U.S. patent application number 12/022966 was filed with the patent office on 2008-05-22 for laser sensitive lithographic printing plate having specific photopolymer composition.
Invention is credited to Gary Ganghui Teng.
Application Number | 20080118869 12/022966 |
Document ID | / |
Family ID | 38285932 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080118869 |
Kind Code |
A1 |
Teng; Gary Ganghui |
May 22, 2008 |
Laser sensitive lithographic printing plate having specific
photopolymer composition
Abstract
High speed violet or ultraviolet laser sensitive lithographic
printing plate comprising on a hydrophilic substrate a specific
photosensitive composition is described. The photosensitive layer
comprises a polymeric binder, a multifunctional (meth)acrylate
monomer, a free-radical initiator, and a sensitizing dye, with
specific weight ratio of the monomer to the polymer. Combination of
multifunctional urethane (meth)acrylate monomer and multifunctional
non-urethane (meth)acrylate monomer can be advantageously used. The
plate is imagewise exposed with a violet or ultraviolet laser at a
dosage of less than 300 .mu.J/cm.sup.2, and then developed with an
aqueous developer or with ink and/or fountain solution.
Inventors: |
Teng; Gary Ganghui;
(Northborough, MA) |
Correspondence
Address: |
Gary Ganghui Teng
10 Kendall Dr.
Northborough
MA
01532
US
|
Family ID: |
38285932 |
Appl. No.: |
12/022966 |
Filed: |
January 30, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11336132 |
Jan 21, 2006 |
7348132 |
|
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12022966 |
Jan 30, 2008 |
|
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Current U.S.
Class: |
430/302 |
Current CPC
Class: |
G03F 7/027 20130101;
G03F 7/38 20130101; G03F 7/11 20130101 |
Class at
Publication: |
430/302 |
International
Class: |
G03F 7/26 20060101
G03F007/26 |
Claims
1. A method of processing a lithographic printing plate comprising
in order: (a) providing a lithographic printing plate comprising
(i) a hydrophilic substrate, (ii) an oleophilic photosensitive
layer comprising an alkaline soluble polymeric binder, a urethane
(meth)acrylate monomer having at least 4 (meth)acrylate groups, a
free radical initiator, and a sensitizing dye, and (iii) a water
soluble or dispersible overcoat; wherein the weight ratio of all
the urethane monomers having at least 4 (meth)acrylate groups to
all the alkaline soluble polymeric binders is at least 0.9; (b)
exposing said plate with a laser having a wavelength of from 250 to
430 nm at a dosage of less than 300 .mu.J/cm.sup.2 according to
digital imaging information to cause hardening of the
photosensitive layer in the exposed areas; and (c) contacting said
exposed plate with an aqueous alkaline developer having a pH of 9.0
to 13.5 to remove the non-exposed areas of the photosensitive
layer.
2. The method of claim 1 wherein said weight ratio is from 1.2 to
6.0.
3. The method of claim 1 wherein said weight ratio is from 1.8 to
5.0.
4. The method of claim 1 wherein said weight ratio is from 2.4 to
4.0.
5. The method of claim 1 wherein said urethane monomer has at least
5 (meth)acrylate groups.
6. The method of claim 1 wherein said urethane monomer has at least
6 (meth)acrylate groups.
7. The method of claim 1 wherein said urethane monomer has at least
6 (meth)acrylate groups, and the weight ratio of all the urethane
monomers having at least 6 (meth)acrylate groups to all the
alkaline soluble polymeric binders is at least 0.9.
8. The method of claim 1 wherein said monomer is an acrylate
monomer.
9. The method of claim 1 wherein said photosensitive layer further
comprises a non-urethane (meth)acrylate monomer.
10. The method of claim 1 wherein said free radical initiator is a
hexaarylbiimidazole or titanocene compound.
11. The method of claim 1 wherein said free radical initiator is a
hexaarylbiimidazole compound.
12. The method of claim 1 wherein said sensitizing dye is a
dialkylaminobenzophenone compound.
13. The method of claim 12 wherein said dialkylaminobenzaphenone
compound is a 4,4'-bis(dialkylamino)benzophenone compound.
14. The method of claim 1 wherein said photosensitive layer further
comprises a hydrogen donor compound.
15. The method of claim 14 wherein said hydrogen donor compound is
selected from the group consisting of 2-mercaptobenzoxazole,
2-mercaptobenzimidazole, 2-mercaptobenzothiazole,
3-mercapto-1,2,4-triazole, N,N-dialkyl benzoic alkyl ester,
N-phenylglycine ethyl ester, and N-phenylglycine benzyl ester.
16. The method of claim 1 wherein said free radical initiator is a
hexaarylbiimidazole compound, said sensitizing dye is a
4,4'-bis(dialkylamino)benzophenone compound, and said
photosensitive layer further includes a hydrogen donor
compound.
17. The method of claim 1 wherein said photosensitive layer is
semisolid at 25.degree. C.
18. The method of claim 1 wherein said substrate is a grained and
anodized aluminum sheet (with or without further hydrophilic
treatment) having a reflection optical density of from 0.30 to
0.50.
19. The method of claim 1 wherein said developer has a pH of from
10.0 to 13.0.
20. The method of claim 1 wherein said plate is heated to an
elevated temperature of 50 to 200.degree. C. for 1 to 600 seconds
after said laser exposure (step b) and before said development
(step c).
Description
RELATED PATENT APPLICATIONS
[0001] This application is a divisional of application Ser. No.
11/336,132 filed Jan. 21, 2006.
FIELD OF THE INVENTION
[0002] This invention relates to lithographic printing plates. More
particularly, it relates to lithographic printing plates having a
photosensitive layer comprising a multifunctional (meth)acrylate
monomer and a polymeric binder, suitable for image exposure with a
violet or ultraviolet laser.
BACKGROUND OF THE INVENTION
[0003] Lithographic printing plates (after process) generally
consist of ink-receptive areas (image areas) and ink-repelling
areas (non-image areas). During printing operation, an ink is
preferentially received in the image areas, not in the non-image
areas, and then transferred to the surface of a material upon which
the image is to be produced. Commonly the ink is transferred to an
intermediate material called printing blanket, which in turn
transfers the ink to the surface of the material upon which the
image is to be produced.
[0004] At the present time, lithographic printing plates
(processed) are generally prepared from lithographic printing plate
precursors (also commonly called lithographic printing plates)
comprising a substrate and a photosensitive coating deposited on
the substrate, the substrate and the photosensitive coating having
opposite surface properties. The photosensitive coating is usually
a photosensitive material, which solubilizes or hardens upon
exposure to an actinic radiation. In positive-working systems, the
exposed areas become more soluble and can be developed to reveal
the underneath substrate. In negative-working systems, the exposed
areas become hardened and the non-exposed areas can be developed to
reveal the underneath substrate. Conventionally, the actinic
radiation is from a lamp (usually an ultraviolet lamp) and the
image pattern is generally determined by a photomask that is placed
between the light source and the plate.
