EP0269851B1 - Aluminium or aluminium alloy based carrier materials for offset printing plates, and process for manufacturing them - Google Patents

Description

The invention relates to an improved carrier material based on aluminum or its alloys for offset printing plates.

The invention also relates to a method for producing the carrier material.

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 in a photomechanical way. After a printing form has been produced from the printing plate, the layer support carries the image areas which will guide the color during later printing and at the same time forms the hydrophilic image background for the lithographic printing process at the areas which are free of image (non-image areas) during 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 strahlungsempfindlichen Schicht vor bzw. der druckenden Teile der Schicht nach der Bestrahlung (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 have to be developed be easy to remove residue-free from the support to generate 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 high affinity for water, that is to say it must 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 radiation-sensitive layer before or the printing parts of the layer after the irradiation (exposure) must be sufficient.
• The carrier material is said to have good mechanical resistance, e.g. 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 commonly used in electrolytes such as H₂SO₄, H₃PO₄, H₂C₂O₄, H₃BO₃, 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 H₂SO₄ or H₃PO₄ solution are used. For electrolytes containing H₂SO₄, reference is made, for example, to EP-B 0 004 569 (= US-A 4 211 619) and the prior art mentioned therein.

In aqueous, H₂SO₄ containing electrolytes produced aluminum oxide layers are amorphous and usually have a layer weight of about 0.5 to 10 g / m² in offset printing plates, corresponding to a layer thickness of about 0.15 to 3.0 microns. A disadvantage of the use of such an anodized substrate, in particular for offset printing plates, is the relatively low resistance of the oxide layers produced in H₂SO₄ electrolytes to alkaline solutions, such as are increasingly being used, for example, in the processing of presensitized offset printing plates, preferably in contemporary developer solutions for irradiated ones negative- or in particular positive-working radiation-sensitive layers. In addition, these aluminum oxide layers often tend to more or less irreversible adsorption of substances from the applied reproduction layers, which can lead, for example, to a coloration of the oxide layers (“fogging”). The so anodized Beams are relatively dark and mechanical abrasion levels are poor.

The anodic oxidation of aluminum in phosphorus oxygen acids and aqueous electrolytes optionally containing further compounds is also known and is described, for example, in DE-A 32 06 470, where the prior art is also discussed in detail. The plates produced in this way are somewhat lighter in appearance than those anodized with sulfuric acid and, for example, also have better abrasion resistance and alkali resistance, but the plates are not yet silvery - as desired and tend to be under-exposed.

Electroless alkaline treatments of aluminum oxide surfaces are also known, e.g. from DD-A 208 176, JP-A 58/177497 and JP-A 56/051388 and DE-A 32 19 922.

JP-A 57/085998 and JP-A 57/085996 describe a method for anodizing solar energy collectors in which an electrolyte is used which, in addition to an alkali metal hydroxide, also contains an acid and sodium phosphate, a polyhydric alcohol or a fluoride. Because of the additives, this electrolyte has a pH which is too low to be used in the process according to the invention. Therefore, under practical conditions it is not possible to achieve oxide layers as thick as those for lithographic ones Purposes would be desirable. The addition of fluoride also increases the corrosiveness of the electrolyte, which leads to an unsightly gray surface.

EP-A 0 048 988 describes a multi-stage process for coloring the surface of aluminum, in which strip-shaped patterns are produced. Material is used that was previously anodized. In the second step - the coloring step - the process uses an electrolyte that contains alkali metal ions and additives that lead to the stripe pattern. Alkali metal phosphates or borates or alkaline earth metal compounds and an acid with which the pH is adjusted below 5.0 are mentioned as additives.

Some alkaline electrolytes are known to form a thin, but very dense, electrically insulating barrier layer that prevents an oxide layer that is sufficiently thick for lithographic purposes from being built up (see, for example, Wernick and Pinner, "The Surface Treatment and Finishing of Aluminum and its Alloys ", Vol. 1, pp. 304ff., Robert Draper Ltd., Teddington 1972). This applies to anodizing in alkali metal phosphate solutions, which are described, for example, in JP-A 54/031047 and DE-A 28 42 396, as well as for electrolytes, the main constituents of which are borates, as in EP-A 0 008 212 JP-A 49/035239 and GB-A 1 243 741, as well as for ammonium salt-containing electrolytes, which JP-B 9453/73 recommends.

