U.S. patent application number 09/864570 was filed with the patent office on 2003-04-03 for negative-working thermal imaging member and methods of imaging and printing.
This patent application is currently assigned to Eastman Kodak Company. Invention is credited to Bailey, David B., Lander, Charles W..
Application Number | 20030064317 09/864570 |
Document ID | / |
Family ID | 25343558 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030064317 |
Kind Code |
A1 |
Bailey, David B. ; et
al. |
April 3, 2003 |
Negative-working thermal imaging member and methods of imaging and
printing
Abstract
A negative-working imaging member can be used as a lithographic
printing plate without ablation. The imaging member comprises a
support and an imaging layer that includes a dispersion of at least
0.05 g/m.sup.2 of a cyanoacrylate polymer that is thermally
degradable below 200.degree. C., a photothermal conversion material
that is present in an amount to provide a dry weight ratio to the
cyanoacrylate polymer of from about 0.02:1 to about 0.8:1, and a
hydrophilic binder to provide a dry weight ratio of a hydrophilic
binder to the cyanoacrylate polymer of up to 1:1. Thermal imaging
energy causes the exposed areas of the imaging layer to adhere to
the support while unexposed areas can be readily washed off and/or
simultaneously inked for press runs.
Inventors: |
Bailey, David B.; (Webster,
NY) ; Lander, Charles W.; (Wayland, NY) |
Correspondence
Address: |
Paul A. Leipold
Patent Legal Staff
Eastman Kodak Company
343 State Street
Rochester
NY
14650-2201
US
|
Assignee: |
Eastman Kodak Company
|
Family ID: |
25343558 |
Appl. No.: |
09/864570 |
Filed: |
May 24, 2001 |
Current U.S.
Class: |
430/270.1 ;
430/281.1; 430/302; 430/303 |
Current CPC
Class: |
B41C 2210/04 20130101;
B41C 1/1008 20130101; B41C 2210/24 20130101; B41C 2210/22 20130101;
Y10S 430/146 20130101; Y10S 430/165 20130101; B41C 2210/08
20130101; Y10S 430/145 20130101 |
Class at
Publication: |
430/270.1 ;
430/281.1; 430/302; 430/303 |
International
Class: |
G03F 007/038 |
Claims
We claim:
1. A negative-working imaging member comprising a support having
thereon a hydrophilic imaging layer comprising a dispersion of at
least 0.05 g/m.sup.2 of a cyanoacrylate polymer that is thermally
degradable below 200.degree. C., a photothermal conversion material
that is present in an amount to provide a dry weight ratio to said
cyanoacrylate polymer of from about 0.02:1 to about 0.8:1, and a
hydrophilic binder to provide a dry weight ratio of said
hydrophilic binder to said cyanoacrylate polymer of up to 1:1.
2. The imaging member of claim 1 wherein said hydrophilic imaging
layer comprises said hydrophilic binder and said cyanoacrylate
polymer to provide a dry weight ratio of from about 0.01:1 to
1:1.
3. The imaging member of claim 2 wherein said hydrophilic imaging
layer comprises said hydrophilic binder and said cyanoacrylate
polymer to provide a dry weight ratio of from about 0.15:1 to
0.75:1.
4. The imaging member of claim 1 wherein said hydrophilic imaging
layer has a dry thickness of from about 0.05 to about 20 .mu.m.
5. The imaging member of claim 4 wherein said hydrophilic imaging
layer has a dry thickness of from about 0.5 to about 4 .mu.m.
6. The imaging member of claim 1 wherein the dry weight ratio of
said photothermal conversion material to said cyanoacrylate polymer
is from about 0.1:1 to about 0.5: 1.
7. The imaging member of claim 1 comprising a polyester or aluminum
support.
8. The imaging member of claim 1 wherein said support is an
on-press printing cylinder.
9. The imaging member of claim 1 wherein said cyanoacrylate polymer
is a poly(alkyl cyanoacrylate), poly(aryl cyanoacrylate), or
poly(alkoxyalkyl cyanoacrylate) and has a molecular weight of at
least 5000 g/mole.
10. The imaging member of claim 1 wherein said cyanoacrylate
polymer is: poly(methyl cyanoacrylate), poly(ethyl cyanoacrylate),
poly(methyl cyanoacrylate-co-ethyl cyanoacrylate),
poly(methoxyethyl cyanoacrylate), poly(n-butyl cyanoacrylate),
poly(phenyl cyanoacrylate), poly(2-ethylhexyl cyanoacrylate),
poly(methyl 2-cyanoacrylate-co-methoxye- thyl
2-cyanoacrylate-co-ethyl-2-cyanoacrylate), poly(methyl
2-cyanoacrylate-co-methyl acrylate), or a mixture of two or more of
these.
11. The imaging member of claim 1 wherein said cyanoacrylate
polymer is composed of recurring units derived from one or more
cyanoacrylate polymerizable monomers and recurring units derived
from one or more additional ethylenically unsaturated polymerizable
monomers, the recurring units derived from one or more said
cyanoacrylate polymerizable monomers comprising at least 50 mol %
of the total recurring units in said cyanoacrylate polymer.
12. The imaging member of claim 1 wherein said hydrophilic polymer
is poly(vinyl alcohol), poly(vinyl pyrrolidones),
polyethyleneimine, poly(ethyloxazoline), polyacrylamide, gelatin
(and its derivatives), polyacrylic acid (and salts thereof), or
mixtures thereof.
13. The imaging member of claim 1 wherein said photothermal
conversion material is an IR dye, an IR-sensitive pigment, or a
carbon black.
14. The imaging member of claim 1 wherein said photothermal
conversion material is a carbon black or an IR dye that is
bis(dichlorobenzene-1,2-t- hiol)nickel(2:1)tetrabutyl ammonium
chloride, tetrachlorophthalocyanine aluminum chloride, or one of
the following compounds: 3IR Dye 2 is the same as IR Dye 1 but with
C.sub.3F.sub.7CO.sub.2 as the anion. 4
15. A method of imaging comprising: A) providing the imaging member
of claim 1, and B) imagewise exposing said imaging member with
thermal energy to provide exposed and unexposed areas in said
hydrophilic imaging layer of said imaging member, whereby said
exposed areas are adhered to said support, and C) washing off said
unexposed areas to form a negative image in said hydrophilic
imaging layer.
