EP0139111B1 - Process for two step anodic oxidation of aluminium carrier materials for offset printing plates - Google Patents

Description

The invention relates to a two-stage anodic oxidation process for aluminum, which is used as a carrier material for offset printing plates.

Carrier materials for offset printing plates are provided either by the consumer directly or by the manufacturer of precoated printing plates on one or both sides with a radiation (light) sensitive layer (reproduction layer), with the help of which a printing image is generated photomechanically. After a printing form has been produced from the printing plate, the layer support carries the image points which will guide the color during later printing and at the same time forms the hydrophilic background for the lithographic printing process at the image-free locations (non-image points) during the later printing.

• - Die nach der Belichtung relativ löslicheren Teile der strahlungsempfindlichen Schicht müssen durch eine Entwicklung leicht zur Erzeugung der hydrophilen Nichtbildstellen rückstandsfrei vom Träger zu entfernen sein, ohne daß der Entwickler dabei in größerem Ausmaß das Trägermaterial angreift.
• - Der in den Nichtbildstellen freigelegte Träger muß eine große Affinität zu Wasser besitzen, d. h. stark hydrophil sein, um beim lithographischen Druckvorgang schnell und dauerhaft Wasser aufzunehmen und gegenüber der fetten Druckfarbe ausreichend abstoßend zu wirken.
• - Die Haftung der lichtempfindlichen Schicht vor bzw. der druckenden Teile der Schicht nach der Belichtung muß in einem ausreichenden Maß gegeben sein.
• - Das Trägermaterial soll eine gute mechanische Beständigkeit z. B. gegen Abrieb und eine gute chemische Resistenz, insbesondere gegenüber alkalischen Medien besitzen.

The following requirements must therefore be placed on a layer support for reproduction layers for the production of offset printing plates:

• - The parts of the radiation-sensitive layer which are relatively more soluble after exposure must be easy to remove from the support without residues by development in order to produce the hydrophilic non-image areas, without the developer attacking the support material to a greater extent.
• - The carrier exposed in the non-image areas must have a great affinity for water, ie be highly hydrophilic, in order to absorb water quickly and permanently during the lithographic printing process and to be sufficiently repellent to the bold printing ink.
• - The adhesion of the light-sensitive layer before or the printing parts of the layer after exposure must be sufficient.
• - The carrier material should have good mechanical resistance, for. B. against abrasion and good chemical resistance, especially against alkaline media.

Aluminum, which is roughened on the surface by known methods by dry brushing, wet brushing, sandblasting, chemical and / or electrochemical treatment, is used particularly frequently as the base material for such layer supports. To increase the abrasion resistance, electrochemically roughened substrates in particular are subjected to an anodization step to build up a thin oxide layer. These anodic oxidation processes are usually carried out in electrolytes such as H2S04, H ₃ PO ₄ , H ₂ C ₂ 0 ₄ , H ₃ B0 ₃ , amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof. The oxide layers built up in these electrolytes or electrolyte mixtures differ in structure, layer thickness and resistance to chemicals. In the production of offset printing plates, in particular aqueous H ₂ SO ₄ or H ₃ PO ₄ solution are used. For electrolytes containing H ₂ S0 ₄ , reference is made, for example, to EP-B-0 004 569 (= US-A-4 211 619) and the prior art mentioned therein.

Aluminum oxide layers produced in aqueous electrolytes containing H ₂ S0 ₄ are amorphous and usually have a layer weight of about 0.5 to 10 g / m ² in offset printing plates, corresponding to a layer thickness of about 0.15 to 3.0 μm. A disadvantage of using such anodized substrate for offset printing plates is the relatively low resistance of the oxide layers produced in H ₂ S0 ₄ electrolytes to alkaline solutions, such as are increasingly being used, for example, in the processing of presensitized offset printing plates, preferably in modern developer solutions for irradiated, negative- or in particular positive-working, radiation-sensitive layers.

• In der DE-B-16 71 614 (= US-A-3 511 661) wird ein Verfahren zur Herstellung einer lithographischen Druckplatte beschrieben, bei dem der Aluminiumträger bei einer Temperatur von mindestens 17°C in einer mindestens 10 %igen wäßrigen H₃P0₄-Lösung anodisch oxidiert wird, bis die Aluminiumoxidschicht eine Dicke von mindestens 50 nm hat.

The anodic oxidation of aluminum in aqueous electrolytes containing phosphoric acid or phosphates is also known per se:

• DE-B-16 71 614 (= US-A-3 511 661) describes a process for the production of a lithographic printing plate in which the aluminum support is at least 17 ° C. in an at least 10% aqueous H ₃ P0 ₄ solution is anodized until the aluminum oxide layer has a thickness of at least 50 nm.

From DE-A-18 09 248 (= US-A-3 594 289) a method is known in which a printing plate support material made of aluminum in a 50% aqueous H ₃ P0 ₄ solution at a current density of 0.5 to 2.0 A / dm ² and a temperature of 15 to 40 ° C is anodized.

The process for the anodic oxidation of aluminum supports, in particular for printing plates, according to DE-A-23 28 311 (= US-A-3 836 437) is carried out in a 5 to 50% strength aqueous Na ₃ PO ₄ solution at a temperature of 20 to 40 ° C, a current density of 0.8 to 3.0 A / dm ² and carried out for a period of 3 to 10 min. The aluminum oxide layer produced in this way should have a weight of 10 to 200 mg / m ² .

