CA1103084A - Photopolymerizable composition containing an o- nitroaromatic compound as photoinhibitor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A photopolymerizable coating composition comprising (1) a nongaseous, ethylenically unsaturated, polymerizable compound, (2) a specified nitroaromatic compound, and (3) an organic radiation-sensitive, free-radical generating system is useful for making a positive or negative polymeric image on a substrate.

Description

~3~

BACKGROUND OF THE INVENTION
(1) Field of the Invention This invention relates to photopolymerizable compositions, and to methods of producing positive and negative polymeric images from these compositions.

(2) Description of the Prior Art Conventional polymeric imaging systems are of the negative polymeric image type; that is, the photo-polymerizable coating is exposed to radiation through a - 10 process transparency and a negative polymer~c image is produced. By "negative polymeric image" is meant a polymeric image which corresponds to the transparent portions of the process transparency.
Recently systems which provide a positive poly-meric image have been developed. One such system is i~ described by Nebe in Belgian Patent 818,371. In this system . .
(a) a ~ubstrate is coated with a photopolymerizable ' composition containing (1) a nongaseous, ethylenically unsaturated, ; polymerizable compound, (2) 0.001 to 1.0 part by weight per part of polymerizable compound of an organic, radiation-sensitive, free-radical generating system, and

(3) 0.1 to 10~ by weight, based on the photopolymerizable composition, of a nitroso dimer (b) the photopolymerizable coating is exposed through a pro-cess transparency to radiation at least some of which ~. ' .
- 2 - ~.

:, ~

..
.

-li~3~

has a wavelength less than 3400 ~ whereby the nitroso dimer is dissociated to a polymerization-inhibiting nitroso monomer in the radiation-struck areas, and (c) a greater portion of the photopolymerizable coating is exposed to radiation substantially limited to wavelengths greater than 3400 A whereby a positive polymeric image is formed in the areas struck by the second radiation but not struck by the first imagewise radiation.
Although this system can produce excellent positive 10 ~ polymeric images, a limited time factor is involved. The second exposure must be carried out soon after the first exposure since the nitroso monomer formed during the first exposure can recombine to form inactive nitroso dimer. It would also be desirable to have a system which is not dependent on exposure to such short wavelength radiation.
Another system for producing positive polymeric images is described by Margerum in U.S. 3,556,794. In this system, a photopolymerizable material comprising (1) an ethylenically unsaturated monomer, (2) a photopolymerization initiator system comprising a photo-oxidant dye and a reducing agent for the dye, and (3) an ionizable desensitizing agent having a nitro-benzyl moiety in combination with a carboxylate group, is imagewise exposed to radiation in the wavelength range of 2000-4000 A, thereby inhibiting polymerization by the desensitization of the initiator system, and exposing the photopolymeriæable material to radiation in the wavelength range of 3800 to 7200 A, thereby producing a polymeric image in the area not exposed to the imagewise radiation. This fiystem suffers from the drawback that the desensitizing effect of the desensitizing agent is only temporary.
Margerum states that the desensitization lasts ~for up to about fifteen or more minutes". In Example 1 the second exposure follows the imagewise exposure by 30 seconds.

`: SUMMARY OF THE INVEN~ION
,:
This invention provides a photopolymerizable composition which comprises (a) a normally nongaseous, ethylenically unsaturated compound capable of addition polymerization by free-radical initiated chain propagation, (b) about 0.004 to about 0.7 part by weight, per part of component (a), of nitroaromatic compound of the - formula ~- ~ Rl R2 ~ ~0 2 R3 ~ CHR5R6 wherein R4 Rl, R2, R3 and R4, alike or different, are H, OH, halogen, NO2, CN, alkyl of 1 to 18 carbons, alkoxy in which the alkyl is of 1 to 18 carbons, aryl of 6 to 18 carbons, benzyl, halogen-substituted phenyl, polyether of 2 to 18 carbons and 1 to 6 oxygens, dialkylamino ; ~ in which each alkyl is of 1 to 18 carbons, thioalkyl in which the alkyl is of 1 to 18 carbons, or thioaryl in which the aryl is of 6 to 18 carbons, or any two of Rl, R2, R3 and

- 4 -.

~ 3~
:' R4,taken together,are the residue of a second benzene ring fused into the benzene nucleus, with the proviso that not more than one of Rl, R2, R3 and R4 is OH or NO2, R5 is H, alkyl of 1 to 18 carbons, halogen, phenyl, or alkoxy in which the alkyl is of 1 to 18 carbons, R6 is H, OH, alkyl of 1 to 18 carbons, phenyl, or alkoxy in which the alkyl is of 1 to 18 carbons, with the proviso that only one of R5 and R6 is H, or R5 and R6 together are =0, =CH2, -0-CH2-, =NC H =NC H N ~alkyl)2 in which each alkyl is of 1 to 18 carbons, -0-C1H4-O-, or N2 ~ R2 =~(hydrocarbylene) N=CH~ in which the hydrocarbylene group is of 1 to 18 carbons, or - 2 0 --C .L--C--NH--C = C--in which R8 and R9, alike or different, are H or alkyl of 1 to 4 carbons, and R7 and R , alike or different, are -CN, -COR
in which Rll is alkyl of 1 to 5 carbons, or -COOR12 in which R12 is alkyl of 1 to 6 carbons which may be interrupted by an oxygen atom, alkenyl of 2 to 5 carbons, or alkynyl of 2 to 5 carbons,or R7 and R8 together, or R9 and R10 together, complete ~ 3~L

a 6-membered carbocyclic ring containing a keto group, and (c) about 0.001 to about 10 parts by weight, per part of component (a), of an organic,radiation-sensitive,free-radical generating system, activatable by actinic - radiation that does not significantly rearrange the nitroaromatic compound to an inhibitor of free-radical polymerization.
Positive polymeric images are produced on a sub-strate by the process which comprises (1) coating the substrate with the above photopolymer-izable composition, (2) imagewise exposing a portion of the photopolymer-:~ izable coating through an image-bearing transparency to radiation at least about 20% of which has a . wavelength of about 200 to about 380 nm, thereby rearranging at least some of the nitroaromatic compound to polymerization-inhibiting nitroso-. . aromatic compound, and (3) subjecting the coating to a second exposure whereby a greater portion of the coating, including the portion exposed during the image-wise exposure,is exposed to radiation substantially limited to wavelengths greater than about 380 nm, whereby a positive polymeric image is formed in the areas exposed during the second exposure, but not exposed during the imagewise exposure.
The image formed in step (3) is developed by removing the nonpolymerized portion of the photopolymerizable coating in the areas exposed to the imagewise exposure 3~8 , radiation, or by differential adhesion of a pigment toner to the unpolymerized portion of the photopolymerizable coating in the areas exposed to the imagewise exposure radiation.
Negative polymeric images are produced on a sub-strate by the process which comprises ~1) coating the substrate with the above photopolymer-izable composition, and (2) imagewise exposing a portion of the photopolymer-izable coating through an image-bearing transparency to radiation substantially limited to wavelengths greater than about 380 nm, whereby a negative polymeric image is formed in the areas exposed to ; to the radiation.
.`: DESCRIPTION OF ~HE PREFERRED EMBODIMENTS :
~ In a preferred embodiment of the photopolymerizable ; coating composition, component (a) is an unsaturated ester of a polyol and an a-methylenecarboxylic acid selected from the group consisting of acrylic and methacrylic acids, any alkyl groups in component (b) are of 1 to 6 carbons, and component (c) has at least one component having an active radiation absorption band with a molar extinction coefficient ;~ of at least about 50 within the range of greater than 380 to 800 nm, and most preferably within the range of 400 to 600 nm, and is selected from the group consisting of phenanthrenequinones and 2,4,5-triarylimidazole dimers.
Preferably component (b) is present in the amount of about 0.04 to about 0.15 part by weight of component (a), and component (c) is present in the amount of about 0.01 to about 2 parts by weight per part of component (a).

In a preferred embodiment of the method of making ~3~ 34 positive polymeric images at least about 30~ of the radiation in the imagewise exposure has a wavelength of about 200 to about 380 nm, and the radiation in the second exposure has wavelengths substantially limited to greater than about 380 to about 800 nm, and most preferably substantially limited to about 400 to about 600 nm.
This invention is based on the discovery that certain nitroaromatic compounds in which the nitro group is ortho to a hydrogen-bearing alpha-carbon substituent do not significantly retard or inhibit free-radical polymerization in certain photopolymerizable systems, but are photochemically rearranged to nitrosoaromatic inhibitors of free-radical polymerization by exposure to radiation having a wavelength of about 200 to about 380 nm. These nitroaromatic compounds are relatively unaffected by radiation of longer wavelength.
On the other hand, certain radiation-sensitive, free-radical initiators absorb radiation of longer wavelength, especially in the presence of added sensitizers, to provide sufficient radicals for polymerization of a polymerizable monomer in the absence of an appreciable concentration of inhibiting nitrosoaromatic species.
The nitroso compounds formed by irradiation of the nitroaromatic compounds described herein with short wave-length radiation interfere with the normal free-radical induced polymerization process. Thus, when using the shorter wavelength region of the spectrum in the presence of a nitrosoaromatic compound, an insufficient number of initiating and propagating free radicals is available, and polymerization does not occur. When a composition of this lnvention is e~posed to radiation of wavelength gre~ter than ~ 3~
about 380 nm, the nitroaromatic compound is relatively unaffected, and the photoinitiator system operates to pro-duce initiating radicals. These radicals are able to effect chain propagation in the usual way and polymerization occurs.
Suitable polymerizable compounds for use as - component (a) of the photopolymerizable coating compositions of this invention are the normally nongaseous, ethylenically unsaturated compounds described by Burg et al. in U.S.
Patent 3,060,023; Martin et al., in U.S. Patent 2,927,022;
and Hertler in Belgian Patent 769,694. By "normally nongas-eous" is meant compounds which are not gases under atmos-pheric conditions. They are preferably monomeric, having a boiling point above 90C at normal atmosphere pressure, and contain at least one terminal ethylenic group, but may con-tain 2-5 terminal ethylenic groups. Monomers which contain two or more terminal ethylenic groups are particularly preferred.
Suitable polymerizable compounds include unsaturated esters of polyols, particularly such esters of ~-methylenecarboxylic acids, for example, ethylene glycol diacrylate, diethylene glycol diacrylate, glycerol diacry-late, glyceryl triacrylate, mannitol polyacrylate, sorbitol polyacrylates, ethylene glycol dimethacrylate, 1,3-propane-diol dimethacrylate, 1,2,4-butanetriol trimethacrylate, l,l,l-trimethylolpropane triacrylate, triethylene glycol diacrylate, 1,4-cyclohexanediol diacrylate, 1`,4-benzenediol dimethacrylate, pentaerythritol di-, tri-, and tetrameth-acrylate, dipentaerythritol polyacrylate, pentaerylthritol di-, tri-, and tetraacrylates, 1,3-propanediol diacrylate, 1,5-pentanediol dimethacrylate, the bis-acrylates and _ 9 _ - :' ' - - ~ -.

