AU608973B2 - Hard water-stabilizing additive to activating agents for zinc phosphating - Google Patents

Description

i fid~aJg~$~ S F Ref; 82620 FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: S Related Art: T;is document contains the lai.:'Inclments made under S-".tion 49 and is correct for Jpriiting.

4 t.n a Name and Address of Applicant: Address for Service: Henkel Kommanditgesellschaft auf Aktien Henkelstrasse 67 4000 Dusseldorf FEDERAL REPUBLIC OF GERMANY Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Hard Water-Stabilizing Additive to Activating Agents for Zinc Phosphating The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/4 Registered Patent Attorney TO: THE COMMISSICNER OUR REF: 82620 S&F CODE: 55370 OF PATENTS APPLICATION ACCEPTED AND AMENDMENTS ALLOW ED 2 S007050 5845/3 27/04/89 e I, HARD WATER-STABILIZING ADDITIVE TO ACTIVATING AGENTS FOR ZINC PHOSPHATING Abstract of the Disclosure The invention relates to hard water-stabilizing additives to treatment baths for the activation of metal surfaces composed of iron or steel, zinc, galvanized iron or steel, aluminum or aluminated iron or steel prior to the step of phosphating said surfaces with phosphating baths containing zinc ions, said additives consisting of poly(aldehydocarboxylic acids).

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inventors to the said applicant 4. The basic application referred to in paragraph 2 of this Declaration was the first application made in a Convention country in respect of the invention the subject of the application, Declared atDlsseldorf this 3 day of January 1989 Signatur 'o eclarant Dr 7n'4"' Ir, a~P on 0 S0 oo 00 0 0 00 00 0 0 0 00 0 QO 0o 00 0 o 00 0 0 0 00 00 O 00 00 0 0 00 00 0 0 94 0 t II HARD WATER-STABILIZING ADDITIVE TO ACTIVATING AGENTS FOR ZINC PHOSPHATING The invention relates to additives to treatment baths for the activation of metal surfaces composed of iron or steel, zinc or galvanized steel as well as aluminum or aluminated steel prior to phosphating said surfaces with phosphating baths containing zinc ions, and more specifically prior to so-called low-zinc phosphating wherein the ratio of zinc ions to phosphate ions in the treatment solution is less than 1:12. The invention also relates to the use of said additives.

Processes for producing phosphate layers on iron or steel surfaces by means of solutions of phosphoric acid containing various polyvalent metal cations and additives acting as accelerators oxidants) have been proven prior art for long. Such processes are employed, more particularly, in the automotive industry to achieve an improved protection from corrosion of the automotive bodies. The phosphated surfaces are subsequently coated with paints, preferably by cathodic electro-dipcoating.

Phosphated are the materials conventionally used in automotive body construction, usually iron or steel 2 sheets, more recently also electrogalvanized or hotgalvanized steel or materials having a surface composed of zinc alloys containing, for example, iron, nickel, cobalt or aluminum as alloying elements. Phosphating such surfaces for corrosion inhibition is usual not only in automobile construction but also in the manufacture of household appliances such as washing machines or refrigerators.

Prior to the above-mentioned treatment the work pieces are cleaned, rinsed and activated in order to obtain a thin and uniform phosphate layer to be produced which is known to be one pre-requisite for a good protection from corrosion. In the "high-zinc phosphat- 00 0 0o ing process" used for a long time it was possible in one S0O process step to remove adherent oils, fats and other 0°o contaminants including those due to machining from the o 000 oo 00 metal surface and at the same time to activate said 0 0 oa o0 metal surface for the following zinc phosphating step.

0 STreatment baths in accordance therewith have been described, for example, in the German Patent Specifico °o ations Nos. 2 951 600 and 3 213 649 within the scope of 0o o 0 processes for pre-treating metal surfaces prior to Sphosphating.

A0 A o c Meanwhile, more recently-there have been used to an increasing extent so-called "low-zinc phosphating processes" such as those set forth, for example, in the SGerman Patent Specification No. 2 232 067. These processes in combination with the usually following electro-dipcoating procedure result in a clearly improved corrosion resistance. However, these processes more sensitively respond to changes in the process parameters and to contaminations which are introduced 21 1__11- I~ 00 0 So 0 oo 01 0 a O O *o 00 0 a0 0 0 0 D0 0 0 0 i 0. t t Oi. 9 3 into the phosphating bath with the sheets to be coated.

