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
  • C23C22/78—Pretreatment of the material to be coated
  • C23C22/80—Pretreatment of the material to be coated with solutions containing titanium or zirconium compounds

Definitions

• the invention relates to an improved method for activating metal surfaces made of iron or steel and zinc or galvanized steel or aluminum or aluminized steel before phosphating said surfaces with phosphating baths containing zinc ions, in particular before so-called low-zinc phosphating.
• the cleaning, degreasing and activation solutions were usually applied to the metal surfaces to be treated in a spray, immersion or combined spray-immersion process and - when adjusted to a weakly acidic to alkaline pH value - contained surface-active substances (wetting agents, emulsifiers) builder substances (Sodium hydroxide, alkali metal carbonates, alkali metal phosphates) and optionally also silicates and borates and substances which have a layer-refining and activating effect, for example titanium compounds such as titanium phosphates.
• aqueous solutions which have a cleaning and activating effect at the same time, are described in the context of processes for pretreating metal surfaces before phosphating in DE-PS 29 51 600 and 32 13 649.
• DE-AS 12 87 892 also discloses the use of aqueous alkaline solutions which contain an alkali borate and which can contain wetting agents and / or activators and are preferably free of silicate for the treatment of iron and steel surfaces before phosphating with a zinc phosphate solution.
• Such alkali borate solutions also combine the cleaning, degreasing and activation step and are usually applied by spraying, which is why they contain little foaming, surface-active substances in order to prevent excessive foaming.
• low-zinc phosphating processes have increasingly been used, as are described, for example, in DE-PS 22 32 067. These enable significantly better corrosion protection for the usually subsequent electrocoating.
• Such low-zinc phosphating processes are much more sensitive to changes in the process parameters and impurities that are introduced into the phosphating bath with the metal sheets to be coated, so that the step of activating the metal surface is of much greater importance.
• a destabilization of the activation baths occurs, for example, in that so-called "hardness agents" of the rinsing water are introduced into the activation baths from the rinsing baths connected between cleaning and activation.
• Such destabilization can be avoided in various ways.
• demineralized water can be used for rinsing. However, this would make the entire process drastically more expensive.
• tap water for the intermediate rinse cycle a different water hardness should be expected. This necessitated a formulation of the activation baths that was adapted to the respective water conditions.
• the quality of the zinc phosphate layer applied by phosphating was satisfactory only within very narrow limits, which are sometimes difficult to achieve in practical operation, of the free acid content in the phosphating bath. Only if the free acid content in the phosphating solution was kept within narrow limits by adding alkali could zinc phosphate layers be obtained, which formed a good basis for the subsequent electrocoating. Even with a low free acid content, there is an increased accumulation of sludge in the bathroom.
• the object of the present invention was to provide a bath which was stable against the abovementioned influences for the separate activation prior to zinc phosphating in particular a low-zinc phosphating, which not only allows rapid and economical phosphating of metal surfaces, but also enables improved corrosion protection through the subsequent phosphating.
• the activating bath should make it possible to expand the relatively narrow limits of the process parameters for the subsequent phosphating and, in particular, make it possible to keep the free acid content in the subsequent phosphating bath within further limits compared to earlier. These advantages should be particularly noticeable on steel surfaces.
• the invention relates to a method for activating metal surfaces made of iron, steel, zinc, galvanized iron or steel, aluminum or aluminized iron or steel between the steps of cleaning / rinsing and phosphating with phosphating baths containing zinc ions, in particular low-zinc phosphating, using aqueous solutions , alkaline solutions containing titanium ions and phosphate ions, which is characterized in that the activation solutions to a pH of 8 to 10 adjusts and additionally they disodium tetraborate and / or other soluble alkali or alkaline earth metal borates in such amounts that the weight ratio based on B2O7 PO4: borate is 1:> 1.
• cleaning and degreasing solutions of conventional composition can be used in a cleaning and degreasing step with subsequent water rinsing.
• These solutions usually have a pH in the range from 6 to 13 and usually contain builders, such as, for example, phosphates, carbonates, silicates or hydroxides of the alkali metals. Corresponding ammonium compounds can also be used for this.
• emulsifiers such as, for example, adducts of ethylene oxide with fatty alcohols, alkylphenols, fatty amines or polyoxypropylene glycols.
• Condensed phosphates or other complexing compounds are usually also used as builders of the cleaning solutions.
• hydroxypolycarboxylic acids such as citric acid, nitrilotriacetic acid or ethylenediaminetetraacetic acid, phosphonic acids or other common complexing agents are suitable.
• the activation solutions used in the process according to the invention contain titanium ions in amounts of up to 100 ppm.
• the content is usually in the range between 1 and 100 ppm, a range from 1 to 20 ppm being preferred.
• Activation solutions which contain titanium ions in amounts of 1 to 10 ppm are used with particular advantage in the process according to the invention.
• the phosphate ion content can be up to 3000 ppm. It is usually in the range from 100 to 3000 ppm and preferably in the range from 200 to 1500 ppm. Activation solutions containing phosphate ions in amounts of 200 to 600 ppm are used with particular advantage.
