EP0536531A2 - Process for graining of aluminum and aluminum alloys respectively for supports for printing plates and a printing plate - Google Patents

Abstract

The invention relates to a method for roughening aluminum or aluminum alloys as a carrier material for printing plates, in which two electrochemical roughening steps follow one after the other, followed by a pickling step. Printing plates are produced from this carrier material by coating with light-sensitive layers, which expose and develop corresponding printing forms with a very uniform topography, high circulation stability and good dampening solution management.

Description

The invention relates to a method for roughening aluminum or aluminum alloys as a carrier material for printing plates, in which two electrochemical roughening steps follow one after the other, and a printing plate made of a carrier material that is produced by the method.

Printing plates, especially offset printing plates, generally consist of a support and at least one radiation-sensitive layer arranged thereon, this layer being applied by the consumer in the case of non-precoated plates or by the manufacturer in the case of precoated plates.

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 for producing printing plate supports and / or precoated printing plates, a combination of the above-mentioned processing steps is often used applied, 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, e.g. B. aqueous HCl or HNO₃ solutions, or in aqueous salt solutions, for. B. 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 R _z , 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. The arithmetic mean of the individual roughness depths of five adjacent individual measuring sections is calculated as the average roughness depth R _z .

The roughening takes place u. a. to improve the adhesion of the reproduction layer on the support and the dampening solution guide 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 also 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 get into the ink emulsify, the pressure becomes flat. Watermarks may also occur, causing the paper to become damp. Registration problems can also occur and there is an increased risk of tearing the paper web in 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). The consequences of too high and too low dampening solution management are discussed there. This term is more appropriate than the term "water supply", since offset printing generally does not use pure water for dampening, but rather several components are usually 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 of the printing press can deliver for design or other reasons, other non-printing parts of the printing plate can also take on color and also print, whereby especially fine screen areas are 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 non-image areas, free of color, but which also has a neutral behavior shows large amounts of dampening solution and still delivers flawless prints even if the supply of dampening solution temporarily exceeds normal levels due to operational fluctuations.

The fountain solution consumption of a printing plate can be measured objectively with sufficient accuracy, but not the fountain solution guidance, since it is responsible for some of the above-mentioned disadvantageous phenomena, e.g. B. 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". It will be described later in the context of the explanation of the examples under which conditions these adjectives are used as a basis for the assessment.

Another quality feature of an offset printing plate is the brightness and the uniformity of the brightness of the carrier material. For example, the brightness can be measured as described in the DIN standard 6174 in the version from January 1979. It also mentions how the uniformity of the color impression can be quantified. The value δE _{ab *} , which can be calculated from the three color values L ^* , a * and b *, serves as a measure of the uniformity. A support must not be too dark so that too much of the incident light is not absorbed by the support surface itself and is thus lost in the actual light-sensitive layer for photochemical reactions. The surface should also be uniformly bright so that the sensitivity to light does not vary from place to place on the printing plate.

By exposing or irradiating and developing or de-coating the reproduction layers that work electrophotographically, the image points that guide the color during later printing and the non-image points that carry the dampening agent, which are generally the exposed carrier surface, and thus the actual printing form, are produced on the printing plate created. 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 for 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, 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 0.5 and 2% HCl, there are only minor changes in the hole structure below 0.5% HCl, there is only a local attack on the surface and, at high values, an irregular dissolution of aluminum. 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. 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.

In pure hydrochloric acid electrolytes, it is difficult to set a flat and uniform surface topography, 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.

• Monocarbonsäuren, z. B. Essigsäure, in der DE-A 28 16 307 (= US-A 4 172 772),
• Gluconsäure in der US-A 3 963 594,
• Citronen- und Malonsäure in der EP-A 0 036 672 und
• Weinsäure in der US-A 4 052 275

beschrieben. Alle diese organischen Elektrolytbestandteile haben den Nachteil, bei hoher Strombelastung, die mit hoher Spannungsbelastung gleichzusetzen ist, elektrochemisch instabil zu werden und sich zu zersetzen.Additions to the HCl electrolyte have the task of preventing an adverse local attack in the form of deep holes. So is the addition of

• Monocarboxylic acids, e.g. B. acetic acid, in DE-A 28 16 307 (= US-A 4 172 772),
• Gluconic acid in US Pat. No. 3,963,594,
• Citric and malonic acid in EP-A 0 036 672 and
• Tartaric acid in US-A 4,052,275

described. All these organic electrolyte components have the disadvantage that they become 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-A 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.

