CA1190510A - Anodically anodizing aluminium in organic polybasic acid for printing plate support - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process is disclosed for anodically oxidizing materials in the form of sheets, foils or strips, comprising aluminum or aluminum alloys, in an aqueous-electrolyte which contains at least 0.05% by weight of at least one polybasic organic acid, if appropriate after a foregoing mechanical, chemical and/or electrochemical roughening, in which the polybasic organic acid is poly-meric and is selected from the group consisting of phosphonic acid, sulfonic acid and carboxylic acid. The resulting anodized and sealed metal sheets have improved corrosion resistance and are especially suitable for lithography.
Lithographic sheets made by this invention exhibit improved adhesion for light sensitive coating, improved run length, and lessened wear on the press, greater shelf life and improved hydrophilicity in non-image areas.

Description

I'his in~ention relates to simultaneously anodizing and sealing the surface of metal sheets with novel electrolytes and the products thereby obtained.
The resulting anodi~ed and sealed metal sheets have improved corrosion resistance and are suitable, among other uses, for architectural applications. They are particularly useful as supports in lithography, particularly if aluminum or its alloys are selected. Such lithography sheets exhibit improved adhesion for light sensitive coatings, i~nproved run length, and lessened wear on the press hoth in image and non-image areas, greater shelf life and improved hydrophilicity in non-image areas. Such anodically generated coatings are more economically ob-tained than with conventional anodizing.
Anodization is an electrolytic process in which the metal is made the anode in a suitable electrolyteO When electric current is passed, the surface of the metal is converted to a form of its oxîde having decorative, protective or other properties. The ca-thode is either a metal or graphite, at which the only important reaction is hydrogen evolution. The metallic anode is consumed and converted to an oxide coatingO This coating progresses from the solution side, outward rom the metal, so the last-~ormed oxide is adjacent to the metal. The oxygen required originates from the electrolyte used.
Although anodizing can be used for other metals, aluminum is by far the most important.
Anodic oxide coatings on aluminum may be of two main types. One is the so-called barrier layer which forms when the anodi~ing electrolyte has little capacity for dissol~ing the oxide. These coatings are essentially nonporous;
their thic'kness is limited to about 13A/volt applied. Once this limiting thic'k-ness is reached, it is an effective barrier to further ionic or electron flow.
T he current drops to a low leakage value and oxide formation stops. Boric acid ~.

35~3 and tartaric acid are used as electrolytes for this process.
When the electrolyte has appreciable solvent action on the oxide, the barrier layer does no~ reach its limiting thickness: curren~ continues to flow, resulting in a "porous" oxide structure. Porous coatings may be quite thick:
up to several tens of micrometers, but a thin barrier oxide layer always remains at the metal-oxide interfaceO
Electron microscope studies show the presence of billions of close-packed cells of amorphous oxide through ~he oxide layer, generally perpendicular to the metal-oxide interface.
Sulfuric acid is the most widely used electrolyte, with phosphoric also popular. Anodic films of aluminum oxide are harder than air~oxidized surface layers.
Anodizing ~or decorative7 protective and adhesive bonding properties has used strong electrolytes such as sulfuric acid and phosphoric acid. United States 2,703,781 employs a mixture of these two electrolytes.
United States 39227,639 uses a mixture of sulfophthalic and sul~uric acids to produce protective and decorative anodic coatings on aluminum. Other aromatic sulfonic acids are used ~ith sulfuric acid in United States 3,804,731.
As a post-treatment after anodi7ation, the porous surface is sealed according to numerous processes to determine the final properties of ~he coating.
Pure water at high temperature may be usedO I~ is believed tha~ some oxide is dissolved and reprecipitated as a voluminous hydroxide ~or hydra~ed oxide) inside the pores. O~her a~ueous sealants contain metal salts whose oxides may be coprecipitated with ~he aluminum oxide.
United States 3,900,370 employs a sealant composition of calcium ions, a water-soluble phosphonic acid ~hich complexes ~ith a divalent metal to protect

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anodized aluminum or anodized aluminum alloys against corrosion. Polyacrylamide has been proposed as a sealant.
United States 3,915,811 adds an organic acid (ace~ic acid, hydroxy acetic acid, or amino acet~c acid) to a mixture of sulfuric and phosphoric acidsto form the electrolyte in preparation for electroplating the so-formed anodic aluminum coating.
United States 4,115,211 anodizes aluminum by A.C., or superimposed A.C.
and ~.C.~ wherein the electroly~te solution contains a water~soluble acid and a ~ater-soluble salt of a heavy me~al. The water-soluble acid may be oxalic, tar-taric, citric, malonic, sulfuric, phosphoric, sulfamic or boric.
United States 3,988,217 employs an electrolyte containing quaternary ammonium salts, or aliphatic amines and a water-soluble thermosetting resin to anodize aluminum for protective, ornamental or corrosion resistant applications.The advan~ages of anodized aluminum as a carrier for lithographic prin*ing plates were early recognized. Processes employing as electrolytes sulfuric acidJ phosphoric acid, mixtures of these, or either o these in suc-cession have been proposedO Prior to anodiæing, the sheet may be roughened mechanically or chemicallyO The need for a subcoa~ing prior to application as a photosensitive layer to impart adhesion to the coa*ing and hydrophilicity to thenon-image areas was recognized. United States 3,181,461 uses an aqueous alkalinesilicate treatment following the anodization step.
United States 2~594J289 teaches ~Col. 1, lines 42-54~ that porous anodic films but not nonporous anodic films are suitable for li~hographic purpo-ses~ "since the porous film confers a better water receptive surface to the non-image areas of the plate and allows image-forming material to anchor effectivelyto the surface by penetrating the pores."

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3~1r3 United Sta~es 3,511,661, since disclaimed, describes al~inum sheet or a lithographic printing surface anodized in aqueous phosphoric ~cid having an anodic film wi~h a cellular pattern of aluminum oxide having cells with porous o o openings o~ about ~OOA to 700A in average diameter and a surface with 10 to 200 mg per square meter of aluminum phosphateO
United States 3,658,66~ describes the electrochemical silication of a cleaned, etched aluminum plate to achieve a measure of hydrophilization.
In United States 3,902,976 a conventionally anodized aluminum sheet is electrolytically post-treated in an aqueous solution of sodium silicate to form a hydrophilic abrasion-resistant and corrosion-resistant layer suitable as a support for a presensi~ized lithographic sheet.
United States 4,0~2,670 carries out anodization of aluminum sheets in an aqueous solution of a mixture of polybasic mineral acid such as sulfuric and a higher concentration of a polybasic aromatic sulfonic acid such as sulfophtha-lic acid to produce a porous anodic oxide surface to which a photosensitive layer ma~ be directly applied.
There is described in United States 4,090,880~ a two-step process whereby a cleaned aluminum sheet is first coated with an interla~er material such as alkali silicate, Group IV-B metal fluorides, polyacrylic acid, or alkali zir-conium fluoride and then anodized conventionally in aqueous sulfuric acid.Enhanced shelf life when overcoated with diazo sensitizers is claimed.
United States 4,153,461 employs a post-treatment with aqueous polyvinyl phosphonic acid at temperatures from 40 to 95C after conventional anodizing to a thickness of at least 0~2uo The treatmen~ provides good adhesion of a subse-quently applied light sensitive layer, good shelf life and good hydrophilization ~f non-image areas after exposure and development as well as long press runs.

Plates of the above construction, particularly when the light sensi-tive layer is a diazo compound have enjoyed considerable commercial success.
Nevertheless, certain improvements would be desirable. These include freedom from occasional coating voids, occasional unpredictable premature image failure on the press, faster, more dependable roll-up on the press and freedom from other inconsistencies. Still greater press life is desirable as well as a pro-cess that would be more economical -than conventional anodizing followed by a second operation of sealing or post-treating in preparation for coating with a light sensitive layer.
In the case of protective and decorative applications, improved corro-sion resistance and production economy over known anodizing processes is desired.
Tlle invention is based on the known process for anodically oxidizing materials in the form of sheets, foils or strips, comprising aluminum or aluminum alloys, in an aqueous electrolyte which contains at least 0.05% by weight of one polybasic organic acid, if appropriate after a preceding mechani-cal, chemical and/or electrochemical roughening; the process of the invention being characterized in that the polybasic organic acid is polymeric and is selected from the group consisting of phosphonic acid, sulfonic acid and carboxylic acid.
Transmission electron microscopy (TEM) of at least 55,000 times magni-fication of aluminum oxide films obtained according to the invention shows no porosity of the surface of the procluct of the invention, whereas conventionally anodized aluminum shows typical porosity at as little as 5,000 times magnifica-tion. Further ESCA (Electron Spectroscopy Eor Chemical Analysis) examination of polyvinyl phosphonic acid treated aluminum shows a high ratio of phosphorus to aluminum (P/Al) in the metal oxide-organic complex surface film. In contrast, conventionally anodized aluminum using even phosphoric acid has a very low P/Al s~

rati~ Conventionally anodized aluminum post~t~eated b~ simple thermal immersion in aqueous polyvinyl phosphonic acid tnon-electrochemical) has an intermediate, significantl~ lower P/Al ratio. This is evidence of ~he incorporation of the electrolyte molecules into the structure of the insoluble metal oxide-organic complex which comprises the surface film of ~he products of this invention.
Copending Canadian patent application Serial No. 386,627, filed on even date here~ith, discloses and claims a process for anodically oxidizing materials in the form of sheets, foils or stripsJ cornprising aluminum or aluminum alloys, in an aqueous e]ectrol~te ~hich contains at least one polybasic organ~c acid, after, if appropriate, a preceding mechanical, chemical and/or electrochemical roughening, in which, as the polybasic acid, one employs either phytic acid, nitrilo triacetic acid, phosphoric acid mono (dodecyloxy-polyoxyethylene)ester, tridecyl benzene sulfonic acid, dinitro-stilbene disulfonic acid, dodecyl naphthalene disulfonic acid, dinonyl naphthalene disulfonic acid, di-n-butyl naphthalene disulfonic acid, ethylene diamine tetraacetic acid, or hydroxyethyl ethylene diamine triacetic acid; or a mixture of at least two o~ these acids is used.
The metal substrates to be subjected to elactrochemical treatment according to the inven~ion are first cleaned. Cleaning may be accomplished by a ~ide range of solvent or aqueo~s alkaline treatments appropriate to the metal and to the final end-purpose.
Typical alkaline degreasing trea~ments include. hot aqueous solutions containing alkalis such as sodium hydroxide, potassium hydroxide, trisodium phosphate, sodium silicate, aqueous alkaline and surface active agents. A
proprietary composition of this type is Ridolene* 57, manufactured by Amchem *trademark " ~
: "

