Claims:We Claim:

1. A curable elastomer composition comprising:
- atleast 50 % (w/w) of an elastomer;
- atleast 30 % (w/w) of precipitated silica having a CTAB surface area in a range of 110-170 m2g; a BET surface area in a range of 100-170 m2g, a BET/ CTAB ratio in a range of 1.1- 1.25; a DBP oil absorption in a range of 240-320 ml/100g, a CDBP co-efficient (DA) in range of 0.5-.0.9, a sears number (V2) in a range of 10 to 25 ml/ (5g), and a sears number (V2)/CTAB ratio in a range of 0.16-0.20 ml/(5 m2).

2. A curable elastomer composition as claimed in claim 1, wherein the precipitated silica has a Wk coefficient number less than 3.

3. A curable elastomer composition as claimed in claim 1, wherein the precipitated silica has an average particle size ranging from 10-30 nm.

4. A curable elastomer composition as claimed in claim 1, wherein the precipitated silica has an average particulate aggregate size ranging from 50-3000 nm.

5. A curable elastomer composition as claimed in claim 1, wherein the precipitated silica has a pore volume ranging from 0.01 to 0.02 cm³/g.

6. A curable elastomer composition as claimed in claim 1, wherein the precipitated silica has a pore size distribution ranging from 4.0-10.0 (g nm)/ml.

7. A curable elastomer composition as claimed in claim 1, wherein the precipitated silica has a moisture loss of 2 to 5% by weight on drying for two hours at 105°C.

8. A curable elastomer composition as claimed in claim 1, further comprising one or more of additives selected from a group consisting of processing aids, antioxidants, an-tiozonants, and fillers.
9. A curable elastomer composition as claimed in claim 1, wherein the elastomer is se-lected from a group consisting of polybutadienes, polyisoprenes, natural rubber, buta-diene-styrene copolymers, butadiene-isoprene copolymers, butadiene-acrylonitrile co-polymers, isoprene-styrene copolymers, butadiene-styrene-isoprene copolymers and mixtures thereof.

10. A curable elastomer composition as claimed in claim 1, upon curing has a modulus 100% of 1.5-3.0MPa, a modulus 300% of 8.5-11.5MPa, and a reinforcement index of around 4.5.

11. A tyre having at least one component comprising the curable elastomer composition claimed in any of the preceding claims.

