Note: Descriptions are shown in the official language in which they were submitted.
2 ~ ~ ~ 3 ~ ~
89/~ 033 Tra~slation
Photosensitive mixture and recording material produced
therefrom
The present invention relates to a photosensitive mixture
which can be developed with aqueous solutions, which contains
a polymeric binder and a photocurable compound or combination
of compounds, and which is suitable for the production of
photosensitive recording materials, in particular of
planographic printing plates and photoresists.
DE-A 20 24 244 (corresponding to US-A 3,867,147) discloses
the use of photosensitive recording materials comprising
cocondensation products of diazonium salts capable of conden-
sation and other, non-photosensitive compounds, capable of
condensation, if appropriate combined with polymeric binders,
for producing printing plates. These photosensitive materials
are distinguished by their high photosensitivity and long
print runs. The number of prints obtained is particularly
high, if water-insoluble binders, for example, polyvinyl
formal, are used, but such layers can only be properly
processed by means of developers containing a considerable
amount of volatile organic solvents. For ecological reasons
it is desirable to make it possible to develop printing
plates with purely aqueous solutions. In the most favorable
cases, the mentioned printing plates can be developed with
relatively aggressive acidic or alkaline purely aqueous
solutions by suspending the non-image areas of the layer in
the developer, in the form of flakes or relatively small
particles. There is, however, the danger of uncontrolled
redeposition of flaky matter in non-image areas of the plates
whereby the plates are rendered unusable.
2 ~
EP-A 152,819 dlscloses photosensitive mixtures comprised of
diazonium salt polycondensation products and binders con-
taining carboxyl groups, which are obtained by reacting
hydroxyl group-containing polymers with acid anhydrides.
Plates produced using these mixtures can be developed with
aqueous-alkaline solutions, and the mixtures are suited for
the production of lithographic printing forms giving high
print runs. It is, however, desirable to achieve even better
print runs. For this purpose, the publication proposes the
addition of minor amounts of other polymers, for example,
polyurethanes, in order to increase the abrasion resistance.
However, this combination results in a poorer copying perfor~
mance, such as undesired dot gain. Furthermore, the develop-
ing behavior and shelf life of the plates are impaired. Like
other mixtures prepared with carboxyl-containing binders,
these mixtures also suffer from the draw-back that upon being
processed with developers based on tap water there is the
risk of the formation of precipitates in the form of
sparingly soluble calcium salts, which are deposited in the
developing machines and cause disturbances.
~ixtures of the above generic type, where polyurethanes are
employed as polymeric binders, are known from US-A 3,660,097
and DE-A 27 39 774. It is a disadvantage of these mixtures
that the binders are sparingly soluble in the solvents
conventionally used for coatings and that the solutions have
to be filtered several times to remove insoluble residues.
The developability of these mixtures in aqueous-alkaline
media is very limited and the print runs are inadequate for
high-performance machines.
A similar mixture is known from EP-A 0,030,001. The binder
contained therein is a branched polyurethane. Using this mix-
ture, relatively high print runs can be achieved but it still
has a number of drawbacks. For example, acidic aqueous deve-
loper solutions with an addition of organic solvents are pre-
2~c3~
ferably employed for achieving a scum-free, rapid development
of the photocured layer. When used for automatic processing,
these developers may cause corrosion problems at the light
metal parts of the processing equipment.
EP-A 167 963 describes a negative working photosensitive mix-
ture which is suitable for the production of planographic
printing plates and comprises a diazonium salt polyconden-
sation product, an ethylenically unsaturated compound which
can be polymerized by a free-radical process, a ph~to-
initiator and a water-insoluble polymeric binder. High print
runs can be achieved when polyvinyl acetals are used as bin-
ders. In this case development can, however, be only per-
formed with solutions comprising a predominant amount of
organic solvents.
EP-A 274,075 discloses photocurable mixtures which comprise a
photocurable substance and a polyvinyl acetal obtained by
reacting vinyl alcohol polymers with hydroxy-containing
aldehydes. These mixtures, which are suitable for the
production of planographic printing plates and photoresists,
can be developed with neutral or weakly alkaline aqueous
solutions. They give printing plates of relatively high print
runs, but the number of prints which can be obtained is
inferior to the print run of plates which cannot be developed
with purely aqueous solutions.
In DE-A 37 32 089 graft polymers are described, which com-
prise a polyurethane as the graft backbone and grafted-on
vinyl ester units, which are at least partially saponified
to give vinyl alcohol units. The polymers are suitable as
binders for pigments; for preparing printing inks,
thermoplastic adhesives and solvent-containing adhesives;
as constituents of varnishes or coatings for fibers, films
and metals, and for thermoplastic shaped articles.
2~ 9s~
JP-A 246,047/87 describes photopolymerizable mixtures
wherein graft polymers of polyurethanes and polyvinyl
alcohol with mercapto groups are contained as binders.
Graft polymers obtained from the graft polymers described
in DE-A 37 32 089 above by acetalizing with aldehydes, are
described in the prior German Patent Application
P 38 35 840.9.
The prior German Patent Application P 38 24 146.3 discloses
photocurable elastomeric mixtures which contain a compound
being polymerizable by a free-radical process, a photo-
initiator and, as the binder, a graft polymer according to
DE-A 37 32 089, which is soluble or dispersible in an aqueous
solution.
It is an object of the present invention to provide a photo-
sensitive mixture which is suitable for use in the production
of printing plates, particularly lithographic printing
plates, or of photoresists; which has all the advantages of
the known photosensitive mixtures; which can be developed by
means of virtually solvent-free, aqueous solutions, without
resulting in disturbing deposits when developer solutions
containing tap water are employed; and which, at the same
time, yields printing plates of high photospeed and image
resolution, which give high print runs and have a good ink
acceptance and long shelf life, properties which could up to
now only be achieved with printing plates requiring the
addition of relatively large amounts of organic solvents in
the developing process.
In accordance with the instant invention, a photosensitive
mixture is provided which contains, as essential
constituents, a photocurable compound or combination of
compounds and a polymeric binder possessing repeating vinyl
acetal units.
3 ~ ~
The mixture of this invention is characterized in that the
binder is a graft polymer where the graft backbone is a
polyurethane onto which chains containing vinyl alcohol units
and vinyl acetal units derived from hydroxyaldehydes are
grafted.
In accordance with the instant invention, there is also pro-
posed a photosensitive recording material comprising a layer
support and a photosensitive layer wherein said photosen-
sitive layer is comprised of the mixture defined above.
