WO2011000133A1 - Hydrophilic silica as filler for silicone rubber formulations - Google Patents
Hydrophilic silica as filler for silicone rubber formulations Download PDFInfo
- Publication number
- WO2011000133A1 WO2011000133A1 PCT/CN2009/000754 CN2009000754W WO2011000133A1 WO 2011000133 A1 WO2011000133 A1 WO 2011000133A1 CN 2009000754 W CN2009000754 W CN 2009000754W WO 2011000133 A1 WO2011000133 A1 WO 2011000133A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- weight
- precipitated silica
- silicone rubber
- value
- silica
- Prior art date
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- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 title claims abstract description 188
- 239000000377 silicon dioxide Substances 0.000 title claims abstract description 90
- 229920002379 silicone rubber Polymers 0.000 title claims abstract description 64
- 239000004945 silicone rubber Substances 0.000 title claims abstract description 56
- 238000010058 rubber compounding Methods 0.000 title claims abstract description 38
- 239000000945 filler Substances 0.000 title claims description 11
- 238000000034 method Methods 0.000 claims abstract description 35
- LZZYPRNAOMGNLH-UHFFFAOYSA-M Cetrimonium bromide Chemical compound [Br-].CCCCCCCCCCCCCCCC[N+](C)(C)C LZZYPRNAOMGNLH-UHFFFAOYSA-M 0.000 claims abstract description 31
- 230000008569 process Effects 0.000 claims abstract description 24
- 239000000203 mixture Substances 0.000 claims description 61
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 55
- 238000001556 precipitation Methods 0.000 claims description 32
- 239000000725 suspension Substances 0.000 claims description 28
- 238000002360 preparation method Methods 0.000 claims description 22
- 239000002535 acidifier Substances 0.000 claims description 20
- 239000002245 particle Substances 0.000 claims description 20
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 claims description 18
- 238000010521 absorption reaction Methods 0.000 claims description 17
- 238000001035 drying Methods 0.000 claims description 16
- 229910052915 alkaline earth metal silicate Inorganic materials 0.000 claims description 15
- 229910052910 alkali metal silicate Inorganic materials 0.000 claims description 11
- 238000005406 washing Methods 0.000 claims description 10
- 239000002253 acid Substances 0.000 claims description 9
- 235000012239 silicon dioxide Nutrition 0.000 claims description 7
- 239000007787 solid Substances 0.000 claims description 7
- 238000001914 filtration Methods 0.000 claims description 6
- 230000032683 aging Effects 0.000 claims description 5
- 229910000272 alkali metal oxide Inorganic materials 0.000 claims description 5
- 229910000287 alkaline earth metal oxide Inorganic materials 0.000 claims description 5
- 229910052500 inorganic mineral Inorganic materials 0.000 claims description 5
- 239000011707 mineral Substances 0.000 claims description 5
- 238000003756 stirring Methods 0.000 claims description 5
- 150000007513 acids Chemical class 0.000 claims description 4
- 229910052731 fluorine Inorganic materials 0.000 claims description 4
- DWAQJAXMDSEUJJ-UHFFFAOYSA-M Sodium bisulfite Chemical compound [Na+].OS([O-])=O DWAQJAXMDSEUJJ-UHFFFAOYSA-M 0.000 claims description 3
- 239000003513 alkali Substances 0.000 claims description 3
- 229910052740 iodine Inorganic materials 0.000 claims description 3
- 235000010267 sodium hydrogen sulphite Nutrition 0.000 claims description 3
- 239000004289 sodium hydrogen sulphite Substances 0.000 claims description 3
- 238000001694 spray drying Methods 0.000 claims description 3
- 238000004821 distillation Methods 0.000 claims description 2
- 238000001223 reverse osmosis Methods 0.000 claims description 2
- 101150068888 MET3 gene Proteins 0.000 claims 1
- 101100022915 Neurospora crassa (strain ATCC 24698 / 74-OR23-1A / CBS 708.71 / DSM 1257 / FGSC 987) cys-11 gene Proteins 0.000 claims 1
- 101100022918 Schizosaccharomyces pombe (strain 972 / ATCC 24843) sua1 gene Proteins 0.000 claims 1
- 239000003795 chemical substances by application Substances 0.000 claims 1
- 230000008719 thickening Effects 0.000 abstract description 6
- 230000003014 reinforcing effect Effects 0.000 abstract description 4
- 150000001875 compounds Chemical class 0.000 description 57
- 239000000243 solution Substances 0.000 description 57
- -1 for e.x ample Chemical class 0.000 description 40
- 230000000052 comparative effect Effects 0.000 description 31
- 238000009472 formulation Methods 0.000 description 25
- DOIRQSBPFJWKBE-UHFFFAOYSA-N dibutyl phthalate Chemical compound CCCCOC(=O)C1=CC=CC=C1C(=O)OCCCC DOIRQSBPFJWKBE-UHFFFAOYSA-N 0.000 description 21
- 238000004448 titration Methods 0.000 description 21
- 150000003254 radicals Chemical class 0.000 description 19
- 239000000523 sample Substances 0.000 description 19
- 229920001296 polysiloxane Polymers 0.000 description 18
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 17
- 238000005259 measurement Methods 0.000 description 17
- 239000000047 product Substances 0.000 description 17
- 238000010348 incorporation Methods 0.000 description 16
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 15
- 239000001117 sulphuric acid Substances 0.000 description 15
- 235000011149 sulphuric acid Nutrition 0.000 description 15
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 14
- 238000012360 testing method Methods 0.000 description 13
- 238000013329 compounding Methods 0.000 description 12
- 235000019353 potassium silicate Nutrition 0.000 description 12
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 12
- 229920001971 elastomer Polymers 0.000 description 11
- 239000003431 cross linking reagent Substances 0.000 description 10
- 239000000806 elastomer Substances 0.000 description 10
- 239000000463 material Substances 0.000 description 10
- 238000012545 processing Methods 0.000 description 10
- 238000004073 vulcanization Methods 0.000 description 10
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 9
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 9
- 229920000642 polymer Polymers 0.000 description 9
- 229910001220 stainless steel Inorganic materials 0.000 description 9
- 239000010935 stainless steel Substances 0.000 description 9
- 239000000126 substance Substances 0.000 description 9
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 8
- 239000008367 deionised water Substances 0.000 description 8
- 239000012153 distilled water Substances 0.000 description 8
- 229910052742 iron Inorganic materials 0.000 description 8
- 230000003287 optical effect Effects 0.000 description 8
- 239000012086 standard solution Substances 0.000 description 8
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 7
- 239000000470 constituent Substances 0.000 description 7
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 description 7
- KJFMBFZCATUALV-UHFFFAOYSA-N phenolphthalein Chemical compound C1=CC(O)=CC=C1C1(C=2C=CC(O)=CC=2)C2=CC=CC=C2C(=O)O1 KJFMBFZCATUALV-UHFFFAOYSA-N 0.000 description 7
- 125000000391 vinyl group Chemical group [H]C([*])=C([H])[H] 0.000 description 7
- WFDIJRYMOXRFFG-UHFFFAOYSA-N Acetic anhydride Chemical compound CC(=O)OC(C)=O WFDIJRYMOXRFFG-UHFFFAOYSA-N 0.000 description 6
- 230000008901 benefit Effects 0.000 description 6
- 125000004432 carbon atom Chemical group C* 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 6
- 229910052801 chlorine Inorganic materials 0.000 description 6
- 229910021641 deionized water Inorganic materials 0.000 description 6
- 239000003921 oil Substances 0.000 description 6
- 239000004944 Liquid Silicone Rubber Substances 0.000 description 5
- 125000003545 alkoxy group Chemical group 0.000 description 5
- 229910052794 bromium Inorganic materials 0.000 description 5
- 239000003153 chemical reaction reagent Substances 0.000 description 5
- 238000012937 correction Methods 0.000 description 5
- 238000002474 experimental method Methods 0.000 description 5
- 239000012065 filter cake Substances 0.000 description 5
- 239000007788 liquid Substances 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 238000003801 milling Methods 0.000 description 5
- 150000001451 organic peroxides Chemical class 0.000 description 5
- 125000006850 spacer group Chemical group 0.000 description 5
- 229920002554 vinyl polymer Polymers 0.000 description 5
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 4
- 125000003302 alkenyloxy group Chemical group 0.000 description 4
- 125000000217 alkyl group Chemical group 0.000 description 4
- 239000002585 base Substances 0.000 description 4
- 239000007795 chemical reaction product Substances 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 238000004132 cross linking Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 229910017604 nitric acid Inorganic materials 0.000 description 4
- 229920000058 polyacrylate Polymers 0.000 description 4
- 229920002239 polyacrylonitrile Polymers 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 3
- 229910019142 PO4 Inorganic materials 0.000 description 3
- 239000004793 Polystyrene Substances 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 239000004411 aluminium Substances 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 125000003118 aryl group Chemical group 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000011088 calibration curve Methods 0.000 description 3
- 239000012482 calibration solution Substances 0.000 description 3
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 3
- 239000003054 catalyst Substances 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 229920005645 diorganopolysiloxane polymer Polymers 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 3
- 230000031700 light absorption Effects 0.000 description 3
- 230000007774 longterm Effects 0.000 description 3
- 229910052748 manganese Inorganic materials 0.000 description 3
- 150000002978 peroxides Chemical class 0.000 description 3
- 125000001997 phenyl group Chemical group [H]C1=C([H])C([H])=C(*)C([H])=C1[H] 0.000 description 3
- 239000010452 phosphate Substances 0.000 description 3
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 3
- 229920002223 polystyrene Polymers 0.000 description 3
- 229920002689 polyvinyl acetate Polymers 0.000 description 3
- 239000011118 polyvinyl acetate Substances 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 239000012763 reinforcing filler Substances 0.000 description 3
- 229910052710 silicon Inorganic materials 0.000 description 3
- 239000010703 silicon Substances 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- 229910052717 sulfur Inorganic materials 0.000 description 3
- 239000012085 test solution Substances 0.000 description 3
- 238000009210 therapy by ultrasound Methods 0.000 description 3
- QAQSNXHKHKONNS-UHFFFAOYSA-N 1-ethyl-2-hydroxy-4-methyl-6-oxopyridine-3-carboxamide Chemical compound CCN1C(O)=C(C(N)=O)C(C)=CC1=O QAQSNXHKHKONNS-UHFFFAOYSA-N 0.000 description 2
- OVSKIKFHRZPJSS-UHFFFAOYSA-N 2,4-D Chemical compound OC(=O)COC1=CC=C(Cl)C=C1Cl OVSKIKFHRZPJSS-UHFFFAOYSA-N 0.000 description 2
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 239000004262 Ethyl gallate Substances 0.000 description 2
- KKCBUQHMOMHUOY-UHFFFAOYSA-N Na2O Inorganic materials [O-2].[Na+].[Na+] KKCBUQHMOMHUOY-UHFFFAOYSA-N 0.000 description 2
- 229910020175 SiOH Inorganic materials 0.000 description 2
- DGEZNRSVGBDHLK-UHFFFAOYSA-N [1,10]phenanthroline Chemical group C1=CN=C2C3=NC=CC=C3C=CC2=C1 DGEZNRSVGBDHLK-UHFFFAOYSA-N 0.000 description 2
- 125000003668 acetyloxy group Chemical group [H]C([H])([H])C(=O)O[*] 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- 125000003368 amide group Chemical group 0.000 description 2
- 239000007900 aqueous suspension Substances 0.000 description 2
- 125000004104 aryloxy group Chemical group 0.000 description 2
- 235000010323 ascorbic acid Nutrition 0.000 description 2
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- OGZPYBBKQGPQNU-DABLZPOSSA-N (e)-n-[bis[[(e)-butan-2-ylideneamino]oxy]-methylsilyl]oxybutan-2-imine Chemical compound CC\C(C)=N\O[Si](C)(O\N=C(/C)CC)O\N=C(/C)CC OGZPYBBKQGPQNU-DABLZPOSSA-N 0.000 description 1
- SIJBDWPVNAYVGY-UHFFFAOYSA-N 2,2-dimethyl-1,3-dioxolane Chemical compound CC1(C)OCCO1 SIJBDWPVNAYVGY-UHFFFAOYSA-N 0.000 description 1
- IQUPABOKLQSFBK-UHFFFAOYSA-N 2-nitrophenol Chemical compound OC1=CC=CC=C1[N+]([O-])=O IQUPABOKLQSFBK-UHFFFAOYSA-N 0.000 description 1
- 125000003903 2-propenyl group Chemical group [H]C([*])([H])C([H])=C([H])[H] 0.000 description 1
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- OMPJBNCRMGITSC-UHFFFAOYSA-N Benzoylperoxide Chemical compound C=1C=CC=CC=1C(=O)OOC(=O)C1=CC=CC=C1 OMPJBNCRMGITSC-UHFFFAOYSA-N 0.000 description 1
- CPELXLSAUQHCOX-UHFFFAOYSA-M Bromide Chemical compound [Br-] CPELXLSAUQHCOX-UHFFFAOYSA-M 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
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- 239000004115 Sodium Silicate Substances 0.000 description 1
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 1
- 239000012963 UV stabilizer Substances 0.000 description 1
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 description 1
- CARRLWRDCUHXCK-UHFFFAOYSA-N [SiH3]NC1CCCCC1 Chemical compound [SiH3]NC1CCCCC1 CARRLWRDCUHXCK-UHFFFAOYSA-N 0.000 description 1
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- TVJPBVNWVPUZBM-UHFFFAOYSA-N [diacetyloxy(methyl)silyl] acetate Chemical compound CC(=O)O[Si](C)(OC(C)=O)OC(C)=O TVJPBVNWVPUZBM-UHFFFAOYSA-N 0.000 description 1
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- 150000002367 halogens Chemical class 0.000 description 1
- 125000004051 hexyl group Chemical group [H]C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])C([H])([H])* 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 125000004435 hydrogen atom Chemical group [H]* 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- NYMPGSQKHIOWIO-UHFFFAOYSA-N hydroxy(diphenyl)silicon Chemical class C=1C=CC=CC=1[Si](O)C1=CC=CC=C1 NYMPGSQKHIOWIO-UHFFFAOYSA-N 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 238000007603 infrared drying Methods 0.000 description 1
- 239000001023 inorganic pigment Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- NLYAJNPCOHFWQQ-UHFFFAOYSA-N kaolin Chemical compound O.O.O=[Al]O[Si](=O)O[Si](=O)O[Al]=O NLYAJNPCOHFWQQ-UHFFFAOYSA-N 0.000 description 1
- 239000002655 kraft paper Substances 0.000 description 1
- 239000001115 mace Substances 0.000 description 1
- 238000003760 magnetic stirring Methods 0.000 description 1
- FPYJFEHAWHCUMM-UHFFFAOYSA-N maleic anhydride Chemical compound O=C1OC(=O)C=C1 FPYJFEHAWHCUMM-UHFFFAOYSA-N 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 238000011022 operating instruction Methods 0.000 description 1
- 239000012860 organic pigment Substances 0.000 description 1
- 125000005375 organosiloxane group Chemical group 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 235000011837 pasties Nutrition 0.000 description 1
- 125000002467 phosphate group Chemical group [H]OP(=O)(O[H])O[*] 0.000 description 1
- 229910052615 phyllosilicate Inorganic materials 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 239000004014 plasticizer Substances 0.000 description 1
- 229920000435 poly(dimethylsiloxane) Polymers 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 229910052573 porcelain Inorganic materials 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 description 1
- 229910052913 potassium silicate Inorganic materials 0.000 description 1
- NNHHDJVEYQHLHG-UHFFFAOYSA-N potassium silicate Chemical compound [K+].[K+].[O-][Si]([O-])=O NNHHDJVEYQHLHG-UHFFFAOYSA-N 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000011085 pressure filtration Methods 0.000 description 1
- 125000001436 propyl group Chemical group [H]C([*])([H])C([H])([H])C([H])([H])[H] 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 239000012744 reinforcing agent Substances 0.000 description 1
- 239000005871 repellent Substances 0.000 description 1
- 230000002940 repellent Effects 0.000 description 1
- 230000000979 retarding effect Effects 0.000 description 1
- 229910052895 riebeckite Inorganic materials 0.000 description 1
- 229920002631 room-temperature vulcanizate silicone Polymers 0.000 description 1
- 239000005060 rubber Substances 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 230000007017 scission Effects 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 229910000077 silane Inorganic materials 0.000 description 1
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical class O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Inorganic materials [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- ABTOQLMXBSRXSM-UHFFFAOYSA-N silicon tetrafluoride Chemical compound F[Si](F)(F)F ABTOQLMXBSRXSM-UHFFFAOYSA-N 0.000 description 1
- 229920005573 silicon-containing polymer Polymers 0.000 description 1
- 229920002545 silicone oil Polymers 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- FQENQNTWSFEDLI-UHFFFAOYSA-J sodium diphosphate Chemical compound [Na+].[Na+].[Na+].[Na+].[O-]P([O-])(=O)OP([O-])([O-])=O FQENQNTWSFEDLI-UHFFFAOYSA-J 0.000 description 1
- APSBXTVYXVQYAB-UHFFFAOYSA-M sodium docusate Chemical compound [Na+].CCCCC(CC)COC(=O)CC(S([O-])(=O)=O)C(=O)OCC(CC)CCCC APSBXTVYXVQYAB-UHFFFAOYSA-M 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000007655 standard test method Methods 0.000 description 1
- 125000001424 substituent group Chemical group 0.000 description 1
- 150000003467 sulfuric acid derivatives Chemical class 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- GJBRNHKUVLOCEB-UHFFFAOYSA-N tert-butyl benzenecarboperoxoate Chemical compound CC(C)(C)OOC(=O)C1=CC=CC=C1 GJBRNHKUVLOCEB-UHFFFAOYSA-N 0.000 description 1
- SWAXTRYEYUTSAP-UHFFFAOYSA-N tert-butyl ethaneperoxoate Chemical compound CC(=O)OOC(C)(C)C SWAXTRYEYUTSAP-UHFFFAOYSA-N 0.000 description 1
- 235000019818 tetrasodium diphosphate Nutrition 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 238000002604 ultrasonography Methods 0.000 description 1
- 238000009834 vaporization Methods 0.000 description 1
- 230000008016 vaporization Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
- 238000009736 wetting Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
- C01B33/187—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates
- C01B33/193—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates of aqueous solutions of silicates
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
- C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black
- C09C1/28—Compounds of silicon
- C09C1/30—Silicic acid
- C09C1/3081—Treatment with organo-silicon compounds
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
- C09D183/04—Polysiloxanes
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/51—Particles with a specific particle size distribution
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/11—Powder tap density
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/19—Oil-absorption capacity, e.g. DBP values
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
Definitions
- the present invention relates to hydrophi..ic prec Lpitated silicas which are well suited for use in jsilicone rubber formulations (RTV-I, RTV-2, HTV and LSR), particularly well suited for use in HTV silicone rubber formulations, a process for the preparation thereof and the use thereof for thickening and reinforcing silicone rubber formulations.