Thereby, the step of activating the metal surface becomes much more important than before. It has proven to be particularly advantageous to carry out the activation in a separate process step subsequently to the step of cleaning and degreasing. This is all the more applicable if phosphating according to the low-zinc method is effected by a dipcoat procedure, while it is likewise relevant for zinc-phosphatjng according to spray or combined spray-dipcoat as well as dipcoat-spray procedures.

The activation of the metal surface has the following objectives: Increase of the rate of formation of nuclei and, hence, the number of crystal nuclei in the start phase of zinc phosphating, which results in a layer refinement; the porosity of the desired zinc phosphate layer is reduced due to the crystals being situated closely side by side. This results in the formation of a uniform and continuous zinc phosphate layer over the entire metal surface at a low surface area weight (indicated in grams of metal phosphate per 1 m 2 of metal surface), low surface area weights having proven to be beneficial as primer for paints.

Reduction of the minimum phosphating time, i.e. time required to completely cover the metal surface with a continuous zinc phosphate layer.

These effects provided by the activating agent finally result in that the paint layers to be applied 00 00 i 0 N F

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4 will be well anchored through the dense zinc phosphate layers containing fine particles and, thus, a good protection from corrosion will be attained which is the main object of zinc phosphating.

As efficient activating agents having the demanded properties, in practice exclusively products have proven to be valuable which contain polymeric titanium(IV) phosphate, such as those already described by Jernstedt, for example in the U.S. Patent Specifications Nos.

2,456,947 and 2,310,239. Today, these activating agents are preferably used in a separate rinsing bath immediately prior to the zinc phosphating step, while, however, they may also be previously added to an at best mildly "o alkaline cleansing bath.

a O °o Since the technical production of such activating o0C o agents of a constant and high quality is difficult, 0 0 o 0o O there has not been a lack in attempts to develop activa ating agents based on materials other than titanium phosphate.

00 0 o Thus, Jernstedt describes activating agents based 0 0 n on zirconium phophate or on reaction products of water- B" o soluble t.'n and lead compounds with disodium hydrogen 0 00 0 phosphate in the U.S. Patent Specifications Nos.

2,456,947 and 2,462,196. In the German Patent Specific- So. ation No. 29 31 712 there are described organic titanium compounds which are stable to hydrolysis as activating agents for zinc, zinc-manganese or manganese surfaces.

Said compounds are obtained by the reaction of a beta-diketone titanyl acetylacetonate with gluconic acid or gluconates in the presence of a hydrogen halide salt of an aliphatic aminoalcohol.

I.

1--3 -uurrrrrrrnn~ul 5 A further option for increasing the rate of formation of nuclei on steel is the treatment of the surface with diluted aqueous copper sulfate or copper nitrite solutions as well as with oxalic acid. However, the latter is only allowed to produce weak etching of the iron surface; the activation effect will disappear if a continuous iron oxalate layer will have been formed Patent Specification No. 2,164,024 and German Patent Specification No. 17 71 924).

The European Patent Specification No. 0 056 675 describes a process for the pre-treatment of steel wire prior to zinc phosphating using a bath containing sodium salts of oxalic, tartaric or citric acids as activating 0 9 agents.

9 i o9 0 The phosphate-containing activating agents are rapidly rendered unusable by the hardness elements of ,t water. Therefore, in practice it is necessary to employ 4 t the activating agents at least in partially de-salted water, better effects being attained in fully de-salted a' water. This is as costly as is the alternative of replenishing the activating baths with fresh activa-ing Smixture after only a short period of use.

As one possible solution to this problem there has been proposed in the European Patent Application No.

0 180 523 the use of phosphonic acids for complexing the water hardness or for hard water-stabilizing the activating agents. In application tests the process resulted in a well satisfactory activation at a markedly extended bath use-life as compared to activating baths containing no phosphonic acid. However, said process has the drawback of that the waste water to be disposed F--i -i r 7 0 0 So o S0 0 04 g 0 44 o 4 0 0 0 r 400 0 00a 1 0 0 0 0 4O 0 r Q i il

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of is additionally contaminated by the organophosphorus compounds which are biodegradable only with great difficulty.

