Process for the one-stage anodic oxidation of aluminum bases for offset printing plates

84 MOW 367 JADE I 33 PROCESS FOR THE -NE-srrAGE-A-NoDIc OXIDATION OF ALUMINUM BASE FOR OFFSET PRINTING PLATES BACKGROUND OF THE INVENTION ___ _ _ The present invention relates to a one-stage anodic oxidation process or alwninum which is employed as a base for offset printing plates, the base resulting from this process and the offset printing plate itself.

vases for offset printing plates are provided, either directly by the user or by the manufacturer of precoated printing plates, with a radiation-sensitive or photosensitive layer (reproduction layer) on one or both sides, with the aid of which layer a printable image is produced by photomechanical means.

After prodiction of a printing form prom the printing plate, the base carries the image areas which convey ink during subseqllent printing and, in the areas which are imagefree Turing subsequent printing (non-image areas), also forms the h~drophilic image background for the lithographic printing process.

Bases for reproduction layers or the pricklion of offset printing plates therefore have to meet the following requirements:

Jo - I 3 - The areas of the radiation-sensitive layer which are relatively more soluble aster exposure just - be capable ox being readily removed from the base without leaving a residue to produce the nydrophilic non-image areas, this hying done without the developer attacking the base to any great extent:.

- The base bared in eke non-image areas must have a great affinity or water, i.eOI must be very hydrophilic, in order in the lithographic printing process, to take up water rapidly and permanently and to have a sufficiently repellent action toward the fatty printing ink.

the adhesion of the photosensitive layer before exposure, and of the printing areas of the layer aster exposure, must be adequate.

- The base should possess good mechanical stability, for example to abrasion, and good chemical resistance, in particular to alkaline media.

particularly frequently used starting material for such bases is aluminum, the surface of which is roughened by conventional methods, for example, ho dry-brushing, ~qet-brushing, sand blasting, chemical treatment and/or electrochemical treatment To increase the abrasion-resistance, electrochemically roughened substrates, in particular, are subjected to an anodizing step to build up a thin oxide layer.

These anodic oxidation processes are usually carried out in electrolytes such as H2SO4, H3PO4, H2C2O4, H3BO3, amidosulfonic acid, sulfosuccinic acid, sulfasalicylic acid or mixtures of these.

The oxide layers produced in these electrolytes or mixtures of electron lyres 3ifEer in structure, layer thickness and resistance to chemicals.

In practice, in offset 33 pri.nrl!lg ovate production, an aqlleous ~2S0~ ox H3P0 solution is particularly employed. with regard Jo ~S0~-contai.ning electrolytes, reference may be Ned o, for example, USE Patent Jo. 4,211,~1q and the prior art mentioned therein.

aluminum oxide layers produced in aqueous H2S0 contailling electrolytes are amorphous and, when used in offset printing plates, usually have a weight per unit area ox about 0.5 to 10 my correspondiilg to a layer thickness ox about 0.15 to 3~0 em.

The dozedvantage of using such an anodically oxidized base for offset printing plates is the tact that the oxide layers produced in H2S04 electrolytes have a relati~-~ly Luke resistance to alkaline solutions as used to an increasing extent in, for example, the processing ox presensiti~ed offset printing plates, preferably in modern developer solutions for irradiate negativeworking or, in particular, positive-working radiationsensitive layers.

The anodic oxidation ox aluminum in aqueous electrolytes containing ~'nosphorus oxyacids or pros plates is Lucas known per so:

US.

Patent Jo. 3,511,~61 describes a process for the production of a lithographic orienting plate, in which the aluminum base is oxidized anodically at a temperature of at least 17C in an at least 10~ strength aqueous rd3P04 solution, until the aluminum oxide layer has a thickness of at least 50 no.

US.

Patent No. 3,594,289 discloses a process in which a printing plate base made ox aluminum is oxdozed anodically in a 50~ strength aqueous H3P04 solution at a current density ox 0.5 to 2.0 Audi and at a temperature of 15 to 40C.

Lo 33 The process for tune antic oxidation ox Allahnut bases in particular or printing plates, according to US.

Patent No. 3,836,437 is carried out in a 5 to I strength aqueous Nope solution at a temperature ox 20 to 40C and a current 1ensity of I to 3.0 ~/dm2 and for a period ox 3 to 10 minutes.

The aluminum oxide layer thus produced should have a weight ox 10 to 200 mg/m2.

The aluminum can also be mechanically or chemically roughened or etched Bufferin.

The aqueous bath for the electrolytic treatmint of aluminum which is to be subsequently coated with a water-soluble or water-dispersible substance contains, according to US.

Patent No. 3,960,676, 5 to 45% of silicates, 1 to I of permanganates, or 'Orates, phosphates, chromates, molybdates or vendettas in an amount from 1% to saturation.

