Conductive curable liquid silicone rubber composition

Abstract

The present invention relates to a conductive curable liquid silicone rubber composition comprising carbon black and carbon nanotubes. The conductive curable liquid silicone rubber composition comprising carbon black and carbon nanotubes can be cured to dimensional change-resistant conductive silicone rubber compositions which surprisingly have a very low decrease of conductivity upon dimensional changes, in particular, after elongation or bending compared to silicone rubber compositions comprising only carbon black.

Description

[0001] CONDUCTIVE CURABLE LIQUID SILICONE RUBBER COMPOSITION

[0002] DESCRIPTION

[0003] The present invention relates to conductive curable liquid silicone rubber compositions comprising carbon black and carbon nanotubes. The conductive curable liquid silicone rubber compositions comprising carbon black and carbon nanotubes can be cured to dimensional change-resistant conductive silicone rubber compositions which surprisingly have a very low decrease of conductivity upon dimensional changes, in particular, after elongation or bending compared to silicone rubber compositions comprising only carbon black. At the same time the cured silicone rubber compositions show satisfactory mechanical properties like elongation and tensile strength. These properties allow in particular the application of the conductive silicone rubber compositions in electronic parts, where the high conductivity of the silicone rubber composition must be retained even at dimensional changes, such as elongation or bending, occurring for example in cable connectors, in particular, for high-voltage applications. Technical Problem

[0004] When two cables are connected inside a cable connector at the connection between the two cables there is a need for the presence of a conductive polymer in the connector to smoothen the high electrical fields created because of the metallic surfaces touching (sharp edges). The conductive polymer needs to retain its conductivity even if its dimensions are changed in the process of connecting the cables with the connector. Therefore, there is a strong need for a conductive polymer that should have conductive properties over a wide range of changes in the shape of the cable connector and satisfactory mechanical properties. For this reason, the volume resistivity of the conductive polymer in the cable connector should be stable during assembly of the cable connector with the cables to avoid a loss of efficiency in shielding of the high electric field between the two cables and avoid moisture creeping inside the cable connector.

[0005] US2020 / 0017685A1 discloses a silicone rubber composite composition comprising solid silicone rubber (HCR) having no fluidity and carbon nanotubes having an average length / diameter (L / D) value of 500 or more and 5000 or less. They are cured with peroxides to a hardness (Shore A) of 60 or more which is very hard and does not allow them to be used in common applications where significant dimensional changes of the silicone rubber may occur. The use of solid silicone rubbers also limits the possible applications of these silicone rubber composite composition in contrast to a LSR composition.

[0006] CN103937258B describes silicone rubber compositions comprising modified conductive fillers, which include a combination of modified carbon nanotubes and modified conductive carbon black, having a ratio of carbon black to carbon nanotubes of 3:1. According to CN107964247A the conductive silicone rubber of CN 103937258B has low elongation and poor tearing. Similarly, CN109486193B discloses an extrusion type silicone rubber system, comprising 100 parts of silicone rubber, 5-10 parts of hollow carbon black, and 3-10 parts of pre-dispersed single-wall carbon nanotube silicone rubber. Further CN 117757266 A, CN 108976809 A, CN111785409 A, and CN103160128B describe the use of combinations of carbon nanotubes and conductive carbon black.

[0007] US 11 ,939,471 B2 discloses a conductive liquid silicone rubber composition, comprising an electrically conductive filler comprising; (i) extra conductive carbon black present in an amount of from 1.5 to 5.5% by weight of the composition, and (ii) single walled carbon nanotubes present in an amount of from 0.05 to 1 % by weight of the composition. In the examples the maximum amount of the extra conductive carbon black is 4.18% by weight. In the comparative examples 1 and 2, 6.00% by weight of the extra conductive carbon black are used. Larger amounts of carbon black (>6% by weight) are to be avoided because of the consequential high viscosities resulting from the high levels of carbon black in the uncured LSR compositions resulting in poor workability of the compositions during injection moulding and coating applications, adverse effects on the cure of the silicone rubber and the poorer mechanical properties of the resulting cured rubbers.

[0008] It has been surprisingly found that the addition of carbon nanotubes (CNT) to LSR containing relatively high amounts of carbon black (CB) leads to a stable volume resistivity under mechanical stress and good mechanical properties as required for the silicone rubber used in electronic applications in particular in electronic components for high voltage applications.

[0009] The present invention therefore provides a liquid hydrosilylation curable silicone rubber composition (LSR) (subsequently sometimes referred to as the composition according to the invention) comprising:

[0010] (A) at least one polyorganosiloxane having one or more alkenyl groups,

[0011] (B) at least one polyorganosiloxane having one or more SiH groups,

[0012] (C) at least one filler component selected from one or more silicas,

[0013] (D) at least one transition metal hydrosilylation catalyst,

[0014] (E) at least one carbon black (CB),

[0015] (F) at least one carbon nanotube (CNT),

[0016] (G) optionally one or more auxiliary additives, wherein the weight ratio of component (E) to (F) is more than about 5 : 1 , and the content of component (E) is more than about 6.0 weight percent based on the total amount of the composition.

[0017] In general liquid silicone rubber compositions (LSR) contain silicone polymers of relatively lower molecular weight and hence shorter chains. Usually, they have better flow properties than solid silicone rubber compositions often referred to as HCR (= high consistency rubber). Liquid silicone rubber compositions can be processed as a liquid at room temperature and can be cured thermally or by irradiation as a rule with an addition-curing, i.e. hydrosilylation catalyst, for example, in an injection molding process. LSRs are commonly supplied as 2- component systems, where the so-called A component contains the hydrosilylation catalyst, while the so-called B component contains the SiH crosslinker and optionally the inhibitor. The viscosities of LSRs (mixture of A and B components and the respective A and B components) typically lay in the range of about 200 to about 1000 Pa.s at 25 °C measured at a shear rate of 10 s'1according to DIN 53019. In contrast, solid silicone rubber compositions (HCR) contain polymers with a high molecular weight and relatively long polymer chains, which are often peroxide-curing and delivered as solid bars or the like.

[0018] In the following preferred embodiments of components (A) to (G) are described.

[0019] (A) Polyorganosiloxane having one or more alkenyl groups

[0020] The liquid hydrosilylation-curable silicone rubber composition according to the invention comprises at least one, such as one, two or more polyorganosiloxanes having one or more alkenyl groups.

[0021] The composition according to the invention comprises as a base polymer one, two or more polyorganosiloxanes having one, two or more alkenyl groups (A) preferably at least two alkenyl groups.

[0022] Preferably the polyorganosiloxanes (A) are selected from the group of one or more polyorganosiloxanes having organic substituents R, i.e. having at least one carbon atom and being bond to the silicon atom by a carbon atom, preferably selected form the group which consists of optionally substituted alkyl groups, such as methyl or halogen alkyl groups such as fluorine-substituted propyl groups, optionally substituted aryl groups, such as phenyl, and one or more alkenyl groups R1, in particular vinyl groups, and preferably an average degree of polymerisation (Pn) between 100 to 12000 siloxy units, calculated in particular from the number average molecular weight which may be determined by GPC measurement versus polystyrene standard, following in particular the procedure according to ASTM D5296 - 11.

[0023] The composition according to the invention comprises at least one polyorganosiloxane as component (A) having alkenyl groups, preferably in average at least two alkenyl groups. Suitable components (A) may be described by the general formula (I),

[0024] (MaDbTcQdR2e)m (I) wherein the indices in formula (I) represent the ratios of the siloxy units M, D, T and Q (according to the common nomenclature on silicones), which may be distributed blockwise or randomly in the polyorganosiloxane (A). Within a polyorganosiloxane (A) each siloxane unit may be identical or different and a = 0 - 10 b = 0 - 12000 c = 0 - 50 d = 0 - 1 e = 0 - 300 m = 1 - 1000, preferably m = 1 , wherein the indices a, b, c, d and m being such that the viscosity of component a) at 20 °C is preferably less than 50 kPa.s (measured at a shear rate of D=1 s-1at 20 °C), whereby not all indices of a to e can be 0, preferably (a + b) is > 0,

[0025] The viscosity of component (A refers to the viscosity of a single component a) or a mixture of components (A). The latter case of the mixture includes, in particular, the presence of individual components (A1) and (A2) as described below that may have a viscosity exceeding 1 kPa.s at 20 °C, and for example resinous components (A3) that comprise Q and orT units, as described also below.

[0026] In formula (I) “(Ea-d) x m” should represent the average polymerisation degree Pnbased on the number-average molecular mass Mn.

[0027] In the formula (I):

[0028] M= RaSiOi / 2, or M*

[0029] D= R2SiO2 / 2, or D*

[0030] T= RSiC>3 / 2, or T*

[0031] Q=SiO4 / 2,

[0032] R2= divalent bridging group between two siloxy groups, in particular, alkylene (or alkanediyl) groups, wherein each R, which may be the same or different, and each be an organic group, which is preferably selected from optionally substituted alkyl with up to 12 carbon atoms, most preferably methyl, optionally substituted aryl with up to 12 carbon atoms, most preferably phenyl, the groups R being free of aliphatic unsaturation, and

[0033] M*= R1PR3-pSiOi / 2,

[0034] D*= R1qR2-qSiO2 / 2,

[0035] T*= R1SiO3 / 2, wherein p= 0-3, preferably 1-3, q= 1-2, and

[0036] R is preferably selected from n-Ci-Ci2-, iso-C3-Ci2-, ortertiary-C4-Ci2-alkyl, alkoxyalkyl, Cs-Ci2- cyclic alkyl, or C6-Ci2-aryl, alkylaryl, which groups may be substituted in addition by one or more O-, CI-, CN- or F-atom, or poly(C2-C4)-alkylene ethers with up to 500 alkylene oxy units the groups R being free of aliphatic unsaturation. Examples of suitable monovalent hydrocarbon radicals R include alkyl radicals, preferably such as CH3-, CH3CH2-, (CHs^CH-, C8Hi7- and C H2I-, and cycloaliphatic radicals, such as cyclohexylethyl, aryl radicals, such as phenyl, tolyl, xylyl, aralkyl radicals, such as benzyl, 2-phenylethyl and 2-phenylpropyl. Preferable monovalent halohydrocarbon radicals have the formula CnF2n+iCH2CH2- wherein n has a value of from 1 to 10, such as, for example, CF3CH2CH2-, C4F9CH2CH2- , C6F13CH2CH2-, C2F5-0(CF2-CF2-0)I-IOCF2-, F(CF(CF3)-CF2-0)I-5-(CF2)O-2-, C3F7-OCF(CF3)- and C3F7- OCF(CF3)-CF2-OCF(CF3)-. The most preferred groups for R in the polyorganosiloxane (A) of the inventive composition are selected form the group which consists of methyl, phenyl, and 3,3,3-trifluoropropyl groups, still more preferred R is methyl.