[0005] Laser sources have been increasingly used to imagewise
expose a lithographic printing plate that is sensitized to a
corresponding laser. This allows the elimination of the photomask
film, reducing material, equipment and labor cost. Among the lasers
useful are infrared lasers (about 830 nm or 1064 nm), FD-YAG laser
(about 532 nm), violet laser (about 405 nm), and ultraviolet laser
(such as about 375 nm). Violet and ultraviolet laser sensitive
plates are quite attractive because of their yellow light handling
capability (in contrast to red light handling for FD-YAG sensitive
plate) and higher quantum efficiency (than infrared laser sensitive
plate). However, the energy output of a violet or ultraviolet laser
diode is much lower than that of an infrared laser diode. In order
to be imaged with a violet or ultraviolet laser imager at a
practical speed, a violet or ultraviolet laser sensitive plate
should have a sensitivity of less than 300 .mu.J/cm.sup.2,
preferably less than 200 .mu.J/cm.sup.2, more preferably less than
100 .mu.J/cm.sup.2, which is significantly lower than the
sensitivity required for an infrared laser sensitive plate
(typically 50 to 300 mJ/cm.sup.2) or a conventional plate exposed
with an ultraviolet lamp through a photomask (typically 50 to 300
mJ/cm.sup.2).
[0006] Silver halide based violet laser sensitive plate has
recently been introduced as the first lithographic printing plate
suitable for imaging with violet laser, utilizing the inherently
high sensitivity of silver halide. Examples include U.S. Pat. No.
6,541,176. However silver halide based plates have the
disadvantages of relatively low run length and generating hazardous
silver waste.
[0007] Photopolymerizable composition based (also called
photopolymer) violet or ultraviolet laser sensitive plates are very
attractive because of the high durability of photopolymer plates.
However, because of the extremely high sensitivity requirement of
the violet or ultraviolet laser sensitive plate, a commercially
viable violet or ultraviolet laser sensitive photopolymer plate can
not be achieved by simple addition of a laser absorbing sensitizer
into a conventional photopolymer plate but will require certain
specific photopolymerizable composition. The selection of the
monomers is crucial in achieving a commercially viable violet or
ultraviolet laser sensitive photopolymer plate.
[0008] U.S. Pat. No. 6,689,537 (Urano et al) describes some
specific compositions for violet photopolymer plate, wherein the
photosensitive layer comprises multifunctional (with 3 or more
functional groups) urethane acrylate monomers, difunctional
non-urethane acrylate monomers and a polymeric binder, and the
weight ratio of the multifunctional monomers to the polymeric
binders is less than 0.75.
[0009] U.S. Pat. No. 6,423,471 (Sorori et al) describes some
specific compositions for violet photopolymer plate, wherein the
photosensitive layer comprises a monomer and a polymeric binder at
a weight ratio of 0.75.
[0010] U.S. Pat. No. 6,749,995 (Matsumura) describes some specific
compositions for violet photopolymer plate, wherein the
photosensitive layer comprises polyfunctional urethane acrylate
monomers, trifunctionality non-urethane acrylate monomer and
polymeric binder; the weight ratio of the multifunctional monomers
to the polymeric binders is 1.0, and the weight ratio of the
polyfunctional urethane acrylate monomer to the polymeric binder is
0.25.
[0011] U.S. Pat. App. Pub. No. 2004/0157153 (Takamuki) describes
some specific compositions for violet photopolymer plate, wherein
the photosensitive layer comprises a monofunctional acrylate
monomer, a difunctional methacrylate monomer, a multifunctional
urethane (meth)acrylate monomer, and a polymeric binder; the weight
ratio of the monomers to the polymeric binder is 1.125 and the
weight ratio of the multifunctional urethane monomer to the
polymeric binder is 0.625.
[0012] U.S. Pat. App. Pub. No. 2003/0186165 (Gries et al) describes
some specific compositions for violet photopolymer plate, wherein
the photosensitive layer comprises difunctional (meth)acrylate
monomer and a polymeric binder at a weight ratio of about 1.6 to
2.4. While photosensitive layers having a trifunctional
non-urethane monomer and a polymeric binder at a weight ratio of
about 1.63 or having a penta functional non-urethane acrylate
monomer and a polymeric binder at a weight ratio of about 1.50 are
also described in the patent application as comparative examples,
such photosensitive layers are reported in the same patent
application to give no hardening upon exposure to the violet
laser.
[0013] While multifunctional monomers and higher content of the
total monomers in an aqueous alkaline developable violet plate are
described in the patents, there is no teaching of the weight ratio
of the multifunctional monomers to the polymeric binders of higher
than 1.7, or of the weight ratio of the multifunctional urethane
monomers to the polymeric binders of larger than 0.8. Apparently,
higher content of the multifunctional monomer might be thought to
cause difficulty in development with aqueous alkaline developer,
since multifunctional monomers are generally larger in size and
less soluble or dispersible in aqueous developer than
monofunctional or difunctional monomers.
[0014] The inventor has found, surprisingly, violet or ultraviolet
laser sensitive lithographic printing plate having, between a
hydrophilic substrate and a water soluble or dispersible overcoat,
a photosensitive layer comprising multifunctional (meth)acrylate
monomers and polymeric binders at a weight ratio of at least 1.8 or
comprising multifunctional urethane (meth)acrylate monomers and
polymeric binders at a weight ratio of at least 0.9, can be
developed with an aqueous alkaline developer and give significantly
better photospeed and press durability than plate with lower
monomer-to-polymer weight ratio or with lower monomer
functionality. In addition, combination of multifunctional urethane
(meth)acrylate monomer and multifunctional non-urethane monomer in
the photosensitive layer can give excellent photospeed and press
durability as well as developability.
SUMMARY OF THE INVENTION
[0015] According to the present invention, there has been provided
a method of lithographically printing images on a receiving medium,
comprising in order: [0016] (a) providing a lithographic printing
plate comprising (i) a hydrophilic substrate, (ii) an oleophilic
photosensitive layer comprising an alkaline soluble polymeric
binder, a (meth)acrylate monomer having at least 3 (meth)acrylate
groups, a free radical initiator, and a sensitizing dye, and (iii)
a water soluble or dispersible overcoat; wherein the weight ratio
of the monomers having at least 3 (meth)acrylate groups to the
alkaline soluble polymeric binders is at least 1.8; [0017] (b)
exposing said plate with a laser having a wavelength of from 250 to
430 nm at a dosage of less than 300 .mu.J/cm.sup.2 according to
digital imaging information to cause hardening of the
photosensitive layer in the exposed areas; and [0018] (c)
contacting said exposed plate with an aqueous alkaline developer
having a pH of from 9.0 to 13.5 to remove the non-exposed areas of
the photosensitive layer.
[0019] According to another aspect of the present invention, there
has been provided a method of lithographically printing images on a
receiving medium, comprising in order: [0020] (a) providing a
lithographic printing plate comprising (i) a hydrophilic substrate,
(ii) an oleophilic photosensitive layer comprising a polymeric
binder, a urethane (meth)acrylate monomer having at least 4
(meth)acrylate groups, a free radical initiator, and a sensitizing
dye, and (iii) a water soluble or dispersible overcoat; wherein the
weight ratio of said urethane monomers to the polymeric binders is
at least 0.9; [0021] (b) exposing said plate with a laser having a
wavelength of from 250 to 430 nm at a dosage of less than 300
.mu.J/cm.sup.2 according to digital imaging information to cause
hardening of the photosensitive layer in the exposed areas; and
[0022] (c) contacting said exposed plate with an aqueous alkaline
developer having a pH of 9.0 to 13.5 to remove the non-exposed
areas of the photosensitive layer.