Preparation of bases for printing plates is not mentioned, nor is prior roughening of the material.

British Patent No. 1,587,260 discloses a base or printing plates which carries an oxide layer which is produced by anodic oxidation of aluminum in an aqueous solution of H3PO~ or a mixture of H2SO~ and H3PO3.

This relatively porous oxide layer is then covered with a second oxide film of the "barrier layer" type, which can be formed, for example, by anodic oxration in aqueous solutions containing boric acid, tartang acid or borate.

Both the first stage (Example 3, 5 mint and the second stage (Example 3, 2 mint are carried out very slowly, and furthermore, the second stage is carried out a a relatively high temperature (80) It is true that an oxide layer produced in l3PO4 is often more resistant to alkaline media than is an oxide layer produced in an electrolyte 'oases on -SUE solution. this oxide layer while having some other advantages, such as a paler surface, better ate rink balance or less adsorption of dyes S staining in the non image arousal also possesses significant disadvantages.

In a modern conveyor line for the production of printing plate 'vases, it is ~ossib]e, using voltages and residence times conforming to practice, to produce oxide layers 'having a weight per unit area of, for example, only up to about 1.5 g/m2, which corresponds to a layer thickness winch of course provides less protection from mechanical awrysoon than does a thicker oxide layer produced in an -SUE electrolyte.

Because of the relatively large pore ~olune and pore diameter of an oxide layer produped in H3PO4, the mechanical stability of the oxide itself is lower, and this results in d further loss with respect to abrasion-resistance. where can also be problems of adhesion in certain negative-working layers, so that a printing plate base anodized in H3PO4 cannot be employed in all cases.

The prior art oxide layers produced in an aqueous electrolyte containing ape require, on the one hand, a treatment time which is too long or a modern 'nigh-speed manufacturing line and, by having a weight per unit area of up to only no mg/m2, are furthermore unsuitable for pro tooting the fine pore structure of an electrochemically roughened aluminum surface sufficiently against mochaNikolai abrasion.

For this purpose, weights per unit area of more than 500 mum in particular of more than 800 mg/m2, are required for the high-performance printing plates demanded commercially today.

7~.~`3 Processes have also been proposed which seek to combine the advantages of two different electrolytes by employing a twostage treatment procedures; this also applies to the use of solutions containing phosphate ions in one of the two stages.

German Offenlegungsschrift No 32 06 published 09/01/1983 Applicant: Hoechst AG),which has not been previously published and has an earlier priority date, describes a two stage oxidation process for the production of bases for offset printing plates, in which the anodic oxidation is carried out in a) an aqueous electrolyte based on sulfuric acid and b) an aqueous electrolyte containing phosphoroxo, phosphorfluoro and/or phosphoroxofluoro anions. These two-stage oxidation processes can result in bases, for offset printing plates, which are usable and good in practice and which have the same or similar allele resistance of an oxide produced in the H3PO4-containing aqueous electrolytes. However, the bases still require more expensive apparatus since anodic oxidation must be carried out in two baths, frequently also with the intermediate use of a rinsing bath. Such a plant then requires additional units and monitoring procedures, as a result of which, inter alias additional sources of error can arise.

I, 3 3 7 20731-868 SUMMARY OF THE INVENTION It is therefore an object of the present invention to propose a process for the anodic oxidation of bases for offset printing plates based on roughened and anodically oxidized aluminum, which can be carried out relatively rapidly and without great expenditure on apparatus and process technology in a modern manufacturing line.

Another object of the present invention is to provide a process of the type described above which produces bases which are distinguished by increased resistance to alkaline media and by very good mechanical stability.

Yet another object of the present invention is to provide a process as described above in which the anodic oxidation is performed in one slave.

In accomplishing the foregoing objects, there has been provided according to one aspect of the present invention a process for the production of bases for offset printing plates in the form of sheets, foils or webs from roughened aluminum or one of its alloys by means of a one-stage anodic oxidation in an aqueous elect trolyte comprising phosphorus-containing anions, comprising the steps of electrochemically roughening a base material comprising aluminum or its alloys, anodically oxidizing the roughened base matonal in an aqueous H3PO~-free electrolyte comprising dissolved inorganic phosphoroxo anions of inorganic phosphoroxo compounds select ted from the group consisting of metaphosphoric, pyrophosphoric or polyphosphoric acids or alkali metal or alkaline earth metal or ammo Nemo salts of orthophosphoric, metaphosphoric, pyrophosphoric or I, 3~.3 - pa - 20731-868 polyphosphoric acids for a period of about 1 to 90 sea, at a voltage between about 10 and 100 V and at a temperature of about 10 to 80C.

to produce a metal oxide layer having a weight per unit area of at least 0.5 g/m2.

