Classifications

• • 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
• • 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

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.
• aqueous acids such as aqueous HCl or HN0 3 solutions or in aqueous salt solutions such as aqueous NaCl or Al (N0 3 ) 3 solutions 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.
• the roughening is carried out, inter alia, in order to improve the adhesion of the reproduction layer on the substrate and the water flow of the printing plate resulting from the printing plate by irradiation (exposure) and development.
• irradiation and development or decoating in the case of reproduction layers working electrophotographically
• the image points which carry color during later printing and the water-bearing non-image points are produced on the printing plate, whereby the actual printing form is created.
• Various parameters have an influence on the later topography of the aluminum surface to be roughened, which may be exemplified by the following explanations of the prior art:
• the essay "The Alternating Current Etching of Aluminum Lithography Sheet” by AJ Dowell in Transactions of the Institute of Metal Finishing, 1979, Vol. 57, pp. 138 to 144 contains basic explanations made to roughen aluminum in aqueous hydrochloric acid solutions, the following process parameters varied and the corresponding effects were examined.
• the electrolyte composition is (3 0 + H) ion concentration changes after repeated use of the electrolyte, for example, in terms of H + (measured via the p H value) and the A13 + ion concentration, said effects are observed on the surface topography.
• the temperature variation between 16 ° C and 90 ° C shows a changing influence only from about 50 ° C, which is expressed, for example, by the sharp decline in the formation of layers on the surface.
• the roughening time change between 2 and 25 min also leads to an increasing metal dissolution with increasing exposure time.
• the variation of the current density between 2 and 8 A / dm 2 results in higher roughness values with increasing current density. If the acid concentration is in the range 0.17 to 3.3% of HCl, then only insignificant changes in the hole structure occur between 0.5 and 2% of HCl, below 0.5% of HC1 there is only a local attack on the Surface and at the high values an irregular dissolution of Al instead.
• the addition of S 04 2- ions or Cl ions in salt form [e.g. B. by adding Al 2 (SO 4 ) 3 or N aCl] can also influence the topography of the roughened Aluminum. The rectification of the alternating current shows that both types of half-wave are obviously required for a uniform roughening.
• 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 known organic additives to aqueous acid electrolytes such as HC1 or HN0 3 solutions have the aftermath partly that they become electrochemically unstable at high current loads (voltage) in modern continuously operating conveyor systems and at least partially decompose.
• 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.
• the previously known complexing additives generally accelerate the "trapping" of released Al 3+ ions to dissolve the aluminum and thus lead to an increase in 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 further ionic halogen compound under the action of alternating current.
• the process according to the invention is then characterized in that the ionic halogen compound is an inorganic fluorine compound which is present as an acid or alkali metal salt and whose anion contains fluorine and at least one further element.
• the aqueous electrolyte solution contains 0.5 to 10% by weight, in particular 0.8 to 5.0% by weight, of HCl and 0.05 to 5.0% by weight, in particular 0.1 up to 2.0% by weight of the fluorine compound.
• the inorganic ionic fluorine compound is in particular a complex-like compound or a compound comparable to it.
• Preferred examples of such fluorine compounds are acids or alkali salts (including the ammonium salts) with the anions: SiF 6 2- , TiF 6 2- , ZrF 6 2- , BF 4 - , PF 6 - and PO 3 F 2- ;
• compounds with the following anions can also be used: NbF 6 - , TaF 6 - , FeF 6 3- , SbF 6 - , HfF 6 2- and SO 3 F-.
• the compounds are preferably used individually, but can also be used as a mixture of several.
• Suitable base materials for the material to be roughened according to the invention include those made of aluminum or one of its alloys, which have, for example, a content of more than 98.5% by weight of Al and proportions of Si, Fe, Ti, Cu and Zn.
• This aluminum carrier mat Materials can also be roughened mechanically (e.g. by brushing and / or with abrasive treatments) before the electrochemical stage, if necessary after pre-cleaning. All process steps can be carried out discontinuously with plates or foils, but they are preferably carried out continuously with tapes.
• the process parameters particularly in a continuous process, in the electrochemical roughening in the following areas: the residence time the temperature of the electrolyte between 20 and 60 0 C, the current density 3-200 A / dm 2, a roughened material point in the electrolyte of between 3 and 100 sec and the electrolyte flow rate at the surface of the material to be roughened between 5 and 100 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 ⁇ m, in particular from 1.5 to 8.0 ⁇ m.
• the aqueous electrolyte can also in addition aluminum ions in the form of aluminum salts, in particular 0.5 to 5.0% by weight of AlC1 3, are also added to the components already mentioned above.
• 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 Connect aluminum for example to improve the abrasion and adhesion properties of the surface of the carrier material.
• the usual electrolytes such as H 2 S0 4 , H 3 P0 41 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 it is used either by the manufacturer of presensitized printing plates or a radiation-sensitive coating applied directly or by the consumer to the carrier material on one or both sides.
• 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.
• photo semi-conductive layers as described in the D E C 11 17 391, 15 22 497, 15 72 312 23 22 046 and 23 22 047, for example, be applied to the according to the invention carrier materials, whereby high-photosensitive, electrophotographic printing plates are created.
• 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 .
• EXAMPLES 1 TO 30 AND COMPARATIVE EXAMPLES V1 TO V12 An aluminum sheet is first pickled for 60 seconds in an aqueous solution of 20 g NaOH per liter at room temperature and then freed from 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 the conditions listed there. After roughening, an anodic oxidation is carried out in an aqueous electrolyte containing H 2 S0 4 and A1 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.
• 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 rolled 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.
• 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 immersed in a solution of 35 parts by weight of sodium metasilicate 9 H 2 O, 140 parts by weight of glycerol, 550 parts by weight of ethylene glycol and 140 parts by weight of ethanol for 60 seconds .
• the plate is then rinsed off with a powerful jet of water, removing the areas of the photoconductor layer not covered with toner.
• 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)

Applications Claiming Priority (2)

Publications (3)

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• 1984
  • 1984-01-05 DE DE19843400248 patent/DE3400248A1/de not_active Withdrawn
  • 1984-12-21 DE DE8484116021T patent/DE3463681D1/de not_active Expired
  • 1984-12-21 EP EP84116021A patent/EP0151304B1/fr not_active Expired
  • 1984-12-27 JP JP59274253A patent/JPS60159093A/ja active Granted
  • 1984-12-31 ES ES539251A patent/ES8700338A1/es not_active Expired
• 1985
  • 1985-01-04 CA CA000471470A patent/CA1256059A/fr not_active Expired
  • 1985-01-04 US US06/689,001 patent/US4566959A/en not_active Expired - Fee Related
  • 1985-01-04 BR BR8500015A patent/BR8500015A/pt not_active IP Right Cessation
  • 1985-01-04 ZA ZA8590A patent/ZA8590B/xx unknown

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