DE2125963A1 - Aqueous pretreatment liquid for grain refinement for iron and zinc-containing metal surfaces and their use - Google Patents

Description

Aqueous pretreatment liquid for grain refinement for iron and zinc-containing metal surfaces and their use

The invention relates to aqueous, grain refining metal pretreatment processes and fluids Stabilizers for use in these fluids and on aqueous metal pretreatment fluids which are so stabilized are.

Metal pretreatment liquids are to be understood here as liquids which are used to treat metal surfaces be used so that they provide a cheap substrate on which a protective coating and / or a decorative Coating, for example a paint oil or wax film, can be applied subsequently. In the present

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In this context, particular reference is made to aqueous liquids which are used in connection with a phosphate coating step and prior to this, can be used in a metal pretreatment process.

It is known that the corrosion resistance of iron and zinc-based metal surfaces (e.g. Zinc or "galvanization") can be usefully improved by looking at the. Surfaces a crystalline zinc phosphate

coating is deposited, which is then completed with a suitable top coating. Before applying the zinc phosphate coating the metal surface must be cleaned to remove contaminants such as oil, grease and dirt, for what purpose an aqueous cleaning liquid is usually used. The one on the cleaned metal surface deposited phosphate coating tends to form a mass of relatively coarse, loosely packed crystals, if not specific ones Precautions are taken to avoid this. P It has been found that coatings with these properties are deficient Show flexibility and adhesion to the metal. They also have a further disadvantage than surface appearance an applied, otherwise glossy paint film interrupt and spoil.

It has been proposed to add certain complex titanium / phosphate compounds, commonly known as titanium grain refining compounds, to the aqueous liquid used to clean the metal, thereby creating

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the subsequently applied zinc phosphate coatings become denser and finer crystalline and adhere more firmly to the metal substrate. Such surfaces are also considered to have superior corrosion resistance to that of a metal surface which is coated with a coarser, less dense zinc phosphate film.

Titanium grain refining compounds of this class are the so-called "Jernstedt" salts, which are described, for example, in Australian patent specification 224/61 and in US patent specification 2,310,239. Even if the exact nature of these salts is not known, titanium / phosphate complexes appear to be present in the pretreatment solution as finely dispersed contaminants, possibly in colloidal dimensions, which supply titanium ions to the liquid.

Although the usefulness of an aqueous metal pretreatment liquid predictably decreases when active ingredients are withdrawn from the liquid, it was observed that the effectiveness of a titanium grain refining compound present in the liquid is also time dependent is. Even if the cleaning function or other function of the liquid is usually unaffected by storage remains, its grain refining ability may decrease remarkably over time, even if the liquid does not is used, i.e. the grain refinement can be carried out very quickly fall off. In addition, the rate of fall of the grain

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the ability to refine the pH of the liquid addicted. If the liquid is moderately alkaline, for example Has a pH of 8 to 9, its grain refining ability can be more usable for hours or even days Be height. On the other hand, if the liquid is acidified or its pH is raised above about 10, the Grain refinement properties are destroyed for all practical purposes «There was therefore an internal limit to the pH value the aqueous liquid in which a titanium grain refining compound can be used. For example, for For some purposes, moderately acidic cleaning baths are particularly effective cleaning or etching agents for metal surfaces, but in these Media usually degrade titanium grain refining compounds too rapidly to be commercially useful.

To estimate some limitations, which one is pH dependent May exhibit a drop in grain refinement ability in metal pretreatment processes, it is appropriate to use a typical industrial process for cleaning and zinc phosphating of metal objects.

The metal is mechanically followed by a series of Dipping or spraying stages conveyed through which one after the other rinses the metal with a series of liquids, the stages in combination forming what is essentially a single, continuous metal treatment unit is. When using spray stages, it is normal practice to drain the treated metal in a basin at the bottom of each

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To collect stage and, for the sake of economy, return it to the spray stages. Because of the close proximity of neighboring Stages one usually encounters a splash of liquid from one stage to the next, so that a gradual one Contamination growth occurs in the liquid of each stage. In a typical setup, in sequence the following stages are present: alkaline metal cleaner, one or more water rinses, sink phosphating solution and finally water rinse.

