SE432094B - HYDROPHOBERATED FELLOW-SILIC ACID, PROCEDURE FOR ITS PREPARATION AND USE OF ITS SAME - Google Patents

Description

7807329-3 2 Water wettability ¿0, l Carbon content% 2,5 É 0,6 Water uptake at 30 ° C and + 30% relative humidity% 1,2 - 0,4 at 30 ° C and + 70% relative humidity% 1, In a preferred embodiment of the hydrophobic precipitated silicic acid according to the invention, the drying loss may be from 2.5 to 0.0%. The conductivity of the hydrophobic precipitated silicic acid according to the invention can be 50 - 300¿uS. The water-wettability can amount to 0 - 0.05.

The invention also relates to a process for the preparation of the hydrophobic precipitating silicic acid according to the invention, which process is characterized in that in an original precipitating suspension of a precipitating silicic acid having the following physicochemical properties (properties obtained after separation of the precipitating suspension for intensive long-term drying of the hydrophilic precipitating silicic acid): EET surface area according to DIN es 131 m2 / g _ 160 É Average size of the primary particles over EM uptake nm 14 - 22 Drying loss according to DINO 55 921 after 2 hours. at 105 DEG C. 2.5 ~ 4.0 The first annealing (calculated on the 2 hours at 105 DEG C. dried substance) according to DIN 55 921%% 3.5 pH value Ci 5% aqueous slurry) according to DIN 53 200 7.0 - 8.5 Conductivity (in 4% water slurry) y / uS ¿6 00 Shake density for the non-aerated substance according to DIN 53 194 g / l 140 SO content (based on the 2 hour at 10 ° C dried substance)% 0.3 40 O Na O content (based on the 2 hour f at 105 ° C dried substance)% 0.3 7807329-3 feeds a hydrophobicizing agent while maintaining an alkaline pH value, after-stirring the mixture thus obtained, separating, long-term dryers, tempering the obtained product for 60-180 minutes, preferably 70-130 minutes at a temperature of 200-400 ° C and grinding.

The original precipitation suspension of the hydrophilic precipitating silicic acid can be obtained as follows: In a reaction vessel a volume of water is charged in advance.

Slowly add 0.5 - 0.25 parts by volume of water glass solution (proportion SiO 2: Na 2 O = 3.5 and 26% SiO 2) and 0.015 - 0.025 parts by volume of H 2 SO 4 (96%) with stirring to the publisher, during which an alkaline pH is carefully observed. -value in the mixture. After completion of the addition of water glass and H 2 SO 4, the pH value of the suspension obtained is in the slightly alkaline range.

As hydrophobicizing agents, organosilicon compounds which are reacted with the hydrophilic precipitated silicic acid suspended in the aqueous phase can be used those which have hitherto been used for such a reaction. Preferred are those of the general formula (R 3 Si) aZ, wherein R represents the same or different, monovalent, optionally substituted and / or polymeric hydrocarbon groups, a is 1 or 2 and Z is halogen, hydrogen or a group of the formula -OH, -OR, -NRX, -ONR2, -SR, OOCR, -O-, -N (X) ~ or -S-, wherein R has the meaning given above and X is hydrogen or has the same meaning as R. Example of such organosilicon compounds are hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trime- tyletoxisilan, triorganosilylmerkaptan such as trimethylsilyl mercaptan triorganosilylacylatersåsom vinyldimetylacetoxi- silane, triorganosilylaminersåsom trimetylsilylisopropylamin, trimetylsilyletylamin, dimetylfenylsilylpropylamin and vinyl dimetylsilylbutylamin, triorganosilylaminoxiföreningar as 7807329-3 dietylaminoxitrimetylsilan and dietylaminoxidimetylfenylsilan, _vidare hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane and 1,3-diphenylhexamethyldisilazane.

