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
  • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
  • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
• • 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
  • C23C22/18—Orthophosphates containing manganese cations
  • C23C22/182—Orthophosphates containing manganese cations containing also zinc cations

Definitions

• the invention relates to an improved method for producing fine crystalline, closed conversion layers, consisting predominantly of zinc phosphate, 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 strips.
• the process is not limited to "pure zinc layers". Steel strips that have been given a zinc alloy coating can also be treated. In addition to zinc, iron, nickel and cobalt are examples of alloy components.
• the treatment times were over 5 seconds; targeted belt speeds of 90 to 120 m / min, for example, were impossible or difficult to achieve and with quality losses, such as non-closed layers.
• DE-AS 19 55 002 proposes the use of acid phosphating solutions to which a carbohydrate obtained from starch, starch derivative or polysaccharide by acidic decomposition is added in order to produce thin, adhesive and corrosion-resistant zinc phosphate layers on, for example, electrolytically galvanized steel surfaces.
• Zinc phosphate layers with mass per unit area of, for example, 1.2 to 1.8 g / m 2 should form in treatment times of 3 to 10 seconds.
• DE-OS 21 00 021 proposes to form thin closed phosphate layers with mass per unit area of ⁇ 1.0 g / m 2 to treat the metal surfaces with phosphating solutions which essentially contain nickel ions as layer-forming cations.
• nickel ions in addition to the nickel ions, further metal ions, in particular zinc ions, can be present.
• the molar ratio of the nickel ions to the other divalent metal ions should be in the range from 1: 0.001 to 1: 0.7.
• nickel phosphate layers are deposited. In contrast to the desired zinc phosphate layers, they always require a subsequent coating with, for example, a varnish in order to achieve acceptable corrosion protection. This is a serious disadvantage.
• a process proposed in DE-OS 32 45 411 represents an essential step in the desired direction.
• a process for the phosphating of electrolytically galvanized steel strips is described. In treatment times of not significantly more than 5 seconds, mostly in 5 or less, zinc phosphate layers with mass per unit area of less than 2 g / m 2 , preferably 0.6 to 1.9 g / m 2 , are deposited, which are without loss of the required corrosion protection, both in the unpainted and in the lacquered state, which do not have disadvantages due to the high layer coverage.
• the weight ratio of Zn 2+ / NO 3 - is kept in the range of 1 / (1 to 8)), the weight ratio of PO 4 3- / NO 3 - in the range of 1 / (0.1 to 2.5).
• nickel ions are also used, the Zn 2+ content always predominating. Particularly useful ratios may 20-2 parts by weight of Zn 2+ ions to a part by weight of Ni 2 + - be ions. Most of the time, nickel cannot be detected analytically in the deposited layer, so it is only present in the layer in traces that remain below the detection limit.
• the phosphating takes place in the temperature range from 50 to 70 ° C., preferably in the range from 60 to 65 ° C. The process is suitable for both spray and dip application.
• electrolytically galvanized steel strip is also increasingly being used in body construction; in many cases the phosphating is already applied in combined galvanizing and pre-treatment lines and the material is supplied as galvanized, "pre-phosphated" steel.
• the phosphating should therefore also be suitable for subsequent cathodic electrocoating. Since iron cannot be built into the phosphate layer in the present case, layers with a cubic or cuboid structure must be created.
• the object of the invention is a method described below which fulfills the requirement.
• Acid phosphating solutions which, in addition to zinc, manganese and phosphate ions, can contain further metal cations and / or anions of oxygen-containing acids with accelerating action.
• the phosphate layers produced have mass per unit area of less than 2 g / m 2 , the preferred range is 0.9 to 1.6 g / m2. Layers in the range from 0.6 to 1.9 g / m 2 can be deposited.
• the acidic phosphating solutions are characterized in that the zinc cation content is in the range from 0.1 to 0.8 g / l, preferably 0.25 to 0.6 g / l.
• the content of manganese II cations is kept in the range of 0.5 to 2 g / 1, preferably 0.75 to 1.25 g / l.
• the free acid content is kept in a range from 4 to 8 points, preferably 5 to 7 points.
• the acid ratio (total acid / free acid) is kept in the range of 2.5 to 5 points, the preferred range is 2.8 to 4.5.
• the free acid score is defined as the number of milliliters of 0.1 N 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 of 0.1 N NaOH required to titrate 10 ml bath solution against phenolphthalein as an indicator until the first pink color.
• the process according to the invention is further characterized in that the phosphating baths contain nitrate.
• the cobalt content is preferably one part of cobalt per 100 to 150 parts of Zn and Mn 2+ .
• treatment times are deliberately kept short in view of the modern systems for the electrolytic galvanizing and phosphating of steel strips, 90 to 120 m / min speed of the strip. 5 seconds are not significantly exceeded, treatment times of 2.5 to 5 seconds are generally used.
