Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/12—Anodising more than once, e.g. in different baths
• • 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
  • Y10S205/00—Electrolysis: processes, compositions used therein, and methods of preparing the compositions
  • Y10S205/917—Treatment of workpiece between coating steps

Definitions

• the invention relates to a two-stage anodic oxidation process for aluminum, which is used as a carrier material for offset printing plates.
• Carrier materials for offset printing plates are provided either by the consumer directly or by the manufacturer of precoated printing plates on one or both sides with a radiation (light) sensitive layer (reproduction layer), with the help of which a printing image is generated photomechanically.
• the layer support After a printing form has been produced from the printing plate, the layer support carries the image points which will guide the color during later printing and at the same time forms the hydrophilic background for the lithographic printing process at the image-free locations (non-image points) during the later printing.
• Aluminum which is roughened on the surface by known methods by dry brushing, wet brushing, sandblasting, chemical and / or electrochemical treatment, is used particularly frequently as the base material for such layer supports.
• electrochemically roughened substrates in particular are subjected to an anodization step to build up a thin oxide layer.
• electrolytes such as H2S04, H 3 PO 4 , H 2 C 2 0 4 , H 3 B0 3 , amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof.
• the oxide layers built up in these electrolytes or electrolyte mixtures differ in structure, layer thickness and resistance to chemicals.
• aqueous H 2 SO 4 or H 3 PO 4 solution are used.
• Aluminum oxide layers produced in aqueous electrolytes containing H 2 S0 4 are amorphous and usually have a layer weight of about 0.5 to 10 g / m 2 in offset printing plates, corresponding to a layer thickness of about 0.15 to 3.0 ⁇ m.
• a disadvantage of using such anodized substrate for offset printing plates is the relatively low resistance of the oxide layers produced in H 2 S0 4 electrolytes to alkaline solutions, such as are increasingly being used, for example, in the processing of presensitized offset printing plates, preferably in modern developer solutions for irradiated, negative- or in particular positive-working, radiation-sensitive layers.
• the aluminum oxide layer produced in this way should have a weight of 10 to 200 mg / m 2 .
• a support material for printing plates which carries an oxide layer which consists of anodic oxidation of aluminum in an aqueous solution of H 3 P0 3 or a mixture H Z S0 4 / H 3 POg is generated; then this relatively porous oxide layer is overlaid with a second oxide film of the "barrier layer" type, which can be formed, for example, in aqueous solutions containing boric acid, tartaric acid or borates by anodic oxidation.
• Both the first stage (example 3, 5 min) and the second stage (example 3, 2 min) are carried out very slowly, as well as the second at a relatively high temperature (80 °).
• An oxide layer produced in these electrolytes is often more resistant to alkaline media than an oxide layer produced in an electrolyte based on H 2 SO 4 solution; it also has some other advantages, such as a lighter surface, better water flow or low adsorption of dyes ("fog" in the non-image areas), but it also has significant disadvantages.
• oxide layer weights of up to about 1.5 g / m 2 can be produced, a layer thickness that naturally offers less protection against mechanical abrasion than a thicker one in an H 2 S0 4 electrolyte produced oxide layer. Due to the larger pore volume and diameter of an oxide layer built up in H 3 P0 4 , the mechanical stability of the oxide itself is also lower, which results in a further loss in terms of abrasion resistance.
• the actual oxide layer should have a weight per unit area of 1 to 6 g / m 2 , this weight decreasing significantly when immersed in the aqueous H 3 P0 4 solution, for example by about 2 to per minute immersion time in an aqueous H 3 P0 4 solution 3 g / m 2 .
• US Pat. No. 3,940,321 also describes a two-stage electrochemical treatment in an electrolyte based on H 2 S0 4 and then in an electrolyte based on H 3 P0 4.
• the two-stage anodic oxidation or treatment method leads to the fact that the oxide layer built up in the H 2 S0 4 electrolyte is redissolved to an excessive extent in the H 3 P0 4 solution under the previously known conditions.
• support materials for printing plates made of aluminum are anodized so that they act as central conductors first through a bath with aqueous 45% H 3 P0 4 and an anode and then into a bath aqueous 15 % H 2 S0 4 and a cathode run.
• the two electrodes can also be connected to an AC voltage source.
• the treatment with H 3 PO 4 can be a pure immersion treatment or that neutral or alkaline solutions would also be possible instead of the acids.
• a two-stage anodic oxidation process for printing plate support materials made of aluminum in which in the first stage an aqueous electrolyte containing H 3 P0 4 and in the second stage an aqueous electrolyte containing H 2 S0 4 and H 3 P0 4 can be used.
• a solution is used which contains at least 250 g H 3 P0 4 per 1. Bath monitoring for a mixed electrolyte is always difficult and expensive to control, so that the use of mixed electrolytes is avoided as far as possible in modern conveyor systems.
• Oxide layers primarily produced in aqueous electrolytes containing H 3 PO 4 are known to form a relatively compact barrier layer, which in itself contributes to increasing the alkali resistance of the oxide and thus to protecting the underlying aluminum.
