CA1190509A - Anodizing aluminium support for printing plates with organic acid - 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 aqeuous electrolyte which contains at least 0.05% by weight of at least one acid, if appropriate after a foregoing mechanical, chemical and/or electro-chemical roughening, in which, the said acid or acidic ester is selected from the group conisting of phytic acid, nitrilo triacetic acid, phosphoric acid mono(dodecyloxypolyoxyethlene) 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, hydroxyethyl ethylene diamine triacetic acid or a mixture of at least two of said acids is used. The resulting anodized and sealed metal sheets have good corrosion resistance and are especially suitable for lithography. Lithographic plates made in accordance with this invention exhibit improved adhesion for light sensitive coatings, improved run length, lessened wear on the press, greater shelf life and improved hydrophilicity in non-image areas.

Description

This invention relates to simultaneous anodizing and sealing the surface of metal sheets with novel electrolytes and the products thereby ob-tained. The resulting anodized and sealed metal sheets have improved corrosion resistance and are suitable, among other uses, for architectural applications.
They are especially useful as supports in lithography, particularly if aluminum or its alloys are selected, such sheets exhibit improved adhesion for light sensitive coatings, improved run length, and lessened wear on the press both 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 electrolyte. When electric curren-t is passed, the sur-face of the metal is converted to a form of its oxide having decorative, pro-tective or other properties. The cathode 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 coating. This coating progresses from the solution side, ou~ward from the metal, so the last-formed 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 anodizing electrolyte has little capacity for dissolving the oxide. These coatings are essentially non-porous; their thickness is limiked to about 13A/volt applied. Once this limit-ing thickness is reachedg it is an effective barrier to further ionic or elec-tron flow. The current drops to a low leakage value and oxide formation stops.
Boric acid and tartaric acid are used as electrolytes for this process.

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~ Vhen the electrolyte has appreciable solvent action on the oxide, the barrier layer does not reach its limiting thickness: current 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 interface.
ELectron microscope s~udies show the presence of billions of close-packed cells of amorphous oxide through the 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 sur-face layers.
Anodizing for decorative, 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 3~227,639 uses a mixture of sulfophthalic and sulfuric acids to produce protective and decorative anodic coatings on aluminum. Other aromatic sulfonic acids are used with sulfuric acid in United States 3~804,731.
As a post-treatment after anodization, the porous surface is sealed according to numerous processes to determine the final properties of the coat-ing. Pure water at high temperature may be used. It is believed that someoxide is dissolved and reprecipitated as a voluminous hydroxide (or hydrated oxide) inside the pores. Other aqueous sealants contain metal salts whose oxides may be coprecipitated with the aluminum oxide.
United States 3,900,370 employs a sealant composition of calcium ions, a water-soluble phosphonic acid which complexes with a divalent metal to protect anodized aluminum or anodized aluminum alloys against corrosion. Polyacryl-amide has been proposed as a sealant.

