CA1064755A - Photopolymerizable composition containing n-vinyl pyrrolidone and vinyl acetate as polymeric blend or copolymer thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A photopolymerisable composition comprising:-(a) 50%-95% by weight of a mixture of poly (N-vinyl pyrrolidone) and polyvinyl acetate, or a copolymer of N- vinyl pyrrolidone and vinyl acetate;
(b) 5%-50% by weight of an addition-polymerisable monomer comprising at least two non-conjugated ethylenic double bonds and which is soluble in or compatible with a solvent or dispersing medium for (a); and (c) a photoinitiator capable of initiating polymerisation of the monomer whereby the composition may be rendered water-insoluble by radiation. The compositions are of use in water developable photosensitive plates and in the preparation of relief plates.

Description

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This invention relates to photopolymerisable comp-ositions and to methods of production and use thereof.
Photopolymerisable compositions are known comprising a soluble polymeric material together with an addition-polymerisable monomer. Such a composition may be employed e.g~
to produce a relief printing plate by exposing a sheet of the composition to light through a negative, so that further polymerisation occurs in those parts of the composition which have been exposed to light, and subsequently removing the unexposed areas with a suitable solvent down to the desired dapth of relief.
The present invention provides a Photopolymerisable composition which can be developed (that is, unexposed areas removed) by treatment with water or ah aqueous liquid.
The photopolymerisable composition of the present invention comprises essentiall~:-(a) a water-soluble or water-dispersible polymer or co-polymer~ or a polymer or copolymer mixture in which one or more of the components is water-soluble or water-dispersible;-(b) an additlon-polymerisable monomer which, is preferably, though not essentially, water insoluble but is soluble in or compatible with a solvent or disPersing medium for (a); and (c~ a photoinitiator capable of initiating polymerisation of the monomer whereby the composition ma~ be rendered water-insoluble by suitable radiation.

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- 3 - ~064~55 Typical water-soluble polymers include polyacrylic acid, polym~thylacrylic acid, polyvinyl alcohol, hvdroxy-ethyl cellulose,lvinyl pyridine, sulphonated poly~tyrene, and partially hydrolysed polyvinyl acetate.
Component (a) comprises a water soluble ~olymer either alone or in admixture or copolymerised with one or more less water-soluble polymers or monomers (as appropriate), examples of which are polyacrylates, poly-alkyl acrylates (e.g. polymethyl acrylate, 2-ethyl hexyl 10- acrylate), polyalkyl methacrylates (e.g. polymethyl methacryla~e, lauryl methacrylate), dialkyl maleates (e.g.
di-iso-octyl maleate, di-butyl maleate, diethyl maleate).
Selection of the ingredient(s) of component (a) will be made i~ the light of the requirement that it should be capable of being washed from a film of material using an aqueous liquid, preferably water,i.e. that it should be water-soluble or water dispersible. Preferably also the composition is soluble in an alcohol or other convenient solvent for ease of film formation.
Our preferred component (a) comprises poly(N-vinyl-pyrrolidone), either alone or in admixture with polyvinY
acetate, or a copolymer of N-vinylpyrrolidone and vinyl acetate. The poly(N-vinylpyrrolidone) and the copolymer of N-vinylpyrrolidone and vinyl acetate are both water and lower alcohol (e.g. methanol and ethanol) soluble, and we have found this advantageous because formation of the composition of the invention into a film from a , ~0~4755 solution in one of the lower alcohols (i.e. u~ to C4) is preferred.
The component (a) will usually be present in the composition in an amount forming from 50~ to 95% by weight, the water soluble polymer preferably forming 30-70~ of the total of (a).
The monomer employed is one which is preferably, although not necessarily, water insoluble. It is desirable of course that the monomer be highly compatible with the polymeric and any other components of the composition, and capable of polymerising with at least one of component (a) to form a water-insoluble product. Preferably the monomer comprises at least two non-conjugated ethylenic double bonds, and preferably has terminal unsaturation.
As examples of suitable monomers we would mention R
(1~ N (CH2CH201CI - C CH2)2 ~ o where R = H or CH3; in which the benzene ring may contain one or more substituents which may be the same or different, including alkyl groups up to 4 carbon atoms, -COOH, ~ halogen, -COORlin which R, is a lower (i.e. up to 4~carbon atoms) alkyl group, -S02 NR2 R3 or -CONR4R5 where R2, R3, R4 and R5 each represents H or a lower alkyl group.
e.g. N N-bis-(~-acryloyl oxyethyl) aniline M:N-bis-(~-methacryloyloxyethyl) m toluidine N:N (acryloyloxyethyl) -chloro aniline ~0~475S