[0023] According to yet another aspect of the present invention,
there has been provided a method of lithographically printing
images on a receiving medium, comprising in order: [0024] (a)
providing a lithographic printing plate comprising (i) a
hydrophilic substrate, (ii) an oleophilic photosensitive layer
comprising a polymeric binder, a urethane (meth)acrylate monomer
having at least 4 (meth)acrylate groups, a non-urethane
(meth)acrylate monomer having at least 4 (meth)acrylate groups, a
free radical initiator, and a sensitizing dye, and (iii) a water
soluble or dispersible overcoat; [0025] (b) exposing said plate
with a laser having a wavelength of from 250 to 430 nm at a dosage
of less than 300 .mu.J/cm.sup.2 according to digital imaging
information to cause hardening of the photosensitive layer in the
exposed areas; and [0026] (c) contacting said exposed plate with an
aqueous developer or with ink and/or fountain solution to remove
the non-exposed areas of the photosensitive layer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The substrate employed in the lithographic printing plates
of this invention can be any support that provides a hydrophilic
surface. Such a support may be a metal sheet, a polymer film, or a
coated paper. Aluminum (including aluminum alloys) sheet is a
preferred support. Particularly preferred is an aluminum support
that has been grained and anodized, with or without further
hydrophilic treatment. Surface graining can be achieved by
mechanical graining or brushing, chemical etching, and/or AC
electrochemical graining. The grained aluminum is typically treated
with a basic or acid solution to remove the smut (called desmut
treatment), and then subjected to an electrochemical anodization
process utilizing an acid such as sulfuric acid and/or phosphoric
acid. The anodization process serves to form an anodic oxide layer
and is preferably controlled to create a layer of at least 0.1
g/m.sup.2. The desmut is typically controlled to achieve a
reflection optical density of preferably from 0.10 to 1.0, more
preferably from 0.20 to 0.70, and most preferably from 0.30 to 0.50
for the final substrate.
[0028] The electrochemically grained, anodized aluminum can be
further treated with a hydrophilic material to form a hydrophilic
barrier layer. Suitable hydrophilic materials include metal
silicate such as sodium silicate, phosphate fluoride (formed from a
solution containing sodium dihydrogen phosphate and sodium
fluoride, called phosphate fluoride solution), phosphoric acid, and
hydrophilic polymer such as polyvinyl phosphonic acid,
polyacrylamide, polyacrylic acid, polybasic organic acid,
copolymers of vinyl phosphonic acid and acrylamide. Polyvinyl
phosphonic acid and its copolymers are preferred polymers. The
hydrophilic material can be formed on the aluminum surface by
thermal or electrochemical method. By thermal method, the grained
and anodized aluminum passes through or is immersed for a certain
time in a solution containing the hydrophilic material at a certain
temperature including elevated and room temperature. By
electrochemical method, a DC or AC electricity is applied to the
aluminum while passing through or immersed in the solution
containing the hydrophilic material. Processes for forming a
hydrophilic barrier layer on aluminum in lithographic printing
plate application are well known in the art, and examples can be
found in U.S. Pat. Nos. 2,714,066, 4,153,461, 4,399,021, 5,368,974,
and 6,555,205.
[0029] According to the first aspect of the current invention, the
photosensitive layer comprises an alkaline soluble polymeric
binder, a (meth)acrylate monomer having at least 3 (meth)acrylate
groups, a free radical initiator, and a sensitizing dye. A hydrogen
donor compound is preferably added. The weight ratio of the
monomers having at least 3 (meth)acrylate groups to the alkaline
soluble polymeric binders is at least 1.8, preferably from 2.0 to
6.0, more preferably from 2.3 to 5.0, and most preferably from 2.6
to 4.0. The monomer preferably has at least 4 (meth)acrylate
groups, more preferably 5 (meth)acrylate groups, and most
preferably 6 (meth)acrylate groups. A non-alkaline soluble
polymeric binder can be added, preferably at an amount less than
the alkaline soluble polymeric binder.
[0030] According to the second aspect of the current invention, the
photosensitive layer comprises a polymeric binder, a urethane
(meth)acrylate monomer having at least 4 (meth)acrylate groups, a
free radical initiator, and a sensitizing dye. A hydrogen donor
compound is preferably added. The weight ratio for said urethane
monomers to the polymeric binders is at least 0.9, preferably from
1.2 to 6.0, more preferably from 1.8 to 5.0, and most preferably
from 2.4 to 4.0. The monomer preferably has at least 5
(meth)acrylate groups, and more preferably at least 6
(meth)acrylate groups. A non-urethane (meth)acrylate monomer can be
added. The polymeric binder is preferably alkaline soluble.
[0031] According to the third aspect of the current invention, the
photosensitive layer of this invention comprises a polymeric
binder, a urethane (meth)acrylate monomer having at least 4
(meth)acrylate groups, a non-urethane (meth)acrylate monomer having
at least 4 (meth)acrylate groups, a free radical initiator, and a
sensitizing dye. A hydrogen donor compound is preferably added. The
weight ratio of the urethane (meth)acrylate monomers to the
non-urethane (meth)acrylate monomers is preferably from 0.10 to
10.0, more preferably from 0.20 to 5.0, and most preferably from
0.30 to 3.0. The weight ratio of the monomers having at least 4
(meth)acrylate groups to the polymeric binders is at least 0.5,
preferably from 1.0 to 6.0, more preferably from 1.5 to 5.0, and
most preferably from 2.0 to 4.0. The urethane monomer preferably
has at least 5 (meth)acrylate groups, and more preferably at least
6 (meth)acrylate groups.
[0032] In the photosensitive layers of this invention (including
last three paragraphs), a preferred initiator is a titanocene or
hexaarylbiimidazole compound, more preferably a hexaarylbiimidazole
compound; and a preferred sensitizing dye is a
dialkylaminobenzophenone compound, more preferably a
4,4'-bis(dialkylamino)benzophenone compound. Preferred hydrogen
donor compounds are 2-mercaptobenzoxazole, 2-mercaptobenzimidazole,
2-mercaptobenzothiazole, 3-mercapto-1,2,4-triazole, N,N-dialkyl
benzoic alkyl ester, N-phenylglycine ethyl ester, and
N-phenylglycine benzyl ester. Various additives, such as
surfactant, colorant (dye or pigment), exposure indicating dye
(such as leuco crystal violet, leucomalachite green, azobenzene,
4-phenylazodiphenylamine, and methylene blue dyes), and free
radical stabilizer (such as methoxyhydroquinone) can be added.
Monomers with lower (meth)acrylate functionality can be added.
[0033] In a preferred embodiment for the violet or ultraviolet
laser sensitive lithographic plates of this invention, the
photosensitive layer comprises a polymeric binder, a monomer having
at least 3 (meth)acrylate group, a hexaarylbiimidazole or
titanocene compound, a dialkylaminobenzophenone compound, and a
hydrogen donor compound. The monomer-to-polymer weight ratio is at
least 1.8, preferably from 2.0 to 6.0, more preferably from 2.3 to
5.0, and most preferably from 2.6 to 4.0. A hexaarylbiimidazole
compound is preferred among hexaarylbiimidazole and titanocene
compounds. A preferred dialkylaminobenzophenone compound is a
4,4'-bis(dialkylamino)benzophenone compound.
[0034] In another preferred embodiment for the violet or
ultraviolet laser sensitive lithographic plates of this invention,
the photosensitive layer comprises a polymeric binder, a urethane
monomer having at least 4 (meth)acrylate group, a
hexaarylbiimidazole or titanocene compound, a
dialkylaminobenzophenone compound, and a hydrogen donor compound.