The aqueous bath for the electrolytic treatment of aluminum, which is then to be provided with a water-soluble or water-dispersible coating substance, according to DE-B-23 49 113 (= US-A-3 960 676) contains 5 to 45% of silicates, 1 to 2.5% of permanganates or from 1% to saturation of borates, phosphates, chromates, molybdate or vanadates.

From DE-A-27 29 391 (= GB-A-1 587 260) a support material for printing plates is known which carries an oxide layer which consists of anodic oxidation of aluminum in an aqueous solution of H ₃ P0 ₃ or a mixture H _Z S0 _{4 /} H ₃ POg is generated; then this relatively porous oxide layer is overlaid with a second oxide film of the "barrier layer" type, which can be formed, for example, in aqueous solutions containing boric acid, tartaric acid or borates by anodic oxidation. Both the first stage (example 3, 5 min) and the second stage (example 3, 2 min) are carried out very slowly, as well as the second at a relatively high temperature (80 °).

An oxide layer produced in these electrolytes is often more resistant to alkaline media than an oxide layer produced in an electrolyte based on H ₂ SO ₄ solution; it also has some other advantages, such as a lighter surface, better water flow or low adsorption of dyes ("fog" in the non-image areas), but it also has significant disadvantages. In a modern belt system for the production of printing plate carriers, with practical tensions and dwell times, for example, only oxide layer weights of up to about 1.5 g / m ² can be produced, a layer thickness that naturally offers less protection against mechanical abrasion than a thicker one in an H ₂ S0 ₄ electrolyte produced oxide layer. Due to the larger pore volume and diameter of an oxide layer built up in H ₃ P0 ₄ , the mechanical stability of the oxide itself is also lower, which results in a further loss in terms of abrasion resistance.

Methods have also become known which attempt to combine the advantages of both electrolytes by means of a two-stage treatment.

The process for the production of printing plate support materials made of aluminum according to DE-A-22 51 710 (= GB-A-1 410 768) is carried out in such a way that the aluminum is first anodized in an electrolyte containing H ₂ S0 ₄ and then this oxide layer in a 5 to 50% by volume aqueous H ₃ PO ₄ solution is aftertreated without the action of electric current. The actual oxide layer should have a weight per unit area of 1 to 6 g / m ² , this weight decreasing significantly when immersed in the aqueous H ₃ P0 ₄ solution, for example by about 2 to per minute immersion time in an aqueous H ₃ P0 ₄ solution 3 g / m ² . An electrochemical treatment in the H ₃ P0 ₄ solution should also be possible (Example 11) or the use of a mixed electrolyte made of H ₃ P0 _{4 /} H ₂ S0 ₄ (Example 12), with an oxide layer being removed in these cases as well.

US Pat. No. 3,940,321 also describes a two-stage electrochemical treatment in an electrolyte based on H ₂ S0 ₄ and then in an electrolyte based on H ₃ P0 _4. The two-stage anodic oxidation or treatment method leads to the fact that the oxide layer built up in the H ₂ S0 ₄ electrolyte is redissolved to an excessive extent in the H ₃ P0 ₄ solution under the previously known conditions.

• - in der EP-A-0 008 212 eine Elektrolyse in einem Borationen enthaltenden Bad vor der anodischen Oxidation in einem zweiten Bad (z. B. einer wäßrigen H₂S0₄-Lösung), der pH-Wert des ersten Bades sollte bei 9 bis 11 liegen und die Behandlungstemperatur bei 50 bis 80° C; die Stärke der ersten Schicht soll bei mindestens 2 um liegen, die der zweiten bei höheren Werten (z. B. bei etwa 20 um),
• - in der DE-B-26 51 346 (= GB-A-1 523 030) eine Elektrolyse in einer wäßrigen Lösung aus einem Salz (wie einem Borat oder Phosphat) und gegebenenfalls einer Säure oder einem Salz als Sperrschicht-Bildner (z. B. Borsäure oder Ammoniumborat).

It is also occasionally described to carry out certain surface modifications in H ₂ SO ₄ solutions before the anodic oxidation, for example

• - in EP-A-0 008 212 an electrolysis in a bath containing borate ions before the anodic oxidation in a second bath (e.g. an aqueous H ₂ SO ₄ solution), the pH of the first bath should be 9 to 11 and the treatment temperature at 50 to 80 ° C; the thickness of the first layer should be at least 2 µm, that of the second at higher values (e.g. around 20 µm),
• - in DE-B-26 51 346 (= GB-A-1 523 030) electrolysis in an aqueous solution of a salt (such as a borate or phosphate) and optionally an acid or a salt as a barrier layer former (e.g. B. boric acid or ammonium borate).

However, both publications only refer to aluminum, which is to be used for window frames, panels (paneling) and fastenings for building structures or decorative aluminum moldings for vehicles or household items. In addition, the formation of thinner layers would lead to them being too easily dissolved again during the second treatment.

