Process for treating aluminum oxide layers and use in the manufacture of offset-printing plates

A process is disclosed for manufacturing sheets, foils, or strips which involves chemically, mechanically, and/or electrochemically roughening and anodically oxidizing aluminum or aluminum alloy surfaces, followed by two post-treatment steps. In the first step, the metal surface is treated with an aqueous alkali metal silicate solution; thereafter, the surface is treated with an aqueous solution comprising alkaline earth metal ions. The materials produced according to this process are particularly used as supports for offset-printing plates.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for post-treating roughened and 
anodically oxidized aluminum with aqueous solutions of an alkali metal 
silicate. The treated aluminum is particularly useful as a support 
material for offset-printing plates. 
Support materials for offset-printing plates are provided, on one or both 
sides, with a radiation-sensitive coating (reproduction coating). The 
coating is provided either directly by the user or by manufacturers of 
precoated printing plates. This coating permits the photomechanical 
production of a printing image of an original. Following the production of 
this printing form from the printing plate, the coating support has image 
areas which are ink-receptive during the subsequent printing steps. Also, 
simultaneously with image-production, a hyrophilic image-background for 
lithographic printing is formed in the areas which are free from an image 
(non-image areas). 
A coating support for reproduction coatings used in the manufacture of 
offset printing plates must meet the following requirements: 
Those portions of the photosensitive coating which have become 
comparatively more soluble following exposure must be capable of being 
easily removed from the support, by a developing operation, in order to 
produce the hydrophilic non-image areas without leaving a residue. 
The support, which has been laid bare in the non-image areas, must possess 
a high affinity for water, i.e., it must be strongly hydrophilic, in order 
to accept water, rapidly and permanently, and to repel greasy printing ink 
during the lithographic printing operation. 
The photosensitive coating must exhibit an adequate degree of adhesion 
prior to exposure, and those portions of the coating which print must 
exhibit adequate adhesion following exposure. 
Suitable base materials for coating supports of this kind include aluminum, 
steel, copper, brass, or zinc foils. Plastic sheets or paper may also be 
used. By appropriate modifications, such as, for example, graining, matte 
chromium-plating, surface oxidation, and/or application of an intermediate 
layer, these base materials are converted into coating supports for 
offset-printing plates. The surface of the base material, presently most 
frequently aluminum, is roughened according to known methods, e.g., 
dry-brushing, slurry-brushing, sandblasting, or chemical and/or 
electrochemical treatment. In order to increase resistance to abrasion, 
the roughened substrate may additionally be treated in an anodizing step 
to produce a thin oxide layer. 
In practice, the support materials, and particularly anodically oxidized 
aluminum-based support materials, are often subjected to a further 
treatment step, before applying a photosensitive coating, in order to 
improve the adhesion of the coating, increase the hydrophilic properties 
of the support material, and/or improve the developability of the 
photosensitive coatings. Such treatments are, for example, carried out 
according to the following methods: 
German Pat. No. 907,147 (corresponding to U.S. Pat. No. 2,714,066), German 
Auslegeschrift No. 1,471,707 (corresponding to U.S. Pat. Nos. 3,181,461 
and 3,280,734), and German Offenlegungsschrift No. 2,532,769 
(corresponding to U.S. Pat. No. 3,902,976) describe processes for 
hydrophilizing support materials for printing plates made of aluminum 
which has optionally been anodically oxidized. In these processes, the 
materials are treated, with or without the application of an electrical 
current, with an aqueous solution of sodium silicate. 
German Pat. No. 1,134,093 (corresponding to U.S. Pat. No. 3,276,868) and 
German Pat. No. 1,621,478 (corresponding to U.S. Pat. No. 4,153,461) 
describe the use of polyvinyl phosphonic acid or copolymers based on vinyl 
phosphonic acid, acrylic acid, and vinyl acetate to hydrophilize support 
materials for printing plates, comprising aluminum which has optionally 
been anodically oxidized. 
Although these post-treatment methods often yield adequate results, they 
cannot meet all of the frequently very complex requirements which are 
demanded of a support material for printing plates, and which comprise the 
present standards for high-performance printing plates used in practice. 
Thus, for example, upon treating the supports with alkali metal silicates 
which produce a good developability and good hydrophilic properties, a 
certain deterioration of the storability of the applied reproduction 
coatings must be accepted. In supports which are treated with 
water-soluble organic polymers, the good solubility of these polymers, 
particularly in the aqueous-alkaline developers which are commonly used 
for developing positive-working reproduction coatings, leads to a decrease 
in the hydrophilizing action of the post-treatment. In addition, 
resistance to alkali, which is particularly necessary when 
high-performance developers are used in the field of positive-working 
reproduction coatings, is not present to a sufficient degree. Depending on 
the chemical compositions of the reproduction coatings, tinting in the 
non-image areas is occasionally encountered. This tinting is probably 
caused by absorptive effects. 
