Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/12—Process control or regulation
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/12—Process control or regulation
  • C25D21/14—Controlled addition of electrolyte components
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/16—Regeneration of process solutions
  • C25D21/18—Regeneration of process solutions of electrolytes

Definitions

• This invention belongs to the field of chemistry and metallurgy and it is specifically related to a process for the electrolytic and electrophoretic production of electrochemical coatings with a bath from trivalent decorative chromium solutions on a metal or plastic substrate with trivalent chromium ions, sulfate ions, graphite anodes, hexavalent chromium control and false cathode purifications in a continuous industrial operation.
• Chromium is a very important metal for a large range of industry applications. Over more than 70 years chromate plating decorative and functional process of has been carried out with electrolytes from chromium acid, process with a high content of the Cr+6 ion, considered by the WHO as a carcinogen for operators and personnel entering in contact with companies where it is used which is manifested in ulcers in the nasal septum. Hexavalent chromium has a strong impact in water environment.
• Electrochemical coatings of trivalent chromium has been stigmatized throughout the time due to their cost and the process color and stability; these has caused that its implementations is not that popular in large sites or small workshops.
• Trivalent chromate plating baths have been developed from two technologies: sulfate and chloride.
• Trivalent chromium baths from chloride ions have some disadvantages: a darker color, more sensitivity to metal contaminants and chlorine detachments in the anodes causing safety and occupational health risks, besides of equipment corrosion.
• Trivalent chromium baths from sulfate ions are more noble, are whiter, close more to the chromate plating from hexavalent ions, are more tolerant to metal and organic contaminants, they do not produce detachment of noxious gases and do not cause safety and occupational health risks.
• Trivalent chromate plating baths from chloride ions work preferably with graphite anode. Anode is produced by the formation of chlorine gas, there is no oxygen production, which causes the formation of Cr+6.
• the bath composition may include additives from Br— and HCOO— ions which prevent the evolution of Cr+3 to Cr+6.
• the trivalent chromate plating process from chloride ions mainly uses graphite anodes
• the trivalent chromate plating from sulfate ions also uses graphite anodes.
• U.S. Pat. No. 5,560,815 defines the development of trivalent chromate plating baths from SO 4 ⁇ 2 ions, describing the use of anodes coated with iridium and tantalum oxide with the characteristic of a potential lower than the oxygen and as consequence it inhibits the evolution of the Cr+3 to Cr+6.
• This type of anodes after a work time in continuous industrial productions, have proven to make easier the formation of Cr+6 in the bath, due to the exhausting of the iridium oxide layer, causing the restriction of the current pass in the anode and defects related to the Cr+6 contaminant.
• patent EP0088192 defines a trivalent chromate plating bath different from the chloride ions, it refers to the use of graphite anodes in the trivalent chromate plating processes from sulfate ions and how the release of oxygen in this kind of anodes causes surface erosion and carbon particles release that accumulates in the chromium producing coating defects.
• Patent WO2010051118 refers to the use of manganese ions as additive to inhibit the formation of Cr+6 and increase the shelf-life of insoluble anodes used in the chromate plating process from trivalent and sulfate ions, including lead, lead alloy, platinized titanium anodes or metal anodes that consist of the coating of surface with iridium oxide, ruthenium oxide or mixed iridium/tantalum oxide. Although the shelf-life of this type of anodes increases, they will eventually collapse. In a continuous industrial production 24/6/360, it is difficult to determine the time when they exhaust and the Cr+6 production starts. On the other hand, concentration of Mn ion bath has to be closely controlled due to the risk of an excess that may cause a deposit with chromium changing the coating color and affecting the corrosion resistance.
• HEAT-TREATABLE CHROMIUM refers to a bath that is part of a hexavalent chromium and an alloy of iridium to reduce it to trivalent chromium through methanol, ammonium formate and sodium sulfate as catalyzer, where the reaction is made from the contaminant hexavalent chromium that reacts in the process with platinum and graphite anodes in order to obtain functional non-uniform chromium.
