U.S. patent application number 11/266817 was filed with the patent office on 2007-05-10 for method of processing laser sensitive lithographic printing plate.
Invention is credited to Gary Ganghui Teng.
Application Number | 20070101886 11/266817 |
Document ID | / |
Family ID | 38000889 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070101886 |
Kind Code |
A1 |
Teng; Gary Ganghui |
May 10, 2007 |
Method of processing laser sensitive lithographic printing
plate
Abstract
A method of developing a laser sensitive lithographic printing
plate with ink and/or fountain solution is described. The printing
member comprises on a substrate a photosensitive layer soluble or
dispersible in ink and/or fountain solution and capable of
hardening upon exposure to a laser. The plate is exposed with a
laser and deactivated under a safe light or in the dark, and then
on-press developed with ink and/or fountain solution preferably
under white light. Alternatively, the plate is developed with ink
and/or fountain solution or the likes off press, and then mounted
on press for lithographic printing.
Inventors: |
Teng; Gary Ganghui;
(Northborough, MA) |
Correspondence
Address: |
Gary Ganghui Teng
10 Kendall Dr.
Northborough
MA
01532
US
|
Family ID: |
38000889 |
Appl. No.: |
11/266817 |
Filed: |
November 4, 2005 |
Current U.S.
Class: |
101/450.1 |
Current CPC
Class: |
B41C 2210/08 20130101;
B41C 2210/22 20130101; B41C 1/1008 20130101; B41C 1/1016 20130101;
B41C 2210/04 20130101; G03F 7/38 20130101; B41C 2201/02 20130101;
B41C 2210/24 20130101; G03F 7/033 20130101; B41C 2201/14
20130101 |
Class at
Publication: |
101/450.1 |
International
Class: |
B41F 1/18 20060101
B41F001/18 |
Claims
1. A method of lithographically printing images on a receiving
medium, comprising in order: (a) providing a lithographic plate
comprising (i) a substrate, and (ii) a photosensitive layer capable
of hardening upon exposure to a laser having a wavelength selected
from 200 to 1200 nm and soluble or dispersible in ink and/or
fountain solution; wherein said photosensitive layer exhibits an
affinity or aversion substantially opposite to the affinity or
aversion of said substrate to at least one printing liquid selected
from the group consisting of ink and an abhesive fluid for ink; (b)
exposing the plate with a laser according to digital imaging
information to cause hardening of the photosensitive layer in the
exposed areas; (c) overall applying to the exposed plate (i) a
deactivating agent, (ii) heat, or (iii) a radiation that has a
different wavelength from the laser and does not cause hardening of
the photosensitive layer, to deactivate the photosensitive layer;
and (d) contacting said deactivated plate with ink and/or fountain
solution on a lithographic press to remove the photosensitive layer
in the non-hardened areas and to lithographically print images from
said plate to the receiving medium; wherein said steps (a) to (c)
are performed with the plate under lightings (including darkness)
that will not cause hardening of the photosensitive layer, and said
step (d) is performed under a lighting that will cause hardening of
the non-deactivated photosensitive layer.
2. The method of claim 1 wherein said steps (a) to (c) are
performed with the plate under lightings that contain no or
substantially no radiation below a wavelength selected from 400 to
650 nm, or in the dark or substantially dark; and said step (d) is
performed under a white light.
3. The method of claim 1 wherein said laser exposed plate is
deactivated by applying a solution containing a deactivating
agent.
4. The method of claim 1 wherein said laser exposed plate is
deactivated by applying heat.
5. The method of claim 1 wherein said photosensitive layer contains
a latent-deactivating agent, and said laser exposed plate is
deactivated by applying heat.
6. The method of claim 1 wherein said laser exposed plate is
deactivated by applying a radiation which has wavelength different
from the laser radiation and does not cause hardening of the
photosensitive layer.
7. The method of claim 1 wherein said photosensitive layer
comprises a free radical polymerizable monomer, a free radical
initiator, and a sensitizing dye.
8. The method of claim 1 wherein said plate further comprises a
water soluble or dispersible overcoat.
9. The method of claim 1 wherein said plate further comprises a
water soluble or dispersible overcoat, and said overcoat is removed
with water or an aqueous solution after the laser exposure (step b)
and before the deactivation (step c).
10. The method of claim 1 wherein said laser is a violet or
ultraviolet laser having a wavelength selected from 300 to 430 nm
and said plate is exposed at a dosage of from 1 to 400
.mu.J/cm.sup.2 (0.001 to 0.400 mJ/cm.sup.2).
11. A method of lithographically printing images on a receiving
medium, comprising in order: (a) providing a lithographic plate
comprising (i) a hydrophilic substrate; (ii) an oleophilic
photosensitive layer comprising a polymeric binder, a free radical
polymerizable ethylenically unsaturated monomer, a free radical
initiator, and a sensitizing dye; and (iii) a water soluble or
dispersible overcoat; (b) imagewise exposing the plate with a laser
having a wavelength selected from 300 to 430 nm to cause hardening
of the photosensitive layer in the exposed areas; (c) applying an
aqueous solution containing a deactivating agent to said exposed
plate to deactivate the photosensitive layer; and (d) contacting
said deactivated plate with ink and fountain solution on a
lithographic press to remove the photosensitive layer in the
non-hardened areas, and to lithographically print images from said
plate to the receiving medium; wherein said steps (a) to (c) are
performed with the plate under lightings (including darkness) that
will not cause hardening of the photosensitive layer, and said step
(d) is performed under a lighting that will cause hardening of the
non-deactivated photosensitive layer.
12. The method of claim 11 wherein said steps (a) to (c) are
performed with the plate under lightings that contain no or
substantially no radiation below a wavelength selected from 450 to
650 nm, or in the dark or substantially dark; and said step (d) is
performed under a white light.
13. The method of claim 11 wherein said deactivating agent is an
acid or alkaline compound which can react with one or more
compounds in the photosensitive layer.
14. The method of claim 11 wherein said photosensitive layer
further comprises a hydrogen donor, and said deactivating agent can
react with said initiator, sensitizing dye, or hydrogen donor.
