Note: Descriptions are shown in the official language in which they were submitted.
~ FN 914,771
PHOTOPOI.Y~ERIZABLE COMPOSITION
Field of_the Invention
This invention relates to novel photopolymerizable
compositions, photoimagable recording element, and a pro-
cess for imaging with photopolymerizable compositions.
Prior Art
Photopolymerizable compositions have been used in
photosensitive elements, such as printing plates, for a
number of years. Such compositions have been.satisfactory
only where contact printing of the plate and relatively
long time exposures can be tolerated. Most representative
of the prior art are compositions disclosed in U.S. Patents
Nos. 3,218,167 and 3,887,450. In U.S. Patent No. 3,218,167
photosensitive compositions comprising 1) an ethylenically
unsaturated compound (e.g., pentaerythritol polyacrylate),
2) a sensitizing dye, and 3) a thermoplastic binder (e.g.,
cellulose ether or polyvinyl ether). In U.S. Patent No.
3,887,450 a radiation sensitive composition is described
which comprises 1) an acrylic monomer (e.g. pentaerythritol
triacrylate), 2) a photosensitive dye, and 3) a binder com-
prising a copolymer of styrene and a carboxyl containlng
comonomer (e.g., acrylic or malelc acid). This latter com-
position has the advantage of being developable (i.e. solu-
ble in non-irradiated areas) by basic developers. The com-
position is relatively slow, however, and must be exposedin the absence of oxygen.
Radiation sensitive elements which are oxygen in-
sensitive have been produced by overcoating the elements
.. ~
- 1~.22~9~
with an oxygen barrier layer as in U.S. Patent No. 3,895,
949. Here a support bearing a photopolymerizable composi-
tion comprising a glycidyl acrylate adduct of a styrene/
maleic anhydride adduct, and ethylenically unsaturated
monomer (e.g., pentaerythritol tetraacrylate), and a photo-
initiator is overcoated with an oxygen/moisture barrier
layer (e.g., a copolymer of an acrylic acid and copolymer-
izable ethylenically unsaturated compound). Such elements
are relatively oxygen insensitive (by reason of the bar-
rier layer), and with proper selection of the barrier layercan be developed with basic solutions after exposure. These
elements remain relatively slow and require the additional
coating operation to provide the barrier layer. In addi-
tion to the time and cost factors resulting from the over-
coating operation, careful control of solvents and condi-
tions in this step must be observed to avoid sensitometric
damage to the photosensitive layers.
Other radiation sensitive compositions known in
the art include those of U.S. Patent No. 3,827,956. This
ultraviolet radiation sensitive compositlon comprises 1)
an acrylic monomer (e.g., pentaerythritol triacrylate),
2) an acrylate ollgomer (e.g., the reactlon product of
toluene dlisocyanate wlth two equlvalents of 2-hydroxyethyl
methacrylate), and 3) a halogenated polynuclear lactone
catalyst. U.S. Patents Nos. 3,297,745; 4,017,649; and
4,065,627 describe other acrylate end-capped urethane oli-
gomers which can be homopolymerized or copolymerlzed with
other ethylenically unsaturated compounds. These materials
are photopolymerizable with relatively high radiation sen-
- 1~.2Z9~?9
--3--
sitivity and low oxygen sensitivity, but they are not base
soluble and have no base developable printing plate capa-
bility because o~ this. These compositions also have poor
bonding characteristics to metal surraces such as zinc and
aluminum.
Summary of the Invention
It has been found that high speed radiation sensi-
tive photopolymerizable compositions with excellent adhe-
sion to certain substrates, especially aluminum surraces,
which compositions arè suitable for use in radiation sensi-
tive printing plates and color proofing sheets can be made.
These compositions also can have extensive shelf stability
and oxygen insensltivity, and the polymers produced there-
from are tough and have a long service life. The composi-
tions are also base soluble and can be developed in basicsolutions in printing plate processes.
The photosensitive compositions of the present
invention comprise 1) an ethylenically unsaturated free
radical polymerizable end-capped oligomer, the bridging
oligomeric portion between the unsaturated capping groups
having carboxyl group substitution thereon, 2) a polymeric
binder, 3) at least one free radlcal polymerizable monomer
having at least one ethylenically unsaturated ~roup, and
Il) a radiation sensitive initiator system capable of ini-
tiating free radical polymerization upon absorption ofelectromagnetic radiation.
A storage stable photosensitive imaging element
of particular use in providing base developable printing
1~.2Z~9
--4--
plates can be made by applying the photosensitive composi-
tions of the present invention to a support layer.
Particularly improved compositions comprising the
photosensitive oligomers, limited classes of binder, poly-
merizable monomers, and photoinitiation systems have unex-
pectedly high radiation sensitivity and no oxygen or mois-
ture sensitivity.
Details Of the Invention
There are basically four essential ingredients of
the radiation sensitive compositions o~ the present inven-
tion, l) an oligomer, 2) a binder, 3) a polymerizable mon-
omer, and 4 ) a photoinitiation system. All four of these
materials must be present in the polymerizable composition
for it to work well in photoimagable recording elements as
in lithographic printing processes. Generally, the compo-
sitions comprise per 100 parts total:
10 to 60 parts by weight of oligomer,
lO to 60 parts by weight of binder,
lO to 60 parts by weight of monomer, and
0.1 to 12.0 parts by wetgh~ of photoinitiator
system. It is pre~erL-ed to have as the photoinitiator sys-
tem a photosensitizer and a compound which when photosensi-
tized is capable of initiating free radical polymerization.
In the practice of this invention the second compound is
defined as an initiator. The photoinitiator system is more
preferably present in an amount Or 0.5 to 10 parts. Pre-
ferably, the photosensitive composition comprises per 100
parts total:
~zzg~9
--5--
15 to 45 parts by weight of oligomer,
15 to 35 parts by weight of binder~
25 to 50 parts by weight of monomer,
0.2 to 10 parts by weight of initiator
(more preferably 2 to 8).
0.1 to 5 parts by weight of photosensitizer
(more preferably 1 to 4j.
Most preferably the compositions of the present invention
comprise per 100 parts total, by weight:
20 to 35 parts oligomer,
20 to 30 parts binder,
30 to 50 parts monomer,
2 to 6 parts initiator, and
1 to 3 parts photosensitizer.
Generally, the photosensitive compositions of the
invention are prepared by mixing the components in a low
boiling (at atmospheric pressure boiling at less than about
150C) polar solvent that is not reactive with carboxyl
groups or ethylenically unsaturated groups, such as methan-
ol ethanol, propanol, acetone, methylethyl ketone, tetrah-
hydro~urane or mixtures thereof. There may even be water
present although less than 50% by wieght of water ln the
solvent is preferred. The amount of solvent used (gene-
rally 0 to 98% by weight, preferably 10 to 96% by weight
and in lithographic applications 85 to 95% by weight sol-
vent is most preferred) depends upon the desired viscosity
and desired coating thickness. It is often desirable to
add a surfactant or coating aid, but these aids, including
the solvent are not functionally required for practice of
the invention, but are merely better modes of practice.
-6~ i~Z;~9
0.001 to 2% of surfactant, particularly silicone or fluor
carbon surfactants will ususlly be sufficient.
These compositions may contain any number of addi-
tional useful additives such as dyes, pigments, coating
aids, surfactants, etc.
The coating weight of the compositions of the pre-
sent invention is usually 0.3 to 9 g/m2, preferably 0.5 to
5 g/m2, and most preferably o.8 to 2.4 g/m2. Suitable sub-
strates include resin coated paper, various transparent or
opaque plastic sheet or film, metal sheets and foils (pre-
ferably aluminum substrates that have been grained and an-
odized).The coated substrates must be maintained in the
absence of light unless the element is sensitized to a
narrow range of the electromagnetic spectrum outside the
range of normal light and the element is provided with a
filter layer which excludes normal visible light.
The preferred utility of the photopolymerizable
compositions of the present invention is as a presensitized
plate for use in printing operations such as in the forma-
tion of lithographic plates. This structure comprises agrained and anodized aluminum substrate coated with from
0.3 to 9 g/m2 of the compositions of the present lnvention.
Grained substrates are surfaces which have been textured
or rou~hened. This treatment is well known in the art and
can be effected by brush graining (roughening with an abra-
sive material), chemical etching, or electrochemical grain-
ing. Anodizing is the well known anodic oxidation of metal
surfaces. Polymer top coat layers used in these construc-
tions must be dissolvable in aqueous alkaline solutions of
. ,
-7- ~ ZZ9~99
pH 8-13 such as the aqueous developers of the examples.
