HK1029326A - Improved silica product for use in elastomers - Google Patents

Description

Modified silica products for elastomers

Background

Technical Field

The present invention relates to a novel precipitated silica product and a process for its preparation. More particularly, the invention relates to an amorphous precipitated silica product that is used as an additive in an elastomer formulation for the manufacture of shaped products, particularly rubber passenger tire (passenger tire) treads.

Description of the Related Art

The precipitated silica product is used in particular as a filler for rubber, as described in Kirk-Othmer encyclopedia of chemical technology (third edition, volume 20, John Wiley Sons, New York, page 779 (1982)). Fillers, which are commonly used as reinforcing agents, improve the mechanical properties of rubber or other elastomers.

The various fillers used in the elastomer art should be easy to handle and easy to formulate into elastomer mixtures. Powdered silica products are difficult to handle due to their poor flowability and the generation of large amounts of dust. Furthermore, the low bulk density of the powdered silica product makes it difficult to incorporate into elastomers.

Even though shaped silica products overcome these drawbacks to some extent, shaped silica products are difficult to disperse in elastomers and achieve reinforcement effects that are inferior to those achieved with powdered silica products. The desired reinforcing characteristics are generally obtained if the silica product is uniformly dispersed throughout the elastomer matrix in a finely divided state. Thus, an ideal shaped silica product would be one that is easily mixed with an elastomeric matrix and then disaggregated or dispersed in the matrix as a fine powder, which is easily dispersed into a homogeneous state.

In addition, the silica filler should minimize the need for expensive coupling agents in the rubber formulation. The coupling agent used is typically a trialkoxysilane which bears amino, mercapto, polysulfide or other functional groups and is used to reduce heat accumulation/thermal hysteresis and enhance the improvement in mechanical properties provided by the silica filler.

In rubber formulations in the tire industry, especially in solution-polymerized styrene-butadiene rubber (s-SBR) for the preparation of car tire treads, there are several useful rubber tread characteristics which are still mutually contradictory, and which are strongly influenced by the physical properties of the filler used. The ability of the tread to adhere to the ground is of paramount importance, and silica fillers which provide good tire adhesion under a variety of conditions, whether the ground is dry, wet, snow-covered or ice-covered, are well known. However, known silica fillers that enhance grip do not simultaneously reduce rolling resistance, reduce the rate of tread wear and limit structural deformation, which are also desirable for tires. Similarly, silica fillers have been prepared in the past to improve rolling and tire tread durability, but this has been done at the expense of reduced adhesion and generally requires the inclusion of large amounts of expensive coupling agents to improve adhesion. Furthermore, the known highly dispersible silica fillers for rubbers do not enhance the processability of the rubber.

Accordingly, there has been considerable research in silica filler/passenger tire tread formulations in an attempt to develop a highly dispersible silica filler that desirably combines these mutually opposing tread characteristics while enhancing processability. See, for example, U.S. patents 5089554, 5227425, and 5403570 and international applications WO95/09127 and WO 95/09128. However, the best results of these studies are also unsatisfactory and do not simultaneously compromise the more demanding properties. Accordingly, there is a long felt need in the art for highly dispersible silica fillers that provide enhanced processability, low rolling resistance, long-term durability, high all-weather adhesion, and reduced coupling agent requirements for passenger car tire treads or other rubber/elastomer dynamic applications formed therefrom when incorporated into rubber compounds, particularly rubber blends of solution SBR and one or more other polymers.

Object of the Invention

It is therefore an object of the present invention to provide a highly dispersible precipitated amorphous silica product suitable as a filler for elastomeric compositions.

It is another object of the present invention to provide an improved highly dispersible precipitated amorphous silica filler for passenger car tire treads.

Other objects of the present invention will be apparent from the following description. Summary of the invention

Briefly, the present invention provides a precipitated amorphous silica product having a CTAB specific surface area of about 10 meters²Per gram to less than 140 m²Per gram, preferably about 10-110 m²Per gram, more preferably from about 10 to less than 100 meters²Per gram; multiple point BET surface area of about 50-225 m²Per gram; a 5% pH of about 5.0-8.5; DBP oil adsorption value of about 160-310 cm³100 g; the adsorption value of linseed oil is about 150-300 cm³100 g; projected surface area no greater than about 4000 nm²Preferably no greater than about 3500 nanometers²(ii) a The pore volume ratio of pore diameter at 175-275 angstroms to all pore diameters less than 400 angstroms is from about 10% to less than 50%.

The precipitated amorphous silica product of the present invention is preferably subjected to shaping processes such as granulation, nozzle spray drying and the like. If shaping is to be carried out, the product of the invention preferably has a bulk density (pour point density) of about 0.16 to 0.30 g/ml, more preferably about 0.16 to 0.27 g/ml, and is present in an amount of no greater than about 20 weight percent, preferably no greater than about 10 weight percent, less than a 200 mesh screen.

The process of the invention comprises adding an acid at a substantially constant rate to a mixture of water and alkali metal silicate, the mixture having a temperature of from about 60 ℃ to about 90 ℃ and a molar ratio of silicate of from about 2.4 to about 3.3. When the pH of the reaction mixture reaches about 10.0 to 6.5, preferably about 7.8 to 7.5, a further amount of silicate is added together with the acid. The pH of the reaction mixture is maintained at about 10.0 to 6.5, preferably about 7.7 to 7.3, by adjusting the rate of addition of acid. The silicate addition is stopped after about 0 to 60 minutes, preferably about 30 minutes, and the acid addition is continued until the pH of the reaction mixture reaches about 4.5 to 6.5, preferably about 5.1 to 5.5. The reaction mixture is digested at about 60-99 deg.C for about 0-60 minutes, after which the pH is readjusted with acid to about 4.5-6.5, preferably about 5.1-5.5. An electrolyte, preferably sodium sulfate, may be added at any stage of the synthesis by digestion. The silica slurry was filtered from the reaction mixture and washed. The degree of washing is preferably such that the sodium sulfate content of the washed silica product is no greater than about 4.5%. The pH of the washed silica slurry is preferably adjusted to about 6.0 to 7.0 with an acid. The washed silica slurry is then dried, preferably to a pH of H₂The content of O is not greater than about 8%.

