Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
  • B41C3/00—Reproduction or duplicating of printing formes
  • B41C3/08—Electrotyping; Application of backing layers thereon
• • 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 direct current in an nitrate-containing 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 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.
• hydrochloric acid or nitric 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 nitric 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.
• 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 with direct current, 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, and also Energy is saved.
• the finished printing plates should have a large print run and low wiping water consumption.
• the invention is based on a process for the combined roughening of aluminum, wherein first mechanical roughening and then electrolytic roughening are carried out in an nitrate-containing electrolyte.
• the step that characterizes the invention is that electrolytic roughening is carried out with direct current.
• the mechanical roughening is preferably carried out with a moist abrasive (wet brushing), but other mechanical pre-structuring, such as dry brushing, sandblasting, spherical grain, embossing and similar processes, can also be used.
• moist abrasive wet brushing
• other mechanical pre-structuring such as dry brushing, sandblasting, spherical grain, embossing and similar processes, can also be used.
• the sheet is preferably cleaned by an etching step with metal removal.
• This etching step pickling
• a nitrate electrolyte is used, the concentration of the nitrate compound being between 1.0 g / l and the saturation limit, particularly preferably between 5.0 g / l and 100.0 g / l.
• Aluminum nitrate and / or nitric acid and / or sodium nitrate is used as the preferred compound containing nitrate ions. Combinations of other compounds containing nitrate ions are of course also within the scope of the invention.
• the current density used is less critical than the total amount of charge.
• 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 electrochemical roughening are in the following ranges: the temperature of the electrolyte between 20 and 80 ° C, the current density between 1 and 300 A / dm2, the residence time of a material point to be roughened in the electrolyte between 1 and 300 s, preferably between 2 and 60 s, and the electrolyte flow rate at the surface of the material to be roughened between 5 and 1000 cm / s.
• 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.
• pulsed, corrugated and differently shaped direct currents can also be used as long as the plate does not change polarity during the entire roughening process.
• 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 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 H2SO4, H3PO4, H2C2O4, amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof be set.
• 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, causing a surface removal 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 one or multiple post-treatment levels can be recreated.
• These post-treatment stages serve in particular to additionally increase the hydrophilicity of the aluminum oxide layer, which is already sufficient for many areas 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 usual carrier materials.
• the light-sensitive reproduction layers include such as z. B. 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); 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-diazo-quinones such as naphthoquinonediazides, p-diazo-quinones or diazonium salt condensates (Kosar, Chapter 7).
• the suitable layers also include the electrophotographic layers, ie those which contain an inorganic 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 Pat.
• Negative working, mixed condensation products of aromatic diazonium compounds for example according to DE-A 2024244, 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 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 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-A 20 64 079 and 2,361,041.
• Suitable photoinitiators include benzoin, benzoin ethers, multinuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives or synergistic mixtures of various ketones.
• a variety of soluble organic polymers can be used as binders, e.g. B.
• Negative working layers according to DE-A 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.
• photo-semiconducting layers such as are described, for example, in DE-C 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047, to the support materials, thereby producing highly light-sensitive, electrophotographic layers.
• 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
• the method according to the invention is particularly successful in producing flat, scar-free supports.
• Comparative examples V1 to V5 show in direct comparison with examples 1 to 4 the effect of direct current in electrolytes containing nitrate ions as a means of achieving uniform surfaces which have significant advantages in printing in terms of reducing the wiping water requirement and increasing the circulation . These surface properties can be realized without any great expenditure on equipment.
• An aluminum sheet is pre-structured wet with cutting abrasives using rotating brushes to a roughness depth R z of 4.3 ⁇ m, then pickled in a 3% sodium hydroxide solution for 30 s, in the next step with a direct current of 20 A / dm2 for 10 s anodically roughened at 40 ° C in an electrolyte of 20 g / l HNO3 and 50 g / l Al (NO3) 3 ⁇ 9 H2O and then cleaned for 1 min in a bath of 2.5% NaOH at 60 ° C.
• the water consumption is 25 divisions.
• Example 2 A prepared and coated as in Example 1, but in 10% aluminum nitrate solution at 20 A / dm2 for 5 s anodically roughened plate, which was cleaned in 2.5% NaOH at 60 ° C for 60 s, prints 150,000 copies under the same conditions with a water consumption of 30 scale divisions.
• a plate produced and coated analogously to Example 1, but anodically roughened with an alternating current of 20 A / dm 2 for 20 s has a circulation of 120,000 and a water consumption of 40 scale parts.
• a plate manufactured and coated as in Comparative Example V4, but anodically roughened in 12 g / l HCl and 50 g AlCl3 ⁇ 6 H2O has a circulation of 115,000 and a water consumption of 39 scale parts.
• the printing was carried out under the same conditions using the same printing press (Roland Favorit).
• the application quantity of the wiping water is determined by a display device in a dampening unit from Dahlgren. These are relative comparative measurements. The lower the scale divisions, the lower the water consumption.

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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)
• Manufacturing & Machinery (AREA)
• Printing Plates And Materials Therefor (AREA)
• Battery Electrode And Active Subsutance (AREA)

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• 1986
  • 1986-10-17 DE DE19863635304 patent/DE3635304A1/de not_active Withdrawn
• 1987
  • 1987-10-07 DE DE8787114630T patent/DE3786327D1/de not_active Expired - Fee Related
  • 1987-10-07 EP EP87114630A patent/EP0268058B1/fr not_active Expired - Lifetime
  • 1987-10-13 US US07/106,588 patent/US4824535A/en not_active Expired - Fee Related
  • 1987-10-15 JP JP62258490A patent/JPS63104890A/ja active Pending
  • 1987-10-17 KR KR870011536A patent/KR890000246A/ko not_active Ceased

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