SILICA PARTICULATES

Abstract: A particulate silica which has been treated with a polymer oil jelly.

Description: SILICA PARTICULATES This invention relates to silica particulates, in particular precipitated silica particulates. It is well known to use particles of silica as a re-inforcing filler material for elastomeric and rubbery materials. Thus they have been used as a white re-inforcing filler in elastomers, for example those used in the manufacture of vehicle tyres. As with any filler material, the silica must be easy to handle and to formulate. One of the problems with silica in powder form is that it tends to form a dust. Apart from the environmental difficulties that this leads to, this dust formation tends to hinder the incorporation of the filler since it gives it a low apparent density. In addition, rubber mixing requires very accurate metering techniques for which powdery fillers are often unsuitable. This is because of the difficulty of pouring them. it is possible to overcome problems of dusting by shaping the filler material into a granule or the like but such granules often are difficult to disperse adequately in the elastomer and the degree of re-inforcement ultimately obtained is quite often lower than would be obtained using the same quantity of filler in powder form. It is known in this art that if a filler is to provide optimum re- inforcing properties it must be present in the elastomer matrix in a form which is both as finely divided as possible and as homogenously distributed as possible. It will be appreciated that these requirements are somewhat incompatible. Accordingly, there is a need to provide silica particles which are finely divided but which can be homogenously distributed throughout the elastomer without significant dusting. It has surprisingly been found that silica particles which have been treated with a polymer oil jelly (POJ) eliminate, or generally reduce, the problems of dusting without causing a deterioration of the other properties of the resulting elastomer. Indeed the resulting elastomer may possess various technical advantages. In particular, it has been found that the treated particles possess a higher density. Also the incorporation of the treated particles in the elastomer gives rise to a somewhat reduced viscosity in the uncured elastomer while at the same time reducing abrasion losses. Further the treated particles can be incorporated more quickly into the elastomer, thus resulting in shorter mixing times and, in consequence, less power. According to the present invention there is provided the particulate silica which has been treated with a polymer oil jelly. Polymer oil jellies are materials obtained by mixing an oil extender with a thermoelastic polymer to form a substantially homogenous blend. Typically, the oil extender is a mineral oil, for example a naphthenic process oil. Preferred thermoelastic polymers are copolymers of ethylene, propylene and, optionally, a diene, for example with an ethylene content of 60 to 90% by weight more particularly 60 to 75% by weight while the propylene content is 10 to 35%, particularly 20 to 30%, by weight with the remainder (if any), preferably 2 to 10% by weight diene. Specific polymers include those with the following (a) ethylene 68.5%, propylene 27% and ENB 4.5%, (b) ethylene 70.5%, propylene 25% and ENB 4.5% and (c) ethylene 72.5%, propylene 25% and hexadiene 2.5%. Typical dienes include hexadiene and ENB (ethylidenenorbornene). Generally the oil extender will predominate and will typically account for 80%, for example 85 to 95%, by weight of the composition with the copolymer representing up to 50% by weight, for