Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/02—Etching
  • C25F3/04—Etching of light metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41N—PRINTING PLATES OR FOILS; MATERIALS FOR SURFACES USED IN PRINTING MACHINES FOR PRINTING, INKING, DAMPING, OR THE LIKE; PREPARING SUCH SURFACES FOR USE AND CONSERVING THEM
  • B41N3/00—Preparing for use and conserving printing surfaces
  • B41N3/03—Chemical or electrical pretreatment
  • B41N3/034—Chemical or electrical pretreatment characterised by the electrochemical treatment of the aluminum support, e.g. anodisation, electro-graining; Sealing of the anodised layer; Treatment of the anodic layer with inorganic compounds; Colouring of the anodic layer

Definitions

• the invention relates to a method for the electrochemical roughening of aluminum for printing plate supports, which is carried out with alternating current in an aqueous mixed electrolyte.
• Printing plates generally consist of a support and at least one radiation-sensitive reproduction layer arranged thereon, this layer either from the consumer (in the case of non-precoated plates) or from the industrial one Manufacturer (for pre-coated boards) is applied to the substrate.
• Aluminum or one of its alloys has established itself as a layer material in the printing plate field.
• 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 grain or etching in literature), chemical or electrochemical oxidation and / or treatment with hydrophilizing agents.
• a combination of the above-mentioned Mo Types of dification applied, in particular a combination of electrochemical roughening and anodic oxidation, optionally with a subsequent hydrophilization step.
• the roughening is carried out, for example, in aqueous acids such as aqueous HCl or HN0 3 solutions, in aqueous salt solutions such as aqueous NaCl or Al (N0 3 ) 3 solutions or in combinations of these components using alternating current.
• the roughness depths that can be achieved in this way are in the range from about 1 to 15 / ⁇ m, in particular in the range from 2 to 8 / ⁇ m.
• the roughness depth is determined in accordance with DIN 4768 in the version from October 1970, the roughness depth R z is then the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections.
• aqueous HCl solutions as an electrolyte solution for the electrochemical roughening of support materials made of aluminum must therefore be assumed to be known. It can be obtained - as many examples of commercial printing plates show - a uniform grain size, which is particularly suitable for the field of application of lithography and is within a roughness range that is generally useful in practice. For certain areas of application of printing plates (e.g.
• the previously known organic additives to aqueous acid electrolytes such as HCl or HN0 3 solutions have the disadvantage that they become electrochemically unstable and at least partially decompose at high current loads (voltage) in modern continuously operating conveyor systems.
• the known inorganic additives such as phosphoric, chromic or boric acid have the disadvantage that the intended protective effect frequently breaks down locally and individual, particularly pronounced scars then develop there. So z. B. the addition of H 3 P0 4 lead to flat roughened surfaces, which, however, have the disadvantage of many deep individual holes.
• the previously known complexing additives generally accelerate the "trapping" of released Al 3+ ions and dissolve the aluminum ren thereby to reinforce the roughening attack; However, this often leads to the fact that no additional hole nuclei are created, but that already formed nuclei and holes continue to grow, ie there is then increased scar formation.
• the previously known inhibitory additives generally have the effect that the hole growth of individual holes is stopped relatively soon and new hole nuclei can arise; However, they have the decisive disadvantage that this protective effect due to defects, alloy components and the like. ⁇ . can collapse; this then leads to deep holes in an otherwise flat and evenly roughened surface. Backing materials with such imperfections are unsuitable for lithographic purposes.
• the object of the present invention is therefore to propose a method for the electrochemical roughening of aluminum for printing plate supports, which makes it possible to achieve a uniformly roughened surface topography with a wide range in the mean roughness depth values and to achieve long bath service lives.
• the invention is based on the known process for the electrochemical roughening of aluminum or its alloys for printing plate supports in an aqueous mixed electrolyte solution containing HCl and at least one organic acid under the action of alternating current.