- pa 20731-~68 In a preferred embodiment, the anodic oxidation step is carried out for a period of about 5 to 70 sea, at a voltage between about 20 and 80 V and at a temperature of about 15 to 70~C, most preferably, for a period of about 10 to 60 sea, at a voltage between about 30 and 60 V and at a temperature of about 25 to 60C.

In accordance with another aspect of the present invention, there has been provided a base for offset printing plates in thy form of a sheet, a foil or a web produced by the process described above In accordance with another aspect of the present invention, there has been provided an offset printing plate, comprising a base material produced by the process described above, and a radiation-sensitive or photosensitive coating applied to the base material.

Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments which follows.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention concerns a process for the production of bases for offset printing plates in the form of sheets, foils or webs from roughened aluminum or one of its alloys by means of a one-stage anodic oxidation in an aqueous electrolyte comprising phosphorus-containing anions.

In the process according to the invention, the aluminum is first roughened, electrochemicallY and then anodically oxidized (stage a) in an aqueous 2~'7~33 electrolyte Salk thdll H3?0~ comprising dissolved ooze oroxo anions or a period of about 1 to 90 sea, at a voltage between about 10 and 100 V and at a themportray of about 10 to ~0C.

In preferred embodiment of tune process according to the invention, stage a) i, carried out for a period of about 5 to 70 sea, at a voltage between about 20 and 80 V and at a temperatllre ox about 15 to 70C, especially about 10 to I sea, about 30 to I V and about 25 to ~0C.

The aqueous electrolyte with the stated content ox phosphoroxo anions preferably comprises a salt possessing tune corresponding anion, in particular a salt possessing an alkali metal, alkaline earth metal or ammonium cation and a phosphoroxo anion; however, it is also possible to employ acids, preferably oligoand polyphosp'noric acids. the concentration of eke aqueous electrolyte can be varied within a wide range without variance in effect.

Preferably the concent ration ranges between about 20 9/1 and the partitular saturation limit of the salt at the given temperature in general a concentration ox more than 500 9/1 does not yield any advantages.

Examples of suitable electrolyte compounds include:

sodium dihydroqen phosphate Nope disodium hydrogen phosphate, Nope trisodium phosphate, Nope phosphorous acid, H3PO3 sodium dihydrogen phosphate, Nope disodium phosphate, Nope diphosphoric acid (pyrophosphoric acid), H4P2O7 sodium pyrophospnate9 ape triphosphoric acid, HsP3Olo ~.37~ 3 sodium triphospllate, Apple polyphosphoric acid, Hn~2PnO3n~1 hexasodium tetrapolyphosphate, Nope hexasodium ~etap'nosphate, Nope metaphosphoric acid, Hn(P03)n us used herein, the term "phosphoroxo anion" is intended to refer to anions co,~prisin-3 one or more atoms of phosphorus bonded to oxygen atoms as in the foregoing example confounds.

Similarly, the corresponding ammonium salts an, in particular, potassium salts can be used.

A preferred embodiment of the anodization procuss according to the present invention employs a soullion of trisodium phosphate (Nope) or a tripotassiun phosphate (~3P04) in fully de-ionized water as the electrolyte.

The weight per unit area of the oxide layer which is to be attained by the process according to the present invention increases with increasing electrolyte concentration and increasing voltage.

Chile weights per unit area ox the oxide layer up to about 1 g/m2 can be achieved at electrolyte concentrations of less than about 60 g/l, at voltages up to about 60 V and for residence times up to about 90 sea, higher electrolyte concentrations surprisingly give weights per unit area of the oxide layer which are even greater than about 3 g/m2 The highest growth of the oxide layer when the stated phosphoroxo anions are used is achieved, as a rule, with R3P04 or Nope.

Surprisingly, the oxide layer thicknesses which can be achieved in this electrolyte can all be in the range of an oxide produped in an H2S04-containing electrolyte.

The stated effect of the concentration tune electrolyte on the -- 10 - 37~33~3 weight per unit area ox the oxide layer which can be achieved cannot ye determined when H3PO~ it use in a concentration greater than lo g/l, this being in contrast Jo tile electrolytes used accorr3ing to the proKent invention.

on unexpected effect on the growth ox the oxide layer is also observed when an acid containing phosphoroxo anions is replaced with a corresponding salt solution.

In tile series ox electrolytes stated lo above, higher weights per unit area ox the oxide layer are achieved, as a rule, using the salts of the acids containing phosphoroxo anions.

The current-time curves for the anodization in the various electrolytes employed according to the present invention show that the current flow remains constant over the period only when Nope or K3PO4 is used.

This means that, when Nope or K3PO4 is used in an aqueous electrolyte for anodization, the growth ox the oxide layer is dependent on the anodization time.

However, in the case of long anodization times, it is also necessary to take into account the fact that the oxide may redissolve in the anodization electrolyte.