The monomer-to-polymer weight ratio is at least 0.9, preferably
from 1.2 to 6.0, more preferably from 1.8 to 5.0, and most
preferably from 2.4 to 4.0. A hexaarylbiimidazole compound is
preferred among hexaarylbiimidazole and titanocene compounds. A
preferred dialkylaminobenzophenone compound is a
4,4'-bis(dialkylamino)benzophenone compound. A non-urethane
(meth)acrylate monomer can be added.
[0035] In yet another preferred embodiment for the violet or
ultraviolet laser sensitive lithographic plates of this invention,
the photosensitive layer comprises a polymeric binder, a urethane
monomer having at least 4 (meth)acrylate group, a non-urethane
monomer having at least 4 (meth)acrylate groups, a
hexaarylbiimidazole or titanocene compound, a
dialkylaminobenzophenone compound, and a hydrogen donor compound.
The weight ratio of the urethane (meth)acrylate monomer to the
non-urethane (meth)acrylate monomer is preferably from 0.10 to
10.0, more preferably from 0.20 to 5.0, and most preferably from
0.30 to 3.0. The weight ratio for said monomers to the polymeric
binders is preferably at least 0.5, more preferably from 1.0 to
6.0, even more preferably from 1.5 to 5.0, and most preferably from
2.0 to 4.0. A hexaarylbiimidazole compound is preferred among
hexaarylbiimidazole and titanocene compounds. A preferred
dialkylaminobenzophenone compound is a
4,4'-bis(dialkylamino)benzophenone compound.
[0036] In this patent, the term monomer includes both monomer and
oligomer, and the term (meth)acrylate includes both acrylate and
methacrylate (A monomer means a monomer or an oligomer, and a
(meth)acrylate monomer means an acrylate monomer, a methacrylate
monomer, or a monomer with both acrylate and methacrylate groups.).
The term monomer to polymer weight ratio means the weight ratio of
all the specific monomers to all the polymeric binders (which are
solid film-forming polymers); liquid polymer such as nonionic
surfactant is not considered polymeric binder and is not included
in the monomer to polymer weight ratio calculation. The term
"comprises a . . . " means "comprises at least one . . . "; for
example, the term "comprising a monomer" means "comprising at least
one monomer."
[0037] The photosensitive layer of this invention can be solid or
semisolid at 25.degree. C. In one embodiment, semisolid
photosensitive layer is preferably used to achieve fast photospeed,
and/or developability with ink and/or fountain solution or with an
aqueous developer. Here the term semisolid photosensitive layer is
defined as a photosensitive layer which, when coated on a flat and
smooth surface at a thickness of at least 1 micron, is able to form
fingerprints when pressed with a finger at a force (or weight) of 2
kg and is tacky to touch by fingers at 25.degree. C.
[0038] Polymeric binder for the photosensitive layer of this
invention can be any solid film-forming polymer. The polymer may or
may not have (meth)acrylate groups or other ethylenic groups (such
as allyl groups). Examples of suitable polymers include
(meth)acrylic polymers and copolymers (such as
polybutylmethacrylate, polyethylmethacrylate,
polymethylmethacrylate, polymethylacrylate,
butylmethacrylate/methylmethacrylate copolymer,
methylmethacrylate/methylmethacrylic acid copolymer,
polyallylmethacrylate, and allylmethacrylate/methacrylic acid
copolymer), polyvinyl acetate, polyvinyl butyrate, polyvinyl
chloride, styrene/acrylonitrile copolymer, styrene/maleic anhydride
copolymer and its partial ester, nitrocellulose, cellulose acetate
butyrate, cellulose acetate propionate, vinyl chloride/vinyl
acetate copolymer, butadiene/acrylonitrile copolymer, and
polyurethane binder. The alkaline soluble polymeric binder suitable
for the alkaline developable photosensitive layer of this invention
can be any polymeric binder that is soluble in an aqueous alkaline
solution having a pH of from 9.0 to 13.5, preferably from 10.0 to
13.0. Preferred alkaline soluble polymers are polymers with
carboxylic acid groups. The acid number is preferably from 20 to
300, more preferably from 40 to 200, and most preferably from 60 to
150 mg KOH/g polymer. (The acid number is defined as the amount in
mg of KOH required to neutralize 1 g of the polymer.) The polymeric
binder suitable for the photosensitive layer of this invention has
a weight average molecular weight of at least 5,000, preferably
from 10,000 to 1,000,000, more preferably from 20,000 to 500,000,
and most preferably from 50,000 to 200,000 Dalton.
[0039] Suitable free-radical polymerizable monomers (including
oligomers) include, for example, multifunctional acrylate monomers
or oligomers, such as (meth)acrylate esters of ethylene glycol,
trimethylolpropane, pentaerythritol, ethoxylated ethylene glycol
and ethoxylated trimethylolpropane, multifunctional urethanated
(meth)acrylate, and epoxylated (meth)acrylate; and oligomeric amine
diacrylates. The monomers can be urethane (meth)acrylate, or
non-urethane (meth)acrylate. Combination of both urethane
(meth)acrylate and non-urethane (meth)acrylate monomers can be
used. The monomers, preferably has at least 3 (meth)acrylate
groups, more preferably at least 4 (meth)acrylate groups, even more
preferably at least 5 (meth)acrylate groups, and most preferably at
least 6 (meth)acrylate groups. However, monofunctional or
difunctional (meth)acrylate monomer can be added into the
photosensitive layer having multifunctional (meth)acrylate
monomers; the total amount of such monofunctional or difunctional
monomers is preferably less than 50% by weight of the total
monomers, more preferably less than 30%, and most preferably less
than 10%. Acrylate monomer is preferred over methacrylate monomer
because of the faster photospeed of acrylate group over
methacrylate group. The monomer has a molecular weight of less than
4,000, preferably from 100 to 3,000, more preferably from 200 to
2,000, and most preferably from 300 to 1,500 Dalton.