Dated this 29th day of February, 2016

Sneha Agarwal
Of Obhan & Associates
Agent for the Applicant
Patent Agent No. 1969 , Description:Field of Disclosure
The present disclosure relates to a curable elastomer composition reinforced with precipitated silica. Specifically, the present disclosure provides a curable elastomer com-position reinforced with highly dispersible precipitated silica having specific morphology, structure, surface area, pore volume, pore size distribution and silanol group density.
Background
Silica is well-known for use as a reinforcing filler in elastomer compositions, such as those used to form tyres. The reinforcing fillers used in tyre compounding are critical to achieving the performance requirements and substantially assist in strengthening the rubber network thereof, resulting in a substantial increase in stiffness, tensile strength, and resistance to abrasion. This in effect contributes in increasing the longevity of tyres while reducing the fuel consumption. The silica used in the tyre industry is generally precipitated silica, in particular characterized by its particle size, structure and surface activity.
An essential parameter for characterizing precipitated silica is the surface area which is determined either by the adsorption of nitrogen (commonly referred to as BET (after Brunauer, Emmett and Teller) surface area) or, by the adsorption of Cetyl trimethyl ammonium bromide (CTAB) on the surface of silica (commonly referred to as CTAB sur-face area). BET surface area provides total surface area, whereas CTAB surface area pro-vides external surface area of silica. The ratio of said two parameters viz. BET/ CTAB provides a measure of microporosity. Pore volume and pore size distribution are also im-portant factors which determine the elastomer and filler interaction.
Once silica is synthesized, primary particles condense into aggregates having di-mensions of 100-200 nm. These are the real reinforcing species in elastomer compounds. As the concentration of the aggregate particles increases, an interaction between them leads to the formation of bigger agglomerates. The degree of condensation in aggregates is designated by structure, determines the inter-particle void volume and pore diameter with-in the aggregates. The measurement of this “structure” is based on the adsorption of dibu-tyl phthalate (DBP) and is determined by the amount of absorbed DBP.
Another significant parameter which determines the dispersibility of silica is CDBP coeffficient (DA). This coefficient is calculated according to the difference in the DBP absorption between the primary uncompressed sample (DBPO) and sample after its compression at 40 MPa (Compressed DBP or CDBP), as shown in formula below:
DA =1—(CDBP/DBPO)
This coefficient theoretically ranges from 0 to 1, whereas the higher the value of the coefficient, the weaker is the structure of the silica.
Another parameter, Wk coefficient, is the ratio of the peak height of the non-degradable particle, the maximum of which lies in the range of 1.0-100 microns, to the peak height of the degraded particles, the maximum of which lies in the range of <1 mi-cron. The Wk coefficient provides a measurement of the “degradability” (dispersibility) of the precipitated silica.
It is known that the properties of precipitated silica affect the reinforcement prop-erties thereof. It necessitates the need to identify the characteristic attributes of silica suit-ed for different requirement profile of different applications. Depending on the require-ment profile, these properties may vary.
For instance, EP 0 937 755 discloses that precipitated silicas which possess a BET surface area from about 180 to about 430 m2/g and a CTAB surface area from about 160 to 340 m2/g and a BET to CTAB ratio of about 1.1 to 1.3 are particularly suitable as carrier material. However, such precipitated silica is not meant for application in elastomer and rubber compositions.
US20030082090 discloses that precipitated silica having very different BET (?135 m2/g)and CTAB surface areas (?75 m2/g) while remaining above minimum values are particularly suitable as fillers.
Apart from surface area, surface activity of silica, which is usually defined in terms of Sears number influences the properties of silica. Sears number is a measurement of the concentration of silanol groups on the precipitated silica. The silanol groups on the surface of precipitated silica function as potential chemical reaction sites for a coupling reagent, which permit coupling of the silica to the elastomer matrix. The ratio of Sears Number/ CTAB surface area provides the concentration of silanol groups for a given level of CTAB surface area.
US 7566433 discloses precipitated silica having a relative breadth ?of pore size distribution of 4.0-10.0 (g nm)/ml, a Sears Number of 28-40 ml/(5 g), a Sears Number /CTAB ratio of 0.18-0.28 ml/(5 m2), and CTAB of ?100-200 m2/g and suggests that such precipitated silica are particularly suitable as reinforcing fillers. Further, disclosed precipi-tated silica has a BET/CTAB ratio greater than 1.3 and a zeta potential at pH 5 from -12 to -30 mV. The precipitated silica is obtained by controlling the addition of sulphuric acid such that prevailing alkali number in the reaction medium is 30.0 + 0.3. Additionally, the process employs organic / inorganic salt, as a result of which it contains residues of Al2O3 ranging from 0.01 to 5%.
US 7790131 discloses that highly dispersible silica having BET surface area 200–300 m2/g, CTAB surface area ?170 m2/g, DBP number 200–300 g/(100 g), and Sears number 23–35 ml/(5 g) are particularly suited for use as a tyre filler for utility vehicles, motor cycles and high speed vehicles. The precipitated silica having said properties is ob-tained by using organic and/or inorganic salt in the aqueous solution of 0.01 to 5 mol/l to get the desired properties.
There is still a requirement for elastomer compositions which could exhibit superior physical and mechanical properties over conventional silica reinforced elastomer com-positions. It is further desirable that such elastomer composition could be used to manu-facture tyre compound having low rolling resistance, improved handling, and resistance to wear.
Summary
A curable elastomer composition is disclosed. Said curable elastomer composition comprises atleast 50 % (w/w) of an elastomer; atleast 30 % (w/w) of precipitated silica having a CTAB surface area in a range of 110-170 m2g; a BET surface area in a range of 100-170 m2g, a BET/ CTAB ratio in a range of 1.1- 1.25; a DBP oil absorption in a range of 240-320 ml/100g, a CDBP coefficient (DA) in range of 0.5-.0.9, a sears number (V2) in a range of 10 to 25 ml/ (5g), and a sears number (V2)/CTAB ratio in a range of 0.16-0.20 ml/(5 m2).