A generic structural formula for the urethane
oligomers can be drawn as follows:
1l
(E-D ~ R--tOCA)b
wherein E is an ethylenically unsaturated, free
radical polymerizable group, preferably selected
from acryloyloxyalkoxy (alternatively named
acryloxyalkoxy), methacryloylalkoxy (alternatively
named methacryloxyalkoxy), vinylalkoxy, and allyloxy,
D is the residue of polyisocyanate (preferably
a diisocyanate) having at least two of its -N=C=0
groups reacted to form -NHC- groups, D bonding E to R,
A is a carboxylic acid containing group, (e.g.,
O O
~CH2)mC ~ , -C6H4!COH, etc.),
0~1
a is a number having an average value between
2 and 20,
b is a number havlng an average value between
0.3 and 10, and
m = 1 to 6,
R is the residue of a polyol having at least
a + b hydroxyl groups and a number average molecular
weight between 90 and 10,000, the residue formed by
removal of hydrogen from the hydroxyl groups.
-8- 1~.2~
The backbone of the oligomer, group R, may be any
aromatic or aliphatic polyol having a molecular weight be-
tween 90 and lO,000. The backbone of the oligomer may be
any oligomer with the requisite molecular weight and num-
ber of hydroxyl groups, but polyesterpolyols and polyoxy-
alkylene polyols are preferred. Linear oligomeric polyols
are useful but the branched or three-dimensional polyols
such as polycaprolactone polyols are preferred. The back-
bone may be prepared by any of the many well known methods
of forming polyhydroxyl substituted oligomers having a mo-
lecular weight between 90 and lO,000. The polyols must
have a hydroxy equivalent weight of between 45 and 5,000 to
be useful according to the present invention. Preferably
the polyol has a hydroxy equivalent wieght between 90 and
4,000 and most preferably between 200 and 2,000.
The oligomeric backbone may be homopolymeric, co-
polymeric, graft polymeric, or mixtures thereof. For ex-
ample, polycaprolactone polyols may be used, or lower mo-
lecular weight polycaprolactone polyols (average molecular
weights of less than, for example, 500) may be ~oined by
polyacids (preferably dicarboxylic acids) or by polyiso-
cyanates (preferably diisocyanates) to form higher molecu-
lar weight oligomer backbones.
In the synthesis of the oligomers useful in the pre-
sent invention, it is preferred to ~oin the E-D substituent
to the oligomeric backbone R by first separately forming
an adduct of the polyisocyanate of which D is a residue by
reacting one mole of the diisocyanate with one mole of an
ethylenically unsaturated free radical polymericable mono-
`~:
`
~,2~.C~
- 9 -
mer having one hydroxyl group. The adduct formed is then
reacted with a hydroxyl group on the oligomer polyol back-
bone (the reaction being with an isocyanate group). In an
alternative method where the compound with the free radi-
cal polymerizable group with one hydroxyl group and the
polyisocyanate are added to the oligomeric polyhydroxy
backbone before forming the E-D adduct, the polyisocyanate
will act both as a polymer extender for the oligomer and as
an adduct former with the free radical containing compound.
In such a reaction there would be far less control over the
final product and there would be a tendency for the oligo-
mer to gel. Therefore the free radical polymerizable mon-
omer and the polyisocyanate (preferably diisocyanate) in an
independently run synthesis form, for example, an isocyan-
atoalkylacrylate, isocyanatoalkylmethacrylate, an isocyan-
ato alkyl ether, or isocyanatoalkylvinyl ether adduct.
The adduct (E-D) formed in that step is then caused
to react with the polyhydroxy containing backbone so that
the remaining isocyanate group of the adduct reacts with
some, but not all,of the hydroxyl groups on the oligomer
to bond thereto.
The carboxyllc acld groups are added to the oll-
gomerlc backbone preferably after addltlon of the free ra-
dlcal polymerlzable moletles by reactlon of remalnlng hy~
droxyl groups on the ollgomeric backbone with a compound
having free carboxyl groups. Preferably such a compound is
a dicarboxylic acid or anhydrlde so that the linklng bond
to the oligomeric backbone is an ester group. An isocyan-
ate linkage can be formed by first making an acid-isocyanate
.
~ 2Z~9
--10--
adduct.
A more specific formula representing preferred
oligomeric materials is as follows:
(E-D-RltaR2--tRl-C-R3-C-oH)b
wherein D, a, and b are as defined above,
E ~s selected from ~CH2~nO-C-C=CH2, ~CH2~nO-I=CH2,
4 R4 R4
and ~CH2~nO-CH2-CH=CH2, where R is -H or -CH3 and
n is an interger of from 2 to 4 inclusive,
R is the residue formed by the removal of active
hydrogen atoms and hydroxyl groups from oligomeric
Q-hydroxy carboxylic acids or the residue formed by the
removal of active hydrogen atoms and hydroxyl groups
from oligomeric diols,
R is a residue, having a valence of a plus b, of
an aliphatic polyol having the formula R5(oH)a+b after
removal of a + b hydrogens from hydroxyl groups, or
a polyol having the formula
(HO ~ R5-o-D-o-R5(oH) =
after removal of a + b-l hydrogens from hydroxyl groups
wherein R5 is the residue of an aliphatic polyol rad-
ical formed by having the OH groups removed therefrom
and having 3 to 10 valences substituted with OH groups
and which can have one or two ether oxygen atoms in the
aliphatic backbone, and
1~.'2Z9~9
R3 is the residue of a dicarboxylic acid having
o
both -C-OH groups removed therefrom.
Preferably the molecular weight of (Rlt-aR2(Ri)b
is between 2QO and 5,000.
Particularly desirable aliphatic polyols from
which R is formed are polyether polyols, polyester polyols,
polyactone polyols, polyolefin polyols, polydiene polyols,
polysiloxane polyols, poly (alkylacrylate) polyols, and
poly (glycidyl ether) polyols.
A particularly desirable material is represented
by the structural formula
[Hoc-R3-c-o~ R7~oCNH-R6-NHCo~CH ~--OCC-CH ]
wherein R3 and R are as defined above,
c is 2 to 5 inclusive,
p is a number average value of 2 to 7.7,
q is a number average value of 0.3 to 4,
R6 is the residue of a diisocyanate having two
-N=C=O groups removed therefrom and pre~erably is an
aromatic resldue thereor, and
R7 is an organic triyl radlcal which ls the
residue of an organic polyol with at least three
hydroxyl groups removed therefrom and having a
molecular weight of from 90 to lO,OOO, preferably
selected from aliphatic triols, tetrols and pentols,
poly(oxyalkylene)triols, tetrols and pentols, poly-
1~ 2~
-12-
estertriols, tetrols and pentols, polyactonetriols,
tetrols and pentols, polyolefintriols, tetrols and
pentols, polyacrylatetriols, tetrols and pentols,
polyalkylacrylatetriols, tetrols and pentols, and
polysiloxanetriols, tetrols and pentols.
Another particularly desirable material can be
represented by
8~ ~ O~C~ H2)d~elR3~ oH3 f
R tM ~0 (CH2)d~e7 o ll
~O:~C~CH2~dO3-elCIl'lHR6Mlllco~cH2~eocc~ h-fll2
wherein R3 and R are defined above,
d is 1 to 6 inclusive,
e is an average value Or 0.5 to 5 inclusive,
f is an average value of 1 to 6 inclusive,
R8 is the dival.ent hydrocarbon radical which is
the residue of an organic polyisocyanate (prererably
diisocyanate) with two lsocyanate groups re~oved there-
from,
R9 is an alkanepolyyl radical having a valence of
h + 1 that is the residue of an alkanepolyol having
h + 1 hydroxyl groups removed therefrom ( preferably
having h + 1 hydroxyl groups before removal), said
alka~epolyol having a molecular weight of from 100 to
.2zg~
-13-
10,000 and preferebly 200 to 2,000, wherein h is an
integer of from 2 to 8.
The general method of preparing the oligomers of
the present invention is as follows.
STEP ONE - Preparation of a one-to-one adduct of a
hydroxyalkyl (free radical polymerizable) material and a
polyisocyanate, preferably a diisocyanate. This is done
by reacting the two materials in a one-to-one ratio.
