Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~V3~
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Compositions capable of being converted under the
influence of actinic light to solid, insoluble, tough struc-
tures have become increasingly important in the preparation
of printing plates. U.S. Patent 2,760,863 to Plambeck con-
tains an early disclosure of such compositions. In theprocess of the Plambeck patent, printing plates are produced
directly by exposing to actinic light through an image
bearing transparency a layer of an essentially transparent
polymerizable composition containing an addition polymeriza-
tion initiator which composition cross-links on exposure to
actinic light. The layer of polymerizable composition,
which is supported on a suitable support, is exposed until
substantial polymerization of the composition occurs in the
~ exposed areas while substantially no polymerization occurs
; 15 in the unexposed areas. The unchanged material in the
latter areas is then removed, as by treatment with a suit-
able solvent in which the polymerized composition in the
exposed areas is insoluble. The result is a rasied relief
image, corresponding to the transparent areas in the trans-
parency, which is suitable for use as a printing plate, as
in letterpress and dry off-set work.
Photopolymerizable layers of the type described by
Plambeck were usually prepared from polymeric components
which are soluble in organic solvents. Due to the toxicity,
high volatility and generally low flash point of low cost
organic solvents, their use often gave rise to hazardous
conditions. As a consequence, further research was direc-
ted toward the development of photopolymer compositions
which are soluble in water or aqueous alkali. U.S. Patents
3,794,494 to Kai et al and 3,960,572 to Ibata et al describe
water or aqueous alkali dispersible compositions that are
. . .
., . , :
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~ 3~35
suitable for use in rigid or elastic flexographic printingplate preparation. These compositions comprise polyester-
polyether urethane-linked block polymers containing acrylate
or methacrylate end groups (U.S. Patent 3,960,572), or un-
saturated polyesters (U.S. Patent 3,794,494), in combinationwith unsaturated monomers and a photopolymerization initi-
ator. However, the compositions of U.S. Patents 3,960,572
and 3,794,494 are not appropriate for making printing plates
to be used with the type of inks containing acrylate mon-
omers with no solvents which are cured by ultraviolet radia-
tion. Such ultraviolet inks require soft printing plates to
;provide maximum ink transfer and print quality. Soft plates
made from unsaturated polyester compositions generally have
poor physical properties and do not withstand the printing
or plate cleaning processes, while the polyester-polyether
urethane-linked block polymer formulations produce plates
which swell and disintegrate when used with such ultraviolet
inks and plate cleaning materials.
According to the invention, a photopolymer composition
~;20 comprises a liquid polymer containing at least two terminal,
olefinically unsaturated groups linked by a carbamoyl (i.e.,
urethane) linkage to a hydroxy-terminated polymer, a liquid
unsaturated polyester produced from an alcoholic component
,comprising a polyol and an acid component comprising a di-
carboxylic acid or dianhydride or a diester, at least one of
the two said components being unsaturated, an ethylenically
unsaturated, addition-polymerizable monomer, and an inhib-
itor for thermal polymerization. The said carbamoyl linkage
is to polyether, polyester (which may be saturated or con-
tain unsaturation in the acid or polyol components), orblock polyester-polyether polymers, or to other hydroxy-
terminated polymers.
The compositions according to the invention, when fully
cured by actinic radiation, have better physical properties
and better solvent resistance and "washout" characteristics
in automatic washout equipment than fully cured compositions
containing only the urethane-linked component. These im-
~~provements in physical properties and solvent resistance
'
~ 3~8~;
--4
make the compositions of this invention well suited for usein preparing printing plates which are to be used with inks
cured by ultraviolet radiation. This invention also relates
to photopolymer elements, for example, printing plates em-
bodying a layer of such compositions, to processes formaking printing reliefs from such elements, and to coating
applications.
