WO1999048813A1

WO1999048813A1 - Precipitated silica particulates with improved dispersability

Info

Publication number: WO1999048813A1
Application number: PCT/IL1999/000134
Authority: WO
Inventors: Alexander Josef; Michael Lerner
Original assignee: Rotem Amfert Negev Ltd.
Priority date: 1998-03-26
Filing date: 1999-03-08
Publication date: 1999-09-30
Also published as: AU3271699A; IL123841A0

Abstract

The present invention provides a particulate dispersible silica, comprising on its surface an adsorbed material such that the volume of pores of diameter smaller than 175 Å is preferentially reduced, and a process for preparing such silica.

Description

-1-

PRECIPITATED SILICA PARTICULATES WITH IMPROVED

DISPERSABILITY

Field of the Invention

The present invention relates to a process for preparing precipitated silica particulates with improved dispersability, particularly for use as a reinforcing filler material for elastomeric and rubber matrices.

Background of the Invention

Precipitated silica particulates have been used as filling material in mixtures for tires (as described in EP-A 0520862 and EP-A 0157703), and in rubber material (S. Wolff, v. 7, page 674, (1988), Kautschuk und Gummikunst).

Dispersible precipitated silica particulates - beads, powders and granulates - have been described as having characteristic particle sizes BET and CTAB specific surface areas (EP-A 0520862, corresponding to US 5,403,570).

In general, it is known in this specific art that if a filler is to provide optimum reinforcing properties, it must be as homogeneously distributed as possible (U.S. 5,403,570).

In the particular case where the filler is introduced initially in a granular state, the granules have the capacity for incorporation into the matrix when mixed with the elastomer, and for disintegration in the form of a powder, and the powder can in turn be dispersed homogeneously within the elastomer matrix (U.S. 5,587,416). For the reinforcement of elastomers, the art describes particles having characteristic BET and CTAB specific surface areas for total pore volume and pore size distribution. The specific surface area is described by the BET Brunauer-Emmet-Teller method (J. Amer. Chem. Soc, Vol. 60, p. 309, 1938). The CTAB specific surface area is the -2-

external surface area, determined in accordance with French NFT Standard 45007 (November 1987).

US 5,587,416 discloses silica granules having a preferred BET specific surface area/CTAB specific surface area ratio which varies between 1:1 to 1.2:1. Examples of commercially available silicas, which satisfy this requirement, are shown in Table I below:

Table I

Product B.E.T. CTAB BET/CTAB

Hi-Sil-255 (PPG) 162 152 1.06

Hi-Sil-233 (PPG) 157 147 1.07

VN-3 (Degussa) 186 162 1.15

US 5,723,529 discloses preciptated silica aggregates, the surface of which is treated and modified by various methods. The minimal theoretical BET/CTAB ratio is considered to be, according to US 5,723,529, 1/1.

International patent application No. PCT/IL98/634, filed December 31, 1998, by the same applicants hereof, the full description of which is incorporated herein by reference, describes an optimally dispersible precipitated silica particulate, which possesses a Δ-value, corresponding to the peak value of the Differential Intrusion located at the Median Pore Diameter, as measured by Hg porosimeter, such that the following inequality is satisfied:

Δ(m//g - ) x l0³ > 0.141 x CTAB(m² /g) - b

wherein the median pore diameter is comprised between 100 and 400 A, the value of CTAB is between 90 and 400 m²/g, and preferably between 90 and 210 m²/g, and the intercept b is 10 or less, and is preferably between 7.5 and -3-

9.79, and more preferably between 8 and 9, and is most preferably 8.64. A preferred range of CTAB for many uses is between 120 and 180 m²/g. According to PCT/IL98/00634, the optimally dispersible precipitated silica particulate has a Δ-value of at least 0.01 ml/g A and a CTAB surface area comprised between 134 - 170 m²/g.