STEP TWO - Reaction of an organic polyol having X
number of hydroxyl groups with up to X - 1 moles of the
adduct of STEP ONE. This forms a urethane oligomer having
both ethylenically unsubstituted groups and at least one
free hydroxyl group. Although, of course, in this reaction
some individual oligomeric moieties may have all X hydroxyl
groups reacted with the isocyanate, by control of the pro-
portions of' isocyanate adduct and polyol, the number aver-
age of free hydroxyl groups on the urethane oligomer will
be at least one.
STEP THREE - The f'ree hydroxyl ~,roups on the pro-
duct of STEP TWO are esterirled with a polycarboxylic acidtpreferably a dicarboxylic acid and most preferably an
anhydride of a diacid). This reaction f`orms the carboxyl-
substituted, ethylenically unsaturated urethane oligomer of'
the invention.
The adduct of the hydroxyalkylacrylate and the
diisocyanate of STEP ONE has the general formula:
O O
OCN-R6-NHC-0(R10)OCC-CH2
1~.229~99
--14--
wherein R6, R4 and a are as defined above, and
R6 is preferably tolyl, and
R10 is an aliphatic group and preferably is
2)2-6
It is preferred to use diisocyanates such as tol-
ylene-2,4- diisocyanate and isophorone diisocyanate because
of the great differential between reactivities of the iso-
cyanate groups thereon. Without this differential, the
product would have to be purified or else there would be
less control over the subsequent product.
Such adducts are prepared by the addition of about
0.9 to 1.1 molar equivalent of the hydroxyalkylacrylate to
one mole of organic diisocyanate while stirring the reac-
tion mixture. Generally, it is desirable to hold the
temperature below about 30C during the addition. The
reaction can be complete after stirring the mixture for 10
minutes to an hour or more. If not completed that quickly,
the reaction may be completed by further heating the mix-
ture at temperatures of 50 or more for at least an hour.
Since many of the reaction products are vlscous liquids
or solids (the reaction product of 2-hydroxyethyl methacry-
late and 2,4-toluene-diisocyanate is a solld) it is prefer-
able to add 0.25 to about 35 parts by weight of a non-
functional group containing solvent, such as methylethyl
ketone, acetone, tetrahydrofurane or the like. The solvent
can be added at the beginning of the reaction, or along
with the addition of the hydroxyalkylacrylate. Although
not always necessary, it is often desirable to add a cata-
lyst to effect the reaction between the hydroxyl group of
' '
,
~.2 ~9 ~ 9
-15-
the hydroxyalkylacrylate and one of the isocyanate groups
of the organic diisocyanate. Suitable catalysts for the
reaction are well known; an example of which is dibutyltin
dilaurate.
STEP TWO is accomplished by adding over a period
of one to five or more hours either the product of STEP
ONE to an organic polyol as defined above while heating
the mixture at about 50 to 100 or vice-versa. As for
STEP ONE, a catalyst such as dibutyltin dilaurate can be
used to facilitate the reaction. It is often desirable
to add a polymerization inhibitor such as 2,6-di(t-butyl)
-4-methylphenol to prevent premature polymerization. The
ratio of diisocyanate-hydroxyalkylacrylate adduct to organ-
ic polyol is chosen so that one mole of oligomer obtained
by the reaction contains at least two acrylic groups but
leaves at least 0.3 equivalents unreacted hydroxyl groups.
STEP THREE is carried out, generally without iso-
lating the product of STEP TWO, by esterification of un-
reacted hydroxyls in the product of STEP TWO with an anhy-
drlde of a dicarboxylic acid. Preferably, the esterifi-
cation is accomplished by adding an amount of an anhydride
of a dicarboxylic acid such as preferably succinic acid
anhydride or adipic acid anhydride and continuing heating
50 to 100C for 3 to about 10 hours, the higher the temper-
ature, the shorter the heating time required. Depending onthe extent of carboxylation desired, there is used from
about 0.3 to about 4 moles of anhydride per mole of organic
polyol originally present in the reaction mixture. The
esterification, however, can be preformed using in place of
.
-16-
the anhydride an ester of the dicarboxylic acid, viz., the
methyl or ethyl ester and by ester interchange distill of
the corresponding methanol or ethanol formed. Esterifica-
tion can also be preformed using other reactive deriva-
tives of the dicarboxylic acid such as the diacid chlorideand removing the hydrogen chloride formed. Sometimes it is
necessary to add a basic catalyst, such as lithium acetate,
to increase the rate of this reaction.
Controlling the ratio of the number of acid (car-
boxylic acid) groups on the oligomer to the gram molecularweight of the oligomer is an effective way of controlling
the bondability of the composition to a substrate after
photoinitiated reaction. With increasing acid concentra-
tion, the composition is removed more easily in development.
A wide range of ratios can be used, depending upon the per-
formance characteristics desired in the final product. A
composition having a ratio of molecular weight to acid
groups between 67 and 17,000 is useful. It is preferred to
have the ratio of molecular weight to acid groups in the
oligomer between 500 and 5,000, and most preferably between
800 and 3,000.
Binders
The second of the critical elements in the photo-
polymerizable compositions of the present invention is the
binder. This material is an organic film forming polymer
having a molecular weight of at least 6,ooo, prererably
12,000 and most preferably at least 15,000. It is desira-
ble, but not essential for practice of the present inven-
tion, for the binder to have a labile hydrogen or easily
1~ 2~
-17-
abstractable hydrogen thereon. The polymer preferably has
a molecular weight of no greater than 100,000, preferably
no greater than 80,000 and most preferably no greater than
50,000, although binders with molecular weights up to
2,000,000 or 3,000,000, are known in the art. To be a la-
bile or easily abstractable hydrogen, a hydrogen in the
binder must be attached to a carbon atom having an adjacent
heteroatom selected from N, S, Se, and O. Preferably the
heteroatom is N~ S, or O. It is also preferred that the
carbon having the easily abstractable hydrogen thereon is
in a 5`, 6, or 7-membered heterocyclic ring comprised of C,
N, S, and 0 atoms, with preferably two heteroatoms ad~acent
to the carbon atom having the labile hydrogen. The carbon
atom bearin~ the labile hydrogen can be primary, but is
preferably secondary or tertiary. The greater the ease of
abstractability the lower the proportion of binder that the
composition needs, althou&h not necessarily in a linear re-
lationship. Preferred binders are the polyvinyl acetals
such as polyvinyl formal, polyvinyl butyral, and mixtures
thereof. Poly-(vlnyl methylether), polyvinyl alcohol, hy-
droxyalkylcellulose (e.~., hydroxypropylcellulose), polya-
mides, polyvlnylacetate, polyvinylacetate-polyvinylchloride
copolymers, polyehtyleneoxides, and polyacrylates (e.g.
polyalkylmethacrylates have also been found to work well).
The rate or quantum efficiency of double bond con-
version (i.e., polymerization) and the photosensitivity of
various coatings exposed in air are a function of the type
of polymeric binder used. While some polymers give no in-
crease in rate and photosensitivity to the composition,
~,2
-18-
many polymers have been found that give surprisingly
large increases. Amongst the polymers that have been shown
to give an increase in the rate of conversion of double
bonds include polyvinylacetals, polyvinylalcohol, hydroxy-
alkylcellulose (e.g.~ hydroxypropylcellulose), polymides,polyvinylacetate, polyvinylacetatevinylchloride, polyethyl-
eneoxide, and polyalkylmethacrylates. Polymers that do
not give an increase include certain aliphatic hydrocarbon
resins, cellulose acetatebutyrate, certain polyurethanes
such as EstaneR, and linear saturated polyesters.
It should be understood by those knowledgeable in
the art that not all polymers that give a rate increase
are necessarily the best binders for lithographic plate
coatings although they are still useful and desirable in
other imaging processes such as duplicating film and proof-
ing systems. Other properties such as solubility, water
sensitivity and adhesion must be considered in choosing a
polymeric binder for lithographic plates.
The exact function of the binder ln the composi-
tions of the present :Lnvention is, not understood. Thelabile hydrogen thereon is belleved to be desl,rable, as
many materials without a :labile hydrogen do not appear ~o
work as well as those w:l.th labile hydroKens, although some
do ln fact work well. Oxygen barr:ler characteristics may
be additionally desirable in the binder polymer but such
characteristics are not known to be essential.
