DE3689442T2 - Acidic, aqueous phosphate coating solutions for a process for phosphate coating of metallic surfaces. - Google Patents

Abstract

Acidic, aqueous, substantially chlorate-free phosphate solution contains in S/L:- 0.1-1.5 Zn ions; 5-50 phosphate ions; 0.2-4 Mn ions; min 0.05 fluoride ions; less than 0.5 chloride ions; and at least one of the following phosphate accelerators:- 0.01-0.2 nitrite ions; 1-15 nitrate ions; 0.5-5 H2O2 (based on 100% H2O2); 0.05-2 m-nitrobenzene-sulphonate ions; 0.05-2 m-nitrobenzoate ions and 0.05-2 p-nitrophenol.

Description

The present invention relates to an acidic aqueous phosphate coating solution for use in a process for phosphating metal surfaces. More particularly, it relates to a solution for forming a phosphate film which is particularly suitable for cationic electroplating and is particularly applicable to metal surfaces comprising both an iron-based surface and a zinc-based surface.

Japanese Laid-Open Publication No. 107784/1980 (laid open on August 19, 1980) discloses a method for treating a metal surface by dipping treatment and subsequent spraying treatment with an acidic aqueous phosphate solution containing 0.5 to 1.5 g/l of zinc ions, 5 to 30 g/l of phosphate ions and 0.01 to 0.2 g/l of nitrite ions and/or 0.05 to 2 g/l of m-nitrobenzenesulfonate ions. It is reported that the method is capable of providing a phosphate film effective for forming a coating by cationic resistance on complicated articles having many pocket-like parts such as automobile bodies.

Japanese Laid-Open Patent Application No. 145180/1980 (laid open on November 12, 1980) discloses a method for treating a metal surface by spraying an acidic aqueous phosphate solution containing 0.4 to 1.0 g/l of zinc ions, 5 to 40 g/l of phosphate ions, 2.0 to 5.0 g/l of chlorate ions and 0.01 to 0.2 g/l of nitrite ions. Furthermore, Japanese Laid-Open Patent Application No. 1512183/1980 (published on November 27, 1980) discloses an acidic aqueous phosphate solution containing 0.08 to 0.20 wt% of zinc ions, 0.8 to 3.0 wt% of phosphate ions, 0.05 to 0.35 wt% of chlorate ions, 0.001 to 0.10 wt% of nitrite ions and complex fluoride ions in an amount is calculated according to the formula 0.4 ≥ y ≥ 0.63 x - 0.042, where z is the concentration of zinc ions in wt.% and y is the concentration of complex fluoride ions in wt.%. It is stated that these prior art methods are capable of imparting excellent adhesion and corrosion resistance to the cationic electroplating coating.

To the extent relevant, it is also noted that British published patent application GB 2 148 951 A, according to its abstract, discloses that a protective coating can be formed on steel or other metal surfaces at low temperatures, for example below 40°C, by contact with a solution which is generally free of chlorate and chloride and which contains 0.5 to 1.5 parts of silicofluoride or borofluoride, 0.8 to 2.5 parts of zinc, 10 to 25 parts of phosphate, 1.5 to 10 parts of nitrate, 0.1 to 1.2 parts of nickel and 0.25 to 2 parts of sodium nitrobenzenesulphonate. The composition may also contain 0 to 0.7 parts of manganese.

A recent development in the automotive industry has been to use steel components plated with zinc or alloyed zinc on one side only for automotive bodies, with the aim of further improving corrosion resistance after application of the siccative coating. However, it has been recognized that when the above prior art compositions and methods are applied to such materials (i.e., to the metal surfaces having both an iron-based surface and a zinc-based surface), a phosphate film can be formed on the iron-based surface which is suitable as a substrate to be coated by cationic electroplating, but that a phosphate film formed on a zinc-based surface is significantly inferior to that formed on the iron-based surface.

A composition and a process have been developed to solve the above-mentioned problems that occur with surfaces based on zinc Base in components having both an iron-based surface and a zinc-based surface. This is the invention disclosed in Japanese Laid-Open Publication No. 152472/1982 (published on September 20, 1982). This publication discloses immersing the composition in an acidic aqueous phosphate solution containing 0.5 to 1.5 g/l of zinc ions, 5 to 30 g/l of phosphate ions, 0.6 to 3 g/l of manganese ions and a phosphating accelerator.