15. The method of claim 11 wherein said plate is rinsed with water
to remove the overcoat after the laser exposure (step b) and before
the deactivation (step c).
16. The method of claim 11 wherein said overcoat is partially or
completely removed by the aqueous solution containing the
deactivating agent.
17. The method of claim 11 wherein said laser is a violet laser
having a wavelength selected from 390 to 430 nm and said plate is
exposed at a dosage of from 5 to 200 .mu.J/cm.sup.2.
18. A method of lithographically printing images on a receiving
medium, comprising in order: (a) providing a lithographic plate
comprising (i) a hydrophilic substrate; and (ii) an oleophilic
photosensitive layer comprising a polymeric binder, a free radical
polymerizable monomer, a free radical initiator, and a sensitizing
dye; (b) imagewise exposing the plate with a laser having a
wavelength selected from 200 to 1200 nm to cause hardening of the
photosensitive layer in the exposed areas; (c) contacting said
exposed plate off press with ink and fountain solution to remove
the photosensitive layer in the non-hardened areas; and (d)
mounting said developed plate on a lithographic press to
lithographically print images from said plate to the receiving
medium; wherein said steps (a) to (c) are performed with the plate
under lightings (including darkness) that will not cause hardening
of the photosensitive layer, and said step (d) is performed under a
lighting that will cause hardening of the non-deactivated
photosensitive layer.
19. The method of claim 18 wherein said plate further comprises a
water soluble or dispersible overcoat.
20. The method of claim 18 wherein said laser is a violet or
ultraviolet laser having a wavelength selected from 300 to 430 nm
and said plate is exposed at a dosage of from 1 to 400
.mu.J/cm.sup.2.
Description
FIELD OF THE INVENTION
[0001] This invention relates to lithographic printing plates. More
particularly, it relates to a method of deactivating or developing
a laser sensitive lithographic plate after imagewise exposure and
before printing on press.
BACKGROUND OF THE INVENTION
[0002] 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.
[0003] 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, optionally with further
post-exposure overall treatment. 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. The exposed plate is usually
developed with a liquid developer to bare the substrate in the
non-hardened or solubilized areas.
[0004] On-press developable lithographic printing plates have been
disclosed in the literature. Such plates can be directly mounted on
press after exposure to develop with ink and/or fountain solution
during the initial prints and then to print out regular printed
sheets. No separate development process before mounting on press is
needed. Among the patents describing on-press developable
lithographic printing plates are U.S. Pat. Nos. 5,258,263,
5,516,620, 5,561,029, 5,616,449, 5,677,110, 5,811,220, 6,014,929,
6,071,675, and 6,482,571).
[0005] Conventionally, the plate is exposed with an actinic light
(usually an ultraviolet light from a lamp) through a separate
photomask film having predetermined imaging pattern which is placed
between the light source and the plate. While capable of providing
plate with superior lithographic quality, such a method is
cumbersome and labor intensive.
[0006] Laser sources have been increasingly used to imagewise
expose a printing plate which is sensitized to a corresponding
laser wavelength. This allows the elimination of the photomask
film, reducing material, equipment and labor cost. Suitable lasers
include infrared lasers (such as laser diode of about 830 nm and
NdYAG laser of about 1064 nm), visible lasers (such as
frequency-doubled NdYAG laser of about 532 nm, violet laser diode
of about 405 nm), and ultraviolet laser (such as ultraviolet laser
diode of about 350 to 370 nm). Among them, infrared laser diode,
violet laser diode, and ultraviolet laser diode are most
attractive.
[0007] Laser sensitive plates generally have higher sensitivity
(than conventional film based plate) because of the limited laser
power and the desire for fast imaging speed. Accordingly,
photosensitive plates designed for laser imaging generally have
limited room light stability. For example, before being developed
to remove the non-hardened areas, frequency-doubled NdYAG laser
sensitive plates usually require red room light for handling,
violet laser sensitive plates usually require orange or yellow room
light for handling, and infrared laser sensitive photopolymer
plates usually require yellow room light for handling and have only
limited white light stability (due to the use of certain initiator
which has spectral sensitivity in the ultraviolet region).
[0008] Such limited room light stability is an inherent barrier for
the design and use of laser sensitive lithographic plates. It would
be desirable if the exposed laser sensitive plate can be handled
under white room light before development or printing.
SUMMARY OF THE INVENTION
[0009] According to the present invention, there has been provided
a method of lithographically printing images on a receiving medium,
comprising in order: [0010] (a) providing a lithographic plate
comprising (i) a substrate, and (ii) a photosensitive layer capable
of hardening upon exposure to a laser having a wavelength selected
from 200 to 1200 nm and soluble or dispersible in ink and/or
fountain solution; wherein said photosensitive layer exhibits an
affinity or aversion substantially opposite to the affinity or
aversion of said substrate to at least one printing liquid selected
from the group consisting of ink and an abhesive fluid for ink;
[0011] (b) exposing the plate with a laser according to digital
imaging information to cause hardening of the photosensitive layer
in the exposed areas; [0012] (c) overall applying to the exposed
plate (i) a deactivating agent, (ii) heat, or (ii) a radiation that
has a different wavelength from the laser and does not cause
hardening of the photosensitive layer, to deactivate the
photosensitive layer; and [0013] (d) contacting said deactivated
plate with ink and/or fountain solution on a lithographic press to
remove the photosensitive layer in the non-hardened areas and to
lithographically print images from said plate to the receiving
medium; [0014] (e) wherein said steps (a) to (c) are performed with
the plate under lightings (including darkness) that will not cause
hardening of the photosensitive layer, and said step (d) is
performed under a lighting that will cause hardening of the
non-deactivated photosensitive layer.
