DE3814391A1 - Activation of metal surfaces before zinc-phosphating - Google Patents

Abstract

The invention relates to products based on aqueous solutions and/or dispersions of titanium phosphates for the activation of metal surfaces before zinc-phosphating, which are characterised in that they give a pH from 7 to 10 in water and contain titanium, phosphates and finely particulate layer silicates having a cation exchange capacity, of the type of alkali metal magnesium silicate or alkali metal silicate, whose primary particles predominantly have a diameter of less than 30 mu m, and, if appropriate, also further components usual in activating agents, and to a process for activating metal surfaces with such aqueous solutions and/or dispersions at temperatures in the range from 10 to 40@C.

Description

The invention relates to means and a method for activation of metal surfaces before zinc phosphating, whereby defi layered silicates can be used.

The zinc phosphating, i.e. the treatment of metal upper surfaces with aqueous solutions containing zinc ions is a long-used process with which surfaces made of iron, steel, zinc or galvanized steel or aluminum or aluminized steel with regard to their corrosion resistance be improved and thus be prepared at the same time that uniform training and liability later on brought organic coating on the metal surfaces is guaranteed. Is of interest in application technology In this context, the so-called "low zinc Ver drive ", in which the ratio of zinc to phosphate ions in of the treatment solution is 1: (12 to 110) and the metal surface areas from the above-mentioned group especially for the Be layering with surface lacquers by means of cathodic elec Trotauchlackierung (K (E) TL) prepared.

Pretreat the respective metallic surfaces The actual phosphating step has an eminent part big influence on the training of a high quality Zinc phosphate layer and thus also has a direct influence  to the desired procedural goals, namely a high cor protection against corrosion and good paint adhesion on the metalli surfaces.

Therefore, the procedural steps that the The actual zinc phosphating are upstream: The cleaning with an alkaline and / or acidic cleaner and the closing activation of the metallic surfaces. While acidic cleaners often have an adverse impact on training of the zinc phosphate layers, which i.a. to a ver coarsening of the layer structure and an extension of the time leads to the formation of a uniform surface covering zinc phosphate layer is required, the Activation step the undesirable effects of cleaning counteracting reagents. Usually both are today Steps separated, especially if the Phosphating solution in the low zinc phosphating process in to be applied to a diving process.

One differentiates between mechanical activation of the metal surfaces on the one hand, usually by brushing, Sanding or sandblasting the surfaces and chemical activation on the other. In the course of Chemical activation is achieved through special pre-rinse solutions before the actual phosphating, crystal seeds first the cleaned metal surfaces on which the Kri installation of zinc phosphate can begin. In practice only effective as nucleating agents are titanium (IV) proven orthophosphate. These activating agents will come before moves in a separate rinsing bath immediately in front of the phospha brought into contact with the metal surfaces. In out In some cases it is also possible to use an activating agent if necessary add a mildly alkaline detergent bath.  

Activation by such titanium orthophosphate solutions causes a uniform and closed zinc phosphate layer to form on the entire metal surface. Crystals of zinc phosphate should form as close as possible to one another as quickly as possible (increase in the nucleation rate). This layer refinement is aimed at reducing the porosity of the resulting phosphate layer. In this way it can also be achieved that the weights per unit area (masses per unit area of the zinc phosphate layers, often also referred to as "layer weight") decrease. These are given in g zinc phosphate / m metal surface; The industry is demanding surface weights of 1.2 to 4.0 g / m ² as a primer for paints. In addition, the minimum phosphating time, ie the time until the metal surfaces are completely covered with a closed zinc phosphate layer, can be significantly reduced by activating the metal surfaces.

Activation of metal surfaces with titanium orthophosphates is usually part of a multi-stage process, in where the metal surfaces are mechanically and chemically cleaned, pickled, activated and phosphated. It can be done before be partaking of the steps of treating the metal surface with the different chemicals through steps of Rinse the workpieces with water to separate them.

The stabilization of bathroom solutions in which - separately from the cleaning step - metal surfaces are to be activated by treatment with titanium orthophosphates is a problem that has not yet been solved satisfactorily to this day. In contrast to baths, which combine the cleaning, degreasing and activation of the metal surfaces with each other and whose cleaning effectiveness can be maintained over a long period of time, no stable activation baths could be made available that make it possible, despite a constant concentration of activating agent in the Bad to perform a good activation of metal surfaces over a long period of time. In practical operation, ie in a large number of successive process steps of cleaning, rinsing, activating, rinsing and subsequent phosphating, the activation baths containing titanium orthophosphate are exhausted. Despite maintaining the level of activating agent in the bath solution, the activating effect wears off relatively quickly.

This is significantly reflected in an increase in the area weight of the zinc phosphate formed on the metal surfaces phatschichten down. The desired, initially small areas ch weights on metal surfaces in fresh activation Activation baths are activated on workpieces that follow activation baths are activated for a longer period of time values that are no longer acceptable to users.

In addition, it was repeatedly found that the following phosphate layers formed then phosphating had great roughness, if a lot of work pieces have been treated in the respective activation bath were. This also indicated an insufficient or bad one Activation of the metal surfaces.

