Planographic printing member and process for its manufacture

A planographic printing member comprising a substrate, an oleophilic layer, an infra-red sensitive/ablatable layer, and a hydrophilic layer. The hydrophilic layer is derived from a silicate solution, optionally containing particulate materials such as alumina and/or titania. The printing member may be exposed to radiation from a laser which ablates the infra-red sensitive/ablatable layer to reveal areas of the oleophilic layer. An exposed printing member may be used in wet lithographic printing.

BACKGROUND OF THE INVENTION 
Lithographic processes involve establishing image (printing) and non-image 
(non-printing) areas on a substrate, substantially on a common plane. When 
such processes are used in printing industries, non-image areas and image 
areas are arranged to have different affinities for printing ink. For 
example, non-image areas may be generally hydrophilic or oleophobic and 
image areas may be oleophilic. In "wet" lithographic printing, a dampening 
or fountain (water-based) liquid is applied initially to a plate prior to 
application of ink so that it adheres to the non-image areas and repels 
oil based inks therefrom. In "dry" printing, ink is repelled from 
non-image areas due to their release property. 
There are numerous known processes for creating image and non-image areas. 
Recently, much work has been directed towards processes which use laser 
imaging, in view of the ease with which lasers can be controlled 
digitally. 
For example, Lewis U.S. Pat. No. 5,339,737 (Presstek) describes 
lithographic printing plates suitable for imaging by means of laser 
devices that emit in the near-infrared region. One plate described 
includes a substrate having an oleophilic layer, an ablatable layer over 
the oleophilic layer and a top hydrophilic layer. Imagewise laser exposure 
ablates areas of the ablatable layer which areas (together with the 
portions of the hydrophilic layer fixed thereto) are removed. A plate for 
use in wet lithographic printing which is described in Lewis U.S. Pat. No. 
5,339,737 has a hydrophilic layer derived from polyvinyl alcohol which is 
a water-soluble polymer. As a result, the hydrophilic layer gradually 
dissolves into the water-based dampening or fountain solution, thereby 
leading to a gradual acceptance of ink by non-image areas. Consequently, 
the number of prints obtainable from such a plate is severely limited. 
WO94/18005 (Agfa) describes a substrate coated with an ink receptive layer 
over which an ablatable layer is provided. A hardened hydrophilic layer 
comprising titania, polyvinyl alcohol, tetramethylorthosilicate and a 
wetting agent is provided over the ablatable layer. Disadvantageously, the 
hydrophilic layer needs to be hardened at an elevated temperature for a 
period of at least several hours and for some cases up to a week (see U.S. 
Pat. No. Hauquier 5,462,833) in order to provide a viable product. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to address problems associated 
with known planographic printing members and methods for their 
preparation. 
According to the invention, there is provided a method of preparing a 
planographic printing member comprising a support, an ablatable layer and 
a hydrophilic layer, said method including forming said hydrophilic layer 
by application of a fluid comprising a silicate.

DETAILED DESCRIPTION OF THE INVENTION 
Preferably, said planographic printing member is a printing plate. 
Said hydrophilic layer may be applied over said support, suitably so that 
it is between the support and said ablatable layer or it may be applied so 
that said ablatable layer is between the support and said hydrophilic 
layer. The latter described arrangement is preferred. Preferably, the 
planographic printing member is arranged such that, on ablation of said 
ablatable layer, areas of the hydrophilic layer over areas of the 
ablatable layer which are ablated are removed. 
Said silicate preferably does not include organic functional groups, for 
example alkyl groups. 
Said silicate is preferably substantially water soluble. Preferably, said 
fluid applied in said method comprises a silicate solution, suitably an 
aqueous silicate solution, in which said particulate material is 
dispersed. Said silicate solution may comprise a solution of any soluble 
silicate including compounds often referred to as water glasses, 
metasilicates, orthosilicates and sesquisilicates. Said silicate solution 
may comprise a solution of a modified silicate for example a borosilicate 
or phosphosilicate. 
Said silicate solution may comprise one or more, preferably only one, metal 
or non-metal silicate. A metal silicate may be an alkali metal silicate. A 
non-metal silicate may be quaternary ammonium silicate. Preferably, said 
silicate is an alkaline silicate. 