In Yost ox the other electrolytes investigate, with the exception of 'POW (not claimed), and H3PO3, the current walls from high initial values to values of less than about l to 2 Adam in the course ox about lo to 30 sea (dependent on the electrolyte) at a given voltage.

As a result, relatively long anodization times play only a very minor role in producing a further increase in the weight per unit area ox the oxide layer.

In contrast to the weight per unit area of the oxide layer, the alkali-resistance measured in the -- 11 - .

20731-868 zinc ate test) of the oxide is no longer significantly dependent on the concentration of the electrolyte for concentrations greater than about 60 g/l. After the maximum zinc ate test time has been reached at a concentration between about 60 and 100 g/l of, for example, Nope, the further increase in the concentration of the electrolyte does not result in an increase in the zinc ate test time. In fact, a slight decrease is observed at high voltage.

At a given concentration and voltage, the anodization time likewise has only a minor effect on the alkali-resistance o-f the oxide.

The principal factor affecting the alkali-resistance is the applied anodization voltage. The increase in the zinc ate test times runs parallel with the increase in the voltage.

Suitable base materials to be oxidized according to the invention include those comprising aluminum or one of its alloys which includes, for example, more than 98.5% by weight of Al and proportions of Six Fe, Tip Cut and Zen. These aluminum base materials are first cleaned, if necessary, and then roughened electrochemically (for example, by treatment with arc. current in aqueous Hal, HNO3 or salt solutions). All process stages can be carried out bushes, but are preferably carried out continuously.

In general, the process parameters in the roughening stage are in the following ranges, particularly in the case of the continuous procedure: the temperature of the electrolyte is between about 20 and I 3 Hayakawa, the asset compound (acid or salt) concentration is between about 2 and 100 g/l (or higher in the case ox salts), the current density is between about 15 and 7.50 Adam, the residence tire is between about 3 and LOO eye and tune slow rate of the electrolyte at the slurs of the article to he treated is between about 5 and 100 cm/sec.

The type ox current used is generally arc. current; however, it is also possible to employ modified types ox current, such as arc. current with different current amplitudes for the annul current and cathode current.

In this procedure, the average peakto-valley height Rz of the roughened surface is in the range from about 1 to 15 em. the peak-to-valley height is determine in accordance with DIN 4768 in the Yensoon ox October 1970, and the average peak-to-valley height Rz is then the arithmetic mean ox the individual ~eak-to-valley heights of five individually measured areas lying adjacent to one another.

Toe precleaning step comprises, for example, treatment with aqueous Noah solution, with or without degreasiny agents and/or complex Wormers, inch. loroethylene, acetone methanol or other commercial, suckled aluminum pickles.

the roughening step can be hollowed by an additional etching treatment whereby, in particular, a maximum of 2 g/m2 is removed.

If there are several roughening stages, etching treatment can also be carried out between the individual stages, with up to 5 g/1n2 being removed between the stages.

The etchin solutions used are in general aqueous alkali metal hydroxide solutions or aqueous solutions of alkaline salts or aqueous acid solutions based on H~03, H2S04 or H3P04.

In addition to an etching treatment stage I 7~33 between the roughening stage and the anodization stage, non-electrochemical treatments are also known kick Inertly have a rinsing and/or cleaning action and are useful, for example, or removing deposits ("smut formed during the roughening Rockies or simply for removing residual electrolyte.

For example, dilute aqueous alkali metal hydroxide solutions or water are used or these purposes.

The anodic oxidation of the aluminum base material can also be hollowed by one or more posttreatment stages, although these are often unnecessary, particularly in the present process.

Post-treatment is understood as meaning, in particular, a chemical or electrochemical treatment of the aluminum oxide layer lo to render it hydrophilic, for example, treatment of the material by i!nmer:,io~ in an aqueous polyvinylphosphonic azalea solution in accordance with British Patent No. 1,~30,447, treatment by immersion in an aqueous alkali metal silicate solution in accordance with US.

Patent LOWE. 3,1~1,461 or an electrochemical treatment (anodization) in an aqueous alkali metal silicate soullion in accordance with US.

Patent No. 3,902,976.

In these post-treatment stages, in particular, the hydrophilicity of the aluminum oxide layer, which is frequently already sufficient, is increased further while retaining the remaining conventional properties ox this layer being at least retained.

The materials produced according to the prosent invention are used as bases for offset printing plates, i.e., a ra~iation-sensitive coating is applied on one or both sides of the base material, either by the manufacturer of presensitized printing plates or directly by the user.

Suitable radiation-sensitive or .

~3~7~i~3 photosensitive layers are, in principle, all layers which, Atari irradiation (exposure) and with or without subsequent development and/or mixing, judge an i~age~7ise ,l~rFace which can be used or printwheel.

