U.S. patent application number 11/854596 was filed with the patent office on 2008-03-20 for processless lithographic printing plate precursor.
Invention is credited to Brian J. Collister, Graham Darling, Jonathan W. Goodin, Jacqueline L. Ricafrente, Susan A. Wilkinson, Yisong Yu.
Application Number | 20080070163 11/854596 |
Document ID | / |
Family ID | 33134890 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080070163 |
Kind Code |
A1 |
Yu; Yisong ; et al. |
March 20, 2008 |
PROCESSLESS LITHOGRAPHIC PRINTING PLATE PRECURSOR
Abstract
A radiation-sensitive medium comprises hydrophilic polymer
particles, the particles comprising a thermally softenable
hydrophobic polymer, a hydrophilic polymer and a bonding compound
capable of chemically bonding to the hydrophobic polymer and to the
hydrophilic polymer. The radiation-sensitive medium further may
comprise a substance capable of converting radiation into heat. The
radiation-sensitive medium is aqueous-ineluable when coated and
dried, and becomes hydrophobic under the action of heat. The
polymer particles are made by polymerization of at least one
hydrophobic monomer and at least one bonding compound in the
presence of the hydrophilic polymer. The radiation-sensitive medium
may be provided as a coatable composition to be applied to
substrates to form a processless radiation-imageable lithographic
printing precursor, which may further be provided with an aqueous
eluable hydrophilic overcoat. The processless radiation-imageable
lithographic printing precursor so created may be imaged using
absorbed radiation that is imagewise converted to heat, resulting
in areas of hydrophobic property, while unimaged areas retain their
hydrophilic property. This allows the latent image so formed to be
employed in creating a negative-working lithographic printing
master. The negative-working lithographic printing master so
created is irreversible, does not require a substrate of controlled
hydrophilicity and provides great toughness in the exposed areas.
The radiation-sensitive medium may be coated on-platesetter or
on-press onto a suitable substrate, including the drum of the
press. It may also be coated off-press on a suitable substrate to
create a precoated processless radiation-imageable lithographic
printing precursor.
Inventors: |
Yu; Yisong; (Vancouver,
CA) ; Collister; Brian J.; (Burnaby, CA) ;
Goodin; Jonathan W.; (Wake Forest, NC) ; Darling;
Graham; (Burnaby, CA) ; Ricafrente; Jacqueline
L.; (Surrey, CA) ; Wilkinson; Susan A.;
(Vancouver, CA) |
Correspondence
Address: |
Andrew J. Anderson;Patent Legal Staff
Eastman Kodak Company
343 State Street
Rochester
NY
14650-2201
US
|
Family ID: |
33134890 |
Appl. No.: |
11/854596 |
Filed: |
September 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11181039 |
Jul 13, 2005 |
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11854596 |
Sep 13, 2007 |
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10647913 |
Aug 25, 2003 |
7323288 |
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11181039 |
Jul 13, 2005 |
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60436182 |
Apr 14, 2003 |
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Current U.S.
Class: |
430/302 |
Current CPC
Class: |
B41C 2210/22 20130101;
B41C 2210/08 20130101; B41C 1/1016 20130101; B41M 5/366 20130101;
Y10S 430/145 20130101; B41C 1/1008 20130101; B41C 2210/04 20130101;
B41C 1/1041 20130101; B41C 2210/24 20130101 |
Class at
Publication: |
430/302 |
International
Class: |
G03F 7/12 20060101
G03F007/12 |
Claims
1. A method for making a negative-working lithographic printing
master, the method consisting essentially of, in the order stated:
imagewise thermally irradiating a processless radiation-imageable
lithographic printing precursor comprising a substrate, a dried and
aqueous-ineluable coating of a radiation-sensitive medium on the
substrate and, optionally, an aqueous eluable hydrophilic overcoat
over the coating of a radiation-sensitive medium, the
radiation-sensitive medium comprising: a. a substance capable of
converting radiation into heat, b. hydrophilic polymer comprising
an amine group, and c. at least one thermally softenable or
heat-fusible copolymer of a hydrophobic monomer and a monomer that
has a carboxylic acid group, wherein the dried and
aqueous-ineluable coating becomes hydrophobic under the action of
heat, and treating the precursor with an aqueous medium to remove
only said aqueous eluable hydrophilic overcoat, when present.
2. The method of claim 1 wherein the aqueous eluable hydrophilic
overcoat comprises a water-soluble organic polymer.
3. The method of claim 2 wherein the water-soluble organic polymer
is at least one of poly(vinyl alcohol), poly(vinyl acetate),
poly(acrylic acid), poly(meth)acrylic acid, an alkali metal salt of
poly(meth)acrylic acid, an amine salt of poly(meth)acrylic acid,
poly 2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, polyvinyl
methyl ether, polyvinyl methyl ether/maleic anhydride copolymer,
poly(vinyl pyrrolidone), poly-2-acrylamide-2-methylpropane sulfonic
acid, an alkali metal salt of poly-2-acrylamide-2-methylpropane
sulfonic acid, an amine salt of poly-2-acrylamide-2-methylpropane
sulfonic acid, alginic acid, a salt of alginic acid, protan jelly,
carageenin, tragacanth, laminarin sulfate, starch, animal glues,
vegetable mucilages, gum arabic, cellulose, a modification product
of cellulose and a polysaccharide.
4. The method of claim 1, wherein the substance capable of
converting radiation into heat is hydrophobic.
5. The method of claim 1 wherein the irradiating is carried out
using infrared radiation.
6. The method of claim 1 wherein the at least one hydrophilic
polymer is at least one of a saccharide, a chitosan polymer, a
polyethyleneimine polymer, a polyamine polymer, a polyvinylamine
polymer, a polyallylamine polymer, a polydiallylamine polymer, an
amino(meth)acrylate polymer, a polyamide polymer, a
polyamide-epichlorohydrin polymer, a polyamine-epichlorohydrin
polymer, a polyamidepolyamine-epichlorohydrin polymer, a
dicyandiamide-polycondensation product polymer and a copolymer
thereof.
7. The method of claim 6 wherein the at least one hydrophilic
polymer is a chitosan polymer.
8. The method of claim 1 wherein said optional hydrophilic overcoat
further comprises a water-soluble dye, colorant, or surfactant.
9. The method of claim 1 that is carried out without any wash-off
development.
10. The method of claim 1 wherein said aqueous medium is water or a
fountain solution.
11. The method of claim 1 wherein said coated and dried
aqueous-ineluable coating is not removable in said aqueous medium
either before or after said imagewise irradiating.
12. The method of claim 1 wherein said hydrophilic polymer and said
copolymer are bonded in thermally softenable or heat-fusible
particles.
13. The method of claim 12 wherein said thermally softenable or
heat-fusible particles comprise a core predominantly of said
copolymer predominantly and a shell of said hydrophilic
polymer.
14. A method for making a negative-working lithographic printing
master, the method comprising the steps of: providing a precursor
comprising a dried and aqueous-ineluable coating of a
radiation-sensitive medium on a substrate and, optionally, an
aqueous eluable hydrophilic overcoat over the coating of a
radiation-sensitive medium, the radiation-sensitive medium
comprising particles of chitosan and at least one thermally
softenable or heat-fusible hydrophobic polymer, the coating being
hydrophilic and capable of becoming hydrophobic under the action of
heat, imagewise irradiating the precursor with infrared imaging
radiation of wavelength between 700 nm and 1200 nm, and treating
the precursor with an aqueous medium to remove said optional
hydrophilic overcoat.
15. The method of claim 14 wherein the aqueous eluable hydrophilic
overcoat comprises a water-soluble organic polymer.
16. The method of claim 15 wherein the water-soluble organic
polymer is at least one of poly(vinyl alcohol), poly(vinyl
acetate), poly(acrylic acid), poly(meth)acrylic acid, an alkali
metal salt of poly(meth)acrylic acid, an amine salt of
poly(meth)acrylic acid, poly 2-hydroxyethyl(meth)acrylate,
poly(meth)acrylamide, polyvinyl methyl ether, polyvinyl methyl
ether/maleic anhydride copolymer, poly(vinyl pyrrolidone),
poly-2-acrylamide-2-methylpropane sulfonic acid, an alkali metal
salt of poly-2-acrylamide-2-methylpropane sulfonic acid, an amine
salt of poly-2-acrylamide-2-methylpropane sulfonic acid, alginic
acid, a salt of alginic acid, protan jelly, carageenin, tragacanth,
laminarin sulfate, starch, animal glues, vegetable mucilages, gum
arabic, cellulose, a modification product of cellulose and a
polysaccharide.
17. The method of claim 14 wherein the overcoat further comprises
at least one of a light-to-heat converting agent, a water-soluble
dye, a colorant and a surfactant.
18. The method of claim 14 that is carried out without any wash-off
development.
19. The method of claim 14 wherein said particles comprise a core
predominantly of said hydrophobic polymer and a shell of
chitosan.
20. The method of claim 14 wherein said hydrophobic polymer is
derived from at least an acrylic acid, methacrylic acid, sulfonated
styrene, or phosphonated styrene, and optionally from one or more
of substituted or unsubstituted styrene, esters of (meth)acrylic
acid, vinyl halide, (meth)acrylonitrile, vinyl ester,
silicon-containing polymerizable monomer, and polyether.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. Ser. No.
11/181,039 filed Jul. 13, 2005, that is a Continuation-in-part of
U.S. Ser. No. 10/647,913, filed Aug. 25, 2003 that is based on U.S.
provisional application 60/436,182 filed on Apr. 14, 2003.
FIELD OF THE INVENTION
[0002] This invention relates to image formation in printing plates
and printing plate precursors and to the formation of images
directly from electronically composed digital sources without
wash-off development.
BACKGROUND OF THE INVENTION
[0003] For many years, it has been a goal of the printing industry
to form printing images directly from an electronically composed
digital database, for example, by a so-called "computer-to-plate"
system. The advantages of such a system over the traditional
methods of making printing plates are the elimination of the costly
intermediate silver-containing film and processing chemicals; a
saving of time; and the ability to automate the system with
consequent reduction in labor costs.