Further examples of organosilicon compounds which can be reacted with aqueous, alkaline phase-suspended, hydrophilic precipitated silicic acid within the scope of the invention are dimethyldichlorosilane, dimethyldiethoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilanethoxymethanylethoxymethanimethane Si-bonded hydroxyl group with 2 to 12 siloxane units per molecule.

Mixtures of different organosilicon compounds can be reacted with the precipitated silicic acid present in the original aqueous precipitating suspension. In a preferred embodiment of the invention, dimethyldichlorosilane can be used as the hydrophobing agent.

The organosilicon compounds which are reacted with the hydrophilic precipitated silica present in the aqueous alkaline suspension are preferably used in amounts of 5 to 30% by weight, based on the weight of the precipitated silicic acid to be reacted therewith. The invention further relates to the use of the hydrophobic precipitated silicic acid according to the invention as reinforcing fillers in elastomer-curable compositions based on diorganopolysiloxanes. Thus, in a preferred embodiment, the hydrophobic precipitated silicic acid of the invention can be used in 1-component silicone rubber sealants.

In addition, they can be used in room temperature curable organopolysiloxane elastomers, such as preferably, for example, in a two-component silicone impression composition. According to the invention, the hydrophobic precipitated silicic acid can be used in hot-vulcanizing diorganopolysiloxane elastomer. These can, for example, be used as cable insulation compound.

As diorganopolysiloxanes you can use all diorganopolysiloxanes that have been used so far resp. could be used as a basis for organopolysiloxane elastomers at room temperature (RTV) only slightly elevated temperature (LTV) or high temperature (HTV) curable resp. hardening masses. They can be represented, for example, by the general formula Z si (R) -o- E10:) 01- 3- R __z n 3-21 2 x 1 (š_àn wherein R denotes the same or different, monovalent, optionally substituted and / or polymeric hydrocarbon groups, Z represents a hydroxyl group, hydrolysable group and / or hydrolyzable atom or in the case of only slightly elevated temperature curable masses of alkenyl groups, n is 1, 2 or 3 and x is an integer having a value of at least 1 .

Examples of hydrocarbon groups R are alkyl groups such as methyl, ethyl, propyl, butyl, hexyl and octyl groups; alkenyl groups such as vinyl, allyl, ethylallyl and butadienyl groups; and aryl groups such as phenyl and tolyl groups.

Examples of substituted hydrocarbon groups R are in particular halogenated hydrocarbon groups, such as the 3,3,3-trifluoropropyl group, the chlorophenyl and bromotolyl group; and cyanoalkyl groups, such as the beta-cyanethyl group.

Examples of polymeric (also as "modifying" designable) substituted and unsubstituted hydrocarbon groups R are over carbon to silicon bonded polystyryl, polyvinyl acetate, polyacrylate, polymethacrylate and polyacrylonitrile groups. 7807329-3 At least the predominant part of the groups R consists mainly of methyl groups, mainly due to the easier availability. The optionally present other groups R are in particular vinyl and / or phenyl groups.

Particularly in the case of water-storable masses which, during the exclusion of water, can be stored at room temperature to elastomer-curing masses, these are usually hydrolysable groups. Examples of such groups are amino, amido, aminoxy, oxime, alkoxy, alkoxyalkoxy (eg CH 3 OCH 2 CH 2 O-), alkenyloxy (eg H 2 C = (CH 3) CO-), acyloxy and phosphate groups. In particular due to the easier availability, acyloxy groups, in particular acetoxy groups, are preferred as Z. However, excellent results are also obtained, for example, with oxime groups, such as those of the formula -ON = C (CH 3) (C 2 H 5), as Z.

Examples of hydrolyzable atoms Z are halogen and hydrogen atoms.

Examples of alkenyl groups Z are in particular vinyl groups.

Same or different Z can be attached to a Si atom.

Mixtures of different diorganopolysiloxanes can be used.

