EP0796356A1

EP0796356A1 - Method of applying phosphate coatings to metal surfaces

Info

Publication number: EP0796356A1
Application number: EP95941068A
Authority: EP
Inventors: Thomas Wendel; Hardy Wietzoreck; Klaus Bittner; Peter Schiefer; Marcus Schinzel; Helmut HÜLSMANN
Original assignee: Metallgesellschaft AG
Current assignee: Chemetall GmbH
Priority date: 1994-12-09
Filing date: 1995-12-05
Publication date: 1997-09-24
Anticipated expiration: 2015-12-05
Also published as: ATE173034T1; JPH10510322A; ZA9510440B; CN1169165A; AU700492B2; CN1066207C; CA2207932C; EP0796356B1; US5904786A; DE59504172D1; MX9704126A; WO1996017977A1; CA2207932A1; AU4259996A; ES2124032T3; KR970707322A; DE4443882A1

Abstract

The proposed method of applying phosphate coatings to surfaces of zinc, iron, aluminium or alloys of those metals, involves wetting the surfaces with a phosphatising solution which contains no sub-group 5 or 6 elements, 0.5-8 g/l nickel, 2-20 g/l manganese, 18-170 g/l phosphate (in the form of P2O5) and has an acid number of 0.4-0.8. The wetting is done in such a way that, after the subsequent drying-on process, a phosphate layer with a weight per unit area of 0.3-3.0 g/m2 is produced. In the case of surfaces of iron, aluminium or alloys thereof, the phosphatising solution must contain 0.5-5.0 g/l of zinc. In the case of zinc or zinc alloy surfaces, the solution need not, and preferably should not, contain zinc. The process according to the invention can be used to particular advantage in the phosphatisation of zinc-plated or zinc alloy-plated steel strip.

Description

Process for applying phosphate coatings on metal surfaces

description

The invention relates to a method for applying phosphate coatings on surfaces of zinc, iron, aluminum or their alloys by wetting them with a phosphate solution containing divalent cations and phosphate and then drying the liquid film.

The process of producing phosphate coatings using aqueous zinc phosphate solutions is widely used in the metalworking industry. The phosphate layers created with this process on the treated metal surfaces are used in particular to facilitate sliding, to prepare for non-cutting cold forming, as well as to protect against corrosion and as a paint primer.

Such phosphating solutions usually have a pH between about 1.8 and 3.8 and contain zinc and phosphate ions as process-determining components. In addition to the cation zinc, other cations, for example ammonium, calcium, cobalt, iron, potassium, copper, sodium, magnesium, manganese, may also be present. In order to accelerate the formation of the phosphate layer, oxidizing agents such as bromate, chlorate, nitrate, nitrite, organic nitro compounds, perborate, persulfate or hydrogen peroxide are generally added to the phosphating solutions. In order to optimize the layer formation on certain materials, additives such as Fluoride, silicon fluoride, boron fluoride, citrate and tartrate. Due to the large number of individual components and their possible combinations, there are a multitude of different compositions of the phosphating solutions.

The so-called low-zinc processes represent a special embodiment of the phosphating processes. The phosphating solutions used here contain zinc in concentrations of only about 0.4 to 1.7 g / l and, particularly on steel, produce phosphate layers with a high proportion of phosphophyllite, which is better Provides paint adhesion and a higher resistance to paint infiltration when exposed to corrosion than is customary in the production of phosphate layers based on Hopeit from phosphating solutions with a higher zinc content. (DE-A-22 32 067, EP-A-15 021, EP-A-39 093, EP-A-56 881, EP-A-64 790, K. Wittel:

"Modern zinc phosphating process-low zinc technology", industrial painting, 5/83, page 169 and 6/83, page 210).

A comparatively new development is represented by phosphating processes, which experts call the trication process. These are low-zinc phosphating processes, in which the use of nickel in e.g. Quantities of 0.3 - 2.0 g / 1 and manganese in quantities of e.g. 0.5 - 1.5 g / 1 phosphate coatings are obtained, which are characterized by an increased alkali resistance and are therefore of importance for cathodic electrocoating, in particular for car bodies.

Processes have been developed specifically for the phosphating of electrolytically galvanized or hot-dip galvanized steel strip, which allow the formation of a phosphate layer in accordance with the trication process within a contact time of 3 to 8 seconds. (EP-A-111 246).

