CA1218284A - Phosphating metal surfaces - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
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 subsequent electrocoating.

Description

3Z~3~

- PHOSP~IATING METAL SURF~CES
. ~
This invention relates to phosphating metal surfaces.
Japanese Patent Publications (unexamined) No. 107784/1980 and No. 152183/1980 (both in the name rlippon 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 use~ 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 containin~ 0.5 to 1.5 g/l of zinc ion, 5 to 30 ~/1 of phosphate ion~ and 0.01 to 0.2 g/l of nitrite ion and/or 0.05 to 2 g/l of m-nitrobenzene--sulfonate ion at a bath temperature of 40 to 70C 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.~ to 1.0 g/l of zinc ion, 5 to 40 g/l of phosphate ion, 0.01 to 0.2 g/l of nitrite ion and 2.0 to 5.0 g/l of chlorate ion at 40 to 70C for 40 seconds or more.
Recently, in the automotive industry, with the aim of further improving corrosion-resistanc~ 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 3~

metal sur~aces), the iron-based surfaces are provided with a phospha~e coating film having a low film thickness ~ith uniforln and ~ense cubic or plate-like cr~stals, as well a~ 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 surraces, the resistance to sait water spraying after the application of a ca~ionic electro-coating thereto is insufficient, and secondary adhesion(tested by immersion of the surface bearin~ 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 propo~ed phosphating methods has succeeded in giving satisfactory results, 30 especially with the above-mentioned combination of substrate materials.
Japanese Patent J50139-039 (JA 197511) discloses a conversion coating solution containing man~anese ions for the treatment of zinc surfaces. However, this prior art solution contains from 3 to 20 g/l of zinc ions, which results in a conversion coating havi~

3;Z8~

- PHOSPilATI~lG METAL SURFACES
.
This invention relates to phosphating metal surfaces.
Japanese Patent Publications (unexamined) No. 107784/1~80 and No. 152183/1980 (both in the name ~ippon 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 use~ extensive~ly in this industr~. The phosphating method of Japanese Patent Publication No. 107784/l9~0 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/l of zinc ion, 5 to 30 ~tl of phosphate ion~ and 0.91 to 0.2 g/l of nitrite ion and/or 0.05 to 2 g/l of m-nitro~enzene--sulfonate ion at a bath temperature of 40 to 70C 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 ollto the metal surface an acidic aqueous solution containing 0.4 to l.O g/l of zinc ion~ 5 to 40 g/l of phosphate ion, 0.01 to 0.2 g/l of nitrite ion and 2.0 to 5.~ g/l of chlorate ion at 40 to 70C for ~0 seconds or more.
Recently, in the automotive industry, with the aim of further improvin~ 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 3Z~3~
metal sur~aces), the iron-based surfaces are provided with a phosphate coating film having a low film thickness ~ith uni~or~n and dense cubic or plate-like cr~stals, as well as excellent adhesion and corrosion-r~sistance.
Such a phosphate coating on the iron-based surface is suitable as a substrate for cationic electrocoating.
However, in the case of the phosphate coàting film formed on the zinc-based surraces, the resistance to sait water spraying after the application of a ca~ionic electro-coating thereto is insuf~icient, and secondary adhesion(tested by immersion of the surface bearin~ 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 containin~ zinc, manganese, phosphate, nitrate, and nitrite, as essential ingredients, in stated proportions. -Cerman 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 propoced phosphating methods has succeeded in giving satisfactory results, 30 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/l of zinc ions, which results in a conversion coatlng havin, The invention provides also an aqueous concentrate which upon dilution with water forms a solution for use in the application of a conversion coating to iron- or zinc-based metal surfaces, which concentrate comprises:
(a) at least 25 g/l, preferably 50 to 130 g/l of zinc ion;
~ b) from 2.5 to 300 parts by weight of phosphate ion;
(c) from 0.1 to 30 parts bv 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.
The invention provides also 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 - 4a --- ~LZ1828~
non-leaf-like crystal structure on iron-based surfaces.
Tl1e metal surface can be contacted with the acidic aqueous solution by spraying the solution onto the surface o~' the metal, by dipping the metal sur-face into the solution, or by a combination of dippin~
and spraying steps.
In a particular, preferred, embodiment, the solution contains 0.1 to-0.4 g/l of zinc ion. In another particular, preferred, embodiment, the 10solution contains 1.6 to 2.0 g/l ol zinc ion. In another particular, preferred, embodiment, the solu-tion contains 0.2 to 0.5 g/l of manganese ion.
In a particularly surprising and preferred embodiment, the present process consists essentially of contacting-the metal surface with the solution by spraying the metal surface with the solution by optionally after spraying dipping the metal surface in the solution. This is distinguished from a contacting which consists of dipping or dipping followed by 20spraying. In the present embodiment, the contacting can be by spraying more than once optionally interrupted by dipping.
- Optionally, the present acidic aqueous solution may also contain one or more of the following:
(e) from about 0.1 to about 4 g/l, preferably about 0.3 to about 2 g~l, of nic~el ion;
(f) from about 1 to about 10 g /1 7 preferably about 2 to about 8 g/l, of nitrate ion;~nd (g) from about 0.05 to about 3 g/l (for example

