Liquid silicone rubber composition

Abstract

A conductive liquid silicone rubber composition containing superconductive carbon black and single-walled carbon nanotubes as conductive fillers, a method for making the composition, and a method for curing the composition, which cures to form an elastomeric product suitable for high voltage applications such as cable joints, cable termination applications, cable accessories, and connectors. [Selection diagram] None

Description

[Technical Field]

[0001] This disclosure relates to addition curing of conductive liquid silicone rubber (LSR) compositions, their methods of preparation, and cured elastomeric articles made from the compositions, which are cured to form elastomeric articles suitable for high voltage applications such as cable joints, cable termination applications, cable accessories and connectors.

[0002] Liquid silicone rubber ("LSR") compositions containing conductive components such as metal powders, e.g., silver, nickel, and copper, and carbonaceous powders, e.g., carbon black, graphite powder, and / or carbon fiber, are well known. However, such compositions suffer from various problems, such as high resistance and / or volume resistivity values, temperature-dependent and / or variable resistance and time-dependent resistance. While increasing the amount of the conductive components solves these problems, such compositional changes generally result in a significant increase in viscosity in the pre-cured composition, resulting in impaired handling characteristics. As a solution to the high viscosity problem, such compositions have been diluted with non-reactive silicones or organic solvents. However, this has been found to result in compatibility issues, such as the diluent bleeding over time from the subsequently cured silicone elastomer product, and further, such products do not always overcome the resistance and resistivity problems.

[0003] For example, when a highly conductive cured silicone elastomer product with a volume resistivity of <100 ohm·cm is required to fabricate a cable joint with direct contact and a covalent interface with the insulating material of a shielded cable or a conductive or semi-conductive cable, the dielectric parameters for the joint material must be carefully selected and / or adjusted. Preferred conductive fillers for such applications include types of carbon black sometimes referred to as "ultra" conductive carbon black. While these types of carbon black improve conductive properties, they are essentially non-reinforcing in terms of filler to the silicone composition. High loading levels of these carbon blacks (i.e., >6% by weight of the composition) can lead to undesirable dispersion and bubble problems associated with the resulting high viscosity due to the high concentration of carbon black in the uncured LSR composition, potentially reducing the composition's handleability during injection molding and coating applications. Furthermore, the resulting cured silicone elastomer materials not only exhibit poor physical properties, such as low elasticity to the point of brittleness, but also poor mechanical properties, such as elongation (<500% or even <400%), upon curing the composition into an elastomeric product.

[0004] As previously mentioned, inappropriately high viscosity resulting from high loading levels of conductive fillers in LSR compositions can result in undesirable bubbles and poor dispersion, particularly of the conductive carbon black material therein, which in turn can further cause poor physical properties and / or damage upon expansion to extrude high voltage insulation (HVI) cable accessories and the like.

[0005] Therefore, there has been a long-standing need in the industry to provide a suitable conductive silicone rubber that can solve the problems of the prior art described above. However, it should be understood that many of the above problems are contradictory, for example, that adding more conductive fillers, such as carbon black, to improve conductivity results in a decrease in mechanical properties such as elongation and a significant and unnecessary increase in the viscosity of the composition. Furthermore, an excessive amount of carbon black may adversely affect the curing of silicone rubber elastomer products due to surface properties and / or impurities.

[0006] As used herein, a conductive liquid silicone rubber composition is provided, (a) one or more polydiorganosiloxanes having at least two alkenyl groups per molecule; (b) at least one organohydrogenpolysiloxane; and (c) 10 to 25 weight percent of the composition of at least one reinforcing filler; (d) at least one hydrosilylation catalyst; (e) (i) 1.5 to 5.5 weight percent of the composition of superconducting carbon black; and (ii) a conductive filler containing single-walled carbon nanotubes in an amount of 0.05 to 1% by weight of the composition.

[0007] It has been discovered that while the introduction of multi-walled carbon nanotubes has little effect, the introduction of small amounts of single-walled carbon nanotubes into the composition eliminates the need to incorporate large amounts of carbon black, in this case, superconductive carbon black, into the composition. By reducing the amount of superconductive carbon black, the poor physical properties and resulting potentially brittle elastomer properties caused by high concentrations of carbon black in the composition are avoided. Indeed, incorporating only low concentrations of single-walled carbon nanotubes advantageously significantly improves electrical conductivity while minimizing the impact on mechanical properties and viscosity, thereby helping to provide the physical properties sought after within the industry for this type of liquid silicone rubber composition. Furthermore, the ability to avoid the addition of higher concentrations of superconductive carbon black allows for the inclusion of additional reinforcing fillers, resulting in the desired improved physical properties.

[0008] Ingredients of the composition: a) Polydiorganosiloxane having at least two alkenyl groups in one molecule Component (a) is one or more polydiorganosiloxanes containing at least two silicon-bonded alkenyl groups per molecule. Suitable alkenyl groups in component (a) typically contain 2 to 10 carbon atoms, with preferred examples being vinyl, isopropenyl, allyl, and 5-hexenyl. Component (a) typically further contains a silicon-bonded organic group other than the alkenyl group. Typically, such silicon-bonded organic groups are selected from monovalent saturated hydrocarbon groups typically containing 1 to 10 carbon atoms and monovalent aromatic hydrocarbon groups typically containing 6 to 12 carbon atoms. These hydrocarbon groups are either unsubstituted or substituted with groups (e.g., halogen atoms) that do not interfere with the curing of the composition of the present invention. Preferred species of silicon-bonded organic groups include alkyl groups such as methyl, ethyl, and propyl, halogenated alkyl groups such as 3,3,3-trifluoropropyl, and aryl groups such as phenyl.

[0009] The molecular structure of the or each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule of component (a) is typically linear, although some branching may be present due to the presence of trivalent siloxane units within the molecule. To achieve useful levels of physical properties in the elastomers prepared by curing the LSR compositions of the present invention, the or each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule in component (a) should have a viscosity of 150 mPa·s to 150,000 mPa·s, measured using a rotational viscometer such as a Brookfield rheometer, or a capillary viscometer, particularly a Brookfield DV-III Ultra Programmable rheometer for viscosities of ≥ 50,000 mPa·s, or a Brookfield DV 3T rheometer for viscosities less than 50,000 mPa·s, unless otherwise specified. Unless otherwise specified, all viscosity measurements are made at 25° C. The upper viscosity limit of the or each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule of component (a) is not particularly limited and is typically limited only by the processability of the LSR composition of the present invention.

