[0001] This invention relates to a method for the production of a support for use as a substrate
for a lithographic printing plate. More specifically, the invention provides a method
for the surface treatment of a support material, whereby a substrate having particularly
favourable lithographic properties may be obtained.
[0002] The material used as the support material depends upon the specific purpose for which
the printing plate is to be used and may be, for example, a metal, paper or plastics
material. Generally for printing plates, however, the preferred substrate is aluminium,
most preferably electrochemically roughened aluminium which includes a surface layer
of anodic aluminium oxide. Optionally, said aluminium may be laminated to another
metal, such as copper or zinc, or to a plastics material, for example a polyester
material such as poly(ethylene terephthalate).
[0003] Conventionally, aluminium substrates intended for use as support materials for lithographic
printing plates and their precursors have been subjected to surface treatments prior
to application of a light sensitive coating material. These treatments serve to improve
the lithographic properties of the aluminium, in particular, its hydrophilicity. This
is important during printing operations, since the basis of lithography is the ability
of the lithographic plate to accept ink in image areas whilst rejecting ink and accepting
water in background (non-image) areas, so that the printed image remains free from
dirt and other contamination in said background areas. Thus, the light-sensitive coating
of a lithographic printing plate precursor is imagewise exposed to radiation in order
to change the solubility characteristics of the coating in the radiation-struck areas.
The soluble areas are subsequently dissolved away by treatment with a developing solution,
to expose the aluminium surface which must be capable of rejecting ink and accepting
water.
[0004] A typical surface treatment comprises an initial graining treatment, wherein the
aluminium surface is roughened by either mechanical or electrochemical means, and
a subsequent anodising treatment, by means of which a layer of aluminium oxide is
formed on the surface of the aluminium. Anodising treatments may, for example, be
carried out by passing a grained aluminium web through a bath of a suitable anodising
acid, such as sulphuric or phosphoric acid, or a mixture thereof, whilst an electric
current flows through the anodising bath and the web serves as the anode. The presence
of a surface anodic layer greatly enhances the hydrophilicity of the aluminium surface,
and the adhesion of the subsequently formed image layer is found to be much improved
when the surface of the aluminium is subjected to a graining treatment prior to anodising.
[0005] Additionally, there is generally a requirement for a further surface treatment following
the anodising process. Such a treatment - referred to as a post-anodic dip - is usually
applied in order to improve specific lithographic printing properties of the substrate,
such as clean up of background areas, coating adhesion or corrosion resistance, and
will typically involve treating the aluminium with a solution, often an aqueous solution,
of the chosen reagent. Commonly used post-anodic dips include aqueous solutions containing,
for example, various inorganic salts or organic derivatives such as poly(acrylic acid)
or various aqueous-soluble copolymers.
[0006] Thus, EP-A-567178 discloses the treatment of grained and anodised aluminium with
an aqueous solution of an alkali metal bicarbonate, whilst the use of solutions containing
anions including chloride, fluoride, nitrate, carboxylate, sulphate and phosphate
for application to anodised aluminium is described in JP-A-10129143. In addition,
GB Patent No 1128506 deals with a process wherein anodised aluminium is treated with
an aqueous solution of titanium, zirconium or hafnium tetrachloride - or the corresponding
double fluoride formed with, for example, alkali metal fluorides - and subsequently
dipped in an aqueous alkaline solution of potassium tetrapyrophosphate. Indeed, the
successful use of various fluoride derivatives of titanium, hafnium and zirconium
for post-anodic dip treatments has been widely reported; for example, GB Patent No
1504503 teaches the use of potassium titanium fluoride in combination with a vegetable
tannin compound and a soluble lithium compound in the treatment of anodised aluminium
surfaces in order to improve corrosion resistance, whilst EP-A-178020 discloses a
treatment process for otherwise untreated aluminium which provides excellent corrosion
resistance and paint adhesion characteristics and involves sequentially contacting
the surface with (1) an aqueous acidic solution containing hafnium, zirconium and/or
titanium ions, fluoride ions, a tannin compound and a sequestering agent and (2) a
solution comprising a polyphenolic compound or acid salt thereof.
