CA1054425A - Method of producing positive polymer images - Google Patents

Abstract

METHOD OF PRODUCING POSITIVE POLYMER IMAGES Positive polymer images are produced on substrates having applied thereto a layer of photopolymerizable composition containing (1) a non-gaseous ethylenically unsaturated compound capable of polymerization by free-radical initiated chain propagation, (2) a dinitroso compound which is a noninhibitor of free-radical polymerization and is photochemically converted by ultraviolet radiation to an inhibitor of free-radical polymerization, and (3) a photoactivatable organic free-radical generating system. These images are produced by imagewise exposing a portion of the photopolymerizable layer through a transparency bearing an opaque image to ultraviolet radiation that converts the dinitroso compound to an inhibitor of free-radical polymerization, exposing a greater portion of the photopolymerizable layer, including the area exposed to the imagewise exposure radiation, to actinic radiation that activates the freeradical generating system but does not convert the dinitroso compound to an inhibitor of free-radical polymerization, whereby a positive polymeric image is formed in the areas not exposed to the imagewise exposure radiation.

Description

1~5~4Z5 BACKGROUND OF T~IE INVENTION
(1) Field of the Invention This inven~ion relate~ to a method of producing positive images using photopolymerizable compositions contain-ing compounds having a din~troso group, and more particularly to such a method lnvolving two expo~ures to radiation.

(2) Description o~ the Prior Art It is known that cer~ain aromatic nitroso compounds are useful as polymerization inhibltors. For example, Hungarian Patent 150,550 (19~3) describes the use of p-aminonitrosobenzene and a-nitroso-~-naphthol as inhibitors ~or the free-radical polymerization of styrene. Similarly3 the use o~ 4-nitrosophenol, 1,4-dinltrosobenzene, nitroso-resorcinol, p-nitrosodimethylaniline and other nitroso compounds as inhibitors for styrene and vinyl acetate poly-merizations is described by Hartel ln Chimia (Aarau), 19, p. 116 (1965), and Tyudesh et al., in Kinetics and Catalysis (USSR), 6, p. 175-181 (1965).
It is also known that al~hatic nitroso dimers can be dissociated to nitroso monomers, either thermally or by irradiation with short wavelength ultraviolet radiation (Bluhm and Weinstein, Nature, 215, p. 1478, 1967).
SUMMARY OF THE INVENTION
.
It has now been discovered that positive polymer images can be produced on a ~ubstrate by the process which comprises ~a) applying to the substrate a layer of photo-polymerizable composition containing (1) non-gaseous ethylenically unsaturated compound capable of addition polymerization ~y free-radical initiated chain propagation, - 2 ~:

' ' 10~44~:~
(23 about 0.1 10~ by weight, based on the photopolymeri-zable composition, of a compound contalning a dinitroso group which ~s a noninhibitor of free-radical polymeriza-tion and is photochemically converted by ultraviolet radiatlon to an inhibitor of ~ree-radical polymerization, and (3) about 0.001-1.0 part by weight, per part of un-saturated compound, of an organic free-radical generating system activatable by actinic radiation -that does not convert the dinitroso compound to an inhibitor of free-radical polymerization, (b) imagewise e~posing a portion of the photo-polymerizable layer through an image-bearing transparency consisting solely of substantially opaque and substanti- :.
ally transparent areas to ultraviolet radiation that converts the dinitroso compound to an inhibitor of free-radical polymerization, thereby inhibit~ng photopoly-merization in the exposed areas~
(c) exposing a greater portion of the photo-polymerizable layer, including the areas exposed to the imagewise exposure radiation, ~o actinic radiation that activates the free-radical generating system but does not convert the dinitroso compound to an inhibitor of free-radical polymer~zation, whereby a positive polymeric image is formed in the areas not exposed to the imagewise exposure radiation.
DETAILED DESCRIPTION OF THE INVENTION
In accordance wi-th the present invention positi~e polymeric images are produced by a two-exposure process.
The firs~ exposure ls an imagewise exposure which 3o photochemically produces polymerization inhi~itor in the 1: . .
54~42S
- exposed areas and the second exposure is an overall act~nic radiation exposure which causes photopolymerlzation ln the areas not exposed to the imagewise exposure radiation.
Thi~ invention is based on the fact that com-. . .
pounds containing dinitroso groups are not free-radical polymerization inhibitors, but are photochemically con-verted to inhibitors of free-radical polymerization by ex-posure to ultraviolet radiation having wavelengths o~ about 2000-3400A,and in some cases about 2000-3800A. The actinlc radiation exposure is conducted using radiation that in-cludes wa~elengths which activate ~he ~ree-radical genera-ting system but does not include waveleng~hs which photo-chemically convert the dinitroso compound to inhibitor.
. . . -- .
The specific wavelengths which ef~ect conversion ; of the dinitroso compound depend on ~he particular dinitroso compound involved. Generally, the w~vëlengths which cause this result are less than about 3400A, in which case the actinic radiation exposure is done with radiation substan-~ially limited to wavelengths greater than about 3400A. In ~20 tne case of certain aromatic dinitroso compounds, wavelengths -~ up to about 3800A effect this result, and thus the actlnic ; radiation exposure is carried out using radiation substan-- tially limited to wavelengths greater than about 3800A.
` During the acti4ic radiation exposure free-.. ..
- radicals are generated in the area struck by the imagewise exposure radiatiGn just as they are in the other areas struck ;-i by the actinic radiation. In the area struck by the ^~
;~ imagewise exposure, however, the inhibitor formed by !,C
~-, irradiation of the dinitroso compound interferes with the - . ~
`30 ~
. ..
~ .
~ 4~
.. ~,~ .

lOs44es normal free-radical induced polymerization process~
Although the nature o~ the inhibitor ~ormed by - the photochemical conversion of the dinitroso compound is not in all cases fully understood, it ls belle~ed to be a nitroso monomer, a nitroxide or nitric oxide. Most commonly, the dinitroso compound is in thermal equilibrium with a mononitroso compound. m e dinitroso compounds which are subject to this èquilibrium are re~erred to herein as "n~troso dimers" and the equilibrium mononitroso compounds are referred to as "nitroso monomers'l. me nitroso dimer is convertea to the nitroso monomer by ultraviolet radiation.
In those cases where the inhibitlng species is nitroso monomer, it is believed that the nitroso monomer re acts with free-radicals or with photoactivated nitroso monomer to form ætable nitroxide radicals which do not propagate the free-radical cha~n process and hence serve as e~ficient chain terminators. The processes believed to be operating are out-lined ~n equations 1-3, wherein RN = NR represents a typical nitroso dimer and RN0*

represents a photoexclted ni~roso monomer species RN = ~R ~ RN0 ~ RN0 R
N - 0 + N0 (1) N - 0- (2) - RN0 _hv~ R- + N0 ) \N - 0~ (3) R
mus, upon generatlon o~ ~ree radlc~l~ ln th~ ~rea~
struck by the imagewise radlation, elther during the image-. .
. ' ' ' , , ' ~ ' . ' - . ., ' ' wise exposure or the actinic radiation exposure, the inhibitor specles reacts with at least some of the free radicals to form inhibitin~ nitroxide radicals and poly-merization does not take place in these areas. When por-tions of the photopolymeriza~le layer not exposed to the imagewise exposure radiation are exposed to actinic radiation substan~ially limited to wavelen~ths greater than those that ' cause photochemical conversion of the dinitroso compound, the photoinitiator system operates to produce initiating radicals.
These radicals are able to effect chain propagation in the usual way and polymerization can occur.
The photopolymerizable coating compositions used in accordance with this invention must contain ~1) the unsaturated compound, (2) the photochemically convertible dinitroso compound and (3) the organic free~radical generat-ing system. Suitable unsaturated compounds are ~he non-gaseous ethylenically unsaturated co~pounds capable of addition polymerization by free-radi~al initiated chain propagation described in Burg et al., U.S. Patent 3~060,023; Martin et al., U.S. Patent 2,927,022; and Hertler, Belgian Patent - 76g,694. The photocrosslinkable polymers disclosed in Schoenthaler, U.SO Patent 3,418~295, and Celeste, U.S.
Patent 3,~48,o~9, may also be used. They are preferably monomeric~ have a boiling point above 90~. at normal at-mospheric pressure, and contain at least one terminal ethylenic group3 but may contain 2-5 terminal ethylenic -~ groups. Monomers which contain three terminal ethylenic groups are par~icularly preferred.
Suitable unsaturated compounds lnclude unsaturated 3o esters of polyols, particularly such esters of a-methylene-. , .