Brief Description of Drawings
Figures 1a and 1b illustrate extrudate smoothness (before moulding) of a conven-tional elastomer composition and the elastomer composition of the present disclosure, re-spectively.
Figures 2a and 2b illustrate extrudate smoothness (after moulding) of a conven-tional elastomer composition and the elastomer composition of the present disclosure, re-spectively.
Figures 3a and 3b illustrate appearance of the mileage tested tyre tread formed from a conventional elastomer composition and the elastomer composition of the present disclosure, respectively.
Detailed Description
For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclo-sure is thereby intended, such alterations and further modifications in the disclosed com-position and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.
It will be understood by those skilled in the art that the foregoing general descrip-tion and the following detailed description are exemplary and explanatory of the disclo-sure and are not intended to be restrictive thereof. It will be further understood by those skilled in the art that the parameters such as BET surface area, CTAB surface area, CDBP coefficient (DA), DBP absorption, Wk coefficient, sears number, have the same meaning as generally understood in the art, unless specifically stated otherwise.
Reference throughout this specification to “one embodiment”“an embodiment”or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present dis-closure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment”and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
In its broadest scope, the present disclosure relates to a curable elastomer composi-tion reinforced with precipitated silica. Specifically, the present disclosure provides a cur-able elastomer composition reinforced with highly dispersible precipitated silica having the following physico-chemical characteristic data:
- a CTAB surface area in a range of 80 to 230 m2/g;
- a BET surface area in a range of 100 to 250 m2/g;
- a BET/ CTAB ratio in a range of 0.8- 1.35;
- a DBP oil absorption in a range of 240-320 ml/100g;
- a CDBP coefficient (DA) in range of 0.4-.0.9;
- a sears number (V2) in a range of 10 to 30 ml/ (5g); and
- a sears number (V2)/CTAB ratio in a range of 0.16-0.20 ml/(5 m2).
It has been observed by the present inventors that aforesaid curable elastomer composition exhibits improved reinforcibility Index. Specifically, said curable elastomer composition exhibits improved dispersion of silica in the elastomer; improved processing i.e. it requires less number of mixing stages; better extrudate smoothness upon extrusion and better appearance compared to conventional elastomer compositions.
In accordance with a preferred embodiment, the precipitated silica has the CTAB surface area in the range of 130 to 170 m2/g. In accordance with another preferred embod-iment, the precipitated silica has the BET surface area in the range of 100-170 m2/g. In accordance with yet another preferred embodiment, the BET/CTAB of the precipitated silica is in the range of 1.1 to 1.25. In accordance with a further preferred embodiment, the DBP oil absorption of the precipitated silica is in the range of 280-320 ml/100g. In ac-cordance with a further preferred embodiment, the CDBP coefficient (DA) is in the range of 0.5 to 0.9. In accordance with a further preferred embodiment, the precipitated silica has the sears number (V2) in the range of 10 to 25 ml/ (5g).
In accordance with an embodiment, the precipitated silica has a Wk coefficient number less than 3. Preferably, the precipitated silica has the Wk coefficient number rang-ing from 1 to 3.
In accordance with an embodiment, the precipitated silica has an average primary particle size ranging from 8 to 50 nm. Preferably, the precipitated silica has the average primary particle size ranging from 10 to 30 nm.
In accordance with an embodiment, the precipitated silica has an average particu-late aggregate size ranging from 50 to 3000 nm. Preferably, the precipitated silica has the average particulate aggregate size ranging from 50 to 600 nm.
In accordance with an embodiment, the precipitated silica has a micro pore volume ranging from 0.01 to 0.06 cm³/g. Preferably, the precipitated silica has the micro pore vol-ume ranging from 0.01 to 0.02 cm³/g.
In accordance with an embodiment, the precipitated silica has a micro pore area ranging from 6 to 35 m2/g. Preferably, the precipitated silica has the micro pore area rang-ing from10 to 25 m2/g.
In accordance with an embodiment, the precipitated silica has a pore diameter ranging from 250 Å to 350 Å. Preferably, the precipitated silica has the pore diameter ranging from 250 Å to 300 Å.
In accordance with an embodiment, the precipitated silica has a moisture loss of 2 to 6% by weight, on drying for two hours at 105°C. Preferably, the precipitated silica has the moisture loss of 2 to 5% by weight, on drying for two hours at 105°C.
In accordance with an embodiment, the precipitated silica has a tapped density in a range of 0.12 – 0.3 g/cc. Preferably, the precipitated silica has the tapped density in a range of 0.18 to 0.25 g/cc.
In accordance with an embodiment, the precipitated silica has a bulk density in a range of 80 – 140 g/l. Preferably, the precipitated silica has the bulk density in the range of 100 to 120 g/l.
In accordance with a embodiment, the precipitated silica has a pH value of 6 – 6.5 (5 % in water).
In accordance with an embodiment, the precipitated silica has a SiO2 content of greater than 96 %. Preferably, the precipitated silica has the SiO2 content of 97%.
In accordance with an embodiment, the precipitated silica has a soluble salt content of 0.5 to 1%. Preferably, the precipitated silica has the soluble salt content of less than 0.5%.
