WO1998000367A1

WO1998000367A1 - Cerium and alkaline or alkaline earth molybdate, method of its preparation and use as colouring pigment

Info

Publication number: WO1998000367A1
Application number: PCT/FR1997/001129
Authority: WO
Inventors: Catherine Hedouin; Pierre Macaudiere
Original assignee: Rhodia Chimie
Priority date: 1996-06-28
Filing date: 1997-06-25
Publication date: 1998-01-08
Also published as: FR2750415A1; FR2750415B1; AU3448297A; ZA975668B

Abstract

The invention concerns one cerium and alkaline or alkaline earth molybdate, method of its preparation and use as colouring pigment. The molybdate is characterised in that it has an alkaline and/or alkaline earth/cerium atomic ratio less than 1. It has a deformed scheelite and monoclinic crystallographic structure. It can be prepared by a method that comprises the following steps: an alkaline and/or alkaline earth molybdate and a cerium salt are brought together; the medium thus formed is precipitated; the resulting precipitate is calcined. The molybdate can be used as pigment in plastic materials, paints, surface coating, rubber, ceramics, glazing, paper, ink, cosmetic products, dyes, leather, laminated coatings and materials based on or obtained from at least a mineral binder.

Description

MOLYBDATE OF CERIUM AND ALKALINE OR ALKALINE EARTH. ITS PREPARATION PROCESS AND ITS USE AS A COLORING PIGMENT

The present invention relates to a molybdate of cerium and alkali and / or alkaline earth, its process of preparation and its use as coloring pigment.

Mineral coloring pigments are already widely used in many industries, particularly in paints, plastics and ceramics. In such applications, the properties of, among others, thermal and / or chemical stability, dispersibility (ability of the product to disperse correctly in a given medium), compatibility with the medium to be colored, intrinsic color, coloring power and opacifying power are all particularly important criteria to take into consideration when choosing a suitable pigment.

Unfortunately, the problem is that 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 use is becoming more and more severely restricted, 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 yellow pigments of the lead chromate or molybdate type. We therefore see that there is a significant need for new substitute mineral pigments.

The object of the present invention is therefore to provide a substitution pigment in the range of yellow or yellow-orange.

For this purpose, the molybdate according to the invention is a molybdate of cerium and at least one metal chosen from alkali or alkaline-earth metals and it is characterized in that it has an atomic ratio of alkali and / or alkali metal - earthy / cerium less than 1.

The molybdate, according to the invention, of cerium and at least one metal chosen from alkali or alkaline-earth metals is also characterized in that it has a crystallographic structure of the deformed Scheelite type and of the monoclinic type.

The invention also relates to a process for preparing a molybdate which, according to a first embodiment, is characterized in that it comprises the steps following: an alkali and / or alkaline-earth molybdate and a cerium salt are brought into contact; the medium thus formed is precipitated; the precipitate obtained is calcined.

According to a second embodiment, the method for preparing molybdate is characterized in that it comprises the following steps: a suspension is formed comprising an alkali and / or alkaline-earth salt other than a molybdate, a cerium salt and an ammonium molybdate; the suspension is dried, in particular by atomization; the product obtained in the previous step is calcined.

Other characteristics, details and advantages of the invention will appear even more completely on reading the description which follows and the appended drawing in which:

- The single figure is an X-ray diffraction spectrum of a product according to the prior art and of a product according to the invention.

The molybdate of the invention is a molybdate of cerium and another metal, this other metal being an alkali metal or an alkaline earth metal. The invention also relates to a molybdate of cerium and two other metals, one being an alkali metal, the other an alkaline earth metal.

The molybdate of the invention can be characterized first of all by the fact that it has an alkali metal or alkaline earth metal / cerium atomic ratio of less than 1. It can also be characterized by its structure. It has a crystallographic structure of the Scheelite type, that is to say the structure of the calcium tungstate CaWOψ II, however, it is a deformed structure. Indeed, while the Scheelite structure is of the quadratic type, that of the molybdate of the invention is of the monoclinic type. This deformation is due to the fact that the alkaline and / or alkaline-earth element is present in the mesh in an amount less than that in which it is present in the double molybdate of formula Cefv MoO ^.

