PRECIPITATED SILICIC ACIDS, PROCESS FOR THEIR PREPARATION AND USE THEREOF

Abstract

Precipitated silicas having, a N-cetyl-N,N,N-trimethylammonium bromide (CTAB) surface area ≤115 m.sup.2/g, a dioctyl adipate (DOA) absorption ≥130 ml/(100 g), a RoTap for >300 μm of ≥86%, and a pore volume distribution of V (d5−d50)/V (d5−d100)<0.66. A method of producing the precipitated silicas.

Claims

1. Precipitated silicas, having: a N-cetyl-N,N,N-trimethylammonium bromide (CTAB) surface area ≤115 m.sup.2/g, a dioctyl adipate (DOA) absorption ≥130 ml/(100 g), a RoTap for >300 μm of ≥86%, and a pore volume distribution of V (d5−d50)/V (d5−d100)<0.66.

2. The precipitated silicas according to claim 1, having a CTAB surface area ≤90 m.sup.2/g.

3. The precipitated silicas according to claim 1, having a PV value at 0.0042 MPa-414 MPa, and 140°, in the range of 1.00-3.00 ml/g.

4. The precipitated silicas according to claim 1, having a silanol group density ≥5.4 OH/nm.sup.2.

5. The precipitated silicas according to claim 1, having a bulk density of at least 180 g/l.

6. The precipitated silicas according to claim 1, having a grain length ≥1 mm.

7. A method of producing the precipitated silicas according to claim 1, comprising: a) forming an aqueous solution of an organic and/or inorganic salt and/or an alkali metal or alkaline earth metal silicate and/or an organic and/or inorganic base with a pH ≥9; b) adding a waterglass and an acidifying agent simultaneously into the aqueous solution while stirring at 80-98° C. for 60-120 minutes; c) adding acid only in a smaller amount than in b) in order to attain a mixture with a pH (measured at 60° C.) of 9.0-10.0; d) stirring the mixture at a temperature >85° C. for 45 min to 200 min, without adding further reactants; e) adding sulfuric acid for acidification to a pH of about 3.5-4.5 (measured at 60° C.); and f) filtering, drying to a drying loss of <8%, and forming a pellet.

8. A rubber mixture comprising: (A) a rubber or a mixture of rubbers; and (B) at least one of the precipitated silicas according to claim 1.

9. A method of producing the rubber mixture according to claim 8, comprising: mixing the rubber or the mixture of rubbers, the precipitated silica, and optionally further rubber auxiliaries in a mixing unit.

10. A material comprising the rubber mixture of claim 8, wherein the material is selected from the group consisting of tyres, cable sheaths, hoses, drive belts, conveyor belts, roll coverings, footwear soles, gasket elements and damping elements.

Description

EXAMPLES

Example 1

[0194] A reactor with a propeller stirrer system is initially charged with 1140 l of water and 150 kg of waterglass, and heated up to 88.8° C. Within 100 minutes, 727.9 kg of waterglass (density 1.345 kg/l, 27% S102, 8% Na.sub.2O) and 77.6 kg of sulfuric acid (density 1.84 kg/l, 96% H.sub.2SO.sub.4) are added simultaneously, such that the AN in the reaction mixture is 24-27.

[0195] Subsequently, sulfuric acid (density 1.84 kg/l, 96% H.sub.2SO.sub.4) is added, such that the pH in the reaction mixture is 8.6 (measured at 60° C.).

[0196] The temperature in the precipitation vessel is increased to 94° C. within 5 minutes, and the suspension is subjected to ageing while stirring at 94° C. for 55 minutes.

[0197] Thereafter, further sulfuric acid (density 1.84 kg/l, 96% H.sub.2SO.sub.4) is fed in at a metering rate of kg/min until a pH of 7 (measured at 60° C.) has been attained. Then further sulfuric acid is added at a metering rate of 0.35 kg/min to a pH of 4.0 (measured at 60° C.).

[0198] The resulting suspension is filtered and washed with water as usual and subjected to spin-flash drying. The powder thus obtained is pelletized, i.e. compacted in a roll compactor and then crushed by means of a crusher.