- Silicone rubbers are materials which can be converted into the elastomeric state and contain, as base polymers,
- crosslinking reactions Predominantly suitable as such are H- atoms, OH groups and vinyl groups which are present at the chain ends but may also be incorporated into the chain.
- Fillers such as, for example, hydrophilic precipitated silicas, are incorporated as reinforcing agents into this system, the type and amount of which substantially influence the mechanical and chemical behaviour of the -vulcanizates .
- Silicone rubbers can be coloured by inorganic pigments.
- HTV and RTV room temperature vulcanizing silicone rubber types
- LSR liquid silicone rubber
- the first group (RTV-IC) polymerizes slowly at room temperature under the influence of atmospheric humidity, the crcsslinking taking place by condensation of SiOH groups with formation of Si-O bonds.
- the SiOH groups are formed by hydrclysis of SiX groups of a species formed as an intermediate from a polymer having terminal OH groups and a so-called crosslinking agent R-SiX 3 (e.g. X - -Q-CO-CH 3 , -NHR) .
- RTV-2C two -component rubbers
- silicic acid esters ⁇ e.g. ethyl silicate
- silicas are used for thickening ard reinforcing RTV-IC silicone rubber. Owing to the sen ⁇ itivity of the silicone sealing compounds to hydrolysis, they must introduce as little moisture as possible into the system. To date, virtually exclusively fumed silicas have therefore been used for this application. However, EP 1860066 also discloses novel hydrophilic precipitated silicas having a special surface character, which are suitable for thickening .FTV-IC
- RTV-IC silicone rubber formulations are very sensitive to any introduction of water and therefore set special requirements for the fillers with regard to the introduction of water, this problem does not occur to this extent in the case of HTV silicone rubber formulations.
- good processibility of the formulation after introduction of filler and a high mechanical load capacity of the silicone rubber product, in particular long-term load capacity, must be ensured.
- the fillers should lead to as little
- the introduction of water into the system is not of great importance since the silicone rubber producers specially pretreat or aftertreat thu filler, for example hydrophilic precipitated silicas.
- the silicas are rendered water repellent during the
- ⁇ specific object of the present invention was to provide precipitated silicas which can be readily incorporated and dispersed in silicone rubber formulations, in particular HTV formulations, and impart good mechanical properties, in particular good long-term load capacity, to them. Moreover, it was a specific object of the present inventior to provide precipitated silicas which permit the preparation of HTV formulations (compounds and vulcanizates) having very high transparencies, preferably in combination with very little di scolouration .
- the present invention therefore relates to hycrophilic
- precipitated silicas which are characteri2.ed in that they have a BET surface area of 185 to 260 tn'Vg
- the present invention furthermore relates to a process for the preparation of the precipitated silicas according to the invention, characterized in that it comprises the following steps :
- the .ilka.,.i metal silicate and/or alkaline earth metal silicate used ir, steps a) and/or b) has an alkali metal oxide or alkaline earth metal oxide content in the range from 4 to 7% by weig:it and a silicon dioxide content in the range from 12 to 28% b/ weight
- the acidifying agent used in step b) aid/or c) is an acidifying agent selected from the group consisting of concentrated mineral acids and carbonic acid (or CO2 gas) and sodium hydrogen sulphite (or SO 2 gas) in th.s correspondingly possible concentrations, and in that ":he Y value of the precipitation suspension is kept constant at a value between 10 and 30 during the precipitation, keeping constant meaning that the Y value varies by not more 3% about the starting Y value, i.e. the value directly before the oeginning of the simultaneous addition of acidifying agent and alkali metal silicate or alkaline earth metal silicate, Ln the course
- the present invention also relates to silicone rubber
- the inventors have surprisingly found that the precipitated silicas according to the invention can be very readily
- a further advantage of the precipitated si lies s according to the invention is that silicone rubber compouncs, i.e. as yet uncured mixtures and cured vulcanizates, containing the precipitated silicas according to the inventicn have a high transparency (translucence) .
- the precipitated silicas according to the invention have a high BET surface area of 185 to 260 m 2 /g.
- the EET surface area is preferably in the range from 185 to 210 mVg aid particularly preferably 190 to 205 mVg.
- the BET surface area is in the range from 210 to 260 m 2 /g, preferably 211 to 260 m 2 /g, particularly preferably 215 to 250 m 2 /g and very particularly preferably 220 ":o 250 m 2 /g.
- the BET surface area influences the reinforcing potential of the precipitated silica. The higher the BET surface area, the greater is the reinforcement. However, a high BET surface area also leads to a deterioration of the possibility of incorporating the precipitated silica into the silicone rubber formulation. The inventors have now found that this
- the precipitated silicas according to the invention are therefore distinguished by a CTAB surface area of 100 to
- 160 m ? 7g preferably 110 to 150 mVg, particularly preferably 120 - 150 m 2 /g and very particularly preferably 126 to 145 mVg and a BET/CTAB ratio of 1.2 to 2.6, preferably 1.25 - 2.3, particularly preferably 1.3 to 2 and very particularly
- the BET/CTAB ratio is an independent parameter, i.e. an independent characteristic of the
- precipitated silica according to the invention which has a CTAB of 160 m 2 /g must have at least a BET of 2)0 m ? /g.
- the CTAB surface area characterizes the rubber-accessible surface.
- the inventors are of the view that the BET/CTAB ratio also influences the
- refractive index of the precipitated silica which refractive index reflects properties in the region of interfaces, which in turn are dependent on the differently determined surface areas of the silica used, and hence contributes to the good transparency of the precipitated silicas according to the invention .
- a further important feature of the precipitated silicas according to the invention is the median particle size dso.
- the precipitated silicas ⁇ iccoiding to the invention therefore preferably have a median particle size d 5 o of 5 to 95 ⁇ m,
- diffraction is in the range from 5 to 25 ⁇ m, preferably 8 to 24 ⁇ m, particularly preferably 10 to 20 ⁇ iri anc very
- the proportion of very fine particles, expressed by the ds value, in this variant is 4 to 10 ⁇ m, in particular 4.3 to 6 ⁇ m.
- particles which are too small lead to disadvantages in the incorporation into the silicone rubber formulation.
- the ds value can be kept
- the median particle size is in the range from 25 to 95 ⁇ m, preferably 30 to 90 ⁇ m, particularly preferably 30 to 80 ⁇ m and especially preferably 40 to 75 ⁇ m.
- this variant has the advantage that no milling of the dried precipitated silica is necessary. At the same time, however, a deterioration in the dispersibility may be
- a further substantial feature of the precipitated silicas according to the invention is the low conductivity thereof/ i.e. the low content of salts, such as, for e.x ample,
- the precipitated j.ilicas according to the invention have a conductivity of less 1 han 250 ( ⁇ S)/cm, preferably less than 200 ( ⁇ S) /cm, particularly preferably 1 to 200 ( ⁇ S)/cm, very particularly preferably 5 tc 150 ( ⁇ S) /cm, especially preferably 5 to 100 ( ⁇ S)/cm anc very especially preferably 10 to 50 ( ⁇ S) /cm.
- the positive properties of the precipitated silicas according to the invention can be further enhanced if they have a low- tamped density.
- the inventors are of the view that the tamped density is conducive to a particularly good dispersibility.
- the median particle size ⁇ $or measured by mean.- of laser diffraction is in the range from 5 to 25 ⁇ m, preferably 8 to 24 ⁇ m, particularly preferably 10 to 20 ⁇ m and very
- the tamped density of the precipitated silicas according to the invention is preferably 50 to 150 g/1, particularly preferably 80 to 150 g/1, very particularly preferably 90 to 14 D g/1 and especially preferably 100 to 130 g/1.
- the tamped density of the precipitated silicas according to the invention is preferably IbO to
- precipitated silicas according to the invention have a
- the precipitated silicas according to the invention can be readily incorporated into extrudable HTV silicone rubber formulations, in spite of the relatively high moisture content of 5 to 7% by weight. This is surprising since considerable efforts are made in the prior art to prepare precipitated silicas having a low moisture content and low water absorption. Owing to the special parameter combination, the precipitated silicas according to the invention can be readily used as reinforcing filler for elastomer mixtures even in the case of a high moisture content. This leads to considerable cost reductions in the preparation, transport and storage of tie precipitated silicas .
- the precipitated silicas according to the inveition preferably have a DBP absorption of 240 to 300 g/100 g, particularly preferably 250 to 300 g/100 g and very particularly preferably 260 to 290 g/100 g.
- Precipitated silicas having this DBP absorption possess particularly good dispersibility
- the pH of the precipitated silicas according to the invention is preferably in the range from 5 to 8, particularly
- the precipitated silicas according to the invention can be prepared by a process which comprises the following steps:
- the aIlea. ' i metal silicate and/or alkaline earth metal silicate used in steps a) and/or b) has an alkali metal oxide or alkaline earth metal oxide content in the range from 4 to 7% by weight and a silicon dioxide content in the range from 12 to 28% by weight
- the acidifying agent used in step b) a:id/or c) is an acidifying agent selected from the group consisting of concentrated mineral acids and carbonic acid (or CO2 gas) and sodium hydrogen sulphite (or SO 2 gas) ir tho correspondingly possible concentrations, and in that 1:he Y value of the precipitation suspension is kept constant at a value between 10 and 30 during the precipitation, keeping constant meaning that the Y value varies by not more 3% about the starting Y value, i.e.
- silicate solution and alkali metal silicate solution and/or alkaline earth metal silicate solution are used synomously.
- the alkali metal oxide or alkaline earth metal oxide content in the silicate solution used according to the invention is in the range from 4 to 7% by weight, preferably in the range from 5 to 6.5% by weight, particularly preferably from 5.5 to 6,5% by weight.
- the silicate solution used in the process according to the invention is sodium silicate solution (waterglass) or potassium silicate solution. In a particularly preferred embodiment of the present invention, highly pure silicate solution is used.
- Highly pure silicate solution is characterized by a content of Fe 2" of less than or equal to 200 mg/kg, p.;efe2.ably less than or equal to 180 mg/kg, particularly preferably less than or equal to 150 mg/kg, and an AI 2 O 3 content oJ: Ie. s than or equal to 0.55% by weight, preferably less than or eqjal to 0.45% by weight, particularly preferably less than or equal to 0.25% by weight .
- the silicon dioxide content in the silicate solution used according to the invention is 12 to 23% by weight, preferably 13 to 23% by weight, particularly preferably 14 to 18% by weight.
- the modulus, i.e. the weight ratio of silicon dioxide to alkali metal oxide or alkaline earth metal oxide in the silicate solution used according to the invention is
- concentrated mineral acids such as hydrochloric acid, sulp.iuric acid, nitric acid or phosphoric acid, or CO 2 are preferably used as the acidifying agent.
- Concentrated minera] acid means a concentration of 36 to 47.2% by weight, prefeiably 40 to 47% by weight, in the case of hydrochloric ac ⁇ d, a concentration of 90 to 98.5% by weight, preferably 93 to 98.5% by weight and very particularly preferably 96 to 98% by weiciht, in the case of sulphuric acid, a concentration of 60 to 6H% by weight in the case of nitric acid and a concentration of 80 to 100% by weight, preferably 80 to 90% by weight, particularly
- denineralized water preferably water purified by distillation or reverse osmosis
- water purified by distillation or reverse osmosis is used as water in at least one ⁇ step of the process according to the invention, preferably at least during the washing process .
- the initially introduced mixture in step a) consists of water to which a base is added, or an aqueous solution of a base; it preferably comprises at least one alkali tretal silicate and/or alkaline earth metal silicate. It has proved advantageous if the initially introduced mixture is heated to a temperature of 40 to 90 0 C before the beginning of the precipitation, i.e. the addition of acidifying agent and silicate solution together.
- the Y value of the initially introduced mixture is adjusted to tha value to be maintained during the precipitation.
- the adjustment of the Y value of the initially introduced mixture is preferably effected with the silicate solution which is also used for the precipitation.
- th'2 Y value remains constant in the course of the simultaneous addition ot acidifying agent and alkali metal silicate or alkaline earth metal silicate, i.e. varies by not more than 3% about the starting Y value, i.e. the value directly befcre the beginning of the simultaneous addition of acidifying agent and alkali metal silicate or alkaline earth metal silicate.
- the Y value expresses the alkali metal ion concentration in the reaction solution. The Y value therefore reflects the chemical
- the Y value is kept constant in the range from 10 to 30, preferably from 15 to 25 and very particularly preferably from 18 to 22 during the precipitation.
- the precipitation is carried out at a temperature of 80 to 95 0 C, preferably 85 to 9O 0 C.
- the pure precipitation time i.e. the duration of the addition of silicate solution and
- acidifying agent together - without taking intD account interruption times - is 60 to 90 min, preferably 65 to 85 min, very particularly preferably 70 to 80 min.
- the flow rates of the acidifying agent and of the silicate solution are chosen so that the desired precipitation time but at the same time also the desired Y value variation of the precipitation suspension can be maintained.
- step c) the reacidification of the precipitation
- suspension is effected, preferably to a pK of 1 to 1,
- step d) ageing of the precipitation suspension for 5 to 50 min, preferably 10 to 40 min, particularly preferably 10 to 30 min and very particularly preferably 15 to 25 min takes place in step d) .
- This ageing step has, inter alia, an influence on the establishment of the BET and CTAB surface areas.
- the suspension is not harmful if the suspension is stored for up to 48 hours after step c) , for example in a suspension tank. This permits a higher flexibility of production.
- the precipitated silica suspensions preparec by the process according to the invention are filtered in step e) and the filter cake is washed with water.
- a plurality of washing steps can be carried out.
- demineralized water is used in at least one washing step.
- washing can preferably oe effected with the normal water first and with demineralizod water only in the latter stages or the last stage, T " -iis reduces the preparation costs.
- the filtration, fluidization (for example, according to DE 2447613) and long- or short-term drying of the silicas according to the invention, are familiar to th ⁇ person skilled in the art and are described, for example, in the documents mentioned in this description.
- the filtration and the washing of the silica preferably take place in such a way that the conductivity of the end product is less than 250 ( ⁇ S) /cm, preferably less than 200 ( ⁇ S) /cm, particularly preferably 1 to 200 ( ⁇ S) /cm, very particularly preferably 5 tc 150 ( ⁇ S)/cm, especially preferably 5 to 100 ( ⁇ S)/cm and very especially preferably 10 to 50 ( ⁇ S) /cm.
- the silica according to the invention is dried in a pneumatic dryer, spray dryer, rack dryer, belt dryer,
- Buttner dryer rotary tube dryer, flash dryer, spin-flash dryer or nozzle tower dryer.
- These drying variants include operation with an atomizer, a one-fluid or two-fluid nozzle or an integrated fluidized bed.
- Spray drying, in particular with an atomizer, is particularly preferred. This can be carried out, for example according to US 4094771. Particularly
- the spray drying is carried out with a feed having a solids content of 15 to 20% by weight and a pH of 4 to 7, preferably 5 to 6.
- the spray-dried particles can have median diameters of more than 15 ⁇ m, preferably 25 - 55 ⁇ m,
- the dried precipitated silicas are billed.
- Impact mills or opposed jet mills or mechanical mills are preferably used for milling the silicas according to the
- the milling parameters are preferacly chosen so that the median particle size dso of the precipitated silicas according to the invention, measured by means of laser
- diffraction is in the range from 5 to 25 ⁇ m, preferably 8 to 25 ⁇ m, particularly preferably 10 to 20 ⁇ i, very particularly preferably 12 to 18 ⁇ m, and/or the d* > value is in the range from 4 to 10 ⁇ m, in particular 4.3 to 6 ⁇ m.
- the precipitated silicas according to the invention are preferably used as fillers in silicone rubber formulations of the RTV-IC, RTV-2C and LSR systems, in partici lar in HTV silicone rubber formulations.
- Organopolysiloxanes which may be used are ⁇ 11 polysiloxanes which have been used to date, or which it has been possible to use to date, as the base for organopolysilox ⁇ ne elastomers in the case of room temperature vulcanizable or vulcanizing materials (RTV), materials vulcanizable or vu-canizing at only slightly elevated temperature (LTV) or iigh temperature vulcanizable or vulcanizing materials (HTV) .
- RTV room temperature vulcanizable or vulcanizing materials
- LTV room temperature vulcanizable or vulcanizing materials
- HTV iigh temperature vulcanizable or vulcanizing materials
- radicals Z and R may be identical or different or the radicals R and Z themselves can however also be identical or different, and in which the radicals are definad as follows:
- R alkyl, alkoxy, aryl, hydroxy, hydride or alkenyl radicals having 1-50 carbon atoms, unsubstituted or substituted by 0, S, F, Cl, Dr, I, in each case identical or different, and/or polys ryrene, polyvinyl acetate, polyacrylate, po.Lymel hacrylate and polyacrylonitrile radicals havirg 5C-10 000 repeating units .
- n 1 - 3
- X 100 - 15 000, preferably 100 - 11 )00, particularly preferably 100 - 8000.
- Polysiloxanes especially suitable for RTV-IC silicone rubber formulations may have, for example, the following structure
- R alkyl, acetoxy, oxime, alkoxy, amido, aryl or alkenyl radicals having 1 to 50 carbon atoms, unsubstituted or substituted by 0, S, F, Cl, Br, I, in each case identical or d: fferent, and/or polystyrene, polyvinyl acei.ate, polyacrylate, polymethacrylate and polyacrylonitrile radicals having 50 - 10 000 repeating units.
- Z OH, Cl, Br, acetoxy, amino, a ⁇ iido, aminoxy, oxime, alkoxy, alkenyloxy, acryloyioxy or phosphate radicals, it being possible for the organic radicals :o carry up to 20 carbon atoms ,ind said organic radicals being identical or different in each case.
- n 1 - 3
- X 100 - 15 000, preferably 100 - 11 000, particularly preferably 100 - 8000.
- siloxane units within or along the siloxane chain in t ⁇ e abovementioned formulae, other siloxane units, generally present only as impurities, can also be present as diorganosiioxane units, for example those of the formulae RSiC- 3/ 2, RjOi/ 2 and SiCv2, in which R in each case has the meanings stated above therefor.
