GB1603700A - Developers for lithographic printing plates - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO DEVELOPERS FOR LITHOGRAPHIC PRINTING PLATES (71) We, VICKERS LIMITED, a British Company, of Vickers House, Millbank Tower, Millbank, London SWI do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to developers suitable for processing lithographic printing plates.

Lithographic printing plates comprise ink receptive water repellant printing area and water receptive ink repellant non-printing areas. The printing and non-printing areas are essentially coplanar. During printing, an aqueous medium is applied to the plate.

This wets the non-printing areas but is repelled by the printing areas. An oleophilic printing ink is applied and this is accepted by the printing areas but repelled by the wet non-printing areas. Ink is then transferred from the printing areas to the member being printed.

Such printing plates are conventionally produced photomechanically. In this technique a suitable substrate is coated with a radiation sensitive material and the resultant radiation sensitive plate is imagewise exposed to radiation. This is effected using a transparent film having an opaque areas. A negative transparency of the image desired to be reproduced is used for exposing a so-called negative-acting radiation sensitive plate, and a positive transparency is used for exposing a socalled positive-acting radiation sensitive plate. In the case of negative-acting plates radiation passes through the clear areas of the transparency, which correspond to the image, and causes a reaction in the radiation sensitive coating that insolubilises the coating in the image area. Radiation does not pass through the opaque areas of the transparency, however, so that the radiation sensitive coating underlying such areas remains unaffected. The exposed plate is then developed by selectively removing the non-radiation struck areas of the coating to reveal the underlying surface of the substrate. If the revealed surface is not hydrophilic, it is then made so and serves as the non-printing areas of the plate.

The insolubilised coating remaining on the substrate after development then consistutes the printing areas of the plate.

Typical of the radiation-sensitive materials commonly used for negative acting plates is a photopolymerisable.

material containing groups of the structure -CH=CH-CO-, for example polyvinyl cinnamate. Whilst printing plates formed from radiation sensitive plates based on these materials are satisfactory from the aspect of printing life, i.e. the number of satisfactory copies produced, and the radiation sensitive plates have a satisfactory storage life, i.e. they may be stored for a considerable period prior to being exposed and developed, the materials have a disadvantage with regard to the organic solvent liquids which have to be used for the developing step. Many of these solvents are toxic, unpleasant to use, or produce problems with regards to their disposal.

Examples of such solvents are cyclohexanol, methoxybutyl acetate, 2methoxyethyl acetate and dimethyl formamide.

In view of the increasing concern over health and pollution, the printing plate manufacturing industry sought to provide a negative-working presensitised plate that did not require the use of these solvents, but which would still be satisfactory in terms of printing and storage life.

The problem was partially solved by the use of a water soluble diazo resin as the radiation sensitive material, for example the condensation product of 4-diazodiphenylamine phosphate and formaldehyde. Whilst such materials were satisfactory from the aspect of development in that water could be used as the developer, printing plates formed then did not have a good enough printing life unless given suitable treatment with, for example, a reinforcing lacquer, and radiation sensitive plates formed from them did not have a good enough storage life. Organic solvent soluble diazo resins are now known that do not suffer from the above disadvantage yet can still be processed with developers consisting substantially of water, for example an aqueous solution containing n-propanol, a sulphonic acid and an ionic surfactant. In some cases, however, the amount of npropanol or sulphonic acid required to remove the non-radiation struck areas is such that the radiation struck areas are also attacked causing over development of the plate.

According to the present invention, there is provided a developer suitable for processing image-wire exposed radiation sensitive plates comprising an aqueous alkaline solution of (a) an organic compound, (b) a water miscible organic solvent, and (c) a surface active agent.

wherein said organic compound has the general formula

wherein R1 and R2 which may be the same or different each represents a hydrogen atom, an optionally substituted alkyl, group having up to 5 carbon atoms, an optionally substituted aryl group, or together represent either an optionally substituted alkylene group or an optionally substituted carbon chain including a hetero atom: R is an optionally substituted alkylene group or an optionally substituted arylene group X is COO-, S03-, OPT,: or OSO,-; m and n are zero when R is an optionally substituted alkylene group; and m and n are independently integers of from 0 to 4 when R is an optionally substituted arylene group.

