CA2201891A1 - A process for making a flexographic printing plate - Google Patents

Abstract

A process for making a flexographic printing plate from a flexographic element having an infrared ablatable layer capable of being selectively removed by a laser beam is described.

Description

J~ W096/16356 2 2 0 1 8 9 1 PCr/US95/l4430 TLE
A PROCESS FOR MAK~G
A FLEXOGRAP~C PRINTING PLATE
FIELD OF THE INYENTION
This invention relates to a ~ v~ printmg element amd, more pal li~ lally, to a flr ~ element having an infrared ablatable layer capable of bemg ~ul~,.,liv~ly removed by a laser beam. This mvention also relates to a process for makmg a flexographic printmg plate from such an 10 element.
BACKGROUND OF THE INVENTION
Flr~ printing plates are well known for use in letter~ress printmg, patticularly on sutfaces which are soft amd easily ,lrr... ,. ~l~lr 15 such as packaging materials, e.g, cardboard, plastic films, etc.
Flr~ ~v ~ ` printing plates can be prepared from ~I.,t~,lJGly~ al,lc c~ , such as those described in U.S. Patents 4,^23,637 amd 4,427,749. The l l 1 olyl.lcri_~hie comp~sitions generally comprise an ~' - bimder, 2t least one mol~omer 2nd a ~llui ~
20 Pl .l.., ... ~ l; vc elements generally have a ~llulu~,~ly ..l~ ablc layer interposed between a support and a coversheet or multilayer cover element.
Upon imagewise exposure to actirlic radiatiorl, polyml~ri7:~tinn, and hence, in~n~ lhili7s~inn of the phOtopoly.l.~ al,lc layer occurs m the exposed areas. Treatment with a suitable solution removes tbe I , ' areas of 25 the photopol~ ~le layer leaving a printmg relief which can be used for flr,~,glAl,hi~. prmting.
T ~ e exposure of a 1~ ve element requires the use of a phototool which is a mask having clear and opaque areas covering the photopolymerizable layer. The phototool prevents exposure amd 30 polyr^~.ri7qii.^,n in the opaque areas. The phototool allows exposure to radiation itl the clear areas so that these areas polymerize and remain on the support after the development step. The phototool is usually a ^. negative of the desired printmg image. If corrections are needed in the final image a new negative must be made. This is a time-35 c~.~.~,.,.,;..~ process. In addition, the phototool may chatlge sllghtly indimension due to changes in L~lllp~ Lul~ amd hutîlidity. Thus, the same WO96/16356 220~18g1 PCIIUS95114430 phototool, when used at different times or in different ~ ., may give different results and could cause ~ lioll problems.
Thus, it would be desirable to eliminate the phototool by directly recordmg r ~ on a ~ r - -;1; v~ element, e.g., by means of a 5 laser beam. The image to be developed could be translated into digital r ~ amd the digital infimnS~ti~ used to place the laser for imaging.
The digital r ' could even be i ~ from a distant location.
Corrections could be made easily and quickly by adjusting the digitized image. In addition, the digitized image could be either positive or negative, 10 ~ ' g the need to have both positive-working and negative-working 1 ' v~ materials, or positive and negative phototools. This saves storage space and, thus, reduces cost. Another advantage is that registration can be precisely controlled by machine during the imagmg step. Digitized imaging without a phototool is p~ ~ly well-suited for 15 making seamless, ~ prmting forms.
rn general, it has not been very practical to use lasers to image the elements which are used to prepare flrY~ . printing plates. The elements have low ~ ' vi~y amd require long exposure times even with high powered lasers. In addition, most of the pllo~ olylll~li~l,.l~
20 materials used m these elements have their greatest sensitivity m the ultraviolet range. Wlule W lasers are known, E ' and reliable UV
lasers with high power are generally not available. However, non-UV=
lasers are available which are relatively . v~, and which have a useful power output amd which can be utilized to form a mask image on top

2~ of flPY~gr~rhic printing elements.
SUMMARY OF THE INVENTION
The present mvention reiates to a ~ ; v~ eiement used to prepare fl. ~ printing plates c~rrieingJ in the order listed:
(a) a support (b) a photopolyll.~li ,~lc layer ~ g an ~ l.-- ~ .. ;~
binder; at least one monomer and an initiator having sensitivity to non-infrared actinic radiatlon, said layer being swellable, soluble, or ~ in a developer solution;5 W096116356 ~ 18 91 PClJrlS9~i/14430 (c) at least one barrier layer which is 11y i to non-infrared actinic radiation; removable during development; amd wherein said barrier layer is insoluble m the developer solution before d~, v~lu~ ul~ and (d) at least one layer of infrared radiation sensitive material which is s lhetq~ltiAIIy opaque to non-infrared actinic radiation;
wherein the infrared-sensitive material is ablatable from the surface of the barrier layer upon exposure to infrared laser radiation and removable during d~v.l~, The invention further relates to a ~ ;v~ element as described above, c~
(a) an aqueous IJluc~sail~lc ~JIIutopGl~ dll~ layer and (b) at least one barrier layer which is msoluble in an aqueous developmg solution amd to a l~ s~ v~ element wherein the aqueous ~luc~aa~l~
ph~l~",oly..l~ ~lc layer comprises a microgel bmder having a core of poly(l ' ,'aLyrene) and a shell of poly~u~.di~ ,al~l.,lylic acid).
The at least one barrier layer may comprise polyamide.
The present invention also relates to a process for making a flP~ rqrhi~ printmg plate, which comprises (1) providing a 1 ' v~ element , _, in the order listed;
(a) a support:
(b) aphotopoly 1-layerc.~ am Pl ~1.. , ,;.
binder; at least one monomer and an initiator having sensitivity to non-infrared actinic radiation, said layer being swellable, soluble, or ~lierPreihl~ in a developer solution;
(c) at least one barrier layer which iâ 5l-h5~q~ltiq11y Ll~lla,U~UI~ to non-infrared actinic radiation;
removable during development; and wherein said ~ barrier layer is insoluble in the aeveloper solution before dcvch,l,.ll~ , and (d) at least one layer of infrared radiation sensitive material which is ' lly opaque to ~
actinic radiation; wherein the infrared sensitive material is ablatable from the surface of the balrier layer upon exposure to infrared laser radiation and removaWe during dcvch,~~
(2) imagewise ablating layer (d) with infrared laser radiation to form a mask;

(3) overall exposing the r' ve element to actinic radiation through the mask; and

(4) treatmg the product of step (3) with at least one developer solution to remove during d~v~ (i) the infrared-sensitive material which was not removed during step (2), (ii) at least the areas of the barrier layer which were not exposed to non-infrared actinic radiation, and (iii) the areas of the photopoly.~ ,.dbl~ layer (b) which were not exposed to non-infrared actinic radiation.
The present invention also relates to a process for making a fl~ ,;C printing plate which comprises:
(1) providing a ~ iv~ element with am aqueous-processable photopoly u.~ able layer and at least one barlier layer which is insoluble in am aqueous d~, v .,L
solution;
(2) imagewise ablating layer (d) with infrared laser radiation to for~n a mask;
(3) overall exposing the r~- ~lu~ ;v~ element to actinic radiation through the mask; and (4) d~v~l~",il.g the product of step (3) in a rotary processor and in an aqueous solution to remove during d~, v~lo~ the infrared-sensitive layer; the at least one aqueous insoluble barrier layer amd the umpolymerized aqueous ~ /GGi.~ibl~
photopolyl.~ 11c layer;
and to a process as described above wherein the aqueous processible photopolymerizable layer comprises a microgel 3~ binder having a core of poly(butadiene/styrene) amd a shell of poly(l U~h~ ,lyliG acid).

~ WO96/16356 2 ~ O ~ 8 9 7 PCT/~S95/14430

- 5 -The mvention also relates to a process wherein the at least one barrier layer is a polyamide and to;
a process wherein d~ . utilizes water and a surfact~mt to remove (i) the infrared ablatable layer; the balrier layer; and the 5 unpolymerized l ' r lyll~ al~lG layer.
DETAILED DESCRIPTION OF Tl~E INVENTION
The element and process of the invention combine the: ~ ~Ifi.,llcc and sensitivity of infrared laser i~naging with cull~.lLu.lal 10 PI~UIU~ c~ to produce fl~ ,.r~P ;r' prmting plates with known good printing quality quickly,, ly, and by digital imaging means.
The ~ ;vc element of the invention comprises, in order, a support, a phOtopol~ ~al,l~ layer, at least one balrier layer, and a layer 15 of ir~ared radiation sensitive material.
The support can be any flexible material which is Gull~
used with l.l...l..~ .. .:liv~ elements used to prepare flPY~v l~ ' printing plates. Examples of suitable support materials include polymeric films such those formed by addition polymers and linear c~ .. ,.l. . - ~' ;-. polymers, 20 llalla~Jal1ll1 foams and fabrics. A prefeIred support is a polyester film;
particularly preferred is polyethylene ~ rla~. The support typically has a thickness from 2 to 10 mils (0.0051 to 0.025 cm), with a preferred thickness of 3 to 8 mils (0.0076 to 0.020 cm).
As used herein, the term "l,llulupûlyl..~ al~le" is intended to 25 ~ systems which are photopoly~ i,~ble, L:l~ulu~ P, or both. The photopolyll..,li~,l,l~ layer comprises an ~' - binder, at least one monomer and an initiator, where the initiator has a sensitivity to non-infrared actinic radiation. In most cases, the initiator will be sensitive to visible or ultraviolet radiation. Any photopolyl.l~,l.,ablG c~mrocitil~nc 30 whicharesuitablefortheformationofflr~..,,.,;.l.;rprintingplatescanbe used for the present invention. Examples of suitable G~ " ' '1''~`'1 '' ~ l` have been disclosed, for example, in Chen et al., U.S. Patent 4,323,637, Gliir~ .. et al., U.S. Patent 4,427,749 and Feinberg et al., U.S. Patent 4,894,3 15. =~ =
The rl ~ mPriC binder can be a single polymer or miYture of polymers which can be soluble, swellable or l;~ lr in water, aqueous,

