AU754720B2

AU754720B2 - Method for preparing a rare earth sulphide comprising an alkaline element, resulting composition and application as colouring pigment

Info

Publication number: AU754720B2
Application number: AU42721/99A
Authority: AU
Inventors: Stephane Romero; Jean-Christian Trombe
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 1998-06-26
Filing date: 1999-06-25
Publication date: 2002-11-21
Anticipated expiration: 2019-06-25
Also published as: EP1112226A1; AU4272199A; JP2002519445A; CA2335901A1; WO2000000431A1; FR2780393A1; FR2780393B1; KR20010053198A

Description

PREPARATION OF A RARE EARTH SULPHIDE COMPRISING AN ALKALI ELEMENT FROM AN ALKALI ELEMENT PHOSPHATE OR BORATE, THE COMPOSITION OBTAINED, AND ITS APPLICATION AS A COLOURING

PIGMENT

The present invention relates to a process for preparing a rare earth sulphide comprising an alkali element from an alkali element phosphate or borate, to the composition obtained by this process and to its application as a colouring pigment.

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Mineral colouring pigments are already widely used in many industries, in particular the paint, plastics and ceramics industries.

However, the majority of mineral pigments for applications such as those described above which are in current use on an industrial scale generally use metals (in particular cadmium, lead, chromium, cobalt) the use of which is becoming more strictly regulated or even prohibited under the legislation of many countries, due to their very high toxicity. Non limiting examples that can be cited are red pigments based on cadmium selenide and/or cadmium sulphoselenide, for which substitutes based on rare earth sulphides have already been proposed by the Applicant. Compositions based on rare earth sesquisulphides and alkali elements have been described in this regard in European patent EP-A-O 545 746. Such compositions, obtained by a process consisting essentially of heating a mixture based on rare earth compound, an alkali element and sulphur, have shown themselves to produce substituents of particular interest.

However, there is a need for products with even further improved properties.

It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

In a broad aspect, the present invention provides a process for preparing a rare earth sesquisulphide comprising at least one alkali element in a quantity of at most of the molar quantity of rare earth wherein at least one rare earth compound is brought into contact with an alkali element phosphate or borate and heated in the presence of at least one gas selected from hydrogen sulphide or carbon disulphide.

The invention also concerns a rare earth sesquisulphide when prepared by the I process of the invention.

-2- Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

Other characteristics, advantages and details of the invention will become clear from the following description and non-limiting examples that illustrate it.

It should be noted that the term "rare earth" as used throughout the description means elements from the group constituted by yttrium and elements from the periodic table with atomic numbers 57 to 71 inclusive.

The first characteristic of the process of the invention is the nature of the starting products. The rare earth is provided in the form of a compound that can be an oxide, a hydroxide or a salt. The salt can be inorganic or an organic salt. Preferably, a nitrate or a carbonate or a hydroxycarbonate is used.

It should be noted here that the whole of the description of the invention is also applicable to mixed rare earth sulphides, sulphides comprising more than one rare earth.

The alkali element is provided in the form of a phosphate. The term "alkali phosphate" means products resulting from reacting phosphoric acids with an alkali hydroxide, these acids possibly being orthophosphoric acid, polyphosphoric acids or metaphosphoric acids. More particularly, alkali orthophosphates are used, still more particularly alkali dihydrogen phosphates. More particularly, the alkali is sodium or lithium.

The alkali element can also be supplied in the form of the borate. Borates that can be mentioned are polyborates of the type NaBO 2 Na 2

B

4 0 7 and Na 3

B

6

O

10 A further characteristic of the process of the invention is the nature of the sulphiding gas. This gas can be hydrogen sulphide or carbon disulphide. In a preferred implementation of the invention, a mixture of these two gases is used. The sulphiding gas or gas mixture can be used with an inert gas such as argon or nitrogen.

Heating is to a temperature in the range 700°C to 1000 0 C. The high temperatures encourage the production of phase-pure products.

The heating period corresponds to the time required to obtain the desired sulphide; the higher the temperature, the shorter the period.

The reaction is generally carried out with a partial pressure of hydrogen sulphide and/or carbon disulphide in the range 0.1 x 105 Pa to 1 x 10 5 Pa.