The invention therefore also covers a molybdate of cerium and at least one metal chosen from alkali or alkaline-earth metals which has a crystallographic structure of the deformed Scheelite type and of the monoclinic type and whose atomic ratio of alkali and / or alkali metal - earthy / cerium is less than 1. The atomic ratio of alkali metal and / or alkaline earth metal / cerium can in particular be between 0.01 and 0.9 and more particularly between 0.2 and 0.7, the values of the limits being included.

The alkali metal may in particular be sodium or lithium. The alkaline earth can be calcium. The molybdate of the invention has a sustained yellow coloring. This color can be appreciated by the chromatic coordinates of the product.

The chromaticity coordinates L *, a * and b * are given here and for the rest of the description in the CIE 1976 system (L *, a * and b *) as defined by the Commission Internationale d'Eclairage and listed in the Collection of French Standards (AFNOR), colorimetric n ° X08-12, n ° X08-14 (1983). They are determined for the measurements made on products and plastics using a colorimeter sold by the company Pacific Scientific. The nature of the illuminant is D65. The observation surface is a circular patch 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.

Thus, the molybdate of the invention can have a b * coordinate of at least 50, more particularly at least 55 and which can exceed 60. The component a * can be greater than -5 and in particular greater than -2.

Thanks to the preparation processes which will be described below, the molybdate of the invention has a particle size which makes it perfectly suitable for its use as a pigment. Thus, the molybdate resulting from the methods of the invention usually has an average size of at most 10 μm, more particularly at most 5 μm. The particle size, here and for the entire description, is measured by GLAS particle size. In addition, the molybdate thus obtained is disaggregable, that is to say it can be in the form of agglomerates of the aforementioned size, these agglomerates being able to consist of agglomerated and / or slightly sintered grains from which it is possible to obtain whole grains by simple disaggregation. Whole grain means grain that has not been broken or broken. Grains can indeed be broken or broken during grinding. Scanning electron microscopy photos can show that the grains have not been broken. After disagglomeration, by any suitable means, the average grain size can be at most 4 μm, more precisely at most 2 μm and advantageously between 1 and 2 μm.

For the whole of the description, the size and dispersion index characteristics are measured by the laser diffraction technique using a granulometer of the GLAS HR 850 type (volume distribution).

The processes for preparing the molybdate of the invention will now be described. Two possible embodiments will be given.

The method according to the first mode comprises a first step in which an alkaline molybdate and a cerium salt are brought into contact. Any cerium salt may be suitable. Inorganic salts or organic salts can be used. As inorganic salts, mention may be made more particularly of cerium chloride or nitrate. The salts are introduced in the quantities necessary to obtain the desired alkaline / cerium ratio. The bringing together of the two salts causes the precipitation of a double molybdate of cerium and alkali. The precipitate obtained is separated from the reaction medium by any known means. It is washed and dried if necessary. According to a variant, the drying can be done by atomization. In this case, the precipitate separated from the reaction medium, after optional washing, is resuspended in water and then the suspension thus obtained is atomized. Any known type of atomizer can be used. The gas outlet temperature can be between 100 and 150 ° C.

The dried product is then calcined. This calcination makes it possible to obtain the crystallographic structure which has been described above. Calcination takes place in air. It can also be done in a neutral medium, under nitrogen for example, or in a slightly reducing medium. The calcination takes place at a temperature which is generally at least 600 ° C. More particularly, this temperature can be between 700 and 800 ° C. The duration can vary between 1 and 5 hours. The increase in the calcination temperature makes it possible to obtain a more yellow color for the product. Above 800 ° C, sintering may occur and there is therefore a risk of obtaining a product of grain size ill-suited to the application as a pigment. The method of the second embodiment comprises a first step in which a suspension is formed comprising an alkali and / or alkaline earth salt other than a molybdate, a cerium salt and an ammonium molybdate. The alkaline and / or alkaline earth salt can be chosen from organic or inorganic salts. Mention may be made of oxalates by way of example. The cerium salt can be of the same type as that described for the first process. In a second step, the suspension obtained above is dried, this drying possibly being carried out by atomization. Finally, the dried product obtained in the previous step is calcined. The calcination makes it possible to obtain the molybdate of cerium and alkali and or alkaline-earth in the desired structure. As regards the atomization and calcination conditions, these are the same as those given for the first embodiment. The method of the second mode which has just been described makes it possible to control more precisely the alkaline and / or alkaline-earth / cerium ratio.