[0037] R1is selected from unsaturated groups, comprising C=C-group-containing groups (alkenyl groups), e.g.: n-C2-Ci4-, iso-Cs-Cu-, or tertiary- C4-Ci4-alkenyl or Ce-C -cyclic alkenyl, C6-C14- cycloalkenyl, Cs-Cu -alkenylaryl, cycloalkenylalkyl, vinyl, allyl, methallyl, 3-butenyl, 5-hexenyl, 7-octenyl, ethyliden-norbornyl, styryl, vinylphenylethyl, norbornenyl-ethyl, limonenyl, optionally substituted by one or more O- or F-atoms. The alkenyl radicals are preferable attached to terminal silicon atoms, with the olefin function at the end of the alkenyl group of the higher alkenyl radicals, because of the more ready availability of the alpha-, omega-dienes used to prepare the higher alkenyl siloxanes.

[0038] Preferred groups for R1are vinyl, allyl, 5-hexenyl, cyclohexenyl, limonyl, styryl, vinylphenylethyl.

[0039] The group R2includes for example divalent aliphatic or aromatic n-, iso-, tertiary- or cycloalkylene with up to 14 carbon atoms, arylene or alkylenearyl groups. R2forms bridging elements between two siloxy units. The content of the R2groups does not exceed 30 mol.% preferably not exceed 20 mol.% of all siloxy units. Preferably R2is absent. Preferred examples of suitable divalent hydrocarbon groups R2include any alkylene residue, preferably such as -CH2-, -CH2CH2-, -CH2(CH3)CH-, -(CH2)4-, -CH2CH(CH3)CH2-, -(CH2)6-, -(CH2)8- and -(CH2)i8-; cycloalkylene radical, such as cyclohexylene; arylene radicals, such as phenylene, xylene and combinations of hydrocarbon radicals, such as benzylene, i.e. -CH2CH2-C6H4- CH2CH2-, -C6H4CH2-. Preferred groups are alpha, omega-ethylene, alpha, omega- hexylene,1 ,4-phenylene or 1 ,4-ethylenephenyl. Further examples include divalent halohydrocarbon radicals R2e.g. any divalent hydrocarbon group R2wherein one or more hydrogen atoms have been replaced by halogen, such as fluorine, chlorine or bromine. Preferable divalent halohydrocarbon residues have the formula -CH2CH2(CF2)I- CH2CH2- such as for example, -CH2CH2CF2CF2CH2CH2- or other examples of suitable divalent hydrocarbon ether radicals and halohydrocarbon ether radicals including -CH2CH2OCH2CH2-, -C6H4-O-C6H4-, -CH2CH2CF2OCF2CH2CH2-, and -CH2CH2OCH2CH2CH2-.

[0040] Component (A) comprising R, R1and / or R2radicals are e.g. alkenyl-dimethylsiloxy or trimethylsiloxy terminated poly(dimethylsiloxy)(alkenylmethylsiloxy)siloxanes, which may contain other siloxane units than alkenylmethylsiloxy groups or dimethylsiloxy groups such as poly(dimethyl-co-diphenyl)siloxanes. Broadly stated component (A) of the compositions of this invention may be any polyorganosiloxane compound containing two or more silicon atoms linked by oxygen and optionally divalent groups R2wherein the silicon is bonded to 0 to 3 monovalent groups per silicon atom, with the proviso that the polyorganosiloxane compound contains one or more preferably two or more alkenyl groups, in particular, vinyl groups.

[0041] The siloxane units with radicals R and / or R1may be equal or different for each silicon atom. In a preferred embodiment component (A) has the structure

[0042] R1pR3-pSiO(R2SiO)mi(R1RSiO)nSiR1pR3-p (1) with p = 0 - 3, preferably 1 , ml = 10-3000, preferably 100-2000, n = 0- 3000, preferably 3-2000, more preferred 5-500, most preferred n = 0. In a particularly preferred embodiment formula (1) n is 0. With other words a,o-alkenyl- terminated polyorganosiloxanes, in particular, dimethylvinylsiloxy-terminated polydimethylsiloxanes are particularly preferred.

[0043] A preferred polyorganosiloxane component (A) for the composition of this invention is thus a substantially linear polyorganosiloxane (A1). The expression “substantially linear” includes polyorganosiloxanes (A1) that do not contain more than 0.2 mol.% (trace amounts) of siloxy units of the branched type T or Q. This means the polymer (A) is preferably a linear, flowable fluid (A1):

[0044] R1pR3-pSiO(R2SiO)miSiR3-pRp1(1 a) wherein R1, R, p and ml are as defined above, with the proviso, that there are at least two alkenyl groups per molecule. Preferred structures include

[0045] VipMe3-pSiO(Me2SiO)io-3ooo SiMes-p Vip(1b),

[0046] (p is as defined above), PhMeViSiO(Me2SiO) -2ooo SiPhMeVi (1 c),

[0047] (Vi = Vinyl, Me = Methyl and Ph = Phenyl).

[0048] In the group of alkenyl comprising siloxanes (A) the addition of a second or a third siloxane as component (A2) and / or (A3) is preferred. The purpose of component (A2) and (A3) so-called vinyl rich polymers is to modify mechanical properties and crosslinking density.

[0049] Polyorganosiloxanes particular suitable for LSR (Liquid Silicone Rubber) are selected from the group of siloxane polymers with about 100 to about 2000 siloxy units.

[0050] The polymers (A2) are selected either from the group consisting of polymers of the formulas (1d) to (1 i), i.e. linear polyorganosiloxanes having additional alkenyl side groups wherein the concentration of T- and Q-groups are below 0.2 mol.% or polyorganosiloxanes having a higher concentration of T- and Q-groups than the previous polymer types (A1) or (A2).

[0051] The polymers (A2) are represented preferably for example by the formulas 1d)- 1f):

[0052] R1PR3-p(R2SiO)bi(R1R SiO)bixSiR3-pRP1(ld)

[0053] Me3SiO(Me2SiO)bi(MeR1SiO)bixSiMe3(le),

[0054] R1Me2SiO(Me2SiO)bi(Me R1SiO)bixSiMe2R1(lf), whereby b1 = > 0 - 2000 b1x = > 0 - 2000 b1 + b1x = > 10 - 2000

[0055] R1, R, p are as defined above,

[0056] R1= preferably vinyl, allyl, hexenyl, cyclohexenyl, limonyl, styryl, vinylphenylethyl. Preferred groups for R are methyl, phenyl, 3,3,3-trifluoropropyl.

[0057] Other preferred structures of (A2) are

[0058] VipMe3-pSiO(Me2SiO)i-2ooo (MeViSiO)io-isoo SiMea-pVip (1 g),

[0059] Me3SiO(Me2SiO)i-2ooo (MeViSiO)io-isooSiMe3 (1 h),

[0060] PhMeViSiO(Me2SiO)i-2ooo (MePhSiO)io-i5ooSiPhMeVi (1 i) and wherein Me= methyl, Vi= vinyl, Ph= phenyl, and p= 0 to 3, preferred p=1.

[0061] The third component of polymer (A), branched polymers (A3), are preferably selected from those of the formula (la) wherein the polyorganosiloxane (A3) comprising alkenyl groups have more than 0.2 mol.% of T=RSiO3 / 2 or Q=SiO4 / 2-units.

[0062] (M 0.4-4D0-1 oooT 0-50Q0-1 ) 1-1000 ( la) wherein:

[0063] M= R3SiOi / 2, or M*

[0064] D= R2SiO2 / 2, or D*

[0065] T= RSiO3 / 2, or T*

[0066] Q=SiO4 / 2 as defined above, wherein M*, D* and T* are as defined above, carrying unsaturated groups R1. The amount of such M*, D* and T* units is preferably 0.001 to 20 mol.%, more preferably 0.01 to 15 mol.%, most preferably 0.1 to 10 mol.% based on all siloxy units.

[0067] The range of the sub-indices defines a range of the possible average polymerization degrees Pnaccording to the number average molecular weight Mn.

[0068] The indices relate to suitable viscosities as defined later on and describe polymers without any solvent for a viscosity adjustment.

[0069] The polyorganosiloxanes (A2) and (A3) have usually a higher concentration of unsaturated groups R1. Branched polymers (A3) are described e.g. in US 5109095. Preferably the branched vinyl-rich polymers (A3) are soluble in xylene > 10 wt.% resin and have a range of D : T > 10 : 1 preferably > 33 : 1 and / or respectively

[0070] (M : Q) = (0.5 to 4) : 1 , such as e.g. (MO.7M*O.O5Q)IO-5OO (1j).

[0071] All these polymers may be prepared by any of the conventional methods for preparing triorganosiloxane-terminated polydiorganosiloxanes. For example, a proper ratio of the appropriate hydrolyzable silanes, e.g., vinyldimethylchlorosilane, trimethylchlorosilane, tetrachlorosilane, methyltrichlorosilane and dimethyldichlorosilane, or its corresponding alkoxysilanes, may be co-hydrolyzed and condensed. Other reaction routes may run alternately over equilibration reactions of 1 ,3-divinyltetraorganodisiloxane, e.g. symmetrical divinyldimethyldiphenylsiloxane or divinyltetramethylsiloxane, which furnishes the endgroups of the polydiorganosiloxane, which may be equilibrated with an appropriate polydiorganosiloxane, e.g., octamethylcyclotetrasiloxane, in the presence of an acidic or basic catalyst.

[0072] The vinyl-rich polymers are in particular the branched polymers having MQ or MDQ structures and Si-alkenyl or SiH groups can replace the filler component (C) partly and provide nevertheless high mechanical reinforcement. This could be an additional option to reduce viscosity and modify electrical properties.

[0073] In a preferred embodiment the polymer component (A) is a mixture of polymers of the formula (la) and / or of the formula (1d) and / or (1j) whereby the mixture has an alkenyl content in average of preferably below 2 mol.% of all siloxy units of the mixture a), whereby polymer (A1) is present in a higher amount than (A2) or (A3).

[0074] The polyorganosiloxanes (A) which are defined above for the purposes of this invention, are preferably essentially free of cyclic polydiorganosiloxanes (less than 1 wt.%, more preferably 0.5 wt.% measured for 1 h at 150 C and 20 mbar).

[0075] In the preferred embodiment of Liquid Silicone Rubber (LSR) compositions it is preferred to use viscosities of less than 1 kPa.s; with respect to polydimethylsiloxanes this relates roughly to Pnvalues of <2500 siloxy units. In both embodiments vinyl functionalized polydimethylsiloxanes are preferred.

[0076] The viscosity of the polyorganosiloxane (A) for LSR is preferably 100 to 1000*103mPa.s at 20°C at a shear rate of D = 10 s-1and the number of siloxy units Pnis preferably > 10 to 2500. In a preferred embodiment for the LSR polymer (A) a mixture of e.g. 2-4 polymers of component (A) can be used which has a viscosity of less than 200,000 mPa.s at 20 °C at a shear rate of D= 10 s’1, in order to ensure a sufficiently low viscosity for liquid silicone rubber composition. Such a low viscosity is advantageous for the manufacture of compositions comprising reinforcing fillers and processing these compositions in a LSR injection molding process.