In accordance with an embodiment, the precipitated silica has a zeta potential in a range of -20 mV to -50 mV. Preferably, the precipitated silica has the zeta potential in the range of -30mV to -40 mV.
In accordance with an embodiment, the precipitated silica has an electrical conduc-tivity (4% in water) of less than 1300 µS/ cm. Preferably, the precipitated silica has the electrical conductivity (4% in water) of less than 1200 µS/ cm.
The present disclosure also provides a process of preparing aforesaid precipitated silica. Said process comprises of:
- reacting an aqueous solution of a metal silicate with a mineral acid in the pres-ence of a surfactant solution comprising gelatin and C8-C20 sulfosuccinate blend, at a reaction temperature in a range of about 70 to 100 ºC with constant stirring such that a reaction mixture having a pH of about 10 + 0.3 is obtained;
- optionally, allowing the reaction mixture to age at a temperature in a range of about 70 to 100 °C for a time period in a range of 10 minutes to 30 minutes;
- adjusting the pH of the reaction mixture to about 4, followed by aging said mixture at a temperature in a range of about 70 to 100 ºC for a time period in a range of 10 minutes to 2 hours; and
- recovering the precipitated silica from the reaction mixture.
In accordance with an embodiment, the reaction of the aqueous solution of metal silicate with the mineral acid is carried out by separately adding the aqueous solution of metal silicate, the mineral acid, and the surfactant solution to an aqueous medium heated up to the reaction temperature. In accordance with an embodiment, a reactor containing the aqueous medium and connected to a heater is simultaneously charged with the aqueous solution of the metal silicate, the mineral acid, and the surfactant solution to carry out afore-said reaction. In accordance with an alternate embodiment, the reactor containing the aqueous medium and connected to the heater is first charged with the surfactant solu-tion, followed by the addition of the metal silicate and the mineral acid. In accordance with a related embodiment, the surfactant solution is added to the aqueous medium at a temperature lower than the reaction temperature; and the aqueous medium comprising the surfactant solution is then heated till the reaction temperature.
In accordance with an embodiment, the aqueous solution of metal silicate, the min-eral acid, and the surfactant solution are added in a continuous manner. In accordance with an alternate embodiment, the addition may be stopped intermittently to allow intermittent aging of the reaction mixture. The intermittent aging may be carried out for 10-30 minutes.
In accordance with an embodiment, the aqueous solution of metal silicate, the min-eral acid, and the surfactant solution are simultaneously added to the aqueous medium over a time period in a range of 30 minutes to 2 hours. In accordance with a related em-bodiment, the addition rate of the metal silicate solution and the mineral acid is such that the metal silicate solution and the mineral acid are in a ratio of about 1:1 (based on vol-ume). The addition rate of the metal silicate solution, and the mineral acid, may further be adjusted to maintain the pH of 10 +0.3. In accordance with an embodiment, the surfactant solution is added such that the surfactant solution has a concentration of about 2.25 to 2.5 % w/w with respect to the silica content of the metal silicate solution. Preferably, the sur-factant solution is added such that the surfactant solution has a concentration of about 2.45 % w/w with respect to the silica content of the metal silicate solution. For example, to prepare 450 grams of precipitated silica from 2 kg (1.5 litres) sodium silicate having a total solid content of 32% and silica content of 23%, the surfactant solution comprising .98 % (i.e. 4.5 grams) of gelatin and 1.47% (i.e. 6.75 ml) of Surfactant- OT 85 AE w.r.t. silica content of sodium silicate is added.
In accordance with an embodiment, the reaction is carried out at the reaction tem-perature in a range of about 70 to 100 ºC. Preferably, the reaction temperature is 95 ºC. In accordance with an embodiment, the reaction mixture comprising metal silicate solution, the mineral acid, and the surfactant solution is continuously stirred. The stirring is carried out at a stirring rate in a range of 50 to 700 rpm. Preferably, the stirring is carried out at 400 rpm.
In accordance with an embodiment, once the reaction mixture has attained the pH of 10+0.3, it is allowed to age at the temperature in a range of about 70 to 100 ºC for a time period of 10- 100 minutes. Preferably, the aging is carried out for 60 minutes at 95 ºC.
In accordance with an embodiment, after the completion of the reaction at the pH of 10+0.3, the pH of the reaction is rapidly brought down to the pH of around 4. The pH of the reaction mixture is adjusted to about 4 from 10+0.3 by addition of the mineral acid. In accordance with an embodiment, the pH of the reaction mixture is first adjusted to about 2 from 10+0.3 and then to about 4. The pH of the reaction mixture is adjusted to about 2 from 10+0.3 by addition of the mineral acid and then to around 4 by addition of a base. The base may be any base known to a person skilled in the art. Preferably, the base is sodium hydroxide.
In accordance with an embodiment, the reaction mixture is allowed to age at the pH of about 4 for a time period in a range of 10 minutes to 2 hours. Preferably, the reac-tion mixture is allowed to age for 1 hour. In accordance with a related embodiment, the aging is carried out at a temperature in a range of 70 to 100 ºC. Preferably, the aging is carried out at 95 ºC. In accordance with an embodiment, the aging is carried out while continuously stirring the reaction mixture.
