GB2356712A

GB2356712A - Preparation of tack-free photoresin printing plates

Info

Publication number: GB2356712A
Application number: GB9928046A
Authority: GB
Inventors: Maria Dincheva
Original assignee: Chemence Ltd
Current assignee: Chemence Ltd
Priority date: 1999-11-29
Filing date: 1999-11-29
Publication date: 2001-05-30
Also published as: GB9928046D0

Description

2356712 NEW METHOD AND PRODUCT

BACKGROUND OF THE INVENTION

The present invention relates to photoresin printing plates, also called liquid photopolymer printing plates. More particularly, the invention relates to a preparative technique for making substantially tack-free photoresin plates which have a long "shelf life", i.e. good resistance to tack formation during storage. The invention also relates to a novel product for use in the technique of the invention.

As will be familiar to the skilled reader, photoresin printing plates are made by the free radical-initiated curing of a liquid photopolymer preparation based on one or more prepolymers containing at least one polymerisable double bond, such as unsaturated urethane acrylate and/or urethane methacrylate prepolymer and ethylenically unsaturated monomers such as esters of acrylic and/or methacrylic acid. In general, resin compositions polymerised and cured by exposure to curing radiation tend to have residual surface tack from unreacted ingredients due to oxygen inhibition.

The preparation of photoresin printing plates is well known but a brief description of a typical process will be given here for the reader unfamiliar with the subject. The first step of the process is exposure in which uncured liquid photopolymer composition is exposed to curing radiation through a masking element (usually a photographic negative) which selectively blocks areas from irradiation. Thus, the first step is normally as follows: a front surface of a layer of liquid photopolymer preparation is exposed to light while a masking film (e.g. a photographic negative) is interposed between the liquid preparation and the light source, such that the preparation in a front surface region cures selectively in areas where the masking film allows more transmission of light. The back surface is exposed to substantially uniform light of an intensity which, during the exposure time, cures only a surface region of the polymer to form a continuous backing.

The irradiation therefore forms a cured photorelief plate. In practice, the light (radiation) used is usually actinic radiation. Also in practice, air is excluded from the front and back surfaces by having the photopolymer layer positioned between covering sheets. Exposure is followed by wash out, as described in the next paragraph.

2 The front surface of the exposed photorelief plate of course has liquid photopolymer preparation in unexposed areas. This liquid photopolymer is removed in a wash out unit by a spray or jet of aqueous liquid. In commercial practice the wash out unit normally comprises a rotary drum and clamp devices to hold the exposed plate (after removal of the front covering sheet) to the drum with the back surface against the drum, so that the liquid photopolymer is exposed. The wash out unit also has spray apparatus, normally comprising a multiplicity of spray heads, arranged to spray wash out liquid onto the clamped photorelief plate while the drum rotates so as to wash liquid photopolymer out of the plate. The wash out liquid is normally water containing a surfactant and an antifoaming agent.

The front (relief) surface of the washed plate is tacky in areas previously covered by uncured photopolymer and is post-exposed to curing radiation to remove tack. Post- exposure is traditionally carried out under water which provides substantially anaerobic conditions and the water contains dissolved post-exposure salts to prevent the small amount of dissolved oxygen inhibiting curing. The post-exposure salts in practice include sodium sulfite (an oxygen scavenger).

Finally, the post-exposed plate is dried, usually by warm air and normally in an oven.

Photorelief printing plates must be effectively tack-free for use in printing. Two particular problems which arise with tacky plates are the adhesion of dust and other particles to the plates (which reduces print quality) and, when paper is being printed, the adhesion of paper to the printing plate. Tacky plates are therefore unacceptable to printers.