~3~
methacrylates of polyethylene glycols of molecular weight 200-4000, and the like; unsaturated amides, particularly those of ~-methylenecarboxylic acids, and especially those ~: of ~-~- diamines and oxygen-interrupted ~-diamines, such as methylene bis-acrylamide, methylene bis-methacrylamide, .- ethylene bis-methacrylamide, 1,6-hexamethylene bis-acryl-` amide, bis(y-methacrylamidopropoxy)-ethane and ~-methacryl-amidoethyl methacrylate; vinyl esters such as divinyl . succinate, divinyl adipate, divinyl phthalate, divinyl terephthalate, divinyl benzene-1,3-disulfonate and divinyl butane-1,4-disulfonate; styrene and derivatives thereof;
unsaturated aldehydes, such as hexadienal; and the like;
and mixtures thereof.
A preferred group of polymerizable compounds, because of the good physical properties of compositions containing them, includes N-phenyl-N-methylacrylamide, N-vinylphthalimide, diacetone acrylamide, N-vinylsuccinimide, : p-xylylene diacrylate, 1,4-bis(2-acryloxyethyl)benzene, pentaerythritol triacrylate, 4-acryloxybenzophenone, 4-methacryloxybenzophenone, N-(2-acryloxyethyl)succinimide, : l,l,l-trimethylolpropane triacrylate, pentaerythritol tetraacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, , :

' 3~

- l,l,l-trimethylolpropane trimethacrylate, 4-acryloxydiphenylmethane, N-(2-acryloxypropyl)succinimide, 2,4-diacryloxybenzophenone, 4-(~,~-dimethylbenzyl)phenyl acrylate, 3-acryloxybenzophenone, 2-acryloxybenzophenone, 2-acryloxy-4-octyloxybenzophenone, and mixtures thereof. The most preferred polymerizable compounds are esters of ~-methylenecarboxylic acids selected from the group consisting of acrylic and methacrylic acids.
Many of the polymerizable compounds listed above are swbject to thermal polymerization, especially when stored for long periods or at elevated temperatures. When such compounds are supplied commercially, it is customary for them to contain a small, but effective, amount of a thermal polymerization inhibitor. These inhibitors may be left in the monomers when the photopolymerizable coating compositions of this invention are prepared, as was done in the examples which follow. The resulting compositions ; usually have satisfactory thermal stahility. If unusual thermal exposure is anticipated, or if monomers containing little or no thermal polymerization inhibitor are employed, compositions with adequate shelf like can be obtained by incorporating up to 5 percent, by weight of monomer, of a thermal polymerization inhibitor such as hydroquinone, methylhydroquinone, p-methoxyphenol, and the like.
The photopolymerizable coating compositions also contain a nitroaromatic compound of the formula described above. In this formula, the preferred alkyl groups are ;

; lower alkyl groups containing 1 to 6 carbon atoms. In the ~ bis compounds, the term "hydrocarbylene" represents any -~ divalent radical composed solely of carbon and hydrogen containing 1 to 18 carbon atoms. Typical radicals include o-, m-, and p- phenylene, vinylene r 2-butynylene, 1,3-buta-dienylene, hexamethylene, octamethylene, octadecamethylene, naphthylene (1,2; 2,3; 1,4; and 1,5), ~CH2~, ~3CH2{~}, . , ~ CH2-CH2 ~ , ~ CH=CH ~ , ; and the like.
It has been found that the nature of the R5 and R6 substituents in the nitroaromatic compounds is very important. The unsubstituted compounds in which R5 and R6 are H do not rearrange to photoinhibitor and thus do not work. Furthermore, some R and R substituents deactivate the CH moiety toward rearrangement, for example, substitu-ents which are normally considered to destabilize positive charges, such as nitro, cyano, carboxy and 2-pyridyl. It has been found, for instance, that C~2CO2 2 do not work in accordance with this invention.
Suitable nitroaromatic compounds include _-nitrobenzyl alcohol, _-nitrobenzaldehyde, ~-phenyl-_-nitrobenzyl alcohol, :

. .
~-1 .~

~i3~84 o-(diphenylmethyl)n~trobenzene, a-phenyl~m~no-o-nitrotoluene~
~,a_diethoxy-o-nitrotoluene, a,_ethylenedi oXy - o-nitrotoluene, 3-methoxy-2-nitrobenzalde~yde, 4-methoxy-2-nitrobenzaldehyde, ~,4-dimethoxy-2-n~trobenz~ldehyde, 3,4-dimethoxy-2-nitrobenzyl alcohol, 4-cyano-2-nitrobenzaldehyde,

5-hydroxy-2-nitrobenzaldehyde, ~-hydroxy-3-methoxy-2-nitrobenzaldehyde, l-nitro-2-naphthaldehyde, 2,3,4,5-tetr~methyl-6-nitrobenzyl alcohol, ~,4,5-trichloro-2-nitrobenzaldehyde,~
3,5-dibromo-4,6-d$chloro-2-nitrobenzaldehyde, 4,5-dimethoxy-2-nitrobenzyl alcohol, 4,5-dimethoxy-2-nitrobenzaldehyde, 2,4-dinitrobenzaldehyde, 5-tolyl-2-nitrobenzaldehyde, ..
5-benzyl-2-nitrobenzaldehyde, 5-(m-chlorophenyl)-2-nitrobenzaldehyde, 4-(2-methoxyethoxy)-2-nitrobenzaldehyde, 4-ethoxyethyl-2-nitrobenzaldehyde, 3-diethylamino-2-nitrobenzaldehyde, 4-butylthio-2-nitrobenzaldehyde, 4-phenylthio-2-nitrobenzaldehyde, 2-nitrostyrene, 4,5-dimethoxy-2-nitrostyrene, ~ -dimethylaminophenyl)imino-2-nitrotoluene, : . 30 4,5-dimethoxy-2-nitro-~-phenyliminotoluene, ~i~)3~38`~

2-nitrostyrene oxide, 2-nitrocumene, 4,5-dimethoxy-2-nitrobenzyl chloride, ,~-ethylenedioxy-2-nitrotoluene, N,N'-bis(4,5-dimethoxy-2-nitrophenylmethylene)-1,6-hexanediamine, N,N'-bis(2,4-dinitrophenylmethylene)-2,5-dimethyl-2,5-hexanediamine, N,N'-bis(4,5-dimethoxy-2-nitrophenylmethylene)-~-phenylenediamine, '-bis(4,5-dimethoxy-2-nitrophenylmethylene)-~-phenylenediamine N,N'-bis(4,5-dimethoxy-2-nitrophenylmethylene)-~,~'-bi-p-toluidine, N,N'-bis(4,5-dimethoxy-2-nitrophenylmethylene)-4,4'-stilbenediamine, dimethyl ester of 2,6-dimethyl-~-(2'-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, diethyl ester of 2,6-dimethyl-4-(2'-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, diethyl ester of 2,6-dimethyl 4-(2'-nitro-4',5'-dimethoxyphenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, di-n-propyl ester of 2,6-dimethyl-4-(2'-nitro-~ phenyl)-1,4-dihydropyridine-3,5-dicarboxylic :~ acid, diisopropyl ester of 2,6-dimethyl-4-(2'-nitro-phenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, di( ~ethoxyethyl)ester of 2r6-dimethyl-4-(2'-3~

nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, diallyl ester of 2,6-dimethyl-4-(2'-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, dipropargyl ester of 2,6-dimethyl-4-(2'-nitro-phenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, 3-methyl-5-ethyl ester of 2,6-dimethyl-4-(2'-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, 3-isopropyl-5-methyl ester of 2,6-dimethyl-4-: (2'-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid, ethyl ester of 4-(2'-nitrophenyl)-2,6-dimethyl-3-aceto-1,4-dihydropyridine-5-carboxylic acid, 2,6-dimethyl-4-(2'-nitrophenyl)-3,5-diaceto-1,4-dihydropyridine, 2,6-dimethyl-4-(2'-nitrophenyl)-3,5-dicyano-~ 20 1,4-dihydropyridine, ethyl ester of 2-methyl-4-(2'-nitrophenyl)-1,4,5-

6,7,8-hexahydro-5-oxoquinoline-3-carboxylic acid, methyl ester of 2-methyl-4-(2'-nitrophenyl)-1,4,5,6,7,8-hexahydro-5-oxoquinoline-3-. carboxylic acid, isopropyl ester of 2-methyl-4-(2'-nitrophenyl)-: 1,4,5,5,6,8-hexahydro-5-oxoquinoline-3- carboxylic acid, 1,2,3,4,5,6,7,8,9,10-decahydro-9-(2'-nitro-. .