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Products, Pennsylvania. Currently less popular because of environmental and health considerations, is solvent degreasing, using trichloroethylene, l,l,l-tri-chloroethane, and perchloroethylene. Solvent degreasing is accomplished by immersion, spray or vapor washing. Aluminum alloys 1100, 3003 and A-19, products of Consolidated Aluminum Company among othcrs, may be used for lithographic pur-poses and are preEerred. Typical analyses of these three lithographic alloys will now be shown on a weight percent basis:
Alloy Al Mg Mn Fe Si Cu lloo 99 2 - - .375 .375 .05 3003 99.0 - .7 .15 .2 .05 A-l9 98.3 .9 - .375 .375 .05 The metal surface may be smooth or roughened. Conventional surface roughening techniques may be employed. They include~ but are not restricted to, chemical etching in alkaline or acid solutions, graining by dry abrasion with metal brushes, wet abrasion with brushes and slurries of abrasive particles, ball graining and electrochemical graining. The surface roughness and topography varies with each of these processes. For best results according to the practice of this invention, the clean surface should be electrotreated immediately before the formation of an aerial oxide. The term "aerial oxide" refers to the build-up of oxidized areas on the plate sur:Eace during usual storage in air (the degree of build-up depends on storage time and weather conditions). In other words, such term refers to oxide layers in an indefinite form, contrary to those layers that are provided, for example, by oxidizing anodically. Prior to immer-sion of a previously cleaned, degreased and optionally roughened plate in the organic electrolyte solution Eor electrodeposition, the plate should be etched to remove aerial oxide which, as is stated above, usually grows during the stor-, 5~

age period of the plate materials in ~he absence of electric current. Such etching can be accomplished by known etching means including acid and alkaline and electrolytic treatments with the above followed by rinsing. A method Eor removal of said aerial oxide is stripping the plate - 7a -with a standard etchant such as phosphoric acid/chromic acid solution. Thus immediately after cleaning and roughening (if this step is desired) and etching it is preferable that the metal surface should be rinsed with wa-ter and electro-treated while still wet, although useful products may be obtained if this pre-caution is not rigidly adhered to.
After cleaning and after roughening, if desired, the metal may be optionally anodized conventionally prior to electrodeposi-tion of the organic electrolyte of this invention.
Specific electrolytes include the condensation product of benzene phosphonic acid and formaldehyde (polybenzene phosphonic acid), hydrolyzed, copolymers of me-thylvinyl ether and maleic anhydride at various molecular weights, copolymers of methylvinyl ether and maleic acid, polyvinyl sulfonic acid, polystyrene sulfonic acid, alginic acid, poly-n-butyl benzene sulfonic acid, polydiisopropyl benzene sulfonic acid, polyvinyl phosphonic acid, poly-diisopropyl naphthalene disulfonic acid, polydecyl benzene sulfonic acid, poly-acrylic acid, polymethacrylic acid, polynaphthalene sulfonic acid, and mixtures of any of the foregoing. All of the above are water-soluble.
For lithographic applications, a high degree of hydrophilicity and firm adhesion of the image is necessary. Preferable electrolytes include the condensation product of benzene phosphonic acid and formaldehyde, lower molecul-ar weight copolymers of methylvinyl ether and maleic anhydride, copolymers of methylvinyl ether and maleic acid, polyvinyl sulfonic acid, polyvinyl phosphonic acid, poly-diisopropyl naphkhalene sulfonic acid, and mixtures of any of the foregoing.
The rnost preferred electrolytes, particularly for critical lithographic 5~
applications, include the condensation product of benzene phosphonic acid and formaldehyde, polyvinyl phosphonic acid, and mixtures of any of the foregoing.
The concentration of the electrolyte, the electrolysis conditions used, e.g. voltage, current density, time, temperature all play significant roles in determining the properties of the coated metal.
The integrity of the metal oxide-organic complex of which the electro-deposited film is composed may be measured by the potassium zincate test for anodizedsubstrates. This test is described in United States 3,940,321. A solu-tion of potassium zincate (ZnO 6.9%, KOH 50.0%, H2O 43.1%) is applied to the surface of the coating. An untreated plate gives a rapid reaction to form a black film. As a barrier layer is formed, the time for the zincate solution to react is increased. For comparison, an aluminum plate anodized in sulfuric acid to an oxide weight of 3.0 g/M2 will show a reaction in about 30 seconds. A
plate anodized in phosphoric acid having an oxide weight of ca. 1.0 g/M2 will take about two minutes to react. Tests with electrotreated plates using poly-vinyl phosphonic acid as the electrolyte, consistently take substantially longer to react, unless very low extremes of concentration or operating conditions are used. While it has been found that the zincate test gives clearly recognizable end points for anodic coatings of the prior art, say up to about one mimlte, the products of this invention produce more difficulty in recognizing end points, particularly as the reaction time increases. The stannous chloride test des~
cribed below, not only is more rapid, but produccs a more easily recognized end point, particularly when observations are conducted under a magnifying lens.
Nevertheless, with both reagents, the longer reaction times re~uire some experi-ence for correct interpretation.

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United States 3,902,976 describes the use of a stannous chloride solu-tion for the same purposeO The end point is a visible hydrogen evolution, fol-lowed by a black spot formation. Representative samples tested with zincate and wlth stannous chloride show the lat*er to be about 4 times faster. Conventional-ly anodized aluminum using sulfuric acid and/or phosphoric acid as electrolyte has been used for architec~ural applications because of superior resistance to weathering. Typical stannous chloride tests for such materials are about 4 to 10seconds, while for the aluminum sheets of this invention such times are about 15seconds for a 0.1% solution to more than 200 seconds for a 5% solution. The ~incate and stannous chloride tests are believed to correlate with corrosion resistance, a key property in protective and decorative metal applications.
The metal oxide-organic complex film weight is determined quantita-tively by stripping with a standard chromic acid/phosphoric acid bath ~1.95% CrO3, 3.41% H3PO4, 85% balance H2O) at 180F for 15 minutes.
The bonding of an electrolytically deposited film is much greater than when prior art thermal immersion is used after anodizing. A 1.0 N NaOH solution removes most of such thermally deposited coating but virtually none of an elec-trolytically deposited film ~hich is therefore insoluble in reagents of equal orlo~er aggressiveness.
2Q For lithographic applications~ pla~es are tested after electrodeposi-tion o the metal oxide-organic complex and before coating with a light sensi~ive layer. The plate is wet or dry inked3 the lat~er test being more severe. After inking, the plate is rinsed under running water or sprayed with water and lightly rubbed. The ease and completeness of ink removal indicates the hydrophilicity ofthe surface.
Typically, plates prepared in accordance with the invention9 when dry ~9~5~
inked and baked in an oven at 100C, rinsed totally free of ink. By contrast, plates which were either unanodized or conventionally anodized and then subjected to a thermal immersion in an a~ueous solution of polyvinyl phosphonic acid are irreversibly scummed when aged even under less severe conditions.
Using the inking tests, plates, both with and without photosensitive coatings, were aged a~ various times and temperatures and chec~ed or retention of hydrophilic properties. Plates coated Wit}l various diazo coatings were checked by aging for stepwedge consis~ency, resolu~ion, retention of background hydrophilicity, and ease of development. Suitable light sensitive materials willbe discussed below.
Fînally, for lithographic applications, plates including controls, are run on press. Dif~erences in topwear, dot sharpening, stepwedge rollback, speed and cleanllness of roll-up, and length of run were observed. In general, in all cases, plates electrodeposited within an extensive range of concentration, time,temperature, voltage, and current density were superior to prior art plates withlittle criticality in the variablesbeing shown. However, within the confines of the inven*ion, certain variables proved more important than others and certain parameters of those variables were more critical in obtaining best results. Thisis discussed in more detail below.
~he succession o even~.s with increased time in a typical electrodepo-sltion trial may be described. por example7 polyvinyl phosphonic acid at 1%
concentra~ion is used as an electrolyte at a temperature of 20C at 10 volts ~.C.
with a cleaned and etched aluminum plate as the anode and a carbon rod as the e]ectrode.
The aluminum oxide-organic complex which co~prises the surface film forms very rapidly at first. In the first second it is over 1~0 mg/M2. By the third second it is 250 mg/M2 and in five seconds it is starting ~o level off at 275 mg/M2. There is no appreciabl increase in layer weight up to 300 secs.
During this period the voltage remains substantially constant.
The amperage is no* a prime variable but is set by the other conditions selected, particularly the voltage and electrolyte concentration. The amperage begins to decline very shortly after the beginning of electrolysis.
The picture is that of a self-limiting process, in which an electro-deposited barrier layer is formed composed of a metal oxide-organic complex~
which restricts the further flow of current. The restriction is not as severe as in the case of boric acid anodization, in ~hich the maximum film thickness is 13-16A/volt as found by typical surface analytical technique ~i.e., Auger analy-sis) coupled with ion sputtering.
Thc stannous chloride test parallels the coating weight gain, up to 250 seconds. There is a rapid increase in reaction time, rising to 150 seconds ~corresponding to 630 seconds for a potassium zincate test~ which remains con-stant to an electrodeposition time of 250 seconds, after which there is a small fall~off in stannous chloride reaction *imeO
At higher voltages, the weight gain is higher. However, the stannous chloride test time, which initially parallels the weight gain rise, falls off m~ch sooner. The explanation is found from transmission el0ctron microscope examinationO Whereas the surface is nonporous and featurel~ss up to about 55,000X magnification for treatment times up to the clecline in the stannous chloride test reaction time, thereafter it is marked by pits tha~ could be due to arclng. Ink samples confirm this appearance.
It is believed, based upon experiments at various voltages and times, that the metal oxide-organic complex film upon the metal surface acts as a capacitor. As long as the dielectric strength is not exceeded during electro-lysis, there is no further weight gain with time, the film is unbroken and the stannous chloride test time remains constant. l,~hen the dielectric strength is exceeded, perforation of the film takes place with loss of film integrity. The stamlous chloride test time corresponds to this perforation. The aforementioned breakdown is primarily a function of voltage with 70 vol-ts the lowest potential at which breakdown takes place quickly. However, even at 30 volts, provided the time is prolonged beyond 250 seconds, :in the example cited, some breakdown is observed.
The boundary of breakdown conditions will therefore depend upon the process variables selected. Within this boundary, readily tested by procedures disclosed, there lie the most preferred conditions for the performance of the inventive process and the obtaining of the corresponding products. }loweverg it should be remembered that within a much wider range of conditions which are com-paratively non-critical, there are obtained products all of which are improve-ments over the prior art.
The concentration of electrolyte that may be used ranges from about 0.05% to saturation, with solutions above about 30% impractical because of viscosity, and does not depend greatly upon its chemical structure. At the lower end, solution conductivity is very low, e.g. 619000Q in the case of poly-vinyl phosphonic acid at 0.001%. Nevertheless, even at a concentration of 0.05%
a metal oxide-organic complex film is formed which confers properties of corro-sion resistance, aging resistance, hydrophilicity and lithographic properties superior to typical products of the prior art such as an aluminum plate conven-tionally anodized and then thermally sealed in a solution of polyvinyl phosphonic acid as :