' -!~, ' ,, :; : ~

1~5~425 carboxylic aclds, ~or example, ethylene ~lycoi diacryla~e~
diethylene glycol diacrylate, glycerol diacrylate, glyceryl triacrylate, mannitol polyacrylate, sorbitol polyacrylates, ethylene glycol dimethacrylate, 1,3-propanediol dimethacry- :
late, 1,2,4-butane~riol trimethacrylate, trimethylolpropane triacrylate, triethylene glycol diacrylate, 1,4-cyclohexane-diol diacrylate, 1,4-benzenediol dimethacrylate, pentaeryth-ritol di-, tri-, and te.tramethacrylate, dipentaerythrlt~l polyacrylate~ pentaerylthritol di-, tri-, and tetraacr~lates, 1,3-propanediol diacrylate,1,5-~entanediol dimethacrylate, the bis-acrylates and methacrylates of polyethylene ~lycols.
of molecular weight 200 - 4000, and the like; unsaturated . amides, particularly those of a-methylenecarboxylic acids, and especially those Or a,~- diamines and oxygen-interrupted ; w-diamines, such as methylene bis-acrylamide, methylene bis-methacrylamide, ethylene bis-methacrylamide, 1,6-hexa-methylene bis-acrylarnide, bis(r-methacrylamidopropoxy)-ethane and ~-methacrylamiaoe~hyl rnethacrylate; vinyl esters such as divinyl succinate, divinyl adipate, divinyl phthal-ate~ divinyl terephthalate, divinyl benzene-1,3-disulfonate and divinyl butane-1,4-disulfonate; styrene and derivatives thereof; unsaturated aldehydes~ such as hexad~.ienal; and the like.
A preferred group of unsaturated compounds, because of the good physical properties of compositions containing them,include N-phenyl-N-methylacrylamide, N-vinylphthalimide, diacetone acrylamide, 3o N-vinylsuccinimide, '' ~ ' ' ' ', . .' ~ ~ 5 ~4 ~ 5 - p-xylylene diacrylate, 1,4~bis(2-acryloxyethyl)benzene, pentaerythritol triacrylal;e, ~-acryloxybenzophenone, ~-methacryloxybenzophenone, N-(2-acryloxyethyl)succini~ide, trimethylolpropane triacrylate, polyoxyethylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, triethylene glycol diacrylate, - trie~hylene glycol dimethacrylate, trimethylolpropane trimethacrylate~
4-acryloxydiphenylmethane, N-(2-acryloxypropyl)succinimide, 2,4-diacryloxybenzophenone, ~-(a,a-dimethylbenzyl)phenyl acrylate,

3-acryloxybenzophenone, 2-acryloxybenzophenone, 2-acryloxy-~-octylox~benzophenone, and mix~ures . thereo~.
The p~otopolymerizable composition also contains a co~pound containing a dinitroso group which is a non-inhibitor o~ frèe-radical polymer~zation but is photo-chemically converted by ultraviolet radiation to an inhi-bitor of free-radical polymeriza~ion. The dinitroso group can be o~ the structure O O
-N=N- or -N-0-N= .

30 The structure o~ the-remainder o~ the compound is not - 8 ~

.

; ~ ~ 5 44~ S
- important provided it does not contain groups which inhibit free-radlcal polymerization. The actual form of the dinl-troso ~roup of the structure ' ~
-N=N , whether cis or trans~ ~ immaterial~ but the form is believed to be mainly trans except when constrained to the cis form by a ring structure.
Most commonly, the dinitroso compound is a nitroso dimer which is in thermal equilibrium with a nitroso monomer. These nitroso dimers generally have a di~socia-tion constant of about 10-2 - 10-1 And a dissociation half-life of at least about 30 seconds in solution at 25C.
The dissociation half-life of the dimer can be determined using known techniques, for example, by measuring the rate o~ colored nitro~o monomer formation by ~isible spectroscopy.
A typical nitroso dimer o~ the ~irst structure photodissociates in accordance with the equation:

- T`
N = N ~ ~ 2 ~ N0 The nitroso monomer may contain one or more nitroso groups. When the nitroso monomer contains two or more ni-troso groups, the a~sociation of the nitroso groups in the nitroso dimer may be intramolecular rather than intermole-cular. A typical nitroso dimer o~ the flrst structure ln which the association of the nltroso groups is intramole-cular photodissociates in accordance with the equation:

_ g _ 1 ~ 5 4 4Z 5 N = N N0 ~0 0 ' `' ` I
A typical ni~roso dimer ~f ~he ~econd structure photo- ¦
dissociates in accordance with the equat~on:
~ ~ ~ N0 The preferred nitroso dimers are those which~ ln the monomeric form, have at least one nitroso gr~up attached .
to a primary or secondary carbon atom, although nitroso dimers in which the nitroso group is attached to an activated tertiary carbon atom are also useful.
The most preferred dinitroso compounds are those in ~hich a~ least one of the nitrogen atoms,~n the noninhlbitor or ~nhibitor for~ is ~ttached ~o a 6-membered aromatic ring or to ~he beta car~on o~ a vinyl 20 group attached to a 6-membered aromatic ring. These com-pounds Are re~erred to herein~ ~or simplic~ty~ as arom~t~c -.
din~troso compounds. Aromatic d~nltroso compounds Are pre-ferred because they are sensitive to radiation havin~ wave-lengths in the range o~ about 32oo-38ooA which are readily b' passed by polyethylene terephthalate film. Radiation wave-length~ below about 3200~ are largely screened out by poly- -ethylene terephth~.a~e, ThuS, the aromatlc d~nitro~o com- ~:
pounds ~re mo~t suitable ~or use with the most modern lmage-bearing transparency materials.

Suitable examples o~ dinitro~o compo~nds include 0 5~42 5 ~ ~ ~ 2 [ 0 NO )2 (n c3H7cH ~ NO) C3H7) CH3 CHco2c2H5 (c2H5lcHco2c2H5)2 ((CH3)2CHN0)2 (CH3CH(N0)C2H5)2 (n-c~H9cH(No)co2c2H5)2 ((cH3)2cHcH2cH2cH(No)co2czHs)2 ~
(C2H502CCH2CH(NO)c02c2H5)2 H3 _ 2 ~C~s)2CHc~tNO)cH9i~2 - (CH3COCH(G02G~H5~C~(NO)C02C2H5)2~ /

(CH3COCH(NO)COC6~5)2 (C~3)2 ~ \ ~

5cocH(No~coc6H3) 2 .

- ~-CX30C6X~COCH(NO)COC6H5)2 lH3 C ~ ~ 0 NC - C - N0 2 _ Cl LCH~

10~4425 CH3 CO2CHC~I ( NO ~I C~
CH3CO2CH~CH(NO)CH3¦ ~

_ . ~ OC2H5 2 OCH~ _ 2 [ ~ CH~NO~CH~

~H3C02CHCH(NO)C2'3l V J 2 OCH3 ~ [ V -NO~

[ ~ C~(NO)C ~ L ~ NO 3 2 (n~4~ C~(NO)c~2~H2C~2oH)2 Cl (n-C6Hl3cH(NO)~K3)2 [ ~ ~ 2 `

(~3C]~(~O)cl) (HO(C~12)6NO) 2 r ~ C2X5~ ~

(( 3)3cc~l2c}l(~lo)c(cH3)2oNo2)2 L ~ 2 : ~-(CH3CH~Cl)CH(~10) CH3) 2 . ~ O

(CH3C~(Cl~CH(~tO)C2H~2 ' ~ CO~C2H5 2 ~; :
_ _ .
(C6H5~H~Cl)CH(~0~H3) 2 -` .............. ~ COCH3¦ ~ :

((~H3~C(Cl)CH(NO)CH3)2 ~ J 2 ~.