[0007] The present inventors have found, however, that the use of fluoride derivatives of
this type can give rise to problems during the platemaking process, thereby resulting
in the production of printing plates of inferior quality. Specifically, it was observed
that the ease of performing deletions was adversely affected, such that corrections
to the plate surface could only be carried out with difficulty. As a consequence,
costly delays were experienced during platemaking, and the vigorous treatments required
in order to effect the corrections gave rise to damage to the plate surface, with
a resulting deleterious effect on printing performance.
[0008] It is, therefore, an object of the present invention to provide a post-anodic dip
treatment for grained and anodised aluminium which eliminates the problem of poor
ease of deletion during printing platemaking which is associated with the use of fluoride
derivatives of titanium, hafnium and zirconium, whilst at the same time retaining
the advantageous properties which are associated with the use of these materials.
[0009] Initially, the present inventors studied the possible addition of further materials
to the post-anodic dip to study their effects in combination with the said fluoride
derivatives. Specifically, a series of experiments was carried out with an aqueous
solution of potassium hexafluorozirconate to which various other salts had been added;
the intention was to examine the potential benefits of several alternative anions
in combination with the hexafluorozirconate. It was found that particularly beneficial
results were achieved when orthophosphate salts were present in the post-anodic bath,
and that the resulting printing plates showed good ease of deletion. Unfortunately,
however, severe practical difficulties were associated with this procedure, and the
addition of orthophosphate salts to the post-anodic bath in this way was shown to
give rise to severe precipitation problems during manufacture, to the extent that
the resulting process could not be considered to be commercially viable. Hence, the
inventors sought an alternative process, by means of which the beneficial results
of the treatment could be maintained, whilst at the same time eliminating the said
practical problems.
[0010] According to the present invention there is provided a process for the manufacture
of a substrate for use in the production of lithographic printing plates, said process
comprising the steps of:
(a) providing an aluminium substrate;
(b) graining at least one surface of said substrate;
(c) applying an anodic layer to said at least one grained surface;
(d) treating said at least one grained and anodised surface with an aqueous solution
comprising at least one salt of a metal from Group IB, IIB, IVA, IVB, VB, VIA, VIB,
VIIB or VIII of the Periodic Table; and
(e) treating said at least one treated surface with an aqueous solution comprising
at least one orthophosphate salt of an alkali metal.
[0011] Said treatment of said at least one grained and anodised surface with an aqueous
solution comprising at least one salt of a metal from Group IB, IIB, IVA, IVB, VB,
VIA, VIB, VIIB or VIII of the Periodic Table is preferably carried out by treating
said substrate with an aqueous solution, preferably containing from 0.01% to 10.0%
(w/w) (more preferably from 0.05% to 1.5%) of said salt at a preferred temperature
of from 10° to 90°C (more preferably from 40° to 80°C) for a preferred dwell time
of from 0.1 second to 5 minutes (more preferably from 0.2 second to 30 seconds) at
a pH which preferably lies between 1 and 6, most preferably between 3.5 and 5.5. Various
coating techniques may be employed for application of the salt, such as dip coating,
slot coating, reverse roll coating or electrochemical coating; most preferred, however,
is spray coating. Single pass processes are also preferred since they facilitate the
avoidance of contamination which could otherwise occur as a consequence of re-circulation
of the solution.
[0012] Suitable salts which may be used for the said treatment include, for example, salts
of titanium, zirconium, hafnium, molybdenum, tungsten, vanadium, manganese, nickel,
copper, zinc, tin, niobium, tantalum, cerium, selenium, silicon, cobalt or iron. Said
salts may include the metal either as the cation, for example in halide, sulphate
or nitrate salts, or as part of a complexed anion. Particularly favourable results
are achieved with salts of titanium, zirconium or hafnium, such as hafnium sulphate,
zirconium phosphate, titanium nitrate, hafnium acetate, zirconium fluoride and titanium
chloride. Most preferably, however, the hafnium, zirconium or titanium salt comprises
a salt wherein the metal is present in a metal-complex anion, such as a chlorotitanate
or fluorozirconate anion. Especially preferred in this regard are the alkali metal
fluorozirconates, particularly potassium hexafluorozirconate.