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a second stepO
Curren~ carrying capacity increases rapidly with concentration, resul-ting in shorter process times and lower voltage requirements.
There appears to be li-ttle diference in the properties of products bet~een 1% and 5% while characteristic properties are still obtained at 30%, despite the high viscosity of the electrolyteO Purther, there is a decline in the rate of increase in film thickness at constant voltage with increase in concentration. Based upon considerations of ~roperties obtained~ processing ease, film thickness obtained, and cost of electrolyte, a preferred concentrati~n range lies between about 0~8% and about 5%.
There is a reasonably linear relationship between the weight of insol-uhle metal oxlde-organic complex film formed and the direct current vol*age employed. In tests with 1% polyvinyl phosphonic acid, at 10 volts ~DC), the film weight is about 40 mg~ At 110 volts, the film weight is about 860 mg. Figures are found wl~h an electrolysis period of 60 seconds. At all w ltages over about 5 volts, the electrodeposited ~llm that is formed confers corrosion resistance and llthographic properties superior to prior artO
As the voltage is raised to 70 volts ~DC)9 the stannous chloride test time increases apparently in response to the increase in film weight and thick-ness. Beyond 70 volts~ the stannous chloride test time decreases, a resultbelieved to be due to the loss in film integrity as the dielectric strength o the film is exceeded and it becomes perforated. This view is confirmed by transmission electron microscopy in which perforation is seen. Corrosion resis-tance is thus favored by operation under 70 volts.
Press tests are longer with plates electrolyzed at lower voltages. In a typical test comparing diazo coated plates electrol~zed at 109 20 and 40 volts 5~

respectively, the order of run length was inversely proportional to the electro-l~sis voltage and to the metal oxide-organic compl0x film thlckness. The elec-trodeposition treatment of this invention provides superior sealing of the metal substrate and bonding of the electrodeposited layer ko the light sensitive layer overall. The printing trial results show that lower voltages favor better bonding to the light sensitive layer, particularly diazo based layers, with the range from bet~een about 10 volts to about 30 volts preferred. Direct current is required for the process, althougll alternating current may be superimposed.
Square waves from pulse pla-ting sources are particularly useful.
Amperage is at a maximum at the beginning of electrodeposition and declines with time as the metal oxide-organic complex film builds upon the metal surface and reduces current carrying capacit~. Within 3~ seconds it has declined to a level at ~hich further current consu~ption becomes minimal~ This is a major ~actor in processing econom~, as a useful, desirable ~ilm has already been depa-sited.
Using as electroly~e a 1% solution o~ pQlyvillyl phosphonic acid depen-ding upon the impressed voltage and specimen geome~ry~ the amperage surged to about 10 amps~dm2 and then declined to about 120 milliamps/dm2. This decline to very lo~ current levels is characteristic ~f the process using the organic ~0 electrolytes o~ this invention. By contrast, in normal anodi~ing using strong electrol~tes above, the current drops slo~l~ and remains at levels around 10 to 15 amperes for the balance of the process.
A~perage is thus a dependent variable, with electrolyte identity, concentration and voltage the independent variables. Current densitles of from abou-t 1.3 amps/dm2 to abollt 4.3 amps/dm2 are characteristic of favorable process operating conditions and are preferred.

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The temperature at which the process is conducted may range from abou~-2C. ~near the freezing point of the electrolyte) to about 60C. Best r~sults based on tests of surface hardness, stannous chloride test times, image adhesion, hydrophilicit~, and aging charac~eristics are obtained a~ 10C. However, de-crease in performance from 10C to room ~emperature and even up to 40C is not very grea~D Operation at very low tempera~ures would require expensive cooling capacity. Accordingly, a temperature range between about :lOC and 35C is pre-ferred and an operating temperature of about 20C to about 25C is still further preferred because of operating economy and minimal loss of performance.
Over 60% of the metal oxide-organic complex film is produced within the first five seconds (0008 minu~es) of electrodeposition. Times be~ond five min-utes are not beneficial for lithographic uses since no further film is produced, but they are not harmful as long as voltage is low as discuss~d above. A time range of between about 0.16 minutes and about 1 minute is prefe~red.
From a process point of view, the short time, low temperature ~room temperature with little need for auxiliary heating or cooling) and low current consumption are all favorable economic factors compared to conventional anodizing followed by thermal substrate treatments characteristic of prior art processes.
Light sensitive compositions suitable for preparation of printing forms 2Q b~ coating upon the metal oxide-organic complex films of ~his invention include iminoquinone diazides, o-quinone diazides, and condensation products o aromatic diazonium compounds together with appropriate bindersO Such sensitizers are described in United States Patent Nos; 3,175,906; 3,046,118; 2,063,631; 2,667,415;
3,867,147 with the compositions in the last being in general preferred. Fur~her suitable are photopolymer systems based upon ethylenically unsaturated monomers with photoinitiators which may include matrix polymer binders. Also suitable are _16-s~

photodimerization systems such as polyvinyl cinnamates and those based upondiallyl phthalate prepolymers. Such systems are described in Uni~ed States Patent Nos= 3,497,356; 3~615,435; 3,926,643; 2,670,~86; 3,376jl38 and 3,376,139.
It is to be emphasized that the aforementioned specific light sensitive systems which may be employed in the present invention are conven-tional in the art. Although all compositions are useul~ the diazos are generally preferred as they tend to adhere best to the metal oxide-organic complex and to exhibit higher resolution in printing.
The physical appearance of the surfaces of electrodeposited coatings of organic electrolytes of this inven~ion has been examined by kransmission electron microscopy. When viewed at magnifications of at least 55,000X, a non-porous surface is seen. In contrast, conventionall~ anodized surfaces show typical pores at as little as 5,000 magnification. Accordingly, when the term "nonparous" is used herein, it is meant that pores are not visible at 55,000X
magnification using transmission electron microscopy.
Physical-chemical analysis by ESCA ~Electron Spectroscopy for Chemical Analysis) has been described above and shows that the electrolyte is tightly bonded with metal oxide to the surEace of the metal surface to form an insoluble metal~organic complex.
~0 ESCA results with phosphonic acid treated aluminum shows ~ ~ ~o~s/
aluminum ratios of 0~6-0~9:1 for ~hermal treatment versus 1.10 to 2.54:1, ~average=1.54) when electrolytically treated.
A third form o:E analysis uses the Auger techni~ue to de~ermine the thickness of the layer formed on the surface of the metal by electrochemical action. ~he thickness of layers of constant composition can be measured and compared for the different electrochemical processes. As ~he voltage used in each process is known, results can be stated in A/volt.

