EP0437761A2 - Process for the electrochemical graining of aluminum for printing plate supports - Google Patents

Abstract

A description is given of a process for the graining of aluminium or its alloys for printing plate supports. In this process, an electrochemical graining is carried out in a graining step by means of alternating current in an acidic sulphate- and chloride-ion-containing electrolyte which contains chloride ions in the form of aluminium chloride. In a preceding or subsequent graining step, a mechanical dry or moist graining or an electrochemical graining is carried out by means of alternating current in an electrolyte. The electrolyte contains hydrochloric acid and aluminium ions, nitric acid and aluminium ions or sulphuric acid and chloride ions.

Description

The invention relates to a method for the electrochemical roughening of aluminum for printing plate supports according to the preamble of claim 1.

DE-A 37 17 654 discloses such a process for the electrochemical roughening of aluminum or its alloys for printing plate supports by means of alternating current in an electrolyte containing sulfate and chloride ions, the acidic, sulfate-containing electrolyte containing chloride ions in the form of aluminum chloride. Very uniform, scar-free carrier surfaces with fine roughening are obtained, which have excellent lithographic properties, but because of the fine roughening, the anchoring of the color-carrying organic layer on the carrier is not sufficient, which leads to a lower circulation compared to one Printing form in which a carrier was used which is produced by a process in which electrolytes containing sulfate-free, chloride or nitrate ions are used.

Printing plates, especially offset printing plates, generally consist of a carrier and at least one radiation-sensitive layer arranged on it, this layer being applied to the layer carrier by non-pre-coated plates by the consumer or, in the case of pre-coated plates, by the industrial manufacturer.

Aluminum or one of its alloys has established itself as a layer support in the printing plate field. In principle, these substrates can also be used without a modifying pretreatment, but they are generally modified in or on the surface, for example by mechanical, chemical and / or electrochemical roughening, sometimes also called graining or etching, chemical or electrochemical oxidation and / or treatment with hydrophilizing agents.

In the modern, continuously operating high-speed systems of the manufacturers of printing plate supports and / or precoated printing plates, a combination of the above-mentioned types of modification is often used, in particular a combination of electrochemical roughening and anodic oxidation, optionally with a subsequent hydrophilization step.

The roughening can be carried out in aqueous acids such as aqueous HCl or HNO₃ solutions or in aqueous salt solutions such as aqueous NaCl or Al (NO₃) ₃ solutions using alternating current. The roughness depths of the roughened surface which can be achieved in this way, given, for example, as mean roughness depths Rz, are in the range from 1 to 15 μm, in particular in the range from 2 to 8 μm. The roughness depth is determined in accordance with DIN 4768 in the version from October 1970. This is called the average roughness depth Rz arithmetic mean calculated from the individual roughness depths of five adjacent individual measuring sections.

The roughening takes place u. a. to improve the adhesion of the reproduction layer on the substrate and the dampening solution of the printing plate resulting from the printing plate by exposure and development.

The water flow is an important quality feature for offset printing plates. It is defined as the dosage and control in the document "Determining an optimal water flow to increase the performance of offset printing" (Albrecht, J .; Rebner, W., Wirz, B., Westdeutscher Verlag, Cologne and Opladen 1966, page 7) the moistening of the printing form during the print run. The water flow depends, among other things, on the surface roughness of the printing form, ie the grain size of the surface. The problems of inadequate water supply are well known: If too much water is required to keep the non-printing parts of a printing form free of ink, more water can emulsify into the ink and the print becomes flat. Watermarks may also occur, causing the paper to become damp. Registration problems can also occur and there is an increased risk of the paper web tearing when using web offset printing. These are just a few of the problems. Information on the importance of correct water flow can also be found in the document "Contribution to the analysis of the offset process", pages 17, 18 (Decker, P .; Polygraph Verlag, Frankfurt am Main). There is about the consequences too high and too low dampening solution management discussed. This term is more appropriate than the term "water supply", since in the case of offset printing generally pure water is not used for dampening, but usually several components are added to the water.

The above-mentioned disadvantages of excessive dampening solution guidance are listed in the cited document. However, an insufficient amount of dampening solution is also a disadvantage. If too little dampening solution is offered to the printing plate in the printing press due to a setting of the dampening unit that is too low or if the printing plate requires more dampening solution than the dampening unit can supply to the printing press for design or other reasons, other non-printing parts of the printing plate can also take on color and also print, fine screen areas are particularly sensitive to co-printing. The printing of non-image areas within grid areas is known as "smearing".

It is therefore desirable to have a printing plate that requires very little dampening solution to keep fine screens, but also large areas of non-image, free of color, but which on the other hand also show a neutral behavior towards large amounts of dampening solution and still deliver flawless prints, if due to operational reasons Fluctuations in the dampening solution supply sometimes exceed the normal level.

The dampening solution consumption of a printing plate can be measured objectively with sufficient accuracy, but not the dampening solution guidance, since for some of the above-mentioned adverse phenomena such as smearing, there is no objective measurement method (Decker, P., in "Contribution to Analysis .. . ", Page 18). Therefore the dampening solution guidance of a printing plate is assessed qualitatively with the adjectives "very good", "good", "satisfactory", "sufficient", "moderate", "bad", "very bad".