[0040] Urethane (meth)acrylate monomers include any compounds
having at least one urethane linkage (--NHCOO--) and at least one
(meth)acrylate group. Preferred urethane (metha)acrylate monomers
are those with at least 3 (meth)acrylate groups, more preferably at
least 4 (meth)acrylate groups, even more preferably at least 5
(meth)acrylate groups, and most preferably at least 6
(meth)acrylate groups. Urethane (meth)acrylate monomer is usually
formed by reacting a compound having at least one isocyanate group
with a (meth)acrylate compound having a hydroxy group. Urethane
monomer with 2 or more (meth)acrylate groups are usually formed
from a compound having one or more isocyanate groups and a
(meth)acrylate compound having a hydroxy group and one or more
(meth)acrylate groups. For example, a tetrafunctional urethane
(meth)acrylate monomer can be formed from a compound having one
hydroxy group and 2 (meth)acrylate groups with a bifunctional
isocyanate compound. Suitable isocyanate compounds include, for
example, aromatic diisocyanate such as p-phenylene diisocyanate,
2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
4,4'-diphenylmethane diisocyanate, naphthalene-1,5-diisocyanate and
tolydine diisocyanate; aliphatic diisocyanale such as hexamethylene
diisocyanate, lysinemethyl ester diisocyanate,
2,4,4-trimethylhexamethylene diisocyanate and dimer acid
diisocyanate; alicyclic diisocyanate such as isophorone
diisocyanate, and 4,4'-methylenebis(cyclohexylisocyanate),
aliphatic diisocyanate having an aromatic ring, such as xylylene
diisocyanate; triisocyanate such as lysine ester triisocyanate,
1,6,11-undecane triisocyanate,
1,8-diisocyanate-4-isocyanatemethyloctane, 1,3,6-hexamethylene
triisocyanate, bicycloheptane triisocyanate, tris(isocyanate
phenylmethane) and tris(isocyanatephenyl)thiophosphate; and
polyisocyanate formed from condensation of three or more
diisocyanate compounds such as 2,4-tolylene diisocyanate
isocyanurate trimer, 2,4-tolylene diisocyanate-trimethylolpropane
adduct, 1,6-hexanediisocyante isocyanurate trimer. Suitable
(meth)acrylate compounds with one hydroxy group include
pentaerythritol tri(meth)acrylate, dipentaerythritol
penta(meth)acrylate, ditrimethylolpropane tri(meth)acrylate and
pentaerythritol di(meth)acrylate monostearate. Various urethane
(meth)acrylate monomers are described in U.S. Pat. No. 6,232,038
and U.S. Pat. Pub. No. 2002/0018962, and can be used as the
urethane (meth)acrylate monomers of this instant invention. Among
the urethane (meth)acrylate monomers, urethane acrylate monomer is
preferred. Either aromatic urethane (meth)acrylate monomer (which
contains at least one aromatic group in the molecule) or aliphatic
urethane (meth)acrylate monomer (which does not contain any
aromatic group in the molecule) or both can be used in a
photosensitive layer of this invention.
[0041] Suitable non-urethane (meth)acrylate monomers can be any
(meth)acrylate monomers without urethane linkage (--NHCOO--) in the
molecule. Suitable non-urethane (meth)acrylate monomers with 3 or
more (meth)acrylate groups include any non-urethane (meth)acrylate
monomer with 3 or more (meth)acrylate groups, such as
trimethylolpropane triacrylate, pentaerythritol
tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate,
dipentaerythritol hexa(meth)acrylate, di(trimethylolpropane)
tetra(meth)acrylate. Among the non-urethane (meth)acrylate
monomers, non-urethane acrylate monomer is preferred.
[0042] The free-radical initiators useful in this instant invention
can be any compound capable of generating free radicals to cause
the polymerization of the (meth)acrylate monomer in the presence of
a violet or ultraviolet laser sensitizing dye upon exposure to a
violet or ultraviolet laser at a dosage of from 1 to 300
.mu.J/cm.sup.2. Suitable free-radical initiators include, for
example, onium salts such as diaryliodonium hexafluoroantimonate,
diaryliodonium hexafluorophosphate, diaryliodonium triflate,
(4-(2-hydroxytetradecyloxy)phenyl)phenyliodonium
hexafluoroantimonate, (4-octoxyphenyl)phenyliodonium
hexafluoroantimonate, bis(4-t-butylphenyl)iodonium
hexafluorophosphate, triarylsulfonium hexafluorophosphate,
triarylsulfonium p-toluenesulfonate, (3-phenylpropan-2-onyl)triaryl
phosphonium hexafluoroantimonate and N-ethoxy(2-methyl)pyridinium
hexafluorophosphate, and the onium salts as described in U.S. Pat.
Nos. 5,955,238, 6,037,098 and 5,629,354; borate salts such as
tetrabutylammonium triphenyl(n-butyl)borate, tetraethylammonium
triphenyl(n-butyl)borate, diphenyliodonium tetraphenylborate, and
triphenylsulfonium triphenyl(n-butyl)borate, and the borate salts
as described in U.S. Pat. Nos. 6,232,038 and 6,218,076; haloalkyl
substituted s-triazines such as
2,4-bis(trichloromethyl)-6-(p-methoxy-styryl)-s-triazine,
2,4-bis(trichloromethyl)-6-(4-methoxy-naphth-1-yl)-s-triazine,
2,4-bis(trichloromethyl)-6-piperonyl-s-triazine, and
2,4-bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen-1-yl]-s-triazine,
and the s-triazines as described in U.S. Pat. Nos. 5,955,238,
6,037,098, 6,010,824, and 5,629,354; hexaarylbiimidazole compounds
such as
2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-biimidazole,
2,2'-bis(2-ethoxyphenyl)-4,4',5,5-tetraphenyl-1,1'-biimidazole, and
2-(1-naphthyl)-4,5-diphenyl-1,2'-biimidazole; and titanocene
compounds such as
bis(.eta..sup.9-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-py-
rrol-1-yl)phenyl)titanium. The hexaarylbiimidazole compounds and
titanocene compounds are preferred initiators, and
hexaarylbiimidazole compounds are more preferred. One or more
initiators can be added in a photosensitive layer. The initiator is
added in the photosensitive layer preferably at 0.5 to 40% by
weight of the photosensitive layer, more preferably at 2 to 30%,
and most preferably at 5 to 20%.
[0043] The hexaarylbiimidazole compound is a biimidazole compound
having three aryl groups on each of the two imidazole moieties.
Examples of hexaarylbiimidazole compounds include
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenylbiimidazole,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(p-methoxyphenyl)biimidazole,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(p-methylphenyl)biimidazole,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(p-ethoxycarbonylphenyl)biimidazo-
le,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(p-fluorophenyl)biimidazole,
2,2'-bis(o-bromophenyl)-4,4',5,5'-tetra(p-iodophenyl)biimidazole,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(p-chloronaphthyl)biimidazole,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(p-chlorophenyl)biimidazole,
2,2'-bis(o-bromophenyl)-4,4',5,5'-tetra(p-chlor-p-methoxyphenyl)biimidazo-
le,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(o,p-dichlorophenyl)biimidazol-
e,
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetra(o,p-dibromophenyl)biimidazole,
2,2'-bis(o-bromophenyl)-4,4',5,5'-tetra(o,p-dichlorophenyl)biimidazole,
or
2,2'-bis(o,p-dichlorophenyl)-4,4',5,5'-tetra(o,p-dichlorophenyl)biimid-
azole. Of these compounds, preferred is a hexaphenylbiimidazole
compound, particularly preferred is one which has the
ortho-positions of the benzene rings at the 2,2'-positions on the
imidazole rings replaced % with halogen, more preferred is one
having benzene rings at the 4,4',5,5'-positions on the imidazole
rings not replaced, replaced with halogen or replaced with
alkoxycarbonyl, and most preferred is a combination of embodiments
of the two hexaphenylbiimidazole compounds.
[0044] Suitable titanocene compounds include titanium compounds
having a dicyclopentadienyl structure and a biphenyl structure,
such as dicyclopentadienyl titanium dichloride, dicyclopentadienyl
titanium bisphenyl, dicyclopentadienyltitanium
bis(2,4-difluorophenyl), dicyclopentadienyl titanium
bis(2,6-difluorophenyl), dicyclopentadienyl titanium
bis(2,4,6-trifluorophenyl), dicyclopentadienyl titanium
bis(2,3,5,6-tetrafluorophenyl), dicyclopentadienyl titanium
bis(2,3,4,5,6-pentafluorophenyl),
di(methylcyclopentadienyl)titanium bis(2,6-difluorophenyl),
di(methylcyclopentadienyl)titanium
bis(2,3,4,5,6-pentafluorophenyl), and dicyclopentadienyl titanium
bis[2,6-difluoro-3-(1-pyrrolyl)phenyl]. A preferred compound is one
having the o-positions of the biphenyl ring replaced with a halogen
atom.
