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
  • 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

Definitions

• the invention relates to a two-stage anodic oxidation process for aluminum, which is used as a carrier material for offset printing plates.
• Backing 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 light-sensitive layer (copying layer), with the aid of which a printing image is generated photomechanically.
• the support carries the printing image areas and at the same time forms the hydrophilic background for the lithographic printing process in the non-image areas (non-image areas).
• 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 2C2 0 4 , H 3 B0 31 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 this way are amorphous and, in the case of offset printing plates, usually have a layer weight of approximately 1 to 8 g / m 2 , corresponding to a layer thickness of approximately 0.3 to 2.5 ⁇ m.
• the oxide layers are characterized by a fine channel-like structure; they have good mechanical resistance, which in particular protects the filigree structure of an electrochemically roughened aluminum against abrasion.
• 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 exposed negative- or especially positive-working light-sensitive layers.
• the process for the anodic oxidation of aluminum supports, in particular for printing plates, according to DE-OS 23 28 311 (US Pat. No. 3,836,437) is carried out in a 5 to 50% strength aqueous Na 3 PO 4 solution at a temperature of 20 to 40 ° C, a current density of 0.8 to 3.0 A / dm 2 and carried out for a period of 3 to 10 min.
• the aluminum oxide layer produced in this way should have a weight of 10 to 200 mg / m 2 .
• a carrier material for printing plates which carries an oxide layer, which by anodic oxidation of aluminum in an aqueous solution of H 3 P0 3 or a mixture of H 2 S0 4 / H 3 P0 3 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 (8 00) .
• 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 stabili Activity of the oxide itself lower, which leads to 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.
• carrier materials for printing plates made of aluminum are anodized so that they act as central conductors first through a bath with aqueous H 3 P0 4 and an anode and then into a bath with aqueous H 2 S0 4 and run on a cathode.
• the two electrodes can also be connected to an AC voltage source.
• the treatment with H 3 PO 4 can also be a pure T treatment or that neutral or alkaline solutions would also be possible instead of the acids.
• a salt of silicic acid, phosphoric acid, molybdenum acid, vanadium acid, permanganic acid, tin acid or tungsten acid This treatment is said to result in a greater layer thickness, improved toughness, a finer structure and thus greater corrosion resistance (e.g. against acids or alkali).
• 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 SO 4 solution.
• the invention is based on a method for manufacturing. Development of plate, foil or ribbon-shaped carrier materials for offset printing plates made of chemically, mechanically and / or electrochemically roughened aluminum or egg ner of its alloys by a two-stage anodic oxidation in a) an aqueous electrolyte based on sulfuric acid and then b) an aqueous electrolyte different from that in stage a).
• stage b) in an aqueous electrolyte containing dissolved oxo anions of boron, vanadium, molybdenum, tungsten and / or carbon for a period of 1 to 60 seconds at a voltage between 10 and 100 V and is carried out at a temperature of 10 to 60 ° C.
• oxo anions also includes anions of heteropolyacids, ie those which, in addition to oxygen, also contain other atoms such as phosphorus or silicon.
• stage b) 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 50 ° C.
• the aqueous electrolyte with the stated content of oxo anions of boron, vanadium, mblybdenum, tungsten and / or carbon contains either an acid or preferably a salt with the corresponding anion, in particular a salt with an alkali, alkaline earth or ammonium cation.
• concentration of the aqueous electrolyte can be varied within wide limits, preferably between 5 g / 1 and the respective saturation limit. Examples of suitable compounds in the electrolyte are:
• the current profile can be characterized approximately so that after a very short-term initial current density of about 3 to 10 A / dm 2, this drops to values of less than 1 A / dm 2 after only about 2 to 5 sec, in order to drop towards 0 after about 10 to 20 sec.
• Aluminum carrier materials are still mechanical (e.g. by brushing and / or with abrasive treatments), chemical (e.g. by etching agents) or electrochemical (e.g. by AC treatment in aqueous HCI, HN0 3 - or in salt solutions ) roughened.
• Aluminum printing plates with electrochemical roughening are used in particular in the process according to the invention.
• the process parameters in the roughening stage are in the following ranges: the temperature of the electrolyte between 20 and 60 ° C, the active substance (acid, salt) concentration between 5 and 100 g / l, the current density between 15 and 130 A / dm 2 , the residence time between 10 and 100 sec and the electrolyte flow rate on the surface of the workpiece to be treated between 5 and 100 cm / sec; AC is usually used as the type of current, but modified types of current such as AC with different amplitudes of the current strength are also possible for the anode and cathode currents.
• the average roughness depth R z of the roughened surface is in the range from about 1 to 15 ⁇ m, in particular in the range from 3 to 8 ⁇ m.
• the roughness depth is determined in accordance with DIN 4768 in the version from October 1970, the roughness depth R is then the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections.
• the individual roughness depth is defined as the distance between two parallels to the middle line, which touch the roughness profile at the highest or lowest point within the individual measuring sections.
• the individual measuring section is the fifth part of the length of the part of the roughness profile which is used directly for evaluation and is projected perpendicularly onto the middle line.
• the middle line is the line parallel to the general direction of the roughness profile from the shape of the geometrically ideal profile, which divides the roughness profile in such a way that the sum of the material-filled areas above it and the material-free areas below it are equal.
• a first anodic oxidation of the aluminum then follows in a further process step [step a) J.
• This is carried out in an electrolyte based on 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, for example in the form of Al 2 (SO 4 ) 3 .
• the A1 3+ content can also be set to values of more than 12 g / 1.
