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
  • C23C22/07—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 phosphates
  • C23C22/08—Orthophosphates
  • C23C22/12—Orthophosphates containing zinc cations
  • C23C22/13—Orthophosphates containing zinc cations containing also nitrate or nitrite anions
• • 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
  • C23C22/07—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 phosphates
  • C23C22/08—Orthophosphates
  • C23C22/12—Orthophosphates containing zinc cations

Definitions

• the invention relates to an improved method for producing closed, finely crystalline zinc phosphate layers with a low mass per unit area in very short treatment times on electrolytically galvanized metal products, in particular ferrous metals, for example on electrolytically galvanized steel sheets.
• DE-AS 19 55 002 proposes to apply thin, corrosion-resistant and adhesive zinc phosphate coatings to metal surfaces, to treat these, for example, galvanized metal surfaces with an acidic solution, the at least one of starch, a starch derivative or a polysaccharide, which is caused by acidic decomposition Starch or a starch derivative has been prepared, existing carbohydrate has been added.
• zinc phosphate coatings with a low coating weight of, for example, 1.2 to -1.8 g / m 2 and a uniform appearance should be able to be formed over a period of 3 to 10 seconds.
• the incorporated organic components are decomposed aurch the temperature and pH-value with increasing bath lifetime.
• the initially low phosphate requirements increase significantly.
• the decomposition products lead to strong odor nuisance.
• the extremely strong sludge formation is also particularly undesirable.
• DE-OS 21 00 021 proposes to form thin, coherent phosphate coatings with a layer weight of ⁇ 1.0 g / m, to treat the metal surfaces with solutions which essentially contain nickel ions as layer-forming cations.
• nickel ions layer-forming cations of another divalent metal, in particular zinc ions, can also be used are available.
• the molar ratio of nickel ions to the other divalent metalations is clearly above 1. It should be in the range from 1: 0.001 to 1: 0.7.
• Essentially nickel phosphate layers were deposited here. The formation of the zinc phosphate layers required in practice is not successful.
• the thin nickel phosphate layers according to this proposal of the prior art are also subject to drastic restrictions. So they always demand a subsequent overcoating with other coating agents to ensure lasting protection.
• the invention is based on the object of forming high-quality and improved zinc phosphate layers on electrolytically galvanized materials, in particular ferrous metals, despite substantially reduced processing times in the phosphating stage.
• the invention deliberately intends to accept the coating layers of the phosphate layers without, however, having to give up the uniform covering of the galvanized material with a finely crystalline, firmly adhering, self-contained zinc phosphate layer.
• the method according to the invention it is possible, for example, with a duration of the phosphating step of a maximum of about 5 seconds to form uniform, closed phosphate layers on electrolytically galvanized steel sheets which have surface masses that are half as low as known methods, but at the same time guarantee corrosion protection which at least approximately achieves that of "thick-layer phosphating" Properties, however, even differ significantly from the known thicker phosphate layers.
• the adhesion of organic coatings during and after deformation steps - for example when folding, deep drawing, flanging and the like - is improved compared to the results that have been achievable so far.
• the invention also wants to make it possible, for example, to be able to drive electrolytic galvanizing lines with subsequent phosphating at very different belt speeds without any significant differences in the phosphate coating being associated therewith.
• the belt speeds occurring in aer practice today are, for example, in the range between 20 and 120 m / min.
• the quality of the phosphate coating is constant, in particular also in the range of high belt speeds, that is to say for example in the range from 100 to 120 m / min. enables.
• the invention accordingly relates to a process for the phosphating of electrolytically galvanized metal products, in particular electrolytically galvanized steel strips, by short-term treatment with acid phosphating solutions which, in addition to zinc and phosphate ions, can contain further metal cations and / or anions of oxygen-containing acids with accelerating action, with the formation of zinc phosphate layers a mass per unit area below 2 g / m 2 , this method being characterized in that with acidic phosphating solutions works, aeren content of Zn 2+ cations is about 1 to 2.5 g / 1, while the free acid content in the range of 0.8 to 3 points and the acid ratio of total acid to free acid in the range of 5 to 10 and the duration of the treatment of the electrolytically galvanized material with the phosphating solution is not significantly extended over the period of 5 seconds.
• This process of the invention produces zinc phosphate coatings of 0.6 to 1.9 g / m 2 , which have a closed, finely crystalline structure and give the electrolytically galvanized sheet a desired uniform, light gray appearance.
• An electrolytically galvanized steel strip which has been phosphated in this way can also be processed further without subsequent coating.
• the thin phosphate layers produced by the method according to the invention behave more favorably in many deformation processes than the phosphate layers of a higher mass per unit area produced with the previous conventional methods.
• organic coatings applied subsequently also show markedly improved adhesion compared to the prior art, both during and after deformation processes.
• the free acid content of the phosphating bath used according to the invention is preferably in the range from 1.2 to 1.8 points.
• the preferred acid ratio of total acid to free acid is in the range from 6 to 8.
• the definitions of free acid, total acid and the primary phosphates mentioned below in phosphating baths are referred to pertinent printed state of the art referred, in particular to the publication Christian Ries "Monitoring of phosphating baths" Galvanotechnik, 59 (1968) No. 1, pages 37 to 39 (Eugen G. Leuze Verlag, Saulgau (Württ)). In this publication, both the terms of the parameters mentioned here and their determination are described in detail.
