Note: Descriptions are shown in the official language in which they were submitted.
2~ ~3~
89/X 032 Tran~lation
Photopolymerizable mixture and recording material produced
therefrom
The present invention relates to a photopolymerizable mixture
which can be developed with aqueous solutions, wich contains
a polymeric binder, a polymerizable compound having at least
one ethylenically unsaturated double bond in the molecule,
and a photoinitiator or photoinitiator system, and which is
suitable for the production of photosensitive recording
materials, in particular of planographic printing plates
and photoresists.
Photopolymerizable mixtures containing water-soluble binders
are known from DE-B 15 22 362 and DE-A 19 17 917. As a rule,
these mixtures can be developed readily and without scumming,
but they suffer from the disadvantage that in planographic
printing the hardened image areas, which contain the water-
soluble binder, are wetted more easily by the dampening
solutions and are attacked by the latter during the
production of high print runs.
Mixtures of the above generic type are also described in
DE-A 20 53 363. The binders contained therein comprise
reaction products obtained from a polymer containing
hydroxyl groups or amino groups and at least one saturated
alkyl sulfonyl isocyanate, alkoxy sulfonyl isocyanate, aryl
sulfonyl isocyanate or aryloxy sulfonyl isocyanate. In
combination with diazonium salt condensation products or
photopolymerizable mixtures, the binder is processed to
give photosensitive layers. However, the resulting mixtures
can only be developed with aqueous-alkaline solutions if the
2 ~
binders employed have high acid numbers, which adversely
affect the abrasion resistance and printing properties of the
hardened layers.
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 photo-
initiator and a water-insoluble ~olymeric 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.
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.
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 pho~o-
2 ~
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-
polymerizable mixture which is suitable for use in the
production of printing plates, particularly lithographic
printing plates, or of photoresists; which has all the advan-
tages of the known photopolymerizable compositions; 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, proper-
ties 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 photopoly-
merizable mixture is provided which contains, as essential
constituents,
a) a polymeric binder possessing repeating vinyl
acetal units,
b) a free-radically polymerizable compound possessing
at least one terminal ethylenically unsaturated
group and having a boiling point of more than
100 C at normal pressure, and
c) a compound or a combination of compounds which
under the action of actinic light is capable of
initiating the polymerization of compound b).
2~ 3~6
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 are grafted.
In accordance with the instant invention, there is also pro-
posed a photopolymerizable recording material comprising a
layer support and a photopolymerizable layer wherein said
photosensitive layer is comprised of the mixture defined
above.
The graft polymers contained in the mixture of the instant
invention are described in the prior German Patent Applica-
tion P 38 35 840.9. For preparing them, a carboxylic acid
vinyl ester and optionally another ethylenically unsaturated
compound copolymerizable therewith is grafted onto a
polyurethane graft backbone and saponified completely or
partially. The polymers having vinyl alcohol units, which
are obtained in this way, are further reacted with aldehydes
to give 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 employedO
Cycloaliphatic diols, such as cyclohexanediols, and in
particular aliphatic diols having 2 to 12 carbon atoms are
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, are also preferred; polyethylene oxides with
molecular weights of between 200 and 10,000, and more pre-
ferably 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-butane-
diol, 1,3-propanediol, ethylene glycol, diethylene glycol,
1,2-hexanediol, 1,2-propanediol, pentanediol or cyclohexane-
diol. 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
polyurethane. Vinyl acetate and/or vinyl propionate, in
particular vinyl acetate, are particularly preferred.
2~36~
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 carboxyli~ 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 being
at 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 known methods.
Aliphatic aldehydes having 1 to 20 carbon atoms, which may be
substituted, and aromatic aldehydes, which may also be sub-
stituted, are employed for acetalizing. Preference is given
to aliphatic aldehydes having 1 to 5 carbon atoms, such as
n-butyraldehyde, isobutyraldehyde, propionaldehyde or
formaldehyde. Substituted or unsubstituted benzaldehydes,
2 ~
such as benzaldehyde, p-chlorobenzaldehyde or
p-methoxybenzaldehyde are also suited. It is also possible
to employ combinations of several of these aldehydes.
The degree of acetalization of the graft polyvinyl acetals
used as binders in accordance with this invention is pre-
ferably selected such that the content of non-acetalized
polyvinyl alcohol units in the graft polyvinyl acetals is
18 to 60 mole %, and particularly preferably 20 to 45 mole ~,
each time relative to the molar amount of vinyl alcohol units
contained in the saponified graft polymers used, it being
possible for up to 55 mole %, relative to the original
amount, to be present as vinyl ester units. The hydroxyl
number of the ready-for-use binder should be in the range
of 100 to 600, preferably of 200 to 500.
