NO761006L - - Google Patents

Description

"Photopolymerizable mixture".

The invention relates to radiation polymerizable mixtures.

Belgian Patent No. 820,404 describes photopolymerizable mixtures comprising (a) a water-soluble or water-dispersible polymer or copolymer, or a polymer or copolymer mixture where one or more of the components is water-soluble or water-dispersible; (b) an addition polymerizable monomer which is soluble in or compatible with a solvent or dispersing medium for (a); and (c) a photoinitiator capable of initiating the polymerization of the monomer whereby the mixture can be rendered water-insoluble by irradiation.

Belgian Patent No. 789,950 describes the photopolymerization of ethylenically unsaturated material using a photoinitiator comprising

(I) at least one photosensitizer having the structural formula

where X is >C=0, >CR1R2 or ;>CR3OR4; R 3 to R 4 , which may be the same or different, are hydrogen or hydrocarbon radicals; n is 0 or 1, and the groups A, which may be the same or different, are hydrocarbon or substituted hydrocarbon residues, the groups A being aromatic or substituted aromatic when n is 1 and X is >CR^R2 and when n is 0, and ( II) at least one reducing agent capable of reducing the photosensitizer when it is in a photostimulated state.

The applicant has now found that it can be beneficial to . use as the polymer or copolymer in the photopolymerizable mixture according to patent no. 820,404 a compound which is able to act also as the reducing agent according to patent no. 789,950, in connection with the photoinitiator according to the latter patent.

Therefore, the invention provides a photopolymerizable mixture comprising (a) a water-soluble or water-dispersible polymer or copolymer, or a polymer or copolymer mixture in which one or more of the components is water-soluble or water-dispersible, (b) an addition polymerizable monomer which is soluble in or compatible with a solvent or dispersing medium for (a); and (c) at least one photosensitizer having the structural formula

where X is C=0; >CR R or ^CR^OR., R, to R„, which may be

1 2 3 4 1 4

the same or different, are hydrogen or hydrocarbon residues,

n is 0 or 1, and the groups A, which may be the same or different, are hydrocarbon or substituted hydrocarbon residues, the groups A being aromatic or substituted aromatic when n is 1 and X is ^CR-^I^°9n^r n is 0, the polymeric component (a) being able to reduce the photosensitizer (c) when it is in a stimulated state, to effect addition polymerization of at least part of the components (a) and (b) in the mixture.

The polymeric component (a) preferably comprises a reducing component which has the structure B-M-B where M is an

B

meant from group Vb in the periodic table, in that at least one of the units B has a carbon atom that forms part of the polymer chain in the polymeric component (a) and at least one other of the units B, which is hydrogen, hydrocarbon residue, substituted hydrocarbon residue, or a group where two units B together with the element M form a ring system, and where the element M is linked directly to an aromatic group, with at least one of the other groups B having a -C- group linked to M. H

Preferably, the polymeric component (a) comprises a poly-(N-vinylpyrrolidone) and optionally a vinyl acetate component.

The reducing component in the polymer should have such a reduction potential that, in the concentration in which it is incorporated into the mixture, it is able to reduce the photosensitizer when it is in a stimulated state, but still unable to reduce the photosensitizer when the latter is not stimulated by irradiation . The reducing component should, at the concentration in which it is present in the photopolymerizable mixture, have little or no inhibitory effect on polymerization.

The periodic table referred to above is that published in "Advanced Inorganic Chemistry", Item 2nd Edition, by F.A. Cotton and G. Wilkinson (Interscience 1966), and element M can e.g. be phosphorus or, more preferably, nitrogen. If desired, M can be arsenic or antimony, and

throughout this description where reference is made to specific examples of reducing components where M is nitrogen, corresponding examples where M is phosphorus, arsenic or antimony will be included in suitable places.

The reducing component can be primary, secondary

B

or tertiary. This means that in the structure B-M-B two, one or none of the units B can be hydrogen atoms. For example, the reducing component can originate from a primary, secondary or tertiary amine or phosphine.

One or more of the groups B can be a hydrocarbon residue, and the hydrocarbon residue can e.g. be alkyl, cycloalkyl or alkaryl. Preferably, one or more of group B is an alkyl group with 1-10 carbon atoms.

