CA2023251A1

CA2023251A1 - Water-soluble or water-dispersible photopolymerizable mixture and its use for printing purposes

Info

Publication number: CA2023251A1
Application number: CA002023251A
Authority: CA
Inventors: Dieter Littmann
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1989-08-26
Filing date: 1990-08-14
Publication date: 1991-02-27
Also published as: FI904160A0; EP0415187A3; EP0415187B1; DE3928289A1; DE59006676D1; EP0415187A2; AU6132090A; JPH03170932A; AU629972B2

Abstract

O.Z. 0050/41056 Abstract of the Disclosure: The novel water-soluble or water-dispersible photopolymerizable mixture, comprising the following components:
A) from 46 to 53% by weight, based on the total weight of the mixture, of a binder consisting of a1) from 20 to 80% by weight, based on the total weight of the binder, of a polyvinyl alcohol resin having a degree of hydrolysis of from 75 to 85% and a number average degree of polymer-ization ?n of from 250 to 350, a2) from 20 to 80% by weight, based on the total weight of the binder, of one or more graft copolymers of vinyl alcohol and alkylene oxides having a degree of hydrolysis of more than 80%
containing from 10 to 40% by weight of alkylene oxide units and possessing a weight average degree of polymerization ?w of from 300 to 500, and a3) from 0 to 60% by weight, based on the total weight of the binder, of one or more polyvinyl alcohol resins having a degree of hydrolysis of more than 75% and a number average degree of polymerization ?n of from 350 to 450, B) from 35 to 44% by weight, based on the total weight of the mixture, of one or more water-soluble mono-functional monomers, C) from 6 to 9% by weight, based on the total weight of the mixture, of one or more polyfunctional monomers and D) from 0.4 to 5% by weight, based on the total weight of the mixture, of one or more photopolymerization initiators is very useful for the production of photopolymerizable recording layers of novel photosensitive recording elements. The said recording elements are particularly suitable for the production of newspaper printing plates.