2.1 to 3 g~l), preferably about 0.05 to about 1.9 g/l, and more preferably about 0.2 to about 1.5 g/l, of chlorate ion for both dipping and spraying use. However where a spray process is used with a zinc ion concentrationof more than 1 g/l~ i.e.from >1.0 g/l toabout 2.0 g/l Or ~inc ion, then up t~about 5 g/l (for example ~ to 5g/ljof chlorate ion ean te -` ~2~8;~84 pr,esent in the solution. Use of chlorate concerltrations in excess of these ranges is not advisable since at higher chlorate levels the phosphating rate becomes too rapid for satisfactory control.
The present process is carried out preferably at a temperature of from about 40 to about 70C, especially about 45 to about 60C, and preferably for a contact time of at least 5 seconds, more preferably at least 15 seconds, especially about 30 to about 180 seconds, and most preferably about 30 - to about 120 seconds, as hereinafter discussed. The , period of treatment is generally at least about 15 seconds for dipping and at least about 5 seconds for spraying. It should be noted that at temperatures below about 40C coatings can be formed, but the coating is sparse, coating formation is relativel~f slow and longer times are required to form satisfactory coatings. At temperatures above 70C~ the conversion coating accelerators begin to dqcompose 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

3 surfaces, zinc-based surfaces, and zinc alloy-based surfaces. Zinc-based and zinc alloy-based surfaces include, for example, zinc plated ~teel plate formed by hot dipping, alloyed zinc plated steel plate formed by hot dipping, zinc platedsteel plate formed by electroplating, and alloyed zinc plated steel plate formed by electroplating.

1~8'~
An important advantage of the present invention is that surfaces of metal component3, 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 t~ 60C 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 about 40 to about 70C 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 a preferred embodiment of the invention, use is made of a dipping procedure. In this embodiment, the 30 acidic aqueous solution preferably contains (a') from about 0.5 to about 1.5 g/l, more preferably about 0.7 to about 1.2 g/l, of zinc ion;
(b') from about 5 to about 30 g/l, more preferably bou~ 10 to about 20 gJl, of phosphate ion;

(c') from about 0.6 to about 3 g/l, more preEerably about 0.8 to about 2 g/l, of manganese ion; and (d') the conversion coating accelerator, preferably that and its quantities specified above, on the proviso that when the solution contains from about 0.6 to about 3 g/l of manganese ion, the zinc ion is not present in an amount from about 0.5 to about 1.5 g/l.
Most preferably the acidic aqueous solution contains (a) from 1.5 -2 g/l of zinc ion;
(b) from 10 to 20 g/l of phosphate ion;
(c) from 0.6 to 3 g/l of manganese ion; and ~ d~ conversion coating accelerator.
While these ranges are preferred, they can be adjusted within the broader limits stated above depending on the intended objects, materials and conditions used. However, certain general criteria for this dip process may be usefully stated here as follows: When the amount of zinc ion is less than about 0.5 g/l, an even phos-phate film is usually not formed on an iron-based surface, and a partially blue-coloured film is often formed. When the amount of zinc ion exceeds about 1.5 g/l, then though an even phosphate film is formed, the film formed on an iron-based surface tends to be in the form of leaf-like crystals, which are unsuitable as a substrate for cationic electrocoating. When the amount of phos-phate ion in the solution is less than about 5 g/l, an uneven film results. When the amount of phosphate ion exceeds about 30 g/l, no further improvement in the phosphate film is realized and hence, while not harmful, use of phosphate ion above about 30 g/1 j ~l lZ~8~