Various modifications of the silicating processes have been described 
previously. These modifications include, for example: 
Adding surfactants containing non-ionic and anionic moieties and, as 
optional ingredient, gelatin to an aqueous silicate solution used in an 
immersion treatment for aluminum printing-plate supports, and subsequently 
heating the supports, according to Japanese Published Applications No. 
55,109,693) published Aug. 23, 1980) or No. 55,082,695 (published June 21, 
1980); 
adding a combination of non-ionic and anionic surfactants to aqueous alkali 
metal silicate solutions used in an immersion treatment for aluminum 
printing plate supports, at temperatures ranging from 80.degree. to 
100.degree. C., according to French Pat. No. 1,162,653; 
adding water-soluble organic polymers, such as, for example, polyvinyl 
alcohol, polyacrylic acid, polyacrylamide, polysaccharides or polystyrene 
sulfonic acid, to aqueous alkali metal silicate solutions used in an 
immersion treatment for aluminum at a temperature exceeding 40.degree. C., 
according to European Published Application No. 0,016,298, this treatment 
being especially applicable to aluminum containers; 
using a three-step process for producing a hydrophilic adhesive layer on 
aluminum printing plate supports according to German Auslegeschrift No. 
1,118,009 (corresponding to U.S. Pat. No. 2,922,715), comprising the steps 
of (a) a chemical or mechanical roughening treatment, (b) an immersion 
treatment at a temperature above 85.degree. C. in an aqueous alkali metal 
silicate solution, and (c) a final immersion treatment at room temperature 
in an aqueous solution of citric or tartaric acid, in order to neutralize 
the alkali produced in step (b); 
subjecting silicate layers on aluminum printing-plate supports, which 
layers were produced by an immersion treatment in aqueous alkali metal 
silicate solutions, to a hardening after-treatment in an aqueous solution 
of Ca(NO.sub.3).sub.2 or, generally, in a solution of an alkaline earth 
metal salt, according to U.S. Pat. Nos. 2,882,153 and 2,882,154, using, as 
a rule, concentrations of alkaline earth metal salt above 3% by weight, 
the support materials being only chemically or mechanically roughened, 
without anodic oxidation treatment; 
using a process according to German Offenlegungsschrift No. 2,223,850 
(corresponding to U.S. Pat. No. 3,824,159) for coating aluminum moldings, 
sheets, castings, or foils (for use, inter alia, as offset printing 
plates, but especially for use in capacitors). This process comprises an 
anodic oxidation in an aqueous electrolyte composed of an alkali metal 
silicate and an organic complex-forming compound. Such compounds include 
amines, amino acids, sulfonic acids, phenols, glycols and, additionally, 
salts of organic carboxylic acids, for example, maleic acid, fumaric acid, 
citric acid, or tartaric acid; or 
using a process for producing grain-like or textured surfaces on aluminum, 
according to German Auslegeschrift No. 2,651,346 (corresponding to British 
Pat. No. 1,523,030), which process is carried out directly on the 
aluminum, using an alternating current in an electrolyte which contains, 
in an aqueous solution, from 0.01 to 0.5 mol/l of a hydroxide or salt of 
an alkali metal or alkaline earth metal (e.g., a silicate and, optionally, 
from 0.01 to 0.5 mol/l of a compound which forms a barrier layer. The 
reference discloses that compounds that form barrier layers include, among 
others, citric acid, tartaric acid, succinic acid, lactic acid, malic acid 
or the salts thereof. 
However, these known modifications of silication, anodic oxidation, or 
surface texturing processes using electrolytes which contain organic acids 
or the salts thereof, even when they are applicable to aluminum printing 
plate supports at all, do not produce a surface which is suitable for 
high-performance printing plates, i.e., technologically, the silicate 
layers are not improved to such an extent that they fully meet the 
above-indicated requirements. 
German Auslegeschrift No. 2,364,177 (corresponding to U.S. Pat. No. 
3,860,426) discloses a hydrophilic adhesion-promoting layer for 
presensitized lithographic printing plates, which is present on an 
anodically oxidized aluminum support and comprises a water-soluble salt of 
Zn, Ca, Mg, Ba, Sr, Co or Mn, in addition to a cellulose ether, for 
example, sodium carboxymethyl cellulose or hydroxyethyl cellulose. Such 
adhesion-promoting layers are intended to impart a longer useful life to 
the plate and to prevent "scumming" in the non-image areas during printing 
with a printing form produced from this plate. An appreciable increase of 
the resistance to alkali is, however, not obtained by means of this layer. 