[0013] Said treatment of at least one treated surface with an aqueous solution comprising
at least one orthophosphate salt of an alkali metal is preferably carried out by treating
said substrate with an aqueous solution, preferably containing from 0.01% to 10.0%
(w/w) (more preferably from 0.05% to 1.5%) of an orthophosphate salt of an alkali
metal at a preferred temperature of from 5° to 90°C (more preferably from 40° to 80°C)
for a preferred dwell time of from 0.05 second to 5 minutes (more preferably from
0.1 second to 30 seconds) at a pH which preferably lies between 3 and 7, most preferably
around 4.5. Various coating techniques may be employed for application of the orthophosphate
salt of an alkali metal, such as dip coating, slot coating, reverse roll coating or
electrochemical coating; most preferred, however, is spray coating. Single pass processes
are also preferred since they facilitate the avoidance of contamination which could
otherwise occur as a consequence of re-circulation of the solution.
[0014] Particularly suitable orthophosphate salts of alkali metals which may be used for
the said treatment are the orthophosphates of sodium or potassium, including the hydrogen
and dihydrogen orthophosphates. It has been found that these materials provide superior
results, and are therefore preferred. Other phosphorus-containing compounds, such
as hypophosphonate, hypophosphate, pyrophosphonate, pyrophosphate, phosphonate, polyphosphonate
or metaphosphonate derivatives have been reported in the prior art, but generally
provide printing plates of lower quality than those obtained by the application of
orthophosphate salts.
[0015] In addition, the use of alkali metal fluorophosphates or difluorophosphates, phosphosilicates
and phosphoborates, all of which facilitate the controlled release of phosphate into
the coating bath, and various organic materials, such as the copolymer of acrylic
acid and vinyl phosphonic acid, has been investigated. However, from an economic viewpoint,
the cheaper orthophosphates are the most preferred materials, giving excellent performance
at optimum cost, with sodium dihydrogen orthophosphate and, most particularly, potassium
dihydrogen orthophosphate being especially preferred.
[0016] The orthophosphate salt of an alkali metal may be applied to the substrate simultaneously
with the salt of a metal from Group IB, IIB, IVA, IVB, VB, VIA, VIB, VIIB or VIII
of the Periodic Table, or it may be applied in a separate treatment, subsequent to
the application of the said salt; in either case, plates showing excellent ease of
deletion, as well as other desirable properties, are obtained. However, precipitation
problems which are associated with the simultaneous treatment method are not apparent
when the treatments are carried out as separate stages, with the orthophosphate salt
of an alkali metal being applied subsequent to the treatment with the salt of a metal
from Group IB, IIB, IVA, IVB, VB, VIA, VIB, VIIB or VIII of the Periodic Table.
[0017] Additionally, other materials may be incorporated in the aqueous solution of the
salt of a metal from Group IB, IIB, IVA, IVB, VB, VIA, VIB, VIIB or VIII of the Periodic
Table, or the aqueous solution of at least one orthophosphate salt of an alkali metal
- or the combined solution, if this is to be employed. Specifically, the solution
or solutions may include materials such as sequestering agents, tannin, sulphuric
acid, fluorides and other additives which are known to improve the lithographic properties
of a substrate, including various organic and inorganic polymeric materials.
[0018] Optionally, said substrate may be rinsed with water following said treatment with
an aqueous solution comprising at least one salt of a metal from Group IB, IIB, IVA,
IVB, VB, VIA, VIB, VIIB or VIII of the Periodic Table, and prior to said treatment
with an aqueous solution comprising at least one orthophosphate salt of an alkali
metal.