It is a common practice to compound titanium grains incorporated into the alkaline cleaning liquid, which then, however, as mentioned above, to a maximum pH is limited to around 8 to 9.

Another suggestion to avoid this pH limitation is to use the titanium grain refining compound leave the cleaning stage and introduce them to a water rinsing stage immediately before the phosphating stage. Provided that an adequate water rinse is interposed between the cleaning stage and the grain refining stage becomes, the alkali impurity becomes the titanium grain refinement connection thereby avoided. An objection to this one However, it is suggested that the back-spraying of acid phosphating solution reduces the effectiveness of the titanium compound in the Grain refinement stage can quickly destroy. Even if this is presumably done immediately by interposing an additional rinse stage could be prevented before the phosphating stage, so

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after all, this is an economically unattractive solution.

It has now been found, surprisingly, that the time-dependent loss of conical refinement capacity of a liquid containing titanium grain refinement compound can be inhibited over a wide pH range by adding certain polymeric substances to the liquid, which are defined below. When using the polymeric substances in the 'above cleaning and rinsing liquids, these substances have no ansich grain refinement function and appropriate description of their effect without them, however, any particular functional mechanism suz-us rub ₈ whether they are referred to as Kornverfeinerungsstabilisatorert.

According to the invention, an aqueous pretreatment liquid for grain refinement for iron and zinc-containing metal surfaces is created, this liquid having a pH value of at least ¹ J.5 and titanium grain refining compound, together with a soluble grain refinement stabilizer, the latter consisting of an addition copolymer of the monomer (a ) and the monomer (b) in essentially equimolar proportions, the monomer (a) being at least one unsaturated polybasic carboxylic acid or anhydride from the group consisting of maleic acid, maleic anhydride, fumaric acid and citraconic acid, and the monomer (b) being at least one unsaturated Monomer from the group of ethylene, methyl vinyl ether, ethyl vinyl ether and cyclohexyl vinyl ether, and wherein the copolymer

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has a viscosity of at least 3.5 centipoise at 25 ° C when ^{tested as a 1} J weight / C solution in aqueous sodium hydroxide solution at pH 9.

It is a particular and unexpected advantage of the invention that titanium grain refining compounds are applied thereto Way can be stabilized in aqueous liquids, which have a pH value of 4.5 to greater than 12. The invention is therefore applicable not only to conventional moderately alkaline pretreatment liquids, but both on acidic as well as on relatively strongly alkaline metal pretreatment fluids.

The aqueous metal pretreatment liquid can be an acidic or moderately alkaline cleaning or etching liquid be, which has at least a pH of M.5. at a particular embodiment of the invention, in which from the stormy cleaning effect of strongly alkaline liquids can be taken advantage of, has the aqueous metal pretreatment liquid has a pH of at least 9 and has titanium grain refining compound along with the above defined polymeric grain refinement stabilizer.

The aqueous metal pretreatment liquid can, however, also be a water rinse consisting essentially of water, together with grain refinement stabilizer and titanium grain refinement compound. In this embodiment of the invention, the liquid can satisfactorily be used as the last grain-size

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finer water rinsing stage, immediately before a zinc phosphate coating stage, be used. For purely economic reasons, it is unlikely to splash back from the neighboring acidic zinc phosphate level to a pH of the water rinse from 4.5 and moderately acidic under such Under these conditions, the stabilizer of the present invention withstands the grain refinement degradation to an acceptable level.

When the aqueous metal treatment liquid is an alkaline cleaning liquid, it can essentially consist of an aqueous alkali solution, for example sodium and potassium carbonates, bicarbonates and hydroxides a concentration required to create the desired pH. Other substances such as polyphosphates (e.g. alkali pyrophosphates and tripolyphosphates), alkali silicates, and anionic or nonionic surfactants Agents are usually added to the liquid in order, for example, to increase its cleaning effect.

The polymeric stabilizers are generally easily soluble in alkaline liquids with which they are exposed Formation of soluble alkali salts can react. In acidic solutions or solutions which are likely with acidic liquids Can be contaminated, it is necessary to use as stabilizers those compounds defined above select which are soluble in the liquid at the desired pH and working concentration.

