Note: Descriptions are shown in the official language in which they were submitted.
:~SX~3~
O.Z~ D050/36307
Dye-conta;ning layer of a photopolymer;zable mixture,
and the production of relief plates and printing plates
._ ~
The present invention relates to layers of im-
proved photopolymer;zable mixtures for the production
of reLief plates and printing plates, which ~ontain, as
additives~ one or more compounds possessing one or more
photopolymer;zable olefin;cally unsaturated doublr bonds,
a photoinitiator and, to obtain a better relief image and
in particular to improve the depth of shadow wells in
the production of relief plates, a small amount of a
combination of certa;n organic compounds~
Layers of photopolymerizable mixtures for the
product;on of rel;ef plates and pr;nting plates have
been descr;bed in a large nu~ber of publications~ If,
for example, such conventional mixtures are used to pro~
duce relief printing plates having a thickness of about
0.025 - 1 mm, which is the usual thickness used for
letterpress plates in the printing industry, these
plates usually do not exhibit a sharp relief image,
and often have side walls which are not steep enough.
It is known that improved relief plates can be
obtained by employing certain arti-fices during exposure
of the photopolymer plate, ie. of the layer of photo-
polymerizable mixture applied to the base, through the
image-bearing negative; us1ng multi-layer photopolymer
plates; or arranging other layers which influence the
sidewall structure of the relief beneath the actual
photopolymerizable recording layer. However, these methods
are involved.
It is also known that the relief imag~e can be
improved by adding small amounts of certain organic
compoundsu For example, German Laid-Open Applications
DOS 2,720,560 and DOS 2,720~559 describe the use of
10,10'-bisanthrones and 9-nitroanthracene for this
purpose. Even handling of the compounds, for example
in the dissolving process, is critical, and, owing to
their natural color, the compounds have an ad-
~S~
- 2 - O~Zu 0050/36307
verse effect on the visual assessment of the photopoly-
mer layer before and after development~ They also make
it difficult to distinguish the unexposed and the
exposed areas of the undeveloped plate from one another.
The same applies to thioanthraquinone derivatives,
which are recommended in German Laid-Open Application
DOS 2~759,163 for improving the relief image.
It is an object of the present ;nvention~ in the
production of relief plates by a conventional method from
layers of photopolymerizable mixtures, to improve the
relief image by adding small amounts of chemicals to
these layers, without the additives adversely
affecting the other properties of the photopolymeri~able
mixtures to any great extent during the production of
the relie~ plate~ Preferably, these additives should
not have a disadvantageous effect on the requisite
minimum exposure time~ and also be toxicologicalLy
acceptable and easy to handle~ It is a particular
object of the invention to provide additives for the
photopolymerizable mixtures which improve the relief image
and at the same time, by changing the absorption character-
istics~ enable the imagewise exposed plate to be assessed
visually before the development step, so that this time-
and energy-consuming step can be omitted in the event
of exposure errors.
We have found that these objectsareachieved and
that, surprisingly~ a layer of a photopolymeri2able
mixture for the production of relief plates and printing
plates gives substantially improved relie1 inages having
the desired process;ng propert;es, if it contains~
(a) one or more compounds having one or more photo-
polymerizable olefinically unsaturated double
bonds,
(b) one or more photoinitiators uhich, ~hen exposed
to act;nic light~ initiate- rapid photopoly-
mQrization in the layer and
(c) a combination which, when exposed to actinic
Light, does not initiate any appreciable photo-
3~
- 3 ~ 3.~ 0050/3~3~7
polymerization in the Layer, and which comprises
tc1) from 0.0001 to 1, preferably from 0.001 to 0.2,
% by weight, based on the total dry weight of
the mixture, of a sol~ble dye of the formula (I)
S ~ ~ 3 (1
~here ~ is N~ 0, S or CR7, R1 is hydrogen,
C1-C~-alkyL or unsubstituted or substituted
phenyl or naphthyl~ R2 and R3 are identical or
d;fferen~ and are each hydrogen, hydroxyl, C1-C4-
alkoxy~ phenoxy, unsubstituted or substituted
diarylmethyl, or NHz ~here some or all of the
hydrogen atoms can be substituted by ;d~ntical or
different unsubstituted or substituted alkyl,
aryl or aralkyL radicals, R~ and R5 are ;dentical
different and are each hydrogen, C1 C4-alkyl,
phenyl, hydroxyl, C1~C~-alkoxy, sulfo or NH2
where so~e or all of the hydrogen atoms can be
substituted ty identical or different unsubstituted
or substituted acyl, alkyl9 aryl or aralkyl
radicals, R6 is hydrogen, hydroxyl, C~oC4-alkoxy~
carboxyl~ carbalkoxy~ N-acylamino or h3logen, R7
is hydrogen, C1-C4-alkYl or unsubst;tuted
or substituted aryl or aralkyl9 ~ is an acid
anion, and A and B are identical or different
and are each hydrogen or a fused benzocyclic,
naphthocycl;c or heterocyclic system which is
fused on at the a~ b or c posit;onO with the
proviso that ~hen A is a fused ring system of
~he stated type, one of the radicals R2 and R4
is absent, and
3~
- ~ ~ o~z. oosa/36307
~c2) an adequate amount of a reducing agent which
does not reduce the dye ~c1) in the absence of
acrinic Light but, on exposure, is c3pab~e of
reducing the dye in the excited electronic
state.
The present invention furthermore reLates to a
process for the production of reLief pLates and printing
plates by exposing image~ise a novel layer of a
photopolymerizable mixture which is applied to a base
to actinic light and developing the resulting relief
plate or printing plate by subsequently removing, in
particular washing out, the unexposed areas of the layer.
r he process is useful for the production OT reLief
iplates for letterpress printing as well as, surprisingly~
particularly for the production of photopolymer relief
plates for intaglio printing.
