WO2000000431A1

WO2000000431A1 - Method for preparing a rare earth sulphide comprising an alkaline element, resulting composition and application as colouring pigment

Info

Publication number: WO2000000431A1
Application number: PCT/FR1999/001535
Authority: WO
Inventors: Stéphane ROMERO; Jean-Christian Trombe
Original assignee: Rhodia Chimie
Priority date: 1998-06-26
Filing date: 1999-06-25
Publication date: 2000-01-06
Also published as: AU754720B2; KR20010053198A; AU4272199A; FR2780393A1; FR2780393B1; JP2002519445A; CA2335901A1; EP1112226A1

Abstract

The invention concerns a method for preparing a rare earth sulphide comprising an alkaline element from a phosphate or a borate of the alkaline element, the composition resulting from said method and its use as a colouring pigment. Said method is characterised in that it consists in contacting at least a rare earth compound with a phosphate or a borate of the alkaline element and heating them in the presence of at least a gas selected among hydrogen sulphide or carbon sulphide.

Description

PREPARATION OF A RARE EARTH SULFIDE COMPRISING AN ALKALINE ELEMENT, COMPOSITION OBTAINED AND APPLICATION AS A COLORING PIGMENT

The present invention relates to a process for the preparation of a rare earth sulfide comprising an alkaline element, from a phosphate or a borate of the alkaline element, the composition obtained by this process and its application as a coloring pigment.

Mineral coloring pigments are already widely used in many industries, particularly in paints, plastics and ceramics. However, most of the mineral pigments which are suitable for applications such as above and which are actually used to date on an industrial scale, generally use metals (cadmium, lead, chromium, cobalt in particular) whose employment is becoming more and more severely regulated, even banned, by the laws of many countries, taking into account their toxicity, which is reputed to be very high. Mention may more particularly be made, by way of nonlimiting examples, of the case of red pigments based on cadmium selenide and / or cadmium sulfoselenide, and for which substitutes based on rare earth sulfides have already been proposed. by the Applicant. Compositions based on rare earth sesquisulfides and alkaline elements have thus been described in EP-A-545746. These compositions, which are obtained by a process essentially consisting in heating a mixture based on a rare earth compound, of an alkaline element and sulfur, have proved to be particularly interesting substitutes.

However, the need was felt to have products with even better pigmentary qualities.

The object of the present invention is to provide such products. For this purpose, the process according to the invention for the preparation of a composition based on a rare earth sulfide comprising at least one alkaline element is characterized in that at least one rare earth compound is brought into contact with a phosphate or a borate of an alkaline element and they are heated in the presence of at least one gas chosen from hydrogen sulfide or carbon sulfide. The invention also relates to a composition based on a rare earth sulfide comprising at least one alkaline element which is characterized in that it is capable of being obtained by the process described above.

Other characteristics, details and advantages of the invention will appear even more completely on reading the description which follows, as well as various concrete but nonlimiting examples intended to illustrate it.

It will be noted here for the whole of the description that by rare earth is understood the elements of the group constituted by yttπum and the elements of the periodic classification of atomic number included inclusively between 57 and 71. A first characteristic of the process of invention lies in the nature of the starting materials. The rare earth is brought in the form of a compound which can be an oxide, a hydroxide or a salt. As the salt, an inorganic salt or an organic salt can be used. Preferably, a nitrate or a carbonate or a hydroxycarbonate is used. It will be noted here and for the whole of the description that the invention also applies to mixed sulfides of rare earths, that is to say to sulfides comprising more than one rare earth.

The alkaline element is provided in the form of a phosphate. The term “alkaline phosphate” is understood to mean the products resulting from the reaction of phosphoric acids with an alkali hydroxide, these acids possibly being orthophosphoric acid, polyphosphoric or metaphosphoric acids. Use is more particularly made of alkaline orthophosphates and even more particularly alkaline dihydrogen phosphates. As alkali, sodium or lithium are used more particularly.

The alkaline element can also be provided in the form of borate. As borate, mention may be made in particular of polyborates of the NaBθ2, Na2B4θ7 type and

Na ₃ B ₆ Oιo-

Another characteristic of the process of the invention is the nature of the sulfurizing gas.

This gas can be hydrogen sulfide or carbon sulfide. According to a preferred embodiment of the invention, a mixture of these two gases is used. The gas or the mixture of sulfurizing gas can be used with an inert gas such as argon or nitrogen.

Heating takes place at a temperature between 700 and 1000 ° C. The high temperatures favor the production of phasically pure products.

The duration of the heating corresponds to the time necessary to obtain the desired sulphide and this duration is shorter the higher the temperature.