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 an 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 and mixed with an 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. Thereby, 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-precipita-
tion.
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 reactionis 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.
9 2 ~
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 acid.
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.
The preparation of the graft polyvinyl acetals is also
described in the former German Patent Application
P 38 35 ~40.9.
In combination with 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-
lo ~ 6~
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 photopolymerizable mixtures contain 20 to 90,
preferably 30 to 75, % by weight of polymeric binder, rela-
tive 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 any
of a great number of customary binders. Examples of suitable
compounds are: polyamides, polyvinyl esters, polyvinyl
acetals, polyvinyl ethers, epoxide resins, polyacrylic acid
esters, polymethacrylic acid esters, polyesters, alkyd
resins, polyacryl amides, polyvinyl alcohols, polyethylene
oxides, polydimethylacrylamide, polyvinylpyrrolidone, poly-
vinylmethylformamide, polyvinylmethylacetamide, and copoly-
mers of the monomers forming the homopolymers enumerated.
Advantageously, these binders, too, are water-insoluble but
soluble or at least swellable in aqueous-alkaline solutions.
Examples of polymers of this generic type include: maleate
resins, polymers of ~-(methacryloyloxy)-ethyl N-)p-tolyl-
sulfonyl)-carbamate and copolymers of these and similar mono-
mers with other monomers, as well as vinyl acetate/crotonicacid copolymers, styrene/maleic anhydride copolymers, alkyl
methacrylate/methacrylic acid copolymers and copolymers of
methacrylic acid, higher alkyl methacrylates and methyl
methacrylate and/or styrene, acrylonitrile and others.
The mixtures and materials according to the invention contain
free-radically polymerizable compounds with at least one
terminai ethylenic double bond. Preferably, esters of acrylic
or methacrylic acid with mono- or polyhydric, preferably
primary, alcohols are used as the polymerizable compounds.
Preferably, the polymerizable compounds should possess more
3 ~ ~
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, diethy-
lene 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 of a
hydroxyalkyl acrylate or hydroxyalkyl methacrylate are parti-
cularly 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 monG-
mers 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 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-
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-
12 ~ 3~
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 types and quantities of such additions depend upon thefield of application for which the photosensitive mixture is
intended. In principle, care must be taken that the added
substances do not absorb an excessive portion of the actinic
light which is required for cross-linking, because this would
result in a reduction of the practical sensitivity to light.
The photopolymerizable mixtures can also be combined with
other, negative working photosensitive compounds, in particu-
lar with diazonium salt polycondensation products. Suitable
3i~
13
diazonium salt polycondensation products are condensation
products of condensible aromatic diazonium salts, 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 cond~nsation productsare 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 (R1-R2-)pR3-N2X, in
which
X is the anion of the diazonium compound,
p is an integer from 1 to 3,
Rl 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~l
-O- ( CH2 ) r-NR4 -,
-S-(CH2)r-NR4-,
-S-CH2CO-NR -,
-o-R5_0_
--O--,
-S-, or
-Co-NR4-
where
2~ ~ 93~
14
q is a number from O to 5,
r is a number from 2 to 5,
R4 ~s 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 havir.g from 6 to
12 carbon atoms, and
R5 is an arylene group having from 6 to 12 carbon
atoms.
10 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 diazonium salt polycondensation products are contained in
the mixture in an amount of 0 to 40 ~ by weight, preferably
of O to 30 % by weight, relative to the non-volatile consti-
tuents of the mixture.
In addition, the photopolymerizable mixtures can contain dyes
and/or pigments which may serve to enhance the contrast upon
exposure and also to harden the layer. Suitable dyes are, for
example, specified in US-A 3,218,167 and US-A 3,884,693. Par-
ticularly suitable are, for example, Victoria Pure Blue FGA,
Victoria Pure Blue BO (C.I. 42,595), Malachite Green,
Victoria Blue B (C.I. 44,045), Renol Blue B2G-H (C.I.
74,160), Crystal Violet, Fatty Red 5B (C.I. 26,125), Neo7apon
Blue FLE (C.I. Solvent Blue 70), Brilliant Blue Salt Acetate,
Samarone Navy-Blue, Orasol Blue GN, Zapon Fast Fire-Red B
(C.I. 13,900:1) or Rhodamine 6 GDN (C.I. 45,160). To enhance
3 ~ ~
the image contrast after exposure, Metanil Yellow (C.I.
