EP1831297A2

EP1831297A2 - Use of specific silicas for increasing the rigidity of a thermoplastic while maintaining or improving its impact resistance

Info

Publication number: EP1831297A2
Application number: EP05850622A
Authority: EP
Inventors: Yves Bomal; Antoine Guiu
Original assignee: Rhodia Chimie SAS
Current assignee: Rhodia Chimie SAS
Priority date: 2004-12-30
Filing date: 2005-12-27
Publication date: 2007-09-12
Also published as: FR2880351B1; US8334334B2; US20090326139A1; WO2006072704A2; FR2880351A1; WO2006072704A3

Abstract

The invention relates to the use of a silica having a BET specific surface of at least 60 m2/g for increasing the rigidity of a thermoplastic polymeric material while maintaining i.e. improving its impact resistance. The silica used is of the type obtained according to a method involving the drying of a silica suspension obtained by reacting a silicate with an acidulant according to the following successive steps: (i) forming an aqueous starter having a pH between 2 and 5; (ii) simultaneously adding silicate and the acidulant while keeping the pH between 2 and 5; (iii) continuing with only the addition of silicate until a pH between 7 and 10 has been reached; (iv) simultaneously adding silicate and acidulant while keeping the pH of the reaction medium between 7 and 10, and; (v) continuing with only the addition of the acidulant until a pH value lower than 6 has been obtained. The invention also relates to the materials obtained within this scope.

Description

Use of specific silicas to increase the stiffness of a thermoplastic by maintaining or improving its impact resistance

The present invention relates to the reinforcement of thermoplastic polymer materials, and more specifically relates to the stiffening of thermoplastic polymer materials, and in particular that of materials based on polyolefins, such as polypropylene.

The rigidity of a thermoplastic polymer composition can in particular be measured by its flexural modulus, which reflects the pressure that it is necessary to apply to the material to deform it. By "flexural modulus" is meant more specifically, in the sense of the present description, the Young's modulus of the bending material. For a given thermoplastic polymer material, this flexural modulus may in particular be measured according to the method of ISO 178, which consists in providing a test piece made of the material to be tested, in supporting it on two supports spaced apart by a given distance, and applying a constant rate of deformation to the center of the test piece, continuously measuring the load applied to the test piece, in order to deduce the stress as a function of the displacement.

It is often desirable to improve the stiffness of the polymeric materials used for the constitution of materials, particularly when it is desired to obtain thin pieces having good mechanical properties. Rigidification of this type is in particular often necessary for polyolefin-based materials such as polypropylene, which generally have a relatively low flexural modulus in the raw state.

In general, it is known that in order to stiffen thermoplastic polymer materials, inorganic, natural or synthetic fillers can be incorporated therein. However, if the addition of such mineral fillers certainly has a positive impact on the rigidity, it usually induces, in return, a decrease in the impact resistance of the material. In the sense that it is used in the present description, the term

"impact resistance" (or "impact resistance") of a polymeric material means the more or less high ability of this polymeric material to resist rupture under the effect of impact, especially under the effect of a high-speed impact. The impact resistance of a polymer can in particular be measured by the so-called "impact test" method. This type of test generally involves notching a test piece consisting of the material to be tested (U-notch or, most often, V-shaped notch), then breaking the notched test piece under the impact of a weight (pendulum or hammer). , and to measure the energy absorbed by the fracture of the specimen, which reflects the breaking strength energy (or "resilience") of the material. The higher the energy absorbed, the more the material is shock resistant. In this context, the impact resistance of a polymer material may in particular be determined by the so-called "Charpy impact test" method, for example according to the specific method of the ISO 179 standard.

In the most general case, the reduction in the impact resistance which is observed when mineral fillers are introduced into a thermoplastic polymer material results, concretely, in a weakening of the material, while at the same time increasing the rigidity.

To avoid such embrittlement, a first solution that has been proposed is to modify the polymer, for example by adding an elastomeric resin, as proposed in US Pat. No. 4,209,504, or else other specific polymers, such as those envisaged, for example in US Patent 5,525,703 or US 5,041,491.

Another solution provided for this purpose is to treat the inorganic filler used by organic compounds such as fatty acids. In this context, it is particularly known from Polymer, vol. 44, pp. 261-275 (2003), to use calcium carbonates treated with stearic acid. In more general terms, reference can also be made to application WO 00/49081.

An object of the present invention is to provide mineral fillers that improve the rigidity of the material, but without adverse effect on its impact resistance. In this context, the invention aims in particular to provide mineral fillers capable of ensuring such an effect, without having to modify the composition of the polymer by adding specific polymeric fillers of the type. above, or to use mineral fillers treated with fatty acid compounds.

For this purpose, the subject of the present invention is the use of particular silicas, especially having a BET specific surface area of at least 60 m ² / g, as mineral filler in a thermoplastic polymer material to increase the rigidity of said material, while maintaining or improving its impact resistance.

More specifically, the inventors have now demonstrated that the specific silicas of the type described in application WO 03/016215 provide such an effect in thermoplastic polymer materials, when they have a BET specific surface area of at least 60 m ² / g. For the purposes of the present description, the term "BET surface area" refers to the specific surface area of the silica as determined according to the method of BRUNAUER-EMMET-TELLER described in The Journal of the American Chemical Society, Volume 60, page 309, February 1938, and corresponding to the international standard ISO 5794/1 (Annex D).

Thus, against all expectations, the inventors have now discovered that, when dispersed silicas of the type of those described in WO 03/016215 and having a BET surface area of at least 60 m ^z / g in a polymeric material thermoplastic, there is an increase in the stiffness of the material, which is not accompanied by a joint decrease in the impact resistance of the material. This result is quite surprising insofar as it is known that the incorporation of a mineral filler in a polymer material tends, as a rule, to reduce the impact resistance, in particular when the mineral filler is not pretreated with a fatty acid type agent.

Even more unexpectedly, it turns out that by using silicas of the type described in application WO 03/016215 and having a BET specific surface area of at least 60 m ² / g, it is even possible to observe, in in some cases, an increase in the impact resistance of the material, for example when the silica is finely dispersed in the material. In other words, we in this case, increases both the impact resistance and the rigidity of the material. The possibility of such a joint improvement of these two parameters by the implementation of a single charge in the polymer is quite surprising. Indeed, most often, when introducing a charge into a polymer material, there is a selective improvement in either the impact resistance or the stiffness of the material, and the improvement of one of these properties is in general to the detriment of the other, which usually requires the use of a mixture of different types of charges when it is desired to obtain both an increase in the properties of rigidity and impact resistance.

In addition, the work of the inventors has shown that in addition to the aforementioned advantages, the incorporation of a silica of the type described in application WO 03/016215 and having a specific surface area of at least 60 m ² / g in a thermoplastic polymer material leads, in most cases, to an unexpected improvement in other mechanical characteristics of the material. In particular, the incorporation of such silicas increases, as a rule, the tensile elongation characteristics of the material (in particular the elongation at break in tension of the material, as measured for example according to the ISO 527 standard). may be advantageous especially when the material is intended to be subjected to strong bending, for example when it is used in injected parts of complex shapes, or when it is intended to act as a hinge between two parts .

Furthermore, it turns out that the incorporation of a silica of the type described in WO 03/016215 in a thermoplastic polymer material usually induces an increase in the scratch resistance of the material.

The silicas which are used in the context of the present invention are preferably silicas as described in application WO 03/016215, and which specifically have a BET specific surface area of at least 60 m ² / g. Alternatively, they may be analogous silicas having similar properties and having a BET specific surface area of at least 60 m ² / g. More specifically, the silicas that can be used according to the invention will be described in detail in the description that follows. According to a first particularly advantageous embodiment, the silica used according to the invention is a silica, called "silica S" below, which has a BET specific surface area of at least 60 m ² / g and which is obtained (or more generally that is obtainable) according to a process (referred to as "method P" in the following description) which comprises the reaction of a silicate with an acidifying agent whereby a suspension of silica is obtained , then separating and drying this suspension, and wherein the reaction of the silicate with the acidifying agent is carried out according to the following successive steps:

(i) forming an aqueous starch having a pH of from 2 to 5, preferably at a pH of at least 2.5;

(ii) at the same time, said silicate and acidifying agent are added to said base stock, such that the pH of the reaction medium is maintained between 2 and 5,

(iii) stopping the addition of the acidifying agent while continuing the addition of silicate in the reaction medium, until a pH value of the reaction medium of between 7 and 10 is obtained,

(iv) silicate and acidifying agent are added simultaneously to the reaction medium, in such a way that the pH of the reaction medium is maintained between 7 and 10, (v) the addition of the silicate is stopped while continuing to addition of the acidifying agent in the reaction medium until a pH value of the reaction medium of less than 6 is obtained.

Preferably, the silica S used according to this first embodiment is a silica directly obtained according to process P as defined above. In view of its particular steps, in particular the first simultaneous addition of acidifying agent and silicate in acid medium of step (ii) and the second simultaneous addition of acidifying agent and silicate in basic medium of the step ( iii), the process P gives the silica obtained particular characteristics and properties. Alternatively, the silica S may be a silica prepared according to another process but having characteristics similar to those of silicas obtained in the process P. Generally, the silica S is rather a precipitated silica silica.

In the aforementioned process P, any common form of silicate, for example a metasilicate and / or a disilicate, may be used as the silicate. Advantageously, the silicate employed is an alkali metal silicate, such as sodium silicate or potassium silicate. Preferably, it is a sodium silicate, which advantageously has a weight ratio SiO ₂ / Na ₂ O of between 2.5 and 4, for example between 3.2 and 3.8 (typically between 3.4 and 3.7, for example between 3.5 and 3.6) Whatever its nature, the silicate is typically used in the form of a solution, generally aqueous, having a concentration (expressed in SiU2) included between 40 and 330 g / l, typically between 60 and 300 g / l, in particular between 60 and 260 g / l (for example of the order of 200 to 250 g / l, in particular of the order of 230 g / l). 1, especially when using sodium silicate).

Moreover, the acidifying agent used in process P is generally a strong mineral acid such as sulfuric acid, hydrochloric acid or nitric acid, or, alternatively, an organic acid such as acetic acid, formic acid or carbonic acid, for example. Whatever its nature, the acidifying agent can be used in the diluted or concentrated state. It may for example be used in the form of a solution, generally aqueous, of normality for example between 0.4 and 36 N, in particular between 0.6 and 1.5 N.

