EP2147051A2 - Use of ferrocene or ferrocene-derivatives for producing insulators - Google Patents

Abstract

The invention relates to the use of ferrocene or ferrocene-derivatives for producing hardenable polyorganosiloxane rubber compositions that can be used as high-voltage insulators. The elastomers containing ferrocene or ferrocene derivatives have an increased arc resistance and/or creep resistance.

Description

 Use of ferrocene or ferrocene derivatives for the production of insulators

The invention relates to the use of ferrocene or ferrocene derivatives for the production of insulators, in particular high-voltage insulators. Ferrocene or derivatives thereof in particular increase the arc resistance and / or tracking resistance of the insulators. The invention further relates to curable polyorganosiloxane rubber compositions containing ferrocene or derivatives thereof, cured polyorganosiloxane rubber compositions obtainable by curing said curable organosiloxane rubber compositions, elastomeric molded articles therefrom, such as insulators such as high voltage insulators, anode caps, cable insulators, cable terminations , Spark plug caps, etc.

High-voltage isoizers can be made of ceramic materials but also of duromer, thermoplastic or elastic materials. The use of elastomer materials such as EPDM, but in particular of silicone elastomers, requires stabilization against damage caused by electrical flashovers such as electric arcs or leakage currents, in particular insulator surfaces that have become capable of conductivity due to environmental effects. The life of elastomeric high voltage insulators is limited, inter alia, by the resistance of the elastomeric material to these effects. In particular, the destruction of the surface by erosion of glow discharges, leakage currents and / or arcs are a problem for the life of an insulator. The literature teaches numerous measures for stabilizing insulating silicone elastomer surfaces. The technically most important measure is the addition of relatively large amounts of oxidic fillers such as SiO ₂ , ZnO, Zn-borate, Al (OH) ₃ , TiO ₂ , CeO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , ZrO ₂ , low-melting ceramic glasses or frit compositions, etc. For stabilizing arc and Kriechstromfesten Siükonelastomeren was proposed in US 3,965,065 or EP-AO 928 008, aluminum oxide hydroxide ( ^' aluminum trihydrate ^' ) to use. EP-AO 218 461 discloses how, by addition of platinum and the like TΪO ₂ can improve the resistance to the damage caused by arcing. Finally, WO 02-24813 discloses compositions which have sufficiently good arc resistance without the use of pigmenting fillers or fillers which modify the dielectric properties of silicones. Ferrocene has been described for the thermal stabilization of silicone oils (EP-A-0166279). Furthermore, the use of combinations of ferrocene and quinoline compounds for improving the dielectric strength of polyolefins, in particular polyethylene, has been disclosed. Furthermore, DE-A-1116396 describes the use of 1, 1 'bis (trtorgano-silyl) dicyclopentadienyl iron as a stabilizer for polyorganosiloxanes, in particular for the preparation of lubricants, hydraulic fluids and damping fluids. Similarly, DE-A1-2135984 discloses the use of carbamoyl-bonded metallocene organosilane or siloxane compounds to stabilize polydimethylsuloxane oils. However, ferrocene or ferrocene derivatives-containing curable silicone elastomer compositions for insulators are not known from the prior art.

In the search for effective additives, problems such as mass loss and the reduction of the number of holes in one of the standard tests for evaluation of high-voltage creep current strength such as DIN 57 303 / IEC 587 VDE 303 of insulators could not yet be solved satisfactorily, especially if the amounts of expensive additives such as Platinum compounds should be kept low in quantity.

The inventors found now completely surprising how to prevent the surfaces of high voltage insulators against destruction by glow discharges, in particular based on polyorganosiloxane elastomers, in which is achieved by addition of very small amounts of ferrocene or ferrocene derivatives even at low platinum contents excellent stabilization of the insulator surfaces based on polyorganosiloxane elastomers against damage caused by high-voltage creepage currents. The invention thus provides the use of ferrocene or ferrocene derivatives for the preparation of insulators, in particular high voltage insulators, based on polyorganosiloxane elastomer compositions.

Insulators in the sense of the invention are, in particular, those which make it possible to insulate electrical currents at voltages above approximately 0.2 kV.

Insulators, in particular high-voltage insulators, for the purposes of the invention are those based on polyorganosiloxane-eggastomer compositions, i. they have a polymer matrix consisting essentially of polyorganosiloxanes. They are thus preferably obtained by curing curable organopolysiloxan rubber compositions. Preferred curable polyorganosiloxane rubber compositions contain the following components:

a) one or more polyorganosiloxanes having reactive groups, b) one or more crosslinkers and / or chain extenders for the

Component a), c) one or more transition group metals selected from platinum, rhodium and ruthenium, or compounds thereof, d) one or more ferrocene compounds, e) optionally one or more fillers.

Component a)

Polyorganosiloxane polymer of component a) having reactive groups are, in particular, those whose reactive groups can be reacted free-radically or by a hydrosilylation reaction with themselves or with a crosslinker or chain A extenders can be reacted to form and cure into elastomeric moldings, extrudates or coatings.

¹ shear rates of 1 s ^~ keitsgefälle D), in accordance with the invention used in silicone rubber compositions used are preferably alkenyl-containing polyorganosiloxanes a) with a viscosity range of 0.025 to 100,000 Pa (25 ⁰ C. The polyorganosiloxane a) may consist of a uniform polymer or mixtures of different Polyorganosiioxane a1) or a1) and a2) and / or a3). Generally, the polyorganosiloxane A) comprises siloxane units selected from the group consisting of the units M = R ¹ R ₂ SIOI _{/ 2,} D = R ¹ RSi0 _2/2, T = R ¹ Si0 _3/2, Q = SiO ₄ ^ and optionally the divalent units R ² , wherein R, R ¹ and R ^{2 are} as defined below.

The polyorganosiloxane a) can be described by the general formula (I):

[M _a D _b T _c Q _d ] m (I)

Therein, the siloxy units M, D, T and Q can be distributed in blocks or randomly in the polymer chain and linked together. Within the polyorganosiloxane chain, each siloxane unit may be the same or different. The indices are preferably as follows and are expediently selected in accordance with the desired viscosity: m = 1-1000 a = 1-10 b = 20-10000 c = 0-50 d = 0-1.