Monomers
Another of the critical materials in the photo-
polymerizable compositions of the present invention is
1~.2Z~9
--19--
the monomer. This material is a free radical polymerizable
monomer having one or more ethylenically unsaturated groups,
and preferably 2 to 4 ethylenically unsaturated groups such
as acrylate, methacrylate, vinyl and allyl. Preferred are
compounds having multiple acrylate and methacrylate groups,
e.g., acrylic esters o~ low molecular weight polyols, such
as trimethylolpropanetriacrylate, pentaerythritol tetraacry-
late and triacrylate, etc. Preferably these monomers have
a molecular weight of less than 2,000 and more preferably
less than 1,000.
Suitable free radical polymerizable monomers use-
ful in the compositions of the invention are well known
and listed in many patents, e.g., U.S. Patent Nos. 3,8~5,
949 and 4,037,021. Preferred monomers are the polyacrylate
and polymethacrylate esters of alkanepolyols, e.g., pent-
aerythritol tetraacrylate, tris(2-acryloxyethyl) isocyanu-
rate, tris(2-methyacryloxyethyl)-isocyanurate, 2-acetoxy-
ethyl methacrylate, tetrahydrofurfuryl-methacrylate, l-aza-
5-acryloxymethyl-3,7-dioxabicyclo [3Ø0] octane (ADOZ)
bis[4-(2-acryloxyethyl)phenyl]dimethyl methane, dlacetone
acrylamide, and acrylamidoethyl methacrylate.
Initiator
The compositions Or the present invention must also
have a radiatlon sensitive system capable of initiating
free radical polymerization upon absorption of radiation.
Free radical initiators are materials known in the art,
such as F e-Radical Chemistry, D. C. Nonhebel and J. C.
Walton, University Press (1974). Particularly suitable
free radical generators can be selected from many classes
-20-
of organic compounds including, for example, organic
peroxides, azo compounds, aromatic dlazonium salts, aromatic
iodonium salts, aromatic sulfonium salts, aromatic phos-
phonium salts, quinones, benzophenones, nitroso compounds,
acyl halides, aryl halides, hydrazones, mercapto compounds,
pyrylium compounds, triarylimidazoles, biimidazoles,
chloroalkyltriazines, etc. These materials, in general,
must have photosensitizers therewith to form a photo-
initiator system. Photosensitizers are well known in the
art.
Additional reference in the art to free radical
photoinitiator systems for ethylenically unsaturated
compounds are included in U. S. Patent No. 3,887,450
(e.g., column 4), U. S. Patent No. 3,895,949 (e.g.,
column 7), and U. S. Patent No. 4,043,819. Preferred
initiators are the onium salts as disclosed in U. S.
Patent Nos. 3,729,313; 4,058,400; and 4,058,401. Other
desirable initiators are biimidazoles; and chloroalkyl-
triazines as disclosed in U. S. Patent No. 3,775,113.
These references also disclose sensitizers therein.
Another good reference to photoinitiator systems is
Li~ht-Sensitive Systems, J. Kosar, 1965, J. Wiley and
Sons, Inc., especially Chapter 5.
Preparation I
A polycaprolactone hexol is prepared for use
in forming a carboxyl substituted urethane oligomer.
63.5 grams dipentaerythritol, 228 grams epsilon-
carprolactone, and 0.02 grams 2,6-di-t-butyl-4-methyl phenol
(as an oxidation inhibitor)were added to a 500 ml, three-
neck flask which hadbeen fitted with an overhead mechanical
' ~ ,
` ~
~.2;;~9~?9
-21-
stirrer and a condenser. The liquid was deoxygenated for
20 minutes by bubbling with dry nitrogen from a gas dis-
persion tube. This tube was then replaced with a gas in-
let adapter and the reaction mixture was heated while main-
taining a slight positive pressure with nitrogen. Themixture was maintained at 170C for 5 hours under contin-
ual stirring. The reaction mixture was then allowed to
cool to room temperature under a nitrogen atmosphere. This
material is referred to as P-I. This procedure is similar
to that in U.S. Patent No. 3,169,945.
Preparation II
A urethane oligomer (hereinafter P-II) was pre-
pared according to the following procedures.
A 1000 ml three-neck flask was fitted with an
adapter, mechanical stirrer, thermometer, addition funnel,
and drying tube. To this flask was charged 175 grams of
polycaprolactone hexol P-I and 60 ml of methylethyl ketone.
A solution of 13 grams of 2,4-tolylene diisocyanate in 9
ml of methylethyl ketone was slowly dripped into the first
solution wlth stirring at toom temperature. The additlon
was completed in 20 minutes and the reaction mixture
stirred for 90 minutes at 30C, after which time infrared
spectoscopy showed that essentially all the isocyanate had
reacted.
To a second flask fitted with an overhead mechan-
ical stirrer, thermometer, addition funnel, and drying tube
was charged 86.1 grams of 2,4-tolylene diisocyanate. To
the addition funnel was added 70.2 grams 2-hydroxyethylme-
thacrylate (hereafter HEMA) and 0.02 grams of the inhibitor
.
1~.2Z9!~9
-22-
of the previous preparation, which was then slowly added
with stirring to the diisocyanate while maintained below
or at 30C. The addition was completed in 15 minutes and
after 40 minutes of reaction time, a white solid formed.
The solid was dissolved in 45 ml of methylethyl ketone by
heating to 45C and held at that temperature for lO min-
utes to complete the reaction.
The flask containing the reaction product (adduct)
of the polycaprolactone hexol (P-I) and the 2,4-tolylene
diisocyanate was heated to 67C and the solution of the
HEMA/2,4-tolylene diisocyanate adduct in methylethyl ketone
was added slowly with stirring over a period of 2 hours.
27 grams of succinic anhydride was then added with an addi-
tional 0.02 grams of the inhibitor. Heating and stirring
was continued until the anhydride had completely reacted
(about 5-6 hours).
The final product is a carboxyl substituted ure-
thane oligomer, P-II.
Preparation III
The preparation of a second carboxyl substituted
urethane oligomer ls here described.
To a 500 ml three-neck flask was charged 29.2
grams of a poly(propylene oxide)tr:lol having a molecular
weight of 740, 25 ml ethyl acetate, and 0.007 grams of
methylhydroquinone as a reaction inhibitor. The flask
was heated ln a 65C oil bath with stirring and 13.0 grams
HEMA and 17.4 grams tolylene diisocyanate were added simul-
taneously from addition funnels. After addition of one
half of these reactants, the reaction mixture was stirred
~ Z~9~
-23-
for another 30 minutes. Then 0.001 grams SnC12 catalyst
and 0.004 grams 3,4-epoxycyclohexylmethyl-3,4-epoxycyclo-
hexane carboxylate were added. The reaction mixture was
stirred another 30 minutes and then the remainder of the
HEMA and diisocyanake were added slowly. Stirring was
continued overnight. Infrared analysis showed no free
isocyanate groups after that time. To this reaction mix-
ture was added, with stirring, 1.4 grams succinic anhy-
dride. The temperature was raised to 93C and held there
until the anhydride was completely reacted. The mixture
was then cooled and diluted to 50% weight solution of
P-III oligomer in ethyl acetate.
Preparation IV
A 250 ml flask was charged with 21.2 grams of a
polycaprolactone polyol having a molecular weight of about
540, 25.1 ml of ethyl acetate and 0.007 grams methylhydro-
quinone as an antioxidant. 17.4 grams of tolylene-2,4-dii-
socyanate and 13.0 grams of 2-hydroxyethylmethacrylate
(HEMA) were individually added to addition funnels on the
flask. The polyol solution was heated to 67C and the
diisocyanate and IIEMA werc added dropwise with rapid stir-
ring until half of each material was added. ~t th:ls point
stirring and heating were continued for 30 mlnutes. 0.002
~rams SnC12 and 0.008 grams of` 3,~1-epoxycyclohexylmethyl-3,
4-epoxycyclohexane carboxylate were added and the solution
stirred for another 30 minutes. The remainder of the
diisocyanate and HEMA was added dropwise and then an addi-
tional 5 ml of ethyl acetate was added. The mixture was
stirred at 67C overnight. When isocyanate was no longer
24- 1~,2 ~ g ~ ~
detectable by in~rared analysis, 1.4 grams of succinic an-
hydride was added along with 10 ml of ethyl acetate. The
temperature was raised to 100C and the reaction of the an-
hydride was indicated by infrared analysis as essentiallycomplete after five hours.
This resulting material, a carboxylic substituted
urethane oligomer, is referred to as P-IV and is useful in
the practice of the present invention.