Precipitated silica particulate can be prepared by a number of processes, for instance, using the process disclossed in PCT/IL98/00634 or PCT/IL98/00635. According to said process, silicate solution is acidified, to precipitate the silica therefrom. The silicate solution is provided by dissolving water-soluble silicate, which is preferably selected from among alkali metal silicates, and in particular sodium silicate, in water. These water-soluble silicates may be obtained by treating a silica-containing mineral, such as, for example, porcelanite, with NaOH solution under elevated temperature, which preferably ranges between 120 to 150° C, to provide the aqueous silicate solution. Upon removal of solids therefrom, this solution is further diluted before the introduction of the acidifying agent thereto, to reduce the concentration of Siθ2 in said solution.

The silica is precipitated by introducing an acidifying agent into the aqueous silicate solution, said agent being preferably an inorganic acid selected from among the group consisting of H2SO4, NaHSO.4, H2CO3 or NaHCO3, the most preferred being a combination of H2SO4 and NaHSO4 wherein the H2SO₄/NaHSO concentration ratio is comprised between 1 and 3, the concentration of free H₂SO being in the range 4% - 10%, or a combination of H2CO3 and NaHCO3, wherein the EbCOs/NaHCOs concentration ratio is comprised between 0.64 and 1.92, the concentration of CO2 being in the range 1.5% - 5.0%. The introduction of the acidifying agent into the reaction medium, executing the precipitation of the silica, is carried out at elevated, constant temperature, while the solution is maintained under agitation. Preferably, the acidifying agent is provided in the form of a -4-

liquid solution, the introduction of which may be carried out in a continuous mode of operation at a constant flow, until a pH value of about 8.5 is attained.

Upon increasing the temperature of the reaction mixture to a value of about 95 ° C, additional amounts of sodium silicate are introduced thereto, preferably in several equal quantities which are added successively to the solution, simultaneously with appropriate amounts of an acidifying agent, to maintain the pH of the solution at a substantially constant value, which is typically about 7.5. Optionally, the introduction of the silicate and the acidifying agent may be carried out via a continuous mode of operation.

Upon accomplishing the introduction of the total amount of silicate into the reaction medium, the pH is further lowered and adjusted to a value in the range between 4.5 to 5.0, preferably by continuing the introduction of said acidifying agent for an additional period of time. The total reaction time is about 4 hours.

The separation of the precipitated silica from the reaction medium is carried out by known techniques, preferably by filtration under pressure. The pulp of precipitated silica thus obtained is preferably subjected to washing, typically containing between 75 to 87 weight % of water.

The wet silica precipitate is mixed with appropriate quantities of dry silica, to form a mixture having a moisture content not higher than 75 weight %, and preferably between 60 to 73%, the mixture being concurrently granulated, and the granules obtained are subsequently dried in a fluidized bed. -5-

The above description of a possible process is provided only as an example. Other processes well known in the art can also be used in conjunction with the invention to be described below.

The applicant has found that various silicas which have a given dispersability in a polymeric matrix, when tested after even a short period of time after their production has lapsed, show a deterioration of their dispersion ability. This aging adversely affects the quality of the resulting silica, and makes it difficult to provide silica of constant and finite properties. Even the dispersability of the excellent silica disclosed in PCT/IL98/00634 may be diminished because of said aging effect, although it is able to retain final dispersion properties which are superior in comparison to currently available silica.

In order to monitor and study this effect, the applicant has employed a simple test, the "Dispersability Test", to which reference is made herein, which has been developed by the applicant. The test described below directly correlates with the ability of silica particles to disperse in rubber: this test reflects the ability of the silica according to the present invention to undergo disintegration and to provide finely divided particles. This property, which is of a significant importance for various applications, in particular, when the silica is intended for rubber reinforcing applications, is measured by the D50 parameter, indicating the mean diameter of the finely divided particles obtained from the silica particulates.

