MXPA01001714A - Use of titanium dioxide as anti-uv agent in a rubber composition - Google Patents

Abstract

The invention concerns the use as anti-UV agent, in an elastomer rubber composition, titanium dioxide particles of not more than 20 mn in size, said particles being coated with a silica, silico-aluminate or alumina layer. The invention also concerns rubber compositions comprising such an anti-UV agent and finished products based on said composition.

Description

USE OF TITANIUM DIOXIDE AS AN ANTI-UV AGENT IN A RUBBER COMPOSITION The present invention describes the use of specific particles of titanium dioxide as an anti-UV agent in rubber compositions. Likewise, reference is made to finished articles derived from these compositions and especially to tire coatings. Rubber compositions that can be used for the manufacture of finished articles generally contain, inter alia, one or more elastomers, a reinforcing filler and a coupling agent (facilitating a coupling between the elastomers and the surface of the reinforcing filler) . It is known that the use of systems for protection against ultraviolet (UV) radiation in rubber compositions in order to limit the aging of these due to light and, consequently, to avoid the degradation of their mechanical properties . However, the performance of known UV absorbers is not always good, especially those, such as phenolic derivatives, used in rubber compositions. "light colored", ie those that do not contain carbon black. One of the objects of the invention is therefore to propose an anti-UV agent for rubber compositions that is effective, does not migrate to the surface, different organic UV absorbers, and in this way can preferably retain their protective activity with time. Another object of the invention is to have an anti-UV agent that can be used in rubber compositions containing a reinforcing filler that is not predominantly carbon black and, in particular, in "light colored" rubber compositions, that is, those that do not contain carbon black: thus, one of the objects of the invention is to propose a colorless UV stabilizer that is transparent and therefore does not tint the "light colored" rubber compositions in which it is going to to incorporate. In order to achieve these objectives, the central point of the present invention is the use as an anti-UV agent, in a rubber composition, of the titanium dioxide particles having an average size of 80 nm, at most , and at least partially coated with at least one layer of at least one metal oxide, hydroxide or oxohydroxide. ^^^^^^^^ fe ^^^ ji ^^^ jg ^^^^^^^^^^ J ^^^^^^^^^^^^^^^^ gjj ^^ j ^^ g ^^ o ^^^^^^^^^^^^^^ j ^^^^^^ giL ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The invention relates to rubber compositions comprising at least one elastomer and an anti-UV (or UV absorbent) agent. Finally, another central factor of the invention relates to finished articles derived from these rubber compositions, especially tire coatings. The invention relates in the first place to the use as an anti-UV agent, in a rubber composition, of titanium dioxide particles having an average size of at most 80 nm, and at least partially coated with at least one layer of at least one metal oxide, hydroxide or oxohydroxide. In general, the composition of this layer is chosen in such a way that it is chemically inherent with respect to the elastomers included in the rubber composition to be protected and can react with the coupling agent that is normally found in this composition. Accordingly, this layer can be a layer of at least one silicone and / or aluminum oxide, hydroxide or oxohydroxide. Consequently, it can be derived from alumina. According to the preferred input, it is derived from silica or an aluminosilicate.

According to another preferred embodiment, it is derived from a layer of silica and aluminum hydroxide or oxohydroxide, in particular with a weight content of SiO2 of approximately 15% and a weight content of Al203 of approximately 5%. In general, the weight ratio between the layer and titanium dioxide is between 5 and 100%; normally it is almost 60%; the mass of the layer is measured with the fluorescence of X-rays in suspended particles. 10 This layer is very thin; It usually has a thickness of between 0.5 and 5 nm, especially between 1 and 3 nm (measured with the electron microscopy), and is generally dense.15 It must be taken into account. that said titanium dioxide particles can at least be partially coated: with a first layer of at least one compound of cerium and / or iron, and with a second layer as already described. or iron are precursors of cerium or iron oxide, that is to say they can be thermally divided into cerium oxide or iron, they can be cerium or iron salts, it is preferred to cerium compounds.

