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
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
• • 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
  • C25D11/30—Anodisation of magnesium or alloys based thereon
• • 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
  • C25D11/34—Anodisation of metals or alloys not provided for in groups C25D11/04 - C25D11/32

Definitions

• the present invention relates to the electrolytic surface treatment of metal plates and the use of the products obtained.
• the treated metal plates have increased corrosion resistance and are suitable for use in planographic printing, among other things.
• they When used as a support for planographic printing plates, they are notable for increased adhesive strength of the photosensitive layers, longer print runs, less wear on the image and non-image areas, longer shelf life and improved hydrophilicity in the non-image areas. This is especially true when using aluminum or aluminum alloys.
• Anodic oxidation is an electrolytic process in which the metallic workpiece is treated as an anode and treated in a suitable electrolyte.
• electrical current flows from a cathode through the electrolyte to the metallic workpiece, the surface of the metal is converted to one of its oxide forms with decorative, protective, or other properties.
• the cathode is made of metal or graphite, and the only significant reaction that occurs on it is the evolution of hydrogen.
• the oxide layer is formed from the solution side, that is, outside the metal, so that the oxide formed is directly adjacent to the metal.
• the oxygen required for oxide formation comes from the respective electrolyte.
• the oxide layer does not reach its final limit thickness if the electrolyte exerts a noticeable solution on the oxide: current continues to flow and the oxide layer contains a "porous" structure.
• Porous structures can be quite thick, that is, they can reach a thickness of a few 10 pm, but a thin barrier layer made of oxide is always retained at the boundary between metal and oxide.
• Sulfuric acid is used as the electrolyte in most cases, and phosphoric acid is also frequently used.
• Anodically produced aluminum oxide layers are harder than oxide layers obtained under the influence of air.
• US Pat. No. 3,227,639 describes the use of a mixture of sulfophthalic and sulfuric acids for producing protective and decorative anodic oxide layers on aluminum.
• Other aromatic sulfonic acids are used in accordance with US Pat. No. 3,804,731 in a mixture with sulfuric acid.
• Anodization is followed by an aftertreatment step in numerous processes in which the porous surface is sealed, as a result of which the final properties of the layer are determined.
• pure water can be used for this at high temperatures. It is believed that part of it the oxide layer is dissolved and precipitated again as a voluminous hydroxide (or hydrated oxide) within the pores.
• Other aqueous sealants contain metal salts, the oxides of which can be precipitated together with the aluminum oxide.
• an organic acid (acetic acid, hydroxyacetic acid or aminoacetic acid) is added to a mixture of sulfuric and phosphoric acid in order to produce an anodic oxide layer on a plate which is then to be galvanized.
• US Pat. No. 4,115,211 describes the anodic oxidation of aluminum by means of alternating current or superimposed alternating and direct current.
• the electrolyte used contains a water-soluble acid and a water-soluble salt of a heavy metal.
• the water-soluble acid can be oxalic, tartaric, citric, malonic, sulfuric, phosphoric, sulfamic or boric acid.
• porous anodized layers are suitable for planographic printing, while non-porous anodized layers are unsuitable because the porous layer gives the non-image areas on the plate a surface with improved water flow and the adhesive strength of the material forming the image areas on the plate surface is increased by the fact that it can penetrate into the pores.
• US Pat. No. 3,511,661 describes aluminum foils for planographic printing which have been anodized in aqueous phosphoric acid, the oxide layers having a structure with pore-like openings, which has aluminum oxide cells whose average diameter is approximately 200 to 700 A, and on the surface of which a layer of about 10 to 200 mg / m 2 of aluminum phosphate is located.
• an aluminum foil which has been anodized in a conventional manner is electrolytically aftertreated in an aqueous solution of sodium silicate in order to obtain a hydrophilic, abrasion and corrosion-resistant layer and thus a presensitized support suitable for planographic printing.
• the anodic oxidation of aluminum foils is carried out in an aqueous solution of a mixture of a polybasic mineral acid, for example sulfuric acid, and a larger proportion of a polybasic aromatic sulfonic acid, for example sulfophthalic acid, whereby anodically produced porous Oxide layer is formed, which can be directly coated with a light-sensitive coating.
• a polybasic mineral acid for example sulfuric acid
• a polybasic aromatic sulfonic acid for example sulfophthalic acid
• US-A 4 090 880 describes a two-stage process in which a cleaned aluminum foil with an intermediate layer, e.g. from alkasilicate, fluorides of metals from group IV-B, polyacrylic acid or alkali zirconium fluoride, and then anodized in a conventional manner in aqueous sulfuric acid.
• the plate pretreated in this way is said to have an increased shelf life after being coated with light-sensitive diazo compounds.