In DE-A 16 21 115 (= US-A 3 632 486 and US-A 3 766 043) a direct current roughening is diluted Hydrofluoric acid mentioned, wherein the aluminum strip is connected as a cathode.

• Wechselstrom, bei dem die Anodenspannung und der anodische coulombische Eingang größer als die Kathodenspannung und der kathodische coulombische Eingang sind (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 29 12 060 (= 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 (DE-A 14 46 026 = US-A 3 193 485),
• die Unterbrechung des Stromflusses während 10 bis 120 s und ein Stromfluß während 30 bis 300 s, wobei Wechselstrom und als Elektrolyt eine wäßrige 0,75 bis 2 n HCl-Lösung mit NaCl- oder MgCl₂-Zusatz eingesetzt werden (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 to improve the uniformity is to modify the current form used. These include, 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 (DE-A 26 50 762 = US-A 4 087 341), the anodic half-period time of the alternating current generally being less than the cathodic half-period time is set; this method is also used, for example, in DE-A 29 12 060 (= 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 increased compared to the cathode voltage (DE-A 14 46 026 = US-A 3 193 485),
• the interruption of the current flow for 10 to 120 s and a current flow for 30 to 300 s, alternating current and an aqueous 0.75 to 2 N HCl solution with NaCl or MgCl₂ addition being used as the electrolyte (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).

The methods mentioned result in aluminum surfaces which, although they have a relatively uniform hole size distribution, require a relatively large outlay on equipment and are also only within very narrow parameter limits applicable. In addition, the carriers are difficult to produce with uniform brightness.

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 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 one chemical cleaning (pickling) which may take place with an electrochemical roughening by means of modified alternating current in electrolytes containing hydrochloric or nitric acid is described, it being possible for a further cleaning step to subsequently take place.

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

From DE-A 38 36 810 a double roughening with two electrochemical roughening steps and an etching treatment taking place between the two roughening steps is known.

Various two-stage processes are known for the production of capacitors from aluminum foils. In the 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 can meet the high demands placed on offset printing plates today.

Two-stage processes that use electrochemical processes in both stages have also become known. In the method 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 JP-A 86/051 396. Although these known processes 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 DE-A 37 17 654.

US-A 4 437 955 discloses a two-stage electrochemical roughening process for the production of 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 foil 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 in the last two methods optimized for electrolytic capacitors are too pitted for use in lithography.

DE-A 38 36 810 describes a process in which aluminum is also roughened in two steps for the production of printing plate supports. Pickling is carried out there between the first and the second roughening step. This method has the disadvantage that the plates, especially when chloride-containing electrolytes are used in the last pickling step, become superficially uneven and quite dark.

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 uniformly bright, very fine, grain-free, area-covering roughening structure of the aluminum surface of the printing plate supports, very good reprographic and printing properties, in particular high ones Print runs of the finished printing forms can be obtained.

Furthermore, it is an object of the present invention to provide a method which allows the targeted production of printing plate 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 the changing market requirements without any changes in the system.

This object is achieved in that the first electrochemical roughening step in an electrolyte containing hydrochloric, nitric or sulfuric acid and chloride ions or nitrate ions, the subsequent second electrochemical roughening step in an electrolyte with the same or different concentration proportions of the additives as in the first roughening step and that finally a pickling of the substrate surface is carried out.

The further embodiment of the method results from the features of claims 2 to 15.

The pickling step removes undesirable deposits that make the surface uneven and dark from the surface of the carrier material.

It was found that in addition to the excellent reprographic properties and good dampening solution management, there were excellent printing properties, such as a longer print run.

