EP0135622B1

EP0135622B1 - Phosphating metal surfaces

Info

Publication number: EP0135622B1
Application number: EP83304846A
Authority: EP
Inventors: Yasutake Mino; Ryoichi Murakami; Koichi Saito
Original assignee: Nippon Paint Co Ltd
Current assignee: Henkel Corp
Priority date: 1983-08-22
Filing date: 1983-08-22
Publication date: 1988-12-07
Also published as: DE3378641D1; MX161907A; EP0135622A1; ATE39134T1; BR8400392A; ES8607423A1; CA1218284A; ES535314A0

Abstract

Surfaces of iron-based metals or zinc-based metals are phosphated by contacting the metal surfaces with an acidic aqueous solution containing from 0.1 to 2.0 g/l of zinc ion, from 5 to 30 g/l of phosphate ion, from 0.2 to 3 g/l of manganese ion, and a conversion coating accelerator. The phosphated metal surfaces are then suitable for electrocoating.

Description

This invention relates to phosphating metal surfaces.
Japanese Patent Publications (unexamined) No. 107784/1980 and No. 152183/1980 (both in the name Nippon Paint Co. Ltd.) disclose phosphating methods for treating iron-based metal surfaces which are particularly suitable for treating manufactured products having complicated surfaces, such as automobile bodies. The phosphating methods are in use commercially in the automotive industry for pre-treating automobile bodies prior to cationic electrocoating, which is a coating process now used extensively in this industry. The phosphating method of Japanese Patent Publication No. 107784/1980 is carried out by first subjecting the metal surface to a dipping treatment with an acidic aqueous solution containing 0.5 to 1.5 g/I of zinc ion, 5 to 30 g/I of phosphate ion, and 0.01 to 0.2 g/I of nitrite ion and/or 0.05 to 2 g/I of m-nitrobenzenesulfonate ion at a bath temperature of 40° to 70°C for 15 seconds or more, followed by spraying with the above-mentioned solution for 2 seconds or more. The method of Japanese Patent Publication No. 152183/1980 comprises spraying onto the metal surface an acidic aqueous solution containing 0.4 to 1.0 g/I of zinc ion, 5 to 40 g/I of phosphate ion, 0.01 to 0.2 g/I of nitrite ion and 2.0 to 5.0 g/I of chlorate ion at 40° to 70°C for 40 seconds or more.
Recently, in the automotive industry, with the aim of further improving corrosion-resistance after the application of a siccative coating, steel components which are plated on one surface only with zinc or a zinc alloy have come to be used as materials for automobile bodies. When the processes of these Japanese Patent Publications are applied to such materials (i.e. to metal components having both iron-based metal surfaces and zinc-based metal surfaces), the iron-based surfaces are provided with a phosphate coating film having a low film thickness with uniform and dense cubic or plate-like crystals, as well as excellent adhesion and corrosion-resistance. Such a phosphate coating on the iron-based surface is suitable as a substrate for cationic electrocoating. However, in the case of the phosphate coating film formed on the zinc-based surfaces, the resistance to salt water spraying after the application of a cationic electrocoating thereto is insufficient, and secondary adhesion (tested by immersion of the surface bearing the film with cross-hatched scratches in warm water) after the sequence cationic electrocoating-intermediate coating-top coating is greatly inferior to that on the iron-based surfaces.
In addition to these Japanese Patent Publications, the following references disclose phosphating compositions for metal surfaces:
U.S. Patent 3,338,755 (Jenkins et al) discloses a process for phosphating metal surfaces with a phosphating solution containing zinc, manganese, phosphate, nitrate, and nitrite, as essential ingredients, in stated proportions.
German Patent 29 31 693 (Fosfa-Col) discloses a phosphating process using a solution containing zinc, manganese, phosphate, nitrate, and chlorate ions in stated gram-atom relationships.
However, none of the above proposed phosphating methods has succeeded in giving satisfactory results, especially with the above-mentioned combination of substrate materials.
Japanese Patent J50139-039 (JA 197511) discloses a conversion coating solution containing manganese ions for the treatment of zinc surfaces. However, this prior art solution contains from 3 to 20 g/I of zinc ions, which results in a conversion coating having leaf-like crystals on iron-based surfaces. Such leaf-like crystals are unsuitable as a substrate for cationic electrocoating. Hence, the solutions of this patent are unsuitable for treating both zinc-based and iron-based surfaces.
EP-A-0 018 841 discloses a coating composition for forming a zinc phosphate coating on a metal surface, which composition comprises an acidic, aqueous solution containing about 0.4 to about 1 g/I of zinc, about 5 to about 40 g/I of phosphate, and about 0.01 to about 0.2 g/I of nitrite. The specification states that there are applications where advantages can be realized by applying the composition utilizing intermittent spraying, and that for these applications, the composition includes also about 2 to about 5 g/I of chlorate. The specification states also that the aqueous coating solution may contain, in addition to the aforementioned ingredients, one or more of: nickel, cobalt, calcium and manganese ions, and one or more of nitrate, chloride and complex fluoride ions.
EP-A-0 060 716 discloses a process for phosphating an iron- or zinc-based metal surface comprising subjecting the metal surface to a dipping treatment in an acidic aqueous solution characterized in that the solution contains:

