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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12993—Surface feature [e.g., rough, mirror]

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 acidic electrolyte containing chloride and ammonium ions.
• Printing plates (this term means offset printing plates in the context of the present invention) generally consist of a carrier and at least one radiation-sensitive reproduction layer arranged on it, this layer either by the consumer (in the case of non-precoated plates) or is applied by the industrial manufacturer (in the case of pre-coated boards) to the layer support.
• 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 called grain or etching in the relevant literature), a chemical one or electrochemical oxidation and / or treatment with hydrophilizing agents.
• the roughening is carried out, for example, in aqueous acids such as aqueous HCI or HN0 3 solutions or in aqueous salt solutions such as aqueous NaCl or Al (NO 3 ) 3 solutions using alternating current.
• aqueous acids such as aqueous HCI or HN0 3 solutions
• aqueous salt solutions such as aqueous NaCl or Al (NO 3 ) 3 solutions using alternating current.
• the thus obtainable surface roughness (expressed for example as the average roughness depth R z) of the roughened surface are in the range of about 1 to 15 1 1m, in particular in the range of 2 to 8 microns.
• the roughness depth is determined in accordance with DIN 4768 (as of October 1970).
• the roughness depth R z is then the arithmetic mean of the individual roughness depths of five adjacent individual measurement sections.
• the roughening is a. therefore carried out in order to improve the adhesion of the reproduction layer on the layer support and the water flow of the printing plate resulting from the printing plate by irradiation (exposure) and development.
• irradiation and development or de-coating 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, as a result of which the actual printing form is created.
• Very different parameters have an influence on the later topography of the roughened aluminum surface.
• the following references provide information:
• 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 HCI, then between 0.5 and 2% of HCI only minor changes occur in the hole structure, below 0.5% of HCI there is only a local attack on the Surface and at the high values an irregular dissolution of aluminum instead.
• the addition of S0 4 2-- or CI - ions in salt form [e.g. B. by adding Al 2 (S0 4 ) 3 or NaCl] can also influence the topography of the roughened aluminum.
• the rectification of the alternating current shows that obviously both half-wave types are required for a uniform roughening.
• hydrochloric acid as an electrolyte for roughening aluminum substrates can therefore be assumed to be known.
• a uniform grain size can be obtained which is suitable for lithographic plates and is within a useful roughness range.
• pure hydrochloric acid electrolytes the setting of a flat and uniform surface topography is difficult, and it is necessary to maintain the operating conditions within very narrow limits.
• JP application 91 334/78 describes AC roughening in a combination of hydrochloric acid and an alkali halide to produce a lithographic base material.
• DE-C 120 061 describes a treatment for producing a water-attracting layer by using electricity, which can also take place in hydrofluoric acid.
• JP application 93 108/78 describes the production of a capacitor film; it is first roughened in an electrolyte from 0.3 to 1.5% hydrochloric acid and 15 to 25% ammonium acetate with alternating current (with 200 to 400 C / dm 2 ) and then further electrolyzed in HCl with pulsed current.
• these anticorrosive agents increase the roughness depth compared to pure hydrochloric acid electrolytes.
• the methods mentioned can be used to make relatively evenly roughened aluminum surfaces lead, but they sometimes require a relatively large amount of equipment and can only be used within very narrow parameter limits.
• the object of the present invention is therefore to propose a method for the electrochemical roughening of aluminum for printing plate supports with alternating current, which results in a uniform, scar-free and area-wide roughening structure and which can be dispensed with a large expenditure on equipment and / or particularly narrow parameter limits.
• the invention relates to a process for the electrochemical roughening of aluminum or its alloys for printing plate supports in an acid electrolyte containing chloride ions and ammonium ions under the action of alternating current.
• the process according to the invention is characterized in that an ammonium ion-containing compound is added to the electrolyte in a concentration of 40 g / 1 up to the saturation limit and the pH is adjusted to less than 4.5.
• an HCI electrolyte is used, the hydrochloric acid concentration being between 0.01 and 50.0 g / l, particularly preferably between 0.01 and 30.0 g / l, and the concentration of the ammonium compound preferably between 70.0 g / I and the saturation limit.
• Ammonium chloride is used as the preferred compound containing ammonium ions. Within the scope of the invention it is also provided to use combinations of ammonium salts as long as the requirement is met that the pH value is adjusted to ⁇ 4.5, preferably ⁇ 3.0.
• the process according to the invention is carried out either discontinuously or preferably continuously with strips made of aluminum or its alloys.
• the process parameters in continuous processes during roughening are in the following ranges: the temperature of the electrolyte between 20 and 60 ° C, the current density between 3 and 130 A / dm 2 , the residence time of a material point to be roughened in the electrolyte between 10 and 300 s and the electrolyte flow rate at the surface of the material to be roughened between 5 and 100 cm / s.
• the current densities required tend to be in the lower part and the residence times are in the upper part of the ranges specified; the flow of the electrolyte can also be dispensed with.
• the method according to the invention can also be applied to other aluminum alloys.
• an anodic oxidation of the aluminum can then 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.
• an alkaline but preferably an acidic, intermediate pickling can be carried out to remove any coating or to improve the water flow.
• 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 ⁇ m.
• a modification can also be applied which causes surface abrasion from the roughened surface, as described, for example, in DE-A 30 09 103.
• Such a modifying intermediate treatment can u. a. allow the build-up of abrasion-resistant oxide layers and a lower tendency to tone when printing later.
• the stage of 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.
• a light-sensitive reproduction layer is applied to the material.
• all layers are suitable as light-sensitive reproduction layers which, after exposure, possibly with a subsequent development and / or fixation, provide an image-like area from which printing can take place and / or which represent a relief image of an original.
• the materials for printing plate supports roughened by the process according to the invention have a very uniform topography, which has a positive influence on the support stability and the water flow during printing of printing forms made from these supports.
• "scars" compared to the roughening of the surroundings: distinctive depressions
• Comparative examples 9 to 12 and 41 to 49 show, in comparison with the other examples, the effect of the addition of ammonium while maintaining a pH value of ⁇ 4.5 as an aid for achieving flatter and nevertheless uniform surfaces.
• An aluminum sheet (DIN material no. 3.0255) 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 at 40 ° C.
• the classification into the quality classes is carried out by visual assessment under the microscope, whereby a homogeneously roughened and scar-free surface is assigned quality level "1" (best value).
• Quality level "10" (worst value) is assigned to a surface with thick scars of a size of more than 30 11 m and / or an extremely unevenly roughened or almost rolled surface.

Applications Claiming Priority (2)

Publications (3)

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• 1985
  • 1985-02-06 DE DE19853503927 patent/DE3503927A1/de not_active Withdrawn
• 1986
  • 1986-01-25 EP EP86101024A patent/EP0194429B1/de not_active Expired
  • 1986-01-25 DE DE8686101024T patent/DE3667077D1/de not_active Expired
  • 1986-02-04 US US06/825,937 patent/US4666576A/en not_active Expired - Lifetime
  • 1986-02-05 CA CA000501182A patent/CA1280997C/en not_active Expired - Fee Related
  • 1986-02-05 KR KR1019860000784A patent/KR930005014B1/ko not_active IP Right Cessation
  • 1986-02-05 BR BR8600495A patent/BR8600495A/pt not_active IP Right Cessation
  • 1986-02-06 JP JP61023075A patent/JPH0667674B2/ja not_active Expired - Lifetime

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