Said silicate solution may be formed from silicate wherein the ratio of the 
number of moles of Si species, for example SiO.sub.2, to the number of 
moles of cationic, for example metal species is in the range 0.25 to 10, 
preferably in the range 0.25 to about 6, more preferably in the range 0.5 
to 4. 
Said silicate is most preferably an alkali metal silicate. In this case, 
the ratio of the number of moles of SiO.sub.2 to the number of moles of 
M.sub.2 O in said silicate, where M represents an alkali metal may be at 
least 0.25, suitably at least 0.5, preferably at least 1, more preferably 
at least 1.5. Especially preferred is the case wherein said ratio is at 
least 2.5. Said ratio may be less than 6, preferably less than 5 and more 
preferably less than 4. 
Preferred alkali metal silicates include lithium, sodium and potassium 
silicates, with lithium and/or sodium silicate being especially preferred. 
A silicate solution comprising only sodium silicate is most preferred. 
Said fluid may comprise 2 to 30 wt % of silicate (e.g. dissolved sodium 
silicate solid), preferably 5 to 20 wt %, more preferably 8 to 16 wt %. 
The fluid may be prepared using 10 to 60 wt %, preferably 30 to 50 wt %, 
more preferably 35 to 45 wt % of a silicate solution which comprises 30 to 
40 wt % silicate. 
Said fluid preferably comprises said silicate and particulate material. 
Said fluid may include 5 to 60 wt % of particulate material. Preferably, 
the fluid includes 10 to 50 wt %, more preferably 15 to 45 wt %, 
especially 20 to 40 wt % of particulate material. 
The ratio of the weight of silicate to the weight of particulate material 
in the fluid is preferably in the range 0.1 to 2 and, more preferably, in 
the range 0.1 to 1. Especially preferred is the case wherein the ratio is 
in the range 0.2 to 0.6. 
Said fluid may include more than 20 wt %, preferably more than 30 wt %, 
more preferably more than 40 wt %, especially more than 45 wt % water 
(including water included in, for example said silicate solution). Said 
fluid may include less than 80 wt %, preferably less than 70 wt %, more 
preferably less than 65 wt %, especially less than about 60 wt % water. 
Said particulate material may be an organic or an inorganic material. 
Organic particulate materials may be provided by latexes. Inorganic 
particulate materials may be selected from alumina, silica, silicon 
carbide, zinc sulphide, zirconia, barium sulphate, talcs, clays (e.g. 
kaolin), lithopone and titanium oxide. 
Said particulate material may comprise a first material which may have a 
hardness of greater than 8 Modified Mohs (on a scale of 0 to 15), 
preferably greater than 9 and, more preferably, greater than 10 Modified 
Mohs. 
Said first material may comprise generally spherical particles. 
Alternatively, said material may comprise flattened particles or 
platelets. 
Said first material may have a mean particle size of at least 0.1 .mu.m and 
preferably at least 0.5 .mu.m. 
Said first material may have a mean particle size of less than 45 .mu.m, 
preferably less than 20 .mu.m, more preferably less than 10 .mu.m. 
The particle size distribution for 95% of particles of the first material 
may be in the range 0.01 to 150 .mu.m, preferably in the range 0.05 to 75 
.mu.m, more preferably in the range 0.05 to 30 .mu.m. 
Said first material preferably comprises an inorganic material. Said first 
material preferably comprises alumina which term includes Al.sub.2 O.sub.3 
and hydrates thereof, for example Al.sub.2 O.sub.3.3H.sub.2 O. Preferably, 
said material is Al.sub.2 O.sub.3. 
Said particulate material in said fluid may include at least 20 wt %, 
preferably at least 30 wt % and, more preferably, at least 40 wt % of said 
first material. Said fluid may include 5 to 40 wt %, preferably 5 to 30 wt 
%, more preferably 7 to 25 wt %, especially 10 to 20 wt % of said first 
material. 
Said particulate material may comprise a second material. Said second 
material may have a mean particle size of at least 0.001 .mu.m, preferably 
at least 0.01 .mu.m. Said second material may have a mean particle size of 
less than 10 .mu.m, preferably less than 5 .mu.m and, more preferably, 
less than 1 .mu.m. 
Mean particle sizes of said first and second materials suitably refer to 
the primary particle sizes of said materials. 