The hydrophobic precipitated silicic acid according to the invention is prepared by mixing with diorganopolysiloxanes and possibly additional substances at room temperature or only slightly elevated temperature, possibly after the addition of crosslinkers, to elastomer-curable masses, in particular with the exclusion of water-storable, upon access of water at room temperature to elastomer curing masses. This mixing can take place in any known manner, for example in mechanical mixing devices.

Preferably, the fillers according to the invention are used in amounts of S-50% by weight, calculated on the total weight of the masses which can be cured to "$ 0? 329-3 elastomers. In the case of HTV organopolysiloxane elastomers 5 - 50% by weight can be used. In the case of RTV organopolysiloxane elastomers, 5 to 35%, preferably 5 to 25% by weight can be used.

If in the reaction-prone diorganopolysiloxanes which contain terminal units as the only reaction-prone terminal units there are those with Si-bonded hydroxyl groups, then these diorganopolysiloxanes must, in order to be cured in a manner known per se, resp. to be transferred to through the water contained in the air, possibly with the addition of additional water, to elastomer-curing compounds are reacted with crosslinking agent, possibly in the presence of a condensation catalyst in a known manner. In the case of HTV diorganopolysiloxane elastomers, organic peroxides can be used at correspondingly high temperatures, for example bis-2,4-dichlorobenzoyl peroxide, benzoyl peroxide, dicumyl peroxide, tert. butyl perbenzoate or tert. butyl peracetate is used as a crosslinker.

As hot-vaporizing organosiloxanes one can use those whose organic substituents consist of methyl, ethyl, phenyl, trifluoromethylphenyl {: F3CC6H4-1 or trimethylsilylmethylene groups ç (CH3) 3SiCH2-J, for example dimethyl-, diethyl-, phenylmethyl-, phenylethyl- , ethylmethyl, trimethylsilylmethylenemethyl, trimethylsilylmethyleneethyl, trifluoromethylphenylmethyl or trifluoromethylphenylethylsiloxanes resp. copolymers of such compounds. In addition, the polymers may contain limited amounts of diphenylsiloxane, bis-trimethylsilylmethylensiloxane, bis-trifluoromethylphenylsiloxane units as well as siloxanes having units of the formula RSiO1, 5 and R3SiOOI5, wherein R is one of the above groups.

Examples of crosslinkers are in particular silanes of the general formula R4_tsiz't, in which R has the meaning given above, Z represents a hydrolysable group and / or a hydrolysable atom and t is 3 or 4. The above examples concerning hydrolyzable groups Z and hydrolyzable atoms Z also apply in full to the hydrolyzable groups Z 'and the hydrolyzable atoms Z'.

Examples of silanes of the above formula are methyltriacetoxysilanes, isopropyltriacetoxysilane, isopropoxytriacetoxysilane, vinyltriacetoxysilane, methyltrisdietylaminooxysilane, methyltris (-cyclohexylamino) -silano-methylsilan-methylsilan-methylsilan-methylsilan-methylsilan-methylsilane.

Instead of or in mixture with silanes of the formula given above, it is also possible to use, for example, polysiloxanes, which per molecule contain at least 3 Z 'groups resp. atoms in which case they do not pass through Z 'groups resp. atoms saturated the silicon valencies are saturated by siloxic acid atoms and possibly R groups. The best known examples of crosslinkers of the latter type are polyethylsilicate with a SiO2 content of about 40% by weight, hexaethoxydisiloxane and methylhydrogenpolysiloxanes.

The best known examples of condensation catalysts are tin salts of fatty acids, such as dibutyltin dilaurate, dibutyltin diacetate and tin (II) octoate.

If in the reaction-prone diorganopolysiloxanes which contain terminal units as the only reaction-prone, terminal units, there are those with alkenyl groups, then the curing to elastomers can take place in a known manner with organopolysiloxanes, which on average contain at least 3.Si-bonded hydrogen. atoms per molecule, such as methylhydrogenpolysiloxane, in the presence of catalysts that promote the storage of alkenyl groups to Si-bonded hydrogen, such as platinum (IV) -chloric acid. At room temperature or only slightly elevated temperature (usually 50 - 80 ° C) there are curable (LTV) pulps.

