FR2608619A2 - Composite pigment intended for protecting metal surfaces against corrosion and process for its preparation - Google Patents

Abstract

Each pigment particle comprises a core of an electrically conductive compound, especially a metal, metal salt or alloy coated with a surface layer of an anodic metal such as zinc, and the particle is treated chemically in a bath containing an active product chosen from hexavalent chromium salts, fluorine salts, boron nitrogen, or a product originating from the reaction between aminotriazole and the anhydride of hydrocarbylsuccinic acid, the surface layer of the pigment thus being made an electron emitter.

Description

The present invention relates to developments in the pigment described and claimed under the main patent, the pigment according to the main patent consisting of particles comprising a core of conductive and preferably metallic material, the core being coated with a surface coating layer. of an anodic metal such as zinc.

The advantages of this composite pigment, the unitary particles of which have a core on the one hand and a coating surface on the other, have been described in the main patent, and which makes it possible to obtain considerably improved results in cathodic protection of surfaces. against corrosion, in particular of metallic surfaces and more particularly of iron and steel surfaces.

In addition to a considerably improved yield, the pigment according to the main patent has advantages in terms of economic profitability because it makes it possible to use, to form the core of the pigment particles, an electrically conductive material of low cost price.

It is thus possible according to the main patent to produce a pigment which is particularly effective for the protection and coating of a metallic surface, after incorporation of the pigment in an appropriate binder, from a percentage (in the composition of the pigment) limited to a rate of the order of 25% of a rich metal such as zinc, the rest of the composition being supplied by an inexpensive metal product such as particles of iron or iron alloy.

It being specified that in all cases the iron or iron alloy constitutes the core of the pigment particles, the surface of which consists of a coating of zinc, the whole being obtained by grinding under conditions described in the main patent.

This Certificate of Addition relates to developments in the technique and in the pigment products provided for in the main patent, a development which considerably improves the effectiveness and the durability of action of the product.

The applicants have in fact found that the pigment according to the main patent and obtained by a physical grinding process, resulting in the coating of a core of an inexpensive metal (such as iron) with an anodic metal (such as zinc), could be improved by a subsequent chemical treatment leading to stabilization of the coating and to an electrochemical passivation making it possible to improve the anodic action of the protective coating constituting the active element of the pigment according to the invention.

And the present Certificate of Addition therefore relates to developments in the main patent relating to the pigment of the princ-pa 'patent improved in its effectiveness and its durability of action by a chemical treatment following the physical coating treatment.

To this end, the invention relates to a pigment for protecting metallic surfaces against corrosion and capable of being incorporated in a binder such as based on a synthetic or natural resin, to be applied as a film to the surface of the metal wall to be protected, and the pigment is made up according to claim 1,2,3,4 or 5 of the main patent by particles each comprising a core chosen from electrically conductive compounds, in particular metals, their salts or their alloys, such as carbides, phosphide, nitride, boride, silicide, or alloy of metals such as iron, cobalt, nickel, moybde'ne, titanium, chromium, zirconium, vanadium, tungsten, thorium, tantalum, cadmium, the core being coated with a coating layer made of an anodic metal such as zinc, and the pigment is characterized in that said coating layer has undergone a passivation treatment by immersion in a chemical reagent in liquid phase, and such that said layer coating becomes an electron emitter.

According to another characteristic, the core of the pigments can receive a surface coating layer of metals chosen from the family comprising magnesium, aluminum, zinc, chromium, lead, copper or silver, forming a layer of interpenetrating coating, by ionic diffusion, with the surface of the nucleus.

According to another important characteristic of the invention, the reagent used for the treatment of pigmentary particles is chosen from the family comprising hexavalent chromium salts.

Alternatively, the chemical reagents for the treatment of the coating surface of the pigment particles are chosen from the family comprising the fluorine, nitrogen or boron salts.

According to a particularly advantageous embodiment, the pigment according to the invention comprises a finely ground metallic lead core, of particle size between 1 and 50 microns, and coated with zinc, the pigment thus produced having been treated with a chosen chemical reagent in the family comprising hexavalent chromium salts, fluorine, nitrogen or boron salts.