In DE-B-24 31 793 (= GB-A-1 412 929) an aluminum surface is treated with hot water or steam (to form a boehmite layer) and then electrolysis in an aqueous solution of a salt of the silica , Phosphoric, molybdenum, vanadium, permangan, tin or tungstic acid performed. This treatment is said to lead to a greater layer thickness, improved toughness, a finer structure and thus greater corrosion resistance (e.g. against acids or alkali). A similar process is also described in DE-B-24 32 364 (= US-A-3 945 899), the surface of the aluminum being present not only as a boehmite layer, but also as a chemical “conversion layer” as a result of a chromate or phosphate treatment can. The electrolysis times in the examples are in the range from 2 to 10 minutes. However, both treatment steps are too lengthy for modern belt systems, and in addition the non-electrolytically produced aluminum layers are less suitable for the practical requirements placed on high-performance printing plates (e.g. with regard to abrasion resistance and the interactions with the light-sensitive layer).

In EP-B-0 007 233 and 0 007 234, support materials for printing plates made of aluminum are anodized so that they act as central conductors first through a bath with aqueous 45% H ₃ P0 ₄ and an anode and then into a bath aqueous 15 % H ₂ S0 ₄ and a cathode run. The two electrodes can also be connected to an AC voltage source. It is also stated, but not further specified, that the treatment with H ₃ PO _{4 can be} a pure immersion treatment or that neutral or alkaline solutions would also be possible instead of the acids.

From GB-A-20 88 901 a two-stage anodic oxidation process for printing plate support materials made of aluminum is known, in which in the first stage an aqueous electrolyte containing H ₃ P0 ₄ and in the second stage an aqueous electrolyte containing H ₂ S0 ₄ and H ₃ P0 ₄ can be used. In the first stage a solution is used which contains at least 250 g H ₃ P0 ₄ per 1. Bath monitoring for a mixed electrolyte is always difficult and expensive to control, so that the use of mixed electrolytes is avoided as far as possible in modern conveyor systems. The use of higher acid concentrations on H ₃ P0 ₄ has been shown to be disadvantageous due to the large back dissolving effects, this also applies to the use of alternating current in two-stage anodization. If both electrodes are connected to one Power source are connected, this can also be disadvantageous, since such a variant is more difficult to control in terms of production technology.

Oxide layers primarily produced in aqueous electrolytes containing H ₃ PO ₄ are known to form a relatively compact barrier layer, which in itself contributes to increasing the alkali resistance of the oxide and thus to protecting the underlying aluminum. In a subsequent treatment in aqueous electrolytes containing H ₂ S0 ₄ , however, such a compact barrier layer can often prove to be more of a hindrance since its electrical resistance first has to be overcome, as a result of which high voltages are required. This increases the risk of "burns", ie breakdowns through the primarily formed oxide layer, which cannot be accepted for use in the lithography field.

The prior art also includes US Pat. No. 4,188,270. However, this is a partially two-stage electrolytic polishing process for non-roughened aluminum using sodium phosphate with the addition of organic or inorganic acids or their salts for the production of shiny objects. The statements made above for bathroom monitoring also apply to this method. The object of the present invention is therefore to propose a method for increasing the alkali resistance of support materials for offset printing plates on the basis of roughened and anodized aluminum, which can be carried out relatively quickly and without great effort in a modern belt system, in which the proportion of the oxide redissolution is low or a back solution does not occur and which maintains the positive property of the oxide layer known from the anodic oxidation in aqueous H ₂ S0 ₄ solution and in which the process product has a high chemical resistance.

The invention relates to a process for the production of plate, film or tape-shaped carrier materials for offset printing plates made of chemically, mechanically and / or electrochemically roughened aluminum or one of its alloys by a two-stage anodic oxidation in a) an aqueous electrolyte which contains inorganic compounds Contains phosphorus oxo anions and then b) in an aqueous electrolyte containing sulfuric acid. The process according to the invention is then characterized in that stage a) in an aqueous electrolyte containing 5 to 500 g / l of compounds containing phosphorus oxo anions, with the exception of an electrolyte consisting of aqueous H ₃ PO ₄ , for a period of time of 1 to 60 sec, at a voltage between 10 and 100 V and at a temperature of 10 to 80 ° C until an oxide layer weight of 0.4 to 1.4 g / m ^{2 is} reached and then the anodized material in stage b) treated in an electrolyte with a sulfuric acid content of 100 to 250 g / l and at least 5 g / l of A1 ^{3 + -} ions at a temperature of 20 to 60 ° C until an oxide layer weight of up to 3 g / m2 is reached.

In a preferred embodiment of the process according to the invention, stage a) is carried out for a period of 5 to 60 seconds, at a voltage between 20 and 80 V and at a temperature of 15 to 60 ° C.

• Natriumdihydrogenphosphat NaH₂P0₄
• Dinatriumhydrogenphosphat Na₂HPO₄
• Trinatriumphosphat Na₃P0₄
• Phosphorige Säure H₃P0₃
• Dinatriumphosphit Na₂HP0₃
• Diphosphorsäure (Pyrophosphorsäure) H₄P₂0₇
• Natriumpyrophosphat Na₄P₂0₇
• Triphosphorsäure H₅P₃O₁₀
• Natriumtriphosphat Na₅P₃0₁₀
• Polyphosphorsäure H_n+2P_nO_3n+1
• Hexanatriumtetrapolyphosphat Na₆P₄0₁₃
• Hexanatriummetaphosphat Na₆(PO₃)₆

