U.S. patent application number 17/312517 was filed with the patent office on 2022-03-03 for lithographic printing plate precursor.
The applicant listed for this patent is AGFA NV. Invention is credited to Thomas Billiet, Peter Hendrikx, Katleen Himschoot, Johan Loccufier.
Application Number | 20220066318 17/312517 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-03 |
United States Patent
Application |
20220066318 |
Kind Code |
A1 |
Hendrikx; Peter ; et
al. |
March 3, 2022 |
LITHOGRAPHIC PRINTING PLATE PRECURSOR
Abstract
A lithographic printing plate precursor is disclosed including a
support and a coating comprising a sensitizer and an onium salt
wherein the onium salt and the sensitizer are capable of inducing a
print-out image upon UV light exposure.
Inventors: |
Hendrikx; Peter; (Mortsel,
BE) ; Billiet; Thomas; (Mortsel, BE) ;
Loccufier; Johan; (Mortsel, BE) ; Himschoot;
Katleen; (Mortsel, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AGFA NV |
Mortsel |
|
BE |
|
|
Appl. No.: |
17/312517 |
Filed: |
December 9, 2019 |
PCT Filed: |
December 9, 2019 |
PCT NO: |
PCT/EP2019/084232 |
371 Date: |
June 10, 2021 |
International
Class: |
G03F 7/004 20060101
G03F007/004; B41C 1/10 20060101 B41C001/10; G03F 7/016 20060101
G03F007/016; G03F 7/029 20060101 G03F007/029 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2018 |
EP |
18211235.9 |
Claims
1. A negative-working lithographic printing plate precursor
comprising: a coating comprising at least one sensitizer and an
onium salt; wherein the sensitizer and the onium salt are capable
of inducing a print-out image upon UV light exposure.
2. The lithographic printing plate precursor according to claim 1
wherein the coating is stable for at least five minutes in office
light.
3. The lithographic printing plate precursor according to claim 1
wherein the sensitizer is represented by Formula II: ##STR00011##
wherein R.sup.1 to R.sup.14 independently represent hydrogen, an
alkyl group, an alkoxy group, a cyano group or a halogen.
4. The lithographic printing plate precursor according to claim 3
wherein at least one of R.sup.1 to R.sup.10 represents an alkoxy
group having more than 1 carbon atom.
5. The lithographic printing plate precursor according to claim 1
wherein the sensitizer is a mixture comprising Formulas III, IV,
and V: ##STR00012##
6. The printing plate precursor according to claim 1 wherein the
sensitizer has an absorption maximum in a wavelength range from 320
nm and 500 nm.
7. The printing plate precursor according to claim 1 wherein the
onium salt is an optionally substituted iodonium or sulfonium
compound.
8. The printing plate precursor according to claim 1 wherein the
onium salt is an optionally substituted diaryliodonium or triaryl
sulfonium compound.
9. The printing plate precursor according to claim 1 wherein the
onium salt has hexafluorophosphate as counter ion.
10. The printing plate precursor according to claim 1 wherein the
onium salt is present in an amount comprised between 1% wt and 25%
wt.
11. The printing plate precursor according to claim 1 wherein the
coating further comprises a radical polymerisation initiator, a
radically polymerisable compound, and a binder polymer.
12. The printing plate precursor according to claim 1 wherein the
coating further comprises a diazonium compound.
13. A method for making a printing plate comprising: image-wise
exposing the printing plate precursor as defined in claim 1 to UV
radiation whereby a lithographic image consisting of image areas
and non-image areas is formed and whereby a colour change in the
image areas is induced; and developing the exposed precursor.
14. The method according to claim 13 wherein the colour change is
characterized by a CIE 1976 colour distance .DELTA.E between the
image and non-image areas of at least 5.
15. The method according to claim 13 wherein the energy density of
the UV radiation is between 10 mJ/cm.sup.2 and 150 mJ/cm.sup.2.
16. A method for making a printing plate comprising: image-wise
exposing the printing plate precursor as defined in claim 3 to UV
radiation whereby a lithographic image consisting of image areas
and non-image areas is formed and whereby a colour change in the
image areas is induced; and developing the exposed precursor.
17. The method according to claim 16 wherein the colour change is
characterized by a CIE 1976 colour distance .DELTA.E between the
image and non-image areas of at least 5.
18. The method according to claim 16 wherein the energy density of
the UV radiation is between 10 mJ/cm.sup.2 and 150 mJ/cm.sup.2.
19. A method for making a printing plate comprising: image-wise
exposing the printing plate precursor as defined in claim 5 to UV
radiation whereby a lithographic image consisting of image areas
and non-image areas is formed and whereby a colour change in the
image areas is induced; and developing the exposed precursor.
20. The method according to claim 19 wherein the colour change is
characterized by a CIE 1976 colour distance .DELTA.E between the
image and non-image areas of at least 5.
Description
BACKGROUND ART
[0001] Lithographic printing typically involves the use of a
so-called printing master such as a printing plate which is mounted
on a cylinder of a rotary printing press. The master carries a
lithographic image on its surface and a print is obtained by
applying ink to said image and then transferring the ink from the
master onto a receiver material, which is typically paper. In
conventional lithographic printing, ink as well as an aqueous
fountain solution (also called dampening liquid) are supplied to
the lithographic image which consists of oleophilic (or
hydrophobic, i.e. ink-accepting, water-repelling) areas as well as
hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling)
areas. In so-called driographic printing, the lithographic image
consists of ink-accepting and ink-adhesive (ink-repelling) areas
and during driographic printing, only ink is supplied to the
master.
[0002] Lithographic printing masters are generally obtained by the
image-wise exposure and processing of a radiation sensitive layer
on a lithographic support. Imaging and processing renders the
so-called lithographic printing plate precursor into a printing
plate or master. Image-wise exposure of the radiation sensitive
coating to heat or light, typically by means of a digitally
modulated exposure device such as a laser, triggers a
(physico-)chemical process, such as ablation, polymerization,
insolubilization by cross-linking of a polymer or by particle
coagulation of a thermoplastic polymer latex, solubilization by the
destruction of intermolecular interactions or by increasing the
penetrability of a development barrier layer. Although some plate
precursors are capable of producing a lithographic image
immediately after exposure, the most popular lithographic plate
precursors require wet processing since the exposure produces a
difference in solubility or difference in rate of dissolution in a
developer between the exposed and the non-exposed areas of the
coating. In positive working lithographic plate precursors, the
exposed areas of the coating dissolve in the developer while the
non-exposed areas remain resistant to the developer. In negative
working lithographic plate precursors, the non-exposed areas of the
coating dissolve in the developer while the exposed areas remain
resistant to the developer. Most lithographic plate precursors
contain a hydrophobic coating on a hydrophilic support, so that the
areas which remain resistant to the developer define the
ink-accepting, hence printing areas of the plate while the
hydrophilic support is revealed by the dissolution of the coating
in the developer at the non-printing areas.
[0003] Photopolymer printing plates rely on a working-mechanism
whereby the coating--which typically includes free radically
polymerisable compounds--hardens upon exposure. "Hardens" means
that the coating becomes insoluble or non-dispersible in the
developing solution and may be achieved through polymerization
and/or crosslinking of the photosensitive coating upon exposure to
light. Photopolymer plate precursors can be sensitized to blue,
green or red light i.e. wavelengths ranging between 450 and 750 nm,
to violet light i.e. wavelengths ranging between 350 and 450 nm or
to infrared light i.e. wavelengths ranging between 750 and 1500 nm.
Optionally, the exposure step is followed by a heating step to
enhance or to speed-up the polymerization and/or crosslinking
reaction.
[0004] In general, a toplayer or protective overcoat layer over the
imageable layer is required to act as an oxygen barrier to provide
the desired sensitivity to the plate. A toplayer typically includes
water-soluble or water-swellable polymers such as for example
polyvinylalcohol. Besides acting as barrier for oxygen, the
toplayer should best be easily removable during processing and be
sufficiently transparent for actinic radiation, e.g. from 300 to
450 nm or from 450 to 750 nm or from 750 to 1500 nm.
[0005] The classical workflow of photopolymer plates involves first
an exposure step of the photopolymer printing plate precursor in a
violet or infrared platesetter, followed by an optional pre-heat
step, a wash step of the protective overcoat layer, an alkaline
developing step, and a rinse and gum step. Over the past years,
there is a clear evolution in the direction of a simplified
workflow where the pre-heat step and/or wash step are eliminated
and where the processing and gumming step are carried out in one
single step or where processing is carried out with a neutral gum
and then gummed in a second step. Alternatively, on-press
processing wherein the plate is mounted on the press and the
coating layer is developed by interaction with the fountain and ink
that are supplied to the plate during the press run, has become
very popular. During the first runs of the press, the non-image
areas are removed from the support and thereby define the
non-printing areas of the plate.
[0006] Besides allowing for the evaluation of the image quality, a
high contrast between the image and the hydrophilic support is
required in order to obtain a good image registration (alignment)
of the different printing plates in multi-colour printing in order
to ensure image sharpness (resolution) and a correct rendering of
the colours in the images present. In order to be able to evaluate
the lithographic printing plates for image quality, such as for
example image resolution and detail rendering (usually measured
with an optical densitometer) before mounting them on the press,
the lithographic printing plate precursors often contain a colorant
such as a dye or a pigment in the coating. Such colorants provide,
after processing, a contrast between the image areas containing the
colorant and the hydrophilic support where the coating has been
removed which enables the end-user to evaluate the image quality
and/or to establish whether or not the precursor has been exposed
to light.