By exposing or irradiating and developing or de-coating in reproduction layers that work electrophotographically, the image areas that guide the color during later printing and the non-image areas that conduct moisture, which are generally the exposed carrier surface, are produced on the printing plate, as a result of which the actual printing form arises. Very different parameters influence the later topography and thus the dampening solution management of the surface to be roughened. For example, the following references provide information:

In the article "The Alternating Current Etching of Aluminum Lithographic Sheet" by AJ Dowell in Transactions of the Institute of Metal Finishing, 1979, Vol. 57, pp. 138 to 144, basic explanations are given on the roughening of aluminum in aqueous hydrochloric acid solutions, the following process parameters varied and the corresponding effects are examined.

The electrolyte composition is changed with repeated use of the electrolyte, for example with regard to the H⁺ (H₃O⁺) ₋ ion concentration (measurable via the pH value) and the Al³⁺ ion concentration, with effects on the surface topography being observed. The temperature variation between 16 ° C and 90 ° C shows a changing influence only from about 50 ° C, which is noticeable, for example, by the sharp decline in the formation of layers on the surface. The roughening time between 2 and 25 min leads to an increasing metal dissolution with increasing exposure time. The variation of the current density between 2 and 8 A / dm² results in higher roughness values with increasing current density. If the acid concentration is in the range of 0.17 to 3.3% HCl, between 0.5 and 2% HCl only minor changes occur in the hole structure, below 0.5% HCl there is only a local attack on the surface and high values an irregular dissolution of aluminum instead. If pulsed direct current is used instead of alternating current, it can be seen that both types of half-wave are obviously required for uniform roughening. Already in this reference it is pointed out that the addition of sulfate ions increasingly leads to undesired, coarse, non-homogeneous roughening structures which are not suitable for lithographic purposes.

The use of hydrochloric acid to roughen aluminum substrates is known. A uniform grain size can be obtained which is suitable for lithographic plates and within a useful one Roughness range. In pure hydrochloric acid electrolytes, setting a flat and uniform surface topography is difficult, and it is necessary to maintain the operating conditions within very narrow limits.

• Die DE-A 22 50 275 (=GB-A 1 400 918) nennt als Elektrolyten bei der Wechselstrom-Aufrauhung von Aluminium für Druckplattenträger wäßrige Lösungen eines Gehaltes von 1,2 bis 1,5 Gew.-% an HNO₃ oder von 0,4 bis 0,6 Gew.-% an HCl und gegebenenfalls 0,4 bis 0,6 Gew.-% an H₃PO₄·,
• die DE-A 28 10 308 (=US-A 4 072 589) nennt als Elektrolyten bei der Wechselstrom-Aufrauhung von Aluminium wäßrige Lösungen eines Gehaltes von 0,2 bis 1,0 Gew.-% an HCl und 0,8 bis 6,0 Gew.-% an HNO₃.

The influence of the composition of the electrolyte on the roughening quality is also described, for example, in the following publications:

• DE-A 22 50 275 (= GB-A 1 400 918) mentions, as electrolytes in the AC roughening of aluminum for printing plate supports, aqueous solutions with a content of 1.2 to 1.5% by weight of HNO 3 or 0, 4 to 0.6% by weight of HCl and optionally 0.4 to 0.6% by weight of H₃PO₄ ·,
• DE-A 28 10 308 (= US-A 4 072 589) names as electrolytes in the AC roughening of aluminum aqueous solutions containing 0.2 to 1.0% by weight of HCl and 0.8 to 6 , 0 wt .-% of HNO₃.

• die DE-A 28 16 307 (=US-A 4 172 772) den Zusatz von Monocarbonsäuren wie Essigsäure zu Salzsäureelektrolyten,
• die US-A 3 963 594 von Gluconsäure,
• die EP-A 0 036 672 von Citronen- und Malonsäure und
• die US-A 4 052 275 von Weinsäure.

Additions to the HCl electrolyte have the task of preventing an adverse local attack in the form of deep holes. So describes

• DE-A 28 16 307 (= US-A 4 172 772) the addition of monocarboxylic acids such as acetic acid to hydrochloric acid electrolytes,
• US Pat. No. 3,963,594 to gluconic acid,
• EP-A 0 036 672 of citric and malonic acid and
• U.S. 4,052,275 to tartaric acid.

All these organic electrolyte components have the disadvantage that they are electrochemically unstable and decompose at high current loads, which can be equated with high voltage loads.

DE-A 35 03 927 describes ammonium chloride as an inorganic additive to an HCl electrolyte.

Inhibiting additives such as those described in US Pat. No. 3,887,447 as phosphoric or chromic acid, in DE-A 25 35 142 (= US Pat. No. 3,980,539) as boric acid have the disadvantage that the protective action is often local collapses and there can be individual, particularly pronounced scars.

From JP application 91 334/78 an alternating current roughening in an electrolyte from hydrochloric acid and an alkali halide for producing a lithographic carrier material is known.