A particular variant of the molybdate of the invention will now be described. According to this variant, the molybdate comprises a layer based on at least one transparent oxide, deposited on its surface or on its periphery.

For this variant, reference may be made with regard to the transparent oxide and the preparation process to the French patent application FR-A-2703999 in the name of the Applicant, the teaching of which is incorporated here.

According to this variant, the product of the invention comprises a molybdate, of the type described above, which forms a core and, coating this core, a peripheral layer of transparent oxide.

Of course, some variations around this structure are possible. In particular, the peripheral layer coating the molybdate may not be perfectly continuous or homogeneous. However, preferably, the products according to the invention consist of a uniform coating layer and of controlled thickness of transparent oxide, and this so as not to alter the original color of the molybdate before coating. By transparent oxide is meant here an oxide which, once deposited on the molybdate in the form of a more or less fine film, absorbs little or no light rays in the visible range, and this of so as not to mask the original intrinsic color of the molybdate or little. In addition, it should be noted that the term oxide, which is used for convenience in this part of the present description, should be understood as also covering hydrated type oxides. These oxides, or hydrated oxides, can be amorphous and / or crystallized. As an example of such oxides, mention may more particularly be made of silicon oxide (silica), aluminum oxide (alumina), zirconium oxide (zirconia), titanium oxide, silicate zirconium ZrS ^' 104 (zircon) and rare earth oxides. According to a preferred embodiment of the present invention, the coating layer is based on silica. Even more advantageously, this layer is essentially, and preferably only, made of silica.

A process for preparing the coating layer products may consist in bringing the molybdate as it was obtained after calcination into contact with a precursor of the oxide forming layer, and in precipitating this oxide. The methods of precipitation of the oxides and the precursors to be used are described in particular in FR-A-

2703999.

In the case of silica, mention may be made of the preparation of silica by hydrolysis of an al-yl-silicate, by forming a reaction medium by mixing water, alcohol, molybdate which is then suspended, and optionally of a base, and then introducing the alkyl silicate, or alternatively a preparation by reaction of molybdate, of a silicate, of the alkaline silicate type, and of an acid.

In the case of an alumina-based layer, molybdate, an aluminate and an acid can be reacted, whereby alumina is precipitated. This precipitation can also be obtained by bringing together and reacting molybdate, an aluminum salt and a base.

Finally, alumina can be formed by hydrolysis of an aluminum alcoholate. As regards titanium oxide, it can be precipitated by introducing into an aqueous suspension of molybdate according to the invention and a titanium salt on the one hand such as TiGφ TiOCl2 or T1OSO4, and a base on the other hand . One can also operate for example by hydrolysis of an alkyl titanate or precipitation of a titanium sol.

Finally, in the case of a zirconium oxide-based layer, it is possible to proceed by cohydrolysis or coprecipitation of a suspension of molybdate from the invention in the presence of an organometallic compound of zirconium, for example a zirconium alkoxide such as zirconium isopropoxide.

The molybdate of the invention having the characteristics mentioned above or as obtained by the processes which have just been described can be used very particularly as coloring pigment.

The product of the invention has in fact a coloring power and a covering power and, therefore, is suitable for coloring many materials, such as plastics, paints and others.

Thus, and more precisely, it can be used in the coloring of polymers for plastics which may be of the thermoplastic or thermosetting type, these polymers being capable of containing traces of water.