13,065), Methyl Orange (C.I. 13,025) or phenylazo-
diphenylamine can be used.
The support material is coated from appropriate organic
solvents or solvent mixtures, generally by flow-coating,
spraying or dipping. The coating method depends on the
desired layer thickness, the dried layers usually having
thicknesses between 0.5 and 200 ~m.
Suitable supports are, for example, magnesium, zinc, copper,
mechanically, chemically and electrochemically grained
aluminum, anodically oxidized aluminum, steel, and also poly-
ester film or cellulose acetate film, Perlon gauze etc., the
surface of which may have been subjected to a pretreatment.
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.
Employing the mixture according to the invention, 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.
The recording material which is prepared using the photopoly-
merizable 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.
Preferably, the mixtures are used for the production of
lithographic printing plates, in which aluminum is the pre-
ferred support material. It is particularly preferred topretreat 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 ceilulose derivatives is advanta-
geous.
The recording materials obtained from the mixtures are
processed in the conventional manner, by exposing it
imagewise and washing-out the unexposed areas of the layer
with a suitable developer.
2~3~
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 laserirradiation. 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 CO2 lasers, which emit at about 10.6 ~m, or YAG lasers
emitting at about 1.06 ~m.
As the developer solutions, neutral or preferably alkaline
aqueous solutions are used, which have a pH value in the
range from 8 to 14, preferably from 8.5 to 13, 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 appro-
priate, water-soluble polymers. The solution can also contain
minor amounts, for example, up to 5 percent by weight, pre-
ferably 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
developer solutions which from an ecological point of view
are virtually neutral.
2~
The large 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. To achieve even higher print
runs, the plates can be post-heated after exposure and/or the
developed plates can be post-exposed.
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
~5 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
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 NCO groups.
2~93~
19
Table 1
Poly- Diol Reaction Molar ratioMcalc
urethane component temperature diol com-
(PU) PEG/PU (o C) ponent/
(molar ratio) diisocyanate
A 7 : 3 80 1 : 0.96,470
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
E 7 : 3 78 l : 0.95 13,200
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 diisocyanate.
b) Preparatlon 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.
2 ~
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 Cr Start Meter- Post- Graft- JO calc.
poly- g/g g/g temp. ing react. ed-on mole-
mer PU PU C time min monom. ml/ cular
min wt %g weight
_
AV A 4 0 75 420 45 79.821.9 31,300
BV B 2.32 0 73 420 45 69.318.3 21,000
CV C 3.16 0 75 300 45 74.726.3 72,500
DV D 3.16 0 75 420 45 74.528.7 78,000
EVCr E 3.03 0.126 75 300 45 75.3 31.5 53,000
VAc = Vinyl acetate
JO = intrinsic viscosity
Cr = Crotonic acid
All products were prepared employing 0.2 mole % of
dibenzoyl peroxide (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 ~
c) Saponification of the qraft ~olvmers
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 using
conventional mills, 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 Degree of Mcalc
polyvinyl polyvinyl NaOH per hydrolysis
alcohol acetate ester unit in %
F AV 1.92 98.2 22,000
G BV 5.00 98.9 14,000
H CV 1.92 98.0 47,000
I DV 1.97 98.4 44,000
_ EVCr 2.00 94.5 * 36,000
0 * found by determination of the acid present following
saponification; the crotonic acid present in the polymer
is also measured.
. ~
~2~ ~3~
d) Pre~aration of the araft polw inyl 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
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.
Table 4
Graft Graft
vinyl poly Aldehyde OH-number
acetal alcohol
L F Pr+4-ClBz 3) 302
M G Bu 290
N H Pr 336
O I i-Bu 268
P K Bu 401
Q I 4-CH3OBz+Bu 1) 214
R Pr+Bu 2) 312
Bu = n-butyraldehyde
i-Bu = isobutyraldehyde
4~CHqOBz = 4-methoxy-benzaldehyde
4-ClBz = 4-Chloro-benzaldehyde
Pr = propionaldehyde
~ 23
1) Molar ratio 1 : 3
2) Molar ratio 1 : 2
3) Molar ratio 3 : 4
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.
