Note: Descriptions are shown in the official language in which they were submitted.
~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--
R7 R8 R9 R10
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
-- 6 --
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
- 7 -
~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
- 8 -
~ 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,
,
:
-- 10 --
'
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,
:
- 12 -
. .
~-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,
- 13 -
~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'-
- 14 -
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-
-- 15 -- -
. .
: `: ~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
- 16 -
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-
- 17 -
.
34
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
- 18 -
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.
- 19 -
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,
- 20 -
~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
- 21 -
~ .
~: .
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
- 22 -
"
`~ 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.
- 23 -
' ~
' . :
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.
- 24 -
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
- 25 -
'.
........
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
. ~
- 26 -
~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
- 27 -
" ~,
:'' .
3084
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.
:
- 28 -
'
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:
..
- 29 -
' "
~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
- 30 -
:
':
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.
. ' .
~,
- 31 -
:, ~
.. . . .
. . .
3~84
i H
~ a 0OOO0 0OOOO0O0OOO0O
U~
O
X ~ ~
E~ g
00 O O O O O O O O O O O O O O O O O O
' 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 4
~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 ~ ~ ~
--32
. .
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-
N02
:
CH= ~ (CH3)2
d = ~
2
e = CH 5HH2
2
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):
.~,
X - 33 -
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.
- 34 -
~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
- 36 -
'' -
~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:
:.
., .
- 37 -
-~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
- 38 -
.~.. .
. ~
''' ' - ' ' "' ' ' ' " ' ' '
~ 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.
- 39 -
~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
- 41 -
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.
- 42 -
'-:
~ 3~4
TABLE IV
Positive/~egative-Working Photopolymerization Speed
Example Exposures tsec.) Positive Negative
~o. <380 nm >380 nm Modea Modeb
2/6 8/14
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
.,
- 43 -
~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
.
- 45 -
'
~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
- 46 -
.
:
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
R4
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
.~
- 47 -
~3~
t-butyl, or - C = C - NH - C = C - in which
R7 R8 R9 R10
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
- 48 -
.~
. .
.
~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
- 49 -
' ~,.
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.
- 50 -
'. '~
: . ~
. :