This value, hereinafter termed "D50", is obtained as follows. The silica is charged into an ultrasonic bath. The bath employed in the following examples was integral with a MasterSizer Micro device (ex Malvern Instruments Ltd.), for the analysis of particle size distribution. The ultrasonic transducer operated at 40 kHz and 75 W. -6-

The samples are passed through a 18 Mesh (-1 mm) screen. About 0.2 gr of the sample are then dispersed into 600 ml demineralized water at room temperature. The dispersion is stirred with a mechanical stirrer at 2070 r.p.m., and the ultrasonic bath is operated for 5 minutes. At the end of this 5 minute period, the particle size distribution and the D50 parameter are determined. The lower the D50, the higher the dispersability of the silica and the better its quality.

It is an object of the invention to provide silicas that present improved dispersibility.

It is another object of the invention to provide dispersible silica particles that overcome the aforementioned aging effect, and thus provide constant quality of the finite product.

Other objects of the invention will become apparent as the description proceeds.

SUMMARY OF THE INVENTION

The invention is primarily directed to a particulated dispersible silica, comprising on its surface an adsorbed material such that the volume of pores of diameter smaller than 175A is reduced. According to a preferred embodiment of the invention the silica has an at least partially coated surface.

The adsorbed material can be any suitable material which can be adsorbed and/or coat the surface of the silica, and which is compatible for further use of the silica. According to a preferred embodiment of the invention the adsorbed material is a polar organic molecule. According to another preferred embodiment of the invention the adsorbed material is a molecule which forms hydrogen bonds with the silica surface. According to another -7-

preferred embodiment of the invention the adsorbed material is a polymeric material. According to a preferred embodiment of the invention, however, the polymeric material is a water soluble material. Other suitable materials are known to the skilled person and are described, inter alia, in "The Chemistry of Silica", by Ralph K. Her, pp. 288-298, John Wiley and Sons, 1979 Ed. (U.S.A.).

Illustrative and non-limitative examples of suitable polymers are polyethers, such as polyethylene oxides and methylcellulose, polyamine salts, such as polyethylene i ine, polyalcohols, such as polyvinyl alcohol, polyvinylpyrrolidone and proteins, such as gelatin and albumin.

According to a preferred embodiment of the invention the adsorbed material is a glycol. A preferred glycol is polyethylene glycol (PEG). Preferably, but non-limitatively, the polyethylene glycol has a molecular weight between 400 and 1500, more preferably between 600 to 1000. PEG shows an excellent selectivity of coating, so that pores smaller than 175A are preferentially coated. As will be appreciated by the skilled person, it is suprising that adsorption of a material on the silica is selective and not all pores are coated essentially in the same way.

The silica of the invention has a n/N ratio, wherein n is the number of open pores of diameter <175A, and N is the number of open pores of diameter >175A, which is smaller than that of the corresponding, uncoated silica. The ratio n/N can be measured indirectly in a variety of ways, e.g., by the aforementioned BET and CTAB tests, or in any other suitable manner.

The silica of the invention has a BET/CTAB ratio smaller than 1. This is surprising, since according to the prior art, highly dispersible silica is characterized by BET/CTAB ratios between 1.0 and 1.2. The prior art, in fact, was unable to produce silica with ratios smaller than 1, and this result -8- cannot be practically achieved, as far as is known to the applicants, other than through the practice of the present invention. The present invention thus provides silica particulate characterized by BET/CTAB value smaller than 1, and preferably, smaller than 0.9.

The invention is further directed to a process for manufacturing an improved dispersible silica, comprising manufacturing a precipitated silica and bringing it into contact with a material which is capable of being adsorbed onto the silica surface, in a concentration and under conditions suitable to obtain at least a partial and selective coating of the silica particle surface by said material, which results in a preferential closure of pores of less than 175A.

As explained hereinbefore, the preparation of precipitated silica generally involves acidifying an aqueous silicate solution, to form a silica precipitate- containing suspension, followed by the separation of said precipitate, preferably by filtration. According to a preferred embodiment of the present invention, the improved dispersible silica is produced by bringing the silica precipitate- containing suspension into contact with the material which is capable of being adsorbed onto the silica surface, before the separation step. In another variant, the silica is brought into contact with a material which is capable of being adsorbed onto the silica surface subsequent to the separation step, by treating the silica filter cake with said material, by washing or otherwise contacting said filter cake with an aqueous solution containing said material.