• a conventional anodic oxidation which is carried out up to an oxide layer thickness of at least 0.2 pm, is followed by an aftertreatment with aqueous polyvinylphosphonic acid, at temperatures between 40 and 95.degree.
• the treatment improves the adhesion of a subsequently applied coating, the shelf life of the plate and the hydrophilicity of the non-image areas after exposure and development and the print run.
• the process also strives for an even higher print run, the process being more economical than the conventional anodic oxidation, which is followed by a second operation for sealing and post-treating the oxide layer before the photosensitive coating can be applied.
• an electrolyte for anodizing metal plates by means of direct current which contains at least one water-soluble organic acid which is capable of forming an insoluble organometallic oxide complex
• the characteristic feature of which is that the electrolyte is compatible with it contains compatible base and a pH from 3 to 10 and an electrochemical process with the aid of which a firmly adhering, insoluble complex of metal oxide and organic component is applied to a metal surface, the metal serving as the anode and the electrolyte used as a water-soluble mixture based on polybasic organic acid
• the a characteristic feature is that a compatible base is added in an amount sufficient to adjust the pH of the electrolyte in the range between about 3 and 10.
• the polybasic acid can be a polyvinylphosphonic, polycarbonate or polysulfonic acid and is advantageously a polymeric acid.
• Polyvinylphosphonic acid (PVPS) is preferably used as the electrolyte.
• the process is operated with direct current.
• the insoluble complex of metal oxide and organic component formed during electrolysis consists of a combination of anodically generated oxide and polyacid, which forms a protective layer on the metal with improved corrosion resistance.
• the complex of metal oxide and organic component is well suited for anchoring light-sensitive layers.
• Printing plate carrier materials produced according to the invention result in a longer shelf life, better printing properties and a longer print run than carriers produced using conventional methods.
• the manufacturing method according to the invention also includes cleaning and adhering to a metal object finally, the anodic oxidation of the metal object by means of direct current in an aqueous organic solution in which a water-soluble organic acid or a mixture of two or more organic acids, the acid in the case of carboxylic acids in each case should be at least three-base, and a base, where the amount of base is chosen so that the pH of the solution is between 3 and 10.
• the electrolysis is carried out under conditions such that an insoluble complex of metal oxide and organic component is formed in which the organic acid is contained and which adheres firmly to the surface of the metal object.
• An examination of the surface of the product produced according to the invention shows that it is essentially non-porous.
• the metal supports are cleaned before the electrochemical treatment according to the invention. This can be done using a variety of different solvents or aqueous alkaline solutions, the choice of which depends on the type of metal used and the purpose for which the support is to be used.
• Typical alkaline degreasing agents are, for example, hot aqueous solutions which contain alkalis such as sodium hydroxide, potassium hydroxide, trisodium phosphate, sodium silicate, aqueous, alkaline products and wetting agents.
• alkalis such as sodium hydroxide, potassium hydroxide, trisodium phosphate, sodium silicate, aqueous, alkaline products and wetting agents.
• Such a mixture is, for example, ( R ) Ridolene 57 (manufacturer Amchem Products, Pennsylvania).
• Degreasing treatments with solvents such as trichlorethylene, For some time, 1,1,1-trichloroethane and perchlorethylene have been used less frequently because of health and ecological concerns. Degreasing with solvents is done by dipping, spraying or steaming.
• Suitable metals that can be treated according to the invention are steel, magnesium and preferably aluminum and aluminum alloys.
• Suitable carriers for planographic printing plates are e.g. the aluminum alloys 1100, 1050, 3003 and A-19, which are offered by the companies Alcoa and Consolidated Aluminum Company, among others.
• Typical aluminum alloys for planographic printing plates contain the following components (in% by weight):
• the chemical composition of the alloy used probably also has a certain influence on the effectiveness of the electrolytic deposition of organic electrolytes.
• Other alloy components that are not normally analyzed can also have an impact.
• the surface of the metal to be treated can be smooth or roughened.
• the roughening is done with the help Known methods, such as chemical roughening in alkaline or acidic etching solutions, dry brushing, wet brushing with abrasive suspensions, roughening with abrasive balls and electrochemical roughening. Each of these processes results in a different roughening and surface topography.
• the cleaned surface is treated electrolytically immediately, that is to say before an air oxide layer can form.
• the plate Before immersing the cleaned, degreased and possibly roughened plate in the organic electrolytic solution for electrolytic deposition, the plate should be etched to remove air oxide. The etching is done in a known manner, e.g. in one of the acidic or alkaline media or electrolytes described.