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The concentration of stabilizer required to give the fluid a useful grain refining life depends on the nature and concentration of the titanium grain refining compound used in the fluid. The effectiveness of the titanium complex again seems to depend to a certain extent on the method by which it was prepared. Although concentrations as low as 0.0005 wt -.% (In terms of titanium ions) in the liquid may be effective, but are the more useful working concentrations in the order of magnitude from 0.005 to 0.05 Gew.-Jf. In general, it is found that a weight of stabilizer equal to the total weight of titanium in the grain refining compound is the minimum amount which can benefit from the invention, although higher concentrations of stabilizer in the fluid can be employed. It is common practice to prepare a series of aqueous liquids with increasing stabilizer contents but otherwise identical formulations and then to control the lifetime of active grain refinement of the liquids. When this is done, it is usually found that for a particular grain refining compound there is a definite stabilizer concentration at which the liquid exhibits a maximum grain refining life which is not extended by using higher stabilizer concentrations. In order to achieve a useful working life of the fluid, it is preferred that it contain at least 0.005 wt% stabilizer, with the most useful working concentration range under normal working conditions being 0.01-0.02

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Weight-ί is. For example, if a cleaning fluid to be used industrially on heavily soiled metal which has a titanium grain refinement compound, so it may be found necessary to use even higher concentrations of stabilizer, presumably because of the adverse effect of the impurities on the stabilizer.

The degree of improvement that can be achieved in terms of the useful active life of the metal pretreatment fluid depends on a number of factors which are characteristic of the particular fluid being stabilized. For example, if the liquid is moderately alkaline, ie below about pH 9.5 to 10, the improvement that can be achieved is useful, but often relatively small; for example, the active life can be extended by just a few hours. However, at pH values of 11 and above or when the liquid is acidic, the liquid can actually in the absence of the grain refinement stabilizer have no useful grain refining effect at all, whereas in the presence of the stabilizer according to the invention, a pronounced grain refinement capacity can exist for more than 72 hours. It has been observed that the maximum attainable grain refining ability of a particular fluid can vary according to the source of titanium grain refining compound contained therein. Although these substances are known as a class , the nature of individual compounds appears to vary somewhat and this is reflected in their performance in grain refining liquids. In particular, it has been observed that

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when using the grain refining titanium compound in an aqueous pretreatment liquid, the pH of which is greater than about 9, some titanium compounds, which otherwise work satisfactorily as grain-refining substances, completely lose their activity seem to lose when the liquid is alkali polyphosphates, for example alkali pyrophosphates and tripolyphosphates having. It has been observed that this loss of grain refining potency appears to be complete Solubility of the titanium compound in the liquid is associated. For example, the addition of a grain refining titanium compound confers to an aqueous pretreatment liquid, the liquid usually has a slight turbidity, whereas in a clear liquid is usually formed in the above cases. Although this observed effect is not of any particular one Mechanism can be attributed, it seems, that in relatively strongly alkaline solutions and in the presence of alkali polyphosphates, certain substances that are widely used by experts as titanium compounds that refine grains Scope are accepted, react quickly with such liquids and are then not recorded as grain-refining titanium compounds can be. It is believed that a titanium / phosphate complex, which is known in the art as a grain refining compound is recognized to be at least partially insoluble in the liquid in which it is to be used. Because of this addiction the service life of an unstabilized, a grain-refining titanium compound having! Liquid from the pH the fluidity and the variation in the nature of the

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grain-refining compound itself and taking into account, that the purpose of the stabilizer is to extend the active life of a grain refining fluid and not to accelerate its activity or to increase it in any other way, there must be some improvement in the fluid using the stabilizer according to the invention brings with it, be related to the performance of the work special liquid in the absence of the stabilizer and not for the work of another pretreatment liquid.