In German Offenlegungsschrift No. 3,219,922, a process for post-treating 
roughened and anodically oxidized aluminum supports for printing plates is 
described. In this process, an aqueous alkali metal silicate solution of 
the above-mentioned kind is used, additionally containing an aliphatic 
monobasic, dibasic or tribasic hydroxycarboxylic acid, an aliphatic 
dicarboxylic acid, or a water-soluble salt of these acids. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a process for 
post-treating sheet aluminum after the anodic oxidation of the aluminum, 
which process results in an aluminum oxide layer that particularly meets 
the above-described use requirements for a high-performance printing 
plate. 
It is a further object of the present invention to provide a support for 
offset-printing plates of improved hydrophilicity in non-image areas, 
reduced tinting tendency, enhanced resistance to alkali, and a steeper 
gradation of image. 
In accomplishing the foregoing objects, there has been provided, in 
accordance with one aspect of the present invention, a process for 
treating a surface of aluminum or of aluminum alloy, which process 
comprises roughening and anodically oxidizing the surface, then treating 
the surface with an aqueous alkali metal silicate solution, and, 
thereafter, treating the surface with an aqueous solution of at least one 
alkaline earth metal salt. 
In accordance with another aspect of the present invention, there has been 
provided an offset-printing plate comprising a support subjected to a 
process as described in the preceding paragraph, to which is applied a 
radiation-sensitive coating. 
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The invention proceeds from the known process for manufacturing materials 
in the form of sheets, foils, or strips which involves chemically, 
mechanically, and/or electrochemically roughening and anodically oxidizing 
aluminum or an aluminum alloy and then post-treating the aluminum oxide 
layers with an aqueous alkali metal silicate solution. In the process of 
the invention, the treatment (a) with an aqueous alkali metal silicate 
solution is followed by an additional treatment (b) with an aqueous 
solution of alkaline earth metal salts. 
In preferred embodiments, the alkaline earth metal salts used are 
water-soluble calcium or strontium salts, particularly nitrates. The 
solution contains, in particular, from 0.1 to 10% by weight, preferably 
from 0.5 to 3% by weight, of alkaline earth metal salts. 
The two treatment steps (a) and/or (b) can be carried out in an immersion 
process. Step (a) can also be performed during an electrochemical process. 
Often the electrochemical process itself causes a certain increase in the 
resistance to alkali of material which has not yet been subjected to 
process step (b). For an electrochemical process, direct or alternating 
current, trapezoidal, rectangular, or triangular current, or superimposed 
forms of these current types are preferably used. The current density 
generally ranges from about 0.1 to 10 A/dm.sup.2 and/or the voltage ranges 
from 1 to 100 V; moreover, the parameters are, for example, also dependent 
on the electrode distance and the electrolyte composition. Materials can 
either be discontinuously or continuously treated using modern strip 
processing equipment. Treating times for each treatment step are 
appropriately in the range from about 0.5 to 120 seconds, and treating 
temperatures are about 15.degree. to 80.degree. C., particularly about 
20.degree. to 75.degree. C. In general, the aqueous alkali metal silicate 
solution of step (a) contains from about 0.5 to 15% by weight, 
particularly from about 0.8 to 12% by weight, of an alkali metal silicate 
(for example, sodium metasilicate or the sodium trisilicates and sodium 
tetrasilicates contained in "waterglass"). It is assumed that a firmly 
adhering covering layer is formed in the pores of the aluminum oxide 
layer, which protects the oxide against attacks. The previously produced 
surface topography (e.g., roughness and oxide pores) remains virtually 
unchanged or is only negligibly changed by the post-treatment, so that the 
process of the invention is especially suitable for treating materials 
when it is very important to retain surface topography, such as, for 
example, in support materials for printing plates. 
Suitable base materials for use in the process of the invention, in 
particular for the manufacture of printing plate supports, include 
aluminum or an aluminum alloy which contains, for example, more than 98.5% 
by weight of Al and Si, Fe, Ti, Cu, and Zn constituents. 
Before the photosensitive coatings are applied to the aluminum support 
materials which are conventionally used for printing plates, the supports 
are roughened by mechanical (e.g., brushing and/or abrasive treatments), 
chemical (e.g., etchants) or electrochemical processes (e.g., treatment 
with an alternating current in aqueous acid or salt solutions to which, 
e.g., corrosion inhibitors, may be added). For the purpose of the present 
invention, aluminum printing plates which have been electrochemically 
roughened in aqueous HCl and/or HNO.sub.3 solutions are preferably used. 