According to an advantageous embodiment, the acidifying agent used in process P is sulfuric acid. In this case, it is preferably used in the form of a solution, generally aqueous, having a concentration of between 40 and 180 g / l, for example between 60 and 130 g / l (typically of the order of 80 g / l).

Preferably, in process P, sulfuric acid is used as acidifying agent, and sodium silicate as silicate. In process P, whatever the nature of the acidifying agent and the silicate, the reaction between these compounds is in a very specific manner according to the following steps.

Firstly, in step (i), an aqueous base stock having a pH of between 2 and 5 is formed. Preferably, this base of the tank has a pH of between 2.5 and 5, in particular between 3 and 5. and 4.5. This pH is for example between 3.5 and 4.5, and it is typically of the order of 4.

The initial stock of step (i) can be obtained by adding an acidifying agent to water so as to obtain a pH value of the bottom of the tank between 2 and 5, preferably between 2.5 and 5, especially between 3 and 4.5 and for example between 3.5 and 4.5.

According to another embodiment, the initial stock of step (i) can be obtained by adding the acidifying agent to a water / silicate mixture so as to obtain this pH value. This base of the tank may also be prepared by adding an acidifying agent to a base stock containing silica particles previously formed at a pH of less than 7, so as to obtain a pH value between 2 and 5, preferably between 2 and 5. , 5 and 5, especially between 3 and 4.5 and for example between 3.5 and 4.5 (typically, this pH is of the order of 4).

Furthermore, the stock formed in step (i) may optionally comprise an electrolyte. Nevertheless, preferably, no electrolyte is added to the stock in step (i). More generally, it is preferable to add no electrolyte to the medium during process P.

For the purposes of the present description, the term "electrolyte" is understood in its usual acceptation, that is to say as designating any ionic or molecular substance which, when in solution, decomposes or dissociates to form ions or charged particles. As an example of an electrolyte that may be present in the stockstock, mention may be made especially of a salt of the group of alkali and alkaline earth metal salts, in particular the salt of the metal of the silicate used and of the acidifying agent, for example the sulphate. in the case of the reaction of a sodium silicate with sulfuric acid, or sodium chloride in the case of the reaction of a sodium silicate with hydrochloric acid.

In step (ii) of process P, the acidifying agent and the silicate are added simultaneously (ie jointly and generally progressively). This simultaneous addition is carried out in such a way that the pH of the reaction medium is maintained between 2 and 5, preferably between 2.5 and 5, in particular between 3 and 4.5, for example between 3.5 and 4.5, at during the addition. This maintenance of the pH in the ranges indicated can in particular be ensured by controlling the respective introduction rates of acidifying agent and silicate. Typically, for this purpose, the silicate is introduced at a constant rate (generally between 150 and 250 l / h, for example of the order of 180 to 200 l / h), and the acidifying agent is introduced together with a variable flow, which is controlled to maintain the pH at the desired value.

The simultaneous addition of step (ii) is advantageously carried out in such a way that the pH value of the reaction medium is constantly equal (within ± 0.2 units, and preferably to within ± 0.1 pH value between 3 and 4.5, in general the pH value reached at the end of step (i) (typically, the pH is maintained at a value of 4 to ± 0.2 unit, and preferably within ± 0.1 unit). In the subsequent step (iii), the addition of acidifying agent is stopped, while the addition of silicate is continued in the reaction medium. It follows therefore an increase in the pH of the medium, which is used to achieve a pH value of the reaction medium of between 7 and 10, preferably between 7.5 and 9.5, for example between 7.5 and 8.5. Typically, the pH reached at the end of step (iii) is of the order of 8.

Between step (iii) and the subsequent step (iv), that is to say just after stopping the addition of silicate and before the second simultaneous addition, the reaction medium may optionally be cured. . If necessary, this ripening is advantageously carried out by allowing the medium to evolve to the pH obtained at the end of stage (iii), generally with stirring. Such ripening is typically conducted for a duration of the order of 2 to 45 minutes, for example between 5 and 25 minutes. Preferably, this maturing does not involve addition of acidifying agent, no addition of silicate. More generally, no compound is usually added to the medium during such ripening.

According to a particular embodiment, acidifying agent may be added to the reaction medium between step (iii) and step (iv), for example between the aforementioned ripening (when it takes place) and the step (iv), or immediately after stopping the silicate addition of step (iii). In this case, however, the pH of the reaction medium at the end of this addition of acidifying agent remains between 7 and 9.5, preferably between 7.5 and 9.5.

After step (iii) and the possible ripening and / or addition of acidifying agent mentioned above, step (iv) is followed by a new simultaneous addition of acidifying agent and silicate, so that the pH of the reaction medium is maintained between 7 and 10, preferably between 7.5 and 9.5, for example between 7.5 and 8.5. Again, the maintenance of the pH in the ranges indicated is generally ensured by controlling the respective introduction rates of acidifying agent and silicate, typically, by introducing the silicate at a constant flow rate (generally between 150 and 250 l / l). h, for example of the order of 180 to 200 l / h), and by jointly introducing the acidifying agent with a variable flow, controlled to maintain the pH to the desired value.

The simultaneous addition of step (iii) is advantageously carried out in such a way that the pH value of the reaction medium is constantly equal (at

± 0.2 unit, and preferably to within ± 0.1 unit) at a pH value between 7 and 10, preferably between 7.5 and 9.5, for example between 7.5 and 8.5 , in general at the pH value reached at the end of the preceding step (typically, in step (iv), the pH is maintained at a value of 8 to ± 0.2 units, and preferably at ± 0,1 unit).

Finally, in step (v), the addition of the silicate is stopped while continuing the addition of acidifying agent in the reaction medium so as to obtain a pH value of the reaction medium of less than 6, preferably between 3 and 5.5, in particular between 5 and 5.5, for example of the order of 5.2.

After this step (v), namely just after stopping the addition of acidifying agent, it may be advantageous to carry out a maturing of the medium reaction. In this case, the ripening is advantageously carried out by allowing the medium to evolve to the pH obtained at the end of stage (v), generally with stirring. This ripening is typically conducted for 2 to 45 minutes, for example between 5 and 25 minutes. Preferably, it comprises neither addition of acidifying agent nor addition of silicate. More generally, no compound is usually added to the medium during such ripening.

The reaction chamber in which the entire reaction of the silicate with the acidifying agent is carried out is usually provided with appropriate stirring equipment and heating equipment. The entire reaction of the silicate with the acidifying agent is generally carried out between 70 and 95 ° C., in particular between 75 and 90 ^° C.

According to one variant of the invention, the entire reaction of the silicate with the acidifying agent is carried out at a constant temperature, usually between 70 and 95 ^° C., in particular between 75 and 90 ^° C., typically between 80 and 90 ^° C. 90 ⁰ C.

According to another variant, the end-of-reaction temperature is higher than the reaction start temperature. According to this variant, the temperature is preferably maintained between 70 and 85 ^° C. at the beginning of the reaction (for example during steps (i) to (iii) and any subsequent maturing), then the temperature is increased, preferably to a value between 85 and 95 ^° C., the value at which it is maintained until the end of the reaction (for example during steps (iv) and (v) and any subsequent maturing ).

In the process P, at the end of the steps which have just been described, a suspension of silica is obtained. This silica suspension is then subjected to separation, generally of the liquid / solid type. This separation usually comprises a filtration, which is optionally followed by washing, if necessary, for example with water, which makes it possible in particular to remove unreacted silicates, the acidifying agent, and / or or at least a portion of the salts formed. The above-mentioned filtration is carried out according to any suitable method, for example by means of a filter press, a belt filter, or a vacuum filter. At the end of this separation, a silica slurry is recovered, namely an aqueous medium enriched in silica and depleted of water (filter cake, in the case where the separation is a filtration).

The concentrated silica slurry thus obtained is then dried. Preferably, this drying is done by atomization. For this purpose, any suitable type of atomizer may be used, such as a turbine, nozzle, liquid pressure or two-fluid atomizer. In general, when the filtration is carried out using a filter press, a nozzle atomizer is used, and when the filtration is carried out using a vacuum filter, a turbine atomizer is used.

It should be noted that the concentrated silica slurry filter cake type is not always under conditions allowing its atomization, especially given its generally high viscosity. In a manner known per se, the cake is then subjected to a disintegration operation prior to spray drying. This disintegration operation can be performed mechanically, by passing the cake in a colloid mill or ball. The disintegration is generally carried out in the presence of an aluminum compound, in particular sodium aluminate and, optionally, in the presence of an acidifying agent as described previously (in the latter case, the aluminum compound and the acidifying agent are generally added simultaneously). The disintegration operation makes it possible in particular to lower the viscosity of the suspension to be dried later.

When the drying is carried out using a nozzle atomizer, the silica obtained after drying is usually in the form of substantially spherical beads. After drying, a grinding step can optionally be carried out on the recovered product to obtain the silica in the form of a powder.

When the drying is carried out using a turbine atomizer, the silica obtained is most often in the form of a powder. The silica obtained in powder form, as obtained for example after nozzle spray and grinding, or as obtained after drying by turbine atomizer, may optionally be subjected to a subsequent agglomeration step, for example by direct compression, wet granulation (that is to say with use of a binder such as water, silica suspension, etc.) extrusion or, preferably, dry compaction. When the latter technique is used, it may be advisable, before compacting, to deaerate (operation also called pre-densification, or degassing) the powdery products so as to eliminate the air included in those and ensure more regular compaction. The silica obtained by this agglomeration step is generally in the form of granules. Thus, the silica S likely to be obtained according to the method P may be in the form of powder, beads or compacted granules.

Advantageously, the silica S used according to the invention is in powder form. Preferably it is the aforementioned powders, obtained by nozzle atomization drying and grinding, or obtained after drying by turbine atomizer. Alternatively, it may also be a powder resulting from the grinding of the compacted silica granules described above.

