Classifications

• • 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
• • 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
• • 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

Definitions

• 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: In the article "The Alternating Current Etching of Aluminum Lithographic Sheet" by AJ Dowell in Transactions of the Institute of Metal Finishing, 1979, Vol. 57, pp.
• the electrolyte composition is changed with repeated use of the electrolyte, for example with regard to the H+ (H3O+) ion concentration (measurable via the pH) and the Al3+ ion concentration, with 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.
• hydrochloric acid 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-A 17 580/80 describes an AC roughening in a combination of hydrochloric acid and one Alkali halide for the production of 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.
• aluminum chloride is used as the salt and hydrochloric acid is optionally added.
• Such a saturated aluminum chloride solution ( ⁇ 500 g / l AlCl3 x 6 H2O), especially in the acidic range, represents an extremely high risk of corrosion for the materials used.
• the surface quality achievable using added sulfuric acid as an added mineral acid in the examples would be , as the comparative examples V24 to V33 show, very pitted and not usable for lithographic applications.
• JP-B 006 571/76 describes the alternating current roughening of an aluminum sheet for lithographic printing plates in electrolytes which contain 1 to 4% HCl and 0.1 to 1% H2SO4.
• electrolytes which contain 1 to 4% HCl and 0.1 to 1% H2SO4.
• the comparative examples V34 to V53 show, only irregularly roughened surface profiles that do not correspond to the prior art can be achieved.
• GB-A 1 392 191 describes the influence of sulfate ions in concentrations of more than 10 to 15 ppm in hydrochloric acid electrolytes as harmful for the production of a lithographic support material and uses a phosphoric acid additive as a remedy.
• EP-A 132 787 describes a roughening of aluminum in 1000 to 40000 ppm nitric acid, which contains 50 to 4000 ppm (up to 0.4%) sulfate ions; again the harmful influence of higher concentrations is spoken of. Roughening is even prevented from 5000 ppm.
• US Pat. No. 1,376,366 describes the electrochemical lowering of metals in particular steel with direct current in a solution of ammonium chloride, sulfuric acid and nitric acid.
• the aim is to shape a workpiece.
• the aim of roughening for lithographic surfaces is a very fine (1 to 10 ⁇ m), coating-free structuring of the surface, good anchoring of the copying layer and retention of the dampening water during the printing process has to task.
• the coating during roughening can be suppressed by using alternating current.
• US-A 3,284,326 describes the roughening of an aluminum foil for the capacitor production, using direct current, in order to achieve a high capacitance of the capacitor.
• a solution of chloride and phosphate is used as the electrolyte, the type of cation for the capacitor foil roughening - with the exception of the disadvantageous aluminum - being immaterial.
• Up to 10 mol% of the cation can also be replaced by H+; however, it emphasizes that it is not a good idea to start with an acidic electrolyte.
• GB-A-2 100 751 discloses an electrochemical etching process of aluminum foils for the production of capacitors with alternating current in electrolytes which contain hydrochloric acid, sulfuric acid and aluminum chloride.
• the fundamentally different roughening for printing plate supports serves to anchor the layer and to guide the water thus be very homogeneous and scar-free in a narrow rough depth area.
• the object of the present invention is therefore to improve the method described above for the electrochemical roughening of aluminum for printing plate supports with alternating current in such a way that a uniform, scar-free and area-covering roughening structure, without the need for a large amount of apparatus and special material selection for reasons of corrosion protection and / or particularly narrow parameter limits are obtained.
• the object is achieved by a process for the electrochemical roughening of aluminum or its alloys for printing plate supports by means of alternating current in an acidic electrolyte containing sulfate and aluminum chloride, the sulfate ion concentration in the electrolyte being between 5 and 100 g / l and the chloride ion concentration between 1 and 100 g / l is set.
• the presence of aluminum ions for uniformizing the surface is absolutely advantageous for the process according to the invention for the production of printing plate supports.
• examples V60 and V61 show, the use of direct current also leads to very grained surfaces that are absolutely unsuitable for lithographic purposes. In addition, an undesirable white coating occurs and the sheets are not roughened all over.
• the electrochemical roughening for the production of lithographic printing plates with sulfate ions in a relatively high concentration of 5 to 100 g / l is surprisingly achieved by adding chlorides in the form of aluminum chloride.
• Lower concentrations of e.g. B. sulfuric acid cause an uneven surface structure.
• an H2SO4 electrolyte is used, the sulfate ion concentration between 5 and 100 g / l, particularly preferably between 20 and 50 g / l, and the concentration of the chloride ions between 1 and 100 g / l, particularly preferably between 10 and is 70 g / l.
• chloride ions are used as AlCl3 x 6 H2O in a concentration between 20 and 250 g / l, particularly preferably between 50 and 200 g / l.
• the invention also provides for combinations of different compounds containing chloride ions to be used.
• a solution containing sulfuric acid or removal in sodium hydroxide solution is particularly 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 current density between 3 and 180 A / dm2, the residence time of a material point to be roughened in the electrolyte between 6 and 300 s, preferably between 6 and 30 s, and the electrolyte flow rate at the surface of the material to be roughened between 5 and 100 cm / s. Due to the continuous driving style and the simultaneous release of Al ions and the consumption of H+, constant adjustment of the electrolyte composition by the corresponding diluted acids is necessary.
• 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.
• 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.
• 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, 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. 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 in Exposure isomerized, rearranged, cyclized or crosslinked (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-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, 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 24 244, which
• 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 off by acid (e.g.
• 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 23 61 041.
• Suitable photoinitiators include benzoin, benzoin ethers, multinuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives or synergistic mixtures.
• 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 the photosensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as the 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.
• Undesirable "scars" compared to the roughening of the surroundings: distinctive depressions
• the comparative examples V24 to V33 and V34 to V53 show in comparison with the other examples the effect of the electrolyte system according to the invention to achieve flat and nevertheless uniform surfaces. These surface properties can be realized without any great expenditure on equipment.
• 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 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 ⁇ m and / or an extremely unevenly roughened or almost rolled surface.

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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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• 1987
  • 1987-05-26 DE DE19873717654 patent/DE3717654A1/de not_active Withdrawn
• 1988
  • 1988-05-13 DE DE8888107659T patent/DE3876291D1/de not_active Expired - Lifetime
  • 1988-05-13 EP EP88107659A patent/EP0292801B1/de not_active Expired - Lifetime
  • 1988-05-25 BR BR8802559A patent/BR8802559A/pt not_active IP Right Cessation
  • 1988-05-25 KR KR1019880006114A patent/KR960016059B1/ko not_active IP Right Cessation
  • 1988-05-25 CA CA000567633A patent/CA1325788C/en not_active Expired - Fee Related
  • 1988-05-25 US US07/198,307 patent/US4840713A/en not_active Expired - Lifetime
  • 1988-05-26 JP JP63127239A patent/JP2776830B2/ja not_active Expired - Fee Related

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