The titanium dioxide particles used in the present invention have an average size of almost 80 nm, preferably between 20 and 70 nm (measured with the electron transmission microscope, TEM). This average size is more specifically between 30 and 60 nm, in particular between 40 and 50 nm. Although the titanium dioxide forming part of said particles may have a predominantly rutile crystal structure, it advantageously has a The structure is predominantly anatase crystal, that is, 50% of the weight of said titanium dioxide is anatase structure. Preferably 80%, or even almost 100%, of the weight of said titanium dioxide is of anatase structure. In general, said particles of titanium dioxide have a specific surface area of BET of at least 40 m2 / g, in particular at least 70 m2 / g, for example at least 100 m2 / g; it can be, at the most, 250 m2 / gr, it is particular almost 200 m2 / gr. The area of surface area of BET by nitrogen absorption according to ASTM D 3663-78, based on the BRUNAUER-EMMET-TELLER method described in "The Journal of the American Chemical Society", Vol. 60, page 309 , February 1938.

The titanium dioxide particles used in the present invention typically have a relative density of between 2.0 and 2.7. Preferably, this relative density is between 2.3 and 2.7 when a layer of at least one cerium and / or iron compound is found and is between 2.0 and 2.4, when said layer is not found. Finally, it is recommended to use it in its powder presentation. The titanium dioxide particles used in the present invention are preferably processed by the precipitation of at least one metal oxide, hydroxide or oxohydroxide on the surface of the titanium dioxide particles with an average size of at least 80 nm, in general with a predominantly anatase crystal structure and usually with a BET specific surface area of at least 200 m2 / g and a relative density of between 2.3 and 2.7. Optionally, at least one compound of cerium and / or iron is precipitated in advance to the surface of these starting titanium dioxide particles. It is possible to carry out said precipitation by: introducing, in a dispersion of titanium dioxide particles with the above characteristics - «- ...". ^, .., ^ ¿^; ..- i¿a¿a ^ fe ... L ^ á, ^ ...,. , jd¡ ^ aaa¡aáÉtt-fefe afc ^ afefe «^. ,, -. ^. A - ^ - - ^ - ... ^. ia.: .. _ ,,,, mentioned, precursors of the compounds of cerium and / or iron and metal oxides, hydroxides or oxohydroxides, usually in the form of aqueous salt solutions, and then modify the pH in order to precipitate these compounds or oxides, hydroxides or oxohydroxides in the dioxide particles of titanium. In general, this precipitation occurs when a temperature of 50 ° C is recorded, at least. The titanium dioxide particles used according to the invention are normally not calcined, that is to say that they do not usually have a coating with cerium and / or iron oxides. The cerium and / or iron compounds are usually cerium or iron salts or hydroxides. In the case of cerium, the compound can be a cerium salt which is chosen from cerium acetate, cerium sulfate or cerium chloride. Also, by containing iron, the compound can be an iron chloruor, an iron sulfate or an iron acetate. 20 Cerium acetate and / or iron chloride are most frequently used. In general, the cerium and / or iron compounds are precipitated at a pH of between 4 and 10.