[0045] Violet or ultraviolet laser sensitizing dyes useful in the
violet laser sensitive photosensitive layer of this invention
include any dyes capable of absorbing the violet or ultraviolet
laser (about 250 to 430 nm) at a dosage of less than 300
.mu.J/cm.sup.2 to activate the free radical initiator to cause
polymerization of the monomers. Suitable violet or ultraviolet
laser sensitive dyes include, for example, cyanine dyes (including
polymethine dyes); chromanone compounds such as
4-diethylaminobenzilidene chromanone; dialkylaminobenzene compounds
such as ethyl 4-dimethylaminobenzoate and dialkylaminobenzene;
dialkylaminobenzophenone compounds such as
4,4'-bis(dimethylamino)benzophenone,
4,4'-bis(diethylamino)benzophenone,
2-(p-dimethylaminophenyl)benzooxazole,
2-(p-diethylaminophenyl)benzooxazole,
2-(p-dimethylaminophenyl)benzo[4,5]benzooxazole,
2-(p-dimethylaminophenyl)benzo[6,7]benzooxazole,
2,5-bis(p-diethylaminophenyl)1,3,4-oxazole,
2-(p-dimethylaminophenyl)benzothiazole,
2-(p-diethylaminophenyl)benzothiazole,
2-(p-dimethylaminophenyl)benzimidazole,
2-(p-diethylaminophenyl)benzimidazole,
2,5-bis(p-diethylaminophenyl)1,3,4-thiadiazole,
(p-dimethylaminophenyl)pyridine, (p-diethylaminophenyl)pyridine,
2-(p-dimethylaminophenyl)quinoline,
2-(p-diethylaminophenyl)quinoline,
2-(p-dimethylaminophenyl)pyrimidine or
2-(p-diethylaminophenyl)pyrimidine; unsaturated cyclopentanone
compounds such as
2,5-bis{[4-(diethylamino)phenyl]methylene}-(2E,5E)-(9Cl)-cyclopen-
tanone and bis(methylindolenyl)cyclopentanone; coumarin compounds
such as 3-benzoyl-7-methoxy coumarin and 7-methoxy coumarin; and
thioxanthene compounds such as 2-isopropylthioxanthenone.
Dialkylaminobenzene compounds (including
bis(dialkylamino)benzophenone compounds) are particularly suitable
for ultraviolet laser sensitive plate.
Bis(dialkylamino)benzophenone compounds are particularly suitable
for violet laser sensitive plate. The sensitizing dyes as described
in U.S. Pat. Nos. 5,422,204 and 6,689,537, and U.S. Pat. App. Pub.
No. 2003/0186165 can be used for the photosensitive layer of this
invention. The violet laser sensitizing dye is added in the
photosensitive layer preferably at 0.1 to 20% by weight of the
photosensitive layer, more preferably 0.5 to 15%, and most
preferably 1 to 10%.
[0046] The photosensitive composition of the present invention
preferably contains one or more hydrogen donor compound as a
polymerization accelerator. Examples of the hydrogen donor compound
include compounds having a mercapto group such as
2-mercaptobenzothiazole, 2-mercaptobenzimidazole,
2-mercaptobenzoxazole and 3-mercapto-1,2,4-triazole, N,N-dialkyl
benzoic alkyl ester, N-aryl-.alpha.-amino acids, their salts and
esters such as N-phenylglycine, salts of N-phenylglycine, and alkyl
esters of N-phenylglycine such as N-phenylglycine ethyl ester and
N-phenylglycine benzyl ester.
[0047] The photosensitive layer developable with an aqueous
alkaline developer must be soluble or dispersible in an aqueous
developer in the non-hardened areas. The photosensitive layer
preferably comprises at least one alkaline soluble polymer.
[0048] The photosensitive layer suitable for on-press developable
plate of this invention must be soluble or dispersible in ink
and/or fountain solution and can be developed off on a lithographic
press with ink and/or fountain solution.
[0049] Various surfactants may be added into the photosensitive
layer to allow or enhance the on-press developability with ink
and/or fountain solution or developability with an aqueous
solution. Both polymeric and small molecule surfactants can be
used. However, it is preferred that the surfactant has low or no
volatility so that it will not evaporate from the photosensitive
layer of the plate during storage and handling. Nonionic
surfactants are preferred. The nonionic surfactant used in this
invention should have sufficient portion of hydrophilic segments
(or groups) and sufficient portion of oleophilic segments (or
groups), so that it is at least partially soluble in water (>1 g
surfactant soluble in 100 g water) and at least partially soluble
in organic phase (>1 g surfactant soluble in 100 g
photosensitive layer). Preferred nonionic surfactants are polymers
and oligomers containing one or more polyether (such as
polyethylene glycol, polypropylene glycol, and copolymer of
ethylene glycol and propylene glycol) segments. Examples of
preferred nonionic surfactants are block copolymers of propylene
glycol and ethylene glycol (also called block copolymer of
propylene oxide and ethylene oxide); ethoxylated or propoxylated
acrylate oligomers; and polyethoxylated alkylphenols and
polyethoxylated fatty alcohols. The nonionic surfactant is
preferably added at from 0.1 to 30% by weight of the photosensitive
layer, more preferably from 0.5 to 20%, and most preferably from 1
to 15%.
[0050] For plates with rough and/or porous surface capable of
mechanical interlocking with a coating deposited thereon, a thin
water soluble interlayer may be deposited between the substrate and
the photosensitive layer. Here the substrate surface is rough
and/or porous enough and the interlayer is thin enough to allow
bonding between the photosensitive layer and the substrate through
mechanical interlocking. Such a plate configuration is described in
U.S. Pat. No. 6,014,929, the entire disclosure of which is hereby
incorporated by reference. Preferred releasable interlayer
comprises a water-soluble polymer. Polyvinyl alcohol (including
various water-soluble derivatives of polyvinyl alcohol) is the
preferred water-soluble polymer. Usually pure water-soluble polymer
is coated. However, one or more surfactant and other additives may
be added. The water-soluble polymer is generally coated from an
aqueous solution with water as the only solvent. A water-soluble
organic solvent, preferably an alcohol such as ethanol or
isopropanol, can be added into the water-soluble polymer aqueous
coating solution to improve the coatability. The alcohol is
preferably added at less than 40% by weight of the solution, more
preferably at less than 20%, and most preferably at less than 10%.
The releasable interlayer preferably has an average coverage of 1
to 200 mg/m.sup.2, more preferably 2 to 100 mg/m.sup.2, and most
preferably 4 to 40 mg/m.sup.2. The substrate preferably has an
average surface roughness Ra of 0.2 to 2.0 microns, and more
preferably 0.4 to 1.0 microns.
[0051] The water soluble or dispersible overcoat preferably
comprises a water-soluble polymer, such as polyvinyl alcohol
(including various water-soluble derivatives of polyvinyl alcohol).
Combination of two or more water-soluble polymers (such as a
combination of polyvinyl alcohol and polyvinylpyrrolidone) may also
be used. Polyvinyl alcohol is a preferred water-soluble polymer.