In addition to the Salk 'nal.ide~containing fevers used in Inane fields r various other layers are also known, as .r1escri~ed in, for example "I.ight-~en~itive Systems" by Jaromir Caesar, yu'~lished by John Wiley &

sons, New York 1965: killed layers containing chromates and dichromates (Xosar, chapter 2); layers containing unsaturated compounds winch undergo isomerization, rearrangement, cyclization or cross linking on exposure (Caesar, chapter 4); layers containing photopolymeritable compounds and in which monomers or prepolymers undergo polymerization on exposure, if appropriate with the aid of an initiator (Rosen, chapter 5); and layers containing o diazoquinones, such as diazonaphthoqùinones, p-diazoquinones or diazonium salt condensates (Rosen, chapter 7).

Suitable layers also include the electrophotographic layers, i.e., those which contain an inorganic or organic p'notoconductor.

In addition to the p'notosensitlve substances these layers can, ox course, also contain other components, such as, for example, resins, dyes or plasticizers.

In particular, the hollowing photosensitive compositions or compounds can be employed in coating the bases produced by the process according to the present invention:

- positive-working reproduction layers weaken are described tin, for example, German Patents No. 854,890; No. 865,109; No. 879,203; No. 894,959;

No. 938,233; No. lug; No. 1,144,705;

No. 1~118,606; No. 1,120,273; No. 1,124,817 and - 15 US No. 2,331,377 and European Patent Applications No. 0,021,428 (published 01/07/1981 Applicant: Hoechst AG)and No 0,055,814 (published 07/14/1982 Applicant: Hoechst A), and which contain, as the photosensitive compound, o-diazoquinones, in particular o-diazonaphthoquinones, such as 2 dozily, 2-naphthoquinonesulfonie acid esters or asides, which can be of low molecular weight or high molecular weight;

- negative-working reproduction layers containing condensation products owe aromatic diazonium salts and compounds possessing active carbonyl groups, preferably condensation products of diphenylaminediazonium salts and formaldehyde, which are described in, for example, German Patents No. 596,731; No.

1,138,399; No. 1,138,400; No. 1,138,401; No. 1,142,871 and No.

1,154,123, United States Patents No. 2,679,498 and No. 3,050,502, and British Patent No. 712,606, - negative-working reproduction layers, for example as described in German Patent No. 20 65 published 08/21J1975 Applicant: American Host Corporation), which contain co-condensalion products of aromatic diazonium compounds, the layers contain in products which contain at least one unit each of a) condensable aromatic diazonium salt compound and b) a condensable compound such as a phenol ether or an aromatic thither, bonded through a diva lent bridge member, such as a ethylene group, which is derived from a condensable carbonyl compound;

- positive-working layers as described in German offenlegungsschrift No. 26 10 published 09/30/1976 Applicant:

Host Agrimony Patent No. 27 18 published 11/02/1978 Applicant: Host Agree German Offenlegungssehrift No. 29 28 636 - I I (published 02/12/1981 Applicant: Hoechst A), which contain a compound which splits off acid on exposure, a monomeric or polymeric compound which possesses at least one COOK group which can be split off by means of an acid (for example an ortho carboxylate group or a carboxamidoacetal group), and, if appropriate, a binder;

- negative-working layers consisting of photopolymerizable monomers, photo initiators, binders and, if appropriate, further additives; the monomers used are, for example, acrylates and methacrylates or reaction products of di-isocyanates with partial esters of polyhydric alcohols, as described in, for example, United States Patents No. 2,760,863 and No. 3,060,023 and German Offenlegungsschriften No. 20 64 079 (published 07/13/1972 Applicant: Katie AGO and No. 23 61 041 (published 06/12/1975 Applicant: Hoechst A), and - negative-~orking layers as described in German Offenlegungsschrift No 30 36 077 (published 05/06/1982 Applicant:

Hoechst A), which contain, as the photosensitive compound, a diazonium salt polycondensation product or an organic Acadia compound and, as the binder, a high molecular weight polymer possessing alkenylsulfonyl or cycloalkenylsulfonylurethane side groups.

Photosemiconducting layers as described in, for example, German Patents No 11 17 391 (published 11/16/1961 Applicant: Katie lo A), No. 15 22 497 (published 09/11/~ Applicant: Katie A), No.

15 72 312 (published 01/08/1970 Applicant: Hoechst A), No.

23 22 046 (published 11/07/1974 Applicant: lushest AGO and No.

23 22 047 (published 11/07,/1974 Applicant: Hoechst AGO can also be ,~"~' ~37~ applied onto the bases produced according to the invention, to produce highly photosensitive electrophotographic printing plates.

