Lithographic plate, and method for making, having an oxide layer derived from a type A sol

A lithographic plate comprising a substrate carrying an oxide layer derived from a Type A sol is disclosed. The substrate may be metal, e.g. aluminum or steel, and may be in a mill finished state or grained or otherwise profiled. Type A sols have polynuclear cations but no specific particles and may be formed by peptising basic salts with acids. The sol may include an inorganic passenger powder which may impart a desired topography to the coating layer.

This invention concerns a method of preparing the substrate of lithographic 
printing plates, and lithographic plates so prepared, which eliminates the 
need to electrograin and anodise but is capable of producing a range of 
controlled topographies and high quality plates. 
BACKGROUND OF THE INVENTION 
Lithographic printing processes rely on the differential wetting 
characteristics of hydrophobic and hydrophilic surfaces. In practice an 
aluminum surface is roughened, anodised, conditioned and then coated with 
a light sensitive coating. Positive and negative images are normally 
formed on the surface of the printing plate by photographic methods. 
Development of the image results in removal of the organic coating from 
either the exposed or unexposed areas. The organic areas are oleophilic 
and will accept oil-based inks but will not water wet. In contrast the 
conditioned anodic oxide has a high surface energy and can accept either 
water or ink, however, when wet it will not accept ink. The roughening 
stage is critical for print quality and requires uniform topographies with 
surface features in the range 0.01-4 .mu.m. The actual range employed for 
any particular plate depends predominantly on the quality of paper and 
required print finish. 
The most common method of achieving the high standard of roughening 
required for lithographic plates is to electrochemically treat the 
surface. However, the process has several limitations. Specifically it can 
only be run at slow speeds and it requires very high quantities of 
electrical power and the use of specialist materials. Production of these 
materials demands special and costly practices in order to ensure the high 
quality of the final product. Also, expensive waste treatment plant is 
required to treat the waste chemicals from anodising and graining 
aluminum. The present invention will increase line-speeds, require less 
power usage, will eliminate costly production methods, increase the range 
of alloys that can be used to make lithographic printing plates, and 
permit the use of other metallic and non-metallic substrates. Also, the 
treatment is environmentally good as it does not give rise to significant 
waste disposal problems. 
It is known to prepare a lithographic printing plate by applying to a 
substrate a suspension or sol of preformed particles, and removing the 
liquid to leave a coating comprising the particles. The particles may be 
bound together by means of a polymer or by partial sintering, but organic 
polymers may affect the hydrophilic lipophilic balance of the surface 
while partial sintering may require heating to such high temperatures as 
to damage the substrate. Particulate surface coatings of this kind are 
described in U.S. Pat. No. 4,293,625; 4,330,605; 4,445,998; 4,456,670; 
4,457,971; 4,420,549; 4,542,089; and 4,687,729. 
U.S. Pat. No. 3,231,376 describes a lithographic plate coated with a Type B 
sol derived from a titanium or zirconium alkoxide. 
U.S. Pat. No. 3,419,406 describes a lithographic plate comprising a grained 
aluminum substrate coated with a sol derived from an alkyl titanate. The 
grained substrate is responsible for the surface topography. 
U.S. Pat. No. 4,522,912 describes a lithographic plate in which a metal 
substrate carries an electrodeposited chromium layer of rough crag-like 
character with recesses covered by glass-like films derived from an 
ammonium zirconate carbonate solution. 
SUMMARY OF THE INVENTION 
In one aspect the present invention provides a lithographic plate 
comprising a substrate carrying an oxide layer derived from a type A sol 
which is itself derived from an inorganic precursor. 
In another aspect the invention provides a method of making a lithographic 
plate, which method comprises applying to a substrate a fluid composition 
comprising a type A sol derived from an inorganic precursor and curing the 
composition to form an oxide layer on the substrate. 
Type A sols consist of basic units which are polynuclear ions which form an 
inorganic polymer and are formed by hydrolysis and polymerisation of 
monomeric cations. The molecular weight of the polynuclear cations will 
depend on the degree of hydrolysis but these sols normally have an anion 
to metal ratio of approximately 1:1. The polymeric species are not large 
enough to scatter light efficiently, so the sol and the resultant gel are 
optically clear. The gel has a high density, low porosity and the x-ray 
diffraction pattern consists of very broad bands. See J. D. F. Ramsay 
"Neutron and Light Scattering Studies of Aqueous Solutions of Polynuclear 
Ions. Water and Aqueous Solutions", 207-218 1986 (ed G. W. Neilson and J. 