It is surprising that layers of photopolymer-
izable mixtures containing even very small amounts of
the novel additives substantially improve the relief
image of the desired relief plates, while the additives
do not adversely affect the other properties of the
photopolymerizable mixtures to any great extent. In the
preferred cases, the minimum exposure time of the layers
is not altered to any great extent. Moreover, some Q~ the
dyes used according to the invention impart a pleasing in-
:r;ns;c coloration to the photopolymerizable mixtures.
Ln principle, virtualLy any desired hue can be produced
in the m;xture by appropriate ~hoice of the dyes added
according to the invent;on. In practice, dyes ~hich
are preferably added are those which permit the most
advan~ageous visual assessment of the exposed plate~ In
this context, red hues are very par~ticuLarly preferred;
~owever, the ;nvention is not restricted to these.
An extrem~ely rapid change in ~he absorption
characteristics of the dye addit;ves dur;ng image~ise
exposure ;s part;cuLar~y advantageous, provided that
this change does not adversely affect the processing
properties of the photopolymerizable composi-tion to any
great extent. Moreover~ depending on the particular dye chosen on the
-
3~
- S - O~Z. ~050/3~307
basis of the dye struc~ures stated aboYe, a very large
variety of desired effects can be achieved~ ranging
from total bleaching of the dyes to a shift in hue, for
example from blue to red. In the novel process for the
production of relief plates and printing plates, ~his
property of the layer according to the invention sub-
stantially facilitates the evaluation of the exposed
plate before and after development.
~o better assess the quality of the image in different
sections of the relief of one and the same plate, it
is known to be advantageous to measure the depth of
shadow wells in halftone areas produced with screens
of different ruling and tone value, and for negative
dots, having a diameter of 400 ~m, in a solid area~
Fig. 1 shows how, after exposure of a layer L of a photo-
polymerizable composition with actinic lioht through a
negative N and development by washing outthe non-polymeriz2d
areas of the layer L with a developer solution, a relief
hav;ng a rel;ef height hR and a shadow well depth tz in a
halftone area of 50Xa tone value, this depth being referred
to hereinafter as ''tz(50)''~ is produced. The same is
shown in Fign 2 for an opaque dot (in negative N) having
a diameter of 0u~ mm in a clear area which is large in
relation thereto, here and hereinafter referred to as
"negative dot", the shadow dot depth being referred to
hereinafter as t~tnP400~. As the Examples described
below show~ a considerable improvement in the shadow
well depth and hence in the structure of fine image sections
can be achieved with the compositions of the invention.
I~ is known that compounds and dye of the
generaL formula (I)D which contain ~ instead of ~
and in which a bridge Z between the t~o aryl nuclei does
not exist~ ie. di- or triphenylmethane dyes which are
structurally similar to the dyes used according to the
invention, can be employed. However, these do not
~ 6 - 0.~. OOS0/3630?
result in an improvement in the relief image. The struc-
turally si~ilar xanthene dyes of the general formula (I)
wh;ch are frequently used in photopolymerizable layers
and in ~hich N~ is replaced with ~ and Z is 0 aLso do
not give the effects achieved with the novel mixtures and neither
improve the relief image nor change their absorptior
character;stics on exposure.
The novel layers contain~ as an essential component (a),
one or more compounds containing one or more photopoly-
merizable olefinically unsaturated double bonds. Su;t-
able co~pounds are the conventional monomers, oligomers
and unsaturated polymers used for the production of
relief plates and of photopolymer plates for letterpress,
gravure and offset pr;nting; the type of compound used
depends on the intended use o~ the mixture, on the nature
of the other components of the mixture and, where poly-
meric binders are preferably present in the ~ixture, on
their type and the compatability of the compound with these binders.
~1onomers con~aining two or more olefinically unsaturated photo-
pslymerizable double bonds are preferred, either alone or
as ~ mixture w;th monomers containing only one olefinic~
ally unsatur3ted photopo Lymerizable double bond~ Poly-
mers containing several olefinically unsaturated double
bonds in sideocha;ns or several terminaL olefinically un-
saturated double bonds can be used instead of the monomers
or as a m;xture with the~e. Examples of suitable monomers
are the di and polyacrylates and -methacrylates, as can
be prepared by esterification of a diol or polyol with
acrylic acid or me~hacrylic acid~ eg~ di- and triacryl-
ates and -methacrylates of e~hylene gly~ol, die~hylene
glycoL~ tr;ethyLene glycol or polyethylene glycols ha\ling
3 ~olecular weight of up to about 500, propane~ diol,
propane~1,3 diol, neopentylglycol t2~2-dimethylpropane-
diol~ butane-1,4 diol, 1,1,1-trimethylolpropane~ gLycerol
or pentaerythritol, the monoacrylates and monome.hacryl-
ates o~ such diols and polyols, eg. ethyLene glycolO
diethylene glycol~ triethylene glycol or tetraethylene
3~
- 7 ~ O.Z. 0050J36307
glycol monoacrylate~ and monomers containing ~wo or more
olef;nically unsaturated bonds and urethane and/or a~;de
groups, such as the lo~ molecular ~eight compounds pre-
pared fro~ al;phat;c d;ols of the above type, organ;c
d;isocyanates and hydroxyalkyl acrylates or methacrylates.
Other examples ;nclude acrylic ~cid, methacrylic acid and
the;r der;vati~es, eg. acrylamideO methacrylam;de, N hyd-
roxymethylacrylamide, N-hydroxymethylmethacrylamide and
the acrylates or methacrylates of monoalcohols of 1 to 6
carbon atoms.