The aforementioned polyorganosifoxanes a) or mixtures thereof containing the polyorganosiloxanes a1) and a2), preferably have a structure of the general formula (Ia) for the polyorganosiloxanes a1), which are substantially linear and have a content of unsaturated organic groups, which is preferably between 0.22 to 7.4 mol.% Based on Si atoms and correspondingly at 0.03 to 1, 0 mmoi / g for vinyl-containing polydimethylsiloxanes. The content of unsaturated organic groups in mmol / g preferably refers to polymethylvinyldimethylsiloxanes and is to be adjusted within the given viscosity limits to siloxy groups having a higher molecular weight.

R ¹ R ₂ SiO (R ¹ RSiO) _b iSiR ₂ R ¹ (Ia), preferably of the formula (Ia ')

R ¹ R ₂ SiO (R ₂ SiO) MSiR ₂ R ¹ (Ia ') where

R, R ¹ and R ^{2 are} as defined below and b1 = 20-10,000.

In the above radicals, R is an organic group, which is preferably excluded selects: unsubstituted and substituted hydrocarbon radicals, such as n-, iso-, tert- or -C ₁₂ alkyl or C ₆ -C ₃₀ aryl, C ₁ -C ₂ alkyl (C ₆ -C ₁₀ ) aryl, which may optionally be substituted by one or more O or F atoms and are, for example, ethers.

Examples of suitable monovalent hydrocarbon radicals R include alkyl groups, preferably CH ₃ -, CH ₃ CH ₂ -, (CH ₃ ) ₂ CH-, C ₈ H ₁₇ - and C ₁₀ H ₂₁ groups, cycloaliphatic groups, such as cyclohexylethyl, Aryl groups such as phenyl, aralkyl groups such as 2-phenylethyl groups. Preferred monovalent halohydrocarbon radicals R have the formula C _n F _{2n +} - _I CH ₂ CH ₂ - wherein n has a value of 1 to 10, such as, for example, CF ₃ CH ₂ CH ₂ -, C ₄ F ₉ CH ₂ CH ₂ - and C ₆ Fi ₃ CH ₂ CH ₂ -, the more preferred radical is the 3,3,3-trifluoropropyl group.

Particularly preferred radical R is methyl, phenyl, 3,3,3-trifluoropropyl. In the above groups, R ^{1 is} an alkenyl-containing organic group, which is preferably selected from unsubstituted and substituted alkenyl-containing hydrocarbon radicals, such as C ₂ -C ₁₂ n-, iso-, tert-or cyclic alkenyl, vinyl, allyl, hexenyl, C ₆ -C ₃₀ cycloalkenyl, cycloalkenylalkyl, Norbornenylethyl, Limonenyl, C ₈ -C ₃ o-alkenyl aryl, which are optionally substituted by one or more O- or F-atoms, for example ether. Preferred radicals R ¹ are groups such as vinyl, allyl ₁ 5-hexenyl, cyclohexenylethyl, limonenyl, norbornenylethyl, ethylidene norbornyl and styryl, particularly preferably vinyl.

The optional radical R ² bridges two siloxy units of the type M, D or T. In each case, the divalent units R ² bridge two siloxane units, for example -DR ² -D-. In this case, R ² is selected from divalent aliphatic or aromatic n-, iso-, tert-, or cyclic -C ₁₄ alkylene, C ₆ -C ₁₄ arylene or -Alkylenarylgruppen.

Examples of suitable divalent hydrocarbon groups R ² which can bridge siloxy units include all alkylene and dialkylarylene radicals, preferably those such as -CH ₂ -, -CH ₂ CH ₂ -, CH ₂ (CH ₃ ) CH-, - <CH ₂ ) ₄ , -CH ₂ CH (CH ₃ ) CH ₂ -, - (CH ₂ J ₆ - - (CH ₂ J ₈ - and - (CH ₂ ) ₁₈ -cycloalkylene groups such as cyclohexylene, arylene groups such as phenylene, xylene 30 mol .-% of all siloxy units are not Preferred are groups such as alpha, omega-ethylene, alpha, omega-hexylene or alpha, omega-phenylene The term substantially linear polyorganosiloxanes comprises a), preferably not more than 0.1 mol contain -% of siloxane units, which are selected from the T = RSiO ₃ ^ - or Q = SiO _4/2 units.

In the polyorganosiloxanes a1), the radical R is preferably present as methyl radical with at least 90 mol% (ie, 90 to 99 mol% based on Si atoms), preferably with at least 95 mol%. The polyorganosiloxanes a1) contain at least 2 unsaturated organic radicals. Preferably, they contain from 0.03 to 1.0 mmol / g, more preferably from 0.05 to 0.8 mmol / g alkenyl groups. The content of unsaturated organic groups refers to polymethylvinylsiloxanes and must be adapted within the given viscosity limits to siloxy groups with a higher molecular weight. The alkenyl groups may be attached either to the chain end of a silioxane molecule or as a group to a silicon atom in the siloxane chain. Preferably, the alkenyl groups are present only at the chain end of the siloxane molecule. When alkenyl groups are present on silicon atoms of the siloxane chains, their content is preferably less than 0.01 mmol / g (0.074 mol% based on the Si atoms).

In order to improve the mechanical properties, such as the tear propagation resistance of the crosslinked products, it is expedient to use mixtures of different polymers (ie at least 2 polymers a1) or at least a1) and a2) or a1) and a3) with different alkenyl content and / or different chain length , Wherein the total content of the polymer mixtures of unsaturated groups 1, 0 mmol / g in the component a) suitably does not exceed. However, the vinyl content in the polymers a2) or a3) itself can be up to 11 mmol / g or 100 mol.% Per Si atom. Preferred siloxy units are, for example, alkenyl units, such as dimethylvinylsiloxy, alkyl units, such as trimethylsiloxy, dimethylsiloxy and methylsiloxy units, aryl units, such as phenylsiloxy units, such as dimethylphenylsiloxy, diphenylsiloxy, phenylmethylvinylsiloxy, phenylmethylsiloxy units. The polyorganosiloxane a) preferably has a number of siloxy units of from 20 to 10,000, particularly preferably from 100 to 6,000 (average degree of polymerization P _n , which relates to polymethylvinylsiloxanes and is to be adjusted within the given viscosity limits to higher molecular weight siloxy groups.) The alkenyl content is determined here by ¹ H-NMR-see AL Smith (Ed.): The Analytical Chemistry of Silicones, J. Wiley & Sons 1991 Vol. 112, p.356 et seq. in Chemical Analysis ed. by JD Winefordner.