The present invention includes an elastomeric formulation comprising a precipitated amorphous silica product or a shaped silica product as described herein. The elastomer is preferably s-SBR, more preferably s-SBR and at least one other polymer. The other polymer is preferably a diene. The present invention also includes an elastomeric formulation useful in a tire tread comprising a precipitated amorphous silica product or a shaped silica product as described herein. Detailed description of the invention

We have disclosed a highly dispersible silica product which, when incorporated into a rubber composition for use as a filler in the production of a passenger car tire tread, can achieve a compromise in various characteristics of the tread product, such as enhanced processability, rolling resistance, durability and adhesion, at levels not achieved in the prior art. More specifically, the present invention provides an excellent compromise between various advantages that have previously been considered mutually contradictory; i.e., excellent rubber processability, low rolling resistance, good wet adhesion, good ice adhesion, enhanced rubber extrudability, minimal coupler requirements, good abrasion resistance, and high tensile and modulus. When formed, the present invention is also easy to handle and produces minimal dust.

The silica product of the invention has an excellent compromise between several physical properties, in particular a CTAB specific surface area of about 10 m²Per gram to less than 140 m²Per gram, preferably about 10-110 m²Per gram, more preferably about 10 meters²Per gram to less than 100 m²Per gram; multiple point BET surface area of about 50-225 m²Per gram; a 5% pH of about 5.0-8.5; DBP oil adsorption value of about 160-310 cm³100 g; the adsorption value of linseed oil is about 150-300 cm³100 g; projected surface area no greater than about 4000 nm²Preferably no greater than about 3500 nanometers²(ii) a The pore volume ratio of pore diameter at 175-275 angstroms to all pore diameters less than 400 angstroms is from about 10% to less than 50%.

When formed, the present invention preferably has a bulk density (pour point density) of about 0.16 to 0.30 g/ml, more preferably about 0.16 to 0.27 g/ml, and a content of less than 200 mesh sieve preferably no greater than about 20 wt%, more preferably no greater than about 10 wt%. Granulation, spheronization and/or other known forming means may be used. The shaped silica products of the present invention produce little dust, are easy to handle and are easy to mix with elastomer formulations.

It is well known that a single physical property, such as surface area or particle size, is hardly descriptive of a silica product or is predictive of the performance of the product in a particular application. The controlled mechanism of how a particular silica product affects performance in a given end use can be extremely complex and often unclear; thus, it is extremely difficult, and perhaps misleading, to combine one or even several conventionally measured physical properties of silica products with the performance characteristics of a particular end use application. We have discovered that our invention makes it extremely unexpected that the products described herein can be used in passenger car tire treads much better than known precipitated amorphous silica products having some similar conventionally measured physical properties, as clearly demonstrated by the tests which we have conducted and described herein. We do not exclude the possibility that new silica product testing techniques may be developed that are capable of determining other physical characteristics of the present invention and the prior art, further explaining the significant and unexpected performance advantages brought about by the present invention.

The process of the invention comprises adding an acid to a mixture of water and an alkali metal silicate, the temperature of the mixture being from about 60 ℃ to about 90 ℃. The water and/or silicate may be heated separately or mixed and then heated. The alkali metal silicate used is not particularly limited and may include any alkali metal or alkaline earth metal silicate and disilicate. The silicate is preferably present in a molar ratio of about 2.4 to 3.3, and an aqueous solution having a silicate concentration of about 10.0 to 30.0% is preferably added. An electrolyte may also be added to the reaction medium or mixed with one or more reactants prior to or simultaneously with the addition of the reactants to the reaction medium. The addition of the electrolyte can also be carried out during any stage of the synthesis by digestion, preferably during the first half of the reaction. Any known electrolyte may be used, with sodium sulfate being preferred.

The rate of addition of acid is substantially constant. Preferably, an acid solution having a concentration of about 5.0-30.0% is added. Sulfuric acid is preferably used, but other acids such as H can also be used successfully₃PO₄、HNO₃、HCl、HCO₂H、CH₃CO₂H and carbonic acid.

When the pH of the reaction mixture reaches about 10.0 to 6.5, preferably 7.8 to 7.5, more silicate is added to the reaction mixture while the acid is continuously added. Precipitation occurs simultaneously with the addition, and the pH of the precipitate is maintained at about 10.0 to 6.5, preferably about 7.7 to 7.3, by adjusting the rate of addition of acid. The silicate addition is stopped after about 0 to 60 minutes and the acid addition is continued until the pH of the reaction mixture reaches about 4.5 to 6.5, preferably about 5.1 to 5.5.

After the acid addition is stopped, the reaction mixture is digested for about 0-60 minutes at a digestion temperature of about 60-99 ℃. An electrolyte, such as sodium sulfate, may be added at any stage from the synthesis to the digestion step. After the digestion reaction, the pH of the reaction mixture is readjusted with an acid to about 4.5-6.5, preferably about 5.1-5.5.

The product silica slurry was then filtered from the reaction mixture and washed. Filtration as used herein includes various separation methods known in the art, such as rotary filtration, pressure filtration, plate filtration, and frame filtration, among others. Preferably, the washing is carried out until the sodium sulfate content is less than about 4.5%. The pH of the washed silica slurry is readjusted to about 6.0-7.0 with acid prior to drying.

The washed silica slurry is then dried to obtain a silica product. Drying may be carried out by wheel pressure spray drying, nozzle spray drying, flash drying, rotary drying or any other drying method known in the art. Preferably, drying should be such that the moisture content of the silica product reaches about 8% or less.

If desired, the silica product can be formed by various forming processes, such as granulation, spheronization and/or other known forming methods, and placed in a low-dust/readily dispersible form. A granulation process is preferred which compresses the silica product into a compact and then breaks the compact into small particles. The fine particulate fraction is then recovered and blended with more silica product and the blend is pressed into a more dense compact. The compact is broken up and sieved through a sieve of desired size to form a granular product. To aid in densification, vacuum may be applied to various stages of the process. The spray dried silica may be milled prior to granulation. The forming process may be carried out with or without the aid of other additives, such as water, corn syrup, etc.

As will be described below, the elastomeric compositions, in particular tire tread compositions, containing the silica products of the invention have improved processability combined with the use properties not known from the elastomeric compositions of the prior art. The elastomeric composition preferably contains the elastomer s-SBR and may contain other polymers, preferably dienes. The elastomeric composition may be used in any dynamic application including, but not limited to, tire treads and engine mount applications.