: `: ~3~8~

phenyl)-1,8-dioxoacridine, and 1,2,3,4,5,6,7,8,9,10-decahydro-3,3,6,6-tetra-methyl-9-(2'-nitrophenyl)-1,8-dioxoacridine.
The nitroaromatic compounds are ordinarily employed in concentrations of about 0.004 to about 0.7 part by weight per part of polymerizable compound. The preferred amount in any specific case will depend upon the particular ; monomer/free-radical generating system employed. In general, the preferred amount of nitroaromatic compound is about 0.04 to about 0.15 part by weight per part of polymerizable compound. ;
The thlrd componen~ which the photopolymerizable -~ coatin~ composition must contain ls an organic, radiation-sensitive, free-radical generating system which initiates polymerization of the monomer and does not subsequently terminate the polymerization. The word "organic" is used here and in the claims to designate compounds which contain carbon, and one or more of oxygen, hydrogen, nitrogen, sulfur and halogen, but are free of metal.
The rree-radical generating system absorbs actlnic radiation wlth wavelengths within the range of about 200 to about 800 nm that does not significantly re-arrange the nitroaromatic compound to an inhibitor of free-radical polymerization. By "actinic radiation" is meant radiation which is active to produce the free radicals necessary to initiate polymerization of the monomeric material. The free-radical generating system can comprise one or more compounds which directly furnish free radicals when activated by radiation. It can also comprise a plurality of compounds, one of which yields the free radicals after having been caused to do so by a sensitizer which is activated by the radiation. Preferably the free-radical generating system has at least one component having a radiation absorption band with a molar extinction coefficient of at least about 50 within the range of greater than about 380 to about 800 nm, and more preferably about 400 to about 600 nm.
A large number of free-radical generating compounds can be utilized in the practice of this invention including aromatic ketones such as benzophenone, Michler's ketone (4,4'-bis(dimethylamino)benzophenone), 4,4'-bis(diethylamino)-benzophenone, 4-acryloxy-4'-dimethylaminobenzophenone, 4-acryloxy-4'-diethylaminobenzophenone, 4-methoxy-4'-dimethyl-aminobenzophenone, phenanthrenequinone, 2,7-di-t-butylphenan-threnequinone, and other aromatic ketones; benzoln ethers such as benzoin methyl ether, benzoin ethyl ether and benzoin phenyl ether, methylbenzoin, ethylbenzoin and other benzoins; 2,4,5-triarylimidazole dimers such as 2-(o-chlcr-ophenyl)-4,5-diphenylimidazole dimer, 2-(o-chlorophenyl)-4, ; 20 5-di(m-methoxyphenyl)imidazole dimer, 2,2'-bis(2-chloro-phenyl)-4,4',5,5'-tetrakis(3-methoxyphenyl)blimidazole, 2-(o-fluorophenyl)-4,5-di-phenylimidazole dimer, 2-(o-meth-oxyphenyl)-4,5-diphenylimidazole dimer, 2-(~-methoxyphenyl)-4,5-diphenylimidazole dimer, 2,4-di(~-methoxyphenyl)-5-; phenylimidazole dimer, 2-(2,4-dimethoxyphenyl)-4,5-diphenyl-lmldazole dimer, 2-(~-methyl-mercaptophenyl)-4,5-diphenyl-imidazole dimer, and the like disclosed in ~.S. Patent 3,479,185 and in Brltlsh Patents 997,396, publlshed July 7, 1965, and 1,047,569, publlshed November 9, 1966.
The imidazole dimers may be used with hydrogen do-.

nors such as 2-mercaptobenzoxazole or 2-mercaptobenzothiazole, - with or without sensitizers such as Michler's ketone, 2,5-bis(4'-diethylamino-2'-methylbenzylidene)cyclopentanone, and various dyes. Additional examples of suitable initia-tors are disclosed by Plambeck in U.S. Patent 2,760,863.
Redox. systems, especially those invo~ving dyes, may also be used. These include combinations such as Rose Bengal/2-dibutylaminoethanol; 2-o-chlorophenyl-4,5-di(m-methoxy-phenyl)imidazole dimer/2-mercaptobenzoxazole; 2-o-chloro-phenyl-4,5-di~m-methoxyphenyl)imidazole dimer/2-mercapto-benzothiazole; and the like.
A preferred group of free-radical generating systems characterized by good efficiency includes the phenanthre~nequinones and 2,4,5-triarylimidazole dimers, with or without hydrogen donors such as 2-mercaptobenz-oxazole, and 2-mercaptobenzthiazole, especially in the presence of sensitizers. The concentration of the free-radical generating system is about 0.001 to about 10.0 parts by weight per part of polymerizable compound, and preferably about 0.01 to about 2.0 parts by weight.
The coating composltlons used herein can also contain other components, if desired. For example, the ; coating can be of the monomer/binder type containing addltlonally a thermoplastlc macromolecular organlc polymer blnder. The coatlng can also be of the substantlally dry, predomlnately crystalline type, described by Hertler ln Belgian Patent 769,694, wherein the coating contains a solid ethylenically unsaturated polymerizable compound, an organic radiation-sensitive,free-radical generating system, and a nonpolymeric normally liquid or solid organic substance which does not inhibit polymerization, in addition to a suitable nitroaromatic compound.
Suitable thermoplastic macromolecular organic polymer binders for use in a monomer/binder system are described by Chang in U.S. 3,661,588, and include such polymeric types as (a) copolyesters based on terephthalic, isophthalic, sebacic, adipic and hexahydroterephthalic acids; (b~ nylons or polyamides; (c) vinylidene chloride copolymers; (d) ethylene/vinyl acetate copolymers; (e) cellulosic ethers; (f) polyethylene; (g) synthetic rubbers;
(h) cellulose esters; (i) polyvinyl esters including poly-vinyl acetate/acrylate and polyvinyl acetate/methacrylate copolymers; (j) polyacrylate and poly-~-alkylacrylate ' esters, e.g., polymethyl methacrylate and polyethyl meth-acrylate; (k) high molecular weight ethylene oxide polymers (polyethylene glycols) having average molecular weights from 4000-4,000,000; (1) polyvinyl chloride and copolymers; (m) polyvinyl acetal; (n) polyformaldehydes; (o) polyurethanes;
(p) polycarbonates; and (q~ polystyrenes.
In a particularly preferred embodiment of the invention, the polymeric binder is selected so that the unexposed photopolymerizable coating is soluble in predom-inantly aqueous solutions, for example dilute aqueous alkaline solutions, but upon exposure to actinic radiation becomes relatively insoluble therein. TypicalIy~ polymers which satisfy these requirements are carboxylated polymers, for example vinyl addition polymers containing free carboxylic acid groups. Another preferred group of binders includes polyacrylate esters and poly--alkylacrylate esters, particularly polymethyl methacrylate.

3~8~

When a monomer/binder system is employed, the amount of polymeric binder present is about 10 to about 80%
by weight based on the total solids content, and preferably about 25% to about 75~. Polymerizable compounds which con-- tain only one site of ethylenic unsaturation are generally - not satisfactory for use in a monomer/binder system.
When the substantially dry, predominantly crystalline system, described in the Hertler Belgian Patent, is employed, in one aspect of the invention, the system may contain in addition to the polymerizable compound, about 0.01 to about 0.25 part by weight, per part of polymerizable compound, of a nonpolymeric, normally liquid organic compound which does not inhibit the polymerization of the polymeriz-able material and does not absorb so much of the incident radiation as to prevent the initiation of the polymerization by the free-radical generating system. In another aspect of the invention, the system may contain about 0.01 to about 250 parts by weight, per part of polymerizable compound, of a nonpolymerizable, crystalline organic solid which does not ; 20 inhibit polymerization of the polymerizable compound and also does not absorb the incident radiation to such an extent as to prevent initiation of polymerization by the free-radical generating system.
Illustrative examples of suitable organic compounds which may be added include octadecanol, triethanolamine, stearlc acid, cyclododecane, l,10-decanediol, dimethylamino-benzonitrile, acetone oxime, desoxybenzoin, naphthalene, N,N'-dimethylhexamethylenediamine, p diethoxybenzene, 1,2-diphenylethane, biphenyl, dotriacontane, tetramethylurea, tributylamine, 2-dimethylaminoethanol, pentamethylbenzene, ~3~
1,12-dodecanediol, 1,2-diphenoxyethane, octacosane, trichloroxylene, cyclododecanol, and the like. A preferred group of solid compounds includes bibenzyl, biphenyl, 1,2-diphenoxyethane, _-diethoxybenzene, octacosane, l-octadecanol and cyclododecanol.
The photopolymerizable compositions described herein may be coated on a wide variety of substrates. By "substrate" is meant any natural or synthetic support, prefer-ably one which is capable of existing in a flexible or rigid film or sheet form. For example, the substrate could be a metal sheet or foil, a sheet or film of synthetic organic resin, cellulose paper, fiberboard, and the like, or a compo-site of two or more of these materials. Specific substrates include alumina-blasted aluminum, alumina-blasted polyethylene terephthalate film, polyethylene terephthalate film, polyvinyl alcohol-coated paper, crosslinked polyester-coated paper, nylon, glass, cellulose acetate film, heavy paper such as lithographic paper, and the like.
The particular substrate will generally be determined by the use application involved. For example, the compositions and method of this invention are particularly useful for producing printed circuits using as the substrate a plate which is a copper coating on fiberboard. When the photopolymerizable compositions are coated on metal surfaces, they are useful for making presensitized lithographic printing plates. For example, such a plate can be prepared from a grained aluminum base in combination with a photopolymerizable coating. After the image has been developed, the plate is first coated with water and then contacted with a roller which wets only the photopolymer image with ink. The inked plate ~ .