Example 2

[0199] A reactor with a propeller stirrer system is initially charged with 1164 l of water and 150 kg of waterglass (AN 25-26), and heated up to 89.0° C. The following are added simultaneously within 100 minutes: waterglass at an average metering rate of 7.3 kg/min (density 1.345 kg/l, 27% S102, 8% Na.sub.2O) and sulfuric acid (density 1.84 kg/l, 96% H.sub.2SO.sub.4) at an average metering rate of 0.82 kg/min.

[0200] Subsequently, further sulfuric acid (density 1.84 kg/l, 96% H.sub.2SO.sub.4) is added, such that the pH in the reaction medium is 8.5 (measured at 60° C.).

[0201] The temperature in the precipitation vessel is increased to 94° C. within 5 minutes, and the suspension is subjected to ageing while stirring at 94° C. for 55 minutes.

[0202] Thereafter, further sulfuric acid (density 1.84 kg/l, 96% H.sub.2SO.sub.4) is added at a metering rate of 0.70 kg/min, at first down to a pH of 7 (measured at 60° C.), and then acidification is continued at a metering rate of 0.35 kg/min down to a pH of 4.0 (measured at 60° C.).

[0203] The resulting suspension is filtered and washed with water as usual and subjected to spin-flash drying. The powder thus obtained is pelletized, i.e. compacted in a roll compactor and then crushed by means of a crusher.

[0204] The silicas have the analytical parameters reported in Table 1.

TABLE-US-00003 TABLE 1 Inventive Inventive silica I silica II Reference Example Example Parameter Unit silica I 1 2 BET surface area m.sup.2/g 74 77 90 (N.sub.2, multipoint) CTAB surface m.sup.2/g 80 82 90 area DOA absorption ml/(100 g) 123 148 169 Ro-Tap > 300 μm % 84.5 94.3 94.9  Ro-Tap < 75 μm % 3.5 1.3 1.5 Sears ml/(1.5 g) 10.6 11.7 12.4 number.sub.original Silanol group OH/nm.sup.2 5.3 5.7 5.5 density Drying loss % 6.1 5.7 5.4 pH 7.7 6.5 7.1 Electrical μS/cm 806 1180 176 conductivity Ignition residue % 4.1 4.4 4.1 Bulk density g/l 347 314 298 TAR % not 22.4 21.0 measurable V(d5-d50)/ 0.65 0.64 0.64 (d5-d100) PV ml/g 1.27 1.42 1.54 Pore maximum nm 61 61 57

[0205] Reference silica 1 is ZEOSIL® 1085 GR from Solvay S. A.

Example 3

[0206] Examination of Rubber Characteristics The formulation (green tyre compound) used for the rubber mixtures is specified in Table 2 below.

[0207] In this table, the unit phr means parts by weight based on 100 parts of the crude rubber employed.

TABLE-US-00004 TABLE 2 Formulation of the green tyre mixture Rubber mixture 1 Inventive Inventive (compar- rubber rubber ative) mixture mixture with 2 with 3 with Con- Production/ reference inventive inventive Name stituent supplier silica I silica I silica II Stage 1 phr phr phr Buna S-SBR; ARLANXEO 96.25 96.25 96.25 VSL see Deutschland 4526-2 note .sup.1 GmbH Buna Nd-BR; ARLANXEO 30.00 30.00 30.00 CB 24 see Deutschland note .sup.2 GmbH Reference Solvay S.A. 90.00 silica I Inventive Evonik 90.00 silica I Resource Efficiency GmbH Inventive Evonik 90.00 silica II Resource Efficiency GmbH Si 266 Bifunc- Evonik 5.80 5.80 5.80 tional Resource silane Efficiency GmbH N330 Industrial Orion 5.00 5.00 5.00 carbon Engineered black Carbons GmbH ZnO RS ZnO Carl 2.00 2.00 2.00 RAL Arnsperger 844 C Chemikalien GmbH & Co. Edenor Stearic Caldic 2.00 2.00 2.00 ST1 GS acid Deutschland GmbH Vivatec TDAE H&R GmbH 8.75 8.75 8.75 500 Co. KGaA Vulkanox TMQ LANXESS 1.50 1.50 1.50 HS/LG Deutschland GmbH Vulkanox 6PPD LANXESS 2.00 2.00 2.00 4020/LG Deutschland GmbH Protektor Wax Paramelt 2.00 2.00 2.00 G 3108 B.V., the Stage 2 Netherlands Stage 1 batch Rhenogran DPG Rhein 2.50 2.50 2.50 DPG-80 80% Chemie Stage 3 additives Stage 2 GmbH batch Richon TBzTD WEBER & 0.20 0.20 0.20 TBZTD- SCHAER OP GmbH & Co. KG (produced by Dalian Richon) Vulkacit CBS LANXESS 1.60 1.60 1.60 CZ/EG-C Deutschland GmbH Sulfur Ground HENSELER 2.00 2.00 2.00 sulfur GmbH .sup.1 Buna ® VSL 4526-2 HM is a solution styrene-butadiene rubber extended with 37.5 phr TDAE oil; Mooney (1 + 4 @ 100° C.): 62 ME; vinyl: 44.5%; styrene: 26% The rubber mixture is produced in three stages in an internal mixer in accordance with the tabular listing below (Table 3):