Alternatively, the silica S used according to the invention may be in the form of substantially spherical beads, obtainable by the aforementioned nozzle spray drying. According to a particularly advantageous variant, the process P for preparing the silica S comprises (and for example consists of) the following successive steps:

(i) forming an aqueous base stock having a pH of between 3 and 4.5, preferably between 3.5 and 4.5 (typically of the order of 4); (ii) at the same time, silicate and acidifying agent are added to said base stock so that the pH of the reaction medium is maintained at the value reached at the end of step (i) at ± 0 , 2 units, and preferably within ± 0.1 units;

(iii) after possibly allowing the medium to mature, the addition of the acidifying agent is stopped while continuing the addition of silicate in the reaction medium until a pH value of the reaction medium is obtained between 7 and 9.5, preferably between 7.5 and 9.5 (typically of the order of 8);

(iv) silicate and acidifying agent are added simultaneously to the reaction medium, so that the pH of the reaction medium is maintained at the value reached at the end of step (iii) at ± 0, 2 units, and preferably within ± 0.1 units;

(v) stopping the addition of the silicate while continuing the addition of the acidifying agent in the reaction medium until a pH value of the reaction medium of between 3 and 5.5 is obtained, preferably between 5 and 5.5 (typically of the order of 5.2);

(vi) the medium is allowed to mature, preferably with stirring, typically for 2 to 20 minutes, for example for 5 minutes;

(vii) filtering the silica suspension obtained at the end of step (vi), whereby a filter cake is obtained; (viii) the filter cake is disintegrated mechanically in the presence of sodium aluminate;

(ix) the disintegrated cake obtained is dried, and optionally the dried silica obtained is crushed.

According to this specific variant of the process P, the steps (i) to (vi) are advantageously carried out at a temperature of between 75 and 95 ° C., preferably between 80 and 90 ^° C. (at a temperature of the order of 80 ⁰ C or 86 ° C, for example).

Furthermore, the silicate used according to this specific variant is advantageously a sodium silicate, advantageously having a weight ratio SiO ₂ / Na ₂ O of between 3.2 and 3.8, typically between 3.5 and 3.6, for example of the order of 3.52. This silicate is preferably used in the form of a solution having a concentration (expressed as SiO ₂ ) of between 200 and 250 g / l, typically of the order of 230 g / l. This solution is generally introduced with a constant flow rate of between 150 and 250 l / h, for example between 180 and 200 l / h, typically of the order of 190 l / h in steps (iii) and (v). The acidifying agent is, for its part, preferably sulfuric acid, advantageously in the form of a solution having a concentration of between 60 and 130 g / l, for example between 70 and 100 g / l, typically of the order of 80 g / l.

According to a second advantageous embodiment of the invention, the silica used is a silica, called "silica S1", which has the following characteristics:

a BET specific surface area of between 60 and 550 m ² / g;

a CTAB specific surface area of between 40 and 525 m ² / g;

an object size distribution width Ld measured by XDC granulometry after ultrasound deagglomeration of at least 0.91; and

- a pore volume distribution such that the ratio V A / (d5 - DIØØ) _(d5 d5 _0.) Is at least 0.66.

This silica S1 is advantageously a precipitation silica. According to a particular embodiment, it is a silica obtained according to the method P defined above in the present description.

The "CTAB specific surface area" referred to herein, as in the rest of the present description, refers to the external surface as determined according to standard NF T 45007 (November 1987) (5.12).

Furthermore, the "XDC granulometric analysis method" referred to in the present description is a method of particle size analysis centrifugal sedimentation, by which one can measure, on the one hand, the widths of object size distribution of a silica, and, on the other hand, the XDC mode illustrating its size of objects. This method is described below:

Materials Needed - BI-XDC Centrifugal Sedimentation Granulometer (BROOKHAVEN-INSTRUMENT X DISC CENTRIFUGES) marketed by Brookhaven Instrument Corporation)

- high shape beaker of 50 ml

- graduated cylinder of 50 ml - BRANSON ultrasonic probe 1500 watts, without tip, diameter 13 mm,

- permutated water

- crystallizer filled with ice

- magnetic stirrer Measuring conditions

- DOS version 1.35 of the software (supplied by the manufacturer of the granulometer)

- fixed mode

- rotation speed

- duration of the analysis: 120 minutes - density (silica): 2.1

- volume of suspension to be taken: 15 ml

Sample preparation

Add 3.2 g of silica and 40 ml of deionized water to the tall beaker. Put the beaker containing the suspension in the crystallizer filled with ice. Immerse the ultrasound probe in the beaker.

Deagglomerate the suspension for 16 minutes using the 1500 watts BRANSON probe (used at 60% of maximum power). When the disaggregation is complete, place the beaker on a magnetic stirrer. Preparation of the granulometer

Turn on the appliance and let it heat for 30 minutes. Rinse the disc twice with deionized water.

Introduce into the disc 15 ml of the sample to be analyzed and stir. Enter in the software the measurement conditions mentioned above. Take the measurements.

When the measurements have been made:

Stop the rotation of the disc.

Rinse the disc several times with deionized water.

Stop the device. Results

In the device register, record the values of the diameters passing at 16%, 50% (or median) and 84% (% mass) as well as the value of the Mode (the derivative the cumulative granulometric curve gives a frequency curve whose abscissa of the maximum (abscissa of the main population) is called the "Mode").

The "object size distribution width Ld", measured by XDC granulometry, after ultrasonic deagglomeration (in water), is equal to the ratio (d84 - d16) / d50, in which each of the terms dn (n = 16, 50 and 84) designates the size for which one% of particles (in mass) of size smaller than this size (the width Ld of distribution is thus calculated on the cumulative granulometric curve, taken in its entirety). For a silica S1 this object size distribution width Ld, measured by XDC granulometry, after ultrasonic deagglomeration (in water) is at least 0.91, for example at least 0.94, and it can be at least 1, 04.

In the present description, reference is also made to "an object size distribution width d less than 500 nm", measured by XDC particle size, after ultrasonic deagglomeration (in water). This width d is equal to the ratio (d84 - d16) / d50 in which each of the terms dn (n = 16, 50 and 84) designates the size for which one% of particles (in mass), with respect to the particles. less than 500 nm, smaller than this size (the width The distribution d is therefore calculated on the cumulative granulometric curve, truncated above 500 nm).

In addition, a mean (mass) particle size (i.e., secondary particles or aggregates), denoted by _w , can be measured using the XDC granulometric analysis method by centrifugal sedimentation. after dispersion, by deagglomeration with ultrasound, silica in water. The method differs from that previously described in that the suspension formed (silica + deionized water) is deagglomerated, on the one hand, for 8 minutes, and on the other hand, using an ultrasonic probe VIBRACELL 1, 9 cm (marketed by Bioblock) of 1500 watts (used at 60% of the maximum power). After analysis (sedimentation for 120 minutes) the mass distribution of the particle sizes is calculated by the granulometer software. The geometric mean mass of particle sizes ("mean geometry (Xg)", denoted by _dw , is computed by the software from the following equation: log d _w = (Σ (i = 1 to i = n) rrijlogdj ) / Σ (i = 1 to i = n) rrij, where each of the terms mi (for i = 1 to n) denotes the mass of the set of objects in the size class d |.

On the other hand, when reference is made to porous volumes in the present description, these are porous volumes as measured by mercury porosimetry, the preparation of each sample being as follows: each sample is dried beforehand for 2 hours in an oven at 200 ⁰ C, then placed in a test vessel within 5 minutes after leaving the oven and degassed under vacuum, for example using a pump with rotary drawers; the pore diameters (MICROMERITICS Autopore III 9420 porosimeter) are calculated by the WASHBURN relationship with a theta contact angle equal to 140 ° and a gamma surface tension equal to 484 Dynes / cm (or N / m). For the purposes of the present description, the so-called "V s-dso ^" pore volume denotes the pore volume constituted by the pores of diameters between d5 and d50, and the so-called "V _(d5 - _d 100o ₎ " porous volume represents the pore volume constituted by the pores of diameters between d5 and d100, where each of the dn denotes here the pore diameter for which n% of the total surface of all the pores is provided by the pores with a diameter greater than this diameter (the total pore area (st _ot ) can be determined from the mercury intrusion curve).

The ratio of volumes V ^ s. _d50 ) A / (ds - dioo) is characteristic of the distribution of the pore volume.

In a silica S1, the ratio V _(d5 dso.) A / _(d 5 - _d ioo) is at least 0.66, for example at least 0.68, and typically at least 0.71 . This ratio V _(d5 - d50) A / (d5 - dioo) may be at least 0.73, in particular at least 0.74. In some cases, this ratio is at least 0.78, especially at least 0.80, or even at least 0.84.

One can, on the other hand, determine a "porous distribution width Idp" from the porous distribution curve representing pore volume (in ml / g) as a function of the pore diameter (in nm). More precisely, as indicated in the application WO 03/016215, this porous distribution width Idp is determined as follows: the coordinates Xs (in nm) and Ys (in ml / g) of the point corresponding to the main population (typically , the maximum of the porous distribution curve). We draw a line of equation Y = Ys / 2; this line intersects the porous distribution curve at two points A and B having abscissa respectively X _A and X _B (in nm) on either side of Xs. The porous distribution width is equal to the following ratio:

ldp = (X _A - X _B ) / Xs-

The pore size distribution width may optionally also be reflected by the parameter "L / IF" determined by mercury porosimetry. The measurement is carried out using the PASCAL 140 and PASCAL 440 porosimeters marketed by ThermoFinnigan, operating as follows: a sample quantity of between 50 and 500 mg (in the present case 140 mg) is introduced into a cell measurement. This measuring cell is installed on the measurement station of the PASCAL 140 device. The sample is then degassed under vacuum, for the time necessary to reach a pressure of 0.01 kPa (typically of the order of 10 minutes). . The measuring cell is then filled with mercury. The first part (pressures below 400 kPa) of the mercury intrusion curve Vp = f (P), where Vp is the mercury intrusion volume and P the applied pressure, is determined on the PASCAL 140 porosimeter. measuring cell is then installed on the measurement station of the porosimeter PASCAL 440, the second part of the mercury intrusion curve Vp = f (P) (pressures between 100 kPa and 400 MPa) being determined on the porosimeter PASCAL 440 The porosimeters are used in "PASCAL" mode, so as to continuously adjust the rate of intrusion of the mercury as a function of variations in the volume of intrusion. The velocity parameter in "PASCAL" mode is set to 5. The pore radii Rp are calculated from the pressure values P using the WASHBURN relation, with a hypothesis of cylindrical pores, by choosing an angle of theta contact equal to 140 ° and a gamma surface tension equal to 480 Dynes / cm (or N / m). The porous volumes Vp are related to the mass of silica introduced and expressed in cm ³ / g. The signal Vp = f (Rp) is smoothed by combining a logarithmic filter (smooth dumping factor filter parameter F = 0.96) and a moving average filter (number of points to average filter parameter f = 20 ). The pore size distribution is obtained by calculating the dVp / dRp derivative of the smoothed intrusion curve. The fineness index IF is the value of pore radius (expressed in angstroms) corresponding to the maximum of the pore size distribution dVp / dRp. We denote L the width at half height of the pore size distribution dVp / dRp.

