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
  • C25D11/18—After-treatment, e.g. pore-sealing
  • C25D11/24—Chemical after-treatment
• • 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
  • B41N3/038—Treatment with a chromium compound, a silicon compound, a phophorus compound or a compound of a metal of group IVB; Hydrophilic coatings obtained by hydrolysis of organometallic compounds
• • 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
  • Y10S205/921—Electrolytic coating of printing member, other than selected area coating

Definitions

• the invention relates to an aftertreatment process for roughened and anodically oxidized aluminum, in particular of support materials for offset printing plates with aqueous solutions containing alkali silicate.
• 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 radiation-sensitive layer (reproduction layer), with the aid of which a printing image of a template is generated photomechanically.
• 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 non-image points (non-image points) during later printing.
• Aluminum, steel, copper, brass or zinc, but also plastic films or paper can be used as the base material for such layers. These raw materials are modified by suitable modifications such.
• Aluminum, which is probably the most frequently used base material for offset printing plates today, is roughened on the surface by known methods by dry brushing, wet brushing, sandblasting, chemical and / or electrochemical treatment. In order to increase the abrasion resistance, the roughened substrate can also be subjected to an anodization step to build up a thin oxide layer.
• a cellulose ether such as sodium carboxymethyl cellulose or hydroxyethyl cellulose
• a water-soluble Zn, Ca Contains Mg, Ba, Sr, Co or Mn salt.
• Such adhesive layers are intended to give the plate a longer service life and prevent "non-toning" of the non-image areas of a printing form produced therefrom during printing, but this layer does not achieve any appreciable increase in alkali resistance.
• the object of the present invention is to propose a method for the aftertreatment of flat aluminum, which can be carried out in addition to anodic oxidation of the aluminum and leads to a surface on the aluminum oxide produced in this way, which in particular meets the practical requirements of a high-performance printing plate described at the outset.
• the invention is based on the known process for the production of plate, sheet or strip-shaped materials based on chemically, mechanically and / or electrochemically roughened and anodically oxidized aluminum or one of its alloys, the aluminum oxide layers of which are post-treated with an aqueous alkali silicate solution.
• the process according to the invention is then characterized in that after carrying out treatment a) with an aqueous alkali silicate solution, a treatment b) is additionally carried out with a solution containing aqueous alkaline earth metal salts.
• water-soluble calcium or strontium salts in particular nitrates, are used as the alkaline earth metal salts.
• the solution contains in particular 0.1 to 10% by weight of the alkaline earth metal salts, preferably 0.5 to 3% by weight.
• stage a) can also be carried out electrochemically, the latter procedure often already bringing about a certain increase in the alkali resistance of the material not yet treated with b).
• the electrochemical process variant is carried out in particular with direct or alternating current, trapezoidal, rectangular or triangular current or overlapping forms of these types of current; the current density is generally 0.1 to 10 A / dm 2 and / or the voltage is 1 to 100 V, the rest of the parameters depend on z. B. from the electrode spacing or the electrolyte composition.
• the treatment of the materials can be carried out discontinuously or continuously in the modern belt systems, the treatment times - for the respective treatment stage - expediently in the range from 0.5 to 120 seconds and the treatment temperatures at 15 to 80 ° C, in particular 20 to 75 ° C.
• the aqueous alkali silicate solution in stage a) generally contains 0.5 to 15% by weight, in particular 0.8 to 12% by weight, of an alkali silicate (such as sodium metasilicate or the sodium nitrate contained in the "water glass” and tetrasilicates). It is assumed that a firmly adhering cover layer forms in the pores of the aluminum oxide layer, which protects the oxide from attacks.
• the procedure used changes the previously generated surface topography (such as roughness and oxide pores) practically not or only insignificantly, so that the inventive method is particularly suitable for the treatment of materials in which the Maintaining this topography plays a major role, for example for printing plate substrates.
• Suitable base materials for use in the process according to the invention, in particular for the production of printing plate supports include those made of aluminum or one of its alloys, which have, for example, a content of more than 98.5% by weight of Al and portions of Si, Fe, Ti , Cu and Zn.
• the aluminum support materials for printing plates found in practice are mechanically (e.g. by brushing and / or with abrasive treatments), chemically (e.g. by etching agents) or electrochemically (e.g. by alternating current treatment) before the photosensitive layer is applied in aqueous acid or salt solutions, which may also contain additives such as corrosion inhibitors).
• Aluminum printing plates with electrochemical roughening in aqueous HCl and / or HN0 3 solutions are used in particular for the present 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 / 1 (in the case of salts also higher), the current density between 15 and 130 A / dm 2 , the residence time between 10 and 100 sec and the electrolyte flow rate in continuous processes 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 2 to 8 ⁇ m.
