U.S. patent application number 09/263110 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 Eric Verschueren. Invention is credited to DAMME, MARC VAN, HABERHAUER, HELMUTH, HAUQUIER, GUIDO, JUNG, JORG, VERMEERSCH, JOAN, VERSCHUEREN, ERIC.
Application Number | 20010001700 09/263110 |
Document ID | / |
Family ID | 27239288 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001700 |
Kind Code |
A1 |
VERSCHUEREN, ERIC ; 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 but
not in water and less than 5% by weight versus the polymer, soluble
in the aqueous alkaline solution of a hydrophilic polymer and a top
layer on the same side of the lithographic base as the first layer
which top layer is IR-sensitive and unpenetrable for or insoluble
in an alkaline developer wherein said first layer and said top
layer may be one and the same layer; characterized in that said top
layer contains a compound selected from the group consisting of a
polymer in an amount from 30 mg to 500 mg/m.sup.2, a triaryl
methane dye and a phthalocyanine dye.
Inventors: |
VERSCHUEREN, ERIC;
(MERKSPLAS, BE) ; DAMME, MARC VAN; (HEVERLEE,
BE) ; VERMEERSCH, JOAN; (DEINZE, BE) ;
HAUQUIER, GUIDO; (NIJLEN, BE) ; JUNG, JORG;
(FLORSHEIM, DE) ; HABERHAUER, HELMUTH;
(TAUNUSSTEIN, DE) |
Correspondence
Address: |
BREINER & BREINER
P O BOX 19290
ALEXANDRIA
VA
223200290
|
Assignee: |
Eric Verschueren
|
Family ID: |
27239288 |
Appl. No.: |
09/263110 |
Filed: |
March 5, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60081996 |
Apr 16, 1998 |
|
|
|
Current U.S.
Class: |
430/271.1 ;
430/270.1; 430/284.1; 430/302 |
Current CPC
Class: |
B41C 2210/262 20130101;
B41C 2210/22 20130101; B41C 2210/02 20130101; B41C 2210/14
20130101; B41C 2210/266 20130101; B41C 2210/06 20130101; B41C
2210/24 20130101; B41C 1/1016 20130101; B41C 2210/20 20130101 |
Class at
Publication: |
430/271.1 ;
430/270.1; 430/284.1; 430/302 |
International
Class: |
G03C 001/76; G03F
007/00; G03F 007/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 6, 1998 |
EP |
98200709.8 |
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 but not in water and less than 5% by weight versus the
polymer, soluble in the aqueous alkaline solution of a hydrophilic
polymer and a top layer on the same side of the lithographic base
as the first layer which top layer is IR-sensitive and unpenetrable
for or insoluble in an alkaline developer wherein said first layer
and said top layer may be one and the same layer; characterized in
that said top layer contains a compound selected from the group
consisting of a polymer in an amount from 30 mg to 500 mg/m.sup.2,
a triaryl methane dye and a phthalocyanine dye.
2. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein the IR-sensitive layer contains
carbon black.
3. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein the IR-sensitive layer contains
a polymer with a glass transition temperature of at least
35.degree. C., capable of forming a film by drying at high
temperature.
4. A heat mode imaging element for making a lithographic printing
plate according to claim 3 wherein said polymer is a
polyurethane.
5. A heat mode imaging element for making a lithographic printing
plate according to claim 4 wherein said polyurethane has been
hardened with a melamine.
6. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein said polymer is cellulose or a
cellulose derivative.
7. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein said top layer contains a
phthalocyanine dye.
8. A heat mode imaging element for making a lithographic printing
plate according to claim 1 wherein said top layer contains a
triaryl methane dye.
9. 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.
10. 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 said 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.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a heat mode imaging element
for preparing a lithographic printing plate comprising an IR
sensitive top layer.
[0002] More specifically the invention is related to a heat mode
imaging element for preparing a lithographic printing plate with a
higher scratch resistance.
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] GB-A-1 208 415 discloses a method of recording information
comprising information-wise heating a recording material comprising
a support bearing, with or without an inter-layer, a heat-sensitive
recording layer constituted so that such information-wise heating
creates a record of the information in terms of a difference in the
water-permeability of different areas of the recording layer,
treating the recording material with an a aqueous liquid which
penetrates through the water-permeable or more water permeable
areas of the recrding layer and is constituted so as to effect a
permanent physical and/or chemical change of at least the surface
portions of the underlying support or inter-layer in the
corresponding areas, and removing the whole of the recording layer
to expose said information-wise changed underlying support or
inter-layer.
