GB2110401A - Developer solutions and processes for making lithographic printing plates - Google Patents

Abstract

A single-phase developer liquid for lithographic printing plates sensitized with diazo or diazonium compounds and incorporating a resin that is not light sensitive but has better mechanical properties than the said compound. The resin may be mixed with the sensitiser or may be coated over it. The developer includes 10 to 20 parts of a water-immiscible solvent for the resin present in the plate and correspondingly 80 to 90 parts water together with sufficient solubilisers to obtain a single-phase solution. The solubilisers include both an anionic surfactant and a non-ionic surfactant. The anionic surfactant is relatively hydrophilic (at least as hydrophilic as sodium nonyl sulphate) and the non-ionic surfactant is relatively organophilic. By using two surfactants of this kind together, rapid action without the separation of large flakes of resin can be obtained, and the tendency to foam is usefully reduced.

Description

SPECIFICATION Developer solutions and processes for making lithographic printing plates This invention relates to developer solutions for certain lithographic printing plates. More particularly, it relates to the processing of plates sensitised with diazo or diazonium compounds, either positive-working or negative working.

In view of their high cost and relatively poor abrasion resistance, these sensitive substances are in most cases used in conjunction with an inexpensive resin that is not light sensitive but has better mechanical properties; the resin may be mixed with the sensitiser or it may be coated over it.

Developers for such a plate must have sufficient affinity for the resin to disperse resin particles from areas of the plate in which the sensitiser has become, or remained, soluble in the background areas of the plate, without attacking the image areas; and in the case of over-coated plates it must penetrate through the resin layer fast enough to give an acceptably short development time.

A range of developers that has been found useful consists basically of an organic liquid that would dissolve the resin mixed with water to establish the required differential solubility; as the most effectively penetrating organic liquids have very limited solubility in water, it has been proposed to add a third ingredient (a solubiliser) to allow the formation of a single-phase mixture containing a higher proportion of the organic liquid than would otherwise dissolve. Anionic and non-ionic surfactants are suitable solubilisers, and it has been recognised that they might be mixed, but it has not hitherto been suggested that there was any merit in the use of mixtures.

The developer in accordance with the present invention comprises: 10 to 20 parts of a waterimmiscible solvent for the resin; 80 to 90 parts water; and sufficient solubilisers to obtain a single-phase solution, the solubilisers comprising an anionic surfactant that is relatively hydrophilic and a non-ionic surfactant that is relatively organophilic.

Developers in accordance with the invention can be formulated to give rapid penetration, and consequently rapid development without the risk of resin flakes or other large particles appearing in the liquor, as is liable to happen if a single surfactant solubiliser of high hydrophilicy is used; and at the same time the tendency to generate foam when sprayed or brushed is reduced.

Suitable organic solvents include (subject to compatibility with the resin chosen) ketone, halogenated hydrocarbons, alkylated aromatic hydrocarbons, carboxylic esters and those alcohols that are not freely miscible with water.

Specific examples include ethyl butyl ketone, metho iso butyl ketone, cyclohexanone, methylene chloride, ethylene chloride, monochlorobenzene, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, benzyl acetate, ethylene glycol, monobutyl ether acetate, ethylene glycol, mono iso amyl ether, benzyl alcohol, neopentyl alcohol, and xylene. When the resin is a polyvinyl acetal, benzyl alcohol is particularly preferred.

The ratio of organic solvent to water must be chosen, within the range indicated, to secure adequate differential solubility as between exposed and unexposed areas of the plate to be processed.

By a relatively hydrophilic surfactant is meant one that is at least as hydrophilic (in terms of partition coefficient between xylene and water) as the sodium salt of nonyl sulphate. With few exceptions these will include a sulphate, phosphate, sulphonate or phosphonate group and an organic group containing from six to nine carbon atoms.

By a relatively organophilic surfactant is meant one that is more organophilic (in terms of its partition coefficient between xylene and water) than the sodium salt of nonyl sulphate. Ether and hydroxy surfactants such as alcohol ethoxylates and alkyl phenol ethoxylates and the long-chain ethers and esters of di- and poly-ethylene glycol, polypropylene glycol and sorbitol are preferred, but non-ionic sulphate or phosphate surfactants, e.g. laurel methyl sulphate, could be used if desired.

The invention will be further described, by way of example with reference to certain specific lithographic printing plates.