Said particulate material in said fluid may include at least 20 wt %, 
preferably at least 30 wt % and, more preferably, at least 40 wt % of said 
second material. Said fluid may include 5 to 40 wt %, preferably 5 to 30 
wt %, more preferably 7 to 25 wt %, especially 10 to 20 wt % of said 
second material. 
Said second material is preferably a pigment. Said second material is 
preferably inorganic. Said second material is preferably titanium dioxide. 
Said first and second materials preferably define a multimodal, for example 
a bimodal particle size distribution. 
Where the fluid comprises a silicate and said particulate material 
comprises a first material and a second material as described, the ratio 
of the wt % of silicate (e.g. dissolved sodium silicate solid) to the wt % 
of said first material may be in the range 0.25 to 4, preferably in the 
range 0.5 to 1.5 and more preferably about 1. Similarly, the ratio of the 
wt % of silicate to the wt % of said second material may be in the range 
0.25 to 4, preferably in the range 0.5 to 1.5 and more preferably about 1. 
The ratio of the wt % of first material to the wt % of second material may 
be in the range 0.5 to 2, preferably in the range 0.75 to 1.5, more 
preferably about 1 to 1. 
Said particulate material may include a third material which is preferably 
adapted to lower the pH of the fluid. Said third material may be a 
colloid, suitably colloidal silica or an inorganic salt, suitably a 
phosphate, with aluminum phosphate being preferred. Where a third material 
is provided, preferably less than 30 wt % more preferably less than 20 wt 
%, especially less than 10 wt % of said particulate material is comprised 
by said third material. 
The pH of said fluid may be greater than 9.0, is preferably greater than 
9.5 and, more preferably, greater than 10.0. Especially preferred is the 
case wherein the pH is greater than 10.5. The pH is suitably controlled so 
that the silicate remains in solution and does not form a gel. A gel is 
generally formed when the pH of a silicate solution falls below pH9. The 
pH of said fluid is preferably less than 14, more preferably less than 13. 
The pH of the fluid is believed to be important, in some cases, for 
ensuring adequate adhesion of the hydrophilic layer to an underlying 
layer. 
The fluid may include other compounds for adjusting its properties. For 
example, the fluid may include one or more surfactants. Said fluid may 
include 0 to 1 wt % of surfactant(s). A suitable class of surfactants 
comprises anionic sulphates or sulphonates. The fluid may include 
viscosity builders for adjusting the viscosity. Said fluid may include 0 
to 10 wt %, preferably 0 to 5 wt % of viscosity builder(s). Also, the 
fluid may include dispersants for dispersing the inorganic particulate 
material throughout the liquid. Said fluid may include 0 to 2 wt % of 
dispersant(s). A suitable dispersant may be sodium hexametaphosphate. 
Hydrophilic layers of planographic printing plates have been proposed which 
incorporate organic polymers, for example polyvinyl alcohol and/or 
polyvinyl acetate. Said fluid used in the method of the present invention 
may include less than 30 wt %, preferably less than 15 wt %, more 
preferably less than 5 wt %, especially less than 1 wt % of polyvinyl 
alcohol and/or polyvinyl acetate and/or any other organic polymeric or 
polymerizable material. 
Said fluid may have a viscosity of less than 100 centipoise when measured 
at 20.degree. C. and a shear rate of 200s.sup.-1 using a Mettler Rheomat 
180 Viscometer incorporating a double gap measuring geometry. Preferably, 
said viscosity is less than 50 centipoise, more preferably less than 30 
centipoise when measured as aforesaid. Especially preferred is the case 
wherein the viscosity is less than 20 centipoise. 
Said fluid may be applied to said support by any suitable means which is 
preferably non-electrochemical. 
Said fluid may be applied to both sides of said support in order to form a 
hydrophilic layer over both sides. A support with such a layer over both 
sides may be used to prepare a double-sided lithographic plate. Said fluid 
is preferably applied over only one side of said support. 
Said fluid may be applied to form a hydrophilic layer having an average 
thickness after drying, of less than 20 .mu.m, preferably less than 10 
.mu.m and, more preferably, less than 5 .mu.m. Especially preferred is the 
case wherein the average thickness is less than 3 .mu.m. 
The thickness of the hydrophilic layer may be greater than 0.1 .mu.m, 
preferably greater than 0.3 .mu.m and, more preferably, greater than 
0.5.mu.m. 