In accordance with an embodiment, the precipitated silica obtained upon comple-tion of reaction is filtered followed by washing. Washing is done to eliminate the by prod-ucts, such as sodium sulphate, obtained as a result of reaction. Thus obtained precipitated silica is then subjected to a drying step. The drying step may be carried out by spray dry-ing, spin flash drying, or vacuum tray drying. Alternatively, the wet cake is subjected to short-term drying, followed by addition of a dispersing agent in a suitable solvent. The dispersion may then be dried to obtain precipitated silica. In accordance with an embodi-ment, the dispersion of silica is prepared using a dispersing agent selected from a group consisting of metal salt of saturated and unsaturated fatty esters with long hydrocarbon chain/ fatty acids in an appropriate solvent selected from a group consisting of butanol, butanone, toluene and acetone.
In accordance with an embodiment, the surfactant solution is prepared by dissolv-ing gelatin in water followed by addition of C8-C20 sulfosuccinate blend at 50 to 80 °C. In accordance with an embodiment, the surfactant solution comprises gelatin and C8-C20 sulfosuccinate blend in a ratio ranging from 1:1 to 1:3, and preferably 1: 1.5. For example, the surfactant solution may be obtained by combining 4.5 grams of gelatin with 6.75 ml of a C8-C20 sulfosuccinate blend, such as Surfactant- OT 85 AE, commercially available from CYTEC.
In accordance with an embodiment, the metal silicate is selected from a group con-sisting of an alkali metal silicate, an alkaline earth metal silicate and mixture thereof. Pref-erably, sodium silicate is used as the metal silicate. The metal silicate can contain from 7-30 wt% SiO2, and preferably 23 wt% SiO2. In accordance with an embodiment, the aqueous solution of metal silicate is prepared by mixing the alkali metal silicate and/or alkaline earth metal silicate with water for a predetermined time period, preferably for 15 minutes, while stirring. In accordance with a related embodiment, the metal silicate has a pH between 11 - 14, and preferably about 12.5 ±0.5.
In accordance with an embodiment, the mineral acid is selected from a group con-sisting of sulphuric acid, hydrochloric acid, nitric acid. In accordance with a related em-bodiment, the mineral acid has a molarity in a range of 0.1 M to 2 M, and preferably around 0.625 M.
In accordance with an embodiment, the aqueous medium is formed of water only.
In accordance with an embodiment, the silica may be pre-treated with a silane cou-pling agent or may be reacted with a coupling agent in-situ within the curable elastomer composition. The silane coupling agent may be any known silane coupling agent and is preferably disulfidic or tetrasulfidic in nature.
In accordance with an embodiment, the elastomer may comprise of a natural and/or synthetic rubber. In accordance with an embodiment, the elastomer is a diene elastomer selected from a group consisting of polybutadienes (BR), polyisoprenes (IR), natural rubber (NR), butadiene-styrene copolymers (SBR), butadiene-isoprene copolymers (BIR), butadiene-acrylonitrile copolymers (NBR), isoprene-styrene copolymers (SIR), butadiene-styrene-isoprene copolymers (SBIR) and mixtures thereof. In accordance with an embodiment, the elastomer comprises 40-60 % of the curable elastomer composition.
In accordance with an embodiment, the elastomer composition may further com-prise of one or more additives such as processing aids, antioxidants, antiozonants, and fill-ers. In accordance with an embodiment, the processing aids may include plasticizers, tackifiers, extenders, chemical conditioners, homogenizing agents. The processing aids may be added in an amount ranging between 1.0-8.0 phr. In accordance with an embodi-ment, the fillers used in the curable elastomer composition may comprise of one or more of reinforcing fillers. The reinforcing filler may be selected from a group consisting of carbon black and silica. The reinforcing filler is added in an amount ranging between 30-50%.
Curing agents are added to cause the vulcanization of the elastomer composition. Any known curing agent may be employed. Preferably, sulfur-based curing systems are used. In accordance with a related embodiment, curing agent is added in an amount rang-ing between 1-3 phr. Accelerators are added to the elastomer composition to control the time and/or temperature required for vulcanization and to improve the properties of the elastomer composition. In accordance with an embodiment, the accelerator may be select-ed from a group consisting of sulfenamide, guanidine and thiuram. The accelerator may be added in an amount ranging between 2-5 phr.
The present disclosure also provides a process of compounding said precipitated silica with elastomer composition. Any known process of compounding elastomer compo-sition with silica may be used. Preferably, to prepare the curable elastomer composition, a master compound is formed by blending elastomer(s), silica along with any other additive and curing agent and accelerator in a single step or in multiple steps in an internal mixer, such as a Banbury, Intermesh mixer or extruder, or on a mill. The mixing is carried out until a homogenized blend is obtained. Subsequently, this master compound is subjected to a forming process, preferably extrusion, which gives the curable elastomer composition the desired profile. The formed master compound is then allowed to cure in predetermined conditions depending on the elastomer and other ingredients.