• the roughness depth is determined in accordance with DIN 4768 in the version from October 1970, the roughness depth R z is then the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections.
• 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 electrolyte is in particular an aqueous solution containing H 2 S0 4 and / or H 3 P0 4 .
• the layer weights of aluminum oxide range from 1 to 10 g / m 2 , corresponding to a layer thickness of approximately 0.3 to 3.0 ⁇ m.
• a radiation-sensitive coating is applied to 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-PS 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.
• offset printing plates obtained from the carrier materials according to the invention are converted into the desired printing form in a known manner by imagewise exposure or irradiation and washing out of the non-image areas with a developer, preferably an aqueous developer solution.
• a developer preferably an aqueous developer solution.
• offset printing plates whose base support materials have been post-treated by the two-stage process according to the invention compared to plates in which the same base material has been post-treated in one stage with aqueous solutions containing only silicates, are characterized by improved hydrophilicity of the non-image areas, a lower tendency to form color fog, and an improved resistance to alkali and achieving a steeper gradation (measured with a halftone step part).
• Zinc certificate (according to US Pat. No. 3,940,321, columns 3 and 4, lines 29 to 68 and lines 1 to 8):
• the rate at which the layer dissolves in an alkaline zincate solution is used as a measure of the alkali resistance of an aluminum oxide layer.
• the layer is more alkali-resistant the longer it takes to dissolve it.
• the layer thicknesses should be roughly comparable, since of course they also represent a parameter for the dissolution rate.
• a drop of a solution of 500 ml of distilled H 2 O, 480 g of KOH and 80 g of zinc oxide is placed on the surface to be examined and the period of time until the appearance of metallic zinc is determined, which can be seen from the darkening of the examination site.
• test pieces are immersed in an aqueous solution containing Na 3 SiO 3 .5H 2 O (for duration, concentration and temperature, see Table 1), then with dist. H 2 0 rinsed (this intermediate cleaning can also be omitted, see Table 1) and then or immediately after the silication in immersed in the aqueous solution of an alkaline earth metal nitrate at room temperature (duration, type of cation and concentration see Table 1).
• the contact angle and / or the light-sensitive coating again with dist. H 2 0 rinsed and dried or dried directly (see Table 1).
• the contact angles in the comparative examples V1 and V5 are 74.0 ° and 19.0 ° and in examples 9 and 21 7.0 ° and 11.3 °.
• stage b) is generally omitted, and stages a) and b) are also omitted.
• Table I and the wetting angle measurements show the clear difference in the better hydrophilicity and the better alkali resistance of the products treated according to the invention compared to the prior art.
• the use of the intermediate rinses also shows a certain influence in the alkali resistance, it is generally better in the case of samples that have not been rinsed after the silicatization stage than in the case of intermediate rinsed samples, but is also still significantly better in these than in the prior art.
• Example 35 The procedure described in Example 35 is followed, but the two-stage treatment with silicates and alkaline earth metal salts is not used, but with an aqueous polyvinylphosphonic acid solution aftertreated.
• the gradation of the image areas in V19 is one to two wedge steps softer (ie less steep) than in Example 35, and the print run is 130,000 prints.
• Example Groups 1 to 23 The procedure described in Example Groups 1 to 23 is followed, but the two-stage treatment with silicates and alkaline earth metal salts is not used, but the roughened and oxidized aluminum samples are immersed in aqueous solutions with a content of 2 g / l of sodium carboxymethyl cellulose (in V20 with a viscosity of 300 mpas, in V20 with a viscosity of 30,000 mPa .s, each with a degree of substitution of about 0.7) and 2 g / 1 of Sr (N0 3 ) 2 immersed at 25 ° C (based on DE-AS 23 64 177).
• the zincate test times are 31 seconds for samples not rinsed after this treatment and for those with dist.
• H 2 0 rinsed samples at 25 sec, ie this type of aftertreatment has practically no or only a minor effect on the alkali resistance of the oxide layer.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Printing Plates And Materials Therefor (AREA)
• Electrochemical Coating By Surface Reaction (AREA)

Applications Claiming Priority (2)

Publications (3)

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• 1982
  • 1982-09-01 DE DE19823232485 patent/DE3232485A1/de not_active Withdrawn
• 1983
  • 1983-08-17 CA CA000434745A patent/CA1225961A/en not_active Expired
  • 1983-08-18 ZA ZA836092A patent/ZA836092B/xx unknown
  • 1983-08-18 JP JP58149729A patent/JPS5959897A/ja active Granted
  • 1983-08-19 US US06/524,591 patent/US4492616A/en not_active Expired - Lifetime
  • 1983-08-19 AU AU18147/83A patent/AU553196B2/en not_active Ceased
  • 1983-08-22 EP EP83108259A patent/EP0105170B1/de not_active Expired
  • 1983-08-22 DE DE8383108259T patent/DE3375307D1/de not_active Expired
  • 1983-08-31 BR BR8304765A patent/BR8304765A/pt not_active IP Right Cessation

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