Preferably, the alkenyi group content is represented by alkenyldimethylsiloxy units as end-of-chain siloxy units. In these cases of severe difunctionality, the alkenyl content also defines the viscosity. Thus, in these preferred for the polymer a1) embodiment, the alkenyl content clearly linked to the chain length or the degree of polymerization and thus the viscosity.

The polyorganosiloxane a1) and the mixture of a1) and a2) have a viscosity of 0.025 to 100,000 Pa.s, very particularly preferably 0.2 to 30,000 Pa.s at 25 ⁰ C. The viscosity is s ^{"measured 1} according to DIN 53019 at 25 ⁰ C and a shear velocity gradient D =. 1

Another class of preferred polymers a), which together with a1) form component a), are essentially linear polyorganosiloxanes a2) with alkenyl-containing side groups on the silicon and polyorganosiloxanes a3) with additional branching units. The polymers a2) and a3) can be used to increase, for example, the tear resistance or tensile strength in combination with other polyorganosiloxanes, such as those defined above, if no or little reinforcing filler of component c) is used. The polyorganosiloxanes a3), such as. As disclosed in US 3,284,406, US 3,699,073, contain an increased content of unsaturated radicals R ¹ , but in contrast to these have an increased proportion of branched or branching siloxane units T = RSiO _3/2 - or Q = SiO _{4 / 2} units which are present in more than 0.1 mol%, based on the Si atoms present. However, the amount of branching units should be limited by the fact that this component should preferably be liquid, low-melting (mp <16O ⁰ C) or with the other polymers a) miscible, transparent silicone compositions (> 70% transmission at 400 nm and 2 mm layer thickness).

The above-mentioned highly branched polyorganosiloxanes are polymers containing the aforementioned M, D, T and Q units. They preferably have the general ratio formulas (II), (IIa) to (IIb):

([R ₁ SiO ₃ Z ₂ ] [R ³ O ₁ Z ₂ ] HiImI (IIa)

{[SiO _4/2 }] [R ³ O _1/2 ] ni [R ₂ R ¹ SiO ₁₀ ] o, oi-io [RSiO _3/2 ] o-so [R2S1O2 / 2] o- ₅ oo} mi (Hb) wherein R ^{3 is} a C ₁ to C ₂₂ organic radical such as alkyl, aryl or arylalkyl.

The radical R ³ Oi _{/ 2} is preferably methoxy, ethoxy or hydroxy with the preferred indices n1 m1 = 1 to 1000 n1 = 0.001 to 4 a2 = 0.01 to 10 b2 = 0 to 1000 c2 = 0 to 50 d2 = 1. The molar ratio M: Q can assume values of 0.1 to 4 to 1 or M: T of 0.1 to 3: 1, the ratio of D: Q or D: T from 0 to 333: 1, the Units M, D and T may contain the radicals R or R ¹ . The alkenyl group-rich branched polyorganosiloxanes a3) include, in particular, liquid polyorganosiloxanes, solid resins or liquid resins soluble in organic solvents, which preferably consist of trialkylsiloxy (M units) and silicate units (Q units), and which preferably contain vinyldimethylsiloxy units in an amount of contain at least 0.2 mmol / g. These resins may also have up to a maximum of 10 mol% of aikoxy or OH groups on the Si atoms. In the abovementioned branched polyorganosiloxanes a3), the radical R is preferably present as the methyl radical with at least 50 mol% (ie 50 to 95 mol% based on Si atoms), preferably at least 80 mol%. The alkenyl group-rich, preferably vinyl group-rich, polyorganosiloxane a3) preferably has an alkenyi group content of more than 0.35 mmol / g to 11 mmol / g, which refers to polymethylvinylsiloxanes and is to be adapted within the given viscosity limits to siloxy groups with a higher molecular weight. The polyorganosiloxanes a) can in principle be mixed with one another in any ratio of a1) to a2) or a3). Preferably, the ratio a1): a2) is more than 2.5: 1. A preferred mixture of polyorganosiloxanes a) contains two substantially linear alkenyl endstopped polyorganosiloxanes a1) having different alkenyl, preferably vinyl, contents. By this measure, on the one hand, the lowest possible viscosity of the silicone composition should be specified, on the other hand, a crosslinking structure with high strength should be achieved.

In a further preferred embodiment, the polyorganosiloxanes a) have substantially linear alkenyl endstopped polyorganosiloxanes a1) or a2), wherein more than 50% by weight a) consist of polymers having an alkenyl content of more than 0.2 mol%, more preferably more than 0.4 mol%, which are selected from Alkenyldimethyl- or as alkenyl methylsiloxy. It has been found that polymers with this content of reactive groups lead to a particularly low mass loss and low number of holes in the arc or high-voltage creepage test.

Component b) is selected from molecules which can crosslink the reactive groups of the component. Component b) is selected from siloxanes or silanes which have two or more than two groups which can react with the reactive groups of component a) and form covalent bonds, or prefer the reactive groups of component a) by free-radical activation with themselves intermolecular reaction. SiH-containing siloxanes or peroxides are preferably used for this purpose.

The polyorganohydrogensiloxanes b) are preferably linear, cyclic or branched polyorganosiloxanes whose siloxy units are suitably selected from M = R ₃ SiO _{1 Z 2} , M ^H = R ₂ HSiO _1/2! D = R ₂ SiO ₂ Z ₂ , D ^H = RHSiO _2/2 , T = RSiO _{3 / 2l}

T ^H = HSiθ _3/2 , Q = SiO _4/2 , in which these units are preferably made of MeHSiO- or

Me ₂ HSiOo _I5 units in addition to optionally other organosiloxy, preferably dimethylsiloxy, are selected. The polyorganosiloxanes b) can be described, for example, by the general formula (III) in which, for the sake of brevity, the symbols M * for M and M are ^H , D ^* for D and D ^H and T ^* for T and T ^H are:

[M ^* _a4 DVT ^* _c4 Qd4] m2 (Hf) m2 = 1 to 1000 a4 = 1 to 10 b4 = 0 to 1000 c4 = O to 50 d4 ~ 0 to 1.

The siloxy units can be present in blocks or randomly linked to one another in the polymer chain. Each siloxane unit of the polyorganosiloxane chain may carry identical or different radicals.

The indices of the formula (III) describe the average degree of polymerization P _n, measured as number average M _n per GPC, which relate to polyhydrogenmethylsiloxanes and are to be adapted within the given viscosity limits to siloxy groups having a higher molecular weight.