• the new invention comes from trivalent chromium, it does not use sodium sulfate as catalyzer but sodium sulfate as a result of the reaction of a crystallization sub process.
• Iron or alloys can not be used in the new process since iron is a bath contaminant that leaves black veins in the finishing and increases the possibility of corrosion in the final finishing. Likewise, it does not need any temperature changes and the trivalent chromium batch may be applied on plastic or metal for decorative finishing.
• the present invention solves the contamination problem when hexavalent chromium is generated in a low-cost efficient process, proposing a continuous industrial process and corrosion-resistant product with uniform finishing and non contaminant from a bath with trivalent chromium ions, sulfate ions and graphite anodes in a combination appropriate for a continuous industrial operation.
• this invention the difficulties of the previous state-of-the-art are overpassed, such as wear and final collapse of titanium electrodes covered with noble metals, the control and purification of contaminants affecting the process have been eliminated generating a continuous rejuvenation of process, reducing risks, costs and allowing replicating the novelty without technological difficulties.
• the invention proposes a chromate plating process from Cr+3, having SO 4 ⁇ 2 ions and preferably using graphite anodes, obtaining a chromium coating with strong adherence to substate, with mechanical, physical and chemical properties reproducible in continuous industrial productions.
• the specifications of products of color, thickness and resistance to corrosion and wearing maintains his stability in time and to temperature changes.
• composition of the bath has proven stability in 24 hours continuous productions with the application of appropriate controls and maintenance.
• the bath has been noble to changes of temperature, pH, components concentration and tolerant to different contaminants.
• the process of this invention mainly uses graphite anodes that have qualities such as good conducer of electricity, mechanized facility to be adapted to different conformations, good chemical and mechanic resistance, good resistant to anodic corrosion and high relation of surface-volume providing a very good anodic area, they are cost-effective compared to titanium electrodes coated with noble metals.
• the use of graphite anodes is not limited and also lead and stainless steel anodes are used. With the use of graphite anodes in trivalent chromate plating solutions with SO 4 ⁇ 2 ions, a better anode-cathode relation can be used as well as better current density without affecting the electrodes, compared to titanium electrodes coated with noble metal which tend to crack when subjected to high current densities.
• graphite anodes must not have pores, since they cause penetration of the bath solution and an electrical reactions when releasing oxygen that cause an early erosion leaving too much carbon residues.
• Graphite anode must be put in acid-resistant fabric bags as those used in the nickel plating process to avoid the pass of anode eroded particles to the solution.
• the continuous filtration is used at a speed of 4 times to 8 times and preferably from 4 times to 6 times the bath volume per hour. This secures that carbon particles in the batch are controlled and protects the coating quality.
• the bath relationship of anode/cathode must be 3:1 and preferable a relation of 2:1, a greater relation and a greater direct current improve the process efficiency, producing a best cathode coating area.
• the density of current applied must be between 4 dm2 to 12 A/dm2 and preferable between 5 A/dm2 to 8 A/dm2.
• the bath prepared for the use with graphite anodes contains Cr+3 ions, the Cr+3 ions concentration in the bath is between 10 g/l to 30 g/l, preferably between 15-g/l to 25 g/l.
• the Cr 2 (SO 4 ) 3 salt is used as the Cr+3 source.
• the bath prepared contains organic and organic chromium complexes that are stable, forming bonds that allow the Cr+3 ion and its reduction to Cr0 in the cathode surface forming a metal sheet with mechanic, physical and chemical properties with strong adherence to the substrate and reproducible in continuous industrial production.
• Chromium complexes of this preparation also have properties allowing an easier degradation when residual waters treatment is made, with which a reduction of the environmental impacts is assured.
• H3BO3 in an electrolytic solution, between 40-g/l to 60 g/l, preferably between 45 g/l to 50 g/l increases conductivity and acts as a buffer agent and also as an inhibitor of the anode decreasing the attack and detachment of the graphite anode by the presence of B— ions which reduce the O2 overproduction.