E. Enderby: Bristol. Adam Hilger). Type A sols may be formed from the 
polynuclear ions listed in this paper including those containing 
Al(III) Fe(III) Zr(IV) Th(IV): for example: 
Al.sub.13 O.sub.4 (OH).sub.24 (H.sub.2 O).sub.12.sup.7+. 
Type B sols consist of basic units or particles with a definite shape, e.g. 
spherical, rod or plate-like, and which are amorphous or microcrystalline. 
The sol is formed by extensive hydrolysis of a salt and has a low anion to 
metal atom ratio of approximately 0.3:1. The sols can also be prepared by 
peptization of fresh precipitates. The colloidal units are not aggregated 
and the sol and the resultant gel may both be clear. Type B sols include 
Al(III) Zr(IV) Ce(IV) Ti(IV) Fe(III). Preparation of Type B Al(III) sols 
is described in GB 1,174,648. Preparation of Ce Type B sol is described in 
GB 1,342,893. Type B Alumina Sols are available commercially. 
In the type C sol the basic colloidal units are aggregated. They are 
crystalline and the gels formed by removal of water have a low density. 
These sols scatter light and are therefore opaque. The sols formed from 
ultrafine powders prepared by vapour phase techniques, i.e. flame 
hydrolysed powders, belong to this category. 
Type A and B sols when dehydrated yield gels which are &gt;45% of the 
theoretical density of the oxide. The gels derived from a type C sol are 
porous and have a density &lt;45% of the theoretical density of the oxide. 
The inorganic sol for use in this invention is a hydrous oxide sol, 
preferably a hydrous metal oxide sol, that is to say a Type A (but not 
Type B or Type C) sol. Examples are zirconia sols, ceria sols, titania 
sols, hafnia sols, alumina sols, and iron oxyhydroxide sols. Silica sols 
exemplify non-metal oxide sols. 
Zirconia Type A sols are readily formed by peptising basic zirconium 
carbonate in mineral acid. The constitution of zirconia sols when the 
associated anion is nitrate or bromide or chloride is discussed in a UKAEA 
Research Group Report, reference AERE-R5257 (1966) by J. L. Woodhead and 
J. M. Fletcher. Zirconia sols contain extensively hydrolysed inorganic 
polymers with a primary particle size of less than 10 nm. The polymer is 
thought to be built up of hydrated oxy-hydroxide species of zirconium. 
When nitric acid is used, the species is believed to have the formula: 
EQU [Zr.sub.4 (OH).sub.12 (NO.sub.3).sub.2 (H.sub.2 O).sub.4 ].sub.n 
(NO.sub.3).sub.2n.2nH.sub.2 O, 
where n is thought to be approximately one in dilute sols and greater than 
one at higher concentrations. Ceria and titania and other hydrous metal 
oxide Type A sols may be formed by peptising the corresponding hydrated 
metal oxide with a mineral acid. Alumina type A sols may be prepared by 
denitration of an aqueous aluminium nitrate solution using an organic 
water-immiscible amine such as that sold under the Trade Mark PRIMENE JMT. 
Type A sols can also be formed by controlled hydrolysis of metal alkoxides. 
The alkoxide is provided in solution in an organic solvent, and a 
controlled amount of water added to form polynuclear cations. The same 
technique is available for forming type A silica sols from organic 
solutions of alkoxysilanes. However, this route is unsatisfactory; organic 
groups may need to be removed from the coating; organic solutions are a 
fire hazard. The Type A sols used in this invention are derived from 
inorganic precursors (including carbonates). 
On gelling Type A sols, the polynuclear cations polymerise by a chemical 
reaction to form a crosslinked inorganic network. By contrast on gelling 
type B or type C sols, the sol particles merely aggregate or physically 
fuse together. As a result, coatings formed from type A sols are more 
coherent than those formed from type B or type C sols, and without the 
need to cure at temperatures high enough to sinter the particles. 
The nature of the substrate is not critical. Substrates which are 
conventionally used for lithographic plates may be used in this invention. 
The most common substrate is aluminum sheet, but other metals including 
steel are used, as are plastics sheet, metallised plastics and even paper. 