[0010] An example of component (a) is a polydiorganosiloxane containing two alkenyl groups at its ends, which can be represented by the general formula (I). R'R''R'''SiO-(R''R'''SiO) m -SiOR'''R''R' (I) In formula (I), each R' is an alkenyl group, typically containing from 2 to 10 carbon atoms, such as vinyl, allyl, and 5-hexenyl. Alternatively, each R' is vinyl. Typically, the alkenyl content, e.g., the vinyl content of the polymer, is 10.01 to 3 weight percent of each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule of component (a), alternatively 0.025 to 2.5 weight percent of component (a), alternatively 0.025 to 2.0 weight percent of the or each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule of component (a), as determined by H nmr.

[0011] R" contains no ethylenic unsaturation, and each R" may be the same or different and is independently selected from monovalent saturated hydrocarbon groups, typically containing 1 to 10 carbon atoms, and monovalent aromatic hydrocarbon groups, typically containing 6 to 12 carbon atoms. R" may be unsubstituted or substituted with one or more groups (such as halogen atoms) that do not interfere with curing of the composition, as described above. R'" is R' or R". m represents a degree of polymerization suitable for component (a) having a viscosity of 150 mPa s to 150,000 mPa s at 25°C, unless otherwise indicated, measured using a rotational viscometer such as a Brookfield rheometer, or a capillary viscometer, particularly a Brookfield DV-III Ultra Programmable rheometer for viscosities ≥ 50,000 mPa s, or a Brookfield DV 3T rheometer for viscosities less than 50,000 mPa s.

[0012] Typically, all R" and R" groups contained in the compound according to formula (I) are methyl groups. Alternatively, at least one R" and / or R" groups in the compound according to formula (I) is a methyl group and the others are phenyl or 3,3,3-trifluoropropyl groups. This choice is based on the availability of reactants typically used to prepare polydiorganosiloxanes (component (a)) and the properties desired for cured elastomers prepared from compositions containing such polydiorganosiloxanes.

[0013] Typical examples of the or each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule of component (a) containing ethylenically unsaturated hydrocarbon groups only at the terminal groups include, but are not limited to, dimethylvinylsiloxy-terminated polydimethylsiloxane, dimethylvinylsiloxy-terminated polymethyl-3,3,3-trifluoropropylsiloxane, dimethylvinylsiloxy-terminated dimethylsiloxane-3,3,3-trifluoropropylmethylsiloxane copolymer, and dimethylvinylsiloxy-terminated dimethylsiloxane / methylphenylsiloxane copolymer. When R''' is R', the polymer may be dimethylvinylsiloxy-terminated polyvinylmethylsiloxane or dimethylvinylsiloxy-terminated polydimethylvinylmethylsiloxane.

[0014] Generally, the or each polydiorganosiloxane containing at least two silicon-bonded alkenyl groups per molecule of component (a) will have a viscosity of from 150 mPa s to 150,000 mPa s, alternatively from 200 mPa s to 125,000 mPa s, alternatively from 200 mPa s to 100,000 mPa s at 25° C., measured using a rotational viscometer such as a Brookfield rheometer, or using a capillary viscometer, particularly a Brookfield DV-III Ultra Programmable rheometer for viscosities of ≥ 50,000 mPa s, or a Brookfield DV 3T rheometer for viscosities less than 50,000 mPa s, unless otherwise indicated.

[0015] In one alternative, the composition may comprise two or more polydiorganosiloxanes containing at least two silicon-bonded alkenyl groups per molecule, e.g., relatively high viscosity polymers. The relatively high viscosity polymers may have a viscosity in the range of, for example, 50,000 to 100,000 mPa s at 25°C, alternatively 50,000 to 75,000 mPa s at 25°C, alternatively 55,000 to 70,000 mPa s at 25°C, as measured using a Brookfield DV-III Ultra Programmable Rheometer, and may contain 0.04 to 0.2 wt% ( 1 1H nmr); or 0.04 to 0.15 wt% ( 1 1H nmr); in combination with a medium viscosity polymer and / or a low viscosity polymer, the medium viscosity polymer has a viscosity in the range of 5,000 to 20,000 mPa·s at 25°C, alternatively 5,000 to 17,500 mPa·s at 25°C, alternatively 7,500 to 15,000 mPa·s at 25°C, measured using a Brookfield DV 3T rheometer, and has a vinyl content of 0.075 to 0.2 wt.% ( 1 1H nmr); or 0.1 to 0.175 wt% ( 1 the low viscosity polymer has a viscosity in the range of 150 to 1000 mPa·s at 25°C, alternatively 150 to 750 mPa·s at 25°C, alternatively 150 to 600 mPa·s at 25°C, as measured using a Brookfield DV 3T rheometer, and a vinyl content of 0.075 to 0.2 wt.% ( 1 1H nmr); or 0.1 to 0.175 wt% ( 1 It has a vinyl content of 1H (as determined by H nmr).

[0016] (b) Organohydrogenpolysiloxane Component (b) is an organohydrogenpolysiloxane that functions as a crosslinker for crosslinking polymer (a), undergoing a hydrosilylation (addition) reaction via silicon-bonded hydrogen atoms with the alkenyl groups in component (a) catalyzed by one or more hydrosilylation catalysts described below. Component (b) typically contains three or more silicon-bonded hydrogen atoms that react with the alkenyl groups of component (a) to form a network structure. When component (a) has more than two alkenyl groups per molecule, some or all of component (b) may instead have two silicon-bonded hydrogen atoms per molecule.

[0017] The molecular structure of component (b) is not particularly limited and may be linear, branched, or cyclic. The viscosity of component (b) is typically 20 to 5000 mPa s at 25°C, alternatively 20 to 2500 mPa s at 25°C, alternatively 20 to 500 mPa s at 25°C, as measured using a Brookfield DV-3T rheometer.

[0018] Component (b) may typically be added in an amount such that the molar ratio of the total number of silicon-bonded hydrogen atoms in component (b) to the total number of all alkenyl groups in component (a) is from 0.5:1 to 5:1, alternatively from 0.5:1 to 4:1, alternatively from 1:1 to 3:1. If this ratio is less than 0.5:1, a sufficiently cured composition will not be obtained. If this ratio is greater than 5:1, the hardness of the cured composition will tend to increase when heated.