• the pH of the activation solutions is now set to a range from 8 to 10. According to the invention, this range must not be exceeded or fallen short of, since a satisfactory activation of the metal surfaces mentioned is not possible at pH values less than 8 and greater than 10. Rather, falling below the pH value means that the phosphate layers formed are no longer closed and / or their layer weight increases in an undesirable manner. Exceeding the pH value above 10 likewise leads to a significant deterioration in the quality of the phosphating layers applied subsequently. In addition then a shorter service life of the activation bath is to be expected, ie the time in which the bath works effectively.
• disodium tetraborate and / or other soluble alkali metal or alkaline earth metal borates are also added to the activation solutions in addition to the titanium ions and phosphate ions.
• Preferred borate additive is borax, i.e. Disodium tetraborate decahydrate.
• borax i.e. Disodium tetraborate decahydrate.
• other soluble alkali or alkaline earth metal borates instead or together therewith. Borates of sodium or potassium, for example, are suitable as such.
• the amount of borate added or borates added is in such a range that the weight ratio PO4: borate or PO4: borate, based on B2O7, is 1:> 1, ie that in the activation solutions used for the process according to the invention there is always an excess by weight Borate or borates versus phosphate is present.
• the weight ratio which is purely mathematically based on B2O7, is preferably 1: 1.01 to 1:20 and is particularly advantageously in the range from 1: 2 to 1:10, i.e. it is particularly advantageous to use a 2- to 10-fold excess weight of borate compared to the amount of phosphate used.
• the temperature of the activation bath can generally range from 10 to 50 ° C.
• the activation solutions to be used in the process according to the invention can be applied to the metal surfaces by spraying, dipping or in a combined spraying / dipping process.
• the use of the method according to the invention leads to significant improvements in the activation of metal surfaces made of iron, steel, galvanized iron or steel, aluminum or aluminized iron or steel.
• the activation baths are stable against the influence of any hardness-forming agents even when using tap water and cannot be destabilized by alkali or dirt from the metal surfaces to be activated. Accordingly, re-sharpening of the activation solutions with activating components and / or fully demineralized water is only necessary to maintain the excellent activating effect to the extent that the bath volume carried out with a larger metal throughput is supplemented.
• the treatment of the metal surfaces by the activation method according to the invention also enables a faster and better quality phosphating of the metal surfaces mentioned. It also shows that the dependence of the subsequent phosphating step with respect to the free acid content is substantially less and that this process is therefore significantly less dependent on the process parameters. For example, the free acid content in the subsequent phosphating step can fluctuate within substantially larger limits, so that an alkali addition is essential in the process step is less often required. In addition, the sludge formation in the phosphating bath is significantly reduced, which significantly extends the maintenance intervals of the phosphating bath.
• all phosphating baths based on zinc phosphate are generally suitable, which may also contain other layer-forming cations.
• the method according to the invention is suitable for a subsequent so-called "low zinc phosphating", as described for example in DE-PS 22 32 067.
• the phosphating solutions to be used here are characterized by a weight ratio of zinc to phosphate such as 1: (12 to 110).
• a surprising additional advantage results from the fact that the activation solution according to the invention alone has a significantly less influence on the subsequent phosphating step due to its chemical composition.
• the activation solution which may have been carried into the subsequent phosphating bath, has a buffering effect due to its borate or borate content and does not impair the effectiveness of the phosphating solution.
• the process according to the invention for activating the metal surfaces before zinc phosphating can optionally also be carried out with solutions which, in addition to titanium and phosphate ions and the abovementioned borates, also contain other components which are customary for activation solutions.
• the known additives for example polycondensed phosphates, citrates, salts of ethylenediaminetetraacetic acid, nitrilotriacetates, etc., can be mentioned as such. However, it should be emphasized that these components are in no way necessary. This is a simplification compared to previously used cleaning and activation solutions.
• a rinse cycle with water can optionally be inserted after the activation step and before the actual phosphating.
• this flushing is not mandatory and does not add anything to the advantageous effects of using the separate activation method according to the invention.
• Example 1a according to the invention:
• the steel parts were then sprayed for 2 minutes at 48 ° C. with a phosphating bath which had the following composition: PO4: 20.2 g / l Zn: 1.0 g / l ClO3: 1.5 g / l NO2: 0.05 g / l Free acid score: 1.0 Total Acid Score: 24.2
• the phosphated steel parts were then rinsed with water, rinsed with distilled water and dried in a drying oven.
• the phosphate layers formed were finely crystalline, closed and very uniform. These excellent phosphate layers also resulted after the bath had been in operation for about 8 hours. Resharpening of the activation bath was not necessary.
• the layer weight of the phosphate layers was 1.4 g / m2.
• the phosphate layers formed were initially fine-crystalline and closed. After approx. 4 hours of operation, however, problems occurred in the layer formation: the phosphate layers became coarsely crystalline and were no longer closed. They had a layer weight of 3.5 g / m2.
