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
  • C23C22/34—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 fluorides or complex fluorides

Definitions

• the latter consist of small quantities of complex fluorides of iron, titanium, zirconium or silicon and small amounts of nitrate ions or similar oxidizer in water.
• the pH must carefully be maintained at 1.8 to 3.5.
• the solutions act on the metal surfaces very rapidly, i.e., within 3 to 45 seconds, and are applied at temperatures between 5 and 95 C., preferably at room temperature. Applicataion to the surfaces can be in a bath, by a spray or by roller coating.
• a passivation post-treatment may be applied in the form of aqueous dilute chromic and/ or phosphoric acid or acid salts thereof.
• the invention relates to the deposition of protective coatings on iron, preferably steel, zinc and zinc-clad surfaces, particularly on continuous sheet or coils, by means of acid solutions, whereby the same baths can even simultaneously be used under like conditions for all of these metals. A process for this deposition also is described.
• Another object of the invention is to supply suitable solutions to carry out this process.
• aqueous solution free of chromic, phosphoric and oxalic acids which contains complex fluorides of iron, titanium, zirconium or silicon in amounts of 0.1 to 5 g./l. (grams per liter), calculated on the total cations, and further 0.3 to 10 g./l. nitrate ions or a corresponding amount of other oxidizers.
• the solutions have a pH of 1.8 to 3.5.
• the temperatures are between 5 and C., preferably ambient (room) temperature, i.e., between 10 and 50 C.; and the treatment is carried out within 3 to 45 seconds, and preferably 5 to 30 seconds.
• the values named are the effective amounts, pH, temperatures and times.
• the cations are added to the aqueous bath solutions in the form of their soluble salts whereby, in the case of titanium, zirconium and silicon, their fluoride complexes are most applicable.
• titanyl sulfate or zirconyl chloride can be employed.
• Iron can be added either as complex fluoride or, e.g., as sulfate, nitrate or chloride.
• the baths may contain mixtures of these metals or mixtures of several metal salts,
• the fluoride ions When not entered in the form of complexes, the fluoride ions are incorporated in the baths as hydrofluoric acid or its neutral or acid soluble salts. A slight excess of fluoride ions over the stoichiometrical amount needed for complex formation does not have any adverse effect.
• the bath solutions according to the invention preferably contain soluble nitrates as oxidizer. This permits operation of the baths at particularly low temperatures and short time cycles, thus resulting in very easy procedures.
• the process can be carried out using a solution of iron-III-nitrate and hydrofluoric acid.
• oxidizing agents can be used in lieu of nitrates.
• agents which are known as oxidizing accelerators for phosphatizing solutions, such as sodiumand potassium nitrates, chlorates, bromates, hydrogen peroxide and its adducts, e.g., melamine perhydrate or urea perhydrate (percarbamide), aliphatic and aromatic nitroand nitrosocompounds, e.g., nitroguanidine, picric acid, nitrophenols, monoand dinitrobenzenesulfonic acids. Mixtures of several of these materials may be employed.
• the treating baths are to be practically free from chromic acid and chromium-VI-compounds, of oxalic acid, oxalates, phosphoric acid and phosphates. These compounds or their anions, respectively, inhibit the formation of the layers according to the invention because they themselves are layer-forming anions. Even comparatively small quantities, e.g., of phosphates, decrease the adhesion of organic coatings. Chromic acid and chromium- VI-compounds, moreover, are poisonous, and the effiuents must be decontaminated.
• the pH of the solutions must be adjusted to 1.83.5, and preferably is between 2 and 3. Adjustment can be carried out with alkali solutions or acids other than named in the preceding paragraph. Only when these pH values and the concentrations previously named are maintained, equally good surface layers are produced on iron, steel, zinc and galvanized metal.
• the treatment time is exceedingly short and usually lies between 3 and 45 seconds, preferably to 30 seconds. This time is short enough to carry the conveyors in continuous plants at high speed without the need for particularly large baths or spray zones.
• the temperature of the baths is kept between 5 and 95 C.
• Preferred temperatures are ambient temperatures, i.e., substantially room temperature, between substantially and 50 C. This constitutes a further advantage of the process according to the invention because the baths do not require heating nor necessarily the maintenance of a given temperature.
• the solutions can be applied to the metals by immersion, coating, or spraying. Coating rolls can successfully be employed.
• the metal surfaces are cleaned and degreased prior to the treatment, using the customary organic solvents or alkaline, acid or neutral cleansers.
• the pretreatment is governed by the degree of soiling of the materials.
• a passivation of the layers produced by the process according to the invention is desirable. This can be accomplished by using dilute aqueous phosphoric and/ or chromic acid, or their sodium-, potassiumor ammonium salts, respectively.