Preferably, the layer of ~he photopolymerizable
mixture also conta;ns a polymer;c b;nder. Su;~able org-
anic polymeric binders for the photopolymerizable mix-
tures for the production of relief plates and printing
plates are the conventional polymers used for this pur
pose; these binders should generally be compatible ~ith
the monomers present and, as is obvious to the skilled
~orker, should be soluble or dispersible in the developer
so that th~ unexposed and non crosslinked areas of a layer
2Q of the photopoly~erizabLe composition can be washed out
after it has been exposed imagewisen Suitable polymeric
saturated or oLefinically unsaturated binders are unsatu-
rated polyesters~ linear nylons and in particular alcohol-
soluble nylon copolymers, as described in French Patent
1,52û,856, cellulose derivatives, in particular ~hose which
can be washed out with an aqueous alkaline developer, vinyl
alcohol polymers and polymers and copolymers of vinyl
esters of aliphat;c monocarboxyl~c acids of 1 to 4 carbon
atoms~ egO those obtained from vinyl ace~ate and having
Yar;ous de~rees of hydrolysis, polyurethanes, such as
polye~her-urethanes and polyester-urethanes, polyacryla~es
and poLymethacrylates, styrenefbutad;ene~ styrene/iso-
prene and styrene/butad;ene/isoprene copolymers, styrene
maleic anhydride ropalymers~ copolymers of styrene ~;th
male;c acia es~ers or half-esters9 styrene/maleic anhy~ride/acFYlic
acid or ~e~hacrylic acid copolymers~ modified polyvinyl
alcohol deriva~ives, eg. poly~inylbu~yral or the reaction
product, mentioned in German La;d-Open Application DOS
~ 8 O~Z. ~050/36307
3,015,340, of a polyvinyl alcohol ~;th a certa;n amount
of acrylic or methacrylic anhydr;de. O~her polymeriG
binders ~hich are su;table for the production of reLief
printing pLates for flexographic printing are elastomeric
diene polymers and copoly~ers, such as those of butadiene
and/or isoprene, of which block copolymers which contain
butadiene and/or isoprene homopolymer blocks and polymer
blocks of styrene or ~-methylstyrene are particularly
suitable. The amount of polymeric binder present ;n the
pho~opolYmer;zable m;xtures depends on the;r use; it is
;n generel about 5-90, ;n particu~ar 45-80, % by ~eight,
based on the sum of the amounts of polymers and photo-
polymer;zable monomers. Which ~onomers~ unsaturated oli-
gomers or unsaturated polymers can be advantageously GOm-
b;ned with ~hich polymeric binders is disclosed inthe patent literature.
Thenovel layers of the photopolymerizable mixtures contain,
as is customary in the art, one or more photoinitiators9 gener-
ally ;n amounts of from OnO1 to 10~ ;n particular from
0.01 to 3, ~ by weight, based on the dry wei~ht of the
mixture. Su;table photoin;t;ators are those compounds
~h;ch are capable of forming free radicals un~er the
action of ac~in;c light, and ;nitiate rap;d photopoly-
merization i!l the layer. Examples of suitable photo-
initiators are acyloins and acyLoin ethersy aromaticdiketones and the;r derivatives, and polynuclear quinones.
Yery useful compounds are benzoin and ~-hydro~ymethylben-
zoin and particularly their alkyl ethers of 1 to 8 carbon
atomsg eg~ benzoin isopropyl ether, ~-hydroxymethylben-
zoin methyl ether or benzoin methyl ether, benz;L monoketals, eg. benzil dimethyl ketal~ benzil methyl ethyl
ketal, benz;l methyl benzyl ketal or benzil neopentyl
ketal, and diarylphosphine oxides, as described in German
LaidoOpen Application DOS Z~909~9~2 Preferred
photoinitia~ors req~lire onlr-
short minimum exposure times, preferably no more ~han a
few minutes, for initiat;ng photopolymerization on
3~
- 9 - 0.7. 0050/36307
imagewise exposure to actin;c light~ ;n particular UV
light. Pref~rably~ the photoinitiators tb~ are not dyes.
A particular feature of the layers according to
the invention is that~ in addition to the photo7nitiators~
they contain a mixture of a certain dye (c1) with a m;ld
reducing agent (c2) for the particular dye (c1) used.
The mixture (c1) ~ tc2) should notiniti~te any--ap~!reciable
ibLe photopolymerization in the layer of the pho~opoly-
merizable mixture on imagewise exposure to actinic l;ghtr
this can be established by ~eans of a few exper;mentsa
If, for example, the exposure t;me for the noYel, prefer-
ably essentially solvent-free layer of the photopolymeriz-
able mixture containing the photoinitiator (b) is X
seconds or minutes, the corresponding layer ~h;ch does
not contain the photoin;tiator tb) should~ even ~hen the
exposure time is increased 10-fold, advantageously not
contain any appreciable amounts of photopolymerized
CQmpOsi~iOn when the relief plateis subsequently developed by
~ashing out; in any case, less than 20% by weight of the
Z0 exposed amounts of monomPrs should have undergone photo~
po lymeri zationa
Par~icularly suitable dyes tc1) of the above for-
mula (I) for the photopolymerizable mixtures are those
from the series comprising the phenoxazine dyes of the
ZS formula (II)~
F~S ( II )
p6 - Rl X
where ~O A9 ~, R1~ RZ, R3, R4, R5 and R6 have th~
above meanings. Examples of very useful dyes are Capri
blue GN (C.I. 51000~, zapon fast blue 3 G tC.I. 51005),
gallo blue E ~C.I. 51040), fast ne~ blue 3 R (C.I. 51175),
Nile blue A tC.I. 51180)~ fast green M tCoI~ 51210)~ fast
black L tC~Ia 51215), and rhodanil blue, the salt or
3~
- 10 - ~.Z. 0050/}63Q7
amide obtained from rhodam;ne B tbasic violet 10, C.I.
45170) and Nile blue (basic blue 12~ C.I. 51180).