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United States 3,915,811 adds an organic acid ~acetic acid, hydroxy acetic acid, or amino acetic acid) to a mixture of sulfuric and phosphoric acids to form the electrolyte in preparation for electroplating the so-formed anodic aluminum coating.
United States ~,115,211 anodizes aluminum by A.C. or superimposed A.C. and DoC~ wherein the electrolyte solution contains a water-soluble acid and a water-soluble salt of a heavy metal. The water-soluble acid may be oxalic, tartaric, citric, malonic, sulfuric, phosphoric, sulfamic or boric.
United States 3,988,217 employs an electrolyte containing quarternary ammonium salts, or aliphatic amines and a water-soluble thermosetting resin to anodize aluminum for protec~ive, ornamental or corrosion resistant applications.
The advantages of anodized aluminum as a carrier for lithographic printing plates were early recognized. Processes employing as electrolytes sulfuric acid, phosphoric acid, mixtures of these or either of these in suc-cession have been proposed. Prior to anodizing the sheet may be roughened mechanically or chemically. The need for a subcoating prior to application a photosensitive layer to impart adhesion to the coating and hydrophilicity to the non-image areas was recognized. United States 3,181,461 uses an aqueous alkaline silicate treatment following the anodization step.
United States 2,594,289 teaches ~Col. 1, lines 42 - 54) that porous anodic films but not nonporous anodic films are suitable for lithographic pur-poses, "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 ef-fectively to the surface by penetrating the pores."
United States 3,511,661, since disclaimed, describes aluminum sheet for a lithographic printing surface anodized in aqueous phosphoric acid having an anodic film with a cellular pattern of aluminum oxide having cells with o o porous openings of about 200A to 700A in average diameter and a surface with 10 to 200 mg per square meter of aluminum phosphate.
United States 3,658,662 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 sultable as a support for a presensitized lithographic sheet.
United Sta~es 4,022,670 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 sulfophthalic acid to produce a porous anodic oxide surface to which a photosensitive layer may be directly applied.
There is described in United States 4,090,8~0, a two-step process whereby a cleaned aluminum sheet is first coated with an interlayer material such as alkali silicate, Group IV-B metal ~luorides, polyacrylic acid, or alkali zir-conium fluoride and then anodized conventionally in aqueous sulfuric acid. En-hanced 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 95G after conventional anodizing to a khickness of at least 0.2u. The treatment provides good adhesion of ~ subse-quently applied light sensitive layer, good shelf life and good hydrophilization of ~ non-image areas after exposure and development as well as long press runs.
Plates of the above construction, particularly when the light sensitive layer is a diazo compound have enjoyed considerable commercial success. Never-theless, 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 process that would be more economical than conventional anodizing followed by a second opera-tion of sealing or post-treating in preparation for coating with a light sensitive layer.
In the case of protective and decorative applications, improved corrosion resistance and production economy over known anodizing processes is desired.
The invention is based on a process for anodically oxidizing mater-ials in the form of sheets, foils or strips, comprising aluminum or aluminum alloys having less than 1% by weight of copper, in an aqueous electrolyte which contains at least 0.05% by weight of at least one acid or acidic ester, if appropriate after a preceding mechanical, chemical and/or electrochemical roughening; the process of the invention being characterized in that the said acid or acidic ester is selected from the group consisting of phytic acid, nitrilo triacetic acid, phosphoric acid mono(dodecyloxy-polyoxyethylene)ester, tridecyl benzene sulfonic acid, dinitro-stilbene disulfonic acid, dodecyl naphthalene disulfonic acid, dinonyl napthalene disulfonic acid, di-n-butyl naphthalene disulfonic acid, ethylene diamine tetraacetic acid, hydroxyethyl ethylene diamine triacetic acid.
Transmission electron microscopy ('IEM) of at least 55,000 times mag-nification of aluminum oxide films obtained according to the invention, whereas conventionally anodized aluminum shows typical porosity at as little as 5,000 times magnification.
Copending Canadian patent appli.cation, serial No. 386,628, filed on even date herewith, discloses and claims a process for anodically oxidizing materials in the -Eorm of sheets, foils or strips, comprising aluminum or alum~
inum alloys, in an aqueous electrolyte which contains at least one poly'oasic organic acid, if appropriate after a foregoing mechanical, chemical and/or electro-- 5a -5~
chemical roughenillg, in ~hich the polybasic acid has at least five acid func-tions and is selected from the group consisting of phosphonic acid, sulfonic acid and carboxylic acid. Additional to the acids or acidic esters of the pre-sent invention, the aqueous electrolyte may contain at least one of the poly-basic organic acids of said copending application.
The metal substrates to be subjected to electrochemical treatment according to the invention are first cleaned. Cleaning may be accomplished by a wide range of solvent or aqueous alkaline treatments appropriate to the metal and to the final end-purpose.
Typical alkaline degreasing treatments include: hot aqueous solutions containing alkalis such as sodium hydroxide, potassium hydroxide, trisodium phosphate, sodium silicate, aqueous alkaline and surface active agents. A pro-prietary composition of this type is Ridolene* 57, manufactured by Amchem Products, Pennsylvania. Currently less popular because of environmental and health considerations, is solvent degreasing, using trichloroethylene, 1,1,1-trichloroethane, and perchloroethylene. Solvent degreasing is accomplished by immersion, spray or vapor washing. Aluminum alloy 1100, 3003 and A-l9, products of Consolidated Aluminum Company among others, may be used for lithographic pur-poses and are preferred. Typical analyses of these three lithographic alloys will now be shown on a weight percent basis:
Alloy _ Mg Mn Fe Si Cu_ 1100 99.2 - - .375 .375 .05 3003 99.0 - .7 .15 .2 .05 A-19 98.3 .9 - .375 .375 .05 It is surmised that the specific chemical composition of the alloy may have an influence upon the effectiveness of electrodeposition of organic elec-trolytes. Further other components not usually analyzed may also have an influ-ence.