[0007] However, for photopolymer lithographic printing plates which
are processed on-press and thus development of the plate is not
carried out before mounting the plate on the press, a previous
inspection and discrimination of the plate including colorants is
not possible. A solution has been provided in the art by including
components to the coating which are able to form upon exposure a
so-called "print-out image", i.e. an image which is visible before
processing. In these materials however, often the photo-initiating
system is a reacting component, which induces formation of the
print-out image upon exposure, and therefore the lithographic
differentiation may be reduced.
[0008] Contrast-providing colorants obtained from the so-called
leuco dyes that switch colour upon changes in pH, temperature, UV
etc, have been widely used in the art. The leuco dye technology
involves a switch between two chemical forms whereby one is
colourless. If the colour switch is caused by for example pH or
temperature, the transformation is reversible. Irreversible
switches are based on redox reactions.
[0009] Formation of a print-out image for violet sensitized
photopolymer systems have been disclosed in for example U.S. Pat.
Nos. 3,359,109; 3,042,515; 4,258,123; 4,139,390; 5,141,839;
5,141,842; 4,336,319; 4,232,106; 4,425,424; 5,030,548; 4,598,036;
EP 434 968; WO 96/35143.
[0010] Despite the solutions which have been provided in the prior
art, there is still an interest in photopolymer plate coating
formulations which offer an improved contrast between the image
areas and background areas and which are preferably designed for
direct on-press development.
SUMMARY OF INVENTION
[0011] It is therefore an object of the present invention to
provide a negative-working, violet sensitive printing plate based
on photopolymerisation and/or crosslinking which offers an
excellent visual contrast upon imaging, even before processing.
[0012] This object is realised by the printing plate precursor
defined in claim 1 with preferred embodiments defined in the
dependent claims. The invention has the specific feature that the
printing plate material includes a coating comprising an onium
compound having an anion as counter ion and at least one sensitizer
which are capable of forming a printout image upon UV exposure.
[0013] It has surprisingly been observed that upon UV light
exposure of the coating according to the present invention, a
print-out image is formed without the presence of any additional
components such as for example a colorant.
[0014] It is a further object of the present invention to provide a
method for making a lithographic printing plate comprising the
steps of: [0015] image-wise exposing the printing plate precursor
including the coating as defined above to UV radiation whereby a
lithographic image consisting of image areas and non-image areas is
formed and whereby a colour change in the image areas is induced;
[0016] developing the exposed precursor.
[0017] The CIE 1976 colour distance .DELTA.E measured before
development and after exposure with UV light having an energy
density between 10 and 150 mJ/cm.sup.2, more preferably between 15
and 120 mJ/cm.sup.2, most preferably of maximum between 20 and 100
mJ/cm.sup.2, between the exposed and non-exposed areas preferably
has a value of at least 5.
[0018] The development is preferably carried out by treating the
precursor with a gum solution, however more preferably by mounting
the precursor on a plate cylinder of a lithographic printing press
and rotating the plate cylinder while feeding dampening liquid
and/or ink to the precursor.
[0019] Other features, elements, steps, characteristics and
advantages of the present invention will become more apparent from
the following detailed description of preferred embodiments of the
present invention. Specific embodiments of the invention are also
defined in the dependent claims.
DESCRIPTION OF EMBODIMENTS
[0020] The Sensitizer
[0021] The lithographic printing plate precursor of the current
invention comprises a coating including at least one sensitizer.
Preferred sensitizers are blue, light absorbing sensitizers having
an absorption spectrum between 320 nm and 500 nm. Preferably, the
sensitizer has a structure according to the following Formula's I
or II:
##STR00001##
[0022] wherein R.sup.1' to R.sup.5' and R.sup.1'' to R.sup.5''
independently represent hydrogen, an alkyl group, an alkoxy group,
a cyano group or a halogen;
##STR00002##
[0023] wherein R.sup.1 to R.sup.14 independently represent
hydrogen, an alkyl group, an alkoxy group, a cyano group or a
halogen.
[0024] One of R.sup.1' to R.sup.5' or R.sup.1'' to R.sup.5'' in
Formula I preferably represents an alkoxy group having more than 1
carbon atom.
[0025] More preferably, R.sup.1', R.sup.5', R.sup.1'', R.sup.5'' in
Formula I independently represent hydrogen, fluorine, chlorine,
R.sup.2' to R.sup.4' and R.sup.2'' to R.sup.4'' in Formula I
independently represent an alkoxy group; and at least two of the
alkoxy groups are branched and have from 3 to 15 carbon atoms
[0026] Even more preferred, R.sup.1', R.sup.5', R.sup.1'', R.sup.5
in Formula I represent hydrogen and R.sup.2' to R.sup.4' and
R.sup.2'' to R.sup.4'' in Formula I independently represent an
alkoxy group; and at least two of the alkoxy groups are branched
and have from 3 to 15 carbon atoms.
[0027] Most preferred, R.sup.2', R.sup.4', R.sup.2'', R.sup.4'' in
Formula I represent a methoxy group and R.sup.3' and R.sup.3'' in
Formula I independently represent branched alkoxy groups having 3
to 15 carbon atoms.
[0028] One of R.sup.1 to R.sup.10 in Formula II preferably
represents an alkoxy group having more than 1 carbon atom.
[0029] More preferably, R.sup.1, R.sup.5, R.sup.6, R.sup.10,
R.sup.11, R.sup.12, R.sup.13 and R.sup.14 in Formula II
independently represent hydrogen, fluorine, chlorine, R.sup.2 to
R.sup.4 and R.sup.7 to R.sup.9 in Formula II independently
represent an alkoxy group; and at least two of the alkoxy groups
are branched and have from 3 to 15 carbon atoms
[0030] Even more preferred, R.sup.1, R.sup.5, R.sup.6, and R.sup.10
in Formula II represent hydrogen and R.sup.2 to R.sup.4, and
R.sup.7 to R.sup.9 in Formula II independently represent an alkoxy
group; and at least two of the alkoxy groups are branched and have
from 3 to 15 carbon atoms.
[0031] Most preferred, R.sup.2, R.sup.4, R.sup.7 and R.sup.9 in
Formula II represent a methoxy group and R.sup.3 and R.sup.8 in
Formula II independently represent branched alkoxy groups having 3
to 15 carbon atoms.
[0032] The sensitizers can be used as single compound or as mixture
of several compounds. The overall amount of these compounds is
preferably comprised between 0.1 to 25% by weight, more preferably
between 0.5 to 20% by weight by weight and most preferably between
1.0 to 15% by weight with respect to the total weight of the
non-volatile compounds in the composition. The print-out image is
already obtained at a low concentration of sensitizer; for example
at an amount of 0.1% wt to 6% wt.
[0033] The following structures are examples of preferred
sensitizers used in the present invention.
##STR00003## ##STR00004## ##STR00005##
[0034] The coating of the printing plate precursor of the present
invention most preferably contains at least one of the following
compounds:
##STR00006##
[0035] The three sensitizers according to Formulae III to V may be
used in the coating as a mixture. The mixture preferably contains
between 30 and 45% by weight of Formula (III); between 35 and 55%
by weight of Formula (IV) and between 5 and 25% by weight of
Formula (V).
[0036] The Onium Compound
[0037] The coating of the printing plate precursor includes at
least one onium salt including an anion as counter ion. Preferred
onium salts include iodonium salts and sulfonium salts. One or a
mixture of two or more onium salts may be present in the
coating.
[0038] Preferred examples of iodonium salts without being limited
thereto include optionally substituted diaryl iodonium salts or
diheteroaryl iodonium salts. Diaryl iodonium salts or diheteroaryl
iodonium salts substituted with Specific examples of the
diaryliodonium salts include diphenyliodonium,
4-methoxyphenyl-4-(2-methylpropyl) phenyliodonium,
4-chlorophenyl-4-phenyliodonium, 4-(2-methylpropyl) phenyl-tolyl
iodonium, 4-hexyloxyphenyl-2,4,6-trimethoxyphenyliodonium,
4-hexyloxyphenyl-2,4-diethoxyphenyliodonium,
4-octyloxyphenyl-6-trimethoxyphenyliodonium, bis
(4-tert-butylphenyl) iodonium and bis (4-isopropylphenyl) iodonium,
4-octyloxyphenyl phenyliodonium,
[4-[(2-hydroxytetradecyl)-oxy]phenyl]phenyliodonium,
4-methylphenyl-4'-hexylphenyliodonium tetraphenylborate,
4-methylphenyl-4'-cyclohexylphenyliodonium,
4-hexylphenyl-phenyliodonium,
4-methylphenyl-4'cyclohexylphenyliodonium,
4-cyclohexylphenyl-phenyliodonium,
2-methyl-4-t-butylphenyl4'-methylphenyliodonium. Mixtures of two or
more of these onium salts can be selected.
[0039] Preferred examples of the triarylsulfonium salts without
being limited thereto include triphenylsulfonium,
dialkylphenacylsulfonium, dialkyl-4-hydroxyphenylsulfonium, bis
(4-chlorophenyl) phenylsulfonium, triphenylsulfonium benzoyl
formate, bis (4-chlorophenyl) phenylsulfonium benzoyl formate, bis
(4-chlorophenyl)-4-methylphenylsulfonium bis
(4-chlorophenyl)-4-methylphenylsulfonium, tris (4-chlorophenyl)
sulfonium, tris 2,4-dichlorophenyl) sulfonium, bis
(2,4-dichlorophenyl) phenyl sulfonium and bis (2,4-dichlorophenyl)
4-methoxyphenyl sulfonium. Mixtures of two or more of these onium
salts can be selected.
