U.S. patent application number 09/260062 was filed with the patent office on 2001-05-24 for heat mode sensitive imaging element for making positive working printing plates.
This patent application is currently assigned to Joan Vermeersch. Invention is credited to HAUQUIER, GUIDO, VAN DAMME, MARC, VERMEERSCH, JOAN, VERSCHUEREN, ERIC.
Application Number | 20010001699 09/260062 |
Document ID | / |
Family ID | 27239313 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001699 |
Kind Code |
A1 |
VERMEERSCH, JOAN ; et
al. |
May 24, 2001 |
HEAT MODE SENSITIVE IMAGING ELEMENT FOR MAKING POSITIVE WORKING
PRINTING PLATES
Abstract
According to the present invention there is provided a heat mode
imaging element for making a lithographic printing plate having on
a lithographic base with a hydrophilic surface a first layer
including a polymer soluble in an aqueous alkaline solution, and a
top layer on the same side of the lithographic base as the first
layer that is IR-sensitive and unpenetrable for an aqueous alkaline
developer wherein said first layer and said top layer may be one
and the same layer; characterized in that the surface of said
element upon exposure and treatment with an aqueous alkaline
developer is such that a) the contact angle between the unexposed
areas of the imaging element and the aqueous alkaline developer
changes for at most 6.degree. during the first minute of contact
with said developer; b) the contact angle between the exposed areas
of the imaging element and the aqueous alkaline developer changes
more than 15.degree. during the first minute of contact with said
developer; c) the difference in contact angle between on the one
side the unexposed areas and on the other side the exposed areas of
the imaging element with the aqueous alkaline solution at the onset
of the measurement is not higher than 10.degree..
Inventors: |
VERMEERSCH, JOAN; (DEINZE,
BE) ; VAN DAMME, MARC; (HEVERLEE, BE) ;
VERSCHUEREN, ERIC; (MERKSPLAS, BE) ; HAUQUIER,
GUIDO; (NIJLEN, BE) |
Correspondence
Address: |
BREINER & BREINER
PO BOX 19290
ALEXANDRIA
VA
223200290
|
Assignee: |
Joan Vermeersch
|
Family ID: |
27239313 |
Appl. No.: |
09/260062 |
Filed: |
March 2, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60089287 |
Jun 15, 1998 |
|
|
|
Current U.S.
Class: |
430/270.1 ;
430/278.1; 430/302 |
Current CPC
Class: |
Y10S 430/146 20130101;
B41C 2210/262 20130101; Y10S 430/145 20130101; B41C 2210/14
20130101; B41C 1/1016 20130101; B41C 2210/24 20130101; B41C 2210/22
20130101; Y10S 430/165 20130101; B41C 2210/02 20130101; B41C
2210/06 20130101 |
Class at
Publication: |
430/270.1 ;
430/278.1; 430/302 |
International
Class: |
G03F 007/038; G03F
007/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 1998 |
EP |
98201216.3 |
Claims
1. A heat mode imaging element for making a lithographic printing
plate having on a lithographic base with a hydrophilic surface a
first layer including a polymer soluble in an aqueous alkaline
solution, and a top layer on the same side of the lithographic base
as the first layer that is IR-sensitive and unpenetrable for an
aqueous alkaline developer wherein said first layer and said top
layer may be one and the same layer; characterized in that the
surface of said element upon exposure and treatment with an aqueous
alkaline developer is such that a) the contact angle between the
unexposed areas of the imaging element and the aqueous alkaline
developer changes for at most 6.degree. during the first minute of
contact with said developer; b) the contact angle between the
exposed areas of the imaging element and the aqueous alkaline
developer changes more than 15.degree. during the first minute of
contact with said developer; c) the difference in contact angle
between on the one side the unexposed areas and on the other side
the exposed areas of the imaging element with the aqueous alkaline
solution at the onset of the measurement is not higher than
10.degree..
2. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein the contact angle between the
unexposed areas of the imaging element and the aqueous alkaline
solution at the onset of the measurement is at least
100.degree..
3. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein the change in contact angle
between the exposed areas of the imaging element and the aqueous
alkaline developer during the first minute of contact is more than
20.degree..
4. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein the polymer soluble in an
aqueous alkaline solution is a novolac polymer or a polymer
containing polyhydroxystyrene units.
5. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein the top layer contains a
compound selected from the group consisting of low molecular acids
and benzophenones.
6. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein the lithographic base is an
electrochemically grained and anodized aluminum.
7. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein said imaging element contains an
IR absorbing compound.
8. A method for making a lithographic printing plate comprising the
steps of a) exposing imagewise to IR-radiation a heat mode imaging
element according to claim 1; and b) developing said imagewise
exposed heat mode imaging element with an aqueous alkaline
developer whereby the exposed areas of the first and the top layer,
which may be the same, are dissolved and the unexposed areas of the
first layer remain undissolved.
9. A method for making a lithographic printing plate according to
claim 8 wherein said aqueous alkaline developer contains
alkalimetalsilicates and has a pH of at least 12.
10. A method for making a lithographic printing plate according to
claim 8 wherein the laser exposure has a pixel dwell time between
0.005 and 20 .mu.s.
Description
DESCRIPTION
FIELD OF THE INVENTION
[0001] The present invention relates to a heat mode imaging element
for preparing a lithographic printing plate.
[0002] More specifically the invention is related to a heat mode
imaging element for preparing a lithographic printing plate whereof
the difference in the top layer of being penetrated and/or
solubilised in the exposed areas and in the non-exposed areas by an
aqueous developer is increased.
BACKGROUND OF THE INVENTION
[0003] Lithography is the process of printing from specially
prepared surfaces, some areas of which are capable of accepting
lithographic ink, whereas other areas, when moistened with water,
will not accept the ink. The areas which accept ink form the
printing image areas and the ink-rejecting areas form the
background areas.