[ ~ CH3 1 ` (C~H5~oC(CH3)(NO)CH3)2 NO ~ 2 [ ~ COC2H5~

Cl 2 :
.~C6~3 _ :
_ ~N0 _ 2 1 ~TO . ,, ~C02C 2H5 2 ' ,~,.

- 12 _ - `
!

1054425 ' ((~H3)2CHcoc(cH3)t~lo)cH3~ 2 (CH3 COC ( CH3 ) ( NO ) C~I3) 2 ~NO

(~ CH3 ) E~CHCH2COC ( CH3 ~ (NO ) CH3) 2 ~02C2X~ 2 ([(CH3)c~C]2CHNO)2 CH3 ) 2C NO 2 -- .
~,C6HsC0c(c~3~ (~o)co2c~H5)2 (C~3N0) 2 ~~ l ( CH3 ) 2 L oZC2H5¦2 N
O O . ' (CH3C( CH( CH3 ) 2) 2C~2NO)2 (CH3 ( CH2 ) 1~jCH2N~)2 (CH3 ( CH2 ) 10CH2N) 2 .
=CH-~0] [~

[(~C = CH-No]

[C'~3)3c (~01 = CH~ 0~{

' (> C;) lOS44~5 ~ClJ~CI' ~Cl~CI

2 C~H5 2 ~ . I . - . `
-- NO - - C2 C~2 CH2 OH_ 2 L~3C~ rH3~ 2 ~ ~ N ~ 2 O--N~
N~

~0~ )' - 2 32 ~H5 - CH - CH - No3 2 ~6~3 - C - Cn2 - NOl r CH
~/ - C~2i~O I
CE3 . --2 _ ~2 12 ~ , [CH3)3C~CH - CH21 [6~5~CH = C~-N3 1~3 N

J~N/ - ;

:

~OS~42~

~ ~ 2 .' , ...... . . . .
[C~13)3C~--CH = (~c(c~3~3 , .~ ..
. . . .

;~(CH3)3 C ~ C = C4 - N~ ~ N

.. - ~ . .. , l .

[~3 (C~2 ) 112 C~ . ~ 2 -, ' "- , . ' ' ' -., -,' ' ', :; ' [ 3 ~H ~12 `

. . !

3 )3C <~>~C (CH3 )3 CH3 (C~'2 ) 11 ~ L1~3 N N=~
G O . O O
)'3 ~3 i"

C 13 co~3~(~\ COC-13 d3 c~l ~

1`

- 15 _Re~p~G/ ~ pub~

- : ~

~ 544Z~ :
- _ NO l _ ~c~ ~ ~ Tl ~ d ~1 ~ f .. . . . . . .

~ ~Z

.. . : .

- ... ,; . ' ,' '- '-~ ' ' .'.' ,-~ - '-_ ~,o I . .'.'-'~.~0 L ~c H5 ~2 ~ 2 .- . ' ~
'' )5~42~

~'JO -- -. ~0 C~ 2 L /i~

. ~o -- ........... ` - ,' ~10 . - '' , .

L ~o ~2 ~

.

~ [~ C13~C~3)2 . ' . O , ;, . .
.: . . .
:, ` COCo~i5 , -'. -- :' CH3~(cy~)2 '.` ' ' ' ' O ': . ' ' :.
.~ ' .'- ', ' C02CE~3 . ,`' ~V~o . ~C'I2``& (C~113 )2 C~30 CH3 CO,~f~ -o , : ` :
. . ~

1~54~25 m e dinitroso compound is ordinarily employed in concentrations o~ about 0.1-10~ by weight based on the dry photopolymerizable composition. The preferred amount in any specific case will depend upon the particular unsaturated compound/~ree-radical generating system employed and whether it is a simple system, a binder system~ or an essentially crystalline system. In general, the preferred amount of dinitroso compound will be about 0.2-2~ by weight based on the photopolymerizable composition.
The photopolymerizable composition also contains ~ -an organic free-radical generating system which initiates the polymerixation of the unsa~urated compound and does not subsequently terminate the polymerization. The word "organic"
is used here and in the claims to designate compound~ which contain carbon, and one or more of oxygen, hydrogeng nitrogen, sulfur and halogen, but are free o~ metal.
The free-radical generating system absorbs radiation within the ra~ge of about 2000-80QoA and has at least one component that has an active radiation absorption band with a molar extinction coe~ficient of at least about 50 within the rsnge o~ about 3400-8000A, and pre~erably 3800-5000A.
"Active radiation absorption band" means a band of radiation which is active to produce the free r~dicals necessary to ini~iate the polymerization of the unsaturated material. The free-radical generatin3 ~ystem can comprise one or more com-pounds which directly furnish ~ree radicals when activated by radiation. It can also comprise a plurality of compounds, one o~ which yields the ~ree radicals after having been caused to do so by a sensitizer which is activated by the rsdiation.

~ ~ ~0s~42~

A large ~umber of such compounds can be utilized in the practice o~ this invention including aromatic ketones such as benzophenone, Michler's ketone (4g4~-bis(dimethyl-amino)benzophenone), 4,4'-bis(diethylamino)benzophenone,

4-acryloxy-4'-dimethylaminobenzophenone, 4-acryloxy-4'- -die~hylaminobenzophenone, 4-methox~-4'-dimethylaminoben o-phenone, phenanthrenequinone, and other aromatic ketones;
benzoin, benzoin ethers such as benzoin methyl ether, benzoin ethyl ether and benzoin phenyl ether, methylbenzoin, ethyl-benzoin and other benzoins; 2~4,5-triarylimidazolyl dimers such as 2-(o-chlorophenyl)-4,5-diphenylimidazolyl dimer, 2-- (o-chloropheny1)-4,5-di(m-methoxyphenyl)imidazolyl dimer, 2-~ (o-fluorophenyl)-4,5-diphenylimidazolyl dimer3~2-(o-methoxy-; phenyl)-4,5-diphenylimida~olyl dimer, 2-(p-methoxyphenyl)-4,5-diphenylimidazolyl dimer, 2,4-di(~-methoxyphenyl)-5-phenylimidazolyl dimer, 2-t2~4-dimetkoxyphenyl)-4~5 diphenylimidazolyl dimer, 2-(p-methylmercaptophenyl)-4,5-diphenylimidazolyl dimer, and the like as disclosed in U.SO
Patents 3,479~185 and 3~784,557 and in British Patents 997,396, published July 7~ 1965, and 1,047,569, published November 9, 1966; and bis(p-aminophenyl~ -unsaturated) ketones AS described in U.S. Patent 3,652,275.
The lmidazolyl dimers may be used with compounds such as 2-mercaptobenzoxazole with or wi~hout sensitizers such as Michler's ketone and vArious dyes. Additional examples of suitable initiators are disclosed by Plambeck in UOS. Patent 2,760,863. Redox systems may also be usedO
mese include combinations such as Rose Bengal/2-dibutyl-aminoethanol; phenanthrenequlnone/trie~hanolamine; 2~o- -chlorophenyl)-4,5-di(m-methoxyphenyl)imidazolyl dimer/2- ~

~ 19 ~ r .

