FR2831176A1 - Pigment composition, e.g. useful for coloration of plastics, paints, rubber, ceramics, glazes, paper, inks and cosmetics, comprises a dye covalently bound to rare earth metal sulfide particles through a coupling agent - Google Patents

Abstract

Pigment composition comprises a dye covalently bound to rare earth metal sulfide particles through a coupling agent. Independent claims are also included for: (1) production of the pigment composition by contacting the sulfide particles with the coupling agent in a liquid medium and reacting the dye with the coupling agent; (2) coloration of plastics, paints, rubber, ceramics, glazes, paper, inks, cosmetics, dyes and multilayer coatings using the pigment composition.

Description

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PIGMENT COMPOSITION BASED ON RARE EARTH SULFIDE, DYE AND, IF POSSIBLE, A COUPLING AGENT,
ITS PREPARATION METHOD AND USE
The present invention relates to a pigment composition based on a rare earth sulphide, a dye and, optionally, a coupling agent, its method of preparation and its use.

 The inorganic pigments for coloring are already widely used in many industries, particularly in the fields of paints, plastics and ceramics.

 Most of the inorganic pigments which are suitable for applications as above and which are actually used today on an industrial scale, generally use metals (cadmium, lead, chromium, cobalt in particular) whose use becomes more and more heavily regulated, even banned, by the legislation of many countries, given their very high toxicity. More particularly, by way of nonlimiting examples, mention may be made of red pigments based on cadmium selenide and / or cadmium sulphoselenide, for which rare earth sulphide-based substitutes 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 pigments have proved to be particularly interesting substitutes.

 However, the need has been felt to have improved pigment quality products especially for applications in plastics.

 The object of the present invention is to provide such products.

 For this purpose and according to a first embodiment, the pigment composition of the invention is characterized in that it comprises: a support based on a rare earth sulphide; a dye bound to said support via a chemical function Rs of said dye which is capable of creating a bond between the support and the dye by complexation, by adsorption, of the electrostatic or covalent type.

 According to a second embodiment, the pigment composition of the invention is characterized in that it comprises: a support based on a rare earth sulphide; a coupling agent linked to said support via a chemical function R's of said agent which is capable of creating between the support and the agent

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e une liaison par complexation, par adsorption, du type électrostatique ou covalente ; - un colorant lié audit agent de couplage par une liaison covalente.

a complexing bond, by adsorption, of the electrostatic or covalent type; a dye bonded to said coupling agent by a covalent bond.

 Other features, details and advantages of the invention will appear even more fully on reading the description which follows, as well as various concrete but non-limiting examples intended to illustrate it.

 For rare earth is meant for the entire description the elements of the group consisting of yttrium and the elements of the periodic classification of atomic number inclusive between 57 and 71.

 The composition of the invention firstly comprises a support which is based on a rare earth sulphide.

 As sulfides of this type, there may be mentioned those of formula Ln2S3, in which Ln denotes a rare earth, and described in EP-A-203838. We can also mention rare earth sulphides of beta form.

 More particularly, the support may be based on a rare earth sulphide and may contain at least one alkaline and / or alkaline earth element. This alkaline or alkaline earth element may be included partly or totally in the crystal lattice.

 With regard to such a type of sulphide, reference may be made to the teaching of the European patent application EP-A-545746. It may be recalled that the alkaline element may be chosen in particular from lithium, sodium or potassium. Of course, the sulfide may include several alkali or alkaline earth elements.

 The sulphide may be more particularly a sesquisulphide.

 The sesquisulphide may in particular have a cubic crystallographic structure of Th3P4 type, which has gaps in the cation network; this lacunar structure can be symbolized by giving to the sesquisulphides the formula M1 0, 66 [] 1, 33 S16 (see in this regard, WH ZACHARIASEN, "Crystal Chemical Studies of the 5f-Series of Elements." The Ce2S3-Ce3S4 Type of Structure, "Acta Cryst., (1949), 2, 57).