It is possible to heat the dispersion of particles during this phase. When the silica and an aluminum hydroxide or oxohydroxide are precipitated, precipitation can be carried out at an acidic or basic pH. The pH can be controlled by incorporating an acid such as sulfuric acid or by introducing at the same time or alternatively an alkaline silicone compound and an acid aluminum compound. In this case, the preferred range of pH ranges from 8 to 10. It is possible to precipitate the silica from a silicone salt such as an alkali silicate. It is possible to precipitate aluminum hydroxide or oxohydroxide from an aluminum salt such as alumina sulfate, sodium aluminate, basic ammonium chloride or aluminum diacetate. After precipitation, the particles obtained after treatment can be recovered and washed, one or more times, before they dry or, preferably, redispersed. This phase can be carried out by centrifugation and washing or by ultrafiltration washing. Fortunately, the pH of the rinse water is about 5.5. Then, optionally after one or more rinses of this type, the particles are redispersed preferably, usually in water, and then they are dried, usually at a temperature below 110 ° C; advantageously, this drying phase consists in drying a suspension that preferably contains from 8 to 30% of the weight of said particles by means of an atomizer, for example an APV type atomizer, with an outlet temperature of less than 110 °. , in general. Starting titanium dioxide particles have an average number-size of up to 80 nm, preferably between 20 and 70 nm (measured with the electron transmission microscope, TEM). This average size is more specifically between 30 and 60 nm, especially between 40 and 50 nm. Although the titanium dioxide constituting said starting particles may predominantly have a rutile crystal structure, it advantageously has a structure predominantly of anatase crystal, ie the anatase structure represents 50% of the weight of said titanium dioxide. . Preferably, the anatase structure represents 80%, or even up to 100%, of the weight of said titanium dioxide. The starting particles normally have a BET specific surface area of at least 200 m2 / g, for example 250 m2 / g, at least. «- ij¡g | ^ £ In general, its relative density is in a range between 2.3 and 2.7. This relative density is obtained in particular thanks to the following formula: 1 Relative density = 1 / p + Vi in which: p is the relative density of anatase, ie 3.8; Vi is the volume generated by the pores between the particles and is measured using the BJH method. The expression "the volume measured using the BJH method" shall be understood as the volume measured using the BARRETT-JOYNER-HELENDA method described in the article entitled "Texture des solides poreux ou divises [Texture of the porous or divided solids "] contained in the Techiques work of 1 'Ingénieur, pp 3645-1 to 3645-13 In order to measure the volume given by the pores between the particles according to the invention, when it is dispersed, it is It is essential to follow the measurement protocol which consists in eliminating the liquid phase of the dispersion and then vacuum drying the particles at a temperature of 150 ° C for a minimum period of four hours.