Examples of suitable reducing components where one or more of the units B is a hydrocarbon residue are those which conceptually derive from propylamine, n-butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, di-n-butylamine, dipentylamine, trimethylamine, triethylamine, tripropylamine, tri-n-butylamine, tripentylamine, dimethylaminoethyl methacrylate and long-chain fatty amines, e.g. C,QH NMe .

IO3 I 2.

Thus, the reducing component is conveniently introduced into the polymer by copolymerization. Suitable reducing comonomers in which one or more of the units B is a hydrocarbon residue are e.g. the following esters of a methacrylic acid:

2-aminoethyl

3-amino-2-hydroxypropyl

2-aminopropyl

4-aminobutyl

5-aminopenty1

6-aminobenzy1

N-methylaminoethyl

2- N-ethylaminoethyl

3- N-propylaminopropyl1

N-methylaminomethyl

4- N-butylaminobutyl

5 N-pentylaminopentyl

N,N-Dimethylaminomethyl

2 N,N-Dimethylaminoethyl

3 N,N-dipropylaminopropyl

4 N,N-dibutylaminobuty1

N,N-dipentylaminopentyl

Examples of reducing components containing aromatic groups include those conceptually derived from N,N'-dimethylaniline, N-methyldiphenylamine, p-(N,N-climethylamino)-styrene, 2-anilinoethyl methacrylate, 2-p-methoxyanilinoethyl methacrylate, 2 -anilino-1-methylethyl acrylate.

One or more of the units B can be a substituted hydrocarbon residue and in particular the hydrocarbon residue can have a substituted

tuent with the structural formula

where M is an element

from group Vb in the periodic table, and the unit R2 e.g. is an alkylene chain, and the units R, which may be the same or different, are hydrogen atoms or hydrocarbon residues, especially alkyl-(especially C₁-C₂) groups.

Examples of reducing components that have struc-

B

the tour B-M-B where at least one of the units b is a substituted hydrocarbon residue includes conceptual derivatives of the structure

where n is an integer of at least two, and the groups R^, which may be the same or different, are hydrogen atoms or hydrocarbon residues, especially alkyl groups. For example, the reducing component can be conceptually derived from ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine or hexamethylenediamine, or an N-hydrocarbon residue, especially N-alkyl derivatives thereof.

Examples of such copolymerizable monomers are the following esters of (meth)acrylic acid:

1,3 bis-(dimethylamino)isopropyl

1,3 bis-(diethylamino)isopropyl

N-(diethylaminoethyl)-N-methylaminomethyl

Other suitable reduction components include conceptual derivatives of compounds with the structure

where one or more of the hydrogen atoms in the -CH unit are substituted with one

group, especially a -NH2~ group.

Examples of reducing components where the element M forms part of a ring system include those conceptually derived from piperidine, and an N-hydrocarbon residue, especially N-alkyl, derivatives of piperidine, e.g. 1,3-bis-di-piperidino-methyl)isopropyl methacrylate.

Other reducing components include such as

conceptually derived from triallylamine,

(allyl) 2-N-CH2-

CH2_N-(allyl), allylthiourea, o-tolylthiourea, soluble salts of aromatic sulfinic acids, e.g. S-benzyl-iso-thiuronium, p-toluenesulfinate, and sodium diethyldithiophosphate.

Incorporation of the reducing component in the polymeric component in the mixture, or production of a polymeric component containing such a reducing component according to the invention, can take place by known techniques for polymer production and will not present any difficulty for the person skilled in the field. Suitable preparative methods include copolymerizing the polymeric component of the mixture with a material which comprises the reducing component and is copolymerizable with said polymeric component.

A particularly suitable method for incorporating it. reducing component is by free radical copolymerization using e.g. aminoalcohol esters of (meth)acrylic acid.

The reducing component can also be introduced by conversion of an existing polymer, e.g. polyvinyl alcohol, with an aminoaldehyde. Monomers containing acid functions should

not used.

Polycondensation techniques can also be used where appropriate.

The concentration of the reducing component in the mixture may suitably be in the range of 0.001 to 50% by weight of addition polymerizable or ethylenically unsaturated material in the mixture, although concentrations outside these ranges may be used if desired. The reducing component is preferably present in a concentration of 1 to 10% by weight of the ethylenically unsaturated material in the mixture.