16. The method of claim 15 wherein said imagewise exposing is
carried out using an IR radiation emitting laser, and said imaging
member is a lithographic printing plate having an aluminum support
or an on-press imaging cylinder having a cylindrical support.
17. The method of claim 15 wherein said imagewise exposing is
accomplished using a thermoresistive head.
18. A method of printing comprising: A) providing the imaging
member of claim 1, B) imagewise exposing said imaging member with
thermal energy to provide exposed and unexposed areas in said
hydrophilic imaging layer of said imaging member, whereby said
exposed areas are adhered to said support, C) washing off said
unexposed areas to form a negative image in said hydrophilic
imaging layer, and D) simultaneously with or subsequent to step C,
contacting said imagewise exposed imaging member with a
lithographic printing ink, and imagewise transferring said printing
ink from said imaging member to a receiving material.
19. A method of imaging comprising: A) spray coating a dispersion
comprising at least 0.05 g/m.sup.2 of a cyanoacrylate polymer that
is thermally degradable below 200.degree. C., a photothermal
conversion material that is present in an amount to provide a dry
weight ratio to said cyanoacrylate polymer of from about 0.02:1 to
about 0.8:1, and a hydrophilic binder to provide a dry weight ratio
of said hydrophilic binder to said cyanoacrylate polymer of up to
1:1, onto a support to provide a negative-working imaging member,
and B) imagewise exposing said imaging member with thermal energy
to provide exposed and unexposed areas in said hydrophilic imaging
layer of said imaging member, whereby said exposed areas are
adhered to said support.
20. The method of claim 19 wherein said unexposed areas are washed
off said imaging member and said imaging member is inked and used
in press runs.
21. The method of claim 19 wherein said imagewise exposing is
carried out using an IR radiation emitting laser.
22. The method of claim 19 wherein said support is an on-press
printing cylinder.
23. A method of imaging comprising: A) providing the imaging member
of claim 1 on press, B) imagewise exposing said imaging member with
thermal energy to provide exposed and unexposed areas in said
hydrophilic imaging layer of said imaging member, whereby said
exposed areas are adhered to said support, and C) without wet
processing, washing off said unexposed areas to form a negative
image in said hydrophilic imaging layer.
Description
FIELD OF TIE INVENTION
[0001] This invention relates in general to negative-working
thermal imaging members (particularly lithographic printing
plates). The invention also relates to a method of imaging such
imaging members, and to a method of printing.
BACKGROUND OF THE INVENTION
[0002] The art of lithographic printing is based upon the
immiscibility of oil and water, wherein an oily material or ink is
preferentially retained by an imaged area and the water or fountain
solution is preferentially retained by the non-imaged areas. When a
suitably prepared surface is moistened with water and ink is
applied, the background or non-imaged areas retain the water and
repel the ink while the imaged areas accept the ink and repel the
water. The ink is then transferred to the surface of a suitable
substrate, such as cloth, paper or metal, thereby reproducing the
image.
[0003] Very common lithographic printing plates include a metal or
polymer support having thereon an imaging layer sensitive to
visible or UV light. Both positive- and negative-working printing
plates can be prepared in this fashion. Upon exposure to a
patterned light image, and perhaps post-exposure heating, either
imaged or non-imaged areas are removed using wet processing
chemistries.
[0004] "Direct-write" imaging avoids the need for patterned light
imaging and chemical processing. Direct-write using an infrared
radiation laser is a thermally driven process and is more desirable
because the laser heats only a small region at a time. Moreover,
computer control allows for high-resolution images to be generated
at high speed since the images can be produced directly on the
imaging member surface, pixel by pixel. The conventional chemical
processing steps may also be eliminated in such imaging
techniques.
[0005] Examples of thermally sensitive printing plates are
described in U.S. Pat. No. 5,372,915 (Haley et al.). They include
an imaging layer comprising a mixture of dissolvable polymers and
an infrared radiation absorbing compound. While these plates can be
imaged using lasers and digital information, they still require wet
processing using alkaline developer solutions.
[0006] It has been recognized that a lithographic printing plate
could be created by ablating an IR absorbing layer. For example,
Canadian 1,050,805 (Eames) discloses a dry planographic printing
plate comprising an ink receptive substrate, an overlying silicone
rubber layer, and an interposed layer comprised of laser energy
absorbing particles (such as carbon particles) in a self-oxidizing
binder (such as nitrocellulose). Such plates were exposed to
focused near IR radiation with a Nd++YAG laser. The absorbing layer
converted the infrared energy to heat thus partially loosening,
vaporizing or ablating the absorber layer and the overlying
silicone rubber. Similar plates are described in Research
Disclosure 19201, 1980 as having vacuum-evaporated metal layers to
absorb laser radiation in order to facilitate the removal of a
silicone rubber overcoated layer. These plates were developed by
wetting with hexane and rubbing. Other publications describing
ablatable printing plates include U.S. Pat. No. 5,385,092 (Lewis et
al.), U.S. Pat. No. 5,339,737 (Lewis et al.), U.S. Pat. No.
5,353,705 (Lewis et al.), U.S. Reissue Pat. No. 35,512 (Nowak et
al.), and U.S. Pat. No. 5,378,580 (Leenders).
[0007] The noted printing plates have a number of disadvantages.
The process of ablation creates debris and vaporized materials that
must be collected. The laser power required for ablation can be
considerably high, and the components of such printing plates may
be expensive, difficult to coat, or unacceptable for resulting
printing quality. Such plates generally require at least two coated
layers on a support.
[0008] Thermal or laser mass transfer is another method of
preparing processless lithographic printing plates. Such methods
are described for example in U.S. Pat. No. 5,460,918 (Ali et al.)
wherein a hydrophobic image is transferred from a donor sheet to a
microporous hydrophilic crosslinked silicated surface of the
receiver sheet. U.S. Pat. No. 3,964,389 (Peterson) describes a
process of laser transfer of an image from a donor material to a
receiver material requiring a high temperature post-heating
step.
[0009] Still another method of imaging is the use of materials
comprising microencapsulated hydrophobic materials as described for
example in U.S. Pat. No. 5,569,573 (Takahashi et al.). Upon thermal
imaging, the microcapsules rupture in an imagewise fashion to
provide an ink-receptive image.
