EP0577486B1 - Process for corrosion protection of metal objects and metal objects obtained - Google Patents

Abstract

Process for temporary corrosion protection of a pickled metal article, especially of a metal sheet, characterised in that it comprises the stages consisting in: - applying to at least a part of the said metal component an emulsion obtained by dispersing in water from 3 to 13 % by volume of an oily phase comprising from 75 to 90 % by volume of at least mineral oil, from 5 to 10 % by volume of at least one surface-active agent and from 5 to 15 % by volume of at least one corrosion inhibitor, - drying the said coated metal article until a dry film is obtained.

Description

The subject of the present invention is a process for temporary protection against corrosion of a metal part, in particular of a metal sheet.

The problem of protecting metal surfaces and, more particularly, metal sheets, against atmospheric corrosion, is a constant concern of manufacturers.

Methods of protecting metal surfaces are described in patents US-A-3,597,152, WO-A-9,105,033 and FR-A-2,325,730.

Indeed, after the hot rolling operations of the flat products and cold rolling in order to reduce the thickness, the sheets obtained are subjected to pickling, then they are stored in a warehouse. The sheets are then often exposed directly to the aggressions of the ambient environment and corrode over time before reaching the user.

Any alteration or degradation of the surface condition of the metal sheets significantly disrupts the subsequent treatments performed on the sheets, in particular phosphating, stamping and welding.

In order to avoid these drawbacks, the sheets should be isolated from the ambient environment by covering them with a waterproof material which is resistant to attack by the ambient environment.

After chemical etching and rinsing of metal products, in particular flat products such as sheets, these are treated differently depending on whether they are delivered without further treatment or whether they undergo different finishing operations before their delivery to users.

In the first case, protection must be granted for a minimum of three months. A known process for protecting metal sheets against corrosion for a period of at least three months consists in applying to the previously pickled and dried sheets a film formed of an oil, by soaking the sheets in an oil bath in order to give them a fatty coating with a surface density of the order of 1 to 3 g / m ² .

In the second case, the previously pickled products are first of all protected for a period of the order of a few days by corrosion inhibitors, such as amine-based corrosion inhibitors, for example the product RC 305 sold. by CRODA. After the finishing operations, the products are protected more durably by applying a fatty protective film as described above or are delivered to the user without special protection.

The process consisting in applying to the pickled products having possibly undergone finishing operations a fatty film of oil, has several important drawbacks.

Indeed, the user must before any use, for example painting, enameling or galvanizing, degrease the surfaces of said products for a long time to avoid unnecessary pollution of tools (shears, splitters) and installations, and to allow adhesion of coatings.

In addition, these fatty films pollute the cleaning baths which must therefore be frequently renewed.

Thus, to overcome the problems inherent in the presence of the fatty protective film on pickled metal products and in particular on sheets, one can choose either to not protect the products, or to use conventional products against corrosion but having corrosion resistance limited in time, of the order of a few days.

Beyond this period, the corrosion phenomenon appears and very quickly degrades the pickled products.

The object of the present invention is therefore to remedy the drawbacks of the prior art by proposing a method which makes it possible to protect effectively against corrosion of metal parts, in particular metal sheets, and to overcome the cleaning operations of said products. before use.

• sécher ladite pièce métallique,
• appliquer sur une partie au moins de ladite pièce métallique une émulsion obtenue par dispersion dans de l'eau de 3 à 13 % en volume d'une phase huileuse comprenant de 75 à 90 % en volume d'au moins une huile minérale, de 5 à 10 % en volume d'au moins un agent tensioactif et de 5 à 15 % en volume d'au moins un inhibiteur de corrosion,
• sécher ladite pièce métallique revêtue, par chauffage à une température comprise entre 70° et 100°C,

de façon à obtenir un film sec comprenant de 300 à 800 mg/m² de produit déposé.The present invention thus relates to a process for temporary protection against corrosion of a pickled metal part, in particular of a sheet metal, characterized in that it comprises the steps consisting in:

• drying said metal part,
• applying to at least part of said metal part an emulsion obtained by dispersion in water of 3 to 13% by volume of an oily phase comprising from 75 to 90% by volume of at least one mineral oil, of 5 10% by volume of at least one surfactant and 5 to 15% by volume of at least one corrosion inhibitor,
• drying said coated metal part, by heating to a temperature between 70 ° and 100 ° C,

so as to obtain a dry film comprising from 300 to 800 mg / m ² of product deposited.