Said particulate material (when provided) preferably defines formations in 
said hydrophilic layer which render said layer non-planar. 
The method preferably includes the steps of providing suitable conditions 
for the removal of water from the fluid after it has been applied. 
Suitable conditions may involve passive or active removal of water and may 
comprise causing an air flow over the hydrophilic layer and/or adjusting 
the humidity of the air. Preferably, the method includes the step of 
arranging the support over which said hydrophilic layer has been applied 
in a heated environment. Said support may be placed in an environment so 
that its temperature does not exceed 230.degree. C., preferably does not 
exceed 200.degree. C. and, more preferably, does not exceed 175.degree. C. 
Especially preferred is the case wherein the support temperature does not 
exceed 150.degree. C. The support may be arranged in the heated 
environment for less than 180 seconds, preferably less than 120 seconds 
and, more preferably, less than 100 seconds. Advantageously, it is found 
that no further prolonged treatment of the hydrophilic layer is needed to 
produce a useful printing member. 
The method may include the further step of treating the hydrophilic layer 
with a liquid to adjust its properties. For example, the pH of the surface 
of the hydrophilic layer may be adjusted, for example by contacting the 
surface with aluminum sulphate. 
Said support may be any type of support used in printing. For example, it 
may comprise a cylinder or a plate. The latter is preferred. 
Said support may include a metal surface over which said ablatable layer 
and hydrophilic layer are provided. Preferred metals include aluminum, 
steel, tin or alloys of any of the aforesaid, with aluminum being most 
preferred of the aforesaid. Said metal may be provided over another 
material, for example over plastics or paper. 
Alternatively, said support may not include a metal surface described, but 
may comprise plastics, for example a polyester, or a coated paper, for 
example one coated with a polyalkylene material, for example polyethylene. 
Where the ablatable layer is provided between the support and the 
hydrophilic layer, an oleophilic surface is preferably defined between the 
support and ablatable layer, suitably so that said oleophilic surface and 
said ablatable layer are abutting. Said oleophilic surface may be defined 
by an oleophilic layer which may be a resin, for example a phenolic resin. 
Said ablatable layer is suitably arranged to ablate on application of 
radiation, for example by means of a laser preferably arranged to emit in 
the infrared region and, more preferably, arranged to emit in the near-IR 
region, suitably between 700 and 1500 nm. Preferably, the lambda (max) of 
the radiation is in the range 700 to 1500 nm. Said laser may be a solid 
state laser (often referred to as a semi-conductor laser) and may be based 
on gallium aluminum arsenide compounds. 
Said ablatable layer may include a first binder and a material capable of 
converting radiation into heat or may consist essentially of a 
substantially homogenous material which is inherently adapted to be 
ablated. 
Preferred first binders are polymeric, especially organic polymers, and 
include vinylchloride/vinylacetate copolymers, nitrocellulose and 
polyurethanes. 
Preferred materials for converting radiation into heat include particulate 
materials such as carbon black and other pigments, metals, dyes and 
mixtures of the aforesaid. 
Said ablatable layer may include a second binder material adapted to 
increase the adhesion of the ablatable layer to said hydrophilic layer as 
compared to when said second material is not present. Said second binder 
material is preferably inorganic. It is preferably a material which is 
described herein as an essential or optional component of the hydrophilic 
layer. Preferably, said second binder material is a particulate material 
with titanium dioxide being especially preferred. 
Where the ablatable layer comprises a substantially homogenous material as 
described, it may comprise a layer of metal. Suitable metals may be 
selected from aluminum, bismuth, platinum, tin, titanium, tellurium or 
mixtures thereof or alloys containing any of the aforesaid. Preferably, 
said layer of metal is selected from aluminum and titanium or alloys 
thereof. 
The ablatable layer may have a thickness of at least 50 nm, preferably at 
least 100 nm, more preferably at least 150 nm, especially 200 nm or more. 
The ablatable layer may have a thickness of less than 10 .mu.m, suitably 
less than 8 .mu.m, preferably less than 6 .mu.m, more preferably less than 
4 .mu.m, especially 2 .mu.m or less. 
The ablatable layer and hydrophilic layer may be contiguous. 
