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 HNO 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 measurement 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 HN03 solutions have the disadvantage that they become electrochemically unstable and at least partially decompose under 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.
• 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 results in no additional hole germs are created, but already formed germs and holes continue to grow, ie there is an increased formation of scars.
• 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 carboxylic acid under the action of alternating current.
• the aqueous electrolyte solution contains 0.5 to 10.0%, in particular 0.8 to 5.0%, of HCl and 0.1 to 8.0%, in particular 0.2 to 5.0%, of haloalkanoic acid (n).
• Suitable base materials for the material to be roughened according to the invention include those made of aluminum or one of its alloys, which for example have a content of more than 98.5% by weight of Al and proportions of Si, Fe, Ti, Cu and Zn. These aluminum carrier materials can also be roughened mechanically (for example by brushing and / or with abrasive treatments) before the electrochemical stage, if appropriate 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 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 on 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 thereby in the range from 1 to 15 / um, in particular from 1.5 to 8.0 / um.
• Aluainium ions in the form of aluminum salts, in particular 0.5 to 5.0% of AlCl 3 can also be added to the aqueous electrolyte in addition to UCl and at least one of the halocarboxylic acids.
• 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 S0 4 or H 3 PO 4 are used as removal solutions.
• non-electrochemical treatments which essentially have only a rinsing and / or cleaning action and are used, for example, to remove deposits formed during roughening (“Schmant”) or simply to remove 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 in order 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 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, i. H. a radiation-sensitive coating is applied to one or both sides of the carrier material either by the manufacturer of presensitized printing plates or directly by the consumer.
• a radiation-sensitive coating is applied to one or both sides of the carrier material either by the manufacturer of presensitized printing plates or directly by the consumer.
• all layers are suitable as radiation (light) sensitive layers which, after irradiation (exposure), optionally with subsequent development and / or fixation, provide an imagewise surface from which printing can take place.
• photo-semiconducting layers such as e.g. 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.
• Examples 1 to 21 and Comparative Examples VI to V17 An aluminum sheet is first pickled for 60 seconds in an aqueous solution of 20 g NaOH per liter at room temperature and then briefly Dipping in a solution corresponding to the roughening electrolyte frees of any alkali residues present. 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 / um or an extremely unevenly roughened or almost mill-finished 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.
• An aluminum sheet prepared according to Example 12 is immersed at 40 ° C. for 30 seconds in an aqueous solution containing 5 g / 1 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 according to Example 18 is coated with the following solution in order to produce an electrophotographically operated 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 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.

Landscapes

• 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)

Family

ID=6234306

Family Applications (1)

Country Status (4)

Cited By (1)

Families Citing this family (20)

Citations (2)

Family Cites Families (7)

• 1984
  • 1984-04-25 DE DE19843415338 patent/DE3415338A1/de not_active Withdrawn
• 1985
  • 1985-04-16 DE DE8585104603T patent/DE3560642D1/de not_active Expired
  • 1985-04-16 EP EP85104603A patent/EP0162281B1/fr not_active Expired
  • 1985-04-23 US US06/726,242 patent/US4600482A/en not_active Expired - Fee Related
  • 1985-04-24 JP JP60086649A patent/JPS60234895A/ja active Granted

Patent Citations (2)

Also Published As

Similar Documents

Legal Events