KR100260328B1 - Novel method for preparing precipitated silica, novel zinc-containing precipitated silicas, and use thereof for reinforcing elastomers - Google Patents

Abstract

The present invention relates to a new process for producing precipitated silica with good dispersibility and very satisfactory reinforcement. The present invention also relates to novel precipitated silica in the form of a powder, substantially round beads or granules. The silica has a CTAB specific surface area of 90-250 m ² / g, BET specific surface area of 90-250 m ² / g, DOP oil absorption of 300 ml / 100 g or less, and zinc content of 1-5 wt% And the number N of stearic acid molecules consumed per 1 nm ^{2 of} silica surface is characterized by being at least 1 when stearic acid is reacted with a xylene solution of the silica at 120 ° C. for 2 hours. In addition, the present invention also relates to the use of such silicas as reinforcing fillers for elastomers, in particular for the purpose of enhancing their rheological properties.

Description

NOVEL METHOD FOR PREPARING PRECIPITATED SILICA NOVEL ZINC-CONTAINING PRECIPITATED SILICAS, AND USE THEREOF FOR REINFORCING ELASTOMERS

It is well known that precipitated silica has long been used as the white reinforcing filler for elastomers.

However, as with any other reinforcing filler, this is suitable if it is easy to handle on the one hand and, above all, easily homogeneous in the mixture.

In order to obtain the optimum reinforcement imparted by the filler, it is generally known that it is appropriate that the filler be present in the elastomer matrix in the final form as finely pulverized as possible and distributed as homogeneously as possible. However, these conditions, on the one hand, are very good in terms of the ability of the filler to be homogeneously mixed in the matrix during mixing with the elastomer (homogeneous mixing of the filler), which can be collapsed or deagglomerated in the form of very fine powders. It should be very good in terms of performance (disintegration of the filler), and on the other hand, it can only be achieved if the powder produced during the disintegration process is completely and uniformly dispersed (dispersibility of the powder) in the elastomer itself. .

Moreover, due to mutual affinity, the silica particles have an undesirable tendency to aggregate with each other in the elastomer matrix. These silica / silica interactions have the decisive consequence of limiting the reinforcement to a level substantially below the theoretically possible values, except where all silica / elastomer interactions are actually obtained, which can occur during the mixing process ( Theoretical figures of this silica / elastomer interaction, as is well known, are directly proportional to the outer surface of the silica used).

Moreover, in the raw state, such silica / silica interactions tend to increase the stiffness and consistency of the mixture and thus make its processing more difficult.

While the size can be relatively large, there is a problem of improving the rheological properties of the elastomer and advantageously obtaining a filler having good dispersibility in the elastomer.

The present invention relates to a new process for the production of precipitated silica, in particular precipitated silica in the form of powder, substantially in the form of beads or granules, and its application as reinforcing fillers of elastomers.

An object of the present invention is to overcome the above disadvantages and the above problems.

More precisely, the object of the present invention is advantageously very good dispersibility (and disintegration) and very satisfactory reinforcement, especially when used as a reinforcing filler of an elastomer, to impart good mechanical properties. At the same time, it is to propose a new method for producing precipitated silica that gives good rheological properties.

In addition, the present invention is relatively large in size and has good dispersibility (and disintegration), very satisfactory reinforcement, and preferably in the form of powder, substantially spherical beads or, optionally, granules. Phosphorus precipitated silica.

Finally, the present invention relates to the use of the precipitated silica as a reinforcing filler for elastomers.

In the following specification, the BET specific surface area is listed in the Journal of the American Chemical Society, Volume 60, page 309 (February 1938) and corresponds to NFT standard 45007 (November 1987). As determined by the Brunauer-Emmett-Teller law.

CTAB specific surface area is the external surface area determined according to NFT standard 45007 (November 1987) (5.12).

DOP oil uptake is measured according to NFT standard 30-022 (March 1953) using dioctyl phthalate.

Packing density (PD) is measured according to NFT standard 030100.

The pH is measured according to ISO standard 787/9 (the pH of the suspension at 5% aqueous solution concentration).

Finally, a given micropore volume is measured by a mercury porosimetry, and the micropore diameter can be calculated from the Washburn relationship of 130 ° contact angle θ and surface tension γ of 484 dyne / cm (Micromeritics 9300 porosimeter).

The dispersibility and disintegration properties of the silicas according to the invention can be quantified by non-collapse tests.

The collapse test is carried out according to the following method:

Assessing the aggregation of aggregates by particle size measurement (using laser scattering method) in silica suspensions previously disintegrated by sonication; The disintegration of the silica is measured (breaking the material up to 0.1 to several tens of microns). Ultrasonic disruption is performed using a Vibracell Bioblock (600 W) sonic transducer equipped with a 19 mm diameter probe. Particle size measurements are performed by laser scattering on a Sympatec particle size analyzer.

2 g of silica was weighed into a sample tube (height: 6 cm, diameter: 4 cm) and desalted water was added to make 50 g or less; An aqueous suspension containing 4% silica is prepared, which is homogenized by magnetic stirring for 2 minutes. Ultrasonic collapse is then carried out as follows: With a probe immersed at a depth of 4 cm, the output is adjusted so that the needle deflection on the output dial is 20% (this is 120 watts / scattered by the end of the probe). corresponds to an energy of cm ² ). Run the decay for 420 seconds. Subsequently, a homogeneous suspension of known volume (expressed in ml) is introduced into the cell of the particle size analyzer, followed by measurement of the particle size.