The polyorganohydrogensiloxane b) comprises, in particular, all liquid, flowable and solid polymer structures of the formula (III) having the degrees of polymerization resulting from the abovementioned indices. Preference is given to the polyorganosiloxanes b) having a low molecular weight, ie less than about 60,000 g / mol, preferably less than 20,000 g / mol, which are liquid at 25 ^° C.

The preferred polyorganohydrogensiloxanes b) are structures selected from the group which can be described by the formulas (Illa-Ille)

HR ₂ SiO (R ₂ SiO) ₂ (RHSiO) _P SiR ₂ H (purple) HMe ₂ SiO (Me ₂ SiO) _z (MeHSiO) _p SiMe ₂ H (IMb)

Me ₃ SiO ₂ (Me ₂ SiO) ₂ (MeHSiO) _P SiMe ₃ (IHc)

Me ₃ SiO (MeHSiO) _p SiMe ₃ (MId)

{[R ₂ YSiO _1/2 ] o-3 [YSiO ₃₇₂ ] [R ³ OWW (HIe) _{[SiO4 / _2}] [R ³ O _1/2] π2 [R ₂ YSi0i / _2] 0.01-10 [YSiO ₃ Z _2] o-so [ryšio _2/2] 0-1000} m2 ( Ulf)

z = (z1 + z2) = 0 to 1000 p = 0 to 100 z + p = b4 = 1 to 1000 where R ³ Ov _{2 is} an alkoxy radical on the silicon,

Y = hydrogen (H) or R, both of which can occur simultaneously in one molecule. R is defined above, preferably R = methyl.

A preferred embodiment of the compound class (IIe) and (IIIf) are, for example, monomeric compounds such as [(Me ₂ HSiO ₄ ) Si] of the polymeric compounds such as [(Me ₂ HSiOi _{/ 2} ) o, 7 - <4Q] i-iooo The SiH concentration is preferably in the range of 0.1 to 10 mmol / g (to 80 mol.% Based on Si), which refers to Polyhydrogenmethylsiioxane and is within the given viscosity limits to siloxy groups with higher molecular weight to adjust.

Another preferred group of crosslinkers is selected from the group described by the general formulas (IIIa) and (IIIc) and wherein z> p.

The preferred SiH concentrations for compounds of the formulas (IIIa) and (IIIc) are less than 50 mol% (SiH groups based on all silicon atoms corresponding to about 7 mmol / g for polyhydrogenmethylsiioxanes), more preferably less than 30 mol% ,

The polyorganosiloxanes b) are preferably liquid at room temperature or siloxaniöslich, that is, they preferably have less than 1000 siloxy units, that is, they preferably have viscosities below 40 Pa, s at 25 ⁰ C and D = 1 ^{s' 1.}

The SiH content is determined in the present invention by ¹ H-NMR see AL Smith (Ed.): The Analytical Chemistry of Silicones, J. Wiley & Sons 1991 Vol. 12 p. 356 et seq. In Chemical Analysis ed. By JD Winefordner. The preferred amount of the polyorganohydrosiloxanes b) is 0.1 to 200 parts by weight, based on 100 parts by weight of component a).

The preferred amount of polyorganohydrogensiloxanes b) is selected such that the molar ratio of the total amount of Si-H to the total amount of Si-alkenyl in component a) is from 0.5 to 5: 1, preferably from 1.0 to 3.2: 1, more preferably 1.5 to 2.5: 1.

On the one hand rubber-mechanical properties and the crosslinking rate can be controlled via the ratio of SiH to Si-alkenyl units, but this ratio also contributes to the stabilization of the surface against destruction by arc action.

As is known, the rate of the hydrosilylation reaction can be influenced by a series of compounds which are grouped under the name of inhibitors. They are counted here to the excipients.

In the case that the component a) is crosslinked with peroxides, they are selected from the group consisting of organic and inorganic peroxides. Preference is given to dialkyl peroxides, alkylaryl peroxides, peroxycarbonates, diaryl peroxides, such as, for example, di-tert-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-bis-2-5-di-tert-butylpyoxyhexane, dibenzoyl peroxide, bis-2,4-dichlorobenzyl peroxide , Bis-2-methylbenzoyl peroxide, bis-4-methyl-benzoyl peroxide, etc.

In this case, it is possible to dispense with at least the predominant part of the SiH compounds, but not with component d).

The peroxides are preferably used in amounts of from 0.1 to 2% by weight, based on the components a) to e). DiO component c) is used to cure the rubbers with the SiH-containing compounds of component b) to give elastomers via a hydrosilylation reaction to form a shaped article. The component c) is also needed as a stabilizer to improve the arc resistance or creep resistance. Component c) is selected from the group of transition group metals consisting of platinum, rhodium, ruthenium, palladium, nickel, iridium or compounds thereof.

The hydrosilylation catalyst c) or stabilizer can be used in metallic form, in the form of a complex compound and / or as a salt. The catalysts can be used with or without support materials in colloidal or powdered state.

Platinum or compounds of platinum are preferably used as component c).

The amount of component c), in particular of the platinum catalyst is 0.1-1000 ppm, calculated as metal, based on the weight of components a) to b).

More preferred are 1-50 ppm of metal or metal compounds, especially platinum or platinum compounds, with the amount referring to the metal (especially platinum), more preferably 2-24 ppm, even more preferably 3 to 15, most preferably 4 to 9, 5 ppm.

In the group of Pt, Rh, Ir, Pd, Ni and Ru compounds, ie their salts, complexes or metals, the component c) is selected, for example, from the Pt catalysts, in particular Pt ° complex compounds with olefins, particularly preferably with vinylsiloxanes, such as, for example, 1: 1 complexes with 1,3-divinyltetramethyldisiloxane and / or tetravinyltetramethyltetracyclosiloxane, amine, azo or phosphite complex compounds. These Pt catalysts are exemplified in US 3,715,334 or US 3,419,593. The preferred Pt.alpha.-olefin complexes are prepared in the presence of 1,3-di-vinyltetramethyldisiloxane (M.sub.1) by reduction of hexachloro-platinic acid or other platinum chlorides.

Likewise, of course, other platinum compounds, as far as they allow rapid crosslinking, can be used, such as the photoactivatable Pt catalysts of EP 122008, EP 146307 or US 2003-0199603.

The rate of hydrosilylation is determined by the selected catalyst compound, its amount, and the type and amount of additional inhibitor component in component f).

