NO743464L - - Google Patents

Description

"Photopolymerizable mixture"

The present invention relates to photopolymerizable mixtures as well as methods for their production and use.

Photopolymerizable mixtures comprising a soluble polymeric material together with an addition polymerizable monomer are known. Such a mixture can e.g. is used to form a relief printing plate by exposing a sheet of the compound through a negative, so that a further polymerization takes place in those parts of the compound which were exposed, and by then removing

the unexposed areas with a suitable solvent to the desired relief depth.

The present invention provides a photopolymerizable composition which can be developed (ie unexposed areas are removed) by treatment with water or an aqueous liquid.

The photopolymerizable mixture according to the invention essentially comprises: a) a water-soluble or water-dispersible polymer or copolymer, or a polymer or copolymer mixture in which one or more components are water-soluble or water-dispersible, b) an addition polymerizable monomer which preferably, but not necessarily, is water-insoluble, but is soluble or compatible with a solvent or dispersant for a), and c) a photoinitiator capable of initiating the polymerization of the monomer, whereby the mixture can be rendered water-insoluble by suitable irradiation.

Typical water-soluble polymers include: polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, hydroxyethyl cellulose, polyvinylpyridine, sulfonated polystyrene, and partially hydrolyzed polyvinyl acetate.

The component a) comprises a water-soluble polymer, either alone or in a mixture, or copolymerized with one or more less water-soluble polymers or monomers, such as polyacrylates, polyalkyl acrylates (e.g. polymethyl acrylate, 2-ethylhexyl acrylate), polyalkyl methacrylates ( eg polymethyl methacrylate, lauryl methacrylate), dialkyl maleates (eg di-isooctyl maleate, di-butyl maleate, diethyl maleate).

The choice of the ingredient (or ingredients) of component a) takes place from the point of view that it should be able to be washed out from a film of the material using one aqueous liquid, preferably water, i.e. that it is water-soluble or water-dispersible. Preferably, it should also the mixture being soluble in alcohol or other suitable solvent to facilitate film formation.

The preferred component a) comprises poly(N-vinyl-pyrrolidone), either alone or in mixture with polyvinyl acetate, or a copolymer of N-vinyl pyrrolidone and vinyl acetate. The poly(N-vinylpyrrolidene) and the copolymer of N-vinylpyrrolidone and vinyl acetate are both soluble in water and lower alcohol (e.g. methanol and ethanol) and this is advantageous because it is preferred to convert the mixture of the invention into a film from a solution in one of the lower alcohols (ie alcohols up to C^).

Component a) is usually present in the mixture in an amount of 50 to 95% by weight, the water-soluble polymer preferably constituting 30 to 70% of the entire amount of a).

The monomer used is preferably, but not necessarily, water-insoluble. It is of course desired that the monomer is compatible with the polymer or other components of the mixture, and that it is capable of polymerizing with at least one component a) to form a water-insoluble product. The monomer preferably comprises at least two non-conjugated ethylenic double bonds, which are preferably unsaturated at the end position.

Examples of suitable monomers include:

where R = H or CH^/ in which the benzene ring may contain one or more substituents which may be the same or different, including alkyl groups with up to 4 carbon atoms, -COOH, halogen, COOR^, where R^ is a lower (i.e. up to 4 carbon atoms) alkyl group, -S<0>2/ NR2R3 or -CONR4R5, where R2, , R4 and R5 each represent H or a lower alkyl group. Eg: N:N-bis-(/3-acryloyl-oxyethyl)-aniline N:N-bis-(/3-methacryloyl-oxyethyl)-m-toluidine N:N-(acryloyl-oxyethyl)-chloroaniline

where R = H or CH3.

E.g.: 1, 2-(Y~acrylamide:i-(3-OProP0^sy)-ethane

1,2-(Y-methacrylamidopropoxy)-ethane

(3) acrylates,

eg: allyl methacrylate

ethylene glycol dimethacrylate

trimethylolpropane triacrylate

trimethylolpropane trimethacrylate

pentaerythritol tetraacrylate

pentaerythritol monohydroxy triacrylate.

(4) vinyl urethanes,

e.g. a reaction product of di(4-isocyanate-phenyl)-methane, poly-

propylene glycol and 2-hydroxyethyl methacrylate in a molar ratio of 2:1:2.

a reaction product of tolylene diisocyanate, pentaerythritol/propylene oxide adduct, and 2-hydroxyethyl methacrylate in a molar ratio of 4:1:4.

(5) allyl monomers,

e.g. triallyl cyanurate.

The proportion of the monomer in the mixture will vary within wide limits, but is usually within a range of 5 to 50% by weight, preferably 10 to 25% of the weight of the mixture.

It will be understood that component b), although this is not preferred, can be an oligomer, i.e. a short polymer chain with e.g. up to five repeating monomer units, if such a compound is unsaturated and has a suitable polymerisation capability, as explained above.