~: .

can then be used in lithographic printing in the usual way.
Preferably the substrate is impermeable to oxygen.
The coated compositions can also serve as photo-resists in making etched or plated circuits or in chemical milling applications. They are also useful for preparing colored images from color separation negatives suitable for color-proofing. The images formed with these elements may also be used for making copies by thermal transfer to a substrate. Specific uses will be evident to those skilled in the art; many uses for positive images on substrates are disclosed in U.S. Patents 2,760,863;
3,060,023; and 3,060,026.
Processes for coating the substrate are described in the patents listed in the preceding paragraph. Processes using coating compositions of the substantially dry, predom-inantly crystalline type are of five general types: those in which (1) the components of the coating composition are melted together generally to form a homogeneous melt which is coated onto the substrate; (2) the components of the coating composition are dissolved together in a solvent in which the components are preferably completely soluble and the resulting solution is poured or painted onto the sub-strate; (3) the components of the coating composition are dissolved in a volatile solvent and the resulting solution is sprayed as a fine mist against the substrate; (4) the components of the coating composition are melted together and the melt is sprayed as a fine mist onto the substrate;
(5) the components of the coating composition are mixed together in a heated vessel which contains an inner surface that is cooled in which the distance from the mixture to "

`~ 3~

the cooled, surface can be varied, whereby the components are sublimed onto the cooled surface. Further details of these processes can be found in the Belgian patent of Hertler, cited above. A preferred coating method involves solution coating as in (2) above.
- One of the special features of the photopolymer-izable coating compositions of this invention is that they can be used to prepare either positive or negative polymeric images. Positive polymeric images are prepared by a two exposure procedure while negative polymeric images are prepared by the one exposure technique.
The compositions of the invention are exposed to radiation of wavelength in the 200-800 nm range. Suitable sources of such radiation, in addition to sunlight, include carbon arcs, mercury-vapor arcs, fluorescent lamps with ultraviolet radiation-emitting phosphors, argon and xenon glow lamps, electronic flash units, and photographic-flood lamps. Other fluorescent radiation sources such as the tracings on the face of a cathode ray tube may be used.
Electron accelerators and electron beam sources through an appropriate mask may also be used.
; Where artificial radiation sources are used, the distance between the photosensitive layer and the radiation source may be varied according to the radiation sensitivity of the composition and the nature of the photopolymerizable polymer. Customarily, mercury-vapor arcs are used at a distance of 1~5 to 20 inches from the photopolymerizable layer. Radiation fluxes of 10-10,000 ~w/cm2 are generally suitable for use.

' ~

' . :

3~

During the first exposure in preparing a positive polymer image, radiation having a wavelength of about 200 to about 380 nm i5 used, but it is not necessary that the wavelength be limited to this range. The radiaticn may have wavelengths over the entire range of about 200 to about 800 ; nm. In order to form an effective amount of inhibitor in the first exposure, at least about 20% of the radiation should be between about 200 and about 380 nm; and preferably at least about 30~ of the radiation is within this range.
The radiation used during the second exposure should be substantial]y limited to wavelengths greater than - about 380 nm. By "substantially limited" it is meant that the radiation is filtered to exclude greater than about 95~
of the radiation at about 380 nm and below, or is otherwise limited to radiation greater than about 380 nm. Preferably, the radiation in the second exposure has wavelengths substan-tially limited to greater than about 380 to about 800 nm, and most preferably about 400 to about 600 nm.
Although all of the photopolymerizable composit;`ons of this invention can be imaged with the second exposure radiation having wavelengths down to about 380 nm, shorter exposure times are generally experienced when wavelength$
up to about 420 nm are filtered out since many of the ni`tro-aromatic compounds absorb radiation that far out into the visible range. During the second exposure, a greater portion of the coating, typically the entire coated area, is struck by radiation with the result that free radicals are generated and polymerization takes place in the areas struck by radia-tion during the second exposure but not during the first exposure.

11~3~

The length of time for which the compositions are exposed to radiation may vary upward from fractions of a second. The exposure times wlll vary, in part, according to the nature and concentration of the polymerizable com-pound and initiator, and the type of radiation. Exposure can occur over a wide range of temperatures, as for example, from about -80C up to about +150C with selected composi-tions. Preferred exposure temperatures range from about ` -30 to about +35C. There is an obvious economic advantage to operating the process at room temperature.
; Imagewise exposure, for example in preparing printing plates, is conveniently carried out by exposing a layer of the photoactive composition to radiation through a process transparency; that is, an image-bearing trans-- parency consisting solely of areas substantially opaque and substantially transparent to the radiation being used where the opaque areas are substantially of the same optical den-sity; for example, a so-called line or halftone ne~ative or positive. Process transparencies may be constructed Qf any suitable materials including cellulose acetate film and ; polyethylene terephthalate film. An example is the prepa-ration of a positive working lithographic plate using the novel system of this invention. In a positive imaging i system, polymer is ultimately formed under the opaque areas of the process transparency; that is, the areas not struck by radiation passing through the transparency. Exposure of a plate coated with the nitroaromatic compound-containing photoactive composition to the full spectrum of a mercury-vapor lamp through a cellulose acetate or polyethylene ; 30 terephthalate film negative causes rearrangement of the '.

........

1~3~8~
nitroaromatic compound to a nitrosoaromatic compound in the radiation-struck areas. The areas struck by radiation during the first exposure will become non-image areas since no polymerization will be initiated in these areas.
Removal of the process transparency followed by a second exposure of the plate to radiation substantially limited to wavelengths greater than about 380 nm causes polymerization to occur in the areas which were not struck by radiation during the first exposure. Radiation of this wavelength is insufficiently absorbed by the nitroaromatic ! compound to rearrange it to a nitroso compound. The portions of the coating exposed in this manner become the polymeric image areas. Development of the doubly exposed plate provides a positive working plate suitable for use in lithography.
The exposed photosensitive layer may be developed by removing the unpolymerized, ethylenically unsaturated compound from the coatiny, leaving behind a polymeric replica of the original. This may be accomplished by heating the coating under conditions which result in some or all of the volatile components being vaporized, whereby the photo-polymer is left behind. The conditions of thermal develop-ment selected will depend upon the nature of the substrate, the volatility of the components to be removed, and the thermal stability of the components. AlternativeIy, devel-opment may be achieved by solvent washout, thermal trans-fer, pressure transfer, or differential adhesion of the exposed versus unexposed areas, and the like. Preferably, polymeric images are developed by solvent washout. Alternatively, they may be developed without washout by differential adhes;`on of . ~

~1~3~84 '.;
a pigment toner to the tacky unpolymerized areas.
The photopolymerizable compositions of this invention have the advantage that the same compositions used for the two-exposure positive-working applications described above may also be used to form negative polymeric images by the single exposure procedure. For this applica-tion, a layer of any of the photopolymerizable nitroaromatic compound-containing compositions described above is exposed through an image-bearing transparency to radiation substan-tially limited to wavelengths above about 380 nm until polymer is formed in the exposed areas. Unpolymerized por-tions of the photopolymerizable layer are then removed by solvent washout, or any of the other removal methods des-cribed above, to leave a negative polymeric image of the ,' pattern of the transparency employed.
The photopolymerizable compositions of this inven-tion have the very special advantage that the imagewi,se exposure of the positive-working process can be carried out using polyethylene terephthalate process transparencies.
This is possible because the ~itroaromatic compounds are sensitive to radiation of wavelength about 366 nm which is readily passed by polyethylene terephthalate fi,lm. Most of the previously known sources of ni,troso inhibitors in positive-working photopolymerizable compositions have' required activation by radiation having wavelengths beIow about 330 nm which is screened out by polyethylene tere-phthalate film. Thus, the present invention is useful with the latest, and most preferred, image-bearing transparencies.
The following examples further illustrate the " ~, :'' .

compositions and methods of this invention. All parts and percentages are by weight unless otherwise specified.
Example 1 Part A
To 3.5 ml of l,l,l-trimethylolpropane triacrylate containing about 200 ppm of hydroquinone and/or methylhydro-quinone inhibitor was added 0.153 g of o-nitrobenzyl alcohol and 0.021 g of phenanthrenequinone. A layer of the resulting clear solution was doctored onto each of two glass micro-scope slides, and the coated slides were covered with a thin film of polyethylene terephthalate and another microscope slide. The exposures below were carried out at room temperature.
Part B
One of the slide assemblies described above was exposed through an image-bearing transparency to the total radiation from a 275 watt G.E. sunlamp for one minute at a distance of six inches. This lamp gives radiation of wave-leng~s in the range of 280 to 600 nm with approximately 40%
20 in the range of 280 to 380 nm. The exposure caused formation of o-nitrosobenzaldehyde in the irradiated areas of the photopolymerizable layer. The image-bearing transparency was then replaced by a filter eliminating all radiation of wave-length below 400 nm (Dow Corning 3-73 filter) and the assembly was again exposed to the same lamp for one minute. The film of polyethylene terephthalate next to the photopolymerizable layer was then peeled off. The presence of a positive poly-meric image in the areas not exposed during the first exposure (e.g. areas under the opaque image on the transparency) was demonstrated by lightly dusting the layer with carbon black.
:

' 11~3~84 The carbon black adhered to the tacky unpolymerized areas containing o-nitrosobenzaldehyde inhibitor and left clear the remaining dry areas which had polymerized during the second exposure.
:; Part C
The second slide assembly was exposed by a sin~le exposure process through the image-bearing transparency used in Part B to radiation from the sunlamp used in Part B
which passed through the filter described in Part B to screen out all radiation below about 400 nm for one minute at a distance of six inches. The areas receiving the filtered radiation polymerized because phenanthrenequinone is an effective photoinitiator with radiation of wavelength about 410 nm. The film of polyethylene terephthalate next to the photopolymerizable layer was peeled off. The presence of a negative polymeric image in the areas struck by radiation coming through the transparency (e.g., in the areas not shielded by the opaque image on the transparency) was demonstrated by lightly dusting the layer with carbon black. The carbon black adhered to the tacky unexposed areas and left the remaining dry, polymerized areas clear.
Examples 2-18 ; ~ The following examples illustrate the usefulness of the inventive compositions in a process in which images are formed by photohardening and applying a colorant.
A stock solution was prepared containing the fol-lowlng lngredients:

..