If one or more of the groups B in the reducing component B-M-B is aromatic, then it is preferred to have a concen-B

tration of reducing component in the photopolymerizable mixture in the range of 0.01 to 0.5% by weight of ethylenically unsaturated material in the mixture.

Typical water-soluble polymers include hydroxyethyl cellulose, polyvinylpyridine, sulfonated polystyrene, and partially hydrolyzed polyvinyl acetate.

Component (a) comprises a water-soluble polymer either alone or in mixture or copolymerized with one or more less water-soluble polymers or monomers (as appropriate), and examples of these are polyacrylates, polyalkyl acrylates (e.g. polymethyl acrylate, 2- ethylhexyl acrylate), polyalkyl methacrylates (e.g. polymethyl methacrylate, lauryl methacrylate, dialkyl maleates (e.g. di-iso-octyl maleate, di-butyl maleate, diethyl maleate).

Selection of the component(s) in component (a) will be made in light of the requirement that it must be able to be washed out of a film or material using an aqueous liquid, preferably water, i.e. that it must be water-soluble or water-dispersible. The mixture is preferably also soluble in an alcohol or other suitable solvent to facilitate film formation.

The applicant's preferred component (a) comprises poly(N-vinylpyrrolidone), either alone or in admixture with polyvinyl acetate, or a copolymer of N-vinylpyrrolidone and vinyl acetate. Pply(N-vinylpyrrolidone) and the copolymer of N-vinylpyrrolidone and vinyl acetate are both water soluble and soluble in lower alcohol (eg methanol and ethanol) and the applicant has found this advantageous, as one of the lower alcohols (ie up to C^) is preferred when forming the mixture according to the invention into a film from a solution. Substitution derivatives of the components can of course also be used where appropriate.

Component (a) will usually be present in the mixture in an amount of from 50 to 95% by weight, the water-soluble polymer preferably constituting 30 to 40% of the entire amount of (a).

The monomer used is one which preferably,

but not necessarily, is water-insoluble. It is naturally desirable that the monomer is highly compatible with the polymer and any other components in the mixture and is able to polymerize with at least one of component (a) to form a water-insoluble product. The monomer preferably comprises at least two non-conjugated ethylenic double bonds and preferably has terminal unsaturation. Examples of suitable monomers are mentioned

where R = H or CH^' > where 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, -COOR.^ where R^ is lower (e.g. eg up to 4 carbon atoms) alkyl group, -SO»NR R_ or -CONR.Rrh R„, R_, R. and R_ each represent-Å £ 545 2 j 4 5 .

teres H or a lower alkyl group.

Eg: N:N-bis-(f-acryloyloxyethyl)aniline N :N-bis-(13-methacryloyloxyethyl)-m-toluidine N:N (acryloyloxyethyl)-chloroaniline

where R = H or CH3.

E.g.: 1,2-(v-acrylamidopropoxy)ethane 1,2-(V-methacrylamidopropoxy)ethane (3) acrylates,

eg: allyl methacrylate

ethylene glycol dimethacrylate

trimethylolpropane triacrylate

trimethylolpropane trimethacrylate

pentaerythritol tetraacrylate

pentaerythritol monohydridoxytriacrylate.

(4) vinyl urethanes,

e.g. a reaction product of di(4-isocyanatophenyl)methane, polypropylene glycol and 2-hydroxyethyl methacrylate in the molar ratio 2:1:2.

The reaction product of tolylene diisocyanate, penta-erythritol/propylene oxide adduct, and 2-hydroxyethyl methacrylate in the molar ratio 4:1:4;

(5) allyl monomers

e.g. triallyl cyanurate.

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

It will be understood that component (b), although it does not

is preferred, could be an oligomer, i.e. a short polymer chain with up to 8, e.g. 5, repeating monomer units.

The reducing component in the polymer should, of course, be one which does not adversely affect the water-soluble or water-dispersible property of the polymer to an undesirable degree, and it will be selected accordingly.

The photosensitizer used according to the invention can be any suitable compound. In particular, it is preferred according to the invention to use

a photosensitizer as described, and in the proportions indicated,

in Belgian Patent Document No. 789,950.