[0077] The alkenyl content of the components a) may be determined here by way of1H NMR - see A.L. Smith (ed.): The Analytical Chemistry of Silicones, J. Wiley & Sons 1991 Vol. 112 pp. 356 et seq. in Chemical Analysis ed. by J.D. Winefordner.

[0078] In a preferred embodiment of the invention Component (A) comprises at least one of component (A11), and at least one of component (A21), which are preferable as follows: (A11) at least one polyorganosiloxane of the formula (la), wherein each R is independently selected from saturated or aromatic organic groups as defined above, each R1is independently selected from alkenyl groups as defined above, and x is > 0,

[0079] (A21) at least one polyorganosiloxane of the formula (lb), wherein x, R and R1are as defined above; R2is selected from R or R1, and y is > 1 .

[0080] In a preferred embodiment of the invention in the curable silicone rubber composition the molar ratio of the alkenyl groups R1in component (A21) to the alkenyl groups R1in component (A11) is in the range of 0.3 to 8, preferably 0.6 to 6, more preferably 1 to 5. Component (A11)

[0081] The inventive composition preferably comprises at least one polyorganosiloxane (A11) of the formula (la): wherein each R is as defined above, and R1is as defined above, and x is > 0, preferably x is

[0082] > 10, more preferably x is > 100, and preferably x is less than 2000, more preferably less than 1500, and even more preferably less than 1000.

[0083] Preferably the viscosity of component (A11) at 25 °C is less than 100000 mPa.s, preferably the viscosity is more than 5000 mPa.s (measured at a shear rate of D=10 s-1at 25 C).

[0084] The viscosities of such polymers are preferably in the range of 10 to 100,000 mPa.s, more preferred 40 to 70,000 mPa.s (measured at a shear rate of D=10 s-1at 25 C).

[0085] The viscosity of component (A11) refers to the viscosity of a single component (A11) or a mixture of components (A11). The latter case of the mixture includes with it the presence of individual components (A11) that may have a viscosity exceeding 100000 mPa.s at 25° C. x is an average value calculated from the number-average molecular weight Mnof the polydiorganosiloxanes of the formula (la), which is determined by gel permeation chromatography using polystyrene standard. x is preferably 10 - 2000, more preferably 100-1000.

[0086] The average number molecular weight Mn(determined by gel permeation chromatography using polystyrene standard) is preferably in the range of up to 200000 g / mol, the more preferred range is up to 100000 g / mol.

[0087] Preferred structures of the polydiorganosiloxane (A11) include:

[0088] ViMe2SiO(Me2SiO) 10-2000 SiMe2Vi (11a),

[0089] ViPhMeSiO(Me2SiO)io-2ooo SiMePhVi (11 b), wherein Vi is a vinyl group, Me is a methyl group and Ph is a phenyl group. Particularly preferred are polydiorganosiloxanes of formula (1a).

[0090] In a preferred embodiment of the invention a mixture of at least two polydiorganosiloxanes (A11) is used which differ in their chain lengths. Preferably, a mixture of the following two polydiorganosiloxanes (A11-1) and (A11-2) is used:

[0091] (A11-1):

[0092] R1R2SiO(R2SiO)xiSiR2R1 wherein x1 is 10 to 700, and R and R1are as defined above, preferably R is methyl and R1is vinyl, (A11-2):

[0093] R1R2SiO(R2SiO)x2SiR2R1wherein x2 is > 700, preferably > 800, and R and R1are as defined above, preferably R is methyl and R1is vinyl.

[0094] The weight ratio (A11-1) to (A11-2) is preferably 99:1 to 1:99, preferably 49 : 51 to 10 : 90. Component (A21)

[0095] The inventive composition preferably comprises at least one polyorganosiloxane (A21) of the formula (lb): wherein x, R and R1are as defined above; and R2is selected from R or R1as defined above and y is > 1.

[0096] The siloxane units with radicals R and / or R1can be equal or different for each silicon atom. In a preferred embodiment the structure is

[0097] R1pR3-pSiO[R2SiO]x[R1RSiO]ySiR1pR3-p (11c) wherein R and R1are as defined above, p = 0 - 3, preferably 1 , x = 10 - 2000, preferably 100-1000, y = 1-500, preferably 1-200, more preferably 1-100, even more preferably 1-50.

[0098] The purpose of component (A21) a so-called alkenyl rich, suitably vinyl rich polymer again is to modify mechanical properties and crosslinking density.

[0099] Preferred polydiorganosiloxanes (A21) are represented by the formulas Me3SiO(Me2SiO)x(MeR1SiO)ySiMe3(11 d), R1Me2SiO(Me2SiO)x(MeR1SiO)ySiMe2R1(11e), whereby x = > 0 - 2000, preferably 10 to 800, more preferably 50 to 700, y = > 0 - 500, preferably 5 to 200, more preferably 7 to 100, x + y = > 10, preferably > 15, more preferably > 50, more preferably > 57, more preferably > 70, more preferably > 75, R1, R are as defined above,

[0100] More preferred polydiorganosiloxanes (A21) are represented by the formula (11e). In a preferred embodiment of the invention a mixture of at least two polydiorganosiloxanes (A21) is used which differ in their chain lengths. Preferably a mixture of the following two polydiorganosiloxanes (A21-1) and (A21-2) is used: (A21-1): R1Me2SiO(Me2SiO)xi(MeR1SiO)yiSiMe2 R1(11f), x1 = > 100 - 2000, preferably 200 to 800, more preferably 300 to 700, y1 = > 10 - 500, preferably 15 to 200, more preferably 30 to 100, x1 + y1 = > 110, preferably >215, more preferably > 300, more preferably > 330, more preferably > 500

[0101] R1, R are as defined above,

[0102] (A21-2):

[0103] R1Me2SiO(Me2SiO)x2(MeR1SiO)y2SiMe2R1(11f), x2 = > 10 - 100, preferably 20 to 100, more preferably 30 to 90, y2 = > 1 - 100, preferably 5 to 70, more preferably 7 to < 30, x2 + y2 = > 11 , preferably > 30, more preferably > 50, R1, R are as defined above,

[0104] The weight ratio (A21-1) to (A21-2) is preferably 99:1 to 1 :99, preferably 51 : 49 to 90 : 10. Further preferred structures of polydiorganosiloxane (A21) are VipMe3-pSiO(Me2SiO)io-2ooo (MeViSiO)i-iooo SiMea-p Vip(11 f) ,

[0105] Me3SiO(Me2SiO) -2ooo (MeViSiO)i-ioooSiMe3 (11g),

[0106] PhMeViSiO(Me2SiO)w-2ooo (MeViSiO)i-ioooSiPhMeVi (11 h) wherein Me = methyl, Vi = vinyl, Ph = phenyl, and p= 0 to 3, preferred p=1.

[0107] The average number molecular weight Mnis preferably in the range of up to 100000 g / mol, the more preferred range up to 50000 g / mol, which is determined preferably using GPC with polystyrene standards.

[0108] In a preferred embodiment the weight ratio of the polydiorganosiloxane (A11) to polydiorganosiloxane (A21) is 100 : 1 to 1 : 1 , preferably 20 : 1 to 2 : 1.

[0109] It is also possible in the present invention that Component (A) comprises only at least one of component (A11) or only at least one of component (A21), that is components (A11) and (A21) are not used together but are used alone.

[0110] (B) at least one polyorganosiloxane having one or more SiH groups

[0111] The curable silicone rubber composition comprises component (B), that is, at least one organohydrogensiloxane having one or more such as at least two SiH groups, wherein component (B) is selected from one or more polyorganohydrogensiloxanes of the general formula (2): [MaDbTcQdZe]m (2) wherein: M = R3SiOi / 2, and / or MH*

[0112] D = R2SiO2 / 2, and / or DH*

[0113] T = RSiO3 / 2, and / or TH*

[0114] Q = SiO4 / 2, with MH*= HR2SiOi / 2, DH*= HRSiO2 / 2, TH*= HSiO3 / 2,

[0115] Z is a divalent optionally substituted hydrocarbyl bridging group with up to 14 carbon atoms between two siloxy groups, which siloxy groups are as defined before, and R is as defined above, a = 0.01-10 preferably = 2-5, most preferably =2 b = 0-1000 preferably = 10-500 c = 0-50 preferably= 0 d = 0-5 preferably = 0 e = 0-3 preferably = 0 m = 1-1000, preferably = 1-500, most preferably =1 , with the proviso that there are one or more such at least two groups selected from MH*, DH* and TH*.

[0116] Preferably, the component (B) is selected from polysiloxanes that have only methyl or phenyl groups, even more preferably only methyl groups as organic residues.

[0117] Preferably, the polyorganohydrogensiloxanes (B) have at least 10, preferably at least 15, more preferably at least 20, still more preferably at least 25 and most preferably at least 30 silicon atoms.

[0118] The siloxy units can be distributed blockwise or randomly in the polymer chain.

[0119] The aforementioned indices should represent the average polymerization degree Pnbased on the average number molecular mass Mn.

[0120] The range for M-, D-, T- and Q-units present in the molecule basically can cover nearly all values representing fluids, flowable polymers, liquid and solid resins as long as they are suitable for the LSR compositions. It is preferred to use liquid linear, cyclic or branched siloxanes. Optionally these siloxanes can comprise additional traces of Ci-Ce-alkoxy or Si- hydroxy groups remaining from the synthesis.

[0121] Preferred structures of component (B) in the compositions of this invention are siloxanes of formula (2a) to (2e).

[0122] Hai(R)3-aiSi[RHSiO]p[R2SiO]q[RR1SiO]zSi(R)3-aiHai (2a) more specifically:

[0123] HR2SiO(R2SiO)q(RR1SiO)z(RHSiO)pSiR2H (2b)

[0124] HMe2SiO(Me2SiO)q(RR1SiO)z(MeHSiO)pSiMe2H (2c)

[0125] Me3SiO(MeHSiO)pSiMe3(2d)

[0126] Me3SiO(Me2SiO)q(RR1SiO)z(MeHSiO)pSiMe3(2e) wherein R and R1are as defined above, R is preferably methyl and / or phenyl, R1is preferably vinyl, and index 'a1 ' is 0 or 1 , p = 0 - 1000, preferably = 0-500, q = 0 - 650, preferably = 0-100, z = 0 - 65, preferably = 0

[0127] 2 < p + q + z <1000, preferably 10 < p + q + z < 650.

[0128] Most preferred is

[0129] HR2SiO(R2SiO)q(RR1SiO)z(RHSiO)PSiR2H (2b) with p, q, z as defined before, with z is preferably 0 and p is preferably 0, and q is preferably 5 to 50, more preferably 10 to 30.

