EP0187597A1 - 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 clean concentrate to allow 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 metallic 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 H₃P^O ₄#
• - 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 ₃ P ^O 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 _. vs.

• - 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 numerous chemical conversion baths, some of which contain free or complex fluorides in the form including hydrofluoric acid ^(HF), f ^l uorosilici ^q ue (H ₂ SiF ₆₎ or fluobo- America (HBF _4).

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.

• F - PO₃ 2-qui peut être amené sous la forme de l'acide correspondant, d'un de ses sels alcalins, alcalino-terreux ou d'ammonium ou de son sel de zinc.

It follows that the chemical conversion bath at zinc in accordance with the invention comprises, in addition to the conventional constituents, an effective amount of at least one compound comprising at least one fluorine atom chemically bonded to a phosphorus atom, preferably an effective amount of fluorophosphate ion of formula:

• F - PO ₃ 2-which can be brought in the form of the corresponding acid, one of its alkaline, alkaline-earth or ammonium salts or its zinc salt.

According to an advantageous embodiment, the abovementioned bath comprises from 1 to 10 g / 1, preferably from 2 to 7 g / 1, of zinc ion and from 1 to 10 g / 1, preferably from 2 to 7 g / 1, fluorophosphate ion.

The chemical conversion process in accordance with the invention consists in implementing the above-mentioned bath on the substrates to be treated by spraying or by quenching the substrates, the bath temperature 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.

The concentrate according to the invention comprises the fluorophosphate ion, the zinc ion and the conventional constituents of the chemical conversion bath according to the invention in proportions such that this bath can be obtained by dilution with the appropriate quantity of water.

• - 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.

According to an advantageous embodiment, said concentrate has 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 number of other provisions which will be discussed later and, in part culier, 1 ^- application of 1 fluorophospnaze ion in the chemical conversion baths.

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 according to 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 / l, of fluorophosphate ion.

• - de l'acide orthophosphorique H₃PO₄,
• - 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.

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 PO 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 ZnPO 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 a com taken between 3 and 20 gll, preferably between 3 and 15 g / l, and the nickel ion in an amount between 0.5 and 2 g / 1, preferably 0.5 to 1 g / 1.

The accelerator can be present in an amount between 40 and 150 mg / 1.

Conventional ions such as Fe, Ca, Mn can be present in an amount between 0 and 5 g / 1.

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 comprising 3.8 g of K ₂ PO ₃ 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 respectively the concentrate and the aqueous solution of K ₂ ^P0 ₃ ^F.

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 compared to the results obtained with conventional baths, some of which are based on compounds comprising 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 monofluorophosphate ion participate favorably, metal substrates treated in the baths according to the invention have been subjected to accelerated corrosion tests such as that known as "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 × 10 cm, constituted by

• - 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 stades étant caractérisés
  • - pour le premier :
    • . par une concentration de 1,8 Z en volume de RIDOLINE 1550 CF/2 + 10 X, 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/1 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 _. ) an alkaline soaking degreasing (in two stages) using a degreasing bath constituted by 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 brand "RIDOLINE 1550 CF / 2" and "RIDOSOL 550 CF", the two stages being characterized
  • - for the first :
    • . by a concentration of 1.8% by volume of RIDOLINE 1550 CF / 2 + 10 X, relative to the charge, of RIDOSOL 550 CF,
    • . at a temperature of 65 ° C,
    • . by 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 / 1 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 treated in bath A for 150 seconds, then rinsed and finally baked 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 test 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 X 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 1 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 under 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 Z 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 (8)

1. Bath for chemical conversion to zinc, characterized in that it comprises, in addition to the conventional constituents, an effective amount of at least one compound comprising at least one fluorine atom chemically bonded to a phosphorus atom, preferably an amount effective fluorophosphate ion of formula:
F - PO ₃ ^2-
which can be brought in the form of the corresponding acid, one of its alkaline, alkaline-earth or ammonium salts or its zinc salt. 2. Bath according to claim 1, characterized in that it comprises from 1 to 10 g / l, preferably from 2 to 7 g / l, of zinc ion and from 1 to 10 g / l, preferably from 2 to 7 g / 1, of fluorophosphate ion. 3. Bath according to claim 1, characterized in that it has the following composition:

4. own concentrate to prepare a chemical conversion bath according to one of claims 1 to 3, characterized in that it has the composition cen _- tésimale follows: - 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. 5. Process for the chemical conversion of metallic substrates, in particular based on iron, zinc, aluminum and alloys of these metals, comprising: - 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,
characterized in that it comprises the use on the substrate to be treated of a chemical conversion bath according to one of claims 1 to 3 by spraying or by quenching the substrate, 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. 6. Application to the constitution of a chemical conversion bath to zinc of the fluorophosphate ion of formula F-PO ₃ ^2- brought in the form of the corresponding acid, of one of its alkali, alkaline-earth or ammonium or its zinc salt. 7. Kit comprising in two separate containers respectively the concentrate according to claim 4 and an aqueous solution of alkaline monofluorophosphate.