DE2327304A1 - PROCESS FOR APPLYING PHOSPHATUE COATINGS TO METALS - Google Patents

Description

METALLGESEIiSCHAFT Frankfurt / M., May 28th 73

Public company DrBr / MSchu

Prov. No. 7181 M.

Process for applying phosphate coatings to metals

The invention relates to an improved process control when applying phosphate coatings to metals, in particular iron, zinc, aluminum and their alloys, among Use of aqueous acidic solutions to form layers

Phosphates that contain oxidizing agents as accelerators,

Layer-forming phosphating processes, especially those based on the zinc phosphate, optionally with the use of further layer-forming cations, are in widely used in practice. The phosphate baths usually have an oxidizing agent content, which considerably reduces the minimum phosphating time. The most common industrial oxidation accelerators include nitrates, nitrites, chlorates and, in particular, mixtures thereof. They are often in the form of the Alkali salts introduced into the bath. Of the many other oxidation accelerators described in the literature only have peroxide accelerators, such as hydrogen peroxide, perborates: and other persalts

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attained a certain technical importance. However, they are mostly used in combination with the other more common ones Oxidizing agents.

In addition to oxidizing agents, a number of other bath additives are common, e.g. to increase the layer weight of the coatings formed influence or improve the film-forming ability of the solution.

The rinsing and Wastewater therefore contains, depending on the composition of the baths used, to a greater or lesser extent substances, which exert a damaging influence on the environment can and therefore require careful and, in many cases, time-consuming processing. There is therefore the Desire to avoid the related disadvantages of the procedures customary in practice, without going too high Pho spherical er speed and good formation of the desired coatings to do without.

According to the invention, a method is proposed for applying phosphate coatings to metals, in particular Using iron, zinc, aluminum and their alloys of aqueous acidic solutions of layer-forming phosphates that contain oxidizing agents as accelerators, which is characterized in that the Surfaces are brought into contact with a solution,

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the phosphate ions, layer-forming cations and peroxide accelerators contains and largely free of. those components that are used in a neutralization of the solution Ca (OH ^ water-soluble salts yield, is and held will.

The chemicals used to make up and replenish the phosphating bath are selected so that only those anions and cations get into the phosphating bath which lead to poorly soluble or insoluble salts _{when the solution is neutralized with Ca (OH) 2.}

As layer-forming cations are suitable for the invention Working method especially zinc ions. The solution preferably contains at least one further type of layer-forming agent Cations. The concentration of zinc ions and, if applicable Other cations can be selected depending on the desired layer and is suitably in the range from 0.5 to 60 g / l. The zinc content is preferably in the range from 0.5 to 20 g / l. The concentration of the other cations in the Bath can be from about 1 mg / l to about 50 g / l, depending on the type of cations used. Come as more cations in particular calcium ions are considered, the content expediently in the range of about 120 mg / l to 50 g / l * If nickel ions are also used, their amount is expediently in the range from 5 to 1000 mg / l. More usable Cations and their appropriate amounts are, for example

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_ 4 - subsequentSioh ' gsä.ndari:

Cu (1-30 mg / 1); Mn (100 mg / 1 - 5 g / L); Li (40 mg / 1 - · 20 g / l); Co (5-10ODmg / 1); Pb (1-100 mg / l); Cd (0.5 20 g / l); Mg, Sr, Ba (120 mg / 1 - 50 g / l).

The phosphate ion content of the bath is at least so high that all cations are present as primary phosphate and so much free P _{2 is} present to keep the bath in or near the phosphating equilibrium.

A particularly suitable peroxide accelerator is HpOp. However, perphosphates, percarbonates, ozone, for example, can also be used. The peroxide accelerator content of the bath should expediently be in the range from 5 to 150 mg / l, preferably in the range from 30 to 120 mg / l, calculated as H ₂ O ₂ .