[0015] 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: [0016] (a) providing a
lithographic plate comprising (i) a hydrophilic substrate; and (ii)
an oleophilic photosensitive layer comprising a polymeric binder, a
free radical polymerizable monomer, a free radical initiator, and a
sensitizing dye; [0017] (b) imagewise exposing the plate with a
laser having a wavelength selected from 200 to 1200 nm to cause
hardening of the photosensitive layer in the exposed areas; [0018]
(c) contacting said exposed plate off press with ink and/or
fountain solution, or with an organic solvent-based or oil-based
liquid or paste and/or an aqueous solution, to remove the
photosensitive layer in the non-hardened areas; and [0019] (d)
mounting said developed plate on a lithographic press to
lithographically print images from said plate to the receiving
medium; [0020] (e) wherein said steps (a) to (c) are performed with
the plate under lightings (including darkness) that will not cause
hardening of the photosensitive layer, and said step (d) is
performed under a lighting that will cause hardening of the
non-deactivated photosensitive layer.
[0021] The deactivation or off-press development of step (c) allows
the plate to be processed or handled under a lighting which is not
safe (causing hardening) to the original, non-deactivated
photosensitive layer.
[0022] Preferably, for both above processes, said steps (a) to (c)
are performed with the plate under lightings that contain no or
substantially no radiation below a wavelength selected from 400 to
650 nm (such as 400, 450, 500, 550, or 600 nm), or in the dark or
substantially dark; and said step (d) is performed under a white
light (which can be a white fluorescence light, incandescent light,
sunlight, or any other office white light). Here, the steps (a) to
(c) can be under different or the same lightings (including
darkness).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] The substrate employed in the lithographic plates of this
invention can be any lithographic support. Such a substrate may be
a metal sheet, a polymer film, or a coated paper. Aluminum
(including aluminum alloy) sheet is a preferred metal support.
Particularly preferred is an aluminum support that has been grained
and anodized (with or without deposition of a barrier layer).
Polyester film is a preferred polymeric film support. A surface
coating may be coated to achieve desired surface properties. For
wet plate, the substrate should have a hydrophilic or oleophilic
surface, depending on the surface properties of the photosensitive
layer (with opposite philicity to the substrate); commonly, a wet
lithographic plate has a hydrophilic substrate and an oleophilic
photosensitive layer. For waterless plate, the substrate should
have an oleophilic or oleophobic surface, depending on the surface
properties of the photosensitive layer (with opposite philicity to
the substrate).
[0024] Particularly suitable hydrophilic substrate for a wet
lithographic plate is an aluminum support that has been grained and
anodized; such a substrate is preferably further deposited with a
hydrophilic barrier layer. Surface graining can be achieved by
mechanical graining or brushing, chemical etching, and/or AC
electrochemical graining. The roughened surface can be further
anodized to form a durable aluminum oxide surface using an acid
electrolyte such as sulfuric acid and/or phosphoric acid. The
roughened and anodized aluminum surface can be further thermally or
electrochemically coated with a layer of silicate or hydrophilic
polymer such as polyvinyl phosphonic acid, polyacrylamide,
polyacrylic acid, polybasic organic acid, copolymers of vinyl
phosphonic acid and acrylamide to form a durable hydrophilic layer.
Polyvinyl phosphonic acid and its copolymers are preferred
polymers. Processes for coating a hydrophilic barrier layer on
aluminum in lithographic 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, and 5,368,974. Suitable polymer film supports
for a wet lithographic plate include a polymer film coated with a
hydrophilic layer, preferably a hydrophilic layer that is
crosslinked, as described in U.S. Pat. No. 5,922,502.
[0025] For preparing lithographic printing plates of the current
invention, any photosensitive layer is suitable which is capable of
hardening upon exposure to a laser having a wavelength selected
from 200 to 1200 nm, and is soluble or dispersible in ink (for
waterless plate) or in ink and/or fountain solution (for wet
plate). Here hardening means becoming insoluble and non-dispersible
in ink and/or fountain solution. Hardening is generally achieved
through crosslinking or polymerization of the resins (polymers or
monomers). A laser sensitive dye or pigment is usually used in the
photosensitive layer. The photosensitive layer preferably has a
coverage of from 100 to 4000 mg/m.sup.2, and more preferably from
400 to 2000 mg/m.sup.2.
[0026] Preferably, the photosensitive layer comprises a
polymerizable monomer and an initiating system, optionally with
addition of a polymeric binder. The initiating system generally
comprises an initiator; an initiator and a sensitizing dye; or an
initiator, a sensitizing dye and a hydrogen donor; depending on the
specific photosensitive layer. Either one species (such as 1
initiator or 1 polymer) or more than one species of the same
component type (such as 2 different initiators or 3 different
monomers) can be added in the same photosensitive layer. The
composition ratios (such as monomer to polymer ratio) are usually
different from conventional plates designed for development with a
regular liquid developer. Various additives may be added to, for
example, allow or enhance on-press developability. Such additives
include surfactant, plasticizer, water soluble polymer or small
molecule, and ink soluble polymer or small molecule. The addition
of nonionic surfactant is especially helpful in making the
photosensitive layer dispersible with ink and fountain solution, or
emulsion of ink and fountain solution. Various additives useful for
conventional photosensitive layer can also be used. These additives
include pigment, dye, exposure indicator, and stabilizer.
[0027] In this patent, the term monomer includes both monomer and
oligomer, and the term (meth)acrylate includes acrylate and/or
methacrylate (acrylate, methacrylate, or both acrylate and
methacrylate). In calculating the weight ratio of the monomer to
the polymeric binder, the weight of the monomer includes the total
weight of all monomers and the weight of the polymeric binder
includes the total weight of all polymeric binders. The term yellow
or red light means yellow light, red light, or any light with a
color between yellow and red such as orange light. The term safe
light means a light with a certain wavelength range being cut off,
including yellow light or red light, so that it does not cause
hardening of a certain photosensitive layer. The term white light
means a white fluorescence light, white incandescence light,
sunlight, or any white office light.
[0028] Photosensitive materials useful in wet plates of this
invention include, for example, photosensitive compositions
comprising a polymerizable monomer, an initiator, a sensitizing
dye, and optionally a polymer.
[0029] Photosensitive oleophobic materials useful in waterless
plates of this invention include, for example, compositions
comprising a monomer having perfluoroalkyl or polysiloxane groups
and crosslinkable terminal groups, an initiator, and a sensitizing
dye.