The coated offset printing plates obtained from the bases produced by the process according to the present invention are converted to the desired printing form in a known manner by images exposure or - aye ,~, it 76f33 irradiation and washing out ox the non-image areas Will a developer, or example an aqueous alkaline developer option t h r; I I The one-stagelprocess according to the invent lion combines, inter alias the following advantages:

e alkali-resistance of the oxide produsted is substantially slipperier to that ox the oxide produced in an ~25O4-containing aqueous electrolyte, and ~arke~Jly superior to that of the oxide produced in lo an H3PO4-containing aqueous electrolyte - The resulting weight per unit area of the oxide layer reaches the values of the oxide layer produped in an 112SO4~containing electrolyte, and, with respect to the layer thickness, is Nancy jar superior to the oxide produced in H3PO4-containing electrolytes.

.

- The oxide layer is very hydrophilic, so that it may be possible to dispense with one of the post-treatment steps or hydrophilization which are conventionally used in printing plate production techlogy - The bases can be used for all positiveworking, negative working and electrophotographicallyworming reproduction layers.

In the above description and the examples below, percentages denote percentages by weight, unless stated otherwise. Parts by weight bear the same rotalion to parts by volume as that of g to cm3.

otherwise, Noah hollowing methods have been used in the - 18 it 3 20731-868 examples in order to test the alkali-resistance of the surface, and the results of the particular examples have been summarized in tables.

Nate test (according to US.

Patent No. 3,940,321, columns 3 and 4, lines 29 to 68 and lines 1 to 8:

The Nate of dissolution, in sea, of an aluminum oxide layer in an alkaline zinc ate solution is taken as a measure of the alkali-resistance of the layer. The longer the layer requires for dissolution, the greater is its resistance to alkalis. The layer thicknesses should be roughly comparable, since of course they also constitute a parameter with regard to the dissolution rate. A drop of a solution of 480 g of KOCH and 80 g of zinc oxide in 500 ml of distilled water is applied to the surface to be investigated, and the time which elapses before the appearance of metallic zinc is determined, this being recognizable from the dark coloration which appears at the point being investigated.

Gravimetrically determined corrosion rate A sample of defined size which is protected on the reverse side by means of a surface coating film is agitated in a bath which contains an aqueous solution containing 6 g/l of Noah. The weight loss suffered in this bath is determined gravimetrically. Times of 1, 2, 4 or 8 minutes are chosen as treatment times in the alkaline bath.

-- 19 - ~317~i.6~ Comparative Example Al 20731-868 A mill finished aluminum sheet which is 0.3 mm thick is decreased using an aqueous alkaline pickling solution at a temperature of 5Q to 70C. Electrochemical roughening of the aluminum surface is carried out using arc. current in an HNO3-containing electrolyte, and a surface roughness having an Rz value of about 6 em is obtained.

Subsequent anodic oxidation is carried out in accordance with the process described in European Patent No. 0,004,569 (published 11/03/1932 Applicant: Hoechst A), in an aqueous electrolyte containing H2SO4 and ASSAY, this procedure leading to a weight per unit area of the oxide layer of 2.8 g/m .

Comparative Example V2 An aluminum web which has been roughened as described in Comparative Example Al is oxidized anodically in an aqueous elect trolyte containing 100 g/l of H3PO4, at a voltage of 40 V in the course of 40 sea The resulting weight per unit area of the oxide layer is 0.9 g/m .

samples 1 to 40 An aluminum web roughened electrochemically as described in Comparative Example V1 is rinsed with fully de-ionized water and then subjected to anodic oxidation in the aqueous electrolytes listed in Table It and under the conditions likewise stated in that Table.

Table I also shows the results of the determinations of the weight per unit area of the oxide layer, and the zinc ate test times as a measure of the alkali-resistance.

Table II contains comparative data for determining alkali-resistance by means of the gravimetrically determined corrosion rate in Noah solution.

- 20 3 I TWILL Example Electrolyte Conch Voltage Time Weight Per Zonk Sultan trash Unit Aria Test Contains of the of Oxide Elect Layer owlet I (V~~sec) (9/~2) Seiko) I V1 H~S04/A 200/7 25 40 3.0 27 V2 H3P0~, - 100 40 40 0 . 8 1 Z 1 Nope Z0 40 60 OHS 138 2 ape 40 40 60 0 . 8 153 3 4 60 40 pa 0 . 7 195 4 Nope, Tao 20 60 O . 7 117 Nope 80 40 60 1.1 Z31 I_ , , _ .