The alkylene or arylene groups may be substituted with for example COO-, OH, NH2, halogen, alkoxy, optionally substituted alkyl, optionally substituted aryl, or heterocyclic groups. By way of example, the organic compound may be an N-heterocyclic compound substituted with, for example, a COO- or 503 group. It will be apparent from the foregoing general formula that the organic compound may be based on a heterocyclic ring including one or more hetero atoms. For example it may include a morpholino group. With regard to the defined general formula, in the case where R1 and R2 together represent an alkylene group or a carbon chain including a hetero atom, the ring may be substituted with a group having the formula CH2)nRCH2)rnX, where R, X, n and m are as defined above.

According to a further preferred feature the developer comprises from 5 to 25 ó w/v of the organic compound, from 5 to 30 Ó w/v of water miscible organic solvent and from 5 to 50% w/v surfactant.

Preferred organic compounds are the salts (particularly the sodium salts) of amino benzoic acids, particularly 2- or 4-amino benzoic acid; 6-aminohexanoic acid: amino acetic acid; 4-aminophenylacetic acid; 3 dimethylaminobenzoic acid; 5-amino phthalic acid; sulphanilic acid; pyrrole carboxylic acid: pyridine carboxylic acid; leucine, and tryptophan.

The developer preferably contains a buffer to maintain the pH in the alkaline range up to 11.

The water miscible solvent is preferably a solvent completely miscible with water such as one of the lower alcohols, such as ethanol, n-propanol or iso-propanol, or tetra hydrofurfuryl alcohol. However, less miscible solvents such as cyclohexanol or benzyl alcohol may be added in small amounts. Examples of suitable surface active agents are sodium dodecyl benzene sulphonate, sodium lauryl ether sulphate, sodium dioctyl sulphosuccinate, sodium n decyl biphenyl ether disulphonate, and sodium dodecyl biphenyl ether disulphonate.

Thickening agents to slow down the rate of evaporation of the solvent, biocides, anti foaming agents and/or colourants may be added to the developer.

The following Examples illustrate the invention.

EXAMPLE 1 A sheet of aluminium was cleaned, electrochemically grained, anodised and finally treated with sodium silicate according to U.S. Patent No. 2,714,066.

The sheet was coated with the product obtained by reacting the condensation product of diazodiphenylamine bisulphate and formaldehyde with hexafluoro phosphoric acid at a coating weight of 0.8 g/m2.

The resultant radiation sensitive plate was cut in half and both halves were exposed under a negative transparency and a stepwedge to an ultra violet source for identical times. One plate, plate A, was developed with the following solution (Developer A) benzene disulphonic acid 10% w/v sodium dodecyl benzene sulphonate 5% w/v isopropanol losd w/v water to 1000/, The other plate, Plate B, was developed with the following solution (Developer B) sodium aminobenzoate 10% w/v sodium dodecyl benzene sulphonate 5 Ó w/v isopropanol 10% w/v aqueous buffer solution (pH 10) to 1000i: Both plates were desensitised and linkedup in the conventional manner. The stepwedge reproduction on Plate A showed step 4 solid, step 8 tail whereas the step-wedge reproduction on Plate B showed step 6 solid, step 9 tail. When placed on an offset press, Plate A gave only 20,000 satisfactory copies whilst Plate B gave 80,000 satisfactory copies.

EXAMPLE 2 A sheet of aluminium was prepared as in Example 1 and coated with the reaction product of diazodiphenylamine bisulphate/formaldehyde and sodium triisopropyl-naphthalene sulphonic acid at a coating weight of 0.7 gm-2.

The resultant radiation sensitive plate was cut in half and both halves were exposed under a negative transparency and a stepwedge to an ultra violet source of identical times.

One of the plates was developed with the following solution (Developer C) Phosphoric acid 5% w/v sodium lauryl ether sulphate 5% w/v ethanol 25% w/v water to 100% The other plate was developed with the following solution (Developer D) sodium dimethylamino benzoic acid sodium lauryl ether 10% sulphate 595 w/v ethanol 25Uo w/v aqueous buffer solution (pH9) to 100% Both plates were desensitised and inked up in the conventional manner. The step wedge reproduction on the first plates showed step 4 solid, step 7 tail, whilst the step-wedge reproduction on the other plate showed step 6 solid, step 10 tail. When placed on an offset press, the first plate gave only 10,000 copies whilst the second plate gave 75,000 copies.

