Note: Descriptions are shown in the official language in which they were submitted.
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HYDROPHILIC COPOI,YMERS AND THEIR
USE IN REPROGRAPHY
Backqround of the Invention
The invention relates to hydrophilic
copolymers, built up from polymeric chains, which
carry acidic and basic side groups, and to the use
of these copolymers for hydrophilizing lithographic
printing plates and as binders in light-sensitive
lithographic layers.
To produce offset printing plates, suitable
layer supports are provided on one or both sides
with a light~sensitive layer (resist layer), by
means of which a printing Lmage is generated by
photomechanical means. After the printing image has
been produced, the layer support carries the
printing image areas and, in the image-free areas
(non-image areas) forms at the same time the
hydrophilic image background for the lithographic
printing process.
A layer support for light-sensitive layers,
suitable for producing lithographic plates, mu~t
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therefore meet the following requirements. First,
the parts of the liyht-sensitive layer applied to
the layer support, which are relatively readily
soluble after exposure, must be detachable easily
and without residue from the support in a developing
process to produce the non-image areas. The support
bared in the non-image areas must be highly
hydrophilic, i.e. have a high affinity to water, so
that it can rapidly absorb and permanently hold
water during the lithographic printing step and thus
sufficient~y repel the greasy printing ink. The
light-sensitive layer must also have adequate
adhesion to the layer support; even the printing
areas of the layer, which have remained after
exposure and development, must still adhere suffi-
ciently strongly to the support in order to achieve
a long print run.
Foils of aluminum, steel, copper, brass or
zinc and also plastic films or paper can be used as
the starting material for such layer supports.
These raw materials are converted to layer supports
for offset printing plates by a suitable treatment
of their surface, such as graining, matte chromium-
plating, superficial oxidation and/or application of
an interlayer. Aluminum, which is probably the most
widely used base material for offset printing plates
nowadays, is superficially roughened by known
methods such as dry brushing, wet brushing,
sandblasting, chemical and/or electrochemical
treatment or a combination thereof. To increase the
abrasion resistance, the aluminum thus roughened can
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also be subjected to an anodic oxidation in order to
build up a thin oxide layer.
In practice, the support materials,
especially aluminum-based, anodically oxidized
support materials, are frequently subjected to a
further treatment step before a light~sensitive
layer is applied, for improving the layer adhesion,
for increasing the hydrophilic character and/or for
enhancing the developability of the light-sensitive
layers. These include, for example, the following
methods known from DE-C-907,147 (= U.S. Pat. No.
2,714,066), DE-B-1,471,707 (= U.S. Pat. No.
3,181,461 and U.S. Pat. No. 3,280,734) or DE-A-
2,532,769 (= U.S. Pat. No. 3,902,976), which
disclose processes for hydrophilizing printing plate
support materials based on aluminum which may have
been anodically oxidized. These materials are
treated with aqueous sodium silicate solution,
without or with the use of e].ectric current.
DE-A-1,134,093 (= U.S. Pat. No. 3,276,868)
and DE-C-1,621,~78 (= U.S. Pat. No. 4,153,461) have
disclosed the use of polyvinyl-phosphonic acid or
copolymers based on vinyl phosphonic acid, acrylic
acid and vinyl acetate for hydrophilizing printing
plate support materials basedl on aluminum which may
have been anodically oxidizecl. The use of salts of
these compounds is also mentioned, but not specified
in more detail.
The use of complex fluorides of titanium,
zirconium or hafnium according to DE-B-1,300,415 (=
U.S. Pat. No. 3,440,050) also leads to additional
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hydrophilizing of aluminum oxide layers on printing
plate support materials.
In addition to these most widely known
hydrophilizing methods, the use of numerous polymers
5 in this f ield of application has also been
described. For example, in DE-B-1, 056, 931t the use
of water-soluble, linear copolymers based on alkyl
vinyl ethers and maleic anhydrides in light-
sensitive layers for printing plates is described.
10 In addition, those copolymers in which the maleic
anhydride component has been reacted partially or
fully with ammonia, an alkali metal hydroxide or an
alcohol are also mentioned.
DE-B-1, 091, 433 has disclosed hydrophilizing
15 of printing plate support materials based on metals
by means of film-forming organic polymers, such as
polymethacrylic acid or sodium carboxymethyl-
cellulose or sodium hydroxyethyl-cellulose for
aluminum supports or by means of a copolymer of
20 methyl vinyl ether and maleic anhydride for
magnesium supports.