[0019] EP-A-823 327 discloses a positive photosensitive composition
showing a difference in solubility in alkali developer as between
an exposed portion and a non-exposed portion, which comprises as
components inducing the difference in solubility
[0020] (a) a photo-thermal conversion.material, and
[0021] (b) a high molecular compound, of which the solubility in an
alkali developer is changeable mainly by a change other than a
chemical change.
[0022] U.S. Pat. No. 5,641,608 discloses a process for the direct
production of an imaged pattern of resist on a substrate, which
process utilizes thermo-resist rather than photoresist, i.e.
compositions which undergo thermally-induced, rather than
photo-induced, chemical transformations. A film of thermo-resist
composition applied to the surface substrate is scanned by a
focused heat source in a predetermined pattern, without a
phototool, to bring about localized thermally-induced chemical
transformations of the composition which either directly produce
the resist pattern or produce in the film a developable latent
image of the pattern.
[0023] GB-A-1 154 568 discloses a method of recording a graphic
original having contrasting light-absorbing and light-transmitting
areas, wherein a recording material comprising a supported layer
composed mainly of gelatin the water-solubility or water-absorptive
capacity of which increases if the layer is sufficiently heated,
such layer also having light-absorbing substance(s) distributed
therein, is placed with such gelatin layer in contact with the
light-absorbing areas of the original and the said gelatine layer
is exposed to light through the original, the intensity of the
light and the duration of the exposure being such that the areas of
the gelatin layer in contact with the light absorbing areas of the
original are substantially unaffected by heat conduction from such
light-absorbing areas, but the water solubility or water-absorptive
capacity of the other areas of the gelatin layer is increased by
heating thereof due to absorption of copying light by the
light-absorbing substance(s) in those other areas of the gelatin
layer.
[0024] GB-A-1 245 924 discloses an information-recording method
wherein a recording material is used comprising a heat-sensitive
recording layer of a composition such that the solubility of any
given area of the layer in a given solvent can be increased by
heating that area of the layer, wherein the said layer is
information-wise heated to produce a record of the information in
terms of a difference in the solubilities in the said solvent of
different areas of the recording layer , and wherein the whole
layer is then contacted with such solvent to cause the portions of
the recording layer which are soluble or most soluble in such
solvent to be removed or penetrated by such solvent, the said
method being characterized in that the said recording layer is
wholly or mainly composed of one or more heat-sensitive polymeric
compounds.
[0025] FR-A-1 561 957 discloses a processus in order of registering
or reproducing information by means of electromagnetic radiation
and also discloses elements sensible for heat containing substances
wherein heat is produced by exposure to electromagnetic
radiation.
[0026] GB-A-1 155 035 discloses a method of recording information,
wherein a recording material is used comprising a layer of a
polymeric material which when any given area of the layer is
sufficiently heated undergoes in that area a modificarion resulting
in a decrease in the solubility of that area of the layer in water
or an aqueous medium, such layer also incorporating a substance or
substances distributed over the whole area of the layer and being
capable of being heated by exposing the layer to intense radiant
energy which is absorbed by such substance or substances, and
wherein the said material is exposed to intense radiant energy
which is distributed over the material in a pattern determined by
the information to be recorded and which is at least partly
absorbed by said distributed substance or substances, so that a
corresponding heat pattern is generated in the material, whereby
such information is recorded in terms of a difference in the
solubilities in water or an aqueous medium of different areas of
said layer.
[0027] GB-A-1 160 221 discloses a method of recording information,
wherein a recording material is used comprising a water permeable
recording layer which incorporates hydrophobic thermoplastic
polymeric material in the form of particles solid at room
temperature and which can be rendered water-impermeable or
substantially less water-permeable by the action of heat, said
recording material also incorporating, in heat-conductive
relationship to said polymer particles, a substance or substances
which is or are distributed over the whole area of such material
and is or are capable of being heated by exposing the material to
intense electromagnetic radiation which is absorbed by such
substance or substances; and wherein the recording material is
exposed to such an amount of electromagnetic radiation which is
absorbed by said distributed substance or substances and is
distributed over the recording material in a pattern determined by
the information to be recorded, that a corresponding heat pattern
is generated in the recording material whereby such information is
recorded in terms of a difference in the water-permeabilities of
different areas of said recording layer.