Typical barrier layers using boric and tartaric acids have thicknesses O O
of 13A-16A/volt and are nonporous.
Conventionally anodized aluminum using sulfuric acid or phosphoric acid have thicknesses of 100-150A/volt and are porous as determined by TEM.
Aluminum electrolyzed in a 1% solution of polyvinyl phosphonic acid (typical electrolyte of this invention) develops a coating of 50A/volt to 30A/
volt at 10 and 30 volts respectively, and is nonporous. It must be remembered that the coating develops very rapidly and does not increase in thickness with further increase in electrolysis time. Thus the products of this invention are nonporous, have coating thicknesses of 30 to 50A/volt and, at least when phos-phonic acids are used as electrolyte, additionally have high phosphor~us to aluminum ratios showing the incorporation of molecules or ions of the electrolyte together with metal oxide in the insoluble metal oxid0-organic complex of which the electrodeposited coating is composed.
In a process variant, the aqueous electrolyte additionally contains inorganic acid(s) from the group phosphoric acid, phosphorous acid or a mixture of phosphoric acid and sulfuric acid or phosphorous acid.
Alternative to the use of a single organic acid with a strong mineral acid, there may be employed a mixture of one or more such organic acids. As a further alternative there may be added another strong inorganic acid provided that a phosphorous oxo acid is always present. The characteristics of the variant are the initial surge in current during electrodeposition followed by a fall to a much lower level (to about 2 amps as shown in the examples), and a nonporous surface as shown by transmission electron microscopy. The benefits are an increased corrosion resistance as sho~n by the potassium zincate test, ,. ~".,i ':

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and/greatly improved ~ hydrophilicity/in appropriate tests described below, and comparable printing run lengths a-~ appreciably lower electrodeposited coating weights compared to eonventional anodi3ing.
Conventionally anodized products, in contrast, do not show the initial current surge as markedly, and ~he drop in current is less severe, levelling off at its steady state at a much higher level, typicall~ 10-15 amperes. Such anodic coatings have characteristic porosity and corrosion resistance and are not suf-ficiently hydrophilic until given supplementary treatments. By the addition of an effective or sufficient concentration of the above organic acids to phosphoric acid, or to a mlxture of phosphoric and sulfuric acids, the desirable character-istics may be obtained and recognize~ by the test procedurcs described herein.
Typically, although dependent upon the total composition, the addition of at least about 0.25% of organic acid produces the products of this invention if the inorganic acid is phosphoric although a minimum of 0.5% is preferable. In the case of ternary mixtures of phosphoric, sulfuric and organic acid, the addi-tion of at least about 0O5% of organic acid is desirable ~hile 1% is preferable to obtain nonporGus surfaces.
The concen~ration of the eleçtrolyte, the electrolysis conditions used, e.g. voltage, current density, time, temperature all play significan~ roles in determining the properties of the coa~ed metal.
The successlon of events ~ith ~ncreased time in a typical electrodepo-sition trial may be described. For example, an electrolyte composed of 100 g/l phosphoric acid with polyvinyl phosphonic acid at 1% concentration is used at a temperature of 20C at 10 volts ~.C~ with a cleaned and etched aluminum plate as the anode and a carbon rod as the cathodeO
The aluminum oxide-arganic complex which comprises the surface film forms very rapidly at first~
During this p0riod the voltage remains substan~ially constant.
The amperage is not a prime variable but is set by the other conditions selected, particularly -the voltage and electrolyte concentration. The amperage begins to decline very shortly after the beginning of electrolysis.
The boundary of conditions will therefore depend upon the process variables selected. Within this boundar~, readily tested by procedures disclosed, /,e, there ~s the most preferred conditions for the performance of the inventive process and the obtaining of the corresponding products. However, it should be remembered that within a much wider range of condi~ions ~hich are comparatively non~critical, ~here are obtained products all of which are improvements over the prior art.
Binary systems of phos~horic acid with organicacidsmay range in con-centration from about 10 g/l of H3P04 to about 2Q0 g/l of H3P04. A preferred range is from about 20 g/l of H3P0~ to 100 g/l. To this is added at least about 0,25% of organic acid and preferably a~ least about 0.5% ts secure the above described characteristics and benefits in the electrodeposited metal shee~.
In the case of ternary systems in which another strong inorganic acid such as sulfuric or phosphorous acid is added to phosphoric acid, such mixture may vary over the en~ire composition range. High H2S0~/H3P0~ ratios require more organic acid to ensure nonporosity, i.e., greater than about 1%; however, ~ery high H2S04/H3P04 may prevent formation of a nonporous film. ~ower H2S0~/
H3P04 ratios need onl~ about 0.5% of organic to achieve nonporosi~y. In any event, ~here is no harm in the use of a higher organic acid content.
Current carrying capacity increases rapidly with concentration, resul-ting in shorter process times and lower voltage requirements.

35~

There is a reasonably linear relationship between ~he weight of insol-uble metal oxide-organic complex film formed and the direct curren~ voltage employed. At all voltages over about 5 volts, the electrodeposited film that is formcd confers corrosion resistance and lithographic properties superior to prior art.
Direct current is required for the process, although alternating cur-rent may be superimposedO Square waves -~rom pulse plating sources are particu-larly usefulO
A~perage is a~ a max~mum at the beginning of electrodeposition and declines with tims as the metal oxide~organic complex film builds upon the metal surface and reduces current carrying capacity, ~ithin 30 seconds i~ has declined to a level at which further current consumption decreases. This is a major factor in processing economy, as a useful, desirable film has already been deposited.
Electrodep~sition voltages range from 5 VDC to 75 VDC and higher. High electrodeposited coating weights are more readily obtained in ~he presence of a strong inorganic acid; hence~ neither h~gh voltages, nor long treatment times are necessar~O To achieve the desired products of this invention, voltages from about 5 VDC to about 40 VDC for both binary systems and ternary systems are pre-~0 ferred.
Amperage is thus a dependent variableJ with electrolyte identity, concentration and voltage the independent variables. Current densities of from about 0.2 amperes/dm to about 6 amperes/dm2 are characteristic of favorable process operating condi-tions and are preferred.
The temperature at which the prccess is conducted may range from about W2C~ ~near the free~ing point of the electrolyte) to about 60C. Best results are based on tests of lithographlc properties. 0peration at very low tempera-tures ~ould require expensive cooling capacity. Accordingly, a temperature range between about 10C and 35C is preferred and an operating temperature of about 20C to about 25C is still further preferred because of operating economy and minimal loss of performance.
Aluminum electrolyzed in a solution of 100 g/l H3PO4 with a 1% poly-vinyl phosphonic acid ~typical elec*roly~e of this invention) develops a coating of 10~A/volt at 25 volts3 and is nonporousO It must be remembered that the coa~ing develops very rapidly. Thus the products of this invention are nonpor-ous, have coating thicknesses of about 10~A/~olt or more and at least when phos-phonic acids are used as co-electrolyte, additionally 20 have high p~ ~ to alumin~n ratios showing the incorporation of molecules of the electroi~te togeth-er with metal oxide in the insoluble metal oxide-organic complex of which the electrodeposited coating is composed.
~xample 1 Several sections of 3003 alloy aluminum (17.75 cm ~ 19.00 cm x .05 cm) were prepared for electrotreatment by degreasing both sides with Ridoline* 57, Amchem Products, an inhibited alkaline degreaserw ~ he degreased sectio~ of aluminum was then e*ched with a 1.0 N NaOH
solution a~ room ~emperature for 20 seconds.
After etchingg the aluminum plate was thoroughly water rinsed and immediately placed in an electrically insulated tank containing a 1.0% solution of polyvinyl phosphonic acid ~PVPA). On each side of the aluminum were placed lead electrodes with dimensions corresponding to the aluminum plate. The elec-trodes were equidistan~ from the aluminum with a gap of 10 cm.
*trademark s~

Using a D.C. output, t~e aluminum was made anodic and the lead elec-trodes were made cathodicO The temperature of the bath was main~ained at 25C.
The current was turned on ~ith the voltage preset to 60 VDC. The process was allowed to run for 30 secondsO ~he E~F was turned off~ the plate removed from the bath and rinsed well. The plate was then ~lotted dry.
Several drops of saturated solution of stannous chloride were placed upon the surface. The stannous chloride reacts ~ith the aluminum once it has migrated through the layer generated by the electrochemical process. Discrete black spots of ~etallic tin signal the end of the test.
The surface produced as described required 182 seconds for the SnC12 to *otally migrate through the electrodeposited surface film. The aluminum oxide -organic complex sur~ace film weight was 648 mg/M2 as determined by stripping with chromic acid/phosphoric acid solutionO ~Iydrophilicity o~ the surface was tested by applying a heavy rub-up ink without the benefit of any water. A dry applîcator pad was used.
The pla~e was perfectly clean when immediatel~ dry inked and water washed. Additional pieces of the plate were aged at room temperature for seven calendar days, at 50C for sev0n calendar days and at 1~0C for one hour. After aging, the plates were dry inked and rinsed. In all cases the plates rinsed ink-2Q free.
Finally, the plate was coated with a solution containing a pigment,polyvinyl formal binder and a dia~onium condensation product of United States 3,867,147. When exposed through a standard negative flat and developed with an aqueous alcohol developer, the ~ackground cleared easily leaving an in~ense image that under magnification was considered very good. It was not necessary to dampen the plate prior to inking to prevent scumming.
~23.