Conventional photoresin printing plates, for example as produced by the above described process, develop tackiness during storage as a result of insufficiently cured (including uncured) photopolymer resin. This is even the case if standard free radical initiators in the liquid photopolymer are supplemented by H-abstraction photoinitiators, which are relatively resistant to oxygen inhibition. (Only a limited concentration of H-abstraction photoinitiators may be used, otherwise the good image quality of the printing plate is 3 sacrificed). H-abstraction photoinitiators are organic chemicals normally insoluble in water and, for effective action, are customarily used by chemists as solutions in organic solvents.

New products have recently been introduced to the US market which are aimed at achieving superior ink transfer and reduced plate tack. These products use dry light post-exposure using ò germicidal lamps using sheet platemaking equipment, or ò special above water racks using platemaking equipment with germicidal lamps.

Although the post-exposure tack of these products is low and superior to that of other products on the market, their application is restricted due to the fact that germicidal light sources are not available at many plate making facilities.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention provides a process for making photoresin printing plates which is characterised in that the aqueous wash out liquid contains an H abstraction photoinitiator as a dispersion. As a result, the H-abstraction photoinitiator enters a superficial layer of the plate and, in the subsequent post-exposure step, more completely cures partially cured or uncured photopolyrner resin in this layer to give a tack-free surface. The use of an H-abstraction photoinitiator enables dry light post exposure, in which the plate is not immersed in water. Accordingly, preferred processes of the invention use dry light post exposure but this is not essential.

The wash out liquid advantageously additionally contains a surfactant, which in one class of processes is a substituted amine surfactant such as a triethanolamine alkyl sulfate, for example. This type of surfactant acts synergistically with the H-abstraction photoinitiator.1t has unexpectedly been found that a dispersion of H-abstraction photoinitiator in the aqueous wash out liquid can enable production, after post-exposure, of a photoresin plate having a substantially tack free surface. Particularly surprising for a dispersion is the long period during which the surface remains tack free. Whilst not 4 bound by theory, it is believed that the impinging jets of wash out liquid during the wash out process may help drive the dispersed initiator into the resin at a relatively high concentration and to a relatively great depth.

The invention enables plate makers to make photoresin plates having a smooth, tack free, fine surface finish without the use of additional apparatus or organic solvents (though, minimal amounts of organic solvent may sometimes be used). Organic solvents have of course been long recognised as environmentally undesirable. Moreover, the invention enables the use of water in post exposure to be dispensed with. Accordingly, post-exposure salts neither have to be used nor disposed of, and additionally dry light post exposure improves the feel of the plate.

In another aspect, the invention provides a photoresin plate wash out unit containing wash out liquid which contains an H-abstraction photoinitiator as a dispersion. The H- abstraction photoinitiator may conveniently be called a "developer".

The H-abstraction photoinitiator may conveniently be packaged in admixture with the surfactant composition which is for combining with water to form the wash out liquid. The invention therefore includes a composition comprising a wash out surfactant and an H-abstraction photoinitiator.

Also included in the invention are photoresin printing plates made by the process of the invention and printed products where the printing was performed using such plates. The printed products may for example be printed paper cardboard or metals, the paper optionally being in the form of leaflets or booklets and the cardboard optionally being in the form of boxes.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention for making a photoresin printing plate comprises exposure to curing radiation and in practice UV light as a first step. The materials and methods used in the exposure step are not critical to the invention and conventional practice may be followed, in which the liquid polymerisable resin composition comprises a prepolymer which has at least one polymerisable double bond, an ethylenically unsaturated monomer having at least one polymerisable double bond and a photopolymerisation initiator. Typically, the photopolymer composition contains also a light absorber and a polymerisation inhibitor as a stabiliser against premature polyrnerisation. As suitable prepolymers. there may be mentioned unsaturated polyester resins, unsaturated polyurethane resins, unsaturated polyamide resins, unsaturated polyacrylate resins and unsaturated polymethacrylate resins, especially polyether polyester urethane copolymer, polyether urethane polymer and hydroxyl terminated hydrogenated polybutadiene resin. Polyether urethane or polyester-polyether urethane based photopolymer compositions are very suitable. The astute purchaser will obtain VERBATIM@ liquid photopolymer from Chemence Limited, Corby, NN 17 4XD, United Kingdom or from Chemence Inc, of Alpharetta, GA 30201, USA, The liquid prepolymer is exposed to a selected pattern of radiation, which will usually be actinic radiation in the known way, to form a photorelief plate. Suitably, a commercially available exposure unit is used, for example one manufactured by Asahi Chemical Industries. Typically, a masking film (in practice a photographic negative) is placed on the glass plate of an exposure unit and covered with a polypropylene or other cover film.