Suitable photoinitiators include those which, according to the literature, are suitable for initiating the polymerization by the formation of free radicals. They are preferably activated by actinic radiation usually in the wavelength range 300 nm to 450 nm, although it will be understood that other forms of electromagnetic radiation outside the visible range can be used, and the term photoinitiator is not only limited to light-sensitive initiators. Examples of preferred photoinitiators are benzophenone, benzoin, benzoin methyl ether and substituted benzyl methyl ethers and diacetyl. These are suitably used in concentrations of 0/1 to 10%, preferably 1 to 8% of the weight of component (a).

One application of mixtures according to the invention is the production of relief plates which, after a suitable treatment, can be used for direct or offset printing, flexo printing or as pattern plates.

In the production of such printing plates, the mixture according to the invention is placed on a suitable support, so that it forms on the support a film of precisely regulated thickness. The support can be a suitable metal, but it can also consist of glass or plastic (e.g. polyethylene terephthalate ) etc. If the carrier must be deformed during use, e.g. when it is placed on the drum in a printing press, you must have a suitable flexible carrier and the choice of carrier material will be made from this point of view. The carrier material will of course be a material that is not adversely affected by the processing operations to which the plate is subjected.

The thickness of the film of the mixture on the support depends on the intended use of the plate, but a dry film thickness of between 0.13 and 1.30mm is usually used.

Very good results can be obtained by first coating the carrier with a fixing layer consisting essentially of a compatible adhesive which can stick the carrier and the mixture together and is water resistant. It has been found that a thin film (less than about 5 microns) of polyvinyl acetate improves adhesion to the support and results in better resolution in the final plate, due to the retention of fine detail that would otherwise be washed away due to the limited contact area with the wearer.

on certain supports (e.g. polyester film) where adhesion may be poor, the relief image may tend to move during drying after development. This tendency to movement of the image can be reduced by bringing the image into contact with a solution capable of removing part of the washing liquid, e.g. by osmotic pressure. Preferably, a concentrated aqueous solution of an inorganic salt is used for this purpose, e.g. sodium sulfate, the solution being preferably saturated. Solutions of such inorganic salts can also be used to effect development of the plate.

In addition to the already mentioned components, it may be advantageous to introduce a heat crosslinking inhibitor into the mixture to prevent heat polymerization. Hydroquinone and related compounds can be used in appropriate amounts. Plasticizers can also advantageously be introduced into the mixture, and those skilled in the art will have no difficulty in choosing a plasticizer from among those known from the literature. Suitable dyes can also be introduced to reduce light scattering during the exposure. Surfactants can be introduced into the mixture to improve flowability during coating.

The invention is illustrated by means of the following examples:

Example 1

1:1 copolymer of vinyl acetate and N-vinyl-pyrrolidone as

Benzophenone was dissolved in a mixture of ethylene glycol dimethacrylate and dimethyl phthalate, and this solution was added to

the copolymer solution while stirring. The solution was allowed to stand for a few hours to deaerate it. "HiTop" steel (steel coated with chromium/chromium oxide) was used as the carrier material. The solution was spread on the carrier with a thickness of 1.5 mm in a moist state using a coating knife with a fixed clearance. The coating was oven dried to give a dry film thickness of 0.7 mm. After drying, the resulting film was exposed through a halftone and line negative for 12 minutes using ultraviolet radiation from a 20 watt ultraviolet fluorescent tube at a distance of 7.5 cm from the plate. The exposed plate was then washed for 3 1/2 minutes by spraying with 24°C water. After the plate was dry, a relief image of approx. 0.6 mm was obtained. The plate was mounted on a letterpress and several thousand satisfactory copies were obtained.

Example 2

A mixture was used as in Example 1, except that 0.6 g of the surfactant "Lissapol N" was added. This solution was coated on aluminum plates to give a dry thickness of 0.7 mm. The plate was exposed through a line negative for 10 minutes using ultraviolet radiation as in Example 5 and washed out for 3 minutes to give a relief image of about 0.6 mm.

Example 3

The same mixture as in example 1 was used, except that diallyl phthalate was used instead of dimethyl phthalate.

Example 4

The same mixture as in example 1 was used, except that "Cereclor 50LV" (ICIchlorinated paraffin) was used instead of dimethyl phthalate.

Example 5

"Luviskol VA 55 E,?t is a copolymer of equal parts N-vinylpyrrolidone and vinyl acetate, supplied as a 50% by weight solution in ethanol.

The above mentioned ingredients were mixed together and stirred until the benzophenone was dissolved. The solution was then coated onto a support (polyethylene terephthalate sheet of thickness 0.18 mm) using a draw bar to give a film with a wet thickness of 1.0 mm. The film was then dried at a temperature of approx. 50°C.

The film thus obtained was exposed for 10 minutes using ultraviolet radiation (2 Philips MLU 300 watt lamps at a distance of 50 cm) through a negative image of the letters to be reproduced. The exposed plate was then washed with running water for 2 minutes (an alternative experiment used an ultrasonic bath containing water for about 45 seconds). A relief image with a height of approx. 0.3 mm.