 The alkaline or alkaline-earth elements can be introduced into these cationic vacancies, until saturation or not of these latter. The presence of this element in the sulphide or sesquisulphide can be evidenced by simple chemical analysis. Moreover, the X-ray diffraction analyzes show that in the case of this variant, there is preservation of the crystalline phase in Th3P 4 of the sesquisulphide, with in some cases a more or less significant modification of the mesh parameters, which is a function of of the nature and quantity of the alkaline or alkaline-earth element introduced.

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 In the case of sesquisulphide, the rare earth may be more particularly cerium, samarium or lanthanum. Even more particularly, the rare earth sesquisulphide is a sesquisulphide Ce2S3 and cubic.

 Generally, the amount of alkaline or alkaline earth element is at most 50% of the rare earth molar amount of sulfide or sesquisulphide.

 The molar amount of alkali or alkaline earth is generally at least 0.1%, and advantageously between 5% and 50% and more particularly 5 and 20%, of the molar amount of rare earth.

 Mention may also be made as rare earth sulfides used as support in the context of the present invention, those described in the European patent application EP-A-680930 to the description of which we can refer. These rare earth sulfides comprise at least one alkaline element and they consist of monocrystalline whole grains of average size of at most 1.5um. They are obtained by a process in which at least one rare earth carbonate or hydroxycarbonate is brought into contact with at least one compound of an alkaline element and the mixture is heated in the presence of at least one gas chosen from hydrogen or carbon disulfide.

These products also have an average size (CILAS particle size) generally less than 2 μm, more particularly between 0.7 and 1.5 μm. After deagglomeration under mild conditions, the average size may be at most 1.5, and preferably between 0.3 and 0.8um.

 According to a variant of the invention, the support of the composition may further comprise a layer based on at least one transparent oxide deposited on the surface of the support. This peripheral layer coating the support may not be perfectly continuous or homogeneous. However, preferably, the compositions according to this embodiment comprise a uniform coating layer and a controlled thickness of transparent oxide, and this so as not to alter the original color of the support before coating.

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

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 These oxides, or hydrated oxides, can be amorphous and / or crystallized.

 By way of example of such oxides, mention may be made more particularly of silicon oxide (silica), aluminum oxide (alumina), zirconium oxide (zirconia), titanium oxide and silicate. zirconium ZrSiO4 (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 solely, silica.

 This layer may be deposited on the support by a precipitation method for example.

 Reference may also be made to a product of this type comprising such a layer, and to its method of preparation, to the European patent application EP-A-620254.

 According to another variant of the invention, the support may further contain a metal element at the surface. This element is generally advantageously chosen from divalent metal elements (such as magnesium, calcium, strontium, barium, zinc for example), trivalent metallic elements (in particular aluminum and trivalent rare earth elements), the elements tetravalent metals (titanium, zirconium and / or cerium and tetravalent rare earths) These elements may be present as a mixture The quantity of metallic elements present on the surface of the support may be between 30 elements per nm 2, typically between 1 and 10 elements per nm 2, and this amount is preferably greater than 2 elements per nm 2, and preferably greater than 3 elements per nm 2.

 In the particular case of zinc, this element may have been introduced onto the support by reaction of a zinc precursor with ammonia and / or an ammonium salt. The zinc precursor may be a zinc oxide or hydroxide which is used in suspension. This precursor may also be a zinc salt, preferably a soluble salt. It may be an inorganic acid salt such as a chloride, or an organic acid salt such as an acetate. The form in which this zinc compound thus obtained is not precisely known, but it may be thought that zinc is present in the form of a zinc-ammonia complex of formula Zn (NH 3) x (A) y in which A represents an anion such as OH-, Cl-, the acetate anion or a mixture of anions, x being at most equal to 4 and y at most equal to 2. We can refer for the case of zinc to teaching of the European Patent Application EP-A-876434.

 The support may further comprise fluorine atoms on its surface.

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 For such a support, it will also be possible to refer more particularly to the arrangement of the fluorine atoms with the patent application EP-A-628608.