• a compact barrier layer can often prove to be more of a hindrance since its electrical resistance first has to be overcome, as a result of which high voltages are required. This increases the risk of "burns", ie breakdowns through the primarily formed oxide layer, which cannot be accepted for use in the lithography field.
• the object of the present invention is therefore to propose a method for increasing the alkali resistance of support materials for offset printing plates on the basis of roughened and anodized aluminum, which can be carried out relatively quickly and without great effort in a modern belt system, in which the proportion of the oxide redissolution is low or a back solution does not occur and which maintains the positive property of the oxide layer known from the anodic oxidation in aqueous H 2 S0 4 solution and in which the process product has a high chemical resistance.
• the invention relates to a process for the production of plate, film or tape-shaped carrier materials for offset printing plates made of chemically, mechanically and / or electrochemically roughened aluminum or one of its alloys by a two-stage anodic oxidation in a) an aqueous electrolyte which contains inorganic compounds Contains phosphorus oxo anions and then b) in an aqueous electrolyte containing sulfuric acid.
• stage a) is carried out for a period of 5 to 60 seconds, at a voltage between 20 and 80 V and at a temperature of 15 to 60 ° C.
• the alkali resistance of the layers produced by the process according to the invention when using the phosphoroxo anions, with the exception of Na 3 P0 4 , generally remains in a comparable order of magnitude, irrespective of the electrolyte concentration, provided that the zincate test times are taken as the basis.
• the current course of the anodization can be characterized approximately in such a way that after a very brief initial current density of approximately 18 to 25 A / dm 2, this drops to values of less than 10 A / dm 2 after approximately 2 to 5 seconds, after approximately 10 to 20 sec already fall towards 0. If Na 3 P0 4 is used, a constant current density of approximately 5 to 20 A / dm 2 is maintained for the duration of the anodization, depending on the voltage applied.
• Na 3 P0 4 also forms a certain exception with regard to the alkali resistance of the oxide layers produced with it, since an increase in the electrolyte concentration also leads to a significant increase in the zincate test times.
• the use of higher voltages generally also increases the alkali resistance of the layers.
• Suitable base materials for the material to be oxidized according to the invention include those Aluminum or one of its alloys, which have, for example, a content of more than 98.5% by weight of Al and proportions of Si, Fe, Ti, Cu and Zn. These aluminum carrier materials are still, optionally after a pre-cleaning, mechanical (e.g. by brushing and / or with abrasive treatments), chemical (e.g. by etching agents) and / or electrochemical (e.g. by AC treatment in aqueous HCl) -, HN0 3 - or in salt solutions) roughened.
• materials with electrochemical or a combination of mechanical and electrochemical roughening are used in the method according to the invention. All process steps can be carried out batchwise, but they are preferably carried out continuously.
• the process parameters are in the roughening stage in the following ranges: the temperature of the electrolyte between 20 and 60 ° C., the active substance (acid, salt) concentration between 2 and 100 g / l (also in the case of salts higher), the current density between 15 and 250 A / dm 2 , the dwell time between 3 and 100 sec and the electrolyte flow rate on the surface of the workpiece to be treated between 5 and 100 cm / sec; alternating current is usually used as the type of current, but it is also modified current types such as alternating current with different amplitudes of the current strength for the anode and cathode current are possible.
• the mean roughness depth R z of the roughened surface is in the range of about 1 to 15 ⁇ m.
• the roughness depth is determined in accordance with DIN 4768 in the version from October 1970, The roughness depth Rz is then the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections.
• Pre-cleaning includes, for example, treatment with aqueous NaOH solution with or without degreasing agent and / or complexing agents, trichlorethylene, acetone, methanol or other commercially available aluminum stains.
• the roughening or, in the case of several roughening stages, also between the individual stages, an abrasive treatment can additionally be carried out, in particular a maximum of 2 g / m 2 being removed (up to 5 g / m 2 between the stages);
• aqueous solutions of alkali metal hydroxide or aqueous solutions of alkaline salts or aqueous acid solutions based on HN0 3 , H 2 SO 4 or H 3 PO 4 are used as abrasive solutions.
• stage b) is carried out in an electrolyte containing H 2 S0 4 , as described at the outset in the assessment of the prior art.
• a suitable electrolyte will also contain Al 3 + ions, which either arise during the process or are added from the start [e.g. B. as Al 2 (SO 4 ) 3 ].
• the electrolyte in stage b) contains 100 to 250 g / l of H 2 SO 4 , at least 5 g / l of A1 3 + ions, and the stage is carried out at 20 to 60 ° C.
• Direct current is preferably used for anodic oxidation in these stages, however alternating current or a combination of these types of current (e.g. direct current with superimposed alternating current) can also be used.
• the process time in both stages is preferably about 5 to 60 seconds.
• the layer weights of the oxide layer produced in stage a) generally range between about 0.4 to 1.4 g / m 2 , corresponding to a layer thickness of about 0.01 up to 0.4 ⁇ m; they are preferably about 0.6 to 1.0 g / m 2 , corresponding to about 0.02 to 0.3 ⁇ m.