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The metal surface may be smooth or roughened. Conventional surfaceroughening 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. T}le surface roughness and topo-graphy varies with each of these processes. For best results according to the practice of this invention, the clean surface should be electrotreated immedi-ately before the formation of an aerial oxide. The term "aerial oxide" refers to the build-up of oxidized areas on the plate surface 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 produced, for example, by oxidizing anodically. Prior to immersion of a previously cleaned, degreased and optionally roughened plate in the organic electrolyte solution for electrodeposition, the plate should be etched to remove aerial oxide which, as is stated above, usually grows during the storage period of the plate materials in the 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 for removal of said aerial oxide is stripping the plate with a standard etchant such as phosphoric acid/chromic acid solution. Thus immediately after cleaning, roughening ~if this step is desired) and etching it is preferable that the metal surface be rinsed with water and electrotreated while still wet, although useful produc~s may be obtained if this precaution is not rigidly adhered to.
After cleaning and after roughening, if desired, the metal may be optionally anodized conventionally prior to electrodeposition of the organic electrolyte of this invention.

The concentration of the electrolyte, the elec-trolysis 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 o-f which the electro-deposited film is composed may be measured by the potassium zincate test for anodized substrates. This test is described in United States 3.9~0,321. A
solution of potassium zincate (ZnO 6.9%, KOH 50.05%, 1l2O ~3.1%) 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. l.O g/M will take about two minutes to react. Zincate tests show that electro-treated plates using polyvinyl phosphonic acid in the aqueous electrolyte, consistently take substantially longer to react, unless, for example, very low values of concen-tration 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 minute, the products o:E this invention produce more difficulty in recogniz-ing end points, particularly as the reaction time increases. The stannous chloride test described below, not only is more rapid, but produces a more easily recognized end point, particularly when observations are conducted under a magnifying lens. Nevertheless, with both reagents, the longer reaction times require some experience or correct interpretation.
United States 3,902,976 describes the use of a stannous chloride solution for the same purpose. The end point is a visible hydrogen evolution, followed by a black spot formation. Representative samples tested with zincate and with stannous chloride show the latter to be about ~ times faster. Conven-tionally anodized aluminum using sulfuric acid and/or phosphoric acid as elec-trolyte has been used for architectural applications because of superior resis-tance to weathering. Typical stannous chloride tests for such materials are about 4 to 10 seconds, while for the aluminum sheets of this invention such times are about 15 seconds for a 0.1% solution to more than 200 seconds for a 5% solution. The zincate and stannous chloride tests are believed to corre-late with corrosion resistance, a key property in protective and decorative metal applications.