In some cases, it may be desirable to arrange a binder layer between the 
ablatable and hydrophilic layers suitably for adhesion purposes. Said 
binder layer may comprise a polymeric, for example an organic polymeric 
material, optionally in combination with an inorganic material, especially 
an inorganic particulate material. A preferred material for said binder 
layer may be selected from resins, latexes and gelatin or gelatin 
derivatives. Said binder layer preferably includes a material which is 
described herein as an essential or optional component of said hydrophilic 
layer. Said binder layer preferably includes titanium dioxide. 
In other cases, it may be desirable to treat the ablatable layer prior to 
providing said hydrophilic layer over said ablatable layer. Preferred 
treatments are arranged to modify the exposed surface of the ablatable 
layer and may include the use of solvent etches or a corona discharge. In 
some circumstances, for example when said ablatable layer comprises 
titanium, said ablatable layer may be subjected to a surface treatment 
which may comprise contacting the surface of an ablatable layer with an 
alkaline solution, for example comprising a metasilicate. 
The invention extends to a planographic printing member preparable by the 
method described. 
The invention further extends to a planographic printing member comprising 
a support, an ablatable layer and a hydrophilic layer, said hydrophilic 
layer comprising a material, for example a binder material, derived or 
derivable from a silicate. 
Said binder material may be derived from at least 60 wt %, preferably at 
least 70 wt %, more preferably at least 80 wt %, especially at least 90 wt 
% silicate. Most preferably, said binder is derived essentially completely 
from silicate. 
Said silicate may be as described in any statement herein. 
Preferably, particulate material is dispersed in said binder material. 
Said particulate material may be as described in any statement herein. 
Preferably, 30 to 80 wt %, more preferably 40 to 70 wt %, of said 
hydrophilic layer is composed of said particulate material. 
Said particulate material preferably includes a first material as described 
in any statement herein. 
Said first material may have a mean particle size and/or particle size 
distribution as described above for said first material when in said 
fluid. 
Said particulate material on said substrate may include at least 20 wt %, 
preferably at least 30 wt %, more preferably, at least 40 wt % of said 
first material. 
Said particulate material preferably includes a second material as 
described in any statement herein. 
Said second material may have a mean particle size and/or particle size 
distribution as described above for said second material when in said 
fluid. 
Said particulate material on said substrate may include at least 20 wt %, 
preferably at least 30 wt %, more preferably, at least 40 wt % of said 
second material. 
In the layer, the ratio of the wt % of first material to the wt % of second 
material may be in the range 0.5 to 2, preferably in the range 0.75 to 
1.5, more preferably, about 1 to 1. 
Said particulate material may include a third material as described in any 
statement herein. 
Said hydrophilic layer may include less than 30 wt %, preferably less than 
15 wt %, more preferably less than 5 wt %, especially less than 1 wt % of 
organic polymeric material. 
Said hydrophilic layer preferably has an average thickness of less than 20 
.mu.m, preferably less than 10 .mu.m and, more preferably, less than 5 
.mu.m. 
Said hydrophilic layer preferably has an average thickness of greater than 
0.1 .mu.m, preferably greater than 0.3 .mu.m, more preferably, greater 
than 0.5 .mu.m. 
Said hydrophilic layer may have an Ra, measured using a stylus measuring 
instrument (a Hommelmeter T2000) with an LV-50 measuring head, in the 
range 0.1 to 2 .mu.m, suitably in the range 0.2 to 2 .mu.m, preferably in 
the range 0.2 .mu.m to 1 .mu.m, more preferably in the range 0.3 to 0.8 
.mu.m, especially in the range 0.4 to 0.8 .mu.m. 
Said hydrophilic layer may include 1 to 20 g of material/m.sup.2 of 
substrate. Preferably said layer includes 5 to 15 g, more preferably 8 to 
12 g, of material/m.sup.2 of substrate. Most preferably, said layer 
includes about 10 g of material/m.sup.2. 
It is believed that said binder material derived from a silicate of the 
type described contains extremely small three-dimensional silicate polymer 
ions carrying a negative charge. Removal of water from the system as 
described is believed to cause condensation of silanol groups to form a 
polymeric structure which includes--Si--O--Si-- moieties. Accordingly, the 
invention extends to a planographic printing member comprising a support, 
an ablatable layer and a hydrophilic layer which includes a binder 
material comprising a polymeric structure which includes--Si--O--Si-- 
moieties. Preferably a particulate material is arranged in said binder 
material. 