[0130] In the above formulas (2a) to (2e) the molar ratio of SiH-groups to all Si-atoms is preferably more than 0.01 and preferably up to 0.7, and the total number of Si atoms is preferably at least 7, more preferably at least 15 and even more preferably at least 20.

[0131] Furthermore, the use of resinous polyorganohydrogensiloxanes of the following formula is preferred:

[0132] {[T][R290l / 2]n}m (2f)

[0133] {[Q][R29Ol / 2]n[M]0,01-1o[T]0-50, preferably o[D]o-1OOO, preferably o}m (2g) wherein

[0134] Q, T, M, D are as defined above, n = 0 to 3, preferably n = 0, m is as defined above,

[0135] R29is hydrogen, Ci-C2s-alkyl, such as methyl, ethyl, n-propyl, iso-propyl, n-, iso- and tert.-butyl, alkanoyl, such acyl, aryl, -N=CHR, such as butanonoxime, alkenyl, such as propenyl, with the proviso that there are at least two groups selected from M*, D* and T*. Most preferred resinous polyorganohydrogensiloxanes are of the formula consisting of Q and M* units, 6.Q. {[Q][M*]o, 01-10, preferably 1-1o}m (2h) wherein Q, M* and m are as defined above, and m is preferably 1 to 20.

[0136] One preferred embodiment of the compounds (2g) is provided by way of example by monomeric to polymeric compounds which can be described via the formula [(Me2HSiOo.s)kSi04 / 2]i-iooo wherein index k is from 0.3 to 4. Such liquid or resinous molecules can contain significant concentrations of SiOH- and / or (Ci-Ce)-alkoxy-Si groups of up to 10 mol.% related to the silicon atoms.

[0137] Particular preferred resinous polyorganohydrogensiloxanes (B) include e.g.

[0138] M*2D -30,

[0139] Q(M*)4,

[0140] M2DIO-3OD*IO-3O, and

[0141] [M* Q]I-40. Preferred viscosities of the resinous polyorganohydrogensiloxanes (B) are 1 to 100 mPa.s at 25 C at a shear rate of D=10 s-1.

[0142] Specific examples of preferred suitable compounds for component (B) in the compositions of this invention include

[0143] M eaSi O- (M e H S i O) 2-50- Si M 63 ,

[0144] Me3SiO-(MeHSiO)2-5o(Me2SiO)i-iooSiMe3,

[0145] (MeHSiO)3-7,

[0146] HMe2SiO-(MeHSiO)o-6o(Me2SiO)i-25oSiMe2H

[0147] HMe2SiO(Me2SiO)o-3o(MePhSiO)o-3o(MeHSiO)2-5oSiMe2H, Me3SiO(Me2SiO)o-3o(MePhSiO)o-3o(MeHSiO)2-5oSiMe3, Me3SiO(Me2SiO)o-3o( h2SiO)o-3o(MeHSiO)2-5oSiMe3, wherein in each formula the molar ratio of SiH-groups to all Si-atoms is preferably more than 0.01 and the total number of Si atoms is preferably at least 7, more preferably have at least 10, more preferably at least 15, most preferably at least 20 atoms.

[0148] The SiH-content of the polyorganohydrogensiloxanes (B) is preferably at least 0.1 mmol / g, more preferably at least 0.2 mmol / g, and at most preferably 17 mmol / g, more preferably at most 15 mmol / g, more preferably 0.1 to 17 mmol / g, and most preferably 0.2 to 13 mmol / g. If more than one component (B) is used, these Si-contents apply for each specific component (B) used.

[0149] Most preferred are compounds of the formula HMe2SiO-(MeHSiO)o-6o(Me2SiO)i-25oSiMe2H even more preferred in admixture with at least one resinous polyorganohydrogensiloxane (B), preferably of formula [MH*I-4Q]I-4O, preferably in a weight ratio of HMe2SiO-(MeHSiO)o-6o(Me2SiO)i-25oSiMe2H / [MH*I-4Q]I-4O in the range of 49 : 51 to 1 : 99.

[0150] The component (B) can be used as a single component of one polyorganohydrogensiloxane or preferably as mixtures of at least two thereof. Most preferred are mixtures of linear polyorganohydrogensiloxanes consisting of D and / or DH* and M and / or MH* units and resinous polyorganohydrogensiloxanes, consisting of Q and M and / or MH* units, preferably in a weight ratio of 49 : 51 to 1 : 99.

[0151] If an increase of the cure rate is required, it is preferred to use some organopolysiloxanes (B) having HMe2SiOo,s- units or homo MeHSiO-polymers to adjust the cure rate to shorter times.

[0152] If it is necessary to still further increase the cure rate, this can be achieved by way of example via an increase of the molar ratio of SiH to Si-alkenyl, or an increased amount of catalyst (D). The component (B) has preferably a viscosity at 25 °C from 2 to 2000 mPa s, preferably from 1 to 1000 mPa s, still more preferably 2 to 100 mPa s (preferably measured at a shear rate of D=10 s-1). Preferably, the crosslinker (B) should have at least 2, more preferably at least 3, in some instances also more than 15 and more than 20 SiH-groups per molecule.

[0153] In a preferred embodiment of the invention the curable silicone rubber composition comprises at least one resin based organohydrogensiloxane comprising at least one unit selected from T, TH* and Q, preferably Q.

[0154] In a particularly preferred embodiment of the invention in the curable silicone rubber composition, at least two different organohydrogensiloxanes B) are used. Furthermore, in the curable silicone rubber composition according to the invention preferably the organohydrogensiloxanes (B) are selected from the group of (B1) a resin based organohydrogensiloxane having > 2 terminal SiH groups, preferably comprising at least one unit selected from T, TH* and Q, preferably Q, and (B2) an organohydrogensiloxane having 2 or more SiH groups and being different from (B1).

[0155] (C) at least one filler component selected from one or more silicas

[0156] The curable silicone rubber composition according to the invention comprises at least one reinforcing filler (C) which is selected from one or more preferably reinforcing silicas preferably from at least one, preferably surface-treated, silica filler.

[0157] Preferably, the liquid curable liquid silicone rubber composition according to the invention comprises about 3 to 30, preferably about 5 to 25, more preferably about 10 to 20 weight percent of the one filler component (C) based on the total amount of the composition.

[0158] Preferably the reinforcing filler (C) is a silica filler which is selected from the group of fumed silica and precipitated silica, having a BET from 50 to 500 m2 / g preferably measured according to DIN-ISO 9277 with nitrogen. Most preferably, the reinforcing filler (C) is a silica filler selected from a surface-treated filler.

[0159] Preferably the surface treatment of the silica filler can be done though reaction with hydrophobic organosilicon compounds selected from the group of disilazanes, silylamines, silanols, bis(polyorganosiloxanyl)amine of the formula [RaRbRcSi (OSi(Me)2)t]2NH where Rais methyl, ethyl, or phenyl; Rbis methyl or ethyl, Rcis vinyl or allyl; and t is an integer of from 2 to 12 inclusive, trimethylsilanol, trimethylchlorosilane, trimethylethoxysilane, triorganosilyloxyacylates, such as vinyldimethylacetoxysilane, triorganosilylamines, such as trimethylsilylisopropylamine, trimethylsilylethylamine, dimethylphenylsilylpropylamine and vinyldimethylsilylbutylamine, triorganosilylaminooxy compounds, such as diethylaminooxytrimethylsilane and diethylaminooxydimethylphenylsilane, and additionally hexamethyldisiloxane, 1 ,3-divinyltetramethyldisiloxane, 1 ,3-diphenyltetramethyldisiloxane and 1 ,3-diphenyltetramethyldisilazane.

[0160] Other examples of organosilicon compounds are dimethyldichlorosilane, dimethyldiethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, vinylmethyldimethoxysilane, methyltriethoxysilane, octamethylcyclotetrasiloxane and / or dimethylpolysiloxanes having from 2 to 12 siloxane units per molecule and containing a hydroxyl group bonded to Si in each of the terminal units.

[0161] Most preferably the reinforcing filler (C) is at least one silica filler surface-treated with at least one silazane, preferably an organosilazane, e.g. of the formula R’3Si-[NH-SiR’2]n-NH-SiR’3 (with n being > 0) and R’ being an organic group, preferably selected from methyl and / or vinyl. Most preferred are divinyltetramethyldisilazane and hexamethyldisilazane and a mixture thereof. In a particular preferred embodiment the silica filler (C) is subjected to an extended surface treatment with one or more organosilazanes, which may include a single step treatment for an extended period of time, such as at least 2 or 3 hours, or a multiple step surface-treatment. In further particularly preferred embodiment the surface-treated silica filler, is prepared by the surface-treatment of silica in a two-step process comprising subsequent reaction of said silica with at least two charges of silazanes. Preferably the at least one silica filler (C) is a surface-treated silica filler, which is obtained by the following steps: a) providing a mixture comprising the components A), B) and at least one silica filler C), b) adding at least one silazane having at least one alkenyl group and at least one silazane which does not have alkenyl groups to said mixture, c) heating to at least 100°C for at least 1 h, d) removal of the volatiles, and e) further adding at least one silazane which preferably does not have alkenyl groups, f) heating to at least 100°C for at least 1 h, and g) removal of the volatiles.

[0162] Preferred silica fillers are preferably those known as reinforcing silicas, which also permit production of elastomers having sufficient transparency for irradiation. Preferred are reinforcing silicas, in particular those increasing the strength. Examples are silicas whose BET surface areas are from 50 to 400 m2 / g, preferably 80 to 350 m2 / g preferably measured according to DIN-ISO 9277 with nitrogen, in particular, fumed or precipitated silicas. Preferably, these fillers are surface-hydrophobicized. The amount of reinforcing filler (C) is preferably from 1 to 100 parts by weight, more preferably from 5 to 90 parts by weight, even more preferably from 10 to 80 parts by weight, even more preferably from 15 to 70 parts by weight based on 100 parts by weight of the total amounts of components (A) and (B).

[0163] Fillers whose BET surface areas are above 50 m2 / g permit production of silicone elastomers with improved properties. In view of strength and transparency fumed silicas are preferred, and even more preferred silicas are, for example, Aerosil® 200, 300, HDK® N20 or T30, Cab-O- Sil® MS7 or HS5 having more than 200 m2 / g BET surface area. As BET surface area rises, the transparency of the silicone mixtures in which these materials are present also rises. Examples of trade names of the materials known as precipitated silicas, or wet silicas, are Vulkasil®VN3, or FK 160 from Evonik (formerly Degussa), or Nipsil®LP from Nippon Silica K.K. and others.

[0164] It is preferred to use silica fillers having BET-surface areas of 50 m2 / g or more, preferably having a BET-surface of at least 150 m2 / g. Such compositions can be also photo-activated if desired due to sufficient transparency.