example from 5 to 15% by weight. In one embodiment, the polymer represents about 6.5% by weight of the POJ, the remainder being oil. Suitable polymer oil jellies for use in the present invention include those disclosed in GB-A-1430768. The amount of polymer oil jelly used to treat the silica particles can vary within quite wide limits although, generally, the POJ is used in an amount from 2.5 to 40%, typically 5 to 30%, particularly 5 to 20% preferably from 10 to 20% and more preferably from 10 to 15%, by weight based on the weight of the silica. Use of an amount from, say, 10 to 15% by weight is generally sufficient to reduce the tendency to dust very significantly without adversely affecting any properties of the elastomer into which the particles are introduced. The incorporation of the POJ into the silica particles can be achieved quite simply by mixing the two components together while the POJ is sufficiently fluid. In general, a temperature of at least 50°C is required for this purpose. The upper temperature is not particularly critical but, in general, too high a temperature can give rise to discolouration. A general range is, therefore, 50 to 1 10°C with a preferred range being from 60 to 90°C, especially about 80°C. In a preferred embodiment the POJ is preheated to the desired temperature. The silica particles are placed in a mixer and then the POJ added gradually. Mixing is generally complete in, say, five minutes. The present invention is applicable to all types of precipitated silicas. While the present invention is particularly applicable to silica powders, the invention is also applicable to silicas in the form of granules, beads or spherules such as micro pearls. They are advantageously dispersable precipitated silica particulates. The silica can be in the form of a powder, spherical beads or granules generally having a CTAB (cetyl trimethyl ammonium bromide) specific surface [determined in accordance with French NFT standard 45007] of 60 to 240 m 2 /g, for example 90 to 180 m 2 /g, in particular 130 to 5 1 70 m 2 g, and a BET specific surface (determined by the Brunauer - Emmet - Teller method, described in The Journal of the American Chemical Society, vol 60, page 309 (February 1938) and corresponding to French NFT standard 45007 (November 1987)) of 70 to 250 m 2 /g, for example 100 to 190 m 2 /g, in particular 140 to 180 m 2 /g". The silica may also have a CTAB specific surface 0 of 100 to 240 m 2 /g in particular 140 to 200 m 2 /g, especially about 160 to 165 m 2 /g. They can also have a high ultrasonic desegregation factor (obtained following the procedure described in, for example WO95/09128). The silica will generally have a mean particle size of at least 60 μm, generally at least 80 μm and preferably from 100 to 300, especially 1 50 to 300, μm. Typical silica 5 which can be used include those disclosed in EP-A-520862, WO95/09127 and WO95/09128. Thus the silica used in the present invention can be silica prepared using a particular chemical process, for example for reacting a silicate with an acidifying agent as in EP-A-520862. 0 The median diameter after ultrasonic deagglomeration (0 50 ) and the ultrasonic deagglomeration factor (F D ), along with the pore size distribution which are mentioned in these patent specifications and which are suitable for the particles of silica used in the present invention are those measured before treatment with POJ. 5 The initial granulometry of the silica used has in general a great importance: The most preferred silicas have a mean particle size of at least 60 μm, preferably of at least 80 μ and in particular of at least 100 μm. The improvement from