CA1101586A

CA1101586A - Photosensitive compositions

Info

Publication number: CA1101586A
Application number: CA135,271A
Authority: CA
Inventors: Arnel D. Potter; Michael J. Lowe; Maclean R. Hess
Original assignee: WR Grace and Co Conn
Current assignee: P T Sub Inc
Priority date: 1971-05-17
Filing date: 1972-02-22
Publication date: 1981-05-19
Also published as: NL7206691A; AU4228872A; GB1395822A; FR2137942B1; FR2137942A1; DE2223808A1; IT958889B

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to relief printing plates prepared from compositions consisting of I) a monovinyl-arene-diene block copolymer; II) an addition-photo-polymerizable polyunsaturated ester derived from acrylic or methacrylic acid; III) an addition polymerization initiator activatable by actinic radiation, and option-ally a low molecular weight liquid rubber.

Description

S~il6 ~AS~a~ ~D ~

This invention relates to new photosensitive compositions ~or the production o~ relief printing plates which are characterized by excellent so~tness, ~lexibility, resilienca and wear characteristics. More particularly, the invention relates to relief' printing plates prepared ~rom compositions consisting of' I) a monovinylarene-diene block copolymer; II) an addition-photopolymerizable polyunsaturated ester derived from acrylic or methacrylic acid, III) an addition-polymeriza-tion initiator activatable by actinic radiation and op-tionally a low molecular weight liquid rubber.

DESCRIPTION OF THE PRIOR ART
~: , A well-known process ~or preparing relief print-ing plates is the photoengraving process, wherein a metal coated with a photosensitive~acid resist is exposed to actinic radiation through an image bearing process trans-parency thereby forming a reverse image in the coating on the metal surface. Selective etching o~ this surface with a concentrated acid yields a positive metal relie~
plate. A negative relief is then made from the positive metal relie~ in a thermosetting resin. The relief plate used in the printing process is then molded from the negative relief' using suitable rubber or resinous com-' 25 poun~s. The process entails many man-hours of' skilled ~' labor and correspondingly much expense in time and ma-, . .
terials Another well-known process ~or the preparation of' relief' printing plates involves the use of' composi-- 30 tions capable of' addition photopolymerization under the , . , :

- ~2~

in~luence Or actinic radiation as disclosed in U~S. Pat-ents 2,760,863 and 2,791,804. In the processe~ de-scribed in these patents, rigid polymeric printirlg re-lie~s are produced by exposing to aetinic llght, throu~h an image bearing process transparency, a layer com-prising an addition polymerizable, ekh~lenically un-saturated compound and polymerization lnitiator. In~
solubilization, due to the photopolymerization occurs in the exposed areas, but no such polymerization occurs in the non-exposed areas. Removal of the non exposed areas by treatment with a suitable solvent yields a rigid printing reliefO Subsequent U.S. Patentæ

2,902,365; and 2J927~022; 2,g27,023 disclose polyvinyl alcohol and celluloslc matrix materials respectively which may be used in c~nlu~ction with an ethylenicall-~
unsaturated compound and initiator to ~orm photopoly-meriæed polymeric platesO Printing reliefs prepared in accordance with these patents are generally hard, ~rittle, and rigidO UOSo Patent~ 299489611 and 3,024,180 disclose poly(ether) urethane and chloroprene matrix materials respectively which are ~imilarly used to ~orm printing relie~s characterized by reduced brittleness.
However, none o~ these photopolymer1zable relief plates provide the combination of softness, flexibilityJ re-sillence, wear, and other properties eharacteri~tic o~
the relie~ prinking plates of the present invention~
An ob~ect of this invention is to provide new addition photopoJ.ymerizable eompositions and elements which are u3e~ul in making printing relie~s particularly ~or use in ~lexographic and letterpress printing An-other ob~ect is to provide compositions which are cap-able of being formed into so~t, resilient, abra~ion-5~6

-3 -resistant printing reliefs of great durability. A fur-ther ob~ect is to provide printlng reliefs which have excellent resistance to pxinting ink ~olvents, ex-cellent ink tran~fer properties~ and excellent ~harp-ness o~ image. Other ob~ects are ko provide photo-polymerizable compositions which have good storage life and are economlcal to make and u~e. In addition, an ob~ect of this invention is to provide printing re-llefs having the combination o~ properties character-istic of molded rubber printing plates, ~hich are es-pecially suitable for printing on coarse "antique ~
paper~. Still other obJects and advantages wlll be apparent from the following description o~ the in~en tion.