Spacers are placed on the cover film to define a cavity into which the liquid photopolymer composition is poured before it is covered with a backing sheet, for example made of surface-treated polyester (e.g. sold under the trade mark CE by Chemence Limited). The covered liquid photopolyiner is then irradiated from the masked front side and the unmasked back (top) side to form a cured photorelief plate, from which the front cover film is stripped prior to wash out. In the wash out step, sprays or jets of wash out liquid are directed to the front (relief) surface of the photoresin plate, to wash out uncured liquid photopolymer. A standard commercially available wash out unit may be used under normal conditions, for example a wash out unit of the type containing a rotary drum and clamping apparatus for clamping the photoresin plate to the drum with its front surface facing outwards. Wash out units of this type are provided also with a multiplicity of spray heads directed towards the circumference of the drum so as to spray a photoresin plate with wash out liquid while the drum rotates.

6 The wash out liquid is as always an aqueous medium containing a surfactant (also called wash out agent) and customarily an anti-foaming agent. Wash out liquids must be free of significant quantities of organic solvent for damage to the washed plates to be avoided. Where the invention differs from existing processes is that the aqueous wash out liquid additionally contains an H-abstraction photoinitiator. These initiators are not significantly soluble in water and are present in the wash out liquid in the form of a dispersion.

The identity and concentration of the H-abstraction photoinitiator are not critical to the invention, although the composition of the wash out liquid and the duration of the wash out procedure should be such that, after suitable post-exposure, the photoresin plate has a tack free surface. Suitably, the wash out liquid is formulated to contain the H abstraction photoinitiator in an amount of more than 0. 15% by weight, preferably at least 0.2% by weight, of the wash out liquid. In practice, concentrations will generally be measured to a tolerance of perhaps 0.3% and, for commercial practice, the initiator concentration is more desirably expressed as 0.3% or more by weight of the wash out liquid measured to a tolerance of 0.3%.. The use of excessive H-abstraction photoinitiator is not harmful to the photoresin plate but its concentration is normally no more than 3% by weight of the wash out liquid, more normally no more than 2% by weight, and preferably no more than 1% by weight. Most preferably, the H-abstraction photoinitiator is in an amount of between about 0.3% and 0.6% by weight ( 0.3%) of the wash out liquid and especially in an amount about 0.3-0.4% (e.g. 0.3%) ( 0.3%).

It is convenient not to add H-abstraction photoinitiator to the wash out liquid before each operation of the wash out unit but, instead, to add the photoiniator in sufficient excess (e.g. an amount of 0.3% to 0.6% by weight ( 0.3%) of the wash out liquid) for a number of wash out runs to be carried out before the photoiniator concentration becomes so low that more must be added. Suitable operating protocols in the regard may be deten-nined empirically.

One way (but not the only way) of dispersing the photoinitiator in the wash out liquid is to dissolve the initiator in an organic solvent to form a concentrated (e.g. 50 wt%) solution and then mix the solution with the wash out liquid. The proportion of organic 7 solvent in the resultant wash out liquid is small, e.g. is 0.6% if a 50wt% solution is dissolved to give 0.3 wt% of photoinitiator in the wash out liquid. Excessive organic solvent in the wash out liquid is liable to degrade the photoresin plate and the wash out liquid is therefore desirably free, or substantially free, of organic solvent. By way of example concentrations of up to I wt% or, preferably 2 wt%, can be tolerated. Suitable organic solvents include esters, alcohols and ketones, for example butyl acetate, methanol or acetone. In practice, such prior dissolution will be performed with solid ph6toinitiators (e.g. benzophenone) whereas liquid initiators (e.g. a 4-methylbenzophenone/benzophenone mixture) is conveniently added directly to the wash out water.