The reaction is generally carried out with a partial pressure of hydrogen sulfide and / or carbon sulfide which is between 0.1 × 10 ^ Pa and 1.10 ^ Pa. The product obtained after heating usually has an average size of less than 2 μm, more particularly less than 1.5 μm. However, if it is desired to obtain a finer particle size, the product can be deagglomerated. Generally, disagglomeration under mild conditions, for example grinding of the air jet type, is sufficient to obtain an average size which can be less than 1.5 μm and for example at most 1 μm and advantageously between 0, 3 and 0.8μm. For the whole of the description, the particle size characteristics are measured by a CILAS technique (CILAS 850 device).

Generally an amount of alkaline element is used which is at most 50% of the molar amount of rare earth. According to a preferred characteristic, the molar amount of alkali is at least equal to 0.1%, and advantageously between 5% and 50% and more particularly 5 and 20%, of the molar amount of rare earth.

According to a particular embodiment of the invention, cerium, samarium and lanthanum, or a combination thereof, are used as the rare earth. The process of the invention applies very particularly to the preparation of a rare earth sesquisulfide and, in particular, of a sesquisulfide of crystallographic structure of the Th3P4 type. In the case of cerium, in particular the cubic cerium sesquisulfide Ce2S3 γ is prepared.

The present invention also relates to a composition based on a rare earth sulphide which is characterized in that it is capable of being obtained by the process which has just been described. Consequently, all the process characteristics which have been given above also apply here for the definition of the product. It is added here that the process makes it possible to obtain a composition in which the alkaline element is included at least in part in the crystal lattice of the sulfide or sesquisulfide. Preferably, the alkaline element is included essentially or totally in the crystal lattice.

The sesquisulfide of the composition of the invention, of cubic crystallographic structure of the TI ^ P type, can thus have gaps at the level of the cation network; this lacunar structure can be symbolized by giving the sesquisulfides the formula Mι _υ , 66 t 3l, 33 S ^ 6 ( ^{see in} particular on this subject, WH ZACHARIASEN, "Crystal Chemical Studies of the 5f-Series of Elements. The Ce2S3-Ce3S Type of Structure ", Acta Cryst., (1949), 2, 57).

According to another variant, the composition of the invention comprises on the surface of the particles or of the grains which constitute it, a layer based on at least one transparent oxide. Reference may be made, with regard to a product of this type comprising such a layer, to European patent application EP-A-620 254, in the name of the Applicant, the teaching of which is incorporated here. This peripheral layer coating the composition may not be perfectly continuous or homogeneous. However, preferably, the compositions according to this variant comprise a uniform coating layer and of controlled thickness of transparent oxide, and this so as not to alter the original color of the composition before coating.

By transparent oxide is meant here an oxide which, once deposited on the particle or the grain in the form of a more or less fine film, absorbs little or no light rays in the visible range, and this so as not to mask the original intrinsic color of the particle or the grain. In addition, it should be noted that the term oxide, which is used for convenience throughout this description concerning this variant, should be understood as also covering oxides of the hydrated type.

These oxides or hydrous oxides can be amorphous and / or crystalline, Examples of such oxides, mention may more particularly be mentioned ^the silicon oxide (silica), aluminum oxide (alumina), the zirconium oxide (zirconia), titanium oxide, zirconium silicate ZrSiθ4 (zircon) and rare earth oxides. According to a preferred variant, the coating layer is based on silica. Even more advantageously, this layer is essentially, and preferably only, made of silica. According to another variant, the composition can contain fluorine atoms.

In this case, reference may also be made, with regard to the arrangement of the fluorine atoms, to European patent application EP-A-628608, in the name of the Applicant, the teaching of which is incorporated here.

The fluorinated compositions can exhibit at least one of the following characteristics:

- The fluorine atoms are distributed according to a decreasing concentration gradient from the surface to the core of the particles or grains constituting said compositions.

- the fluorine atoms are mainly distributed at the outer periphery of the particles or grains constituting the compositions. By external periphery is meant here a thickness of material measured from the surface of the particle, of the order of a few hundred Angstroms. Furthermore, the majority means that more than 50% of the fluorine atoms present in the sesquisulfide are found in said external periphery. the percentage by weight of the fluorine atoms present in the compositions does not exceed 10%, and preferably 5%. - the fluorine atoms are present in the form of fluorinated or sulfofluorinated compounds, in particular in the form of rare earth fluorides or rare earth sulfofluorides (thiofluorides).

According to another variant, the compositions of the invention can also comprise a zinc compound, this zinc compound possibly being more particularly deposited on the surface of the particles or grains constituting these compositions. For this variant, reference may be made to French patent application FR-A-2741629, in the name of the Applicant, the teaching of which is incorporated here.