In another aspect, the invention is directed to a method for producing a reinforced elastomer/rubber matrix, comprising the steps of:

a) providing non-cross-linked components mixture of the matrix; b) providing dispersible silica pariculates, comprising on its surface an -9-

adsorbed material such that the volume of pores of said silica, of diameter smaller than 175A, is lower in comparison to the volume of said pores in corresponding silica which is free of said adsorbed material; c) homogeneously dispersing said silica particulates in said component mixture; and d) vulcanizing said mixture.

Thus, the invention is also directed to a reinforced elastomer/rubber matrix comprising finely divided, uniformly dispersed silica particles, resulting from silica particulates which comprise on their surface an adsorbed material such that the volume of pores of said silica particulates, of diameters smaller than 175A, is lower in comparison to the volume of said pores in corresponding silica particulates which are free of said adsorbed material.

Brief Description of the Drawings

- Fig. 1 is a graph showing the specific pore volume (ml/g) as a function of the CTAB, for pores with a diameter smaller than 175A;

- Fig. 2 is a graph showing the dependence of the D50 on the CTAB; and

- Fig. 3 is a graph that illustrates the aging effect in silicas with different CTAB.

Detailed Description of Preferred Embodiments

All percentages given herein are by weight, unless specifically otherwise stated. The experimental methods described herein are conventional methods employed in the industry, with the exception of the aforementioned Dispersability Test. The measurements of the other technical parameters were conducted in accordance with the procedures described in EP 520862, corresponding to US 5,403,570. -10-

Preparation A

For the purpose of the comparison with the improved silica according to the present invention (the preparation of which is illustrated hereinafter), a particularly excellent silica was chosen, the silica according to PCT/IL98/00634. The following illustrates the preparation of said comparative silica samples used in the examples to follow.

A solution of sodium sihcate was prepared from porcelanite. 6371 g of solution, containing 17.8% SiO₂ (module 3.0) and 105 ppm organic compound, and 12,031 g water were placed into a 25 liter reactor provided with a mixer and double-jacketed heater. The mixture was heated to 82°C, and agitation was maintained. 8,301 g of solution containing H2SO (5.53%) and NaHSO (2.17%) were added until a pH value of 8.8 was attained in the reactor medium after 85 minutes. The temperature was then increased to 95°C, and 1124 g of sodium silicate solution was added to the silica sediment in two equal parts, with an interval of 30 minutes.

The simultaneous addition of sulfuric acid (6.5%) was carried out, while constantly maintaining a pH of 7.5. Adding additional H₂SO to the reaction mixture adjusted the pH to 4.0.

A suspension of precipitated silica was thus obtained, which was then filtered under vacuum. The silica cake was washed twice with 1.5 liters of water. 8,420 g of a silica pulp was obtained (85% moisture). Dry silica was combined with the pulp silica, to obtain a mixture of 28% solids by weight (1646 g). The mixing and granulation were carried out in a change-can mixer (KENWOOD). The product was then dried to 5% moisture in a fluidized bed with dry air (90°C). The dried granules were passed through a screen of mesh and the diameter of the granules obtained was in the range 0.5-3.0 mm. ^■11-

In different examples changes were made in the above procedure, as described in the aforementioned copending international patent application no. PCT/IL98/00634, to obtain varied properties.

Example 1

Dependence of the surface area of the pores on the diameter of the pores

The dependence of the surface area of the pores on their diameter was investigated. Silicas were tested in a liquid nitrogen absorption/desorption test (using a COULTER SA - 3100, Coulter Corporation, Miami, Florida, USA), and from the data obtained in this test the specific pore surface area (m²/ml) was calculated. Table II shows average results of the pore specific surface area in different ranges of pore diameters, for different samples having different CTAB surface areas between 140 - 175 m²/g (deviation between samples ±6%).