Various additives, such as surfactant, wetting agent, defoamer,
leveling agent and dispersing agent, can be added into the overcoat
formulation to facilitate, for example, the coating or development
process. Examples of surfactants useful in the overcoat of this
invention include polyethylene glycol, polypropylene glycol, and
copolymer of ethylene glycol and propylene glycol, polysiloxane
surfactants, perfluorocarbon surfactants, alkylphenyl ethylene
oxide condensate, sodium dioctylsulfosuccinate, sodium
dodecylbenzenesulfonate, and ammonium laurylsulfate. Various
organic or inorganic emulsion or dispersion may be added into the
overcoat to, for example, reduce the tackiness or moisture
sensitivity of the plate. For plate developable with a regular
liquid developer, the overcoat preferably has a coverage of from
0.1 to 5.0 g/m.sup.2, more preferably from 0.5 to 3.0 g/m.sup.2,
and most preferably from 1.0 to 2.0 g/m.sup.2. For on-process
developable plate, the overcoat preferably has a coverage of from
0.001 to 3.0 g/m.sup.2, more preferably from 0.01 to 1.0 g/m.sup.2,
and most preferably from 0.05 to 0.5 g/m.sup.2.
[0052] For conventional wet press, usually fountain solution is
applied (to contact the plate) first, followed by contacting with
ink roller. For press with integrated inking/dampening system, the
ink and fountain solution are emulsified by various press rollers
before being transferred to the plate as emulsion of ink and
fountain solution. However, in this invention, the ink and fountain
solution may be applied at any combination or sequence, as needed
for the plate. There is no particular limitation. The recently
introduced single fluid ink that can be used for printing wet
lithographic plate without the use of fountain solution, as
described in for example U.S. Pat. No. 6,140,392, can also be used
for the on-press development and printing of the on-press
developable plate as well as for the printing of the aqueous
developable plate of this invention.
[0053] The alkaline aqueous developer is an aqueous solution
comprising 60-99% by weight of water, and 0.2 to 20%, preferably
0.5 to 10%, by weight of alkaline compound and having a pH of at
least 9.0, preferably from 9.5 to 13.5, more preferably from 10.0
to 13.0, and most preferably from 10.5 to 12.5. More than one
alkaline compound can be used. Suitable alkaline compounds include
inorganic alkaline compounds such as potassium silicate, sodium
silicate, potassium hydroxide, and sodium hydroxide, and organic
amine compounds such as triethylamine, diethylamine,
triethanolamine, and diethanolamine. One or more surfactants (ionic
or nonionic or both) are preferably added. Various additives such
as dye or pigment, defoamer, and hydrophilization agent can be
added. One or more organic solvents, preferably water soluble
organic solvents, can be added at 0.1 to 20% by weight of the
developer. Preferably, no organic solvent is added.
[0054] The non-alkaline aqueous developer is an aqueous solution
comprising 60-99% by weight of water and 0.5 to 40% by weight of an
alcohol solvent and having a pH of 3.0 to 8.9. The alcohol solvent
is defined as a water-soluble liquid organic compound having at
least one hydroxyl group. The alcohol solvent must be soluble or
capable of forming stable emulsion in water at the added
concentration. Liquid alkyl alcohol (including arylalky alcohol)
and its liquid derivatives are preferred alcohol solvents. Alcohol
solvents useful for the developer of this invention include, for
example, various liquid water-soluble alkyl alcohol, arylalkyl
alcohol, alkoxyalkyl alcohol, arylalkoxyalkyl alcohol, aroxyalkyl
alcohol, oxydialkanol, and alkyl lactate. Other functional group,
such as ester, ether, epoxy, or ethylenic group, may be attached to
the alkyl or aryl group. Examples of useful alcohol solvents are
benzyl alcohol, phenethyl alcohol, isopropyl alcohol, 1-propyl
alcohol, ethyl alcohol, butyl alcohol, ethyl lactate, propyl
lactate, butyl lactate, methoxyethanol, ethoxyethanol,
propoxyethanol, butoxyethanol, methoxypropanol, ethoxypropanol,
propoxypropanol, butoxypropanol, diethylene glycol
(2,2'-oxydiethanol), phenoxyethanol, and phenoxypropanol. For the
alcohols with isomers, all liquid isomers can be used. Benzyl
alcohol is a particularly useful alcohol solvent. Usually one
alcohol solvent is used in the developer. However, two or more
alcohol solvents can also be used in the same developer. The
alcohol solvent is added preferably at 1 to 30% by weight of the
developer and more preferably at 2 to 20%. The non-alkaline aqueous
developer preferably has a pH of 3.0 to 8.9, more preferably 5.0 to
8.5, most preferably 6.0 to 8.0. While a pH of close to neutral (pH
of about 7.0) is preferred, the pH may be slightly to moderately
basic or acidic due to addition of certain additives for improving,
for example, the hydrophilicity of the substrate. For example,
phosphoric acid or citric acid may be added to improve the
hydrophilicity of certain substrate; and small amount of
diethanolamine may be added to adjust the pH to slightly basic to
improve the hydrophilicity of certain substrate.
[0055] Various surfactants can be added into the developer to, for
example, help the wetting of the developer on the plate, improve
the developability, reduce solid residue in the developer, and
condition the bared substrate. Either ionic or nonionic
water-soluble surfactant or both can be used. Examples of useful
surfactants include polyethylene glycol, polypropylene glycol, and
copolymer of ethylene glycol and propylene glycol, polysiloxane
surfactants, ionic perfluorocarbon surfactants, nonionic
perfluorocarbon surfactants, sodium dioctylsulfosuccinate, sodium
dodecylbenzenesulfonate, sodium butylnaphthalenesulfate, sodium
alkylnaphthalenesulfate, sodium cumenesulfonate, and ammonium
laurylsulfate. The surfactant is preferably added at from 0.01 to
20% by weight of the developer, more preferably from 0.1 to 10%,
and most preferably from 1 to 5%. Various other additives, such as
defoamer, bactericide, dye, and substrate conditioner (such as gum
arabic, and maltodextrin), can be added. Certain salts, such as
sodium chloride, potassium phosphate and ammonium sulfite, may be
added to, for example, improve the hydrophilicity of the bared
substrate.
[0056] The laser exposed plate can be directly developed with an
aqueous solution or with ink and/or fountain solution.
Alternatively, the laser exposed plate can be overall heated to an
elevated temperature (such as from 50 to 200 oC for 1 to 600
seconds) to further harden the exposed areas before development.
Such a heating process is also called preheat. The plate can be
heated by any method that does not cause hardening of the
photosensitive layer in the non-exposed areas. Suitable heating
method include, for example, hot air, contacting with a heated
material such as a metal plate, or applying a radiation with a
wavelength of at least 550 nm such as an infrared radiation.
[0057] Violet or ultraviolet lasers useful for the imagewise
exposure of the lithographic printing plates of this invention
include any laser having a wavelength of from 250 to 430 nm.
Examples of such lasers include violet diode laser of about 405 nm,
ultraviolet laser of about 375 nm, and ultraviolet LEDs. Violet
laser diode is especially useful because of its small size and
relatively lower cost. Laser diodes are preferred ultraviolet
lasers. The exposure dosage is preferably less than to 300
.mu.J/cm.sup.2, more preferably from 1 to 200 .mu.J/cm.sup.2, and
most preferably from 5 to 100 .mu.J/cm.sup.2, depending on the
sensitivity of the photosensitive layer.