5~

Using a 21-s~ep Stouffer step wedge, exposure was made ~o give a solid six after development with an aqueous alcohol developer.
Examples 2 through 19 In like manner as described in Example 1, the electrolytes tabulated below were substituted for PVPA and subsequently processed. After preparation, in the manner described in Example 1, the metal oxide~organic complex film weight~
stannate test time and ink tes~ response were determined for each plate prepared.
The results are tabulated belowO
Time ~ilm (Secs.) Wt2 ~xample Acid SnCl2 mg/M Ink ~est 2 Poly benzene phosphonic acid 87 138 C
3 Gantrez AN 119 ~ AF Corp., ~low viscosity) 91 142 C
polyvinyl methyl ether maleic anhydride

4 Gantrez AN-139 ~ A~ ~or~., (med~um 73 127 C
viscosity) polyvinyl methyl ether maleic anhydride Gantrez AN-169 ~GAF Corp., (high 57 118 T
viscosity) polyvinyl methyl ether maleic anhydride 6 Gantrez AN-179 ~GAF Corp., (high 53 107 viscosity) polyvinyl methyl ether maleic anhydride 7 Gantrez S-95 ~GAF Corp. 102 149 C
(polyvinyl methyl ether maleic acid) 8 polyvinyl sulfonic acid 90 191 CT
9 polystyrene sulfonic acid 106 197 S
10 alginic acid 39 85 S
11 pol~-n-butyl benzene sulfonic acid 36 213 S
12 poly -diisopropyl benzene sulfonic ac.id 48 217 S
13 poly~diisopropyl naph~halene sulfonic acid 44 20~ S
~4-Time Film (Secs.)Wt 2 Example Acid SnC12 mg/M Ink Test polydecyl benzene sulfonic acid 61 220 S
16 polyacrylic acid 43 102 CT
17 polymethacrylic acid 37 93 T
19 polynaphthalene sulfonic acid 35 181 T
C = Rinsed totally clean, suitable for critical lithographic applications T = Slightly toned or peppered S = Scummed, unsuitable for litho CT= Intermediate between C and T
Comparison Example Cl A plate was prepared in like manner, as described in Example 1. In this case the electrolyte was phosphoric acid added to the extent of 75 g/l.
The voltage was dropped to 30 VDC because of the tremendous current flow that would occur at 60 VDC. The time was increased from 30 to 60 seconds. After, processing, the pla-te was rinsed and blotted dry~
The plate was found to have an oxide weight of 871 mg/M . The stan-nous chloride reaction time was 8 seconds. The result of dry in~ing the surface was a scummed plate. The application of a light sensitiva coating and subse-quent exposure, development and inking gave a scummed plate.
Comparison Example C2 A plate WQS prepared as described in Example Cl, excep-t that, after re-moval from the electrotrea-ting bath the plate was rinsed and immersed in a bath of 0.2% PVPA in tap water at a temperature of 150F for 30 secs. After

5~0 treatment, the plate was rinsed and blotted dry.
The plate ~ras found to have an oxide complex weight of 909 mg/M2. The stannous chloride reaction time was 10 seconds. Upon dry inking the plate, it was not possible to totally remove the ink. That which was removable required conslderable effort. Upon coating the substrate with a light sensitive solution,previousl~ described, and exposing, developing and inking, it was Eound that ~heplate was acceptable only if the background was dampened before inking.
Comparison Example C3 A plate was degreased and etched as described in Example 1. Instead rec7-hnc~>~
of e~ e~e~s~}Rg with PVPA, the etched plate was immersed in a bath of 0.2%
P~PA maintained at a temperature of 150~ ~6S.5C), ~thermally treated). It was allowed to remain immersed for 60 seconds, at which point it was removed, rinsedand blot~ed dry.
~he stannous chloride test gave an immediate reaction (<1 second).
5tripping the fllm gave a ~eight of 37 mg/M20 On a freshly made plate, dry ink wiped clean with relative ease. With aging as described in Example 1, it was found that this surface became increasingly difficult to wipe clean when inked.
~ithin the period of one week, the surface irreversibly scummed when ink tested.A light sensitive coating as described in ~nited States Patent No.
3,867,147, was applied to the plate, exposed, developed and inked. When wet inked, the background was acceptableO Dry inking resulted in a background that left some ink hanging after rinsing.
Comparison Example C4 A plate wa~ cleaned and etched as described in ~xample 1. It was immediately placed in an electrically insulated ba~h containing 150 g/l of H2S04(96%). The plate was made anodic and was processed with 18 VDC for 60 seconds.

The voltage was kept constantO The ~em~erature of the bath was maintained at 40C. The plate processed in this fashion was ~aken from the bath and well rinsed and blotted dry. The oxide complex ~eight was 3213 mg/~2.
The time necessary for the stannous chloride to react was only four seconds. Dry inking of a freshly prepared surface resulted in an irreversibly scummed plate. Aging was therefore not at~empted.
The plate was also coated ~ith negative light sensitive coating as in Example 1l exposed, developed and in~ed. Both wet inked and dry inked samples showed scummed backgrounds.
Comparison Example C5 A plate was prepared exactly as described in Comparison Example C4, except that, as an additional step~ the plate was thermally treated with a 0.2%
solution of PVPA at 150F ~65.5C) for 60 seconds. This step was conducted imme-diately after the plate was anodi~ed and rinsed. After thermal processing with PVPAJ the plate was well rinsed and blotted dry.
Using the stripping method described in Example 1~ the plate was found to ha~e a film weight of 3~67 mg/~ . The stannous chloride reaction time was low at 6 seconds. Dry lnking of a freshly produced plate permitted ink removal with reasonable ease. Under aging conditions described in Example 1, the ink would remain in spots after 24 hours. In 48 hours, the surface was unacceptable in that ink could not be removedO
Application of a negative light sensitive coating, as in Example 1, on a freshly produced surface permit~ed acceptable imaging and development. After, aging, as in Example 1, the background was found to invariably scum.
Com~arison Exam~le C6 A plate was cleaned and etched as described in Example 1. A tank was S~
charged with sodium silicate having a sodil~l oxide/silicon dioxide ratio of 2.5:1to a final concentration of 7O0% Cw/w)O The solution was heated to and main-tained at 180~ {82.2C?o The plate was next immersed into this solution for 60 seconds. After that time the plate was removed and thoroughly rinsed immediate-lyO After the water rinse, the pla~e was immersed into a 1.0% H3P04 ~85%) solution 30 at room temperature for 30 seconds. Upon removal, the plate was water rinsed and blotted dry.
The stannous chloride reaction time was 10 seconds. Wet and dry inking of the freshly prepared plate was acceptable in that all of the ink was easily removedO Plates aged at 5QC for one week and 100 C for one hour showed failure in the dry inking test. Plates freshly made and coated with a negative coating solutionJ as in Example 1, were acceptable after exposing, developing and inking the plate. When the plate was aged and then coa~ed, or coated and then aged, after 7 days at 50C and 4 weeks at room temperature, the background was unaccep-table, after dry inking.
Comparison Examp~le C7 A plate was prepared as described in Comparison Example C6, except that the silication was electrochemical instead of thermal. The plate in the hot sodium silicate solution was made anodic. A potential of 30 VPC was applied for 30 seconds and then water rinsed. An immersion into a 3.0% ~w/w) solution of H3PO4 (85%) immediately followed. Water rinsing was once more conduc~ed, with the plate then being blotted dry. This corresponds to the practice of United States 3~658J662O
The stannous chloride reaction time was increased to 46 seconds~ Dry inking of a freshly produced plate permitted easy removal of ink. Plates aged at room temperature lost hydrophilicity, shown as toning after eight weeks when 5~

applying the dry ink test. At 50C, the plates showed toning when dry inked after fifteen days aging.
Plates coated, developed and inked, as in Example 1, when fresh were acceptable as judged by the background. Plates coated with a negative solution of light sensitive material were considered to be lithographically non-usable at18 weeks at room temperature and 22 days at 50C.
~ ar ________mple C8 A plate ~as degreased and etched as in Example 1 The plate was then anodized in a solution of H3PQ~ ~85%) added in the amount of 75 g/l. The voltageused was 30 ~DC, applied for 60 seconds.
Immediately after anodizing~ the surface was well rinsed and silicated thermally as described in Comparison Example C6.
All testing gave essentially the same results as those obtained with the plate of Comparison Example C6 ~simple thermal sillcation). The stannous chloride test reaction time was 9 seconds. At 50C and 100C, the dry ink test sho~ed failure at seven da~s and one hour respectively. Coated plates failed after 3Q days at room temperature and seven days a~ 50C. ~he only benefit to anodizing prior to thermal silication was observed in an increased num~er of impressions in printing trials.
Com~arison Example C9 A plate was anodized according to the procedure of Comparison E~ample C4 and then elec~rochemically silicated in a 7.0% solu~ion of sodium silicate heated to 180~ ~82.2C). An EMF of 30 VDC was used for 60 seconds. This corresponds to ~he practices of United S~ates 3,902,976~
The stannous chloride reaction time was 55 seconds. Dry inking of a freshly produced plate gave a clean surface that r~nsed free quickly and easil~
_~

~,0 5:3 ~

Plates aged at room *emperature tc~ned when dry inked after ten weeks. At 50C
the plates toned at 19 daysO Plates freshly made were coated with a solution containing negative light sensitive material as in Example l. When aged at room temperature, the plates were rated as non-usable after 19 weeks and at 50C, loss of quality occurred at 22 daysO Again~ the benefit of post-treating an anodized plate by electrosilicating was not so much the improvement of hydrophilicity, as increasing the length of run. See Comparison Example C8.
Exam~les 20 to 23 ~ ixtures of organic electrolytes were made to a total concentration of 1.0%. The mixture ~as used as electroly~e. Electrolysis was conclucted at 30 VDC, for 30 seconds at room temperature on aluminum sheets previously degreased, slurry grained and etched, The compositions, aluminum oxide-organic film weights, stannous chloride reaction times and behavior in the dry inking test are shown in the follo~ing tableO In all cases corrosion resistance and hydrophilicity ~ere high.