[0028] 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 or insoluble in an alkaline
developer containing SiO.sub.2 as silicates
[0029] Said last three heat-mode imaging element have the
disadvantage that the upper layer is very sensitive for scratches.
Covering said layer with a protective layer results in a lower
resolution and in a lower development lattitude, due to a smaller
difference in the rate of penetration of the developing liquid
between exposed and non-exposed areas. A solution for said problem
would be appreciated
OBJECTS OF THE INVENTION
[0030] It is an object of the invention to provide a heat mode
imaging element for making a lithographic printing plate with a
wide lattitude of development.
[0031] It is an object of the invention to provide a heat mode
imaging element for making a lithographic printing plate with a
high resolution.
[0032] It is further an object of the present invention to provide
a heat mode imaging element for making a lithographic printing
plate with an improved scratch resistance.
[0033] Further objects of the present invention will become clear
from the description hereinafter.
SUMMARY OF THE INVENTION
[0034] 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
but not in water and less than 5% by weight versus the polymer,
soluble in the aqueous alkaline solution of a hydrophilic polymer
and a top layer on the same side of the lithographic base as the
first layer which top layer is IR-sensitive and unpenetrable for or
insoluble in an alkaline developer wherein said first layer and
said top layer may be one and the same layer; characterized in that
said top layer contains a compound selected from the group
consisting of a polymer in an amount from 30 mg to 500 mg/m.sup.2,
a triaryl methane dye and a phthalocyanine dye.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The top layer is also called the second layer.
[0036] The first layer comprises preferably not more than 1% by
weight, more preferably none hydrophilic polymer.
[0037] Suitable polymers which can be used as scratch resistance
increasing agents are preferably polymers with a glass transition
temperature of at least 35.degree. C., more preferably above
40.degree. C. capable of forming a film by drying at high
temperature
[0038] Representative polymers which can be used as scratch
resistance increasing agents are eg acrylates, selfcrosslinking
acrylates, acrylates in combination with melamine-hardeners. These
polymers can be added as a solution to the coating but also as a
dispersion to the coating.
[0039] Another class of polymers which can be used as scratch
resistance increasing agents are of the type of polyvinylalcohol
and modified derivates, which can be hardened with well known
harderners of the type of orthosilicates, orhotitanates,
aldehyde-type compounds,
[0040] Other polymers that can be used as scratch resistance
increasing agents are polymetylmethacrylates, styrene-maleic
anhydride copolymers, polycarbonates, polyamides, terpolymers of
styrene-methylmethacrylate-mal- eic acid, selfcrosslinking
terpolymers acrylates-styrene-maleic acid.
[0041] One of the preferred classes of polymers that can be used as
scratch resistance increasing agents is these of the polyurethanes.
Polyurethanes can be obtained from the polymerisation of following
polyisocyanates and polyhydric alcohols.
[0042] As polyhydric alcohols can be used the simple polyhydric
alcohols as ethylene glycol, propylene glycol, 1,3-propanediol,
1,4-butanediol, 1,4 butylene glycol, 1,5 pentanediol, 1,6
hexanediol, diethylene glycol, dipropylene glycol, neopentyl
glycol, triethylene glycol, p-xylylene glycol, bisphenol A,
hydrogenated bisphenol A, bisphenol dihydroxypropyl ether,
glycerol, trimethylolethane, trimethylolpropane,
trishydroxymethylaminomethane, pentaerythritol, dipentaerythritol,
sorbitol, sucrose, degraded starch. As polyhydric alcohols can also
be used condensation polyester polyols with hydroxyl groups at both
ends obtained by polycondensation between any of these polyhydric
alcohols and dicarboxylic acids or anhydrides as succinic acid, the
three isomeric phtalic acids, phtalic anhydride, adipic acid,
hexahydrophtalic acid, isophtalic acid, hydroxy-functional
polylactons produced by transesterification of diphenyl carbonate
with glycols. Another process for manufacturing hydroxyl-terminated
polyesters include ring-opening polymerisation of
.epsilon.-caprolactone in the presence of glycol.