A surface produced by the method according to the invention is a highly uniform carrier surface with excellent lithographic properties. It has brightnesses that can be varied in the range from L = 60 to L = 90, and irregularities in the brightness of not more than δEab * = 2. The values for the brightness and the unevenness are measured as described in the DIN standard 6174 in the version from January 1979.

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 are in the following ranges: the temperature of the electrolyte between 20 and 80 ° C, the current density between 3 and 180 A / dm², the residence time of a material point to be roughened in the electrolyte between 5 and 300 s and Electrolyte flow rate on the surface of the material to be roughened between 5 and 200 cm / s. 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 / dm² and the residence times between 30 and 300 s. The flow of the electrolyte can also be dispensed with.

• "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.

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

The process can also be used successfully with other aluminum alloys.

At the end of the roughening process, an anodic oxidation of the aluminum takes place, for example, which improves the abrasion and adhesion properties of the surface of the carrier material.

• 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.-% (363 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 ^oC, 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 up to 8 to 10% by weight. H₂SO₄ (about 100 g / l H₂SO₄) reduced or increased to 30 wt .-% (363 g / l H₂SO₄) and more.
• The "hard anodization" is carried out with an aqueous electrolyte containing H₂SO₄ at a concentration of 166 g / l H₂SO₄ (or approx. 230 g / l H₂SO₄) at an operating temperature of 0 to 5 ^o C, at a current density of 2 to 3 A / dm², an increasing 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 processes for the anodic oxidation of printing plate support materials already mentioned in the previous paragraph, the following processes can also be used, for example: the anodic oxidation of aluminum in an aqueous electrolyte containing H₂SO₄, the Al³⁺ ion content of which is more than 12 g / l is set in an aqueous electrolyte containing H₂SO₄ and H₃PO₄ or in an aqueous electrolyte containing H₂SO₄, H₃PO₄ and Al³⁺ ions.

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 surface removal from the roughened surface, can also be applied. This treatment can be carried out in both acidic and basic media.

Such a modifying intermediate treatment provides by removing fine structures and. a. a uniformly bright surface, and the surface improves the water flow of the panels.

The anodic oxidation of the aluminum printing plate support material can 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 immersion treatment of the material in an aqueous polyvinylphosphonic acid solution, immersion treatment in an aqueous alkali silicate solution or electrochemical treatment (anodization) in an aqueous alkali silicate solution. 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.

A carrier material produced by the method according to the invention becomes a printing plate by coating with a light-sensitive 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 either at the manufacturer applied by presensitized printing plates 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 contain other components, e.g. 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 according to the invention have a uniform brightness and a very uniform topography, which has a positive influence on the print run stability and the dampening solution guidance when printing printing forms 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.

The process according to the invention is described in more detail below with reference to the examples and comparative examples given in the tables below.

An aluminum support material is first pickled for 60 s in an aqueous solution containing 20 g / l NaOH at room temperature. The roughening takes place in the specified electrolyte systems of the roughening stages A, B, C, D by combining two roughening steps, all possible combinations of the electrolyte systems of the roughening steps A to D, including the combination of one of the roughening steps with themselves, e.g. B. A-A, B-B, C-C, D-D, is possible.

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 a microscope, whereby a homogeneously roughened and scar-free surface is assigned quality level "10" (best value). A quality level "0" (worst value) is assigned to a surface with thick scars of a size of more than 30 µm and / or an extremely unevenly roughened or almost rolled surface.

Another criterion for the quality is the brightness and the uniformity of the brightness of the support surface, which are given as L-value and δE-value in the tables below. The greater the L value, the greater the brightness, and the greater the δE value, the more the brightness fluctuates from place to place on the carrier surface.

A

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,

B

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,

C

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

D

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 steps A to D are used:

A

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,

B

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,

C.

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

D

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 2 of the following tables shows the roughening process used in the first step, columns 3 and 4 the roughening time and the current density, column 5 shows the roughening process used in the second step, columns 6 and 7 the roughening time and the current density, the column 8 contains the L value explained above, the one The measure of the brightness is, and column 9 contains the classification of the carrier in quality classes, which was explained in the previous section, column 10 shows the uniformity δE of the brightness.