The amounts of catalyst are limited by the costs incurred upwards and the reliable catalytic effect down. Therefore are

Amounts above 100 ppm Metali mostly uneconomic, amounts below 1 ppm unreliable. It was recognized that by the addition of component d) the

Amount of transition metals to stabilize the surfaces against the

Arc effect and Kriechstromwegbildung can be significantly reduced.

As carriers for the catalysts, all solids can be selected unless they undesirably inhibit hydrosilylation. The carriers may be selected from the group of powdered silicas or gels or organic resins or polymers and used in accordance with the desired transparency, preference is given to non-opacifying carriers.

The transition group metals or compounds thereof can also be used in conjunction with one or more complexing agents. The complexing agents can be used in advance in the preparation of the transition group metal compounds, or the Kompiexbildner ^" KB ^' can also ^' in situ ^'be used. That is, the complexing agents can be used separately in addition to a transition group metal compound and optionally also in stoichiometric excess to transition group metal compound, ie, be added to the curable Polyorganosiioxankautschuk compositions.

By using an excess of said complexing agents, regardless of the complexation of the transition metal, occasionally further positive effects on the high voltage strength of the insulators can be observed.

Such complexing agents are selected, for example, from the group consisting of amines, amides, azo compounds such as azobisisobutyronitrile, azo dicarbonamide, hydrazine compounds such as dialkyl and / or diaryl compounds, guanidines such as cyanoguanidine, sulfides such as bisalkyl and or aryl sulfides, phosphines such as triorganophosphines such as trialkyl and / or aryl phosphines, phosphites such as trialkyl and / or aryl phosphites, and phosphonates such as trialkyl and / or aryl phosphonates, tetramethylpiperindinyl siloxanes such as Uvasil 299, benzotriazoles such as types 26, 27 and 55 lowilites, Quinolines such as polymeric 2,2,4-trimethyldihydroquinoline or hydroquinones, primary or secondary antioxidants.

Particularly preferred complexing agents are phosphites, benzotriazoles, quinoline and quinoline derivatives, azobisisobutyronitrile, azodicarbonamide.

These compounding agents can be added to the curable polyorganosiloxane rubber compositions in an amount of 0.001 to 10 parts by weight based on the amounts of components a) and b). Preferably, a molar ratio of transition group metal to the complexing agent is selected, which is preferably 1: 1 to 100, based on the molar amount of the metal.

Component d)

According to the invention, ferrocene and / or ferrocene derivatives (hereinafter both referred to as ferrocene derivatives or ferrocene compounds) are used.

Ferrocene is known to be bicyclopentadienyliron of the formula:

Fe

With a melting point (mp) of 172 ⁰ C and a boiling point (bp) of 249 ° C. Ferrocene derivatives in the context of the invention are derived by substitution of one or more hydrogen atoms on one or both of the cyclopentadienyl ligands on the ferrocene base body and include in particular:

Alkyl or alkenyl-substituted ferrocene, such as iron bis (alkylcyclopenta- dienyl), such as iron, bis (methylcyclopentadienyl), bis (ethylcyclopenta- dienyl) iron liquid at 25 ⁰ C, bis (i-propylcyclopentadienyl) iron liquid at 25 ⁰ C , bis (vinyl-cyclopentadienyl) iron mp: 51-53 ° C, bp: 80-85 / 0.2 mm Hg, or bis (n-butyl-cyclopentadienyl) iron bp: 230 ⁰ C / 630mm, bis (t -butyi-cyclopentadienyl) iron Bis (tetramethyl-cyclopenta-dienyl) iron, bis (pentamethyl-cyclopentadienyi) iron. Organosiloxanyl and silyl-substituted ferrocenes, such as bis (trimethylsilylcyclopentadienyl) iron,

Contain ferrocene with hydrocarbon-substituted cyclopentadiene ligands, O, P, S, or N, such as acetyl ferrocene, 1, 1 ferrocene ^'-bis (di-t-butyi- phosphino) Butyroferrocen, ferrocene carboxaldehyde (OHCC ₅ H ₄ - - Fe- (C ₅ H ₅ ) mp: 124 ⁰ C, 1, 1 ^' -ferrocene-dicarboxylic acid, ferrocene monocarboxylic acid (HOOCC ₅ H ₄ Fe ₁ ferrocenyl-acetic acid ((C ₅ H ₅ ) Fe C ₅ H ₄ CH ₂ COOH, α-Hydroxyethylferrocen ((C ₅ H ₅₎ FeC ₅ H _4n -CHOHCH ₃₎ mp: 76-77 ⁰ C, hydroxymethyl ((C ₅ H ₅₎ FeC ₅ H ₄ CH ₂ OH) mp: 66 -

70 ⁰ C, the Ci-Ce-Aikyl and C ₆ -C ₁₀ aryl, Alkylenaryl esters of the aforementioned carboxyl and hydroxyl-containing ferrocenes, such as the dimethyl ester of 1, 1 ^" ferrocene dicarboxylic mp: 113-115 ⁰ C, ferrocenylacetonitrile mp: 81-83 ⁰ C, α- (N, N-dimethylamino) -ethylferrocen _((C5 H5) Fe {C ₅ H4) CH (CH3) N _(CH3) 2) bp: 110 ⁰ C. / 0.45 mm, N, N-dimethylaminomethyl-ferrocene ((C ₅ H ₅ ) Fe (C ₅ H ₄ ) CH ₂ N (CH ₃ ) 2) bp: 91-92 ° C / 0.45 mm , their acid addition salts or their quaternized with alkyl groups Haiogenide,

Bisferrocenyl- bridged compounds, such as 1, 1 '-lsopropyliden- bis (ethyl ferrocene) (Catocene mp: <- 10 ⁰ C),

The ferrocene derivatives may or may not have a mirror plane. Preferred are ferrocene derivatives which have a mirror plane.

Preferably, component d) is selected from the group consisting of ferrocene, bis (ethylcyclopentadienyl) iron, bis (i-propylcyclopentadienyl) iron, bis (vinylcyclo-pentadienyl) iron, Hydroxy-methylferrocene, ferrocenylacetonitrile, 1, 1'-isopropylidene-bis- (ethylferrocene) (catocenes) of the formula:

and triorganonylsilyl-substituted ferrocene derivatives.

The ferrocene derivatives are preferably added in quantitative ranges based on the iron content of 0.01-5% by weight, more preferably 0.02-2% by weight, more preferably 0.05-1% by weight of Fe, based on total amount of the composition.