The median diameter Φ ₅₀ obtained is proportionally smaller as the degree of disintegration of silica is higher. In addition, the ratio of the optical density (optical density of about 20) of the suspension detected by (volume (in ml) x 10) of the introduced dispersion / particle size analyzer is determined. This ratio is an index indicating the proportion of fine particles, ie, particle content below 0.1 μm, which is not detected by the particle size analyzer. This ratio, called the ultrasonic decay index (F _D ), increases proportionally as the higher the degree of disintegration of silica.

Another subject of the invention is a process for preparing precipitated silica of the type comprising reacting an acidifying agent with a silicate, thereby obtaining a suspension of precipitated silica, and then separating and drying the suspension, wherein precipitation is carried out in the following manner. :

(i) forming an initial basal liquor containing silicate and an electrolyte, wherein the silicate concentration of the initial basal liquor (denoted as SiO ₂ ) is 100 g / l or less and the electrolyte concentration of the initial basal liquor is 17 g / l or less,

(ii) adding an acidulant to said basal stock to bring the pH of the reaction mixture to at least approximately 7,

(iii) simultaneously adding an acidifying agent and a silicate to the reaction mixture,

And drying the suspension having a solids content of 24% by weight or less, which method comprises the following two operations (a) or (b):

(a) adding at least one zinc compound to the reaction mixture after step (iii) and then adding a base agent, if said separation involves filtration and the collapse of the mass resulting from this filtration, the collapse Preferably carried out in the presence of at least one aluminum compound,

(b) adding the silicate and the at least one zinc compound simultaneously to the reaction mixture after step (iii) and if the separation involves filtration and the collapse of the mass resulting from this filtration, the collapse is preferably at least one Operation carried out in the presence of an aluminum compound.

Its feature is that it includes one of the following.

Thus zinc combined with low concentrations of silicate (represented by SiO ₂ ) in the initial basal liquor, which is according to a particular method, and the appropriate solids content of the suspension to be introduced and dried, are of good properties, in particular remarkable, to the product obtained. It has been found that important conditions are imparted to impart dispersibility and very satisfactory reinforcement (particularly for the rheology of the elastomer).

In general, it is worth noting that the relevant method is the method of synthesizing precipitated silica, i.e., the acidifying agent reacts with the silicate under very specific conditions.

The choice of acidifier and silicate is by known methods.

It will be appreciated that the acidifiers generally used are strong inorganic acids such as sulfuric acid, nitric acid or hydrochloric acid, or organic acids such as acetic acid, formic acid or carbonic acid.

The acidifying agent may be diluted or concentrated, and its normal concentration may be 0.4 to 36 N, such as 0.6 to 1.5 N.

In particular, when the acidifier is sulfuric acid, the concentration may be 40 to 180 g / l, such as 60 to 130 g / l.

Furthermore, as silicates it is possible to use any form of silicates such as metasilicates, disilicates and advantageously alkali metal silicates, in particular sodium or potassium silicates.

The silicates may exhibit concentrations of 40 to 330 g / l, such as 60 to 300 g / l, in particular 60 to 250 g / l, based on silica.

It is common to use sulfuric acid as the acidifier and sodium silicate as the silicate.

When using sodium silicate, it is common for the SiO ₂ / Na ₂ O weight ratio to be 2-4, such as 3.0-3.7.

As far as the production process of the invention is concerned in particular, sedimentation is carried out in a special manner according to the following steps.

First of all, a basic stock solution containing some silicate and electrolyte is prepared (step (i)). It is advantageous that the amount of silicate present in the initial basal liquor is only a fraction of the total amount of silicate introduced into the reaction.

The term electrolyte is used herein in its usual sense, that is to be understood as referring to any ionic or molecular material that will disintegrate or dissociate in solution to form ions or charged particles. The electrolytes which may be mentioned include salts selected from the group consisting of alkali metal and alkaline earth metal salts, in particular sodium sulfate in the reaction of metal salts of the starting silicates with acidifying agents such as sulfuric acid and sodium silicate.

One feature of the production process according to the invention is that the concentration of the electrolyte in the initial basal liquor is at least 0 g / l and at most 17 g / l, preferably at most 14 g / l.

Another feature of the production process according to the invention is that the silicate concentration in the initial basal liquor is 100 g or less (at least 0 g / l and) per liter of SiO ₂ . This concentration is preferably 90 g / l or less, in particular 85 g / l or less. In some cases, it may be 80 g / l or less.

The second step consists in adding an acidulant to the basal stock of the composition described above (step (ii)).

This addition is accompanied by a corresponding drop in pH of the reaction mixture, which is carried out until a pH value of at least approximately 7, generally 7-8, is obtained.

Once the desired pH value is reached, the simultaneous addition of acidifying agent and silicate is carried out (step (iii)).

This simultaneous addition is preferably carried out so that the pH value is continuously the same (in the range of +/- 0.1) as reached in the last step of step (ii).

According to a very important feature of the production method of the present invention, the production method comprises one of the two operations (a) or (b) described above:

(a) adding at least one zinc compound to the reaction mixture after step (iii) and then adding a base agent, if the separation used in the process involves filtration and the collapse of the mass from the filtration. , Performing the decay preferably in the presence of at least one aluminum compound,

(b) adding silicate and at least one zinc compound simultaneously to the reaction mixture after step (iii), and if said separation used in the process involves filtration and the collapse of the mass resulting from this filtration, the collapse Preferably carried out in the presence of at least one aluminum compound.