A common feature of the aforementioned phosphating processes is that the phosphating solution is brought into contact with the workpiece surfaces to be treated in immersion, flooding or spraying. After the chemical reaction has taken place and the solid, Critalline phosphate layer requires a rinsing treatment to remove any phosphating chemicals remaining on the surface, which is usually carried out in several stages. This results in rinsing solutions that cannot be disposed of in this form, but must be sent to a wastewater treatment plant.

There have been various proposals to reduce the amount of rinsing water or to eliminate it entirely, for example rinsing in a so-called rinsing water cascade is associated with a considerable reduction in the amount of rinsing water that is produced. However, it is inevitable that the rinse water, even in a reduced amount, will be worked up. In order to avoid rinsing water, it has been proposed to use a zinc phosphating process whose phosphating solutions are composed in such a way that practically all components can be precipitated with calcium hydroxide. In this way, the rinse water treatment is made considerably easier, and at the same time the method has the advantage that water of sufficiently good quality can be recovered for the process. (DE-C-23 27 304). A disadvantage of such a procedure, however, is that the requirement for the constituents of the phosphating solution to be able to precipitate gives the freedom to adapt the composition of the phosphating solution to

Practice needs are severely limited. Finally, methods for producing a conversion coating are known, in which coating solutions are applied after any cleaning and water rinsing that may be required, and then dried on. The treatment solution can be applied by dipping or spraying with subsequent squeezing of the excess solution or by roller application, in which only the required amount of liquid is applied to the metal surface. The drying-up following the application of the treatment liquid can in principle already take place at room temperature. In general, however, it is common to use higher temperatures, preferably temperatures between 50 and 100 ° C. One such method, which is intended for preparing metal surfaces for subsequent coating with organic coatings, is to wet the metal surface with a phosphating liquid which has a pH of 1.5 to 3, is chromium-free and contains, in addition to metal phosphate, soluble molybdate, tungstate, vanadate, niobate and / or tantalate ions (EP-B-15 020). The cationic component of the metal phosphate in the solution can be formed by calcium, magnesium, barium, aluminum, zinc, cadmium, iron, nickel, cobalt and / or manganese.

A disadvantage of the last-mentioned process is that due to the necessary additions of molydate, tungstate, vanadate, niobate and tantalate ions, the process is more cost-intensive than the conventional phosphating processes, another that the phosphate coatings obtained do not meet all requirements today e.g. B. with regard to alkali resistance and thus resistance in a subsequent cathodic electrocoating and the desired corrosion resistance, in particular in connection with a subsequent painting, are sufficient.

The object of the invention is to provide a method for applying phosphate coatings on surfaces of zinc, iron, aluminum or their alloys, which does not have the known, in particular the aforementioned disadvantages, is nevertheless inexpensive and simple to carry out and leads to high-quality phosphate coatings.

The object is achieved by the method of the type mentioned according to the invention is designed such that the

Surfaces with a phosphating solution that are free from elements of the

5th and 6th subgroup of the Periodic Table of the Elements,

0.5 to 8 g / 1 nickel

2 to 20 g / 1 manganese

Contains 18 to 170 g / 1 phosphate (calculated as P _: 0 ₅ ) and has an S value of 0.4 to 0.8, wetted in such a way that a phosphate layer weight of 0.3 to 3.0 after drying g / m ² results, the phosphating solution in the case of

Phosphating of surfaces made of iron, aluminum or their

Alloys necessarily contain 0.5 to 5 g / 1 zinc and in the case the phosphating of surfaces made of zinc or zinc alloys can contain zinc ions.

The aforementioned formulation with regard to the zinc content is intended to express that in the case of the treatment of surfaces made of iron, aluminum or their alloys, a zinc content in the concentrations mentioned is essential. When treating zinc or zinc alloy surfaces, the phosphating solution can also contain zinc, but a zinc content is not required. Elements of the 5th and 6th subgroup of the Periodic Table of the Elements are vanadium, niobium, tantalum, chromium, molybdenum and tungsten.

In order to avoid that the phosphate coating has a content of water-soluble compounds after drying, the S value is expediently set with nickel oxide, manganese oxide or possibly zinc oxide or with ammonia solution.

An expedient embodiment of the invention provides that, in the case of the treatment of zinc or zinc alloys, the surfaces are wetted with a phosphating solution which is zinc-free. In this particular case, the amount of zinc required to form the coating comes from the surface of the treated material.