The graft polymers contained in the mixture of the instantinvention are novel. For preparing them, a carboxylic acid
vinyl ester and optionally another ethylenically unsaturated
compound copolymerizable therewith is grafted onto a
polyurethane graft backbone and thereafter saponified
completely or partially. The polymers having vinyl alcohol
units obtained in this way, are known from DE-A 37 32 089 and
are further reacted with hydroxyaldehydes to give the novel
polyvinyl acetals.
The proportion of the grafted-on components is in general
10 to 95, preferably 30 to 90 and in particular 40 to 80 %
by weight, based on the total graft polymer.
The graft backbones consist of polyurethanes having at least
two urethane groups in the molecule, the number of urethane
groups per molecule being subject to no particular upper
limit and in general having values higher than 2.
The polyurethanes employed as graft backbone can be produced
from diols and diisocyanates by conventional processes of
polyurethane synthesis. In principle, all of the diols custo-
marily used in polyurethane synthesis can be employed.
Cycloaliphatic diols, such as cyclohexanediols, and in
particular aliphatic diols having 2 to 12 carbon atoms are
2~ 93~
preferred. Polyetherdiols, for example polypropylene oxides,
polybutylene oxides and copolymers of ethylene oxide, propy-
lene oxide and butylene oxide, preferably the block copoly-
mers thereof, or poly-1,4-butanediols are also preferred;
polyethylene oxides with molecular weights of between 200 and
10,000, and more preferably of between 400 and 1,500 are
particularly preferred. The polyetherdiols are advantageously
employed in combination with low-molecular aliphatic diols,
for example 1,4-butanediol, 1,3-propanediol, ethylene glycol,
diethylene glycol, 1,2-hexanediol, 1,2-propanediol,
pentanediol or cyclohexanediol. The molar ratio of
polyetherdiol to low-molecular aliphatic diol is preferably
from 1 : 0.1 to 1 : 0.7.
Diisocyanate components which can be employed are aromatic
diisocyanates. Aliphatic and/or cycloaliphatic diisocyanates
are preferred. Preferred aliphatic diisocyanates are those
having 2 to 12 carbon atoms in the aliphatic radical, for
example ethylene diisocyante, propylene diisocyanate, tetra-
methylene diisocyante and 2,2,4-trimethylhexamethylene
diisocyante. Preferred cycloaliphatic diisocyantes are,
for example, 1,4-diisocyanato-cyclohexane,
dicyclohexylmethane-4,4'-diisocyante and isophorone
diisocyanate. Hexamethylene diisocyanate and isophorone
diisocyanate are particularly preferred.
The molar ratio of diol component to diisocyanate component
is preferably between 1 : 0.99 and 1 : 0.5, in particular
between 1 : 0.98 and 1 : 0.7. The average molecular weights
of the polyurethanes are preferably between 200 and 100,000,
in particular between 1,000 and 50,000 and particularly
preferentially between 3,000 and 25,000.
Carboxylic acid vinyl esters having 3 to 20 and preferably
4 to 14 carbon atoms are employed for grafting onto the
2 ~ 6 ~
polyurethane. Vinyl acetate and/or vinyl propionate, in
particular vinyl acetate, are particularly preferred.
Mixtures of vinyl acetate and/or vinyl propionate and vinyl
versatate are also preferred. In particular in the case of
partial or complete saponification of the products following
the graft polymerization, the co-use of vinyl propionate in
addition to vinyl acetate during grafting is advantageous.
Moreover, copolymerizable mixtures of carboxylic acid vinyl
esters can be grafted, preferably mixtures of vinyl acetate
and minor amounts of vinyl versatate.
Grafting with different carboxylic acid vinyl esters in the
form of block copolymers, optionally in combination with
further ethylenically unsaturated and copolymerizable mono-
mers, can also be advantageous. Furthermore, the carboxylic
acid vinyl esters can also be grafted together with other
ethylenically unsaturated and copolymerizable monomers,
in particular acids, such as maleic acid, itaconic acid,
mesaconic aicd, crotonic acid, acrylic acid or the esters
thereof.
The graft polymers obtained can be converted by hydrolysis,
alcoholysis or transesterification into partially or comple-
tely saponified products, the degree of hydrolysis beingat least 30 mol%, preferably 45 to 99 mol%, based on the mole
number of saponifiable monomer units in the graft polymer.
The production of graft polymers with a polyurethane graft
backbone is described in DE-A 37 32 089.
The saponified graft polymers can be acetalized in an acidic
medium by means of methods known per se. For the
acetalization reaction, aliphatic C2 to C20 hydroxyaldehydes,
which may be substituted, are employed. Preference is thereby
given to aldehydes corresponding to one of formulae I and II
2~ ~3~
OH R2
HO - Rl - CHO R5 - C - C - CHO
l4 R3
(I) (II)
in which
Rl is a substituted or unsubstituted alkylene
group containing 1 to 6 carbon atoms,
R2 and R3 are identical to or different from one another
and denote hydrogen atoms, alkyl radicals
containing 1 to 6 carbon atoms, alkoxy
radicals containing 1 to 4 carbon atoms,
hydroxyalkyl radicals containing 1 to 3 carbon
atoms or hydroxyl groups,
R4 is a hydrogen atom or an alkyl radical
containing 1 to 6 carbon atoms, and
R5 is a hydrogen atom, an alkyl, hydroxyalkyl or
alkoxyalkyl radical containing 1 to 6 carbon
atoms or a substituted or unsubstituted aryl
radical containing 6 to 10 carbon atoms.
Suitable hydroxyaldehydes are described in EP-A 274,075.
In the compounds of formulae I and II, the symbols preferably
have the following meanings:
R1 may contain, in particular, halogen atoms or alkoxy
groups as substituents and has in total 1 to 6,
preferably 2 to 5 carbon atoms.
R2 and R3 are preferably hydrogen atoms, alkyl radicals
containing 1 to 4 carbon atoms or hydroxymethyl
radicals.
R4 is preferably a hydrogen atom.
2~ 3
R5 is preferably a hydrogen atom or an alkyl radical
containing 1 to 4 carbon atoms, a hydroxyalkyl
radical or an alkoxyalkyl radical containing 1 to 4
carbon atoms.
The hydroxyaldehydes corresponding to formulae I and II
contain at least one and up to three, preferably up to 2
hydroxyl groups.
Among the hydroxyaldehydes, preference is given to the auto-
condensation products of acetaldehyde and its higher
homologues and to the condensation products of acetaldehyde
with propionaldehyde or higher aliphatic aldehydes, and also
to 4-hydroxybutanal and 5-hydroxypentanal.
Apart from the hydroxyaldehydes, aliphatic aldehydes having
1 to 20 carbon atoms, which may be substituted, and aromatic
aldehydes, which may also be substituted, are preferably
employed. Preference is given to aliphatic aldehydes having
1 to 5 carbon atoms, such as n-butyraldehyde,
isobutyraldehyde, propionaldehyde or acetaldehyde.