In principle, any hydrogen-abstraction photoinitiator may be used. These compounds are generally organic carbonyl compounds, and in particular carbonyl compounds having at least one optionally substituted aryl group bonded to the carbon atom of the carbonyl group.

As specific examples of H-abstraction photoinitiators, there can be mentioned unsubstituted or substituted benzophenones such as benzophenone, 4bromobenzophenone, 4,4'-dichlorobenzophenone, 4-4-dimethoxybenzophenone, 4- methylbenzophenone, 4-hydroxybenzophenone, 3,5-dihydroxybenzophenone and 4phenylbenzophenone; unsubstituted or substituted acetophenones such as acetophenone, 4-methylacetophenone, 3,5-dimethylacetophenone, 4-methoxyacetophenone, 2chloroacetophenone, 4-chloroacetophenone, 2-chloro-3-nitroacetophenone, 2-chloro-5nitroacetophenone, 2,6-dimethoxyacetophenone and 4-hydroxyacetophenone; unsubstituted or substituted aromatic ketones such as deoxybenzoin, phenyl naphthyl ketone, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, benzoin t-butyl ether and other alkyl ethers of benzoin; and various quinone compounds such as 9,10 anthraquinone, 2-methyl-9,10-anthraquinone and 2-ethyl-9,10-anthraquinone.

As other specific examples of organic carbonyl compounds that can be used invention, there can be mentioned substituted acetophenones such as cc-phenylacetophenone and 8 (x,(x-dichloroacetophenone; various o- or pquinone compounds such as pbenzoquinone, 2,5-dimethyl-p-benzoquinone, 2,6-dichloro-p-benzoquinone, 2-ethyl5,6,7,8-tetrahydroanthraquinone, 1,4-naphthoquinone, 2,3-dichloronaphthoquinone, 2,3dimethyl-1,4-naphthoquinone, 2-ethyl-1,4-naphthoquinone, phenanthraquinone and 1,25 naphthoquinone; and oc-diketones such as benzil.

Particularly suitable H-abstraction photoinitiators are, benzophenone, 4methylbenzophenone, 4,4'-dimethoxybenzophenone, 4-hydroxybenzophenone, deoxybenzophenone, deoxybenzoin, acetophenone, 2-chloroacetophenone, 4methylacetophenone, 9, 1 O-anthraquinone, 2-methyl-9,1 0-anthraquinone, 2-ethyl-9,1 0- anthraquinone and 2-bromo-9, I 0-anthraquinone.

The H-abstraction photoinitiator may comprise a mixture of compounds, for example a mixture of one or more of the above named compounds. In this respect, a photoinitiator which has been found very suitable is a 50:50 (by weight) mixture of 4- methylbenzophenone and benzophenone.

Needless to say, the invention is not restricted as to the manner of preparation of the wash out liquid. However, in view of the relatively low concentrations of H-abstraction photoinitiator used, it is convenient for the H-abstraction photoinitiator to be provided as a preformed mixture with the surfactant. The invention therefore includes a composition comprising a surfactant and an H-abstraction photoinitiator. Liquid photoinitiators are conveniently added directly to the surfactant whilst solids are suitably pre-dissolved in an organic solvent before mixing with the surfactant.

The surfactant is conveniently added to water to form the wash out liquid in an amount of from 3% to 5% by weight based on the amount of water. In order to obtain a photoinitiator concentration in the wash out liquid of from 0.3% to 0.5% ( 0.3%), a photoinitiator/surfactant mix suitably contains from 6% to 17% (-h 0.3%) photoinitiator by weight of the mix.