In each of the cases specified in Table 1, the supports are still alkali pickled in a third step after both roughening steps. In this case, an aqueous solution of 20 g / l NaOH and 2 g / l sodium carbonate (anhydrous) at room temperature of 20 to 24 ° C. is used as the pickling solution. The concentration of both salt and acid can be varied. Then the temperature or the pickling time may have to be adjusted. The pickling time is 15 s, but can be between 5 and 120 s. Under no circumstances should it be longer than 300 s in this pickling solution. Table 1 1st roughening step 2nd roughening step 1 2nd 3rd 4th 5 6 7 8th 9 10th No. method Time s Current density A / dm² method Time s Current density A / dm² Brightness L * grade δE 1 A 20th 100 D 15 40 65.5 7 0.4 2nd A 20th 100 D 20th 40 69.2 7 0.3 3rd C. 10th 40 B 15 40 71.4 10th 0.3 4th C. 10th 40 B 20th 40 80.0 10th 0.6 5 B 30th 60 D 10th 40 83.4 7 0.8 6 C. 30th 60 D 15 60 81.2 6 0.8 7 D 8th 35 B 20th 40 78.6 9 0.7 8th B 15 80 B 25th 40 69.8 8th 0.8 9 B 30th 40 A 25th 90 75.8 8th 0.9 10th A 20th 100 A 10th 60 77.6 7 1.2 11 C. 20th 100 C. 13 60 74.1 7 0.9 12th A 20th 100 C. 17th 60 72.4 7 0.8 13 D 30th 60 C. 10th 40 77.3 7 0.5 14 D 30th 60 C. 15 40 78.3 7 0.6 15 D 30th 60 D 40 90 79.4 6 0.8 16 B 30th 60 C. 10th 80 75.6 7 1.1 17th B 30th 60 C. 10th 40 73.5 7 0.8 18th D 30th 60 A 15 80 75.1 8th 0.5 19th B 30th 60 D 10th 40 81.4 7 0.8 20th A 30th 80 B 15 40 82.1 8th 1.1 21 A 10th 80 C. 10th 40 81.1 7 0.9 22 C. 30th 60 D 15 60 81.3 6 0.8 23 C. 10th 40 B 15 40 79.6 10th 0.4 24th C. 10th 40 A 20th 40 71.6 10th 0.5 25th C. 10th 40 A 10th 60 72.0 8th 0.6

Table 2 contains comparative examples of supports that were not made by the methods of the invention. Except for the pickling step after the two roughening steps, the carriers were produced under identical conditions as the carriers in Table 1. Instead of the pickling step after the two roughening steps, a pickling step was inserted between the two roughening steps. This pickling step, not listed in Table 2 is an alkaline pickling. In this case, an aqueous solution of 20 g / l NaOH and 2 g / l sodium carbonate (anhydrous) at room temperature from 20 to 24 ° C. was used as the pickling solution. The diving time was 30 s. The poorer quality of the carriers can be seen from Table 2 in comparison to Table 1. The carriers are darker than those produced according to the invention, the brightness is more irregular. Table 2 1st roughening step 2nd roughening step 1 2nd 3rd 4th 5 6 7 8th 9 10th No. method Time s Current density A / dm² method Time s Current density A / dm² Brightness L * grade δE V1 A 20th 100 D 15 40 59.5 6 3.4 V2 A 20th 100 D 20th 40 59.2 5 2.3 V3 C. 10th 40 B 15 40 59.4 4th 2.3 V4 C. 10th 40 B 20th 40 60.0 5 6.6 V5 B 30th 60 D 10th 40 59.9 6 3.1 V6 C. 30th 60 D 15 60 50.2 4th 3.8 V7 D 8th 35 B 20th 40 59.5 4th 6.7 V8 B 15 80 B 25th 40 59.8 3rd 4.8 V9 B 30th 40 A 25th 90 55.6 6 2.9 V10 A 20th 100 A 10th 60 55.6 4th 2.2 V11 C. 20th 100 C. 13 60 54.1 5 2.9 V12 A 20th 100 C. 17th 60 52.4 6 4.8 V13 D 30th 60 C. 10th 40 57.3 6 15.5 V14 D 30th 60 C. 15 40 58.3 7 0.6 V15 D 30th 60 D 40 90 59.4 5 6.8 V16 B 30th 60 C. 10th 80 55.6 4th 5.1 V17 B 30th 60 C. 10th 40 55.6 4th 6.8 V18 D 30th 60 A 15 80 55.1 4th 5.5 V19 B 30th 60 D 10th 40 51.4 7 2.8 V20 A 30th 80 B 15 40 52.1 6 2.1 V21 A 10th 80 C. 10th 40 53.1 6 5.9 V22 C. 30th 60 D 15 60 51.3 4th 5.8 V23 C. 10th 40 B 15 40 69.6 7 4.4 V24 C. 10th 40 A 20th 40 61.6 6 5.5 V25 C. 10th 40 A 10th 60 62.0 6 6.6