Example 1 A conventional anodised and silicated aluminium plate substrate was coated with 0.1 g/m2 of the toluene sulphonic acid salt of diazo diphenylamine/formaldehyde condensation product and then over-coated with a solution containing 5 parts by weight of polyvinyl formal (Formvar 12/85 from Monsanto) and one part by weight of ball milled pigment Monastral Blue BG dissolved in 94 parts by weight of ethylene dichloride and dried to give a coating weight of 0.8g/m2.

After exposure the plate could be developed with the following known developer: Pentrone ON (33% active) 48g Benzyl Alcohol 1 4g Sodium Hydroxide 0.1g Water 37.9g (Pentrone ON is a commercial sodium ethyl-hexyl sulphate).

The clear solution developed the plate quickly but flakes of coating material up to about 1 mm in diameter became dispersed in it and some foaming was observed.

However, if in accordance with the invention some of the Pentrone ON was replaced with an alkyl phenol ethoxylate (Ethylan 44 from Diamond Shamrock) to produce the following formula according to this invention: Pentrone ON (33% active) 30g Benzyl Alcohol 14g Sodium Hydroxide 0.1g Ethylan 44 6g Water 49.9g this clear solution developed the plate quickly with the removed part of coating finely dispersed in the developer. The developer of this invention could be used in a processor (Howson Algraphy Negative 30) in which it is sprayed and brushed on a plate without deleterious foaming, whilst the developer without the alkyl phenol ethoxylate could not.

Example 2 A conventional anodised and silicated aluminium plate substrate was coated with 0.9g of the naphthalene sulphonic acid salt of the diazo diphenylamine/formaldehyde condensation product and then over-coated with the following ball milled dispersion (see co-pending Application MJP/J9210 filed on the same day as this application): Polyvinyl formal (Formvar 12/85 from Monsanto) 5g Copper phthalocyanine pigment (Monastral Blue BG from ICI) 1 g 2,5 di-n-butoxy 4-morpholino benzene fluoroborate 0.3g Metanil Yellow 0.15g Toluene: ethyl alcohol (95%) 60:40 by weight 94g to a coating weight of 0.6g/m2.

The plate could be developed with the following solution: Benzyl Alcohol 1 2g Pentrone ON 36g Trisodium Citrate 2g Water 50g The solution developed the exposed plate relatively quickly but flakes of coating material up to about 1 mm in diameter became dispersed in it.

However, if in accordance with the invention some of the Pentrone ON anionic surfactant was partially replaced with an alkyl phenyl ethoxylate (Ethylan HA from Diamond Shamrock) as follows: Benzyl Alcohol 1 2g Pentrone ON 24g Trisodium Citrate 2g Ethylan HA 5g Water 57g no such flakes were observed. The developer containing the nonionic surfactant also showed a lower tendency to foam.

Example 3 A conventional anodised and silicated aluminium plate substrate was coated with a 4% solution of the condensation product of diphenylamine 4 diazonium chloride, half zinc chloride salt and formaldehyde and then overcoated with the same inert resin coating as in Example 2.

After exposure the plate could be developed with the following solution: Benzyl Alcohol 11 g Pentrone ON 33g Disodium Tetraborate 2g Water 54g The plate developed quickly but flakes of coating material up to 1 mm in diameter became dispersed in it.

If however, in accordance with the invention some of the Pentrone ON anionic surfactant were replaced by an alcohol ethoxylate (Ethylam CD919 from Diamond Shamrock) as follows: Benzyl Alcohol 11 g Pentrone ON 22g Disodium Tetraborate 2g Ethylan CD919 8g Water 57g development was equally quick without any flakes being apparent. The foaming of the developer was also reduced.

Example 4 A conventional grained anodised and silicated aluminium plate substrate was coated with the toluene sulphonic acid salt of the diazo diphenylamine/formaldehyde condensation product, coating weight 0.1 g/m2, and then overcoated with a solution containing 5 parts by weight of a polyvinyl acetal resin (BM18 from Wacker Chemie) to a coating weight of 1 g/m2.

After exposure the plates could be developed with the following solution: Ethylene Glycol Mono Phenyl Ether 20g Pentrone ON 20g Sodium Carbonate 1.5g Water 63.5g Development was rapid but some slight signs of image attack were apparent and flakes of coating material up to 1 mm diameter became dispersed in the developer.

If, however, in accordance with the invention some of the Pentrone anionic surfactant were replaced by an alcohol ethoxylate Tergitol 15-S12 (from Union Carbide) as follows: Ethylene Glycol Mono Phenyl Ether 20g Pentrone ON 1 5g Sodium Carbonate 1 .5g Tergitol 15-S-12 5g Water 63.5g development was equally rapid with no signs of image attack and no coating flakes were apparent.