Substituted or unsubstituted benzaldehydes, such as
benzaldehyde, p-chlorobenzaldehyde or p-methoxybenzaldehyde
are also suited.
It is also possible to employ the corresponding acetals with
lower alcohols, for example, 2-methoxy-acetaldehyde dimethyl
acetal, bromo- or chloroacetaldehyde diethyl acetal or the
reaction products of phenols with halogenoalkyl-dialkyl
acetals, instead of the free aldehydes. The acetals can be
reacted with the polymer directly or after having been
hydrolysed to give the aldehyde.
The graft copolyvinyl acetals used in the mixture according
to this invention thus contain at least two, preferably four,
different types of units in the grafted-on side chains.
2~ ~3~
a) vinyl alcohol units,
b) optionally carboxylic acid vinyl ester units,
c) vinyl acetal units with free OH groups, and
d) optionally vinyl acetal units without free OH groups.
The amounts of the individual units are for:
a) 15 to 70, preferably 20 to 50, mole %,
b) 0 to 65, preferably 1 to 50, mole %,
c) 5 to 70, preferably 7 to 65, mole %,
d) 0 to 75, preferably 10 to 70, mole %.
The hydroxyl number of the ready-for use binder should be in
the range of 100 to 800, preferably of 150 to 600.
The acetalization can be performed employing two different
methods:
In accordance with the first process variant, the graft poly-
mer is dissolved or dispersed in an alcohol or in a
water/alcohol mixture, mixed with a catalytic amount of an
organic or inorganic acid and the aldehyde or aldehyde mix-
ture, and heated. The resulting polymer solution, which where
appropriate also contains an anti-oxidant, can either be used
directly for preparing the mixtures according to this inven-
tion, or alternatively, the polymer can be precipitated and
purified by dropwise adding the solution to a non-solvent.
In accordance with the second process variant, the graft
polymer is dissolved in water or a water/alcohol mixture and
mixed with the aldehyde or aldehyde mixture. Subsequently, an
aqueous solution of an inorganic or strong organic acid -
if appropriate with the addition of a surfactant and of an
antioxidant - is added dropwise at a low temperature,
preferably between -10 ~C and room temperature. Thereby,
2~1 93~
11
the acetalized graft polymer is often precipitated. The
reaction is completed at an increased temperature of about
20 to 60 C. The isolated polymer is purified by washing with
water or re-precipitation. This second process variant gives
more uniform products.
To prepare the graft polyvinyl acetals in an aqueous medium,
known methods are employed to produce 1 to 50 % strength,
preferably 5 to 20 % strength, aqueous solutions of the graft
polyvinyl alcohols, preferably at elevated temperatures, the
acid catalyst is added, the solutions are then cooled to tem-
peratures of less than 25 C, and the acetalization reaction
is finally performed by metering in the aldehyde with
agitating, preferably within a time of 3 to 300 minutes.
As is known, the aldehyde conversion is incomplete in most
cases, and therefore an excess of aldehyde, preferably of
10 to 20 mole percent, is usually added.
In a preferred process variant, the aqueous solution is
allowed to stand for at least about 30 minutes at tempera-
tures of 0 to 5 C prior to the start of the reaction,
whereupon the graft polyvinyl acetal formed is generally
separated off after a short time, as a pulverulent substance.
To complete the reaction, the reaction mixture is slowly
heated to room temperature, and where appropriate it is post-
reacted at elevated temperatures, for example at 25 to 70 C,
during about one to three hours. The added amount of acid
catalyst depends, inter alia, on the degree of acetalization
to be achieved and may preferably be up to 1.1 mole, relative
to the molar content of vinyl alcohol units.
The resulting graft polyvinyl acetal is isolated by suction,
washed with weakly alkaline water (pH 9 to 12) and dried.
Acetalization products which do not precipitate from the
aqueous reaction solution can be isolated by the addition of
precipitating agents, purified and dried.
2~ 93~
The acetalization can also be performed in organic solvents.
Suitable solvents include water-miscible solvents, in parti-
cular water-soluble alcohols, such as ethanol and/or metha-
nol, to which water may be added~
Preferred acid catalysts are organic sulfonic acids, for
example, toluene sulfonic acids, and also mineral acids, for
example sulfuric acid, phosphoric acid, hydrochloric acid or
nitric acid. Among these, perference is given to phosphoric
acid and hydrochloric asid.
For performing the preparation in organic solvents, the acid
catalyst, the aldehyde and the graft polyvinyl alcohol are
dispersed or dissolved in the solvent, and the mixture is
refluxed. It may also be expedient to add the aldehyde in
the course of the reaction. The graft polyvinyl alcohols
which are insoluble in the organic solvents gradually dis-
solve as a consequence of the acetalization in progress.
When the acetalization reaction is completed the reaction
product is precipitated by adding non-polar solvents, for
example, aliphatic hydrocarbons, or by pouring the reaction
solution into ice-cold water or an ice-cold water/alcohol
mixture, isolated by suction, washed with weakly alkaline
water (pH 9 to 12), and dried.
In combination with various negative working photosensitive
substances, such as diazonium salt polycondensation products,
azido compounds, p-quinonediazides or photopolymerizable
mixtures comprising polymerizable compounds and photoinitia-
tors, the polymers obtained in this way result in layers
which can be developed easily and without scumming. Depending
on their individual composition, the layers can be developed
with aqueous solutions of inorganic salts and/or surfactants
or with aqueous-alkaline solutions. The layers are distin-
2 ~
13
guished by a high abrasion resistance, good ink acceptanceand adequate shelf lives and can therefore be used for nume-
rous applications, in particular for producing planographic
printing plates, screen printing stencils and photoresists.
In general, the photosensitive mixtures contain 20 to 90,
preferably 30 to 75, % by weight of polymeric binder,
relative to the weight of all non-volatile constituents of
the mixture. Up to 50 % by weight, preferably up to 20 % by
weight, of the total amount of binder can be replaced by
customary binders.
Suitable photocurable compounds include, in particular,
diazonium salt polycondensation products, for example, of
diphenylamine-4-diazonium salts, with aldehydes, preferably
with formaldehyde. It is particularly advantageous to use
cocondensation products containing, in addition to the
diazonium salt units A-N2X, other, non-photosensitive units B
which are derived from condensible compounds, particularly
from aromatic amines, phenols, phenol ethers, aromatic
thioethers, aromatic hydrocarbons, aromatic heterocyclic com-
pounds and organic acid amines. These condensation products
are described in DE-A 20 24 244. Generally, all diazonium
salt polycondensation products described in DE-A 27 39 774
are suitable.