DE-A 16 21 115 (= US-A 3 632 486 and US-A 3 766 043) mentions direct current roughening in dilute hydrofluoric acid, the Al strip being connected as the cathode.

• Wechselstrom, bei dem die Anodenspannung und der anodische coulombische Eingang größer als die Kathodenspannung und der kathodische coulombische Eingang sind, gemäß DE-A 26 50 762 (=US-A 4 087 341), wobei im allgemeinen die anodische Halbperiodenzeit des Wechselstromes geringer als die kathodische Halbperiodenzeit eingestellt wird; auf diese Methode wird beispielsweise auch in der DE-A 2 912 060 (=US-A 4 301 229), der DE-A 30 12 135 (=GB-A 2 047 274) oder der DE-A 30 30 815 (=US-A 4 272 342) hingewiesen,
• Wechselstrom, bei dem die Anodenspannung deutlich gegenüber der Kathodenspannung erhöht ist, gemäß der DE-A 14 46 026 (=US-A 3 193 485),
• die Unterbrechung des Stromflusses während 10 bis 120 sec und ein Stromfluß während 30 bis 300 sec, wobei Wechselstrom und als Elektrolyt eine wäßrige 0,75 bis 2 n HCl-Lösung mit NaCl- oder MgCl₂-Zusatz eingesetzt werden, gemäß der GB-A 879 768. Ein ähnliches Verfahren mit einer Unterbrechung des Stromflusses in der Anoden- oder Kathodenphase ist auch in der DE-A 30 20 420 (=US-A 4 294 672) beschrieben.

Another known way of improving the uniformity is to modify the current form used, for example

• Alternating current, in which the anode voltage and the anodic coulombic input are greater than the cathode voltage and the cathodic coulombic input, according to DE-A 26 50 762 (= US-A 4 087 341), the anodic half-period time of the alternating current generally being less than that cathodic half period is set; this method is also used, for example, in DE-A 2 912 060 (= US-A 4 301 229), DE-A 30 12 135 (= GB-A 2 047 274) or DE-A 30 30 815 (= US-A 4,272,342),
• AC current, in which the anode voltage is significantly higher than the cathode voltage, according to DE-A 14 46 026 (= US-A 3 193 485),
• the interruption of the current flow for 10 to 120 sec and a current flow for 30 to 300 sec, alternating current and an aqueous 0.75 to 2 N HCl solution with NaCl or MgCl₂ addition being used as electrolyte, according to GB-A 879 768. A similar method with an interruption of the current flow in the anode or cathode phase is also described in DE-A 30 20 420 (= US-A 4 294 672).

Although the methods mentioned produce relatively uniformly roughened aluminum surfaces, they require a relatively large outlay on equipment and can also be used only within very narrow parameter limits.

Another method known from the patent literature is the combination of two roughening methods. This has the advantage over a one-step process that, depending on the process control, the influence of one or the other step can predominate within certain limits specified by the properties of the individual steps.

In the patents US-A 3 929 591, GB-A 1 582 620, JP-A 123 204/78, DE-A 30 31 764 (= GB-A 2 058 136), DE-A 30 36 174 (= GB -A 2 060 923), EP-A 0 131 926, DE-A 30 12 135 (= GB-A 2 047 274) and JP-B 16 918/82 are the combination of a pre-structuring which takes place mechanically in the first step, followed by an optional chemical cleaning (pickling) with an electrochemical roughening by means of modified alternating current in electrolytes containing hydrochloric or nitric acid is described, wherein a further cleaning step can then take place.

These methods take advantage of double roughening, with mechanical roughening as the first step, which in particular saves electricity.

Various two-stage processes are known for the production of capacitors from aluminum foils. US Pat. No. 4,525,249 describes a process which uses hydrochloric acid in the first stage and electrolessly treats the aluminum foil in the second stage with a dilute nitric acid which also contains aluminum in the form of aluminum nitrate. This process does not produce surfaces that are used today on offset printing plates high requirements can meet.

Two-stage processes that use electrochemical processes in both stages have also become known. In the process according to US Pat. No. 4,721,552, the first electrolyte contains hydrochloric acid, while the second electrolyte can also contain hydrochloric acid in addition to nitric acid. A similar process is described in Japanese publication JP 61 05 1396. Although these known methods provide surfaces which can be used for lithographic purposes, the fineness of the surface structure does not match those which are achieved according to the teaching of published patent application DE-A 37 17 654.

US Pat. No. 4,437,955 discloses a two-stage electrochemical roughening process for producing capacitors with an electrolyte containing hydrochloric acid in the first step and an electrolyte containing chloride and sulfate ions in the second step. The second stage electrolyte is not acidic, and DC is used in this stage.

Another, two-stage, electrochemical method for producing a capacitor film is described in US Pat. No. 4,518,471. There the electrolytes in both baths are identical and contain dilute hydrochloric acid and aluminum ions. The baths are operated at different temperatures, namely in the first stage at 70 to 85 ° C and in the second stage at 75 to 90 ° C.