The invention is described below by means of specific examples. The examples are not intended to limit the scope of the invention, which is defined by the appended claims. Example 1

The precipitated amorphous silica product of the present invention is prepared as follows: in one reactor, 260 liters of water and 200 liters of 24.7% sodium silicate (silicate molar ratio 3.3, excess silicate 82.9%; excess silicate 100 × volume of silicate initially present in the reaction medium divided by the total volume of silicate used in the reaction) were mixed and the reaction medium was heated to 82 ℃. To the heated reaction medium was added 9.5 kg of anhydrous sodium sulfate. Then, to the heated reaction medium was added 33 ℃ sulfuric acid (7.4%) at an acid addition rate of 4.5 liters/min. When the pH of the reaction medium reached about 7.5, the rate of addition of acid was slowed to 1.81 liters/min and the addition of 24.7% sodium silicate (molar ratio 3.3) was started at a rate of 1.38 liters/min. The pH of the precipitate was maintained at 7.5 by adjusting the rate of addition of acid while adding. After 30 minutes, the addition of silicate was stopped, but the addition of acid was continued at a rate of 1.81 liters/minute until the pH of the reaction mixture reached 5.1. The reaction mixture was then digested for 10 minutes at 82 ℃ after which the pH was adjusted to 5.1 with more acid.

The precipitated silica slurry was rotary filtered from the reaction mixture and washed with water until the sodium sulfate content was reduced. The silica slurry is then spray dried.

The physical properties of the final product were measured as follows, and the results are summarized in Table 1. Average Particle Size (APS)

The particle size was determined using a Leeds and Northrup Microtrac II apparatus. During the measurement, a projected laser beam is passed through a transparent container containing a moving stream of particles suspended in a liquid. Light impinging on the particles is scattered through an angle inversely proportional to the particle size. The light sensing array measures the amount of light at several predetermined angles. The electrical signal, which is proportional to the measured light flux value, is then processed by a microcomputer system to form a multi-channel histogram of the particle size distribution. Multipoint BET

The surface area of the solid material was measured using a Gemini III2375 surface area Analyzer (Micromeritics, Inc.). During the measurement, an analysis gas (nitrogen gas) was measured while being supplied to the sample tube and the control tube (blank sample). The internal volume and ambient temperature of the two tubes remain the same, the only difference being the sample contained in the sample tube.

The sample and control tubes were immersed in a single liquid nitrogen bath in which the temperature of both tubes was maintained the same. The analyte gas delivered to the control and sample tubes is metered through separate servo valves. A differential pressure sensor is used to determine the pressure imbalance between the two tubes, which is caused by the adsorption of the analyte gas by the sample. When the sample adsorbs the analyte gas, the pressure balance of the two tubes is maintained by the servo valve feeding more gas into the sample tube. The net result is that the Gemini maintains a constant pressure of the analyte gas on the sample while varying the rate of delivery of the analyte gas to match the rate at which the sample adsorbs the gas. Bulk fines and pellet distribution of compacted products

Bulk fines and pellet distribution of the compacted product were determined by weighing the portions retained on or passing through an 8 inch diameter stainless steel U.S. sieve having a mesh size of 50 mesh and 200 mesh, respectively, and a pore size of 297 microns and 74 microns, respectively.

A10.0 + -0.1 gram sample was placed on top of the stacked screens. The sieve was covered and shaken on a portable sieve shaker (RX-24, model C-E Tyler, W.S. Tyler Co., Ltd.) for 5 minutes. The percentage of sample that passes through or remains on the predetermined screen size is determined by weighing. Bulk density of the particles (bulk or pour point density of the compact product)

A funnel, the opening of which can be sealed, was mounted directly above the mouth of a standard pint cup, the fixed height of the funnel from the pint cup being 3 inches. The sealed funnel was filled with granules. The funnel was opened to allow the particles to flow freely into and fill the cup. The particles were scraped off along the rim of the cup with the flat edge of a spatula. The weight of the filled cup is weighed and the weight of the empty cup is subtracted from this weight to obtain the weight of the pellet (measured in grams to the nearest 0.1 gram). The bulk density (in g/ml) was obtained by dividing the weight of the particles by the standard volume of the cup (in ml). Pore volume method

Pore volume (mercury pore volume) was determined using an Autopore II 9220 porosimeter (Micromeritics, Inc.). The instrument measures the pore volume and pore size distribution of various materials. Mercury is forced into the pores by the action of pressure and the volume of mercury intrusion per gram of sample at each pressure setting is calculated. The total pore volume expressed here refers to the cumulative volume of mercury intrusion from vacuum up to 60000 psi. Plotting the volume increase (in centimeters) at each pressure setting³In grams) and increments set in correspondence with pressureHole radius plot. The peak-pore radius curve of the invaded volume corresponds to the way the pore size is distributed for determining the most common pore size of the sample. Oil adsorption

The oil adsorption of linseed oil or DBP (dibutyl phthalate) oil was measured by the elimination (rub-out) method. The method comprises mixing linseed oil and silica product by wiping with a spatula on a flat surface until a viscous putty-like paste is formed. The oil absorption value of the silica product was determined by determining the amount of oil required to saturate the silica product, i.e., the amount of oil required to form the silica/cream-like mixture (which curls when laid flat). The oil adsorption value was calculated as follows:

oil adsorption value ═ cm (cm)³Adsorbed oil x 100 divided by silica product weight (g)

Is equal to centimeter³Oil/100 grams silica product CTAB surface area

The external surface area of the silica product was determined by the value of CTAB (cetyltrimethylammonium bromide) adsorbed on the surface of the silica product, the excess CTAB was removed by centrifugation and determined by titration with sodium dodecyl sulfate with a surfactant electrode. The external surface area of the silica product was calculated from the amount of CTAB adsorbed (CTAB analysis values before and after adsorption).

Specifically, about 0.5 g of the silica product was loaded into a 250 ml beaker containing 100.00 ml of CTAB solution (5.5 g/l). The solution was mixed on an electric stirring plate for 1 hour and then centrifuged at 10000rpm for 30 minutes. To 5 ml of clear supernatant in a 100 ml beaker was added 1 ml of 10% Triton X-100. The pH was adjusted to 3.0-3.5 with 0.1N HCl and the endpoint was determined by titration with sodium dodecyl sulfate using a surfactant electrode (Brinkmann SUR 1501-DL). Projected surface area

The average projected surface area of the silica product was determined by the following method. 150 mg of silica product was placed in a beaker containing a mixture of 10 ml of water and 20 ml of isopropanol; the mixture was shaken with ultrasound (L & R-PC5 Ultrasonic Cleaning Systems) for 60 minutes while maintaining the temperature below 30 ℃. Ultrasonic vibration was then continued while 10. mu.l of liquid was removed from the beaker with a micropipette and dropped onto three 200 mesh copper grids, which had been coated with a carbon-containing polyvinyl formal resin (CarbonFormvar). After the drop was allowed to stand for 20 seconds, excess liquid was removed by wicking (contacting the drop with the sharp corners of the filter paper) in order to prevent reagglomeration of the particles. The average projected area of 1000 aggregates was determined by image analysis.

