GB1600350A

GB1600350A - Radiation sensitive materials

Info

Publication number: GB1600350A
Application number: GB2526178A
Authority: GB
Original assignee: VICKRS Ltd
Current assignee: VICKRS Ltd
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-10-14

Description

(54) IMPROVEMENTS IN OR RELATING TO RADIATION SENSITIVE MATERIALS (71) We, VICKERS LIMITED, a British Company, of Vickers House, Millbank Tower, Millbank, London SW1, 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 radiation sensitive materials and is concerned with radiation sensitive materials suitable for use in the production of radiation sensitive plates for lithographic printing plate manufacture.

In the manufacture of printing plates such radiation sensitive plates, the radiation sensitive coating is image-wise exposed to radiation. The radiation renders the radiation struck areas of the coating either more or less soluble in solvents for the nonradiation stuck areas (depending on the nature of the radiation sensitive material).

By subsequently developing the image-wise exposed plate using such a solvent as de veloper. the more soluble areas can be selectively removed to leave an image constituted by the less soluble areas.

Radiation sensitive plates comprises a substrate coated with a condensation product of a 4-diazodiphenylamine salt and formaldehyde are known. Such plates can be stored for a considerable period before being processed into lithographic printing plates. In order to be commercially satisfactory, the radiation sensitive material should have as high a radiation sensitivity as possible and also should be soluble in a suitable solvent medium to enable it to be coated on the substrate.

The light sensitivity of condensation products of 4-diazo diphenylamine salts and formaldehyde is dependent on the conditions under which the condensation is carried out. It has been found that a good guide to the light sensitivity can be obtained from the ratio of aromatic ring protons to aliphatic protons in bridging the methylene groups of the condensation product. This ratio can be determined by nuclear magnetic resonance (NMR) techniques.

The lower this ratio, the more condensed, and hence the more light sensitive, is the product likely to be. There are indications that an increased level of condensation will result in a smaller residual hydroxy methyl content and it is believed that the presence of this particular grouping reduces the solubility differential between the radiation struck and non-radiation struck areas of the coating and possibly the stability of the product.

In order to produce a radiation sensitive plate, the radiation sensitive material is applied to the substrate in solution in a suitable solvent. Ideally, the solvent used should have a high evaporation rate and cause no problems in respect of health and/or pollution. Examples of preferred organic solvents used hitherto are ethanol, ethyl methyl ketone and a mixture of toluene and isopropanol.

Those condensation products of 4diazodiphenylamine and formaldehyde which are soluble in water only are not satisfactory for use in the production of radiation sensitive plates because water is not particularly suitable as a coating medium and the resultant plates generally have a relatively short storage life. Many attempts have been made to produce radiation sensitive materials suitable for the production of radiation sensitive plates for lithographic printing plate manufacture by converting these water soluble condensation products into organic solvent soluble materials by a change of anion. However, many of these materials still have disadvantages.

In some cases, the material is soluble only in organic solvents that are unsatisfactory from the health/pollution aspect such as ethylene glycol monomethyl ether, cyclohexanone, dimethyl formamide, 1,4-diethylene dioxide or tetrahydrofuran. In other cases the material with a different anion precipitates as an oil rather than a solid which makes it difficult to isolate. In yet other cases, the product has good solubility in suitable coating solvents but the light sensitivity of plates made therefrom is inadequate. In particular, it has been found that known materials soluble in the above preferred solvents give radiation sensitive plates having very poor light sensitivity. Examples of anions giving such materials are lauryl sulphate, paradodecyl benzene sulphonate and dioctyl sulphosuccinate.

It has now surprisingly been found that radiation sensitive materials which are satisfactory for use in the production of storage stable radiation sensitive plates for lithographic printing plate manufacture, can be formed by reacting a condensation product of 4-diazodiphenylamine and formaldehyde having a suitable proton ratio with certain naphthalene sulphonic acids or derivatives thereof or with certain mixtures of surfactants and acid compounds such as sulphonic acids or derivatives thereof.

According to the present invention, there is provided a radiation sensitive material comprising the reaction product of (i) a condensation product of a salt of an optionally substituted 4-diazodiophenylamine and formaldehyde having a ratio of aromatic ring protons to aliphatic protons in bridging methylene groups of less than or equal to 2.3:1 and (ii) either a) an alkyl naphthlene sulphonic acid or salt or other derivative thereof or b) a mixture of at least two acidic compounds or salts or other derivatives thereof, at least one of which is a surfactant, and preferably at least one of which is a aryl or heterocyclic sulphonic acid or salt or other derivative thereof.

As is well known, a surfactant is a material having one or several strongly polar groups and one or (more rarely) a few large non polar residues in one molecule.