Preferred compounds are those from the series
comprising the phenazin;um dyes of the formula tIII):
S R ~ ~ (II})
~here ~, A, ~ R1, R2, R3, R40 R5 and R6 have the
above meanings. Examples of very useful dyes of this
type are neutral red (C.I~ 50040), neutral vioLet (C.I~
50030), azine scarlet ~ ~C.I~ 50045), rhoduline helio-
trope 3 B tC.I. 50055), neutr2l blue C (C.I. 50150),az;ne green GB (C.I. 50155), safranine B (C.I. 50200)~
indamine blue B (G~I. 50204), rhoduline red 6 ~CgI~
5021~), rhoduline blue 6G extra tC~I~ 50220), indazine GB
(C.I. 50221)~ safran;ne T tC.I. 50Z40), mauveine (C.I.
50245)~ naphthyl red tC~I~ 50370) and nigrosine black T
.(C.I. 50415).
Acridinium dyes of the Formula tIV)
,-~ R7 '~~
R2 ~ C ~ R3
6 R X~ tIV)
R
where ~ A, B, R1, R2, ~30 R4~ R5 R6 an~ R7
have the above mean;ngs~ may also be used; suitable
dyes of this typ~ are acriflavine (C.I. 46000), acridine
oranye tC.I. 46005)~ acridine scarlet J tC~Io 46015)~
acridine yellow G tCoI~ 46025)~ aurazine ti (C~Io 46030)~
C.I. Basic Orange 4-11 (C.I. 46035), phosphine E (C~I.
46045), flaveosin tC~I~ 4bO60~, benzoflavine tC~I~ 4~065)
and rheonine A tC.I. 46075).
æ~30
~ O.Z. 0050/36307
Other suitable dyes are the phenothiazlnium dyes
of the formula tI~ ~here Z is S, eg. methylene blue or
thionine.
To enable the formulae ~I) to ~IV) to be better
understood, examples of radicals~ R1, R2, R3~ R4, R5,
R6, R7, A~ B and X~ of suicable dyes are gi~len below:
R1 is, for example, hydrogen, methyl, ethyl, phenyl, 2-
methoxyphenyl, 4-methylphenyl~ Z,4-dimethylphenyl, 20
methylphenyl, 4 sulfophenyl, 2 methyl-3-sulfophenyl,
naphth-1~yl, naphth 20yl or 5,8 disulfonaphth-2 yl. R2
and R3 are identieal or different and are eac~, for example, hydrogen,
hydroxyl, methoxy, di-(p~diethylaminophenyl)-methyl, amino, ~-me~hyl-
amino, N-ethyla~ino~ dime~hylamino, die~hylamino, N-
phenylamino, N-t4-sulfophenyl)-aminoJ N-~2~4~disulfo-
phenyl)-amino, N~t2-sulfo-4 aminophenyl)-amino, N-S2-
methylphenyl~-amino, N~(3-methoxyphenyl~-amino, N-t4-
diethylaminophenyl)-amino~ N (4-dimethylaminophenyl)~
amino, N-(2-sulfo-4-methylamino-5-methylphenyl)-am;no, N--
(5r8-d;sulfonaphthyl)-amino, N-ethyl-N-ben~ylamino,
phenaziniumylamino, oxaziniumylamino~ or rhoda~inylamino~
R and R are identical or different and are each, for example,
hydrogen, methyl, methoxy, sulfo, i~-methylaMino, N-ethylaminoj dimethyl-
amino, diethylamino, N-phenylamino or N-(4-diethylamino-
phenyl)-am;no. R6 is, for example, hydrogen, hydroxyl,
methoxy, chloro, bromo, carboxyl, carbometho~y or N-
acetyla~ino. R7 is, for example, hydrogen, Inethyl,
ethyl, phenyl, 4-aminophenyl or 2-carboxyphenyl.
Examples of the ac;d an;ons are Cl~ Cl046
HS04aand CH3S04~ and similar conventional acid anions, in
particular monovalent inorganic and organic ones. The
chlorohydrates are frequently very useful salts. A and ~
are~ for example, hydrogen, benzo CaJ, d;benzo Ca~c3, di-
benzo Ca~f~, dibenzo Ca,d~D tetraben20 Ca,G,t~,fJ, unsub-
stituted or substituted~
~ ~ b ~0 ~ O
33~
- 12 - 0.~. 0050/36307
O ~ ~ 0 ~ a~d ~ ~ ~ 0 X
The cho;ce of ~he dye tc~ used in the photopoly
merizable mixture is governed mainl~-~by esthet;c cons;dera-
tions. For example~ ~isual assessment of the printing
plates is part;cularly easy w;th the compounds neutral
red tC.I~ 50040~ safran;ne T tC.I. 50240) and rhodanile
blue ~see above~, and these are preferably used in the
photopolymerizable m;xture~
The novel layers contain, in combination with the
dye (c1), an amount of a reducing agent which is suf~
f;c;ent for this dye and does not reduce it in the absence
of actin;c light but, on exposure, is capable of redu~ing
the dye in the excited electronic state, in partisular to
g;ve the semiquinone. Examples of such m;ld rsducing
agents are ascorbic acid~ anethole~ thiourea, die~hyl-
allylth;ourea and hydroxylamin~ der;vat;ves, ;n part;cu~
lar N-allylthiourea and preferably salts of N-n;troso~
cycLohexyLhydroxylamine~ ;n part;cular the potassium and
aluminum salts. The latter are also conventionally used
as thermal polymer;zat;on inh;bitors ;n photopolymer;zable
mixtures. The amount of reducing a~ent added ;s ;n g~ne-
ral about 0.005 - 5, ;n particular 0.01 - 1~ X by weight,
based on the total dry l~eight of the m;xture, and should
not be less than the reduct;on equ;valent of the amount
of the dye ~c1) used. In ~any cases, the addition of
from 3 to 10 t;mes the a~ount of dye (c1) used has proven
useful~
In general, the photopolymeri~able mixtures also
contain thsrmal polymerization inhib;tors, eg. hydroquinone,
3û p-methoxyphenol, d;nitrobenzene, p-qu;none~ methylene
blue, ~ naphthol9 N-n;trosam;nes, such as N nitrosodi-
phenylamine~ phenothiazine, phosphites~ such as triphenyl
phosphite, or the salts~ in particular the aLkali metaL
and aluminum salts~ of N-nitrosocyclohexylhydroxylamine.