[0165] The reinforcing silica filler (C) may be subject of any suitable conventional surface-treatment with suitable surface-treatment agents belonging to hydrophobizing treatment with a suitable hydrophobizing agent, dispersing treatment with suitable dispersing agents, which influence the interaction of the filler with the silicone polymer, e.g. influence thickening action. The surface treatment of the fillers is preferably a hydrophobization with silanes or with siloxanes. It can by way of example take place in situ via addition of silazanes, such as hexamethyldisilazane and / or 1,3-divinyltetramethyldisilazane, with addition of water, and 'in- situ '-hydrophobation is preferred. It can also take place with other familiar filler-treatment agents with polyorganosiloxanediols whose chain lengths are from 2 to 50 and which bear unsaturated organic radicals, with the aim of providing reactive sites for the crosslinking reaction. Examples of commercially available silicas pre-hydrophobized with various silanes are: Aerosil® R 972, R 974, R 976, or R 812, or, for example, HDK 2000 or H30 Examples of trade names for materials known as hydrophobized precipitated silicas or wet silicas are e.g. Sipernat D10 or D15 from Evonik (formerly Degussa).

[0166] Rheological properties, i.e. technical processing properties, of the non-cured silicone rubber mixtures can be influenced by the selection of the type of the filler, its amount, and the nature of hydrophobization.

[0167] (D) At least one transition metal hydrosilylation catalyst

[0168] The curable silicone rubber compositions according to the invention comprise at least one transition metal hydrosilylation catalyst (D).

[0169] Component (D) is preferably selected from the group of organometal compounds, salts or metals, having the ability to catalyze hydrosilylation wherein the metal is selected from the group of Ni, Ir, Rh, Ru, Os, Pd and Pt compounds as taught in US 3,159,601; US 3,159,662; US 3,419,593; US 3,715,334; US 3,775,452 and US 3,814,730. Most preferred are platinum compounds.

[0170] Preferably component (D) is selected from hydrosilylation catalysts comprising at least one metal selected from the group consisting of platinum, rhodium, palladium, ruthenium and iridium.

[0171] The catalyst component (D) for the hydrosilylation reaction of the inventive composition is a compound, which facilitates the reaction of the silicon-bonded hydrogen atoms of component (B) with the silicon-bonded olefinic hydrocarbon substituents of component (A). The metal or organometal catalyst compound is preferably based on a platinum group metal. Without wishing to be bound by theory, it is believed that the catalyst (D) includes complexes with sigma- and pi-bonded carbon ligands as well as ligands with S-, N, or P atoms, metal colloids or salts of the afore mentioned metals. The catalyst can be present on a carrier such as silica gel or powdered charcoal, bearing the metal, or a compound or complex of that metal. Preferably, component (D) is selected from any platinum complex compound.

[0172] A typical platinum containing catalyst component in the polyorganosiloxane compositions of this invention is any form of platinum (0), (II) or (IV) compounds, which are able to form complexes. Preferred complexes are Pt-(O)-alkenyl complexes, such alkenyl, cycloalkenyl, alkenylsiloxane such vinylsiloxane, because of its easy dispersibility in polyorganosiloxane compositions. A particularly useful form of the platinum complexes are the Pt(0)-complexes with aliphatically unsaturated organosilicon compound such as a 1 ,3- divinyltetramethyldisiloxane (Vinyl-M2 or Karstedt catalyst): as disclosed by e.g. US 3,419,593 incorporated herein by reference are especially preferred, cyclohexene- Pt, cyclooctadiene-Pt and tetravinyltetramethyl-tetracyclosiloxane (Vinyl-D4)-Pt, e.g. Ashby’s catalyst, a Pt(O) complex in tetramethyltetravinylcyclotetrasiloxane with the empirical formula Pt[(C3HeSiO)4]x.

[0173] Most preferred catalyst component (D) is a Pt° complex with tetramethyl- tetravinylcyclotetrasiloxane that contains about 1 to 3 wt% Pt, preferably 2 wt% Pt, in particular, Ashby’s catalyst.

[0174] Also preferably is a so-called Lamoreaux catalyst, which is a platinum (II) complex compound, obtained from chloroplatinic acid hexahydrate and octyl alcohol (as described for example in US 3,197,432 or US 3,220,972). Preferably are Pt(O) or Pt(ll) catalysts, with preference to Ashby and Lamoreaux platinum catalysts.

[0175] The amount of platinum-containing catalyst component that is used in the compositions of this invention is not narrowly limited as long as there is a sufficient amount to accelerate the hydrosilylation between (A) and (B) at the desired temperature in the required time (B) in the presence of all other ingredients of the inventive composition. The exact necessary amount of said catalyst component will depend upon the particular catalyst, the amount of other inhibiting compounds and the SiH to olefin ratio and is not easily predictable. However, for platinum catalysts said amount can be as low as possible due to cost reasons. Preferably, one should add more than one part by weight of platinum for every one million parts by weight of the organosilicon components (A) and (B) to ensure curing in the presence of other undefined inhibiting traces. For the compositions of this invention, the amount of platinum containing catalyst component to be applied is preferably sufficient to provide from 1 to 200 ppm preferably 2 to 100 ppm, especially preferred 4 to 60 ppm by weight platinum per weight of polyorganosiloxane components (A) plus (B). Preferably, said amount is at least 4 ppm platinum by weight per sum of (A) and (B).

[0176] The hydrosilylation catalyst can also be selected from the group of catalysts capable of being photoactivated. These photo-activatable catalysts preferably contain at least one metal selected from the group composed of Pt, Pd, Rh, Co, Ni, Ir or Ru. The catalysts capable of being photoactivated preferably comprise platinum compounds. Catalyst capable of being photo-activatable is preferably selected among organometallic compounds, i.e. comprise carbon-containing ligands, or salts thereof. In a preferred embodiment, photoactive catalyst (D) has metal carbon bonds, including sigma- and pi-bonds. Preferably, the catalyst capable of being photo-activated (D) is an organometallic complex compound having at least one metal carbon sigma bond, still more preferably a platinum complex compound having preferably one or more sigma-bonded alkyl and / or aryl group, preferably alkyl group(s). Sigma-bonded ligands include in particular, sigma-bonded organic groups, preferably sigma-bonded Ci-Ce-alkyl, more preferably sigma-bonded methyl groups, sigma-bonded aryl groups, like phenyl, Si and O substituted sigma bonded alkyl or aryl groups, such as triorganosilylalkyl groups, sigma- bonded silyl groups, like trialkyl silyl groups. Most preferred photo-activatable catalysts include r|5-(optionally substituted)-cyclopentadienyl platinum complex compounds having sigma- bonded ligands, preferably sigma-bonded alkyl ligands.

[0177] Further catalysts capable of being photoactivated include (r|-diolefin)-(sigma-aryl)-platinum complexes (see e.g. US 4,530,879).

[0178] The catalyst capable of being photoactivated can be used as such or supported on a carrier. Examples of catalysts capable of being photo-activated include r|-diolefin-o-aryl-platinum complexes, such as disclosed in US 4,530,879, EP 122008, EP 146307 (corresponding to US 4,510,094 and the prior art documents cited therein), or US 2003 / 0199603, and also platinum compounds whose reactivity can be controlled by way of for example using azodicarboxylic esters, as disclosed in US 4,640,939 or diketonates.

[0179] Platinum compounds capable of being photo-activated that can be used are moreover those selected from the group having ligands selected from diketones, e.g. benzoylacetones or acetylenedicarboxylic esters, and platinum catalysts embedded into photodegradable organic resins. Other Pt-catalysts are mentioned by way of example in US 3,715,334 or US 3,419,593, EP 1 672 031 A1 and Lewis, Colborn, Grade, Bryant, Sumpter, and Scott in Organometallics, 1995, 14, 2202-2213, all incorporated by reference here. Catalysts capable of being photo-activated can also be formed in-situ in the silicone composition to be shaped, by using Pt(0)-olefin complexes and adding appropriate photo- activatable ligands thereto.

[0180] The catalysts capable of being photo-activated that can be used here are, however, not restricted to these above-mentioned examples.

[0181] The most preferred catalyst capable of being photo-activated to be used in the process of the invention are (r|5-cyclopentadienyl)-trimethyl-platinum, (r|5-cyclopentadienyl)-triphenyl- platinum complexes, in particular, (r|5-methylcyclopentadienyl)-trimethyl-platinum.

[0182] The amount of the catalyst capable of being photo-activatable is preferably 1 to 500 ppm and preferably in the same lower range as defined for the heat-activatable hydrosilylation catalysts mentioned above.

[0183] The most preferred curable silicone rubber composition according to the invention comprises a hydrosilylation catalyst (D) comprising platinum.

[0184] (E) at least one carbon black (CB)

[0185] The curable silicone compositions according to the invention contain at least one or one or more carbon blacks (CB) (E), which are preferably incorporated into the curable silicone compositions of the invention by mixing the other components of the curable compositions with non-curable CB compositions, i.e. carbon black masterbatches.

[0186] The amount of the one or more carbon blacks (E) in the curable silicone compositions of the invention is more than about 6.0 weight percent, preferably more than about 6.1 weight percent, preferably more than about 6.2 weight percent, preferably equal to or more than about 6.3 weight percent each based on the total amount of the composition. Preferably the amount of component (E) is from about 6.0 to about 12 weight percent, more preferably from 6.0 to about 10 weight percent based on the total amount of the silicone rubber composition. Preferably the curable compositions of the invention contain only one kind of carbon black.

[0187] As carbon blacks (E), basically, all kinds of carbon blacks may be used (such as acetylene black, channel black, furnace black, lamp black or thermal black). As is well known to a skilled person in the art carbon black is a form of paracrystalline carbon that has generally a high surface-area-to-volume ratio, albeit lower than that of activated carbon. It is dissimilar to soot in its much higher surface-area-to-volume ratio and significantly lower (negligible and non- bioavailable) polycyclic aromatic hydrocarbon (PAH) content.

[0188] In a preferred embodiment of the invention component (E) is a conductive carbon black, preferably furnace carbon black, i.e. manufactured by the furnace black process.

[0189] In a preferred embodiment the one or more carbon blacks (E) comprise at least one carbon black selected from conductive carbon blacks having a BET surface of > 30 m2 / g and / or an average primary particle size of Dso between 5 to 500 nm. In a further preferred embodiment, the one or more carbon blacks (E) comprise at least one carbon black selected from conductive carbon blacks having one or more of the following properties:

[0190] • a BET surface area of > 100 to 1500 m2 / g, more preferably > 100 to 1400 m2 / g, more preferably > 100 to 1000 m2 / g, more preferably > 250 to 1000 m2 / g, more preferably > 500 to 1000 m2 / g, and / or

[0191] • a primary particle size of Dso between 5 to 500 nm, more preferably 10 to 200 nm, and / or

[0192] • a DBP pore volume 300-600 ml / 100g, more preferably 300-550 ml / 100g, more preferably 300-400 ml / 100g, and / or

[0193] • iodine adsorption 700-1200 mg / g, more preferably 700-1150 mg / g, more preferably 700-1000 mg / g, more preferably 700-900 mg / g, and / or

[0194] • pH 8-11 , more preferably pH 9-11 , more preferably pH 9-10.5 and / or

[0195] • metal content < 50 ppm, and / or

[0196] • sulphur content < 150 ppm, and / or

[0197] • water content < 0.5 wt.%, and / or

[0198] • volatiles content < 1 wt.%, and / or

[0199] • fines <125 micron in pellets < 10 wt.-%, and / or

[0200] • grit content: < 50 mg / kg, and / or

[0201] • ash content: < 0.1 wt.-%.