The photopolymerizable compositions o~ the pres-ent invention comprise at least 40~ by weight o~ a rub -~
bery monovinylarene-diene block copolymer~ and at leask 5~ by weight of an addition-photopolymerizable polyun-~aturated acr~lic or methacrylic acid ester, and cata-lyti¢ amounts o~ an addition polymerization initiator activatable by actinic lighto ~he relie~ plate o~ the pre~ent inventlon, comprising a layer o~ the a~oresaid ~ -~
photopolymerlzable composition 2 to 200 mil~ in thick~
ne~, adherent upon a flexible backing~ hereinafter to be re~erred to a~ the sub~trate, is exposed to actinic ~adiation through an image bearihg proce~ tran~parency, con~isting of ~ub~tantially clear and opaque areas, placed in intlmate contact with the photopolymerizable layer. Addition-photopolymerization occur~ in the area .

-3~

of the layer corresponding to the clear area of the process transparency, but substantially no polymerization takes place in the areas corresponding to the opaque areas of the process transparency. Removal of the non-polymerized areas (hereinafter referred to as unexposed areas) by treatment with a suitable solvent, which dissolves the non-polymerized areas, but which has substantially no effect on the photopoly-merized areas (hereinafter referred to as exposed areas) yields a relief printing plate.
The monovinylarene-diene block copolymers are elastomeric polymers having the general formula:
A - B - A
wherein A is an independently selected resinous polymer block having an average molecular weight of 2,000 - 100,000 and a glass transition temperature above 25C., the total block con-tent A being 10 to 50% by weight of the copolymer, and B is an elastomeric polymer block having an average molecular weight of 25,000 - 1,000,000 and a glass transition temperature below 10C.
The end blocks (A) comprising monovinylarene polymer blocks, which may be the same or different, are derived from monoalkenyl aromatic compounds having the general formula:

X
A) C = CH2 (Y)n ~
wherein X represents hydrogen or a lower alkyl radical such ~ as a methyl or ethyl radical; Y represents a member of the : group consisting of hydrogen and lower alkyl radicals ~ :

containing from 1 to 4 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, sec- butyl and tert-butyl radicals;
and n represents an integer from 1 to 5. Illustrative of the Y,i -D~
. ,, ~

5~16 alkenyl aromatic compounds which are included within the scope of the above noted formula A, are for example: styrene, ~-methyl s-tyrene, tert- butyl styrene, vinyl toluene, ortho- and para-methyl styrenes, ortho- and para- methyl-~-methylstyrenes, ortho-and para- ethyl styrenes, and the like.
The elastomeric block (B) comprises a diene polymer block derived from conjugated diene hydrocarbon compounds having the general formula:

B) CH2 C C ~ CH2 R
wherein R represents hydrogen or a lower alkyl radical such as a methyl or ethyl radical. Illustrative of the conjugated diene hydrocarbon compounds which are included in the scope of the above noted formula s, are for example: 1,3-butadiene, 2-methyl-1,3-butadiene, and the like.
Monovinylarene-diene block copolymers, as described above are uniquely suited for application in the invention because such copolymers possess both resinous and elastomeric properties. The resinous properties provide excellent dimensional stability and storage life both prior to and after formation of the relief plate. The elastomeric properties provide relief plates having excellent softness and flexibility characteris-tics. An additional advantage of such block copolymers is their ease of solubility in many organic solvents, thereby permittiny rapid removal of the non-photopolymerized areas during fabrica-tion of the relief plate. I'ypical examples of the monovinylarene-diene block copolymers, useful in th~e present invention, are described in U.S. patent 3,265,765, issued August 9, 1966.

Suitable polyunsaturated esters useful in the present invention are those derived from acrylic or methacrylic acid.
Examples are:

i, ~5~
...... .