Table II

Pores Specific Surface .Area Pores Diameter m²/ml A

460 <175

153.5 175 - 400

77.6 >400

Example 2 Dependence of the Specific Pore Volume on the CTAB

Silica samples were tested in a mercury porosimeter, and their specific pore volume (ml/g) was determined for pores with diameters less than 175A. The results are shown in Fig. 1, which is a graph showing the specific pore -12-

volume (ml/g) as a function of the CTAB, for pores with a diameter in the range <175A. It can be easily seen that the specific pore volume increases strongly with increasing CTAB.

Example 3 Dependence of the Dso on the CTAB

Several samples having CTAB values between 121.5 and 171 were prepared and left to cure in a closed vessel, under identical conditions for all samples, for one month. The D50 values of all samples were measured after one month, and the resulting values are plotted in Fig. 2.

These tests show that the dispersability of the silica is inversely proportional to the CTAB, and therefore the Dso values increase with increasing CTAB.

The preceding examples assert the hypothesis represented hereinbefore, according to which the pores of diameter <175A play a critical role in determining the dispersability of the silica in rubber compositions, as expressed by the D50 parameter.

Example 4 Aging

Three silicas having different CTAB values (141, 158 and 174 m²/g) were prepared and tested in the Dispersion Test immediately after preparation, and after 3, 10 and 25 days. The D50 values were determined, and the results are reported in Fig. 3.

Fig. 3 clearly shows the aging effect, represented by the increase of the D50 values with time. Curve (a) represents results for a silica with CTAB 174 m²/g, while the points of curve (b) represent two samples, with a CTAB of 158 and 141 m²/g. Curve (c) is a silica according to the invention, having an -13-

initial CTAB 174 m²/g, coated with PEG (MW 600). The improvement of curve (c) as compared with curve (a) is, as it can be seen, dramatic.

Example 5 PEG Treatment

Aqueous solutions of polyethylene glycol (PEG) of various molecular weights were used to prepare a number of samples. The samples were prepared with the same procedure, which involved preparing a 4% solution of PEG in water, which was then mixed in a 1:1 weight ratio with a silica cake from the filter after washing (pH 5.5). Mixing was effected in a stirred vessel for 20 minutes. At the end of the mixing, the suspension was re-filtered and the resulting silica cake was granulated and dried in a fluidized bed drier. For the experiments of this example the silica was chosen with a CTAB of 174 m²/g. The results are shown in Table III.

A review of the results of Table III shows an unequivocal relation between the effect of the various PEGs on the pore distribution induced thereby in the silica, and the dispersability of the silica, as expressed by the D50 test. The results below also show the selectivity in the coating of pores having diameters in the range 0-175A. The best results are obtained, with PEG, using a molecular weight in the range 400 - 1500, more preferably in the range between 600 - 1000.