According to DE-B-l,173,917 (= UK 907,719),
water-solu~le polyfunctional synthetic
amino/urea/aldehyde resins or sulfonated synthetic
25 urea/aldehyde resins, which are cured on the metal
support for conversion into a water-insoluble state,
are used for hydrophilizing printing plate support
materials of metals.
To produce a hydrophilic layer on printing
30 plate support materials, a) an aqueous dispersion of
a modified urea/formaldehyde resin, of an alkylated
methylolmelamine resin or of a
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melamine/formaldehyde/polyalkylenepolyamine resin
and b~ an aqueous dispersion of a polyh~droxy
compound or polycarboxy compound, such as sodium
carboxymethylcellulose are applied, according to DE-
B-1,200,847 (= U.S. Pat. No. 3,232,783),
successively to the support and the substrate c)
thus coated is then treated with an aqueous solution
of a salt of Zr, Hf, Ti or Th.
In DE-B-1,257,170 (= U.S. Pat. No. 2,991,204)
a copolymer which, in addition to units of acrylic
acid, acrylate, acrylamide or methacrylamide, also
contains Si-trisubstituted vinylsilane units, is
described as a hydrophilizing agent for printing
plate support materials.
DE-A-1,471,706 (= U.S. Pat. No. 3,298,852)
has disclosed the use of polyacrylic acid as a
hydrophilizing agent for printing plate support
materials of aluminum, copper or zinc.
According to DE-C-2,107,901 (= U.S. Pat. No.
3,733,200), the hydrophilic layer on a printing
plate support material is formed from a water-
insoluble hydrophilic homopolymer or copolymer of
acrylate or methacrylate, having a water absorption
of at least 20~ by weight.
In DE-B-2,305,231 t= UK 1,~14,575)
hydrophilizing of printing plate support materials
is described, in which a solution or dispersion of
a mixture of an aldehyde and a synthetic
polyacrylamide is applied to the support.
DE-A-2,308,196 (= U.S. Pat. No. 3,861,917)
has disclosed hydrophilizing of roughened and
anodically oxidized aluminum printing plate supports
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with ethylene/maleic anhydride copolymers or ~ethyl
vinyl ether/maleic anhydride copolymers, with
polyacrylic acid, carboxymethylcellulose, sodium
poly(vinylbenzene-2,4-disulfonic acid) or
polyacrylamide.
In DE-B-2,364,177 (= U.S. Pat. No.
3,860,426), a hydrophilic adhesion layer for
aluminum offset printing plates is described, which
layer is located between the anodically oxidized
sur~ace of the printing plate support and the light-
sensitive layer and which. in addition to a cel-
lulose ether, also contains a water-soluble salt of
Zn, Ca, Mg, Ba, Sr, Co or Mn. The layer weight of
cellulose ether in the hydrophilic adhesion layer is
0.2 to 1.1 mg/dm2, and the same layer weight is also
quoted for the water-soluble salts. The mixture of
cellulose ether and salt is applied to the support
in aqueous solution, if appropriate with the
addition of an organic solvent and/or of a
surfactant.
According to U.S. Pat. No. 3,672,966,
anodically oxidized aluminum surfaces are, before or
during the sealing with hot water, treated with
aqueous solutions of acrylic acid, polyacrylic acid,
polymethacrylic acid, polymaleic acid or copolymers
of maleic acid with ethylene or vinyl alcohol in
order to avoid seal deposits.
According to U.S. Pat. No. 4,049,746,
hydrophilizing agents for printing plate support
materials contain salt-like reaction products of
water-soluble polyacrylic resins having carboxyl
groups and polyalkyleneimine/urea/aldehyde resins.
In UX 1,246,696, hydrophilic colloids such as
hydroxyethylcellulose, polyacrylamide, polyethylene
oxide, polyvinylpyrrolidone, starch or gum arabic,
are described as hydrophilizing agents for
anodically oxidized aluminum printing plate
supports.
EP-B-0,149,490 describes, for hydrophilizing,
compounds which additionally contain carboxyl groups
or carboxylate groups, sulfo groups or hydroxyl
groups, apart from amino groups. These compounds
have a molecular weight of at most 1000.
The state of the art has also disclosed the
use of metal complexes, which contain low-molecular
ligands, for hydrophilizing printing plate support
materials. Examples of such complexes are: complex
ions of divalent or polyvalent metal cations and
ligands, such as ammonia, water, ethylenediamine,
nitric oxide, urea or ethylenediamine tetraacetate
(DE-A-2,807,396 = U.S. Pat. No. 4,208,212); iron
cyanide complexes such as K,~(Fe(CN)6) or Na3(Fe(CN)6)
in the presence of heteropolyacids, such as
phosphomolybdic acid or salts thereof, and of
phosphates (U.S. Pat. No. 3,76'3,043 and/or U.S. Pat.