• This oxide layer is then further treated in step b), if appropriate after rinsing with water, it being possible for the oxide weight to be increased to values of, for example, 1 to 3 g / m 2 (corresponding to 0.3 to 1 ⁇ m).
• the aluminum oxide layers also contain A1 2 (SO 4 ) 3 and AIP0 4 .
• the stages of anodic oxidation of the aluminum support material can also be followed by one or more post-treatment stages, although this is often not necessary, particularly in the present process.
• These post-treatment stages serve in particular to additionally increase the hydrophilicity of the aluminum oxide layer, which is often sufficient, while at least the other known properties of this layer are retained.
• the materials produced according to the invention are used as supports for offset printing plates, i. H. a radiation-sensitive coating is applied to one or both sides of the carrier material either by the manufacturer of presensitized printing plates or directly by the consumer.
• a radiation-sensitive coating is applied to one or both sides of the carrier material either by the manufacturer of presensitized printing plates or directly by the consumer.
• all layers are suitable as radiation (light) sensitive layers which, after irradiation (exposure), optionally with subsequent development and / or fixation, provide an image-like area from which printing can take place.
• 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, applied to the carrier materials produced according to the invention, whereby highly light-sensitive, electrophotographic printing plates are formed.
• the sample of a defined size protected on the back by a layer of lacquer is moved in a bath which contains an aqueous solution of 6 g / l of NaOH.
• the weight loss experienced in this bath is determined gravimetrically. Times of 1, 2, 4 or 8 minutes are selected as the treatment time in the alkaline bath.
• a bright rolled aluminum sheet with a thickness of 0.3 mm is degreased with an aqueous alkaline pickling solution at a temperature of 50 to 70 ° C.
• the electrochemical roughening of the aluminum surface is carried out using alternating current in an electrolyte containing HN0 3 , a surface roughness having an R z value of about 6 ⁇ m being obtained.
• the subsequent anodic oxidation is carried out in accordance with the process described in EP-B-0 004 569 in an aqueous electrolyte containing H 2 S0 4 and Al 2 (SO 4 ) 3 , resulting in a layer weight of 2.8 g / m 2 leads.
• An aluminum sheet pickled and roughened according to the specifications of comparative example V1 is anodically oxidized at room temperature at a direct voltage of 40 V in an aqueous solution containing 100 g / l of NagP0 4 for 30 seconds. After rinsing with demineralized water the sheet in a second stage, containing oxidized, an aqueous solution of 200 g / I of H 2 S0 4 and 50 g / I sec to A1 2 (SO 4) 3 at 20 V for 30 also anodically . The oxide weight determination gives a value of 1.3 g / m 2 . For further results and process variations, see Table I.
• the pressure plate can be developed quickly and free of fog. Due to the bright appearance of the carrier surface there is a very good contrast between image and non-image areas. The number of copies printed from the printing form is 200,000.
• An aluminum strip prepared in accordance with Example 1 and two-stage anodized is coated with the following positive-working light-sensitive solution to produce an offset printing plate:
• the coated tape is dried in the drying tunnel at temperatures up to 120 ° C.
• the printing plate thus produced is exposed under a positive template and developed with a developer of the following composition:
• the printing form obtained is perfect in terms of copying and printing technology and has a very good contrast after exposure, the print run is 150,000.
• An aluminum sheet pickled and roughened according to the specifications of comparative example V1 is anodized at room temperature at a direct voltage of 40 V in an aqueous solution containing 100 g / l of H 3 PO 4 for 30 seconds. After rinsing with deionized water, the sheet is subjected to a second anodic oxidation as described in Example 1. No current flow can be determined under the conditions of Example 1; the anodization reaction occurs abruptly only when the voltage is increased to 35 to 40 V. At the end of the second anodizing stage, the sheet clearly shows burns on the surface.
• the oxide layer weight is 0.75 g / m 2 .
• Example 3 An aluminum strip prepared according to the information in Example 3 is immersed in a further treatment step (additional hydrophilization) in a 0.2% aqueous solution of polyvinylphosphonic acid at 50 ° C. for 20 seconds. After drying, the support material additionally hydrophilized in this way is further processed as described in Example 3, it being possible to improve the ink-repelling effect of the non-image areas.
• An even more favorable hydrophilization is achieved with the complex-type reaction products described in DE-A-31 26 636 from a) polymers such as polyvinylphosphonic acid and b) a salt of an at least divalent metal cation.

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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)
• Electrochemical Coating By Surface Reaction (AREA)

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• 1983
  • 1983-08-03 DE DE19833328048 patent/DE3328048A1/de not_active Withdrawn
• 1984
  • 1984-07-25 DE DE8484108776T patent/DE3467192D1/de not_active Expired
  • 1984-07-25 EP EP84108776A patent/EP0139111B1/de not_active Expired
  • 1984-07-26 US US06/634,550 patent/US4606975A/en not_active Expired - Fee Related
  • 1984-08-03 JP JP59163019A patent/JPS6056093A/ja active Granted

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