For image analysis, the TEM micrograph is placed on a dual-purpose slide projector attachment to an image analysis computer. The area of all measurable particles on the micrograph was determined by means of the area function. Only particles that include all features and whose boundaries are clearly defined on the micrograph are analyzed. In this case, the particles are defined as aggregates of silica particles. Various size ranges are selected based on the applicability of the image analysis. The number of particles in each size range is the measured data. 5% pH

The 5% pH was determined as follows, 5.0 g of the silica product was weighed into a 250 ml beaker, 95 ml of deionized or distilled water was added, mixed on a magnetic stir plate for 7 minutes, and the pH was measured with a pH meter which had been previously standardized with two buffers falling within the desired pH range. Percentage of sodium sulfate

A13.3 g sample of the silica product was weighed out and 240 ml of distilled water was added. The slurry was mixed on a hamilton beach mixer for 5 minutes. The slurry was transferred to a 250 ml graduated cylinder and distilled water was added to make 250 ml of slurry. The samples were mixed and the temperature of the slurry was measured. The conductivity of the solution was measured with Solu-Bridge suitably adjusted by a temperature compensator. The percentage of sodium sulfate was determined using a standard calibration chart. Percentage of humidity (water)

About 2.0 grams of the sample was weighed to the nearest 0.0001 gram on a pre-weighed weighing pan. The sample was placed in an oven at 105 ℃ for 2 hours, and then the sample was removed and cooled on a desiccator. The cooled sample is weighed and the difference in weight is divided by the original weight of the sample and multiplied by 100 to obtain the percent humidity. Example 2

The precipitated amorphous silica product of the present invention is prepared as follows: in one reactor, 235 liters of water and 166 liters of 30.0% sodium silicate (silicate molar ratio 2.5, excess silicate 84.7%) were mixed and the reaction medium was heated to 87 ℃. To the heated reaction medium was added 33 ℃ sulfuric acid (11.4%) at a rate of 2.7 liters/min. When the pH of the reaction medium reached about 7.5, the rate of addition of acid was slowed to 1.4 liters/minute and the addition of 30.0% sodium silicate (molar ratio 2.5) was started at a rate of 1.0 liter/minute. The pH of the precipitate was maintained at 7.5 by adjusting the rate of addition of acid while adding. After 30 minutes, the addition of silicate was stopped, but the addition of acid was continued at a rate of 1.3 liters/minute until the pH of the reaction mixture reached 5.5. The reaction mixture was then digested for 10 minutes at 87 ℃ after which the pH was adjusted to 5.5 with more acid.

The precipitated silica slurry was rotary filtered from the reaction mixture and washed with water until the sodium sulfate content was reduced. The pH of the washed silica slurry was adjusted to 6.5 with more acid and then the silica slurry was spray dried.

The physical properties of the final product were measured in the same manner as in example 1, and the results are summarized in Table 1. Example 3

The precipitated amorphous silica product of the present invention is prepared as follows: in one reactor, 2568 gallons of 1.8% sodium sulfate and 1707 gallons of 24.7% sodium silicate (3.3 mole ratio silicate, 76.4% excess silicate) were mixed and the reaction medium was heated to 180 ° F. To the heated reaction medium was added 90 ° F sulfuric acid (7.4%) at a rate of 34.0 gallons per minute. When the reaction medium reached a pH of about 7.8, the acid addition rate was slowed to 17.6 gallons/minute and 24.7% sodium silicate (3.3 mole ratio) was started at an addition rate of 11.9 gallons/minute. The pH value of the precipitate is kept between 7.3 and 7.7 by adjusting the acid addition speed at the same time of adding. After 30 minutes, the silicate addition was stopped, but the acid addition was continued at a rate of 17.6 gallons per minute until the reaction mixture reached a pH of 5.5. The reaction mixture was then digested for 10 minutes at a temperature of 180 ° F, after which the pH was adjusted to 5.5 with more acid.

The precipitated silica slurry was rotary filtered from the reaction mixture and washed with water until the sodium sulfate content was reduced. The silica slurry is then spray dried.

The physical properties of the final product were measured in the same manner as in example 1, and the results are summarized in Table 1. Example 4

The silica product was prepared as in example 2 and then granulated. The silica product was compacted between small tandem rolls and then crushed into small particles to complete granulation at a pressure of 700 psi. The fine fraction of the small particles (less than 16 mesh) was recovered and returned to the tandem rolls with the other silica product, pressed into a denser dense silica product, which was then crushed and sieved to produce a granulated silica product having a particle bulk density of 0.281 g/ml, a particle size distribution of 83.3% +50 mesh and 5.4% -200 mesh. To evacuate the gases from the silica mass, a vacuum is applied to the granulation system before and during compaction.

The physical properties of the final product were measured in the same manner as in example 1, and the results are summarized in Table 1. Example 5

The precipitated amorphous silica product of the present invention is prepared as follows: in one reactor, 2732 gallons of water and 1749 gallons of 30% sodium silicate (2.5 mole ratio silicate, 83.6% excess silicate) were mixed and the reaction medium was heated to 87 ℃. Sulfuric acid (11.4%) at 33 c was then added to the heated reaction medium at a rate of 30.2 gallons per minute. When the reaction medium reached a pH of 7.5, the acid addition rate was slowed to 15.6 gallons/minute, and 30% sodium silicate (2.5 mole ratio) was started at an addition rate of 11.4 gallons/minute. The pH of the precipitate was maintained at 7.5 by adjusting the rate of addition of acid while adding. After 30 minutes, the silicate addition was stopped, but the acid addition was continued at a rate of 14.5 gallons per minute until the reaction mixture reached a pH of 5.5. The reaction mixture was then digested for 10 minutes at 87 ℃ after which the pH was readjusted to 5.5 with more acid.

The precipitated silica slurry was rotary filtered from the reaction mixture and washed with water until the sodium sulfate content was reduced. The spray dried silica slurry was then spray dried and the spray dried silica product granulated as in example 4 except that the pressure of the tandem roll was changed to 200psi and no vacuum was applied to the system.