• the steel parts were then sprayed for 2 minutes at 48 ° C. with a phosphating solution which had the following composition: PO4: 20.0 g / l Zn: 1.0 g / l ClO3: 1.5 g / l NO2: 0.05 g / l Free acid score: 1.0 Total Acid Score: 24.2
• the steel parts were then rinsed with water, rinsed with distilled water and dried in a drying oven.
• the phosphate layers formed were initially fine-crystalline and closed. After an operating time of about 4 hours, the phosphate layers became coarsely crystalline and were no longer closed. The layer weight of the phosphate layers was 3.2 g / m2.
• Example 1a above shows the advantages of the method of operation according to the invention: phosphate layers, which have a desired, low layer weight, result even with a longer operating time.
• examples 1b and 1c according to the prior art result in poorer quality phosphate layers after a certain operating time, which also had a higher layer weight.
• the parts were then sprayed for 2 minutes at 52 ° C. with a phosphating bath which had the following composition: PO4: 19.0 g / l Zn: 0.7 g / l ClO3: 1.8 g / l m-nitrobenzenesulfonic acid: 0.4 g / l Free acid score: 1.5 Total Acid Score: 23.0
• the parts were then rinsed with water, rinsed with distilled water and dried in a drying oven.
• the phosphate layers formed were finely crystalline, closed and very uniform. Even after an operating time of approx. 8 h, these excellent phosphate layers resulted, which had a layer weight of 1.5 g / m2. It was not necessary to sharpen the activation bath. Due to the procedure according to the invention, the phosphating bath could be operated with a higher free acid score. This immediately results in less sludge in the phosphating bath during the operating time.
• Examples 2a to 2c above show the advantage of the procedure according to the invention: the subsequent phosphating bath can also be run with a high number of free acid without the phosphate layers formed having any loss in quality. This means that when the method according to the invention is carried out, a considerably wider range of points with regard to the number of free acids in the subsequent phosphating bath is possible. Furthermore, phosphate layers with a lower layer weight result when the method according to the invention is carried out. In addition, a higher free acid content in the phosphating bath has a positive effect on the reduction of incrustations on the heating registers of the phosphating bath.
• Electrolytically galvanized steel parts were cleaned for 3 minutes by immersion at 55 ° C. with a commercially available alkaline cleaning solution (containing 20 g / l NaHCO3, 6 g / l Na3PO4 and 4 g / l nonionic surfactant) and rinsed with water.
• the parts were then treated with an activation solution containing the following components for 2 minutes at 20 ° C.: PO4: 600 mg / l Ti: 15 mg / l Na2B4O7. 10 H2O: 5200 mg / l pH: 8.9 Water with 4 ° dH was used to prepare this solution.
• the steel parts were then treated for 3 minutes in a dipping bath at 55 ° C. with a phosphating bath ches had the following composition: PO4: 19.5 g / l Zn: 1.3 g / l ClO3: 2.0 g / l NO2: 0.03 g / l Free acid score: 1.3 Total Acid Score: 23.5
• the parts were then rinsed with water, rinsed with distilled water and dried in a drying oven.
• the phosphate layers formed were finely crystalline, closed and very uniform; they had a layer weight of 2.5 g / m2.
• the phosphate layers formed in the subsequent phosphating were coarsely crystalline and uneven; they had a layer weight of 4.5 g / m2. Furthermore, corrosion products in the form of white defects were observed on the surface.
• Examples 3a and 3b above also show the advantages of the process according to the invention: the result is a comparatively low layer weight of the phosphate layers formed for electrolytically galvanized steel parts; there was no speck formation (white missing parts).
• the parts were then sprayed for 2 minutes at 52 ° C. with a phosphating bath which had the following composition: PO4: 19.0 g / l Zn: 0.7 g / l ClO3: 1.8 g / l m-nitrobenzenesulfonic acid: 0.4 g / l Free acid score: 1.5 Total Acid Score: 23.0
• the parts were then rinsed with water and dried in a drying oven.
• the phosphate layers formed were coarsely crystalline and not closed; they had a layer weight of 3.5 g / m2.

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• 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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• 1985
  • 1985-11-28 DE DE19853541997 patent/DE3541997A1/de not_active Withdrawn
• 1986
  • 1986-11-19 EP EP86116027A patent/EP0224190B1/fr not_active Expired - Lifetime
  • 1986-11-19 DE DE8686116027T patent/DE3681562D1/de not_active Expired - Fee Related
  • 1986-11-24 US US06/933,832 patent/US4707193A/en not_active Expired - Fee Related
  • 1986-11-26 CA CA000523837A patent/CA1267062A/fr not_active Expired - Fee Related
  • 1986-11-26 ES ES8603187A patent/ES2002664A6/es not_active Expired
  • 1986-11-27 ZA ZA868990A patent/ZA868990B/xx unknown
  • 1986-11-28 JP JP61285816A patent/JPS62133082A/ja active Pending

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