[0019] Examples of component (b) include: (i) trimethylsiloxy-terminated methylhydrogenpolysiloxane, (ii) trimethylsiloxy-terminated polydimethylsiloxane-methylhydrogensiloxane; (iii) dimethylhydrogensiloxy-terminated dimethylsiloxane-methylhydrogensiloxane copolymer; (iv) dimethylsiloxane-methylhydrogensiloxane cyclic copolymer; (v)(CH3)2HSiO 1 / 2 Units and SiO 4 / 2copolymers consisting of units, and (vi)(CH3)3SiO 1 / 2 Units: (CH3)2HSiO 1 / 2 units, and SiO 4 / 2 Examples include, but are not limited to, copolymers consisting of units.

[0020] (c) Reinforcing filler Reinforcing fillers, such as ultrafine fumed or precipitated silica, are used in LSR compositions to achieve the high levels of physical properties that characterize some types of cured elastomers that can be prepared using the LSR compositions. Often, silica and other reinforcing fillers are treated with one or more known filler treating agents to prevent a phenomenon known as "creping" or "crepe hardening" during processing of the curable composition.

[0021] Finely divided silica, such as fumed and / or precipitated silica, is a preferred reinforcing filler. Typically, at least 50 ml 2 Fumed silica is particularly preferred because it has a relatively large surface area of ​​100 to 600 m / g measured according to the BET method according to ISO 9277:2010. 2 / g, or 100-500m 2 / g (using the BET method according to ISO9277:2010), or 200-400m 2 Fillers with a surface area of ​​0.1g / g (using the BET method according to ISO 9277:2010) are typically used.

[0022] The amount of finely divided silica or other reinforcing filler used in the LSR compositions of the present invention is typically present in an amount of about 10-25% by weight of the composition, alternatively 11-20% by weight of the composition, alternatively 11-18% by weight of the composition.

[0023] When the filler is naturally hydrophilic (e.g., untreated silica filler), it is typically treated with a treating agent. This treatment can be done either prior to introduction into the composition or in situ (i.e., by mixing the other components of the LSR composition of the present invention together in the presence of at least some of the components until the filler is completely treated and uniformly dispersed into a homogeneous material). In the presence of component (a), the untreated filler can be used in situ with the treating agent.

[0024] Typically, the filler may be surface-treated with, for example, a fatty acid or fatty acid ester such as stearic acid, or with an organosilane, polydiorganosiloxane, or organosilazane hexaalkyldisilazane, or a short-chain siloxanediol to render the filler hydrophobic and thus easier to handle and to achieve a uniform mixture with other components. The surface treatment of the filler in component (c) renders the filler hydrophobic, making it more easily wetted by the silicone polymer in the composition, most importantly, component (a), which is usually mixed to prepare the base. This improves the mechanical properties of the uncured composition at room temperature.

[0025] Typically, the filler treating agent may be any low molecular weight organosilicon compound disclosed in the art that can be applied to prevent creping of organosiloxane compositions during processing.

[0026] Examples of treating agents include, but are not limited to, hydroxyl-terminated polydiorganosiloxanes, hexaorganodisilazanes, and the like, each molecule of which contains an average of 2 to 20 repeating diorganosiloxane units. The hexaorganodisilazanes hydrolyze to form organosilicon compounds containing hydroxyl groups under the conditions used to treat the filler. Typically, at least a portion of the silicon-bonded hydrocarbon groups present in the treating agent are identical to the majority of the hydrocarbon groups present in components (a) and (b). A small amount of water may be added with the silica treating agent as a processing aid.

[0027] The fillers may be treated with a treating agent before compounding, and treated fillers are commercially available.

[0028] (d) Hydrosilylation catalyst Curing of the LSR compositions of the present invention is catalyzed by a hydrosilylation catalyst, component (d), which is one of the platinum metals (platinum, ruthenium, osmium, rhodium, iridium, and palladium), or a compound of one or more of such metals. Platinum and platinum compounds are preferred due to the high activity levels of these catalysts in hydrosilylation reactions.

[0029] Examples of preferred curing catalysts include, but are not limited to, platinum black, platinum on various solid supports, hexachloroplatinic acid, alcohol solutions of hexachloroplatinic acid, and complexes of hexachloroplatinic acid with ethylenically unsaturated compounds such as olefins and organosiloxanes containing ethylenically unsaturated silicon-bonded hydrocarbon groups. The catalyst is platinum metal, platinum metal deposited on a support such as silica gel or powdered charcoal, or a compound or complex of a platinum group metal.

[0030] Examples of suitable platinum-based catalysts include: (i) complexes of chloroplatinic acid with organosiloxanes containing ethylenically unsaturated hydrocarbon groups, as described in U.S. Pat. No. 3,419,593; (ii) chloroplatinic acid in either the hexahydrate or anhydrous form; (iii) platinum-containing catalysts obtained by a process comprising reacting chloroplatinic acid with an aliphatically unsaturated organosilicon compound such as divinyltetramethyldisiloxane; (iv) alkene-platinum-silyl complexes described in U.S. Pat. No. 6,605,734, such as (COD)Pt(SiMeCl) (where “COD” is 1,5-cyclooctadiene); and / or (v) Karstedt's catalysts, which are typically platinum divinyltetramethyldisiloxane complexes containing about 1% by weight of platinum in a solvent such as toluene, as described in U.S. Patent Nos. 3,715,334 and 3,814,730.

[0031] The catalyst is present throughout the composition in a catalytic amount, i.e., an amount or quantity sufficient to promote its reaction or cure under the desired conditions. Varying levels of catalyst can be used to tailor the reaction rate and cure reaction rate. The catalytic amount of the catalyst is generally from 0.01 ppm to 10,000 parts by weight of platinum group metal per million parts (ppm), based on the total weight of composition components (a) and (b); alternatively, from 0.01 to 5000 ppm; alternatively, from 0.01 to 3,000 ppm; alternatively, from 0.01 to 1,000 ppm. In specific embodiments, the catalytic amount of the catalyst can range from 0.01 to 1,000 ppm, alternatively, from 0.01 to 500 ppm, alternatively, from 0.01 to 100 ppm, alternatively, from 0.01 to 750 ppm of metal, based on the weight of the composition. The ranges may relate to only the metal content in the catalyst, or to the entire catalyst (including its ligands), as specified, but typically these ranges relate only to the metal content in the catalyst. The catalyst may be added as a single species or as a mixture of two or more different species. Typically, depending on the form / concentration in which the catalyst package is provided, the amount of catalyst present is in the range of 0.001 to 3.0 wt.% of the composition.

[0032] The mixture of components (a), (b), and (d) can begin to cure at ambient temperature. Therefore, the liquid silicone rubber composition is generally stored in two parts that are mixed together immediately before use. The two parts, generally referred to as part (A) and part (B), are designed to separate components (b) the crosslinker and (d) the catalyst to avoid premature curing.