The aqueous electrolyte with the stated content of phosphoroxo anions preferably contains a salt with the corresponding anion, in particular a salt with an alkali, alkaline earth or ammonium cation and a phosphoroxo anion, but also acids, preferably oligo- and polyphosphoric acids applicable. The concentration of the aqueous electrolyte can be varied within wide limits, preferably as long as it is between 5 and 500 g / l, in particular between 10 and 200 g / l. Examples of suitable compounds in the electrolyte are:

• Sodium dihydrogen phosphate NaH ₂ P0 ₄
• Disodium hydrogen phosphate Na ₂ HPO ₄
• Trisodium phosphate Na ₃ P0 ₄
• Phosphorous acid H ₃ P0 ₃
• Disodium phosphite Na ₂ HP0 ₃
• Diphosphoric acid (pyrophosphoric acid) H ₄ P ₂ 0 ₇
• Sodium pyrophosphate Na ₄ P ₂ 0 ₇
• Triphosphoric acid H ₅ P ₃ O ₁₀
• Sodium triphosphate Na ₅ P ₃ 0 ₁₀
• Polyphosphoric acid H _{n + 2} P _n O _{3n + 1}
• Hexasodium tetrapolyphosphate Na ₆ P ₄ 0 ₁₃
• Hexasodium metaphosphate Na ₆ (PO ₃ ) ₆

The alkali resistance of the layers produced by the process according to the invention, when using the phosphoroxo anions, with the exception of Na ₃ P0 ₄ , generally remains in a comparable order of magnitude, irrespective of the electrolyte concentration, provided that the zincate test times are taken as the basis. The current course of the anodization can be characterized approximately in such a way that after a very brief initial current density of approximately 18 to 25 A / dm ^2, this drops to values of less than 10 A / dm ² after approximately 2 to 5 seconds, after approximately 10 to 20 sec already fall towards 0. If Na ₃ P0 ₄ is used, a constant current density of approximately 5 to 20 A / dm ^{2 is} maintained for the duration of the anodization, depending on the voltage applied. Na ₃ P0 ₄ also forms a certain exception with regard to the alkali resistance of the oxide layers produced with it, since an increase in the electrolyte concentration also leads to a significant increase in the zincate test times. The use of higher voltages generally also increases the alkali resistance of the layers.

Suitable base materials for the material to be oxidized according to the invention include those Aluminum or one of its alloys, which have, for example, a content of more than 98.5% by weight of Al and proportions of Si, Fe, Ti, Cu and Zn. These aluminum carrier materials are still, optionally after a pre-cleaning, mechanical (e.g. by brushing and / or with abrasive treatments), chemical (e.g. by etching agents) and / or electrochemical (e.g. by AC treatment in aqueous HCl) -, HN0 ₃ - or in salt solutions) roughened. In particular, materials with electrochemical or a combination of mechanical and electrochemical roughening are used in the method according to the invention. All process steps can be carried out batchwise, but they are preferably carried out continuously.

In general, the process parameters, especially in the case of continuous process control, are in the roughening stage in the following ranges: the temperature of the electrolyte between 20 and 60 ° C., the active substance (acid, salt) concentration between 2 and 100 g / l (also in the case of salts higher), the current density between 15 and 250 A / dm ² , the dwell time between 3 and 100 sec and the electrolyte flow rate on the surface of the workpiece to be treated between 5 and 100 cm / sec; alternating current is usually used as the type of current, but it is also modified current types such as alternating current with different amplitudes of the current strength for the anode and cathode current are possible. The mean roughness depth R _{z of} the roughened surface is in the range of about 1 to 15 µm. The roughness depth is determined in accordance with DIN 4768 in the version from October 1970, The roughness depth Rz is then the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections.

Pre-cleaning includes, for example, treatment with aqueous NaOH solution with or without degreasing agent and / or complexing agents, trichlorethylene, acetone, methanol or other commercially available aluminum stains. The roughening or, in the case of several roughening stages, also between the individual stages, an abrasive treatment can additionally be carried out, in particular a maximum of 2 g / m ^{2 being} removed (up to 5 g / m ² between the stages); In general, aqueous solutions of alkali metal hydroxide or aqueous solutions of alkaline salts or aqueous acid solutions based on HN0 ₃ , H ₂ SO ₄ or H ₃ PO ₄ are used as abrasive solutions. In addition to an abrasive treatment stage between the roughening stage and the anodizing stages, such non-electrochemical treatments are also known which only have a rinsing and / or cleaning effect and, for example, for removing deposits formed during roughening ("Schmant") or simply for removing electrolyte residues serve; For example, dilute aqueous alkali hydroxide solutions or water are used for these purposes.

After the roughening process, the procedure described further above then follows in the further process steps as the first anodic oxidation step a) of the aluminum. A rinse stage can be switched on before stage b). Stage b) is carried out in an electrolyte containing H ₂ S0 ₄ , as described at the outset in the assessment of the prior art. In addition to H ₂ S0 ₄ and water in the main, a suitable electrolyte will also contain Al ^{3 +} ions, which either arise during the process or are added from the start [e.g. B. as Al ₂ (SO ₄ ) ₃ ]. In particular, the electrolyte in stage b) contains 100 to 250 g / l of H ₂ SO ₄ , at least 5 g / l of A1 ^{3 +} ions, and the stage is carried out at 20 to 60 ° C. Direct current is preferably used for anodic oxidation in these stages, however alternating current or a combination of these types of current (e.g. direct current with superimposed alternating current) can also be used. The process time in both stages is preferably about 5 to 60 seconds. The layer weights of the oxide layer produced in stage a) generally range between about 0.4 to 1.4 g / m ² , corresponding to a layer thickness of about 0.01 up to 0.4 µm; they are preferably about 0.6 to 1.0 g / m ² , corresponding to about 0.02 to 0.3 μm. This oxide layer is then further treated in step b), if appropriate after rinsing with water, it being possible for the oxide weight to be increased to values of, for example, 1 to 3 g / m ² (corresponding to 0.3 to 1 μm). The aluminum oxide layers also contain A1 ₂ (SO ₄ ) ₃ and AIP0 ₄ .