6 22018 9 ~ PCrlUS95/14430 II~

semi-aqueous or organic solution developers. Bimders which are soluble or lr im aqueous or semi-aqueous developers have been disclosed in Alles U.S. Patent 3,458,311; Pohl U.S. Patent 4,442,302; Pine U.S. Patent 4,361,640; Inoue et al., U.S. Patent 3,794,494; Proskow U.S. Patent 5 4,177,074; Proskow U.S. Patent 4,43l,723; and Worns U.S. Patent 4,517,279. Binders which are soluble, swellable or ~ m organic solution d~v~,lv,u~ include natural or synthetic polymers of c, ;
diolefin lly~ilUUallJVlls, including polyisoprene, 1,2-polyl 1~4-pOlyl)~tal~ ta~ /a~,ly 1-~ Iyl.
11 ."",~1 I;r f1_~;" .;- block CUAUV1Y~-I~ andothercopolymers. The block cul,~ly discussed in Chen U.S. Patent 4,323,636; Heinz et al., U.S. Patent 4,430,417; and Toda et al., U.S. Patent 4,045,231 can be used.
It is preferred that the bmder be present in at least an amoumt of 65% by weight of the ~ ; vt: layer.
The term binder, as used herein, , core shell microgels and blends of microgels and preformed ~ polymers, such as those disclosed in Fryd et al., U.S. Patent 4,956,252.
The IJllululJolylll~ all~ layer can contain a smgle monomer or mixture of monomers which preferably is cr--p '~ '~ with the binder to the 20 extent that a clear, non-cloudy l ' v~ layer is produced.
M~n-~mf rg that cam be used in the phOtopolyll,~ al,l~ layer are well known in the art. Examples of such monomers can be foumd m Chen U.S.
Patent 4,323,636; Fryd et al., U.S. Patent 4,753,865; Fryd et al., U.S
Patent 4,726,877; and Feinberg et al., U.S. Patent 4,894,315. It is preferred 25 that the monomer be present im at least an amount of 5% by weight of the pllulu~Olylllr,li~al~l~ layer.
The l~l,,.l..;,.;l; ~ .. can be any smgle compoumd or ~ (m Of ,ulllluvllllds which is sensitive to non-infrared act~nic radiation, generatingfree radicals which initiate the polymf ri7~tir of the monomer or 30 monomerswithoutexcessiveI rl1 ;1l-l;~1l/ Therh~: ' isgenerally sensitive to visible or ultraviolet radiation, preferably ultraviolet radiation.It should be thermally inactive at and below 18~C. Examples of suitable pl- .l..,..;l;.,t~ include the ..h~ rd and, ' ~ polyl~
quinones. Examples of suitable systems have been disclosed in G~ l,. . U.S. Patent 4,460,675 and Femberg et al., U.S. Patent W096/16356 22 0 18 9 1 PCIJUSg5J14430

-7-4,894,315. ~ : are generally present in amounts from 0.001%
to 10.0%basedontheweightofthe r~ a~lcc~n~o~if The photopoly~ dl,l~ layer can contain other additives depending on the final properties desired. Such additives include s~nr;fi7~r~ rheology 5 modifiers, thermal ~oly.. .;,~l ;r~ inhibitors, tackifiers, colorants, Pntin~riAO~f~ ~70nont~ or fillers.
The thickness of the photopolymeri_able layer can vary over a wide range depending upon the type of printing plate desired. For so called "thin plates" the phOtopolylll~ ahlc layer can be from about 20 to 50 mils 10 (0.05 to 0.13 cm) in thickness. Thicker plates will have a photopolyul~.li, alJI~ layer up to 100-250 mils (0.25 to 0.64 cm) in thickness or greater.
At least one batrier layer is mterposed between the photopoly .~ al~lc layer and the layer of ir~ared-sensitive material. The 15 batrier layer serves two i1nportant functions. First, it m=es migration of materials between the pllU~U,UOlylu~ ,dlJl~ layer amd the infrared-sensitive layer because monomers and p1 ~ can migrate over time if they are ~ . with the materials in the other layer. If such migration occurs into the infrared-sensitive layer, then the infrared sensitivity of that 20 layer can be altered. In addition, this can cause smeating and tackifying of the infrared sensitive layer after imaging. If there is no . . ' ' y between the two layers there will be no migration.
Second, the batrier layer shields the photopoly ' '- layer from d~ oxygen when the photopolylll.,li ~alJI~ layer is overall exposed 25 to actinic radiation. The poly;,-l;reactions require longer exposure times or higher mtensity radiation sources, and the results are less l~,uludu.,ilJlc when oxygen is present. It is possible to apply a temporary CUV~ prior to exposure to actinic radiation or to catry out that exposure step in a vacuum frame. However, the phOtopolylll~li al,lc layer is usually inherently tacky and steps must be taken to prevent the temporary coversheet or vacuum frarne cover from sticking to and/or damaging the sutface of the photopolymerizable laycr. The presence of a non-tacky batrier layer which mrnunizes the ~ A1;.~ of oxygen to the phOtopoly~ ablc layer addresses these problems.
The batrier layer must be ~h~f~ntiAlly llall*)a.~ to actinic radiation so that when the element is exposed to actinic radiation through WO96/16356 2 2 0 1 ~ 9 1 PCTIIJS95114430 ~
the infrared-sensitive layer, the radiation passes through the ablated areas of the infrared-sensitive layer to the photopol~ layer without 5:~...;1;. . " - in intensity. It is preferred that the barrier layer should also initially (i e., prior to exposure to actinic radiation) be 5 insoluble in the developer solution for `the 1 ' r -lyll.~i~ lc layer amd removable in the developer solution. This is so that the barrier layer will be removed by the developer in at least those areas which are not exposed to actinic radiation, ie., in those areas where the photopoly~ li,~lc layer is also removed.
Two types of barrier layers cam be used. The first type is one which is ill~C~ilivc to actinic radiation and is insoluble amd removable in developer solutions for the photopoly ' ' layer both before and after exposure to actinic radiation. This type of barrier layer is ~,ul~l~Jlct~ly removed in both exposed and -nP~rosed areas, along with the, ^-~r. ee~l 15 areas of the pllulu~oly ' ' - layer, during processing with the developer.
Examples of materials which are suitable for use as the barrier layer of this first type include those materials which are cu~ llliu..ally used as a release layer in fl~ nl~hl~ printing elements, such as polyamides, 20 polyvinyl alcohol, hydroxyaLIcyl cellulose, copolymers of ethylene amd vinyl acetate"...,l,h(.~ mterpolymers, cellulose acetate butyrate, aLlcyl cellulose, butyral, cyclic rubbers, and ~ ' thereof.
The second type of barrier layer is one which is msoluble in the developer solution prior to exposure to actirlic radiation, but is not affected 25 by the developer solution after exposure to actinic radiation. When this type of barrier layer is used it is removed by the developer solution only in those areas which are not exposed to actinic radiation. The areas of the barrier layer which have been exposed to actirlic radiation remain on the surface of the polymerized areas of the photopolymerizable layer and 3û become the actual printing surface of the printing plate.
This type of barrier layer can be l~l.u~u,. .,~;I;vc itself, ie., contain monomer and initiator, or it can become 1.l.,.l..~....;I;vc when m contact with the lul~ulu~olymerizable layer. This second type of barrier layer is usually a layer of an ~ . composition. The cf~mroeitil~n cam 35 consist simply of a nonphuluJ~ ivc ~ etl m~ liC bmder layer similar to the bmder im the photopoly--l~ ~lc layer or it cam be the binder in ~ W096/16356 2 2 0 1 8 ~ i PCTnJS95/144t3D
c~l-irqtilm with a monomer amd initiator. A preferred barrier layer is an ...... ;. C,-mroeitil~n~ anfl ~-,.. ; polymericbmder,a second polymeric bmder and optionally a - ~ y dye or pigment.
TheP~ polymericbindermthe f~ ;' C~rOeitl'~ is generaUy the same as or sirnilar to the ~ binderpresent m the pl~ olymcr layer. Suitable c~ for the barrier layer are those disclosed as e~ - m the multilayer cover element described m Ch~ h. . et al., U.S. Patents 4,427,759 and 4,460,675.
It is also possible to use more tham one balrier layer. For example, an ~ ;. barrier layer may be present next to the photopolylllc;l~lc layer amd this, m turn, may be UVC;I~ ' ' with a barrier layer which is soluble both before and after exposure to actinic radiation. The exact choice of barrier layer(s) will depend on the nature of the r'- r t'~/ 1 ' layer and the infrared-sensitive layer and other physical 1C;4LLil~ of the printing element.
The barrier layer, of either type, should be thick enough to act as an effective barrier to prevent migration and air pPrrAPqfif)n and also be thin enough to minimize its effect on the exposure of the pll~ lc layer to actinic radiation In general, the barrier layer or layers will have a total thickness m the range of 0 002 to 3 mils (to 0.076 mm) A preferred thickness range is 0 005 to 2.5 mils (to 0 064 mm).
Over the barrier layer, there is at least one layer of infrqred radiation sensitive material which must be ablatable, L e., vaporized or ablated, by exposure to infrared laser radiation.
The infrared-sensitive layer should be capable of absorbmg infrared radiation and should be opaque to actinic radiation This can be dC ~ ' usimg a single material or a - ' of materials. Also, a binder can be present if desired. This layer may be referred to as the "infrared-sensitive layer" or the "actinic radiation opaque layer" (radiation opaque layer). Although the infrared-sensitive layer is referred to hereim as a single layer, it will be Imderstood that two or more infrared-sensitive layers can be used. The properties of the infrared-sensitive layer can be modified by usmg other 1l.~, " , such as, for example, pl tt~i7Prc, pigment .l ;~ ,, r~ , and coating aids, provided that they do 35 ~not adversely affect the imaging properties of the element.

