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.
• Sources of error include, for example, non-closed layers of the phosphate coating and thus poorer protection against corrosion as well as unsatisfactory deformation and paint adhesion properties. Treatment times in the phosphating stage of less than 5 seconds cannot be achieved with the known methods used in practice.
• DE-B-19 55 002 relates to a method for applying thin, corrosion-resistant and adhesive zinc phosphate coatings on metal surfaces, for example on those made of galvanized or hot-dip galvanized steel.
• the metal surfaces are treated with acid phosphating solutions to which at least one carbohydrate consisting of starch, a starch derivative or a polysaccharide, which has been produced by acidic decomposition of starch or a starch derivative, has been added.
• the acidic, aqueous phosphating solutions also contain zinc and phosphate ions, nickel cations, nitrate and also fluorides. With such phosphating solutions, galvanized or hot-dip galvanized steel plates are sprayed at temperatures in the range from 40 to 70 ° C.
• FR-A-2033717 (corresponding to GB-A-1237996) describes a method for phosphating electrolytically galvanized steel surfaces, which results in phosphate layers which have a layer weight of up to 21.5 mg / dm 2 (corresponding to 2.1 g / m 2 ), preferably in the range from 5.3 to 16.1 mg / dm 2 (corresponding to 0.5 to 1.6 g / m 2 ).
• the phosphating solutions used for this purpose contain 0.12 to 0.50 percent by weight zinc ions, 0.55 to 2.20 percent by weight phosphate ions and 0.009 to 0.036 percent by weight nickel ions; the total acid content is in the range from 7.5 to 30 points, the temperature of the phosphating solution is 38 to 60 ° C.
• nitrate ion content of the phosphating solutions which should be 0.001 to 0.02 percent by weight, preferably 0.005 to 0.015 percent by weight. It is said that a nitrate content of more than 0.02 percent by weight causes layer weights of more than 21.5 mg / dm 2 .
• the duration of treatment in this procedure should be between 2 to 45 seconds; the example speaks of a treatment duration of 15 seconds.
• DE-A-21 00 021 suggests treating the metal surfaces with solutions which essentially contain nickel ions as layer-forming cations.
• layer-forming cations of a further divalent metal, in particular zinc ions can also be present.
• the molar ratio of nickel ions to the other divalent metal cations is clearly above 1. It should be in the range from 1: 0.001 to 1: 0.7.
• Essentially nickel phosphate layers are 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 require a subsequent layering 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 thin layers of the phosphate layers without, however, having to give up the uniform covering of the galvanized material with a fine crystalline, firmly adhering, self-contained zinc phosphate layer.
• the method according to the invention it is possible, for example, to form uniform, closed phosphate layers on electrolytically galvanized steel sheets with a duration of the phosphating step of a maximum of about 5 seconds, which at the same time guarantee corrosion protection that at least approximately achieves that of "thick-layer phosphating", but has other properties even significantly different 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 furthermore wants to make it possible, for example, to be able to drive electrolytic galvanizing lines with subsequent phosphating at very different strip speeds, without any significant differences in the phosphate coating being associated therewith.
• the belt speeds that occur in practice today are, for example, in the range between 20 and 120 m / min.
• a constant quality of the phosphate coating is achieved, in particular also in the range of high belt speeds, that is, for example, in the range from 100 to 120 m / min. enables.
• 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 without subsequent coating.
• the thin phosphate layers produced by the method according to the invention behave more favorably in many shaping processes than the phosphate layers of a higher mass per unit area produced with the previous conventional methods.
• organic coatings applied subsequently also show significantly 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 free acid score is accordingly defined as the number of milliliters n / 10 NaOH required to titrate 10 ml bath solution against dimethyl yellow, methyl orange or bromophenol blue.
• 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 inventive design of the desired thin but nevertheless homogeneously closed layers.
• the bath solution has a comparatively high content free acid is used, 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 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 1.9 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 NO 3 - is in the range from 1 to (1 to 8).
• the phosphate and nitrate content of the phosphating bath is adjusted to one another in such a way that the weight ratio of PO 4 3- to NO 3 - is in the range from 1 to (0.1 to 2.5).
• the ratio of zinc cations to primary phosphate is chosen such that weight ratios of Zn 2+ to H 2 P0 4 - are kept in the range from 1 to (1 to 8) in the treatment bath.
• nickel cations are also used in the process according to the invention. However, these are used in minor amounts, 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 are used according to the invention. It is interesting in this context 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 takes place at moderately elevated temperatures 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 oil must be removed by means of known, suitable means and processes prior to phosphating.
• the water-wettable 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-A-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 the 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 process according to the invention or the zinc phosphate layers produced thereafter can also be advantageous for the process according to the invention or the zinc phosphate layers produced thereafter to passivate the phosphate layers produced in a subsequent process step.
• Such passivation can take place, for example, with dilute chromic acid and / or phosphoric acid.
• the concentration of chromic acid and / or phosphoric acid is generally between 0.01 and 1.0 g / l. It is possible to post-treat the protective layers with dilute chromic acid, which contains chromium (III) ions.
• the application concentrations of the hexavalent chromium are between 0.2 and 4.0 g / l Cr0 3 and those of the trivalent chromium between 0.5 and 7.5 g / l Cr 2 0 3 . It is expedient 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 of 0.1 N NaOH, which are required to titrate 10 ml of 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 2 .
• 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.
• the tape had a uniform, light gray appearance.
• the phosphate layer formed was closed and had a mass per unit area of 1.1 g / m 2 .
• 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 poorer 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)
• Catalysts (AREA)
• Electrolytic Production Of Metals (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Glass Compositions (AREA)
• Manufacture And Refinement Of Metals (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (3)

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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 EP EP83112008A patent/EP0111246B1/de not_active Expired
  • 1983-11-30 DE DE8383112008T patent/DE3378481D1/de not_active Expired
  • 1983-11-30 AT AT83112008T patent/ATE38692T1/de not_active IP Right Cessation
  • 1983-12-07 ZA ZA839106A patent/ZA839106B/xx unknown
  • 1983-12-07 ES ES527886A patent/ES527886A0/es active Granted
  • 1983-12-07 AU AU22172/83A patent/AU561151B2/en not_active Ceased
  • 1983-12-07 KR KR1019830005789A patent/KR910002568B1/ko not_active IP Right Cessation
  • 1983-12-07 CA CA000442768A patent/CA1205727A/en not_active Expired
  • 1983-12-08 JP JP58232618A patent/JPS59116383A/ja active Pending

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