a dusting standpoint is usually the highest with silicas showing a mean particle size from 100 to 300 μm. As indicated above, such particulate silicas are typically used for incorporation in natural of synthetic elastomers and rubbers and especially, elastomers used to manufacture vehicle tyres and shoe soles. Such elastomers include butadiene polymers such as styrene-butadiene rubber and neoprene elastomers. Typically the silica is present in an amount from 25 to 150, for example from 40 to 100, parts per 100 parts, by weight of the elastomer. One might expect that the suppression of dust could be achieved using oil. However, it has been found that the same dust suppression effect can be achieved using a smaller quantity of POJ than that of oil. The following Examples further illustrate the present invention. In these working Examples two grades of silica were employed designated A and B. A is a powdered silica having a CTAB specific surface area of 1 60 m 2 /g and a mean particle size of 270 μm. B differs from A in having a mean particle size of 120 μm. For these were incorporated amounts of POJ corresponding to 10, 1 5, 20 and 30%. Example 1 The silica together with the varying amounts of POJ (P0J10 = 10% by weight POJ) . was tested for its tapped density (TD) and dust index (D1 ). The dust index was measured optically via the "cloud" generated by the fall of the powder in a black box. The 50 g of the powder is allowed to fall under standard conditions across an optical axis provided by a light source and a photoresistor cell. The dust index is given as the maximal initial peak (mV) as read by the photoresistor cell. The tapped density was measured by compacting a known mass of powder in a measuring container by means of a reciprocating tapping arm applied to an anvil placed on top of the powder. A total of 1250 taps was used (French NFT standard 030100). The oil used to prepare the POJ silicas has a final density of 0.87. The values obtained are shown in the following Table. Silica A has a very low dust level so that improvements are difficult to achieve. Nevertheless, the incorporation of POJ reduces the dust index by about a half, even when used in an amount of only 10% by weight. The values obtained should be regarded as excellent. With silica B which has a higher dust level, the dust index is reduced more. SILICA TD Dl A 0.285 4 POJ 10 A 0.317 2.1 POJ 1 5 A 0.339 2.2 POJ 20 A 0.355 2.7 POJ 30 A 0.41 5 2 B 0.287 40.6 POJ 10 B 0.321 22.7 POJ 1 5 B 0.344 10.6 PO 20 B 0.351 10.9 POJ 30 B 0.399 9.5 ULTRASIL VN3 0.37 29.4 GRANULAR * AKZO KS 404 0.373 21.3 GRANULAR * marketed by Degussa Example 2 An assessment was made of the effect of the incorporation of the POJ silica on particular styrene-butadiene rubbers. The formulation was as follows, using either aromatic oil and silica or POJ and silica. The amounts of oil/filler allow for a full comparative evaluation of the POJ silicas: COMMON PART phr (parts by weight) SBRe 1509 50 BR 1220 25 NR SMRL 25 SILANE X50S 11.15 5.6 AM STEARIC ACID 0.5 ACTIVE ZnO 2.5 6 PPD 2 SULPHUR 1 .5 CBS 1.78 DPG 2 AROM.OIL SILICA COLL. IDENT A 37.5 70 R959 B 37.5 70 R960 POJ 10 A 29.7 77.8 R961 POJ 15 A 25.1 82.4 R962 POJ 20 A 20 87.5 R963 POJ 30 A 7.5 100 R964 POJ 10 B 29.7 77.8 R965 POJ 15 B 25.1 82.4 R966 POJ 20 B 20 87.5 R967 POJ 30 B 7.5 100 R968 SBRe 1 509 is an emulsion polymerised styrene butadiene rubber from the 1500 series. BR1220 is a 1220 grade cis 1 ,4 butadiene rubber. NR SMRL is a natural rubber (Standard Malaysian Rubber) produced from latex. Active ZnO is a rubber quality zinc oxide. 