WO96/16356 2;20 18 ~1 PCT/IJS95/14430 ~

The infrared-absorbmg material should have a strong ~ .u.~; in the region of the infrared imaging radiation, typically 750 to 20,000 nm.
Examples of suitable infrared-absorbimg materials include, poly( ' ')phthalocyanine G" ~ J"~ cyanine dyes; s4ua.yLuul 5 dyes; rhql~ o~ y~ylc~ylidene dyes, bis( l ~ y~ylo)polymethine dyes; oxyindolizine dyes; bis(aminoaIyl)polymethine dyes; Ill~lu~ ~
dyes; croconium dyes; metal thiolate dyes; amd quinoid dyes. Also suitable are dark inorganic pigments such as carbon black, graphite, copper chromite, chromium oxides and cobalt chrome aluminate; metals such as 10 ~' , copper or zinc; and alloys of bismuth, imdium and copper. The metallic materials generally function as both infrared-absorbimg material amd radiation-opaque material. They are generally applied without a bimder.
Infrared-absorbing materials can be present im any c-~
15 which is effective for the imtended purpose. In general, for the organicG- ~ u-- Ic, C r-~ of 0.1 tû 80% by weight, based on the total weight of the layer, have been found to be effective.
Any material which prevents the i of actmic ligbt to the ~JI.ulu~ol~ 1 l layer can be used as the radiation-opaque material.
20 Examples of suitable materials mclude dyes, pigments and G~
thereo As initiators used m the photopolymerizable layer are often sensitive to actinic radiation in the ultraviolet amd/or visible region, it is preferred to use carbon black and/or graphite to provide W/visible opacity. When carbon black and/or graphite is used it may not be 25 necessaly to use an additional infrared-sensitive material.
The - of the radiation-opaque material is chosen so as to achieve the desired optical density, i. e., so that the layer prevents the 1, .".;~ . of actinic radiation to the photopol~ .blc layer. In general, a l, ," ,~ optical density greater than 2.0 is preferred. The 30 :~ ~,.., .. ~ .. I ..,- ;l m of radiation-opaque material which is needed, deGreases with increasmg thickness of the layer. In general a c ~ of l-90% by weight, based on the total weight of the layer cam be used. It is preferred to use 2-80% by weight, based on the total weight of the layer.
The optional binder for the infrared sensitive layer is a polymeric 35 material which should satisfy several .,, ~ t~. (1) The bimder should be ~ rrc.,,i ,~ly removed by the heat generated by the infrared-absorbing 2 ;! 0 1 8 ~ ~
~ ~VO 96/16356 PC'r/US95/i4430 material when the layer is exposed to infrared laser radiation. (2) The binder should be removable from tbe surface of the photopoly ' '-Iayer after the infrared imaging step. This condition generally is met if the binder is soluble, swellable or ~ in the developer solution for the 5 1 ~ r ~ ly~ layer. The binder may also be removed m a separatestep, e.g, the binder can be soluble, swellable or .1;~ ,1;. in a second solution which does not affect the polymeri4ed areas of the photopol~ ~ l layer. (3) The binder should be one in which the other materials in the iùfrared-sensitive layer can be uniformly dispersed. (4) 10 The binder should be capable of for~ing a unifolm coating on the baIrier layer. Examples of organic binders which can be used include self-oxidizing polymers such as ~ uC~" ' - , non-self-oxidizing polymers such as ethylcellulose, polyacrylic acids and the metal aLcali salts thereof;
~TmA~rl~^mirAAlly ~ , - ~ l polymers such as homopolymers and 15 copolymers of acrylates, ~ LA~ly~ ' ~ and styrene; butadiene, isoprene, and their copolymers (i. e., polymers of two or more monomers) and block copolymers with styrene and/or olefins, ,UYIUIY4AI~I~ fihns such as polyvinyl alcohol, polyvinyl chloride, and polyaclylorlitrile, . ' -interpolymers; and mixtures thereof. It is frequently a~ to use 20 those materials which are C011~1 ' 'Iy used as a release layer in flf-Yn~rhic printing elements, such as pol~ ' polyvinyl alcohol, hydroxyaLkyl cellulose, copolymers of ethylene and vinyl acetate, ,.,lllll..lrl ;~. interpolymers, cellulose acetate butyrate, aLkyl cellulose, butyral, cyclic rubbers and c-..,.l,;.. ~;.1,,~ thereof.
25 = The binder of the infrared sensitive layer may also be removed in a single step from the surface of the pLu~ uoly~ Iayer even if the binder is not typically soluble, swellable or dispersible in the developer for the photopolymer layer. It is possible to remove the infrared sensitive layer using the developer solution for the photopolymer layer with the aid of 30 .~ brushing action and optionally pressure during IJIuC~aahlg~ I IA t~ IY
during the dcvcl~,ull.~.lt or washout step. For example, an infrared sensitive layer containing a binder which is soluble, swellable, or Jrl ~;I.lr in a solvent developer solution can be applied to a photopolyll..,li ~ ~Ic layer m which the PIA~ binder is soluble, 35 swellable, or dispersible in water, or an aqueous or semi-aqueous developer solution and the infrared sensitive layer can be removed by the W096/16356 2 2 0 1 8 9 1 PCT/IJS95/14~30 -- ' --same process used to remove the I , ~ ~ portions of the photopolymer layer. Thus, the lulu~ ai~ of such a phulua~;live element is simplified simce the infrared sensitive layer can be removed without a separate ,Ul~ " g step.
Similarly, the barrier layer may also be removed during 1.. u~
of the l~ t~ ; I i v~ element even if the barrier layer generally is not soluble or swellable in the developer solution for the pllvL~ layer.
In this case, it is possible to remove the barrier layer using the developer solution for the photopolymer layer with the aid of brushing action and 10 optionally pressure during processing, pa~icul~ly during the d~v~,lu,ulll~
or washout step. For example, a barrier layer contairling a binder which is soluble, swellable or ~ in a solvent developer solution (e.g, imsoluble in aqueous or s .~ ul~ solution) can be removed from a lullu~u~ layer in which the i ' - bmder is soluble, 15_ swellable, or liCr~r~ in a water, or an aqueous or ~ ., developer solution.
As is -~ d by those sl~lled in the art, in the cases that the l.l.~.l,.,...~:~iv~ element has (i) an infrared sensitive layer, or (ii) a barrier layer/s or (iii) am infrared sensitive layer amd a barrier layer/s, which 20 generally are not soluble, swellable, or .l;~ ,lr in the developer solution of the photopolylll~li, ..I,lc layer, the ~;ulllluOailiull of each of the infrared sensitive layer, barrier layers/s, and the photopoly ~ t_ layer are chosen so that the fnal adhesion between each of the layers in the element have the desired balance, while g desired ~ ' y.
A dispersant is generally added when a pigment is present in the infrared-sensitive layer in order to disperse the fine particles and avoid ~ncclllq~ n and q~l( ~ nn A ,vide ramge of .1.~ is cullull~l~,;ally available. Suitable .l;~l.. . --.t~ are the A-B .1;~
generally described m "Use of A-B Blockpolymers as Dispersants for Non-aqueous Coatmg Systems" by H. K. J~L .,l. --,~L_c Journal of Coating Technology, Vol. 58; Number 736; pages 71-82. Useful A-B di are disclosed in U.S. Patents 3,684,771; 3,788,996; 4,070,388 and 4,032,698. The dispersant is generally present m am amount of about 0.1 to 10% by weight, based on the total weight of the layer.
A plasticizer can be added to adjust the film fornung properties of the binder. Suitable l lZ~ include, for example, triphenyl phosphite, ~ WO96116356 2 ~ ~ 1 8 9 11 PCr/US95/~443D