[0033] Component (e) Conductive filler Component (e) is a conductive filler, (i) 1.5 to 5.5 weight percent of the composition of superconducting carbon black; and (ii) The composition contains 0.05 to 1% by weight of single-walled carbon nanotubes.

[0034] Superconductive carbon black has the following properties: (i) each of which has a length of at least 500 m, as measured by ASTM D 6556; 2 / g BET surface area, or 500-1600 m 2 / g, or 500-1500m 2 / g, or 600-1300m 2 / g, or 750-1250m 2 BET surface area in / g; (ii) D50 aggregate particle size of 5–500 nm or 10–200 nm, as measured using photosedimentation (DCP) according to ISO 15825:2017; (iii) highly conductive carbon black having at least one of a dibutyl phthalate (DBP) pore volume of 300 to 600 ml / 100 g, alternatively 300 to 550 ml / 100 g, alternatively 300 to 400 ml / 100 g, as measured using ASTM D-2414.

[0035] ISO 15825:2017 specifies a method for determining the size distribution of carbon black aggregates using a disc centrifuge photosedimentometer. This method is based on the hydrodynamic behavior of carbon black in a centrifugal field. Determining the aggregate size distribution is important for the evaluation of carbon blacks used in the rubber industry.

[0036] The superconducting carbon black is present in the compositions herein in an amount from 1.5 to 5.5% by weight of the composition, alternatively from 1.5 to 5.0, alternatively from 1.75 to 5% by weight of the composition.

[0037] Carbon nanotubes (CNTs) are nanomaterials made of graphene sheets, consisting of carbon atoms arranged in a hexagonal honeycomb, rolled up into tubes with diameters ranging from about a few nanometers to a few hundred nanometers. Carbon nanotubes exhibit unique electrical, mechanical, and physicochemical properties due to their unique electronic structure resulting from their nanometer-order diameter.

[0038] Carbon nanotubes are classified as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Single-walled carbon nanotubes (SWNTs) are seamless cylinders composed of layers of graphene. Multi-walled carbon nanotubes (MWNTs) consist of multiple rolled layers of graphene. MWNTs are not well-defined due to their structural complexity and diversity compared to SWNTs. Nevertheless, MWNTs offer advantages over SWNTs, such as ease of mass production, lower per-unit product cost, and improved thermal and chemical stability. As can be seen from the examples, it has surprisingly been found that the compositions herein can be strengthened using SWNTs, while multi-walled carbon nanotubes have the opposite effect. SWNTs are present in the composition in an amount of 0.05 to 1 wt. % of the composition, alternatively, 0.05 to 0.75 wt. % of the composition, or alternatively, 0.075 to 0.75 wt. % of the composition. In one alternative, the SWNTs may be provided in a masterbatch or solvent, for example, trimethyl-terminated polydimethylsiloxane. When in solution or in a masterbatch, an equal amount of carbon nanotubes must be incorporated into the composition as when added in the absence of a solvent / masterbatch, etc.

[0039] Inhibitor To obtain a longer working time and pot life of the LSR compositions of the present invention, suitable inhibitors may be used to retard or inhibit the activity of the catalyst.

[0040] Inhibitors for hydrosilylation catalysts, generally platinum metal-based catalysts, are known in the art. Hydrosilylation or addition reaction inhibitors include hydrazines, triazoles, phosphines, mercaptans, organic nitrogen compounds, acetylenic alcohols, silylated acetylenic alcohols, maleates, fumarates, ethylenically or aromatic unsaturated amides, ethylenically unsaturated isocyanates, olefinic siloxanes, unsaturated hydrocarbon monoesters and diesters, conjugated eneynes, hydroperoxides, nitriles, and diaziridines.

[0041] One group of known inhibitors for platinum catalysts includes the acetylenic compounds disclosed in U.S. Patent No. 3,445,420. Acetylenic alcohols, such as 2-methyl-3-butyn-2-ol, constitute a preferred class of inhibitors that suppress the activity of platinum-containing catalysts at 25° C. Typically, compositions containing these inhibitors must be heated to temperatures above 70° C. in order to cure at a practical rate.

[0042] Examples of acetylenic alcohols and their derivatives include 1-ethynyl-1-cyclohexanol (ETCH), 2-methyl-3-butyn-2-ol, 3-butyn-1-ol, 3-butyn-2-ol, propargyl alcohol, 2-phenyl-2-propyn-1-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynylcyclopentanol, 1-phenyl-2-propynol, 3-methyl-1-penten-4-yn-3-ol, and mixtures thereof.

[0043] When present, in some cases, inhibitor concentrations as low as 1 mole of inhibitor per mole of metal in catalyst (d) provide sufficient storage stability and cure speed. In other cases, inhibitor concentrations of 500 moles of inhibitor or less per mole of metal in catalyst (d) are required. The optimum concentration for a given inhibitor in a given composition can be readily determined by routine experimentation. Depending on the concentration and form in which the selected inhibitor is commercially provided / available, inhibitors, if present in the composition, are typically present in amounts of 0.0125 to 10 weight percent of the composition.

[0044] Additional Optional Ingredients Additional optional ingredients may be present in the liquid silicone rubber composition depending on its intended end use. Examples of such optional ingredients include thermally conductive fillers, pot life extenders, flame retardants, lubricants, non-reinforcing fillers, pigments and / or colorants, adhesion promoters, chain extenders, mold release agents, UV light stabilizers, fungicides, wetting agents, heat stabilizers, compression set additives, plasticizers, and mixtures thereof.

[0045] Pot life extenders such as triazoles may be used but are not considered essential within the scope of the present invention, and therefore the liquid curable silicone rubber composition may be free of pot life extenders.

[0046] Examples of flame retardants include aluminum trihydrate, chlorinated paraffins, hexabromocyclododecalane, triphenyl phosphate, dimethylmethylphosphonate, tris(2,3-dibromopropyl)phosphate (brominated tris), and mixtures or derivatives thereof.

[0047] Examples of lubricants include tetrafluoroethylene, resin powder, graphite, fluorinated graphite, talc, boron nitride, fluorinated oil, silicone oil, molybdenum disulfide, and mixtures or derivatives thereof.When present in the composition, flame retardants are typically present in an amount of 0.1 to 5% by weight of the composition.