is uneconomical. When the amount of mangan~se ion is less than about 0.6 g/l, the manganese content in the film formed on the zinc-based surface is insufficient, resulting in inadequate adhesivity of the coating film to the phosphate substrate a~ter cationic electrocoating. When the amount of manganese ion exceeds about 3 g/l, no further improvement in the phosphate coating is realized, and hence, it is uneconomical to use amounts in excess of about 3 g/l.
With respect to the conversion coating accelerator, when the amount of these accelerators is less than the lower amounts given above, the conversion coating on iron-based surfaces is inadequate, forming - 8a --` i218Z84 yellow rust, etc. When the amount of accelerator exceeds the higher amounts given above, a blue-coloured uneven film is formed on iron-based surfaces.
In another preferred embodiment of the invention, use is made of a spraying procedure. In this embodiment, the acidic aqueous solution desirably contains (a"~ from about 0.1 to about 2.0 g/l, preferably about 0.5 to about 1.5 g/l, and more preferably about 0.7 to about 1.2 g/l, of zinc ion;
(b") from about 5 to about 30 g/l, preferably about 10 to about 20 g/l, of phosphate ion;
(c") from about 0.2 to about 3 g/l, preferably about 0.6 to about 3 g/l, of manganese ion; and (d") the conversion coating accelerator, preferably - that and its quantitiesspecified abo~e.
Here again, t-hese ranges can be adjusted dependin~ ~n the intended objects, materials and conditions used. ~owe~er, when the amount of zinc ion is less than 0.1 g/1, an e~en phosphate ~ilm will seldom form on an iron-b~sed surface, and a partially blue-coloured-film is formed. On the other hand, when the amount of æinc ion is in excess of 2.0 g/l, then the film tends to be in the for~ 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/l, no further improvement in the phosphate film is realized and hence, the use of greater quantities of phosphate is uneconomical. When the amc;lnt 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 .

_ g -- lZ1~2~34 reali~ed and nence, uqe of a greater ~uantity is unec?nomicaL. ~urthermore, sport rusting of iron--based surfaces will increase. With respect to the quantities of conversion coating accelerator, very similar results to those stated above i~ connection with the solution for dipping use are obtained.
In audition to the dipping and spray applic-ations described above, certain commercial conditions may warrant contacting the metal surface with the coating solution a plurality Or times, such as by intermittent spraying of the metal surface, by spraying followed by dipping, cr dipping followed by spraying. A combination of dipping and spraying treat~
ments may be employed. The coating composition can be ~pplied by these methods without a loss in coating formation. For example, the coating solution can be applied by intermittent spray, where the metal substrate is sprayed for about 5 to about 30 seconds1 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.
Furthermore, in treating metal components having compli-cated surface profiles, such as car bodies, the compon-ents can be subjected first to dipping treatments for about 15 seconds or more, preferably about 30 to about 90 seconds, and then to spray treatment with the solution for about 2 seconds or more, preferably for about 5 to about 45 seconds. In order to wash out the sludge which adheres durin~ dipping, the spray treatment is preferably carried out for as long a period within the above range as the speed of the production line will permit. Dipping treatment is preferred to spray treatment, but dipping followed by spraying is more preferred. Alternatively however t~e coating can be applied by first spraying the metal surface for from about 2 to about15 seconds, and then dipping the metal surface into the coating solution 120 seconds. This method of applying the coatir.g composition helps to eliminate "hash" marks on the metal surface as the metal surface - enters the dip coating solution. The "hash" marks res-ult when the conveyor system fails to move the sub-strate at a constant velocity, or when the substrate "sways" in a direction perpendicular to the direction of conveyor movement.
Of eourse, the above-mentioned treating times and treating sequences can be ehanged according to the composition of the metal substrate to be treated and the treating solution and conditions to be used.
For spray applications, the coating solution is con-veniently applied at a spraying pressure of from about 0.5 to about 2 Kg/em2.
Irreqpeetive of the applieation means and the contae-ting solution used, the resulting phosphate film present oil the zinc-based surface should preferably eontain from about 1.0 ~o about 20Yo by weight, more preferably from about 2 to about 18% by weight, and most preferably from about 5 to about about 18,' by weight of manganese ion, which is very important for the subsequent eationie eleetroeoating. The zine ion is usually present in from about 28 to about 450/D 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 4h by weight, preferably about 0.5 to about 4% by weight of nickel is usually present in the coating. The remainder of the eoating is usually phosphate and water, exeept for qu~ntities of other ions such as sodium, ealeium and magnesium, whieh usually total less than 1% by weight.
It has also been ~ound that as the content of manganese in the bath increases, inereased manganese eoating results. However, increasing the manganese level of the eoating above the ranges given above does not improve eoating quality.
As examples of sources of zinc ions for use in the ~21~328~
. .