This zinc compound can be obtained by reacting a zinc precursor with ammonia and / or an ammonium salt. The form in which this zinc compound is present in the composition is not known precisely. In some cases, however, it may be thought that zinc is present in the form of a zinc-ammonia complex of formula Zn (NH3) _x (A) _v in which A represents an anion like OH ", CI ^" , the anion acetate or a mixture of anions, x being at most equal to 4 and y equal to 2.

Of course, the invention also relates to the combination of the variants which have been described previously. Thus, it is possible to envisage a composition in which the particles or the grains comprise an oxide layer with in addition fluorine atoms, these compositions possibly also containing zinc. In particular, for compositions comprising an oxide layer, the zinc may be included in the oxide layer or situated on the surface thereof.

For the variants which have been described above and for which the compositions comprise a transparent oxide, fluorine and / or a zinc compound, these compositions are prepared by implementing the methods described in the abovementioned patent applications EP-A- 620254, EP-A-628608 and FR-A-2741629.

The invention also relates to colored pigments comprising a composition based on at least one sulfide of the above type or obtained by the process described above.

The compositions based on sulphide or sesquisulphide or the pigments according to the invention have improved colorimetric coordinates. They are ideal for coloring many materials, such as plastics, paints and others.

Thus, and more precisely still, they can be used in the coloring of plastics which can be of the thermoplastic or thermosetting type. As thermoplastic resins capable of being colored according to the invention, mention may be made, purely by way of illustration, of polyvinyl chloride, polyvinyl alcohol, polystyrene, styrene-butadiene, styrene-acrylonitrile, acrylonitrile-butadiene-styrene copolymers. (ABS), acrylic polymers including polymethacrylate methyl, polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, cellulose derivatives such as for example cellulose acetate, cellulose aceto-butyrate, ethylcellulose, polyamides including polyamide 6 -6. As regards the thermosetting resins for which the compositions or pigments according to the invention are also suitable, mention may, for example, be made of phenoplasts, aminoplasts, in particular urea-formaldehyde, melamine-formaldehyde copolymers, epoxy resins and thermosetting polyesters.

The compositions or pigments of the invention can also be used in special polymers such as fluoropolymers, in particular polytetrafluoroethylene (P.T.F.E.), polycarbonates, silicone elastomers, polyimides.

In this specific application for coloring plastics, the compositions or pigments of the invention can be used directly in the form of powders. It is also possible, preferably, to use them in a pre-dispersed form, for example in premix with a part of the resin, in the form of a paste paste or of a liquid which makes it possible to introduce them to n ' no matter what stage of resin manufacturing.

Thus, the compositions or pigments according to the invention can be incorporated into plastics such as those mentioned above in a weight proportion generally ranging either from 0.01 to 5% (reduced to the final product) or from 40 to 70 % in the case of a concentrate.

The compositions or pigments of the invention can also be used in the field of paints and stains and more particularly in the following resins: alkyd resins, the most common of which is called glycerophthalic; long or short oil modified resins; acrylic resins derived from esters of acrylic (methyl or ethyl) and methacrylic acid optionally copolymerized with ethyl acrylate, 2-ethylhexyl or butyl; vinyl resins such as, for example, polyvinyl acetate, polyvinyl chloride, butyralpolyvinyl, formalpolyvinyl, and copolymers of vinyl chloride and vinyl acetate or vinylidene chloride; the aminoplast or phenolic resins most often modified; polyester resins; polyurethane resins; epoxy resins; silicone resins.

Generally, the compositions or pigments are used in an amount of 5 to 30% by weight of the paint, and from 0.1 to 5% by weight of the stain.

Finally, the compositions or pigments according to the invention are also capable of being suitable for applications in the rubber industry, in particular in floor coverings, in the paper and inks industry. printing, in the field of cosmetics, as well as many other uses such as for example, and not limited to, dyes, finishing of leathers and laminate coatings for kitchens and other worktops, ceramics, glazes. The invention also relates to the compositions of colored matter, in particular of the plastics, paints, stains, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes and laminated coatings, characterized in that they comprise a composition or a colored pigment. of the type described above. Concrete but non-limiting examples will now be given. In this description, the chromaticity coordinates L *, a * and b * are given in the CIE 1976 system (L *, a *, b *) as defined by the International Lighting Commission and listed in the Collection of Standards French (AFNOR), colorimetric n ° X08-12 (1983). They are determined using a colorimeter sold by the company Pacific Scientific. The nature of the illuminant is D65. The observation surface is a circular pastilie of 12.5 cm ^ of surface. The observation conditions correspond to a vision under an opening angle of 10 °. In the given measurements, the specular component is excluded.