The curable elastomer composition can be used for the manufacture of tyre and other rubber products. The curable elastomer composition of this invention can specifically be used to manufacture tyre treads and/or sidewalls, bead fillers, components of the bead area, including the bead compound, tread cushion, liner cushion, belt , inner liner, overlay , and carcass of a tyre.
Specific Embodiments are discussed below
A curable elastomer composition comprising atleast 50 % (w/w) of an elastomer; and atleast 30 % (w/w) of precipitated silica having a CTAB surface area in a range of 110-170 m2g; a BET surface area in a range of 100-170 m2g, a BET/ CTAB ratio in a range of 1.1- 1.25; a DBP oil absorption in a range of 240-320 ml/100g, a CDBP coeffi-cient (DA) in range of 0.5-.0.9, a sears number (V2) in a range of 10 to 25 ml/ (5g), and a sears number (V2)/CTAB ratio in a range of 0.16-0.20 ml/(5 m2).
Said curable elastomer composition, wherein the precipitated silica has a Wk coef-ficient number less than 3.
Said curable elastomer composition, wherein the precipitated silica has an average particle size ranging from 10-30 nm.
Said curable elastomer composition, wherein the precipitated silica has an average particulate aggregate size ranging from 50-3000 nm.
Said curable elastomer composition, wherein the precipitated silica has a pore vol-ume ranging from 0.01 to 0.02 cm³/g.
Said curable elastomer composition, wherein the precipitated silica has a pore size distribution ranging from 4.0-10.0 (g nm)/ml.
Said curable elastomer composition, wherein the precipitated silica has a moisture loss of 2 to 5% by weight on drying for two hours at 105°C.
Said curable elastomer composition, further comprising of one or more of one or more of additives selected from a group consisting of processing aids, antioxidants, anti-ozonants, and fillers.
Said curable elastomer composition, wherein the elastomer is selected from a group consisting of polybutadienes, polyisoprenes, natural rubber, butadiene-styrene copolymers, butadiene-isoprene copolymers, butadiene-acrylonitrile copolymers, isoprene-styrene copolymers, butadiene-styrene-isoprene copolymers and mixtures thereof.
Said curable elastomer composition, upon curing has a modulus 100% in a range of 1.5-3.0 MPa, a modulus 300% in a range of 8.5-11.5 MPa, and a reinforcement index of about 4.5.
A tyre having at least one component comprising said curable elastomer composi-tion.
Examples
The following examples are provided to explain and illustrate the preferred embod-iments of the present disclosure and do not in any way limit the scope of the disclosure as described:
EXAMPLE 1: Process of preparing precipitated silica in accordance with present disclosure.
Sodium silicate solution used for the silica synthesis has a solid content of ~ 30.1% by wt.(Na2O to SiO2 ratio= 1: 3.1, silica percentage by wt. = 23 %, Na2O percentage by wt.= 7.1%). This solution has a pH value of 12.5 ±0.5.
1.25 M sulphuric acid solution was prepared by adding slowly 680 mililitre of con-centrated sulphuric acid (% of sulphuric acid in the solution = 98%, Sp. Gr. of the solution = 1.84) to distilled water to make 10 litre solution.
To prepare the surfactant solution, 600 milliliter of distilled water was heated at 50-60°C. 7.5 grams of gelatin is added and stirred to dissolve gelatin in water. 11.2 milliliter of C8 to C20 sulfosuccinate blend surfactant was further added to the above solution and stirred to mix.
In order to synthesize precipitated silica, 3 litres of distilled water was taken in a properly cleaned 25 litre jacketed reactor. The heater was set at 95°C and the stirrer of the reactor was set at a stirring rate of 400 rpm. In the first stage, 3 litres of 1.25 M sulphuric acid and 3 litres of sodium silicate solution were taken in two separate beakers. 300 milli-litre of surfactant solution was slowly added to the reactor while mixing. Three metering pumps were calibrated: 1st for acid, 2nd for sodium silicate addition and 3rd for water addi-tion. The addition rate of all the three pumps was set at 30 millilitres/minute. When the temperature of the reactor reached 95°C, the sodium silicate pump and the water metering pump were switched on simultaneously. Sodium silicate and water were then pumped at an addition rate of 30 millilitres/minute for 10 minutes to the reaction chamber. The pH of the solution in the reaction chamber was checked. At this point, it was ensured that the pH of the reaction mixture is between pH 9.7 to 10. Further on, the reaction was carried out in two stages. In the first stage, the sulphuric acid metering pump was switched on and sul-phuric acid solution was added at an addition rate of 30 millilitres/minute to the reaction chamber, while continuing the addition of both sodium silicate and water at the addition rate of 30 millilitres/minute. The reaction mixture is stirred at 400 rpm. After 30 minutes, the addition of sulphuric acid, sodium silicate and water were stopped while continuing the stirring at 400 rpm and 95°C reactor temperature. The reaction mixture was then al-lowed to age for 30 minutes. The pH of the solution in the reaction chamber was checked. At this point, it was ensured that the pH of the reaction mixture is between pH 9.7 to 10. In the second stage, 300 millilitres of the surfactant solution was added to the reactor. The addition of sulphuric acid and sodium silicate was started at the addition rate of 30 millili-tres/minute and water at the addition rate of 45 millilitres/minute while stirring at 95°C for next 60 minutes. The pH of the solution in the reaction chamber was checked. It was en-sured that the pH of the reaction mixture is between pH 9.7 to 10. The addition of sul-phuric acid, sodium silicate and water were stopped. The reaction mixture was allowed to age for another 70 minutes while stirring at 95°C. After 70 minutes of aging, sulphuric acid was added to the reaction mixture at 100 millilitres/minute. The pH was measured till the reaction mixture attained a pH of 4.0 –4.7. After pH adjustment, the addition of sul-phuric acid was stopped. The reaction mixture was allowed to age for 1 hour at 95°C with continuous stirring.
At the end of the reaction, the precipitates were collected from the reactor. The precipitate was centrifuged at 4000 rpm for 5 minutes. The cake was collected and washed thoroughly with approximately 5 litre of distilled water to remove sodium sulphate. The solid content of the wet cake thus obtained was checked and found to be 12-15% by dry-ing at 125 ºC. 2-4% (w/w) metal salt of saturated and unsaturated fatty esters with long hydrocarbon chain/ fatty acids was added to the silica cake as dispersing agent followed by homogenization. Silica cake was then spray dried to powder. The moisture content of spray dried silica should be in the range of 2 - 5%. Post synthesis, a detailed characteriza-tion of synthesized precipitated silica was carried out. The properties were tabulated in the below table, table 1.