EXAMPLE 3 A sheet of aluminium was cleaned, electrochemically grained, and anodised. It was then treated with poly(vinyl phosphonic)acid according to G.B. Patent No. 1,230,447.

The sheet was coated with the product obtained by reacting the condensation product of diazodiphenylamine bisulphate and formaldehyde with sodium dodecycl benzene sulphonate, at a coating weight of 0.7 gm-2. The resultant radiation sensitive plate was exposed under a negative to an ultra violet source and developed with the following solution (Developer E).

disodium-5-aminophthalic acid 20% w/v sodium dioctylsulpho succinate 5% w/v tetrahydrofurfuryl alcohol 30% w/v aqueous buffer solution (pH 7.5)to 100% The plate developed quickly and cleanly.

After desensitising and inking-up the plate was placed on an offset press, where 50,000 good quality copies were produced with little sharpening of the image.

EXAMPLE 4 A sheet of aluminium was cleaned, electrochemically grained and anodised and then treated with potassium zirconium fluoride solution.

The sheet was coated with the product obtained by reacting the condensation product of diazodiphenylamine bisulphate and formaldehyde with nitrobenzene sulphonic acid at a coating weight of 1.0 gm-2.

The resultant radiation sensitive plate was exposed under a negative and a step-wedge to an ultra violet source and developed with the following solution (Developer F).

sodium pyridine-2 carboxylate 10% w/v sodium n-decylbiphenyl ether disulphonate 10% w/v n-propanol 3/o w/v aqueous buffer solution (pH 10) to 100% The plate developed quickly and cleanly leaving the non-image areas completely clear of coating. The plate was desensitised and inked-up in the normal manner. The step-wedge reproduction showed a sharp cut-off.

When placed on an offset press, the plate gave 50,000 copies with no sign of image break down occurring.

EXAMPLE 5 A sheet of aluminium was treated as in Example 1 and coated with the product obtained by reacting the condensation product of diazodiphenylamine bisulphate and formaldehyde with 4-suiphosalicyclic acid, at a coating weight of 0.9 gm-2. The resultant radiation sensitive plate was exposed under a negative and developed with the following solution.

sodium 2-amino-4-methyl pentanoate 8% w/v sodium dodecyl biphenyl ether disulphonate 40% w/v isopropanol 18% w/v aqueous buffer solution (pH 9) to 100% The plate developed quickly and cleanly and gave 70,000 good quality copies when placed on an offset press.

WHAT WE CLAIM IS: 1. A developer suitable for processing image-wise exposed radiation sensitive plates comprising an aqueous alkaline solution of (a) an organic compound, (b) a water miscible organic solvent, and (c) a surface active agent.

wherein said organic compound has the general formula

wherein R1 and R2, which may be the same or different, each represents a hydrogen atom, an optionally substituted alkyl group having up to 5 carbon atoms, an optionally substituted aryl group, or together represent either an optionally substituted alkylene group or an optionally substituted carbon chain including a hetero atom; R is an optionally subsituted alkylene group or an optionally substituted arylene group, X is COO-, S03-, OPO3- or OSO3-, m and n are zero when R is an optionally subsitituted alkylene group: and m and n are independently integers of from 0 to 4 when R is an optionally substituted arylene group.

2. A developer as claimed in Claim 1 wherein the organic compound is a salt of (i) an amino benzoic acid, (ii) 6-aminohexanoic acid, (iii) aminoacetic acid, (iv) 4aminophenylacetic acid, (v) 3-dimethylaminobenzoic acid, (vi) 5-aminophthalic acid; (vii) sulphanilic acid; (iix) leucine; or (ix) tryptophan.

3. A developer as claimed in Claim í wherein the organic compound is a N- heterocyclic compound substituted with a COO- or SO3- group.

4. A developer as claimed in Claim 3 wherein the organic compound is pyrrole carboxylic acid or pyridine carboxylic acid.