The physical properties of the final product were measured in the same manner as in example 1, and the results are summarized in Table 1. Example 6

The precipitated amorphous silica product of the present invention is prepared as follows: in one reactor 3041 gallons of water and 1692 gallons of 30% sodium silicate (2.5 mole ratio silicate, 83.2% excess silicate) were mixed and the reaction medium was heated to 78 ℃. Sulfuric acid (11.4%) at 33 c was then added to the heated reaction medium at a rate of 29.3 gallons per minute. When the reaction medium reached a pH of 7.5, the rate of addition of acid was slowed to 15.6 gallons/minute, and 30% sodium silicate (2.5 mole ratio) was started at an acid addition rate of 11.4 gallons/minute. The pH of the precipitate was maintained at 7.5 by adjusting the rate of addition of acid while adding. After 30 minutes, the silicate addition was stopped, but the acid addition was continued at a rate of 15.6 gallons per minute until the reaction mixture reached a pH of 5.3. The reaction mixture was then digested for 10 minutes at a digestion temperature of 78 deg.C, after which the pH was readjusted to 5.3 with more acid.

The precipitated silica slurry was rotary filtered from the reaction mixture and washed with water until the sodium sulfate content was reduced. After adjusting the pH of the washed silica slurry to 6.5 with more acid as needed, the silica slurry was spray dried.

The physical properties of the final product were measured in the same manner as in example 1, and the results are summarized in Table 1. Example 7

A silica product was prepared as in example 6 and then granulated as in example 4. Except that the tandem roll pressure was changed to 620psi and no vacuum was applied to the system.

The physical properties of the final product were measured in the same manner as in example 1, and the results are summarized in Table 1.

In addition to the above examples, the physical properties of 3 commercially available precipitated amorphous silica products were tested as in example 1 and the results are summarized in Table 2. Comparative example 1 is Zeofree  (product of j.m. huber limited), comparative example 2 is Zeosil  1165MPND (product of Rhone-Poulenc Chimie), and comparative example 3 is Zeopol  8741 (product of j.m. huber limited).

TABLE 1

Physical Properties	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Example 7
								Shape of	Powder of	Powder of	Powder of	Granules	Powder of	Powder of	Granules
CTAB specific surface area (meter)2Pergram)	87	55	114	61	76	93	95
								BET specific surface area (m)2Pergram)	133	75	150	83	91	132	187
5％pH	6.9	7.0	7.0	7.0	7.4	6.9	6.9
								Mercury intrusion into the peak diameter position, angstrom	640	1020	360	640	790	610	500
Total pore volume for mercury intrusion, (centimeters)3Pergram)	4.2676	3.7618	4.5191	1.8637	5.5669	4.8330	2.6777
								Mercury intrusion pore volume ratio (V2/V1)*100	20.4	21.2	28.6	23.8	19.2	23.4	23.6
Bulk density of the pellets, (g/ml)	****	****	****	0.281	0.197	****	0.225
								％Na2SO4	1.3	1.2	1.5	1.3	2.6	1.3	1.8
APS micro-scanning of powder (micron)	54.2	28.6	66.6	****	****	62.5	****
								Projected surface area, (nanometer)2)	3098	****	****	****	****	****	****
The granules retained on a 50 mesh sieve%	****	****	****	83.3	81.2	****	91.8
								Granules passing through a 200 mesh sieve%	****	****	****	5.4	5.6	****	3.4
Free water content%	5.3	5.0	4.7	5.7	6.8	5.9	5.3
								Adsorption value cm of linseed oil3Per 100 g	204	218	233	203	169	210	177
DBP oil adsorption in cm3Per 100 g	210	248	248	229	202	242	205

TABLE 2

Physical Properties	Comparative example 1	Comparative example 2	Comparative example 3
				Trade name	Zeofree80	Zeosil1165	Zeopol8741
Shape of	Powder of	Microbeads	Powder of
				CTAB specific surface area (meter)2Pergram)	55	153	143
BET specific surface area (m)2Pergram)	85	164	183
				5％pH	7.0	6.4	7.2
Mercury intrusion into the peak diameter position, angstrom	700	250	285
				Total pore volume for mercury intrusion, (centimeters)3Pergram)	19.9	3.0799	4.9975
Mercury intrusion pore volume ratio (V2/V1)*100	81.0	56.6	39.7
				％Na2SO4	1.9	0.51	1.8
APS micro-scanning of powder (micron)	14.2	268	45
				Free water content%	5.7	5.5	5.0
Projected surface area, (nanometer)2)	4211	9627	1967
				Adsorption value of linseed oil in cm3Per 100 g	202	185	185
DBP oil adsorption in cm3Per 100 g	222	233	298

To compare the properties imparted to the rubber compositions by the silica products, various loadings of each of the silica products of the present invention in Table 1 and the prior art silica products in Table 2 were added to the same rubber matrix. In addition, the rubber composition was prepared with carbon black filler (no silica filler/no coupling agent). Table 3 shows the composition of the rubber matrix, while table 4 shows the exact shape (powder or granules) and loading of the silica. The resulting rubber compositions were tested according to industry standards: mooney viscosity (ASTM D1646), M_{Maximum value}(ASTM D2084)，t_s2(ASTM D2084), T90(ASTM D2084), 100, 200 and 300% modulus (ASTM D412), Tensile at Break (ASTM D412), elongation at Break (ASTM D412), mold groove tear strength (ASTM D624), DIN abrasion resistance (ISO-4649 method B), NBS abrasion resistance (ASTM D1630), Faston operating temperature (ASTM D623), -25, 22 and 100 ℃ Zvyvale rebound (ASTM 1504), 1% and 12% DSA at 60 ℃ (measured in RPA 2000 from Monsanto). The results are summarized in table 4.

TABLE 3

Composition (I)	Carbon black N-234 formulations	Silicon dioxide formulation
			Solution polymerization SBR-JSR-SL574*	75	75
Polybutadiene CB11**	25	25
			Reinforcing filler	80	80
Stearic acid	1	1
			Coupling agent X-50S	0	0.00-12.80
Aromatic hydrocarbon 8125	32.5	32.5
			Zinc oxide	2.5	2.5
Sunolite 240TG***	1.5	1.4
			Santoflex 13	2	2
Sulfur	1.35	1.7
			Delac S	1.35	1.7
DPG	0	2
			Total of phr	222.2	224.80-237.60

:

TABLE 4

Physical and service characteristics of rubber	Rubber containing N-234 carbon black	Rubber containing the Filler of comparative example 1	Rubber containing the Filler of comparative example 2	Rubber containing the Filler of comparative example 2	Rubber containing the Filler of comparative example 3	Rubber containing the Filler of comparative example 3	Rubber containing the Filler of example 1	Rubber containing the Filler of example 1	Rubber containing the Filler of example 3	Rubber containing the Filler of example 5	Rubber containing the Filler of example 6	Rubber containing the Filler of example 7
													Shape of silica filler	****	Powder of	Microbeads	Microbeads	Powder of	Powder of	Powder of	Powder of	Powder of	Granules	Powder of	Granules
Coupling agent (phr)	0.00	7.20	12.80	8.96	12.80	8.96	12.8	7.20	10.0	7.00	7.0	7.0
													MMaximum value(Nm)	6.5	7.9	9.0	8.5	8.0	7.6	8.9	7.3	8.1	6.9	8.0	9.6
Ts2 (minutes)	3.8	2.2	1.9	1.8	1.9	1.7	1.9	2.3	2.2	2.3	2.8	2.5
													T90 (minutes)	7.3	3.8	9.3	13.0	6.4	9.3	5.5	4.7	6.8	4.0	5.5	5.6
Mooney viscosity at 100 ℃ MM(1+4)(mu)	70.9	50.0	92.0	97.0	82.0	86.0	57.2	59.4	72.5	49.3	50.8	60.3
													100% modulus (MPa)	2.01	2.74	2.90	2.53	2.85	2.30	3.94	2.45	2.94	2.64	2.63	2.87
200% modulus (MPa)	4.31	6.98	7.03	6.17	8.24	6.34	10.7	6.50	7.10	7.36	6.13	6.95
													300% modulus (MPa)	8.07	12.7	14.4	12.0	13.2	13.1	***	12.1	9.24	13.2	10.5	12.0
Breaking force (MPa)	18.9	15.4	17.8	16.8	18.2	19.1	14.4	16.4	15.0	15.6	14.3	14.8
													Elongation at break%	618	341	346	371	367	386	251	372	344	344	384	346
DIN abrasion resistance index	****	***	112	102	134	129	***	***	***	127	136	123
													NBS abrasion resistance (%)	4190	4392	9500	11500	9060	11300	9928	11065	7041	***	***	8082
Faston working temperature, deg.C	150	94	104	107	99	102	97	94	100	***	***	***
													Zivweike rebound at 100 ℃ (%)	50	73	65	63	68	67	62	70	70	79	70	69
Zivweike rebound at 22 ℃ (%)	35	63	50	51	54	55	60	58	56	62	57	61
													Zivweike rebound at-25 ℃ (%)	11.0	7.6	7.6	7.6	6.6	6.8	6.4	8.4	7.6	5.8	7.8	7.0
The tangent delta value is 12% DSA at 60 DEG C	0.353	0.087	0.155	0.139	0.110	0.110	0.101	0.102	0.118	0.100	***	***

Physical and service characteristics of rubber	Rubber containing N-234 carbon black	Rubber containing the Filler of comparative example 1	Rubber containing the Filler of comparative example 2	Rubber containing the Filler of comparative example 2	Rubber containing the Filler of comparative example 3	Rubber containing the Filler of comparative example 3	Rubber containing the Filler of example 1	Rubber containing the Filler of example 1	Rubber containing the Filler of example 3	Rubber containing the Filler of example 5	Rubber containing the Filler of example 6	Rubber containing the Filler of example 7
													The tangent delta value is 12% DSA at 60 DEG C	0.353	0.087	0.155	0.139	0.110	0.110	0.101	0.102	0.118	0.100	***	***
1% DSA at 60 ℃ for the tangent delta value	0.289	0.057	0.118	0.103	0.090	0.079	0.084	0.086	0.098	0.064	***	***

Further silica products according to the invention were prepared according to example 6, the specific gravity of the silicate used, the excess rate of silicate, the reaction temperature, the digestion temperature and the pH of the spray-dryer batch being shown in Table 5. The silica products of the invention were added separately to the rubber formulations shown in Table 6, as well as for comparison purposes, prior art silica products (Zeopol  8745, product of J.M. Huber, Inc.). Rubber formulations made according to the passenger car tire industry standard test (test as described in table 4) and the results are summarized in table 7.

TABLE 5

Synthesis parameters, physical characteristics	Example 8	Example 9	Example 10	Example 11	Example 12	Example 13	Example 14	Example 15
									Shape of	Powder of	Powder of	Powder of	Powder of	Powder of	Powder of	Powder of	Powder of
Silicate specific gravity of reaction medium	1.120	1.120	1.135	1.135	1.135	1.135	1.135	1.135
									Excess of silicate, percent	83.7	83.7	83.7	83.7	83.7	83.7	83.7	83.7
Reaction temperature of	80	80	80	80	68	68	68	68
									Digestion temperature of	80	80	80	80	68	68	93	93
pH of spray dryer Material	6.8	6.2	6.8	6.2	6.8	6.2	6.8	6.2
									CTAB specific surface area, meter2Per gram	80	90	72	72	118	119	104	110
BET specific surface area, rice2Per gram	120	152	130	153	243	261	170	220
									5％pH	7.35	6.87	7.14	7.25	7.48	6.99	7.2	7.1
Mercury intrusion peak diameter location (angstroms)	590	580	850	830	450	420	400	410
									Total pore volume for mercury intrusion, (centimeters)3Pergram)	4.7917	4.3743	4.4631	4.3070	4.4379	4.4070	4.5979	3.4736

TABLE 5 (continuation)

Synthesis parameters, physical characteristics	Example 8	Example 9	Example 10	Example 11	Example 12	Example 13	Example 14	Example 15
									Mercury intrusion pore volume ratio (V2/N1)*100	24.2	22.2	24.9	21	32.6	32.9	30.7	31.9
％Na2SO4	2.32	1.14	2.39	1.06	1.29	1.14	4.28	1.61
									APS micro-scanning of powders	46.4	43.0	58.6	55.8	84.1	49.3	66.6	56.8
Free water content%	4.7	4.7	5.1	4.5	6.6	5.8	5.0	4.4
									Adsorption value of linseed oil in cm3Per 100 g	235	225	218	214	245	237	237	242
DBP oil adsorption in cm3Per 100 g	251	268	231	241	279	272	256	255

TABLE 6

Composition (I)	Silicon dioxide formulation
		Solution polymerization SBR	70.00
Polybutadiene	30.00
		Reinforcing filler	70.00
Coupling agent X-50S	11.00
		Process aid	33.50
Sulfur	1.70
		Curing agent	9.20
Total of phr	225.10