[0048] Further additives include silicone fluids such as trimethylsilyl or OH-terminated siloxanes. Such trimethylsiloxy or OH-terminated polydimethylsiloxanes typically have a viscosity of less than 150 mPa.s at 25°C, measured using a Brookfield DV 3T rheometer. When present, such silicone fluids can be present in the liquid curable silicone rubber composition in an amount ranging from 0.1 to 5 wt%, based on the total weight of the composition, and can function as mold release agents.

[0049] Examples of pigments include titanium dioxide, chromium oxide, bismuth vanadium oxide, iron oxide, and mixtures thereof.

[0050] Examples of colorants for textile coatings include pigments, vat dyes, reactive dyes, acid dyes, chrome dyes, disperse dyes, cationic dyes, and mixtures thereof.

[0051] In a preferred embodiment of the present invention, the pigment and dye are used in the form of a pigment masterbatch consisting of the pigment and dye dispersed in a low viscosity polydiorganosiloxane (component (a)) in a ratio of 25:75 to 70:30.

[0052] Examples of adhesion promoters include alkoxysilanes containing methacryl or acryl groups, such as methacryloxymethyl-trimethoxysilane, 3-methacryloxypropyl-trimethoxysilane, 3-methacryloxypropyl-methyldimethoxysilane, 3-methacryloxypropyl-dimethylmethoxysilane, 3-methacryloxypropyl-triethoxysilane, 3-methacryloxypropyl-methyldiethoxysilane, 3-methacryloxyisobutyl-trimethoxysilane, or similar methacryloxy-substituted alkoxysilanes; 3-acryloxypropyl-trimethoxysilane, 3-acryloxypropyl-methyldimethoxysilane, 3-acryloxypropyl-dimethyl-methoxysilane, 3-acryloxypropyl-triethoxysilane, or similar acryloxy-substituted alkyl-containing alkoxysilanes; zirconium(IV) tetraacetylacetonate, zirconium(IV) hexafluoroacetylacetonate, ... zirconium chelate compounds such as zirconium(IV) trifluoroacetylacetonate, tetrakis(ethyltrifluoroacetylacetonate)zirconium, tetrakis(2,2,6,6-tetramethylheptanethionate)zirconium, zirconium(IV) dibutoxybis(ethylacetonate), diisopropoxybis(2,2,6,6-tetramethylheptanethionate)zirconium, or similar zirconium complexes with β-diketones (including their alkyl- and fluorine-substituted forms); epoxy-containing alkoxysilanes such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 4-glycidoxybutyltrimethoxysilane, 5,6-epoxyhexyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

[0053] Examples of chain extenders include disiloxanes or low molecular weight polyorganosiloxanes containing two silicon-bonded hydrogen atoms at the terminal positions. Chain extenders typically link two or more molecules of component (a) by reacting with the alkenyl groups of component (a), increasing the effective molecular weight and the distance between potential crosslinking sites.

[0054] Disiloxanes are typically represented by the general formula (HR a 2Si)2O. When the chain extender is a polyorganosiloxane, it has the general formula HR a 2SiO 1 / 2 and terminal units of formula R b 2SiO. In these formulas, R a and R b independently represent an unsubstituted or substituted monovalent hydrocarbon group free of ethylenic unsaturation, including, but not limited to, alkyl groups containing 1 to 10 carbon atoms, substituted alkyl groups containing 1 to 10 carbon atoms (such as chloromethyl and 3,3,3-trifluoropropyl), cycloalkyl groups containing 3 to 10 carbon atoms, aryl groups containing 6 to 10 carbon atoms, alkaryl groups containing 7 to 10 carbon atoms (such as tolyl and xylyl), and aralkyl groups containing 7 to 10 carbon atoms (such as benzyl).

[0055] Further examples of chain extenders include tetramethyldihydrogendisiloxane or dimethylhydrogen-terminated polydimethylsiloxane.

[0056] When component (a) has two vinyl groups per molecule, crosslinker (b) has three or more SH groups per molecule to ensure the formation of a crosslinked network. Crosslinker (b) may have only two Si-H groups per molecule when polymer (a) has three or more vinyl groups per molecule. However, when the polymer has two Si-vinyl groups per molecule, a chain extender, as described above, may optionally be added. When present, the chain extender may be present in any amount up to 3% by weight of the composition, alternatively, the chain extender may be present in an amount of 0.1% to 3% by weight of the composition, alternatively, the chain extender may be present in an amount of 0.1% to 2.5% by weight of the composition.

[0057] Suitable chain extenders for use in the present compositions have a viscosity, measured using a Brookfield DV 3T rheometer, of about 1 mPa·s to 1000 mPa·s at 25°C, alternatively 1 mPa·s to 500 mPa·s at 25°C, alternatively 1 mPa·s to 100 mPa·s at 25°C.

[0058] Examples of heat stabilizers include metal compounds such as red iron oxide, yellow iron oxide, ferric hydroxide, cerium oxide, cerium hydroxide, lanthanum oxide, and copper phthalocyanine. Also included are aluminum hydroxide, fumed titanium dioxide, iron naphthenate, cerium naphthenate, cerium dimethylpolysilanolate, and acetylacetonates of metals selected from copper, zinc, aluminum, iron, cerium, zirconium, titanium, and the like. The amount of heat stabilizer present in the composition may range from 0.01% to 1.0% by weight of the total composition.

[0059] Therefore, the present invention provides (a) one or more polydiorganosiloxanes having at least two alkenyl groups per molecule; (b) at least one organohydrogenpolysiloxane, or at least one organohydrogenpolysiloxane in an amount such that the molar ratio of the total number of silicon-bonded hydrogen atoms in component (b) to the total number of all alkenyl groups in component (a) is from 0.5:1 to 5:1; (c) 10 to 25 weight percent of the composition of at least one reinforcing filler; (d) at least one hydrosilylation catalyst; (e) (i) 1.5 to 5.5 weight percent of the composition of superconducting carbon black; and (ii) a conductive filler containing single-walled carbon nanotubes in an amount of 0.05 to 1% by weight of the composition; and

[0060] The composition may also contain one or more additives selected from the list of inhibitors, mold release agents, chain extenders, heat stabilizers, flame retardants and pigments / colorants. Thus, the composition may contain any combination of the following: (a) one or more polydiorganosiloxanes having at least two alkenyl groups per molecule; (b) at least one organohydrogenpolysiloxane, or at least one organohydrogenpolysiloxane in an amount such that the molar ratio of the total number of silicon-bonded hydrogen atoms in component (b) to the total number of all alkenyl groups in component (a) is from 0.5:1 to 5:1; (c) 10 to 25 weight percent of the composition of at least one reinforcing filler; (d) at least one hydrosilylation catalyst in an amount of from 0.01 parts per million (ppm) to 10,000 parts by weight of a platinum group metal, based on the combined weight of components (a) and (b); and (e) (i) 1.5 to 5.5 weight percent of the composition of superconducting carbon black; and (ii) a conductive filler comprising single-walled carbon nanotubes in an amount of 0.05-1% by weight of the composition, and optionally any one or more of an inhibitor, a mold release agent, a chain extender, a heat stabilizer, a flame retardant, and a pigment / colorant, provided that the total weight percent of the composition is 100%.