Description

~ O.Z. 0050/41056 Water-soluble or water-dispersible phot~opoly~erizable mixture and its use for printing purposes The present invention relates to a novel water-soluble or water-dispersible photopolymerizable mixture which, in brief, contains two or more polyvinyl alcohol resins (A) of different compositîons, one or more water-soluble monofunctional ethylenically unsaturated photo-polymerizable monomers (B), one or more polyfunctional ethylenically unsaturated photopolymerizable monomers (C) and one or more photopolymerization initiators (D).
Photopolymerizable mixtures of this typa are known. They are used in particular for the production of photopolymerizable recording layers of photosen~itive recording elements which, after they have been exposad imagewise to actinic light and developed with water, are u~ed as le~terpress printing plates, in particular for newspaRer printing.
For example, EP-A-0 266 06g disclo3es a photo-polymerizable mixture which contains from 35 to 41% by weight o~ one or more water-soluble monofunctional ethylenically unsaturated photopol~merizable monomers, ~rom 6.5 to 8.5% by weight of one or more polyfunctional ethylenically unsaturated photopolymsri~able monomer~ and from 47.S to 63, in particular from 49 to 52, % by weight of one or mlore partially hydrolyzed polyvinyl alkan~-carboxylate~ r th~ percentages being based on the total amount of the ~aid mixture. The partially hydroiyzed polyvinyl alkanecarboxylata i8 said to have a degree of polymeriza~ion P of from 200 to 400, but it is not stated whether the degree o~ polymerization P is the number ayerag2 (~n) or the weight averag~ ) degr~e of polymer-ization. Furthermore, the abovementioned partially h~drolyzed polyYi~yl alkanecarboxylate can be used together with a smaller amount of par~ially hydrolyzed polyvinyl alkanecarboxylate having a degree of polymeriz-ation P o~ 500, the weight ratio being preferably 3 : 1.
In addition, the mean de~ree of hydroly~is of ~hese ~ 3 - 2 - O.Z. 0050/41056 polyvinyl alcohol xesins is said to be about 78 to 84% of the alkanecarboxylate group~ originally present, and individual polyvinyl alcohol resins may have a degree of hydrolysis of from 65 to 90%.
If this known photopolymerizabl~ mixture is used 2S a photopolymerizable recording layer in a photo-sensitive recording element, it is said to Lmprove the processing properties of the photosensitive recording elemant and finally to lead to ~etter prints. It is said that the photosensitive recording element~ are capable of being exposed more rapidly to actinic light and there-after of being wa~hed out more rapidly than other known photosensitive recording elQments, the improvement being said to be from 10 to 15~. It is also said that the photosensitivity of tha photopolymerizable recording layers can be aven further increased by the pre~ence of a substrate layer which ~trons~ly re~lects W light.
Furthermore~ the letterpres~ printing plates produced from the photosen~itive recording alement~ ara said to transfer printing inks better and more rapidly.
A ~urther photopolymerixable mixture o~ the type stated a~ the outset is disclolsed in US-A-4 272 611~
Here, a mixture of partially hydrolyzed polyvinyl alkane-carboxylate having a degr2e of polymerization P of from 200 to 3,000, in paxticular from 250 to 700, and a degree of hydrolysi~ from 65 to 100~, in particular from 80 to 88%, nd a partially h~drolyzed graft copolymer of vinyl alkaneca~boxylates and alkylen~ oxides is used as tha binder. Thi~ graft copolymer may contain from 5 to 75%
by weight of alkylene oxide uni~s and have a degrae of hydrolysis of from 70 to 100% and a molecular weight of from 5,000 to 2~105, specific example~ baing gra~t copoly-mers which contain 24% by weight of alkylene oxide units and hava a degree of hydroly~is of 85% and a molecular weight of from 30,000 to 35,000 or those which contain 54~ by weight of alkylene oxid~ unit~ and hava a de~reQ
of hydrolysis o~ 83 mol % and a molecular weight o~ ~rom - 3 - O.Z. 0050/41056 35,000 to 50,000 or tho~e which have a weight average degree of polymerization Pw of 460. These specifically stated graft copolymers are used in p~rticular together with a partially hydrolyzed polyvinyl alkanecarboxylate having a degree of polymerization P of 500.
The use of this known photopolymerizable mixture is also said to simplify the production of photosensitive recording element~ because the photopolymeri~able mixture permits the production of cl0ar homogeneous iolutions and doe~ not exhibit pha~e separation or exudation of compon-ents of the mixture either during casting of the mixture or during drying and stoxage of the mlxture. The photo-polymeri~able recording layers produced with the aid of this photopolymerizable mixture are said to be nontacky, so that photographic transparencies placed thereon should not cause any damage. In addition, the washout tima a~ter imagewise expoYure to actinic light i~ said to be shorter than in the case of other Xnown photopolymeri~-able recording layars or othor known photosen~itive recording elements. Furthermore, the photosensitive recording elements of US-A-4 272 611 are said to give letterpress prin~ing plates which are le~s sensi~ive to moi~ture and less brittle and have improved ink tran~fer prop~r~ies.
A further photopolymerizable mixture of the type ~tated at the out~et i~ di~closed in DE-A-37 38 215. This known photopolymerizable mixture contain~, as a binder, a partialqy hydrolyzed polyv~nyl alkanecarboxylate having a degree o~ hydrolysis of from 65 to 90 mol ~ and a degree of polymerization P of from 50 to 2,000, in particular from 200 to 1,000 and a partially hydrolyzed polyvinyl alkanecarboxylate having a degree of hydroly~is of les~ than 65~ and a degreo of polymerization of not more ~han 2,000, in particular not more than 500. The la~t-mentioned polyvinyl alcohol resin may furthexmore contain ionic group~, in particular anionic groups, such a~ alkali metal ~ulfonate group~. T~o two poly~inyl ~. `.` ~f' ,,` . ., ',_ 4 _ O.Z. ~050/41056 alcohol resins are used in ratios of from 50 : 50to 98 :2.
This known photopolymeri~able mixture is sai~ to be capable of being dissol~ed in particularly high con-centration in water. Th~ photopolymarizable recording layers obtained from this known photopolymerizable mix-ture are said to have Lmproved flexibility. In addition, a substantially improved resolution is said to be achieved, so that letterpres~ printing plates can be more e f f ic iently produced.
A further example of a photopolymerizable mixture of the type stated at the outset is described in US-A-3 801 328. This known photopolymerizable mixture con-tains a partially hydrolyzed polyvinyl alkane~arboxylate having a msan degree of polymerization P of 500 and a degree of hydrolysis of 80.5% and a partially hydrolyzed polyvinyl alkanecarboxylate having a mean degrea of polymerization P of 500 and a degree o~ hydroly~is of 88.5%. Thi~ known photopolymerizable mixture is ~aid to give hard and stable letterpre~ printing plates, and the photosensitive recording element~3 used for the production of these letterpre3~ printing plates are said to dispense with antihalation agent~ and adhesive layer~.
Furthermore, EP-A-0 295 545 d~sclose3 a photo-polymeri~able mixture which is u~ed for the production of hot ~tamping pl~tes crosslinkable by photopolymerization and hot stamping die~ obtained therefrom. The known photopolymerizable mixture contain~, a~ a binder, one or more par~ially or virtually completely hydroly2ed poly-vinyl alkanecarboxylates in combination with one or more alkenecarbo~ylatasand/oralkenecarbonylamino-~-methylene e~her of partially or virtuslly completsly hydrolyzed polyvlnyl alkanecarboxylates and/or alkenecarboxylates and/or alkenecarbonylamlno-N-methylane ethers of partial-ly or virtually completely hydrolyzed gra~t copolymors of vinyl alkanecarb~xylates and alkylane oxide~. In par-~icular, binder mixtures of partially hydrolyzed poly-vinyl acetate having a de~ree o~ hydrolysis of 80~ and a b ~ d 5 _ o.z. 0050/41056 number average molecular weight ~ of 2-104, correspond-ing to a number average degree of polymerization P~ of about 400, and (i) acrylates of partially hydrolyzed polyvinyl acetate having a degree of hydrolysis of 82%
5 and a number average molecular weight M~ of 2 10S, (ii) acrylates of a partially hydrolyzed ethylene oxide/vinyl ac~tate graft copolymer having a number average molecular weight ~ of 2~104 and containing 25% by weight of ethylene oxide units, (iii) acrylamido-N-me~hylene ethers of a partially hydrolyzed polyvinyl acetate having a degree of hydrolysi~ of 82% and a number average mole-cular weight ~ of 2,1 o4 or ( iY ) acrylamido-N-methylene ethers of the abo~ mentioned graft copolymer are used.
The patent reco~mends using these binders in conjunction with one or more alkenecarbonylamino-N-methylena ethers of a polyhydric alcohol as a polyfunctional ethylenically unsaturated photopolymerizable monomer.
The hot stamping plates produced with the aid o~
thi~ known photopolymerizable mi.xture are said, as such, to have high thermal stability and a long shel~ life and are al~o supposed to be capable of being disposed of in an environmentally compatible manner. They are also said to have shorter exposure and dsvelopment times than other known photopolymerizable mixture~, so that overall shorter proces~ time~ and hence higher space-~Lme yield3 result durin~ the production of hot ~tamping die~. ~ore-over, it is said that the drying times for the hot stamp-ing dies can be reduced because their performance charac-teristics are ~upposed not to be advarsely affected by a comparatively high re~idual watar content. Moreover, their relief layers are said to be so hard, heat-rQ~istant and dimensionally s~a~le that they show no di~-advantageous changes even a~ter being u~ed 10 times ~or hot ~t~mping.
Furthermore, EP-A-0 295 547 disclo~es a photo-pol~merizable mixture o~ the type stated~at the outse~
which contain~, a~ a binder, a mixture of a methacryla~e - 6 - O.Z. 0050/41~56 of a partially hydrolyzed polyvinyl alkanecarboxylate having a degree of hydrolysis of 80~ and a number average molecular weight M~ of 2.5-104 and a partially hydrolyzed polyvinyl alkanecarboxylate having a degree of hydrolysis of 80 mol % and a number average molecular weight ~ of 2.5-104. In addition to the photopolymerizable monomers and the photopolymerization initiator, this known photo-pol~meri2able mixture also contains glyoxal. With the aid of this compound, it is said that the letterpress printing plates which are produced from photosensitive recording elements which contain photopolymerizable recording layers and/or adhesive layers of this kn~wn photopolymerized mixture exhibit better Lmage reproduc-tion, have great hardness, very little sensitivity to water and excellent ink acceptance and show no damage due to swelling and no pitting.
Accordinglyt it i~ still necesYa~y to prepare in each case a special photopolymerizabla mixture of the typs stated a~ the outset if it is intended t~ achieve one of the abovementioned proper~.y profiles or one of the ~tated technical effects, becau~e none of the known photopolymerizable mixtures i3 suitable for fully meeting all re~uirements in practice. The necessity o~ preparing a special photopolymerizable mixture for each intended use i8 a seriou~ disadvantage, requiring very expen~ive pre~aration of the individual components and frequently making it e~ential for the producer and the printing works to make modifications to the apparatuse~ or the production of the photopol~merizable mixtures~ of the photopol~merizable recording lay~rs, of the photosensi-tive recording elements and of tha letterpxess printing plates.
If, on the other hand, it i3 in~ended to optimize a known photopol~merizable mixture in order to use it ~or other purpose , new problQms ari~e. I~hu~, photopolymer-izable mixtures which permit a rela~ively hlgh casting concentration during the production of the photo8en8itive _ 7 _ o.~. 0050/41056 recording elements and hence are economically more attractive and lead to shorter development and drying times in the production of letterpress printing plates have greater brittleness in the photopolymerized state.
Furthermore, the cohesion of the relevant photopolymeriz-able recording layer is often reduced, so that cracking occurs. The disadvantage of the great tendency to embrittlement could be counteracted, for example, by adding plasticizers. However, this measure leads to other very well known problems, for example the reduction in the mutual compatibility of the components of the photopolymerizable mixture, which leads ~o exudation of photopolymerizable monomers, plasticizers and other low molecular weight components and to opacity.
Thus, it is not possible, on tha basis of the conventional photopolymerizable mixtures or of the binder combinations present therein, to produce a property profile which includes the advantage~ of a high solids concen~ration in solution and a greatly reduced washo~t and drying time in the production of printing plates without incorporating the disadvantages, such as great brittleness and low cohesion o~ tha photopolymerizable recording layer. It i~ even more di~icult ts vary the conventional photopolymerizable mixtures in such a way tha~ ~he compatibility of the components present therein~
high resolution and graat expo~ure latitude in imagewise exposure, shorter exposure times and le9~ soiling o the washers used or development are achieved. Accordingly, in tha case of the letterpre~s printing plates which were produced with the aid of the~e known photosensitive mixtures, i~ is not possible to obtain a property profile which includes a uniform smooth sur~ace, better ink co~erage in solid areas in the print, very smooth ~ido waLls in the relie, less tendency to picklng and to linting and a long press life.
It i~ an ob~ect o~ the presant invention to provide a no~el photopol~merizable mix~ura which no ë i~ J `' - 8 - O. Z . (:~050/41056 longer has the disadvantage~ of the prior art a~d with the aid of which it is possible to realize the d~ired advantages required in practice.
We have found that this object is achieved, 5 surprisingly, if two or more specially selected partially hydroly~ed polyvinyl alkanecarboxylates of differ2nt com-positions are used in certain, exactly ~pecified amount~
as the binder for the novel photopolymerizable mixture.
The choice of certain, exactly specified amount~ of water-~oluble monofunctional ethylenically unsaturated photopolymerizable monomers, polyfunctional ethylenically unsaturated photopolymerizable monomers and photopolymer-ization initiators has contribut~d to this surprising achievement.
In view of the prior art, it wa~ surprising that the desired advantage~ required in practice can be achieved with the aid of the novel photopolymerizable mixture without the prior art disadvantages occurring.
The present invention accordingly relates ~o a water-soluble or water-dispersible photopolymerizable mixture, compri~ing the following components:
A) from 46 to 53% by waight, based on the total weight o~ the mixture, of a binder consisting of a1) from 20 to 80% by weight, based on the total weight of the binderOof one or more partially hydrolyzed polyvinyl alkanecarboxylate~ having a degree of hydroly~is of from 75 to 85% of the alkanecarboxylate groups originally present and a number average degree of polymerization PD of from 250 to 350, a2) from 20 to 80% by weight, based on the total weight of the binder, of one or more par~ially hydrolyzed graft copolymers of vinyl alkanecar-boxylate3 and alkylene oxldes havinq a degree of hydroly3i-~ of more than 80~ of the alkane-carboxyla~e groups originally present, contain-ing from 10 to 40% by weight of alkylene oxide ~ r~ r~