[0010] Thermally switchable polymers have been described for use as
imaging materials in printing plates. By "switchable" is meant that
the polymer is rendered from hydrophobic to relatively more
hydrophilic or, conversely from hydrophilic to relatively more
hydrophobic, upon exposure to heat. U.S. Pat. No. 4,034,183 (Uhlig)
describes the use of high powered lasers to convert hydrophilic
surface layers to hydrophobic surfaces. A similar process is
described for converting polyamic acids into polyimides through a
transparency mask in U.S. Pat. No. 4,081,572 (Pacansky). The use of
high-powered lasers is undesirable in the industry because of their
high electrical power requirements and because of their need for
cooling and frequent maintenance.
[0011] U.S. Pat. No. 4,634,659 (Esumi et al.) describes imagewise
irradiating hydrophobic polymer coatings to render exposed regions
more hydrophilic in nature. While this concept was one of the early
applications of converting surface characteristics in printing
plates, it has the disadvantages of requiring long UV light
exposure times (up to 60 minutes), and the plate's use is in a
positive-working mode only.
[0012] U.S. Pat. No. 4,405,705 (Etoh et al.) and U.S. Pat. No.
4,548,893 (Lee et al.) describe amine-containing polymers for
photosensitive materials used in non-thermal processes. Thermal
processes using polyamic acids and vinyl polymers with pendant
quaternary ammonium groups are described in U.S. Pat. No. 4,693,958
(Schwartz et al.). U.S. Pat. No. 5,512,418 (Ma) describes the use
of polymers having cationic quaternary ammonium groups that are
heat-sensitive.
[0013] WO 92/09934 (Vogel et al.) describes photosensitive
compositions containing a photoacid generator and a polymer with
acid labile tetrahydropyranyl or activated ester groups. However,
imaging of these compositions converts the imaged areas from
hydrophobic to hydrophilic in nature.
[0014] EP-A 0 652 483 (Ellis et al.) describes direct-write
lithographic printing plates imageable using IR lasers that do not
require wet processing. These plates comprise an imaging layer that
becomes more hydrophilic upon imagewise exposure to heat. This
coating contains a polymer having pendant groups (such as t-alkyl
carboxylates) that are capable of reacting under heat or acid to
form more polar, hydrophilic groups.
[0015] Additional imaging materials described in, for example, U.S.
Pat. No. 6,030,750 (Vermeersch et al.) utilize thermoplastic
polymer particles that are believed to be capable of coalescing
under the influence of heat.
[0016] U.S. Pat. No. 5,605,780 (Burberry et al.) describes printing
plates that are imaged by an ablation method whereby exposed areas
are removed from the heat generated by a focused high-intensity
laser beam. The imaging layer is composed of an IR-absorbing
compound in a film-forming cyanoacrylate polymer binder. In order
for thermal ablation to be successful in such printing plates, the
imaging later thickness is generally less than 0.1 .mu.m and the
weight ratio of IR-absorbing compound to the cyanoacrylate polymer
is at least 1:1. Thus, the imaging layers are quite thin and have a
significant amount of IR-absorbing compound.
[0017] There is a need in the graphic arts industry for a means to
provide processless, direct-write, negative-working lithographic
imaging members that can be imaged without ablation, or the other
problems noted above, to provide high sensitivity, high imaging
speed, long shelf life, and long press life.
SUMMARY OF THE INVENTION
[0018] The problems noted above are overcome with a
negative-working imaging member comprising a support having thereon
a hydrophilic imaging layer comprising a dispersion of at least
0.05 g/m.sup.2 of a cyanoacrylate polymer that is thermally
degradable below 200.degree. C., a photothermal conversion material
that is present in an amount to provide a dry weight ratio to the
cyanoacrylate polymer of from about 0.02:1 to about 0.8:1, and a
hydrophilic binder to provide a dry weight ratio of hydrophilic
binder to the cyanoacrylate polymer of up to 1:1.
[0019] This invention also includes a method of imaging comprising
the steps of:
[0020] A) providing the imaging member as described above, and
[0021] B) imagewise exposing the imaging member to thermal energy
to provide exposed and unexposed areas in the hydrophilic imaging
layer of the imaging member, whereby the exposed areas are adhered
to the support, and
[0022] C) washing off the unexposed areas to form a negative image
in the imaging layer.
[0023] A method of printing comprises the steps of carrying out
steps A, B, and C noted above, and additionally:
[0024] D) simultaneously with or subsequently to, contacting the
imagewise exposed imaging member with a lithographic printing ink,
and imagewise transferring that printing ink from the imaging
member to a receiving material.
[0025] Still further, this invention comprises a method of imaging
that comprises the steps of:
[0026] A) spray coating a dispersion comprising at least 0.05
g/m.sup.2 of a cyanoacrylate polymer that is thermally degradable
below 200.degree. C., a photothermal conversion material that is
present in an amount to provide a dry weight ratio to the
cyanoacrylate polymer of from about 0.02:1 to about 0.8:1, and a
hydrophilic binder to provide a dry weight ratio of the hydrophilic
binder to the cyanoacrylate polymer of up to 1:1, onto a support to
provide a negative-working imaging member, and
[0027] B) imagewise exposing the imaging member with thermal energy
to provide exposed and unexposed areas in the hydrophilic imaging
layer of the imaging member, whereby the exposed areas are adhered
to the support.
[0028] The present invention also provides a method of imaging
comprising:
[0029] A) providing the imaging member described above on
press,
[0030] B) imagewise exposing the imaging member with thermal energy
to provide exposed and unexposed areas in the hydrophilic imaging
layer of the imaging member, whereby the exposed areas are adhered
to the support, and
[0031] C) without alkaline processing, washing off the unexposed
areas to form a negative image in the hydrophilic imaging
layer.
[0032] The negative-working imaging members of this invention have
a number of advantages and avoid the problems of known printing
plates. Specifically, the problems and concerns associated with
ablation imaging (that is, imagewise removal of a surface layer)
are avoided because imaging is accomplished in the imaging layer by
adhering (preferably, irreversibly) exposed areas of the printing
surface and washing off unexposed areas before or during printing.
Thus, the imaged (exposed) areas are adhered to the support during
and after imaging (that is, no ablation imaging occurs). The
resulting printing members formed from the imaging members of this
invention are negative working in nature.