Table 3 again contains comparative examples which were not produced by the process according to the invention. Here no pickling was carried out between the two roughening steps nor after the roughening steps. The supports are overall more uneven than the comparative examples in Table 2, the supports of which were pickled after the first roughening step. Table 3 1st roughening step 2nd roughening step 1 2nd 3rd 4th 5 6 7 8th 9 10th No. Procedure time Current density Procedure time Current density brightness grade δE ren s A / dm² ren s A / dm² L * V26 A 20th 100 D 15 40 58.5 6 3.0 V27 A 20th 100 D 20th 40 58.2 5 3.3 V28 C. 10th 40 B 15 40 57.4 4th 3.3 V29 C. 10th 40 B 20th 40 58.0 5 7.7 V30 B 30th 60 D 10th 40 59.4 6 4.1 V31 C. 30th 60 D 15 60 50.2 4th 4.1 V32 D 8th 35 B 20th 40 58.5 4th 6.7 V33 B 15 80 B 25th 40 59.8 3rd 4.8 V34 B 30th 40 A 25th 90 54.6 6 4.9 V35 A 20th 100 A 10th 60 55.6 4th 4.2 V36 C. 20th 100 C. 13 60 53.1 5 2.9 V37 A 20th 100 C. 17th 60 52.4 6 4.8 V38 D 30th 60 C. 10th 40 56.3 6 15.5 V39 D 30th 60 C. 15 40 58.3 7 3.6 V40 D 30th 60 D 40 90 56.4 5 6.8 V41 B 30th 60 C. 10th 80 54.6 4th 5.1 V42 B 30th 60 C. 10th 40 55.2 4th 7.8 V43 D 30th 60 A 15 80 54.1 4th 6.5 V44 B 30th 60 D 10th 40 51.1 7 3.8 V45 A 30th 80 B 15 40 52.1 6 2.7 V46 A 10th 80 C. 10th 40 54.4 6 6.5 V47 C. 30th 60 D 15 60 50.3 4th 5.9 V48 C. 10th 40 B 15 40 69.4 7 4.4 V49 C. 10th 40 A 20th 40 61.2 6 5.3 V50 C. 10th 40 A 10th 60 61.5 6 6.7 V51 A 20th 50 - - - 59.8 5 2.3 V52 B 20th 80 - - - 57.6 6 3.0 V53 C. 10th 100 - - - 62.3 7 2.5 V54 D 10th 90 - - - 62.4 7 2.2

Examples V51 to V54 in the table above are supports which have been subjected to roughening in only one stage.