- 8a -The metal oxide-organic complex film weight is determined quantitative-ly by stripping with a standard chromic acid/phosphoric acid bath ~1.95% CrO3, 3.~1% H3PO~ 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 which is therefore insoluble in reagents of equal or lower aggressiveness.
For lithographic applications, plates are tested af~er electrodeposi-tion of the metal oxide-organic complex and before coating with a light sensitive layer. The plate is wet or dry inked, the latter 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 of the surface.
Typically, plates prepared in accordance with the invention, when dry 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 subjec~ed to a thermal immersion in an aqueous solution of polyvinyl phosphonic acid are irreversibly scummed when aged even under less severe conditions.
Using the inking tests, plates, both with and wi-thout photosensitive coatings, were aged at various times and temperatures and checked for retention of hydrophilic properties. Plates coated with various diazo coatings were checked by aging for stepwedge consistency, resolution, retention of background hydrophilicity, and ease of development. Suitable light sensitive materials will be discussed below.
Finally, for lithographic applications, plates including controls, are run on press. Differences in topwear, dot sharpening, stepwedge rollback, speed 5~

and cleanliness of roll-up, and length of run are observed. In general, in all cases, plates electrodeposited within an extensive range of concentration, t;me, temperature, voltage, and current density were superior to prior art plates wi~h little criticality in the variables being shown. However, within the confines of the invention, certain variables proved more important than others and cer-tain parameters of those variables were more critical in obtaining best results.
This is discussed in more detail below.
The amperage is not a prime variable but is set by the other condi--t;ons 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 anodi~ation, in which the maximum film thickness is 13 - lGA/volt as found by typical surface analytical technique [i.e., Auger analysis) coupled with ion sputtering.
The 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 ~incate test) which remains con-stant for an electrodeposition time up to 250 seconds, above which there is a small fall-off in stannous chloride reaction time.
At higher voltages, the weight gain is higher. However, the stannous chloride test time, which initially parallels the weight gain rise, falls off much sooner. The explanation is found from transmission electron microscope examination. Whereas the surface is nonporous and featureless even up to about 55,000X magnification for treatment times up to the decline in the stannous chloride test reaction time, thereabove it is marked by pits that could be dueto : - 10 -..,~

arcing. Ink samples confirm this appearance.
It is believed, based upon experimcnts 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 strengt}l is not exceeded during elec-trolysis, there is no further weight gain with time, the film is unbroken and the stannous chloride test time remains constant. ~len the dielectric strength is exceeded, perforation of the film takes place with loss of film integrity.
The stannous chloride test time corresponds to this perforation. Although the picture is believed to represent the situation, it is only a speculation and the validi.ty of the invention does not rest UpOII it. The aforementioned breakdown is primarily a function of voltage with 70 volts 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. However~ it should be remembered that within a much wider range of conditions which are com-paratively non-critical, there are obtained products all of wllicll are improve-ments over the prior art.
The concentration of electrolyte that may be used ranges from about 0.01% to saturation with solutions above about aO% impractical because of viscos-ity, and does not depend greatly upon its chemical structure. At the lower end, solution conductivity is very low, e.,g. 61,000 Q in the case of polyvinyl phos-phonic acid at 0.001%. Nevertheless, even at a concentration of 0.05% a metal oxide-organic complex film is formed which confers properties of corrosion resis-tance, aging resistance, hydrophilicity and lithographic properties superior to typical products of the prior art such as an aluminum plate conventionally anodized and then thermally sealed in a solution of polyvinyl phosphonic acid as a second step.
Current carrying capacity increases rapidly with concentration, result-ing in shorter process times and lower voltage requirements.
There appears to be little difference in the properties of produc~.s between 1% and 5% while characteristic properties are still obtained at 30%, despite the high viscosity of the electrolyte. Further, there is a decline in the rate of increase in film thickness at constant voltage with increase in con-centration. Based upon considerations of properties obtained, processing ease, film thickness obtained, and cost of electrolyte, a preferred concentration range lies between about 0.8% and about 5%.
l`here is a reasonably linear relationship between the weight of in-soluble metal oxide-organic complex film ~ormed and the direct current voltage employed.
As the voltage is raised to 70 volts (DC), 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 result be-lieved to be due to the loss in film integrity as the dielec-tric s~rength of the film is exceeded and it becomes perforated. This view is confirmecl by trans-mission electron microscopy in which perforation is seen, corrosion resistance is thus favored by operation under 70 volts.
Press tests are longer with plates electrolyzed at 10, 20 and ~0 volts respectively, the order of run length was inversely proportional to the electro-lysis voltage and to the metal oxide-oTganic complex film thickness. The elec-trodeposition treatment of this invention provides superior sealing of the metal substrate and bonding of the electrodeposited layer to the light sensitive layer . .