The diazonium salt units A-N2X are preferably derived from
compounds corresponding to the formula (Rl-R2-)pR3-N2X, in
which
2~ 3~
14
X is the anion of the diazonium compound,
p is an integer from l to 3,
R1 is an aromatic radical which is capable, in at
least one position, of condensation with an active
carbonyl compound,
R3 is an arylene group, preferably a phenylene group
which may be substituted,
R2 is a single bond or one of the groups:
~(CH2)q~NR4~~
-O- ( CH2 ) r-NR ~ ~
-S- ( CH2 ) r-NR4 -,
-S -CH2 Co-NR4 -,
-o-R5-o~
-0-,
-S-, or
-Co-NR4- 1
where
q is a number from 0 to 5,
r is a number from 2 to 5,
R4 is a hydrogen atom, an alkyl group having from 1 to
5 carbon atoms, an aralkyl group having from 7 to
12 carbon atoms or an aryl group having from 6 to
12 carbon atoms, and
R5 is an arylene group having from 6 to 12 carbon
atoms.
Further advantageous polycondensation products are obtained
by condensing an optionally substituted diphenylamine diazo-
nium salt first with an aromatic compound R'-O-CH2-B and then
with an aromatic compound R'-O-CH2-B-CH2-O-R', R' denoting a
hydrogen atom, an alkyl radical or an aliphatic acyl radical,
and B denoting the radical of any one of the condensible com-
pounds listed above. These condensation products are
described in detail in EP-A 126,875. The added amount of
diazonium salt polycondensation products generally varies
2~3~
between 5 and 70 % by weight, preferably between 10 and 50 %
by weight, relative to the non-volatile constituents of the
mixture.
Low- or high-molecular weight azido derivatives are also
suitable for use as photocurable compounds for certain
applications, preference being thereby given to low-molecular
weight azido compounds having at least two azido groups per
molecule. Examples of suitable compounds include 4,4'-
diazido-stibenes, 4,4'-diazidobenzophenones, 4,4'-diazido-
benzalacetophenones, 4,4'-diazidobenzalacetones and 4,4'-
diazidobenzalcyclohexanones. Where appropriate, the
photospeed of azido compounds of this type can be increased
by adding suitable sensitizers, for example 1,2-benzanthra-
quinone. It is also possible to use polyfunctional azides
whose absorption is shifted such, as a result of conjugation
with double bonds in the molecule, that no additional
sensitization is required upon exposure. Further suitable
azido compounds are described in GB-A 790,131, DE-C 950,618
and US-A 2,848,328. The mixtures according to the present
invention generally comprise from 5 to 60, preferably from
10 to 40, percent by weight of azido compounds, relative to
the non-volatile constituents of the mixture.
To stabilize the photosensitive mixtures containing diazonium
salt polycondensation products, it is advantageous to add a
compound having an acidic character. Compounds which can be
used include mineral acids and strong organic acids, with
phosphoric acid being preferred. The mixtures may furthermore
contain dyes and/or pigments which serve both as contrast-
enhncers and to stabilize the layer.
As the photocurable substances, the mixtures and materials
according to the invention may also contain combinations of
free-radically polymerizable compounds with photoinitiators.
Preferably, esters of acrylic or methacrylic acid with mono-
7~
16
or polyhydric, preferably primary, alcohols are used as the
polymerizable compounds. Preferably, the polymerizable
compounds should possess more than one, in particular 2 to 4,
polymerizable groups. Examples of suitable polyhydric
alcohols are ethylene glycol, propylene glycol, butane-1,4-
diol, butane-1,3-diol, diethylene glycol, triethylene glycol
or polyethylene glycols or polypropylene glycols with
molecular weights from about 200 to 1,000, neopentyl glycol,
glycerol, trimethylolethane, trimethylolpropane,
pentaerythritol, bisphenol-A derivatives and reaction
products of these compounds with ethylene oxide and/or
propylene oxide. Bis-acrylates and bis-methacrylates which
contain urethane groups and which are obtained by the
reaction of 1 mole of a diisocyanate with 2 moles o f a
hydroxyalkyl acrylate or hydroxyalkyl methacrylate are
particularly suited. The diisocyanate may also be an
oligomeric product obtained by the reaction of a diol with a
molar excess of a monomeric diisocyanate. These and similar
monomers containing urethane groups are described
in DE-A 20 64 079, DE-A 28 22 190, DE-A 30 48 502 and
DE-A-35 40 480.
In addition to the esters mentioned above, amides of acrylic
or methacrylic acid can be employed. Examples are methylene-
bis-(meth)acrylamide, ethylene-bis-(meth)acrylamide and
m-xylylene-bis-(meth)acrylamide.
The amount of monomers contained in the mixture generally is
about 10 to 80 % by weight, preferably 25 to 70 % by weight,
of the non-volatile constituents.
A large number of substances can be used as photoinitiators.
Examples include benzoins; benzoin ethers; polynuclear quino-
nes, such as 2-ethyl-anthraquinone; acridine derivatives,
such as 9-phenylacridine or benzacridine; phenazine derivati-
ves, such as 9,10-dimethylbenz(a)phenazine; quinoxaline deri-
2~3~
17
vatives or quinoline derivatives, such as 2,3-bis-(4-methoxy-
phenyl)quinoxaline or 2-styrylquinoline; quinazoline com-
pounds; or acyl-phosphineoxide compounds. Photoinitiators of
this type are described in DE-C 20 27 467, DE-C 20 39 861,
DE-A 37 28 168, EP-B 0,011,786 and EP-A 0,220,589. Hydrazo-
nes, mercapto compounds, pyrylium salts or thiopyrylium
salts, xanthones, thioxanthones, benzoquinones, acetopheno-
nes, benzophenones, synergistic mixtures with ketones or
hydroxy ketones and dyestuff redoxy systems may also be used.
Particular preference is given to photoinitiators possessing
photo-cleavable trihalomethyl groups, especially to
corresponding compounds of the triazine or thiazoline series.
Compounds of this type are described in DE-A 27 18 259, DE-A
33 33 450 and DE-A 33 37 024. 2-(4-Methoxystyryl)-4,6-bis-
trichloromethyl-s-triazine is a preferred example. It is
advantageous to combine these compounds with photooxidizable
dyes, photoreducible compounds and optionally further
coinitiators, as is described, for example, in EP-A 0,284,939
and EP-A 0,287,817.
The photoinitiators are generally employed in a quantity from
0.1 to 15, and preferably from 0.5 to 10, % by weight,
relative to the non-volatile constituents of the mixture.