The process parameters in the roughening step, particularly in a continuous 
procedure, are generally within the following ranges: temperature of the 
electrolyte between 20.degree. and 60.degree. C., concentration of active 
substance (acid, salt) between 5 and 100 g/l (or even higher in the case 
of salts), current density between 15 and 130 A/dm.sup.2, dwell time 
between 10 and 100 seconds, and flow rate of the electrolyte in continuous 
processes, measured on the surface of the workpiece to be treated, of 
between 5 and 100 cm/second. The type of current used is in most cases 
alternating current. It is also possible, however, to use modified current 
types, e.g., an alternating current with different amplitudes of current 
strength for the anode and cathode current. The mean peak-to-valley 
roughness, R.sub.z, of the roughened surface is in the range from about 1 
to 15 .mu.m, particularly in the range from 2 to 8 .mu.m. The 
peak-to-valley roughness, R.sub.z, is determined according to DIN 4768, 
October 1970, as the arithmetic mean calculated from the individual 
peak-to-valley roughness values of five, mutually adjacent, individual 
measurement lengths. 
The roughening process is followed by anodic oxidation of the aluminum in a 
further process step, in order to improve, for example, the abrasion and 
adhesion properties of the surface of the support material. Conventional 
electrolytes, such as H.sub.2 SO.sub.4, H.sub.3 PO.sub.4, H.sub.2 C.sub.2 
O.sub.4, amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid, or 
mixtures thereof, may be used for the anodic oxidation. By way of example, 
the following standard methods are representative of the use of aqueous 
electrolytes, containing H.sub.2 SO.sub.4, for the anodic oxidation of 
aluminum (see, in this regard, e.g., M. Schenk, Werkstoff Aluminium und 
seine anodische Oxydation (The Material Aluminum and its Anodic 
Oxidation), Francke Verlag, Bern, 1948, page 760; Praktische 
Galvanotechnik (Pratical Electroplating), Eugen G. Leuze Verlag, Saulgau, 
1970, pages 395 et seq., and pages 518-519; W. Huebner and C. T. Speiser, 
Die Praxis der anodischen Oxidation des Aluminiums (Practical Technology 
of the Anodic Oxidation of Aluminum), Aluminium Verlag, Duesseldorf, 1977, 
3rd Edition, pages 137 et seq.): 
The direct current sulfuric acid process, in which anodic oxidation is 
carried out in an aqueous electrolyte which conventionally contains 
approximately 230 g of H.sub.2 SO.sub.4 per 1 liter of solution, for 10 to 
60 minutes at 10.degree. to 22.degree. C., and at a current density of 0.5 
to 2.5 A/dm.sup.2. In this process, the sulfuric acid concentration in the 
aqueous electrolyte solution can also be reduced to 8 to 10% by weight of 
H.sub.2 SO.sub.4 (about 100 g of H.sub.2 SO.sub.4 per liter), or it can 
also be increased to 30% by weight (365 g of H.sub.2 SO.sub.4 per liter), 
or more. 
The "hard-anodizing process" is carried out using an aqueous electrolyte, 
containing H.sub.2 SO.sub.4 in a concentration of 166 g of H.sub.2 
SO.sub.4 per liter (or about 230 g of H.sub.2 SO.sub.4 per liter), at an 
operating temperature of 0.degree. to 5.degree. C., and at a current 
density of 2 to 3 A/dm.sup.2, for 30 to 200 minutes, at a voltage which 
rises from approximately 25 to 30 V at the beginning of the treatment, to 
approximately 40 to 100 V toward the end of the treatment. 
In addition to the above-described processes for the anodic oxidation of 
aluminum, the following processes can also be used: the anodic oxidation 
of aluminum in an aqueous, H.sub.2 SO.sub.4 -containing electrolyte, in 
which the content of Al.sup.3+ ions is adjusted to values exceeding 12 g/l 
(according to German Offenlegungsschrift No. 2,811,396=U.S. Pat. No. 
4,211,619), in an aqueous electrolyte containing H.sub.2 SO.sub.4 and 
H.sub.3 PO.sub.4 (according to German Offenlegungsschrift No. 
2,707,810=U.S. Pat. No. 4,049,504), or in an aqueous electrolyte 
containing H.sub.2 SO.sub.4, H.sub.3 PO.sub.4 and Al.sup.3+ ions 
(according to German Offenlegungsschrift No. 2,836,803=U.S. Pat. No. 
4,229,266). Direct current is preferably used for the anodic oxidation, 
but it is also possible to use alternating current or a combination of 
these types of current (for example, direct current with superimposed 
alternating current). The electrolyte is, particularly, a H.sub.2 SO.sub.4 
and/or H.sub.3 PO.sub.4 -containing aqueous solution. The layer weights of 
aluminum oxide range from 1 to 10 g/m.sup.2, which corresponds to a layer 
thickness of from about 0.3 to 3.0 .mu.m. 