-~q~

t, h ~

.
I~ o o~
~ ~ ~ ,1 o ~
a~
E~
_ _ . _.. _. ......... .... ... ~
a~ o ~ oo ~D ~ t` Ln ... . . .... ....... ._.. _ . ~ I
3 It~ Lt) In n r` N
~_ O O O O
o\ U~
~ . ... _. ~ ~

0 q~ ~ ~

h ,_~ ~ o ~C
O O .,1 ~
~ F~ ~ o rl ~1 ~ h t~
o ~.C ¢ ¢ ¢ .~
C~ .~ , p., ~i o ~ ~ ~. :7 h ~ ~ ~ D~ ~
___ =........ . S~
_ . ,,,.,.",,,...........
U~
o\_ O ~ o o ,~
___ ______ V~
~ .
rl ~1 0 O

h ;- o li~ p, t.) ~1 ~ ¢ 5~41 '~ O ~ ~ ~d O
Lq ~ ~ ~ ~ ~ O
o U~ o p~ o 4 ,~
... _ _ . . ._ .. _.. _ . . . .. _. __A' _ _.. __.. __ a) ;~
a~
-~ ~ R ~ ~

, 3 i~

5~13 Comparison Exam~
A section o 3003 aluminum was degreased as described in Example 1.
The surface was mechanically roughened b~ using the combined abrading action of a quartz slurry and rotating nylon brushes. After roughening, the aluminum was thoroughly washed to remove all ~uartz par~icles~ After water ~ashing and before the aluminwn could dry, it was immersed into a ~.2% ~w/w) solution of PVPA
heated to a temperature of 150~ ~505C~. Th0 time of treatment was 60 seconds after which th0 web was water ~ashed and dried.
The sample produced in the described manner was found to have a film ~e~ghing 37mg/~2 and a resistance to stannous chloride of 6 seconds.
On the freshly prepared plate, the dry ink test indicated a hydrophilic surface in that the ink could be removed with light rubbing. A plate aged at room temperature for seven days was partly scummed when dry inked and totally scummed after aging for ten days when dry inked~
~ hen the substrake ~as coated ~ith a light sensitive negative coating and aged ~ith the various times and t0mperatures as in Fxample 1, the background ~as unacceptable in that it was irreversibly scummed.
Ex~ e 24 A plate was procèssed as described in Comparison Example C10, exc0pt that the pla~e was electrochemically proc0ssed in a 1.0% ~w/w~ solution at room temp0rature using 30 VDC for 30 s0conds. Afker the current ceased flowing~ the plate was rinsed and blotted dr~.
The stannous chlorid0 reaction time was 122 seconds. A film weight of 395 mg/~2 was measured using the chromic acid/phosphoric acid procedure.
The dry inking test conducted as described in Exampl0 1 gave extremely good results in that no test failedO Coating with the negative coating solution :' :
' also described in Example 1, and subse~uently exposing~ developing and inkingprovided a plate having a totally clean hackground along ~ith a well attached image possessing high resolution.
Example 25 Substituting aluminum 11~0 alloy for the 3003 alloy, the procedure was repeated exactly as stated i.n Example 24. The results in terms of stannous chloride reaction ~ime, film weight9 dry ink test, aging and coating tests ~ere identical, There was an improvement ln all characteristics when compared to the control of Comparison Example C10.
Example ?6 and Comparison Example Cll A sec~ion of 3003 alumir~um alloy was degreased and dried. The sheet was then mechanically roughened, using a dry method which utilizes a rotating brush made of steel br;s~les ~wire brushing~. After the roughening, the sheet ~as etched to activate the surace, rinsed and immersed into an electrically isolated bath containing a 100% ~W/W) solution of PVPA. A potential of 30 VDC
was applied through the solution ~o the plate for 30 seconds. The plate was then rinsed and blotted dry.
: The electrically generated surface had a stannous chloride resistance time of 127 secondsO The weight of the electrically generated film was 415 mg/
M2.
Using the aging techniques for dry inking that are described in Example 1, the surface was shown to possess good hydrophilicity that was re-tained with time.
Coating with a light sensitive negative coating composition as de-scribed in ~xample 1, *he electrodeposition o PVPA on a wire ~rushed surface showed an improvement over the thermally t~eated control ~0.2% sol PVPA @ 150 F
~33-for 60 sec~) in tha~ the resolution, developer resistance and adhesion of the image ~as improved. Further, the background was considerably more hydrophilic than the control.
Exam~le 27 and C'omparison Exam~le C12 A degreased sheet of 1100 alloy aluminum was electrochemically grained and rinsed with water. It was immediately placed into a 0~1% PVPA solution and electrodeposited at room temperature with a potential of 30 VDC for 30 seconds.
After treatment, the plate was rlnsed and blotted dry.
The surface formed had a stannous chloride resistance time of 103 seconds and a weight of 396 mglM2. Pry inked, a freshly prepared plate rinsed free of inkO Using the aging test described in Example 1 for dry ink tests, the surface generated on an electrochemically grained substrate was satisfactory in all cases.
~urther~ the appllcatlon o a nega~ive light sensitive coating as in ~xample 1, was an improvement over an electrochemically grained substrate ther-mally reacted with PVPA. AdheslGn ~as better as well as resistance to developer. Ex mple ?8 and Comparison Example~C13 A section of aluminum alloy 11~0 was etched and electrochemically grained. The plate was subsequently rinsed and placed into a bath containing 150 g/l of H2S04 ~96%). By applying an electric potential of 18 VDC across the solution for 60 seconds, the aluminum b~ virtue of being anodic was electricallyoxldized. This plate was then rinsed ~ell with water and placed into a bath containing a 100% (W~W) solution of PVPAo At room te~perature~ a potential of 30 VDC was applied for 30 seconds. This surface was compared to a plate preparedin the same fashion except that a thermal PVPA ~0.2% @ 150F for 60 sec.) was administered rather than electrical~ The control had a film ~eight of 2876 mg/M2 ~3~-~L~9~
and a stannous chloride resistance time of 8 seconds. The test plate made with the electrotreatment of PVPA had a film weight of 2919 mg/~2 with the stannous chloride resistance time increased to 114 seconds.
The dry inking of both plates freshly prepared was acceptable. How-ever, the control plate displayed a loss of hydrophilici~y in a short period of time, (~4 days at R~T., 1 day at 50C and 30 min ~ 100C).
When coated, the PVPA electrically treated plate gave better image adhesion and developer resistance than did the control.
Examples 29 to 31 and Com~arison Example C14 Sheets of 1100 alloy, 3003 alloy and A-l9 alloy (manu~actured by Consolida~ed Aluminutn Co., St. Louis, M0) were hand grained in a wet fashion using quartz slurry and a nylon scrubbing brush. With a light-sectioning micro-scope, all three were found to have the satne average depth of grain (i.e., 2.25 0.2~). They were then processed with PVPA in accordance with Example 24.
The plates were then c~aked to the same coating weight with a negative coating solution described in Example lo They were subsequently exposed, deve-loped and flnishedO The plates were run to breakdown on a sheet-fed press.
Under abrasive conditions having a wear factor of 2.5, the A-19 plate ran 45,000 impressions b~fore image failure occurred. The 3003 plate ran 36,000 impressions ZO ~ith the 1100 alloy lasting 29,000 impressionsO
A control plate using 3003 alloy that was thermally treated with PVPA
as described in Comparison Example ClO,but otherwise processed the same as the above test plates, failed at 17,000 impressions.
Exam~es 32 to 35 and Comparison F:xamples C15 to C18 Several plates were made exactly as described in Example 24. These were to serve as the substrate for several coating solutions. Serving as a 5~
control were plates made as described in Comparison Example C10, in which PVPA
was thermally applied from solution.
Coating #l was a photo dimeri~able coating which was first described in United States Patent 2J670~286~
Coating ~2 was photo crosslinking non-diazo coating based upon the free radical initiation of polyfunctional acrylic resins. This composition was disclosed in United States Pa~ent 3~615,~35.
Coating #3 was a non-diazo containing photo polymerizable coating which was disclosed in United States Patent ~,161,588.
Coating #4 is a positive working ~photo solubilizable) coating based upon diazo naphthol sulfo esters. Such a coating is described in United States Patent 3~0~6,118.
Coatings ~tl, #2 and #3 are applied to control and test plates alike, and are exposed with a negative exposure flat using a conventional metal halogen exposure frame and an equal number of light integration units. The plates were developed using a prescribed processing solution detailed in the respective patent. All plates are then inked and comparedO
The images on the control plates all were less intense than the cor-responding image on the test plates with the step-wedge reading ~21-step Stou-ffer Scale) being two steps lower in all cases. The highlight areas on the control plate were lost; whereas on the electrodeposited plates~ all highlight areas were retained. Further, the control plates had toning in the background.
The P~PA electrotreated plates were all clean.
The positive coating referred to above was coated on both *est and control plates. Using a positive exposure 1at, exposure was made so as to give a knock-out 2 on the ~l~step Stou-ffer Scale after development wi~h a standard ~36-~3: ~5~

alkaline developer.
The control plate had a knock~out 2 ~ith 10 ghost steps. The electro-chemically PVPA treated plate had a knock-out 2 and 14 ghost steps. Further, the highlights were lost on th0 control and re~ained on the other.
Examples 36 to M and Comparison Fxamples Cl9 and C20 The procedure of Example 2~ was used, except that the concentration of polyvinyl phosphonic acid was 0.01% and the tests were conducted at room tempera-ture. Electrodeposition periods of 10, 60 and 300 seconds were used at each of 5, 30 and 90 VDC. S-tannous chloride tests were run and alumin~ oxide-organic complex surface film weights determined by the standard procedure. These data are recorded in Tahle lo Table 1 0.01% PVPA at R~To ... .. ._, _ . . .
Time 5 VDC 30 VDC 90 VDC