[0040] According to the present invention, the counter ion of the
onium salts is selected from hexafluorophosphate (PF.sub.6.sup.-),
SbF.sub.6.sup.- or AsF.sub.6.sup.-.
[0041] The onium salts are preferably present in the coating in an
amount between at least 1% wt and 25% wt, more preferably in an
amount between at least 5% wt and 20% wt, most preferably in an
amount between at least 10% wt and 15% wt, all based on the total
dry weight of the photopolymerisable and/or crosslinkable
layer.
[0042] The colour difference between the exposed and non-exposed
areas of the coating calculated from the L*a*b* values of the
exposed areas of the image areas (exposed areas) of the coating and
the L*a*b* values of non-image areas (non-exposed areas) of the
coating, is denoted as .DELTA.E. It has surprisingly been found
that upon exposure of the coating of the present invention with UV
radiation, a print-out image is formed characterised by a CIE 1976
colour difference .DELTA.E of at least 5, more preferably at least
6 and most preferably at least 10. .DELTA.E is the CIE 1976 colour
distance Delta E that is defined by the pair wise Euclidean
distance of the CIE L*a*b* colour coordinates. CIE L*a*b* colour
coordinates are obtained from reflection measurement in 45/0
geometry (non-polarized), using CIE 2.degree. observer and D50 as
illuminant. More details are described in CIE S 014-4/E: 2007
Colourimetry--Part 4: CIE 1976 L*a*b* Colour Spaces and CIE
publications and CIE S 014-1/E:2006, CIE Standard Colourimetric
Observers.
[0043] The CIE 1976 colour coordinates L*, a* and b* discussed
herein are part of the well-known CIE (Commission Internationale de
l'Eclairage) system of tristimulus colour coordinates, which also
includes the additional chroma value C* defined as
C*=[(a).sup.2+(b).sup.2].sup.1/2. The CIE 1976 colour system is
described in e.g. "Colorimetry, CIE 116-1995: Industrial Colour
Difference Evaluation", or in "Measuring Colour" by R. W. G. Hunt,
second edition, edited in 1992 by Ellis Horwood Limited,
England.
[0044] CIE L*a*b* values discussed and reported herein have been
measured following the ASTM E308-85 method.
[0045] At the exposed areas of the coating the L*, a* and b*
coordinates are enhanced due to absorption in the visual wavelength
range whereby a clear print-out image is formed. The print-out
image is visible due to the contrast of the image which is defined
as the colour difference between the exposed areas and the
non-exposed areas. This contrast is preferably as high as possible
and enables the end-user to establish immediately after imaging
whether or not the precursor has already been exposed, to
distinguish the different colour selections and to inspect the
quality of the image on the plate precursor.
Definitions
[0046] The optionally substituted aryl herein is preferably an
optionally substituted phenyl, benzyl, tolyl or an ortho-meta- or
para-xylyl, naphtyl, anthracenyl, phenanthrenyl, and/or
combinations thereof. The heteroaryl group is preferably a
monocyclic or polycyclic aromatic ring comprising carbon atoms and
one or more heteroatoms in the ring structure, preferably, 1 to 4
heteroatoms, independently selected from nitrogen, oxygen, selenium
and sulphur. Preferred examples thereof include an optionally
substituted furyl, pyridinyl, pyrimidyl, pyrazoyl, imidazoyl,
oxazoyl, isoxazoyl, thienyl, tetrazoyl, thiazoyl, (1,2,3)triazoyl,
(1,2,4)triazoyl, thiadiazoyl, thiofenyl group and/or combinations
thereof and the optionally substituted heteroaryl is preferably a
five- or six-membered ring substituted by one, two or three oxygen
atoms, nitrogen atoms, sulphur atoms, selenium atoms or
combinations thereof. Examples thereof include furan, thiophene,
pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole,
tetrazole, oxazole, isoxazole, thiazole, isothiazole, thiadiazole,
oxadiazole, pyridine, pyridazine, pyrimidine, pyrazine,
1,3,5-triazine, 1,2,4-triazine or 1,2,3-triazine, benzofuran,
benzothiophene, indole, indazole, benzoxazole, quinoline,
quinazoline, benzimidazole or benztriazole.
[0047] The term "alkyl" herein means all variants possible for each
number of carbon atoms in the alkyl group i.e. methyl, ethyl, for
three carbon atoms: n-propyl and isopropyl; for four carbon atoms:
n-butyl, isobutyl and tertiary-butyl; for five carbon atoms:
n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl and
2-methyl-butyl, etc. Preferably, the alkyl group is a C.sub.1 to
C.sub.20-alkyl group; more preferably the alkyl group is a C.sub.1
to C.sub.6-alkyl group. Most preferably the alkyl is a methyl
group. Cycloalkyls include for example, substituted or
unsubstituted cyclopropyl, cyclopentyl, cyclohexyl,
4-methylcyclohexyl, and cyclooctyl groups.
[0048] The term "substituted", in e.g. substituted alkyl group
means that the alkyl group may be substituted by other atoms than
the atoms normally present in such a group, i.e. carbon and
hydrogen. For example, a substituted alkyl group may include a
halogen atom or a thiol group. An unsubstituted alkyl group
contains only carbon and hydrogen atoms.
[0049] The optional substituents represent an alkyl, cycloalkyl,
alkenyl or cyclo alkenyl group, an alkynyl group, an aryl or
heteroaryl group, an alkylaryl or arylalkyl group, an alkoxy group
such as methoxy, ethoxy, iso-propoxy, t-butoxy,
(2-hydroxytetradecyl)oxy, and various other linear and branched
alkyleneoxyalkoxy groups; an aryloxy group, a thio alkyl, thio aryl
or thio heteroaryl group, a hydroxyl group, --SH, a carboxylic acid
group or an alkyl ester thereof, a sulphonic acid group or an alkyl
ester thereof, a phosphonic acid group or an alkyl ester thereof, a
phosphoric acid group or an alkyl ester thereof, an amino group, a
sulphonamide group, an amide group, a nitro group, a nitrile group,
a halogen such as fluoro, chloro, or bromo, or a combination
thereof.
[0050] A suitable alkenyl group herein is preferably a C.sub.2 to
C.sub.6-alkenyl group such as an ethenyl, n-propenyl, n-butenyl,
n-pentenyl, n-hexenyl, iso-propenyl, iso-butenyl, iso-pentenyl,
neo-pentenyl, 1-methylbutenyl, iso-hexenyl, cyclopentenyl,
cyclohexenyl and methylcyclohexenyl group.
[0051] A suitable alkynyl group herein is preferably a C.sub.2 to
C.sub.6-alkynyl group; a suitable aralkyl group is preferably a
phenyl group or naphthyl group including one, two, three or more
C.sub.1 to C.sub.6-alkyl groups; a suitable alkaryl group is
preferably a C.sub.1 to C.sub.6-alkyl group including an aryl
group, preferably a phenyl group or naphthyl group.
[0052] A cyclic group or cyclic structure herein includes at least
one ring structure and may be a monocyclic- or polycyclic group,
meaning one or more rings fused together.
The Lithographic Printing Plate Precursor
[0053] The lithographic printing plate precursor according to the
present invention is negative-working, i.e. after exposure and
development the non-exposed areas of the coating are removed from
the support and define hydrophilic (non-printing) areas, whereas
the exposed coating is not removed from the support and defines
oleophilic (printing) areas. The hydrophilic areas are defined by
the support which has a hydrophilic surface or is provided with a
hydrophilic layer. The hydrophobic areas are defined by the
coating, hardened upon exposing, optionally followed by a heating
step. Areas having hydrophilic properties means areas having a
higher affinity for an aqueous solution than for an oleophilic ink;
areas having hydrophobic properties means areas having a higher
affinity for an oleophilic ink than for an aqueous solution.
[0054] "Hardened" means that the coating becomes insoluble or
non-dispersible for the developing solution and may be achieved
through polymerization and/or crosslinking of the photosensitive
coating, optionally followed by a heating step to enhance or to
speed-up the polymerization and/or crosslinking reaction. In this
optional heating step, hereinafter also referred to as "pre-heat",
the plate precursor is heated, preferably at a temperature of about
80.degree. C. to 150.degree. C. and preferably during a dwell time
of about 5 seconds to 1 minute.
[0055] The coating includes at least one layer including a
photopolymerisable and/or crosslinkable composition. The layer
including the mainly photopolymerisable composition is also
referred to as the "photopolymerisable layer", the layer including
the mainly crosslinkable composition is also referred to as the
"crosslinkable layer". The coating may include an intermediate
layer, located between the support and the photopolymerisable
and/or crosslinkable layer. The lithographic printing precursors
can be multi-layer imageable elements.
[0056] The lithographic printing plate precursor can be prepared by
applying on a support the coating as described below and drying the
precursor.
[0057] The printing plate of the present invention is preferably
exposed with UV radiation having an energy density comprised
between 10 mJ/cm.sup.2 and 150 mJ/cm.sup.2; preferably between 15
mJ/cm.sup.2 and 120 mJ/cm.sup.2; most preferably between 20
mJ/cm.sup.2 and 100 mJ/cm.sup.2. The printing plate precursor of
the present invention has the specific feature that it is not
sensitive to the portion of the electromagnetic spectrum starting
from about 500 nm and higher. In other words, the printing plate of
the present invention is stable for at least five minutes in office
light (i.e. for example 800 lux). Stable means that the quality of
the printing plate precursor remains high and that the precursor
does not have an increased tendency to toning and/or formation of
defects in the coating after such light exposure. Also, the
sensitivity of the plate precursor does not reduce after such light
exposure. Thus the quality of the printing plate remains high i.e.
no/limited loss of sensitivity, no/limited formation of defects in
the coating, and/or no/limited tendency of toning after exposure to
office light up to five minutes.