The stages of anodic oxidation of the aluminum support material can also be followed by one or more post-treatment stages, although this is often not necessary, particularly in the present process. Aftertreatment is understood in particular to mean a hydrophilizing chemical or electrochemical treatment of the aluminum oxide layer, for example an immersion treatment of the material in an aqueous polyvinylphosphonic acid solution according to DE-C-16 21 478 (= GB-A-1 230 447), an immersion treatment in one aqueous alkali silicate solution according to DE-B-14 71 707 (= US-A-3 181 461) or an electrochemical treatment (anodization) in an aqueous alkali silicate solution according to DE-A-25 32 769 (= US-A- 3 902 976). These post-treatment stages serve in particular to additionally increase the hydrophilicity of the aluminum oxide layer, which is often sufficient, while at least the other known properties of this layer are retained.

The materials produced according to the invention are used as supports for offset printing plates, i. H. a radiation-sensitive coating is applied to one or both sides of the carrier material either by the manufacturer of presensitized printing plates or directly by the consumer. In principle, all layers are suitable as radiation (light) sensitive layers which, after irradiation (exposure), optionally with subsequent development and / or fixation, provide an image-like area from which printing can take place.

• positiv-arbeitende, o-Chinondiazide, insbesondere o-Naphthochinondiazide wie Naphthochinon-(1,2)-diazid-(2)-sulfonsäureester oder -amide, die nieder- oder höhermolekular sein können, als lichtempfindliche Verbindung enthaltende Reproduktionsschichten, die beispielsweise in den DE-C-854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273, 1 124 817 und 2 331 377 und den EP-A-0 021 428 und 0 055 814 beschrieben werden;
• negativ-arbeitende Reproduktionsschichten mit Kondensationsprodukten aus aromatischen Diazoniumsalzen und Verbindungen mit aktiven Carbonylgruppen, bevorzugt Kondensationsprodukte aus Diphenylamindiazoniumsalzen und Formaldehyd, die beispielsweise in den DE-C-596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123, den US-A-2 679 498 und 3 050 502 und der GB-A-712 606 beschrieben werden;
• negativ-arbeitende, Mischkondensationsprodukte aromatischer Diazoniumverbindungen enthaltende Reproduktionsschichten, beispielsweise nach der DE-C-20 65 732, die Produkte mit mindestens je einer Einheit aus a) einer kondensationsfähigen aromatischen Diazoniumsalzverbindung und b) einer kondensationsfähigen Verbindung wie einem Phenolether oder einem aromatischen Thioether, verbunden durch ein zweibindiges, von einer kondensationsfähigen Carbonylverbindung abgeleitetes Zwischenglied wie einer Methylengruppe aufweisen;
• positiv-arbeitende Schichten nach der DE-A-26 10 842 der DE-C-27 18 254 oder der DE-A-29 28 636, die eine bei Bestrahlung Säure abspaltende Verbindung, eine monomere oder polymere Verbindung, die mindestens eine durch Säure abspaltbare C-O-C-Gruppe aufweist (z. B. eine Orthocarbonsäureestergruppe oder eine Carbonsäureamidacetalgruppe) und gegebenenfalls ein Bindemittel enthalten;
• negativ-arbeitende Schichten aus photopolymerisierbaren Monomeren, Photoinitiatoren, Bindemitteln und gegebenenfalls weiteren Zusätzen; als Monomere werden dabei beispielsweise Acryl- und Methacrylsäureester oder Umsetzungsprodukte von Diisocyanaten mit Partialestern mehrwertiger Alkohole eingesetzt, wie es beispielsweise den US-A-2 760 363 und 3 060 023 und den DE-A-20 64 079 und 23 61 041 beschrieben wird;
• negativ-arbeitende Schichten gemäß der DE-A-30 36 077, die als lichtempfindliche Verbindung ein Diazoniumsalz-Polykondensationsprodukt oder eine organische Azidoverbindung und als Bindemittel ein hochmolekulares Polymeres mit seitenständigen Alkenylsulfonyl- oder Cycloalkenylsulfonylurethan-Gruppen enthalten.