Table 1: Properties of precipitated silica of the present disclosure
Sr. No. Properties Units Value Method
1 Appearance White fluffy powder
2 Crystal structure Amorphous X-ray Diffraction
3 Surface area (N2) m2/g 160 Multipoint-BET N2 absorption method
4 CTAB surface area (CTAB) m2/g 140 CTAB surface area (ASTM 3765)
5 DBP absorption value ml/100 g SiO2 320 Oil absorption tester (ASTM D 2414)
6 Sears Number ml/(5g) 25 Method used as per US 7,871,588
7 CDBP coeffficient (DA) Number 0.69 ASTM D-3493
8 BET/ CTAB surface area Number 1.142 ----
9 Sears number/CTAB surface area ml/5m2 0.178 ---

Example 2: Process of preparing precipitated silica in accordance with present disclosure.
Sodium silicate solution was prepared by mixing 6 kilograms of sodium silicate (Solid content ~45.5% by wt.; Na2O to SiO2 ratio= 1 : 2.5; SiO2 % by wt.= 32.5 %) in 6 litre of distilled water with stirring at 400 RPM for 15 minutes. The obtained sodium silica solution has a pH value of 12.5 ±0.5. Further, 1.25 M sulphuric acid solution is prepared by adding slowly 680 millilitres of concentrated sulphuric acid (% of sulphuric acid in the solution = 98%, Sp. Gr of the solution = 1.84) to distilled water to make 10 litre solution. The 1.25 M sulphuric acid solution is diluted 2 times by mixing 1.5 litre of 1.25 M sul-phuric acid solution and 1.5 litre of water. The resultant sulphuric acid solution has a mo-larity of 0.625 M and pH 1 ±0.3. Gelatin and C8-C20 sulfosuccinate blend surfactant is prepared by first taking 600 millilitres of distilled water and heating it up to 50-60°C fol-lowed by adding to it 3.75 grams of gelatin. The resultant mixture is stirred to dissolve gelatin in water. Subsequently, 5.6 milliliter of C8-C20 sulfosuccinate blend surfactant is added to it followed by stirring to obtain gelatin and C8-C20 sulfosuccinate blend surfac-tant.
To prepare precipitated silica, 3 litre of distilled water is taken in a properly cleaned 25 litre jacketed reactor connected to a heater. The heater and stirrer of the reactor are set at temperature of 95°C and stirring rate of 400 rpm respectively. 600 ml of gelatin and C8-C20 sulfosuccinate blend surfactant is added to the reactor when temperature thereof reaches 70°C. Further, the reaction mixture in the reactor reaches 95°C, 3 litre of 0.625 M sulphuric acid solution and 3 litre of sodium silicate solution are simultaneously added thereto at an addition rate of 30 millilitres/minute. This reaction mixture was stirred at 400 rpm. After completion of the addition, the pH of the reaction mixture was checked. At the end of the reaction, pH should be 10 ±0.3. Once pH of 10 ±0.3 is obtained in the reaction mixture, 1.25 M sulfuric acid solution is added to the reactor to adjust the pH of the reaction mixture to 2 ±0.5 followed by addition of 5% NaOH solution to bring the pH to 4 ±0.5. Thereafter, the solution mixture was aged/ maintained at 95 ?C for 1hour while stirring at 400 rpm. At the end of the reaction, precipitate was collected from the reactor.
The precipitate was centrifuged at 4000 rpm for 5 minutes. The filter cake thus ob-tained was collected and washed thoroughly with approximately 5 litre of distilled water to remove sodium sulphate. The solid content of the wet cake was checked and found to be 12-15% by drying at 125 ºC. A dispersion of 6 - 10 % solid content was prepared there-after by adding distilled water to obtain silica slurry. Once silica slurry is prepared, metal salt of saturated and unsaturated fatty esters with long hydrocarbon chain/ fatty acids was used as dispersing agent with a 2-4% w/w loading in an appropriate solvent (e.g. butanol, butanone, toluene and acetone) and added slowly to the 6 - 10 % silica slurry by homoge-nizing in a high shear mixer for 15 minutes at 2000 rpm. The 6-10% silica slurry was then spray dried to powder. The moisture content of spray/ spin flash dried silica should be in the range of 2 - 5%. Post synthesis, a detailed characterization of synthesized precipitated silica was carried out. The properties were tabulated in the below table, table 2.