[0043] As isocyanates can be used the following compounds:
hexamethylene diisocyanate, trimethylhexamethylene diisocyanate,
diphenyl ether isocyanate, dimeric acid diisocyanate,
bicycloheptane triisocyanate, paraphenylene diisocyanate, 2,4- or
2,6-toluylene diisocyanate, 4,4-diphenylmethane diisocyanat,
tolidine diisocyanate, hydrogenated xylylene diisocyanate,
cyclohexane diisocyanate, metaxylylene diisocyanate,
2,6-diisocyanate methylcaproate, 4,4'-methylenebis(cyclohex-
ylisocyanate), methylcyclohexane 2,4(2,6)diisocyanate,
1,3-(isocyanateomethyl)cyclohexane, isophorone diisocyanate,
tetramethylxylylene diisocyanate, polymethylenepolyphenyl
isocyanate, triarylmethane triisocyanate, tris(isocyanatophenyl)
thiophosphate, tetramethylxylylene diisocyanate, lysine ester
triisocyanate, 1,6,11-undecane triisocyanate,
1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-hexamethylene
triisocyanate, . . .
[0044] The above mentioned polyurethanes can be hardened with
melamine-derivates. As a preferred melamine derivate can be used a
methylated melamine-formaldehyde reaction product. For the
hardening of these systems the addition of strong acids functions
as catalyst.
[0045] Said urethanes are used in a amount preferably between 30
and 200 mg/m.sup.2.
[0046] Another preferred class of polymers that can be used as
scratch resistance increasing agents is these of cellulose and
derivatives. As nitrocellulose can be used the esterified product
of cellulose with nitrating acid with a nitrogen content of the
final product lower than 12.6%. As cellulose can be used natural
cellulose.
[0047] Said celluloses are used in a amount preferably between 30
and 120 mg/m.sup.2.
[0048] The triaryl methane dyes are used preferably in an amount
ranging from 30 to 500 mg, more preferably in an amount between 50
and 200 mg/m.sup.2.
[0049] The phthalocyanine dyes can be metal containing dyes or
metal-free dyes. They are used preferably in an amount ranging from
40 to 600 mg, more preferably in an amount between 80 and 250
mg/m.sup.2.
[0050] 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 or insoluble in an alkaline developer containing
SiO.sub.2 as silicates.
[0051] 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 at
least two acid groups, more preferably with at least two sulphonic
groups. Still more preferably are cyanines dyes with two indolenine
and at least two sulphonic acid groups. Most preferably is compound
I with the structure as indicated 1
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] The development with the aqueous alkaline solution is
preferably done within an interval of 5 to 120 seconds.
[0059] 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 descibed 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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. No. 3,971,660, 4,284,705 and EP-A-514 490.
[0070] 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.
[0071] 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.
[0072] 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 or insoluble
in an alkaline developer containing SiO.sub.2 as silicates.
[0073] 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.
[0074] The IR-dyes are present preferably in an 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.
[0075] 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 descibed 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] To prepare a lithographic plate, the heat-mode imaging
element is image-wise exposed and developed.
[0081] 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.s and 20 .mu.s.
[0082] 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 as
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.
[0083] In the present invention, the composition of the developer
used is also very important.
[0084] 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.
[0085] 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 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.
[0086] 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.
[0087] 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.
[0088] 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,
[SiO.sub.2]/[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.
[0089] 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 mqnophenyl 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.
[0090] 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 (C8.about.C22) 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.3Na 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.
[0091] In order to enhance developing stability of the developers
and replenishers used in the invention, the following compounds may
simultaneously be used.
[0092] 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(NH3)6]Cl3 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.
[0093] 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.
[0094] 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.
[0095] 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 lenght of the printing plate.
[0096] The following examples illustrate the present invention
without limiting it thereto. All parts and percentages are by
weight unless otherwise specified.
EXAMPLE 1
(Comparative Example)
[0097] Preparation of the Lithographic Base
[0098] 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/m.sup.2 to form a
surface topography with an average center-line roughness Ra of 0.5
mm.
[0099] 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.
[0100] 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.
Preparation of the Heat-Mode Imaging Element 1
[0101] On the above described lithographic base was first coated a
layer from an 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 and 12% of
3,4,5-trimethoxybenzoic acid.
[0102] Upon this layer was then coated with a wet coating thickness
of 20 .mu.m the IR-sensitive layer from a 0.735% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black 11.5 mg/m.sup.2 of nitrocellulose, 2.1 mg/m.sup.2
of Solsperse 5000, 11.3 mg/m.sup.2 of Solsperse 28000, 2.0
mg/m.sup.2 of Tego Wet 265 and 5.0 mg/m.sup.2 of Tego Glide
410.