[0058] Support
[0059] The lithographic printing plate used in the present
invention comprises a support which has a hydrophilic surface or
which is provided with a hydrophilic layer. The support is
preferably a grained and anodized aluminum support, well known in
the art. Suitable supports are for example disclosed in EP 1 843
203 (paragraphs [0066] to [0075]). The surface roughness, obtained
after the graining step, is often expressed as arithmetical mean
center-line roughness Ra (ISO 4287/1 or DIN 4762) and may vary
between 0.05 and 1.5 .mu.m. The aluminum substrate of the current
invention has preferably an Ra value below 0.45 .mu.m, more
preferably below 0.40 .mu.m and most preferably below 0.30 .mu.m.
The lower limit of the Ra value is preferably about 0.1 .mu.m. More
details concerning the preferred Ra values of the surface of the
grained and anodized aluminum support are described in EP 1 356
926. By anodising the aluminum support, an Al.sub.2O.sub.3 layer is
formed and the anodic weight (g/m.sup.2 Al.sub.2O.sub.3 formed on
the aluminum surface) varies between 1 and 8 g/m.sup.2. The anodic
weight is preferably .gtoreq.3 g/m.sup.2, more preferably
.gtoreq.3.5 g/m.sup.2 and most preferably .gtoreq.4.0 g/m.sup.2
[0060] The grained and anodized aluminum support may be subjected
to so-called post-anodic treatments, for example a treatment with
polyvinylphosphonic acid or derivatives thereof, a treatment with
polyacrylic acid, a treatment with potassium fluorozirconate or a
phosphate, a treatment with an alkali metal silicate, or
combinations thereof. Alternatively, the support may be treated
with an adhesion promoting compound such as those described in EP 1
788 434 in [0010] and in WO 2013/182328. However, for a precursor
optimized to be used without a pre-heat step it is preferred to use
a grained and anodized aluminum support without any post-anodic
treatment.
[0061] Besides an aluminum support, a plastic support, for example
a polyester support, provided with one or more hydrophilic layers
as disclosed in for example EP 1 025 992 may also be used.
[0062] The Photopolymerisable Layer
[0063] The photopolymerisable layer includes, besides the
sensitizer and the onium salt discussed above, a polymerisable
compound, optionally a binder and a polymerization initiator
capable of hardening said polymerisable compound in the exposed
areas. The photopolymerisable layer has a coating thickness
preferably ranging between 0.2 and 5.0 g/m.sup.2, more preferably
between 0.4 and 3.0 g/m.sup.2, most preferably between 0.6 and 2.2
g/m.sup.2.
[0064] Polymerisable Compound and Initiator
[0065] The polymerisable compound is preferably a monomer or
oligomer including at least one epoxy or vinyl ether functional
group and the polymerisation initiator is a Bronsted acid generator
capable of generating free acid, optionally in the presence of a
sensitizer, upon exposure, hereinafter the Bronsted acid generator
is also referred to as "cationic photoinitiator" or "cationic
initiator".
[0066] Suitable polyfunctional epoxy monomers include, for example,
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate,
bis-(3,4-epoxycyclohexymethyl) adipate, difunctional bisphenol
A-epichlorohydrin epoxy resin and multifunctional
epichlorohydrintetraphenylol ethane epoxy resin.
[0067] Suitable cationic photoinitiators include, for example,
triarylsulfonium hexafluoroantimonate, triarylsulfonium
hexafluorophosphate, diaryliodonium hexafluoroantimonate, and
haloalkyl substituted s-triazine. It is noted that most cationic
initiators are also free radical initiators because, in addition to
generating Bronsted acid, they also generate free radicals during
photo or thermal decomposition.
[0068] According to a more preferred embodiment of the present
invention, the further polymerisable compound is a polymerisable
monomer or oligomer including at least one terminal ethylenic
group, hereinafter also referred to as "free-radical polymerisable
monomer", and the polymerisation initiator is a compound capable of
generating free radicals upon exposure, optionally in the presence
of a sensitizer, hereinafter said initiator is referred to as "free
radical initiator". The polymerisation involves the linking
together of the free-radical polymerisable monomers.
[0069] Suitable free-radical polymerisable monomers include, for
example, multifunctional (meth)acrylate monomers (such as
(meth)acrylate esters of ethylene glycol, trimethylolpropane,
pentaerythritol, ethoxylated ethylene glycol and ethoxylated
trimethylolpropane, multifunctional urethanated (meth)acrylate, and
epoxylated (meth)acrylate), and oligomeric amine diacrylates. The
(meth)acrylic monomers may also have other double bond or epoxide
group, in addition to (meth)acrylate group. The (meth)acrylate
monomers may also contain an acidic (such as carboxylic acid) or
basic (such as amine) functionality.
[0070] Suitable free-radical polymerisable monomers are disclosed
in [0042] and [0050] of EP 2 916 171 and are incorporated herein by
reference.
[0071] The coating contains a free radical initiator capable of
generating free radicals upon exposure directly and/or in the
presence of a sensitizer. Suitable free-radical initiators are
described in WO 2005/111727 from page 15 line 17 to page 16 line 11
and EP 1 091 247 and may include for example hexaaryl-bisimidazole
compound (HABI; dimer of triaryl-imidazole), aromatic ketones,
aromatic onium salts, organic peroxides, thio compounds, ketooxime
ester compounds, borate compounds, azinium compounds, metallocene
compounds, active ester compounds and further compounds having a
carbon-halogen bond.
[0072] The photopolymerisable layer may also comprise a
co-initiator. Typically, a co-initiator is used in combination with
a free radical initiator. Suitable co-initiators for use in the
photopolymer coating are disclosed in U.S. Pat. Nos. 6,410,205;
5,049,479; EP 1 079 276, EP 1 369 232, EP 1 369 231, EP 1 341 040,
US 2003/0124460, EP 1 241 002, EP 1 288 720 and in the reference
book including the cited refences: Chemistry & Technology UV
& EB formulation for coatings, inks & paints--Volume
3--Photoinitiators for Free Radical and Cationic Polymerisation by
K. K. Dietliker--Edited by P. K. T. Oldring--1991--ISBN 0
947798161. Specific co-initiators, as described in EP 107 792, may
be present in the photopolymerisable layer to further increase the
sensitivity. Preferred co-initiators are disclosed in EP 2 916 171
[0051] and are incorporated herein by reference.
[0073] The Binder
[0074] The photopolymerisable layer preferably includes a binder.
The binder can be selected from a wide series of organic polymers.
Compositions of different binders can also be used. Useful binders
are described in WO2005/111727 page 17 line 21 to page 19 line 30,
EP 1 043 627 in paragraph [0013] and in WO2005/029187 page 16 line
26 to page 18 line 11.
Further Ingredients
[0075] The photopolymerisable layer may also comprise particles
which increase the resistance of the coating against manual or
mechanical damage. The particles may be inorganic particles,
organic particles or fillers such as described in for example U.S.
Pat. No. 7,108,956. More details of suitable spacer particles
described in EP 2 916 171 [0053] to [0056] are incorporated herein
by reference.
[0076] The photopolymerisable layer may also comprise an inhibitor.
Particular inhibitors for use in the photopolymer coating are
disclosed in U.S. Pat. No. 6,410,205, EP 1 288 720 and EP 1 749
240.
[0077] The photopolymerisable layer may further comprise an
adhesion promoting compound. The adhesion promoting compound is a
compound capable of interacting with the support, preferably a
compound having an addition-polymerisable ethylenically unsaturated
bond and a functional group capable of interacting with the
support. Under "interacting" is understood each type of physical
and/or chemical reaction or process whereby, between the functional
group and the support, a bond is formed which can be a covalent
bond, an ionic bond, a complex bond, a coordinate bond or a
hydrogen-bond, and which can be formed by an adsorption process, a
chemical reaction, an acid-base reaction, a complex-forming
reaction or a reaction of a chelating group or a ligand.
[0078] The adhesion promoting compound may be selected from at
least one of the low molecular weight compounds or polymeric
compounds as described in EPA 851 299 from lines 22 on page 3 to
line 1 on page 4, EP-A 1 500 498 from paragraph [0023] on page 7 to
paragraph [0052] on page 20, EP-A 1 495 866 paragraph [0030] on
page 5 to paragraph [0049] on page 11, EP-A 1 091 251 from
paragraph [0014] on page 3 to paragraph [0018] on page 20, and EP-A
1 520 694 from paragraph [0023] on page 6 to paragraph [0060] on
page 19. Preferred compounds are those compounds which comprise a
phosphate or phosphonate group as functional group capable of
adsorbing on the aluminum support and which comprise an
addition-polymerisable ethylenic double bond reactive group,
especially those described in EP-A 851 299 from lines 22 on page 3
to line 1 on page 4 and EP-A 1 500 498 from paragraph [0023] on
page 7 to paragraph [0052] on page 20. Also preferred are those
compounds which comprises a tri-alkyl-oxy silane groups,
hereinafter also referred to as "trialkoxy silane" groups, wherein
the alkyl is preferably methyl or ethyl, or wherein the trialkyloxy
silane groups are at least partially hydrolysed to silanol groups,
as functional group capable of adsorbing on the support, especially
silane coupling agents having an addition-polymerisable ethylenic
double bond reactive group as described in EP-A 1 557 262 paragraph
[0279] on page 49 and EP-A 1 495 866 paragraph [0030] on page 5 to
paragraph [0049] on page 11. Also the adhesion promoting compounds
described in EP 2 916 171 [0058] are incorporated herein by
reference.
