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
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions
• • 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
  • C23C22/78—Pretreatment of the material to be coated

Definitions

• the invention relates to a method for producing phosphate coatings on composite parts made of steel and galvanized steel by alkaline cleaning, rinsing with an aqueous rinsing bath and zinc phosphating, and its use for preparing these composite parts for the subsequent painting, in particular electrocoating.
• the object of the invention is now to provide a method for producing phosphate coatings on composite parts made of steel and galvanized steel, the use of which does not give rise to the abovementioned disadvantages and which is nevertheless simple in terms of process and can be carried out without significant additional cost.
• 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 the cleaned composite parts are rinsed with a rinsing bath containing at least 0.2 g / l alkali borate, at least 0.1 g / l alkali silicate and at least 0. Contains 05 g / l alkali nitrite.
• the term steel is understood to mean unalloyed to low-alloy steel, as it e.g. in the form of sheets for body construction.
• galvanized steel includes e.g. Galvanizing by electrolytic and hot-dip and refers to zinc and zinc alloys, e.g. ZnNi, ZnFe, ZnAl.
• the process step of alkaline cleaning is carried out with aqueous alkaline, surfactant-containing solutions and the aim is to free the metal surfaces of oil, grease and dirt at least as far as is necessary for a subsequent, perfect phosphating.
• Disodium and trisodium phosphate condensed alkali phosphates, alkali silicates, alkali carbonates, alkali borates and alkali hydroxides can be used.
• Complexing agents such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, polyhydroxycarboxylic acid and phosphonates serve to avoid precipitation and to improve cleaning performance.
• titanium phosphate By adding titanium phosphate, the cleaning agent can be activated to activate the subsequent zinc phosphating.
• the surfactants are usually selected from the group of nonionic and anionic products.
• the pH of the solutions is usually in the range from 9 to 12, preferably between 9.5 and 11.5.
• the concentration of the cleaning baths is e.g. 1 to 40 g / l. They can be used in diving and / or spraying at temperatures between 30 and 95 ° C.
• the zinc phosphating processes used in the context of the invention work with aqueous treatment solutions which contain 0.4 to 1.7 g / l Zn and in which the weight ratio of Zn: P2O5 is set to about 1: (6 to 60) and is maintained.
• the phosphating baths can additionally contain one or more further divalent cations. These preferably include Ni, Mn, Mg and Ca. They are usually added in concentrations of 0.1 to 2 g / l, partly incorporated into the phosphate layer and lead to a further improved layer quality under special conditions.
• the phosphating baths also contain at least one oxidizing agent from the group consisting of chlorate, bromate, nitrate, nitrite, peroxide and organic nitro compound, e.g. meta-nitrobenzenesulfonate.
• the dosage is carried out in the amount and manner customary in phosphating technology.
• the phosphating baths can also contain other additives known per se, such as single and complex fluorides, chlorides, sulfates, polyhydroxycarboxylic acids, polyphosphates, ammonium, alkali, copper, cobalt ions and surfactants.
• the phosphating baths are used in spraying and / or dipping at bath temperatures of 25 to 70 ° C and treatment times of 0.45 to 10 minutes.
• the rinsing baths used in the process according to the invention contain additives which are selected, for example, from the group of sodium and potassium borates, sodium and potassium silicates and sodium and potassium nitrite.
• the rinsing treatment can take place in one step or in several steps.
• the cleaned composite parts should be treated with a rinsing bath which Contains alkali borate, alkali silicate and alkali nitrite in a total amount of maximum 5 g / l.
• a further advantageous embodiment of the invention provides for the composite parts to be activated before the zinc phosphating with an activation bath containing titanium phosphate, to which tetraalkali pyrophosphate is added in an amount of at least 1 g / l.
• tetraalkali pyrophosphate as such or e.g. in the form of another pyrophosphate-containing substance and the amount of alkali required for neutralization. It is easiest to add tetrasodium and / or tetrapotassium pyrophosphate to the activation bath.
• the maximum concentration of tetraalkali pyrophosphate is preferably 4 g / l.
• the activation bath gradually loses its effectiveness over time. Accordingly, it is supplemented with a concentrate containing fresh titanium phosphate. In order to avoid an excessive increase in the salt concentration, a part of the bath can be drained off and reattached from time to time.
• the tetraalkali pyrophosphate is preferably metered in such a way that the optimum concentration is maintained in the bath.
• the temperatures of the rinsing and activating baths are preferably kept below 40 ° C.
• the treatment times should be chosen so that a complete exchange of the liquid adhering to the composite parts from the previous treatment stage is ensured. Depending on the shape of the parts and the type of flushing, dipping or spraying - 0.2 to 1 min are sufficient. In many cases, the contact times with the rinsing bath and activation bath are significantly longer due to the specified system dimensions and the transport speed of the workpieces. The advantages of the method according to the invention are particularly evident under these conditions.
• the process according to the invention produces phosphate coatings of high uniformity.
• the formation of stripes and specks is avoided.
• rinsing with a rinsing bath containing alkali borate, silicate and nitrite is sufficient as a condition to to get perfect phosphate coatings.
• the phosphate coatings produced with the method according to the invention can be used with advantage in all fields in which phosphate coatings have been used. However, they are preferably suitable as a preparation of composite parts made of steel and galvanized steel for painting, in particular electro-dip painting.
• Example 1 in which steps 3 and 4 were only rinsed with water and in which the activation bath was free of tetraalkali pyrophosphate, led to deficient phosphate coatings.
• Example 2 shows in particular that the addition in the rinsing baths leads to an improvement, but speck formation on the galvanized area of the composite part is not yet avoided.
• Example 3 illustrates that, with a suitable choice of the rinsing bath, flawless phosphate layers are obtained on the steel parts, but because of the activation bath used, without the required addition of tetraalkali pyrophosphate, specks still occur on the galvanized area of the composite parts.
• Example 4 the steel surface is slightly streaky because of the insufficient addition of effective rinsing components with perfect formation of phosphate layers in the galvanized area.
• Example 5 with the correctly selected additives both in the rinsing bath and in the activation bath leads to flawless results in both areas of the composite parts.
• Example 6 which represents a repetition of Example 5 while omitting a separate activation treatment, shows that in this case too, perfect phosphate layers can be obtained on both surface areas. However, the weight per unit area of the phosphate layers is somewhat higher than in Example 5.

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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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• 1986
  • 1986-10-17 DE DE19863635343 patent/DE3635343A1/de not_active Withdrawn
• 1987
  • 1987-08-19 CA CA000544880A patent/CA1306929C/fr not_active Expired - Lifetime
  • 1987-10-03 DE DE8787201891T patent/DE3768599D1/de not_active Expired - Lifetime
  • 1987-10-03 EP EP87201891A patent/EP0264151B1/fr not_active Expired - Lifetime
  • 1987-10-03 ES ES87201891T patent/ES2020552B3/es not_active Expired - Lifetime
  • 1987-10-07 US US07/106,165 patent/US4867853A/en not_active Expired - Lifetime
  • 1987-10-15 JP JP62258497A patent/JP2607549B2/ja not_active Expired - Lifetime
  • 1987-10-19 AU AU79913/87A patent/AU7991387A/en not_active Abandoned
  • 1987-10-19 GB GB8724432A patent/GB2199850B/en not_active Expired - Fee Related

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