[0033] The thermally sensitive imaging polymers used in the imaging
members of this invention can be readily prepared or purchased from
a number of commercial sources. Thus, the imaging members are
simple to make.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0034] "Photothermal conversion materials" are inorganic or organic
compounds that absorb radiation from an appropriate energy source
(such as a laser) and converts that radiation into heat. More
details of such compounds are provided below.
[0035] As known in the lithographic printing art, materials that
release or repel oil-based inks are referred to as having
"oleophobic", "hydrophilic", or "ink-repelling" character, and
conversely, materials that accept oil-based inks are referred to an
"oleophilic" or "hydrophobic."
[0036] "Wet processing" refers to washing off unexposed regions of
the imaging layer after imaging using water or a fountain solution.
It does not refer to contacting the imaging member with alkaline
developers or other chemical processing solutions used in
conventional lithographic developing methods.
[0037] "Dry weight ratio" refers to a weight ratio in dry form
(coated or uncoated).
[0038] When referring to the cyanoacrylate polymers as "thermally
degradable," we mean that greater than 50% (preferably greater than
90%) of the polymer weight is lost, as measured by
thermogravimetric analysis. Thus, it is considered that the
cyanoacrylate polymers used in the practice of this invention are
not "thermoplastic" materials. Thermoplastic materials are known in
the art to be materials that undergo no chemical change when heated
to a temperature where "flow" can occur.
[0039] The imaging members of this invention comprise a support and
one or more layers thereon that include a dried thermally sensitive
composition as described herein. The support can be any
self-supporting material including polymeric films, glass,
ceramics, cellulosic materials (including papers), metals or stiff
papers, or a lamination of any of these materials. The thickness of
the support can be varied and should be sufficient to sustain the
wear from printing and thin enough to wrap around a printing form.
A preferred embodiment uses a polyester support prepared from, for
example, polyethylene terephthalate or polyethylene naphthalate,
and having a thickness of from about 100 to about 310 .mu.m.
Another preferred embodiment uses aluminum sheets (grained or
ungrained, anodized or unanodized) having a thickness of from about
100 to about 600 .mu.m. The support should resist dimensional
change under conditions of use. The aluminum and polyester supports
are most preferred for the imaging members of this invention.
[0040] The support may also be a cylindrical support that includes
imaging or printing cylinders on-press as well as printing sleeves
that are fitted over printing cylinders. The use of such supports
to provide cylindrical imaging members is described in U.S. Pat.
No. 5,713,287 (Gelbart). The thermally sensitive composition (or
dispersion) described herein can be coated or sprayed directly onto
the cylindrical surface that is an integral part of the printing
press.
[0041] The backside of the support may be coated with antistatic
agents and/or slipping layers or matte layers to improve handling
and "feel" of the imaging member.
[0042] The imaging members, however, preferably have only one layer
on the support, that is a heat-sensitive surface layer that is
required for imaging. This layer is prepared from a heat-sensitive
composition described herein and includes one or more thermally
sensitive cyanoacrylate polymers described below and one or more
photothermal conversion materials (both described below) as the
only essential components for imaging. Because of the particular
thermally sensitive polymers used in the imaging layer, the exposed
(imaged) areas of the layer are rendered water-insoluble because
they are adhered to the support. The unexposed areas remain
relatively hydrophilic in nature and can be washed off using water
or a fountain solution.
[0043] In an alternative embodiment, the imaging member comprises
one or more thermally sensitive polymers as described herein in a
surface imaging layer, and one or more photothermal conversion
materials in a separate layer directly over or underneath, or in
thermal contact with, the imaging layer. The photothermal
conversion materials can diffuse into the imaging layer prior to or
during imaging.
[0044] The cyanoacrylate polymers used in the present invention
have many advantageous properties for use in image-forming layers
of lithographic printing plates, including relatively low
decomposition (typically below 200.degree. C.), good ink affinity,
excellent adhesion to the surface of the support (especially
anodized aluminum), good resistance to common pressroom chemicals,
and high wear resistance.
[0045] Useful cyanoacrylate polymers include homopolymers derived
from a single cyanoacrylate ethylenically unsaturated polymerizable
monomer, copolymers derived from two or more such cyanoacrylate
monomers, or copolymers derived from one or more such cyanoacrylate
monomers and one or "additional" ethylenically unsaturated
polymerizable monomers (that are not cyanoacrylates). Where the
polymers include recurring units derived from the "additional"
monomers, at least 50 mol % of the recurring units in the polymers
are derived from one or more cyanoacrylate monomers. The polymers
generally have a molecular weight of at least 5000 g/mole, and
preferably of at least 10,000 g/mole.
[0046] Useful "additional" monomers that can be copolymerized with
one or more cyanoacrylate monomers include, but are not limited to,
acrylamides, methacrylamides, acrylates and methacrylates (such as
ethyl acrylate, ethyl methacrylate, n-butyl acrylate, methyl
methacrylate, t-butyl methacrylate, and n-butyl methacrylate),
acrylonitrile and methacrylonitrile, styrene and styrene
derivatives, acrylamides and methacrylamides, vinyl ethers, vinyl
pyridines, vinyl pyrrolidones, vinyl acetate, vinyl halides (such
as vinyl chloride, vinylidene chloride, and vinyl bromide), and
dienes (such as ethylene, propylene, 1,3-butadiene, and
isobutylene). Acrylates, acrylamides and styrene (and its
derivatives) are preferred.
[0047] Preferably, the cyanoacrylate polymers used in the present
invention are poly(alkyl cyanoacrylates), poly(aryl
cyanoacrylates), or poly(alkoxyalkyl cyanoacrylates) wherein an
alkyl, aryl or alkoxyalkyl group is present as the ester group.
Useful substituted or unsubstituted alkyl groups can have 1 to 12
carbon atoms and be linear or branched groups. Useful substituted
or unsubstituted alkoxyalkyl groups can have 2 to 14 carbon atoms
and be linear or branched groups. Useful substituted or
unsubstituted aryl groups are carbocyclic aromatic groups having 6
to 10 carbon atoms in the aromatic ring. Useful substituents on
these groups can include any monovalent chemical moiety that a
skilled artisan would understand as not harmful to the desired
function of the cyanoacrylate polymer.
[0048] Representative cyanoacrylate polymers include the following.
Molar ratios are shown where the polymers are derived in part from
"additional" ethylenically unsaturated polymerizable monomers.