[0004] The introduction of laser technology provided the first
opportunity to form an image directly on a printing plate precursor
by directing a laser beam at sequential areas of the printing plate
precursor and modulating the beam so as to vary its intensity. In
this way, radiation sensitive plates comprising a high sensitivity
photocrosslinkable polymer coating have been exposed to imagewise
distributions of radiation from various laser sources and
electrophotographic printing plate precursors having sensitivity
ranging from the visible spectral region into the near infra-red
region (including thermal sensitivity) have been successfully
exposed using low powered air-cooled argon-ion lasers and
semiconductor laser devices.
[0005] While lithographic printing precursors that are
post-exposure developable using aqueous media, preferably alkaline
aqueous media, are well known and widely used in the printing
industry, there is a more specific subset of precursors that may be
developed on press by the action of the fountain solution employed
during wet offset printing. A newer class of lithographic media is
based upon the general concept of employing polymeric particles in
an otherwise hydrophilic binder, often along with a substance to
convert light into heat. This kind of media is exemplified by U.S.
Pat. No. 6,001,536. The unilluminated areas of a lithographic
precursor based on this generic media may be removed by treatment
with fountain solution on a printing press. This kind of precursor
is therefore pseudo-processless, in that no specific separate
development step with a specific developer, as such, is required to
obtain a master. The illuminated areas are rendered hydrophobic and
hence the master is in effect negative-working. These precursors
allow lithographic printing masters to be made relatively easily
on-press, but suffer from poor run length. The quality of the
printed image rendered is directly dependent on the choice and
quality of hydrophilic substrate used, as this substrate is exposed
and has to carry the fountain solution during the wet offset
printing process.
[0006] A more specific category of lithographic precursors employs
mechanisms and compositions that cause the sensitive layer on the
substrate to switch between hydrophilic and hydrophobic, without
any material being required to be removed with a development step.
That is, there is no removal of material at all, even by fountain
solution. These are true processless precursors.
[0007] By way of example, U.S. Pat. No. 6,410,202 describes a
composition for thermal imaging comprising a hydrophilic
heat-sensitive polymer having recurring ionic groups within the
polymer backbone or chemically attached thereto. The imaging
members of this particular invention do not require post-imaging
wet processing and are generally negative-working in nature. In
some cases, the polymers are crosslinked upon exposure and provide
increased durability to the imaging members. In other and preferred
cases, the polymers are crosslinked upon application to a support
and curing. A further example of this class of precursor is
provided by U.S. Pat. No. 5,985,514. That patent describes an
imaging member that is composed of a hydrophilic imaging layer
having a hydrophilic heat-sensitive polymer containing
heat-activatable thiosulfate groups, and optionally a photothermal
conversion material. Upon application of energy that generates
heat, such as from IR irradiation, the polymer is crosslinked and
rendered more hydrophobic. The exposed imaging member can be
contacted with a lithographic printing ink and a fountain solution
and used for printing with or without post-imaging wet processing.
U.S. Pat. No. 4,081,572 describes making hydrophilic printing
masters comprising coating a self-supporting master substrate with
a specific hydrophilic polymer containing carboxylic acid
functionality and selectively converting this polymer in image
configuration to a hydrophobic condition by heat. The polymer is
selectively converted to a hydrophobic condition in image
configuration through heat-induced cyclodehydration reactions. In
other examples the precursor is inherently positive-working, as in
the case of U.S. Pat. No. 4,634,659. That particular patent
describes a method of making a processing-free planographic
printing plate comprising irradiating a plate surface comprised of
a hydrophobic organic compound capable of being converted, upon
exposure to radiation, from hydrophobic to hydrophilic, carrying
out the exposure in an image pattern, thereby selectively
converting said surface, in the image pattern, from hydrophobic to
hydrophilic, thereby making the precursor positive-working.
[0008] A yet more specific category of true processless
lithographic precursors, is based on media comprising polymer-based
particles or microcapsules:
[0009] In U.S. Pat. No. 6,550,237 a heat-sensitive material is
described for making a negative working non-ablative lithographic
printing plate including in a heat sensitive layer thermoplastic
polymer beads and a compound capable of converting light into heat
on a surface of a hydrophilic metal support. The layer is free of
binder, and is characterized in that the thermoplastic polymer
beads have a diameter between 0.2 .mu.m and 1.4 .mu.m. Argument is
provided for the requirement that the thermoplastic particles
should have a specific size range. It is explained that, when the
polymer particles are subjected to a temperature above the
coagulation temperature they coagulate to form a hydrophobic
agglomerate so that at these parts the metallic support becomes
hydrophobic and oleophilic. Preferably, the polymer particles are
selected from the group consisting of polyvinyl chloride,
polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole
etc., copolymers or mixtures thereof. Most preferably used are
polystyrene, polyacrylate or copolymers thereof and polyesters or
phenolic resins. No indication is given that the polymer particles
should be hydrophilic, or that there may be more than one polymer
in the particles.
[0010] In U.S. Pat. No. 6,653,042, a lithographic printing plate
precursor requiring no development step is described. It comprises
a support, having provided thereon a layer comprising a hydrophilic
medium, wherein the layer comprising a hydrophilic medium contains
a hydrophobitization precursor having a hydrophilic surface and a
light/heat converting agent which is hydrophilic in itself, or at
least on the surface. Various implementations of the invention are
presented in which the hydrophobitization precursor having a
hydrophilic surface is a particle dispersion of composite
constitution containing a hydrophobic substance at the core part
and having a surface layer of specifically superficial
hydrophilicity. All forms of particles disclosed are composed of
either one or two distinct materials. Various materials may be at
the core, including hydrophobic polymeric materials and
crosslinking materials. A light-to-heat converting material, which
is specifically chosen to be hydrophilic, is also added. The
lithographic printing plate precursor as described above, further
comprises a water-soluble protective layer.
[0011] U.S. Pat. Nos. 5,569,573 and U.S. Pat. No. 6,171,748
describe a thermosensitive lithographic printing original plate
comprising a substrate, a hydrophilic layer containing a
hydrophilic binder polymer, and a microcapsuled oleophilic material
which forms an image area by heating; the hydrophilic binder
polymer having a three-dimensional cross-link and a functional
group which chemically combines with the oleophilic material in the
microcapsule when the microcapsule is ruptured, and the
microcapsuled oleophilic material having a functional group which
chemically combines with the hydrophilic binder polymer when the
microcapsule is ruptured. Among the many hydrophilic binder
polymers listed are polysaccharides. The lithographic printing
plate has a hydrophilic polymer thin film layer on the surface of
the hydrophilic layer. This hydrophilic thin film layer inhibits
the surface from accepting tinting materials.
[0012] U.S. Pat. Nos. 5,677,108, U.S. Pat. No. 5,677,110 and U.S.
Pat. No. 5,997,993 disclose an on-press developable lithographic
printing plate precursor comprising a lithographic hydrophilic
printing plate substrate, a photohardenable photoresist, and a
layer of polymeric protective overcoat. The overcoat functions as
an oxygen barrier, as well as imparting the plate with a non-tacky
surface and an enhanced resistance to the adverse influence of
ambient humidity. The overcoat contains a polyphosphate salt and
may further contain a fountain soluble or dispersible crystalline
compound to facilitate on-press removability. U.S. Pat. No.
6,387,595 discloses an on-press developable lithographic plate
comprising on a substrate a photosensitive layer and a top
ultra-thin ink and/or fountain solution soluble or dispersible
overcoat with coverage of 0.001 to 0.150 g/m.sup.2.
[0013] Heat-sensitive lithographic printing plates not requiring a
wet development step after exposure have been desired by the
industry for a long time. One approach to no-process lithographic
printing plates relies on ablation to physically remove the imaging
layer from the printing plate precursor. Unfortunately, ablative
printing plates can only be exposed on imaging devices that are
fitted with a vacuum device to collect the by-products of the
ablative imaging step (particulate and gaseous debris). Recently
the use of a laser transparent, water-soluble top coating over an
ablatable imaging layer such that when ablatively removed with a
laser, the ablative debris is contained by the top coating, has
been proposed. See for example WO99/41077, U.S. Pat. No. 6,397,749,
U.S. Pat. No. 6,468,717 and U.S. Pat. No. 6,468,717.
[0014] A water-soluble overcoat may also be provided to protect the
hydrophilic layer during storage and handling and to improve
lithographic latitude. See for example U.S. Pat. No. 5,997,993,
U.S. Pat. No. 6,171,748, U.S. Pat. No. 6,468,717, U.S. Pat. NO.
6,503,684 and U.S. Pat. No. 6,513,433.
[0015] There remains a requirement for negative-working, true
processless, lithographic precursors having long run-length,
suitable sensitivity to laser-diode-based imaging radiation, and
which are easy to prepare, preferably from aqueous media, and show
consistent high quality press performance and good handling
characteristics.
SUMMARY OF THE INVENTION
[0016] A radiation-sensitive medium comprises hydrophilic polymer
particles, the particles comprising a thermally softenable
hydrophobic polymer, a hydrophilic polymer and a bonding compound
capable of chemically bonding to the hydrophobic polymer and to the
hydrophilic polymer.
[0017] The radiation-sensitive medium further may comprise a
substance capable of converting radiation into heat. The
radiation-sensitive medium is aqueous-ineluable when coated and
dried, and becomes hydrophobic under the action of heat. The
polymer particles are made by polymerization of at least one
hydrophobic monomer and at least one bonding compound in the
presence of the hydrophilic polymer. The radiation-sensitive medium
may be provided as a coatable composition to be applied to
substrates to form a processless radiation-imageable lithographic
printing precursor, which may further be provided with an aqueous
eluable hydrophilic overcoat. The processless radiation-imageable
lithographic printing precursor so created may be imaged using
absorbed radiation that is imagewise converted to heat, resulting
in areas of hydrophobic property, while unimaged areas retain their
hydrophilic property. This allows the latent image so formed to be
employed in creating a negative-working lithographic printing
master. The negative-working lithographic printing master so
created is irreversible, does not require a substrate of controlled
hydrophilicity and provides great toughness in the exposed areas.
