EP0187597B1 - Composition and process for coating metal surfaces with a conversion coating of zinc phosphate - Google Patents

Abstract

Chemical conversion bath with zinc characterized by the fact that it comprises, besides the conventional constituents, an effective amount of fluorophosphate ion of the formula: F-PO32- which can be introduced in the form of the corresponding acid, one of its alkali, alkaline-earth or ammonium salts or its zinc salt.

Description

The subject of the invention is a bath and a process for the chemical conversion to zinc of metallic substrates, in particular those based on iron, zinc, aluminum and alloys of these metals.

It also targets a concentrate and a kit suitable for the preparation of the above baths.

It will be recalled that, by the expression "chemical conversion _" , is meant the surface transformations of metals, in particular in an acid medium, making it possible to modify their intrinsic properties and to confer on them new physical or physicochemical characteristics, in particular with a view to increase their corrosion resistance and promote the adhesion of film-forming coatings applied subsequently.

Traditionally, this chemical conversion of metal substrates is carried out - by conventional zinc phosphating treatments and leads to the deposit on the surface of the metal of a thin layer of insoluble phosphate.

• - de l'acide phosphorique H_SP0₄,
• - un phosphate métallique primaire (H₂PO₄)₂Me, Me représentant souvent le zinc et/ou le fer, mais pouvant aussi représenter le manganèse, le nickel, le cuivre, le calcium, le magnésium ou leurs mélanges,
• - un accélérateur constitué par des éléments tels que les chlorates, les nitrites et/ou les nitrates, le métanitrobenzènesulfonate de sodium, les peroxydes.

In general, conventional phosphating treatments use acid solutions which, before use, contain the following constituents:

• - phosphoric acid H _S P0 ₄ ,
• a primary metal phosphate (H ₂ PO ₄ ) ₂ Me, Me often representing zinc and / or iron, but which can also represent manganese, nickel, copper, calcium, magnesium or their mixtures,
• - An accelerator consisting of elements such as chlorates, nitrites and / or nitrates, sodium metanitrobenzenesulfonate, peroxides.

These treatments can be carried out by spraying the above-mentioned solutions onto the objects to be treated or by immersing them in baths formed by these solutions, generally at temperatures above 30 ° C.

• - une ou plusieurs étapes de dégraissage,
• - une ou plusieurs étapes de rinçage,
• - de préférence, une étape de conditionnement de la surface du substrat à traiter,
• - l'étape de conversion chimique au zinc proprement dite,
• - une étape de rinçage,
• - de préférence, une étape de passivation en milieu chromique,
• - une étape de rinçage,
• - une étape de séchage ou d'étuvage.

The spraying or immersion treatment is part of a sequence of operational steps as follows, which may include:

• - one or more degreasing steps,
• - one or more rinsing steps,
• preferably, a step of conditioning the surface of the substrate to be treated,
• - the stage of chemical conversion to zinc proper,
• - a rinsing step,
• - preferably, a passivation step in a chromic medium,
• - a rinsing step,
• - a drying or baking step.

There are already very many chemical conversion baths, some of which contain free or complex fluorides in the form in particular of hydrofluoric (HF), fluorosilicic (H ₂ SiF _s ) or fluoboric (HBF ₄ ) acids.

There are also chemical chromatography baths of metal bands using the fluophosphoric ion (FR-A-1 477179).

Faced with the ever-increasing demands of users in terms of corrosion resistance of objects based on iron, zinc, aluminum and their alloys, the Applicant Company has worked to improve the existing chemical conversion baths and had the merit of finding, after extensive research, that the implementation in a zinc phosphating bath of an effective amount of at least one compound comprising at least one fluorine atom chemically bonded to an atom phosphorus, preferably an effective amount of fluorophosphate ion, allowed to achieve the desired goal.

• - de 1 à 10 g/l d'ion fluorophosphate de formule :
  

• - de 1 à 10 g/I d'ion zinc,
• - entre 3 et 20 g/I d'ion phosphate et
• - entre 0,5 et 2 g/l d'ion nickel.

It follows that the zinc phosphating bath in accordance with the invention comprises:

• - from 1 to 10 g / l of fluorophosphate ion of formula:
  

• - from 1 to 10 g / I of zinc ion,
• - between 3 and 20 g / I of phosphate ion and
• - between 0.5 and 2 g / l of nickel ion.

The fluorophosphate ion can be introduced into the bath using the corresponding acid or one of its alkaline, alkaline-earth or ammonium salts or its zinc salt.

According to an advantageous embodiment, the above-mentioned bath preferably comprises from 2 to 7 gA of zinc ion and from 2 to 7 g / I of fluorophosphate ion.

The phosphating process according to the invention consists in using the above-mentioned substrates to be treated by spraying or by soaking the substrates, the temperature of the bath being from 30 to 70 ° C., preferably from 50 to 55 ° C. , the contact between bath and substrate being maintained for 5 to 200 seconds.