In weakly alkaline solutions, as described, for example, in JP-A 52/120238, it is not possible to achieve sufficiently thick oxide layers with practical voltages in such short times as are necessary in modern, continuously operating systems.

JP-A 53/011843 recommends an electrolyte that can be acidic or alkaline and contains chloride. An aluminum material treated with this electrolyte has an unsightly, irregularly gray surface due to the corrosive chloride ions.

From US-A 4,166,777 a method for producing a carrier material for offset printing plates is known, in which plate-shaped aluminum is mechanically roughened and anodized in an aqueous alkaline sodium silicate electrolyte at a pH of 13 and a voltage of 6 or 36 volts. The electrolyte of this known method contains 1.56 or 4.05% by weight of sodium silicate, defined by 1 Na₂O: 2.5 SiO₂, which as the sodium salt of weak silica in aqueous solution reacts strongly alkaline and has a pH of 13.

The object of the present invention is to provide a carrier material based on aluminum or its alloys, which at the same time has a higher resolution of the plates coated with a light-sensitive layer, high contrast between non-image areas and image areas, high oxide layer weight, high abrasion resistance, high alkali resistance and good adhesion between the support and the photosensitive layer.

It is furthermore an object of the present invention to propose a process for the anodic oxidation of bright-rolled or roughened, flat aluminum, suitable as a carrier material for offset printing plates, which can be carried out relatively quickly in a modern installation and without great outlay in terms of apparatus and process engineering.

The invention is based on a plate, foil or tape-shaped carrier material for offset printing plates made of bright rolled, mechanically and / or chemically or mechanically and electrochemically roughened aluminum or its alloys anodized in alkaline solutions.

The characteristic of the invention is that the carrier material has a reflectometer value at 60 ° (measured according to DIN 67530, 1982) of> 5, an abrasion of the oxide layer of <0.5 g / m² and an alkali resistance of> 140 s. The carrier material preferably has a reflectometer value of ≧ 15. The preferred value for the abrasion of the oxide layer is ≦ 0.3 g / m² and that of the alkali resistance is ≧ 160 s. The carrier material preferably has an oxide basis weight of> 0.8 g / m 2.

The manufacture of the carrier material is based on a process in which plate, foil or strip-shaped aluminum or its alloys are roughened mechanically and / or chemically or mechanically and electrochemically and anodized in an aqueous alkaline electrolyte at a voltage greater than 36 V. will. It is characteristic that the applied voltage is set in a range from 42 to below 50 V and that the pH value is in the range greater than or equal to 12.5 to less than or equal to 13.4. In one embodiment of the method, the electrolyte contains sodium hydroxide. Furthermore, the electrolyte contains a strongly alkaline salt such as alkali metal octyl sulfate, carbonate, aluminate, borate, silicate or phosphate of a weak acid. The alkali metal salt in 1% by weight aqueous solution has a pH of at least 10.5. In addition to water, the electrolyte also contains 0.1 to 20% by weight, preferably 0.5 to 10% by weight, of solids. The anhydrous solids content of the electrolyte is too at least 60% by weight preferably from alkali metal hydroxide. The rest can consist of a weak acid alkali metal salt, surfactants and aluminum ions, these components not being essential for the operation of the process.

Alkali metal salts of weak acids form alkaline solutions in water. Among the alkali metal salts of weak acids, those salts are selected in the process according to the invention whose 1% by weight aqueous solutions (of the anhydrous salts) have a pH of at least 10.5. For example, some alkali metal carbonates, alkali metal silicates and alkali metal phosphates and alkali metal aluminates are suitable.

The choice of surfactants is relatively uncritical. It should be a substance that does not decompose too quickly under the conditions of anodic oxidation so that the electrolyte does not have to be regenerated too often. For example, sodium octyl sulfate can be added. An amount of one percent by weight is sufficient, but more can be used without adverse consequences.