[0079] The adhesion promoting compound may be present in the
photopolymerisable layer in an amount ranging between 1 and 50 wt
%, preferably between 3 and 30 wt %, more preferably between 5 and
20 wt % of the non-volatile components of the composition.
[0080] The adhesion promoting compound may be present in an
optional intermediate layer in an amount of at least 25 wt %,
preferably at least 50 wt %, more preferably at least 75 wt %, of
the non-volatile components of the composition. Alternatively, the
intermediate layer may consist of the adhesion promoting
compound.
[0081] Various surfactants may be added into the photopolymerisable
layer to allow or enhance the developability of the precursor;
especially developing with a gum solution. Both polymeric and small
molecule surfactants for example nonionic surfactants are
preferred. More details are described in EP 2 916 171 [0059] and
are incorporated herein by reference.
[0082] The Crosslinkable Layer
[0083] Based on a Diazonium Compound
[0084] The crosslinkable layer may include a diazonium compound and
preferably a binder.
[0085] Diazonium compounds are preferably characterized by the
generic structure A-N.sub.2.sup.+X.sup.-, wherein A is an aromatic
or heterocyclic residue and X is the anion of an acid. Specific
examples of light sensitive diazonium coatings include higher
molecular weight compositions obtained, for example, by the
condensation of certain aromatic diazonium salts in an acid
condensation medium with active carbonyl compounds such as
formaldehyde, as disclosed for example in U.S. Pat. Nos. 2,063,631
and 2,667,415. Suitable examples include condensation products of
diazonium salts of p-amino-diphenylamines, such as
diphenylamine-4-diazonium chloride or diphenylamine-4-diazonium
bromide or diphenyl-amine-4-diazonium phosphate, with formaldehyde
in phosphoric acid of high concentration. The term phosphoric acid
also includes pyrophosphoric acid, metaphosphoric acid, and
poly-phosphoric acid.
[0086] Another preferred class of diazonium compounds is described
in U.S. Pat. No. 3,849,392. The compounds are the polycondensation
product of 3-methoxy-4-diazo-diphenyl amine sulfate and 4,
4'-bis-methoxy methyl-diphenyl ether, precipitated as mesitylene
sulfonate, as taught in U.S. Pat. No. 3,849,392. The most preferred
diazonium salt is benzenediazonium, 2-methoxy-4-(phenylamino),
2,4,6-trimethylbenzenesulfonate (1:1), polymer with
1,1'-oxybis[4-(methoxymethyl)benzene]. The preparation of this
diazonium salt is disclosed in DE 2024244A. Other diazonium salts
disclosed in this document are suitable to be contained in the
crosslinkable layer.
[0087] The diazonium salt is preferably present in the coating
composition in an amount of from about 20% to about 100% by weight
of the solid composition components. A more preferred range is from
about 25% to 50% and most preferably from about 30% to 45%.
[0088] The binder may be added to the diazonium compound to improve
mechanical resistance of the crosslinkable layer and/or the
processing behaviour of the plate.
[0089] Suitable binders are polyvinyl acetates, epoxy resins based
on bis-phenol-A-epichlorohydrin, p-(vinyl butyral-co-,vinyl
acetate-co-vinyl alcohol), unplasticized urea resin of an
approximate acid number of 2 (Resamin 106 F), Recinene-modified
alkyd resin, Resins comprising a polyvinyl acetate resin and a
styrene/maleic acid half ester copolymer,
[0090] Suitable polyvinyl acetate resins have a weight average
molecular weight in the range of from about 40.000 to less than
800.000. A preferred weight average molecular weight maximum is
about 700.000; more preferably 680.000. The most preferred average
molecular weight is in the range of about 80.000 to 200,000.
Preferred binders are the butyl semi-ester of the maleic acid
anhydride/styrene copolymers (such as Scripset.RTM. 540, available
from Monsanto) and the styrene/maleic acid half ester copolymers as
disclosed in U.S. Pat. No. 4,511,640A. A more preferred binder is
obtained by reacting p-[vinylbutyral-co-vinyl alcohol-co-vinyl
acetate] such as Mowital B30T or Mowital B60T (from Kuraray Europe
GmbH) with maleic acid anhydride to a half-ester and half acid,
with the OH of the polyvinylalcohol as disclosed in Preparation
Example 5 in U.S. Pat. No. 5,695,905.
[0091] The binder is preferably present in the coating composition
in an amount of from about 8% to about 60% by weight of the solid
composition components. A more preferred range is from about 12% to
50% and most preferably from about 18% to 45%.
[0092] The weight ratio of binder to diazonium compound does not
exceed 20, preferably equal to or less than 10, more preferably
between 0.8 and 1.2.
[0093] The coverage of the crosslinkable layer is preferably
between 0.1 and 1.2 g/m.sup.2, more preferably between 0.5 and 0.8
g/m.sup.2.
[0094] The crosslinkable layer may further comprise additives, such
as for example acid stabilizers including phosphoric, citric,
tartaric and p-toluene sulfonic acids. The acid stabilizer may be
present in the coating composition in an amount of from about 1.5%
to about 4.5% by weight of the solid composition components, a more
preferably from about 2.0% to 4.0% and most preferably from about
2.5% to 3.5%.
[0095] Exposure indicators including para phenyl azo diphenyl
amine, Calcozine Fuchine dyes and Crystal Violet and Methylene Blue
dyes may be present in an amount from about 0.05% to about 0.35% by
weight of the solid composition components. A more preferred range
is from about 0.10% to 0.30% and most preferably from about 0.15%
to 0.25%.
[0096] Suitable solvents which may be used as a medium to combine
the ingredients of the coating include Methyl Cellosolve, ethylene
glycol ethers, butyrolactone, alcohols as ethyl alcohol and
n-propanol, and ketones such as methyl ethyl ketone.
[0097] Based on o-quinonediazide
[0098] Alternatively, the crosslinkable layer may include an
o-quinonediazide compound and preferably a binder.
[0099] o-quinonediazide compounds are well-known and are for
example described in Light-Sensitive Systems written by J. Kosar
(Published by John Wiley & Sons. Inc.) pp. 339-352. Suitable
o-quinonediazide compounds are for example o-naphthoquinonediazide
sulfonic acid esters of aromatic hydroxyl compounds,
o-naphthoquinonediazide carboxylic acid esters of aromatic hydroxy
compounds, o naphthoquinonediazide sulfonic acid amides of aromatic
amino compounds and o-naphthoquinonediazide carboxylic acid amides
of aromatic amino compounds.
[0100] Preferred binders are alkali-soluble resins include novolak
resins such as for examples phenol-formaldehyde resins,
cresol-formaldehyde resins, p-tert-butylphenol-formaldehyde resins,
phenol modified xylene resins, i.e., a formaldehyde condensate of
phenol and xylene, and phenol modified xylene mesitylene resins,
i.e., a formaldehyde condensate of phenol, xylene and mesitylene.
Other useful alkali-soluble resins include polyhydroxystyrene,
polyhalogenated hydroxystyrene, and copolymers of acrylic acid or
methacrylic acid and other vinyl compounds (for example, methyl
methacrylate).
[0101] The amount of o-quinonediazide compounds in coating
composition is preferably from 10 to 50% by weight, preferably from
20 to 40% by weight, based on the total solid composition
components. The amount of the alkali-soluble resins added is
preferably between 90 and 50% by weight, preferably between 80 and
60% by weight, based on the total solid weight.
[0102] The coating may include on the photopolymerisable or on the
crosslinkable layer, a toplayer or protective overcoat layer which
acts as an oxygen barrier layer including water-soluble or
water-swellable binders. Printing plate precursors which do not
contain a toplayer or protective overcoat layer are also referred
to as overcoat-free printing plate precursors. In the art, it is
well-known that low molecular weight substances present in the air
may deteriorate or even inhibit image formation and therefore
usually a toplayer is applied to the coating. A toplayer should be
easily removable during development, adhere sufficiently to the
photopolymerisable layer or optional other layers of the coating
and should preferably not inhibit the transmission of light during
exposure. Preferred binders which can be used in the toplayer are
polyvinyl alcohol and the polymers disclosed in WO 2005/029190;
U.S. Pat. No. 6,410,205 and EP 1 288 720, including the cited
references in these patents and patent applications. The most
preferred binder for the toplayer is polyvinylalcohol. The
polyvinylalcohol has preferably a hydrolysis degree ranging between
74 mol % and 99 mol %, more preferably between 88-98%. The weight
average molecular weight of the polyvinylalcohol can be measured by
the viscosity of an aqueous solution, 4% by weight, at 20.degree.
C. as defined in DIN 53 015, and this viscosity number ranges
preferably between 1 and 26, more preferably between 2 and 15, most
preferably between 2 and 10.
[0103] The overcoat layer may optionally include other ingredients
such as inorganic or organic acids, matting agents or wetting
agents as disclosed in EP 2 916 171 and are incorporated herein by
reference.