Example 1
A coating solution comprised of
1.20 pbw of polymer N,
1.00 pbw of a technical-grade mixture of
pentaerythritol triacrylate and
pentaerythritol tetraacrylate,
0.15 pbw of 2-(p-trichloromethyl-benzoylmethylene)-3-
ethyl-benzothiazoline and
0.03 pbw of a blue azo dye obtained by coupling
2,4-dinitro-6-chlorobenzenediazonium salt with
2-methoxy-5-acetylamino-N-cyanoethyl-N-
hydroxyethyl-aniline, in
50.00 pbw of 2-methoxyethanol
was applied to a 0.3 mm thick aluminum foil which had 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
was performed such that a dry layer weight of 1.1 g/m2
resulted.
The plate was then coated with a 3.5 ~ strength aqueous
solution of polyvinyl alcohol (12 % of residual acetyl
groups, K value 4). After drying, a protective layer having a
weight of 0.8 g/m2 was obtained. The printing plate obtained
was exposed for 40 seconds using a 5 kW metal halide lamp at
24
a distance of 110 cm under a 13-step exposure wedge having
density increments of 0.15 and on which a silver film of
uniform optical density (density 1.57) and uniform absorption
over the effective spectral range had additionally been
mounted as neutral density filter. After exposure, the plate
was developed in a developer of the following composition
with the aid of a plush pad:
5.0 pbw of sodium octyl sulfate,
l.0 pbw of sodium metasilicate x 5 H2O, and
94.0 pbw of distilled water.
The non-exposed layer areas were completely removed within a
few seconds. Step 4 of the wedge step was rendered solid on
the copy. Even the finest elements of the original were
reproduced.
Example 2
A coating solution was prepared from
1.000 pbw of polymer M,
1.500 pbw of trimethylolethane triacrylate,
0.200 pbw of 2,4-bis-trichloromethyl-6-(4-styryl
phenyl)-s-triazine and
0.015 pbw of Crystal Violet (C.I. 42,555), in
50.000 pbw of 2-methoxyethanol
and applied to the layer support of Example 1, in a way such
that a dry layer weight of 1.5 g/m2 was obtained.
A protective cover layer as described in Example 1 and having
a weight of 0.6 g/m2 was applied. Exposure and development
were performed as in Example 1, with the exception that the
exposure time was 18 seconds only.
2 ~
Example 3
A coating solution was prepared as in Example 1, except that
polymer N was replaced by the same amount of polymer P. The
solution was applied to a support material as described in
Example 1, such that a dry layer weight of 1.3 g/m2 was
obtained. The cover layer had a weight of 0.8 g/m2. Exposure
and development were performed as in Example 1. A copy
exhibiting excellent resolution and good ink acceptance was
obtained~
Example 4
A coating solution was prepared from
1.560 pbw of polymer L,
0.910 pbw of a diazonium salt polycondensation product
prepared from 1 mole of 3-methoxy-
diphenylamine-4-diazonium sulfate and l mole
of 4,4'-bis-methoxy-methyl-diphenylether,
isolated as mesitylene sulfonate,
0.049 pbw of phosphoric acid (85 % strength),
0.162 pbw of 2-(4-methoxystyryl)-4,6-bis-trichloro-
methyl-s-triazine,
1.750 pbw of a technical-grade mixture of
pentaerythritol tri- and tetraacrylate and
0.550 pbw of the azo dye described in Example 1, in
70.000 pbw of butanone,
4.000 pbw of ethanol and
2.000 pbw of butyl acetate
and applied to an aluminum foil which had been
electrochemically grained, anodically oxidized and post-
treated with polyvinylphosphonic acid. Application took place
such that a dry layer weight of 2.1 g/m2 resulted.
Q~ ~'
26
The layer was exposed for 25 seconds through a negative
original, with a solid step 4 being obtained on the test
wedge. Development was performed with a developer having the
following composition~
5.0 pbw of sodium octyl sulfate,
1.5 pbw of sodium metasilicate x 5 H2O,
1.5 pbw of trisodium phosphate x 12 H2O, and
92.5 pbw of distilled water.
The printing plate was clamped into a sheet-fed offset press
where it readily accepted printing ink. 280,000 good prints
could be run.
Example 5
A coating solution was prepared from
2.50 pbw of polymer O,
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 1, 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 resulted after drying at 100 C.
The dry resist film prepared in this way was laminated at
120 ~C onto a phenoplast laminate board clad with a 35 ~m
thick copper foil, employing a customary laminating device.