- the amount of these other siloxane units should not exceed 10 mol%.
- R having the meaning alkyl iadical are, for example, methyl, ethyl, propyl, butyj , hexyl and octyl radicals; vinyl, allyl, ethylallyl and butadisnyl radicals may be used as alkenyl radicals; and phenyl and tolyl radicals may be used as aryl radicals.
- substituted hydrocarbon radicals R are in particular halogenated hydrocarbon radicals such as the 3,3,3- trifluoropropyl radical, chlorophenyl and bromotolyl radical; and cyanoalkyl radicals, such as the G ⁇ cyanoethyl radical.
- radical R examples include polystyrene, polyvinyl acetate, polyacrylate, polymethacrylate and polyacrylonitrile radicals bonded to silicon via carbon.
- the pnsdom .nant part of the radicals R preferably consists of methyl groups .
- the other radicals R are in particular vinyl and/or phen/1 groups.
- Z are hydrolysable groups.
- acyloxy groups in particular acetoxy groups, are preferred as Z.
- hydrolysable atoms Z are halogen and hydrogen atoms.
- alkenyl groups Z are in particular vinyl groups .
- the viscosity of the organopolys iloxanes used in the invention does not exceed 500 000 cP at 25°C, particularly preferably 150 000 cP at 25°C. Accordingly, the value x preferably does not exceed 40 000. It is also possible to use mixtures of different organopolysiloxanes .
- the silicas used according to t.ie invention are employed in amounts of 0,5 to 60% by weiqht, preferably 5% to 60% by weight, particularly preferably 10% -;o 40% by weight and very particularly preferably 20 to 3Oo by weight, based on the total weight of the materials curable to give elastomers.
- 5% to 60% by weight particularly preferably 10% -;o 40% by weight and very particularly preferably 20 to 3Oo by weight, based on the total weight of the materials curable to give elastomers.
- very particularly preferably 20 to 3Oo by weight based on the total weight of the materials curable to give elastomers.
- up to 60% by weight can likewise be used.
- the proportion of the abovementioned organc-polysiloxanes is preferably 30 - 99.5% by weight, based on the total weight of the material curable to give elastomers.
- Si-bonded hydroxyl groups are present as the only reactive terminal units in the reactive diorganopolysiloxanes containing terminal units, these diorganopolysiloxanes must be reacted in a known manner with crosslinking agents, optionally in the presence of a condensation catalyst, in order to cure them in a manner known per se or to cc nvert them into compounds curing by the water present in the air, optionally with addition of further water, to giv ⁇ 5 elastomers.
- organic peroxides such as, for example 2, 5-dimethy1-2, 5- (di-tert- butylperoxy) hexane, bis-2, 4-dichlorobenzoyl peroxide, benzoyl peroxide, tert-butyl perbenzoate or tert -butyl peracetate in an amount of 0.5 - 5.0% by weight can be used at correspondingly advantageous temperatures.
- Preferably used high temperature vulcan/.zinq organosiloxanes are those in which the organic substituents consist of methyl, ethyl, phenyl, trifluoromethylphenyl [F3CC6H4] or trimethylsilmethylene radicals [ (CH 3 ) 3 SiCII 2 -] , e.g. dimethyl-, diethyl-, phenylmethyl-, phenylethyl-, ethylmethyl-, trimethylsilmethylenemethyl-, trimethyls Llmethyleneethyl-, trifluoromethylphenylmethyl- or trifluororasthylphenylethyl- siloxanes or copolymers of such compounds.
- the organic substituents consist of methyl, ethyl, phenyl, trifluoromethylphenyl [F3CC6H4] or trimethylsilmethylene radicals [ (CH 3 ) 3 SiCII 2 -] , e.g
- the polymers can preferably contain lLmitud amounts of diphenylsiloxane, bistrimethylsilraethylenesiloxane, or bistrifluoromethylphenylsiloxane units and also siloxanes having units of the formula RSiO x ,5 and RjS- O 0 ,5/ in which R represents one of the above radicals.
- the formulations according to the invention can be crosslmked by addition of silanes.
- the silicone rubber formulations may therefore additionally contain 0.01 to 20% by weight, preferably 0.5 - 5% by weight, of a crosslinking agent having the general formula
- Z' H, OH, Cl, Br, amino, aminoxy, alkenyloxy, aryloxy or phosphate radicals, it being possible for the organic radicals to carry up to 20 carbon atoms and to be in each case identical or different.
- silanes of the aboveme ⁇ tioned formula are methyltriacetoxysilane, ethyltriacetoxys llanu, isopropyltri- acetoxysilane, isopropoxytriacetoxysilane, vinyltriacetoxy- silane, methyltrisdiethylaminooxysilane , tiethyltris (cyclo- hexylamino) silane, methyltris (diethylphosphato) silane and methyltris (methylethylketoximo) silane.
- silicone rubber formulations according to the invention additionally to contain 0.5 to 99.5% by weight, preferably 2.0 to 30.0% by weight, of an unfunctionalized polysilo ⁇ ane, in addition to the organopolysiloxane and the crosslinking agsnt.
- the polysiloxanes used here may have a viscosity of up to 500 000 cP (500 Pa -s).
- Baysilone MS 10 viscosity 10 - 20 mPa'S
- the distributor oil Si 200 viscosity about 28 mPa*s
- RTV-2C silicone rubbers for example, the oil M ICO i viscosity about 100 mPa-s) of the same manufacturer can be used.
- the s: lice s according to the invention, crosslinking agents and crossl- nking catalysts, formulations according to the invention can oi course
- fillers generally or
- fillers havine a surface area below 50 m 2 /g such as quartz powder, kaolin, phyllosilicates, tau minerals, diatomaceous earth, furthermore zirconium
- oiganic resins such as polyvinyl chloride powder, organopolysj loxane resins, fibrous Cillers, such as asbestos, glass fibres, and organic pigments, soluble dyes, fragrances, corrosion inhibitors, compositions stabilizing materials to the influence of water, such as acetic anhydride, compositions retarding curing, such as benzotriazole, and plasticizers, such as
- formulation constituerts and additives are carbon blacks for establishing antistatic properties or specific electrical conductivities, UV stabilizers, anti- discolouration compositions, such as, for exairple, the product TSF-484 (Momentive Performance Materials) or HF 99 (Shin-Etsu Silicones) .
- the silicone rubber formulations may additionally contain 0.01 to 6% by weight of organic or iiiDrganic compounds of the metals Pt, Sn, Ti and/or Zn as a catalyst and/or 0.01 to 6% by weight of inhibitors and/or 0.01- 6% by weight of fungicides or bactericides and/or 0.01 to 6% by weight of adhesion promoters.
- RTV-IC silicone rubber formulations may oDtioially contain 0.1 - 20, preferably 0.1 - 15, particularly preferably 0.1 - 10, % by weight (based on the total amount of the formulation) of water-binding substance.
- Suitable substances for this purpose are, for example, carboxylic anhydrides, e.g. acetic anhydride or maleic anhydride, and/or carbonic acid est ⁇ rs, such as, for example, diethyl carbonate, ethylene carbonate, and/or alkenyloxy compounds and/or ketals, such as, for example dimethyldioxolane. It is possible to use one or more of these substances .
- preferred HTV silicone rubber formulation is to be understood as meaning the following formulation constituents:
- polysiloxane (vinyl content about 0.15%) and having a
- crosslinking agent organic peroxide, (2 , 5-dirnethyl-2, 5- di-tert-butylperoxy)hexane, definable by the following
- DHBP-C8BS DHBP paste with a pei oxide
- the physicochemical parameters of the precipitated silicas according to the invention and the process paiameters are determined as follows.
- the Y value is determined by means of sulphuric acid as standard solution and phenolphthalein as an indicator.
- 100 ml of the sample to be investigated e.g a precipitation suspension
- 100 ml of the sample to be investigated are introduced into a 500 'Til beaker and about 10 ml of water and 3-5 drops of phenolphthalein solution are added.
- the mixture is stirred by means of a magnetic stirrer and the sulphuric acid solution is added by means of a burette until the colour of phenolphthalein chan ⁇ ies from red to faint pink. 3 - 5 further drops of phenolphthalein are added and titration is continued. This process is repeated until a colour change is no longer detectable.
- the Y value is calculated as follows:
- V volume of the sulphuric acid consumed :i n the titration, in ml
- a sample of 50 - 100 ml of the initially introduced mixture or the precipitation suspension is taken and the pH is determined at 6O 0 C.
- the solids content (SC) in % is determined according to
- the determination of the pH of the silica is effected as a 5% strength aqueous suspension at room temperature on the basis of DIN EN ISO 787-9. The weights taken were changed compared with the specifications of this standard (5.0U g of silica per 100 ml of deionized water) .
- the moisture content of silica is determined according to ISO 787-2 after drying for 2 hours in a circulation drying oven at 105 0 C. This loss on drying consists pjedo ⁇ inantly of water moisture .
- the specific nitrogen surface area (referred to below as BET surface area) of the pulverulent, spherical cr granular silica is determined according to ISO 5794-1/Annex D using an AREA Meter (from Strohlein, JUWE) .
- the method is based on the adsorption of CfAB (N-hexadecyl- N,N,N-trimethylammonium bromide) on the "external" surface of the silica, according to ASTM 3765 or NFT 45-007 (section 5.12.1.3) .
- CfAB N-hexadecyl- N,N,N-trimethylammonium bromide
- CTAB adsorption of CTAB takes place in aquecus solution with stirring and ultrasonic treatment.
- u ⁇ adsorbed CTAB is determined by back-titration with NDSS (sodium dioctyl sulphosuccinate solution, "Aerosol OT" solution) using a titroprocessor, the end point being given bv the maximum of the turbidity of the solution and beincr determined using a phototrode.
- NDSS sodium dioctyl sulphosuccinate solution, "Aerosol OT" solution
- the temperature during all operations carried out is 23 - 25 0 C, in order to prevent CTAB from crystallizing out.
- the back-titration is based on the following equation:
- Membrane filter comprising cellulose nitiate, pore size
- CTAB 0.015 mol/1 in deionized water
- the consumption of NDSS solution for the tit- ation of 5 ml of CTAB solution should be checked once a day before each measurement series.
- the phol:otrode is set at 1000 + 20 mV before the beginning of the titration (corresponding to a transparency of 100%) .
- 10.0 g of the pulverulent, spherical or grant lar silica having a moisture content of 5 ⁇ 2% ⁇ moisture content is optionally adjusted by drying at 105 ⁇ C in a drying oven or uniform moistening) are comminuted using a mill (fr ⁇ n Krups, Model KM 7b, article No. 2030-70) for 30 seconds.
- a mill fr ⁇ n Krups, Model KM 7b, article No. 2030-70
- Exactly 500.0 mg of the comminuted sample (weight E taken) are transferred to a 150 ml titration vessel with magnetic stirring rod, and exactly 100.0 ml of CTAB solution (Ti) are metered in.
- the titration vessel is closed with a cover and stirred with an Ultra Turrax T 25 stirrer (stirrer shaft KV-18G, 18 mm diameter) at 18 000 rpm for not more thai: 1 ⁇ in until wetting is complete.
- the titration vessel is screv7 ⁇ d to the DL 70 titroprocessor and the pH of the suspension is adjusted to a value of 9 ⁇ 0.05 with KOH (0.1 mol/1) .
- Ultrasonic treatment of the suspensior for 4 minutes is effected in the titration vessel in an nitre sonic bath (from Bandelin, Sonorex RK 106 S, 35 kHz, 100 W ei fective or 200 W peak power) at 25°C. Thereafter, immediate prassure filtration through a membrane filter at a nitrogen pressure of 1.2 bar is effected. The forerun of 5 ml is discarded.
- nitre sonic bath from Bandelin, Sonorex RK 106 S, 35 kHz, 100 W ei fective or 200 W peak power
- V n consumption of NDSS solution in ml on use of the filtrate
- CcTAB concentration of the CTAB solution in : ⁇ ol/l
- the CT ⁇ B surface area is based on the anhydrous silica, and it is for this reason that the following corrs ction is carried out .
- the moisture content of the silica is derernuned according to the described method "Determination of the ' moisture content”.
- DBP number which is a measure of the absorptivity of the precipitated silica, is determined on the basis of the standard DIN 53601, as follows:
- V consumption of DBP in ml
- the DBP absorption is defined for the anhydrous, dried silica.
- the correction value K should be taken into account for ca. culating the DBP absorption. This value can be determined with the following correction table; for example, a water ccnter.t of 5.8% in the silica would mean an addition of 33 g/(100 g) for the DBP absorption.
- the moisture content of the silica is determined according to the method ⁇ Determination of moi.sture content or of the loss on drying".
- Table 1 Moisture correction table for dibutyl phthalate absorption (anhydrous)
- the determination of the electrical conductivity of silicas is carried out as a 4% strength aqueous suspension at room
- the sample preparation and measurement are effected with a dispersion liqu.id (0.05 m-% Tetra- Sodium-diphosphate in demineralised water] in the case of hydrophilic precipitated silica.
- a dispersion liqu.id 0.05 m-% Tetra- Sodium-diphosphate in demineralised water] in the case of hydrophilic precipitated silica.
- pure ezhanol / water mixture (ration by volume 1 : 1) in the case of precipitated silica nor sufficiently wettable with water.
- the laser diffraction apparatus LS 230 (from Beckmann Coulter, Art. -No. 6605210) and the liquid module (Small Volume Module Plus, 120 ml, from Beckmanr, Coulter with internal ultrasonic finger (diameter 6 mm), Art. -No. 6605506) including a ultrasonic processor SONICS Vibracell (Modul VCX 130) are allowed to warm up for 2 h and the module is washed three times with the dispersion liquid, calibrated, and washed three times with ethansl / water mixture in the case of hydrophobic precipitat ⁇ d silicas.
- the liquid module Small Volume Module Plus, 120 ml, from Beckmanr, Coulter with internal ultrasonic finger (diameter 6 mm), Art. -No. 6605506) including a ultrasonic processor SONICS Vibracell (Modul VCX 130) are allowed to warm up for 2 h and the module is washed three times with the dispersion liquid
- Suspensions are prepared from the silica ⁇ ampl.es to be investigated.
- a redispersion is conducted by ultrasonic treatment for 1 rai ⁇ ute by means of ultrasonic processor model VC 70 T from Vibra Cell (70 W) and an ultrasound finger CV 181.
- the dispersing is effected by circulation for 1 minute by means of a pump in the Small Volume Module Plus.
- the homogeneous suspension of 1 g of silica in 40 ml of demineralized water is added by means of a 2 til one-way pipette to the liquid module of the apparatus in such a way that a constant concentration with a light absorption of 8 to 12% is achieved and the apparatus reports X ⁇ OK".
- the software calculates the particle size distribution (d ⁇ value) and the d ⁇ o value (median valuel on the basis of the volume distribution taking into account the MLe theory and the optical model parameters ( . rfd file).
- silicate solutions evaporated to dryness are heated in a mixture of hydrofluoric acid and sulphuric acid. This results in the formation of gaseous silicon tetraf luoride, which is evaporated with fuming, and the silicon is th/js removed.
- the metal salts remaining behind are taken up in rydrochloric acid and diluted with water.
- the iron content of the metal salt solution i ⁇ determined by means of atomic absorption .spectroscopy by measurement of the light absorption at a wavelength of 248.3 nm.
- the numbers in Brackets represent the content of the reagent respectively deionised water in the mixture ir (parts by volume / parts by volume) .
- the first number stands for the content of the reagent while the second nv.mbei represents the content of deionised water) .
- o-Phenanthroline solution 1% by weight is prepared with an ethanol solution 100 ml (1+1) .
- Chromazurine S solution 0.2% by weight is prepared with an ethanol solution 100 ml (1+3) ,
- Al standard solution 10 ⁇ g/ml is prepared by introducing 1 ml of the Al standard solution of 1000 ug/ml and 2 ml of hydrochloric acid solution into a 100 mL graduated flask and making up to 100 ml with distilled water.
- Mn standard solution 1000 ⁇ g/ml Mixed solution of Cu, Fe, Mn having a metal content of 10 ⁇ g/ml is prepared by introducing in each case 1 ml of the Fe, Mn and Cu standard solutions and 2 mJ of concentrated hydrochloric acid into a 100 ml graduated flask and diluting to the mark with distilled water.
- the concentrated waterglass solution is diied for 1.5 h at 105 0 C in an oven, and allowed to cool.
- 1.5 g (i 0.1 ⁇ g) of the dried sample is wetted with deionized water ir a platinum crucible and mixed with 10 ml of hydrofluoric acid and 0.5 ml of sulphuric acid.
- the mixture is concentratec by means of a heating stirrer until white fumes form and is allowed to cool, 5 ml of hydrofluoric acid are added again and concentration is effected again until white fumes form.
- the coc led residue is taken up with 5 ml of hydrochloric acid and heated until all solids have dissolved.
- the cooled solution is transferred to a 20 ml flask and diluted to the 10 ml mark witlr distilled water. Test solution A is thus obtained. Carrying out the measurements
- test solution A 1 ml is transferred to a 100 m] graduated flask, 2 ml of hydrochloric acid are added and the sclution is made up to the 100 ml mark with distilled water. T ⁇ st solution B is thus obtained.
- analysis of the sample is -effected with consultation of the operating instructions of the AAS
- 0, 10, 20, 30 and 50 ⁇ g (addition of 0, 1, 2 r 3 and 5 ml of an Ai calibration solution having an Al content cf 10 ⁇ g/ml) are introduced into a 100 ml graduated flask. Thereafter, 1 drop of nitrophenol (0.1% by weight) is added, diluted with 20 ml distilled water, 2% by weight .of nitric acid and 2% by weight of ammonia solution are added so that the yellow solution becomes colourless. Immediately thereafter, 5 nl of a 4% by weight nitric acid are added and thoroughly mixed. After 20 - 30 minutes, 1 ml of ascorbic acid is added and shaking is vigorously effected again.
- test solution B cf. determination of the iron content above
- blank solution a 100 ml graduated flask
- the suspension obtained is filtered with , ⁇ chamber filter press and the filter cake is washed with water.
- the filter cake is then fluidized in a dissolver.
- the s .lica feed having a solids content of about 18.9% by weight aid a pH of about 5.7 is then spray-dried so that a pH of 6.3, measured as 5% strength suspension, is established in the end product.
- the spray-dried product is then mil] ed by means of a mechanical mill having a classifier (Vortex Pulverizing Mill QWJ-60) .
- Example Ia The physicocheraical data of a representative sample of the spray-dried and unmilled product obtained (Example Ia) and of the milled product (Example Ib) are listed in Table 2.
