elecphobic and hydrophilic properties of the surrounding support surface are relative in nature to some extent. When using an image bearing plate for printing, both ink and water are applied and the support is sufficiently hydrophilic to acceptwater but not the geasy ink, while the image accepts the ink but not the water. Hence to obtain good prints it is necessary that the diiference in hydrophilic and oleophilic properties of the image and v the background surface is sufiiciently great that when water and ink are applied, the image will accept sufiicient ink without the background accepting any ink at all. Hence lithographic printing plates are supports the nature of whose surface is such that when wetted it will not accept the ink although if ink is applied when the surface is dry the ink so applied is not removed by subsequent wetting.

The practice inmaking a photolithographic printing plate is to produce an oleophilic image on the hydrophilic support which can be put into an inking machine whereby large numbers of copies can usually be made very rapidly from the one plate.

Where only a few hundreds of copies are required,

or even up toabout a thousand copies, it is quite common to use a paper type. printing plate, but where many thousands of copies are required it is necessary to use i a more substantial type of printing plate and the ones commonly used are made of aluminium sheet or zinc sheet. From these metal sheets it is a common practice in the art to take as many as twenty thousand copies. Aluminium sheet employed in the art is provided with an inert hydrophilic surface. This is often done by treating the aluminium to produce thereon an aluminium compound which is hydrophilic for instance aluminium oxide as in the case of anodised aluminium, aluminium silicate and chromatiscd aluminium.

When making such printing plates, usually an ordinary negative is first made and then this is used for making a positive oleophilic image on the printing plate. A large number or" processes have been used and suggested for doing this.

A printing process employing greasy ink on metal plates was suggested many years ago by K. W. C.Webb in which process, for instance the polished copper plate, were not as such suitable asllithographic printing plates and it was necessary to etch the bare copper parts after theimage a had been formed. One object of the present invention is to provide a process which entirely avoids etching after formation of the image by making the image areas very oleophilic compared with the background areas.

In view of the wide variety of commercial uses of photolithographic copying, it is very desirable to have a process which is both simple and easy for the user.

An object of the present invention is to provide a process which satisfies these requirements in a verysurprisingly simple way namely by forming a silver image on a lithographic printing plate and merely treating it with a special type of organic compound which is adsorbed to the surface of the silver and renders it oleophilic while having no appreciable elfect on the hydrophilic proper-,

ties of the background. This treatment of the silver image with the solution can be very easily done by swabbing or rubbing a solution of the organic compound over the image for a few seconds using cotton wool. An important advantage is that there is nothing critical about this treatment. It is believed that the organic compound is rapidly adsorbed to the surface of the silver and this takes place immediately the solution is applied thus rendering the time of application very short and not critical.

Accordingly the present invention provides a'lithographic printing process which comprises forming on a lithographic printing surface a photographic silver image and bath ng the silver image in a solution of a sulphur or selenium organic compound containing an oleophilic group in the molecule and being a compound which when brought into contact with the silver at ordinary room temperature becomes integrated to the surface of, and only in the region of the silver and thereby renders the surface of the silver oleophilic by virtue of the oleophilic groups, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press. Preferably the support is free of metals and metal salts which are readily converted into oleophilic metal derivatives of said organic compound. By integrated only to the surface we mean that the compound is adsorbed to the surface of the silver but does not chemically react with the bulk of the silver. Whether the adsorption of a chemical to the surface of a metal is purely a physical phenomenon is open to doubt since it is believed that surface adsorption of this kind may involve some surface chemical action of some kind which is not thoroughly understood. Y

The development of the diffusing silver halide must be sufiiciently greatto ensure that the developed image on the printing surface is built up to a suit-able high density at the surface.

In a preferred embodiment there is provided a lithographic printing process which comprises forming on a lithographic printing surface containing a silver precipitating agent a silver image from the diffusing silver halide of an exposed and developed silver halide emulsion layer in contact with the printing surface and then bathing the silver image so formed in a solution of an organic compound containing an oleophilic group in the molecule and being a compound which when brought into contact with the silver at ordinary room temperature becomes integrated to the surface of, and only in the region of'the silver and thereby renders the surface of the silver oleophilic by virtue of the oleophilic groups, inking the silver a image with greasy printing ink and printing therefrom in a lithographic printing press.

