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
  • 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
• • 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
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12993—Surface feature [e.g., rough, mirror]

Definitions

• the invention relates to a method for roughening aluminum or its alloys for printing plate supports, in which in a roughening step an electrochemical roughening takes place by means of alternating current in a first electrolyte which contains sulfate ions introduced as sulfuric acid in a concentration of 5 to 100 g / l and aluminum chloride. which provides chloride ions in a concentration of 1 to 100 g / l.
• EP-A-0 292 801 discloses such a process for the electrochemical roughening of aluminum or its alloys for printing plate supports by means of alternating current in an electrolyte containing sulfate and chloride ions, the acidic, sulfate-containing electrolyte containing chloride ions contains in the form of aluminum chloride. This process is a one-step roughening process.
• Printing plates especially offset printing plates, generally consist of a support and at least one radiation-sensitive layer arranged thereon, this layer being applied by the consumer in the case of non-precoated plates or by the industrial manufacturer in the case of precoated plates.
• Aluminum or one of its alloys has established itself as a layer support in the printing plate field.
• these supports can also be used without a modification pretreatment, but they are generally modified in or on the surface, for example by mechanical, chemical and / or electrochemical roughening, sometimes also called graining or etching, chemical or electrochemical oxidation and / or treatment with hydrophilizing agents.
• the roughening can be carried out 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 of the roughened surface which can be achieved in this way, given, for example, as mean roughness depths Rz, are in the range from 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. This is called the average roughness depth Rz arithmetic mean calculated from the individual roughness depths of five adjacent individual measuring sections.
• the roughening takes place u. a. to improve the adhesion of the reproduction layer on the substrate and the dampening solution of the printing plate resulting from the printing plate by exposure and development.
• the water flow is an important quality feature for offset printing plates. It is defined as the dosage and control in the publication "Determining an optimal water flow to increase the performance of offset printing” (Albrecht, J .; Rebner, W., Wirz, B., West Germanr Verlag, Cologne and Opladen 1966, page 7) the moistening of the printing form during the print run.
• the water flow depends, among other things, on the surface roughness of the printing form, ie the grain size of the surface.
• the problems of inadequate water supply are well known: If too much water is required to keep the non-printing parts of a printing form free of ink, more water can emulsify into the ink and the print becomes flat. Watermarks may also occur, causing the paper to become damp.
• the dampening solution consumption of a printing plate can be measured objectively with sufficient accuracy, but not the dampening solution guidance, since for some of the above-mentioned adverse phenomena such as smearing, there is no objective measurement method (Decker, P., in "Contribution to Analysis .. . “, Page 18). Therefore, the dampening solution guidance of a printing plate is assessed qualitatively with the adjectives "very good”, “good”, “satisfactory”, “sufficient”, “moderate”, “bad”, “very bad”.
• 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 noticeable, for example, by the sharp decline in the formation of layers on the surface.
• the roughening time between 2 and 25 min 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.
• hydrochloric acid to roughen aluminum substrates.
• a uniform grain size can be obtained which is suitable for lithographic plates and within a useful one Roughness range.
• pure hydrochloric acid electrolytes it is difficult to set a flat and uniform surface topography, and it is necessary to maintain the operating conditions within very narrow limits.
• DE-A 35 03 927 describes ammonium chloride as an inorganic additive to an HCl electrolyte.
• US Pat. No. 4,437,955 discloses a two-stage electrochemical roughening process for producing capacitors with an electrolyte containing hydrochloric acid in the first step and an electrolyte containing chloride and sulfate ions in the second step.
• the second stage electrolyte is not acidic, and DC is used in this stage.
• the object of the present invention is to improve a method for roughening aluminum for printing plate supports of the type described above in such a way that, in addition to a uniform, very fine, grain-free, surface-covering roughening structure of the aluminum surface of the printing plate supports, very good reprographic and printing properties, in particular long print runs of the finished printing forms. Furthermore, it is an object of the present invention to provide a method which permits the targeted production of supports, the properties of which can be controlled in a wide range and which provides differently structured surfaces of the printing plate supports without changing the plant technology in accordance with changing market requirements.