The liquid, urethane-linked polymers used in the compo-
sitions according to the invention preferably have the
structure
O H H O / O H H O \ / O H H O\
Il I 1 11 11 1 1 11 11 1 1 11
X-C-N-Q-N-C- -O-D-O-C-N-Q-N-C-O m -D'-O-C-N-Q-N-C- _~ I
where m and n are integers from 0 to 10 and m + n is at
least 1, D and D' are polymeric backbones selected from
hydroxy-terminated homopolymers of butadiene, isoprene,
chloroprene, styrene, isobutylene, ethylene, epichloro-
hydrin, ethylene glycol, propylene glycol or neopentyl
glycol; or hydroxy-terminated copolymers of butadiene and
acrylonitrile, butadiene and styrene, butadiene and iso-
prene, ethylene and neohexene, isobutylene and styrene,
- isobutylene and acrylonitrile; hydroxy-terminated polyesters
of saturated or unsaturated dibasic acids and saturated or
unsaturated glycols; hydroxy-terminated polyester-polyether
block copolymers; or combinations of such polymeric back-
bones; Q is a radical selected from C4-C10 alkylenel C5-C8
cycloalkylene, arylene containing 1-2 rings, C6-C12 alkar-
ylene, and alkylene oxyalkylene radicals containing 4-8
carbon atoms and 1-3 oxygen atoms; X is selected from the
radical of an alcohol containing one to three ethylenically
unsaturated bonds from which a hydrogen atom has been re-
moved from the hydroxyl group, the radical of a primary or
secondary alkyl or aralkyl amine containing unsaturation in
the alkyl group, from which a hydrogen atom has been removed
from the amine group, or the radical of a carboxylic acid
selected from acrylic acid and methacrylic acid from which
the hydrogen atom on the carboxyl group has been removed.
- The polymeric backbones D and D' preferably have number
.
. ' . - . :
-
. ' . ' ' , .~ , .
3C)85
-5-
average molecular weights in the range of about 500 to about
20,000, more preferably about 500 to about 2,000.
These urethane-linked polymers are conventionally pre-
pared by reacting a hydroxy-terminated polymer, copolymer,
polyester or polyester-polyether block copolymer with a di-
isocyanate, and reacting the resulting isocyanate-terminated
compound with a compound selected from the group consisting
of (I) an alcohol having one to three ethylenically unsatur-
ated bonds, (II) an amine having one to two ethylenically
unsaturated bonds, and (III) a carboxylic acid having one
ethylenically unsaturated bond.
The preferred photopolymer mixtures of this invention
comprise about 10% to about 45% (more preferably about 30%
to about 40~) by weight of the said liquid polymer (herein-
after referred to as a urethane-linked polymer) having a
molecular weight (Mn) of about 5,000-26,000 and a room
temperature viscosity of about 100,000-300,000 cps. They
also comprise about 10% to about 45% (more preferably about
20% to about 30%) by weight of the liquid unsaturated poly-
, 20 ester polymer used in the composition, with the latter hav-
ing a molecular weight (Mn) of about 2,000-8,000 and a
viscosity of about 1,000-3,000 cps. at 100C. (lO0,000-
700,000 cps. at room temperature).
Preferably about 5% to about 55% (more preferably about
10% to about 30%) by weight of the ethylenically unsaturated
addition-polymerizable monomer is used. It is preferably
selected from acrylonitrile, styrene, methyl substituted
styrenes and monomers having unsaturation in the form of at
least one
O O~ R'
H2C = C - C - O - or H2C = C - C - N -
R R
group where R is hydrogen or Cl-C3 alkyl, and R' is hydro-
gen, Cl-C3 alkyl or phenyl.
The preferred amounts of the photoinitiator are from
about 0.05% to about 4% by weight, and of the thermal polym-
erization inhibitor, from about 0.01% to about 0.2% by
,, weight. These percentages are based on the total weight of
:
'
, : ,
116~3~5
--6--
the liquid polymer components and ethylenically unsaturated
monomer component.
The liquid unsaturated polyesters useful in this inven-
tion may be an ester, carboxyl or hydroxyl terminated poly-
ester prepared from a dibasic acid or ester and a glycol,the dibasic acid, glycol, or both containing unsaturation.
Such polyesters may be prepared using, e.g., fumaric or
itaconic acids, or 1,4-butenediol or trimethylolpropane
monoallyl ether. As indicated previously, the molecular
weight of these liquid unsaturated polyesters is between
2,000 and 8,000.
The ethylenically unsaturated monomer components of
the compositions of this invention have their unsaturation
in the form of acrylonitrile, methacrylonitrile, styrene,
methyl-substituted styrene or compounds containing one or
R l
more CH2=C-C- groups, wherein R is hydrogen or a Cl-C3
alkyl group.