invention, one or more of the following can be employ~d:
zinc oxide, ~inc carbonate, and ~.inc nitrate. As cxamples of sources of phosphate ions, one or more o~~ the following can be used: sodium phosphate, zinc phosphate, and manganese phosphate. As examples of sources of manganese ions, one or more o~ the followin~ can be employed: manganese carbonate, man~anese nitrate, manganese chloride, and manganesephosphate. As examples of sources of conversion coating accelerators, sodium nitrite, ammonium nitrite, sodium m-nitrobenzene-- sul~onate, and hydrogen pero~ide can be employed.
With respect to the optional in~redients that can be present in the acidic aqueous solution, the addition o~
nickel ion ~o the man&anese-containin~ composition results in further improve~ent in the performance of the phosphate conversion coatin~, so that the adhesion and the corrosion-resistance of the ~ilm produced by cationic electrocoating are also further improved.
As sources of the optional ingredients, nickel carbonate, nickel ~itrate, nickel chloride, nickel phosphate,etc. can be used for nickel ions;
sodium nitrate, ammonium nitrate, ~inc nitrate, ~.an~anese nitrate, nickel nitrate, etc~ for nitrate ions and chloric acid, sodiu~ chlorate, ammonium chlorate, etc.
ror chlarate ions.
The acidic aqueous treating solutions are conveniently prepared by dilutin~ an aqueous concentrate which contains a number of the solution ingredients in proper wel~ht ratios, and then adding other .:
.

~2 ~8284 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 gtl , and more pre-fer-ably from about 50 g/l to 130 g/l, of ~inc ion.
The phosphated metal surface is preferably rinsed and electrocoated.
The in~ention is illustrated by the following Examples.

; - 13 -1~82i~3~
, - EXAMPLES I - XIV

Examples I to IX are Examples of the process and compositions of the invention. Examples X to XIV are Examples using known compositions, given for comparison purposes. The treating process used, which is common to all of E~amples I - XIV, 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 ofall 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 60C
for 1 minute, followed by dipping in the solution for 2 minutes;
tb) 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 soluti~n specified in Table 1 at 52C 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 3 water at room temperature for 15 3econds;
(g) the surfaces were then dried in hot air at 100C
for 10 minutes. At this stage, the appearance and film weight of the treated metal surfaces was determined, with the results set forth in a o~ 1 a ~
_ 14 -:, ' iL2~ 8~
Table 2; and (h) a cationic electrocoating material (~ippon Paint Co., "Power Top U-30 Dark Gray") was coated to 20,u thic~ness onto the treated metal surfaces (voltage 180 V., treatment time 3 minutes), followed by baking at 180C 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 ~0778 Cray") to 30 thickness, followed by baking at 140C for 20 minutes, and a top coating material (Nippon Paint Co., "ORGA
T0626 Margaret White") in 40 ~ thickness was then applied, followed by baking as above. Accordingly, coated plates with a total of 3 coatings and 3 bakings ~ere 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-2~71): -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 deioni~ed water at 50C for 10 days, grids (100 squares) were made at lmm intervals or at 2 mm intervals using a sharp cutter; an adhesive tape was attached to each surface t and the number of squares of coating film that remained on the plate after the removal of the adhesive tape was counted.

2~8~

(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-C-4404, hardness Hv 700 or higher) weighing 1.00 g and 14.0 mm in total length was dropped repeatedly from a distance o~ 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 SDray test (JIS-Z-2871, 24 hours), second, a moisture test (temperature of 40C, relative humidity 85%, 120 hours), and third, standing at room temperature (24 hours) Test.
results are shown in Table 2.
.