[0019] Said aluminium substrate may comprises pure aluminium or an aluminium alloy containing
small amounts of, for example, manganese, nickel, cobalt, zinc, iron, copper, magnesium,
titanium, vanadium, silicon or zirconium. Said substrate is generally provided in
the form of a continuous web or roll of material.
[0020] Preferably, said substrate is subjected to a degreasing treatment prior to said graining
treatment. Said degreasing treatment is most conveniently carried out by means of
an aqueous alkaline solution. Typically, said treatment involves passing said substrate
through a bath containing a 1-20% w/v solution of, for example, sodium or potassium
hydroxide at a temperature of 30-80°C for a dwell time of from 5-60 seconds. Following
said degreasing treatment, said substrate is rinsed with water prior to further treatment.
[0021] Any of the known techniques may be utilised for graining the substrate. Said graining
treatment can involve mechanical graining, wherein the surface of the substrate is
subjected to mechanical forces which may, for example, be achieved by the use of a
slurry of very small metal balls or via brush graining techniques. Alternatively,
and most preferably, electrochemical graining may be employed; said technique typically
comprises passing a substrate through a solution of a mineral or organic acid, or
a mixture thereof, such as a mixture of hydrochloric and acetic acids, whilst applying
an electric current to the acid solution. Alternatively, solutions of suitable inorganic
salts in mineral acids are also found to provide highly acceptable results; particularly
favoured in this respect is a mixed electrolyte comprising hydrochloric acid, hydrated
aluminium chloride and hydrated aluminium sulphate. By way of illustration, suitable
graining conditions could involve the use of a bath of aqueous hydrochloric acid at
a concentration of from 1-30 g/l and a temperature of 5-70°C, with a dwell time of
from 1-60 seconds at a charge density of 200-800 C/dm
2 and an applied potential of from 1-60 V. The grained substrate is then rinsed with
water prior to further processing.
[0022] Following electrochemical graining, said grained substrate should be subjected to
a desmutting treatment in order to remove by-products formed during the course of
said electrograining treatment, and deposited on the surface of the substrate. Typically,
the process involves treatment of the grained substrate with an aqueous acid or alkali
according to the methods well known in the art. Suitable desmutting conditions could,
for example, involve treatment of the grained substrate with aqueous phosphoric acid
at a concentration of around 20-400 g/l at a temperature in the region of 20-80°C
for a dwell time of the order of 1 second to 5 minutes; alternatively, a higher temperature
treatment - using sulphuric acid at 50-300 g/l and 30-80°C for a shorter dwell time
of around 8 seconds - may be employed, or an alkaline treatment, with 2-20 g/l aqueous
sodium hydroxide at 5-60°C, would suffice. The substrate is rinsed with water following
desmutting.
[0023] Anodising of the grained substrate is carried out by means of any of the standard
techniques well known in the art, and typically involves passing the substrate through
a bath containing an aqueous mineral acid, such as sulphuric, phosphoric, nitric,
hydrofluoric or chromic acid, or an aqueous solution of an organic acid, for example
oxalic, tartaric, citric, acetic or oleic acid, or a mixture of these acids, whilst
applying an electric current to the anodising bath. Suitable anodising conditions
would involve the use of a bath of sulphuric acid at a concentration of from 10 to
300 g/l, preferably 100-150 g/l, and a temperature in the range of from 20-60°C, preferably
40-60°C, with a dwell time of from 1 to 120 seconds, preferably 3 to 40 seconds, an
applied potential of from 5-60 V, preferably 10-50 V, and a charge density of from
100-500 C/dm
2, preferably 200-400 C/dm
2. The grained and anodised substrate is then rinsed with water prior to further processing.
[0024] The process provided by the present invention may be successfully employed using
various forms of process and coating technology. Principally, said process is suitable
for use with the different forms of cell alignment associated with flat bed technology
and vertical cell technology, both of which are well known to those skilled in the
art.