From all this it is clear that the constant control of the Concentrations of all components of an activation bath or resharpening it with individual components alone not sufficient to activate the metal surface well ensure over a longer term. This is particularly disadvantageous if - as with the so-called "low zinc phosphating" of zinc surfaces or galvanized steel surfaces, such as those recently used in Ka rosseriebau are used more often - a bad act immediately to rough, poorly formed phosphate stratification leads. The immediate result is mistakes  in the painting of such poorly activated and after following insufficiently phosphated metal surfaces.

One of the many causes of destabilization of the Activation baths containing titanium phosphate are introduced of alkaline earth metal ions from the rinsing bath, which in total ver drive between cleaning the metal surfaces and the Activation is arranged. The introduction of the so-called "Hardening agents" in the rinsing water could be avoided by that you use demineralized water for rinsing. This however, the procedure would be significantly more expensive. As a result Tap water used for the intermediate rinse cycle, must have different water hardness and therefore different content of alkaline earth metal ions in the rinsing water will. Suitable complexing agents, such as phosphates, EDTA, nitrilotriacetate, phosphonylated organic compounds or citrates would have to be in the activation bath in concentrations be added by the content of hardness in the rinse water are dependent. However, such additives interfere with activation and subsequent phosphating of the metal surfaces in un desirable way. They also complicate automation of the overall process because of the need to recipe the Activation bath always the current process parameter to adapt.

In DE-PS 33 07 158 the use of natural highly swellable sodium bentonites to stabilize Activation baths described. Crucial application technology The disadvantages of these stabilizing agents lie therein founds that the layer-refining effect by the named layered silicates is greatly reduced. Coarse crystalline, uneven zinc phosphate layers result in their Addition to the activating agents containing titanium phosphate. The  further disadvantages lie in the fact that the above Layer silicates themselves because of their mineral origin high cleaning effort and admixtures (e.g. aluminum minium silicates), which have the activation in particular by dissolving aluminum ions through the acidic phospha animal solution.

The object of the present invention was to fight against destabi Influencing influences stable bath for separate activation of metal surfaces before zinc phosphating, in particular prior to low-zinc phosphating make a compared to previously known activation baths significantly longer service life with the same quality of shares crossing of metal surfaces. The over a long time consistently good activation should be followed by a quick one le and economical phosphating of the metal surfaces possible ben and thus the corrosion protection of the phosphate layer on the improve treated metal surfaces. Another job the invention was the quality of the activation of Me tall surfaces over a large number of treated sheets without Change the bath fluid and thus improve the relative narrow limits of the process parameters for the following Expand phosphating.

Surprisingly, it has now been found that activation of Me metal surfaces through activation baths containing titanium phosphate at a high quality level with long service life of the bathrooms depending on the water hardness of the preparation water used for this is possible if you use the separate activation baths finely divided synthetic, mica-like, trioctahedral Al Potassium magnesium and / or alkali silicates with pronounced cat ion exchange properties and acid resistance added.  

The invention relates to compositions based on aqueous solutions and / - or dispersions of titanium (IV) phosphates to activate Metal surfaces before zinc phosphating caused by this are characterized in that they have a pH of 7 to in water Have 10 and 0.001 to 0.2 g / l titanium, 0.1 to 4 g / l one or more phosphates and 0.05 to 20 g / l one or more rer, cation-exchanging synthetic alkali magnesium and / or alkali silicates with layer structure and given if still more, usual in such activating agents Components included.

The invention also relates to a method for activation of metal surfaces using one or more titanium aqueous solutions and / or dispersions containing phosphates after alkaline cleaning and rinsing with water and before Phos phating with aqueous solutions containing zinc phosphates, which is characterized in that the metal surfaces in a manner known per se at temperatures from 10 to 40 ° C., preferably at 20 to 40 ° C, particularly preferably from 25 to 30 ° C, treated with aqueous solutions and / or dispersions, which have the above composition.

Metal surfaces with the activation according to the invention detached from alkaline cleaning and degreasing can be activated for the subsequent phosphating Surfaces made of iron, steel, zinc, galvanized iron or Steel, aluminum or aluminized iron or steel. Be The activating agents according to the invention are particularly suitable for the activation of surfaces made of steel, zinc, galvanized Iron or galvanized steel, as has recently been used for provision of motor vehicle bodies will.  

Before activation, such metal surfaces are usually used surfaces in a separate cleaning and degreasing step of surface contamination or grease residues exempted from previous machining processes. Such Cleaning and degreasing solutions have one in technology common composition today. The pH of 1% solutions is usually in the range of 6-13, the more in alkaline pH values are preferred. The Cleaning and degreasing solutions usually contain Builders such as phosphates, carbonates, silicates and / or hydroxides the alkali metals. Corresponding ammonium compounds find use. Additional components of such common ones Cleaning solutions are anionic or non-ionic mesh agents and emulsifiers, such as addition products of ethylene oxide on fatty alcohols, alkylphenols, fatty amines and / or polyoxypropylene glycols. Ent for complexation in water alkaline earth metals are also usually condensate based phosphates or others, per se from the prior art known complexing agents such as polycarboxylic acids (Citric acid, nitrilotriacetic acid or ethylenediaminetetra acetic acid), phosphonic acids or other common com plexer included.

After cleaning the metal surfaces with such, mostly alkaline cleaners are treated with Water to make cleaner residue more or less complete to remove from the metal surfaces and such residues not to be dragged into the subsequent baths.