• another roughening step is carried out, which comprises at least one roughening step which consists of mechanical, dry or wet roughening of the printing plate carrier, electrochemical roughening by means of alternating current in a second electrolyte from hydrochloric acid and aluminum chloride, which supplies aluminum ions, in a third electrolyte is selected from nitric acid and aluminum nitrate, which provides aluminum ions, and a fourth electrolyte is selected from sulfuric acid and aluminum chloride, which provides chloride ions.
• the invention is based on a process for the combined roughening of aluminum, an electrolyte is used in one step, which contains sulfate ions in a relatively high concentration of 5 to 100 g / l, with the addition of chloride ions in the form of aluminum chloride.
• a conventional roughening in electrolytes containing hydrochloric acid or nitric acid or a mechanical roughening is carried out.
• the roughening step in the sulfate-containing electrolyte can also be carried out as a second step.
• a chloride ion-containing, sulfate-free electrolyte can be used as the electrolyte.
• acidic or alkaline cleaning can optionally be carried out.
• Carriers with good reprographic qualities can indeed be produced according to the teaching of DE-A 37 17 654, but printing plates which have been produced with these carriers do not achieve the high print runs which result in plates whose carriers are made according to the prior art corresponding process can be produced, in which an electrolyte based on nitric acid is used.
• Printing forms the supports of which were produced by one of the processes mentioned above, with the exception of the process described in DE-A 37 17 654, have poorer reprographic properties and poorer fountain solution guidance than the printing plate supports produced according to the invention.
• roughening in an electrolyte containing sulfate ions and chloride ions is combined with a further roughening step.
• the sulfate can be introduced into the electrolyte as sulfuric acid and the chloride as aluminum chloride.
• the preceding or subsequent roughening step can be carried out, for example, in an electrolyte which contains 1 to 20 g / l hydrochloric acid (calculated as 100% HCl) and 10 to 200 g / l Al3+ ions, introduced as aluminum chloride.
• the electrochemical roughening then typically takes place in a temperature interval of 35 to 55 ° C., at current densities of 20 to 150 A / dm2 and, depending on the current density, in times of 5 seconds to 200 seconds.
• This roughening step can also take place in an electrolyte which contains, for example, 20 to 35 g / l HNO3 and 30 to 50 g / l Al3+ ions, introduced as aluminum nitrate.
• the electrochemical roughening can then be carried out at temperatures from 22 to 50 ° C. and with current densities of 15 to 80 A / dm2, the exposure times being 2 to 100 seconds.
• Mechanical graining can also be carried out as a roughening step. This can be a roughening with damp Abrasives (wet brushing), but the roughening can also be carried out dry, for example with wire brushes, by sandblasting, ball grit, embossing and similar processes. Mechanical roughening should be followed by thorough pickling in acidic or alkaline media.
• the process can be carried out discontinuously or continuously with strips made of aluminum or its alloys.
• the process parameters in the continuous process during the roughening step in the chloride- and sulfate-containing electrolyte 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 roughened material point 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. 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 required current densities are between 3 and 40 A / dm2 and the residence times between 30 and 300 seconds.
• the flow of the electrolyte can also be dispensed with.
• the method can also be used with other aluminum alloys.
• an anodic oxidation of the aluminum takes place, for example, whereby the abrasion and the adhesion properties of the surface of the carrier material are improved.
• 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 modifying treatment which causes a surface removal from the roughened surface, can be used, as described for example in DE-A 30 09 103.
• a modifying intermediate treatment provides the structure, among other things abrasion-resistant oxide layers and a lower tendency to tone when printing later.
• the 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, without impairing the other known properties of this layer.
• all layers are suitable as light-sensitive reproduction layers which, after exposure, subsequent development and / or fixing, provide an image-like area from which printing can take place and / or which represent a relief image of an original.
• the reproduction layers are applied either by the manufacturer of presensitized printing plates, by means of dry resist or directly by the consumer on 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), such as B.
• 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).
• o-diazo-quinones such as naphthoquinonediazides, p-diazo-quinones or diazonium salt condensates
• Suitable layers also include the electrophotographic layers, i. H. those containing an inorganic or organic photoconductor. In addition to the light-sensitive substances, these layers can of course also other components such.