The surfaces produced by the last two methods optimized for electrolytic capacitors are too pitted for use in lithography.

The object of the present invention is to improve a method for roughening aluminum for printing plate supports of the type described above in such a way that, in addition to a uniform, very fine, scar-free, area-covering roughening structure of the aluminum surface of the printing plate supports, very good reprographic and printing properties, in particular long print runs of the finished printing forms. Furthermore, it is an object of the present invention to provide a method which allows the targeted production of supports, the properties of which can be controlled in a wide range and which delivers differently structured surfaces of the printing plate supports in accordance with changing market requirements without any changes in the system.

This object is achieved in that in a preceding or subsequent roughening step, mechanical, dry or wet roughening or electrochemical roughening is carried out by means of an alternating current in an electrolyte, the hydrochloric acid and aluminum ions, introduced as aluminum chloride, nitric acid and aluminum ions introduced as aluminum nitrate or sulfuric acid and chloride ions introduced as aluminum chloride.

The further embodiment of the invention results from the measures of the subclaims.

The invention is based on a process for the combined roughening of aluminum, an electrolyte is used in one step which contains sulfate ions in a relatively high concentration of 5 to 100 g / l with the addition of chloride ions in the form of aluminum chloride. Before or after this roughening step, conventional roughening in hydrochloric acid or nitric acid-containing electrolytes or mechanical roughening is carried out.

The roughening step in the sulfate-containing electrolyte can also be carried out as a second step.

In the first roughening step, a chloride ion-containing, sulfate-free electrolyte can be used as the electrolyte.

Before the first roughening step, between the two roughening steps and after the second roughening step, acidic or alkaline cleaning can optionally also be carried out.

Surprisingly, it was found that in addition to the excellent reprographic properties and good dampening solution management, which is characteristic of carriers produced in sulfate-containing electrolytes according to the teaching of DE-A 37 17 654, there are excellent printing properties, such as the higher print run.

Carriers with good reprographic qualities can indeed be produced according to the teaching of DE-A 37 17 654, but printing plates which have been produced with these carriers do not achieve the high print runs which result in plates whose carriers are made according to the prior art corresponding process can be produced, in which an electrolyte based on nitric acid is used.

Printing forms, the supports of which were produced by one of the processes mentioned above, with the exception of the process described in DE-A 37 17 654, have poorer reprographic properties and poorer fountain solution guidance than the printing plate supports produced according to the invention.

According to the invention, roughening in an electrolyte containing sulfate ions and chloride ions, the sulfate ion concentration being from 5 to 100 g / l and the chloride ion concentration being 1 to 100 g / l, is combined with a further roughening step.

A range from 20 to 50 g / l sulfate ions and 10 to 70 g / l chloride ions is preferred. The sulfate can be introduced into the electrolyte as sulfuric acid and the chloride as aluminum chloride.

Higher chloride ion concentrations increase the local attack on the aluminum surface and result in unwanted scars. Combinations of different compounds containing chloride ions are also used in the context of the invention.

The preceding or subsequent roughening step can be carried out, for example, in an electrolyte which contains 1 to 20 g / l hydrochloric acid (calculated as 100% HCl) and 10 to 200 g / l Al³⁺ ions, introduced as aluminum chloride. The electrochemical roughening then typically takes place in a temperature interval of 35 to 55 ° C., at current densities of 20 to 150 A / dm² and, depending on the current density, in times of 5 seconds to 200 seconds.

This roughening step can also be carried out in an electrolyte which contains, for example, 20 to 35 g / l HNO₃ and 30 to 50 g / l Al³⁺ ions, introduced as aluminum nitrate. The electrochemical roughening can then be carried out at temperatures from 22 to 50 ° C. and with current densities of 15 to 80 A / dm², the exposure times being 2 to 100 seconds.

Mechanical graining can also be carried out as a roughening step. This can be a roughening with damp Abrasives (wet brushing), but the roughening can also be carried out dry, for example with wire brushes, by sandblasting, ball grit, embossing and similar processes. Mechanical roughening should be followed by thorough pickling in acidic or alkaline media.

A surface produced by the method according to the invention is a highly uniform carrier surface with excellent lithographic properties and has surface roughness ranges which can be varied for Rz = 3 to 9 and which, depending on requirements, can also be adapted to market requirements without having to convert the production facilities.

The process can be carried out discontinuously or continuously with strips made of aluminum or its alloys. In general, the process parameters in the continuous process during the roughening step in the chloride- and sulfate-containing electrolyte lie in the following ranges: the temperature of the electrolyte between 20 and 60 ° C, the current density between 3 and 180 A / dm², the residence time of a roughened material point in the electrolyte between 10 and 300 sec and the electrolyte flow rate on the surface of the material to be roughened between 5 and 100 cm / sec. Due to the continuous driving style and the simultaneous release of Al ions and the consumption of H⁺, constant adjustment of the electrolyte composition by the corresponding diluted acids is necessary.

In the batch process, the required current densities are between 3 and 40 A / dm 2 and the residence times between 30 and 300 seconds. The flow of the electrolyte can also be dispensed with.