In the subsequent process step, those to be treated Activate metal surfaces in a separate bathroom with solutions fourth, the activating component titanium (IV) phosphate in contain aqueous solutions and / or dispersions. Such  Titanium phosphates can be according to the prior art known methods are prepared and are the expert then available to activate metal surfaces.

The activating agents according to the invention, without exception Based on aqueous systems are composed, have a pH in Range from 7 to 10. This area must not over- or are below, because at pH values <7 and <10 a be peaceful activation of the metal surfaces not possible is. Falling below the pH value means that due to poor activation in the following phospha formation step no longer formed are closed. In addition, the weight per unit area increases Phosphate layers in an undesirable manner. An override The pH value also has a value above 10 poor activation performance, so that in the after subsequent phosphating also a significant deterioration to observe the quality of the applied phosphate layer pay attention. In addition, an overshoot of the pH value shortens to values above 10, the service life of the activation bathes, so that an effective activation of the metal surfaces for phosphating over a much shorter time possible is.

In addition to their pH, the activity according to the invention due to their content of the components titanium, phos phat (e) and cation-exchanging layered silicates draws. According to the invention, the total titanium content moves in the activating agents in the range of 0.001 to 0.2 g / l Titan in the activation solution. Activation are preferred medium containing 1 to 100 mg / l titanium, particularly preferably 5 to Contain 30 mg / l titanium. The activation solutions included the titanium, which is almost exclusively in the oxidation  stage (IV) exists, in bound form. Those in the asset Titanium compounds are mainly used Titanium phosphates, where such phosphates predominate, the two or contain more phosphate residues condensed together.

Another component of the activating agent according to the invention are phosphates that are present in the activation solutions in both Titan bound state, as well as in ionic form can. The latter are mostly in the solutions as Orthophos Contain phat ions made of polymer, two or more Phosphate groups condensed together contain phosphates arise through hydrolysis. It follows that the Akti vation solutions usually several different Phos contain phat species, but it is also possible that both the bound and the ionic phosphates finally are attributable to a species and for example Can be orthophosphates.

The content of one or more phosphates in Invention The activating agent is 0.1 to 4 g of one or more phosphate / l activation solution (100 to 4000 ppm). Be preferred quantity ranges of the phosphates are 0.1 to 3 g / l, be particularly preferably 0.2 to 1.5 g / l of one or more Phos phate. In particularly preferred and regarding their Akti result of excellent activation solutions the phosphate content is 0.2 to 0.6 g of one or more Phosphate / l application solution. Of these, the Orthophos phate can be used with particular advantage.

Another essential component of the shares according to the invention Cation-exchanging agents are layer silicates. According to the invention, it is possible in the activating agents certain layered silicates characteristic of this type  to use cation-exchanging properties. It However, it is also possible to use several layer silicates next to one another to be used, with the same properties can or may be similar or in their properties ten are different, so that they differ in their properties ten, especially their cations exchanging and swelling Ability to complement properties.

The quantity range in which the layered silicate (s) in the Activating agents are contained, is in the range of 0.05 up to 20 g of one or more layers that exchange cations silicates per liter of aqueous solution and / or dispersion of Activating agent. The exact salary depends on the Composition and combination of the layered grapes used cate, their cations exchanging properties in the foregoing the reason.

The mica-like layered silicates used according to the invention are derived from pyrophyllite and talc. By isomorphic sub institutions in the tetrahedron and octahedron layer receive the Layers of negative charges caused by interlayer cations be compensated. The general formula for this is

Me _x (H₂O) _n {Mg _2-3 (OH) ₂ [Si _{4- y} Al _y O₁₀]} with
Me = Na, K and Li; y = 0 to 0.5 and x = 0 to 1.

In these synthetic mica-like layered silicates, the magnesium ions predominate as cations in the octahedral layers. The Al ₃ O ₃ content in the layered silicates claimed according to the invention is below 10% by weight, preferably below 5% by weight.

Suitable from the series of trioctadic magnesium silicates synthetic hectorite and saponite to stabilize the Activation solutions particularly good.

The group of alkali metal phyllosilicates becomes magadiite
= Na₂Si₁₄O₂₉ · 11 H₂O and Kanemit = NaHSi ₂ O ₅ × 3 H ₂ O and similar Lich silicate-rich species present in the sodium form preferred according to the invention.

Technical details of classification, structure and chemistry important magnesium and alkali phyllosilicates can be Literature, for example

• - Ullmann's Encyclopedia of Technical Chemistry, 4th edition, Verlag Chemie, Weinheim (1982), Volume 21, pp. 365 ff;
• - Römpps Chemie-Lexikon, 8th edition, Franckh'sche Verlag Buchhandlung, Stuttgart (1987), Volume 5, pp. 3845-3847;
• - Rex W. Grimshaw, The Chemistry and Physics of Clays and Allied Ceramic Materials, 4th edition, Ernest Benn Ltd., London (1971), pp. 97-170;
• - R. C. Evans, Introduction to Crystal Chemistry, Walter de Gruyter, Berlin (1976), pp. 22-228;
• - F. Liebau, Structural Chemistry of Silicates, Springer Verlag, Berlin (1985);
• - H. Struntz, Mineralogische tables, 6th edition, Acade mix publishing company Geest & Protig KG, Leipzig (1977), pp. 429-469;

remove.