The wetting of the respective metal surfaces can e.g. by immersion and subsequent draining, by pouring over and spinning off, by brushing, by spraying with compressed air, air-les and electrostatically. A particularly elegant method of applying the phosphating solution is carried out by rolling with structured or smooth rollers in the same direction or in the opposite direction.

The drying following the wetting of the metal surface can in principle already take place at room temperature. However, it is advantageous to work at higher temperatures because this considerably reduces the time for the formation of the phosphate layer. Drying is preferably carried out at temperatures between 50 and 200'C, but an object temperature of 90 "C should not be exceeded.

A preferred development of the invention is that

Wetting surfaces with a phosphating solution

0.8 to 6 g / 1 nickel,

3 to 16 g / 1 manganese,

30 to 140 g / 1 phosphate (calculated as P-O and in the case of phosphating surfaces made of iron or

Aluminum or its alloys contains 0.8 to 4 g / 1 zinc. The aforementioned embodiment of the invention leads to particularly high quality phosphate coatings.

An additional improvement in the quality of the phosphate coatings can be achieved if, according to an advantageous embodiment of the

Invention wetted the surfaces with a phosphating solution, the additional

2 to 10 g / 1 Si0 ₂ and

Contains 0.05 to 0.5 g / 1 fluoride (calc. As F). As SiO _: because of its good dispersibility, pyrogenic silica is particularly suitable. It is advantageously added dispersed in water. Fluoride is conveniently in the form of

Hydrogen fluoride or their aqueous solution introduced. These additives in particular bring about the formation of a uniform and closed coating which practically does not tend to stick.

Further advantageous embodiments of the invention consist of wetting the surfaces with a phosphating solution which has an S value of 0.5 to 0.7 or wetting the surfaces with the phosphating solution in such a way that after drying a phosphate layer weight of 0, 5 to 2 g / m ^: results.

The setting of the preferred S value of 0.5 to 0.7 is particularly important in the treatment of zinc surfaces with zinc-free phosphating solutions, since the pickling attack of the phosphating solution on the zinc surface responsible for the zinc content of the phosphate coating is particularly optimal runs. The embodiment of the invention with a phosphate coating weight of 0.5 to 2 g / m ^* enables the phosphate coating to be formed in a particularly short time and, moreover, of particularly high quality.

When using the method according to the invention

Phosphate layers produced that 0.5 to 3 wt .-% nickel

1.5 to 8 wt% manganese

1.0 to 35 wt% zinc

Contain 25 to 40 wt .-% phosphate (calculated as P, 0 _; ).

The metal surfaces must be sufficiently clean to ensure proper wetting with the phosphating solution. This is generally the case when e.g. B. strip material is treated immediately after the galvanizing by the method according to the invention. However, if the metal surface is oiled or dirty, degreasing or cleaning must be carried out using methods known per se and then rinsed.

The one to be used in the method according to the invention

Phosphating solution is expediently used at a temperature in the range from 20 to 80 ° C. The amount of the solution is usually between 2 and 10 ml per m ^{2 of} metal surface Surface, ie after an exposure time of about 0.5 to 5 see.

The present invention provides a method capable of producing phosphate coatings in a matter of seconds. Another advantage over known processes is that an activating pretreatment before phosphating can be omitted. The phosphate coatings produced are particularly of high quality with regard to the adhesion imparting of subsequently applied paints, plastics or adhesives. Their quality is similar to that of the phosphate layers produced using the so-called trication process. This is surprising insofar as the phosphate coatings obtained by the process according to the invention are generally are amorphous, whereas the layers formed by the trication method are always crystalline.

Another important advantage of the invention is that phosphate layers are produced which significantly improve the forming behavior of the metals treated in this way, without the weldability being significantly impaired thereby.

The phosphate coatings produced using the method according to the invention can be used well in all fields in which phosphate coatings are used. A particularly advantageous application is the preparation of the metal surfaces for the subsequent painting, in particular the electrocoating.

The method according to the invention is of particularly outstanding importance for its application to the phosphating of galvanized or alloy-galvanized steel strips. The term galvanized or alloy-galvanized steel strip is understood to mean strips which are a coating of Elektroytzmk (ZE), hot-dip zinc (Z), alloys based on zinc / nickel (ZNE), zinc / iron (ZF) or zinc / aluminum (ZA or AZ) ) exhibit. To the latter, alloys with z. B. 55 wt .-% Al and 45 wt .-% Zn counted.