[0030] Infrared laser sensitive materials useful for wet
lithographic plates of this invention include, for example,
thermosensitive compositions comprising a polymerizable monomer, an
initiator, an infrared absorbing dye, and optionally a polymer.
[0031] Visible or ultraviolet light sensitive materials useful for
wet plates of this invention include, for example, photosensitive
compositions comprising a polymerizable monomer, an initiator, a
visible or ultraviolet light sensitizing dye, and optionally a
polymer. A hydrogen donor is preferably added to accelerate the
polymerization.
[0032] Polymeric binder for the photosensitive layer of this
invention can be any film-forming polymer. The polymers may or may
not have (meth)acrylate groups or other polymerizable double bonds
such as allyl groups. Examples of suitable polymers include
(meth)acrylic polymers and copolymers (such as
polybutylmethacrylate, polyethylmethacrylate,
polymethylmethacrylate, polymethylacrylate,
butylmethacrylate/methylmethacrylate copolymer, and
methylmethacrylate/methylmethacrylic 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.
[0033] 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. Urethanated (meth)acrylate with at least six
(meth)acrylate groups and non-urethanated (meth)acrylate with at
least four (meth)acrylate groups are preferred monomers because of
their fast curing speed. Combinations of urethanated (meth)acrylate
and non-urethanated (meth)acrylate are especially useful. Various
monomer combinations are described in U.S. patent application Ser.
No. 10/720,882, the entire disclosure of which is hereby
incorporated by reference, and can be used for the preparation of
the photosensitive layer of this invention.
[0034] Suitable free-radical initiators include, for example, the
derivatives of acetophenone (such as
2,2-dimethoxy-2-phenylacetophenone, and
2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one), onium
salts such as diaryliodonium hexafluoroantimonate, diaryliodonium
hexafluorophosphate, diaryliodonium triflate,
(4-(2-hydroxytetradecyl-oxy)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; titanocene such as
bis(.eta..sup.9-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-y-
l)phenyl) titanium; 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,
2-(1-naphthyl)-4,5-diphenyl-1,2'-biimidazole; and derivatives of
acetophenone such as 2,2-dimethoxy-2-phenylacetophenone, and
2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one.
Triarylsulfonium salts, diaryliodonium salts, and
triarylalkylborate salts are particularly suitable for infrared
laser sensitive plate. Titanocene compounds and hexaarylbiimidazole
compounds are particularly suitable for visible or ultraviolet
laser sensitive plate. The initiator is added in the photosensitive
layer preferably at 0.1 to 40% by weight of the photosensitive
layer, more preferably 1 to 30%, and most preferably 5 to 20%.
[0035] Infrared sensitizing dyes useful in the infrared sensitive
photosensitive layer (also called thermosensitive layer) of this
invention include any infrared absorbing dye effectively absorbing
an infrared radiation having a wavelength of 750 to 1200 nm. It is
preferable that the dye has an absorption maximum between the
wavelengths of 800 and 1100 nm. Various infrared absorbing dyes are
described in U.S. Pat. Nos. 5,858,604, 5,922,502, 6,022,668,
5,705,309, 6,017,677, and 5,677,106, and in the book entitled
"Infrared Absorbing Dyes" edited by Masaru Matsuoka, Plenum Press,
New York (1990), and can be used in the thermosensitive layer of
this invention. Examples of useful infrared absorbing dyes include
squarylium, croconate, cyanine (including polymethine),
phthalocyanine (including naphthalocyanine), merocyanine,
chalcogenopyryloarylidene, oxyindolizine, quinoid, indolizine,
pyrylium and metal dithiolene dyes. Cyanine and phthalocyanine dyes
are preferred infrared absorbing dyes.
[0036] Visible or ultraviolet sensitizing dyes useful in the
visible or ultraviolet sensitive photosensitive layer of this
invention include any dyes having a wavelength maximum of from 200
to 600 nm and capable of directly or indirectly causing
polymerization of the monomers upon exposure to the corresponding
laser. Usually, the visible or ultraviolet dye activates an
initiator to cause the polymerization of the monomer upon exposure
to a laser. Suitable visible and ultraviolet sensitive dyes
include, for example, cyanine dyes (including polymethine dyes);
rhodamine compounds such as rhodamine 6G perchloride; 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 and 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.
patent application Pub. No. 2003/0186165 can be used for the
photosensitive layer of this invention.
[0037] The photosensitive composition of the present invention
preferably contains a 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.
[0038] Various surfactants can be added into the photosensitive
layer to allow or enhance the on-press developability with ink
and/or fountain. 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%.
[0039] The deactivating agent can be any compound that can
deactivate the hardening capability of the photosensitive layer.
The deactivating agent can be applied from a solution to the
photosensitive layer (with or without overcoat). Preferably, the
deactivating agent is soluble in water and is applied from an
aqueous solution. Certain additives, such as dye, dispersed
pigment, bactericide, stabilizer, reducer, thickening agent,
cosolvent, and surfactant, can be added. For free radical
polymerizable photosensitive layer, the deactivating agent can be a
compound that can react with a component of the free radical
initiating system (such as initiator, sensitizing dye, or hydrogen
donor).
[0040] The solution containing the deactivating agent can be
applied to the photosensitive layer of the plate through any means,
such as spray, dipping, roller coating, slot coating, etc. For
plate with an overcoat, the deactivating solution can be applied
with or without the overcoat being removed first. When the overcoat
is not removed before applying the deactivating solution, the
deactivating solution may penetrate through the overcoat without
removing the overcoat, or partially or completely remove the
overcoat.
[0041] For photosensitive layer having an amine group in the
initiator, sensitizing dye, or hydrogen donor, an acid compound
(including organic acid and inorganic acid) can be used as the
deactivating agent. Suitable organic acid include, for example,
organic compounds having at lease one carboxylic acid group, a
sulfonic acid group, or phosphonic acid group. Suitable inorganic
acids include, for example, phosphoric acid, boric acid, and
hydrochloride acid. Preferred acids are those with moderate
acidity, such as carboxylic acid-functional organic compounds,
phosphoric acid, and boric acid. Water-soluble organic compounds
having at least one carboxylic acid group are preferred organic
acids. Suitable organic acids include, for example, citric acid,
acetic acid, salicylic acid, glycolic acid, malic acid, and lactic
acid. Citric acid and malic acid are particularly suitable because
they are widely used natural organic acids and are non-hazardous to
the environment.