 The fluorinated supports may have at least one of the following characteristics: the fluorine atoms are distributed according to a gradient of decreasing concentration of the surface at the core of the support.

 the fluorine atoms are mainly distributed at the outer periphery of the support. By outer periphery is meant a thickness of material measured from the surface of the support, of the order of a few hundred Angstroms. In addition, it is generally understood that more than 50% of the fluorine atoms present in the support are in said outer periphery.

 the percentage by weight of the fluorine atoms present in the support 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 sulfofluorides (thiofluorides) of rare earths.

 According to the first embodiment of the invention, the pigment composition further comprises a dye chemically bonded to the support.

 By dye is meant any compound having absorption or light-emitting properties in the field of visible light or in a wider range, from near ultraviolet to near infrared. The bond between the dye and the support can be of different types. It may be first of all a bond by chemical complexation between the dye and a cation present on the surface of the support. This connection can also be of electrostatic nature between the dye and the surface of the support, for example of positive charge. This bond can also be done by adsorption between the dye and the surface of the support. These bonds may also be demonstrated by various techniques, for example by adsorption curve determinations according to techniques known to those skilled in the art; by spectroscopic techniques of the Raman or infrared type. Finally, the bond between the dye and the support may be covalent. This covalent bond can be demonstrated by spectroscopic techniques of the Raman, NMR and infrared type.

 These bonds, which are strong bonds between the dye and the support, can also be evidenced by a test which consists in subjecting the composition of the invention, ie the support on which the graft is grafted.

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 dye, washing with water at a rate of 3 ml of water per gram of composition. It is found that less than 5% of the graft dye, advantageously less than 2% thereof and preferably less than 1% are found in the free state in the washing water obtained.

 It should be noted that the different types of link given above can coexist.

 The dye has a chemical function Rs or comes from a compound which has this function Rs which is likely to create between the support and the latter a connection of the type described above.

 As Rs function of this type can be mentioned carboxylic functions-CCH, or carboxylate-CO2M '; sulfonate -SO3M ', sulphosuccinate-CO2-CH2-CH (SO3M') - CO2H, M'Designing a metal, especially an alkali metal or the suffonic acid-SOsH function or sulfate -O-SO3. Thus, there may be a bond by chemical complexation between the carboxyl, carboxylate, sulfonate or sulfonic group in ionized form and a cation present on the surface of the support. A connection of electrostatic nature can also be established between the group-COO or SO 2 'ionized dye and the surface of the positive charge carrier. More particularly, the Rs function may be a carboxylate function present with an amine function.

 The Rs function can also be a phosphonate-PO (OH) 2 or phosphinate = PO (OH) or phosphate-O-PO (OH) function, especially in the case where the bond with the support is of covalent type. Still in this same specific case, the function Rs may be a silane function, and advantageously a function-SiZZ, where Z \ Z2 and Z3 each represent a group capable of being hydrolyzed in the form of an OH group. Thus, each of the groups Z1, Z2 and Z3 may, for example, designate a halogen atom (in particular Cl, Br, l or F), or a group-Or, where r denotes an alkyl group or an aryl group.

 The dyes used may of course have several of these functions of the same type or of different types in combination. One can thus mention the particular case of dyes having both one or more carboxylate functions and one or more amine functions.

 The dye of the dispersion of the invention may be of any type insofar as it has the aforementioned Rs function or even if it comes from a compound having this function. Water-soluble dyes can especially be used.

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 Examples of dyes which may be suitable in the context of the present invention are given below, the names and numbers given here and in the remainder of the description are those of the Color Index (CI).

 Thus, the dye may be selected from the family of azo, ie compounds having a group -N = N-. Among the dyes of this family, one can use the monoazo CI N016035, CI N015985, CI N01551 0, CI N015850, CI N015585, CI N012085 or the diazo for example Ci N020170. The dye may be an element of the xanthene family, for example Rhodamine B (CI N045170) or IC N045430. It is also possible to mention the dyes of the indigo family as Ci N073015. Suitable dyes are also those of the triphenylmethane type such as Erioglaucine (CI No. 449090) or CI N042053 or CI N042090.

 The dyes of the family of pyrazolones Ci? 19140 or orange B, those of the anthraquinone family: Ci N061570 for example, those of the pyrene family: CI N059040 in particular, quinolines: Ci N047005 for example or nitro dyes like CI? 10315.