The radiation-sensitive medium may be coated on-platesetter or
on-press onto a suitable substrate, including the drum of the
press. The radiation-sensitive medium of the present invention may
be coated off-press on a suitable substrate to create a precoated
processless radiation-imageable lithographic printing
precursor.
DETAILED DESCRIPTION OF THE INVENTION
[0018] In a first aspect of the invention there is provided a
radiation-sensitive medium comprising hydrophilic polymer
particles, the particles comprising a thermally softenable
hydrophobic polymer, a hydrophilic polymer and a bonding compound
capable of chemically bonding to the hydrophobic polymer and to the
hydrophilic polymer. The radiation-sensitive medium further may
comprise a substance capable of converting radiation into heat. The
radiation-sensitive medium is aqueous-ineluable when coated and
dried, and becomes hydrophobic under the action of heat.
[0019] In a further aspect of the invention there is provided a
method for making the radiation-sensitive medium of the invention
by polymerization of at least one hydrophobic monomer and at least
one bonding compound in the presence of the hydrophilic
polymer.
[0020] In a further aspect of the invention, there is provided a
precoated processless radiation-imageable lithographic printing
precursor, comprising a first layer of the radiation-sensitive
medium of the present invention, precoated onto a substrate and
dried, and an aqueous eluable hydrophilic overcoat, comprising at
least one hydrophilic polymer, precoated and dried onto the first
layer.
[0021] In a further aspect of the invention there is provided a
method for making a precoated processless radiation-imageable
lithographic printing precursor, comprising the coating of the
radiation-sensitive medium of the invention onto a substrate and
drying the coated radiation-sensitive medium, followed by the
coating and drying of a aqueous eluable hydrophilic overcoat,
comprising at least one hydrophilic polymer.
[0022] In yet a further aspect of the invention there is provided a
method for making a negative working lithographic printing master
using the precoated processless radiation-imageable lithographic
printing precursor. The precoated processless radiation-imageable
lithographic printing precursor may be imaged using absorbed
radiation that is imagewise converted to heat, transforming
hydrophilic areas to hydrophobic areas, resulting in areas of
hydrophilic and areas of hydrophobic property. This allows the
latent image so formed to be employed in making a negative-working
lithographic printing master. The imaging process is irreversible
when performed. That is, the coated and dried radiation-sensitive
medium remains hydrophobic after imagewise exposure to imaging
radiation. The method may be performed on a plate-setting machine
or fully on-press.
[0023] Definitions:
[0024] The term "negative-working lithographic printing master" is
used herein to describe a lithographic printing master on which,
during the process of transferring printing ink from the master to
a printing medium for receiving printing ink, the printing ink
adheres to those areas that were irradiated or written to in any
way whatsoever by an imaging head and, conversely, on which
printing ink does not adhere to those areas that were not
irradiated or written to in any way by that imaging head. Whether
the master is referred to as negative-working or positive-working
is therefore not determined by the means of creating ink-bearing
and non-ink-bearing areas on the master, but rather by whether the
positive image to be created on the printing medium for receiving
the printing ink, or the negative of it, respectively, is
transferred to the master from the imaging head. In brief, on a
"negative-working lithographic printing master", those areas that
are written by the imaging head will carry printing ink.
[0025] The phrase "processless radiation-imageable lithographic
printing precursor" is used herein to describe a
radiation-imageable lithographic printing precursor that requires
no imagewise removal of, or imagewise addition to, any part of the
precursor after imagewise exposure of the precursor to radiation in
order to form a lithographic printing master.
[0026] The phrase "precoated processless radiation-imageable
lithographic printing precursor" is used herein to describe a
processless lithographic printing precursor that comprises a
radiation-sensitive medium coated onto a substrate.
[0027] Substrates may specifically include printing press drums or
sleeves, the drums or sleeves being precoated with
radiation-sensitive medium, or with radiation-sensitive medium and
an adhesion-promoting layer.
[0028] The term "eluent" refers to any fluid, either liquid or
gaseous, which is capable of dissolving or otherwise placing the
unpatterned coating of the radiation-sensitive medium into a
dispersible form.
[0029] The term "dispersible" means, with respect to a layer of
given material that the material is capable of displacement or
removal, including lifting off, by physical or chemical action of a
fluid.
[0030] The term "aqueous eluable" is used to describe a property of
an overcoat layer coated over a aqueous ineluable
radiation-sensitive layer, whereby the hydrophilic overcoat layer,
but not the aqueous ineluable radiation-sensitive layer, is
removable by dissolving and/or dispersing it in an aqueous medium
like water or fountain solution as used on printing presses.
[0031] The term "aqueous-ineluable" is used to describe a property
of a radiation-sensitive medium coated on a substrate, whereby the
radiation-sensitive medium is not dissolved or otherwise
dispersible by an aqueous eluent. It must be remembered that nearly
any material may be etched or dissolved, so that this term applies
only to fluids that are intended to be used in the treatment of the
layer (e.g., water, low alkaline content aqueous solutions, acidic
solutions, aqueous solutions with low amounts of organic compounds
such as 10% isopropanol or methoxypropanol, and other fountain
solutions used on printing presses.)
[0032] The term saccharide is used herein as defined by IUPAC,
being inclusive of monosaccharides and di-, oligo- and
polysaccharides, the di-, oligo- and polysaccharides being made up
of a plurality of monosaccharide units linked to each other by a
glycosidic bond.
[0033] Composition of the Radiation-Sensitive Medium
[0034] In a first embodiment of the present invention, a
radiation-sensitive medium comprises a continuous phase and
hydrophilic polymer particles. The hydrophilic polymer particles
comprise a thermally softenable hydrophobic polymer, a hydrophilic
polymer and a bonding compound capable of chemically bonding to the
hydrophobic polymer and to the hydrophilic polymer. The polymer
particles are made by polymerization of at least one hydrophobic
monomer and at least one bonding compound in the presence of the
hydrophilic polymer. The radiation-sensitive medium of the present
invention, when coated and dried, is aqueous-ineluable and a layer
of the radiation-sensitive medium becomes hydrophobic when imaged
using absorbed radiation that is imagewise converted to heat. A
substance capable of converting radiation into heat is preferably
added to the composition to create a suitably radiation-sensitive
medium.
[0035] The hydrophilic polymer particles are hydrophilic to a
substantial depth, with only a core region of the particles being
hydrophobic. A "substantial depth" means a depth that is
sufficiently large that when a lithographic printing master made
from a coated precursor in accordance with the invention is
employed in printing, the hydrophilic areas of the coating will not
erode sufficiently to expose the hydrophobic core of the particles
and thereby detrimentally affect printing quality to a material
degree. Being hydrophilic to a substantial depth stands in contrast
to the various particle types discussed in U.S. Pat. No. 6,653,042,
which are either entirely hydrophilic or have only a superficial
hydrophilic surface region or coating. The polymer particles of the
present invention are distinctly hydrophilic, compared with the
hydrophobic particles disclosed in U.S. Pat. No. 6,550,237. Without
wishing the invention to be limited in any way, the inventors
believe that the cores of the particles are dominated by the
hydrophobic polymer derived from the hydrophobic monomer, while the
rest of any given particle is dominated by the hydrophilic polymer.
It is believed that there is a transition region wherein there are
co-polymers of both the hydrophobic monomer and the hydrophilic
polymer with the bonding compound (itself preferably hydrophilic as
a polymer), producing thereby a particle that has three regions,
namely, an inner hydrophobic core, a transition region that is
largely hydrophilic, due to the nature of the preferred bonding
compounds, and the rest of the particle, being dominated by the
hydrophilic polymer.
[0036] The hydrophobic monomer of the present invention is selected
from electrically neutral ethylenically unsaturated monomers such
as ethylene, propylene, styrene, other vinyl monomers (e.g. methyl
methacrylate), and electrically neutral derivatives of these
ethylenically unsaturated monomers. The term "electrically neutral"
is well understood in the art and includes primarily non-polar
compounds, although monomers with internal charge distributions and
overall electrical neutrality (e.g., Zwitterions) are
acceptable.
[0037] The bonding compound of the present invention is preferably
selected from within the classes of water-soluble/dispersible
ethylenically unsaturated monomers, especially acryloyl or
methacryloyl monomers and anionic-substituted styrene monomers, and
especially acryloyl acids (i.e., acrylic acid, and methacrylic and
other substituted acrylic acids) and sulfonated or phosphonated
styrenes (e.g., with alkali or alkaline metal or ammonium
counterions such as Na, Li, K and the like).
[0038] The hydrophilic polymer of the present invention is
preferably selected from chitosan polymers (which includes
derivatized chitosan as described herein), polyethyleneimine
resins, polyamine resins (for example polyvinylamine polymers,
polyallylamine polymers, polydiallylamine resins and
amino(meth)acrylate polymers), polyamide resins,
polyamide-epichlorohydrin resins, polyamine-epichlorohydrin resins,
polyamidepolyamine-epichlorohydrin resins, as well as
dicyandiamide-polycondensation products (for example,
polyalkylenepolyamine-dicyandiamide copolymers). These polymers may
be employed alone or in a mixture or copolymer of two or more
thereof. The polymers preferably have a molecular weight of 5,000
to 500,000, more preferably 5,000 to 200,000. The content of
hydrophilic polymer is preferably 5 to 65% by weight, based on the
total weight of the imageable layer.
[0039] The hydrophilic polymer of the present invention may also
comprise saccharides, such as cellulose or starch, or a mixture of
such saccharides. The present invention allows for the hydrophilic
polymer to be comprised of a mixture of hydrophilic cationic resins
and saccharides. Furthermore, the hydrophilic polymer of the
present invention may be a derivative of a saccharide and mixtures
thereof with any one or more other hydrophilic cationic resin and
saccharide.