No. 4,420,549); and iron cyanide complexes in the
presence of phosphates and complex formers such as
ethylenediamine tetraac:etic acid for
electrophotographic printing plates having a zinc
oxide surface (U.S. Pat. No. 3,672,885).
In EP-A-0,069,320 (= U.S. Pat. No.
4,427,765), a process is describ~d in which salts of
polyvinylphosphonic acids, polyvinylsulfonic acids,
,,
polyvinylmethylphosphonic acids and other polyvinyl
compounds are used as aftertreatment agents.
In DE-A-2,615,075 (= UK 1,~95,895), a process
for treating image-bearing offset printing plates
with polyacrylamide or a mixture of polyacrylamide
and polyacrylic acid is used.
In SU-A-547,142, a copolymer of acrylamide
and vinyl monomers is used for hydrophilizing offset
printing plates.
10DE-C-1,091,433 describes a process for the
aftertreatment of offset printing plate supports
with polymers of methacrylic acid, methyl vinyl
ether and maleic anhydride.
Acrylamide for the treatment of printing
15plate supports is also mentioned in DE-A-2,540,561.
For the same purpose, especially for
improving the storage stability of printing plates,
DE-A-2,947,708 describes, inter alia, Ni salt
solutions of acrylamide and acrylic acid and also0 acrylamide and vinylpyrrolidone.
All the methods de~;cribed above, are,
however, affected by greater or lesser
disadvantages, so that the sllpport materials thus
produced frequently no longer meet the current
demands of offset printing with respect to developer
resistance, hydrophilic properties, free-running
behavior and steady print runs. Thus, after the
treatment with alkali metal silicates, which lead to
good developability and hydrophilic character, a
certain deterioration in the storage stability of
light-sensitive layers applied thereto must be
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accepted, and the print run of a printing plate thus
aftertreated drops drastical:ly.
Although the complexes of the transition
metals in principle promote the hydrophilic
character of anodically oxidized aluminum surfaces,
they have the disadvantage of being very readily
soluble in water, so that they can easily be removed
during the development of the layer with aqueous
developer systems which recently increasingly
contain surfactants and/or chelate formers which
have a high affinity to these metals. As a result,
the concentration of the transition metal complexes
on the surface is reduced to a greater or lesser
extent, and this can lead to a weakening of the
hydrophilic effect.
In the treatment of supports with water-
soluble polymers without scope for anchorage, their
high solubility, especially in aqueous-alkaline
developers such as are predominantly used for
developing positive-wor~ing, light-sensitive layers,
also leads to a marked weakening of the hydrophiliz-
ing effect.
Monomeric h~drophilic c:ompounds such as those
described, for example, in EP-B-0,149,490, quite
generally have the disadvantas~e of being washed away
relatively rapidly .from the bared non-image area
surface during the development and printing process
and losing their hydrophilic- effect, since the
anchorage points in the surface are insufficient.
The combination of a mixture of a water-
soluble polymer, such as a cellulose ether, and a
water-soluble metal salt leads, since the layer
weights and hence the layer thic~ness are selected
at a relatively high level (see DE-B-2,364,177), to
reduced adhesion of the resist- layer, and this can
manifest itself, for example, in parts of the
developer fluid undermining image areas during the
development.
Summary of the Invention
Accordingly, it is an object of the present
invention to provide a high-polymeric hydrophilizin~
agent for support materials for offset printing
plates which does not adversely affect the storage
stability of the light-sensitive layers of the
offset printing plates.
Another object of the present invention is to
provide an agent which, in addition to good adhesion
to the surface of the aluminum support on the one
hand and to the light-sensitive layer on the other
hand, effects a durable hydrophilic character of the
non-image areas of the finished developed offset
printing plates.
A further object of the present invention is
to provide an agent which is difficult to wash out
of the support material treated with it.
Still another object of the present invention
is to provide a binder ill a light-sensitive
photopolymer system which can be stripped in an
aqueous medium.
Yet another object of the present invention
is to provide a process for producing the agent and
binder.