In a first other form of method of the manufacturing method according to the invention (ie, when the method comprises operation (a)), the following series of steps comprise steps (i), (ii) as described above And after carrying out the precipitation according to (iii), it is advantageous:

(iv) adding at least one zinc compound to the reaction mixture (ie the reaction mixture or slurry obtained),

(v) adding a base agent to the reaction mixture, preferably bringing the pH of the reaction mixture to 7.4 to 10, in particular 7.8 to 9,

(vi) adding an acidifying agent to the reaction mixture, preferably bringing the pH of the reaction mixture to at least 7, in particular from 7 to 8.5, for example from 7 to 8.

It may be advantageous to age the reaction mixture after the simultaneous addition in step (iii), for example by sustaining the maturation for 1 to 60 minutes, in particular 3 to 30 minutes.

In a first alternative method, it may be desirable to add an additional amount of acidifying agent to the reaction mixture between step (iii) and step (iv), especially before the selective maturing above. Such addition is usually carried out until the pH of the reaction mixture reaches 3 to 6.5, in particular 4 to 6.

The acidifiers used during this addition are generally the same as those used during steps (ii), (iii) and (vi) of the first other form of the production process according to the invention.

The maturing of the reaction mixture is usually carried out between steps (v) and (vi), in particular from 2 to 60 minutes, in particular from 5 to 45 minutes.

Similarly, the maturing of the reaction mixture is in most cases carried out after step (vi), for example 2 to 60 minutes, in particular 5 to 30 minutes.

The base agent used during step (iv) may be an aqueous ammonia solution or, preferably, a sodium hydroxide (or soda) solution.

In another second form of the production process according to the invention (i.e. comprising process (b)), step (iv) is followed by steps (i), (ii) and (iii) as described above. This step consists in adding the silicate and one or more zinc compounds to the reaction mixture at the same time.

It may be advantageous to carry out the aging of the reaction mixture after the simultaneous addition of step (iv), which may for example last for 2 to 60 minutes, in particular 5 to 30 minutes.

In this second alternative form of process, it may be desirable to add an additional amount of acidifying agent to the reaction mixture after step (iv), in particular after such selective ripening. Such addition is usually carried out until the pH of the reaction mixture reaches 7 or more, in particular 7 to 8.5, for example 7 to 8.

The acidifiers used during this addition are generally the same as those used during steps (ii) and (iii) of the second, different form of the production process according to the invention.

After addition of the acidifying agent, it is common to carry out the aging of the reaction mixture, for example for 1 to 60 minutes, in particular for 3 to 30 minutes.

The zinc compound used in the production process according to the invention is usually an organic or inorganic zinc salt.

Examples of organic salts may in particular mention salts of carboxylic acids or polycarboxylic acids, such as acetates, citrates, tartarates or oxalates and the like.

As examples of inorganic salts, halides and oxyhalides (chlorides and oxychlorides), nitrates, phosphates, sulfates and oxysulfates and the like can be mentioned.

In practice, the zinc compound can be used in the form of a solution, usually an aqueous solution.

It is preferable to use zinc sulfate as the zinc compound.

The temperature of the reaction mixture is generally 70 to 98 ° C.

According to another aspect of the present invention, the reaction is carried out at a constant temperature of 75 to 96 ℃.

According to another (preferred) form of the invention, the temperature at the end of the reaction is higher than the temperature at the beginning of the reaction; It is preferable that the temperature of the reaction initial stage is maintained at 70-96 degreeC; It is preferable to raise the temperature for several minutes, preferably 80 to 98 ° C. or lower, and to maintain this temperature until the end of the reaction; Operation (a) or (b) is therefore usually carried out at this constant temperature value.

As a result of the steps just described a silica slurry is obtained which is then separated (liquid-solid separation).

In a first alternative form of production process according to the invention (i.e. comprising operation (a)), the separation process generally comprises filtration (with washing if necessary) and collapse, The decay is preferably carried out in the presence of at least one aluminum compound, preferably in the presence of an acidifying agent as described above (in this latter case it is advantageous to add the aluminum compound and the acidifying agent simultaneously). .

The decay operation can be carried out, for example, by passing the filter mass in the form of a colloid or bead through a grinder, in particular making it possible to lower the viscosity of the suspension to be dried later.

In a second, different form of the production process according to the invention (ie, in the case of operation (b)), the separation process generally comprises filtration (with washing if necessary) and decay. Is preferably carried out in the presence of at least one aluminum compound and, in general, in the presence of an acidifying agent as described above (in this latter case it is advantageous to add the aluminum compound and the acidifying agent simultaneously).

Aluminum compounds generally consist of alkali metals, in particular potassium, or very preferably sodium, aluminate.

The amount of the zinc compound used in the production process according to the invention is preferably such that it contains 1 to 5% by weight, in particular 1.5 to 4% by weight, such as 1.5 to 2.5% by weight, of zinc in the precipitated silica produced.

The separation process used in the production process of the present invention generally includes filtration performed using a suitable method, such as a belt filter, a rotary vacuum filter or, preferably, a filter press.

The suspension (filtration mass) of the recovered precipitated silica is then dried.

According to one feature of the production process according to the invention, this suspension should have a solids content of up to 24% by weight, preferably up to 22% by weight, immediately before drying.

Such drying can be carried out by any method known in the art.

Drying is preferably carried out by a nebulizer.

Examples of suitable sprayers that can be used for this purpose are in particular turbines, nozzles, hydraulic or two-fluid sprayers and the like.

According to one embodiment of the invention, the solids content of the suspension to be dried is at least 15% by weight, preferably at least 17% by weight, such as at least 20% by weight. At this time, the drying is preferably performed using a multi-nozzle sprayer.