3~
- 13 - O.Z. 0050/36307
The inhibitors are mixed with the photopolymerizable mix-
tures in gener3l in an amount of from 0.001 to 3, in par-
ticular from 0.003 to 1, X by ~eight, based on the
mixture.
The ~ tures according
tc the invention can also contain other conventional
aodit;ves~ eg. plast;c;zers, saturated Low~moLecuLar
weight compounds conta;ning amide or alcohol groups~
waxes, pigments, etc. For example, preferred m;xtures
for the product;on of gravure printing plates contain
f:neLy d;v;ded p;gments, such as quartz ~owd~.
Examples of very usefuL soL;d layers of photo
polymerizable mixtures contained
a) from 35 to 90% by ~e;ght of a polymer;c binder~ such
as a nylon copolymer or polyvinyl alcohol or an elas~o-
mer;c homopolymer or copolymer,
b) from 6 to 60~ in particular from 8 to 45, X by weight
of one or more lo~ molecular ~eight compounds (a~ conta;n-
;ng more than one photopolymerizable olef;nically unsatu-
rated double bond, or of a mixture of these with a ls~molecular we;ght compound contain;ng only one photopoly-
merizable olef;nically unsaturated double bond,
c~ from 0.2 to 6X by we;ght of a photo;nitiator (b),
d) from OoOOl to 2X by ~eight of a thermopolymerization
;nhib;tor,
e~ from 0.0001 to 1, preferably from 0 oO001 to 0.1, % by
we;ght of a dye ~c13 of the formula SI) and
f) from 0~005 to SX by ~e;ght of a reduc;ng agent tcZ).
Examples of very useful layers of liqu;d photo-
polymer;zable m;xtures containeda) f rom 45 to 75% by we;ght of an unsaturated poLyester
having an ac;d number of from 100 to 1509
b~ from 15 to 25, in particular from 10 to 20, X by
weight of a monomer conta;n;ng one or more allyL groups
and two olef;n;cally unsaturated double bonds,
c) from 5 to 2$% by we;ght of a monomer contain;ng
one or more acrylate or methacrylate groups,
d~ from 1 to 10X by weight of a saturated or olef;nically
~5~3~
~ .Z. 0~50/30307
unsaturated low moLecular weight compound containing one
or more am;de groups,
e) from 0~2 to 4% by weight of a photoin;tiator tb),
f3 from 0,003 to 1X by ~eight of a thermal poly~erization
inhibitor,
g) from 0~0001 to 1, preferably from O.OOG1 to 0.1, % by
weight of a dye (c1) of the formula tI) and
h) from 0.005 to 5X by ~eight of a reducing agent (c2~.
Regarding suitable photopolymerizable mixtures
19 for the product;on of gravure printing plates, ~ith which
reduc;ng a~ents ~G2) and dyes ~c1~ which are soluble
according to the invention can be mixed, reference may be
made to 6erman Laid-Open AppLication DOS 30128,949. ~hey
contain, as polymeric binder, in particular an alcohol-
soluble nylon copolymer of the above type, advantageouslyin an amount of from 20 to 93~ in particular from 45 to
87~ X by weightO The compositions con~ain, as an intimate
m;xture, a finely divided pigment, preferably very fine
quartz powder, in an amount of from 2 to 50, in -
2n particular frsm 5 to Z5~ X by weight, based on the mixture. A compound having photopolymer;zable olefinically
unsaturated double bonds which has prsven particularly
useful in combination with alrohol soluble nylon copoly-
mers is the diether obtained from Z moles of N-methylol
acrylamide ~ith 1 moLe of ethylene glycol; it is gener-
ally used in an amount of from 2 ~o 50, in particular from
5 to 25, X by ~eight. It is surprising that, even ~hen
used for producing gravure printing plates, the novel
layers result in such a substantial improvement in the
3D plate obtained, and- in the depth and shape of its wellsr
even when overexposure occurs.
Processing of the photopolymer;zable mixture into a
photopolymer printing plate9 which has a relief;forming
layer of the mixture on a base, can be carried out in a
conventional mannerO and depends on the type of mixture
used and on whether the mixture is liqu;d or solid~ Proces-
sing of the b!ank material into relief plates
is carried out in a conventional manner by image~ise exposure
- 15 - 0~. 0050/36307
to actin;c light, in particu~ar us;ng light sources whieh
have emission maxima in the range of the absorption of
the photoinitiators used, in general from 390 to 400 nm,
and emit a sufficient proportion of Light in the range
of the absorption band of the dye ~c1) used, eg. medium-
pressure mercury la~ps, high-pressure nr low-pressure Lamps
or superactinic fluorescent tubes. After the image~ise
exposure, the unexposed areas of the layer of the photo-
polymerizable mixture are removed mechanically in a ~on-
ventional manner and/or are washed out with a developer,and the resulting d~veloped relief plate is dried. In- -
some cases it may be a~van~a~eous to p~st-e~pose the entire,
r~lief. In the productior, of gr~vure printing
pl?tes, prolonged drying at about 70 - 100C is advan~
tageous, In the Examples and Comparative Experiments ~hich
follo~ parts and percentages are by weight, unless stated
otherwise, Parts by weight bear the same relation to parts
by volume as the kilogram to the liter.