6PPD is N-(1 ,3-dimethylbutyl)-N'- phenyl p-phenylene diamine. CBS is N-cyclohexyl 2-benzothiazyl sulphenamide accelerator. DPG is diphenylguanidine accelerator. Silane X50S is a silica/rubber coupling agent (marketed by Degussa) comprising a 50 wt % dispersion of Silane Si69 on N339 carbon black. The materials were processed in a Banbury mixer at 55 °C. The elastomer was added. One minute later two thirds of the silica, oil and silane were added. After two minutes the remaining third of the silica was added along with the stearic acid, zinc oxide and PPD. After 5 minutes the mixer was stopped with the temperature at 1 65 °C. Then in an open mill at 30°C the sulphur, CBS and DPG were incorporated . The resulting material was cut up and calendered with vulcanization for 40 minutes at 1 50°C. It can be seen that the values remain at least constant despite the POJ treatment. A slight improvement in the abrasion loss and tan delta at 70°C will be noticed. In the following tables the data headed RH M100S was obtained using a Monsanto 100S Rheometer. The data headed RH MDR 2000E was obtained using a Monsanto moving die Rheometer 200 (enhanced). MT = maximal torque; mT = minimal torque; delta-T = delta torque (MT-mT); Ts2 = scorch time; T90 = time corresponding to 90% delta torque; E100 and E300 - elongation modulus at 100% and 300% elongation; DRC = compression set. RHEOLOGICAL PROPERTIES 01594.XLS RH M100S 50mπ 150°C IDENT. R959 R960 R961 R962 R963 R964 R965 R966 R967 R968 rr CD NATURE A B POJ10 A POJ15 A POJ20 A POJ30 A POJ10 B POJ15 B POJ20 B POJ30 B CD CΛ c MT in.lb 72.2 71.5 69 68.9 67.6 68.5 70.4 70.5 70.4 69.2 o Λ 13 1 1 .9 13.1 e mT in.lb 14 12.7 1 1.9 12.7 12.2 13.3 12.8 rxH- 0 ύ . dβlta-T in.lb 58.2 58.8 57.1 56.2 54.6 56.6 57.3 58.3 57.1 56.4 ■ D CD Q. TS2 mn 5 5.6 5.7 5.5 6 6.1 5.4 5.2 5.3 5.6 CD T90% mn 11.25 11.9 12.5 11.3 13.65 13.2 11.5 11.8 10.9 12.1 . CQ REVERS. MT 0 0 0 0 0 0 0 0 0 0 < CD 3 MOONEY MV2000E 100°C VISCOSITY =r CD > ML 1 +4 MU 55.5 55 52.5 53 50 52 54.5 51 54.5 52.5 δ " z. CQ MOONEY MV2000E 121 °C SCORCHING 0) σ CD delta 5 mn 43.9 41 36 37 41.6 40 32.1 31 .7 31.1 35.3 delta 10 mn 45.1 42 39.2 40.1 46.4 43.9 35.5 34.1 33.9 38.5 MECHANICAL PROPERTIES IDENT. R959 R960 R961 R962 R963 R964 R965 R966 R967 R968 NATURE A B P0J10A P0J15 A POJ20 A P0J30A POJ10B POJ15 POJ20 B POJ30 B SHA HARDN. 61 62 61 59 59 59 62 61 60 61 CO c 03 E100 MPa 2.68 2.66 2.6 2.52 2.39 2.53 2.4 2.55 2.47 2.41 E300 MPa 10.8 10.7 10.6 10.3 9.7 10 9.8 10.2 10.4 10.1 Mi TENSILE MPa 20 20.8 20.2 20.2 19.6 19.1 19.4 19.1 19.4 18.3 ELONGAT. % 505 529 515 522 530 506 525 502 500 484 TEAR R. kN/m 42 47 45 34 38 33 43 33 34 38 3» DENSITY 1.22 1.22 1.21 1.2 1.19 1.18 1.21 1.2 1.19 1.18 ABR. LOSS 75 79 68 70 73 72 73 66 67 68 mm 3 DRC 22h70°C 16.3 16 16.6 16.7 18.4 17.3 16 16.5 16 16.1 % Example 3 A similar evaluation was carried out on EPDM elastomer. The formulation used along with the amounts of silica used are given below: COMMON PART phr (parts by weight) EPDM 6630 130 STEARIC ACID 3 ACTIVE ZnO 4 PEG 4000 3 WAX CERELUX 120 2 WAX EPOLENE N34 2 SILANE SI69 1 ACC. MBT 1 ACC. TMTD 1 ACC. DPTT 2 VARIABLES phr (parts by weight) NAPHT.OIL SILICA COLL.IDENT A 50 50 R969 B 50 50 R970 POJ 10 A 45.5 55.5 R972 POJ 1 5 A 41 .2 58.8 R973 POJ 20 A 37.5 62.5 R974 POJ 30 A 28.6 71 .4 R975 POJ 10 B 45.5 55.5 R976 POJ 1 5 B 41 .2 58.8 R977 POJ 20 B 37.5 62.5 R978 POJ 30 B 28.6 71 .4 R979 Si69 is bis-(triethoxy propyl silyl) tetra sulphur (Degussa). EPDM 6630 is an oil extended grade of EPDM DEG 4000 is a polyethylene glycol with a molecular weight of 4000. MBT is a mercapto benzothiazole accelerator. TMTD is tetramethylthiuram disuiphide accelerator. DPTT is dipentamethylenethiuram hexasulphide accelerator. The materials