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12~828~

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.

EXAMPLES X~ - XXXI
.

Examples X~ to XXV are Examples of the process and compositions of the invention. Examples XXVI to XXXI
are Examples using known compositions, given for comparison purposes.
The treating process used, which is common to all of Examples XV - XXXI, is given below, with the aqueous coating composition of each Example being set forth ih T.~ble 3, while the metal treated and the test results oi~tained 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 60C for 2 minutes;
- (b) the metal surfaces were then washed with tap water at room temper~ture for 15 seconds;
(c) the metal surfaces were then sprayed with the acidic aqueous solution specified in Table 3 at 52C for 120 seconds, (in ~x. XX~I, 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 I5 seconds;
(e) the metal surfaces were then dipped into deionized water at room temperature for 15 seconds;

12~
(f) the surfaces were then dried in hot air at 100C for 10 minutes. At this stage, the appearance and ~ilm wei~ht of the treated metal surfaces were determined, with the results set forth in Tabi~ 4; and - tg) a cationic electrocoating material (Nippon Paint Co., "Power Top U-30 Dark Gray") was coated to 20 ~ thickness onto the treated metal surfaces (voltage 180 V., treatment time 3 minutes), followed by baking at 180C 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 To778 Gray") to 30 thic~ness, followed by baking at 140C for 20 minutes, and a top coating material (Nippon Paint Co., "ORGA
To626 Margaret White") in 40 ~u 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-cut~ 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 ~later at 50C 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;

Z~8Z8~
and the number Or squares Or coating film that remained on the plate after the removal Or 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 scratch~s were made on the coated surfa~e.
Subsequently, the coated plate was subjected to 4 cycles of testing, each cycle consist ng o~
first,the brine spray test (JIS-Z-2871, 24 hours), second,a moisture test (tempe~ature of 40C, relative humidity 85%, 120 hours), and third, standing at room temperature (24 hours). After testing, the average value (mm) of the lar~es' diameter of rust spots and ~listers W2S
obtained, with the results shown in Table 4.
~) Determination of Mn in coating:
- A phosphated plate was dipped in 2 5~0 aqueous chromic acid solurlon (75C) for 5 minutes, and - the weight of the conversion coating was ; calculated from the weight difference of the Dlate before and after this treatment. Next, the amount of manganese dissolved out and contained in the aqueous chromie âcid was determined by the atomic-absorption method, and manganese in the conversion coating was calculated therefrom.
Mn(%) in the conversion coating = WM~I~c .Y 100 (%) ~'~C = Wl - W2 /S
WM = A.iM/S
wherein .

:

-` iZ~ 84 Wl stands for weight (g) of plate before chromic acid treatment;
~2 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/l); and WM stands for amount of Mn in unit area (m2) of coating.

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Table 4 ~conti nued) Metal Test item EX.XXIII EX.XXX ¦ EX.XXXI
_ l Hot Film appearance good evenness good evenness good evennessdipp~d & density zinc Film weight(g/m2) 2.4 3.7 2.0 alloy Brine spray plated ~ave.in mm) 2.5 4.0 4.5 on Adhesivity steel 2 mm cuts100/100 0/100 60/100 plate 1 mm cuts100/100 0/100 j 0/100 Electro- Film appearance good evenness good evenness good evenness plated 2 & density zinc on Film weight(g/m ) 1.9 3.0 1.8 steel Brine spray plate (ave.in mm) 3.5 8.6 7.5 Adhesivity 2 mm cuts 100/100 0/100 34/100 1 mm cuts 95/1000/100 0/100 Electro- Film appearance good evenness good evenness good evenness plated 2 & density zinc Film weight(g/m ) 2.2 3.6 2.2 alloy Brine spray on (ave.in mm) 2.5 3.0 4.0 steel Adhesivity plate 2 mm cuts 100/100 0/100 ~8/100 1 mm cuts 100/100 0/100 12/100 cold Film appearance good evenness good evenness yellow rust rolled & density uneven steel Film weight(g/m2) 1.2 2.2 1.1 plate Brine spray (ave in mm) 2.0 3.5 4.5 Adhegivity 2 mm cuts100/100 0/10080/100 1 mm cuts100/100 0/10030/100 Spot rusting (ave.in mm)1.00 4.52 5.02

Claims (24)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for phosphating an iron- or zinc-based metal surface comprising contacting the metal surface with an acidic aqueous solution com-prising:
(a) from 0.1 to 2.0 g/l of zinc ion;
(b) from 5 to 30 g/l of phosphate ion;
(c) from 0.2 to 3 g/l of manganese ion; and (d) a conversion coating accelerator, on the proviso that when the solution contains from about 0.6 to about 3 g/l of manganese ion, the zinc ion is not present in an amount from about 0.5 to about 1.5 g/l.