Since the phosphating bath is as free of such components as possible and should be kept, the water-soluble salts when the solution is neutralized with Ca (OH) p result, only those chemicals are suitable for the preparation and supplementation of the bath, due to the small ions that are too lead to such salts. Sodium, potassium and ammonium compounds can therefore not be used. the Layer-forming cations cannot therefore be introduced into the bath via nitrates, chlorates, etc. Oxalates, Sulphates and fluorides can be present or desirable in the bath. - 5 -

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The admissibility of bathroom components can thereby be checked be that a bath sample with Ca (OH) p to a pH value of 8.5 and then the salt content (anions and cations) in the supernatant water is determined. Under "Essentially free of those components which, when the solution is neutralized with Ca (OH) ρ, are water-soluble salts result ", a salt content is understood that is not significantly higher than the usual service water, i.e. not significantly higher than about 500 mg / l. It is preferred to use those bath components that are used after neutralization with Ca (OH) ρ an additional salinity of not bring in more than 100 mg / l. Particularly favorable conditions are present when the salinity after neutralization Does not exceed 50 mg / l.

If you also have hot water in the bathroom If you want to avoid introduced salts, it is advisable to use fully demineralized water for the preparation and addition of the bath to use.

The phosphating solution used in the process according to the invention is expediently supplemented with peroxide to maintain a concentration of 5 to 150 mg / l, preferably 30 to 120 mg / l, calculated as H ^ O _{2 I.}

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The process can be carried out with particular advantage by contributing to maintaining the effectiveness of the phosphating bath the addition of at least some of the cations to the phosphating bath in the form of oxide and / or hydroxide and / or carborate and / or hydride is added. These compounds are preferably introduced into the bath as an aqueous solution or suspension or as an aqueous paste. One could, in principle, use the entire amount required for the supplement Adding cations to the bath in the above manner; however, it is only more expedient and advantageous to supplement some of the cations in the form of oxide or hydroxide or carbonate or hydride or mixtures thereof and also to be supplemented with a phosphoric acid concentrate. The peroxide can be supplemented separately or added to the phosphoric acid supplement concentrate. For the Partial addition of the cations are e.g. calcium carbonate, calcium hydroxide, Zinc oxide, zinc hydroxide, zinc carbonate, manganese carbonate, calcium hydride, nickel carbonate are suitable. Calcium hydroxide is preferably used.

In the phosphoric acid supplement concentrate, which contains zinc ions, where appropriate, other cations, phosphate and optionally contains desired and permissible anions, the molar ratio of / "zinc + other cations should be 7 J ^? ^ 5 preferably less than 0.8: 1. The other cations are calculated as divalent cations. - 7 -

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Vorzugswelse is supplemented with zinc, further cations and phosphate to maintain the phosphating bath of cations and phosphate in a molar ratio of / "zinc + further cations_7: P ₂ Oc = (0.9 to 2.0): 1 The molar ratio of zinc: other cations, calculated as divalent cations, are preferably in the range from 1: (0.01 to 2.3).

The aforementioned supplementary recommendation requires more cations per Pp ^ * than is to be brought in via the preferably phosphoric acid supplement concentrate. The resulting difference As stated above, cations are separated in the form of oxide or hydroxide or carbonate or hydride or mixtures supplemented by this.

It has been found to be particularly beneficial as a supplement of the phosphating bath is an acidic zinc phosphate concentrate to use and also to meter calcium hydroxide in the form of an aqueous suspension into the bath.

The inventive method can be carried out at temperatures zwisehen room temperature and 80 ⁰ C. Temperatures below 60 ^° C. are preferably used.

The workpieces to be phosphated can be placed on any Sometimes they are brought into contact with the coating solution,

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e.g. in diving, spraying, flooding. An injection treatment is preferably carried out.

To monitor the phosphating bath and the replenishment, the known and customary automatic control and metering devices used.

Normally the phosphating solution will be prepurified Use fittings. It is, however, also possible to add substances to the phosphate-making bath that pre-clean it make unnecessary, such as surfactants.

The method of operation according to the invention has the considerable advantage that from the process sequence described accumulating rinsing water through simple neutralization with alkaline earth compounds, e.g. calcium hydroxide, all undesirable, the wastewater polluting salts are precipitated and easily separated by sedimentation or filtration and the solids-free solutions can be reused in the process cycle without further processing. A particularly favorable possibility is that the rinse water also according to the reverse osmosis process can be worked up, with the permeate in the water cycle and the retentate in the phosphating bath again can be added.