9 ~ O ~ 2 ~ 0~50~41056 units and having a weight a~erage degree of polymerization ~w of from 300 to 500, calculated from the weight average molecular weight ~
determined by viscosity measurements using dilute solutions, in accordance with the equation M~ = PW (86 minus 0.42 . degree of hydrolysis) and a3~ from 0 to 60% by weight, based on the total weight of the binder of one or more partially hydrolyzed polyvinyl alkanecarboxylates having a degree of hydrolysis of more than 75% of the alkanecarboxylata groups originally present and a number average degree of polymerization Pn of from 350 to 450, B) from 35 to 44% by weight, based on the total weight o~ the mixture, of one or more water-~oluble mono-functional ethylenically unsaturated photopolymeriz-able monomer~ which are compatible with the binder (A), C) from 6 to 9% ~y weight, based on the total wPight of the mixture, of one or more pc:lyfunctional ethyleni-cally unsatura~ed pho~opolymerizable monomer~ which are compatible wi~h the bindex (A) and D) from 0.4 to 5% by weight, ba~ed on ~he total weight of the mixture, of one or more photopolymerization initiators .
For the sake of brevity, the novel water-solùble or water-dispersibla pho~opolymerizable mixture is refer-red to below as the novel mixture.
Tho component, e~sential or the invention~ of the novel mixture is the novel bindor mixtura tA). This is pre~ent in tha ~ovel mixture in an amount of from 46 to 53% by weight. Although it i~ also possible to use othar amoun~ , for exampla from 40 to 46% by weigh~ or ~rom 53 to 60~ by weight, ~he par~icular advantages of - 10 - O.Z. 0050/41056 the novel mixture are then sometLmes not obtained with the required reliability. Accordingly, the range from 46 to 53% by weight is an optimum within which the amount of the novel binder mixture (A) may be freely chosen and adapted in an advantageou~ manner to the particular intended use. Within this range, the range from 49 to 51% by weight is particularly noteworthy because novel mixtures which contain the novel binder mixture (A) in these amounts are very particularly advantageous and are therefore preferably used according to the invention~
The novel binder mixture (A) contains from 20 to 80% by weight, based on its total amount, of one or more partially hydrolyzed polyvinyl alkanecarboxylates having a degree of hydrolysis of from 75 to 85% of the alkane-carboxylate group~ originally present and a numberaverage degree of polymerization ~n f from 250 to 350 (b~nder a1).
If the novel binder mixture (A) contains the binder (al) in amount~ of less than 20% by weight or greater than 80~ by weight, the advantages achieved according to the invention are no longer reliably ob-tained. ~ccordingly, the range Erom 20 to 80% by weight i~ an optimum within which the proportlon of the binder (a13 in the novel binder mixture ~A) may be ~reely chosen and adapted in an excellent manner to the particular intended u~e. Very particular advantages result from the u~e of from 25 to 50% by weight o~ bind~r (a1), becau~e the noveI mixturQs which contain a novel binder mixture (~) having such a content of binder (al) have particular-ly good performance characteristic~0 ~ he hinder (a1) must, accordin~ to the inventionrhave a degxee of hydrolysis of from 75 to 85% o~ the alkanecarboxylate group~ originally prasent. Binders having higher or lower deqraes o~ hydroly~is are not suitable for use in the novel binder mixture (A) or in the novel mixture. According ~o the invention, it is advantageous if ~he degree of hydrolysis o~ ~he blnder rr, ~ "~