TABLE 7

Characteristic of use	Zeopol  8745 filler-containing rubber	Rubber containing the Filler of example 8	Rubber containing the Filler of example 9	Rubber containing the Filler of example 10	Rubber containing the Filler of example 11	Rubber containing the Filler of example 12	R contains examples13-filled rubber	Rubber containing the Filler of example 14	Rubber containing the Filler of example 15
										Shape of	Granules	Powder of	Powder of	Powder of	Powder of	Powder of	Powder of	Powder of	Powder of
MMaximum value(Nm)	64.6	65.6	66.3	67.0	68.0	65.4	65.0	66.1	67.1
										Ts2 (minutes)	5.0	4.0	4.2	3.8	3.8	4.8	4.4	4.6	4.9
T90 (minutes)	12.1	7.1	7.4	7.0	8.3	10.1	14.4	9.9	13.6
										Mooney viscosity at 100 ℃ M1(1+4)(mu)	81.0	81.7	84.2	81.0	81.7	84.8	91.3	88.7	92.9
100% modulus (MPa)	2.26	2.57	2.62	2.59	3.02	2.43	2.46	2.52	2.67
										200% modulus (MPa)	6.67	6.94	7.33	6.99	7.80	6.33	6.73	6.92	7.75
300% modulus (MPa)	13.4	12.7	13.5	12.7	13.5	12.1	12.8	13.2	14.8
										Breaking force (MPa)	21.7	18.9	19.2	16.8	17.0	19.3	19.5	19.6	18.3
Elongation at break%	420	399	393	378	364	421	395	401	360
										Molded groove-tear Strength (kilonewtons/meter)	46	25	27	25	25	47	47	36	31
The tangent delta value is 12% DSA at 60 DEG C	0.128	0.104	0.102	0.090	0.099	0.113	0.119	0.111	0.112
										1% DSA at 60 ℃ for the tangent delta value	0.078	0.066	0.062	0.061	0.065	0.074	0.078	0.073	0.073

Table 8 summarizes the relevant properties of the silica products as reflected by the rubber characteristics listed in tables 4 and 7. Tables 4, 7 and 8 show that the properties measured in each respect of the rubber compositions comprising the silica products of the invention are comparable to or better than those of the rubber compositions comprising the prior art silica products. From the results reflected in the rubber use properties, these tables also show that the silica products of the invention are excellent compared with the carbon black fillers used in the prior art. More specifically, the rubber compositions filled with the silica products of the invention have exactly the same advantages as those filled with the silica products of the prior art, while also improving the abrasion resistance of the rubber compositions. The rubber compositions filled with the silica products of the invention are processable better than with the highly dispersed silica fillers of the prior art and to the level achieved when filled with carbon black fillers. Furthermore, the table also shows that the novel silica products for use as rubber fillers have a reduced demand for coupling agents, reduced heat build-up and improved temperature/ice adhesion compared to carbon black and prior art silica products.

TABLE 8

Use performance	Preferred value	The silica products of the examples of the invention are comparable to carbon black	Granulated silica product of the inventive example compared with comparative example 1	The silica products of the examples of the invention are compared with comparative examples 2 and 3
					Shape of	Granules	Are identical to each other	Is excellent in	Identity/better
Coupling dose (Si-69)	Lower/cost	Is poor	Is preferably used	Is excellent in
					MMaximum value(Nm)	Is larger	Is poor	Identity/better	Are identical to each other
ts2(minutes)	Is longer	Is shorter	Are identical to each other	Is preferably used
					T90 (minutes)	Is shorter	Is preferably used	Are identical to each other	Is preferably used
Mooney viscosity ML(1+4)At 100 deg.C (mu)	Low/processability	Is preferably used	Identity/poor	Is excellent in
					100% modulus (MPa)	Is lower than	Worst case	Are identical to each other	Are identical to each other
200% modulus (MPa)	Is higher than	Is preferably used	Are identical to each other	Are identical to each other
					300% modulus (MPa)	Is higher than	Is preferably used	Are identical to each other	Identity/better
Breaking force (MPa)	Is higher than	Is poor	Are identical to each other	Are identical to each other
					Elongation at break%	Is higher than	Is poor	Are identical to each other	Are identical to each other
NBS abrasion resistance (%)	Is higher than	Is excellent in	Is excellent in	Are identical to each other
					Faston operating temperature (DEG C)	Is lower than	Is excellent in	Are identical to each other	Is excellent in
Zivweike rebound at 100 ℃ (%)	Is larger	Is excellent in	Are identical to each other	Are identical to each other
					Zivweike rebound at 22 ℃ (%)	Is larger	Is excellent in	Are identical to each other	Are identical to each other
Zivweike rebound at-25 ℃ (%)	Is lower than	Is excellent in	Identity/better	Identity/better
					The tangent delta value is 12% DSA at 60 DEG C	Is lower than	Is excellent in	Are identical to each other	Is excellent in
1% DSA at 60 ℃ for the tangent delta value	Is lower than	Is excellent in	Are identical to each other	Is excellent in

These examples do demonstrate that the silica products of the present invention unexpectedly improve the processability and the service properties of rubber compositions used to prepare tire treads. In particular, the silica product of the invention most advantageously combines the use properties of rubber tire tread formulations previously considered to be contradictory, such as reduced rolling resistance (as evidenced by low Faston service temperature, high Zivzvke 100 ℃ rebound and low tan delta at 60 ℃), improved adhesion under various conditions (as evidenced by low Zivke rebound at-25 ℃) and excellent wear resistance (as evidenced by NBS wear resistance values).

The advantages of mixing and extrusion of the rubber provided by the silica product of the invention are evidenced by the low Mooney viscosity values described above. In addition, low T90 (associated with increased productivity) and high T_s2The (scorch) values demonstrate improved processability with the silica products of the invention without premature setting of the composition.

Although the present invention has been described herein with reference to particular and preferred embodiments, it is to be understood that various changes, modifications, substitutions and omissions may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (37)

1. A precipitated amorphous silica product comprising:

CTAB specific surface area of about 10 m²Per gram to less than 140 m²Per gram;

multiple point BET surface area of about 50-225 m²Per gram;

a 5% pH of about 5.0-8.5;

DBP oil adsorption value of about 160-310 cm³100 g;

the adsorption value of linseed oil is about 150-300 cm³100 g;

small projected surface areaAt about 4000 nm²(ii) a And

the pore volume ratio of pore diameter at 175-275 angstroms to all pore diameters less than 400 angstroms is from about 10% to less than 50%.

2. The precipitated amorphous silica product according to claim 1 wherein said CTAB specific surface area is about 10 to 110 meters²Per gram.

3. The precipitated amorphous silica product according to claim 1 wherein said CTAB specific surface area is about 10 meters²Per gram to less than 100 m²Per gram.