The subject of the invention also relates to a coated sheet as defined in claim 9 and to its uses as defined in claims 10 to 13.

The oil contained in the oily phase of the emulsion can consist of a vegetable or animal oil.

Advantageously, the mineral oil of the oily phase is a paraffinic type oil.

It is preferred to use as surfactant for the oily phase a surfactant of polyoxyethylene type.

A carboxylic acid, a barium or sodium alkyl sulfonate or a salt is advantageously used as an inhibitor of corrosion of the oily phase. amine and fatty acid.

Advantageously, the aqueous emulsion is applied by spraying.

• sécher ladite pièce métallique en la chauffant à une température comprise entre 30°C et 90°C pendant une durée comprise entre 2 et 20 secondes,
• appliquer sur une partie au moins de ladite pièce métallique une émulsion obtenue par dispersion dans de l'eau de 3 à 13 % en volume d'une phase huileuse comprenant de 75 à 90 % en volume d'au moins une huile minérale, de 5 à 10 % en volume d'au moins un agent tensioactif et de 5 à 15 % en volume d'au moins un inhibiteur de corrosion,
• sécher ladite pièce métallique revêtue jusqu'à obtention d'un film sec, de préférence en chauffant ladite pièce métallique à une température comprise entre 70 et 100°C pendant une durée comprise entre 2 et 20 secondes.

Advantageously, the method comprises the steps consisting in:

• drying said metal part by heating it to a temperature between 30 ° C and 90 ° C for a period of between 2 and 20 seconds,
• applying to at least part of said metal part an emulsion obtained by dispersion in water of 3 to 13% by volume of an oily phase comprising from 75 to 90% by volume of at least one mineral oil, of 5 10% by volume of at least one surfactant and 5 to 15% by volume of at least one corrosion inhibitor,
• drying said coated metal part until a dry film is obtained, preferably by heating said metal part to a temperature of between 70 and 100 ° C. for a period of between 2 and 20 seconds.

The prior drying operation promotes the reactivity of the sheet as well as the attachment mechanisms of the product which will be applied subsequently to said sheet.

A preferred example of the oily phase used in the aqueous emulsion consists of the product sold under the name PREVOX 6767 ^R by HENKEL.

Another example is the product sold under the name 112 STS ^R by QUAKER.

The metal part is preferably a metal sheet, the dry film being formed on at least one face of said sheet.

The subject of the invention is also a metal sheet coated with a dry protective film against corrosion obtained by the process according to the invention, characterized in that the dry film comprises from 300 to 800 mg / m ² of deposited product obtained from the applied emulsion, the quantity of product being determined by chemical determination of the surfactant according to standard NFT 73258.

The invention will be better understood with the aid of the following examples relating to a steel sheet previously pickled and implemented on a processing line, for example from a hot-rolled sheet, and in the single figure representing the evolution of corrosion over time of an untreated sheet, of a sheet treated with a conventional corrosion inhibitor and of sheets treated according to the method of the invention.

The steel sheet is first pickled by pickling in acid baths, for example in hydrochloric acid, in order to remove the chemical substances, such as the iron oxides constituting the scale, adhering to the surface of the sheet. and which would interfere with the subsequent application of a coating. Then the sheet is immersed in the rinsing water tanks to remove all traces of acid.

The emulsion according to the invention is then applied by spraying onto the sheet.

In order to determine the protection efficiency of the dry protective film on the surface of the sheet, a chemical dosage of the film is carried out in accordance with standard NFT 73258 relating to the determination of surfactants and detergents.

According to the above-mentioned standard, the product constituting the film is removed from a determined surface area equal to S (m ² ) of the sheet by washing with chloroform. The sample is collected in a 200 ml volumetric flask to which 10 ml of water are added.

ce qui correspond à une teneur d'agent tensioactif de y g/m².A volumetric assay of the sample is then carried out using a mixed indicator, the hyamine, the hyamine solution being titrated at 0.004 mol / l until the pink color turns blue. By designating by V the volume of hyamine poured (ml) and by S the sampling surface, the amount of surfactant content present on the surface of the sheet has the value: $$\frac{\text{104}}{\text{S}}{\text{x V x 0.004 = x µeq / <figure-callout id="2" label="m" filenames="imgf0001.png" state="{{state}}">m</figure-callout>}}^{\text{2}}$$

which corresponds to a surfactant content of yg / m ² .