In order that the organic compound shall be adsorbed to the surface of the silver it must contain in the molecule one or more groups having an aflinity for silver. Such groups include the following:

(2) --SR where R is a group which can easily be hydrolyzed off leaving SH, such as acoyl, aroyl, amidinium or NHR when R is alkyl, aryl, aralkyl, cyclo alkyl, heterocyclyl.

(3) Thio-acid groups.

(4) Thio-amide groups.

(5 Selenium analogues of the foregoing groups (1), (2),

(3) and (4).

(6) Isothiocyanate group.

In order that the organic compound shall confer oleophilic properties on the silver, it must contain one or more oleophilic groups in the molecule. In general it is found that suitable oleophilic characteristics are conferred on the silver image if the organic compound contains a. fatty chain or a substituent containing at least four carbon atoms, e.g., potassium butyl xanthate.

In some cases however where there are no additional groups in the molecule that detract from its hydrophobic properties the fatty chain may be one of less than four carbon atoms, e.g., S-methyl isothiuronium salts, ethyl isothiuronium salts which split in alkaline solutions to give S-methyl mercaptan and ethyl mercaptan respectively, triazole mercaptans and tetrazole mercaptans.

Organic compounds which contain the aforesaid groups in the molecule and therefore may be used in the present invention include the following:

(1) Dodecyl mercaptan, benzothiazole-Z-thiol, and the triazine thiols of the general Formula I wherein R is an alkyl or cycloalkane, preferably of, but not limited to, the range C to C These compounds have good stability when dissolved or dispersed in water or aqueous solutions of gum arabic or carboxy methyl cellulose.

R is H2 H FORMULA 1 Compounds of this class can be prepared by the method of or analogous to the method described by Burke J.A.C.S., 69, 236-7 (1947). Examples of triazine thiols are l-dodecyl-l,2,4,5-tetrahydro-1,3,5-triazine-4thiol and l-octyl-1,2,4,5-tetrahydro-1,3,5-triazine-4-thiol.

(2) S-diethylamino ethyl isothiuronium chloride hydrochloride.

(3) Thio acids and their salts such as thio-benzoic acid or potassium octylxanthate, dithiocarbamates, for exam ple diethyldithiocarbamate, zinc dibutyldithiocarbamate, the polysulphide derivatives of dithiocarbamates which are activated by alkali, e.g., tetraethylthiuramdisulphide.

(4) Thio amides, e.g., phenylthiourea, N-(N-octylthiocarbamoyl) glycine, thiopropionanilide, phenylthiosemicarbazide.

(5) The selenium analogues of the above, e.g., phenyl selenosemicarbazide, 2-selenylbenzothiazole.

(6) Isothiocyanates, e.g., phenylisothiocyanate.

The silver precipitating agents such as development nuclei on the lithographic printing support should preferably be free of particles of compounds such as zinc sulphide because many of the said organic compounds having the properties required for making the surface of the silver oleophilic chemically react with zinc sulphide to convert it into the metal derivative of said organic compound, and we have found that such conversion of the zinc sulphide nuclei in the background renders those nuclei sufficiently oleophilic to cause the background to accept visible amounts of ink unless the plate is wetted extensively when making the copies therefrom. On the other hand it is believed than any surface action, such as adsorption by metal or metal salt nuclei is not practically detrimental and for this reason nuclei of for instance silver or silver sulphide, which are not converted into particles of a silver salt of the organic compound are the preferred kind of nuclei to employ in this invention. If a low concentration of zinc sulphide nuclei is used in order to try to avoid this difficulty caused by the conversion, there are insutficient nuclei to yield a sufficiently strong surface image.