As a further example of the curing to elastomers can end- TSG? (IJ FJ ao I 04) it is mentioned by means of polycyclic organopolysiloxanes in the presence of equilibration catalysts, such as phosphoronitrile chlorides.

Of course, in addition to diorganopolysiloxanes, precipitated silicic acid according to the invention, bridging silicas and crosslinking catalysts, the elastomer-curable compositions may optionally contain conventional fillers commonly used or often curable in elastomeric compositions. Examples of such substances are fillers with an area below 50 m2 / g, such as quartz flour, diatomaceous earth, further zirconium silicate and calcium carbonate, further untreated, pyrogenically produced silica, organic resins such as polyvinyl chloride powder, organopolysiloxane resins, fibrous fillers, fibrous glass fibers and organic fibers, pigments, soluble dyes, perfumes, corrosion inhibitors, agents which stabilize the masses against the action of water, such as acetic anhydride, agents which delay curing, such as benzotriazole, and plasticizers, such as dimethylsoloxyl groups which are terminally blocked by trimethylsiloxy groups.

The stated combination of physico-chemical substance data for the hydrophobic precipitated silicic acid according to the invention leads, thanks to its excellent dispersibility, to a highly effective reinforcing filler. The significantly reduced equilibrium moisture content compared with the known precipitated silicas entails advantages in the processing, for example in the case of tn fl clumsy vulcanization, in which, in comparison with the use of the known, hydrated precipitated silicic acid, less blown vulcanizate is obtained. The low electrolyte content in combination with the low moisture content ultimately leads to good electrical properties for the vulcanizate. In cold-hardening silicone rubber sealing compositions, the hydrophobic precipitated silicic acid according to the invention shows advantages due to its low water content with regard to the storability of the uncured mes.

The invention is further illustrated by the following examples which describe the preparation, physicochemical data and use of the hydrophobic precipitated silicic acid according to the invention. N Example gel l Preparation of the original precipitate suspension of a hydrophilic precipitated silicic acid for subsequent wet hydrophobing.

In a reaction vessel, 50.0 m3 of water are charged in advance. While stirring, slowly add 9.2 m of water glass solution and 0.9 m 3 of H 2 SO 4 to the publisher, observing an alkaline pH in the mixture during the addition. After completion of the addition of water glass and H 2 SO 4, the pH value of the suspension obtained is in the alkaline range.

To characterize the hydrophilic precipitated silicic acid, part of the suspension is filtered, washed with low electrolyte, then dried in a drying cabinet at 105 ° C to constant weight and ground by means of a pin mill.

The resulting hydrophilic precipitated silicic acid has the following physicochemical properties: BET surface area according to DIN 66 131 m2 / g 155 Average size of the primary particles from EM uptake nm 18 - 20 Drying loss according to DIN 0 55 921 after 2 hours at 105 C% 3.0 Annealing loss based on the 2 hr. at 105 ° C dried substance) according to DIN 55 921% 3.3 pH value (in 5% aqueous slurry) according to DIN 53 200 7.7 Conductivity (in 4% aqueous slurry) uS 240 Shake density for the non-deaerated substance according to DIN 53 194 g / 1 140 SO -halš (based on the 2 h. dried at 105 ° C)% 0.22? 8Û '? 329 ~ 3 ll Na O-haate (based on the 2 hours at 105 ° C the substance dried)% 0.18 Carrying out the determination of the electrical conductivity.

A sample of 4.0 g of silicic acid was heated with 50 ml of completely desalinated water in a 150 ml beaker and boiled with stirring. Then the suspension is transferred to a 100 ml graduated flask, cooled and filled with completely desalinated water up to the mark. After shaking, the measuring cell of the conductivity measuring device is first pre-flushed with the suspension to be measured and then filled resp. the measuring cell is immersed in the suspension. The electrical conductivity is read on the measuring device and the temperature of the suspension during the measurement is determined.