EXAMPLE 1

The sheet, pickled with hydrochloric acid and rinsed, is heated to a temperature of 60 ° C. for drying, using hot air dryers.

After drying, an aqueous emulsion containing 5% by volume of an oily phase consisting of the product sold under the name PREVOX 6767 ^R by HENKEL is sprayed onto one face of the pickled steel sheet.

The spraying is carried out by means of conventional spray nozzles of the "VEEJET" type with an opening angle of 65 ° which makes it possible to cover a square of 25 cm side on substrate placed 20 cm from the nozzle.

The product being thus distributed over the face of the sheet, the coated sheet is heated to a temperature of 90 ° C. by means of hot air dryers arranged in an appropriate manner.

A dry and thin film is thus formed on the surface of the pickled steel sheet to protect it against corrosion for a minimum of three months.

The coated sheet is then wound and placed in a storage hall.

The coils can be directly delivered to users without receiving any special treatment, these then have a period of three months to proceed with the transformation of the sheet in complete safety from corrosion.

Painting tests were carried out using samples from such coils directly on the sheet coated with its dry anticorrosion film, on the one hand with a polyurethane type primer and on the other hand, with a powder paint of the type polyester.

The adhesion tests of the paint coating (grid, so-called "chevron" test) made it possible to show that the ability to paint said sheet which is not degreased, that is to say not stripped of its film dry, is as good as that of bare sheet metal.

The same is true for hot dip galvanizing and enamelling by electrostatic spraying.

A simple degreasing is sufficient to remove all traces of product on the surface of the sheet and users are also assured not to pollute their installations.

In addition, the coils can be unwound to complete the sheets and possibly be split before being delivered to users.

• S = 0,016 m²
• V = 2 ml

ce qui correspond à une quantité d'agent tensioactif de 50 µeq/m², soit une teneur de l'ordre de 0,5 g/m².The dosage of the dry film deposited in accordance with the method described above gave the following values:

• S = 0.016 m ²
• V = 2 ml

which corresponds to a quantity of surfactant of 50 μeq / m ² , ie a content of the order of 0.5 g / m ² .

EXAMPLE 2

The sheet is previously pickled as described above in Example 1, rinsed and then dried using hot air dryers by heating to a temperature equal to 60 ° C to promote the reactivity of the sheet as well as the attachment mechanisms of the product.

An aqueous emulsion containing 5% by volume of an oily phase consisting of the product sold under the name 112 STS ^R by QUAKER is then sprayed onto one face of the pickled steel sheet and dried.

The spraying is carried out by means of conventional spray nozzles of the "VEEJET" type with an opening angle of 65 ° which makes it possible to cover a square of 25 cm side on a substrate placed 20 cm from the nozzle.

After having distributed the product on the surface of the sheet, it is heated by means of hot air dryers at a temperature of 90 ° C in order to dry it and therefore to favor the evaporation of the water present on its surface .

The sample is then assayed volumetrically using a 0.004 mol / l titrated hyamine solution as described above.

• S = 0,013 m²
• V = 0,12 ml

ce qui correspond à une quantité d'agent tensioactif de 45 µeq/m², soit une teneur de l'ordre de 0,5 g/m².The dosage of the dry film deposited in accordance with the method described above gave the following values:

• S = 0.013 m ²
• V = 0.12 ml

which corresponds to a quantity of surfactant of 45 μeq / m ² , ie a content of the order of 0.5 g / m ² .

The sheet thus protected against corrosion for a period of at least three months can then be directly delivered to the user or undergo a finishing operation as explained for example 1.

The Applicant has noticed quite unexpectedly that the protective film of the sheet did not affect its suitability for further processing, such as phosphating and painting.

The results of the test described below make it possible to demonstrate significantly the properties of the sheets coated by the process of the invention.

TRIAL

The test is carried out on test specimens of steel sheets of dimensions 50 × 100 mm which have been etched in a hydrochloric acid solution, the concentrations of free acidity and of ferrous chlorides being respectively equal to 80 g / l and 90 g / l, at a temperature of 85 ° C.

After pickling, the test pieces are then rinsed in two successive tanks of water and then dried by rotation of the test pieces.