' "

~3~
Component (Function)Amount (g) Pentaerythritol triacrylate (monomer)25 containing 0.1-0.25~ p-methoxyphenol (inhibitor) Methyl methacrylate polymer (binder, low mol. wt., density = 1.13 g/cc) 25 Triethylene glycol diacetate (plasticizer) 6.5 Methylene chloride (solvent) 508.5 Coating solutions were prepared using 10-g portions of the above stock solution, 2,7-di-_-butyl phenanthrenequinone as photoinitiator, and, in all except the control, an o-nitro-aromatic compound as photoinhibitor; the amounts of photo-initiator and photoinhibitor added, calculated as a percentage based on the total solids in the coating, are indicated in Table I.
Each coating solution was coated in duplicate at room temperature on the resin side of a 0.1 mm polyethylene terephthalate film which had been resin-coated by the proce-dure of U.S. Patent 2,779,68~, Example IV. The coating was dried at 55C and the dried coating was 0.0076 mm thick. A
; 0.025 mm cover sheet of polyethylene terephthalate was pres-sure laminated onto the coating at room temperature. One set of films was then exposed in a vacuum frame through a step wedge process transparency in which the transmittance of radiation between steps increases successively by a factor of ~ , to radiation above 380 nm to determine conventional photopolymerization speed. The radiation source was a 1000-watt, quartz-iodide lamp, placed 81.2 cm from the sample; the exposure times are listed in Table I.
Following exposure, the polyethylene terephthalate cover sheet was removed and a finely-divided, blue pigment :

':
toner was applied to the photopolymer surface. After removing excess toner with a cotton pad, a replica of the step wedge remained. That is, toner did not adhere to polymerized areas, but did to the tacky, unpolymerized portions. Thus, the number of clear, i.e. polymerized, steps found on the replica gave a relative comparison of the photopolymerization speed in the presence of the o-nitro-aromatic compound. The results are shown in Table below.
; 10 The second set of films was initially exposed in a vacuum frame through the step wedge process transpar-ency to radiation of wavelength between 310 and 430 nm with approximately 88% between 310 and 380 nmt this initial exposure source was a device containing eight Sylvania~
Blacklite Blue lamps (Model No. F15T8-BLB) 5.08 cm from the sample films. This exposure (see Table I for exposure time) was effective in producing aromatic nitroso inhibitor from the o-nitroaromatic compound in the film, in amounts inversely related to the optical densities of the steps on the step wedge. Consequentl~, when the process transparency was removed, and the sam~le irradiated with actinic radiation having a wavelength greater than 380 nm using the ~uartz-iodide lamp as above, photopolymerization occurred only where the concentration of nitroso inhibitor was negligible-to-low. Following removal of the cover sheet and toning as above, pigment adhered to the tacky, unpolymerized areas corresponding to those steps which contained a high concen-tration of nitroso inhibitor from the initial exposure, i.e., the lower numbered steps. The data observed in this two-exposure process are also summarized in Table I.

. ' .
~, :, ~

.. . . .

. . .

3~84 i H
~ a 0OOO0 0OOOO0O0OOO0O
U~
O
X ~ ~
E~ g ' V
h ,~
~ a) a) 0 4 ~1 O tq v v O ~P
E~
En .

o ~1 ~1 ~D ~ ~D ~ ~ ~ ~ ~1 ~ U~ ~1 ~ O
.. ~ ~ U~ V V V V V V
a)~ o u~
O ~ Q
Q U~
.,. O

H N ~ I u~ ~ ~ U ) Lf~ N
~:1 ~1 ~1 O O a~
a) ~ o\o . . . . . . . . . . . . .
.,1 _1~1~1 ~ ~ ~ ~t~
. _ . E~ O H
p Co Co Co (~ ~1 O Ir) o el~~r ~ ~ ~ ~r ~ t~ d' d' ~ CS~ I` ~ O~
... . . . . . . . . . . . . . .
I 0 ~1 0 0 0 ~1 ~1 o o~1 o o ~ o O
P~
~ .
., O
'~

S~ O
O ~ ~ ~
O I I ~ Ul rl 1~1 O X X a) x I , ~, o x ~ O ~ O ~ 0~ ~ ~ O
a) o: ~ ~ ~ ~1 ~ I I C~rl P ~ O o ~ x ~) a ~ I ~1 0 ~1 ,~ O N O ~~ ~1 0 E~ ~ ~ ~ O a~ ~ ~ e~ O

~1 ~ O ~1 ~ ~ ~ ~ O
:~ I O ~1) I ~ I a) I r-l O ~~1 X a N 11~ ~I N ~ O ~ 0 i4 ~ `
~U ~r a) d' ~ ~) ~) ~ O O O ~ a O O ~ O O (~J ~ O O ~ O ~ O O O
4 ~I N ~ 1 N rl ~1 ~1 1 4 1 ~1 ~1 i4 4 N
Z Z Q Z Z ~ ~ Z Z ~1 ~ ~I
N ~`I
~1) ~0 .,i, P~
~ O ~ ~ ~ ~ u~ ~ r~ co a~ o ~ ~ ~

. .

Table I Legend a = Number of full ~ step wedge steps toned, i.e., not polymerized, tacky.

b = Number of full ~ step wedge steps remaining clear, i.e., polymerized, nontacky.

C = (0 2N<~CH=N- C ( CH 3 ) 2 - CH 2 32-:
CH= ~ (CH3)2 d = ~

e = CH 5HH2 f = for both single and two step exposures.
Examples 19-20 The following two examples illustrate applica-bility of the compositions of this invention for preparing lithographic films. In these examples, the unpolymerized areas were completely removed, down to the base substrate, by washing out with an a~ueous alkali solution. The poly-merized portions, which were not dissolved by the solvent, were opaque since they contained a high concentration of colloidal carbon. Thus, the resulting film could serve as a photomask for further copy preparation, e.g., lithographic films.
Coating solutions were prepared containing the following ingredients (percentage based on total solids):

.~, Component Amount (g) %

Triethylene glycol dimethacrylate containing 100-300 ppm p-methoxyphenol inhibitor 1.05 33.8 - Copolymer (l:l)of styrene and maleic anhydride, partially esterified with iso-propanol; mol.wt. 1700, acid No. 270 1.18 37.9 Terpolymer of ethyl acrylate (56~), methyl methacrylate (37%) and acrylic acid (7%);
acid No. 76-85, mol.wt. ca. 260,000 0.30 9.5 Colloidal carbon 0.30 9.5 Triethylene gl~col diacetate 0.10 3.3 2,2' -Bis (2-chlorophenyl)-4,4! ,5,5'-tetrakis (3-methoxyphenyl) biimidazole 0.09 2.9 2-Mercaptobenzothiazole 0.009 0.29 2,5-Bis(4 ! -diethylamino-2'-methyl-benzylidene) cyclopentanone 0.036 1.2 Photoinhibitor 0.054 1.7 Methylene chloride 12.7 ml Duplicate coatings were prepared as in Examples 2-18 using a cover sheet of polyethylene terephthalate, 0.013 mm thick. The dried coating thickness was 0.0051 mm.
The negative-working mode for these examples was ascertained in a manner similar to the single exposure tests of Examples 2-18. Thus, one set of films was exposed for 90 seconds through a ~ step wedge, to radiation above 380 nm to determine conventional, negative-working, photopolymeriza-tion speed. The exposure device was a commercial nuArc~
vacuum frame (Model FT26L) containing a 2000 watt, pulsed xenon source, 43.2 cm from the polymerizable layer. Radiation of wavelengths less than 380 nm was excluded by inserting an appropriate filter between the source and sample; either a Wratten Light Filter lA or 2C, manufactured by Eastman Kodak Co., was used.
Following exposure, the cover sheet was removed and the unpolymerized steps were washed out with a dilute aqueous solution of Na2CO3 and NaHCO3, pH = 9.3, at 44.4C.

~1 ; The polymerized steps were readily visible due to the ; colloidal carbon dispersed through the photopolymer.
The positive-working mode of the compositions was determined by an initial 60-second exposure to radiation, <380 nm, from Blacklite Blue lamps in the configuration described above, through the step wedge process transparency of Examples 2-18 followed by a 90-second exposure to actinic radiation, >380 nm, from the filtered pulsed xenon source described above without the step wedge, followed by aqueous alkali washout development as described above. The data observed are shown in Table II.

Table II
Positive/Negative-Working Photopolymerization Speed Positive Negative Ex. No. PhotoinhibitorModea Modeb Control -- -- 8 19 2-Nitro-5-methoxy-` benzyl alcohol 4 7 alpha-Phenylimino-2-nitrotoluene 3 5 , a = Number of full ~ step wedge steps washed off and clear i.e., not polymerized.
b = Number of full ~ step wedge steps not washed off, i.e. polymerized and black.

Equally satisfactory results were obtained on laminating the above, or similar, compositions at 65C to drafting film substrates as described in U. S. 2,964,423. In this manner, either positive- or negative-working, wash-off, sharp, black engineering reproduction films are produced.
; 30 Example 21 This example illustrates the applicability of the compositions of this invention for making photoresists.