EXAMPLE 1
400 parts of a mix~ure of equal amounts of tetra-~
ethylene glycol dimethacrylate and diallyl phthalate~ 55
parts of methacrylamide9 2 parts of hydroquinone~ ln4
parts of N-allylthiourea and 8 parts of benzoin ethyl
ether werelnixed with 650 parts of an unsaturated poly-
ester obtained from fumaric acid, trimellitic anhydride
and diethylene glycol and having an acid number of 140.
0.0075X by ~e;ght of safranine T tC.I. 50240)waS mixed
with the resulting liquid mixture.
A reLief plate was produced from the photopolymerizable mixture
in a conventional manner:
r he liquid mixture was cast in a layer onto a steel sheet coated
with a layer of adhesive,serving as support~ the applie~ layer was broughttO
a thickness of 800 /um using a doctor blade~ and was then
covered with a 9 /um thick transparent polyester film, the
formation of air bubbles being avoidedO
The liquid resin layer was then exposed imagewise
3~
- 16 ~ O.Z. 0050~36307
~ith a commercial ~edium-pressure UV lanp, through 3 ne~a-
tive laid on top of the polyester film. The negative and
the polye~ter film w~re removed, and the unexposed areas
of the layer of the mixture~ere therl ~ashed out ~ith a
û.5% strength aqueous solution of sod;um carbonate. The
resulting relief plate ~s dried anf! th~n post~exposed for
2 minutes.
Evaluation of the resulting relief image showed
that the shoulders were non-tacky and sharply defined,
and that the shadow well depths in a halftone area of
50% tone value (tz(50)) and for a negative dot (tz(nP400~)
were advantageous (cf. Table 1).
COMPARATIVE EXPRI~ENT 1
The procedure described in Example 1 ~ias follQwed
exactly, excep~ tha~ the addition of safranine T to the
photopolymerizable mixture was omitted. Eualuation
of the relief image showed that the shado~ well depth-s
t7 (50) and tz (nP400) were inadequate and ~hat the
shoulder shape was unfavorable; the shoulders ~ere also
very tacky (cf~ Table 1).
TABLE 1
Evaluation of the relief images prod~lced in accordance
~ith Example 1 and Compara~ive Experiment 1 (screen:
28 lines/cm)
Example 1 Comparative
.... ~
Minimum exposure time ~equired to
reproduce a 3X highl;ght dot 20 sec. 20 sec.
___ ... . . _ _.
Shado~ well depth in a halftone arec
of 50X tone valLe~ t (50) 155 ~m
,_ , , z . . __
Shadow well depth for a ne~ati`ve
dot 0 4 mm in diameter, t (nP400)
z~ 3~0 ~m _ 48 ~m
__
Shoulders non-tacky, tacky, poorly
~h~rp~y ~ef;ned defined
_ ~_
33~
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EXAMPLE 2
A solution of 16~ parts of a polystyrene/polybuta~
dienetpolyisoprene three-block copolymer containing 18
of styrene ;n the form of copolymer;zed units, 12.5
parts of a styrene prepolymer, 0.33 part of 2,6-di-tert.-
butyl-4-methy'phenol, lG parts of hexanediol 1,~-diacry
late, 6.7 parts of lauryl acrylate, 2 parts of ~-methylol-
benzoin methyl ether and 0.2 part of the aluminum salt of
N nitrosocyclohexylhydroxylamine in 160 parts of toluene
and 10 parts of n-propanol was mixed ~ith 0~1X by weight
of neutral red tC.I. 50040) and 1% by weight of ascorbic
acidO the percentages being based on the solids content
of the mixture~ and the m;xture W35 then appl;ed,'using a
doctor bLade~ to a 125 lum thick polyester film, coated
~ith an adhesion promoter, and the layer wasdried. The
resulting photopolymer printing plate having a 670 ~m
thick layer of the photopolymerizable mixture wasexposed
imagewise to actinic light, and the relief plate was
developed in a spray washer with a trichloroethylene/iso-
2D propanol m;xture by washing out the unexposed areas. The
results of the evaluation sf the relief images are shown
;n Table 2. Advantageous; s-hadow' well depth's were obtained
at the minim~m- exposu~e time.-
COMPARATIVE EXPERIMENT 2
The procedure descr;bed in Example 2 wasfollowed
exactly~ except that the neutral red wasnot added.
Evaluation of the relief image, showed th~t thæ~shadow
well depths tz(50) and tz(nP400) were inadequate`
~cf. Table 2).
3~
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TABLE 2
Evaluation of the relief images produced in accordance
~ith Example 2 and Comparativ~ Experiment 2
(screen: 28 !;nes/cm)
Example 2 Comparative
Experiment 2
Minimum exposure time required to
12 min. 12 min.
reproduce a 3% hi~hliqht dot
. .
Shadow well depth in a halftone
area of 50X tone value, tz (50~ 105 ,um 45 ~m
Shadow~well depth for a negative I
~ .
~ hen theprin~ing plate from Example 2 was exposed
for tw;ce the required min;mum exposure time, ~2 (nP400)
decreased from 165 to 140 ~m, whereas the plate
descr;bed in Comparative xperiment 2 ha~ virtually no
shadow welts (tz~nP400) C15 /um) afterexposure for 24 minu~es.
EXAMPLE 3
A 65X strength methanolic solution of a photo~
poLymerizable mixture comprising 60% of a nylon copolymer
obtained from adipic ac;d, hexamethylenediamine, 4,4'-di-
aminodicyclohexyl~ethane and ~-caprolacta~, 25X of a
diether obta;ned from 1 ~ole of ethylene glycol and 2
moles of N-hydroxyme~hylacrylamide, 13.5X of benzene-
sulfonamide~1.5% of benzoin tetrahydropyranyl ether,
0.2X of the potassium salt of N-nitrosocyclohexylhydroxyl-
amine and 0c02X of safranine T (C~I. 50Z40) is preparedO
Alayer of the solution of the mixture was applied to a steel
sheet coated wtth a layer of adhesive (reflectance: about 15%)
in such- a thickness that, after drying at about 70C~ the layer of
the photopolymeri2able mixture was sao ~m thickc This layer
~printing plate)was exposed imagewise through an image-
30t
- 19 - O Z. 0050~36307
bearing transparency. During exposure in a commercial
flat-pLate exposure uni~ equipped with superac~inir fluo~
rescent tubes (~max ~ 350 - 400 nm)~ the color of the
exposed areas of the layer changed from red to pale red.