In addition to the layers containing silver halides used in many fields, various others are also known, such as e.g. B. in "Light-Sensitive Systems" by Jaromir Kosar, John Wiley & Sons Verlag, New York 1965: the colloid layers containing chromates and dichromates (Kosar, chapter 2); the layers containing unsaturated compounds in which these compounds are isomerized, rearranged, cyclized or crosslinked during exposure (Kosar, Chapter 4); the layers containing photopolymerizable compounds, in which monomers or prepolymers optionally polymerize during exposure by means of an initiator (Kosar, Chapter 5); and the layers containing o-diazo-quinones such as naphthoquinonediazides, p-diazo-quinones or diazonium salt condensates (Kosar, Chapter 7). The suitable layers also include the electrophotographic layers, ie those which contain an inorganic or organic photoconductor. In addition to the light-sensitive substances, these layers can of course also other components such. B. contain resins, dyes or plasticizers. In particular, the following light-sensitive compositions or compounds can be used in the coating of the carrier materials produced by the process according to the invention:

• positive-working, o-quinonediazides, in particular o-naphthoquinonediazides such as naphthoquinone- (1,2) -diazid- (2) -sulfonic acid esters or amides, which can be of low or higher molecular weight, as a photosensitive compound-containing reproduction layers, for example in the DE-C-854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273, 1 124 817 and 2 331 377 and EP-A-0 021 428 and 0 055 814;
• negative working reproduction layers with condensation products from aromatic diazonium salts and compounds with active carbonyl groups, preferably condensation products from diphenylamine diazonium salts and formaldehyde, which are described, for example, in DE-C-596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123, US-A-2 679 498 and 3 050 502 and GB-A-712 606;
• Negative-working, mixed condensation products of aromatic diazonium compounds containing reproduction layers, for example according to DE-C-20 65 732, the products with at least one unit each from a) a condensable aromatic diazonium salt compound and b) a condensable compound such as a phenol ether or an aromatic thioether by a double bonded intermediate derived from a condensable carbonyl compound such as a methylene group;
• positive-working layers according to DE-A-26 10 842, DE-C-27 18 254 or DE-A-29 28 636, which contain a compound which releases acid when irradiated, a monomeric or polymeric compound which contains at least one acid has cleavable COC group (e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally contain a binder;
• negatively working layers made of photopolymerizable monomers, photoinitiators, binders and optionally other additives; the monomers used are, for example, acrylic and methacrylic acid esters or reaction products of diisocyanates with partial esters of polyhydric alcohols, as described, for example, in US Pat. Nos. 2,760,363 and 3,060,023 and DE-A-20 64 079 and 23 61 041;
• Negative-working layers according to DE-A-30 36 077, which contain a diazonium salt polycondensation product or an organic azido compound as the light-sensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as the binder.

It can also be photoconductive layers such as z. B. in DE-C-11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 are described, applied to the carrier materials produced according to the invention, whereby highly light-sensitive, electrophotographic printing plates are formed.

• - die beim Einsatz von HgP0₄ in der Stufe a) zu beobachtenden "Verbrennungen" treten im erfindungsgemäßen Verfahren nicht auf,
• - die beim Einsatz von H₃P0₄ in der Stufe a) zu ermittelnde Alkaliresistenz der Oxidschicht wird erfindungsgemäß, insbesondere bei Einsatz von Salzen, noch deutlich verbessert,
• - die beim Einsatz von Salzen mit Phosphoroxo-Anionen in der Stufe b), d- h- bei einer Umkehrung des erfindungsgemäßen Verfahrens zu ermittelnde Alkaliresistenz wird bei nahezu gleicher Oxidschichtdicke noch zusätzlich verbessert,
• - die Hydrophilie der Oberfläche wird gegenüber einem Einsatz von Salzen mit Phosphoroxo-Anionen in der Stufe b) (Umkehrung) so stark verbessert, daß möglicherweise eine zusätzliche Hydrophilierung überflüssig wird, und
• - darüber hinaus bleiben die von umgekehrten Verfahren her bekannten Vorteile wie gute Abriebfestigkeit, helle Oberfläche, keine "Farbschleier"-Bildung und vorzügliche Wasserführung mindestens erhalten.

The coated offset printing plates obtained from the carrier materials produced by the process according to the invention are converted into the desired printing form in a known manner by imagewise exposure or irradiation and washing out of the non-image areas with a developer, for example an aqueous alkaline developer solution. Surprisingly, offset printing plates, the support materials of which have been treated by the process according to the invention, are distinguished by considerably improved alkali resistance compared to those plates in which the same support material has been treated without the use of step a). In addition, the carrier materials produced according to the invention or the offset printing plates or printing plates produced from them have the following characteristics:

• the "burns" to be observed when using HgP0 ₄ in stage a) do not occur in the process according to the invention,
• the alkali resistance of the oxide layer to be determined when using H ₃ PO ₄ in stage a) is significantly improved according to the invention, in particular when salts are used,
• the alkali resistance to be determined when using salts with phosphorus oxo anions in stage b), ie if the process of the invention is reversed, is additionally improved with the oxide layer thickness being almost the same,
• - The hydrophilicity of the surface is improved so much compared to the use of salts with phosphorus oxo anions in stage b) (reversal) that additional hydrophilization may become superfluous, and
• - In addition, the advantages known from reverse processes such as good abrasion resistance, bright surface, no "color fog" formation and excellent water flow are at least preserved.

• Zinkattest (nach US-PS-3 940 321, Spalten 3 und 4, Zeilen 29 bis 68 und Zeilen 1 bis 8):
  • Als Maß für die Alkaliresistenz einer Aluminiumoxidschicht gilt die Auflösegeschwindigkeit der Schicht in sec in einer alkalischen Zinkatlösung. Die Schicht ist umso alkalibeständiger je länger sie zur Auflösung braucht. Die Schichtdicken sollten in etwa vergleichbar sein, da sie natürlich auch einen Parameter für die Auflösegeschwindigkeit darstellen. Man bringt einen Tropfen einer Lösung aus 500 ml H₂0 dest., 480 g KOH und 80 g Zinkoxid auf die zu untersuchende Oberfläche und bestimmt die Zeitspanne bis zum Auftreten von metallischem Zink, was an einer Dunkelfärbung der Untersuchungsstelle zu erkennen ist.