The mean size of the product obtained after heating is usually less than 2 ptm, more particularly less than 1.5 ptm. However, if a finer grain size is required, the product can be disagglomerated. In general, disagglomeration is carried out under mild conditions, for example grinding with an air jet, which is sufficient to obtain a mean size that can be less than 1.5 am, for example at most 1 pm and advantageously in the range 0.3 to 0.8 rnm. Throughout the description, the grain size characteristics were measured using a CILAS technique (CILAS 850 apparatus).

In general, the quantity of alkali element is at most 50% of the molar rare earth quantity. In accordance with a preferred characteristic, the molar quantity of alkali is at least 0.1%, advantageously in the range 5% to 50%, more particularly 5% to 20% of the molar quantity of rare earth.

S*:i In a particular embodiment, the rare earth is cerium, samarium or lantnanum, or a S combination thereof.

More particularly, the process of the invention is applicable to preparing a rare earth sesquisulphide, in particular a sesquisulphide with a TH 3 Ph 4 type structure. In the case of cerium, a y cubic cerium sesquisulphide Ce 2

S

3 is used.

The present invention also concerns a composition based on a rare earth sulphide, characterized in that it can be obtained using the process described above. As a result, all of the characteristics of the process given above are also applicable when defining the product. It should also be added that the process can produce a composition in which the alkali element is at least partially included in the crystalline lattice of the sulphide or sesquisulphide. Preferably, the alkali element is essential or totally included in the crystalline lattice.

The sesquisulphide of the composition of the invention, with a Th 3

P

4 type crystallographic structure, can exhibit voids in the cation lattice; this void structure can be symbolised by giving the sesquisulphides a structure with formula M 10 66 ]1.33S16 (see in particular W. H. Zachariasen, "Crystal Chemical Studies of the 5f series of Elements. The Ce 2

S

3 -Ce 3

S

4 Type of Structure", Acta Cryst, (1949), 2, 57).

In a further variation, the composition of the invention comprises a layer based on at least one transparent oxide on the surface of the particles or grains constituting them. Regarding a product of this type comprising such a layer, reference should be made to the Applicant's patent EP-A-O 620 254, the disclosure of which is hereby incorporated.

This peripheral layer coating the composition need not be precisely continuous or homogeneous. However, the compositions of this variation preferably comprise a uniform coating layer of transparent oxide of controlled thickness, so as not to alter the original colour of the composition before coating.

The term "transparent oxide" as used here means an oxide that, once deposited on the *.o particle or grain in the form of a thin or thick film absorbs little or no visible light so that it only slightly, or does not at all mask the intrinsic colour of the particle or grain. Further, it should be noted that the term "oxide", used for convenience throughout the present description concerning this oooo• variation, also encompasses hydrated type oxides.

These oxides or hydrated oxides can be amorphous and/or crystalline.

Examples of such oxides that can be cited are silicon oxide (silica), aluminium oxide (alumina), zirconium oxide (zirconia), titanium oxide, zirconium silicate ZrSiO 4 (zircon) and rare earth oxides. In a preferred variation, the coating layer is silica-based. Still more advantageously, this layer is essentially, and preferably completely, constituted by silica.

In a further variation, the composition can contain fluorine atoms.

In this case, regarding the disposition of the fluorine atoms, reference should be made to the Applicant's European patent EP-A-0 628 608, the teaching of which is hereby incorporated.

Fluorinated compositions can have at least one of the following characteristics: 0 the fluorine atoms are distributed in accordance with a concentration gradient that decreases from the surface to the core of the particles or grains constituting said compositions; 0 the fluorine atoms are mainly distributed at the outer periphery of the particles or grains constituting the compositions. The term "outer periphery" as used here means a material thickness, measured from the particle surface, of the order of a few Angstroms. In this context, the term "mainly" means more than 50% of the fluorine atoms present in the sesquisulphide are in said outer periphery; 0 the percentage by weight of fluorine atoms present in the compositions does not exceed 10%, preferably the fluorine atoms are present in the form of fluorinated or sulphofluorinated compounds, in particular in the form of rare earth fluorides or rare earth sulphofluorides to: (thiofluorides).