- 11 - O.Z. ~050/41056 (a1) is from 78 to 83%.
The binder tal) has a number average degree of polymerization ~n of from 250 to 350. Binders having a higher or a lower number average degree of polymeriza~ion 5 Pn are, on the other hand, unsuitable for the intended use according to the invention, since they result in a deterioration in the property profile of the relevan~
binder mixture and therefore of the relevant photopoly-merizable mixture. Accordingly, the range from 250 to 350 is an optimum within which the number average degree of polymerization ~ may be freely chosen and adapted in an excellent manner to the particular intended use of the novel mixture. Particular advantages of the novel mixtures are obtained if the binder (al) has a number average degree of polymerization ~n Of 300 The binder ~al) is a polyvinyl alkanecarboxylate, which is also referred to by the skilled worker as poly-vinyl alcohol or polyvinyl alcohol resin. All polyvinyl alkanecarboxylates which can be prepared in a 31mple manner and selectively hydrolyzed and have the property profile described above in detail are sui~able for tha intended use accordLng to the invention. Example~ o~
3uitable polyvinyl alkanecarboxylates are polyvinyl acetate, propionate and butyrate.
The binder~ (al) and their preparation are known per se and ~re disclosed in, for example, the prior art ~ta~ed at the out3et.
The novel binder mixture (~) contain~ from 20 to 80~ by weight, based on its total amount, o~ a binder (a2). Higher or lower contents of binder (a2) in the novel binder mixture (~) are unsuitable for the purposes of the present invention since they lead to a deteriora-tion in the proper~y profile of the relevan~ bindar mix-ture and of the relevant photopolymeri~able mixture, ~o that they are no longer suitable for the pUrpO~QS 0~ the present invention. Accordingly, the range from 20 to 80%
by weight is an op~imum wi~hin wh~ch the proportion o~