When, as is preferred, the development nuclei comprises silver or silver sulphide it is necessary to use as little colloidal binder as possible for holding the nuclei on the surface of the support since if too much binder is used, the silver image which is formed is protected by the binder and is not sufficiently strong at the surface to operate satisfactorily in the linking process. It is preferable to obtain adherence between the nuclei and the surface by means other than using a colloidal binder. We have found that an excellent support to use in our invention is aluminum the surface of which comprises a hydrophilic aluminum compound, for example we prefer anodised aluminum. Other supports may be used in the present invention for example, grained zinc chemically treated to produce a hydrophilic lithographic surface, and paper lithographic supports. In the case of paper supports it is preferable to render the paper waterproof or of low water permeability and to apply to the surface a thin hydrophilic layer, such as a layer of casein or silica or polyvinyl alcohol with suitable fillers if necessary and then silver nuclei may be deposited thereon and will adhere thereto. Various plastics may also be used as supports, for example surface hydrolyzed cellulose ester sheetings.

A suitable nucleated surface can be produced on aluminium which has been treated to convert the surface into a hydrophilic aluminium compound for use in making printing plates by the present invention by merely bathing the surface of the aluminium with a colloidal solution of silver or gold or silver sulphide. An alternative but less convenient way of forming such nuclei on the aluminium surface is to bathe the aluminium surface first with a solution of silver nitrate followed by bathing with sodium sulphide thus producing nuclei of silver sulphide.

If the nucleating layer is formed by simply bathing the anodised aluminium in a simple aqueous colloidal solution of silver this ensures that the amount of the silver which is absorbed by the anodised aluminium surface per unit area is extremely low and no colloid binder is necessary. Colloidal solutions of silver which may be used for this purpose are, for instance, those giving yellow, red or black solutions and containing between 0.1 and 0.001 mol of silver per litre.

The simplest way of treating the silver image with the organic compound according to our invention is to form the silver image first and then merely apply to it a solution of the organic compound. However, the silver image may be formed in the presence of the said organic compound.

We have also discovered that the image can be treated with the organic compound by coating the organic compound on the aluminium plate before forming the image thereon and in this case the organic compound becomes adsorbed to the silver as the image is formed. However, in this case it is believed that adsorption of the organic compound by the silver image depends on whether the support has been specially coated with development nuclei, such as colloidal silver or silver sulphide particles and the concentration of such nuclei. If the concentration of nuclei is high then a black image of metallic silver is obtained with the organic compound adsorbed or partly adsorbed thereto. However if the concentration of nuclei is very low or nil a whitish image may result which comprises largely or wholly the silver derivative of the said organic compound formed by double decomposition of the silver halide with the organic compound. 7

It is also possible to produce an oleophilic image if the said organic compound is present in the developing solution when the silver image is formed by the silver salt diffusion process and both the receiving support and the silver halide emulsion layer are immersed therein during the formation of the image.

If desired a two layer material may be usedin the present invention namely one in' which the receiving layer (which may contain development nuclei) is coated beneath the light sensitive silver halide layer it only being necessary to remove, such as by washing away, the latter layer after the silver image has been formed in the receiving layer. In this .case the emulsion layer may be for instance, a cellulose dib'asic acid ester emulsion layer described in the Yackel et al., US. Serial No. 586,705, filed May 23, 1956.

Example 1 A silver sol is prepared by the classical Carey Lea method and is Well Washed and finally diluted to 1 gram in 100 cos. of distilled water. A sheet of aluminium 0.005 inch thickand anodised to give a tihckness of aluminium oxide of about 0.5 gram per square metre is bathed in this solution, the excess removed and the sheet dried.

A high contrast negative material such as Kodak Chemical Transfer Negative Paper comprising a sensitive silver chloride emulsion is exposed either by transmission or by reflex and in conjunction with the prepared'metal receiving sheet is fedthrough a normal processing machine for the silver diffusion process such as the Remington Rand TC; 35, containing a developer of the following composition:

7 Grams Sodium hydroxide 11.25 Sodium sulphite (anhydrous) 75.00 Hydroquinone 18.0 1-phenyl-3-pyrazolidone 1.0 Potassium bromide 0.25 Hypo 3.5

Water to 1 litre.