It is possible to obtain said starting particles by hydrolysis of at least one titanium compound A in the presence of at least one compound B chosen from: (i) organic phosphoric acids of the following formula: HO 0 R2 0 OH \ 11 I I / - (O - - P / P_ \ HO Rl OH OH where n and m are integers between 1 and 6, p an integer between 0 and 5, R1, R2, R3, which are identical or different, representing a hydroxyl, amino, aralkyl, aryl or alkyl or hydrogen group; (ii) acids that have: ^^^ s ^^^? ^^^^^ g ^ jj ^^^^^^^^? gjgga ^ g ^^^^^^^ or a carboxyl group and at least two hydroxyl and / or amino groups, or at least two carboxyl groups and a hydroxyl and / or amino group; (iii) compounds capable of releasing sulphate ions in some acid medium; (iv) salts of the aforementioned acids; and in the presence of titanium dioxide, normally anatase, seeds that positively have a size of up to 8 nm and in a weight ratio (Ti02 present in the seeds) / (titanium present before introducing the seeds in the hydrolysis medium, expressed as Ti02) preferably between 0.01 and 3%. It is preferred that the starting solution, which is intended to be hydrolyzed, is aqueous in its entirety; optionally, another solvent may be added, for example an alcohol, just as the titania compound A and the compound B used are then substantially soluble in this mixture. As the titanium compound A, a compound selected from halides, oxyhalides, titanium alkoxides, sulfates, and more in particular, synthetic sulfates is generally used. The expression "synthetic sulfates" is understood as the solutions of sulphate titanyl produced by the exchange ^^^ ^^ g ^^^^^ i ^ Jj S = s --- "To ion solutions using very pure titanium chloride or by reaction of sulfuric acid in a alkoxide of titanium. It is preferred to use titanium compounds of the halide or titanium oxyhalide type. The halides or titanium oxyhalide which were used more specifically in the present invention are fluorides, chlorides, bromides and iodides (oxyflorides, oxychlorides, oxybromides and oxyiodides, respectively) of titanium. According to a particularly preferred contribution, the titanium compound is titanium oxychloride TiOCl. The amount of the titanium compound A present in the solution to be hydrolyzed is not crucial. The initial solution also contains at least one compound B as already mentioned. Below are listed without limitation not limitative compounds B: hydroxypolycarboxylic acids and more specifically hydroxydicarboxylic acids or hydroxytricarboxylic, such as citric acid, maleic acid and tartaric acid; - (polyhydroxy) monocarboxylic acids, such as glucoheptonic acid and gluconic acid; poly (hydroxycarboxylic) acids, such as tartaric acid; ^ ^ ^^^^^^^^^^^^^^^ L »« ^ ígÉa ^ fc, ^^^^? G ^^^^^^ jHl ^^^^ d ^^^^ ll ^^ ^^^ s ^^^^ ^^^^^^^^^^^^^^^^^^ and monocarboxylic and dicarboxylic corresponding amides, such as aspartic acid, asparagine and glutamic acid; hydroxylated or non-hydroxylated monocarboxylic amino acids, for example lysine, serine and threonine; aminotri (methylene phosphonate), ethylene diaminotetra (methylene phosphonate), triethylene tetraaminohexa (methylene phosphonate), tetraethylene pentaaminohepta (methylene phosphonate) or pentaethylene hexaaminoocta (methylene phosphonate); methylenediphosphonate, 1,1 '-ethylenediphosphonate, 1,2-ethylenediphosphonate, 1,1'-propylene diphosphonate, 1,3-propylenediphosphonate, 1,6-hexamethylenediphosphonate, 2,4-dihydroxypentamethylene-2,4-diphosphonate, 2, 5- 15 dihydrosihexamethylene-2, 5-diphosphonate, 2,3-dihydroxybutylene-2,3-diphosphonate, 1-hydroxybenzyl-1, 1'-diphosphonate, 1-aminoethylene-1-diphosphonate, hydroxymethylene diphosphonate, 1-hydroxyethylene-1, 1 ' - diphosphonate, 1-hydroxyprop leno-ll '-difosfonato, 1- 20 hydroxybutylene-1-l-diphosphonate or 1-hidroxihexametileno-1- 1' -difosfonato?. As already indicated, it is also possible to use, as compound B, all the salts of the aforementioned acids. In particular, those salts that are salts of ^^^^^^^^^ g ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^ a ^ BS ^ fa ^. ^^ | ^ CTS ^ g ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^ & alkali metal, more specifically sodium salts, or ammonium salts. These compounds can also be chosen from sulfuric acid and ammonium or potassium sulfates, among others. The compounds B as defined above are generally compounds comprising hydrocarbons of the aliphatic type. In this case, the length of the main chain comprising hydrocarbons preferably does not exceed 15 carbon atoms, for example 10 carbon atoms. The preferred compound B is citric acid. The amount of compound B is not crucial. The molar concentration of compound B in relation to that of titanium compound A is generally between 0.2 and 10% and preferably between 1 and 5%. 