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
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S204/00—Chemistry: electrical and wave energy
  • Y10S204/09—Wave forms

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 one of the customary acid and / or salt electrolytes.
• 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 the literature), chemical or electrochemical oxidation and / or treatment with hydrophilizing agents.
• a combination of the above-mentioned types of MDdification is often used tion 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 or in aqueous salt solutions such as aqueous NaCl or Al (NO 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:
• 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 changed with repeated use of the electrolyte, for example with regard to the H + (H 3 O + ) ion concentration (measurable via the pH value) and the A1 3 + ion concentration, 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 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 HC1, then between 0.5 and 2% of HC1 there are only insignificant changes in the hole structure, 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 SO 4 2- ions or Cl - ions in salt form [e.g. B. by adding A1 2 (SO 4 ) 3 or NaCl] 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.
• the influence of frequency changes or of superimpositions of currents of different frequencies has not been investigated; the frequency was always 50 Hz.
• aqueous solutions with several components in the roughening of aluminum can lead to more or less uniformly roughened surfaces, but the monitoring of the bath composition, particularly in the currently preferred continuously operating high-speed belt systems, is very complex, but necessary in practice, because the composition of the electrolyte changes frequently during the process.
• the invention is based on the known method for the electrochemical roughening of aluminum or its alloys for printing plate supports in an aqueous electrolyte under the action of alternating current.
• the method according to the invention is then characterized in that an alternating current is used which is generated by superimposing at least two types of alternating current of different frequencies.
• the AC type with the lowest frequency is referred to as the carrier current and the AC type (s) with the higher frequency (s) is referred to as the superimposed current.
• the frequency of the superimposing alternating current type (s) is a factor of 3 to 100 greater than the frequency of the carrier alternating current, and the ratio of the amplitudes of superimposing alternating current to carrier alternating current is between 0.1 and 10, in particular between 0.2 and 2.
• Only two types of alternating current are expediently superimposed on one another in the method according to the invention.
• the shape of the alternating current - with a graphical representation of the course of the current density or voltage as a function of time - can, for example, have a rectangular, trapezoidal or sinusoidal shape; in the method according to the invention, a combination of rectangular shape for the carrier alternating current and sinusoidal shape for the superimposing alternating current is preferred .
• 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 electrolyte (acid and / or salt) concentration between 1 and 250 g, in particular between 5 and 100 g / l, 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 sec and the electrolyte flow rate on the surface of the material to be roughened between 5 and 100 cm / sec.
• Direct current is preferably used for anodic oxidation, however alternating current or a combination of these types of current (e.g. direct current with superimposed alternating current) can also be used will.
• the layer weights of aluminum oxide range from 1 to 10 g / m, 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-OS 30 09 103.
• a modifying intermediate treatment can, among other things, enable the build-up of abrasion-resistant oxide layers and a lower tendency to tone during later printing.
• the stage of anodic oxidation of the aluminum printing plate support material can also be followed by one or more post-treatment stages.
• These post-treatment stages serve, in particular, to further increase the hydrophilicity of the aluminum oxide layer, which is already sufficient for many fields of application, the remaining known properties of this layer being at least retained.
• all layers are suitable as light-sensitive reproduction layers which, after exposure, optionally with 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. They are applied either by the manufacturer of presensitized printing plates or by so-called dry resists, or directly by the consumer to one of the carrier materials roughened according to the invention.
• the reproduction layers include those such as z. B.
• Suitable layers also include the electrophotographic layers, ie those which contain an inorganic or organic photoconductor. In addition to the light-sensitive substances, these layers can of course also other components such.
• Resins, dyes, pigments, wetting agents, sensitizers, adhesion promoters, indicators, plasticizers or other conventional auxiliaries can be used in the coating of the carrier materials:
• Positive-working o-quinonediazide preferably o-naphthoquinonediazide compounds, which are described, for example, in DE-PS 854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273 and 1 124 817.