dimethyl phthalate, diethyl phthalate, L~, '~'~ yl phthalate, ~,y, ' ' yl ber~7yl phthalate, dibutoxy ethyl adipate, ethyleneglycol 1;1,, , p~ ylLiLul Ir~ ', glycerol diacetate, glyceryl carbonate, polyethylene glycol rnr~ , methyl phthalyl ethyl glycolate, o~-5 ~ul r ', N-ethyl ~t~ r ', and N-.,y~ ' ' yl-~
The plasticizer should be present in an amoumt effective for the mtended purpose which depends on the properties of the binder, the rl~ti~.i7Pr, and the other ~ , of the layer. hn general, the amount of p~ tiri7Pr when present, is 1-30% by weight, based on the 10 weight of the layer.
The thickness of the infrared-sensitive layer should be in a range to optimize both sensitivity and opacity. The layer should be thin enough to provide good sensitivity, ie., the infrared-sensitive layer should be removed rapidly upon exposure to mfrared laser radiation. At the same lS time, the layer should be thick enough so that the areas of the layer which remain on the ~ ul~ ~le layer after imagewise exposure effectively mask the photopolymerizable layer from actinic radiation. In general, this layer will have a thickness from about 20 Angstroms to about 50 ~ ull.ctcrs. It is preferred that the thickness be from 40 Angstroms to 20_ 40 ",i~", The 1~ 1;V~ element of the invention can also mclude a temporaly c~,vt:,~l.e~. on top of the infrared-sensitive layer. The purpose of the cov~ I,e~l is to protect the infrared-sensitive layer during storage amd handling. It is important that the coversheet be removed prior to exposing 25 the infrared-sensitive layer to infrared laser radiation. Examples of suitable materials for the coversheet include thin films of polystyrene, polyethylene, polypropylene, poly.,~ul,, , fluoropolymers, p~l~ idc or polyester, which can be subbed with release layers.
The rl-.,l.,~. .. :~ ,vc element of the mvention is generally prepared by 30 first preparing the photopoly,ll~,i~hlc layer on the support amd then applying the barrier and infrared-sensitive layers by coating or 1~in~tinn tPr.hniq -PC
The photopoly,l,~ dblc layer itself can be prepared in many ways by admixing the binder, monomer, initiator, and other ill~dh".L;,. It is 35 preferred that the photopolymerizable mixture be formed into a hot melt and then .,~ ld~l ~d to the desired thickness. An extruder can be used to WO96116356 220 18 9 ~ PCIIUS95/14430 perform the functions of melting, mixing, deaeratmg amd filtering the Culllr - The extruded mixture is then ~ d between the support and a temporary c~ ,l or a tempora-y c~Jv~l~L~. which has been v;u~ly coated with the barrier layer. In the latter case it is arranged so 5 that the barrier layer is next to the photopoly~l ., dl~l_ layer during the 1 ~ process. The adhesion bet~-veen the barrier layer and the temporary cu v, ' - should be low, so that the barrier layer will remain mtact on the phulu~ dlJlf layer when the temporary c~,v~l~L~.,L is removed. Alternatively, the photopoly ' '^ material can be placed 10 between the support and the temporary coversheet or the barrier layer coated temporaTy cu~ in a mold. The layers of material are then pressed flat by the -~ ;.. of heat andlor pressure.
The infrared-sensitive layer is generally prepared by coating the infrared-sensitive material onto a second temporary coversheet. The 1~ infrared-sensitive layer can be applied using amy known coating technique including spray coating. It also can be applied by vapor deposition under vacuum or by sputtering. The last methods are p~llLicul~llly useful for metal layers.
The adhesion of this second temporary c~,vt:l~h~L should also be 20 low so that the sheet is easily removed. The infrared-sensitive layer cam then be ~vc;l-,o- L~d with the barrier layer or the two layers cam be coated The fmal element is prepared by (1) removmg the temporary v~ Le~,~ from the photopolyl.._li~ble layer amd placing it together with 25 the second element (second temporary ~ he~ d-sensitive layer/barrier layer) such that the barrier layer is adjacent to the p~Jlu~Jolymerizable layer; or (2) removing the temporary c~ lle~l from the barrier layer on the photopolyl~ dl,lc layer amd placing it together with the second element (second temporary cuv~ e~;/i~alc:d-sensitive 30 layer) such the infrared-sensitive layer is adjacent to the barrier layer. This composite element is then pressed together with moderate pressure. The second temporaly c~lvc;l~llc~l can remain in place for storage, but must be removed prior to IR 1~1 Lll~iug.
Altematively, the three layers cam all be prepared on temporary 35 c~,v~l~llc-~L~. the photopolylll.,.i,~lc layer by extrusion amd f q~ f-rinn or pressing in a mold; the barrier amd infrared-sensitive layers by coating.

~ 2 ~ 1 8 ~ 1 ~ WO 96n6356 rCTllJ595/14430 The final element is p}epared by removing the temporary cuv~ from the ~ element, applymg the barrier layer such that the barrier layer is adjacent to the ~Luluuol~ Wc layer, removing the temporaly cuvcl~h~ from the barrier layer, and applying the irlfrared-5 sensitive layer such that the infrared-sensitive layer is adjacent to the balrier layer. The composite st~ucture is larninated together as each new layer is added or one time for all the layers. The temporaly cuv~,~h~,~.. on the infrared-sensitive layer can remam in place for storage, but must be removed prior to imaging.
The infrared-sensitive layer cam also be coated directly onto the barrier layer which is on the pllulu~oly..l~li~11c layer.
The process of the invention involves (1) providing a l l : v~:
prmting element as described above; (2) imagewise ablating layer (d) of the elementtoformamask;(3)overallexposmgthel,1,.,t.~ ;v~elementto actinic radiation through the mask; amd (4) treating the product of step (3) with at least one developer solution to remove (i) the infrared-sensitive material which was not removed durmg step (2), (ii) at least the areas of the barrier layer which were not exposed to non-infrared actinic radiation, arld ~lii) the areas of the photopolyll~.i~ layer (b) which were not 2û expQsed to non-infrared actinic radiation.
The first step m the process of the mvention is to provide a i ve printing element c"" ~ in the order listed:
(a) a support, (b) a photopoly~ .i~blc layer ~,~ 1 g an ~ bmder, at least one monomer amd am initiator having sensitivity to non-infrared actinic radiation, said layer bemg soluble, swellable or ~lierPrcihl~ m a developer solution;
(c) at least one barrier layer which is ellhcf-~ ly j~ ,U~U~III to actinic radiation, and 3û (d) at least one layer of infrOred radiation sensitive material which is Ylhsfonfiolly Qpaque to non-infrared actinic radiation.
Suitable methods for preparing this element have been discussed m detail above.
The next step m the process of the invention is to hll~,v~i~e ablate layer (d) to form a mask. This exposure is given to the side of the 1.1...1--~..- ';vc element bearing the ir~frared-sensitive layer. :~a temporary cu ~ h_~l is present in the element, it should be removed prior to the exposure step. The exposure can be carried out usimg various types of infrared lasers. Diode lasers emitting im the region of 750 to 880 nm offer 5..hst~.lti ~1 adv _ im terms of their small size, low cost, stability, S reliability, ,,,, ' amd ease of ...,~ Diode lasers emitting in the range of 780 to 850 nm may be used to advantage. Such lasers are ~u.. ~ lly available from, for example, Spectra Diode T. l (San Jose, CA). YAG lasers emitting at 1060 mn are also very effective.
In the infrared ~ v~ ablating step, material in the infrared-10 sensitive layer is removed, ie., ablated, im the areas exposed to the infrared laser radiation. The areas exposed to laser radiation m the infrared-sensitive layer Cull~ -r ~ to those areas im the ~ ulu~ ~lc layer which will be polymerized to form the fmal prmtmg plate. After laser ablation, a pattern of actmic radiation-opaque material remains on the 15 barrier layer over the lullulu~ol~l..~li~l~lc layer. The areas in which the infrared-sensitive layer remains cull~l.ulld to the areas of the photopoly 1 lc layer which will be washed out m the formation of the final printing plate.
The next step in the process of the mvention is to overall expose the 20 r.~ ;I;vc element to actinic radiation through the mask. The type of radiation used is dependent on the type of pllui m the photopoly~ ,li~blc layer. The radiation-opaque material m the infrared sensitive layer which remains on top of the barrier layer on the photopolyl~ layer prevents the material beneath from bemg 25 exposed to the radiation amd hence those areas covered by the radiation-opaque material do not pol~ c. The areas not covered by the radiation-opaque material are exposed to actinic radiation amd polymerize.
Any conventional sources of actinic radiation can be used for this exposure step. Examples of suitable visible or UV sources include carbon arcs, 30 mercury-vapor arcs, nuul~ ;lll lamps, electron flash units, electron beam units and photographic flood lamps. The most suitable sources of UV
radiation are the merculy-vapor lamps, ~ iulJkuly the sum lamps. A
standard radiation source is the Sylvania 350 Blacklight n~ ccllL lamp (FR 48T12/350 VL/VHO/180, 115 w) which has a central wavelength of 35 emission around 354 nm.