ethylene glycol diacrylate and dimethacrylate, propylene glycol diacrylate and dimethacrylate, 1,4 - butane diol diacrylate and dimethacrylate, 1,5 - pentane diol diacrylate and dimethacrylate, 1,6 - hexane diol diacrylate and dimethacrylate, 1,10 - decamethylene glycol diacrylate and dimethacryla te, diethylene glycol diacrylate and dimethacrylate, triethylene glycol diacrylate and dimethacrylate, tetraethylene glycol diacrylate and dimethacrylate, dipropylene glycol diacrylate and dimethacrylate, tripropylene glycol diacrylate and dimethacrylate, : 10 tetrapropylene glycol diacrylate and dimethacrylate, octapropylene glycol diacrylate and dimethacrylate, nonapropylene glycol diacrylate and dimethacrylate, ~ decapropylene glycol diacrylate and dimethacrylate, ; 2,2 dimethyl propane diacrylate and dimethacrylate, glyceryl triacrylate and trimethacrylate trimethylolpropane triacrylate and trimethacrylate, -~
pentaerythritol tetra-acrylate and tetramethacrylate, neopentyl glycol diacrylate and dimethacrylate, ethylene diacrylate, glycerol diacrylate, glycerol triacrylate, 1,4 - cyclohexanediol diacrylate, and 1,4 - benzene-diol dimethacry:Late.
Such polyunsaturated acrylic and methacrylic acid esters -are particularly well suited to the present invention since they are capable of addition photopolymerization at rapid rates.
Moreo~er the plurality of sltes of unsaturation results in the relatively rapid:establishment of a network polymer structure which is .
~ .

~ /
,....
".

o7~

subst~ltially insoluble in the solvent used to remove the non~photopolymerized areas in preparation o~ the relief printing plate.
Initiator o~ catalysts which are operative in the present invention are those which are capable of initiat-ing addition photopolymerization under the in~luence o~
actinic light. The prererred catalyst or initiators are substantially soluble in the photopolymericable polyun-saturated estera and are effective in promoting rapid polymerization, by which the composition is cured. Suit-able photopolymerization initiators or catalysts include vicinal ketaldonyl compounds such as diacetyl, benzil, etc.; ~ -ketaldonyl alcohols such as benzoin, pivaloin, etc.; acryloin ethers such as benzoin methyl or ethyl ethers, hydrocarbon substituted aromatic acyloins includ~
ing ~ -methylbenzoin, ~ -alkylbenzoin, and ~-phenyl benzoin, etc.; diaryl ketones such as benzophenone.
In the compositions of the present invention, the monovinylarene~diene block copolymer constitutes at least 40~ by weight of the total composition~ The polyunsatu-rated acrylic or methacrylic acid ester is present in the amount o~ at least 5~ by weight of the total composition The addition-polymerization initiator is present in cata-lytic amounts, i.e., from 0.1 to 10~ by weight of the total composition.
Optionally, a low molecular weight liquid rubber polymer may be incorporated in cornpositions o~ the present invention in order to increase the so~tness of relief plates made there~rom. Suitable liquid rubber polymers have molecular weights of 750 to 3000 and comprise buta-diene homopolymers and copolymers containing at least 60~ butadiene with the remainder being either styrene or acrylonitrile. The addition o~ such liquid rubber poly-mers should not constitute greater than 50~ by weight o~
the total composition.
As a pre~erred embodîment, compositions o~ the present invention comprise I) ~rom about 60~ to about 85~ by weight o~ a styrene-butadiene block copolymer, II) from about 40% to about 15~ by weight o~ ethylene glycol diacrylate or methacrylate, trimethylolpropane triacrylate or methacrylate, pentaerythritol tetra-acrylate or methacrylate, and III) ~rom about 1.5~ toabout ~.0~ by wei~ht o~ benzophenoneO Another pre~er-red embodiment is the a~oresaid composi~ion containing ; between about 5 and 30~ liquid butadiene.
The method of mixing the photosensitive composi-tions of the present invention is not critical, and does not constitute part o~ the invention. ~t has been ~ound that optimum homogeneity results when the addition poly-merization initiator is combined with the polyunsaturated acrylic or methacrylic acid ester prior to incorporation into the monovinylarenediene block copolymer The re-sultant polymerizable compositions may be in a ~orm of a liquid solution, liquid dispersion, or as a solid mix.
The liquid solution or liquid dispersion may be cast di-j rectly upon the substrate, or first case upon a sultable wheel or belt, stripped, and then a~ixed to the surface of the same substrate The solid mix may be extruded or calendered directly upon the substrate or as a sel~-sup porting sheet and then a~ixed to the~sur~ace o~ the same substrate.
For example, solutions and dispersions o~ the photopolymerizable compositions can be made with such solvents as chlorinated hydrocarbons, e.g., chloroform, -8_ S13~ ~
-8a-carbon tetrachloride, trichlorethylene and chlorotolu-ene; ketones, e.g., methyl ethyl ketone, diethyl ketone and methyl isobutyl ketone~ aromatic hydrocarbons, eOg., benzene, toluene and xylene and blends thereo~ o~ such solvents.
Cn the other hand, solid mixes rnay be prepared by mixing the components on a mill or in an internal mixer such as a Banbury.
The substrate which acts as a support for the ~ -photosensitive compound may be practically any natural or synthetic product capable o~ existing in ~ilm or .
.