- waterglass (as .specified above) and sulphuric acid (as specified above) are then added while maintaining a constant precipitation temperature of 86 0 C (maximum variation ⁇ 0.2 0 C) in such a way "hat the Y value remains constant, i.e. is subject to a maximi m variation of ⁇ 3,1% about the starting value.
- the addition of waterglass is stopped and the sulphuric acid is further added until a pH of 3.74 is reached. Thereafter, 1 he suspension is stirred for 20 min at a pH between 3.74 and 3.78.
- the suspension obtained is filtered with a. chamber filter press and the filter cake is washed with water which was fully demineralized beforehand via rever.se osmosis.
- the filter cake is then fluidized in a dissolver.
- the silica feed having a solids content of about 18.2% by weight and a pH of about 5.7 is then spray-dried so that a pH of 6.5, measured as 5% strength suspension, is established in the end product.
- the spray-dried product is then mill.ed by means of a mechanical mill having a classifier (Vortex Pulverizing Mill QWJ-60) .
- a classifier Vortex Pulverizing Mill QWJ-60
- the physico-chemical data of a represent,ative sample of the spray-dried and unmilled product obtained (Example 2a) and of the milled product (Example 2b) are listed in Table 2.
- Comparative Example 1 A conventionally prepared standard silica ULtrasil VN3 from Evonik Degussa GmbH was chosen as Comparativs Example 1. In Comparative Examples 2 to 4, precipitated silicas which are developed and sold specially for the reinforcement of silicone rubber elastomers were chosen. Comparative Example 2 is Nipsil LP from Nippon Silica. In Comparative Examples 3 and 4, two different samples of Zeosil 132 from Rhodia Chimie were tested. These two samples show very different properties. The reason is not known to the applicant,, It might be, for example, that Rhodia Chimie sells different product qualities under the same name. Table 2
- the comparative experiments shown in Table 3 are based on compounding by means of a laboratory kneader.
- the comparative experiments shown in Table 4 are once again based on compounding by means of a two-roll mill. The experiments were carried out as follows:
- Taiwan Taiwan
- DHBP-C8BS paste (45%) from Qiangsheng Chemical. Co., Ltd.
- the incorporation time required for the silica was determined i noted). After incorporation of the complete amount of silica, the heating power of the kneader thermostat is set at 17C°C and
- Datacolor 400 can be effected.
- HTV polymer At room temperature, 200 g of HTV polymer are applied to the two-roll mill and dispersed until the compound is present in homogenized form, i.e. the faster roll is completely coated with said compound and has a smooth surface. Hor this purpose, the two-roll mill is stopped and about 10? of the amount of silica (total amount of silica is 80 g) are introduced in the middle between the two rolls. Thereafter, the complete amount of processing auxiliary (6.4 g of distributor oil) is metered to the silica already applied. By starting the two-roll mill again, the incorporation of the silica into the polymer is now achieved. The addition of further amounts of isilica is
- silica effected very slowly and stepwise. After about 50% of the total amount of silica were added and incorporated, the compound is removed from the roll, folded and applied again to the roll. The remaining 50% of silica are now incorporated stepwise. Small amounts of silica may fall under the two-roll mill through the roll nip. In this context, it should be ensured that the amounts of this silica are collected on a clean underlay and applied to the two-roll mill again for complete incorporation.
- the incorporation time required for the silica is determined (noted) .
- the homogenization of the compound is now continued in order to ensure the complete dispersing of the silica. During this procedure, the compound is removed a further five times from the two-roll mill, folded and applied again. The total subsequent dispersing time should be not more than 5 minutes. After the compounding, the compound is removed from the roll in the form of a single long compound hice. ⁇ he compound hide is now folded into 4 uniform layers and stored on a stainless steel plate at 17O 0 C for one hour in a hct-air oven.
- the compound is removed from the oven and is stored for one hour at room temperature fcr cooling.
- the compound is again plasticized by rolling with 5 - 10 minutes (depending on silica properties), i.e. applied again to the two-roll mill and dispersed until the compound is present in homogenized form, i.e. the faster roll is completely coated with said compound and said compound has a smooth surface.
- the vulcanization is effected after compounding by means of a laboratory kneader or after compounding by means of a two- * roll mill.
- vulcanizates or HTV test specimens having a thickness of 2 mm (for determining the tensile strength, elongation at break and tear propagation resistance) and having a thickness of 6 mm ⁇ for determining the hardness and the optical properties of the HTV vulcanizates) are required.
- H 1 IV compound is applied to the two-roll mill and dispersed until a completely replasticized compound (compound plasticiz.ed by rolling) has formed.
- the peroxide addition can be effected.
- DHBP-45-PSI (2, 5-dimethyl-2 , 5-di-tert- butylperoxy) hexane based on the mass of compound used, are now added and dispersed.
- dispersing is effected for a further 8 minutes. During this rolling time, the compound is removed frcm the ro] 1 8 times altogether, folded and applied again to the coll.
- the compound After the peroxide has been dispersed, the compound is now stored for 24 hours away from dust. Before tire actual vulcanization, the compound is completely replasticized again by rolling.
- the actual vulcanization is effected.
- the following polished stainless steel plates are used: For the 2 mm thick test specimens, 2 stainless steel plates having the dimensions 330 mm • 330 mm • 2 mm and a spacer plate of rhe same thickness with 4 recesses having the dimensions 130 mm • 130 mm are used.
- the vulcanization of the 2 mm HTV test specimens (weight taken: 4 times 35 g of compound) is effected in the heating press at 170°C for 7 min and at a pressure of about 15 bar (15 mPa) .
- the vulcanization of the 6 mm HTV test specimens (weight taken: 2 times 25 g of compound) is effected in the heating press at 170 0 C for 10 min and at a pressure of about 15 bar (15 mPa) .
- vulcanizates may be adversely effected.
- circulation oven at least 120 1 of fresh ai c per minute and per kg of HTV vulcanizate are required at 200 0 C for 4 hours.
- the precipitated silicas according to the invention have substantially reduced incorporation time in comparison with conventionally prepared precipitated silicas (Comparative Example 1), i.e. they can be more rapidly incorporated and more rapidly dispersed/homogenized. If only the precipitated silicas according to the invention (Examples Ib and 2b) are considered, they too have substantially more advantageous incorporation times than precipitated silicas which are already available on the market and are offered especially for silicone rubber applications (Comparative Example 1)
- Example 3 The Williams plasticity, a measure of the
- Examples Ia, Ib, 2a and 2b in direct comparison with Comparative Examples 2 and 3 is likewise advantageous since a lower vulca ⁇ iza ⁇ e hardness permits increased silica addition (based on the formulation) .
- the mechanical properties, such as, for example, tensile strength and tear propagation resistance, of Examples Ib and 2b are at a similarly high level in compai ison with
- Example IIa Comparative Examples 2 and 3
- the results obtained for Example Ia are to be singled out in this lespect. Although this is an unmilled silica, an acceptable ten ⁇ .ile strength and an acceptable tear propagation resistance can already be achieved in comparison with a milled silica (Comparative Example 2) . According to the prior art at present, this is not achievable with conventional unmilled precipitated silicas. However, the following advantages of the precipitated silicas according to the invention are to be singJ ed cut in
- Example Ia, Ib, 2a and 2b show an extremely high translucency of the vulcanizates as a measure of the transparency and clarity of the crosslinked silicone systems. 'Ihis permits use in novel silicon products which require extrertely high transparencies. All Comparative Examples ⁇ l, 2 and 3) show substantially lower translucency values arid the lightness of the vulcanizates, too, was determined with substantially lower values for Comparative Examples 1 and 2,
- Examples 2a and 2b not only have a
- the Williams plasticity a measure of the thickening and rheological properties of the compounds, Is comparable for all examples shown in Table 4.
- a further advantage of the precipitated silicas according to the invention is found on consideration of the compound translucency .
- precipitated silicas according to the invention are to be singled out in particular.
- a low b value is equivalent to very little yellow discolouration of the compound. If the b values of Examples Ia, Ib, 2a and 2b are ⁇ DW compared with Comparative Examples 2 to 4, it becomes clsar that the compounds based on the precipitated silicas according to the invention have substantially less yellow discolouration.
- the relatively small difference between the b values does not ir.ake this as clear as the simple visual assessment of the compounds (even by means of photographs, this difference readily visible to the eye in daylight unfortunately cannot JOB shown in a reproducible manner) .
- vulcanizate hardness permits an increased, silica addition (based on the formulation) .
- the mechanical properties, such as, for example, tensile strength and tear propagation resistance, Df Example 2b are at a similarly high level in comparison with Comparative Examples 2 and 3. In this respect, however, the results obtained for Examples Ia and 2a are to be singled out in particular. Although these are unmilled siLicas, tear propagation resistances which are just as iigh can be achieved in comparison with the milled precipitated silicas (Comparative Examples 2 and 3) .
- Examples Ia, Ib, 2a and 2b show a high traislucency of the vulcanizates as a measure of the transpare icy and clarity of the crosslinked silicone systems in comparison with a conventional precipitated silica (Comparative Example 1) , This permits use in highly transparent si-icone products, In the case of highly transparent vulcanizates, an
- Examples 2a and 2b not or.Iy have a substantial improvement in comparison with conventional precipitated silicas (Comparative Example 1) but could also be substantially improved in direct comparison with the precipitated silicas already established in the market, which are offered for silicone rubber applications
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Abstract
Provided is a hydrophilic precipitated silica which is well suited to use in silicone rubber formulations (RTV-1, RTV-2, HTV and LSR), particularly well suited to use in HTV silicone rubber formulations. It has a BET surface area of 185~260 m2/g, a CTAB surface area of 100~160 m2/g, a BET/CTAB ratio of 1.2~2.6, and a conductivity of <250μS/cm. Also provided are a process for producing the precipitated silica and the use of the precipitated silica for thickening and reinforcing silicone rubber formulations.
Description
HYDROPHILIC SILICAAS FILLER FOR SILICONE RUBBER FORMULATIONS
The present invention relates to hydrophi..ic prec Lpitated silicas which are well suited for use in jsilicone rubber formulations (RTV-I, RTV-2, HTV and LSR), particularly well suited for use in HTV silicone rubber formulations, a process for the preparation thereof and the use thereof for thickening and reinforcing silicone rubber formulations.
Silicone rubbers are materials which can be converted into the elastomeric state and contain, as base polymers,
polydiorganosiloxanes which have groups accessible to
crosslinking reactions. Predominantly suitable as such are H- atoms, OH groups and vinyl groups which are present at the chain ends but may also be incorporated into the chain.
Fillers, such as, for example, hydrophilic precipitated silicas, are incorporated as reinforcing agents into this system, the type and amount of which substantially influence the mechanical and chemical behaviour of the -vulcanizates .
Silicone rubbers can be coloured by inorganic pigments. A distinction is made between high temperature vulcanizing and room temperature vulcanizing silicone rubber types (HTV and RTV) . In the case of the high temperature vulcanizing silicone rubber types, a distinction may furthermore be made between HTV silicone rubber and liquid silicone rubber (LSR) .
In the case of the room temperature curing or RTV silicone rubber materials, a distinction may be mace between one- component systems and two-component systerrs. The first group (RTV-IC) polymerizes slowly at room temperature under the influence of atmospheric humidity, the crcsslinking taking place by condensation of SiOH groups with formation of Si-O bonds. The SiOH groups are formed by hydrclysis of SiX groups
of a species formed as an intermediate from a polymer having terminal OH groups and a so-called crosslinking agent R-SiX3 (e.g. X - -Q-CO-CH3, -NHR) . In the case of two -component rubbers (RTV-2C) , for example, mixtures of silicic acid esters {e.g. ethyl silicate) and organotin compounds are used as crosslinking agents, the formation of an Si-O-Si bridge from ≡ Si-OR and ≡ Si-OH (- = methyl group; R = organic radical) by alcohol elimination taking place as a cross linking
reaction.
Inter alia, silicas are used for thickening ard reinforcing RTV-IC silicone rubber. Owing to the senεitivity of the silicone sealing compounds to hydrolysis, they must introduce as little moisture as possible into the system. To date, virtually exclusively fumed silicas have therefore been used for this application. However, EP 1860066 also discloses novel hydrophilic precipitated silicas having a special surface character, which are suitable for thickening .FTV-IC
formulations. Furthermore, US 5,395,605, US 2C08/0019898 and WO 2003/055801 describe various precipitated silicas for silicone rubber formulations which silicas are distinguished in each case by a low water absorption. Precipitated silicas having a low water absorption require very special and complicated preparation methods. Furthermore, preparation and transport require a considerable effort.
While, owing to the water crosslinking, RTV-IC silicone rubber formulations are very sensitive to any introduction of water and therefore set special requirements for the fillers with regard to the introduction of water, this problem does not occur to this extent in the case of HTV silicone rubber formulations. Here in particular good processibility of the formulation after introduction of filler and a high mechanical load capacity of the silicone rubber product, in particular long-term load capacity, must be ensured. Furthermore,
particularly in the case of transparent sjliccne rubber formulations, the fillers should lead to as little
discolouration as possible and permit high transparency.
In the case of the RTV-2C silicone rubber and liquid silicone rubber formulations, too, the introduction of water into the system is not of great importance since the silicone rubber producers specially pretreat or aftertreat thu filler, for example hydrophilic precipitated silicas. Thus, for example, the silicas are rendered water repellent during the
compounding in situ so that the moisture introduced by the silica escapes or is reduced during this preparation process.
EP 1557446 describes HTV silicone rubber ioriUvlations which do not foam during the extrusion. Here too, s recuction of the water absorption of the precipitated silica i,= proposed as a solution.
There is therefore still a need for fillers fcr silicone rubber formulations, in particular HTV formulations, which can be used even in the case of a relatively high water content and exhibit good processing properties.
It was therefore an object of the present invention to provide novel precipitated silicas which do not have at least some of the disadvantages of the precipitated silicas of the prior art or do so only to a reduced extent. Furthermore, it is intended to provide a process for the preparation cf ths novel
precipitated silicas.
Δ specific object of the present invention was to provide precipitated silicas which can be readily incorporated and dispersed in silicone rubber formulations, in particular HTV formulations, and impart good mechanical properties, in
particular good long-term load capacity, to them. Moreover, it was a specific object of the present inventior to provide precipitated silicas which permit the preparation of HTV formulations (compounds and vulcanizates) having very high transparencies, preferably in combination with very little di scolouration .
Further objects not explicitly mentioned arise from the overall context of the following description, examples and claims .
The abovementioned objects are achieved by the precipitated silicas defined in more detail in the followirg description, the examples and the claims and by the process defined in more detail there.
The present invention therefore relates to hycrophilic
precipitated silicas which are characteri2.ed in that they have a BET surface area of 185 to 260 tn'Vg
a CTAB surface area of 100 to 160 m:Vg
a BET/CTΛB ratio of 1.2 to 2.6 m:7g
a conductivity of < 250 (μS)/cm.
The present invention furthermore relates to a process for the preparation of the precipitated silicas according to the invention, characterized in that it comprises the following steps :
a) preparation of an initially introduced m .xture having a Y value of 10 to 30,
b) simultaneous metering of alkali metal silicate and/or alkaline earth metal silicate and acidifying agent into this initially introduced mixture with stirring at 80 to 95°C for 60 to 90 min,
c) reacidification of the precipitation suspension, d) ageing of the suspension for 5 to 50 min,
e) filtration, washing and drying,
and which is characterized in that the .ilka.,.i metal silicate and/or alkaline earth metal silicate used ir, steps a) and/or b) has an alkali metal oxide or alkaline earth metal oxide content in the range from 4 to 7% by weig:it and a silicon dioxide content in the range from 12 to 28% b/ weight, in that the acidifying agent used in step b) aid/or c) is an acidifying agent selected from the group consisting of concentrated mineral acids and carbonic acid (or CO2 gas) and sodium hydrogen sulphite (or SO2 gas) in th.s correspondingly possible concentrations, and in that ":he Y value of the precipitation suspension is kept constant at a value between 10 and 30 during the precipitation, keeping constant meaning that the Y value varies by not more 3% about the starting Y value, i.e. the value directly before the oeginning of the simultaneous addition of acidifying agent and alkali metal silicate or alkaline earth metal silicate, Ln the course of the simultaneous addition of acidifying agent, and alkali metal silicate or alkaline earth metal silicate.
The present invention also relates to silicone rubber
formulations, in particular HTV silicone rubber formulations, containing the precipitated silicas according to the
invention, and to the use of the precipitated silicas
according to the invention as a reinforcing filler for
silicone rubber formulations.
The inventors have surprisingly found that the precipitated silicas according to the invention can be very readily
incorporated into silicone rubber formulations, i.e. have short incorporation times. Thus, it is possible to achieve good dispersibility and high loads with the precipitated
silicas according to the invention, i,e, to incorporate a large amount of reinforcing filler into the silicone rubber formulation .
Furthermore, the precipitated silicas according to the
.invention impart good mechanical properties to the silicone rubber formulations. Particularly in the case of a high load, the precipitated silicas according to the invention lead to a good long-term capacity of the silicone rubbeα formulations.
A further advantage of the precipitated si lies s according to the invention is that silicone rubber compouncs, i.e. as yet uncured mixtures and cured vulcanizates, containing the precipitated silicas according to the inventicn have a high transparency (translucence) . The precipitated silicas
according to the invention can therefore be incorporated in particular into highly transparent formulations. Especially in the particularly preferred embodiments, they lead to very little discolouration here.
The subjects of the present invention are described in detail below.
The precipitated silicas according to the invention have a high BET surface area of 185 to 260 m2/g. Cn a preferred embodiment of the present invention, the EET surface area is preferably in the range from 185 to 210 mVg aid particularly preferably 190 to 205 mVg. In another preferred embodiment, the BET surface area is in the range from 210 to 260 m2/g, preferably 211 to 260 m2/g, particularly preferably 215 to 250 m2/g and very particularly preferably 220 ":o 250 m2/g. The BET surface area influences the reinforcing potential of the precipitated silica. The higher the BET surface area, the greater is the reinforcement. However, a high BET surface area
also leads to a deterioration of the possibility of incorporating the precipitated silica into the silicone rubber formulation. The inventors have now found that this
disadvantage does not occur, i.e. very good incorporation properties can be achieved, if the precipitate-d silicas have a fairly low CTAB surface area and a high ratio of BET to CTAB surface area in addition to the high BET surface area,
The precipitated silicas according to the invention are therefore distinguished by a CTAB surface area of 100 to
160 m?7g, preferably 110 to 150 mVg, particularly preferably 120 - 150 m2/g and very particularly preferably 126 to 145 mVg and a BET/CTAB ratio of 1.2 to 2.6, preferably 1.25 - 2.3, particularly preferably 1.3 to 2 and very particularly
preferably 1.4 to 1.9. The BET/CTAB ratio is an independent parameter, i.e. an independent characteristic of the
precipitated silicas according to the invention. From the subset of the ratios which can be calculated from the ranges generally stated for the BET and the CTAB, i.e. which can theoretically be calculated therefrom, these which have these initial parameters are distinguished according to the
invention by the BET/CTAB ratio. In other words, a
precipitated silica according to the invention which has a CTAB of 160 m2/g must have at least a BET of 2)0 m?/g. The CTAB surface area characterizes the rubber-accessible surface.