Calculation: The electrical conductivity is given in / ns attributed to 20 ° C.

Example 2 Preparation of a hydrophobic precipitated silicic acid obtained by wet hydrophobing according to the invention.

To 10 l of an original aqueous precipitating suspension of the precipitating silicic acid according to Example 1 with a solids concentration of 57.9 g / l is added while observing a pH value for the suspension of 8.5 193 g of dimethyldichlorosilane for a period of 30 minutes and for intense stirring. After a subsequent mixing time of 60 minutes, the precipitated silicic acid coated with dimethyldichlorosilane is separated off to 25%, dried at 100 DEG C., tempered at 350 DEG C. for 2.0 hours and then ground.

The resulting hydrophobic precipitated silicic acid exhibits the following physicochemical properties:? .8Û7329 ~ 3 12 solvents at 1 ° C according to DIN 55 921% 5.5 thereof moisture at 100 ° C according to DIN 55 921% 0.4 pH value according to DIN 53 200 8.0 EET surface according to DIN 66 131 m2 / g 89 Water wettability f% 0,05 Conductivity IMS 160 C content _% 2,2 Water uptake at 30 ° C and 30% relative humidity%, 1,2 at 30 ° C oc 70% relative humidity -% 2,0 Shake density of the non-deaerated substance according to DIN ss 194 ~ g / 1 130 Determination of the water-wettability of hydrophobic silicic acids The following analytical method describes the determination of the water-wettable proportions of hydrophobic silicic acid.

Carrying out the determination: 0.2 g of hydrophobic silicic acid is charged with 50 ml of distilled water into a 250 ml shaker funnel and shaken for one minute using a highest speed Turbula mixer.

After a short time of depositing the wet portions, 45 ml of the suspension is discharged after gentle swirling in an evaporation bowl, evaporated on a water bath and then dried at 105 ° C. Remaining after drying. 100 =% water-wettable Calculation: proportions Weighted amount Determination of moisture uptake In determining the moisture uptake, the maximum or time-dependent moisture uptake for silicas is determined as a function of temperature and relative humidity.

Carrying out the determination: Weigh, to the nearest 0,1 mg, a silica sample of approximately 2,5 g in a dry dewaxed weighing glass and dry for two hours at 10 ° C.

After cooling, the weight of an analysis scale is determined. The open-wave glass with the sample is then stored in a climate cabinet at a predetermined temperature and relative humidity. You can then determine either a moisture uptake time diagram or the maximum moisture uptake.

The determination is usually carried out at 30 ° C and 30% relative humidity 30 ° C and 70% relative humidity. Calculation: 9 weighted amount, 100% moisture absorption and weighted amount X) x) dried sample Example 3 Use of a hydrophobic precipitated silica according to the invention in cold-curing 1-component silicone rubber compounds.

In this example, the hydrophobic precipitated silicic acid according to the invention in Example 2 is tested as a reinforcing filler and thixotropic agent in a 1-component silicone rubber sealant (cold vulcanizing).

In the experiments, the silicic acid Aerosil l50R from the company Degussa and the commercial product HDK H2000 from the company Wacker are tested as a comparison in the same silicone rubber compound.