In general, the group A in the photosensitizer will be aliphatic or aromatic, and it should be understood that the groups A can be the same or different, e.g. say in the photosensitizer of structural formula I, both groups A may be aromatic, or both may be aliphatic, or one group A may be aromatic and the other aliphatic, provided that when n is 1 and X is ^CR-j^»and when n is 0, both groups A are aromatic. However, for convenience in preparing the photosensitizer, the groups A are preferably the same.

Within the scope of the designation aliphatic groups are included cycloaliphatic groups and aliphatic groups that carry aromatic substituents, i.e. alkaryl groups. Similarly, included within the scope of the designation aromatic group are groups that carry alkyl substituents, i.e. aralkyl groups.

The aromatic group may be a benzenoid aromatic group, e.g., the phenyl group, or it may be a non-benzenoid cyclic group recognized in the art to possess the characteristics of a benzenoid aromatic group.

The groups A, especially when they are aromatic, may carry substituent groups other than hydrocarbon residues, e.g. halogen or alkoxy, provided that the photosensitizer containing the substituent groups is not present in the photopolymerizable mixture in such a concentration as to result in substantial inhibition of the polymerization of the ethylenically unsaturated material in the mixture.

.1 the photosensitizer having the structure I, the group X preferably has the structure ?C=0 or ?CR3OR4 where R3

and R^ are as described above.

The groups R 1 , R 2 , R 3 and R 3 can be hydrogen or hydrocarbon residues, e.g. alkyl. The groups R^ to R^ are preferably hydrogen.

In the photosensitizer having the structure I, the groups A can further be connected by a direct bond, or by a divalent group, e.g. a divalent hydrocarbon residue,

ie that in addition to the binding via the group

the groups A can be further connected so that they form a cyclic ring system. For example, if the groups A are aromatic, the photosensitizer may have the structure where X and n are as described above. Y is >CH2 , or a hydrocarbon derivative thereof, and m is 0, 1 or 2. The group Y is preferably linked to the aromatic groups in ortho-positions to the group

The groups A can together form a fused aromatic ring system.

Particularly preferred photosensitizers in view of the high rates at which the ethylenically unsaturated material can be polymerized are α-diketones of the structure I where X is

C=0 and n is 1. In general, the α-diketones are capable of being stimulated by irradiation in the visible region of the spectrum, i.e. by light having wavelengths greater than 400 mu, e.g. in the wavelength range 400 mu - 500 mu, although ultraviolet irradiation or a mixture of ultraviolet irradiation and visible light may be used. Suitable α-diketone photosensitizers include bi-acetyl where both groups A are methyl, benzyl where both groups A are phenyl, α-diketones where both groups A are fused aromatic, e.g. ar-naphthyl and B-naphthyl, and α-diketones where the groups A are aralkyl groups, e.g. p-tolyl. As an example of a suitable α-diketone photosensitizer where the groups A are non-benzenoid aromatics, mention can be made of furil where the groups A have the structure

, e.g. 2:2'-furyl. In the a-diketone photosensitizer

the groups A may carry non-hydrocarbon residues, for example the photosensitizer may be p,p'-dihydroxybenzyl, e.g. p,p'-dimethoxybenzyl, or p,p'-dihalobenzyl, e.g. p,p'-dichloro-benzyl, or p-nitrobenzyl.

In the photosensitizer having the structure I, n may be 0, in which case the groups A are aromatic or substituted aromatic. An example of such a photosensitizer is benzophenone where both groups A are phenyl.

Other suitable photosensitizers include those having the structure I where n is 1 and X is >CR.jOR 4 . For example, the photosensitizer can be benzoin where R^ and R^ and H and both groups A are phenyl, an alkylbenzoin where R^ is hydrogen and R^ is alkyl, e.g. methyl, α-naphthoin and ph-naphthoin where both groups A are fused aromatic, p,p'-di-alkoxybenzoin, e.g. p,p'-dimethoxybenzoin, and p,p'-dihalobenzoin, e.g. p,p'-dichlorobenzoin, where the groups A carry non-hydrocarbon residues, and furoin where the groups A are non-benzenoid aromatic and have struc-

the trip

e.g. 2,2'-furoin.