According to an embodiment of the present invention, the precipitated silica obtainable, preferably using a filter press, is advantageously in the form of a substantially round bead, preferably having an average size of at least 80 μm.

It should be noted that dry matter, for example silica in pulverized form, may also be added to the filter mass after filtration in a subsequent step of the process.

After drying, a grinding step is carried out on the recovered product, in particular on the product obtained by drying the suspension with a solids content of at least 15% by weight. The precipitated silica obtainable at this time is generally in the form of a powder having an average size of at least 15 μm, in particular 15 to 60 μm, such as 20 to 45 μm.

The grinding product of the desired particle size can be separated from the ineligible product, for example, by using a vibrating screen with a suitable mesh size, so that the recovered ineligible product can be subjected to the grinding step again.

Likewise, according to another preferred embodiment of the invention, the suspension to be dried has a maximum of 15% by weight of solid components. At this time, the drying is generally performed using a turbine sprayer. According to this embodiment of the invention, preferably, the precipitated silica obtainable using a rotary vacuum filter is in the form of a powder having an average size of at least 15 μm, in particular from 30 to 150 μm, such as 45 to 120 μm. It is common.

Finally, the dried (particularly in suspensions with up to 15% by weight of solids) or ground product can be subjected to a flocculation step, according to another embodiment of the invention.

Coagulation means here a process by which the finely divided objects can be combined with one another to form larger and mechanically stronger objects.

Such processes include, inter alia, direct compression, wet type granulation (ie by the use of binders such as water, silica slurries), extrusion and, preferably, dry compression.

Using this last technique, before entering the compression step, the air of the grinding product (also called predense or degassing) is removed to remove the air contained therein and to ensure a more uniform compression. Giving can be advantageous.

Precipitated silica obtainable according to an embodiment of the invention is advantageously in the form of granules which are at least 1 mm in size, in particular 1 to 10 mm.

At the end of the coagulation step the product can be sorted by desired size, for example by screening, and then packaged for later use.

Not only the beads of the precipitated silica obtained by the process according to the invention but also powders are, among other things, in a simple, efficient and economical method, in particular by conventional molding operations, for example, granulation or compression. It provides the advantage of obtaining granules as described above and can block or even extinguish the good intrinsic properties associated with the powder or the beads, which may be in the prior art when using conventional powders. There is no cause of even collapse.

Other subjects of the present invention advantageously provide good mechanical properties while imparting good rheological properties to the elastomers, especially when used as reinforcing fillers of elastomers, having good dispersibility (and disintegration) and very satisfactory reinforcement. Is in the new precipitated silica.

therefore,

CTAB specific surface area of 90 m ² / g to 250 m ² / g, for example 120 m ² / g to 230 m ² / g,

A BET specific surface area of 90 m ² / g to 250 m ² / g, for example 120 m ² / g to 240 m ² / g,

The DOP oil intake is 300 ml / 100 g or less, preferably 200 ml / 100 g to 295 ml / 100 g,

Zinc content is from 1% to 5% by weight, preferably from 1.5% to 4% by weight,

And the number N of stearic acid consumed per 1 nm ² of silica surface is at least 1, preferably at least 1.2, in particular at least 1.5 when the stearic acid is reacted with the xylene solution of silica at 120 ° C. for 2 hours. A new precipitated silica is now proposed, in accordance with the present invention.

The silica according to the invention preferably has a zinc content of 1.5 to 4% by weight; This content is particularly preferably 1.5 to 2.5% by weight.

One of the very important properties of the precipitated silica according to the invention is that it consumes one component of rubber vulcanization (stearic acid) in a typical medium (xylene).

Applicants have thus found that precipitated silica, exhibiting a certain number N, can, in conjunction with other properties mentioned herein, provide satisfactory mechanical properties, in particular giving the elastomer good rheological properties. .

To determine this property (number N), stearic acid is reacted at 120 ° C. for 2 hours in the presence of a xylene solution of silica. The amount of stearic acid remaining in the xylene after the reaction is then determined by infrared (IR) spectroscopy; The amount of stearic acid consumed by the silica can then be estimated and thus the number N of stearic acid molecules consumed per 1 nm ^{2 of} silica surface can be estimated.

The manipulations used to determine these properties are described in more detail below.

60.2 g (ie 70 ml) of xylene are added into a round bottom flask containing 3.17 g of stearic acid. Cap the flask and stir with magnet for several minutes.

Then 12.04 g of silica are added. The flask is placed under reflux in an oil bath at 120 ° C. (equipped with a condenser). The flask is then stirred with magnet for 105 minutes. The stirring is then stopped and the flask is left in the oil bath for another 15 minutes. The total reaction time at 120 ° C. is therefore 2 hours.

Remove the condenser and remove the flask from the oil bath.

The contents of the flask are filtered on a microfiltration system (Millipore device (micropore size: 0.45 μm) using a Durapore membrane filter made of polyvinylidene fluoride).

10 g of the filtrate obtained are then diluted in 10 g of xylene; Solution S is obtained.

In parallel, standard solutions of stearic acid are prepared (stearic acid content is 2% by weight or less) and their respective IR spectra (from 400 cm ⁻¹ to 4000 cm ⁻¹ ) are obtained. The characteristic peak of stearic acid is located at 1710 cm ⁻¹ . The intensity of this peak in relation to the stearic acid content of the solution makes it possible to graph the straight line of the stearic acid content of the solution as a function of the IR absorbance at 1710 cm ⁻¹ ; The equation of the calibration straight line is obtained by linear regression.