Depending on their intended use and on their desired proper-
ties, the photopolymerizable mixtures may contain a number of
various additives, such as, for example, inhibitors to pre-
vent thermal polymerization of the monomers, hydrogen donors,
dyes, colored and uncolored pigments, color formers, indica-
tors, plasticizers and chain transfer agents.
The photopolymerizable mixtures can also be combined with
other, negative working photosensitive compounds, in
particular with diazonium salt polycondensation products.
18 2~93~
Processing of the mixtures according to this invention into
photosensitive recording materials is performed in a known
manner by coating a suitable support with a solution of the
mixture and drying the applied coating, so that a layer
having the desired thickness is obtained. Suitable supports
include metals and also polyester film or cellulose acetate
film, Perlon gauze etc.. The support material may function as
the final support or as a temporary support material from
which the photosensitive layer is transferred by lamination
to the workpiece to be processed.
The recording material which is prepared using the photosen-
sitive mixtures of the invention serves, on the one hand, to
produce images on suitable supports or receptor sheets and,
on the other hand, to produce reliefs which are used as
printing plates, screens, resists, and the like. In addition,
it is also possible to use the photosensitive mixtures for
the formulation of UV-hardenable printing inks or for the
preparation of lacquers which are hardenable by ultraviolet
radiation and may be used for the protection of surfaces.
Primarily, the compositions are used for the production of
lithographic printing plates, in which aluminum is the pre-
ferred support material. It is particularly preferred to
pretreat the aluminum used for this purpose in the usual
manner, for example, by a mechanical, chemical or electro-
chemical graining process which is, optionally, followed by
an anodic oxidation. A further treatment of this support
material, for example, with polyvinyl phosphonic acid, alkali
metal silicate, phosphate, hexafluorozirconate, chromate,
borate, polyacrylamide and cellulose derivatives is
advantageous.
The recording materials obtained from the mixtures are
processed in the conventional manner, by exposing imagewise
19
and washing-out the unexposed areas of the layer with a
suitable developer.
The recording material is exposed under an original, as is
known in the art, using light sources which emit light with
the highest possible spectral fraction in the near ultra-
violet region. The material can also be exposed by laser
irradiation. Suitable lasers for irradiation are shorter-wave
lasers of adequate performance, for example, Ar lasers,
krypton ion lasers, helium/cadmium lasers, emitting in the
region between about 300 and 600 nm and, for some layers,
even C02 lasers, which emit at about 10.6 ~m, or YAG lasers
emitting at about 1.06 ~m.
As the developer solutions, water or neutral or alkaline
aqueous solutions are used, which have a pH value in the
range from 6 to 14, preferably from 7.5 to 12, and which con-
tain buffer salts, for example, water-soluble alkali metal
phosphates, alkali metal silicates, alkali metal borates,
alkali metal carbonates, alkali metal acetates or alkali
metal benzoates. Additional constituents used are wetting
agents, preferably anionic wetting agents and, if
appropriate, water-soluble polymers. The solution can also
contain minor amounts, for example, up to 5 percent by
weight, preferably not more than 2 percent by weight, of
water-miscible organic solvents. It is preferred to use
difficultly volatile solvents, for example, araliphatic
alcohols, the vapor pressure of which is of no consequence in
the handling of the developer. Development can be performed
in the conventional manner by dipping, spraying, brushing or
wiping-over with a pad. If desired, the developed material
can be treated with a gumming solution.
The photosensitive recording materials of this invention are
distinguished by good reproduction properties and an adequate
shelf life. They can be easily developed without scum, using
2~
developer solutions which from an ecological point of view
are virtually neutral. The long print runs and the good ink
acceptance obtained with printing forms prepared using the
material of the present invention are particularly
advantageous. The printing stencils are also highly resistant
to alkaline developers and other processing solutions.
If the mixture according to the invention contains a
photopolymerizable combination of compounds, it is not
absolutely necessary to exclude the access of atmospheric
oxygen during exposure. Nevertheless, it is generally
favorable to keep the mixture away from the influence of
atmospheric oxygen during the photopolymerization. When the
mixture is used in the form of thin copying layers, it is
advisable to apply a suitable protective film which is
substantially impermeable to oxygen. This film can be self-
supporting and can then be peeled off before development of
the copying layer. For this purpose, polyester films, for
example, are suitable. The protective film can also comprise
a material which dissolves in the developer liquid or can be
removed during development, at least from the non-hardened
areas. Materials which are suitable for this purpose are, for
example, polyvinyl alcohol, vinyl alcohol/vinyl acetate
copolymers, polyvinylpyrrolidone, vinylpyrrolidone/vinyl
acetate copolymers, polyacrylic acid, butadiene/maleic acid
copolymers, polyvinylmethyl ethers, polyphosphates, sugars
etc.. Such protective layers generally have a thickness of
0.1 to 10 ~m, preferably of 0.5 to 5 ~m.
When photopolymerizable mixtures are employed, the print runs
can be increased by post-heating the exposed plates or by
post-exposing the developed plates. The two process steps can
also be combined. But even without an additional
heattreatment or post-exposure high print runs are achieved.
21 2~
A thermal post-treatment is also a suitable means for
additionally strengthening photosensitive layers containing
other photosensitive compounds, such as diazonium salt
polycondensation products. Such a treatment is particularly
recommended for planographic printing forms. It comprises
heating the gummed printing form to a temperature of between
180 C and 240 C. The duration of the treatment depends on
the temperature and generally is two to twenty minutes. With
this thermal post-treatment no surfactant is required. It is
assumed that under these conditions the graft polyvinyl
acetals split off water and are converted into polymers
having unsaturated side groups which are able to undergo an
additional photochemical or thermal crosslinking reaction. It
may therefore be expedient to add a thermal crosslinking
agent to the photosensitive mixture, such as, for example, an
organic peroxide, which has a scorch temperature of at least
100 C and above this temperature is capable of forming free
radicals of the type described in EP-A 247,461. Examples of
suitable peroxides include peroxy-esters, peroxyketals,
bisaralkyl peroxides, dialkyl peroxides and bis-dialkyl
peroxides. The ink acceptance of the photosensitive layers is
substantially improved by this thermal post-treatment, in
particular, if the polymers employed have high hydroxyl
numbers.
Furthermore, the mixtures according to the present invention
are suitable for the production of resist stencils exhibiting
excellent image resolution and possessing satisfactory
thermal stability and shelf lives. In this case, too, very
mild developer solutions can be used, which are little toxic
or even untoxic. The manufacture of screen printing stencils
is yet another field of application. They are distinguished
by favorable processing characteristics and long shelf lives.