The non-polar groups possess a much lower surface energy than the polar groups. When dissolved in water or other polar solvent these compounds have a higher concentration in the surface than in the interior of the solution: the non-polar groups then form a new surface with a lower surface energy than the original solvent surface. The proton ratio is the ratio, of the aromatic ring protons to the aliphatic protons in methylene bridging groups, discounting any protons to be found in the anion. The proton ratio is measured by nuclear magnetic resonance spectroscopy. For consistency and ease of measurement it is desirable that the NMR determinations should be carried out using condensation products having a common proton free anion. Preferably the anion is proton-free. Whilst any proton-free anion is usable, it is preferred that an anion conferring on the condensation product solubility in solvents other than water, such as BF4 or PF6, is used. The reason for using such anions is that separation of the condensation product from low molecular weight material, notably uncondensed reactants, the presence of which might give an incorrect proton ratio measurement, is facilitated.

It is particularly preferred for the condensation produce to include no, or only a small proportion of, hydroxymethyl groups. The condensation product may be produced by reacting formaldehyde per se with the diazodiphenylamine salt. Alternatively the formaldehyde may be in polymeric form or in the form of another substance which liberates formaldehyde.

According to a preferred feature of the invention, the alkyl naphthalene sulphonic acid or derivative thereof has at least 7 aliphatic carbon atoms. Examples of suitable alkyl naphthalene sulphonic acids or derivatives thereof are diisobutylnaphthalene sulphonic acid (or sulphonate) and tri-isopropylnaphthalene sulphonic acid (or sulphonate).

According to a further preferred feature of the invention, the acidic compound having surfactant properties in the mixture is a sulphate or a sulphonic acid or derivative thereof such as sodium dioctyl sulphosuccinate, sodium dodecyl benzene sulphonate, sodium dicyclohexyl sulphosuccinate, sodium lauryl sulphate, sodium alkyl phenol ether sulphate, sodium diamyl sulphosuccinate or sodium ethoxylauryl sulphate and the other acidic compound is fluoroboric acid, hexafluorophosphoric acid or a sulphonic acid such as acetyl benzene sulphonic acid, benzaldehyde sulphonic acid, xylene sulphonic acid, sulphosalicyclic acid, naphthalene-2-sulphonic acid, mesitylene sulphonic acid, camphor sulphonic acid or octylphenol sulphonic acid.

The following Examples illustrate the invention.

Example 1 29.3g (0.1mol) of 4-diazodiphenylamine bisulphate was added to 80 g of 98% sulphuric acid at a temperature below 5"C.

4.5 g (0.15 mol) of paraformaldehyde was then added slowly, the temperature being kept below 5"C. After 2 hours, the solution was poured onto 200g of ice and made up to a 1 litre solution with distilled water.

For test purposes 100ml of the solution was dripped into a mixture of 1.12 g sodium fluoroborate in 100ml distilled water to produce the BF4 salt. NMR analysis showed a proton ratio of 1.6:1.37.52g (0.llmol) of sodium di-isobutyl naphthalene sulphonate was dissolved in a mixture of 0.5 litre isopropanol and 1.25 litre of water. The above condensation product solution was dripped into this mixture and the precipitated resin was filtered, washed with distilled water and dried.

3.0g of the resin product was dissolved in a 60:40 toluene/isopropanol. mixture and whirler coated on to an electrochemically grained, anodised and silicated sheet and dried. The coating weight was 0.8gm-2. The resultant radiation sensitive plate was exposed beneath a half tone negative and a step wedge to a 4Kw pulsed xenon lamp at a distance of 1 metre for 1 minute.

The plate was developed with a solution of sodium dodecylbenzene sulphonate containing 20% isopropanol and buffered at pH 9. After development the plate was densitised and inked-up in the normal manner.

On subsequent exposure to a step wedge the step-wedge reproduction showed a step 6 solid and a step 9 tail. When placed on a web offset press the plate produced 100,000 satisfactory copies.

Example 2 Example 1 was repeated except that the di-isobutylnaphthalene sulphonate was replaced by 39.27g (0.11 mol) of sodium tri-isopropylnaphthalene sulphonate. The plate was again satisfactory giving a step wedge reprodction of a step 6 solid and a step 9 tail and 100.000 copies.

Example 3 Example 1 was again repeated except that the di-isobutylnaphthalene sulphonate was replaced by a mixture of 13.15 g (0.055 mol) of nitrobenzene sulphonic acid and 24.42 g (0.055 mol) of sodium dioctyl sulphosuccinate. The plate was again satisfactory giving a step-wedge reproduction of step 5 solid and step 9 tail and 60,000 copies.

Example 4 Example 1 was repeated except that the di-isobutyl naphthalene sulphonate was replaced by a mixture of 16.94 g (0.055 mol) of 2-hydroxy-4-methoxy benzophenone-5sulphonic acid and 15.84g (0.055 mol) of sodium lauryl sulphate. Results similar to those of Example 3 were obtained.