• - ion zinc compris entre 2 et 20 g, de préférence entre 2 et 14 g pour 100 g de concentré,
• - ion monofluorophosphate compris entre 2 et 20 g, de préférence entre 1 et 14 g pour 100 g de concentré,
• - ion phosphate compris entre 6 et 40 g, de préférence entre 6 et 30 g pour 100 g de concentré,
• - ion nickel entre 1 et 4 g, de préférence 1 à 2 g pour 100 g de concentré.

The concentrate specific to the preparation of the phosphating bath according to the invention obtained by dilution with the appropriate quantity of water is characterized by the following percentage composition:

• - zinc ion between 2 and 20 g, preferably between 2 and 14 g per 100 g of concentrate,
• - monofluorophosphate ion between 2 and 20 g, preferably between 1 and 14 g per 100 g of concentrate,
• - phosphate ion between 6 and 40 g, preferably between 6 and 30 g per 100 g of concentrate,
• - nickel ion between 1 and 4 g, preferably 1 to 2 g per 100 g of concentrate.

The invention also relates to a kit, as defined in claim II, for the preparation of the bath of the invention.

The invention also relates to a certain number of other arrangements which will be discussed below.

It can, in any case, be well understood with the aid of the additional description which follows and of the examples, the said additional description and the said examples being relative to advantageous embodiments.

Proposing, therefore, to constitute the chemical conversion bath in accordance with the invention, a conventional chemical conversion bath to zinc is made to contain an amount of 1 to 10 g / l, preferably 2 to 7 g / l , of zinc ion and from 1 to 10 g / l, preferably from 2 to 7 g / I, of fluorophosphate ion.

• - de l'acide orthophosphorique H₃P0₄,
• - l'ion nickel,
• - éventuellement les ions classiques utilisés dans les bains de conversion chimique, à savoir Ca, Fe, Mn et autres,
• - un accélérateur choisi dans le groupe comprenant les nitrites et/ou les nitrates, les chlorates et autres.
• - L'anion fluorophosphate peut être amené sous forme de monofluorophosphate alcalin ou d'ammonium, notamment de potassium K₂PO₃F, de monofluorophosphate de zinc ZnP0₃F et autres, ou de leurs mélanges.

The above bath is acidic, preferably of pH 2.6 to 3.3, and comprises, in addition to the zinc ion and the fluorophosphate ion,

• - orthophosphoric acid H ₃ P0 ₄ ,
• - the nickel ion,
• - optionally the conventional ions used in chemical conversion baths, namely Ca, Fe, Mn and others,
• - an accelerator chosen from the group comprising nitrites and / or nitrates, chlorates and others.
• - The fluorophosphate anion can be brought in the form of alkaline monofluorophosphate or ammonium, in particular potassium K ₂ PO ₃ F, zinc monofluorophosphate ZnP0 ₃ F and others, or their mixtures.

The zinc ion can be brought in any suitable way and in particular in the form of its salts such as nitrate or phosphate or of its oxide.

The nickel ion can be brought in any suitable way and in particular in the form of its salts such as carbonate or nitrate.

The best results are obtained when zinc is brought in combined form of the monofluorophosphate anion.

The phosphate ion is present in an amount between 3 and 20 g / l, preferably between 3 and 15 g / l, and the nickel ion in an amount between 0.5 and 2 g / l, preferably 0 , 5 to 1 g / I.

The accelerator can be present in an amount between 40 and 150 mg / l.

Conventional ions such as Fe, Ca, Mn can be present in an amount between 0 and 5 g / I.

Particular compositions of conversion bath in accordance with the invention are given in the examples.

An advantageous composition of concentrate is as follows:

To optionally adjust the K ₂ PO ₃ F content, a solution of this product containing 3.8 g of K ₂ PO _s F in 96.2 g of industrial water can be provided.

It is also possible to provide for the marketing of the concentrate in the form of a "kit" with two receptacles containing the concentrate and the aqueous solution of K ₂ PO ₃ F respectively.

To prepare the bath according to the invention from such a concentrate, it is diluted with about 95% industrial water.

The implementation of the bath according to the invention in the context of the process according to the invention leads to conversion layers having a remarkable resistance to corrosion, clearly superior to that presented by the layers obtained according to conventional phosphating processes.

In the examples which follow, the advantageous results obtained using compounds in which a fluorine atom is chemically linked to a phosphorus atom are compared with the results obtained with conventional baths, some of which are based on compounds having a free or complexed fluorine atom. To illustrate the corrosion resistance of the conversion layers in the construction of which the compounds used in accordance with the invention and in particular the monofluoro ion phosphate participates favorably, metallic substrates treated in the baths in accordance with the invention have been subjected to accelerated corrosion tests such as that known as “with salt spray according to standard NF x 41-002.