The German Unexamined Patent Application 36 15 294 describes the use of anionic copolymers from unsaturated carboxylic acids and acrylic acid derivatives, isobutylene and/or styrene as well as anionic condensation products of naphthalenesulfonic acid and formaldehyde for "stabilizing" activating baths. This is understood to mean the delay of "ageing" of the baths, i.e. the phenomenon that activating baths once prepared will rapidly lose their activity even upon use of fully de-salted water, irrespectively of whether or not they will have been used. As a side-effect due to the use of polymers there has been indicated that for the preparation of the activating baths water of a lesser grade than so far usual may be used. As a parameter for the grade of the water there is used the specific conductivity.

However, said parameter which is commonly used in practice for characterizing the water quality by nature fails to tell anything about the presence of hardness elements in the water. Appropriate tests using hard water even proved the inefficiency of the decribed polymers for stabilizing in hard water. Similar copolymers which also do not contain any aldehyde groups have been claimed in the German Unexamined Patent Application 21 25 963 as additives to cleaning baths containing grain-refining titanium compounds to extend the pH range as required for the activating effect.

In contrast thereto, it is the object of the present invention to achieve a stabilization of the activating agents with respect to the hardness elements -7- 0e 0 0 00 0 0 "0 0s 0 0 0 0 0B 0* of water by using complexing agents which only contain the elements carbon, hydrogen and oxygen which under ecological aspects involve lesb problems.

Surprisingly it was found that polymers bearing aldehyde groups in addition to carboxyl groups offset the sensitivity to hard water of the activating agents without adversely affecting the activating effect.

According to a first embodiment of the present invention there is provided a method of using poly(aldehydocarboxylic acids) and/or their water-soluble alkali metal salts as hard water-stabilizing additives for treatment baths in the activation of metal surfaces composed of iron, steel, zinc, galvanized or alloy-galvanized iron or steel, aluminum or aluminated iron or steel comprising adding said additive to said treatment 00 bath prior to the step of phosphating said surfaces with phosphating baths o containing zinc ions.

According to one embodiment of the present invention there are 15 obtainable poly(aldehydocarboxyllc acids) and/or their water-soluble alkali metal salts by the reaction of hydrogen peroxide, acrolein and acrylic acid, which have a viscosity number within the range of from 5 to 50 ml/g, an acid value within the range of from 450 to 670, an acid equivalent weight within the range of from 125 to 0'0 a setting point of less than O"C, o a content of carboxyl groups within the range of from 55 to by mole, and a molecular weight within the range of from 1,000 to 20,000.

a0 0 00 *0 0 o 0 'Fluuu~ c I: ~.arnan~~~ 8 While according to the invention the poly(aldehydocarboxylic acids) are employed in the acid form, one embodiment of the present invention consists of that the poly(aldehydocarboxylic acids) are employed as alkali metal salts, the sodium salts being particularly preferred.

Furthermore, the present invention relates to the use of the additives according to the invention in treatment baths for the activation of metal surfaces in an amount of from 0.05 to 3 g/l.

One preferred embodiment of the present invention consists of that the poly(aldehydocarboxylic acids) are employed in an amount of from 0.5 to 1 g/l in treatment of baths for the activation of metal surfaces.

00 9Q0 o ©a .4 oI While basically the additives according to the o present invention may be employed in any conventional S0 phosphating process, one further preferred embodiment of the present invention consists of that the additives are employed prior to a low zinc-phosphating procedure.

One further preferred embodiment of the present o invention consists of that the additives are employed in treatment baths for the activation of metal surfaces in activating baths having a pH value of from 5 to 9.

H 0 The poly(aldehydocarboxylic acids) used according to the invention are commercially available and are marketed by the company DEGUSSA AG, Frankfurt (West Germany), for example under the designations POC OS POC HS 0010, POC HS 2020, POC HS 5060, POC HS 65 120 and POC AS 0010, POC AS 2020, POC AS 5060 or POC AS 65 120.