In addition to sinusoidal AC voltages with mains frequency, superimposed AC voltages and voltages lower than the mains frequency can also be used.

• "Reinaluminium" (DIN-Werkstoff Nr. 3.0255), d. h. bestehend aus mehr als 99.5 % Al und den folgenden zulässigen Beimengungen von (maximale Summe von 0,5 %) 0,3 % Si, 0,4 % Fe, 0,03 % Ti, 0,02 % Cu, 0,07 % Zn und 0,03 % Sonstigem, oder
• "Al-Legierung 3003" (vergleichbar mit DIN-Werkstoff Nr. 3.0515), d. h. bestehend aus mehr als 98,5 % Al, den Legierungsbestandteilen 0 bis 0,3 % Mg und 0,8 bis 1,5 % Mn und den folgenden zulässigen Beimengungen von 0,5 % Si, 0,5 % Fe, 0,2 % Ti, 0,2 % Zn, 0,1 % Cu und 0,15 % Sonstigem.

The materials to be roughened are used, for example, as a plate, film or tape:

• "Pure aluminum" (DIN material no. 3.0255), ie consisting of more than 99.5% Al and the following admissible admixtures of (maximum sum of 0.5%) 0.3% Si, 0.4% Fe, 0.03 % Ti, 0.02% Cu, 0.07% Zn and 0.03% other, or
• "Al alloy 3003" (comparable to DIN material no. 3.0515), ie consisting of more than 98.5% Al, the alloy components 0 to 0.3% Mg and 0.8 to 1.5% Mn and the following admissible admixtures of 0.5% Si, 0.5% Fe, 0.2% Ti, 0.2% Zn, 0.1% Cu and 0.15% other.

However, the method can also be used with other aluminum alloys.

At the end of the roughening process, for example, anodic oxidation of the aluminum takes place, as a result of which the abrasion and the adhesion properties of the surface of the carrier material are improved.

• Das Gleichstrom-Schwefelsäure-Verfahren, bei dem in einem wäßrigen Elektrolyten aus üblicherweise ca. 230 g H₂SO₄ pro 1 Liter Lösung bei 10 bis 22 °C und einer Stromdichte von 0,5 bis 2,5 A/dm² während 10 bis 60 min anodisch oxidiert wird. Die Schwefelsäurekonzentration in der wäßrigen Elektrolytlösung kann dabei auch bis auf 8 bis 10 Gew.-% H₂SO₄ (ca. 100 g/l H₂SO₄) verringert oder auch auf 30 Gew.-% (365 g/l H₂SO₄) und mehr erhöht werden.
• Die "Hartanodisierung" wird mit einem wäßrigen H₂SO₄ enthaltenden Elektrolyten einer Konzentration von 166 g/l H₂SO₄ (oder ca. 230 g/l H₂SO₄) bei einer Betriebstemperatur von 0 bis 5 °C, bei einer Stromdichte von 2 bis 3 A/dm², einer steigenden Spannung von etwa 25 bis 30 V zu Beginn und etwa 40 bis 100 V gegen Ende der Behandlung und während 30 bis 200 min durchgeführt.

The usual electrolytes such as sulfuric acid, phosphoric acid, oxalic acid, amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof can be used for anodic oxidation. Reference is made, for example, to the following standard methods for the anodic oxidation of aluminum (see, for example, BM Schenk, material aluminum and its anodic oxidation, Francke Verlag, Bern 1948, page 760; practical electroplating, Eugen Leutze Verlag, Saulgau 1970, pages 395 ff . and pages 518/519; W. Hübner and CT Speiser, The Practice of Anodic Oxidation of Aluminum, Aluminum Verlag, Düsseldorf 1977, 3rd edition, pages 137 ff.):

• The direct current sulfuric acid process in which in an aqueous electrolyte from approximately 230 g H₂SO₄ per 1 liter of solution at 10 to 22 ° C and a current density of 0.5 to 2.5 A / dm² for anodic for 10 to 60 min is oxidized. The sulfuric acid concentration in the aqueous electrolyte solution can also be reduced to 8 to 10% by weight of H₂SO₄ (approx. 100 g / l H₂SO₄) or increased to 30% by weight (365 g / l H₂SO₄) and more.
• The "hard anodizing" is carried out with an aqueous electrolyte containing H₂SO₄ with a concentration of 166 g / l H₂SO₄ (or approx. 230 g / l H₂SO₄) at an operating temperature of 0 to 5 ° C, with a current density of 2 to 3 A / dm², a rising voltage of about 25 to 30 V at the beginning and about 40 to 100 V towards the end of the treatment and for 30 to 200 min.

In addition to the methods for the anodic oxidation of printing plate support materials already mentioned in the previous paragraph, the following methods can also be used, for example: the anodic oxidation of aluminum in an aqueous electrolyte containing H₂SO₄, the Al³⁺ ion content of which is adjusted to values of more than 12 g / l is (according to DE-A 28 11 396 = US-A 4 211 619), in an aqueous electrolyte containing H₂SO₄ and H₃PO₄ (according to DE-A 27 07 810 = US-A 4 049 504) or in an aqueous, H₂SO₄, H₃PO₄ and Al³⁺ ions containing electrolytes (according to DE-A 28 36 803 = US-A 4 229 226).