Useful monofunctional ethylenically unsaturated mono-
mers include acrylonitrile, methacrylonitrile, styrene,alpha-methylstyrene, alpha-p-dimethylstyrene, acrylic acid,
methacrylic acid, esters of acrylic acid and methacrylic
acid containing up to 22 carbon atoms, acrylamide, mono- and
di-N- alkyl-substituted acrylamides and methacrylamides con-
; 25 taining up to 10 carbon atoms in the alkyl group, and di-
acetoneacrylamide.
Useful trifunctional monomers include 1,3,5-triacryl-
oylhexahydro-1,3,5-triazine or 1,3,5-triallylcyanurate.
Suitable difunctional monomers may be defined by the
structural formula:
O O
CH2 = C-C-~-A-~-C-C = CH2 II
X R R
wherein ~ is -HN- or -O-, A is alkylene, substituted alkyl-
ene or alkylene oxyalkylene, and R is hydrogen or Cl-C3
alkyl.
A preferred monomer having this formula is N,N'-
oxydimethylene-bis(acrylamide).
.
. : .
--7--
, ~(
When ~ in formula II is -NH- but A is alkylene or sub-
stituted alkylene, this is descriptive of another preferred
monomer, N,N'-methylene-bis(acrylamide). This compound is
one member of a valuable group of monomers represented by
compounds having the formula:
CH2 = C-C-N-(CHR')b-N-C-CI = CH2 III
R
where R is hydrogen or a Cl-C3 alkyl group, R' is hydrogen,
or a Cl-C3 alkyl group or phenyl, b is 1 to 6, and the total
: number of carbon atoms in (CHR')b is no more than ten.
Representative of compounds of formula III above are
N,N'-methylene-bis(acrylamide), N,N'-methylene-bis(meth-
acrylamide), N,N'-methylene-bis(2-ethylacrylamide), N,N'-
methylene-bis(2-propylacrylamide), N,N'-1,6-hexamethylene-
bis(acrylamide), N,N'-ethylidene-bis(acrylamide), N,N'-
ethylidene-bis(methacrylamide), N,N'-benzylidene-bis(acryl-
amide), N,N'-butylidene-bis(methacrylamide) and N,N'-
propylidene-bis(acrylamide). These compounds may be pre-
pared by conventional reactions well known in the art, forexample, see U.S. Patent 2,475,846.
Other useful monomers are those wherein ~ in formula II
is -O- and A is alkylene or substituted alkylene. These
compounds are di-, tri- and tetra-acrylates of certain poly-
hydric alcohols. These acrylates may be il~ustrated by thegeneral formula:
R12 l
CH = C-C-O-(C) -(CR"CR' )b-(CR2)a 1 2 IV
R R2 R
wherein R is hydrogen or a Cl-C3 alkyl group, a is 0 or 1,
R2 is hydrogen, a Cl-C3 alkyl group, OH, -CH2OH,
-CH -OC-C = CH2, or -O-C-C = CH2,
R R
R" is hydrogen, Cl-C3 alkyl, -OH, -CH2OH,
I Rl O Rl
-CH2-O-C-C=CH2 or -O-C-C=CH2,
R"' is hydrogen, a Cl-C3 alkyl group, b is 1 to 6 and the
~.
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--8--
total of carbon atoms in -~CR"CR"')b- is no more than
eleven. Representative of these compounds are ethylene
glycol diacrylate, ethylene glycol dimethyacrylate, ethylene
glycol di(2-ethylacrylate), ethylene glycol di(2-propyl-
acrylate), 1,5-pentanediol dimethacrylate, glycerol diacry-
late, glycerol triacrylate, trimethylolpropane triacrylate,
trimethylolpropane trimethacrylate, pentaerythritol diacry-
late, pentaerythritol triacrylate, pentaerythritol tetra-
methacrylate, and pentaerythritol tetracrylate.
Closely related to the preceding acrylates are those
which are derived from di-, tri- and tetra-ethylene glycol
- and di- and tri-propylene glycol. These compounds are
~- those of formula II wherein ~ is -O- and A is alkylene oxy
alkylene, and they may be more specifically illustrated by
the formula.