Preparation V
A particularly useful binder material for the oli-
gomers was prepared as follows. A low molecular weight
polyvinyl alcohol (88% hydrolyzed polyvinylacetate) was
reacted with butyraldehyde and acrolein using an acid cata-
lyst, preferably sulfuric acid. The proportion of reac-
tants was 100/43.2/6.4 respectively. The product was preci-
pitated from water with a dilute weak basic solution (r~a-
HC03). Analysis of the product showed the empirical for-
mula to be close to that based on the stoichiometry of the
reaction,
1l
ol~l f - C - (~l3
~C~12-~1)5. IJ(C~C~12-C~l~C~-12f~
O~ 0 0~0
CH2C~2C1~3 DC~
C~12
This material is hereinafter referred to as P-V.
~.2Z9~9
-25-
Preparations VI-XI
Six additional oligomers were prepared for eval-
uation in the present invention.
P-VI was prepared by first placing 128.8 gof2,4-
toluenediisocyanate into a three-neck, 250 ml flask equi-
pped with a mechanical stirrer and a pressure equalizing
dropping funnel. The flask was maintained at room temp-
erature with a water bath. Hydroxyethylmethacrylate
(106.6 g) and o.o89 butylated hydroxy toluene and 100 g
methylethyl ketone were added slowly over a 30 minute per-
iod. The reaction was stirred for one hour at room temper-
ature. Methylethyl ketone was added and the reaction mix-
ture was heated to 45C for 3 hours to complete the reac-
tion.
P-I (350 g of 79% solids in methylethyl ketone)
was placed into a 500 ml, three-neck flask equipped with a
mechanical stirrer, pressure equalizing dropping funnel
and 26.0 g 2,4-toluenediisocyanate was added over a 30 min-
ute period. The temperature rose to 32C. The mixture
was cooled to room temperature and stlrred over the week-
end. The first reaction product from the above synthesis
was added over a four hour period to this second solution
which had been heated to 65C. Heating was continued for
ten hours to form the second reaction product.
1.8 g of succinic anhydride and 0.1 g lithium
acetate were added to 112.4 g (71% solids in methylethyl
ketone) of the second reaction product and the entire mix-
ture heated to 78C for twelve hours to complete the reac-
tion and form oligomer P-VI.
.,
~ ,
$~ zg~
-26-
P-VII was prepared by placing 112.4 g (71~ solids
in ~ethylethyl ketone) of the second reaction product in
the preparation of P-VI into a 500 ml three-neck flask
with stirrer and condenser and then adding 2.4 g succinic
anhydride and 0.1 g lithium acetate. The mixture was
heated to 78C for 12 hours until the reaction was com-
plete to form P-VII.
P-~III was formed by placing 112.4 g (71% solids
in methylethyl ketone) of the second reaction product in
the preparation of P-VI into a 500 ml three-neck flask
with stirrer and condenser with 5.5 g succinic anhydride
and 0.1 g lithium acetate. The reaction mixture was then
heated to 78C for 32 hours until the reaction was complete
to form P-VIII.
P-IX was formed by first preparing a polycapro-
lactone hexol by introducing 342 g caprolactone and 127 g
dipentaerythritol into a 1000 ml reaction kettle equipped
with a thermometer, mechanical stirrer and condenser.
The reaction mixture was deoxygenated by bubbling dry
nitrogen through a gas dispersion tube for about 30 minutes.
The gas dispersion tube was then replaced with a gas inlet
adapter and the reaction was maintained under a slight
positive nitrogen pressure. The reaction mixture was heat-
ed in an oil bath at 165-170C with continuous stirring
for 24 hours. The product wa:, allowed to cool to room
temperature while under a nitrogen atmosphere.
141.0 g of the polycaprolactone hexol and 50 g of
methylethyl ketone were placed in a 1000 ml flask equipped
with a pressure equali~ing dropping funnel and a mechanical
1~.2~9~9
-27-
stirrer. This solution was maintained at room temperature
by using a water bath while 2,4-toluene diisocyanate
(13.0 g) in 20 g of methylethyl ketone was added over a
25 minute period through the dropping funnel with contin-
uous stirring. Stirring at roorn temperature was continuedfor 22 hours to form the second reaction product.
38.2 g of 2,4~toluene diisocyanate and 0.2 buty-
lated hydroxytoluene were introduced into a 250 mlthree-
neck flask equipped with mechanical stirrer, pressure
equalizing dropping funnel and thermometer. Hydroxyethyl
methacrylate (31.2 g) was added with continuous stirring
over fifteen minutes at a temperature below 30C. The
mixture was stirred for one hour and a white solid formed.
20 ml of methylethyl ketone was added and the mixture heat-
ed to 45C for three hours to complete formation of thethird reaction product.
69.7 g of' the second reaction product and 0.02 g
butylated hydroxy toulene were added to a 500 ml three-neck
flask with a mechanical stirrer, condenser, and pressure
equalizing dropping funnel. This solut:lon was heated to
69C with continuous stirrln~. The entire portlon of` the
third reaction product was added to thls solution over one
hour. Heating and stirrin~ were continued for thirteen
hours to form the fourth reaction product.
13.0 g of succinic anhydride and 0.4 g of lithlum
acetate were added to the fourth reaction product and the
solution heated at 70C to 80C with continuous stirring
to form P-IX.
P-X was prepared by first forming a polyol by
1~ 229~?~
-28-
placing 93.1 g tripentaerythritol and 303.2 g caprolactone
in a 1 liter reaction kettle equipped with mechanical stir-
rer, condenser, and thermometer. The reaction mixture was
purged with dry nitrogen for 30 minutes, and a gas inlet
tube affixed thereto. Positive nitrogen pressure was
maintained over the reaction mixture as it was heated to
165-170C for 9-1/2 hours, then allowed to cool to room
temperature.
300 g of this polyol and 75 g of methylethyl
ketone were introduced into a 1000 ml flask equipped with
stirrer, dropping funnel and thermometer. 16.4 g of 2,4-
toluene diisocyanate was added through the dropping
funnel over 10 minutes. The temperature of the mixture
rose to between 28-32C and continued for about 3-1/2
hours to form the first reaction product. 153 g of this
product (as 80% solids in methylethyl ketone) was added
with 0.04 g butylated hydroxytoluene into a flask and
heated to 65-70C. Over a period of 2 hours the third
reaction product of preparation IX was added to this solu-
tion and heated for an additional three hours.
18.5 g of succinic anhydride and 0.5 g of lithium
acetate was added to the above resulting solution and the
mlxture heated at 70-80C for 22 hours to product P-X.
P-XI was prepared by first forming an adduct of
25 2,4-toluene diisocyanate (26.8 g) and hydroxyethylmethacry-
late (22 g) in 30 ml of methylethyl ketone with 0.02 g
butylated hydroxytoluene in the same procedure used in
forming the third reaction product of preparation IX. This
product was added over a one hour period to the product of
~.,2zg~9
-29-
the second solution of P-VI (87.'7 g as 80% solids in meth-
ylethyl ketone) and 0.02 g butylated hydroxytoluene and
heated to 65-70C. Heating was continued for 7-1/2 hours
at about 67C.
19.6 g of succinic anhydride and 0.4 g lithium
acetate were then added to the solution and heated at 75C
for 84 hours to form P-XI.
Preparation XII
A urethane oligomer (hereinafter P-XII) was pre-
pared according to the following procedure.
A 1000 ml three-neck flask with adapter fitted
with an overhead mechanical stirrer, thermometer, addi-
tion funnel and drying tube was charged with 180 g of a
polypropylene oxide polyol of molecular weight 600 and 90
ml of methylethyl ketone. A solution of 34.8 g 2,4-toluene
diisocyanate in 30 g of methylethyl ketone was added with
stirring at room temperature. The addition was completed
after 80 minutes and stirring was continued at room tem-
perature for 90 minutes. After the addition of 0.02 g 2,6-
di-t-butyl-4-methyl phenol, the temperature was increased
to 45-55C for about 15 hours at which time isocyanate
groups were no longer detected by infrared analysis.
To a 250 ml one-neck flask with a magnetic stirrer
and drying tube was charged 95.7 g 2,4-toluene diisocyanate.
78 g of 2-hydroxyethylmethacrylate was added over a period
of about 10 minutes while maintaining the temperature at
less than 30C with a cold water bath. After about 40 min-
utes of total reaction time a white solid formed and 45 ml
of methylethyl ketone was added. The solution solidified
l~..ZZ9!~3
\
-3o-
on standing overnight and was redissolved by warming to
about 45C.