[0058] Laser imaging devices are currently widely available
commercially. Any device can be used which provides imagewise laser
exposure according to digital imaging information. Commonly used
imaging devices include flatbed imager, internal drum imager, and
external drum imager, all of which can be used for the imagewise
laser exposure in this invention.
[0059] The on-press developable plate is usually exposed on an
exposure device, and then mounted on press to develop with ink
and/or fountain solution and then print out regular printed sheets.
However, the plate can also be exposed on a printing press (such as
by mounting on the plate cylinder or sliding through a flatbed
imager mounted on the press), and the exposed plate can be directly
developed on press with ink and/or fountain solution and then print
out regular printed sheets. The ink and/or fountain
solution-solubilized or dispersed photosensitive layer and/or
overcoat can be mixed into the ink and/or the fountain solution on
the rollers, and/or can be transferred to the blanket and then the
receiving medium (such as paper). The fountain solution roller is
engaged (to the plate cylinder as for conventional inking system or
to the ink roller as for integrated inking system) for preferably 0
to 100 rotations, more preferably 1 to 50 rotations and most
preferably 5 to 20 rotations (of the plate cylinder), and the ink
roller is then engaged to the plate cylinder for preferably 0 to
100 rotations, more preferably 1 to 50 rotations and most
preferably 5 to 20 rotations before engaging the plate cylinder and
feeding the receiving medium (such as paper). Good quality prints
should be obtained preferably under 40 initial impressions, more
preferably under 20 impressions, and most preferably under 5
impressions. The plate may be rinsed or applied with an aqueous
solution, including water and fountain solution, to remove the
water soluble or dispersible overcoat and/or to dampen without
developing the plate, after imagewise exposure and before on-press
development with ink and/or fountain solution.
[0060] The laser exposure and development is preferably performed
under a safe light which does not have radiation below a certain
cutoff wavelength (such as an orange light with a cutoff wavelength
of 550 nm or a yellow light with a cutoff wavelength of 450 nm), or
in a light-tight box. The developed plate can be handled under any
light, including white light. Alternatively, the laser exposed
plate can be treated with a deactivating agent to deactivate the
photosensitive layer so that the plate can be handled under white
light before and during development, as described in U.S. patent
application Ser. No. 11/266,817, the entire disclosure of which is
hereby incorporated by reference.
[0061] The laser exposed plate can be directly developed with an
aqueous solution or with ink and/or fountain solution.
Alternatively, the laser exposed plate can be rinsed with water or
an aqueous solution to remove the overcoat without developing the
photosensitive layer before development.
[0062] The laser exposed on-press developable plate (with or
without preheat) can be applied with a deactivating agent to
deactivate the photosensitive layer before development, preventing
any hardening of the photosensitive layer in the non-exposed areas
and allowing handling of the plate under regular office light
before and during on-press development. Such a deactivating agent
is described in U.S. patent application Ser. No. 11/266,817, the
entire disclosure of which is hereby incorporated by reference.
[0063] The invention is further illustrated by the following
non-limiting examples of its practice.
Examples 1-10
[0064] Ten sheets of electrochemically grained, anodized and
polyvinylphosphonic acid treated aluminum substrates were coated
with the photosensitive layer formulations PS-1 to PS-10 (as listed
in Table 1), respectively, with a #6 Mayer rod, followed by hot air
blow drying and baking in an oven at 90.degree. C. for 2 min.
TABLE-US-00001 TABLE 1 (all values are by weight) Component PS-1
PS-2 PS-3 PS-4 PS-5 PS-6 PS-7 PS-8 PS-9 PS-10 Carboset 527 (Polymer
with acid 2.69 2.69 2.69 2.69 2.69 2.69 2.69 4.56 4.56 4.56 number
of 80, from B. F. Goodrich) Sartomer CN975 6.43 3.22 3.22 3.22 4.56
(Hexafunctional urethane acrylate monomer from Sartomer Company)
Sartomer SR-399 6.43 3.22 4.56 (Pentafunctional non-urethane
acrylate monomer from Sartomer Company) Sartomer SR-295 6.43 3.22
(Tetrafunctional non-urethane acrylate monomer from Sartomer
Company) Sartomer SR-349 (Difunctional 6.43 3.22 4.56 non-urethane
acrylate monomer from Sartomer Company) Renol Blue B2G-HW (60 parts
0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 0.57 blue pigment
dispersed in 40 parts polyvinylbutyral from Ciba- Geigy) Pluronic
L43 (Nonionic 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14 0.14
surfactant from BASF) 2,2'-Bis(2-chlorophenyl)- 1.21 1.21 1.21 1.21
1.21 1.21 1.21 1.21 1.21 1.21 4,4',5,5'-tetraphenyl-1,1'-
biimidazole 4,4'-Bis(diethylamino) 0.72 0.72 0.72 0.72 0.72 0.72
0.72 0.72 0.72 0.72 benzophenone 2-Mercaptobenzoxazole 0.24 0.24
0.24 0.24 0.24 0.24 0.24 0.24 0.24 0.24 1-Methoxy-2-propanol 61.60
61.60 61.60 61.60 61.60 61.60 61.60 61.60 61.60 61.60 2-Butanone
26.40 26.40 26.40 26.40 26.40 26.40 26.40 26.40 26.40 26.40 Monomer
to polymeric binder 2.20 2.20 2.20 2.20 2.20 2.20 2.20 0.95 0.95
0.95 weight ratio Multifunctional monomer to 2.20 2.20 2.20 0.00
2.20 2.20 1.10 0.95 0.95 0.00 polymeric binder weight ratio
Multifunctional monomer to 2.39 2.39 2.39 0.00 2.39 2.39 1.19 1.00
1.00 0.00 alkaline soluble polymeric binder weight ratio
[0065] Each of the photosensitive layer coated plates was further
coated with a water-soluble overcoat OC-1 using a #6 Mayer rod,
followed by hot air blow drying and baking in an oven at 90.degree.
C. for 2 min. The above coating and drying were performed under red
light and the plates were kept in a light-tight box before
development. TABLE-US-00002 OC-1 Component Weight ratios Airvol 203
(Polyvinyl alcohol from Air Products) 15.0 Triton X-100 (Surfactant
from Union Carbide) 0.20 Water 85.0
[0066] The above coated plates (Plates #1 to #10, with PS-1 to
PS-10, respectively) were exposed with a violet laser imager
equipped with a 60 mw laser diode emitting at about 405 nm (MAKO 8
from ECRM) at a dosage of 65 .mu.J/cm.sup.2. The exposed plates
were developed with an alkaline aqueous developer containing 2.0%
by weight of potassium silicate and 3.0% by weight of a nonionic
surfactant, and rinsed with water. The laser exposure was performed
under an orange light (with a cut off wavelength of 550 nm-no light
below 550 nm), and the development was performed under a red light.
The developed plates were evaluated for the imaging pattern and
background, with the results listed in Table 2. TABLE-US-00003
TABLE 2 Plate #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 Photosensitive layer
PS-1 PS-2 PS-3 PS-4 PS-5 PS-6 PS-7 PS-8 PS-9 PS-10 Imaging pattern
Good Good Good Wash Good Good Fair Fair Poor Wash off off
Background Clean Clean Clean Clean Clean Clean Clean Clean Clean
Clean Highlight resolution 2% 2% 2% Wash 2% 2% 20% 20% >20% Wash
off off
* * * * *