A silica S1 useful according to the invention may for example have the following characteristics:

- a width Ld ((d84 - d16) / d50) of object size distribution measured by XDC granulometry after deagglomeration with ultrasound of at least 1, 04; and

- a pore volume distribution as a function of the size of the pores such that the ratio V _(d5 dso / Vys -. _D ioo) is at least 0.71, for example at least 0.73, in particular of at least 0.74, and in some cases at least 0.78, especially at least 0.80, or even at least 0.84.

According to a third advantageous embodiment of the invention, the silica used is a silica, called "silica S2", which has the following characteristics: a BET specific surface area of between 60 and 550 m ² / g;

a CTAB specific surface area of between 40 and 525 m ² / g;

a porous distribution width Idp greater than 0.70.

This silica S 2 is advantageously a precipitation silica. Preferably, it is a silica obtained according to the method P defined above in the present description.

The silica S2 may in particular have a porous distribution width Idp greater than 0.80, for example greater than 0.85. In some cases, this porous distribution width Idp is greater than 1.05, for example greater than 1.25, or even greater than 1.40. Moreover, the silica S2 preferably has a width Ld ((d84-d16) / d50) of object size distribution measured by XDC granulometry after deagglomeration with ultrasound (in water) of at least 0.91, for example at least 0.94, especially at least 1, typically at least 1.04.

According to a fourth advantageous embodiment, the silica used according to the present invention is a silica, called "silica S3", which has the following characteristics:

a BET specific surface area of between 60 and 550 m ² / g;

a CTAB specific surface area of between 40 and 525 m ² / g; - a width The d ((d84 - d16) / d50) of object size distribution less than

500 nm, measured by XDC granulometry after deagglomeration with ultrasound, of at least 0.95; and

- a distribution of the pore volume such as the ratio dioo) of at least 0.71.

This silica S3 is advantageously a precipitation silica. Preferably, it is a silica obtained according to the method P defined above in the present description.

The silica S3 may in particular have a ratio V (d5 - d50) / V (d5 - d100) of at least 0.73, in particular at least 0.74. This ratio may be at least 0.78, especially at least 0.80, or even at least 0.84.

Finally, according to a fifth advantageous embodiment of the invention, the silica used according to the present invention is a silica, called "silica S4", which has the following characteristics:

a BET specific surface area of between 60 and 550 m ² / g; a CTAB specific surface area of between 40 and 525 m ² / g;

a width of the d ((d84-d16) / d50) of object size distribution of less than 500 nm, measured by XDC particle size after deagglomeration with ultrasound, of at least 0.90, in particular of at least 0.92; and - a distribution of the pore volume such that the ratio V (d5-d5θ) A / (d5 - dioo) of at least 0.74.

This silica S4 is advantageously a precipitation silica. Preferably, it is a silica obtained according to the method P defined above in the present description.

This silica S4 may for example have a ratio V ( _d 5 - _d 5 O) A / ( _d 5 - dioo) of at least 0.78, especially at least 0.80, or even at least 0.84.

According to a particular variant, the above-mentioned silicas S, S1, S2, S3 and S4 have the following characteristics: a BET specific surface area of between 70 and 350 m ² / g, in particular between 90 and 320 m ² / g; and

a CTAB specific surface area of between 60 and 330 m ² / g, for example between 80 and 290 m ² / g.

In this context, their BET specific surface area may be between 110 and 270 m ² / g, especially between 115 and 250 m ² / g, for example between 135 and 235 m ² / g. Furthermore, their CTAB specific surface area may be between 90 and 230 m ² / g, in particular between 95 and 200 m ² / g, for example between 120 and 190 m ² / g.

According to another variant, the silicas S, S1, S2, S3 and S4 have the following characteristics: a BET specific surface area of between 60 and 400 m 2 / g, in particular between 60 and 300 m 2 / g; and

a CTAB specific surface area of between 40 and 380 m 2 / g, in particular between 45 and 280 m 2 / g.

According to this other variant, their BET specific surface area may be between 120 and 280 m ² / g, in particular between 150 and 280 m ² / g. Moreover, their CTAB specific surface area may be between 115 and 260 m ² / g, in particular between 145 and 260 m ² / g.

In general, the silicas S, S1, S2, S3 and S4 may have a certain microporosity. Thus, most often, the difference between their BET surface area and their CTAB specific surface area (SBET - SCTAB) is greater or equal to 5 m ² / g, typically greater than or equal to 15 m ² / g, for example greater than or equal to 25 m ² / g, this difference remaining, however, most often less than 50 m ² / g, preferably less than 40 m ² / g.

On the other hand, in the silicas S, S1, S2, S3 and S4, the pore volume provided by the larger pores is usually the largest part of the structure.

These silicas S1, S2, S3 and S4 may have a pore volume consisting of pores with diameters of between 3.7 and 80 nm of at least 1.35 cm3 / g, in particular at least 1.40 cm3 / cm3. g, or even at least 1.50 cm3 / g.

On the other hand, the silicas S, S1, S2, S3 and S4 can have both an object size distribution width Ld of at least 1, 04 and a width distribution width D d of objects less than 500 nm of not less than 0.95.

The object size distribution width Ld of the silicas S, S1, S2, S3 and S4 may, in some cases, be at least 1, 10, in particular at least 1, 20; it may be at least 1, 30, for example at least 1, 50 or even at least 1.60.

Likewise, the width D of the object size distribution less than 500 nm of the silicas S, S1, S2, S3 and S4 may be, for example, at least 1.0, in particular at least 1, 10, especially at least 1, 20.

It should also be noted that the silicas S, S1, S2, S3 and S4 generally have a high object size, which is atypical. Thus, the mode of their particle size distribution as measured by XDC granulometry after deagglomeration with ultrasound (in water) can for example satisfy the following condition: Mode XDC (nm)> (5320 / CTAB surface (m2 / g)) +8 or even the following condition:

XDC (nm) mode> (5320 / SCTAB (m2 / g)) + 10.

The silicas S, S1, S2, S3 and S4 which are useful according to the invention can moreover possess a particular surface chemistry, such that they have a ratio (Sears number x 1000) / (BET surface area) less than 60, preferably less than 55, e.g. less than 50. '

The "Sears number" referred to herein corresponds to the volume of 0.1 M sodium hydroxide solution that is required to raise the pH of 4 to 9 of a suspension of the silica tested to 10 g / l. in 200 g / l sodium chloride medium, as determined by the method described by GW SEARS in Analytical Chemistry, vol. 28, No. 12, December 1956.

For a given silica, this number of Sears is determined under the following conditions. A solution of sodium chloride at 200 g / l acidified to pH 3 with a 1M hydrochloric acid solution is prepared from 400 g of sodium chloride. The weighings are carried out using a weighing scale. Precision METTLER. 150 ml of this sodium chloride solution are added gently into a 250 ml beaker into which a mass M (in g) of the sample to be analyzed corresponding to 1.5 grams of dry silica has been introduced beforehand. Ultrasound was applied to the dispersion for 8 minutes (1500 W BRANSON ultrasound probe, 60% amplitude, 13 mm diameter), the beaker being in a crystallizer filled with ice. Then the solution obtained is homogenized by magnetic stirring, using a magnetic bar of dimensions 25 mm × 5 mm. It is checked that the pH of the suspension is less than 4, adjusting it if necessary with a 1M hydrochloric acid solution. Next, using a Metrohm titration meter pH meter (titroprocessor 672, dosimat 655), previously calibrated with buffer solutions pH 7 and pH 4, 0.1 M sodium hydroxide solution at a flow rate of 2 ml / min. (The titration pH meter has been programmed as follows: 1) Call the program "Get pH", 2) Enter the following parameters: pause (waiting time before start of titration): 3 s, reagent flow: 2 ml / min, anticipation (adaptation of the titration rate to the slope of the pH curve): 30, pH stop: 9.40, critical EP (detection sensitivity of the equivalence point): 3, report (parameters of printing of the titration report): 2,3,5 (ie creation of a detailed report, list of measuring points, titration curve)). The exact volumes V ₁ and V ₂ of the added sodium hydroxide solution are determined by interpolation to obtain a pH of 4, respectively. and a pH of 9. The number of Sears for 1, 5 grams of dry silica is equal to the ratio:

((V ₂ - V ₁ ) X iSO) Z (ES x M) with the following meanings: Vi: volume of 0.1 M sodium hydroxide solution at pHi = 4

V ₂ : volume of 0.1 M sodium hydroxide solution at pH ₂ = 9 M: mass of the sample (g) ES: dry extract in%

Furthermore, the silicas S, S1, S2, S3 and S4 that are useful according to the invention generally have at least one, and preferably all, of the following three characteristics:

• the mass geometric mean particle size (d _w ) as measured using the XDC granulometric analysis method satisfies the following condition: d _w ≥ (16500 / S _C TA _B ) - 30, where SCTAB denotes the CTAB specific surface area expressed in m2 / g;

• the porosity is such that the L / IF ratio satisfies the following condition:

L / IF> - 0.0025 SCTAB + 0.85 where S _C TA _B designates the CTAB specific surface area expressed in m2 / g; ^• the number of silanols per unit area (Nsi _{θH /} nm ₂₎ is such that:

N _S i0H / nm2 ≤ "S ₀ 0.027 TAB + 10.5 where: -. SCTAB refers to the CTAB surface area expressed in m2 / g; and

the number of silanols per nm ² of surface is determined by grafting methanol on the surface of the silica, preferably under the conditions set out below:

1 g of crude silica is suspended in 10 ml of methanol in a 110 ml autoclave (Top Industrie, reference 09990009). A magnetic bar is introduced and the autoclave, hermetically sealed and heat-insulated, is heated at 200 ^° C. (40 bar) on a heating magnetic stirrer for 4 hours. The autoclave is then cooled in a cold water bath. The grafted silica is recovered by decantation and the Residual methanol is evaporated under a stream of nitrogen. Finally, the grafted silica is dried at 130 ^° C. under vacuum for 12 hours. The carbon content is determined by elemental analyzer (NCS 2500 analyzer from CE Instruments) on the raw silica and on the grafted silica. This assay on the grafted silica is carried out within three days

The end of drying, the humidity of the air or the heat can indeed cause a hydrolysis of methanol grafting. The number of silanols per nm ² is then calculated by the following formula: N _S i0H / nm2 = [(% C _g -% C _b) × 6.023 × 10 ^23] / [SBET x 10 ¹⁸ x 12 x 100] with following meanings:

% C _g : mass percentage of carbon present on the grafted silica% C _b : mass percentage of carbon present on the crude silica SBET: BET specific surface area of the silica (expressed in m ² / g)

Whatever the exact mode of preparation of the silica used according to the invention and its characteristics of porosity, granulometry, and surface chemistry, an important characteristic of this silica is its specific surface, which is greater than or equal to 60 m ² / g, which makes it possible to obtain the increase in rigidity of the desired material according to the invention.