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In accomplishing the foregoing objectives,
there has been provided, in accordance with one
aspect of the present invention, a hydrophilic
copolymer having the general structure:
... -(A)~-.. -(B) D- - (C) o~ - (D)p-
in which
A is at least one polymerizablQ
monomer having an acidic side
group,
B is at least one polymerizable
monomer having a basic side group,
C is at least one polymerizable
monomer having a non-polar, non-
hydrophilic side group, and
D is at least one polymerizable
monomer capable of increasing the
hydrophilic character of monomer A
or to form a chelate with monomer
A,
m, n, o
and p are the monomer contents of
monomers A, B, C and D,
respectively, in mol%, with m + n
+ o + p = 100 mol%, with the
proviso that m and n are each > 2
mol% and p is > 1 mol%,
wherein the copolymer is a linear copolymer
having a random structure o~ the above-desrribed
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monomers. Preferably, the polymerizable monomers
are free-radically polymerizable.
In accordance with another aspect of the
present invention there is provided a process for
producing the above-described hydrophilic copolymer
which comprises the step of free-radically
polymerizing monomers A, B, C and D in the presence
of a free-radical initiator.
Lithographic and offset printing plates
comprising the inventive copolymer as a
hydrophilizing agent, light-sensitive mixtures
comprising the inventive copolymer as a binder, and
light-sensitive recording materials comprising
light-sensitive layers which include the inventive
copolymer as a binder are also provided.
Other objects, features and advantages of the
present invention will become apparent to those
skilled in the art from the following detailed
description. It is to be understood, however, that
the detailed description and speciEic examples,
while indicating preferred embodiments of the
present invention, are given by way of illustration
and not limitation. Many changes and modifications
within the scope of the present invention may be
made without departing from the spirit thereof, and
the invention includes all such modifications.
Detailed DescriPtion of the Preferred Embodiments
The copolymers of the type described above
are not only highly effective hydrophilizing agents
which, in addition, can be prepared in a simple
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manner, but they can also be used with advantage as
binders in light-sensitive layers. The degree of
the solubility of the light-sensitive layer can be
varied as desired and very advantageously adjusted
by varying the type and quantity of the basic
monomers.
The concentration of the hydrophilic groups
can be selected such that the polymers according to
the invention are suitable as binders for light-
sensitive layers, with aqueous or aqueous/alcoholicstripping. At an even higher concentration of the
hydrophilic groups, they can also be used as
hydrophilizing agents. The hydrophilic polvmers are
distinguished by having, along a polymeric chain,
acidic and basic side groups which are ionizable and
capable of forming salts.
The hydrophilic copolymers which, inter alia,
are used as hydrophilizing agents, are linear
polymers with acidic and basic side groups and have
the following structure:
...~(A)m~...-(B)~-...~(C)O-...-(D)p-..
with m + n + o ~ p = 100 mol~.
The values of m and n are in the range from
about 2 to 97 mol% and fol].ow mutually opposed
curves, i.e. a high value of m corresponds to a low
value of n, and vice versa. Preferably, however, m
and n are approximately equal, i.e., A and B are
present in an approximately e~uimolar ratio. The
resulting range for the value o is about 0 to 95
mol%, and that ~or p is a~out 1 to 96 mol~. In
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particular, the values o and p are ~ithin the ranges
of about 10 to 50 mol% and about l to 20 mol%
respectively.
The polymeric hydrophilizing agents have a
random structure and average molecular weights of at
least 1,000, preferably about S,000 to 50,000, but
polymers having a molecular weight even higher than
50,000 can also be used with technical advantage.
The monomer types A, B, C and D are
exemplified below:
Monomer type A: Acrylic acid, methacrylic acid,
maleic acid, fumaric acid, itaconic acid, and
monoesters of aliphatic and cycloaliphatic alcohols
having 1 to 17 carbon atoms with maleic acid,
fumaric acid, and itaconic acid, vinylsulfonic acid,
vinylbenzoic acid, vinylphosphonic acid and other
polymerizable monomers containing acidic groups.
Monomer type B: Dimethylaminoethyl acrylate and
methacrylate, diethylaminoethyl acrylate and
methacrylate, dimethylaminopropyl acrylate and
methacrylate, dimethylaminobutyl acrylate and
methacrylate, and other monomers suitable for
polymerization and containing amino groups.
Vinylpyridine, styrenes containing dialkylamino
groups and many others are also suitable.
Monomer type C: Acrylates, methacrylates, maleates,
fumarates, and itaconates of aliphatic and
cycloaliphatic alcohols having 1 to 17 carbon atoms,
styrene and substituted styrenes, vinyl chloride and
other non-polar, non-hydrophilic monomer units. The
use of the monomer type C and the concentration
thereof allow a defined adjustment of the solubility
of the copolymers.