r;, ~ f '~
- 12 - O Z. 0050/41056 binder (a2) in the novPl binder mixture (A) may be freely chosen and adapted in an excellent manner to the particu-lar intended use of the novel photopolymerizable mix~ure.
Within thi_ range, the range from 25 to 56% by weight is particularly noteworthy, because th~ use of these ~ounts o~ binder ~a2) results in particularly advantageous binder mixtures (A) and novel mixture~, which can be easily prepared and give excellent photopolymerizable recording layers, photosensitive recording elements and letterpress pxinting plates.
The binder (a2) is a partially hydrolyzed graft copolymer of vinyl alkanecarboxylates and alkylene oxides. Examples of suitable vinyl alkanecarboxylates are vinyl acetate, propion~te and butyrate, among which ~inyl acetate is preferred. Examples of suitable alkyl-ene oxide~ are ethylene oxide and propylene oxide, ethylene oxide being preferred.
The degree of hydrolysis of the binder~ (a2) i~
more than 80% of the alkanecarboxylate group~ pre~ont.
On the other hand, lower degree3 of hydroly~is should not be used since the excellent water 301ubility of the binder (az) suf~ers as a result. Degree~ o~ hydrolysis of ~rom ~2 ~o 90%, ln particular 85~, are particularly advantageous ~ince binder~ (a2) having such a degree of hydrolysis posses~ particularly advantageous performance charac~eri~ics.
The content of alkylene oxide units in the binder (a2~ i~ from 10 to 40~ by weight, based on the binder (a2). The use of ~maller or larger amount~ of alkylene oxide unit~ i~ possible but i8 not advisable because this results in a property pro~ile which is no longer optLmal-ly tailored to the novel intended u~e of the binders (a2).
Accordingly, ~he range from 10 to 40~ by weight iq an optimum within which the content of alkylene oxide units in the binders (a2~ may be freely chosen and ~dapted in an excellent manner to the particular intanded use of the photopolymerizable mixture~. Wi~hin thi~ range, the - 13 - O.Z. 005~t41056 range from 20 ~o 30% by weight is particularly noteworthy since binders (a2) having such a content of alkylene oxide units exhibit particular advan~ages during preparation and use.
The binders (a2) have a weight avPrage degree of polymeri.zation Pw of from 300 to 500, which is calculated in a conventional and known m nner from the weight average molecular weights ~ determined by viscosity measurements on dilute solutions, in accordance with the equation ~ w (86 - 0.42 d~gree of hydrolysis).
The use of binder~ (a2) having a different weight average degree of polymerization ~w i~ not advisable because this results in binder mixtures and photopolym~rizable mix-tures which no longer have the advantages of the novel mixtures. Accordingly, the range from 300 to 500 is an optimum within which the weight average degree o~ poly-merization ~w may be freely chosen and adapted to the par~icular intended use of the novel mixtures. Within this range, the ranqe from 440 to 480 is noteworthy because the b.inders (az) having th~is weight average degree of polymarization Pw have partic1l1arly advantageous pro-perties and, according to the invention, are therefore particularly preferably used.
The novel binder mix~ure (A) has additional advantages if it contain~ not more than 60, in particular not more than 50, % by weight, based on it8 total amount, o the binder (a3). The u~e of larger amount~ o the binder (a3) is not advisable since ~hi~ results in dis-ad~an~ageou~ binder mixtures and photopolymerizable mixtures.
The binder (a3) differs from the bindor (a1) in its degree of hydrolysis and its number average degree o polymerization Pn~ Thu~ the degree o~ hydroly~i~ of the binder (a3) is greater than ?5~ of the alkanecarboxylic acid groups originally present, degree~ of hydroly~is of less than 75~ being un~ui~able. Additional ad~antage3 - 14 - O.Z. 0050J41056 are obtained if the binder (a3) ha~ a degree of hydrolysi~
of more than 78%. The number average degree of poly-merization ~n Of the binder (a3) should be from 350 to 450. On the other hand, the use of binders (a3) having other number average degrees of polymerization ~n is dis-advantageous. Binders (a3) which have a number average degree of polymerization Pn Of about 400 may be particu-larly advantageously used.
The properties and the preparation of the binders (a2) and (a3) are al~o known and are disclosed in, for example, the prior art stated at the outset.
~ he noveI mixture contains from 35 to 44% by weight, based on its total ~mount, of a monomer (B).
Although the monomers (B) may also be present in larger or smaller amounts in the novel mixture, the rel~vant photopol~merizable mixtures then do not always meet the expectations and requirement~ -~et. It is therefore not advisable to depart from thi~ optimum range. Within this optimum range, the range from 41 to 43~ by weight i8 noteworthy since ~he novel mixture~ having such a content of monomers (B) can be particularly readiiy proce~sed to the photopolymerizable recording layers o~ photo~ensi~ive racording element~ and letterpre~ printing plates.
Suitable monomer~ tB) to be used according to the invention are all the water-soluble monofunctional ethylenically unsaturated photopolymerizable monomer~
which are compatible with the nov21 binder mixture (A).
~ xample~ of particularly ~uitable monomers (B) to ba u~ed according to the invention are the acrylic and methacryllc monoesters and the alkenecarbonylamino-N
methylene monoe~her~ of polyfunctional alcohol~, such a~
e~hylenQ glycol, glycerol, diglycerol, diethylene glycol, triethylene gly~ol, polyethylene glycol, trimethylol-ethane or trime~hylolpropane~ among which 2-hydroxyethyl acrylate and methacrylate ars particularly preferred.
The no~el mixture contain~ from 6 to 9~ by weight, based on its total ~mount, of one or more mono-- 15 - O. Z . 0050/41056 mers (C). Although it is possible to use smaller or larger amounts of monomers (C), this does not result in any further particular advantages, so that such a measure is not advisable. Within the range from 6 to 9% by weight, the range from 7 to 8% by weight is particularly noteworthy since the novel mixtures having such a content of monomers (C) are particularly advantageous to prepare and to use.
Suitable monomers (C) to be used according to the invention are all the polyfunctional ethylenically un-saturated photopolymerizable monomexs which are com-patible with the novel binder mixture ~A). Suitable monomers (C) are tho~e which are soluble or at least readily dispersible in water.
Ex~mples of particularly suitable monomers (C) are the polyfunctional acrylates and methacrylates having a molecular weight of not more than 2,000 and containing 2 or more acryloyl or methacryloyl groups in one and the 9ame molecule and having a number of hydroxyl groups which does not exceed the number of the acryloyl or meth-acryloyl groups in on~ and the s,lme molecule. The total number of carbon atom~ in the~0 monomer3 (C) should be from 6 to 40.
Examples of very particularly suita~le monomers (C) of thi~ type are glycerol diacrylate, glycerol di-methacrylate, trLmethylolpropane diacrylate, trimethylol-propane dimethacrylate, pentaerythritol diacrylate, pentaerythritol dimethacrylate, pentaerythritol tri-acrylate, pentaerythritol trimethacrylate, trimothylol-ethane diacrylate, trimethylolethane dimethacrylate,~etramethylolethane triacrylate and tetramethylolethanQ
trimethacrylate.
Further examplas o~ suitable monomer~ (C) to be u~ed according to ths invention are the polyfunctional acrylate3 and methacrylate~ having from 2 to S acryloyl or methacryloyl group~ and the ~ame numb~r o~ hydroxyl ~roup~ in the molecule, these being J r~
- 16 - O.Z. 005~/41056 reaction products of glycidyl ethers of polyhydric alcohols ha~ing from 2 to 30 carbon atoms and from 2 to 5 hydroxyl groups in the molecule with ethylenically un-saturated carboxylic acids having from 3 to 15 carbon atoms in the molecule, or the reaction product~ o an unsaturated alcohol haviny from 4 to 15 carbon atoms in the molecule with glycidyl ethers of polyfunctional alcohols having from 2 to 30 carbon atoms and from 2 to 5 hydroxyl groups in the molecule.
Examples of particularly suitable monomers (C) of this type are disclosed in EP-A-0 081 964.
Other examples of suitable monomers (C) are ethylene glycol di(meth)acrylate, diethylene glycol di-(meth)acrylate, triethylene glycol di(meth)acrylate,tetraethylene glycol di(meth)acxylate and polyethylsnQ
glycol di(meth)acrylate, propanediol di(meth)acrylate, 1,4-butanediol di(me~h)acrylate, 1,5-pentanediol di-(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,1,1-trimekhylolpropane tri(meth)acrylate, pentaerythritoltetra(meth)acrylate, divinyl ethers, such as 1,4-butane-diol divinyl ether, and the alkenecarbonylamino-N-methylene ethers of polyhydric alcohols, such as ethylena glycol bi~-, propanediol bis-, l,4-but~nediol bi~-, diethylene glycol bis-, glycerol tris- and pentaeryth-ritol tetrakis-~methacrylamido-N-methylane ether), or the corresponding acrylamido-N-methylene ethers.
The novel mixture contain~ from 0.4 to 5, in particular from 0.5 to 2.0, % by weight, based on itq total amount, of one or more photopolymerization in-itiators ~D). Becauqe of the particular ad~antageou~
propertie~ obtained with the novel binder mixture (A) and ~he abovementioned monomers (B) and (C), these small amount~ of photopolymerization initiator~ (D) are com-pletely ~ufficient.
~ xamples of ~uitable pho~opolymerization in-ltiator~ (D) to be u~ed ac&ording to the invention are - 17 ~ O.Z. 0050/41056 benzoin and benzoin derivatives, such as its methyl, isopropyl, n~butyl or isobutyl ether, symmetric~lly or asymmetrically substituted benzil acetals, such a~ ben~il dimethyl acetal or benzil 1-methyl l-ethyl acetal; acyl-S diarylphosphine oxides and acylarylpho6phonic acid derivatives, such as 2,6-dLmethoxybenzoyldiphenylphos-phine oxide, 2,4,6-trimethylbenzoyldiphenylphisphine oxide, sodium 2,4,6-trLmethylbenzoylphenylphosphinate or ethyl 2,4,6-trimethylbenzoylphenylphosphinate; and substituted and unsubstituted quinone3, such as ethyl anthraquinone, benzanthraquinone, benzophenone or 4,4' bis-(dLmethylamino)-benzophenone, which may be used alone or as a mixture with one another.
The novel mixtures may furthermore contain other prior art polyvinyl alcohol re~ins in minor amounts which do not have a disadvantageous effect on the property profile of the novel mixtl~re~. Examples of the~e poly-vinyl alcohol re~ins are disclo~ed in the prior art stated at the outset.
The novel mixture3 may also contain further addi~ives, ~uch as thermal polymerization inhibitors, plasticizer~, dyes, pigments, photochromic additives, reducing agents, agents for improving the relief struc-ture, antioxidants, fillers, reinforcing fillers, etc., in effective amount~.
The praparation of the novel mixtures from their components has no special featurss in term~ of the method, instead the conventional kneading, mixing and dis~olution methods may be used for mixing thecomponents.
The novel mixture~ thu~ obtained may be used for a very wide range of applications, where they display their particular advantageou~ prQper~ies. However, they are used in particular for the production of novel photosensitive recordin~ alements. For thi~ purposel ~hey are formed into novel layers o~ ~he desired thick-ne~s in a canventional manner by casting rom a solution, hot pressing/ calendering or extru~ion. Tho ~hickne~s of '?~ `J '!.~ `l - 18 - O.Z. 0050/41056 these novel layers depends primarily on whether they are to ~8 used in the novel photosensitive recording elements as a novel photopolymerizable recording layer or as a noYel phetopolymeri2able adhesive layer. The thicknass of the novel photopolymerizable recording layers in turn depends on the intended use of the novel photosensitive recording element.s and varies in general from 0.001 to O.8 mm, whereas the novel adhesive layers are usually ~rom 0.0005 to 0.1 mm thicXc The novel photosensitive recording elements con-tain either at least one novel photopolymerizable record-ing layer or at least one novel adhesive layer of the novel mixture. However~ the novel photosen~itive record-ing elements whose novel photopolymerizable recording layer and adhesive layer consist of the novel mixture are very particularly advantageous.
In the novel photo~en~itive recording elementl the novel photopolymeri2able recording layer is usually ~irmly bonded to a dimensionally stable substrate.
Furthermore, a conventional and known top layer or a conventional and known cover sheet may be applied to that side of the novel photopolymerizable recording layer whlch faces away from khe sub3trate.
If the top layer and covar sheet are used to-gether, the top layer is located directly on the novelphotopolymeri~able recording l~yer, and a further conven-tional and known antiadhesion layer may be present between the ~op layer and cover sheat. Furthenmore, a firm bond may be achieved between the said recording layer and the cover sheet wi~h the aid of an adhesive layer.
Conventionally used dimensionally stable 5ub-strates axe sheets, films or sleeves of metal~, such a~
steel, aluminum, copp~r or nickel, or of high polymers, such as polyethylene ~erephthalate, polybutylene tereph-thalate~ polyamide or polycarbonata. Woven fabrics and nonwovens, such as gla~s fiber ~abrics, or laminates of, - 19 - O.Z. 005~t41~56 for example, glass fibers and high polymers are also suitable.
The adhesive layers used may be conventional and known 0.0005-0.1 mm thick adhesive layers. However, the novel adhesive layers of the novel mixtures are advant-ageous. The adhesive layers are crosslinked either by photopolymerization by uniform exposure or thermally by heat treatment before application of the novel photo-polymeri able recording layer, or by photopolymerization after application of the said recording layer. Cross-linking before application of the said recording layer is preferred here.
Con~entional top layers are from 0.5 to 20 ym thick and may conqist of a polymer which forms soluble, nontacky, transparent and strong films, for example poly-amide, copolyamide, polyurethane, polyYinyl alcohol rosins of a wide range of type~, polyvinylpyrrolidone, polyethylene oxide or cyclo rubber. The top layer can, if necessa~y, be matt.
Conventional cover sheets are from 20 to 150 ~m thick and con~ist of a polymer, such as polyamide or polyethylene terephthalate.
Conventional antiadhesion layers are from 0.1 to 0.5 ~m thlck and consis~ of, for example, silicone re~ins.
If highly raflective sheets or films are used as sub~trate~, they may contain conventional antihalation agent~, ~uch a~ carbon black or manganese dioxide. How-ever, the antihalation agents can al90 be pre~ent as a separate layer on the sub~trate or may be contained in the adhesive layer or the novel photopolymsrizable recording layer.
The production of the novel photosansitive recording element3 has no special features in ~exms of 3S the method. Usually, thi~ is carried out by applying the novel photopolymerizable recording layer ~o the ~ub-~tratet provided with a novel or a conventional and known - 20 - O.~. 0050~41056 adhesive layer, by casting from solution, hot pres3ing, calendering or extrusion. The other layers can then be applied in a known manner to such a novel photosensitive recording element. However, it is also possible first to apply the said recording layer to that side of a cover sheet which i~ covered with a top layer and then firmly to bond the uncovered side of the said recording layer to the substrate.
Letterpress printing plates, in particular news-paper printing plates, can be produced from these novelphotosensitive recording elements in a conventional and known manner by photopolymeri2ation. The production has no special features in terms of the method but is carried out, if necessary after a pretreatment, by Lmagewise exposure of the novel photosensitive recording element3 to actinic light having a wavelength ~ of from 300 to 450 nm, ad~antageously from 320 to 400 nm, through a photo-graphic negative placed on top, washing out of the un-exposed and therefore nonpolymerized parts o~ the image-wi~e exposed novel photosensitiva recording element~ withwater or a conventional aqueou4 solution and drying of the letterpres~ printing plates which have been obtained in thi~ manner and now contsin a relief layer.
Conventional pretrea~ments are, for example, removal of any cover sheet present in ~he novel photo-sen~itive recording element or uniform exposure of the novel photopolymerizable recording~layar and/or of the novel or conventional and known adhe~ive layer to actinic light from the back, ie. from the side which sub~equently face~ away from the printing surface.
Examples of suitable sources of actinic light are commercial W fluorescent tube~, medium pres~ure, high pre~sure and low pressure mercury lamps, superactinic 1uorescent tubes, pulsed xenon lamp~, lamps doped with metal iodides or carbon arc lamps and laser light.
A conventional aftertreatment i~ uniform post-expoqura of ~h~ letterpress printing pla~e~ to actinic ~ P~,~`?J'3 - 21 - O.Z. 0050/41056 light.
Tha thickness of the relief layer of the letter-press printing plates obtained in this manner varies from 0.001 to 0.8 mm, depending on the intended use.
The letterpress printing plates obtained in this manner can be clamped on printing cylinders in a conven-tional and known manner and used for continuous letter-press printing, in particular newspaper printing.
The novel mixtures have particular unexpected advantages over the prior art in their preparation, processing and use. Thus, no special measures need be taken during their preparation; instead, the preparation methods conventionally used for such mixturPs may be employed. The novel mixtures may be dissolved in par-ticularly high concentration~ in water, which dramatical-ly reduces the energy consumption for their preparation and further proces~ing. Because of their high thermal stability, the novel mixtures can be very readily pro-cessed by the conventional methods to ~ive a very wide range of products without it baing necessary to take special precautions for this pur]posa. They have an ex-cellent shelf life and can be disposed of in an environ-mentally compatible manner, which i~ a great advantage in industry.
The novel photosensitive recording element~ which contain the novel photopolymsrizable recording layers consisting of ~he novel mixtures likawise have par-ticularly`unexpacted technical eect~.
For example, their novel photopQlymerizabla re ording layers have a nontacky surface, so that the photographic negative~ can be readily placed on top and removed. ~he said recording layers are no longer brittle and have high cohe~ion, so tha~ they no longer crack during storage. E~en after prolonged ~torage at elevated ~empera~ure~, a~ occur, for axample, in the middle of summer or in tropical ragions, the said recording layers exhibit ab~olu~aly no opaci~y and no axudation of their ~ S~