However, during zinc phosphate treatment of galvanized steel, an abnormal coating with white spots is often formed, each spot having a diameter of 1 mm to 2 mm. This is particularly true for electroplated galvanized steel and especially during dip treatment of the same. These white spots create craters during subsequent treatment and thus result in poor coatings. The mechanism by which the white spots are formed is believed to be as follows: In a first stage, many pits appear, at the peripheral parts of which the galvanized layer is gradually dissolved in the form of concentric circles by an excessive reaction of etching. As each pit grows, zinc phosphate is deposited in the central part of it. However, at the peripheral parts, the ion surface is exposed, which forms a galvanic cell with the zinc metal, thereby continuing the dissolution of zinc.

As a result, an excess amount of zinc phosphate crystals is precipitated and accumulates as "snow" on the peripheral parts of the spots, which can be easily observed with the naked eye.

Unfortunately, no solution to this problem has yet been found to consistently prevent the formation of such white spots.

It is the aim of the present invention to provide a phosphating solution, especially for treating a substrate under cationic electrocoating, capable of imparting excellent adhesion and corrosion resistance, in particular to cationic electrocoating coatings on a variety of metal surfaces, including iron-based surfaces, zinc-based surfaces and aluminum-based surfaces, even when treated at low temperatures and even on objects that may have different metal surfaces and/or a complicated shape, such as a motor vehicle body... and in particular to provide an acidic aqueous phosphate solution that does not cause white spots or at least only insignificant spots on galvanized steel even when dipping it.

We have found that phosphating compositions which are chlorate-free or at least substantially chlorate-free and which have a chloride ion concentration below 0.5 g/l provide excellent coatings on iron, zinc and aluminum based surfaces without the formation of harmful white spots. It is important to the beneficial results of the present invention that the chloride ion level be kept consistently below 0.5 g/l, which means that not only chloride ions themselves but also chlorate ions should not be added to the phosphating compositions since in use of the phosphating compositions the chlorate ions are reduced to chloride ions.

According to the present invention there is provided an acidic aqueous phosphate solution for use in a process for phosphating metal surfaces, which contains at most 0.2 g/l and preferably no chlorate ions at all and the lowest practical concentration of chloride ions, but never exceeding 0.5 g/l chloride ions, the solution further comprising:

a) 0.1 to 1.5 g/l zinc ions,

b) 5 to 50 g/l phosphate ions,

c) at least 0.8 to 4 g/l manganese ions,

d) at least 0.05 g/l fluoride ions and

e) at least one of the following phosphating accelerators in the following concentrations:

i) 0.01 to 0.2 g/l nitrite ions,

ii) 1 to 15 g/l nitrate ions,

iii) 0.5 to 5 g/l hydrogen peroxide (based on 100% H₂O₂)

(iv) 0.05 to 2 g/l m-nitrobenzenesulfonate ions,

v) 0.05 to 2 g/l m-nitrobenzoate ions and

(vi) 0,05 to 2 g/l p-nitrophenol.

As stated above, the metal surfaces treated according to the present invention include iron-based surfaces, zinc-based surfaces, aluminum-based surfaces, and surfaces based on their respective alloys. These metal surfaces can be treated either separately or in combination. The advantage of the present invention is most apparent when the treatment is carried out on metal surfaces that include both an iron-based surface and a zinc-based surface, such as in an automobile body. Examples of zinc-based surfaces include galvanized steel plates, hot-dip galvanized steel plates, electrogalvanized steel plates, zinc alloy electroplated steel plates, complex electrogalvanized steel plates, etc.

If the content of zinc ions in the above acidic phosphate solution is less than 0.5 g/l, a uniform phosphate film is not formed on the iron-based surfaces. If the content of zinc ions exceeds about 1.5 g/l, then continued formation of the phosphate film takes place on both iron-based and zinc-based surfaces, causing the film to build up, with The result is that the film shows a decrease in adhesion and becomes unsuitable as a substrate for cationic electroplating.

If the content of phosphate ions in the above solution is less than about 5 g/l, there is a risk of an uneven phosphate film being formed. If the content of phosphate ions is greater than 50 g/l, no further benefits are obtained and for this reason it is economically disadvantageous to use additional amounts of phosphate chemicals.