The invention is illustrated by the following examples, for example and in more detail.

The values for free acid and total acid given in the examples were determined as follows:

To determine the free acid, 1 ml bath solution after dilution to approx. 50 ml with distilled water, if necessary with the addition of K ₃ (Co (CN) or K ₄ (Fe (CN) to remove interfering metal cations, using dimethyl yellow as an indicator Titrate with n / 10 NaOH until it changes from pink to yellow. The ml n / 10 NaOH consumed give the free acid. 1 ml of n / 10 sodium hydroxide solution corresponds to 7.098 mg of free P, oc. The total number of points (GS) is determined by titrating 1 ml of the phosphating solution after dilution with water to about 50 ml using phenolphthalein as an indicator until the color changes from colorless to red. The number of ml n / 10 sodium hydroxide used for this gives the total number of points.

The so-called S value is obtained by dividing the free acid by the total P, 0 ₅ . Here, the total P ₂ 0 _{5 is} determined by, following the determination of the free acid, the titration solution after adding 20 ml of 30% strength neutral potassium oxalate solution against phenolphthalein as an indicator until the color changes to red with n / 10 NaOH is titrated. The consumption of ml n / 10 NaOH between the envelope with dimethyl yellow and the envelope with phenolphthalein gives the total P, 0 ₅ . (See W. Rausch "The Phosphating of Metals" Eugen G. Leuze-Verlag 1988, p. 300ff)

Example 1:

Immediately after the hot-dip galvanizing of steel strip, a surface was heated to 35 "C

Phosphating solution applied, which contained the following components - dissolved in deionized water.

Phosphate 69 g / 1 (calculated as P _: 0 ₅ )

Manganese 7.5 g / 1

Nickel 2.7 g / 1

The phosphating solution had a temperature of 25 ^* C, a pH value of 1.7 and an S value of 0.6. The content was

Free acid 5.9 ml, total acid 17.1 ml.

The application of the phosphating solution was carried out with the help of a roll coating machine (roll coater), as it is also used for coil coating. The applied wet film of 5 ml phosphating solution per m ^{2 of} metal surface was dried after an exposure time of 2 seconds in a continuous furnace at 200 "C. When leaving the furnace, the strip had an object temperature of 60 ^* C. The phosphate coating applied was uniform, closed and had a dry layer weight of

1.1 g / m ^:. It contained 30% by weight of P-0 ₅ , 20% by weight of zinc,

3.5% by weight of manganese and 1.4% by weight of nickel.

The tape provided with a phosphate coating by the process according to the invention showed excellent behavior during deformation, both in the lacquered and in the unpainted state. The adhesion and corrosion protection values of subsequently applied organic coatings also met today's requirements.

The strip phosphated by the process according to the invention can also pass through the process usual in the automotive plant. This means that the individual body parts can first be shaped in a customary manner and assembled by welding to form the body and then the treatment system cleaning-rinsing-activating-

Pass through phosphating-rinsing-rinsing. This is where the

Phosphating during a treatment time of 3.5 min and one

Temperature of the phosphating solution of 52 ^* C. The composition of the

Phosphating solution is:

14 g / 1 phosphate (calculated as P _: 0 ₅ )

1.4 g / 1 zinc

1.0 g / 1 manganese

1.0 g / 1 nickel

70 mg / 1 sodium nitrite

185 mg / 1 free fluoride.

The free acid content was 1.5 and the total acid content 27.8

Points were measured using a 10 ml bath sample. de

S value was set to 0.08.

The phosphate coating produced in this way has a weight per unit area of 2.56 g / m ² and contained 31% by weight of P ₂ O ₅ , 35% by weight of zinc, 6.4% by weight of manganese 1.7% by weight. % Nickel.

Following the phosphating treatment, the bodies are first provided with a cathodic electrodeposition paint and then with the customary automotive paint structure. Test sheets with which the aforementioned process was simulated were subjected to the following tests:

Stone chip test plus VDA alternating test, outdoor weathering, cross-cut plus 240 h condensation water constant climate test.

The tests showed that the results met expectations in every respect. In particular, it was found that the phosphating in the 1st stage led to the same good results as the phosphating by the conventional trication methods.