Materials which have been pretreated in this manner are particularly used 
as supports for offset printing plates, i.e., a radiation-sensitive 
coating is applied to the support material, either by the manufacturers of 
presensitized printing plates or directly by the user. Suitable 
radiation-sensitive (photosensitive) coatings basically comprise any 
coatings which, after irradiation (exposure), optionally followed by 
development and/or fixing, yield a surface having an image configuration, 
which can be used for printing. 
In addition to the coatings which contain silver halides, which are used in 
many fields, various other coatings are also known, such as those 
described, for example, in "Light-Sensitive Systems," by Jaromir Kosar, 
published by John Wiley & Sons, New York, 1965. These include colloid 
coatings containing chromates and dichromates (Kosar, Chapter 2); coatings 
containing unsaturated compounds which, upon exposure, are isomerized, 
rearranged, cyclized, or crosslinked (Kosar, Chapter 4); coatings 
containing compounds which can be photopolymerized, which, upon exposure, 
undergo polymerization of the monomers or prepolymers, optionally with the 
aid of an initiator (Kosar, Chapter 5); and coatings containing 
o-diazoquinones, such as naphthoquinone-diazides, p-diazoquinones, or 
condensation products of diazonium salts (Kosar, Chapter 7). Other 
suitable coatings include the electrophotographic coatings, i.e., coatings 
which contain an inorganic or organic photoconductor. In addition to the 
photosensitive substances, these coatings can, of course, also contain 
other constituents, such as for example, resins, dyes or plasticizers. In 
particular, the following photosensitive compositions or compounds can be 
employed in the coating of support materials prepared according to the 
process of the present invention: 
positive-working reproduction coatings which contain, as the photosensitive 
compound, o-quinone diazides, particularly o-naphthoquinone diazides, for 
example, 1,2-naphthoquinone-2-diazide-sulfonic acid esters or amides, 
which may have low or higher molecular weights, as described, for example, 
in German Pat. No. 854,890, No. 865,109, No. 879,203, No. 894,959, No. 
938,233, No. 1,109,521, No. 1,144,705, No. 1,118,606, No. 1,120,273, No. 
1,124,817 and No. 2,331,377 and in published European Patent Applications 
No. 0,021,428 and No. 0,055,814; 
negative-working reproduction coatings which contain condensation products 
from aromatic diazonium salts and compounds with active carbonyl groups, 
preferably condensation products formed from diphenylaminediazonium salts 
and formaldehyde, which are described, for example, in German Pat. No. 
596,731, No. 1,138,399, No. 1,138,400, No. 1,138,401, No. 1,142,871, and 
No. 1,154,123, U.S. Pat. No. 2,679,498 and No. 3,050,502 and British Pat. 
No. 712,606; 
negative-working reproduction coatings which contain co-condensation 
products of aromatic diazonium compounds, for example, according to German 
Offenlegungsschrift No. 2,024,244, comprising products which possess, in 
each case, at least one unit of (a) an aromatic diazonium salt compound 
which is capable of condensation and (b) a compound, such as a phenol 
ether or an aromatic thioether, which is capable of condensation, 
connected by a bivalent intermediate member derived from a condensable 
carbonyl compound, for example, a methylene group; 
positive-working coatings according to German Offenlegungsschrift No. 
2,610,842, German Pat. No. 2,718,254 or German Offenlegungsschrift No. 
2,928,636, which contain a compound which, on being irradiated, splits off 
an acid, a monomeric or polymeric compound which possesses at least one 
C--O--C group, which can be split off by acid (e.g., an orthocarboxylic 
acid ester group, or a carboxamide-acetal group), and, if appropriate, a 
binder; 
negative-working coatings, composed of photopolymerizable monomers, 
photo-initiators, binders and, if appropriate, further additives. In these 
coatings, for example, acrylic and methacrylic acid esters, or reaction 
products of diisocyanates with partial esters of polyhydric alcohols, are 
employed as monomers, as described, for example in U.S. Pat. No. 2,760,863 
and No. 3,060,023, and in German Offenlegungsschriften No. 2,064,079 and 
No. 2,361,041; 
negative-working coatings according to German Offenlegungsschrift No. 
3,036,077, which contain, as the photo-sensitive compound, a diazonium 
salt polycondensation product, or an organic azido compound, and which 
contain, as the binder, a high-molecular weight polymer with 
alkenylsulfonylurethane or cycloalkenylsulfonylurethane side groups. 