Aluminum ions are brought into the electrolyte anyway by dissolving the anode material during the anodizing process. They can also be added to the electrolyte before the start of the anodization in order to change the relative composition of the electrolyte in the course of the anodization by dissolving the anode material to diminish. However, an increased content of aluminum ions in the electrolyte reduces the current flow during anodization. Aluminum ions can be added until the weight ratio of alkali metal hydroxide to aluminum ions is about 6: 1, but it makes sense to use less. Aluminum can be added to the electrolyte, for example, in the form of alkali metal aluminate.

The concentration ranges of the electrolyte components are checked at regular intervals, since they are of crucial importance for an optimal process, and the electrolyte is then regenerated discontinuously or continuously. The process according to the invention itself can be carried out batchwise or in particular continuously. Good electrolyte circulation is preferred in the practice of the invention. This can be generated by stirring or pumping around the electrolyte. In the case of a continuous process, care must be taken that the electrolyte is conducted as parallel as possible to the strip to be treated under turbulent flow at high speed while ensuring good material and heat exchange. The flow rate of the electrolyte relative to the strip is then expediently more than 0.3 m / s. Direct current is used in particular as the type of current, however alternating current or a combination of these types of current (e.g. direct current with superimposed alternating current or asymmetrical types of current) can also be used. The voltages are generally between 2 and 50 V, the current densities between 3 and 50 A / dm², the temperatures between 10 and 50 ° C and the time periods between 5 and 500 seconds.

The oxide layer weight to be achieved by the method according to the invention increases with increasing current density and longer anodizing time, but the current yield decreases with increasing duration of the anodizing.

Although the strongly alkaline electrolyte is very aggressive and aluminum oxide can dissolve quickly, surprisingly oxide layer weights of 2 g / m² and more can be achieved here.

The oxide layer's weight also increases the resistance of the oxide layer to mechanical abrasion. The correction contrast (due to corrections, the appearance of light areas on a tinted background) and the "fog" are largely independent of the electrolyte concentration. As the anodizing time increases with the same oxide layer weight, the mechanical abrasion values generally become more favorable.

The oxide layers achieved in this way combine all the advantages known per se from supports anodized in phosphoric acid, such as, for. B. a bright, shiny silver color, a very good alkali resistance and low tendency to fog with the advantage of an anodized in sulfuric acid, which consists in its relatively high oxide layer weight and the associated favorable values of mechanical abrasion.

Suitable base materials for the material to be oxidized according to the invention include those made of aluminum or one of its alloys, which have, for example, more than 98.5% by weight of Al and proportions of Si, Fe, Ti, Cu and Zn. These aluminum support materials are roughened, optionally after a preliminary cleaning, mechanically (e.g. by brushing and / or with abrasive treatments) and electrochemically (e.g. by AC treatment in aqueous HCl, HNO₃ or in salt solutions) or only electrochemically. All process steps can be carried out batchwise, but they are preferably carried out continuously.

In general, the process parameters, particularly in the case of continuous process control, in the electrochemical roughening stage are 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 (in the case of salts also higher), the current density between 15 and 250 A / dm², the dwell time between 3 and 100 s and the electrolyte flow rate on the surface of the workpiece to be treated between 5 and 100 cm / s; AC is usually used as the type of current, but modified types of current such as AC with different amplitudes of the current strength are also possible for the anode and cathode currents. The average roughness depth R _{z of} the roughened surface is in the range from about 1 to 15 μm. The roughness depth is determined in accordance with DIN 4768 in the version from October 1970, the roughness depth R _z 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 additional abrasive treatment can be added, in particular a maximum of 2 g / m² being removed (between the stages up to 5 g / m²); as abrasive solutions are generally used aqueous alkali metal hydroxide solutions or aqueous solutions of alkaline salts or aqueous acid solutions based on HNO₃, H₂SO₄ or H₃PO₄. 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. However, such treatment is often not necessary since the anodizing electrolyte has a sufficient ablative effect.

The stage 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. Post-treatment involves in particular a hydrophilizing chemical or electrochemical treatment understood the aluminum oxide layer, for example immersion treatment of the material in an aqueous polyvinylphosphonic acid solution according to DE-C 16 21 478 (= GB-A 1 230 447), immersion treatment in an aqueous alkali silicate solution according to DE-B 14 71 707 ( = US-A 3 181 461). 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.