Herein the designation HS refers to the acid form, and

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9 the designation AS refers to the sodium salt form of the poly(aldehydocarboxylic acids). They may be prepared by a specific process developed by the company Degussa, the "oxidative polymerization" of acrolein. In said process, acrolein alone or in admixture with acrylic acid in an aqueous solution is treated with hydrogen peroxide. The H202 acts as a polymerization initiator and a molecular weight modifier. At the same time part of the aldehyde groups of the acrolein is oxidized by hydrogen peroxide to form carboxyl groups. Thereby polymers are formed which have pendant aldehyde and carboxyl groups, namely the poly(aldahydocarboxylic acids).

"f Indications on the above-described preparation of o the poly(aldehydocarboxylic acids) and on possible uses 0°o thereof are found in a company brochure by DEGUSSA AG under the title "POC-Umweltfreundliche Polycarbonsauren mit vielfaltigen Anwendungsm6glichkeiten" (Print note: SCH 215-3-3-582 Vol). In accordance therewith, the poly- (aldehydocarboxylic acids) may be used, for example, as o hardness stabilizers with respect to an inhibition of a 0 crystallization of calcium and other alkaline earth o metal salts, as inhibitor of deposit formation in sea water de-salting, as dispersing agent for aqueous pigment dispersions which are rich in solids, and as matrix material (builder) for washing and cleansing agents. Furthermore in said company brochure there may be found indications on respectively relevant patent literature, for example the German Patent Specification No. 10 71 339 (preparation), German Unexamined Patent Application No. 19 04 940 (complex-forming agents), German Unexamined Patent Application No. 19 04 941 (polyoxycarboxylic acids), German Patent Specification

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10 No. 19 42 556 (complex-forming agents), German Unexamined Patent Application No. 21 54 737 (rust-preventive treatment), German Unexamined Patent Application No.

23 30 260 and German Patent Specification No. 23 57 036 (preparation).

The free poly(aldehydocarboxylic acids) can be neutralized with alkali solutions to form the corresponding salts, e.g. with NaOH to form sodium poly- (aldehydocarboxylates).

The contents of carboxyl and carbonyl groups and the average molecular weight of the various grades of poly(aldehydocarboxylic acids) may be varied by selecting suitable reaction conditions. The general Sformula represents the fundamental structure of the poly(aldehydocarboxylic acids) to be used according to t, the invention.

S* HO[(CH2-CH-) (CH2-CH) y] -OH (I) COOH CHO 9 I 0 The poly(aldehydocarboxylic acids) are poly- (aldehydocarboxylic acids) which have been mostly linearly linked via carbon-carbon bonds and comprising many pendant carboxyl groups and a few pendant carbonyl groups and terminal hydroxyl groups. The chemical constitution thereof is more specifically characterized by the general formula The average degrees of polymerization are indicated by the viscosity numbers. These are usually between and 50 ml/g, based on 100% solids, measured as a 2% solution in 0.1N NaBr at 25 "C and a pH of 10 in an 11 a Qo s t 4 44e i6 r 0 dl a f 4 4 *Dl 4 4 4r p.

e «D I a 4 4 44a 4 4 0 4 4 4 Ubbelohde viscosimeter, capillary No. Oa. The steric linkage of the monomer constituents may be assumed to be atactic, the sequence of linkage may be assumed to be at random.

The content of carboxyl groups, expressed as by mole of COOH, may be calculated from the acid value (DIN 53402) of the dried polymers. The acid value of aqueous poly(aldehydocarboxylic acids) is unsuitable for calculating the molar percentage of COOH, since the technical grades contain minor amounts of formic acid, acetic acid and B-hydroxypropionic acid as by-products.

The sodium poly(aldehydocarboxylates) will have to be converted into the H form prior to the determination of the acid value by ion exchange.

Whereas upon use of commercially available activating agents in hard water (city tap water of hardness 18 in the subsequent zinc phophation coarse crystals are immediately formed due to an insufficient activation, the addition of the poly(aldehydocarboxylic acids) according to the invention produces phosphate layers having values of the area-based mass ("area weights") which otherwise are obtained only if fully de-salted water is used in the preparation of the baths of activating agents. Under the hardness conditions as investigated, the addition of an amount of polymer of 0.5 g/l proved to be sufficient, whereas higher amounts resulted in a coarse appearance of the phosphate layers.