In principle, all good cations can not be exchanged water-soluble silicates with layer structure for hard water Use stabilization of the activation baths. The one here observed stabilizing effect is in accordance with the invention  preferably used layered silicates larger than that by the Cation exchange capacity alone would be expected. thats why the cation exchange capacity (e.g. calcium binding capacity as a measure of this) is only a selection criterion.

The causes of the observed additional effects are not yet enlightened. It is surprising, however, that in particular the alkali phyllosilicates and the mica-like trioctahedral Layer silicates show this additional effect.

As is also known from the literature mentioned above, the layered silicates differ in their solids properties and especially with regard to their swelling and cat ion exchange ability significantly different.

Are preferred in the activating agents according to the Invention used layered silicates whose cat ion exchange capacity at room temperature 20 mg CaO / g active sub punch exceeds, this cation exchange ability is given here as calcium binding capacity. Especially before Layer silicates whose calcium binding capacity are added at room temperature exceeds 50 mg / g of active substance.

A significant influence on the cation exchange capacity of the Layered silicate has the type of cation that the layer silicate is released to the aqueous phase, while at the same time Application-disturbing, hardness-forming cations of the Water bound. Layer silicates are therefore preferred in their sodium or potassium form in the activating agents used; Layer silicates are very particularly preferred of the sodium type.

Na⁺ or K⁺ ions are released into the aqueous phase, wäh calcium ions in the interstices of the silicates be stored.  

The layered silicates mentioned are alone or side by side usable according to the invention.

Since it is one of the tasks of the cation exchange layer silicate is to remove the hardness from the water, the optimal application quantity of the layer or layers results silicates from their calcium binding capacity and the water hardness of the aqueous phase. Activating agents according to the invention contain such an amount of layered silicates that the total cat ion binding capacity of the layer silicate (s) per liter Ak tivierungsbad the amount of hardness in the water by min at least 50 mg, preferably by 10 to 30 mg per liter of bath steps. The amount of layered silicates is calculated on the amount of CaO in the water, the amount of hardness is equivalent in the aqueous phase. Preferred execution forms of the activating agent according to the invention contain as Layered silicate component magadiite, kanemite, saponite and / or Hectorite in an amount of 0.05 to 20 g of the layered silicate per liter of activation bath.

In addition to the components listed above, the Activating agents according to the invention optionally also contain other components in such activation are common and generally known. Examples of this are known additives such as polycondensed phosphates, citrates and similar connections. The addition of such components is but not absolutely necessary, but worsens the achievable with the activating agents according to the invention results of the activation of metal surfaces. Just the possibility of adding such otherwise essential additives in the Not to have to use activating agents according to the invention sen is one of the advantages of the invention.  

Significant improvements in the activation of metal upper surfaces before the step of phosphating can be Aqueous activating agents described in more detail above by the achieve method according to the invention. After an alkaline Clean and rinse with water and before the step of the phos phatens with aqueous solutions containing zinc phosphates metal surfaces, especially steel surfaces, Zinc surfaces or galvanized steel surfaces, under use aqueous one containing one or more titanium phosphates Activate solutions and / or dispersions by these metal surfaces in a manner known per se at Tempe temperatures from 10 to 40 ° C with aqueous solutions and / or dispersers sions in contact, which is described in detail above and have a pH in the range of 7-10 and 0.001 to 0.2 g / l titanium, 0.1 to 4 g / l one or more Phosphates and 0.05 to 20 g / l of cations exchanging Contain layer silicates, the primary particles of which predominantly part have a diameter of less than 30 microns.

A preferred temperature range for the treatment of the Me talloberflächen with such aqueous solutions and / or dis persions is 20 to 40 ° C, the range of 25 to 30 ° C is particularly preferred. The raising of the asset Solutions and / or activation dispersions follows processes known per se from the prior art. So can NEN spraying process, immersion process or combined Spraying / dipping procedures are applied to the activation to bring medium into contact with the metal surfaces.

Also in the inventive method for activating the Metal surfaces can be customary, per se from the prior art Technically known individual steps can also be carried out in order to to achieve special results. So it is according to the invention  possible after the activation step and before the actual one Phosphating rinsing the activated workpieces with Water. However, this flushing is usually undesirable and contributes to the beneficial effects of using the he inventive method not. It is therefore in the sense of Invention preferred, the phosphating step immediately to connect the activation step according to the invention.

The application of the method according to the invention leads to significant improvements in the activation of metal surfaces. This is shown in the subsequent phosphating. The Phos phatierungsschritt can - as compared with activation processes of the prior art - are faster and brings phosphate layers that are much more finely divided than in herkömm Licher activation. In addition, the layer weights of the phosphate layers are significantly lower after the activation according to the invention. This advantage is particularly noticeable in the so-called "low-zinc phosphating. Low coating weights have always been sought for such phosphating processes in particular, but could only be achieved permanently in a few cases.

Another advantage is the fact that the activation bathrooms themselves are more stable against external influences, for example wise results from the composition of the invention Activation baths an increased stability against the influence any hardships that advance from the activation who rinsed in going rinsing step of the metal surfaces the. Also brought in from previous cleaning steps Alkali or loose dirt adhering to the metal surfaces, which is carried into the activation baths destabilizes not this one. A re-sharpening of the activation baths, i.e. the subsequent supply of activating components (titanium, phospha  te and / or layered silicates) and / or the subsequent addition of water, are excellent for maintaining activating effect of the activating agents according to the invention only required to the extent that the bath volume or content of active components with greater throughput of metal works pieces is added.