The product from the reaction of the polyol and
2,~-toluene diisocyanate was heated to 67C and the pro-
duct from the 2-hydroxyethylmethacrylate and 2,4-toluene
diisocyanate was added over a period of about 30 minutes.
After 6 hours 27 g of succinic anhydride and 1.05 g of
lithium acetate were added. After about 28 hours of
heating at 53C to 70C the anhydride was determined to be
completely reacted by infrared analysis.
Examples 1-4
A solution was prepared (in parts by weight) from
3.32 parts pentaerythritol tetraacrylate, 1.87 parts P-II,
0.17 parts triethylamine, 0.34 parts of diphenyliodonium
hexafluorophosphate, 0.17 parts 4,4'-bis(dimethylamino)-
benzophenone (a photosensitizer for the iodonium catalyst)
and 91.62 parts of n-propanol/water azeotrope (71.8% n-
propanol and 28.2% water). Aliquots of this solution were
prepared and 2.50 parts by weight of different organic
polymeric binders were added to the solutlon.
Alumlnum sheets whlch had been grained and ano-
dlzed were coated with these solutions uslng a #14 wlre
wound rod and then dried with a heat gun. The coated alu-
minum was then exposed for 13 seconds ln a vacuum frame to
a carbon arc having about 5000 watt output and at about
1 meter distance through a 21 step sensitivity guide and a
neutral density o.51 filter. Exposed plates were developed
by wiping with a weak basic aqueous solution of 0.63% so-
dium metasilicate and 0.23% sodium (lower alkyl) naphtha-
~.229~9
--31--
lene sulfonate.
The binders used ln the examples were:
1. P-V,
2. Poly(vinyl methyl ether),
3. Poly(vinyl formal), prepared from a poly-
vinyl acetate starting material and hav-
ing 85% of the acetate groups replaced
by alcohol and formal groups (the poly-
vinyl acetate having a viscosity of about
12 cp at 25C, as 86 grams in 1000 ml of
benzene), and
4. Poly(vinyl butyral).
The following table shows the polymer retained
after exposure to a certain number of steps and develop-
ment by the weak basic solution.
Steps
Example Solid Ghost
1 8 10
2 4 6
3 4 5
4 2 4
The "ghost" values indicate the lowest exposure
from which photopolymer was retained on the plate. The
"solid" values indicate the exposure level at which the
developed image density can no lon~er be differentiated
from the background andis believed to be cured to the de-
sired level.
The numbers of the steps consecutively indlcate
an increase of about 40% in filtering strength. The high-
er the step number remaining after development, the corres-
pondingly higher sensitivity of the composition exposed
and developed.
;,'
~.2Z~9
Example 5
The usefulness of the compositions of the present
invention in conventional newspaper printing operations
~as evaluated here.
A solution was prepared having 17.2 grams pentae-
rythritol tetraacrylate, 13.5 grams P-II (70% by weight in
methylethyl ketone), 171.6 grams of polyvinyl formal in a
6% by weight solution in the azeotrope, 295 grams of the
n-propanol/water azeotrope, 4.3 grams of 20% triethylamine 5
3.7 grams of red pigment (Pigment Red 48, C115865 in the
Color Index) in a composition of 1:2 weight ratio to poly-
vinyl formal (as described above), 1.74 grams diphenyllo-
donium hexafluorophosphate and 0.65 grams 4,4'-bis(dimethy-
lamino)benzophenone photosensitizer. This composition was
coated on grained anodized aluminum using a squeeze roll
coater fitted with a rubber gravure sleeve. The coating
weight was about 1.72 grams/m2. The coating was exposed
in a vacuum frame by a carbon arc for 40 seconds through
a neutral density 0.5 filter and a newspaper negative. The
coatlng was developed with the aqueous developing solution
of Examples 1-4 and then gummed with a standard substrac-
tive plate gum. The resulting printing plate was mounted
on a high speed web press using direct lithographic tech-
niques and produced 95,000 newspaper impression without de-
gradation of the image line copy or half-tones.
Exam~le 6
A solution was prepared from 7.72 grams of P-V,
327.4 grams of the n-propanol/water azeotrope, 12.8 grams
of pentaerythritol tetraacrylate, 10.3 grams of a 69% by
i~..Z~9~
-33-
weight solution of P-II in the azeotrope, 3.2 grams of a
20% solution of triethylamine in the azeotrope, 15.7 grams
of Pigment ~ed 48 dispersed in P-V and the azeotrope
(4 8 88), 1.3 grams of diphenyliodonium hexafluorophosphate
and o.65 grams of the benzophenone sensitizer of' the pre-
vious examples. This solution was coated onto grained ano-
dized aluminum using a squeeze roll caoter fitted with a
rubber gravure sleeve at a coating weight of about 1.72
grams/m . The coatings were exposed from a pasteup with
a laser imaging system, using primarily the 351 and 364 nm
lines of an argon ion laser, (at 4 milliJoules/cm2 exposure)
and developed with the mild basic aqueous developing solu-
tion of the previous examples, and gummed with a commercial
substractive plate gum. The printing plates were mounted on
a web offset press and produced high quality impressions.
Example 7
A solution was prepared from 12.8 grams of poly-
vinyl formal from a 6% by weight solution in the n-propanol/
wate,r azeotrope, 1.28 ~rams of pentaerythrlto] tetraacry-
late, 1.42 ~rams of P-IIIas a 50% by weight solution in
ethyl acetate, 24 grams Or the azeotropic solution, 0.28
grams of Plgment Red 48 in polyvinyl formal (1:2 wei~ht
ratio), 8 drops of a 20% solutlon of triethylamine in the
azeotrope, 0.13 grams of' dip~lenyliodonium hexafulorophos-
phate and o.o65 grams o* the benzophenone sensitizer ofthe previous examples.
This solution was coated onto grained anodized
aluminum using the #14 wire wound rod. After exposure
(from a 5000 watt output carbon arc for 13 second through
-34- l~.Z~9
neutral density 0.51 filter) and development with the weak
basic solution of the previous examples, a solid image at
step 6 was obtained~ and a ghost image at step 7 was ob-
tained.
Example 8
A solution was prepared from 1.54 grams of P-V,
2.56 grams of pentaerythritol tetraacrylate, 2.06 grams
of P-II as a 70% by weight solution in methylethyl ketone,
o.64 grams of triethylamine as a 20% by weight solution
in the azeotrope, 4.7 grams of a dispersion of Pigment Red
48 in P-V and the azeotrope (4:8:88), 65.6 grams of the
azeotrope, 0.25 grams of diphenyllodonium hexafluorophos-
phate, and 0.13 grams of 4,4'-bis(dimethylamino)benzophen-
one. This solution was coated with a #14 wire wound rod
onto a substrate comprising polyethylene film with a top
coat of TiO2 and CaCO3 in a polyurethane binder. This
coating was air dried with a heat gun and overcoated with
a 10% solution of low molecular weight (88% hydrolyzed
polyvinyl acetate) poly(vinyl alcohol) with a small amount
of inert surfactant as a coating aid. A #10 wire wound
rod was used to coat this solution. The dried coating was
exposed in a vacuum frame to a carbon arc for 13 seconds
through a 0.5 neutral density filter, a half-tone negative,
and a sensitivity guide. The exposed coating was developed
with an aqueous solution of o.63% sodium metasilicate and
0.23% sodium (lower alkyl)naphthalene sulfonate. A strong
magenta image on a white background was obtained. Solid
3 and ghost 5 steps were visible and sharp 3-97% dots of
at least a 110 line screen were obtained.
~..2zg~9
-35-
Examples 9-15
The following examples show the necessity and in-
teraction o~ the different components of the system of the
present invention. The effect of poly(vinyl alcohol) top-
coats, normally used in the art as an oxygen barrier, wasalso investigated.
