This invention is concerned with improvements in and relating to photocurable materials, the preparation thereof and compositions containing them.

The use of materials containing ethylenic unsaturation, particularly that derived from an unsaturated carboxylic acid such as acrylic or methacryliσ acid, in photocurable or photopolymerisable compositions is well known and established. Such compositions, when adapted to be cured by the action of UN light, generally also contain a photosensitizer in conjunction with the ethylenically unsaturated material. Such photocurable compositions are widely used as coating compositions; being firstly applied to a substrate by an appropriate method and then later being cured in situ on the substrate by the action of UN light.

It is a particular object of the present invention to provide a photocurable material which is suitable for use as a component in photocurable lithographic inks (i.e. inks to be applied to a substrate by a lithographic printing process and subsequently cured by exposure to UV radiation).

It has now been found, in accordance with the present invention, that certain reaction products of epoxy resins with fatty acids and unsaturated acids have unexpectably useful properties as components of photocurable lithographic inks. GB-A-1580115 discloses reaction products of a variety of epoxy resins with a combination of- certain unsaturated fatty acids and unsaturated lower carboxylic acids, the fatty acid forming at least 25 mole % of the acid mixture. Such products are not satisfactory for use in lithographic printing inks.

In accordance with a first embodiment of the present invention there is provided as an ethylenically unsaturated material, suitable for use in photocurable compositions, comprising the reaction product of an epoxy novolac resin with (i) an ethylenically unsaturated carboxylic acid and (ii) a long chain fatty acid, the long chain fatty acid forming from 2.5 to 15 _/ preferably 6 to 12, ^' mole % of the total components (i) and (ii).

Epoxy novolac resins (sometimes referred to as epoxidised novolac resins and which term is intended to embrace both epoxy phenol novolac resins and epoxy cresol novolac resins) are polyepoxy compounds,

(in which R is a hydrogen atom or lower alkyl, e. g. methyl groups; and n is 0 or an integer).

Epoxy novolac (including epoxy cresol novolac resins) resins are readily commercially available, for example under the Trade Names DEN, Quatrex, Grilonit (ESN) and Araldite (ECN). The materials of commerce- generally comprise mixtures of various species of the above formula and a convenient way of characterising such mixtures is by reference to the average, n' , of the values of n for the various species. Preferred epoxy novolac resins for use in accordance with the invention are those in which n' has a value of from 0.2 to 6.0, more preferably from 1.1 to 4.0.

Preferred ethylenically unsaturated carboxylic acids for reaction with the epoxy novolac resin are acrylic acid and methacrylic acid, especially the former.

The fatty acid used to modify the epoxy novolac/unsaturated acid reaction product suitably contains at least 8 carbon atoms and is preferably one containing from 12 to 20 carbon atoms. Typical examples of suitable fatty acids are caprylic, capric, lauric, myristic, palmitic, stearic and arachidic acids. Mixtures of such acids, for example those such as may be derived, directly or indirectly, from vegetable or animal sources may be used.

The curable materials in accordance with ^" the invention may be produced in one or two stages, namely by:

(a) reacting the epoxy novolac resin with a mixture of the ethylenically unsaturated carboxylic acid and the fatty acid; or

(b) reacting the epoxy novolac resin with the ethylenically unsaturated carboxylic acid to produce a reaction product (hereinafter, for convenience, simply referred to as an "epoxy acrylate" ); and reacting the reaction product (epoxy acrylate) with the fatty acid.

Reaction of the epoxy novolac with the aσid(s) is carried out by reacting the resin with the acid(s), generally at elevated temperature, e.g. 70 to 110'C, and possibly in the presence of a catalyst. such as triphenyl phosphine.

In the course of reaction of the ethylenically unsaturated acid with the novolac resin, the epoxy groups of the resin and the carboxylic acid groups of the acids react to link the acids to the resin by an ester linkage whilst at the same time giving rise to free secondary hydroxyl groups.

The ratio of total carboxyl groups to epoxy oxygen atoms should be substantially 1: 1. The final product should have an epoxy value below lOmgKOH/g, preferably below 5 mgKOH/g, and an acid value below 4 mgKOH/g, preferably below 2 mgKOH/g.

The curable materials (esters) in accordance with the invention are readily photopolymerisable or photocurable by the action of ultra violet light in the presence of a conventional photoinitiator.

Accordingly, the invention also provides a photocurable composition comprising a photocurable material as defined above together with a photoinitiator. Such compositions may also, and indeed, generally will, contain other ingredients such as, for example, diluents, colourants or fillers.

Suitable photosensitizers or photoinitiators for use in photocurable compositions according to the invention include benzophenone, substituted benzophenones, 2-chlorohioxanthone, isopropyl- thioxanthene, di-alkyl-p dimethylamine benzoates (including the diethyl, amyl/isoamyl and ethyl hexyl compounds), and 2-cleavage initiators, such as these sold under the trade names Darocur 1173, Irgacure 174, Irgacure 184, Irgacure 651, Irgacure 907, Irgacure 369, Esacure KIP, and Lucirin 7PO. Commonly an initiator system will comprise a mixture of two or more compounds as listed above.

The diluents possibly employed in the photocurable compositions may be reactive or non-reactive diluents. Thus, reactive diluents are diluents which themselves contain ethylenically unsaturation and will co-polymerise with the curable esters in the composition, during irradiation thereof, to afford a cured composition. Examples of such reactive diluents include esters of acrylic acid and methacrylic acids such as tripropylene glycol diacrylate. trimethylolpropane triacrylate, alkoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, alkoxylated pentaerythritol triacrylate, di-tetramethylolpropane triacrylate, alkoxylated

neopentyl glycol diacrylate, alkoxylated glyceryl triacrylates, dipentaerythritol penta- and hexa-acrylates and dianol diacrylate.