L * gives a measure of reflectance (light / dark shade) and thus varies from 100 (white) to 0 (black); a * and b * are the values of the colored trends. L * therefore represents the variation from black to white, a * the variation from green to red and b * the variation from yellow to blue.

Examples will now be given. EXAMPLE 1

This example relates to the preparation of a cerium sulphide comprising sodium in an Na / Ce atomic ratio of 0.1.

The necessary proportions of a cerium hydroxycarbonate are introduced into a mortar, having a CILAS particle size of 0.8 μm (measurement carried out on a dispersion of the product (200 mg) in 50 ml of an aqueous solution at 0.625 mg / l by weight of sodium hexametaphosphate and which has previously undergone a passage to the ultrasonic probe for 3 minutes 450W) and a sodium dihydrogen phosphate (NaH2PO4). The whole is then ground so as to obtain a homogeneous mixture. This mixture is then brought (8 ° C / min.) To 800 ° C and then maintained for 1 hour at this temperature under a continuous sweep of a gaseous mixture containing argon, hydrogen sulfide and sulfide of carbon at the respective flow rates of 13.21 / h, 4.61 / h and 91 / h.

After heating, the product is deagglomerated under mild conditions. The chromatic characteristics of the product are given in the table below. EXAMPLE 2

The procedure is as in Example 1 but using cerium nitrate Ce (NO ₃ ) ₃ , 1, 7H ₂ O. The chromatic characteristics of the product are given in the table below.

COMPARATIVE EXAMPLE 3

The procedure is as in Example 1, but using sodium carbonate Na2CO ₃ instead of sodium dihydrogen phosphate.

The chromatic characteristics of the product are given in the table below.

COMPARATIVE EXAMPLE 4

The same operating conditions of Example 1 are used, but using cerium nitrate Ce (NO ₃ ) ₃ , 1, 7H2θ and sodium carbonate.

The chromatic characteristics of the product are given in the table below.

It is seen from the results of the table and by comparing the products of Examples 1 and 3 on the one hand and 2 and 4 on the other hand, that by using an alkaline phosphate instead of an alkali carbonate, the compound of starting rare earth remaining the same, the chromaticity coordinates are clearly improved.

Claims

1- Process for the preparation of a composition based on a rare earth sulfide comprising at least one alkaline element, characterized in that at least one rare earth compound is brought into contact with a phosphate or a borate of a alkaline element and they are heated in the presence of at least one gas chosen from hydrogen sulfide or carbon sulfide.

2- A method according to claim 1, characterized in that an oxide, a hydroxide or a salt is used as the rare earth compound.

3- A method according to claim 2, characterized in that as the rare earth compound is used a nitrate, a carbonate or a hydroxycarbonate.

4- Method according to one of the preceding claims, characterized in that a mixture of hydrogen sulfide and carbon sulfide is used.

5- Method according to one of the preceding claims, characterized in that the rare earth sulfide is a sesquisulfide.

6- Method according to one of the preceding claims, characterized in that an amount of alkaline element is used which is at most 50% of the molar amount of rare earth and which is more particularly between 5 and 50% of that amount.

7- Method according to one of the preceding claims, characterized in that a composition based on a sulfide is prepared which has a crystallographic structure of the Th ₃ P4 type.

8- Method according to one of the preceding claims, characterized in that the alkaline element is sodium or lithium.

9- Method according to one of the preceding claims, characterized in that a composition is prepared based on a cerium sesquisulfide Cβ2S ₃ cubic γ.

10- Composition based on a rare earth sulfide comprising at least one alkaline element, characterized in that it is capable of being obtained by a process according to one of the preceding claims. 11- Composition according to claim 10, characterized in that it comprises on the surface of the particles constituting it, a layer based on at least one transparent oxide.

12- Composition according to claim 10 or 11, characterized in that it further comprises fluorine atoms, the fluorine atoms can be more particularly distributed in a decreasing gradient from the surface to the core of the particles constituting the composition.

13- Composition according to one of claims 10 to 12, characterized in that it further comprises a zinc compound, this zinc compound can be more particularly deposited on the surface of the particles constituting it.

14- Composition according to claim 13, characterized in that the zinc compound was obtained by reaction of a zinc precursor with ammonia and / or an ammonium salt.

15- Colored pigment, characterized in that it comprises a composition based on a rare earth sulphide according to one of claims 10 to 14.

16- Use of a composition according to one of claims 10 to 14 or of a colored pigment according to claim 15 in plastics, paints, stains, rubbers, ceramics, glazes, papers, inks, cosmetics, dyes and laminate coatings.

17 - Compositions of colored matter in particular of the plastics, paints, stains, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes and laminated coatings, characterized in that they comprise a composition or a colored pigment as defined in one of claims 10 to 15.