,~

' ~3~

A coating composition was prepared containing the following ingredients (percentages based on total solids):

Component Amount (%) Methyl methacrylate polymer (low mol. wt., density = 1.13 g/cc) 50.22 Trimethylol propane triacrylate (monomer) containing 235-265 ppm hydroquinone (inhibitor) 33.76 2,2-Bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl biimidazole 8.66 Triethylene glycol diacetate 2.68 2-Mercaptobenzothiazole 0.43 2,5-Bis(4'-diethylamino-2'-methylbenzylidene) cyclopentanone 1.74 2-Nitro-4,5-dimethoxybenzaldehyde 2.60 ' These ingredients were added to enough methylene chloride to give a 10% solids solution. This solution was coated onto 0.025 mm thick polyethylene terephthalate using a : doctor knife and air dried; the dried coating thick-ness was about 0.038 mm. This layer was then laminated to a piece of copper clad, epoxy-fiber glass board substan-tially as described in U.S. 3,469,982, Ex. I, lines 46-55.
The positive~ and negative-working modes were then evaluated by exposing the laminate, through a ~ step wedge process transparency, through the polyester film side, as described in Examples 2-18. The one-step exposure was for 2 minutes to a quartz iodide lamp. The two-step exposures were for one minute to radiation having wave-lengths ~380 nm, followed by 2 minutes to actinic radiation ; 30 having wavelengths ~380 nm. After exposure, the polyester film was removed by stripping, and the unpolymerized portions '' -~3~3~4 of the replica were dissolved away in a 15-sec. spray of l,l,l-trichloroethane, leaving a protective, polymeric resist on the copper surface. In the single-exposure, negative-working mode, areas corresponding to steps 1-6 were polymerized (a resist), while areas under the higher steps were not. In the two-exposure, positive-working mode, however, areas of the replica corresponding to steps 1-4 of the step wedge were clean copper, while the higher steps were polymerized (a resist).
The unprotected copper in both of the above, as - taught in U.S. 3,469,982, could be etched with ferric chloride. Then, following removal of the resist, e.g.
with CH2C12, printed circuit boards would result, one a positive and the other a negative of the step wedge target.
. .
Examples 22-24 .
These examples illustrate the applicability of compositions of this invention containing different photo-, inhibitors for preparing lithographic films.

A stock solution (10% solids) was prepared con-taining the following ingredients:
:.
., .

-~L~`3~
Component Amount (g) Trimethlolpropane triacrylate (monomer) containing 235-265 ppm hydroquinone (inhibitor) 1.64 Triethylene glycol dimethacrylate (monomer) containing 235-265 ppm hydro~uinone (inhibitor) 13.82 Copolymer (1:1) of styrene and maleic anhydride, partially esterified with isopropanol; mol. wt. 1700, acid No.
270 24~18 Terpolymer of ethyl acrylate (56~), methyl methacrylate (37~), and acrylic acid (7~); acid No. 76-85, mol. wt. ca. 260,000 11.4 Colloidal carbon 11.4 Methylene chloride 541.3 2-Ethoxyethanol 20.5 Coating solutions were pre~ared using the above stock solution, 2,2-bis(2-chlorophenyl)-4 7 4' ,5,5'-tetraphenyl biimidazole as the photoinitiator, 2,5-bis(4'-diethyl-amino-2'-methylbenzylidene)cyclopentanone as sensitizer, and a photoinhibitor or mixture of photoinhibitors as indicated in Table III. The amounts of photoinhibitor, ~ photoinitiator and sensitizer are reported in percentages ; based on total solids content.
Duplicate coatings were prepared by a procedure similar to that used in Examples 19-20. The coatings were air-dried at room temperature for 30 minutes; the polyethy-lene terephthalate cover sheet was laminated to the coating 30 at 65.6C at a rate of 0.91 meters/minute. Dried coating .~.. .
. ~
''' ' - ' ' "' ' ' ' " ' ' ' ~ 1~3 :' thicknesses were approximately 0.005 mm.
The negative-working mode was ascertained as ` described in Examples 19-20, using a nuArc~ 2000 watt xenon ; source and a Wratten 2C filter to exclude raaiatiGn at ~avelensths les~ than 380 nn; exposure times are shown ir.
; Table III.
Following exposure, the cover sheet was removed and the unpolymerized steps were washed out with a dilute aqueous solution of Na2CO3 and NaHCO3, pH - 9.3, at 25.5C, and then rinsed with water at 32C, accompanied by light rubbing with a sponge. The number of steps polymerized '~ are reported in Table III.
The positive-working mode of the compositions was determined by an initial exposure through the step wedge process transparency of Examples 2-18 to unfiltered radia-tion from the nuArc~ 2000 watt xenon source containing approximately 25% radiation below 380 nm, followed by an overall exposure to actinic radiation limited to wavelengths above 380 nm from the pulsed xenon source described above with a UV filter, followed by wash out using an aqueous alkali solution in which the unpolymerized areas were completely removed down to the base substrate. The polymer-ized portions, which were not dissolved by the solvent, were opaque since they contained a high concentration of colloidal carbon. The initial exposure time is shown in Table III.
The exposure time for the single-exposure, negative-working mode was identical to the second exposure time for the two-exposure, positive-working process, as indicated in Table III.

~5C3 ,.
' ~ o o o .~ W ~ ~
N d ~ l 1~ r ~ i N ~ ~ ~ ~ ~ ~ 5 O~ ~ C D 1l ; 9 &IO~ ~,~, o 0~ ~
? u~ Ir~
~ l ~

Q~ 1~ 1 ~ &O &o ~
~ ~ ~ o ~ 0 ~ o~
, ' ~ ~ 3 ~ o 0 ~ ~0 ~0 ~0 ~0 ~ C~ ' ~ l 1 ~c ~ ~ ~ ~
~ 11 U ~

K N ~ ~

- 40 ~

3~

Example 2S
This example illustrates the applicability of compositions of this invention for preparing positive-working lithographic printing plates, similar to those - described by Alles in U.S. Patent 3,458,311.
; A photosensitive composition was prepared containing the following ingredients:
Component Parts Methyl methacrylate/methacrylic acid copolymer (9:1) 36.0 10 Trimethylol propane triacrylate (monomer) containing 235-265 ppm hydroquinone (inhibitor)35.3 ; Di(2-ethylhexyl)phthalate 12.3 ; 2,2'-Bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl biimidazole 10.0 ; 4,S-Dimethoxy-2-nitro-a-phenyliminotoluene 3.1 ; 2,5-Bis(4'-diethylamino-2'-methylbenzylidene) cyclopentanone 1.5 C.I. Solvent Red 109 1.5 Leuco Crystal Violet 0.3 A coating solution was prepared by dissolving the ingredients in enough 2-ethoxyethanol to yield a solution containing 18.6% solids. The solution was then spin coated on an anodized aluminum plate; after drying at 38C, the dried photopolymerizable coating weight was 20.4 mg/dm2.
After being cooled to room temperature, the coated plate was then overcoated with an oxygen-barrier polymer using an aqueous solution (10% solids) of polyvinyl alcohol (medium viscosity, 87-89~ hydrolyzed). After drying also at 38C, the overcoat weight was 18.9 mg/dm2.
The negative- and positive-working modes for the l~G3~P~4 plate were then evaluated by exposure, through a ~ step wedge process transparency, through the overcoat layer, as described in Examples 22-24; the exposure times are shown in Table IV.
Following exposure, the overcoat layer and the unpolymerized steps were washed out (developed) using a solution of sodium carbonate (1.8%) and diethyleneglycol monobutyl ether (8%) in distilled water at 22C.
Development was complete in 60 seconds at 25C. The plate was then rinsed with water, lightly rubbed with a cotton pad, and blotted dry. The results obtained are shown in Table IV.
The polymerized areas on the developed plate accepted conventional lithographic greasy inks and the clear areas of the aluminum support were readily wetted with water to yield a high quality lithographic plate.
Example 26 Example 25 was repeated except that the photo-sensitive composition contained,in addition to the components 20 present in Example 25, 0.04 part of 1,4,4-trimethyl-2,3-diazobicyclo(3.2.2)non-2-ene-N,N'-dioxide as a supplement to the hydroquinone thermal inhibitor. The resulting lithographic printing plate, containing a small amount of superior thermal inhibitor, exhibited increased shelf life and improved thermal stability when compared with the plate of Example 25. The photopolymization speeds obtained are shown in Table IV.

'-:

~ 3~4 TABLE IV
Positive/~egative-Working Photopolymerization Speed Example Exposures tsec.) Positive Negative ~o. <380 nm >380 nm Modea Modeb 26 45 90 3/7 7/lO

a = Number of full ~ step wedge steps that do not accept greasy ink, i.e., not polymerized/first step that accepts ink to maximum density, i.e., totally polymerized.
b = Number of full ~ step wedge steps that accept greasy ink to maximum density, i.e., totally polymerized/last step to accept ink, i.e., partially polymerized.
Example 27 This example illustrates the applicability of a composition of this invention for preparing a positive-working relief printing plate similar to those described by Munger in U.S. Patent 2,923,673.
A photosensitive composition was prepared containing the following ingredients:

Component Amount (g) Styrene/maleic anhydride copolymer, partially esterified with l_butyl alcohol, acid No. 180, average mol. wt. 20,000, softening point 210C 66.25 Trlethylene glycol diacrylate (monomer)containing 0.044 g of p-methoxyphenol (inhitibor) 22.0 2-Ethylhexyl-diphenyl phosphate ll.0 2-Nitro-4,5-dimethoxybenzaldehyde 0.3 2,6-Di-t-butyl-4-methylphenol 0.2 p-Methoxyphenol 0.15 30 Phenanthrenequinone 0.1 ., ~1&`3~