The invention further extends to a planographic printing member comprising 
a support, an ablatable layer and a hydrophilic layer, wherein said 
ablatable layer includes a binder material adapted to increase the 
adhesion of the ablatable layer to the hydrophilic layer as compared to 
when said second material is not present. 
The invention further extends to a method of preparing a planographic 
printing member having ink-accepting and non-ink-accepting areas, the 
method comprising exposing a planographic printing member as described in 
any statement herein to radiation to cause the ablatable layer of the 
member to ablate. 
In a preferred embodiment, said method comprises exposing a planographic 
printing member comprising a support, an ablatable layer and a hydrophilic 
layer which includes a material derived or derivable from a silicate, to 
radiation which causes ablation of said ablatable layer in exposed areas. 
Said radiation delivered in said method is preferably delivered using a 
laser. A preferred type of laser has been described above. The power 
output of a laser used in the method may be in the range 40 mW to 10,000 
mW, suitably in the range 40 mW to 5,000 mW, preferably in the range 40 mW 
to 2,500 mW, more preferably in the range 40 mW to 1,000 mW, especially in 
the range 40 mW to 500 mW. 
The invention further extends to a method of printing using a planographic 
printing plate as described in any statement herein, the method using a 
fountain fluid and ink. Thus, the method is preferably a "wet" printing 
method. 
Any feature of any invention or embodiment described herein may be combined 
with any feature of any other invention or embodiment described herein. 
EXAMPLES 
The invention will now be described by way of example, with reference to 
FIGS. 1 to 4 which are schematic cross-sections through various 
lithographic plates. 
The following products are referred to hereinafter: 
BKR 2620 BAKELITE.RTM.phenolic resin--refers to a 
phenol-formaldehyde-cresol resin of formula (C.sub.7 H.sub.X O. C.sub.6 
H.sub.6 O. CH.sub.2 O).sub.X obtained from Georgia-Pacific Resins Inc, 
Decatur, Georgia, USA. 
MICROLITH.RTM.Black C-K pigment--refers to carbon black predispersed in 
vinyl chloride/vinyl acetate copolymer obtained from Ciba pigments of 
Macclesfield, England. 
Luconyl Black 0066 --refers to carbon black (40 wt %) in water/butylglycol 
obtained from BASF Plc of Cheshire, England. 
NEOREZ.RTM.R old synthetic resin--refers to a dispersion of aliphatic 
urethane (34 wt %) in water (47.3 wt %), N-methyl-2-pyrrolidone (17 wt %) 
and triethylamine (1.7 wt %) obtained from Zeneca Resins of AC-Waalwijk, 
Holland. 
EPIKOTE.RTM.1004 synthetic resin--an epoxy resin obtained from Shell 
Chemicals of Chester, England. 
Dispercel Tint Black STB-E--a carbon black/plasticised nitrocellulose 
dispersion obtained from Runnymede Dispersions Limited of Gloucestershire, 
England. 
Nitrocellulose DHX 3-5- high nitrogen grade (11.7-12.2%) nitrocellulose in 
chip form, obtained from ICI Explosives of Ayrshire, Scotland. 
DOWFAX.RTM.2A1surface active agent--refers to an anionic surfactant 
comprising a mixture of mono- and di-sulphonates from Dow Chemicals of 
Middlesex, England. 
Titanium dioxide--refers to rutile titanium dioxide provided with an 
inorganic coating of Al.sub.2 O.sub.3, ZnO and ZnPO.sub.4. The mean 
crystal size is 0.23 .mu.m. It was obtained from Tioxide (Europe) of 
Billingham, England. 
In the figures, the same or similar parts are annotated with the same 
reference numerals. 
Example 1 
Preparation of Aluminium 
A 0.3 mm gauge aluminum alloy sheet of designation AA1050 was cut to a size 
of 230 mm by 350 mm, with the grain running lengthways. The sheet was then 
immersed face up in a solution of sodium hydroxide dissolved in distilled 
water 100g/l at ambient temperature for 60seconds and thoroughly rinsed 
with water. 
Example 2 
Oleophilic formulation 
comprises a solution of BKR 2620 thermosetting phenolic resin (resole) (10 
wt %) dissolved in methoxypropanol (90 wt %). 