[0042] Alkaline solution can also be used as the deactivating agent
because it can react with the free radical initiating system
(initiator, sensitizing dye, or hydrogen donor) or monomer.
Suitable alkaline compounds include, for example, sodium silicate,
potassium silicate, sodium carbonate, and organic amines. Preferred
alkaline compounds are water-soluble compounds with moderate
basicity, such as sodium silicate, potassium silicate, ammonium
hydroxide, and organic amines. Suitable water-soluble organic
amines include regular amine compounds such as triethylamine,
triethanolamine, 2-amino-2-methyl-1-propanol,
tris(hydroxymethyl)aminomethane and N-methyl-2-pyrrolidone, and
polymeric amines such as polyethyleneamine.
[0043] The latent deactivating agent can be any compound that can
generate a deactivating agent at an elevated temperature of from 80
to 200.degree. C., preferably from 100 to 150.degree. C. Suitable
latent deactivating agents include any thermal acid generators
capable of producing free acid at such elevated temperature.
Various thermal acid generators have been described in the patent
literature, such as U.S. Pat. Nos. 5,955,238, 6,037,098, and
6,159,655, and can be used as the thermal acid generator of the
current invention. Examples of useful thermal acid generators are
ammonium benzoate, and ammonium acetate.
[0044] The photosensitive layer may contain a compound that can
react with a component in the initiating system (initiator,
sensitizing dye and hydrogen donor) of the photosensitive layer at
elevated temperature of from 80 to 200.degree. C., preferably from
100 to 150.degree. C., causing deactivation of the photosensitive
layer.
[0045] Photosensitive layer containing a thermally decomposable
sensitizing dye or hydrogen donor can be deactivated by applying
heat. The thermally decomposable sensitizing dye or hydrogen donor
can be any sensitizing dye or hydrogen donor having a decomposition
temperature of from 80 to 200.degree. C., preferably from 100 to
150.degree. C. Here the decomposition temperature is a temperature
at which the compound rapidly decomposes to two or more smaller
compounds.
[0046] The heat can be applied to the plate by any means, such as
hot air, contacting the back of the plate with a heated material,
exposing the back of the plate with a radiation such as an infrared
radiation, exposing the front of the plate (having photosensitive
layer) with a radiation which has different wavelength from the
laser and does not cause hardening of the photosensitive layer.
[0047] The photosensitive layer may be exposed with a radiation to
cause deactivation of the photosensitive layer through
photochemical reaction. Such radiation must have a different
wavelength from the laser and does not cause hardening of the
photosensitive layer. The photosensitive layer can contain a latent
deactivating agent which can generate a deactivating agent upon
exposure to a radiation that has different wavelength from the
laser and does not cause hardening of the photosensitive layer.
Suitable photosensitive latent deactivating agent includes photo
acid generators and photo base generators which can generate an
acid or base upon exposure to a radiation different from the laser
and does not cause hardening of the photosensitive layer.
[0048] 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 water-soluble
organic solvent is preferably added at less than 20% by weight of
the solution, more 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.
[0049] The photosensitive layer may be conformally coated onto a
roughened substrate (for example, with Ra of larger than 0.4
microns) at thin coverage (for example, of less than 1.2 g/m.sup.2)
so that the plate can have microscopic peaks and valleys on the
photosensitive layer coated surface and exhibit low tackiness and
good block resistance, as described in U.S. Pat. No. 6,242,156, the
entire disclosure of which is hereby incorporated by reference.
[0050] A water soluble or dispersible overcoat can be coated on the
photosensitive layer to, for example, improve the photospeed,
surface durability, and/or developability of the plate. The
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. The overcoat
preferably has a coverage of from 0.001 to 4.0 g/m.sup.2, more
preferably from 0.01 to 2.0 g/m.sup.2, and most preferably from 0.1
to 1.0 g/m.sup.2.
[0051] In a preferred embodiment for the thermosensitive
lithographic printing plates of this invention, the thermosensitive
layer comprises at least one polymeric binder (with or without
ethylenic functionality), at least one polymerizable ethylenically
unsaturated monomer having at least one terminal ethylenic group,
at least one free-radical initiator, and at least one infrared
absorbing dye or pigment. Other additives such as surfactant, 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) may be added. The monomer-to-polymer weight
ratio is preferably larger than 1.0, more preferably larger than
1.5, and most preferably larger than 2.0.
[0052] In another preferred embodiment for the thermosensitive
lithographic printing plates of this invention, the thermosensitive
layer comprises a polymeric binder, a urethane (meth)acrylate
monomer having at least 6 (meth)acrylate groups, a non-urethane
(meth)acrylate monomer having at least 4 (meth)acrylate groups, a
free-radical initiator, and an infrared absorbing dye. The weight
ratio of the urethane (meth)acrylate monomer to the non-urethane
(meth)acrylate monomer is preferably from 0.10 to 3.0, more
preferably from 0.15 to 2.0, even more preferably from 0.20 to 1.5,
and most preferably from 0.30 to 1.0.
[0053] In a preferred embodiment for visible or ultraviolet light
sensitive lithographic printing plates of this invention, the
photosensitive layer comprises at least one polymeric binder (with
or without ethylenic functionality), at least one polymerizable
ethylenically unsaturated monomer having at least one terminal
ethylenic group, at least one free-radical initiator, and at least
one visible or ultraviolet sensitizing dye. A hydrogen donor is
preferably added to increase the photospeed. Other additives such
as surfactant, dye or pigment, exposure-indicating dye, and
free-radical stabilizer may be added. The monomer-to-polymer weight
ratio is preferably larger than 1.0, more preferably larger than
1.5, and most preferably larger than 2.0.
