Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
  • C23C22/26—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also organic compounds
  • C23C22/28—Macromolecular compounds

Definitions

• the passivation is a method to protect metal against corrosion in mild mediums.
• the passivation can be obtained in different ways, among them the chemical ones, with the formation of a surface film of metal oxide, for instance chromate plating.
• the passive state must not be considered as a state in which there is no corrosion, but that one in which the reaction is inhibited by a passive film controlling the diffusion speed with a very low density of dissolution current, of about 10 A per cm2.
• Zinc is the protection metal most currently used, but cadmium is as well largely used. However these metals have a high tendency to corrosion in industrial atmospheres as well as in urban and marine ones.
• the chromium plating is the most usual passivation procedure onto metal zinc and cadmium surfaces.
• a typical chromium plating is composed by solutions of 50 to 200 grs/l of Na2 Cr2 07 and 3 to 6 ml of H2 SO4, this producing a greenish-brown film after about ten seconds of dipping, the optimum application pH of these solutions is between 1 ⁇ 2 and 1 ⁇ 6, and the procedure comprehends three phases:
• the protection process for zinc or cadmium plated surfaces would comprehend a chromating bath, dipping the pieces to treat in periods from 5 to 10 seconds, to 2 or 3 minutes. Afterwards there would be a cold or hot water rinsing, depending on the process, and an immersion in a protective organic product. A correct squeezing and afterwards a room temperature drying, or a hot air one.
• the purpose of present invention is to develop a product with at the same time a chromium plating of zinc or cadmium surface, as well as laying an organic polymer.
• organo-inorganic films are obtained, with a high anticorrosive protection and a decorative finishing similar to the above described traditional passivations.
• the product developed in present invention provides a corrosion protective film onto zinc (or cadmium) plated surfaces, with a decorative finishing in different colours, as per the final composition employed. Different finishings can be obtained : blueish-white, olive-green, iridiscent yellow, and black.
• the application process is extremely simple as the chemical conversion and the polymer laying are performed in the same single bath, not requiring further rinsings.
• the process can be schematized as follows : - Zinc plating. - Rinsing. - Bright dipping. - Rinsing. - Conversion + Polymer. - Drying.
• the basic operation principle of this invention consists in a simultaneous action of the different elements of the composition to form a mixed insoluble film of chromates and polymers, of high anticorrosive resistance and a decorative colour as above described.
• the different elements of this invention act as follows : the existing mineral acids attack the zinc surface with formation of ions of Zn++ and H+. These rising ions will provoke a reduction of existing hexavalent chromium, with a change in the pH value in the interface of the polymer next to the metal surface with the subsequent unstabilization, coagulation and unsolubilization of the polymer. Afterwards, the polymer reticulates with the metalic polyvalent ions present, performing a "closed" film highly resistant to corrosion.
• a characteristic of this procedure is the fact that the treatment time can modify and control the thickness of the coating obtained, the protective film being thicker when treatment time is longer, so that some limits have been fixed to make possible the industrial application of this process, which are scheduled between 20 seconds and 120 seconds of treatment time.
• films with thicknesses of 0,5 up to 2 microns can be obtained, corresponding to a weight of 0,75 to 3 grs/m2.
• Anticorrosion The high anticorrosive protection reached is explained by the high weight of coat laid by the product of this invention, and also by the structure itself of the coating, which because of being highly reticulated, presents a surface with a poor porosity, with an effective isolation of the corrosion circuit between anode and cathode.
• an iridescent-yellow coating with a layer weight of about 1 to 1,7 gr/m2, can protect from corrosion up to 250-300 hours as per Salt Spray ASTM-B-117, up to white rust.
• a blueish-white coating with layer thickness of 1 gr/m2, has a resistance of 100 to 125 hours.
• the Cr VI Salts which will be in the system shaped as soluble anions, will give under a reduction process chromiun ions (III). As well, the Cr VI Salts will give the anions which will precipitate with the present cations, which are solved or formed, as per the different solubility of every chromate or dichromate. Therefore there will be a precipitate of inorganic salts onto the zinc plated surface dipped in the system.
• the mineral acids which will attack the zinc or cadmium plated surface, solving in the medium Zn++ or Cd++ ions, forming at the same time hydrogen which will provoke the reduction of the Cr VI salts to Cr+++ ions.
• these acids will give to the system a low pH, preventing the precipitation of the hydroxides of the different cations present in the system.
• the anions derivated from these acids will also enter in the precipitated film, forming slats with the adequate precipitating cation.
• the inorganic Salts which provide the system with cations and anions, which will form salts with the cations being solubilized, which in their turn precipitate by supersaturation or by coprecipitation onto the zinc or cadmium plated surface.
• the colours of the film laid, will above all depend of the choice of these inorganic salts.
• Organic component of the system henceforth named component "A”.
• the organic product being the base of the formation of a polymeric film onto the treated part, will enter in the final product in an aqueous dispersion shape.
• the resin produced by the system of polymerisation in emulsion will contain polymers of acids and esters such as acrylic, metacrylic, ethyl-acrylate, butil-acrylate, and other monomers like styrene.
• component "A” An important part of component "A” is the incorporation, by means of the procedure of emulsion inside the polymerisation, or by further incorporation to the system, of other polymers of low molecular weight, giving to the surface of dry organic film, lubricating properties.
• pieces specially screws and nuts
• the inorganic fraction of the system that is the one producing a first attack to zinc, and the formation of chromates and insoluble salts, will be named henceforth component "B”. It is evident that chemical composition of component "B” will vary in some of its ingredients depending of the colour of the passivate finishing to obtain, although always maintaining the hexavalent chromium as a common and main element.
• component "B” The choice of products entering in component "B” comprehends 3 basic groups, forming the conversion layer onto the zinc surface.
• Composition hexavalent chromium, occasionally trivalent, like chromates, dichromates, chromium dioxide, chromium +3 salts ; strong mineral acids, to start the attack, like sulfuric acid, nitric acid, fluorhidric, acid florures. They will also maintain the control of the pH value of the product.
• components of the inorganic fraction of component "B” will be as follows :
• Example A to obtain a olive green coating, of above mentioned qualities component "A” - as per above description - 75 to 120 cc.
• component "B” as per first example - 75 to 120 cc. Distilled water - up to 1000 cc.
• Example B for a yellow iridiscent coating, with above mentioned qualities component "A” - as per above description - 50 to 100 cc. component “B” - as per second example - 50 to 100 cc. Distilled water - up to 1000 cc.
• Example C to obtain a blueish-white coating, with above mentioned qualities component "A” - as per former description - 50 to 100 cc.
• Example D to obtain a black coating, of above mentioned qualities component "A” - as per above description - 80 to 120 cc.
• component "B” - as per fourth example - 70 to 100 cc.
• component "C” - as per above description - distilled water - up to 1000 cc.

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)

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Cited By (6)

Citations (5)

• 1986
  • 1986-10-21 EP EP86114575A patent/EP0264472A1/en not_active Withdrawn
• 1987
  • 1987-07-06 JP JP16958687A patent/JPS63109177A/ja active Pending

Patent Citations (5)

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