In the photosensitizer, the groups A can be linked together by a direct bond or by a divalent hydrocarbon residue to form a cyclic ring system. E.g. the photosensitizer, if the groups A are aliphatic, can be camphorquinone.

If the photosensitizer has the structural formula II, suitable photosensitizers include fluorenone where n and m are both 0 bg the aromatic groups A are linked together by a direct bond that is ortho to the group

and phenanthraquinone where X is>C=0, n is 1, and m is 0, the aromatic groups A being linked together by a direct bond that is in the ortho position to the group

Photosensitizers

the torus can be acenaphthenquinone where the groups A in structure I together form a fused aromatic ring system.

The photosensitizer can e.g. be present in the photopolymerizable mixture in a concentration in the range of 0.001 to 10% by weight of the ethylenically unsaturated material in the mixture, although concentrations outside these ranges may be preferable.

The method of mixing the photosensitizer with the ethylenically unsaturated material may affect the success or otherwise of achieving the desired concentrations of photosensitizer and reducing agent in the mixture.

Therefore, if the photosensitizer is not sufficiently soluble in the ethylenically unsaturated material, or if either can be dissolved only with difficulty, the applicant has found that dissolution of the photosensitizer can be remedied by adding to the ethylenically unsaturated material a small amount of a diluent in which the photosensitizer is soluble and which is miscible with the ethylenically unsaturated material. The photosensitizer can preferably be introduced into the ethylenically unsaturated material in the form of a solution in such a diluent.

According to a further embodiment of the invention, a method for the production of a polymeric material is provided, comprising irradiation of a photopolymerizable mixture as described here, with irradiation of a wavelength that can be absorbed by the photosensitizer so that the photosensitizer is converted into a stimulated state.

The irradiation can take place with visible light or ultraviolet rays or rays which in their crack spectrum include rays with both visible and ultraviolet wavelengths. The rays may preferably have a wavelength in the range 230 mu - 600 mu. Sunlight can be used as a radiation source, although the wavelength of the rays used will be determined by the particular photosensitizer in the mixture, the rays being of such a wavelength being absorbed by the photosensitizer to convert the photosensitizer into a stimulated state. A suitable wavelength can be selected using simple experiments, e.g. by measuring the electronic absorption spectrum of the photosensitizer.

In general, the polymerization of the ethylenically unsaturated material proceeds readily at ambient temperature when the mixture is irradiated with rays of a wavelength which converts the photosensitizer to the stimulated state. However, the polymerization rate can generally be increased by the polymerization being carried out at a temperature above ambient temperature.

The invention provides photopolymerizable compositions which can be developed (ie unexposed areas are removed) by treatment with water or an aqueous liquid, and the composition can e.g. is used in the production of coated sheet materials that carry a layer of the mixture. Such sheet materials can e.g. used as printing plates. Other uses for the compounds include lightfast applications.

According to another aspect of the invention, a carrier is therefore provided which has deposited on it a photopolymerizable mixture as described here. The carrier will preferably be a sheet together with a layer of the mixture deposited on at least one surface thereof. A special application of such a sheet product is in the production of relief plates which, after suitable processing, can be used both for direct or offset book printing, flexo printing, or as pattern plates, as fully described in Belgian patent document no. 820,404, and consequently provides another aspect of the invention a method for producing relief plates by selectively exposing a mixture according to the invention to suitable irradiation, e.g. through a negative, and development of the exposed mixture (preferably in the form of a sheet on a substrate)..

In the following, the invention will be illustrated by examples.

Example 1

Production of polymer

A mixture of 100 g of vinyl acetate, 100 g of vinyl pyrrolidone, 4 g of dimethylaminoethyl methacrylate and 2 g of azobisisobutyronitrile was added to refluxing methylated industrial alcohol (160 g). The mixture was boiled under reflux in a nitrogen atmosphere for a total of 14 hours. A viscous, straw-colored solution was obtained.

Production of printing plates comprising the polymer

100 g of the above solution was mixed with 11 g of ethylene glycol dimethacrylate, 1.65 g of benzyl and 5.5 g of dimethyl phthalate. The mixture was spread over a steel sheet and dried by heating at 60°C for 1 hour and 85°C for 1 hour so that a 0.5 mm thick coating was obtained.