(a) from 0.5 to 1.5 g/I of zinc ion;
(b) from 5 to 30 g/l of phosphate ion;
(c) from 0.6 to 3 g/I of manganese ion; and
(d) a conversion coating accelerator.

The specification states that the conversion coating accelerator is preferably at least one of the following:

(i) from 0.01 to 0.2 g/I, preferably 0.04 to 0.15 g/l, of nitrite ion;
(ii) from 0.05 to 2 g/I, preferably 0.1 to 1.5 g/I, of m-nitrobenzene-sulphonate ion; and
(iii) from 0.5 to 5 g/I, preferably 1 to 4 g/I, of hydrogen peroxide (based on 100% H₂0₂).

The specification states also that optionally the acidic aqueous solution may also contain one or more of the following:

(e) from 0.1 to 4 g/I, preferably 0.3 to 2 g/l, of nickel ion;
(f) from 1 to 10 g/I, preferably 2 to 8 g/I, of nitrate ion; and
(g) from 0.05 to 2 g/I, preferably 0.2 to 1.5 g/l, of chlorate ion.

The present inventors have surprisingly found that by the inclusion of defined quantities of manganese ion in certain acidic aqueous phosphating solutions, very satisfactory results can be attained when the resulting solutions are applied by spraying more than once. The inventors have further found that the amounts of chlorate ion can be markedly lower than those of known compositions.
Accordingly, the present invention provides an improved phosphating method for metal surfaces, which is particularly suitable for treating metal surfaces, such as those of car bodies, which have both iron-based surfaces and zinc-based surfaces. The method is especially advantageous for forming phosphate coating films suitable for electrocoating, particularly cationic electrocoating.
Accordingly, the invention provides a process for phosphating an iron- or zinc-based metal surface comprising contacting the metal surface with an acidic aqueous solution containing:

(a) from 0.1 to 2.0 g/l, preferably 0.5 to 1.5 g/I, and more preferably 0.7 to 1.2 g/I, of zinc ion;
(b) from 5 to 30 g/I, preferably 10 to 20 g/l, of phosphate ion;
(c) from 0.2 to 3 g/l, preferably 0.6 to 3 g/l, and more preferably 0.8 to 2 g/l, of manganese ion;
(d) as conversion coating accelerator from 0.01 to 0.2 g/l, preferably 0.04 to 0.15 g/l, of nitrite ion; and
(e) from 0.05 to 1.9 g/I of chlorate ion, in which process the contact is by spraying the metal surface with the solution more than once. Additional conversion coating accelerator can also be present, in particular at least one of-the following:
- (i) from 0.05 to 2 g/I, preferably 0.1 to 1.5 g/I, of m-nitrobenzene-sulfonate ion; and
- (ii) from 0.5 to 5 g/l, preferably 1 to 4 g/I, of hydrogen peroxide (based on 100% H₂0₂₁.

The solution can be formed by a method comprising diluting with water a concentrate which comprises:

a. at least 25 g/I of zinc ion;
b. from 2.5 to 300 parts by weight of phosphate ion;
c. from 0.1 to 30 parts by weight of manganese ion; and optionally
d. from 0.05 to 40 parts by weight of nickel ion; the parts by weight being per 1 part by weight of zinc ion.

Using the present phosphating process, there can be produced a metal substrate having an iron- or zinc-based surface, which surface is coated with a zinc phosphate conversion coating which contains from 1 to 20%, preferably 2 to 15%, especially 2 to 7%, by weight of manganese, and which coating has a non-leaf-like crystal structure on iron-based surfaces.
In a particular, preferred, embodiment, the solution contains 0.1 to 0.4 g/I of zinc ion. In another particular, preferred, embodiment, the solution contains 1.6 to 2.0 g/I of zinc ion. In another particular, preferred, embodiment, the solution contains 0.2 to 0.5 g/I of manganese ion.
Optionally, the present acidic aqueous solution may also contain one or more of the following:

(f) from 0.1 to 4 g/l, preferably 0.3 to 2 g/I, of nickel ion;
(g) from 1 to 10 g/I, preferably 2 to 8 g/l, of nitrate ion.