W096116356 2 2 0 1 8 9 ~ PC~/lJSg5~14430 It is c , ' ' that the ,, ;De exposure to infrared radiation alld the overall exposure to actinic radiation can be carried out in the same It is preferred that this be done using a drum Le~ the ~' v~ element is moumted on a drum which is rotated to allow for exposure of different areas of the element first to infrared laser radiation and then to non-infrared actinic radiation.
The actinic radiation exposure time can vary from a few seconds to minutes, depending upon the imtensity and spectral energy ~' ' of the radiation, its distance from the ~ ;v~ element, and the nature amd amoumt of the ~,hulu~oly~ dlJI~ ;lLJ.I. Typically a mercury vapor arc or a sunlamp is used at a distance of about 1.5 to about 60 inches (3.8 to 153 cm) from the i l v~ element. Exposure i , are preferably ambient or slightly higher, i.e., about 20 to about 35C
The process of the imvention usually mcludes a back exposure or backflash step. This is a blanket exposure to actinic radiation through the support. It is used to create a shallow layer of polymerized material, or a floor, on the support side of the photopoly.l.cli~lc layer and to sensitize the photopoly~ dl,l~ layer. The floor provides improved adhesion between the I~Lolu~olylll~ ~lc layer amd the support helps highlight dot resolution and also ~C~Ihl~ c the depth of the plate relief. The backflash exposure can take place before, after or during the other imaging steps. It is preferred that it take place just prior to the imagewise exposure to infrared laser radiation on the irlfrared-sensitive layer side of the element, p~ulL~ulally when the overall exposure is carried out on a drum.
Any of the conventional radiation sources discussed above can be used for the backflash exposure step. Exposure time generally range from a few seconds ur~ to about a minute.
Following overall exposure to UV radiation tnrough the mask formed by the actinic radiation-opaque material, the image is developed by washing with a suitable developer. The developer removes (i~ the infrared-sensitive material which was not removed during the ablation step, (ii) the barrier layer in at least the areas which were not exposed to non-infrdred actinic radiation, and (iii) the phOtopolyll.c;..,.al,lc layer in the areas which were not exposed to non-infrared actinic radiation. Development is usually 35 carried out at about room l~ c. The developers cam be orgarlic solutions, water, aqueous or semi-aqueous solutions. The choice of the WO96116356 2 2 0 ~ 8 9 1 PCTIIlS9S114430 ~
developer will depend on the chemical nature of the l,LULUl,UI~ ' ' material to be removed. Suitable organic solution d~,v~,lv~ a include aromatic or aliphatic lly~ ub~ll and aliphatic or aromatic halollyJ.u.,all" solutions, or mixtures of such solutions with suitable 5 alcohols. Other organic solution d~,v~lu~ a have been disclosed in published German ~ ' 38 28 551. Suitable ~ r developers usually contain water and a water miscible orgaluc solution and an aL~aline material. Suitable aqueous d~_v~,lu~ a usuaUy contain water and an alkaline material. Other suitable aqueous developer are described in U.S. Patent No. 3,796,602.
D~,v~l~r ~ time can valy, but it is preferably in the range of about 2 to 25 minutes. Developer can be applied in any C~J11 v~ ' malmer, including spraying and brush or roller L~ Brushing aids can be used to remove the unpolymerized portions of the c~lmr~ ~iti~m 15 However, washout is frequently carried out in an automatic l,.uc~ unit which uses developer and mf-rh~ l brushing action to removed the . ^1~ ,~ ~1 porlions of the plate, leaving a relief ,, the exposed image and the floor.
A pre-development step may be necessary if the infrared-sensitive 20 layer is not removable by the developer solution. An additional developer, which does not effect the polymerized 1)1.. 1.. ~;I;v~ material can be applied to remove the infrared-sensitive layer frrst. This is IJ~ Li.,ul~ly truewhen metallic materials are used. In such cases, etching solutions are used, such as 2% aqueous KOH solution.
The process of this invention r~iay be simplified by removing in the treating step with brushing the infrared sensitive layer, and/or the barrier layer at the same time as the removal of the ..,.- ~ 5; d portions of the photopolymer layer. The pretreating step may not be necessaTy in the situation in which the l~1...l(.3. .~:l;v~ element includes a infrared sensitive30 layer and/or barrier layer which is not ~3~ on~iolly soluble, swellable, 1 llr, or li*able in the developer solution for the photopolymer layer.
The infrared sensitive layer and the barrier layer are generally much thinner than the photopolymer layer such that with the aid of brushing or brushing with pressure, the infrared and barrier layers can be easily 35 removed from the photopolymer layer. Since automatic ~IU~,Caaiug units which use ...~ ~1"..,;,.~1 brushing action are in use co~ ,;dlly for ~ W096116356 2 2 0 1 8 9 ~ PCr/USss/l4430 d~,v.,lu, f I ' r ~ ,.ic plates, the need for brushing action during waskout is easily a~c~ . .l.l;~l.. ,1 Fo-aowing solution d~v, ' r t, the relief printing plates are generally blotted or wiped dry, and then dried in a forced air or infrared 5 oven. Drying times and ~ . may vary, however, typicaUy the plate is dried for 60 to 120 minutes at 60C. High t~ ..allL~ are not lCC~1--.. I.lf d because the support can shrink and tbis can cause registration problems.
Most flrY~ printing plates are uniformly post-exposed to 10 ensure that the photopolym.-n7~tinn process is complete and that the plate will remain stable during printing and storage. This post ~AlUU~ step utilizes the same radiation source as the main exposure.
Dl ' ~ is an optional post-d~, v.~ r ' treatment wkich can be applied if the surface is still tacky, such tackiness not generally 15 being removed im post-exposure. Tackiness cam be eliminated by methods well known in the art, such as treatment witk. bromine or chlorine solutions. Such treatments have been disclosed in, for example, G~ k U.s. Patent 4,400,459, Fickes et al., U.S. Patent 4,400,460 amd German Patent 28 23 300. D~ .. can also be , ' ' 20 by exposure to radiation sourc~es having a ~ L,l.~a- not longer than 300 mm, as disclosed in European Published Patent ~rrlir~ti~n o 017927 and Gibson U.S. Patent 4,806,506.
These elements cam be used to particular advantage in the formation of seamless, c~ printing elements. The photopoly..l~li ~lf flat 25 sheet elements can be ~-u.,c, . ,~d by wrappimg the element around a cylmdrical form, usually a printing sleeve or the printing cylinder itself, and fusmg the edges together to form a seamless, ~ element. In a preferred method, the pl~u~ul~c~ly~ ~lf layer is wrapped aroumd the cylindrical form and the edges joined. One p}ocess for joining the edges 30 has been disclosed in German patent DE 28 44 426. The photopolyl.lcli~l~lf layer can then be spray coated with, at least one barrier layer and then with at least one mfrared-sens7ltive layer.
Continuous printing elements have slrrli~ n~ in the fl(.~
printing of ~...l;.. ...~ designs such as in wallpaper,~decoration and gift 35 wrapping paper. Fu. hc;llllul~, such ~..l;....~.. printing elements are well- suited for mouriting on conventional laser ~qlljrm~nt The sleeve or WO96/lC356 ~2 2 0 1 8 9 1 PCr/~JS95/14430 ~

cylinder on which the printing element is wrapped when the edges are fused, can be moumted direc'dy into the laser apparatus where it functions as the rotating drum during the laser exposure step.
In addition, it has been found that the process of the invention can 5 be performed while the plate is mounted in the roumd, i.e., wrapped around a cylindrical form. Thus, i~ vvi~C ablation, overall exposure, d~ lv~ and any additional steps can be performed while the plate is mounted in the round. Other ~d~ ,, which cam be obtained usmg the imstant process include increased process speed, better ~ L~II and 10 reduced or in some cases no extra moumting time.
Unless otherwise mdicated, the term ~ ' printing plate or element" A plates or elements in any form suitable for flPYov , ' - prmting, mcluding, but not limited to, flat sheets and seamless c, forms. All pllhl~ ti~ r~ nn~d herein are hereby 15 i~Cu~ ' by reference unless otherwise indicated.
GLOSSARY
Base 1 ~ Di~ Lul~lo~;lllylmethacrylate BD Butadiene BHT Butylated llyJIu~yi ' 25 DAM Diallyl Maleate, MTM- ILudwi~ , Inc.
(Elgin, SC) DDM Dodecyl mercaptan 30 t-DDM Tertiary dodecyl mercaptam HMDA 1,6-h~ l diacrylate HEC Hydroxyethyl Cellulose HPC ~ Hydlu~y~ulul,yl cellulose, Klucel~ E-F
from Hercules, Inc. (Wilmington, DE) ~ WO96116356 ~12 0 1 8 9 ~ PCT/US9~/14430 Initiator 2-phenyl-2~2-dilL~ u~y~ tu-phenone Inhibitor 2,3-di~dl~,~,y~,1O[3.2.2]non-2-ene, 1,4,4-trimethyl-N,N'-dioxide, CAS No.

IsoparV C14 18 iiv~ u~ ull~
CAS No. 64742-46-7, from Exxon Co.
10 (Houston, TX) Lomar PW ~"~ sulfonic acid r polymer, sodium salt, CAS No. 9û84-06-4, fromHenlcel Corp. (M;...,~
15 MN!
MAA Methaclylic Acid NaDDBS Sodium dodecyl ben~ene sulfonate NLA n-Laulyl acrylate Piccotex~ Substituted polystyrene from Hercules, Inc. (Wilm ington DE) = - ~ :
PVP-VA Poly(vinyl pyrrolidone/vinyl acetate) Rodo No.0 : Blend of oils used as odor masking agent, from R. T.~Vanderbilt (Norwalk, . . _ CT) TBP : ~ Tributoxyethyl phosphate Tinuvin~9 130 Mixture of polyethylene glycol mono(2-2(2H-b~ .. ,... I .; ,. ,.~ ,1 -2-yl)-6-t-butyl-4-(3 -~: == methoxy-3-oxypropyl) phenyl)ether and polyethylene glycol bis(2-2(2H-Wo96/16356 ~2 0 18 9 1 PCI`/IJS95/14430 1~..~u; zol-2-yl)-6-t-butyl ~-(3-methoxy-3-oxypropyl) phenyl) ether, from Ciba-Geigy.
5 TKPP T~ r ~ylul h , ' , from Monsanto Compamy (St. Louis, MO) Vazo(~) 67 2,2"-Azo-bis(2 .. ~,ll~lbulylv-nitrile), from E. 1. du Pont de Nemours amd Company, (Wilmington, DE) Zapon(~) 335 Red dye, CAS No. 73297-15-1 EXAMPLES
E~ample 1 This examples illustrates the preparation of a l.l,..l., . .~;I;v~ element having a layer which is sensitive to infrared radiation amd two types of batrier layers.
An infrared sensitive laycr was obtained by using an infrared-sensitive W opaque film having a support (T .:leFrM~ekTM. made by James River Graphics, Inc, South Hadley, MA) A photopol~ li~blc layer was obtained by using a Cyrel~) 107 PLS+ prmting element (E I du Pont de Nemours amd Company, ~7ih.~.~,tUII, DE) In the prmting element, the photopolymerizable layer is U~ with an F~ Iayer, which furictions as one barrier layer, amd which is further overcoated with a polyamide release layer, which fimctions as a second barrier layer.
A sheet of the infrared-sensitive UV opaque film was sprayed with a mixture of methamol amd ethanol (2:1 w/w) to soften the coating The 3û Cyrel(~9 107 PLS+ cuvc;~ .l was removed amd the softened coatmg side of the infrared-sensitive film was plaGed on top of the release layer This was laminated at room t~l.lU-,I~lW~ to squeeze out the excess solution The IR
support was then removed frorn the infrared-sensitive layer and the element was air dried The density of the infrared-sensitive layer on the element was increased by l~rninsltin~ additional infrared-sensitive films, with the coating softened, onto the element four more times WO96/163S6 a~o 18 9 1 PCTICS95/14430 Example 2 This example illustrates the use of a Nd:YAG laser for the imaging step m the process of the invention.
The laser used was a Quamta DCR- I I model (Spectra Physics Corp., 5 Moumtam View, CA) at a ~ of 1064 nm. The laser was Q-switched with a 20 ns pulse.
A i l vc: element prepared as described m Example I was given 50, 100, 250 amd 500 mj exposures m a shadow dot pattern with the above laser, usmg one pulse per shadow dot. Holes were ablated m the 10 infrared-sensitive layer resulting m a pattern of rows of shadow dots with a distdnce of 250 IlP~l,l~ between the dots.
After q,, ~;~., laser ablating the infrared sensitive layer, the element was given a backflash exposure for 50 seconds on a Cyrel~ 3040 light source (E. I. du Pont de Nemours and Compamy, Wilmington, DE), 15 and then given a top exposure, L e., tbrough the imaged infrared-sensitive coatmg, for 10 minutes usmg the same light source without a vacuum. The exposed element was developed m a Cyrel~9 rota~y processor for 5.5 minutes using 3:1 mixture (wl/vol) of Perclene amd butanol. The black mask amd the polyamide batrier layer were removed in the developer. The 20 photopoly~ . . ,dl,l~ layer and the ~ "" . ;~. bamer layer were removed in the ....~ d areas only. The plate was oven dried for two hours at 60C amd then lt?~l~ollcly post exposed amd light finished m a Cyrel~
light finishing unit for 10 minutes. Highlight dots were obtained for all exposures except the 50 mj exposure.
~ =
Example 3 This example illustrates the process of the mvention usmg a diode laser for the imagewise laser ablatmg step.
A phUL(J~ iLiv~ element prepared as described m Example 1 was 30 imaged usmg a Crosfield 645 scalmer modified with an IR diode laser head havmg 780 to 840 mm output as described m Kellogg et al., Journal of ImagmgScience and Technology, Vol. 36, No. 3, pages 220-224 (May/Jume I 992), the disclosure of which is hereby illc~ ,ul~ d by reference. The moumted assembly was given am imagewise exposure usimg 35 signals sent from the Crosfield 645 reader. A halftone image was used (150 lines per inch screen) amd the exposure energy was 1200 mj/Cm2.