In addition to the layers containing silver halides used in many fields, various others are also known, as are described, for example, 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 contain other constituents such as 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;
Reproductive layers containing negative-working, mixed condensation products of aromatic diazonium compounds, for example according to DE-C 20 65 732, the products with at least one unit each of a) a condensable aromatic diazonium salt compound and b) a condensable compound such as a phenol ether or an aromatic thioether, connected by have 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 cleaves off under irradiation, a monomeric or polymeric compound which has at least one COC which can be cleaved off by acid 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. 2,760,863 and 3,060,023 and DE-A 20 64 079 and 2,361,041;
Negative-working layers according to DE-A 30 36 077, which contain a diazonium salt polycondensation product or an organic azido compound as a photosensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as a binder.

It is also possible to use photo-semiconducting layers such as e.g. in DE-C 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 are described, are applied to the carrier materials produced according to the invention, thereby producing highly light-sensitive, electrophotographic printing plates.

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.

• Die Nichtbildstellen von Druckplatten sind - auch ohne hydrophilierende Nachbehandlung - nach dem Entwickeln "schleierfrei". Damit ist die erfindungsgemäß erzeugte Oxidoberfläche einer in H₂SO₄ oder in H₃PO₄ oder in H₂SO₄/H₃PO₄-Gemische enthaltenden Elektrolyten erzeugten Oberfläche vergleichbaren Oxidschichtgewichts deutlich überlegen.
• Die Alkaliresistenz des erzeugten Oxids ist dem in einem H₂SO₄ oder H₃PO₄ oder H₂SO₄/H₃PO₄-Gemische enthaltenden wäßrigen Elektrolyten erzeugten Oxid deutlich überlegen.
• Das erzielte Oxidschichtgewicht kann die Werte der in einem H₂SO₄ enthaltenden Elektrolyten erzeugten Oxidschicht erreichen und ist damit bezüglich der Schichtdicke dem in üblichen H₃PO₄ enthaltenden Elektrolyten erzeugten Oxid überlegen.
• Die Oxidschicht besitzt eine gute Hydrophilie, so daß gegebenenfalls auf einen der in der Technik der Druckplattenherstellung bekannten hydrophilierenden Nachbehandlungsschritte verzichtet werden kann.
• Durch den hohen direkt reflektierten Anteil von > 5 des auf den Träger fallenden Lichtes, was sich in einem glänzenden Aussehen bemerkbar macht, haben die mit einer lichtempfindlichen Schicht beschichteten Träger eine deutlich bessere Auflösung als die in nicht erfindungsgemäßen Elektrolyten anodisierten Träger vergleichbarer Aufrauhung.
• Die sehr hellen Nichtbildstellen der fertigen Druckform liefern einen starken Kontrast zu den Bildstellen, was sich insbesondere dann positiv bemerkbar macht, wenn mit modernen, optisch arbeitenden Meßgeräten der Anteil von Bildstellen und Nichtbildstellen gemessen werden soll.
• Die lichtempfindliche Schicht haftet auf der Oberfläche der Träger außerordentlich gut, wodurch man mit diesen Druckplatten deutlich höhere Auflagen erzielt als mit nicht erfindungsgemäß anodisierten Trägern vergleichbaren Typs.
• Der mechanische Abrieb ist wesentlich geringer als der anders erzeugter Träger vergleichbaren Oxidschichtgewichts.
• Durch die gute Leitfähigkeit des Elektrolyten und der Elektrodensysteme kann man mit niedrigeren Spannungen arbeiten.
• Daneben bietet das erfindungsgemäße Verfahren einen weiteren, verfahrenstechnischen Vorteil: Wird das Aluminium vor der Aufrauhung einer Reinigung in einer alkalischen Beize unterworfen, so kann diese Beizlösung, sofern sie eine erfindungsgemäße Zusammensetzung hat, auch zur Anodisierung benutzt werden.