Direct current is preferably used for the anodic oxidation, but alternating current or a combination of these types of current (eg direct current with superimposed alternating current) can also be used. The layer weights of aluminum oxide range from 1 to 10 g / m², corresponding to a layer thickness of approximately 0.3 to 3.0 µm.

After the electrochemical roughening and before an anodic oxidation, a modifying treatment, which causes a removal of the surface from the roughened surface, can be used, as described for example in DE-A 30 09 103. Such a modifying intermediate treatment provides the structure, among other things abrasion-resistant oxide layers and a lower toning tendency when printing later.

The anodic oxidation of the aluminum printing plate support material can also be followed by one or more post-treatment stages. Aftertreatment is understood to mean in particular 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 an 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 already sufficient for many areas of application, without impairing the other known properties of this layer.

In principle, all layers are suitable as light-sensitive reproduction layers which, after exposure, subsequent development and / or fixing, provide an image-like area from which printing can take place and / or which represent a relief image of an original. The reproduction layers are applied either by the manufacturer of presensitized printing plates, using a dry resist or directly by the consumer on one of the usual carrier materials.

The light-sensitive reproduction layers include such as z. B. in "Light-Sensitive Systems" by Jaromir Kosar, John Wiley & Sons Verlag, New York 1965, are described: The layers containing unsaturated compounds in which these compounds are isomerized, rearranged, cyclized or crosslinked during exposure (Kosar, chapter 4) such as B. Cinnamate; 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).

Suitable layers also include the electrophotographic layers, i.e. H. those containing an inorganic or organic photoconductor. In addition to the light-sensitive substances, these layers can of course also other components such. B. Resins, dyes, pigments, wetting agents, sensitizers, adhesion promoters, indicators, plasticizers or other conventional auxiliaries.

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, are applied to the support materials, whereby highly light-sensitive, electrophotographic layers are formed.

The materials for printing plate supports roughened by the process have a very uniform topography, which has a positive effect on the print run stability and the dampening solution guidance when printing printing plates made from these supports. Undesirable "scars" occur less frequently, which form distinctive depressions compared to the roughening of the surroundings; these can even be completely suppressed. In particular, the method succeeds in producing a very wide spectrum of differently roughened carriers, which can be seen from the achievable roughness depths Rz = 3 µm to 9 µm. This succeeds without having to make changes to the equipment in production plants.

Examples

An aluminum sheet is first pickled for 60 seconds in an aqueous solution containing 20 g / l NaOH at room temperature. The roughening takes place in the specified electrolyte systems.

The classification into the quality classes, taking into account the surface topography with regard to uniformity, freedom from scars and area coverage, is carried out by visual assessment under the microscope, whereby a homogeneously roughened and scar-free surface is assigned quality level "10" (best value). A surface with thick scars larger than 30 µm and / or an extremely unevenly roughened or almost bare surface, the quality level "0" (worst value) is assigned.

A -

Drahtbürstung,

B -

Naßbürstung,

C -

elektrochemische Aufrauhung in einem Elektrolyten, der 10 g/l HCl (gerechnet als 100%ig) und 65 g/l Aluminiumchlorid (AlCl₃·6H₂O) enthält, bei einer Temperatur von 35 °C,

D -

elektrochemische Aufrauhung in einem Elektrolyten, der 9 g/l Salpetersäure (gerechnet als 100%ig) und 67 g/l Aluminiumnitrat (Al[NO₃]₃·9H₂O) enthält, bei einer Temperatur von 40 °C,

E -

elektrochemische Aufrauhung in einem Elektrolyten, der 28 g/l Schwefelsäure und 100 g/l Aluminiumchlorid (AlCl₃·6H₂O) enthält, bei einer Temperatur von 45 °C und

F -

elektrochemische Aufrauhung in einem Elektrolyten, der 25 g/l Schwefelsäure und 130 g/l Aluminiumchlorid (AlCl₃·6H₂O) enthält, bei einer Temperatur von 40 °C.

The following roughening methods are used:

A -

Wire brushing,

B -

Wet brushing,

C -

electrochemical roughening in an electrolyte containing 10 g / l HCl (calculated as 100%) and 65 g / l aluminum chloride (AlCl₃ · 6H₂O) at a temperature of 35 ° C,

D -

electrochemical roughening in an electrolyte containing 9 g / l nitric acid (calculated as 100%) and 67 g / l aluminum nitrate (Al [NO₃] ₃ · 9H₂O) at a temperature of 40 ° C,

E -

electrochemical roughening in an electrolyte containing 28 g / l sulfuric acid and 100 g / l aluminum chloride (AlCl₃ · 6H₂O) at a temperature of 45 ° C and

F -

electrochemical roughening in an electrolyte containing 25 g / l sulfuric acid and 130 g / l aluminum chloride (AlCl₃ · 6H₂O) at a temperature of 40 ° C.