In general, the greater the specific surface area of a silica used according to the invention, the greater the improvement in rigidity obtained is pronounced.

From this point of view, it is therefore preferred in most cases use of silicas having a BET surface area of at least 80m ² / g, - or even at least 90 m ² / g, more preferably at least 100 m ² / g. According to an advantageous embodiment, the silica used at a BET specific surface area of at least 120 m ² / g, or even at least 150 m ² / g, for example at least 170 m ² / g.

Moreover, it is most often preferred that a silica used according to the invention be present in the form of objects (particles, aggregates and / or agglomerates) which are as finely divided and dispersed as possible, which proves to be particularly advantageous in regarding the impact resistance of the material. Thus, without wishing to be bound to a particular theory, the work of the inventors allows to establish that we observe an increase in the impact resistance even more pronounced that the silica is finely dispersed in the material.

It should be noted that the silicas S, S1, S2, S3, and S4 which have been described above in the present description are silicas which have BET specific high surface areas, typically greater than or equal to 60 m ² / g. In addition, these specific silicas are generally dispersed in the form of very small objects in thermoplastic polymer materials where they are introduced as mineral filler (typically they are found essentially in the form of objects smaller than 5 microns in size, and most often less than 1 micron, or even lower). These silicas are therefore of particular interest for the implementation of the present invention.

In this regard, it should be emphasized that the silicas S, S1, S2, S3, and S4 often have a very good dispersibility, especially in thermoplastic polymers. This dispersibility (and disagglomeration) ability can be quantified in particular by means of the following specific disagglomeration tests:

A first deagglomeration test is carried out by appreciating the cohesion of the agglomerates by a granulometric measurement (by laser diffraction) carried out on a suspension of silica previously deagglomerated by ultra-sonification. The ability of the silica to deagglomerate (rupture of the objects from 0.1 to a few tens of microns) is thus measured.

In this test, the deagglomeration under ultrasound is performed using a VIBRACELL BIOBLOCK sonicator (600 W), equipped with a 19 mm diameter probe. The particle size measurement is carried out by laser diffraction on a SYMPATEC granulometer. 2 grams of silica are weighed into a pillbox (height: 6 cm and diameter: 4 cm) and the mixture is made up to 50 grams by addition of deionized water: a 4% aqueous suspension of silica is thus obtained which is homogenized during 2 minutes by magnetic stirring. Deagglomeration under ultrasound is then carried out as follows: the probe being immersed over a length of 4 cm, the output power is adjusted so as to obtain a power dial needle deflection indicating 20%. The disagglomeration is carried out for 420 seconds. The granulometric measurement is then carried out after introducing into the vat of the granulometer a known volume (expressed in ml) of the homogenized suspension. The value of the median diameter 0 ₅ bone (or "medial diameter Sympatec") that is obtained is even lower than the silica has a high ability to deagglomerate. It is also possible to determine the ratio (10 x volume of suspension introduced (in ml)) / optical density of the suspension detected by the granulometer (this optical density is of the order of 20). This ratio is indicative of the rate of particles smaller than 0.1 μm which are not detected by the granulometer. This ratio is called ultrasonic deagglomeration factor (Sympatec) (F _D s) -

Another deagglomeration test is carried out by appreciating the cohesion of the agglomerates by a granulometric measurement (by laser diffraction), carried out on a suspension of silica previously deagglomerated by ultra-sonification. The ability of the silica to deagglomerate (rupture of the objects from 0.1 to a few tens of microns) is thus measured.

In this test, the deagglomeration under ultrasound is carried out using a VIBRACELL BIOBLOCK (600 W) sonifier, used at 80% of the maximum power, equipped with a 19 mm diameter probe. The granulometric measurement is carried out by laser diffraction on a MALVERN granulometer (Mastersizer 2000). A gram of silica is weighed into a pillbox (height: 6 cm and diameter: 4 cm) and the mixture is made up to 50 g by addition of deionized water: an aqueous suspension of 2% silica, which is homogenized during 2 minutes by magnetic stirring. Deagglomeration is then carried out under ultrasound for 420 seconds. The granulometric measurement is then carried out after the whole of the homogenized suspension has been introduced into the vat of the particle size analyzer.

The median diameter value 0 ₅ OM (OR "Malvern median diameter") that is obtained is much lower than the silica has an aptitude for deagglomeration. One can also determine the ratio (10 x darkness value of the blue laser) / darkness value of the red laser. This report is indicative of the rate of particles smaller than 0.1 μm. This ratio is called ultrasonic deagglomeration factor (Malvern) (F _D M).

• A deagglomeration rate, denoted α, can be measured by means of another ultrasonic deagglomeration test, at 100% power of a 600 watt probe, operating in pulsed mode (ie: 1 second ON, 1 second OFF) to prevent excessive heating of the ultrasonic probe during measurement. This known test, in particular the subject of the application WO99 / 28376 (see also the applications WO99 / 28380, WO00 / 73372, WO00 / 73373), makes it possible to measure continuously the evolution of the average size (in volume) of the agglomerates of particles during sonication, as indicated below. The assembly used consists of a laser granulometer (type "MASTER RS I ZE RS", marketed by Malvern Instruments - He-Ne laser source emitting in the red, wavelength 632.8 nm) and its preparer (" Malvern Small Sample Unit MSX1 "), between which was interposed a continuous flow treatment unit (BIOBLOCK M72410) equipped with an ultrasonic probe (12.7 mm type VIBRACELL type 600-watt sonifier marketed by Bioblock). A small amount (150 mg) of silica to be analyzed is introduced into the preparator with 160 ml of water, the circulation speed being set at its maximum. At least three consecutive measurements are carried out to determine, according to the known Fraunhofer calculation method (Malvern 3 $$ D calculation matrix), the average initial diameter (in volume) of the agglomerates, denoted d _v [0]. The sonification (pulsed mode: 1 s ON, 1 s OFF) is then established at a power of 100% (ie 100% of the maximum position of the "tip amplitude") and the evolution of the average diameter is followed for about 8 minutes. (in volume) d _v [t] as a function of time "t" at the rate of one measurement every 10 seconds approximately. After an induction period (about 3-4 minutes), it is observed that the inverse of the mean diameter (in volume) 1 / d _v [t] varies linearly, or substantially linearly, with the time "t" (stable deagglomeration regime). The deagglomeration rate α is calculated by linear regression of the evolution curve of 1 / d _v [t] as a function of time "t", in the zone of stable deagglomeration regime (in general, between 4 and 8 minutes approximately ); it is expressed in μm ^"1 .mn ^{" 1} . The application WO99 / 28376 describes in detail a measuring device that can be used for carrying out this ultrasound disagglomeration test. This device consists of a closed circuit in which a flow of agglomerates of particles suspended in a liquid can flow. This device essentially comprises a sample preparer, a laser granulometer and a treatment cell. Atmospheric pressure, at the level of the sample preparer and the treatment cell itself, allows the continuous removal of air bubbles that form during sonication (action of the ultrasound probe). The Sample Dispenser ("Malvern Small Sample Unit MSX1") is intended to receive the test silica sample (in suspension in the liquid) and to circulate it through the circuit at the preset speed (potentiometer - maximum speed). about 3 l / min), in the form of a liquid suspension stream. This preparer is simply a receiving tank which contains, and through which circulates, the suspension to be analyzed. It is equipped with a stirring motor, at variable speed, in order to avoid sedimentation of the particle agglomerates of the suspension; a centrifugal mini-pump is intended to ensure the circulation of the suspension in the circuit; the inlet of the preparator is connected to the open air via an opening intended to receive the test sample to be tested and / or the liquid used for the suspension. To the preparator is connected a laser granulometer ("Mastersizer S") whose function is to continuously measure, at regular intervals of time, the average volume size "d _v " of the agglomerates, at the passage of the flow, thanks to a cell of measurement to which are coupled the means for recording and automatic calculation of the granulometer. It will be briefly recalled here that the laser granulometers use, in a known manner, the principle of diffraction of light by solid objects suspended in a medium whose refractive index is different from that of the solid. According to Fraunhofer's theory, there is a relation between the size of the object and the diffraction angle of light (the smaller the object, the higher the angle of diffraction).

In practice, it is sufficient to measure the amount of light diffracted for different diffraction angles to be able to determine the size distribution (in volume) of the sample, d _v corresponding to the average volume size of this distribution (d _v = Σ (njdj ⁴ ) / Σ (njdj ³ ) where each of the ni denotes the number of objects of the size class or diameter already ).

Interleaved between the preparator and the laser granulometer is finally a treatment cell equipped with an ultrasonic probe, which can operate in continuous or pulsed mode, intended to continuously break the particle agglomerates at the passage of the flow. This flow is thermostatically controlled by means of a cooling circuit arranged at the level of the cell in a double envelope surrounding the probe, the temperature being controlled for example by a temperature probe immersed in the liquid at the level of the preparer.