Example 3 
IR sensitive/ablatable formulations 
Formulation A 
comprises a 5 wt % dispersion of MICROLITH.RTM.Black C-K pigment in 
methylethylketone (95 wt %). 
Formulation B 
comprises nitrocellulose DHX 3-5 (4.13 wt %), Dispercel Tint Black STB-E 
(8.10 wt %) in methylethylketone (87.77 wt %). 
Formulation C 
comprises NEOREZ.RTM.R961 Synthetic resin (56 wt %), Luconyl Black (24 wt 
%) and water (20 wt %). 
Formulation D 
comprises a dispersion of MICROLITH.RTM.Black C-K pigment (1.0 g), titanium 
dioxide (2.0 g) in methylethylketone (12.0 g). 
Formulation E 
comprises a dispersion of nitrocellulose DHX 3-5 (0.7 g), Dispercel Tint 
Black STB-E (1.25 g), titanium dioxide (4.0 g) in methylethylketone (23.0 
g). 
Formulation F 
comprises NEOREZ.RTM.R961 Synthetic resin (3.0 g), Luconyl Black 0066 (1.25 
g), titanium dioxide (4.0 g) and water (20.0 g). 
Example 4 
Binder formulation 
Formulation G 
comprises EPIKOTE.RTM.1004 Synthetic resin (3 g), titanium dioxide (10 g) 
dispersed in methyl lactate (46.3 g) and benzyl alcohol (0.7 g). 
Example 5 
Hydrophilic coating formulation 
Formulation H 
The following reagents were used in the preparation: 
Sodium silicate solution having a ratio SiO.sub.2 : Na.sub.2 O in the range 
3.17 to 3.45 (average about 3.3); a composition of 27.1-28.1 wt % 
SiO.sub.2, 8.4-8.8 wt % Na.sub.2 O, with the balance being water; and a 
density of about 75 Twaddel (.degree.Tw), equivalent to 39.5 Baume 
(.degree.Be) and a specific gravity of 1.375. 
Deionized water having a resistivity of 5 Mohm.cm 
Al.sub.2 O.sub.3 powder comprising alumina (99.6%) in the shape of 
hexagonal platelets. The mean particle size is 3 .mu.m. The powder has a 
hardness of 9 Moh (on a 0-10 hardness scale). 
Deionized water (48 g; 24 wt %) and sodium silicate solution (80 g; 40 wt 
%) were added to a 250mL beaker and the solution sheared using a Silverson 
high shear mixer operating at maximum speed. Titanium dioxide powder (36 
g; 18 wt %) was then added in portions of approximately 2 g every ten 
seconds. On completion of the addition, the liquid was sheared for a 
further two minutes. Then, alumina powder (36 g; 18 wt %) was added in 
portions of approximately 2 g every ten seconds. On completion of the 
addition, the liquid was sheared for a further two minutes. Finally, 
DOWFAX.RTM.2AL surface active agent (0.18 wt %) was added with stirring. 
The viscosity of the liquid was found to be about 10 centipoise when 
measured at 20.degree. C. and a shear rate of 200s.sup.-1 using a Mettler 
Rheomat 180 Viscometer incorporating a double gap measuring geometry. 
Preparation of Lithographic Plates 
In Examples 6 to 8, lithographic plates were prepared having the 
construction shown in FIG. 1, wherein reference 2 represents a substrate, 
reference 4 represents an oleophobic layer, reference 6 represents an IR 
sensitive/ablatable layer and reference 8 represents a hydrophilic layer. 
Example 6 
An aluminum substrate, prepared as described in Example 1, was coated using 
a Meyer bar with the oleophilic formulation of Example 2to give a wet film 
weight of about 1.2 .mu.m.sup.-2 and oven-dried at 160.degree. C. for 5 
minutes to produce oleophilic layer 4. 
Layer 4 was then coated using a Meyer bar with Formulation A to give a wet 
film weight of about 0.5 .mu.m.sup.-2 and oven-dried at 130.degree. C. for 
30 seconds to produce a layer 6. 
Layer 6 was then coated using a Meyer bar with Formulation H to give a wet 
film weight of about 8 .mu.m.sup.-2 and oven-dried at 130.degree. C. for 
80 seconds to produce a hydrophilic layer 8. This was then post-treated by 
immersion in aluminum sulphate (0.1M) for thirty seconds, followed by 
spray rinsing with tap water and fan drying. 