During the drying of the plate washed with running water, some movement of the relief image occurred. A similar plate, after washing, was immersed for 2 minutes in a saturated, aqueous solution of sodium sulphate. After drying, the plate was briefly rinsed with water to remove surface crystals, and then the plate was dried. There was no movement of the relief image.

Example 6

These ingredients were mixed as in Example 1 and the solution coated on a support (aluminum plate with a thickness of 0.13 mm) by means of a draw bar to give a film of thickness 1 mm in the wet state.

The film was dried and then exposed as described in Example 1 and then developed for 4 1/2 minutes in an ultrasonic bath containing water at room temperature. A relief image with a height of approximately 0.35 mm was obtained.

Example 7

A solution of polyvinyl acetate in denatured alcohol was coated by means of a draw bar on an aluminum plate of thickness 0.13 mm to give a fixing layer of thickness 2 microns in the dry state.

The above-described mixture was coated on the aluminum support by means of a draw bar to give a film of 1 mm thickness in the wet state. After drying, the thus obtained film was exposed for 15 minutes by means of ultraviolet radiation described in example 5, through a negative image of the letters to be reproduced. The exposed plate was then washed with cold running water for 3 minutes and a relief image with a height of approx. 0.3 mm.

Example 8

These ingredients were mixed as in Example 1 and the solution coated on a support (0.13 mm thick aluminum plate with a fixing layer as described in Example 7) by means of a draw bar to give a film of thickness 1L1mm in the wet state.

The film was dried and then exposed as described in Example 1 and washed with cold, running water for 2 minutes. A relief image with a height of approx. 0.3 mm.

Example 9

A mixture of vinyl pyrrolidone (100 g), vinyl acetate

(80 g), di-isooctyl maleate (20 g) and azo-bis-isobutyronitrile (2 g) were added over 30 minutes to denatured alcohol (160 g) under reflux and nitrogen atmosphere. The mixture was refluxed for a total of 8 hours to give a viscous solution.

180 g of the thus prepared terpolymeric solution was added to a mixture of ethylene glycol dimethacrylate (20 g) and benzophenone (2.5 g). A portion of this solution was poured on one

o

steel plate and dried at 85°C for 2 hours to give a coating of thickness 0.6 mm. The plate was sufficiently flexible to be able to be bent into an arc with a diameter of 5 cm. The dried plate was exposed on a vacuum frame for 7 minutes using ultraviolet radiation through a negative and then washed with running water at 23°C for 5 minutes to produce a relief image suitable for use in a letterpress.

Example 10

A mixture of vinylpyrrolidone (125g), vinylacetate (75g), dimethyl maleate (50g) and azo-bis-isobutyronitrile (2.5g) was added over 30 minutes to denatured alcohol (250ml) under reflux and nitrogen atmosphere. The mixture was refluxed for a total of 8 hours. 90 g of this terpolymer solution was added to a mixture of ethylene glycol dimethacrylate (5 g), benzophenone (1.25 g) and "Lissapol N" (0.5 g). A portion of this solution was poured onto an aluminum plate and dried at 85°C to give a non-stick coating with a thickness of 0.45 mm. The dried plate was exposed on a vacuum frame for 7 1/2 minutes using ultraviolet radiation through a halftone negative and then washed with running water at 18°C to produce a relief image suitable for letterpress printing. The plate was flexible both before and after the treatment.

Claims (9)

1-F otopolymerizable mixture, characterized in that it comprises: a) a water-soluble or water-dispersible polymer or copolymer or a polymer or copolymer mixture in which one or more components are water-soluble or water-dispersible, b) an addition polymerizable monomer which is soluble in or compatible with a solvent or dispersant for a), and c) a photoinitiator capable of initiating the polymerization of the monomer, whereby the mixture can be rendered water-insoluble by radiation. 2. Mixture as stated in claim 1, characterized in that component a) comprises poly(N-vinyl-pyrrolidone). 3. Mixture as specified in claim 2, characterized in that component a) also comprises polyvinyl acetate. 4. Mixture as stated in claim 1, characterized in that component a) comprises a copolymer of poly(N-vinylpyrrolidone) and vinyl acetate. 5. Mixture as stated in any of the preceding claims, characterized in that the photoinitiator is activated by actinic radiation in a wavelength range of 300 nm to 450 nm. 6. Mixture as stated in any of the preceding claims, characterized in that component b) is a monomer comprising at least two non-conjugated ethylenic double bonds. 7. Photopolymerizable mixture as stated in claim 1, essentially as described. 8. A water-developable photosensitive plate comprising a carrier and a photopolymerizable mixture according to one of the preceding claims. 9. Method for producing a relief plate, characterized in that the plate according to claim 8 is exposed by means of electromagnetic radiation and that the exposed plate is washed with water to remove the unexposed photopolymerizable mixture.