Metal substrates may carry a continuous electroplated coating e.g. of 
nickel or chromium. The aluminum or steel or other substrate may have a 
grained or profiled surface, but it is an advantage of the invention that 
the substrate may be used in a mill finished state or otherwise as 
supplied, without the need for special surface profiling. 
Also applied to the surface, according to one aspect of the invention, is a 
fluid which gels the sol and/or a powder passenger on the surface. For 
example, Al.sub.2 O.sub.3 Type B or C sol powder passenger may be gelled 
on the surface by phosphoric acid. This fluid may be in the vapour phase, 
for example a low molecular weight amine such as ethylamine or preferably 
ammonia, which is applied after the composition and simply serves to gel 
and thereby fix the layer on the surface. More preferably, the fluid is a 
liquid, particularly an aqueous liquid containing a gelling agent for the 
sol. This liquid may be applied to the surface to deposit the gelling 
agent thereon, prior to application of the sol. Alternatively, the liquid 
can be applied to the surface already carrying a layer of the sol. It is 
preferred, though not essential, that the layer of sol be dried prior to 
application of the gelling fluid. Gelling of the layer causes or may cause 
shrinkage, and care may need to be taken to prevent cracking of the layer 
at this stage. Drying may be effected at temperatures below 100.degree. 
C., conveniently at ambient temperature. 
The composition may also contain a powder passenger, which can be used to 
give the protective coating a desired surface topography. The powder is 
preferably an inert metal oxide such as silica, zirconia, titania or 
alumina. This may be a type C sol, or a powder produced by comminution, 
for example. Powder loadings of 1 to 300 gl.sup.-1, preferably 5-150 
gl.sup.-1, more particularly 10-75 gl.sup.-1 are appropriate. The powder 
may have an average particle size below 10 .mu.m, preferably below 5 
.mu.m, e.g. in the range 3-500 nm, and is preferably of substantially 
uniform particle size. When a fluid brings about gelation of the sol, the 
powder becomes incorporated in the layer on the substrate surface. 
The oxide layer is sufficiently hydrophilic to be capable of being wetted 
by water. The texture and thickness of the layer are such that it is 
capable of holding water to an extent to prevent deposition of lipophilic 
inks. The roughness of the surface should not be so great as to impair 
print definition, or to give rise to abrasion or ink pick up on high 
spots. These factors affect size and loading of the powder passenger. 
The composition generally has an acid pH, typically in the range 1.5 to 7. 
Sol concentration is chosen to achieve a convenient application viscosity. 
The sol may typically contain from 1 to 200 gl.sup.-1 metal oxide 
equivalent. 
The surface to which the composition is to be applied may be cleaned by 
conventional means appropriate to the substrate concerned. For aluminum 
this may be an acid or alkaline cleaning treatment, using commercially 
available chemicals such as those sold by ICI under the trade marks 
RIDOLENE 124 and 124E. Alternatively, the metal surface may be pretreated 
to form thereon an artificially applied oxide layer. Such treatments 
include acid etching (Forest Products Laboratories), and anodising 
treatments with sulphuric, chromic or phosphoric acid. It has been shown 
by means of transmission electron microscopy that phosphoric acid 
anodising treatment produces fine oxide protrusions of greater length and 
magnitude than other surface treatments. This pretreatment may help to 
extend lithographic plate life. By virtue of their small sol unit size, 
the aqueous compositions of this invention can be applied to such profiled 
surfaces in layers so thin and uniform that the profiled surface 
topography is substantially maintained. It is believed that the 
artificially applied oxide layer provides improved initial adhesion for 
subsequently applied artificial coatings by mechanical interlocking. 
The sol may itself provide a desired degree of profiling to a smooth 
substrate, either of itself or by virtue of containing a suitable powder 
passenger. Or a sol without a powder passenger may be applied to a 
profiled substrate, and form thereon a uniform coating which maintains the 
profiling and protects it from abrasion. Or profiling may result in part 
from a profiled substrate and in part from a powder passenger contained in 
the sol. What is not envisaged is an excessively rough or profiled 
substrate with a solderived deposit merely filling in holes and pores of 
the substrate. 
The composition may be applied to the substrate surface (optionally 
carrying a profiled surface) by any convenient technique, such as spin 
coating, immersion, flow or roller coating, brushing, or by spraying. For 
aluminum strip, roller coating is likely to be an attractive option. The 
formulation may need to be adjusted to provide a convenient viscosity for 
application by the desired method. After application and drying, the 
coating on the surface is cured. Curing temperatures are from ambient up 
to 700.degree. C., usually (though not always) below those required to 
fully sinter the particles, and may typically be at a temperature in the 
range 50.degree. to 400.degree. C. at which the substrate is stable. 