[0202] Commercially available carbon blacks include in particular PrintexXE2, PrintexHV (Evonik), Black Pearls 2000, VulcanoxC72, VulcanoxC72 (Cabot), Ketjen Black EC300J, Ketjen Black EC600JD (Akzo Nobel), Ensaco 360 g, Ensaco 350 g, Ensaco 350 p, Ensaco 250 g (Timcal), CL-08 (Continental Carbon), Denka Black HS100, Denka Black HS100, Denka Black HS100 (Denka Chemicals), CD 7087 (Columbian Chemicals), TokaBlack5500 (TokaiCarbon), Chezacarb A (Unipetrol) etc.

[0203] Particularly preferred carbon blacks are conductive carbon blacks marketed under the trademark Ketjenblack (from Akzo Nobel), especially Ketjenblack EC-300J, and electroconductive carbon black (CAS number 1333-86-4) in the form of pellets.

[0204] The carbon black component (E) is preferably introduced in the form of a carbon black master batch such as described in WO2022 / 084434 which is prepared by comprises the extrusion of one or more polyorganosiloxanes (E) with one or more carbon blacks (E). As described therein the process comprises the extrusion of one or more polyorganosiloxanes with one or more carbon blacks. The disclosure of WO2022 / 084434 is here fully incorporated by reference to such patent application. (F) At least one carbon nanotube (CNT)

[0205] The silicone rubber composition according to the invention comprises at least one or one or more carbon nanotube materials (F). Preferably component (F) is selected from single wall carbon nano tubes.

[0206] As is known in art, a carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometre range (nanoscale). In the present invention for example single-walled carbon nanotubes (SWCNTs) having average diameters of around 0.5-2.0 nanometres and average lengths in the range of for example 2 to 60 pm, such as 5 to 55 pm or 5 to 35 pm or 20 to 55 pm, and multi-walled carbon nanotubes (MWCNTs) consisting of single-wall carbon nanotubes in a nested, tube-in-tube structure, including double- and triple-walled carbon nanotubes can be used. Preferably the carbon nanotubes (F) have an average length / diameter (L / D) value of 500 or more and 5000 or less. The specific surface area of the carbon nanotubes can be in the range of for example 200 to 700, preferably 35 to 600 m2 / gram. It is also possible to use functionalized (e.g. carboxy or hydroxy functionalized) carbon nanotube materials, although this embodiment is less preferred. While MWNTs exhibit cost advantages over SWNTs and show enhanced thermal and chemical stability, the use of SWNTs is preferred in respect to lower the decrease of conductivity upon dimensional changes of the cured compositions. Commercial products to be used in the present invention are for example M2013L4, M2013L5 (Ocsial) in particular the TLIBALL™ MATRIX concentrates (Black flakes paste with a standard dosage 0.4%-10%).

[0207] In the liquid curable silicone rubber composition according to the invention preferably the amount of component (F) is less than about 1 weight percent, preferably less than about 0.500 weight percent, more preferably less than about 0.350 weight percent, still more less than about 0.300 about weight percent, still more preferably less than 0.220 weight percent, still more preferably less than about 0.150 weight percent, based on the total amount of the silicone rubber composition. The lower limit is preferably at least about 0.005 weight percent, preferably at least about 0.010 weight percent, more preferably at least about 0.020 weight percent. Further preferably the amount of component (F) is from about 0.005 to about 1 weight percent, preferably about 0.010 to about 0.500 weight percent, more preferably about 0.015 to about 0.350 weight percent, still more preferably about 0.020 to about 0.300 about weight percent, still more preferably about 0.023 to about 0.220 weight percent, still more preferably about 0.028 to about 0.150 weight percent, based on the total amount of the silicone rubber composition.

[0208] In an embodiment the liquid curable silicone rubber composition according to the invention comprises about 0.03 to about 0.50 wt.-% of component (F) and more than about 6.0 % preferably more than about 6.1 weight percent, preferably more than about 6.2 weight percent, preferably equal to or more than about 6.3 weight percent of the component (E) each based on the total amount of the composition.

[0209] Component (F) can be preferably provided as a masterbatch preferably with any silicone oil or component (A) as a carrier material.

[0210] (G) Auxiliary Additives

[0211] The curable silicone rubber composition according to the invention comprises optionally up to 100 parts by weight of one or more auxiliary additives (G) based upon 100 parts by weight of component (A) as defined above. The auxiliary additive (G) is different from any of the other components (A), (B), (C), (D), (E), and (F) as defined herein, and is preferably selected from the group consisting of low compression set additives, surface-treating agents, lubricating oils, oil bleeding agents, hydrosilylation inhibitors etc.

[0212] The auxiliary additive (G) may include in particular:

[0213] - low compression set additives, such as acetylene alcohols having the formula: H-C=C-R”- OH, wherein R” is a divalent organic group, preferably a cyclic saturated or unsaturated hydrocarbyl group such as cyclohexane-diyl, fluorene-diyl, e.g. 1-ethynyl-1 -cyclohexanol ("ECH"), 9-ethynyl-fluorenol, and the like, preferably ECH and 9-ethynyl-9-fluorenol, most preferably ECH (these compounds act also as hydrosilylation inhibitors),

[0214] - curing retardant or flame retardants such as a triazole compound selected e.g. from the group consisting of 1 ,2,3-triazole, 1 ,2, 4, -triazole, benzotriazole, 1-methyl-1 ,2,3-triazole, 1-phenyl-

[0215] 1.2.3-triazole, 4-methyl-2-phenyl-1 ,2,3-triazole, 1-benzyl-1 ,2,3-triazole, 4- hydroxy- 1 ,2,3- triazole, 1-amino-1 ,2,3-triazole, 1-benzamido-4-methyl-1 ,2,3-triazole, 1-amino-4,5-diphenyl- 1 ,2, 3, -triazole, 1 ,2,3-triazole-4-aldehyde, 4-cyano-1 ,2,3-triazole, 1-methyl-1 ,2,4-triazole, 1 ,3- diphenyl-1 ,2,4-triazole, 5-amino-3-methyl-1 ,2,4-triazole, 3-mercapto-1 ,2,4-triazole, 1-phenyl-

[0216] 1.2.4-triazole-5-one, 1-phenylurazole, 1 -methylbenzotriazole, 5,6-dimethylbenzotriazole, 2- phenylbenzotriazole, 1 -hydroxybenzotriazole and methyl 1 -benzotriazolecarboxylate, a metal salt, carbon black, phthalocyanine compounds or metal derivatives of said compound where said metal is selected from the group consisting of copper, nickel, cobalt, iron, chromium, zinc, platinum, palladium, vanadium.

[0217] - surface-treating agents,

[0218] - lubricating oils,

[0219] - oil bleeding agents,

[0220] - hydrosilylation inhibitors,

[0221] - coloring agents or pigments, such as inorganic pigments, and organic dyes,

[0222] - adhesion promoters,

[0223] - stabilizers, such as heat stabilizers,

[0224] - fillers, such as reinforcing and non-reinforcing fillers, such as quartz powder and diatomaceous earth, calcium carbonate, - dispersants,

[0225] - flow improvers,

[0226] - plasticizers,

[0227] - slip agents,

[0228] - toughening agents,

[0229] - conductive stability improvers, such as carbon black or graphite, and

[0230] - foam forming additives, e.g. alcohols,

[0231] - anti-oxidants,

[0232] - thixotropic agents,

[0233] - foam stabilizers,

[0234] - ultraviolet stabilizers, and

[0235] - water which may be used in the preparation of the curable silicone rubber compositions.

[0236] In a preferred embodiment of the invention the curable silicone rubber composition does not comprise quartz. In a preferred embodiment of the invention the curable silicone rubber composition comprises at least one hydrosilylation inhibitor, preferably 1-ethynyl-1- cyclohexanol ("ECH").

[0237] In a preferred embodiment of the invention, the curable silicone rubber composition comprises at least one coloring agent or pigment. Such coloring agents or pigments can be colourless, like for example colourless metal oxides, or colored, and may include inorganic pigments, and organic dyes. In this respect, the curable silicone rubber composition according to the invention can be in particular provided as a colourless curable silicone rubber composition, i.e. which does not comprise any coloring agent or pigment. However, from such colourless curable silicone rubber compositions according to the invention, colored curable silicone rubber compositions can be easily obtained by mixing the colourless curable silicone rubber compositions according to the invention with at least one coloring agent or pigment, such as red iron oxide etc.

[0238] The curable silicone rubber composition according to the invention optionally comprises melamine cyanurate. Melamine cyanurate, also known as melamine-cyanuric acid adduct or melamine-cyanuric acid complex, is a crystalline complex formed from a 1 :1 mixture of melamine and cyanuric acid:

[0239]

[0240] Component (G) may also include colorless metal oxides, selected from the group consisting of aluminum oxide, titanium oxide, magnesium oxide, cerium oxide, zirconium oxide, tin oxide and zinc oxide, and mixtures thereof, colored metal oxides, selected from the group consisting of oxides of transition metal compounds and mixtures thereof, such as iron oxide pigments (e.g. yellow iron oxide, red iron oxide, black iron oxide and mixtures thereof), mixed phase metal oxide pigments such as COAI2O4 and Co(AI,Cr)2C>4, synthetic and natural ultramarines, and chromic oxides, and mixtures of colorless metal oxides and colored metal oxides.

[0241] Further preferred embodiments

[0242] In a preferred embodiment of the invention in the liquid curable silicone rubber composition the total amount of carbon nanotubes (F) and carbon black (E) is less than about 12 weight percent, preferably less than about 10 weight percent, and still more preferably less than about 8 weight percent based on the total amount of the silicone rubber composition.

[0243] Further, preferably the weight ratio of carbon black component (E) to the carbon nano tubes component (F) is about 800 : 1 to about 5 : 1 , preferably about 500 : 1 to about 8 : 1 , more preferably about 300 : 1 to about 6 : 1.

[0244] Further preferably neither the carbon black component (E) nor component (F) are modified or surface-modified.

[0245] The liquid curable silicone rubber composition according to the invention preferably has a viscosity at 25°C of 200 to 1000 Pa.s at a shear rate of 10s-1determined according to DIN 53019.