[0049] Poly(methyl 2-cyanoacrylate),
[0050] Poly(ethyl 2-cyanoacrylate),
[0051] Poly(methyl 2-cyanoacrylate-co-ethyl 2-cyanoacrylate),
[0052] Poly(methoxyethyl 2-cyanoacrylate),
[0053] Poly(n-butyl 2-cyanoacrylate),
[0054] Poly(phenyl 2-cyanoacrylate),
[0055] Poly(2-ethylhexyl 2-cyanoacrylate),
[0056] Poly(methyl 2-cyanoacrylate-co-methoxyethyl
2-cyanoacrylate-co-ethy- l-2-cyanoacrylate), and
[0057] Poly(methyl 2-cyanoacrylate-co-methyl acrylate)(90:10 mol
ratio).
[0058] Mixtures of the cyanoacrylate polymers can be used as well,
particularly mixtures of two or more of the specific listed
polymers.
[0059] A preferred polymer used in the practice of this invention
is poly(methyl 2-cyanoacrylate-co-ethyl 2-cyanoacrylate) and its
use is demonstrated in the examples.
[0060] The cyanoacrylate polymers useful in this invention can be
readily prepared using known polymerization techniques and commonly
available starting materials and reagents. Other details of
preparation are provided in U.S. Pat. No. 5,605,780 (noted
above).
[0061] While its presence is not essential for all embodiments, it
is preferred to include one or more hydrophilic binders in the
hydrophilic imaging layer (formulation) described herein. Thus, the
imaging layer can be free of such binders, but generally they are
present to provide a dry weight ratio of binder(s) to the total
cyanoacrylate polymers of at least 0.01:1 and preferably at least
0.15:1. The dry weight ratio of such binder(s) to cyanoacrylate
polymer(s) can be as high as 1:1, but preferably it is up to
0.75:1. Dry weight ratios greater than 1:1 tend to diminish the
effectiveness of the cyanoacrylate polymer(s) as imaging components
in the imaging layer. Such binders must be water-soluble or
water-dispersible so they can be removed from the support in
unexposed areas.
[0062] Examples of useful hydrophilic binders include, but are not
limited to, poly(vinyl alcohol), poly(vinyl pyrrolidones),
poly(ethyleneimine) (PEI), poly(ethyloxazoline), polyacrylamide,
gelatin (and its derivatives), polyacrylic acid (and salts
thereof), and other similar hydrophilic materials that would be
readily apparent to one skilled in the art. Mixtures of hydrophilic
binders can also be used. Poly(vinyl alcohol) is the preferred
hydrophilic binder material. Commercial sources for such materials
are well known to skilled artisans.
[0063] The imaging layer of the imaging member can also include
minor amounts (less than 20 weight %, based on total dry weight of
the layer) of additional binder or polymeric materials that will
not adversely affect its imaging or printing characteristics.
However, the imaging layer comprises no additional materials that
are needed for imaging commonly used in printing plates that are
wet processed using alkaline developer solutions.
[0064] The imaging and any other layers in the imaging member can
also include one or more conventional surfactants for coatability
or other properties, dyes or colorants to allow visualization of
the written image, or any other addenda commonly used in the
lithographic art, as long as the concentrations are low enough so
they are inert with respect to imaging or printing properties.
[0065] It is essential that the imaging member include one or more
photothermal conversion materials. Preferably, they absorb
radiation in the infrared and near-infrared regions of the
electromagnetic spectrum. The photothermal conversion materials
useful in this invention include infrared radiation (IR) dyes, a
carbon black (including polymer grafted carbons), IR-sensitive
pigments, evaporated pigments, semiconductor materials, alloys,
metals, metal oxides, metal sulfides or combinations thereof, or a
dichroic stack of materials that absorb radiation by virtue of
their refractive index and thickness. Borides, carbides, nitrides,
carbonitrides, bronze-structured oxides and oxides structurally
related to the bronze family but lacking the WO.sub.29 component,
are also useful. Useful absorbing dyes for near infrared diode
laser beams are described, for example, in U.S. Pat. No. 4,973,572
(DeBoer). Particular dyes of interest are "broad band" dyes, that
is those that absorb over a wide band of the spectrum. Mixtures of
one or more types of these compounds can be used if desired. Carbon
blacks and IR dyes are preferred photothermal conversion
materials.
[0066] Still other useful photothermal conversion materials include
multisulfonated IR dyes as described U.S. Pat. No. 6,159,657
(Fleming et al.), the disclosure of which is incorporated herein by
reference.
[0067] Useful IR dyes are sensitive to radiation in the
near-infrared and infrared regions of the electromagnetic spectrum.
Thus, they are generally sensitive to radiation at or above 700 nm
(preferably from about 800 to about 900 nm, and more preferably
from about 800 to about 850 nm).
[0068] Examples of useful IR dyes of several classes include, but
are not limited to,
bis(dichlorobenzene-1,2-thiol)nickel(2:1)tetrabutyl ammonium
chloride, tetrachlorophthalocyanine aluminum chloride, and the
following compounds: 1
[0069] IR Dye 2 is the same as IR Dye 1 but with
C.sub.3F.sub.7CO.sub.2.su- p.- as the anion. 2
[0070] IR Dyes 1-7 can be prepared using known procedures
or-obtained from several commercial sources (for example, Esprit,
Sarasota, Fla.). IR dyes 8-14 can be prepared using known
procedures, as described for example in U.S. Pat. No. 4,871,656
(Parton et al.) and reference noted therein (for example, U.S. Pat.
No. 2,895,955, U.S. Pat. No. 3,148,187 and U.S. Pat. No.
3,423,207), all incorporated by reference. Other useful IR dyes are
described in U.S. Pat. No. 5,605,780 (noted above), incorporated
herein by reference. IR Dye 2 is one particularly useful
photothermal conversion material for use in the practice of this
invention.
[0071] As noted above, the one or more photothermal conversion
materials can be formulated in a separate layer that is in thermal
contact with the heat-sensitive imaging layer. Thus, during
imaging, the action of the additional photothermal conversion
material can be transferred to the heat-sensitive imaging layer.
Preferably, the one or more photothermal conversion materials are
formulated in a dispersion comprising the one or more cyanoacrylate
polymers and optional hydrophilic binders.