W096/16356 2 2 0 1 8 9 1 Pcr/usgsn4430 ~

The black, UV-opaque material was removed in the areas which had been exposed to the laser.
After ,, v~;ac laser ablating the infrared sensitive layer, the element was exposed and developed as described in Example 2. An image 5 was obtained.
Examl~le 4 This example illustrates the preparation of a different infrared sensitive layer which is used with a single barrier layer which is c A 1 ' ~/
10 removed in the developer solution.
S-B-S, a styrene-~ ' ~ styrene block CU~JOIY~ (Kraton~9 1102, Shell Chemical Co., Houston, TX) was ~.c~ -'ifd with carbon black to a level of 10 phr in a Moriyama batch mixer. An infrared sensitive c-~mr~ition was prepared by dispersmg amd dissolving the followmg c-~ .l.. ~ .. l~ in methylene chloride as a 15% solution:
ComDonent Amommt (~) S-B-S, 10 phr carbon 33.û
MABSa 16.5 20BHTb 0 5 Final %C 6.06 a MABS = tetrapolymer of ~ lyhl~ ly~ /
acry-lonitril~l~u~ lc/a~yl~
25 = Blendex(~9 491 from General Electric Co., p . L .~ , WV
b BHT = but,vrated hydroxy toluene The coversheet was removed from a Cyrel(~9 112 HO printing 30 element (E. I. du Pont de Nemours and Company, Wilmington, DE), amd the infrared sensitive c- mrocifion was coated onto the release layer of the Cyrel~ plate, which fi~ fi~nPd as ~e barrier layer, usmg a 10 mil (0.025 cm) doctor knife to form a 1 mil (0.0025 cm) dry coatmg The W~density of the resulting plate was 3.61. ~ :

WO96/16356 25- PCI~ S95/14430 The element was tben laser ablated as described in Example 2 except that exposures of 100, 200, 300, 400 and 500 ~Lj and 1 and 2 mj were used.
After ~ v~;~e laser ablating the infrared sensitive layer, the 5 element was exposed and developed as described in Example 2. In the development step, tbe black and the barrier layer are , ' ~y removed along witb the ~ ;1 areas of the ~Lul~ a11~ layer. An image with good relief higblight dots was obtained with all exposures levels except 100 and 200 Example 5 This example illustrates the use of a spray-coated infrared sensitive layer. This process is pa~ lally usefill in the formation of c, printing elements.
An infrared sensitive ~ was prepared by dispersing and dissolving the cu...r given in Example 4 in toluene to form a 15%
solution. Using a Jet Pak Power Unit (Spray-on Products, Inc., Cleveland, OH), tbe infrared sensitive c~.. l'~;l.. was sprayed onto a Cyrel~D 112 HO printing element from which the coversheet had been removed leaving 20 the release layer as the barrier layer. The coating was ~ in 4 passes. The toluene solution did not attack the barrier or PI~UIOIJOIYI~ .alJIc layers and a good element was obtained.
Example 6 An infrared-sensitive ~ was prepared from the following:

=

Wo96/16356 220 18 9 1 ~cr/US9S/14430 ~

Component Amount (~) Methylene chloride 283 S-B-S, 50 phr carbon 33 MABS 16.5 5 BHT ~: 0.5 Surfactamta 0.2 ml a FC-430 made by 3M Company (St. Paul, MN) 10 Using a 4 mil (0.010 cm) doctor knife, the infrared sensitive solution WaS
coated onto a 1 mil (0.0025 cm) sheet of silicone-release treated Mylar~9 polyester. The dry coating weight was 115.2 g/dm2 and the resulting optical density was 4.79. After the infrared sensitive coating was dTy, it was U~ ' 'I with a barrier layer coatmg of 85% poly 15 (1` ~ u~ ) 6900 from Henkel Corp., M;.. ~ -I ol;~ MN) and 15%
A I ~ .~,1.. .~. . ;~. ,.,lt~ ,l (40% N-t-o~,~yla~lyl~ullide~ 34% methyl yl~ 16% acrylic acid, 6% hydluAylulu,uyl methacrylate, and 4% t-butyl anuno ethylmethacrylate), as a 10% propanol solution, usmg a 4 mil (0.010 cm) doctorknife. .
The coversheet and release layer were removed from a Cyrel(~) 30 CP printing element (E. I. du Pont de Nemours and Compamy, Wihnington, DE), leaving the photopolymer layer as the top layer. The infrared sensitive composite was then laminated to the printing element such that the barrier layer was adjacent to the pl~ut~ layer.
. The silicone-release Mylar~) coversheet was removed amd the infrared sensitive layer of the element was ~ .g~ C ablated using a ~;UI~ ;AI laser engraving apparatus equipped with a Nd:~AG laser. The element was mounted on the exterior of a rotatmg drum. The laser beam was directed parallel to the axis of the drum, and was directed toward the sample surface with a folding mirror. The folding mirror was stationary and the drum moved parallel to its axis. The laser beam was then focused to impinge on the sample mounted on the drum. As the drum rotated amd translated relative to the laser beam, the sample was exposed m a spiral fashion. The laser beam was modulated with image data, i. e., dots, lines and text characters. The laser was operated at 2 watts and the drum was rotated at 104 rpm with a 25 Illi~,lUlll~tW advamce rate. This resulted in a ,~ WO96116356 a 2 0 1 8 9 ~ PCI~/US95~14430 W-opaque patterned rnask on the surface of the ~ element with a tonal range of 2-98% and isolated fme lines, and dots resolved using a 60 lines per inch screen.
After ~ i~c laser ablating the infrared sensitive layer, the 5 element was given a backflash exposure for 12 seconds on a Cyrel 19 3040 light source, and then given a top exposure, i. e., through the imaged infrared-sensitive coating, for 7 minutes usmg the same light source without a vacuum. The exposed element was developed in a Cyrel~ rotary processor for 3 minutes using 3:1 mixture (vol/vol) of Perclene and 10 butanol. The black mask, the barrier layer amd the I , ~ areas of the rh~ S~ ;l;v~ layer were removed. The plate was oven dried for one hour at 60C and then ~ ly post exposed and light fmished in a Cyrel~ light frnising unit for 5 minutes.
Printing tests were carried out with the developed plate on a Mark Andy press System 830 (('~ rfif 1~1, MO) usimg Film m Dense Black EC8630 ink (~llVil~ 1 ~ks & Coatings, Ml~r~lt l~, NC) diluted with EIC Aqua Refresh EC1296 to a viscosity of 20 seconds as measured using a Zahn #2 cup. Printing was done on Hi Gloss 40FS S246 paper (Fasson, Painesville, OH). All samples were run at optimum i..l~ ;UII as judged 20 by the operator at 150 feet per minute. ~ood printed images were obtamed.
Examl)le 7 T_is example illustrates the ~ Ll~iUII of a very thin infrared-25 sensitive coating which can be used with the Cyrel~9 printmg elements inthe above examples.
S-B-S was ~I~C~ rd with carbon black to a level of 50 phr m a Moriyama batch mixer. An infrared sensitive c, l was prepared by dispersmg and dissolving the following Cull.~,o~ in methylene 30cloride as a 15% solution:
Cornponent = Amount (~) S-B-S, 50 phr carbon 49.5 BHT 0.5 W096/16356 2 ~ 0 18 9 1 PCT/US95/14430 Usmg a 1 mil (0.0025 cm) doctor knife, the infrared sensitive solution was coated onto a 1 mil (0.0025 cm) sheet of silicone-release treated Mylar(~9 polyester. The dry coating weight was 33.7 g/dm2 and the resulting optical density was 2.45.
Example 8 The procedure of Example 6 was repeated ~- -l -~l; 1- 1; -g a Cyrel~) 67 HO prmtmg element (E. L du Pont de Nemours and Compamy, Wilmington, DE) for the Cyrel(g) 30CP printing element. The composite 10 element was exposed and developed as described in Example except that the backflash exposure was 15 seconds, the top exposure was 9 minutes and the d~,v~lv~ time was 6 mmutes.
Usmg the prmting conditions of Example 6, a good print image was obtained.
Example 9 An infrared sensitive c~ citi~ was prepared by coating the following mixture to a 5 mil Mylar~) (polyester) to achieve a dry optical density of 2.64.
Component Amoumt (~) Black Polyamide (5oo/ol5oo/o)a 2 Polyamide But~nol/methyl ethyl ketone(80/20) 21 a Polyamide (Macromelt 6900, Henkel Corp.) was "uullded with equal amount of carbon black in a Banbuly mixer.
After the infrared sensitive coating was dry, it was overcoated with a 30 polyamide barrier layer (50 mg/dm2 dry coating weight) from a solution and allowed to dry.
The coversheet and release layer were removed from a Cyrel~ 112 HO printing element (E. I. du Pont de Nemours and Compamy, Wilmington, DE) leaving the photopolymer layer as the top layer. The 35 infrared sensitive composite was then laminated to the printing element such that the barrier layer was adjacent to the photopolymer layer.