15 Finally, the starting solution consists of titanium dioxide seeds used in a specific way. Therefore, the titanium dioxide seeds favorably used have a size smaller than 8 nm, measured by X-ray diffraction. Preferably titanium dioxide seeds with a size between 3 and 5 nm are occupied. Then, the weight ratio between the titanium dioxide present in the seeds and the titanium present in the medium .. ^^^ .. aa - ^ -, ^. ^. "_ > ^ ... AA- ^ .. A., .. ^ fe .. - .. ^^^^ - gf AI ^ - * & - • - - "^ of hydrolysis before the introduction of seeds, is say contributed by the compound A of titanium, and expressed as Ti02 is between 0.01 and 3%, this ratio can be between 0.05 and 1.5% Combining these two conditions relative to the seeds (size and weight ratio), together with the process already described, allow a more precise control of the final size of the titanium dioxide particles, associating the content of a seed with the size of a particle. Typically, titanium dioxide seeds are used in anatase in order to induce the precipitation of titanium dioxide in the anatase form. Also, due to its small size, these seeds have the form of crystallized anatase. Normally, the seeds are in the form of an aqueous suspension composed of titanium dioxide. In general, they can be achieved in the customary manner by a neutralization process of a titanium salt by means of a base. The next phase consists of hydrolyzing this solution by any means known to a person skilled in the art and, generally, by heat. In the latter case, the hydrolysis may preferably be carried out at a temperature greater than 70 ° or equal. Also, it is possible to operate, firstly, below a boiling temperature of the medium and, ^^ ¿¿¿^ ^ j ^^^^^ then keep the level of the hydrolysis medium at a boiling temperature. Once the hydrolysis was carried out, the titanium dioxide particles obtained by separating the precipitated solid derived from mother liquors are recovered before being redispersed in a liquid medium in order to obtain a dispersion of titanium dioxide. . This liquid medium can be acidic or basic. A basic solution is preferred, for example an aqueous solution of sodium hydroxide. Derived from this dispersion, the precipitation phase of metal oxides, hydroxides or oxohydroxides will be carried out, as already mentioned. According to an alternative specific form, after recovering the particles obtained after the hydrolysis and before they are redispersed, the particles are neutralized and subjected to at least a single washing operation. It is possible to recover the particles, for example by centrifuging the solution resulting from the hydrolysis; subsequently they are neutralized with a base, for example a solution of sodium or aqueous ammonium hydroxide, subsequently washed by re-dispersing them in an aqueous solution and, finally, the particles are separated from the aqueous washing phase. After one or more, as preferred, washing operations of the same type, the ^ i > ^^ ^ particles are redispersed in a liquid or basic solution before the precipitation phase of metal oxides, hydroxides or oxohydroxides. In general, the mass of the titanium dioxide particles used in the invention is between 0.5 and 8%, preferably between 1 and 5%, of the total mass of the rubber composition. Rubber compositions in which said titanium dioxide particles are used as anti-UV agents typically have as base one or more elastomers. More specifically, elastomers with a glass transition temperature between -150 ° and + 20 ° C can be among the recommended elastomers. As possible elastomers, one can speak of diene elastomers. For example, mention may be made of natural rubber, polymers or copolymers derived from aliphatic or aromatic monomers, containing at least one unsaturated group (such as, in particular, ethylene, propylene, butadiene, isoprene and styrene), polybutyl acrylate or combinations of any of them. Similarly, silicone elastomers and halogenated elastomers can be mentioned.