EXAMPLE 2
[0103] On the lithographic base described in example 1, was first
coated a layer from an 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 and 12% of 3,4,5-trimethoxybenzoic acid.
[0104] Upon this layer was then coated with a wet coating thickness
of 20 .mu.m, the IR-sensitive layer from a 1.0520% wt solution in
methylethylketcne/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 63.0 mg/m.sup.2 of ALMACRYL XPE-1676, 11.5
mg/m.sup.2 of nitrocellulose, 2.1 mg/m.sup.2 of Solsperse 5000,
11.3 mg/m.sup.2 of Solsperse 28000, 2.0 mg/m.sup.2 of Tego Wet 265
and 5.0 mg/M.sup.2 of Tego Glide 410. ALMACRYL XPE-1676.RTM. is a
urethane modified polyester commercially available from Image
Polymers Europe.
EXAMPLE 3
[0105] On the lithographic base described in example 1, was first
coated a layer from an 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 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 1.3057% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 114.1 mg/m.sup.2 of ALMACRYL XPE-1676, 11.5
mg/m.sup.2 of nitrocellulose, 2.1 mg/m.sup.2 of Solsperse 5000,
11.3 mg/m.sup.2 of Solsperse 28000, 2.0 mg/m.sup.2 of Tego Wet 265
and 5.0 mg/m.sup.2 of Tego Glide 410.
EXAMPLE 4
[0106] On the lithographic base described in example 1, was first
coated a layer from an 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 and 12% of 3,4,5-trimethoxybenzoic acid.
[0107] Upon this layer was then coated with a wet coating thickness
of 20 .mu.m, the IR-sensitive layer from a 1.052% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 43.7 mg/m.sup.2 of ALMACRYL XPE-1676, 11.5
mg/m.sup.2 of nitrocellulose, 18.9 mg/m.sup.2 of CYMEL 303, 0.63
mg/m.sup.2 of p-toluene sulphonic acid, 2.1 mg/m.sup.2 of Solsperse
5000, 11.3 mg/m.sup.2 of Solsperse 28000, 2.0 mg/m.sup.2 of Tego
Wet 265 and 5.0 mg/m.sup.2 of Tego Glide 410. CYMEL 303.RTM. is a
methylated melamine-formaldehyde crosslinking agent commercial
available from CYANAMID.
EXAMPLE 5
[0108] On the lithographic base described in example 1, was first
coated a layer from an 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 and 12% of 3,4,5-trimethoxybenzoic acid.
[0109] Upon this layer was then coated with a wet coating thickness
of 20 .mu.m, the IR-sensitive layer from a 0.777% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 20 mg/m.sup.2 of nitrocellulose, 2.1 mg/m.sup.2 of
Solsperse 5000, 11.3 mg/m.sup.2 of Solsperse 28000, 2.0 mg/m.sup.2
of Tego Wet 265 and 5.0 mg/m.sup.2 of Tego Glide 410.
EXAMPLE 6
[0110] On the lithographic base described in example 1, was first
coated a layer from an 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 and 12% of 3,4,5-trimethoxybenzoic acid.
[0111] Upon this layer was then coated with a wet coating thickness
of 20 .mu.m, the IR-sensitive layer from a 0.927% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 50 mg/m.sup.2 of nitrocellulose, 2.1 mg/m.sup.2 of
Solsperse 5000, 11.3 mg/m.sup.2 of Solsperse 28000, 2.0 mg/m.sup.2
of Tego Wet 265 and 5.0 mg/m.sup.2 of Tego Glide 410.
EXAMPLE 7
[0112] On the lithographic base described in example 1, was first
coated a layer from an 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 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 1.177% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 100 mg/m.sup.2 of nitrocellulose, 2.1 mg/m.sup.2
of Solsperse 5000, 11.3 mg/m.sup.2 of Solsperse 28000, 2.0
mg/m.sup.2 of Tego Wet 265 and 5.0 mg/m.sup.2 of Tego Glide
410.
EXAMPLE 8
[0113] On the lithographic base described in example 1, was first
coated a layer from an 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 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 1.177% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 11.5 mg/m.sup.2 of nitrocellulose, 2.1 mg/m.sup.2
of Solsperse 5000, 11.3 mg/m.sup.2 of Solsperse 28000, 100
mg/m.sup.2 of HELIOGEN BLAU D7565, 2.0 mg/m.sup.2 of Tego Wet 265
and 5.0 mg/m.sup.2 of Tego Glide 410. HELIOGEN BLAU D7565 also
named C.I. Pigment Blue 16 is a copper and chloride free
phtalocyanin dye, commercially available from BASF.