With the reduction of the content of manganese ions, the manganese content in the phosphate film formed on zinc-based surfaces becomes smaller, and in fact, it can be found that if it is less than 0.2 g/l, the adhesion between the substrate and the coating after cationic electroplating becomes insufficient. If the manganese ions are present in an amount of more than 4 g/l, no further beneficial effects are obtained for the coating and the solution forms excessive precipitates, making it impossible to obtain a stable solution.

The manganese content in the phosphate film formed on the metal substrates should be in the range of about 1 to about 20 wt.%, based on the weight of the film, in order to have a phosphate film that meets the performance requirements for a cationic electrocoating.

The manganese content in the phosphate film can be determined by conventional methods. For example, a phosphated specimen [S (m²); W₁ (g)] is immersed in an aqueous solution of 5 wt% chromic acid at 75°C for 5 minutes to dissolve the film, and the weight of the specimen [W₂ (g)] is measured. The amount of the film [Wc (g/m²)] is calculated by the formula [Wc = (W₁-W₂)/S]. Then, the amount of manganese dissolved in the aqueous chromic acid solution [A(1)] is determined by the atomic light absorption method [M (g/l)] to obtain the total amount of dissolved manganese [WM = A · M/S (g/m²)]. Using the amount thus obtained and the above amount of film, the manganese content in % can be calculated from the formula (WM/Wc) · 100.

If the amount of fluoride ions in the phosphating solution is less than 0.05 g/l, micronization of the phosphate film, improvement of corrosion resistance after coating and phosphating treatment at a reduced temperature cannot be obtained. The fluoride ions may be present in an amount above 3 g/l, but the use of them in such amounts does not provide greater effects than those achievable with the range of 0.05 to 3 g/l. Preferably, the fluoride ion is contained in the form of a complex fluoride ion, e.g. the fluoroborate ion or the fluorosilicate ion, although the F- ion itself can also be used.

It has been found that when the chloride ion concentration in the phosphating solution reaches or exceeds 0.5 g/l (500 ppm), an excessive etching reaction takes place, resulting in undesirable white spots on zinc surfaces. Although the presence of chlorate ions may not directly cause the development of white spots, chlorate ions are gradually converted to chloride ions and accumulate in this form in the bath liquid, causing the white spots, as mentioned above.

Furthermore, it was found that the combination of manganese and fluoride ions is effective for formulating usable phosphating solutions that do not contain chlorate ions.

In the phosphating solutions of the invention, it is preferable that the weight ratio of zinc ions to phosphate ions is 1:(10 to 30). Within this ratio, a uniform phosphate film is obtained which meets all the performance requirements for a cationic electrocoating. The weight ratio of zinc ions to manganese ions is preferably 1:(0.5 to 2). Within this ratio it is possible to economically obtain a phosphate film which contains the required manganese and which exhibits all the beneficial effects made available by the present invention.

In the phosphating solutions of the invention, it is desirable that the solutions have a total acidity of 10 to 50 points, a free acidity of 0.3 to 2.0 points and an acid ratio of 10 to 50. With a total acidity in the above range, the phosphate film can be obtained economically, and with a free acidity in the above range, the phosphate film can be obtained uniformly without excessive etching of the metal surface. Adjustments in the solution to obtain and maintain the above points and ratio can be achieved, as required, by means of an alkali metal hydroxide or ammonium hydroxide.

Sources of the components of the phosphating solutions of the invention include the following: as regards zinc ions, zinc oxide, zinc carbonate, zinc nitrate, etc. can be used; as regards phosphate ions, phosphoric acid, zinc phosphate, zinc monohydrogen phosphate, zinc dihydrogen phosphate, manganese phosphate, manganese monohydrogen phosphate, manganese dihydrogen phosphate, etc. can be used; as regards manganese clays, manganese carbonate, manganese nitrate, the above-mentioned manganese phosphate compounds, etc. can be used; as regards fluoride ions, hydrofluoric acid, fluoroboric acid, fluorosilicic acid, fluorotitanic acid and their metal salts (e.g. zinc salt, nickel salt, etc. - however, sodium salt is excluded, since it does not produce the desired effect); and as for the phosphating accelerator, one can use sodium nitrite, ammonium nitrite, sodium m-nitrobenzenesulfonate, sodium m-nitrobenzoate, aqueous hydrogen peroxide, nitric acid, zinc nitrate, manganese nitrate, nickel nitrate, etc.