Examples 7 and 8 
The procedure of Example 6 was followed except that Formulation B (Example 
7) and Formulation C (Example 8) were used instead of Formulation A to 
produce an ablatable layer 4. 
In Examples 9 to 11, lithographic plates were prepared having the 
construction shown in FIG. 2, wherein a binder layer 10 is arranged 
between layers 6 and 8 of FIG. 1. 
Example 9 
The procedure of Example 6 was followed except that Formulation G was 
coated over layer 6, before coating with Formulation H as described above 
to produce hydrophilic layer 8. 
Examples 10 and 11 
The procedure of Example 9 was followed except that Formulation B (Example 
10) and Formulation C (Example 11) were used instead of Formulation A to 
produce an ablatable layer 4. 
In Examples 12 to 14, lithographic plates were prepared having the 
construction shown in FIG. 3, wherein a layer 12 which is IR 
sensitive/ablatable and arranged to bind layer 8 to layer 4 is provided 
between layers 8 and 4. 
Example 12 
The procedure of Example 6was followed except that layer 4 was coated, 
using a Meyer bar, with Formulation D to give a wet film weight of about 
2.5 gm.sup.-2 and oven-dried at 130.degree. C. for 30 seconds to produce 
layer 12 prior to coating with Formulation H to produce hydrophilic layer 
8. 
Examples 13 and 14 
The procedure of Example 12 was followed except that Formulation E (Example 
13) and Formulation F (Example 14) were used instead of Formulation D to 
produce layer 12. 
Example 15 
Referring to FIG. 4, an aluminized polyester film 20 comprises a polyester 
layer 22 and an aluminum layer 24. Formulation H was applied over the 
layer 24 as described in Example 6 to produce hydrophilic layer 8. 
Example 16 
Imaging the lithographic plates 
The plates prepared as described in Examples 6 to 15 were cut into discs of 
105 mm diameter and placed on a rotatable disc that could be rotated at a 
constant speed of either 100 or 250 revolutions per minute. Adjacent to 
the rotatable disc, a translating table held a laser beam source so that 
it impinged normal to the disc, while the translating table moved the 
laser beam radially in a linear fashion with respect to the rotatable 
disc. The exposed image was in the form of a spiral whereby the image in 
the center of the spiral represented slow laser scanning speed and long 
exposure time and the outer edge of the spiral represented fast scanning 
speed and short exposure time. 
The laser used was a single mode 830 nm wavelength 200 mW laser diode which 
was focused to a 10 micron spot. The laser power supply was a stabilized 
constant current source. 
Example 17 
Processing after Imaging 
The exposed disc was immersed in fount solution which removed the imaged 
coating areas leaving the exposed spiral image. The larger the diameter of 
the resulting spiral image the less the exposure time required to form the 
image. 
Results 
(i) Discs having layers of type 6, 12 and 24 can be ablated imagewise when 
subjected to IR radiating to produce printing plates having oleophilic 
image layers comprised by layer 4 (FIGS. 1 to 3) or layer 22 (FIG. 4) and 
hydrophilic layers comprised by layer 8. 
(ii) Adhesion of layer 8 to the underlying layer is strongest for discs 
having a separate binder layer 10 (FIG. 2) or a binder material (e.g. 
titanium dioxide) incorporated in the IR sensitive/ablatable layer as in 
layer 12 (FIG. 3). 
(iii) Discs were produced which, at a speed of 100 rpm, produced a 
well-defined image at up to 40 mm radius; were fully ablated at up to 7 mm 
radius; and accepted ink in imaged areas at up to 10 mm radius. 
All of the features disclosed in this specification (including any 
accompanying claims, abstract and drawings), and/or all of the steps of 
any method or process so disclosed, may be combined in any combination, 
except combinations where at least some of such features and/or steps are 
mutually exclusive. 
Each feature disclosed in this specification (including any accompanying 
claims, abstract and drawings), may be replaced by alternative features 
serving the same, equivalent or similar purpose, unless expressly stated 
otherwise. Thus, unless expressly stated otherwise, each feature disclosed 
is one example only of a generic series of equivalent or similar features.