The method according to the invention combines the following advantages:

• The non-image areas of printing plates are "fog-free" after development - even without hydrophilizing aftertreatment. The oxide surface produced according to the invention is therefore clearly superior to a surface of comparable oxide layer weight produced in electrolytes containing H₂SO₄ or in H₃PO₄ or in H₂SO₄ / H₃PO₄ mixtures.
• The alkali resistance of the oxide produced is clearly superior to that produced in an aqueous electrolyte containing H₂SO₄ or H₃PO₄ or H₂SO₄ / H₃PO₄ mixtures.
• The oxide layer weight achieved can reach the values of the oxide layer produced in an electrolyte containing H₂SO₄ and is therefore superior to the oxide produced in conventional electrolyte containing H₃PO₄ in terms of layer thickness.
• The oxide layer has good hydrophilicity, so that one of the hydrophilizing aftertreatment steps known in the art of printing plate production can optionally be dispensed with.
• Due to the high directly reflected portion of> 5 of the light falling on the carrier, which is noticeable in a shiny appearance, they have with a light-sensitive layer coated carrier has a significantly better resolution than the comparable roughening carrier anodized in electrolytes not according to the invention.
• The very bright non-image areas of the finished printing form provide a strong contrast to the image areas, which is particularly noticeable when the proportion of image areas and non-image areas is to be measured with modern, optically operating measuring devices.
• The light-sensitive layer adheres extremely well to the surface of the supports, as a result of which significantly higher runs are achieved with these printing plates than with comparable types of supports not anodized according to the invention.
• The mechanical abrasion is considerably less than the oxide layer weight of a differently produced carrier.
• Due to the good conductivity of the electrolyte and the electrode systems, one can work with lower voltages.
• In addition, the process according to the invention offers a further advantage in terms of process technology: if the aluminum is subjected to cleaning in an alkaline pickle before it is roughened, this pickling solution, if it has a composition according to the invention, it can also be used for anodizing.

In the above description and the following examples,% data always mean% by weight, unless stated otherwise. Parts by weight relate to parts by volume in the ratio of g to cm³. In addition, the following methods were used to test the properties of the surface in the examples, the results of which were summarized in Tables I and II.

• A. Zinkat-Test (nach US-A 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 s 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., 480g 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.
• B. Bestimmung des Flächengewichtes von Aluminiumoxidschichten durch chemisches Ablösen (nach DIN 50 944 in der Ausgabe vom März 1969):
  Die Aluminiumoxidschicht wird durch eine Lösung aus 37 ml H₃PO₄ (Dichte von 1,71 g/ml bei 20 °C entsprechend 85 % H₃PO₄), 20 g CrO₃ und 963 ml H₂O dest. bei 90 bis 95 °C während 5 min vom Grundmetall abgelöst und der dabei entstehende Gewichtsverlust durch Wiegen der Probe vor und nach dem Ablösen bestimmt. Aus dem Gewichtsverlust und dem Gewicht der mit der Schicht bedeckten Oberfläche wird das Flächengewicht der Schicht berechnet und in g/m² angegeben.
• C. Bei der Messung des Abriebs wird ein Reibrad über die Oberfläche eines unbeschichteten Plattenstücks geführt und dabei (bezogen auf eine Standardbehandlungszeit) der Massenverlust der Oberfläche pro Flächeneinheit bestimmt. Für die Bestimmung wird ein Reibrad Taber-Abraser Typ 503 mit Reibrollen CS 10 F der Firma Teledyne Taber, North Tonawanda, USA, verwendet. Es wurden 200 Umdrehungen mit 1 U/s durchgeführt, wobei das Auflagegewicht 500 g betrug. Das Verfahren zur Durchführung solcher Abriebmessungen ist z. B. in der US-A 2 287 148 beschrieben.
• D. Die Bestimmung des Reflektometerwertes bei 60° wurde nach DIN 67 530 (Ausgabe Januar 1982) vorgenommen, wobei der Primärstandard dort in Kapitel 4.2.1 beschrieben ist.