[0025] The support provided by the method of the present invention may subsequently be coated
with a light-sensitive coating to give a lithographic printing plate precursor. Various
coatings of the types well known to those skilled in the art may be applied for this
purpose, for example, positive-working coatings incorporating quinone diazide derivatives,
negative-working coatings incorporating diazo or azide resins or photocrosslinkable
resins or silver halide based coatings. The coatings may be applied by any of the
standard coating techniques known to the skilled person, such as curtain coating,
dip coating, meniscus coating, slot coating, reverse roll coating, and the like.
[0026] The thus-obtained lithographic printing plate precursor may then be imagewise exposed
and the non-image areas can be developed away to provide a lithographic printing plate
which is subsequently used on a printing press to produce copies.
[0027] Lithographic printing plates produced from aluminium supports obtained by the method
of the present invention show excellent performance in terms of ease of deletion,
as well as good corrosion resistance, solvent resistance, clean-up and roll-up on
press. No background staining is observed and plates exhibit excellent ink-water balance
and damping latitude performance, as well as good run length.
[0028] The invention will now be illustrated, though without limitation, by reference to
the following examples:
EXAMPLES
Example 1
[0029] An aluminium alloy substrate comprising Al ≥99.1%, Si ≤0.2%, Fe ≤0.4%, Cu ≤0.05%,
Mn ≤0.05%, Mg ≤0.05%, Zn ≤0.07%, Ti ≤0.05% and V ≤0.05% was conventionally degreased,
rinsed and subjected to an electrochemical graining treatment using a liquor comprising
hydrochloric acid (9 g/l) and acetic acid (25 g/l) at a temperature of 30°C for a
dwell time of 20 seconds at a charge density of 500 C/dm
2. Following water rinsing and desmutting in a solution of phosphoric acid (260 g/l)
at 45°C for 20 seconds, the grained substrate was subjected to an anodising process
by treating with sulphuric acid (145 g/l) at 45°C for a dwell time of 20 seconds at
a charge density of 250 C/dm
2, then rinsed with water.
[0030] The grained and anodised aluminium substrate was then treated by spray coating for
20 seconds with an aqueous solution of potassium hexafluorozirconate (5 g/l) having
pH 4.0 at 60°C, then spray coated with an aqueous solution of potassium dihydrogen
orthophosphate (12 g/l) having pH 4.5 at 60°C for 20 seconds. No evidence of precipitation
was observed during, or subsequent to, either treatment.
[0031] The resulting substrate was rinsed with water and coated with a solution of a naphthoquinone
diazide photosensitive resin and a cresol novolak support resin in 2-methoxypropanol
to produce a light-sensitive coating layer, and the coated substrate was baked at
130°C for 5 minutes. The resulting lithographic printing plate precursor was imagewise
exposed to UV light at 100-300 mJ/cm
2 and the non-image areas were developed away with an aqueous alkaline developer solution
by immersion for 30 seconds at 20°C. The resulting lithographic printing plate was
rinsed with water and dried in a stream of cool air and subsequently produced 250,000
excellent quality copies on a Drent Web Offset press. The plate showed excellent roll-up
and clean-up, with no background staining, on press. Ink/water balance, damping latitude
and solvent resistance were also all exceptionally good. On treatment with Posidel
A (a commercial deletion fluid supplied by Agfa-Gevaert) the plate showed excellent
ease of deletion and little evidence of residual staining.
Example 2
[0032] An aluminium alloy substrate comprising Al ≥98.0%, Si ≤0.5%, Fe ≤0.7%, Cu ≤0.05%,
Mn 1.0-1.5%, Mg ≤0.15%, Zn ≤0.1%, Ti ≤0.05% and V ≤0.05% was degreased, grained, desmutted
and anodised as described in Example 1.
[0033] The grained and anodised aluminium substrate was then treated by spray coating for
a dwell time of 3.5 seconds with an aqueous solution of potassium hexafluorozirconate
(5 g/l) having pH 4.0 at 80°C, then further spray coated with an aqueous solution
of potassium dihydrogen orthophosphate (8 g/l) having pH 4.5 at 70°C for 0.5 second.
No evidence of precipitation was observed during, or subsequent to, either treatment.