Example 5 Example 1 was repeated using a mixture of 17.27g (0.055mol) of diisopropylnaphthalene sulphonate and 24.4g (0.055 mol) of sodium di-octyl sulpho succinate instead of the di-isobutyl naphthalene sulphonate. Results similar to those of Example 3 were obtained.

Example 6 29.3g (0. 1mol) of 4-diazodiphenylamine bisulphate was added to 80 g of 88% phosphoric acid at a temperature below 40"C. 3.15g (0.05 mol) of paraformaldehyde was then added slowly, the temperature being kept below 40"C. After 20 hours the solution was poured on to 200 g of ice and made up to a 1 litre solution with distilled water.

A 100 ml sample of the solution was dripped into sodium fluoroborate as before to produce the BF4 salt. NMR analysis showed a proton ratio of 2.18:1.

The above condensation product was reacted with sodium di-isobutyl naphthalene sulphonate as in Example 1. The resultant radiation sensitive material was used to form a radiation sensitive plate in the manner of Example 1. The plate was exposed and developed as in Example 1 and gave a step-wedge reproduction of step 6 solid, step 9 tail and 100,000 copies.

Example 7 Example 6 was repeated except that the sodium di-isobutyl naphthalene sulphonate was replaced with sodium tri-isopropyl naphthalene sulphonate. Results similar to those of Example 2 were obtained.

Example 8 Example 6 was repeated except that the di-isobutyl naphthalene sulphonate was replaced with a mixture of nitrobenzene sulphonic acid and sodium dioctyl sulphosuccinate as in Example 3. Results similar to those of Example 3 were obtained.

Example 9 The condensation product of 4diazodiphenylamine and formaldehyde prepared as in Example 1 was reacted with 38.24 (0.11 mol) of sodium dodecyl benzene sulphonate. A radiation sensitive plate was prepared from the resultant radiation sensitive material. The plate was processed in the same way as in Example 1. The step wedge reproduction showed a step 4 solid, step 7 tail and produced only 30,000 copies.

Example 10 Example 9 was repeated except that the sodium dodecyl benzene sulphonate was replaced with 48.84 g (0.11 mol) of sodium dioctyl sulphosuccinate. Similar results were obtained.

Example 11 Example 9 was repeated except that the sodium dodecyl benzene sulphonate was replaced by 26.30g (0.llmol) of nitrobenzene sulphonic acid.

The resulting radiation sensitive material was insufficiently soluble in toluene/isopropanol for coating purposes and it was necessary to use 2-methoxy ethanol as coat ing solvent.

Example 12 A small sample of a commercially available diazo resin believed to be a chlorozinacate salt of the condensation product of 4-diazodiphenylamine and formaldehyde was reacted with sodium fluoroborate to produce the BF4 salt. NMR analysis showed a proton ratio of 2.75:1. 35.0 g of the resin were reacted with 34.54g (0.11 mol) sodium tri-isopropyl naphthalene sulphonate to form a radiation sensitive material. 3.0 g of this material was dissolved in 60:40 toluene/ isopropanol and used to coat a sheet in the manner of Example 1. The resultant radiation sensitive plate was exposed and processed as in Example 1. The processed plate showed a step wedge reproduction of step 3 solid, step 6 tail and produced only 20,000 copies.

Example 13 The resin preparation of Example 6 was repeated except that the reaction was terminated after 2 hours.

NMR analysis of a sample of the resin converted to the BF4 salt showed a proton ratio of 2.96:1.

The resin was reacted with di-isobutyl naphthalene sulphonic acid and the resultant radiation sensitive material was used to produce a radiation sensitive plate as in Example 1. The plate was exposed and developed as in Example 1 and gave a step wedge reproduction of only step 2 solid, step 6 tail.

Example 14 A condensation product of 4diazodiphenylamine bisulphate and formaldehyde prepared as in Example 1 was reacted with a mixture of sodium lauryl sulphate (29.6g. = 0.0825mol) and 2hydroxy-4-methoxy benzophenone sulphonic acid (8.47 = 0.0275mol).

The product was completely soluble in a mixture of toluene and isopropanol. Following the procedure of Example 1, it was used to produce a radiation sensitive plate which was then exposed and developed as in that Example. The results were similar to those obtained in Example 3.

Example 15 A condensation product of 4diazodiphenylamine bisulphate and formaldehyde prepared as in Example 1 was reacted with a mixture of sodium dodecyl benzene sulphonate (28.71g = 0.0825 mol) and 2-hydroxy-4-methoxybenzophenone sulphonic acid (8.47g = 0.0275 mol). The product was completely soluble in a mixture of toluene and isopropanol. It was used to produce a radiation sensitive plate in the manner of Example 1 which was then processed as in that Example. The results were similar to those obtained in Example 3.