• concentrations generally are between 0.01 and 5 g./l.
• the protective layers produced are passivated with aqueous dilute chromic acid which contains chromium-III-ions.
• the effective concentrations generally are 0.2-2 g./l. CrO and 0.05-1 g./l. Cr O
• the layers then are dried after passivation. Prior to the passivation, a water rinse is opportune but not a strict requirement, especially when squeeze rolls are used.
• the baths preferably are renewed with solutions of concentrates, respectively, which contain complex fluorides of iron, titanium, zirconium and/ or silicon and at least one oxidizer and have a ratio of free acid to total acid of 1:1.05 to 1.75.
• the process according to the invention produces uni- .formly thin and readily deformable coatings on iron, steel zinc and galvanized surfaces which impart good corrosion resistance and excellent adhesion of organic coatings subsequently applied.
• the coating layers produced on steel are taupe to bluish-iridescent, those on zinc are gray and, slightly yellowish-iridescent.
• the process is easy to carry out, and the baths have a long working life.
• EXAMPLE 1 A continuous device for coiled or long-strip bands was used, wherein steel and galvanized bands were simultaneously treated by an automatic spray at a dwelling time of 10 seconds in all treatment zones. The surfaces first were degreased with an aqueous alkaline solution of customary composition, and rinsed with cold water, followed by an exposure to an aqueous solution containing Fer, 1.25 NO3 1.5
• Layers thus formed on the steel and zinc surfaces were uniform, thin and well deformable. These layers promoted excellent adhesion of organic coatings, e.g., paints, lacquers and plastic coatings.
• the color of the steel band was taupe to weakly bluish-iridiscent; that of the galvanized bands gray to weakly yellowish-iridescent.
• the spray solution was renewed to maintain it at con stant point using an aqueous concentrate containing Percent Fe(No -9 H O 4 HF (40%) 3 HNO;; (60%) 3
• the protective layer formed did not change from the original even after frequent renewals and much use of the solution.
• EXAMPLE 2 A similar device was used as in Example 1 with a dwelling time of 12 seconds. Iron-, steel and hot dip galvanized (sendzimierverzinkte) iron bands were degreased, rinsed and then simultaneously sprayed with a solution containing G./l. FeF 1.7 N0 3.5
• Iron and steel bands were passivated with 0.1% NaH PO, solution; the galvanized bands with 0.02% chromic acid solution.
• Passivation is an optional step and in many instances is not required.
• Example 1 The spray was the same for all materials which attained thin, uniform and well deformable protective layers. These exhibited excellent adhesion to organic coatings as named in Example 1. When changing over from one band material to another, no changes were required in treatment conditions, i.e., time, pH or temperature.
• a continuous process for the simultaneous deposition of protective surface layers on surfaces of longstn'p bands of like and different metals selected from the group consisting of iron, steel, zinc and zinc-clad iron and steel which consists essentially of continuously passing said bands through a contact zone and continuously contacting said surfaces of said bands with an aqueous solution which is free from phosphoric, chromic and oxalic acids, and which contains complex fluorides of cations selected from the group consisting of iron, and zirconium, in amounts of 0.1 to 5 g./l., calculated on the total cations present, plus 0.1 to 10 g./l.
• oxidizer selected from the group consisting of nitrate ions, sodium and potassium chlorates, sodium and potassium bromates, hydrogen peroxide, melamine perhydrate, urea perhydrate, nitroguanidine, picric acid, nitrophenols and monoand dinitrobenzenesulfonic acid; said aqueous solution having a pH of 1.8 to 3.5 and a temperature of substantially 5 to C.; said bands being continuously contacted with said aqueous solution over a period of time of 3 to 45 seconds; and continuously removing said bands from said contact zone.
• an oxidizer selected from the group consisting of nitrate ions, sodium and potassium chlorates, sodium and potassium bromates, hydrogen peroxide, melamine perhydrate, urea perhydrate, nitroguanidine, picric acid, nitrophenols and monoand dinitrobenzenesulfonic acid
• a passivation step is carried out by a second contacting step to an aqueous solution of a substance selected from the group consisting of phosphoric acid, chromic acid, sodium-, potassiumand ammonium salts of said acids, or mixtures thereof.

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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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Citations (3)

• 1967
  • 1967-11-20 US US684491A patent/US3539402A/en not_active Expired - Lifetime
  • 1967-12-06 GB GB55391/67A patent/GB1193460A/en not_active Expired
• 1968
  • 1968-02-15 ES ES350547A patent/ES350547A1/es not_active Expired
  • 1968-02-16 BE BE710840D patent/BE710840A/xx not_active IP Right Cessation
  • 1968-02-16 FR FR1554415D patent/FR1554415A/fr not_active Expired

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