The median diameter δ ₅₀ of the silicas S, S1, S2, S3 and S4, after deagglomeration with ultrasound, is generally less than 8.5 μm; it may be less than 6.0 μm, for example less than 5.5 μm.

Similarly, the median diameter 0 ₅ OM silicas S, S1, S2, S3 and S4, after ultrasonic disintegration, is in general less than 8.5 microns; it may be less than 6.0 μm, for example less than 5.5 μm.

The silicas S, S1, S2, S3 and S4 may moreover have a deagglomeration rate α, measured according to the ultrasonic deagglomeration test in the pulsed mode described above, at 100% power of a 600 ultrasound probe. watts, at least 0.0035 μm ^'1 .mn ^"1 , in particular at least

0.0037 μm ^"1 .mn ^{" 1} .

The silicas S, S1, S2, S3 and S4 may moreover have an ultrasonic deagglomeration factor (SDS) greater than 3 ml, in particular greater than 3.5 ml, especially greater than 4.5 ml. Their ultrasonic deagglomeration factor (F _D M) may mean greater than 6, in particular greater than 7, especially greater than 11.

On the other hand, the silicas according to the present invention may have an average size (in mass) of particles, measured by XDC granulometry after deagglomeration with ultrasound, d _w , between 20 and 300 nm, in particular between 30 and 300 nm, by example between 40 and 160 nm. The work of the inventors now makes it possible to establish that the particularly interesting results that have been observed with the specific silicas S, S1, S2, S3, and S4 mentioned above can be generalized to other silicas, provided that these silicas (1 °) have a BET surface area of at least 60 m ² / g, and (2 °) are dispersed as objects in the sufficiently divided state in the thermoplastic polymer material where they are incorporated.

In this context, according to another particular aspect, the subject of the present invention is the use of any silica (hereinafter referred to as "silica S ₀ ") having a BET specific surface area of at least 60 m ² / g, and presents in the polymer essentially in the form of dispersed objects having a size of less than 5 microns (and preferably less than 1 micron), as a mineral filler in a thermoplastic polymer material, to increase the rigidity of said material, while maintaining or improving its impact resistance.

By way of example, it is possible to use, as silica So of the aforementioned type, the specific silicas S, S1, S2, S3, and S4 described above in the present description. Other silicas which have the required surface area, coupled with sufficient dispersibility within the polymeric material, are also suitable for the practice of the present invention. In general, the silica So is preferably a precipitation silica. Most often, silicas having very high specific surface areas have relatively limited dispersibility properties, and as a result it is generally difficult to disperse them in a polymeric material in the form of very small objects. Therefore, in practice, is typically used as silica S ₀ silicas having a lower BET specific surface area equal to 300 m ² / g, for example less than or equal to 250 m ² / g. Thus, a silica that is used as silica S has, as a rule, a BET specific surface area of between 60 and 300 m ² / g, for example between 100 and 250 m ² / g, and especially between 150 and 200 m ² / g. . However, the use of silicas having higher specific surface areas is not excluded, provided that they can be dispersed in the material essentially in the form of dispersed objects having a size of less than 5 microns, and preferably less than 1 micron. Moreover, irrespective of their exact nature, an important characteristic of the So type silicas is their state of dispersion in the material in which they are incorporated. As a general rule, the impact resistance properties of the material obtained by using an S ₀ type silica depend to a large extent on this state of dispersion, especially as the specific surface area of the silica used is high.

In this context, it is generally preferable for the silica So to be present in the material in the form of aggregates, agglomerates and / or particles of which at least 90% by number, preferably at least 95% by number, and advantageously at least 98% by weight. % in number, have dimensions less than 5 microns, preferably 1 micron, the rest of the particles generally having dimensions less than 10 microns.

Advantageously, the silica So is dispersed in the form of objects (aggregates, agglomerates and / or particles) of which at least 80% by number, preferably at least 90% by number, and advantageously at least 95% by number, have dimensions between 30 nm and 1000 nm, for example between 50 and 900 nm, in particular between 100 nm and 800 nm. With such silica dispersion conditions, an increase in both stiffness and impact resistance of the material is most often obtained. The state of dispersion of the silica in a thermoplastic polymer material of the type of that of the invention can moreover be quantified by analysis of several scanning electron microscopy (typically with a magnification × 1000) micrographs taken on several flat sections of the material obtained by ultracryotomy (typically cuts of dimensions 110 μm × 70 μm). The image analysis of this type of image allows, by image analysis, to determine the fraction of the surface of the image occupied by objects larger than 5 μm. In this context, a surface fraction "FS 5 _μm ^" (equal to the area occupied by the objects of size greater than 5 μm relative to the total surface area of the image) is determined, the ratio of this surface fraction FS 5 _{μm being} brought back to the volume fraction. Silica FV in the material (ratio of the volume occupied by the silica in the material to the total volume of the material) is characteristic of the dispersion of silica in the material. A suitable dispersion according to the invention generally corresponds to a ratio FS 5 _μm / FV less than or equal to 4, preferably less than or equal to 3, advantageously less than or equal to 2, and more preferably less than or equal to 1. Typically, the surface fraction FS _δμ m to which reference is made above can be measured under the following conditions:

Sample preparation

Flat sections of the sample are made by pre-cutting with an ultratrim (Reichert-Jung). The final surfacing of the sample is carried out using an ultra-microtome ULTRACUT E (Reichert-Jung) equipped with DIATOME diamond knives of width 3 mn. The block surface obtained has a width of 2mn and a length close to 4mn.

observations

The surface block obtained is then observed by scanning microscopy for the evaluation of the macrodispersion. The microscope used is a SEM / FEG

(Field Emission) LEO 1525. For each sample, a series of at least 10 secondary electron images are made at different locations of the material, to obtain a representative measurement of the material. The size of each image is 1024 * 768 pixels. Image analysis

The digital images obtained are then processed by image analysis using the VISILOG software, according to the following steps:

• thresholding I binarization: the thresholding makes it possible to extract from the image all the pixels having a value in a given interval, it thus makes it possible to discriminate the particles within the matrix; binarization consists in assigning to each pixel of the image a numerical value (0 or 1) according to its membership in the matrix or the load (0 for the matrix, 1 for the load).

• Erosion / dilation: An erosion of the image obtained by a structuring element of size 2.5 microns makes it possible to subtract from the image all the objects having a size smaller than 5 microns. A Expansion of the resulting image then makes it possible to reconstruct the image.

• Measure: we add the value of all the pixels of the image then we normalize by the surface; the value obtained then corresponds to the surface rate of objects having a size greater than 5 microns.

More generally, the silicas S, S1, S2, S3, S4 and So that are useful according to the invention preferably have a BET specific surface area of between 60 and 300 m ² / g, for example between 100 and 250 m ² / g. , and especially between 150 and 200m ² / g.

Furthermore, the silicas S ₁ S ₁ , S ₂ , S 3, S 4 and S ₀ useful according to the invention preferably have a pH of between 6.3 and 7.8, especially between 6.6 and 7.5. This pH is that measured according to the ISO 787/9 standard (pH of a suspension of the silica tested at 5% in water).

The silicas S, S1, S2, S3, S4 and So also have an intake of DOP oil that varies, for the most part, between 220 and 330 ml / 100 g, for example between

240 and 300 ml / 100g. The DOP oil uptake to which reference is made in the present description is determined according to standard NF T 30-022 (March 1953) using dioctyl phthalate.

On the other hand, the silicas S, S1, S2, S3, S4 and _S0 useful according to the invention are advantageously in the form of powders, preferably powders having an average size of at least 15 .mu.m, for example of between 15 and 60 μm (in particular between 20 and 45 μm) or between 30 and 150 μm (especially between

45 and 120 μm).

Alternatively, the silicas S, S1, S2, S3, S4 and S ₀ used according to the invention may also be in the form of substantially spherical beads of average size of at least 80 .mu.m. This average size of the beads may be at least 100 μm, for example at least 150 μm; it is generally at most 300 μm and is preferably between 100 and 270 μm. This average size is determined according to standard NF X 11507 (December 1970) by dry sieving and determination of the diameter corresponding to a cumulative refusal of 50%.

Regardless of their precise nature, the S silicas, S1, S2, S3, S4 and _S0 above are particularly suitable as inorganic fillers to improve the stiffness material thermoplastic polymer, without decreasing the impact resistance, even by improving this impact resistance in some cases, and at the same time improving, at the same time, other characteristics, such as the tensile elongation of the material and the scratch resistance. For the purposes of the present description, the term "thermoplastic polymer material" is understood to mean a material comprising as majority constituent a thermoplastic polymer or a mixture of thermoplastic polymers, and generally behaving like a thermoplastic polymer. Thus, a thermoplastic polymer material in the sense of the present description generally comprises at least 50% by weight of a thermoplastic polymer or a mixture of thermoplastic polymers, most often at least 75% by weight, for example at least 80% by weight. in bulk, and typically at least 90%, or even at least 95% by weight. In addition to this or these thermoplastic polymer (s) and the silica used as a filler, the thermoplastic polymer material may comprise other ingredients such as additives allowing the conservation or the proper use of the polymer, or additives to further improve the impact properties of the material (for example polymeric fillers or surface fillers treated with fatty acids). The silica of the invention may also be used in combination with other mineral fillers, such as other silicas, talc, wollastonite, kaolin, mica, calcium carbonate, glass fibers, and the like. or silicates. The presence of these additional agents may make it possible to further improve the effect of improving the rigidity desired according to the invention, and / or to improve other characteristics of the material, in particular the impact resistance. In particular, the use of the silica of the invention together with other mineral fillers may be advantageous for improving the scratch resistance of the material. Nevertheless, the presence of such additional components is not required to achieve the effect of improving the rigidity sought according to the invention. According to a particular embodiment, the silica of the invention is used as sole mineral filler in the thermoplastic polymer material.

Moreover, it should be emphasized that the silica used according to the invention does not generally require any surface treatment, in particular with organic molecules such as fatty acids, to ensure the effect of improving the rigidity of the invention. Nevertheless, according to one conceivable embodiment, the polymeric material may comprise an additive chosen from silanes, fatty acids, phosphonic acids, titanates, polypropylene waxes, polyethylene waxes and / or maleic anhydride grafted polypropylenes, which makes it possible in particular to ensure better compatibility between silica (and any other mineral fillers present) and thermoplastic polymers.