For the phospha following the process according to the invention All phosphating baths generally occur the base of zinc phosphate in question, which may also be can also contain other layer-forming cations. In particular in particular, the method of activation according to the invention shows of metal surfaces have a good impact on a subsequent one "Low zinc phosphating". This is from the state of the art nik known and described for example in DE-PS 22 32 067 ben. Those in such processes of "low zinc phosphate bathroom solutions are identified by a Weight ratio of zinc: phasphate from 1:12 to 110.

Particularly good results are in the activation and after following phosphating of zinc surfaces or galvanized Steel surfaces achieved. The corrosion protection on zinc top areas are particularly significantly improved. The repeated observed so-called "speck formation", i.e. the appearance badly phosphated - because poorly activated - stains on the metal surfaces, after activation with the he occurs activating agents according to the invention no longer.

The characterization and suitability assessment of means for Activation of metal surfaces, especially inventions according to the invention, titanium, one or more phosphates, cations exchanging layered silicates and possibly other ones Solutions or dispersions containing customary components requires experience in application technology. It is used  only possible and sensible when using the products according to the invention prepared aqueous dispersions, Test sheets treated with it, i.e. activated and then be phosphated. Only through this phosphating resulting quality of the zinc phosphate layers at a lot Number of sheets over a variety of activation and phos Phating cycles provide a secure basis for the appraisal sharing the activating effect of such Activationsmit tel. The test conditions are in the examples below described in detail and clarify that the invention and activation used in the described method medium a reproducibly high activation performance guarantee ren.

The following examples illustrate the invention explained.

1. General information

To the effect of the activating agents according to the invention Application of the proposed method compared to Pro To determine products of the prior art, the waiters surfaces of steel coupons (material St 1405 m, dimensions 10 cm × 20 cm × 0.75 mm) or of electrolytically galvanized steel sheet metal of the same dimensions in a standardized condition brought and then by means of a standardized dive phosphating process phosphated.

2. Individual steps of the phosphating process

• a) Mechanical cleaning and degreasing with absorbent paper;
• b) Dry cleaning and degreasing using a strongly alkaline cleaner at 80 ° C for 5 min .;  
• c) Rinsing with tap water (untreated city water with 18 ° d) at 20 ° C, 1 min ,;
• d) Activation with titanium phosphates (usual concentrations the dispersions in demineralized water: 20 mg titanium / l; 1300 mg phosphate / l; pH = 8.5; the dispersions were made by dispersing titanium phosphate powder in Water), application: 2 min at 25 ° C.
• e) Dip phosphating with a commercially available phosphate 4% by volume; Treat duration of the treatment: 3 min at 55 ° C;
• f) rinsing with tap water (see (c)) for 1 min at 20 ° C;
• g) rinsing with fully desalinated, i.e. demineralized water over 1 min at 20 ° C; and
• h) Drying with compressed air at 20 ° C to dryness.

In the following examples there are deviations from the ge named process steps listed separately.

The Phos used for this and the following examples Phating agent (see above list of procedures steps, step (s)) was selected so that the influence of the Activating agent on the layer weights of the phosphating, the morphology of the zinc phosphate crystals and the bath capacity the activation baths (for bath capacity: see below) in particular it became clear and the effectiveness of the activating agents was already clearly visible under standard conditions. In the this, as obtained in the examples below  can be generalized and are therefore also for others Process of zinc phosphating, especially for the so-called called "low-zinc" process, valid.

The steel coupons to be checked were part of the above be described standard phosphating method using Activation solutions treated, which layer silicates according to the characteristics given in Table 1 stopped. The preparation water for the activity according to the invention The hardness was 10 ° d. Type and amount of layered silicates added and those from the addition resul Table 2 below shows the pH values to take. The phosphating bath for the after activation used phosphating of the metal sheets contained (per liter):

• - 12.8 g phosphate,
• - 1.56 g zinc,
• - 1.35 g of chlorate and
• - 0.012 g nitrite.

The free acid score was 1 to 2.3, the score of total acid 16 to 18, the toner point number 1 to 2.

The score of free acid or total acid corresponds the amount n / 10 sodium hydroxide solution measured in ml, which is used for the Titra tion of 10 ml of a sample of the phosphating bath against 0.1% aqueous methyl orange solution (free acid) or 0.1% alcoholic phenolphthalein solution (total acid) ver was needed.

3. Characterization of the layer silicates used

The activating agents according to the invention have been exemplified with the four different layer silicate types hectorite, Saponite, Kanemite and Magadiite made.  

For comparison purposes, activating agents were also not used according to the invention, i.e. unsuitable in the sense of the invention,

Layered silicates (bentonite containing montmorillonite, a non-cation exchanging magnesium layer silicate talc as well a layer silicate type called "Dis-Thix-Extra") produced.

The average particle sizes  were in aqueous slurry the layer silicate using a laser beam device type SYM PATEC HELOS® determines. The slurries were for 20 sec treated with ultrasound, then in a closed circuit measure within 20 sec with gentle stirring. Means computer-aided evaluation of the diagram can then un indirectly  remove. The indication of the chosen destination method is particularly special for particle size measurements Importance. Other methods are usually used because of man if oversize sizes are taken into account too low average determined particle sizes.  