TABLE-US-00005 TABLE 3 Method for mixture production Mixer HF MIXING GROUP (Harburg-Freudenberger Maschinenbau GmbH) Stage 1 GK 1.5 N, fill level 0.73; 70 rpm; chamber temperature: 70° C.; friction 1:1.11 min:sec Target batch temperature: 145° C.-155° C. Mixing time 00:00- At 00:00: Add polymers; Vulkanox HS; Vulkanox 4020; 00:15 close plunger and mix for 15 s 00:15- At 00:15: Add 45 phr of silica, Si 266; 01:15 close plunger and mix for 60 s 01:15 Move plunger halfway up, for ventilation and cleaning of the plunger 01:15- Open oil bag (LD-PE plastic bag 150 × 200 mm, IGEFA 02:15 Handelsgesellschaft) before commencement of the mixing stage and put the carbon black into the bag; at 01:15: a) add prepared bag b) 1/2 silica c) Protektor G 3108 d) close plunger and mix for 60 s 02:15- At 02:15: Add ZnO and stearic acid; close plunger and mix 03:45 for 90 s; maintain the target batch temperature by varying the speed at 150° C. +/− 5° C. 03:45 Discharge mixture and check the batch by weighing Apply the discharged batch to a laboratory roll heated to 60° C. and form a sheet thereon within 45 s at a roll nip of 4 mm and suitable rotation speeds. In so doing, do not cut into, turn over or fold over the sheet. Thereafter, take the sheet off the roll and take a sample if necessary, and cut to the weight for the second mixing stage. The intermediate storage of the sheet for the second mixing stage is 24 +/− 3 h at 23 +/− 3° C. The wait time between mixing stages 1 & 2 should be understood such that all mixtures belonging to a mixing series, after commencement of the mixing of the first compound in the series, are mixed further in direct succession without further interruptions. Stage 2 GK 1.5 N, fill level 0.70; 75 rpm; chamber temperature: 75° C.; friction 1:1.11 min:sec Target batch temperature: 145° C.-155° C. Mixing time 00:00- At 00:00: Add the stage 1 batch; close plunger and mix for 60 s 01:00 01:00- At 01:00: Add Rhenogran DPG-80; close plunger and mix 03:00 for 120 s; maintain the target batch temperature by varying the speed at 150° C. +/− 5° C. 03:00 Discharge mixture and check the batch by weighing Apply the discharged batch to a laboratory roll heated to 60° C. and form a sheet thereon within 45 s at a roll nip of 4 mm and suitable rotation speeds. In so doing, do not cut into, turn over or fold over the sheet. Thereafter, take the sheet off the roll and take a sample if necessary, and cut to the weight for the third mixing stage. The intermediate storage of the sheet for the third mixing stage is 4 h up to 24 h at 23 +/− 3° C. The wait time between mixing stages 2 & 3 should be understood such that all mixtures belonging to a mixing series, after commencement of the mixing of the first compound in the series, are mixed further in direct succession without further interruptions. Stage 3 GK 1.5 N, fill level 0.68; 50 rpm; chamber temperature: 50° C.; friction 1:1.11 min:sec Batch temperature: 90° C.-110° C. Mixing time 00:00- At 00:00: Add the stage 2 batch and TBzTD, CBS, 02:00 sulfur; close plunger and mix for 120 s 02:00 Discharge mixture and check the batch by weighing Apply the discharged batch to a laboratory roll heated to 60° C. and form a sheet thereon within 20 s at a roll nip of 4 mm and suitable rotation speeds. Cut into the sheet three times from the right and turn over each time, cut in three times from the left and turn over each time, and fold over tightly three times. For sampling thereafter, discharge the sheet in the appropriate thickness necessary, take sample, fold together again and put back onto the rotating roll until all the necessary samples have been taken.