In the individual case, the optimum amount of complexing agents will have to be determined for the local hardness conditions of the used (tap) water by way of a test series.

12

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12 In the preparation of the ready-to-use activating bath the amount to be employed may be flexibly adapted to the water hardness available at the respective site of use by the addition of the poly(aldehydocarLoxylic acids) according to the invention.

EXAMPLES

In order to determine the activating effect provided by the agents prepared according to the invention and by products used for comparison, the surfaces of steel specimens (material St 1405, dimensions cm x 20 cm, about 1 mm in thickness) were phosphated °o '5 by means of standardized phosphating processes according o o, to Table 1 (dipcoat phosphating, normal-zinc process).

00 0* Bo The "area weight" of the metal phosphate layer is 0 0 Sunderstood to mean the mass relative to the area, in 0 grams per square meter, determined according to DIN 50 492. For the determination of the bath capacity, oo0o two liters each of a 0.2% aqueous preparation of the So activating agent was loaded with test sheets which were subsequently phosphated. The average area weights of four subsequent test specimens were determined initially and after each tenth test sheet. The average values calculated therefrom are set forth in Table 3. The baths were considered to have been exhausted, if ten 4 t t sheets in a series upon being zinc phosphated exhibited defects or coarsely crystalline regions. The bath capacity is expressed as 'square meter of activatable area per two liters of activating bath.

13- Comparative Example 1 As product for comparison there was employed a commercially available titanium phosphate containing activating agent of the company Collardin, Cologne (Fixodine® The results of activation obtained thereby are set forth in Table 3.

Comparative Example 2 An ethylene-maleic anhydride copolymer EMA 1103 of the company MONSANTO according to the German Unexamined Patent Application 36 15 294 was employed in the same molar amount as the additive according to the invention. The result (see Table 3) shows the inefficiency of this polymer o o for hard water-stabilization.

S. amples 1 to 6 The Examples furnish evidence of the efficiency of the additive according to the invention in combination with differently formulated o, 5 activating agents. Employed were the poly(aldehydocarboxylic acids) o POC HS 5060, POC HS 0010 and POC HS 65 120 of the company DEGUSSA AG, Frankfurt, which are characterized in greater detail in Table 2. The obtained results are also summarized in Table 3.

00 0 0 0 I S0 o 0 C i A

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0 0 0 0 0 0 0 0 0 0 -e o' 3 r a a 00 0 C o3 0 oo c o c o o 0 0 C 0 0000 C 0co o c o a o o c o S0 00 Table 0 0 T ab le 1 Treatment steps in the course of the standard phosphating process Stage Treatment Treatment Concentration Temperature Period of Treatstep with by weight ment (min) 1 Mechanical bibulous paper cleansing and 20 degreasing 2 Chemical Ridoline(R) cleansing and C 1051 1) 5 80-90 degreasing 3 Rinsing Tap water 2 20 1 3) 4 Mordanting Chemapix(R) ACM 30 20 1 Rinsing Tap water 2 20 1 6 Activation Activating agent according to 0.2 20 2 Table 3 Continued rco pr r e I c -ir r o J ci c ci ci3 d ci ci1 ci D c DoD cic DoD ci c c ci c aa ci a o o ci c i c ci ci Dci Dci0 DODOD i ci ci c ccic Table 1 continued Stage Treatment step Treatment with Concentration Temperature Period of Treatby weight ment (min) 7 Phosphating Granodine(R) 4) 3.0 60-70 8 Rinsing VE water 5) 20 1 9 Drying Compressed air -20 to dryness I) Commercially available strongly alkaline phosphate-containing immersion cleaner, of the company Collardin, Cologne.

2) Untreated city water of 18 "d.

3) Commercially available rust-removing and descaling agent containing hydrochloric acid and inhibitor, of the company Collardin, Cologne.

4) Commercially available nitrate/nitrite accelerated phosphating agent, of the company Collardin, Cologne.