• the process according to the invention is then characterized in that the organic acid is a compound from the group of diphosphonic acids, polyphosphone acids and gallic acid.
• the aqueous electrolyte solution contains 0.5 to 10.0% X, in particular 0.8 to 5.0%, of HCl and 0.05 to 5.1%, in particular 0.1 to 2.0%, of the organic acid.
• the phosphorus acids which can be used in the process according to the invention include, in particular, di- and polyphosphonic acids (ie compounds having at least 3 phosphonic acid groups) with aliphatic organic radicals, ie preferred alkanedi- or polyphosphonic acids from C 1 to C 6 and with up to 6 phosphonic acid groups, which, if appropriate may also have further functional groups such as hydroxyl or amino groups as substituents on the alkane moiety.
• the phosphonic acid groups are preferably located as substitutes on carbon atoms, but they can also be linked to hetero atoms.
• Gallic acid is 3,4,5-trihydroxy-benzoic acid.
• Suitable base materials for the present invention include those materials roughened aluminum or one of its alloys, for example, have a content of more than 98.5 parts by weight X of Al and proportions of Si, F e, Ti, Cu, and Zn. These aluminum carrier materials can also, if necessary after pre-cleaning, mechanically (e.g. by brushing and / or with an abrasive treatment) before the electrochemical stage lungs) are roughened. All process steps can be carried out discontinuously with plates or foils, but they are preferably carried out continuously with tapes.
• the process parameters are in the following ranges: the temperature of the electrolyte between 20 and 60 ° C, the current density between 3 and 200 A / dm 2 , the residence time of a material point to be roughened in the electrolyte between 1 and 300 sec and the electrolyte flow rate at the surface of the material to be roughened between 1 and 300 cm / sec; in the batchwise process, the required current densities tend to be in the lower part and the dwell times are in the upper part of the ranges specified, and the flow of the electrolyte can also be dispensed with.
• alternating current with a frequency of 50 to 60 Hz is used as the type of current, but modified types of current such as alternating current with different amplitudes of the current strength for the anode and cathode current, lower frequencies, current interruptions or superimposition of two currents of different frequency and waveform are also possible.
• the average roughness depth R z of the roughened surface is in the range from 1 to 15 / um, in particular from 1.5 to 8.0 / um.
• aluminum ions in the form of aluminum salts in particular 0.5 to 5.0% of AlC1 3 can be added.
• Pre-cleaning includes, for example, treatment with aqueous NaOH solution with or without degreasing agent and / or complexing agents, trichlorethylene, acetone, methanol or other commercially available aluminum stains.
• the roughening or, in the case of several roughening stages, also between the individual stages, an abrasive treatment can additionally be carried out, in particular a maximum of 2 g / m 2 being removed (up to 5 g / m 2 between the stages);
• aqueous solutions of alkali metal hydroxide or aqueous solutions of alkaline salts or aqueous acid solutions based on HN0 3 , H 2 SO 4 or H 3 PO 4 are used as abrasive solutions.
• non-electrochemical treatments are also known which essentially only have a rinsing and / or cleaning effect and, for example, for removing deposits formed during roughening ("Schmant") or simply for Serve removal of electrolyte residues; For example, dilute aqueous alkali hydroxide solutions or water are used for these purposes.
• an anodic oxidation of the aluminum can then preferably follow in a further process step to be used, for example to improve the abrasion and adhesion properties of the surface of the carrier material to improve rials.
• the usual electrolytes such as H 2 S0 4 , H 3 P0 4 , H 2 C 2 0 4 , amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof can be used for anodic oxidation; in particular, H 2 S0 4 and H 3 P0 4 are used alone, in a mixture and / or in a multi-stage anodizing process.
• the stage of anodic oxidation of the aluminum support material can also be followed by one or more post-treatment stages.
• These post-treatment stages serve in particular to additionally increase the hydrophilicity of the aluminum oxide layer, which is often sufficient, while at least the other known properties of this layer are retained.