Aqueous cleaning fluids according to the invention are prepared by adding to a conventional cleaning fluid, or in the case of a water rinse, in a rinse liquid, the required amount of grain-refining titanium compound and grain refinement stabilizer is stirred in. In the case of alkaline liquids it may be necessary to add an additional Add amount of alkali to compensate for a drop in pH as the stabilizer dissolves. Man but can also, especially in the case of an alkaline cleaner, all solid components of the cleaner as dry Premix the powder and the grain refining liquid is then prepared by dissolving the powder in water, which is optional contains previously dissolved components, e.g. conventional surfactants, which are suitable for rapid wetting and dispersing the powder.

As mentioned above, the ability to use the Korn-109850/1830

refinement has a useful practical life To maintain this in a moderately acidic liquid, apply a grain-refining rinse before the coating with zinc phosphate, regardless of the measures which are applied to the metal to be phosphated to pre-clean. For best results, it is preferable to rinse cleaning fluid off the metal before putting it in the grain-refining rinsing stage occurs. Accordingly, according to a preferred embodiment of the invention, a method created for zinc phosphating of steel or metal surfaces based on zinc, the metal successively an aqueous Cleaning liquid, at least two water rinses and a zinc phosphating liquid is subjected, wherein the method is characterized in that the water rinse immediately before the zinc phosphating liquid comprises a titanium grain refining compound and a grain refinement stabilizer as defined above and a pH value of at least 4.5.

Zinc phosphating fluids are well known and are useful in selecting a suitable phosphating fluid no special requirements need to be met in order to carry out the method according to the invention. They are generally known to be essentially acidic solutions of zinc orthophoephates.

The invention is now based on the following details

management examples explained in more detail, in Depeji all parts

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given are based on weight.

example 1

Effect of an acidic cleaning liquid which does not contain a polymeric stabilizer according to the invention, as Pretreatment for zinc phosphated steel.

A bath of acidic cleaning fluid is prepared by dispersing 0.1% of the following mixture in water at a concentration based on weight:

Monosodium orthophosphate 77.00 parts

Disodium prthophosphate 9.00 parts

Diatomaceous earth · 2.00 parts

'.- anionic surfactant

Medium 4.00 parts

non-ionic surfactant

Medium 8.00 parts

The nonionic surfactant used is a commercially available octylphenol / ethylene oxide condensate and the anionic surfactant is a commercially available aryl sulfonate.

The solution has a pH of 5.8. The bath is ^{heated to 60 °} C. and a steel panel, which has been given a pre-wash with hydrocarbon cleaning solvent, is sprayed with the solution for one minute. The board is then rinsed free of this solution by spraying it with pure water for 30 seconds, and then it is placed in a commercially available

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lichen zinc phosphate coating bath coated with zinc phosphate. on A light, flaky, relatively coarse, discontinuous coating of zinc phosphate forms on the steel.

Additions of a polymeric stabilizer as defined above, namely poly (maleic anhydride / methyl vinyl ether) with a viscosity of 200 centipoise at 25 ° C (k X solution in aqueous sodium hydroxide, pH 9) to the cleaner without a grain-refining titanium compound, have no visible effect on the Nature of the zinc phosphate coating formed on the steel.

Example 2

Effect of polymeric stabilizers and grain refiners Titanium compound according to the invention, on the action of an acidic cleaning bath.

An acidic cleaning bath is prepared according to Example 1, which, however, additionally contains 0.01% by weight of stabilizer according to Example 1 and 0.025% by weight of grain-refining titanium compound (as titanium). The titanium grain refiner compound is prepared by 2Ί parts water to 9 * I ^O C heated and for this purpose with continuous mechanical stirring, 95 parts of anhydrous Dinatriura hydrogen phosphate adds, Mixing is continued while 5 parts of anhydrous potassium Pluotitanat to the bath in added in small amounts over a period of 30 minutes. Mixing and heating continues,

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until a dry mass is formed, which is then ground to less than 60 mesh, a de kornverfeinerr titanium compound with about 1 wt -.% titanium is formed.

If the testing according to Example 1 is carried out on steel panels, a dense, flat, fine-grained one is formed Zinc phosphate coating on the steel.

The example is repeated using the titanium grain refining compound, but leaving the stabilizer open. A relatively coarse, discontinuous one forms Zinc phosphate coating on the board, demonstrating the effectiveness of the combination of grain refining titanium compounds and stabilizer according to the invention.