 The composition of the invention may also be in a second embodiment which will now be described.

 The main feature of this second mode is the presence of a coupling agent bound to the support of the composition and a dye which is bound to the coupling agent by a covalent bond.

 The bond between the coupling agent and the support is of the same type as that described above for the first embodiment with regard to the carrier-dye bond, that is to say that a bond by chemical complexation between the coupling agent and a cation present on the surface of the support or a connection of electrostatic nature between the coupling agent and the support surface, for example a positive charge or finally an adsorption bond between the coupling agent and the surface of the support. Likewise, the bond between the coupling agent and the support may also be covalent.

 This bond is established by a chemical function R's which is of the same type as the function Rs mentioned above. What has been described previously about Rs therefore also applies here.

 Furthermore, according to this second embodiment, the dye is bonded to the coupling agent by a covalent bond.

 In order to ensure the covalent dye-coupling agent binding, the coupling agent must come from a first compound which has a

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 Rc function capable of reacting to form a covalent bond. This first compound must also have a function R's of the type described above for the connection with the support. Moreover, the dye must also come from a second compound which has a chemical function R'c capable of reacting to form a covalent bond.

 The chemical functions Rc and R'c mentioned above may be amine, aldehyde, alcohol, isocyanate, thiol, silane or halogen functions.

 The amine function can be more particularly -NH2. The halogen may be more particularly chlorine.

dans laquelle R1 est un groupement alkyle comprenant de 1 à 12 atomes de carbone, Z1 est un groupe-CO2H, carboxylate-C02M'ou-SO3M', M' désignant un métal, notamment un métal alcalin, Z1 pouvant être aussi un groupe phosphate ou phosphonate, Z2 désigne un halogène ou un groupe - NHR2, ou-NR3R2, ou-NH4+, R2 et R3, identiques ou différents, désignant un hydrogène ou un groupement alkyle comprenant de 1 à 8 atomes de carbone. The coupling agent may more particularly come from a compound of formula (1):

in which R 1 is an alkyl group comprising from 1 to 12 carbon atoms, Z 1 is a group -CO 2 H, carboxylate-CO 2 M 'or -SO 3 M', M 'denoting a metal, in particular an alkaline metal, Z 1 may also be a phosphate group or phosphonate, Z2 denotes a halogen or a group - NHR2, or - NR3R2, or - NH4 +, R2 and R3, which may be identical or different, denoting a hydrogen or an alkyl group comprising from 1 to 8 carbon atoms.

 The group R 1 can be linear or branched. It may more particularly have a number of carbon atoms of between 4 and 10 or even more particularly between 4 and 8.

 Z2 can be especially chlorine or NH2.

 The compound (1) may especially be an amino acid, more particularly an aliphatic amino acid. It may be in particular a C4-C10 acid and preferably a C4-CS acid. An example of an acid that may be mentioned is aminocaproic acid.

 As in the case of the first embodiment of the invention, the coloring compound of the composition according to the second embodiment may be any type of compound having absorption or light-emitting properties in the field of visible light or in a wider range, from near ultraviolet to near infrared, in the measure, moreover, where it comes from a compound having the function R'c above.

 The chemical functions Rc and R'c are chosen so as to create a covalent bond between the coupling compound and the dye compound.

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 By way of example, mention may be made of the coloring compounds chosen from the monoazo family, such as CI? 12085 or CI N015585, those of the xanthenes family as CI N045370: 1, CI N045425: 1, CI N045425 and CI? 45410 and also those of the anthraquinone family such as Disperse Violet 1.

 According to a variant of the second embodiment of the invention, the dye may further comprise a chemical function R 'which is capable of creating a bond between the support and the dye by complexing, by adsorption or by electrostatic or covalent type. In this case, the dye is bound to the support of the composition both via the coupling agent and by a chemical bond of the same type as that described in the case of the first embodiment of the invention. 'invention. The description that has been made on this link and on the chemical function Rs therefore applies here.