Preferred ferrocene derivatives are low melting compounds, preferably having a melting point below 200 ⁰ C, more preferably below 12O ⁰ C, more preferably below 80 ° C and a boiling point above 230 ⁰ C, preferably above 280 ⁰ C, at least by weight: 5.% in siloxane or a C ₅ -C _O - aliphatic, Cj-Cβ-aromatic solvent, Ci-C ₆ -chlororganischen solvents are soluble.

In principle, other so-called τr complexes are also compounds which contain metals of group III to VIII, which can build up a metallocene with aryl compounds, in particular cyclopentadiene, as component d). For this purpose, the metal is additionally selected from the group consisting of titanium, vanadium, chromium, manganese, cobalt, zirconium, niobium, molybdenum, technetium, hafnium, tantalum, tungsten and rhenium. Iron complexes, however, are preferred. For incorporation of the ferrocene compounds, these are preferably dispersed in a polyorganosiloxane, in particular component a) optionally a mixture of component a) and e). The ferrocene compounds can also be dissolved in a solvent or dispersed in the polyorganosiloxane introduced. In this case, a concentrated with respect to the ferrocene masterbatch is obtained, for example, with a concentration of up to 20 wt.% Of the ferrocene compound

With regard to component e), the silicone rubber mixtures according to the invention may optionally contain fillers. Component e) serves to increase the mechanical strength, such as tensile strength DIN 53 504, elongation at break and tear resistance, e.g. according to ASTM 624 test specimen B. If component e) is used, these are so-called reinforcing fillers.

These are preferably inorganic or organic fillers such as silicates, carbonates, oxides, carbon blacks or silicas. The fillers are preferably so-called reinforcing silicas which allow the production of opaque to transparent elastomers, ie those which improve the rubber-mechanical properties after crosslinking, increase the strength, such as, for example, fumed or precipitated silica having BET surfaces between 20 and 400 nfVg, which are preferably rendered hydrophobic surface superficially. The term filler also includes fillers including their surface-bound hydrophobizing agents, optionally converted by reaction with water or silanols, dispersants or ^' process aids ^' , which influence the interaction of the filler with the polymer, for example the thickening effect. The hydrophobing can be done before or during the mixing process. Such water repellents are known in numerous ways.

These are, on the one hand, saturated hydrophobizing agents selected from the group consisting of disilazanes, siloxane diols of chain length 1 to 60, alkoxysilanes, such as methyltriaoxyloxy or dimethyldialkoxy or trimethylalkoxysilane, silylamines, silanols, such as trimethylsilanol, acetoxysiloxanes, acetoxysilanes, chlorosilanes , Chlorosiloxanes and aikoxysiloxanes, on the other hand optionally an unsaturated hydrophobing agent selected from the group consisting of polyvinyl substituted methyldisilazanes such as 1, 3-divinyltetramethyldisilazane, and methylsilanols and alkoxysilanes each having unsaturated radicals selected from the group consisting of alkenyl, alkenylaryl, acrylic and methacryi.

The surface-modified -before the mixing or ^'in-situ' -treated filler, when it is used, from 10 to 70 parts by weight share-in amounts of 1 to 100 parts by weight, preferably, more preferably 10 to 50 parts by weight , based on 100 parts by weight of component a) used. Fillers with BET surface areas above 50 m ² / g allow the production of silicone elastomers with improved rubber-mechanical properties. The fumed silicas, such as Aerosil® 200, 300, HDK® N20 or T30, Cab-O-Sil® MS 7 or HS 5, lead to improved rubber mechanical strength and increase transparency with increasing BET surface area. Trade names for so-called precipitated silicas, engl. ^' Wet Siiicas ^' are Vulkasil® VN3 or FK 160 from Degussa or Nipsil LP from Nippon Silica KK It is preferred to use pyrogenic silicas, in particular with surfaces of 50 to 300 m ² / g. In addition, in addition or as a substitute, non-reinforcing extender fillers, such as quartz flour, diatomaceous earths, cristobalite flours, mica, aluminum oxides, hydroxides, Ti, Fe, Zn oxides, chalks or carbon blacks with BET surfaces of 0.2-50 m ² / g can be used. These fillers are available under a variety of trade names such as Sicron®, Min-U-Sil®, Dicalite®, Crystallite®, Wollastonite, Bayferrox®, Titanium Dioxide P25, Xonotlite or Martinal®, Hymod® or Micral®.

Quartz flour, aluminum oxide hydroxides, Ti, Fe, Zn oxides, and / or Zn borate are preferably used, preferably in amounts of 50-300 parts by weight per 100 parts by weight of component a). The addition of these fillers also increases the resistance in the arc or high-voltage creepage test. The adjuvants f) are selected, for example, from the group consisting of: inorganic or organic pigments, further stabilizers against embrittlement by hot air, such as organic salts, alcohols, chitates of titanium, zirconium, cerium, manganese, iron, lanthanum, the not defined and included under d).

The term auxiliaries f) also includes inhibitors with which the rate of curing to elastomers can be controlled by means of a hydrosilylation reaction. Inhibitors are selected from the group consisting of alkynols, maleates, fumarates, etc., which are not defined and included among complexing agents of component c).

Also preferred as an auxiliary are silicone oils without reactive groups which are selected from polydimethylsiloxanes, polyphenylmethylsiloxanes, polydiphenyl-dimethylsiloxanes having viscosities of 10-1000 mPa.s at 25 ° C. They are used to produce increased, sustainably regenerating hydrophobic surfaces of insulators that are exposed to damage from weather, glow discharges and arcing effects.

A preferred embodiment of the curable polyorganosiloxane rubber compositions contains the following components:

a) one or more polyorganosiloxanes having reactive groups, b) one or more crosslinker and / or chain extenders for component a), c) one or more transition group metals selected from

Platinum, rhodium, iridium, palladium, nickel and ruthenium, or compounds thereof, d) one or more ferrocene compounds, e) optionally one or more fillers, f) optionally one or more auxiliaries. Platinum, rhodium and ruthenium are particularly preferred.

A more preferred embodiment of the curable polyorganosiloxane rubber composition contains the following components:

a) one or more polydimethylsiloxanes having at least two alkenyl groups, b) one or more polydimethylsiloxanes having at least two SiH groups, c) one or more platinum compounds, d) one or more ferrocene compounds selected from ferrocene, vinylferrocene, Alkylferrocene, 1, 1'-Isopropylidenbis (ethy! Ferrocene) (Catcenes) and siloxanyl or triorganosilyl-substituted ferrocene derivatives, e) at least one silica-containing filler having a BET surface area of 50 to 400 m ² / g.