• photoconductive layers such as z. B. 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 have a very uniform topography, which has a positive influence on the print run stability and the dampening solution guidance when printing printing plates made from these supports.
• Undesirable "scars" occur less frequently, which form distinctive depressions compared to the roughening of the surroundings; these can even be completely suppressed.
• An aluminum sheet is first pickled for 60 seconds in an aqueous solution containing 20 g / l NaOH at room temperature. The roughening takes place in the specified electrolyte systems.
• the classification into the quality classes taking into account the surface topography with regard to uniformity, freedom from scars and area coverage, is carried out by visual assessment under the microscope, whereby a homogeneously roughened and scar-free surface is assigned quality level "10" (best value). A surface with thick scars larger than 30 ⁇ m and / or an extremely unevenly roughened or almost bare surface, the quality level "0" (worst value) is assigned.
• Column 1 of the following tables shows the roughening process used in the first step, columns 2 and 3 the roughening time and the current density (if applicable), column 5 specifies the roughening process used in the second step, columns 6 and 7 the roughening time, and the Current density, if applicable, column 8 contains the Rz value explained above, which is a measure of the roughness, and column 9 contains the classification of the carrier in quality classes, which was explained in the previous section.
• the carriers can still be pickled.
• Table 2 contains comparative examples of supports that were not made according to the methods of the invention.
• Alkaline pickling which was carried out on all supports between the first and the second roughening step, is not mentioned in Table 2.
• the immersion time was uniformly 30 seconds.
• Neither of the two roughening steps took place in an electrolyte which has the composition described above of 5 to 100 g / l of sulfate ions with the addition of chloride ions, for example in the form of Al chloride.
• the table shows the poorer quality of the roughening.
• Aluminum sheets were roughened in two stages according to the processes described in Table 3 and anodized in sulfuric acid (100 g / l) at 30 ° C. and a current density of 5 A / dm2 for 30 seconds.
• Table 3 No. 1st roughening step 2nd roughening step Water supply Edition of 1000 method Time sec Current density A / dm2 method Time sec Current density A / dm2 65 D 30th 60 F 10th 60 Well 210 66 D 10th 60 F 30th 60 very good 140 67 F 10th 60 D 30th 60 Well 190 68 F 30th 60 D 10th 60 very good 130 90 F 15 70 E 10th 40 very good 140 91 E 20th 80 F 13 60 Well 170
• the developed plates were used to print and the plates were tested with regard to print run and dampening solution management. It has been shown that these properties can be influenced as desired by controlling the two stages of the roughening process and are consistently good.
• 1st roughening step 2nd roughening step Water supply Location in 1000 method Time sec Current density A / dm2 method Time sec Current density A / dm2 V69 A B 10th 40 satisfied. 40 V70 A C. 15 80 satisfied. 60 V71 A D 13 40 bad 120 V72 B A Well 25th V73 B C. 7 80 Well 55 V74 B D 6 40 moderate 65 V75 C. 8th 70 A Well 40 V76 C. 12th 75 B Well 65 V77 C. 20th 60 D 6 40 bad 95 V78 D 6 40 A moderate 80 V79 D 8th 35 B satisfied. 45 V80 D 12th 30th C. 7 80 moderate 110

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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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• 1990
  • 1990-01-19 DE DE4001466A patent/DE4001466A1/de not_active Withdrawn
  • 1990-12-17 DE DE59010198T patent/DE59010198D1/de not_active Expired - Fee Related
  • 1990-12-17 EP EP90124403A patent/EP0437761B1/de not_active Expired - Lifetime
• 1991
  • 1991-01-17 JP JP3016979A patent/JP2969134B2/ja not_active Expired - Lifetime
  • 1991-01-17 CA CA002034426A patent/CA2034426A1/en not_active Abandoned
  • 1991-01-18 BR BR919100220A patent/BR9100220A/pt not_active Application Discontinuation
  • 1991-01-22 US US07/644,296 patent/US5156723A/en not_active Expired - Fee Related

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