 As a dye which may be used in the composition of the composition according to this variant, mention may be made of those of the azo type, such as Cl 2 NO 5 1585 with sulphonate and chlorine functional groups or Cl 2 N017200 (Acid red 33) with functional groups. fonate and - NHs or the compounds of formula (1) of EP-A-437184 or of formula (1) of WO 97/30125, the brilliant Cibacron Red 3B-A or the Procion Red MX-5B (ref 22845 -1 and 40436-5 respectively from Aldrich) with sulfonate and chlorine functions.

 Mention may also be made of anthraquinone-type products with sulfonate and NH2 functions such as Reactive Blue 2 or Procion Blue HB Ref 24 222-5 from Aldrich or PX3R brilliant blue.

 According to another variant of the second embodiment of the invention, in the case of a support which comprises a layer based on a transparent oxide, in particular silica, the coupling agent can come from an aminosilan.

dans laquelle les radicaux R4, R5, R6 et R7, identiques ou différents, représentent chacun un atome d'hydrogène ou un groupement alkyle ou aryle possédant de 1 à 8 atomes de carbone ; et le radical Ra représente un groupement alkylène comportant de 1 à 18 atomes de carbone. This aminosilan can respond more particularly to the following formula (2):

in which the radicals R4, R5, R6 and R7, which are identical or different, each represent a hydrogen atom or an alkyl or aryl group having from 1 to 8 carbon atoms; and the radical Ra represents an alkylene group having from 1 to 18 carbon atoms.

 The dye concentration in the composition of the invention may vary. Generally, the ratio R: moles of dye / moles of rare earth sulphide is between 0.001 and 0.1, preferably between 0.001 and 0.01.

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 The concentration of coupling agent can also vary. It can be between 0.01 and 0.6 mole of coupling agent per mole of rare earth sulfide.

 The preparation of the composition according to the first embodiment of the invention consists in bringing the support into contact with a dye having a chemical function Rs in a liquid medium capable of solubilizing the dye, whereby the presence of this dye is obtained. Rs function or the reaction thereof with the support, a bond between the support and the dye.

 In the case of the second mode, the method comprises a first step in which the support is brought into contact with a first compound having a chemical function R 'and Rc in a liquid medium capable of solubilizing said first compound, whereby one obtains, by the presence of the R's function or the reaction thereof with the support, a bond between the support and the coupling agent from the first aforementioned compound; and a second step in which the product from the preceding step is brought into contact with a second compound having a function R'c in a liquid medium capable of solubilizing said second compound, whereby the functions Rc and R'c, a bond between the coupling agent and the dye from the above-mentioned second compound.

 Preferably, these processes are carried out in an aqueous medium, and even more preferably in the absence of any organic solvent.

 The pH of the medium in which the support is brought into contact with the other abovementioned compounds in order to create the support / dye or support / coupling agent / dye bonds is generally at least 6, it may be more particularly between 6 and 10. It is also possible to heat the medium to facilitate the formation of bonds.

 When these processes are carried out in an aqueous medium, it is generally preferred, especially to optimize the yield, that the coupling agent and the dye compound used are water-soluble compounds. By "water-soluble compounds" is meant compounds which have a solubility in water at 25 ° C (after possible hot dissolution) of at least 25 g / l, and preferably greater than 50 g / l.

 In the implementation of the process for preparing the compositions having a coupling agent, the compounds whose functions are chosen from the following pairs (Rc / R'c) are especially used: (amine / halogen), (halogen / amine) ), (alcohol / isocyanate), (isocyanate / alcohol), (thiol / halogen), (halogen / thiol), (amine / aldehyde), or (aldehyde amine).

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 A specific embodiment of the process of the invention which proves to be particularly advantageous consists in using aminosilan coupling agents and coloring compounds having a reactive chemical function R'c of halogen type, preferably a CI-radical. or-Br.

 The present invention also relates to the use as dye of the compositions described above.

 The compositions or products of the invention have indeed a coloring power and a covering power and, therefore, are suitable for coloring many materials, such as plastics, paints, rubbers, ceramics, glazes, papers, inks, cosmetics, dyes and laminates.