It is also possible to apply photo-semiconducting coatings to the support 
materials manufactured according to the invention, such as described, for 
example, in German Pat. No. 1,117,391, No. 1,522,497, No. 1,572,312, No. 
2,322,046 and No. 2,322,047, resulting in highly photosensitive 
electrophotographic printing plates. 
The coated offset-printing plates which are obtained from the support 
materials according to the invention are converted into the desired 
printing form, in a known manner, by imagewise exposure or irradiation, 
and rinsing the non-image areas with a developer, preferably an aqueous 
developing solution. Surprisingly, compared to plates in which the same 
base materials have been post-treated in a one-step process with aqueous 
solutions which merely contain silicates, offset-printing plates whose 
base support materials have been post-treated according to the two-step 
process of the invention exhibit improved hydrophilic properties of the 
non-image areas, a reduced tendency to tinting, an improved resistance to 
alkali, and a steeper image gradation (measured with the aid of a 
continuous-tone step wedge). 
In the preceding description and in the examples which follow, percentages 
always denote percentages by weight, unless otherwise indicated. Parts by 
weight are related to parts by volume as the g is related to the cm.sup.3. 
Moreover, the following methods were used in the examples for the 
determination of parameters: 
The hydrophilic character of the support materials manufactured according 
to the invention is tested by measuring the contact angle of a water 
droplet placed on the support. In this method, the angle formed between 
the support surface and a tangent line passing through the contact point 
of the droplet is determined; in general the angle is between 0 and 90 
degrees. The better the wetting is, the smaller the angle. 
Zincate test (according to U.S. Pat. No. 3,940,321, columns 3 and 4, lines 
29 to 68 and lines 1 to 8): The rate, in seconds, at which an aluminum 
oxide layer dissolves in an alkaline zincate solution is a measure of its 
resistance to alkali. The longer the layer requires to dissolve, the 
greater is its resistance to alkali. The layer thicknesses should be 
approximately comparable, since, of course, they also represent a 
parameter for the rate of dissolution. A drop of a solution, composed of 
500 ml of distilled H.sub.2 O, 480 g of KOH and 80 g of zinc oxide, is 
placed on the surface to be tested, and the time which elapses before the 
appearance of metallic zinc is measured, this event being recognizable by 
a dark coloration of the test spot.

EXAMPLES 1 TO 23 AND COMATIVE EXAMPLES C 1 to C 8 
Aluminum foil is electrochemically roughened in a dilute aqueous HNO.sub.3 
solution, using alternating current, and is then anodically oxidized in a 
dilute aqueous H.sub.2 SO.sub.4 solution, using direct current. In the 
subsequent treatment step (a), samples are immersed in an aqueous solution 
containing Na.sub.2 SiO.sub.3.5H.sub.2 O (see Table I for duration, 
concentration and temperature), then rinsed with distilled H.sub.2 O (this 
intermediate rinsing can be omitted, see Table I) and, after rinsing or 
directly after silicating, immersed in an aqueous solution of an alkaline 
earth metal nitrate at room temperature (see Table I for duration, kind of 
cation, and concentration). Before determining the zincate test time, the 
contact angle and/or before coating with the photosensitive layer, the 
samples are again rinsed with distilled H.sub.2 O and dried without 
previously rinsing (see Table I). The contact angles are 74.0.degree. and 
19.0.degree. in Comparative Examples C 1 and C 5, respectively, and 
7.0.degree. and 11.3.degree. in Examples 9 and 21, respectively. 
Generally, step (b) is omitted in the Comparative Examples and in one case 
both steps (a) and (b) are omitted. Table I and the measurements of 
contact angles show that, compared with prior art products, the 
hydrophilic character and the resistance to alkali are clearly improved in 
the products treated according to the invention. Similarly, the 
application of intermediate rinsing shows a certain influence on the 
resistance to alkali. Samples which have not been intermediately rinsed 
after the silicating step generally have a better resistance to alkali 
than samples which have been intermediately rinsed, but even the latter 
still have a markedly better alkali resistance than prior art products. 
EXAMPLES 24 TO 29 
These examples are carried out as indicated for the group comprising 
Examples 1 to 23, but the silicating step is carried out by an 
electrochemical process, at room temperature (see Table II). 