■14-

Table III

Sample -► Silica Silica+ Silica+ Silica+ Silica+ Silica+ Silica÷ Silica+

Parameter Blank PEG PEG PEG PEG PEG PEG PEG

* 400 600 1000 1500 2000 4000 6000

4-

Total Fore

Volume** 1.8785 1.8590 1.9215 1.8449 1.8511 1.9139 1.8434 1.9548 ml/g

Specific Pore

Volume** ml/g

D<175A 0.2177 0.1046 0.0918 0.0760 0.0812 0.1130 0.1144 0.1284

175<D<400A 0.7254 0.6750 0.6535 0.6472 0.6487 0.6672 0.6452 0.6622

D>400A 0.9353 1.0793 1.1761 1.1217 1.1211 1.1337 1.084 1.1642

Total Pore

Area** 249.8 200.0 183.1 174.4 177.3 192.2 194.1 204.0 m²/g

Median Pore

Diameter, A 194 212 215 216 216 211 210 208

Dispersion

Test

Dso; t=0 10.7 8.0 7.9 8.1 8.85 8.1 9.6 9.9

Dso; t=10 13.9 8.7 8.7 10.2 11.9 10.7 - - days

Dso; t=30 17.5 12.6 9.5 11.4 12.5 11.4 12.7 12.6

days

* Surface Area (CTAB) 174 m²/g ** Mercury Porosimeter data

Example 6 Treatment of Different Silicas

Example 5 was repeated, with the following changes. Three different silicas were chosen each having a different CTAB. Silica #322 with a CTAB of 141 m²/g, SUica #316 with a CTAB of 158 m²/g, and Sihca #315 with a CTAB of 174 m²/g. The PEG employed (ex Aldrich Chemical Company) had a molecular weight of 600. PEG treatment of the silica was carried out with PEG concentrations varying between 0.4% and 4%. The results are summarized in Tables IV through VI below. -15-

Table IV Silica #322

PEG Concentration in Solution

Property 0 0.4 1.0 2.5

V (<175A), ml g 0.1085 0.0902 0.0837 0.0486

V(175-400A), ml/g 0.8238 0.7950 0.8372 0.7664

V >400A, m g 1.5676 1.4923 1.4064 1.4742

Δ x 10³, ml/g ^• A 9.3 10 10 7.8

T.P.A., m²/g⁽ⁱ⁾ 223 213.1 211 172.9

M.P.D., A⁽²⁾ 248 253 261 279

B.E.T. (lp.), m²/g 146 135.4 125 106

C.T.A.B., m²/g 141 141 139 129

BET/CTAB 1.03 0.96 0.899 0.82

Dso, t=0 9.8 9.8 9.5 9.3

D50, t=10 days 11.1 10.8 10.5 10.1

D50, t=30 days 13.2 12.8 12.3 11.1

(1) Total Pore Area

(2) Median Pore Diameter

Table V Silica #316

PEG Concentrai tion in So ution

Property 0 0.4 1.0 2.5

V (<175A), ml/g 0.1592 0.1124 0.1208 0.0938

V(175-400A), mUg 0.7441 0J827 0J769 0J326

V >400A, ml/g 1.1092 1.1793 1.2212 1.2281

Δ x 10³, ml/g ^• A 12.0 12.5 12.5 10.5

T.P.A., m²/ ω 231.1 208.6 220.2 199.8

M.P.D., A<²> 210 225 222 232

B.E.T. (lp.), m²/g 170 149 139 118

C.T.A.B., m²/g 158 161.5 156 149.5

BET/CTAB 1.08 0.92 0.89 0J9

Dso, t=0 9.06 10.22 8.38 8.85

D50, t=10 days 11.76 12.6 10.85 10.7

D50, t=30 days 14.4 13.1 12.5 11.8

(1) Total Pore Area

(2) Median Pore Diameter -16-

Table VI Silica #315

PEG Concentration in Solution

Property 0 0.4 1.0 2.5 4.0

V (<175A), ml g 0.2177 0.1885 0.1785 0.1434 0.0918

V(175-400A), ml/g 0.7254 0J357 0J568 0.6935 0.6535

V >400A, ml g 0.9353 1.138 1.1133 1.1200 1.1761

Δ x 10³, ml/g ^• A 13.8 14.5 14.5 11.5 10.2

T.P.A., m²/g⁽D 250 244J 247.8 213 183.1

M.P.D., A® 194 199 201 206 215

B.E.T. (lp.), m²/g 185 162 151 129 120

C.T.A.B., m²/g 173.5 171 169 157.6 147.5

BET/CTAB 1.07 0.95 0.89 0.82 0.81

Dso, t=0 10.3 10.9 9.5 9.0 7.9

Dso, t=10 days 13.5 13.1 12.6 11.5 8.7

D50, t=30 days 16.6 15.2 14.5 13.5 9.5

(1) Total Pore Area (2) Median Pore Diameter

Furthermore, it is seen that there is a critical PEG concentration (about 1%), up to which the CTAB value is essentially fixed. Above the 1% concentration, the CTAB value drops substantially. The BET value, on the other hand, decreases constantly with decreasing pore volume smaller than 175A pores. It should be noted that the drastic drop in the CTAB value takes place concurrently with a similar drop in the pore volume of 175-400A pores.