Yisual assessment. good. ~ - ~
~The unexposed areas of the layer of the mixture were then
~ashed out with an aLcohol/water mixturea
Evaluation of the resuLting relief image showed
that the shoulders were non-taGky and sharply defined,
and that the shadow well depths in a halftone area of
50~ tone value (tz(50)) and for a negative dot (tz(nP400
were advantageous (cf. Table 3).
EXAMPLE 3a
The procedure described in Example 3 was followed,
except that, ;nstead of the potass;um salt of N-nitroso-
cyclohexylamine, the same amount of N-allylthiourea is
used. ~he results of the èvaluat;on of the relief image are shown in
Table 3.
COMPARATIVE XPERIMENT 3
Z The procedure described in Example 3 was follo~ed~
except that the addition of safranine T to the photo-
poLymerizable mixture waso~itted~ Evaluation
of the rel;ef ;~age showed that the shado~ weLl depths
tz (50) and t7 (nP400) were inadequate and that the
shoulder shape was unfavorable (cf.rable 3). No color cnanye
occurred during exposure. Consequently, it was virtually impossibLe
to evaluate the exposed plate before washout~
~5~33~
- 2D - O.Z. OOSO/36307
TABLE 3
Evaluation of the relief images produced in accordance
with Examples 3 and 3a and Compara~ive Exper;ment 3
(screen: 60 lines/cm)
Example 3 Example 3a~ Comparative
1 Experiment
_ ~ _ ~ .. _ _ _
Minimum exposure time require
to reproduce a 3~ highl;ght
dot ` 2~0 min. 202 min. 2.0 min.
. e ~ ~ .
Shadow well depth in a half-
tone area of 50~ tone value,
tz (50~ 64 ~m 45 um 20 ~m
Shadow well depth for a
negative dot 0 4 mm in dia-
240,um 160 ~m 17~m
EXAMPLE 4
The procedure described in Example 3was follo~ed,except that, instead of safranine T, 0.03X of rhodanil
bLue (~ee above)was used as the dye. During exposure in
the exposure unit used inExa~ple 3, the color changed from
dark blue to bright red, which perm;tted very good visual
assessment of the exposed relief plate before washout.
After the washout operarion (cf. Example 3), the
desired relief plate ~as obtained.
Evaluation of the resulting relief image sh4wed
~hat the shoulders were non-tacky and sharply defined~
and that the shadow well depths in a halftone area of
50% tone value ttz(50)) and for a negat;ve dot (tz(nP400))
were advantageous (cf. Table 4~. -
COMPARATIVE EX~ERIMENT 4
The procedure descr;bed in Example 4 was followed,
except that, instead of adding rhodanil blueO the tri
phenylmethane dye crystal violet (C.I. 42 555)was used ;n
a concentration of 0~01X. Virtually no color change~ 20 occur~redon exposure, and consequently the plate could not be
assessed before the washout operation. Evaluation
of the relief image showed that the shadow well depths tz (50) and
tz (nP400) were inadequa-te and that the shoulder shape was unfavorable
(cf~ Table 4).
33~
- 21 - 0.~. 0050~36307
TABLE 4
Evaluation of the reli f images produced in accordance
with Example 4 and Comparative Experiment 4
(screen: 60 l;nes/cm)
Example 4 Compara~ive
Experiment
-.. ~ . . . - . .. .
Minimu~ exposure time required to
reproduce a 3% highlight dot 4.0 min. 2.1 min.
. -
Shadow well depth in a halftone area
of 50% tone value,~ltz (50) 36 ~m 22 ,um
~ . .. .. . . ., ...
Shado~ we!l depth for a negative
= 133
EXAMPL 5
The procedure descrihed ;n Example 3 wasfollowed,
except that, instead of safranine T, 0.02X of neu~ral red
(C.I. 50040) was used as th~ dye. During exposure, the color
changed from red to yello~ish brown, and this permitted
good visual assessmen~ of the printing plate before
development.
Evaluation of the resulting relief image showed
that the shoulders were non-tacky and sharply defined,
and that the shadow well depths in a halftone area of
50% tone value (tz(50)) and for a negative dot (tz(nP400))
were advantageous (cf. Table ~).
EXAMPLE ~
The procedure described in Example 5was follo~ed9
except that~ instead of neutral red, 0.02% of ~hionine
~C.I. 52~00)was used as the dye~ During exposure~ com-
plete bleaching of the dye occurr~the coLor changing
from dark blue to cslorlessO Visual assessment could be
readily carr;ed out.
3~
- 22 - O~Z. C050/36307
Evaluation of the relief image showed that the
shado~ well depths tz(5Q) and tz(nP400) and shoulder shape
werP be~ter than in the case of the relief image obtained ;n
Comparative Experiment 3 (cfo Table 5).
TAPLEvaLuation or the relief images produced in accordance
with Examples 5 and 6(screen: 60 Lines/cm)
Example 5 ExampLe 6
,
.... ... . ,.. _.
Ninimum exposure ~ime required to
reproduce a 3% highlight dot 2~0 min. 10 min.