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overall. The printing trial results show that lower voltages favor better`bond-ing to the light sensitive layer, particularly diazo based layers, with the range from between about 10 volts to about 30 volts preferred. nirect current is required for the process, although alternating current may be superimposed.
Square waves from pulse plating sources are particularly useful.
Amperage is at a maximum at the beginning of electrodeposition and de-clines with time as the metal oxide-organic complex film builds ~u~4~ the metal surface and reduces current carrying capacity. Within 30 seconds it has de-clined to a level at which further curren-t consumption becomes minimal. This is a major factor in processing economy, as a useful, desirable film has already been deposited.
Amperage is thus a dependent variable, with electrolyte identity, con-centration and voltage the independent variables. Current densities of from about 1.3 amps/dm2 to about 4.3 amps/dm2 are characteristic of favorable process operating conditions and are preferred.
The temperature at which the process is conducte~ may range from abou~
-2C. (near the freezing point o the electrolyte) to about 60C. Best results based on tests of surface hardness, stannous chloride test times, image adhesion, hydrophilicity~ and aging characteristics are obtained at 10C. However, de-crease in performance from 10C to room temperature and even up to ~0C is not very great. Operation at very low temperatures would require expensive cooling capacity. Accordingly, a temperature range between about 10C 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.
Qver 60% of the metal oxide-organic complex film is produced within the first five seconds (0.08 minutes) of electrodeposition. Times beyond five minutes are not beneficial for lighographic uses since no further film is pro-s~

duced, but ~hey are not harmful as long as voltage is low as discussed above.
A time range of between abou~ 0.16 minutes and about 1 mimlte is preferred.
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 by coating upon the metal oxide-organic complex films o~ this invention include iminoquinone diazides, o-quinone diazides, and condensation products of aromatic diazonium compounds together with appropriate binders. Such sensitizers are described in United S~ates Patent Nos; 3,175,906; 3,046,118; 2,063,631; 2,667,415;
3,867,147 wi~h the compositions in the last being in general preferred. Further suitable are photopolymer systems based upon ethylenically unsaturated monomers with photoinitiators which may include matrix polymer binders. Also suitable are photodimerization systems such as polyvinyl cinnamates and those based upon di-allyl phthalate prepolymers. Such systems are described in United States Patent Nos. 3J4979356; 3~615,435; 3,926,643; 2,670,285; 3,376,138 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 conventional in the art. Although all compositions are useful, 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 invention has been examined by tr~nsmission elec-tron microscopy. When viewed at magnifications of at least 55,000X, a nonporous surface is seen. In contrast, conventionally anodized surfaces show typical pores at as little as 5,000 magnification. Accordingly, when ~he ~erm "non-s~