[0004] In the art of photolithography, a photographic material is
made imagewise receptive to oily or greasy inks in the
photo-exposed (negative-working) or in the non-exposed areas
(positive-working) on a hydrophilic background.
[0005] In the production of common lithographic printing plates,
also called surface litho plates or planographic printing plates, a
support that has affinity to water or obtains such affinity by
chemical treatment is coated with a thin layer of a photosensitive
composition. Coatings for that purpose include light-sensitive
polymer layers containing diazo compounds, dichromate-sensitized
hydrophilic colloids and a large variety of synthetic
photopolymers. Particularly diazo-sensitized systems are widely
used.
[0006] Upon imagewise exposure of the light-sensitive layer the
exposed image areas become insoluble and the unexposed areas remain
soluble. The plate is then developed with a suitable liquid to
remove the diazonium salt or diazo resin in the unexposed
areas.
[0007] Alternatively, printing plates are known that include a
photosensitive coating that upon image-wise exposure is rendered
soluble at the exposed areas. Subsequent development then removes
the exposed areas. A typical example of such photosensitive coating
is a quinone-diazide based coating.
[0008] Typically, the above described photographic materials from
which the printing plates are made are camera-exposed through a
photographic film that contains the image that is to be reproduced
in a lithographic printing process. Such method of working is
cumbersome and labor intensive. However, on the other hand, the
printing plates thus obtained are of superior lithographic
quality.
[0009] Attempts have thus been made to eliminate the need for a
photographic film in the above process and in particular to obtain
a printing plate directly from computer data representing the image
to be reproduced. However the photosensitive coating is not
sensitive enough to be directly exposed with a laser. Therefor it
has been proposed to coat a silver halide layer on top of the
photosensitive coating. The silver halide may then directly be
exposed by means of a laser under the control of a computer.
Subsequently, the silver halide layer is developed leaving a silver
image on top of the photosensitive coating. That silver image then
serves as a mask in an overall exposure of the photosensitive
coating. After the overall exposure the silver image is removed and
the photosensitive coating is developed. Such method is disclosed
in for example JP-A-60-61 752 but has the disadvantage that a
complex development and associated developing liquids are
needed.
[0010] GB-1 492 070 discloses a method wherein a metal layer or a
layer containing carbon black is provided on a photosensitive
coating. This metal layer is then ablated by means of a laser so
that an image mask on the photosensitive layer is obtained. The
photosensitive layer is then overall exposed by UV-light through
the image mask. After removal of the image mask, the photosensitive
layer is developed to obtain a printing plate. This method however
still has the disadvantage that the image mask has to be removed
prior to development of the photosensitive layer by a cumbersome
processing.
[0011] Furthermore methods are known for making printing plates
involving the use of imaging elements that are heat-sensitive
rather than photosensitive. A particular disadvantage of
photosensitive imaging elements such as described above for making
a printing plate is that they have to be shielded from the light.
Furthermore they have a problem of sensitivity in view of the
storage stability and they show a lower resolution. The trend
towards heat mode printing plate precursors is clearly seen on the
market.
[0012] For example, Research Disclosure no. 33303 of January 1992
discloses a heat mode imaging element comprising on a support a
cross-linked hydrophilic layer containing thermoplastic polymer
particles and an infrared absorbing pigment such as e.g. carbon
black. By image-wise exposure to an infrared laser, the
thermoplastic polymer particles are image-wise coagulated thereby
rendering the surface of the imaging element at these areas
ink-acceptant without any further development. A disadvantage of
this method is that the printing plate obtained is easily damaged
since the non-printing areas may become ink accepting when some
pressure is applied thereto. Moreover, under critical conditions,
the lithographic performance of such a printing plate may be poor
and accordingly such printing plate has little lithographic
printing latitude.
[0013] U.S. Pat. No. 4,708,925 discloses imaging elements including
a photosensitive composition comprising an alkali-soluble novolac
resin and an onium-salt. This composition may optionally contain an
IR-sensitizer. After image-wise exposing said imaging element to
UV--visible--or IR-radiation followed by a development step with an
aqueous alkali liquid there is obtained a positive or negative
working printing plate. The printing results of a lithographic
plate obtained by irradiating and developing said imaging element
are poor.
[0014] EP-A-625 728 discloses an imaging element comprising a layer
which is sensitive to UV- and IR-irradiation and which may be
positive or negative working. This layer comprises a resole resin,
a novolac resin, a latent Bronsted acid and an IR-absorbing
substance. The printing results of a lithographic plate obtained by
irradiating and developing said imaging element are poor.
[0015] U.S. Pat. No. 5,340,699 is almost identical with EP-A-625
728 but discloses the method for obtaining a negative working
IR-laser recording imaging element. The IR-sensitive layer
comprises a resole resin, a novolac resin, a latent Bronsted acid
and an IR-absorbing substance. The printing results of a
lithographic plate obtained by irradiating and developing said
imaging element are poor.
[0016] Furthermore EP-A-678 380 discloses a method wherein a
protective layer is provided on a grained metal support underlying
a laser-ablatable surface layer. Upon image-wise exposure the
surface layer is fully ablated as well as some parts of the
protective layer. The printing plate is then treated with a
cleaning solution to remove the residu of the protective layer and
thereby exposing the hydrophilic surface layer.
[0017] EP-A-97 200 588.8 discloses a heat mode imaging element for
making lithographic printing plates comprising on a lithographic
base having a hydrophilic surface an intermediate layer comprising
a polymer, soluble in an aqueous alkaline solution and a top layer
that is sensitive to IR-radiation wherein said top layer upon
exposure to IR-radiation has a decreased or increased capacity for
being penetrated and/or solubilised by an aqueous alkaline
solution.