(2) CH2 = C - CoNH(cH2)3o(cH2)2o(cH2)3 2 where R = H or CH3.
e.g. l,2-(yacrylamidopropoxy)ethane ~2-(ymethacrylamidopropoxy)ethane (3) Acrylates, e.g. allyl methacrylate ethylene glycol dimethacrylate trimethylol propane triacrylate trimethylol propane trimethacryiate pentaerythritol tetra acrylate pentaerythritol mono hydroxy trlacrylate.

(4) vinyl urethanes, e.g. a reaction product of di(4-isocyanatophenyl)methane, polypropylene glycol and 2-hydroxyethyl methacryla~e in moIe ratio 2:1:2.
reaction product of tolylene diisocyanate, penta-erythrltol/propylene oxide adduct, and 2-hydroxyethyl methacrylate i~n mole ratio 4:1:4;

(5) Allyl monomers e.g. triallyl cyanurate.
The proportion of monomer in the composition will vary within wide limits but will usually Iie within the range 5% to 5Q~ by weight, preferably lO to 25% by weight of the composition.
It will be appreciated that, although not preferred, component (b) could be an oligomer~ that is a short polymeric chain having up to, say, 5 repeating monomeric units, if such a compound has an appropriate unsaturation and polymerisation capabiliiy as explained above.
Suitable photoinitiators include those described in the literature as being suitable for the initiation of polymerisation by free radical generation. Preferably they are activated by actinic radiation usually in the wavelength region 300 nm to 450 nm although it will be appreciated that other forms of electromagnetic radiation, outside the visual range, may be employed and the term photoinitiator is not limited to light sensitive initiators only. Examples of preferred photoinitiators are benzo-phenone, benzoin, benzoin methyl ether and substituted benzyl~methyl ethers and diacetyl. These are conveniently employed in concentrations of the order of 0.1% to 10%, preferably 1% to 8% of the weight of component (a).
One use of the compositions of the invention is in the production of relief plates which are capable, after suitable processing, of being used for direct or offset letterpress printingj flexo printing or as pattern plates.
In the production of such a printing plate the composition of the invention is applied to a suitable support so that it forms a film thereon of accurately controlled thickness. The support may be of a suitable metal! bu~ it may also be of glass or of plastic (e.g.
polyethylene terephthalate), etc. Where the support must be deformed in use, as where it is applied to the drum of ~ 7 - ~06~755 a printing press, then an appropriately flexible support is necessary and the choice of support material will be made in the light of this requirement. The support material will, of course be such that it is not dis-advantageously affected by processing operations to which the plate is subjected.
The thickness of the film of composition uPon the support will depend upon the intended application of the plate, but in general we have used a dry film thickness between 0.13 and 1.30 mm.
Superior results can be obtained by first coating the support material with a keying layer which is essentially a compatible adhesive capable of adhesively bonding to the support and the composition, and is water resistant. We have found a thin film (less than about 5 microns) of polyvinyl acetate tends to improve adhesion to the support and results in better resolution in the final plate because of the retention of fine detail which might otherwise wash off due to the limited area of contact with the support.
on some supports (e.g. polyester film) where adhesion may be poor, the relief image may tend to move during drying after development. This tendency to image movement may be reduced by contacting the image with a solution capable of withdrawing a proportion of the wash-out liquid, as by osmosis pressure. We prefer to use for this purpose a concentrated aqueous solution of an inorgan1c salt, ~L~64~55 for example sodium sulphate; the solution is preferably saturated. Solutions of such inorganic salts may be employed also to effect development of the plate.
In addition to the components already listed it may be desirable to include in the comPosi~ion a thermal cross-linking inhibitor to prevent polymerisation by heat.
~ydroquinone and related compounds in appropriately effective quantities may be used. Plasticisers too, advantageously may be included in the composition, and the skilled man will have no difficulty in making a selection from those described in the literature. The inclusion of suitable dyes may also be preferred, to reduce light scattering during exposure. Surfactants may also be included in the composition to improve even-ness of flow on coating.
The invention is further illustrated by the following Examples.
Example 1 1:1 copolymer of vinyl acetate and N-vinyl pyrrolidone as 60% w/w solution in ethanol 166.7 gm Ethylene glycol dimethactylate 20.0 gm Dimethyl phthalate (plasticiser) 10.0 gm Benzophenone 2.5 gm The benzophenone was dissoIved in a mixture of the ethylene glycol dimethacrylate and the dimethyl phthalate and this solution was added to the copolymer solutian with stirring. This solution was allowed to stand for ~` - 9 - ~0~75S