The rubber compositions are sulfides prone to vulcanization. Also, the invention discloses rubber compositions further containing at least one reinforcing filler (for example carbon black, alumina and / or precipitated silica) and, alternatively, at least one coupling agent and / or a coating agent. It is preferred that the rubber composition contain precipitated silica and a favorably high dispersion as reinforcing filler. In general, this reinforcing filler is formed, especially considering the weight, of precipitated silica, preferably precipitated silica and with a high dispersion, as described in the applications EP 0520862, WO 95/09127 15 and WO 95/09128. The invention offers even greater advantages when the rubber composition is a "light colored" composition, ie it does not contain carbon black. The rubber composition may also contain, inter alia, an organic antioxidant. Also, the invention also encompasses finished articles derived from the rubber compositions described above. As finished items, it is possible that ^^^^^^^^^^ £ ^^ ^ ^^^ g ^^ * j ^^ g ^^^^^^^^^^^^^^^^^^^^^^^ ^^^^? ^^^^^ Bfe ^ j «| ^^^^^^^^^^^ g ^^^^^^^^^^^^^^^^^^ reference to tire coatings, shoe soles, etc. The following examples serve to illustrate the invention, without limiting its scope to them.

EXAMPLE 1 The preparation of titanium dioxide particles with an average size of 60 nm, by means of a surface treatment. 10 1-H? Drolysis The following was added in place of 394.7 g of a 1.9 mol / Kg titanium oxychloride solution: 42.02 g of 36% hydrochloric acid; 15 - 4.73 g of citric acid; 574.1 gr of purified water; 5.68 gr (0.1% / TiO2) of a suspension containing 1.06% by weight of anatase seeds with a size between 5 and 6 nm. The mixture was heated to its boiling point and held at that point for 3 hours. 2 - . 2 - . 2 -Recovery of the particles and redispersion ^^^^^^^? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^ B ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The obtained particles were washed with water until the chlorides were completely removed. The particles were redispersed with a pH of 9 (controlled by the incorporation of sodium hydroxide). The dispersion obtained had a solids content of 20% by weight. This dispersion was stable. 60 nm was the average particle size measured by TEM. X-ray analysis shows that the particles were based on titanium dioxide only in the anatase form. 300 m2 / gr measured its BET specific surface area. 2.52 (Vi = 0.14 cm3 / gr) was its relative density. 3 - . 3 - Surface treatment of the particles 15 750 gr of starting dispersion was introduced into a reactor fitted with a stirrer. Then 750 g of purified water was added and the temperature reached 90 ° C. The pH of the dispersion was adjusted to 9 by adding sodium hydroxide. First, a solution of sodium silicate (solution containing 335 gr / 1 of Si02) containing the equivalent of 22.5 gr. of Si02 and a sulfuric acid solution of 80 gr / 1 were added constantly and at the same time in the proper amount to maintain the pH at 9. The rate of introduction of the silicate solution of S ^^^ fc ^^^^^^^^^^^ S ^ y ^ w ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^ ggJ ^^^^ sodium was established at 2 ml / min. Then, the ripening time of one hour at 90 ° C was respected. Then, an aqueous solution of sodium aluminate (solution of Al203 of 240 gr / 1) that contains the equivalent of 7.5 g of Al203 was added consistently with a pH of 9 and at 90 ° C. The rate of introduction of the aluminate solution was 2 ml / min. , the pH being controlled at 9 while incorporating an aqueous solution of 6 N sulfuric acid at the same time. When the reagents were added, the dispersion was matured for a period of two hours at 90 ° C and then cooled. The dispersion so prepared was centrifuged. The mass obtained with water was washed three times and then redispersed in water. The pH of the obtained dispersion was about 7.7 and the dispersion has a solids content of 10% by weight. Then, the dispersion was dried using an APV type atomizer, in a turbine configuration, with the inlet temperature of 250 ° C, the outlet temperature of 90 ° C and the feed rate of almost 20 kgr / h. 4 - Characteristics of the particles obtained 60 nm was the average size of the particles measured by TEM. 135 m2 / gr was its specific surface area of BET. * < ta > ", - * tB- ^ -.- z ^ A ^ a ± JlSß? u! ^ - t¿. ^ .c- -. aMM *» The content of Si02, measured by fluorescence, weighted 14.9% and the of Al203, 5% with respect to titanium dioxide 2.15 was the relative density of the prepared particles.

EXAMPLE 2 The preparation of the titanium dioxide particles with an average size of 45 nm with surface treatment. 1-Hydrolysis The following was added in place of 394.7 g of a titanium oxychloride solution of 1.9 mol / kg: 42.02 g of 36% hydrochloric acid; - 4.73 g of citric acid; 574.1 gr of purified water; 11.36 gr (0.2% / TiO2) of a suspension containing 1.06% by weight of anatase seeds with a size between 5 and 6 nm. The mixture was heated to its boiling point and held at that point for 3 hours. 2 -Recovery of the particles and redispersion Then, the solution was filtered and the particles obtained were washed with water until the chlorides were completely eliminated. The particles were redispersed with a pH of 9 (controlled by the incorporation of sodium hydroxide). The dispersion obtained had a solids content of 20% by weight. This dispersion was stable. 60 nm was the average particle size measured by TEM. X-ray analysis shows that the particles were based on titanium dioxide only in the anatase form. 300 m2 / gr measured its BET specific surface area. 2.52 (Vi = 0.14 cm3 / gr) was its relative density. 3 - . 3 - Surface treatment of the particles 15 750 gr of starting dispersion was introduced into a reactor fitted with a stirrer. Then 750 g of purified water was added and the temperature reached 90 ° C. The pH of the dispersion was adjusted to 9 by adding sodium hydroxide. First, a solution of sodium silicate (solution containing 335 gr / 1 of Si02) containing the equivalent of 22.5 gr. of Si02 and a sulfuric acid solution of 80 gr / 1 were added constantly and at the same time in the proper amount to maintain the pH at 9. The rate of introduction of the silicate solution of ^^^^^^^ a ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ J ^^^^ j ^^ ^^^^^^^^^^^^^^ j ^^^^^^^^^ j ^^ sodium was established at 2 ml / min. Then, the ripening time of one hour at 90 ° C was respected. Then, an aqueous solution of sodium aluminate (solution of Al203 of 240 gr / 1) that contains the equivalent of 7.5 g of Al203 was added consistently with a pH of 9 and at 90 ° C. The rate of introduction of the aluminate solution was 2 ml / min. , the pH being controlled at 9 while incorporating an aqueous solution of 6 N sulfuric acid at the same time. When the reagents were added, the dispersion was matured for a period of two hours at 90 ° C and then cooled. The dispersion so prepared was centrifuged. The mass obtained with water was washed three times and then redispersed in water. The pH of the dispersion obtained was about 7.7 and the dispersion has a solids content of 10% by weight. Then, the dispersion was dried using an APV type atomizer, in a turbine configuration, with the inlet temperature of 250 ° C, the outlet temperature of 90 ° C and the feed rate of almost 20 kgr / h. 0 4 - Characteristics of the particles obtained 45 nm was the average size of the particles measured by TEM. 150 m2 / gr was its specific surface area of BET. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^ ji ^^^^^^^ The content of Si02, measured by fluorescence weighed 14.9% and that of Al203, 5% compared to titanium dioxide. 2.15 was the relative density of the prepared particles.