EXAMPLES 30 TO 33 AND COMATIVE EXAMPLES C 9 to C 18 
These Examples are carried out as indicated for the group comprising 
Examples 1 to 23. However, Comparative Examples C 9 to C 14 follow the 
teaching of U.S. Pat. No. 2,882,154 (however, at a lower salt 
concentration), using a slurry-brushed support material (abrasive and 
nylon brushes in C 9 to C 12) and a wire-brushed support material (in C 13 
and C 14) which have not been anodically oxidized, Comparative Examples C 
15 and C 16, Examples 30 and 31 use a support material which has been 
slurry-brushed and anodically oxidized in an aqueous solution containing 
H.sub.2 SO.sub.4, and Comparative Examples C 17 and C 18 and Examples 32 
and 33 use a support material which has been electrochemically roughened 
and anodically oxidized in an aqueous solution containing H.sub.3 
PO.sub.4. The examples clearly show (see Table III) that, in a 
mechanically roughened aluminum sample which has not been anodically 
oxidized, the resistance to alkali is nearly unaffected, or is only 
insignificantly increased, by a two-step treatment with silicates and 
alkaline earth metal salts, i.e. based on the teaching of U.S. Pat. No. 
2,882,154, the process of the invention and the advantages obtainable 
therewith could not be anticipated. 
TABLE I 
__________________________________________________________________________ 
Treating with Alkaline 
Silicating Earth Metal Salt Solution 
Concen- 
Temper- 
Dura- 
Interme- Concen- 
Dura- 
Interme- 
Zincate 
tration 
ature 
tion 
diate 
Kind of 
tration 
tion 
diate 
Test 
Example 
(%) (.degree.C.) 
(sec) 
Rinsing 
Cation 
(%) (sec) 
Rinsing 
(sec) 
__________________________________________________________________________ 
C 1 -- -- -- -- -- -- -- -- 28 
C 2 4 40 1 no -- -- -- -- 29 
C 3 4 40 5 " -- -- -- -- 34 
C 4 4 40 10 " -- -- -- -- 38 
C 5 4 40 30 " -- -- -- -- 38 
C 6 4 40 60 " -- -- -- -- 45 
1 4 40 1 " Ca.sup.2+ 
0.10 
10 no 61 
2 4 40 5 " " 0.10 
10 " 64 
3 4 40 10 " " 0.10 
10 " 66 
4 4 40 30 " " 0.10 
10 " 72 
5 4 40 60 " " 0.10 
10 " 80 
6 4 25 30 yes " 0.01 
10 yes 36 
7 4 25 30 " " 0.10 
10 " 48 
8 4 25 30 " " 1.00 
10 " 59 
9 4 25 30 no " 1.00 
10 no 90 
10 4 25 30 yes Sr.sup.2+ 
0.01 
10 yes 38 
11 4 25 30 " " 0.10 
10 " 57 
12 4 25 30 " " 1.00 
10 " 72 
13 1 25 1 no " 0.10 
1 " 38 
14 1 25 1 " " 10.00 
1 " 67 
15 1 70 1 " " 0.10 
1 " 34 
16 1 70 1 " " 10.00 
1 " 112 
C 7 4 25 30 yes -- -- -- -- 27 
C 8 4.sup.+ 
25 30 " -- -- -- -- 32 
17 4 25 30 no Sr.sup.2+ 
1.00 
10 yes 84 
18 4.sup.+ 
25 30 " " 1.00 
10 " 66 
19 1 25 30 " " 1.00 
10 no 69 
20 2 25 30 " " 1.00 
10 " 111 
21 4 25 30 " " 1.00 
10 " 153 
22 10 25 30 " " 1.00 
10 " 167 
23 4 25 30 " Ba.sup.2+ 
1.00 
10 " 35 
__________________________________________________________________________ 
.sup.+ in these Examples waterglass is used instead of N.sub.2 
SiO.sub.3.5H.sub.2 O 
TABLE II 
__________________________________________________________________________ 
Treating with Alkaline 
Silicating Earth Metal Salt Solution 
Concen- 
Vol- 
Dura- 
Interme- Concen- 
Dura- 
Interme- 
Zincate 
tration 
tage 
tion 
diate 
Kind of 
tration 
tion 
diate 
Test 
Example 
(%) (V) 
(sec) 
Rinsing 
Cation 
(%) (sec) 
Rinsing 
(sec) 
__________________________________________________________________________ 
24 4 20 30 no Sr.sup.2+ 
1.00 
10 yes 90 
25 4 20 60 " " 1.00 
10 " 82 
26 4 40 30 " " 1.00 
10 " 99 
27 4 40 60 " " 1.00 
10 " 116 
28 4 60 30 " " 1.00 
10 " 128 
29 4 60 30 " " 1.00 
10 " 126 
__________________________________________________________________________ 
TABLE III 
__________________________________________________________________________ 
Treating with Alkaline 
Silicating Earth Metal Salt Solution 
Concen- 
Tempe- 
Dura- 
Interme- Concen- 
Dura- 
Interme- 
Zincate 
tration 
rature 
tion 
diate 
Kind of 
tration 
tion 
diate 
Test 
Example 
(%) (.degree.C.) 