[0208] The general method for producing rubber mixtures and vulcanizates thereof is described in the following book: “Rubber Technology Handbook”, W. Hofmann, Hanser Verlag 1994.

[0209] The vulcanization time for each of the test specimens at 165° C. is 15 min. Rubber testing is effected in accordance with the test methods specified in Table 4.

TABLE-US-00006 TABLE 4 Procedures for performance of physical tests Raw mixture Test/ Vul- Physical Test method canizate parameter Unit conditions Standard MDR; R Delta dNm Test at DIN 165° C.; torque 165° C.; 53529/3, 0.5°: Delta MDR 0.5° ISO 6502 torque Tensile V Ultimate MPa Test at DIN 53504, test: tensile 23° C.; ISO 37 strength standard ring R1; takeoff speed 500 mm/min Tensile V Stress MPa Test at DIN 53504, test: value 23° C.; ISO 37 Tensile at 200% standard strength elongation ring 200% R1; takeoff modulus speed 500 mm/min Tensile V Stress — Test at DIN 53504, test: value 23° C.; ISO 37 200%/ at 200% standard 50% elongation ring modulus divided R1; takeoff by the speed 500 stress mm/min value at 50% elongation, corresponds to the reinforce- ment ratio Tensile test: V Elongation % Test at DIN 53504, Elongation at break 23° C.; ISO 37 at break standard ring R1; takeoff speed 500 mm/min DIN V DIN mm.sup.3 10 N DIN ISO abrasion abrasion: 4649, Loss of ISO 2781, volume Method A Tear V Tear N/ Test at DIN 53515 resistance resistance mm 23° C.; test DIE C; DIE C; standard specimen 23° C. 23° C. test without specimen; incision takeoff speed 500 mm/min Tear V Tear N/ Test at DIN 53515 resistance resistance mm 23° C.; GRAVES; standard 23° C. test specimen; takeoff speed 500 mm/min Tear V Tear N/ Test at DIN 53515 resistance resistance mm 60° C.; GRAVES; standard 60° C. test specimen; takeoff speed 500 mm/min Ball V Resilience/ % Fall height ASTM D rebound; % 500 mm, 2632 23° C. steel ball with d = 19 mm, 28 g RPA strain V Complex MPa RPA: 2nd ASTM D sweep; shear strain sweep 6601-02 60° C.: G* modulus G* on the vulcanizate 1.6 Hz; 60° C.; 0.28%- 42% test at 60° C., 1.6 Hz, 0.28%- 42.0% “Operators Manual RPA 2000” from Alpha Tech- nologies, February 1997 ZWICK V Complex 16 Hz, DIN 53513, force modulus E* initial ISO 4664-1 controlled; force 50 N 60° C.: and E* amplitude force 25 N, heat treatment time 5 min, parameters recorded after 30 s testing time ZWICK V Loss factor — 16 Hz, DIN 53513, force tan δ initial ISO 4664-1 controlled; force 50 N 0° C.: and tan δ amplitude force 25 N, heat treatment time 5 min, parameters recorded after 30 s testing time Dispersion: V Rating % Works ISO 11345 : DisperTester on the settings; 2006; 3000 plus basis of rating-the ASTM D (100×) undispersed higher the 7723 particles value, the better the dispersion Dispersion: V Roughness % Roughness In TOPO- on on accordance Peak area account of account of with ASTM undispersed un- D 2663; particles dispersed described particles => in DE the lower 199 17 the value, 975 C 2 the better Deter- the mination dispersion by means of a topographic method, described in: “Ent- wicklung eines Ver- fahrens zur Charak- terisierung der Füllstoff- dispersion in Gummi- mischungen mittels einer Oberflächen- topographie [Develop- ment of a surface- topography method for character- izing filler dispersion in vulcanized rubber mixtures]” A. Wehmeier; Degree thesis 1998 at the Münster University of Applied Sciences, Steinfurt site, in the Chemical Engineering Department and “Filler dispersion Analysis by Topography Measure- ments” Degussa AG, Applied Technology Advanced Fillers, Technical Report TR 820. Dispersion: V Number of — Number of In TOPO- defects on defects accordance Considered account of resulting with sum undispersed from ASTM D of peaks particles inadequate 2663; dispersion described => in DE 199 the lower 17 975 C 2 the value, Deter- the better mination by the means of a dispersion topographic method, described in: “Ent- wicklung eines Verfahrens zur Charak- terisierung der Füllstoff- dispersion in Gummimi- schungen mittels einer Oberflächen- topographie” A. Wehmeier; Degree thesis 1998 at the Münster University of Applied Sciences, Steinfurt site, in the Chemical Engineering Department and “Filler dispersion Analysis by Topography Measure- ments” Degussa AG, Applied Technology Advanced Fillers, Technical Report TR 820.