• Negative-working condensation products from aromatic diazonium salts and compounds with active carbonyl groups preferably condensation products from diphenylamine diazonium salts and formaldehyde, which are described, for example, in DE-PS 596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123 U.S. Patents 2,679,498 and 3,050,502 and British Patent 712,606.
• Negative mixed condensation products of aromatic diazonium compounds for example according to DE-OS 20 24 244, which each have at least one unit of the general types A (-D) n and B connected by a double-bonded intermediate member derived from a condensable carbonyl compound.
• A is the remainder of a compound containing at least two aromatic carbocyclic and / or heterocyclic nuclei, which is capable of condensing with an active carbonyl compound in an acidic medium at at least one position.
• D is a diazonium salt group attached to an aromatic carbon atom of A; n is an integer from 1 to 10; and B is the remainder of a compound free of diazonium groups and capable of condensing with an active carbonyl compound in an acidic medium at at least one position on the molecule.
• Positive-working layers according to DE-OS 26 10 842 which contain a compound which splits off acid when irradiated, a compound which has at least one C-O-C group which can be split off by acid (e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and, if appropriate, a binder.
• acid e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group
• the monomers used here are, for example, acrylic and methacrylic acid esters or reaction products of diisocyanates with partial esters of polyhydric alcohols, as described, for example, in US Pat. Nos. 2,760,863 and 3,060,023 and DE-OSes 20 64 079 and 23 61 041.
• photoinitiators are u. a. Benzoin, benzoin ethers, multinuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives or synergistic mixtures of different ketones.
• soluble organic polymers can be used as binders, e.g. B. polyamides, polyesters, alkyd resins, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, gelatin or cellulose ether.
• Negative working layers according to DE-OS 30 36 077 which contain a diazonium salt polycondensation product or an organic azido compound as a photosensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as a binder.
• photoconductive layers such as z. B. in DE-PS 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 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 topography, which has a positive influence on the support stability and the water flow during printing of printing forms made from these supports.
• "scars" marked depressions compared to the roughening of the surroundings
• These surface properties can be realized without particularly great expenditure on equipment and without continuous qualitative and quantitative bath monitoring.
• the uniformity of the roughening may be due to the fact that the gas bubbles formed on the aluminum surface during the electrochemical reaction can be detached from the surface more easily in the process according to the invention.
• Example 7 a rectangular current is always used as the carrier alternating current and a sine current as the superimposing alternating current; in example 7, a sinusoidal current is also used as the carrier alternating current.
• 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 which may be present by briefly immersing it in a solution corresponding to the roughening electrolyte.
• the roughening takes place either under galvanostatic or potentiostatic control in the specified electrolytes, with the latter either the reference electrode saturating the Ag / AgCl system (Ex. 32, V8, 34 and 35) or the counterpart. electrode (Ex. 33).
• Examples 1 to 31 and VI to V7 are galvanostatically (Table I) and Examples 32 to 35 and V8 (Table II) controlled potentiostatically.
• the electrolysis is started at room temperature of the electrolyte.
• An aluminum plate roughened according to example 2 is oxidized anodically in an electrolyte made of H 2 SO 4 and Al 2 (SO 4 ) 3 according to the specifications of DE-OS 28 11 396 up to an oxide layer thickness of 2.8 pm.
• the roughened and anodized aluminum support is provided with the following negative working light-sensitive layer:
• a print run of 125,000 can be printed from this printing form.
• a printing plate which has been anodically oxidized and coated in accordance with Example 36, but which is roughened in accordance with Comparative Example V2, results in a printing form after development, of which only 75,000 sheets can be printed.

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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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• 1982
  • 1982-05-10 DE DE3217499A patent/DE3217499A1/de not_active Withdrawn
• 1983
  • 1983-04-28 EP EP83104146A patent/EP0093961B1/fr not_active Expired
  • 1983-04-28 DE DE8383104146T patent/DE3372001D1/de not_active Expired
  • 1983-05-02 US US06/490,567 patent/US4468295A/en not_active Expired - Lifetime
  • 1983-05-03 CA CA000427269A patent/CA1209522A/fr not_active Expired
  • 1983-05-06 AU AU14300/83A patent/AU550815B2/en not_active Ceased
  • 1983-05-09 JP JP58079472A patent/JPS58207374A/ja active Granted
  • 1983-05-09 BR BR8302397A patent/BR8302397A/pt not_active IP Right Cessation

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