The two sheets are squeegeed together as they emerge from the developer and are left in contact for /2 minute after which they are stripped apart and the transferred silver image on the aluminium receiving sheet is rinsed and then is swabbed for a few seconds with the following solution:

l octyl 1,2,4,5 tetrahydro 1,3,5 triazine- 4-thiol grams 0.5

Acetone ccs 50 Water do 50 The excess is removed'with a sponge moistened with a weak solution of gumarabic after which the image may be inked in the usual way either by hand or on a lithographic printing machine, and will give several thousands of copies.

Further examples of solutions which may be used for treating the silver image in the foregoing are: (a) 1 dodecyl vl,2,4,5 tetrahydro 1,3,5 tritetrah.ydrol,3,5 -triazine-4thiol in acetone is shaken vigorously with 50 ml. of a 5% aqueous. solution of carboxy, methyl cellulose to form a crude emulsion. i 0

Water .j.... ccs 100 The colour of theimage is hardly affected at all by treatment with any of the solutions described with reference to the foregoing example. j

Further examples of nucleated supports which may be used in the present invention are:

Example 2 1 gram of chloroauric acid H(AuCl is dissolved in 500 ml. of distilled water, it is neutralized with 0.1 N potassium carbonate and heated. A few drops of a solution of White phosphorus in ether are added to produce a gold sol. This gold sol. is washed and diluted to 1 litre and a sheet of anodised aluminium bathed in it and dried.

- E ple 3 This is the same as Example 2v except that the metal sheet instead of being anodised aluminium is a sheet of aluminium on the surface of which a fine sharp lithographic grain has been produced by a chemical etching technique to produce for instance an aluminum silicate or chromate surface, a suitable material being that sold commercially by Addressograph Multigraph for conventional lithographic platemaking.

Examples of further solutions which may be used in the foregoing Example 1 where somewhat less strong oleophilic characteristics in the treated silver image are desired or can be tolerated are: i (d) Ethyl 'iso-thiourea grams Sodium hydroxide do 1 Water ccs 30 Ethanol ccs 70 (e) Dipentamethylene thiuram tetrasulphide grams; 0.25 Sodium hydroxide do 1.0 i Water ccs 30 Ethanol L ccs 70 (f) 2-seleny1 benzothiazole grams 1 Water ccs 30 Ethanol ccs 70 (g) Phenyl selenosemicarbazide grams 1 Water ccs 30 Ethanol ocs 70 (h) Zinc dibutyldithiocarbamate ?ms 1 Water ccs 30 Ethanol ccs 70 (i) S-diethylaminoethyl iso thiuronium chloride hydrochloride grams 1 Sodium hydroxide do 1 Water Q ccs 100 While as stated above it isvery desirable to have the background free of metals and metal salts which are readily converted in metal derivatives of the organic compound used to treat the silver, we have found that in the case of some paper supports which have on the surface -a much thicker hydrophilic layerxthan is the case with anodised aluminium and'the like, it is possible to use zinc sulphide nuclei and then by keeping the printing plate very well wetted during printing several dozen good copies I can be obtained, as in the following example.

Example 4 A lithographic paper plate sold by the Addressograph Multigraph Corporation under the name Blue Duplimat is first treated with a solution of 1% sodium sulphide in water for about 20 seconds and then washed for 2 to 3 minutes and dried off. This treatment is believed to form zinc sulphide in the Duplimat'coating by'the reaction with a soluble zincsalt already incorporated during manufacture of the material. Such treatment provides a suitable nucleated receiving layer. V

The paper plate is now wiped over with the following solution and'dried off: Hypo V -gram-.. 2 Sodium carboxy methyl cellulose (high Viscosity) then ink accepting by wiping over with:

Potassium butyl xanthate "grams" 2 Water ccs 100 The colour of the image is hardly changed at all by this treatment but now readily accepts greasy ink while the background refuses the ink if maintained in a well wetted condition by applying plenty of water in the printing machine. Several hundred copiescan be run off.

An example illustrating the treatment of the silver image by incorporating the organic compound in the developing solution is as follows:

Example 5 A sheet of negative paper such as Kodak Chemical Transfer paper is exposed as in Example 1 and then together with a sheet of anodised aluminium carrying silver nuclei is fed through a processing machine as in Example 1, and using the same developer but also containing 5 grams per litre of 1-hexyl-l,2,4,5-tetrahydro-l,3,5-triazine-4-thiol. When the two sheets are separated the aluminium sheet carries a positive silver image which is oleophilic. It is wiped over with a 2% solution of gum arable and then inked in the usual way.