[0072] Wherever the photothermal conversion materials are located,
the total amount is generally sufficient to provide an optical
density of at least 0.1, and preferably of at least 1.0. The
particular amount required for a given material and formulation
could be readily determined by a skilled worker in the art using
routine experimentation. In the thermally sensitive imaging
compositions used to provide hydrophilic imaging layers, the
photothermal conversion material(s) is generally present in an
amount of from about 5 to about 35% of the total solids (prior to
drying). The dry weight ratio of photothermal conversion material
to the one or more cyanoacrylate polymers is from about 0.02:1 to
about 0.8:1, and preferably from about 0.1:1 to about 0.5:1.
[0073] In the typical manufacture of the imaging members of this
invention, a thermally sensitive imaging composition is formed by
combining the one or more cyanoacrylate polymers, the photothermal
conversion material(s), any hydrophilic binder, and any optional
addenda in a suitable solvent or mixture of solvents to form a
coating solution or dispersion. Various mixing or dispersing
techniques may be used that do not adversely affect the performance
of the individual composition components.
[0074] A layer of the resulting dispersion or composition is then
formed on the suitable support and dried in any suitable manner.
During coating and drying, solvents, conditions, and equipment are
selected to assure suitable adhesion to the support for handling
prior to imaging. However, the adhesion is not so strong that the
unexposed areas cannot be readily washed off while exposed areas
are more strongly adhered to the support.
[0075] The thermally sensitive imaging compositions are generally
formulated in and coated from water or water-miscible organic
solvents including, but not limited to, water-miscible alcohols
(for example, methanol, ethanol, isopropanol, 1-methoxy-2-propanol
and n-propanol), methyl ethyl ketone, tetrahydrofuran, acetonitrile
and acetone. Water, methanol, ethanol and 1-methoxy-2-propanol are
preferred. Mixtures (such as a mixture of water and methanol) of
these solvents can also be used if desired. By "water-miscible" is
meant that the organic solvent is miscible in water at all
proportions at room temperature.
[0076] In such thermally sensitive imaging compositions (including
solvent), the one or more cyanoacrylate polymers are generally
present in an amount of at least 1% solids, and preferably at least
2% solids. A practical upper limit of the amount of cyanoacrylate
polymer(s) in the composition is 20% solids. The amount of
cyanoacrylate polymer(s) present in the dried imaging layer is
generally at least 0.05 g/m.sup.2, and preferably from about 0.5 to
about 2 g/m.sup.2 (dry weight). The amounts of photothermal
conversion material(s) and any hydrophilic binders can be readily
determined from the amount of cyanoacrylate polymer(s).
[0077] The dried imaging layer generally has an average dry
thickness of from about 0.05 to about 20 .mu.m, and preferably from
about 0.5 to about 4 .mu.m.
[0078] The imaging member of this invention can also include a
protective overcoat or surface layer over the hydrophilic imaging
layer. Such layers can be composed of one or more hydrophilic
binders as described above that are water-soluble or
water-dispersible. Preferably, such binders are coatable out of
water or one or more water-miscible organic solvents such as ethyl
acetate.
[0079] The thermally sensitive imaging composition described herein
can be applied to a support using any suitable equipment and
procedure, such as spin coating, knife coating, gravure coating,
dip coating or extrusion hopper coating. In addition, the
composition can be sprayed onto a support, including an on-press
cylindrical support (such as an on-press cylinder or sleeve), using
any suitable spraying means for example as described in U.S. Pat.
No. 5,713,287 (noted above) to provide an imaging member.
[0080] The negative-working imaging members of this invention can
be of any useful form including, but not limited to, printing
plates, printing cylinders, printing sleeves and printing tapes
(including flexible printing webs), all of any suitable size or
dimensions. Preferably, the imaging members are lithographic
printing plates having an aluminum support or on-press imaging
cylinders having the imaging layer disposed thereon.
[0081] To provide an image, the negative-working imaging members of
this invention are exposed to a suitable source of energy that
generates or provides heat, such as a focused laser beam (for
example, from an IR radiation emitting laser) or a thermoresistive
head (or "thermal head"), in the foreground areas where ink is
desired in the printed image, typically from digital information
supplied to the imaging device. A laser used to expose the imaging
member of this invention is preferably a diode laser, because of
the reliability and low maintenance of diode laser systems, but
other lasers such as gas or solid state lasers may also be
used.
[0082] The combination of power, intensity and exposure time can be
readily adjusted by a skilled artisan to adhere the exposed regions
of the imaging layer to the support and to avoid significant
ablation as described in U.S. Pat. No. 5,605,780 (noted above).
Otherwise, the imaging conditions for practicing the methods of
this invention are not critical. More importantly to providing the
desired imaging effects is the amount of photothermal conversion
material used in the imaging members.
[0083] Suitable imaging equipment for this type of imaging is well
known in the art, including that described in U.S. Pat. No.
5,168,288 (Baek et al.) and U.S. Pat. No. 5,339,737 (Lewis et al.),
incorporated herein by reference.
[0084] The imaging apparatus can operate on its own, functioning
solely as a platemaker, or it can be incorporated directly into a
lithographic printing press. In the latter case, printing may
commence immediately after imaging, thereby reducing press set-up
time considerably. The imaging apparatus can be configured as a
flatbed recorder or as a drum recorder, with the imaging member
mounted to the interior or exterior cylindrical surface of the
drum.
[0085] In the drum configuration, the requisite relative motion
between an imaging device (such as laser beam) and the imaging
member can be achieved by rotating the drum (and the imaging member
mounted thereon) about its axis, and moving the imaging device
parallel to the rotation axis, thereby scanning the imaging member
circumferentially so the image "grows" in the axial direction.
Alternatively, the beam can be moved parallel to the drum axis and,
after each pass across the imaging member, increment angularly so
that the image "grows" circumferentially. In both cases, after a
complete scan by the laser beam, an image corresponding to the
original document or picture has been formed in the surface of the
imaging member.
[0086] In the flatbed configuration, a laser beam is drawn across
either axis of the imaging member, and is indexed along the other
axis after each pass. Obviously, the requisite relative motion can
be produced by moving the imaging member rather than the laser
beam.
[0087] While laser imaging is preferred in the practice of this
invention, imaging can be provided by any other means that provides
or generates thermal energy in an imagewise fashion. For example,
imaging can be accomplished using a thermoresistive head (thermal
printing head) in what is known as "thermal printing", described
for example in U.S. Pat. No. 5,488,025 (Martin et al.). Such
thermal printing heads are commercially available (for example, as
Fujitsu Thermal Head FTP-040 MCS001 and TDK Thermal Head F415
HH7-1089).