Example 2:

Using a roll coater, a phosphating solution with a temperature of

27 "C applied, had the following composition:

Phosphate 134 g / 1 (calculated as P _: 0 ₅ )

Manganese 14.8 g / 1

Nickel 5.42 g / 1.

The solution had an S value of 0.62, a free acid content of 10.3 and a total acid content of 29.7 (based on a

Bath sample of 1 ml). The wet film of the solution on the belt surface was

3 ml / m ² .

After drying the wet film at an oven temperature of 200 ° C., a uniform, closed phosphate coating with a layer weight of 1.6 g / m ^{2 was} obtained.

A review of the phosphate coating with regard to composition, deformability, weldability, adhesion and corrosion protection of subsequently applied organic lacquer coatings showed results that can otherwise be produced using the conventional phosphating process in accordance with the trication process. Example 3:

A wet film of 5 ml / m ^{2 of} a phosphating solution, which had the following composition, was applied to a cleaned and rinsed steel strip surface using a roller mill at room temperature:

134 g / 1 phosphate (calculated as P _: 0 ₅ )

14.8 g / 1 manganese

5.42 g / 1 nickel

3.33 g / 1 zinc.

The solution had an S value of 0.56, a free acid content of 9.4 and a total acid content of 29.2 (based on 1 ml

Bath sample).

After drying the wet film at a temperature of 150 ° C, a uniform and closed phosphate coating with a

Layer weight of 1.0 g / m ^: obtained, which had the following composition:

37% by weight P, 0 ₅ , 4.2% by weight manganese, 1.6% by weight nickel,

2.1 wt% zinc.

A review of the phosphate coating with regard to adhesion and corrosion protection of subsequently applied organic lacquer coatings showed that the requirements were fully met.

Example 4:

6 ml / m ^{2 of} the phosphating solution from Example 3 were applied to the surface of cleaned and rinsed aluminum sheets of the alloy AlMgSi at room temperature with the aid of a roller and the wet film was dried at 150 ° C. for 15 seconds in a forced air oven. The dry phosphate layer had a basis weight of 1.95 g / πr and a composition of 37% by weight p, 0 ₃ 3.9% by weight manganese, 1.5% by weight nickel and 1.9% by weight zinc here were the properties of the phosphate layer in terms of adhesion and Corrosion protection in connection with a subsequently applied coating as expected.

Claims

claims

1. A process for applying phosphate coatings to surfaces of zinc, iron, aluminum or their alloys by wetting with a phosphate solution containing divalent cations and phosphate and then drying the liquid film, characterized in that the surface is covered with a phosphate solution which is free of Elements of the 5th and 6th subgroup of the Periodic Table of the Elements,

0.5 to 8 g / 1 nickel

2 to 20 g / 1 manganese

Contains 18 to 170 g / 1 phosphate (calculated as P, 0 ₅ ) and has an S value of 0.4 to 0.8, wetted in such a way that a phosphate layer weight of 0.3 to 3.0 after drying g / m ² results, the phosphating solution necessarily containing 0.5 to 5 g / 1 zinc in the case of phosphating surfaces made of iron, aluminum or their alloys and may contain zinc in the case of phosphating surfaces made of zinc or zinc alloys.

2. The method according to claim 1, characterized in that in the case of the phosphating of surfaces made of zinc or zinc alloys, a phosphating solution is used which is zinc-free.

3. The method according to claim 1, characterized in that the surfaces are wetted with a phosphating solution, the

0.8 to 6 g / 1 nickel

3 to 16 g / 1 manganese

30 to 140 g / 1 phosphate (calculated as P, 0 ₅ ) and in the case of phosphating surfaces made of iron,

Contains aluminum or their alloys 0.8 to 4 g / 1 zinc.

4. The method according to claim 1, 2 or 3, characterized in that the surfaces are wetted with a phosphating solution, the additional

2 to 10 g / 1 SiO, and

Contains 0.05 to 0.5 g / 1 fluoride (calc. As F). 5. The method according to one or more of claims 1 to 4, characterized in that the surfaces are wetted with a phosphating solution which has an S value of 0,

5 to 0.7.

6. The method according to one or more of claims 1 to 5, characterized in that the surfaces are wetted with the phosphating solution in such a way that a phosphate layer weight of 0.5 to 2 g / m ² results after drying.

7. Application of the method according to one or more of claims 1 to 6 to the phosphating of galvanized or alloy-galvanized steel strip.