Shadow well depth in a halftone area
Of 50% tone value~ tz (50) ~2 ~m 3û ~m
~ ~ _
Shadow well depth for a negative
dot 0.4 mm in d;ameter, tz ~nP400) Z50 ~m 140 ym
EXAM~LE 7
A 200 ~m thick layer of a photopolymerizable mix-
ture having the folLowing composition was applied to a
240 ~U~l thick steel sheet provided with a polyurethane
adhesive layer:
o1 parts of an alcohol soluble nylon copolymer
obtained from about equal parts of hexamethylenediamine
adipate, 4~4'-diaminodicyclohexylmethane adipate and
~-caprolactam~ 27 parts of a diether obtained from 1 ~ole
of ethylene glycol and 2 moles of N-methylolacrylaM;de,
10 parts of fine quartz powder, 2 parts of benzil dimethyl
ketal~ 0.3 part of the potass;um salt of N-nitrosocyclo-
hexyl~ydroxyla~ine and 0.02 part of the dye safranine r
tC.I. 50240)~
These components were mixed together to
give an intimate mix~ureO The layer of the photopoly-
merizable ~ixture was exposed for Z minu~es through an
image-bearing transparency for intaglio printing.
- 23 O.Z. ~050/36307
The still soluble areas of the layer of ~he photopoly-
merizable mixture ~ere ~ashed out with an ethanol/w3ter
- mixture, and the result;ng intaglio print;ng plate
was dried fQr 30 ~-inutes at 80Cc The
5 wells of the Plate were as deep as 80 lu~-but the
surface of the plate wascompletely flat.
Another intagli~ pr;nt;ng platewas produced as
described above~ except that an exposure time of 10 min
utes was used: the wellswere just as deep as those of the
plate exposed for 2 minutes.
COMPARATIVE EXPERIMENT ~
A in~io printing plate wasproduced as described
in Example 7, except that the addition of the dye safra-
n;ne T was omitted. After exposure ~or 2 minutes,
the ~ells ~ere 40 ~m deep, the screen lines being a few
lum de~per than the non~printing areas. After exposure
for 4 minutes9 the wells were-only 25 ym deepr while after
exposure for 10 minutes they were less than 5 ~m deepO
zo EXAMPLE 8
The procedure described ;r, Fxa~pLe 3 was fo~lo~ed,
except that, instead of safranine T~ 0.02X of acridine
orange (C.I. 46005) was used as the dye. Dur;ng exposure,
bleaching of the dye took place in the exposed areas of
the layer~ The results ~f the evaluation of the relief image
are shown in Table 6.
EXAMPLE 9
The procedure described ;n Exa~ple 8 ~as follo~ed,
except that the salt of ~-nitrosocyclohexylamine ~as
3Q replaced by 0.4% ~y ~eight of N-allylthiourea. The
results of t-he evaluation of the relief image are~g;ve~ ;n~
Table 6.
- 24 - 0uZ. 005~/36307
TABLEEvaluation of the relief images produced in accordance
with~ Examples 8 and 9 tscreen: 60 lines/cm)
Example 8 Example 9
____ __ ~
Minimum exposure time required to
reproduce a 3% highlight cor 1.5 min. 1.7 min.
_~ _ ~_
Shad~w well depth in a halftone area
of 50~O tone value, tz (50~ 33 ~m 30 ~m
.. ~ ~ ................. ..
Shadow well depth for a negative
120,u- 80 rm
EXAMPLE 10
A 60% strength aqueous solution of a m;xture of
60X of a polyvinyl alcohoL, having a deyree of hydrolysis
of ~0 mole% and a mean molecu~ar weight of about 25,000,
23% of a diether obtain~d from 1 mole of ethylene glycol
and 2 moles of N hydroxymethylacry~amide, 18X of 2-hyd-
roxyethyl methacrylate, 1.5X of benzoin isopropyl ether,
0.02% of safranine T ~C.I~ 50240) and 0.48X of the potas
sium salt of N-n;trosocyclohexylhydroxylamine waspre-
pared. A layer of the solution was applied to a steel-sheet coated
with a la~(er Df a~bes;ve (reflectance: about 15%) in su~h a thickness
that after dryin3 at about 70C, the layer of the
photopolymerizable composition was 500 ~m thick. The
photopolymer prin~ing pla~e was exposed image~ise through
an image~bearing transparency in a commerc,al flat-plate exposure
unit equipped with superactinic fluorescen~ tubes ~ maX~J350 -
400 nm), the color changing from red to pale red. Visual
assessment: good~ The unexposed areas of the layer were
then washed out with water at 40C.
Evaluation of the resulting relief image showed that
the shoulders were non-tacky and sharply defined and that the
shadow well depths in a halftone area of SOX tone value
(tz(SO)) and for a negative dot (tz(nP400)) were advantageous
(cf~ Table 7).
~Z~
25 - O.Z~ 0050/3~307
EXAMPLE 11
The procedure described in Example 10 was folLo~ed
exactly, except that, instead of the potassium salt of N
n;trosocycLohexylhyaroxylam;ne, a miYture of 0.3~ of
h~droqu;none monomethyl ether and OO~X of L( )-ascorbic
acid wasused~ The results of the eval~at;on of the-rel;ef ;mage
are shown inTable 7.
COMPARATIV EXPERIMENT 6
The procedure descr;bed in Exam~le 11 was fo!lo~ed
exactly, except that the addition of L(+3-ascorb;c acid
was om;tted. Evaluation of the relief image showed that the
shadow weLl depths tz (50~ and tz (nP400) were ;nadequate
and that the shoulder shape was unfavorable (cf~ r abLe ?).
TABLE 7
Evaluation of the relief images produced ;n accordance
with Examples 10 and 11 and Comparative Experiment 6
(screen: 60 L;nes/cm)
Example ExampLe Comparative
11 Experiment
_____
Minimum exposure time
required .o reproduce a-3%
highl;ght dot 3 mln. 10 mln. 8 mln.
Shadow welL depth in a-halftone
area of 50,'0 .one value, tz (50)
37 ~m 35lum 28~um
~ ~_~
Shadow well depth for a negativ
dot 0.4 mm in diameter,
t (nP400) 200 ~m 105 ~m 32~m
, , _ ____ ~