~, .
: ::

-8a_ i8~

sheet form, which is dimensionally stable and flexible.
It is a common practice, known to those skilled in the art, to use sheet metals such as aluminum or steel, or plastics such as polyester or polyamide, as substrates. In either case, such materials are rendered non-reflective, where necessary, by coat-ing with an antihalation layer~ Suitable antihalation coatings can be made by dispersing in a solution or aqueous dispersion of a resin or polymer a finely divided dye or pigment which sub-stantially absorbs actinic light. The antihalation layer may also be formulated such that it acts as a binder or adhesive layer between the substrate and photosensitive composition. Anti-halation pigments include carbon black, manganese dioxide and dyes, e.g., Acid Blue Black (CI 20470) and Acid Magenta O (CI
42685). A dyed metal plate is also useful.
The source of actinic radiation used in exposing the photosensitive compositions of the present invention is not a part of the present invention. Practically any source of high intensity light may be used. Included, for example, are those sources such as mercury vapor lights, pulsed Xenon lights, and carbon arc lights. The light source may emanate from point sources or be in the form of parallel rays or divergent beams.
It is preferred that the light source have sufficient intensity so that the compositions of the invention may be photopolymerized within a relatively short period of time.
The image bearing process transparency through which the printing plate is e~posed is that conventionally used in photo-graphy, photolithography, graphic arts processes, etc. In order to obtain the sharpest detail, so-called "black-black"
transparencies such as Du Pont Ortho-D*type, Kodak Estar*, or similar types, especially made for graphic arts processes, are preferred. The sharpest images are also obtained, when the image bearing process transparency is placed in intimate contact *Trademarks _ g _ . . .

J~5~6 wi-th ~he photosensi-tive printing plate.
To make possible easy removal of the image bearing transparency Erom the printing plate after photopolymerization, it is desirable to coat the printing plate with a "parting"
layer or slip coat. Suitable coatings include the conventional acrylic latex slip coats, silicone yreases, etc.
After exposure of the plates, the unexposed areas are removed by means of a suitable solvent liquid which has good solvent action on the monovinylarene-diene block copolymer and relatively little action on the insolubilized, photopolymer-ized image or upon the substrate, antihalation coating, or anchor layer, in the period required to remove the non-polymerized por-tions. Suitable organic solvents include aliphatic hydrocarbons such as hexane, octane, mineral oil, naphthas, etc., aromatic solvents such as toluene, xylene, etc.j halogenated organic solvents such as methylene chloride, Freon ~, etc., and blends thereof of such so]vents. To a large e~tent, the specific solvent which is best is determined by the exact composition of the photosensitive printing plate. In the development step where the relief is formed the solvent may be applied in any convenient manner, as by pouring, immersion, or spray. Brushing or agitation aid in the removal of the non-polymerized portion of the composi-tion. The use of ultrasonic washing ~, j, --10--ii ..",,.~"

5~1~

techniques ls a convenient means of removing the non- :
polymerized areas o~ the relie~ printing plate, The relief plate of' the present lnvention com~
prises a layer o~ khe photopolymerizable composition 2 t,o 200 mlls i.n thickness adherent to a flexible backing, Layers ranging from 3 to 60 mils in'thick ness will be used ~or the maJority of the letterpress printing plates. Layers thicker than 50 to 60 mil~ ~-can be used for the printlng o~ designs and relatlvely large areas in letterpress prlnking plakes. In gen~
eralJ the relie~ helght-~orming stratum o~ the photo- -polymerlzable layer should be essentially non-light scattering, It is important that the ~inal photo-sensitive composition possess su~ic~ent clarity so as to permlt the passage of llght in su~ic:lent quantity to e~rect ~he addlkion~phokopolymer:lzation, mls invention provides a slmple, e~ective relief printing plate utilizing inexpensive materlals and mlnimal labor requirements, The images obtained are sharp and show fldelity to the original trans-parency both in small details and overall dimen~ions~
A signi~icant advantage arises ~rom the ~act that the Roftness and ~lexibiliky of the photopolymerized print~
ing plates makes possible the use of "kiss impresslon"
- prlnting techniques. This prlnting technlque is pre-~erred especially by the book publishing indus~ry as it allows use o~ coarse "antique" papers, as well as higher press speeds. The abrasion resistance o~ the photopolymerized printing plates make the plate more durable than those presently available, An important commerlcal advantage is their lightness in weight, The following examples are included in order 5i!~6 to i.llustrate the invention ln greater detail, but are not to be construed as limitin~ thereto.
', ""':