As thermoplastic resins which can be 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, in particular polymethyl methacrylate, 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 product according to the invention is also suitable, mention may, for example, be made of phenoplasts, aminoplasts, in particular urea-formaldehyde, melamine-formaldehyde copolymers, epoxy resins and thermosetting polyesters.

The product 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 product of the invention can be used directly in the form of powders. It is also possible, preferably, to use it in a pre-dispersed form, for example in premix with a part of the resin, in the form of a paste concentrate or of a liquid which makes it possible to introduce it at n no matter what stage of resin manufacturing.

Thus, the products 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 20 to 70% in the case of a concentrate.

The products 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; oil-modified resins long or short; 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, butyral polyvinyl, 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 products 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.

In addition, the products 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 printing ink industry, in the cosmetic field. , as well as many other uses such as for example, and not limited to, dyes, in leathers for the finishing thereof and laminate coatings for kitchens and other worktops, ceramics and glazes.

The products of the invention can also be used in the coloring of materials based on or obtained from at least one mineral binder. This mineral binder can be chosen from hydraulic binders, aerial binders, plaster and binders of the anhydrous or partially hydrated calcium sulphate type.

By hydraulic binders is meant substances having the property of setting and hardening after addition of water by forming hydrates insoluble in water. The products of the invention apply very particularly to the coloring of cements and, of course, of concretes produced from these cements by adding thereto water, sand and / or gravel.

In the context of the present invention, the cement may, for example, be of the aluminous type. By this is meant any cement containing a high proportion either of alumina as such or of aluminate or of both. By way of example, mention may be made of cements based on calcium aluminate, in particular those of the SECAR type.

The cement can also be of the silicate type and more particularly based on calcium silicate. PORTLAND cements can be given as an example and, in this type of cements, Portland cures with rapid or very rapid setting, white cements, those resistant to sulfates as well as those comprising blast furnace slag and / or fly ash and / or meta-kaolin.

We can also mention cements based on hemihydrate, calcium sulphate as well as magnesium cements known as Sorel cements. The products of the invention are also used for coloring aerial binders, that is to say binders hardening in the open air by the action of CO2, of the calcium or magnesium oxide or hydroxide type.

The products of the invention are finally used for coloring plaster and binders of the anhydrous or partially hydrated calcium sulphate type (CaSθ4 and CaSθ4, 1 / 2H2O).

Finally, the invention relates to compositions of colored material, in particular of the plastics, paints, stains, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes, leathers, laminated coatings or of the type based on or obtained from at least one mineral binder, which comprise, as coloring pigment, a product according to the invention or obtained by methods of the type described above.

Examples will now be given.

In the examples, the particle size was determined according to the aforementioned Glas technique. It is further specified that the measurement was carried out on a dispersion of the product in an aqueous solution at 0.05% by weight of sodium hexametaphosphate and which has previously undergone passage through your ultrasonic probe (probe with tip of

13mm diameter, 20KHz, 120W) for 3 minutes.

EXAMPLE 1

500 ml of a solution (0.18 molar) of sodium molybdate Na2Moθ4.2H2θ are introduced into a reactor with a capacity of 1.51 equipped with a stirrer. With constant stirring, 500 ml of a 0.12 molar solution of cerium nitrate Ce (Nθ3) 3, xH2θ is added slowly (10 ml / min). A yellow precipitate immediately forms. This precipitate is filtered and washed with water. The precipitate obtained is then resuspended in water at a concentration of 150g / l and then atomized with Buchi®. The inlet and outlet temperatures of the atomizer gases are respectively 210 ° C and 100 ° C. The dried solid is calcined for 2 hours at 600 ° C or 2 hours at 800 ° C (rising speed 5 ° C / min). The products obtained at the end of the calcination have an Na / Ce atomic ratio of 0.33. These products can be easily disaggregated with an air jet. The following particle size characteristics are obtained (average diameter):

The chromaticity coordinates of the disaggregated products are as follows

The deagglomerated products are incorporated in a proportion of 0.5% and 1% by weight of powder in polypropylene. Double thickness (2 and 3mm) parallelipipedic specimens are formed by injection at 230 ° C. The measurement of the chromaticity coordinates is carried out on a white background. The% of transition reflects the opacity of the wafer. The values measured on the thick part of the plate are given below.