• the materials produced according to the invention are used as supports for offset printing plates, ie a radiation-sensitive coating is applied to one or both sides of the coating either by the manufacturer of presensitized printing plates or directly by the consumer Carrier material applied.
• a radiation-sensitive coating is applied to one or both sides of the coating either by the manufacturer of presensitized printing plates or directly by the consumer Carrier material applied.
• all layers are suitable as radiation (light) sensitive layers which, after irradiation (exposure), optionally with subsequent development and / or fixation, provide an image-like area from which printing can take place.
• photoconductive layers as described, for example, in DE-C 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 are described, are applied to the carrier materials produced according to the invention, thereby producing highly light-sensitive, electrophotographic printing plates.
• coated offset printing plates obtained from the carrier materials produced by the process according to the invention are converted into the desired printing form in a known manner by imagewise exposure or irradiation and washing out of the non-image areas with a developer, for example an aqueous alkaline developer solution.
• a developer for example an aqueous alkaline developer solution.
• % data always mean% by weight, unless stated otherwise. Parts by weight relate to parts by volume in the ratio of g to cm 3 .
• An aluminum sheet is first pickled for 60 seconds in an aqueous solution of 20 g NaOH per 1 at room temperature and then freed of any alkali residues that may be present by briefly immersing it in a solution corresponding to the roughening electrolyte.
• the roughening takes place in the electrolyte systems shown in the following tables and under those there listed conditions.
• an anodic oxidation is carried out in an aqueous electrolyte containing H 2 S0 4 and Al 3+ ions up to a layer weight of 3.0 g / m 2 .
• the classification into the quality classes takes place by visual assessment under the microscope, whereby the quality level "1" (best value) is assigned to a homogeneously roughened and scar-free surface.
• a quality level "10" (worst value) is assigned to a surface with thick scars of a size of more than 100 ⁇ m or an extremely unevenly roughened or almost bare surface.
• Intermediate qualities are rated “2" to "9". All examples and the comparative examples are carried out with symmetrical alternating current at a frequency of 50 Hz, one electrode being the aluminum sheet and the other a graphite plate.
• Example 2 An aluminum sheet prepared according to Example 1 is immersed at 40 ° C. for 30 seconds in an aqueous solution containing 5 g / l of polyvinylphosphonic acid and then rinsed with deionized water and dried. To produce a lithographic printing plate, the sheet is coated with the following negative-working light-sensitive solution:
• a carrier material produced in accordance with Example 4 is coated with the following solution in order to produce an electrophotographic offset printing plate:
• the layer is negatively charged to about 400 V in the dark by means of a corona.
• the charged plate is exposed imagewise in a repro camera and then with an electrophotographic suspension developer, which by dispersing 3.0 parts by weight of magnesium sulfate in a solution of 7.5 parts by weight of pentaerythritol resin ester in 1200 parts by volume of an isoparaffin mixture with a Boiling range of 185 to 210 "C. was obtained.
• the developer is fixed and the plate is 60 sec in a solution of 35 parts by weight of sodium metasilicate 9 H 2 0, 140 parts by weight of glycerol, 550 parts. Parts of ethylene glycol and 140 parts by weight of ethanol are dipped in.
• the plate is then rinsed off with a powerful water jet, the areas of the photoconductor layer which are not covered with toner being removed, and the printing form is then ready for printing.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Printing Plates And Materials Therefor (AREA)

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• 1984
  • 1984-04-25 DE DE19843415363 patent/DE3415363A1/de not_active Withdrawn
• 1985
  • 1985-04-16 DE DE8585104604T patent/DE3560490D1/de not_active Expired
  • 1985-04-16 EP EP85104604A patent/EP0162282B1/fr not_active Expired
  • 1985-04-23 US US06/726,245 patent/US4626328A/en not_active Expired - Fee Related
  • 1985-04-24 JP JP60086651A patent/JPS60234897A/ja active Pending

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