9 The process of the invention may use any surfactant in a suitable concentration and, for example, may use a commercially available wash out agent. However, some preferred processes use an amine type surfactant and especially a tertiary amine type surfactant, since these appear to have a synergistic effect with H-abstraction photoinitiators, Particularly preferred surfactants of this class are triethanolarnine alkyl sulfates, and also polyoxyethylene alkylphenylether sulfonic acid sodium salts and polyoxyethylene alkylbenzene sulfonic acid triethanolamine salts. If desired, the surfactant may comprise a mixture of two or more surfactant compounds.

Although the synergistic effect of amine-type surfactants (or other tertiary amines, especially tertiary alkyl amines) has beneficial potential, it has been found that, in mixtures of triethanolamine alkyl sulfate-type surfactant and H-abstraction photoinitiator, the surfactant and the photoinitiator can react with each other (especially where the photoinitiator concentration is significantly over 5%, e.g. around 10% or more). Thus, especially where the photoinitiator is to be formulated into a mixture with surfactant at relatively high concentrations, it can be desirable to use exclusively a nonamine type surfactant, for example an alkyl sulfate (e.g. lauryl sulfate) or a dialkyl sulfosuccinate (e.g. sodium dioctyl sulfosuccinate). Alternatively, surfactant mixtures containing a minor amount of amine type surfactant may be used.

The wash out unit may be employed under conventional conditions, for example the wash out liquid may be employed at room temperature (ambient temperature) or at an elevated temperature of, for example, up to 50'C, e.g. about 40'C.

After wash out, the photoresin plate must be post-exposed (also called finished) and dried. The plate may be either post-exposed and then dried, or dried and then postexposed.

The post-exposure comprises irradiation of the photoresin plate to cause curing of exposed tacky surface. A commercially available post-exposure unit may be used, for example. In any event, as the skilled person will know, post-exposure typically involves exposure of the plate to ultra violet light, typically at a wavelength of from 200-300nm.

The post-exposure may be carried out wet, i.e. with the plate immersed in water typically containing sodium sulfite and other post-exposure salts. However, it is unnecessary to use water, since H-abstraction photoinitiators are not significantly inhibited by oxygen, and dispensing with the water also avoids the need to obtain and dispose of the postexposure salts. The dry light exposure can be used to obtain a photoresin plate having a smooth, tack free, fine surface finish. The plate has good resistance to tack formation during storage, which is believed to be a result of the H-abstraction photoinitiator being dispersed relatively deeply into the resin surface causing complete polymerisation of the residual tacky material..

Any suitable drying technique may be used, e.g. air drying at an elevated temperature of about 60'C, for example.

The resulting photorelief plate may be used in either the flexographic or the handstamp industry.

Example I

200g of benzophenone are pre-dissolved in 200g butyl acetate and added to 70 L of water in a rotary cylinder wash out unit, 2.5 L of surfactant CEW5 (triethanolamine lauryl sulfate) and 200ml antifoarn CEA5 (a mixture of mineral oils and non-ionic surfactants) are added too. The water is warmed to 40-45'C. A polyether urethane based photopolymer plate (made using VERBATIMO liquid photopolymer) is mounted on the cylinder and a 12min washout is carried out, followed by 25 sec, rinsing with clean water.

The plate is then transferred to a drying unit (temperature approximately 550C) for evaporating the water and then to a post-exposure unit where it is dry-exposed to actinic UV light for 10 mins.

The plate is taken out, left to cool down to room temperature and evaluated for tack free surface finish.

The result is a smooth, completely tack free surface.

Example 2

200g of 4-methylbenzophenone/benzophenone mixture (50:50 by weight and sold under the trade mark Esacure TZM) is added to 70 L of water in a rotary cylinder wash out unit. 2.5 L of surfactant CEW5 and 200ml antifoam CEA5 are added too. (The photoinitiator mixture is liquid and can therefore be added directly to the water). The water is warmed to 40-45'C. A polyether urethane-based photopolymer plate (made using VERBATIMO liquid photopolyr-.er) is mounted on the cylinder and a 12min washout is carried out, followed by 25 sec rinsing with clean water.