[0040] In one embodiment of the invention, the coatable
compositions comprise latices in aqueous carriers, the latices
comprising dissolved chitosan and particles comprised of thermally
softenable hydrophobic polymer, hydrophilic polymer and the bonding
compound, bonding the hydrophobic polymer and the hydrophilic
polymer. In this embodiment, therefore, there is dissolved chitosan
present, in addition to chitosan that may be the hydrophilic
polymer of the hydrophilic polymer particles. The composition may
also contain additives to assist in the imaging steps and/or the
coating steps. For example, a substance capable of converting the
imaging radiation into heat is particularly desirable in the
compositions so that the imaging radiation is efficiently absorbed
and converted to heat to assist in the softening and coalescing of
the polymer particles. The composition preferably contains at least
0.05 to 10% by weight of solids of a substance capable of
converting radiation to heat. The substance capable of converting
radiation to heat may be a pigment, such as, but not limited to,
carbon black, or a dye. Infrared and near infrared (NIR) dyes are
particularly suitable for use with infrared (IR) lasers.
[0041] In a preferred embodiment of the present invention the
substance capable of converting radiation to heat absorbs radiation
over the range 700 nm to 1200 nm, more preferably over the range
800 nm to 1100 nm, and most preferably over the range 800 nm to 850
nm, and converts it to heat. Examples of such substances are
disclosed in JOEM Handbook 2 Absorption Spectra of Dyes for Diode
Lasers, Matsuoka, Ken, bunshin Shuppan, 1990 and Chapter 2, 2.3 of
Development and Market Trend of Functional Colouring Materials in
1990's, CMC Editorial Department, CMC, 1990, such as polymethine
type coloring material, a phthalocyanine type coloring material, a
dithiol metallic complex salt type coloring material, an
anthraquinone type coloring material, a triphenylmethane type
coloring material, an azo type dispersion dye, and an
intermolecular CT coloring material. The representative examples
include
N-[4-[5-(4-dimethylamino-2-methylphenyl)-2,4-pentadienylidene]-3-methyl-2-
,5-cyclohexadiene-1-ylidene]-N,N-dimethylammonium acetate,
N-[4-[5-(4-dimethylaminophenyl)-3-phenyl-2-pentene-4-in-1-ylidene]-2,5-cy-
clohexadiene-1-ylidene]-N,N-dimethylammonium perchlorate,
bis(dichlorobenzene-1,2-dithiol)nickel(2:1)tetrabutyl-ammonium and
polyvinylcarbazol-2,3-dicyano-5-nitro-1,4-naphthoquinone complex.
Some specific commercial products that may be employed as substance
capable of converting radiation to heat include Pro-jet 830NP, a
modified copper phthalocyanine from Avecia of Blackley, Lancashire
in the U.K., ADS 830A, an infa-red absorbing dye from American Dye
Source Inc. of Montreal, Quebec, Canada, and S0094, S0306, S0391
and S0451, all infrared absorbing dyes from FEW Chemicals GmbH of
Wolfen, Germany. Hydrophobic forms of these dyes are particularly
preferred as this property makes these dyes more compatible with
the hydrophobic aspect of the particles, thereby facilitating heat
transfer to the thermally softenable hydrophobic polymer when
radiation is being absorbed and heat produced during irradiation of
the medium coated on a lithographic base.
[0042] Cosolvents (e.g., alcohols, ketones, and other organic
solvents), surfactants, blowing agents, and filler (e.g., silica,
titania, zinc oxide, zirconia, etc.) are also useful additives, and
may be present in non-limiting exemplary amounts of up to 25% by
weight of total solids, and the like. The use of filler particles,
preferably having volume average particle sizes of between 0.01 to
0.5 micrometers, and less than 50% of the volume average size of
the polymeric particles, is particularly desirable. Especially when
using inorganic filler particles, such as metal or semimetal oxides
or silica, the particles can add a surprisingly higher level of
on-press durability to lithographic printing masters prepared from
the radiation-sensitive medium of the present invention.
[0043] Preferably, the polymer or polymers that constitute the
thermally softenable hydrophobic polymer component of the particles
have a film forming temperature above ambient temperature (e.g.,
20.degree. C.) and may comprise any thermally softenable or
heat-fusible polymer, and, by way of non-limiting examples, may be
an addition polymer comprising residues derived from one or more of
styrene, substituted styrenes, esters of (meth)acrylic acid, vinyl
halides, (meth)acrylonitrile, vinyl esters, silicon-containing
polymerizable monomers or polyethers. It may also be a polyester,
polyamide or polyurethane, or any thermally fusible oleophilic
material or composition capable of forming a hydrophobic
center/hydrophilic outer layer structure by polymerization with one
or more anionic monomers. Preferred materials are addition polymers
containing 50% or more by weight of styrene or substituted
styrenes. Most preferred materials are polymers containing 50% or
more by weight of esters of (meth)acrylic acid. The hydrophobic
centers of the polymer particles preferably soften at temperatures
such as from 30.degree. C. to 300.degree. C., and more preferably
from 50.degree. C. to 200.degree. C. to allow coalescence, flow,
phase change or any other phenomenon to occur within or between the
particles to effect the hydrophilicity decrease in the surface of
the layer. Suitable examples of esters of (meth)acrylic acid
include, but are not limited to, methyl(meth)acrylate,
ethyl(meth)acrylate, propyl(meth)acrylate, butyl(meth)acrylate and
lauryl(meth)acrylate. Suitable examples of substituted styrenes
include, but are not limited to, alpha-methylstyrene and
vinyltoluene. Suitable examples of substituted vinyl esters
include, but are not limited to, vinyl acetate and vinyl
propionate. Suitable examples of vinyl halides include, but are not
limited to, vinyl chloride and vinylidene chloride.
[0044] Co-monomers used with these monomers may include up to 50%
by weight of polymerizable monomers having carbon-carbon double
bonds including, but not limited to monomers having various types
of carboxyl groups, such as acrylic acid, methacrylic acid,
crotonic acid, itaconic acid, fumaric acid, maleic acid, citraconic
acid and their salts; monomers having various types of hydroxyl
groups, such as 2-hydroxyethyl(meth)acrylate,
2-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,
monobutylhydroxyl fumarate and monobutylhydroxyl itaconate; various
types of nitrogen-containing vinyl monomers such as
(meth)acrylamides, diacetone acrylamides, N-methylol acrylamides;
sulphonamide- or phosphorus-containing vinyl monomers; various
types of conjugated dienes such as butadiene; dicarboxylic acid
half-esters of hydroxyl group-containing polymers, such as
phthalic, succinic or maleic acid half esters of a polyvinyl acetal
and, in particular, of a polyvinyl butyral; and alkyl or aralkyl
half esters of styrene- or alkyl vinyl ether-maleic anhydride
copolymers, in particular alkyl half esters of styrene-maleic
anhydride copolymers.
[0045] In a preferred embodiment of the invention, the hydrophilic
polymer is chitosan, which is normally prepared from chitin.
Chitosan, an aminopolysaccharide, is bio-friendly. Despite its
abundance in nature, chitin has not been effectively utilized
because of its low solubility in aqueous solutions. Owing to this
problem, chitin is difficult to form into fibers or films and thus,
has found limited applications. In an effort to overcome this
problem, chitin is often converted into chitosan. A deacetylation
technique is generally used for the conversion of chitin into
chitosan. U.S. Pat. No. 3,533,940 discloses a method for preparing
chitosan from chitin, along with its application to fibers and
films. For possible applications, the prepared chitosan is
dissolved in aqueous organic solutions.
[0046] Chitosan may be provided in the practice of the present
invention in a wide range of properties as long as its hydrophilic
surface properties are maintained. A non-limiting example of the
types of chitosan that are particularly useful in the practice of
the invention are chitosan which ranges in molecular weight from
5,000 to 500,000, more preferably 5,000 to 200,000, and in
deacetylation degree from 60 to 99%, more preferably from 70 to
95%. The chitosan also provides an emulsifying agent for the
thermally softenable or fusible polymer particles when in the
coating composition.
Synthesis of the Radiation-Sensitive Medium
[0047] A preferred mode of synthesis of the radiation-sensitive
medium of the present invention is performed via the following
steps, illustrated by, but not limited to, the use of chitosan as
hydrophilic polymer. The hydrophilic polymer is dissolved in a
suitable solvent and the hydrophobic monomer is added. An initiator
may be added in either of these steps. The resultant mixture is
polymerized by heating. The bonding compound may be added either
during or after the polymerization of the hydrophobic monomer. The
substance capable of converting radiation to heat is added prior to
coating. Minor amounts of co-solvents, blowing agents, fillers and
surfactants may be added at various stages of the synthesis.
[0048] Any solvent may be used that dissolves the chitosan and not
the hydrophobic monomer, selected from aqueous acidic solutions,
aqueous inorganic salt solutions and organic solvents. To obtain an
aqueous acidic solution, which is a desired route in practicing the
invention, water is added with 0.1-20 wt % of an acid, which is
selected from the group consisting of organic acids, such as acetic
acid and lactic acid, and inorganic acids, such as hydrochloric
acid. Available inorganic salt solutions that can assist in the
dissolving of chitosan include, by way of non-limiting examples, an
inorganic salt at an amount of 10-70 wt % in water. The inorganic
salt is particularly desirably selected from the group consisting
of alkali metal (e.g., sodium) thiocyanate, metal chlorides (e.g.,
zinc chloride, calcium chloride, sodium chloride, potassium
chloride, lithium chloride, and mixtures thereof). Organic solvents
that may be useful in carrying the dissolved chitosan in the
present invention are polar, examples of which include
dimethylacetamide, N-methylpyrrolidone, dimethylformamide,
diethylacetamide, trifluoroacetic acid, trichloroacetic acid, and
mixtures thereof. In order to obtain higher polarity, one or more
selected from the above-mentioned inorganic metal salts may be
added at an amount of 0.1-10 wt % to the organic solvent. The
polymerization process can be effected as described by Wen-Yen Chiu
et al. in Journal of Polymer Science A (Polymer Chemistry) volume
39, 2001, pp 1646-1655. The co-monomer, e.g. (meth)acrylic acid,
can be copolymerized with the primary component of the hydrophobic
polymer composition, e.g. styrene or methyl methacrylate. In the
polymerization process, an initiator (e.g.,
persulfate-metabisulfite) must be present. Other commonly known
initiators for radical polymerization can also be used to give
satisfactory polymers as described by Odian in Principles of
Polymerization, 3.sup.rd Edition, publisher John Wiley & Sons,
NY (1991) pp 212-215, 219-225 and 229-232.