~Seconds) g/M ¦ SnC12 g/M SnC12 g/~ SnC12 ,- ~ ~ , __ 0.016 2 ~.0~1 ~ 0.027 6 . ... _ ~ . ___ ~ ~
0O02~ 3 0~023 5 ~.035 17 8 0.037 41 Each of the plates prepared according to the conditions given in Table 1 above were tested for hydrophilicity by dry inking and aging and then by dry lnking by procedure of Example 1, and compared with control plates prepared according to Comparlson ~xa~ples C3 and C5. In all cases the plates prepared according to these examples rinsed totall~ free v ink ~here the controls either did not rinse completely clean or required rubbing to free them of ink. Thus coatings of the kind produced by this invention, have superior hydrophilicity even when the coating weight is as low as oO16 g/M2 ~10 secs., 5 VDC~.

s~
A coating of .008 g/M2, produced at 5 V~C in one second, not shown in the above tabul~tion, had equall~ good hydrophllicit~ by the same ~est. For corrosion resistance the electrolyte concentration i~ somewhat low to produc~
good corrosion resistanceO
Exam~les 45 to 53 The procedure of Examples 36 to 44 was followed, except that the elec-trolyte concentration was raised to 001%. The results are shown in Table 2. It can be seen tha~ at either longer electrodeposition times or increased voltage, at this concentration, corrosion resistance is increased. As before in Examples 36 to 44, all coatings showed a high degree of hydrophilicity by the dry inking and aging tests when compared to the control plates, Comparison Examples Cl9 and Table 2 0.1% PVPA at R.T.
_ ~
Time 5 VDC 30 VUC 30 VDC

~Seconds~ ~ SnC12 g/M2 SnCl2 ~/M2 SnC12 ., _~_. _ 0.043~1 0~llO 12 O.lS7 24 0.05014 0.163 _ 18 0 .

300 0.05114 0.198 18 0.222 4 _ _ _ .~ ~___. . . . .. .. ._ ~xa ples 54 ~o 82 The procedure of Examples 36 to 44 was followed, except that ~he elec-trolyte concentra~ion was 1~0%o In addition, plates were electrotreated at 20, 40 and 80 seconds at 30 and 60 vol~s DoC~ These results are included ln Tahle 3 below in their logical places to show stannous chloride reaction time. Moreover, each o~ the pla~es prepared a~ 20, 4~0 and 80 seconds ~ere used as carriers for pr~ss tests. The procedure for plate prepara~ion and results are given in Table 3.

' 5~0 Table 3 1.0% PVPA a~ R.T.
.. .
Time 5 VDC 30 VDC 60 VDC 90 VDC
.
(Seconds) g/M2 SnC12 g/M2 SnC12 g/M2 SnC12 g/M2 SnC12 ... _ .... __ _ ~ _ . 0O043 7 0.2l7 26 0.398 73 0.5~7 t36 0.271 31 0.461 98 ~ ~ l 0.083 19 0.373 , 85 ~.592 120 0.782 165 0.38S , 103 0.620 134 . _ . . _ 0.088 21 0O396 122 0.648 148 0O861 173 . _. _ 0.~14, ,, 125 0.654 164 -- _ _ .,_ _. ___ 0~093 20 0.431 ,12~-0.661 180 0.873 190 . _ ___ ..
~.430 ,129, 0.694 208 _ , ~.. ~ ~ ........ ~
120 0.430 13~ 0O72~ 237 . ~ _ 300 . ~ 0.431 _ . 0O758 191 0.902 213 As before, as in Examples 36 to 44, all plates sho~n in Table 3, were highly hydrophilic in dry inking and aging tests.
~xa~ples 83'to 91 The procedure of Bxamples 36 ~o 44 ~as used except that the electrolyte c~ncen~ration was 5.0%. The results are recorded in Table 4.
Table 4 5.0% PYPA at R.T.

. ,'Time,, 5 VDC 30 y~c ~0 YVC
. .. ~ .. . ., _~, .. ..
. (SecQnds~g/~ SnC12 g/M4 ~ SnC12 0 04 124 21 0.417- :''' 1~1 0.779 4-12 ' _ , _ _ .
60 0.288 44 0O545 ' :: 315 0.936 ?ol ~ ~ ~ . . _ 300 0.389 63 00 690 '313 1.069 7~7, ~ . . . _ ~11 plates shown in Table 4 were highly hydrophilic in dry inking and aging -39.

~ests~

~ ___to 100 The procedure of Examples 36 to 44 was followed, except that the elec-trolyte concentration was 10,0%. The results are recorded in Table 5.

Table 5 10% PVPA at R.T.

Time 5 VDC30 VDC 90 VDC
_ ~ ~ .
~Seconds) g/M SnC12 . SnC12 g/M SnC12 0O156 13 0O431 81 0O~3~ 166 _ . _, 0~ 299 23 0~558 118 1 ~ 012 Z56 300 ~:). 417 27 OJ 701 11~ 1 ~ 046 244 All plates shown in Table 5 ~ere highly hyd~ophilic in dry inXing and aging tests A

Exa~les lQl ~o 10~
The procedure of Examples 36 to 44 was followed9 except that the elec-trolyte concentration was 30~0%O The results are given in Table 6.

'rable 6 30% PVPA at R.T.
-.. _................... _ _ _. .
Time 5 VDC. . 30 ~PC 90 VPC
~2 ~ ---2- - 2 ~Seconds) _ _ _ SnCl~ ~ g/M SnCl2 g/M SnC12 . . _ _ _ _ O A 162 0.4 2 9 9 3 0.853 158 0.311 19 0.56~ 117 1 ~ 041 246 300 0O381 19 0. 727 118 1 ~ 087 ~37 .~ _ _ . ~
All plates shown in Table 6 were highly hydrophilic in dry inking and aging tests.

~Or .

6~ 1 s~

~xamples 110 to 120 The procedure of Examples 36 to 44 ~1.0% PVPA~ was followedJ except that ~he temperature ~as 10C. The results are sho~n in Table 7.
Table 7 1.0% P~PA at 10C
_ ................ _ .
Time 5 VDC 30 VDC 90 VDC
, _ ~ i _ Seconds) g/M I SnC12 g/M2 SnC12 g/M2 SnCl~
~ _ _ ~_ ,_ . ._ 1 0.222 ~2 ... _ ~ . ~ ~ ~ __ _ 0.282 66 . . _ __~ ,~
0O0~4 47 0.368 98 0.8~2 197 ~ _ _ _. .
0O093 66 0.453 137 0.901 263 . _. _ _ ~ _ 300 OOO99 77 0.469 132 0.943 253 ; All plates shown in Table 7 were highly hydrophilic in dry inking and aging tests.
Ex~_ples 121 to 131 The procedure of Examples 36 to 44 was followed except that ~he tem-perature was held at 40Co Table 8 1.0% PVPA at 40C
~ , _ _ Time 5 VDC 30 YDC 90 VOC
_ _ 2 - - 2 (Seconds~ g/M2 SnCl~ g/M SnCl2 g/~ SnCl~
_ . _ ~
1 _ 0.187_ ~ _ ~ _ _ 0.201 17 __ 0.079 13 0O311 36 0.742 95 , ~ _ _ _ _ , OOO90 13 0. 417 59 Oo 857 171 _ _ _ __ __ : 300 0.09~ 13 O450 54 0.867 198 All plates shown in Table 8 were highly hydrophilic in dry inking and aging ~ests.

Printing trials were conduc-ted on some of the plates prepared in the previous examplesO In all cases a Solna sheet fed press was used with a Dahlgren ountain solution at pl-l 3.9-4Ø Plates were overpacked 0.004 inches and printed with an abrasive ink which increased the normal wear ra~e by a factor of 2.4.
The paper l~as Mead White Offset Moistrite~ Bond (20 lb.~.
In the following table, ~he numbers indicate when dct sharpening and step~wedge rollback begins and not when the plate becomes unusable.

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., .. . .

5~

The controls are Comparison Examples C21 to C23, and are all commer-cially successful plates. The inventive plates outran the best control plates in seven cases in resistance to dot sharpening and in four cases in step-wedge rollback. The inventive plates outran the int~rmediate control plate in nine cases in resistance to dot sharpening and in seven cases in step-wedge rollback.
The inventive plates outran *he poorest plate in 12 cases in resistance to dot sharpening and in 12 cases in step-wedge rollback.
Exam~le 144 An anodic film was grown in 1% Gantre ~ S-95 resin solution by a pro-cedure similar to that of Example 1, TE~ examination of the isolated aluminumoxide-organic film at 55,000X magnification showed a smooth surface with no visible porosityO
am~le l~S and Co~arisan Example C24 18.3 cm x 1708 cm x ,03 cm samples of 3003 aluminum alloy were pre-pared for electrotreatment by degreasing with Ridoline* 57 ~supplied by Amchem Products), an inhibited alkaline degreaser.
The degreased samples were -then etched with about 1.0 N NaOH for 10-15 seconds, After etchingl a sample was water washed and dried with a jet of air.
The sample was clamped to a conducting bar and suspended between ~wo lead plates at about 20 cm from these plates in an insulated tank. ~he tank contained about 8 liters of a solution of 50 g/l H2SO~; 50 g/l H3PO~ and 0.5% polyvinyl phos-phonic acid ~PVPA~o Using a D.C. output, the aluminum was made anodic and the lead elec-trodes were made cathodicO The temperature of the bath was ambient but remained at 22C ~ 2C for the test. The current l~as turned on ~ith the voltage preset *trademark ~4 to lO V~C, The electrotreatn1ent ~as run for 60 seconds. Initial amperage rose to 5 ampsO, ~t dropped to a 1-2 a~psO level very rapldly, and ~emained at that level for the duration of the trea~mentO ~he contact ~as broken, the plate was rem~ved from the bath and was rinsed ~i~h wa~er and finally blo~ted dry.
The aluminum oxide-organic complex .surface film weight was lO8 mg/m as de~ermined by gravimetry ~efore and after stripplng with a chromic acid/phosphor-ic acid solution. Hydrophilicity of the surface wa~ ~ested b~ applying a heavy rub-up ink without the benefi~ of ~ater using a dry applica~or pad.
The plate ~as considerably~cleaner than conventionally prepared plates when immedia~ely dry inked and water washed.
Several drops of potassiu~ zincate solution ~vide supra) were placed on the surface. The zinc ions are reduced to zinc metal at the aluminum oxide-organic film/metal interface thus giving a vlvid dark spo~ signifying the end ofthe testO
The surface produced in this example required 35-40 seconds to the end point. By contrast, standard anodiæed~ thermall~ treated ~PVPA) plates took 25-30 seconds.
Finally, the plate ~as coated with a solution con~aining a pigment, polyvinyl formal binder and a diazonium condensation product of United States 3,867,l47. When exposed through a standard negative flat and developed with an aqueous alcohol developer, the background cleaned out easily leaving a vivid lmage in ~he exposed areasO
Using a 21-step Stouffer stepwedge, exposure was made to give a solid six after development with an aqueous alcohol developer.
Transmission electron microscopic ~TEM) examination of the isolated aluminum oxide-organic film at 55,000X magnifica~ion showed a smooth surface s~