. O
CH2 = C-C-O-(CHR""CH2O)d-C-C = CH2 V
R R
- wherein R is hydrogen or a Cl-C3 alkyl group, R"" is hydro-
gen or methyl, d is 2 to 10 when R"" is hydrogen and is 2 to
3 when R"" is methyl. Representative of these compounds
are diethylene glycol diacrylate, diethylene glycol dimeth-
acrylate, triethylene glycol diacrylate, triethylene glycol
dimethacrylate, tetraethylene glycol diacrylate, tetraeth-
ylene glycol dimethacrylate, dipropylene glycol diacrylate,dipropylene glycol dimethacrylate, tripropylene glycol di-
acrylate and tripropylene glycol dimethacrylate.
Monofunctional monomers may also be employed in combin-
ations with the polyunsaturated monomers. The amount of
monomer or monomers used to effect cross-linking of the
polymer component of the compositions of this invention will
be from about 5 to 55%, preferably from about 10 to about
30%, by weight.
The specific photoinitiator used will depend upon the
other components as well as the light source employed. Typ-
ical photoinitiators are the benzoins, such as benzoin,
benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl
ether, benzoin isopropyl ether, alpha-methylbenzoin,
~lC3~
_9_
alpha-ethylbenzoin, alpha-phenylbenzoin, alpha-allylbenzoin,
etc.; the anthraquinones, such as anthraquinone, chloro-
anthraquinone, methylanthraquinone, ethylanthraquinone,
etc.; the diketones, such as benzil, diacetyl, etc.; the
2,2-dialkoxy substituted acetophenones, such as 2,2-diethoxy
acetophenone, etc., the 2,2-dialkoxy-2-phenyl substituted
acetophenones, such as 2,2-dimethoxy-2-phenylacetophenone,
etc.; the disulfides, such as diphenyldisulfide, tetraethyl-
thiuramidsulfide, etc.; 2-naphthalene-sulfonyl chloride,
etc. The amount of photoinitiator may be from about 0.05
to about 10%, preferably from about 0.1 to about 5~, by
weight based on the polymer in the photopolymer composition.
For the purpose of inhibiting premature cross-linking
during thermal processing and storage of the photopolymer
compositions of this invention, the incorporation of a
thermal polymerization inhibitor or inhibitors is desirable.
Such inhibitors also are well known in the art, and they are
exemplified by di-t-butyl-p-cresol, hydroquinone monomethyl
ether, pyrogallol, quinone, hydroquinone, methylene blue,
t-butyl catechol, hydroquinone monobenzyl ether, methyl
hydroquinone, amyl quinone, amyloxy hydroquinone, n-butyl
phenol, phenol, hydroquinone monopropyl ether, phenothiazine
and nitrobenzene, used separately or in combination. When
used in an amount within the range of from about 0.01 to
about 2% by weight of the pclymer, these stabilizers are
quite effective in preventing cross-linking of the photo-
polymer composition during processing and storage. During
exposure such amounts of stabilizer also delay and, thus,
prevent cross-linking due to scattered light in the nonex-
posed areas of the compositions, but do not greatly inter-
fere with or delay the cross-linking of the composition in
strongly exposed areas, thus, aiding in formation of a
plate of optimum depth and surface configuration.
When the photopolymer elements in this invention are
exposed to actinic light at a wavelength of from about 3000
to 4000 A through a photographic negative or positive, the
polymer beneath the exposed areas becomes insolubilized,
whereas the polymer beneath the unexposed areas remains
. _. .
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water dispersible. Subsequent washing of the plate removes
the dispersible polymer, leaving a replica of the negative
or positive in relief. Washing will normally be carried
- out with dilute aqueous solution of an anionic or nonionic
detergent. Anionic detergents such as alpha-olefin sulfon-
ates, alkylaryl sulfonates, lauryl sulfate, alkyl esters of
sulfosuccinic acid or sulfated ethylene oxide condensates
of alkyl phenols or fatty alcohols, and nonionic detergents
such as alkyl phenol, fatty alcohol Gr fatty acid ethylene
oxide condensates may be used. Alpha-olefin sulfonates are
particularly useful. Detergent concentrates of about 0.2 to
2% will normally be employed, generally at temperatures of
25-60C. Washing may frequently be accelerated by brush-
ing or scrubbing. In large-scale work, application of the
water solvent will advantageously be carried out by means of
jets or sprays. In some instances, it may be helpful to use
minor quantities of organic solvents such as the short chain
aliphatic alcohols and ketones. Suitable solvents of these
types include methanol, ethanol, and acetone, and they gen-
erally will be used in amounts no greater than 25-35%, pref-
erably less than 1-5% of the water or aqueous detergent
developer. Following development of the plate, residual
surface water and any organic solvent which also might be
present may be removed by passing a current of warm air over
the relif.