[0054] In another preferred embodiment for visible or ultraviolet
light sensitive lithographic printing plates of this invention, the
photosensitive layer comprises a polymeric binder, a urethane
(meth)acrylate monomer having at least 6 (meth)acrylate groups, a
non-urethane (meth)acrylate monomer having at least 4
(meth)acrylate groups, a free-radical initiator, and a visible or
ultraviolet sensitizing dye. A hydrogen donor is preferably added
to increase the photospeed. The weight ratio of the urethane
(meth)acrylate monomer to the non-urethane (meth)acrylate monomer
is preferably from 0.10 to 3.0, more preferably from 0.15 to 2.0,
even more preferably from 0.20 to 1.5, and most preferably from
0.30 to 1.0.
[0055] On-press developable lithographic plates as described in
U.S. Pat. Nos. 6,482,571, 6,576,401, 5,548,222, and 6,541,183, and
U.S. patent application Ser. Nos. 10/720,882, 11/075,663 and
11/175,518, the entire disclosures of which are hereby incorporated
by reference, can be used for the instant invention.
[0056] A hydrophilic or oleophilic micro particles may be added
into the photosensitive layer to enhance, for example, the
developability and non-tackiness of the plate. Suitable micro
particles include polymer particles, talc, titanium dioxide, barium
sulfate, silicone oxide, and aluminum micro particles, with an
average particle size of less than 10 microns, preferably less than
5 microns, more preferably less than 2 microns, and most preferably
less than 1 microns. A suitable particular dispersion is described
in U.S. Pat. No. 6,071,675, the entire disclosure of which is
hereby incorporated by reference.
[0057] The photosensitive layer should exhibit an affinity or
aversion substantially opposite to the affinity or aversion of the
substrate to at least one printing liquid selected from the group
consisting of ink and an abhesive fluid for ink. For example, a wet
plate can have a hydrophilic substrate and an oleophilic
photosensitive layer, or can have an oleophilic substrate and a
hydrophilic photosensitive layer; a waterless plate can have an
oleophilic substrate and an oleophobic photosensitive layer, or can
have an oleophobic substrate and an oleophilic photosensitive
layer. An abhesive fluid for ink is a fluid that repels ink.
Fountain solution is the most commonly used abhesive fluid for ink.
A wet plate is printed on a wet press equipped with both ink and
fountain solution, while a waterless plate is printed on a
waterless press equipped with ink.
[0058] Infrared lasers useful for the imagewise exposure of the
thermosensitive plates of this invention include laser sources
emitting in the near infrared region, i.e. emitting in the
wavelength range of from 750 to 1200 nm, and preferably from 800 to
1100 nm. Particularly preferred infrared laser sources are laser
diodes emitting around 830 nm or a NdYAG laser emitting around 1060
nm. The plate is exposed at a laser dosage that is sufficient to
cause hardening in the exposed areas but not high enough to cause
substantial thermal ablation. The exposure dosage is preferably
from 1 to 400 mJ/cm.sup.2, more preferably from 5 to 200
mJ/cm.sup.2, and most preferably from 20 to 150 mJ/cm.sup.2,
depending on the sensitivity of the thermosensitive layer.
[0059] Visible lasers useful for the imagewise exposure of the
visible light sensitive plates of this invention include any laser
emitting in the wavelength range of from 390 to 600 nm. Examples of
suitable visible lasers include frequency-doubled Nd/YAG laser
(about 532 nm), argon ion laser (about 488 nm), violet diode laser
(about 405 nm), and visible LEDs. Violet laser diode is especially
useful because of its small size and relatively lower cost. The
exposure dosage is preferably from 0.0001 to 5 mJ/cm.sup.2 (0.1 to
5000 .mu.J/cm.sup.2), more preferably from 0.001 to 0.5 mJ/cm.sup.2
(1 to about 500 .mu.J/cm.sup.2), and most preferably from 0.005 to
0.10 mJ/cm.sup.2 (5 to 100 .mu.J/cm.sup.2), depending on the
sensitivity of the photosensitive layer.
[0060] Ultraviolet lasers useful for the imagewise exposure of the
ultraviolet light sensitive plates of this invention include any
laser having a wavelength of from 200 to 390 nm. Examples of
ultraviolet lasers include ultraviolet diode lasers or LEDs having
a wavelength of from 350 to 390 nm. Laser diodes are preferred
ultraviolet lasers. The exposure dosage is preferably from 0.0001
to 5 mJ/cm.sup.2 (0.1 to 5000 .mu.J/cm.sup.2), more preferably from
0.001 to 0.5 mJ/cm.sup.2 (1 to about 500 .mu.J/cm.sup.2), and most
preferably from 0.005 to 0.10 mJ/cm.sup.2 (5 to 100
.mu.J/cm.sup.2), depending on the sensitivity of the photosensitive
layer.
[0061] 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.
[0062] For on-press development, the plate is exposed on an
exposure device under a safe light or in the dark, deactivated with
a deactivating agent, and then mounted on press to develop 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. Good quality prints should be obtained preferably
under 40 initial impressions, more preferably under 20 impressions,
and most preferably under 5 impressions.
[0063] 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 plate of this
invention.
[0064] The ink used in this application can be any ink suitable for
lithographic printing. Most commonly used lithographic inks include
"oil based ink" which crosslinks upon exposure to the oxygen in the
air and "rubber based ink" which does not crosslink upon exposure
to the air. Specialty inks include, for example, radiation-curable
ink and thermally curable ink. An ink is an oleophilic, liquid or
viscous material which generally comprises a pigment dispersed in a
vehicle, such as vegetable oils, animal oils, mineral oils, and
synthetic resins. Various additives, such as plasticizer,
surfactant, drier, drying retarder, crosslinker, and solvent may be
added to achieve certain desired performance. The compositions of
typical lithographic inks are described in "The Manual of
Lithography" by Vicary, Charles Scribner's Sons, New York, and
Chapter 8 of "The Radiation Curing: Science and Technology" by
Pappas, Plenum Press, New York, 1992.