 Thus, and more specifically, they 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 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 and acrylonitrile-butadiene-styrene copolymers. (ABS), acrylic polymers including polymethyl methacrylate, polyolefins such as polyethylene, polypropylene, polybutene, polymethylpentene, cellulose derivatives such as for example cellulose acetate, cellulose acetate butyrate, ethylcellulose, polyamides including polyamide 6-6.

 As regards the thermosetting resins for which the compositions according to the invention are also suitable, mention may be made, for example, of phenoplasts, aminoplasts, in particular the urea-formaldehyde, melamine-formaldehyde copolymers, epoxy resins and thermosetting polyesters.

 The compositions of the invention can also be used in special polymers such as fluorinated polymers, in particular polytetrafluoroethylene (P.T. F.F.), polycarbonates, silicone elastomers and polyimide.

 In this specific application for coloring plastics, it is possible to use the compositions of the invention directly in the form of powders. They can also preferably be used in a pre-dispersed form, for example by premixing with part of the resin,

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 in the form of a paste concentrate or a liquid which allows them to be introduced at any stage of the manufacture of the resin.

 Thus, the products according to the invention can be incorporated in plastics such as those mentioned above in a proportion by weight ranging generally from 0.01 to 5% (referred 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 varnishes and more particularly in the following resins: alkyd resins, the most common of which is called glycerophthalic acid; resins modified with long or short oil; acrylic resins derived from esters of acrylic acid (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 products are used in a proportion of 5 to 30% by weight of the paint, and 0.1 to 5% by weight of the stain.

 Finally, the compositions according to the invention are also likely to be suitable for applications in the rubber industry, especially in floor coatings.

 Examples will now be given.

 These examples relate to the incorporation of pigment compositions of the invention into polypropylene Eltex HV 001 powder. The color measurements were made on the polypropylene.

The implementation was carried out as follows: - Blends in a plastic bag of 34.65g of pigment, 7g of antioxidant
B225 (0.2%) and 3458.35g of polypropylene for Examples 1 and 2, and 35g of pigment, 7g of the same antioxidant and 3458g of polypropylene for Examples 3 to 6; Homogenization of the mixture in a cube mixer for 15 minutes; - Extrusion at 1800C in a co-rotating twin-screw extruder Werner ZSK 30; The granules obtained at the outlet of the granulator are injected at 220 ° C. in the form of platelets 2 mm thick in an Arburg press, with a mold temperature of 40 ° C. and a cooling time of 40 seconds.

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The color of the platelets obtained was measured with a Minolta CM 508d spectrocolorimeter (diffuse reflection and gloss included).

The chromatic coordinates L *, a * and b * are given in the CIE 1976 system (L *, a * and b *) as defined by the International Commission on Illumination and listed in the French Code of Standards (AFNOR), color color n X08-12 (1983). The nature of the illuminant is the D65. The observation surface is a circular pellet of 12.5 cm 2 area. The observation conditions correspond to a vision with an aperture angle of 100.

Example 1
A light orange pigment based on cerium sesquisulphide of formula Ce2S3 encapsulated by a layer of silica representing 4.6% by weight of the mass of Ce2S3 was incorporated in polypropylene according to the conditions described above.

Example 2
An orange sesquisulphide pigment of formula Ce2S3 encapsulated by a silica layer representing 4.6% of the mass of Ce2S3 and containing 10% of ZnO expressed relative to the mass of Ce2S3 was incorporated into polypropylene according to conditions previously described.

Example 3
In what follows, a method of grafting a red dye on the surface of the pigment of Example 1 is described.

 102 g of light orange pigment of this example are dispersed with stirring in 2 liters of water. The pH of the suspension obtained is reduced to 9 by adding 1 mol / l aqueous NaOH solution.

 In parallel, a basic solution of aminopropyltrietoxysilane (APS) is prepared by adding 8 g of APS in 20 g of H 2 O and then raising the pH to 12 by addition of an aqueous NaOH solution at 1 mol / l.