The silicas of the invention are particularly advantageous as mineral fillers in thermoplastic polymer materials based on one or more polymers chosen from polyolefins, polyamides (in particular polyamides 6, polyamides 66, polyamides 11, polyamides 12, polymetaxylylenediamines, mixtures and copolymers based on these polyamides), polyesters, poly (arylene) oxides, polyvinyl chlorides, polyvinylidene chloride, polyvinyl acetate, mixtures of these polymers and copolymers based on these polymers.

In particular, the silicas of the invention are particularly suitable for improving the impact resistance of thermoplastic polymer materials based on one or more polyolefins, and in particular on polymeric materials which comprise:

a homopolyolefin selected from polyethylene, polypropylene, polybutylene, or poly (methylpentene); a copolymeric polyolefin based on at least two types of units chosen from ethylene, propylene, butylene and methylpentene units; or a mixture of two or more of said homopolyolefins and / or said copolymeric polyolefins.

The silicas that are useful according to the invention are, for example, well suited as fillers in thermoplastic materials based on polypropylene, polyethylene or on the basis of mixtures of these polymers or of their copolymers. According to an interesting embodiment, the thermoplastic polymer material in which the silica filler according to the invention is incorporated is a material based on polypropylene or a copolymer of propylene and ethylene.

Whatever the nature of the thermoplastic material, the silica used as a filler according to the invention is generally in a content between

0.5% and 10% by weight, for example between 1 and 7%, for example between 2 and 6%, relative to the total mass of the thermoplastic polymer material including silica.

The incorporation of the silica into the material can be done by any means known per se for the incorporation of mineral fillers in a thermoplastic polymer matrix, provided that it leads to a dispersion of the silica as required according to the invention . To this end, this incorporation is preferably carried out by mixing under stress and the silica or polymeric material beyond their glass transition temperature, optionally in the presence of additives, for example thermal stabilizers of the type of I'IRGANOX ^® B225 sold by the company Ciba, advantageously using devices of the internal mixer or extruder types.

According to a particular aspect, the invention also relates to thermoplastic polymer materials comprising a silica S, S1, S2, S3, S4, or SO, of the aforementioned type, as mineral filler improving their rigidity.

These materials are particularly suitable for the manufacture of coating layers, mechanical parts or parts for the automobile, and in particular for the manufacture of thin parts having good mechanical properties. More specifically, the invention also relates to thermoplastic polymer materials of this type which comprise one or more polyolefins as a major constituent (namely constituting more than 50% by weight, generally at least 75% by weight, for example at least 90% or even 95% by weight of the material), and more specifically materials of this type comprising polypropylene as a major constituent. In these materials, the introduction of the silica of the invention as a mineral filler usually leads to obtaining polymeric materials having similar optical properties to the unfilled material, contrary to what is observed with most mineral fillers that lead to a change in the shade of the material, its transparency or its light scattering properties. The preservation of optical properties of the starting material is often such that the introduction of silica into the material does not lead to a change in the appearance of the material visually. The modification of the properties of the material can moreover be more accurately quantified, for example by spectro-colorimetry, from which it appears most often that the introduction of a silica according to the invention into a polymer material based on A polyolefin such as polyethylene leads at most to very slight changes in the properties of transparency, light transmission and coloring of the material. These properties make it possible in particular to obtain impact-resistant thermoplastic polyolefinic materials having good transparency properties.

Various aspects and advantages of the invention will emerge from the illustrative and nonlimiting examples given below, in which silica, S, which is a silica with a BET specific surface area of greater than 5%, is used as the silica according to the invention. 100 m ² / g, which is obtained according to the method P as defined above in the present description. EXAMPLE 1

Use of silica S to improve the impact resistance of a thermoplastic polypropylene material (incorporation of silica into the material by means of an internal mixer)

Silica S has been used as a mineral filler for the improvement of the impact resistance of a polymeric material having the following Formulation (1) (the percentages given are percentages by weight relative to the total mass of the formulation ):

- polypropylene: 96.8% - thermal stabilizer: 0.2%

- silica S: 3%

The polypropylene used in this example is the polypropylene sold under the name PPH 4060 by the company Atofina (polypropylene homopolymer having a melt index (230 ^° C. under 2.16 kg) of 3 g / 10 min). The thermal stabilizer is meanwhile I'1RGANOX ^® B225 marketed by Ciba (mixed-based antioxidant phenolic compounds).

The polymeric material incorporating the silica was prepared by introducing 35 g of polypropylene, 0.07 g of thermal stabilizer and 1.1 g of silica S into a Brabenber internal mixer initially heated to a temperature of 150 ^° C., with a filling 0.7, where the tank of the internal mixer is provided with two rotors of type W50 for thermoplastic, rotating at a speed of 125 revolutions per minute.

Was performed a mixing of the constituents introduced into these conditions for 5 minutes, the temperature rising in the mixture in view of the internal shear, leading to a final temperature of about 180 ⁰ C.

Part of the formulation thus obtained was molded by pressing into a parallelepiped mold of dimensions 100 mm × 100 mm × 10 mm, between two compression plates heated to 200 ^° C., under a pressure of 200 bar (2.10 ^"3 Pa) for 2 minutes The mold was then cooled between the two plates brought to 18 ⁰ C under a pressure of 200 bar for 4 minutes.

On the obtained polymer plate, several electron microscopy images were made at different locations on the basis of which the surface fraction FS 5 _μm (the proportion of area occupied by the objects larger than 5 μm in the images obtained) was determined. by image analysis under the specific conditions defined above in the description. The surface fraction FS 5 _μm thus measured is 4%.

In this example, the volume fraction FV of silica in the material (ratio of the volume occupied by the silica in the material reduced to the total volume of the material) is 1.4% (mass fraction of 3%). The FS _5μm / FV ratio of the material is therefore 2.93 in this example.

Furthermore, in the polymer plate obtained at the end of the molding, two parallelepiped test pieces of dimensions 80 mm × 4 mm × 10 mm were cut.

On the first specimen, the flexural modulus was measured under the conditions of ISO 178 at 23 ° C.

On the second specimen, the fracture energy was measured according to the Charpy impact test at 23 ° C. on a notched specimen, under the conditions of ISO 179 at 23 ° C.

For comparison, the same tests were carried out on specimens prepared under the same conditions, but from a control formulation (T1) without silica.

The results obtained are reported in Table I below, from which it appears that the presence of silica as a mineral filler in the formulation increases both rigidity (increase in flexural modulus) and impact resistance ( increased breaking energy). Table I

EXAMPLE 2

Use of silica S to improve the impact resistance of a polypropylene thermoplastic material (incorporation of silica into the material by means of an extruder)

Silica S was used as a mineral filler for the improvement of the impact resistance of a polymer material having generally the same formulation as that of Example 2, but differing by the silica incorporation mode. More specifically, in this example, the polymeric material has the following Formulation (2):

polypropylene PPH 4060: 96.8%

- IRGANOX ^® B225 thermal stabilizer: 0.2%

- silica S: 3%

The incorporation of the silica in the material was carried out by introducing 2420 g of polypropylene, 5 g of thermal stabilizer and 75 g of silica S into a cube mixer and mixing for 10 minutes at 150 ^° C., and then introducing the mixture. in a WERNER twin screw extruder ZSK30 (die), with a temperature profile in the extruder of 168 ° C / 168 ^O C / 182 ^O C / ^188o C / 182 ° C, a speed of rotation of the screws co-rotating 230 rpm, and a feed rate of the constituents at the inlet adjusted to obtain a torque of 45% of the maximum torque of the extruder. The rod obtained on exiting the die was cooled and then cut into granules, then the obtained pellets were introduced into an injection mold ARBLJRG with a temperature profile of 180 ° C / ^180o C / ^180o C / ^180o C / 40 ° C, and an injection pressure set at 55% of the maximum pressure of the machine, so as to form a polymer plate.

On this polymer plate, as in the preceding example, several electron microscopy photos were taken at different locations on the basis of which the surface fraction FS 5 _μm was determined by image analysis under the specific conditions defined above in _FIG. the description. The surface fraction FS 5 _.mu.m thus measured is, in this example, 5.5%. Here again, the volume fraction FV of silica in the material is 1.4% (mass fraction of 3%). The FS _5μm / FV ratio of the material is therefore 4.

In addition, two parallelepiped test pieces of dimensions 80 mm × 4 mm × 10 mm were cut from the polymer plate, which were used as in Example 1: on the first specimen, the flexural modulus was measured in the conditions of ISO 178.

on a second test piece, the fracture energy was measured according to the Charpy impact test at 23 ° C. on a notched specimen, under the conditions of the ISO 179. Furthermore, a dumbbell test specimen was also cut out. to determine elongation at break in tension according to ISO 527.

The dynamic scratch resistance properties of the material were also measured and a diamond stylet having an internal angle of 90 ° and a tip radius of 90 microns was moved on the surface of a sample of the material at the speed of 1 mm / s, applying a normal controlled force on the surface. This operation was carried out several times to make several scratches on the material with increasing applied forces (0.25N, 0.5N, 1N, 5N) until a scratch of at least 200 microns wide was obtained. being then analyzed using an ALTI SURF 500 profilometer to measure the topological characteristics of the stripes (depth, width, profile). The scratch depth was measured for an applied force of 1N, and the scratch hardness Hs for 100 microns (determined according to the formula Hs = 4F // 7D ² , where F is the normal force to be applied to create a dynamic crack of 100 microns thick and D denotes this scratch width of 100 microns).

For comparison, the same tests were performed on specimens prepared under the same conditions, but from a control formulation (T2) without silica.

The results obtained are reported in Table II below, which shows that, again, the incorporation of silica into the polymer material induces both an increase in the impact resistance and stiffness, with, in addition an increase in elongation at break in tension.

Table II

Table II (continued)

In this example, the optical properties of the two materials were also compared using a MINOLTA CM508 spectrophotometer. The results obtained are reported in Table III below, from which it appears that the two materials have similar optical qualities.