Without being tied to a specific theory, the inventors are of the view that the BET/CTAB ratio also influences the
refractive index of the precipitated silica, which refractive index reflects properties in the region of interfaces, which in turn are dependent on the differently determined surface areas of the silica used, and hence contributes to the good transparency of the precipitated silicas according to the invention .
A further important feature of the precipitated silicas according to the invention is the median particle size dso. Thus, it has been found that particles which ere too small are difficult to incorporate into the silicone rut ber formulations since they float on the silicone rubber formulation and do not sink. Consequently, the incorporation time increases.
Particles which are too large, on the other h.=nd, may have problems in the dispersing of the silica in tJ"e silicone rubber mixture. The precipitated silicas εiccoiding to the invention therefore preferably have a median particle size d5o of 5 to 95 μm,
In a first specific variant of the present indention, the median particle size dso, measured by mean;* of laser
diffraction, is in the range from 5 to 25 μm, preferably 8 to 24 μm, particularly preferably 10 to 20 μiri anc very
particularly preferably 12 to 18 μm. Particularly preferably, the proportion of very fine particles, expressed by the ds value, in this variant is 4 to 10 μm, in particular 4.3 to 6 μm. As already indicated above, particles which are too small lead to disadvantages in the incorporation into the silicone rubber formulation. The ds value can be kept
correspondingly high by suitable milling.
In a second preferred variant of the present invention, the median particle size is in the range from 25 to 95 μm, preferably 30 to 90 μm, particularly preferably 30 to 80 μm and especially preferably 40 to 75 μm. Compared with the first variant, this variant has the advantage that no milling of the dried precipitated silica is necessary. At the same time, however, a deterioration in the dispersibility may be
associated with the relatively large particle size. A person skilled in the art can determine by simple manαal experiments whether he is using precipitated silicas of variant 1 or of
variant 2 for the respective silicone rubber iormulation.
A further substantial feature of the precipitated silicas according to the invention is the low conductivity thereof/ i.e. the low content of salts, such as, for e.x ample,
sulphates, chlorides and nitrates. This promotes the good incorporation properties; in particular., the decolouration of compound and vulcanisate and an undesired increase in
viscosity after the preparation of the silicone rubber
formulations are prevented. The precipitated j.ilicas according to the invention have a conductivity of less 1 han 250 (μS)/cm, preferably less than 200 (μS) /cm, particularly preferably 1 to 200 (μS)/cm, very particularly preferably 5 tc 150 (μS) /cm, especially preferably 5 to 100 (μS)/cm anc very especially preferably 10 to 50 (μS) /cm.
The positive properties of the precipitated silicas according to the invention can be further enhanced if they have a low- tamped density. Without being tied to a specific theory, the inventors are of the view that the tamped density is conducive to a particularly good dispersibility.
In a preferred embodiment of the present invenbion in which the median particle size ά$or measured by mean.- of laser diffraction, is in the range from 5 to 25 μm, preferably 8 to 24 μm, particularly preferably 10 to 20 μm and very
particularly preferably 12 to 18 μm and preferably at the same time the proportion of very fine particles, expressed by the d5 value, is 4 to 10 μm, in particular 4.3 to 6 μn, the tamped density of the precipitated silicas according to the invention is preferably 50 to 150 g/1, particularly preferably 80 to 150 g/1, very particularly preferably 90 to 14 D g/1 and especially preferably 100 to 130 g/1.
In a second preferred embodiment of the presert invention in which the median particle size d^or measured by means of laser diffraction, is in the range from 25 to 95 μm, preferably 30 to 90 μm, particularly preferably 30 to 80 μm and especially preferably 40 to 75 μm, the tamped density of the precipitated silicas according to the invention is preferably IbO to
350 g/1, particularly preferably 180 to 3CO g/1, very
particularly preferably 200 to 300 g/1 and especially
preferably 210 to 290 g/1.
Preferably, zhe precipitated silicas according to the
invention have a moisture content of less than 7% by weight. In a special variant of the present invention, the
precipitated silicas according to the invention have a
moisture content of 5 to 7% by weight, particularly preferably 5.5 to 7% by weight. It has in fact been found that the precipitated silicas according to the invention can be readily incorporated into extrudable HTV silicone rubber formulations, in spite of the relatively high moisture content of 5 to 7% by weight. This is surprising since considerable efforts are made in the prior art to prepare precipitated silicas having a low moisture content and low water absorption. Owing to the special parameter combination, the precipitated silicas according to the invention can be readily used as reinforcing filler for elastomer mixtures even in the case of a high moisture content. This leads to considerable cost reductions in the preparation, transport and storage of tie precipitated silicas .
The precipitated silicas according to the inveition preferably have a DBP absorption of 240 to 300 g/100 g, particularly preferably 250 to 300 g/100 g and very particularly preferably 260 to 290 g/100 g. Precipitated silicas having this DBP absorption possess particularly good dispersibility ,
The pH of the precipitated silicas according to the invention is preferably in the range from 5 to 8, particularly
preferably 6 to 7.
The precipitated silicas according to the invention can be prepared by a process which comprises the following steps:
a) preparation of an initially introduced mixture having a Y value of 10 to 30,
b) simultaneous metering of alkali motal silicate and/or alkaline earth metal silicate and acidifying agent into this initially introduced mixture with .tirring at 80 to 950C for 60 to 90 min,
c) reacidification of the precipitation suspension,
d) ageing of the suspension for 5 to 50 min,,
e) filtration, washing and drying,
and which is characterized in that the aIlea.' i metal silicate and/or alkaline earth metal silicate used in steps a) and/or b) has an alkali metal oxide or alkaline earth metal oxide content in the range from 4 to 7% by weight and a silicon dioxide content in the range from 12 to 28% by weight, in that the acidifying agent used in step b) a:id/or c) is an acidifying agent selected from the group consisting of concentrated mineral acids and carbonic acid (or CO2 gas) and sodium hydrogen sulphite (or SO2 gas) ir tho correspondingly possible concentrations, and in that 1:he Y value of the precipitation suspension is kept constant at a value between 10 and 30 during the precipitation, keeping constant meaning that the Y value varies by not more 3% about the starting Y value, i.e. the value directly before the beginning of the simultaneous addition of acidifying agent and alkali metal silicate or alkaline earth metal silicate, ;.n the course of the simultaneous addition of acidifying agent and alkali metal silicate or alkaline earth metal silicate.
The terms precipitated silica and silica are csed synomously in the context of the present invention. Furthermore, the terms silicate solution and alkali metal silicate solution and/or alkaline earth metal silicate solution are used synomously. The alkali metal oxide or alkaline earth metal oxide content in the silicate solution used according to the invention is in the range from 4 to 7% by weight, preferably in the range from 5 to 6.5% by weight, particularly preferably from 5.5 to 6,5% by weight. Specifically, the silicate solution used in the process according to the invention is sodium silicate solution (waterglass) or potassium silicate solution. In a particularly preferred embodiment of the present invention, highly pure silicate solution is used.
Highly pure silicate solution is characterized by a content of Fe2" of less than or equal to 200 mg/kg, p.;efe2.ably less than or equal to 180 mg/kg, particularly preferably less than or equal to 150 mg/kg, and an AI2O3 content oJ: Ie. s than or equal to 0.55% by weight, preferably less than or eqjal to 0.45% by weight, particularly preferably less than or equal to 0.25% by weight .
The silicon dioxide content in the silicate solution used according to the invention is 12 to 23% by weight, preferably 13 to 23% by weight, particularly preferably 14 to 18% by weight. The modulus, i.e. the weight ratio of silicon dioxide to alkali metal oxide or alkaline earth metal oxide in the silicate solution used according to the invention is
preferably 2.0 to 5.75, particularly preferabl/ 2.5 to 4,5, very particularly preferably 3 to 4 and especially preferably 3.2 to 3.7.
In the process according to the invention, concentrated mineral acids, such as hydrochloric acid, sulp.iuric acid,
nitric acid or phosphoric acid, or CO2 are preferably used as the acidifying agent. Concentrated minera] acid means a concentration of 36 to 47.2% by weight, prefeiably 40 to 47% by weight, in the case of hydrochloric acάd, a concentration of 90 to 98.5% by weight, preferably 93 to 98.5% by weight and very particularly preferably 96 to 98% by weiciht, in the case of sulphuric acid, a concentration of 60 to 6H% by weight in the case of nitric acid and a concentration of 80 to 100% by weight, preferably 80 to 90% by weight, particularly
preferably 80 to 85% by weight, in the case of phosphoric acid.
Furthermore, it has proved advantageous if denineralized water, preferably water purified by distillation or reverse osmosis, is used as water in at least one^ step of the process according to the invention, preferably at least during the washing process .
The initially introduced mixture in step a) consists of water to which a base is added, or an aqueous solution of a base; it preferably comprises at least one alkali tretal silicate and/or alkaline earth metal silicate. It has proved advantageous if the initially introduced mixture is heated to a temperature of 40 to 900C before the beginning of the precipitation, i.e. the addition of acidifying agent and silicate solution together. By adding the silicate solution or a base, the Y value of the initially introduced mixture is adjusted to tha value to be maintained during the precipitation. The adjustment of the Y value of the initially introduced mixture is preferably effected with the silicate solution which is also used for the precipitation.
The inventors have furthermore found that it is essential for the process according to the invention that th'2 Y value
remains constant in the course of the simultaneous addition ot acidifying agent and alkali metal silicate or alkaline earth metal silicate, i.e. varies by not more than 3% about the starting Y value, i.e. the value directly befcre the beginning of the simultaneous addition of acidifying agent and alkali metal silicate or alkaline earth metal silicate. The Y value expresses the alkali metal ion concentration in the reaction solution. The Y value therefore reflects the chemical
reactions during the precipitation, in particular the
incorporation of ions into the silica skeleton. Inferences about the fundamental structure of the silica can be drawn therefrom and accordingly statements about the quality and reproducibility of the relevant production can be made before the physicochemical analysis of the end product. In the process according to the invention, the Y value is kept constant in the range from 10 to 30, preferably from 15 to 25 and very particularly preferably from 18 to 22 during the precipitation.
The precipitation is carried out at a temperature of 80 to 950C, preferably 85 to 9O0C. The pure precipitation time, i.e. the duration of the addition of silicate solution and
acidifying agent together - without taking intD account interruption times - is 60 to 90 min, preferably 65 to 85 min, very particularly preferably 70 to 80 min. The flow rates of the acidifying agent and of the silicate solution are chosen so that the desired precipitation time but at the same time also the desired Y value variation of the precipitation suspension can be maintained.
It may be particularly advantageous for the process according to the invention if high shear forces act on tie precipitated silica particles in one of the steps of the process according to the invention, preferably during the precipitation or
fluidizing steps, for example by means of an internal or external shearing unit.
In step c) , the reacidification of the precipitation
suspension is effected, preferably to a pK of 1 to 1,
particularly preferably 2 to 5, very particularly preferably 3 to 4. As a result of this step, the precipitation reaction is stopped and residual waterglass in the precipitation
suspension is reacted with the acidifying ager.t.
After the quenching of the precipitation reaction in step c) , ageing of the precipitation suspension for 5 to 50 min, preferably 10 to 40 min, particularly preferably 10 to 30 min and very particularly preferably 15 to 25 min takes place in step d) . This ageing step has, inter alia, an influence on the establishment of the BET and CTAB surface areas.
For the precipitated silicas according to the invention, it is not harmful if the suspension is stored for up to 48 hours after step c) , for example in a suspension tank. This permits a higher flexibility of production.
The precipitated silica suspensions preparec by the process according to the invention are filtered in step e) and the filter cake is washed with water. A plurality of washing steps can be carried out. As already mentioned, it is particularly advantageous if demineralized water is used in at least one washing step. Thus, washing can preferably oe effected with the normal water first and with demineralizod water only in the latter stages or the last stage, T"-iis reduces the preparation costs.
The filtration, fluidization (for example, according to DE 2447613) and long- or short-term drying of the silicas
according to the invention, are familiar to thε person skilled in the art and are described, for example, in the documents mentioned in this description. The filtration and the washing of the silica preferably take place in such a way that the conductivity of the end product is less than 250 (μS) /cm, preferably less than 200 (μS) /cm, particularly preferably 1 to 200 (μS) /cm, very particularly preferably 5 tc 150 (μS)/cm, especially preferably 5 to 100 (μS)/cm and very especially preferably 10 to 50 (μS) /cm.
Preferably, the silica according to the invention is dried in a pneumatic dryer, spray dryer, rack dryer, belt dryer,
Buttner dryer, rotary tube dryer, flash dryer, spin-flash dryer or nozzle tower dryer. These drying variants include operation with an atomizer, a one-fluid or two-fluid nozzle or an integrated fluidized bed. Spray drying, in particular with an atomizer, is particularly preferred. This can be carried out, for example according to US 4094771. Particularly
preferably, the spray drying is carried out with a feed having a solids content of 15 to 20% by weight and a pH of 4 to 7, preferably 5 to 6. The spray-dried particles can have median diameters of more than 15 μm, preferably 25 - 55 μm,
particularly preferably 30 - 80 μm, very particularly preferably 30 - 75 μm and especially preferably 40 to 75 μm, measured by means of laser diffraction. The contents of' US 4094771 and EP 0 937755 are hereby explicitly incorporated into the content of the present application.
In a preferred variant of the process according to the
invention, the dried precipitated silicas are billed.
Techniques for milling the precipitated silicas according to the invention are known to a person skilled in the art and described, for example, in Ullmann, 5th edition, B2, 5-20.
Impact mills or opposed jet mills or mechanical mills are
preferably used for milling the silicas according to the
Invention. The milling parameters are preferacly chosen so that the median particle size dso of the precipitated silicas according to the invention, measured by means of laser
diffraction, is in the range from 5 to 25 μm, preferably 8 to 25 μm, particularly preferably 10 to 20 μπi, very particularly preferably 12 to 18 μm, and/or the d*> value is in the range from 4 to 10 μm, in particular 4.3 to 6 μm.
The precipitated silicas according to the invention are preferably used as fillers in silicone rubber formulations of the RTV-IC, RTV-2C and LSR systems, in partici lar in HTV silicone rubber formulations.
Organopolysiloxanes which may be used are < 11 polysiloxanes which have been used to date, or which it has been possible to use to date, as the base for organopolysiloxαne elastomers in the case of room temperature vulcanizable or vulcanizing materials (RTV), materials vulcanizable or vu-canizing at only slightly elevated temperature (LTV) or iigh temperature vulcanizable or vulcanizing materials (HTV) . They can be described, for example, by the general formula
Zn Si R3-n -0-[Si R2 O]x -Si R3_T -Zn in which radicals Z and R may be identical or different or the radicals R and Z themselves can however also be identical or different, and in which the radicals are definad as follows:
R = alkyl, alkoxy, aryl, hydroxy, hydride or alkenyl radicals having 1-50 carbon atoms, unsubstituted or substituted by 0, S, F, Cl, Dr, I, in each case identical or different, and/or polys ryrene, polyvinyl acetate, polyacrylate, po.Lymel hacrylate and
polyacrylonitrile radicals havirg 5C-10 000 repeating units .
'A = H, OH, Cl, Br, amino, aminoxy, slker.yloxy, aryloxy or phosphate radicals, it being possible for the organic radicals to carry up to 20 carbon atoms and said organic radicals being identical or different in each case. n = 1 - 3
X = 100 - 15 000, preferably 100 - 11 )00, particularly preferably 100 - 8000.
Polysiloxanes especially suitable for RTV-IC silicone rubber formulations may have, for example, the following structure
Zn Si R3.n -0-[Si R2 O]x -Si R3-n -Z'n where R = alkyl, acetoxy, oxime, alkoxy, amido, aryl or alkenyl radicals having 1 to 50 carbon atoms, unsubstituted or substituted by 0, S, F, Cl, Br, I, in each case identical or d: fferent, and/or polystyrene, polyvinyl acei.ate, polyacrylate, polymethacrylate and polyacrylonitrile radicals having 50 - 10 000 repeating units.
Z = OH, Cl, Br, acetoxy, amino, aπiido, aminoxy, oxime, alkoxy, alkenyloxy, acryloyioxy or phosphate radicals, it being possible for the organic radicals :o carry up to 20 carbon atoms ,ind said organic radicals being identical or different in each case.
Z' - oxime, alkoxy, amido or acetoxy radicals.
n = 1 - 3
X = 100 - 15 000, preferably 100 - 11 000, particularly
preferably 100 - 8000.
Within or along the siloxane chain in tϊ e abovementioned formulae, other siloxane units, generally present only as impurities, can also be present as diorganosiioxane units, for example those of the formulae RSiC-3/2, RjOi/2 and SiCv2, in which R in each case has the meanings stated above therefor. The amount of these other siloxane units should not exceed 10 mol%.
Examples of R having the meaning alkyl iadical are, for example, methyl, ethyl, propyl, butyj , hexyl and octyl radicals; vinyl, allyl, ethylallyl and butadisnyl radicals may be used as alkenyl radicals; and phenyl and tolyl radicals may be used as aryl radicals.
Examples of substituted hydrocarbon radicals R are in particular halogenated hydrocarbon radicals such as the 3,3,3- trifluoropropyl radical, chlorophenyl and bromotolyl radical; and cyanoalkyl radicals, such as the G~cyanoethyl radical.
Examples of polymers as radical R are polystyrene, polyvinyl acetate, polyacrylate, polymethacrylate and polyacrylonitrile radicals bonded to silicon via carbon.
Owing to the easier accessibility, the pnsdom .nant part of the radicals R preferably consists of methyl groups . The other radicals R are in particular vinyl and/or phen/1 groups.