The following measurement methods were used:

• A. Zinkat test (according to US Pat. No. 3,940,321, columns 3 and 4, lines 29 to 68 and lines 1 to 8):
  The rate of dissolution of the layer in s in an alkaline zincate solution is 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 H₂0 dist., 480 g of KOH and 80 g of zinc oxide is brought onto 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.
• B. Determination of the basis weight of aluminum oxide layers by chemical detachment (according to DIN 50 944 in the March 1969 edition):
  The aluminum oxide layer is through a solution of 37 ml of H₃PO₄ (density of 1.71 g / ml at 20 ° C corresponding to 85% H₃PO₄), 20 g of CrO₃ and 963 ml of H₂O dest. detached from base metal at 90 to 95 ° C for 5 min and the resulting weight loss determined by weighing the sample before and after detachment. The weight per unit area of the layer is calculated from the weight loss and the weight of the surface covered with the layer and is given in g / m 2.
• C. When measuring the abrasion, a friction wheel is passed over the surface of an uncoated plate piece and the mass loss of the surface per unit area is determined (based on a standard treatment time). A Taber Abraser Type 503 friction wheel with CS 10 F friction rollers from Teledyne Taber, North Tonawanda, USA is used for the determination. 200 revolutions were carried out at 1 rev / s, the coating weight being 500 g. The method for performing such abrasion measurements is e.g. B. described in US-A 2,287,148.
• D. The reflectometer value at 60 ° was determined in accordance with DIN 67 530 (January 1982 edition), the primary standard being described there in Chapter 4.2.1.

The invention is described with the aid of the following examples, without however restricting the embodiments.

Examples 1 to 18

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 takes place with alternating current in an electrolyte containing HCl. The subsequent anodic oxidation is carried out in the following electrolytes: 1. 10.0 g / l NaOH (pH 13) 2nd 8.0 g / l NaOH (pH 13) 1.5 g / l Na₂CO₃ 0.1 g / l sodium octyl sulfate 3rd 0.6 g / l NaOH (pH 12.5) 0.4 g / l Na₂CO₃ 4th 5.0 g / l NaOH (pH 12.5) 1.0 g / l sodium octyl sulfate 5. 5.0 g / l NaOH (pH 12.5) 2.0 g / l sodium aluminate 6. 12.0 g / l NaOH (pH 12.7) 2.3 g / l Na₂CO₃ 0.2 g / l sodium octyl sulfate 7. 14.0 g / l KOH (pH 13.4) 8th. 18 g / l NaOH (pH 12.6) 12 g / l sodium borate

The proportions given here and in the rest of the text are those at the beginning of the anodization. They can change during the process, in particular due to the dissolution of aluminum from the anode material.

The voltage for all settings was 42 V (direct current), which enables easy handling in practice.

The anodization results are summarized in Table I. The table proves that oxide layers of 0.8 and preferably 2 g / m 2 and more can be achieved with the electrolytes according to the invention and that the supports have only a low abrasion. The alkali resistance, measured with the zincate test, is excellent for all carriers, and all show a silvery surface with a good 60 ° reflectometer value measured according to DIN 67 530 and with the aforementioned good properties.

Comparative Examples V1 to V13

Other than the alkaline electrolytes according to the invention often tend to form an insulating barrier layer during anodization, which allows only a small current flow at moderate voltages and therefore does not allow the build-up of sufficiently thick oxide layers within practical times. The carriers usually do not show the desired gloss, which brings the previously mentioned positive properties.

If electrolytes are used which contain alkali metal hydroxide and salts of strong acids, e.g. Sulphates, this is how shiny surfaces are obtained which, however, after anodizing under practical conditions, do not have sufficiently thick oxide layers. This is demonstrated by comparative examples 14 to 16. With additives whose 1% aqueous solution only reacts weakly alkaline (pH 8.5 to 10.5), relatively thin, light to matt gray surfaces are obtained, some of which have small spots through micro-burns.

The voltage in the comparative tests was 42 V here too. For most electrolytes, this relatively high voltage was necessary in order to force a sufficiently high current flow. The comparative experiments were carried out with the following electrolytes: A. Sodium acetate 20.5 g / l (pH 8) not according to the invention, alkali metal hydroxide pH too low, none B. sodium 33 g / l (pH 11.5) not according to the invention, alkali metal hydroxide pH too low, none C. Sodium bicarbonate 10 g / l (pH 8.6) not according to the invention, alkali metal hydroxide pH too low, none D. Lithium hydroxide 5.8 g / l (pH 11.9) not according to the invention, pH too low E. Sodium acetate 47.5 g / l (pH 12.1) NaOH 2.5 g / l not according to the invention, alkali metal hydroxide pH too low, too little F. Na₂CO₃ 0.95 g / l (pH 11.8) NaOH 0.05 g / l not according to the invention, alkali metal hydroxide pH too low, too little G. Sodium metasilicate 9.9 g / l (pH 12.4) NaOH 0.1 g / l not according to the invention, alkali metal hydroxide pH too low, too little