Similarly, the IR spectrum of solution S is obtained. The characteristic peaks of stearic acid in relation to the equation of the calibration straight line allow the determination of the content of stearic acid in solution S; The stearic acid content of the filtrate from the reaction is obtained by taking account of the amount of xylene added during dilution. The content of stearic acid consumed by silica during the reaction, and therefore the amount, is estimated from the initial stearic acid content and the stearic acid content after the reaction (the latter is the content of stearic acid in the filtrate). The number N of stearic acid molecules consumed per 1 nm ^{2 of} silica surface is then determined.

The zinc present in the precipitated silica according to the invention is preferably in an amorphous rather than crystalline form (which can be determined by X-ray diffraction).

According to another (preferred) form of the invention, the precipitated silica is:

CTAB specific surface area of 90 m ² / g to 185 m ² / g, in particular 120 m ² / g to 185 m ² / g, for example 140 m ² / g to 180 m ² / g,

The median diameter φ ₅₀ after collapse by ultrasonic waves is 4 μm or less, preferably 3 μm or less,

The ultrasonic disruption factor (F _D ) is at least 6 ml, preferably at least 10 ml

It is characterized by that.

The median diameter φ ₅₀ of the precipitated silica according to this another aspect of the invention after collapse by ultrasonic waves may be 2.8 μm or less, for example 2.5 μm or less.

The ultrasonic disruption factor (F _D ) of the precipitated silica according to this another form of the invention may be at least 11 ml, for example at least 14 ml.

The BET specific surface area of the precipitated silica according to this another form of the invention is generally 90 m ² / g to 195 m ² / g, in particular 120 m ² / g to 195 m ² / g, for example 150 m ² / g To 190 m ² / g.

According to another form of the invention, the precipitated silica is:

-CTAB specific surface area not less than 185 m ² / g and not more than 220 m ² / g,

The median diameter φ ₅₀ after collapse by ultrasonic waves is 7 μm or less, preferably 5.5 μm or less

It is characterized by that.

The median diameter φ ₅₀ of the precipitated silica according to this another aspect of the invention after collapse by ultrasonic waves may be 4 μm or less.

The ultrasonic disruption factor (F _D ) of the precipitated silica according to this another form of the invention may be at least 6 ml.

The BET specific surface area of the precipitated silica according to this other form of the invention is generally from 185 m ² / g to 230 m ² / g.

According to one particular embodiment of the invention, one of the properties of silica is in the distribution, or dispersion, of the micropore volume, in particular in the distribution of the micropore volume formed by micropores having a diameter of 400 mm 3 or less. This micropore volume corresponds to the useful micropore volume of the filler used to reinforce the elastomer. Silica according to a particular method of the present invention exhibits a micropore volume consisting of micropores having a diameter of 175 to 275 mm 3 and at least 50%, such as at least 60% of the micropore volume consisting of micropores having a diameter of 400 mm 3 or less. It can be seen through the analysis of microporosity to have a micropore distribution.

According to another highly preferred form of the invention, the ratio of the BET specific surface area / CTBA specific surface area of silica exhibits 1.0 to 1.2, ie preferably very low micromicroporosity.

The pH of the silica according to the invention is generally 8.0 to 9.0, such as 8.3 to 8.9.

The silicas according to the invention can be in the form of powders, substantially spherical beads or, in some cases, granules, and in particular are relatively large in size and very satisfactory reinforcement, and preferably good dispersibility and disintegration properties. It has that feature. Thus, they can exhibit very good dispersibility and disintegration that are advantageous over those of prior art silicas of the same or near specific surface area and size.

The silica powder according to the invention preferably has an average size of at least 15 μm; This average size is, for example, 15 to 60 μm (particularly 20 to 45 μm) or 30 to 150 μm (particularly 45 to 120 μm).

These, Preferably, it is preferable that DOP oil absorption amount is 240-290 ml / 100g.

The packing density (PD) of the powder is generally at least 0.17, for example 0.2 to 0.3.

The powders generally have a total micropore volume of at least 2.5 cm ³ / g, more particularly 3 to 5 cm ³ / g.

They make it possible in particular to obtain a very good compromise between workability and mechanical properties in the vulcanized state.

They are also preferred precursors for the synthesis of the granules described later.

Substantially spherical beads according to the invention preferably have an average size of at least 80 μm.

According to another aspect of the present invention, this average bead size is at least 100 μm, such as at least 150 μm, generally at most 300 μm, preferably 100 to 270 μm. This average size is measured according to NF standard X 11507 (December 1970) by dry screening and measurement of diameters corresponding to cumulative transient sizes of at least 50%.

They preferably have a DOP oil absorption of 240 to 290 ml / 100 g.

The packing density (PD) of the beads (or pearls) is generally at least 0.17, such as 0.2 to 0.34.

They generally have a total micropore volume of at least 2.5 cm ³ / g, more particularly of 3 to 5 cm ³ / g.

As noted above, silica in the form of substantially spherical beads, which are advantageously solid, uniform, low in impurity and good in fluidity, has excellent disintegration and dispersibility. This also shows good reinforcement. Such silicas are also one of the preferred precursors for the synthesis of powders or granules according to the invention.

Such silica in substantially spherical bead form constitutes another very advantageous form of the invention.

The dimension of the granules according to the invention is preferably at least 1 mm, in particular 1 to 10 mm, along the axis of its longest dimension (length).

They preferably have a DOP oil absorption of 200 to 260 ml / 100 g.

The granules can have a wide variety of shapes. Shapes that may be specifically mentioned are, for example, spheres, cylinders, cubes, tablets, flakes, spherical or polylobed precipitates and extrudates.