Example 5 A conventional anodised and silicated aluminium plate substrate was coated with 0.12g of the 2-hydroxy-4-methoxy benzophenone 5sulphonic acid salt of diazo diphenylamine formaldehyde condensation product and then over-coated with a solution containing 5 parts by weight of polyvinyl formal (Formvar 12/85 from Monsanto) and one part by weight of ball milled pigment Monastral Blue BG dissolved in 94 parts by weight of ethylene dichloride to a coating weight of 0.8g/m2.

After exposure the plate could be developed with the following solution: G2209 (45% active postassium salt of a phosphoric ester) (ex Atlas Chemical Ind. UK Ltd) 40g Benzyl Alcohol 15g Sodium Acetate 2g Water 43g The clear solution develops the plate quickly but flakes of coating material up to about 1 mm in diameter became dispersed in it.

However if in accordance with the invention some of the G2209 is replaced with a polyoxethylene sorbitol mono-acetate (Tween 80 from Atlas Chemical Industries Ltd) as follows: G2209 35g Benzyl Alcohol 15gel Sodium Acetate 2g Tween 80 4g Water 43g the clear solution develops the plate quickly with the coating finely dispersed in the developer.

Example 6 A plate as described in Example 5 could also be developed after exposure with the following solution: Sodium Ethyl Hexanoate 19g Benzyl Alcohol 15g Water 66g Sodium Hydroxide sufficient to adjust the PH to 10 The plates developed quickly with the clear solution but flakes of coating material up to 1 mm dispersed in it.

However, if in accordance with the invention, 5g of the sodium ethyl hexanoate was replaced with a nonyl phenol ethoxylate ((Synperonic NP8 from ICI Limited) the developer worked quickly and the coating was finely divided in the developing solution. In this case no noticeable alteration in the foaming level was observed with the addition of the nonionic surfactant, as the solution without it was already of a low foaming nature.

Example 7 A conventional anodised and silicated aluminium plate substrate was coated with 0.1 gm2 of the toluene sulphonic acid salt of diazo diphenylamine-formaldehyde condensation product and then over-coated with a solution containing 4 parts by weight of Vinylite VROH 1 part by weight of ball milled pigment Monastral Blue B dissolved in 95 parts by weight 2 ethoxyethyl acetate and dried to give a coating weight of 0.7g/m2.

After exposure the plate could be developed with the following solution: Pentrone ON (33% active) 45g Methyl Isobutyl Ketone 1 3g Potassium Carbonate 1g Water 41g The clear developer develops the plate quickly but shows signs of attacking the image area in streaks and shows flakes of coating material up to 1 mm in diameter.

If, however, in accordance with the invention 5g of Supronic B25 (obtained from BM Limited was added to the developer formula, the plate was developed equally quickly without any signs of image attack.

When each developer was used in a developing machine to develop plates, a lower foaming tendency was demonstrated by the developer containing the nonionic surfactant Supronic B25.

Claims (7)

Claims

1. A developer comprising 10 to 20 parts of a water-immiscible solvent for a resin; 80 to 90 parts water and sufficient solubilisers to obtain a single-phase solution, characterised in that the solubilisers comprise an anionic surfactant that is relatively hydrophilic and a non-ionic surfactant that is relatively organophilic.

2. A developer in accordance with Claim 1 characterised in that the solvent is selected from ketones, halogenated hydrocarbons, alkylated aromatic hydrocarbons, carboxylic esters and those alcohols that are not freely miscible with water.

3. A developer as claimed in either of the preceding claims in which the relatively hydrophilic surfactant is a compound including a sulphate, phosphate, sulphonate or phosphonate group and an organic group containing from six to nine carbon atoms.

4. A developer as claimed in any one of the preceding claims in which the organophilic surfactant is an ether or hydroxy surfactant.

5. A developer as claimed in Claim 4 in which the relatively organophilic surfactant is selected from alcohol ethoxylates, alkyl pheno ethoxylates and the long-chain ethers and esters of di and poly-ethylene glycol, propylene glycol and sorbitol.

6. A developer in accordance with the invention substantially as described in any one of Examples 1 to 6.

7. A method of developing a lithographic printing plate sensitized with a diazo or diazonium compound mixed with or over-coated with a resin that is not light sensitive but has better mechanical properties than the diazo or diazonium compound, characterised by the use of the developer claimed in any one of the preceding claims.