Table 4 shows the results of supports which were roughened in the same way as the supports in Table 1. They differ from those described in Table 1 by the pickling. In each of the cases listed in Table 4, the carriers are pickled in a third processing step after both roughening steps. In this case, an aqueous solution of 100 g / l H₂SO₄ and 5 g / l aluminum sulfate (anhydrous) at 45 ° C is used as the pickling solution. These concentrations can be varied. The acid concentration can range from 10g / l to 500g / l, and the aluminum concentration can also be changed. With low acid concentrations, it is advisable to increase the temperature. The pickling time is 60 s, but can be between 10 and 300 s. Under no circumstances should it be longer than 500 s in this pickling solution. Table 4 1st roughening step 2nd roughening step 1 2nd 3rd 4th 5 6 7 8th 9 10th No. method Time s Current density A / dm² method Time s Current density A / dm² Brightness L * grade δE 26 A 20th 100 D 15 40 64.5 7 0.6 27th A 20th 100 D 20th 40 68.2 7 0.4 28 C. 10th 40 B 15 40 69.8 10th 0.8 29 C. 10th 40 B 20th 40 79.5 10th 0.9 30th B 30th 60 D 10th 40 83.0 7 0.7 31 C. 30th 60 D 15 60 81.0 6 1.9 32 D 8th 35 B 20th 40 78.2 9 1.4 33 B 15 80 B 25th 40 69.2 8th 0.9 34 B 30th 40 A 25th 90 75.1 8th 0.9 35 A 20th 100 A 10th 60 76.6 7 1.3 36 C. 20th 100 C. 13 60 73.1 7 1.1 37 A 20th 100 C. 17th 60 72.0 7 1.8 38 D 30th 60 C. 10th 40 77.2 7 0.7 39 D 30th 60 C. 15 40 78.1 7 0.7 40 D 30th 60 D 40 90 79.1 6 0.9 41 B 30th 60 C. 10th 80 75.6 7 1.5 42 B 30th 60 C. 10th 40 72.4 7 0.9 43 D 30th 60 A 15 80 74.0 8th 0.8 44 B 30th 60 D 10th 40 80.1 7 0.9 45 A 30th 80 B 15 40 81.8 8th 1.5 46 A 10th 80 C. 10th 40 81.0 7 1.2 47 C. 30th 60 D 15 60 80.3 6 1.2 48 C. 10th 40 B 15 40 77.6 10th 0.8 49 C. 10th 40 A 20th 40 68.6 10th 0.7 50 C. 10th 40 A 10th 60 71.0 8th 0.8

Some of the plates made in this way were selected for further experiments. The plates were coated with a solution which has the following composition (Gt = parts by weight, Vt = parts by volume): 6.6 pbw Cresol-formaldehyde novolak with a softening range from 105 to 120 ° C according to DIN 53 181, 1.1 Gt 4- (2-phenyl-prop-2-yl) phenyl ester of naphthoquinone- (1,2) -diazide- (2) -sulfonic acid- (4), 0.6 pbw 2,2'-bis- (naphthoquinone- (1,2) -diazide- (2) -sulfonyloxy- (5)) - dinaphthyl- (1,1 ') - methane, 0.24 pbw Naphthoquinone- (1,2) -diazide- (2) -sulfochloride- (4), 0.08 pbw Crystal violet, 91.36 pbw Solvent mixture of 4 parts ethylene glycol monomethyl ether, 5 parts tetrahydrofuran and 1 part butyl acetate.

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 pbw Sodium metasilicate · 9H2O 3.4 pbw Trisodium phosphate 0.3 pbw Sodium dihydrogen phosphate (anhydrous) 91.0 pbw Water.

sehr schlecht

Die Feuchtmittelmenge muß in einem sehr engem Unterbereich des gesamten Einstellbereiches der Feuchtmitteldosierung gehalten werden und die Druckplatte benötigt mehr als 100 Bogen um freizulaufen.

schlecht

Die Feuchmittelmenge muß in einem engen Unterbereich des gesamten Einstellbereiches der Feuchtmitteldosierung gehalten werden und benötigt 50-100 Bogen um freizulaufen.

ausreichend

Die Feuchtmittelmenge kann innerhalb eines Bereiches von 20% des möglichen Feuchtmittel-dosierungsbereiches ohne Schaden an der Qualität des Druckes gefahren werden und ist nach weniger als 50 Bogen freigelaufen.

befriedigend

Die Feuchtmittelmenge kann innerhalb eines Bereiches von 25% des möglichen Feuchtmittel-dosierungsbereiches ohne Schaden an der Qualität des Druckes gefahren werden und ist nach weniger als 30 Bogen freigelaufen.

gut

Die Feuchtmittelmenge kann innerhalb eines Bereiches von 25% des möglichen Feuchtmittel-dosierungsbereiches ohne Schaden an der Qualität des Druckes gefahren werden und ist nach weniger als 20 Bogen freigelaufen.

sehr gut

Die Feuchtmittelmenge kann innerhalb eines Bereiches von 25% des möglichen Feuchtmitteldosierungsbereiches ohne Schaden an der Qualität des Druckes gefahren werden und ist nach weniger als 15 Bogen freigelaufen.