Fully desalted (demineralized) water.

i L C 5 0 0 0 9 00 C 00 0 C0 0 0z 9 0 0 000 'Ji Ta bl1e 2 Solids pH Value Density (g/ml) viscosity at 20 'C (mPa. s) S etting point Color Value viscosity DIN 6162 number* (ml/g) POC HS 5060 40 1.3 1.1 240 -9 2 28 POC HS 0010 50 1.0 1-2 115 -9 7 8 POC HS 65 120 35 1.7 1.1 380 -9 3 47 The viscosity number was based on 100% solids, measured with a 2% solution in 0.1N NaBt at 25 'C and pH 10; Ubbelohde viscosimeter, capillary Oa.

1 -01 g--n~ n

B

17 Table 3 Influence of additives for the hard-water stabilization of activating baths

EX-

AMPLE

Activating Agenta) Additive (1 g/l) Area Weight g/m 2 Capacityb) 4r 4 446 4 a4 9I 94 44P 4 4 4.1 4, o Q 4l A 9 V.4 Asn 4 V.4 Comparative FIXODINE® 6 c) NONE d) 1 Comparative same EMA 1103 4 .5-7.5d) 2 1 same POC HS 5060 2.9 2 same POC HS 0010 2.4 2.4 3 same POC HS 65 120 2.6 4 e) POC HS 5060 2.4 3.2 POC HS 5060 2.5 2.8 6 e) POC HS 5060 2.5 3.3 (0.5 g/1) a)a Batch 0.2% by weight in city water of 18 "d.

b) Activatable area in m 2 per 2 liters of activating bath.

c) c .'est substance: Activating agent containing titanium phosphate by the company Collardin, Cologne.

d Coarse crystals due to an insufficient activating effect.

18 e Activating agent containing titanium phosphate, prepared with 1.7% by weight of POC HS 5060.

f) Activating agent containing titanium phosphate, prepared with 2.4% by weight of 1-amino-l-phenylmethane-1,1-diphosphonic acid.

The activating agents containing titanium phosphate used in the Examples 4, 5 and 6 (cf. the annotations e) and have been described in the German Patent Application No. P 38 14 287.2 which has not been previously published.

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Claims (8)

1. A method of using poly(aldehydocarboxylic acids) and/or their water-soluble alkali metal salts as hard water-stabilizing additives for treatment baths in the activation of metal surfaces composed of iron, steel, zinc, galvanized or alloy-galvanized iron or steel, aluminum or aluminated iron or steel comprising adding said additive to said treatment bath prior to the step of phosphating said surfaces with phosphating baths containing zinc ions.

2. A method according to claim 1, characterized in that the poly(aldehydocarboxylic acids) and/or their water-soluble alkali metal o salts are obtained by the reaction of hydrogen peroxide, acrolein and S acrylic acid, and have a*°o a viscosity number of 5 to 50 ml/g, oo an acid value of 450 to 670, an acid equivalent weight of 125 to a setting point of less than 0OC, a content of carboxyl groups of 55 to 90% by mole, and a molecular weight of 1,000 to 20,000.

3. A method according to claim 1 or 2, characterized in that the alkali salts of the poly(aldehydocarboxylic acids) are sodium salts.

4. A method according to any one of claims 1 to 3 wherein the poly(aldehydocarboxylic acids) and/or their water-soluble alkali metal salts are present in an amount of from 0.05 to 3 g/l. 0 o

5. A method according to claim 4 wherein the amount is from 0.5 to 1 g/l.

S6. A method according to any one of claims 1 to 5 wherein the o. additive is added prior to a low zinc-phosphating procedure.

7. A method according to any one of claims 1 to 6 where the pH value of the treatment baths is from 5 to 9. 7 I 20

8. A method of using poly(aldehydocarboxylic acids) and/or their water-soluble alkali metal salts as hard water-stabilizing additives for treatment baths in the activation of metal surfaces composed of iron, steel, zinc, galvanized or alloy-galvanized iron or steel, aluminum or aluminated iron or steel prior to the step of phosphating said surfaces with phosphating baths containing zinc ions substantially as hereinbefore described with reference to the Examples but excluding the Comparative Examples. I- I 1 1* I I( I ~8 C O C DATED this FOURTEENTH day of JANUARY 1991 Henkel Kommanditgesellschaft auf Aktien Patent Attorneys for the Applicant SPRUSON FERGUSON "CC" C C CC 'I I I r Io I CO rI b8R6 PE .1\