~ithout porosity~O
r~
A plate was prepared in like manner, as described in Example 145, except that the electroly~e was pho~phoric acid at 75 g/l. At 30 VDC for 60 secands a plate having an oxlde weigh~ of 871 mg/m2 was obtained. The potassium ~incate end point was about 2 minu~es and ~he result of dry lnking was a severely scummed plate. The application of a light sensitive coating and subsequent ~xpusure resulted iJI a scummed plate upon inking after development in an aqueous alcohol developer. This is a prior art procedure.
Comparison Examp e C26 A plate was prepared as described in Comparison Example C25. After removal from the anodizing bath the plate was rinsed and immersed in a bath of 0.2% PVPA (no strong inorganic acid) in tap water at a temperature of 150F for 30 seconds. After this treatment, the pla~e was rinsed and blotted dry.
The plate was found to have an oxide weight of 909 mg/m2. The p~tassium zincate end point was about 2 minutes. Upon dry inking ~he plate, the ink was ~ery difficult to remove wit~ some areas remaining scummedn Upon coating the substrate with a light sensitive solution, previously describedJ and exposing, de~eloping and inking, it was found that the plate was acceptable only with ~20 adequate dampening before inking. This is a prior art procedure.
~x~le ~46 A plate was degreased and e~ched as described in ~xample 145. The e~ched plate was immersed in a bath o~ 63 g/l ll2S04; 37g/1 H3P04 and 1% PVpA.
Electrotreatmen~ for 30 seconds at 15 V. ~10 amps. initially dropped to 1-2 amps.
within 5 seconds) resulted in an aluminum oxide~organic film weight of about 500 mg/m2. The potassium zincate time ~as 42 seconds and the drr inked sample :, ~3~5~C3 c~uld be reasonably~cleaned ~ith a wet ap~licat~r ~ad. Coated samples could bedeveloped cleanly ~ith aqueous alcohol developer.
TE~ examination of ~he isolated alumino oxide-organic film sho~ed a smooth, seemingly pore free, surfaceO
Exa~ple 147 A plate was degreased a~d ekched as described in ~xample 145. The e~ched plate ~as i~ersed in a ba~h o 23 g/l H~P04 and 0.25~ PVPA. Electro-tr~atment for 60 seconds at 30 vqlts ~.C. resulted in an aluminum oxide-organic film weight of 198 mg/m2. TE~ analysis of the isolated aluminum oxide-organic film at 55,000X magnification showed essentially a structurelcss su~face with some discontinuities. This surface was not tested functionally because of the discontinui~ies notedO
~ 148 A plate was degreased and etched as described in Example 145. The sample was electrotreated in a bath of ~3 g/l H3P0~ and 0.6% PVPA. The s~mple was treated at 20 VDC for 60 seconds to deposit 101 mg/m2 of an aluminwn oxide-organic film.
A potassium zincate time of 2S0 ~eco~ds was recorded for this sample.
After dry inking the plate could be cleaned fairly readily with a damp applica~or 2Q pad~ and coated samples could be readily developed with aqueous alcohol developer after exposure through a negativeO
TEM examination of the isolated film at 553000X magnification sho~ed a smoothJ uniform surface, free of apparent porosity~
Example 149 A plate was degreased and etched as described in Exan~ple 145 The sample was electrotreated in a ba~h of 7S g/l H2SO~;25 g/l H3PO~ and 0.5% PVPA

5~

at 15 VDC for 60 seconds to gi~e an alumlnum oxide~organic fllm weight of about 50~ mg~m2. The po~asslum zincate end point was 30-35 seconds. A dry inked plate cQuld ~c relat~vel~ cleaned by vigorous rubbing wlth a ~et cotton applicator pad.
Exposed and aqueous alcohol developed coated pla~es were fairly clean and scum ~ree, hut storage stabilit~ was limited.
TE~ analysis at 55,000X magnificatl~n showed incipient porosity.

The sample was prepared and electrotreated as described in Example 145, except that the electrotr0atment was run at 25 VDC for 60 seconds (amperage started at 25 ampsO and rapidly dropped to about 2 amps. for duration of treat-ment)O The aluminum oxide-organic film weight was 522 mg/m2, The plate was comparable lithographically to that obtained in Example 145.
~ tSl A sample was prepared and electrotreated as in Example 150, excep*
that the treatment time was 120 seconds. The aluminum oxide-organic film weight ~as 1085 mg/m2. The plate obtained was lithographically comparable to that obtained ln Example 145.
Exampl_ 152 A plate was degreased and etched as described in Example 145. The plate was elec~rotreated at 16 V for 60 seconds in a bath o~ 100 g/l H3PO4 and 1% PVPA to give 113 mg/m2 of aluminum oxide-organic film. 99 seconds was required to reach the potassium zlncate end point.
After dry inking, the plate could be cleaned very easily by rinsing with water and lightly wiping with cotton applicator pad. A plate coated with a diazonium coating described in Example 145 could be developed cleanly and efficiently af~er exposure with aqueous alcohol developer.
-48~

3~

;ex~
A plate was prepared as in ~xample 146, except that the eleckrotreat-ment v~lkage ~as 50 VDC. The resultlng plate wa5 comparable lithographlcally to that of Example 1460 ~ plate was prepared as in ~xample 146, except that the electrotreat-menk temperature ~as 40Co The resul~ing plate was comparable likhographlcally to that of Example 146.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for anodically oxidizing materials in the form of sheets, foils or strips, comprising aluminum or aluminum alloys, in an aqueous electro-lyte which contains at least 0.05% by weight of at least one polybasic organic acid, in which the polybasic organic acid is polymeric and is selected from the group consisting of phosphonic acid, sulfonic acid and carboxylic acid.

2. A process according to claim 1, in which the aqueous electrolyte con-tains from 0.05 to 30% by weight of the polybasic acid(s).

3. A process according to claim 1, in which the aqueous electrolyte con-tains at least 0.5% by weight of the polybasic acid(s).

4. A process according to claim 1, or 2, or 3, in which prior to oxidiz-ing, the material to be oxidized is roughened mechanically, chemically, or electrochemically.

5. A process according to claim 1, in which the aqueous electrolyte additionally contains inorganic acid(s) from the group consisting of phosphoric acid, phosphorous acid and a mixture of phosphoric acid with sulfuric acid or phosphorous acid.

6. A process according to claim 5, in which the aqueous electrolyte con-tains from 10 to 200 g/l of said inorganic acid(s).

7. A process according to claim 1, or 2, or 3, in which an anodic oxida-tion in an electrolyte comprising an aqueous sulfuric acid solution is addition-ally carried out, before the anodic oxidation in the electrolyte comprising a polybasic polymeric organic acid.

8. A process according to claim 1, or 2, or 3, in which anodic oxidation is carried out at a voltage from 1 to 30 volts, a current density from 1 to 5 A/dm2, for a period of time from 0.08 to 5 minutes and at a temperature from -2°C
to 60°C.

9. A process according to claim 1, or 2, or 3, in which anodic oxidation is carried out at a voltage of at least 5 volts, a current density from 1.3 to 4.3 A/dm2, during a period of time from 0.16 to 1 minute and at a temperature from 10°C to 35°C.

10. A process according to claim S or claim 6, in which anodic oxidation is carried out at a voltage from 5 to 40 volts, a current density from 0.2 to 6 Adm2, during a period of time from 0.08 to 5 minutes and at a temperature from -2°C to 60°C.

11. A process according to claim 1, or 2, or 3, in which at least one of the polybasic polymeric organic acids is a phosphonic acid.

12. A process according to claim 1, or 2, or 3, in which the polybasic polymeric organic acid(s) used is/are polybenzene phosphonic acid, hydrolyzed copolymers of methylvinyl ether and maleic anhydride, copolymers of methylvinyl ether and maleic acid, polyvinyl sulfonic acid, polystyrene sulfonic acid, alginic acid, polyvinyl phosphonic acid, poly-diisopropyl naphthalene disulfonic acid, polydecyl benzene sulfonic acid, polyacrylic acid, polymethacrylic acid, polynaphthalene sulfonic acid or a mixture comprising at least two of said organic acids.

13. A process according to claim 1, or 2, or 3, in which at least one of said polybasic polymeric organic acids is polyvinyl phosphonic acid.

14. A support material in the production of printing plates carrying a light-sensitive layer comprising an aluminum sheet, foil or strip which has been anodically oxidized in accordance with the process of claim 1, or 2, or 3.