` 1054~L2~
mercaptobenzoxazole; 2-(o-chlorophenyl)-4,5-diphenyl-lmidazolyl dimer/2,5-bis(4'-die~h~lamino-2'-methylbenzyl-idene)cyclopentanone; and the like.
A preferred group o~ free~radlcal generating systems characterized by good e~ic~ency includes methyl, ethyl and phenyl benzoin ethers, methylbenzoin and its ethers~ phenanthrenequinone, phenànthrenequinone/triethanol-amine, and 2,4,5-triaryllmidazolyl dimers/2-mercaptobenzox-azolé. The concentration of the ~ree-radical generRting system employed fihould be about 0.001-1.0 part by weight per part of unsaturated compound, pre~erably about 0.01-0.7 part by weight.
The photopolymerizable compositions used herein ~-can also contain other components, if desired. For example, the composition can be o~ the unsaturated compound~binder type which conbains a thermoplastic macromolecular organic polymer binder. The composition can also be o~ the substantially dry, predominately crystalline type, described by Hertler in Belgian Patent 76~,694 which contains a solid ethylenically unsaturated compound, an organic radiation- -sensitive free-rQdical generating system, and a nonpolymeric normally liquid or solid organic substance which does not inhibit the polymerization o~ the unsaturated compound, in ;~ ;
addition to a suitable nitroso dimer.
Suitable thermoplastic macromolecular organic polymer binders for use in an unsaturated compound~binder system are described by Chang in U.S. Patent 3,661,588, and include such polymeric types as (a) copolyesters based on terephthalic~ isophthalic, sebacic, adipic and hexahydro 3o terephthalic acids3 (b) nylons or polyamides; (c) vinylidene _ 20 -:
. .

. . . - - . -. .. . . . . .

chloride copolymers; (d) ethylene~inyl acetate copolymers;
~e) cellulosic ethers; (f) polyethylene; (g) synthetic rubbers; (h) cellulose esters; (i) polyvinyl esters including polyvinyl acetate/acrylate and polyvinyl acetate/methacrylate ,;, .
copolymers; (J) polyacrylAte and a-alkylpolyacrylate esters, e.g., polymethyl methacrylate, polyethyl methacrylate, and polymethyl methacrylate/ethylacrylate copolymers; (k) ....
high molecular weight polyethylene oxides o~ polyglycols having average molecular weights o~ about 4000-1,000~000;
10 (1) polyvinyl chloride and copolymers; ~m) polyvinyl acetal;
(n) poly~ormaldehydes; (o) polyurethanes; (p) polycarbonates;
q3 polystyrenes. A pre~erred group o~ binders includes :
- the polyacrylates and a-alkylacrylate esters, particularly .: . .
polymethyl methacrylate and polymethylmethacrylate/ethyl-acrylate copolymers.
When an unsaturated compound/binder system is employed, the binder is normally employed in concentrations o~ about 3-95% by weight, based on the photopolymerizable composition, and preferably about 25-75% by weight. Unsaturated 20 compounds which contain only one ethylenic group are generally not satisfactory for use in a binder system.
- When the substantially dry, predominantly crystal-line system, described in the Hertler Belgian Patent is employed, in one aspect of the invention, the system may contain in addition to the unsaturated compound, about 0.01- -0.25 part by weight, per part o~ unsaturated compound, o~ a non-polymeric, normally liquid org~nic compound ~hich does not inhibit polymeriæation o~ the unsaturated compound and doe~
- not absorb so much o~ the incident radiation as to prevent ~30 the initiation o~ the polymer~zation by the ~ree-radical - 21 ~

5~L425 -:
generating system. In ~nother aspect o~ the invention~ about 0.01-250 parts by welgh~, per part of unsaturated compound, o~
a nonpolymerizable, crystalline or~anic solid which does not inhibit polymerization of the unsaturated compound and also ~- does not absorb the incident radiation to such an extent as to prevent the initiation of the polymeri2atio~ by the free-:....
`' rad~cal generating system may be added.
'. Illustrative examples of suitable liquid and solid i compounds which may be added include octadecanol, tri-- 10 ethylanolamine, s~earlC acid, cyclododecane, 1,10- ' ' decanediol, dimethylaminobenzonitrile, acetone oxime, '' -~ desoxybenzoin, naphthalene, N~N'-dlmethylhexamethylene-'~ diaminel p-diethoxybenzene, biphenyl, dotriacontane, tetra~
- methylurea, 'tributylamine, 2-dimethylaminoethanol, bibenzyl3 pentamethylbenzene, 1,12-dodecanediol, 1,2-diphenoxyethane, octacosane, trichloroxylene, cyclododecanol, and the like.
A pre~erred group o~ solid compounds include~ bibenzyl, - biphenyl, 1,2-diphenoxyethane, p-diethoxybenzene, octaeosane, ' ' l-octadecanol and cyclododecanol. ' -:' 20 When the polymer is a hard, high~meltlng compound~ ;
a plasticizer is usually used to lower the glass transition temperature and facilitate selective development. The plasti-cizer may be any of the common plasticizers compatible with the polymeric binder. Among the common plasticizers are dialkyl phthalates, alkyl phosphates, polyethylene glycol, ;
polyethylene gylcol esters, and polyethylene glycol ethers.
; The photopolymerizable compositions described ~erein may be applied to a wide variety of natural and synthetic substrates. By "substrate" is meant any ~lexi~le or rigid support which is capable o~ exlsting in ~ilm or . .
.. . . ~ .
. . : . .

~ ~ 1054~25 . .
. .. .
or sheet form. For example, the substrate could be a metal shee~ or foil, a sheet or film o~ synthetic organic resin, cellulose paper, fiberboard, and the like~ or a composite o~ two or more o~ these materials. Speci~ic substrates in-clude copper~ alumina-blas~ed aluminum, oriented polyester .,. ~
film, alumina-blasted oriented polyester film, polyvlnylidene chloride-coated oriented polyester ~ilm~ polyvinyl alcohol-coated paper, crosslinked polyester-coated paper, nylon, glass, heavy paper such as lithographic paper, polypropylene ' 10 film and the like. Preferably the substrate is polyv~nyli-- dene chloride-coated oriented polyester film or alumina-blasted ;- aluminum.
The particular substrate will generally be determined by the use application involved. For example, the method of this invention is particularly use~ul ~or producing printed : circuits using a copper-clad fiber-reinforced resin board as the substrate.
When the photopolymerizable compositions are coated on metal sur~aces, they are useful ~or making presensitized lithographic printing plates. For example, application o~ a photopolymerizable layer to a grained ; aluminum base results in a lithographic printing plate. In - use, the developed plate is ~ir~t coated with water and is ; then contacted with a roller which wets only the pho~opoly-mer image with ink. The inked plate can then be used in lithographic printing in the usual way.
The photopolymerizable compositions can also serve t as photoresists in making etched or plated circuits or in chemical milling applications. ~or example~ the photopoly-merizable composition may be applied in liquid ~orm to a sub-:. ~ - . . .. . . . -: `:

54~25 .
strate ~ollowed by drying. A removable cover sheet may be applied ~o the æur~ace of the resultant layer of the compo-sition in order to protect it during handlingO Upon removing the cover sheet if present, the dry layer can be laminated to another substrate for lts ultimate use, using conventional -laminating equi~ment to apply pressure and generally using , ........ .
heat. The original substrate now becomes a cover sheet~
This technique is particularly use~ul in applying the compo-sitions for use as photoresists, such as described in U.S0 Patent 3,469,982, wherein the original substrate is a poly-meric ~ilm and the substrate to which the layer is trans~erred generally has a metal or ceramic sur~ace.
The photopolymerizable compositions are also useful ~or preparing colored images ~rom color separation negatives suitable for color-proo~ing. The ~mages ~ormed with these elements may also be used ~or making copies by thermal transfer to a substrate. Speci~ic uses will be evident to those skilled in the art; many uses for positive images on substrates are disclosed in U.S. Patents 2,760,8633 3,060,023; and 3,060,026.
Processes for applying a layer o~ photopolymerizable composition either in the liquid or dry s~ate to a substrate are well known. Processes starting with compositions of the substantially dry, predominantly crystalline type are o~ ~ive general types: those in which (1) the components of the compo-sition are melted toge~her generally ~orming a homogeneous melt which is coated onto the substrate; ~2) the components of the composition are dissolved together in a solvent in which the components are pre~erably completely soluble and the resulting solution is poured or painted onto the sub-, . . . . . . .
,, ~ .