Monomer tY~e D: Monomer units which are able to
boost the hydrophilic character of monomer type A
and/or to form chelates with monomer type A, for
example hydroxylated acrylates of the type of
hydroxyethyl acrylate or polyethylene glycol
monoacrylate or polypropylene glycol monoacrylate,
or the corresponding monomethacrylates.
More than one of each of monomer types A, B,
C and/or D can be used in producing the hydrophilic
agents according to the invention.
lS The synthesis of the hydrophilizing agents is
advantageously carried out by a polymerization,
initiated by free radicals, in organic solvents.
The free-radical initiators used can be the
conventional compounds, such as peroxides, for
example benzoyl peroxide, or azo compounds such as
azobisisobutyronitri.le (AIB~). In addition,
regulators for adjusting the molecular weight can be
used. The polymerization in non-polar solvents,
carried out as a precipitation polymerization, has
the advantage that low-molecular, oligomeric and
chemically inhomogeneous ~ractions, for example
products which contain only a few ionizable groups,
remain in solution and can thus easily be separated
from the precipitated polymers. This type of
polymerization also has the advantage that it is
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simple and economical. The precipitation
polymerization in organic solvents such as, for
example, in petroleum spirit fractions in the suit-
able boiling point range from 100 to 140C can be
carried out very easily and with good yield of
copolymers in which the ionizable monomer units of
types A and B are present in the preferably used
concentrations of m = n = lO to 50 mol~. At
concentrations in the range of m and n = 2 to 10
mol%, the polymers are isolated by distilling off
the organic solvent.
The examples which follow explain the
fundamental polymerization method for some preferred
copolymers, but the invention is not restricted to
the examples given.
The support materials used are preferably
aluminum supports such as are described in German
Application P 40 23 267.0 (corresponding to docket
No. 1687~/403), filed simultaneously. The manner in
which these aluminum supports are coated or surface-
treated with the hydrophilizing agents according to
the invention is also descri~ed in detail in this
application. The hydrophilizing a~ents are anchored
in the way of an "absorption", a "complex formation"
or a "salt formation" on the specially pretreated
aluminum surface in such a way that a permanent
hydrophilic character is obtained.
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Example 1
A copolymer of methacrylic acid,
dimethylaminoethyl methacrylate, ethyl acrylate and
a hydroxyethyl methacrylate chain-extended with 4.5
5 mol of ethylene oxide per mole is prepared. For
this purpose
524 g of dimethylaminoethyl methacrylate
300 g of ethyl acrylate
287 g of methacrylic acid and
1034 g of hydroxyethyl methacrylate which
was reacted for chain extension
with 4.5 mol of ethylene oxide per
mole, were dissolved in
1145 g of methyl ethyl ketone (MEK).
114S g of methyl ethyl ketone, 20% by weight of the
solution of monomers described above and 1% by
weight of azobisisobutyronitri.le (AIBN), relative to
the total weight of the monomers, are introduced
under a nitrogen blanket gas atmosphere into a
three-necked flask provided ~ith a stirrer, reflux
condenser, dropping funnel with pressure balance
line and a gas inlet tube, and polymerized for 1
hour. Using a dropping funnel, the remaining
monomer mixture is then added within 1 hour and the
whole is polymerized for a further 2 hours under
reflux. A further 0.5% by weight of azobisisobuty-
ronitrile is then added and the polymerization is
continued for 2 hours under reflux. The product is
worked up by filtering off the precipitate formed
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with suction and washing the precipitate with three
tlmes 500 ml of methyl ethyl ketone.
The product is dried at 70C.
Yield: 78%
The copolymer has outstanding hydrophilizing
properties for aluminum supports. It forms a clear
solution in an aqueous 2 N Na2CO3 solution.
Completely analogously to the polymerization
method described in Example 1, the copolymers listed
in the following table (Examples 2 and 3) can be
prepared.
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Example 2 Example 3
Monomer A Methacrylic acid Vinylphosphonic
30 mol% acid 20 mol%
Monomer B DMAEMA1) DMAEMA
30 mol% 20 mol%
Monomer C Ethyl acrylate Ethyl acrylate
30 mol% 50 mol%
Monomer D Esterification Esterification : .
product of PEG product of PEG .
(350)2) (350)2)
monomethyl ether monomethyl
with methacrylic ether with
acid 10 mol% methacrylic
l _ acid 10 mol%
S Solvent MEK MEK
67 parts by 67 parts by
weight weight
AIBN 1.5% by weight, 1.5% by weight,
relative to relative to
monomer monomer
I
¦Yield 92% by weight 90% by weight
1) DMAEM = dimethylaminoethyl methacrylate
2) PEG (350) = polyethylene glycol of molecular
weight 350
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