The curable polyorganosiloxane rubber compositions preferably have the following composition:

100 parts by weight of component a), - 0.1 to 50 parts by weight of component b),

1 to 100 ppm of component c), wherein the amount given to platinum metal and the total amount of a) and b), 0.01 to 25 parts by weight of component d), based on the iron contained therein, - 0 to 300 parts by weight of component e).

Most preferably, the curable polyorganosiloxane rubber compositions contain:

100 parts by weight of component a), 0.5 to 10 parts by weight of component b),

5 to 25 ppm of component c), the amount given being based on platinum metal and the total amount of a) and b), 0.05 to 5 parts by weight of component d), based on the iron contained therein,

15 to 50 parts by weight of component Θ).

The curable polyorganosiloxane rubber compositions may additionally comprise one or more adjuvants f) which are different from the components a) to e).

In a preferred embodiment of the invention, the molar ratio of the reactive Si-alkenyl groups in component a) to the SiH groups in component b) is chosen such that an average of 0.5 to 5 per reactive group in component a): 1, preferably 1, 0 to 3.2: 1, more preferably 1, 5 to 2.5: 1 SiH groups are selected per alkenyl groups.

Preferably, the content of component c) is below 25 ppm, in a particularly preferred embodiment of the invention it is 2-24 ppm, more preferably 3 to 15, most preferably 4 to 9 _r 5 ppm.

Component c) is preferably used together with a complexing agent ^' KB ^' . The most preferred molar ratio between metal ^' Me ^' of component c) and the complexing agent ^' KB ^' is Me: KB such as 1: 2-50, more preferably 1: 2-4.

In a further preferred embodiment of the invention, the content of component d) is less than 10 parts by weight, based on 100 parts by weight of components a) and b) based on that in component d) containing iron. The invention further relates to curable polyorganosiloxane rubber compositions which are as defined above.

The invention further relates to cured polyorganosiloxane rubber compositions obtainable by curing the aforementioned curable polyorganosiloxane rubber compositions. The curing includes in particular the heating of the curable polyorganosiloxane rubber compositions in the range of preferably 20 to 200 ° C. Furthermore, in the case of radiation-curing polyorganosiloxane rubber compositions, the irradiation with light in a wavelength range of 150 to 700 nm or electron radiation.

The invention further relates to elastomeric molded articles obtainable by curing the curable polyorganosiloxane rubber compositions of the invention. The elastomeric molded articles are preferably selected from the group of insulators, such as high voltage insulators, anode caps, cable insulators, cable terminations, spark plug caps, and high voltage plug insulation, such as picture tubes or ignition coils.

The invention further relates to a process for producing cured polyorganosiloxane rubber compositions or elastomeric molded articles obtainable by curing the curable polyorganosiloxane rubber compositions of the invention.

The invention further relates to the use of ferrocene or derivatives thereof for increasing the arc resistance and / or the creep resistance of insulators, such as high-voltage insulators, in particular based on cured polyorganosiloxane rubber compositions. The invention is further illustrated by the following examples. Examples

The following examples serve to illustrate the invention without being limiting.

Testbedinqungen

The elastomers obtained in the following examples were evaluated in a test device for high-voltage creepage according to DIN 57 303 / IEC 587 VDE 303 Part 10. For this purpose, 5 to 10 test plates 6 x 50 x 120 mm with respect to the maximum permissible limiting current 60 mA, the depth of the hole and the loss of mass at a given high voltage were tested. In the evaluation, u.a. determined the ratio of observed holes to the number of plates tested in which a depth of hole (erosion depth) greater than 6 mm was found. The mass loss was determined after cleaning as the average of the weight losses measured in each case. For this purpose, the erosion products (ash, slag), which are easily removable from the elastomer plate, were first mechanically separated and, finally, the remaining constituents were wiped off with a coarse cloth.

The classification into the voltage classes was carried out essentially according to the current limit criterion, ie. h not exceeding 60 mA for 2 sec. within the test period of 6 hours.

Preparation of premix 1)

In a kneader, 350 g of a vinyl-containing polyorganosiloxane as

Component a1-1) (SiVi content = 0.03 mmol / g, viscosity at 25 ° C = 65 Pa.s) and 120 g of vinyl-containing polyorganosiloxane as component a1-2) (SiVi content = 0.05 mmol / g , Viscosity at 25 ° C = 10 Pa.s) with 47 g of hexamethyldisilazane and 0.15 g of 1, 3-DivinyltetramethyIdisilazan each as a water repellent for component e) and 17 g of water under N 2 blanket gas mixed. This was followed by 250 g of fumed silica Aerosil 300 having a BET surface area of 300 m ^z / g as component e) in 5 portions was added and mixed all Ingredients evenly to a homogeneous paste. The paste was left for 20 min. heated to 90 to 100 ⁰ C under reflux. Subsequently, the temperature was raised to 150 to 160 ⁰ C, and while passing N ₂ , the volatiles were removed. It was cooled to 100 ⁰ C and again led to 120 g of the vinyl-containing polyorganosiloxane as component a1-1) and 110 g of the vinyl-containing polyorganosiloxane as component a1-2). Subsequently, the resulting paste was cooled to 40 to 50 ⁰ C and obtained ca, 1000 g of the premix 1).

The cooled premix 1) was divided into 2 partial mixtures on 1a) and 1 b).

To 500 g of the mixture 1 a) was added 28 g of a vinyl-containing polyorganosiloxane as component a2-1) (SiVi content = 0.8 mmol / g, viscosity at 25 ⁰ C = 20 Pa.s), 0.06 g of a Pt- (0) -vinylsiloxane complex with 0.15 wt .-% Pt (determined by AA spectroscopy), corresponding to a platinum amount based on the below prepared mixture of the sub-mixtures 1a) and 1 b) of 8.5 ppm ,

To 500 g of the sub-mixture 1b) was added 14.5 g of M ^H ₂ Di ₇ (1, 4 mmol / g SiH), 13.5 g of M ₂ D ₂ oD ^H 2o (about 7 mmol / g SiH as component b ) and 0.4 g of 1-ethynylcyclohexanol (inhibitor as adjuvant according to component f). The amount of SiH was adjusted so that in the mixture of mixtures 1a) and 1b) prepared below a molar ratio of SiH groups to Si-vinyl groups of 2.5: 1 resulted.