~ 22 ~ O~ Z ~ 0050~41056 components. They can be particularly rapidly exposed imagewis2 to actinic light and exhibit particularly high resolution and a particularly wide exposure latitude.
Their short washout times are particularly notew~rthyO
Because of the especially good solubility of the non-photopolymerized parts of the novel photopolymerized recording layers, there is no longer any soiling of the washers used for their development.
The letterpress printing plate~, in particular newspaper printing plates, obtained from the novel photo-sensitive recording elements have a particularly uniform and smooth surface, which leads to substantially impro~ed ink coverage in solid areas during printing. Their relief layers have very smooth side walls r SO that their tendency to linting during printing i~ substantially reduced. Overall, the result is printing propertie~
which are substantially improved over the prior art and a longer pres~ life.
Surpri~ingly, the novel mixtures can ba used not only in the novel photopolymerizable recording layer~ of the novel photosensitiva recording element~ but also in the adhesive layers present therein. In thls function too, the particular unexpected advantages of the novel mixtures are eviden~. For example, th~ use of the novel adhe ion-promoting layerq in ~he novel photosensitive recording elements result~ in an Lmprovement in the re~istance to swelling, the water resistance, the dimen-3ional s~ability, the ink fastnes~ and the abra~ion resistance in the letterpre ~ printing plates produced therefxom, so that, inter alia, ~here is no delamination of relief parts even during very long print runs.
~ exy particular advantages are obkained if the novel mix~ures are used for the production of the novel adhesive layer~ and the novel photopolymeriz~ble record-ing layers. This re~ults in novel photosen~itive record-ing elemen~ in which the abovementioned ~pecial tech-nical ef~ect~ mutually reinforce one ano~her. A

- 23 - O.Z. 0050/41056 particular example here is the sensitivity of known photosensitive recording elements to overwashing, this sensitivity being extremely troublesome in practice and being absent in the novel photosensitive recording elements.
The advantages of the novel mixtures are des-cribed below with reference to their use for the produc tion of novel photosensitive recording elements.