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example

In a run-Spritzphosphatieranlage car wheels were purified from steel with a weakly alkaline titanium-containing cleaner _f then rinsed and in the phosphate! Erungszone 75 sec at a temperature of 54-56 C in the syringes. With a solution treated in the 1.75 g / l zinc, 7.0 g / l P ₂ O ₅ , 0.95 g / l calcium, 0.035 g / l nickel and 75 mg / 1 H ₂ O ₂ (i-OQ # ig). The ratio of free acid to total acid was approx. 0.07.

To replenish the bath, a concentrate was used which contained 11.7 _{% by weight of zinc, 32.5% by weight of P 2} O ₅ and 0.044% by weight of nickel. It was metered into the bath while maintaining a total acid score of 12-14. H ₂ O ₂ was added to the bath in an amount such that an HpOp concentration of 50 to 100 mg / 1 H ₂ O _{2 was maintained} in the bath. In addition, the bath would be replenished with a 7.5% strength aqueous suspension of Ca (OH) ₂ in such an amount that the molar ratio of Zn: Ca: PpOc in the replenishment was 0.8: 0.8: 1. With this addition, a ratio of free acid to total acid of 0.06 to 0.08 was maintained in the bath.

When supplementing, the H ₂ O _{2 can} also be added to the supplement concentrate and metered into the bath together with it.

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The phosphated wheels were then used for 30 seconds Cold water, then rinsed with deionized water and dried.

Simultaneously with the car wheels were also in the plant Test plates made of steel of the quality St 1405 m in the same Way with treated.

During a total throughput of 17,862 m of surface were evenly formed, thin, firmly grown phosphate coatings with a on the treated surfaces Layer weight of 0.8 to 1.5 g / m is obtained.

The phosphated work pieces were then electrophoresed primed with a black varnish and provided with a conventional top coat.

For comparison, other car wheels and test panels were treated in the same way, but in the phosphating zone a nitrate-nitrite accelerated zinc phosphate solution came to use in the usual way.

The examination of the workpieces treated in both series showed that they phosphated according to the proposal according to the invention Parts with regard to corrosion protection and primer for the subsequent painting according to the usual

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The parts treated are at least equivalent are. "..--" _ ■

The advantage of the treatment carried out according to the invention If the phosphating result is at least equivalent, the result is that only such rinsing water is used which from a technical and economic point of view in simple Way can be subjected to a total circulation in the system.

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- claims

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Claims (5)

Claims . Process for applying phosphate coatings to ketals, in particular iron, zinc, aluminum and their alloys • using aqueous acidic solutions of layer-forming phosphates which contain oxidizing agents as accelerators, characterized in that the surfaces are in contact with a solution which contains phosphate ions, layer-forming cations and peroxide accelerators and is essentially free of those components which give water-soluble salts _{when the solution is neutralized with Ca (OH) 2, and is kept.} 2. The method according to claim 1, characterized in that that as layer-forming cations zinc ions, preferably in a mixture with at least one v / supernier Kind of layer-forming cations. 3. The method according to claim 1 and 2, characterized in that that the phosphating bath with peroxide to maintain a concentration of 5 to 150 mg / l, preferably 30 to 120 mg / l, calculated is added as iLpOrjj. - 13 - 4 0 9 8 5 0/1011 4. The method according to claim 1 "to 3» thereby g e k ennz ei chn e t that the phosphating bath the supplement at least part. (Ie ^ i rations in the form of oxide and / or hydroxide and / or 3 garonate and / or Hydride is added. 5. The method according to claim 1 to 4, characterized ge k e η η ζ ei ch η et that the phosphating bath with zinc, other cations and phosphate in a molar ratio of / "zinc + other Kationen_7:? 2 ° 5 ⁼ (0.9 Ms 2.0): 1 supplement, being the mole ratio of zinc: further cations preferably in the: range from 1: (0.01 to 2.3). 409850/1011 . ORIGINAL INSPECTED