Examples illustrating the application of the organic compound to the receiving support prior to the formation of the silver image thereon are as follows:

Example 6 A sheet of anodised aluminium foil nucleated by treatment with a silver sol. as in Example 1 is coated with a thin layer of 0.5% solution of 1-octyl-l,2,4,5-tetrahydro- 1,3,5-triazine-4-thiol in ethyl alcohol and then dried off.

A sheet of light sensitive halide negative material such as Kodak Chemical Transfer paper is exposed to a positive image and then in conjunction with the sheet of coated anodised aluminum foil is fed through a Remington Rand TC. 35 machine containing the same developer as in Example 1. When the sheets have been separated the aluminum sheet bearsja black positive image. This sheet is then wiped with a swab containing ethyl alcohol to remove the unused triazine compound. A 2% solution of gum arabic is then wiped on the aluminium and then it is inked in the usual way.

Example 7 A sheet of Blue Duplimat is treated with sodium sulphide as in Example 4.

The paper plate is now wiped over with a 2% solution of hypo in water and dried 01f. A sheet of light sensitive silver halide negative material such as that supplied for the solvent transfer process, e.g., Kodak Chemical Transfer paper is exposed to a positive image, developed for about 20 seconds in the developer used in Example '1 but omitting the hypo, and then while still containing the developer it was laminatedinto contact with the paper Duplimat. After a few-seconds the sheets are separated and a positive image is visible on the Duplimat sheet. The surface of this sheet is now moistened with Platex solution or with a mixture of:

Platex is a proprietory solution sold by Addressograph Multigraph Limited for treating Duplimat sheets.

l i The excess liquid is removed with a damp sponge and this is followed by rubbing over with greasy lithographic ink on a pad or cloth but it will be seen that it is not possible to get much ink to adhere to the silver image. Instead of using the above prepared Duplimat another sheet is taken and after being treated with the sodium sulphide solution is wiped over with the following solution and dried 01f:

Hypo grams 2 Potassium butyl xanthate do 1 Water ccs The remainder of the process is then carried out as before. It will be found that the transferred silver image which is almost black in colour readily accepts lithographic ink when applied from the cloth.

Alternative solutions which may be used in this example for coating on to the Duplimat sheet after treatment with the sodium sulphide are:

When these solutions are used the images are again black in colour.

An example Where the support is coated with the organic compound before the image is formed thereon and the image is formed by double decomposition of the diffusing silver halide with the organic oompound, is as follows:

Example 8 A sheet of brush grained aluminium foil is surface anodized in the known manner to give an aluminium oxide layer of about 0.5 gram per square metre and coated with the following solution:

Potassium octyl xanthate grams 1 Hypo do 2 Water ccs 100 An exposed negative paper is developed and then washed and laminated to the treated aluminium surface and left for about 30 seconds. It is then stripped away and there is seen on the aluminum surface a whitish positive image of silver xanthate. The surface is then wiped over with a gum-phosphoric acid mixture and then rinsed off. This image readily accepts greasy ink.

We claim:

1. A lithographic printing process which comprises forming on a support containing a silver precipitating agent a silver image from the diffusing silver halide of an exposed and developed silver halide emulsion layer in contact with the support and then directly bathing the silver image so formed in a solution of a compound of the class consisting of oleophilic organic compounds containing a thiol group, oleophilic organic compounds generating a thiol group, and selenium analogues of said compounds, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press.

2. A lithographic printing process comprising forming on a support having development nuclei coated thereon a silver image by development of the diffusing silver halide from an exposed and developed silver halides layer in contact therewith and directly bathing the silver image on the support in a solution of a compound of the class consisting of oleophilic organic compounds containing a thiol group, oleophilic organic compounds generating a thiol group, and selenium analogues of said compounds, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing. press.

3. A lithographic printing process according to claim 1 wherein the support is free of metals and metal salts which are readily converted into metal derivatives of said organic compound.