4. A precipitated amorphous silica product according to claim 3 wherein said projected surface area is no greater than 3500 nm²。

5. A shaped precipitated amorphous silica product comprising:

CTAB specific surface area of about 10 m²Per gram to less than 140 m²Per gram;

multiple point BET surface area of about 50-225 m²Per gram;

a 5% pH of about 5.0-8.5;

DBP oil adsorption value of about 160-310 cm³100 g;

the adsorption value of linseed oil is about 150-300 cm³100 g;

projected surface area no greater than about 4000 nm²(ii) a And

the pore volume ratio of pore diameter at 175-275 angstroms to all pore diameters less than 400 angstroms is from about 10% to less than 50%.

6. A shaped precipitated amorphous silica product according to claim 5 wherein said CTAB specific surface area is about 10 to 110 meters²Per gram.

7. A shaped precipitated amorphous silica product according to claim 5 wherein saidCTAB specific surface area of about 10 meters²Per gram to less than 100 m²Per gram.

8. A shaped precipitated amorphous silica product according to claim 5 further comprising a bulk density of from about 0.16 to about 0.30 g/ml.

9. A shaped precipitated amorphous silica product according to claim 5 further comprising a bulk density of from about 0.16 to about 0.27 g/ml.

10. A shaped precipitated amorphous silica product according to claim 5 further comprising less than 200 mesh in an amount of no greater than about 20% by weight.

11. A shaped precipitated amorphous silica product according to claim 10 wherein said content of less than 200 mesh is no greater than about 10% by weight.

12. A process for the preparation of a precipitated amorphous silica product comprising the steps of:

(a) adding an acid to a mixture of water and an alkali metal silicate at a substantially constant rate until the reaction mixture reaches a pH of about 10.0 to 6.5, said mixture having a temperature of about 60 to 90 ℃, said silicate having a molar ratio of about 2.4 to 3.3;

(b) adding more of said silicate to said reaction mixture for a time period of about 0 to 60 minutes while controlling said rate of addition of acid such that said reaction mixture maintains a pH of about 10.0 to 6.5;

(c) discontinuing the addition of the silicate and continuing the acid addition until the reaction mixture reaches a pH of about 4.5-6.5;

(d) digesting the reaction mixture for about 0-60 minutes at a digestion temperature of about 60-99 ℃;

(e) filtering the reaction mixture to recover a silica slurry;

(f) washing the silica slurry to form a washed silica product; and

(g) drying the washed silica product to produce a dried silica product.

13. The method of claim 12, wherein said washing step is carried out until the washed silica product has a sodium sulfate content of no greater than about 4.5%.

14. The method according to claim 12, further comprising adjusting the pH of the washed silica product to about 6.0-7.0.

15. The method of claim 12 wherein said drying step is carried out to H of said dried silica product₂The O content is no greater than about 8%.

16. The method according to claim 12, wherein an electrolyte is added during at least one step selected from the group consisting of adding acid to a mixture of water and alkali metal silicate, adding more silicate to the reaction mixture, discontinuing and continuously adding silicate, and digesting the reaction mixture.

17. The method of claim 16, wherein the electrolyte is sodium sulfate.

18. An elastomeric composition comprising an elastomer and a precipitated amorphous silica product, said silica product comprising:

CTAB specific surface area of about 10 m²Per gram to less than 140 m²Per gram;

multiple point BET surface area of about 50-225 m²Per gram;

a 5% pH of about 5.0-8.5;

DBP oil adsorption value of about 160-310 cm³100 g;

the adsorption value of linseed oil is about 150-300 cm³100 g;

projected surface area no greater than about 4000 nm²(ii) a And

the pore volume ratio of pore diameter at 175-275 angstroms to all pore diameters less than 400 angstroms is from about 10% to less than 50%.

19. The elastomeric composition according to claim 18, wherein the silica product has a CTAB specific surface area of about 10-110 meters²Per gram.

20. The elastomeric composition according to claim 18, wherein the silica product has a CTAB specific surface area of about 10 meters²Per gram to less than 100 m²Per gram.

21. An elastomeric composition according to claim 18, wherein said precipitated amorphous silica product is a shaped silica product.

22. The elastomeric composition according to claim 21, wherein said shaped silica product has a bulk density of about 0.16 to 0.30 g/ml.

23. The elastomeric composition according to claim 21, wherein said shaped silica product has a bulk density of about 0.16 to 0.27 g/ml.

24. The elastomeric composition of claim 21, wherein said shaped silica product is present in an amount of less than about 20 weight percent of a 200 mesh screen.

25. The elastomeric composition of claim 18, wherein said elastomer is a solution polymerized styrene butadiene rubber.

26. The elastomeric composition of claim 25, wherein said elastomer further comprises at least one other polymer.

27. The elastomeric composition according to claim 26, wherein said other polymer is a diene.

28. A passenger car tire tread comprising an elastomer and a precipitated amorphous silica product, said silica product comprising:

CTAB specific surface area of about 10 m²Per gram to less than 140 m²Per gram;

multiple point BET surface area of about 50-225 m²Per gram;

a 5% pH of about 5.0-8.5;

DBP oil adsorption value of about 160-310 cm³100 g;

the adsorption value of linseed oil is about 150-300 cm³100 g;

projected surface area no greater than about 4000 nm²(ii) a And

the pore volume ratio of pore diameter at 175-275 angstroms to all pore diameters less than 400 angstroms is from about 10% to less than 50%.

29. A passenger car tire tread according to claim 28 wherein said silica product has a CTAB specific surface area of about 10-110 meters²Per gram.

30. A passenger car tire tread according to claim 28 wherein said silica product has a CTAB specific surface area of about 10 meters²Per gram to less than 100 m²Per gram.

31. A passenger tire tread according to claim 28 wherein said silica product is a shaped silica product.

32. A passenger tire tread according to claim 31, wherein said shaped silica product has a bulk density of from about 0.16 to about 0.30 g/ml.

33. A passenger tire tread according to claim 31, wherein said shaped silica product has a bulk density of from about 0.16 to about 0.27 g/ml.

34. A passenger car tire tread according to claim 31 wherein said shaped silica product is present in an amount of less than 200 mesh in an amount of no more than about 20 weight percent.

35. A passenger car tire tread according to claim 28 wherein said elastomer is solution polymerized styrene butadiene rubber.

36. The passenger tire tread of claim 35, wherein said elastomer further comprises at least one other polymer.

37. A passenger tire tread according to claim 36 wherein said other polymer is a diene.