[0049] The post-polymerization mix may generally comprise the
following:
[0050] solvent (40-97 w/w % of total mix)
[0051] excess dissolved hydrophilic solubilizable polymer (0.01-50
w/w % of total mix)
[0052] particles comprising electrically neutral hydrophobic
polymer (2-59 w/w % of total mix)
[0053] The post-polymerization mix comprises a continuous phase and
a dispersed phase, the dispersed phase comprising 50-99.9 w/w % of
polymerized electrically neutral hydrophobic monomer and 0.1-50 w/w
% polymerized anionic monomer. The post-polymerization mix may
contain suspended solids in the size range from 0.01 to 5
microns.
[0054] Minor amounts of additives may be added at various stages of
the polymerization or particle formation process. Surfactants can
be added (e.g., silicone-polyether,) to improve film forming
quality when the composition is coated onto a surface. A
plasticizer may be added at any time before coating of the
composition, but is preferably present well before the coating to
allow it to mix with the polymer.
[0055] In a further step 0.05 to 10 w/w % of solids of the
substance capable of converting radiation into heat is added. Other
additives, including the co-solvents, surfactants, blowing agents
and fillers, can be added in amounts from 0-25 w/w % of solids.
Aqueous Eluable Hydrophilic Overcoat
[0056] The lithographic printing plate precursor of the present
invention preferably comprises an aqueous eluable hydrophilic
overcoat provided on the heat-sensitive hydrophilic layer to
improve the overall performance of the lithographic printing plate.
The inventors have found that an aqueous-soluble or
aqueous-dispersible hydrophilic overcoat on top of the
heat-sensitive hydrophilic layer will prevent the surface of the
heat-sensitive layer from being contaminated and/or scratched
during storage and/or handling. The aqueous-soluble or
aqueous-dispersible hydrophilic overcoat provided on the
heat-sensitive hydrophilic layer of the lithographic printing plate
precursor also significantly improves start-up on press. A further
benefit stems from the fact that the overcoat provides a higher
optical reflectivity value, which is particularly useful in
platesetter systems that employ an autofocus arrangement to focus
the imaging radiation on the imageable layer. Since many
lithographic printing plate precursors tend to exhibit changes in
characteristics with time, temperature and humidity, the overcoat
also helps in minimizing these effects.
[0057] As the lithographic printing plate precursor of the
invention does not require a wet processing step after exposure,
the hydrophilic overcoat eluable in aqueous media has been designed
to be easily removable, at least in the imaged areas, during
start-up on press. Some of the specific requirements taken into
consideration during the design, were the eluability in water or
fountain, a high thermal stability to ensure minimal thermal
degradation during imaging, minimal compatibility with the
heat-sensitive hydrophilic layer to allow rapid removal, chemical
inertness to satisfy product shelf life requirements. The overcoat
thus comprises a resin, or a mixture of resins, selected from the
group of water-soluble organic polymers.
[0058] Representative examples of these resins include
polyvinylalcohol, poly(vinyl acetate), poly(acrylic acid),
poly(meth)acrylic acid or its alkali metal salt and amine salt,
poly 2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, poly(vinyl
methyl ether), poly(vinyl methyl ether)/maleic anhydride copolymer,
poly(vinyl pyrrolidone), poly(2-acrylamide-2-methylpropane sulfonic
acid) and alkali metal or amine salt thereof, alginic acid or its
salts, protan jelly, carageenin, tragacanth, laminarin sulfate,
starch, animal glues, vegetable mucilages, gum arabic, cellulose
and modification product thereof, polysaccharides such as dextran,
pullulan, or chitosan. The term saccharide is used herein as
defined by IUPAC, being inclusive of monosaccharides and di-,
oligo- and polysaccharides, the di-, oligo- and polysaccharides
being made up of a plurality of monosaccharide units linked to each
other by a glycosidic bond.
[0059] The aqueous eluable hydrophilic overcoat may comprise
additional ingredients, such as a second polymer, a plasticizer to
give the coating flexibility and reduce cracking, a
light-to-heat-converting agent to counteract any speed loss due to
the additional coating thickness, a surfactant or wetting agent to
improve coatability, a water-soluble visible dye or colorant to
help with the QC of the hydrophilic overcoat, and a highly
water-soluble crystalline compound to accelerate the breakdown of
the structural integrity of the overcoat during roll-up on press.
The aqueous eluable hydrophilic overcoat may also comprise
ingredients, such as small carboxylic acid molecules (e.g. citric
acid), polyvinylphosphonates, and other materials commonly found in
plate storage gum solutions, e.g. phosphates, sodium
hexametaphosphate, sodium gluconate, tartaric acid. Representative
examples of suitable plasticizers are ethylene glycol, glycerin,
sorbitol, carboxymethylcellulose. Preferably, the light-to-heat
converting agent is a water-soluble IR dye, for example, a
water-soluble cyanine dye as described in U.S. Pat. No. 6,159,657,
U.S. Pat. No. 6,397,749, U.S. Pat. No. 6,410,202, or as
commercially available from FEW Chemicals, but other IR-absorbing
dyes may be used as well. Acid Green 25 is one example for a useful
water-soluble visible dye. Useful examples of highly water-soluble
crystalline compounds have been described in U.S. Pat. No.
5,677,110. An especially preferred highly water-soluble crystalline
compound is glucose.
[0060] The coating weight of the aqueous eluable hydrophilic
overcoat preferably is 0.5 g/m.sup.2 or less. More preferably the
coating weight is 0.1 g/m.sup.2 or less. Most preferably the
coating weight of the overcoat is between 0.01 and 0.05 g/m.sup.2.
This coating weight of the protective layer is low enough not to
negatively affect the oleophilicity of the imaged areas or to
result in a significant increase of the exposure energy required
for optimum image formation.
Preparation of the Precoated Processless Radiation-Imageable
Lithographic Printing Precursor
[0061] The radiation-sensitive medium is applied to a substrate and
dried by the standard coating and drying methods employed in the
manufacture of printing plate precursors and other metal, plastic,
ceramic and paper products, to create a radiation-imageable layer.
Similarly, after the layer of radiation-sensitive medium has been
applied and dried, the aqueous eluable hydrophilic overcoat may be
applied and dried using standard coating and drying methods. The
two coatings, however, do not have to use the same coating or
drying techniques. The drying temperature for the protective
aqueous eluable hydrophilic overcoat preferably is low enough not
to cause any negative effects on the coated and dried
radiation-imageable layer. For example if the drying temperature of
the aqueous eluable hydrophilic overcoat is too high (more than
100.degree. C.) a bleaching of the coated and dried
radiation-imageable layer may be observed. The substrate material
used depends upon the purpose for which the image is to be used and
may be, for example, formed of metal, polymer material (such as,
but not limited to, PET), paper, ceramic, or composite material.
The substrate is preferably aluminum and more preferably chemically
treated aluminum, grained aluminum, anodized aluminum, aluminum
coated substrates, or combinations thereof. Preferably, the
substrate is sufficiently flexible to facilitate mounting on
presses. To the extent that the precoated processless
radiation-imageable lithographic printing precursor of the present
invention does not require any water carrying or water abhesive
quality from the substrate, the substrate being not exposed during
printing, there is wide scope of choice for the materials of which
the substrate may be composed.
[0062] According to another embodiment in connection with the
present invention, the substrate comprises a flexible support, such
as e.g. paper or plastic film, provided with a further
adhesion-promoting layer of cross-linked polymer. A suitable
cross-linked hydrophilic layer may be obtained from a hydrophilic
(co-) polymer cured with a cross-linking agent such as a hydrolysed
tetra-alkylorthosilicate, formaldehyde, glyoxal or polyisocyanate.
Particularly preferred is the hydrolysed tetra-alkylorthosilicate.
For the purposes of the present invention, this layer must be
capable of being wetted by the radiation-sensitive medium to give a
good quality of coating and is therefore usually hydrophilic. The
hydrophilic (co-) polymers that may be used comprise for example,
homopolymers and copolymers of vinyl alcohol, hydroxyethyl
acrylate, hydroxyethyl methacrylate, acrylic acid, methacrylic
acid, acrylamide, methylol acrylamide or methylol methacrylamide.
The hydrophilicity of the (co-) polymer or (co-) polymer mixture
used is preferably higher than that of polyvinyl acetate hydrolyzed
to at least an extent of 60 percent by weight, preferably 80
percent by weight.
[0063] In a further embodiment of the invention, an
adhesion-promoting layer is coated on the substrate. Suitable
adhesion-promoting layers for use in accordance with the present
invention comprise a hydrophilic (co-) polymer binder and colloidal
silica as disclosed in EP 619524, and EP 619525. Preferably, the
amount of silica in the adhesion-promoting layer is between 0.2 and
0.7 mg per m.sup.2. Further, the ratio of silica to hydrophilic
(co-) polymer binder is preferably more than 1 and the surface area
of the colloidal silica is preferably at least 300 m.sup.2 per
gram.
Preparation of the Negative-Working Lithographic Printing
Master
[0064] The preparation of the negative-working lithographic
printing master may be performed on a platesetter machine or
directly on the printing press. In both cases, the precoated
processless radiation-imageable lithographic printing precursor of
the invention may be mounted on the platesetter or printing press.