• the Na 2 SO 4 salt is added as a conducer, between 30 g/l to 60 g/l, preferable between 40 g/l to 50 g/l.
• this salt is added only to form the bath since during the process it produces and increases its concentration due to the different reactions of oxide-reduction.
• the bath of the present invention also includes salts containing Na+, K+ and (NH) 4 + ions.
• the chromium complex discomposes by action of the electrical current and deposits Cr0 on the cathode and releases SO 4 ⁇ 2 anion which combines with sodium ions present in the solution forming Na 2 SO 4 . Also during the mechanism of reduction from Cr+6 to Cr+3, an increase of acidity is produced by the formation of H 2 SO 4 , the control of acidity is made with NaOH, Na 2 CO 3 , neutralizing the solution with formation of Na 2 SO 4 . In this type of bath using graphite anodes, it always tends to become acid.
• pH must be controlled between 3.4 of pH to 4.0. High pH values favor the formation of oxygen and promotes the attack of graphite anode.
• the bath superficial tension must be between 30 dynes to 70 dynes. Adjustment is made by adding moistening agents such as octyl alcohol.
• Process temperature must be between 40° C. to 60° C., preferably between 45° C. to 50° C. Due to the constant reduction from Cr+6 to Cr+3, bath is concentrating from Na 2 SO 4 , and a reduction of temperature may cause the crystallization of this salt.
• the process of the present invention does not require purification with selective resins allowing a reduction of contaminants produced in the regeneration and a reduction of costs.
• the use of sequestering agents as EDTA for metal purification is not recommendable in this process because if produce side effects as progressive accumulation by making strong organometallic complexes that affect coating quality and causes problems in the effluent treatment.
• Addition of reducers is made controlling the consumption of amperes-hour and maintaining the Cr+6 between 0 ppm to 40 ppm, preferably between 0 ppm 20 ppm, rank in which there is no side effect in the coating quality.
• Results have been obtained with the bath of the present invention from Cr+3 and SO 4 ⁇ 2 ions by using graphite anodes, in Hull Cell the penetrations were between 80% to 92% even after five trials with the same solution and photometric analysis in presence of diphenylcarbazide with results of Cr+6 between 20 ppm to 30 ppm, concentration that did not affect coating quality, color was white to almost the hexavalent chromium color without dark veins formation.
• the thickness of coating obtained in decorative coatings from Cr+3, is between 0.3 ⁇ m to 2 ⁇ m, very similar to those obtained with the process of traditional Cr+6.
• the invention is a novelty preparation of a trivalent chromium bath from SO 4 ⁇ 2 ions offering the advantage to preferably work with graphite anodes and we have solved the control of Cr+6 generation and control and elimination of the different contaminants, obtaining a chromium coating with strong adherence to the substrate with excellent mechanical, physical and chemical properties, commercially reproducible in continuous industrial productions. Product specifications of color, thickness, resistance to corrosion and wearing have been stable throughout the time.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Automation & Control Theory (AREA)
• Electroplating And Plating Baths Therefor (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 2014
  • 2014-02-11 CO CO14028206A patent/CO7190036A1/es unknown
• 2015
  • 2015-02-09 RU RU2016135556A patent/RU2016135556A/ru not_active Application Discontinuation
  • 2015-02-09 WO PCT/IB2015/050974 patent/WO2015121790A2/es active Application Filing
  • 2015-02-09 CN CN201580019366.6A patent/CN106164340A/zh active Pending
  • 2015-02-09 US US15/118,460 patent/US20170167040A1/en not_active Abandoned
  • 2015-02-09 MX MX2016010449A patent/MX2016010449A/es unknown
  • 2015-02-09 EP EP15748593.9A patent/EP3106544A4/en not_active Withdrawn
  • 2015-02-09 BR BR112016018584A patent/BR112016018584A2/pt not_active IP Right Cessation

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