l~;
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strate, which ls the pre~erred method; (3) the components of the composition are dissolved in a volatile solvent and the resulting solution ls sprayed as a ~ine mist aga~nst the substrate; (4) the components of the composition are melted together and the melt is sprayed as a fine mist onto the ;` substrate; (5) the components o~ the composition are mi~ed together in a heated vessel which contains an ~nner surface -~ that is cooled in ~hich the distance from the mixture to the cooled surface can be varied whereby the components are sub-o l~med onto the cooled surface. Further details of these pro-cesses can be round in the Belgian Patent o~ Hertler, cited - above.
- m e photopolymerizable compositions of this inven-tion are exposed to radiation in the wavelength range of about 2000-8000A. Suitable sources of such radiation, in ; addition to su~light, include carbon arcs~ mercury-vapor arcs, fluorescent lamps with ultraviolet radiation-emitting phosphors, argon glow lamps, electronic flash units and i photographic ~lood lamps. Other fluorescent ~adiation sources such as the tracings on the face o~ a cathode ray tube may be used. Electron accelerators and electron beam sources through an appropriate mask may also be used.
Nhere artificial radiation sources are use~, the distance between the photopolymerizable layer and the ràdiation source may be varied according to the radiation sensitivity of t~e composition and the nature of the un-saturated compound. Cu~tomarilyg mercury-vapor arcs are used at a distance o~ about 1.5-20 inches (3.8 - 50.8 cm) from the photopolymeri~able layer. Radiation fluxes o~
3 about 10-10~000 ~w/cm2 are generally suitable for use.

~.

~ - 25 -.~`` ~
..':.
The radiation used during the imagewi~e exposure - may have wavelengths over the entire range of about 2000-8000A, provided at least some o~ the radiation is o~ wave-lengths o~ ul~raviolet radiation that photochemically con-vert the dinitroso compound to ilihibitor. The radiation used during the exposure that activates the ~ree-radical generating system should be sub~tantially limited to wave-lengths that do not convert the dinitroso compound to inhib~tor. For example, if wavelengths of about 3400A and shorter cause conversion of the dinitroso compound, then the exposure activating the free-radical generating system should preferably exclude greater than about 99~ of the radiation below about 3400A. Likewise, if wavelengths o~
about 3800A and shorter cause the conversion, then the actinic radiation exposure should preferably exclude greater than about 99% of the radiation below about 3800A. During ` the activating exposure, a greater portion of the photopoly-merizable layer, typically the entire layer, is struc~ by the radiation with the result that free radicals are generated and polymerization takes place in the portion s~ruck by the activating radiation but not by the imagewise exposure - ~ radiation.
The length of time the compositions are exposed to radiation may vary upward from a fraction of a second. The exposure times will vary depending on the nature and concen-tration of the unsaturated compound and the free-radical generating system, and the type of radiation. Exposure can occur over a wide range of temperatures, as for example, from about -80C up to about 45C. Preferred exposure temperatures range from about -30C to about 35C. There ' .

fi .:
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.

i6 an obvious economic advantage to operating the pro-cess at room temperature. However, because o~ the slower rate at which nitroso monomers reassociate to nitroso dimers at lower temperatures, for exam;ple about 0 to -30C, improved :
image relier can be achieved by using nitroso di~ers at these temperatures. Accordingly, these lower temperatures will be --~ preferred where improved relief, such as that required when operating on a micro scale, is desired.
Imagewise exposure is conveniently carried out by ; 10 exposing a layer of the photopolymerizable composition to ultraviolet radiation through a process transparency; that is, an image-bearing transparency consisting sole~y of areas substantially opaque and substantially transparènt to the radiation being used,where the opaque areas are substantially o~ the same optical density; ~or example, a so-called line or halftone negative or positlve. Process transparencies may be constructed of any suitable materials including cellu-lose acetate film and polyester ~ilm. Exposure o~ the layer of photopolymerizable composition to the ~ull spectrum o~
a mercury-vapor lamp through a cellulose acetate or poly-ester film negative causes conversion o~ the dinitroso compound to inhibitor in the radiation struck areas. m ese areas ul~imately become non-image areas since no polymeri-zation will be initiated in these areas dur~ng the actinlc radiation exposure step.
Removal of the process transparency followed by exposure ~o the activating radiation, e.g~ radiation sub-stantially limited to wavelengths greater than about 3400A, or about 3800A as the case may be~ causes polymerization to occur in the areas which were not struck by the radiation ... - - . . . ... ..

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during the imagewise exposure. Racliation o~ this wavelength is insufficiently absorbed by the clinltroso compound to con-vert it to inhibitor. The areas exposed in this manner be-come the image areas. Development o~ the twice exposed layer provides a positive image, i.e.~ the photopolymerized portion of the layer remaining after development corresponds to the `
opaque region o~ the process transparency.
m e exposure to ac~inic radiation must be carried out while the amount OI' inhibitor present in the areas . . . .
exposed to the imagewise exposure raaiation is su~fi~ient that inhibition of polymerization is e~ected in these areas. When the dinitroso compound is a nitroso dimer~ the inhibitor species may be the nitroso~-monomer as such or a more persistent inhibitor species such as the nitro~ide radicals ~ormed in equations (1), (2) and (3) may be presentO
For best results the exposure to actinic radiation should be carried out within a reflsonable time after the imagewise exposure, for example, ~ithin about one hour, preferably within about 30 minutes, and most pre~erably withln about 15 minutes.
It is not necessary that the two exposures to radiation be carrled out in sequence, i.e., the imagewise exposure first~ ~ollowed by the activating exposure. It ~;
is also possible to use simultaneous exposure ~o radiation of the dif~erent w~velengths required. For example, exposure o~ the photopolymerizable layer to the ~ull spectrum of a mercury-vapor lamp through a process trans-parency spaced apart from the surface o~ the layer may be carried oùt while simultaneously pro~ecting radiation of wavelengths greater than about 3400R, or about 3800A as the - 2~ -'' . ~. ." ' ;' : ~354425 !
case m~y be, onto the layer without passing throu~h the transparency. It is also suitable cluring simultaneous exposures to pro~ect the actinic racliation from the reverse 1 side of the substrate when the subst;rate supporting the photopolymerizable layer is transparent to such radiation.
The exposed photosensitive layer can be developed by removing the unpolymerized unsaturated compound ~rom ~he layer, leaving behind a polymeric replica o~ the opaque areas of the process transparency; i.e., a positive image.
The unpolymerized unsaturated compound can be removed by heating under conditions which result in some or all of the volatile components being vaporized-whereby the photo-polymer is le~t behind. The conditions o~ ~hermal develop-ment selected will depend upon the na~ure of the substra~e9 ~he volatility o~ the components to be removed, and the thermal stability of the components. Alternatively, develop-ment may be achieved by solvent washout, thermal transfer, pressure trans~er~ di~erential adhesion of the exposed ver-sus unexposed areas, and the like. Pre~erably, positive polymeric images are developed by solvent washout. Nega-~ive ~mages are preferabl~ developed by dif~eren~ial adhesion of a pigment toner to the tacky unpolymerized areas.
The following examples further illustrate the method !~` of this invention All percen~ages are by weight unless . .
otherwise speci~ied.
EXAMPLE_l A mixture o~ 0.851 g of 1,2-diphenoxyethane, 0.082 g of 2,4-dime~hyl-2-nitroso-3-pentanone dimer, 0.082 g of 4-(a,a-dimethylbenz~l)phenyl acrylate, and 0~040 g o~
benzoin methyl ether was dis~olved i~ 15 ml of chloro~or~

~ ~.

;` - and the solution was sprayed onto d 12.7 x 12.7 cm aluminum `-~ plate. The plate was heated to melt the coating, and it was -- cooled to give a uniform melt-crystallized coating. m e plate was exposed for 3 minutes to 3130A radiation from a high pressure mercury lamp (light flux o~ 46 ~w/cm2) with a por-~- tion of the plate covered and obscured from the rad~ation.
~ To eliminate shorter and longer wavelength radiation 0-54 and ;- 7-54 filters available ~rom Corning ~lass Works and a nickel sulfate/potassium chromate/potassium biphthalate filter solu-~- 10 tion were used. m e filters were replaced with 0-53 and 7-51 filters and a 3660A interference filter to give an out-` put limited to 3660A radiation (38 ~w/cm2 light flux) and the entire plate was irradiated for 2.0 minutes. l'he plate was developed by washout with a 90~ n-hexane/10% chloro~orm - solution. A positive image was produced in which polymer ` was present in the area not exposed to the 3130A ~irst ~; irradiation.