• the plate can also be removed with an etchant, e.g. a solution of phosphoric and chromic acid. It is preferred to rinse the metal surface with water immediately after cleaning and, if necessary, to roughen it, and to subject it to the electrolytic treatment according to the invention while it is still wet, although satisfactory results are also achieved if the procedure is not so careful.
• a conventional anodic oxidation of the metal optionally follows the cleaning and any roughening before the electrolytic deposition process according to the invention is carried out.
• Preferred electrolytes are therefore the condensation product from Ben zolphosphonklare and formaldehyde, low molecular weight copolymers of methyl vinyl ether and maleic anhydride, copolymers of methyl vinyl ether and maleic acid, polyvinyl sulfonic acid, phytic acid, polyvinylphosphonic acid, Dodecylpolyoxyethylenphosphorklare, Diisopropylpolynaphthalinsulfonklare, 2-Ethylhexylpolyphosphorklare, ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, or mixtures of several of these compounds.
• condensation product of benzenephosphonic acid and formaldehyde, phytic acid, polyvinylphosphonic acid, 2-ethylhexylpolyphosphoric acid and mixtures of these compounds are particularly preferably used in planographic printing.
• a very suitable electrolyte mixture for example, a mixture of phytic acid and Polyvinylphosphon - acid.
• the properties of the coated metal depend essentially on the concentration of the electrolyte and the electrolysis conditions, such as voltage, current density, time or temperature.
• a compatible base is contained in the electrolyte solution according to the invention in an amount such that the solution has a pH in the range from 3 to 10.
• the pH is between 4 and 8, very particularly preferably between 6 and 7.
• the anodic oxide layer undesirably dissolves. It was found that the closer the pH is to the neutrality limit, the better the adhesion between the metal workpiece and the acid component. In addition, the workpiece does not need to be rinsed off after the anodic oxidation. By promoting the metallic bond, the anchoring of the acid component in the anodic oxide layer is also improved. This can be seen in a higher print run of a printing plate made from a carrier treated according to the invention.
• Bases suitable according to the invention are, for example, hydroxides, such as sodium, lithium, potassium and ammonium hydroxide. It is possible that a harder anodic oxide layer will form in the specified pH range due to the decreasing solubility in aluminum oxide.
• Plates intended for planographic printing are subjected to a test immediately after the electrolytic deposition of the complex of metal oxide and organic component, that is to say before the photosensitive layer has been applied.
• the plates are stained wet or dry, with the second test being stricter. After staining, the plate is rinsed under running water or sprayed with water and lightly rubbed off. The ease and completeness with which the paint can be removed is a measure of the hydrophilicity of the plate surface.
• the printing ink runs off completely when rinsed with water from printing plates produced according to the invention, which have been colored dry and dried at 100.degree.
• printing plates which have not been anodized or are conventionally anodized and have been subjected to a thermal immersion treatment in an aqueous polyvinylphosphonic acid solution give rise to an irreversible fogging, even if milder test conditions are used in the heat treatment.
• plates with and without a light-sensitive coating are subjected to an aging treatment over different periods of time and at different temperatures. Then it is examined to what extent it have retained their hydrophilic properties. Plates coated with various diazo compounds are examined after the treatment with regard to step wedge resistance, image resolution, retention of the hydrophilicity at the image background sites and easy developability. Suitable photosensitive materials are described below.
• the printing plates according to the invention together with comparison samples, are used in a printing press.
• the differences in surface abrasion, the resolution of the grid wedge, the speed and purity of the freewheel and the height of the print run are assessed.
• the complex of aluminum oxide and organic compound that makes up the surface layer initially forms very quickly. After a second, the layer thickness is already more than 0.12 pm. After three seconds it is up to 0.17 pm and after five seconds the increase in the layer thickness slowly stops at 0.20 pm. Even after 120 seconds there is no further appreciable increase.
• the voltage is kept practically constant during the entire period of electrolytic deposition.
• the amperage is not an independent variable, but depends on the other process conditions, in particular the voltage and electrolyte concentration. The amperage begins to drop very shortly after the start of electrolysis.
• the layer consisting of the complex of metal oxide and organic compound on the plate surface acts as a capacitor.
• the dielectric strength is not exceeded during the electrolysis, there will be no further weight gain as the time progresses and the layer will be retained throughout. If the dielectric strength is exceeded, the layer is perforated and its integrity is lost. While it is believed that this assumption accurately describes the facts, it is based purely on speculation and is in no way the basis for the present invention.
• the breakdown mentioned depends primarily on the voltage, with a potential of 70 V quickly breaks down. However, a certain breakdown is already registered at 30 V if the time is extended to over 250 seconds.