Calcination of the coating at temperatures above 400.degree. C. is 
possible but not usually necessary. Removal of water takes place 
progressively and is still not complete at 400.degree. C. 
The surface preferably carries the coating at a rate of from 0.01 to 5 
gm.sup.-2, preferably between 0.02 and 1.0 gm.sup.-2, and most preferably 
from 0.05 to 0.7 gm.sup.-2. If more pronounced surface texture is 
required, thicker coatings e.g. of up to 5 gm.sup.-2 may be preferred and 
passenger powders with average particle sizes up to 1 micron or even up to 
10 microns may be used. The invention envisages as an additional method 
step the application to the oxide layer of one or more subsequent layers 
such as are conventional in lithography. 
The lithographic sheet may comprise a photosensitive layer on the oxide 
layer. This may be applied by the manufacturer before distribution; or by 
the user by a wipe-on-technique before use. When using silver salt 
diffusion transfer principles, the lithographic plate may comprise a 
silver-receptive layer on the oxide layer.

Description of the Preferred Embodiments 
The following examples illustrate the invention. Preparation of the sols is 
described in EPA-358338 published on Mar. 14, 1990 and to which reference 
is directed. 
EXAMPLE 1 
Sols were deposited on AA1050A alloy at 0.4 mm gauge in either the as 
rolled or as commercially grained condition. The plates produced were; 
______________________________________ 
A 5% Zirconia sol Electrograined 
sheet 
B 5% Zirconia sol As rolled sheet 
C 2.5% Zirconia sol and 
As rolled sheet 
2.5% Bacosol (Bohmite) 
D 2.5% Zirconia sol and 
As rolled sheet 
2.5% Bacosol (Bohmite) 
E 5% fumed silica (A200) 
As rolled sheet 
and 5% Zirconia Sol 
______________________________________ 
A positive light sensitive coating (Esterified resin of 
2,1-naphthoquinone-diazide-5-sulphonic acid) was applied as the 
recommended 10 wt % solids content solution in Cellosolve. Bar coating was 
used to apply the coatings and the approximate film weight was 4 
gm.sup.-2. In general control over the uniformity of the films deposited 
was not optimised; specifically, in examples A and B, coatings were 
thinner than optimum. 
A series of standard test images designed to show the resolution and range 
of tones were developed on to the plates using standard UV 
exposure/developing techniques. Exposure time was 75 seconds in a Howson 
Algraphy Apollo contact printer and Howson Algraphy "Posidev" solution was 
used to develop the plates. For comparative purposes, a standard Howson 
Algraphy "Super Amazon" plate was also developed. After development the 
plates were coated with synthetic gum. 
Printing Trails 
Printing trials were carried out on a single stand of a five-colour 
Heidelberg Offset Lithographic Printing Press. Preliminary trails with an 
uncoated plate A showed total "Blocking out" of the non-image area, i.e. 
ink was deposited on all areas of the plate and not lifted from the 
sol-gel coated non-image area. A separate fountain solution, applied to 
the plate in addition to the ink, normally wets the non-image area 
preventing ink adhesion. During the course of the work it was established 
that the treatment with the developer which contains sodium metasilicate 
overcame "blocking out". 
For the printing tests the plates were mounted "side-by-side" in the press 
and 320 impressions made. Impressions from the C, D and E treated plates 
were of almost identical quality to those obtained from the commercial 
Howson "Super Amazon" plate. It should be noted that the Howson plate is 
one of the best available commercially. Poorer quality (but acceptable) 
impressions were obtained from examples A and B but this was attributed to 
the low thickness of the original photoresist on the plate surface. None 
of the plates showed any deterioration during the print run. Throughout 
the trials the fountain solution was used at a minimum rate. In addition, 
during each trial the fountain solution was turned off until complete 
"blocking out" of the plates had occurred. Low fountain solution levels 
were then restored and recovery of the plates recorded. It was also 
observed that at very low fountain solution levels the commercial plate 
was tending to "block out". This did not happen on any of the test plates. 
Examples 2-20 
Sol Preparation 
a) Zirconia Sol 
In a typical preparation 2 kg of zirconium carbonate (44.8 w/v ZrO.sub.2, 
7.2 moles) was added with stirring to 0.91 of 8M HNO.sub.3 (7.2 moles). 