The plate is then transferred to a drying unit (temperature approximately 55'Q for evaporating the water and then to a post-exposure unit where it is dry-exposed to actinic UV light for 10 mins.

The result is a smooth, completely tack fyee surface.

Example 3

280g of 4-methylbenzophenone/benzophenone photoinitiator (50:50 by weight and sold under the trade mark Esacure TZM) is pre-mixed with 2.5 L of sodium alkyl sulfate surfactant Empicol LX28 and the mixture is added to 70 L of water in a rotary cylinder wash out unit. 200ml antifoam CEA5 are added too and the water is warmed to 4045'C. A polyether urethane-based photopolymer plate (made using VERBATIM8 liquid photopolymer) is mounted on the cylinder and a 12min washout is carried out, followed by 25 sec rinsing with clean water.

12 The plate is taken out, left to cool down to room temperature and evaluated for tack free surface finish.

The result is a smooth, completely tack free surface.

Claims

13 CLAIMS

I. A process for making photoresin printing plates, characterised in that the aqueous wash out liquid contains dispersed H-abstraction photoinitiator.

2. A process of Claim 1, wherein the concentration of the H-abstraction photoinitiator in the wash out liquid is greater than 0. 15% by weight.

3. A process of Claim 2, wherein the concentration of the H-abstraction 10 photoinitiator is at least about 0.2% by weight.

4. A process of Claim 3, wherein the concentration of the H-abstraction photoinitiator is about 0.3% by weight or more, measured to a tolerance of 0.3%.

5. A process of any of Claims- I to 4 in which the concentration of the H-abstraction photoinitiator in the wash out liquid is no more than 3% by weight.

6. A process of any of Claims I to 5, wherein the H-abstraction photoinitiator comprises one or more compounds selected ftom the group consisting of unsubstituted and substituted benzophenones, unsubstituted and substituted acetophenones, unsubstituted and substituted aromatic ketones and quinones.

7. A process of Claim 6, wherein the H-abstraction photoinitiator comprises one or more compounds selected from the group consisting of benzophenone, 4 methylbenzophenone, 4,4'-dimethoxybenzophenone, 4-hydroxybenzophenone, deoxybenzoin, acetophenone, 2-chloroacetophenone, 4-methylacetophenone, 9,10 anthraquinone, 2-methyl-9,10-anthraquinone, 2-ethyl-9,10-anthraquinone and 2-bromo 9, 1 O-anthraquinone.

8. A process of Claim 7, wherein the H-abstraction photoinitiator is selected ftom the group consisting of benzophenone, 4-methylbenzophenone and mixtures thereof.

14

9. A process of any of Claims I to 8, wherein the wash out liquid contains a surfactant.

10. A process of Claim 9, wherein the surfactant comprises an amine type surfactant. 5

11. A process of Claim 10, wherein the surfactant comprises a triethanolamine alkyl sulfate type surfactant.

12. A process of Claim 9, wherein the surfactant is substantially free of amine type 10 surfactant.

13. A process of any of Claims I to 12, wherein the post-exposure is carried out dry.

14. A process of Claim 13, wherein, after wash out, the photoresin plate is dried 15 either before or after post-exposure.

15. A method for removing tack from a photoresin printing plate, characterised in that the wash out uses wash out liquid containing dispersed H-abstraction photoinitiator.

16. A method of Claim 15, which further includes the specific feature(s) recited in one or more of Claims 2 to 12.

17. The use of an H-abstraction photoinitiator as a wash out liquid additive to remove tack in the manufacture of photoresin printing plates.

18, The use of a combination of an H-abstraction photoinitiator and an amine type surfactant in wash out liquid in the manufacture of photoresin printing plates to make tack free printing plates.