In the above description and the examples below, 0 / o data always mean% by weight, unless stated otherwise. Parts by weight relate to parts by volume in the ratio of g to cm ³ . Furthermore The following methods were used to test the alkali resistance of the surface in the examples, the results of which were summarized in tables:

• Zinc certificate (according to US Pat. No. 3,940,321, columns 3 and 4, lines 29 to 68 and lines 1 to 8):
  • The rate at which the layer dissolves in an alkaline zincate solution is used as a measure of the alkali resistance of an aluminum oxide layer. The layer is more alkali-resistant the longer it takes to dissolve it. The layer thicknesses should be roughly comparable, since of course they also represent a parameter for the dissolution rate. A drop of a solution of 500 ml of distilled H ₂ O, 480 g of KOH and 80 g of zinc oxide is placed on the surface to be examined and the period of time until the appearance of metallic zinc is determined, which can be seen from the darkening of the examination site.

Gravimetric removal

The sample of a defined size protected on the back by a layer of lacquer is moved in a bath which contains an aqueous solution of 6 g / l of NaOH. The weight loss experienced in this bath is determined gravimetrically. Times of 1, 2, 4 or 8 minutes are selected as the treatment time in the alkaline bath.

Comparative Example V1

A bright rolled aluminum sheet with a thickness of 0.3 mm is degreased with an aqueous alkaline pickling solution at a temperature of 50 to 70 ° C. The electrochemical roughening of the aluminum surface is carried out using alternating current in an electrolyte containing HN0 ₃ , a surface roughness having an R _z value of about 6 μm being obtained. The subsequent anodic oxidation is carried out in accordance with the process described in EP-B-0 004 569 in an aqueous electrolyte containing H ₂ S0 ₄ and Al ₂ (SO ₄ ) ₃ , resulting in a layer weight of 2.8 g / m ² leads.

example 1

An aluminum sheet pickled and roughened according to the specifications of comparative example V1 is anodically oxidized at room temperature at a direct voltage of 40 V in an aqueous solution containing 100 g / l of NagP0 ₄ for 30 seconds. After rinsing with demineralized water the sheet in a second stage, containing oxidized, an aqueous solution of 200 g / I of H ₂ S0 ₄ and 50 g / I sec to A1 ₂ (SO _{4) 3} at 20 V for 30 also anodically . The oxide weight determination gives a value of 1.3 g / m ² . For further results and process variations, see Table I.

• 0,70 Gew.-Teile des Polykondensationsproduktes aus 1 Mol 3-Methoxy-diphenylamin-4-diazoniumsulfat und 1 Mol 4,4'-Bis-methoxymethyl-diphenylether, ausgefällt als Mesitylensulfonat,
• 3,40 Gew.-Teile 85 %ige Phosphorsäure,
• 3,00 Gew.-Teile eines modifizierten Epoxidharzes, erhalten durch Umsetzen von 50 Gew.-Teilen eines Epoxidharzes mit einem Molgewicht unterhalb 1000 und 12,3 Gew.-Teilen Benzoesäure in Ethylenglykolmonomethylether in Geqenwart von Benzyltrimethvlammoniumhvdroxid,
  

To produce an offset printing plate, this support is coated with the following negative-working light-sensitive solution:

• 0.70 parts by weight of the polycondensation product from 1 mol of 3-methoxy-diphenylamine-4-diazonium sulfate and 1 mol of 4,4'-bis-methoxymethyl-diphenyl ether, precipitated as mesitylene sulfonate,
• 3.40 parts by weight of 85% phosphoric acid,
• 3.00 parts by weight of a modified epoxy resin obtained by reacting 50 parts by weight of an epoxy resin with a molecular weight below 1000 and 12.3 parts by weight of benzoic acid in ethylene glycol monomethyl ether in the presence of benzyltrimethylammonium hydroxide,
  

entwickelt.After exposure through a negative mask, a solution of

developed.

The pressure plate can be developed quickly and free of fog. Due to the bright appearance of the carrier surface there is a very good contrast between image and non-image areas. The number of copies printed from the printing form is 200,000.

Example 2

An aluminum strip prepared in accordance with Example 1 and two-stage anodized is coated with the following positive-working light-sensitive solution to produce an offset printing plate:

The coated tape is dried in the drying tunnel at temperatures up to 120 ° C. The printing plate thus produced is exposed under a positive template and developed with a developer of the following composition:

The printing form obtained is perfect in terms of copying and printing technology and has a very good contrast after exposure, the print run is 150,000.

Comparative example V2

An aluminum sheet pickled and roughened according to the specifications of comparative example V1 is anodized at room temperature at a direct voltage of 40 V in an aqueous solution containing 100 g / l of H ₃ PO ₄ for 30 seconds. After rinsing with deionized water, the sheet is subjected to a second anodic oxidation as described in Example 1. No current flow can be determined under the conditions of Example 1; the anodization reaction occurs abruptly only when the voltage is increased to 35 to 40 V. At the end of the second anodizing stage, the sheet clearly shows burns on the surface. The oxide layer weight is 0.75 g / m ² .