(sec) 
Rinsing 
Cation 
(%) (sec) 
Rinsing 
(sec) 
__________________________________________________________________________ 
C 9 -- -- -- -- -- -- -- -- 13 
C 10 4 25 30 yes -- -- -- -- 13 
C 11 4 25 30 no Sr.sup.2+ 
1.00 
10 yes 16 
C 12 4 25 30 yes " 1.00 
10 " 13 
C 13 -- -- -- -- -- -- -- -- 10 
C 14 4 25 30 no Sr.sup.2+ 
1.00 
10 yes 11 
C 15 -- -- -- -- -- -- -- -- 28 
C 16 4 25 30 yes -- -- -- -- 29 
30 4 25 30 no Sr.sup.2+ 
1.00 
10 yes 41 
31 4 25 30 yes " 1.00 
10 " 41 
C 17 -- -- -- -- -- -- -- -- 95 
C 18 4 25 30 yes -- -- -- -- 101 
32 4 25 30 no Sr.sup.2+ 
1.00 
10 yes 130 
33 4 25 30 yes " 1.00 
10 " 120 
__________________________________________________________________________ 
EXAMPLE 34 
A support material prepared as indicated in Example 17 is coated with the 
following positive-working photosensitive composition: 
6.00 parts by weight of a cresol/formaldehyde novolak (with softening range 
of 105.degree. to 120.degree. C., according to DIN 53 181), 
1.10 parts by weight of 4-(2-phenyl-prop-2-yl)-phenyl-1, 
2-naphthoquinone-2-diazide-4-sulfonate, 
0.81 part by weight of polyvinyl butyral, 
0.75 part by weight of 1,2-naphthoquinone-2-diazide-4-sulfochloride, 
0.08 part by weight of crystal violet, 
91.36 parts by weight of a mixture composed of 4 parts by volume of 
ethylene glycol monomethyl ether, 5 parts by volume of tetrahydrofuran, 
and 1 part by volume of butyl acetate. 
The printing form obtained after exposure and development yields a print 
run of 100,000 copies. 
EXAMPLE 35 
A support material prepared as indicated in Example 17 is coated with the 
following negative-working photosensitive composition: 
50.0 parts by weight of the reaction product obtained by reacting a 
polyvinyl butyral (having a molecular weight of 80,000 and containing 75% 
of polyvinyl butyral units, 1% of vinyl acetate units and 20% of vinyl 
alcohol units) with propenylsulfonyl isocyanate having an acid number of 
140, 
16.5 parts by weight of the polycondensation product of 1 mole of 
3-methoxydiphenylamine-4-diazonium-sulfate and 1 mole of 
4,4'-bismethoxymethyl-diphenylether, condensed in an 85% strength H.sub.3 
PO.sub.4 and precipitated as the salt of mesitylene sulfonic acid, 
1.5 parts by weight of an 85% strength H.sub.3 PO.sub.4, 
2.0 parts by weight of Victoria Pure Blue FGA, 
1.0 part by weight of phenylazodiphenylamine, 
2,500.0 parts by weight of ethylene glycol monomethyl ether. 
The printing form obtained after exposure and development yields a print 
run of over 150,000 copies. 
COMATIVE EXAMPLE C 19 
The example is carried out as indicated in Example 35, but the two-step 
treatment with silicates and alkaline earth metal salts is replaced by a 
post-treatment with an aqueous solution of polyvinyl phosphonic acid. In C 
19, the gradation of the image area is about one to two wedge steps softer 
(i.e. less steep) than in Example 35, and a print run of about 130,000 
copies is obtained. 
COMATIVE EXAMPLES C 20 AND C 21 
These examples are carried out as in Examples 1 to 23. However, the 
two-step treatment with silicates and alkaline earth metal salts is not 
applied; instead, the roughened and oxidized aluminum samples are immersed 
for 30 seconds at 25.degree. C. in aqueous solutions containing 2 g/l of 
sodium carboxymethyl cellulose (having a viscosity of 300 mPa.s in C 20 
and a viscosity of 30.000 mPa.s in C 21 and having a degree of 
substitution of about 0.7, in each case) and 2 g/l of Sr(NO.sub.3).sub.2 
(in accordance with German Auslegeschrift No. 2,364,177). In these two 
Comparative Examples, the zincate test times are about 31 seconds for 
samples which have not been rinsed after post-treating and about 25 
seconds for samples which have been rinsed with distilled H.sub.2 O. This 
kind of post-treatment has practically no influence or only a slight 
influence on the resistance of the oxide layer to alkali.