An aqueous emulsion containing 3% by volume of oily phase consisting of the product sold under the name PREVOX 6767 ^R by HENKEL (1) is then sprayed onto a first part of the test pieces.

An aqueous emulsion containing 3% by volume of oily phase consisting of the product sold under the name 112 STS ^R by QUAKER (2) is sprayed onto a second part of the test pieces.

An aqueous emulsion containing 3% by volume of oily phase constituted by the product sold under the name RC 305 ^R by CRODA CHEMICALS (3) is also sprayed onto a third part of the test pieces. This product, known for its anti-corrosion properties, consists essentially of amines.

A test piece which has not undergone any corrosion treatment serves as a control sample (4).

All the test pieces are dried using hot air dryers whose temperature is also 90 ° C.

The test pieces are then exposed to atmospheric conditions in a storage hall at a temperature of the order of 30 ° C and a relative humidity of the order of 70%.

For several days, the different test pieces are observed, taking into account the appearance of corrosion as a function of time. The corrosion aspect is noted on a rating scale ranging from 1 to 4, the coefficient 1 being assigned to a test piece on which the first pits appear, the coefficient 4 corresponding to the entire corroded surface.

The curve shown in the appended figure represents the comparative evolution of corrosion over time for the four tests.

The results of the tests show the superiority of the products in accordance with the invention over a conventional corrosion inhibitor such as RC 305, the degradation process of the sheets engaging very quickly with the latter.

The sheets coated with the anticorrosion dry film according to the invention can undergo, without prior degreasing, the coating operations of the dip galvanizing, painting or enamelling type, while benefiting from very good anticorrosion protection, even after a long period of storage. In addition, degreasing the sheets remains very easy after prolonged storage.

Claims (13)

1. A process for temporarily protecting against corrosion in a pickled metal part, in particular a sheet, characterized in that it comprises steps consisting in:

   - drying the said metal part,

   - applying to at least part of the said metal part an emulsion obtained by dispersing in water from 3 to 13% by volume of an oil phase comprising from 75 to 90% by volume of at least one mineral oil, from 5 to 10% by volume of at least one surfactant and from 5 to 15% by volume of at least one corrosion inhibitor,

   - drying the said coated metal part by heating it to a temperature between 70° and 100°C,

   so as to obtain a dry film comprising from 300 to 800 mg/m² of deposited product.
2. A process according to Claim 1, characterized in that the mineral oil of the oil phase is a paraffin-type oil.
3. A process according to Claim 1, characterized in that the surfactant of the oil phase is a polyoxyethylene-type surfactant.
4. A process according to Claim 1, characterized in that the corrosion inhibitor of the oil phase is a carboxylic acid, a barium or sodium alkylsulphonate or an amine and fatty acid salt.
5. A process according to Claim 1, characterized in that the aqueous emulsion is applied by spraying.
6. A process according to one of Claims 1 to 5, characterized in that the first stage of drying is carried out by heating the said metal part to a temperature between 30 and 90°C for a period of between 2 and 20 seconds.
7. A process according to Claim 6, characterized in that the said coated metal part is dried for a period of between 2 and 20 seconds.
8. A process according to any one of the preceding claims, characterized in that the metal part is a metal sheet, the dry film being formed on at least one face of the said sheet.
9. A metal sheet coated with a dry film for protecting against corrosion, obtained by the process according to any one of Claims 1 to 7, characterized in that the dry film comprises from 300 to 800 mg/m² of deposited product obtained from the emulsion applied according to any one of the preceding claims.
10. The use of a metal sheet coated with a dry film obtained by previously drying the said metal sheet and applying an emulsion obtained by dispersing in water from 3 to 13 % by volume of an oil phase comprising from 75 to 90% by volume of at least one mineral oil, from 5 to 10% by volume of at least one surfactant and from 5 to 15% by volume of at least one corrosion inhibitor, then drying the metal part by heating it to a temperature of between 70 and 100°C so as to obtain a dry film comprising from 300 to 800 mg/m² of deposited product, for applying a coating directly to the said sheet, without previous degreasing.
11. The use of a sheet according to Claim 10 for painting without previous degreasing.
12. The use of a sheet according to Claim 10 for enamelling without previous degreasing.
13. The use of a sheet according to Claim 10 for dip galvanizing without previous degreasing.

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