2 ~
22
The preparation of the polyvinyl acetals used in the Examples
is described below.
a) Preparation of polvurethane qraft backbones
In each case, the diol component and the catalyst were
first introduced into a reaction vessel equipped with a
stirrer and supplied with a nitrogen atmosphere, and the
mixture was heated to a reaction temperature of between
65 C and 100 C. Then the diisocyanate component was
metered in whereby care was taken that the temperature
of the reaction mixture did not exceed 120 C, and
preferably did not exceed 100 C. After the complete
addition of the diisocyanate component, the mixture was
post-heated to a temperature between 80 C and 100 C
~5 for a period of up to two hours in order to complete the
reaction. The completion of the conversion and thus the
end of the reaction were determined by an analysis of
the diisocyanate consumption with the aid of known
methods (p.e., IR-spectroscopy, titration).
The detailed composition of the reaction mixtures used
in the Examples and the calculated mean molecular
weights (MCalc) of the resulting polyurethanes (PU) are
compiled in Table 1 below. The molecular weights result
from the molar ratio diol component/diisocyanate,
assuming a complete conversion of the NC0 groups.
21~9~
23
Table 1
Poly- Diol Reaction Molar ratio Mcalc
urethane component tem~erature dlol com-
(PU) PEG/PU ( C) ponent/
(molar ratio) diisocyanate
A 7 : 3 80 1 : o.96,470
B 7 : 3 72 1 : 0.96,470
C 3 : 2 78 1 : 0.97 18,300
D 7 : 3 75 1 : 0.97 19,900
PEG = Polyethylene glycol, molecular weight 600
Bu = 1,4-butanediol
All products were prepared using isophorone diisocyanate
as the diisocyanate component. In each case, 1,4-dimethyl-
piperazine was used as the catalyst in an amount of
0.48 mole %, relative to the diisoc~yanate.
b) Preparation of the qraft Polvmers
In each case, the polyurethane graft backbone was melted
in a reaction vessel in a nitrogen atmosphere or was
dissolved, respectively, by adding small amounts of
methanol, and heated to a temperature between 60 C and
100 C. The monomers to be grafted on, which had
optionally been dissolved in a solvent (e.g. methanol),
including the free-radical initiator dissolved in the
monomer, were then slowly metered to the polyurethane
graft backbone, in a way such that the homopolymer
formation was largely suppressed.
24 2~3~
The maximum temperature of the reaction mixture should
be 120 C, more preferably 100 C.
When the post-reaction was completed, excess monomer
remainders were removed by azeotropic distillation with
methanol. The compositions of the individual reaction
mixtures and the reaction parameters are compiled in
Table 2 below.
Table 2
_
Graft PU VAc Start Meter- Post- Graft- Jo calc.
poly- ~/g temp. ing react. ed-on mole-
mer PU ~C time min monom. ml/g cular
min wt % _ weight _
AV A 4 75 420 45 79.8 21.9 31,300
BV B 2.32 73 420 45 69.3 18.3 21,000
CV C 3.16 75 300 45 74.7 26.3 72,500
DV D 3.16 75 420 45 74.5 28.7 78,000
VAc = Vinyl acetate
JO = intrinsic viscosity
All products were prepared employing 0.2 mole % of
dibenzoyl pero~ide (relative to the monomer used in each
case). The intrinsic viscosities were determined at
25 C in tetrahydrofuran, using an Ostwald Viscosimeter,
with the measured concentrations being selected such
that a Hagenbach correction was not necessary. The
grafted-on amount of monomer, in % by weight, is related
to the weight of the total polymer.
2~3~
c) Saponification of the qraft polvmers
The graft polymers of Table 2 were transesterified or
saponified within two hours at room temperature. For
this purpose, the products were dissolved in methanol
to give 50 % strenghth solutions and mixed with
methanolic soda lye (10 % strength). Depending
on the added amount of alkali and the degree of
grafting of the graft polymer, polymeric hydrolysis
products having different degrees of hydrolysis were
obtained. The resulting gels were granulated, the
granules were washed with methanol (where appropriate
with an addition of acetic acid to neutralize the soda
lye) and dried. The process parameters and results are
compiled in Table 3 below.
Table 3
Graft Graft mole % of mole % of Degree of Mcalc
polyvinyl polyvinyl NaOH per H20 per hydrolysis
alcohol acetate ester unit ester unit in %
E AV 1.92 0 98.2 22,000
F BV 5.00 0 98.9 14,000
G CV 1.92 0 98.0 47,000
H DV 1.97 0 98.4 44,000
CV 0.50 11.13 56.5 58,000
d) PreParation of the araEt polw invl acetals
The graft polymers listed in Table 3 were dissolved in
about eight times their amount of distilled water. The
corresponding amount of aldehyde and a small amount of
2,6-di-tert.-butyl-4-methylphenol were added at room
temperature. A solution comprising a small amount of
sodium octyl sulfate, 1/3 of the weight amount of the
aldehyde of concentrated hydrochloric acid and water
was dropwise added to this solution, with agitating.
The mixture was stirred for one hour at room
26 2~
temperature, then heated to 40 ~C, and stirring was
continued for another two hours. Thereafter concentrated
hydrochloric acid (the same weight amount as the
aldehyde) was added and stirring was continued at 40 C
for a further two hours. When the mixture had cooled
down to room temperature the aqueous phase was decanted
from the precipitated polymer, the polymer was dissolved
in ethanol and precipitated by pouring it into an excess
amount of water. The polymer was dried in a vacuum drier
at 40 C until its weight remained constant.
Tabelle 4
Graft poly- Graft poly Molar OH
vinyl vinyl Aldehyde rationumber
acetal alcohol
K E Prl+4-ClBz 1 : 2 302
L F Bu1+4-CH30Bz 1 : 1 416
M G Bul+Bu 1 : 1 441
N H Acl+Bu 1 : 1 394
O I Tri+Bu 3 : 1 551
P H Prl+Bz 1 : 2 332
Q F Tri+Bu 1 : 2 270
R G Tri+Bu 1 : 3.7 187
S H Bul+Ac 1 : 1 419
T E Tri+Pr 1 : 2 244
Ac = acetaldehyde
Acl = acetaldol
Pr = propionaldehyde
Prl = propionaldol
Bu = butyraldehyde
Bul = butyraldol
Bz = benzaldehyde
4-CH3OBz = 4-methoxy-benzaldehyde
4-ClBz = 4-chlor-benzaldehyde
Tri = triglinaldehyde
(3-hydroxy-pentanal)
2~ 3
Preferred embodiments of the invention are described in the
Examples which follow~ In most cases, amounts are indicated
in parts by weight (pbw). Unless otherwise specified,
percentages and proportions are given in weight units.