Alternatively, in the case of either machine, the
radiation-sensitive medium and the aqueous eluable hydrophilic
overcoat may be applied to the substrate and to the coated and
dried first layer of radiation sensitive medium while the substrate
resides on the relevant machine. The substrate may be an integral
part of the press or it may be removably mounted on the press. In
this embodiment, the imageable coating may be dried by means of a
curing unit integral with the press, as described in U.S. Pat. No.
5,713,287 (Gelbart). It is also possible to coat a cylinder of a
printing press with a layer of radiation-sensitive medium when the
cylinder is separate from the press. Before applying the imageable
coating to the substrate, the substrate may be treated to enhance
the adhesion of the imageable coating.
[0065] In a preferred embodiment of the invention, the
radiation-sensitive medium of the coating is imagewise converted by
means of the spatially corresponding imagewise generation of heat
within the coating to form a hydrophobic area corresponding to
areas imagewise irradiated. The imaging process itself may be by
means of scanned laser radiation as described in U.S. Pat. No.
5,713,287. The wavelength of the laser light and the absorption
range of the converter substance are chosen to match each other.
The heat to drive the process of converting the irradiated areas of
the precursor from hydrophilic to hydrophobic is produced via the
substance capable of converting radiation into heat. The
radiation-sensitive medium of the present invention, when coated
and dried on a suitable substrate, therefore becomes hydrophobic
under the action of heat. The aqueous eluable hydrophilic overcoat
of the precursor remains largely unaffected in this imaging
process. During subsequent wet lithographic offset printing, the
on-press fountain solution, being an aqueous medium, removes the
aqueous eluable hydrophilic overcoat, at least in the imaged areas,
to expose the underlying layer of image-wise irradiated imageable
coating for use in printing. Any small amounts of aqueous eluable
hydrophilic overcoat remaining in the unimaged areas after such
treatment with fountain solution do not constitute a problem in
printing, since the aqueous-ineluable coating of a
radiation-sensitive medium in that area remains hydrophilic
anyway.
[0066] The exposed areas of the imageable coating will be
hydrophobic and the lithographic printing ink will adhere
preferentially to these areas, as water or fountain solution will
be adhering to the hydrophilic areas. This makes the processless
printing master of the present invention inherently
negative-working. The method does not require a substrate of
controlled hydrophilicity and provides great toughness in the
exposed areas of the precursor, thereby extending the run length of
the negative-working lithographic printing master. The aqueous
eluable hydrophilic overcoat assures a trouble-free startup on
press, even for plates that have aged.
[0067] Without limiting the scope of the invention in any way, the
mechanism by which the irradiated areas of the layer become
hydrophobic is believed to be as follows. When the
radiation-imageable layer is imaged, the substance capable of
converting radiation into heat provides imagewise distributed heat.
This imagewise distributed heat provides the activation energy
required to turn the imageable layer from, what the inventors
believe to be, a metastable state into a thermodynamically stable
state. The majority of the copolymer is the thermally softenable
hydrophobic polymer. However, when the imageable layer is coated
and dried, the particles are locked into a metastable state in
which the more hydrophilic surface regions of the polymer particles
dominate the surface energy, rendering the layer hydrophilic. It is
believed that this happens because the coating occurs out of a
highly polar solvent mix, which favors the hydrophilic state. After
drying, the solvents are removed, but the solids remain in the
metastable hydrophilic state. Upon exposure to radiation that gets
converted to heat by the substance capable of converting radiation
into heat, the required activating energy is provided for the
polymer particles in the exposed areas to relax to the
thermodynamically stable hydrophobic state and at least partially
coalesce. In the unirradiated areas, where the activating energy
has not been provided, the coated layer remains hydrophilic. During
wet offset printing, the irradiated regions form the ink-accepting
image-areas, whereas the unirradiated areas of the layer remain
hydrophilic and take fountain solution, thereby being abhesive to
ink.
[0068] The imaging process is irreversible when performed. The
areas of the composition exposed to imaging radiation remain
hydrophobic and cannot be reversed to form a useable processless
radiation-imageable lithographic printing precursor by way of
thermal treatment (heating or cooling), radiation treatment to the
same or different imaging range of radiation. The composition and
radiation-sensitive medium is aqueous-ineluable when coated and
dried and is specifically not removable by water or
fountain-solution when coated and dried.
[0069] As is evident, the radiation-sensitive medium and
lithographic printing precursors of the present invention allow the
combination of the benefits of the newer generation of polymer
particle/coalescence-type of thermally sensitive media with the
substrate-independence of a switchable polymer approach to
plate-making. With the particles having a substantially hydrophilic
nature, rather than merely superficial, there is also reduced
scumming, a phenomenon that occurs when the water-bearing area of
the master loses some of its hydrophilic nature and starts to take
ink. This provides a master with excellent run-length, which is
nevertheless producible from an aqueous based radiation-sensitive
medium.
EXAMPLES
[0070] All materials used in the following examples are readily
available from standard commercial sources, such as Aldrich
Chemical Co. (Milwaukee, Wis.), Polysciences, Inc. (Warrington,
Pa.) or VWR Canlab, (Mississauga, Canada), unless otherwise
specified.
[0071] Chitosan was obtained as "High Viscosity Chitosan" from
Vanson, Redmond, Wash., USA or as "Chitosan" from Primex,
Siglufjordur, Iceland.
[0072] The infrared dyes are S0094 and S0391 from FEW Chemicals
GmbH in Wolfen, Germany.
[0073] The wetting agent is BYK-345 from BYK-Chemie, Wallingford,
Conn., USA.
[0074] Triton X-405 was obtained from Dow Chemical Company,
Midland, Mich., USA.
[0075] Gum Arabic was obtained as "100% Pure Gum Arabic" from
Anchor, Orange Park, Fla., USA.
[0076] All infrared laser exposure was at 830nm wavelength using a
Creo Trendsetter.TM. platesetting machine.
Example 1
[0077] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PS copolymer (13 wt % Chitosan and
87% Styrene) aqueous dispersion with 10% solids in aqueous and 9 g
of 2 wt % infrared dye in ethanol. After drying at room temperature
for 5 minutes, the plate was imaged using infrared laser exposure
of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was mounted onto a
press (Ryobi), dampened with fountain solution for 30 seconds
before the ink was applied to the plate. 1000 impressions were
printed on coated paper with little deterioration of printing
quality. During printing, the surface on background remains
unchanged.
Example 2
[0078] A plate was produced by coating the following formulation on
to ungrained, unanodized aluminum plate to give a dry coating
weight of 1 g/m.sup.2: 30 g Chitosan/PS copolymer (13 wt % Chitosan
and 87% Styrene) aqueous dispersion with 10% solid and 9 g of 2 wt
% infrared dye in ethanol. After drying at room temperature for 5
minutes, the plate was imaged using infrared laser exposure of 500
mJ/cm.sup.2 at 15 Watts. The imaged plate was mounted onto a press
(Ryobi), dampened with fountain solution for 30 seconds before the
ink was applied to the plate. 1000 impressions were printed on
coated paper with little deterioration of printing quality. During
printing, the surface on background remains unchanged.
Example 3
[0079] A plate was produced by coating the following formulation on
to a Ceramic Paper to give a dry coating weight of 1 g/m.sup.2: 30
g Chitosan/PS copolymer (13 wt % Chitosan and 87% Styrene) aqueous
dispersion with 10% solid and 9 g of 2 wt % infrared dye in
ethanol. After drying at room temperature for 5 minutes, the plate
was imaged using infrared laser exposure of 500 mJ/cm.sup.2 at 15
Watts. The imaged sample was mounted onto a press (Ryobi), dampened
with fountain solution for 30 seconds before the ink was applied to
the plate. 3000 impressions were printed on coated paper with
little deterioration of printing quality. During printing, the
surface on background remains unchanged.
Example 4
[0080] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PS/AN copolymer (13 wt % Chitosan,
78% Styrene, 9% Acrylonitrile) aqueous dispersion with 10% solid
and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minute, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 5
[0081] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PS/AA copolymer (13 wt % Chitosan,
78% Styrene, 9% Acrylic acid) aqueous dispersion with 10% solid and
9 g of 2wt % infrared dye in ethanol. After drying at 60.degree. C.
for 2 minutes, the plate was imaged using infrared laser exposure
of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was mounted onto a
press (Multi), dampened with fountain solution for 30 seconds
before the ink was applied to the plate. 5000 impressions were
printed on uncoated paper. During printing, the surface on
background remains unchanged.
Example 6
[0082] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 15 g Gelatin/PS/AN copolymer (13 wt % Gelatin, 78%
Styrene, 9% Acrylonitrile) aqueous dispersion with 10% solid and 15
g Chitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methyl
methacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid
and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 5000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 7
[0083] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 15 g Starch/PS/AN copolymer (13 wt % Starch, 78%
Styrene, 9% Acrylonitrile) aqueous dispersion with 10% solid and 15
g Chitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methyl
methacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid
and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 5000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 8
[0084] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 24 g Chitosan/PS copolymer (13 wt % Chitosan and
87% Styrene) aqueous dispersion with 10% solid and 6 g
Chitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methyl
methacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid
and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 9
[0085] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 24 g Chitosan/PS/AN copolymer (13 wt % Chitosan,
78% Styrene, 9% Acrylonitrile) aqueous dispersion with 10% solid
and 6 g Chitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methyl
methacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid
and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 10
[0086] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PS/AA copolymer (13 wt % Chitosan,
78% Styrene, 9% Acrylic acid) aqueous dispersion with 10% solid and
9 g of 5 wt % carbon black (CAB-O-JET 200) in water. After drying
at 60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 800 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 11
[0087] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Starch/PS/AA copolymer (13 wt % starch, 78%
Styrene, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 g
of 2 wt % infrared dye in ethanol. After drying at 60.degree. C.
for 2 minutes, the plate was imaged using infrared laser exposure
of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was mounted onto a
press (Multi), dampened with fountain solution for 30 seconds
before the ink was applied to the plate. 500 impressions were
printed on uncoated paper. During printing, the surface on
background remains unchanged.