• direct current is preferably used, however alternating current or a combination of these types of current (eg direct current with superimposed alternating current) can also be used.
• alternating current or a combination of these types of current (eg direct current with superimposed alternating current) can also be used.
• This oxide layer is then treated further in step b) after rinsing with water.
• These roughened and two-stage anodically oxidized carrier materials are used in the production of offset printing plates having a light-sensitive layer, although they can also be additionally hydrophilized beforehand, for example, as explained in the description of the prior art.
• all layers are suitable as light-sensitive layers which, after exposure, optionally with subsequent development and / or fixation, provide an imagewise surface from which printing can take place. They are either applied by the manufacturer of presensitized printing plates or directly by the consumer on one of the usual carrier materials.
• 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-PS 596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123 U.S. Patents 2,679,498 and 3,050,502 and British Patent 712,606.
• Negative mixed condensation products of aromatic diazonium compounds for example according to DE-OS 20 24 244, 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, in an acidic medium, is capable of condensing with an active carbonyl compound 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 remainder of a compound free of diazonium groups and capable of condensing with an active carbonyl compound in an acidic medium at at least one position on the molecule.
• Positive-working layers according to DE-OS 26 10 842 which contains a compound which splits off acid when irradiated, a compound which has at least one COC group which can be split off by acid (e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally contain a binder.
• acid e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group
• optionally contain a binder e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group
• the monomers used are, for example, acrylic and methacrylic acid esters or reaction products of diisocyanates with partial esters of polyhydric alcohols, as is described, for example, in US Pat. Nos. 2,760,863 and 3,060,023 and DE-OSes 20 64 079 and 23 61 041.
• photoinitiators are u. a. Benzoin, benzoin ethers, multinuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives or synergistic mixtures of different ketones.
• soluble organic polymers can be used as binders, e.g. B. polyamides, polyesters, alkyd resins, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, gelatin or cellulose ether.
• Negative working layers according to DE-OS 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.
• photoconductive layers such as z. B. in DE-PSen 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 are described, to the invention manufactured carrier materials are applied, which results in highly light-sensitive, electrophotographic printing plates.
• the sample of a defined size, protected on the back by a layer of lacquer, is moved in a bath containing 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 was degreased with an aqueous alkaline pickling solution at a temperature of about 50 to 70 ° C.
• the electrochemical roughening of the aluminum surface was carried out with 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 was carried out in accordance with the process described in DE-OS 28 11 396 in an aqueous electrolyte containing H2 S0 4 and Al 2 (SO 4 ) 3 , resulting in a layered. weight of 2.8 g / m 2 .
• the printing plate thus produced was quick to develop and free of fog.
• the bright appearance of the carrier surface resulted in a very good contrast between image and non-image areas.
• the circulation was more than 150,000.
• An aluminum strip prepared and anodically aftertreated in accordance with Example 2 was coated with the following positive-working light-sensitive solution to produce an offset printing plate:
• the coated tape was dried in the drying tunnel at temperatures up to 120 ° C.
• the printing plate thus produced was exposed under a positive template and developed with a developer of the following composition:
• the printing form obtained was perfect in terms of copying and printing technology and had a very good contrast after exposure, the print run was 180,000.
• An aluminum sheet prepared according to the comparative example V1 was anodized with the aqueous electrolyte solutions listed in Table 2 at room temperature for 30 seconds. The voltages and concentrations used for this are also shown in this table.
• a support which was anodically aftertreated in accordance with Example 31 with a voltage of 60 V for 30 seconds was coated with the following solution to produce an electrophotographically operated offset printing plate:
• the layer was negatively charged to about 400 V in the dark using a corona.
• the charged plate was exposed imagewise in a repro camera and then developed with an electrophotographic suspension developer which also contains a dispersion of 3.0 parts by weight of magnesium sulfate in a solution of 7.5 parts by weight of pentaerythritol resin ester in 1200 parts by volume of an isoparaffin mixture represents a boiling range of 185 to 210 ° C.
• the developer was fixed and the plate was poured into a solution for 60 seconds submerged. The plate was then rinsed off with a powerful jet of water, removing the areas of the photoconductor layer not covered with toner, and the plate was then ready for printing.
• Example 2 An aluminum strip prepared as described in Example 2 was 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 was further processed as described in Example 2, the ink-repelling effect of the non-image areas being able to be improved. An even more favorable hydrophilization was achieved with the complex-type reaction products described in DE-OS 31 26 636 from a) such polymers 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)
• Handling Of Sheets (AREA)
• Electrochemical Coating By Surface Reaction (AREA)
• Reinforced Plastic Materials (AREA)
• Laminated Bodies (AREA)

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• 1982
  • 1982-02-23 DE DE19823206469 patent/DE3206469A1/de not_active Withdrawn
• 1983
  • 1983-01-20 AT AT83100461T patent/ATE21861T1/de not_active IP Right Cessation
  • 1983-01-20 DE DE8383100461T patent/DE3365748D1/de not_active Expired
  • 1983-01-20 EP EP83100461A patent/EP0086956B1/fr not_active Expired
  • 1983-02-09 CA CA000421170A patent/CA1206912A/fr not_active Expired
  • 1983-02-14 US US06/466,087 patent/US4554216A/en not_active Expired - Fee Related
  • 1983-02-16 AU AU11475/83A patent/AU1147583A/en not_active Abandoned
  • 1983-02-18 JP JP58024939A patent/JPS58153699A/ja active Pending

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