The packing density (PD) of the granules is generally at least 0.27 and may reach up to 0.37.

They generally have a total micropore volume of at least 1 cm ³ / g, more particularly of 1.5 to 2 cm ³ / g.

The silica according to the invention, in particular in the form of powder or substantially spherical beads or granules, is preferably prepared according to one of the other suitable forms of the production process according to the invention described above.

The silicas according to the invention or the silicas produced by the process according to the invention can be particularly advantageously applied to the reinforcement of natural or synthetic elastomers. They give good elastomeric properties, generally good wear resistance, while giving the elastomer excellent rheological properties. In addition, it is preferable that these elastomers are not easy to be heated.

The present invention therefore also relates to the use of said silicas for use in improving the rheological properties of elastomers (described for example by Mooney consistency, minimum torque, etc.).

The following examples illustrate the invention in detail, but do not limit the scope of the invention.

Example 1 (comparative)

Silica (referenced A1) is prepared according to Example 12 of European Patent Application EP-A-0520862 (Application No. 92401677.7).

The properties of silica A1 obtained in the form of substantially round beads are as follows:

-CTAB specific surface area 160 m ² / g

-BET specific surface area 170 m ² / g

-DOP oil suction 276 ml / 100 g

Zinc weight content 〈0.005%

-micropores with d ≤ 400 Å

Indicated micropore volume V1 0.90 cm ³ / g

-Micropores with 175 2 ≤ d ≤ 275 Å

Micropore volume V2 0.55 cm ³ / g

61% V2 / V1 ratio

pH 6.5

-Average particle size 260 μm

The number N of stearic acid molecules consumed per 1 nm ² of the silica surface is 0.5 when stearic acid is reacted with the xylene solution of silica A1 at 120 ° C. for 2 hours (according to the operating procedure outlined in the specification).

This silica A1 is subjected to the collapse test as defined above in the specification.

After disintegration by ultrasonic waves it has a median diameter of 4.3 μm (φ ₅₀ ) and an ultrasonic disintegration factor (F _D ) of 6.5 ml.

Example 2

The following is introduced in a stainless steel reactor equipped with a stirring system using a propeller and a heating system using a jacket:

-624 liters of water

-Na ₂ SO ₄ 11.2 kg

310 liters of an aqueous sodium silicate solution having a SiO ₂ / Na ₂ O weight ratio of 3.45 and a relative density of 1.230 at 20 ° C.

The silicate concentration in the initial base stock solution is 79 g / l when expressed by SiO ₂ . The mixture is then stirred while heating to a temperature of 80 ° C. Dilute sulfuric acid with a relative density of 1.050 at 20 ° C. is then introduced at a flow rate of 7.0 l per minute to obtain a pH value 8.0 (measured at its temperature) in the reaction mixture. The reaction temperature is 80 ° C. during the first 30 minutes; The temperature then rises from 80 ° C. to 94 ° C. in approximately 15 minutes and then held at 94 ° C. until the end of the reaction.

The reaction mixture was then subjected to an aqueous solution of sodium silicate of the above kind at a flow rate of 2.4 l per minute, and also of the aforementioned type, sulfuric acid, during the introduction period, the pH of the reaction mixture was continuously maintained at 8.0 ± 0.1. The flow rate is controlled so that it is introduced together for 30 minutes.

Next, after this simultaneous addition, an aqueous solution containing 85 g / l of zinc sulfate is introduced therein for 12 minutes at a flow rate of 9.3 l per minute. At the end of this addition an aqueous solution containing 180 g / l sodium hydroxide is introduced into the reaction mixture to bring the pH of the reaction mixture to 8.0.

The introduction of sodium hydroxide is then stopped and the reaction mixture is stirred for 10 minutes.

Sulfuric acid of the above kind is then introduced to bring the pH of the reaction mixture to 7.1.

The introduction of acid is then stopped and the reaction mixture is aged for 5 minutes at a temperature of 94 ° C.

Total reaction time is 128 minutes.

A slurry or suspension of precipitated silica is thus obtained, which is then filtered and washed with a filter press.

The resulting mass is then fluidized by mechanical and chemical action (simultaneous addition of sulfuric acid and sodium aluminate in an amount corresponding to an Al / SiO ₂ weight ratio of 0.20%). The resulting slurry after this decay operation is sprayed with a nozzle nebulizer, with a pH of 8.4 and an ignition loss of 78.0% (thus 22.0% by weight of solids).

The properties of silica P1 obtained in the form of substantially round beads are as follows:

-CTAB specific surface area 151 m ² / g

-BET specific surface area 158 m ² / g

-DOP oil suction 262 ml / 100 g

Zinc content 1.80%

-micropores with d ≤ 400 Å

Micropore volume indicative V1 0.92 cm ³ / g

-Micropores with 175 2 ≤ d ≤ 275 Å

Micropore volume V2 0.47 cm ³ / g

-V2 / V1 ratio 51%

pH 8.5

-Average particle size 260 μm

The number N of stearic acid molecules consumed per 1 nm ^{2 of} silica surface is 1.2 when stearic acid is reacted with the xylene solution of silica P1 at 120 ° C. for 2 hours (according to the operating procedure outlined in the specification).

This silica P1 is subjected to the collapse test as defined above in the specification.

After disintegration by ultrasound it has a median diameter (φ ₅₀ ) of 2.2 μm and an ultrasonic disintegration factor (F _D ) of 14.1 ml.

Example 3

This example specifically illustrates the use and function of silica according to the invention and silica not according to the invention in the formulation of industrial rubber.