Production of a novel photosensitive recording element having a novel photopolymerizable recording layer of a novel mixture; production method:
250 g of a polyvinyl acetate having a number average degree of polymerization ~n of 300 and a degree of hydrolysis of 83~ and 250 g of a vinyl alcohol/ethylene oxide ~raft copolymer containing 25% by weight of eth-ylene oxide units and having a degree of hydrolysis of 85% and a weight average degree of polymerization ~w of about 460 were dissolved in 270 g of distilled water in the course of ~0 minutes a~ 90C. Thereafter, 400 g of 2-hydroxyethyl methacrylate, 80 g of 1,4-butanediol di-methacrylate, 9 g of 2,4,6-tr.~methylphenylbenzoyldi-phenylphosphine oxide, 3 g of Kerobit TBK (2,6-di-tert-butyl-p-cresol) and 0.024 g of Dulasyn Basic Red TH (C.I.
50,240) were added to the solution. The casting solution thus obtained wa~ then cast on a steel sheet pro~ided with an antihalation coating, after which the resulting WQt layer was drie~ without any cracking to give a novel 500 ~m photopolymerizable recording layer.
After imagewise exposure, development with water and dryin~ of the novel photosensitivQ recording element, a lettarpress printing plate having a 500 ~m thick relief layer was obtained.
The advantageous performance characteristics of the novel photosensLtive recording elament and of the letterpress prin~ing plate produced therefrom are evident ~rom the Table~

?.~ i`.l ~,.J ~;.

- 24 - O.Z. 0050/41056 Production of a novel photosen~itive recording element having a novel photopolymerizable recording layer of a novel mixture; production method:
175 g of a polyvinyl acetate having a number average degree of polymerization Pn of 300 a~d a degree of hydrolysis o~ 82%, 175 g of a polyvinyl ace~ate having a number average degree of polymerization Pn of 400 and a degree of hydrolysis of 80% and 145 g of the graft co-pol~mer of Example 1 were dissolved in 300 g o~ distilled water in the course of 30 minutes. Thereafter, 400 g of 2-hydroxyethyl acrylate, 75 g of 1,4-butanediol dimeth-acrylate, 8 g of 2,4,6-$rLmethylbenzoyldiphenylphosphine oxide, 3 g of Kerobit TBK and 0.02 g of Duasyn Basic Red T~ were added. The resulting casting solution was further processed to a novel photosensitive recording element and thereafter to a letterpress printing plate, these steps being carried out as described in Example 1.
The ad~antageou~ performance characteristics of the resulting novel photo~en~itive recording elemen~ and of the letterpres~ printing plate produced therefrom are likewise evident rom the Table.
CO~PAR~TIVE EXP]ERIMENT
Production of a known photosensitive recording element having a known photopolymerizable recording layer of a known photopolymPrizable mixture7 production method:
A known le~terpress printing plate is produced by the metho^d described in Example~ 1 and 2, except that, in~tead of the novel mixture~ de~cribed there, the con-vantional mixture con~isting o~ 151 g of a polyvinyl acetate hsvlng a num~er average degree o~ polymerization Pn of 500 and a degree of hydroly~is of 82%, 161 g of the polyvinyl acetate ha~ing a number average degree of poly-merization ~n of 400 according to Example 2, 138 g o the gra~t copolymer according to Example 1, 3S0 g of distil-led water, 3~0 g of 2-hydro~yethyl methacrylate, 80 g o~
Cetamoll BMB (N-n-butylbenzenesulfonamide), ~ g of 2,4,6-- 25 - O.Z. 0050/4105~
trLmethylbenzoyldiphenylphosphine oxide and 0.3 g of Kerobit TBK was used. It was found that one hour was required for dissolution of the polyvinyl alcohol resins in water, more than twice as long as in the case of Examples 1 and 2.
The performance characteristics of the known photosensitive recording element and of the letterpress printing plates produced there$rom are compared in the Table with the much more advantageous performance charac-teristics of the novel photosensitive recording elementsand letterpress printing plates of Examples 1 and 2.
The comparison of the values stated in the Table shows that the improvement over the prior art achieved using the novel mixture was on average about 57%, which makes the particular unexpected technical effect of the novel mixture very particularly clear.

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Claims

1. A water-soluble or water-dispersible photopoly-merizable mixture, comprising the following components:
A) from 46 to 53% by weight, based on the total weight of the mixture, of a binder consisting of a1) from 20 to 80% by weight, based on the total weight of the binder, of one or more polyvinyl alkanecarboxylates having a degree of hydrol-ysis of from 75 to 85% of the alkanecarboxylate groups originally present and a number average degree of polymerization ?n of from 250 to 350, a2) from 20 to 80% by weight, based on the total weight of the binder, of one or more partially hydrolyzed graft copolymers of vinyl alkane-carboxylates and alkylene oxides having a degree of hydrolysis of more than 80% of the alkanecarboxylate groups originally present, containing from 10 to 40% by weight of alkylene oxide units and possessing a weight average degree of polymerization ?w of from 300 to 500, calculated from the weight average molecular weight ?w determined by viscosity measurements using dilute solutions, in accordance with the equation ?w = ?w (86 - 0.42 ? degree of hydrolysis), and a3) from 0 to 60% by weight, based on the total weight of the binder, of one or more partially hydrolyzed polyvinyl alkanecarboxylates having a degree of hydrolysis of more than 75% of the alkanecarboxylate groups originally present and a number average degree of polymerization ?n of from 350 to 450, B) from 35 to 44% by weight, based on the total weight of the mixture, of one or more water-soluble mono-functional ethylenically unsaturated - 28 - O.Z. 0050/41056 photopolymerizable monomers which are compatible with the binder (A), C) from 6 to 9% by weight, based on the total weight of the mixture, of one or more polyfunctional ethylen-ically unsaturated photopolymerizable monomers which are compatible with the binder (A) and D) from 0.4 to 5% by weight, based on the total weight of the mixture, of one or more photopolymerization initiators.

2. A photopolymerizable mixture as claimed in claim 1, wherein the binder (A) contains from 5 to 40% by weight, based on the total amount of the binder, of the partially hydrolyzed polyvinyl alkanecarboxylate (a3).

3. A photopolymerizable mixture as claimed in claim 1, wherein the degree of hydrolysis of partially hydrol-yzed polyvinyl alkanecarboxylate (a1) is from 78 to 83%.

4. A photopolymerizable mixture as claimed in claim.
1, wherein the number average degree of polymerization ?n of the partially hydrolyzed polyvinyl alkanecarboxylate (a1) is 300.

5. A photopolymerizable mixture as claimed in claim 1, wherein the degree of hydrolysis of the partially hydrolyzed polyvinyl alkanecarboxylate (a2) is 85%.

6. A photopolymerizable mixture as claimed in claim 1, wherein the content of alkylene oxide units in the graft copolymer (a2) is from 20 to 30% by weight, based on the copolymer.

7. A photopolymerizable mixture as claimed in claim 1, wherein the weight average degree of polymerization ?w of the graft copolymer (a2) is from 400 to 500.

8. A photopolymerizable mixture as claimed in claim 1, wherein the degree of hydrolysis of the partially hydrolyzed polyvinyl alkanecarboxylate (a3) is greater than 80%.