porous" is used herein, it is meant tha~ pores are not visible at 55,000X magni fication using transmission electron microscopy.
In a process variant, the aqueous elcctrolyte additionally contains inorganic acid(s) from the group phosphoric acid, phosphorous acid or a mixturc of phosphoric acid and sulfuric acid or phosphorous acid.
Alternative to the use of a single of said acids with a strong mineral acid, there may be employed a mixture of one or more such acids. As a further alternative there may be added another strong inorganic acid provided that a phosphorous oxo acid be always present. The characteristics of the variant are the initial surge in current during electrodeposi~ion followed by a fall to much lower level ~to about 2 amps as shown in the examples), and a nonporous sur~ace as shown by transmission electron microscopy. The benefits are an increased cor-rosion resistance as shown by the potassium zincate test, and greatly improved hydrophilicity in appropriate tests described below, and comparable printing run lengths at appreciably lower electrodeposited coating weights compared to conven-tional anodizing.
Conventionally anodized products, in contrast, do not show the initial current surge as markedly and the drop in current is less severe, leveling off at its steady state at a much higher level, typically 10 - 15 amperes. Such anodic coatings have characteristic porosity and corrosion resistance and are not sufficiently hydrophilic until given supplementary treatments. By the addi-c~ ~ci~/~`c esfcrs tion of an effective or sufficient concentration of the above acids~to phosphoric acid, or to a mixture of phosphoric and sulfuric acids, the desirable character-istics may be obtained and recognized by the test procedures described herein.
Typically, although dependent upon the total composition, the addition of at least about 0.25% of said acids produces the products of this invention i-f the inorganic acid is phosphoric although a minimum o-f 0.5% is preferable. In ,, ~

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the case of ternary mixtures of phosphoric, sulfuric and said acids, the addition of at least about 0.5% of said acids is desirable while 1% is preferable to ob-tain nonporous surfaces.
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 aluminum oxide-organic complex which comprises the surface film forms very rapidly at first.
During this period the voltage remains substantially constant.
l~le amperage is not a prime variable but is se~ 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 o~ conditions will therefore depend upon the process vari-ables selected. Within this boundary, readily tested by procedures disclosed, ~5~ ' there ~ 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 conditions which are comparatively non-critical, there are obtained products all of which are improvements over the prior art.
Binary systems of phosphoric acid with said acids may range in con-centration from about 10 g/l of H3P04 to about 200 g/l of H3P04. A preferred range is from about 20 g/l of H3P04 to 100 g/l. To this is added at least about 0.25% of said acid and preferably at least about 0.5% to secure the above de-scribed characteristics and beneEits in the electrodeposited metal sheet.
In the case of ~ernary systems in which another strong inorganic acid such as sulfuric or phosphorous acid is adcled to phosphoric acid, such mixture may vary over the e~tire composition range. High H2S04/H3P04 ratios require more . .~