HDK HZOOOR is a highly dispersed silicic acid which is produced by flame hydrolysis of volatile silicon compounds and then hydrophobized by reaction with organosilanes. It is therefore densely coated with trimethylsilyl groups at the surface and has the following physicochemical properties: Surface according to BET mz / g 170 ï 30 SiO2 content weight% _> 97 Shake weight unpressed g / l approx. 90 Humidity according to DIN 53 1980 Procedure A 2 tim. at 105 C wt% ¿0.6 Annealing loss according to DIN ~ 52 911 2 hrs. at 1000 C wt% <2.5 pH value according to DIN 53 200 in 4% dispersion in water-methanol = 1: 1 6.7 - 7.7 Grit according to Mocker (DIN 53 580) wt% <0, Adherent HCl wt% <0.020 Al2O3 wt% ¿0.05 Fe2O3 wt% ¿0.005 TiO2 wt% ¿0.003 c wt% in ε 3 Aerosil 150R is a pyrogenically produced silicic acid with the following physicochemical properties: Surface according to BET m2 / g 150 in 50 Average size for primary particles nm 14 Drying loss (DIN 53 198 / A) (2 hours at 105 C). 0.5 Annealing loss (DIN 52 911) (2 hours at 1000 DEG C.) 1 pH value (DIN 53 200) (in 4% aqueous dispersion) 3.6 - 4.5 SiO2 2)% 99.8 Al2O3 % 0.05 Fe2O3% 0.003 TiO2% 0.03 HCl% 0.025 Grit according to Mocker (DIN 53 580)% 0.05 Wetting ratio K hydrophilic x) based on the 2 hr. at 1000 ° C the substance was annealed. The following recipe is based on acetate hardener: 68.4 parts by weight of dimethylpolydisiloxane with hydroxyl end groups viscosity 50,000 cSt. 271 parts by weight of dimethylpolysiloxane with trimethylsiloxy end groups, viscosity 1000 cSt. 4.5 parts by weight of methyltriacetoxysilane (crosslinker) 0.005 parts by weight of dibutyltin diacetate plus silicic acid to be tested.

The silicic acid is incorporated after the bridge builder has been added to an evacuable planetary mixer.

The still pastear fi e joint sealant resp. its seven days in air-cured vulcanizates were then subjected to the following test: a) extrudability according to ASTM 2452-69 b) durability according to the Hütchen method c) modulus at 100% elongation according to DIN 53 504 d) tensile strength according to DIN 53 504 e) elongation at break according to DIN 53 504 f ) tear propagation strength according to DIN 53 515 g) Shore-A hardness according to DIN 53 505 The results of these tests are summarized in the following Table I. In doing so, the following technical advances can be determined compared to the known pyrogenic hydrophilic silicic acids Aerosil 150 and the hydrophobic silicic acid HDK H2000: Aerosil 150 can only be incorporated up to 8% into the 1-component sealing compound. A higher degree of filling leads to a difficult-to-process pulp. The level obtained at a degree of filling of 8% for the mechanical values corresponds to the state of the art up to now.

On the other hand, with the silicic acid according to the procedure of Example 2, at a degree of filling of 20%, a significantly higher level is achieved for the mechanical values which meet the requirements set for high-strength sealing compositions. The extrusionability of the composition is completely satisfactory at this mass. Storage stability is also good.

On the other hand, at a degree of filling of 20%, the value level of the mechanical values for the commercial product is HDK H2000, which represents the state of the art; not comparable to the vulcanizate filled with the precipitated silicic acid according to the invention. This applies in particular to the tensile strength and the elongation at break, both of which are 45% below the corresponding values for the silicic acid according to the invention. Only when raising the fill rate to 25% can the data picture for HDK H2000 become fully comparable. Consequently, it was surprisingly found that using only 20% of the precipitated silicic acid according to the invention, a to some extent clearly better property image (a 25% HDK HZOOO) can be achieved. With the noticeably low production costs in comparison with pyrogenic hydrophobic silicic acid, this opens up further possible uses.

Table I Test of a hydrophobic precipitated silicic acid according to the invention according to Example 2 in a 1-component silicone sealant compared to fumed silica according to the prior art.

G3 C) N! Silica type Storage Stability- Resistance injectable- TYPE! (%) * Tet (Hütchen method unit (g / min) Silica in V enL ex_ 2: ao good good ß after o days Acrosil 150 3 3 HH 8 O - š ^ 28 HDX Uzonü; 20 HH 19 "0 3 22 .. 28 -: g - 25 n 'ui]' l" Q {l: f; u | I: | _._- ..> ..... - f. Ä vikt -% calculated on the total mixture 7807329-3 17 a ^! 1 I% Silicic acid type M ° du1 100 'Tensile-% Fracture- = Rivfort-; Shore-A- ä firmness increase âí: 3: še_; hardness É T ._.