' mis example illustrates the use of 4-acryloxy-i. .
benzophenone as t~e unsaturated compound.
- A plate was coated as described in Example 1 with `~ a solution of o.800 g o~ 1~2-diphenoxyethane, o.o80 g of 4-acryloxybenzophenone, 0.040 g of 2,4-dimethyl-2-nitroso--- 3-pentanone dimer and o.o40 g of benzoin methyl ether in 15 ml of chloro~orm. A high-quality positive image was ; prepared by exposure of the plate to 3130A radiation for - 3.0 minutes through a cellulose acetate process trans-parency, followed by exposure for 1.0 minute to radiation limited ~o 3660~ with the process transparency removed. ~he plate was developed by-washlng with 90% hexane/10~ chloroform solution.

_ 30 -:. . . , .

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; E MPLE 3 miS example lllustrates ~he use of nitroso-~ cyclohexane dimer as the nitroso dimer. Nitrosocyclohexane j dimer (trans form~ has an equilibrium constant of 10-7 and ~ . . .
a dissociatlon half-life of 10 hours in acetonitrile at room temperature (Wa~er et al., Rec. Trav. Chim " Vol. 91~ p.
565-577, 1972).

. A plate was coated as described in Example 1 with - a solution of o.800 g of 192-diphenoxyethane, o.o80 g of 10 4-(a,-dimethylbenzyl)phenyl acrylate, o.o60 g of nitrosocyclo-hexane d~mer and 0.040 g o~ benzoin methyl ether ln 15 ml of ~- chloroform. A high-quality positlve image was prepared by exposure of the plate to 3130A radiation for 3~0 minutes through a cellulose acetate process transparency which ls ` followed by exposure for 1.0 minute to radiation limited :~; to 3660A with the process transparency removed. The plate was developed by washing with 90% hexane/10% chloroform r ~ " solution.
. ~:XAMPLE 4 . .
This example illustrates the use of 4,4~biæ~
~- (acryloxy)-2,2-diphenylpropane as the unsaturated compound.
; A plate was coated as in Example 1 with a solutlon of 0.800 g of 1,2-diphenoxyethane, o.o60 g of nitrosocyclo~
hexane~dimerj 0.040 g of benæoin methyl ether and o.o80 g of 4,4'-bis(acryloxy)-2,2-diphenylpropane in 15 ml o~ chloro-form to form a crystalline system. The plate was lrradiated ~: wlth the full spectrum of the high pres~ure mercury lamp, without filters, for 1 mlnute through a cellulose acetate process tr~nsparency (300 ~w/cm~ light flux). The proces~
transparency was removed and the irradlation was continued :;. ~

- ; - 31 -: . -. .
. ~ , .

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for 0.5 mlnute using light limited to wavelengths greater than 3400A, obtained by use of a CORNING* 0-52 ~ilter. A~ter development with a 50% hexane/50~ chloro~orm solution, a . .; . .
`- high-quality positive image remained.
~, EXAMPLE 5 : mis example illustrates the use of pentaerythri-tol triacrylate as the unsaturated compound in a crystalline - system.
r; l-Nitroso-3-methylcyclohexane dimer was prepared as follows: Ace-tic anhydride (55 g) was added over a 30-minute periodg to a solution o~ 12.2 ml of 90% hydrogen peroxide and one drop o~ concentrated sulfuric acid in 50 ml of methylene chloride, while the temperature ~as maintalned at 0C. This solution was then added slowly to 22.8 g of 3-methylcyclohexylamine in 75 ml of methylene chloride while .
the temperature was maintained at 15C. After the addition of the peracetic acid solution was com~leted, the reaction mixture was allowed to warm to room temperature and ~tirred an additional 10 hours. me solution ~as extracted w~th 200 ml ~ water, 100 ml of cold 15~ ammonium hydroxide, 100 ml of 10% sulfuric acid and 100 ml of water, ~d dried over ; a~hydrous m~gnesium sulfate. The methylene chloride was re- -moved by distillation to lea~e a pale blue solid. mis solid was recrystallized from methanol-water to give 5.0 g of l-nitroso-3-methylcyclohexane dimer as a ~hite solid, mp 81-83C. The structure was confirmed by IR, UV and NMR spectra.
Anal- Calcd for C14H26N202: C, 66.10, H, 10.30~ N~ 11.01 Found: C, 66.o6; H, 10.41, N, 10.77 66.~5 10.22 10.78 A mixture o~ 0.800 g o~ 1,2-diphenox~ethane, o.o60 g 3 o~ l-nitroso-3-methylcyclohexane dimer, prepared as described * denotes trade mark - .

- -.; , . :

s~
above, 0.040 g of benzoin methyl ether and 0.100 g of penta-erythritol triacrylate~ HOCH2C(CH,~02CCH=CH2)3~ was dissolved in a mixture Or 6 ml of methyl e-thyl ketone and 1 ml o~
2-ethoxyethanol and the solution was poured onto a 30,5 x 30.5 cm aluminum plate. me solvent waæ evaporated by heating the plate at 80C with an ln~rarecl lamp. me residual coat-ing crystallized.
The plate was exposed through a cellulose acetate process transparency to the ~ull spectrum of a high pressure mercury lamp for 1 minute. me process transparency was removed, and the plate was reexposed to radiation limited to wavelengths .: O
greater than 3400A (COR~ING 0-52 filter) ~or 20 seconds.
After development with 50~ hexane/50% chloro~orm solution, a ~ high-quality positive image was obtalned.
.~

This example illustrates the use o~ a triar~limida-zolyl dimer and 2-mercaptobenzoxazole as the ~ree-radical ; generating system. -~ A mixture of 0.800 g of lJ2-diphenoxyethane, 0.100 g of 4-(~ , ~ -dimethylbenzyl)phenyl acrylate3 o.o60 g of l-nitroso-3-methylcyclohexane dimer, 0.015 g of 2-o chlorophenyl-4,5-bis(m-methoxyphenyl)imidazolyl dimer and 0.005 g Or 2-mercapto-benzoxazole was dissolved in a mixture of 6 ml of methyl ethyl ketone and 1 ml of 2-ethoxyethanol, and the solution was poured onto a 30.5 x 30.5 cm aluminum plate. me solvent was evaporated by heating the plate at 80~C with an infrared lamp. me residual coating cry tallized.
e plate was exposed through a paper process transparenc~ to the full spectrum o~ a mercury lam~ ~or 1 minute, followed by a 15-second exposure to radiation l~mited .

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5 ~ ~5 to wavelengths greater than 34QoA (CORNIN~ 0-52 rilter) without the process transparency. A high-quality positive image wa~ ;
obtained after development.
. . , ... ~XAMPIE 7 mis example illustrates the use o~ polymethyl methacrylate in a binder system.
.-.;.
A mixture Or 1025 g Or trimeth~lolprop~ne tri-acrylate, 0.80 g o~ triethylene glycol diacrylate, 0.125 g of benzoin methyl ether, 0.05 g Or l-nitroso-3-methylcyclo-10 hexane dimer, and 2.78 g o~ polymethyl methacrylate resin .... . .
; ~s dissolved in 20 ml o~ methylene chloride and the solu-fX tion was coated onto a 30~5 x 30.5 cm alllminum plate with a - doctor knife set at 0.0127 cm thickness. The solvent was evaporated and the residual film was coated with an aqueous polyvinyl alcohol solution.
The plate w~s exposed through a cellulose acetate process tr~nsparency to the rull spectrum Or a medium pres-.. . .
~ sure mercury lamp ror 4 minutes, the transparency was removed, j,J
and the plate Wa8 exposed rOr 2 minute~ to radiation limited 20 to wavelengths greater than 3400A (CORNING 0-52 rilter). me -~ plate was developed by washing with water followed by methyl chlorororm. A high-quali~y pvsltlve image was obtained.

me composition o~ Example 7 was used except that three times as much l-nitroso-3-methylcyclohexane dimer (0.15 g) was employed. A 30.5 x 30.5 cm aluminum plate was coated as described in Example 7.
A portio~ o~ the plate was irradiated with the full spectrum o~ a mRdium pressure mercury lamp for 2 minutes .. . .