[0065] The fountain solution used in this application can be any
fountain solution used in lithographic printing. Fountain solution
is used in the wet lithographic printing press to dampen the
hydrophilic areas (non-image areas), repelling ink (which is
hydrophobic) from these areas. Fountain solution contains mainly
water, generally with addition of certain additives such as gum
arabic and surfactant. Small amount of alcohol such as isopropanol
can also be added in the fountain solution. Water is the simplest
type of fountain solution. Fountain solution is usually neutral to
mildly acidic. However, for certain plates, mildly basic fountain
solution is used. The type of fountain solution used depends on the
type of the plate substrate as well as the photosensitive layer.
Various fountain solution compositions are described in U.S. Pat.
Nos. 4,030,417 and 4,764,213.
[0066] Emulsion of ink and fountain solution is an emulsion formed
from ink and fountain solution during wet lithographic printing
process. Because fountain solution (containing primarily water) and
ink are not miscible, they do not form stable emulsion. However,
emulsion of ink and fountain solution can form during shearing,
compressing, and decompressing actions by the rollers and
cylinders, especially the ink rollers and plate cylinder, on a wet
lithographic press. For wet press with integrated inking system,
ink and fountain solution are emulsified on the ink rollers before
transferred to the plate.
[0067] For off-press development with ink and/or fountain solution,
or with an organic solvent- or oil-based liquid or paste and/or an
aqueous solution, a developing device which carries ink and/or
fountain solution, or an organic solvent- or oil-based liquid or
paste and/or an aqueous solution, can be used. Preferably, the
plate is developed with (i) ink, (ii) both ink and fountain
solution, (iii) an organic solvent-based or oil-based liquid or
paste, or (iv) both an organic solvent- or oil-based liquid or
paste and an aqueous solution, and the device carries corresponding
developing fluid or fluids (i, ii, iii, or iv). For plate
developable with ink, a regular ink or single-fluid ink can be
used.
[0068] For plate requiring more than one developing fluid
(including paste), the ink (or the solvent- or oil-based liquid or
paste) and the fountain solution (or the aqueous solution) can be
applied by any means and at any sequence or combination. The same
developing fluid may be applied more than once, and different
compositions of the same type of fluid (such as different aqueous
solutions) can be used in the same developing device. Preferably,
the fountain solution (or the aqueous solution) is applied first
(for example, by spray, dipping, roller coating, or slot coating)
to dampen the plate, followed by applying ink (for example, with
one or more ink rollers) to remove the photosensitive layer in the
non-hardened areas. After applying ink, the plate may be further
applied with the fountain solution (or the aqueous solution) or a
gum solution (plate finisher), to further clean the background
areas and/or to protect the lithographic surface of the plate. For
plate with a water soluble or dispersible overcoat, the overcoat
can be removed by contacting with fountain solution or the aqueous
solution during the off-press development. Alternatively, the
overcoat can be removed by rinse with water or other aqueous
solution in a separate step before the development.
[0069] The organic solvent- or oil-based liquid or paste can be any
liquid or paste materials with organic solvent or oil as the main
solvent, which can dissolve or disperse (and therefore develop) the
photosensitive layer of this invention. Ink is one of such
materials. The liquid or paste may or may not contain pigment or
dye. The oil can be a petroleum oil, vegetable oil, animal oil, or
synthetic oil. The aqueous solution can be any water-based
solutions that can dampen the substrate surface of the plate, or
can be water. Fountain solution is one of such aqueous solutions.
The aqueous solution can be neutral, slight acidic, or slightly
basic, preferably with a pH of 4.0 to 10.0, more preferably 5.0 to
9.0, and most preferably 6.0 to 8.0.
[0070] For plate with a water soluble or dispersible overcoat, the
plate can be rinsed with water or other aqueous solution, to remove
the water soluble or dispersible overcoat after imagewise exposure
and before deactivation or off-press development.
[0071] The laser exposure, and deactivation or off-press
development of this invention are performed with the plate under
lightings (or darkness) that will not cause hardening of the
photosensitive layer. Preferably, these are performed under
lightings containing no or substantially no radiation below a
wavelength selected from 400 to 650 nm (such as 500 nm), or in the
dark or substantially dark; more preferably under lightings
containing no radiation below a wavelength selected from 400 to 650
nm, or in the dark. Such lighting is usually a yellow or red light.
This includes a light that is from a fluorescence or incandescence
lamp that is covered with a filter that cuts off all or
substantially all (at least 99%) of the radiation below a
wavelength selected from 400 to 650 nm; preferably the lamp is
covered with a filter that cuts off all of the radiation below a
wavelength selected from 400 to 650 nm. The laser exposure and the
deactivation or off-press development can be performed with the
plate under the same or different lightings.
[0072] The term "substantially no radiation below a wavelength"
means the intensity of the radiation below that wavelength is less
than 1% of that for a regular 100-watt incandescence light (for
home use, not focused) at a distance of 2 meters. The term
"substantially dark" means the intensity of the radiation is less
than 1% of that for a 100-watt incandescence light at a distance of
2 meters.
[0073] The lighting that contains no or substantially no radiation
below a wavelength selected from 400 to 650 nm (usually as a yellow
or red light) allows a working lighting condition for the
operators. Alternatively, the plate can be handled automatically in
the dark, including in a dark room or in a light-tight box of any
shape. Preferably, during the handling before deactivation or
off-press development, the plate is in a lighting or lightings that
contain no or substantially no radiation below a wavelength
selected from 400 to 650 nm, or in the dark or substantially
dark.
[0074] In one embodiment of the instant invention, both the laser
exposure and deactivation or off-press development are performed
with the plate under a lighting that contains no or substantially
no radiation below a wavelength selected from 400 to 650 nm; the
lightings for the laser exposure and deactivation or off-press
development can be the same or different. In the second embodiment,
the laser exposure is performed with the plate under a lighting
that contains no or substantially no radiation below a wavelength
selected from 400 to 650 nm and the deactivation or off-press
development is performed with the plate in the dark or
substantially dark. In the third embodiment, the laser exposure is
performed with the plate in the dark or substantially dark and the
deactivation or off-press development is performed with the plate
under a lighting that contains no or substantially no radiation
below a wavelength selected from 400 to 650 nm. In the fourth
embodiment, both the laser exposure and the deactivation or
off-press development are performed with the plate in the dark or
substantially dark.