[0018] EP-A-97 203 129.8 and EP-A-97 203 132.2 disclose a heat mode
imaging element consisting of a lithographic base with a
hydrophilic surface and a top layer which top layer is sensitive to
IR-radiation, comprises a polymer, soluble in an aqueous alkaline
solution and is unpenetrable for an alkaline developer containing
SiO.sub.2 as silicates
[0019] Said last three heat-mode imaging element have the
disadvantage that the difference between the solubility in the
exposed areas and in the non-exposed aqreas is not very great so
that also non-exposed areas are dissolved during the processing of
said element so that said plates could not be used as lithographic
plates.
OBJECTS OF THE INVENTION
[0020] It is an object of the invention to provide a heat mode
imaging element for making in an easy way lithographic printing
plates.
[0021] It is another object of the invention to provide a heat mode
sensitive imaging element for making positive lithographic printing
plates having excellent printing properties, developable in a
selective, rapid, convenient and ecological way.
[0022] It is further an object of the present invention to provide
a heat mode sensitive imaging element having a high infrared
sensitivity.
[0023] It is also an object of the present invention to provide a
heat mode sensitive imaging element which has a great difference in
developability in a developer between the exposed areas and the
non-exposed areas.
[0024] Further objects of the present invention will become clear
from the description hereinafter.
SUMMARY OF THE INVENTION
[0025] According to the present invention there is provided a heat
mode imaging element for making a lithographic printing plate
having on a lithographic base with a hydrophilic surface a first
layer including a polymer soluble in an aqueous alkaline solution,
and a top layer on the same side of the lithographic base as the
first layer that is IR-sensitive and unpenetrable for an aqueous
alkaline developer wherein said first layer and said top layer may
be one and the same layer; characterized in that the surface of
said element upon exposure and treatment with an aqueous alkaline
developer is such that
[0026] a) the contact angle between the unexposed areas of the
imaging element and the aqueous alkaline developer changes for at
most 6.degree. during the first minute of contact with said
developer;
[0027] b) the contact angle between the exposed areas of the
imaging element and the aqueous alkaline developer changes more
than 15.degree. during the first minute of contact with said
developer;
[0028] c) the difference in contact angle between on the one side
the unexposed areas and on the other side the exposed areas of the
imaging element with the aqueous alkaline solution at the onset of
the measurement is not higher than 10.degree..
DETAILED DESCRIPTION OF THE INVENTION
[0029] The top layer is also called the second layer.
[0030] The contact angle is measured with a contact angle
goniometer.
[0031] The contact angle between the unexposed areas of the imaging
element and the aqueous alkaline solution at the onset of the
measurement is preferably at least 100.degree.. The change in
contact angle between the exposed areas of the imaging element and
the aqueous alkaline developer after the first minute of contact is
preferably higher than 20.degree., more preferably higher than
25.degree..
[0032] In a first embodiment the first layer and the top layer are
different. In said embodiment there is provided a heat mode imaging
element for making lithographic printing plates having on a
lithographic base with a hydrophilic surface a first layer
including a polymer, soluble in an aqueous alkaline solution and a
top layer on the same side of the lithographic base as the first
layer which top layer is sensitive to IR-radiation and which is
unpenetrable for an alkaline developer.
[0033] The top layer, in accordance with the present invention
comprises an IR-dye or pigment and a binder resin. A mixture of
IR-dyes or pigments may be used, but it is preferred to use only
one IR-dye or pigment. Preferably said IR-dyes are IR-cyanines
dyes. Particularly useful IR-cyanine dyes are cyanines dyes with
two indolenine groups. Most preferably is compound I with the
structure as indicated 1
[0034] Particularly useful IR-absorbing pigments are carbon black,
metal carbides, borides, nitrides, carbonitrides, bronze-structured
oxides and oxides structurally related to the bronze family but
lacking the A component e.g. WO2.9. It is also possible to use
conductive polymer dispersion such as polypyrrole or
polyaniline-based conductive polymer dispersions. The lithographic
performance and in particular the print endurance obtained depends
on the heat-sensitivity of the imaging element. In this respect it
has been found that carbon black yields very good and favorable
results.
[0035] The IR-absorbing dyes or pigments are present preferably in
an amount between 1 and 99 parts, more preferably between 50 and 95
parts by weight of the total amount of said IR-sensitive top
layer.
[0036] The top layer may preferably comprise as binder a water
insoluble polymer such as a cellulose ester, a copolymer of
vinylidene chloride and acrylonitrile, poly(meth)acrylates,
polyvinyl chloride, silicone resins, etc. Preferred as binder is
nitrocellulose resin.
[0037] The total amount of the top layer preferably ranges from
0.05 to 10 g/m.sup.2, more preferably from 0.1 to 2 g/m.sup.2.
[0038] In the top layer a difference in the capacity of being
penetrated and/or solubilised by the aqueous alkaline solution is
generated upon image-wise exposure for an alkaline developer
according to the invention.
[0039] In the present invention the said capacity is increased upon
image-wise IR exposure to such degree that the imaged parts will be
cleaned out during development without solubilising and/or damaging
the non-imaged parts.
[0040] The development with the aqueous alkaline solution is
preferably done within an interval of 5 to 120 seconds.
[0041] Between the top layer and the lithographic base the present
invention comprises a first layer soluble in an aqueous alkaline
developing solution with preferentially a pH between 7.5 and 14.
Said layer is preferably contiguous to the top layer but other
layers may be present between the top layer and the first layer.