[0061] In each case, the aforementioned optional ingredients, if present, are in the following ranges: an inhibitor in an amount of 1 to 500 moles per mole of metal in catalyst (d); a release agent in an amount of 0.1 to 5% by weight of the composition; a chain extender in an amount of 0.1 to 3% by weight of the composition; a heat stabilizer in an amount of 0.01 to 1.0% by weight of the total composition; The flame retardant is present in an amount of 0.1 to 5% by weight of the composition.

[0062] The composition is stored in two parts, Part A and Part B, to separate components (b) and (d) and prevent premature curing. Typically, the Part A composition contains components (a), (c), and (d), and Part B contains components (a), (b), and (c), and, if present, an inhibitor. Component (e) above can be present in either or both Parts A and B.

[0063] Additives, if present in the composition, can be present in either Part A or Part B, so long as they do not adversely affect the properties of any other components (e.g., catalyst deactivation). Parts A and B of the liquid silicone rubber composition are mixed together immediately before use to initiate curing of the overall composition to form a silicone elastomer material. The composition can be designed to be mixed in any suitable ratio; for example, Part A:Part B can be mixed in a ratio of 10:1 to 1:10, or 5:1 to 1:5, or 2:1 to 1:2, with a 1:1 ratio being most preferred.

[0064] The components of Part A and / or Part B may be mixed together individually, or may be introduced into the composition in a pre-prepared combination, e.g., to facilitate mixing of the final composition. For example, components (a) and (c) are often mixed together to form the LSR polymer base before adding the other components. These may then be mixed directly with the other components of the part being manufactured, or may be used to make pre-prepared concentrates, commonly referred to in the industry as masterbatches.

[0065] In this case, to facilitate mixing of the components, one or more masterbatches can be utilized to facilitate mixing of the components to form the Part A and / or Part B compositions. For example, a "fumed silica" masterbatch can be prepared. This is essentially an LSR silicone rubber base containing several optional additives. Any suitable additives may be incorporated into such a masterbatch. Alternatively or additionally, a conductive filler masterbatch can be utilized as a means of introducing the conductive filler. Such a masterbatch may include, for example, components (a), (c), and (e), along with suitable optional additives, or may be a mixture of the aforementioned fumed silica masterbatch and conductive filler (e). Any other suitable combination of components can be utilized to form a concentrate / masterbatch to improve ease of incorporation.

[0066] The composition of the present invention can be prepared by mixing all of the components at ambient temperature. Any mixing technique and equipment disclosed in the prior art can be used for this purpose. The specific equipment used will depend on the viscosity of the components and the final curable coating composition. Suitable mixers include, but are not limited to, paddle-type mixers, such as planetary mixers, or kneader-type mixers. It may be desirable to cool the components during mixing to prevent premature curing of the composition.

[0067] However, while the order in which the components are mixed is not absolutely critical, it has been found that the development and use of conductive filler masterbatches, in particular, offers significant advantages in the processing of the composition. While the use of carbon black in conductive compositions has historically been favored in the industry, it has presented processing challenges, particularly the dispersion of carbon black in silicone compositions, especially when high levels are required to provide the desired conductive properties. It has been found that using a roll mill or a three-mill mill to prepare a conductive filler masterbatch containing components (a), (c), and (e) and optional additives improves the stability of conductivity and reduces conductive filler particle dispersion when preparing both Part A and Part B, and when Part A and Part B are mixed together to prepare the final composition immediately before use / curing.

[0068] One of the main advantages of this composition is that the viscosity of the final composition is, in fact, ≤350,000 mPa.s at 25°C and a shear rate of 10 s-1 when measured using an AR2000 EX plate-plate rheometer from TA Instruments (Delaware USA); typically ≤350,000 mPa.s at 25°C and a shear rate of 10 s-1 when measured using an AR2000 EX plate-plate rheometer. -1 or in the range of 150,000 to 350,000 at a shear rate of 10 s at 25 °C when measured using an AR2000EX plate-plate rheometer from TA Instruments (Delaware USA). -1 The viscosity is kept reasonably low at 200,000 to 300,000 mPa.s.

[0069] Accordingly, there is provided a method for producing the aforementioned composition, comprising the steps of: (i) a conductive filler masterbatch, a. a silicone rubber-based material comprising a dimethylvinyl-terminated polydimethylsiloxane (a) and a reinforcing filler (c); b. conductive filler (e); c. one or more dimethylvinyl-terminated polydimethylsiloxanes (a), (ii) introducing the conductive filler masterbatch of (i) into a part A composition containing a dimethylvinyl-terminated polydimethylsiloxane (a), a reinforcing filler (c), and a hydrosilylation catalyst (d), and / or into a part B composition containing a dimethylvinyl-terminated polydimethylsiloxane (a), a reinforcing filler (c), and at least one organohydrogenpolysiloxane (b), wherein part A does not contain the organohydrogenpolysiloxane (b) and part B does not contain the hydrosilylation catalyst (d); (iii) mixing parts A and B together.

[0070] The dimethylvinyl-terminated polydimethylsiloxane (a) in component a in step (i) has a viscosity higher than the viscosity of the one or more dimethylvinyl-terminated polydimethylsiloxanes (a) in component c in step (i). For example, the dimethylvinyl-terminated polydimethylsiloxane (a) in component a in step (i) may have a viscosity of 50,000 to 150,000 mPa·s at 25°C, or 55,000 to 100,000 mPa·s at 25°C, or 55,000 to 80,000 mPa·s at 25°C, in each case, Brookfield DV-III Ultra the one or more dimethylvinyl-terminated polydimethylsiloxanes (a) of component c. in step (i) have a viscosity of 150 mPa·s to 25,000 mPa·s at 25°C, alternatively 200 mPa·s to 20,000 mPa·s at 25°C, as measured using a Brookfield DV 3T rheometer, or a mixture of second and third dimethylvinyl-terminated polydimethylsiloxanes, the second having a viscosity of 5,000 mPa·s to 25,000 mPa·s at 25°C, alternatively 7,500 mPa·s to 20,000 mPa·s at 25°C, as measured using a Brookfield DV 3T rheometer, and the third dimethylvinyl-terminated polydimethylsiloxane having a viscosity of 150 mPa·s to 1,000 mPa·s at 25°C, alternatively 200 to 500 mPa·s at 25°C, as measured using a Brookfield DV 3T rheometer.