• the number of points of the free acid is therefore defined as the number of milliliters of N / 10 NaOH ml for titration of 10 bath solution against dimethyl, M ethyl orange or bromophenol blue is erfoderlich.
• the total acid score is the number of milliliters n / 10 NaOH required to titrate 10 ml bath solution using phenolphthalein as an indicator until the first pink color.
• the concentration of Zn 2 + ions is kept in a low-limited range. This is an important prerequisite for the development of the desired thin but nevertheless homogeneously closed layers.
• a comparatively high free acid content is used in the bath solution, which, as indicated, is in the range from 0.8 to 3.0 points, preferably in the range from 1.2 to 1.8 points.
• the duration of the treatment is deliberately chosen to be short. 5 seconds are not significantly exceeded. A treatment period of 2.5 to 5 seconds is generally used.
• the zinc phosphate layers produced by the new process are preferably in a range from 0.6 to 1.8 g / m 2 , the range from 1.2 to 1.4 g / m 2 being particularly preferred.
• nitrate is also used as the anion of an oxygen-containing acid with an activating effect.
• the weight ratio of Zn 2+ to NO3 is preferably in the range from 1 to (1 to 8).
• the phosphate and the nitrate content of the phosphating bath are expediently adjusted to one another in such a way that the weight ratio of PO 4 3- to NO3 is in the range from 1 to (0.1 to 2.5). It is further preferred to choose the ratio of zinc cations to primary phosphate such that weight ratios of Zn2 + to H 2 PO 4 are kept in the range from 1 to (1 to 8) in the treatment bath.
• Ni 2 + ions In addition to zinc, other cations can also be used in the process according to the invention. However, these are generally used in minor quantities. It is thus possible to use small admixtures of Ni 2 + ions, but the zinc ion content always predominates. Mixing ratios of 20 to 2 parts by weight of Zn 2+ ions to one part by weight of Ni 2+ ions can be particularly useful, for example. It is interesting in this connection that nickel cannot generally be detected analytically in the zinc phosphates deposited by the process according to the invention. At best, it is present in traces in the phosphate coating that are below the detection limit.
• the phosphating itself is advantageously carried out at moderately elevated temperatures, in particular in the temperature range from about 50 to 70 ° C.
• the temperature range from 60 to 65 ° C. can be particularly suitable. Any technically useful way of applying the treatment solution is suitable. In particular, it is therefore possible to carry out the new method both by means of spraying technology and by immersion.
• the electrolytically galvanized surface Before the phosphating solution is applied, the electrolytically galvanized surface must be completely water wettable. This is usually the case in continuously operating conveyor systems. If the surface of the electrolytically galvanized strip is oiled for storage and corrosion protection, this must be removed 01 using suitable means and methods that are already known before phosphating. The water wettable The electrolytically galvanized metal surface is then expediently subjected to an activating pretreatment known per se before the phosphating solution is applied. Suitable pretreatment processes are described in particular in DE-OSes 20 38 105 and 20 43 085.
• the metal surfaces to be subsequently phosphated are treated with solutions which contain, as activating agent, essentially titanium salt and sodium phosphate together with organic components such as gelatin or alkali metal salts of polyuronic acids.
• Soluble compounds of titanium such as potassium titanium fluoride and in particular titanyl sulfate can preferably be used as the titanium component.
• Disodium orthophosphate is generally used as sodium phosphate, but can be replaced in whole or in part by other sodium phosphates such as monosodium orthophosphate, trisodium orthophosphate, tetrasodium pyrophosphate and sodium tripolyphosphate.
• Titanium-containing compounds and sodium phosphate are used in such proportions that the titanium content is at least 0.005% by weight, based on the weight of the titanium-containing compounds and the sodium phosphate.
• the application concentrations of hexavalent chromium are between 0.2 and 4.0 g / l CrO 3 and those of trivalent chromium between 0.5 and 7.5 g / l Cr 2 0 3 . It is advisable to rinse with water between the phosphating and the aftertreatment step. However, this rinsing is not absolutely necessary and can be omitted in particular when working with squeeze rollers.
• the free acidity was 1.3 points and the total acidity was 10.8 points.
• the points free acid and total acid mean the ml 0.1 N NaOH, which are required to titrate 10 ml bath solution against bromophenol blue or phenolphthalein as an indicator.
• the sheet was rinsed with water and then passivated with a solution containing Cr-3 + / Cr-6 + at 50 ° C and dried.
• the mass per unit area of the phosphate coating was 1.6 g / m.
• the corrosion protection test according to SS DIN 50021 was comparable to layers that had been produced using conventional methods and had a mass per unit area of 2.4-2.6 g / m 2 .
• the total acidity of the bath was 9.9 points and the free acidity was 1.4 points.
• An electrolytically galvanized sheet was phosphated with this solution for 5 seconds.
• the sheet had a closed, light gray phosphate layer with a mass per unit area of 1.3 g / m 2 .
• a sheet metal sample was painted and, after drying at elevated temperature, provided with a cross cut according to DIN 53151.
• the adhesion value was perfect both without and with 8 mm Erichsen cupping.
• the free acidity of the bath was 2.1 points and the total acidity 11.3 points. In this case, too, the tape had an even, light gray appearance.
• the phosphate layer formed was closed and had a mass per unit area of 1.1 g / m. The paint adhesion on a sample of this sheet was good.
• a sheet electrolytically galvanized and phosphated by a conventional method with a mass per unit area of 2.3 g / m 2 was coated with the same paint and subjected to the same deformation operation.
• the paint adhesion values were significantly worse than in the case of the sheet phosphated using the method according to the invention.