~ W096/163~6 2 2 0 1 8 9 ~ r~s~l443~

The Mylar~9 polyester next to the i~frared sensitive layer was removed and the element was mounted (secured with a double sided adhesive tape) on the exterior of the rotating drum (24 inch in ci~ ) of an ~ "I l laser apparatus equipped with a 5 Nd:YAG laser. The laser beam was focused to impinge on the sample mounted on the drum As the drum rotated and the laser beam moved parallel to the axis of the dr lm, the sample was exposed in a spiral fashion. The laser beam was - ' ' ' with image data, i.e., dots, lines and text characters. The laser was operated at 25.0 watts at the plate 10 surface and the drum was rotated at 2500 rpm with a 25 llfl~lu~ t~l advance rate. This resulted in a W-opaque pattemed mask on the surface of the photopolymer element with a tonal range of 2-95 /9 and iso_ated fine lines, and dots resolved using a 120 lines per inch screen.
After imagewise laser ablating the infrared sensitive layer, the 15 element was removed from the dmm. The element was given a backflash exposure for 75 seconds on a Cyrel~ 3040 light source, and then given a top exposure, i.e. through the imaged infrared-sensitive coating, for 12 minutes using the same light source without a vacuum and without amy ~uvc,~ . The exposed element was developed in a Cyrel(g) rotaly 20 processor for 9 minutes using 3:1 mixture (vol/vol) of Perclene and butamol. The black mask, the barrier layer amd the lml~Yr~lc~d areas of the l.l .. -l- -~. -:' ivc layer were removed. The plate was oven dried for one hour at 60C and then ! ' ' ' ~ y post exposed and light finished m a Cyrel~ light frnishing unit for 10 mmutes. Excellent image resolution was 25 obtained with this processed plate. Good prmted images were also obtaimed when printed on a Mark Andy press.
Exam~le 10 This example illustrates the process of this invention using a 30 pllulu~,llailivc element having am orgaluc soluble barrier layer and infrared sensitive layer on am aqueous ~u.,c~ photopoly",c,i,~lc layer.
A water dcv~lu~dbl~ photopolymer plate was prepared with a microgel binder prepared as follows:

~Vo96/16356 ~2 0 18 9 1 PCI/llS95/14430 ~

I. p~ dliul~ ûf microgel bmder A. P~,Jlaldl iu~ of Water Phase Solution The water phase solution was composed of the following ~;" '1"'''' ' "
Component Amount C~rams) Lomar PW 56 NaDDBS 239 Deionized water 13093 NaDDBS and Lomar PW were charged to the water under a nitrogen blanket. The cu...~. were mixed until they were dissolved.
B. Preparation of Oil Phase The oil phase solution was composed of the following .
Component ~ Amount (grams) Styrene 1332 Væo(~ 67 35 Isopar V 2244 The DDM amd DAM were dissolved m stvrene umder a nitrogen blanket. The Væo~}) 67 was then added and allowed to dissolve. The Isopar V was slowly added to the styrene solution while under a nitrogen blanket.
C. Preparation of Oil Emulsion : The oil phase was added to the water phase, under a nitrogen blanket, keeping the solution mixed This was then ll.. ~.,., ..; ~r~1 using a Microfluidizer~) M210 (Microfluidics Corp., Newton MA) at 3000-~000 psig umtil the paTticle size measured 100-250 mm (Gaussion ~iie1rih~l*~m NICOMP Submicron Particle Size Analyzer, Model 270, Pacific 35 Scientific).

~ WO96116356 ~ 0 18 9 1 PCr/rJS95/14430 D. Butadiene Poly The following C 1 was used for the poly ComPOnent = _ Amount Deionized water 79.00 pounds 5 Oil emulsion 52.00 pounds FeSO4 0.02 grams TKPP - 33.00 grams BD 43.18 pounds The FeSO4 and TKPP were dissolved m the deionized water under a nitrogen ~ I ' ~. The oil emulsion was added and this was placed in an autoclave. The BD was added and allowed to swell the oil emulsion droplets for one hour while stirring. The t~ l..C was then raised to 60-65C to initiate the pol~, reaction. rul.y . . lr~ m was 15 allowed to proceed until ~,U,~ / 85% of the BD had polymerized.
The following i..~, ' were premixed and pumped in at a~ J 85% . v~ of the BD.
Component ~ Amount MAA 2.27 polmds t-DDM 0.65 pounds NaDDBS 0.31 pounds Deionized Water 22.47 pounds The reaction proceeded to c~mr1~-tirn with ~ Jlu~ y 90-95%
total conversion. The resulting polymer mooney viscosity was 65. The final palticle size was 144nm (Gaussion ~ n NICQMP Submicron Particle Size Analyzer, Model 270 Pacific Scientific).
The above emulsion was freeze dtied to remove the water. The 30 result was a solid microgel binder having a core~of poly(butadiene/stvrene) and a shell of poly(butadiene/ ' ylic acid). The percent MAA was 3.9%.
IL Preparation of r~ " . .; ~; v~ element containing an aqueous 35 developable photopolymer layer.