The phosphating solutions of the invention may further contain, as an optional ingredient, nickel ions. The content of nickel ions should be 0.1 to 4 g/l, preferably 0.3 to 2 g/l. When nickel ions are present together with the manganese ions, the performance of the resulting phosphate film is further improved, i.e. the adhesion and corrosion resistance of the coating obtained after cationic electroplating are further improved. In phosphating solutions containing nickel ions, the weight ratio of zinc ions to the sum of manganese ions and nickel ions is desirably 1:(0.5 to 5.0), preferably 1:(0.8 to 2.5). The source of nickel supply can be, for example, nickel carbonate, nickel nitrate, nickel phosphate, etc.

The phosphate film formed by the solutions of the present invention is a zinc phosphate type film. Such films formed on iron-based metal surfaces contain about 25 to about 40 wt.% zinc, about 3 to about 11 wt.% iron, about 1 to about 20 wt.% manganese, and 0 to about 4 wt.% nickel.

The phosphating solutions of the invention can be used to phosphate metal surfaces by spraying, dipping or a combination of such treatments. The spraying treatment can usually be carried out by spraying for 5 seconds or more to form an adequate phosphate film which exhibits the desired performance characteristics. The spraying treatment can be conveniently carried out using a cycle which comprises an initial spraying treatment of about 5 to about 30 seconds, a subsequent interruption of the treatment of about 5 to 30 seconds, and then a renewed spraying treatment of at least 5 seconds, the total time of the spraying treatment being at least 40 seconds. This cycle can be carried out once, twice or three times.

Dipping is usually more preferable than spraying in the process of the present invention. In order to form adequate films that exhibit the desired performance characteristics, dipping is usually carried out for at least 15 seconds, preferably from about 30 seconds to about 120 seconds. The treatment can also be carried out by first dipping for at least 15 seconds and then spraying for at least 2 seconds. Alternatively, the treatment can be carried out by first spraying for at least 5 seconds and then dipping for at least 15 seconds. The aforementioned combination of first dipping and then spraying is particularly advantageous for articles with complicated shapes such as a car body. For such articles, it is advantageous to first dip for 30 to 90 seconds and then spray for 5 to 45 seconds. In this process, it is advantageous to carry out the spray treatment for as long a time as is possible within the limits of an automobile production line in order to remove the sludge that adheres to the article during the dip treatment stage.

In the present process, the treatment temperature may be 30°C to 70°C, preferably 35°C to 60°C. This temperature range is approximately 10°C to 15°C lower than that used in the prior art processes. Treatment temperatures below 30°C should not be used because of an unacceptable increase in the time required to produce an acceptable coating. Conversely, if the treatment temperature is too high, the phosphating accelerator will decompose and an excessive precipitate will be formed, resulting in an imbalance of the components in the solution and making it difficult to obtain satisfactory phosphate films.

For spray treatments, a suitable spray pressure is an overpressure of 0.6 to 2 kg/cm².

As described above, a preferred mode of treatment using the solutions of the present invention is a dip treatment or a combined treatment in which first a dip treatment and then a spray treatment are applied.

An advantageous procedure for treating metal surfaces using a series of procedures preceding coating and subsequent phosphating with the solutions of the present invention is as follows:

A metal surface is first subjected to a dip treatment and/or a spray treatment with an alkaline degreasing agent for 2 minutes at a temperature of 50°C to 60°C, followed by the steps of: washing with tap water; spray treatment and/or dip treatment with a surface conditioning agent for 10 to 30 seconds at room temperature; dip treatment with the solution of the present invention for at least 15 seconds at a temperature of about 30°C to about 70°C; washing with tap water and then with deionized water, in that order. It is desirable to then follow with an acidified rinsing solution commonly used in the industry, such as a dilute chromate solution. This post-treatment is preferably carried out even if the phosphating is carried out by spray treatment or by a combined treatment comprising a spray treatment followed by a dip treatment. By introducing this post-treatment, a phosphate film can be obtained, which gives a siccative coating greater corrosion resistance.