• the phosphating is expediently carried out at elevated temperatures, in particular in the temperature range from 40 to 70 ° C., the temperature range from 45 to 55 ° C. being particularly suitable. Any technically useful way of applying the treatment solution is applicable. It is particularly interesting that the process according to the invention can be carried out both by 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 conveyor systems. If the surface of the electrolytically galvanized strip is oiled for the purpose of temporary corrosion protection, this oil must be removed by known, suitable means and methods before phosphating.
• the water-wettable electrolytically galvanized metal surface is expediently treated with activating solutions known per se before phosphating.
• the activators essentially contain titanium salts and phosphates, together with organic components. Information on suitable activation methods can be found in DE-OS 20 38 105 and DE-OS 20 43 085.
• the process according to the invention can also be advantageous for the process according to the invention to passivate the deposited conversion layers with dilute chromic acid and / or phosphoric acid.
• the chromic acid concentration is generally between 0.01 and 1 g / l. It is also possible to passivate the protective layers with dilute chromic acid, which contains chromium III ions.
• the concentrations generally used are 0.2 to 4.0 g / 1 CrO 3 (hexavalent chromium) and 0.5 to 7.5 g / 1 cr203 (trivalent chromium).
• phosphate layers are produced on electrolytically galvanized steel, which clearly show a cuboid or cuboid structure. This is proven by scanning electron microscope images. With the previously known method, also with the method described in DE-OS 32 45 411, this was not possible. Crystals with a needle-like shape were deposited. The method according to the invention thus achieves the object of providing a conversion layer suitable for the subsequent cathodic electrocoating on electrolytically galvanized steel produce. The type of layer described is also achieved on steel galvanically coated with a zinc-nickel alloy.
• a lighter colored conversion layer is produced. This is particularly desirable when the electrolytically galvanized and phosphated steel is used without further coating. In this case, phosphating is expected to significantly delay or suppress both the occurrence of the so-called “white rust” (formation of zinc corrosion products) and the “red rust” (iron corrosion products).
• the layers deposited from the acidic phosphating solutions according to the invention fulfill this task significantly better than layers deposited from conventional treatment baths.
• the acidic phosphating baths according to the invention work very low in sludge. This is a not insignificant advantage for practical use.
• the deposited layers consist predominantly of Zn phosphate.
• the small amounts of cobalt contained in the phosphating baths lead one to expect that, given the low surface masses deposited according to the invention, cobalt can no longer be detected in the layers, since the content is below the detection limit. It is surprising, however, that manganese is only found in very small amounts in the layers deposited from the acid phosphating solutions according to the invention.
• An electrolytically galvanized surface was treated at 30 ° C. with a solution which contained an activating agent containing titanium, as described in DE-OS 20 38 105, in an amount of 3 g / l.
• the activated surface was then treated with a solution of the following composition at 50 ° C:
• the free acidity was 6 points and the total acidity was 19.6 points.
• the sheet was rinsed with water and then passivated with a solution containing Cr 6+ + Cr 3+ and dried.
• the mass per unit area of the phosphate coating was 1.15 g / m 2 .
• a sheet treated in the same way was cathodically electrocoated and provided with a filler and topcoat that are common in the automotive industry.
• the painted surface was bombarded with steel granules under defined conditions and then stored at 40 ° C. for 40 h in a 5% saline solution. Then the sheet was again bombarded with steel granules.
• the sheet according to Example 1 was given characteristic values 3 to 4.
• Example 1 The activation of the sheets was carried out as shown in Example 1, as was the passivation following the phosphating.
• the phosphating time and the temperatures also correspond to Example 1.
• the same amounts g / 1 as in Example 1 were used, but the solution contained no cobalt.
• Free acid and total acid as in Example 1.
• the weight per unit area of the phosphate coating was 1.3 g / m2.
• Test sheets made using conventional methods e.g. according to the method proposed in DE-OS 32 45 411, show a significantly poorer behavior after the tests described.

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

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• 1985
  • 1985-10-18 DE DE19853537108 patent/DE3537108A1/de not_active Withdrawn
• 1986
  • 1986-10-10 EP EP86114075A patent/EP0219779B1/fr not_active Expired - Lifetime
  • 1986-10-10 DE DE8686114075T patent/DE3682865D1/de not_active Expired - Fee Related
  • 1986-10-10 AT AT86114075T patent/ATE70314T1/de not_active IP Right Cessation
  • 1986-10-17 ZA ZA867903A patent/ZA867903B/xx unknown
  • 1986-10-17 KR KR1019860008719A patent/KR930010339B1/ko not_active IP Right Cessation
  • 1986-10-17 AU AU64156/86A patent/AU581789B2/en not_active Ceased
  • 1986-10-17 ES ES8602645A patent/ES2002422A6/es not_active Expired
  • 1986-10-18 JP JP61248251A patent/JPH086183B2/ja not_active Expired - Lifetime
  • 1986-10-20 CA CA000520902A patent/CA1240905A/fr not_active Expired
  • 1986-10-20 US US06/921,665 patent/US4762572A/en not_active Expired - Fee Related

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