EXAMPLE 2

This example relates to the preparation of molybdates according to the invention at different sodium levels. Sodium oxalate, cerium chloride and ammonium heptamolybdate are mixed. The amounts of sodium oxalate used vary according to the Na / Ce ratio sought. The mixture thus obtained is atomized under the same conditions as in Example 1 and the atomized product is calcined for 7 hours at 700 ° C.

The characteristics of the products obtained are given below. The chromaticity coordinates were determined on the powdered products after deagglomeration of the air jet.

FIG. 1 shows the spectrum (identified by the number 1) of comparative product 2-4 with an Na / Ce ratio of 1. The spectrum identified by the number 2 corresponds to the product of Example 1 calcined at 800 ° C.

EXAMPLE 3

The procedure is as in Example 2 using calcium chloride in stoichiometric amounts such that the product of formula is obtained

After disaggregation with an air jet, an orange product with a particle size of 3.5 μm and a chromaticity coordinate L = 85, a * = 2.8, b * = 66.7 is obtained.

Claims

1 - Cerium molybdate and at least one metal chosen from alkali or alkaline earth metals, characterized in that it has an alkali metal and / or alkaline earth cerium atomic ratio of less than 1.

2- Molybdate of cerium and at least one metal chosen from alkali or alkaline-earth metals, characterized in that it has a crystallographic structure of the deformed Scheelite type and of the monoclinic type.

3- Molybdate according to claim 2, characterized in that it has an alkali metal and / or alkaline earth metal / cerium atomic ratio of less than 1.

4- Molybdate according to one of the preceding claims, characterized in that it has an atomic alkali and / or alkaline-earth metal / cerium atomic ratio between

0.01 and 0.9 and more particularly between 0.2 and 0.7.

5- Molybdate according to one of the preceding claims, characterized in that it is in the form of grains of average size of at most 4 μm, more particularly at most 2 μm.

6- Molybdate according to claim 5, characterized in that the grains are whole.

7- Molybdate according to one of the preceding claims, characterized in that the alkali metal is sodium.

8- Molybdate according to one of the preceding claims, characterized in that it comprises a layer based on at least one transparent oxide, deposited on its surface or on its periphery.

9- Process for preparing a molybdate according to one of the preceding claims, characterized in that it comprises the following steps:

- an alkali and / or alkaline earth molybdate and a cerium salt are brought into contact;

- The medium thus formed is precipitated; - The precipitate obtained is calcined.

10- A method according to claim 9, characterized in that before calcination, the precipitate is dried by atomization. 1 1 - Process for the preparation of a molybdate according to one of claims 1 to 7, characterized in that it comprises the following steps:

- A suspension is formed comprising an alkali and / or alkaline-earth salt other than a molybdate, a cerium salt and an ammonium molybdate;

- The suspension is dried, in particular by atomization;

- The product obtained in the previous step is calcined.

12- Method according to one of claims 9 to 11, characterized in that calcining at a temperature of at least 600 ° C, more particularly between 700 and 800 ° C.

13- A process for preparing a molybdate according to claim 8, characterized in that the molybdate obtained by the process according to one of claims 9 to 1 1 and a precursor of the oxide forming a layer are brought into contact, and this oxide is precipitated.

14- Use of a molybdate according to one of claims 1 to 8 or obtained by a process according to one of claims 9 to 13, as a coloring pigment.

15- Use according to claim 14, characterized in that molybdate is used as a pigment in plastics, paints, stains, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes , leathers, laminate coatings and materials based on or obtained from at least one mineral binder.

16- Colored material compositions, in particular of the plastics, paints, stains, rubbers, ceramics, glazes, papers, inks, cosmetic products, dyes, leathers, laminated coatings or of the type based or obtained from at least one mineral binder , characterized in that they comprise, as coloring pigment, a molybdate according to one of claims 1 to 8 or obtained by a process according to one of claims 9 to 13.