In a variation, the compositions of the invention can also comprise a zinc compound, this eoooo zinc compound more particularly also being' deposited on the surface of the particles or grains constituting these compositions. Reference in this regard should be made to the Applicant's French p n 7 patent FR-A-2 741 629, hereby incorporated by reference.

•o 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 presented in the composition is not accurately known. In some cases, however, the zinc can be considered to be present in the form of a zinc-ammonia complex with formula Zn(NH 3 )x(A)y where A represents an anion such as OH', Cl", the acetate anion or a mixture of anions, x being at most 4 and y being 2.

Clearly, the invention also concerns a combination of the variations described above. Thus, a composition can be envisaged in which the particles or grains comprise a layer of oxide and fluorine atoms, these compositions also containing zinc. In particular, with compositions comprising a layer of oxide, the zinc can be included in the oxide layer or located on the surface thereof.

For the variations described above and where the compositions comprise a transparent oxide, fluorine and/or a zinc compound, these compositions are prepared using the processes described in the patent applications cited above, namely EP-A-0 620 254, EP-A-0 628 608 and FR-A-2 741 629.

The invention also concerns coloured pigments comprising a composition based on at least one sulphide of the type described above or obtained by the process described above.

Compositions based on a sulphide or sesquisulphide or pigments of the invention have improved colorimetric co-ordinates. They are ideal for colouring a number of materials such as plastics, paint and the like.

9 Thus, and more precisely still, they can be used for colouring plastic materials, which may be thermoplastics or thermosets.

Illustrative examples of thermoplastic resins that can be coloured in accordance with the invention and which can be cited are polyvinyl chloride, polyvinyl alcohol, polystyrene, styrenebutadiene copolymers, styrene-acrylonitrile copolymers, acrylonitrile-butadiene-styrene (ABS) copolymers, acrylic polymers, in particular polymethylmethacrylate, polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, cellulose derivatives such as cellulose acetate, cellulose acetobutyrate, ethylcellulose, and polyamides including polyamide 6-6.

Examples of thermoset resins for which the compositions or pigments of the invention are also suitable and which can be cited are phenoplasts, aminoplasts, in particular urea-formol copolymers, melamine-formol copolymers, epoxy polymers and thermoset polyesters.

It is also possible to use the compositions or pigments of the invention in special polymers such as fluorinated polymers, in particular polytetrafluoroethylene (PTFE), polycarbonates, silicone elastomers and polyimides.

In this specific application for colouring plastics, the compositions or pigments of the invention can be used directly in the form of powders. It is preferable to use them in a pre-dispersed form, for example as a pre-mixture with a portion of the resin, in the form of a concentrated paste or a liquid that allows them to be introduced at any point in the resin manufacture process.

The compositions or pigments of the invention can be incorporated into plastics materials such as those mentioned above in a proportion by weight that is generally either 0.01% to 5% (with respect to the final product) or 40% to 70% in the case of a concentrate.

The compositions or pigments of the invention can also be used in the field of paint and finishes, more particularly in the following resins: alkyd resins, the most common of which are known as oil-based paints; short- or long- oil modified resins; acrylic resins derived from acrylic S0@ acid esters (methyl or ethyl) and methacrylic acid esters, possibly co-polymerised with ethyl, 2ethylhexyl or butyl acrylate; vinyl resins such as polyvinyl acetate, polyvinyl chloride, 000.0: 0 polyvinylbutyral, polyvinylformal and copolymers of vinyl chloride and vinyl acetate or vinylidene chloride; aminoplast resins or phenol resins, usually modified; polyester resins; polyurethane resins; epoxy resins; silicone resins.

In general, the compositions or pigments are used in an amount of 5% to 30% by weight for a paint, and 0.1% to 5% by weight for a finish.

Finally, the compositions or pigments of the invention are also suitable for applications in the rubber industry, in particular for floor coverings, in the paper industry and in printing inks, in cosmetics, and in other fields, non limiting examples of which are dyes, leather finishing and laminated coatings for kitchens and other work surfaces, ceramics, glazes.

The invention also concerns coloured compositions, in particular plastics, paints, finishes, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes and laminated coatings, characterized in that they comprise a composition or a coloured pigment of the type described above.