The following combinations are used (parts expressed by weight):

-SBR rubber ⁽¹⁾ 50

-KBR01 Rubber ⁽²⁾ 25

-SMR5L natural rubber 25

Silica 51

Active ZnO ⁽³⁾ 1.82

-Stearic acid 0.35

-6DPD ⁽⁴⁾ 1.45

-CBS ⁽⁵⁾ 1.1

DPG ⁽⁶⁾ 1.4

Sulfur ⁽⁷⁾ 0.9

Silane X50S ⁽⁸⁾ 8.13

(1) Styrene Butadiene Copolymer Solution Buna VSL 1955 S25 Type

(2) polybutadiene

(3) rubber grade zinc oxide

(4) N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine

(5) N-cyclohexyl-2-benzothiazylsulfenamide

(6) diphenylguanidine

(7) vulcanizing agent

(8) Silica / Rubber Coupling Agents (marketed by Degussa)

The formulation is prepared in the following way:

In a sealed mixer [Banbury type], the following is introduced, in that order and at the time and temperature indicated in parentheses:

-SBR, KBR01 and natural rubber

(t ₀ ) (60 ° C)

-2/3 of X50S and silica (t ₀ + 1 min)

(80 ℃)

ZnO, stearic acid, 6PPD and 1/3 of silica (t ₀ + 2 min) (100 ° C.)

Release from the mixer (mixing droplets) occurs when the chamber temperature reaches 165 ° C. (ie at approximately t ₀ + 5 minutes 15 seconds). This blend is introduced into a roll mill and the roll is kept at 30 ° C. and rolled thereon. This mill introduces CBS, DPG and sulfur.

After homogenization and three good passes of the test, the final mixture is rolled in the form of sheets of thickness 2.5 mm to 3 mm.

The results of the test were as follows:

1-rheological properties

Measurements are taken on unprocessed blends.

The results are reported in Table 1 below. The apparatus used to perform the measurements is shown.

A1 P1 Mooney consistency ⁽¹⁾ 105 92 Torque (ln lb) ⁽²⁾ 25.0 20.8

(1) Mooney MV 2000E Viscometer (Money Broad (1 + 4) measurement at 100 ° C)

(2) Monsanto 100 S rheometer

The blend obtained from the silica according to the invention gives the lowest value results.

This shows even greater processability of the formulations prepared from the silica according to the invention, especially for the extrusion and rolling operations which are often carried out during the preparation of the elastomeric composition (a reduction in the energy costs for processing the formulations, of injection during formulation). Increased ease, reduced shrinkage during rolling, etc.).

2-mechanical properties

Measurements are made on vulcanized formulations.

Vulcanization is performed by heating the blend to 150 ° C. for 40 minutes.

The following criteria were used:

(i) Tensile test (tensile strength, elongation at break):

NFT 46-002 or ISO 37-1977

(ii) wear resistance test

DIN 53-516

The results are listed in Table 2 below.

A1 P1 Tensile strength (MPa) 18.6 20.2 Elongation at Break (%) 456 521 Abrasion Resistance (mm ³ ) ⁽¹⁾ 52 51

(1) The measured value is the decrease in wear: the lower it is, the better the wear resistance.

These last results demonstrate the good reinforcing effect that the silica according to the invention provides.

Thus, while apparently bringing better rheological properties, the silica according to the present invention provides at least equally or even better mechanical properties that can be sensed at least as much as the mechanical properties obtained from prior art silicas.

The high reinforcement of the silica according to the invention is supported by the high values obtained for tensile strength and elongation at break.

In addition, it can be seen that the silica according to the present invention has a satisfactory effect on wear resistance.

3-kinematic properties

Measurements are made on vulcanized formulations.

Vulcanization is obtained by heating the blend to 150 ° C. for 40 minutes. The results (showing a rise in temperature) are reported in Table 3 below (the lower the value, the lower the rise in temperature). The apparatus used to perform the measurements is shown.

A1 P1 Tangent Delta 70 ° C ⁽¹⁾ 0.140 0.125

(1) Instron viscoelastic system

The temperature rising tendency obtained in the silica according to the invention is quite low.

Claims (30)