Particularly in the case of the presence of f ^rmulations which are storable in the absence of water and cure on admission of water at room temperature to give elastomers, Z are hydrolysable groups. Examples of such groups are amino, aminoxy, alkenyloxy (e.g. H2C=(CH3CO-)), acylcxy and phosphate
groups. Especially because of the easier accessibility, acyloxy groups, in particular acetoxy groups, are preferred as Z. Examples of hydrolysable atoms Z are halogen and hydrogen atoms. Examples of alkenyl groups Z are in particular vinyl groups .
PreferabLy, the viscosity of the organopolys iloxanes used in the invention does not exceed 500 000 cP at 25°C, particularly preferably 150 000 cP at 25°C. Accordingly, the value x preferably does not exceed 40 000. It is also possible to use mixtures of different organopolysiloxanes .
The mixing of these organopolysiloxanes Vvith the silicas according to the invention and optionally the further constituents of the formulation according to :he invention can be effected in any known manner, for exampLe in mechanical mixing apparatuses. It takes place very rapidly and easily, regardless of the sequence in which the addition of the constituents of the mixture is carried out.
Preferably, the silicas used according to t.ie invention are employed in amounts of 0,5 to 60% by weiqht, preferably 5% to 60% by weight, particularly preferably 10% -;o 40% by weight and very particularly preferably 20 to 3Oo by weight, based on the total weight of the materials curable to give elastomers. In the case of HTV organopolysiloxane elastomers, up to 60% by weight can likewise be used.
The proportion of the abovementioned organc-polysiloxanes is preferably 30 - 99.5% by weight, based on the total weight of the material curable to give elastomers.
If such Si-bonded hydroxyl groups are present as the only reactive terminal units in the reactive diorganopolysiloxanes
containing terminal units, these diorganopolysiloxanes must be reacted in a known manner with crosslinking agents, optionally in the presence of a condensation catalyst, in order to cure them in a manner known per se or to cc nvert them into compounds curing by the water present in the air, optionally with addition of further water, to giv<5 elastomers. In the case of HTV diorganopolysiloxane elastomers, organic peroxides, such as, for example 2, 5-dimethy1-2, 5- (di-tert- butylperoxy) hexane, bis-2, 4-dichlorobenzoyl peroxide, benzoyl peroxide, tert-butyl perbenzoate or tert -butyl peracetate in an amount of 0.5 - 5.0% by weight can be used at correspondingly advantageous temperatures.
Preferably used high temperature vulcan/.zinq organosiloxanes are those in which the organic substituents consist of methyl, ethyl, phenyl, trifluoromethylphenyl [F3CC6H4] or trimethylsilmethylene radicals [ (CH3) 3SiCII2-] , e.g. dimethyl-, diethyl-, phenylmethyl-, phenylethyl-, ethylmethyl-, trimethylsilmethylenemethyl-, trimethyls Llmethyleneethyl-, trifluoromethylphenylmethyl- or trifluororasthylphenylethyl- siloxanes or copolymers of such compounds. In addition, the polymers can preferably contain lLmitud amounts of diphenylsiloxane, bistrimethylsilraethylenesiloxane, or bistrifluoromethylphenylsiloxane units and also siloxanes having units of the formula RSiOx,5 and RjS- O0,5/ in which R represents one of the above radicals.
The formulations according to the invention can be crosslmked by addition of silanes. The silicone rubber formulations may therefore additionally contain 0.01 to 20% by weight, preferably 0.5 - 5% by weight, of a crosslinking agent having the general formula
R'4-t Si Z' 4
where R' = alkyl, alkoxy, aryl or alkenyl radicals having 1 to 50 carbon atoms, unsubstituted or substituted by O, S, F, Cl, Br, I, in each case identical or different, and/or polystyrene, polyvinyl acetate, polyacrylate, polyraethacrylate and polyacrylonitrile radicals having 5 - 5000 repeating mirs.
Z' = H, OH, Cl, Br, amino, aminoxy, alkenyloxy, aryloxy or phosphate radicals, it being possible for the organic radicals to carry up to 20 carbon atoms and to be in each case identical or different.
t = 3 or 4.
Examples of silanes of the abovemeπtioned formula are methyltriacetoxysilane, ethyltriacetoxys llanu, isopropyltri- acetoxysilane, isopropoxytriacetoxysilane, vinyltriacetoxy- silane, methyltrisdiethylaminooxysilane , tiethyltris (cyclo- hexylamino) silane, methyltris (diethylphosphato) silane and methyltris (methylethylketoximo) silane.
It is furthermore possible for the silicone rubber formulations according to the invention additionally to contain 0.5 to 99.5% by weight, preferably 2.0 to 30.0% by weight, of an unfunctionalized polysiloκane, in addition to the organopolysiloxane and the crosslinking agsnt.
The polysiloxanes used here may have a viscosity of up to 500 000 cP (500 Pa -s). For example, in particular Baysilone MS 10 (viscosity 10 - 20 mPa'S) or the distributor oil Si 200 (viscosity about 28 mPa*s), both available from Momentive Performance Materials, are suitable for tie HTV silicone rubbers according to the invention. For RTV-2C silicone rubbers, for example, the oil M ICO i viscosity about 100 mPa-s) of the same manufacturer can be used.
In addition to organopolysiloxanes, the s: lice s according to the invention, crosslinking agents and crossl- nking catalysts, formulations according to the invention can oi course
optionally conventionally contain fillers generally or
frequently used in materials curable to g_ ve elastomers .
Examples of such substances are fillers havine a surface area below 50 m2/g, such as quartz powder, kaolin, phyllosilicates, tau minerals, diatomaceous earth, furthermore zirconium
silicate and calcium carbonate, furthermore untreated
pyrogenically produced silicon dioxide, oiganic resins, such as polyvinyl chloride powder, organopolysj loxane resins, fibrous Cillers, such as asbestos, glass fibres, and organic pigments, soluble dyes, fragrances, corrosion inhibitors, compositions stabilizing materials to the influence of water, such as acetic anhydride, compositions retarding curing, such as benzotriazole, and plasticizers, such as
dimethylpolysiloxanes endcapped by trimethylsiloxy groups.
Further examples of formulation constituerts and additives are carbon blacks for establishing antistatic properties or specific electrical conductivities, UV stabilizers, anti- discolouration compositions, such as, for exairple, the product TSF-484 (Momentive Performance Materials) or HF 99 (Shin-Etsu Silicones) .
Furthermore, the silicone rubber formulations may additionally contain 0.01 to 6% by weight of organic or iiiDrganic compounds of the metals Pt, Sn, Ti and/or Zn as a catalyst and/or 0.01 to 6% by weight of inhibitors and/or 0.01- 6% by weight of fungicides or bactericides and/or 0.01 to 6% by weight of adhesion promoters.
RTV-IC silicone rubber formulations may oDtioially contain 0.1 - 20, preferably 0.1 - 15, particularly preferably 0.1 - 10, %
by weight (based on the total amount of the formulation) of water-binding substance. Suitable substances for this purpose are, for example, carboxylic anhydrides, e.g. acetic anhydride or maleic anhydride, and/or carbonic acid estϊrs, such as, for example, diethyl carbonate, ethylene carbonate, and/or alkenyloxy compounds and/or ketals, such as, for example dimethyldioxolane. It is possible to use one or more of these substances .
The quantity ranges described above are net to be regarded as being additives. The person skilled in the art understands that he must choose the components within the abovementioned quantity ranges so that he arrives at 100% by A/eight
altogether .
Further silicone rubber formulations or modifications of the abovementioned silicone rubber formulations ace known to the person skilled in the art. Examples of these are described, for example, in EP 1557446 Al. The precipitated silicas according to the invention can also be used in these
formulations .
In the context of the present invention, a particularly
preferred HTV silicone rubber formulation is to be understood as meaning the following formulation constituents:
1st formulation constituent:
100 parts of HTV silicone polymer, vinyl-funci; Lonal
polysiloxane (vinyl content about 0.15%) and having a
molecular weight of 600 000 g/mol, definable b/ the following structural formula.
R = methyl group, phenyl group
Ri = vinyl group
Product name: Dongjue 110-2, Manufacturer: Narjing Dongjue, China.
2nd formulation constituent:
40 parts of the precipitated silicas accoidinc to the
invention.
3rd formulation constituent:
3.2 parts of processing auxiliary, short-chain OH-functional silicone oil (α, ω-dihydroxysiloxane) havirg an OH
concentration of about 8%, definable. by the fcllowing
structural formula.
Manufacturer: Shanghai HuaRun Chemical Co., Ltd., China.
4th formulation constituent:
1% of crosslinking agent, organic peroxide, (2 , 5-dirnethyl-2, 5-
di-tert-butylperoxy)hexane, definable by the following
structural formula.
Product name: DHBP-C8BS (DHBP paste with a pei oxide
concentration of 45%) ,
Manufacturer: Qiangsheng Chemical Co., Ltd., China.
The physicochemical parameters of the precipitated silicas according to the invention and the process paiameters are determined as follows.
Determination of the Y value;
The Y value is determined by means of sulphuric acid as standard solution and phenolphthalein as an indicator.
Reagents
- phenolphthalein solution in ethanol having a concentration of 10 g/1
sulphuric acid solution having a concentration of 1 mol/1
Procedure
100 ml of the sample to be investigated, e.g a precipitation suspension, are introduced into a 500 'Til beaker and about 10 ml of water and 3-5 drops of phenolphthalein solution are added. The mixture is stirred by means of a magnetic stirrer and the sulphuric acid solution is added by means of a burette until the colour of phenolphthalein chanςies from red to faint
pink. 3 - 5 further drops of phenolphthalein are added and titration is continued. This process is repeated until a colour change is no longer detectable.
The Y value is calculated as follows:
Y = C * V * N
where :
C = concentration of the sulphuric acid in mo] /1
V = volume of the sulphuric acid consumed :i n the titration, in ml
N = normality of the acid
Determination of the pH of the initially intrsducad mixture or precipitation suspension
A sample of 50 - 100 ml of the initially introduced mixture or the precipitation suspension is taken and the pH is determined at 6O0C.
Determination of the solids oontent of the siiilica feed prior to drying
10 g of sample (weight E taken) are dried in a porcelain dish (45 mm diameter) under an infrared drying lairp at 120 - 14O0C to constant weight. Thereafter, the sample is cooled to room temperature in a desiccator cabinet with silica gel as drying agent. The final weight A is determined graviinetrically .
The solids content (SC) in % is determined according to
SC - A / E * 100%,
where A = final weight in g and E - weight taksn in g.
Determination of the pH of the silica (end proAuct)
The determination of the pH of the silica is effected as a 5% strength aqueous suspension at room temperature on the basis of DIN EN ISO 787-9. The weights taken were changed compared with the specifications of this standard (5.0U g of silica per
100 ml of deionized water) .
Determination of the moisture content
The moisture content of silica is determined according to ISO 787-2 after drying for 2 hours in a circulation drying oven at 1050C. This loss on drying consists pjedoπ inantly of water moisture .
Determination of the BΞT surface area
The specific nitrogen surface area (referred to below as BET surface area) of the pulverulent, spherical cr granular silica is determined according to ISO 5794-1/Annex D using an AREA Meter (from Strohlein, JUWE) .
Determination of the CTAB surface area
The method is based on the adsorption of CfAB (N-hexadecyl- N,N,N-trimethylammonium bromide) on the "external" surface of the silica, according to ASTM 3765 or NFT 45-007 (section 5.12.1.3) .
The adsorption of CTAB takes place in aquecus solution with stirring and ultrasonic treatment. Excess, uπadsorbed CTAB is determined by back-titration with NDSS (sodium dioctyl sulphosuccinate solution, "Aerosol OT" solution) using a titroprocessor, the end point being given bv the maximum of the turbidity of the solution and beincr determined using a phototrode. The temperature during all operations carried out is 23 - 250C, in order to prevent CTAB from crystallizing out. The back-titration is based on the following equation:
(C20H3VO4)SO3Na + BrN(CHs)3(Ci5H33) <=>
(C2OH37O4)SO3N(CH3)S(Ci6H33) + NaBr
NDSS CTAB
Apparatuses
METTLER Toledo type DL 55 titroprocessor and METTLER Toledo
hype DL 70 titroprocessor, equipped in eaci case with: pH electrode, Mettier brand, type DG 111 and ph jtotrode, Mettler brand, type DP 550
100 ml polypropylene titration beaker
] 50 ml titration glass vessel with cover
Pressure filtration apparatus, 100 ml capacity
Membrane filter comprising cellulose nitiate, pore size
0.1 μm, 47 mm diameter, e.g. Whatman (Order No. 7181-004)
Reagents
The solutions of CTAB (CCTAB = 0.015 mol/1 in deionized water) and NDSS (concentration = 0.00423 mol/1 in deionized water) are obtained in ready-to-use form (froTi Bdrnd Kraft GmbH, 47167 Duisburg: Order No, 6056.4700 CTAB solution of concentration 0.015 mol/1; Order No. 6057.4730 NDSS solution 0.00423 mol/1) , stored at 25°C and used within one month.
Procedure
1. Blank titration
The consumption of NDSS solution for the tit- ation of 5 ml of CTAB solution should be checked once a day before each measurement series. For this purpose, the phol:otrode is set at 1000 + 20 mV before the beginning of the titration (corresponding to a transparency of 100%) .
Exactly 5.00 ml of CTAB solution are pipetted into a titration beaker and 50.0 ml of deionized water are added. While stirring, the titration with NDSS solution i. effected by the method of measurement familiar to those skd .led in the art, using the DL 55 titroprocessor, up to maximum turbidity of the solution. The consumption VΛ of NDSS solution is determined in ml. Each titration should be carried oi t as a triple determination .
2. Adsorption
10.0 g of the pulverulent, spherical or grant lar silica having a moisture content of 5 ± 2% {moisture content is optionally adjusted by drying at 105σC in a drying oven or uniform moistening) are comminuted using a mill (frαn Krups, Model KM 7b, article No. 2030-70) for 30 seconds. Exactly 500.0 mg of the comminuted sample (weight E taken) are transferred to a 150 ml titration vessel with magnetic stirring rod, and exactly 100.0 ml of CTAB solution (Ti) are metered in. The titration vessel is closed with a cover and stirred with an Ultra Turrax T 25 stirrer (stirrer shaft KV-18G, 18 mm diameter) at 18 000 rpm for not more thai: 1 αin until wetting is complete. The titration vessel is screv7βd to the DL 70 titroprocessor and the pH of the suspension is adjusted to a value of 9 ± 0.05 with KOH (0.1 mol/1) .
Ultrasonic treatment of the suspensior for 4 minutes is effected in the titration vessel in an nitre sonic bath (from Bandelin, Sonorex RK 106 S, 35 kHz, 100 W ei fective or 200 W peak power) at 25°C. Thereafter, immediate prassure filtration through a membrane filter at a nitrogen pressure of 1.2 bar is effected. The forerun of 5 ml is discarded.
3. Titration
5.00 ml of the remaining filtrate are pipettsd into a 100 ml titration beaker and made up to 50.00 ml with deionized water. The titration beaker is screwed to the DL !>5 titroprocessor and the titration with NDSS solution is effected with stirring to maximum turbidity. The consumption VB of ND3S solution in ml is determined. Each titration should be carried out as a triple determination.
Calculation
O CTTAA tBJ / (no *t moisture-correc *ted Λ)\ =— VΛ— VB CCTAB • M—CTAB - Tl - P
VA £■
VA -- consumption of NDSS solution in ml in the titration of the blank sample
Vn = consumption of NDSS solution in ml on use of the filtrate
CcTAB = concentration of the CTAB solution in :τ ol/l
McTAB = molar mass of CTAB = 364 . 46 g/mol
Ti = added amount of CTAB solution in 1
P = space requirement of CTAB = 578.435 m2/g
E = weight of silica taken
The CTΛB surface area is based on the anhydrous silica, and it is for this reason that the following corrs ction is carried out .
- CTAB (not moisture-corrected) in mVg • 100%
100% - moisture content in %
The moisture content of the silica is derernuned according to the described method "Determination of the' moisture content".
Determination of the DBP absorption
The DBP absorption (DBP number), which is a measure of the absorptivity of the precipitated silica, is determined on the basis of the standard DIN 53601, as follows:
12.50 g of pulverulent or spherical silica having a moisture content of 0 10% (the moisture content is optionally adjusted by drying at 1050C in a drying ovei.) are introduced into the kneader chamber (article nurrber 279061) of the Brabender absorptometer "E" (without vaporization of the exit filter of the torque transducer) . In the case of granules, a sieve fraction of 1 to 3.15 mm (stainless steel sieves from Retsch) is used (by gentle pressing of the granules with a plastic spatula through the sieve of 3.1^ mm pore size). With
constant mixing (circulation speed of th^ kneader blades 125 rpm) , dibutyl phthalate is added diopwise at a rate of 4 ml/min to the mixture at room temperature by means of the "Dosimat Brabender T 90/50", Mixing requires only a little force and is monitored on the basis of the digital display. Towards the end of the determination, the mixture becomes pasty, which is indicated by means of a steep increase in the force required. At a display of 600 digits {torque of 0.6 Nm), both the kneader and the DBP metering are switched off by an electrical contact. The synchronous motor for the DBP feed is coupled to a digital counter so that the consumption of DBP can be read in ml.
The DBP absorption is stated in g/(100 g) and calculated on the basis of the following formula:
V-D - 100 e
DBP=—IT- -Ϊ^Ϊ + κ
where DBP = DBP absorption in g/ (100 g)
V = consumption of DBP in ml
D = density of DBP in g/ml (1.047 g/ml ac 2O0C)
E = weight of silica taken in g
K = correction value according to moistuce correction table in g/ (100 g)
The DBP absorption is defined for the anhydrous, dried silica. With the use of moist precipitated silicas . the correction value K should be taken into account for ca. culating the DBP absorption. This value can be determined with the following correction table; for example, a water ccnter.t of 5.8% in the silica would mean an addition of 33 g/(100 g) for the DBP absorption. The moisture content of the silica is determined according to the method ^Determination of moi.sture content or of the loss on drying".
Table 1: Moisture correction table for dibutyl phthalate absorption (anhydrous)
Determination of the electrical conductivity
The determination of the electrical conductivity of silicas is carried out as a 4% strength aqueous suspension at room
temperature on the basis of DIN EN ISO 787-14. The weights taken were changed compared with the specifications of this standard (4.00 g of silica per 100 ml of ceioπized water) .
Determination of the particle size by means of laser diffraction
The use of laser diffraction for determining particle sizes of powders is based on the phenomenon that P'3rti':les scatter monochromatic light with a different intensity pattern in all directions. This scattering is dependent on t.ie particle size. The smaller the particles, the greater are thu scattering angles .