~ome hours to dea2~ate. Support material used ~as "Hi Top" steel(Trade Mark for steel coated with chromium/chromium oxide)~
The solution was spread on this support at 1.5 mm wet ~hickness using a fixed clearance coating knife. The coating was oven dried to give a dry film thickness of 0.7 mm. After dryiny the film so obtained was exposed through a half tone and line negative for 12 mins to a U.V. source of 20 watt U.V. fluorescent tubes at 3 inches from the plate. The exposed plate was then washed for 3% mins with a spray of water at 24C. Ater drying the - plate a relief image of approximately 0.6 mm was obtained.
The plate was mounted on a letter press printing'machine and several thousand satisfactory copies were obtained.
~, Example 2 Composition as in Example 1 except that 0.6 g of the surfactant"Lissapoi"N(Tradè Mark) was added. This soiution was coated on aluminium sheets to give a dry thickness of 0.7 mm. The plate was exposed through a line negative for 10 mins to a U.V. source as in Example 5 and washed out in 3 mins to give a relief image of approximately 0.6 mm.
Example 3 Composition as in Example 1 except that diallyl-phthalate was used in place of dimeth~l phthalate.
Example 4 Composition as in Example 1 except that 'Cereclor' 50 LV (Trade Mark for ICI chlorinat~d ~a~a~in)was used in place of dimethyl p;hthalate, ~B

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"~uviskol" ~A 55 E* 20 gm bis (~ acryloyloxye~hyl) aniline 2,5 gm Methanol 2,5 gm Benzophenone 0~5 gm *"Luviskol" VA 55 E (Registered Trade Mark)is copolymer of equal-parts of N-vinyl pyrrolidone and vinyl acetate supplied as a 50% by weight solution in ethanol, The above componen~s were mixed together and stirred until the benzophenone dissolved, The solution was then coated onto a support (polyethylene tarephthalate sheet 0,18 mm thick) by a draw bar to give a 1.0 mm wet film thickness, The film was then dried at a temperature of about 50C, - The film so obtained was exposed for 10 mins to a U.V. source (2"Philips" MLU (Trade Mark) 300 w lamps at 20 inches) through a negative transparency of the characters to be reproduced, The exposed plate was then washed under a cold water tap for 2 mins (in an alternative experiment an ultrasonic bath containing water was used for about 45 seconds), A relief image of approximately 0,3 mm in height was obtained, During drying of the tap water-washed plate some movement of the relief image occurred. A similar plate after washing was immersed for 2 mins in a saturated aqueous solution of sodium sulphate. A~ter drying the plate was given a short water rinse to remove surface crysta's and then dried, No movement of the relief image had occurred, ~

V A
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Exam~le 6 *Luviskol VA 37 E 20 gm Trimethylol propane trimethacrylate 0.9 gm Benzophenone 0.5 gm S *Luviskoi VA 37 E (Registered rrrade Mark) being a co-polymer with comonomers N-vinyl pyrrolidone and vinyl acetate in the ratio 3:7 supplied as a 50~ by weight solution in ethanol.
The above components were mixed as in Example 1 and lQ the solu*ion coated onto a support (aluminium sheet 0.13 mm thick) by a draw bar to give a 1 mm wet film thickness.
The film was dried and subsequently exposed as described in Example 1 then developed for 4% mins in an ultrasonic bath containing water at room temperature.
A relief image of approximately 0.35 mm in height was obtained~
Exam~le 7 ~Luviskol VA 64 10 gm ~ Ethylene glycol dimethacrylate 2.5 gm Dimethyl phthalate 2.0 gm - Benzophenone 0.5 gm Nylomine (Trade Mark)acid black 0.75 mgm Industrial methylated spirits 10 gm *Luviskol VA 64 (Registered Trade Mark) is a copolymer whose comonomers M-vinyl pyrrolidone and vinyl acetate are in the ratio 6:4.