Exam~le 1
A coating solution comprised of
3.90 pbw of polymer N,
1.30 pbw of a diazonium salt polycondensation product
prepared from 1 mole of 3-methoxy-
diphenylamine-4-diazonium sulfate and 1 mole
of 4,4'-bis-methoxy-methyl-diphenylether,
isolated as mesitylene sulfonate,
0.06 pbw of phosphoric acid (85 % strength),
0.02 pbw of phenylazodiphenylamine and
0.35 pbw of Victoria Pure Blue FGA
(C.I. Basic Blue 81), in
100.00 pbw of 2-methoxyethanol
is applied to a 0.3 mm thick aluminum foil which has been
electrochemically grained in nitric acid, anodically oxidized
in sulfuric acid and post-treated with a 0.1 % strength
aqueous solution of polyvinyl phosphonic acid. Application is
performed such that a dry layer weight of 1.2 g/m2 results.
The photosensitive layer obtained in this way is exposed for
30 seconds through a standard test original by means of a
5 kW metal halide lamp. The exposed layer exhibits a clear
contrast between the exposed and unexposed areas and is
developed with a developer solution having the following
composition:
5.0 pbw of sodium octyl sulfate,
1.0 pbw of sodium metasilicate x 5 H20, and
94.0 pbw of distilled water.
3 ~ ~
The non-exposed layer areas are removed within a short time
without remainders being left behind. The plate is then
rinsed with water and dri~d. Even the finest image elements
of the original are reproduced on the copy. More than 210,000
prints can be run in a sheet-fed offset press with the
printing plate produced in this way.
Exam~le 2
A coating solution comprised of
1.00 pbw of polymer L,
1.00 pbw of a diazonium salt polycondensation product
prepared as in Example 1, but isolated as the
methane sulfonate,
1.00 pbw of a diazonium salt polycondensation product
obtained from diphenylamine-4-diazonium chlo-
ride and para-formaldehyde, prepared in 85 %
strength phosphoric acid,
0.15 pbw of Basonyl Red 583 (C.I. 45,170), in
23.00 pbw of methanol,
23.00 pbw of propyylene glycol monomethylether and
9.00 pbw of distilled water
is applied to an aluminum foil pretrated as described in
Example 1, in a way such that a dry layer weight of 0.8 g/m2
is obtained.
The plate is exposed for 40 seconds and then developed by
spraying with a water jet, whereby the non-exposed layer
areas are removed within a short time, and is then dried.
2 ~
Example 3
A coating solution comprised of
2.60 pbw of polymer O,
1.30 pbw of the diazonium salt polycondensation product
described in Example 1,
0.06 pbw of phosphoric acid (85 % strength),
0.02 pbw of Metanil Yellow (C.I. 13,065) and
0.30 pbw of Victoria Pure ~lue FGA, in
80.00 pbw of 2-methoxyethanol
is applied to an aluminum foil pretreated as described in
Example 1, such that the dried layer has a weight of
0.9 g/m2. The layer is exposed as described in Example 1.
Development is performed with the aid of plush pad, using a
developer solution having the following composition:
5.0 pbw of sodium octyl sulfate,
1.5 pbw of sodium metasilicate x 5 H2O,
1.0 pbw of trisodium phosphate x 12 H20,
0.5 pbw of disodium hydrogen phosphate x 12 H20,
92.0 pbw of distilled water.
The non-exposed areas are removed within 30 seconds. The
further treatment is performed as in Example 2. On the copy,
step 4 of a silver film continuous tone step wedge having a
density range of 0.05 to 3.05 with increments of 0.15 is
reproduced solid. Even the finest lines and screen dots of
the original are fully reproduced. When clamped into a sheet-
fed off~et press, the resulting printing plate gives more
than 195,000 prints.
2 ~
Example 4
A coating solution is prepared from
1.560 pbw of polymer K,
0.910 pbw of a diazonium salt polycondensation product
of Example 1,
0.049 pbw of phosphoric acid (85 % strength),
0.162 pbw of 2-(4-methoxyst~ryl)-4,6-bis-trichloro-
methyl-s-triazine,
1.750 pbw of a technical-grade mixture of penta-
erythritol tri- and tetraacrylate, and
0.550 pbw of an azo dye obtained by coupling 2,4-
dinitro-6-chlorobenzenediazonium salt with
2-methoxy-5-acetylamino-N-cyanoethyl-N-
hydroxyethylaniline, in
70.000 pbw of butanone,
4.000 pbw of ethanol and
2.000 pbw of butylacetate
and applied to the layer support material described in
Example 1, in a way such that a dry layer weight of 2.1 g/m2
is obtained.
The layer is exposed through a negative original for 25
seconds, with a solid step 4 resulting. Development is
performed with a solution of the following composition:
5.0 pbw of sodium octyl sulfate,
1.5 pbw of sodium metasilikate x 5 H2O,
1.0 pbw of trisodium phosphate x 12 H2O,
l.0 pbw of phenoxyethanol and
91.5 pbw of distilled water.
3 1
The resulting printing form is clamped into a printing press
where it readily accepts ink. The printing test is stopped
after 220,000 prints.
Exam~le 5
A coating solution is prepared from
6.20 pbw of polymer M,
2.10 pbw of a diazonium salt polycondensation product
of Example 1,
0.30 pbw of Victoria Pure Blue FGA (C.I. Basic Blue 81)
0.24 pbw of phosphoric acid (85 % strength),
0.24 pbw of 45 % strength 2,5-dimethylhexane-2,5-di-
tert.-butyl peroxide, as granules with chalk
(INTEROX DHBP-45-IC/G made by Peroxid-Chemie
GmbH) and
0.07 pbw of phenylazodiphenylamine, in
257.00 pbw of 2-methoxyethanol and
78.00 pbw of tetrahydrofuran,
applied to an aluminum foil pretreated as described in
Example 1, and dried. The resulting copying layer, which has
a dry weight of 1.1 g/m2, is exposed through a negative
original for 30 seconds by means of a 5 kW metal halide lamp.
The exposed layer is developed with the developer solution
specified in Example 4, with the aid of a plush dabber and
subsequently rinsed with water and dried. The non-exposed
layer areas are completely removed by development with;~a few
seconds. Step 4 of the silver film continuous tone step wedge
described in Example 3 is solid on the copy.
2 ~
The printing plate is treated in a drying cabinet at 200 C
for 5 minutes and then allowed to cool down. A printing test
in a sheet fed offset press is stopped after 260,000 prints,
although no loss ir. quality is stated.
Example 6
A coating solution is prepared as described in Example 1,
except that polymer P is substituted for polymer N. The
solution is applied to plates made of the support material
described in Example 1, such that a dry layer weight of
1.2 g/m2 is obtained.
Four of the plates prepared as described above are stored at
100 C in a drying oven for a period of 1 to 4 hours. After
this heat treatment the plates are imagewise exposed and
developed with the developer solution of Example 4. To render
visible any layer residues (toning) remaining in the non-
image areas, the dried plates are dyed with a protective ink.