used were prepared using a Banbury mixer initially at 60°C when the EPDM was added. One minute later the silica, silane, oil, stearic acid and polyethylene glycol were added, the temperature having risen to 80°C. After 3 minutes the zinc oxide and waxes were added; the temperature was 105°C. The mixing was terminated after 53 minutes when the temperature was 130°C. Subsequently, the material was open milled at 60°C and calendered to 2.5 mm. Vulcanization took place at 160°C. The results obtained were shown in the resulting tables. Best results were generally obtained with the 10% POJ particles. RHM 100S and Mooney mV2000E = rheometer (Flexys). RH M100S 24mn 160°C IDENT. R969 R970 R972 R973 R974 R975 R976 R977 R978 R979 NATURE A B P0J10 A P0J15 A POJ20 A P0J30 A P0J10 B P0J15 B P0J20 B P0J30 B MT in.lb 44 48.3 46.5 46.9 46.7 46.8 49.1 49.3 49 49.2 mT in.lb 7.7 7.5 7.7 7.3 7.3 7.2 7.7 7.8 7.6 7.5 delta-T in.lb 36.3 40.8 38.8 39.6 39.4 39.6 41.4 41 .5 41 .4 41 .7 TS2 mn 3 2.5 2.6 2.75 2.9 2.75 2.4 2.6 2.75 2.6 T90% mn 9.4 10.45 9.7 10.35 10.2 10.3 9.8 10 10.1 9.9 MECHANICAL PROPERTIES IDENT. R969 R970 R972 R973 R974 R975 R976 R977 R978 R979 NATURE A B POJ10 A P0J15 A P0J20 A POJ30 A P0J10 B POJ15 B POJ20 B POJ30 B INST.SH.A HARDN. 47 47 47 47 46 46 47 48 47 47 15 s SH.A HARDN. 43 43 42 42 43 42 43 45 43 43 MODULUS 100% MPa 1.09 1 .09 1 .09 1.12 1.08 1.06 1.08 1.1 1 .1 1 .08 MODULUS 300% MPa 2.68 2.74 2.66 2.77 2.6 2.56 2.6 2.66 2.59 2.73 TENSILE STR.MPa 12.5 9.9 1 1 1 1.1 10.6 9.7 9.4 9.4 9 8.7 ELONGATION % 719 670 699 686 702 695 686 685 689 709 COMP. SET 25% 22H 70°c 19.7 18.9 18.8 20.5 ? 18.2 19.1 17.5 18 17.4 18.3 Example 4 Tests were carried out on a neoprene rubber using the formulation set up below. COMMON PART phr (parts by weight) NR SMR L 100 CB N339 35 SILANE X50S 5.8 STEARIC ACID 3.4 AOX IPPD 1 .5 AOX TQ 1 .5 ACTIVE ZnO 3.5 CBS 1 .75 SULPHUR 1 .75 RETARD. PVI 0.15 VARIABLES phr (parts by weight) AROM.OIL SILICA COLL.IDENT A 10 25 R980 B 10 25 R981 POJ 10 A 7.2 27.8 R983 POJ 1 5 A 5.6 29.4 R984 POJ 20 A 3.75 31 .25 R985 POJ 30 A 0 35.7 R986 POJ 10 B 7.2 27.8 R987 POJ 1 5 B 5.6 29.4 R988 POJ 20 B 3.75 31 .25 R989 POJ 30 B 0 35.7 R990 CB N339 is carbon black with ASTM designation N339, a high abrasion furnace grade. AOX IPPD is an N-isopropyl-N-phenyl- paraphenylenediamine antioxidant/antiozonant. AOX TQ is a 1 ,2-dihydro-2,2,4- trimethylquinoline antioxidant. Retard PVI is an N-(cyclo - hexyD-thiophthalimide pre-vulcanisation inhibitor. Processing was conducted in three stages. In the first stage the neoprene rubber AOX, silica, silane, zinc oxide, stearic acid and oil were mixed, initially at 80°C for 5.5-5.75 minutes when the temperature had reached 145°C. In the second stage the resulting material was mixed at 80°C together with the MB and CB. Mixing was stopped after 3.5-3.75 minutes, the temperature being at 130°C. In the third step, the resulting material was added to the Banbury mixer initially at 50°C and the MB, CBS, sulphur and PVI added and mixed for 2-2.25 minutes when the temperature was 105°C. Subsequently, open milling was carried out at 60°C. Vulcanization was carried out for 40 minutes at 140°C. The results obtained are shown on the resulting Tables. It can be seen that the values remain at least constant despite the POJ treatment. A slight improvement in the abrasion loss and tan delta at 70°C will be noticed. RHEOLOGICAL PROPERTIES RH M100S 60mn 140°C IDENT. R980 R981 R983 R984 R985 R986 R987 R988 R989 R990 NATURE A B POJ10 A P0J15 A POJ20 A POJ30 A POJ10B POJ15 B POJ20 B POJ30 B MT in.lb 81.1 83.8 81.9 82.9 82.2 80.5 83 82.4 82.4 79.7 mT in.lb 18.8 17.5 17.2 17.2 17.7 17.2 17.5 