Example 12
[0088] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Gelatin/PS/AA copolymer (13 wt % Gelatin, 78%
Styrene, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 g
of 2 wt % infrared dye in ethanol. After drying at 60.degree. C.
for 2 minutes, the plate was imaged using infrared laser exposure
of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was mounted onto a
press (Multi), dampened with fountain solution for 30 seconds
before the ink was applied to the plate. 500 impressions were
printed on uncoated paper. During printing, the surface on
background remains unchanged.
Example 13
[0089] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Cellulose/PS/AA copolymer (13 wt % Cellulose,
78% Styrene, 9% Acrylic acid) aqueous dispersion with 10% solid and
9 g of 2 wt % infrared dye in ethanol. After drying at 60.degree.
C. for 2 minutes, the plate was imaged using infrared laser
exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 500 impressions
were printed on uncoated paper. During printing, the surface on
background remains unchanged.
Example 14
[0090] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PMMA/AA copolymer (13 wt % Chitosan,
78% Methyl methacrylate, 9% Acrylic acid) aqueous dispersion with
10% solid and 9 g of 2 wt % infrared dye in ethanol. After drying
at 60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 15
[0091] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PS/PMMA/AA copolymer (13 wt %
Chitosan, 39% Styrene, 36% Methyl methacrylate, 9% Acrylic acid)
aqueous dispersion with 10% solid and 9 g of 2 wt % infrared dye in
ethanol. After drying at 60.degree. C. for 2 minutes, the plate was
imaged using infrared laser exposure of 500 mJ/cm.sup.2 at 15
Watts. The imaged sample was mounted onto a press (Multi), dampened
with fountain solution for 30 seconds before the ink was applied to
the plate. 500 impressions were printed on uncoated paper. During
printing, the surface on background remains unchanged.
Example 16
[0092] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 25 g Chitosan/PS/AA copolymer (13 wt % Chitosan,
78% Styrene, 9% Acrylic acid) aqueous dispersion with 10% solid, 5
g of 10% Zinc oxide in ethanol and 9 g of 2 wt % infrared dye in
ethanol. After drying at 60.degree. C. for 2 minutes, the plate was
imaged using infrared laser exposure of 500 mJ/cm.sup.2 at 15
Watts. The imaged plate was mounted onto a press (Multi), dampened
with fountain solution for 30 seconds before the ink was applied to
the plate. 500 impressions were printed on uncoated paper. During
printing, the surface on background remains unchanged.
Example 17
[0093] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 25 g Chitosan/PS/AA copolymer (13 wt % Chitosan,
78% Styrene, 9% Acrylic acid) aqueous dispersion with 10% solid 5 g
of 10% SiO.sub.2 in ethanol and 9 g of 2 wt % infrared dye in
ethanol. After drying at 60.degree. C. for 2 minutes, the plate was
imaged using infrared laser exposure of 500 mJ/cm.sup.2 at 15
Watts. The imaged plate was mounted onto a press (Multi), dampened
with fountain solution for 30 seconds before the ink was applied to
the plate. 5000 impressions were printed on uncoated paper. During
printing, the surface on background remains unchanged.
Example 18
[0094] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PnBMA/AA copolymer (13 wt % Chitosan,
78% n-butyl methacrylate, 9% Acrylic acid) aqueous dispersion with
10% solid and 9 g of 2 wt % infrared dye in ethanol. After drying
at 60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 19
[0095] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PtBMA/AA copolymer (13 wt % Chitosan,
78% t-Butyl methacrylate, 9% Acrylic acid) aqueous dispersion with
10% solid -and 9 g of 2 wt % infrared dye in ethanol. After drying
at 60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 20
[0096] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PEMA/AA copolymer (13 wt % Chitosan,
78% Ethyl methacrylate, 9% Acrylic acid) aqueous dispersion with
10% solid and 9 g of 2 wt % infrared dye in ethanol. After drying
at 60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 500 impressions
were printed on uncoated paper. During printing, the surface on
background remains unchanged.
Example 21
[0097] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PtBS/AA copolymer (13 wt % Chitosan,
78% 4-t-Butyl styrene, 9% Acrylic acid) aqueous dispersion with 10%
solid and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 10,000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 22
[0098] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PCS/AA copolymer (13 wt % Chitosan,
78% 4-Chloro styrene, 9% Acrylic acid) aqueous dispersion with 10%
solid and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 4000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 23
[0099] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/P.alpha. MS/AA copolymer (13 wt %
Chitosan, 78% a-methyl styrene, 9% Acrylic acid) aqueous dispersion
with 10% solid and 9 g of 2 wt % infrared dye in ethanol. After
drying at 60.degree. C. for 2 minutes, the plate was imaged using
infrared laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged
plate was mounted onto a press (Multi), dampened with fountain
solution for 30 seconds before the ink was applied to the plate.
4000 impressions were printed on uncoated paper. During printing,
the surface on background remains unchanged.
Example 24
[0100] A plate was produced by coating the following formulation on
to a grained, anodized aluminum plate to give a dry coating weight
of 1 g/m.sup.2: 30 g Chitosan/PMS/AA copolymer (13 wt % Chitosan,
78% 4-methyl styrene, 9% Acrylic acid) aqueous dispersion with 10%
solid and 9 g of 2 wt % infrared dye in ethanol. After drying at
60.degree. C. for 2 minutes, the plate was imaged using infrared
laser exposure of 500 mJ/cm.sup.2 at 15 Watts. The imaged plate was
mounted onto a press (Multi), dampened with fountain solution for
30 seconds before the ink was applied to the plate. 1000
impressions were printed on uncoated paper. During printing, the
surface on background remains unchanged.
Example 25
[0101] To a 10 L glass reactor equipped with thermometer,
mechanical stirring, nitrogen inlet and heating bath, set to
60.degree. C., containing a stirring solution under nitrogen of 120
g chitosan, 8.52 g of potassium persulfate and 8.53 g of sodium
metabisulfite in 159 g of acetic acid and 7910 g of water, was
added 712 g of styrene and 80 g of acrylic acid. After 6 hours,
stirring was stopped and the reactor contents were filtered to give
an opaque white liquid, 3 g of which was mixed with 1 g of 1%
infrared dye in ethanol and 1 g of 0.2% wetting agent in water.
When coated onto an aluminum substrate, dried, imaged with 830 nm
laser radiation with an exposure of 300 mJ/cm.sup.2 the resulting
plate printed to over 5,000 pages without loss of coating in either
exposed or unexposed areas.
Example 26
[0102] To a 10 L glass reactor equipped with thermometer,
mechanical stirring, nitrogen inlet and heating bath, set to
60.degree. C., containing a stirring solution under nitrogen of 120
g chitosan, 8.52 g of potassium persulfate and 8.53 g of sodium
metabisulfite in 159 g of acetic acid and 7910 g of water, was
added 633 g of styrene, then 158 g of acrylic acid. After 6 hours,
stirring was stopped and the reactor contents were filtered to give
an opaque white liquid, 3 g of which was mixed with 1 g of 1%
infrared dye in ethanol and 1 g of 0.2% wetting agent in water.
When coated onto an aluminum substrate, dried, imaged with 830 nm
laser radiation with an exposure of 300 mJ/cm.sup.2, the resulting
plate printed to over 5,000 pages without loss of coating in either
exposed or unexposed areas.
Example 27
[0103] In a 2 L glass vessel equipped with mechanical stirring and
nitrogen atmosphere was prepared a mixture of 791.99 g deionized
water, 19.27 g acetic acid, 12.10 g chitosan and 0.0723 g iron
gluconate having a viscosity of 32.6 cps at 25.degree. C.; to this
was added 57.47 g methyl methacrylate, 6.39 g acrylic acid, 0.229 g
Triton X-405 and 80.24 g more deionized water, then, after stirring
at 1200 rpm and 60.degree. C. for 15 minutes, a solution of 0.980 g
of ammonium sulfite and 1.080 g of 50% aqueous glyoxylic acid in
12.36 g of deionized water with rinsing by 1.0 g of deionized
water, then after 10 minutes still stirring at 1200 rpm, 1.188 g of
55% pinane hydroperoxide in pinane, then after a further 10 minutes
at 800 rpm, a further 0.584 g of 55% pinane hydroperoxide in
pinane, then after a further 5 minutes at 800 rpm then 10 minutes
at 400 rpm, a further solution of 0.979 g of ammonium sulfite and
1.079 g of 50% aqueous glyoxylic acid in 12.34 g of deionized water
with rinsing by 1.0 g of deionized water. During this time the pot
temperature had risen by 7.degree. C.; after a further 90 minutes
at 400 rpm, the hot opaque white liquid was passed through
successive filters having nominal ratings of 100, 10 then 1
microns. The resulting filtrate was a latex containing particles
having d(50) diameter of 0.138 microns by light-scattering, for
7.94% nonvolatile solids (expected 8.00% from the monomers).
[0104] 38.7 g of a latex made according to the above recipe was
mixed with 7.9 g of 2% acetic acid and 3.4 g of
1-methoxy-2-propanol containing 2.8% IR dye and 0.84% of a wetting
agent and 0.025% glyoxal when coated on a grained and anodized
aluminum substrate, dried to give a dry coatweight of ca. 1.8 g,
imaged using infrared exposure of 275 mJ/cm.sup.2 at 15 Watts. The
imaged plate was mounted onto a press, dampened with fountain
solution for 30 seconds before the ink was applied to the plate.
Over 25,000 impressions without loss of coating in either exposed
or unexposed areas were printed. During printing, the surface on
the background remains unchanged.