[0071] Step (i) of the method may include premixing the components in a mixer to form an initial mixture, and then mixing the resulting initial mixture on a three-roll mill. This has been found to result in more stable conductivity and improved dispersion of the conductive filler in the composition. Preferably, the viscosity of the conductive filler masterbatch is less than 10 s as measured using an AR2000 EX plate-plate rheometer from TA Instruments (Delaware, USA). -1 At a shear rate of 500,000 to 1,200,000 mPa.s at 25°C.

[0072] Typically, parts A and B are mixed in about a 1:1 ratio just prior to use to avoid premature curing.

[0073] Alternatively, the liquid silicone rubber composition may be further processed by injection molding, encapsulation molding, press molding, dispenser molding, extrusion molding, transfer molding, press vulcanization, centrifugal casting, calendar molding, bead application, or blow molding.

[0074] Curing of the liquid curable silicone rubber composition can be carried out at any suitable temperature. Typical curing temperatures may range from 80 to 200°C, or alternatively, from 90 to 150°C. If desired, samples can be additionally post-cured by heating to a temperature of 130 to 200°C for 4 hours.

[0075] Curing can be carried out, for example, in a mold to produce a molded silicone article. The composition can be, for example, injection molded to form an article, or the composition can be overmolded by injection molding around an article or onto a substrate.

[0076] Considering the electrical applications for which this material was developed, the industry generally recommends a hardness in the 30-50 range when cured, or ASTM D22 40 There is a need for an elastomeric product having a Shore A hardness of 35 to 48 when measured according to ASTM D412. The aforementioned composition can meet this requirement while also having an elongation of ≥ 500%, e.g., 550 to 600% when tested according to ASTM D412, and a 10 s elongation of ≥ 500% when measured using a TA Instruments (DELAWARE USA) AR2000 EX plate-plate rheometer. -1The composition has a viscosity of ≤350,000 mPa·s at 25°C, e.g., 250,000-300,000 mPa·s, at a shear rate of 100 s. Depending on the concentration of carbon black in the composition, this combination of properties has historically proven problematic for conductive silicone rubber materials. Not only does this composition meet the above requirements, but it also has a stable volume resistivity of <100 Ω·cm, e.g., about 30-60 Ω·cm, as demonstrated by the Chinese National Test Method GB / T3048.3-2007, and is capable of adhering to other liquid silicone rubber materials, particularly insulating-based materials. Bonding to insulating LSR products has also been determined to be acceptable for the intended purpose.

[0077] In one embodiment, the present invention relates to articles cured from the liquid curable silicone rubber composition, including those that can be used in high voltage alternating current (AC) applications such as cable joints, cable termination applications, cable accessories, e.g., high voltage insulated (HVI) cable accessories, and connectors, automotive parts such as electrical insulators, single wire seals, plug connector seals, connector seals, electrical and electronic components such as copier rolls and packing in microwave ovens.

[0078] The liquid curable silicone rubber composition can be cured into silicone elastomer articles such as tubes, strips, solid cords, or custom profiles according to manufacturer's sizing specifications.

[0079] The cured silicone elastomer obtained by curing the liquid curable silicone rubber composition of the present invention can provide a composite part that is mechanically or chemically bonded to a substrate.

[0080] In one embodiment, the present invention relates to a composite part comprising a silicone elastomer cured from a liquid curable silicone rubber composition on a substrate.

[0081] The aforementioned compositions, once cured, can be used by themselves as conductive elastomers, but they can also be used in combination with other materials well known in the design of high-voltage AC applications. For example, the insulation of such cable joints or cable terminations is often a multi-layer design, with at least one material providing high conductivity, such as an elastomer cured from the present compositions being part of the joint as a shielding material, and other materials, such as silicone rubber insulating materials, can be used in combination. Some of these cable accessories can have the form of a tube or tubular trumpet, and can therefore be manufactured by extrusion. Example All viscosities were measured at 25° C. unless otherwise noted. Viscosities of individual components in the following examples were measured using a Brookfield DV-III Ultra Programmable Rheometer for viscosities ≧50,000 mPa s and a Brookfield DV 3T Rheometer for viscosities less than 50,000 mPa s, unless otherwise noted.

[0082] The following examples used the liquid silicone rubber bases disclosed in Table 1. As a first step, silicone-based compositions having the compositions listed in Table 1 below were prepared in a kneader mixer. [Table 1]

[0083] The base compositions prepared according to the formulations shown in Table 1 were then used to prepare conductive filler masterbatch compositions according to Table 2. [Table 2]

[0084] The components of the conductive filler masterbatch composition were premixed in a planetary mixer and then further mixed using a three-roll mill.

[0085] Rather than making a final composition, as described above, to avoid premature curing, three compositions were prepared as described above, each having a Part A composition containing a hydrosilylation catalyst (Pt) and no crosslinker (Table 3) and a Part B composition containing a crosslinker and no catalyst (Table 4), prepared individually using the compositions detailed in Tables 3 and 4 below. [Table 3]

[0086] The platinum catalyst solution is about 1.43 wt% platinum divinyltetramethyldisiloxane complex (CAS#68478-92-2) or a platinum catalyst / vinyl polymer dispersion having about 0.7 wt% platinum group metal. [Table 4]

[0087] Table 5 below shows the total filler content in weight percent for the three examples above, as previously stated. [Table 5]

[0088] The resulting Part A and Part B compositions were mixed together in a suitable mixer, and the resulting final composition was cured for 10 minutes at a temperature of 120° C. and post-cured for 4 hours at a temperature of 150° C. After mixing and / or curing, the physical properties of the three examples were evaluated and are summarized in Table 6 below. [Table 6]

[0089] Bonding using the insulating LSR test was performed by subjecting the samples to a 180° peel test using an Inston tensiometer at a crosshead speed of 50 mm / min.

[0090] It can be seen that all of the above examples exhibited the desired properties, particularly low viscosity, stable volume resistivity, higher elongation, and acceptable bond strength, as compared to the comparative examples.