w096~l63s6 2 2 0 1 8 9 1 PCI/US9!i/1443~

A~ lu~ ;1;v~ .n~ waspreparedfromthefollowing C~""1""" "1`
Component Parts by Wei~ht Microgel binder (prepared in A) 65.1 5 HMDA 4.0 NLA 4.9 Base 1 9.8 Initiator 3 0 B~IT 2.0 Inhibitor o I
Piccotex~) 5.0 PVP-VA 1.0 Zapon~) 335 0.01 5 Tinuvin~9 1130 0.1 Rodo(~l No. 0 0.1 A coversheet was prepared by coating a 5 rnil (0.013 cm) sheet of polyethylene l~l.r' ~ 1 with a layer of a blend of HPC and ~C at a 20 coating weight of 20 mg/dm2.
A support was 7 mil (0.018 cm) polyethylene l~ 1 which was flame-treated.
The c~ .. ,1.. ,1~ of the pllu: v~ , were fed into a 30 mm twin screw extruder which performed the functions of melting, 25 mixing, deaerating and filtering the 1' , The material was extruded at 135C through a die into the rotating bank of a two-roll calender, and then calendered between the support film and the cover sheet.
30 ~ In~ Preparation of rh.~ 5~ ;v~ element from step n with a barrier layer and infrared sensitive layer.
The infrared-sensitive composite film including the polyamide barrier layer was prepared as described in Example 9. The infrared sensitive composite filrn was laminated to the freshly extruded aqueous 35 developable flexoplate prepared above by temporarily attaching the infrared-sensitive composite flm to the coversheet, i.e., piggy-back mode, ~ W096/16356 ~2 0 1 8 9 1 rcuus~s/l4430 such that the polyamide barrier layer of the composite film was adjacent to the aqueous I ' ' r ~ layer. After ' ' ~, the portion of the ;ve element having the infrared sensitive layer amd barrier layer was cut out of the ' ' cd element. Smce there was no adhesive layer or 5 ~JIl~Di~ i.D between the coversheet and the Mylar~) polyester support of the infiared sensitive composite film, the original coversheet was easily removed from the composite film.
The resultmg ~,1 ,l,,, ..~;I;v~ element had a total thickness of 0.062 in (1.57 mm). The l ' '( v~ element also had the desired adhesion 10 balance m that the organic soluble barrier layer adhered to the aqueous photopolymer surface amd the lowest adhesion of the layers for the element structure was the Mylar(~9 polyester to the infrared sensitive layer.
IV. Process for making a flPY~ l ' ~ printing plate = The l.l . .l .~- ~; I; ve element formed m step m was given a back flash exposure of 30 seconds on Cyrel~ 3040 exposure unit. The Mylar~
polyester was removed from the infrared sensitive layer of the rh. .l. .s~ ; vc element amd the infrared sensitive layer was imagewise ablated as described in Example 9 using the Nd:YAG laser with 4 joules/cm2 fluence. A tonal range of 2-95% was resolved using 120 line per inch screen.
After imagewise laser ablating the infrared sensitive layer, the i l ~ ve element was given a top exposure, i e., through the UV-opaque patterned mask, for 3 mmutes without the vacuum. The element was developed m a rotary processor using brushes amd with tap water at room Lc~ Jcldtl,.c for 10 minutes. The infrared-sensitive layer amd the polyamide barrier layer were removed with the umpolymerized aqueous photopolymer as desired. It was rmsed with fresh water and then dried irl a 60 degree centigrade oven for 15 minutes. Good images were obtamed.
== . = = = :
Exam~le 11 ~ ~
This example illustrates the process of this mvention usmg a rh .lu~- ~;I;ve element having a solvent-soluble infrared sensitive layer on aqueous developable plate with the aqueous barrier layer.
An aqueous dcvcl~ r~ s ~ ,~; I; vc plate was prepared as described m Example 10 amd was extluded and calendared between the ~20 18 91 support film amd the Guvl ' ' The layer of HPC and HEC on the cu~L~l was an aqueous d~v.,~ release layer which ~ - ' as an aqueous d~, v ~,h~dlJlc barrier layer. The resulting plate was such that the aqueous bar~ier layer was in direct contact with the aqueous d~,v~lul ' '^
phulupoly ~ layer. The thickness of the plate (without the cuvcl~h~ ) was 0.067 in.
The plate was given a back flash exposure of 30 seconds. The plate was modified by removing the coversheet and dip coating the plate with the solvent soluble, infrared sensitive Cull~u~;llu~ described in Example 9.
The infrared sensitive coating formed a layer having a dried coating weight of 29 mg/dm2 and a density of 2.73, on top of the aqueous barrier layer, to create a ~ ; vc element. The I ' vc element was imagewise ablated as in Example 9 using Nd: :YAG laser with 3 .6 Joule/cm2 fluence. A tonal range of 2-95 % was resolved using 120~LPI
screen. After imagewise laser ablation, the element was given an overall main exposure for 3 minutes using vacuum. The element was developed in a rotary processor using brushes and tap water at room t~ UCId~C as the developer solution for 10 minutes. The solvent soluble infrared-sensitive layer and the aqueous soluble barrier layer were removed with the umpolymerized aqueous photopolymer as desired. The element was rinsed with fresh water, dried in a 60C oven for 15 minutes and post exposed and fmished ~ ly for 5 minutes. Good images were obtained.
Examl~le 12 An infrared sensitive layer was obtained by using an infrared-sensitive W opaque film having a polyester support (T qcPr~ rM, made by James River Graphics, Inc., South Hadley MA). A sheet of the infrared-sensitive W opaque film was dipped coated with a polyarnide solution (5% solid in butamol/toluene solution) to form a bar~ier layer, and allowed to dly. A coversheet and a release layer were removed from a Cyrel~ 67 HO plate leaving the photopolymer as the top layer. The infrared sensitive UV opaque film with the barrier layer was laminated to the plate such that the barrier layer was adjacent to the photopolymer layer, to form a~rl vc element.
The polyester support of the I qc~rMqckTM film ~ CIIIU v .,d and the infrared sensitive layer of the elcment was imagewise ablated using the W096/16356 22 0 1 a ~ e~ PCI'IUS95/14431) laser write engine as described im Example 9 with fluence of 1.5 joule/cm2.
The element was back _ash exposed, main exposed, developed, amd post exposed amd light finished as described m the Example 9. Good images were obtained.
Example 13 This example illustrates the process of the invention usmg an aqueous d~, v ~,lop~ ; vc element which is Cu~
available and which was modified to include an infrared sensitive layer.
An aqueous d~v~ d~l~ photopolymer layer was obtained from am aqueous developable n. ~ . plate, identified as aqueous plate for fl~ from Nlppon Zeon Co. (0.067 in thickness) having a cover sheet and a release layer. The plate was modified by discarding the cu v~ L~ and removing the tack-free release layer by wipmg the plate 15 surface with a wet towel (soaked with water). The plate surface of the photopolymer layer became tacky after allowing to dry m the room. The modified plate was then hot laminated with the irlfrared-sensitive composite film as described m the Example 9 such that the solution soluble ba~Tier layer, i.e., polyamide barrier layer, was adjacent to the aqueous 20 photopolymer layer. The resultmg 1.l -,l,,,. .. -;I;vc eleme~t had good black density and good a&esion balamce such that the Mylar~ polyester ....v, was removed cleanly from the infrared-sensitive layer of the s~ ;vc element~ The element was imagewise ablated with Nd:yAG
laser at the fluence of 3.6 joule/cm2 as described in Example 9. The 25 element was back flashed 20 seconds, amd was given a main W overall exposure through the laser ablated, W opaque mask for 3 min:utes (without vacuum). The element was developed m hot water (150F) with 1% surfactant in a processor with brushes for 10 minutes amd dried for 15 minutes m 60'rC. Good images were obtained.

Claims (11)

What is claimed is:

1. A photosensitive element used to prepare flexographic printing plates comprising, in the order listed:
(a) a support (b) a photopolymerizable layer comprising an elastomeric binder; at least one monomer and an initiator having sensitivity to non-infrared actinic radiation, said layer being swellable, soluble, or dispersible in a developer solution;
(c) at least one barrier layer which is substantially transparent to non-infrared actinic radiation; removable during development; and wherein said barrier layer is insoluble in the developer solution before development;
and (d) at least one layer of infrared radiation sensitive material which is substantially opaque to non-infrared actinic radiation;
wherein the infrared-sensitive material is ablatable from the surface of the barrier layer upon exposure to infrared laser radiation and removable during development.

2. A photosensitive element according to Claim 1, comprising (a) an aqueous processable photopolymerizable layer and (b) at least one barrier layer which is insoluble in an aqueous developing solution.

3. A photosensitive element according to Claim 2 wherein the aqueous processable photopolymerizable layer comprises a microgel binder having a core of poly(butadiene/styrene) and a shell of poly(butadiene/methacrylic acid).

4. A photosensitive element according to Claim 2 wherein the at least one barrier layer comprises polyamide.

5. A process for making flexographic printing plate, which comprises (1) providing a photosensitive element comprising, in the order listed;
(a) a support:
(b) a photopolymerizable layer comprising an elastomeric binder; at least one monomer and an initiator having sensitivity to non-infrared actinic radiation, said layer being swellable, soluble, or dispersible in a developer solution;
(c) at least one barrier layer which is substantially transparent to non-infrared actinic radiation;
removable during development; and wherein said barrier layer is insoluble in the developer solution before development; and (d) at least one layer of infrared radiation sensitive material which is substantially opaque to non-infrared actinic radiation; wherein the infrared sensitive material is ablatable from the surface of the barrier layer upon exposure to infrared laser radiation and removable during development;
(2) imagewise ablating layer (d) with infrared laser radiation to form a mask;
(3) overall exposing the photosensitive element to actinic radiation through the mask; and (4) treating the product of step (3) with at least one developer solution to remove during development (i) the infrared-sensitive material which was not removed during step (2), (ii) at least the areas of the barrier layer which were not exposed to non-infrared actinic radiation, and (iii) the areas of the photopolymerizable layer (b) which were not exposed to non-infrared actinic radiation.

6. A process for making a flexographic printing plate according to Claim 5, which comprises:
(1) providing a photosensitive element with an aqueous-processable photopolymerizable layer and at least one barrier layer which is insoluble in an aqueous developing solution;
(2) imagewise ablating layer (d) with infrared laser radiation to form a mask;
(3) overall exposing the photosensitive element to actinic radiation through the mask; and (4) developing the product of step (3) in a rotary processor and in an aqueous solution to remove during development the infrared-sensitive layer; the at least one aqueous insoluble barrier layer and the unpolymerized aqueous processible photopolymerizable layer.

7. A process according to Claim 6, wherein the aqueous processible photopolymerizable layer comprises a microgel binder having a core of poly(butadienne/styrene) and a shell of poly(butadienne/methacrylic acid).

8. A process according to Claim 6, wherein the at least one barrier layer is a polyamide.

9. A process according to Claim 6, wherein development utilizes water and a surfactant to remove (i) the infrared ablatable layer; the barrier layer; and the unpolymerized photopolymerizable layer.

10. A photosensitive element used to prepare flexographic printing plates, comprising, in the order listed:
(a) a support;
(b) a photopolymerizable layer comprising an elastomeric binder; at least one monomer and an initiator having sensitivity to non-infrared actinic radiation, said layer being swellable, soluble or dispersible in an aqueous developer solution;

(c) at least one barrier layer which is substantially transparent to non-infrared actinic radiation; removable during development; and soluble in the aqueous developer for the photopolymerizable layer;
(d) at least one layer of solvent-soluble infrared sensitive material which is substantially opaque to non-infrared actinic radiation; wherein the infrared sensitive material is ablatable from the surface of the barrier layer upon exposure to laser radiation and removable during development.

11. A process for making flexographic printing plates, which comprises (1) providing a photosensitive element comprising, in the order listed:
(a) a support;
(b) a photopolymerizable layer comprising an elastomeric binder; at least one monomer and an initiator having sensitivity to non-infrared actinic radiation, said layer being swellable, soluble or dispersible in an aqueous developer solution;
(c) at least one barrier layer which is substantially transparent to non-infrared actinic radiation;
removable during development and soluble in the aqueous developer for the photopolymerizable layer;
(d) at least one layer of solvent soluble infrared sensitive material which is substantially opaque to non-infrared actinic radition; wherein the infrared sensitive material is ablatable from the surface of the barrier layer upon exposure to infrared laser radiation and removable during development;
(2) imagewise ablating layer (d) with infrared laser radiation to form a mask;
(3) overall exposing the photosensitive element to actinic radiation through the mask; and (4) treating the product of step (3) with at least one developer solution to remove during development (i) the infrared sensitive material which was not removed during step (2), (ii) at least the areas of the barrier layer which were not exposed to non-infrared actinic radiation, and (iii) the areas of the photopolimerizable layer (b) which were not exposed to non-infrared actinic radiation.