Table 1

Chemical composition, average particle diameter

d

, Calcium binding capacity and swelling capacity of the layer used silicates; the types mentioned under a to d are fiction moderate, the types mentioned under e to g are in the sense of the Erfin unsuitable.

To further characterize the layered silicates, they were first dried in vacuo at 100 ° C. for 15 h. The samples were then triturated well. X-ray diffraction spectra were recorded from the powder samples obtained in this way. All products showed the X-ray diffraction reflections characteristic of the respective type, which correspond to the reflections specified in the literature with regard to the position and relative intensity of the individual reflections. The calcium binding capacity of 1 g of layered silicate (active substance "AS") / l at an initial hardness of 30 ° d was used as a measure of the cation exchange capacity of the respective crystalline layered silicate. To determine the calcium binding capacity, 1 l of an aqueous solution containing 0.594 g of CaCl ₂ (corresponding to 300 mg of CaO / l = 30 ° d) was adjusted to a pH of 10 with dilute sodium hydroxide solution and 1 g of the layered silicate was added. The suspension formed was then for a period of 15 min. stirred vigorously at a temperature of 22 ± 2 ° C. After the layered silicate had been filtered off, the residual hardness X in the filtrate was determined by complexometric titration with ethylenediaminetetraacetic acid. The calcium binding like, expressed in mg CaO / g AS, was calculated from the titration result using the formula

CabV = (30- X) · 10

4. Determination of the basis weights (area-related masses, also called "layer weights")

The weights per unit area of a zinc phosphate layer applied after activation (given in g zinc phosphate / m ² metal surface) provide easily determinable, quantitative indications of the effectiveness of activating agents. The better the activation, the lower the resulting basis weights after the phosphating step. This is attributed to the layer-refining effect (smaller crystals, thinner layers) of the activating agent. As already mentioned above, thin, finely crystalline layers are particularly desirable in terms of application technology, since they form a particularly good basis for organic coatings or topcoats to be applied subsequently. In practice, the weights per unit area that are not activated but are otherwise based on the standard process of phosphated steel surfaces are between 4.5 and 6 g / m ² . After activation according to methods known from the prior art, the basis weights of zinc phosphate layers deposited on steel surfaces are between 3.0 and 4 g / m ² , in the case of very well activated steel surfaces 1.6 to 3 g / m ² .

To determine the grammages, the steel coupons described above were weighed after activation and phosphating and subsequent conditioning in accordance with the above-mentioned standard method. Then they were 10 min. long with 5% chromic acid solution (chromium trioxide) in demineralized water) at 70 ° C. As a result, the zinc phosphate layers formed were completely removed. The steel coupons were then immediately weighed again. The weights per unit area were determined from the weight difference between the phosphated and chromic acid-treated test sheets, ie the phosphate layer which had been removed. Because of the experimental fluctuation range (± 0.3 g / m ² ), 10 determinations were carried out in each case. The values were averaged over all 10 determinations.

Examples 1 to 8

Activation baths were prepared in the manner described above which contained the layered silicate type according to the invention in two different concentrations. The basis weights of the phosphate layers obtained after activation with such activating agents according to the present invention during the phosphating are shown in Table 2, with experimental deviations of about 0.1 g / m ² such basis weights were also after an operating time of the activation bath still reached by 8 hours, without having to visually add any of its components to the bath. The phosphate layers were finely crystalline and closed.

Comparative Examples 9 to 16

In the case of activation baths with layer silicates which are not according to the invention, ie unsuitable, faults occurred after just one hour of operation: the phosphate layers became increasingly coarsely crystalline and were no longer closed. They had basis weights of <3.5 g / m ² .

Activation baths without the addition of layered silicate already followed three hours on the same faults.

Without activating agent, only coarsely crystalline, inhomogeneous, not closed phosphate layers with basis weights <5 g / m ^{2 were} obtained from the beginning.

Table 2

Phosphating results depending on the addition of layered silicate to the activation bath containing titanium phosphate
Examples 1 to 8: Activating agents with layered silicates according to the invention
Examples 9 to 14: Activating Agents with Unsuitable Layered Silicates (Comparative Examples)
Example 15: Activating agent without layered silicate additive (comparative example)
Example 16: Without Activating Agent (Comparative Example)

Examples 17 to 24

Activation baths were prepared analogously to Examples 1 to 8 sets that in addition to those in the general procedure mentioned above amounts of titanium and phosphate (Step (d)) indicated in Table 3 below Contained amounts of different layered silicates. The Amounts of layered silicate and those after the layered silicate addition pH values measured in the activation bath correspond to the Data in Table 2 for Examples 1 to 8.

In a modification of Examples 1 to 8, the steel coupons after activation with a phosphating bath (normal Zinc process), which contains 5.6 g / l Zn, 9.85 g / l phosphate, Contained 6.6 g / l nitrate and 0.38 g / l nitrite.

The after activation with the activation according to the invention averaged basis weights obtained in the phosphating Phosphate layers are shown in Table 3 below men. The phosphate layers formed during the phosphating were consistently fine crystalline, closed and very similar moderate, which shows good activation.