YP (d) * 2 I snn fl ighe fi I P (N / mm) (N / mm) (ß) (N / mm) É; Silica E å, enl- GX- 2 20 = u, 6 45 780 16 É 18. '' u ''s Åerosil 150 8 3.0 10 # 00 2,5 É 20. 3 ¿I a Unn nzooo 20 5.0 25 430, 1 "§ 2h §! 1 3 f 25 6.0 å 45 H90 18; 32 § *% by weight, calculated on the total mixture Example 4 Preparation of a obtained by wet hydrophobing , hydrophobic precipitated silicic acid according to the invention.

To 12 liters of an original precipitated suspension of the precipitated silicic acid of Example 1 with a solids concentration of 57.9 g / l is added while maintaining a pH value for the suspension of 8.5 l75.6 g of dimethyldichlorosilane for a period of 30 minutes for intense stirring. After a subsequent mixing time of 60 minutes, the precipitated silicic acid coated to 20% with dimethyldichlorosilane is dried at 105 ° C, tempered at 300 ° C for 1.5 hours and then ground. The precipitated silicic acid obtained has the following physicochemical properties: solvent loss at 100 ° C according to DIN 55 92l% 5.5 thereof moisture at 100 ° C according to DIN 55 921% 0.4 pH value according to DIN 53 200 7, 5 BET surface according to DIN see 131 amz / g 94 Water wettability 0.06 Conductivity / uS 9 2 Cahalt% 2.1 Water uptake 'at 3000 and Z 30% relative humidity% 1.3 at 30 ° C and 70 % relative humidity% 2.0 Shake density of the non-aerated substance according to DIN 53 194 g / l 137 Example 5 * Use of a hydrophobic precipitated silicic acid according to the invention in cable masses based on organopolysiloxanes.

In this example, the hydrophobic precipitated silicic acid of Example 4 according to the invention is incorporated as a reinforcing filler in hot-vaporizing silicone rubber and is tested for internal resistivity to the heat-produced vuikanisate.

Thanks to its excellent dielectric properties, hot-vaporizing silicone rubber is also used as a high-quality cable insulation material. As the reinforcing filler, highly active fumed silica is usually used in this case due to its uniformity and favorable dielectric properties. It is known that the insulation properties are further improved if the cured masses are subjected to a further longer tempering process (at least 6 hours) at higher temperatures (about 200 ° C). In the tests in this example, the following recipe was used: 100 parts by weight of dimethylpolysiloxane with trimethylsiloxy end group per and a content of vinyl groups 40 parts by weight of silicic acid 1.4 parts by weight of bis-2,4-dichlorobenzoyl peroxide (50% as paste in silicone oil) soaking = 7 min. at 13o ° c Temperature: 0 or 6 hours. at ZOOOC of 7329 ~ 3 19 Conditioning: 24 hrs. at 22 ° C and 80% relative humidity.

The results of the test in comparison with Aerosil 200R X), a fumed silica from Degussa, are shown in Fig. 1.

As can be seen from the curves, the precipitated silicic acid according to the invention can surprisingly achieve as good resistivity values as with the pyrogenic silicic acid. Furthermore, it was surprisingly found that with the silicic acid according to the invention the good electrical properties could be achieved even without the above-mentioned expensive tempering process. In addition to the more favorable manufacturing costs, there is an additional advantage here for the precipitated silicic acid according to the invention.