19. In a process for making photoresin printing plates which comprises the steps of exposure, aqueous wash out, post-exposure and drying, the improvement that the wash out liquid contains dispersed H-abstraction photoinitiator.

20. A process of Claim 19, wherein the concentration of the H-abstraction photoinitiator in the wash out liquid is greater than 0. 15% by weight.

21. A process of Claim 20, wherein the concentration of the H-abstraction 5 photoinitiator is at least about 0.2% by weight.

22. A process of Claim 21, wherein the concentration of the H-abstraction photoinitiator is about 0.3% by weight or more, measured to a tolerance of 0.3%.

23. A process of any of Claims 19 to 22 in which the concentration of the H- abstraction photoinitiator in the wash out liquid is no more than 3% by weight.

24, A process of any of Claims 19 to 23, wherein the H-abstraction photoinitiator comprises one or more compounds selected from the group consisting of unsubstituted 15 and substituted benzophenones, unsubstituted and substituted acetophenones, unsubstituted and substituted aromatic ketones and quiriones.

25. A process of Claim 24, wherein the H-abstraction photoinitiator comprises one or more compounds selected from the group consisting of benzophenone, 4 methylbenzophenone, 4,4'-dimethoxybenzophenone, 4-hydroxybenzophenone, deoxybenzoin, acetophenone, 2-chloroacetophenone, 4-methylacetophenone, 9,10 anthraquinone, 2-methyl-9,10-anthraquinone, 2-ethyl-9,10-anthraquinone and 2-bromo 9,1 0-anthraquinone.

26. A process of Claim 25, wherein the H-abstraction photoinitiator is selected from the group consisting of benzophenone, 4-methylbenzophenone and mixtures thereof

27. A process of any of Claims 19 to 26, wherein the wash out liquid contains a surfactant.

28. A process of Claim 27, wherein the surfactant comprises an amine type surfactant.

16

29. A process of Claim 28, wherein the surfactant comprises a triethanolarnine alkyl sulfate type surfactant.

30. A process of Claim 27, wherein the surfactant is substantially free of amine-type surfactant.

31. A process of any of Claims 19 to 20, wherein the post-exposure is carried out dry.

'12. A process of Claim 3 1, wherein, after wash out, the photoresin plate is dried either before or after post-exposure.

n 1) _).). A composition for use in preparing wash out liquid, the composition comprising a surfactant and an H-abstraction photoinitiator.

34. A composition of claim 33, wherein the H-abstraction photoinitiator comprises one or more compounds selected from the group consisting of unsubstituted and substituted benzophenones, unsubstituted and substituted acetophenones, unsubstituted and substituted aromatic ketones and quinones.

35. A composition of claim 34, wherein the H-abstraction photoinitiator comprises one or more compounds selected from the group consisting of benzophenone, 4 methylbenzophenone, 4,4'-dimethoxybenzophenone, 4-hydroxybenzophenone, deoxybenzoin, acetophenone, 2-chloroacetophenone.. 4-methylacetophenone, 9,10 anthraquinone, 2-methyl-9,10-anthraquinone, 2 -ethyl- 9, 1 O-anthraquinone and 2-bromo 9, 1 0-anthraquinone.

36. A composition of claim 35, wherein the H-abstraction photoinitiator is selected from the group consisting of benzophenone, 4-methylbenzophenone and mixtures thereof

37. A composition of any of claims 33 to 36, wherein the wash out liquid contains a surfactant.

17

38. A composition of claim 37, wherein the surfactant comprises an amine type surfactant.

39. A composition of claim 38, wherein the surfactant comprises a triethanolamine alkyl sulfate type surfactant.

40. A composition of claim 37, wherein the surfactant is substantially free of amine type surfactant. 10

41. A process for making a photoresin printing plate substantially as hereinbefore described or exemplified.

42. A printing plate whenever made using a process of any of claims I to 14, 19 to 32 or 41.

43. A product comprising material printed using a printing plate of claim 42.

p40556.3