Solutions were prepared with di~ferent combina-
tions of representative additives. P-V was used as the
binder, P-II as the carboxyl containing free radical poly-
merizable oligomer, pentaerythritol tetraacrylate as thefree radical polymerizable monomer, diphenyliodonium hexa-
fluorophosphate (as 0.04 parts by weight) as the free
radical initiator,
N ~ N \ C7H15, here~nafter re~erred
C2H5 CH2C02H
to as CEBI-I (0.01 parts by weight) as sensitizer, and poly
(vinyl alcohol) as a topcoat. The solu~lons havin~, the
compositions noted below in the table were coated on
grained and anodized aluminum to g:lve dry coating weigllts
of ~rom 1. o6 to 1.61 grams/m2. Where a topcoat was present,
the poly(vinyl alcohol) was applled at about the same coat-
ing weight as the base coat. In the examples the solutions
were made from isopropanol or methanol-methylethyl ketone-
water solvents. Triethylamine was added in all examples in
amounts equivalent to the acid in P-II.
z,~ 9
-36-
The dried samples were exposed through a 21 step
sensitivity guide for 2 seconds with a 16,000 foot candle
tungsten source. The exposed samples were developed by
wiping with an aqueous solution of 0.35% sodium metasili-
cate and 0.25% sodium (lower alkyl)naphthalene sulfonate.Exam~le_No. P-V P-II Monomer Top Coat Steps
9 0.3 0.0 0.4 No
0.3 0.4 0.0 No
11 0.0 0.5 0.4 No 0
12 0.0 0.5 0.4 Yes10
13 0.3 0.2 0.4 No 9
14 0.3 0.4 0.2 No10-11
0.3 0.4 0.2 Yes14
As can be seen from these results, the absence
f any one of the three lngredients (blnder, oligomer, or
monomer) produces poor or useless photopolymerizable com-
posltions. When a top coat is put on the composition with-
out the binder (Example 12), the oxygen sensitivity of the
system is reduced and it polymerizes well. Surprising]y,
systems having the three components of the present inven-
tion work as well as the top coated system (Examples 13
and 14), and when the systems of the present invention
ar-e combined with a top coat, even f`urther improved re-
sults are obtained (Example 15). These results are sur-
prising and hlghly desirable.
Example 16
A solution was prepared from 4 parts poly)m-dial-
lylphthalate), 2 parts P-II, 4 parts pentaerythritol
-37-
tetraacrylate, 5 parts methanol, 0.4 parts diphenylio-
donium hexafluorophosphate, 0.1 part CEBH, 0.4 parts of
Phthalocyanine Blue GS, and methylethyl ketone to 100
parts. This was coated onto grained and anodized aluminum
to give a dry coating weight of about 1.34 grams/m2.
This was overcoated with poly~vinyl alcohol) at about the
same coating weight as the base coat. The coating was
air dried, then exposed and developed as in Examples 9-15.
The photopolymer was retained through step 12.
Example 17
The same procedure as in Example 16 was used ex-
cept that 4 parts of tris-methacryloxyethyl isocyanurate
was substituted for the pentaerythritol tetraacrylate.
The photopolymer was again retained through step 12.
Examples 18-21
A solution was prepared from 0.3 grams P-V, 0.4
grams pentaerythritol tetraacrylate, 0.22 grams P-II,
0.04 grams diphenyliodonium hexafluorophosphate, 0.02
grams of CEBH, 1.28 grarns methylethyl ketone, 0.47 grams
water, 7.36 grams isopropanol, and 6 drops of a 20% by
weight solution of triethylamine in n-propanol. The
solution was coated w.tth wire wound rods onto grained and
anodized aluminum at coating weights of 0.95, 1.36 and
2.0ll grams/m2. Some of the coatings were overcoated with
a 10% by weight solution of poly(vinyl alcohol) using a
#8 wire wound rod. The coatings were exposed using an
argon laser at 488 nm and developed by wiping with a pad
and an aqueous solution of a 0.35% sodium metasilicate
and 0.25% sodium (lower alkyl)naphthalene sulfonate. The
l~.Z29~9
-38-
laser beam was passed through a 21 step sensitivity guide.
The exposure values (in milliJoules/cm ) listed are the
exposures needed to give a solid step 6 for the various
coating weights.
Example Goating Weight g/m2 Top Coat Exposure
18 .95 Yes 1.8
19 1.36 Yes 1.8
1.36 No 10-14
21 2.04 No 10
As can be seen, the top coat improves the compo-
sitions, but the uncoated materials are still of excellent
speed and quality even when exposed in the presence of
air.
Examples 22-32
Solutions were prepared as in Example 16 except
that different photolnitiation systems were evaluated.
Exposure was to a mercury vapor lamp having an output of
500 watts/inch at a distance of about 34 cm through an
interference filter having a maximum transmission at 366
nm and a 21 step sensitivity guide. The table indicates
the relative sensitivity of the system for the minimum
exposure required to give retained photopolymer with
development as in Example 16.
-39-
Approx.
Absorption Relative
Ex. Photoinitiation System at 366 nm Exposure
22 4,4'-bis(dimethylamino) 0.3 0.26
benzophenone
2-o-chlorophenyl-4,5-di
(m-methoxyphenyl)imidazole
dimer
2-o-chlorophenyl-4,5-di-
phenylimidazole dimer
2-mercaptobenzoxazole
23 Same as Example 22 0.01 o.88
24 4,4'-bis(dimethylamino) 0.1 2.2
benzophenone
diphenyliodonium hexaflu-
orophosphate
tetraphenyl benzidine 0.2 3.3
diphenyliodonium hexaflu-
orophosphate
26 tetraphenyl benzidine 0.1 4.8
diphenyliodonium hexaflu-
orophosphate
27 tetraphenyl benzidine 0.02 13
diphenyliodonium hexaflu-
orophosphate
28 2,4-bis(trichloromethyl)-6- 0.2 6.6
(4-methoxylstyryl)-s-
triazlne
29 3-carboxymethyl-5(3-ethyl 0.02 13
-2-benzothiazolinylidene)
-2-(3-heptyl-4-oxo-2-thio
-5-thiazolinylidene)-4-
thiazolidone
diphenyliodonium hexaflu-
orophosphate
chlorothioxanthone 0.2
diphenyliodonium hexaflu-
orophosphate
9099
-40-
Approx.
Absorption Relative
Ex. Photoinitiation System at 366 nm Exposure
31 ethyldimethoxy antracene 0.02 40
diphenyliodonium hexaflu-
orophosphate
32 4,4'-bis(dimethylamino)-
benzophenone 0.1 40
Examples 33-39
A stock solution was prepared by mixing 5.13
grams pentaerythritol tetraacrylate, 4.03 grams P-II,
25.5 grams of a 10% by weight solution Or polyviny formal
in the azeotropic solution of n-propanol and water, 119
grams of methylethyl ketone and 1.5 grams of a 20% by
weight solution of triethylamide in the azeotrope. To
aliquots of 20 grams of this solution were added various
photoinitiation systems. The photoinitiation systems and
amount of each are shown in the following table. The
solutions were then coated on a grained anodized aluminum
substrate with a #L4 wlre wound rod and drled with a
heat gun. The result:Lng coating,s were exposed for 13
seconds to a carbon arc through a 21 step sensltivity
guide and a 0.5 density filter. The exposed coatings
were developed by wiping with an aqueous solution of o.63%
by weight sodium metasilicate and 0.23% by weight of
sodium (lower alkyl)naphthalene sulfonate. The number
of solid steps observed after gumming and inking were re-
corded. As in previous examples, the higher the number
of steps retained, the greater the sensitivity of the
coating.
-41-
Weight Solid
Ex.Photoinitiation System (Grams) Steps
33 4,4'-bis(dimethylamino)benzophenone 0.035 0
34 4,4'-bis(dimethylamino)benzophenone 0.035 7
diphenyliodonium hexafluorophosphate 0.070
7-diethylamino-4-methylcoumarin 0.035 0
36 7-diethylamino-4-methylcoumarin 0.035 4
diphenyliodonium hexafluorophosphate 0.070
37 2,4-bis(trichloromethyl)-6-(4- 0.070 2
methoxystyryl)-s-trazine
38 2,4-bis(trichloromethyl)-6-(4- 0.14 3
methoxystyryl)-s-triazine
39 4,4'-bis(dimethylamino)benzophenone 0.035 11
2-o-chlorophenyl-4,5-di(m-methoxy- 0.10
phenyl)-imidizole dimer
2-o-chlorophenyl-4,5-diphenyl 0.10
imidizole dimer
2-mercaptobenzoxazole 0.07
None of these compositions had top coats.