Example 19

An aluminum substrate produced in accordance with Example 8 is provided with the following negative-working photosensitive layer:
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 12.8 parts by weight of benzoic acid in ethylene glycol monomethyl ether in the presence of benzyltrimethylammonium hydroxide,
0.44 part by weight of finely ground heliogen blue G (CI74 100)
62.00 parts by volume of ethylene glycol monomethyl ether,
30.60 parts by volume of tetrahydrofuran and
8.00 parts by volume of butyl acetate.

After exposure through a negative mask, a solution of
2.80 parts by weight of Na₂SO₄.10H₂O,
2.80 parts by weight of MgSO₄.7H₂O,
0.90 parts by weight of 85% phosphoric acid,
0.08 part by weight of phosphorous acid,
1.60 parts by weight of nonionic wetting agent,
10.00 parts by weight of benzyl alcohol,
20.00 parts by weight of n-propanol and
60.00 parts by weight of water
developed.

The printing plate produced in this way can be developed quickly and free of fog. The print run with a printing form produced in this way is 130,000. A carrier material produced in accordance with Comparative Example V7 and coated with the same formulation can only be developed under difficult conditions. After development, a yellow haze remains in the non-image areas, which may be caused by adhering particles of the diazonium compound. If a carrier material according to comparative example V3 is used, then after printing about 90,000 prints, a clear gloss is found in the non-image areas, which increases with increasing circulation. After 100,000 prints, the print quality has dropped to a level that is no longer accepted in practice.

Example 20

An aluminum substrate produced as described in Example 10 is coated with the following positive-working photosensitive solution:
6.00 parts by weight cresol-formaldehyde novolak (with a softening range of 105 to 120 ° C according to DIN 53 181)
1.10 parts by weight of the 4- (2-phenyl-prop-2-yl) phenyl ester Naphthoquinone- (1,2) -diazide- (2) -sulfonic acid- (4),
0.81 part by weight of polyvinyl butyral,
0.75 part by weight of naphthoquinone- (1,2) -diazide- (2) -sulfonic acid chloride- (4),
0.08 part by weight of crystal violet,
91.36 parts by weight of solvent mixture of 4 parts by volume of ethylene glycol monomethyl ether,
5 parts by volume of tetrahydrofuran and
1 part by volume of butyl acetate.

The 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:
5.30 parts by weight of Na₂SiO₃ · 9 H₂0,
3.40 parts by weight of Na₃PO₄ · 12 H₂0,
0.30 parts by weight of NaH₂PO₄ (anhydrous),
91.00 parts by weight of water.

The printing form obtained is perfect in terms of copying and printing technology and has an excellent resolution. The print run is 150,000.

A corresponding plate made from the carrier material of comparative example V6 shows a blue haze in the non-image areas. With prolonged exposure to the developer, there is a clear light-dark shading in the non-image areas, which indicates an attack by the developer solution of the oxide.

Example 21

An aluminum substrate produced according to the information in Example 16 is provided with the following negative-working photosensitive layer:
16.75 parts by weight of an 8.0% solution of the reaction product of a polyvinyl butyral with a molecular weight of 70,000 to 80,000, consisting of 71% by weight of vinyl butyral, 2% by weight of vinyl acetate and 27% by weight of vinyl alcohol Units, with propylene sulfonyl isocyanate,
2.14 parts by weight of 2,6-bis- (4-azido-benzene) -4-methylcyclohexanone,
0.23 parts by weight of ^(R) Rhodamine 6 GDN extra and
0.21 part by weight of 2-benzoylmethylene-1-methyl-β-naphthothiazoline in
100 parts by weight of ethylene glycol monomethyl ether and
50 parts by weight of tetrahydrofuran.
The dry layer weight is 0.75 g / m². The reproduction layer is exposed under a negative original for 35 s using a metal halide lamp with a power of 5 kW. The exposed layer is covered with a plush pad with a developer solution of the composition
5 parts by weight of sodium lauryl sulfate
1 part by weight of Na₂SiO₃ · 5 H₂O
94 parts by weight of water
treated, the non-image areas are removed.