The alkali soluble binders used in this layer are preferably
hydrophobic binders as used in conventional positive or negative
working PS-plates e.g. novolac polymers, polymers containing
hydroxystyrene units, carboxy substituted polymers etc. Typical
examples of these polymers are described in DE-A-4 007 428, DE-A-4
027 301 and DE-A-4 445 820. The hydrophobic binder used in
connection with the present invention is further characterised by
insolubility in water and partial solubility/swellability in an
alkaline solution and/or partial solubility in water when combined
with a cosolvent.
[0042] Furthermore this aqueous alkali soluble layer is preferably
a visible light- and UV-light desensitised layer. Said layer is
preferably thermally hardenable. This preferably visible light- and
UV-desensitised layer does not comprise photosensitive ingredients
such as diazo compounds, photoacids, photoinitiators, quinone
diazides, sensitisers etc. which absorb in the wavelength range of
250 nm to 650 nm. In this way a daylight stable printing plate may
be obtained.
[0043] Said first layer preferably also includes a low molecular
acid, preferably a carboxylic acid, still more preferably a benzoic
acid, most preferably 3,4,5-trimethoxybenzoic acid or a
benzophenone.
[0044] The ratio between the total amount of low molecular acid or
benzophenone and polymer in the first layer preferably ranges from
2:98 to 40:60, more preferably from 5:95 to 20:80. The total amount
of said first layer preferably ranges from 0.1 to 10 g/m.sup.2,
more preferably from 0.3 to 2 g/m.sup.2.
[0045] In the imaging element according to the present invention,
the lithographic base may be an anodised aluminum for all
embodiments. A particularly preferred lithographic base is an
electrochemically grained and anodised aluminum support. The
anodised aluminum support may be treated to improve the hydrophilic
properties of its surface. For example, the aluminum support may be
silicated by treating its surface with sodium silicate solution at
elevated temperature, e.g. 95.degree. C. Alternatively, a phosphate
treatment may be applied which involves treating the aluminum oxide
surface with a phosphate solution that may further contain an
inorganic fluoride. Further, the aluminum oxide surface may be
rinsed with a citric acid or citrate solution. This treatment may
be carried out at room temperature or may be carried out at a
slightly elevated temperature of about 30 to 50.degree. C. A
further interesting treatment involves rinsing the aluminum oxide
surface with a bicarbonate solution. Still further, the aluminum
oxide surface may be treated with polyvinylphosphonic acid,
polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl
alcohol, polyvinylsulphonic acid, polyvinylbenzenesulphonic acid,
sulphuric acid esters of polyvinyl alcohol, and acetals of
polyvinyl alcohols formed by reaction with a sulphonated aliphatic
aldehyde It is further evident that one or more of these post
treatments may be carried out alone or in combination. More
detailed descriptions of these treatments are given in GB-A-1 084
070, DE-A-4 423 140, DE-A-4 417 907, EP-A-659 909, EP-A-537 633,
DE-A-4 001 466, EP-A-292 801, EP-A-291 760 and U.S. Pat. No.
4,458,005.
[0046] According to another mode in connection with the present
invention, the lithographic base having a hydrophilic surface
comprises a flexible support, such as e.g. paper or plastic film,
provided with a cross-linked hydrophilic layer for all embodiments.
A particularly suitable cross-linked hydrophilic layer may be
obtained from a hydrophilic binder cross-linked with a
cross-linking agent such as formaldehyde, glyoxal, polyisocyanate
or a hydrolysed tetra-alkylorthosilicate. The latter is
particularly preferred.
[0047] As hydrophilic binder there may be used hydrophilic
(co)polymers such as for example, homopolymers and copolymers of
vinyl alcohol, acrylamide, methylol acrylamide, methylol
methacrylamide, acrylate acid, methacrylate acid, hydroxyethyl
acrylate, hydroxyethyl methacrylate or maleic
anhydride/vinylmethylether copolymers. The hydrophilicity of the
(co)polymer or (co)polymer mixture used is preferably the same as
or higher than the hydrophilicity of polyvinyl acetate hydrolyzed
to at least an extent of 60 percent by weight, preferably 80
percent by weight.
[0048] The amount of crosslinking agent, in particular of
tetraalkyl orthosilicate, is preferably at least 0.2 parts by
weight per part by weight of hydrophilic binder, more preferably
between 0.5 and 5 parts by weight, most preferably between 1.0
parts by weight and 3 parts by weight.
[0049] A cross-linked hydrophilic layer in a lithographic base used
in accordance with the present embodiment preferably also contains
substances that increase the mechanical strength and the porosity
of the layer. For this purpose colloidal silica may be used. The
colloidal silica employed may be in the form of any commercially
available water-dispersion of colloidal silica for example having
an average particle size up to 40 nm, e.g. 20 nm. In addition inert
particles of larger size than the colloidal silica may be added
e.g. silica prepared according to Stober as described in J. Colloid
and Interface Sci., Vol. 26, 1968, pages 62 to 69 or alumina
particles or particles having an average diameter of at least 100
nm which are particles of titanium dioxide or other heavy metal
oxides. By incorporating these particles the surface of the
cross-linked hydrophilic layer is given a uniform rough texture
consisting of microscopic hills and valleys, which serve as storage
places for water in background areas.
[0050] The thickness of a cross-linked hydrophilic layer in a
lithographic base in accordance with this embodiment may vary in
the range of 0.2 to 25 .mu.m and is preferably 1 to 10 .mu.m.
[0051] Particular examples of suitable cross-linked hydrophilic
layers for use in accordance with the present invention are
disclosed in EP-A-601 240, GB-P-1 419 512, FR-P-2 300 354, U.S.
Pat. Nos. 3,971,660, 4,284,705 and EP-A-514 490.