The paste rapidly dissolved (exothermic 43.degree. C.) to give a sol 
containing 444 gl.sup.-1 ZrO.sub.2 equivalent. When cooled to 20.degree. 
C. the dispersion (NO.sub.3 /ZrO.sub.2 mole ratio=1.0) has a viscosity of 
16 centipoise and a density of 1.55 g/cm.sup.3. 
For coating the sol was diluted to 25% or 1% of the original concentration. 
b) Ammonium zirconium carbonate (AZC) 
Obtained commercially. 
c) Titania Sol 
In a typical preparation 2.8M titanium (IV) chloride is added to ammonium 
hydroxide to form a gelatinous precipitate of titanium (IV) hydroxide. 
Following water washing a controlled amount of nitric acid is added to 
condition and peptise the hydrous colloidal titania sol. The colloidal 
particles are 50-250 nm in size and comprise 5-10 nm crystallites of 
anatase. 
d) Titania P-25 
Titania P-25 comprising of anatase particles with an average primary size 
of 30 nm was obtained commercially. 
e) Ceria Sols 
This sol was formed by controlled aqueous deaggregation of ceria hydrate. 
Nitric acid is added to a slurry of ceria hydrate in water to deaggregate 
particles into their primary crystallites. Following coagulation excess 
nitric acid is decanted and water is added to form the sol. The 
concentration of the sol formed is 400 g/l and its density is 1.4 
g/cm.sup.3. 
f) Iron (III) Oxide 
The method of preparation is similar to that described for titania sol. The 
precursor was hydrated iron (III) nitrate. This forms a type A sol. 
g) Silica Sol 
12 nm particle size Aerosil 200 was obtained commercially. 
h) `Syton` Silica Sol 
Silica in the form of non-aggregated spherical particles with diameters 
approximately 25 nm was obtained commercially. 
Additions 
Low sodium Bacosol 3A and 3C were obtained commercially and comprise 
aluminum oxide monohydrate (Bohmite) particles of 0.1-0.2 .mu.m. Bacosol 
3A has a pH of 10 and 3C 3.5. Both are Type B sols. 
Coating 
Sols were either bar coated or whirler coated at 5 Hz on to AA1050A alloy 
at 0.4-0.3 mm gauge in either the as rolled or as commercially grained 
condition. 
A positive light sensitive coating (Esterified resin of 
2.1-naphthoquinone-diazide-5-sulphonic acid) was applied as the 
recommended 10 wt % solids content solution in Cellosolve. Bar coating or 
whirler coating at 5 Hz gave film weights of approximately 4 gm.sup.-2. 
Plate Testing 
Prior to light sensitive coating all plates were screened by simple 
sellotape testing. The resistance of the plates to chemicals used during 
printing and developing was evaluated by spotting the concentrated 
solutions on to the plate for periods of 60 seconds and 1 hour. 
A series of standard test images designed to show the resolution and range 
of tones were developed on to the plates using standard UV 
exposure/developing techniques. Exposure time was 75 seconds in a Howson 
Algraphy Apollo contact printer and Howson Algraphy "Posidev" solution was 
used to develop the plates. After development the plates were coated with 
synthetic gum. 
Developer resistance of the light sensitive coated plates were evaluated by 
spotting the concentrated developer solution on to the test areas of the 
plate for periods of 15, 30 and 60 seconds and observing the removal of 
the developed photoresist. 
Results showed that some removal of the photoresist on the thinner coatings 
occurred. Thicker coatings, however remained almost unchanged. 
Printing Trials 
Printing trials were carried out using suitable plates on a single stand of 
a five-colour Heidelberg MOFP Offset Lithographic Printing Press. Apart 
from evaluating the printing characteristics of the plates, the effect of 
varying the amount of fountain solution was examined. In addition, wear 
trials were carried out in which excess pressure was loaded onto the 
blanket by over packing. The non-compressible blanket was over packed by 
0.15 mm over a 210 mm section. From previous experience such loading 
results in a ten fold acceleration in the wear rate of the plate. 
Examples 
Pure Type A sols 
2. A 1050A aluminum alloy in the as rolled condition was cleaned in sodium 
hydroxide solution and whirler coated with a 25% dilution of the pure 
zirconia sol using the method described above. The light sensitive coating 
was also applied by whirler coating and after drying an image developed. 