The printing reliefs made in accordance with this in-
vention can be used in all classes of printing, but are most
applicable to those wherein a distinct difference in height
between printing and nonprinting areas is required. These
classes include those in which the ink is carried by the
raised portion of the relief, such as in dry off-set print-
ing and ordinary letterpress printing. Because of the flex-
ibility, abrasion resistance, resilience, and solvent
resistance, relief plates prepared using these compositional
blends are particularly useful for printing applications in
which ultraviolet curing inks are employed.
This invention is illustrated by the following examples
in which all parts are by weight unless otherwise indicated.
~ 3~5
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Example 1
This example illustrates the preparation of a polyester-
polyether urethane-linked block copolymer, the preparation
of an unsaturated polyester, and the use of a photopolymer-
izable composition containing a blend of the polyester-
polyether urethane-linked block copolymer and the unsatur-
ated polyester in making printing plates.
A polyester-polyether urethane-linked block copolymer
;~ (I) is prepared by reacting 26.1 g. of a mixture of 2,4-
toluene diisocyanate and 2,6-toluene diisocyanate (in an
80/20 weight ratio respectively) under nitrogen with 200 g.
of a hydroxyl-terminated polyethylene adipate (molecular
weight approximately 450) at 70C. with stirring in the
presence of 0.1 9. dibutyltin dilaurate for two hours. The
resulting isocyanate terminated polyester is further reacted
with 100 g. polypropylene glycol diol (molecular weight ap-
proximately 1000) at 70C. for two hours. Then 300 g. of
the resulting polyester-polyether urethane-linked block
copolymer (I) is reacted at 70C. for two hours under air
sparge with 25 g. of 2-hydroxypropyl methacrylate containing
0.09 g. of 2,6-di-tert-butyl-p-cresol as stabilizer.
Seventy parts of this prepolymer are added to 12 parts
of 2-hydroxypropyl methacrylate, 16 parts of n-butyl acryl-
amide, 2 parts of acrylamide, 0.04 part of di-tert-butyl-p-
cresol, 0.04 part of hydroquinone methyl ether and 1.8 partsof benzoin isobutyl ether. This composition, designated as
polyurethane I, is doctored as a 40 mil layer onto a photo-
graphic negative which is covered by a protective film. The
layer is photocured by a 30 second exposure with BL-F-20T12
fluorescent lamps (General Electric) followed by a 120 second
; exposure with a 2Kw medium pressure mercury arc lamp. The
photocured plate has a tensile strength of 1900 lbs./in.2,
hardness of 68A, modulus of 1300 lbs./in.2 and elongation of
155%.
An unsaturated polyester prepolymer (II) having an av-
erage molecular weight of 3,100 and an acid number of 18 is
prepared by reacting under an inert atmcsphere of nitrogen
gas, 33.5 parts of diethylene glycol, 5.1 parts of propylene
~,
3~1S
-12-
glycol, 9.76 parts of fumaric acid, 21 parts of phthalic an-
hydride and 30.7 parts of adipic acid at a maximum tëmpera-
ture of 190C. for about 10 hours in the presence of 0.5
g. of p-toluenesulfonic acid as catalys~ and 0.2 g. of
hydroquinone anti-gelation agent.
This unsaturated polyester (100 parts) is added to 50
parts of styrene, 50 parts of triethylene glycol dimethac-
rylate, 0.07 part of di-tert-butyl-p-cresol, 0.03 part of
methyl ether of hydroquinone and 1.1 parts of alpha, alpha-
dimethoxyphenylacetophenone. This unsaturated polyestercomposition, designated as unsaturated polyester II, when
photopolymerized as described above has a hardness of 67A, a
modulus of 990 lb./in.2, a tensile strength of 370 lb./in.2
and an elongation of 35%.