- 34 _ ,' , .. ~ .

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I ,~. ' ' . .. .
. ` ...
:~ through a cellulose acetate process transparency, the tx~ns-.-parency was removed, and the plate was exposed for 4 minutes to radiation limited to wavelengths grcater than 3400A
` (CORNING 0-52 filter). The plate was developed by washout with water ~ollowed by meth~l chloroform. A high-~uality . . -- ~ positive image w~s obtained.
Another portion of the plate was exposed through a polyester process transparency to the full spectrum of the ~. .
lamp for 4 minutes, the transparency was removed, and the ~` 10 plate was exposed ~or 3 minutes to radiation limited to wave -` lengths greater than 3400A. ~fter development as above~ a high-quality positive image was obtained.
- EXA~LE 9 me composition of Example 7 was employed except that the l-nitroso-3-methylcyclohexanP dimer was replaced by 0.15 g of nitrosocyclohexane dimer. A 30.5 x 30.5 cm al~ml-num plate was coated as described in Example 7.
The plate was irradiated through a polyester process transparency with the full spectrum o~ a medium pressure mer-cury lamp ~or 4 minutes~ the transparency was removea, and theplate was exposed for 4 minutes to radiation limited to ~ave-lengths greater than 3400A. The plate was developed by wash-out with water followed by methyl chloroform. A high-quali-ty positi~e image~was obtained.
E~a.MPIE 10 ~, This example illustrates the use o~ 2-nitroso-3-methylbutane dimer as the nitroso dimer.
A mixture of 1.25 g o~ trimethylolpropane tri--~ acrylate, 0.80 g of triethylene glycol diacrylate, 2.78 g o~
polymethyl methacrylate resin, 0~125 g of be~zoin methyl . .

, 3~

; ~ ~, ~ ,- .

~ ether and 0.100 g o~ 2-nitroso-3-methylbu*ane dimer was dis-,. .
solved in 20 ml of methylene chloride and the solution was . `~; .
; coated onto an aluminum plate as described in Example 7.
The plate was exposed t;hrough a cellulose acetate process transparency to the full spectrum o~ a medium pressure mercury lamp for 4 minutes, the transparency was .
, removed, and the plate was exposed for 3 minutes to radiation -- limited to wavelengths greater than 3400A. The plate was developed by washout with water followed by methyl chloro-.
~ 10 form. A high-quality positive image was obtained.

`. This e~ample illustrates the use of simultaneous exposure with radiation of different wavelengths.
The composition of Example 8 was used. A
~r'` 30.5 x 30.5 cm aluminum plate was coated as described in Example 7. The plate was exposed through a process trans-parency spaced from the surface of the photopolymerizable layer to the full spectrum radiation of a medium pressure mercury lamp, while the plate was simultaneously exposed to 20 radiation limited to wavelengths greater than 3400A
(CORNING 0-52 ~ilter) ~or 4.0 minutes by directing the radia-tion into the space between the t,ransparency and the photo-- polymerizable layer. A high-quality positive image was obtained in which no polymer was present, in the area struck `~
~ by the full spectrum radiation and polymer was present in i the area struck by r diation o~ wavelength greater than 34~.
E~AMPL~ 12 ..
This example illu~trates the improved relie~
obtained by photoimaging at 0C.

, 36 .
4gl ., 5~
A stock solutlon o~ a mixture o~ 1.25 g of tri-methylolpropane triacrylate, 0.8 g o~ triethyleneglycol ~, .
diacetate, and 2~77 g o~ polymethyl methacrylate resin r',~ di~solved in 20 ml of methylene chloride ~as prepared. To - one-half o~ this solution, 0.18 g of benzoin methyl ether was added. The resulting solution was again ~ivided in hal~
-' and to one hal~ 0.02 g o~ nitrosocyclohexane dimer was added - and this solution used to coat an aluminum plate. The sol-vent was evaporated at 25C, and the coating, r_l mil 10 (0.0254 mm) in thicknes~, was subsequently top-coated with an aqueous polyvinyl alcohol solution to a thickness of less than 0.05 mil (0.0012~ mm). The coated plate was - cooled at 0C in a ni-trogen atmosphere and exposed to a - 100 W AX4 medium pressure mercury resonance lamp through a o.636 cm quartz plate and a test pattern transparency on a cellulose acetate base. me lamp was placed 6.36 cm from ; the coated plate.
The plate was exposed initially for 2 minutes~ the transparency removed and replaced by ~ CORNING 0-52 ~ilter to remove radiation of less than 3400A, and the plate reexposed for 1.5 minutes. A~ter development, a high quality positive image was obtained with 0.0254 mm relief.
~AMPLE 13 ~ .
mis example illustrates the preparation of a printed circuit.
A mixture o~ 36.61 g o~ trimethylolpropane tri-acrylate, 5.23 g of polymethyl me-thacrylate resin, 52.71 g o~ a polymethyl methacrylate/acryllc acid copolymer resin, 5.23 g of a conventional plasticizer, 0.21 g o~ a conventional , :
adhesion promoter, 2.5 g of benzoin me-thyl ether and 3~0 g .

. ~ . . .. . . . .. .

- of nitrosocyclohexane dimer was dissolved in 900 ml o~
methylene chlorider A portion of this æolution was applied ;- to an epoxy resin board laminated with copper ~rom ~ doctor knife set at 10 mils (0.254 mm~, The dried coating was ~ subsequently top-coated with a 5~ aqueous polyvinyl alcohol _ solution from a doctor knife setat l mil (0.0254 mm).
~ The board was exposed t~ough a cellulose acetate ... .
,r~`~ process transparency to the ~ull spectrum of a 100 watt high c` ~ .
pressure mercury resonance la~p for 4 minutes, the transpar~
ency was removed, and the board was exposed ~or 6 minutes to .. O
- radiation limited to wavelengths greater than 3400A (CORNING
0-52 filter). The board was developed by washout with . , .
water followed by~a solution of 40 g of borax and 500 g o~
2-ethoxyethanol in ~ liters of water~ A positive image resulted.
The board was etched with a ferric chloride 801u-tion until all the copper had been dissolved from the areas not covered by polymer. Residual polymer was removed by `~ washout with methylene chloride to le~ve a positive copper ;i 20 image~ i.e., copper was presen-t in the areas not struck by radiation during the first exposure.
E~U~PIES 14-25 . ~
These examples illuætrate the use of aromatic dinitroso compounds.
A stock solution was prepared containing the following ingredients:
1~ .;
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Component _ Pentaerythritol triacrylate 25 klethyl methacrylate polymer 25 - (low mol. wt.;
density - 1.13 g/cc) Triethylene glycol diacetate 6.5 - Methylene Chloride 508.5 ' ~ r` . .
."'- , .. ' :
Photopolymerizable solutions were prepared using the - above stock solution (10-g portions), 2,7-di-t-butyl-phenan-- 10 threnequinone as the free-radical generating system (initiator), and a dinitroso compound; the amounts of initiator and dinitroso compound added, as well as the struc-; ture of the latter, are indicated in Table Io Each photopolymerizable solution was coated with a doctor knife onto oriented, heat-set, polyethylene tere-~ phthalate film ~0.076 mm thick). After air drying (dry coating thickness ca. o.oo76 mm), a cover sheet of poly-` ethylene (0.025 mm thick) was laminated over the dried ;. . . .
layer; lamination was conducted at room temperature with modest pressure, i.e., via a hand-held squeegee applicator. `
All samples were exposed within two minutes after lamination.
Each film WQS initially exposed in a vacuum - - fr&me through a 21-step ~ stepwedge process transparency, in which the transmittance of radiation bet~een steps di~ers by a ~- factor of ~ to ~adiation of wavelength essentially between 3200-3800A; thi6 initial e~posure ~ource was a device contalning eight Sylvania~ Blacklite Blue lamp~ (Model ~o. F15T8-BLB) ~paced ; 5.o8 cm from the s~mple fllmr This exposure (see Table I
for e~posure time) produced inhibitor in the film in 30 amounts inversely related to the optlcal den~ities of the ' , _ 39 _ . .