2. A process according to claim 1 wherein the solution contains 0.1 to 0.4 g/l of zinc ion.

3. A process according to claim 1 wherein the solution contains 1.6 to 2.0 g/l of zinc ion.

4. A process according to any one of claims 1-3 characterized m that the solution contains 0.2 to 0.5 g/l of manganese ion.

5. A process according to claim 1 consisting essentially of contacting the metal surface with the solution by spraying the metal surface with the solution and optionally after spraying dipping the metal surface in the solution.

6. A process according to claim 5 characterised in that the contact is by spraying the metal surface with the solution for about 2 - 15 seconds, followed by dipping the metal surface in the solution for at least 15 seconds.

7. A process according to claim 5 characterised in that the contact is by spraying the metal surface with the solution for at least 5 seconds.

8. A process according to claim 7 characterized 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.

9. A process according to any one of claims 5, 7 and 8 characterized in that the contact is by spraying the metal surface with a solution containing:
(a) from 1.5 - 2, g/l of zinc ion;
(b) from 10 to 20 g/l of phosphate ion;
(c) from 0.6 to 3 g/l of manganese ion; and (d) a conversion coating accelerator.

10. A process according to claim 1 characterized in that the solution also contains 0.05 - 3 g/l of chlorate ion.

11. A process according to any one of claims 5, 7 and 8 characterized in that the contact is by spraying the metal surface with the solution and the solution contains from 2 to 5 g/l of chlorate ion and from 1 to 2 g/l of zinc ion.

12. A process according to claim 1 wherein the metal treated includes both an iron-based surface and a zinc-oased surface.

13. A process according to claim 1 wherein the phosphated metal surface is rinsed and electrocoated.

14. An aqueous concentrate composition which, upon dilution with water, forms a solution for use in the application of a conversion coating to iron -or zinc- based metal surfaces, the composition comprising zinc ion, phosphate ion and manganese ion in weight ratios of 0.1 - 2:5 - 30: 0.2 - 3.

15. The composition of claim 14 further comprising nickel ion in an amount of 0.1 - 4 by weight.

16. The composition of claim 15 which contains at least 25 g/l of zinc ion.

17. An acidic aqueous composition for phosphating an ion - or zinc -based metal surface which comprises:
(a) from 0.1 to 2.0 gtl of zinc ion;
(b) from 5 to 30 g/l of phosphate ion;
(c) from 0.2 to 3 g/l of manganese ion; and (d) a conversion coating accelerator, on the proviso that when the solution contains from about 0.6 to about 3 g/l of manganese ion, the zinc ion is not present in an amount from about 0.5 to about 1.5 g/l.

18. The composition of claim 17 wherein the solution contains 0.1 to 0.4 g/l of zinc ion.

19. The composition of claim 18 wherein the solution contains 1.6 to 2.0 g/l of zinc ion.

20. The composition of claim 17, 18 or 19, wherein the composition contains 0.2 to 0.5 g/l of manganese ion.

21. An acidic aqueous composition for phosphating an ion - or zinc -based metal surface which comprises:
(a) from 1.5 - 2, g/l of zinc ion;
(b) from 10 to 20 g/l of phosphate ion;
(c) from 0.6 to 3 g/l of manganese ion; and (d) conversion coating accelerator.

22. The composition of claim 21 further comprising 0.05 - 3 g/l of chlorate ion.

23. The composition of claim 21 wherein 1 to 2 g/l of zinc ion is present and also from 2 to 5 g/1 of chlorate ion.

24. A metal substrate having an iron- or zinc-based surface characterized in that the surface is coated with a zinc phosphate conversion coating which contains from 1 to 20% of manganese, and which coating has a non-leaf-like crystal structure on iron-based surfaces.