EXAMPLE 3 The following formulations were made for industrial rubber (Table 1: compositions in parts by weight) containing or not titanium dioxide particles obtained in Example 1.

Table 1 (1) Styrene-butadiene copolymer of Buna type VSL 5525-0; (2) Filler formed by a precipitated silica of Example 12 of EP-A-0520862; (3) Filling coupling agent / industrial rubber (sold by Dégussa); (4) Anti-UV agent obtained from Example 1 above; (5) Phenolic antioxidant agent that does not stain, called Wingstay L.

The compounds were obtained using a Brabender laboratory extruder and then placed at a pressure of 100 ° C for 50 minutes in the form of a 2 mm thick plate. The formulations were aged for 89 hours with a UV agent (using a UV device WITH ATLAS), only one face being exposed. The chamber was at a temperature of 57 ° C. The determination of the tension behavior of the formulations not exposed and exposed to the UV agent was carried out at a tensile rate of 8 mm / min. Table 2 below gives the values of the tensile force (sb) and the deformation under load (elongation) at a point of rupture (et,), together with the stress values at a strain under load of 10% 20 (s) %), the change in the values of tension to a deformation under load of 10% that shows the hardening of the surface of the material. ttg ^^^^^^ g * ^^^^^^^^^^^^^^ g ^^^^^^^^^^^ J ^^^^^^^^^^^ fij ^^^^^^^^ B ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The values that appear below the headings with the suffix (UV) are those of the formulations exposed to the UV agent for 89 hours at 57 ° C. The values that appear below the headings with the suffix (0) are those of the formulations not exposed to the UV agent (or controls), however these formulations were also stored for 89 hours at 57 ° C, but in the dark. Table 2 eb expressed in% s and O \ LO% expressed in Mpa thickness of the test piece (specimen) = 1.6 mm.

The efficacy as an anti-UV agent of the titanium dioxide particles obtained in Example 1 was determined.

EXAMPLE 4 The following formulations were made for industrial rubber (Table 3: compositions in parts by weight) containing or not titanium dioxide particles obtained in Example 1 (TiO2 (60 mn)) or in Example 2 (Ti02 ( 45 mn)). Table 3 (1) Styrene-butadiene copolymer of Buna type VSL 5525-0; (2) Filler formed by a precipitated silica of Example 12 of EP-A-0520862; (3) Filling coupling agent / synthetic rubber (sold by Dégussa); (4) Anti-UV agent obtained in Example 1 above; (5) Anti-UV agent obtained in Example 2 above; (6) Phenolic antioxidant agent that does not stain, called Wingstay L.

The compounds were obtained using a Brabender laboratory extruder and then placed at a pressure of 150 ° C for 50 minutes in the form of a 2 mm thick plate. The formulations were aged for 89 hours with a UV agent (using a UV device WITH ATLAS), only one face being exposed. The chamber was at a temperature of 57 ° C. The determination of the tension behavior of the formulations not exposed and exposed to the UV agent was carried out at a tensile rate of 8 mm / min. Table 4 below gives the values of the tensioning force (sb) and the deformation under load (elongation) at a breaking point (eb), together with the stress values at a deformation under load of 10% 20 (s? or%), the change in the values of tension to a deformation under load of 10% that shows the hardening of the surface of the material.