WHAT WE CLAIM IS: 1. A radiation sensitive material comprising the reaction product of (i) a condensation product of a salt of a optionally substituted 4-diazo diphenylamine and formaldehyde having a ratio of aromatic ring protons in bridging methylene groups of less than or equal to 2.3:1 and (ii) either (a) an alkyl naphthalene sulphonic acid or derivative thereof of (b) a mixture of at least two acidic compounds or salts or other derivatives thereof, at least one of which is a surfactant.

2. A material as claimed in Claim 1 wherein the alkyl naphthalene sulphonic acid is di-isobutyl naphthalene sulphonic acid or tri-isopropyl naphthalene sulphonic acid.

3. A material as claimed in Claim 1 wherein the alkyl naphthalene sulphonic acid derivative is sodium di-isobutyl naphthalene sulphonate or sodium tr-isopropyl naphthalene sulphonate.

4. A material as claimed in Claim 1 wherein the surfactant is sodium dioctyl sulphosuccinate, sodium dodecyl benzene sulphonate, sodium dicyclohexyl sulphosuccinate, sodium ditridecyl sulphosuccinate, sodium lauryl sulphate, sodium alkyl phenol ether sulphate, sodium diamyl sulphosuccinate or sodium ethoxy lauryl sulphate.

5. A material as claimed in Claim 1 or 4 wherein the surfactant is in admixture with acetyl benzene sulphonic acid, benzaldehyde sulphonic acid, xylene sulphonic acid, sulphosalicylic acid, naphthalene-2sulphonic acid, mesitylene sulphonic acid, camphor sulphonic acid, or octyl phenol sulphonic acid.

6. A material as claimed in any one of the preceding claims wherein the condensation product is substantially free of hydroxy methyl groups.

7. A material as claimed in Claim 1 substantially as hereinbefore described in any one of Examples 1 to 8.

8. A solution of the material claimed in any preceding claim in ethanol, ethyl methyl ketone, or a mixture of toluene and isopropanol as solvent.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ing solvent. Example 12 A small sample of a commercially available diazo resin believed to be a chlorozinacate salt of the condensation product of 4-diazodiphenylamine and formaldehyde was reacted with sodium fluoroborate to produce the BF4 salt. NMR analysis showed a proton ratio of 2.75:1. 35.0 g of the resin were reacted with 34.54g (0.11 mol) sodium tri-isopropyl naphthalene sulphonate to form a radiation sensitive material. 3.0 g of this material was dissolved in 60:40 toluene/ isopropanol and used to coat a sheet in the manner of Example 1. The resultant radiation sensitive plate was exposed and processed as in Example 1. The processed plate showed a step wedge reproduction of step 3 solid, step 6 tail and produced only 20,000 copies. Example 13 The resin preparation of Example 6 was repeated except that the reaction was terminated after 2 hours. NMR analysis of a sample of the resin converted to the BF4 salt showed a proton ratio of 2.96:1. The resin was reacted with di-isobutyl naphthalene sulphonic acid and the resultant radiation sensitive material was used to produce a radiation sensitive plate as in Example 1. The plate was exposed and developed as in Example 1 and gave a step wedge reproduction of only step 2 solid, step 6 tail. Example 14 A condensation product of 4diazodiphenylamine bisulphate and formaldehyde prepared as in Example 1 was reacted with a mixture of sodium lauryl sulphate (29.6g. = 0.0825mol) and 2hydroxy-4-methoxy benzophenone sulphonic acid (8.47 = 0.0275mol). The product was completely soluble in a mixture of toluene and isopropanol. Following the procedure of Example 1, it was used to produce a radiation sensitive plate which was then exposed and developed as in that Example. The results were similar to those obtained in Example 3. Example 15 A condensation product of 4diazodiphenylamine bisulphate and formaldehyde prepared as in Example 1 was reacted with a mixture of sodium dodecyl benzene sulphonate (28.71g = 0.0825 mol) and 2-hydroxy-4-methoxybenzophenone sulphonic acid (8.47g = 0.0275 mol). The product was completely soluble in a mixture of toluene and isopropanol. It was used to produce a radiation sensitive plate in the manner of Example 1 which was then processed as in that Example. The results were similar to those obtained in Example 3. WHAT WE CLAIM IS:

1. A radiation sensitive material comprising the reaction product of (i) a condensation product of a salt of a optionally substituted 4-diazo diphenylamine and formaldehyde having a ratio of aromatic ring protons in bridging methylene groups of less than or equal to 2.3:1 and (ii) either (a) an alkyl naphthalene sulphonic acid or derivative thereof of (b) a mixture of at least two acidic compounds or salts or other derivatives thereof, at least one of which is a surfactant.

9. A radiation sensitive plate comprising

a substrate coated with a material as claimed in any one of Claims 1 to 8.