The sample preparation and measurement (washing of the module, etc.) are effected with a dispersion liqu.id (0.05 m-% Tetra- Sodium-diphosphate in demineralised water] in the case of
hydrophilic precipitated silica. With pure ezhanol / water mixture (ration by volume 1 : 1) in the case of precipitated silica nor sufficiently wettable with water.
Before the beginning of the measurement, the laser diffraction apparatus LS 230 (from Beckmann Coulter, Art. -No. 6605210) and the liquid module (Small Volume Module Plus, 120 ml, from Beckmanr, Coulter with internal ultrasonic finger (diameter 6 mm), Art. -No. 6605506) including a ultrasonic processor SONICS Vibracell (Modul VCX 130) are allowed to warm up for 2 h and the module is washed three times with the dispersion liquid, calibrated, and washed three times with ethansl / water mixture in the case of hydrophobic precipitat≥d silicas.
Tn the control bar of the apparatus software (e.g. Version 3.29), the window "calculate Opt. model" is selected via the menu option "Measurement" and the refractive Indices are specified in an .rfd file: liquid refractive Index R.I. real = 1.332 (1.359 for ethanol) ; material refractive index real = 1.46; imaginary = 0.1; form factor 1. In the window "sample info", "sample name", "file name" for saving :he data of the measurement, "dispersion liquid" are defined and confirmed with "OK". Thereafter in the control bar 'Ameai5urement cycle" is chosen. In this window as a first step "ner.tf sample" has to be confirmed, followed by definition respectively activation of: "offset measurement", "adjustment", "background
measurement", "set samplβ concentration", "irout sample info" (necessary for confirmation of the sample def .ned in "sample info") , "start 1 measurement" and deactivation of PIDS function. In addition the optical model "Traunhofer-rfd" is chosen, "size distribution" (make hook at "during
measurement") and "safe data" are activated, ''he pump speed is set on the apparatus (respectively at the Sma..l Volume Modul) to 30%.
Suspensions are prepared from the silica ϋampl.es to be
investigated. In the case of milled products a redispersion is conducted by ultrasonic treatment for 1 raiαute by means of ultrasonic processor model VC 70 T from Vibra Cell (70 W) and an ultrasound finger CV 181. In the case of unmilled products, the dispersing is effected by circulation for 1 minute by means of a pump in the Small Volume Module Plus. Thereafter, the homogeneous suspension of 1 g of silica in 40 ml of demineralized water is added by means of a 2 til one-way pipette to the liquid module of the apparatus in such a way that a constant concentration with a light absorption of 8 to 12% is achieved and the apparatus reports XΛOK". The
measurement is effected at room temperature. From the raw data curve, the software calculates the particle size distribution (dδ value) and the d^o value (median valuel on the basis of the volume distribution taking into account the MLe theory and the optical model parameters ( . rfd file).
Determination of the tamped denaity
The determination of the tamped density was effected according to DIN EN ISO 787-11.
Determination of the Fe24" and of the AI2O3 content of the waterglass
Measurement principle
The silicate solutions evaporated to dryness are heated in a mixture of hydrofluoric acid and sulphuric acid. This results in the formation of gaseous silicon tetraf luoride, which is evaporated with fuming, and the silicon is th/js removed. The metal salts remaining behind are taken up in rydrochloric acid and diluted with water.
Iron content
The iron content of the metal salt solution iε determined by
means of atomic absorption .spectroscopy by measurement of the light absorption at a wavelength of 248.3 nm.
Aluminium content
The determination of the aluminium content is effected
colorimetrically by means of a stable ternary aluminium- chromazurine S-cetylpyridinium bromide conple..
Reagents required
(The numbers in Brackets represent the content of the reagent respectively deionised water in the mixture ir (parts by volume / parts by volume) . The first number stands for the content of the reagent while the second nv.mbei represents the content of deionised water) .
Ascorbic acid solution 2% by weighc in distilled water (freshly prepared before use)
o-Phenanthroline solution 1% by weight is prepared with an ethanol solution 100 ml (1+1) .
Chromazurine S solution 0.2% by weight is prepared with an ethanol solution 100 ml (1+3) ,
Cetylpyridiniura bromide solution 0 4% by weight cetylpyridinium bromide solution 100 ml (1+3).
Al standard solution 1000 μg/ml .
Al standard solution 10 μg/ml is prepared by introducing 1 ml of the Al standard solution of 1000 ug/ml and 2 ml of hydrochloric acid solution into a 100 mL graduated flask and making up to 100 ml with distilled water.
Sulphuric acid 98%
Hydrochloric acid 36%
Hydrochloric acid (2+5) (V/V)
Hydrofluoric acid 40%
Cu standard solution, 1000 μg/ml.
Fe standard solution, 1000 μg/ml.
Mn standard solution, 1000 μg/ml
Mixed solution of Cu, Fe, Mn having a metal content of 10 μg/ml is prepared by introducing in each case 1 ml of the Fe, Mn and Cu standard solutions and 2 mJ of concentrated hydrochloric acid into a 100 ml graduated flask and diluting to the mark with distilled water.
Mixed solutions of Cu, Fe, Mn having metal contents of 0, 0.2, 0.4, 0.6, 0.8 μg/ml are prepared ii eaαh case in 250 ml graduated flasks by dilution with distilled water.
Apparatuses required
- GGX-9 AAS spectrometer, Beijing Kechuarg Haiguang Instrument Co . , Ltd
- 721E spectrometer, Shanghai Analytical Instrument. Factory, China
- 10 ml, 100 ml and 150 ml graduated flasks
- 1, 2, 3, 5, 10, 15, 20 ml volumetric pipettes
- Drying oven of 105 ± 2°C
Analytical balance having an accuracy of ± 0.1 rug
- Desiccator with silica gel
- Weighing bottle with cover
Sample preparation
The concentrated waterglass solution is diied for 1.5 h at 1050C in an oven, and allowed to cool. 1.5 g (i 0.1 π\g) of the dried sample is wetted with deionized water ir a platinum crucible and mixed with 10 ml of hydrofluoric acid and 0.5 ml of sulphuric acid. The mixture is concentratec by means of a heating stirrer until white fumes form and is allowed to cool, 5 ml of hydrofluoric acid are added again and concentration is effected again until white fumes form. The coc led residue is taken up with 5 ml of hydrochloric acid and heated until all solids have dissolved. The cooled solution is transferred to a 20 ml flask and diluted to the 10 ml mark witlr distilled
water. Test solution A is thus obtained. Carrying out the measurements
Determination of the iron content (Fe mg/kq)
The AAS spectrometer GGX-9 is switched on and allowed to warm up for 15 minutes until it is ready for operation. 1 ml of test solution A is transferred to a 100 m] graduated flask, 2 ml of hydrochloric acid are added and the sclution is made up to the 100 ml mark with distilled water. Tεst solution B is thus obtained. The analysis of the sample is -effected with consultation of the operating instructions of the AAS
spectrometer. Calibration solutions with 0, 0.2, 0.4, 0.6 and 0.8 μg of iron/ml are used.
Determination of the AI2O3 content in %
Recording of the calibration curve
0, 10, 20, 30 and 50 μg (addition of 0, 1, 2r 3 and 5 ml of an Ai calibration solution having an Al content cf 10 μg/ml) are introduced into a 100 ml graduated flask. Thereafter, 1 drop of nitrophenol (0.1% by weight) is added, diluted with 20 ml distilled water, 2% by weight .of nitric acid and 2% by weight of ammonia solution are added so that the yellow solution becomes colourless. Immediately thereafter, 5 nl of a 4% by weight nitric acid are added and thoroughly mixed. After 20 - 30 minutes, 1 ml of ascorbic acid is added and shaking is vigorously effected again. This is followed by dilution of the solution to 70 ml with distilled water and addition of 5 ml of a 0.2% strength by weight chromazurine S solution and 5 ml of a 0.4% strength by weight cetylpyridinium bromide solution and 5 ml of a 30% strength by weight hexamethyltetramine solution. The mixture is vigorously shaken and is allowed to stand for 10 minutes. The light absorption of this calibration solution is then measured by means of a 721E spectrometer at. a
wavelength of 620 run in a 5 cm absorption vessel. The calibration curve is recorded in a coordinate system in which the absorbance is plotted along the horizontal axis and the aluminium content in μg along the vertical ax. s . The gradients Jc1 for Al and k2 for AI2O3 are determined, where
Analysis of the sample
For determining the aluminium oxide content, .n each case 2 ml of test solution B (cf. determination of the iron content above) and of the blank solution are initially introduced into a 100 ml graduated flask and the procedure foi recording the calibration curve is then adopted.
The following examples serve for i..lust ration and for understanding of the present invention but io not limit the scope thereof in any way.
Example X
45.94 m3 of water are initially introduced into a precipitation container having a capacity of 85 m3 and 5.0£ m3 of waterglass (Be - 29.0; weight ratio of Siθ2 to Na2O = 3.23) are added. The initially introduced mixture is then heated to 64.10C. The Y value of the initially introduced mixture at the beginning of the precipitation/ i.e. the addition of waterglass and sulphuric acid together (about 98.0 ± 0 ,.5% by weight) to the initially introduced mixture, is 19.65. Within 75 min, waterglass (as specified above) and sulphuric acid (as specified above) are then added while maintaining a constant precipitation temperature of 870C (maximum variation ± 0,20C) and with introduction of shear energy by means of a turbine, in such a way that the Y value remains constant, i.e. is subject to a maximum variation of ± 1.9% acout the starting value. After 75 rain, the addition of watecglass is stopped and the sulphuric acid is further added until -a pH of 3.68 is
reached. Thereafter, the suspension is stirrel for 20 min at a pH between 3.68 and 3.74.
The suspension obtained is filtered with ,ι chamber filter press and the filter cake is washed with water. The filter cake is then fluidized in a dissolver. The s .lica feed having a solids content of about 18.9% by weight aid a pH of about 5.7 is then spray-dried so that a pH of 6.3, measured as 5% strength suspension, is established in the end product.
The spray-dried product is then mil] ed by means of a mechanical mill having a classifier (Vortex Pulverizing Mill QWJ-60) .
The physicocheraical data of a representative sample of the spray-dried and unmilled product obtained (Example Ia) and of the milled product (Example Ib) are listed in Table 2.
Example 2
20.52 mJ of water are initially introduced into a precipitation container having a capacity of 45 m3 and 2.42 m3 of waterglass (Be = 23; weight ratio of SiO2 to Na2O = 3.2•}; SiO2 content = 14.7 ± 0.5% by weight) are added. The ini1 ially introduced mixture is then heated to 86QC. The Y value of the initially introduced mixture at the beginning of the prscipitation, i.e. the addition of waterglass and sulphuric acid together (about 98.0 1 0.5% by weight) to the initially introduced mixture, is 20.35. Within 75 min, waterglass (as .specified above) and sulphuric acid (as specified above) are then added while maintaining a constant precipitation temperature of 860C (maximum variation ± 0.20C) in such a way "hat the Y value remains constant, i.e. is subject to a maximi m variation of ± 3,1% about the starting value. After 75 min, the addition of waterglass is stopped and the sulphuric acid is further added until a pH of 3.74 is reached. Thereafter, 1 he suspension is
stirred for 20 min at a pH between 3.74 and 3.78.
The suspension obtained is filtered with a. chamber filter press and the filter cake is washed with water which was fully demineralized beforehand via rever.se osmosis. The filter cake is then fluidized in a dissolver. The silica feed having a solids content of about 18.2% by weight and a pH of about 5.7 is then spray-dried so that a pH of 6.5, measured as 5% strength suspension, is established in the end product.
The spray-dried product is then mill.ed by means of a mechanical mill having a classifier (Vortex Pulverizing Mill QWJ-60) .
The physico-chemical data of a represent,ative sample of the spray-dried and unmilled product obtained (Example 2a) and of the milled product (Example 2b) are listed in Table 2.
Comparative Examples 1 -bo 4
A conventionally prepared standard silica ULtrasil VN3 from Evonik Degussa GmbH was chosen as Comparativs Example 1. In Comparative Examples 2 to 4, precipitated silicas which are developed and sold specially for the reinforcement of silicone rubber elastomers were chosen. Comparative Example 2 is Nipsil LP from Nippon Silica. In Comparative Examples 3 and 4, two different samples of Zeosil 132 from Rhodia Chimie were tested. These two samples show very different properties. The reason is not known to the applicant,, It might be, for example, that Rhodia Chimie sells different product qualities under the same name.
Table 2
Physicochemical properties of different si lies s
Example 3
The comparative experiments shown in Table 3 are based on compounding by means of a laboratory kneader. The comparative experiments shown in Table 4 are once again based on compounding by means of a two-roll mill. The experiments were carried out as follows:
Apparatuses:
1. Laboratory kneader with thermostat, model INo. : HI-KD-5
(from Hongyi, Taiwan) .
2. Two-roll mill, model No.: LRM-S-110/3E (frjm Labtech,
Taiwan) .
Roll diameter: 100 mm
Roll length: 200 mm
Roll nip: 1.0 +/- 0.05 mm
Speed: 15 rpm/20 rpm
Friction ; 1:1.3
3. Heating press, model No. GT-7014-A50 (frcra Gotech,
China) .
Pressure : 0 - 5O t
Temperature range: RT - 3000C
Press area: 315 • 288 mm
4. Two stainless steel plates having the dimensions 330 mm
330 mm • 2 mm and a spacer plate of the same thickness with 4 recesses having the dimensions 130 mm • '.130 mm and two stainless steel plates having the ciimensions 300 mm • 300 mm • 6 mm and a spacer plate of the: same thickness with 2 recesses having the dimensions 60 mm ■ 6t> mm.
5. High-temperature oven (from ESPEC, China ι.
6. Tensile tester (from Gotech, China).
7. Datacolor (Datacolor 400TM) .
8. Further testers for measuring the hardness (Shore A), Williams plasticity and sample thickness (from Gotech, China) .
9. Laboratory balance, accuracy at least ± J.01 g.
Raw materials used:
HTV Polymer:
Dongjue 110-2 molecular weight 600 000 g/mol, vinyl content:
0.15%, from Nanjing Dongjue, China
Distributor oil/processing auxiliaries;
α,ω-Dihydroxysiloxane, content OH functional groups approx. :
8%, from Shanghai HuaRun Chemical, China.
Crosslinking agent/organic peroxide:
DHBP-C8BS paste (45%) from Qiangsheng Chemical. Co., Ltd.,
China.
Silicas according to the invention and comparative products (cf. Table 2)
Experimental section:
Part 1 Compounding by means of laboratory kneader
Formulation :
100 parts of HTV polymer (1500 g)
40 parts of silica (600 g)
3.2 parts of distributor oil/processing auxiliaries (48g)
1.0% of crosslinking agent/organic peroxide
Compounding/preparation :
After adjustment of the rotational speed of tie kneader tool to 20 rpm, 1500 g of HTV polymer are introduced into the kneader chamber. The silica and the processing- auxiliary were then added at room temperature in four portiois of (40%, 25%, 20% and 15%) .
1.40% by weight = 240 g of silica + 19.2 g oi processing
auxiliary
2.25% by weight = 150 g of silica + 12.0 g oJ processing
auxiliary
3.20% by weight = 120 g of silica + 9.6 g oi processing
auxiliary
4.15% by weight = 90 g of silica + 7.2 g of processing
auxiliary
After complete dispersing of the silica, the incorporation time required for the silica was determined i noted). After incorporation of the complete amount of silica, the heating power of the kneader thermostat is set at 17C°C and
compounding is then effected for two houi s at a temperature of 1700C (without vacuum) . Thereafter, further dispersing in Lhe kneader is effected for 0.5 hour in vacu; but without heating (cooling process). After cooling of the compound, the Williams plasticity (according to ASTM D 926-67) was measured after 24 h. Before the measurement of the optical properties of the compound, special compound test specimens must be prepared. For the preparation of the 6 mrr thick compound test specimens, 2 stainless steel plates having the dimensions 300 mm • 300 mm • 6 mm and a spacer plate of the same thickness with two recesses having the dimensions 60 mir • 60 mm are used.
The preparation of the 6 mm HTV compound test specimens
(weight taken: 2 times 25 g of compound) is effected in the heating press at room temperature (without addition of the crosslinking agent/peroxide) for 1 rain and at a pressure of about 6 bar (6 mPa) .
After preparation of uniform test specimens, the measurement of the optical properties of the compound by neans of
Datacolor 400 can be effected.
The following were determined:
1. 1, a, b values, yellow discolouration εiccoj ding to the
standard ASTM E 313/DIN 6167.
2. Turbidity according to the standard DIN 53] 46.
3. Transparency according to the standard DIN 53147.
After cooling of the compound and after storage for 24 hours, the vulcanization of the compound can be effected - as described in Part 3 - for determining further performance characteristics .
Part 2 Compounding by means of a two-roll mil."
Formulation :
100 parts of HTV polymer (200 g)
40 parts of silica (80 g)
3.2 parts of distributor oil/processing όiuxiϋiary (6.4 g)
1.0% of crosslinking agent/organic peroxide
Compounding/preparation;
After the two-roll mill has been switched on, important working parameters, such as roll nip (l.C +/- 0.05 mm) and dispersing speed (20 rpm/15 rpm, i.e. a friction of 1:1.3), are set.
At room temperature, 200 g of HTV polymer are applied to the two-roll mill and dispersed until the compound is present in homogenized form, i.e. the faster roll is completely coated with said compound and has a smooth surface. Hor this purpose, the two-roll mill is stopped and about 10? of the amount of silica (total amount of silica is 80 g) are introduced in the middle between the two rolls. Thereafter, the complete amount of processing auxiliary (6.4 g of distributor oil) is metered to the silica already applied. By starting the two-roll mill again, the incorporation of the silica into the polymer is now achieved. The addition of further amounts of isilica is
effected very slowly and stepwise. After about 50% of the total amount of silica were added and incorporated, the compound is removed from the roll, folded and applied again to the roll. The remaining 50% of silica are now incorporated stepwise. Small amounts of silica may fall under the two-roll mill through the roll nip. In this context, it should be ensured that the amounts of this silica are collected on a clean underlay and applied to the two-roll mill again for complete incorporation.
After complete incorporation of the silica and as soon as the compound is present in homogenized form, i.e. the faster roll
is completely coated with said compound and said compound has a smooth surface, the incorporation time required for the silica is determined (noted) .