[0052] As flexible support of a lithographic base in connection
with the present embodiment it is particularly preferred to use a
plastic film e.g. substrated polyethylene terephthalate film,
substrated polyethylene naphthalate film, cellulose acetate film,
polystyrene film, polycarbonate film etc. . . . The plastic film
support may be opaque or transparent.
[0053] It is particularly preferred to use a polyester film support
to which an adhesion improving layer has been provided.
Particularly suitable adhesion improving layers for use in
accordance with the present invention comprise a hydrophilic binder
and colloidal silica as disclosed in EP-A-619 524, EP-A-620 502 and
EP-A-619 525. Preferably, the amount of silica in the adhesion
improving layer is between 200 mg per m.sup.2 and 750 mg per
m.sup.2. Further, the ratio of silica to hydrophilic binder is
preferably more than 1 and the surface area of the colloidal silica
is preferably at least 300 m.sup.2 per gram, more preferably at
least 500 m.sup.2 per gram.
[0054] In a second embodiment the first layer and the second layer
are the same. In said embodiment there is provided a heat mode
imaging element for making lithographic printing plates having on a
lithographic base with a hydrophilic surface a top layer which top
layer is sensitive to IR-radiation, comprises a polymer, soluble in
an aqueous alkaline solution and is unpenetrable for an alkaline
developer.
[0055] The IR-sensitive layer, in accordance with the present
invention comprises an IR-dye or pigment and a polymer, soluble in
an aqueous alkaline solution. A mixture of IR-dyes or pigments may
be used, but it is preferred to use only one IR-dye or pigment.
Suitable IR-dyes and pigments are those mentioned above in the
first embodiment of the present invention.
[0056] The IR-dyes are present preferably in an amount between 1
and 60 parts, more preferably between 3 and 50 parts by weight of
the total amount of said IR-sensitive top layer.
[0057] The alkali soluble polymers used in this layer are
preferably hydrophobic and ink accepting polymers as used in
conventional positive or negative working PS-plates e.g. carboxy
substituted polymers etc. More preferably is a phenolic resin such
as a hydroxystyrene units containing polymer or a novolac polymer.
Most preferred is a novolac polymer. Typical examples of these
polymers are described in DE-A-4 007 428, DE-A-4 027 301 and DE-A-4
445 820. The hydrophobic polymer used in connection with the
present invention is further characterised by insolubility in water
and at least partial solubility/swellability in an alkaline
solution and/or at least partial solubility in water when combined
with a cosolvent.
[0058] Furthermore this IR-sensitive layer is preferably a visible
light- and UV-light desensitised layer. Still further said layer is
preferably thermally hardenable. This preferably visible light- and
UV-light desensitised layer does not comprise photosensitive
ingredients such as diazo compounds, photoacids, photoinitiators,
quinone diazides, sensitisers etc. which absorb in the wavelength
range of 250 nm to 650 nm. In this way a daylight stable printing
plate may be obtained.
[0059] Said IR-sensitive layer preferably also includes a low
molecular acid, more preferably a carboxylic acid, still more
preferably a benzoic acid, most preferably 3,4,5-trimethoxybenzoic
acid or a benzofenone, more preferably trihydroxybenzofenone.
[0060] The ratio between the total amount of low molecular acid or
benzofenone and polymer in the IR-sensitive layer preferably ranges
from 2:98 to 40:60, more preferably from 5:95 to 30:70. The total
amount of said IR-sensitive layer preferably ranges from 0.1 to 10
g/m.sup.2, more preferably from 0.3 to 2 g/m.sup.2.
[0061] In the IR-sensitive layer a difference in the capacity of
being penetrated and/or solubilised by the alkaline developer is
generated upon image-wise exposure for an alkaline developer
according to the invention.
[0062] To prepare a lithographic plate, the heat-mode imaging
element is image-wise exposed and developed.
[0063] Image-wise exposure in connection with the present invention
is an image-wise scanning exposure involving the use of a laser
that operates in the infrared or near-infrared, i.e. wavelength
range of 700-1500 nm. Most preferred are laser diodes emitting in
the near-infrared. Exposure of the imaging element may be performed
with lasers with a short as well as with lasers with a long pixel
dwell time. Preferred are lasers with a pixel dwell time between
0.005 .mu.us and 20 .mu.s.
[0064] After the image-wise exposure the heat mode imaging element
is developed by rinsing it with an aqueous alkaline solution. The
aqueous alkaline solutions used in the present invention are those
that are used for developing conventional positive working
presensitised printing plates, preferably containing SiO.sub.2 in
the form of silicates and having preferably a pH between 11.5 and
14. Thus the imaged parts of the top layer that were rendered more
penetrable for the aqueous alkaline solution upon exposure are
cleaned-out whereby a positive working printing plate is
obtained.
[0065] In the present invention, the composition of the developer
used is also very important.
[0066] Therefore, to perform development processing stably for a
long time period particularly important are qualities such as
strength of alkali and the concentration of silicates in the
developer. Under such circumstances, the present inventors have
found that a rapid high temperature processing can be performed,
that the amount of the replenisher to be supplemented is low and
that a stable development processing can be performed over a long
time period of the order of not less than 3 months without
exchanging the developer only when the developer having the
foregoing composition is used.
[0067] The developers and replenishers for developer used in the
invention are preferably aqueous solutions mainly composed of
alkali metal silicates and alkali metal hydroxides represented by
MOH or their oxyde, represented by M.sub.2O, wherein said developer
comprises SiO.sub.2 and M.sub.2O in a molar ratio of 0.5 to 1.5 and
a concentration of SiO.sub.2 of 0.5 to 5% by weight. As such alkali
metal silicates, preferably used are, for instance, sodium
silicate, potassium silicate, lithium silicate and sodium
metasilicate. On the other hand, as such alkali metal hydroxides,
preferred are sodium hydroxide, potassium hydroxide and lithium
hydroxide.