[0246] Preferably the liquid curable silicone rubber composition according to the invention comprise: 100 parts by weight of component (A) as defined above,

[0247] 0.01 to 100, preferably 0.1 to 20, more preferably 1 to 10 parts by weight of component (B) as defined above,

[0248] 0.01 to 100, preferably 1 to 50, more preferably 5 to 30 parts by weight of component (C) as defined above, 0.5 to 1000 ppm, preferably 1 to 100 ppm of component (D) as defined above, based on the weight amount of the transition metal and based on the total weight of components (A) and B),

[0249] 5 to 20, preferably 6 to 15, more preferably 7 to 10 parts by weight of component (E) as defined above,

[0250] 0.01 to 2, preferably 0.02 to 1 , more preferably 0.03 to 0.6 parts by weight of component (F) as defined above, and

[0251] 0 to 100, preferably > 0 to 10 parts by weight of component (G) as defined above.

[0252] The present invention further relates to cured silicone rubber composition obtained by curing the liquid silicone rubber composition as defined above. The hydrosilylation curing process might be initiated thermally for example at temperatures of about 60 to about 220°C or by irradiation at relatively low temperatures as far as transparency allows so.

[0253] Cured silicone rubber composition according to the invention preferably have a hardness (Shore A) of less than 60, preferably less than 50 (ASTM D 412 (..Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers - Tension").

[0254] Cured silicone rubber composition according to the invention preferably have a volume resistivity of less than 45 ohm*cm, preferably less than 40 ohm*cm, more preferably less than 35 ohm*cm, measured according to ISO 1853.

[0255] Cured silicone rubber composition according to the invention preferably have an S1 volume resistivity at 0% elongation ((S1 (0%)) of less than 45 ohm*cm, preferably less than 40 ohm*cm, more preferably less than 35 ohm*cm, still more preferably of less than 30 ohm*cm, measured according to the method indicated in the example part of the specification.

[0256] Cured silicone rubber composition according to the invention preferably have an S1 volume resistivity at 100% elongation (S1 (100%)) of less than 150 ohm*cm, preferably less than 100 ohm*cm, more preferably less than 50 ohm*cm, still more preferably of less than 40 ohm*cm, measured according to the method indicated in the example part of the specification.

[0257] Cured silicone rubber composition according to the invention preferably have an S1 volume resistivity at 100% elongation after 300% overstretching (S1 (300% 100%)) of less than 200 ohm*cm, preferably less than 150 ohm*cm, more preferably less than 130 ohm*cm, still more preferably of less than 100 ohm*cm, measured according to the method indicated in the example part of the specification.

[0258] Cured silicone rubber composition according to the invention preferably have a ratio of S1 volume resistivity at 100% elongation to S1 volume resistivity at 0% elongation ((S1 (100%) / S1 (0%)) of less than 10, preferably less than 8, more preferably of less than 6 still more preferably of less than 4.

[0259] Cured silicone rubber composition according to the invention preferably have a ratio of S1 volume resistivity at 100% elongation after 300% overstretching to S1 volume resistivity at 0% elongation (S1 (300% 100%)) I S1 (0%)) of less than 10, preferably less than 8, more preferably of less than 6.

[0260] In an embodiment the invention relates to a process for the manufacture of the cured silicone rubber composition according to the invention which comprises the step of providing a composition part A, comprising components (A) and (D) but no component (B), and a composition part B, comprising component (B), mixing composition parts A and B, to provide a liquid curable silicone rubber composition according the invention, and curing said liquid curable silicone rubber composition to obtain the cured silicone rubber compositions according to the invention .

[0261] In an embodiment the invention relates an article comprising the cured silicone rubber composition according to the invention.

[0262] The article is preferably selected from electronic devices or components, such as cable joints, cable terminal applications, cable accessories, spark-plug connectors, electrical insulators, single-wire seals, plug connector, seals, tubing and valves, automobile components such as connector seal and spark plug boots, electric and electronic parts such as rolls in a copying machine and packing in a microwave oven. The article is used in particular for high-voltage applications.

[0263] In an embodiment the invention further relates to the use of the liquid curable silicone rubber composition according to the invention for the manufacture of electronic devices or components such as cable joints, cable terminal applications, cable accessories, spark-plug connectors, electrical insulators, single-wire seals, plug connector seals, tubing and valves, automobile components such as connector seal and spark plug boots, electric and electronic parts such as rolls in a copying machine and packing in a microwave oven.

[0264] In an embodiment the invention further relates to electronic components or devices, comprising the cured silicone rubber composition according to the invention.

[0265] The present invention is further illustrated by the following examples, but it is not limited thereto.

[0266] EXAMPLES

[0267] All parts are weight parts unless otherwise indicated. All percentages are weight percentages unless otherwise indicated.

[0268] Liquid Silicone Rubber (LSR) Compositions with the compositions shown in Table 1 and 2 below were prepared.

[0269] LSR parts A and B according to the Table 1 below were mixed at a weight ratio of 1 : 1 and cured at 175°C for 10 min.

[0270] The volume resistivity and mechanical properties of the cured silicone rubber compositions containing different ratios of carbon black (CB) and carbon nanotubes (CNT) were measured according to the following procedures.

[0271] 1. Testing procedures for the volume resistivity

[0272] The volume resistivities were tested according to ISO 1853 with the so called four-point- method (see Figure 1 and ISO 1853 for details in measuring procedure).

[0273] For the measurement of the volume resistivities at elongation this method was only modified by testing with another specimen. The used specimen was taken from elongation measurements in an elastomer material characterization - so called S1 -dumbbell (see Figure 2 and DIN 53504 method).

[0274] In Figure 2, the control spots determine the length change of the specimen, elongation by 100% means 100% distance increase between both control spots. This definition is in accordance with mechanical testing of elastomers. The described method thus combines ISO mechanical testing of elastomers together with the electrical testing of (semi)-conductive elastomers.

[0275] A direct current (DC) voltage of 5V (UDC) is applied to the sample in accordance with the basic set-up for determining the volume resistivity of weakly conductive elastomers with the corresponding dimensions according to ISO 1853. This causes a constant current flowing through the sample which is measured with a multimeter (Less). A second electrode pair has a fixed distance of 20 mm which measures the resulting voltage in the middle of the specimen between these two electrodes. The geometric parameters width, length and height determine the normalized volume resistivity value in [ohm cm].

[0276] The geometric parameters in the S1 dumbbell were as follows:

[0277] 1. 0% strain: height 0,19 cm; width 0,6cm; length 2cm; volume 0,24ml

[0278] 2. 100% strain: height 0,14 cm; width 0,44cm; length 2cm; volume 0,12ml

[0279] The length between the measuring electrodes (voltage) remains always 2 cm by definition. The changes of height and width confirm the expectation that the volume of the specimen at 100% in the measuring interval is half than the volume at no strain. The volume resistivities were determined in the following sequence with the S1 -dumbbell to examine the resistance of the volume resistivities towards strain or elongation, respectively.

[0280] The following measurements were carried out (see Table 3 - Elongation resistance tests):

[0281] 1. At 0% elongation - normal measurement. 2. At 100% elongation (means double length)

[0282] 3. Overstretching to 300% elongation and relaxing back to 100% elongation.

[0283] 2. Testing procedures for the mechanical properties

[0284] The mechanical properties (elongation and tensile strength) were carried out like a classical elongation testing according to the DIN 53504 method.

[0285] 3. Basic composition

[0286] The basic composition of the Liquid Silicone Rubber Composition is shown in Table 1. Table 1 - Basic Liquid Silicone Rubber Composition

[0287] 1): TUBALL™ MATRIX 613

[0288] 4. Preparation method

[0289] (All viscosities indicated are measured at 20°C and a shear rate of D=10s-1(DIN 53019)).

[0290] Part A

[0291] In a dissolver mixer 60.07 parts carbon black paste (Ketjen Black EC300 (10.5 wt-% carbon black in dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 10 Pa s (at 20°C and a shear rate of D=10s-1), 12.66 parts of a dimethylvinylsiloxyterminated polydimethylsiloxane having a viscosity of 65 Pa s each were mixed with 4.86 parts of hexamethyldisilazane (surface treating agent), 0.020 parts of divinyltetramethyldisilazane (surface treating agent) and 1.82 parts of water. The mixture was then mixed with 14.85 parts of fumed silica having a Brunauer-Emmett-Teller (BET) specific surface area of 300m2 / g (Aerosil® 300 from Evonik) and heated at 100°C for 1h so that a silica filler with a mixture of trimethylsilyl- and vinyldimethylsilyl groups at its surface was formed. Water and resulting volatile compounds from the surface treatment reaction were subsequently removed from the silicone mixture at about 150°C under vacuum (< 80 mbar) for 1h. Resulting volatiles were removed from the silicone mixture at about 150°C under vacuum (< 80 mbar) for 1h. The mixture was later cooled down and diluted with 4.25 parts of dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 10 Pa s (at 20°C and a shear rate of D=10s-1) and 4.69 parts of dimethylvinylsiloxy-terminated polydimethylsiloxane having a viscosity of 65 Pa s (at 20°C and a shear rate of D=10s-1). Subsequently 0.48 parts of a SW-CNT masterbatch containing 10wt-% of SW-CNT (TUBALL™ MATRIX 613) and 0.96 parts of a dimethylvinylsiloxy-terminated poly(dimethylsiloxane-co-methylvinylsiloxane) having a vinyl content of 2.08 mmol / g and a viscosity of 0.2 Pa s is added. Finally, 0.25 parts of a solution of a Pt(O) complex with tetramethyltetravinylcyclotetrasiloxane that contains 1.5 wt% Pt was added (Karstedt catalyst).

[0292] Part B

[0293] In a dissolver mixer 60.08 parts carbon black paste according to Masterbatch Example 1 and 12.65 parts of a dimethylvinylsiloxyterminated polydimethylsiloxane having a viscosity of 65 Pa s were mixed with 4.86 parts of hexamethyldisilazane, 0.02 parts of divinyltetramethyldisilazane and 1.74 parts of water (additive - component f)). The mixture was then mixed with 14.85 parts of fumed silica having a Brunauer-Emmett-Teller (BET) specific surface area of 300m2 / g (Aerosil® 300 from Evonik) and heated at 100°C for 1 h so that a silica filler with a mixture of trimethylsilyl- and vinyldimethylsilyl groups at its surface was formed. Water and resulting volatile compounds from the surface treatment reaction were subsequently removed from the silicone mixture at about 150°C under vacuum (< 80 mbar) for 1 h. Resulting volatiles were removed from the silicone mixture at about 150°C under vacuum (< 80 mbar) for 1h. The mixture was later cooled down and diluted with 3.80 parts of a dimethylvinylsiloxyterminated polydimethylsiloxane having a viscosity of 65 Pa s. Subsequently, 0,48 parts of a CNT masterbatch containing 10 wt-% of SW-CNT (TUBALL™ MATRIX 613) and 2.39 parts of a first crosslinker (linear poly(dimethyl)co(methylhydrogen)siloxane with an SiH content at 1.20 mmol / g and a viscosity of 0.014 Pa.s and 3.83 parts of a second crosslinker (linear poly(dimethyl)co(methylhydrogen)siloxane with an SiH content at 7.40 mmol / g and a viscosity of 0.04 Pa.s, and 0.14 parts of 1-ethynyl-1 -cyclohexanol (ECH) (component f)) were added.