A blend of polyurethane I composition and unsaturated
polyester II composition is made by mixing 50 parts of each
composition. The blend, when fully cured by actinic radia-
tion as described above, has a hardness of 70A, a tensile
strength of 890 lb./in. , an elongation of 70% and a modulus
of 1610 lb./in. . These data show that the cured blend has
strength and elongation substantially higher than that of
the unsaturated polyester II alone.
Printing plates made from the above described blend
are developed by spray washing for two minutes with a 0.5%
sodium hydroxide aqueous solution and an additional 30 sec-
onds with water. The plates exhibited considerably less
tack in its background areas than plates prepared from the
polyurethane I composition alone.
Printing plates made from polyurethane I composition
alone swell and disintegrate after a relatively short use
(less than 5000 impressions) on a press when ultraviolet
curable inks (i.e., prepared by dispersing a pigment in a
polymer-acrylate monomer mixture) are used. Printing plates
made from unsaturated polyester II composition alone are
subject to character chipping and breakage during printing
with the above inks and during plate cleaning such that less
than 5000 impressions can be obtained. Printing plates
prepared from a blend of polyurethane I and unsaturated
.
:' ' ' : ::
3~B5
-13-
polyester II compositions are not subject to plate swelling
or plate breakdown when using ultraviolet curable ink, even
after 100,000 impressions.
Example 2
This example illustrates a photopolymerizable composi-
tion containing a blend of a polyester-polyether urethane-
linked block copolymer and an unsaturated polyester, and the
use of the photopolymerizable composition to make printing
- plates.
A blend is prepared by dissolving 38.5 parts of the
liquid polyester-polyether urethane-linked block copolymer
(I) described above in Example 1, and 38.5 parts of the
liquid unsaturated polyester (II) described in Example 1 in
; 50 parts of styrene, 50 parts of triethyleneglycol dimeth-acrylate, 0.07 part of di-tert-butyl-p-cresol, 0.03 part of
methyl ether of hydroquinone and 1.1 parts of alpha, alpha-
dimethoxyacetophenone. When this blend (viscosity 3840
cps.) is fully cured, as described in Example 1, a cross-
linked polymer results having a hardness of 70A, a tensile
strength of 628 p.s.i., an elongation of 105%, a modulus of
2400 p.s.i.
Example 3
This example illustrates a photopolymerizable composi-
tion containing a blend of a polyester-polyether urethane-
linked block copolymer and an unsaturated polyester, and the
use of the photopolymerizable composition to make printing
plates.
Fifty parts of polyurethane I composition described in
Example 1 are blended with 50 parts of an unsaturated poly-
ester composition, designated unsaturated polyester III,which contains 100 parts of the unsaturated polyester pre-
polymer (II) described in Example 1, 30 parts styrene, 5
parts triethyleneglycol dimethacrylate, 10 parts polyethyl-
eneglycol dimethacrylate (molecular weight 425), 0.07 part
di-tert~butyl-p-cresol, 0.03 part methyl ether of hydroqui-
none and 1.8 part benzoin isobutyl ether. Unsaturated poly-
ester III composition, when cured as described in Example 1,
~_ has a tensile strength of 490 p.s.i., elongation of 80%,
3~ 5
-14-
hardness of 70A and a modulus of 1090 p.s.i. The blend of
polyurethane I composition and unsaturated polyester III
composition, when cured as described in Example 1, has a
tensile strength of 800 p.s.i., elongation of 110%, modulus
of 1440 p.s.i. and hardness of 67A.
Example 4
This example illustrates a photopolymerizable composi-
tion containing a blend of a polyester-polyether urethane-
linked block copolymer and an unsaturated polyester, and the
use of the photopolymerizable composition to make printing
plates.
A polyester-polyether urethane-linked block copolymer
(I) is prepared as described in Example 1. To 70 parts of
this prepolymer (I) are added 10 parts of triethyleneglycol
dimethacrylate, 16 parts n-butyl acrylamide, 4 parts methyl
methacrylate, 0.3 part of hydroquinone methyl ether, 0.3
part of di-tert-butyl-p-cresol, 0.3 part of alpha, alpha-
dimethoxyphenylacetophenone and 1.8 parts of benzoin iso-
butyl ether. This composition is designated polyurethane
IV composition and, when fully cured by actinic radiation
as described in Example 1, has a tensile strength of 2700
p.s.i., 35% elongation, a modulus of 18,300 p.s.i. and hard-
ness of 45D.