[0088] Imaging on printing press cylinders can be accomplished
using any suitable means, for example, as taught in U.S. Pat. No.
5,713,287 (noted above), that is incorporated herein by
reference.
[0089] After imaging, the imaging member can be used for printing
without conventional wet processing with alkaline developers.
Unexposed areas in the imaging surface are washed away using water
or a conventional fountain solution and exposed areas remain
adhered to the support. Ink applied to the imaging member can then
be imagewise transferred to a suitable receiving material (such as
cloth, paper, metal, glass or plastic) to provide one or more
desired impressions. If desired, an intermediate blanket roller can
be used to transfer the ink from the imaging member to the
receiving material. The imaging members can be cleaned between
impressions, if desired, using conventional cleaning means.
[0090] The following examples are presented to illustrate the
practice of this invention and are not intended to be limiting in
any way.
Methods and Materials for Examples
[0091] Thermally sensitive coating dispersions were prepared by
mixing the indicated amounts of cyanoacrylate polymer(s), infrared
sensitive (IR) dye, and water in a sealed metal tube containing 300
g of 1.3 mm-diameter chrome-plated steel balls. The contents were
shaken vigorously for 1.5 hours after which the formulations were
separated from the chrome-plate steel balls.
[0092] After adding other addenda, the coating formulations were
coated at a wet coverage of 21.6 ml/m.sup.2 onto 5.5 mil (140
.mu.m) thick anodized, grained aluminum sheet supports to provide
the dried layer coverage noted in TABLE II below.
[0093] All of the resulting printing plates were dried in a
convection oven at 82.degree. C. for 3 minutes, clamped onto the
rotating drum of a conventional platesetter having an array of
laser diodes operating at a wavelength of 830 nm each focused to a
spot diameter of 23 mm at dosages ranging from 500 to 1500
mJ/cm.sup.2. Each channel provided a maximum of 450 mWatts (mW) of
power incident upon the imaging layer surface. The plates were then
soaked for about 15 seconds in Varn Universal Pink fountain
solution and gently wiped with a soft cloth under a stream of
distilled water.
[0094] Each laser-exposed plate was then mounted on the plate
cylinder of a conventional full-page A.B. Dick 9870 lithographic
duplicator press for actual press runs using VanSon Diamond Black
lithographic printing ink to provide a few thousand impressions on
paper or until failure.
Example 1
[0095] A thermally sensitive Dispersion I was prepared for this
invention using the following components:
1 Poly(methyl cyanoacrylate-co-ethyl cyanoacrylate)(70:30 weight
3.5 g ratio) "PCA" Polymer IR Dye 2 3.5 g Water 63 g
[0096] Dispersion II was similarly prepared using 5.6 g of polymer,
61.2 g of water, and no IR dye.
[0097] A coating formulation was prepared from these dispersions by
mixing 3.6 g of Dispersion I, 4.03 g of Dispersion II, water (5.04
g), a 10% (by weight) solution of poly(vinyl alcohol) (MW 3000,
2.18 g), and a 5% (by weight) solution of FLUORAD FC431 nonionic
coating aid (0.15 g, 3M Corp.).
[0098] The printing results for the resulting printing plates are
shown in TABLE II below.
[0099] Comparative Example 1
[0100] Dispersion III was prepared using the following
components:
2 Poly(methyl methacrylate) "Mm" polymer 3.5 g IR Dye 2 3.5 g Water
63 g
[0101] Dispersion IV was similarly prepared with 5.6 g of polymer,
61.2 g of water, and no IR dye.
[0102] A coating formulation was prepared by mixing 3.6 g of
Dispersion III and 4.03 g of Dispersion IV, water (5.04 g), a 10%
(by weight) solution of poly(vinyl alcohol) (MW 3000, 2.18 g), and
a 5% (by weight) solution of FLUORAD FC431 nonionic coating aid
(0.15 g, 3M Corp.).
[0103] The printing results for the resulting printing plates are
shown in TABLE II below.
Comparative Example 2
[0104] A 27.5% solids latex of poly(methyl methacrylate) (Latex M)
was prepared by mixing methyl methacrylate monomer (30 g), water
(78 g), sodium dioctylsulfosuccinate surfactant (75% solution, 0.9
g), and potassium persulfate polymerization catalyst (0.15 g). The
mixture was heated at 60.degree. C. for 18 hours to form the
desired polymer latex.
[0105] Dispersion V was prepared using the following
components:
3 Latex M 12.73 g IR Dye 2 3.5 g Water 53.8 g
[0106] A coating formulation was prepared by mixing Dispersion V
(3.6 g), Latex M (1.12 g), water (7.95 g), a 10% (by weight)
solution of poly(vinyl alcohol) (MW 3000, 2.18 g), and a 5% (by
weight) solution of FLUORAD FC431 nonionic coating aid (0.15 g, 3M
Corp.).
[0107] The printing results for the resulting printing plates are
shown in TABLE II below.
Examples 2a-2g
[0108] A thermally sensitive Dispersion VI was prepared using the
following components:
4 Poly(methyl cyanoacrylate-co-ethyl cyanoacrylate)(70:30 9.8 g
weight ratio) "PCA" polymer IR Dye 2 3.5 g Water 56.7 g
[0109] A series of coating formulations was prepared by mixing
Dispersion VI (3.6 g), water (see TABLE I), various amounts of a
10% (by weight) solution of poly(vinyl alcohol) (MW 3000, see TABLE
I), and a 5% (by weight) solution of FLUORAD FC431 nonionic coating
aid (0.15 g, 3M Corp.).
[0110] The printing results for the resulting printing plates are
shown in TABLE II below.
Comparative Examples 3a-3g
[0111] A 28.7% solids latex of poly(methyl methacrylate-co-acrylic
acid) (Latex E) was prepared by mixing methyl methacrylate monomer
(29.1 g), methacrylate acid monomer (0.9 g), water (78 g), sodium
dioctylsulfosuccinate surfactant (75% solution, 0.9 g), and
potassium persulfate catalyst (0.15 g). The mixture was heated at
60.degree. C. for 18 hours to form the desired polymer latex.