[0034] The resulting substrate was rinsed with water and coated with a solution of a naphthoquinone
diazide photosensitive resin and a cresol novolak support resin in 2-methoxypropanol
and tetrahydrofuran (1:1) which contained dispersed particles of silica having an
average diameter of approximately 4 µm. The coated substrate was baked at 140°C for
30 seconds to 1 minute to produce a light-sensitive coating layer having a mat surface
layer which promoted good vacuum drawdown performance during imagewise exposure. This
was carried out using UV light at 100-300 mJ/cm
2, after which the non-image areas were developed away with an aqueous alkaline developer
solution by immersion for 30 seconds at 20°C. The resulting lithographic printing
plate was rinsed with water and dried in a stream of cool air and subsequently produced
250,000 excellent quality copies on a Drent Web Offset press. The plate showed excellent
roll-up and clean-up, with no background staining, on press. Ink/water balance, damping
latitude and solvent resistance were also all exceptionally good. On treatment with
Posidel A (a commercial deletion fluid supplied by Agfa-Gevaert) the plate showed
excellent ease of deletion and little evidence of residual staining.
Example 3
[0035] An aluminium alloy substrate as in Example 1 was conventionally degreased, rinsed
and subjected to an electrochemical graining treatment using a liquor comprising hydrochloric
acid (12 g/l) and sulphuric acid (9 g/l) at a temperature of 40°C for a dwell time
of 5 seconds at a charge density of 540-550 C/dm
2. Following water rinsing and desmutting in sulphuric acid (145 g/l) at 70°C, the
grained substrate was subjected to an anodising process by treating with sulphuric
acid (145 g/l) at 57°C for a dwell time of 6 seconds at a charge density of 250 C/dm
2, then rinsed with water.
[0036] The grained and anodised aluminium substrate was slot coated for 5 seconds with an
aqueous solution of potassium hexafluorozirconate (5 g/l) having pH 4.0 at 70°C, then
further treated by slot coating with an aqueous solution of potassium dihydrogen orthophosphate
(4 g/l) having pH 4.5 at 70°C for 1.0 second. No evidence of precipitation was observed
during, or subsequent to, either treatment.
[0037] The resulting substrate was rinsed with water and coated with a solution of a naphthoquinone
diazide photosensitive resin and a cresol novolak support resin in 2-methoxypropanol
to produce a light-sensitive coating layer, and the coated substrate was baked at
130°C for 5 minutes. The resulting lithographic printing plate precursor was imagewise
exposed to UV light at 100-300 mJ/cm
2 and the non-image areas were developed away with an aqueous alkaline developer solution
by immersion for 30 seconds at 20°C. The resulting lithographic printing plate was
rinsed with water and dried in a stream of cool air and subsequently produced 250,000
excellent quality copies on a Drent Web Offset press. The plate showed excellent roll-up
and clean-up, with no background staining, on press. Ink/water balance, damping latitude
and solvent resistance were also all exceptionally good. On treatment with Posidel
A (a commercial deletion fluid supplied by Agfa-Gevaert) the plate showed excellent
ease of deletion and little evidence of residual staining.
Example 5
[0038] An aluminium alloy substrate was degreased, grained, desmutted and anodised as described
in Example 1.
[0039] The grained and anodised aluminium substrate was then treated by spray coating for
a dwell time of 3.5 seconds with an aqueous solution of sodium hexachlorotitanate
(5 g/l) having pH 4.0 at 80°C, then further spray coated with an aqueous solution
of sodium dihydrogen orthophosphate (8 g/l) having pH 4.5 at 70°C for 0.5 second.
No evidence of precipitation was observed during, or subsequent to, either treatment.