Column 1 of the following tables shows the roughening process used in the first step, columns 2 and 3 the roughening time and the current density (if applicable), column 5 shows the roughening process used in the second step, columns 6 and 7 the roughening time, and the Current density, if applicable, column 8 contains the Rz value explained above, which is a measure of the roughness, and column 9 contains the classification of the carrier in quality classes, which was explained in the previous section.

Between the two roughening steps, the carriers can still be pickled. In this case, an aqueous solution of 20 g / l NaOH and 2 g / l sodium carbonate (anhydrous) at room temperature (= 22 ° C.) is used as the pickling solution. Diving times, if applicable, are given in column 4 of the table.

The process steps in the following Table 1, as entered in column 1 and / or 5, correspond to the roughening methods E and F mentioned above.

Table 2 contains comparative examples of supports that were not made by the methods of the invention. Alkaline pickling, which was carried out on all supports between the first and the second roughening step, is not mentioned in Table 2. In this case, an aqueous solution of 20 g / l NaOH and 2 g / l sodium carbonate (anhydrous) at room temperature (= 22 ° C.) was used as the pickling solution. The immersion time was uniformly 30 seconds. Neither of the two roughening steps took place in an electrolyte which has the composition described above of 5 to 100 g / l of sulfate ions with the addition of chloride ions, for example in the form of Al chloride. The table shows the poorer quality of the roughening.

Aluminum sheets were roughened in two stages according to the processes described in Table 3 and anodized in sulfuric acid (100 g / l) at 30 ° C. and a current density of 5 A / dm² for 30 seconds.

6,6 Gew.-Teile

Kresol-Formaldehyd-Novolak (mit dem Erweichungsbereich 105-120 °C nach DIN 53 181),

1,1 Gew.-Teile

des 4-(2-Phenyl-prop-2-yl)-phenylesters der Naphtochinon-(1,2)-diazid-(2)-sulfonsäure-(4),

0,6 Gew.-Teile

2,2'-Bis-(naphtochinon-(1,2)-diazid-(2) -sulfonyloxy-(5))-dinaphthyl-(1,1')-methan,

0,24 Gew.-Teile

Naphthochinon-(1,2)-diazid-(2)-sulfochlorid-(4),

0,08 Gew.-Teile

Kristallviolett,

91,36 Gew.-Teile

Lösemittelgemisch aus 4 Vol.-Teilen Ethylenglykolmonomethylether, 5 Vol.-Teilen Tetrahydrofuran und 1 Vol.-Teil Butylacetat.

The plates were coated with a solution which has the following composition:

6.6 parts by weight

Cresol-formaldehyde novolak (with a softening range of 105-120 ° C according to DIN 53 181),

1.1 parts by weight

4- (2-phenyl-prop-2-yl) phenyl ester of naphthoquinone- (1,2) -diazide- (2) -sulfonic acid- (4),

0.6 parts by weight

2,2'-bis- (naphthoquinone- (1,2) -diazide- (2) -sulfonyloxy- (5)) - dinaphthyl- (1,1 ') - methane,

0.24 parts by weight

Naphthoquinone- (1,2) -diazide- (2) -sulfochloride- (4),

0.08 parts by weight

Crystal violet,

91.36 parts by weight

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.

5,3 Gew.-Teile

Natriummetasilikat · 9H2O

3,4 Gew.-Teile

Trinatriumphosphat

0,3 Gew.-Teile

Natriumdihydrogenphosphat (wasserfrei)

91,0 Gew.-Teile

Wasser.

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

5.3 parts by weight

Sodium metasilicate · 9H2O

3.4 parts by weight

Trisodium phosphate

0.3 parts by weight

Sodium dihydrogen phosphate (anhydrous)

91.0 parts by weight

Water.

The developed plates were used to print and the plates were tested with regard to print run and dampening solution management. It has been shown that these properties can be influenced as desired by controlling the two stages of the roughening process and are consistently good.

For comparison, some carriers were roughened using known methods. The roughening methods can be found in Table 4. The supports correspond to the comparative examples listed in Table 2. These plates were also coated with a solution of the composition given above, exposed, developed and printed. Here it turned out that with some Comparative examples (V72, V73, V75 and V76), although the dampening solution management was only slightly worse than according to the method according to the invention, the circulation was, however, significantly lower. With the plates of the other comparative examples, the circulation range of the printing plates produced according to the invention was reached, but the dampening solution consumption was significantly higher than with the printing plates produced according to the method according to the invention.

Even if the roughening methods C or D are modified, the surfaces of the printing plate carriers cannot be matched to the surfaces of the carriers obtainable with the method according to the invention, as can be seen from Table 5.