[0112] Thermally sensitive dispersion VII was prepared using the
following components:
5 Latex E 34.15 g IR Dye 2 3.5 g Water 32.35 g
[0113] A series of coating formulations was prepared by mixing the
Dispersion VII (3.6 g), water (see TABLE I), a 10% (by weight)
solution of poly(vinyl alcohol) (MW 3000, see TABLE I), and a 5%
(by weight) solution of FLUORAD FC431 nonionic coating aid (0.15 g,
3M Corp.).
[0114] The printing results for the resulting printing plates are
shown in TABLE II below.
Comparative Example 4
[0115] Dispersion VIII was prepared using the following
components:
6 Latex M 34.15 g IR Dye 2 3.5 g Water 32.35 g
[0116] A coating formulation was prepared by mixing Dispersion VIII
(3.6 g), water (9.09 g), a 10% (by weight) solution of poly(vinyl
alcohol) (MW 3000, 2.18 g), and a 5% (by weight) solution of
FLUORAD FC431 nonionic coating aid (0.15 g, 3M Corp.).
[0117] The printing results for the resulting printing plates are
shown in TABLE II below.
7 TABLE I Coating Water PVA Solution Example Dispersion (g) (g)
Example 2a VI 4.44 6.83 Example 2b VI 7.89 3.38 Example 2c VI 9.09
2.18 Example 2d VI 9.84 1.43 Example 2e VI 10.59 0.68 Example 2f VI
10.92 0.34 Example 2g VI 11.26 0 Comparative VII 4.44 6.83 Example
3a Comparative VII 7.89 3.38 Example 3b Comparative VII 9.09 2.18
Example 3c Comparative VII 9.84 1.43 Example 3d Comparative VII
10.59 0.68 Example 3e Comparative VII 10.92 0.34 Example 3f
Comparative VII 11.26 0 Example 3g
[0118]
8 TABLE II Polymer IR Dye Coverage Coverage PVA Coverage Polymer
(mg/m.sup.2) (mg/m.sup.2) (mg/m.sup.2) Imaging/Printing Results
Example 1 PCA 724 259 313 Provided 5000 impressions without failure
Comparative Mm 724 259 313 Failed by 500 impressions* Example 1
Comparative Latex M 724 259 313 Failed by 500 impressions** Example
2 Example 2a PCA 724 259 983 No image Example 2b PCA 724 259 486
Provided 3000 impressions without failure Example 2c PCA 724 259
313 Provided 3000 impressions without failure Example 2d PCA 724
259 205 Provided 3000 impressions without failure Example 2e PCA
724 259 97 Provided 4000 impressions without failure Example 2f PCA
724 259 49 Provided 3000 impressions without failure Example 2g PCA
724 259 0 Provided 3000 impressions without failure Comparative
Latex E 724 259 983 No image Example 3a Comparative Latex E 724 259
486 Failed by 500 impressions*** Example 3b Comparative Latex E 724
259 313 Failed by 500 impressions**** Example 3c Comparative Latex
E 724 259 205 Failed by 500 impressions**** Example 3d Comparative
Latex E 724 259 97 Failed by 500 impressions**** Example 3e
Comparative Latex E 724 259 49 Coating formulation not could not
Example 3f be coated Comparative Latex E 724 259 0 Coating
formulation not could not Example 3g be coated Comparative Latex E
724 259 313 Failed by 500 impressions**** Example 4 *Image was
completely gone. **Non-inking of large areas. ***Image was
completely gone. ****Large areas of image were gone.
[0119] The data in TABLE II for the various Comparative Examples
indicate that printing plates having imaging layers containing
thermoplastic particles formed from various methacrylates ("Mn",
Latex M, and Latex E) failed by at least 500 impressions due to
lack of inking in portions of the image (exposed) areas. Moreover,
if the amount of hydrophilic binder [for example, poly(vinyl
alcohol)] was too high in relation to the cyanoacrylate polymers
(Example 2a), the resulting printing plate failed to provide
suitable imaging properties. All of the printing plates of the
present invention provided several thousand impressions without any
loss of resolution or other imaging or printing failure.
Example 3
[0120] Several additional printing plates of the present invention
were prepared similarly to those described in Example 1 above.
TABLE III below shows the dry coverage of each of the cyanoacrylate
polymer, IR Dye 2, and poly(vinyl alcohol) for each plate including
the Control printing plate that contained no IR Dye 2 and did not
provide an image.
9TABLE III Polymer IR Dye Coverage Coverage PVA Coverage
(mg/m.sup.2) (mg/m.sup.2) (mg/m.sup.2) Imaging/Printing Results 724
130 313 Provided 3000 impressions without failure 724 65 313
Provided 3000 impressions without failure 724 130 97 Provided 3000
impressions without failure 724 65 97 Provided 3000 impressions
without failure 724 32.5 97 Provided 8000 impressions without
failure 724 16.2 97 Provided 8000 impressions without failure 724 0
97 Control N: no image 364 32.5 49 Provided 4000 impressions
without failure 181 16.2 25 Provided 4000 impressions without
failure 90.7 8.6 11.9 Provided 1000 impressions without failure
[0121] It is can be seen from these data that wide ranges of IR
dye, ate polymer, and hydrophilic binder can be used in the
practice of this long as the dry weight ratio of IR dye to
cyanoacrylate polymer is 0.02: 1 to about 0.8: 1, and the dry
weight ratio of hydrophilic binder to ate polymer is up to 1:1.
Example 4
[0122] The use of various hydrophilic binders in the imaging layer
was also explored. Thermally sensitive imaging dispersions and
printing plates were prepared as described in Example 1 except that
the hydrophilic binders listed in the following TABLE IV were
used.
10TABLE IV Polymer IR Dye Binder Imaging/ Coverage Coverage
Coverage Printing (mg/m.sup.2) (mg/m.sup.2) (mg/m.sup.2) Binder*
Results 724 130 97 Poly(ethyloxazoline) Provided 8000 impressions
without failure 724 130 97 Poly(vinyl alcohol), Provided 8000 mol.
weight about impressions 100,000 without failure 724 130 97
Poly(vinyl Provided 8000 pyrrolidone) impressions without failure
724 130 97 Poly(ethyleneimine) Provided 8000 impressions without
failure *These materials are commonly available from several
commercial sources.
[0123] These data indicate that various representative hydrophilic
binder materials can be used to advantage in the practice of the
present invention.
[0124] The invention has been described in detail with particular
reference to preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the spirit and scope of the invention.
* * * * *