Tabelle 5 Träger Auflage Wasserführung 1 170 000 gut 3 180 000 sehr gut 9 150 000 sehr gut 17 330 000 sehr gut 24 190 000 befriedigend 28 130 000 sehr gut 48 145 000 gut The developed plates were used to print and the plates were tested with regard to print run and dampening solution management. It was found that these properties were achieved by the pickling after the two roughening stages Can be influenced and are consistently good. Table 5 shows the selected carriers with their numbers in Tables 1 to 4 and the results of the tests. One of the results is the quality of the water flow. As described above, it is difficult to quantify. The following evaluations were therefore made in Table 5:

very bad

The amount of dampening solution must be kept in a very narrow sub-range of the entire setting range of the dampening solution metering and the printing plate requires more than 100 sheets to run free.

bad

The amount of dampening solution must be kept in a narrow sub-range of the entire setting range of the dampening solution metering and requires 50-100 sheets to run free.

sufficient

The amount of dampening solution can be run within a range of 20% of the possible dampening solution metering range without damaging the quality of the print and is freed after less than 50 sheets.

satisfying

The amount of dampening solution can be run within a range of 25% of the possible dampening solution metering range without damaging the quality of the print and is freed after less than 30 sheets.

Good

The amount of dampening solution can be run within a range of 25% of the possible dampening solution metering range without damaging the quality of the print and is freed after less than 20 sheets.

very well

The amount of dampening solution can be run within a range of 25% of the possible dampening solution metering range without damage to the quality of the print and is freed after less than 15 sheets.

Table 5 carrier Edition Water supply 1 170,000 Good 3rd 180,000 very well 9 150,000 very well 17th 330,000 very well 24th 190,000 satisfying 28 130,000 very well 48 145,000 Good

Table 6 shows the results of some printing forms which were produced from supports not according to the invention and which do not match the printing forms in Table 5 either in the print run or in the water supply. Table 6 carrier Edition Water supply V1 80,000 satisfying V5 60,000 bad V31 150,000 very bad V21 30,000 Good V33 90,000 bad V38 30,000 bad V48 145,000 bad V51 120,000 bad V52 140,000 very bad V53 80,000 satisfying V54 60,000 satisfying

Claims (17)