[0068] The developers used in the invention may simultaneously
contain other alkaline agents. Examples of such other alkaline
agents include such inorganic alkaline agents as ammonium
hydroxide, sodium tertiary phosphate, sodium secondary phosphate,
potassium tertiary phosphate, potassium secondary phosphate,
ammonium tertiary phosphate, ammonium secondary phosphate, sodium
bicarbonate, sodium carbonate, potassium carbonate and ammonium
carbonate; and such organic alkaline agents as mono-, di- or
triethanolamine, mono-, di- or trimethylamine, mono-, di- or
triethylamine, mono- or di-isopropylamine, n-butylamine, mono-, di-
or triisopropanolamine, ethyleneimine, ethylenediimine and
tetramethylammonium hydroxide.
[0069] In the present invention, particularly important is the
molar ratio in the developer of [SiO.sub.2]/[M.sub.2O], which is
generally 0.6 to 1.5, preferably 0.7 to 1.3. This is because if the
molar ratio is less than 0.6, great scattering of activity is
observed, while if it exceeds 1.5, it becomes difficult to perform
rapid development and the dissolving out or removal of the
light-sensitive layer on non-image areas is liable to be
incomplete. In addition, the concentration of SiO.sub.2 in the
developer and replenisher preferably ranges from 1 to 4% by weight.
Such limitation of the concentration of SiO.sub.2 makes it possible
to stably provide lithographic printing plates having good
finishing qualities even when a large amount of plates according to
the invention are processed for a long time period.
[0070] In a particular preferred embodiment, an aqueous solution of
an alkali metal silicate having a molar ratio
[SiO.sub.2]/[M.sub.2O], which ranges from 1.0 to 1.5 and a
concentration of SiO.sub.2 of 1 to 4% by weight is used as a
developer. In such case, it is a matter of course that a
replenisher having alkali strength equal to or more than that of
the developer is employed. In order to decrease the amount of the
replenisher to be supplied, it is advantageous that a molar ratio,
[SiO2]/[M.sub.2O], of the replenisher is equal to or smaller than
that of the developer, or that a concentration of SiO.sub.2 is high
if the molar ratio of the developer is equal to that of the
replenisher.
[0071] In the developers and the replenishers used in the
invention, it is possible to simultaneously use organic solvents
having solubility in water at 20.degree. C. of not more than 10% by
weight according to need. Examples of such organic solvents are
such carboxilic acid esters as ethyl acetate, propyl acetate, butyl
acetate, amyl acetate, benzyl acetate, ethylene glycol monobutyl
acetate, butyl lactate and butyl levulinate; such ketones as ethyl
butyl ketone, methyl isobutyl ketone and cyclohexanone; such
alcohols as ethylene glycol monobutyl ether, ethylene glycol benzyl
ether, ethylene glycol monophenyl ether, benzyl alcohol,
methylphenylcarbinol, n-amyl alcohol and methylamyl alcohol; such
alkyl-substituted aromatic hydrocarbons as xylene; and such
halogenated hydrocarbons as methylene dichloride and
monochlorobenzene. These organic solvents may be used alone or in
combination. Particularly preferred is benzyl alcohol in the
invention. These organic solvents are added to the developer or
replenisher therefor generally in an amount of not more than 5% by
weight and preferably not more than 4% by weight.
[0072] The developers and replenishers used in the present
invention may simultaneously contain a surfactant for the purpose
of improving developing properties thereof. Examples of such
surfactants include salts of higher alcohol
(C.sub.8.about.C.sub.22) sulfuric acid esters such as sodium salt
of lauryl alcohol sulfate, sodium salt of octyl alcohol sulfate,
ammonium salt of lauryl alcohol sulfate, Teepol B-81 (trade mark,
available from Shell Chemicals Co., Ltd.) and disodium alkyl
sulfates; salts of aliphatic alcohol phosphoric acid esters such as
sodium salt of cetyl alcohol phosphate; alkyl aryl sulfonic acid
salts such as sodium salt of dodecylbenzene sulfonate, sodium salt
of isopropylnaphthalene sulfonate,sodium salt of dinaphthalene
disulfonate and sodium salt of metanitrobenzene sulfonate; sulfonic
acid salts of alkylamides such as
C.sub.17H.sub.33CON(CH.sub.3)CH.sub.2CH.sub.2SO.sub.3- Na and
sulfonic acid salts of dibasic aliphatic acid esters such as sodium
dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate. These
surfactants may be used alone or in combination. Particularly
preferred are sulfonic acid salts. These surfactants may be used in
an amount of generally not more than 5% by weight and preferably
not more than 3% by weight.
[0073] In order to enhance developing stability of the developers
and replenishers used in the invention, the following compounds may
simultaneously be used.
[0074] Examples of such compounds are neutral salts such as NaCl,
KCl and KBr as disclosed in JN-A-58-75 152; chelating agents such
as EDTA and NTA as disclosed in JN-A-58-190 952 (U.S. Pat. No.
4,469,776), complexes such as [Co(NH.sub.3).sub.6]Cl.sub.3 as
disclosed in JN-A-59-121 336 (U.S. Pat. No. 4,606,995); ionizable
compounds of elements of the group IIa, IIIa or IIIb of the
Periodic Table such as those disclosed in JN-A-55-25 100; anionic
or amphoteric surfactants such as sodium alkyl naphthalene
sulfonate and N-tetradecyl-N,N-dihydroxythyl betaine as disclosed
in JN-A-50-51 324; tetramethyldecyne diol as disclosed in U.S. Pat.