After blendinq the above ingredients, the composition was placed on a rubber mill preheated to 100C, and milled for about 5 minutes to yield a homogeneous mass.
The mass was then pressed for 2 minutes onto an anodized -~ aluminum plate using a laminating press at 118C and 40,000 psi to yield a photopolymerizable layer or film ; 0.040-inch (0.1 cm) thick. During lamination a flame-` treated film of polyethylene terephthalate, 0.004-inch thick (0.01 cm), was applied as a cover sheet.
The resulting element was then placed in a vacuum frame and the polymer surface was brought into contact with a line process negative. The element was then exposed in a positive-working mode as described in Examples 19-20, except that the imagewise exposure to radiation, <383 nm, from Blacklite Blue lamps was 4.5 minutes. The process transparency was then removed, and the element given an overall exposure for 4 minutes to actinic radiation, ~380 nm, from the filtered pulsed xenon source as described in Examples 19-20.
Following exposure, the cover sheet was removed and the element was developed for 3 minutes in a spray of aqueous NaOH (0.04 N~ at 41C. A positive relief image was obtained with raised photopolymeric areas corresponding to the opaque areas of the process negative. The relief wells were 0.025 inch t0.06 cm) in depth, the wells corresponded to the transparent areas of the process negative.
Example 28 This example illustrates the applicability of a composition of this invention for preparing a positive-working, thin-film resist particularly useful with ,, ~ - 44 -' ' , . ' ' '" ~ -' --: ~ ~(!3 , microelectronic, semiconductor wafers.
A photosensitive composition was prepared ~ containing the following ingredients:
-~ Component Parts Methyl methacrylate/methacrylic acid copolymer (9:1) 59.5 Trimethylol propane triacrylate (monomer) containing 235-265 ppm hydroquinone (inhibitor) 24.5 2,2'-Bis(2-chlorophenyl)-4,4'-5,5'-tetraphenyl biimidazole 6.64 10 Mixture of triethylene glycol dicaproate and triethylene glycol dicaprylate6.64 2-Nitro-4,5-dimethoxybenzaldehyde 1.82 2,5-Bis(4'-diethylamino-2'-methylbenzylidene) cyclopentanone 0.91 A coating solution of the above ingredients was prepared by dissolving them in enough 1,1,2-trichloroethane to yield a solution containing 15% solids. This solution was then coated onto a silicon wafer bearing a siiica (SiO2) surface 0.0012 mm in depth. The coating was made using a spin coater at room temperature; when the coater was operated at about 2500 r.p.m. for 45 seconds, a dry photopolymerizable layer or film about 0.0001-inch (0.0025 mm) thick was obtained.
The coated wafer was then imagewise exposed for 4-6 seconds to radiation, ~380 nm, through a resolution test target (1951 U.S. Air Force) to a 200-watt, 4-inch, high ; pressure mercury arc illuminator (Oriel~ Model No. 8010) at a distance of about 13 inches (33 cm) in a vacuum frame.
The test target was then replaced with a filter for ultra-violet radiation (as described in Examples 19-20) and the .

' ~3~
photopolymerizable layer was exp~sed for 4 minutes to radiation, ~380 nm, rrom the Oriel~ source. The nonpoly-merized portions o~ the layer, corresponding to the trans-parent area~ of the test target, were removed under 20 lbs/in2 (1.41 kg/sq cm) nitrogen pressure via spray development u~ing a mixture of l,l,l-trichloroethane and lsopropanol (90/10 by volume) for 3Q seconds, followed by a 5-secon~ spray wlth the above mlxture plu8 naphtha, and ~lnally wlth a 10-second spray of naphtha alone. The re~ultlng re~lst exhlbited a resolution of 228 l~ne pairs/
mm, an exact replica of the maxlmum resolution provlded by the te~t target.
After baking the r0sist one hour at 120C, the resist-protected sillca-coated ~ilicon wa~r was etched 12 mlnutes at room temperature; the etchant was composed of 210 ml of aqueous (40%) ammonium fluorlde, 30 ml of concentrated (49.2%) hydrofluoric acid, and 15 ml of aque~u~ (0.02~) fluorocarbon ~urfactant FC-95* (Product of Mlnn. Mlnlng & Mfg. Co.). The etched wafer was then rlnsed wlth water and drled. The protectlve re~lst wa~
then removed (~tripped) wlth Caro~ acld at 140-150C for 30 mlnutes to yield a ~illca pattern on the silicon wafer.

* denote~ trade mark .

:
SUPPIEMENTARY DISCLOSURE

Further to the photopolymerizable composition des- -cribed hereinbefore, it has been found that the preferred nitro-aromatic compounds of the for~ula Rl . .
. 2 R \ ~ N2 R3 ~ ~ CHR5R6 R
in the composition include those wherein Rl ls H or methoxy, R2 and R3 are H, alkoxy of 1 to 6 carbons, polyether o~ 2 to 18 carbons and 2 to . 10 10 oxygens, alkyl of 1 to 6 carbons, or acetoxy, or R2 and R3, taken together, are -OCH20- or ~ t CH2CH20 ~-R4 is H;

R5 is H, alkyl of 1 to 6 carbons, alkoxy of 1 to 6 carbons, or phenyl, R6 is OH, alkoxy of 1 to 6 carbons, or ; phenoxy substituted with up to three chlorines, alkyls of 1 to 6 carbons, or : 20 alkoxys of 1 to 6 carbons, or R5 and R6, taken together, are =0, -NC6H5, Rl ., ~ 02N~2 aN(Hydrocarby:Lene)N=CH R3 in which the hydrocarbylene group is of 2 to 6 carbons, =N(alkyl) in which alkyl is n-alkyl of 1 to 6 carbons or .~

~3~

t-butyl, or - C = C - NH - C = C - in which R8 and R9 are alike and are H or methyl, and R7 and R10 are alike and are -CN, -COR
in which Rll is methyl or ethyl, or -COORl in which R12 is methyl or ethyl.
Particularly preferred, because the instant com-positions exhibit high imaging speeds, are nitroaromatic compounds wherein Rl and R4 ~re H;
R2 and R3 are alike and are alkoxy o~ 1 to 6 carbons, R5 is H, or alkyl of 1 to 6 carbons, R6 is alkoxy of 1 to 6 carbons, or phenoxy substituted with up to two alkoxys of 1 to 6 carbons; or R5 and R6, taken together, are =0 or =NC6H5.
ThP present invention is further illustrated by the following example:
Example 29 A photosensitive composition was prepared containing . the following ingredients:
Component~ Parts Methyl methacrylate/methacrylic acid copolymer (9:1) 60.86 Trimethylolpropane triacrylate (monomer) containing 235-265 ppm hydroquinone inhibitor 21.31 Triethylene glycol dicaproate and triethylene glycol dicaprylate 6.75 2-(o-chlorophenyl)-4,5-diphenylimidazolyl dimer6.18 1-(2'-nitro-4'~5'-dimethoxy)phenyl-1-(4-methoxy-phenoxy)ethane 2.81 .~

. .

.

~3~34 Components Parts .
2~5-bis(4'-diethylamino-2'-methylbenzylidene)- -cyclopentanone 0~90 C. I. Solvent Red 109 0.95 Leuco Crystal Violet 0.19 1,4,4'-trimethyl-2,3-diazabieyclo(3.2.2)non-2-ene-N,N'-dioxlde o.o5 A coating solution was prepared by dissolving the components in enough 2-ethoxyethanol to obtain a solu-tion containing 19% solids. The solution was spin-coated onto an anodized aluminum plate; after drying at 38C, the dried photopolymerizable coating weight was 20 mg~dm2. After the plate was cooled to room temperature, it was overcoated with an oxygen-barrier polymer using an aqueous solution (10~ solids) of polyvinyl alcohol (medium viscosity, 87-89%
hydrolyzed). After drying at 38C, the overcoat weight was 19 mg/dm .
The negative- and positive-working modes for the plate were then evaluated by exposure, through a 3~2 step wedge tran~parency in contact with the plate in a vacuum ~rame, ~or 20 units with a 2 Kw Hg photopolymer lamp in a Berkey Askor unit where the distance from plate to bulb is 96.5 cm.
Part of the plate was blocked off with a piece of black poly-ethylene fllm. The transparency was then removed and placed in the area where the black film had been, a UV filter that transmits light above 420 nm was placed over the plate, and an overall exposure to visible light with a 100 unit exposure with the same source was made. The plate was developed as in Example 25 for 30 seconds at 22~C, rinsed with water while lightly rubbing with a cotton pad, and blotted dry. me ' ~,.

i~3~1~4 positive image consisted o~ two completely unpolymerized steps (steps 1 and 2). The negative image consisted of an image where the last partially polymerized ~tep was step 12.
The polymerized areas on the developed plate accepted conventional li~hographic greasy inks and the clear areas o~ the aluminum support were readily wetted with water to yield a high quality positive and negative working lithographic plate.

'. '~
: . ~
. :

Claims (24)

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

1. A photopolymerizable coating composition in which the photosensitive components consist essentially of:
(a) normally nongaseous, ethylenically unsaturated compound selected from the group consisting of unsaturated esters of polyols, unsaturated amides, vinyl esters and unsatu-rated aldehydes, said compound being capable of addition polymerization by free-radical initiated chain propagation, (b) about 0.004 to about 0.7 part by weight, per part of component (a), of nitroaromatic compound of the formula wherein R1, R2, R3 and R4, alike or different, are H, OH, halogen, NO2, CN, alkyl of 1 to 18 carbons, alkoxy in which the alkyl is of 1 to 18 carbons, aryl of 6 to 18 carbons, benzyl, halogen-substituted phenyl, polyether of 2 to 18 carbons and 1 to 6 oxygens, dialkylamino in which each alkyl is of 1 to 18 carbons, thioalkyl in which the alkyl is of 1 to 18 carbons, or thioaryl in which the aryl is of 6 to 18 carbons, or any adjacent two of R1, R2, R3 and R4, taken together, are the residue of a second benzene ring fused onto the benzene nucleus of said nitroaromatic compound, with the proviso that not more than one of R1, R2, R3 and R4 is OH or NO2, R5 is H, alkyl of 1 to 18 carbons, halogen, phenyl, or alkoxy in which the alkyl is of 1 to 18 carbons, R6 is H, OH, alkyl of 1 to 18 carbons, phenyl, or alkoxy in which the alkyl 18 of 1 to 18 carbons, with the proviso that only one of R5 and R6 is H, or R5 and R6 together are =O, =CH2, -O-CH2-, =NC6H5, =NC6H4N(alkyl)2 in which each alkyl is of 1 to 18 carbons, -O-C2H4-O-, in which the hydrocarbylene group is of 1 to 18 carbons, or in which R8 and R9, alike or different, are H or alkyl of 1 to 4 carbons, and R7 and R10, alike or different, are -CN, -COR11 in which R11 is alkyl of 1 to 5 carbons, or -COOR12 in which R12 is alkyl of 1 to 6 carbons, alkyl of 1 to 6 carbon atoms interrupted by an oxygen atom, alkenyl of 2 to 5 carbons, or alkynyl of 2 to 5 carbons, or R7 and R8 together, or R9 and R10 together, complete a 6-membered carbocyclic ring containing a keto group, and (c) about 0.001 to about 10 parts by weight, per part of component (a), of an organic, radiation-sensitive, free-radical generating system, activatable by actinic radiation that does not significantly rearrange the nitroaromatic compound to an inhibitor of free-radical polymerization.