CC -

elektrochemische Aufrauhung in einem Elektrolyten, der 15 g/l HCl (gerechnet als 100%ig) und 30 g/l Aluminiumchlorid (AlCl₃·6H₂O) enthält, bei einer Temperatur von 55 °C,

CCC -

elektrochemische Aufrauhung in einem Elektrolyten, der 6 g/l HCl (gerechnet als 100%ig) und 90 g/l Aluminiumchlorid (AlCl₃·6H₂O) enthält, bei einer Temperatur von 30 °C,

DD -

elektrochemische Aufrauhung in einem Elektrolyten, der 20 g/l Salpetersäure (gerechnet als 100%ig) und 43 g/l Aluminiumnitrat (Al[NO₃]₃·9H₂O) enthält, bei einer Temperatur von 60 °C,

DDD -

elektrochemische Aufrauhung in einem Elektrolyten, der 6 g/l Salpetersäure (gerechnet als 100%ig) und 115 g/l Aluminiumnitrat (Al[NO₃]₃·9H₂O) enthält, bei einer Temperatur von 35 °C,

Modified roughening processes:

CC -

electrochemical roughening in an electrolyte containing 15 g / l HCl (calculated as 100%) and 30 g / l aluminum chloride (AlCl₃ · 6H₂O) at a temperature of 55 ° C,

CCC -

electrochemical roughening in an electrolyte containing 6 g / l HCl (calculated as 100%) and 90 g / l aluminum chloride (AlCl₃ · 6H₂O) at a temperature of 30 ° C,

DD -

electrochemical roughening in an electrolyte containing 20 g / l nitric acid (calculated as 100%) and 43 g / l aluminum nitrate (Al [NO₃] ₃ · 9H₂O) at a temperature of 60 ° C,

DDD -

electrochemical roughening in an electrolyte containing 6 g / l nitric acid (calculated as 100%) and 115 g / l aluminum nitrate (Al [NO₃] ₃ · 9H₂O) contains, at a temperature of 35 ° C,

Claims (21)

Process for roughening aluminum or its alloys for printing plate supports, in which in a roughening step electrochemical roughening takes place by means of alternating current in an acidic sulfate and chloride ion-containing electrolyte which contains chloride ions in the form of aluminum chloride, characterized in that in a preceding or subsequent roughening step a Mechanical, dry or moist roughening or electrochemical roughening is carried out by means of alternating current in an electrolyte which contains hydrochloric acid and aluminum ions, introduced as aluminum chloride, nitric acid and aluminum ions, introduced as aluminum nitrate or sulfuric acid and chloride ions, introduced as aluminum chloride. Process according to claim 1, characterized in that this process is carried out continuously with strips made of aluminum or its alloys. Process according to Claim 2, characterized in that when roughening in the electrolyte containing chloride and sulfate ions, temperatures of 20 to 60 ° C, current densities of 3 to 180 A / dm², exposure times of 10 to 300 sec and electrolyte flow rates at the Surface of the material to be roughened from 5 to 100 cm / sec. Process according to claim 1, characterized in that this process is carried out discontinuously with plates made of aluminum or its alloys. A method according to claim 4, characterized in that current roughness of 3 to 40 A / dm² and exposure times of 30 to 300 sec are used for the roughening in the electrolyte containing chloride and sulfate ions. Method according to claim 1, characterized in that the mechanical, dry roughening is carried out with wire brushes, by sandblasting, spherical grain, embossing or similar steps. Process according to Claim 1, characterized in that the concentration of the sulfate ions introduced as sulfuric acid is 5 to 100 g / l, in particular 20 to 50 g / l. A method according to claim 1, characterized in that the concentration of the chloride ions introduced as aluminum chloride is 1 to 100 g / l, in particular 10 to 70 g / l. A method according to claim 1, characterized in that the hydrochloric acid concentration is 1 to 20 g / l and the aluminum ion concentration is 10 to 200 g / l. A method according to claim 9, characterized in that in a temperature interval of 35 to 55 ° C, at current densities of 20 to 150 A / dm² and depending on the current density with exposure times of 5 to 200 seconds. A method according to claim 1, characterized in that the nitric acid concentration is 20 to 35 g / l and the aluminum ion concentration is 30 to 50 g / l. A method according to claim 11, characterized in that in a temperature interval of 22 to 50 ° C, at current densities of 15 to 80 A / dm² and depending on the current density with exposure times of 2 to 100 seconds. A method according to claim 1, characterized in that an acidic or alkaline cleaning takes place before and / or after each roughening step. A method according to claim 13, characterized in that is cleaned with an aqueous pickling solution of NaOH or NaOH with Na₂CO₃ acting for 30 to 80 sec. A method according to claim 14, characterized in that the sodium hydroxide solution is used in a concentration of 20 g / l NaOH and the sodium carbonate with 2 g / l Na₂CO₃. Method according to Claim 1, characterized in that, in addition to sinusoidal AC voltage with a network frequency, superimposed AC voltages and voltages of a lower frequency are used as the network frequency. A method according to claim 1, characterized in that the aluminum or its alloys are used as a plate, foil or tape. A method according to claim 1, characterized in that an anodic oxidation of the carrier material takes place after the roughening process. A method according to claim 1, characterized in that after the electrochemical roughening, a modified treatment is applied, which causes a surface removal from the roughened surface. A method according to claim 1, characterized in that a hydrophilizing aftertreatment is carried out. A method according to claim 1, characterized in that a photo-semiconducting layer is applied to the carrier material.