[0075] The plate can be imaged on a laser imager and deactivated
with a deactivating device or off-press developed with a developing
device in a room which has a lighting that contains no or
substantially no radiation below a wavelength selected from 400 to
650 nm. The plate can be manually or automatically handled between
the imager and deactivating device or developing device. The imager
and deactivating or developing device can stay open to the room
light.
[0076] In another embodiment, the plate can be packaged in a
light-tight cassette to feed to the exposure device that is
designed to be light-tight for the plate, with the plate covered
with light-tight covers. The plate can be automatically transferred
to the deactivating device or the off-press developing device, with
the plate staying within the light-tight covers all the time until
it has been deactivated or off-press developed. Alternatively, the
above automatic processes can be designed so that the light tight
covers have some light-filtering windows which only passes
radiation above a wavelength selected from 400 to 650 nm (such as
500 nm), so that the operator can visually monitor the plate during
imaging and deactivation or off-press development.
[0077] The lighting (in addition to in the dark or substantially
dark) used for the imaging, or deactivation or off-press
development can be any light that contains no or substantially no
radiation below a wavelength selected from 400 to 650 nm. Such a
cutoff wavelength can be 400, 450, 500, 550, 600, and 650 nm, or
any wavelength between 400 and 650 mm, depending on the spectral
sensitivity of the plate. Usually, such light is achieved by adding
a filtering cover or coating to a white fluorescence or
incandescence lamp to cut off the radiation at shorter wavelength.
Such light includes yellow and red lights (including any light with
color between yellow and red, such as orange light). Various yellow
and red lights are commercially available (such as from EncapSulite
International and General Electric), and can be used for the
instant invention.
[0078] This invention is further illustrated by the following
examples of its practice.
EXAMPLES 1-3
[0079] An electrochemically grained, anodized, and
polyvinylphosphonic acid treated aluminum sheet was first coated
with a 0.1% aqueous solution of polyvinyl alcohol (Airvol 540, from
Air Products) with a #6 Meyer rod, followed by drying in an oven at
100.degree. C. for 2 min. The polyvinyl alcohol coated substrate
was further coated with the photosensitive layer formulation PS-1
with a #8 Meyer rod, followed by drying in an oven at 90.degree. C.
for 2 min. TABLE-US-00001 PS-1 Component Weight ratios Neocryl
B-728 (Polymer from Zeneca) 2.75 DPHA (Acrylic monomer from UCB
Chemicals) 6.56 Pluronic L43 (Nonionic surfactant from BASF) 0.56
2,2-Bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'- 1.21
biimidazole 4,4'-Bis(diethylamino)benzophenone 0.77
2-Mercaptobenzoxazole 0.15 2-Butanone 88.00
[0080] The photosensitive layer coated plate was further coated
with a water-soluble overcoat OC-1 using a #6 Meyer rod, followed
by drying in an oven at 100.degree. C. for 2 min. All the coatings
were performed under a red light and the plate was then stored in a
light tight box. TABLE-US-00002 OC-1 Component Weight (g) Airvol
203 (polyvinyl alcohol from Air Products) 4.84 Silwet 7604
(Surfactant from Union Carbide) 0.02 Triton X-100 (Surfactant from
www.chemistrystore.com) 0.14 Water 95.00
[0081] The plate was exposed with a violet plate imager equipped
with a 60 mw violet laser diode emitting at about 405 nm (MAKO-8
from ECRM) for a dosage of about 90 .mu.J/cm.sup.2. The plate was
imaged in an orange light room (with Fuji Yellow FV30 lights from
Encapsulite), and was kept in a light tight box before and after
imaging.
[0082] The laser exposed plate was cut into 3 pieces under red
light. The first piece was treated with a 5% citric acid aqueous
solution by dipping in the solution for 10 seconds. The second
piece was rinsed with water by dipping in water for 5 seconds to
remove the overcoat. The third piece was not treated. The
treatments were performed under red light.
[0083] Each of the treated plates was tested on a wet lithographic
press (AB Dick 360) under office (white) fluorescence light. The
plate was directly mounted on the plate cylinder of the press.
After starting the press, the fountain roller was engaged for 20
rotations, the ink roller (carrying emulsion of ink and fountain
solution) was applied to the plate cylinder for 20 rotations, and
the plate cylinder was then engaged with the blanket cylinder and
printed with paper for 200 impressions. The printed sheets were
evaluated for on-press developability of the plate, with the
results summarized in Table 1. TABLE-US-00003 TABLE 1 Treatment of
Background at Background at Inking in the plate 20 impressions 200
impressions imaging areas Dip in a 5% citric Clean Clean Good acid
aqueous solution Rinse with water Toning Toning Good No treatment
Inked Inked Good
EXAMPLE 4
[0084] An electrochemically grained, anodized, and silicate treated
aluminum sheet was coated with the photosensitive layer formulation
PS-1 with a #6 Meyer rod, followed by drying in an oven at
90.degree. C. for 2 min. The photosensitive layer coated plate was
further coated with a water-soluble overcoat OC-1 using a #6 Meyer
rod, followed by drying in an oven at 100.degree. C. for 2 min. The
plate was prepared under a red light and then stored in a light
tight box.
[0085] The plate was exposed with a violet plate imager equipped
with a 60 mw violet laser diode emitting at about 405 nm (MAKO-8
from ECRM) for a dosage of about 90 .mu.J/cm.sup.2. The plate was
imaged in an orange light room, and was kept in a light tight box
before and after imaging.
[0086] While under a red light, the laser-exposed plate was rubbed
for 10 times for all areas with a cloth soaked with both ink and
fountain solution. The exposed areas were well inked, and the
non-exposed areas were free of ink.
[0087] The developed plate was mounted on a lithographic press (AB
Dick 360) under office fluorescence light to print to 200
impressions. The printed sheets all showed good inking in the
exposed areas and clean background in the non-exposed areas.
* * * * *
References