In the process for the preparation of precipitated silica of the type comprising the reaction between a silicate and an acidifying agent from which a suspension of precipitated silica can be obtained, followed by separation and drying of the suspension, precipitation is carried out in the following manner: (i) an initial basal stock solution containing silicate and an electrolyte is formed, wherein the silicate concentration of the initial basal stock solution is 100 g / l or less (denoted as SiO ₂ ) and the electrolyte concentration of the initial basal stock solution is 17; g / l or less, (ii) adding an acidifying agent to the base stock solution to bring the pH of the reaction mixture to 7 or more, (iii) adding acidifying agent and silicate simultaneously to the reaction mixture, A process for producing a suspension, wherein the suspension has a solid content of 24% by weight or less, wherein the process comprises one of the following two operations (a) or (b): (a) adding at least one zinc compound to the reaction mixture after step (iii) and then adding a base agent, if said separation involves filtration and the collapse of the mass resulting from this filtration; Can be carried out in the presence of at least one aluminum compound B, (b) adding the silicate and the at least one zinc compound simultaneously to the reaction mixture after step (iii) and if the separation involves filtration and the collapse of the mass resulting from the filtration, the collapse of the at least one aluminum compound Operation that can be performed in the presence. The process of claim 1 wherein a suspension of precipitated silica comprises a reaction between the silicate and the acidifying agent from which it can be obtained, followed by separation and drying of this suspension, -Settling in the following manner: (i) an initial basal stock solution containing silicate and an electrolyte is formed, wherein the silicate concentration of the initial basal stock solution is 100 g / l or less (denoted as SiO ₂ ) and the electrolyte concentration of the initial basal stock solution is 17; g / l or less, (ii) adding an acidifying agent to the base stock solution to bring the pH of the reaction mixture to 7 or more, (iii) adding acidifying agent and silicate simultaneously to the reaction mixture, Then execute the following series of steps: (iv) adding at least one zinc compound to the reaction mixture, (v) adding a base agent to the reaction mixture to bring the pH of the reaction mixture to 7.4 to 10, (vi) adding an acidulant to the reaction mixture to bring the pH of the reaction mixture to at least 7, The separation process includes filtration and the collapse of the mass from the filtration, which is carried out in the presence of at least one aluminum compound, To dry the suspension with a solids content of up to 24% by weight. Characterized in that the method. A process according to claim 2, characterized in that between step (iii) and step (iv), an acidifying agent is added to the reaction mixture to bring the pH of the reaction mixture to 3 to 6.5. The process of claim 1, wherein the suspension of precipitated silica comprises a reaction between the silicate and the acidifying agent from which it can be obtained, followed by separation and drying of the suspension, and precipitation is carried out in the following manner: (i) an initial basal stock solution containing silicate and an electrolyte is formed, wherein the silicate concentration of the initial basal stock solution is 100 g / l or less (denoted as SiO ₂ ) and the electrolyte concentration of the initial basal stock solution is 17; g / l or less, (ii) adding an acidifying agent to the base stock solution to bring the pH of the reaction mixture to at least 7 (iii) simultaneously adding an acidifying agent and a silicate to the reaction mixture, (iv) adding silicate and one or more zinc compounds to this reaction mixture simultaneously, Drying the suspension in which the content of solids exhibits a maximum of 24%. 5. The process of claim 4, wherein after step (iv), an acidifying agent is added to the reaction mixture. 6. A process according to claim 4 or 5, wherein the separation process comprises filtration and the collapse of the mass coming from the filtration, wherein the collapse is carried out in the presence of at least one aluminum compound. The method according to any one of claims 1 to 5, wherein the amount of the zinc compound is about 1 to 5% by weight of zinc contained in the prepared precipitated silica. The zinc compound according to any one of claims 1 to 5, wherein the zinc compound is an organic zinc salt or an inorganic zinc salt, which organic salt is selected from salts of carboxylic acids or polycarboxylic acids, wherein the inorganic salts are halides, Characterized in that it is selected from oxyhalides, nitrates, phosphates, sulfates and oxysulfates. The method according to any one of claims 1 to 5, wherein the zinc compound is zinc sulfate. The method according to any one of claims 1 to 5, wherein the aluminum compound is an alkali metal aluminate. 6. A method according to any one of the preceding claims, wherein said separating process comprises filtration performed by a filter press. The method according to any one of claims 1 to 5, wherein said drying is carried out by spraying. 13. A method according to claim 12, characterized in that the suspension is dried with a content of solids of at least 15% by weight. 12. The method of claim 11, wherein said drying is performed by a multi-nozzle sprayer. 12. The method of claim 11, wherein the dry product is subsequently milled. 16. The method of claim 15, wherein the milled product is thereafter aggregated. 13. Process according to claim 12, characterized in that the suspension is dried with a content of solids of at most 15% by weight. 18. The method of claim 17, wherein the dry product is subsequently aggregated. CTAB specific surface area from 90 m 2 / g to 250 m 2 / g, A BET specific surface area of from 90 m 2 / g to 250 m 2 / g, -DOP oil uptake is 300 ml / 100 g or less, Zinc content is from 1% to 5% by weight And the number N of stearic acid molecules consumed per 1 nm ^{2 of} silica surface is at least 1 when stearic acid is reacted with the xylene solution of silica at 120 ° C. for 2 hours. 20. The silica of claim 19, wherein zinc is not in the form of crystals. The method of claim 19 or 20, CTAB specific surface area from 90 m 2 / g to 185 m 2 / g, -The median diameter (φ ₅₀ ) after collapse by ultrasonic waves is 4 μm or less, -Ultrasonic decay factor (F _D ) is 6 ml or more Silica characterized in that. The method of claim 19 or 20, -CTAB specific surface area not less than 185 m 2 / g and not more than 220 m 2 / g, -The median diameter (φ ₅₀ ) after collapse by ultrasonic waves is 7 µm or less Silica characterized in that. 21. The micropore distribution according to claim 19 or 20, wherein the micropore volume composed of micropores having a diameter of 175 mm 2 to 275 mm is 50% or more of the micropore volume composed of micropores having a diameter of 400 mm 3 or less. Silica characterized by having a. 21. Silica according to claim 19 or 20, characterized in that it is in the form of substantially round beads having an average size of 80 mu m or more. 21. Silica according to claim 19 or 20, characterized in that it is in the form of a powder having an average size of 15 mu m or more. 21. Silica according to claim 19 or 20, which is in the form of granules of size 1 mm or more. Silica obtained by the process according to any one of claims 1 to 5, characterized in that it is used as a filler for reinforcing elastomers. Silica obtained by the process according to any one of claims 1 to 5, characterized in that it is used for the purpose of improving the rheological properties of the elastomer. The silica according to claim 19 or 20, characterized in that it is used as a filler for reinforcing elastomers. The silica according to claim 19 or 20, characterized in that it is used for the purpose of improving the rheological properties of the elastomer.