• - des tôles d'acier laminé à froid,
• - des tôles galvanisées,
• - des tôles électrozinguées.

The substrates used are metallic test pieces of approximately equal dimensions, close to 10 x 10 cm, consisting of:

• - cold rolled steel sheets,
• - galvanized sheets,
• - electrogalvanized sheets.

These test pieces are treated either in a chemical dip bath conventionally used in industry, or in various baths according to the invention.

• 1. un dégraissage alcalin au trempé (en deux stades) utilisant un bain dégraissant constitué par une base minérale à base de soude et par une base mouillante à base de tensio-actifs non ioniques, commercialisé par la Demanderesse sous la forme de deux produits respectivement de marque « RIDOLINE 1550 CF/2 » et « RIDOSOL 550 CF », les deux stages étant caractérisés
  pour le premier :
  • - par une concentration de 1,8 % en volume de RIDOLINE 1550 CF/2+10%, par rapport à la charge, de RIDOSOL 550 CF,
  • - par une température de 65 °C,
  • - par une durée de 4 minutes,
    pour le deuxième :
    • - par une concentration de 0,3 % en volume de RIDOLINE 1550 CF/2,
    • - par une température de 60 °C,
    • - par une durée de 2 minutes,

• 2. un rinçage froid courant au trempé de 2 minutes dans de l'eau industrielle,
• 3. un conditionnement de surface au trempé en eau déminéralisée à l'aide d'un agent d'affinage à base de phosphate de titane, commercialisé par la Demanderesse sous la marque « FIXODINE 5 », la concentration étant de 2 g/I et la durée de 2 minutes.

Prior to this chemical conversion treatment, the test pieces are all subjected to the same range of pretreatments recommended by the Applicant Company, namely:

• 1. alkaline soaking degreasing (in two stages) using a degreasing bath consisting of a mineral base based on soda and by a wetting base based on nonionic surfactants, marketed by the Applicant in the form of two products respectively of the "RIDOLINE 1550 CF / 2" and "RIDOSOL 550 CF" brand, both courses being characterized
  for the first :
  • - by a concentration of 1.8% by volume of RIDOLINE 1550 CF / 2 + 10%, relative to the load, of RIDOSOL 550 CF,
  • - at a temperature of 65 ° C,
  • - for a duration of 4 minutes,
    for the second:
    • - by a concentration of 0.3% by volume of RIDOLINE 1550 CF / 2,
    • - at a temperature of 60 ° C,
    • - by a duration of 2 minutes,

• 2. a standard cold rinse by soaking for 2 minutes in industrial water,
• 3. surface conditioning by soaking in demineralized water using a titanium phosphate-based refining agent sold by the Applicant under the brand name "FIXODINE 5", the concentration being 2 g / l and the duration of 2 minutes.

Then, the test pieces are immersed for 150 seconds in one of the above-mentioned chemical conversion baths.

• - une étape de rinçage,
• - une étape de passivation en milieu chromique,
• - une étape de rinçage,
• - une étape de séchage ou d'étuvage.

Finally, they are subject to:

• - a rinsing step,
• - a passivation step in a chromic medium,
• - a rinsing step,
• - a drying or baking step.

Example 1

This is a comparative example using a conventional bath, hereinafter designated by Bath A and the composition of which is as follows:

Ten samples of each of the types of test pieces identified above are processed in the bath. A for 150 seconds, then rinsed and finally steamed at 110 ° C for 10 minutes.

• - température régnant dans l'enceinte : 35 °C ± 1,
• - solution à 5 % de NaCl, de pH égal à 7, utilisée pour former le brouillard salin,
• - humidité de l'air remplissant l'enceinte : 85 - 90 % (humidité relative) et pression à l'intérieur de l'enceinte : 1 bar.

To assess their resistance to corrosion, the various specimens thus treated are exposed to the aggressiveness of a salt spray, obtained using a salt spray test apparatus. The conditions of these tests were as follows:

• - prevailing temperature in the enclosure: 35 ° C ± 1,
• - 5% NaCl solution, pH 7, used to form the salt spray,
• - humidity of the air filling the enclosure: 85 - 90% (relative humidity) and pressure inside the enclosure: 1 bar.

The effectiveness of the conversion treatment was assessed visually and the results, that is to say the progress of the oxidation expressed in% for a given exposure time, are shown in Table 1.

Example 2

This is an example using a bath in accordance with the invention, hereinafter called Bain B and the composition of which is as follows:

In the same way as in the previous example, ten samples of each of the types of test pieces were immersed for 150 seconds in bath B, then rinsed and then baked at 110 ° C for 10 minutes and finally exposed to salt spray in the conditions set out in Example 1.

The effectiveness of the conversion treatment was assessed visually and the results, that is to say the progress of the oxidation expressed in% for a given exposure time, are shown in Table 1.