Examples 3 to 8

An aluminum sheet pickled and electrochemically roughened in accordance with the information given in Comparative Example V1 is treated anodically with direct voltage in the aqueous electrolyte solutions listed in Table 1. The treatment parameters also given in the table are used for this. Then in a second stage in an H ₂ S0 ₄ containing electrolyte according to Example 1.

Examples 9 to 29

An aluminum sheet pickled and electrochemically roughened in accordance with the information given in Comparative Example V1 is treated anodically with direct voltage in the aqueous electrolyte solutions listed in Table II. The treatment parameters also given in Table 11 are used for this. Then in a second stage in an H ₂ S0 ₄ containing electrolyte according to Example 1.

Example 30

• 10,00 Gew.-Teile 2,5-Bis(4'-diethylaminophenyl)-1,3,4,-oxdiazol
• 10,00 Gew.-Teile eines Mischpolymerisates aus Styrol und Maleinsäureanhydrid mit einem Erweichungspunkt von 210° C
• 0,02 Gew.-Teile Rhodamin FB (C. I. 45 170)
• 300,00 Gew.-Teile Ethylenglykolmonomethylether

A carrier treated according to Example 24 with a voltage of 60 V for 30 seconds in the first anodizing stage and subsequently anodized according to Example 1 is coated with the following solution to produce an electrophotographically operated offset printing plate:

• 10.00 parts by weight of 2,5-bis (4'-diethylaminophenyl) -1,3,4, -oxdiazole
• 10.00 parts by weight of a copolymer of styrene and maleic anhydride with a softening point of 210 ° C.
• 0.02 part by weight of Rhodamine FB (CI 45 170)
• 300.00 parts by weight of ethylene glycol monomethyl ether

• 35 Gew.-Teilen Natriummetasilikat . 9 H₂0,
• 140 Gew.-Teilen Glyzerin,
• 550 Gew.-Teilen Ethylenglykol und
• 140 Gew.-Teilen Ethanol getaucht. Die Platte wird dann mit einem kräftigen Wasserstrahl abgespült, wobei die nicht mit Toner bedeckten Stellen der Photoleiterschicht entfernt werden, die Platte ist dann druckfertig.

The layer is negatively charged to about 400 V in the dark by means of a corona. The charged plate is exposed imagewise in a repro camera and then developed with an electrophotographic suspension developer which also contains a dispersion of 3.0 parts by weight of magnesium sulfate in a solution of 7.5 parts by weight of pentaerythritol resin ester in 1200 parts by volume of an isoparaffin mixture represents a boiling range of 185 to 210 ° C. After removing the excess developer liquid, the developer is fixed and the plate is poured out into a solution for 60 seconds

• 35 parts by weight of sodium metasilicate. 9 H ₂ 0,
• 140 parts by weight of glycerin,
• 550 parts by weight of ethylene glycol and
• 140 parts by weight of ethanol immersed. The plate is then rinsed off with a powerful water jet, the areas of the photoconductor layer which are not covered with toner being removed, and the plate is then ready for printing.

Example 31

An aluminum strip prepared according to the information in Example 3 is immersed in a further treatment step (additional hydrophilization) in a 0.2% aqueous solution of polyvinylphosphonic acid at 50 ° C. for 20 seconds. After drying, the support material additionally hydrophilized in this way is further processed as described in Example 3, it being possible to improve the ink-repelling effect of the non-image areas. An even more favorable hydrophilization is achieved with the complex-type reaction products described in DE-A-31 26 636 from a) polymers such as polyvinylphosphonic acid and b) a salt of an at least divalent metal cation.

Claims (6)

1. A process for the production of sheet-like, film-like or web-like bases for offset printing plates from chemically, mechanically and/or electrochemically roughened aluminum or one of it's alloys by means of a two-stage anodic oxidation in a) an aqueous electrolyte containing inorganic compounds with phosphoroxo anions and then b) in an aqueous electrolyte containing sulfuric acid, wherein stage a) is carried out in an aqueous electrolyte containing 5 to 500 g/I of compounds having phosphoroxo anions, with the exception of an electrolyte consisting of aqueous H₃P0₄, for a period of 1 to 60 sec, at a voltage between 10 and 100 V and at a temperature of 10 to 80°C, until an oxide layer weight of 0.4 to 1.4 g/m² has been reached and the material anodized in this manner is then treated in stage b) in an electrolyte containing 100 to 250 g/I of sulfuric acid and at least 5 g/I of AI^3+-ions at a temperature of 20 to 60°C, until an oxide layer weight of up to 3 g/m² has been reached.

2. The process as claimed in claim 1, wherein a) is carried out for a period of 5 to 60 sec, at a voltage between 20 and 80 V and at a temperature of 15 to 60° C.

3. The process as claimed in claim 1 or 2, wherein, in a), the aqueous electrolyte contains a salt possessing an alkali metal, alkaline earth metal or ammonium cation and a phosphoroxo anion.

4. The process as claimed in any of claims 1 to 3, wherein the aluminum is roughened electrochemically or mechanically and electrochemically.

5. The process as claimed in any of claims 1 to 4, wherein stage b) is carried out for a period of 5 to 60 sec.

6. The process as claimed in any of claims 1 to 5, wherein a hydrophilization step is additionally carried out after stage b).