Example 28
[0105] In a 10 L glass vessel equipped with mechanical stirring and
nitrogen atmosphere was prepared a mixture of 7158.41 g deionized
water, 172.95 g acetic acid, 108.76 g chitosan and 1.160 g iron
gluconate having a viscosity of 18.5 cps at 25.degree. C.; to this
was added 516.88 g methyl methacrylate, 57.43 g acrylic acid, 2.03
g Triton.RTM. X-405 and 698.28 g more deionized water, then, after
stirring at 340 rpm and 60.degree. C. for 10 minutes, a solution of
8.81 g of ammonium sulfite and 9.72 g of 50% aqueous glyoxylic acid
in 111.08 g of deionized water with rinsing by 5.0 g of deionized
water, then after 10 minutes still stirring at 340 rpm, 10.546 g of
55% pinane hydroperoxide in pinane, then after a further 10 minutes
at 340 rpm, a further 5.293 g of 55% pinane hydroperoxide in
pinane, then after a further 15 minutes at 340 rpm, a further
solution of 8.80 g of ammonium sulfite and 9.71 g of 50% aqueous
glyoxylic acid in 110.95 g of deionized water with rinsing by 5.0 g
of deionized water. During this time the pot temperature had risen
by 9.degree. C.; after a further 5 minutes at 340 rpm, then 85
minutes at 180 rpm, the hot opaque white liquid was passed through
successive filters having nominal ratings of 100, 10 then 1
microns. The resulting filtrate was a latex containing particles
having d(50) diameter of 0.133 microns by light-scattering, for
7.88% nonvolatile solids (expected 8.02% from the monomers).
[0106] 34.8 g of a latex of this recipe was mixed with 11.8 g of 2%
acetic acid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR
dye and 0.84% of a wetting agent and 0.025% glyoxal when coated on
a grained and anodized aluminum substrate, dried to give a dry
coatweight of ca. 1.8 g, imaged using infrared exposure of 275
mJ/cm.sup.2 at 15 Watts. The imaged plate was mounted onto a press,
dampened with fountain solution for 30 seconds before the ink was
applied to the plate. Over 25,000 impressions without loss of
coating in either exposed or unexposed areas were printed. During
printing, the surface on the background remains unchanged.
Example 29
[0107] 34.8 g of the latex of example 28 was mixed with 11.8 g of
2% acetic acid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR
dye and 0.84% of a wetting agent and 0.025% glyoxal when coated on
a grained and anodized aluminum substrate, dried to give a dry
coatweight of ca. 1.8 g, a second layer was then applied by
spraying from a solution comprising 0.2 g of 25% gum arabic
solution and 0.005 g wetting agent and 9.8 g DI water, dried to
give a dry coatweight of ca. 0.03 g, imaged using infrared exposure
of 275 mJ/cm.sup.2 at 15 Watts. The imaged plate was mounted onto a
press, dampened with fountain solution for 30 seconds before the
ink was applied to the plate. Over 25,000 impressions without loss
of coating in either exposed or unexposed areas were printed.
During printing, the surface on the background remains unchanged.
The benefit of a topcoat was observed when the plate with and
without a topcoat was press tested after 6 weeks storage under
ambient conditions. The press results are summarized in Table 1
below. TABLE-US-00001 TABLE 1 Number of printed sheets required to
give a tone free background in the printed sheet After 1 week After
6 weeks example 28 .ltoreq.10 700 example 29 .ltoreq.10
.ltoreq.10
Example 30
[0108] 34.8 g of the latex of example 28 was mixed with 11.8 g of
2% acetic acid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR
dye and 0.84% of a wetting agent and 0.025% glyoxal when coated on
a grained and anodized aluminum substrate, dried to give a dry
coatweight of ca. 1.8 g, a second layer was then applied by coating
a solution comprising 2.5% (by weight) gum arabic solution in DI
water, which was then dried to give a dry coatweight of ca. 0.01
gsm. A higher topcoat coatweight was achieved by coating a 5% (by
weight) gum arabic solution, which gave ca. 0.1 g.
[0109] Plates based on example 28 and the present example 30 were
then stored at 30 C and 85% relative humidity for 5 days. The
purpose of this test is to accelerate the aging of the plate seen
at lower temperature and humidity conditions. These plates were
then imaged using infrared exposure of 325 mJ/cm.sup.2 at 17.4
Watts. The imaged plate was mounted onto a press, dampened with
fountain solution for 30 seconds before the ink was applied to the
plate. The number of printed sheets required to give a clean
background on the printed sheet was noted as well as the tendency
towards plugging of the shadows and the print quality of the plate
are summarized in the Table 2. TABLE-US-00002 TABLE 2 Number of
copies Topcoat Aged at to obtain a clean Plugging Presence of 2%
dots Example coatweight 30 C. @85% background on the of the at 240
lpi imaged at number (gsm) RH 5days printed sheet shadows 325
mJ/cm2 28 None No .ltoreq.10 No Complete 28 None Yes >3,000 Yes
Complete 30 ca. 0.05 Yes <10 No Complete 30 ca. 0.1 Yes <10
No Incomplete
Example 31
[0110] 34.8 g of the latex of example 28 was mixed with 11.8 g of
2% acetic acid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR
dye and 0.84% of a wetting agent and 0.025% glyoxal when coated on
a grained and anodized aluminum substrate, dried to give a dry
coatweight of ca. 1.8 g, a second layer was then applied by coating
from a solution comprising 0.11 g of polyvinyl alcohol, 0.02 g of
chitosan, 0.01 g of glucose, 0.22 acetic acid and 9.64 g DI water,
dried to give a dry coatweight of ca. 0.01 g. A higher topcoat
coatweight was achieved by coating a solution comprising 0.22 g of
polyvinyl alcohol, 0.04 g of chitosan, 0.02 g of glucose, 0.44 g
acetic acid and 9.28 g DI water, which gave a topcoat coat weight
of ca. 0.1 g.
[0111] Plates based on example 28 and present example 31 were then
stored at 30 C and 85% relative humidity for 5 days. These plates
were then imaged using infrared exposure of 325 mJ/cm.sup.2 at 17.4
Watts. The imaged plate was mounted onto a press, dampened with
fountain solution for 30 seconds before the ink was applied to the
plate. The number of printed sheets required to give a clean
background on the printed sheet was noted as well as the tendency
towards plugging of the shadows and the print quality of the plate
are summarized in the Table 3. TABLE-US-00003 TABLE 3 Number of
copies Topcoat Aged at to obtain a clean Plugging Presence of 2%
dots Example coatweight 30 C. @85% background on the of the at 240
lpi imaged at number (gsm) RH 5days printed sheet shadows 325
mJ/cm2 28 None No .ltoreq.10 No Complete 28 None Yes 400 Yes
Complete 31 ca. 0.01 Yes <10 No Complete 31 ca. 0.1 Yes <10
No Incomplete
Example 32
[0112] 34.8 g of the latex of example 28 was mixed with 11.8 g of
2% acetic acid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR
dye and 0.84% of a wetting agent and 0.025% glyoxal when coated on
a grained and anodized aluminum substrate, dried to give a dry
coatweight of ca. 1.8 g, a second layer was then applied by coating
from a solution comprising 0.13 g of polyvinyl alcohol and 0.01 g
of glucose and 9.86 g DI water, dried to give a dry coatweight of
ca. 0.01 g. A higher coatweight was achieved by coating a solution
comprising 0.26 g of polyvinyl alcohol and 0.02 g of glucose and
9.72 g DI water, dried to give a dry coatweight of ca. 0.1 g
[0113] Plates based on examples 28 and present example 32 were then
stored at 30.degree. C. and 85% relative humidity for 5 days. These
plates were then imaged using infrared exposure of 325 mJ/cm.sup.2
at 17.4 Watts. The imaged plate was mounted onto a press, dampened
with fountain solution for 30 seconds before the ink was applied to
the plate. The number of printed sheets required to give a clean
background on the printed sheet was noted as well as the tendency
towards plugging of the shadows and the print quality of the plate
are summarized in the Table 4. TABLE-US-00004 TABLE 4 Number of
copies Topcoat Aged at to obtain a clean Plugging Presence of 2%
dots Example coatweight 30 C. @85% background on the of the at 240
lpi imaged at number (gsm) RH 5days printed sheet shadows 325
mJ/cm2 28 None No .ltoreq.10 No Complete 28 None Yes 50 Yes
Complete 32 ca. 0.01 Yes <10 No Complete 32 ca. 0.1 Yes <10
No Incomplete
Example 33
[0114] 34.8 g of the latex of example 28 was mixed with 11.8 g of
2% acetic acid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR
dye and 0.84% of a wetting agent and 0.025% glyoxal when coated on
a grained and anodized aluminum substrate, dried to give a dry
coatweight of ca. 1.8 g, a second layer was then applied by coating
from a solution comprising 0.11 g of polyvinyl alcohol and 0.14 g
of gum arabic and 9.75 g DI water, dried to give a dry coatweight
of ca. 0.01 g. A higher topcoat coat weight was achieved by coating
a solution comprising 0.22 g of polyvinyl alcohol and 0.28 g of gum
arabic and 9.5 g DI water, dried to give a dry coatweight of ca.
0.1 g.
[0115] Plates based on examples 30, 31, 32 and present example 33
were then stored at 30 C and 85% relative humidity for 5 days.
These plates were then imaged using infrared exposure of 325
mJ/cm.sup.2 at 17.4 Watts. The imaged plate was mounted onto a
press, dampened with fountain solution for 30 seconds before the
ink was applied to the plate. The run length performance is
summarized in Table 5. TABLE-US-00005 TABLE 5 Number of copies
Topcoat Aged at to obtain a clean Plugging of Example coatweight 30
C. @85% background on the the number (gsm) RH 5days printed sheet
shadows Run length 28 None No .ltoreq.10 No >30,000 30 ca. 0.1
Yes <10 No >30,000 31 ca. 0.01 Yes <10 No >30,000 32
ca. 0.01 Yes <10 No >30,000 33 ca. 0.01 Yes <10 No
>30,000
[0116] There have thus been outlined the important features of the
invention in order that it may be better understood, and in order
that the present contribution to the art may be better appreciated.
Those skilled in the art will appreciate that the conception on
which this disclosure is based may readily be utilized as a basis
for the design of other compositions, elements and methods for
carrying out the several purposes of the invention. It is most
important, therefore, that this disclosure be regarded as including
such equivalent compositions, elements and methods as do not depart
from the spirit and scope of the invention.
* * * * *