Example 3

This is a comparative example using a conventional bath in which has been incorporated an amount equivalent to that of the previous example of fluoride ion, in free form, in particular in the form of HF, called bath C and of which the composition is as follows:

In the same way as in the previous example, ten samples of each of the types of test pieces were immersed for 150 seconds in bath C, then rinsed and then baked at 110 ° C for 10 minutes and finally exposed to salt spray in the conditions set out in Example 1.

The effectiveness of the conversion treatment was assessed visually and the results, that is to say the progress of the oxidation expressed in% for a given exposure time, are shown in Table 1.

Example 4

This is an example using a bath according to the invention, hereinafter called Bain D and the composition of which is as follows:

In the same way as in the previous example, ten samples of each of the types of test pieces were immersed for 150 seconds in bath D, then rinsed and then baked at 110 ° C for 10 minutes and finally exposed to salt spray in the conditions set out in Example 1.

The effectiveness of the conversion treatment was assessed visually and the results, that is to say the progress of the oxidation expressed in% for a given exposure time, are shown in Table 1.

Example 5

This is an example using a bath in accordance with the invention, hereinafter called Bath E and the composition of which is as follows:

In the same way as in the previous example, ten samples of each of the types of test pieces were immersed for 150 seconds in bath E, then rinsed and then baked at 110 ° C for 10 minutes and finally exposed to salt spray in the conditions set out in Example 1.

The effectiveness of the conversion treatment was assessed visually and the results, that is to say the progress of the oxidation expressed in% for a given exposure time, are shown in Table 1.

As goes without saying and as it already follows from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all its variants.

Claims (11)

1. Phosphatization bath with zinc not containing chromium ion, characterized by the fact that it comprises

- from 1 to 10 g/I of fluorophosphate ion of formula :

- from 1 to 10 g/I of zinc ion,

- between 3 and 20 g/I of phosphate ion and

- between 0,5 and 2 g/I of nickel ion.

2. Phosphatization bath with zinc according to claim 1, characterized by the fact that it comprises from 2 to 7 g/I of fluorophosphate ion.

3. Phosphatization bath with zinc according to one of claims 1 and 2, characterized by the fact that it comprises from 2 to 7 g/I of zinc ion.

4. Phosphatization bath with zinc according to one of claims 1 to 3, characterized by the fact that it comprises between 3 and 15 g/I of phosphate ion.

5. Phosphatization bath with zinc according to one of claims 1 to 4, characterized by the fact that it comprises between 0,5 and 1 g/I of nickel ion.

6. Phosphatization bath with zinc according to one of claims 1 to 5, not containing chromium ion, characterized by the fact that it comprises

- from 2 to 7 g/I of fluorophosphate ion of formula :

- from 2 to 7 g/I of zinc ion,

- between 3 and 15 g/I of phosphate ion and

- between 0,5 and 1 g/I of nickel ion.

7. Bath according to one of claims 1 to 6, characterized by the fact that it has the following composition :

8. Process for the phosphatization with zinc of metal substrates particularly based on iron, zinc, aluminium and alloys of these metals, comprising :

- one or several degreasing steps,

- one or several rinsing steps,

- preferably, a step of conditioning the surface of the substrate to be treated,

- the step itself of phosphatization with zinc,

- a rinsing step,

- preferably, a step of passivation in a chromic medium,

- a rinsing step,

- a drying or stoving step,
characterized by the fact it comprises the employment on the substrate to be treated of a phosphatization bath according to one of claims 1 to 7 spraying or by dipping the substrate, the temperature of the bath being from 30 to 70 °C, the contact between bath and substrate being maintained during 5 to 200 seconds.

9. Process according to claim 8, characterized by the fact that the temperature of the phosphatization bath is from 50 to 55 °C.

10. Concentrate adapted for the preparation of a phosphatization bath according to one of claims 1 to 7 obtained by dilution with an appropriate amount of water, characterized by the fact that it has the following centesimal composition :

- zinc ion comprised between 2 and 20 g, preferably between 2 and 14 g per 100 g of concentrate,

- monofluorophosphate ion comprised between 2 and 20 g, preferably between 1 and 14 g per 100 g of concentrate,

- phosphate ion comprised between 6 and 40 g, preferably between 6 and 30 g per 100 g of concentrate,

- nickel ion comprised between 1 and 4 g, preferably between 1 to 2 g per 100 g of concentrate.

11. Kit for the preparation of the bath according to one of claims 1 to 7, characterized by the fact that it comprises in two separate containers respectively :

- a concentrate according to claim 10 adapted to be diluted with 95 % of water and having the following composition per 100 g :

- a solution of 3,8 g of K₂PO₃F in 96,2 g of industrial water adapted to enable the content of K₂PO_sF to be adjusted.