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 acidic electrolyte containing ⁇ -diketo compounds.
• Printing plates generally consist of a carrier and at least one radiation-sensitive reproduction layer arranged thereon, this layer either by the consumer (in the case of non-precoated plates) or by 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 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 HCl or HNO3 solutions or in aqueous salt solutions such as aqueous NaCl or Al (NO3) 3 solutions using alternating current.
• aqueous acids such as aqueous HCl or HNO3 solutions
• aqueous salt solutions such as aqueous NaCl or Al (NO3) 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 (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 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 reproductive layers working electrophotographically
• the image points which carry color during later printing and the non-image points which carry water generally the exposed carrier surface
• 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 / dm2 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 HCl there is only a local attack on the Ober surface and with the high values an irregular dissolution of aluminum instead.
• the addition of SO42 ⁇ ions or Cl ⁇ ions in salt form [z. B. by adding Al2 (SO4) 3 or NaCl] can also affect the topography of the roughened aluminum.
• the experimental 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 with an alternating current in an electrolyte of 0.3 to 1.5% hydrochloric acid and 15 to 25% ammonium acetate and then further electrolyzed in HCl with pulsed current.
• acetylacetone in simple metal cleaners is e.g. B. described in DE-A 19 26 809.
• object of the present invention is to produce a support material suitable for lithographic purposes with an extremely homogeneous surface topography.
• Another known possibility of improving the uniformity of the electrochemical roughening is to modify the current form used, these include, for example -
• the object of the present invention is therefore to propose a method for the electrochemical roughening of aluminum for printing plate supports, which results in a uniform, scar-free and area-covering roughening structure and which can be dispensed with a large outlay 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 acidic electrolyte under the action of electrical current. Alternating current is preferably used. But as can be seen from Examples 30 to 32, good lithographic surfaces can also be produced by using anodic direct current in the electrolyte according to the invention.
• the process according to the invention is characterized in that an acidic electrolyte is used, to which a ⁇ -diketo compound is added.
• the acid concentration between 0.01 and 50.0 g / l, particularly preferably between 0.01 and 30.0 g / l, and the concentration of the ⁇ - Diketo compound is between 3 g / l and the saturation limit, particularly preferably between 40.0 g / l and the saturation limit.
• Acetylacetone is used as the preferred ⁇ -diketo compound.
• combinations of ⁇ -diketo compounds are used as long as the requirement is met that the pH is adjusted to be acidic.
• the amount of hydrochloric acid released by hydrolysis of the aluminum chloride used may already be sufficient to carry out the process according to the invention.
• 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 / dm2, the residence time of a material point to be roughened in the electrolyte between 10 and 300 sec and that Electrolyte flow rate on the surface of the material to be roughened between 5 and 100 cm / sec.
• 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 following can be used as materials to be roughened, for example, which are either in the form of a plate, film or tape: - "Pure aluminum” (DIN material no. 3.0255), ie consisting of more than 99.5% Al and the following admissible admixtures of (maximum sum of 0.5%) 0.3% Si, 0.4% Fe, 0.03% Ti, 0.02% Cu, 0.07% Zn and 0.03% others, or - "Al alloy 3003" (comparable to DIN material no.
• 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.
• the usual electrolytes such as H2SO4, H3PO4, H2C2O4, amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof can be used for anodic oxidation.
• 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.
• 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 include 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.
• These post-treatment stages serve in particular to ensure that the hydrophilicity is already sufficient for many areas of application To increase the aluminum oxide layer even more, at least the other known properties of this layer are retained.
• 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 a template. 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 usual carrier materials.
• the light-sensitive reproduction layers include layers such as those e.g. in "Light-Sensitive Systems” by Jaromir Kosar, John Wiley & Sons Verlag, New York 1965, are described: The layers containing unsaturated compounds in which these compounds are isomerized, rearranged, cyclized or crosslinked during exposure (Kosar, Chapter 4) , such as Cinnamate; the layers containing photopolymerizable compounds, in which monomers or prepolymers optionally polymerize during exposure by means of an initiator (Kosar, Chapter 5); and the layers containing o-diazoquinones such as naphthoquinonediazides, p-diazoquinones or diazonium salt condensates (Kosar, Chapter 7).
• the layers containing unsaturated compounds in which these compounds are isomerized, rearranged, cyclized or crosslinked during exposure such as Cinnamate
• Suitable layers also include the electrophotographic layers, ie those which are inorganic contain or organic photoconductor.
• these layers can of course also contain other constituents, such as, for example, resins, dyes, pigments, wetting agents, sensitizers, adhesion promoters, indicators, plasticizers or other customary auxiliaries.
• the following light-sensitive compositions or compounds 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-C 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-C 596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123 US-A 2 679 498 and 3 050 502 and GB-A 712 606; negative working mixed condensation products of aromatic diazonium compounds, for example according to DE-A 20 24 24 24
• A is the remainder of at least two aromatic carboxylic and / or heterocyclic nuclei-containing compound which is capable of condensing at least one position in an acidic medium with an active carbonyl compound.
• 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 residue of a diazonium group-free compound capable of condensing with an active carbonyl compound in at least one position of the molecule in an acid medium; positive-working layers according to DE-A 26 10 842, which contain a compound which cleaves off on irradiation, a compound which has at least one COC group which can be cleaved by acid (for example an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally a binder; Negative working layers of photopolymerizable monomers, photoinitiators, binders and optionally other additives.
• the monomers used 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-A 20 64 079 and 23 61 041.
• Suitable photoinitiators include benzoin, benzoin ethers, multinuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives or synergistic mixtures of various ketones.
• binders soluble organic polymers for example polyamides, polyesters, alkyd resins, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, gelatin or cellulose ether; Negative working layers according to DE-A 30 36 077, which contain a diazonium salt polycondensation product or an organic azido compound as the photosensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as the binder.
• 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 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 very uniform topography, which has a positive influence on the support stability and the water supply when printing printing forms made from these supports.
• "scars" compared to the roughening of the surroundings: distinctive depressions
• the comparative examples V4, V13 and V29 show in comparison with the other examples play the effect of the addition of ⁇ -diketo compounds while maintaining an acidic pH value as a tool for achieving flatter, yet uniform surfaces.
• An aluminum sheet (DIN material no. 3.0255) is first pickled for 60 seconds in an aqueous solution of 20 g / l NaOH at room temperature. The roughening takes place in the specified electrolyte systems.
• 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 ⁇ m and / or an extremely unevenly roughened or almost rolled surface.

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• 1985
  • 1985-09-20 DE DE19853533532 patent/DE3533532A1/de not_active Withdrawn
• 1986
  • 1986-09-09 EP EP86112451A patent/EP0215422B1/fr not_active Expired
  • 1986-09-09 DE DE8686112451T patent/DE3663155D1/de not_active Expired
  • 1986-09-17 CA CA000518369A patent/CA1288722C/fr not_active Expired - Fee Related
  • 1986-09-19 JP JP61219890A patent/JPS6280300A/ja active Pending
  • 1986-09-19 US US06/909,311 patent/US4671859A/en not_active Expired - Fee Related

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