[0040] The resulting substrate was rinsed with water and coated with a solution of a naphthoquinone
diazide photosensitive resin and a cresol novolak support resin in 2-methoxypropanol
to produce a light-sensitive coating layer, and the coated substrate was baked at
130°C for 5 minutes. The resulting lithographic printing plate precursor was imagewise
exposed to UV light at 100-300 mJ/cm
2 and the non-image areas were developed away with an aqueous alkaline developer solution
by immersion for 30 seconds at 20°C. The resulting lithographic printing plate was
rinsed with water and dried in a stream of cool air and subsequently produced 250,000
excellent quality copies on a Drent Web Offset press. The plate showed excellent roll-up
and clean-up, with no background staining, on press. Ink/water balance, damping latitude
and solvent resistance were also all exceptionally good. On treatment with Posidel
A (a commercial deletion fluid supplied by Agfa-Gevaert) the plate showed excellent
ease of deletion and little evidence of residual staining.
Comparative Example 1
[0041] An aluminium alloy substrate was degreased, grained, desmutted and anodised as described
in Example 1.
[0042] The grained and anodised aluminium substrate was treated for 20 seconds with an aqueous
solution of potassium hexafluorozirconate (5 g/l) and poly(vinyl phosphonic acid)
(2 g/l) having pH 4.0 at 60°C. No evidence of precipitation was observed during, or
subsequent to, the said treatment.
[0043] The resulting substrate was rinsed with water and coated with a solution of a naphthoquinone
diazide photosensitive resin and a cresol novolak support resin in 2-methoxypropanol
to produce a light-sensitive coating layer, and the coated substrate was baked at
130°C for 5 minutes. The resulting lithographic printing plate precursor was imagewise
exposed to UV light at 100-300 mJ/cm
2 and the non-image areas were developed away with an aqueous alkaline developer solution
by immersion for 30 seconds at 20°C. The resulting lithographic printing plate was
rinsed with water and dried in a stream of cool air and subsequently produced 250,000
excellent quality copies on a Drent Web Offset press. The plate showed excellent roll-up
and clean-up, with no background staining, on press. Ink/water balance, damping latitude
and solvent resistance were also all exceptionally good. On treatment with Posidel
A (a commercial deletion fluid supplied by Agfa-Gevaert) the plate showed moderate
ease of deletion and evidence of residual staining was observed.
Comparative Example 2
[0044] An aluminium alloy substrate was degreased, grained, desmutted and anodised as described
in Example 1.
[0045] After rinsing with water, the grained and anodised aluminium substrate was spray
coated for 20 seconds with an aqueous solution of potassium hexafluorozirconate (5
g/l) having pH 4.0 at 60°C, then treated with an aqueous solution of a poly(vinyl
phosphonic acid) (2 g/l) having pH 3.5 by spray coating at 60°C for 20 seconds. No
evidence of precipitation was observed during, or subsequent to, either treatment.
[0046] The resulting substrate was rinsed with water and coated with a solution of a naphthoquinone
diazide photosensitive resin and a cresol novolak support resin in 2-methoxypropanol
to produce a light-sensitive coating layer, and the coated substrate was baked at
130°C for 5 minutes. The resulting lithographic printing plate precursor was imagewise
exposed to UV light at 100-300 mJ/cm
2 and the non-image areas were developed away with an aqueous alkaline developer solution
by immersion for 30 seconds at 20°C. The resulting lithographic printing plate was
rinsed with water and dried in a stream of cool air and subsequently produced 250,000
excellent quality copies on a Drent Web Offset press. The plate showed excellent roll-up
and clean-up, with no background staining, on press; ink/water balance and damping
latitude were also very good. On treatment with Posidel A (a commercial deletion fluid
supplied by Agfa-Gevaert) the plate showed excellent ease of deletion and little evidence
of residual staining. However, in terms of solvent resistance and corrosion resistance,
the performance was poor.
Comparative Example 3
[0047] An aluminium alloy substrate was degreased, grained, desmutted and anodised as described
in Example 1.
[0048] The grained and anodised aluminium substrate was treated for 20 seconds with an aqueous
solution of potassium hexafluorozirconate (5 g/l) and sodium pyrophosphate (8 g/l)
having pH 4.0 at 60°C. No evidence of precipitation was observed during, or subsequent
to, the said treatment.