[0104] The coating thickness of the optional toplayer is preferably
between 0.25 and 1.75 g/m.sup.2, more preferably between 0.25 and
1.3 g/m.sup.2, most preferably between 0.25 and 1.0 g/m.sup.2. In a
more preferred embodiment of the present invention, the optional
toplayer has a coating thickness between 0.25 and 1.75 g/m.sup.2
and comprises a polyvinylalcohol having a hydrolysis degree ranging
between 74 mol % and 99 mol % and a viscosity number as defined
above ranging between 1 and 26.
[0105] In a preferred embodiment of the present invention, the
photopolymerisable or the crosslinkable layer does not contain an
overcoat layer.
[0106] According to the present invention there is also provided a
method for making a negative-working lithographic printing plate
comprising the steps of imagewise exposing a printing plate
precursor followed by developing the imagewise exposed precursor so
that the non-exposed areas are dissolved in the developer solution.
Optionally, after the imaging step, a heating step is carried out
to enhance or to speed-up the polymerization and/or crosslinking
reaction. The lithographic printing plate precursor can be prepared
by (i) applying on a support the coating as described above and
(ii) drying the precursor.
[0107] Exposure Step
[0108] Preferably, the image-wise exposing step is carried out
off-press in a platesetter, i.e. an exposure apparatus suitable for
image-wise exposing the precursor with a laser such as a laser
diode, for example emitting around 405 nm, or by a conventional
exposure in contact with a mask. In a preferred embodiment of the
present invention, the precursor is image-wise exposed by a laser
emitting UV-light.
[0109] The printing plate precursor is preferably image wise
exposed with UV-light and/or light in the short wavelength region
of the visible light spectrum. The light source preferably emits
light having a wavelength between 360 and 420 nm. The light source
is built in an exposure head. Different modes can be used to expose
the lithographic printing plate precursor, one where the plate is
immobile and the exposure head moves back and forth such is in
image setters having an internal drum, one where the plate is
mounted onto a drum which rotates at high speed while the exposure
head moves from one side of the drum to the other side of the
drum.
[0110] The light source can be a bulb or lamp such as mercury
vapour bulbs. Preferably lasers are used due to the high energy
density achievable, such as fibre-coupled laser diodes emitting at
405 nm. This high energy density makes it possible to achieve high
plate throughput during the exposure step. The image wise exposure
via a laser is done by digital modulation of the current and or
voltage.
[0111] The image wise exposure may be achieved by means of
modulation of the light emitted from the light source. This
modulation can be done by means of digital mirror devices, also
called DMD imaging. UV setters which are suitable to digitally
modulate the light source are available from Luscher AG and
Basysprint from Xeikon International B.V. The digital information
is obtained from a digital image which is made available to the UV
setter.
[0112] Preheat Step
[0113] After the exposing step, the precursor may be pre-heated in
a preheating unit, preferably at a temperature of about 80.degree.
C. to 150.degree. C. and preferably during a dwell time of about 5
seconds to 1 minute. This preheating unit may comprise a heating
element, preferably an IR-lamp, an UV-lamp, heated air or a heated
roll. Such a preheat step can be used for printing plate precursors
comprising a photopolymerisable composition to enhance or to
speed-up the polymerization and/or crosslinking reaction.
[0114] Development Step
[0115] Subsequently to the exposing step or the preheat step, when
a preheat step is present, the plate precursor may be processed
(developed). Before developing the imaged precursor, a pre-rinse
step might be carried out especially for the negative-working
lithographic printing precursors having a protective oxygen barrier
or topcoat. This pre-rinse step can be carried out in a stand-alone
apparatus or by manually rinsing the imaged precursor with water or
the pre-rinse step can be carried out in a washing unit that is
integrated in a processor used for developing the imaged precursor.
The washing liquid is preferably water, more preferably tap water.
More details concerning the wash step are described in EP 1 788 434
in [0026].
[0116] During the development step, the non-exposed areas of the
image-recording layer are at least partially removed without
essentially removing the exposed areas. The processing liquid, also
referred to as developer, can be applied to the plate e.g. by
rubbing with an impregnated pad, by dipping, immersing, coating,
spincoating, spraying, pouring-on, either by hand or in an
automatic processing apparatus. The treatment with a processing
liquid may be combined with mechanical rubbing, e.g. by a rotating
brush. During the development step, any water-soluble protective
layer present is preferably also removed. The development is
preferably carried out at temperatures between 20 and 40.degree. C.
in automated processing units.
[0117] Processing Liquid
[0118] The processing liquid may be an alkaline developer or
solvent-based developer. Suitable alkaline developers have been
described in US2005/0162505. An alkaline developer is an aqueous
solution which has a pH of at least 11, more typically at least 12,
preferably from 12 to 14. Alkaline developers typically contain
alkaline agents to obtain high pH values can be inorganic or
organic alkaline agents. The developers can comprise anionic,
non-ionic and amphoteric surfactants (up to 3% on the total
composition weight); biocides (antimicrobial and/or antifungal
agents), antifoaming agents or chelating agents (such as alkali
gluconates), and thickening agents (water soluble or water
dispersible polyhydroxy compounds such as glycerine or polyethylene
glycol).
[0119] Preferably, the processing liquid is a gum solution whereby
during the development step the non-exposed areas of the
photopolymerisable layer are removed from the support and the plate
is gummed in a single step. The development with a gum solution has
the additional benefit that, due to the remaining gum on the plate
in the non-exposed areas, an additional gumming step is not
required to protect the surface of the support in the non-printing
areas. As a result, the precursor is processed and gummed in one
single step which involves a less complex developing apparatus than
a developing apparatus comprising a developer tank, a rinsing
section and a gumming section. The gumming section may comprise at
least one gumming unit or may comprise two or more gumming units.
These gumming units may have the configuration of a cascade system,
i.e. the gum solution, used in the second gumming unit and present
in the second tank, overflows from the second tank to the first
tank when gum replenishing solution is added in the second gumming
unit or when the gum solution in the second gumming unit is used
once-only, i.e. only starting gum solution is used to develop the
precursor in this second gumming unit by preferably a spraying or
jetting technique. More details concerning such gum development is
described in EP1 788 444.
[0120] A gum solution is typically an aqueous liquid which
comprises one or more surface protective compounds that are capable
of protecting the lithographic image of a printing plate against
contamination, e.g. by oxidation, fingerprints, fats, oils or dust,
or damaging, e.g. by scratches during handling of the plate.
Suitable examples of such surface protective compounds are
film-forming hydrophilic polymers or surfactants. The layer that
remains on the plate after treatment with the gum solution
preferably comprises between 0.005 and 20 g/m.sup.2 of the surface
protective compound, more preferably between 0.010 and 10
g/m.sup.2, most preferably between 0.020 and 5 g/m.sup.2. More
details concerning the surface protective compounds in the gum
solution can be found in WO 2007/057348 page 9 line 3 to page 11
line 6. As the developed plate precursor is developed and gummed in
one step, there is no need to post-treat the processed plate.
[0121] The gum solution preferably has a pH value between 3 and 11,
more preferably between 4 and 10, even more preferably between 5
and 9, and most preferably between 6 and 8. A suitable gum solution
is described in for example EP 1 342 568 in [0008] to [0022] and
WO2005/111727. The gum solution may further comprise an inorganic
salt, an anionic surfactant, a wetting agent, a chelate compound,
an antiseptic compound, an anti-foaming compound and/or an ink
receptivity agent and/or combinations thereof. More details about
these additional ingredients are described in WO 2007/057348 page
11 line 22 to page 14 line 19.
[0122] Drying and Baking Step
[0123] After the processing step the plate may be dried in a drying
unit. In a preferred embodiment the plate is dried by heating the
plate in the drying unit which may contain at least one heating
element selected from an IR-lamp, an UV-lamp, a heated metal roller
or heated air.
[0124] After drying the plate can optionally be heated in a baking
unit. More details concerning the heating in a baking unit can be
found in WO 2007/057348 page 44 line 26 to page 45 line 20.
[0125] The printing plate thus obtained can be used for
conventional, so-called wet offset printing, in which ink and an
aqueous dampening liquid is supplied to the plate. Another suitable
printing method uses a so-called single-fluid ink without a
dampening liquid. Suitable single-fluid inks have been described in
U.S. Pat. Nos. 4,045,232; 4,981,517 and 6,140,392. In a most
preferred embodiment, the single-fluid ink comprises an ink phase,
also called the hydrophobic or oleophilic phase, and a polyol phase
as described in WO 00/32705.
EXAMPLES
[0126] All materials used in the following examples were readily
available from standard sources such as Sigma-Aldrich (Belgium) and
Acros (Belgium) unless otherwise specified.
Example 1
1. Preparation of the Printing Plate Precursors PPP-00 to
PPP-06
[0127] Preparation of the Aluminum Support S-01
[0128] A 0.3 mm thick aluminum foil was degreased by spraying with
an aqueous solution containing 26 g/l NaOH at 65.degree. C. for 2
seconds and rinsed with demineralised water for 1.5 seconds. The
foil was then electrochemically grained during 10 seconds using an
alternating current in an aqueous solution containing 15 g/l HCl,
15 g/l SO.sub.4.sup.2- ions and 5 g/l Al.sup.3+ ions at a
temperature of 37.degree. C. and a current density of about 100
A/dm.sup.2. Afterwards, the aluminum foil was then desmutted by
etching with an aqueous solution containing 5.5 g/l of NaOH at
36.degree. C. for 2 seconds and rinsed with demineralised water for
2 seconds. The foil was subsequently subjected to anodic oxidation
during 15 seconds in an aqueous solution containing 145 g/l of
sulfuric acid at a temperature of 50.degree. C. and a current
density of 17 A/dm.sup.2, then washed with demineralised water for
11 seconds and dried at 120.degree. C. for 5 seconds.