The chlorate concentration in the present solution is preferably 0.2 to 1.5 g/I.
The present process is carried out preferably at a temperature of from 40° to 70°C, especially 45° to 60°C, and preferably for a contact time of at least 5 seconds, more preferably at least 15 seconds, especially 30 to 180 seconds, and most preferably 30 to 120 seconds, as hereinafter discussed. The period of spray treatment is generally at least 5 seconds. It should be noted that at temperatures below about 40°C coatings can be formed, but the coating is sparse, coating formation is relatively slow and longer times are required to form satisfactory coatings. At temperatures above 70°C, the conversion coating accelerators begin to decompose at an unacceptable rate, changing the composition of the solution and resulting in an unacceptable conversion coating; also, precipitates begin to form in the bath.
Following the present treatment, the phosphated metal surface(s) are then usually coated with a siccative coating by a known electrocoating process, preferably by the cationic electrocoating process.
The term "iron- or zinc-based metal surface" as used herein means iron-based surfaces, iron alloy-based surfaces, zinc-based surfaces, and zinc alloy-based surfaces. Zinc-based and zinc alloy-based surfaces include, for example, zinc plated steel plate formed by hot dipping, alloyed zinc plated steel plate formed by hot dipping, zinc plated steel plate formed by electroplating, and alloyed zinc plated steel plate formed by electroplating.
An important advantage of the present invention is that surfaces of metal components, such as car bodies, that contain both iron-based surfaces and zinc-based surfaces can be treated by the process of the invention with excellent results. In fact, the process of the invention produces better conversion coatings than are obtainable with conventional dip or spray treating processes, and the amount of etching of the metal surfaces during the present process is only 2/3 to 4/5 that of conventional processes, so that both the quantity of chemicals used in the process as well as sludge formation is only from 2/3 to 4/5 that of conventional processes. The present process is equally applicable to the treatment of a single metal surface of a type described above.
The metal surface to be phosphated is preferably first degreased by dipping in and/or spraying with a known alkaline degreasing agent at 50° to 60°C for a few minutes; washed with tap water; dipped in and/or sprayed with a known surface conditioner at room temperature for 10 to 30 seconds; and the thus treated metal surface then contacted with the acidic aqueous solution of the invention at 40° to 70°C for at least 5 seconds. Finally, the thus treated metal surface is preferably washed with tap water and then with deionized water. An acidic final chromate rinse can be employed before the rinse with deionized water.
In the present spraying procedure, the acidic aqueous solution contains

(a") from 0.1 to 2.0 g/I, preferably 0.5 to 1.5 g/I, and more preferably 0.7 to 1.2 g/I, of the zinc ion;
(b") from 5 to 30 g/l, preferably 10 to 20 g/l, of the phosphate ion; and
(c") from 0.2 to 3 g/l, preferably 0.6 to 3 g/I, of the manganese ion.