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• Chemical & Material Sciences (AREA)
• Metallurgy (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Electroplating Methods And Accessories (AREA)
• Electrolytic Production Of Metals (AREA)
• Catalysts (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Glass Compositions (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (3)

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ID=6180124

Family Applications (1)

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Cited By (8)

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• 1982
  • 1982-12-08 DE DE19823245411 patent/DE3245411A1/de active Granted
• 1983
  • 1983-11-25 US US06/554,879 patent/US4497668A/en not_active Expired - Lifetime
  • 1983-11-30 AT AT83112008T patent/ATE38692T1/de not_active IP Right Cessation
  • 1983-11-30 DE DE8383112008T patent/DE3378481D1/de not_active Expired
  • 1983-11-30 EP EP83112008A patent/EP0111246B1/fr not_active Expired
  • 1983-12-07 ES ES527886A patent/ES8406564A1/es not_active Expired
  • 1983-12-07 CA CA000442768A patent/CA1205727A/fr not_active Expired
  • 1983-12-07 ZA ZA839106A patent/ZA839106B/xx unknown
  • 1983-12-07 AU AU22172/83A patent/AU561151B2/en not_active Ceased
  • 1983-12-07 KR KR1019830005789A patent/KR910002568B1/ko not_active Expired
  • 1983-12-08 JP JP58232618A patent/JPS59116383A/ja active Pending

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