[0129] The support thus obtained was characterized by a surface
roughness Ra of 0.35-0.4 .mu.m (measured with interferometer
NT1100) and had an oxide weight of 3.0 g/m.sup.2.
Photopolymerisable Layer
[0130] The printing plate precursor PPP-00 to PPP-06 were prepared
by coating onto the above described support S-01 the components as
defined in Table 1 dissolved in a mixture of 35% by volume of MEK
and 65% by volume of Dowanol PM (1-methoxy-2-propanol, commercially
available from DOW CHEMICAL Company). The coating solution was
applied at a wet coating thickness of 30 .mu.m and then dried at
120.degree. C. for 1 minute in a circulation oven. Dry coating
weight 1,295 g/m.sup.2
TABLE-US-00001 TABLE 1 Printing plate precursors PPP-00 to PPP-07
Ingre- PPP- PPP- PPP- PPP- PPP- PPP- PPP- dients 00 01 02 03 04 05
06 mg/m.sup.2 comp comp inv comp inv comp inv Binder (1) 120.0
120.0 120.0 120.0 120.0 120.0 120.0 Tegoglide 1.5 1.5 1.5 1.5 1.5
1.5 1.5 410 (2) Sartomer 240 240 240 240 240 240 240 CN104 (3)
Sartomer 90 90 90 90 90 90 90 CN-UVE 151M (4) Mono 240 240 240 240
240 240 240 Z1620 (5) Disperbyk 45 45 45 45 45 45 45 182 (6) HABI
1-2 3 3 3 3 3 3 3 (7) MBT (8) 21 21 21 21 21 21 21 Sipomer 225 225
225 225 225 225 225 PAM 100 (9) Albritect 30 30 30 30 30 30 30 CP
30 (10) Fluomix 60 -- 60 60 60 60 60 (11) Omnicat -- 200 200 -- --
-- -- 440 (12) Onium-01 -- -- -- 200 -- -- -- (13) Onium-02 -- --
-- 200 -- -- (14) Onium-03 -- -- -- -- 200 -- (15) Onium-04 -- --
-- -- -- 200 (16) 1) Binder represents Alberdingk U180, an
aliphatic polyester polyurethane commercially available as a 50 wt.
% aqueous dispersion commercially available from Alberdingk Boley
2) Tegoglide 410 is a surfactant commercially available from Evonik
Tego Chemie GmbH; 3) CN 104 is an epoxy acrylate oligomer
commercially available from Arkema; 4) CN-UVE 151M is an epoxy
diacrylate monomer commercially available from Sartomer 5) Mono
Z1620 is a solution in MEK containing 30 wt % of a reaction product
from 1 mole of 2-hydroxyethylmethacrylate and 0.5 mole of
2-(2-hydroxyethyl-piperidine); 6) Disperbyk 182 is commercially
available from BYK Chemie GmbH.; 7) HABI 1-2 is a photoinitiator,
commercially available from Hodogaya Chemical; 8) MBT is
2-mercapto-benzimidazool; 9) Sipomer PAM 100 is a methacrylate
phosphonic ester commercially available from Rhodia; 10) Albritect
CP 30, is a copolymer of vinylphosphonic acid and acrylic acid
commercially available as a 20 wt % aqueous dispersion from Rhodia
11) Fluomix is a violet sensitizer mixture consisting of the
following compounds: ##STR00007## ##STR00008## ##STR00009## 12)
Bis(4-methylphenyl)iodonium hexafluorophosphate; 13)
(4-methylphenyl, 4 isobutylphenyl)iodonium hexafluorophosphate; 14)
Bis(4-tert-butylphenyl)iodonium tetraphenylborate; 15)
Tetrabutylammonium tetraphenylborate; 16) Scarat BI85 commercially
available from ABCR GmbH & co; B & S Specialites BV; Cray
Valley Prod LTD manufacturer and having the following structure:
##STR00010##
Overcoat Layer
[0131] On top of the photosensitive layer, a solution in water with
the composition as defined in Table 2 was coated (40 .mu.m) on the
printing plate precursors, and dried at 120.degree. C. for 2
minutes. The so-formed protective top layer OC-1 has a dry
thickness or dry coating weight of 1.35 g/m.sup.2.
TABLE-US-00002 TABLE 2 composition of the overcoat INGREDIENT g
OC-01 Mowiol 4-88 (1) 0.817 Mowiol 4-98 (1) 0.493 Ebotec MB-SF (2)
0.002 Advantage S (3) 0.027 Lutensol A8 (4) 0.014 (1) Mowiol 4-88
is a partially hydrolyzed polyvinylalcohol from Kuraray. Mowiol
4-98 is a fully hydrolyzed polyvinylalcohol from Kuraray; (2)
Ebotec MB-SF is a biocide commercially available from Bode Chemie
Hamburg GmbH; (3) Adavantage S is a dewetting agent commercially
available from; ISP; (4) Lutensol A8 is a surface active agent
commercially available from BASF.
2. Imaging of the Printing Plate Precursors PPP-00 to PPP-06
[0132] Exposure was carried out on a Lucher Expose plate-setter, a
UV contact frame with band filters to select the 405 nm region or a
395 nm UV LED firejet 200 of Phoseon, at an energy density of 25
mJ/cm.sup.2.
3. .DELTA.E Measurement
[0133] .DELTA.E was calculated from the L*, a* and b* values of the
plate precursor before and after imaging.
[0134] Lab measurement executed with a GretagMacBeth SpectroEye
reflection spectrophotometer with the settings: D50 (illuminant),
2.degree. (Observer), No filter; commercially available from
GretagMacBeth. The total colour difference .DELTA.E is a single
value that takes into account the difference between the L*, a* and
b* values of the image areas and the non-image areas:
.DELTA.E= {square root over
(.DELTA.L.sup.2+.DELTA.a.sup.2+.DELTA.b.sup.2)}
[0135] The higher the total colour difference .DELTA.E, the better
the obtained contrast. The contrast between image and non-image
areas results in the occurrence of a print-out image.
4. Results
[0136] A solid pattern was imaged on the printing plate precursors
PPP-00 to PPP-06 and the L*a*b* values of both the non-image areas
and the solid imaged area were measured and the respective delta E
(.DELTA.E) values were calculated. Table 3 (Printing plate
precursors PPP-00 to PPP-06 with an overcoat layer) and Table 4
(Printing plate precursors PPP-00 to PPP-06 without an overcoat
layer) summarise the obtained results.
TABLE-US-00003 TABLE 3 Obtained contrast for PPP-00 to PPP-06 with
an OC Printing plate precursor PPP-0X Fluomix cation Anion .DELTA.E
(1) PPP-00 fluomix -- -- <0.5 Comp PPP-01 -- Iodonium PF.sub.6-
1.87 Comp PPP-02 fluomix Iodonium PF.sub.6- 16.07 Inv PPP-03
fluomix Iodonium PF.sub.6- 13.34 Inv PPP-04 fluomix Iodonium
B(Ph).sub.4- 4.25 Comp PPP-05 fluomix Ammonium B(Ph).sub.4- 1.17
Comp PPP-06 fluomix sulfonium PF.sub.6- 7.72 Inv (1) A good
contrast is defined as .DELTA.E .gtoreq. 5.0.
TABLE-US-00004 TABLE 4 Obtained contrast for PPP-00 to PPP-06
without an OC Printing plate precursor PPP-0x sensitizer cation
anion .DELTA.E (1) PPP-00 -- Iodonium PF.sub.6- <0.5 Comp PPP-01
fluomix -- PF.sub.6- 0.58 Comp PPP-02 fluomix Iodonium PF.sub.6-
12.60 Inv PPP-03 fluomix Iodonium PF.sub.6- 9.65 Inv PPP-04 fluomix
Iodonium B(Ph).sub.4- 1.79 Comp PPP-05 fluomix Ammonium
B(Ph).sub.4- 0.31 Comp PPP-06 fluomix sulfonium PF.sub.6- 8.92 Inv
(1) A good contrast is defined as .DELTA.E .gtoreq. 5.0.
[0137] The results summarised in Tables 3 and 4 show that at an
exposure energy of 25 mJ/cm.sup.2 a good visual contrast
.DELTA.E.gtoreq.5 is obtained for the inventive printing plate
precursors including a coating including the combination of
PF.sub.6.sup.- counter ion as part of an onium structure and
fluomix. The onium salt is preferably iodonium salt.
Example 2
1. Preparation of the Printing Plate Precursors PPP-07 to
PPP-12
[0138] Preparation of the Aluminum Support S-01
[0139] See Example 1 above
[0140] Photopolymerisable Layer
The printing plate precursor PPP-07 to PPP-12 were prepared by
coating onto the above described support S-01 the components as
defined in Table 5 dissolved in a mixture of 35% by volume of MEK
and 65% by volume of Dowanol PM (1-methoxy-2-propanol, commercially
available from DOW CHEMICAL Company). The coating solution was
applied at a wet coating thickness of 30 .mu.m and then dried at
120.degree. C. for 1 minute in a circulation oven.