According to another exemplary embodiment of the invention, the pigment consists of a metal phosphide core such as nickel or iron phosphide coated with a metal chosen from the family comprising lead or metallic copper, the coating having been treated with a chemical reagent chosen from the family comprising hexavalent chromium salts or a product resulting from the reaction between aminotriazole and anhydride of succinic hydrocarbil acid.

The invention also relates to a process for preparing a composite pigment, according to one of claims 6, 7, 8 or 9 of the main patent and in which the particles constituting the core are subjected to a coating, by ionic diffusion, of an anodic metal, in particular by mechanical grinding so as to deposit a layer of anodic metal on the surface of the particles of the material constituting the core, and the preparation process is further characterized in that the pigment particles thus obtained after this mechanical treatment and obtaining a composite pigment consisting of a core and a coating surface, are subjected to a treatment with a chemical reagent in the wet phase to obtain the passiva ion of the coating surface rendered thus emitting electrons.

More particularly and according to a development of the process according to this Certificate of Addition, the composite pigment is treated with a reagent chosen from the family comprising hexavalent chromium salts, fluorine, nitrogen or boron salts.

More particularly, the pigment according to the invention is treated by immersion in a bath chosen from the family comprising, as active product - hexavalent chromium salts at a concentration of between 0.5 and 15; - fluororydric acid at a concentration between 0.5 and 110% - silicon fluoride at a concentration between 0.1 and 25%.

According to a development of the process according to the present
Certificate of Addition, the composite pigment comprising a coating of lead or copper metal and treated in a bath containing as active products a compound chosen from the family comprising: 3-amino - 1 H-1,2,4 triazole, 11 -amino 1,2,4 triazole or 5-amino -1 H -1,2,4 triazole.

According to yet another development of the invention, the pigments thus obtained are mixed in an interstitial binder comprising epoxy, vinyl, alkyd, polyurethane, acrylic and other film-forming materials.

Other characteristics and advantages of the invention will emerge from the description which follows and which is given in connection with a more particular embodiment presented by way of example.

According to one embodiment of the invention, a composite pigment is produced in accordance with the data of the main patent and from the following proportions by weight.

ZINC POWDER: 25%
IRON PHOSPHIDE OR IRON ALLOY: 75%
Zinc powder particles which may be of particle size between 25 and 100 microns are chosen in particular, while the iron phosphide particles can have a size of the order of 5 to 10 microns.

The mixture is introduced into a grinding assembly comprising, for example, a rotary drum into which steel balls 5 to 20 cm in diameter are introduced with the mixture.

The grinding is continued for a period of the order of 2 to 3 hours until a composite pigment is obtained, the particles of which consist of a core or an iron core comprising on their surface a layer coating formed, by ionic diffusion, of zinc resulting from the grinding of the zinc particles initially introduced and which during the operation were crushed and which gradually came to clump together and constitute a surface layer on the surface of the particles harder iron.

The composite pigment thus obtained and in accordance with the data of the main patent, can then be treated wet and according to a chemical process to result in a passivation of its coating layer thus rendered emitting of electrons.

Therefore coating for example zinc in the present example, and reinforced in its electron emitting function will ensure under particularly effective conditions the cathodic protection of the surface to be protected.

The chemical treatment subsequent to the coating phase is carried out by immersing the pigment in a bath, for example an aqueous bath containing compositions such as - hexavalent chromium salts at a concentration in the bath of between 0.5 and 15 - fluoridric acid at a concentration between 0.5 and 110% - silicon fluoride at a concentration between C, 1 and 25.

Other materials can be used as cores.

For example: nickel or iron phosphides coated with lead metal or copper metal.

When the diffusion coating is finished, the lead or copper coating surfaces are treated with special compositions containing CARVI salts or with a product resulting from the reaction between aminotriazole and anhydride of the hydrocarbyl succinic acid.