~`~

lQ5~5 : steps on the step wedge. In other words, as the optical density of the st-eps in the transparency increased, the concentration o~ inhibitor decreased ln the corresponding - portion of the film.
The transparency was then removed and the sample ~- was irradiated with actinic radiaion limited to w~veleng~hs - O
greater than 3800A. me radiation source was a commercial nuAr ~ v cuum frame (Model ~T26L) containing a 2000 watt, ;- pulsed-xenon source, spaced 43.2 cm from the polymerizable ~ 10 layer. Radiation of wavelengths less than 3800A ~as excluded by inserting an appropriate filter between the source and sample, a WRATTEN* Light ~ilter either lA or 2C, manufactured -- by Eastman Kodak CoO, was used. The exposure times are listed in Table I. Photopolymerization occurred only where the concentration o~ inhibitor was negligible or ~ery low.
Following exposure, the polyethylene cover sheet was removed and a blue pigment toner, as described in U.S.
3,649,268, was applied to the photopolymer surface. A~ter removing excess toner with a cotton pad, a replica of the step wedge remained, that is, toner did not adhere to the polymeri~ed areas (higher numbered steps), but did adhere '~ to the tacky, unpolymerized portions (lower numbered steps) which contained a high concentration of inhibitor ~rom the initial exposure. The data which indicate that each o~ the dinitroso compounds functioned to produce inhibitor in this two-exposure proce~s are summarized in Table I.
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Claims (28)

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

1. Method of making a positive polymeric image on a substrate which comprises (a) applying to the substrate a layer of photopoly-merizable composition containing (1) non-gaseous ethylenically unsaturated compound capable of addition polymerization by free-radical initiated chain propagation, (2) 0.1-10% by weight, based on the photopolymerizable composition, of a compound containing a dinitroso group which is a noninhibitor of free-radical polymerization and is photochemically con-verted by ultraviolet radiation to an inhibitor of free-radical polymerization, and (3) 0.001-1.0 part by weight, per part of unsaturated compound, of an organic free-radical generating system activatable by actinic radiation that does not convert the dinitroso compound to an inhibitor of free-radical polymerization, (b) imagewise exposing a portion of the photopoly-merizable layer through an image-bearing transparency con-sisting solely of substantially opaque and substantially transparent areas to ultraviolet radiation that converts the dinitroso compound to an inhibitor of free-radical polymeri-zation, thereby inhibiting photopolymerization in the exposed areas, (c) exposing a greater portion of the photopoly-merizable layer, including the areas exposed to the imagewise exposure radiation, to actinic radiation that activates the free-radical generating system but does not convert the dinitroso compound to an inhibitor of free-radical poly-merization, whereby a positive polymeric image is formed in the areas not exposed to the imagewise exposure radiation.

2. The method of claim 1 in which the free-radical generating system absorbs radiation within the range of 2000-8000.ANG. and has at least one component that has an active radiation absorption band with a molar extinction coefficient of at least 50 within the range of 3400-8000.ANG..

3. The method of claim 2 in which the unsaturated compound is an unsaturated ester of a polyol and .alpha.-methylenecarboxylic acid.

4. The method of claim 3 in which the unsaturated compound is an acrylic ester.

5. The method of claim 4 in which the photopoly-merizable composition contains 0.01-0.7 part by weighty per part of unsaturated compound, of a benzoin ether as the free-radical generating system.

6. The method of claim 5 in which the free-radical generating system is benzoin methyl ether.

7. The method of claim 4 in which the photo-polymerizable composition contains 0.2-2 weight percent, based on the photopolymerizable composition, of 2,4-dimethyl-2-nitroso-3-pentanone dimer.

8. The method of claim 4 in which the photo-polymerizable composition contains 0.2-2 percent by weight based on the photopolymerizable composition of nitroso-cyclohexane dimer.

9. The method of claim 4 in which the photo-polymerizable composition contains 0.2-2 percent by weight based on the photopolymerizable composition of 1-nitroso-3-methylcyclohexane dimer.

10. The method of claim 4 in which the photopoly-merizable composition contains 0.2-2 percent by weight based on the photopolymerizable composition of 2-nitroso-3-methylbutane dimer.

11. The method of claim 1 in which the dinitroso compound is a nitroso dimer which has a dissociation constant of 10-2-10-10 and a dissociation half-life of at least about 30 seconds in solution at 25°C, and is photodissociable to nitroso monomer which is an inhibitor of free-radical poly-merization, at least some of the imagewise ultraviolet radia-tion has a wavelength of less than 3400.ANG., the actinic radiation is substantially limited to wavelengths greater than 3400.ANG., and a positive polymeric image is developed by removing the nonpolymerized portion of the photopolymerizable layer in the areas exposed to the imagewise exposure radiation.

12. The method of claim 11 in which the free-radical generating system absorbs radiation within the range of 2000-8000.ANG. and has at least one component that has an active radiation absorption band with a molar extinc-tion coefficient of at least 50 within the range of 3400-8000.ANG..

13. The method of claim 12 in which the unsaturated compound is an unsaturated ester of a polyl and .alpha.-methylenecarboxylic acid.

14. The method of claim 13 in which the unsaturated compound is an acrylic ester.

15. The method of claim 14 in which the photo-polymerizable composition contains 0.01-0.7 part by weight, per part of unsaturated compound, of a benzoin ether as the free-radical generating system.

16. The method of claim 15 in which the free-radical generating system is benzoin methyl ether.

17. The method of claim 14 in which the photo-polymerizable composition contains 0.2-2 percent by weight based on the photopolymerizable composition, of 2,4-dimethyl-2-nitroso-3-pentanone dimer.

18. The method of claim 14 in which the photo-polymerizable composition contains 0.2-2 percent by weight based on the photopolymerizable composition of nitroso-cyclohexane dimer.

19. The method of claim 14 in which the photo-polymerizable composition contains 0.2-2 percent by weight based on the photopolymerizable composition of 1-nitroso-3-methylcyclohexane dimer.

20. The method of claim 14 in which the photopoly-merizable composition contains 0.2-2 percent by weight based on the photopolymerizable composition of 2-nitroso-3-methylbutane dimer.

21. The method of claim 2 in which at least one of the nitrogen atoms in the dinitroso compound, in the non-inhibitor or inhibitor form, is attached to a 6-membered aromatic ring or to the beta carbon of a vinyl group attached to a 6-membered aromatic ring, at least some of the image-wise ultraviolet radiation has a wavelength of less than 3800.ANG., the actinic radiation is substantially limited to wavelengths greater than 3800.ANG., and the free-radical genera-ting system has at least one component that has an active radiation absorption band with a molar extinction coefficient of at least 50 within the range of 3800-8000.ANG..

22. The method of claim 21 in which the aromatic dinitroso compound is .beta.-nitrosostyrene dimer.

23. The method of claim 21 in which the aromatic dinitroso compound is .beta.-nitroso-p-t-butylstyrene dimer.

24. The method of claim 21 in which the aromatic dinitroso compound is benzo[ c ]cinnolin-N,N'-dioxide.

25. The method of claim 21 in which the aromatic dinitroso compound is benzofuroxan.

26. The method of claim 21 in which the aromatic dinitroso compound is 2,6-dimethyl-4-nitro-1-nitrosobenzene dimer.

27. The method of claim 21 in which the aromatic dinitroso compound is 2-hydroxyethyl 3,5-dichloro-4-nitrosobenzoate dimer.

28. The method of claim 1 in which the image is developed by differential adhesion of a pigment toner to the unpolymerized portion of the photopolymerizable layer in the areas exposed to the imagewise exposure radiation.