The dried plate was exposed through a negative to ultraviolet irradiation for 5 minutes and then washed for 4 minutes with a water shower to obtain a relief image. After drying at 105°C for 10 minutes, the plate was suitable for use as a letterpress plate. The plate was quite flexible and after processing could be shaped around a roller with a diameter of 4 cm.

Example 2

167 parts of a 60% solution of copoly(vinyl acetate/vinylpyrrolidone), prepared by polymerizing a mixture of equal parts by weight of vinylpyrrolidone and. vinyl acetate in methylated spirits, was mixed with 20 parts ethylene glycol dimethacrylate, 10 parts dimethyl phthalate, 2 parts dimethylaminoethyl methacrylate and 2 parts benzyl. Part of the solution was used to produce a printing plate as described in example 1. After exposure and washing, the plate cracked when it was shaped around a roller with a diameter of 4 cm.

Examples 3-11

Plates were produced as described in example 1 using different photoinitiators at different concentrations in the following base mixture:

The dried plates were exposed to UV radiation through a "By Chrome" "screen tint" negative. The exposure times indicated are those required to preserve the 5% dots on the plate after processing as described in Example 1. A plate was made using vinyl pyrrolidone:vinyl acetate copolymer (50:50) instead of the copolymer in the mixture according to Example 11. An exposure of 12 minutes was found to be necessary to preserve the 5% dots.

Examples 13-17

Plates were made as described in example 1, but using polymer with different amounts of reducing agent in the mixture.

The plates were exposed to UV radiation through a "By Chrome" "screen tint" negative, and the exposure time indicated is that required to preserve the 5% dots on the plate after processing.

Example 18

A plate was made as described in Example 1, but by replacing ethylene glycol dimethacrylate with polyethylene glycol dimethacrylate ("Sartomer" 210 - from Sartomer Resins, Inc). The processed plate showed good flexibility and could be shaped around a roller with a diameter of 4 cm.

Example 19

A plate was made using the polymer described in example 1. The composition was:

The plate was exposed through a negative to UV irradiation for 5 minutes. The unexposed areas of polymer were removed by washing with a water shower for 4 minutes. After drying, the plate was applied to a newsprint rotary press. After 300,000 impressions, the prints were still of good quality.

Claims (7)

1. Photopolymerizable mixture, characterized in that it comprises (a) a water-soluble or water-dispersible polymer or copolymer, or a polymer or copolymer mixture where one or more of the components is water-soluble or water-dispersible, (b) an addition polymerizable monomer that is soluble in or compatible with a solvent or dispersing medium for (a); and (c) at least one photosensitizer having the structure where X is'C=0,?CR .| R2 or >CR3OR4,R1 to R^, which may be the same or different, are hydrogen or hydrocarbon residues, n is 0 or 1, and the groups A, which may be the same or different, are hydrocarbon or substituted hydrocarbon residues, the groups A being aromatic or substituted aromatic when n is 1 and X is,?CR-]_R2 °^ n^r n is °' i^et ^a polymeric component (a) is capable of reducing the photosensitizer (c) when the photosensitizer is in a stimulated state, to effect addition polymerization of at least part of the components (a) and (b) in the mixture. 2. Mixture as set forth in claim 1, characterized in that component (a) comprises a reducing component having the structure B-M-B where M is an element from group V b, B at least one of the units B has a carbon atom which forms part of the polymer chain in the polymer component (a) and at least one other of the units B is hydrogen, a hydrocarbon residue, a substituted hydrocarbon residue, or a group where two units B together with M form a ring system. 3. Mixture as stated in claim 1 or 2, characterized in that component (a) comprises a poly-(N-vinylpyrrolidone). 4. Mixture as set forth in any of the preceding claims, characterized in that the reducing component is present in the range of 0.001 to 50% by weight of addition-polymerizable or ethylenically unsaturated material in the mixture. 5. Mixture as stated in any of the preceding claims, characterized in that the photoinitiator is an α-diketone. 6. A plate comprising a carrier associated with a composition as set forth in any of the preceding claims. 7. A process for producing a relief plate comprising exposing a layer of the composition according to any one of claims 1 to 5 to polymerization radiation and developing the composition.