[0294] Cured silicone rubber compositions according to the invention were prepared as follows: Parts A and B were mixed in a 1 :1 weight ratio and cured by heating to 175° C for 10 minutes.

[0295] 5. Examples 1 to 6 and Comparative Example 1

[0296] The above liquid silicone rubber composition according to the basic example was prepared with varying amounts of the SW-CNT masterbatch, and their mechanical and electronic properties for the cured formulations were determined. The results are shown in Table 2. Table 2 - Volume resistivities depending on varying SW-CNT contents at a constant CB content of 6.3 wt.-%

[0297] 1)Volume resistivities were measured according to ISO 1853 on a standard specimen. The values measured can deviate from those measured with the S1-dumbbell below.

[0298] 2)silicone rubber composition according to the basic example without CNT masterbatch

[0299] As can be derived from Table 2 at 0.91% SW-CNT content the lowest volume resistivity was observed but the elongation is reduced. The best compromise between volume resistivity and elongation was found in the range of about 0,03 to about 0.5 wt.-% CNT at a CB content of more than about 6 %. A too high content of SW-CNT leads to poor mechanical properties (tensile strength below 4, elongation below 450) and is also not desirable under cost point of view. In the absence of SW-CNT, the elongation resistance towards strain or elongation is inferior as will be shown below.

[0300] 6. Elongation resistance tests

[0301] Elongation resistance tests were carried out with the cured silicone rubber composition of example 5 and comparative example 1 with an the S1 -dumbbell as described above. The results are shown in Table 3.

[0302] Table 3 - Results of the Elongation resistance tests Very surprisingly the addition of only about 0.05 wt.-% of carbon nanotubes leads already to significant decrease in volume resistivity (S1 at % elongation). Even more surprising, the volume resistivity of the 100 % elongated silicone rubber composition increases only by a factor of about 1 .4 and for an elongation of 300 % back to 100% elongation only by a factor of about 4.4, whereas the volume resistivity of the rubber composition of comparative example 1 having no carbon nanotubes increases by a factor of about 14.8 at 100 % elongation, and for an elongation of 300 % back to 100% elongation by a factor about 23.1. This shows that the volume resistivity of the SW-CNT-comprising cured LSR compositions according to the invention are much less sensitive to elongation or strain respectively, which makes them highly efficient in applications where there are elongated or bend. At the same time the mechanical properties are not substantially impaired by the presence of SW-CNT, when a certain amount of carbon black (CB) and a certain weight ratio of CB / SW-CNT is adjusted.

[0303] 7. Effect of the reduction of carbon black content

[0304] In a further comparative test the amount of carbon clack was reduced to 4.2 wt.-%. Table 4 compares the results of the elongation / Volume resistivity tests with Example 5 and Comparative Example 1 :

[0305] Table 4 - Further results of the Elongation resistance tests

[0306] Table 4 shows that reducing of the carbon black content not only leads to an expected increase in volume resistivity but also to greater sensitivity of the volume resistivity after elongation as expressed by the higher ratios Ratio S1 (100%) I S1 (0%) and Ratio S1 (300 % -^100 %) I S1 (0 %).

Claims

CLAIMS:

1. Liquid hydrosilylation-curable silicone rubber composition (LSR) comprising:(A) at least one polyorganosiloxane having one or more alkenyl groups,(B) at least one polyorganosiloxane having one or more SiH groups,(C) at least one filler component selected from one or more silicas,(D) at least one transition metal hydrosilylation catalyst,(E) at least one carbon black (CB),(F) at least one carbon nanotube (CNT),(G) optionally one or more auxiliary additives, wherein the weight ratio of component (E) to (F) is more than about 5 : 1 , and the content of component (E) is more than about 6.0 weight percent based on the total amount of the composition.

2. Liquid curable liquid silicone rubber composition according to claim 1 , having a viscosity about 200 to about 1000 Pa.s at 25 °C measured at a shear rate of 10 s-1measured according to DIN 53019.

3. Liquid curable liquid silicone rubber composition according to any of the previous claims, wherein the amount of the filler component (C) is about 3 to 30, preferably about 5 to 25, more preferably about 10 to 20 weight percent based on the total amount of the composition.

4. Liquid curable liquid silicone rubber composition according to any of the previous claims, wherein component (F) is selected from single wall carbon nanotubes.

5. Liquid curable liquid silicone rubber composition according to any of the previous claims, wherein component (F) has an average length / diameter (L / D) value of 500 or more and 5000 or less.

6. Liquid curable liquid silicone rubber composition according to any of the previous claims, wherein the amount of component (E) is from about 6.0 to about 12 weight percent, preferably from 6.0 to about 10 weight percent based on the total amount of the silicone rubber composition.

7. Liquid curable silicone rubber composition according to any of the previous claims, wherein the amount of component (F) is less than about 1 weight percent, preferably less than about 0.500 weight percent, more preferably less than about 0.350 weight percent, still more less than about 0.300 about weight percent, still more preferably less than 0.220 weight percent, still more preferably less than about 0.150 weight percent, based on the total amount of the silicone rubber composition.

8. Liquid curable silicone rubber composition according to any of the previous claims, wherein the amount of component (F) is from about 0.005 to about 1 weight percent, preferablyabout 0,0075 to 0,075, more preferably about 0.010 to about 0.500 weight percent, more preferably about 0.015 to about 0.350 weight percent, still more preferably about 0.020 to about 0.300 about weight percent, still more preferably about 0.023 to about 0.220 weight percent, still more preferably about 0.028 to about 0.150 weight percent, based on the total amount of the silicone rubber composition.

9. Liquid curable silicone rubber composition according to any of the previous claims, wherein the total amount of carbon nano tubes (F) and carbon black (E) is less than about 12 weight percent, preferably less than about 10 weight percent, and still more preferably less than about 8 weight percent based on the total amount of the silicone rubber composition.

10. Liquid curable silicone rubber composition according to any of the previous claims, wherein the weight ratio of carbon black component (E) : carbon nano tubes component (F) is about 800 : 1 to about 5 : 1 , preferably about 500 : 1 to about 8 : 1 , more preferably about 300 : 1 to about 6 : 1.

11. Liquid curable silicone rubber composition according to any of the previous claims comprising about 0.03 to about 0.50 wt.-% of the carbon nano tube component (F) and more than about 6.0 % preferably more than about 6.1 weight percent, preferably more than about 6.2 weight percent, preferably equal to or more than about 6.3 weight percent of the carbon black component (E) each based on the total amount of the composition.

12. Liquid curable silicone rubber composition according to any of the previous claims, wherein neither component (E) nor component (F) are modified or surface-modified.

13. Liquid curable silicone rubber composition according to any of the previous claims, comprising:100 parts by weight of component (A) as defined above,0.01 to 100, preferably 0.1 to 20, more preferably 1 to 10 parts by weight of component (B) as defined above,0.01 to 100, preferably 1 to 50, more preferably 5 to 30 parts by weight of component (C) as defined above,0.5 to 1000 ppm, preferably 1 to 100 ppm of component (D) as defined above, based on the weight amount of the transition metal and based on the total weight of components (A) and B),5 to 20, preferably 6 to 15, more preferably 7 to 10 parts by weight of component (E) as defined above,0.01 to 2, preferably 0.02 to 1 , more preferably 0.03 to 0.6 parts by weight of component (F) as defined above, and0 to 100, preferably > 0 to 10 parts by weight of component (G) as defined above.

14. Cured silicone rubber composition obtained from the liquid silicone rubber composition according to any of the previous claims.

15. Cured silicone rubber composition according to the previous claim having a hardness (Shore A) of less than 60 (ASTM D 412 (..Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers - Tension").

16. Cured silicone rubber composition according to any of the previous claims having a volume resistivity of less than 45 ohm*cm, preferably less than 40 ohm*cm, more preferably less than 35 ohm*cm, measured according to ISO 1853.

17. Cured silicone rubber composition according to any of the previous claims having an S1 volume resistivity at 0% elongation ((S1 (0%)) of less than of less than 45 ohm*cm, preferably less than 40 ohm*cm, more preferably less than 35 ohm*cm, still more preferably of less than 30 ohm*cm, measured according to the method indicated in the specification.

18. Cured silicone rubber composition according to any of the previous claims having an S1 volume resistivity at 100% elongation (S1 (100%)) of less than 150 ohm*cm, preferably less than 100 ohm*cm, more preferably less than 50 ohm*cm, still more preferably of less than 40 ohm*cm, measured according to the method indicated in the specification.

19. Cured silicone rubber composition according to any of the previous claims having anS1 volume resistivity at 100% elongation after 300% overstretching (S1100%)) of less than 200 ohm*cm, preferably less than 150 ohm*cm, more preferably less than 130 ohm*cm, still more preferably of less than 100 ohm*cm, measured according to the method indicated in the specification.

20. Cured silicone rubber composition according to any of the previous claims having a ratio of S1 volume resistivity at 100% elongation to S1 volume resistivity at 0% elongation ((S1 (100%) / S1 (0%)) of less than 10, preferably less than 8, more preferably of less than 6 still more preferably of less than 4.

21. Cured silicone rubber composition according to any of the previous claims having a ratio of S1 volume resistivity at 100% elongation after 300% overstretching to S1 volume resistivity at 0% elongation (S1 (300%100%)) I S1 (0%)) of less than 10, preferably less than 8, more preferably of less than 6.

22. A process for the manufacture of a cured silicone rubber composition according to any of the previous claims which comprises the step of providing part A, comprising components (A) and (D) but no component (B), and part B, comprising component (B), mixing parts A and B, to provide a liquid curable silicone rubber composition according to any of the previous embodiments, and curing said liquid curable silicone rubber composition.

23. An article comprising the cured silicone rubber composition according to any of the previous claims.

24. An article according to the previous claim selected from electronic devices or components, such as cable joints, cable terminal applications, cable accessories, spark-plug connectors, electrical insulators, single-wire seals, plug connector, seals, tubing and valves,automobile components such as connector seal and spark plug boots, electric and electronic parts such as rolls in a copying machine and packing in a microwave oven.

25. An article according to the previous claims which is used in high-voltage applications.

26. Use of the liquid curable silicone rubber composition according to any of the previous claims for the manufacture of electronic devices or components such as cable joints, cable terminal applications, cable accessories, spark-plug connectors, electrical insulators, singlewire seals, plug connector seals, tubing and valves, automobile components such as connector seal and spark plug boots, electric and electronic parts such as rolls in a copying machine and packing in a microwave oven.

27. Electronic components or devices, comprising the cured silicone rubber composition according to any of the previous claims.

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