The plates stored in the oven for 1 and 2 hours can be
developed satisfactorily. They do not exhibit any substantial
extension of the continuous tone step wedge. After a storage
time of 3 hours, the continuous tone step wedge is extended
by two steps. Development is insignificantly retarded.
Development of the plate stored for 4 hours is slightly
retarded. These results show that the mixtures according to
this invention are relatively resistant to storage in the
heat.
2 ~
33
Example 7
A coating solution comprised of
2.2 pbw of polymer Q,
2.2 pbw of 4,4'-diazido-stilbene-2,2'-disulfonic acid
sodium salt,
0.3 pbw of Rhodamine 6 GDN extra (C.I. 45,160), and
0.2 pbw of 2-benzoylmethylene-1-methyl-~-naphthothiazoline,
in
30.0 pbw of tetrahydrofuran and
120.0 pbw of water
is applied to the support described in Example 1 such that a
dry layer weight of 0,9 g/m2 is obtained. The copying layer
is exposed for 40 seconds through a negative original and
then developed with pure water, whereby the non-image areas
are removed within a short time.
Example 8
A coating solution is prepared from
2.00 pbw of polymer M,
2.00 pbw of the reaction product obtained from 1 mol of
2,4,4-trimethyl-hexamethylene diisocyanate and
2 mol of hydroxyethyl methacrylate,
0.15 pbw of 2,4-bis-trichlormethyl-6-(4-styrylphenyl)-
s-triazine and
0.10 pbw of the azo dye specified in Example 4, in
100.00 pbw of propylene glycol monomethyl ether
and applied onto the support material specified in Example 1,
such that a dry layer weight of 1.3 g/m2 is obtained. The
plate is exposed for 25 seconds through a continuous tone
step wedge. Development is performed with the developer
solution of Example 1. The plate can be readily developed and
exhibits a solid step 4. In a sheet-fed offset press 90,000
good prints are obtained.
34
Example 9
A coating solution is prepared from
2.50 pbw of polymer R,
5.60 pbw of a technical-grade mixture of
pentaerythritol tri- and tetraacrylate,
0.20 pbw of the triazine specified in Example 4 and
0.03 pbw of the azo dye specified in Example 4, in
25.00 pbw of butanone,
2.00 pbw of ethanol and
1.00 pbw of butyl acetate
and spin-coated onto a 25 ~m thick biaxially stretch-oriented
and heat-set polyethylene terephthalate film, such that a
layer weight of 35 g/m2 results after drying at 100 C.
The dry resist film prepared in this way is laminated at
120 D C onto a phenoplast laminate board clad with a 35 ~m
thick copper foil, employing a customary laminating device.
Exposure is performed for 25 seconds using a customary
exposure device. The original used is a line original having
line widths and spacings down to 80 ~m. Following exposure
the polyester film is carefully peeled off, and the layer is
developed for 90 s~conds in a spray developing station, with
the developer solution specified in Example 1. Thereafter,
the plate is rinsed with tap water for 30 seconds, etched for
30 seconds in a 15 ~ strength ammonium peroxydisulfate
solution and then electroplated in the following
electroplating baths:
2~ b~
1. for 30 minutes in a copper bath from
Messrs. Schloetter, Geislingen/Steige,
West Germany, type "Glanzkupfer-Bad"
(Brilliant Copper Bath).
current density: 2.5 A/cm2
metal build-up: about 12.5 ~m
2. for 30 minutes in a nickel bath from the same
manufacturers, type "Norma".
current density: 4.0 A/cm2
metal build-up: 9.0 ~m
The plate does not exhibit any damage or undercutting.
Decoating is performed at a temperature of 50 C,
using 5 % strength KOH solution. The bared copper
is etched away with customary etchants.
Exam~le 10
A coating solution comprised of
1.00 pbw of polymer S,
1.00 pbw of a technical-grade mixture of
pentaerythritol tri- and tetraacrylate,
0.10 pbw of 2-(4-trichloromethyl-benzoylmethylene-)-
3-ethyl-benzothiazoline and
0.02 pbw of Victoria Pure Blue FGA (C.I. Basic Blue) in
50.00 pbw of propylene glycol monomethyl ether
is applied onto an aluminum foil which has been
electrochemically grained, anodically oxidized and post-
treated with polyvinylphosphonic acid, in a way such that a
dry layer of 1.3 g/m2 is obtained. The resulting printing
plate is exposed through a test original and developed with
the developer solution specified in Example 1.
2~ J~
36
The printing form immediately accepts ink in a sheet-fed
offset press. Even after a prolonged press stand still the
ink is readyly accepted after 2 to 8 sheets only. 95,000 good
prints are obtained, and even the finest lines are completely
reproduced.
Example ll
A coating solution comprised of
l.00 pbw of polymer T,
1.00 pbw of pentaerythritol triacrylate,
0.10 pbw of the triazine specified in Example 8 and
0.03 pbw of Victoria Pure Blue FGA in
50.00 pbw of propylene glycol monomethyl ether
is applied to the support material described in Example 1, in
a way such that a dry layer of 1.1 g/m2 is obtained. The
photosensitive layer is exposed for 30 seconds through a
negative standard original, using a 5 kW metal halide lamp,
and is then developed with the developer specified in Example
1. Step 4 of the step wedge is reproduced solid in the copy.
Even the finest screen dots and lines of the original are
completely reproduced. 65,000 good prints can be run in a
sheet-fed offset press.
Example 12
A printing plate produced as in Example 11 is provided with a
0.5 ~m thick protective layer comprised of polyvinyl alcohol
(12% residual acetyl froups, K value 4). The plate is exposed
for 5 seconds through a standard negative original and
developed with the developer solution described in Example 1.
It exhibits a solid step 4 and gives 185,000 good prints in a
sheet-fed offset press.
2~ ~3~
37
This Example illustrates that both the photospeed and the
print run can be increased by applying an oxygen barrier
layer to the photocurable layer., However, a comparison of
Examples 11 and 12 shows that even without a barrier layer a
printing plate yielding high print runs is obtained.
Example 13
Following exposure, a printing plate produced as described in
Example 11 is heat-treated at 100 C for one minute and then
developed. Two additional solid steps are obtained, compared
to the plate of Example 11, which was not post-heated.
The number of prints can be triplicated by the thermal post-
treatment. A similar ncrease is achieved as a result of
post-exposure. ~
Post-treatment Print run
none: 50~000
1 minute, heating to 100 C: 151,000
1 minute, post-exposure (5 kW):156,000
30 seconds, post-exposure (5 kW): 150,000