The print run of the plate in a printing press is 170,000. When using the carrier material produced according to Comparative Example V3, the copy layer has a markedly reduced adhesion, which leads to parts of the layer becoming detached from the image areas after only about 120,000 prints.

Example 22

A support anodized according to Example 5 is coated with the following solution to produce an electrophotographic 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 ^(R) Rhodamine FB (CI 45 170)
300.00 parts by weight of ethylene glycol monomethyl ether
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 a boiling range of 185 to 210 ° C represents. After removing the excess developer liquid, the developer is fixed and the plate is poured out into a solution for 60 s
35 parts by weight of Na₂SiO₃ · 9 H₂O,
140 parts by weight of glycerin,
550 parts by weight of ethylene glycol and
140 parts by weight of ethanol
submerged. 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. The non-image areas of the plate show good hydrophilicity and show no signs of attack even after exposure to alkaline solutions. Several tens of thousands of good prints can be achieved with the printing form.

Example 23

An aluminum sheet prepared according to the information in Example 2 is immersed in a further treatment step (additional hydrophilization) in a 0.2% aqueous solution of polyvinylphosphonic acid at 50 ° C. for 20 s. After drying, the substrate material additionally hydrophilized in this way is further processed as described in Example 19, it being possible to further improve the ink-repelling effect of the non-image areas.

Claims (14)

1. Plate, foil or web-shaped support material for offset printing plates, comprising aluminium or an alloy thereof, which is mill-finished, mechanically and/or chemically or mechanically and electrochemically grained and anodised in alkaline solutions, characterised in that it shows a reflectometer value of >5 at an angle of incidence of 60° (measured according to DIN 67 530; 1982), an abrasion of the oxide layer of <0.5 g/m² and a resistance to alkali of >140 s.
2. A support material as claimed in claim 1, characterised in that it has a reflectometer value of ≧15 at 60° (measured according to DIN 67 530).
3. A support material as claimed in claim 1 or 2, characterised in that it shows an abrasion of the oxide layer of ≦0.3 g/m².
4. A support material as claimed in any of claims 1 to 3, characterised in that it has a resistance to alkali of ≧160 s.
5. A support material as claimed in any of claims 1 to 4, characterised in that its oxide layer has a weight per unit area of >0.8 g/m².
6. Process for the manufacture of a support material as claimed in any one or more of claims 1 to 5, in which a plate, foil or web-shaped aluminium or an alloy thereof is mechanically and/or chemically or mechanically and electrochemically grained and anodised in an aqueous-alkaline electrolyte at a voltage exceeding 36 volts, characterised in that the voltage applied is set in a range from 42 to below 50 volts and that the pH is in the range from ≧12.5 to ≦13.4.
7. A process as claimed in claim 6, characterised in that the electrolyte contains sodium hydroxide.
8. A process as claimed in claim 6 or 7, characterised in that the electrolyte contains a strongly alkaline-reacting salt of a weak acid, such as alkali metal octyl sulfate, carbonate, aluminate, borate, silicate or phosphate.
9. A process as claimed in claim 8, characterised in that the alkali metal salt, in a 1 % by weight strength aqueous solution, has a pH of at least 10.5.
10. A process as claimed in any one or more of claims 6 to 9, characterised in that the electrolyte contains surface-active agents.
11. A process as claimed in any one or more of claims 6 to 10, characterised in that the anodisation is carried out at a current density of 3 to 50 A/dm², at a temperature between 10 and 50 °C, and for a duration of 5 to 500 s, in particular of 10 to 300 s.
12. A process as claimed in any one or more of claims 6 to 11, characterised in that the electrolyte contains 0.1 to 20 % by weight of an alkali metal hydroxide, a strongly alkaline-reacting salt of a weak acid, suface-active agents and aluminium ions.
13. A process as claimed in claim 12, characterised in that the electrolyte contains 0.5 to 10 % by weight of an alkali metal hydroxide, a strongly alkaline-reacting salt of a weak acid, surface-active agents and aluminium ions.
14. A process as claimed in any one or more of claims 6 to 13, characterised in that anodisation is followed by a hydrophilising treatment.