The values that appear below the headings with the suffix (UV) are those of the formulations exposed to the UV agent for 89 hours at 57 ° C. The values that appear below the headings with the suffix (0) are those of the formulations not exposed to the UV agent (or controls), however these formulations were also stored for 89 hours at 57 ° C, but in the dark. Table 4 eb expressed in% s and s10% expressed in MPa thickness of the test piece (specimen) = 1.2 mm.

It can be seen that the yield obtained for the two products of different average sizes is very similar and that the increase in concentration does not cause significantly better results. However, it must be taken into account that the transparency of the formulations with titanium dioxide with an average size of 45 nm is slightly higher than that of the formulations with titanium dioxide with an average size of 60 nm.

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Claims (24)

1. CLAIMS 1. The use as an anti-UV agent, in a rubber composition, of titanium dioxide particles having an average size of at most 80 nm, and at least partially coated with at least one layer of titanium dioxide. , at least, an oxide of metals, hydroxide or oxohydroxide.
2. 2. The use according to claim 1, with the feature that said layer is a layer of at least one silicone and / or aluminum oxide, hydroxide or oxohydroxide.
3. 3. The use according to claim 2, with the feature that said layer is formed from silica, aluminosilicate or alumina.
4. 4. The use according to one of claims 1 to 3, with the feature that said titanium dioxide particles have an average size between 20 and 70 nm, in particular between 30 and 60 nm.
5. 5. The use according to one of claims 1 to 4, with the feature that the titanium dioxide has a structure predominantly of anatase crystal.
6. The use according to one of claims 1 to 5, with the characteristic that said titanium dioxide particles have a specific surface area -B ^ BET of at least 40 m2 / gr, in particular at least 70 m2 / gr.
7. The use according to one of claims 1 to 6, with the characteristic that said particles are used in powder form.
8. The use according to one of claims 1 to 7, with the feature that said rubber composition has at least one elastomer as base, said elastomer preferably having a glass transition temperature of between -150 ° C and + 20 ° C.
9. The use according to one of claims 1 to 8, with the feature that said rubber composition further contains at least one reinforcing filler and, optionally, at least one coupling agent and / or one agent of coating.
10. The use according to one of claims 1 to 9, with the feature that said rubber composition does not contain carbon black.
11. The use according to one of claims 1 to 10, with the feature that said rubber composition includes at least one organic antioxidant.
12. The use according to one of claims 1 to 11, with the characteristic that the mass of the titanium dioxide particles used represents between 0.5 and 8%, preferably between 1 and 5%, of the mass total of said rubber composition.
13. 13. A rubber composition based on at least one elastomer, containing at least one anti-UV agent, with the characteristic that said UV stabilizer is formed by particles of titanium dioxide with an average size of up to 80 nm and partially coated with at least one layer of at least one metal oxide, hydroxide or oxohydroxide.
14. The composition according to claim 13, with the feature that said layer is a layer of at least one silicone and / or aluminum oxide, hydroxide or oxohydroxide.
15. 15. The composition according to claim 14, with the feature that said layer is formed from silica, aluminosilicate or alumina.
16. 16. The composition according to one of claims 13 to 15, with the feature that said titanium dioxide particles have an average size between 20 and 70 nm, in particular between 30 and 60 nm.
17. 17. The composition according to one of claims 13 to 16, with the feature that the titanium dioxide has a structure predominantly of anatase crystal.
18. The composition according to one of claims 13 to 17, with the feature that said titanium dioxide particles have a BET specific surface area of at least 40 m2 / g, in particular at least 70 m2 / gr.
19. 19. The composition according to one of claims 13 to 18, with the feature that said composition is based on at least one elastomer with a glass transition temperature between -150 ° and + 20 ° C.
20. 20. The composition according to one of claims 13 to 19, with the feature that said composition contains at least one reinforcing filler and, optionally, at least one coupling agent and / or a coating agent.
21. 21. The composition according to one of claims 13 to 20, with the feature that said rubber composition does not contain carbon black.
22. 22. The composition according to one of claims 13 to 21, with the feature that said rubber composition includes at least one organic antioxidant.
23. 23. The composition according to one of claims 13 to 22, with the feature that said composition has a weight content of titanium dioxide particles of between 0.5 and 8%, preferably between 1 and 5%.
24. 24. A finished article based on at least one composition as described in one of claims 13 and 23.