TABLE-US-00007 TABLE 5 Performance data of the examples Rubber Inventive Inventive mixture 1 rubber rubber (comparative) mixture 2 mixture 3 MDR: 165° C.; 0.5° dNm 12.7 15.0 14.3 Delta torque MDR Tensile strength MPa 9.5 10.7 10.8 (4 rings R1 @ 23° C.) 200% modulus MPa 5.7 6.8 6.5 200%/50% modulus — 6.6 6.8 6.7 Elongation at break % 300 300 310 DIN abrasion mm.sup.3 94 80 87 Tear resistance N/mm 35 38 36 DIE C, 23° C. Tear resistance N/mm 13 21 16 GRAVES, 23° C. Tear resistance N/mm 22 34 27 GRAVES, 60° C. Ball rebound, 23° C. % 45 41 43 E*; 60° C. MPa 5.4 6.4 1 6.0 tan δ, 0° C. Zwick — 0.393 0.432 0.422 RPA: 2.sup.nd strain MPa 1.6 2.2 1.9 sweep vulcanizate 1.6 Hz, 60° C., 0.28%-42% Modulus Dispersion: % 87.6 94.4 91.3 DisperTester 3000 plus (100×) Dispersion: Peak % 19.2 1.7 7.7 area (Topo) Considered sum — 334 32 140 of peaks

[0210] The rubber data of the rubber mixtures according to the invention that are shown in Table 5 show the superior dispersion/dispersibility of the silicas according to the invention compared to the prior art, rubber mixture 1 (comparative). Inventive rubber mixtures 2 and 3, in the case of direct measurement of the defects in sections through the vulcanizates, clearly have a lower level of undispersed silica by means of tactile topography measurement, and visually by means of the dispersion tester. Combined with this, there is also a distinct improvement in all measurements of relevance in respect of reinforcement: In the tensile test, there was a clear improvement in stress values with the same elongation at break. This is also in accordance with the improved tear results Die C and Graves under various measurement conditions. There is also an improvement in DIN abrasion for the rubber mixtures according to the invention compared to the reference mixture. These advantages indicate that a tyre having a tyre tread including and reinforced by the silicas according to the invention will have a distinct improvement in wear characteristics. The indicators of ball rebound, 23° C., and tan δ at 0° C. additionally also show clearly improved values for the wet skid characteristics of such treads. High stiffness at high temperatures (E*, 60° C. and modulus (max) in RPA) under these measurement conditions additionally also shows improved handling characteristics on dry roads compared to the prior art. All in all, these rubber mixtures and the silicas according to the invention are thus very particularly capable of optimizing and improving the overall performance of winter tyres, for example, or the even more specialized Nordic winter tyres, to a very high degree.