The colourants used in the photocurable compositions may be pigments or dyestuffs. Suitable fillers include mineral fillers such as silicas, bentonite clays, talc, alumina hydrate, barium sulphate, calcium carbonate and magnesium carbonate.

In accordance with a particularly preferred embodiment of the invention, the photocurable composition takes the form of a lithographic ink; generally comprising (I) a photocurable ester of the invention, (II) reactive diluent as discussed above,

(III) a photoinitiator, and (IV) a colorant. The ink suitably comprises from 10 to 80% by weight, preferably 30 to 50% by weight of curable ester (I), from 0 to 30 % by weight, preferably 5 to 15 % by weight, of reactive diluent (II); from 2 to 10 % by weight, preferably 5 to 8%, by weight of photoinitiator (III), and from 5 to 30% by weight, preferably 10 to 20% by weight, of colorant

(IV) in the form of a pigment.

The lithographic inks of the invention may also contain mineral fillers as discussed above and, also, micronised (e.g. having a particle size of 1-20 microns) polyethylene, polypropylene and/or polytetrafluorethylene.

The lithographic inks of the invention can show improved lithographic control on a printing press whilst still maintaining the cure speed required for commercial operation, typically 50 meters per minute under an irradiation of 80 watts per cm.

In order that the invention may be well understood the following examples are given by way of illustration only. In the Example all parts are by weight unless otherwise indicated.

Example 1

A solution of an ethylenically unsaturated material in accordance with the invention in a polymerizable solvent (tripropylene glycol diacrylate) was prepared from the following ingredients.

Quatrex 2410 (Dow Chemical) 39.116

Tripropylene glycol diacrylate 43.868

Inhibitor

(Hydroquinone) 0.167

Catalyst

(Triphenyl phosphine) 0.516

Stannus ^' octoate 0.449

Laurie acid 2.035

Glacial acrylic acid 13.849

The epoxy novolac resin (Quatrex 2410), multifunctional acrylate, inhibitor and stannow octoate were charged to a round-bottom glass reaction vessel, fitted with a stirrer, thermometer and air-sparge (set at 36/kg/hr).

The temperature was raised, gently, to dissolve the epoxy resin in the multifunctional acrylate (σa. 80"C). The acyliσ and fatty acid were then charged with the catalyst over a temperature range of 80-110'C.

This temperature was maintained until the acid value had fallen below 2 mg KOH/g and the epoxide value had fallen to below 5 mg KOH/g.

The batch was then cooled to 70'C, and discharged through a filter.

Example 2

An ester was prepared, following the procedure of Example 1, from the following ingredients.

Quatrex 2010 (Dow Chemical) 44.95 Tripropylene glycol diacrylate 33.814 Inhibitor

(Hydroquinone) 0.198 Catalyst

(Triphenyl phosphine) 0.609

Stannus octoate 0.530

Coconut oil fatty acid 3.870

Glacial acrylic acid 16.034

Example 3

Following the procedure of Example 1 a modified epoxy novolac acrylate was made from the following components: -

Epoxy novolac 42.705 parts

(DEN 438)

Inhibitor 0.183 parts

(hydroquinone)

Catalyst 0.563 parts

(triphenylphosphine)

Stannous octoate 0.490 parts

Acrylic acid (glacial) ' 15.652* parts

Octanoic acid 1.443 parts

Multifunctional acrylate 38.764 parts

(tripropylene glycol diacrylate)

Examples 4 and 5

Modified epoxy novolac resins were prepared, following the procedure of Example 1 from the following ingredients.

Example 4

Epoxy novolac resin 35.015 parts (quatrex 2410)

Inhibitor 0.153 parts (hydroquinone)

Catalyst 0.468 parts

(triphenyl phosphine)

Stannous octoate 0.408 parts

Acrylic acid 12.071 parts

Coconut oil fatty acid 2.914 parts

Multifunctional acrylate (ethoxylated trimethylol propane 48.971 parts triacrylate)

Exampl e 5

Epoxy novolac resin 40.300 parts

(Quatrex 2010)

Inhibitor 0.184 parts

(hydroquinone)

Catalyst 0.561 parts

(triphenyl phosphine)

Stannous octoate 0.490 parts

Acrylic acid 13.208 parts

Laurie acid 6.497 parts

Multifunctional (acrylate) 38.765 parts

(Propoxylated glyσenol triacrylate)

Lithographic printing inks were prepared from the modified resins produced in Examples 3, 4 and 5, in accordance with the following formulations.

Example 6

Modified resin of 55.0 parts Example 3

Ethoxylated 15.0 parts trimethylol propane triacrylate

Pigment Blue (15:3) 20.0 parts

Benzophenone 3. 0 parts

Ethyl p-dimethylamino-benzoate 2.0 parts

Irgacure 651 2.0 parts

Bentone 500 2.0 parts

Polyfluo 190 1.0 parts

Example ^' 7

Modified resin of 58.0 parts' Example 4

Alkoxylated pentaerythritol 16.0 parts triacrylate

Pigment Yellow 13 14.0 parts

Benzophenone 3.0 parts

2-Chiorothioxanthone 1.0 parts

Isuamyl dimethylaminobenzoate 3.0 parts

Calcium carbonate 3.0 parts

Shamrock wax 55TU 2.0 parts

Exampl e 8

Modified acrylate of 55. o parts Example 5

Propoxylated glycenol triacrylate 14.0 parts

Pigment Red 112 18.0 parts

Benzophenone 3.0 parts

Isopropyl-thioxanthone -1. o parts

Ethyhexyl dimethylaminobenzoate 2.0 parts

Daraσur 1173 2.0 parts

Aerosil 200 1.5 parts

Lenowax PE 1500 1.5 parts