Example 3

Comparative tests of strongly alkaline, grain-refining metal cleaning fluids, which show the benefits of incorporation of the grain attenuation stabilizer of the present invention demonstrate.

The following mixes are prepared by dry blending:

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- I ₇ - 2125963 3. Component Mixture No. (Parts by weight) 25th 1. έ. 60 Sodium hydroxide 25 25th 8th Sodium carbonate 60 60 7th non-ionic surface
active agent 8 8th 3 commercial grain ver
refining 'Titanver
binding 7 7th Grain refinement
stabilizer 0.5

The nonionic surfactant is an octylphenol / xethylene oxide condensate containing about 11% Ethylene oxide units per phenol group. The grain refining stabilizer is a poly (maleic anhydride / methyl vinyl ether) with molar ratios of about 1: 1, which as a 4 Gew.Jf-ige solution in aqueous sodium hydroxide, pH 9, has a viscosity of 200 centipoise at 25 ° C.

Each dry mixture is ^{stirred into water heated to 71 °} C. to a weight concentration of 0.1% , resulting in alkaline cleaning fluids whose pH is greater than 12.

The cleaning liquid 3 (based on the mixture no, 3) is a liquid according to the invention, which has about 0.00056% by weight of grain- refining titanium compound (as Ti ions) and 0.012% by weight of stabilizer,

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The cleaning fluids are tested using the following method. Rolled steel plates, which with a heavy dirty, oily film are coated with cleaning fluid for one minute at a pressure of 1.4 kg / cm, Rinsed with a spray of pure water for one minute, and then with a commercially available zinc phosphating solution for one minute of the type described, for example, in Australian patent application 9 ^ 78/66. The tablets will be then air dried and checked, visually for cleanliness and microscopically to determine the nature of the coating found on the tablets.

In order to achieve the useful grain refinement life of the. To compare liquids, they are sorted according to the following, at specified time intervals, measured from the time when the dry powder is stirred into the water will. Unless otherwise specified, the liquids are kept at 71 ° C during the holding times to ensure the indu- ™ emulate strial practice. The results are as follows:

Cleaner cover

Fluid
speed no. Time interval 1 immediately ge
tests 1 4 hours 2 immediately
tested 2 8 hours

excellent fine-grained, even,

continually

- dto, - thin, coarsely crystalline

powdery

- dto - fine-grained, even,

continually

- dto - thin, coarse

crystalline, powdery

tested immediately - dto - fine-grained, even, 10985 0/1830 continuous

3 4 hours - dto - - dto -

3 8 hours - dto - - dto -

3 8 hours plus

Cooling overnight,

Reheat

to 71 ⁰ C - dto - - dto -

The limited useful life of the stabilizer-free mass results from the above results in Comparison with cleaning fluid no. 3. Cleaning fluid no. 2, which is less than the recommended Stabili contains satorkonzentration (0.002 wt .- £), is also inferior to the composition according to the invention after 8 hours of storage.

Example * t

Preparation of silicate-containing, alkaline, grain-refining products Metal cleaning fluids according to the invention.

Following the general method of Example 3, an alkaline cleaning liquid is prepared from a dry mixture of the following substances:

Sodium orthosilicate 43 Parts 1098 Tetrasodium pyrophosphate
sodium 22nd
16 Parts
Parts 50 / ' nonionic surfactant
Medium (like example 3) 8th Parts 1830 commercially available grain refiners
Titanium compound 8th Parts Grain refinement stabilizer
(like example 3) 3 Parts

The cleaning liquid, which has a pH value of 12, has about 0.00064 % by weight of a grain-refining titanium compound (as Ti ions) and 0.012% by weight of stabilizer and is slightly cloudy.

The liquid is tested according to the method of Example 3 for its cleaning and grain refinement capacity Time intervals ^ from preparation, from 0 hours, 8 hours, 16 hours and 72 hours (the last time periods inclusive Cooling overnight with subsequent reheating).

In all tests, the liquid shows excellent cleanability and there is no drop in grain refining ability, even on the 72-hour test, apparently. The phosphate coating is dense, finely crystalline and adheres to the metal surface close to.