Comparative Examples 25 to 31

Analogous to Examples 9 to 15 above, activations tion solutions set, but in the sense of the invention unsuitable layered silicates (Examples 25 to 30) or none lei additive (Example 31) contained. The steel coupons were with such activation solutions as in the previous Examples 17 to 24 treated. The results are also summarized in Table 3. The phosphate layers showed coarse-crystalline, inhomogeneous and therefore technically un suitable slices.  

Table 3

Phosphating result depending on the layer silicate additive to the activation bath
Examples 17 to 24 Activating Agents with Layered Silicate Addition According to the Invention;
Comparative Examples 25 to 30 Activating Agents with Unsuitable Sheet Silicates
Comparative Example 31: Activating agent without layered silicate additive.

Examples 32 to 35

Electrolytically galvanized steel coupons were used Activation baths according to the invention after standard cleaning activated and then with under Examples 17 to 24 described phosphating agents phosphated.

The after activation with the activation according to the invention phosphate layers were finely crystalline lin, closed and very even. They also rejected the basis weights given in Table 4 below. These results could still be seen after long use time of the activation bath can be retained unchanged.

Comparative Examples 36 to 39

Analogously to Examples 32 to 35, activation baths were used not according to the invention, i.e. unsuitable layered silicates (Examples 36 to 38) or layered silicate-free (Example 39) used. The results are also the following Table 4.

When using the activating agents described in Comparative Examples 36 to 39, only coarsely crystalline and uneven phosphate layers were obtained after the phosphating. These had layer weights of around 4.0 g / m ² .

A comparison of the results from Examples 32 to 35 with Comparative Examples 36 to 39 clearly show the advantages of the method according to the invention: When adding the fiction  Layered silicates were also used as activators electrolytically galvanized steel parts activated so well that the zinc phosphate formed in the subsequent phosphating layers had the desired layer weight.

Table 4

Phosphating results depending on the addition of layered silicate to the activation bath
Examples 32 to 35 activating agents with layered silicates according to the invention;
Examples 36 to 38 activating agents with layer silicates according to the invention (comparative examples);
Example 39: Activating agent without layered silicate additive (comparative example).

Comparative Examples 40 to 43

In an otherwise unchanged compared to Examples 1 to 8 procedure, the pH values of the fiction  activation baths with sodium hydroxide to a pH value set from 11.5. As shown in Table 5 below can be removed, the obtained after phosphating Phosphate layers clearly too high and application technology unwanted basis weights. They were also trained The phosphate layers coarsely crystalline and not closed.

Comparative Examples 44 to 47

Corresponding to the comparative examples listed in Table 5 40 to 43 were otherwise unchanged Steel coupons with activation solutions or activation disper sions activated, their pH before activation with Phos phosphoric acid had been set to 6.0. The results are also see table 5. As it turned out, were the phosphate obtained in the subsequent phosphating layers coarsely crystalline and not closed.

As the comparative examples 40-47 show, with activation solutions with a pH value outside the essential loading ranges from 7-10, no activation of steel surfaces be achieved to a satisfactory subsequent Phosphating leads. Rather, they are otherwise unchanged different (standardized) conditions of phosphate layers keep that not only coarsely crystalline and not closed are, but also have undesirably high basis weights.

When working within the pH range of 7-10 without exception phosphate layers with low basis weights and fine crystals over the entire metal surface ten.  

Table 5

Comparative examples using layered silicate-containing activation baths with too low or too high pH values

Example 48

The areas obtained in Examples 1 to 47 above Weight alone is not yet a sufficient criterion for the activating effectiveness of the shares according to the invention means of supply. Another criterion results from the optical assessment of the zinc phosphate layers using a grid electron micrographs of those on the metal surface Chen deposited zinc phosphate crystals. The recordings are Experience has shown that the depth of field is high and leaves the under differ in the shape and morphology of the crystals, the macro form a closed zinc phosphate layer, clearly detect. Differences between well activated and bad activated surfaces become clear from such recordings visible.  

In particular, the size of the crystals is affected by the effect of Activating agent determined and can therefore be a further para meters for the effectiveness of the activating agents will. The Kri works with well activated metal surfaces stable growth from a large number of individual points, which as Kri installation germs act. With no or only poorly active fourth metal surfaces is only at isolated points Watch crystal growth.

The crystallite size is with well activated metal surfaces very uniform. The scanning electron micrographs metal surface well activated before phosphating Chen show zinc phosphate crystals in the form of cubes or platelets, who either woke up parallel or perpendicular to the surface are. In the "low-zinc process" at diving applications tion of phosphate layers obtained in the scanning electrons microscopic images give the impression of blocks and / or Convey cuboids.

If the test sheets are not activated or not activated sufficiently, you can see free metal on the scanning electron micrographs surfaces. The crystals formed on the surfaces are heavily branched and have no characteristic shape.

Representative characteristic scanning electron microscopic Recordings both well activated and poorly activated Metal surfaces with consequent satisfactory or unsuitable Zinc phosphate layers can be found in S. Maeda, "Progress in Organic Coatings ", 11, 11 (1983).

Scanning electron micrographs of zinc phosphated Steel surfaces covered with activating agents in the sense of Invention according to Examples 1 to 8 (Tab. 2), 17 to 24 (Tab. 3) and 32 to 35 (Tab. 4) have been activated, show the  Morphology of zinc phosphate layers of excellent quality. The single crystals have a cube or plate shape and grew up parallel or perpendicular to the surface.