A photos;ensitive composition consisting o~ the -.~
~ollowlng mixture was prapared ~ .
a) 100 parts of ~tyrene-butadiene~styrene (S~S) block copolymer b) 20 parts o~ trimethylolpropane trl~crylate c) 2 parts o~ benzophenone The parti.cular SBS copolymer was designated:Krato 1102-1, manu~actured by the Sheil Chemical Company, ; and was composed o~ approximat;ely l~0% by weight styrene equally distrlbuted between the two end blocks, the remainder being bukadieneO me relle~ plate was pre~
pared b~ dissolving the compo6it;ion ln toluene, and subsequently casting this ~oluti.o~ by means o~a doctor kn~e to a thickness o~ approximakèl~ 25 mlls~on a ~ ~
polyester backingO The backi~ was previou~l~ coated : ~.
with 0.002 inch thick~ antihalat~on layer composed o~
~ 20 the pho~o~ensitive composltion with the additlon o~
.~: 0.125 part~ Or carbon blackO
The photosensitive layer was then coated with an acrylic latex dry based sl~p coat 3 A 16-inch by ~ -ll-inch piece o~ the resultQnt plate was placed in a vacuum frame, and the coated photopolymer surfa¢e was brought into contact with a line process negatlveO The element wa~ then exposed to acti~ic radiation from a 1400 watt mercury vapor lamp for 2.75 min. After ex-posure, the negative was stripped f'rom the element, and the element was ~ubJected ko an ultrasonic flux of 5 watts per square inch ~or 5 minute~ in a bath -13~ 5 ~

containi.ng hexane to remove the unexpo3ed polymer A
relie~ image correspondlng to the clea~ areas o~ the negative wa~ obtal~edO The photopolymerized relie~
plate was characterized by excellent softness, re-~ilience and sharpness of image. The plate was placed on a printing cylinder, and excellent prints of the original image were obta.inedO The relief plate also had excellent abrasion resi.stance, durability, and resistance to prinking ink sol~entsO ::
. .
~XAMPLE 2 A relief plate was prepared as in Example 1 ~rom a ~ixture o~ 100 parts o~ the same SBS block co-polymer, 40 parts of trimethylol propane triacr~late and 2 parts of benzophen:one. me printing plate ob-- 15 tained possessed characterlstics similar to those described in Example 1. ~

- EXAMP:LE 3 ::
A relie.~ plate was px-epared aæ in Example 1 ~rom a mixture o~ lC)O parts of the same SES block co-polymer, 20 parts o~ ~rimethylol propane trimethacrylate and 2 parts o~ benzophenone wlkh the exception that the photosensitive compos~tlon was blended in an internal - shear mixer and subsequen~ly calendered onto a coated polyester ba¢kingO The printing plate obtained pos- ~ ~-sessed ¢haracterlstic~ ~imilar ko those descrlbed in :
Example lo ~ ' EXAMpL~ 4 A rellef plate was prepared as in Example 1 from a mixture o~ 100 parts of the same SBS block co-~13-LS~36 polymer, 40 parts of trimethylol propane trimethacrylate and 4 parts of benzophenone. The printing plate obtained pos-sessed characteristics similar to those described in Example 1.

A relief plate was prepared as in Example 1 from a mixture of lO0 parts of the same SBS block copolymer, 20 parts of pentaerythritol tetra-acrylate and 2 parts of benzophenone with the exception that the plate was exposed for 5 minutes with a 9000 watt pulsed Xenon lamp. The printing plate obtained pos-sessed characteristics similar to those described in Example l.

A relief plate was prepared as in Example l from a mix-ture of lO0 parts of the same SBS block copolymer, 40 parts of pentaerythritol tetra-acrylate and 4 parts of benzophenone with the exception that the unexposed soluble areas of the plate were removed with a 20 psi pressure spray of methylene chloride ~or 4 minutes. The printing plate obtained possessed charac-teristics similar to those described in Example 1.