 The basic APS solution is then added to the light orange pigment suspension in 28 minutes and the pH adjusted to 9 by addition of an aqueous solution of H2SO4 at 0.5 mol / L. Once the addition is complete the suspension is heated to 87 C.

 8 g of Procion Red MX5B red dye from Aldrich are then added. The suspension is maintained at 87 ° C. for 1 hour following the addition of the dye.

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 The suspension is then filtered under vacuum and washed with water until the washings are clear and then washed with ethanol and with ether.

 The product obtained is left under a hood overnight to allow the evaporation of volatile solvents.

 A powder is obtained whose solids content is 98% and whose color has markedly turned red. The powder obtained is sieved to 500 microns before incorporation into the plastic.

 This powder contains 1% by weight of dye.

Example 4
In what follows, a method of grafting a red dye on the surface of the pigment of Example 2 is described.

 The grafting process is the same as that described in Example 3.

 A powder is obtained whose solids content is 98% and whose color has markedly turned red. The powder obtained is sieved to 500 microns before incorporation into the plastic.

 This powder contains 1% by weight of dye.

Comparative Example 5
A mechanical powder mixture was made from 34.65g of the light orange CesSs pigment described in Example 1 and 0.35g of Procion Red MX5B red dye. The amount of red dye added corresponds to the same amount of dye grafted on the encapsulated Ce2S3 pigment of Example 1.

 The mixture was homogenized before extrusion in a cube mixer for 15 minutes.

Comparative Example 6
A mechanical powder mixture was made from 34.65 g of the light orange pigment described in Example 2 and 0.35 g of Procion Red MX5B red dye. The amount of red dye added corresponds to the amount of dye grafted onto the encapsulated CesS pigment of Example 2.

 The mixture was homogenized before extrusion in a cube mixer for 15 minutes.

 The following table shows the chromatic coordinates measured after injection into the polypropylene at 220 ° C. of the products described in Examples 1 to 6.

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<Tb>
<Tb>

Example <SEP> L * <SEP> a * <SEP> b *
<tb> 1 <SEP> 55.6 <SEP> 44.2 <SEP> 59.2
<tb> 2 <SEP> 57.4 <SEP> 43, <SEP> 4 <SEP> 59
<tb> 3 <SEP> 47.1 <SEP> 45.9 <SEP> 46.8
<tb> 4 <SEP> 44.5 <SEP> 47.1 <SEP> 40.6
<tb> 5 <SEP> 54.6 <SEP> 43, <SEP> 7 <SEP> 57.4
<tb> 6 <SEP> 55, <SEP> 7 <SEP> 42.9 <SEP> 57
<Tb>

Les résultats de colorimétrie obtenus après dispersion dans le polypropylène montrent que : - le greffage d'un colorant organique en surface du pigment Ce2SS a bien été réalisé dans les exemples 3 et 4 puisqu'il en résulte un changement de colorimétrie significatif ; - le greffage du colorant organique en surface du pigment Cesse permet une meilleur dispersion du colorant et donc une meilleur efficacité puisque la colorimétrie des plaquettes obtenues par simple mélange mécanique colorant/pigment est identique à celle des plaquettes obtenues à partir du pigment Ce2S3 seul.

The colorimetric results obtained after dispersion in the polypropylene show that: the grafting of an organic dye on the surface of the Ce2SS pigment has indeed been carried out in Examples 3 and 4 since this results in a significant colorimetric change; the grafting of the organic dye on the surface of the Cesse pigment allows a better dispersion of the dye and therefore a better efficiency since the colorimetry of the platelets obtained by simple mechanical dye / pigment mixing is identical to that of the platelets obtained from the Ce2S3 pigment alone.