When carrying out the dipping treatment or the dipping treatment followed by spraying treatment, which is the preferred treatment method of the present invention, it is advantageous to use an acidic aqueous phosphate solution of the present invention which

a') 0.5 to 1.5 g/l, preferably 0.7 to 1.2 g/l, zinc ions,

b') 5 to 30 g/l, preferably 10 to 20 g/l phosphate ions,

c') 0.8 to 3 g/l, preferably 0.8 to 2 g/l, manganese ions,

d') at least 0.05 g/l, preferably 0.1 to 2 g/l, fluoride ions,

e') less than 0.5 g/l chloride ions and

f') a phosphating accelerator in an amount specified above

(hereinafter referred to as "immersion solution").

When the above-mentioned dipping solution of the invention is used in the process of the invention on a metal surface, particularly a metal surface including both an iron-based metal surface and a zinc-based metal surface, a fine, uniform and dense phosphate film is economically formed thereon which imparts excellent adhesion and corrosion resistance to coatings formed by cationic electrocoating and which is substantially free of white spots.

Concentrated aqueous compositions are used for formulating the acidic aqueous phosphate solutions of the present invention. The acidic aqueous treating solutions are conveniently prepared by diluting an aqueous concentrate containing a number of the solution ingredients in the appropriate weight ratios and then adding other ingredients as needed to prepare the treating solutions of the present invention.

The concentrates are advantageously formulated to contain zinc ions, phosphate ions, manganese ions, fluoride ions and optionally nickel ions in a weight ratio of 0.1 to 2 : 5 to 50 : 0.8 to 4 : at least 0.05 : 0.1 to 4. The concentrates preferably contain a weight ratio of the above components of 0.5 to 1.5 : 10 to 30 : 0.8 to 3 : 0.1 to 3 : 0.3 to 2.

The concentrates are advantageously formulated to contain at least about 25 g/l, more preferably about 50 g/l to 130 g/l, of zinc ions. However, care must be taken in forming the concentrates. For example, if manganese ions and complex fluoride ions are present in a concentrate along with sodium ions, a precipitate will form. It is also not advisable to add any phosphating accelerator to the concentrate, as the accelerators tend to decompose and cause other problems.

As an example of a useful concentrated aqueous composition, a concentrated composition is formulated comprising 3.0% by weight of zinc oxide, 1.8% by weight of nickel (II) carbonate, 48.2% by weight of 75% phosphoric acid, 10.0% by weight of manganese (II) nitrate hydrate (manganese content 20% by weight), 7.9% by weight of 40% fluorosilicic acid, and 29.1% by weight of water. This concentrate is then diluted with water to 2.5% by volume, and then an aqueous solution of 20% sodium nitrite is added to obtain an acidic aqueous phosphating solution of the invention.

In order that the invention may be well understood, it will now be described by way of practical and preferred embodiments thereof, which are illustrated in the following examples and comparative examples. It should be noted, however, that the present invention is not limited to these examples.

Examples 1 to 3 and comparative examples 1 to 3 (1) Metal to be treated:

Galvanized steel plate

(2) Acidic aqueous phosphate solution:

The compositions listed in Table 1 were used.

(3) Treatment methods:

The surfaces of the above metal were simultaneously treated according to the following procedures:

Degreasing, washing with water, surface conditioning, phosphating, washing with water, washing with pure water, drying, coating.

(4) Treatment conditions: (a) Degreasing

Using an alkaline degreaser ("RTDOLINE SD200", manufactured by Nippon Paint Co., concentration 2 wt%), a spray treatment was carried out at 60ºC for 1 min, followed by an immersion treatment for 2 min.

(b) Washing with water:

Using tap water, washing was carried out for 15 s at room temperature.

(c) Surface conditioning:

Using a surface conditioning agent (“FIXODINE 5N-5”, manufactured by Nippon Paint Co., concentration 0.1 wt%), a spray treatment was carried out for 15 s.

(d) Phosphating:

Using the above acidic aqueous phosphate solution, immersion treatment was carried out at 52°C for 120 s.

(e) Washing with water:

Using tap water, washing was carried out for 15 s at room temperature.

(f) Washing with pure water:

Using deionized water, an immersion treatment was carried out for 15 s at room temperature.

(g) Drying was carried out for 10 min with hot air blower at 100ºC.

The appearance of each phosphated plate thus obtained and the weight of the phosphate film thereon were determined.