Table 2: Properties of precipitated silica of the present disclosure
Sr. No. Properties Units Value Method
1 Appearance White fluffy powder
2 Crystal structure Amorphous
X-ray Diffraction
3 Surface area (N2) m2/g 140 Multipoint-BET N2 absorption method
4 CTAB surface area (CTAB) m2/g 125 CTAB surface area (ASTM 3765)
5 DBP absorption value ml/100 g SiO2 280 Oil absorption tester (ASTM D 2414)
6 Sears Number ml/(5g) 26 Method used as per US 7,871,588
7 CDBP coeffficient (DA) Number 0.7 ASTM D-3493
8 BET/ CTAB surface area Number 1.12 ----
9 Sears number/CTAB surface area ml/5m2 0.208 ---

Example 3: Preparation of curable elastomer composition in accordance with present dis-closure for manufacturing a tyre.
Table 3: Ingredients
Category Ingredient Quantity (in phr*)
Master Compound Synthetic Rubber Styrene Butadiene Rubber (SSBR) 4526HM (From Laxness) 99.0
Polybutadiene Rubber (PBR) 01 Cisamer grade (From Re-liance Industries Limited) 28.0
Zinc Oxide 3.5
Stearic acid 1.5
Anti ageing agent- Vulkanox HS/LG
(From Laxness) 1.5
Anti ageing agent- Vulkanox 4020
(From Laxness) 1.0
Anti ageing agent- Redezon C-250M from Repsol YPF Lubicantes 1.5
N330 Carbon Black (From PCBL) 12.0
Silica 7000GR (from Evo-nik) + Silica of Example 1 65.0
Silane coupling agent- X-50-S (From Evonik) 11.05
Processing Oil Treated Distillate Aromatic Extract (TDAE) oil (from H&R Chem Pharm) 2.5
Curing Agent Sulphur 1.9
Accelerators Vulkacit CZ/C CBS ( From Laxness) 2.0
Perkacit DPG (From Flexsys Rubber Chem. Ltd.) 2.0
*phr : parts per hundred rubber

SAMPLE PREPARATION:
1. Preparation of compound: The mixing was performed in three steps. First a master compound without curing agent and accelerator was prepared in Banbury mixer at 55°C and rotor speed of 70 rpm. The ingredients of the master compound, curing agent and ac-celerator have been illustrated in the Table 3.The mixing time in Banbury mixer was lasted for 7 minutes and Max dump temperature of 165°C was maintained The master compound prepared in the first stage is remilled in the Banbury mixer in the similar conditions of First stage. The mixing time was 3.5 minutes. The mixing was continued on two-roll mill by adding curing agent and accelerator. All compounds were prepared in accordance with ASTM D 3191. The final compound was stored for at least 24 hours before cured sample preparation.
2. Extrusion: Once the mixing is done, obtained compound undergoes a forming process before making tyres and curing it. This forming process give the rubber compound a de-sired profile suitable to the final tyre dimensions.
3. Curing: The compound specimen curing properties were determined with the aid of an MDR dynamic mechanical rheological tester from Alpha Technologies at a temperature of 160°C. The compounds were cured in a laboratory press at 160°C and 20 minutes, corre-sponding to the t90 of the specific compound, irrespective of the variations in dump tem-perature. Once the tyre is assembled the information is used in deciding the time taken to vulcanise the tyre.
Three trials of above disclosed method of compounding using the precipitated silica ob-tained in Example 1 were performed. The properties of the curable elastomer compositions obtained in the three trials have been summarised below.

Experimental Results: Laboratory Stage
Cured samples were prepared based on the ASTM standard for evaluation of filler disper-sion (i.e. ASTM D2663), physical properties check (ASTM D412) i.e. Tensile strength and Reinforcibility index (Modulus @ 300%/Modulus @ 100%). Each of the property was been expressed by index numbers and has been summarised in Table 4, below. The higher the index, the better the value.
Table 4: Properties of the curable elastomer compositions
Key property Trial-1 Trial-2 Trial-3
Dispersion: (Z scale) 89 93 90
Tensile Strength 100 117 106
Reinforcibility Index:
[M300/M100] 100 115 113

Observation: Precipitated silica of present disclosure exhibited improved dispersion in rubber.
3. Experimental Results: Factory Trials stage
Compounding and curing of tyres was done and the observations were made. The observa-tions have been summarised in Table 5 and have been represented as an index of the result of the tyre prepared from conventional elastomer composition regarded as 100. The higher the index, the better.

Table 5: Process validation
Observations in Mixing and Extrusion Conventional elastomer com-position com-prising silica- GR70 from Evonik Elastomer composition comprising silica pre-pared in Example 1
Number of Mixing stages 100 125
Smoothness of the Mixed compound sheets 100 125
Extrudate smoothness 100 130
Observation: Significant reduction [~25%] in mixing stages was observed. Also, phe-nomenal improvement in process ability was observed, as also evident from extrudate smoothness shown in Fig. 1a and 1b, and 2a and 2b.
4. Product Validation:
Developed technology is validated for indoor and outdoor testings, in a representative tyre [185/65 R15].The result was represented as an index of the result of the tyre prepared from conventional elastomer composition regarded as 100. The higher the index, the better.
Table 6: Product validation
Property Conventional elastomer com-position compris-ing silica- GR70 from Evonik Elastomer compo-sition comprising silica prepared in Example 1
High speed endurance (Durability) 100 101
Rolling resistance coefficient (Fuel efficiency) 100 102
Mileage (% wear after running 20,000Kms) 100 101
Ride 100 105
Handling 100 105

Observations: Product validations demonstrate marked improvement as compared to conventional tyres, as also evident from Figures 3a and 3b..