A relief plate was prepared as in Example 1 from a mixture of 100 parts of the same SBS block copolymer, 20 parts of ethylene glycol diacrylate and 2 parts of benzophenone with the exception that the plate was exposed for 5 minutes with black light. The printing plate obtained possessed characteristics similar to those described in Example 1.

~J

5~

. .
A relief plate was prepared as in Example 1 from a mix-ture of lO0 parts of the same SBS block copolymer, 30 parts of ethylene glycol diacrylate and 3 parts benzoin. The printing plate obtained possessed characteristics similar to those described in Example l.

-A relief pla-te was prepared as in Example 1 from a mix-ture of 100 parts of the same SBS block copolymer, 20 parts of ethylene glycol dimethacrylate and 2 parts benzoin methyl ether. The printing plate obtained possessed character-; is~ics similar to those described in Example l.
: :~
EXAMPLE lO
~ relief plate was prepared as in Example l ~rom a mix- -ture of 100 parts of the same SBS block copolymer, 30 parts -of ethylene glycol dimethacrylate and 6 parts benzophenone.
The printing plate obtained possessed characteristics similar to those described in Example 1.

A relief plate was prepared as in Example 1 from a mix-ture of 100 parts of the same SBS block copolymer, 20 parts of l,3-butylene glycol diacrylate and 2 parts benzophenone.
The printing plate obtained possessed characteristics similar to those described in Example 1.

~:

~... .

8~

A relieE plate was prepared as in Example 1 from a mix-ture of 100 parts of the same SsS block copolymer, 20 parts of polyethylene glycol diacrylate and 2 parts benzophenone.
The printing plate obtained possessed characteristics similar to those described in Example 1.

EXA~LE 13 A relief plate was prepared as in Example 1 from a mix-ture of 100 parts of the same SBS block copolymer, 24 parts of diethylene glycol diacrylate and 2 parts of benzophenone with the exception that the photosensitive composition was cast on an aluminum backing. The printing plate obtained pos-sessed characteristics similar to those described in Example 1.

A relief plate was prepared as in Example 1 from a mix-ture of 100 parts of the same SBS block copolymer, 24 parts of polypropylene glycol triacrylate and 2 parts benzophenone.
The printing plate obtained possessed characteristics similar to those described in Example 1.

A relief plate was prepared as in Lxample 1 from a mixture of 100 parts of the same SBS block copolymer, 10 parts of diethy- -lene glycol dimethacrylate, ~ parts of benzophenone and 2 parts of rose bengal as the antihalator. The ~17-printing plate obtained possessed characteristics siml lar to those described in Example 1.

-A relief plate was prepared as in Example 1 from a mixture of 100 parts o~ the same SBS block copolymer, 24 parts o~ polypropylene glycol tetraacrylate and 2 parts benzophenone, The printing plate obtained posses-sed characteristics similar to those described in Example 1.

A relie~ plate was prepared as in Example 1 ~rom a mixture of 100 parts of the same SBS block copolymer, 24 parts o~ polypropylene glycol trimethacrylate and 2 parts benzophenone. The printing plate obtained posses- ;
sed characteristics simiIar to those clescribed in Example 1. ~ ~ ;

To the ~ollowing photosensitive composition~
(a) 100 parts o~ SBS block copolymer (b) 20 parts o~ trimeth~lolpropane triacrylate (c) 2.5 parts benzophenone was added the various amounts o~ liquid rubbers set forth in the headings Table 1 below the composition was put on ~-a backing and exposed ~or 5 minutes using the procedure described in Examp]e 1. The exposed portions were then tested to determine the Shore A hardness, The hardness values are set f'orth in in the body o~ Table 1.

, 1` ` 8 ~ 5~3~

Table 1 SHORE A H~RDr~ESS VAL ES

PARTS LI~UID RUBBER IN COMPOSITION

Liquid Styrene-Butadiene 92 8884 72 73 6865 ~ 42 Containing 20~ styrene) .
Ricon 100)*
Liquid Butadiene 92 _ 77 _ 74 _ 6352 48 (Ricon 150)*

. 10 The addition of the liquid rubbers significantly reduces the Shore A hardness of the composition o~ the present in~en-tlon.

- :

.
.