Claims (23)

1-Pigmentary composition characterized in that it comprises: a support based on a rare earth sulphide; a coupling agent linked to said support via a chemical function R 'of said agent which is capable of creating a bond between the support and the agent by complexation, by adsorption, of the electrostatic or covalent type; a dye bonded to said coupling agent by a covalent bond. 2. Composition according to claim 1, characterized in that the support based on a rare earth sulphide contains at least one alkaline and / or alkaline-earth element of which at least part is included in the crystal lattice of said sulphide. 3-Composition according to one of claims 1 or 2, characterized in that it comprises a layer based on at least one transparent oxide deposited on the surface of the support and at least partially coating it. 4-Composition according to claim 3, characterized in that the transparent oxide is selected from the group consisting of silica, alumina, zirconia, zircon, titanium oxide and rare earth oxides. 5. Composition according to one of Claims 1 to 4, characterized in that the chemical function R 'is a carboxyl, carboxylate, sulphonate or sulphonic acid, sulphosuccinate, phosphonate, phosphinate, phosphate or silane function.  6-Composition according to one of claims 1 to 5, characterized in that the coupling agent is derived from a compound having a chemical function Rc likely to react to form a covalent bond.  7 - Composition according to one of claims 1 to 6, characterized in that the dye comes from a compound having a chemical function R'c capable of reacting to form a covalent bond. <Desc / Clms Page number 17>  8-Composition according to claim 6 or 7, characterized in that the chemical functions Rc and R'c cited above are amine, aldehyde, alcohol, isocyanate, thiol, silane or halogen functions. 9-Composition according to claim 6, characterized in that the coupling agent comes from a compound which corresponds to formula (1):

 in which R 1 is an alkyl group comprising from 1 to 12 carbon atoms, Z 1 is a group -CO 2 H, carboxylate -CO 2 M 'or -SO 3 M', M 'denoting a metal, in particular an alkaline metal, Z1 may also be a phosphate group or phosphonate, Z2 denotes a halogen or a group - NHR2, or - NR3R2, or - Nt-t4, R2 and R3, which may be identical or different, denoting a hydrogen or an alkyl group comprising from 1 to 8 carbon atoms. 10- Composition according to claim 9, characterized in that the compound of formula (1) is an amino acid. 11-Composition according to claim 10, characterized in that the amino acid is an aliphatic acid, more particularly a C4-C10 acid. 12. Composition according to one of claims 6 to 8, characterized in that the coupling agent is an aminosilan. 13- Composition according to one of the preceding claims, characterized in that the support further contains on the surface a metal element which may be more particularly zinc or aluminum. 14-Composition according to one of the preceding claims, characterized in that the support further contains at the surface fluorine atoms. 15-Composition according to one of claims 12 to 14, characterized in that the amino-silane corresponds to the following formula (2):

 in which the radicals R4, Rs, R6 and R7, which are identical or different, each represent a hydrogen atom or an alkyl or aryl group having from 1 to 8 carbon atoms; and the radical Ra represents an alkylene group having from 1 to 18 carbon atoms. <Desc / Clms Page number 18>  16. Composition according to one of the preceding claims, characterized in that the rare earth sulphide is a sesquisulfide.  17 - Composition according to one of claims 2 to 16, characterized in that the amount of alkali element and / or alkaline earth is at most 50% of the molar amount of rare earth and in that it is in particular between 5 and 50% of this quantity. 18-Composition according to one of the preceding claims, characterized in that the sulfide has a ThgP type crystallographic structure. 19- Composition according to one of claims 2 to 18, characterized in that the alkaline element is lithium, sodium or potassium. 20. Composition according to one of the preceding claims, characterized in that the sulphide is cerium sesquisulphide Ce2S3 y cubic.  21-Process for the preparation of a composition according to one of claims 1 to 20, characterized in that it comprises a first step in which the support is brought into contact with a first compound having a chemical function R's and Rc in a liquid medium capable of solubilizing said first compound, whereby a bond is obtained between the support and the coupling agent from the first aforementioned compound; and a second step in which the product resulting from the preceding step is brought into contact with a second compound having a function R'c in a liquid medium capable of solubilizing said second compound, whereby a bond is obtained between the agent of coupling and the dye from the second aforementioned compound.  22. A process according to claim 21, characterized in that it is carried out in an aqueous medium, preferably in the absence of any organic solvent.  23-Process for coloring plastics, paints, rubbers, ceramics, glazes, papers, inks, cosmetics, dyes and laminates, characterized in that a pigment composition is used according to one of claims 1 to 20.