[0049] The resulting substrate was rinsed with water and coated with a solution of a naphthoquinone
diazide photosensitive resin and a cresol novolak support resin in 2-methoxypropanol
to produce a light-sensitive coating layer, and the coated substrate was baked at
130°C for 5 minutes. The resulting lithographic printing plate precursor was imagewise
exposed to UV light at 100-300 mJ/cm
2 and the non-image areas were developed away with an aqueous alkaline developer solution
by immersion for 30 seconds at 20°C. The resulting lithographic printing plate was
rinsed with water and dried in a stream of cool air and subsequently produced 250,000
excellent quality copies on a Drent Web Offset press. The plate showed excellent roll-up
and clean-up, with no background staining, on press. Ink/water balance, damping latitude
and solvent resistance were also all exceptionally good. On treatment with Posidel
A (a commercial deletion fluid supplied by Agfa-Gevaert) the plate showed excellent
ease of deletion and little evidence of residual staining.
1. A process for the manufacture of a substrate for use in the production of lithographic
printing plates, said process comprising the steps of:
(a) providing an aluminium substrate;
(b) graining at least one surface of said substrate;
(c) applying an anodic layer to said at least one grained surface;
(d) treating said at least one grained and anodised surface with an aqueous solution
comprising at least one salt of a metal from Group IB, IIB, IVA, IVB, VB, VIA, VIB,
VIIB or VIII of the Periodic Table; and
(e) treating said at least one treated surface with an aqueous solution comprising
at least one orthophosphate salt of an alkali metal.
2. A process as defined in claim 1 wherein said orthophosphate salt of an alkali metal
comprises trisodium orthophosphate, disodium hydrogen orthophosphate, sodium dihydrogen
orthophosphate, tripotassium orthophosphate, dipotassium hydrogen orthophosphate or
potassium dihydrogen orthophosphate.
3. A process as defined in claim 1 or 2 wherein said salt of a metal from Group IB, IIB,
IVA, IVB, VB, VIA, VIB, VIIB or VIII of the Periodic Table comprises a salt of titanium,
zirconium, hafnium, molybdenum, tungsten, vanadium, manganese, nickel, copper, zinc,
tin, niobium, tantalum, cerium, selenium, silicon, cobalt or iron.
4. A process as defined in any of claims 1 to 3 wherein said salt of a metal from Group
IB, IIB, IVA, IVB, VB, VIA, VIB, VIIB or VIII of the Periodic Table includes the metal
as the cation.
5. A process as defined in claim 4 wherein said salt comprises a sulphate, phosphate,
nitrate, acetate, fluoride or chloride salt of titanium, zirconium or hafnium.
6. A process as defined in any of claims 1 to 3 wherein said salt of a metal from Group
IB, IIB, IVA, IVB, VB, VIA, VIB, VIIB or VIII of the Periodic Table includes the metal
as part of a complexed anion.
7. A process as defined in claim 6 wherein said salt comprises an alkali metal fluorozirconate.
8. A process as defined in claim 7 wherein said alkali metal fluorozirconate comprises
potassium hexafluorozirconate.
9. A process as defined in any preceding claim wherein said metallic substrate comprises
aluminium or an aluminium alloy containing small amounts of at least one of manganese,
nickel, cobalt, zinc, iron, copper, magnesium, titanium, vanadium, silicon or zirconium.
10. A process as defined in any preceding claim wherein said graining treatment comprises
a mechanical or electrochemical graining treatment.
11. A process as defined in claim 10 wherein said electrochemical graining treatment comprises
passing a substrate through a solution of a mineral or organic acid, or a mixture
thereof, whilst applying an electric current to the acid solution.
12. A process as defined in any preceding claim wherein said anodic layer is applied to
said at least on grained surface of the substrate by passing said substrate through
an aqueous mineral or organic acid, or a mixture thereof, whilst applying an electric
current to the acid solution.
13. A lithographic printing plate precursor manufactured by applying a light-sensitive
coating to a substrate obtained according to the process as defined in any preceding
claim.