Example 5

Comparison of the effectiveness of alkaline cleaning fluids with a relatively low pH value, with and without the invention Stabilizer.

Following the general method of Example 3, two cleaning fluids are made from the following dry mixes prepares:

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Component Gladly! sch no. (Qi »Important parts) • Sodium tripoly
phosphate 60 60 sodium 20th 20th non-ionic upper
area active
Medium (like example 3) 10 10

commercially available »grain-refining titanium compound 10 10

Grain refinement stabilization

lizer - 3

Copolymer 11 from Example 6

The cleaning liquids prepared in this way have a pH value of about 9. Both liquids contain about 0.001% by weight of grain-refining titanium compound (calculated as Ti ions) and liquid no. 2 (derived from mixture No. 2) also contains 0.012 wt .- * stabilizer.

The fluids are tested according to the method of the example with the following results:

Liquid time interval cleaning power coating speed no.

1 immediately very good fine-grained, even, tested continually 1 8 hours plus Cooling overnight, Reheat
to 71 C very good thin, coarse - crystalline, powdery 10985 0/1830

2 tested immediately very good fine-grained, even,

continually

2 8 hours plus

Cooling overnight,

Reheat

at 71 C very good - dto -

These results confirm the beneficial effect of the presence of the stabilizer of the invention in the liquid at a pH of 9 »

For example ^

Comparison of polymeric stabilizers according to the invention with other polymeric substances in alkaline cleaning baths.

The polymers tested fall into two different classes. All polymers are soluble at the concentration in which they are tested in an alkaline cleaning liquid at a pH of about 12, but during a Group is structurally closely related to the polymeric stabilizers according to the invention and includes these stabilizers, the other group consists of chemically dissimilar polymers.

The chemically dissimilar polymers are hydroxyethyloellulose, Carboxymethyl cellulose and polyacrylic acid.

Of the other group are all copolymers of

Maleic anhydride and a comonomer ( approximately molar ratio

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ratio of about 1: 1), which is either ethylene or a substituted Ethylene iet. The composition of the comoncmeres is as follows:

Copolymer
No. Comonomer 1 Methyl vinyl
ether 2 - dto - 3 - dto - 1} - dto - 5 Ethyl vinyl
ether 6th Isobutyl
vinyl ether 7th Cyclohexyl
vinyl ether 8th Styrene 9 Vinyl acetate 10 Acrylic acid 11 Ethylene 12th Ethylene

Viscosity (H ige solution) pH 9 at 25 C

less than 3 centipoise

30 centipoise 2000 centipoise 6000 centipoise greater than 3.5 centipoise

greater than 3.5 centipoise greater than 3.5 centipoise

greater than $ 3 5 centipoise greater than 3.5 centipoise greater than 3.5 centipoise 6 centipoise about 10,000 centipoise

The polymers are used for their effectiveness as grain attenuation stabilizers tested by adding them as a stabilizer component to the dry blended mixture of the Example 3 incorporated using the formulation of Mixture No. 3. This mixture is then < combined with a cleaning fluid and tested according to the method of that example, whereby the basis of the selection of a suitable state

1 0 9 8 B 0/1 8 3 0

bilisators is that the stabilizer is a liquid should create what their grain refining ability for at least Maintains 8 hours. The results are as follows:

Tested polymer

Hydroxyethyl cellulose carboxymethyl cellulose Polyacrylic acid

Copolynieres No. 1 (above)

Copolymer # 2

Copolymer # 3

Copolymer # 4

Copolymer # 5

Copolymer # 6

Copolymer # 7

Copolymer # 8

Copolymer No. 9

Copolymer No.

Copolymer No.

Copolymer No.

Time to failure

less than 1 less than 1 less than 1 less than 1 no failure no failure no failure no failure less than 8 72 hours.
less than 4 less than 8 less than 8 72 hours
72 hours

hour

hour

hour

hour

at 72 hours

at 72 hours

at 72 hours

at 72 hours

hours

Hours hours hours

It can be seen that only polymers of the composition of the stabilizers according to the invention, 8 or more hours, i.e., work satisfactorily for the duration of a normal work shift.