2. The composition of Claim 1 in which component (c) has at least one component having an active radiation absorption band with a molar extinction coefficient of at least about 50 within the range of greater than about 380 to about 800 nm.

3. The composition of Claim 2 which also contains about 10 to about 80% by weight, based on the total solids content, of a polymeric binder selected from the group consisting of vinyl addition polymers containing free carboxylic acid groups, polyacrylate esters and poly-.alpha.-alkyl-acrylate esters.

4. The composition of Claim 3 in which component (a) is an unsaturated ester of a polyol and an .alpha.-methylene carboxylic acid selected from the group consisting of acrylic and methacrylic acids.

5. The composition of Claim 4 in which component (c) is present in the amount of about 0.01 to about 2 parts by weight per part of component (a) and includes a compound selected from the group consisting of phenanthrenequinones and 2,4,5-triarylimidazole dimers.

6. The composition of Claim 5 in which component (b) is present in the amount of about 0.04 to about 0.15 part by weight per part of component (a) and any alkyl groups in component (b) are of 1 to 6 carbons.

7. The composition of Claim 6 in which component (c) has at least one component that has an active radiation absorption band with a molar extinction coefficient of at least about 50 within the range of about 400 to about 600 nm.

8. The composition of Claim 7 in which component (a) is trimethylol propane triacrylate, component (b) is 2-nitro-4,5-dimethoxybenzaldehyde and component (c) is 2,2-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl biimadazole.

9. Method of making a positive polymeric image on a substrate which comprises (1) coating the substrate with the photopolymerizable composition of Claim 1, (2) imagewise exposing a portion of the photopolymer-izable coating through an image-bearing transparency to radiation at least about 20% of which has a wavelength of about 200 to about 380 nm, thereby rearranging at least some of the nitroaromatic compound to polymerization inhibiting nitroso-aromatic compound, and (3) subjecting the coating to a second exposure whereby a portion greater than that portion exposed during the imagewise exposure is exposed to radiation substantially limited to wavelengths greater than about 380 nm, whereby a positive polymeric image is formed in the areas exposed during the second exposure but not exposed during the imagewise exposure, and (4) developing the image formed in step (3).

10. The method of Claim 9 in which at least about 30% of the radiation in the imagewise exposure has a wave-length of about 200 to about 380 nm, the radiation in the second exposure has wavelengths substantially limited to greater than about 380 to about 800 nm, and component (c) has at least one component having an active radiation absorption band with a molar extinction coefficient of at least about 50 within the range of greater than about 380 to about 800 nm.

11. The method of Claim 10 in which the positive polymeric image formed in step (3) is developed by removing the nonpolymerized portion of the photopolymerizable coating in the areas exposed to the imagewise exposure radiation.

12. The method of Claim 10 in which the image formed in step (3) is developed by differential adhesion of a pigment toner to the unpolymerized portion of the photopolymerizable coating in the areas exposed to the imagewise exposure radiation.

13. The method of Claim 10 in which the photo-polymerizable composition also contains about 10 to about 80%
by weight, based on the total solids content, of a polymeric binder selected from the group consisting of vinyl addition polymers containing free carboxylic acid groups, polyacrylate esters and poly-.alpha.-alkylacrylate esters.

14. The method of Claim 13 in which component (a) is an unsaturated ester of a polyol and an .alpha.-methylene-carboxylic acid selected from the group consisting of acrylic and methacrylic acids.

15. The method of Claim 14 in which component (c) of the photopolymerizable composition is present in the amount of about 0.01 to about 2 parts by weight, per part of component (a), and includes a compound selected from the group consisting of phenanthrenequinones and 2,4,5-triaryl-imidazole dimers.

16. The method of Claim 15 in which component (b) of the photopolymerizable composition is present in the amount of about 0.04 to about 0.15 part by weight, per part of component (a) and any alkyl groups in component (b) are of l to 6 carbons.

17. The method of Claim 16 in which the radiation in the second exposure has wavelengths substantially limited to about 400 to about 600 nm, and the component (c) has at least one component that has an active radiation absorption band with a molar extinction coefficient of at least about 50 within the range of about 400 to about 600 nm.

18. The method of Claim 17 in which the positive polymeric image is developed by removing the nonpolymerized portion of the photopolymerizable coating in the areas exposed to the imagewise exposure radiation.

19. The method of Claim 17 in which the image is developed by differential adhesion of a pigment toner to the unpolymerized portion of the photopolymerizable coating in the areas exposed to the imagewise exposure radiation.

20. The method of making a negative polymeric image on a substrate which comprises (a) coating the substrate with the photopolymerizable composition of Claim 1, and (b) imagewise exposing a portion of the photopolymer-izable coating through an image-bearing transparency to radiation substantially limited to wavelengths greater than about 380 nm, whereby a negative polymeric image is formed in the areas exposed to the radiation, and (c) developing the image formed in step (b).

21. The composition of Claim 1 in which component (a) has a boiling point above 90°C and contains 2-5 terminal ethylenic groups.

CLAIMS SUPPORTED BY THE SUPPLEMENTARY DISCLOSURE

22. A photopolymerizable coating composition in which the photosensitive components consist essentially of:
(a) normally nongaseous, ethylenically unsaturated compound selected from the group consisting of unsaturated esters of polyols, unsaturated amides, vinyl esters and unsatu-rated aldehydes, said compound being capable of addition polymerization by free-radical initiated chain propagation, (b) about 0.004 to about 0.7 part by weight, per part of component (a), of nitroaromatic compound of the formula wherein R1, R2, R3 and R4, alike or different, are H, OH, halogen, NO2, CN, alkyl of 1 to 18 carbons, alkoxy in which the alkyl is of 1 to 18 carbons, aryl of 6 to 18 carbons, benzyl, halogen-substituted phenyl, polyether of 2 to 18 carbons and 1 to 10 oxygens, dialkylamino in which each alkyl is of 1 to 18 carbons, thioalkyl in which the alkyl is of 1 to 18 carbons, or thioaryl in which the aryl is of 6 to 18 carbons, or any adjacent two of R1, R2, R3 and R4, taken together, are the residue of a second benzene ring fused onto the benzene nucleus of said nitroaromatic compound, or R2 and R3, taken together are -OCH2O- or -O-(CH2CH2O)5-, with the proviso that not more than one of R1, R2, R3 and R4 is OH or NO2, or R2 and R3, alike or different, are acetoxy, R5 is H, alkyl of 1 to 18 carbons, halogen, phenyl, or alkoxy in which the alkyl is of 1 to 18 carbons, R6 is H, OH, alkyl of 1 to 18 carbons, phenyl, phenoxy substituted with up to three chlorines, or alkoxy in which the alkyl is of 1 to 18 carbons, with the proviso that only one of R5 and R6 is H, or R5 and R6 together are =O, =CH2, -O-CH2-, =NC6H5, =NC6H4N(alkyl)2 in which each alkyl is of 1 to 18 carbons, -O-C2H4-O-, =N(alkyl) in which alkyl is n-alkyl of 1 to 6 carbons or t-butyl, in which the hydrocarbylene group is of 1 to 18 carbons, or in which R8 and R9, alike or different, are H or alkyl of 1 to 4 carbons, and R7 and R10, alike or different, are -CN, -COR11 in which R11 is alkyl of 1 to 5 carbons, or -COOR12 in which R12 is alkyl of 1 to 6 carbons, alkyl of 1 to 6 carbon atoms interrupted by an oxygen atom, alkenyl of 2 to 5 carbons, or alkynyl of 2 to 5 carbons, or R7 and R8 together, or R9 and R10 together, complete a 6-membered carbocyclic ring containing a keto group, and (c) about 0.001 to about 10 parts by weight, per part of component (a), of an organic, radiation-sensitive, free-radical generating system, activatable by actinic radiation that does not significantly rearrange the nitroaromatic compound to an inhibitor of free-radical polymerization.

23. The composition of Claim 22 in which in the nitroaromatic compound:

R1 is H or methoxy;
R2 and R3 are H, alkoxy of 1 to 6 carbons, polyether of 2 to 18 carbons and 2 to 10 oxygens, alkyl of 1 to 6 carbons, or acetoxy;
or R2 and R3, taken together, are -OCH2O- or -O?CH2CH2O?5;
R4 is H;
R5 is H, alkyl of 1 to 6 carbons, alkoxy of 1 to 6 carbons, or phenyl;
R6 is OH, alkoxy of 1 to 6 carbons, or phenoxy substituted with up to three chlorines, alkyls of 1 to 6 carbons, or alkoxys of 1 to 6 carbons;
or R5 and R6, taken together, are =O, =NC6H5, in which the hydrocarbylene group is of 2 to 6 carbons, =N(alkyl) in which alkyl is n-alkyl of 1 to 6 carbons or t-butyl, or in which R8 and R9, are alike and are H or methyl, and R7 and R10 are alike and are -CN, -COR11 in which R11 is methyl or ethyl, or -COOR12 in which R12 is methyl or ethyl.

24. Method of making a positive polymeric image on a substrate which comprises (1) coating the substrate with the photopolymerizable composition of Claim 23, (2) imagewise exposing a portion of the photopolymer-izable coating through an image-bearing transparency to radiation at least about 20% of which has a wavelength of about 200 to about 380 nm, thereby rearranging at least some of the nitroaromatic compound to polymerization inhibiting nitroso-aromatic compound, and (3) subjecting the coating to a second exposure whereby a portion greater than that portion exposed during the imagewise exposure is exposed to radiation substantially limited to wavelengths greater than about 380 nm, whereby a positive polymeric image is formed in the areas exposed during the second exposure but not exposed during the imagewise exposure, and (4) developing the image formed in step (3).