6 Nope . 80 60 40 1.4 312 7 Nope 80 60 60 1 . 6 29Z 8 Nope 100 20 60 0 . 8 116 9 Nope 100 40 40 0 . 9 217 Nope to 40 60 1.2 224 11 Nope 100 60 40 1.7 332 12 ape 100 60 60 109 35Z 13 Nope 150 Z0 60 1 . 0 129 14 ape 150 40 40 1.3 218 ape 150 40 60 2 . 2 2~9 16 Nope lS0 60 20 1.3 267 17 Nope 150 60 40 2 . 3 289 18 Nope 150 60 60 2.6 311 19 ape 200 20 60 1.0 126 Z Nope 200 40 40 1 . 7 200 Jo -- 21 - Pi I Rowley I ( count i nude) __ Examplelectrolyte Concern- Voltage Time Weight Per Zinc ate Solut;ontration Unit Area Test Contains of the of Oxide E l cat r Layer oily glue) (V) (sect (g/m2) (sea) 21 K Pi 100 60 60 2.9 249 -Z2 K3PO4150 40 30 1 . 4 173 23 K3P04 Z4033 2.6 154 24 (NH,;)3P04 100 60 60 1.2 132 25 (~H4)3P04~5~60 60 1.4 139 26 Nope 60 0 O 7 149 27 Nope a 80 40 1 .1 157 28 Nal~2P04 - 150 80 40 1,3 aye Z9 H4Pz07 100 I 69 0 . 5 74 Nope 100 60 MU 0.6 117 31 4 3 ) n 1 JO ha 60 1 . 1 , 68 3Z Nope 60 60 1.3 104 6P413 100 69 60 1 . 5 138 3 ape 200 60 60 1 . 2 137 Nope 200 60 60 1.3 143 36 Nope 200 60 60 1.7 152 37 loupe 200 60 60 1.5 126 I Nope 100 40 40 1.32 233 Nope 150 40 40 2.~4 217 Nope 200 40 40 2 . 78 185 . ~_~ 2 Samples 38 Jo 40 tiler oozed anod;cally at 60C.

Al other examples are prepared a 40C.

-- 22 - 3 3 'd 11 I TABLE It Example Residence time (mix) for the gravimetri eel lye determined corrosion rate __ 1 2 4 6 1 8 , 10 __ __ ___ V1 1.21 2.23 3.4Z 4~85 ¦ 6.53 8.38 V2 0 . 34 O . 86 1 . 45 2 . a 1 4 . I 6 . 41 6 0.05 0.10 0.32 0.59 1 aye ' 1043 11 0.05 0.10 0.29 0.49 0.76 j 1.32 0.07 0.13 0.36 0.64 1 0.98 ' 1.69 0.08 0.17 0.38 0.73 1 1.21 ' 1.87 24 0.09 0.19 n.43 0.87, 1.35 i Zoo I . 0.12 0.2S 0.53 0~,94 1.83 i 3.53 30. 0.15 0.29 0.65 ¦ 1.62 2.87 . 4.94 33 t~.13 0.27 0.61 0~99 1.73 3.,16 -- 23 - ~2~7~ Amelia 41 An aluminum substrate prepared as described in example 8 is provided Whitney the following negative-working photosensitive layer:

0.70 part by weight of a polycondensation product of l mole of 3-methoxydiphenylamine-4-diazonium sulfate an l mole of 4,4'bismethoxymethyl~iphenyl ether, precipitoted as ~esitylenesulEonate;

~.40 parts by weight of 85% strength phosphoric acid;

3.00 parts ho welgh-'c ox a notified epoxy resin obtained by reacting 50 parts by weight of an epoxy resin having a molecular weight of less than 1,000 and 12.8 parts by weight of benzoic acid in ethylene glycol moomethyl ether in the presence of benzyltrimethylammonium hydroxide;

0.44 part by weight of finely milled Halogen blue G (KIWI. 74 Lowe;

~2.00 parts by volume of ethylene glycol monomethyl ether;

30.60 parts by volume of tetrahydrofuran; and 8.00 parts Joy volume of bottle acetate.

Following exposure through a negative task, dovelopment is carries out using a solution of 2.80 parts by weight of Nazi Lowe, 2.80 parts by weight of McCoy OWE, 0.90 part by weight of 85% strength phosphoric acid, 0.08 part by weight of phosphorous acid, 1.50 parts by weight Ox a non-ionic wetting agent, Lowe parts by weight ox bouncily alcohol, 20.00 parts by weight of n-propanol, and 50.00 parts by weight ox water.

- 24 ~23~9~ 3 The printing plate produced in this manner can be developed rudely end without staining.

The orient run Obtained using a orienting for produced in this -wanner is 170,000. A base weakly is pro god as described in comparative example YIP and which is quoted with the same ~ormulacion can only be developed under more severe conditions.

After development, yellow fogging, tush Jay be caused ho adhering particles of inn compound, may remain in the non-image areas.

I F a base according to Comparative example V2 is used, it is wound that, during printing, substantial loss occurs in the non-image area after about 90,000 prints, this gloss increases with the length of tune print run.

after 120,000 orients, the print quality has deteriorated to a level which is no longer acceptable in practice.