Exposure was performed for 25 seconds using a customary
exposure device. The original used was a line original having
line widths and spacings down to 80 ~m. Following exposure
the polyester film was carefully peeled off, and the layer
2 ~ 6 ~
was developed in a spray developing station with the
following developer, during 90 seconds:
5.0 pbw of sodium octyl sulfate,
1.5 pbw of sodium metasilicate x 5 H2O,
1.5 pbw of disodium hydrogen phosphate x 12 H2O, in
92.0 pbw of distilled water.
After development, the plate was 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:
1. for 30 minutes in a copper bath from
Messrs. Schloetter, Geislingen/Steige,
West ~ermany, 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 did not exhibit any damage or undercutting.
Decoating was performed at a temperature of 50 C,
using 5 % strength KOH solution. The bared copper
was etched away with customary etchants.
28
Example 6
A coating solution comprised of
1.00 pbw of polymer Q,
1.00 pbw of technical-grade mixture of pentaerythritol
tri- and tetraacrylate,
0.10 pbw of 2,4-bis-trichloromethyl-6-(4-ethoxy-naphth-
l-yl)-s-triazine and
0.02 pbw of Victoria Pure Elue FGA
(C.I. Basic Blue 81), in
50.00 pbw of propylene glycol monomethyl ether
was applied onto the aluminum support material described in
Example 4, such that a dry layer weight of 1.3 g/m2 was
obtained. The resulting printing plate was exposed through a
test original and developed with the developer specified in
Example 5.
When being clamped into the sheet-fed offset press, the
printing form immediately accepted greasy printing ink.
Fven after a prolonged press standstill the plate
excellently accepted ink after printing 2 to 8 sheets.
95,00Q good prints could be run, and even the finest lines
were reproduced.
Four of the plates prepared as described above were stored
at 100 C in a drying oven for a period of 1 to 4 hours.
After this heat treatment the plates were imagewise exposed
and developed with the developer solution specified above.
To render visible any layer residues (toning) remaining in
the non-image areas, the dried plates were dyed with a
protective ink.
2 ~
29
The plates stored in the oven for 1 and 2 hours could be
developed satisfactorily. They do not exhibit any substantial
reduction of the continuous tone step wedge. After a storage
time of 3 hours, the continuous tone step wedge was reduced
by one step. Development was insignificantly retarded.
Development of the plate stored for 4 hours was slightly
retarded. These results show that the mixtures according to
this invention have a relatively good resistance to storage
in the heat.
Example 7
A coating solution comprised of
2.280 pbw of polymer R,
2.280 pbw of pentaerythritol triacrylate,
0.010 pbw of phenylazodiphenylamine
0.211 pbw of the triazine of Example 2, and
0.350 pbw of Renol Blue B2G-H (C.I. 74,160) in
70.000 pbw of propylene glycol monomethyl ether
was applied to the support material described in Example 1,
in a way such that a dry layer weight of 2.5 g/m2 was
obtained. The photosensitive layer was exposed through a
standard negative original for 12 seconds, using a 5 kW metal
halide lamp. The photosensitive layer, which displayed good
differention between exposed and non-exposed areas, was
developed with the developer solution of Example 5 with the
aid of a plush pad. The non-exposed layer areas were removed
within 10 seconds after wetting with the developer solution.
The plate was then rinsed with water and dried.
Step 4 of a silver film continuous tone step wedge having an
optical density range of 0.05 to 3.05 and density increments
of 0.15 was reproduced solid on the copy. Even the finest
screen dots and lines of the original were reproduced.
2 ~
A layer of polyvinyl alcohol (12 % residual acetyl groups,
X-value 4) was applied to a printing plate prepared as
described above, such that a dry layer weight of 0.8 g/m2
was obtained. The photospeed of the photocurable layer was
increased by 30 % as a result of applying this oxygen barrier
layer. When the two printing plates were clamped in a sheet-
fed offset press, the plate provided with the protective
cover layer produced much more prints than the plate without
a cover layer, i.e. the print run was increased by 250 %.
Exam~le 8
Following exposure, plates produced as in Example 7 (with and
without an oxygen barrier layer) were subjected to a heat
treatment at 100 C for 1 minute and then developed. Two
additional solid steps were obtained on the test wedge in
each case, compared to the printing plates of Example 7,
which had not been thermally post-treated.
Post-heating increased the print run as well. The increase
was about 200 % for the plate without a cover layer and about
100 % for the plate with the cover layer. A post-exposure
step represents another possibility of increasing the number
of prints in a comparably way.