The aminotriazoles which can be used for the copper-coated pigment are 3 - amino - 1 H -1,2,4 triazole, 4 - amino 1,2,4 triazole or 5 - amino - 1 H - 1,2,4 triazole.

The pigments thus obtained will be used in binders of the epoxy, vinyl, alkyd, polyurethane, acrylic and other film-forming materials type.

The primers thus obtained will have an anodic action for all corrodible steels and consequently will have a protective action against electrochemical corrosion.

All these pigments can be used in high-performance anti-corrosion primers and free from chromate toxicity.

Claims (10)

1 - Pigment for the protection of metal surfaces against corrosion and suitable for being incorporated in a binder such as based on a synthetic or natural resin, to be applied as a film to the surface of the metal wall to be protected, and the pigment is made up according to one of claims 1,2,3,4 or 5 of the main patent by particles each comprising a core chosen from electrically conductive compounds in particular metals, their salts or their alloys, such as carbide, phosphide , nitride, boride, silicide, or alloy of metals such as iron, cobalt, nickel, molybdenum, titanium, chromium, zirconium, vanadium, tungsten, thorium, tantalum, cadmium, ie the core being coated with a coating layer constituted of an anodic metal such as zinc, characterized in that said coating layer has undergone a passivation treatment by immersion in a chemical reagent in the liquid phase, and such that said coating layer returns emitting electrons. 2 - Pigment according to claim 1, characterized in that the core of the pigment particles has received a surface coating layer of metals chosen from the family comprising magnesium, aluminum, zinc, chromium, lead, copper or silver, achieving an interpenetrating coating layer, by ionic diffusion, with the surface of the nucleus. 3 - Pigment according to one of claims 1 or 2, characterized in that the reagent used for the treatment of pigment particles is chosen from the family comprising hexavalent chromium salts. 4 - Pigment according to one of the fevendieations 1,2 or 3, characterized in that the chemical reagents for the treatment of the coating surface of the pigment particles are chosen from the family comprising the fluorine, nitrogen or boron. 5 - Pigment according to one of claims 1 to 11, characterized in that each particle comprises a finely ground metallic lead core, of particle size between 1 and 50 microns, and coated with zinc, the pigment thus produced having been treated by a chemical reagent chosen from the family comprising hexavalent chromium salts, fluorine, nitrogen or boron salts. 6 - Pigment according to one of claims 1 to 11, characterized in that each pigment particle consists of a metal phosphide core such as nickel or iron phosphide coated with a metal chosen from the family comprising lead or metallic copper, the coating having been treated with a chemical reagent chosen from the family comprising hexavalent chromium salts or a product resulting from the reaction between aminotriazole and anhydride of succinic hydrocarbil acid. 7 - Process for the preparation of a composite pigment, according to one of claims 6,7,8 or 9 of the main patent and in which the particles constituting the core are subjected to a coating, by ionic diffusion, of a metal anodic, in particular by mechanical grinding so as to deposit a layer of anodic metal on the surface of the particles of the material constituting the core, further characterized in that the pigment particles thus obtained after this mechanical treatment and obtaining a composite pigment consisting of a core and a coating surface, are subjected to a treatment with a chemical reagent in the wet phase to obtain the passivation of the coating surface thus rendered emitting of electrons. 8 - Process according to claim 8, characterized in that the particles of the composite pigment are treated with a reagent chosen from the family comprising hexavalent chromium salts, fluorine, nitrogen or boron salts. 9 - Method according to one of claims 7 or 8, characterized in that the pigment according to the invention is treated by immersion in a bath comprising in solution an active product chosen from the family comprising - hexavalent chromium salts at a concentration between 0.5 and 15%; - fluororydric acid at a concentration between 0.5 and 40%; - silicon fluoride at a concentration between 0.1 to 25S. 10 - Process according to claim 7, characterized in that the composite pigment comprising a coating of lead or copper metal is treated in a bath containing as active products a compound chosen from the family comprising: 3-amino - 1 H-1 , 2,4 triazole, 11-amino 1,2,4 triazole or 5-amino -1 H -1,2,4 triazole.