A process for roughening aluminum or aluminum alloys as a support material for printing plates, in which two electrochemical roughening steps and a pickling step take place, characterized in that the first electrochemical roughening step in an electrolyte containing hydrochloric, nitric or sulfuric acid and chloride ions or nitrate ions, the subsequent second electrochemical roughening step takes place in an electrolyte with the same or different concentration proportions of the additives as in the first roughening step and that finally the substrate surface is pickled. Method according to Claim 1, characterized in that two roughening steps from a group of roughening steps A, B, C, D, including the combination of two identical roughening steps, are combined with one another, that the roughening step A in an electrolyte, the hydrochloric acid and aluminum chloride, B in an electrolyte, nitric acid and aluminum nitrate, C in an electrolyte containing sulfuric acid and aluminum chloride and D in an electrolyte that contains less sulfuric acid and more aluminum chloride than the electrolyte of the roughening step C contains, takes place and that the two roughening steps are followed by a purely chemical pickling in an acidic or alkaline bath. A method according to claim 2, characterized in that the electrochemical roughening takes place continuously, during the roughening steps A, B, C, D the temperature of the electrolyte in the individual roughening step between 20 and 80 ° C, the current density between 3 and 180 A / dm² , the dwell time of a substrate to be roughened in the electrolyte is 5 to 300 s and the electrolyte flow rate on the surface of the substrate is 5 to 200 cm / s. A method according to claim 2, characterized in that the electrochemical roughening takes place discontinuously, wherein during the roughening steps A, B, C, D the temperature of the electrolyte in the individual roughening step between 20 and 80 ° C, the current density between 3 and 40 A / dm² , the residence time of a roughened carrier material site in the electrolyte is 30 to 300 s. Process according to claims 1 to 4, characterized in that in the roughening steps A, B, C, D sinusoidal AC voltages with mains frequency or superimposed AC voltages lower frequency than the mains frequency are applied to the electrolyte baths and carrier materials. A method according to claim 3, characterized in that by continuously feeding the correspondingly diluted acids into the electrolytes of the individual Roughening the electrolyte composition is kept constant. A method according to claim 2, characterized in that the roughening step A in an electrolyte containing 10 g / l HCl and 65 g / l aluminum chloride (AlCl₃ · 6H₂O) at a temperature of 35 ° C for a residence time of 10 to 30 s and a current density of 40 to 100 A / dm². A method according to claim 2, characterized in that the roughening step B in an electrolyte containing 9 g / l nitric acid and 67 g / l aluminum nitrate [Al (NO₃) ₃ · 9H₂O], at a temperature of 40 ° C, during a residence time from 15 to 30 s and a current density of 40 to 80 A / dm². A method according to claim 2, characterized in that the roughening step C in an electrolyte containing 28 g / l sulfuric acid and 100 g / l aluminum chloride [AlCl₃ · 6H₂O) at a temperature of 45 ° C for a residence time of 10 to 30 s and a current density of 40 to 100 A / dm². A method according to claim 2, characterized in that the roughening step D in an electrolyte containing 25 g / l sulfuric acid and 130 g / l aluminum chloride [AlCl₃ · 6H₂O] at a temperature of 40 ° C for a residence time of 8 to 40 s and a current density of 35 to 90 A / dm². A method according to claim 2, characterized in that the purely chemical pickling is carried out as an anodic oxidation of the carrier material in an electrolyte, which contains sulfuric acid, phosphoric acid, oxalic acid, amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof. A method according to claim 11, characterized in that the pickling solution is an aqueous acidic solution of 10 to 500 g / l, in particular 100 g / l H₂SO₄ and 3 to 20 g / l, in particular 5 g / l of anhydrous aluminum sulfate and that Pickling time is 10 to 300 s, in particular 60 s, at a temperature of 45 ° C. Process according to Claim 2, characterized in that the pickling solution is an aqueous alkaline solution of 10 to 100 g / l, in particular 20 g / l NaOH and 2 g / l anhydrous sodium carbonate, and that the pickling time is 5 to 120 s, in particular 15 s , at a room temperature of 20 to 24 ° C. Method according to claim 11, characterized in that the anodic oxidation takes place with direct current, alternating current or with a combination of direct current with superimposed alternating current. A method according to claim 12, characterized in that the anodic oxidation, which leads to layer weights of 1 to 10 g / m² of aluminum oxide, corresponding to a layer thickness of about 0.3 to 3.9 µm, one or more hydrophilizing, chemical or electrochemical treatment step (e) follow the alumina layer by dipping in an aqueous polyvinylphosphonic acid solution, an aqueous alkali silicate solution or anodizing in an aqueous alkali silicate solution. Printing plate made of a carrier material which is produced according to one or more of claims 1 to 15, characterized in that the carrier material is coated with a solution of the following composition (Gt = parts by weight, Vt = parts by volume): 6.6 pbw Cresol-formaldehyde novolak with a softening range of 105 to 120 ° C, 1.1 Gt 4- (2-phenyl-prop-2-yl) phenyl ester of naphthoquinone- (1,2) -diazide- (2) -sulfonic acid- (4), 0.6 pbw 2,2'-bis- (naphthoquinone- (1,2) -diazide- (2) -sulfonyloxy- (5)) - dinaphthyl- (1,1 ') - methane, 0.24 pbw Naphthoquinone- (1,2) -diazide- (2) -sulfochloride- (4), 0.08 pbw Crystal violet, 91.36 pbw Solvent mixture of 4 parts ethylene glycol monomethyl ether, 5 parts tetrahydrofuran and 1 part butyl acetate. Printing plate according to claim 16, characterized in that the coated carrier material is dried at temperatures up to 120 ° C.