GB2146582A

GB2146582A - Lithographic fix solution

Info

Publication number: GB2146582A
Application number: GB08325064A
Authority: GB
Inventors: J K Green
Original assignee: Kodak Ltd
Current assignee: Kodak Ltd
Priority date: 1983-09-20
Filing date: 1983-09-20
Publication date: 1985-04-24
Also published as: GB8325064D0

Abstract

A fully aqueous lithographic fix solution containing a hydrophilic colloid (eg gum arabic or carboxymethyl cellulose), an oleophilic argentophile (e.g. a mercapto-substituted nitrogen containing heterocyclic compound) and a cationic surfactant (e.g. an amine quaternised amine or amide containing a polyethoxy or polyglycidyl group) capable of solubilising the oleophilic argentophile, and wherein the solution is substantially free from non-aqueous solvents.

Description

SPECIFICATION Lithographic fix solution The invention relates to an aqueous lithographic fix solution for rendering silver images oleophilic.

It has been commercial practice for some years to make lithographic printing plates by the silver salt diffusion transfer process. In this process a silver image is deposited on a receiving sheet which is then separated from the photosensitive element with which it was laminated during processing. The support on which the receiving layer is carried may vary but a suitably coated hydrophilic polymer or an anodised aluminium support are commonly used.

The silver image so formed is, however, unsuitable for the lithographic process because it is insufficiently ink-attracting (oleophilic). For this reason it has to be treated with a so-called fix solution which will usually contain a compound which is adsorbed strongly to silver and which has a large hydrocarbon group to provide the necessary oleophilic properties. Such compounds are referred to as oleophilic argentophiles.

Although dispersions of such oleophilic argentophiles have been proposed for this task, for example see U.S. Patent 3,223,524, in practice solutions have been adopted commercially. Usually such solutions while sometimes containing water will contain substantial quantities of volatile organic solvents in order to hold the argentophile in solution. Fix solutions containing substantial quantities of organic solvents are described, for example, in U.S. Patent 3,083,097 and British Specification 2,081,183A.

The presence of such solvents (necessary to dissolve the argentophile) is undesirable in that they present hazards in both use and shipping.

The present invention provides a fully aqueous lithographic fix solution for rendering silver images oleophilic.

According to the present invention there is provided an aqueous lithographic fix solution containing a hydrophilic colloid, an oleophilic argentophile and a surfactant characterised in that the solution is substantially free from non-aqueous solvents and in that the surfactant is a cationic surfactant capable of solubilising the oleophilic argentophile.

The preferred cationic surfactants are amines, quaternised amines or amides containing a polyethoxy or polyglycidyl (non-ionic) group. The non-ionic group may vary widely in size but groups having from 2 to 10, preferably 3 to 8 repeating ethoxy or glycidyl units are preferred. A specific example of such a cationic surfactant is Ethoduomeen T25, an ethoxylated diamine of Tallow available from Akzo Chemie.

The hydrophilic colloid may be, for example, gum arabic or carboxymethyl cellulose.

Many oleophilic argentophiles are known including mercapto-substituted nitrogen-containing heterocyclic compounds, e.g. 3-mercapto-4-acetamido-5-n-heptyl-1,2,4-triazole, 1-phenyl-5-mercaptotetrazole, 2- mercaptobenzothiazole and bis-2-mercapto-thiadiazines.

The present fix solutions may also contain nitrate ions, supplied for example by an alkali metal or ammonium nitrate, and a buffer to contro pH. The preferred pH range being from 2 to 6, preferably 4.

Very small quantities, say less than 5% by weight of the total composition of non-aqueous liquids may be present. For example a solvent could be added to improve the ability of the composition to clean the background areas. In addition an oily or resinous liquid could be dispersed therein to improve ink-up of the image, e.g. methyl abietate.

While the proportions of the various constituents of the present fix solutions may vary, preferred ranges of concentration of the essential constituents are given below for guidance.

The hydrophilic colloid should be used at a concentration that imparts the desired viscosity. For example carboxymethylcellulose (7L2P from Hercules Powder Company) is preferably used at 4 to 30 g/l and gum arabic at 100-400 g/l. The oleophilic argentophile is preferably used at 0.1 to 10 g/l. The cationic surfactant should be used in an amount sufficient to solubilise the argentophile, preferably from 1 to 10 g/l.

The following Example is included for a better understanding of the invention Example Ethoduomeen T251 4.0 gm 1-Phenyl-5-mercaptotetrazole 1.8 gum Carboxy methyl cellulose (7L2P)2 12.0 gm Ammonium Nitrate 5.0 gm 10% Citric acid in water to pH4 (approx 20 mls) Water to make 1 litre an ethoxylated diamine of Tallow supplied by Akzo Chemie.

2supplied by Hercules Powder Company.

Images were formed by diffusion transfer onto a nucleated anodised aluminium foil from a projection speed negative. The plates were then treated with the above fix solution. On printing, these plates produced excellent results.

Claims

1. An aqueous lithographic fix solution containing a hydrophilic colloid, an oleophilic argentophile and a surfactant characterised in that the solution is substantially free from non-aqueous solvents and in that the surfactant is a cationic surfactant capable of solubilising the oleophilic argentophile.

2. A lithographic fix solution as claimed in claim 1 in which the cationic surfactant is an amine, quaternised amine or amide containing a polyethoxy or polyglycidyl (non-ionic) group.

3. A lithographic fix solution as claimed in claim 2 in which the non-ionic group comprises from 2 to 10, preferably from 3 to 8 repeating ethoxy or glycidyl units.

4. A lithographic fix solution as claimed in any of claims 1-3 in which the hydrophilic colloid is gum arabic or carboxymethyl cellulose.

5. A lithographic fix solution as claimed in any of claims 1-4 in which the oleophilic argentophile is a mercapto-substituted nitrogen-containing heterocyclic compound.

6. A lithographic fix solution as claimed in claim 5 in which the olephilic argentophile is 3-mercapto-4 actamido-5-n-heptyl-1 2,4-triazole, 1 -phenyl-5-mercaptotetrazole, 2-mercaptobenzothiazole or a bis-2mercapto-thiadiazine.

7. A lithographic fix solution as claimed in any of claims 1-6 which also contains nitrate ions.

8. A lithographic fix solution as claimed in any of claims 1-7 is buffered to a pH of 2-6, preferably 4.

9. A lithographic fix solution as claimed in any of claims 1-8 which contains less than 5% by weight of the total composition of a non-aqueous liquid.

10. A lithographic fix solution as claimed in claim 9 in which the non-aqueous liquid is a solvent to inhibit the inking of background areas or an oily or resinous liquid to improve ink receptivity of the image.

11. A lithographic fix solution as claimed in any of claims 1-10 which contain carboxymethyl cellulose at 4to 30 g/l or gum arabic at 100-400 gull.

12. A lithographic fix solution as claimed in any of claims 1-11 which contains the oleophilic argentophile at 0.1 to lOg/I.

13. A lithographic fix solution as claimed in any of claims 1-12 which contain the cationic surfactant at 1 to 10 g/l.

14. A lithographic fix solution according to claim 1 substantially as described herein and with reference to the Examples.

15. A method of lithographic plate making which includes the step of applying to a silver image-bearing plate a fix composition according to any of claims 1-14.