[0091] Three comparative compositions were also provided using either superconducting carbon black or single-walled carbon nanotubes as the conductive filler. As with Examples 1-3 above, the three comparative compositions were first divided into two parts. Each comparative composition, having a Part A composition containing a hydrosilylation catalyst (Pt) and no crosslinker (Table 7) and a Part B composition containing a crosslinker and no catalyst (Table 8), was separately prepared using the compositions detailed in Tables 7 and 8 below. [Table 7] [Table 8]

[0092] Table 9 below shows the total filler content in weight percent for the three examples above, as previously stated. [Table 9]

[0093] The resulting Comparative Example Part A and Part B compositions were mixed together in a suitable planetary mixer, and the resulting final composition was cured for 10 minutes at a temperature of 120° C. and post-cured for 4 hours at a temperature of 150° C. After mixing and / or curing, the physical properties of the three examples were evaluated and are summarized in Table 10 below. [Table 10]

[0094] Comparative examples containing superconducting carbon black as a conductive filler exhibited viscosities >350,000 mPa.s, much higher volume resistivities than the above examples, variable elongation values, and poor bonding to the insulator. Comparative compositions relying on single-walled carbon nanotubes exhibited lower viscosity values, but came at a high price, with significantly higher Shore A hardness and volume resistivity results. Unlike the above examples, none provided all the desired properties.

Claims

1. A curable, electrically conductive liquid silicone rubber composition, comprising: (a) a first polydiorganosiloxane having at least two alkenyl groups per molecule and having a viscosity in the range of 50,000 to 100,000 mPa·s at 25°C as measured using a Brookfield DV-III Ultra Programmable Rheometer; a second polydiorganosiloxane having at least two alkenyl groups per molecule and having a viscosity in the range of 5,000 to 20,000 mPa·s at 25°C as measured using a Brookfield DV 3T Rheometer; and a third polydiorganosiloxane having at least two alkenyl groups per molecule and having a viscosity in the range of 150 to 1,000 mPa·s at 25°C as measured using a Brookfield DV 3T Rheometer. (b) at least one organohydrogenpolysiloxane; and (c) 10 to 25 weight percent of the composition of at least one reinforcing filler; (d) at least one hydrosilylation catalyst; (e) a conductive filler comprising: (i) and (ii) (i) 1.5 to 5.5% by weight of said composition of superconductive carbon black having the following characteristics: (1) a BET surface area of ​​at least 500 m 2 / g as measured by ASTM D 6556; (2) a D50 aggregate particle size of 5 to 500 nm, as measured using photosedimentation (DCP) in accordance with ISO 15825:2017; (3) A superconducting carbon black having at least one of the following characteristics: a dibutyl phthalate (DBP) pore volume of 300 to 600 ml / 100 g, as measured using ASTM D-2414. (ii) 0.05 to 1% by weight of the composition of single-walled carbon nanotubes Including, A conductive liquid silicone rubber composition that is stored in two parts, Part A and Part B, prior to use to separate components (b) and (d) and avoid premature curing.

2. The reinforcing filler (c) is 100 to 600 m by the BET method. ２ 2. The conductive liquid silicone rubber composition according to claim 1, wherein the silica is a fumed silica having a surface area of ​​1000 nm / g.

3. 3. The conductive liquid silicone rubber composition according to claim 1, wherein the part A composition comprises components (a), (c), and (d), and the part B composition comprises components (a), (b), and (c).

4. The conductive liquid silicone rubber composition of claim 3 wherein part B also contains a cure inhibitor.

5. The composition comprises the following components: (i) an inhibitor in an amount of 1 to 500 moles per mole of metal of catalyst (d); (ii) a mold release agent in an amount of 0.1 to 5% by weight of the composition; (iii) a chain extender in an amount of 0.1 to 3% by weight of the composition; (iv) a heat stabilizer in an amount of 0.01 to 1.0% by weight of the total composition; (v) a flame retardant in an amount of 0.1 to 5% by weight of the composition, and / or (vi) a pigment / colorant; and (vi) a conductive liquid silicone rubber composition according to any one of claims 1 to 4, further comprising one or more additives selected from the group consisting of:

6. A method for producing a composition according to any one of claims 1 to 5, comprising the steps of: (i) a conductive filler masterbatch, a. a silicone rubber base material comprising a first dimethylvinyl-terminated polydimethylsiloxane (a) and a reinforcing filler (c); b. a conductive filler (e); c. one or more dimethylvinyl-terminated polydimethylsiloxanes (a), (ii) introducing the conductive filler masterbatch of (i) into a part A composition containing a dimethylvinyl-terminated polydimethylsiloxane (a), a reinforcing filler (c), and a hydrosilylation catalyst (d), and / or into a part B composition containing a dimethylvinyl-terminated polydimethylsiloxane (a), a reinforcing filler (c), and at least one organohydrogenpolysiloxane (b), wherein part A does not contain the organohydrogenpolysiloxane (b) and part B does not contain the hydrosilylation catalyst (d); (iii) mixing parts A and B together.

7. 7. The method of claim 6, wherein the dimethylvinyl-terminated polydimethylsiloxane (a) in component (a.) in step (i) has a viscosity of 50,000 to 100,000 mPa·s at 25°C, as measured using a Brookfield DV-III Ultra Programmable Rheometer, and the one or more dimethylvinyl-terminated polydimethylsiloxanes (a) in component (c.) in step (i) is a mixture of second and third dimethylvinyl-terminated polydimethylsiloxanes, the second having a viscosity of 5,000 to 20,000 mPa·s at 25°C, as measured using a Brookfield DV 3T rheometer; and the third dimethylvinyl-terminated polydimethylsiloxane having a viscosity of 150 to 1,000 mPa·s at 25°C, as measured using a Brookfield DV 3T rheometer.

8. 8. The method of claim 6 or 7, wherein step (i) of the method can include premixing the ingredients in a mixer to form an initial mixture and then mixing the resulting initial mixture on a three-roll mill.

9. 6. An article cured from the liquid curable silicone rubber composition according to any one of claims 1 to 5, which is selected from automotive parts such as cable joints, cable terminal applications, cable accessories, spark plug connectors, electrical insulators, single wire seals, plug connector seals, tubes and valves, connector seals and spark plug boots, electrical and electronic parts such as photocopier rolls and packing in microwave ovens.

10. 6. Use of a composition according to any one of claims 1 to 5 in the manufacture of electrical and electronic components such as cable joints, cable terminal applications, cable accessories, spark plug connectors, electrical insulators, single wire seals, plug connector seals, tubes and valves, automotive parts such as connector seals and spark plug boots, photocopier rolls and packings in microwave ovens.

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