An unsaturated polyester prepolymer (II) is prepared
as described in Example 1. To 63 parts of this unsaturated
polyester (II) are added 26.7 parts of tetraethyleneglycol
dimethacrylate, 5.6 parts of 2-hydroxyethyl methacrylate,
10.1 parts of diallylphthalate, 0.08 part di-tert-butyl-p-
cresol, 0.04 part hydroquinone methyl ether, 1.8 parts of
benzoin isobutyl ether and 8 parts Bakelite phenoxy resin
(Union Carbide) as viscosity modifier. This composition,
designated unsaturated polyester V composition, has a vis-
cosity of 5740 cps. and, when fully cured by actinic radia-
tion as described in Example 1, a tensile strength of 830
p.s.i., hardness of 88A, elongation of 25%, modulus of 6900
p.s.i. and a peel strength of 4.6 lbs./inO width.
Fifty parts of polyurethane IV composition are blended
with 50 parts of unsaturated polyester V composition. This
:` :
.
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` ` 3~i~3~3S
-15-
blend has a viscosity of 7160 cps. and, when fully cured by
;~ actinic radiation as described in Example 1, a hardness of
35D, tensile strength of 1120 p.s.i., elongation of 20%, and
modulus of 13,000 p.s.i.
Example 5
; This example illustrates the preparation of a multilayer
~ printing plate having layers of differing hardness using a; photopolymerizable composition containing a blend of a
polyester-polyether urethane-linked block copolymer and an
ùnsaturated polyester as one of the layers.
A multilayer printing plate is prepared as follows:
four to five mils of liquid unsaturated polyester VI compo-
sition, prepared by dissolving 100 parts of unsaturated
polyester VI prepolymer (prepared from 2 moles of diethylene
glycol, 2 moles of propylene glycol, 2 moles of adipic acid
and 2 moles of fumaric acid) in 45 parts triethyleneglycol
dimethacrylate, 15 parts N-3-oxobutylacrylamide, 0.038 part
of di-tert-butyl-p-cresol, 0.02 part of the methyl ether of
hydroquinone and 0.5 part benzoin isobutyl ether is doctored
onto a 0.75 mil polypropylene film covering a Bychrome screen
negative. Then 8-9 mils of a liquid photopolymer resin con-
` taining a blend of 38.5 parts of unsaturated polyester VII
prepolymer (prepared from 1 mole diethylene glycol, 1 mole
propylene glycol, 0.5 mole fumaric acid, 0.5 mole phthalic
; 25 anhydride, and 1 mole adipic acid) and 41.08 parts of
polyester-polyether urethane-linked block copolymer (I) from
Example 1, both dissolved in 16 parts of n-butyl acrylamide,
12 parts 2-hydroxyethyl methacrylate, 5 parts styrene, 2
parts acrylamide, 0.04 part di-tert-butyl-p-cresol, 0.04 part
methyl ether of hydroquinone, 0.65 part benzoin isobutyl
ether and 0.55 part alpha, alpha-dimethoxyphenylacetophenone
(which yields a polymer of hardness 61A and 760 modulus when
photocured) is doctored over the unsaturated polyester VI
composition layer.
A Mylar backing sheet approximately 4 mils thick is
coated with an adhesive solution containing a red dye as an
antihalation agent. This backing sheet is laid over the
above liquid resin layers and the whole is irradiated for
.. ,. ~ .
. , .
.
-16- ~3~
10 seconds through the backing sheet with GE F20T12 BL
fluorescent lamps (of intensity 1.2 mwatt/cm2 as measured
. by an Ultraviolet Back-Ray meter). The resin sandwich is
- then irradiated through the negative for 80 seconds with a
2000 watt medium pressure mercury arc lamp (at an intensity
of 7 mwatt/cm2). After exposure, the polypropylene film
is stripped away and the unexposed polymer removed by spray
washing for 2 minutes with a 0.5% sodium hydroxide aqueous
solution and an additional 30 seconds with water. The dry
plate is exposed for 10 minutes under a nitrogen blanket
with fluorescent lamps (of 1.2 mwatt/cm2 intensity).