The ranges can be adjusted depending on the intended objects, materials and conditions used. However, when the amount of zinc ion is less than 0.1 g/l, an even phosphate film will seldom form on an iron-based surface, and a partially blue-coloured film is formed. On the other hand, when the amount of zinc ion is in excess of 2.0 g/I, then the film tends to be in the form of leaf-like crystals and deficient in secondary adhesion, which renders it unsuitable as a substrate for cationic electrocoating. When the amount of phosphate ion in the solution is less than about 5 g/l, an uneven film results, whereas when the amount of phosphate ion exceeds 30 g/I, no further improvement in the phosphate film is realized and hence, the use of greater quantities of phosphate is uneconomical. When the amount of manganese ion is less than about 0.2 g/l, the manganese content in the film formed on the zinc-based surface is insufficient, resulting in inadequate adhesivity of the siccative coating film to the phosphate conversion coating after cationic electrocoating. When the amount of manganese ion exceeds 3 g/l, no further improvement in the phosphate coating is realized and hence, use of a greater quantity is uneconomical. Furthermore, spot rusting of iron-based surfaces will increase. With respect to the nitrite conversion coating accelerator, when its amount is less than 0.01 g/l, the conversion coating on iron-based surfaces is inadequate, forming yellow rust, etc. When the amount of the nitrite accelerator exceeds 0.2 g/l, a blue-coloured uneven film is formed on iron-based surfaces.
The present contact of the metal surface with the coating solution, a plurality of times can be by intermittent spraying of the metal surface. For example, the coating solution can be applied by intermittent spray where the metal substrate is sprayed for about 5 to about 30 seconds, then allowed to stand without any coating application for about 5 to about 30 seconds, and then sprayed for at least 5 seconds, with a total spray time of at least 40 seconds. This cycle can be carried out once, twice or three times.
Of course, the above-mentioned treating times and treating sequences can be changed according to the composition of the metal substrate to be treated and the treating solution and conditions to be used.
For the spray applications, the coating solution is conveniently applied at a spraying pressure of from about 0.5 to about 2 kg/cm^2.
Irrespective of the particular application means and contacting solution used, the resulting phosphate film present on the zinc-based surface should preferably contain from about 1.0 to about 20% by weight, more preferably from about 2 to about 18% by weight, and most preferably from about 5 to about 18% by weight of manganese ion, which is very important for the subsequent cationic electrocoating. The zinc ion is usually present in from about 28 to about 45% by weight, preferably about 28 to about 40% by weight. When nickel ion is used in the solution, then from about 0.3 to about 4% by weight, preferably about 0.5 to about 4% by weight of nickel is usually present in the coating. The remainder of the coating is usually phosphate and water, except for quantities of other ions such as sodium, calcium and magnesium, which usually total less than 1% by weight. It has also been found that as the content of manganese in the bath increases, increased manganese coating results. However, increasing the manganese level of the coating above the ranges given above does not improve coating quality.
As examples of sources of zinc ions for use in the invention, one or more of the following can be employed: zinc oxide, zinc carbonate, and zinc nitrate. As examples of sources of phosphate ions, one or more of the following can be used: sodium phosphate, zinc phosphate, and manganese phosphate. As examples of sources of manganese ions, one or more of the following can be employed: manganese carbonate, manganese nitrate, manganese chloride, and manganese phosphate. As examples of sources of nitrite conversion coating accelerator, sodium nitrite or ammonium nitrite can be employed. As examples of sources of chlorate ions, chloric acid, sodium chlorate or ammonium chlorate can be employed. With respect to the optional ingredients that can be present in the acidic aqueous solution, the addition of nickel ion to the manganese-containing composition results in further improvement in the performance of the phosphate conversion coating, so that the adhesion and the corrosion-resistance of the film produced by cationic electrocoating are also further improved.
As sources of the optional ingredients, nickel carbonate, nickel nitrate, nickel chloride, nickel phosphate, etc. can be used for nickel ions; sodium nitrate, ammonium nitrate, zinc nitrate, manganese nitrate, nickel nitrate, etc. for nitrate ions; and sodium m-nitrobenzene-sulfonate or hydrogen peroxide for additional conversion coating accelerators.
The acidic aqueous treating solutions are conveniently prepared by diluting an aqueous concentrate which contains a number of the solution ingredients in proper weight ratios, and then adding other ingredients as needed to prepare the treating solutions. The concentrates are advantageously formulated to contain zinc ion, phosphate ion and manganese ion, and optionally nickel ion, in a weight proportion of

0.1 to 2: 5 to 30: 0.2 to 3: 0.1 to 4.

The concentrates are preferably formulated to contain at least about 25 g/I, and more preferably from about 50 g/I to 130 g/l, of zinc ion.
The phosphated metal surface is preferably rinsed and electrocoated.
The invention is illustrated by the following Example XXV. Comparative Examples I-XXIV and XXVI-XXXI are presented for purposes of comparison.

Comparative Examples I-XIV

The treating process used, which is common to all of these Examples, is given below, with the aqueous coating compositions of each Example being set forth in Table 1, while the metal treated and the test results obtained following the phosphate treatment are given in Table 2.
Samples of all four metal surfaces specified in Table 2 were treated simultaneously according to the following procedure:

(a) degreasing, using an alkaline degreasing agent (Nippon Paint Co., "Ridoline SD200", 2% by weight) which was sprayed on the metal surfaces at 60°C for 1 minute, followed by dipping in the solution for 2 minutes;
(b) the metal surfaces were then washed with tap water at room temperature for 15 seconds;
(c) the metal surfaces were next dipped into a surface conditioner (Nippon Paint Co., "Fixodine 5N5", 0.1% by weight) at room temperature for 15 seconds;
(d) the metal surfaces were then dipped into the acidic aqueous solution specified in Table 1 at 52°C for 120 seconds;
(e) the metal surfaces were washed with tap water at room temperature for 15 seconds;
(f) the metal surfaces were then dipped into deionized water at room temperature for 15 seconds;
(g) the surfaces were then dried in hot air at 100°C for 10 minutes. At this stage, the appearance and film weight of the treated metal surfaces was determined, with the results set forth in Table 2; and
(h) a cationic electrocoating material (Nippon Paint Co., "Power Top U-30 Dark Gray") was coated to 20 pm thickness onto the treated metal surfaces (voltage 180 V, treatment time 3 minutes), followed by baking at 180°C for 30 minutes. One sample of each electrocoated plate so obtained was subjected to the brine spray test.

A second sample of each electrocoated plate so obtained was coated with an intermediate coating material (Nippon Paint Co., "Orga T0778 Gray") to 30 pm thickness, followed by baking at 140°C for 20 minutes, and a top coating material (Nippon Paint Co., "Orga T0626 Margaret White") in 40 um thickness was then applied, followed by baking as above. Accordingly, coated plates with a total of 3 coatings and 3 bakings were obtained. The coated plates were subjected to the adhesion test, and with the cold rolled steel plate, to the spot rusting test.
The testing procedures referred to above are described below:

(A) Brine spraying test (JIS-Z-2871): Cross-cuts were made on an electrocoated plate; 5% brine was sprayed thereon for 500 hours (zinc plated steel plate) or 1000 hours (cold rolled steel plate).
(B) Adhesion test: After dipping a coated plate in deionized water at 50°C for 10 days, grids (100 squares) were made at 1 mm intervals or at 2 mm intervals using a sharp cutter; an adhesive tape was attached to each surface; and the number of squares of coating film that remained on the plate after the removal of the adhesive tape was counted.
(C) Spot rusting test: A coated plate was set at a 15 degree angle to the horizontal plane, and an arrow with a cone shaped head with a 90 degree vertical angle, made of alloyed steel (material quality, JIS-G-4404, hardness Hv 700 or higher) weighing 1.00 g and 14.0 mm in total length was dropped repeatedly from a distance of 150 cm, until 25 scratches were made on the coated surface. Subsequently, the coated plate was subjected to 4 cycles of testing, each cycle consisting of first, the brine spray test (JIS-Z-2871, 24 hours), second, a moisture test (temperature of 40°C, relative humidity 85%,120 hours), and third, standing at room temperature (24 hours). Test results are shown in Table 2.

In Table 2 above, the brine spray and spot rusting results each indicate average values (mm) of the largest diameter of blisters and rust spots, respectively.

Example XXV and Comparative Examples XV-XXIV and XXVI-XXXI

The treating process used, which is common to all of these Examples, is given below, with the aqueous coating composition of each Example being set forth in Table 3, while the metal treated and the test results obtained following the phosphate treatment are given in Table 4.
Samples of all four metal surfaces specified in Table 4 were treated simultaneously according to the following procedure:

(a) degreasing, using an alkaline degreasing agent (Nippon Paint Co., "Ridoline S102", 2% by weight) which was sprayed on the metal surfaces at 60°C for 2 minutes;
(b) the metal surfaces were then washed with tap water at room temperature for 15 seconds;
(c) the metal surfaces were then sprayed with the acidic aqueous solution specified in Table 3 at 52°C for 120 seconds, (in Ex. XXV, first sprayed for 15 seconds, spraying discontinued for 15 seconds, and again sprayed for 105 seconds) spraying pressure -0.8 kg/cm² (gauge pressure);
(d) the metal surfaces were washed with tap water at room temperature for 15 seconds;
(e) the metal surfaces were then dipped into deionized water at room temperature for 15 seconds;
(f) the surfaces were then dried in hot air at 100°C for 10 minutes. At this stage, the appearance and film weight of the treated metal surfaces were determined, with the results set forth in Table 4; and
(g) a cationic electrocoating material (Nippon Paint Co., "Power Top U-30 Dark Gray") was coated to 20 µtm thickness onto the treated metal surfaces (voltage 180 V, treatment time 3 minutes), followed by baking at 180°C for 30 minutes. One sample of each electrocoated plate so obtained was subjected to the brine spray test.