In the present description, the chromatic co-ordinates a* and b* are given by the 1976 ICI system as defined by the International Commission on Illumination and indexed with the Receuil de Normes Frangaises [AFNOR, French Standards] as colorimetric colour n' X08- 12 (1983). They were determined using a colorimeter sold by Pacific Scientific. The nature of the illuminant was D65. The observation surface was a circular 12.5 cm 2 surface area disk. The observation conditions corresponded to viewing at an opening angle of 100. The specular component was excluded from the measurements given.

L* provides a measure of the reflectance (light/dark) and thus varies from 100 (white) to 0 (black); a* and b* are the colours. L* thus 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 concerns the preparation of a cerium sulphide comprising sodium in a Na/Ce atomic ration of 0.1.

The required proportions of a cerium hydroxycarbonate with a CILAS granulometry of 0.8 jim (measured with a product dispersion (200 mg) in 50 ml of an aqueous 0.625 mg/1 by weight solution of sodium hexametaphosphate which had been subjected to ultrasound for 3 minutes at 450 W) and a sodium dihydrogen phosphate (NaH 2

PO

4 were introduced into a mortar. It was then ground to obtain a homogeneous mixture. This mixture was heated at 8 0 C/min to 800 0 C then kept for 1 hour at this temperature in a continuous stream of a gas mixture containing argon, hydrogen sulphide and carbon disulphide at respective flow rates of 13.2 k/h, 4.6 1/h and 9 1/h.

After heating, the product was disagglomerated under mild conditions.

The Table below shows the chromatic characteristics of the product.

EXAMPLE 2 The procedure of Example 1 was followed, using cerium nitrate Ce(N0 3 3 1.7H 2 0.

The Table below shows the chromatic characteristics of the product.

COMPARATIVE EXAMPLE 3 The procedure of Example 1 was followed, using sodium carbonate Na 2

CO

3 instead of sodium dihydrogen phosphate.

The Table below shows the chromatic characteristics of the product.

COMPARATIVE EXAMPLE 4 The operating conditions of Example 1 were used, using cerium nitrate Ce(N0 3 3 ,1.7H 2 0 and sodium carbonate.

The Table below shows the chromatic characteristics of the product.

Examples 1 50.3/47.6/37.3 3, comparative 48.2/43.8/34.4 2 47.5/45.5/32.2 4, comparative 44.0/37.4/26.8 From the table, and comparing the products of Examples 1 and 3 and 2 and 4, it can be seen that using an alkali phosphate in place of an alkali carbonate, with the starting rare earth compound remaining the same, the chromatic co-ordinates are substantially improved.

Claims

1. A process for preparing a rare earth sesquisulphide comprising at least one alkali element in a quantity of at most 50% of the molar quantity of rare earth wherein at least one rare earth compound is brought into contact with an alkali element phosphate or borate and heated in the presence of at least one gas selected from hydrogen sulphide or carbon disulphide.

2. A process according to claim 1, wherein the rare earth compound is an oxide, a hydroxide or a salt.

3. A process according to claim 2, wherein the rare earth compound is a nitrate, a carbonate or a hydroxycarbonate.

4. A process according to any one of the preceding claims, wherein a mixture of hydrogen sulphide and carbon disulphide is used.

A process according to any one of the preceding claims, wherein the quantity of alkali element is in the range 5% to 50% of the molar quantity of rare earth.

6. A process according to any one of the preceding claims, wherein a composition based on a sulphide is prepared with a Th 3 P 4 type crystallographic structure.

7. A process according to any one of the preceding claims, wherein the alkali element is sodium or lithium.

8. A process according to any one of the preceding claims, wherein a composition based on a y cubic cerium Ce 2 S 3 sesquisulfide is prepared.

9. A process for preparing a rare earth sesquisulphide, substantially as herein described with reference to any one of the examples but excluding comparative examples. A rare earth sesquisulphide when prepared by any one of the preceding claims. DATED this 6th Day of September 2002 RHODIA CHIMIE Attorney: PAUL G. HARRISON Fellow Institute of Patent and Trade Mark Attorneys of Australia of BALDWIN SHELSTON WATERS