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
  • C23C22/30—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 trivalent chromium

Definitions

• the invention relates to a process for the treatment of metal surfaces by applying a chromating agent which contains chromium VI, chromium III ions and at least 5 g / 1 silica and / or silicate and is free from reducing agents.
• the coating is formed by drying the treatment solution.
• the shape of the objects to be treated influences the result by e.g. strongly convex areas are not adequately layered.
• the chromating process described in GB-PS 1 234 181 leads to drying of the treatment solution on smooth surfaces, e.g. on steel strip, to very good results, however, the layer formation on strongly curved surfaces is unsatisfactory.
• the object of the invention is to provide a method for the treatment of To provide metal surfaces, which does not have the aforementioned disadvantages, allows the treatment of outdoor structures of any shape and yet is easy to implement.
• the object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that a chromating agent is applied which contains organic solvent and organic thickener.
• the chromating agent used in the process according to the invention is in particular stable and can have a consistency which is variable within wide limits and which allows application from spraying on to brushing on or brushing on.
• the organic solvents to be used must be resistant to chromium VI compounds. They should preferably be non-toxic and - with a view to a short drying time - sufficiently volatile.
• a chromating agent is applied which contains N-methyl-2-pyrrolidone as the organic solvent. The amounts are preferably 25 to 200 g / l, in particular 70 to 150 g / l.
• the organic thickener which together with the silica and / or the silicate causes the thickening, should be able to increase the consistency until it can be brushed on or brushed on. It must be compatible with the organic solvent and the other components of the chromating agent.
• a chromating agent is preferably applied which contains polyvinylpyrrolidone as the organic thickening agent. The preferred amounts are 10 to 100 g / l, in particular 30 to 75 g / l.
• the chromating agent contains a surfactant that facilitates application, especially when the metal surfaces are dirty.
• the surfactant must also have the necessary stability. It is usually of the nonionic type and is particularly effective, in particular in combination with anionic surfactants, which are advantageously introduced as a sodium compound. Ethylene oxide adducts are particularly suitable as the nonionic surfactant and sodium lauryl sulfate is particularly suitable as the anionic surfactant.
• the amount of the surfactant can be up to 100 g / 1. A content of 5 to 50 g / 1 is preferred.
• the adhesion of the coating to the metal surface can be improved if a compound of a monovalent metal - as described in GB-PS 1 234 181 - or a divalent metal which does not reduce hexavalent chromium is incorporated into the chromating agent.
• Suitable monovalent cations are sodium and potassium. Calcium, magnesium, strontium, barium and nickel, but especially zinc, can be used as divalent cations.
• the amount of mono- or divalent cations can be up to 3 g / 1. The range of 0.05 to 2.5 g / l is preferred.
• the weight ratio of hexavalent chromium - calculated as' Cro 3 - to mono- or polyvalent cation is usually in the range from 5: 1 to 100: 1.
• the chromating agent may otherwise be of the type described in GB-PS 1,234,181. So the pH will preferably be below 4 and generally above 2. The pH range from 2.5 to 3.5 is preferred. The amount of silica and / or silicate is advantageously 5 to 100 g / l. The preferred entry is as pyrogenic or precipitated silica, e.g. with the trade name AEROSIL. However, the other substances described in the GB-PS are also suitable.
• the chromating agent to be used in the process according to the invention is usually produced by partial reduction of an aqueous solution of chromic acid, which may already contain some or all of the other components.
• the chromic acid can also be partially neutralized, ie partially contain water-soluble chromate or bichromate, for example sodium or potassium. Nevertheless, the aqueous solution must be strongly acidic and - before the reduction - have a pH below 2, preferably below 1.5.
• the solution should contain at least 5 g / l, most advantageously 100 to 500 g / l, chromium VI - calculated as Cr0 3 .
• part of the chromium VI is reduced to chromium III using a suitable amount of reducing agent, possibly under the action of heat, so that when the reduction is complete, the chromium VI and chromium III ions, optionally in whole or in part in the form of chromium chromate.
• the chromium VI: total chromium weight ratio in the chromating agent should be between 0.5: 1 and 0.75: 1.
• the amount of total chromium (calculated as Cr0 3 ) is usually 5 to 40, preferably 10 to 40 g / l.
• the content of hexavalent chromium is preferably 5 to 30 g / l - calculated as CrO 3 . If there is an intention to apply a corrosion-protective coating which is then painted, the ratio of chromium VI: total chromium should be as close as possible to 0. 5: 1, insofar as the formation of a precipitate allows this. Generally the ratio will be 0.55: 1 to 0.63: 1.
• the amount of reducing agent results from the intended degree of reduction and its reducing power.
• the reducing agent should be such that the effectiveness of the chromating agent does not deteriorate when it is oxidized form impairing substances. Sulfur-containing reducing agents are therefore advantageously avoided.
• Organic reducing agents are preferred because of the mostly harmless by-products.
• Particularly suitable reducing agents are sugars such as dextrose, glucose and sucrose, starch, alcohols such as methanol, ethanol, ethylene glycol, polyethylene glycol, glycerol, mannitol, sorbitol, alkylolamines such as triethanolamine, hydroquinone.
• Hydroxylamine but possibly not as sulfate, and phosphorous acid can be used as the inorganic reducing agent.
• the usual method of application for the chromating agent to be used according to the invention is brushing or brushing on. Then the chromating agent is allowed to dry in air or under the influence of heat. A subsequent rinsing with water is generally not carried out.
• Aluminum, magnesium, zinc, galvanized steel, but in particular steel itself, and alloys of the aforementioned metals can be treated by the process according to the invention.
• the method according to the invention is particularly advantageous for the treatment of structures which are located outdoors or are to be erected, preferably when laying pipelines, for the treatment of connecting elements therefor and for the repair of damaged coatings of such structures.
• the coatings produced by the method according to the invention are also suitable as a basis for adhesives, for example based on epoxy resin, for connecting metal surfaces to one another (for example in the motor industry).
• the coatings produced also form an excellent basis for painting pipelines and the like with epoxy resin and are more durable than conventional coatings.
• Farther chromating agents used in the process according to the invention are stable over a considerable period of time, for example over several months. If the coatings produced are provided with paint or varnish and the like, they considerably improve their liability.
• a chromating agent was produced which, in parts by weight, contained the following components:
• the chromating agent could easily be brushed onto profiled steel structures such as connecting elements. After drying in the atmosphere, a substantially uniform coating was obtained. A conventional varnish applied afterwards showed satisfactory adhesion.

Landscapes

• 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)
• Application Of Or Painting With Fluid Materials (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10567207

Family Applications (1)

Country Status (7)

Cited By (7)

Families Citing this family (11)

Citations (2)

Family Cites Families (6)

• 1984
  • 1984-09-25 GB GB848424159A patent/GB8424159D0/en active Pending
• 1985
  • 1985-09-09 US US06/773,483 patent/US4644029A/en not_active Expired - Fee Related
  • 1985-09-11 NZ NZ213440A patent/NZ213440A/en unknown
  • 1985-09-13 AU AU47431/85A patent/AU580333B2/en not_active Ceased
  • 1985-09-17 EP EP85201480A patent/EP0177086A1/de not_active Withdrawn
  • 1985-09-24 GB GB08523573A patent/GB2164956B/en not_active Expired
  • 1985-09-25 BR BR8504719A patent/BR8504719A/pt unknown
  • 1985-09-25 JP JP60212010A patent/JPS6184382A/ja active Pending

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events