In contrast, zinc phosphate crystals are after activation of metal surfaces according to the comparative examples without Layered silicate addition in the activating agents (Example 15, Tab. 2; Example 31, Tab. 3; Example 39, Tab. 4) or with Layer silicates not according to the invention (Examples 9 to 14, Tab. 2; Examples 25 to 30, Tab. 3; Examples 36 to 38, tab. 4) as well as those zinc phosphate crystals that have no activation were obtained (Example 16, Table 2) coarse and uneven.

Examples 49-56 and Comparative Examples 57-60

The measurand "bath capacity" should indicate how much metal surface area per mass of activating agent can be activated before the activation bath is exhausted. Activation baths apply then as "exhausted" when 10 consecutive steel sheets missing or rough after the subsequent phosphating have crystalline areas. The measurand "bath capacity" is also a measure of the quality of the activators Effect of the inventive agents, but especially for Durability of the activating effect of the invention Medium.

In order to determine the measurand "bath capacity", fiction, ge moderate activation agent (Examples 49-56), analog activation tion baths without layered silicate (Comparative Example 60) and Activating agents, the layer silicates not according to the invention (Examples 57-59) contained, with test plates of the above given size continuously charged. The sheets were after usual cleaning in the with demineralized water  Activation baths immersed and then within the scope of the Standard phosphating process with those in Examples 1 to 8 (low zinc process) or those in Examples 17 to 24 (normal zinc process) described phosphated process. This process occurred without the addition of activating components the activation baths carried out until in the after following phosphating 10 consecutive sheets failed places or showed coarse crystalline areas.

The results are shown in Table 6 below. As the information about the bath capacity shows, the Badkapa was zity when using activating agents according to the invention in all cases higher than with non-inventive, i.e. unsuitable activating agents.  

Table 6

Bathroom capacities (in m ²

activated steel surfaces per 1 activation bath) depending on the addition of layered silicate to the activation bath
Examples 49 to 56 activation solutions with layered silicates according to the invention;
Comparative Examples 57 to 59 Activation Solutions with Layered Silicates Not According to the Invention;
Comparative Example 60 Activation solution without layered silicate

Examples 61-64 and Comparative Examples 65-68

These examples are intended to illustrate that even when used of non-softened water (water hardness: 10 ° d) for preparation the activation baths by adding Layered silicates can achieve higher bath capacities, i.e. the satisfactory activation of a large number of steel sheets is possible with the same amount of bath.

This significant increase in bath capacity by the inventor agents according to the invention (Examples 61 to 64) compared to Ver Similar examples (65-68) occur both when using the Normal zinc as well as the low zinc process. The results Table 7 below.  

Table 7

Bathroom capacities (in m ²

activated steel surface per 1 activation bath) depending on the layer silicate additive to the activation bath.
Examples 61 to 64 activation solutions with layered silicates according to the invention;
Comparative Examples 65 to 67 Activation Solutions with Layered Silicates Not Appropriate According to the Invention, ie Unsuitable
Comparative Example 68 Activation Solution Without Layered Silicate

Claims (8)

1. Agent based on aqueous solutions and / or dispersions of titanium (IV) phosphates for activating metal surfaces before zinc phosphating, characterized in that they are in water

• a) have a pH of 7 to 10 and
• b) 0.001 to 0.2 g / l titanium,
  0.1 to 4 g / l of one or more phosphates,
  0.05 to 20 g / l of one or more cations exchanging swellable and / or non-swellable alkali magnesium silicates and / or alkali silicates with a layer structure and
• c) optionally also contain other components customary in such activating agents.

2. Activating agent according to claim 1, characterized in that that they are in water 1 to 100 mg / l titanium, preferably 5 to 30 mg / l Titan included. 3. Activating agent according to claim 1, characterized in that that they contain 0.1 to 3 g / l of one or more phosphates in water, preferably 0.2 to 1.5 g / l phosphates, particularly preferably 0.2 contain up to 0.6 g / l phosphates. 4. Activating agent according to claims 1 and 3, characterized records that they are in water 0.2 to 0.6 g / l orthophosphates contain. 5. Activating agent according to claim 1, characterized in that they contain water-swellable and / or non-swellable alkali magnesium silicates and / or alkali silicates with layer structure whose cation exchange capacity, given as calcium binding capacity at room temperature, 20 mg CaO / g active substance, preferably 50 mg CaO / g active substance, whose Al ₂ O ₃ content is <10% and preferably <5% and whose mean particle diameter is <30 µm. 6. Activating agent according to claims 1 and 5, characterized records that they are layered silicates of the types saponite, hectorite, Kanemite and / or Magadiite included. 7. Activating agent according to claims 1, 5 and 6, characterized ge indicates that they have such an amount in water Layered silicate contain total cation binding capacity the layered silicate the amount per liter of activation bath Hardness formers in water by 50 mg, preferably by 10 to 30 mg calculated on the amount of CaO in the water that the Amount of hardness is equivalent. 8. Method for activating metal surfaces under Ver water-containing one or more titanium phosphates Solutions and / or dispersions after alkaline cleaning and Rinsing and before phosphating with zinc phosphates aqueous solutions, characterized in that the metal surfaces in a manner known per se at temperatures of 10 to 40 ° C, preferably at 20 to 40 ° C, particularly preferably at 25 to 30 ° C, with aqueous solutions and / or dispersions treated one or more of claims 1 to 7.