Examples 40 and 41
Two addit.tonal monomers were evaluated in the
compositions of the present inventlon. Two solutions
(A and B) were prepared havin~ the following composition:
Grams
P-II (64% in methylethyl ketone) 3.12
polyvinylformal (10% in the n- 7.6
propanol-water azeotrope)
P-V (12.9% in n-propanol (62%), 4.18
isopropanol (10%, and water (28%)
disperson of Pigment Red 48 and 10.0
polyvinyl formal (10% in the above
azeotrope) in a 2/1 parts by weight
ratio resin/pigment
1~2~9
-42-
4,4'-bis(dimethylamino)benzo- 0.19
phenone
diphenyliodonium hexafluorophos- 0.37
phate
triethylamine (20% by weight in o.96
the azeotrope
n-propanol-water azeotrope 70.0
To solution A was added 3.67 grams of pentaerylthritol
tetraacrylate and to solution B was added 3.67 grams of
tris(2-acryloxyethyl isocyanurate~. `The solutions were~~ ~~
then coated onto grained and anodized aluminum using a
number 18 wire wound rod and dried for one minute at 65C.
The coated plates were then exposed with a 2 kilowatt dia-
zotype lamp for 2, 5, and 10 seconds in air. The exposed
plates were developed by washing with an aqueous solution
of 3% sodium metasilicate, 3% n-propanol, 0.3% sodium dod-
ecyl diphenylether disulfonate, and 0.3% of an alkyl naph-
thalene sulfonate. The number of solid and ghost steps
remaining after development are given in the followin~
table.
2 Sec. 5 Sec. 10 Sec.
Coating Solid/~host Solid/Ghost Solid/Ghost
A 4-5 5-7 6-~
B 7-8 9-10 9-11
Examples 42 and 43
The usefulness of the compositions of the present
invention with lower intensity exposure porcesses was ex-
amined. The compositions as weight percentages were as
follows:
~4 2~9
-43-
Percenta~e Solids
ComponentSolution A Solution B
pentaerythritol tetraacrylate43.1 32.3
P-II 23.7 18
P-V 6.25 17.2
polyvinyl formal (10% in the azeo- 15.2 17.7
trope
pigment dispersion (of Example 40) 3.09 2.8
tri.ethylamine (20% in the azeotrope) 2.15 1.6
10 diphenyliodonium hexafluorophosphate 4.30 8
4,4'-bis(dimethylamino)benzophenone 2.14 2
Solution A was dried for one minute at 180F with a coating
welght of 200 mg/ft . Solution B was dried with a heat gun
at a coating wei~ht of 170 mg/ft2. The substrate in both
cases was grained and anodized aluminum. A c.onventional
micro~ilm en].arger was used and the plates were exposed
with between 10 and 30 milliwatts/cm2 irradiance by a mer-
cury xenon lamp through a 21 step sensitlvity ~uide in
contact with the plate. ~xposure was made in alr. The
exposed plates were developed by washing wlth an aqueous
solution Or 5.25% metaslllcate, 6.37% n-propanol, 8.25%
glycerol and 0.075% alkyl naphthalene sulfonate. The re-
sults are reported below.
Exposure Time
. Steps
Plate Seconds Solid/Ghost
.
A 2 3-5
4 4-6
6 5-6
8 5-7
1~.2~9~9
-44-
Exposure Time Steps
P]ate Seconds Solid/Ghost
B 2 5-7
L~ 6-8
6 6-8
When identical plates were imaged (A for 3 seconds
and B for 1 second) with line copy and half tones on an
aluminum sheet, 10,000 high quality impressions were ob-
tained with no image loss.
Examples 44-50
A standard solution was prepared having the
following weight percentages of ingredients in the n-pro-
panol-water azeotrope:
pentaerythritol tetraacrylate 43.2
P-V 6.35
polyvinyl formal (10% in the 15.1
azeotrope)
Pigment Red 48 3.1
triethylamine 2.15
diphenyliodonium ilexafluoro- 4.1J
phosphate
4~LI~-bis(dimethylamlno)benzo- 2.2
phenone
To seven aliquots of this solution were added 23.5 percent
by weight o~ the oligomers P-II and P-VI through P-XI.
The solutions were coated on grained and anodized alumlnum
using a number 18 wire wound rod and dried for one minute
at 65C.
The dry coatings were exposed in air through a 21 step
sensitivity guide with a mercury metal halide diazo bul~
and developed by wiping with the aqueous developing solu-
-
29g~
_1~5_
tion of Example 40. The results are shown in the follo-
wing table.
Steps
Example Oligomer Solid/Ghost
44 P-VI 4-7
P-VII 4-7
46 P-VIII 3-6
47 P-IX 4-5
48 P-II 3-6
49 P-X 4-5
P-XI 0-2
The above examples show the effect of varying the ratio of
aci.d groups to molecular weight of the oligomer. The
first two compositions (Examples 44 and 45) had ratios of
acid groups to molecular weight of approximately l:4300
and l:3600 respectively and were more difficult to develop
than preferred and had a tendency to hold the ink on the
background, A stronger or more vlgorous developer could
correct that tendency. The ollgomer oI' Example 50 had an
acid to molecular wei~ht ratio of` about l:750 and developed
a lLttle to easily, wit~l much of the photoreact,ed material
bein~ removed, All composJt:Lons were useful and could be
polymerized in air, however. Examples 46 through 49 worked
exceptionally well and had a ratio of the number of acid
groups to molecular weight of between about l:800 and
l:3000, with Example 48 having a ratio of about l:1200.
Compositions without any acid groups do not adhere well to
the substrate. Development does not differentiate between
exposed and unexposed areas with both being removed indis-
~ 2 ~ ~ ~9
-46-
criminately. Compositions without ethylenic unsaturation
do not photoreact and also do not bind to the plate sur-
face.
Example 51
A solution was prepared like those in Examples
44-50 using P-XII in place of the oligomers in the above
examples. Coatings were exposed and developed as in Ex-
amples 44-50. Only one ghost step and no solid steps were
obtained. Prolonged exposure gave more retained steps.
Examples 52-57
A solution was prepared for the comparison of
different binder materials. The solution comprised in
parts by weight:
pentaerythritol tetraacrylate 41.3
15 P-II 22.5
polyvinyl formal 9.95
Pigment Red 4~ 2.94
triethylamlne 2.05
diphenyliodonium hexaf`luoro- 4.2
20 phosphate
4,4'-bis(d1methylalllino)ben~o- 2.1
phenone
selected binders 14.9
The binders selected were
25 52. P-V
53. low molecular weight hydroxypropyl cellulose
54. polyvinyl butyral (MW 38,000-45,000)
"2zg~9
-47-
55. polyamide (ElvamideR nylong resin
supplied by DuPont Co.)
56. polyvinyl formal
57. no resin
The solutions were coated onto salt plates (clear crystals
of sodium chloride), dried, and the infrared spectrum
determined. The coatings were exposed in air to radiation
from a 2 kilowatt mercury metal halide diazo bulb for
various times at various irradiances. The infrared spec-
trum was determined after the exposure and the percentageof double bonds converted by the exposure was calculated
on the basis of the absorption at 810 cm 1. The results
appear below.
Percentage of Dou~le Bonds
15Exam~leConverted at 9 mW/cm Irradiance
52 35
53 32
54 32
27
56 25
2057 15
Examples 58-69
A solution was prepared for the comparlson of
different binder materials. The solutlon compr:lsed ln
parts by wei~ht:
pentaerythrltol tetraacrylate 43.1
P-II 23.7
polyvinyl formal 15.0
Pigment ~ed 48 3.0
triethylamine 2.2
diphenyliodonium hexafluoro- 4.4
phosphate
-48-
4,4'-bis(dimethylamino)benzo- 2.2
phenone
selscted polymeric binders 6.3
The binders selected were
58. P-V
59. polyvinylpyrolidone
60. polyvinyl ~ormal
61. copolymer of vinyl chloride
(81%) and vinyl acetate (19%)
62. polyvinyl acetate
63. polyethylene oxide (MW - 4,000,000)
64. polymethylmethacrylate (low molecular
weight, inherent viscosity - 0.2)
65. low molecular weight polyolefin resin
66. linear saturated polyester resin
67. thermoplastic aromatic polyurethane
68. cell.ulose acetate butyrate
69. no resin.
The results o~ infrared analysis after coating of these
compositions as i.n Examples 52-57 and exposure to 9 milli-
Watts/cm irradiance appears below.
Doubl.e l30nd Converslon
Examp.le __ %
5~ 3
59 3
61 25
62 25
63 2~1
64 23
16
66 15
67 15
68 13
6~ 15
In examp:Les 52-69, exposure time was 10 seconds.