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of said acids to ensure nonporosity~ i.e., greater than about 1%; however, very high H2S0~/H3P0~ may prevent formation of a nonporous film. Lower H2S0~/H3P04 ratios need only about 0.5~ of said acids to achieve nonporosity. In any event, there is no harm in the use of a higher content of said acids.
Current carrying capacity increases rapidly with concentration, result-ing in shorter process times and lower voltage requirements.
There is a reasonably linear relationship between the weight of in-soluble metal oxide-organic complex film Eormed and the direct current voltage employed. At all voltages over about 5 volts, the electro-deposited film that 10 - is formed confers corrosion resistance and lithographic properties superior to prior art.
Direct current is required for the process, al~hough alternating cur-rent may be superimposed. Square waves from pulse plating sources are parti-cularly 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 capacity. Within 30 seconds it has declined to a level at which further current consumption decreases. This is a major factor in processing economy, as a useful, desirable Eilm has already been de-posited.
~lectrcdeposition voltages range from 5 VDC to 75 VDC and higher.
High electrodeposited coating weights are more readily ob~ained in the presence of a strong inorganic acid; hence, neither high voltages, nor long treatment times are necessary. To achieve the desired products of this invention, volt-ages from about 5 VDC to about ~0 VDC for both binary systems and ternary sys-tems are preferred.
Amperage is thus a dependent variable, with electrolyte identity, con-,, ' centration of thc electrolyte and voltage as the independent variables. Current densities of from about D.2 amperes/dm2 to about 6 amperes/dm2 are characteris-tic of favorable process operating conditions and are preferred.
The temperature at which the process is conducted may range from about -2C. (near the freezing point oE the electrolyte) to about 60C. Best results are based on tests of lithographic properties. Operation at very low temperatures would require expensive cooling capacity. Accordingly, a tempera-ture range between about 10C and 35C is preferred and an operating temperature of about 20C to about 25C is still further preferred because o:E operating economy and minimal loss of performance.
Examl~___l - 10 Several sections of 3003 alloy aluminum (17.75 cm x 19.00 cm x .05 cm) were prepared for electrotreatment by degreasing both sides with Ridoline 57, Amchem Products, an inhibited alkaline degreaser.
The degreased secti~n of aluminum was then etched with a 1.0 N NaOH
solution at room temperature for 20 seconds.
After etching, the aluminum plate was thoroughly water rinsed and immediately placed in an electrically insulated tank containing a 1.0% solution of the acid. On each side of the aluminum were placed lead electrodes with dimensions corresponding to the aluminum plate. The electrodes were equidistant from the aluminum with a gap of 10 cm.
Using a D.C. output, the aluminum was made anodic and the lead elec-trodes were made cathodic. The temperature of the bath was maintained at 25C.
The current was turned on with the voltage preset to 60 VDC. The process was allowed to run for 30 seconds. The EMF was turned off, the plate removed :Erom the bath and rinsed well. The plate was then blotted dry.
Several drops of saturated solution of stannous chloride were placed * Trade Mark .,~ ., '7t" `' S~9 upon the surface. The stannous chloride reacts with the aluminum once it has migrated through the layer generated by the electrochemical process. Discrete black spots of metallic tin signal the end of the ~est.
The aluminum oxide-organic complex surface film weight was determined by stripping with chromic acid/phosphoric acid solution. Hydrophilicity of the surface was tested by applying a heavy rub-up ink without the bene-fit of any water. A dry applicator pad was used.
The results are tabulated below.

Time Film ~Secs.) Wt.
Example Acid SnCl~ m~/M2Ink Test 1 Mitrilo triacetic acid 45 87 T

2 myoinositol hexaphosphoric acid113 208 C
ester (phytic acid) =
C6H6(0P03H2)6

3 dodecyl polyoxyethylene phos- 29 179 C
phor;c acid

4 tridecyl benzene sulfonic acid 61 232 S

dinonyl naphthalene disulfonic 47 222 T
acid 6 2,2 -dinitro-4,4 -disulfonic 53 237 CT
acid stilbene 7 dodecyl naphthalene disulfonic 52 211 T
acid 8 di-n-butyl naphthalene di-46 217 T
sulfonic acid 9 ethylene dia~line tetraacetic acid 43 162 CT

hydroxy ethylene diamine tri- 46150 C
acetic acid C = Rinsed totally clean, suitable ~or critical li~ho applications T = Slightly toned or peppered S = Scummed, wnsuitable for litho CT = Intermediate between C and 1 - "

'.

S~)9 Examples 11 to 16 Mixtures of electrolytes were made to a total concentration of 1.0%.
The mixture was used as electrolyte. Electrolysis was conducted 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 following table. In all cases corrosion resistance and hydrophilicity were high.

. "

~9~51;3 ~u o .
~1 E~
__ U
~1 U~ I` ~ ~ N U~ 00 v~ ~ a N ~~I N O~
C~

O ~ 00 ~ 0 I~ O 0~ ~
. _ _ I
r-.
3 U~ U~ U~
~_ ~ U~ N N
o\ O O O O O O
E; _ _ , ~o ~ .
a~ ~ .
s~ O ~ ~ u a>
h ~ C) ~ rl ~ O
~ ~ S ~ rl a) ~ Q) U U
_I
l ~ ~ ~ U U ~ U
O O ~n-,i rl ri ~,~ ~ r~ ~
C~ ~ ~ ~Ud ~ ~ ¢ ~ a~ ~ ~d p~ 0~ ~ .
,_ --- ~ .
u~ u~ u~ h u~ u~ 4~
0\o o o o o o o ~ ~

¢ ~ ~ ~ U h u a>-, O ~ U
u~ h a ¢ ¢ ¢ ~ ~ :~ o :~ a ~ p~ ~
_ _ . , a> ~L
~4 .~ rl Ei ~I N ~) el~ U~ ~0 ~ r-t r-l rl 1~l . I r-l __ ~ .