(h) Coating:

A cationic electrocoating composition ("POWER TOP U-30 Dark Grey", manufactured by Nippon Paint Co.) was coated to a film thickness of 20 µm (voltage: 180 V; exposure time to electricity: 3 min), and the surface was baked at 180ºC for 30 min. A number of each of the resulting electrocoated panels were used for the salt spray test.

The remaining untested electrocoated panels were coated with an intermediate coating composition ("ORGA T0778 Grey", manufactured by Nippon Paint Co.) to a film thickness of 30 µm and then with a topcoat coating composition ("ORGA T0626 Margaret White", manufactured by Nippon Paint Co.) to a film thickness of 40 µm to obtain coated panels with a total of 3 layers and 3 firings, which were then used for the adhesion test and the rust stain test.

(5) Test results:

The test results are shown in Table 2 below. Each test procedure is indicated below.

(a) Salt spray test (JIS-Z-2871)

Cross cuts were made on the electroplated plate, and a 5% saline solution was sprayed onto it for 500 h (zinc-plated steel plate) or 1000 h (cold-rolled steel plate).

(b) Adhesion test

The coated steel plate was immersed in deionized water at 50ºC for 10 days and then grids (100 squares each) were cut at 1 mm and 2 mm intervals using a sharp cutting tool. An adhesive tape was applied to each surface of the thus treated plate, which was then peeled off and the number of remaining coated squares on the coated plates was counted.

(c) White spot test

The presence of white spots was checked by visual observation.

0 . . . no white spot - X . . . white spots

In addition, scanning electron microscopy photography confirmed the presence of white spots of the phosphate film on a galvanized steel plate. Table 1 Composition of acidic aqueous phosphate solution Example (as F ion) Chloride ion Total acidity (points) Acid ratio Composition of acidic aqueous phosphate solution Comparison example (as F ion) Chloride ion Total acidity (points) Acid ratio Table 2 Metal: Galvanized steel plate Tested property Example White spots Film appearance uniform, dense excellent Weight Salt spray test Adhesion Metal: Galvanized steel plate Tested property Comparison example White spots Film appearance poor Weight Salt spray test Adhesion

As can be seen from Table 2 above, the use of solutions formulated as in the examples according to the invention produces more commercially acceptable phosphate coatings, while the use of solutions formulated as in the comparative examples (where the chloride ion content is above 0.5 g/l) produces commercially unsatisfactory coatings. It should be noted that although Example 1 contained a small amount of chlorate ion (0.2 g/l) which did not adversely affect the results obtained using the fresh bath, it is not recommended that the composition of Example 1 be used commercially since maintaining even this low chlorate content in the bath with progressive use of the bath will eventually result in a reduction in the sufficient chlorate ion with an increase in the chloride ion to a level above 0.5 g/l.

The present solution contains not more than 0.2 g/l of chlorate ions. It is particularly preferred that the solution does not contain chlorate.

The present invention is advantageous in terms of preventing white spots, especially on galvanized steel, particularly when the phosphating treatment involves immersion.

In an advantageous embodiment, the present solution contains at least about 1.05 g/l, in particular at least about 1.1 g/l zinc ions, for example about 1.05 to about 1.5 g/l zinc ions, especially when the phosphating treatment comprises immersion.

In another advantageous embodiment, the solution contains at least about 15 g/l phosphate ions, for example about 15 to 50 g/l, in particular about 15 to about 30 g/l, phosphate ions.

In a further advantageous embodiment, the solution contains more than about 4.0 g/l, in particular more than about 5 g/l, nitrate ions. The solution can thus contain about 5 to about 15 g/l, in particular about 5 to about 10 g/l, nitrate ions.

In yet another advantageous embodiment, the solution contains more than about 0.3 g/l, in particular more than about 0.4 g/l, of nickel ions. The solution can thus contain about 0.4 to about 4 g/l, in particular about 0.4 to about 2 g/l, of nickel ions.

These advantageous embodiments are particularly advantageous for avoiding white spots and providing the phosphate surface with other advantageous properties.

When it is stated herein that a solution comprises specified components, in a preferred embodiment it consists essentially of those components.

However, if the fluoride ion is provided, it is always measured as an F ion.