Table III

L *: luminance on a black background a *: colorimetric index (red-green axis) b *: colorimetric index (yellow-blue axis) contrast: contrast black background / white background; reflects the light transmission properties

Claims

1. Use of a silica (S) having a BET surface area of at least 60 nrYg, and which can be obtained by a process (P) comprising the reaction of a silicate with an acidifying agent by which a suspension of silica is obtained, then the separation and drying of this suspension, and the reaction of the silicate with the acidifying agent is carried out according to the following successive steps:

(i) forming an aqueous starch having a pH of from 2 to 5;

(ii) adding to said cell base, simultaneously, silicate and acidifying agent, such that the pH of the reaction medium is maintained between 2 and 5, preferably between 2.5 and 5;

(iii) stopping the addition of the acidifying agent while continuing the addition of silicate in the reaction medium until a pH value of the reaction medium of between 7 and 10 is obtained; (iv) silicate and acidifying agent are added simultaneously to the reaction medium, so that the pH of the reaction medium is maintained between 7 and 10; and

(v) stopping the addition of the silicate while continuing the addition of the acidifying agent in the reaction medium until a pH value of the reaction medium of less than 6 is obtained, as a mineral filler in a thermoplastic polymer material, for increasing the rigidity of said material while maintaining or improving its impact resistance.

2. Use according to claim 1, wherein in step (ii) of the method P, the addition of the acidifying agent and the silicate is carried out in such a way that the pH of the reaction medium is maintained between 3 and 4.5. for example between 3.5 and 4.5 during the addition.

3. Use according to claim 1 or claim 2, wherein the simultaneous addition of step (ii) of the method P is carried out in such a way that the pH value of the reaction medium is constantly equal to the pH value reached. at the end of step (i), to within ± 0.2 unit.

4. Use according to any one of claims 1 to 3, wherein in step (iv) of the method P, the addition of the acidifying agent and the silicate is carried out in such a way that the pH of the reaction medium is maintained 7.5 and 9.5, for example between 7.5 and 8.5.

5. Use according to claim 6, wherein the simultaneous addition of step (iv) of the method P is carried out in such a way that the pH value of the reaction medium is constantly equal to a pH value of 7.5 and 9. , 5, within ± 0.2 units.

6. Use according to any one of claims 1 to 7, wherein in the method P, the drying of the suspension is by atomization.

7. Use according to one of claims 1 to 6, wherein the silica (S) is obtainable by a process comprising the following successive steps

(i) forming an aqueous starch having a pH of from 3 to 4.5, preferably from 3.5 to 4.5; (ii) at the same time, silicate and acidifying agent are added to said base stock so that the pH of the reaction medium is maintained at the value reached at the end of step (i) at ± 0 , 2 unit close;

(iii) stopping the addition of the acidifying agent while continuing the addition of silicate in the reaction medium until a pH value of the reaction medium of between 7 and 9.5 is obtained, preferably between 7.5 and 9.5;

(iv) silicate and acidifying agent are added simultaneously to the reaction medium, so that the pH of the reaction medium is maintained at the value reached at the end of step (iii) at ± 0, 2 unit close; (v) stopping the addition of the silicate while continuing the addition of the acidifying agent in the reaction medium until a pH value of the reaction medium of between 3 and 5.5 is obtained, preferably between 5 and 5.5;

(vi) the medium is allowed to ripen; (vii) filtering the silica suspension obtained at the end of step (vi), whereby a filter cake is obtained;

(viii) the filter cake is disintegrated mechanically in the presence of sodium aluminate;

(ix) the resulting cake is dried.

8. Use of a silica (S1) having the following characteristics:

a BET specific surface area of between 60 and 550 nfYg;

a CTAB specific surface area of between 40 and 525 m ² / g;

an object size distribution width Ld ((d84-d16) / d50) measured by XDC granulometry after ultrasound deagglomeration of at least 0.91, and

a distribution of the pore volume such that the ratio V (d5-d5θ) / V (d5-dioo) is at least 0.66,

as a mineral filler in a thermoplastic polymer material, for increasing the rigidity of said material while maintaining or improving its impact resistance.

9. Use according to claim 8, wherein the silica (S1) is a silica obtained according to the method P as defined in claim 1.

Use according to claim 8 or claim 9, wherein the silica (S1) has: - a width Ld ((d84 - d16) / d50) of object size distribution measured by XDC granulometry after ultrasonic deagglomeration at least

1, 04; and a distribution of the pore volume as a function of the pore size such that the ratio V ( _d 5 -d 5 O) A / ( _d 5-dioo) is at least 0.71.

11. Use of a silica (S2) having the following characteristics:

a BET specific surface area of between 60 and 550 m ² / g; a CTAB specific surface area of between 40 and 525 m ² / g; and

a porous distribution width Idp greater than 0.70,

as a mineral filler in a thermoplastic polymer material, to increase the rigidity of said material while maintaining or improving its impact resistance.

12. Use according to claim 11, wherein the silica (S2) is a silica obtained according to the method P as defined in claim 1.

Use according to claim 11 or claim 12, wherein the silica (S2) has a porous distribution width Idp greater than 0.80.

The use according to any one of claims 11 to 13, wherein the silica (S2) further has a width Ld ((d84 - d16) / d50) of object size distribution measured by XDC granulometry after deagglomeration with ultrasonic waves. 'at least 0.91

15. Use of a silica (S3) having the following characteristics:

a width of the d ((d84-d16) / d50) of an object size distribution of less than 500 nm, measured by XDC particle size after deagglomeration with ultrasound, of at least 0.95;

a distribution of the pore volume such that the ratio V (d5-d5θ) A / (d5-dioo) of at least 0.71, as a mineral filler in a thermoplastic polymer material, to increase the rigidity of said material while maintaining or improving its impact resistance.

16. Use according to claim 15, wherein the silica (S3) is a silica obtained according to the method P as defined in claim 1.

Use according to claim 15 or claim 16, wherein the silica (S3) has a ratio V (d5-d50) / V (d5-d100) of at least 0.73.

18. Use of a silica (S4) having the following characteristics:

a width d ((d84-d16) / d50) of an object size distribution of less than 500 nm, measured by XDC particle size after deagglomeration with ultrasound, of at least 0.90, in particular of at least 0.92; and

a distribution of the pore volume such that the ratio V (d5-d5θ) A / (d5-dioo) of at least 0.74,

19. Use according to claim 18, wherein the silica (S4) is a silica obtained according to the method P as defined in claim 1.

Use according to claim 18 or claim 19, wherein the silica (S3) has a ratio V (d5-d50) / V (d5-d100) of at least 0.78.

21. Use according to any one of claims 1 to 20, wherein the silica used (S, S1, S2, S3 or S4) has: a BET specific surface area between 70 and 350 m ² / g; and a CTAB specific surface area of between 60 and 330 m ² / g.

22. Use according to any one of claims 1 to 20, wherein the silica used (S, S1, S2, S3 or S4) has:

a BET specific surface area of between 60 and 400 m ² / g; and

a CTAB specific surface area of between 40 and 380 m ² / g.

23. Use of a silica (S ₀ ) having a BET surface area of at least 60 m ² / g, and present in the polymer essentially in the form of dispersed objects having a size less than 5 microns, as a filler mineral material in a thermoplastic polymer material to increase the stiffness of said material while maintaining or improving its impact resistance.

24. Use according to claim 23, wherein the silica (So) is a silica (S, S1, S2, S3, or S4) as defined in one of claims 1 to 22.

25. Use according to claim 23 or claim 24, wherein the silica (S ₀ ) has a BET specific surface area of between 60 and 300 m ² / g, for example between 100 and 250 m ² / g.

26. Use according to any one of claims 23 to 25, wherein the silica (So) used is present in the material in the form of aggregates, agglomerates and / or particles of which at least 90% by number have dimensions less than 1. micron, the rest of the particles having dimensions less than 10 microns.

27. Use according to any one of claims 23 to 26, wherein the silica (S ₀ ) is dispersed in the form of objects of which at least 80% in number have dimensions of between 30 nm and 1000 nm.

28. Use according to claim 27, to increase the stiffness of the polymer while improving its impact resistance.

29. Use according to any one of claims 23 to 28, wherein the FS _5μm / FV ratio of the surface fraction (FS _5μm ) of the volume occupied by objects larger than 5 .mu.m on scanning electron micrographs carried out on several flat sections of the material obtained by ultracryotomy, relative to the volume fraction (FV) of silica in the material is less than or equal to 4, preferably less than or equal to 3.

30. Use according to one of the preceding claims, wherein the silica used (S, S1, S2, S3, S4, or S ₀ ) has a BET specific surface area of between 60 and 300 m ² / g, for example between 100 and 250 m ² / g.

31. Use according to one of the preceding claims, wherein the silica used (S, S1, S2, S3, S4, or So) is in powder form.

32. Use according to one of the preceding claims, wherein the thermoplastic polymer material is based on one or more polymers chosen from polyolefins, polyamides, polyesters, poly (arylene) oxides, polyvinyl chlorides, polychloride. vinylidene, polyvinyl acetate, blends of these polymers and copolymers based on these polymers.

33. Use according to one of the preceding claims, wherein the silica (S, S1, S2, S3, S4, or S ₀ ) is introduced into the thermoplastic polymer material in a content of between 0.5% and 10% by weight. , relative to the total mass of the thermoplastic polymer material including silica.

34. Use according to one of the preceding claims, wherein the thermoplastic polymer material is based on one or more polyolefins.

The use of claim 34, wherein the thermoplastic polymeric material comprises:

a homopolyolefin selected from polyethylene, polypropylene, polybutylene, or poly (methylpentene);

a copolymeric polyolefin based on at least two types of units chosen from ethylene, propylene, butylene and methylpentene units; or

a mixture of two or more of said homopolyolefins and / or said copolymeric polyolefins.

36. Use according to claim 35, wherein the thermoplastic polymer material is based on polypropylene or a copolymer of propylene and ethylene.

37. Use according to one of the preceding claims, wherein the silica is introduced into the thermoplastic polymer material in a content of between 0.5% and 10% by weight, relative to the total weight of the thermoplastic polymer material including silica.

38. thermoplastic polymer material comprising a silica (S, S1, S2, S3, S4, _0, or S) as defined in one of claims 1 to 27 as a mineral filler improving the impact resistance.

39. Thermoplastic polymer material according to claim 38, comprising one or more polyolefins as a major constituent.