4. A lithographic printing process according to claim 1 wherein the support is aluminium which has been chemically treated to form a surface layer of a hydrophilic aluminium compound.

5. A lithographic printing process according to claim 1 wherein the support is coated with development nuclei of the class consisting of silver, silver sulfide and gold.

6. In a lithographic printing process which comprises forming on a nucleated support a photographic silver image by diffusing silver halide imagewise from an exposed and developed silver halide emulsion over the said support and removing the said emulsion, the step of directly after formation of the silver image bathing the image in a solution of a compound of the class consisting of oleophilic organic compounds containing a thiol group, oleophilic organic compounds generating a thiol group and selenium analogues of,said compounds, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press.

7. A process for preparing'a photographic image from an exposed silver halide emulsion layer comprising developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to a. support containing a silver precipitating agent in the presence of a silver halide solvent and directly following the formation of the silver image on the said support, contacting the silver image with an organic compound containing an oleophilic group in the molecule and selected from the compounds of the general formula wherein R is a member of the class consisting of alkyl and cycloalkane groups, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press.

8. A process for preparing a photographic image from an exposed silver halide emulsion layer comprising developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to a support containing a silver precipitating agent in the presence of a silver halide solvent and directly following the formation of the silver image on the said support, contacting the silver image with an organic mercaptan containing an oleophilic group in the molecule which is 10 capable of rendering the silver image oleophilic, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press.

9. A process for preparing a photographic image from an exposed silver halide emulsion layer comprising developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to a support containing a silver precipitating agent in the presence of a silver halide solvent and directly following the formation of the silver image on the said support, contacting the silver image with a thio-acid containing an oleophilic group in the molecule which is capable of rendering the silver image oleophilic, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press.

10. A process for preparing a photographic image from an exposed silver halide emulsion layer comprising developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to a support containing a silver precipitating agent in the presence of a silver halide solvent and directly following the formation of the silver image on the said support, contacting the silver image with a thio-amide containing an oleophilic group in the molecule which is capable of rendering the silver image oleophilic, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press.

11. A process for preparing a photographic image from an exposed silver halide emulsion layer comprising developing the emulsion layer, transferring the silver halide from the undeveloped areas of the emulsion layer to a support containing a silver precipitating agent in the presence of a silver halide solvent and directly following the formation of the silver image on the said support, contacting the silver image with an isothiocyanate containing an oleophilic group in the molecule which is capable of rendering the silver image oleophilic, inking the silver image with greasy printing ink and printing therefrom in a lithographic printing press.

References Cited in the file of this patent UNITED STATES PATENTS 2,987,396 Williams et al. June 6, 1961 FOREIGN PATENTS 1,058,844 Germany June 4, 1959 783,793 Great Britain Oct. 2, 1957 758,759 Great Britain Oct. 10, 1956 556,753 Belgium Oct. 17, 1957 1,011,280 Germany June 27, 1957 OTHER REFERENCES Belgium 556,753, abstracted in Photographic Abstracts, pub. by The Royal Photographic Society of Great Britain, London, vol. 38, part 4, 1958, p. 325.

Claims

1. A LITHOGRAPHIC PRINTING PROCESS WHICH COMRPISES FORMING ON A SUPPORT CONTAINING A SILVER PRECIPITATING AGENT A SILVER IMAGE FROM THE DIFFUSING SILVER HALIDE OF AN EXPOSED AND DEVELOPED SILVER HALIDE EMULSION LAYER IN CONTACT WITH THE SUPPORT AND THEN DIRECTLY BATHING THE SILVER IMAGE SO FORMED IN A SOLUTION OF A COMPOUND OF THE CLASS CONSISTING OF OLEOPHILIC ORGANIC COMPOUNDS CONTAINING A THIOL GROUP, OLEOPHILIC ORGANIC COMPOUNDS GENERATING A THIOL GROUP, AND SELENIUM ANALOGUES OF SAID COMPOUNDS, INKING THE SILVER IMAGE WITH GREASY PRINTING INK AND PRINTING THEREFROM IN A LITHOGRAPHIC PRINTING PRESS.