:B

~L~6~755 A solution of poly(vinyl acetate) in industrial methylated spirits was coated by a draw bar onto 0.13 mm thick alumin~um sheet to provide a keying layer of 2 microns dry thickness.
The composition described above was then coated onto the aluminium support by a draw bar to give a 1 mm wet film thickness. After drying, the film so obtained was exposed for 15 mins to the U.V. source described in Example 5, through a negative transparency of the characters to be reproduced. The exposed plate was then washed under a cold water tap for 3 mins and a relief image approximately 0.3 mm in height was obtained.
Example 8 ~Luviskol VA 73 E 20 gm lS Allyl methacrylate 2.5 gm Dimethyl phthalate 1.5 gm Benzophenone 0.5 gm *Luviskol VA 73 E (registered Trade Mark) being a co-polymer with comonomers N-vinylpyrrolidone and vinyl acetate in the ratio 7:3 supplied as a 50~ by weight solution in ~ethanol.
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The above components were mixed as in Example 1 and the solution coated onto a support (aluminium sheet 0.13 mm thick with a keying layer as described in Example 7) by a draw bar to give a 1 mm wet film thickness.
The film was dried and subsequently exposed as described in Example 1 and washed under a cold water tap . ,... , . ,. ' , I

6~755 for 2 mins. A relief image of approximately 0.3 mm in height was obtained.
Example 9 A mixture of vinyl pyrrolidone (100 gm), vinyl acetate (80 gm)j di-isooctyl maleate (20 gm) and azobis-isobutyronitrile (2 gm) was added ov~r a period of 30 mins, to industrial methylated spirits (160 gm) at reflux under a nitrogen blanket. The mixture was refluxed for a total of 8 hours to yield a viscous solution.
180 gm of the terpolymer solution prepared as above was added to a mixture of ethylene glycol dimethacrylate (20 gm) and benzophenone (2.S gm). A portion of this solution was cast onto a steel sheet and dried at 85C
for 2 hours to yield a coating 0.6 mm thick. The plate was sufficiently flexible to be bent round an arc of 5 cm diameter. The dried plate was exposed on a vacuum frame for 7 mins to U.V. radiation through a negative and then washed with tap water at 23C for 5 mins to yield a relief image suitable for use as a letterpress printing plate.
ExamPle 10 A mixture of vinyl pyrrolidone (125 gm), vinyl acetate (75 gm), diethyl maleate (50 gm) and -azobisisobutyronitrile (2.5 gm) was added over a period of 30 mins to industrial methylated spirits (250 ml) at reflux under a nitrogen blanket. The mixture was refluxed for a total of 8 hours;
90 gm of the terpolymer solution prepared as above was added to a mixture of ethylene glycol dimethacrylate - 14 _ 1 ~ 6 4~ S 5 tS gm), benzophenone (1.25 gm) and Lissapol N (0.5 gm) A portion of this solution was cast onto a sheet of aluminlum and dried at 85C to yield a tack-free coating 0.45 mm thick. The dried plate was exposed on a vacuum frame for 7~ mins to U.V. radiation through a half-tone negative and then washed with tap water at 18C to give a relief image suitable for letterpress printing. The plate was flexible both before and after processlng.

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What we claim is:

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A photopolymerisable composition comprising:-(a) 50%-95% by weight of a mixture of poly (N-vinyl pyrrolidone) and polyvinyl acetate, or a copolymer of N- vinyl pyrrolidone and vinyl acetate;
(b) 5%-50% by weight of an addition-polymerisable monomer comprising at least two non-conjugated ethylenic double bonds and which is soluble in or compatible with a solvent or dispersing medium for (a); and (c) a photoinitiator capable of initiating polymerisation of the monomer whereby the composition is rendered water-insoluble by radiation.

2. A composition according to Claim 1 in which the photoinitiator is activated by actinic radiation in the wavelength region 300 nm to 450 nm.

3. A water developable photosensitive plate comprising a support and a photopolymerisable composition according to Claim 1.

4. A method of preparing a relief plate which comprises the imagewise exposure of a plate as claimed in Claim 3 to electromagnetic radiation and the washing of the exposed plate in water to remove unexposed photopolymerisable composition.