Example 42 _ _ _ An aluminum substrate produced as described in Example 11 is coated with the following positiveworking photosensitive solution:

.00 oats by weight of cresol-Eormaldehyde novolak (having a softening range from 105 to 120C according to DIP 53 181), 1.10 parts by weight of 4-(2-phenylprop-2-yl)-phenyl 2-diazo-1,2-naphthoquinone-4sulfonate, 0.81 part by weight of polyvinylbutyral, 0.75 part by weight of 2-diazo-1,2-naphthoquinone-4 sullenly chloride, 0.08 part by weight ox crystal ~iolet,an3 pyrites by weight of a solvent mixture comprising 4 parts by volume of ethylene - 25 I gly~ol monomethyl ether, 5 parts by iamb of tetrahydrofuran and 1 part by volume of butvl acetate.

The coated web is dried in a drying tunnel at temperatures up to kiwi the printing plate produced in this manner is exposed through a photographic postlive and developed with a developer ox the hollowing composition:

S.30 parts by weight of sodium eta silicate . 9 H20, 3.40 warts by weight of trisodium phosphate . 12 H20, 0.30 parts by weight of sodium dihydrogen phosphate lenders) and 91.00 parts by weight of water.

The printing form obtained has satisfactory copying and printing properties and possesses very goon contrast aster exposure.

The print run is 150,000.

A corresponding plate produced from tune base neutral of Comparative Example VI shows blue fogging in the non-image areas.

After the developer has been acting or a fairly long time, the non-image areas display a substantial light-dark shadow effect, which is an indication of attack on the oxide by the developer solution.

ampule _ 3 An aluminum substrate prepared as described in example 14 is provided with the hollowing negativeworking photosensitive layer:

16.75 parts by weight of an 8.0% strength solution of the reaction product of a polyp vinylbutyral having a molecular weight of 70,000 to Snow consitting of 71% by weight of - 26 33 vinylbutyral units, I by weight ox vinyl acetate units and 27~ ho weight OX vinyl alcohol units, it'll ~ropyle~esul'onyl isocyanate, ~.14 parts by weight of 2,~-~is-(4-azido-~enzene)-4 methyl-cyclohexanone, n. 23 Hart by weight of RADIOMEN Glen extra and 0.~.1 part by weight of 2-benzoylmetnylene-1-methyl- B naphthothiazine in 100 warts ho eight ox ethylene glycol ~onomethyl other, and I parts by weight of tetrahydrofuran.

The weight per unit area of the dry layer is 0 75 9/m2 The copying layer is exposed to a 5 ow metal halide lamp through a photographic negative or 35 seconds. the exposed layer is treater, by means of a pad, with a developer solution having the composition:

5 parts by weight of sodium laurel sulfate, 1 part by weight of sodium metasilicate . 5 HO, and 94 parts by weigh ox water, the non-image area being removed.

In a printing press, the plate gives a print run ox 170,000.

When tune base produced as described in Comparative Example V2 is used substantially reduced adhesion of the copying layer is found.

.

Example 44 A base oxidized anodically as described in Example 25 is coated with the following solution to produce an electrophotographically working offset printing plate:

I 33 .

Jo o . no parts by weight of 2,5-bis-(4'-diethylamino phenyl)-1,8,4,-oxdiazole, 10 on warts by weight of a copolymer ox styrenes and ~naleic android, having a softening point of 21~~0.02 part by weight owe radiomen I (C. I. 45 170) and 300.00 parts by weight of ethylene ylycol monomethyl ether.

The layer is negatively charged to about 400 V in the dark by means of a corona.

The charged plate is exposed images in a process camera and then doveloped with an electrophotographic suspension developer which comprises a dispersion of 3.0 parts by weight of magnesium sulfate in a solution ox 7.5 parts by weight ox pentaerythritol resin ester in 1200 parts by volume ox an isopara~Ein mixture having a boiling range from 185 to 210~. after the excess 3eveloper liquid has been removed, the developer is fixed and the plate is immersed for I sea in a solution comprising 35 parts by weight of sodium metasilicate . 9 HO, 140 parts by weight of glycerol, 550 parts by weight ox ethylene glycol and 140 parts by weight of ethanol.

the plate is then rinsed with a strong jet of water, those areas of the photo conductor layer which are not covered with toner being removed; the plate is then ready or printing.

example I An aluminum web prepared as described in example 12 is subjected to a further treatment step (additional hydrophilization) by being immersed for 20 Seiko in a 0.2~ strength aqueous solution of polyvinyl - 28 ~.137~3~ 20731-868 phosphoric acid at 50C. After drying, the base additionally hydrophilized in this manner is processed further as described in Example 3, and the ink-repellent action of the non-image areas can be improved. Hydrophilization which is still more advantageous is achieved using the complex-type reaction products described in German Offenlegungsschrift No. 31 26 636 (published 01/27/1983 Applicant: ~Ioechst A), which comprise a) polymers such as polyvinylphosphonic acid and b) a salt of a metal cation which is at least diva lent.

The foregoing description has been set forth merely to illustrate the invention and is not intended to be limiting.

Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the scope of the invention is to be limited solely with respect to the appended claims and equivalents.

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