The homogenization of the compound is now continued in order to ensure the complete dispersing of the silica. During this procedure, the compound is removed a further five times from the two-roll mill, folded and applied again. The total subsequent dispersing time should be not more than 5 minutes. After the compounding, the compound is removed from the roll in the form of a single long compound hice. ϊhe compound hide is now folded into 4 uniform layers and stored on a stainless steel plate at 17O0C for one hour in a hct-air oven.
After this heating, the compound is removed from the oven and is stored for one hour at room temperature fcr cooling.
Thereafter, the compound is again plasticized by rolling with 5 - 10 minutes (depending on silica properties), i.e. applied again to the two-roll mill and dispersed until the compound is present in homogenized form, i.e. the faster roll is completely coated with said compound and said compound has a smooth surface.
Thereafter, the compound is removed from the coll and the determination of the Williams plasticity (according to ASTM D 926-67) and the preparation of special compound test
specimens for the determination of the optical properties of zhe compound, as also described in Part 1, follow.
Thereafter, the vulcanization of the compound - as described in Part 3 - can also be effected for determining further performance characteristics.
Part 3 Vulcanization:
The vulcanization is effected after compounding by means of a laboratory kneader or after compounding by means of a two- *roll mill.
For determining the performance characteristics, vulcanizates or HTV test specimens having a thickness of 2 mm (for determining the tensile strength, elongation at break and tear propagation resistance) and having a thickness of 6 mm {for determining the hardness and the optical properties of the HTV vulcanizates) are required.
After the two-roll mill has been switched on,, important working parameters, such as roll nip (1.0 +/•- 0.05 mm) and dispersing speed (20 rpm/15 rpm, i.e. a friction of 1:1.3), are set,
At room temperature, the required amount of H1IV compound is applied to the two-roll mill and dispersed until a completely replasticized compound (compound plasticiz.ed by rolling) has formed.
As soon as the compound is present in homogenized form, i.e. the faster roll is completely coated with sale compound, the peroxide addition can be effected.
1.0% by weight of DHBP-45-PSI (2, 5-dimethyl-2 , 5-di-tert- butylperoxy) hexane based on the mass of compound used, are now added and dispersed.
In order to ensure good dispersing of the pecoxide,
dispersing is effected for a further 8 minutes. During this rolling time, the compound is removed frcm the ro] 1 8 times altogether, folded and applied again to the coll.
After the peroxide has been dispersed, the compound is now stored for 24 hours away from dust. Before tire actual vulcanization, the compound is completely replasticized again by rolling.
After the heating press has been preheated tc 17O0C, the actual vulcanization is effected. For this purpose the following polished stainless steel plates are used:
For the 2 mm thick test specimens, 2 stainless steel plates having the dimensions 330 mm • 330 mm • 2 mm and a spacer plate of rhe same thickness with 4 recesses having the dimensions 130 mm • 130 mm are used.
For the 6 mm thick test specimens, 2 stainless steel plates having the dimensions 300 mm • 300 mm • 6 mm and a spacer plate of the same thickness with 2 recess.es having the dimensions 60 mm • 60 mm are used.
The vulcanization of the 2 mm HTV test specimens (weight taken: 4 times 35 g of compound) is effected in the heating press at 170°C for 7 min and at a pressure of about 15 bar (15 mPa) .
The vulcanization of the 6 mm HTV test specimens (weight taken: 2 times 25 g of compound) is effected in the heating press at 1700C for 10 min and at a pressure of about 15 bar (15 mPa) .
What is important is that the stainless steel plates used for the vulcanization must be cooled to room temperature before reuse, since otherwise the optical properties of the
vulcanizates may be adversely effected.
In order to ensure complete vulcanization anc to remove cleavage products from the vulcanizates, all test specimens are subsequently postvulcanized in a high-teirperature
circulation oven (at least 120 1 of fresh ai c per minute and per kg of HTV vulcanizate are required) at 2000C for 4 hours.
The performance characteristics shown in Table 3 and Table 4 can be tested after storage of the HTV vulcanizates in a
conditioned room or conditioned chamber according to the requirements of the respective method of measurement. The following standard test methods were chosen for determining the comparative data:
Hardness (Shore A): DiN 53 505
Tensile strength and elongation at break: ISO 37
Tear propagation resistance: I!!0 34-1
Optical properties
Yellow discolouration, 1, a, b values: ΛϋTM E 313 / DIN
6167
Turbidity: DlN 53146.
Translucence: D.I N 53147.
Table 3
Performance characteristics of different silicas in HTV silicone rubber - compounding by means of laboratory kneader
ωc
ω OD m
ωx
mm
3B
m
K)
CD
Table 3 (continued)
Ul
K>
V
Interpretation of the test results from Table 3
The precipitated silicas according to the invention (Examples Ia, Ib, 2a and 2b) have substantially reduced incorporation time in comparison with conventionally prepared precipitated silicas (Comparative Example 1), i.e. they can be more rapidly incorporated and more rapidly dispersed/homogenized. If only the precipitated silicas according to the invention (Examples Ib and 2b) are considered, they too have substantially more advantageous incorporation times than precipitated silicas which are already available on the market and are offered especially for silicone rubber applications (Comparative
Example 3) . The Williams plasticity, a measure of the
thickening and the rheological properties of "he compounds, is comparable lor all examples shown in Table 3. A further- advantage of the precipitated silicas according to the
invention is found on consideration of the coirpound
translucency .
In this respect, the comparison of the Examples Ia, Ib, 2a and 2b with Comparative Examples 1 and 2 shows that the compound translucency as a measure of the compound transparency is at an extremely high level for all precipitated silicas according to the invention. The same applies to the compound lightness, since the precipitated silicas according to the invention are clearly distinguished from Comparative Example 1, and Examples Ia, Ib, 2a from Comparative Example 2. Even the very good values of Comparative Example 4 are surpassed here.
The lower Shore A hardness of the precipitated silicas
according to the invention (Examples Ia, Ib, 2a and 2b) in direct comparison with Comparative Examples 2 and 3 is likewise advantageous since a lower vulcaπizaτe hardness permits increased silica addition (based on the formulation) . This means that better mechanical properties could be achieved by addition of more silica at theoretically the same hardness. The mechanical properties, such as, for example, tensile
strength and tear propagation resistance, of Examples Ib and 2b are at a similarly high level in compai ison with
Comparative Examples 2 and 3, However, the results obtained for Example Ia are to be singled out in this lespect. Although this is an unmilled silica, an acceptable tenε.ile strength and an acceptable tear propagation resistance can already be achieved in comparison with a milled silica (Comparative Example 2) . According to the prior art at present, this is not achievable with conventional unmilled precipitated silicas. However, the following advantages of the precipitated silicas according to the invention are to be singJ ed cut in
particular;
Example Ia, Ib, 2a and 2b show an extremely high translucency of the vulcanizates as a measure of the transparency and clarity of the crosslinked silicone systems. 'Ihis permits use in novel silicon products which require extrertely high transparencies. All Comparative Examples ιl, 2 and 3) show substantially lower translucency values arid the lightness of the vulcanizates, too, was determined with substantially lower values for Comparative Examples 1 and 2,
In the case of highly transparent vulcanizates, it is usually found that an increased b value is also a measure of the yellow component and an increased yellow oiscc louration.
However, in spite of the highly transparent properties, all vulcanizates based on the precipitated silicas according to the invention show only moderate (Examples1 Ia, Ib) or very low (Examples 2a, 2b) b values and a very sliςrht yellow
discolouration (Examples 2a and 2 b) .
In this respect, Examples 2a and 2b not only have a
substantial improvement in comparison with conventional precipitated silicas (Comparative Example 1) tut could also be substantially improved in direct comparison with the
precipitated silicas already established Jn the market, which
are offered for silicone rubber applications ^Comparative Examples 2 and 3) .
Table 4
Performance characteristics of different silicas in HTV silicone rubber - compounding by means of two-roll mill
ω
c
OD
ω m Ul
ω
x
m
m
3B
m
K)
CD
Table 4 (continued)
ω
c
OD
ω m
ω Ul
x
m
m
70
m
K)
CD
Interpretation of the test results from Table 4
The precipitated silicas according to the invention
(Examples Ia, Ib, 2a and 2b) have a reduced incorporation time in comparison with conventionally prepared
precipitated silicas (Comparative Example 1) . However, with the compounding method by means of the twc-roll mill which is in any case substantially faster (in comparison with the kneader experiments - Table 3) , in some cases substantial differentiation from precipitated silicas which are already available in the market and are offered especially for silicone rubber applications (Comparative Examples 2 to 4) is no longer possible. However, also in comparison with the precipitated silicas which are alreadv available in the market and are offered especially for silicone rubber applications, from Comparative Examples 2 and 4, Examples Ia, Ib according to the invention show up to 20% faster incorporation times.
The Williams plasticity, a measure of the thickening and rheological properties of the compounds, Is comparable for all examples shown in Table 4. A further advantage of the precipitated silicas according to the invention is found on consideration of the compound translucency .
In this respect, the comparison of Examples Ia, Ib, 2a and 2b with a conventional precipitated silica (Comparative Example 1) shows that the compound translusency as a measure of the compound transparency is at a high level. However, the very low b values, determined for all
precipitated silicas according to the invention, are to be singled out in particular. A low b value is equivalent to very little yellow discolouration of the compound. If the b values of Examples Ia, Ib, 2a and 2b are ΠDW compared with Comparative Examples 2 to 4, it becomes clsar that the compounds based on the precipitated silicas according to
the invention have substantially less yellow discolouration. Unfortunately, the relatively small difference between the b values does not ir.ake this as clear as the simple visual assessment of the compounds (even by means of photographs, this difference readily visible to the eye in daylight unfortunately cannot JOB shown in a reproducible manner) .
The lower Shore A hardness of the precipitated silicas according to the invention (Examples
Ia, Ib, 2a and 2b) in direct comparison with Comparative Example 2 is likewise advantageous since a lower
vulcanizate hardness permits an increased, silica addition (based on the formulation) .
The mechanical properties, such as, for example, tensile strength and tear propagation resistance, Df Example 2b are at a similarly high level in comparison with Comparative Examples 2 and 3. In this respect, however, the results obtained for Examples Ia and 2a are to be singled out in particular. Although these are unmilled siLicas, tear propagation resistances which are just as iigh can be achieved in comparison with the milled precipitated silicas (Comparative Examples 2 and 3) .
However, the following advantages of the precipitated silicas according to the invention are to be singled out in particular:
Examples Ia, Ib, 2a and 2b show a high traislucency of the vulcanizates as a measure of the transpare icy and clarity of the crosslinked silicone systems in comparison with a conventional precipitated silica (Comparative Example 1) , This permits use in highly transparent si-icone products, In the case of highly transparent vulcanizates, an
increased b value as a measure of the yellow component and an increased yellow discolouration are alsD usually found.
However, in spite of the highly transparent properties, all vulcanizates based on the precipitated silicas according to the invention show only moderate (Examples Ia, Ib) or very low (Examples 2a, 2b) b values and very little yellow discolouration (Examples 2a and 2 b) .
In this respect, Examples 2a and 2b not or.Iy have a substantial improvement in comparison with conventional precipitated silicas (Comparative Example 1) but could also be substantially improved in direct comparison with the precipitated silicas already established in the market, which are offered for silicone rubber applications
(Comparative Examples 2 and 3) .
Claims
1. Precipitated silica, characterized in that it has a BET surface area of 185 to ,260 m2/g
a CTAB surface area of 100 to .60 m2/g
a BET/CTAB ratio of 1.2 to » .6 m2/g
a conductivity of < 250 CiS) /cm.
2. Precipitated silica according to Claim 1,
characterized in that it has a me'diar particle size d5o of 5 to 25 μm and a tamped de isitv of 50 to
150 g/1.
3. Precipitated silica according to either of Claims 1 and 2, characterized in that the median particle size dso is 8 to 25 μm and/or the ds value is 4 to 10 μm.
4. Precipitated silica according to Claim 1,
characterized in that it has a mediar particle size d50 of 25 to 90 μm and a tamped density of 150 to 350 g/1.
5. Precipitated silica according to any of Claims 1 to 5, characterized in that the conductivity is 1 to
200 (μS)/cm.
6. Precipitated silica according to any of Claims 1 to 5, characterized in that the DBP absorption is 250 to 300 g/100 g.
7. Precipitated silica according to any of Claims 1 to 6, characterized in that the moisture ccntent is less than 7% by weight, preferably 5 to 1% by weight, particularly preferably 5.5 to 7?, by weight.
8. Precipitated silica according to any of Claims 1 to 7, characterized in that the pH. is !:■ to 8, preferably 6 to 7.
9. Process for the preparation of precipitated silicas, characterized in that it comprises tVe following steps:
a) preparation of an initially introduced mixture having a Y value of 10 to 30,
b) simultaneous metering of alkali metal silicate and/or alkaline earth met3. silicate and acidifying agent into this initially introduced mixture with stirring at 80 to 950C for 60 to 90 min,
c) reacidification of the precipitation suspension, d) ageing of the suspension for 5 "co 50 min,
e) filtration, washing and drying,
and which is characterized in that the alkali metal silicate and/or alkaline earth metal silicate used in steps a) and/or b) has an alkali metal oxide or alkaline earth metal oxide content in the range from 4 to 7% by weight and a silicon dioxide content in the range from 12 to 28% by weight, in that the acidifying agent used in step b) and/or c) is an acidifying agent selected from the group consisting of concentrated mineral acids and carbonic ac:.d (or CO2 gas) and sodium hydrogensulphite (or SO2 gas) in the correspondingly possible concentrations, and in that the Y value of the precipitation suspension is kept constant at a value between 10 ard 30 during the precipitation, keeping constant meaning that the Y value varies by not more 3% about the starting Y value, i.e. the value directly before1 the beginning of the simultaneous addition of acid.i.fying agent and alkali metal silicate or aJkaline earth metal silicate, in the course of the simultaneous addition of acidifying agent and alkali, mπtal silicate or alkaline earth metal silicate.
10. Process according to Claim 9, char, cterized in that demineralized water, preferably water purified by distillation or reverse osmosis, is used in at least one step of the process according 1.o the invention, preferably at least during the washing process.
11. Process according to Claim 9 or 10, characterized in that high shear forces act on the1 precipitated silica particles in one of the steps of the process according to the invention.
12. Process according to any of Claims 9 to 11,
characterized in that the drying is effected by means of spray drying, particularly preferably in that that a feed having a solids content of 15 1 o 20% by weight and a pH of 4 to 7 is spray-dried-
13. Use of a precipitated silica according to any of
Claims 1 to 8 as a filler for silicore rubber
formulations, preferably RTV-I, F.TV-2, HTV and LSR silicone rubber formulations.
14. Silicone rubber formulation, preferably RTV-I, RTV-2, HTV and LSR silicone rubber formulat. on, containing at least one precipitated silica according to any of Claims 1 to 8.
Priority Applications (16)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2767072A CA2767072A1 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| BR112012000033-0A BR112012000033B1 (en) | 2009-07-03 | 2009-07-03 | precipitated silica, its use and its preparation process, and silicone rubber formulation |
| MX2011013371A MX2011013371A (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations. |
| EP09846662.6A EP2448865B1 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| HUE09846662A HUE031263T2 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| JP2012518719A JP5506924B2 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as a filler for silicone rubber formulations |
| ES09846662.6T ES2606713T3 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as a filler for silicone rubber formulations |
| RU2012103381/05A RU2516830C2 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silicon dioxide as filling agent for silicone rubber compositions |
| KR1020127000006A KR101601358B1 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| US13/263,110 US9725326B2 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| CN200980160214.2A CN102471080B (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| PT98466626T PT2448865T (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| PL09846662T PL2448865T3 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| PCT/CN2009/000754 WO2011000133A1 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
| TW099121507A TWI476151B (en) | 2009-07-03 | 2010-06-30 | Hydrophilic silica as a filler for silicone rubber formulations |
| ZA2012/00034A ZA201200034B (en) | 2009-07-03 | 2012-01-03 | Hydrophilic silica as filler for silicone rubber formulations |
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| PCT/CN2009/000754 WO2011000133A1 (en) | 2009-07-03 | 2009-07-03 | Hydrophilic silica as filler for silicone rubber formulations |
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| US (1) | US9725326B2 (en) |
| EP (1) | EP2448865B1 (en) |
| JP (1) | JP5506924B2 (en) |
| KR (1) | KR101601358B1 (en) |
| CN (1) | CN102471080B (en) |
| BR (1) | BR112012000033B1 (en) |
| CA (1) | CA2767072A1 (en) |
| ES (1) | ES2606713T3 (en) |
| HU (1) | HUE031263T2 (en) |
| MX (1) | MX2011013371A (en) |
| PL (1) | PL2448865T3 (en) |
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- 2009-07-03 WO PCT/CN2009/000754 patent/WO2011000133A1/en active Application Filing
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| EP3743466B1 (en) | 2018-01-23 | 2021-11-17 | Worlée-Chemie GmbH | Binder composition and use thereof |
| EP3743467B1 (en) | 2018-01-23 | 2021-11-17 | Worlée-Chemie GmbH | Binder composition and use thereof |
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| US11802217B2 (en) | 2018-01-23 | 2023-10-31 | Worlee-Chemie Gmbh | Binder composition and use thereof |
Also Published As
| Publication number | Publication date |
|---|---|
| US20120029136A1 (en) | 2012-02-02 |
| BR112012000033B1 (en) | 2018-12-04 |
| KR101601358B1 (en) | 2016-03-08 |
| PT2448865T (en) | 2016-11-16 |
| US9725326B2 (en) | 2017-08-08 |
| RU2516830C2 (en) | 2014-05-20 |
| EP2448865B1 (en) | 2016-09-21 |
| ES2606713T3 (en) | 2017-03-27 |
| MX2011013371A (en) | 2012-02-21 |
| KR20120101317A (en) | 2012-09-13 |
| EP2448865A4 (en) | 2013-05-22 |
| CA2767072A1 (en) | 2011-01-06 |
| PL2448865T3 (en) | 2017-05-31 |
| TWI476151B (en) | 2015-03-11 |
| HUE031263T2 (en) | 2017-07-28 |
| JP2012531379A (en) | 2012-12-10 |
| RU2012103381A (en) | 2013-08-10 |
| BR112012000033A8 (en) | 2016-10-04 |
| JP5506924B2 (en) | 2014-05-28 |
| ZA201200034B (en) | 2012-09-26 |
| BR112012000033A2 (en) | 2016-03-15 |
| CN102471080B (en) | 2015-04-08 |
| CN102471080A (en) | 2012-05-23 |
| TW201116486A (en) | 2011-05-16 |
| EP2448865A1 (en) | 2012-05-09 |
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