17.8 16.7 16.5 delta-T in.lb 62.3 66.3 64.7 65.7 64.5 63.3 65.5 64.6 65.7 63.2 TS2 mn 11.3 10.9 10.75 10.35 10 10.1 10.9 10.3 10.1 10.1 T90% mn 24 23.25 23.2 22.5 22.35 22.5 23 22.4 22.3 22.25 REVERSION MT 0 0 0 0 0 0 0 0 0 0 MOONEY MV2000E 100°C VISCOSITY IDENT. R980 R981 R983 R984 R985 R986 R987 R988 R989 R990 NATURE A B POJ10A POJ15 A POJ20A P0J30A POJ10B POJ15 B POJ20 B POJ30 B Ml 1 +4 U 73.5 69 70 70.5 72 69 71.5 72 68.5 68 MOONEY MV2000E 121 °C SCORCHING IDENT. R980 R981 R983 R984 R985 R986 R987 R988 R989 R990 NATURE A B POJ10 A P0J15 A POJ20 A POJ30 A POJ10B POJ15 B POJ20 B POJ30 B DELTA 5 mn 33.3 32.9 31 30.1 29.2 28.7 31 29.5 30.6 30.2 DELTA 10 mn 36.3 35.3 33.6 32.6 31.4 30.7 33.4 31.7 32.8 32 APPARENT CROSS LINKING DENSITY (swelling in xylene) IDENT. R980 R981 R983 R984 R985 R986 R987 R988 R989 R990 NATURE A B POJ10 A POJ15 A P0J20 A POJ30 A POJ10B P0J15 B POJ20 B POJ30 B 1/2Mc.10E6 131 135 131 134 133 133 137 136 134 133 MECHANICAL PROPERTIES IDENT. R980 R981 R983 R984 R985 R986 R987 R988 R989 R990 NATURE A B POJ10A P0J15 A P0J20A P0J30 A POJ10B P0J15 B POJ20 B P0J30 B 9 SH.A HARDNESS 15s 67 67 65 65 65 66 67 67 65 65 MODULUS 100% MPa 3.94 4.09 3.82 3.98 4.13 4.06 3.86 3.94 3.91 3.95 300% MPa 16.5 16.9 16.1 16.3 16.7 17.1 16 16.4 16.6 16.4 TENSILE STR. MPa 27.8 28.2 27.5 26.9 27.6 28.2 26.9 28 27.4 27.6 ELONGATION % 521 520 516 502 508 510 503 529 503 513 TEAR R. trouser 20°C 25 27 27 25 23 16 21 19 29 24 kN/m - 80°C kN/m 44 43 47 45 44 31 40 43 33 35 DENSITY 1.19 1.19 1.19 1.19 1.19 1.18 1.19 1.19 1.19 1.18 ABRASION LOSS mm 3 120 116 115 112 108 106 113 105 110 106 REBOUND 20°C % 37 36 37 37 39 38 37 37 37 38 100°C% 45 48 47 46 48 48 47 48 49 51

Claims: CLAIMS 1 . A particulate silica which has been treated with a polymer oil jelly. 2. A silica according to claim 1 in which the amount of polymer oil jelly is 5 from 2.5 to 40% by weight. 3. A silica according to claim 2 in which the amount of polymer oil jelly is from 5 to 30% by weight. 4. A silica according to any one of the preceding claims which has a mean particle size of at least 60 microns. 0 5. A silica according to claim 4 having a mean particle size of at least 80 microns. 6. A silica according to any one of the preceding claims having a CTAB specific surface from 60 to 240 m 2 /g. 7. A silica according to claim 6 having a CTAB specific surface from 90 to 1 5 180 m 2 /g. 8. A silica according to any one of the preceding claims in which the polymer oil jelly is derived from a mineral oil and a copolymer of ethylene, propylene and, optionally, a diene. 9. A silica according to claim 8 in which the copolymer has an ethylene 20 content of 60 to 90% by weight, a propylene content of 10 to 35% by weight and a diene content of 2 to 10% by weight. 10. A silica according to any one of the preceding claims in which the polymer oil jelly is derived from at least 80% by weight of oil. 1 1 . A silica according to any one of the preceding claims which possesses a 25 density in the compacted state of at least 0.23 prior to the treatment. 1 2. A silica according to claim 1 1 in which the silica has a density of 0.27 to 0.35 prior to the treatment. 1 3. Use of a silica as claimed in any one of the preceding claims as a reinforcing filler for elastomers, in particular in shoe soles or tyres.

Inventors: BUTCHER DOUGLAS MARTIN, MACKINNON IAN MALCOLM, BUTCHER, DOUGLAS, MARTIN, MACKINNON, IAN, MALCOLM
Applicants: BUTCHER DOUGLAS MARTIN, MACKINNON IAN MALCOLM, RHONE POULENC CHEMICALS, BUTCHER, DOUGLAS, MARTIN, MACKINNON, IAN, MALCOLM, RHONE-POULENC CHEMICALS LIMITED
Application year: 1996
Main classification: C08K3
IPC codes: B60C1, C08K9, C08L101, C09C1, C09C3