Claims (22)

1. Acidic aqueous phosphate solution for use in the phosphating of a metal surface, the solution containing not more than 0.2 g/l and preferably no chlorate ions at all and the lowest practical concentration of chloride ions, but in no case more than 0.5 g/l of the same, the solution also containing: a) 0.1 to 1.5 g/l zinc ions, b) 5 to 50 g/l phosphate ions, c) at least 0.8 to 4 g/l manganese ions, d) at least 0.05 g/l fluoride ions and e) at least one of the following phosphating accelerators in the following concentrations: i) 0.01 to 0.2 g/l nitrite ions, ii) 1 to 15 g/l nitrate ions, iii) 0.5 to 5 g/l hydrogen peroxide (based on 100% H₂O₂) (iv) 0.05 to 2 g/l m-nitrobenzenesulfonate ions, v) 0.05 to 2 g/l m-nitrobenzoate ions and (vi) 0,05 to 2 g/l p-nitrophenol. 2. Solution according to claim 1, which comprises 0.5 to 1.4 g/l zinc ions. 3. Solution according to claim 2, which comprises 0.7 to 1.2 g/l zinc ions. 4. A solution according to any one of claims 1 to 3, which comprises 5 to 30 g/l of phosphate ions. 5. A solution according to claim 4, which comprises at least 10 g/l of phosphate ions. 6. Solution according to claim 5, which comprises 10 to 20 g/l phosphate ions. 7. A solution according to any one of claims 1 to 3, which comprises 15 to 50 g/l of phosphate ions. 8. A solution according to any one of the preceding claims, which comprises 0.8 to 3 g/l of manganese ions. 9. Solution according to claim 8, which comprises 0.8 to 2 g/l of manganese ions. 10. A solution according to any one of the preceding claims, wherein the solution comprises 0.1 to 3 g/l of fluoride ions. 11. A solution according to claim 10, which comprises 0.1 to 2 g/l fluoride ions. 12. A solution according to any one of the preceding claims, which comprises 1 to 10 g/l of nitrate ions. 13. A solution according to any one of the preceding claims, which comprising one or more of the following accelerators in the following concentrations: (i) 0.04 to 0.15 g/l nitrite ions, ii) 2 to 8 g/l nitrate ions, iii) 1 to 1.5 g/l hydrogen peroxide (based on 100% H₂O₂) (iv) 0.1 to 1.5 g/l m-nitrobenzenesulfonate ions, v) 0.1 to 1.5 g/l m-nitrobenzoate ions and (vi) 0.1 to 1.5 g/l p-nitrophenol. 14. Solution according to any one of the preceding claims, which a) 0.7 to 1.2 g/l zinc ions, b) 10 to 20 g/l phosphate ions, c) 0.8 to 2 g/l manganese ions and d) 0.1 to 2 g/l fluoride ions. 15. A solution according to any one of the preceding claims, which comprises 0.4 to 4 g/l of nickel ions. 16. A solution according to any one of the preceding claims, which comprises 5 to 15 g/l of nitrate ions. 17. A solution according to any one of claims 1 to 15, which comprises 1 to 10 g/l of nitrate ions. 18. A solution according to any one of the preceding claims, which comprises 1.05 to 1.5 g/l of zinc ions. 19. A solution according to any one of the preceding claims, which comprises 15 to 50 g/l of phosphate ions. 20. Solution according to any one of the preceding claims, which is particularly designed for the dip treatment of metal surfaces, comprising a) 0.5 to 1.4 g/l zinc ions, b) 5 to 30 g/l phosphate ions, c) at least 0.8 to 3 g/l manganese ions, d) at least 0.05 g/l fluoride ions and e) at least one of the following phosphating accelerators in the following concentrations: i) 0.01 to 0.2 g/l nitrite ions, ii) 1 to 10 g/l nitrate ions, iii) 0.5 to 5 g/l hydrogen peroxide (based on 100% H₂O₂), (iv) 0.05 to 2 g/l m-nitrobenzenesulfonate ions, v) 0.05 to 2 g/l m-nitrobenzoate ions and (vi) 0,05 to 2 g/l p-nitrophenol. 21. Solution according to any one of the preceding claims, which a) 0.7 to 1.2 g/l zinc ions, b) 10 to 20 g/l phosphate ions, c) 0.8 to 2 g/l manganese ions and d) 0.1 to 2 g/l fluoride ions. 22. A solution according to any one of the preceding claims, which comprises 0.4 to 4 g/l of nickel ions.