TABLE-US-00005 TABLE 5 Printing plate precursors PPP-07 to PPP-12
Printing plate precursor PPP-07 PPP-08 PPP-09 PPP-10 PPP-11 PPP-12
Binder (1) 120.0 120.0 120.0 120.0 120.0 120.0 Tegoglide 410 (2)
1.5 1.5 1.5 1.5 1.5 1.5 Mono Z1620 (3) 240 240 240 240 240 240 HABI
1-2 (4) 3 3 3 3 3 3 MBT (5) 21 21 21 21 21 21 Fluomix (6) 60 60 60
-- 60 60 Omnicat 440 (7) -- 50 -- 50 -- -- NaPF.sub.6.sup.- -- --
18.5 -- 18.5 -- Thioxantone (8) -- -- 60 60 -- BF.sub.4.sup.- -- --
-- -- 18.5 (1) To (7): see Table 1 above; (8) Speedcure ITX
commercially available from Lambson Limited.
[0141] Overcoat Layer
[0142] On top of the photosensitive layer, a solution in water with
the composition as defined in Table 2 above was coated (40 .mu.m)
on the printing plate precursors, and dried at 120.degree. C. for 2
minutes. The so-formed protective top layer OC-1 has a dry
thickness or dry coating weight of 1.35 g/m.sup.2.
2. Imaging of the Printing Plate Precursors PPP-07 to PPP-12
[0143] Exposure was carried out on a Lucher Expose plate-setter, a
UV contact frame with band filters to select the 405 nm region or a
395 nm UV LED firejet 200 of Phoseon, at an energy density of 25
mJ/cm.sup.2.
3. .DELTA.E Measurement
[0144] .DELTA.E was measured before and after imaging following the
method as described in Example 1.
4. Results
[0145] A solid pattern was imaged on the printing plate precursors
PPP-07 to PPP-12 and the L*a*b* values of both the non-image areas
and the solid imaged area were measured and the respective delta E
(.DELTA.E) values were calculated. Table 6 summarise the obtained
results.
TABLE-US-00006 TABLE 6 Obtained contrast for PPP-07 to PPP-12
PPP-0X sensitizer cation anion .DELTA.E (1) PPP-07 fluomix -- --
0.19 Comp PPP-08 fluomix iodonium PF.sub.6- 10.74 Inv PPP-09
fluomix sodium PF.sub.6- 0.45 comp PPP-10 thioxanthone iodonium
PF.sub.6- 0.16 comp PPP-11 fluomix sodium PF.sub.6- 0.16 Comp
thioxanthone PPP-12 fluomix -- BF.sub.4- 0.48 comp (1) A good
contrast is defined as .DELTA.E .gtoreq. 5.0.
[0146] The results summarised in Table 6 show that at an exposure
energy of 25 mJ/cm.sup.2 a good visual contrast .DELTA.E.gtoreq.5
is obtained for the inventive printing plate precursors including a
coating including the combination of PF.sub.6.sup.- counter ion as
part of an onium structure and fluomix.
Example 3
1. Preparation of the Printing Plate Precursors PPP-14 to
PPP-16
[0147] Preparation of the Aluminum Support S-01
[0148] See Example 1 above
[0149] Photopolymerisable Layer
[0150] The printing plate precursor PPP-14 to PPP-16 were prepared
by coating onto the above described support S-01 the components as
defined in Table 7 dissolved in a mixture of 22% by volume of MeOH
and 77% by volume of Dowanol PM (1-methoxy-2-propanol, commercially
available from DOW CHEMICAL Company) and 1% by volume monoethylene
glycol. The coating solution was applied at a wet coating thickness
of 26 .mu.m and then dried at 120.degree. C. for 1 minute in a
circulation oven.
TABLE-US-00007 TABLE 7 Printing plate precursors PPP-14 to PPP-16
Printing plate precursor PPP-14 PPP-15 PPP-16 Binder (1) 436.0
436.0 436.0 Edaplan LA411 (2) 3.3 3.3 3.3 Phosphoric acid 17.3 17.3
17.3 Diazonium polymer (3) 436 436 436 Fluomix (4) -- 50 50 Omnicat
440 (5) -- 175 175 (1) PAL 166, Polyvinylbutyral, vinyl alcohol,
vinylbutyral copolymer, commercially available form Agfa NV; (2)
Edaplan LA411: 10 wt % solution of Edaplan LA 411, a modified
siloxane-glycol copolymer commercially available from MUNZING
CHEMIE, in Dowanol PM; (3) Diazo resin STE1428 commercially
available from Clariant Benelux NV; (4) and (5) see Table 1
above
2. Imaging of the Printing Plate Precursors PPP-14 to PPP-16
[0151] Exposure was carried out on a Lucher Expose plate-setter, a
UV contact frame with band filters to select the 405 nm region or a
395 nm UV LED firejet 200 of Phoseon, at an energy density of 70
mJ/cm.sup.2.
3. .DELTA.E Measurement
[0152] .DELTA.E was measured before and after imaging following the
method as described in Example 1.
4. Results
[0153] A solid pattern was imaged on the printing plate precursors
PPP-07 to PPP-12 and the L*a*b* values of both the non-image areas
and the solid imaged area were measured and the respective delta E
(.DELTA.E) values were calculated. Table 8 summarise the obtained
results.
TABLE-US-00008 TABLE 8 Obtained contrast for PPP-14 to PPP-16
PPP-14 PPP-15 PPP-16 .DELTA.E (1) No color 17.8 15.3 formation (1)
A good contrast is defined as .DELTA.E .gtoreq. 5.0.
[0154] The results summarised in Table 8 show that a good visual
contrast .DELTA.E 5 is obtained for the inventive printing plate
precursors including a coating comprising a diazonium salt, an
onium structure and fluomix.
Example 4
1. Preparation of the Printing Plate Precursors PPP-17 to
PPP-19
[0155] Preparation of the Aluminum Support S-01
[0156] See Example 1 above
[0157] Photopolymerisable Layer
[0158] The printing plate precursor PPP-17 to PPP-19 were prepared
by coating onto the above described support S-01 the components as
defined in Table 9 dissolved in a mixture of 35% by volume of MEK
and 65% by volume of Dowanol PM (1-methoxy-2-propanol, commercially
available from DOW CHEMICAL Company). The coating solution was
applied at a wet coating thickness of 30 .mu.m and then dried at
120.degree. C. for 1 minute in a circulation oven.
TABLE-US-00009 TABLE 9 Printing Plate precursors PPP-17 to PPP-19
Ingredients PPP-17 PPP-18 PPP-19 mg/m.sup.2 inv inv inv Tegoglide
410 (1) 1.5 1.5 1.5 Sartomer CN104 (2) 220.4 220.4 220.4 Sartomer
CN-UVE 151M (3) 81.2 81.2 81.2 Mono Z1620 (4) 220.4 220.4 220.4
HABI 1-2 (5) 2.3 2.3 2.3 MBT (6) 18.6 18.6 18.6 Sipomer PAM 100 (7)
208.8 208.8 208.8 Albritect CP 30 (8) 27.3 27.3 27.3 Fluomix (9)
57.9 57.9 57.9 Omnicat 440 (10) 197.2 197.2 197.2 Aerosil 150 (11)
92.8 92.8 92.8 Gohsefimer L5407 (12) 110.2 220.4 -- Poval LM30 (13)
-- -- 110.2 (1) to (10) see Table 1 above; (11) Fumed unmodified
silica, 20% dispersion in water with Bykjet 9152 (15% aerosil, 5%
Bykjet); (12) Polyvinyl alcohol supplied by Nippon Gohsei; (13)
Polyvinyl alcohol supplied by Kuraray.
[0159] Overcoat Layer
[0160] On top of the photosensitive layer of PPP-18 a solution in
water with the composition as defined in Table 2 above was coated
(40 .mu.m) on the printing plate precursors, and dried at
120.degree. C. for 2 minutes. The so-formed protective top layer
OC-1 has a dry thickness or dry coating weight of 1.35
g/m.sup.2.
2. Imaging of the Printing Plate Precursors PPP-17 to PPP-19
[0161] Exposure was carried out on a Lucher Expose plate-setter, a
UV contact frame with band filters to select the 405 nm region or a
395 nm UV LED firejet 200 of Phoseon, at an energy density of 25
mJ/cm.sup.2.
3. Development and Printing
[0162] Printing plates PP-17 to PP-19 were evaluated for
development on-press.
[0163] The printing plates were mounted on a Heidelberg GTO52
dalhgren press using K+E Skinnex 800 SPEED IK black ink (trademark
of BASF Druckfarben GmbH) and 4 wt % Prima FS303 SF (trademark of
Agfa Graphics) and 8% isopropanol in water as fountain solution. A
compressible blanket was used and printing was performed on
non-coated offset paper. Prior to paper feeding, 10 press
revolution with only the dampening system followed by 5 revolutions
with only the inking rollers was performed. Up to 500 sheets were
printed and visual assessment of every 10 sheets was performed to
evaluate toning (i.e. accepting ink) in the non-image areas.
4. Toning Behaviour
[0164] Toning behaviour of the on-press developed printing plates
was visually assessed every 10 printed sheets. The results are
given in Table 10.
TABLE-US-00010 TABLE 10 Toning behaviour of printing plates PP-17
to PP-19 Printing Plate Overcoat * Toning behaviour** PP-17 no 50
inventive PP-18 no 30 inventive PP-18 yes 100 inventive PP-19 no 20
inventive *see Example 1 above; **amount of sheets required to
obtain toning-free sheets by visual assessment.
[0165] The results in Table 10 indicate that the clean out in terms
of toning behaviour of the inventive printing plates PP-17 to PP-19
including iodonium salt and fluomix is good to very good after
processing on-press.
* * * * *