In the accelerated printing trial the non-image area started to wear after 
4,000 impressions but loss of acceptable printing performance did not 
occur until 12,000 impressions. 
3. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 40 g/l ammonium zirconium carbonate sol started to 
wear after 2,000 impressions but loss of acceptable printing performance 
did not occur until 11,000 impressions. 
4. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 40 g/l iron (III) sol started to wear after 2,000 
impressions but loss of acceptable printing performance did not occur 
until 10,000 impressions. 
5. A plate formed by bar coating a 5% zirconia sol on to alkali cleaned, 
commercially electrograined sheet gave high quality images on printing. 
6. A plate formed by bar coating a 5% zirconia sol on to alkali cleaned, 
as-rolled sheet gave high quality images on printing. 
Type A sols with Type B sols as powder passengers 
7. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 2.5% zirconia sol and 2.5% Bacosol 3C sol started to 
wear after 4,000 impressions but loss of acceptable printing performance 
did not occur until 23000 impressions. 
8. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 10% zirconia sol with 5% Bacosol 3C sol started to 
wear after 2000 impressions but loss of acceptable printing performance 
did not occur until 14,000 impressions. 
9. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 5% zirconia sol with 1% p-25 titania sol started to 
wear after 7,000 impressions but loss of acceptable printing performance 
did not occur until 19,000 impressions. 
10. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 10% zirconia sol with 1% Aerosil 200 silica sol 
started to wear after 3,000 impressions but loss of acceptable printing 
performance did not occur until 11,000 impressions. 
11. In a similar test to that described in Example 1 but using 304 
stainless steel as the substrate, the non image area of a plate coated 
with a 10% zirconia sol with 10% Bacosol 3C sol started to wear after 
2,000 impressions but loss of acceptable printing performance did not 
occur until 14,000 impressions. Prior to coating the stainless steel was 
cleaned by Scotch-Brite brushing and trichloroethylene degreasing. 
12. A plate formed by bar coating a 2.5% zirconia and 2.5% Bacosol 3A on to 
alkali cleaned, as-rolled sheet gave high quality images on printing. 
Comparative Tests 
Type B Sols 
13. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 40 g/l titania sol started to wear after 1,000 
impressions but loss of acceptable printing performance occurred by 3,000 
impressions. 
14. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 10% Ceria sol started to wear after 1,000 
impressions but loss of acceptable printing performance occurred by 3,000 
impressions. 
Type C Sol 
15. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 1% Aerosil 200 type C silica was badly reticulated. 
During printing the reticulated non-image coating picked up ink causing 
badly marked non-image areas. The same silica performed similarly in a 
formulation including 10% zirconia sol. 
Formulation with Insufficient Type A Sol 
16. In a similar test to that described in Example 2, the non image area of 
a plate coated with a 1% zirconia and 1% P25 titania sol was badly marked 
by 1,000 impressions. 
Plate Clean-up Rates 
17. Throughout the tests 2 to 12, the fountain solution was used at a 
minimum rate. In addition, during tests 5, 6 and 12 the fountain solution 
was turned off until complete "blocking out" of the plates had occurred. 
Subsequent application of low levels of fountain solution resulted in the 
plates cleaning up completely within 25 impressions. 
Image Adherence 
18. During the development and rinsing stages of manufacture, the image 
coatings were washed away from plates coated with 2.5 to 10% Syton X30 
silica. 
Pre-press Screening Tests 
19. The sellotape test was applied to all plates produced as a preliminary 
check of the integrity of the coatings. All of the coatings used in the 
printing trials passed successfully. 
20. Plates coated with following compositions were tested for resistance to 
the chemicals used in the printing process. 
2.5% Ceria (.apprxeq.410 gl.sup.-1) sol 
2.5% Zirconia sol/2.5% BaCoSol 3C 
5% Zirconia (.apprxeq.435 gl.sup.-1) sol 
2% Zirconia sol 
1% Zirconia sol/1% P-25 titania 
10% Zirconia sol 
25% Zirconia sol 
50% Zirconia sol 
5% Zirconia sol/1% P-25 titania 
5% Zirconia sol/0.5% P-25 titania 
Plates were found to be resistant to all chemicals for the exposure times 
normally encountered in printing practices. Most of the plates withstood 
exposure for periods of up to 1 hour. The exceptions were the developer 
and deletion fluids but these are extreme tests where commercial plates 
also failed.