5. A developer as claimed in Claim I wherein in the case where R' and R2 represent an alkylene group or a carbon chain including a hetero atom, the ring is substituted with a group having the formula CH2)nRCH2)rnX wherein R, X, m and n have the meanings specified in Claim 1.

6. A developer as claimed in any one of the preceding claims wherein the organic solvent is a lower alcohol or tetrahydrofurfuryl alcohol.

7. A developer as claimed in any one of the preceding claims wherein the surface active agent is sodium dodecyl benzene sulphonate, sodium lauryl ether sulphate, sodium dioctyl sulphosuccinate, sodium ndecyl biphenyl ether disulphonate or sodium dodecyl biphenyl ether disulphonate.

8. A developer as claimed in any one of the preceding claims comprising from 5 to 25% w/v of the organic compound, from 5 to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. gave 50,000 copies with no sign of image break down occurring. EXAMPLE 5 A sheet of aluminium was treated as in Example 1 and coated with the product obtained by reacting the condensation product of diazodiphenylamine bisulphate and formaldehyde with 4-suiphosalicyclic acid, at a coating weight of 0.9 gm-2. The resultant radiation sensitive plate was exposed under a negative and developed with the following solution. sodium 2-amino-4-methyl pentanoate 8% w/v sodium dodecyl biphenyl ether disulphonate 40% w/v isopropanol 18% w/v aqueous buffer solution (pH 9) to 100% The plate developed quickly and cleanly and gave 70,000 good quality copies when placed on an offset press. WHAT WE CLAIM IS:

1. A developer suitable for processing image-wise exposed radiation sensitive plates comprising an aqueous alkaline solution of (a) an organic compound, (b) a water miscible organic solvent, and (c) a surface active agent.

wherein said organic compound has the general formula

wherein R1 and R2, which may be the same or different, each represents a hydrogen atom, an optionally substituted alkyl group having up to 5 carbon atoms, an optionally substituted aryl group, or together represent either an optionally substituted alkylene group or an optionally substituted carbon chain including a hetero atom; R is an optionally subsituted alkylene group or an optionally substituted arylene group, X is COO-, S03-, OPO3- or OSO3-, m and n are zero when R is an optionally subsitituted alkylene group: and m and n are independently integers of from 0 to 4 when R is an optionally substituted arylene group.

2. A developer as claimed in Claim 1 wherein the organic compound is a salt of (i) an amino benzoic acid, (ii) 6-aminohexanoic acid, (iii) aminoacetic acid, (iv) 4aminophenylacetic acid, (v) 3-dimethylaminobenzoic acid, (vi) 5-aminophthalic acid; (vii) sulphanilic acid; (iix) leucine; or (ix) tryptophan.

3. A developer as claimed in Claim í wherein the organic compound is a N- heterocyclic compound substituted with a COO- or SO3- group.

4. A developer as claimed in Claim 3 wherein the organic compound is pyrrole carboxylic acid or pyridine carboxylic acid.

5. A developer as claimed in Claim I wherein in the case where R' and R2 represent an alkylene group or a carbon chain including a hetero atom, the ring is substituted with a group having the formula CH2)nRCH2)rnX wherein R, X, m and n have the meanings specified in Claim 1.

6. A developer as claimed in any one of the preceding claims wherein the organic solvent is a lower alcohol or tetrahydrofurfuryl alcohol.

7. A developer as claimed in any one of the preceding claims wherein the surface active agent is sodium dodecyl benzene sulphonate, sodium lauryl ether sulphate, sodium dioctyl sulphosuccinate, sodium ndecyl biphenyl ether disulphonate or sodium dodecyl biphenyl ether disulphonate.

8. A developer as claimed in any one of the preceding claims comprising from 5 to 25% w/v of the organic compound, from 5 to

30% w/v of said solvent, and from 5 to 50% w/v of said surface active agent.

9. A developer as claimed in any one of the preceding claims and having a pH in the alkaline range up to 11.

10. A developer as claimed in Claim I substantially as described in any one of the foregoing Examples.

I I. A method of processing a suitable image-wise exposed radiation sensitive plate which comprises applying to the plate a developer as claimed in any one of Claims 1 to 10.

12. A processed plate whenever obtained by the method claimed in Claim 11.