Approximately equimolar copolymers of maleic acid / ethyl vinyl ether, Pumaric acid / ethyl vinyl ether (viscosities of 1 Sigen

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Solutions with a pH of 9 at 25 ° C about 30 centipoise) are used in a further series of tests instead of the above copolymer No. 5, used on the same weight basis and, as grain refinement stabilizers, result in an equivalent work- · performance.

Example 7

Metal pretreatment process with a titanium grain refining washing stage according to the invention.

A simulated metal cleaning and phosphating system is put together, in which metal panels are in Successive in an aqueous alkaline cleaning bath (mixture no. 1 of Example ^; however, omitting the grain-refining titanium compound), rinsing with water to remove alkali, then rinsing in a liquid, which consists essentially of water, together with 0.01 wt. JC grain-refining titanium compound (calculated on the titanium content) and 0.02% by weight of a grain refining stabilizer (copolymer 2 from Example 6), the liquid being sufficient sodium hydroxide was added to form the sodium salt of the stabilizer, and then the tablets in a conventional acidic Zinc phosphating bath coated with zinc phosphate.

Steel panels and galvanized steel panels that pass through the system show satisfactorily fine and even phosphate coatings.

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It then becomes the acidic phosphating solution to refine the grain Rinse bath added to bring the pH to 4.5 and - so to simulate a splash back - and other panels pass the plant with satisfactory results. There is no noticeable drop in the quality of the phosphating apparently when panels pass through the facility after the "contaminated" grain refining rinse for up to 24 hours has aged. For comparison, the above experiment is repeated while leaving the stabilizer out of the last rinsing bath. In In this case, once the grain-refining cleaning rinse bath has been "contaminated" as above, a more rapid one occurs Decrease (in less than 15 minutes) in the quality of the phosphate coating that is formed on the outgoing panels. The coating will be coarse and uneven.

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Claims (8)

Claims /1.1 Aqueous pretreatment liquid for grain refinement for iron and zinc-containing metal surfaces, thereby characterized in that the liquid has a pH of at least 4.5 and a grain refining titanium compound, together with a soluble grain refinement stabilizer, the latter being an addition copolymer of the monomer (a) and the monomer (b) in essentially equimolar proportions consists, wherein the monomer (a) is at least one unsaturated polybasic carboxylic acid or its anhydride, namely maleic acid, maleic anhydride, fumaric acid or citraconic acid, and the monomer (b) at least one unsaturated one Monomer, namely ethylene, methyl vinyl ether, ethyl vinyl ether or cyclohexyl vinyl ether, the copolymer when tested as a 4% strength by weight solution in an aqueous sodium hydroxide solution has a viscosity of at least 3.5 centipoise at pH 9 and 25 ° C. 2. Liquid according to claim 1, characterized in that it is an alkaline cleaning liquid with a pH value of at least 9, 3. Liquid according to claim 1, characterized in that it is a water flushing liquid which is substantially from water, together with grain refining stabilizer and grain refining agent Titanium compound exists. 1 09850/1830 4. Liquid according to claim 1 to 3 »characterized in that that the concentration of grain-refining titanium compound in the liquid is about 0.05 to 0.05% by weight, expressed as titanium ions. 5. Liquid according to claim 1 to * J, characterized in that that the concentration of grain refining stabilizer is at least equal to the total weight of titanium in the ) is a grain-refining compound present in the liquid. 6. Liquid according to claim 1 to 4, characterized in that that the concentration of grain attenuation stabilizer is at least 0.005% by weight of the liquid. 7. Liquid according to claim 6, characterized in that the concentration of grain refinement stabilizer is at least 0.01 to 0.02 wt. # Of the liquid. 8. Use of the liquid according to claim 1 to zinc phosphating of steel or zinc-based metal surfaces, the metal being successively subjected to an aqueous cleaning liquid, at least two water rinses and a zinc phosphating liquid, and the water rinsing immediately before the zinc phosphating liquid has a grain-refining titanium compound and the grain refinement stabilizer and has a pH of at least k _t 5. 10 9 8 5 0/1830