~ ,. .

s~

Example 17 In a procedure similar to that of Example 1, an anodic film was formed in a 1% phytic acid solution at 30 VDC for 60 seconds. TEM examination of the isolated aluminum oxide-organic film at 55,000X magnification showed a smooth and apparently structureless surface without visible porosity.
Example 18 18.3 cm x 17.8 cm x .03 cm samples of 3003 aluminum alloy were pre-pared for electrotreatment by degreasing with Ridoline 57, Amchem Products, an inhibited alkaline degreaser.
The degreased samples were then etched wi~h about 1.0 N NaOH for 10 - 15 seconds.
After etching, a sample was water washed and dried with a jet of air.
The sample was clamped to a conducting bar and suspended between two lead plates at about 20 cm from these plates in an insulated tank. The tank contained a solution of 100 g/l H3P04 and 1% phytic acid.
Using a D.C. output~ the aluminum was made anodic and the lead elec-trodes were made cathodic. The temperature of the bath was ambient but re-mained at 22C ~ 2C for the test. The current was turned on with the voltage preset to 16 VDC. The electrotreatment was run for 60 seconds. The contact was broken, the plate was removed from the bath and was rinsed with water and final- , ly blotted dry.
Hydrophilicity of the surface was ~ested by applying a heavy rub-up ink without the benefit of water using a dry applicator pad.
The plate was considerably cleaner than conventionally prepared plates when immediately dry inked and water washed.
Several drops of potassium zincate solution ~vide supra) were placed on the surface. The zinc ions are reduced to zinc metal at the aluminum oxide-'rrademark ~., organic film/metal interface thus giving a vivid dark spot signifying th0 end of the test.
The surface produced in this example required 100 seconds to the end point.
Finally, the plate was coated with a solution containing a pigment, polyvinyl formal binder and a diazonium condensation product of the type dis-closed in United Stat0s Patent 3,867,147. When exposed through a standard negative flat and developed with an aqueous alcohol developer, the background cleaned ou~ easily, leaving a vivid image in the exposed areas.
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 magnification showed a smooth surface without visible porosity.

i~*

Claims (11)

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 having less than 1% by weight of copper, in an aqueous electrolyte which contains at least 0.05% by weight of at least one acid or acidic ester, in which the said acid or acidic ester is selected from the group consisting of phytic acid, nitrilo triacetic acid, phosphoric acid mono(dodecyloxypolyoxyethylene) ester, tridecyl benzene sulfonic acid, dinitrostilbene disulfonic acid, dodecyl naphthalene disulfonic acid, dinonyl naphthalene disulfonic acid, di-ni-butyl naphthalene disulfonic acid, ethylene diamine tetraacetic acid, hydroxyethyl ethylene diamine tri-acetic acid or a mixture of at least two of said acids.

2. A process according to claim 1, in which the aqueous electrolyte contains from 0.05 to 30% by weight of said at least one acid or acidic ester.

3. A process according to claim 1, in which the aqueous electrolyte contains at least 0.5% by weight of said at least one acid or acidic ester.

4. A process according to claim 1, or 2, or 3, in which prior to oxid-izing 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 at least one inorganic acid selected from the group con-sisting of phosphoric acid, phosphorous acid, or a mixture of phosphoric acid and sulfuric acid or phosphorous acid.

6. A process according to claim 5, in which the aqueous electrolyte contains 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 oxidation in an electrolyte comprising an aqueous sulfuric acid solution is additionally carried out, before the anodic oxidation in said electrolyte com-prising said organic acid or organic acid ester.

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

11. A support material for 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.