EXAMPLE 9
[0114] On the lithographic base described in example 1, was first
coated a layer from an 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 and 12% of 3,4,5-trimethoxybenzoic acid.
[0115] Upon this layer was then coated with a wet coating thickness
of 20 .mu.m, the IR-sensitive layer from a 1.177% wt solution in
methylethylketone/methoxypropanol 50/50 ratio. This layer was dried
at a temperature of at least 120.degree. C. for at least 40
seconds. The resulting IR-sensitive layer contained 115 mg/m.sup.2
of carbon black, 11.5 mg/M.sup.2 of nitrocellulose, 2.1 mg/m.sup.2
of Solsperse 5000, 11.3 mg/m.sup.2 of Solsperse 28000, 100
mg/m.sup.2 of BASONYL BLAU 633, 2.0 mg/m.sup.2 of Tego Wet 265 and
5.0 mg/m.sup.2 of Tego Glide 410. BASONYL BLAU 633 also named C.I.
Basic Blue 8, is a triarylmethane dye, commercially available from
BASF.
[0116] Scratching the Heat-mode Imaging Element
[0117] The above mentioned materials in comparative example 1 and
examples 2 till 9 were scratched in the test `Linimark`. In this
test scratches are formed by displacing needles at a speed of 96
cm/min, under well defined loads. The needles are of type robin
with a radius of 1.5 mm. 15 scratches are formed under following
loads: 57 - 85 - 114 - 142 - 170 - 113 - 169 - 225 - 282 - 338 -
400 - 600 - 800 - 1000 en 1200 mN.
[0118] After creation of the 15 scratches the material was
exposed.
Exposing the Heat-mode Imaging Element
[0119] All the above mentioned materials were imaged with a Creo
3244.TM. external drum platesetter at 263 mJ/cm.sup.2 and 2400
dpi.
Developing the Imagewise Exposed Element
[0120] After exposure of the imaging element, the element was
developed in an aqueous alkaline developing solution. These
developing was carried out in a Technigraph NPX-32 processor at a
speed of 1 m/min at 25.degree. C., filled with Ozasol EP262A
(Ozasol EP262A is commercially available from Agfa) and with water
in the rinsing section and Ozasol RC795 gum in the gumming section
The obtained printing plate has an intact image without etching
defects.
Evaluation of the Scratch Resistance
[0121] The 15 scratches are controlled on width of damage and given
a corresponding quotation as indicated in table 1.
[0122] When the depth of the scratch is unto the support, this
means the total layer is removed, an extra value is summated. This
phenomenon is visible by a discoloration from black to white
metallic color on the scratch region. This value is 3 when the
discoloration is locally. When the entire scratch is white a value
of 5 is added.
1 TABLE 1 Quotation Width of scratch 0 no scratch visible 0.5
scratch smaller than 50 .mu.m 1 width between 50 and 100 .mu.m 2
width between 100 and 150 .mu.m 3 width between 150 and 200 .mu.m 4
width greater than 200 .mu.m +3 when scratch is broken white line
+5 when scratch is fully white
[0123] A summation of all given quotations results in the scratch
resistance of te material. The lower the value, the better the
scratch resistance.
Evaluation of Lithographic Quality of the Material
[0124] After evaluation of the scratch resistance of the above
mentioned materials, the plates are printed on a Heidelberg GTO46
printing machine with a conventional ink (K+E) and fountain
solution (Rotamatic). The prints are evaluated on scumming in the
IR-exposed areas and on good ink-uptake in the non-imaged
areas.
2 Results scratch Example resistance Print quality Comp 1 22 OK Ex
2 19 OK Ex 3 18 OK Ex 4 14.5 OK Ex 5 22 OK Ex 6 15 OK Ex 7 11 Light
Scumming Ex 8 18.5 OK Ex 9 19 OK
[0125] Print quality OK means: no visible scumming on non-image
parts and good ink-uptake.
[0126] It is seen from the examples that examples 2 to 4 and 6 to 9
(examples according to the invention) yield (much) better scratch
resistance than the comparative examples 1 and 5
* * * * *