* Trademarks ,

Claims

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

l. A photopolymerizable composition comprising I) at least 40% by weight of an elastomeric monovinylarene-diene block copolymer; II) at least 5% by weight of an addition photopolymerizable polyunsaturated acrylic or methacrylic acid ester; III) 0.1 to 10% by weight of an addition polymerization initiator activatable by actinic light, and optionally up to 50% by weight of a liquid rubber polymer having a molecular weight between 750 and 3000, wherein said monovinylarene-diene block copolymer has the general formula:
A - B - A
wherein A is a resinous polymer block having an average molecular weight of between about 2,000 and 100,000 and a glass transition temperature above 25°C., the total block A content being 10 - 50%
by weight of the copolymer. B is a rubber polymer block having an average molecular weight of betwee:n about 25,000 and 1,000,000 and a glass transition temperature below 10°C.
2. The composition defined in claim 1 wherein A is derived from monoalkenyl aromatic compounds having the general formula:

wherein X represents hydrogen or an alkyl radical containing 1 to 2 carbon atoms; Y represents a member of the group consisting of hydrogen and lower alkyl radicals containing from 1 to 4 car-bon atoms; and n represents an integer from 1 to 5.
3. The composition defined in claim 1 wherein B is derived from conjugated diene hydrocarbons having the general formula:

wherein R represents hydrogen or an alkyl radical containing 1 to 2 carbon atoms.
4. The composition defined in claim 2 wherein B is derived from conjugated diene hydrocarbons having the general formula:
wherein R represents hydrogen or an alkyl radical containing 1 to 2 carbon atoms.
5. The composition defined in claim 4 wherein the monovinylarene-diene block copolymer is a styrene-butadiene block copolymer.
6. The composition defined in claim 5 wherein said ester (II) is selected from the group consisting of ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetra-acrylate, pentaerythritoltetramethacrylate.
7. The composition defined in claim 5 wherein said ester (II) is ethylene glycol diacrylate.
8. The composition defined in claim 5 wherein said ester (II) is ethylene glycol dimethacrylate.
9. The composition defined in claim 5 wherein said ester (II) is trimethylolpropane triacrylate.
10. The composition defined in claim 5 wherein said ester (II) is trimethylolpropane trimethacrylate.
11. The composition defined in claim 5 wherein said ester (II) is pentaerythritol tetra-acrylate.
12. The composition defined in claim 5 wherein said ester (II) is pentaerythritoltetramethacrylate.
13. The composition defined in claim 6 which contains a liquid rubber selected from the group consisting of homo-polymers of butadiene, copolymers of about 60% butadiene and about 40% styrene, and copolymers of about 60% butadiene and about 40% acrylonitrile.
14. The composition defined in claim 13 wherein the initiator (III) is benzophenone.
15. The composition defined in claim 13 wherein said ester (II) is ethylene glycol diacrylate and said rubber is liquid butadiene.
16. The composition defined in claim 13 wherein said ester (II) is ethylene glycol dimethacrylate and said rubber is liquid butadiene.
17. The composition defined in claim 13 wherein said ester (II) is trimethylolpropane triacrylate and said rubber is liquid butadiene.
18. The composition defined in claim 13 wherein said ester (II) is trimethylolpropane trimethacrylate and said rubber is liquid butadiene.
19. The composition defined in claim 13 wherein said ester (II) is pentaerythritol tetra-acrylate and said rubber is liquid butadiene.
20. The composition defined in claim 13 wherein said ester (II) is pentaerythritoltetramethacrylate and said rubber is liquid butadiene.
21. A relief printing plate comprising a substrate formed from a dimensionally stable flexible material, which is coated with a photopolymerizable composition comprising I) at least 40%
by weight of an elastomeric monovinylarene-diene block copolymer;
II) at least 10% by weight of an addition photopolymerizable polyunsaturated acrylic or methacrylic acid ester and; III) 0.1 -10% by weight of an addition polymerization initiator activatable by actinic light, wherein said monovinylarene-diene block copolymer has the general formula:
A - B - A
wherein A is a resinous polymer having an average molecular weight of between about 2,000 and 100,000 and a glass transition tempera-ture above 25°C., the total block A content being 10 - 50% by weight of the copolymer. B is a rubbery polymer block having an average molecular weight of between about 25,000 and 1,000,000 and a glass transition temperature below 10°C.
22. The relief plate defined in claim 21 wherein said substrate is a polyester film.
23. The relief plate defined in claim 22 wherein said coating is 2 to 200 mils in thickness.
24. The relief plate defined in claim 23 wherein A is derived from monoalkenyl aromatic compounds having the general formula:
wherein X represents hydrogen or an alkyl radical containing 1 to 2 carbon atoms; Y represents a member of the group consisting of hydrogen and lower alkyl radicals containing from 1 to 4 car-bon atoms; and n represents an integer from 1 to 5.
25. The relief plate defined in claim 23 wherein B
is derived from conjugated diene hydrocarbons having the general formula:

wherein R represents hydrogen or an alkyl radical containing 1 to 2 carbon atoms.
26. The relief plate defined in claim 24 wherein B is derived from conjugated diene hydrocarbons having the general formula:

wherein R represents hydrogen or an alkyl radical containing l to 2 carbon atoms.
27. The relief plate defined in claim 26 wherein the monovinylarene-diene block copolymer is a styrene-butadiene block copolymer.
28. The relief plate defined in claim 27 wherein said ester (II) is selected from the group consisting of ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylol-propane triacrylate, trimethylolpropane trimethacrylate, penta-erythritol tetraacrylate, pentaerythritoltetramethacrylate.
29. The relief plate defined in claim 27 wherein said ester (II) is ethylene glycol diacrylate.
30. The relief plate defined in claim 27 wherein said ester (II) is ethylene glycol dimethacrylate.
31. The relief plate defined in claim 27 wherein said ester (II) is trimethylolpropane triacrylate.
32. The relief plate defined in claim 27 wherein said ester (II) is trimethylolpropane trimethacrylate.
33. The relief plate defined in claim 27 wherein said ester (II) is pentaerythritol tetraacrylate.
34. The relief plate defined in claim 27 wherein said ester (II) is pentaerythritoltetramethacrylate.
35. The relief plate defined in claim 27 wherein the initiator (III) is benzophenone.
36. The relief plate defined in claim 28 which contains a liquid rubber selected from the group consisting of homopolymers of butadiene, copolymers of about 60% butadiene and about 40% styrene and copolymers of about 60% butadiene and about 40% acrylonitrile.
37. The relief plate defined in claim 36 wherein said ester (II) is ethylene glycol diacrylate and said rubber is liquid butadiene.
38. The relief plate defined in claim 36 wherein said ester (II) is ethylene glycol dimethacrylate and said rubber is liquid butadiene.
39. The relief plate defined in claim 36 wherein said ester (II) is trimethylolpropane triacrylate and said rubber is liquid butadiene.
40. The relief plate defined in claim 36 wherein said ester (II) is trimethylolpropane trimethacrylate and said rubber is liquid butadiene.
41. The relief plate defined in claim 36 wherein said ester (II) is pentaerythritol tetraacrylate and said rubber is liquid butadiene.
42. The relief plate defined in claim 36 wherein said ester (II) is pentaerythritoltetramethacrylate and said rubber is liquid butadiene.
43. The relief plate defined in claim 36 wherein the initiator (III) is benzophenone.
44. A photosensitive, elastomeric composition comprising (1) at least 40% by weight of a solvent-soluble, thermoplastic, elastomeric block copolymer containing two thermoplastic, non-elastomeric polymer blocks having a glass transition temperature above 25°C. and between thermo-plastic, non-elastomeric polymer blocks an elastomeric polymer block having a glass transition temperature below 10°C., (2) at least 5% by weight of an addition-polymerizable, polyunsaturated acrylic or methacrylic acid ester, and (3) a polymerization initiator activatable by actinic radiation in an amount of from 0.1 to 10% by weight.
45. A composition according to claim 44 wherein said thermoplastic, non-elastomeric polymer blocks have an average molecular weight of 2000-100,000 and said elastomeric polymer block has an average molecular weight of about 25,000 to 1, 000, 000.
46. A composition according to claim 45 wherein said thermoplastic, non-elastomeric polymer blocks are the terminal polymer blocks of said copolymer and axe connected by said elastomeric polymer block.
47. A composition according to claim 46 wherein said copolymer is polystyrene-polybutadiene-polystyrene.
48. A photosensitive element comprising the composition of claim 45.
49. A photosensitive element according to claim 48 comprising a layer of said composition coated on a support, said layer having a thickness of from about 0.002 to about 0.200 inch (2-200 mils).
50. A photosensitive element according to claim 49, said support being a sheet support.
51. The composition defined in claim 44 wherein said ester is selected from the group consisting of 1, 4-butane diol diacrylate, 1, 4-butanediol dimethacrylate, 2,2-dimethylol propane diacrylate, tripropylene glycol di-acrylate, trimethylol propane diacrylate, trimethylol propane trimethacrylate and trimethylol propane triacrylate.