Example 7 Preparation of coated silica

A solution of sihcate was prepared from porcelanite. 7222 g of solution containing 15.8% SiO₂ (module 3.0) and 110 ppm organic compound, and 11,908 g water were placed into a 25-liter reactor provided with a mixer and double -jacketed heater. The mixture was heated to 82°C and agitation was maintained. 7574 g of solution containing H₂SO (5.93) and NaHSO₄ (2.37%) were added until a pH value of 8.58 was attained in the reactor medium after 85 minutes. The temperature was then increased to 95°C and -17-

1274 g of sodium silicate solution was added to the silica sediment in two equal parts, with an interval of 30 minutes.

The simultaneous addition of sulfuric acid (7.0%) was carried out, while constantly maintaining a pH of 7.5. Adding additional H2SO4 to the reaction mixture adjusted the pH to 4.0.

A suspension of precipitated silica was thus obtained, which was then filtered under vacuum. The silica cake was washed twice with 1.5 liters of water. 9545 g of a silica pulp was obtained (85% moisture).

The sihca pulp was mixed in a 1:1 weight ratio with a solution of 1.2% P. E.G. 600. Mixing was effected in a stirred vessel for 20 minutes. At the end of the mixing, the suspension was re-filtered, and the resulting sihca cake was granulated and dried in a fluidized bed drier. Some various characteristics of interest are summarized in table VII.

Table VII

B.E.T. C.T.A.B. BET/CTAB Total Median. Pore Dispersibility test

Surface Surface Intrusion Pore Volume Expressed by Dso

Area Area Volume Diameter 0-175 A (μm)

(mVg) (mVg) ml/g (Area, A) ml/g

125 149 0.84 1.93 234 0.101 14.0

It is apparent from the table above, that the sihca according to the present invention, having a BET/CTAB ratio lower than 1:1, is characterized by an excellent dispersibilty in rubber composition, as reflected by the D50 parameter.

Example 8 Comparative Test -18-

A commercially available silica (Zeosil 1165 MP) and the product of example 7 were tested in a green tire compound. The mechanical and dynamical properties are summarized in Table VIII.

Table VIII

1165 MP Example 7

Mooney Vise.

MB (ISO 289-1 1994) 57 63

FB (ISO 289-1 1994) 53 58

Rheometer ts2 (ISO 3417-1991) 1.77 1.42 t5 (ISO 3417-1991) 0.96 0.50 t95 (ISO 3417-1991) 7.2 7.9 torque (ISO 3417-1991) 16.3 17.4

Hardness (ISO 48- 1994) 68 70

Tensile (ISO 37 1994-dumb-bell type 2) 18.2 19.5

Elongation 415 425

100% Mod. (ISO 37 1994) 2.56 2.75

300% Mod. (ISO 37 1994) 11.74 12.01

Tear (ISO 34-1979 Crescent 38 41 with 1 mm cut)

Rebound (ISO 4662-1986 (Schob) 39 39 c.s. 23°C 6 6 c.s. 100°C 44 48

HBU at 100°C (ISO 4666/3-1982) 48 47

Abrasion (ISO 4649-1985) 100 76

Wet grip* 1.22 1.57

Dry grip* 0.0272 0.0201

Ice grip* 0.0275 0.0218

Cornering coefficient* 3.4 4.3

Rolling resistance* 0.155 0.146

#: Tyre performance test was carried out with a frequency of 1Hz, in the temperature range -150 to 200°C.

It is apparent from the above table that the silica according to the present invention possesses excellent properties, and is superior, compared with the commercial silica, concerning certain critical parameters, such as abrasion, wet grip and cornering coefficient. -19-

While embodiments of the invention have been described by way of illustration, it will be understood that the invention can be carried out by persons skilled in the art with many modifications, variations and adaptations, without departing from its spirit or exceeding the scope of the claims.