No. 4,374,920; non-ionic surfactants as disclosed in JN-A-60-213
943; cationic polymers such as methyl chloride quaternary products
of p-dimethylaminomethyl polystyrene as disclosed in JN-A-55-95
946; amphoteric polyelectrolytes such as copolymer of vinylbenzyl
trimethylammonium chloride and sodium acrylate as disclosed in
JN-A-56-142 528; reducing inorganic salts such as sodium sulfite as
disclosed in JN-A-57- 192 952 (U.S. Pat. No. 4,467,027) and
alkaline-soluble mercapto compounds or thioether compounds such as
thiosalicylic acid, cysteine and thioglycolic acid; inorganic
lithium compounds such as lithium chloride as disclosed in
JN-A-58-59 444; organic lithium compounds such as lithium benzoate
as disclosed in JN-A-50 34 442; organometallic surfactants
containing Si, Ti or the like as disclosed in JN-A-59-75 255;
organoboron compounds as disclosed in JN-A-59-84 241 (U.S. Pat. No.
4,500,625); quaternary ammonium salts such as tetraalkylammonium
oxides as disclosed in EP-A-101 010; and bactericides such as
sodium dehydroacetate as disclosed in JN-A-63-226 657.
[0075] In the method for development processing of the present
invention, any known means of supplementing a replenisher for
developer may be employed. Examples of such methods preferably used
are a method for intermittently or continuously supplementing a
replenisher as a function of the amount of PS plates processed and
time as disclosed in JN-A-55-115 039 (GB-A-2 046 931), a method
comprising disposing a sensor for detecting the degree of
light-sensitive layer dissolved out in the middle portion of a
developing zone and supplementing the replenisher in proportion to
the detected degree of the light-sensitive layer dissolved out as
disclosed in JN-A-58-95 349 (U.S. Pat. No. 4,537,496); a method
comprising determining the impedance value of a developer and
processing the detected impedance value by a computer to perform
supplementation of a replenisher as disclosed in GB-A-2 208
249.
[0076] The printing plate of the present invention can also be used
in the printing process as a seamless sleeve printing plate. In
this option the printing plate is soldered in a cylindrical form by
means of a laser. This cylindrical printing plate which has as
diameter the diameter of the print cylinder is slided on the print
cylinder instead of applying in a classical way a classically
formed printing plate. More details on sleeves are given in
"Grafisch Nieuws" ed. Keesing, 15, 1995, page 4 to 6.
[0077] After the development of an image-wise exposed imaging
element with an aqueous alkaline solution and drying, the obtained
plate can be used as a printing plate as such. However, to improve
durability it is still possible to bake said plate at a temperature
between 200.degree. C. and 300.degree. C. for a period of 30
seconds to 5 minutes. Also the imaging element can be subjected to
an overall post-exposure to UV-radiation to harden the image in
order to increase the run length of the printing plate.
[0078] The following examples illustrate the present invention
without limiting it thereto. All parts and percentages are by
weight unless otherwise specified.
EXAMPLE 1
[0079] Preparation of the lithographic base
[0080] A 0.30 mm thick aluminum foil was degreased by immersing the
foil in an aqueous solution containing 5 g/l of sodium hydroxide at
50.degree.C. and rinsed with demineralized water. The foil was then
electrochemically grained using an alternating current in an
aqueous solution containing 4 g/l of hydrochloric acid, 4 g/l of
hydroboric acid and 5 g/l of aluminum ions at a temperature of
35.degree. C. and a current density of 1200 A/m2 to form a surface
topography with an average center-line roughness Ra of 0.5
.mu.m.
[0081] After rinsing with demineralized water the aluminum foil was
then etched with an aqueous solution containing 300 g/l of sulfuric
acid at 60.degree. C. for 180 seconds and rinsed with demineralized
water at 25.degree. C. for 30 seconds.
[0082] The foil was subsequently subjected to anodic oxidation in
an aqueous solution containing 200 g/l of sulfuric acid at a
temperature of 45.degree. C., a voltage of about 10 V and a current
density of 150 A/m.sup.2 for about 300 seconds to form an anodic
oxidation film of 3.00 g/m.sup.2 of Al.sub.2O.sub.3 then washed
with demineralized water, posttreated with a solution containing
polyvinylphosphonic acid and subsequently with a solution
containing aluminum trichloride, rinsed with demineralized water at
20.degree. C. during 120 seconds and dried.
[0083] Preparation of the heat-mode imaging element
[0084] On the above described lithographic base was first coated a
layer from a 8.6% wt solution in tetrahydrofuran/methoxypropanol
55/45 ratio, with a wet coating thickness of 14 .mu.m. The
resulting layer contained 88% of ALNOVOL SPN452.TM. (novolac
available from Clariant, Germany) and 12% of
3,4,5-trimethoxybenzoic acid. Upon this layer was then coated with
a wet coating thickness of 20 .mu.m, the IR-sensitive layer from a
0.81% wt solution in methylethylketone/methoxypropanol 50/50 ratio.
The resulting IR-sensitive layer contained 81.5% of carbon black,
8.2% of nitrocellulose and 10.3% of FLUORAD FC431.TM. (a
perfluoroalkyl surfactant of 3M, USA).
[0085] Exposing the heat-mode imaging element
[0086] This material was imaged with a CREO 3244 TRENDSETTER.TM.
(available from Creo) external drum platesetter at 240 mJ/cm.sup.2
and 2400 dpi, under non-ablative conditions.
[0087] Developing and printing the imagewise exposed element
[0088] The exposed material was developed in an aqueous alkaline
developing solution. These developing was carried out in a
TECHNIGRAPH NPX-32.TM. (available from Technigraph) processor
filled with OZASOL EP26.TM. developer/water 4/1 ratio (OZASOL EP26
is commercially available from Agfa) in the developer section, and
with water in the rinsing section and OZASOL RC795.TM. gum in the
gumming section.