Subsequently, in each case 100 g of the two partial mixtures 1a) and 1b) are combined in a plastic cup and mixed homogeneously with a kitchen mixer. From this mixture, an amount of about 120 to 130 g in a mold plate, led mold plate and cover plate of a transfer press (vulcanization 333 N / cm ² ), pressed, heated for 10 minutes at 150 ⁰ C, took the mold cavity a plate of 6 x 100 mm x 180 mm and tempered for 4 hours at 200 ⁰ C under fresh air in a convection oven.

Comparative Example 1) Preparation of curable polyorganosiloxane rubber composition without ferrocene compound

A mixture consisting of premixes 1a) and 1b) was mixed in a ratio of 1: 1, molded without component d) into 6 mm test plates, cured and tempered after removal in a hot air oven. Subsequently, the test was carried out for the high-voltage creep resistance. The test results are shown in Table 1.

Example 1)

Preparation of curable polyorganosiloxane rubber composition with ferrocene compound

Premixes 1a) and 1b) were prepared as in Comparative Example 1. 0.4 g of ferrocene (corresponding to 0.1% by weight, based on iron) dissolved in 3 ml of chloroform were added to 120 g of the homogeneous mixture obtained and mixed again with a kitchen mixer for 5 minutes. The resulting mixture was shaped analogously to Comparative Example 1 to test plates, vulcanized at 150 ⁰ C and annealed after removal.

Examples 2 to 4

Example 1 was repeated replacing the ferrocene with 0.49 g of acetylferrocene, 0.45 g of vinylferrocene and 0.5 g of catocenes, respectively.

Table 1 shows the test results obtained in Comparative Example 1 and Examples 1 to 4 on the mold plates with an iron content of 0.1% by weight. Table 1

Average of 5 measurements, number / ratio holes with erosion depth> 6 mm per 5 tests

Table 1 shows that the addition of the ferrocene compounds results in a lower mass loss and an improved hole ratio compared to Comparative Example 1.

Examples 5, 6 and 7

Starting from the general composition of Example 1, the amounts of ferrocene were changed as shown in Table 2. 0.1% by weight of Fe correspond to a weight of 0.33 g of ferrocene per 100 of the concentration of Example 1.

Table 2

'Average of 5 measurements

Table 2 shows that the weight loss decreases with increasing amount of ferrocene.

Claims

CLAIMS; 1. Use of ferrocene or derivatives thereof for the production of Insulators based on silicone rubber compositions. 2. Use according to claim 1, wherein the silicone rubber compositions are obtained from curable polyorganosiloxane rubber compositions. 3. Use according to claim 2, wherein the curable polyorganosiloxane rubber compositions contain the following components: a) one or more polyorganosiloxanes having reactive groups, b) one or more crosslinker and / or chain extenders for component a), c) one or more transition group metals selected from platinum, rhodium, iridium, palladium, nickel and ruthenium, or compounds thereof , d) one or more ferrocene compounds, e) optionally one or more fillers, f) optionally one or more auxiliaries. 4. Use according to claim 2 or 3, wherein the curable organopolysiloxane rubber compositions have the following composition: 100 parts by weight of component a), 0.1 to 50 parts by weight of component b), 1 to 100 ppm of component c), the quantity given being based on platinum metal and the total amount of a) and b), 0.01 to 25 parts by weight of component d), based on the iron contained therein, 0 to 300 parts by weight of component e). Use according to any one of claims 2 to 4, wherein the curable polyorganosiloxane rubber compositions additionally contain one or more adjuvants f) other than components a) to e). 6. Use according to claim 5, wherein the component f) is selected from the group consisting of: inorganic or organic pigments, aluminum trihydrate, quartz powder, oxides, carbonates inorganic, organic salts, alcohols or chelates of titanium, zirconium, cerium, lanthanum , organic, inorganic, metal-organic condensation catalysts. 7. Use according to any one of claims 3 to 6, wherein component d) is selected from the group consisting of: ferrocene, bis (ethylcyclopentadienyl) iron, bis (i-propylcyclopentadienyl) iron, bis (vinyl-) cyclo-pentadienyl) iron, hydroxymethylferrocene, ferrocenylacetonitrile, 1, 1 '-isopropylidenebis (ethylferrocene) (Catocene), and triorganonyisilyl-substituted ferrocene derivatives. 8. Use according to any one of claims 3 to 7, wherein component c) is selected from the group consisting of platinum and platinum compounds. 9. Use according to any one of claims 3 to 8, wherein the component b) is a SiH group-containing polyorganosiloxane. 10. Use according to claim 9, wherein the molar ratio of the reactive groups in component a) to the SiH groups in component b) is selected such that each reactive group in component a) has an average of 0.8-3, 5 SiH groups from component b) are present in the curable polyorganosiloxane rubber composition. 11. Use according to any one of claims 3 to 10, wherein the content of component c) is less than 25 ppm. 12. Use according to any one of claims 3 to 11, wherein the content of component d) is less than 10 parts by weight, based on the iron contained therein. 13. Curable Polyorganosiloxane Rubber Compositions Containing: a) one or more polyorganosiloxanes having reactive groups, b) one or more crosslinkers and / or chain extenders for component a), c) one or more transition group metals selected from platinum, rhodium and ruthenium, or compounds thereof, d) one or more Ferrocene compounds, e) optionally one or more fillers, f) optionally one or more auxiliaries. 14. Curable polyorganosiloxane rubber compositions according to claim 13, wherein the curable polyorganosiloxane rubber compositions are as defined in any one of claims 3 to 12. 15. Hardened polyorganosiloxane rubber compositions obtainable by curing the curable polyorganosiloxane rubber compositions according to one of claims 13 or 14. 16. Elastomers obtainable by curing the curable polyorganosiloxane rubber compositions according to one of claims 13 or 14. 17. Elastomeric molded articles according to claim 16, which are insulators. 18. Isoiatoren consisting of elastomers according to claim 16. 19. Insulators according to claim 18 selected from the group consisting of high voltage insulators, anode caps, cable insulators, cable terminations, spark plug caps and high voltage plug insulators. 20. A process for producing cured polyorganosiloxane rubber compositions or elastomeric molded articles obtainable by curing the curable polyorganosiloxane rubber compositions according to any one of claims 13 or 14. 21. Use of ferrocene or derivatives thereof for increasing the arc resistance and / or the tracking resistance of insulators, such as high voltage insulators and for preventing erosion by glow discharge on the surface of the insulators. Use according to claim 21, wherein the insulators are those based on cured polyorganosiloxane rubber compositions.