• the concentration of the electrolyte used is between about 0.01% and the saturation limit and is essentially independent of its chemical composition. Solutions with a concentration of more than 30% are generally not used, while at concentrations close to the lower limit the conductivity of the solution is very low; in the case of 0.001% polyvinylphosphonic acid it is e.g. at 61,000 a. Nevertheless, even at a concentration of 0.05%, a layer of a complex of metal oxide and organic component is formed, thanks to which products are obtained which are different from known products, such as e.g. Aluminum plates, which have been anodized in a conventional way and then heat-sealed with a polyvinylphosphonic acid solution, are characterized by better corrosion resistance, durability, hydrophilicity and printing properties.
• the current conductivity of the electrolyte grows rapidly with increasing concentration, which leads to shorter treatment times and lower voltage requirements.
• the preferred concentration range is between about 0.8% and 5%.
• the electrodeposited layer gives the material a corrosion resistance and printing properties that are superior to conventional materials.
• Direct current is required for the method, but it can also be superimposed by alternating current. Pulsed direct current can also be used. Square waves from pulsed anodizing current sources are particularly suitable.
• the amperage is greatest at the start of the electrical deposition and, over time, it decreases with increasing thickness of the layer composed of the complex of metal oxide and organic compound on the metallic carrier, thus reducing the current conductivity. Within 30 seconds it drops to a level at which the further power consumption is minimal. This contributes significantly to the economy of the process, since the desired useful layer has already been deposited at this point.
• ampere number is therefore a dependent variable, the size of which is determined by the independent variables electrolyte composition, concentration and voltage.
• Current densities between about 1 and 5 A / dm 2 are characteristic of favorable process conditions and are therefore preferred.
• the process can be carried out at temperatures from about -2 ° C (near the freezing point of the electrolyte) to about 60 ° C. Measured against the criteria of surface hardness, image adhesion, hydrophilicity and durability, the best results are obtained at 10 ° C, although the performance drop at temperatures between 10 ° C and room temperature, up to 40 ° C, is only very slight. In order to carry out the process at very low temperatures, complex cooling devices would be necessary. For reasons of economy and because of the low power consumption, the preferred temperature range is around 10 to 35 ° C, in particular around 20 to 25 ° C.
• More than 60% of the layer consisting of the complex of metal oxide and organic component is formed in the first 5 seconds of the electrolytic process.
• a treatment time of more than 5 minutes is not necessary for planographic printing, since no further layer build-up takes place; it also does no harm as long as the voltage is kept low.
• the treatment time is preferably about 0.16 to 1 minute.
• the short period of time, the low temperature (room temperature, so that hardly any additional heating or cooling devices are required) and the low power consumption represent favorable economic factors in comparison to conventional anodizing processes, which as a rule also include additional heat treatment of the carrier material.
• Iminoquinonediazides, o-quinonediazides and condensation products of aromatic diazonium compounds in combination with suitable binders are suitable as photosensitive mixtures which can be applied to the layers according to the invention from the complex of metal oxide and organic component for the production of printing forms.
• Such connections are e.g. in U.S. Patent Nos. 3,175,906, 3,046,118, 2,063,631, 2,667,415 and 3,867,147.
• the mixtures described in the latter document are generally preferred.
• photopolymer systems based on ethylenically unsaturated monomers with photoiniators, which may contain matrix polymer binders can be used. Photodimerization systems, e.g.
• Polyvinyl cinnamates and systems based on diallyl phthalate prepolymers are also suitable. Such systems are described in U.S. Patents 3,497,356, 3,615,435, 3,926,643, 2,670,286, 3,376,138 and 3,376,139.
• Two plates of a 3003 aluminum alloy suitable for printing purposes and roughened in an abrasive suspension are treated for 30 seconds in a 1 N sodium hydroxide solution and rinsed with distilled water at room temperature.
• the anodization is carried out for 60 seconds with lead as the counter electrode at a voltage of 30 V and a maximum of 5 A / d m 2 .
• the plate pieces treated in this way are spin-coated with the following mixture, which is dissolved in a suitable solvent:
• the dry layer weight is approximately 750 mg / m 2 .
• the printing plates obtained are exposed with an exposure device (Berkey Ascor) through a suitable template so that a fully covered step 7 is obtained on a Stauffer wedge.
• the plates are developed with a developer (Enco Negative Subtractive Developer) and then preserved (Enco Subtractive Finisher). Both plates are used under tough test conditions (excessive pressure on the plates and printing ink with strong abrasion properties) in a printing machine (Miehle).
• the following conditions apply to printing: uncoated paper, dampening solution with a pH value of 4.35, relative humidity 53%, non-alcoholic dampening system.

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• Organic Chemistry (AREA)
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