Claims

-20-CLAIMS

1. A particulate dispersible silica, comprising on its surface an adsorbed material such that the volume of pores of diameter smaller than 175 A is preferentially reduced.

2. A silica according to claim 1 having an at least partially coated surface.

3. A silica according to claims 1 to 2, wherein adsorbed material is a polar organic molecule.

4. A silica according to claim 1, 2 or 3, wherein the adsorbed material is a molecule that forms hydrogen bonds with the sihca surface.

5. A silica according to any one of claims 1 to 4, wherein the adsorbed material is a polymeric material.

6. A silica according to claim 5, wherein the polymeric material is a water soluble material.

7. A silica according to claim 6, wherein the polymer is selected from among polyethers, polyamine salts, poly alcohols, polyvinylpyrrolidone and proteins.

8. A silica according to any one of claims 1 to 7, wherein the adsorbed material is a glycol.

9. A silica according to claim 8, wherein the glycol is polyethylene glycol.

10. A silica according to claim 9, wherein the polyethylene glycol has a molecular weight between 400 and 1500. -21-

11. A silica according to claim 10, wherein the molecular weight is between 600 to 1000.

12. A silica according to any one of claims 1 to 11, having a n/N ratio, wherein n is the number of open pores of diameter <175A, and N is the number of open pores of diameter >175A, which is smaller than that of the corresponding, uncoated sihca.

13. A sihca according to any one of claims 1 to 12, having a BET/CTAB ratio smaller than 1, and preferably, smaller than 0.9.

14. A process for manufacturing an improved dispersible silica, comprising manufacturing a precipitated sihca and bringing it into contact with a material which is capable of being adsorbed onto the sihca surface, in a concentration and under conditions suitable to obtain at least a partial coating of the sihca particle surface by said material.

15. A process according to claim 14, wherein the material which is capable of being adsorbed onto the sihca surface is provided in aqueous solution.

16. A process according to claim 14, wherein the precipitated sihca is obtained by a method comprising acidifying an aqueous silicate solution, to form a sihca precipitate- containing suspension, followed by the separation of said precipitate, preferably by filtration.

17. A process according to claim 14 and 16, wherein the sihca is brought into contact with the material which is capable of being adsorbed onto the sihca surface before the separation step, by contacting the sihca precipitate- containing suspension with said material. -22-

18. A process according to claim 14 and 16, wherein the sihca is brought into contact with the material which is capable of being adsorbed onto the sihca surface subsequent to the separation step, by treating a sihca filter cake resulting from said separation, with said material, by washing or otherwise contacting said filter cake with an aqueous solution containing said material.

19. A process according to claim 14, wherein the material which is capable of being adsorbed onto the sihca surface is a polymeric material.

20. A process according to claim 19, wherein the polymer is PEG.

21. A process according to claim 20, wherein the PEG has a molecular weight between 400 and 1500.

22. A process according to claim 21, wherein the molecular weight of the PEG is between 600 to 1000.

23. A method for producing a reinforced elastomer/rubber matrix, comprising the steps of:

a) providing non-cross-hnked components mixture of the matrix; b) providing dispersible sihca pariculates, comprising on its surface an adsorbed material such that the volume of pores of said sihca, of diameter smaller than 175A, is lower in comparison to the volume of said pores in sihca which is free of said adsorbed material; c) homogeneously dispersing said sihca particulates in said component mixture; and d) vulcanizing said mixture.

24. A reinforced elastomer/rubber matrix comprising finely divided, uniformly -23- dispersed sihca particles, resulting from sihca particulates which comprised on their surface an adsorbed material such that the volume of pores of said silica particulates, of diameters smaller than 175A, is lower in comparison to the volume of said pores in corresponding sihca particulates which are free of said adsorbed material.

25. An improved sihca, whenever prepared by the process of any one of claims 14 to 22.

26. A process for manufacturing an improved dispersible sihca, substantially as described and with particular reference to the examples.