9. A photopolymerizable mixture as claimed in claim 1, wherein the number average degree of polymerization ?n - 29 - O.Z. 0050/41056 of the partially hydrolyzed polyvinyl alkanecarboxylate (a3) is 400.

10. A photosensitive recording element comprising a substrate and at least one photopolymerizable recording layer consisting of a water-soluble or water-dispersible photopolymerizable mixture, comprising the following com-ponents:
A) from 46 to 53% by weight, based on the total weight of the mixture, of a binder consisting of a1) from 20 to 80% by weight, based on the total weight of the binder, of one or more polyvinyl alkanecarboxylates having a degree of hydrol-ysis of from 75 to 85% of the alkanecarboxylate groups originally present and a number average degree of polymerization ?n of from 250 to 350, a2) from 20 to 80% by weight, based on the total weight of the binder, of one or more partially hydrolyzed graft copolymers of vinyl alkane-carboxylates and alkylene oxides having a degree of hydrolysis of more than 80% of the alkanecarboxylate groups originally present, containing from 10 to 40% by weight of alkylene oxide units and possessing a weight average degree of polymerization ?w of from 300 to 500, calculated from the weight average molecular weight ?w determined by viscosity measurements using dilute solutions, in accordance with the equation ?w = ?w (86 - 0.42 ? degree of hydrolysis), and a3) from 0 to 60% by weight, based on the total weight of the binder, of one or more partially hydrolyzed polyvinyl alkanecarboxylates having a degree of hydrolysis of more than 75% of the alkanecarboxylate groups originally present and a number average degree of polymerization ?n of from 350 to 450, - 30 - O.Z. 0050/41056 B) from 35 to 44% by weight, based on the total weight of the mixture, of one or more water-soluble mono-functional ethylenically unsaturated photopolymeriz-able monomers which are compatible with the binder (A), C) from 6 to 9% by weight, based on the total weight of the mixture, of one or more polyfunctional ethylen-ically unsaturated photopolymerizable monomers which are compatible with the binder (A) and D) from 0.4 to 5% by weight, based on the total weight of the mixture, of one or more photopolymerization initiators.

11. A photosensitive recording element as claimed in claim 10, wherein the binder (A) contains from 5 to 40%
by weight, based on the total weight of the binder, of the partially hydrolyzed polyvinyl alkanecarboxylate (a3).

12. A photosensitive recording element as claimed in claim 10, wherein the degree of hydrolysis of the par-tially hydrolyzed polyvinyl alkanecarboxylate (a1) is from 78 to 83%.

13. A photosensitive recording element as claimed in claim 10, wherein the number average degree of polymer-ization ?n of the partially hydrolyzed polyvinyl alkane-carboxylate (a1) is 300.

14. A photosensitive recording element as claimed in claim 10, wherein the degree of hydrolysis of the par-tially hydrolyzed polyvinyl alkanecarboxylate (a2) is 85%.

15. A photosensitive recording element as claimed in claim 10, wherein the content of alkylene oxide units in the graft copolymer (a2) is from 20 to 30% by weight, based on the copolymer.

16. A photosensitive recording element as claimed in claim 10, wherein the weight average degree of polymeriz-ation ?w of the graft copolymer (a2) is from 400 to 500.

17. A photosensitive recording element as claimed in - 31 - O.Z. 0050/41056 claim 10, wherein the degree of hydrolysis of the par-tially hydrolyzed polyvinyl alkanecarboxylate (a3) is greater than 80%.

18. A photosensitive recording element as claimed in claim 10, wherein the number average degree of polymeriz-ation ?n of the partially hydrolyzed polyvinyl alkane-carboxylate (a3) is 400.

19. A photosensitive recording element comprising a substrate, an adhesive layer and at least one photopoly-merizable layer, wherein at least one of the said layers consists of a water-soluble or water-dispersible photo-polymerizable mixture, comprising the following compon-ents.
A) from 46 to 53% by weight, based on the total weight of the mixture, of a binder consisting of a1) from 20 to 80% by weight, based on the total weight of the binder, of one or more polyvinyl alkanecarboxylates having a degree of hydrol-ysis of from 75 to 85% of the alkanecarboxylate groups originally present and a number average degree of polymerization ?n of from 250 to 350, a2) from 20 to 80% by weight, based on the total weight of the binder, of one or more partially hydrolyzed graft copolymers of vinyl alkane-carboxylates and alkylene oxides having a degree of hydrolysis of more than 80% of the alkanecarboxylate groups originally present, containing from 10 to 40% by weight of alkylene oxide units and possessing a weight average degree of polymerization ?w of from 300 to 500, calculated from the weight average molecular weight ?w determined by viscosity measurements using dilute solutions, in accordance with the equation ?w = ?w (86 - 0.42 ? degree of hydrolysis), and a3) from 0 to 60% by weight, based on the total - 32 - O.Z. 0050/41056 weight of the binder, of one or more partially hydrolyzed polyvinyl alkanecarboxylates having a degree of hydrolysis of more than 75% of the alkanecarboxylate groups originally present and a number average degree of polymerization ?n of from 350 to 450, B) from 35 to 44% by weight, based on the total weight of the mixture, of one or more water-soluble mono-functional ethylenically unsaturated photopolymeriz-able monomers which are compatible with the binder (A), C) from 6 to 9% by weight, based on the total weight of the mixture, of one or more polyfunctional ethylen-ically unsaturated photopolymerizable monomers which are compatible with the binder (A) and D) from 0.4 to 5% by weight, based on the total weight of the mixture, of one or more photopolymerization initiators.

20. A photosensitive recording element as claimed in claim 19, wherein the binder (A) contains from 5 to 40%
by weight, based on the total amount of the binder, of the partially hydrolyzed polyvinyl alkanecarboxylate (a3).

21. A photosensitive recording element as claimed in claim 19, wherein the degree of hydrolysis of the par-tially hydrolyzed polyvinyl alkanecarboxylate (a1) is from 78 to 83%.

22. a photosensitive recording element as claimed in claim 19, wherein the number average degree of polymer-ization ?n of the partially hydrolyzed polyvinyl alkane-carboxylate (a1) is 300.

23. A photosensitive recording element as claimed in claim 19, wherein the degree of hydrolysis of the par-tially hydrolyzed polyvinyl alkanecarboxylate (a2) is 85%.

24. A photosensitive recording element as claimed in claim 19, wherein the content of alkylene oxide units in _ 33 _ O.Z. 0050/41056 the graft copolymer (a2) is from 20 to 30% by weight, based on the copolymer.

25. A photosensitive recording element as claimed in claim 19, wherein the weight average degree of polymeriz-ation ?w of the graft copolymer (a2) is from 400 to 500.

26. A photosensitive recording element as claimed in claim 19, wherein the degree of hydrolysis of the par-tially hydrolyzed polyvinyl alkanecarboxylate (a3) is greater than 80%.

27. A photosensitive recording element as claimed in claim 19, wherein the number average degree of polymeriz-ation ?n of the partially hydrolyzed polyvinyl alkane-carboxylate (a3) is 400.