X) Aerosil 200R is a highly dispersed silicic acid produced by flame hydrolysis of volatile silicon compounds which has the following physicochemical properties: Surface according to BET mz / g zoo i '25 Average size of primary particles mn 12 Shake volume (DIN 53 194) ml / 100 g 1700 densified product ml / 100 g 1000 drying loss (DIN 53 198 0 procedure A) 2 hours at 105 C% by weight ¿1.5 Annealing loss (DIN 52 911) 2 hours. at 1000 DEG C.% by weight (1.5 pH value (DIN 53 200) in 4% aqueous dispersion - 3.6 - 4.3 SiO2% by weight> 99.8 Al2O3 "Fe2O3" TiO2 " 03 HCl "<0.025 Grit according to Mocker (DIN 53 580)" 0.05

Claims (5)

1. 780? 329-3 ZC PATENT REQUIREMENTS 1. Hydrophobic precipitated silicic acid, characterized by BET surface according to DIN see 131 _ m2 / g 110 É 40 Average size for primary particles from EM recordings nm 15 - 22 Drying loss according to DIN 55 921 after 2 hours. at 105 c% <2.5 Glow reduction (based on the 2 hr. at 105 C dried substance) 1 + according to DIN 55 921% 5.5 1,5 pH value (in 5% water-methanolic I + slurry) according to DIN 53 200 7.5 - 1.0 Conductivity (in 4% water- methanolic slurry) / JS (6 0 0 Shake density for the non-aerated - + substance according to DIN 53 194 g / 1 130 - 40 Water wettability '( 0.1 Carbon content% 2.5 É 0.6 Water uptake at 30 ° C and + 30% relative humidity% 1.2 - 0.4 at 30 ° C and + 70% relative humidity% 1.5 - 0.5 Process for the preparation of the hydrophobic precipitated silicic acid according to Claim 1, characterized in that in an original precipitating suspension of a precipitating silicic acid having the following physicochemical properties (properties obtained after separation of the precipitating suspension, intensive washing procedure) with water and long-term drying of the hydrophilic precipitating silicic acid): BET surface area according to DIN see 131 m2 / g 160 in 40 Average size of the primary particles from EM recordings nm 14 - 22 Drying loss according to DIN 55 921 after 2 hours at 105 C% 2, 5 - 4.0 Annealing loss (based on the 2 hours dried at 105 DEG C.) according to DIN 55 921% 3,5 pH (in 5% aqueous slurry) according to DIN 53 200 7.0 - 8, 5 l + 1.0 7807329-3 21 Conductivity (in 4% aqueous slurry) jus <soo Shake density of the non-aerated substance according to DIN 53 194 g / 1 140 - 40 SO -halš (based on the 2 hours at 105 DEG C. dried substance)% (_0.3 Na2O-halo (base erad on the 2 hr. at 105 DEG C. the substance was dried (% 0.3) in a medium while maintaining an alkaline pH, stirring the mixture thus obtained, separating the hydrophobic precipitated silica, drying for a long time, the product obtained tempering for 60 to 180 minutes, preferably 70 to 130 minutes. minutes at a temperature of 200 - 4000 and grind. Use of a hydrophobic precipitated silicic acid which is characterized by an EET surface according to DIN, see 131 mz / g 110 in 40 Average size of primary particles 7 from EM recordings nm 15 - 22 Drying loss according to DIN 55 921 after 2 hours. at 105 c% (2.5 Glow reduction (based on the _.M 2 hr. at 105 C dried substance) according to DIN ss 921 s _ 5.5 1 ”1.5 pH value (in 5% aqueous methanolic + slurry) according to DIN 53 200 7.5 - 1.0 Conductivity (in 4% ~ - water-methanolic slurry) PS (600 Shake density for the non-deaerated '+ substance according to DIN 53 194 g / 1 130 - 40 hydrogen wettability < 0.1 Ke1he1t% 2.5 i '0.6 Water uptake at 30 ° C and + 30% relative humidity% 1.2 - 0.4 at 30 ° C een + 70% relative humidity% 1.5 - 0.5 7807329- 3 22 as reinforcing agents in elastomer-curable masses based on diorganoplysysiloxanes. Use according to claim 3 in 1-component silicone rubber joint sealants. Use according to claim 3 in silicone rubber cable masses.