A second sample of each electrocoated plate so obtained was coated with an intermediate coating material (Nippon Paint Co. "Orga T0778 Gray") to 30 µm thickness, followed by baking at 140°C for 20 minutes, and a top coating material (Nippon Paint Co., "Orga T0626 Margaret White") in 40 Ilm thickness was then applied, followed by baking as above. Accordingly, coated plates with a total of 3 coatings and 3 bakings were obtained. The coated plates were subjected to the adhesion test, and with the cold rolled steel plate, to the spot rusting test.
The testing procedures referred to above are described below:

(A) Brine spraying test (JIS-Z-2871): Cross-cuts were made on an electrocoated plate; 5% brine was sprayed thereon for 500 hours (zinc plated steel plate) or 1000 hours (cold rolled steel plate).
(B) Adhesion test: After dipping a coated plate in deionized water at 50°C for 10 days, grids (100 squares) were made at 1 mm intervals or at 2 mm intervals using a sharp cutter; an adhesive tape was attached to each surface; and the number of squares of coating film that remained on the plate after the removal of the adhesive tape was counted.
(C) Spot rusting test: A coated plate was set at a 15 degree angle to the horizontal plane, and an arrow with a cone shaped head with a 90 degree vertical angle, made of alloyed steel (material JIS-G-4404, hardness Hv 700 or higher) weighing 1.00 g and 14.0 mm in total length was dropped repeatedly from a distance of 150 cm, until 25 scratches were made on the coated surface. Subsequently, the coated plate was subjected to 4 cycles of testing, each cycle consisting of first, the brine spray test (JIS-Z-2871, 24 hours), second, a moisture test (temperature of 40°C, relative humidity 85%, 120 hours), and third, standing at room temperature (24 hours). After testing, the average value (mm) of the largest diameter of rust spots and blisters was obtained, with the results shown in Table 4.
(D) Determination of Mn in coating: A phosphated plate was dipped in a 5% aqueous chromic acid solution (75°C) for 5 minutes, and the weight of the conversion coating was calculated from the weight difference of the plate before and after this treatment. Next, the amount of manganese dissolved out and contained in the aqueous chromic acid was determined by the atomic-absorption method, and manganese in the conversion coating was calculated therefrom.
- Mn(%) in the conversion coating=W_M/Wcx100 (%)
- W_C=W_l-W₂/S
- W_M=A.M/S
wherein
- W, stands for weight (g) of plate before chromic acid treatment;
- W₂ stands for weight (g) of plate after chromic acid treatment;
- S is surface area (m²) of plate;
- Wc is the coating weight per square metre (g/m²);
- A stands for volume (1) of chromic acid solution used;
- M stands for amount of Mn determined by atomic-absorption method (g/I); and
- W_M stands for amount of Mn in unit area (m²) of coating.

Claims

1. A process for phosphating an iron- or zinc-based metal surface by contacting the metal surface with an acidic aqueous solution containing:

(a) from 0.1 to 2.0 g/I of zinc ion;

(b) from 5 to 30 g/I of phosphate ion;

(c) from 0.2 to 3 g/I of manganese ion;

(d) as conversion coating accelerator from 0.01 to 0.2 g/I of nitrite ion; and

(e) from 0.05 to 1.9 g/I of chlorate ion,

which process is characterised in that the contact is by spraying the metal surface with the solution more than once.

2. A process according to claim 1 characterised in that the treatment is carried out by one to three intermittent spray cycles, each cycle consisting of first spraying for 5 to 30 seconds, then discontinuing spraying for 5 to 30 seconds, and then finally spraying again for at least 5 seconds, the total spray treatment time for each cycle being at least 40 seconds.

3. A process according to claim 1 or 2 characterised in that the contact is by spraying the metal surface with a solution containing:

(a) from 0.5 to 2 g/I of zinc ion;

(b) from 10 to 20 g/I of phosphate ion;

(c) from 0.6 to 3 g/I of manganese ion;

(d) as conversion coating accelerator from 0.01 to 0.2 g/I of nitrite ion; and

(e) from 0.05 to 1.9 g/I of chlorate ion.

4. A process according to claim 3 characterised in that the solution contains 0.5 to 1.5 g/I of zinc ion.

5. A process according to any one of the preceding claims characterised in that the solution also contains from 0.1 to 4 g/I of nickel ion.

6. A process according to any one of the preceding claims characterised in that the solution also contains from 1 to 10 g/I of nitrate ion.

7. A process according to anyone of the preceding claims characterised in that the temperature is from 40 to 70°C.

8. A process according to any one of the preceding claims characterised in that the metal treated includes both an iron-based surface and a zinc-based surface.

9. A process according to any one of the preceding claims characterised in that the phosphated metal surface is rinsed and electrocoated.