[0089] The diptime in the developing solution was 22 seconds.
Printing this material results in a good ink-uptake, runlength,
dotrendering and processing latitude.
[0090] .DELTA. contact angle with 80% EP26 during 1'
[0091] Unexposed 3.degree. (105.degree.->102.degree.)
[0092] Exposed (240 mJ/cm2) 35.degree.
(95.degree.->60.degree.)
[0093] Exposing the material decreases the contact angle with
10.degree..
EXAMPLE 2
[0094] Preparation of the lithographic base
[0095] A 0.30 mm thick aluminum foil was degreased by immersing the
foil in an aqueous solution containing 5 g/l of sodium hydroxide at
50.degree. C. and rinsed with demineralized water. The foil was
then electrochemically grained using an alternating current in an
aqueous solution containing 4 g/l of hydrochloric acid, 4 g/l of
hydroboric acid and 5 g/l of aluminum ions at a temperature of
35.degree. C. and a current density of 1200 A/m2 to form a surface
topography with an average center-line roughness Ra of 0.5
.mu.m.
[0096] After rinsing with demineralized water the aluminium foil
was then etched with an aqueous solution containing 300 g/l of
sulfuric acid at 60.degree. C. for 180 seconds and rinsed with
demineralized water at 25.degree.C. for 30 seconds.
[0097] The foil was subsequently subjected to anodic oxidation in
an aqueous solution containing 200 g/l of sulfuric acid at a
temperature of 45.degree. C., a voltage of about 10 V and a current
density of 150 A/m.sup.2 for about 300 seconds to form an anodic
oxidation film of 3.00 g/m.sup.2 of Al.sub.2O.sub.3 then washed
with demineralized water, posttreated with a solution containing
polyvinylphosphonic acid and subsequently with a solution
containing aluminum trichloride, rinsed with demineralized water at
20.degree. C. during 120 seconds and dried.
[0098] Preparation of the heat-mode imaging element
[0099] The IR-sensitive layer was coated from a 6.65% wt. solution
in tetrahydrofuran/2-methoxypropanol 60/40 at 21 .mu.m wet coating
thickness resulting in a dry coating thickness of 1.24 g/m.sup.2.
The resulting IR-sensitive layer contained: 9.1% of carbon black,
10.3% of 3,4,5-trimethoxybenzoic acid, 78.5% of ALNOVOL PN430.TM.,
0.2% SOLSPERSE 5000.TM., 0.9% SOLSPERSE 28000.TM. (both dispersing
agents from Zeneca Specialities, GB), 1.0% nitrocellulose E950.
[0100] Results
[0101] The change in contact angle with OZASOL EP26.TM.
developer/water 4/1 ratio (OZASOL EP26.TM. is commercially
available from Agfa) at the unexposed areas over a period of 1
minute is 8.degree..
[0102] The thus obtained material is insufficiently resistant to
the developer, which results in a worse dotrendering and inferior
processing latitude as compared to example 1.
EXAMPLE 3
[0103] Preparation of the lithographic base
[0104] A 0.30 mm thick aluminum foil was degreased by immersing the
foil in an aqueous solution containing 5 g/l of sodium hydroxide at
50.degree. C. and rinsed with demineralized water. The foil was
then electrochemically grained using an alternating current in an
aqueous solution containing 4 g/l of hydrochloric acid, 4 g/l of
hydroboric acid and 5 g/l of aluminum ions at a temperature of
35.degree. C. and a current density of 1200 A/m2 to form a surface
topography with an average center-line roughness Ra of 0.5
.mu.m.
[0105] After rinsing with demineralized water the aluminum foil was
then etched with an aqueous solution containing 300 g/l of sulfuric
acid at 60.degree. C. for 180 seconds and rinsed with demineralized
water at 25.degree. C. for 30 seconds.
[0106] The foil was subsequently subjected to anodic oxidation in
an aqueous solution containing 200 g/l of sulfuric acid at a
temperature of 45.degree. C., a voltage of about 10 V and a current
density of 150 A/m.sup.2 for about 300 seconds to form an anodic
oxidation film of 3.00 g/m.sup.2 of Al.sub.2O.sub.3 then washed
with demineralized water, posttreated with a solution containing
polyvinylphosphonic acid and subsequently with a solution
containing aluminum trichloride, rinsed with demineralized water at
20.degree. C. during 120 seconds and dried.
[0107] Preparation of the heat-mode imaging element
[0108] The IR-sensitive layer was coated from a 6.65% wt. solution
in tetrahydrofuran/2-methoxypropanol 60/40 at 21 .mu.m wet coating
thickness resulting in a dry coating thickness of 1.24 g/m.sup.2.
The resulting IR-sensitive layer contained 8.9% of carbon black,
10.1% of 3,4,5-trimethoxybenzoic acid, 76.9% of ALNOVOL PN430.TM.,
0.2% SOLSPERSE 5000.TM., 0.9% SOLSPERSE 28000.TM., 0.9%
nitrocellulose and 2.1% FLUORAD FC431.TM..
[0109] Exposing the heat-mode imaging element
[0110] This material was imaged with a CREO 3244 TRENDSETTER.TM.
external drum platesetter at 190 mJ/cm2 and 2400 dpi.
[0111] Results
[0112] .DELTA. contact angle with 80% EP26 during 1'
[0113] Unexposed 1.degree. (111.degree.->110.degree.)
[0114] Exposed 190 mJ/cm.sup.2 12.degree.
(106.degree.->94.degree.)
[0115] Exposing the material decreases the contact angle with
5.degree..
[0116] The thus obtained printing element shows an unacceptable
clean-out resulting in toning on press and inferior processing
latitude as compared to example 1.
* * * * *